EAMCET Medical

Dams are built for a number of purposes: to generate hydroelectric power; control flooding; safeguard water supplies for irrigation, domestic, or industrial use; provide for recreation; or ease navigation. The earliest known dam was built by the Egyptians across the Garawi Valley in 2800 B.C.E. and measured 370 feet (113 m) along its crest. The masonry shell was filled with earth and rubble, but as it was not sealed against water, the center of the dam was soon washed away. This failure discouraged the Egyptians from further forays into dam construction. The Romans, armed with their knowledge of concrete, were more successful. Their constructions initially relied on sheer weight of material to resist the water, but in the first century they built the first arch- type dam at Glanum in France. The apex of the arch pointed upstream, transferring the force along the dam and into the solid bedrock of more...

"Crystals grew inside rock like arithmetic flowers... obedience to an absolute geometry." Anne Dillard, American author Crystals are solids—like salt, diamond, and quartz— that have their constituent atoms (or molecules) in regular orders. These patterns repeat in all directions. X-rays penetrate solids and are scattered by the clouds of electrons that surround the nuclei of each atom. Because the atomic arrays in crystals are strictly regular, the X-ray scattering is not random. Measuring the intensity of the X-rays in different' directions and the specific angles at which...the scattering occurs enables the separation of the arrays of crystal atoms to be calculated. The study of crystal atom spacing and ordering is known as crystallography. X-rays have wavelengths that are of the same order of magnitude as both the sizes of typical atoms, and also the spacing between solid arrays of atoms. In 1912 Max von Laue (1879-1960) and Paul Ewald (1888-1985) more...

"My notion of a wife at 40 is that a man should be able to change her, like a banknote, for two 20s." When Marco Polo traveled to China in the late thirteenth century he was astonished to see the locals use paper money instead of coins. Prompted by a copper shortage, the Tang Dynasty (618-907) introduced this new monetary system in 806, more than 800 years before the first European banknotes. While commodity money (the trading of goods that have an intrinsic value, such as gold and cattle) has been around since the dawn of civilization, the first standardized coinage is thought to have appeared in Lydia (western Asia Minor) in the seventh century B.C.E. This was the first time that the nominal value of money was higher than the worth of its inherent material. Ancient Greek historian Herodotus criticized the "gross commercialism" that this system induced. Swedish bank more...

"Lactomangulation, n. [Badly] manhandling the 'open here' spout on a milk carton…” Rich Hall, comedian Tetra Pak, a multinational company, revolutionized the food and drink industry with its unique cardboard carton production in the 1940s. It was founded in 1951 by Ruben Pausing (1895-1983) and Erik Wallenberg (1915-1999) in Sweden. Work began in 1943 with development of a new storage medium for milk, which had previously been sold only in glass bottles. The challenge was to provide a hygienic container using minimal materials. Tetra Paks are made from paper, polyethylene, and aluminum foil, arranged in seven layers to create a lightweight product. The original design, the "Tetra Classic," was launched in 1952. This was a four-sided pyramidal milk container sold in Sweden. Initial responses were very positive and the company continued to refine Its designs with the more familiar rectangular "Brik" carton produced in 1959. In 1961 the simple addition more...

It is thought that early man used a primitive drill—perhaps a modified spear—to pierce wood and animal skins. Much later, the woodworkers of ancient Egypt refined this technique by making any necessary holes with a bow drill. Adapted from the fire-stick, it had a cord wrapped round it and was held taut with a bow. Holding the drill vertically, the operator moved the bow backward and forward, pressing downward on alternate turns, with an idle return stroke. (There is also evidence of dental drilling from as long ago as 9000 B.C.E., accomplished by the same means.) The Romans replaced the bow drill with the auger, but the bit froze between turns. It was not until the Middle Ages that use of the carpenter's brace made continuous rotation of the drill possible. The term "drill" may either refer to the machine supplying the rotational energy needed for penetration, or to the more...

In October 1930, a young surgical resident sat vigil as a patient with a blood clot in her pulmonary artery labored to breathe. The surgery she needed had never been successfully performed in the United States. Developed in Germany, the "Trendelenburg operation" had a 6 percent survival rate. After seventeen hours, it was clear the patient was not going to survive without surgery, so, with nothing to lose, the procedure was successfully carried out, but the patient died. For the next twenty-three years, Dr. John Heysham Gibbon (1903-1973) and his wife Mary worked to produce a machine that could supply oxygenated blood while the heart was stopped. In 1935 he used a prototype heart-lung bypass machine to keep a cat alive for twenty-six minutes. Venous blood was fed into the machine where it was spun over a cylinder to provide oxygen/and then pumped back into an artery. Many improvements were more...

"[It] computes the given numbers automatically; adds, subtracts, multiplies, and divides." Wilhelm Schickard Early inventions to speed up calculations focused on manual solutions such as Napier's bones, which consisted of multiplication tables inscribed onto bones for calculating sums. Seeing John Napier's work, the German polymath Wilhelm Schickard (1592-1635) created a mechanical calculator that automated the process of calculation and incorporated Napier's bones. In 1623, he designed and built the "calculating clock." At around the size of a typewriter, it could handle numbers of up to six digits in length. The calculator used a direct gear drive and rotating wheels to add and subtract. When a wheel made a complete turn, the wheel adjacent rotated one-tenth of a turn. Dials on the lower part of the machine were turned one way to perform addition, and the opposite way to perform subtraction. These dials were joined by teeth-bearing internal wheels that carried more...

Public Key Cryptography (PKC) is a technological tool that enables participants to confirm their identity with each other electronically. Traditional signatures have been around for thousands of years, originally being used to mark artwork such as pottery with the identity of the creator. However, as the concept of currency and contracts spread across the globe, so did the use of signatures. Although signatures were adequate for society's needs, and still are as a whole, they clearly did not satisfy the demands of electronic security. When governments began to learn of the potentials of PKC, they endeavored to keep the technology to themselves. In the early 1970s, while working for the British government, James Ellis (1924- 1997), Clifford Cocks (b. 1950), and Malcolm Williamson (b. 1950) contributed to its development. It was only in 1997, under a new government "openness" policy, that it was revealed to the world that Britain had more...

Norwegian Svend Foyn (1809-1894) is regarded as the father of modern whaling and is credited with the invention of the modern harpoon. Foyn's genius was to combine the use of fast steam-powered boats with deck-mounted cannons that could use both harpoons with strong lines attached to them and bomb lances to kill the target whale as quickly as possible. Foyn's purpose-built steam whale "catcher" Spes et Fides {Hope and Faith) first sailed in 1864 to northern Norway. By 1868 Foyn had perfected the technique and "modern" whaling methods began to reap financial rewards. This success soon transformed Norway into the dominant force in whaling, an industry previously dominated by British, American, French, and German ships. During the nineteenth century, whale oil was much in demand for lighting and soap; whale meat, which has been eaten by some cultures since early times, became popular in the twentieth century. Foyn's innovations were more...

"Fogarty's... procedure was the first successful example of 'less invasive'... vascular surgery." Inventor of the Week archive Thomas Fogarty [b. 1934) was working as a scrub technician at the Good Samaritan Hospital, Cincinnati, Ohio, when he noticed the difficulty surgeons had in removing blood clots that formed in arteries and veins. The operation, which often took nine to twelve hours to perform, necessitated opening up the entire length of the vessel and often resulted in the patient dying or having their limb amputated. Fogarty devised a scheme that could be used to overcome the need for invasive surgery. It involved using a urethral catheter, which is flexible and strong enough to be pushed through a blood vessel and penetrate the blood clot. Working in his attic, Fogarty had the further inspiration to use the fly-tying skills he had learned as a fisherman to attach the "fingertip" of a latex glove more...