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There are an increasing number of Egyptian Web hosting companies that provide services to individuals and businesses. While Web hosting is still an emerging industry in most of Africa, it is relatively developed in Egypt. After its first ISP, InTouch Communications, was founded in 1992, the industry has grown to become a leader in the... more »
Computer languages are used to instruct computers to perform tasks that computers are ideal for, such a complex mathematics and processing large amounts of information. Computers speak in a language called "machine language." Higher level computer languages are close to English and are translated to machine language through computer... more »
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Gemstones are rare minerals, rock or organic material that can be found all over the world in different types of environments. Many gemstones are cut into shapes, which then become gems. This is why most jewelry contains gems, which have a finished and polished look. Gemstone properties can be determined by hardness, specific gravity... more »
Carter G. Woodson, an African American historian, created what would become Black History Month in 1926. (Then it was known as Negro Week.) African Americans didn't have the right to vote at this time, and lynchings were not uncommon. Dr. Woodson began Black History Month because the contributions of African Americans weren't... more »
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A ruby is a pink to blood-red gemstone, a variety of the mineral corundum (aluminium oxide). The red color is caused mainly by the presence of the element chromium. Its name comes from ruber, Latin for red. Other varieties of gem-quality corundum are called sapphires. The ruby is considered one of the four precious stones, together with the sapphire, the emerald, and the diamond., Max Bauer, p 2
Prices of rubies are primarily determined by color. The brightest and most valuable "red" called pigeon blood-red, commands a huge premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions may indicate that the stone has been treated. Cut and carat (size) also determine the price.
Physical properties
Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only moissanite and diamond are harder, with diamond having a Mohs hardness of 10.0 and moissonite falling somewhere in between corundum (ruby) and diamond in hardness. Ruby is α-alumina (the most stable form of Al2O3) in which a small fraction of the aluminum3+ ions are replaced by chromium3+ ions. Each Cr3+ is surrounded octahedrally by six O2- ions. This crystallographic arrangement strongly affects each Cr3+, resulting in light absorption in the yellow-green region of the spectrum and thus in the red color of the gem. When yellow-green light is absorbed by Cr3+, it is re-emitted as red luminescence. This red emission adds to the red colour perceived by the subtraction of green and violet light from white light, and adds luster to the gems appearance. When the optical arrangement is such that the emission is stimulated by 694-nanometer photons reflecting back and forth between two mirrors, the emission grows strongly in intensity. This effect was used by Theodore Maiman in 1960 to make the first successful laser, based on ruby.
All nat read more at » http://en.wikipedia.org/wiki/Ruby
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