Seminars, Seminar Topics, Notes on Engineering Computers, Electronics, Mechanical, Mba

STUN

2010-04-03T02:52:00.001-07:00

This is a network protocol which enables a client in a NAT (or multiple NATs) to find out its public address, the type of NAT behind it and the internet side port associated by the NAT with a particular local port and this whole process aids to set up UDP communication between two hosts that are both behind NAT routers. STUN stands for Simple Traversal of UDP (User Datagram Protocol) through NATs (Network Address Translators).

Protocol overview

STUN is a client-server protocol. Any VoIP phone or software package includes a STUN client, which sends a request to the STUN server. As a reply the public IP address of the NAT router and the port was opened by the NAT to allow incoming traffic back in to the network is sent to the STUN client. Such a response also helps the STUN client to identify the NAT being used as different types of NATs handle incoming UDP packets vividly. Its compatible with Full Cone, Restricted Cone, and Port Restricted Cone. (Restricted Cone or Port Restricted Cone NATs, allows packets from the endpoint through to the client from the NAT once the client has send a packet to the endpoint). Symmetric NAT (also known as bi-directional NAT) which is frequently found in the networks of large companies does not work with STUN as the IP addresses of the STUN server and the endpoint is different, and therefore the NAT mapping the STUN server is different from the mapping that the endpoint uses to send packets through to the client. Network address translation could give you more information on this.

After the client discovers its external addresses communication with its peers occurs. When the NATs are full cone,either side can initiate communication and if they are restricted cone or restricted port cone both sides must start transmitting together. The techniques described in the STUN RFC does not necessarily require using the STUN protocol; they can be used in the design of any UDP protocol. STUN comes in handy in the cases of Protocols like SIP which use UDP packets for the transfer of sound/video/text signaling traffic across the Internet. As both endpoints are often behind NAT, a connection cannot be set up in the traditional way. The STUN server communicates on UDP port 3478 but the server will hint clients to perform tests on alternate IP and port number too (STUN servers have two IP addresses).

Hyper Transport Technology

2010-04-02T00:06:00.000-07:00

The demand for faster processors, memory and I/O is a familiar refrain in market applications ranging from personal computers and servers to networking systems and from video games to office automation equipment. Once information is digitized, the speed at which it is processed becomes the foremost determinate of product success. Faster system speed leads to faster processing. Faster processing leads to faster system performance. Faster system performance results in greater success in the marketplace. This obvious logic has led a generation of processor and memory designers to focus on one overriding objective - squeezing more speed from processors and memory devices. Processor designers have responded with faster clock rates and super pipelined architectures that use level 1 and level 2 caches to feed faster execution units even faster. Memory designers have responded with dual data rate memories that allow data access on both the leading and trailing clock edges doubling data access. I/O developers have responded by designing faster and wider I/O channels and introducing new protocols to meet anticipated I/O needs. Today, processors hit the market with 2+ GHz clock rates, memory devices provide sub5 ns access times and standard I/O buses are 32- and 64-bit wide, with new higher speed protocols on the horizon.Increased processor speeds, faster memories, and wider I/O channels are not always practical answers to the need for speed. The main problem is integration of more and faster system elements. Faster execution units, faster memories and wider, faster I/O buses lead to crowding of more high-speed signal lines onto the physical printed circuit board. One aspect of the integration problem is the physical problems posed by speed.

Hyper Transport technology has been designed to provide system architects with significantly more bandwidth, low-latency responses, lower pin counts, compatibility with legacy PC buses, extensibility to new SNA buses, and transparency to operating system software, with little impact on peripheral drivers.

FluidFM: Combining AFM and nanofluidics for single cell applications

2009-10-02T02:28:00.000-07:00

FluidFM: Combining AFM and nanofluidics for single cell applications

The Atomic Force Microscope (AFM) is a key tool for nanotechnology. This instrument has become the most widely used tool for imaging, measuring and manipulating matter at the nanoscale and in turn has inspired a variety of other scanning probe techniques. Originally the AFM was used to image the topography of surfaces, but by modifying the tip it is possible to measure other quantities (for example, electric and magnetic properties, chemical potentials, friction and so on), and also to perform various types of spectroscopy and analysis. Increasingly, the AFM is also becoming a tool for nanofabrication.

Relatively new is the use of AFM in cell biology. We wrote about this recently in a Spotlight that described a novel method to probe the mechanical properties of living and dead bacteria via AFM indentation experimentations ("Dead or alive – nanotechnology technique tells the difference ").
Researchers in Switzerland have now demonstrated novel cell biology applications using hollow force-controlled AFM cantilevers – a new device they have called FluidFM.

"The core of the invention is to have fixed already existing microchanneled cantilevers to an opportunely drilled AFM probeholder" Tomaso Zambelli tells Nanowerk. "In this way, the FluidFM is not restricted to air but can work in liquid environments. Since it combines a nanofluidics circuit, every soluble agent can be added to the solution to be dispensed. Moreover, the force feedback allows to approach very soft objects like cells without damaging them."

As cell biology is moving towards single cell technologies and applications, single cell injection or extraction techniques are in high demand. Apart from this, however, the FluidFM could also be used for nanofabrication applications such as depositing a conductive polymer wire between to microelectrodes, or to etch ultrafine structures out of solid materials using acids as the spray agent. The team has reported their findings in a recent paper in Nano Letters ("FluidFM: Combining Atomic Force Microscopy and Nanofluidics in a Universal Liquid Delivery System for Single Cell Applications and Beyond").

Zambelli originally realized that the technology of the atomic force microscope that is normally used only to image cells could be transformed into a microinjection system. The result of the development by Zambelli and his colleagues in the Laboratory of Biosensors and Bioelectronics at the Institute of Biomedical technology at ETH Zurich and in the Swiss Center for Electronics and Microtechnology (CSEM) in Neuchâtel was the "fluid force microscope", currently the smallest automated nanosyringe currently in existence.

"Our FluidFM even operates under water or in other liquids – a precondition for being able to use the instrument to study cells" says Zambelli.

The force detection system of the FluidFM is so sensitive that the interactions between tip and sample can be reduced to the piconewton range, thereby allowing to bring the hollow cantilever into gentle but close contact with cells without puncturing or damaging the cell membrane.

On the other hand, if membrane perforation for intracellular injection is desired, this is simply achieved by selecting a higher force set point taking advantage of the extremely sharp tip (radius of curvature on the order of tens of nanometers).

To enable solutions to be injected into the cell through the needle, scientists at CSEM installed a microchannel in the cantilever. Substances such as medicinal active ingredients, DNA, and RNA can be injected into a cell through the tip. At the same time, samples can also be taken from a cell through the needle for subsequent analysis.

According to Zambelli, while this approach is similar to microinjection using glass pipettes, there are a number of essential differences.

"Microinjection uses optical microscopy to control the position of the glass pipette tip both in the xy plane and in the z direction (via image focusing)" he explains. "As consequence of the limited resolution of optical microscopy, subcellular domains cannot be addressed and tip contact with the cell membrane cannot be discriminated from tip penetration of the membrane. Cells are often lethally damaged and skilled personnel are required for microinjection."

"The limited resolution of this method and the absence of mechanical information contrast strongly with the high resolution imaging and the direct control of applied forces that are possible with AFM. Precise force feedback reduces potential damage to the cell; the cantilever geometry minimizes both the normal contact forces on the cell and the lateral vibrations of the tip that can tear the cell membrane during microinjection; the spatial resolution is determined by the submicrometer aperture so that injection into subcellular domains becomes easily achievable."

Experiments conducted by the Swiss team demonstrate the potential of the FluidFM in the field of single-cell biology through precise stimulation of selected cell domains with whatever soluble agents at a well-defined time.

"We confidently expect that the inclusion of an electrode in the microfluidics circuit will allow a similar approach toward patch-clamping with force controlled gigaseal formation," says Zambelli. "We will also explore other strategies at the single-cell level, such as the controlled perforation of the cell membrane for local extraction of cytoplasm

"Zambelli and his colleagues are convinced that their technology has great commercial potential. Rejecting offers from well-known manufacturers of atomic force microscopes for the sale of the patent for the FluidFM, they have founded Cytosurge LLC, a company dedicated to commercially develop the instrument.

Today, Zambelli's laboratory contains two prototypes of the instrument, which are being tested in collaboration with biologists.

Virus

2009-10-02T02:19:00.000-07:00

Virus

Do viruses and all the other nasties in cyberspace matter? Do they really do much harm? Imagine that no one has updated your anti-virus software for a few months. When they do, you find that your accounts spreadsheets are infected with a new virus that changes figures at random. Naturally you keep backups. But you might have been backing up infected files for months. How do you know which figures to trust? Now imagine that a new email virus has been released. Your company is receiving so many emails that you decide to shut down your email gateway altogether and miss an urgent order from a big customer.

Imagine that a friend emails you some files he found on the Internet. You open them and trigger a virus that mails confidential documents to everyone in your address book including your competitors. Finally, imagine that you accidentally send another company, a report that carries a virus. Will they feel safe to do business with you again? Today new viruses sweep the planet in hours and virus scares are major news. A computer virus is a computer program that can spread across computers and networks by making copies of itself, usually without the user’s knowledge. Viruses can have harmful side effects. These can range from displaying irritating messages to deleting all the files on your computer.

A virus program has to be run before it can infect your computer. Viruses have ways of making sure that this happens. They can attach themselves to other programs or hide in code that is run automatically when you open certain types of files. The virus can copy itself to other files or disks and make changes on your computer. Virus side effects, often called the payload, are the aspect of mostinterest to users. Password-protecting the documents on a particular day, mailing information about the user and machine to an address somewhere are some of the harmful side effects of viruses. Various kinds of viruses include macro virus, parasitic or file virus, Boot virus, E-mails are the biggest source of viruses. Usually they come as attachments with emails.

The Internet caused the spreading of viruses around the globe. The threat level depends on the particular code used in the WebPages and the security measures taken by service providers and by you. One solution to prevent the viruses is anti-virus softwares. Anti-virus software can detect viruses, prevent access to infected files and often eliminate the infection.

Computer viruses are starting to affect mobile phones too. The virus is rare and is unlikely to cause much damage. Anti-virus experts expect that as mobile phones become more sophisticated they will be targeted by virus writers. Some firms are already working on anti-virus software for mobile phones. VBS/Timo-A, Love Bug,Timofonica,CABIR,aka ACE-? and UNAVAILABLE are some of the viruses that affect the mobile phones

BASIC CONCEPTS
What is a virus?
A computer virus is a computer program that can spread across computers and networks by making copies of itself, usually without the user’s knowledge. Viruses can have harmful side-effects. These can range from displaying irritating messages to deleting all the files on your computer.
Evolution of virus
In the mid-1980s Basit and Amjad Alvi of Lahore, Pakistan discovered that people were pirating their software. They responded by writing the first computer virus, a program that would put a copy of itself and a copyright message on any floppy disk copies their customers made. From these simple beginnings, an entire virus counter-culture has emerged. Today new viruses sweep the planet in hours and virus scares are major news
How does a virus infect computers?

A virus program has to be run before it can infect your computer. Viruses have ways of making sure that this happens. They can attach themselves to other programs or hide in code that is run automatically when you open certain types of files. You might receive an infected file on a disk, in an email attachment, or in a download from the internet. As soon as you launch the file, the virus code runs. Then the virus can copy itself to other files or disks and make changes on your computer.
Who writes viruses?
Virus writers don’t gain in financial or career terms; they rarely achieve real fame; and, unlike hackers, they don’t usually target particular victims, since viruses spread too indiscriminately. Virus writers tend to be male, under 25 and single. Viruses also give their writers powers in cyberspace that they could never hope to have in the real world.
Virus side effects(Payload)
Virus side-effects are often called the payload. Viruses can disable our computer hardware, Can change the figures of an accounts spreadsheets at random, Adversely affects our email contacts and business domain, Can attack on web servers…
 Messages -WM97/Jerk displays the message ‘I think (user’s name) is a big stupid jerk!’  Denying access -WM97/NightShade password-protects the current document on Friday 13th. Data theft- Troj/LoveLet-A emails information about the user and machine to an address in the Philippines
. Corrupting data -XM/Compatable makes changes to the data in Excel spreadsheets. Deleting data -Michelangelo overwrites parts of the hard disk on March 6th.
 Disabling Hardware -CIH or Chernobyl (W95/CIH-10xx)
 attempts to overwrite the BIOS on April 26th, making the machine unusable.
 Crashing servers-Melissa or Explore Zip, which spread via email, can generate so much mail that servers crash.
There is a threat to confidentiality too. Melissa can forward documents, which may contain sensitive information, to anyone in your address book. Viruses can seriously damage your credibility. If you send infected documents to customers, they may refuse to do business with you or demand compensation. Sometimes you risk embarrassment as well as a damaged business reputation. WM/Polypost, for example, places copies of your documents in your name on alt.sex usenet newsgroups.
VIRUSES AND VIRUS LIKE PROGRAMMES
Trojan horses
Trojan horses are programs that do things that are not described in their specifications The user runs what they think is a legitimate program, allowing it to carry out hidden, often harmful, functions. For example, Troj/Zulu claims to be a program for fixing the ‘millennium bug’ but actually overwrites the hard disk. Trojan horses are sometimes used as a means of infecting a user with a computer virus.
Backdoor Trojans
A backdoor Trojan is a program that allows someone to take control of another user’s PC via the internet. Like other Trojans, a backdoor Trojan poses as legitimate or desirable software. When it is run (usually on a Windows 95/98 PC), it adds itself to the PC’s startup routine. The Trojan can then monitor the PC until it makes a connection to the internet. Once the PC is on-line, the person who sent the Trojan can use software on their computer to open and close programs on the infected computer, modify files and even send items to the printer. Subseven and Back Orifice are among the best known backdoor Trojans.
Worms
Worms are similar to viruses but do not need a carrier (like a macro or a boot sector).They are subtype of viruses. Worms simply create exact copies of themselves and use communications between computers to spread. Many viruses, such as Kakworm (VBS/Kakworm) or Love Bug (VBS/LoveLet-A), behave like worms and use email to forward themselves to other users.
Boot sector viruses
Boot sector viruses were the first type of virus to appear. They spread by modifying the boot sector, which contains the program that enables your computer to start up. When you switch on, the hardware looks for the boot sector program – which is usually on the hard disk, but can be on floppy or CD – and runs it. This program then loads the rest of the operating system into memory. A boot sector virus replaces the original boot sector with its own, modified version (and usually hides the original somewhere else on the hard disk). When you next start up, the infected boot sector is used and the virus becomes active. You can only become infected if you boot up your computer from an infected disk, e.g. a floppy disk that has an infected boot sector. Many boot sector viruses are now quite old.
Those written for DOS machines do not usually spread on Windows 95, 98, Me, NT or 2000 computers, though they can sometimes stop them from starting up properly. Boot viruses infect System Boot Sectors (SBS) and Master Boot Sectors (MBS). The MBS is located on all physical hard drives. It contains, among other data, information about the partition table (information about how a physical disk is divided into logical disks), and a short program that can interpret the partition information to find out where the SBS is located. The MBS is operating system independent. The SBS contains, among other data, a program whose purpose is to find and run an operating system. Because floppy diskettes are exchanged more frequently than program files boot viruses are able to propagate more effectively than file viruses.Form -A virus that is still widespread ten years after it first appeared.
The original version triggers on the 18th of each month and produces a click when keys are pressed on the keyboard. Parity Boot - A virus that may randomly display the message ‘PARITY CHECK’ and freeze the operating system. The message resembles a genuine error message displayed when the computer’s memory is faulty.
Parasitic virus (File virus)
Parasitic viruses, also known as file viruses, attach themselves to programs (or ‘executables’) and Acts as a part of the program .When you start a program infected with a file virus, the virus is launched first. To hide itself, the virus then runs the original program. The operating system on your computer sees the virus as part of the program you were trying to run and gives it the same rights. These rights allow the virus to copy itself, install itself in memory or release its payload. these viruses Infects over networks.
The internet has made it easier than ever to distribute programs, giving these viruses new opportunities to spread.
 Jerusalem- On Friday 13th deletes every program run on the computer.
 CIH (Chernobyl) - On the 26th of certain months, this virus will overwrite part of the BIOS chip, making the computer unusable. The virus also overwrites the hard disk.
 Remote Explorer - WNT/RemExp (Remote Explorer) infects Windows NT executables. It was the first virus that could run as a service, i.e. run on NT systems even when no-one is logged in. Parasitic viruses infects executables by companion, link, overwrite, insert, prep end, append techniques

a) Companion virus
A companion virus does not modify its host directly. Instead it maneuvers the operating system to execute itself instead of the host file. Sometimes this is done by renaming the host file into some other name, and then grant the virus file the name of the original program. Or the virus infects an .EXE file by creating a .COM file with the same name in the same directory. DOS will always execute a .COM file first if only the program name is given, so if you type “EDIT” on a DOS prompt, and there is an EDIT.COM and EDIT.EXE in the same directory, the EDIT.COM is executed.
b) Linking Virus
A link virus makes changes in the low-level workings of the file system, so that program names do no longer point to the original program, but to a copy of the virus. It makes it possible to have only one instance of the virus, which all program names point to.

Limits and Fits, Tolerance Dimensioning

2009-10-01T11:58:00.000-07:00

Limits and Fits, Tolerance Dimensioning

Definitions:nominal size: The size designation used for generalidentification. The nominal size of a shaft and a hole are thesame. This value is often expressed as a fraction.basic size: The exact theoretical size of a part. This isthe value from which limit dimensions are computed. Basic size isa four decimal place equivalent to the nominal size. The number ofsignificant digits imply the accuracy of the dimension.

example: nominal size = 1 1/4basic size = 1.2500

design size: The ideal size for each component (shaft andhole) based upon a selected fit. The difference between the designsize of the shaft and the design size of the hole is equal to theallowance of the fit. The design size of a part corresponds to the Maximum Material Condition (MMC). That is, the largest shaft permitted by the limits and the smallest hole. Emphasis is placed upon the design size in the writing of the actual limit dimension, so the design size is placed in the top position of the pair.

tolerance: The total amount by which a dimension is allowed to vary. For fractional linear dimensions we have assumed a bilateral tolerance of 1/64 inch. For the fit of a shaft/holecombination, the tolerance is considered to be unilateral, that is, it is only applied in one direction from design size of the part. Standards for limits and fits state that tolerances are appliedsuch that the hole size can only vary larger from design size and the shaft size smaller.
basic hole system: Most common system for limit dimensions. In this system the design size of the hole is taken to be equivalent to the basic size for the pair (see above). This means that the lower (in size) limit of the hole dimension is equal to design size. The basic hole system is more frequently used since most hole generating devices are of fixed size (for example, drills, reams, etc.) When designing using purchased components with fixed outer diameters (bearings, bushings, etc.) a basic shaft system may be used.

allowance: The allowance is the intended difference in the sizes of mating parts. This allowance may be: positive (indicated with a "+" symbol), which means there is intended clearance between parts; negative("-"), for intentional interference: or "zero allowance" if the two parts are intended to be the "same size".This last case is common to selective assembly.

The extreme permissible values of a dimension are known as limits. The degree of tightness or looseness between two mating parts that are intended to act together is known as the fit of the parts. The character of the fit depends upon the use of the parts. Thus, the fit between members that move or rotate relative to each other, such as a shaft rotating in a bearing, is considerably different from the fit that is designed to prevent any relative motion between two parts, such as a wheel attached to an axle.

In selecting and specifying limits and fits for various applications, the interests of interchangeable manufacturing require that (1) standard definitions of terms relating to limits and fits be used; (2) preferred basic sizes be selected wherever possible to be reduce material and tool costs; (3) limits be based upon a series of preferred tolerances and allowances; and (4) a uniform system of applying tolerances (bilateral or unilateral) be used.

Introduction to CAN (Controlled Area Network)

2009-10-01T11:54:00.001-07:00

Introduction to CAN (Controlled Area Network)

OVERVIEW

CAN was originally developed by the German company, Robert Bosch, for use in cars, to provide a cost-effective communications bus for in-car electronics and as alternative to expensive, cumbersome and unreliable wiring looms and connectors. The car industry continues to use CAN for an increasing number of applications, but because of its proven reliability and robustness, CAN is now also being used in many other control applications. Intra-vehicular communication:
A typical vehicle has a large number of electronic control systems
The growth of automotive electronics is a result of:Customers wish for better comfort and better safety.Government requirements for improved emission controlReduced fuel consumption
Some of such control systemsEngine timingGearbox and carburetor throttle controlAnti-block systems (ABS)Acceleration skid control (ASC)

The complexity of the functions implemented by these electronic control systems necessitates communication between them.In addition, a number of systems are being developed which will cover more than one device. For exampleASC requires the interplay of the engine timing and carburetor control in order to reduce torque when drive wheel slippage occurs.In the electronic gearbox control, the ease of gear changing can be improved by a brief adjustment to ignition timing

How do we connect these control devices?
With conventional systems, data is exchanged by means of dedicated signal lines.
But this is becoming increasingly difficult and expensive as control functions become ever more complex.

In the case of complex control systems in particular, the number of connections cannot be increased much further.

Solution: Use Field bus networks for connecting the control devices

FIELD BUS NETWORKS

Field buses are communication technologies and products used in vehicular, automation and process control industries.
Proprietary Field busesProprietary Field buses are an intellectual property of a particular company or body.

Open Field busesFor a Field bus to be Open, it must satisfy the following criteria.The full Field bus Specification must be published and available at a reasonable price. Critical ASIC components must be available, also at a reasonable price. Well defined validation process, open to all of the Field bus users.

Field bus Advantages:

I.Reduces the complexity of the control system in terms of hardware outlay.
II.Resulting in the reduced complexity of the control system, project design engineering is made simpler, more efficient and conversely less expensive.

III.By selecting a recognized and well established system, this will make the Fieldbus equipment in you plant or plants interchangeable between suppliers.

IV.The need to be concerned about connections, compatibility and other potential problems is eradicated.

What constitutes a Field bus?The specification of a Field bus should ideally cover all of the seven layers of the OSI model as shown below,.

FEATURES OF CANCAN features are as follows:-

CAN is a robust protocol – essential for automotive applicationsSO 11898 and SAE/J2411 are open standardsWell documented and fully supported worldwideChoice of three CAN physical layer optionsHigh-speed (HS)for high data ratesFault-tolerant (FT)for additional robustnessSingle-wire (SW)for minimum wiringAny node can access the bus when the bus is quiet.Non- destructive bit-wise arbitration to allow 100% use of bandwidth without loss of data.Variable message priority based on 11-bit (or 29 bit) packet identifier.Peer- to-Peer and multi-cast receptionAutomatic error detection, signaling and retries.Data packets 8 bytes long

BENEFITS OF CAN

Can is a fast serial Bus that designed to provide An efficientReliable and Very economical link between sensors & actuatorsCan uses a twisted pair cables to communicate at speed up to 1 Mbit/s up to 40 devices.Originally CAN is developed to simplify the wiring in automobiles.CAN field buses are now used in machine and factory automation products as well.

CAN History

In the early 1980s, engineers at Bosch were evaluating existing serial bus systems regarding their possible use in passenger cars. Because none of the available network protocols were able to fulfill the requirements of the automotive engineers, Uwe Kiencke started the development of a new serial bus system in 1983.

The new bus protocol was mainly supposed to add new functionality – the reduction of wiring harnesses was just a by-product, but not the driving force behind the development of CAN. Engineers from Mercedes-Benz got involved early on in the specification phase of the new serial bus system, and so did Intel as the potential main semiconductor vendor. Professor Dr. Wolfhard Lawrenz from the University of Applied Science in Braunschweig-Wolfenbüttel, Germany, who had been hired as a consultant, gave the new network protocol the name ‘Controller Area Network’. Professor Dr. Horst Wettstein from the University of Karlsruhe also provided academic assistance. In February of 1986, CAN was born: at the SAE congress in Detroit, the new bus system developed by Bosch was introduced as ‘Automotive Serial Controller Area Network’. Uwe Kiencke, Siegfried Dais and Martin Litschel introduced the multi-master network protocol. It was based on a non-destructive arbitration mechanism, which would grant bus access to the message with the highest priority without any delays.

There was no central bus master. Furthermore, the fathers of CAN – the individuals mentioned above plus Bosch employees Wolfgang Borst, Wolfgang Botzenhard, Otto Karl, Helmut Schilling, and Jan Unruh – had implemented several error detection mechanisms. The error handling also included the automatic disconnection of faulty bus nodes in order to keep up the communication between the remaining nodes. The transmitted messages were not identified by the node address of the transmitter or the receiver of the message (as in almost all other bus systems), but rather by their content. The identifier representing the content of the message also had the function of specifying the priority of the message within the system.
A lot of presentations and publications describing this innovative communication protocol followed, until in mid 1987 – two months ahead of schedule – Intel delivered the first CAN controller chip, the 82526.

It was the very first hardware implementation of the CAN protocol. In only four years, an idea had become reality. Shortly thereafter, Philips Semiconductors introduced the 82C200. These two earliest ancestors of the CAN controllers were quite different concerning acceptance filtering and message handling. On one hand, the FullCAN concept favored by Intel required less CPU load from the connected micro-controller than the BasicCAN implementation chosen by Philips. On the other hand, the FullCAN device was limited regarding the number of messages that could be received. The BasicCAN controller also required less silicon. In today’s CAN controllers, the ‘grandchildren’, very often different concepts of acceptance filtering and message handling have been implemented in the same module, making the misleading terms BasicCAN and FullCAN obsolete.

IMPLEMENTATION OF CAN

Communication is identical for all implementations of CAN. However, there are two principal hardware implementations. The two implementations are known as Basic CAN and Full CAN.
Basic CAN In Basic CAN configurations there is a tight link between the CAN controller and the associated microcontroller. The microcontroller, which will have other system related functions to administer, will be interrupted to deal with every CAN message.

Full CANFull CAN devices contain additional hardware to provide a message "server" that automatically receives and transmits CAN messages without interrupting the associated microcontroller. Full CAN devices carry out extensive acceptance filtering on incoming messages, service simultaneous requests, and generally reduce the load on the microcontroller.
Network SizesThe number of nodes that can exist on a single network is, theoretically, limited only by the number of available identifiers. However, the drive capabilities of currently available devices impose greater restrictions. Depending on the device types, up to 32 or 64 nodes per network is normal, but at least one manufacturer now provides devices that will allow networks of 110 nodes.

HOW CAN WORKS ?

Principle

Data messages transmitted from any node on a CAN bus do not contain addresses of either the transmitting node, or of any intended receiving node.Instead, the content of the message (e.g. Revolutions per Minute, Hopper Full, X-ray Dosage, etc.) is labeled by an identifier that is unique throughout the network. All other nodes on the network receive the message and each performs an acceptance test on the identifier to determine if the message, and thus its content, is relevant to that particular node. If the message is relevant, it will be processed; otherwise it is ignored. The unique identifier also determines the priority of the message. The lower the numerical value of the identifier, the higher the priority. In situations where two or more nodes attempt to transmit at the same time, a non-destructive arbitration technique guarantees that messages are sent in order of priority and that no messages are lost.

Bit encodingCAN use Non Return to Zero (NRZ) encoding (with bit-stuffing) for data communication on a differential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number of transitions and high resilience to external disturbance.
The physical busThe two wire bus is usually a twisted pair (shielded or unshielded). Flat pair (telephone type) cable also performs well but generates more noise itself, and may be more susceptible to external sources of noise.

The CAN protocol is an international standard defined in the ISO 11898. Beside the CAN protocol itself the conformance test for the CAN protocol is defined in the ISO 16845, which guarantees the interchangeability of the CAN chips.

CAN is based on the “broadcast communication mechanism”, which is based on a message-oriented transmission protocol. It defines message contents rather than stations and station addresses. Every message has a message identifier, which is unique within the whole network since it defines content and also the priority of the message.

This is important when several stations compete for bus access (bus arbitration), as a result of the content-oriented addressing. This allows for a modular concept and also permits the reception of multiple data and the synchronization of distributed processes. Also, data transmission is not based on the availability of specific types of stations, which allows simple servicing and upgrading of the network.

Message formats

CAN distinguishes four message formats: data, remote, error, and overload frames. Here we limit the discussion to the data frame. A data frame begins with the start-of-frame (SOF) bit. It is followed by an eleven-bit identifier and the remote transmission request (RTR) bit. The identifier and the RTR bit form the arbitration field. The control field consists of six bits and indicates how many bytes of data follow in the data field. The data field can be zero to eight bytes. The data field is followed by the cyclic redundancy checksum (CRC) field, which enables the receiver to check if the received bit sequence was corrupted. The two-bit acknowledgment (ACK) field is used by the transmitter to receive an acknowledgment of a valid frame from any receiver.

The end of a message frame is signalled through a seven-bit end-offrame (EOF). There is also an extended data frame with a twenty-nine-bit identifier (instead of eleven bits).The CAN protocol was internationally standardized in 1993 as ISO 11898-1. The development of CAN was mainly motivated by the need for new functionality, but it also reduced the need for wiring. The use of CAN in the automotive industry has caused mass production of CAN controllers. Today, CAN controllers are integrated on many microcontrollers and available at a low cost.

CAN ARCHITECTURE

Any node can access the bus when the bus is quiet
Non-destructive bit-wise arbitration to allow 100% use of the bandwidth without loss of data
Variable message priority based on 11-bit (or 29 bit) packet identifier
Peer-to-peer and multi-cast reception
Automatic error detection, signalling and retries
Data packets 8 bytes long
ERROR HANDLING PERFORMANCE OF CAN
Error detection and error handling are important for the performance of CAN. Because of complementary error detection mechanisms, the probability of having an undetected error is very small. Error detection is done in five different Vehicle Applications of Controller Area Network 7 ways in CAN: bit monitoring and bit stuffing, as well as frame check, ACK check, and CRC. Bit monitoring simply means that each transmitter monitors the bus level, and signals a bit error if the level does not agree with the transmitted signal. (Bit monitoring is not done during the arbitration phase.)

After having transmitted five identical bits, a node will always transmit the opposite bit. This extra bit is neglected by the receiver. The procedure is called bit stuffing, and it can be used to detect errors. The frame check consists of checking that the fixed bits of the frame have the values they are supposed to have, e.g., EOF consists of seven recessive bits. During the ACK in the message frame, all receivers are supposed to send a dominant level. If the transmitter, which transmits a recessive level, does not detect the dominant level, then an error is signalled by the ACK check mechanism.

Finally, the CRC is that every receiver calculates a checksum based on the message and compares it with the CRC field of the message. Every receiver node obviously tries to detect errors within each message. If an error is detected, it leads to an immediate and automatic retransmission of the incorrect message. In comparison to other network protocols, this mechanism leads to high data integrity and a short error recovery time. CAN thus provides elaborate procedure for error handling, including retransmission and reinitialization. The procedures have to be studied carefully for each application to ensure that the automated error handling is in line with the system requirements.

APPLICATIONS

CAN networks can be used as an embedded communication system for microcontrollers as well as an open communication system for intelligent devices. The CAN serial bus system, originally developed for use in automobiles, is increasingly being used in industrial field bus systems, the similarities are remarkable. In both cases some of the major requirements are: low cost, the ability to function in a difficult electrical environment, a high degree of real-time capability and ease of use.Some users, for example in the field of medical engineering, opted for CAN because they have to meet particularly stringent safety requirements.

Similar problems are faced by manufacturers of other equipment with very high safety or reliability requirements (e. g. robots, lifts and transportation systems). CAN controllers and interface chips are physically small. They are available as low-cost, off-the-shelf components. They will operate at high, real-time speeds, and in harsh environments. All these properties have led to CAN also being used in a wide range of applications other than the car industry. The benefits of reduced cost and improved reliability that the car industry gains by using CAN are now available to manufacturers of a wide range of products.

For example:

• Marine control and navigation systems

•Elevator control systems

• Agricultural machinery

• Production line control systems

• Machine tools

• large optical telescopes

• Photo copiers

• Medical systems

• Paper making and processing machinery

VEHICLE APPLICATIONS OF CAN

The Controller Area Network (CAN) is a serial bus communications protocol developed by Bosch in the early 1980s. It defines a standard for efficient and reliable communication between sensor, actuator, controller, and other nodes in real-time applications. CAN is the de facto standard in a large variety of networked embedded control systems.

The early CAN development was mainly supported by the vehicle industry: CAN is found in a variety of passenger cars, trucks, boats, spacecraft, and other types of vehicles. The protocol is also widely used today in industrial automation and other areas of networked embedded control, with applications in diverse products such as production machinery, medical equipment, building automation, weaving machines & wheelchairs.In the automotive industry, embedded control has grown from stand-alone systems to highly integrated and networked control systems. By networking electro-mechanical subsystems, it becomes possible to modularize functionalities and hardware, which facilitates reuse and adds capabilities. Fig. 1 shows an example of an electronic control unit (ECU) mounted on a diesel engine of a Scania truck. The ECU handles the control of engine, turbofan, etc. but also the CAN communication. Combining networks and mechatronic modules makes it possible to reduce both the cabling and the number. The work of K. H. Johansson was partially supported by the European Commission through the ARTIST2 Network of Excellence on Embedded Systems Design, by the Swedish Research Council, and by the Swedish Foundation for Strategic Research through an Individual Grant for the Advancement of Research Leaders.
The work of M. T¨orngren was partially supported by the European Commission through ARTIST2 and by the Swedish Foundation for Strategic Research through the project SAVE of connectors, which facilitates production and increases reliability. Introducing networks in vehicles also makes it possible to more efficiently carry out diagnostics and to coordinate the operation of the separate subsystems.

Heavy Vehicles

Most existing vehicle model libraries are designed primarily for cars. Heavy vehicles have a number of sub-systems which are not present in passenger cars. Particularly the engine/transmission system includes de-vices like an exhaust brake and possibly a retarder. Further, the cooling system also has a more prominent role than in cars, and coolant is often used both by the engine and the transmission.

Signalling Bus

A key issue in an architecture which contains both physical plant and controller models is the handling of electrical signals. The controllers need to exchange data among themselves and they need to exchange signals with sensors and actuators. For our applications the actual signalling behaviour is not that important, an ideal communications model is sufficient. For the communication between a plant and its controller, standard library in-ports and out-ports are used. The communication between the controllers was a tougher case. Two implementations of the same controller may not have the same signalling needs, thus it must be possible to change the set of signals sent between control units. Separate input and output ports for all links between control units in the vehicle would create an un-decipherable graphical mess. Some type of signalling bus is needed. Both the standard library bus connectors and the type of bus used in the vehicle modelling architecture proposal by Tiller Etal were evaluated. We did not find enough information about the inter-controller communication in the Tiller paper to implement that system. Our main problem was to find a way of having compatible connectors in all controllers, without modifying the code of every controller when a signal was added to the bus. The standard library bus does not solve that problem, since it requires all signals to be declared in the connector. Eventually we chose a simpler solution based on a common connector called ”CAN” with a replace-able variable, called ”protocol”, which contains all the signals. The protocol variable can easily be redeclared into a type which contains exactly the signals broad-cast on the bus in a particular model. Different implementations of the CAN connector are used for different signal buses in the vehicle.

Most of our control units are implemented through external function calls, thus the drawback of having no convenient graphical way of converting a signal from inport/ outport to bus format is minor.

Modern Communication Services

2009-08-27T12:39:00.001-07:00

Modern Communication Services

Society is becoming more informationally and visually oriented every day. Personal computing facilitates easy access, manipulation, storage, and exchange of information. These processes require reliable transmission of data information. Communicating documents by images and the use of high resolution graphics terminals provide a more natural and informative mode of human interaction than just voice and data. Video teleconferencing enhances group interaction at a distance. High definition entertainment video improves the quality of picture at the expense of higher transmission bit-rates, which may require new transmission means other than the present overcrowded radio spectrum. A modern Telecommunications network (such as the broadband network) must provide all these different services (multi-services) to the user.
Differences between traditional (telephony) and modern communication services

Conventional telephony communicates using:

* the voice medium only
* connects only two telephones per call
* uses circuits of fixed bit rate

In contrast, modern communication services depart from the conventional telephony service in these three essential aspects. Modern communication services can be:

* Multimedia
* point to point, and
* multi-rate

These aspects are examined Individually in the following three sub-sections.

* Multi-media: A multi-media call may communicate audio, data, still images, or full-motion video, or any combination of these media. Each medium has different demands for communication qualities, such as:
o bandwidth requirement
o signal latency within the network, and
o signal fidelity upon delivery by the network

Moreover, the information content of each medium may affect the information generated by other media. For example, voice could be transcribed into data via voice recognition and data commands may control the way voice and video are presented. These interactions most often occur at the communication terminals, but may also occur within the network .

* Multi-point: A multi-point call involves the setup of connections among more than two people. These connections can be multi-media. They can be one way or two way communications. These connections may be reconfigured many times within the duration of a call. A few examples will be used to contrast point-to-point communications versus multi-point communications. Traditional voice calls are predominantly two party calls, requiring a point-to-point connection using only the voice medium. To access pictorial information in a remote database would require a point-to-point connection that sends low bit-rate queries to the database, and high bit-rate video from the database. Entertainment video applications are largely point-to-multi-point connections, requiring one way communication of full motion video and audio from the program source to the viewers. Video teleconferencing involves connections among many parties, communicating voice, video, as well as data. Thus offering future services requires flexible management of the connection and media requests of a multi-point, multi-media communication call .
* Multi-rate A multi-rate service network is one which allocates transmission capacity flexibly to connections. A multi-media network has to support a broad range of bit-rates demanded by connections, not only because there are many communication media, but also because a communication medium may be encoded by algorithms with different bit-rates. For example, audio signals can be encoded with bit-rates ranging from less than 1 kbit/s to hundreds of kbit/s, using different encoding algorithms with a wide range of complexity and quality of audio reproduction. Similarly, full motion video signals may be encoded with bit-rates ranging from less than 1 Mbit/s to hundreds of Mbit/s. Thus a network transporting both video and audio signals may have to integrate traffic with a very broad range of bit-rates.

Light tree

2009-08-17T00:04:00.000-07:00

Light tree

Definition
The concept of light tree is introduced in a wavelength routed optical network, which employs wavelength -division multiplexing (WDM).
Depending on the underlying physical topology networks can be classified into three generations:

a).First Generation: these networks do not employ fiber optic technology; instead they employ copper-based or microwave technology. E.g. Ethernet.
b).Second Generation: these networks use optical fibers for data transmission but switching is performed in electronic domain. E.g. FDDI.
c).Third Generation: in these networks both data transmission and switching is performed in optical domain. E.g. WDM.

WDM wide area networks employ tunable lasers and filters at access nodes and optical/electronic switches at routing nodes. An access node may transmit signals on different wavelengths, which are coupled into the fiber using wavelength multiplexers. An optical signal passing through an optical wavelength-routing switch (WRS) may be routed from an output fiber without undergoing opto-electronic conversion.

A light path is an all-optical channel, which may be used to carry circuit switched traffic, and it may span multiple fiber links. Assigning a particular wavelength to it sets these up. In the absence of wavelength converters, a light path would occupy the same wavelength continuity constraint.

A light path can create logical (or virtual) neighbors out of nodes that may be geographically far apart from each other. A light path carries not only the direct traffic between the nodes it interconnects, but also the traffic from nodes upstream of the source to nodes upstream of the destination. A major objective of light path communication is to reduce the number of hops a packet has to traverse.

Under light path communication, the network employs an equal number of transmitters and receivers because each light path operates on a point-to-point basis. However this approach is not able to fully utilize all of the wavelengths on all of the fiber links in the network, also it is not able to fully exploit all the switching capability of each WRS.
A light tree is a point to point multipoint all optical channel, which may span multiple fiber links. Hence, a light tree enables single-hop communication between a source node and a set of destination nodes. Thus, a light tree based virtual topology can significantly reduce the hop distance, thereby increasing the network throughput.

Requirements:
1. Multicast -capable wavelength routing switches (MWRS) at every node in the netwok.
2. More optical amplifiers in the network.

LIDAR

2009-08-16T23:54:00.000-07:00

LIDAR

LIDAR (Light Detection and Ranging) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses. Like the similar radar technology, which uses radio waves, which is light that is not in the visible spectrum, the range to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signal. LIDAR technology has application in Geomatics, archaeology, geography, geology, geomorphology, seismology, remote sensing and atmospheric physics.[1] Other terms for LIDAR include ALSM (Airborne Laser Swath Mapping) and laser altimetry. The acronym LADAR (Laser Detection and Ranging) is often used in military contexts. The term laser radar is also in use but is misleading because it uses laser light and not the radiowaves that are the basis of conventional radar.

General description

The primary difference between lidar and radar is that with lidar, much shorter wavelengths of the electromagnetic spectrum are used, typically in the ultraviolet, visible, or near infrared. In general it is possible to image a feature or object only about the same size as the wavelength, or larger. Thus lidar is highly sensitive to aerosols and cloud particles and has many applications in atmospheric research and meteorology.

An object needs to produce a dielectric discontinuity in order to reflect the transmitted wave. At radar (microwave or radio) frequencies, a metallic object produces a significant reflection. However non-metallic objects, such as rain and rocks produce weaker reflections and some materials may produce no detectable reflection at all, meaning some objects or features are effectively invisible at radar frequencies. This is especially true for very small objects (such as single molecules and aerosols).

Lasers provide one solution to these problems. The beam densities and coherency are excellent. Moreover the wavelengths are much smaller than can be achieved with radio systems, and range from about 10 micrometers to the UV (ca. 250 nm). At such wavelengths, the waves are "reflected" very well from small objects. This type of reflection is called backscattering. Different types of scattering are used for different lidar applications, most common are Rayleigh scattering, Mie scattering and Raman scattering as well as fluorescence. The wavelengths are ideal for making measurements of smoke and other airborne particles (aerosols), clouds, and air molecules.

A laser typically has a very narrow beam which allows the mapping of physical features with very high resolution compared with radar. In addition, many chemical compounds interact more strongly at visible wavelengths than at microwaves, resulting in a stronger image of these materials. Suitable combinations of lasers can allow for remote mapping of atmospheric contents by looking for wavelength-dependent changes in the intensity of the returned signal.

Lidar has been used extensively for atmospheric research and meteorology. With the deployment of the GPS in the 1980's precision positioning of aircraft became possible. GPS based surveying technology has made airborne surveying and mapping applications possible and practical. Many have been developed, using downward-looking lidar instruments mounted in aircraft or satellites. A recent example is the NASA Experimental Advanced Research Lidar.

LIDAR is an acronym for LIght Detection And Ranging.
What can you do with LIDAR?

* Measure distance
* Measure speed
* Measure rotation
* Measure chemical composition and concentration

of a remote target where the target can be a clearly defined object, such as a vehicle, or a diffuse object such as a smoke plume or clouds.

Applications

Other than those applications mentioned above, there are a wide variety of applications of LIDAR.

Archaeology

LiDAR has many applications in the field of archaeology including aiding in the planning of field campaigns, mapping features beneath forest canopy, and providing an overview of broad, continuous features that may be indistinguishable on the ground. LiDAR can also provide archaeologists with the ability to create high-resolution digital elevation models (DEMs) of archaeological sites that can reveal micro-topography that are otherwise hidden by vegetation. LiDAR-derived products can be easily integrated into a Geographic Information System (GIS) for analysis and interpretation. For example at Fort Beausejour - Fort Cumberland National Historic Site, Canada, previously undiscovered archaeological features have been mapped that are related to the siege of the Fort in 1755. Features that could not be distinguished on the ground or through aerial photography were identified by overlaying hillshades of the DEM created with artificial illumination from various angles. With LiDAR the ability to produce high-resolution datasets quickly and relatively cheaply can be an advantage. Beyond efficiency, its ability to penetrate forest canopy has led to the discovery of features that were not distinguishable through traditional geo-spatial methods and are difficult to reach through field surveys.

Meteorology

The first LIDARs were used for studies of atmospheric composition, structure, clouds, and aerosols. Initially based on ruby lasers, LIDARs for meteorological applications were constructed shortly after the invention of the laser and represent one of the first applications of laser technology.

Elastic backscatter LIDAR is the simplest type of lidar and is typically used for studies of aerosols and clouds. The backscattered wavelength is identical to the transmitted wavelength, and the magnitude of the received signal at a given range depends on the backscatter coefficient of scatterers at that range and the extinction coefficients of the scatterers along the path to that range. The extinction coefficient is typically the quantity of interest.

Differential Absorption LIDAR (DIAL) is used for range-resolved measurements of a particular gas in the atmosphere, such as ozone, carbon dioxide, or water vapor. The LIDAR transmits two wavelengths: an "on-line" wavelength that is absorbed by the gas of interest and an off-line wavelength that is not absorbed. The differential absorption between the two wavelengths is a measure of the concentration of the gas as a function of range. DIAL LIDARs are essentially dual-wavelength elastic backscatter LIDARS.

Raman LIDAR is also used for measuring the concentration of atmospheric gases, but can also be used to retrieve aerosol parameters as well. Raman LIDAR exploits inelastic scattering to single out the gas of interest from all other atmospheric constituents. A small portion of the energy of the transmitted light is deposited in the gas during the scattering process, which shifts the scattered light to a longer wavelength by an amount that is unique to the species of interest. The higher the concentration of the gas, the stronger the magnitude of the backscattered signal.

Doppler LIDAR is used to measure wind speed along the beam by measuring the frequency shift of the backscattered light. Scanning LIDARs, such as NASA's HARLIE LIDAR, have been used to measure atmospheric wind velocity in a large three dimensional cone. ESA's wind mission ADM-Aeolus will be equipped with a Doppler LIDAR system in order to provide global measurements of vertical wind profiles. A doppler LIDAR system was used in the 2008 Summer Olympics to measure wind fields during the yacht competition. Doppler LIDAR systems are also now beginning to be successfully applied in the renewable energy sector to acquire wind speed, turbulence, wind veer and wind shear data. Both pulsed and continuous wave systems are being used. Pulsed systems using signal timing to obtain vertical distance resolution, whereas continuous wave systems rely on detector focusing.

Geology

In geology and seismology a combination of aircraft-based LIDAR and GPS have evolved into an important tool for detecting faults and measuring uplift. The output of the two technologies can produce extremely accurate elevation models for terrain that can even measure ground elevation through trees. This combination was used most famously to find the location of the Seattle Fault in Washington, USA. This combination is also being used to measure uplift at Mt. St. Helens by using data from before and after the 2004 uplift. Airborne LIDAR systems monitor glaciers and have the ability to detect subtle amounts of growth or decline. A satellite based system is NASA's ICESat which includes a LIDAR system for this purpose. NASA's Airborne Topographic Mapper is also used extensively to monitor glaciers and perform coastal change analysis.

Physics and Astronomy

A world-wide network of observatories uses lidars to measure the distance to reflectors placed on the moon, allowing the moon's position to be measured with mm precision and tests of general relativity to be done. MOLA, the Mars Orbiting Laser Altimeter, used a LIDAR instrument in a Mars-orbiting satellite (the NASA Mars Global Surveyor) to produce a spectacularly precise global topographic survey of the red planet.

In September, 2008, NASA's Phoenix Lander used LIDAR to detect snow in the atmosphere of Mars.

In atmospheric physics, LIDAR is used as a remote detection instrument to measure densities of certain constituents of the middle and upper atmosphere, such as potassium, sodium, or molecular nitrogen and oxygen. These measurements can be used to calculate temperatures. LIDAR can also be used to measure wind speed and to provide information about vertical distribution of the aerosol particles.

At the JET nuclear fusion research facility, in the UK near Abingdon, Oxfordshire, LIDAR Thomson Scattering is used to determine Electron Density and Temperature profiles of the plasma.

Biology and conservation

LIDAR has also found many applications in forestry. Canopy heights, biomass measurements, and leaf area can all be studied using airborne LIDAR systems. Similarly, LIDAR is also used by many industries, including Energy and Railroad, and the Department of Transportation as a faster way of surveying. Topographic maps can also be generated readily from LIDAR, including for recreational use such as in the production of orienteering maps.

In oceanography, LiDAR is used for estimation of phytoplankton fluorescence and generally biomass in the surface layers of the ocean. Another application is airborne lidar bathymetry of sea areas too shallow for hydrographic vessels.

Redwood ecology

The Save-the-Redwoods League is undertaking a project to map the tall redwoods on California's northern coast. LIDAR allows research scientists to not only measure the height of previously unmapped trees but to determine the biodiversity of the redwood forest. Dr. Stephen Sillett who is working with the League on the North Coast LIDAR project claims this technology will be useful in directing future efforts to preserve and protect ancient redwood trees.

Military and law enforcement

One situation where LIDAR has notable non-scientific application is in traffic speed law enforcement, for vehicle speed measurement, as a technology alternative to radar guns. The technology for this application is small enough to be mounted in a hand held camera "gun" and permits a particular vehicle's speed to be determined from a stream of traffic. Unlike RADAR which relies on doppler shifts to directly measure speed, police lidar relies on the principle of time-of-flight to calculate speed. The equivalent radar based systems are often not able to isolate particular vehicles from the traffic stream and are generally too large to be hand held. LIDAR has the distinct advantage of being able to pick out one vehicle in a cluttered traffic situation as long as the operator is aware of the limitations imposed by the range and beam divergence. Contrary to popular belief LIDAR does not suffer from “sweep” error when the operator uses the equipment correctly and when the LIDAR unit is equipped with algorithms that are able to detect when this has occurred. A combination of signal strength monitoring, receive gate timing, target position prediction and pre-filtering of the received signal wavelength prevents this from occurring. Should the beam illuminate sections of the vehicle with different reflectivity or the aspect of the vehicle changes during measurement that causes the received signal strength to be changed then the LIDAR unit will reject the measurement thereby producing speed readings of high integrity. For LIDAR units to be used in law enforcement applications a rigorous approval procedure is usually completed before deployment. Jelly-bean shaped vehicles are usually equipped with a vertical registration plate that, when illuminated causes a high integrity reflection to be returned to the LIDAR, many reflections and an averaging technique in the speed measurement process increase the integrity of the speed reading. In locations that do not require that a front or rear registration plate is fitted headlamps and rear-reflectors provide an almost ideal retro-reflective surface overcoming the reflections from uneven or non-compliant reflective surfaces thereby eliminating “sweep” error. It is these mechanisms which cause concern that LIDAR is somehow unreliable. Most traffic LIDAR systems send out a stream of approximately 100 pulses over the span of three-tenths of a second. A "black box," proprietary statistical algorithm picks and chooses which progressively shorter reflections to retain from the pulses over the short fraction of a second.

Military applications are not yet known to be in place and are possibly classified, but a considerable amount of research is underway in their use for imaging. Their higher resolution makes them particularly good for collecting enough detail to identify targets, such as tanks. Here the name LADAR is more common.

Five LIDAR units produced by the German company Sick AG were used for short range detection on Stanley, the autonomous car that won the 2005 DARPA Grand Challenge.

Vehicles

Lidar has been used to create Adaptive Cruise Control (ACC) systems for automobiles. Systems such as those by Siemens and Hella use a lidar device mounted in the front of the vehicle to monitor the distance between the vehicle and any vehicle in front of it. Often, the lasers are placed onto the bumper. In the event the vehicle in front slows down or is too close, the ACC applies the brakes to slow the vehicle. When the road ahead is clear, the ACC allows the vehicle to speed up to speed preset by the driver.

Imaging

3-D imaging is done with both scanning and non-scanning systems. "3-D gated viewing laser radar" is a non-scanning laser radar system that applies the so-called gated viewing technique. The gated viewing technique applies a pulsed laser and a fast gated camera. There are ongoing military research programmes in Sweden, Denmark, the USA and the UK with 3-D gated viewing imaging at several kilometers range with a range resolution and accuracy better than ten centimeters.

Coherent Imaging Lidar is possible using Synthetic Array Heterodyne Detection which is a form of Optical heterodyne detection that enables a staring single element receiver to act as though it were an imaging array.

Imaging LIDAR can also be performed using arrays of high speed detectors and modulation sensitive detectors arrays typically built on single chips using CMOS and hybrid CMOS / CCD fabrication techniques. In these devices each pixel performs some local processing such as demodulation or gating at high speed down converting the signals to video rate so that the array may be read like a camera. Using this technique many thousands of pixels / channels may be acquired simultaneously. In practical systems the limitation is light budget rather than parallel acquisition.

LIDAR has been used in the recording of a music video without cameras. The video for the song "House of Cards" by Radiohead is believed to be the first use of real-time 3D laser scanning to record a music video.

3D Mapping

Airborne LIDAR sensors are used by companies in the Remote Sensing area to create point clouds of the earth ground for further processing (e.g. used in forestry).

RADAR

2009-08-12T05:40:00.000-07:00

RADAR
Radar is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for radio detection and ranging. The term has since entered the English language as a standard word, radar, losing the capitalization. Radar was originally called RDF (Radio Direction Finder, now used as a totally different device) in the United Kingdom.

A radar system has a transmitter that emits microwaves or radio waves. These waves are in phase when emitted, and when they come into contact with an object are scattered in all directions. The signal is thus partly reflected back and it has a slight change of wavelength (and thus frequency) if the target is moving. The receiver is usually, but not always, in the same location as the transmitter. Although the signal returned is usually very weak, the signal can be amplified through use of electronic techniques in the receiver and in the antenna configuration. This enables radar to detect objects at ranges where other emissions, such as sound or visible light, would be too weak to detect. Radar uses include meteorological detection of precipitation, measuring ocean surface waves, air traffic control, police detection of speeding traffic, determining the speed of basesballs and by the military.

RAdio Detection And Ranging ,in short RADAR relies on sending and receiving electromagnetic radiation, usually in the form of radio waves (see Radio) or microwaves. Electromagnetic radiation is energy that moves in waves at or near the speed of light. The characteristics of electromagnetic waves depend on their wavelength. Gamma rays and X rays have very short wavelengths. Visible light is a tiny slice of the electromagnetic spectrum with wavelengths longer than X rays, but shorter than microwaves. Radar systems use long-wavelength electromagnetic radiation in the microwave and radio ranges. Because of their long wavelengths, radio waves and microwaves tend to reflect better than shorter wavelength radiation, which tends to scatter or be absorbed before it gets to the target. Radio waves at the long-wavelength end of the spectrum will even reflect off of the atmospheres ionosphere, a layer of electrically-charged particles in the earths atmosphere. The challenges for radar are stealth technology,clutter,jamming. It has certain applications like the traffic control,maritime navigation,millitary safety,air traffic control,meteorology etc.

History

Several inventors, scientists, and engineers contributed to the development of radar. The first to use radio waves to detect "the presence of distant metallic objects" was Christian Hülsmeyer, who in 1904 demonstrated the feasibility of detecting the presence of a ship in dense fog, but not its distance.He received Reichspatent Nr. 165546 for his pre-radar device in April 1904, and later patent 169154 for a related amendment for ranging. He also received a patent[9] in England for his telemobiloscope on September 22, 1904.

In August 1917 Nikola Tesla first established principles regarding frequency and power level for the first primitive radar units. He stated, " by their [standing electromagnetic waves] use we may produce at will, from a sending station, an electrical effect in any particular region of the globe; [with which] we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed."

Before the Second World War developments by the Americans, the Germans, the French, the Soviets, and the British led to the modern version of radar. In 1934 the French Émile Girardeau stated he was building a radar system "conceived according to the principles stated by Tesla" and obtained a patent (French Patent n° 788795 in 1934) for a working dual radar system, a part of which was installed on the Normandie liner in 1935. The same year, American Dr. Robert M. Page tested the first monopulse radar and the Soviet military engineer P.K.Oschepkov, in collaboration with Leningrad Electrophysical Institute, produced an experimental apparatus RAPID capable of detecting an aircraft within 3 km of a receiver.[16] Hungarian Zoltán Bay produced a working model by 1936 at the Tungsram laboratory in the same vein.

However, it was the British who were the first to fully exploit it as a defence against aircraft attack. This was spurred on by fears that the Germans were developing death rays. Following a study of the possibility of propagating electromagnetic energy and the likely effect, the British scientists asked by the Air Ministry to investigate concluded that a death ray was impractical but detection of aircraft appeared feasible. Robert Watson-Watt demonstrated to his superiors the capabilities of a working prototype and patented the device in 1935 (British Patent GB593017) It served as the basis for the Chain Home network of radars to defend Great Britain.

The war precipitated research to find better resolution, more portability and more features for radar. The post-war years have seen the use of radar in fields as diverse as air traffic control, weather monitoring, astrometry and road speed control.

Principles

The radar dish, or antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter. The time it takes for the reflected waves to return to the dish enables a computer to calculate how far away the object is, its radial velocity and other characteristics.

Reflection

Electromagnetic waves reflect (scatter) from any large change in the dielectric or diamagnetic constants. This means that a solid object in air or a vacuum, or other significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves. This is particularly true for electrically conductive materials, such as metal and carbon fiber, making radar particularly well suited to the detection of aircraft and ships. Radar absorbing material, containing resistive and sometimes magnetic substances, is used on military vehicles to reduce radar reflection. This is the radio equivalent of painting something a dark color.

Radar waves scatter in a variety of ways depending on the size (wavelength) of the radio wave and the shape of the target. If the wavelength is much shorter than the target's size, the wave will bounce off in a way similar to the way light is reflected by a mirror. If the wavelength is much longer than the size of the target, the target is polarized (positive and negative charges are separated), like a dipole antenna. This is described by Rayleigh scattering, an effect that creates the Earth's blue sky and red sunsets. When the two length scales are comparable, there may be resonances. Early radars used very long wavelengths that were larger than the targets and received a vague signal, whereas some modern systems use shorter wavelengths (a few centimeters or shorter) that can image objects as small as a loaf of bread.

Short radio waves reflect from curves and corners, in a way similar to glint from a rounded piece of glass. The most reflective targets for short wavelengths have 90° angles between the reflective surfaces. A structure consisting of three flat surfaces meeting at a single corner, like the corner on a box, will always reflect waves entering its opening directly back at the source. These so-called corner reflectors are commonly used as radar reflectors to make otherwise difficult-to-detect objects easier to detect, and are often found on boats in order to improve their detection in a rescue situation and to reduce collisions.

For similar reasons, objects attempting to avoid detection will angle their surfaces in a way to eliminate inside corners and avoid surfaces and edges perpendicular to likely detection directions, which leads to "odd" looking stealth aircraft. These precautions do not completely eliminate reflection because of diffraction, especially at longer wavelengths. Half wavelength long wires or strips of conducting material, such as chaff, are very reflective but do not direct the scattered energy back toward the source. The extent to which an object reflects or scatters radio waves is called its radar cross section.

Polarization

In the transmitted radar signal, the electric field is perpendicular to the direction of propagation, and this direction of the electric field is the polarization of the wave. Radars use horizontal, vertical, linear and circular polarization to detect different types of reflections. For example, circular polarization is used to minimize the interference caused by rain. Linear polarization returns usually indicate metal surfaces. Random polarization returns usually indicate a fractal surface, such as rocks or soil, and are used by navigation radars.

Interference

Radar systems must overcome unwanted signals in order to focus only on the actual targets of interest. These unwanted signals may originate from internal and external sources, both passive and active. The ability of the radar system to overcome these unwanted signals defines its signal-to-noise ratio (SNR). SNR is defined as the ratio of a signal power to the noise power within the desired signal.

In less technical terms, SNR compares the level of a desired signal (such as targets) to the level of background noise. The higher a system's SNR, the better it is in isolating actual targets from the surrounding noise signals.

Noise

Signal noise is an internal source of random variations in the signal, which is generated by all electronic components. Noise typically appears as random variations superimposed on the desired echo signal received in the radar receiver. The lower the power of the desired signal, the more difficult it is to discern it from the noise (similar to trying to hear a whisper while standing near a busy road). Noise figure is a measure of the noise produced by a receiver compared to an ideal receiver, and this needs to be minimized.

Noise is also generated by external sources, most importantly the natural thermal radiation of the background scene surrounding the target of interest. In modern radar systems, due to the high performance of their receivers, the internal noise is typically about equal to or lower than the external scene noise. An exception is if the radar is aimed upwards at clear sky, where the scene is so "cold" that it generates very little thermal noise.

There will be also flicker noise due to electrons transit, but depending on 1/f, will be much lower than thermal noise when the frequency is high. Hence, in pulse radar, the system will be always heterodyne. See intermediate frequency.

Clutter

Clutter refers to radio frequency (RF) echoes returned from targets which are uninteresting to the radar operators. Such targets include natural objects such as ground, sea, precipitation (such as rain, snow or hail), sand storms, animals (especially birds), atmospheric turbulence, and other atmospheric effects, such as ionosphere reflections and meteor trails. Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as chaff.

Some clutter may also be caused by a long radar waveguide between the radar transceiver and the antenna. In a typical plan position indicator (PPI) radar with a rotating antenna, this will usually be seen as a "sun" or "sunburst" in the centre of the display as the receiver responds to echoes from dust particles and misguided RF in the waveguide. Adjusting the timing between when the transmitter sends a pulse and when the receiver stage is enabled will generally reduce the sunburst without affecting the accuracy of the range, since most sunburst is caused by a diffused transmit pulse reflected before it leaves the antenna.

While some clutter sources may be undesirable for some radar applications (such as storm clouds for air-defence radars), they may be desirable for others (meteorological radars in this example). Clutter is considered a passive interference source, since it only appears in response to radar signals sent by the radar.

There are several methods of detecting and neutralizing clutter. Many of these methods rely on the fact that clutter tends to appear static between radar scans. Therefore, when comparing subsequent scans echoes, desirable targets will appear to move and all stationary echoes can be eliminated. Sea clutter can be reduced by using horizontal polarization, while rain is reduced with circular polarization (note that meteorological radars wish for the opposite effect, therefore using linear polarization the better to detect precipitation). Other methods attempt to increase the signal-to-clutter ratio.

Constant False Alarm Rate (CFAR, a form of Automatic Gain Control, or AGC) is a method relying on the fact that clutter returns far outnumber echoes from targets of interest. The receiver's gain is automatically adjusted to maintain a constant level of overall visible clutter. While this does not help detect targets masked by stronger surrounding clutter, it does help to distinguish strong target sources. In the past, radar AGC was electronically controlled and affected the gain of the entire radar receiver. As radars evolved, AGC became computer-software controlled, and affected the gain with greater granularity, in specific detection cells.

Clutter may also originate from multipath echoes from valid targets due to ground reflection, atmospheric ducting or ionospheric reflection/refraction. This clutter type is especially bothersome, since it appears to move and behave like other normal (point) targets of interest, thereby creating a ghost. In a typical scenario, an aircraft echo is multipath-reflected from the ground below, appearing to the receiver as an identical target below the correct one. The radar may try to unify the targets, reporting the target at an incorrect height, or - worse - eliminating it on the basis of jitter or a physical impossibility. These problems can be overcome by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below ground or above a certain height. In newer Air Traffic Control (ATC) radar equipment, algorithms are used to identify the false targets by comparing the current pulse returns, to those adjacent, as well as calculating return improbabilities due to calculated height, distance, and radar timing.

Jamming

Radar jamming refers to radio frequency signals originating from sources outside the radar, transmitting in the radar's frequency and thereby masking targets of interest. Jamming may be intentional, as with an electronic warfare (EW) tactic, or unintentional, as with friendly forces operating equipment that transmits using the same frequency range. Jamming is considered an active interference source, since it is initiated by elements outside the radar and in general unrelated to the radar signals.

Jamming is problematic to radar since the jamming signal only needs to travel one-way (from the jammer to the radar receiver) whereas the radar echoes travel two-ways (radar-target-radar) and are therefore significantly reduced in power by the time they return to the radar receiver. Jammers therefore can be much less powerful than their jammed radars and still effectively mask targets along the line of sight from the jammer to the radar (Mainlobe Jamming). Jammers have an added effect of affecting radars along other lines of sight, due to the radar receiver's sidelobes (Sidelobe Jamming).

Mainlobe jamming can generally only be reduced by narrowing the mainlobe solid angle, and can never fully be eliminated when directly facing a jammer which uses the same frequency and polarization as the radar. Sidelobe jamming can be overcome by reducing receiving sidelobes in the radar antenna design and by using an omnidirectional antenna to detect and disregard non-mainlobe signals. Other anti-jamming techniques are frequency hopping and polarization. See Electronic counter-counter-measures for details.

Interference has recently become a problem for C-band (5.66 GHz) meteorological radars with the proliferation of 5.4 GHz band WiFi equipment.

Radar engineering

A radars components are:

* A transmitter that generates the radio signal with an oscillator such as a klystron or a magnetron and controls its duration by a modulator.
* A waveguide that links the transmitter and the antenna.
* A duplexer that serves as a switch between the antenna and the transmitter or the receiver for the signal when the antenna is used in both situations.
* A receiver. Knowing the shape of the desired received signal (a pulse), an optimal receiver can be designed using a matched filter.
* An electronic section that controls all those devices and the antenna to perform the radar scan ordered by a software.
* A link to end users.

Antenna design

Radio signals broadcast from a single antenna will spread out in all directions, and likewise a single antenna will receive signals equally from all directions. This leaves the radar with the problem of deciding where the target object is located.

Early systems tended to use omni-directional broadcast antennas, with directional receiver antennas which were pointed in various directions. For instance the first system to be deployed, Chain Home, used two straight antennas at right angles for reception, each on a different display. The maximum return would be detected with an antenna at right angles to the target, and a minimum with the antenna pointed directly at it (end on). The operator could determine the direction to a target by rotating the antenna so one display showed a maximum while the other shows a minimum.

One serious limitation with this type of solution is that the broadcast is sent out in all directions, so the amount of energy in the direction being examined is a small part of that transmitted. To get a reasonable amount of power on the "target", the transmitting aerial should also be directional.

Parabolic reflector

More modern systems use a steerable parabolic "dish" to create a tight broadcast beam, typically using the same dish as the receiver. Such systems often combine two radar frequencies in the same antenna in order to allow automatic steering, or radar lock.

Parabolic reflectors can be either symmetric parabolas or spoiled parabolas:

* Symmetric parabolic antennas produce a narrow "pencil" beam in both the X and Y dimensions and consequently have a higher gain. The NEXRAD Pulse-Doppler weather radar uses a symmetric antenna to perform detailed volumetric scans of the atmosphere.
* Spoiled parabolic antennas produce a narrow beam in one dimension and a relatively wide beam in the other. This feature is useful if target detection over a wide range of angles is more important than target location in three dimensions. Most 2D surveillance radars use a spoiled parabolic antenna with a narrow azimuthal beamwidth and wide vertical beamwidth. This beam configuration allows the radar operator to detect an aircraft at a specific azimuth but at an indeterminate height. Conversely, so-called "nodder" height finding radars use a dish with a narrow vertical beamwidth and wide azimuthal beamwidth to detect an aircraft at a specific height but with low azimuthal precision.

Types of scan

* Primary Scan: A scanning technique where the main antenna aerial is moved to produce a scanning beam, examples include circular scan, sector scan etc
* Secondary Scan: A scanning technique where the antenna feed is moved to produce a scanning beam, examples include conical scan, unidirectional sector scan, lobe switching etc.
* Palmer Scan: A scanning technique that produces a scanning beam by moving the main antenna and its feed. A Palmer Scan is a combination of a Primary Scan and a Secondary Scan.

Synergetics

2009-08-12T05:33:00.000-07:00

Synergetics

Inpired by the Laser theory and founded by Hermann Haken and Arne Wunderlin, Synergetics is an interdisciplinary science explaining the formation and self-organization of patterns and structures in 'open' systems far from thermodynamic equilibrium. Self-organization requires a 'macroscopic' system, consisting of many nonlinearly interacting subsystems. Depending on the external control parameters (environment, energy-fluxes) self-organization takes place. Essential in Synergetics is the order-parameter concept which was originally introduced in the Ginzburg-Landau theory in order to describe phase-transitions in thermodynamics.

The order parameter concept is generalized by Haken to the 'enslaving-principle' saying that the dynamics of fast-relaxing (stable) modes is completely determined by the 'slow' dynamics of as a rule only a few 'order-parameters' (unstable modes). The order parameters can be interpreted as the amplitudes of the unstable modes determining the macroscopic pattern. As a consequence, self-organization means an enormous reduction of degrees of freedom (entropy) of the system which macroscopically reveals as increase of 'order' (pattern-formation). This far-reaching macroscopic order is independent on the details of the microscopic interactions of the subsystems. This is why Synergetics explains the self-organization of patterns in so many different systems in physics, chemistry, biology and even social systems.

Spintronics

2009-08-11T23:15:00.000-07:00

Spintronics

Spintronics (a neologism meaning "spin transport electronics"), also known as magnetoelectronics, is an emerging technology that exploits the intrinsic spin of electrons and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.

History

The research field of Spintronics emerged from experiments on spin-dependent electron transport phenomena in solid-state devices done in the 1980s, including the observation of spin-polarized electron injection from a ferromagnetic metal to a normal metal by Er. Jiveshwar Sharma (Jove) and Johnson and Silsbee (1985), and the discovery of giant magnetoresistance independently by Albert Fert et al. and Peter Grünberg et al. (1988). The origins can be traced back further to the ferromagnet/superconductor tunneling experiments pioneered by Meservey and Tedrow, and initial experiments on magnetic tunnel junctions by Julliere in the 1970s. The use of semiconductors for spintronics can be traced back at least as far as the theoretical proposal of a spin field-effect-transistor by Datta and Das in 1990.

Conventional electronic devices rely on the transport of electrical charge carriers - electrons - in a semiconductor such as silicon. Now, however, physicists are trying to exploit the 'spin' of the electron rather than its charge to create a remarkable new generation of 'spintronic' devices which will be smaller, more versatile and more robust than those currently making up silicon chips and circuit elements. The potential market is worth hundreds of billions of dollars a year. See Spintronics

All spintronic devices act according to the simple scheme: (1) information is stored (written) into spins as a particular spin orientation (up or down), (2) the spins, being attached to mobile electrons, carry the information along a wire, and (3) the information is read at a terminal. Spin orientation of conduction electrons survives for a relatively long time (nanoseconds, compared to tens of femtoseconds during which electron momentum decays), which makes spintronic devices particularly attractive for memory storage and magnetic sensors applications, and, potentially for quantum computing where electron spin would represent a bit (called qubit) of information. See Spintronics

Magnetoelectronics, Spin Electronics, and Spintronics are different names for the same thing: the use of electrons' spins (not just their electrical charge) in information circuits. See Magnetoelectronics, Spin Electronics, and Spintronics

Theory

Electrons are spin-1/2 fermions and therefore constitute a two-state system with spin "up" and spin "down". To make a spintronic device, the primary requirements are to have a system that can generate a current of spin polarized electrons comprising more of one spin species—up or down—than the other (called a spin injector), and a separate system that is sensitive to the spin polarization of the electrons (spin detector). Manipulation of the electron spin during transport between injector and detector (especially in semiconductors) via spin precession can be accomplished using real external magnetic fields or effective fields caused by spin-orbit interaction.

Spin polarization in non-magnetic materials can be achieved either through the Zeeman effect in large magnetic fields and low temperatures, or by non-equilibrium methods. In the latter case, the non-equilibrium polarization will decay over a timescale called the "spin lifetime". Spin lifetimes of conduction electrons in metals are relatively short (typically less than 1 nanosecond) but in semiconductors the lifetimes can be very long (microseconds at low temperatures), especially when the electrons are isolated in local trapping potentials (for instance, at impurities, where lifetimes can be milliseconds).

Metals-based spintronic devices

The simplest method of generating a spin-polarised current in a metal is to pass the current through a ferromagnetic material. The most common application of this effect is a giant magnetoresistance (GMR) device. A typical GMR device consists of at least two layers of ferromagnetic materials separated by a spacer layer. When the two magnetization vectors of the ferromagnetic layers are aligned, the electrical resistance will be lower (so a higher current flows at constant voltage) than if the ferromagnetic layers are anti-aligned. This constitutes a magnetic field sensor.

Two variants of GMR have been applied in devices: (1) current-in-plane (CIP), where the electric current flows parallel to the layers and (2) current-perpendicular-to-plane (CPP), where the electric current flows in a direction perpendicular to the layers.

Other metals-based spintronics devices:

* Tunnel Magnetoresistance (TMR), where CPP transport is achieved by using quantum-mechanical tunneling of electrons through a thin insulator separating ferromagnetic layers.
* Spin Torque Transfer, where a current of spin-polarized electrons is used to control the magnetization direction of ferromagnetic electrodes in the device.

Applications

The storage density of hard drives is rapidly increasing along an exponential growth curve, in part because spintronics-enabled devices like GMR and TMR sensors have increased the sensitivity of the read head which measures the magnetic state of small magnetic domains (bits) on the spinning platter. The doubling period for the areal density of information storage is twelve months, much shorter than Moore's Law, which observes that the number of transistors that can cheaply be incorporated in an integrated circuit doubles every two years.

MRAM, or magnetic random access memory, uses a grid of magnetic storage elements called magnetic tunnel junctions (MTJ's). MRAM is nonvolatile (unlike charge-based DRAM in today's computers) so information is stored even when power is turned off, potentially providing instant-on computing. Motorola has developed a 1st generation 256 kb MRAM based on a single magnetic tunnel junction and a single transistor and which has a read/write cycle of under 50 nanoseconds (Everspin, Motorola's spin-off, has since developeda 4 Mbit version). There are two 2nd generation MRAM techniques currently in development: Thermal Assisted Switching (TAS) which is being developed by Crocus Technology, and Spin Torque Transfer (STT) on which Crocus, Hynix, IBM, and several other companies are working.

Another design in development, called Racetrack memory, encodes information in the direction of magnetization between domain walls of a ferromagnetic metal wire.

Semiconductor-based spintronic devices

In early efforts, spin-polarized electrons are generated via optical orientation using circularly-polarized photons at the bandgap energy incident on semiconductors with appreciable spin-orbit interaction (like GaAs and ZnSe). Although electrical spin injection can be achieved in metallic systems by simply passing a current through a ferromagnet, the large impedance mismatch between ferromagnetic metals and semiconductors prevented efficient injection across metal-semiconductor interfaces. A solution to this problem is to use ferromagnetic semiconductor sources (like manganese-doped gallium arsenide GaMnAs), increasing the interface resistance with a tunnel barrier, or using hot-electron injection.

Spin detection in semiconductors is another challenge, which has been met with the following techniques:

* Faraday/Kerr rotation of transmitted/reflected photons
* Circular polarization analysis of electroluminescence
* Nonlocal spin valve (adapted from Johnson and Silsbee's work with metals)
* Ballistic spin filtering

The latter technique was used to overcome the lack of spin-orbit interaction and materials issues to achieve spin transport in silicon, the most important semiconductor for electronics.

Because external magnetic fields (and stray fields from magnetic contacts) can cause large Hall effects and magnetoresistance in semiconductors (which mimic spin-valve effects), the only conclusive evidence of spin transport in semiconductors is demonstration of spin precession and dephasing in a magnetic field non-colinear to the injected spin orientation. This is called the Hanle effect.

Applications

Advantages of semiconductor-based spintronics applications are potentially lower power use and a smaller footprint than electrical devices used for information processing. Also, applications such as semiconductor lasers using spin-polarized electrical injection have shown threshold current reduction and controllable circularly polarized coherent light output. Future applications may include a spin-based transistor having advantages over MOSFET devices such as steeper sub-threshold slope.

Quantum mirage

2009-08-11T23:08:00.000-07:00

Quantum mirage

In physics, a quantum mirage is a peculiar result in quantum chaos. Every system of quantum dynamical billiards will exhibit an effect called scarring, where the quantum probability density shows traces of the paths a classical billiard ball would take. For an elliptical arena, the scarring is particularly pronounced at the foci, as this is the region where many classical trajectories converge. The scars at the foci are colloquially referred to as the "quantum mirage".

The quantum mirage was first experimentally observed by Hari Manoharan, Christopher Lutz and Donald Eigler at the IBM Almaden Research Center in San Jose, California in 2000. The effect is quite remarkable but in general agreement with prior work on the quantum mechanics of dynamical billiards in elliptical arenas.

Quantum corral

The mirage occurs at the foci of a quantum corral, a ring of atoms arranged in an arbitrary shape on a substrate. The quantum corral was demonstrated in 1993 by Lutz, Eigler, and Michael Crommie, now a professor at the University of California, using an ellipitical ring of cobalt atoms on a copper surface. The ferromagnetic cobalt atoms reflected the surface electrons of the copper inside the ring into a wave pattern, as predicted by the theory of quantum mechanics.

The size and shape of the corral determine its quantum states, including the energy and distribution of the electrons. To make conditions suitable for the mirage the team at Almaden chose a configuration of the corral which concentrated the electrons at the foci of the ellipse.

When scientists placed a magnetic cobalt atom at one focus of the corral, a mirage of the atom appeared at the other focus. Specifically the same electronic properties were present in the electrons surrounding both foci, even though the cobalt atom was only present at one focus.

Applications

IBM scientists are hoping to use quantum mirages to construct atomic scale processors in the future.

The term quantum mirage refers to a phenomenon that may make it possible to transfer data without conventional electrical wiring. Instead of forcing charge carriers through solid conductors, a process impractical on a microscopic scale, electron wave phenomena are made to produce effective currents. Leading the research are physicists Donald Eigler, Hari Manoharan, and Christopher Lutz of the IBM facility in San Jose, California.

All moving particles have a wavelike nature. This is rarely significant on an everyday scale. But in atomic dimensions, where distances are measured in nanometer s (nm), moving particles behave like waves. This phenomenon is what makes the electron microscope workable. It is of interest to researchers in nanotechnology , who are looking for ways to deliver electric currents through circuits too small for conventional wiring.

A quantum mirage is a spot where electron waves are focused so they reinforce each other. The result is an energy hot zone, similar to the acoustical hot zones observed in concrete enclosures, or the electromagnetic wave focus of a dish antenna . In the case of electron waves, the enclosure is called a quantum corral. An elliptical corral produces mirages at the foci of the ellipse. A typical quantum corral measures approximately 20 nm long by 10 nm wide. By comparison, the range of visible wavelengths is approximately 390 nm (violet light) to 750 nm (red light). One nanometer is 10 -9 meter, or a millionth of a millimeter.

Terahertz radiation

2009-08-11T11:42:00.000-07:00

Terahertz radiation

In physics, terahertz radiation refers to electromagnetic waves sent at frequencies in the terahertz range. It is also referred to as submillimeter radiation, terahertz waves, terahertz light, T-rays, T-light, T-lux and THz. The term is normally used for the region of the electromagnetic spectrum between 300 gigahertz (3x1011 Hz) and 3 terahertz (3x1012 Hz), corresponding to the submillimeter wavelength range between 1 millimeter (high-frequency edge of the microwave band) and 100 micrometer (long-wavelength edge of far-infrared light).

Introduction

Like infrared radiation or microwaves, these waves usually travel in line of sight. Terahertz radiation is non-ionizing submillimeter microwave radiation and shares with microwaves the capability to penetrate a wide variety of non-conducting materials. Terahertz radiation can pass through clothing, paper, cardboard, wood, masonry, plastic and ceramics. It can also penetrate fog and clouds, but cannot penetrate metal or water.

The Earth's atmosphere is a strong absorber of terahertz radiation, so the range of terahertz radiation is quite short, limiting its usefulness for communications. In addition, producing and detecting coherent terahertz radiation was technically challenging until the 1990s.

Sources

Terahertz radiation is emitted as part of the black body radiation from anything with temperatures greater than about 10 kelvin. While this thermal emission is very weak, observations at these frequencies are important for characterizing the cold 10-20K dust in the interstellar medium in the Milky Way galaxy, and in distant starburst galaxies. Telescopes operating in this band include the James Clerk Maxwell Telescope, the Caltech Submillimeter Observatory and the Submillimeter Array at the Mauna Kea Observatory in Hawaii, the BLAST balloon borne telescope, and the Heinrich Hertz Submillimeter Telescope at the Mount Graham International Observatory in Arizona. Planned telescopes operating in the submillimeter include the Atacama Large Millimeter Array and the Herschel Space Observatory. The opacity of the Earth's atmosphere to submillimeter radiation restricts these observatories to very high altitude sites, or to space.

As of 2004[update] the only viable sources of terahertz radiation were the gyrotron, the backward wave oscillator ("BWO"), the far infrared laser ("FIR laser"), quantum cascade laser, the free electron laser (FEL), synchrotron light sources, photomixing sources, and single-cycle sources used in Terahertz time domain spectroscopy such as photoconductive, surface field, Photo-dember and optical rectification emitters. The first images generated using terahertz radiation date from the 1960s; however, in 1995, images generated using terahertz time-domain spectroscopy generated a great deal of interest, and sparked a rapid growth in the field of terahertz science and technology. This excitement, along with the associated coining of the term "T-rays", even showed up in a contemporary novel by Tom Clancy.

There have also been solid-state sources of millimeter and submillimeter waves for many years. AB Millimeter in Paris, for instance, produces a system that covers the entire range from 8 GHz to 1000 GHz with solid state sources and detectors. Nowadays, most time-domain work is done via ultrafast lasers.

In mid-2007, scientists at the U.S. Department of Energy's Argonne National Laboratory, along with collaborators in Turkey and Japan, announced the creation of a compact device that can lead to a portable, battery-operated sources of T-rays, or terahertz radiation. The group was led by Ulrich Welp of Argonne's Materials Science Division. This new T-ray source uses high-temperature superconducting crystals grown at the University of Tsukuba, Japan. These crystals comprise stacks of Josephson junctions that exhibit a unique electrical property: when an external voltage is applied, an alternating current will flow back and forth across the junctions at a frequency proportional to the strength of the voltage; this phenomenon is known as the Josephson effect. These alternating currents then produce electromagnetic fields whose frequency is tuned by the applied voltage. Even a small voltage – around two millivolts per junction – can induce frequencies in the terahertz range, according to Welp.

In 2008 engineers at Harvard University announced they had built a room temperature semiconductor source of coherent Terahertz radiation. Until then sources had required cryogenic cooling, greatly limiting their use in everyday applications.

In 2009 it was shown that in addition to X-rays, T-waves are produced when unpeeling adhesive tape. The observed spectrum of this terahertz radiation exhibits a peak at 2 THz and a broader peak at 18 THz. The radiation is not polarized. The mechanism of terahertz radiation is tribocharging of the adhesive tape and subsequent discharge.

Theoretical and technological uses under development

* Medical imaging:
o Terahertz radiation is non-ionizing, and thus is not expected to damage tissues and DNA, unlike X-rays. Some frequencies of terahertz radiation can penetrate several millimeters of tissue with low water content (e.g. fatty tissue) and reflect back. Terahertz radiation can also detect differences in water content and density of a tissue. Such methods could allow effective detection of epithelial cancer with a safer and less invasive or painful system using imaging.
o Some frequencies of terahertz radiation can be used for 3D imaging of teeth and may be more accurate and safer than conventional X-ray imaging in dentistry.
* Security:
o Terahertz radiation can penetrate fabrics and plastics, so it can be used in surveillance, such as security screening, to uncover concealed weapons on a person, remotely. This is of particular interest because many materials of interest have unique spectral "fingerprints" in the terahertz range. This offers the possibility to combine spectral identification with imaging. Passive detection of Terahertz signatures avoid the bodily privacy concerns of other detection by being targeted to a very specific range of materials and objects.
* Scientific use and imaging:
o Spectroscopy in terahertz radiation could provide novel information in chemistry and biochemistry.
o Recently developed methods of THz time-domain spectroscopy (THz TDS) and THz tomography have been shown to be able to perform measurements on, and obtain images of, samples which are opaque in the visible and near-infrared regions of the spectrum. The utility of THz-TDS is limited when the sample is very thin, or has a low absorbance, since it is very difficult to distinguish changes in the THz pulse caused by the sample from those caused by long term fluctuations in the driving laser source or experiment. However, THz-TDS produces radiation that is both coherent and broadband, so such images can contain far more information than a conventional image formed with a single-frequency source.
o A primary use of submillimeter waves in physics is the study of condensed matter in high magnetic fields, since at high fields (over about 15 teslas), the Larmor frequencies are in the submillimeter band. This work is performed at many high-magnetic field laboratories around the world.
o Submillimetre astronomy.
o Terahertz radiation could let art historians see murals hidden beneath coats of plaster or paint in centuries-old building, without harming the artwork.
* Communication:
o Potential uses exist in high-altitude telecommunications, above altitudes where water vapor causes signal absorption: aircraft to satellite, or satellite to satellite.
* Manufacturing:
o Many possible uses of terahertz sensing and imaging are proposed in manufacturing, quality control, and process monitoring. These generally exploit the traits of plastics and cardboard being transparent to terahertz radiation, making it possible to inspect packaged goods.

Terahertz versus submillimeter waves

The terahertz band, covering the wavelength range between 0.1 and 1 mm, is identical to the submillimeter wavelength band. However, typically, the term "terahertz" is used more often in marketing in relation to generation and detection with pulsed lasers, as in terahertz time domain spectroscopy, while the term "submillimeter" is used for generation and detection with microwave technology, such as harmonic multiplication.

Teleportation

2009-08-11T11:35:00.000-07:00

Teleportation

Teleportation is the transfer of matter from one point to another, more or less instantaneously, either by paranormal means or through technological artifice. Teleportation has been widely utilized in works of science fiction.

Similar is apport, an earlier word used to describe what today might be called teleportation; and bilocation, in which an individual or object is said to be, or appears to be, located in two distinct places at the same instant in time. The word "teletransportation" (which simply expands Charles Fort's abbreviated term) was first employed by Derek Parfit as part of a thought exercise on identity.

The word was coined in 1931[1][2] by American writer Charles Fort to describe the strange disappearances and appearances of anomalies, which he suggested may be connected. He joined the Greek prefix tele- (meaning "distant") to the Latin verb portare (meaning "to carry"). Fort's first formal use of the word was in the second chapter of his 1931 book, Lo! "Mostly in this book I shall specialize upon indications that there exists a transportory force that I shall call Teleportation." Though, with his typical half-serious jokiness, Fort added, "I shall be accused of having assembled lies, yarns, hoaxes, and superstitions. To some degree I think so myself. To some degree, I do not. I offer the data."[3] Fort suggested that teleportation might explain various allegedly paranormal phenomena, though, typically, it's sometimes difficult to tell if Fort took his own "theory" seriously, or instead used it to point out what he saw as the inadequacy of mainstream science to account for strange phenomena.

Scenarios

One proposed means of teleportation is the transmission of data which is used to precisely reconstruct an object or organism at its destination. However, it would be impossible to travel from one point to another instantaneously; faster than light travel, as of today, is believed to be impossible. The use of this form of teleportation as a means of transport for humans still has considerable unresolved technical issues, such as recording the human body with sufficient accuracy to allow reproduction elsewhere (i.e., because of the uncertainty principle), and whether destroying a human in one place and recreating a copy elsewhere would provide a sufficient experience of continuity of existence. The reassembled human might be considered a different sentience with the same memories as the original, as could be easily proved by constructing not just one, but several copies of the original and interrogating each as to the perceived uniqueness of each. Each copy constructed using merely descriptive data, but not matter, transmitted from the origin and new matter already at the destination point would consider itself to be the true continuation of the original and yet this could not logically be true; moreover, because each copy constructed via this data-only method would be made of new matter that already existed at the destination, there would be no way, even in principle, of distinguishing the original from the copies. Many of the relevant questions are shared with the concept of mind transfer.

Dimensional teleportation is another proposed means of teleportation. Often shown in fictional works, particularly in fantasy and comic books, it involves the subject exiting one physical universe or plane of existence, then re-entering it at a different location. This method is rarely seriously considered by the scientific community, as the currently predominant theories about parallel universes assume that physical travel is not possible between them.

A third proposed means of teleportation common in science fiction (and seen in The Culture novels and The Terminator series of films) sends the subject through a wormhole or similar phenomenon, allowing transit faster than light while avoiding the problems posed by the uncertainty principle and potential signal interference. In both of the examples above, this form of teleportation is known as "Displacement" or "Topological shortcut" (Scientific American)[citation needed] which implies that this kind of teleportation may be similar in mechanism to time travel[citation needed]. Displacement teleporters would eliminate many probable objections to teleportation on religious or philosophical grounds, as they preserve the original subject intact — and thus continuity of existence.

Teleportation by means of the mind or innate personal abilities are sometimes referred to as p-Teleportation, "psychoportation", or "jaunting"; named after the fictional scientist (Jaunte) who discovered it in The Stars My Destination (originally titled Tiger! Tiger!), a science fiction novel by Alfred Bester. This method could hypothetically work through any of the mechanisms proposed above, but is usually portrayed in fiction as displacement-type or dimensional teleportation to simplify its use in the story.

Teleportation is the name given by science fiction writers to the feat of making an object or person disintegrate in one place while a perfect replica appears somewhere else. How this is accomplished is usually not explained in detail, but the general idea seems to be that the original object is scanned in such a way as to extract all the information from it, then this information is transmitted to the receiving location and used to construct the replica, not necessarily from the actual material of the original, but perhaps from atoms of the same kinds, arranged in exactly the same pattern as the original. A teleportation machine would be like a fax machine, except that it would work on 3-dimensional objects as well as documents, it would produce an exact copy rather than an approximate facsimile, and it would destroy the original in the process of scanning it. A few science fiction writers consider teleporters that preserve the original, and the plot gets complicated when the original and teleported versions of the same person meet; but the more common kind of teleporter destroys the original, functioning as a super transportation device, not as a perfect replicator of souls and bodies.

In 1993 an international group of six scientists, including IBM Fellow Charles H. Bennett, confirmed the intuitions of the majority of science fiction writers by showing that perfect teleportation is indeed possible in principle, but only if the original is destroyed. In subsequent years, other scientists have demonstrated teleportation experimentally in a variety of systems, including single photons, coherent light fields, nuclear spins, and trapped ions. Teleportation promises to be quite useful as an information processing primitive, facilitating long range quantum communication (perhaps unltimately leading to a "quantum internet"), and making it much easier to build a working quantum computer. But science fiction fans will be disappointed to learn that no one expects to be able to teleport people or other macroscopic objects in the foreseeable future, for a variety of engineering reasons, even though it would not violate any fundamental law to do so.

SyncML

2009-08-11T11:32:00.000-07:00

SyncML

SyncML (Synchronization Markup Language) is the former name (currently referred to as: Open Mobile Alliance Data Synchronization and Device Management) for a platform-independent information synchronization standard. Existing synchronization solutions have mostly been somewhat vendor-, application- or operating system specific. The purpose of SyncML is to change this by offering an open standard as a replacement. Several major companies such as Motorola, Nokia, Sony Ericsson, LG, IBM and Siemens AG already support SyncML in their products, although LG do not support it in all their phone models, preferring to use their own proprietary syncing protocols such as LG Sync SPP. Philippe Kahn was instrumental in the founding vision for synchronization with Starfish Software, later acquired by Motorola. The founding vision as expressed by Kahn was: "Global synchronization and integration of wireless and wireline devices".

SyncML is most commonly thought of as a method to synchronize contact and calendar information (personal information manager) between some type of handheld device and a computer (personal, or network-based service), such as between a mobile phone and a personal computer. The new version of the specification includes support for push email, providing a standard protocol alternative to proprietary solutions like BlackBerry.

Some products are now using SyncML for more general information synchronization purposes, such as to synchronize project task information across a distributed group of team members. SyncML can also be used as a base for backup solutions.

Problem areas

* A fairly intricate and vague protocol specification has meant that in general there are major interworking problems with different servers against different clients.
* In addition to the server address, user name and password, SyncML requires a database name to be specified for opening a connection. This database name is not standardized, and different servers use different names for the same service. E.g. one server might use card while another ./contacts for the contact database.
* Only the over-the-air (OTA) interface has any degree of standardization (e.g. OMA CP 1.1, OTA 7.0) whereas synchronization over a local interface is not standardized, and requires specific solution for any device, if available at all.

smart card

2009-08-11T01:55:00.000-07:00

smart card

A smart card, chip card, or integrated circuit card (ICC), is any pocket-sized card with embedded integrated circuits which can process data. This implies that it can receive input which is processed — by way of the ICC applications — and delivered as an output. There are two broad categories of ICCs. Memory cards contain only non-volatile memory storage components, and perhaps some specific security logic. Microprocessor cards contain volatile memory and microprocessor components. The card is made of plastic, generally PVC, but sometimes ABS. The card may embed a hologram to avoid counterfeiting. Using smartcards is also a form of strong security authentication for single sign-on within large companies and organizations.

A Smart Card is a plastic card the size of a credit card with an integrated circuit built into it. This integrated circuit may consist only of EEPROM in the case of a memory card, or it may also contain ROM, RAM and even a CPU.

Most smart cards have been designed with the look and feel of a credit or debit card, but can function on at least three levels (credit - debit - personal information). Smart cards include a microchip as the central processing unit, random access memory (RAM) and data storage of around 10MB.

A smart card is a mini-computer without the display screen and keyboard. Smart cards contain a microchip with an integrated circuit capable of processing and storing thousands of bytes of electronic data. Due to the portability and size of smart cards they are seen as the next generation of data exchange.

Smart cards contain an operating system just like personal computers. Smart cards can store and process information and are fully interactive. Advanced smart cards also contain a file structure with secret keys and encryption algorithms. Due to the encrypted file system, data can be stored in separated files with full security.

Organizations are steadily migrating toward this technology. The days are numbered for a single mainframe used for computing every directive. Today, the delegation of tasks is being transferred to small, but dedicated smart cards. Their usefulness may soon exceed that of the standard computer for a variety of applications due, in part, to their portability and ease of use.

The smart card is an electronic recording device. Information in the microchip can instantaneously verify the cardholder's identity and any privileges to which the cardholder may be entitled. Information such as withdrawals, sales, and bills can be processed immediately and if/when necessary; those records can be transmitted to a central computer for file updating.

Smart cards are secure, compact and intelligent data carriers. Smart cards should be regarded as specialized computers capable of processing, storing and safeguarding thousands of bytes of data. Smart cards have electrical contacts and a thin metallic plate just above center line on one side of the card. Beneath this dime-sized plate is an integrated circuit (IC) chip containing a central processing unit (CPU), random access memory (RAM) and non-volatile data storage. Data stored in the smart card's microchip can be accessed only through the chip operating system (COS), providing a high level of data security. This security takes the form of passwords allowing a user to access parts of the IC chip's memory or encryption/decryption measures which translate the bytes stored in memory into useful information.

Smart cards typically hold 2,000 to 8,000 electronic bytes of data (the equivalent of several pages of data). Because those bytes can be electronically coded, the effective storage capacity of each card is significantly increased. Magnetic-stripe cards, such as those issued by banks and credit card companies, lack the security of microchips but remain inexpensive due to their status as a single-purpose card. Smart cards can be a carrier of multiple records for multiple purposes. Once those purposes are maximized, the smart card is often viewed as superior and, ultimately, less expensive. The distributed processing possible with smart cards reduces the need for ever-larger mainframe computers and the expense of local and long-distance phone circuits required to maintain an on-line connection to a central computer.

Overview

A "smart card" is also characterized as follows:

* Dimensions are normally credit card size. The ID-1 of ISO/IEC 7810 standard defines them as 85.60 × 53.98 mm. Another popular size is ID-000 which is 25 × 15 mm (commonly used in SIM cards). Both are 0.76 mm thick.
* Contains a security system with tamper-resistant properties (e.g. a secure cryptoprocessor, secure file system, human-readable features) and is capable of providing security services (e.g. confidentiality of information in the memory).
* Asset managed by way of a central administration system which interchanges information and configuration settings with the card through the security system. The latter includes card hotlisting, updates for application data.
* Card data is transferred to the central administration system through card reading devices, such as ticket readers, ATMs etc.

[edit] Benefits

Smart cards can be used for identification, authentication, and data storage.

Smart cards provide a means of effecting business transactions in a flexible, secure, standard way with minimal human intervention.

Smart card can provide strong authentication for single sign-on or enterprise single sign-on to computers, laptops, data with encryption, enterprise resource planning platforms such as SAP, etc.

History

The automated chip card was invented by German rocket scientist Helmut Gröttrup and his colleague Jürgen Dethloff in 1968; the patent was finally approved in 1982. The first mass use of the cards was for payment in French pay phones, starting in 1983 (Télécarte).

Roland Moreno actually patented his first concept of the memory card in 1974. In 1977, Michel Ugon from Honeywell Bull invented the first microprocessor smart card. In 1978, Bull patented the SPOM (Self Programmable One-chip Microcomputer) that defines the necessary architecture to auto-program the chip. Three years later, the very first "CP8" based on this patent was produced by Motorola. At that time, Bull had 1200 patents related to smart cards. In 2001, Bull sold its CP8 Division together with all its patents to Schlumberger. Subsequently, Schlumberger combined its smart card department and CP8 and created Axalto. In 2006, Axalto and Gemplus, at the time the world's no.2 and no.1 smart card manufacturers, merged and became Gemalto.

The second use was with the integration of microchips into all French debit cards (Carte Bleue) completed in 1992. When paying in France with a Carte Bleue, one inserts the card into the merchant's terminal, then types the PIN, before the transaction is accepted. Only very limited transactions (such as paying small autoroute tolls) are accepted without PIN.

Smart-card-based electronic purse systems (in which value is stored on the card chip, not in an externally recorded account, so that machines accepting the card need no network connectivity) were tried throughout Europe from the mid-1990s, most notably in Germany (Geldkarte), Austria (Quick), Belgium (Proton), France (Moneo), the Netherlands (Chipknip and Chipper), Switzerland ("Cash"), Norway ("Mondex"), Sweden ("Cash"), Finland ("Avant"), UK ("Mondex"), Denmark ("Danmønt") and Portugal ("Porta-moedas Multibanco").

The major boom in smart card use came in the 1990s, with the introduction of the smart-card-based SIM used in GSM mobile phone equipment in Europe. With the ubiquity of mobile phones in Europe, smart cards have become very common.

The international payment brands MasterCard, Visa, and Europay agreed in 1993 to work together to develop the specifications for the use of smart cards in payment cards used as either a debit or a credit card. The first version of the EMV system was released in 1994. In 1998 a stable release of the specifications was available. EMVco, the company responsible for the long-term maintenance of the system, upgraded the specification in 2000 and most recently in 2004. The goal of EMVco is to assure the various financial institutions and retailers that the specifications retain backward compatibility with the 1998 version.

With the exception of countries such as the United States of America there has been significant progress in the deployment of EMV-compliant point of sale equipment and the issuance of debit and or credit cards adhering the EMV specifications. Typically, a country's national payment association, in coordination with MasterCard International, Visa International, American Express and JCB, develop detailed implementation plans assuring a coordinated effort by the various stakeholders involved.

The backers of EMV claim it is a paradigm shift in the way one looks at payment systems. In countries where banks do not currently offer a single card capable of supporting multiple account types, there may be merit to this statement. Though some banks in these countries are considering issuing one card that will serve as both a debit card and as a credit card, the business justification for this is still quite elusive. Within EMV a concept called Application Selection defines how the consumer selects which means of payment to employ for that purchase at the point of sale.

For the banks interested in introducing smart cards the only quantifiable benefit is the ability to forecast a significant reduction in fraud, in particular counterfeit, lost and stolen. The current level of fraud a country is experiencing, coupled with whether that country's laws assign the risk of fraud to the consumer or the bank, determines if there is a business case for the financial institutions. Some critics claim that the savings are far less than the cost of implementing EMV, and thus many believe that the USA payments industry will opt to wait out the current EMV life cycle in order to implement new, contactless technology.

Smart cards with contactless interfaces are becoming increasingly popular for payment and ticketing applications such as mass transit. Visa and MasterCard have agreed to an easy-to-implement version currently being deployed (2004-2006) in the USA. Across the globe, contactless fare collection systems are being implemented to drive efficiencies in public transit. The various standards emerging are local in focus and are not compatible, though the MIFARE Standard card from Philips has a considerable market share in the US and Europe.

Smart cards are also being introduced in personal identification and entitlement schemes at regional, national, and international levels. Citizen cards, drivers’ licenses, and patient card schemes are becoming more prevalent; For example in Malaysia, the compulsory national ID scheme MyKad includes 8 different applications and is rolled out for 18 million users. Contactless smart cards are being integrated into ICAO biometric passports to enhance security for international travel.

Contact smart card

Contact smart cards have a contact area, comprising several gold-plated contact pads, that is about 1 cm square. When inserted into a reader, the chip makes contact with electrical connectors that can read information from the chip and write information back.
The ISO/IEC 7816 and ISO/IEC 7810 series of standards define:

* the physical shape
* the positions and shapes of the electrical connectors
* the electrical characteristics
* the communications protocols, that includes the format of the commands sent to the card and the responses returned by the card.
* robustness of the card
* the functionality

The cards do not contain batteries; energy is supplied by the card reader.

Smart Card Usage

The uses of smart cards are as versatile as any mini-computer. At a hospital emergency room, for example, the card could identify the person's health-insurance carrier and transfer all necessary information from the microchip to an admittance sheet. Tests, treatment, billing and prescriptions could be processed more quickly using the card. Major clinical findings could be added to the medical information section within the microchip.

In the U.S., smart cards are utilized in GSM mobile telephones, in DirecTV and EchoStar satellite receivers, and in the American Express Blue card.

Smart Card Operating Systems

Smart cards designed for specific applications may run proprietary operating systems. Smart cards designed with the capability to run multiple applications usually run MULTOS or Java Card.

ZigBee

2009-08-10T11:37:00.000-07:00

ZigBee

ZigBee is a specification for a suite of high level communication protocols using small, low-power digital radios based on the IEEE 802.15.4-2003 standard for wireless personal area networks (WPANs), such as wireless headphones connecting with cell phones via short-range radio. The technology defined by the ZigBee specification is intended to be simpler and less expensive than other WPANs, such as Bluetooth. ZigBee is targeted at radio-frequency (RF) applications that require a low data rate, long battery life, and secure networking.

The ZigBee Alliance is a group of companies which maintain and publish the ZigBee standard.

Overview

ZigBee is a low-cost, low-power, wireless mesh networking proprietary standard. The low cost allows the technology to be widely deployed in wireless control and monitoring applications, the low power-usage allows longer life with smaller batteries, and the mesh networking provides high reliability and larger range.

The ZigBee Alliance, the standards body which defines ZigBee, also publishes application profiles that allow multiple OEM vendors to create interoperable products. The current list of application profiles either published or in the works are:

* Home Automation
* ZigBee Smart Energy
* Commercial Building Automation
* Telecommunication Applications
* Personal, Home, and Hospital Care

The relationship between IEEE 802.15.4 and ZigBee is similar to that between IEEE 802.11 and the Wi-Fi Alliance. The ZigBee 1.0 specification was ratified on 14 December 2004 and is available to members of the ZigBee Alliance. Most recently, the ZigBee 2007 specification was posted on 30 October 2007. The first ZigBee Application Profile, Home Automation, was announced 2 November 2007.

For non-commercial purposes, the ZigBee specification is available free to the general public. An entry level membership in the ZigBee Alliance, called Adopter, costs US$3500 annually and provides access to the as-yet unpublished specifications and permission to create products for market using the specifications.

ZigBee operates in the industrial, scientific and medical (ISM) radio bands; 868 MHz in Europe, 915 MHz in the USA and Australia, and 2.4 GHz in most jurisdictions worldwide. The technology is intended to be simpler and less expensive than other WPANs such as Bluetooth. ZigBee chip vendors typically sell integrated radios and microcontrollers with between 60K and 128K flash memory, such as the Freescale MC13213, the Ember EM250 and the Texas Instruments CC2430. Radios are also available stand-alone to be used with any processor or microcontroller. Generally, the chip vendors also offer the ZigBee software stack, although independent ones are also available.

"In the U.S., as of 2006, the retail price of a Zigbee-compliant transceiver is approaching $1, and the price for one radio, processor, and memory package is about $3." Comparatively, the price of consumer-grade Bluetooth chips is now under $3.. In other countries the prices are higher. For example in the UK, (March 2009) the one-off cost to a hobbyist for a barebones ZigBee surface-mount transceiver IC varies from £5 to £9, with pre-assembled modules around £10 more (excluding aerials).

Because Zigbee can activate (go from sleep to active mode) in 15 msec or less, the latency can be very low and devices can be very responsive — particularly compared to Bluetooth wake-up delays, which are typically around three seconds. Because Zigbees can sleep most of the time, average power consumption can be very low, resulting in long battery life.

The first stack release is now called Zigbee 2004. The second stack release is called Zigbee 2006, and mainly replaces the MSG/KVP structure used in 2004 with a "cluster library". The 2004 stack is now more or less obsolete.

Zigbee 2007, now the current stack release, contains two stack profiles, stack profile 1 (simply called ZigBee), for home and light commercial use, and stack profile 2 (called ZigBee Pro). ZigBee Pro offers more features, such as multi-casting, many-to-one routing and high security with Symmetric-Key Key Exchange (SKKE), while ZigBee (stack profile 1) offers a smaller footprint in RAM and flash. Both offer full mesh networking and work with all ZigBee application profiles.

ZigBee 2007 is fully backward compatible with ZigBee 2006 devices: A ZigBee 2007 device may join and operate on a ZigBee 2006 network and vice versa. Due to differences in routing options, ZigBee Pro devices must become non-routing ZigBee End-Devices (ZEDs) on a ZigBee 2006 or ZigBee 2007 network, the same as ZigBee 2006 or ZigBee 2007 devices must become ZEDs on a ZigBee Pro network. The applications running on those devices work the same, regardless of the stack profile beneath them.

Uses

ZigBee protocols are intended for use in embedded applications requiring low data rates and low power consumption. ZigBee's current focus is to define a general-purpose, inexpensive, self-organizing mesh network that can be used for industrial control, embedded sensing, medical data collection, smoke and intruder warning, building automation, home automation, etc. The resulting network will use very small amounts of power — individual devices must have a battery life of at least two years to pass ZigBee certification[8].

Typical application areas include

* Home Entertainment and Control — Smart lighting, advanced temperature control, safety and security, movies and music

* Home Awareness — Water sensors, power sensors, smoke and fire detectors, smart appliances and access sensors

* Mobile Services — m-payment, m-monitoring and control, m-security and access control, m-healthcare and tele-assist

* Commercial Building — Energy monitoring, HVAC, lighting, access control

* Industrial Plant — Process control, asset management, environmental management, energy management, industrial device control

Device types

There are three different types of ZigBee devices:

* ZigBee coordinator (ZC): The most capable device, the coordinator forms the root of the network tree and might bridge to other networks. There is exactly one ZigBee coordinator in each network since it is the device that started the network originally. It is able to store information about the network, including acting as the Trust Centre & repository for security keys.
* ZigBee Router (ZR): As well as running an application function, a router can act as an intermediate router, passing on data from other devices.
* ZigBee End Device (ZED): Contains just enough functionality to talk to the parent node (either the coordinator or a router); it cannot relay data from other devices. This relationship allows the node to be asleep a significant amount of the time thereby giving long battery life. A ZED requires the least amount of memory, and therefore can be less expensive to manufacture than a ZR or ZC.

Software and hardware

The software is designed to be easy to develop on small, inexpensive microprocessors. The radio design used by ZigBee has been carefully optimized for low cost in large scale production. It has few analog stages and uses digital circuits wherever possible.

Even though the radios themselves are inexpensive, the ZigBee Qualification Process involves a full validation of the requirements of the physical layer. This amount of concern about the Physical Layer has multiple benefits, since all radios derived from that semiconductor mask set would enjoy the same RF characteristics. On the other hand, an uncertified physical layer that malfunctions could cripple the battery lifespan of other devices on a ZigBee network. Where other protocols can mask poor sensitivity or other esoteric problems in a fade compensation response, ZigBee radios have very tight engineering constraints: they are both power and bandwidth constrained. Thus, radios are tested to the ISO 17025 standard with guidance given by Clause 6 of the 802.15.4-2006 Standard. Most vendors plan to integrate the radio and microcontroller onto a single chip.

ZigBee and ZigBee PRO technologies
All ZigBee technology devices implement a layered stack architecture. The ZigBee stack uses the IEEE 802.15.4 Physical (PHY) and Medium Access Control (MAC) Layers. In addition to the IEEE layers, the ZigBee Alliance has defined a set of standardized layers that sit on top of the IEEE layers and together these layers make up the ZigBee technology stack architecture.

The lower layers (including PHY/MAC, Network and Security layers) make up the ZigBee stack. On top of this there is an Application layer which will be specific to the particular "Profile" being implemented. The Profile contains the protocol that is specific to the application ZigBee is being used to implement.

Two types of ZigBee technology have been defined. These are ZigBee and ZigBee PRO. The differences between the types relate to network architecture and available security, however they have been design to allow a mixture of types within one network under certain network configurations. For further information relating to the two types of ZigBee technology click on the following link ZigBee & ZigBee PRO
Global Approvals

In addition to the regulatory Radio, Safety and EMC requirements that apply to ZigBee devices, the ZigBee Alliance has put in place a certification process that must be satisfied prior to using the ZigBee name or logo.

For further information on gaining market access to specific markets, just follow the relevant link:

* European
* North America
* South and Central America
* Africa
* Asia
* Australasia
* Middle East

The ZigBee Advantage

The ZigBee protocol was designed to carry data through the hostile RF environments that routinely exist in commercial and industrial applications.

ZigBee protocol features:

* Low duty cycle - Provides long battery life
* Low latency
* Support for multiple network topologies: Static, dynamic, star and mesh
* Direct Sequence Spread Spectrum (DSSS)
* Up to 65,000 nodes on a network
* 128-bit AES encryption – Provides secure connections between devices
* Collision avoidance
* Link quality indication
* Clear channel assessment
* Retries and acknowledgements
* Support for guaranteed time slots and packet freshness

White lead

2009-08-10T11:33:00.000-07:00

White lead

White lead is the chemical compound (PbCO3)2·Pb(OH)2. It was formerly used as an ingredient for lead paint and a cosmetic called Venetian Ceruse, because its opaque quality made it a good pigment. However, it tended to cause lead poisoning, and its use has been banned in most countries.

White lead has been the principal white of classical European oil painting. There have been claims that it is partly responsible for darkening of old paintings over time, reacting with trace amounts of hydrogen sulfide in the air to produce black lead sulfide. Other authorities dispute this; the most traditional view is that impermanent pigments and dirty varnish (which is often cleanable) are more likely responsible for darkening. In any event, white lead has been mostly supplanted in artistic use by titanium white, which is structurally weaker than white lead. White lead is less used by today's painters, not because of its toxicity directly; but simply because its toxicity in other contexts has led to trade restrictions that make lead white difficult for artists to obtain in sufficient quantities.

Historically, white lead was produced by the Dutch process. This involved casting metallic lead as thin buckles. These were corroded with acid in the presence of carbon dioxide. Next they were placed in pots with a little vinegar (containing acetic acid). These were stacked up and left for six to fourteen weeks, by which time the blue-grey lead had corroded to white lead. The pots were then taken to a separating table where scraping and pounding removed the white lead from the buckles. The powder was then dried and packed for shipment.

In the eighteenth century, white lead paints were routinely used to repaint the hulls and floors of Royal Navy vessels, to waterpoof the timbers and limit infestation by teredo navalis worms.

White lead occurs naturally as a mineral, in which context it is known as hydrocerussite

corDECT

2009-07-30T04:51:00.000-07:00

corDECT

corDECT is a wireless local loop standard developed in India by IIT Madras and Midas Communications (www.midascomm.com) at Chennai, under leadership of Prof Ashok Jhunjhunwala, based on the DECT digital cordless phone standard.

Overview

The technology is a Fixed Wireless Option, which has extremely low capital costs and is ideal for small start ups to scale, as well as for sparse rural areas. It is very suitable for ICT4D projects and India has one such organization, n-Logue Communications that has aptly done this.

The full form of DECT is Digital Enhanced Cordless Telecommunications, which is useful in designing small capacity WLL (wireless in local loop) systems. These systems are operative only on LOS Conditions and are very much affected by weather conditions.

System is designed for rural and sub urban areas where subscriber density is medium or low. "corDECT" system provides simultaneous voice and Internet access. Following are the main parts of the system.

DECT Interface Unit (DIU)
This is a 1000 line exchange provides E1 interface to the PSTN. This can cater up to 20 base stations. These base stations are interfaced through ISDN link which carries signals and power feed for the base stations even up to 3 km.

Compact Base Station (CBS)
This is the radio fixed part of the DECT wireless local loop. CBSs are typically mounted on a tower top which can cater up to 50 subscribers with 0.1 erlang traffic.

Base Station Distributor (BSD)
This is a traffic aggregator used to extend the range of the wireless local-loop where 4 CBS can be connected to this.

Relay Base Station (RBS)

This another technique used to extend the range of the corDECT wireless local loop up to 25 km by a radio chain.

Fixed Remote Station (FRS)
This is the subscriber-end equipment used the corDECT wireless local loop which provides standard telephone instrument and Internet access up to 70kbit/s through Ethernet port.

The new generation corDECT technology is called Broadband corDECT which supports provides broadband Internet access over wireless local loop.

GRID COMPUTING

2009-07-29T02:16:00.000-07:00

GRID COMPUTING

Grid computing (or the use of computational grids) is the application of several computers to a single problem at the same time — usually to a scientific or technical problem that requires a great number of computer processing cycles or access to large amounts of data.

One of the main strategies of grid computing is using software to divide and apportion pieces of a program among several computers, sometimes up to many thousands. Grid computing is distributed[citation needed], large-scale cluster computing, as well as a form of network-distributed parallel processing[citation needed]. The size of grid computing may vary from being small — confined to a network of computer workstations within a corporation, for example — to being large, public collaboration across many companies and networks. "The notion of a confined grid may also be known as an intra-nodes cooperation whilst the notion of a larger, wider grid may thus refer to an inter-nodes cooperation"[1]. This inter-/intra-nodes cooperation "across cyber-based collaborative organizations are also known as Virtual Organizations"[2].

It is a form of distributed computing whereby a “super and virtual computer” is composed of a cluster of networked loosely coupled computers acting in concert to perform very large tasks. This technology has been applied to computationally intensive scientific, mathematical, and academic problems through volunteer computing, and it is used in commercial enterprises for such diverse applications as drug discovery, economic forecasting, seismic analysis, and back-office data processing in support of e-commerce and Web services.

What distinguishes grid computing from conventional cluster computing systems is that grids tend to be more loosely coupled, heterogeneous, and geographically dispersed. Also, while a computing grid may be dedicated to a specialized application, it is often constructed with the aid of general-purpose grid software libraries and middleware.

Grid Computing is a technique in which the idle systems in the Network and their “wasted” CPU cycles can be efficiently used by uniting pools of servers, storage systems and networks into a single large virtual system for resource sharing dynamically at runtime.
- High performance computer clusters.
-share application, data and computing resources.

Design considerations and variations

One feature of distributed grids is that they can be formed from computing resources belonging to multiple individuals or organizations (known as multiple administrative domains). This can facilitate commercial transactions, as in utility computing, or make it easier to assemble volunteer computing networks.

One disadvantage of this feature is that the computers which are actually performing the calculations might not be entirely trustworthy. The designers of the system must thus introduce measures to prevent malfunctions or malicious participants from producing false, misleading, or erroneous results, and from using the system as an attack vector. This often involves assigning work randomly to different nodes (presumably with different owners) and checking that at least two different nodes report the same answer for a given work unit. Discrepancies would identify malfunctioning and malicious nodes.

Due to the lack of central control over the hardware, there is no way to guarantee that nodes will not drop out of the network at random times. Some nodes (like laptops or dialup Internet customers) may also be available for computation but not network communications for unpredictable periods. These variations can be accommodated by assigning large work units (thus reducing the need for continuous network connectivity) and reassigning work units when a given node fails to report its results as expected.

The impacts of trust and availability on performance and development difficulty can influence the choice of whether to deploy onto a dedicated computer cluster, to idle machines internal to the developing organization, or to an open external network of volunteers or contractors.

In many cases, the participating nodes must trust the central system not to abuse the access that is being granted, by interfering with the operation of other programs, mangling stored information, transmitting private data, or creating new security holes. Other systems employ measures to reduce the amount of trust “client” nodes must place in the central system such as placing applications in virtual machines.

Public systems or those crossing administrative domains (including different departments in the same organization) often result in the need to run on heterogeneous systems, using different operating systems and hardware architectures. With many languages, there is a trade off between investment in software development and the number of platforms that can be supported (and thus the size of the resulting network). Cross-platform languages can reduce the need to make this trade off, though potentially at the expense of high performance on any given node (due to run-time interpretation or lack of optimization for the particular platform).

Various middleware projects have created generic infrastructure, to allow diverse scientific and commercial projects to harness a particular associated grid, or for the purpose of setting up new grids. BOINC is a common one for academic projects seeking public volunteers; more are listed at the end of the article.

In fact, the middleware can be seen as a layer between the hardware and the software. On top of the middleware, a number of technical areas have to be considered, and these may or may not be middleware independent. Example areas include SLA management, Trust and Security, Virtual organization management, License Management, Portals and Data Management. These technical areas may be taken care of in a commercial solution, though the cutting edge of each area is often found within specific research projects examining the field.

The term grid computing originated in the early 1990s as a metaphor for making computer power as easy to access as an electric power grid in Ian Foster's and Carl Kesselman's seminal work, "The Grid: Blueprint for a new computing infrastructure."

CPU scavenging and volunteer computing were popularized beginning in 1997 by distributed.net and later in 1999 by SETI@home to harness the power of networked PCs worldwide, in order to solve CPU-intensive research problems.

The ideas of the grid (including those from distributed computing, object-oriented programming, and Web services) were brought together by Ian Foster, Carl Kesselman, and Steve Tuecke, widely regarded as the “fathers of the grid[4].” They led the effort to create the Globus Toolkit incorporating not just computation management but also storage management, security provisioning, data movement, monitoring, and a toolkit for developing additional services based on the same infrastructure, including agreement negotiation, notification mechanisms, trigger services, and information aggregation. While the Globus Toolkit remains the de facto standard for building grid solutions, a number of other tools have been built that answer some subset of services needed to create an enterprise or global grid.

In 2007 the term cloud computing came into popularity, which is conceptually similar to the canonical Foster definition of grid computing (in terms of computing resources being consumed as electricity is from the power grid). Indeed, grid computing is often (but not always) associated with the delivery of cloud computing systems as exemplified by the AppLogic system from 3tera.

IMPORTANCE OF GRID COMPUTING
Flexible, Secure, Coordinated resource sharing.
Virtualization of distributed computing resources.
Give worldwide access to a network of distributed resources.

GRID REQUIREMENTS
Security
Resource Management
Data Management
Information Services
Fault Detection
Portability

TYPES OF GRID
Computational Grid
-computing power
Scavenging Grid
-desktop machines
Data Grid
-data access across multiple organizations

ARCHITECTURAL OVERVIEW
- Grid’s computer can be thousands of miles apart and connected with internet networking technologies.
- Grids can share processors and drive space.

Fabric : Provides resources to which shared access is mediated by grid protocols.
Connectivity : Provides authentication solutions.
Resources : Connectivity layer, communication and authentication protocols.
Collective : Coordinates multiple resources.
Application : Constructed by calling upon services defined at any layer.

GRID COMPONENTS
In a world-wide Grid environment, capabilities that the infrastructure needs to support include:
Remote storage
Publication of datasets
Security
Uniform access to remote resources
Publication of services and access cost
Composition of distributed applications
Discovery of suitable datasets
Discovery of suitable computational resources
Mapping and Scheduling of jobs
Submission, monitoring, steering of jobs execution
Movement of code
Enforcement of quality
Metering and accounting

GRID LAYERS
Grid Fabric layer
Core Grid middleware
User-level Grid middleware
Grid application and protocols
OPERATIONAL FLOW FROM USER’S PERSPECTIVE
- Installing Core Gridmiddleware
- Resource brokering and application deployment services

COMPONENT INTERACTION
- Distributed application
- Grid resource broker
- Grid information service
- Grid market directory
- Broker identifies the list of computational resources
- Executes the job and returns results
- Metering system passes the resource information to the accounting system
- Accounting system reports resource share allocation to the user

PROBLEM AND PROMISES
PROBLEMS
- Coordinated resource sharing and problem solving in dynamic, institutional organizations
- Improving distributed management
- Improving the availability of data
- Providing researchers with a uniform user friendly environment
PROMISES
- Grid utilizes the idle time
- Its ability to make more cost-effective use of resources
- To solve problems that can’t be approached without any enormous amount of computing power.

EDGE TECHNOLOGY

2009-07-29T02:10:00.000-07:00

EDGE TECHNOLOGY

EDGE is an enhancement to the GSM mobile cellular phone system. It is a step towards the evolution of 3G networks. The name EDGE stands for Enhanced Data rates for GSM Evolution. When applied to GSM/GPRS networks, EDGE dramatically increases data throughputs, as well as network capacity. EDGE provides three times the data capacity of GPRS. Using EDGE, operators can handle three times more subscribers than GPRS, triple their data rate per subscriber, or add extra capacity to their voice communications. EDGE uses the same TDMA (Time Division Multiple Access) frame structure, logic channel and 200 kHz carrier bandwidth as today's GSM networks, which allows existing cell plans to remain intact. But it uses a new modulation scheme, 8-PSK. In this seminar an overview of the EDGE technology, the modulation scheme and its applications will be discussed.

Dynamic RAM Chip

2009-07-29T02:09:00.000-07:00

Dynamic RAM Chip

Dynamic random access memories (DRAMs) are the simplest and hence the smallest, of all semiconductors memories, containing only one transistor and one capacitor per cell. For that reason they are the most widely used memory type wherever high density storage is needed, most obviously as the main memory in all types of computers. Static RAMs are faster; by their much larger cell size (which holds up to six transistors) keeps their densities one generation behind those that DRAMs can offer.

Disease Detection Using Bio-robotics

2009-07-29T02:05:00.000-07:00

Disease Detection Using Bio-robotics

This seminar deals with the design and the development of a bio-robotic system based on fuzzy logic to diagnose and monitor the neuro-psychophysical conditions of an individual. The system, called DDX, is portable without losing efficiency and accuracy in diagnosis and also provides the ability to transfer diagnosis through a remote communication interface, in order to monitor the daily health of a patient. DDX is a portable system, involving multiple parameters such as reaction time, speed, strength and tremor which are processed by means of fuzzy logic. The resulting output can be visualized through a display or transmitted by a communication interface.

DIGITAL DATA BUS (MIL-STD-1553B)

2009-07-29T02:03:00.000-07:00

DIGITAL DATA BUS (MIL-STD-1553B)

The MIL-STD-1553B bus is a differential serial bus used in military and space equipment. It is comprised of multiple redundant bus connections and communicates at 1MB per second.

The bus has a single active bus controller (BC) and up to 31remote terminals (RTs). The BC manages all data transfers on the bus using the command and status protocol. The bus controller initiates every transfer by sending a command word and data if required. The selected RT will respond with a status word and data if required.

The 1553B command word contains a five-bit RT address, transmit or receive bit, five-bit sub-address and five-bit word count. This allows for 32 RTs on the bus. However, only 31RTs may be connected, since the RT address (31) is used to indicate a broadcast transfer, i.e. all RTs should accept the following data. Each RT has 30 sub-addresses reserved for data transfers. The other two sub-addresses (0 and 31) are reserved for mode codes used for bus control functions. Data transfers contain up to (32) 16-bit data words. Mode code command words are used for bus control functions such as synchronization.

COMPUTER FORENSICS

2009-07-28T10:36:00.000-07:00

COMPUTER FORENSICS

Computer forensics is a branch of forensic science pertaining to legal evidence found in computers and digital storage mediums. Computer forensics is also known as digital forensics.

The goal of computer forensics is to explain the current state of a digital artifact. The term digital artifact can include a computer system, a storage medium (such as a hard disk or CD-ROM), an electronic document (e.g. an email message or JPEG image) or even a sequence of packets moving over a computer network. The explanation can be as straightforward as "what information is here?" and as detailed as "what is the sequence of events responsible for the present situation?"

The field of computer forensics also has sub branches within it such as firewall forensics, network forensics, database forensics and mobile device forensics.

There are many reasons to employ the techniques of computer forensics:

* In legal cases, computer forensic techniques are frequently used to analyze computer systems belonging to defendants (in criminal cases) or litigants (in civil cases).
* To recover data in the event of a hardware or software failure.
* To analyze a computer system after a break-in, for example, to determine how the attacker gained access and what the attacker did.
* To gather evidence against an employee that an organization wishes to terminate.
* To gain information about how computer systems work for the purpose of debugging, performance optimization, or reverse-engineering.

Special measures should be taken when conducting a forensic investigation if it is desired for the results to be used in a court of law. One of the most important measures is to assure that the evidence has been accurately collected and that there is a clear chain of custody from the scene of the crime to the investigator---and ultimately to the court. In order to comply with the need to maintain the integrity of digital evidence, British examiners comply with the Association of Chief Police Officers (A.C.P.O.) guidelines. These are made up of four principles as follows:-

Principle 1: No action taken by law enforcement agencies or their agents should change data held on a computer or storage media which may subsequently be relied upon in court.

Principle 2: In exceptional circumstances, where a person finds it necessary to access original data held on a computer or on storage media, that person must be competent to do so and be able to give evidence explaining the relevance and the implications of their actions.

Principle 3: An audit trail or other record of all processes applied to computer based electronic evidence should be created and preserved. An independent third party should be able to examine those processes and achieve the same result.

Principle 4: The person in charge of the investigation (the case officer) has overall responsibility for ensuring that the law and these principles are adhered to.

The Forensic Process

There are five basic steps to the computer forensics:
1. Preparation (of the investigator, not the data)
2. Collection (the data)
3. Examination
4. Analysis
5. Reporting

The investigator must be properly trained to perform the specific kind of investigation that is at hand.

Tools that are used to generate reports for court should be validated. There are many tools to be used in the process. One should determine the proper tool to be used based on the case.

Collecting Digital Evidence

Digital evidence can be collected from many sources. Obvious sources include computers, cell phones, digital cameras, hard drives, CD-ROM, USB memory devices, and so on. Non-obvious sources include settings of digital thermometers, black boxes inside automobiles, RFID tags, and web pages (which must be preserved as they are subject to change).

Special care must be taken when handling computer evidence: most digital information is easily changed, and once changed it is usually impossible to detect that a change has taken place (or to revert the data back to its original state) unless other measures have been taken. For this reason it is common practice to calculate a cryptographic hash of an evidence file and to record that hash elsewhere, usually in an investigator's notebook, so that one can establish at a later point in time that the evidence has not been modified since the hash was calculated.

Other specific practices that have been adopted in the handling of digital evidence include:

* Imaging computer media using a writeblocking tool to ensure that no data is added to the suspect device.
* Establish and maintain the chain of custody.
* Documenting everything that has been done.
* Only use tools and methods that have been tested and evaluated to validate their accuracy and reliability.

Some of the most valuable information obtained in the course of a forensic examination will come from the computer user. An interview with the user can yield valuable information about the system configuration, applications, encryption keys and methodology. Forensic analysis is much easier when analysts have the user's passphrases to access encrypted files, containers, and network servers.

In an investigation in which the owner of the digital evidence has not given consent to have his or her media examined (as in some criminal cases) special care must be taken to ensure that the forensic specialist has the legal authority to seize, copy, and examine the data. Sometimes authority stems from a search warrant. As a general rule, one should not examine digital information unless one has the legal authority to do so. Amateur forensic examiners should keep this in mind before starting any unauthorized investigation.

Live vs. Dead analysis

Traditionally computer forensic investigations were performed on data at rest---for example, the content of hard drives. This can be thought of as a dead analysis. Investigators were told to shut down computer systems when they were impounded for fear that digital time-bombs might cause data to be erased.

In recent years there has increasingly been an emphasis on performing analysis on live systems. One reason is that many current attacks against computer systems leave no trace on the computer's hard drive---the attacker only exploits information in the computer's memory. Another reason is the growing use of cryptographic storage: it may be that the only copy of the keys to decrypt the storage are in the computer's memory, turning off the computer will cause that information to be lost.

Imaging electronic media (evidence)

The process of creating an exact duplicate of the original evidentiary media is often called Imaging. Using a standalone hard-drive duplicator or software imaging tools such as DCFLdd or IXimager, the entire hard drive is completely duplicated. This is usually done at the sector level, making a bit-stream copy of every part of the user-accessible areas of the hard drive which can physically store data, rather than duplicating the filesystem. The original drive is then moved to secure storage to prevent tampering. During imaging, a write protection device or application is normally used to ensure that no information is introduced onto the evidentiary media during the forensic process.

The imaging process is verified by using the SHA-1 message digest algorithm (with a program such as sha1sum) or other still viable algorithms such as MD5. At critical points throughout the analysis, the media is verified again, known as "hashing", to ensure that the evidence is still in its original state. In corporate environments seeking civil or internal charges, such steps are generally overlooked due to the time required to perform them. They are essential for evidence that is to be presented in a court room, however.

Collecting Volatile Data

If the machine is still active, any intelligence which can be gained by examining the applications currently open is recorded. If the machine is suspected of being used for illegal communications, such as terrorist traffic, not all of this information may be stored on the hard drive. If information stored solely in RAM is not recovered before powering down it may be lost. This results in the need to collect volatile data from the computer at the onset of the response.

Several Open Source tools are available to conduct an analysis of open ports, mapped drives (including through an active VPN connection), and open or mounted encrypted files (containers) on the live computer system. Utilizing open source tools and commercially available products, it is possible to obtain an image of these mapped drives and the open encrypted containers in an unencrypted format. Open Source tools for PCs include Knoppix and Helix. Commercial imaging tools include Access Data's Forensic Toolkit and Guidance Software's EnCase application.

The aforementioned Open Source tools can also scan RAM and Registry information to show recently accessed web-based email sites and the login/password combination used. Additionally these tools can also yield login/password for recently accessed local email applications including MS Outlook.

In the event that partitions with EFS are suspected to exist, the encryption keys to access the data can also be gathered during the collection process. With Microsoft's most recent addition, Vista, and Vista's use of BitLocker and the Trusted Platform Module (TPM), it has become necessary in some instances to image the logical hard drive volumes before the computer is shut down.

RAM can be analyzed for prior content after power loss. Although as production methods become cleaner the impurities used to indicate a particular cell's charge prior to power loss are becoming less common. However, data held statically in an area of RAM for long periods of time are more likely to be detectable using these methods. The likelihood of such recovery increases as the originally applied voltages, operating temperatures and duration of data storage increases. Holding unpowered RAM below − 60 °C will help preserve the residual data by an order of magnitude, thus improving the chances of successful recovery. However, it can be impractical to do this during a field examination.

Analysis

All digital evidence must be analyzed to determine the type of information that is stored upon it. For this purpose, specialty tools are used that can display information in a format useful to investigators. Such forensic tools include: AccessData's FTK, Guidance Software's EnCase, and Brian Carrier's Sleuth Kit. In many investigations, numerous other tools are used to analyze specific portions of information.

Typical forensic analysis includes a manual review of material on the media, reviewing the Windows registry for suspect information, discovering and cracking passwords, keyword searches for topics related to the crime, and extracting e-mail and images for review.

Reporting

Once the analysis is complete, a report is generated. This report may be a written report, oral testimony, or some combination of the two.

The increasing use of telecommunications, particularly the development of e-commerce, is steadily increasing the opportunities for crime in many guises, especially IT-related crime .Developments in information technology have begun to pose new challenges for policing. Most professions have had to adapt to the digital age, and the police profession must be particularly adaptive, because criminal exploitation of digital technologies necessitates new types of criminal investigation. More and more, information technology is becoming the instrument of criminal activity. Investigating these sophisticated crimes, and assembling the necessary evidence for presentation in a court of law, will become a significant police responsibility. The application of computer technology to the investigation of computer-based crime has given rise to the field of forensic computing. This paper provides an overview of the field of forensic computing.

Coexistence & Migration

2009-07-28T10:35:00.000-07:00

Coexistence & Migration

The migration of IPv4 to IPv6 will not happen overnight. Rather, there will be a period of transition when both protocols are in use over the same infrastructure. To address this, the designers of IPv6 have created technologies and types of addresses so that nodes can communicate with each other in a mixed environment, even if they are separated by an IPv4 infrastructure. This article describes IPv4 and IPv6 coexistence and migration technologies and how these technologies are supported by the IPv6 protocol for the Windows .NET Server 2003 family. This article is intended for network engineers and support professionals who are already familiar with basic networking concepts, TCP/IP, and IPv6.

Brain Computer Interface

2009-07-28T10:34:00.000-07:00

Brain Computer Interface

A Brain Computer Interface is a device that enables people to interact with computer based systems through conscious control of their thoughts. BCI is any system that can derive meaningful information directly from the user’s brain activity in real time. The current and most important application of BCI is the restoration of communication channel for patients with locked-in-syndrome. Most current BCI’s are not invasive. The electrodes pick up the brain’s electrical activity and carry it into amplifiers. These amplifiers amplify the signal approximately ten thousand times and then pass the signal via an analog to digital converter to a computer for processing. The computer processes the EEG signal and uses it in order to accomplish tasks such as communication and environmental control.

Block Oriented Instrument Software Design

2009-07-28T10:32:00.000-07:00

Block Oriented Instrument Software Design

A new method for writing instrumentation software is proposed. It is based on the abstract description of the instrument operation and combines the advantages of a reconfigurable instrument and interchangeability of the instrumentation modules. The proposed test case is the implementation of a microwave network analyzer for nonlinear systems based on VISA and plug and play instrument drivers.

Modern Instruments or Instrumentation setups are likely to be built-up around generic hardware and custom software. The disadvantage is that the amount of software required to operate such a device is very high. An acceptable development time for a reasonably low number of software bugs can therefore only be obtained if the software is maximally reused from earlier developments. Most attempts used a two-step approach. In the first step transport interface between computer and instrument is abstracted. The first step in this approach has always been quite successful. The first transport abstraction stems from the IEEE-488 interface. Afterward SICL and VISA were developed to support multiple transport busses (IEEE-488, RS-232 and later Ethernet and IEE-1394). These methods use a file as the conceptual model for an instrument. The commands sent to the files are independent of the transmission medium, medium dependency is localized only in the initialization call. Most interfaces that can be used for instrumentation control are, hence, supported by these frameworks.

In the second step the instrumentation command is abstracted to empower interchangeability of similar pieces of instrumentation. For this, the situation always has been much less obvious. Only end-users have something to gain in instrument interchangeability. An abstract model to programming instrumentation setups is proposed which is easy and general enough to be used for complex setups.

BIT FOR INTELLIGENT SYSTEM DESIGN

2009-07-28T10:31:00.000-07:00

BIT FOR INTELLIGENT SYSTEM DESIGN

The increasing complexity of microelectronic circuitry, as witnessed by multi-chip modules and system-on-a-chip and the rapid growth of manufacturing process automation require, that more effective and efficient testing and fault diagnosis techniques be developed to improve system reliability, reduce system downtime, and esemnhance productivity. As a design philosophy, built-in-test (BIT) is receiving increasing attention from the research community. This paper presents an overview of BIT search in several areas of industry, including semiconductor, manufacturing.

ACTUATOR ( AS-i)

2009-07-28T10:30:00.000-07:00

ACTUATOR ( AS-i)

In recent years, automation technology has migrated to new methods of transferring information. Increasingly, field-level devices such as sensors and actuators have internal intelligence capabilities and higher communication demands. The AS-i bus system provides the solution for a digital serial interface with a single unshielded two-wire cable which replaces traditional cable harness parallel wiring between masters and slaves.

AS-i technology is compatible with any fieldbus or device network. Low-cost gateways exist to use AS-i with CAN, PROFIBUS, Interbus, FIP, LON, RS-485 and RS-232.

The AS-i uses the Isolation Penetration Technology. The AS-i follows the ISO/OSI model to successfully implement the master/slave communication.

64-Point FT Chip

2009-07-28T10:29:00.000-07:00

64-Point FT Chip

A fixed-point 16-bit word-length 64-point FFT/IFFT processor developed primarily for the application in an OFDM based IEEE 802.11a wireless LAN base band processor. The 64-point FFT is realized by decomposing it in to a two dimensional structure of 8-point FFTs. This approach reduces the number of required complex multiplication compared to the conventional radix-2 64-point FFT algorithm. The complex multiplication operations are realized using shift and add operation. Thus, the processor does not use a two-input digital multiplier. It also does not need any RAM or ROM for internal storage of coefficients. The core area of this chip is 6.8mm². The average dynamic power consumption is 41mW at 20Mhz operating frequency and 1.8Volt supply voltage. The processor completes one parallel-to-parallel 64-point FFT computation in 23 cycles; it can be used for any application that requires fast operation as well as low power consumption.

Microelectronic pill

2009-07-28T10:28:00.000-07:00

Microelectronic pill

A “Microelectronic pill” is a basically a multichannel sensor used for remote biomedical measurements using micro technology. This has been developed for the internal study and detection of diseases and abnormalities in the gastrointestinal (GI) tract where restricted access prevents the use of traditional endoscope. The measurement parameters for detection include real – time remote recording of temperature, pH, conductivity and dissolved oxygen in the GI tract.

This paper deals with the design of the “Microelectronic pill” which mainly consists of an outer biocompatible capsule encasing 4–channel micro sensors, a control chip, a discrete component radio transmitter and 2 silver oxide cells.

Electronic Nose (E-NOSE)

2009-07-28T10:12:00.000-07:00

Electronic Nose (E-NOSE)

An electronic nose is a device intended to detect odors or flavors.

An electronic nose (e-nose) is a device that identifies the specific components of an odor and analyzes its chemical makeup to identify it. An electronic nose consists of a mechanism for chemical detection, such as an array of electronic sensors, and a mechanism for pattern recognition, such as a neural network . Electronic noses have been around for several years but have typically been large and expensive. Current research is focused on making the devices smaller, less expensive, and more sensitive. The smallest version, a nose-on-a-chip is a single computer chip containing both the sensors and the processing components.

An odor is composed of molecules, each of which has a specific size and shape. Each of these molecules has a correspondingly sized and shaped receptor in the human nose. When a specific receptor receives a molecule, it sends a signal to the brain and the brain identifies the smell associated with that particular molecule. Electronic noses based on the biological model work in a similar manner, albeit substituting sensors for the receptors, and transmitting the signal to a program for processing, rather than to the brain. Electronic noses are one example of a growing research area called biomimetics , or biomimicry, which involves human-made applications patterned on natural phenomena.

Electronic noses were originally used for quality control applications in the food, beverage and cosmetics industries. Current applications include detection of odors specific to diseases for medical diagnosis, and detection of pollutants and gas leaks for environmental protection.

Over the last decade, “electronic sensing” or “e-sensing” technologies have undergone important developments from a technical and commercial point of view. The expression “electronic sensing” refers to the capability of reproducing human senses using sensor arrays and pattern recognition systems. Since 1982, research has been conducted to develop technologies, commonly referred to as electronic noses, that could detect and recognize odors and flavors. The stages of the recognition process are similar to human olfaction and are performed for identification, comparison, quantification and other applications. However, hedonic evaluation is a specificity of the human nose given that it is related to subjective opinions. These devices have undergone much development and are now used to fulfill industrial needs.

Other techniques to analyze odors

In industry, aroma assessment is usually performed by human sensory analysis, Chemosensors or by gas chromatography (GC, GC/MS). The latter technique gives information about volatile organic compounds but the correlation between analytical results and actual odor perception is not direct due to potential interactions between several odorous components.

Electronic Nose working principle

The electronic nose was developed in order to mimic human olfaction that functions as a non-separative mechanism: i.e. an odor / flavor is perceived as a global fingerprint.

Electronic Noses include three major parts: a sample delivery system, a detection system, a computing system.

The sample delivery system enables the generation of the headspace (volatile compounds) of a sample, which is the fraction analyzed. The system then injects this headspace into the detection system of the electronic nose. The sample delivery system is essential to guarantee constant operating conditions.

The detection system, which consists of a sensor set, is the “reactive” part of the instrument. When in contact with volatile compounds, the sensors react, which means they experience a change of electrical properties. Each sensor is sensititive to all volatile molecules but each in their specific way. Most electronic noses use sensor-arrays that react to volatile compounds on contact: the adsorption of volatile compounds on the sensor surface causes a physical change of the sensor. A specific response is recorded by the electronic interface transforming the signal into a digital value. Recorded data are then computed based on statistical models.

The more commonly used sensors include metal oxide semiconductors (MOS), conducting polymers (CP), quartz crystal microbalance, surface acoustic wave (SAW), and field effect transistors (MOSFET).

In recent years, other types of electronic noses have been developed that utilize mass spectrometry or ultra fast gas chromatography as a detection system.

The computing system works to combine the responses of all of the sensors, which represents the input for the data treatment. This part of the instrument performs global fingerprint analysis and provides results and representations that can be easily interpreted. Moreover, the electronic nose results can be correlated to those obtained from other techniques (sensory panel, GC, GC/MS).

How to perform an analysis

fingerprint to those contained in its database. Thus they can perform qualitative or quantitative analysis.

Range of applications

Electronic nose instruments are used by Research & Development laboratories, Quality Control laboratories and process & production departments for various purposes:

in R&D laboratories for:

* Formulation or reformulation of products
* Benchmarking with competitive products
* Shelf life and stability studies
* Selection of raw materials
* Packaging interaction effects
* Simplification of consumer preference test

in Quality Control laboratories for at line quality control such as:

* Conformity of raw materials, intermediate and final products
* Batch to batch consistency
* Detection of contamination, spoilage, adulteration
* Origin or vendor selection
* Monitoring of storage conditions.

In process and production departments for:

* Managing raw material variability
* Comparison with a reference product
* Measurement and comparison of the effects of manufacturing process on products
* Following-up cleaning in place process efficiency
* Scale-up monitoring
* Cleaning in place monitoring.

Various application notes describe analysis in areas such as Flavor & Fragrance, Food & Beverage, Packaging, Pharmaceutical, Cosmetic & Perfumes, Chemical companies. More recently they can also address public concerns in terms of olfactive nuisance monitoring with networks of on-field devices.

Deep Web

2009-07-27T22:00:00.000-07:00

Deep Web

The deep Web (also called Deepnet, the invisible Web, dark Web or the hidden Web) refers to World Wide Web content that is not part of the surface Web, which is indexed by standard search engines.

Mike Bergman, credited with coining the phrase, has said that searching on the Internet today can be compared to dragging a net across the surface of the ocean; a great deal may be caught in the net, but there is a wealth of information that is deep and therefore missed. Most of the Web's information is buried far down on dynamically generated sites, and standard search engines do not find it. Traditional search engines cannot "see" or retrieve content in the deep Web – those pages do not exist until they are created dynamically as the result of a specific search. The deep Web is several orders of magnitude larger than the surface Web.

Naming

Bergman, in a seminal, early paper on the deep Web published in the Journal of Electronic Publishing, mentioned that Jill Ellsworth used the term invisible Web in 1994 to refer to websites that are not registered with any search engine. Bergman cited a January 1996 article by Frank Garcia:

"It would be a site that's possibly reasonably designed, but they didn't bother to register it with any of the search engines. So, no one can find them! You're hidden. I call that the invisible Web."

Another early use of the term invisible Web was by Bruce Mount and Matthew B. Koll of Personal Library Software, in a description of the @1 deep Web tool found in a December 1996 press release.

The first use of the specific term deep Web, now generally accepted, occurred in the aforementioned 2001 Bergman study.

Size

In 2000, it was estimated that the deep Web contained approximately 7,500 terabytes of data and 550 billion individual documents. Estimates based on extrapolations from a study done at University of California, Berkeley, show that the deep Web consists of about 91,000 terabytes. By contrast, the surface Web (which is easily reached by search engines) is only about 167 terabytes; the Library of Congress, in 1997, was estimated to have perhaps 3,000 terabytes.

Deep resources

Deep Web resources may be classified into one or more of the following categories:

* Dynamic content: dynamic pages which are returned in response to a submitted query or accessed only through a form, especially if open-domain input elements (such as text fields) are used; such fields are hard to navigate without domain knowledge.

* Unlinked content: pages which are not linked to by other pages, which may prevent Web crawling programs from accessing the content. This content is referred to as pages without backlinks (or inlinks).

* Private Web: sites that require registration and login (password-protected resources).

* Contextual Web: pages with content varying for different access contexts (e.g., ranges of client IP addresses or previous navigation sequence).

* Limited access content: sites that limit access to their pages in a technical way (e.g., using the Robots Exclusion Standard, CAPTCHAs, or no-cache Pragma HTTP headers which prohibit search engines from browsing them and creating cached copies).

* Scripted content: pages that are only accessible through links produced by JavaScript as well as content dynamically downloaded from Web servers via Flash or AJAX solutions.

* Non-HTML/text content: textual content encoded in multimedia (image or video) files or specific file formats not handled by search engines.

Accessing

To discover content on the Web, search engines use web crawlers that follow hyperlinks. This technique is ideal for discovering resources on the surface Web but is often ineffective at finding deep Web resources. For example, these crawlers do not attempt to find dynamic pages that are the result of database queries due to the infinite number of queries that are possible.It has been noted that this can be (partially) overcome by providing links to query results, but this could unintentionally inflate the popularity (e.g., PageRank) for a member of the deep Web.

One way to access the deep Web is via federated search based search engines. Search tools such as Science.gov are being designed to retrieve information from the deep Web. These tools identify and interact with searchable databases, aiming to provide access to deep Web content.

Another way to explore the deep Web is by using human crawlers instead of algorithmic crawlers. In this paradigm, referred to as Web harvesting, humans find interesting links of the deep Web that algorithmic crawlers can't find. This human-based computation technique to discover the deep Web has been used by the StumbleUpon service since February 2002.

In 2005, Yahoo! made a small part of the deep Web searchable by releasing Yahoo! Subscriptions. This search engine searches through a few subscription-only Web sites. Some subscription websites display their full content to search engine robots so they will show up in user searches, but then show users a login or subscription page when they click a link from the search engine results page.

Crawling the deep Web

Researchers have been exploring how the deep Web can be crawled in an automatic fashion. In 2001, Sriram Raghavan and Hector Garcia-Molina presented an architectural model for a hidden-Web crawler that used key terms provided by users or collected from the query interfaces to query a Web form and crawl the deep Web resources. Alexandros Ntoulas, Petros Zerfos, and Junghoo Cho of UCLA created a hidden-Web crawler that automatically generated meaningful queries to issue against search forms.Their crawler generated promising results, but the problem is far from being solved, as the authors recognized. Another effort is DeepPeep, a project of the University of Utah sponsored by the National Science Foundation, which gathered hidden-Web sources (Web forms) in different domains based on novel focused crawler techniques.

Commercial search engines have begun exploring alternative methods to crawl the deep Web. The Sitemap Protocol (first developed by Google) and mod oai are mechanisms that allow search engines and other interested parties to discover deep Web resources on particular Web servers. Both mechanisms allow Web servers to advertise the URLs that are accessible on them, thereby allowing automatic discovery of resources that are not directly linked to the surface Web. Google's deep Web surfacing system pre-computes submissions for each HTML form and adds the resulting HTML pages into the Google search engine index. The surfaced results account for a thousand queries per second to deep Web content.. In this system, the pre-computation of submissions is done using three algorithms: (1) selecting input values for text search inputs that accept keywords, (2) identifying inputs which accept only values of a specific type (e.g., date), and (3) selecting a small number of input combinations that generate URLs suitable for inclusion into the Web search index.

Classifying resources

It is difficult to automatically determine if a Web resource is a member of the surface Web or the deep Web. If a resource is indexed by a search engine, it is not necessarily a member of the surface Web, because the resource could have been found using another method (e.g., the Sitemap Protocol, mod oai, OAIster) instead of traditional crawling. If a search engine provides a backlink for a resource, one may assume that the resource is in the surface Web. Unfortunately, search engines do not always provide all backlinks to resources. Even if a backlink does exist, there is no way to determine if the resource providing the link is itself in the surface Web without crawling all of the Web. Furthermore, a resource may reside in the surface Web, but it has not yet been found by a search engine. Therefore, if we have an arbitrary resource, we cannot know for sure if the resource resides in the surface Web or deep Web without a complete crawl of the Web.

The concept of classifying search results by topic was pioneered by Yahoo! Directory search[citation needed] and is gaining importance as search becomes more relevant in day-to-day decisions. However, most of the work here has been in categorizing the surface Web by topic. For classification of deep Web resources, Ipeirotis et al. presented an algorithm that classifies a deep Web site into the category that generates the largest number of hits for some carefully selected, topically-focused queries. Deep Web directories under development include as OAIster at the University of Michigan, Intute at the University of Manchester, INFOMINE at the University of California at Riverside, and DirectSearch (by Gary Price). This classification poses a challenge while searching the deep Web whereby two levels of categorization are required. The first level is to categorize sites into vertical topics (e.g., health, travel, automobiles) and sub-topics according to the nature of the content underlying their databases.

The more difficult challenge is to categorize and map the information extracted from multiple deep Web sources according to end-user needs. Deep Web search reports cannot display URLs like traditional search reports. End users expect their search tools to not only find what they are looking for quickly, but to be intuitive and user-friendly. In order to be meaningful, the search reports have to offer some depth to the nature of content that underlie the sources or else the end-user will be lost in the sea of URLs that do not indicate what content lies underneath them. The format in which search results are to be presented varies widely by the particular topic of the search and the type of content being exposed. The challenge is to find and map similar data elements from multiple disparate sources so that search results may be exposed in a unified format on the search report irrespective of their source.

Future

The lines between search engine content and the deep Web have begun to blur, as search services start to provide access to part or all of once-restricted content. An increasing amount of deep Web content is opening up to free search as publishers and libraries make agreements with large search engines. In the future, deep Web content may be defined less by opportunity for search than by access fees or other types of authentication.

Content on the deep Web

When we refer to the deep Web, we are usually talking about the following:

* The content of databases. Databases contain information stored in tables created by such programs as Access, Oracle, SQL Server, and MySQL. (There are other types of databases, but we will focus on database tables for the sake of simplicity.) Information stored in databases is accessible only by query. In other words, the database must somehow be searched and the data retrieved and then displayed on a Web page. This is distinct from static, self-contained Web pages, which can be accessed directly. A significant amount of valuable information on the Web is generated from databases.
* Non-text files such as multimedia, images, software, and documents in formats such as Portable Document Format (PDF). For example, see Digital Image Resources on the Deep Web for a good indication of what is out there for images.
* Content available on sites protected by passwords or other restrictions. Some of this is fee-based content, such as subscription content paid for by libraries and available to their users based on various authentication schemes.
* Special content not presented as Web pages, such as full text articles and books
* Dynamically-changing, updated content

This is usually the basic,"traditional" list. In these days of the social Web, let's consider adding new content to our list of deep Web sources. For example:

* Blog postings
* Comments
* Discussions and other communicative activities on social networking sites
* Bookmarks and citations stored on social bookmarking sites

As you can see, based on these few examples, the deep Web is expanding.
Tips for dealing with deep Web content

* Vertical search can solve some of the problems with the deep Web. With vertical search, you can query an index or database focused on a specific topic, industry, type of content, geographical location, language, file type, Web site, piece of data, and so on. For example, consider MedNar and PubMed to search for medical topics. On the social Web, there are search engines for blogs, RSS feeds, Twitter content, and so on. See the tutorial on Vertical Search Engines for more information.
* Use a general search engine to search for a vertical search engine. For example, a Google search on "stock market search" will retrieve sites that allow you to search for current stock prices, market news, etc. This may be thought of as split level searching. For the first level, search for the database site. For the second level, go to the site and search the database itself for the information you want.
* A number of general search engines will search the deep Web for related content subsequent to an initial search. For example, try a search on Google for "World Trade Center" and select the Images tab. This will retrieve many pages of images of the World Trade Center. Look for this type of feature on other search engines.
* Try to figure out which kind of information might be stored in a database.. There is no general rule. But think about large listings of things with a common theme. A few examples of databased content include:
* phone books
* "people finders" such as lists of professionals such as doctors or lawyers
* patents
* laws
* dictionary definitions
* items for sale in a Web store or on Web-based auctions
* digital exhibits
* images and multimedia
* full text articles and books
* Information that is new and dynamically changing in content will appear on the deep Web. Look to the deep Web for late breaking items, such as:
* news
* job postings
* available airline flights, hotel rooms
* stock and bond prices, market averages
* The social Web often jumps on a late-breaking situation with news items and commentary. Blogs, Twitter, and other social networking environments sometimes get out the word before more traditional sources.
* Topical coverage on the deep Web is extremely varied. This presents a challenge, since it is impossible to anticipate what might turn up.

These limitations are, however, being overcome by the new search engine crawlers (like Pipl) being designed today. These new crawlers are designed to identify, interact and retrieve information from deep web resources and searchable databases. Google, for example, has developed the mod oai and Sitemap Protocol in order to increase results from deep web searches of web servers. These new developments will allow the web servers to automatically show the URLs that they can access to search engines.

Another solution that is being developed by several search engines like Alacra, Northern Light and CloserLookSearch are specialty search engines that focus only in particular topics or subject areas. This would allow the search engines to narrow their search and make a more in-depth search of the deep web by querying password-protected and dynamic databases.

KNX (standard)

2009-07-27T21:59:00.000-07:00

KNX (standard)

KNX is a standardised (EN 50090,ISO/IEC 14543), OSI-based network communications protocol for intelligent buildings. KNX is the successor to, and convergence of, three previous standards: the European Home Systems Protocol (EHS), BatiBUS, and the European Installation Bus (EIB). The KNX standard is administered by the Konnex Association.

The standard is based on the communication stack of EIB but enlarged with the physical layers, configuration modes and application experience of BatiBUS and EHS.

KNX defines several physical communication media:

* Twisted pair wiring (inherited from the BatiBUS and EIB Instabus standards)
* Powerline networking (inherited from EIB and EHS - similar to that used by X10)
* Radio
* Infrared
* Ethernet (also known as EIBnet/IP or KNXnet/IP)

KNX is designed to be independent of any particular hardware platform. A KNX Device Network can be controlled by anything from an 8-bit microcontroller to a PC, according to the needs of a particular implementation. The most common form of installation is over twisted pair medium.

KNX is approved as an open standard to:

* International standard (ISO/IEC 14543-3)
* European Standard (CENELEC EN 50090 and CEN EN 13321-1)
* China Guo Biao(GB/Z 20965)

KNX has more than 100 members/manufacturers including:

* ABB
* Bosch
* Miele & Cie KG
* ON Semiconductor
* Schneider Electric Industries S.A.
* Siemens
* Uponor corporation
* Jung

There are three categories of KNX device:

* A-mode or "Automatic mode" devices automatically configure themselves, and are intended to be sold to and installed by the end user.
* E-mode or "Easy mode" devices require basic training to install. Their behaviour is pre-programmed, but has configuration parameters that need to be tailored to the user's requirements.
* S-mode or "System mode" devices are used in the creation of bespoke building automation systems. S-mode devices have no default behaviour, and must be programmed and installed by specialist technicians.

ADSL - Assymetric Digital Subscriber Line

2009-07-15T10:37:00.000-07:00

ADSL - Assymetric Digital Subscriber Line

Digital Subscriber Line (DSL) is a technology that brings high bandwidth information to homes and small businesses over the existing 2 wire copper telephone lines. Since DSL works on the existing telephone infrastructure, DSL systems are considered a key means of opening the bottleneck in the of the existing telephone network, as telephone companies seek cost-effective ways of providing much higher speed to their customers. DSL is a technology that assumes digital data does not require change into analog form and back. This gives it two main advantages. Digital data is transmitted to your computer directly as digital data, and this allows the phone company to use a much wider bandwidth for transmitting it to you, thereby giving the user a huge boost in bandwidth compared to analog modems. Not only that, but DSL uses the existing phone line and in most cases does not require an additional phone line. The digital signal can be separated or filtered, so that some of the bandwidth can be used to transmit an analog signal so that normal telephone calls can be made while a computer is connected to the internet. This gives "always-on" Internet access and does not tie up the phone line. No more busy signals, no more dropped connections, and no more waiting for someone in the household to get off the phone.

Because analog transmission only uses a small portion of the available amount of information that could be transmitted over copper wires, the maximum amount of data that you can receive using ordinary modems is about 56 Kbps (thousands of bits per second). With ISDN you can receive up to 128 Kbps. This shows that the ability of your computer to receive information is constrained by the fact that the telephone company filters information that arrives as digital data, puts it into analog form for your telephone line, and requires your modem to change it back into digital. In other words, the analog transmission between your home or business and the phone company is a bandwidth bottleneck. DSL however offers users a choice of speeds ranging from 144 Kbps to 1.5Mbps. This is 2.5 times to 25 times faster than a standard 56 Kbps dial-up modem. This digital service can be used to deliver bandwidth intensive applications like streaming audio/video, online games, application programs, telephone calling, video conferencing and other high-bandwidth services.

Biochip

2009-07-14T11:13:00.000-07:00

Biochip

The development of biochips is a major thrust of the rapidly growing biotechnology industry, which encompasses a very diverse range of research efforts including genomics, proteomics, and pharmaceuticals, among other activities. Advances in these areas are giving scientists new methods for unraveling the complex biochemical processes occurring inside cells, with the larger goal of understanding and treating human diseases. At the same time, the semiconductor industry has been steadily perfecting the science of microminiaturization. The merging of these two fields in recent years has enabled biotechnologists to begin packing their traditionally bulky sensing tools into smaller and smaller spaces, onto so-called biochips. These chips are essentially miniaturized laboratories that can perform hundreds or thousands of simultaneous biochemical reactions. Biochips enable researchers to quickly screen large numbers of biological analytes for a variety of purposes, from disease diagnosis to detection of bioterrorism agents.

A biochip is a collection of miniaturized test sites (microarrays) arranged on a solid substrate that permits many tests to be performed at the same time in order to achieve higher output and speed. Biochips can also be used to perform techniques such as electrophoresis or PCR using microfluidics technology (Fan, 2009; Cady, 2009).

== History ==oxygen electrode, thereby relating oxygen levels to glucose concentration. This and similar biosensors became known as enzyme electrodes, and are still in use today.

In 1953, Watson and Crick announced their discovery of the now familiar double helix structure of DNA molecules and set the stage for genetics research that continues to the present day (Nelson, 2000). The development of sequencing techniques in 1977 by Gilbert (Maxam, 1977) and Sanger (Sanger, 1977) (working separately) enabled researchers to directly read the genetic codes that provide instructions for protein synthesis. This research showed how hybridization of complementary single oligonucleotide strands could be used as a basis for DNA sensing. Two additional developments enabled the technology used in modern DNA-based biosensors. First, in 1983 Kary Mullis invented the polymerase chain reaction (PCR) technique (Nelson, 2000), a method for amplifying DNA concentrations. This discovery made possible the detection of extremely small quantities of DNA in samples. Second, in 1986 Hood and coworkers devised a method to label DNA molecules with fluorescent tags instead of radiolabels (Smith, 1986), thus enabling hybridization experiments to be observed optically.

Bionics

2009-07-11T11:15:00.000-07:00

Bionics

Bionics (also known as biomimetics, bio-inspiration, biognosis, biomimicry, or bionical creativity engineering) is the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology. The word bionic was coined by Jack E. Steele in 1958, possibly originating from the Greek word βίον, bíon, pronounced [bi:on] ("bee-on"), meaning 'unit of life' and the suffix -ic, meaning 'like' or 'in the manner of', hence 'like life'. Some dictionaries, however, explain the word as being formed from biology + electronics.

The transfer of technology between lifeforms and synthetic constructs is, according to proponents of bionic technology, desirable because evolutionary pressure typically forces living organisms, including fauna and flora, to become highly optimized and efficient. A classical example is the development of dirt- and water-repellent paint (coating) from the observation that the surface of the lotus flower plant is practically unsticky for anything (the lotus effect).

The term "biomimetic" is prefered when reference is made to chemical reactions. In that domain, biomimetic chemistry refers to reactions that, in nature, involve biological macromolecules (for example, enzymes or nucleic acids) whose chemistry can be replicated using much smaller molecules in vitro .

Examples of bionics in engineering include the hulls of boats imitating the thick skin of dolphins; sonar, radar, and medical ultrasound imaging imitating the echolocation of bats. In the field of computer science, the study of bionics has produced artificial neurons, artificial neural networks, and swarm intelligence. Evolutionary computation was also motivated by bionics ideas but it took the idea further by simulating evolution in silico and producing well-optimized solutions that had never appeared in nature. It is estimated by Julian Vincent, professor of biomimetics at the University of Bath in the UK, that "at present there is only a 10% overlap between biology and technology in terms of the mechanisms used"

The name biomimetics was coined by Otto Schmitt in the 1950s. The term bionics was coined by Jack E. Steele in 1958 while working at the Aeronautics Division House at Wright-Patterson Air Force Base in Dayton. However, terms like biomimicry or biomimetics are more preferred in the technology world in efforts to avoid confusion between the medical term bionics. Coincidentally, Martin Caidin used the word for his 1972 novel Cyborg, which inspired the series The Six Million Dollar Man. Caidin was a long-time aviation industry writer before turning to fiction full time.

Often, the study of bionics emphasizes implementing a function found in nature rather than just imitating biological structures. For example, in computer science, cybernetics tries to model the feedback and control mechanisms that are inherent in intelligent behavior, while artificial intelligence tries to model the intelligent function regardless of the particular way it can be achieved.

The conscious copying of examples and mechanisms from natural organisms and ecologies is a form of applied case-based reasoning, treating nature itself as a database of solutions that already work. Proponents argue that the selective pressure placed on all natural life forms minimizes and removes failures.

Although almost all engineering could be said to be a form of biomimicry, the modern origins of this field are usually attributed to Buckminster Fuller and its later codification as a house or field of study to Janine Benyus.

Roughly, we can distinguish three biological levels in the fauna or flora, after which technology can be modeled:

* Mimicking natural methods of manufacture
* Imitating mechanisms found in nature (velcro)
* Studying organizational principles from the social behaviour of organisms, such as the flocking behaviour of birds, optimization of ant foraging and bee foraging, and the swarm intelligence (SI)-based behaviour of a school of fish.

Adaptive cruise control System

2009-07-11T11:13:00.001-07:00

Adaptive cruise control System
An automotive cruise control system that automatically slows down the car if it is moving too close to the vehicle in front of it. A radar or laser unit located behind the grille determines the speed and distance of the vehicle in front. When the distance is computed to be safe again, the system accelerates the car back to its last speed setting. Also called "active cruise control" and "intelligent cruise control.

Autonomous cruise control is an optional cruise control system appearing on some more upscale vehicles. The system goes under many different trade names according to the manufacture. These systems use either a radar or laser setup allowing the vehicle to slow when approaching another vehicle and accelerate again to the preset speed when traffic allows. ACC technology is widely regarded as a key component of any future generations of smart cars.

Types

Laser-based systems are significantly lower in cost than radar-based systems; however, laser-based ACC systems do not detect and track vehicles well in adverse weather conditions nor do they track extremely dirty (non-reflective) vehicles very well. Laser-based sensors must be exposed, the sensor (a fairly-large black box) is typically found in the lower grille offset to one side of the vehicle.

Radar-based sensors can be hidden behind plastic fascias; however, the fascias may look different from a vehicle without the feature. For example, Mercedes packages the radar behind the upper grille in the center; however, the Mercedes grille on such applications contains a solid plastic panel in front of the radar with painted slats to simulate the slats on the rest of the grille.

Radar-based systems are available on many luxury cars as an option for approx. 1000-3000 USD/euro. Laser-based systems are available on some near luxury and luxury cars as an option for approx. 400-600 USD/euro.

Cooperating systems

Radar-based ACC often feature a Precrash system, which warns the driver and/or provides brake support if there is a high risk of a collision. Also in certain cars it is incorporated with a lane maintaining system which provides power steering assist to reduce steering input burden in corners when the cruise control system is activated.

Examples of vehicles with adaptive cruise control

2005 Acura RL
Audi A4 (see a demonstration on YouTube), A5, A6, A8, Q7
BMW 7 Series, 5 series, 6 series, 3 series (Active Cruise Control)
2004 Cadillac DTS, STS, XLR
2007 Chrysler 300C
2006 Ford Mondeo, Taurus, S-Max, Galaxy
2003 Honda Inspire Accord, Legend
Hyundai Genesis (Smart Cruise Control, delayed)
Infiniti M, Q45,QX56, G35, FX35/45/50 and G37
1999 Jaguar XK-R, S-Type, XJ, XF
2000 Lexus LS430/460 (laser and radar), RX (laser and radar), GS, IS, ES 350, and LX 570
Lincoln MKS, MKT
1998 Nissan Cima, Nissan Primera T-Spec Models (Intelligent Cruise Control)
1998 Mercedes-Benz S-Class, E-Class, CLS-Class, SL-Class, CL-Class, M-Class, GL-Class, CLK-Class (Distronic, removed in 2009 from certain US models)
Range Rover Sport
Renault Vel Satis
Subaru Legacy & Outback Japan-spec called SI-Cruise
1997 Toyota Celsior, Sienna (XLE Limited Edition), Avalon, Sequoia (Platinum Edition), Prius, Avensis
Volkswagen Passat, Phaeton, Touareg, 2009 Golf
Volvo S80, V70, XC70, XC60

Database Terms

2009-07-08T11:23:00.001-07:00

Database Terms

* Aggregation - Objects that are composed of other objects.
* Concurrency - Databases must ensure that data is checked when concurrent access is allowed. Concurrent access means more than one application or thread may be reading or updating the same data at the same time.
* Database Garbage Collection - Garbage collection is the process of destroying objects that are no longer referenced, and freeing the resources those objects used. In Java there is a background process that performs garbage collection. Requires bi-directional object relationships. Determines if the database performs garbage collection on objects that are no longer referenced by the database. This keeps external programs from having to track the use of object pointers.
* DBMS - Database management system.
* Distributed Architecture - Object are sharing in a distributed environment or the entire database may be replicated on multiple computers.
* DML - Data Manipulation Language separate from programming languages (for RDBMS) and used as a means of getting and storing data in the database.
* Encapsulation - Data with method storage. Not all databases support the methods but rely upon the classes defined in the schema to reconstruct the object with its methods.
* Fault tolerance - Features that provide for fault tolerence in the event of a hardware of software failure. Normally transaction processing provides software fault tolerance. Data replication to other servers on the network supports hardware fault tolerance.
* Heterogeneous environment - Cross Platform support - The database may be able to run on various builds of computers and with various operating systems.
* Inheritance - Objects inherit attributes from parent objects.
* JDBC - An application program interface (API). Calls are used to execute SQL operations.
* normalized - Elimination of redundancy in databases so that all columns depend on a primary key.
* Notification - Notification may be active or passive. A passive system can minimally determine if an object has changed state. An active system may provide for an application to be informed when an object is modified.
* Object relationships - Object relationships define association with other objects, and whether objects can detect each other in one direction or two directions. Two way object relationships may allow for garbage collection.
* ODBMS - Object Database management system.
* OQL - Object Query Language, is a data manipulation language for Object Databases although many object databases do not support it. They rely on object class extensions or interfaces for their support.
* Persistence - Databases provide persistance which for object databases means object can be stored between database runs.
* RDBMS - Relational database management system.
* Schema - The data structure of the database.
* SQL - Structured Query Language is a standard language for communication with a relational database management system (RDBMS). Structured Query Language, is a data manipulation language which is a standard for getting and storing data in an RDBMS.
* SQLJ - Supports structured query language (SQL) calls for Java. It consists of a language allowing SQL statements to be embedded in it, a translator, and a runtime model.
* Transaction processing - Some databases may have some form of transaction processing which may support concurrency. Transaction processing will ensure that the entire transaction is made or none of it is made. Transactions support concurrency and data recovery. A data failure will cause a rollback of data

ORDBMS Definition

2009-07-08T11:22:00.000-07:00

ORDBMS Definition

An object relational database is also called an object relational database management system (ORDBMS). This system simply puts an object oriented front end on a relational database (RDBMS). When applications interface to this type of database, it will normally interface as though the data is stored as objects. However the system will convert the object information into data tables with rows and colums and handle the data the same as a relational database. Likewise, when the data is retrieved, it must be reassembled from simple data into complex objects.
Performance Constraints

Because the ORDBMS converts data between an object oriented format and RDBMS format, speed performance of the database is degraded substantially. This is due to the additional conversion work the database must do.
ORDBMS Benefits

The main benefit to this type of database lies in the fact that the software to convert the object data between a RDBMS format and object database format is provided. Therefore it is not necessary for programmers to write code to convert between the two formats and database access is easy from an object oriented computer language.

Object Oriented Database Standards

2009-07-08T11:20:00.000-07:00

Object Oriented Database Standards

There are several object oriented standards and groups that oversee them.
Groups

* Object Management Group (OMG) - Develops standards to help make object applications to be portable and communicate between each other (interoperability). They have developed the Component Object Request Broker Architecture (CORBA) standard along with object and OODBMS interfaces.
* Object Database Management Group (ODMG) - Created to define standard interfaces for object databases. The interfaces should allow the databases and applications that use them be portable and communicate between each other.

Standards

* CASE Data Interchange Format (CDIF) - Defines standards for tools to use so tyey may be used with various applications such as database servers, application servers, and other tools.
* Portable Common Tool Environment (PCTE) Standard.
* PDES/STEP - Exchange format standard for product model data. Also called the object interface format.
* Object Query Language (OQL)
* Object Definition Language (ODL) - Extension of OMGs CORBA standard.

Object Database Use and Features

2009-07-08T11:19:00.000-07:00

Object Database Use and Features

Databases provide persistence which for object databases means that objects can be stored between database runs.
Features

The following list of features are capabilities that object databases may support. Object database features include:

* Support of the object oriented language you want to use.
* Support of Object Oriented Concepts.
o Aggregation - Objects that are composed of other objects.
o Encapsulation - Data with method storage. Not all databases support the methods but rely upon the classes defined in the schema to reconstruct the object with its methods.
o Inheritance - Objects inherit attributes from parent objects.
o Polymorphism - Allows two methods to use the same name but have different behavior. Methods for one object can be defined, then the operation specification can be shared with other objects.
* Distributed Architecture - Object are sharing in a distributed environment or the entire database may be replicated on multiple computers.
* Heterogeneous environment - Cross Platform support - The database may be able to run on various builds of computers and with various operating systems.
* Transaction processing - Some databases may have some form of transaction processing which may support concurrency. Transaction processing will ensure that the entire transaction is made or none of it is made. Transactions support concurrency and data recovery. A data failure will cause a rollback of data.
* Concurrency - Databases must ensure that data is checked when concurrent access is allowed. Concurrent access means more than one application or thread may be reading or updating the same data at the same time. This may also be called two phase commit where two processes may work on the same object at the same time. This may use data locking for reads or writes. Some methods of concurrency control include:
o Pessimistic control - Whan one or more processes are reading, updated to the data cannot be made.
o Multiread - Updates are not blocked. Data must be consistant when the transaction was begun. In other words, if the read was done, and the data was changed by another process before the data is saved, the transaction is not valid until the data is read again.
* Object relationships - Object relationships define association with other objects, and whether objects can detect each other in one direction or two directions. Two way object relationships may allow for garbage collection. The best option is two way relationships.
* Database Garbage Collection - Requires bi-directional object relationships. Determines if the database performs garbage collection on objects that are no longer referenced by the database. This keeps external programs from having to track the use of object pointers.
* Relationship cardinality - Supported relationships may include any combination of:
o One to one.
o One to many.
o Many to one.
o Many to many.

The database should support all these.

* Transparent persistence - Consists of direct data manipulation using object oriented language. Many times a persistent capable class or persistent interface is used to implement persistence. This may be considered by some vendors to be transparency. If an interface is used, an intermediate interface may be used to help insulate calls from the particular database, thereby allowing the customer to more easily change database vendors later.
* Database interface methods - These may include SQL, OQL, and some application programming interface (API). See the section under "Communication Support", below.
* Database Integrity - There are two types:
o Structural database integrity ensures database contents are consistent with the database schema. Referential Integrity requires bi-directional object relationships to ensure objects do not contain references to deleted objects.
o Logical integrity - The logical properties of the data are correct. The data has the correct values consistently and concurrent access does not cause incorrect values to be set.
* Object Versioning - A single object represented by multiple versions. Two types are:
o Linear - Prior versions of the object are saved as the object is changed.
o Branch - Multiple users may update the object concurrently.
* Notification - Notification may be active or passive. A passive system can minimally determine if an object has changed state. An active system may provide for an application to be informed when an object is modified.
* Indexing - Additional indexing may be provided to enhance data retrieval efficiency. Hashing and b-trees may be used.
* Security - Data storage and/or transmission encryption may be supported by some databases. Also different authentication methods and levels for access to the database may be provided by various products.
* Archiving and data recovery
* Fault tolerance - Features that provide for fault tolerence in the event of a hardware of software failure. Normally transaction processing provides software fault tolerance. Data replication to other servers on the network supports hardware fault tolerance.
* Data access - Access is normally done using an iterator to access the data as though objects are collections. This way the objects are not required to be loaded into memory before the desired object is obtained.
* Sorting - All objects of a given class or parent class may be obtained.
* Tools that can be used with the database.
* Amount of storage.

Method storage- The code that runs in objects and gives them behavior is stored in the database.
Considerations

* What programming languages does the database support?
* Object relationships - Are they bi-directional?
* Work Group Support - Sharing databases and locking.
* Schema Evolution - How do you tell the database about schema changes? This includes changes to the definition of a class such as attributes or behavior, changes to inheritance, adding, deleting, or renaming a class. Do classes need to be backward compatible?
* How do databases search using polymorphism? Can it give all cars objects that are made by a specific manufacturer?
* How are the database APIs used? Is the database transparent to the applications?
* Tools - Tools are important for product development and support. The database may support some tools or integrate with some. Tools that should be a concern include development tools, testing tools, debugging tools, data modeling tools, and data maintenance tools.
* Object Models - The object modeling to be used and whether the object modeling tools integrate with the database (or whether they should) should be considered.
* Does the database store object methods or rebuild the methods from classes when required? If it does store methods, methods can be executed in database processes without storing the method or recreating the method in the application memory. Non object oriented programs may be able to access the output of the stored methods.

Communications Support

Object databases will use one or more of the following methods to exchange data between applications and the database.

* OQL - The standard language for object database communication is object query language (OQL). Some object databases support it and others do not.
* SQL - The standard language for relational database communication is structured query language (SQL). Some object databases support it and others do not. This is provided to help prospective customers migrate current applications from RDBMS to ODBMS. The object databases use SQL by considering a row an object, and each unit in a column to be an attribute of an object. The table is a collection of objects. The table joins and keys are used to create object relationships.
* Application Programming Interface (API) - Some vendors provide additional classes or programming interfaces that are used to access the database. It consists of direct data manipulation using object oriented language.

The advantage to using a standard interface such as SQL or OQL is that the application is not tied to one specific database. The advantage to using an API is that the access may be faster and possibly even transparent to the application. The application may not even know it is running methods or using data on a database. The API is a mixed bag since it gives some performance advantages and perhaps a little less flexibility. This loss of flexibility may be mitigated by providing a standard interface between the application and the particular database's API.

RDBMS Definition

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RDBMS Definition

Relational databases store data in tables (relations) that are two dimensional. The tables have rows (records or objects) and columns (fields or attributes). Data items at an intersection of a row and a column are called a cell and consist of attribute values. Data stored is simple data such as integers, real numbers or string values. Multiple values may not be stored in one cell. Relational database tables are "normalized" so data is not repeated more often than necessary. All table columns depend on a primary key (a unique value in the column) to identify the column. Once the specific column is identified, data from one or more rows associated with that column may be obtained or changed.

Relational databases are sets of tables. One table file is not a relational database. A relational database server is not the same as a relational database. A relational database can be a file with sets of tables. The relational database server includes the ability to service requestesto get or change data from remote clients.

Relational database servers use Structured Query Language (SQL), as a data manipulation language to interface between itself and the clients. SQL is the standard for getting and storing data in an RDBMS. For information about SQL, see the "Beginner's SQL Guide".

Relational database servers provide:

* Data Management
* Transaction processing
* Data integrity - Provides for multiple access at the same time (concurrency) between multiple processes/users. This is done so data is not displayed nor saved in a fashion where one change is lost. Various locking mechanisms are used to support this.
* Data backup and recovery.
* Data security - Provides for user authentication, and levels of data access privileges.

Primary Keys

In relational databases, the data is not arranged in any particular order in tables. The data in tables requires keys for identification of rows. Each table has rows and columns. Sets of values in a row may describe a particular item such as customers. Consider the following table:

Object Oriented Databases

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Object Oriented Databases

Object oriented databases are also called Object Database Management Systems (ODBMS). Object databases store objects rather than data such as integers, strings or real numbers. Objects are used in object oriented languages such as Smalltalk, C++, Java, and others. Objects basically consist of the following:

* Attributes - Attributes are data which defines the characteristics of an object. This data may be simple such as integers, strings, and real numbers or it may be a reference to a complex object.
* Methods - Methods define the behavior of an object and are what was formally called procedures or functions.

Therefore objects contain both executable code and data. There are other characteristics of objects such as whether methods or data can be accessed from outside the object. We don't consider this here, to keep the definition simple and to apply it to what an object database is. One other term worth mentioning is classes. Classes are used in object oriented programming to define the data and methods the object will contain. The class is like a template to the object. The class does not itself contain data or methods but defines the data and methods contained in the object. The class is used to create (instantiate) the object. Classes may be used in object databases to recreate parts of the object that may not actually be stored in the database. Methods may not be stored in the database and may be recreated by using a class.
Comparison to Relational Databases

Relational databases store data in tables that are two dimensional. The tables have rows and columns. Relational database tables are "normalized" so data is not repeated more often than necessary. All table columns depend on a primary key (a unique value in the column) to identify the column. Once the specific column is identified, data from one or more rows associated with that column may be obtained or changed.

To put objects into relational databases, they must be described in terms of simple string, integer, or real number data. For instance in the case of an airplane. The wing may be placed in one table with rows and columns describing its dimensions and characteristics. The fusalage may be in another table, the propeller in another table, tires, and so on.

Breaking complex information out into simple data takes time and is labor intensive. Code must be written to accomplish this task.
Object Persistence

With traditional databases, data manipulated by the application is transient and data in the database is persisted (Stored on a permanent storage device). In object databases, the application can manipulate both transient and persisted data.
When to Use Object Databases

Object databases should be used when there is complex data and/or complex data relationships. This includes a many to many object relationship. Object databases should not be used when there would be few join tables and there are large volumes of simple transactional data.

Object databases work well with:

* CAS Applications (CASE-computer aided software engineering, CAD-computer aided design, CAM-computer aided manufacture)
* Multimedia Applications
* Object projects that change over time.
* Commerce

Object Database Advantages over RDBMS

* Objects don't require assembly and disassembly saving coding time and execution time to assemble or disassemble objects.
* Reduced paging
* Easier navigation
* Better concurrency control - A hierarchy of objects may be locked.
* Data model is based on the real world.
* Works well for distributed architectures.
* Less code required when applications are object oriented.

Object Database Disadvantages compared to RDBMS

* Lower efficiency when data is simple and relationships are simple.
* Relational tables are simpler.
* Late binding may slow access speed.
* More user tools exist for RDBMS.
* Standards for RDBMS are more stable.
* Support for RDBMS is more certain and change is less likely to be required.

ODBMS Standards

* Object Data Management Group
* Object Database Standard ODM6.2.0
* Object Query Language
* OQL support of SQL92

How Data is Stored

Two basic methods are used to store objects by different database vendors.

* Each object has a unique ID and is defined as a subclass of a base class, using inheritance to determine attributes.
* Virtual memory mapping is used for object storage and management.

Data transfers are either done on a per object basis or on a per page (normally 4K) basis.

Server Types

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Server Types

There are several kinds of databases which include:

* Flat file databases
* Relational databases
* Object databases
* Object relational databases

Flat files are simply files with a table of information which may be seperated by delimeters such as commas, colons, or semi-colons. Relational databases consist of several related tables of simple data. The tables are composed of rows and columns. Object databases store data in an object form rather than in tables. They store attributes and class information, but sometimes they also store and methods (behavior) in the database. Object relational databases are relational databases with data stored in tables, but they have a front end that converts objects to data and data to objects, making it seem to the application that objects are being stored.

Database servers include both a server program that serves remote clients and manages the database. They may use some means of standard communication between client and server to allow management of the data such as structured query language (SQL) for relational database servers.

The most popular databases today are Relational Database Management Systems (RDBMS). However, object database servers may someday overtake the relational database servers.

Relational Databases and Objects

If relational databases are used to store objects, the object must first be disassembled into parts, normalized, and placed in tables. This can take some time to do, and be a labor intensive process required for writing the code. To use the object, it must be reassembled.

Many relational databases are run on one single server and do not use a distributed architecture.

Object Database Servers

Object database servers may use an Object Query Language (OQL) as a standard language for communication. They may use an application programming interface (API) to allow the application to control the data or they may use both the API and OQL.

Current and Future Trends

Relational databases are still the most popular database in use today. There is good reason for this. They are easy to use and are normally efficient.

However as programming has changed, tools related to those changes must also change. Object oriented programming is becomming much more popular and as that occurs a more practical tool for long term storage of data is in demand. This tool must interface easily to the object oriented language in question. It must also be a standard tool so users are not tied to specific vendors amd should have a standard way of exchanging information between applications and the database. OQL was developed for this purpose, but it does not appear to be widely supported yet by object oriented database vendors.

Although object databases were first written many years ago, since they have not yet become popular, it appears that the market is not stable. There are several object oriented database vendors, and it is difficult to tell who will be in the market for the long haul. Therefore, I believe the purchase of an object oriented database is somewhat of a risk. This risk may be somewhat mitigated by the fact that programs can be written in object oriented language to isolate the programs from specific object database products.

If the benefits of the object oriented database are large enough for the particular application they are used for and the specific organization considering them, the risks are likely to be worth taking. However, if the benefits are marginal, it may be worth waiting another year or two for more market stability and uniformity

E-commerce

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E-commerce

E-commerce is the application of information technology to support business processes and the exchange of goods and services. E-cash came into being when people began to think that if we can store, forward and manipulate information, why can't we do the same with money. Both blanks and post offices centralise distribution, information and credibility. E-money makes it possible to decentralise these functions.

Electronic data interchange, which is the subset of e-com, is a set of data definitions that permits business forms to be exchanged electronically. The different payment schemes E-cash, Net-cash and PayMe system and also smart card technology is also. The foundation of all requirements for commerce over the world wide web is secured system of payment so various security measures are adopted over the Internet.
E-commerce represents a market worth potentiality hundreds of billions of dollars in just a few years to come. So it provides enormous opportunities for business. It is expected that in near future, electronic transaction will be as popular, if not more that the credit card purchases today.

Business is about information. It is about the right people having the right information at the right time. Exchanging the information efficiently and accurately will determine the success of the business.
There are three phases of implementation of E-Commerce.

" Replace manual and paper-based operations with electronic alternatives
" Rethink and simplify the information flows
" Use the information flows in new and dynamic ways

Simply replacing the existing paper-based system will reap new benefits. It may reduce administrative costs and improve the level of accuracy in exchanging data, but it does not address doing business efficiently. E-Commerce application can help to reshape the ways to do business