.... a definite possibility for an alternative power source for space program, but the cost and size of the fuel cell stacks were tremendous. By 1983, Geoff Ballard and a small team of physicists were able to develop the Proton Exchange Membrane (PEM) to produce nearly ten times as much energy, while being only a fraction of the size. How the PEM Fuel Cell Works: A fuel cell is an electrochemical device that produces electricity silently, without combustion. Hydrogen fuel, which is one of the most abundant chemicals in the universe, and oxygen from the air are electrochemically combined in the fuel cell to produce electricity. Heat and pure water vapour are the only by-products ....

.... that archaeologists and historians study to try to interpret how people lived. Cultural resources are important because they help us to learn about our past. These tangible remains help us understand other cultures, appreciate architecture and engineering, and learn about past accomplishments. Furthermore, they offer educational and recreational opportunities and provide links to our past. People have lived in North America for at least 12,000 years. Archaeologists and historians have divided this time span into prehistoric and historic periods. The prehistoric period extends from the earliest arrival of humans in North America to the coming of the European explorers. Th ....

.... are more myth than reality. One story tells that a legendary Chinese leader and medical expert, Sheng Nong, discovered tea as a medicinal herb in 2737 B.C. One day while he was boiling water under a tea tree, some tea leaves fell into Sheng's pot of boiling water. After drinking some tea, he discovered its miraculous powers and immediately placed tea on his list of medicinal herbs. John Blofeld, in Chinese Art of Tea, writes that ¡§it can be confidently stated that tea was known in the three kingdoms epoch (AD 222-277).¡¨ More importantly, however, ¡§tea [was] originally drunk for its medicinal properties.¡¨ (Blofeld 4) Evans links the early popularity of tea to Tao ....

.... by-product from the smelting of zinc, lead or copper ores. Cadmium has a number of industrial applications, but it is used mostly in metal plating, pigments, batteries, and plastics. Cadmium in the Environment Small quantities of cadmium occur naturally in air, water, soil and food. For most people, food is the primary source of cadmium exposure, since food materials tend to take up and retain cadmium. For example, plants take up cadmium from soil; fish take up cadmium from water, and so on. It is introduced into the environment from mining and smelting operations. Other cadmium emissions are from fossil fuel use, fertilizer application, sewage sludge disposal or galvanized ....

.... other is secondary hypertension. The cause of primary hypertension is unknown. It just happens but however, there are certain risk factors or associations such as hereditary factors, race, age, environmental and life-style factors (where you live, salt and other chemicals, weight, stress, alcohol, lack of exercise). The difference between primary and secondary hypertension is that we know the causes of secondary hypertension. Usually, the causes of secondary hypertension include renal artery stenosis (or other cause of increased plasma renin), renal parenchymal disease (glomerulonephritis, diabetic nephropathy, polycystic disease, obstructive uropathy), drugs (oral c ....

.... that are just reflections off of the disco ball. (Stars) These spots seem to form different patterns on the walls and move along with the disco ball, but not always at the same rate. (Constellations) There are two very shy people in the room that sometimes leave the room. When they are in the room they stand by the walls and always wink for some reason, so all we can see of them is one of their eyes. (Mercury & Venus) Then there are three very weird people in the room that are always in the middle of the room doing the Waltz. They do this some how by themselves and they to are always winking. They are sometimes on the first floor and sometimes on the second floor. (Ma ....

.... zoom in on someone's nose hairs all the way from space. Robert Gossard (left) was one of the most integral inventors of the satellite. He was born on October 5, 1882. He earned his Masters and Doctoral degree in Physics at Clark University. He conducted research on improving solid- propellant rockets. He is known best for firing the world's first successful liquid-propellant rocket on March 16, 1926. This was a simple pressure-fed rocket that burned gasoline and liquid oxygen. It traveled only 56m (184 ft) but proved to the world that the principle was valid. Gossard Died August 10, 1945. Gossard did not work alone, he was also in partnership with a Russian theorist named ....

.... for networks appears for the first time when Graham Bell set in use the telephone . He was talking with a friend of his with a single line , but later when he wanted to talk to another friend of his he needed to use another line to connect his phone and the phone of his friend . So imagine that he has X friends , he would need X(X-1)/2 lines and X-1 phones , that was impossible so the need of networks come up . The network first developed for the need of the voice communication but after the appearance of data communications need the same network was used . From the time that electricity and electronics had developed there was rapidly changes at the section of the commu ....