Showing papers on "Scattering published in 1986"
TL;DR: In this article, the effect of the exact shape of the microcrystal and the relationship between the width, shift and asymmetry of the Raman line is calculated and is in good agreement with available experimental data.
1,957 citations
TL;DR: The low-lying energy values associated to energy eigenstates describing two stable particles enclosed in a (space-like) box of sizeL are shown to be expandable in an asymptotic power series of 1/L as mentioned in this paper.
Abstract: The low-lying energy values associated to energy eigenstates describing two stable particles enclosed in a (space-like) box of sizeL are shown to be expandable in an asymptotic power series of 1/L The coefficients in these expansions are related to the appropriate elastic scattering amplitude in a simple and apparently universal manner At low energies, the scattering amplitude can thus be determined, if an accurate calculation of two-particle energy values is possible (by numerical simulation, for example)
1,060 citations
TL;DR: In this article, the authors review the use of the Keldysh method for obtaining kinetic equations for normal and superconducting metals, including electron-impurity, electron-phonon, and electron-electron scattering.
Abstract: The authors review the Keldysh method of obtaining kinetic equations for normal and superconducting metals. The use of the method is illustrated by examples involving electron-impurity, electron-phonon, and electron-electron scattering, both within and beyond the quasiclassical approximation.
1,008 citations
TL;DR: A nontrivial squared helicity amplitude is given for the scattering of an arbitrary number of gluons to lowest order in the coupling constant and to leading order inThe number of colors.
Abstract: A nontrivial squared helicity amplitude is given for the scattering of an arbitrary number of gluons to lowest order in the coupling constant and to leading order in the number of colors.
963 citations
Book•
01 Jan 1986
TL;DR: Monumental as discussed by the authors is a compilation of the present engineering state of the art of microwave remote sensing, presented as a survey of the state-of-the-art in the field.
Abstract: Monumental as a compilation of the present engineering state of the art of microwave remote sensing. -- International Journal of Remote Sensing
959 citations
Book•
01 Mar 1986TL;DR: The fundamental principles of radar backscattering measurements, including measurement statistics, Doppler and pulse discrimination techniques, and associated ambiguity functions, are presented in this article, along with the internal and external calibration techniques employed in scattering measurements.
Abstract: The fundamental principles of radar backscattering measurements are presented, including measurement statistics, Doppler and pulse discrimination techniques, and associated ambiguity functions. The operation of real and synthetic aperture sidelooking airborne radar systems is described, along with the internal and external calibration techniques employed in scattering measurements. Attention is given to the physical mechanisms responsible for the scattering emission behavior of homogeneous and inhomogeneous media, through a discussion of surface roughness, dielectric properties and inhomogeneity, and penetration depth. Simple semiempirical models are presented. Theoretical models involving greater mathematical sophistication are also given for extended ocean and bare soil surfaces, and the more general case of a vegetation canopy over a rough surface.
743 citations
TL;DR: In this article, a self-similar random medium is proposed for the crust of the seismic data, which produces waveform variations at high frequencies (15-30 Hz) similar to those reported for actual small-scale seismic arrays with apertures of hundreds of meters.
Abstract: Synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two-dimensional media with random spatial variations in seismic velocity. The results of this study provide important insights about the propagation of short-period ( 5), the self-similar medium is characterized by a scattering Q that is constant with frequency, whereas theory predicts that the apparent Q in an exponential medium is proportional to frequency. These alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal Q at frequencies greater than about 1 Hz, assuming that scattering is responsible for most of the attenuation at these frequencies. Measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation (scattering Q ≤ 200). In these cases, Q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission Q of the medium. The cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium. The self-similar random medium proposed here for the crust produces waveform variations at high frequencies (15–30 Hz) similar to those reported for actual small-scale seismic arrays with apertures of hundreds of meters.
588 citations
01 Jan 1986
Abstract: Recent Quantum Scattering Calculations on the H + H2 Reaction and its Isotopic Counterparts.- Reaction Path Models for Polyatomic Reaction Dynamics From Transition State Theory to Path Integrals.- Reduced Dimensionality Theories of Quantum Reactive Scattering: Applications to Mu + H2, H + H, O(3P) + H2, D2 and HD.- Calculations on Collinear Reactions using Hyperspherical Coordinates.- Reactive Scattering in the Bending-Corrected Rotating Linear Model.- Periodic Orbits and Reactive Scattering:Past, Present and Future.- The Sudden Approximation for Reactions.- Hyperspherical Coordinate Formulation of the Electron-Hydrogen Atom Scattering Problem.- The R-Matrix Method.- The Time-Dependent Wavepacket Method: Application to Collision Induced Dissociation Processes.- The Distorted Wave Theory of Chemical Reactions.- The Representation and Use of Potential Energy Surfaces in the Wide Vicinity of a Reaction Path for Dynamics Calculations on Polyatomic Reactions.- Light-Heavy-Light Chemical Reactions.- Arrangement Channel Quantum Mechanical Approach to Reactive Scattering.- Resonances in Reactions: A Semiclassical View.
577 citations
TL;DR: In this article, a simple expression for the low field mobility in the miniband conduction regime is derived; localization effects, hopping conduction, and effective mass filtering are discussed.
Abstract: New results on the physics of tunneling in quantum well heterostructures and its device applications are discussed. Following a general review of the field in the Introduction, in the second section resonant tunneling through double barriers is investigated. Recent conflicting interpretations of this effect in terms of a Fabry-Perot mechanism or sequential tunneling are reconciled via an analysis of scattering. It is shown that the ratio of the intrinsic resonance width to the total scattering width (collision broadening) determines which of the two mechanisms controls resonant tunneling. The role of symmetry is quantitatively analyzed and two recently proposed resonant tunneling transistor structures are discussed. The third section deals with perpendicular transport in superlattices. A simple expression for the low field mobility in the miniband conduction regime is derived; localization effects, hopping conduction, and effective mass filtering are discussed. In the following section, experimental results on tunneling superlattice photoconductors based on effective mass filtering are presented. In the fifth section, negative differential resistance resulting from localization in a high electric field is discussed. In the last section, the observation of sequential resonant tunneling in superlattices is reported. We point out a remarkable analogy between this phenomenon and paramagnetic spin resonance. New tunable infrared semiconductor lasers and wavelength selective detectors based on this effect are discussed.
555 citations
IBM1
TL;DR: This work investigates the resistance of a series of two (or more) ob- stacles and study the transition from completely coherent transmission through the sample to completely incoherent transmission.
Abstract: Landauer's approach which yields the resistance of an obstacle in an otherwise perfect wire due to elastic scattering at the obstacle is augmented by including localized inelastic scatterers within the sample. The inelastic scatterers invoked consist of an electron reservoir coupled via a lead to the wire. The key advantage of this method is that the effect of inelastic scattering can be studied by solving an elastic scattering problem. We investigate the resistance of a series of two (or more) ob- stacles and study the transition from completely coherent transmission through the sample to completely incoherent transmission. For a sample with a small transmission probability, increasing inelastic scattering decreases the resistance. At an intermediate value of inelastic scattering, the resistance reaches a minimum to increase again when inelastic scattering processes start to dominate the resistance.
552 citations
TL;DR: The pion form factor has been measured in the space-like q 2 region 0.014 to 0.26 (GeV/c ) 2 by scattering 300 GeV pions from the electrons of a liquid hydrogen target.
TL;DR: In this paper, the transport properties of the 2D electron gas in a narrow channel formed by the split gate of a GaAs-AlGaAs heterojunction field effect transistor were investigated.
Abstract: We present results on the transport properties of the 2D electron gas in a narrow channel formed by the split gate of a GaAs-AlGaAs heterojunction field-effect transistor. There are both quantum-interference and interaction corrections to the conductivity. We find that the temperature dependence of the phase relaxation length is in agreement with a recent theory based on scattering by electromagnetic fluctuations. Beyond the regime of quantum interference the conductivity varies with temperature as ${T}^{2}$.
TL;DR: Scanning second-harmonic microscopy has revealed, for the first time, the existence of a discrete network of fine, polar, filamentous or columnar, structures, and, also, the presence of strongly polar surface, or near-surface patches.
TL;DR: It is shown that vibrational surface modes of particles are responsible for this Raman scattering and the frequency of the maximum of scattering is proportional to the inverse diameter of the particles, which are spherical spinel microcrystallites.
Abstract: The observation of very-low-frequency bands by Raman scattering in a nucleated cordierite glass is described. The frequency of the maximum of scattering is proportional to the inverse diameter of the particles, which are spherical spinel microcrystallites. It is shown that vibrational surface modes of particles are responsible for this Raman scattering.
TL;DR: The results show that additional harmonic excitations coexist with sound waves below 1 THz, and that these excitations correspond to relative rotation of ${\mathrm{SiO}}_{4}$ tetrahedra.
Abstract: Measurements of the elastic and inelastic neutron scattering from vitreous silica in the frequency range 0.3 to 4 THz and with scattering vectors in the range 0.2 to 5.3 A${\r{}}^{\mathrm{\ensuremath{-}}1}$ are analyzed in conjunction with heat-capacity measurements on the same samples to provide a microscopic description of low-frequency vibrational modes. The results show that additional harmonic excitations coexist with sound waves below 1 THz, and that these excitations correspond to relative rotation of ${\mathrm{SiO}}_{4}$ tetrahedra.
TL;DR: Using small-angle x-ray scattering, it is shown that porous silica aerogel has a fractal backbone structure that is traced to the underlying chemical and physical growth processes.
Abstract: Using small-angle x-ray scattering, we show that porous silica aerogel has a fractal backbone structure. The observed structure is traced to the underlying chemical (polymerization) and physical (colloid aggregation) growth processes. Comparison of scattering curves for aerogel with silica aggregates confirms this interpretation.
TL;DR: In this paper, cross-section data have been compiled on the cross sections for collisions of electrons and photons with oxygen molecules (O2) for electron collisions, the processes included are: total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational and electronic states, dissociation, ionization, and attachment.
Abstract: Data have been compiled on the cross sections for collisions of electrons and photons with oxygen molecules (O2). For electron collisions, the processes included are: total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational, and electronic states, dissociation, ionization, and attachment. Ionization and dissociation processes are considered for photon impact. Cross‐section data selected are presented graphically. Spectroscopic and other properties of the oxygen molecule are summarized for understanding of the collision processes. The literature was surveyed through August 1987, but some more recent data are included when available to the authors.
TL;DR: Small-angle neutron scattering from normal, compressed, and water-suspended powders of aggregates of fine silica particles has been studied and the intensity of scattering was found to scale with the correlation length in the manner expected for a fractal system.
Abstract: Small-angle neutron scattering from normal, compressed, and water-suspended powders of aggregates of fine silica particles has been studied. The samples possessed average densities ranging from 0.008 to 0.45 g/${\mathrm{cm}}^{3}$. Assuming power-law correlations between particles and a finite correlation length \ensuremath{\xi}, we derive the scattering function S(q) from specific models for particle-particle correlation in these systems. S(q) was found to provide a satisfactory fit to the data for all samples studied. The fractal dimension ${d}_{f}$ corresponding to the power-law correlation was 2.61\ifmmode\pm\else\textpm\fi{}0.1 for all dry samples, and 2.34\ifmmode\pm\else\textpm\fi{}0.1 for the water-suspended samples. The intensity of scattering was found to scale with the correlation length in the manner expected for a fractal system.
TL;DR: In this article, the authors presented matrix formulations for the discrete-ordinate and matrix-operator methods of solving the transfer of solar radiation in a plane-parallel scattering atmosphere, where eigenspace transformations of symmetric matrices are introduced into the method of Stamnes and Swanson instead of using the decomposition of an asymmetric matrix.
Abstract: Matrix formulations are presented for the discrete-ordinate and the matrix-operator methods of solving the transfer of solar radiation in a plane-parallel scattering atmosphere. Eigenspace transformations of symmetric matrices are introduced into the method of Stamnes and Swanson instead of using the decomposition of an asymmetric matrix. The computational stability is considerably improved by this algorithm, especially for single-precision calculations. Representations of the reflection and transmission matrices in the matrix-operator method are also given, in terms of the indicated formulations, by considering a boundary-value problem of the discrete-ordinate method. The solutions of the discrete-ordinate method for inhomogeneous atmospheres are given by combining discrete-ordinate solutions for respective homogeneous sublayers through the addition technique of the matrix-operator method.
TL;DR: In this article, the argon and krypton interatomic potentials are constructed using the HFD-B form with definite advantages over the C6 dispersion coefficient, which can accurately predict the best available spectroscopy, scattering and bulk data.
Abstract: Accurate interatomic potentials are constructed which represent subtle but significant improvements for the argon and krypton interactions The potentials are of the HFD-B form with definite advantages over the HFD-C form These new potentials incorporate recent determinations of the C6 dispersion coefficient and accurately predict the best available spectroscopy, scattering and bulk data, some of which data were published after earlier constructions
TL;DR: In this article, both the Debye-like semi-empirical model and the theoretical Polder-Van Santen mixing model were found to describe adequately the dielectric behavior of wet snow.
Abstract: Microwave dielectric measurements of dry and wet snow were made at nine frequencies betweeo 3 and 18 GHz, and at 37 GHz, using two free-space transmission systems. The measurements were conducted during the winters of 1982 and 1983. The following parametric ranges were covered: 1) liquid water content, 0 to 12.3 percent by volume; 2) snow density, 0.09 to 0.42 g cm-3; 3) temperature, 0 to -5 \deg C and -15\deg C (scattering-loss measurements); and 4) crystal size, 0.5 to 1.5 mm. The experimental data indicate that the dielectric behavior of wet snow closely follows the dispersion behavior of water. For dry snow, volume scattering is the dominant loss mechanism at 37 GHz. The applicability of several empirical and theoretical mixing models was evaluated using the experimental data. Both the Debye-like semi-empirical model and the theoretical Polder-Van Santen mixing model were found to describe adequately the dielectric behavior of wet snow. However, the Polder-Van Santen model provided a good fit to the measured values of the real and imaginary parts of wet snow only when the shapes of the water inclusions in snow were assumed to be both nonsymmetrical and dependent upon snow water content. The shape variation predicted by the model is consistent with the variation suggested by the physical mechanisms governing the distribution of liquid water in wet snow.
Book•
01 Jan 1986
TL;DR: In this paper, the authors present a model of the Inverse Scattering (Diffraction) problem, where a single small body is used to scatter the data at high frequency.
Abstract: I. Scattering by an Obstacle.- 1. Statement of the Problem. Basic Integral Equations.- 2. Existence and Uniqueness of the Solution to the Scattering Problem.- 3. Eigenfunction Expansion Theorem.- 4. Properties of the Scattering Amplitude.- 5. The S-Matrix and Wave Operators.- 6. Inequalities for Solutions to Helmholtz's Equation for Large frequencies.- 7. Representations of solutions to Helmholtz's Equation.- II. The Inverse Scattering (Diffraction) Problem.- 1. Statement of the Problem and Uniqueness Theorems.- 2. Reconstruction of Obstacles from the Scattering Data at High Frequencies.- 3. Stability of the Surface with Respect to Small Perturbations of the Data.- III. Time Dependent Problem.- 1. Statement of the Problems.- 2. The Limiting Amplitude Principle (Abstract Results).- 3. The Limiting Amplitude Principle for the Laplacian in Exterior Domains.- 4. Decay of Energy.- 5. Singularity and Eigenmode Expansion Methods.- IV. T-Matrix Scheme and Other Numerical Schemes.- 1. Statement of the Problem.- 2. Justification of the T-Matrix Scheme.- 3. Numerical Results.- 4. Other Schemes.- V. Scattering by Small Bodies.- 1. Scattering by a Single Small Body.- 2. Scattering by Many Small Bodies.- 3. Electromagnetic Wave Scattering by Small Bodies.- 4. Behavior of the Solutions to Exterior Boundary Value Problems at Low Frequencies.- VI. Some Inverse Scattering Problems of Geophysics.- 1. Inverse Scattering for Geophysical Problems.- 2. Two Parameter Inversion.- 3. An Inversion Formula in Scattering Theory.- 4. A Model Inverse Problem of Induction Logging.- VII. Scattering by Obstacles with Infinite Boundaries.- 1. Statement of the Problem.- 2. Spectral Properties of the Laplacians.- 3. Spectral Properties of the Dirichlet Laplacian in Semi-Infinite Tubes.- 4. Absence of Positive Eigenvalues for the Dirichlet Laplacian Under Local Assumptions at Infinity.- 5. The Limiting Absorption Principle and Compact Perturbations of the Boundary.- 6. Eigenfunction Expansions in Canonical Domains.- Appendix 1. Summary of some Results in Potential Theory and Embedding Theorems.- Appendix 2. Summary of some Results in Operator Theory.- Appendix 4. Stable Numerical Differentiation.- Appendix 5. Limit of the Spectra of the Interior Neumann Problems when a Solid Domain Shrinks to a Plane One.- Appendix 6. Construction of a Surface from its Principal Curvatures.- Appendix 7. Resonances.- Research Problems.- Bibliographical Notes.- List of Symbols.
TL;DR: In this paper, the composite roughness model is applied to bottom backscattering in the frequency range 10-100 kHz and the Kirchhoff approximation is used to obtain better results.
Abstract: The composite roughness model is applied to bottom backscattering in the frequency range 10–100 kHz. For angles near normal incidence, the composite roughness model is replaced by the Kirchhoff approximation which gives better results. In addition, sediment volume scattering is treated, with account taken of refraction and reflection at the randomly sloping interface. In applying the model to published data it is found that sediment volume scattering is dominant in soft sediments except at small and large grazing angles. For coarse sand bottoms, roughness scattering dominates over a wide range of grazing angles. Implications for acoustic remote sensing are discussed.
TL;DR: In this article, a method of moments technique for analyzing electromagnetic scattering by arbitrary shaped three-dimensional homogeneous lossy dielectric objects is presented based on the combined field integral equations.
Abstract: The recent development and extension of the method of moments technique for analyzing electromagnetic scattering by arbitrary shaped three-dimensional homogeneous lossy dielectric objects is presented based on the combined field integral equations. The surfaces of the homogeneous three-dimensional arbitrary geometrical shapes are modeled using surface triangular patches, similar to the case of arbitrary shaped conducting objects. Further, the development and extensions required to treat efficiently three-dimensional lossy dielectric objects are reported. Numerical results and their comparisons are also presented for two canonical dielectric scatterers-a sphere and a finite circular cylinder.
01 Dec 1986
TL;DR: In this article, it was shown that it is possible to measure the complete scattering matrix of an object using data acquired on a single aircraft pass, and can combine the signals later in the data processor to generate radar images corresponding to any desired combination of transmit and receive polarization.
Abstract: It was shown that it is possible to measure the complete scattering matrix of an object using data acquired on a single aircraft pass, and can combine the signals later in the data processor to generate radar images corresponding to any desired combination of transmit and receive polarization. Various scattering models predict different dependence on polarization state of received power from an object. The imaging polarimeter permits determination of this dependence, which is called the polarization signature, of each point in a radar image. Comparison of the theoretical predictions and observational data yield identification of possible scattering mechanisms for each area of interest. It was found that backscatter from the ocean is highly polarized and well-modeled by Bragg scattering, while scattering from trees in a city park possesses a considerable unpolarized component. Urban regions exhibit the characteristics expected from dihedral corner reflectors and their polarization signatures are quite different from the one-bounce Bragg model.
TL;DR: In this paper, the problem of light scattering by a sphere on a substrate is treated using Mie's solution for scattering a sphere in a homogeneous medium and an extension of Weyl's method for the calculation of the reflection of dipole radiation by a flat surface.
Abstract: The problem of light scattering by a sphere on a substrate is treated using Mie's solution for scattering by a sphere in a homogeneous medium and an extension of Weyl's method for the calculation of the reflection of dipole radiation by a flat surface. The developed theory can be applied to spheres with a radius of the order of the wavelength of the incident light. Particular solutions are given for the case of a perfectly conducting substrate and for the so-called static limit. In the latter case it is shown that the solution is equivalent to that obtained by Wind, Vlieger and Bedeaux for small spheres.
TL;DR: In this article, small-angle neutron-scattering experiments were made on bovine serum albumin (BSA)-lithium dodecyl sulfate (LDS) complexes in buffer solutions.
Abstract: Small-angle neutron-scattering experiments were made on bovine serum albumin (BSA)-lithium dodecyl sulfate (LDS) complexes in buffer solutions. As increasing amounts of LDS are added, the scattering data indicate that BSA molecules are successively transformed into random coil conformations with LDS forming globular micelles randomly decorating the polypeptide backbones. A cross-section formula is developed which successfully fits small-angle neutron-scattering spectra over the entire $Q$ range. The fractal dimension, the micellar size, and the extent of the denatured protein are simultaneously extracted.
TL;DR: A theoretical modeling is proposed to predict the efficiency factors for attenuation, total scattering, and backscattering for spherical and homogeneous phytoplanktonic cells in suspension to evaluate the reliability of the model for algal cells of various indices and morphologies.
Abstract: A theoretical modeling is proposed to predict the efficiency factors for attenuation, total scattering, and backscattering for spherical and homogeneous phytoplanktonic cells in suspension. The input parameters of this modeling are the actual size distribution, the spectral values of absorption by the living cells, and an adjustable value of the real part of the refractive index. The variations in these parameters lead to very diverse spectral behavior of the efficiency factors. Theoretical predictions are compared to experimental results for some species to evaluate the reliability of the model for algal cells of various indices and morphologies.