Chalk

December 24, 2009 by · Leave a Comment 

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Soft, fine-grained, easily pulverized, white-to-grayish variety of limestone, composed of the shells of minute marine organisms. The purest varieties contain up to 99% calcium carbonate in the form of the mineral calcite. Extensive deposits occur in western Europe south of Sweden and in England, notably in the chalk cliffs of Dover along the English Channel. Other extensive deposits occur in the U.S. from South Dakota to Texas and eastward to Alabama. Chalk is used for making lime and portland cement and as a soil additive. Finely ground and purified chalk is known as whiting and is used as a filler, extender, or pigment in a wide variety of materials, including ceramics, putty, cosmetics, crayons, plastics, rubber, paper, paints, and linoleum. The chalk commonly used in classrooms is a manufactured substance rather than natural chalk.

Chalk used in school classrooms comes in slender sticks approximately .35 of an inch (nine millimeters) in diameter and 3.15 inches (80 millimeters) long. Lessons are often presented to entire classes on chalk-boards (or blackboards, as they were originally called) using sticks of chalk because this method has proven cheap and easy.

As found in nature, chalk has been used for drawing since prehistoric times, when, according to archaeologists, it helped to create some of the earliest cave drawings. Later, artists of different countries and styles used chalk mainly for sketches, and some such drawings, protected with shellac or a similar substance, have survived. Chalk was first formed into sticks for the convenience of artists. The method was to grind natural chalk to a fine powder, then add water, clay as a binder, and various dry colors. The resultant putty was then rolled into cylinders and dried. Although impurities produce natural chalk in many colors, when artists made their own chalk they usually added pigments to render these colors more vivid. Carbon, for example, was used to enhance black, and ferric oxide (Fe2O3) created a more vivid red.

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Researcher Fine Tunes Optical Tomography

November 1, 2009 by · Leave a Comment 

By Ayub Khan, MMNS

493D Taufiquar Khan, mathematical science professor at Clemson University, and his colleagues are working to make the physical pain and discomfort of mammograms a thing of past, while allowing for diagnostic imaging eventually to be done in a home setting.

The group is fine-tuning Diffuse Optical Tomography (DOT) to create high-resolution images from a scattering of infrared and visible light for the early detection of breast cancer. While the method is less expensive, safer and more comfortable than X-rays used in mammograms, the problem has been generating a strong enough resolution to detect smaller breast cancers.

“The problem with DOT is that it is a 3-D method where photon density waves launched from a source travel in a banana-shaped path due to multiple scattering, whereas X-rays follow straight lines which make the mathematical problem more manageable and the resolution of the image sharper.” said Khan. “With DOT, near-infrared or near-visible photons make the process safer for the body than with the radiation of X-rays, but they are difficult to track because of the scattering and absorption. So we are coming up with equations that will help get us from capturing cancers that are 4 millimeters in size, down to capturing those as small as 1 millimeter.”

Khan says benefits of DOT include the elimination of harmful radiation to the body as well as false positives and negatives caused by mammography X-rays. He adds there are no harmful side effects to DOT, and some version of DOT eventually could be administered in a do-it-yourself setting at home within the next decade. In addition to breast screening, he says it eventually maybe used as part of other diagnostic procedures such as ultrasound.

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