Thursday, December 27, 2007

Computer programming

Computer programming (often shortened to programming or coding) is the process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs. This source code is written in a programming language. The code may be a modification of an existing source or something completely new, the purpose being to create a program that exhibits a certain desired behavior (customization). The process of writing source codes requires expertise in many different subjects, including knowledge of the application domain, specialized algorithms, and formal logic.

Within software engineering, programming (the implementation) is regarded as one phase in a software development process.

In some specialist applications or extreme situations a program may be written or modified (known as patching) by directly storing the numeric values of the machine code instructions to be executed into memory.

Tuesday, December 18, 2007

DNA microarray

A DNA microarray (also commonly known as gene or genome chip, DNA chip, or gene array) is a collection of microscopic DNA spots, commonly representing single genes, arrayed on a solid surface by covalent attachment to a chemical matrix. DNA arrays are different from other types of microarray only in that they either measure DNA or use DNA as part of its detection system. Qualitative or quantitative measurements with DNA microarrays utilize the selective nature of DNA-DNA or DNA-RNA hybridization under high-stringency conditions and fluorophore-based detection. DNA arrays are commonly used for expression profiling, i.e., monitoring expression levels of thousands of genes simultaneously, or for comparative genomic hybridization.

Tuesday, December 11, 2007

Digital Video Interactive

Digital Video Interactive (DVI) was the first multimedia desktop video standard for IBM-compatible personal computers, developed around 1984 by Section 17 of The David Sarnoff Research Center Labs (a division of RCA at the time, later DSRC became a division of General Electric after their purchase of RCA in 1986, and then the technology was sold by GE to Intel in 1988). The DSRC was sold to SRI International and as of 2007, continues research operations in technology and other areas on a contract basis.

DVI technology allowed full-screen, full motion video, as well as stereo audio, still images, and graphics to be presented on a DOS-based desktop computer. DVI content was usually distributed on CD-ROM discs, which in turn was decoded and displayed via specialized hardware installed in the computer. Audio and video files for DVI were among the first to use data compression, with audio content using ADPCM. DVI was the first technology of its kind for the desktop PC, and ushered in the multimedia revolution for PCs.

Thursday, December 06, 2007

Nuclear fuel cycle

Thermal reactors generally depend on refined and enriched uranium. Some nuclear reactors can operate with a mixture of plutonium and uranium. The process by which uranium ore is mined, processed, enriched, used, possibly reprocessed and disposed of is known as the nuclear fuel cycle.

Under 1% of the uranium found in nature is the easily fissionable U-235 isotope and as a result most reactor designs require enriched fuel. Enrichment involves increasing the percentage of U-235 and is usually done by means of gaseous diffusion or gas centrifuge. The enriched result is then converted into uranium dioxide powder, which is pressed and fired onto pellet form. These pellets are stacked into tubes which are then sealed and called fuel rods. Many of these fuel rods are used in each nuclear reactor.

Most BWR and PWR commercial reactors use uranium enriched to about 4% U-235, and some commercial reactors with a high neutron economy do not require the fuel to be enriched at all (that is, they can use natural uranium). According to the International Atomic Energy Agency there are at least 100 research reactors in the world which use highly enriched, weapons-grade uranium (90% enrichment) as their fuel.