纳米晶体线的晶格动力学格林函数及晶格振动

通过求解差分方程,推导了纳米晶体线的晶格动力学格林函数,分析了其晶格振动,并推导了声子数表象中的原子位移及晶格振动哈密顿公式.研究结果表明,纳米晶体线的晶格振动能带分裂为一系列的子带,格波只能沿纳米晶体线的纵向传播,沿纳米晶体线的横截面只存在驻波.     

Surface electron states produced by a Rayleigh wave

The electronic properties of a semiconductor bounded by an uneven surface representing an infinitely high potential barrier are investigated. The surface irregularities are produced by a Rayleigh acoustic wave. It is shown that, on the boundary of a semiconductor, surface electron states (waves) may arise whose dispersion laws are obtained under the conditions when conduction electrons are located either in or outside the field of the acoustic wave. Existence domains of surface electron states are found that are distinguished by their physical properties. These domains are separated by a band gap whose width is determined by the height of irregularities.     

单波驱动的过渡粒子效应

本文讨论单波在环等离子体中引起的过渡粒子及其有关效应。 关键词：     

The use of distributed pressure receivers based on elastic piezoelectric composite materials for measuring the hydrodynamic noise produced by a near-wall turbulence

Receiving electroacoustic transducers with sensing elements made of an elastic piezoelectric composite material are described. The parameters of a composite material that exhibits a bulk piezoelectric effect are presented. Results obtained by measuring the turbulent noise in a hydrodynamic channel with the use of piezoelectric composite receivers are reported. The results are compared with those of the noise measurements by a miniature piezoceramic receiver and are considered in the light of the known models of near-wall turbulence.     

Acoustic wave propagation in a binary mixture of inviscid fluids

Linearized equations governing the thermo-mechanical behaviour of a binary mixture of inviscid fluids are derived. Restrictions which are sufficient for the equations to have a unique solution are imposed on some of the material constants. The propagation of plane harmonic waves of small amplitude in the mixture is examined and the inequalities are shown to ensure a physically reasonable response. As an application of the theory properties of acoustic waves in a binary mixture of ideal gases are evaluated numerically.     

Calculation of temporal, angular, and intensity characteristics of the sound field in a coastal area with an arbitrary bottom relief and a constant sound speed in the medium

Computational algorithms and some computed data are presented for the total sound field in a waveguide whose depth arbitrarily depends on two horizontal coordinates. The sound speed is supposed to be constant, and the bottom slopes are considered as small. The algorithm involves three steps. First, horizontal rays, i.e., horizontal projections of the real rays multiply bottom-and surface-reflected, are calculated. Second, the horizontal rays are set up to a point. Third, the real rays are set up to a point. The computational accuracy is analyzed for a homogeneous wedge lying on a halfspace. Calculations are carried out for a coastal region of the ocean.     

Thermodynamics of electrons in the graphene bilayer

Some problems of the thermodynamics of electrons in a doped graphene bilayer are considered. Analytical expressions are derived for chemical potential and specific heat in the limiting cases of low and high temperatures. The Seebeck and Thomson coefficients are estimated. Landau levels are studied using a semi-classical approach. An expression for thermodynamic potential is obtained and the de Haas-van Alphen oscillations are studied. The oscillations of magnetic entropy and electron temperature in a magnetic field, i.e., the oscillating magnetocaloric effect, are investigated. For all parameters, the cases of graphene bilayer and monolayer are compared.     

Experimental study of the multipolar vortex instability

The instability of a vortex subjected to a stationary dipolar or tripolar constraint is studied experimentally by using a rotating deformable cylinder on which two or three rollers are applied. As the Reynolds number and the aspect ratio of the cylinder are varied, different modes of instability are observed and their wavelength and frequency are compared to theoretical predictions. Secondary instability and cyclic breakup are also evidenced in the elliptic geometry.     

A review of commonly used analytical and empirical formulae for predicting sound diffracted by a thin screen

This paper reviews some useful analytical and empirical formulae that are used for the calculation of sound diffracted by a barrier. A brief historic overview of the study of spherical waves diffracted by a rigid half plane is presented also. The physical principles of sound diffraction by a thin plane are explained. The mathematical expressions are cast in a convenient form for ease of numerical implementation. Accurate analytical solutions are expressed in terms of standard mathematical functions that can be computed readily. Among the approximate solutions quoted, quite a few empirical formulations are adequate for most engineering purposes. The information presented in this paper should also be helpful for those who are interested in the study of sound diffracted by a barrier in a room or in a long industrial space.     

杆的离散系统的某些混合型振动反问题

研究杆的离散系统的混合型振动反问题,即由给定的部分频谱数据和部分模态数据构造一个杆的离散系统的刚度矩阵和质量矩阵.提出3个此类反问题,给出反问题的解法,讨论反问题的解的存在条件,给出相应的计算实例,并分析这类反问题的潜在价值.     

Effect of magnetic field on freely moving superconductors in the audio band

The results of studying the magnetomechanical effects in classical superconductors are analyzed. The energy losses are determined, and a number of macroscopic parameters are calculated using a developed model. The studies of superconductors by the method of rotation of a body suspended without contact are described. The results obtained are analyzed, and the values of some parameters are determined.     

Interference nanolithography with a UV laser

The sensitivity and resolution of a photoresist composed of a two-layer (polymer-metallic indium) film are measured. 2D masks used to create nanodimensional metallic and insulating islands on a silicon substrate are prepared by direct laser action. Conditions are found for preparing submicron periodic structures on TiO₂ films that are applied on a glass substrate by the sol-gel technology. Optical properties of these arrays are measured, and it is shown that they can be used for exciting plane electromagnetic waves.     

The a Posteriori Error Estimates for Chebyshev-Galerkin Spectral Methods in One Dimension

In this paper, the Chebyshev-Galerkin spectral approximations are employed to investigate Poisson equations and the fourth order equations in one dimension. Meanwhile, $p$-version finite element methods with Chebyshev polynomials are utilized to solve Poisson equations. The efficient and reliable a posteriori error estimators are given for different models. Furthermore, the a priori error estimators are derived independently. Some numerical experiments are performed to verify the theoretical analysis for the a posteriori error indicators and a priori error estimations.     

Phase diagram of a traffic roundabout

We propose a simple cellular automaton model to study the traffic dynamics in a roundabout. Both numerical and analytical results are presented. We are able to obtain exact solutions in the full parameter space. Exact phase diagrams are derived. When the traffic from two directions mixed, there are only five distinct phases. Some of the combinations from naive intuition are strictly forbidden. We also compare the results to a signaled intersection.     

Air-lubrication of magnetic disk sliders

Steady-state and dynamic flying of a self-acting magnetic disk slider over a hard disk are considered. Some tasks for computations are formulated and the possibilities of developed numerical codes are illustrated. Numerical results of dynamic flying over a disk surface with an obstacle are in agreement with experimental data.     

时域飞秒散斑的特性与测量

阐述了飞秒激光脉冲在随机介质传播过程中产生时域散斑的原理,并对时域飞秒散斑进行了测量. 时域飞秒散斑的产生是飞秒脉冲在随机介质中经历多重散射形成的随机干涉现象在时域的体现. 初步讨论了时域散斑的统计特性并给出了相应的实验结果. 关键词： 时域散斑 飞秒脉冲 随机介质     

Inelastic processes in the interaction of an atom with an ultrashort electromagnetic pulse

Electron transitions occurring during the interaction of a heavy relativistic atom with a spatially inhomogeneous ultrashort electromagnetic pulse are considered by solving the Dirac equation. The corresponding transition probabilities are expressed in terms of known inelastic atomic form factors, which are widely used in the theory of relativistic collisions between charged particles and atoms. By way of example, the inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The probabilities of ionization and production of a bound-free electron-positron pair on a bare nucleus, which are accompanied by the formation of a hydrogen-like atom in the final state and a positron in the continuum, are calculated. The developed technique makes it possible to take into account exactly not only the spatial inhomogeneity of an ultrashort electromagnetic pulse, but also the magnetic interaction.     

Properties of planar Nb/α-Si/Nb Josephson junctions with various degrees of doping of the α-Si layer

The properties of Nb/??-Si/Nb planar Josephson junctions with various degrees of doping of the amorphous silicon layer are experimentally studied. Tungsten is used as a doping impurity. The properties of the Josephson junctions are shown to change substantially when the degree of doping of the ??-Si layer changes: a current transport mechanism and the shape of the current-voltage characteristic of the junctions change. Josephson junctions with SNS-type conduction are formed in the case of a fully degenerate ??-Si layer. The properties of such junctions are described by a classical resistive model. Josephson junctions with a resonance mechanism of current transport through impurity centers are formed at a lower degree of doping of the ??-Si layer. The high-frequency properties of such junctions are shown to change. The experimental results demonstrate that these junctions are close to SINIS-type Josephson junctions.     

The influence of contacts on the VA-characteristics of thin-layfr systems with amorphous semiconductors

In the paper the VA-characteristics of a sandwich-type thin-layer system with amorphous semiconductor are discussed, where ohmic and non-ohmic contacts are considered. The VA-characteristics are derived which, in the case of ohmic contacts, lead to a linear dependence of the current on voltage and, in the case of non-ohmic contacts (where barriers are supposed), to a nonlinear dependence, so that VA-characteristics with negative resistance are possible as well. These VA-characteristics are compared with the experimental ones, measured on thin-layer metalamorphous Si-metal and metal-amorphous CdTe-metal structures.