Showing papers in "Physics Today in 1984"
TL;DR: In this article, the authors present a statistical model of quantum theory, including symmetry groups in quantum mechanics, and unbiased measurement and optimality of Gaussian states, and supplement - Statistical Structure of Quantum Theory and Hidden Variables.
Abstract: Foreword to 2nd English edition.- Foreword to 2nd Russian edition.- Preface.- Chapters: I. Statistical Models.- II. Mathematics of Quantum Theory.- III. Symmetry Groups in Quantum Mechanics.- IV. Covariant Measurements and Optimality.- V. Gaussian States.- VI Unbiased Measurements.- Supplement - Statistical Structure of Quantum Theory and Hidden Variables.- References.
2,281 citations
999 citations
TL;DR: The authors found that similar difficulties occur among students of different ages and ability, often in spite of formal study in physics, and the persistence of these difficulties suggests that they are not easily overcome, and need to be addressed explicitly during instruction.
Abstract: Over the past decade, physicists, psychologists and science educators have been conducting research that has yielded detailed information about how students learn physics. Some investigators have used physics as a context for examining cognitive processes and approaches to problem‐solving. For others, the primary emphasis has been on conceptual understanding in a particular area of physics such as mechanics, electricity, heat or optics. Regardless of the motivation behind the research, the results indicate that similar difficulties occur among students of different ages and ability, often in spite of formal study in physics. The persistence of these difficulties suggests that they are not easily overcome, and need to be addressed explicitly during instruction.
616 citations
TL;DR: The first attempt to use physical theory to study the functioning of machines was undertaken by the French engineer Sadi Carnot as discussed by the authors, who undertook a systematic study of the physical processes governing steam engines, resulting in his remarkable paper Reflexions sur la puissance motrice du feu (On the Motive Power of Heat) published in 1826.
Abstract: Until the 19th century, technology was essentially the domain of skilled artisans and constructors who relied on practical experience to design and build their machines. One of the first efforts to use physical theory to study the functioning of machines was undertaken by the French engineer Sadi Carnot. Motivated by the concern of the French about the superiority of British steam engines, he undertook a systematic study of the physical processes governing steam engines, resulting in his remarkable paper Reflexions sur la puissance motrice du feu (On the Motive Power of Heat) published in 1826. Among the earliest successes of this new science, thermodynamics, was the formulation of criteria describing how well real processes perform in comparison with an ideal model. Carnot showed that any engine, using heat from a hot reservoir at temperature Th to do work, has to transfer some heat to a reservoir at lower temperature T1, and that no engine could convert into work more of the heat taken in at Th than the...
406 citations
TL;DR: In this article, the authors present a detailed review of materials behavior and property measurement for design and material selection at low temperatures, including temperature, strain, and magnetic fields measurements, and a detailed subject index is included.
Abstract: The aim of this volume is to establish a firm basis for the understanding of materials behavior and property measurement to use for design and materials selection at low temperatures. The fourteen chapters of this book were written and edited by members of the materials group of the Cryogenics Division of the National Bureau of Standards. Each chapter concludes with a lengthy list of references with the full bibliographic citations. A detailed subject index is included. Contents abridged: Elastic properties. Electrical properties. Magnetic properties. Fracture mechanics. Martensitic phase transformation. Composites. Temperature, strain, and magnetic fields measurements.
292 citations
TL;DR: In this article, a simple Lorentz transformation is used to measure the velocity and acceleration of an object in a four-dimensional space, and then the transformation is applied to the velocity of the object in the four dimensions of the space.
Abstract: 1. Kinematics in Inertial Axes.- 1.1 The "Aether" in the Nineteenth Century.- 1.2 Some Experimental Evidence.- 1.3 Einstein's Relativity Postulates.- 1.4 Time and Length Standards. Synchronization.- 1.5 The "Simple" Lorentz Transformation.- 1.6 More General Lorentz Transformations.- 1.7 Time Dilatation and Proper Time.- 1.8 Length Measurements.- 1.9 Volume and Surface Elements.- 1.10 Visual Perception of Objects in Motion.- 1.11 Transformation of Velocities and Accelerations.- 1.12 Four-Vectors.- 1.13 Kinematics in Four Dimensions.- Problems.- 2. Dynamics in Inertial Axes.- 2.1 Equation of Motion of a Point Mass.- 2.2 Mass and Energy.- 2.3 A Few Simple Trajectories.- 2.4 Transformation Equations for Force, Energy, and Momentum.- 2.5 Four-Dimensional Dynamics.- 2.6 Systems of Points.- 2.7 Elastic Collisions.- 2.8 Motion of a Point with Variable Rest Mass.- 2.9 Rocket Acceleration.- 2.10 Inelastic Collisions.- 2.11 Incoherent Matter.- 2.12 The Kinetic Energy-Momentum Tensor.- 2.13 The Total Energy-Momentum Tensor.- Problems.- 3. Vacuum Electrodynamics in Inertial Axes.- 3.1 Transformation Formulas for the Sources.- 3.2 Transformation Equations for the Fields.- 3.3 Force on a Charged Particle.- 3.4 Four-Currents.- 3.5 The Electromagnetic Tensors.- 3.6 Potentials.- 3.7 Transformation of a Plane Wave: The Doppler Effect.- 3.8 The Lienard-Wiechert Fields.- 3.9 Fields of a Charge in Uniform Motion.- 3.10 Fields of a Static Dipole in Uniform Motion.- 3.11 Radiation from an Antenna in Uniform Motion.- 3.12 Radiation from a Moving Oscillation Dipole.- 3.13 Doppler Spectrum from a Moving Source.- Problems.- 4. Fields in Media in Uniform Translation.- 4.1 Polarization Densities.- 4.2 Constitutive Equations.- 4.3 Some Useful Forms of Maxwell's Equations.- 4.4 Point Charge Moving Uniformly in a Dielectric Medium.- 4.5 The Cerenkov Effect.- 4.6 Waves in a Moving Dielectric. The Fresnel Dragging Coefficient.- 4.7 Green's Dyadic for a Moving Dielectric.- 4.8 Electric Dipole Radiating in a Moving Dielectric.- Problems.- 5. Boundary-Value Problems for Media in Uniform Translation.- 5.1 Boundary Conditions.- 5.2 Dielectric Slab Moving in Time-Independent Fields.- 5.3 The Wilsons' Experiment.- 5.4 Sliding Contacts. A Simple Problem.- 5.5 Material Bodies Moving at Low Velocities.- 5.6 Conductors Moving in a Pre-Existing Static Magnetic Field.- 5.7 Circuit Equations.- 5.8 Motional E.M.F..- 5.9 Normal Incidence of a Time-Harmonic Plane Wave on a Moving Mirror.- 5.10 Arbitrary Time-Dependence of the Incident Plane Wave.- 5.11 Oblique Incidence of a Time-Harmonic Plane Wave on a Moving Mirror.- 5.12 A Time-Harmonic Plane Wave Incident on a Dielectric Medium.- 5.13 Reflection of a Plane Wave on a Moving Medium of Finite Conductivity.- 5.14 Revisiting the Boundary Conditions at a Moving Interface.- 5.15 Scattering by a Cylinder Moving Longitudinally.- 5.16 Scattering by a Cylinder Moving Transversely.- 5.17 Three-Dimensional Scattering by Moving Bodies.- 5.18 The Quasistationary Method.- Problems.- 6. Electromagnetic Forces and Energy.- 6.1 Surface and Volume Forces in Vacuum.- 6.2 Maxwell's Stress Tensor.- 6.3 A Few Simple Force Calculations.- 6.4 Radiation Pressure on a Moving Mirror.- 6.5 Radiation Force on a Dielectric Cylinder.- 6.6 Static Electric Force on a Dielectric Body.- 6.7 Magnetic Levitation.- 6.8 Levitation on a Line Current.- 6.9 Electromagnetic Energy in an Inertial System.- 6.10 Four-Dimensional Formulation in Vacuum.- 6.11 The Electromagnetic Energy-Momentum Tensor in Material Media.- Problems.- 7. Accelerated Systems of Reference.- 7.1 Coordinate Transformations.- 7.2 The Metric Tensor.- 7.3 Examples of Transformations.- 7.4 Coordinates and Measurements.- 7.5 Time and Length.- 7.6 Four-Vectors and Tensors.- 7.7 Three-Vectors.- 7.8 Velocities and Volume Densities.- 7.9 Covariant Derivative.- Problems.- 8. Gravitation.- 8.1 Inertial and Gravitational Masses.- 8.2 The Principle of Equivalence.- 8.3 Curvature.- 8.4 Einstein's Equations.- 8.5 The Small-Field Approximation.- 8.6 Gravitational Frequency Shift.- 8.7 Time Measurement Problems.- 8.8 Some Important Solutions of Einstein's Equations.- 8.9 Point Dynamics.- 8.10 Motion in the Schwarzschild Metric.- 8.11 Motion of a Photon in the Schwarzschild Metric.- 8.12 Strongly Concentrated Masses.- 8.13 Static Cosmological Metrics.- 8.14 Nonstatic Cosmological Metrics.- 8.15 Recent Cosmological Observations.- Problems.- 9. Maxwell's Equations in a Gravitational Field.- 9.1 Field Tensors and Maxwell's Equations.- 9.2 Maxwell's Equations in Rotating Coordinates.- 9.3 Transformation Equations for Fields and Sources.- 9.4 Constitutive Equations in Vacuum.- 9.5 Constitutive Equations in a Time-Orthogonal Metric.- 9.6 Constitutive Equations in Material Media.- 9.7 The Co-Moving Frame Assumption.- 9.8 Boundary Conditions.- Problems.- 10. Electromagnetism of Accelerated Bodies.- 10.1 Conducting Body of Revolution Rotating in a Static Magnetic Field.- 10.2 Conducting Sphere Rotating in a Uniform Magnetic Field.- 10.3 Motional E.M.F.- 10.4 Generators with Contact Electrodes.- 10.5 Dielectric Body of Revolution Rotating in a Static Field.- 10.6 Rotating Permanent Magnets.- 10.7 Scattering by a Rotating Circular Dielectric Cylinder.- 10.8 Scattering by a Rotating Circular Conducting Cylinder.- 10.9 Scattering by a Rotating Dielectric Body of Revolution.- 10.10 Scattering by a Rotating Sphere.- 10.11 Reflection from a Mirror in Arbitrary Linear Motion.- 10.12 Reflection from an Oscillating Mirror, at Normal Incidence.- 10.13 Reflection from an Oscillating Mirror, at Oblique Incidence.- 10.14 Scattering by Other Moving Surfaces.- Problems.- 11. Field Problems in a Gravitational Field.- 11.1 Fields Associated with Rotating Charges.- 11.2 Schiff's Paradox.- 11.3 Kennard's Experiment.- 11.4 Optical Rotation Sensors.- 11.5 Scattering by a Rotating Body of Arbitrary Shape.- 11.6 Transformation of an Incident Wave to Rotating Coordinates.- 11.7 Scattered Field in Rotating Coordinates.- 11.8 Two Examples.- 11.9 Low Frequency Scattering by Rotating Cylinders.- 11.10 Quasistationary and Relativistic Fields.- 11.11 Axes in Hyperbolic Motion.- 11.12 The Induction Law.- 11.13 Maxwell's Equations in a Schwarzschild Metric.- 11.14 Light Deflection in a Gravitational Field.- Problems.- Appendix A. Complements of Kinematics and Dynamics.- A.1 Transformation Matrix for the "Parallel" Transformation.- A.2 Transformation with Rotation.- A.3 Transformation of Velocities.- A.4 Relationship Between Force and Acceleration.- A.5 Equations of Motion in Cylindrical Coordinates (r,?,z).- A.6 Equations of Motion in Spherical Coordinates (R,?,?).- Appendix B. Dyadics.- B.1 The Dyadic Notation.- B.2 Operators on Dyadics.- B.3 Green's Dyadic.- Appendix C. Basis Vectors.- Appendix D. Moving Open Circuits.- List of Symbols.- Some Useful Numerical Constants.- References.
161 citations
TL;DR: In economics, the laws of thermodynamics have been used to constrain economic processes to those that reduce available work, increasing the entropy of the universe as discussed by the authors. And the second law of the increase of entropy has been shown to be a constraint on economic processes.
Abstract: While physical sciences deal with the interactions of matter and energy, economics can be said to deal with the production and exchange of goods and services. Because goods and services incorporate matter and energy, the physical sciences are clearly relevant to economics. In particular, one can expect the laws of thermodynamics to impose constraints on economic processes as they do on physical processes (figure 1). It is clear that the laws of conservation—of matter and energy, for example—have implications for the use of resources and for the generation and treatment of wastes. The law of the increase of entropy—the second law of thermodynamics—constrains economic processes to those that reduce available work, increasing the entropy of the Universe.
114 citations
TL;DR: Metallurgists are now able to take any element in the periodic table and implant it in the surface region of virtually any metal as discussed by the authors, although the resulting novel metastable alloys are usually only a fraction of a micron thick, they have potentially important commercial applications and contribute greatly to fundamental research on metals.
Abstract: Metallurgists are now able to take any element in the periodic table and implant it in the surface region of virtually any metal. Although the resulting novel metastable alloys are usually only a fraction of a micron thick, they have potentially important commercial applications and are contributing greatly to fundamental research on metals.
109 citations
TL;DR: The authors are on the verge of a revolution in computing, spawned by advances in computer technology that will make it practical to build very‐high‐performance computers, or “supercomputers,” consisting of very many small computers combined to form a single concurrent processor.
Abstract: We are on the verge of a revolution in computing, spawned by advances in computer technology. Progress in very‐large‐scale integration is leading not so much to faster computers, but to much less expensive and much smaller computers—computers contained on a few chips. These machines, whose cost‐effectiveness is expected to be staggering, will make it practical to build very‐high‐performance computers, or “supercomputers,” consisting of very many small computers combined to form a single concurrent processor.
TL;DR: This paper showed that the water level drops because the close packing of the marbles is disrupted as layers of marbles slide over each other during the twisting motion; as a result, creating space for the water to fill.
Abstract: Almost a hundred years ago, Osborne Reynolds carried out a simple experiment. He filled a leather bag with marbles, topped it with water and then twisted it, thereby inducing a shear. The water level drops because the close packing of the marbles is disrupted as layers of marbles slide over each other during the twisting motion; as a result the marbles are further apart on average, creating space that the water has to fill.
TL;DR: There has been a spectacular resurgence of interest in the soft x-ray and extreme ultraviolet regions of the electromagnetic spectrum in the past few years as mentioned in this paper, and this is due to the development of new xray optical devices that have given us an xray view of the universe on scales ranging from the microscopic to the astronomical.
Abstract: There has been a spectacular resurgence of interest in the soft x‐ray and extreme ultraviolet regions of the electromagnetic spectrum in the past few years. In part, this is due to the development of new x‐ray optical devices that have given us an x‐ray view of the universe on scales ranging from the microscopic to the astronomical (see figure 1).
TL;DR: In this paper, the authors give special attention to the notion that the quantum frequency spectrum of a periodic system reduces to the classical spectrum in this limit and show that the classical result is not always recovered in the limit of large quantum numbers.
Abstract: The correspondence principle addresses the connection between classical and quantum physics. The simple statement that quantum mechanics reduces to classical mechanics in the limit where the principal quantum number n approaches infinity, while found in many textbooks, is not true in general. In this article we will give special attention to the notion that the quantum frequency spectrum of a periodic system reduces to the classical spectrum in this limit. Two simple counter‐examples—a particle in a cubical box, and a rigid rotator—will show us that the classical result is not always recovered in the limit of large quantum numbers. The usual textbook formulation of Bohr's frequency correspondence principle does not apply to all periodic systems, and the limits n→∞ and h→0 are not universally equivalent.
TL;DR: In this paper, the authors discuss a very powerful technique that surface scientists are using in this research: stimulated desorption, the removal of atoms and molecules from surfaces by low-energy ionizing radiation.
Abstract: After spending years wondering how the surface bond is formed, we are now wondering just as hard how it can be broken Investigation of the latter problem—possibly the more challenging of the two—is leading to new insight into chemical bonding and the dynamical processes important in chemical kinetics In this article I discuss a very powerful technique that surface scientists are using in this research: stimulated desorption, the removal of atoms and molecules from surfaces by low‐energy ionizing radiation Concepts from the field of stimulated desorption are already finding their way into other areas For example, we find that we can offer new insight into the problem of beam damage in electron microscopy and that we can contribute to the very important technological area of plasma processing of surfaces Insights into chemistry and into the general problem of radiation‐induced damage could affect our thinking in areas ranging from radiation treatment in medicine to the interaction of radiation with mat
TL;DR: In this paper, the basic structure of intercalation compounds is described, where the atoms in each layer of the guest material are in registry with those in the neighboring layers of the host material.
Abstract: For the past decade, materials research has focused on synthesizing new materials and generating new structural arrangements that exhibit specific desired properties. Some of the greatest advances in this area have come out of work on intercalation compounds, which are formed by the insertion of atomic or molecular layers of a guest chemical species—an intercalant—between layers in a host material. Figure 1 illustrates the basic structure of intercalation compounds. Part a of the figure depicts graphite intercalated with lithium; this structure is described as “commensurate,” because the atoms in each layer of guest material are in registry with those in the neighboring layers of the host material. Part b of the figure shows the incommensurate nature of graphite intercalated with ferric chloride. Although graphite intercalation compounds have been synthesized for over 150 years, it is only very recently that methods have been perfected to the point that one can prepare materials with specific structures a...
TL;DR: In 1687, Isaac Newton wrote a simple equation defining the viscosity of a fluid as the coefficient of proportionality between the shear stress and the velocity gradient.
Abstract: Fluid dynamics is an old subject. In 1687, Isaac Newton wrote a simple equation defining the viscosity of a fluid as the coefficient of proportionality between the shear stress and the velocity gradient. Newton's equation does well at describing gases and liquids made up of “light” molecules—those of molecular weight less than about 1000. By the middle of the last century the mathematical description of the flow of such “Newtonian” fluids was well established. This description is based on use of the laws of conservation of mass and momentum.
TL;DR: The photonics revolution as mentioned in this paper uses beams of laser light for information transmission, which can be traced to a unique combination of basic conceptual advances, the perfection of new materials and the development of new device principles.
Abstract: The great advances in solid‐state electronics can be traced to a unique combination of basic conceptual advances, the perfection of new materials and the development of new device principles. Ever since the invention of the transistor at Bell Laboratories almost forty years ago, we have witnessed a spectacular growth in silicon technology, leading to increasingly higher densities of devices and more complex functions. Almost as revolutionary as the invention of the transistor in 1947 was the invention of the laser a decade later. Thus, nearly concurrent with the electronics revolution, we have seen another technological revolution, the so‐called photonics revolution: using beams of laser light for information transmission. The lasers that provide light for today's lightwave communication systems are made not from silicon but from compound semiconductors. These are generally compounds of elements from group III of the periodic table, such as Ga, Al and In, along with elements from group V, most notably As,...
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TL;DR: The Division of High Polymer Physics of the American Physical Society (APS) was founded in 1944, spurred in large measure by the development of synthetic rubber during the Second World War as mentioned in this paper.
Abstract: The Division of High Polymer Physics of the American Physical Society was founded in 1944, spurred in large measure by the development of synthetic rubber during the Second World War. With the enormous postwar growth of the synthetic polymer industry, the field of polymer physics burgeoned—and along with it, the Division of High Polymer Physics. At the time of the March 1984 APS meeting, the division was an active, thriving community of 1001 members with a variety of scientific interests and activities. In this article, we will attempt to give the flavor of their work. We hope our account is sufficiently specific to be useful and interesting to polymer scientists, yet general enough to be intelligible and interesting to the general reader.
TL;DR: In this paper, a powerful new device joined the arsenal of modulated radiation sources available to scientists attacking problems that require good temporal resolution, called the high energy storage ring (HERS).
Abstract: Many important biological, chemical and physical phenomena take place on time scales of nanoseconds or picoseconds. Those working to unravel the time development of such fast processes have long recognized that pulsed electromagnetic radiation and particle beams often make more incisive probes than do continuous emissions. During the last decade, a powerful new device joined the arsenal of modulated radiation sources available to scientists attacking problems that require good temporal resolution—the high‐energy storage ring.
TL;DR: The mechanisms of switching, storage and communication close enough to fundamental physical limits to bring into awareness for the first time limitations in the engineering of high‐performance systems.
Abstract: Although the title of our article addresses engineering limits, we do not mean to convey a grim outlook. Over the past 20 years, the technology of computer systems has advanced dramatically in terms of performance, cost and reliability. There is every reason to expect this advance to continue, at a rate almost as shocking as we have experienced to date. However, the advance already achieved has pushed the mechanisms of switching, storage and communication close enough to fundamental physical limits to bring into awareness for the first time limitations in the engineering of high‐performance systems.
TL;DR: The timeprojection chamber has proven so useful as a particle detector that some are calling it the "bubble chamber" of the 1980s and 1990s as discussed by the authors, which can not only reconstruct the trajectories of charged particles in 3D space, but also identify particles by measuring the ionization energy that they deposit along their tracks.
Abstract: Since its invention only ten years ago, the time‐projection chamber has proven so useful as a particle detector that some are calling it the “bubble chamber” of the 1980s and 1990s. The enormous appeal of this new detector stems from its ability not only to reconstruct the trajectories of charged particles in three dimensions, but also to identify particles by measuring the ionization energy that they deposit along their tracks. The time‐projection chamber can make these measurements over a large solid angle and in very crowded environments where many tracks are created at the same time.
TL;DR: In fact, I didn't really decide to become a physicist until I was about 23 years old, working as a research engineer at the RCA Laboratories in Princeton, New Jersey.
Abstract: I didn't really decide to become a physicist until I was about 23 years old, working as a research engineer at the RCA Laboratories in Princeton, New Jersey. To understand my decision, you will need some background. Ever since I was a boy I was fascinated by the operation of machines. I liked to take them apart, and often I was even able to put them back together again. I used to make model airplanes and construct mechanical toys. Originally, I wanted to become a civil engineer and design complex mechanisms.
TL;DR: For example, this article pointed out that scientists often seek to explain the unknown by seeking likenesses with known phenomena, and they must be particularly careful when they use this strategy to study the astronomy of other cultures, for we often become enticed into thinking that their motivations and goals were the same as ours.
Abstract: Looking into the past, we find cultures very different from our own, yet we find people doing many of the things we do—discovering celestial order through observation, developing calendars, creating cosmologies. As scientists, we often endeavor to explain the unknown by seeking likenesses with known phenomena. However, we must be particularly careful when we use this strategy to study the astronomy of other cultures, for we often become enticed into thinking that their motivations and goals were the same as ours. Warning of this “presentist” trap in the thick of the Stonehenge controversy two decades ago, a historian commented that every age fabricates the Stonehenge it desires. Perhaps we gain a measure of security if we convince ourselves that prehistoric Newtons and Einsteins were preaching and practicing our outlook millenia ago. But were they?
TL;DR: The 300-year-old discipline of Newtonian mechanics is still the basis for today's computer calculations at our national laboratories as mentioned in this paper, however, computers are prompting important changes within mechanics itself.
Abstract: The 300‐year‐old discipline of Newtonian mechanics is still the basis for today's computer calculations at our national laboratories. However, computers are prompting important changes within mechanics itself. Versions of atomistic mechanics now under development save time by matching numerical techniques to computer capabilities, which—even with the fastest, newest machines—are quite limited when compared to the complexities inherent in modeling the real world.
TL;DR: Newman as discussed by the authors proposed a new theory about light and colors, which was published at once in the Philosophical Transactions of the Royal Society of the United Kingdom, with the title "A New theory about Light and Color".
Abstract: On 18 January 1672 Isaac Newton wrote Henry Oldenburg, Secretary of the Royal Society, that he would send him a paper that he modestly described as “being in my Judgment the oddest if not the most considerable detection wch hath hitherto beene made in the operations of Nature.” Newton was not referring to his theory of gravitation—that was still more than a dozen years away—but rather to his new theory of the nature of white light and color. He had discovered that rays of different color have different degrees of refrangibility—or, as we would put it, that the index of refraction varies with wavelength—and that white light and, in particular, sunlight consist of a mixture of innumerable colors. Less than three weeks later, as Newton promised, he sent to the Royal Society his famous paper, “A New theory about light and colors,” which was published at once in the Philosophical Transactions. In the “New theory” he boldly proclaims: “A naturalist would scearce expect to see ye science of [colours] become math...