Showing papers in "Physics Today in 1970"
TL;DR: In this paper, a measurement is a superposition of vectors, each representing the quantity being observed as having one of its possible values, and the question is how this superposition can be reconciled with the fact that in practice we only observe one value.
Abstract: Despite its enormous practical success, quantum theory is so contrary to intuition that, even after 45 years, the experts themselves still do not all agree what to make of it. The area of disagreement centers primarily around the problem of describing observations. Formally, the result of a measurement is a superposition of vectors, each representing the quantity being observed as having one of its possible values. The question that has to be answered is how this superposition can be reconciled with the fact that in practice we only observe one value. How is the measuring instrument prodded into making up its mind which value it has observed?
464 citations
398 citations
243 citations
TL;DR: The algebra of symmetry index as discussed by the authors is a generalization of the many-body problems, and it can be viewed as a special case of the algebra of algebraic symmetry index.
Abstract: Preface 1. Bosons 2. Fermions 3. Perturbation theory 4. Green functions 5. Some aspects of the many-body problems 6. Relativistic formulations 7. The algebra of symmetry Index.
207 citations
TL;DR: In this paper, the authors investigated the reason for the bicycle's stability and found that the apparent simplicity and ease of the trick conceals much unrecognized subtlety, and they have spent some time and effort trying to discover the reasons for the bicycles' stability.
Abstract: ALMOST EVERYONE can ride a bicycle, yet apparently no one knows how they do it. I believe that the apparent simplicity and ease of the trick conceals much unrecognized subtlety, and I have spent some time and effort trying to discover the reasons for the bicycle's stability. Published theory on the topic is sketchy and presented mainly without experimental verification. In my investigations I hoped to identify the stabilizing features of normal bicycles by constructing abnormal ones lacking selected features (see figure 1). The failure of early unridable bicycles led me to a careful consideration of steering geometry, from which—with the aid of computer calculations—I designed and constructed an inherently unstable bicycle.
143 citations
TL;DR: In this paper, the authors proposed a method for determining the extragalactic distance scale for nearby galaxies and searching for exceedingly distant clusters where the redshift is large, to measure both of these numbers to a precision of 15%.
Abstract: AS RECENTLY AS THE 1950's about all that observational cosmology had succeeded in establishing was that galaxies exist and the universe expands. But beginning in the 1960's a flood of new discoveries has enriched our picture of the universe and has begun to provide a basis on which to distinguish between competing cosmological models. There has been a 30‐year effort, now drawing to a close, to get precise measurements of two parameters that will provide a crucial test for cosmological models. The two key numbers are the rate of expansion (the Hubble constant H0) and the deceleration in the expansion (q0). The hope is that current research, by determining the extragalactic distance scale for nearby galaxies and searching for exceedingly distant clusters where the redshift is large, will measure both of these numbers to a precision of 15%.
TL;DR: In this paper, the fundamental principles of electricity and magnetism are discussed. But the authors do not discuss the application of magnetism in the field of artificial intelligence. And they do not address how to apply magnetism to artificial intelligence applications.
Abstract: Fundamentals of electricity and magnetism , Fundamentals of electricity and magnetism , کتابخانه دیجیتالی دانشگاه علوم پزشکی و خدمات درمانی شهید بهشتی
TL;DR: In this article, high-resolution nuclear magnetic resonance (NMR) spectroscopy has become a powerful technique for investigating the molecular and electronic structure of biological compounds, and the high sensitivity and resolution of recently developed spectrometers with superconducting solenoids has made possible many new applications and yielded data not obtainable by other methods.
Abstract: DURING THE LAST FEW YEARS high‐resolution nuclear magnetic‐resonance (NMR) spectroscopy has become a powerful technique for investigating the molecular and electronic structure of biological compounds. The high sensitivity and resolution of recently developed spectrometers with superconducting solenoids has made possible many new applications and has yielded data not obtainable by other methods. NMR experiments can be done under conditions similar to the physiological environment of the molecules: in aqueous solution and at body temperature. Thus with NMR it is often possible to establish relations between data on the structure of biological compounds in the solid state, obtained by techniques like x‐ray crystallography, and the corresponding molecular properties in solution.
TL;DR: In this paper, a valve closure member does not begin to move until the armature causes the energy storing spring to be stressed to an extent equal to a predetermined stressing of the load spring.
Abstract: The invention relates to a magnetic valve assembly of the type in which an energized armature moves a valve closure member to an open position and a load spring in compression maintains the valve closure member closed when the armature is nonenergized. Relative movement between the armature member and the closure member is provided and an energy storing spring between these members resists the relative movement. In two embodiments the energy storing spring is stressed in compression in one and in tension in the other. The valve closure member does not begin to move until the armature causes the energy storing spring to be stressed to an extent equal to a predetermined stressing of the load spring. With this mode of operation the armature stroke is longer than the stroke of the closure member and this results in a smaller magnetic system being sufficient for a given valve system.
TL;DR: A 180-degree inverted point of view as mentioned in this paper envisions the absence of fundamentals as the ultimate triumph; this is the bootstrap attitude, which is the attitude that failure to find some such fundamental entity is equated with frustration.
Abstract: Physicists usually perceive their discipline's goal as the reduction of nature to fundamentals, and the high‐energy arena has correspondingly been dominated by the search for “basic building blocks.” Finding the quark is for the moment regarded by many as the ultimate prospective triumph; failure to find some such fundamental entity is equated with frustration. There exists, nonetheless, a 180‐degree inverted point of view, which envisions the absence of fundamentals as the ultimate triumph; this is the bootstrap attitude.
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TL;DR: In this paper, a new definition of ionicity, derived from spectroscopically obtained transition energies between bonding and antibonding states of semiconductor crystals, was proposed, and compared with the older one.
Abstract: ADVANCES in quantum chemistry, as in any other field, need novel concepts to keep pace with the great increase in available experimental data and theoretical understanding. The concept of ionicity of the chemical bond is an example. For 35 years Linus Pauling's development of a definition of ionicity, based on heats of formation of binary crystals, was standard. Here I will describe a new definition of ionicity, derived from spectroscopically obtained transition energies between bonding and antibonding states of semiconductor crystals, and show how it compares with the older one.
TL;DR: The discovery of what we have ever since called the "Josephson effect" took place while I was visiting Cambridge, England, for a sabbatical year in 1961-62 as mentioned in this paper.
Abstract: The discovery of what we have ever since called the “Josephson effect” took place while I was visiting Cambridge, England, for a sabbatical year in 1961–62. Recently, when I travelled to Kyoto to accept the London Prize on Brian Josephson's behalf, I put together some reminiscences of that period, which may be more interesting than a mere recapitulation of the bare scientific facts. Lest I appear too central to this account, I should make it clear that at least two other people could have told a similar story from their own points of view. They are Brian Pippard, Josephson's thesis advisor while the work was being done, and David Shoenberg, director at that time of the Mond Laboratory in which Josephson was a research student in experimental physics and where I served as nominal head of the solid‐state theory group.