Tracing of interference fringes using average gray value and simultaneous row and column scan

An algorithm for computer tracing of interference fringes is reported. The method uses the average gray-level value for thresholding, row and column scans for determining the type of the scan and simultaneous row and column scan for tracing. The proposed method yield good result even for low-contrast and high-noise images. The program for the interferogram tracing was written using MATLAB6.     

The experimental investigation of a glow discharge in a toroidal tube

A glow discharge in a toroidal tube with axial discharge current is investigated. The investigation was carried out for a discharge as a whole, not for electrodal zones and the positive column separately. The volt-ampere characteristics for different pressures and Paschen's curves for different gases were measured. The curves obtained are compared with analogous ones for a cylindrical tube. The conditions for the existence of a glow discharge in a toroidal tube and the processes passing there are discussed on the basis of the measured curves. The experiments were carried out in air, helium, argon and neon.     

粉末压片法波长色散X射线荧光光谱分析铁矿石样品的矿物效应校正初探

利用10个国内铁矿石标样,对粉末压片法波长色散X射线荧光光谱分析铁矿石样品中主、次量元素时的矿物效应校正进行了初步探讨。文章采用两种方法试图降低由于矿物效应带来的影响。第一种方法(角度校正法)是在测量每个样品 前(包括校正标样以及未知样),对每个待测元素的2θ角度进行实际测量,以校正可能存在的角度偏移;第二种方法(峰面积法)是用峰面积代替峰强度,以校正由于峰形变化所带来的影响。最后用回归分析后的Ｋ因子进行比较。结果表明, 两种方法对矿物效应进行校正都可以不同程度地改善铁矿石中主要元素的校正曲线,尤其是S的校正曲线改善明显。如果在角度校正法或峰面积法的基础上再用基体校正系数,除总Fe外,其他组分均可以满足分析要求,但总Fe仍需要采取 其他措施。     

Bulk modulus and its pressure derivatives of cuprous halides

The ab initio pseudopotential approach to the total crystal energy is presented using local DF formalism. The expressions for bulk modulus, its first and second pressure derivatives for group I-VII semiconductor binary compounds are derived. The expression for the second pressure derivative of the bulk modulus for four-fold crystal structures is derived for the first time within the pseudopotential framework. The computed results of the bulk modulus for cuprous halides are very close to the available experimental data.     

Probability representation of the quantum evolution and energy-level equations for optical tomograms

The von Neumann evolution equation for the density matrix and the Moyal equation for the Wigner function are mapped onto the evolution equation for the optical tomogram of the quantum state. The connection with the known evolution equation for the symplectic tomogram of the quantum state is clarified. The stationary states corresponding to quantum energy levels are associated with the probability representation of the von Neumann and Moyal equations written for optical tomograms. The classical Liouville equation for optical tomogram is obtained. An example of the parametric oscillator is considered in detail.     

Long range elastic interaction of prismatic dislocation loop with a grain boundary

The expressions for the displacement and the stress field around a prismatic infinitesimal dislocation loop lying near the welded boundary and for the displacement field near the slipping boundary are given. The expression for the total force by which the loop is either attracted or repelled from the grain boundary (welded or slipping) was calculated. The forces are graphically illustrated for different combinations of material constants. The calculations were carried out within the isotropic elasticity.The author is indebted to Dr. F. Kroupa for valuable discussion.     

Scattering matrix for Raman effect in cubic crystals

The scattering matrix for Raman effect in cubic crystals for any general orientation of the crystal and any angle of scattering is given. The averages of the matrix over all possible orientations is also given and checks with the well known value of 6/7 for the depolarisation of degenerate lines for transverse scattering. The scattering matrix for backward scattering in terms of polar angles and for some special cases are also given.     

Nuclear Level Density with Non-zero Angular Momentum

The statistical properties of interacting fermions have been studied for various angular momentum with the inclusion of pairing interaction. The dependence of the critical temperature on angular momentum for several nuclei,have been studied. The yrast energy as a function of angular momentum for 28 Si and 24Mg nuclei have been calculated up to 60.0 MeV of excitation energy. The computed limiting angular momenta are compared with the experimental results for 26Al produced by 12C 14N reaction. The relevant nuclear level densities for non-zero angular momentum have been computed for 44Ti and l36Ba nuclei. The results are compared with their corresponding values obtained from the approximateformulas.     

Helium-3 adsorption refrigerator cooled with a closed-cycle cryocooler

A helium-3 adsorption refrigerator cooled with a pulse-tube cryocooler is developed. The refrigerator has two stages of adsorption pumping. The first stage is designed for the condensing and pumping of helium-4, whose cooling capacity is used for the condensation of helium-3. The second stage is designed for pumping helium-3. The final temperature reached by the refrigerator is 0.305 K. This temperature is retained for at least 24 h. The time required for helium recondensation and the obtainment of low temperature is 1.5 h. The cryostat is a self-contained instrument, as it contains no external gas-supply pipelines and the working gas is stored directly within the working volume of the refrigerator. The work is performed in the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research.     

Theory of infra-red and optical spectra of antiferromagnets

The contributions of magnons to the optical properties of antiferromagnets having the rutile structure are discussed. The properties considered are electric-dipole active two-magnon absorption in the infra-red, and magnon sidebands on sharp-line exciton transitions in the visible. The discussion is based on a thorough treatment of the properties of excitons and magnons in the antiferromagnetically ordered state. The site-group and space-group symmetries of the magnetic excitations are derived and the selection rules for electric and magnetic dipole transitions are determined. The occurrence of magnetic Davydov splittings of the excitons is investigated, and their symmetry properties throughout the Brillouin zone are derived. The functional dependences of exciton energy on wave vector are calculated. Applications of the theory are made to experimental results on excitons and magnons in MnF₂, FeF₂ and CoF₂.

The possible mechanisms for two-magnon and magnon-sideband absorption are discussed, and the influence of crystal symmetry on these mechanisms is described. The two-magnon state responsible for electric-dipole absorption is identified and selection rules for electric-dipole activity are presented. A spin Hamiltonian for the two-magnon process is set up and used to derive expressions for absorption coefficients for electric vector parallel and perpendicular to the crystal c-axis. Comparison with experiment for MnF₂ yields numerical values for the parameters of the basic coupling mechanism. The exciton-magnon states which give rise to magnon-sideband absorption are explicitly constructed and electric-dipole selection rules are derived for all possible types of sideband. Spin Hamiltonians for the various magnonsideband absorption processes are presented and used to derive expressions for sideband shapes. The results are applied to the experimental spectra for MnF₂ and FeF₂ and the sideband shapes in MnF₂ are calculated numerically. The sideband shapes observable in emission spectra are also briefly discussed.     

Relations among temporal acuity, hearing loss, and the perception of speech distorted by noise and reverberation

Eight normal listeners and eight listeners with sensorineural hearing losses were compared on a gap-detection task and on a speech perception task. The minimum detectable gap (71% correct) was determined as a function of noise level, and a time constant was computed from these data for each listener. The time constants of the hearing-impaired listeners were significantly longer than those of the normal listeners. The speech consisted of sentences that were mixed with two levels of noise and subjected to two kinds of reverberation (real or simulated). The speech thresholds (minimum signal-to-noise ratio for 50% correct) were significantly higher for the hearing-impaired listeners than for the normal listeners for both kinds of reverberation. The longer reverberation times produced significantly higher thresholds than the shorter times. The time constant was significantly correlated with all the speech threshold measures (r = -0.58 to -0.74) and a measure of hearing threshold loss also correlated significantly with all the speech thresholds (r = 0.53 to 0.95). A principal components analysis yielded two factors that accounted for the intercorrelations. The factor loadings for the time constant were similar to those on the speech thresholds for real reverberation and the loadings for hearing loss were similar to those of the thresholds for simulated reverberation.     

Scattering of evanescent electromagnetic waves by a cylinder near the flat boundary: the Green function and fast numerical method

The scattering of plane evanescent waves by a cylinder is studied. The Green function for the Helmholtz equation for two dielectrics with flat interface is found and applied for the numerical calculation of the scattered field by the boundary elements method. The Green function keeps close track of scattering, including multiple reflections. The result may be applicable for the data analysis in near-field optical microscopy.     

Electronic Stopping Power for 0.05--10MeV Protons in a Group of Organic Materials

Electronic stopping powers for 0. 05-10 MeV protons in a group of organic materials are systematically calculated. The calculations are based on Ashley＇s dielectric model, and an evaluation approach of optical energy loss function is incorporated into Ashley＇s model because no experimental optical data are available for most of the organic materials under consideration. The Barkas-effect correction and Bloch correction are included. The proton stopping powers for the considered organic materials except for mylar in the energy range from 0.05 to 10 MeV are presented for the first time. The results may be useful for studies of various radiation effects in these materials and for space research.     

Maximum entropy principle for rarefied polyatomic gases

The aim of this paper is to show that the procedure of maximum entropy principle for the closure of the moments equations for rarefied monatomic gases can be extended also to polyatomic gases. The main difference with respect to the usual procedure is the existence of two hierarchies of macroscopic equations for moments of suitable distribution function, in which the internal energy of a molecule is taken into account. The field equations for 14 moments of the distribution function, which include dynamic pressure, are derived. The entropy and the entropy flux are shown to be a generalization of the ones for classical Grad’s distribution. The results are in perfect agreement with the recent macroscopic approach of extended thermodynamics for real gases.     

New hyperbolic models of dusty gas flow

The paper presents hyperbolic models for dusty gas flow formulated for single- and multivelocity approximations with account for inter-fractional heat transfer. Characteristic analysis of equations for the model was performed. The Godunov method and linearized Riemann solver was applied for a solution on curvilinear mesh: the Prandtl?Meyer problem for air-droplet mixture was solved. The simulation results were compared with the self-similar solution.     

表面极化对弱锚定向列液晶盒饱和特性的影响

以修正后的Rapini-Papoular锚定能公式为基础, 用理论分析和数值计算相结合的方法, 详细研究表面极化对液晶盒饱和特性的影响. 得出了求解指向矢分布的数学方程, 推导出了计算正常二级转变饱和电压的解析式, 同时结合最新报道, 给出了异常一级转变饱和电压的数值计算方法. 此外, 本文引入了反映指向矢分布特征的参量, 讨论了表面极化对此参量的影响. 结果表明, 指向矢最大倾角的位置随表面极化的增大将远离中央平面向基板移动. 一级转变饱和电压随弱锚定基板表面极化的增大而减小, 随强锚定基板表面极化的增大而增大. 而对二级转变, 饱和电压随表面极化的变化与一级转变恰恰相反. 本文所得结论对液晶表面物理的理解及液晶实际应用都具有重要的指导意义.     

Nuclear Level Density with Non-zero Angular Momentum

The statistical properties of interacting fermions have been studied for various angular momentum with the inclusion of pairing interaction. The dependence of the critical temperature on angular momentum for several nuclei, have been studied. The yrast energy as a function of angular momentum for 28Si and 24 Mg nuclei have been calculated up to 60.0 MeV of excitation energy. The computed limiting angular momenta are compared with the experimental results for ^26Al produced by ^12C＋ 14N reaction. The relevant nuclear level densities for non-zero angular momentum have been computed for ^44Ti and ^136 Ba nuclei. The results are compared with their corresponding values obtained from the approximate formulas.     

Critical thickness for ferroelectricity and magnetoelectric effect in multiferroic tunnel junction with symmetrical and asymmetrical electrodes

The critical thickness for ferroelectricity and magnetoelectric effects have been investigated for the multiferroic tunnel junction with symmetric and asymmetric metallic electrodes based on density functional theory. The ferroelectric polarization of a barrier is still retained down to 2 unit cells scale for the asymmetric multiferroic tunnel junction. The greater cause, leading to the reduction, or even complete elimination for the critical thickness, is the difference in the work function for the two asymmetrical electrodes. In addition, the effect of magnetoelectric coupling is obvious. The asymmetric multiferroic tunnel junction provides the possibility for the miniaturising and multifunctional spin electronic devices.     

Analytical evaluation of the plasma dispersion function for a Fermi—Dirac distribution

An efficient method for the analytic evaluation of the plasma dispersion function for the Fermi-Dirac distribution is proposed.The new method has been developed using the binomial expansion theorem and the Gamma functions.The general formulas obtained for the plasma dispersion function are utilized for the evaluation of the response function.The resulting series present better convergence rates.Several acceleration techniques are combined to further improve the efficiency.The obtained results for the plasma dispersion function are in good agreement with the known numerical data.     

Preparation of calibrating standards for x‐ray fluorescence spectrometry of trace metals in plastics

Convenient x‐ray fluorescent spectrometry was developed for the determination of V, Cr, Co, Ni, Ge and Sb in plastic materials. The calibrating standards were prepared by casting of polyurethane or polyester including a xylene solution of organometallic compounds as a standard. The calibrating disk had a homogeneous elemental distribution and excellent durability. The calibration curves of six elements showed a good linearity of less than 50 mass ppm for V and Ni, 100 mass ppm for Co and Ge, 200 mass ppm for Cr, and 400 mass ppm for Sb. The lower limits of detection (3σ) of the present method were 0.19 mass ppm for V, 0.42 for Cr, 0.24 for Co, 0.18 for Ni, 0.066 for Ge, and 2.1 for Sb. The proposed method has been applied to several different industrial plastics. The quantitative results are in good agreement with those obtained by the AAS method and x‐ray fluorescent spectrometry using the fundamental parameter calculation method. Copyright © 2003 John Wiley & Sons, Ltd.