Showing papers in "Physics Today in 1991"
TL;DR: In this paper, the authors argue that without quantum physics we could not explain the behavior of solids, the structure and function of DNA, the color of the stars, the action of lasers or the properties of superfluids.
Abstract: Quantum mechanics works exceedingly well in all practical applications. No example of conflict between its predictions and experiment is known. Without quantum physics we could not explain the behavior of solids, the structure and function of DNA, the color of the stars, the action of lasers or the properties of superfluids. Yet well over half a century after its inception, the debate about the relation of quantum mechanics to the familiar physical world continues. How can a theory that can account ith precision for everything we can measure still be deemed lacking? The environment surrounding a quantum system can, in effect, monitor some of the system's observobles. As a result, the eigenstates of those observables continuously decohere and can behave like classical states.
2,040 citations
TL;DR: It was not hard to associate a logic gate with a degree of freedom, then to associate kT with that, and presume that this energy has to be dissipated at every step as discussed by the authors.
Abstract: Thermodynamics arose in the 19th century out of the attempt to understand the performance limits of steam engines in a way that would anticipate all further inventions. Claude Shannon, after World War II, analyzed the limits of the communications channel. It is no surprise, then, that shortly after the emergence of modern digital computing, similar questions appeared in that field. It was not hard to associate a logic gate with a degree of freedom, then to associate kT with that, and presume that this energy has to be dissipated at every step. Similarly, it seemed obvious to many that the uncertainty principle, ΔEΔt∼ℏ, could be used to calculate a required minimal energy involvement, and therefore energy loss, for very short Δt.
611 citations
TL;DR: In this paper, the authors present a model for lattice dynamics of a linear chain of three-dimensional (3D) crystal lattices with respect to an anharmonic elastic continuum.
Abstract: Elements of crystal symmetry: Direct lattice Reciprocal lattice Brillouin zone Crystal structure Point groups Space groups Symmetry of the Brillouin zone Jones zone Surface Brillouin zone Matrix representations of point groups. Lattice dynamics in harmonic approximation - semiclassical treatment: Introduction Lattice dynamics of a linear chain Lattice dynamics of three-dimensional crystals - phenomenological models Density of normal modes Numerical calculation of g(w) Lattice heat capacity. Lattice dynamics in the harmonic approximation - ab initio treatment: Introduction The frozen-phonon approach The linear response approach The planar force constant method. Anharmonicity: Introduction Hamiltonian of a general three-dimensional crystal Effect of anharmonicity on phonon states Effects of the selection rules on three-phonon processes Hamiltonian of an anharmonic elastic continuum Evaluation of three-phonon scattering strengths The quasi-harmonic approximation and Grueneisen's constant. Theory of lattice thermal conductivity: Introduction Relaxation-time methods Gree-Kubo linear response theory Second sound and Poiseuille flow of phonons. Phonon scattering in solids: Boundary scattering Scattering by static imperfections Phonon scattering in alloys Anharmonic scattering Phonon-electron scattering in doped semiconductors Phonon scattering due to magnetic impurities in semiconductors Phonon scattering from tunnelling states of impurities Phonon-photon interaction. Analysis of phonon relaxation and thermal conductivity results: Anharmonic decay of phonons Lattice thermal conductivity of undoped semiconductors and insulators Non-metallic crystals with high thermal conductivity Thermal conductivity of complex crystals Low-temperature thermal conductivity of doped semiconductors. Phonons in low dimensional solids: Introduction Surface vibrational modes Attenuation of surface phonons Phonons in superlattices Thermal conductivity of superlattices. Phonons in impure and mixed crystals: Introduction Localised vibrational modes in semiconductors Experimental studies of long-wavelength optical phonons in mixed crystals Theoretical models for long-wavelength optical phonons in mixed crystals Phonon conductivity of mixed crystals. Phonons in quasi-crystalline and amorphous solids: Introduction Phonons in quasi-crystals Structure and vibrational excitations of amorphous solids Vibrational properties of amorphous solids Low-temperature properties of amorphous solids. Phonon spectroscopy: Introduction Heat pulse technique Superconducting tunnel junction technique Optical techniques Phonons from Landau levels in 2DEG Phonon focusing and imaging Frequency crossing phonon spectroscopy Phonon echoes. Phonons in liquid helium: Introduction Dispersion curve and elementary excitations Specific heat Interactions between the excitations Kapitza resistance Quantum evaporation. Appendices: Density functional formalism The pseudopotential method Evaluation of integrals in sections 6.4.1.4 Negative-definitenss of the phonon off-diagonal operator ^D*L. References. Index.
534 citations
TL;DR: In this paper, it was shown that any alteration of electromagnetism, the fundamental interaction overning atomic, molecular and condensed matter physics, will lead to fundamentally new phenomena in all these areas.
Abstract: Since the beginning of scientific inquiry the nature of light has played a vital role in our understanding of the physical world. Physicists have marveled at the dual nature of light as both corpuscle and wave; we have harnessed the remarkable coherent properties of light through the use of lasers; and the quantum mechanics of the interaction of photons with matter continue to provide fascinating avenues of basic research. In essence, any alteration of electromagnetism, the fundamental interaction overning atomic, molecular and condensed matter physics, will lead to fundamentally new phenomena in all these areas.
420 citations
TL;DR: The St. Petersburg paradox as discussed by the authors was introduced by Nicolas Bernoulli, who introduced a seemingly innocent game, first published in 1713, that yielded a paradoxical result and became known as the St Petersburg paradox.
Abstract: An early theme in probability was calculating the fair ante for various games of chance. Nicolas Bernoulli introduced a seemingly innocent game, first published in 1713, that yielded a paradoxical result. The result has become known as the St. Petersburg paradox, because of an analysis written later by Daniel Bernoulli in the Commentary of the St. Petersburg Academy.
416 citations
TL;DR: The Making of the Natural Philosopher: 1. From the ashes of revolution 2. Clydeside 3. A Cambridge undergraduate 4. The changing tradition of natural philosophy 5. The Transformation of Classical Physics: 6. The language of mathematical physics 7. The kinematics of field theory and the nature of electricity 8. Thermodynamics: the years of uncertainty 10. The years of resolution 11. T & T' of treatise on natural philosophy 12. The hydrodynamics of matter 13. Rule, Britannia: the art of navigation 22. The magnetic compass
Abstract: List of illustrations Preface Footnote abbreviations Part I. The Making of the Natural Philosopher: 1. From the ashes of revolution 2. Clydeside 3. A Cambridge undergraduate 4. The changing tradition of natural philosophy 5. Professor William Thomson Part II. The Transformation of Classical Physics: 6. The language of mathematical physics 7. The kinematics of field theory and the nature of electricity 8. The dynamics of field theory: work, ponderomotive force, and extremum conditions 9. Thermodynamics: the years of uncertainty 10. Thermodynamics: the years of resolution 11. T & T' of treatise on natural philosophy 12. The hydrodynamics of matter 13. Telegraph signals and light waves Thomson versus Maxwell Part III. The Economy of Nature: The Economy of Nature: The Great Storehouse of Creation: 14. The irreversible cosmos 15. The age of the sun controversies 16. The secular cooling of the earth 17. The age of the earth controversies 18. The habitation of earth Part IV. Energy, Economy, and Empire: The Relief of Man's Estate: 19. The telegraphic art 20. Measurement and marketing: the economics of electricity 21. Rule, Britannia: the art of navigation 22. The magnetic compass 23. Baron Kelvin of Largs Bibliography Index.
305 citations
270 citations
TL;DR: The most compelling student critique of traditional introductory physics and chemistry courses comes from college graduates in the humanities who were engaged by Sheila Tobias to take introductory science for credit as discussed by the authors, who paint a devastating portrait of introductory courses as uninteresting, time consuming, narrowly fixated on the procedures of textbook problem solving, devoid of peer cooperation, lacking in student involvement during lectures, crammed with too much material, and biased away from conceptual understanding.
Abstract: Every fall several hundred thousand students enroll in calculus‐based “engineering” physics courses throughout the United States. Informal statistics tell us that over half of them will fail to complete the sequence of introductory courses. These students complain that physics is hard and boring. The most compelling student critique of traditional introductory physics and chemistry courses comes from college graduates in the humanities who were engaged by Sheila Tobias to take introductory science for credit. These students paint a devastating portrait of introductory courses as uninteresting, time consuming, narrowly fixated on the procedures of textbook problem solving, devoid of peer cooperation, lacking in student involvement during lectures, crammed with too much material, and biased away from conceptual understanding.
239 citations
TL;DR: In this paper, the authors focus on a few topics that are widely perceived to hold the key to understanding these fascinating compounds, such as high-temperature superconductors and their properties.
Abstract: Four years of intensive research following J. Georg Bednorz and K. Alex Muller's discovery of high‐temperature superconductors has produced about 18 000 publications. An overview of all physical properties is thus beyond the scope of this article, so I will focus on a few topics that are widely perceived to hold the key to understanding these fascinating compounds.
TL;DR: In this paper, the structure of high-Tc copper oxides has been studied and the properties of the oxide superconductors have been investigated. But the present understanding of the properties depends heavily on a knowledge of their structures.
Abstract: Few superconducting materials have presented us with the structural elegance and complexity displayed by the recently discovered high‐Tc copper oxides. The structures of these materials, consisting of metal‐oxygen layers stacked in a variety of sequences, with the metal atoms often in unusual coordinations, are interesting in their own right. More importantly, our present understanding of the properties of the oxide superconductors depends heavily on a knowledge of their structures.
TL;DR: In this paper, a collection of essays by the authors and other people that deal with scientific opinions that led Einstein and his contemporaries to their views of general relativity is presented, which explores the passage from the special theory through a sequence of gravitational theories to the discovery of the field equations of the grand theory in November 1915.
Abstract: This book is a collection of essays by the authors and other people that deal with scientific opinions that led Einstein and his contemporaries to their views of general relativity. Some of the essays explore Einstein's passage from the special theory through a sequence of gravitational theories to the discovery of the field equations of the grand theory in November 1915. Two other essays discuss Einstein's public and private exchanges with Max Abraham and Tullio Levi-Civita in 1913 and 1914. A sympathetic picture of H.A. Lorentz's reaction to the general theory of relativity is included, and a careful and insightful essay on the early understanding of the Schwarzschild-Droste solution to the field equations of general relativity is presented. One paper presents a discussion on the state of the enterprise of general relativity between 1925 and 1928, and a short essay details the history of steps toward quantum gravitational through canonical quantization. A discussion of the history of derivations of the geodesic equation of motion from the field equation and conservation laws of the general theory is presented. The early history of geometrical unified field theories is included.
TL;DR: The Taylor-Couette flow as mentioned in this paper is a well-known example of the cellular motion that develops with rotation and was discovered and described mathematically by Geoffrey I. Taylor in 1923.
Abstract: The striking flow shown in figure 1 is produced in a simple apparatus: A fluid is confined between two concentric cylinders, with the inner and perhaps the outer cylinder able to rotate. The cellular motion that develops with rotation was discovered and described mathematically by Geoffrey I. Taylor in 1923. A similar apparatus, with the inner cylinder suspended from a torsion fiber and the outer cylinder rotating, was used even earlier as a viscometer. Maurice Couette described this arrangement in his thesis, which he presented in Paris in 1890. For this reason, modern investigators refer to flow between rotating cylinders as Taylor‐Couette flow. In this article I trace the beginnings of the subject back to Isaac Newton and, by discussing the contributions of Newton, George Stokes, Max Margules, Arnulph Mallock, Couette, Taylor, S. Chandrasekhar and others, show how the study of this flow evolved to its place of prominence today.
TL;DR: Biological polymers have a preferred chirality ond can replicate themselves, and physical arguments provide insight into which of these unique and apparently related properties evolved first, and by what mechanism.
Abstract: Biological polymers have a preferred chirality ond can replicate themselves. Physical arguments provide insight into which of these unique and apparently related properties evolved first, and by what mechanism.
TL;DR: The consensus is that there is absolutely no consensus on the theory of high-Tc superconductivity as mentioned in this paper, and this is true even in the scientific Tower of Babel, where one can find groups working with some level of conviction on almost every hypothesis, and there are groups from very diverse backgrounds (such as quantum chemistry, electronic structure and many-body physics) working on the problem.
Abstract: Anderson: The consensus is that there is absolutely no consensus on the theory of high‐Tc superconductivity. I suppose that, in a way, this is true. One can find groups working with some level of conviction on almost every hypothesis, and there are groups from very diverse backgrounds (such as quantum chemistry, electronic structure and many‐body physics) working on the problem, groups that have very little meaningful communication with each other. Looked at relative to this scientific Tower of Babel, I suspect you and I are practically speaking the same language. Would you agree?
TL;DR: Bubbles appear to rise from certain spots on the surface of the glass and rapidly grow in size as they ascend, the volume of each bubble often doubling or more by the time it reaches the top of a glass.
Abstract: Pour yourself a glass of beer and look closely at the rising bubbles. Careful examination shows that they are seldom distributed uniformly throughout the liquid. Instead, streams of bubbles appear to rise from certain spots on the surface of the glass. Closer inspection reveals that the bubbles rapidly grow in size as they ascend, the volume of each bubble often doubling or more by the time it reaches the top of the glass. In addition, the speed of the bubbles increases as they travel upward.
TL;DR: In this model, students are exposed to content through lectures, presentations and readings, and are expected to absorb the transmitted knowledge in ready-to-use form as discussed by the authors, which is not a model of learning per se, but it does make a pivotal assumption about learning.
Abstract: Two main instructional practices are found in American education: One is prevalent, while the other is emerging. We have all experienced the prevalent practice, which results from the so‐called transmission model of instruction. In this model, students are exposed to content through lectures, presentations and readings, and are expected to absorb the transmitted knowledge in ready‐to‐use form. Although it is not a model of learning per se, the transmission model does make a pivotal assumption about learning, namely that the message the student receives is the message the teacher intended. Within this model, students' difficulties in grasping a concept are interpreted as indications that the presentation was not clear or forceful enough to be understood (that is, the signal being transmitted was either weak or garbled). Thus many users of the transmission model believe that if they make the presentation more lucid or persistent—for example, by transmitting at a slower speed or in a louder voice—students wi...
TL;DR: In this article, an account of physical processes governing the formation of stratospheric particles is given in order to dramatize the interactions between polar stratosphere clouds and the Antarctic ozone-destruction mechanism, and the successive stages of particle nucleation, condensation/evaporation and sedimentation/coagulation phenomena are observed.
Abstract: An account is given of physical processes governing the formation of stratospheric particles, in order to dramatize the interactions between polar stratospheric clouds and the Antarctic ozone-destruction mechanism. Attention is given to the successive stages of particle nucleation, condensation/evaporation and sedimentation/coagulation phenomena, and the ways in which polar stratospheric clouds are observed. Considerable evidence exists that polar stratospheric cloud particles are composed of nitric acid. The relatively small Arctic ozone hole depletion is due to the much smaller duration of Arctic stratospheric clouds.
TL;DR: Close as discussed by the authors reveals the true story of the cold fusion controversy, a story ignored until now in spite of the glare of publicity surrounding Martin Fleischmann and Stanley Pons, who held an astonishing press conference, maintaining that they had succeeded, working in secret, in harnessing atomic fusion.
Abstract: Frank Close, a leading physicist and talented popular science writer, reveals the true story of the cold fusion controversy--a story ignored until now in spite of the glare of publicity surrounding Martin Fleischmann and Stanley Pons. On March 23, 1989, these two Utah scientists held an astonishing press conference, maintaining that they had succeeded, working in secret, in harnessing atomic fusion. What was the basis for their claims to have achieved cold fusion in a test tube in a basement laboratory, while other scientists--using magnets as big as houses and temperatures hotter than those in the center of the sun--were failing to produce as much power as they were using? Why did Fleischmann and Pons proclaim their "discovery" at a news conference, when first announcements of scientific results are almost always made within the scientific community? Why did the full-blown media event inspired by their initial report cause governments to reorient their research programs in hopes of cornering the "new technology"? And why did some scientists recklessly abandon their traditional painstaking methods in haste to be first to prove or discredit the experiment? Acquainted at first hand with investigations of cold fusion on two continents, Close is uniquely qualified to probe the motivations behind Fleischmann's and Pons's startling assertions and to explore the intellectual and political turmoil that surrounded the cold fusion debate. Originally published in 1991. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.
TL;DR: In this paper, the relationship between instabilities and the mechanism of high-temperature superconductivity was investigated and the key to the synthesis of superconductors with even higher critical temperatures.
Abstract: From the discovery of oxide superconductors in 1964, there were frequent indications that these materials are metastable. This lack of thermodynamic stability has now become one of the predominant issues in the synthesis of the high‐temperature superconductors. Once prepared, metastable superconductors possess sufficient kinetic stability that we generally need have no concern that they will decompose into more stable phases that are not superconducting. Nonetheless, our understanding of the issues relating to the stability of the known superconductors greatly influences our approaches to synthesizing them. Furthermore, understanding the relationship between instabilities and the mechanism of high‐Tc superconductivity could be the key to the synthesis of superconductors with even higher critical temperatures.
TL;DR: The discovery of a 92 K superconductor in early 1987 by M. K. Wu, Paul Chu and their coworkers at the Universities of Alabama and Houston produced widespread euphoria as discussed by the authors.
Abstract: The discovery of a 92 K superconductor in early 1987 by M. K. Wu, Paul Chu and their coworkers at the Universities of Alabama and Houston produced widespread euphoria. Newspapers and magazines of every conceivable political and social persuasion speculated on the applications of superconductivity. Some even foretold a new age; after the stone, bronze, iron, steel and semiconductor ages would come the superconductor age. Most of the applications envisaged for this new age depended on the generation of strong magnetic fields, frequently in large volumes. Thus the vanishing of resistance in the superconducting state was the key property for these applications, and it is this ability to carry very large current densities without ohmic loss that forms the essential thread of this article.
TL;DR: In this paper, the authors describe how ideas about the unification of the strong, weak and electromagnetic interactions lead to concrete, quantitative predictions about the relative strengths of these interactions, and how these predictions can be used to understand the physical world.
Abstract: Ambitious attempts to obtain a unified description of all the interactions of nature have so far been more notable for their ingenuity, beauty and chutzpah than for any help they have afforded toward understanding concrete facts about the physical world. In this article we wish to describe one shining exception: how ideas about the unification of the strong, weak and electromagnetic interactions lead to concrete, quantitative predictions about the relative strengths of these interactions.
TL;DR: A worldwide effort to develop high-temperature superconductor thin films and electronic devices began within weeks of the initial discovery in early 1987 of superconductivity above liquid-nitrogen temperature.
Abstract: A worldwide effort to develop high‐temperature‐superconductor thin films and electronic devices began within weeks of the initial discovery in early 1987 of superconductivity above liquid‐nitrogen temperature The ensuing period has seen remarkable progress, spurred by innovations in deposition technology, materials characterization and device design Prospects for practical electronic applications of superconductivity have driven the development of high‐temperature‐superconductor thin‐film technology at an unprecedented pace After five years researchers in the field have surmounted many of the initial hurdles in developing the new materials, and they are now working toward the first practical implementations of high‐temperature‐superconductor electronic technology
TL;DR: In this paper, it has been shown that the best mountaintop observatory sites occasionally deliver images as sharp as 0.3 arcsecond, an image quality that many existing telescopes cannot maintain.
Abstract: We are in a period of rapid improvement in the capability of telescopes. Great strides are being taken to improve angular resolution, to increase sensitivity at all wavelengths and to make the most efficient use of wide‐field images. The technical challenges involved in such development are great, for not only do we need mirror surfaces much larger than what we have used before, but we require higher image quality. It has recently become clear that the best mountaintop observatory sites occasionally deliver images as sharp as 0.3 arcsecond, an image quality that many existing telescopes cannot maintain.
TL;DR: The Ebert spectrometer, named for its inventor, the 19th-century German spectroscopist Hermann Ebert, emerged from obscurity after the Second World War to play a significant role in the exploration of the solar system as mentioned in this paper.
Abstract: The Ebert spectrometer, named for its inventor, the 19th‐century German spectroscopist Hermann Ebert, emerged from obscurity after the Second World War to play a significant role in the exploration of the solar system. I had a part in its resurrection, and the Ebert spectrometer has played a dominant role in my scientific career. Therefore I've taken the trouble to look into its history. The evolution of this instrument, now a century old, was curiously haphazard and fraught with mistakes. I have attempted here to put these events into chronological, and somewhat autobiographical, perspective.
TL;DR: A special celebratory session will become an annual custom at large conferences to take time out to survey both the diversity and unity of physics in a common meeting that is undiluted by the multiplicity of parallel sessions that have become the hallmark of our gatherings as mentioned in this paper.
Abstract: I hope that this special celebratory session will become an annual custom at our large conferences—to take time out to survey both the diversity and unity of physics in a common meeting that is undiluted by the multiplicity of parallel sessions that have become the hallmark of our gatherings. Our research endeavors span a wide spectrum of physics, but at the core of every effort is a common creed: to push to the frontiers our understanding of natural phenomena, by measurement and theoretical analysis. In this article, in addition to giving the retiring president's report, I want to address the idea of whether one can identify sources of unity in the science of physics. My remarks may complement those of one of my predecessors and colleagues, Robert R. Wilson, in his 1985 retiring presidential address, “The Sentiment of the Unity of Physics” (PHYSICS TODAY, July 1986, page 26).