摘要:

Matrix theories of elastic and acoustic wave scattering are reviewed and unified, and a new one is devised and discussed. Called MOOT (method of optimal truncation), it has tangible and aesthetic advantages over other methods, particularly its convergence properties and its conceptual straightforwardness. The exposition is, for simplicity, in terms of scalar waves; the following paper contains detailed applications to scattering of elastic waves. A family of matrix equations, which includes the present method and others, is derived in a simple way from the boundary conditions. Integral equations and their solution by matrix methods are discussed, MOOT is developed and compared with other matrix methods, symmetry principles are developed and their enforcement discussed, and certain computational methods, details, and limitations are expounded. Briefly, we proceed by expanding the scattered wave in a truncated series of eigenfunctions of the unperturbed wave equation, and determine the expansion coefficients (scattered amplitudes) by requiring that the mean square of the deviance (discontinuity in value or normal derivative in the scalar case) from the boundary conditions at the surface of the scatterer be minimized. This results in matrix equations for the scattered amplitudes which may, in many cases, be easily solved. The method is useful for computing scattering of acoustic, elastic, or electromagnetic waves from defects which are internally piecewise homogeneous, so that conditions on the wave function derivatives and values at the boundaries characterize the scatterers. Although the method is applicable to general shapes, the computations are accelerated if the scatterers are axially symmetric. The matrix equations are superficially similar to others derived and used in the past, which were not based on an optimization principle. Differences are exhibited and their significance is discussed.

ISSN:0021-8979    

DOI:10.1063/1.327705

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The method expounded in the preceding paper is applied to the calculation of the scattering of elastic waves from axially symmetric voids and rigid obstacles. The eigenfunctions and surface tractions are presented in detail. Results are exhibited for direct and mode‐converted cross sections for a variety of scatterer shapes, including oblate and prolate spheroids with aspect ratios up to 7, pillboxes, and cones forkavarying from 0.1 to 10. Accuracy, computer time, and convergence properties are discussed.

ISSN:0021-8979    

DOI:10.1063/1.327706

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Four kinds of Si(Li) and a high‐purity Ge x‐ray detectors have been tested to measure the thicknesses of gold contact layers by comparing the response of the primary Rb‐K&agr; x‐rays with that of the induced Au‐L&agr; x rays. Observed thicknesses ranged from 140 to 260 A˚. Near the x‐ray energies of Au‐Msubshell absorption edges, the contribution of x‐ray transmission through the observed gold layers to the detection efficiency is greater than or equivalent to that of the inherently attached 7.6‐&mgr;m beryllium window. Hence, one must be careful in the determination of the detection efficiency in x‐ray semiconductor detector when low‐energy x rays of less than about 4 keV are measured.

ISSN:0021-8979    

DOI:10.1063/1.327707

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Common ion sputtering techniques for depth profiles can cause buildup of charge in low‐conductivity regions such asp‐njunctions in semiconductors, leading to erroneous results. We analyzed Ga0.1Al0.9As liquid phase epitaxial (LPE) layers on GaAs with secondary ion mass spectrometry (SIMS) and observed that the profiles of69Ga+and27Al+in the low‐conductivity region of these Zn‐diffused LPE layers were a function of the sample bias. We noticed that this artifact was due to the shift and broadening of the secondary ion energy distributions caused by positive charging of the specimen surface. We also found that this could be effectively remedied by integrating the secondary ion yields over a wide energy range. The use of an electron flood gun reduced this charging effect, but complete charge compensation was not achieved even at electron current densities far exceeding the ion current density. This can be explained by the fact that the electron‐induced secondary electron coefficient of GaAlAs is larger than unity.

ISSN:0021-8979    

DOI:10.1063/1.327657

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Studies have been made of the production of slow (∼1 eV) positrons by high‐energy positrons from a radioactive source. Moderators consisting of thin metallic foils coated with MgO smoke were used in the transmission mode. The thinnest foils gave the largest fluxes of slow positrons. A double moderator, consisting of a MgO‐coated grid following the MgO‐coated thin foil, gave a flux almost double that of either the foil or grid alone. The positron beam machine used is described. It has electrostatic optics for the collection, analysis, and transmission of the slow positrons.

ISSN:0021-8979    

DOI:10.1063/1.327658

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An investigation was made of the domain configurations in uniaxial anisotropic permalloy pole structures for integrated thin‐film heads utilizing the SEM type‐II magnetic contrast mode. The technique was compared with other viable methods including Kerr magneto‐optics and the ferrofluid colloid. Type II was found to be superior for dynamic and high‐magnification studies. ac demagnetized, partially saturated, and remanent configurations were observed in poles of different geometries, after magnetization in both easy and hard directions. A comparison was made with the domain configuration in double‐layer permalloy structures. In the study of complete integrated heads, only the top pole domain configuration was observable using the ferrofluid colloid method, while with 200‐keV type II, the complete magnetic circuit domain structure was imaged. The effect of subsequent head processing on easy axis alignment was found to be minimal.

ISSN:0021-8979    

DOI:10.1063/1.327659

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Fluorescence emission of guest molecules in cholesteric liquid crystal hosts was modulated by an electric‐field‐induced cholesteric‐nematic transition. The contrast ratio between the two states can be greater than 15, and is affected primarily by the scattering properties of the phase and the order parameter of the guest. Data are presented on the dependence of the contrast ratio on the cell parameters and the structure of both guest and host. A simple model is presented accounting for the observed behavior.

ISSN:0021-8979    

DOI:10.1063/1.327660

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A general discussion is given of the properties of electromagnetic plane waves in moving isotropic and anisotropic media. This includes working out the general constitutive relations and the dispersion relation for the isotropic case. Treatment of the moving interface involves determining not only the Doppler shifts but also generalization to a moving interface of the law of reflection, Snell’s law, formula for the critical angle, Brewster’s angle, and the reflection and transmission coefficients. The latter involve generalization of the Slater impedances associated with the incident, reflected, and transmitted waves. The maximum angle of incidence in the frame moving with the interface is shown to be that which represents a flow of energy parallel to the interface.

ISSN:0021-8979    

DOI:10.1063/1.327661

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The stability properties of coupled dipole resonance oscillations in a relativistic electron‐beam–plasma system are investigated within the framework of a rigid beam model. The analysis is carried out assuming sharp‐boundary rectangular density profiles, and distinguishing the two cases: (a) beam‐electron–plasma‐electron dipole resonance oscillations and (b) the ion resonance instability for an intense relativistic electron beam partially charge neutralized by background ions. In case (a), it is shown that the system is most unstable for zero fractional charge neutralization and that the instability growth rate can be significantly reduced by increasing the density ratio ?e’/?e, where ?e’and ?eare the beam‐electron and plasma‐electron densities, respectively. Moreover, the characteristic growth rate for the electron‐electron dipole resonance instability can be a substantial fraction of the beam‐electron cyclotron frequency. In case (b), it is found that the instability growth rate is enhanced considerably by increasing the beam density and energy and that, for sufficiently small fractional charge neutralization, the most unstable mode occurs for long axial wavelengths (kz=0). The characteristic growth rate for the ion resonance instability is also found to be a substantial fraction of the beam‐electron cyclotron frequency.

ISSN:0021-8979    

DOI:10.1063/1.327662

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Laser action at 1.054 &mgr;m was obtained in a neodymium‐doped Gd3Ga5O12crystal pumped by a Xe flashlamp. The output power of laser oscillation at 1.054 &mgr;m have been measured comparable to that of Nd3+ : YAG laser at 1.052 &mgr;m.

ISSN:0021-8979    

DOI:10.1063/1.327663

出版商:AIP    

年代:1980

数据来源: AIP