Showing papers in "Physics Today in 1950"
TL;DR: The theory of communication is extended to include a number of new factors, in particular the effect of noise in the channel, and the savings possible due to the statistical structure of the original message anddue to the nature of the final destination of the information.
Abstract: HE recent development of various methods of modulation such as PCM and PPM which exchange bandwidth for signal-to-noise ratio has intensified the interest in a general theory of communication. A basis for such a theory is contained in the important papers of Nyquist1 and Hartley2 on this subject. In the present paper we will extend the theory to include a number of new factors, in particular the effect of noise in the channel, and the savings possible due to the statistical structure of the original message and due to the nature of the final destination of the information. The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point. Frequently the messages have meaning; that is they refer to or are correlated according to some system with certain physical or conceptual entities. These semantic aspects of communication are irrelevant to the engineering problem. The significant aspect is that the actual message is one selected from a set of possible messages. The system must be designed to operate for each possible selection, not just the one which will actually be chosen since this is unknown at the time of design. If the number of messages in the set is finite then this number or any monotonic function of this number can be regarded as a measure of the information produced when one message is chosen from the set, all choices being equally likely. As was pointed out by Hartley the most natural choice is the logarithmic function. Although this definition must be generalized considerably when we consider the influence of the statistics of the message and when we have a continuous range of messages, we will in all cases use an essentially logarithmic measure. The logarithmic measure is more convenient for various reasons:
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417 citations
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TL;DR: The major weapon psychologists have for their exploration of perceptual processes is the threshold, the breaking point at which an event stops being perceived one way and starts being perceived another as mentioned in this paper, which they call the threshold.
Abstract: The major weapon psychologists have for their exploration of perceptual processes is the threshold, the breaking point at which an event stops being perceived one way and starts being perceived another.
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41 citations
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TL;DR: Recently, a far more intimate and detailed view of the basic processes by which electrons carry current has been made possible by new experiments based upon the invention of the transistor as mentioned in this paper, which has been called the transistor transistor revolution.
Abstract: Recently a far more intimate and detailed view of the basic processes by which electrons carry current has been made possible by new experiments based upon the invention of the transistor
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TL;DR: In fact, we are now in somewhat the same psychological state about the availability of large diffraction gratings as was the world about human flight at the time the Wright brothers began their experiments.
Abstract: Few problems of experimental physics have a more colorful background than that involved in the ruling of large diffraction gratings. Nor is any problem of such great importance more widely misunderstood. After more than a hundred years of trying, by dozens of physicists and their associated instrument makers, by Nobel prizemen and amateurs alike, no one has succeeded in producing gratings having the size and power needed by modern spectroscopists. In fact, we are now in somewhat the same psychological state about the availability of large gratings as was the world about human flight at the time the Wright brothers began their experiments. Flying seemed desirable, but so many able people had tried it and failed that it appeared likely that the problem never would be solved.
TL;DR: The number of those who travel by themselves is only a small fraction of all the able-bodied blind as mentioned in this paper. But despite the remarkable skills of some gifted individuals, despite their remarkable skills, despite being able to travel with remarkable ability, the number of blind individuals who travel alone is still small.
Abstract: Freedom means many things. For the blind, one of its essential elements is independence of movement. Yet, despite the remarkable skills of some gifted individuals, the number of those who travel by themselves is only a small fraction of all the able‐bodied blind. Too often, blindness means staying at home.
TL;DR: In a very interesting article, "The Composition of Our Universe" (Physics Today, April 1950), Dr. Harrison Brown brings forth convincing evidence which suggests strongly that our cosmos is remarkably uniform in its chemical composition.
Abstract: In a very interesting article, “The Composition of Our Universe” (Physics Today, April, 1950), Dr. Harrison Brown brings forth convincing evidence which suggests strongly that our cosmos is remarkably uniform in its chemical composition. In fact, apart from a few notable exceptions which can be easily accounted for by local conditions, the relative abundance of various chemical elements is nearly the same on the earth, on the planets, on the sun and other stars of the Milky Way system, in the diffuse interstellar material, and in the distant spiral galaxies which represent the independent stellar systems of their own.
TL;DR: In this paper, it was shown that vertical threads which to an observer appear to lie in a frontal parallel plane lie actually in a curved surface, and that the threads which appear to be in a straight line lie on a curve.
Abstract: Helmholtz discovered that vertical threads which to an observer appear to lie in a frontal parallel plane lie actually in a curved surface.
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TL;DR: The author considers such general physical problems as the generalization of the problems of optics, if extended to the space time continuum.
Abstract: The author considers such general physical problems as the generalization of the problems of optics, if extended to the space time continuum.
TL;DR: The thirty-ninth meeting of the Acoustical Society of America (ASA) was held at the Pennsylvania State College (PSC) last June 22, 23, and 24.
Abstract: The Pennsylvania State College played host for the thirty‐ninth meeting of the Acoustical Society of America last June 22, 23, and 24. Sessions covering a wide variety of subjects (including such matters as noise, hearing, speech, transducers and recording, the medical and biological effects of sound, the propagation of sound, etc.) were held in the college's Osmond Laboratory. A total of about ninety papers was given, of which something less than ten percent were invited and the remainder were contributed. Three of the meeting's ten sessions are reviewed below.
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TL;DR: The American Association of Physics Teachers (AAPT) summer meeting was held at Wesleyan University in Middletown, Connecticut as mentioned in this paper, which was unique in many ways.
Abstract: The summer meeting of the American Association of Physics Teachers (held June 20, 21, 22 at Wesleyan University in Middletown, Connecticut) was unique in many ways. For one thing, the meeting was completely a physics teachers meeting. No other organization or society was meeting in that vicinity at the time. This was a first for the physics teachers, some one hundred and fifty of whom were registered from at least twenty‐five different states and Canada, and from over eighty different institutions. Of the registrants, about forty‐five were accompanied by their wives or families, so well over two hundred were present, and the pleasingly cosmopolitan nature of the meetings contributed toward the friendly and informal tone of all the sessions. All this was made possible by the excellent program arranged, which everyone found stimulating and valuable, and above all by the graciously provided environment of that ideal campus of Connecticut Wesleyan. Nothing but praise was heard for the local setting.
TL;DR: The typical response of the physicist who wished to contribute to this latest international crisis has been to go to Los Alamos or some other government laboratory for weapon development, for a summer or a year as mentioned in this paper.
Abstract: As far as this writer can discover, the typical response of the physicist who wished to contribute to this latest international crisis has been to go to Los Alamos, or some other government laboratory for weapon development, for a summer or a year. No doubt this has been a valuable contribution to solving the present crisis and no doubt it has made the contributor feel he is “doing his bit”. But is this all the physicist can contribute, the development of more and fancier weapons? Is the only contribution of physics, to the year‐by‐year needs of this country, to be more and fancier gadgets?
TL;DR: On January 31 and February 1, 1950, the Tuesday and Wednesday preceding the New York meeting of the American Physical Society, the Division of Electron Physics of the Society and the Panel on Electron Tubes of the military's Research and Development Board presented a symposium on thermionics.
Abstract: On January 31 and February 1, 1950, the Tuesday and Wednesday preceding the New York meeting of the American Physical Society, the Division of Electron Physics of the Society and the Panel on Electron Tubes of the military's Research and Development Board presented a symposium on thermionics.
TL;DR: In this paper, the advantage of having two widely separated brains of low quality is emphasized approximately in these words: “For he could think, without congestion, Upon both sides of any question.
Abstract: Oliver Herford wrote a poem about the dinosaur in which the advantage of having two widely separated brains of low quality is emphasized approximately in these words:“For he could think, without congestion, Upon both sides of any question.”
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TL;DR: The physical properties of evaporated metal films cannot in general be explained in terms of the bulk metal: it is usually necessary to assume an aggregated structure, particularly in the case of films less than 150 Angstroms in thickness as mentioned in this paper.
Abstract: The physical properties of evaporated metal films cannot in general be explained in terms of the bulk metal: it is usually necessary to assume an aggregated structure, particularly in the case of films less than 150 Angstroms in thickness.
TL;DR: Tate, who was a professor of physics at the University of Minnesota, died of a cerebral hemorrhage on May 27, 1990 as mentioned in this paper, after having recovered to the point of working several hours daily, and he attended the Washington meeting of the American Physical Society, to the great pleasure of his colleagues.
Abstract: John Torrence Tate, Professor of Physics in the University of Minnesota, died of a cerebral hemorrhage on May 27. An earlier attack in December, 1949, had kept him away from work for some time, but he had recovered to the point of working several hours daily, and he attended the Washington meeting of the American Physical Society, to the great pleasure of his fellow members.
TL;DR: The Institute has adopted a plan, effective immediately, for the organization of Student Sections of the American Institute of Physics as discussed by the authors, which will be implemented in the next few weeks, with the goal of increasing the number of students attending classes.
Abstract: The Institute has adopted a plan, effective immediately, for the organization of Student Sections of the American Institute of Physics.
TL;DR: In this article, a high frequency electric field is applied to an ionized gas, and the resulting oscillatory motion of the free electrons will give rise to an alternating current, which can be used to simulate the behavior of a real electric current.
Abstract: If a high frequency electric field is applied to an ionized gas, the resulting oscillatory motion of the free electrons will give rise to an alternating current.
TL;DR: The differences between the spirit of American and French scientists are discussed in this article, where only some impressions received from contact with American researchers and to speak of the differences in spirit of French and American scientists are described.
Abstract: It takes courage to risk speaking of America and Americans after a visit of only two months. Having, moreover, in the course of my trip visited only laboratories and scientists in a specialized field, I was not able to have more than a partial view of the scientific life in that tremendous country. I intend to recount here only some impressions received from contact with American researchers and to speak of the differences between the spirit of American and French scientists.
TL;DR: A number of federal agencies, acting in concert with certain of the professional organizations, are now methodically investigating each of the many factors involved in the present scientific manpower picture in order to see what may be done to insure the country's long-term scientific future.
Abstract: There is no obvious formula for predicting the future scientific manpower needs of the United States, but if we depend upon experience gained during the past several years there is every reason to suppose that these needs will become increasingly pronounced for quite some time to come. A number of federal agencies, acting in concert with certain of the professional organizations, are now methodically investigating each of the many factors involved in the present scientific manpower picture in order to see what may be done to insure the country's long‐term scientific future. The existing state of international unrest may well extend over a considerable number of years, and it is necessary under the circumstances to know as precisely as possible where we stand with respect to an adequate potential reservoir of scientific and technical manpower. This of course depends largely upon the rate at which American scientists are being trained, as well as upon the quality of the finished product, but any meaningful ...