Showing papers in "Physics Today in 1981"

An introduction to atmospheric radiation

Abstract: Fundamentals of Radiation for Atmospheric Applications. Solar Radiation at the Top of the Atmosphere. Absorption and Scattering of Solar Radiation in the Atmosphere. Thermal Infrared Radiation Transfer in the Atmosphere. Light Scattering by Atmospheric Particulates. Principles of Radiative Transfer in Planetary Atmospheres. Application of Radiative Transfer Principles to Remote Sensing. Radiation and Climate.

Glow Discharge Processes: Sputtering and Plasma Etching

Abstract: Gases. Gas Phase Collision Processes. Plasmas. DC Glow Discharges. RF Discharges. Sputtering. Plasma Etching. Appendices. Index.

Experimental High‐Resolution Electron Microscopy

Abstract: The new edition of this practical microscopy guide includes additional material on high-resolution images of periodic structures and associated techniques. It provides both a view of the fundamental principles of electron microscopy and detailed practical information needed to record the images. Various theoretical results are summarized and practical examples given. A considerable fraction of the book has also been set aside for practical information on setting up and using an electron microscope. Applications in materials science, mineralogy, the biology of radiation-sensitive specimens, semiconductor physics and solid-state chemistry are all described for research workers in these fields.

Structural Phase Transitions

Abstract: 1. Structural Phase Transitions Studied by Electron Paramagnetic Resonance.- 2. Comparison of NMR and NQR Studies of Phase Transitions in Disordered and Ordered Crystals.

Acoustics: An Introduction to Its Physical Principles and Applications

Abstract: Electrical & Computer Engineering | Academics | WPIIntroduction to the Governing Equations and Scope of AcousticsL-Acoustics, Mixhalo Partner Up to Advance 5G Live 10 ENGINEERING NOISE CONTROL WHOARCH 12

Organic molecular crystals : their electronic states

Abstract: 1. Introduction: Characteristic Features of Organic Molecular Crystals.- 1.1 Interaction Forces in Molecular Crystals.- 1.2 The Atom-Atom Potential Method.- 1.3 Aromatic Hydrocarbons - Model Compounds of Organic Molecular Crystals.- 1.3.1 Anthracene.- Anthracene as Model Compound.- Molecular Structure.- Basic Molecular Parameters.- Crystal Structure.- Elastic and Optical Properties.- Metastable Phases in Anthracene.- 1.3.2 Naphthalene.- Molecular Structure.- Basic Molecular Parameters.- Crystal Structure.- Elastic and Optical Properties.- 1.3.3 Higher Linear Polyacenes.- Tetracene and Pentacene.- Hexacene.- 1.3.4 Other Model Aromatic Compounds.- 1.4 Specific Properties of Electronic States in a Molecular Crystal.- 1.5 Basic Characteristics of Electronic Conduction States in Molecular Crystals.- 1.5.1 Band Theory Approach.- 1.5.2 Hopping Versus Band Model.- 1.5.3 Band-to-Hopping Transition.- 1.5.4 Electronic Polarization and Charge Carrier Self-Energy.- 1.5.5 Other Types of Interaction.- 2. Electronic States of an Ideal Molecular Crystal.- 2.1 Neutral Excited States in a Molecular Crystal.- 2.2 Ionized States in a Molecular Crystal.- 2.2.1 The Lyons Model of Ionized States.- 2.2.2 A Modified Lyons Model.- 2.3 Electronic Polarization of a Molecular Crystal by a Charge Carrier.- 2.3.1 Some General Considerations.- 2.3.2 Dynamic and Microelectrostatic Approaches to Electronic Polarization in Molecular Crystals.- 2.4 Electrostatic Methods of Electronic Polarization Energy Calculation in Molecular Crystals.- 2.4.1 Microelectrostatic Methods of Zero-Order Approximation.- 2.4.2 Method of Self-Consistent Polarization Field.- 2.5 Determination of Molecular Polarizability Tensor.- 2.5.1 Experimental Methods.- 2.5.2 Theoretical Methods.- 2.6 Selection of Molecular Polarizability Components bi. for Electronic Polarization Energy Calculations.- 2.7 Extended Polarization Model of Ionized States in Molecular Crystal s.- 2.7.1 Intrinsic Electronic Polarization of a Molecule by a Localized Charge Carrier.- 2.7.2 Vibronic Relaxation and Ionic State Formation.- 2.7.3 Extended Polarization Model Including Ionic States of Electronic Conductivity.- 2.7.4 Dynamic Electronic Polaron States in a Molecular Crystal.- 2.8 Charge Transfer (CT) States in Molecular Crystals.- 2.8.1 General on CT States.- 2.8.2 Evaluation of CT-State Energies in Anthracene and Naphthalene Crystals.- 2.8.3 CT States in Photogeneration Processes.- 2.8.4 CT States in Recombination Processes.- 2.9 Experimental Determination of Energy Structure Parameters in Molecular Crystals.- 2.10 Energy Structure of an Anthracene Crystal.- 2.11 Energy Structure of Aromatic and Heterocyclic Molecular Crystals.- 3. Role of Structural Defects in the Formation of Local Electronic States in Molecular Crystals.- 3.1 Statistical Aspects of the Formation of Local States of Polarization Origin.- 3.2 General Considerations on the Role of Specific Structural Defects.- 3.3 Point Defects (Vacancies) in Molecular Crystals, Their Crystallographic and Electronic Properties.- 3.4 Dislocation Defects, Their Role in Local State Formation.- 3.5 Energetics of Dislocations in Molecular Crystals.- 3.5.1 Discrete Configuration of Dislocations.- 3.5.2 Basic Elastic Properties of Anthracene and Naphthalene Crystals.- 3.5.3 Energy Estimates for Basal Edge Dislocations in an Anthracene Crystal.- 3.6 Atomic and Molecular Models of the Dislocation Core.- 3.6.1 Models of Spherical Atoms and Molecules.- 3.6.2 Polyatomic Molecular Models.- 3.7 Dislocation Alignments and Aggregations, Their Configurational and Energetic Properties.- 3.7.1 Interaction Between Dislocations.- 3.7.2 Dislocation Alignments.- 3.7.3 Dislocation Ensembles.- 3.8 Grain Boundaries, Their Energetic Characteristics.- 3.8.1 Energy of Grain Boundaries in Molecular Crystals.- 3.8.2 Relative Lattice Compression on Grain Boundaries of an Anthracene Crystal.- 3.9 Stacking Faults in Molecular Crystals.- 3.9.1 General on Stacking Faults.- 3.9.2 Stacking Faults in Anthracene-Type Crystals, Their Energetic Characteristics.- 3.9.3 Calculations of Equilibrium Configuration of Molecules in Stacking Faults of an Anthracene Crystal.- 3.10 Formation of Predimer States in the Regions of Extended Structural Defects of Anthracene-Type Crystals.- 3.11 Some More Complex Two- and Three-Dimensional Lattice Defects in Molecular Crystals.- 3.12 Observation of Structural Defects in Molecular Crystals.- 3.12.1 Optical Low Resolution Technique.- 3.12.2 Electron Microscopy and Diffraction Techniques.- 3.12.3 X-Ray Methods.- 3.13 Main Characteristics of Dislocation Defects in Some Model Molecular Crystals.- 3.13.1 Dominant Types of Dislocatioas in Anthracene Space Group Crystal s.- 3.13.2 Density of Dislocations in Anthracene Crystals, Its Dependence on Crystal Growth and Treatment.- 4. Local Trapping Centers for Excitons in Molecular Crystals.- 4.1 Theory of Exciton States in a Deformed Molecular Crystal.- 4.2 Electron Level Shifts in Hydrostatically Compressed Molecular Crystal s.- 4.3 Formation of Local Exciton Trapping Centers in Structural Defects of a Crystal.- 5. Local Trapping States for Charge Carriers in Molecular Crystals.- 5.1 Electronic Polarization Energy of a Compressed Anthracene Crystal.- 5.2 Formation of Local Trapping Centers for Charge Carriers in Structural Defects of a Real Molecular Crystal.- 5.3 Energy Spectrum of Local States of Polarization Origin in Stacking Faults of an Anthracene Crystal.- 5.4 Local Surface States of Polarization Origin in Molecular Crystals.- 5.5 Local States of Polarization Origin in the Vicinity of a Lattice Vacancy.- 5.6 Local Charge Carrier Trapping in Covalent, Ionic and Molecular Crystal s.- 5.7 Randomizing Factors Determining Gaussian Distribution of Local States of Structural Origin.- 5.8 Investigation of Local Trapping States by Method of Space Charge Limited Currents (SCLC).- 5.8.1 General Considerations.- 5.8.2 Injecting and Blocking Contacts.- 5.8.3 Conventional SCLC Theories of Discrete and Exponential Approximation of Trap Distribution.- SCLC Theory for an Insulator With Discrete Trap Distribution.- SCLC Theory for an Insulator With Exponential Trap Distribution.- Applicability Limits of Diffusion-Free SCLC Theory Approximation.- 5.8.4 Criteria for Validity of SCLC Conditions.- 5.8.5 Difficulties in Interpreting Experimental CV Characteristics in Terms of Discrete and Exponential Trap Distribution Models.- 5.9 Phenomenological SCLC Theory for Molecular Crystals with Gaussian Distribution of Local Trapping States.- 5.9.1 Conceptual Basis.- 5.9.2 Basic SCLC Theory Equations.- 5.9.3 Validity Range for Different Analytical SCLC Approximations.- 5.9.4 SCLC Dependence on Dispersion Parameter a.- 5.9.5 SCLC Temperature Dependences for Ge (E) and Gg (E) Distributions.- 5.9.6 SCLC Dependence on Et Value.- 5.9.7 Validity Criteria for Exponential and Gaussian Approximations.- 5.9.8 CV Characteristics for Two Sets of Gaussian Trap Distribution.- 5.10 Gaussian SCLC Approximations of Experimental CV Characteristics.- 5.10.1 Analytical Approximations.- 5.10.2 Differential Method of Analysis of CV Characteristics.- 5.11 SCLC Theory for Spatially Nonuniform Trap Distribution.- 5.12 Investigation of Local Trapping States by Thermally Activated Spectroscopy Techniques.- 5.13 Other Experimental Methods for Local Trapping State Study.- 5.14 Correlations Between Distribution Parameters of Local Trapping States and Crystalline Structure.- 5.15 Local Lattice Polarization by Trapped Charge Carrier in Molecular Crystals.- 5.16 Guest Molecules as Trapping Centers in a Host Lattice.- 6. Summing Up and Looking Ahead.- References.- Additional References with Titles.

Applications of optical phase conjugation

Abstract: The recently discovered generation of conjugate waves in the course of observing several nonlinear optical phenomena has attracted a lot of attention in the international technical community Much of the interest arises from a fascination with the idea of “time reversal” and with impressive, almost magical demonstrations in which severely distorted optical beams can be restored to their original, unaberrated state

Thermoluminescence Techniques in Archeology

Abstract: Thermoluminescense as a method of dating archaeological materials has held great promise of providing chronological information complementary to radiocarbon dating because it can be applied to heated, inorganic artifacts. Presented are the basic principles of the method and the methodological details of the dating techniques: inclusion, fine-grain, and pre-dose techniques. For each technique, the sample preparation, measurement procedures, data analysis, age calculation, and sources of error are explained. TL dating by subtraction and by zircon techniques is mentioned. Applications of the dating techniques to archaeological problems are presented. See also AATA 4-3668.

Wiggler and Undulator Magnets

Abstract: To scientists using vacuum ultraviolet and x rays the most important characteristics of an ideal radiation source would be a high intensity within a small solid angle and a high intensity within a small wavelength interval, both extending over a broad range of wavelengths. High spatial brightness (large flux within a small solid angle) permits the delivery of a large number of photons per second to a small sample. High spectral brightness (large flux within a narrow wavelength interval) is essential for high‐resolution spectroscopy. A high‐power tunable vuv and x‐ray laser would be ideal, but unfortunately such a laser does not yet exist. Conventional vuv sources (such as gas‐discharge lamps) and x‐ray sources (such as electron‐impact x‐ray tubes) can produce a large flux of radiation, most of which is indeed within a narrow bandwidth at particular fluorescent lines. However, the flux is diffused over a large solid angle and the wavelength is fixed. The continuum radiation from these sources is less inten...

Concert‐hall acoustics

Abstract: 1. Introduction.- 2. Sound Transmission Systems.- 2.1 Source Signals in Terms of the Autocorrelation Function.- 2.2 Reflection from Finite Surfaces.- 2.3 Reflection from a Periodic Structure of a Wall.- 2.3.1 Analysis.- 2.3.2 Numerical Calculations.- 2.4 Scattering by Diffusing Walls.- 2.5 Physical Hearing System.- 2.5.1 Head, Pinna and External Auditory Canal.- 2.5.2 Eardrum and Bone Chain.- 2.5.3 Cochlea.- 2.6 Nervous System.- 3. Simulation of Sound Fields.- 3.1 Signals at Both Ears.- 3.2 Simulation of Sound Localization.- 3.3 Simulation of Sound Fields in Concert Halls.- 4. Subjective Preference Judgments.- 4.1 Linear Scale Value of Preference.- 4.2 Sound Fields with Single and Multiple Early Reflections.- 4.2.1 Preferred Delay Time of Single Reflection.- 4.2.2 Preferred Direction of a Single Reflection.- 4.2.3 Preferred Amplitude of a Single Reflection.- 4.2.4 Preferred Delay Time of the Second Reflection.- 4.2.5 Preferred Spectrum of a Single Reflection.- 4.2.6 Preferred Delay Time of the Strongest Reflection in Multiple Early Reflections.- 4.3 Sound Fields with Early Reflections and Subsequent Reverberation.- 4.3.1 Scale Values vs Delay Time of Early Reflections and Subsequent Reverberation Time.- 4.3.2 Scale Values vs Listening Level and IACC.- 4.3.3 Scale Values vs Subsequent Reverberation Time and IACC.- 4.3.4 Agreement with Other Preference Judgments.- 5. Prediction of Subjective Preference in Concert Halls.- 5.1 Model of Auditory Pathways.- 5.2 Optimum Design Objectives.- 5.2.1 Listening Level (Temporal-Monaural Criterion).- 5.2.2 Early Reflections After Direct Sound (Temporal-Monaural Criterion).- 5.2.3 Subsequent Reverberation Time After Early Reflections (Temporal-Monaural Criterion).- 5.2.4 Incoherence at Both Ears (Spatial-Binaural Criterion).- 5.3 Theory of Subjective Preference.- 5.4 Calculating Subjective Preference for a Concert Hall.- 6. Design Study.- 6.1 Walls and Ceiling.- 6.2 Floor and Seats.- 6.2.1 Sound Transmission Over Seat Rows.- 6.2.2 Effects of Seat Configuration and Floor Absorption.- 6.2.3 Effects of the Angle of Wave Incidence.- 6.2.4 Effects of a Slit Resonator Under the Floor.- 6.3 Stage Enclosure.- 6.4 Concert Halls.- 7. Acoustic Test Techniques for Concert Halls.- 7.1 Transfer Function or Impulse Response Measurements.- 7.1.1 Single Pulse Method.- 7.1.2 Correlation Method.- 7.1.3 Fast Method Using the Pseudo-Random Binary Signal.- 7.2 Reverberation.- 7.3 Interaural Cross Correlation.- 7.4 Subjective Preference Judgments of Sound Fields in Existing Concert Halls.- Appendices.- A. Subjective Diffuseness.- B. An Example of Individual Difference in Preference Judgment.- C. Perception of Coloration.- D. Correlation Functions at Both Ears.- E. Computation Programs for the Fast Method of Measuring Impulse Responses (Computer: Univac 1100/83 ASCII FORTRAN Compiler, ANSI STANDARD X3.9 -1978).- Glossary of Symbols.- References.

Catalysis of carbon gasification

Abstract: The conversion of carbon to its oxide gases or methane, by interaction with oxygen, steam, hydrogen or carbon dioxide, are reactions of great practical importance. The oxidation of carbon to CO2 and CO provides much of mankind's heat and power, and the formation of “syngas” (a mixture of carbon monoxide and hydrogen) by steam gasification of carbon is an important step in the conversion of coal to synthetic petroleum (PHYSICS TODAY, August 1978, page 32). These reactions, together with the hydrogenation of carbon to form methane, and its interaction with CO2 to form CO, are the principal gasification reactions of carbon.

Electron‐acoustic microscopy

Abstract: Electron‐acoustic microscopy is a new technique enabling us to produce images that show variations in an object's thermal and elastic properties with a resolution on the order of microns. These images appear dramatically different than optical or electron microscope pictures, and contain much information not otherwise available (see figure 1). Because the technique is less than two years old, it is too early to identify with certainty the areas in which electron‐acoustic microscopy will be important; we can, however, name a few possibilities:▸ the non‐destructive examination of complex integrated circuits▸ the in vitro examination of biological materials▸ the mapping of defects and inhomogeneities in amorphous solids▸ the recovery of obscured metal imprints, such as the serial numbers on firearms.

The development of field theory in the last 50 years

Abstract: This article is devoted to the development of quantum field theory, a discipline that began with quantum electrodynamics, which was born in 1927 when P. A. M. Dirac published his famous paper “The Quantum Theory of the Emission and Absorption of Radiation.” Figure 1 reproduces the first page. Note that it was communicated by Niels Bohr himself. Also note the second and third sentences. The latter is an understatement indeed: Nothing had been done up to this time on quantum electrodynamics.

The emperor's new clothes—1981

Abstract: Physicists learn early that no statement should be accepted without question. Indeed at the core of the physicist's approach to both experimental data and theoretical structures is an insistence on asking questions, looking for patterns and checking for consistency. In this context, incorrect data, bad analysis, and overblown claims are subject to immediate challenge to prevent them from being perpetuated and making the already difficult work of understanding natural phenomena even more difficult.

Wandering surface atoms and the field ion microscope

Abstract: Interest in information about individual atoms on crystal surfaces has been strong since the early 1930s. By then it had become clear that to understand technologically important surface phenomena such as crystal and thin‐film growth, heterogeneous catalysis, sintering and surface oxidation, it was necessary to understand atomic processes at crystal surfaces. In response to this need for qualitative and quantitative knowledge physicists and chemists developed detailed models of atomic activity on crystal surfaces. However, for many decades there was no way to confront speculation with actual data on atomic behavior—that would require observations of individual atoms. No less a capability is now available (see figure 1) through the use of the field ion microscope. As we will see, observations of individual atoms have not only provided much interesting information on surfaces but they have also become surprisingly routine.

The future of nuclear energy

Abstract: In many ways nuclear energy is a fantastic success: a completely new source of energy now producing, or soon scheduled to produce, about 20 exajoules per year or almost 10 percent of all the energy man now produces. This energy will come from approximately 500 large reactors in 36 countries (see figure 1). These reactors, if replaced by oil‐fired power plants, would require about 107 barrels of oil per day—that is, about one‐seventh of all the oil produced in the world. Were the output of these plants used for electric resistive heating, in principle 5×106 barrels of oil per heating day could be displaced; if used to recharge electric vehicles, perhaps 10×106 barrels.

Track‐recording solids

Abstract: Since the beginning of the solar system, natural particle detectors have been recording the passage of charged particles from the sun and cosmic rays. Now, in addition to developing the latent images of these fossil trails of damage in solids and learning about the nature of ancient radiation, we are creating new and more sensitive detectors of a similar kind. These detectors, which are finding a wide variety of applications, take advantage of the fact that a highly charged particle penetrating any nonconducting solid leaves a submicroscopic trail that can be chemically amplified. The increased chemical reactivity of the trails of radiationdamaged material is the basis for the so‐called etched‐track process, by which we make the particle tracks large enough to measure in an optical microscope. As we will see, there is sufficient information in the tracks to allow us to determine a particle's charge and velocity.

E Pluribus Boojum: the physicist as neologist

Abstract: I know the exact moment when I decided to make the word “boojum” an internationally accepted scientific term. I was just back from a symposium at the University of Sussex near Brighton, honoring the discovery of the superfluid phases of liquid helium‐3, by Doug Osheroff, Bob Richardson, and Dave Lee. The Sussex Symposium took place during the drought of 1976. The Sussex downs looked like brown Southern California hills. For five of the hottest days England has endured, physicists from all over the world met in Sussex to talk about what happens at the very lowest temperatures ever attained.

The road to superconducting materials

Abstract: In the golden research period immediately following World War II, the three of us took up research work in cryogenics and superconductivity We were fortunate enough to make some discoveries in superconducting materials that laid the groundwork for new avenues of technological development In this article, we present our recollections of the history of these discoveries and some of the human events surrounding them As is well known, scientific progress rarely takes the logical paths usually portrayed in scientific journals; much of it begins with chance encounters or random events We shall mention a few of the unusual factors that affected our work and some of the people who influenced our thinking

Elementary excitations in quantum liquids

Abstract: By 1931 it was already clear that condensed matter was to be a marvelous proving ground for the then newly developed quantum mechanics. The Sommerfeld free electron gas model for a metal; Bloch's theorem; the description of energy bands in solids; the theoretical explanation of why some solids are metals, some insulators, some semiconductors; all these provide eloquent testimony to the ingenuity of the theorist in developing a quantum description of independent electron motion that explained or illuminated experiment. During the succeeding decade, theorists began to examine some consequences of electron–electron interactions. Thus in 1934, when Frederick Seitz and Eugene Wigner developed the first theory of energy bands and cohesion in the alkali metals, they drew upon the pioneering study by Wigner of Coulomb correlations in a quantum plasma (interacting electrons moving in a uniform background of positive charge). In 1937, John Bardeen took into account the screening of ion motions by electrons in his seminal investigation of electron–phonon interactions in metals, while the concept of a pseudopotential to describe the way in which strong short‐range electron correlations influence the electron–ion interaction in solids was put forward by H. Hellman in 1936 and independently by Conyers Herring in 1939.