Showing papers on "Scattering published in 1972"

Radiation and scattering of waves

Abstract: As relevant today as it was when it was first published 20 years ago, this book is a classic in the field. Nowhere else can you find more complete coverage of radiation and scattering of waves. The chapter: Asympotic Evaluation of Integrals is considered the definitive source for asympotic techniques. This book is essential reading for engineers, physicists and others involved in the fields of electromagnetics and acoustics. It is also an indispensable reference for advanced engineering courses.

Floating orbits, superradiant scattering, and the black-hole bomb.

Abstract: Penrose1 and Christodoulou2 have shown how, in principle, rotational energy can be extracted from a black hole by orbiting and fissioning particles. Recently, Misner3 has pointed out that waves can also extract rotational energy (“superradiant scattering” in which an impinging wave is amplified as it scatters off a rotating hole). As one application of super-radiant scattering, Misner has suggested the possible existence of “floating orbits”, that is, orbits in which a particle radiatively extracts energy from the hole at the same rate as it radiates energy to infinity; thereby it experiences zero net radiation reaction.

Determination of aerosol height distributions by lidar

Abstract: A new analytic solution to the lidar equation is presented, which realistically considers the scattering properties of the aerosols and the molecular atmosphere individually. With this solution, it is shown, in turbid atmospheres where the aerosols dominate the scattering properties, that accurate vertical profiles of the volume extinction cross section can be obtained with an uncalibrated lidar, provided that the total transmittance of the atmospheric layer being investigated is known. This solution is applied to data samples collected under very clear and under very dusty conditions.

Homogeneous Dynamical Conductivity of Simple Metals

Abstract: Within the jellium model the zero wave vector, frequency-dependent conductivity is expressed in terms of a regular memory function. This quantity is calculated in lowest order in the impurity concentration and the electron-phonon coupling, thus yielding a reasonable approximation for the conductivity valid in the complete frequency regime. The standard results for the static conductivity including vertex corrections are reproduced. Deviations from Drude's formula a because of spin-flip scattering in a magnetic field, because of resonance scattering, because of phonon creation at low temperatures, and because of breaking of the screening cloud attached to charged impurities are discussed.

Characteristic modes for dielectric and magnetic bodies

Abstract: A theory of characteristic modes for material bodies, both with and without losses, is developed. For loss-free bodies, the modes consist of a set of real characteristic sources which diagonalize the generalized network matrix for the body, and a set of characteristic fields which diagonalize the scattering matrix. Most of the properties of these modes remain the same as those of the corresponding modes for perfectly conducting bodies. For lossy bodies, the corresponding modes have complex characteristic sources. However, in the lossy case there also exists a set of real characteristic sources which diagonalize the generalized network matrix, but their fields do not diagonalize the scattering matrix.

X-Ray Scattering from Liquid Crystals. I. Cholesteryl Nonanoate and Myristate

Abstract: X-ray scattering intensities from unoriented samples of cholesteryl nonanoate and myristate are reported for several temperatures in the smectic $A$, cholesteric, and isotropic liquid phases. The measured Bragg-scattering intensities from the smectic planes are used to test a recent theoretical model of the smectic $A$ phase. Strong pretransition scattering (short-range-order or order-parameter fluctuations) are observed in the cholesteric phase and a Landau theory is constructed to describe this effect.

Polarization transfer and spin correlation experiments in nuclear physics.

Abstract: This review is concerned with nuclear reactions and nuclear elastic scattering in which the spin polarization of more than one of the reactants is measured. If both of the particles whose polarization is known are in the initial channel, or both in the final channel, we refer to a `spin correlation' experiment; if one polarized particle is in the initial and one is in the final channel, we refer to a `polarization transfer' experiment. We consider mainly particles with spin ? and with spin 1; to a minor extent higher spins are included. The state of the art with respect to the production of polarized beams and targets and with respect to polarization analysing devices is briefly reviewed. A considerable amount of space is devoted to the definitions of cartesian polarization transfer and spin correlation coefficients which are suitable for the description of reactions involving spin ? and spin 1 particles. These parameters are generalizations of the triple scattering and spin correlation parameters introduced by Wolfenstein for a description of nucleon-nucleon scattering. Finally, the experiments of these types so far performed are reviewed. Reactions involving photons are excluded, and the nucleon-nucleon problem is only briefly mentioned. This review was completed in March 1972.

Resonance Raman Spectra of Hemoglobin and Cytochrome c: Inverse Polarization and Vibronic Scattering

Abstract: Resonance Raman spectra of hemoglobin and cytochrome c in dilute solution contain prominent bands that exhibit inverse polarization, i.e., the polarization vector of the incident radiation is rotated through 90° for 90° scattering, giving infinite depolarization ratios. This phenomenon is shown to require an antisymmetric molecular-scattering tensor. The antisymmetry, which is characteristic of resonance scattering, is associated with the form of a particular class of vibrations, A20, of the tetragonal heme chromophores. The dependence of the resonance Raman spectra on the wavelength of the exciting radiation, as well as their polarization properties, demonstrates that the prominent bands correspond to vibronically active modes of the first electronic transition of the heme proteins, and provide confirmation of Albrecht's vibronic theory of Raman intensities.

Multiple scattering theory in condensed materials

Abstract: Second-order elliptic differential equations (such as the time-independent single particle Schrodinger equation) may be solved in a finite closed disjoint region of space independently of the rest of space. The solution in all space may then be determined by solving the equations in the exterior region together with boundary conditions at the junction of the two regions. These boundary conditions are determined by the previously found interior solution. This means that such regions may be taken as ‘black boxes’ whose exact details do not matter. The simplest example of this is phase-shift scattering theory from a single scatterer where all the scattering properties are described by the phase shifts, and the exact details of the scattering potential are unimportant. In a macroscopic condensed system, however, there are many core regions and one is really concerned with the multiple scattering which takes place between these different scattering centres. Much of this article is devoted to investiga...

Brillouin Scattering: A Tool for the Measurement of Elastic and Photoelastic Constants

Abstract: After an outline of the Brillouin effect and of elastic waves in crystals, a method for the determination of elastic and photoelastic constants is analyzed. The authors propose a set of conditions with a view to obtaining accurately the numerical values of elastic and photoelastic constants and to ascertain their sign. The Brillouin-line intensities for scattering angles of 90\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{} are presented for all crystal systems, except for the monoclinic and triclinic ones, and for the low-symmetry classes of the rhombohedric system.

Response Functions in the Theory of Raman Scattering by Vibrational and Polariton Modes in Dielectric Crystals

Abstract: The paper begins with a tutorial introduction to the theory of inelastic light scattering by polaritons in dielectric crystals. The treatment is based on a simple two-oscillator model which represents the ionic and electronic motions of a crystal. The model contains a third-order anharmonicity which allows an incident laser beam to mix with the oscillator fluctuations and produce scattered light of frequency different from the incident frequency. The magnitude of the oscillator fluctuations is determined by an application of the Nyquist of fluctuation-dissipation theorem, using the response functions of the oscillators for externally applied forces. The simple model gives results for light scattering cross sections which agree with more rigorous derivations in the existing literature. The response function approach is generalized to apply to crystals having many ionic resonances and of uniaxial or orthorhombic structure. The general formulas reduce in appropriate special cases to results already published. Experimental and theoretical work on light scattering by polaritons and by pure phonons is reviewed in the context of both the two-oscillator model and the general theory. Particular attention is given to resonance scattering in an attempt to achieve consistency between the differing theoretical treatments in the literature. The subject matter of the review overlaps some topics in nonlinear optics, and contact is made with the theories of the electrooptic effect and stimulated Raman scattering.

A noncoherent model for microwave emissions and backscattering from the sea surface

Abstract: The two-scale (small irregularities superimposed upon large undulations) scattering theory proposed by Semyonov was extended and used to compute microwave apparent temperature and the backscattering cross section from ocean surfaces. The effect of the small irregularities upon the scattering characteristics of the large undulations is included by modifying the Fresnel reflection coefficients; whereas the effect of the large undulations upon those of the small irregularities is taken into account by averaging over the surface normals of the large undulations. The same set of surface parameters is employed for a given wind speed to predict both the scattering and the emission characteristics at both polarizations.

Redistribution of resonance radiation. I - The effect of collisions.

Abstract: The techniques of modern line-broadening theory are used to investigate the scattering of polarized radiation in the rest frame of an atom undergoing collisions. The formulation explicitly includes both elastic and inelastic (quenching) collisions. When the lower state has zero width, a form for the redistribution function similar to that of Zanstra is obtained, but with the redistribution in the neighborhood of the resonance line being caused solely by elastic collisions. In the limit of no collisions, but with both levels of finite lifetime, the result of Weisskopf and Woolley is obtained. The effect of level-degeneracy is also explicitly included; in this case the results are a function of the polarization of the light and the different relaxation rates for the multipolar components of the atomic states.

Control of radar scattering by reactive loading

Abstract: A method for obtaining a desired radar scattering pattern by reactively loading a conducting body is given. The theory uses the concept of characteristic modes of a loaded body. Any desired real current can be resonated by reactive loads to make it the dominant mode current of that body. If no other mode is near resonance, the radar scattering pattern becomes nearly the same as the radiation pattern of the resonated current. A quality factor Q is defined as a measure of the broadband behavior of a scatterer. Procedures for computing the real currents having minimum Q and maximum gain-quality ratio are given. A pattern synthesis procedure is developed for obtaining the real current whose radiation field pattern is the least mean-square approximation to a desired field pattern. Numerical examples are given for each procedure discussed.

Neutron inelastic scattering study of the lattice dynamics of strontium titanate: harmonic models

Abstract: Extensive neutron inelastic scattering measurements of the frequencies of normal modes in strontium titanate propagating in the crystallographic directions (0, 0, zeta ), ( zeta , zeta , 0), ( zeta , zeta , zeta ), (1/2, 1/2, zeta ) and ( zeta , zeta , 1/2) are reported. The temperature dependence of the 'soft' modes at points Gamma and R have been investigated with particular emphasis on the mode of symmetry Delta 2, propagating in the direction (1/2, 1/2, zeta ); quantitative estimates of the isotropy of the dispersion surface at Gamma and R are given. Rigid ion, rigid shell, and deformable shell models of the crystal dynamics have been developed. Based on these, the frequency distribution, specific heat, one-phonon X ray scattering intensity. Debye-Waller factor, and two-phonon Raman spectrum have been calculated; where possible, these are compared with the available experimental measurements.

Pulse Broadening due to Multiple Scattering in the Interstellar Medium

Abstract: A previous paper (Williamson, Mon. Not. R. Astr. Soc.; 157-expected widen radiation fron a pulsar travels through an extended scattering medium to the observer. This method is here developed to cover the case in which the scattering medium is an extended screen, but souce and observer are not necessarily embedded in the medium. Pulse shapes for a model with two thin screens are also derived, and the results for the two models compared. It is found that, for thc cascs of interest, a knowledge of the pulse shape sets an upper limit to the fraction of the line of sight in the medium. (auth)

Electron-molecule interactions. IV. Scattering by polyatomic molecules

Abstract: For pt III see abstr. A70819 of 1972. The theory of scattering of low energy electrons by closed shell polyatomic molecules is developed. Coupled inhomogeneous differential equations are obtained describing the motion of the scattered electron in the fixed nuclei approximation. The symmetry group of the molecule is used to reduce these equations to their simplest form and expressions for the total, differential and momentum transfer cross sections are obtained. A transformation to the laboratory frame is then derived and this is used to obtain expressions for the rotational excitation cross sections in terms of the S matrix calculated in the fixed molecular frame. Special emphasis is given in this paper to the C2v and Oh symmetry groups and the equations describing electron scattering by water molecules are discussed in some detail.

Remote measurements of the atmosphere using Raman scattering.

Abstract: Raman optical radar measurements of the atmosphere demonstrate that the technique may be used to obtain quantitative measurements of the spatial distribution of individual atmospheric molecular trace constituents (in particular water vapor) and of the major constituents. It is shown that monitoring Raman signals from atmospheric nitrogen aids in interpreting elastic scattering measurements by eliminating attenuation effects. In general, the experimental results show good agreement with independent meteorological measurements. Finally, experimental data are utilized to estimate the Raman backscatter cross section for water vapor excited at 3471.5 A.

Electron Mobility in Hg1−xCdxTe

Abstract: The electron mobility in Hg1−xCdxTe has been obtained from Hall and resistivity measurements for x as high as 0.6, and in samples with carrier concentrations generally less than 2×1015/cm3. The room‐temperature mobility was found to increase uniformly, as x was varied from CdTe, to a maximum value at the semiconductor‐semimetal transition. With further reduction in x the mobility drops uniformly again to the HgTe value. Estimates are made of the contributions of various scattering mechanisms to the room‐temperature mobility. The effects of optical‐mode scattering were calculated for a nondegenerate parabolic band and were the right order of magnitude for compositions as low as x=0.20, but failed to fit the measured results accurately. The ionized impurity scattering mobility was also calculated, and the model of singly ionized donor scattering centers accounts very well for the low‐temperature mobility. The results indicate that n‐type Hg1−xCdxTe is not compensated to any large extent over a large range i...

Revised parameters of the analytic fits for coherent and incoherent scattered X‐ray intensities of the first 36 atoms

Abstract: Analytical parameters have been recalculated for atomic scattering factors and incoherent scattered intensities of the elements of atomic numbers 2 to 36, based on the tables of Tavard, Nicolas & Rouault [J. Chim. Phys. (1967), 64, 540]. The fit has also been checked with the total scattered intensities.