Biographical encyclopedia
Download 17.33 Mb. Pdf ko'rish
|
|
855 [1400] TOWNES
TOWNES [1400] 1935. He obtained his master’s degree at Duke University, but traveled west to the California Institute of Technology for his Ph.D., which he earned in 1939. He spent World War II and some years thereafter working for Bell Telephone Laboratories on the design of radar bombing systems. In 1948 he met Rabi [1212], who suggested he come to Columbia Univer sity, a suggestion much to Townes’s lik ing. Townes joined the physics depart ment of the university and since 1950 has been a full professor there. Radar technology involves the emis sion and reception of microwaves, that portion of the electromagnetic spectrum that falls between infrared waves and radio waves. At Columbia, Townes fol lowed up this interest in the most general fashion.
Townes felt the strong need for a de vice that would generate microwaves in great intensity. Ordinary mechanical de vices could be used to generate the much longer radio waves, but for those same devices to produce microwaves would require such small-scale construction as to remove the design from the realm of the possible. It struck Townes in 1951 (while sit ting on a park bench in Washington, D.C., early one morning and waiting for a restaurant to open so he might eat breakfast) that something sufficiently small could be found if one turned to molecules rather than to any electronic circuit. Molecules had various fashions of vibration and some of the vibrations would be equivalent to radiation in the microwave region, if the vibrations could be converted into radiation. The ammo nia molecule for instance vibrated 24.000,000,000 times a second under ap propriate conditions and this could be converted into microwaves with a wave length of iVx centimeters. Suppose he got ammonia molecules “excited” by pumping energy into them through heat or electricity. Suppose, next, that he exposed such excited mole cules to a beam of microwaves of the natural frequency of the ammonia mole cule, even a very feeble beam of such microwaves. An individual molecule struck by such a microwave would be stimulated to emit its own energy in the form of such a microwave, which would strike another molecule and cause it to give up its energy. The very feeble inci dent beam of microwaves would act as the igniter of a cascade, a chain reaction, that would in the end produce a flood of microwaves. All the energy originally used to excite the molecule would be converted into one particular kind of ra diation.
Townes thought of all this on the park bench, putting down some quick calcula tions (in the romantic tradition of sci ence) on the back of an old envelope. By December 1953 he and his students finally constructed a gadget that worked, and produced the necessary beam of mi crowaves. The process was described by the phrase “microwave amplification by stimulated emission of radiation.” This was abbreviated to the word “maser.” (Such acronyms are becoming more and more popular in technology.) The maser turned out to have a num ber of interesting uses. The steady, un deviating vibration of the ammonia mol ecules, as measured by the steady, un deviating frequency of the microwaves, could be used to measure time, so that the maser turned out to be an “atomic clock” far more accurate than any me chanical timepiece ever invented. Masers could also be used to send their microwave beams in different direc tions. If an ether existed, then the earth moved through this ether, then the fre quency should alter with direction. The test was attempted in January 1960, and there was no difference in wavelength. The Michelson [835]-Morley [730] ex periment of three quarters of a century earlier was thus confirmed under condi tions of unprecedented accuracy, for a deviation in frequency of one part in a trillion would have been detected. Ein stein’s [1064] theory of relativity was upheld by this, and also by the Moss- bauer [1483] effect, which had just been discovered. Townes felt a more versatile instru ment could be built if gaseous ammonia
[1400] TOWNES
SUTHERLAND [1402] was replaced by molecules of a solid and if the new knowledge of solid-state phys ics pioneered by Shockley [1348] was taken advantage of. In the late 1950s, such solid-state masers were indeed built by Townes and by others. Such masers could amplify microwaves while intro ducing unprecedentedly low quantities of random radiation (“noise”), which meant that ultra-weak signals could be amplified far more efficiently than by any other known means of amplification. The almost vanishingly weak reflected signals from Pierce’s [1351] Echo I satel lite were successfully amplified in this fashion in 1960, as were radar reflections from the planet Venus. Meanwhile, in 1957 Townes began speculating on the possibility of devising a maser that would deliver infrared or even visible light, instead of microwaves. With his brother-in-law, he published a paper on the subject in 1958. In 1960 such a device was put together for the first time by Maiman [1479]—a pink ruby rod that emitted intermittent bursts of red light. The light was coherent; that is, it did not spread outward but main tained a narrow beam almost indefi nitely. Such a beam reaching out to the moon, a quarter of a million miles away, would still have spread so little as to be only a couple of miles wide. There would be so little dissipation of energy that it was quite practical to think of reflecting such maser beams from the moon’s surface and mapping that surface in far more efficient style than was possi ble with an ordinary telescope. The large energies that could be packed into a nar row beam of light could also be made useful in medicine, as in certain eye op erations, and in chemical analysis, where small bits of a substance could be vapor ized and then subjected to spectroscopic study. The light was also more monochro matic than any light previously produced by man. All the light rays were of pre cisely the same wavelength. This meant that such beams could be modulated to carry messages, much as ordinary radio wave carriers are modulated in ordinary radio communication. The advantage of using light waves for the purpose was that at light’s high frequency there is far more room for carrier waves in a given band than in the low frequency radio wave spectrum. The visible-light masers are called “op tical masers” or “lasers” (acronym for “light amplification by stimulated emis sion of radiation”). For this, Townes was awarded the 1964 Nobel Prize for physics, sharing it with Prokhorov [1409] and Basov [1452] who independently worked out the theory. [1401] HILLIER, James Canadian-American physicist Born: Brantford, Ontario, August 22, 1915 Hillier graduated from the University of Toronto in 1937 and obtained his Ph.D. there in 1941. Shortly before the doctorate came through officially, he emigrated to the United States, and be came an American citizen in 1945. While still at the university, he con structed, with his collaborator, Albert F. Prebus, an electron microscope along the lines advanced earlier by Ruska [1322], The new model, however, built in 1937, was much improved. It magnified 7,000 times and produced resolutions sharp enough to be of use in the laboratory. It was the forerunner of over two thousand electron microscopes existing in the world a generation later, some of them capable of magnifying 2,000,000 times and of making visible the most intimate details within the cell, down to large sin gle molecules. [1402] SUTHERLAND, Earl Wilbur, Jr. American physician and pharma cologist
Born: Burlingame, Kansas, No vember 19, 1915 Died: Miami, Florida, March 9, 1974
Sutherland received his M.D. in 1942 from Washington University Medical 857 [1403] ANFINSEN
SHANNON [1404] School in St. Louis. There was then an interlude because of World War II, after which he worked in the laboratory of C. F. Cori [1194] and served on the faculty, attaining professorial status in 1950. In 1953 he went on to Case Western Reserve University in Cleve land and while there, in 1956, he isolated cyclic AMP, an intermediate in the formation of ATP, the vital compound that Lipmann [1221] had uncovered. Cyclic AMP turned out to play an im portant role in many chemical reactions in the body, and for it, Sutherland re ceived the 1971 Nobel Prize for physiol ogy and medicine. [1403] ANFINSEN, Christian Boehmer American biochemist
March 26, 1916 Anfinsen obtained his Ph.D. at Har vard University in 1943, and he has been affiliated with a number of institutions in the United States, Sweden, and Israel. His chief research interest has been in the relationship between the structure and function of enzymes and other pro teins. He wrote an influential book, The Molecular Basis of Evolution, in 1959. For his work, he received a share of the 1972 Nobel Prize for chemistry. [1404] SHANNON, Claude Elwood American mathematician
30, 1916 Shannon graduated from the Univer sity of Michigan in 1936, then went on to earn a Ph.D. in mathematics at the Massachusetts Institute of Technology in 1940. He joined the staff of Bell Tele phone Laboratories in 1941. At the Bell Telephone Laboratories he worked on the problem of most efficiently transmitting information. For a century, ever since the development of Morse’s [473] telegraph, messages in rapidly increasing numbers had been flowing in all direction over wires and cable or through the open air by means of fluctuating electric currents or modu lated electromagnetic radiation. A large number of different systems of trans mitting these messages were used and it was important to know which was most efficient and if the efficiency could be in creased still further. Shannon turned his efforts toward a fundamental understanding of the prob lem and by 1948 had evolved a method of expressing information in quantitative form. The fundamental unit of informa tion is a yes-no situation. Either some thing is or is not. This can be expressed in binary notation as either 1 or 0. Under these circumstances, 1 and 0 are binary digits, a phrase that can be short ened to “bits.” Thus, the unit of infor mation is the bit. More complicated information can be viewed as built up out of combinations of bits. The game of “Twenty Questions” for instance shows how quite compli cated objects can be identified in twenty bits or less, using the rules of the game. Something much more elaborate, such as is seen by the human eye, can also be measured in bits (many more than twenty, of course) since each cell of the retina might be viewed as recording “light” or “dark” (“yes” or “no”) and it is the combination of these yes-no situa tions that makes up the complete pic ture. (The situation is slightly more complicated, but no different funda mentally, if color and other variables are included.) Shannon’s publication in 1949 showed how this quantitation of information could be analyzed by strict mathematical methods. It was possible to measure the likelihood of information being garbled through loss of bits, distortion of bits, addition of extraneous bits, and so on. One could speak with precision of such things as redundancy and noise and even entropy. This branch of mathematics is called information theory. It has proved useful not only in circuit design, com puter design, and communications technology; it is being applied to biology and psychology, to phonetics, and even to semantics and literature.
[1405] DICKE
CRICK [1406] Since 1956 Shannon has been on the faculty of Massachusetts Institute of Technology. [1405] DICKE, Robert Henry American physicist Bom: St. Louis, Missouri, May 6, 1916
Dicke, who obtained his Ph.D. at the University of Rochester in 1941, has been on the physics faculty of Princeton University since 1946. He is best known for his scalar-tensor field theory, perhaps the most carefully thought out and ambitious alternative presented to Einstein’s [1064] theory of general relativity. Einstein’s theory, how ever, remains the simplest mathe matically and of the alternatives seems to be the most nearly in accord with ob servations. The observational differences that can distinguish between Einstein’s theory and others such as Dicke’s, how ever, remain so delicate that a final choice remains difficult to establish. Dicke also carried further Gamow’s [1278] suggestion of a radio-wave resi due of the initial big bang and was in strumental in establishing the importance of the observances of Penzias [1501] and R. W. Wilson [1506] in this respect as strong evidence that the big bang had in deed taken place. [1406] CRICK, Francis Harry Compton English biochemist
1916
Crick was educated at University Col lege in London and went on to obtain his Ph.D. at Cambridge University in 1953. He was a physicist to begin with and worked in the field during World War II, when he was involved in radar research and in magnetic mine develop ment.
The war years, however, had seen the beginnings of a revolution in biochem istry. Martin [1350] and Synge [1394] had developed paper chromatography, which made it easy to separate complex biochemical mixtures into their compo nents. The development of the nuclear reactor meant that radioisotopes were going to be available in quantity and could be used to tag one particular com pound or another. (This work was in deed to come to great results, Calvin’s [1361] work being an example.) At the same time, biochemists were coming to realize that nucleic acids, rather than proteins, were the instru ments whereby physical characteristics were inherited and it was the deoxy ribonucleic acid (DNA) of the chro mosomes that were the key chemicals of life. The orthodox chemistry of the nucleic acids had been worked out by Todd [1331], but something more was needed. The fine details of structure within the intact giant molecule of DNA were sought and the well-established methods of chemistry were insufficient for the purpose. The new methods and instru mentation of physics were required. At the time, under the leadership of Perutz [1389], a veritable galaxy of phys ics-minded scientists was turning to bio chemistry at Cambridge and their refined probings established the science of mo lecular biology, a fusion of biology, chemistry, and physics. One method of studying the internal structure of large molecules is X-ray diffraction. Wilkins [1413] studied DNA in this manner and by 1953 his data yielded specific information on the type of regularities that were to be found in the molecule. The problem was how best to interpret those regularities in atomic terms.
Crick was one of the physicists who turned to biochemistry or, rather, to mo lecular biology, and with him was a young American, James Dewey Watson [1480]. Together they considered Wil kins’ X-ray diffraction data. Pauling [1236] had in 1951 brought forth con vincing evidence to the effect that mole cules of fibrous proteins, such as the collagen of connective tissue, existed in the form of a helix (the shape, that is, of what is usually called a spiral staircase). It was easy to assume that the nucleic 8 5 9
[1406] CRICK
CRICK [1406] acids were similarly constructed, but that alone was not enough. It would be ideal if one could find a structure that would fit the X-ray diffraction data and would also explain the key fact about DNA; to wit, that it was capable of replication. Ever since the time of Flemming [762], three quarters of a century earlier, it had been known that chromosomes formed replicas of themselves during mi tosis, and when Mendel’s [638] work was rediscovered in 1900 it was quickly seen that such chromosome replication was the key to heredity and to the science of genetics. Since the chromosome came to be seen as essentially a string of DNA molecules, it meant that the molecule of DNA itself must be forming a replica of itself.
Crick and Watson took into consid eration the work of men like Chargaff [1291], which showed that within the nucleic acid molecule there was a definite relationship among the ni trogenous bases. There are four such bases in the DNA molecule—adenine, guanine, thymine, and cytosine—-and it seemed that the number of units of adenine was always roughly equal to the number of thymine units, while that of guanine was equal to cytosine. (The ratio between those two pairs could, however, be almost anything.) Crick and Watson, in a classic paper published in 1953, therefore suggested that the DNA molecule consisted of a double helix, each helix made up of the sugar-phosphate backbone known to exist, thanks to Todd’s work, in the nucleic acid molecule. The nitrogenous bases extended in toward the center of the helix from each of the two back bones and approached each other. The nitrogenous bases are of different sizes and if the double helix is to be of uniform width, an adenine unit can ap proach only a thymine or a cytosine, but never a guanine; a thymine could ap proach an adenine or guanine but never a cytosine; and so on. The conditions of uniform width would be met if it were assumed that an adenine base from one backbone always approached a thymine from the other; while a guanine from one backbone always approached a cy tosine from the other. That would neatly account for the fact that the numbers of thymine and adenine were equal and the numbers of guanine and cytosine were equal. Furthermore, it was now reasonable to suggest that in the process of replication, the two strands of the double helix un wound. Each single helix could then serve as a model for its complement. Wherever an adenine existed, a thymine could be selected as its neighbor and vice versa. Wherever a guanine existed, cy tosine could be selected as its neighbor and vice versa. In this way, helix 1 would form a new helix 2, and helix 2 would form a new helix 1. The end re sult would be two 1-2 double helixes, where only one had existed previously. When first advanced, the Watson- Crick model was nothing more than a device plucked out of air to fit the ob served data. However, a decade of furi ous experimental work in many labora tories followed and every painstakingly gathered piece of evidence seemed to confirm the model. It is now generally accepted by biochemists. Crick named his house at Cambridge the Golden Helix, and for him and for the world of science the helix was indeed golden. Crick, Watson, and Wilkins shared the 1962 Nobel Prize in medicine and physiology, while in that same year the prize in chemistry went to other members of the Cambridge group, Perutz [1389] and Kendrew [1415], Four years before, the chemistry prize had gone to Sanger [1426], still another member of the group. Molecular biology was indeed a kind of “wave of the fu ture.”
The new look of the DNA molecule opened fruitful avenues of research. The work of Fraenkel-Conrat [1355], was showing, clearly enough, that the nucleic acid molecule not only formed a replica of itself but was also capable of bringing about the formation of a specific protein. The mechanism by which it could do so (the genetic code) was tougher to eluci date than that of mere replication. Men like Hoagland [1447], Ochoa [1293], and Crick himself had been working as siduously at it, and as the 1960s opened, 8 6 0
|
