Showing papers in "Physics Today in 1977"
TL;DR: In this article, a transient heating of spherical shaped samples is used to determine a material's thermal conductivity, which is an intensive physical property of a material that relates the heat flow through the material per unit area to temperature gradient across the material.
Abstract: Problem: Thermal conductivity is an intensive physical property of a material that relates the heat flow through the material per unit area to temperature gradient across the material. The thermal conductivity of a material is basically a measure of its ability to conduct heat. In a wide variety of applications ranging from building insulation to electronics, it is important to determine a material’s thermal conductivity. Typical methods of thermal conductivity measurement can be categorized as either steady-state or non-steadystate. In steady-state techniques, equilibrium heat flux and temperature gradient are measured. In nonsteady-state techniques, a variable heat flux is produced and the time-variant temperature gradient is measured. The method you are asked to investigate involves the transient heating of spherical shaped samples.
383 citations
TL;DR: In this paper, an introduction to the theory that must be mastered in order to engineer and evaluate the performance of solar energy systems is presented, and the authors build the necessary background and information in successive chapters, culminating in a section on representative applications.
Abstract: This book is an introduction into the theory that must be mastered in order to engineer and evaluate the performance of solar energy systems. An important goal in solar energy applications is the ability to calculate output from a proposed design application and thereby establish the value of the energy delivered and a fair price for the system. To this end the authors build the necessary background and information in successive chapters, culminating in a section on representative applications. (WDM)
229 citations
148 citations
TL;DR: In this paper, the authors define material failure as a process that advances by rate processes that have threshold conditions and characteristic growth kinetics, and all material failure is dynamic, almost by definition.
Abstract: All material failure is dynamic, almost by definition. It advances by rate processes that have threshold conditions and characteristic growth kinetics.
139 citations
107 citations
95 citations
TL;DR: In the medical field, computed tomography has been referred to as computed axial tomography (CAT) as mentioned in this paper, computed tomographic reconstruction from projections (CT-XR), computerized axial projection (CAX) and transaxial reconstruction (Transaxial Tomography).
Abstract: An important new diagnostic technique is making its appearance in our major hospitals. The technique, which uses x rays to render visible thin slices through any section of the human body, has been so dramatic in its development that no general agreement has yet been reached on its name—it has been called “computed tomography,” “computerized axial tomography,” “transaxial tomography” and “reconstruction from projections.” Figure 1 shows one version of the apparatus in a clinical setting.
TL;DR: The similarity of critical behavior in dissimilar systems has long fascinated scientists as mentioned in this paper, and the magnetic equation of state of nickel has attracted much attention in the last few decades, especially for the case of carbon dioxide.
Abstract: The similarity of critical behavior in dissimilar systems has long fascinated scientists. When Pierre Curie, in 1895, measured the magnetic equation of state of nickel, he was struck by how much the curves he obtained by plotting magnetization against temperature looked like the density–temperature isobars of carbon dioxide near the critical point. In 1907 Pierre Weiss fashioned his mean‐field theory describing the equation of state of nickel after Van der Waals's equation for fluids.
TL;DR: In this article, the effect of selective laser radiation on matter has been studied. But this work is limited to a single quantum state of an atom or a molecule with excitation energy in the range 0.1 to 10 eV.
Abstract: Current progress with tunable lasers has made possible the selective excitation of practically any single quantum state of an atom or a molecule with excitation energy in the range 0.1 to 10 eV. Already we can obtain coherent radiation with sufficient intensity to excite a significant fraction of an atomic or molecular sample into chosen quantum states in the wavelength range 2000 A to 20 microns. Systematic studies of the effect of selective laser radiation on matter have been under way since around 1969 and 1970, when substantial progress in the art of quantum electronics made the experiments possible.
TL;DR: In this paper, the authors described a process in which a material would simultaneously absorb one photon and emit another, and the energies of the two photons differed by an amount corresponding to the energy difference between two quantum-mechanical levels of the medium.
Abstract: In 1928 Chandrasekhara Raman reported a process in which a material would simultaneously absorb one photon and emit another. The energies of the two photons differed by an amount corresponding to the energy difference between two quantum‐mechanical levels of the medium. Raman scattering, as the phenomenon came to be known, provided a tool for the spectroscopic investigation of energy levels not accessible by the usual absorption and emission techniques. For the first thirty‐five years Raman scattering was a laborious and exotic technique, important more for the quantum‐mechanical principles it illustrated than for its practical applications.
TL;DR: In this paper, the feasibility of microwave beaming of satellite-collected solar energy to earth for conversion to useful industrial power is evaluated for feasibility, with attention given to system efficiencies and costs, ecological impact, hardware to be employed, available options for energy conversion and transmission, and orbiting and assembly.
Abstract: Microwave beaming of satellite-collected solar energy to earth for conversion to useful industrial power is evaluated for feasibility, with attention given to system efficiencies and costs, ecological impact, hardware to be employed, available options for energy conversion and transmission, and orbiting and assembly. Advantages of such a power generation and conversion system are listed, plausible techniques for conversion of solar energy (thermionic, thermal electric, photovoltaic) and transmission to earth (lasers, arrays of mirrors, microwave beams) are compared. Structural fatigue likely to result from brief daily eclipses, 55% system efficiency at the present state of the art, present projections of system costs, and projected economic implications of the technology are assessed. Two-stage orbiting and assembly plans are described.
TL;DR: The life of every physicist is punctuated by events that lead him to discover that the way physicists see natural phenomena is different from the way nonphysicists see them.
Abstract: The life of every physicist is punctuated by events that lead him to discover that the way physicists see natural phenomena is different from the way nonphysicists see them. Certain patterns of reasoning appear to be more common among physicists than in other groups. These include:▸ focussing on the important variables (such as the force that accelerates the apple, rather than the lump it makes on your head);▸ propositional logic (“if heat were a liquid it would occupy space and a cannon barrel could only contain a limited amount of heat, but this is contrary to my observations, so…”), and▸ proportional reasoning (for example, the restoring force of a spring increases linearly with its displacement from equilibrium).
TL;DR: In this paper, the authors describe the characteristics of a gamma-ray detector, which consists of a piece of solid material in which electrons and holes are produced when a gamma ray is absorbed.
Abstract: Semiconductor gamma‐ray detectors consist essentially of a piece of solid material in which electrons and holes are produced when a gamma ray is absorbed. These electrons and holes are then collected by an electric field in the material to provide an electric signal that is a direct measure of the energy of the gamma ray. This simple statement implies detector‐material characteristics that are by no means easy to achieve, and much of this article will be concerned with these characteristics.
TL;DR: In this article, the authors describe the advantages of Silicon photodiodes, particularly those of the avalanche type, in terms of speed, efficiency, sensitivity and reliability for the systems now in development and future ones at longer wavelengths.
Abstract: Telecommunication with light waves today stands at the threshold of widespread use. Silicon photodiodes, particularly those of the avalanche type, offer speed, efficiency, sensitivity and reliability—both for the systems now in development and future ones at longer wavelengths.
TL;DR: In the field of electron microscopy, it has been shown that the resolution of 2.3 A, close to the interatomic distances in some solids, has been achieved as discussed by the authors.
Abstract: From its beginnings the field of electron microscopy has sought, as its ultimate aim, the ability to study the structure of matter by imaging the individual atoms that compose it. The resolution necessary to attain this goal is obtainable in principle, because the electron wavelengths of the beams normally used are less than 0.1 A, What has kept this goal from realization are practical difficulties in the design and construction of electron microscopes. These difficulties have now been overcome to the extent that resolutions of 2–3 A, close to the interatomic distances in some solids, have been achieved.
IBM1
TL;DR: In the early days, the early practitioners of nuclear magnetic resonance (NMR) probably never dreamed that their sophisticated coherence techniques would one day be adapted to the optical region.
Abstract: The early practitioners of nuclear magnetic resonance [1,2] probably never dreamed that their sophisticated coherence techniques would one day be adapted to the optical region. Coherent radiation sources were needed and in those days, the early 1950’s, lasers were not being discussed. We now know that the subject of coherent optical transients has developed steadily, beginning in 1964 with the initial photon echo measurement of Kurnit, Abella, and Hartmann [3]. Indeed, at the present time, the optical analogs of pulsed NMR transients have to some degree been realized.
TL;DR: Morse's life-long commitment to teaching, through his authorship of a series if standard-setting textbooks and through his personal guidance of unnumbered individual students, has extended this scope to include thermodynamics, statistical mechanics, and the methods of theoretical physics as well as discussed by the authors.
Abstract: Philip Morse has surely been one of the most versatile of American scientists of his generation, the first to be trained largely in his own country. A scientific generalist, he has made significant contributions to atomic physics, quantum mechanics, plasma physics, astrophysics, acoustics, machine computation, and operations research. His life-long commitment to teaching, through his authorship of a series if standard-setting textbooks and through his personal guidance of unnumbered individual students, has extended this scope to include thermodynamics, statistical mechanics, and the methods of theoretical physics as well.Moreover, as this autobiography relates at a fast-moving pace, Morse has also been involved in the high-pressure concerns of war research, scientific administration and consultation, policy formation, the education of key groups and wider publics beyond the classroom, and the real-world utilization of scientific techniques and discoveries.For all these accomplishments, Morse writes that his experience as a scientist and as a participant in the affairs of his time \"has been at the second, rather than at the top, level.\" It may be that this circumstance of being neat, rather than at, the top makes this autobiography more, rather than less, relevant to other and younger scientists, to those considering a life in science, and to general readers curious as to what such a life is really like. Only a miniscule few reach, say. Einsteinian levels, and their lives and work tend to be unique unto themselves; what Morse reports is truer to the experience of the great majority of the members of the scientific community. While his actual accomplishments, his range, and his eminence certainly far exceed those of a \"typical\" scientist, they do so more in degree than in kind.Morse's style is straightforward and nontechnical, direct, and personal. Some of the lighter moments and revealingly human incidents of his experience are recorded along with the problems and breakthroughs in the near-private world of pure science and the public worlds of policy, high-level consultation, and practical applications.
TL;DR: Superconductivity has contained the promise of important applications in energy generation, storage and distribution as well as in transportation as mentioned in this paper, however, the fulfillment of this promise was deferred for half a century; it is only since the mid 1960's that there has been much progress in applied superconductivity.
Abstract: Ever since its discovery by Kamerlingh Onnes in 1911, superconductivity has contained the promise of important applications. The ability of superconductors to carry current without resistance was expected to revolutionize the field of electrical engineering. The fulfillment of this promise, however, was deferred for half a century; it is only since the mid 1960's that there has been much progress in applied superconductivity. Superconductivity, with its ability to generate an intense, large‐volume magnetic field economically, can now offer alternatives in the fields of energy generation, storage and distribution as well as in transportation. Some prototype quasi‐commercial devices are already in use, and approximately 30 million dollars are being spent annually to develop this technology further.
TL;DR: In this paper, the authors show how the conventional Friedman models fare in the light of new developments, particularly the recognition of a whole new class of evolutionary corrections to the properties of distant galaxies.
Abstract: Is the Universe of infinite extent, or is it a finite system? Will it expand forever, or will it reach some maximum size before turning and collapsing upon itself like an inverse Big Bang? Just a few years ago, models of the conventional Friedman types were showing consistent, albeit tentative, evidence for an open, ever‐expanding Universe. Since then, further data and theory have inevitably conspired to blur the appealing simplicity of that picture. In this article I will show how the Friedman models fare in the light of new developments—particularly the recognition of a whole new class of evolutionary corrections to the properties of distant galaxies (see figure 1), and a proposed reinstatement of Einstein's disinherited cosmological constant. We shall see that the basic questions, posed above, are still unanswered.
TL;DR: Laser light can be generated in extremely short pulses as mentioned in this paper, which can operate at wavelengths at which intense conventional sources such as spectral lamps simply have not been available, and thus can enormously enhance the sensitivity and application range of classical spectroscopic methods.
Abstract: Lasers are rejuvenating, even revolutionizing, the field of spectroscopy of atoms and molecules. Compared with the light of conventional sources, laser light is more—sometimes dramatically more—powerful, directional, spectrally pure and coherent. Laser light can be generated in extremely short pulses. Furthermore, tunable lasers can operate at wavelengths at which intense conventional sources such as spectral lamps simply have not been available. Lasers thus can enormously enhance the sensitivity and application range of classical spectroscopic methods, such as absorption spectroscopy, fluorescence spectroscopy and Raman spectroscopy.