X Windows or more properly the X Window System (also known as X11) is the standard graphical user interface for the Unix family of operating systems. X11 was first developed by Digital Equipment Corporation (DEC) and the projectAthena at Massachusetts's Institute of Technology (MIT) and first released as X11R1 in September 1987. XFree86 is the freely available implementation of
X Windows for 80x86 family computers (PCs), ad it was developed by a group called the XFree86 team in 1992. X Windows is more than a simple interface, it is a network-based system comprising a server and clients. X11 #X Windows Research X Windows
Xanthamide (xanthogen amide) is an amido derivative of xanthicacid. It is a white crystalline substance with the formulae C2H5O.CS.NH2. Research Xanthamide
Xanthic acid also known as xanthogenic acid is an organic, heavy, astringent, colourless oil, with the formulae C2H5OCS.SH so named on account of many of its salts being yellow in colour. It has a pungent odour. It is produced by leading carbon disulphide into a hot alcoholic solution of potassiumhydroxide. Research Xanthic Acid
Xanthine is a nitrogenous compound closely allied to uric acid, that occurs in extract of meat and in tea. It forms a colourless powder slightly soluble in water, and yields alloxan and urea on oxidation. Research Xanthine
Xanthophylls are a class of oxygen-containing carotenoid pigments, which provide the characteristic yellow and brown colours of autumn leaves. Research Xanthophyll
Xanthoprotein is a yellow acid substance formed by the action of hot nitric acid on albuminous or proteid matter. It is changed to a deep orange-yellow colour by the addition of ammonia. Research Xanthoprotein
Xara X is an advanced graphic illustration package for personal computers running the Windows operating system. Producing illustrations is quick and easy using the sophisticated drawing tools, and many of the advanced features which Xara pioneered - such as transparency and real-time anti-aliasing - can be applied to both vector and raster images. Xara X can produce compact, highly optimised graphics, making it an ideal choice for creating web graphics. XaraX has an accurate 'auto-trace' facility which allows raster graphic images to be converted to a vector graphic format quickly and easily. Typical of vector drawing packages, XaraX allows curves to be drawn to which text can then be fitted, the text following a curved path. Research Xara X
Xenon is a rare, gaseous element discovered in July 1898. It's symbol is Xe.
Xenon is a heavy (4.5 times heavier than air), unreactive stable gas occurring in air in trace percentages. It is one of the noble gases. Today, xenon is recovered on a commercial scale by the fractional distillation of liquid air. Natural xenon is a mixture of nine stable isotopes in the following percentages; xenon-124 (0.096); xenon-126 (0.090); xenon-128 (1.92); xenon-129 (26.44); xenon-130 (4.08); xenon-131 (21.18); xenon-132 (26.89) ; xenon-134 (10.44); and
xenon-136 (8.87).
The xenon found in some stony meteorites shows a large proportion of xenon-129, believed to be a product of radioactive decay of iodine-129, whose half-life is 17,000,000 years. Study of the xenon- 129 content of meteorites casts light on the history of the solar system. More than a dozen radioactive xenon isotopes produced by fission of uranium and other nuclear reactions are known. For example, xenon-135 (9.2-hour half-life) is produced by uraniumfission in nuclear reactors, where it is troublesome because it absorbs fission-producing neutrons. In 1962, a sample of xenon combined with an ion of platinum and fluorine to produce the first noble gas compound, previously the noble gases were thought to be inert. Now, xenon is known to combine with fluorine, oxygen, cesium, and alkali metals to form the corresponding fluorides, oxides and salts. All xenon compounds are toxic, although the gas itself is not.
Xenon has been used as an aesthetic, and is used as a tracer to measure lung capacity. It is the most popular gas used in strobe lamps and in high speed electronic flash bulbs used in photography. Electrical excitation of xenon atoms produces a brilliant white light. Some of its compounds have limited application as oxidizing agents. Xenon gas also has applications in modern nuclear power reactors. Research Xenon
Xenu's Link Sleuth (named after Xenu, a sort of 'devil' for customers of the Scientology cult) is a free computer program for the Windows operating systems written by Tilman Hausherr, that checks Web sites for broken links. Link verification is done on standard hypertext links, images, frames, plug-ins, backgrounds, local image maps, style sheets, scripts and also on java applets. Xenu displays a continuously updated list of URLs which can be sorted by different criteria and a report can be produced at any time. Research Xenu's Link Sleuth
Xerography is an electrostatic dry-printing process for the reproduction of images or documents, widely employed in commerce and industry in copying machines, such as photo-copiers. The process was invented by the American printer Chester F Carlson in 1937 and first commercially developed in 1950. It makes use of the principle of photoconductivity, that is, that certain substances resist passage of an electric current except when struck by light. Silicon, germanium, and selenium are poor conductors of electricity, but when light energy is absorbed by some of their electrons, the electrons are able to pass from one atom to another, thus allowing a current to flow when a voltage is applied. When the light is removed, their conductivity again becomes low.
Xerography employs a photoconductive insulating layer, such as selenium, on an aluminium or other conductive metal support. The layer is charged electrostatically, either with positive or negative ions, the polarity of the charge depending on the type of photoconductive insulating layer selected. When the plate is exposed, in a camera or photographic machine, those areas of the coating subjected to light lose a varying portion of the charge, depending upon the intensity of the illumination. Thus, the variation of the amount of charge retained on the coated metal plate is established as an electrical or electrostatic pattern of the image. The image is rendered visible by sprinkling over the exposed plate a special, charged powder, which carries an opposite charge to the initial charge applied to the plate and insulating layer. The powder adheres to those areas that have retained their charge. The print is obtained by covering the plate with paper, then applying a charge over the back of the paper of the same polarity as the initial charge
applied to the photoconductive insulating layer. In this way the opposite charged powders are transferred to the paper surface. The powder image is then fused onto the paper by exposure to solvent vapours or heat to make the image permanent. The entire xerographic process can be carried out, in high-speed mechanized equipment, in less than five seconds, and it is comparatively inexpensive to make these images because the photoconductive insulating layer can be recycled many thousand times. The process has found its primary usefulness in copying office documents and in low-volume duplication of data. The xerographic method also permits the making, quickly and cheaply, of paper offset masterplates for low-to-medium-volume runs on office offset-printing presses. The method has also been applied to the production of X-ray images in a technique that is known as xeroradiography and is used in mammography for the early detection of breast cancer. Research Xerography
Xerox FormBase is a computer forms management program. It combines forms management with database techniques, which can be accessed from within the Microsoft Windows environment. FormBase creates professional quality forms while providing facilities to enter, sort, search, retrieve, and print data. Unlike typical forms management packages which allow users to create a single form per file, FormBase lets you create multiple forms, or views, per database file. Each form created is considered a different view of the database. FormBase lets you create subforms and subtables within a form which facilitate entering multiple entries into a field. For example, in a database containing customer information you may want to create a data-entry form containing all the invoices for each customer. Because the information varies for each customer, this form may need to store dozens of entries. FormBase contains features usually found in database packages. The product can perform a lookup from one file to another. Information entered into one
database can be retrieved in another form. Mathematical computations can be built into a form which are similar to formulae found in spreadsheet programs. Formulae can also be created to validate information entered into forms to provide accuracy and consistency during data entry. FormBase allows you to import graphic images from other software programs into a database and to create forms with logos and pictures. FormBase can print out columnar reports and supports laser, dot-matrix, and colour printers. Research Xerox FormBase
Abbreviations
SciTech
Research X Windows