Sunday, May 27, 2007

Compiler

A compiler is a computer program or set of programs that converts text written in a computer language (the source language) into another computer language (the target language). The original sequence is frequently called the source code and the output called object code. Commonly the output has a form appropriate for processing by other programs (e.g., a linker), but it may be a human-readable text file.

The most common reason for wanting to translate source code is to make an executable program. The name "compiler" is primarily used for programs that convert source code from a high level language to a lower level language (e.g., assembly language or machine language). A program that translates from a low level language to a higher level one is a decompiler. A program that translates between high-level languages is generally called a language translator, source to source translator, or language converter. A language rewriter is generally a program that translates the form of expressions without a modify language.

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Sunday, May 20, 2007

World Wide Web

The World Wide Web is a system of interlinked, hypertext documents that runs over the Internet. With a Web browser, a user views Web pages that may include text, images, and other multimedia and navigates between them using hyperlinks. The World Wide Web is the combination of four basic ideas:Hypertext,Resource Identifiers,The Client-server model of computing,Markup language.On the World Wide Web, a client program called a client agent retrieves information resources, such as Web pages and other computer files, from Web servers using their URLs. If the user agent is a kind of Web browser, it displays the resources on a user's computer. The user can then follow hyperlinks in each web page to other World Wide Web resources, whose position is embedded in the hyperlinks.Web pages are often set in collections of related material called Web sites.The act of following hyperlinks from one Web site to another is referred to as browsing or sometimes as surfing the Web.


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Sunday, May 13, 2007

Proteins

Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by a gene and encoded in the genetic code. Although this genetic code specifies 20 "standard" amino acids, the residues in a protein are often chemically altered in post-translational modification: either before the protein can function in the cell, or as part of control mechanisms. Proteins can also work together to achieve a particular function, and they often associate to form stable complexes.

Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of all living organisms and participate in every process within cells. Many proteins are enzymes that catalyze biochemical reactions, and are vital to metabolism. Other proteins have structural or mechanical functions, such as the proteins in the cytoskeleton, which forms a system of scaffolding that maintains cell shape. Proteins are also important in cell signaling, immune responses, cell adhesion, and the cell cycle. Protein is also a necessary component in our diet, since animals cannot synthesise all the amino acids and must obtain essential amino acids from food. Through the process of digestion, animals break down ingested protein into free amino acids that can be used for protein synthesis.


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Sunday, May 06, 2007

Aerial archaeology

Aerial archaeology is the study of archaeological leftovers by examining them from elevation. It is one of the oldest prospecting methods. It is very productive and cheap, Aerial archaeology is frequent opinion that an aerial archaeologist is sitting in an aeroplane, trying to discover archaeological sites and to take a few good photographs of them.To perform aerial archaeology you can also used satellite images, thermal images or airborne radar images.

The advantages of gaining a good aerial vision of the ground had been long appreciated by archaeologists as a high viewpoint permits a enhanced appreciation of excellent details and their relationships within the wider site context. Early investigators attempted to gain birdseye views of sites by hot air balloons, scaffolds or cameras attached to kites. Following the invention of the aeroplane and Aerial photography helps military during the First and Second World Wars, archaeologists were able to more effectively use the technique to find
out and record archaeological sites.


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