28 May 2009

Contact lenses

The invention: Small plastic devices that fit under the eyelids, contact lenses, or “contacts,” frequently replace the more familiar eyeglasses that many people wear to correct vision problems. The people behind the invention: Leonardo da Vinci (1452-1519), an Italian artist and scientist Adolf Eugen Fick (1829-1901), a German glassblower Kevin Tuohy, an American optician Otto Wichterle (1913- ), a Czech chemist William Feinbloom (1904-1985), an American optometrist An Old Idea There are two main types of contact lenses: hard and soft. Both types are made of synthetic polymers (plastics). The basic concept of the contact lens was conceived by Leonardo da Vinci in 1508. He proposed that vision could be improved if small glass ampules filled with water were placed in front of each eye. Nothing came of the idea until glass scleral lenses were invented by the German glassblower Adolf Fick. Fick’s large, heavy lenses covered the pupil of the eye, its colored iris, and part of the sclera (the white of the eye). Fick’s lenses were not useful, since they were painful to wear. In the mid-1930’s, however, plastic scleral lenses were developed by various organizations and people, including the German company I. G. Farben and the American optometrist William Feinbloom. These lenses were light and relatively comfortable; they could be worn for several hours at a time. In 1945, the American optician Kevin Tuohy developed corneal lenses, which covered only the cornea of the eye. Reportedly, Tuohy’s invention was inspired by the fact that his nearsighted wife could not bear scleral lenses but hated to wear eyeglasses. Tuohy’s lenses were hard contact lenses made of rigid plastic, but they were much more comfortable than scleral lenses and could be worn for longer periods of time. Soon after, other people developed soft contact lenses, which cover both the cornea and the iris. At present,many kinds of contact lenses are available. Both hard and soft contact lenses have advantages for particular uses. Eyes, Tears, and Contact Lenses The camera-like human eye automatically focuses itself and adjusts to the prevailing light intensity. In addition, it never runs out of “film” and makes a continuous series of visual images. In the process of seeing, light enters the eye and passes through the clear, dome-shaped cornea, through the hole (the pupil) in the colored iris, and through the clear eye lens, which can change shape by means of muscle contraction. The lens focuses the light, which next passes across the jellylike “vitreous humor” and hits the retina. There, light-sensitive retinal cells send visual images to the optic nerve, which transmits them to the brain for interpretation. Many people have 20/20 (normal) vision, which means that they can clearly see letters on a designated line of a standard eye chart placed 20 feet away. Nearsighted (myopic) people have vision of 20/40 or worse. This means that, 20 feet from the eye chart, they see clearly what people with 20/20 vision can see clearly at a greater distance. Myopia (nearsightedness) is one of the four most common visual defects. The others are hyperopia, astigmatism, and presbyopia. All are called “refractive errors” and are corrected with appropriate eyeglasses or contact lenses. Myopia, which occurs in 30 percent of humans, occurs when the eyeball is too long for the lens’s focusing ability and images of distant objects focus before they reach the retina, causing blurry vision. Hyperopia, or farsightedness, occurs when the eyeballs are too short. In hyperopia, the eye’s lenses cannot focus images of nearby objects by the time those images reach the retina, resulting in blurry vision. A more common condition is astigmatism, in which incorrectly shaped corneas make all objects appear blurred. Finally, presbyopia, part of the aging process, causes the lens of the eye to lose its elasticity. It causes progressive difficulty in seeing nearby objects. In myopic, hyperopic, or astigmatic people, bifocal (two-lens) systems are used to correct presbyopia, whereas monofocal systems are used to correct presbyopia in people whose vision is otherwise normal.Modern contact lenses, which many people prefer to eyeglasses, are used to correct all common eye defects as well as many others not mentioned here. The lenses float on the layer of tears that is made continuously to nourish the eye and keep it moist. They fit under the eyelids and either over the cornea or over both the cornea and the iris, and they correct visual errors by altering the eye’s focal length enough to produce 20/20 vision. In addition to being more attractive than eyeglasses, contact lenses correct visual defects more effectively than eyeglasses can. Some soft contact lenses (all are made of flexible plastics) can be worn almost continuously. Hard lenses are made of more rigid plastic and last longer, though they can usually be worn only for six to nine hours at a time. The choice of hard or soft lenses must be made on an individual basis. The disadvantages of contact lenses include the fact that they must be cleaned frequently to prevent eye irritation. Furthermore, people who do not produce adequate amounts of tears (a condition called “dry eyes”) cannot wear them. Also, arthritis, many allergies, and poor manual dexterity caused by old age or physical problems make many people poor candidates for contact lenses.Impact The invention of Plexiglas hard scleral contact lenses set the stage for the development of the widely used corneal hard lenses by Tuohy. The development of soft contact lenses available to the general public began in Czechoslovakia in the 1960’s. It led to the sale, starting in the 1970’s, of the popular, soft contact lenses pioneered by Otto Wichterle. The Wichterle lenses, which cover both the cornea and the iris, are made of a plastic called HEMA (short for hydroxyethylmethylmethacrylate). These very thin lenses have disadvantages that include the requirement of disinfection between uses, incomplete astigmatism correction, low durability, and the possibility of chemical combination with some medications, which can damage the eyes. Therefore, much research is being carried out to improve them. For this reason, and because of the continued popularity of hard lenses, new kinds of soft and hard lenses are continually coming on the market.

24 May 2009

Computer chips

The invention: Also known as a microprocessor, a computer chip combines the basic logic circuits of a computer on a single silicon chip. The people behind the invention: Robert Norton Noyce (1927-1990), an American physicist William Shockley (1910-1989), an American coinventor of the transistor who was a cowinner of the 1956 Nobel Prize in Physics Marcian Edward Hoff, Jr. (1937- ), an American engineer Jack St. Clair Kilby (1923- ), an American researcher and assistant vice president of Texas Instruments The Shockley Eight The microelectronics industry began shortly after World War II with the invention of the transistor. While radar was being developed during the war, it was discovered that certain crystalline substances, such as germanium and silicon, possess unique electrical properties that make them excellent signal detectors. This class of materials became known as “semiconductors,” because they are neither conductors nor insulators of electricity. Immediately after the war, scientists at Bell Telephone Laboratories began to conduct research on semiconductors in the hope that they might yield some benefits for communications. The Bell physicists learned to control the electrical properties of semiconductor crystals by “doping” (treating) them with minute impurities. When two thin wires for current were attached to this material, a crude device was obtained that could amplify the voice. The transistor, as this device was called, was developed late in 1947. The transistor duplicated many functions of vacuum tubes; it was also smaller, required less power, and generated less heat. The three Bell Laboratories scientists who guided its development—William Shockley, Walter H. Brattain, and John Bardeen—won the 1956 Nobel Prize in Physics for their work.Shockley left Bell Laboratories and went to Palo Alto, California, where he formed his own company, Shockley Semiconductor Laboratories, which was a subsidiary of Beckman Instruments. Palo Alto is the home of Stanford University, which, in 1954, set aside 655 acres of land for a high-technology industrial area known as Stanford Research Park. One of the first small companies to lease a site there was Hewlett-Packard. Many others followed, and the surrounding area of Santa Clara County gave rise in the 1960’s and 1970’s to a booming community of electronics firms that became known as “Silicon Valley.” On the strength of his prestige, Shockley recruited eight young scientists from the eastern United States to work for him. One was Robert Norton Noyce, an Iowa-bred physicist with a doctorate from the Massachusetts Institute of Technology. Noyce came to Shockley’s company in 1956. The “Shockley Eight,” as they became known in the industry, soon found themselves at odds with their boss over issues of research and development. Seven of the dissenting scientists negotiated with industrialist Sherman Fairchild, and they convinced the remaining holdout, Noyce, to join them as their leader. The Shockley Eight defected in 1957 to form a new company, Fairchild Semiconductor, in nearby Mountain View, California. Shockley’s company, which never recovered from the loss of these scientists, soon went out of business.Integrating Circuits Research efforts at Fairchild Semiconductor and Texas Instruments, in Dallas, Texas, focused on putting several transistors on one piece, or “chip,” of silicon. The first step involved making miniaturized electrical circuits. Jack St. Clair Kilby, a researcher at Texas Instruments, succeeded in making a circuit on a chip that consisted of tiny resistors, transistors, and capacitors, all of which were connected with gold wires. He and his company filed for a patent on this “integrated circuit” in February, 1959. Noyce and his associates at Fairchild Semiconductor followed in July of that year with an integrated circuit manufactured by means of a “planar process,” which involved laying down several layers of semiconductor that were isolated by layers of insulating material. Although Kilby and Noyce are generally recognized as coinventors of the integrated circuit, Kilby alone received a membership in the National Inventors Hall of Fame for his efforts. Consequences By 1968, Fairchild Semiconductor had grown to a point at which many of its key Silicon Valley managers had major philosophical differences with the East Coast management of their parent company. This led to a major exodus of top-level management and engineers. Many started their own companies. Noyce, Gordon E. Moore, and Andrew Grove left Fairchild to form a new company in Santa Clara called Intel with $2 million that had been provided by venture capitalist Arthur Rock. Intel’s main business was the manufacture of computer memory integrated circuit chips. By 1970, Intel was able to develop and bring to market a random-access memory (RAM) chip that was subsequently purchased in large quantities by several major computer manufacturers, providing large profits for Intel. In 1969, Marcian Edward Hoff, Jr., an Intel research and development engineer, met with engineers from Busicom, a Japanese firm. These engineers wanted Intel to design a set of integrated circuits for Busicom’s desktop calculators, but Hoff told them their specifications were too complex. Nevertheless, Hoff began to think about the possibility of incorporating all the logic circuits of a computer central processing unit (CPU) into one chip. He began to design a chip called a “microprocessor,” which, when combined with a chip that would hold a program and one that would hold data, would become a small, general-purpose computer. Noyce encouraged Hoff and his associates to continue his work on the microprocessor, and Busicom contracted with Intel to produce the chip. Frederico Faggin, who was hired from Fairchild, did the chip layout and circuit drawings. In January, 1971, the Intel team finished its first working microprocessor, the 4004. The following year, Intel made a higher-capacity microprocessor, the 8008, for Computer Terminals Corporation. That company contracted with Texas Instruments to produce a chip with the same specifications as the 8008, which was produced in June, 1972. Other manufacturers soon produced their own microprocessors. The Intel microprocessor became the most widely used computer chip in the budding personal computer industry and may take significant credit for the PC “revolution” that soon followed. Microprocessors have become so common that people use them every day without realizing it. In addition to being used in computers,the microprocessor has found its way into automobiles, microwave ovens, wristwatches, telephones, and many other ordinary items.