Strategic minerals are minerals essential to the national defense -- the supply of which a country uses but cannot produce itself. 33% to 50% of the 80 minerals used by industry could be classed as strategic minerals. Wealthy countries, such as the United States, stockpile these minerals to avoid any crippling effect on their economy or military strength if political circumstances were to cut off their supplies. The United States, for instance, stockpiles bauxite (14.5 million tons), manganese (2.2 million tons), chromium (1.8 million tons), tin (185,000 tons), cobalt (19,000 tons), tantalum (635 tons), palladium (1.25 million troy ounces), and platinum (453,000 troy ounces). (The Handy Science Answer Book, compiled by the Science and Technology department of the Carnegie Library of Pittsburgh)
Nov 25, 2013
Nov 20, 2013
A microscope that uses electrons instead of visible light to produce highly magnified images of objects. Scientists use electron microscopes in many different fields of research, including medicine, biology, chemistry, metallurgy, entomology (the study of insects), and physics. Since its introduction in the 1930s, the electron microscope has revolutionized the study of microscopic structures and surfaces. See also Microscope.
Microscopes can only resolve structures that are larger than the length of the waves (such as light waves) reflecting off of them. Electron microscopes are able to obtain much higher powers of magnification than standard visible light microscopes because electrons have much shorter wavelengths associated with them than light waves. The highest magnification achievable with light microscopes is about 2,000X (times); modern electron microscopes can achieve magnifications approaching 1,000,000X.
The invention of the electron microscope was made possible by a number of theoretical and experimental advances in physics and engineering. The main concept on which the electron microscope is founded—that electrons have a wavelike nature—was hypothesized by French physicist Prince Louis Victor de Broglie in 1923 (see Quantum Theory). In 1927, de Broglie’s hypothesis was experimentally verified by American physicists Clinton J. Davisson and Lester H. Germer, and independently by English physicist George Paget Thomson. In 1932 German engineers Max Knoll and Ernst Ruska built the first transmission electron microscope. In 1938 Ruska and German engineer Bodo von Borries built the first model of the commercial TEM for the Siemens-Halske Company in Berlin, Germany. The English engineer Sir Charles Oatley invented the SEM in its present form in 1952.
Nov 14, 2013
what is it? Fat packed deep in the abdomen, in and around your internal organs. Women with waists over 35 inches and men with waists over 40 inches are likely to have it. (For people of Asian descent, risk rises with measurements over 31.5 inches for women and 37.5 for men.) A large waist is dangerous even if your body weight is within the " healthy" range for your height. To measure your waist, wrap a tape measure snugly around your midsection at about belly-button height.
What causes it? Too many hamburgers, too much TV, and too much of all those other activities that keep you sitting down, like working and driving. In other words, a diet high in calories and a life devoid of exercise. Chronic stress plays a role, too, especially for women, since the stress hormone cortisol directs your body to store more fat in your abdomen.
1. A high-calorie diet, lack of exercise, and chronic stress conspire to prompt your body to store dangerous fat around your liver, pancreas, and other internal organs.
2. Intra-abdominal fat pumps free fatty acids and inflammatory compounds into the portal vein, the "superhighway" that delivers blood from your lower abdomen to the liver, pancreas, and other internal organs.
3. An influx of free fatty acids causes your liver to produce more “bad” LDL cholesterol, less “good” HDL cholesterol, more blood sugar, and less adiponectin, a hormone that regulates the use of blood sugar and keeps appetite in check. The result: Your risk of heart disease and diabetes rises.
4. The inflammatory compounds secreted by fat cells encourage the growth of plaque inside artery walls, boost blood pressure, and make blood more likely to clot - a recipe for a heart attack. They also make cells resistant to insulin, which in turn contributes to diseases from Alzheimer's to cancer.
Nov 8, 2013
Nov 3, 2013
The incidence of breast cancer in the United States began climbing steadily in the early 1970s, and is now the highest ever seen in human history. Nearly 50,000 American women die of the disease every year. In the face of this tragedy, a great deal of attention has been given to genetics, but the presence of the breast cancer susceptibility gene, called BRCA-1, only accounts for at most 5 percent of breast cancers.
Exercise is very important to breast cancer risk. In fact, women who exercise (walk) for four hours per week lower their risk by 33 percent. And women who exercise more than that lower their risk even further. 
But diet, it turns out, is even more important. . .
What We Know
Death rate from breast cancer in the United States: 22.4 (per 100,000)
Death rate from breast cancer in Japan: 6.3 (per 100,000)
Death rate from breast cancer in China: 4.6 (per 100,000)
Primary reasons for difference: People in China and Japan eat more fruits and vegetables and less animal products, weigh less, drink less alcohol, and get more exercise than people in the United States.