Localisation in disordered systems—I: The disordered spectrum

Starting from a definition of the localisation-delocalisation of electronic, wavefunctions in disordered systems based on the nature of the disordered spectrum, a delocalisation criterion identical to that of Abou-Chacraet al is recovered. The new derivation on provides a very clear picture of the mechanism of delocalisation and brings out its incompatibility with the normalisability of wavefunctions at the transition.     

Estimation of the mobile user position in the cellular communication system in a multipath environment of signal propagation

We consider the problem of locating a mobile object (user) in the cellular communication system on the basis of the triangulation method and the Gaussian multipath-channel model under urban conditions of signal propagation. The probability density function of the maximum likelihood estimate of Cartesian coordinates of the user is found if two or three base stations arbitrarily located with respect to one another are used. It is shown that the user-locating error depends on the distance between the base stations, mutual location of the user and the base stations, and the variance of the user-bearing estimation error for each base station. In this case, using the third base station significantly improves the user-locating accuracy. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 2, pp. 162–170, February 2008.     

A two-beam laser triangulation for measuring the position of a moving object

A two-beam laser triangulation method has been proposed to measure the position of a moving object. The method uses two parallel laser beams to judge the moving direction of an object, allowing us to track it and measure its positions. An uncertainty of 0.2 mm for a measurement range of 50 mm has been obtained. This tracking measurement capability is useful in the calibration of the position of a moving robot arm.     

Magnon propagation in a nanometric magnetic cluster chain: Effects of additional clusters near the chain

A fundamental understanding of nanoscaled materials has become an important challenge for any technical applications. For magnetic nanoparticles, the investigations are in particular stimulated by the magnetic storage devices. In this paper we present a theory of the magnon propagation in a nanometric chain and of the effects of neighbor magnetic clusters. We show that with an appropriate choice of the additional clusters, it is possible to control the transmission spectrum of the magnons. The additional clusters can also create a resonator with zero of transmission. This model could be useful to construct device to transmit or stop the magnon signal.     

Modeling three-dimensional propagation in a continental shelf environment

An acoustic propagation model is applied to predict measurements of three-dimensional (3-D) effects recorded off the southeast coast of Florida. The measured signal is produced by a low frequency source that is towed north parallel to the shelf from a fixed receiving array. The acoustic data show the direct path arrival at the bearing of the tow ship and a second refracted path arrival as much as 30° inshore of the direct arrival. Notably, the refracted arrival has a received level more than 25 dB greater than that of the direct arrival. A geoacoustic model of the environment is created to explain the data. It is shown that the topography of the seafloor plays the largest role in controlling horizontal refraction effects, whereas the range-dependent sediment properties have the most influence on the received level. The modeling approach is based on a 3-D adiabatic mode technique in which the horizontal refraction equation is solved using a parabolic equation in Cartesian coordinates. A modal decomposition of the field provides insight into the variability in the arrival angle and received level of the measured signal.     

Radiative forces acting on point sources moving in a stratified fluid

Both components of the total radiative force acting on uniformly moving mass sources in a stratified incompressible fluid are calculated. These forces are related to the emission of internal gravity waves. One component of the radiative force is directed opposite to the direction of motion. This is the well-known wave drag force. Different useful representations of this component are derived for several typical point sources (monopole, dipole, and others). The other component, directed perpendicular to the direction of the motion, is calculated for the first time. The results obtained are extended to the case of rotating media, where internal inertial-gravity waves exist. Zh. éksp. Teor. Fiz. 112, 507–523 (August 1997)     

Light propagation in a weak gravitational field of a stochastic system of pointlike sources

Trajectories of light rays in a gravitational field created by a homogeneous distribution of pointlike masses are considered in the framework of General Relativity. A method of approximate computation of statistical characteristics of such trajectories is suggested, with the accuracy up to first order in the gravitational constant. The estimates of the shift in the direction of a light ray and of the change in the angular coordinates of the light source are obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 79–83, December, 1986.     

Love-type wave propagation in a pre-stressed viscoelastic medium influenced by smooth moving punch

In the present paper, a mathematical model studying the effect of smooth moving semi-infinite punch on the propagation of Love-type wave in an initially stressed viscoelastic strip is developed. The dynamic stress concentration due to the punch for the force of a constant intensity has been obtained in the closed form. Method based on Weiner–hopf technique which is indicated by Matczynski has been employed. The study manifests the significant effect of various affecting parameters viz. speed of moving punch associated with Love-type wave speed, horizontal compressive/tensile initial stress, vertical compressive/tensile initial stress, frequency parameter, and viscoelastic parameter on dynamic stress concentration due to semi-infinite punch. Moreover, some important peculiarities have been traced out and depicted by means of graphs.     

Spatial unmasking of nearby speech sources in a simulated anechoic environment

Spatial unmasking of speech has traditionally been studied with target and masker at the same, relatively large distance. The present study investigated spatial unmasking for configurations in which the simulated sources varied in azimuth and could be either near or far from the head. Target sentences and speech-shaped noise maskers were simulated over headphones using head-related transfer functions derived from a spherical-head model. Speech reception thresholds were measured adaptively, varying target level while keeping the masker level constant at the "better" ear. Results demonstrate that small positional changes can result in very large changes in speech intelligibility when sources are near the listener as a result of large changes in the overall level of the stimuli reaching the ears. In addition, the difference in the target-to-masker ratios at the two ears can be substantially larger for nearby sources than for relatively distant sources. Predictions from an existing model of binaural speech intelligibility are in good agreement with results from all conditions comparable to those that have been tested previously. However, small but important deviations between the measured and predicted results are observed for other spatial configurations, suggesting that current theories do not accurately account for speech intelligibility for some of the novel spatial configurations tested.     

Green's function estimation using secondary sources in a shallow water environment

This work provides a new way to measure the Green's function between two points in an acoustic channel without emitting a pulse by any of the two points. The Green's function between A and B is obtained from a set of secondary sources in the guide by averaging either the correlation or the convolution of the signals received in A and B. A theoretical approach based on mode propagation in a monochromatic regime is presented. Results are then extended to the time domain. Estimation of the Green's function is performed numerically in a range-independent and a range-dependent environment. Application to discreet acoustic communications is discussed.     

Radiation of extended electromagnetic sources moving near the surface of a chiral medium

Current-carrying and charged filaments moving in vacuum along the plane surface of a semiinfinite chiral medium are investigated. The electromagnetic fields and energy losses due to radiation are found in both cases. The dependence of the radiation losses on the chirality constant is given. State Electrotechnical University of St. Petersburg, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 7, pp. 866–873, July, 1998.     

Ray dynamics of the propagation of sound in nonuniform moving media

This paper presents a new ray theory for the propagation of sound waves in nonuniformly moving media. It is found that the ray equations in weakly inhomogeneous and slowly moving media are analogous to the equations of motion of charged particles in nonuniform electric and magnetic fields. The adiabatic approximation is used to study the problem of the propagation of sound rays in a model of near-ocean-bottom waveguide with horizontal flow and slowly varying parameters along the direction of propagation of the wave. A general formula is derived that describes the transverse displacement of the trajectory of the ray relative to the direction of propagation of the wave.     

次声波在非均匀运动大气中非线性传播特性的研究

基于有限时域差分方法将大气中近似到二阶的非线性波动方程进行离散化,得到了数值模拟所采用的差分方程. 在此基础上,对线阵列辐射的脉冲声波在非均匀运动大气中的垂直和斜向传播进行了二维数值模拟,模拟了武汉地区(114:20°E, 30:37°N)在夏季和冬季UT=29000 s时开始传播的脉冲声波在不同时刻的声压分布. 模拟时通过采用Msise00和HWM93 两个大气模型,考虑了由于大气温度和密度变化以及大气风场存在所引起的大气不均匀性和运动性. 通过研究上述两季有风与无风条件下的声压差值p_r,可以发现:风场对次声波在传播中声压分布的影响较大;由于不同季节和不同传播距离上"有效声速"的不同,导致了两季p_r分布波形存在差异;风场对声波非线性传播的影响要远大于其对线性传播的影响. 关键词： 次声波传播 非均匀运动大气 有效声速