Emission from a Rayleigh layer with irregular boundaries

A theory of microwave emission from an irregular layer of Rayleigh scatterers is developed by combining an existing matrix doubling method for volume scattering with the Kirchhoff method in surface scattering. Effects of the layer boundaries are illustrated by comparing layers with plane boundaries vs layers with rough top or bottom boundaries and irregular layers. It is found that the major effect of an irregular top layer boundary is to slow down the variation of the layer emission as a function of the nadir angle and the major effect of an irregular bottom boundary is to increase the level of the layer emission. Comparisons of the developed layer model with snow emission indicate the potential use of such models in data interpretation.     

不规则区域上并行求解Poisson方程

提出一种并行求解不规则区域上的Poisson方程方法,将不规则区域转化为带约束的三维结构网格表示,在该区域采用红黑排序并行求解Poisson方程.数值实验表明,方法可较好地解决不规则区域上的Poisson并行求解问题.同时评估了不规则区域对并行性能带来的影响.     

Does an irregular sequence of level spacings provide a new representation of quantum chaos?

The recent claim by Hirooka et al. that an irregular sequence of energy level spacings gives an unambiguous representation of quantum chaos is examined. It is shown that observation of an irregular sequence of spacings does not necessarily imply that the dynamics is chaotic.     

On a Modification of the Scintillation Method

We solve the problem of diffraction of fluctuating radiation by an optically thin irregular layer (phase screen) with developed turbulent structure. It is shown that in the case of diffraction of radiation with saturated fluctuations and a narrow-band frequency spectrum by a weakly turbulent moving phase screen, the measured frequency spectrum of intensity fluctuations in the observation plane allows one to obtain information on the form of the spectrum of irregularities of an optically thin irregular layer in a wide size range significantly exceeding the size of the first Fresnel zone. Similarly to the well-known phase method of diagnostics of randomly irregular media, the conventional scintillation method modified in such a way yields undistorted information on the form of the irregularity spectrum. However, in contrast to the phase method, it also allows one to obtain data on the drift velocity of irregularities in the studied irregular layer.     

Analysis of the diffracted wave from a volume hologram stored with an irregular pattern

The theoretical analysis for the diffracted wave from a volume hologram stored with an irregular pattern is presented. The relative diffraction efficiencies with respect to position and wavelength of readout wave are calculated by applying the Born approximation for light diffraction. The results are compared with experimental results and the effects of irregular pattern are discussed.     

Theory of interband optical absorption in a quasiclassical random field

Green's functions are used to study interband transitions in a quasiclassical (i.e. slowly varying in space) irregular field. It is assumed that the irregular field is random, i.e., the mean square of the fluctuation of the potential energy of an electron in such a field is much less than the width of the forbidden band. Explicit expressions are obtained for the coefficient of interband optical absorption for the case of an anisotropic irregular field and for the case when the irregular fields that act on electrons in the conduction and the valence band are different. As examples, we consider a fluctuation random field in ferroelectrics and a random field produced by long-wave acoustic lattice vibrations. The behavior of the tail of the optical absorption coefficient in ferroelectrics in the region of a phase transition is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 121–130, April, 1972.I am most grateful to V. L. Bonch-Bruevich for suggesting the subject and for his constant interest.     

Cycloid motions of grains in a dust plasma

Hypocycloid and epicycloid motions of irregular grains(pine pollen) are observed for the first time in a dust plasma in a two-dimensional(2D) horizontal plane. These cycloid motions can be regarded as a combination of a primary circle and a secondary circle. An inverse Magnus force originating from the spin of the irregular grain gives rise to the primary circle.Radial confinement resulting from the electrostatic force and the ion drag force, together with inverse Magnus force, plays an important role in the formation of the secondary circle. In addition, the cyclotron radius is seen to change periodically during the cycloid motion. Force analysis and comparison experiments have shown that the cycloid motions are distinctive features of an irregular grain immersed in a plasma.     

Correlation measurements on regular and irregular ionization waves in neon

The evolution from regular to fully irregular motion of the s variety of an ionization wave in neon is studied by space correlation measurements. The correlation functions clearly indicate the onset of strongly nonlinear interaction (by a change in the decay constant of correlation function) in the region of coherent wave motion, the transition to irregular wave motion (short distance correlation only) and the stochastic character of fully developed irregular wave motion (correlation only over a few wavelengths and a few periods).     

Bohmian mechanics to high-order harmonic generation

This paper introduces Bohmian mechanics (BM) into the intense laser-atom physics to study high-order harmonic generation. In BM, the trajectories of atomic electron in an intense laser field can be obtained with the Bohm--Newton equation. The power spectrum with the trajectory of an atomic electron is calculated, which is found to be irregular. Next, the power spectrum associated with an atom ensemble from BM is considered, where the power spectrum becomes regular and consistent with that from quantum mechanics. Finally, the reason of the generation of the irregular spectrum is discussed.     

MRI of uterine leiomyosarcoma

We report a case of a patient with uterine leiomyosarcoma. At MR imaging, the patient was found to have a bilobed uterine mass with two components. While the caudal portion of the mass had the MRI appearance of a simple leiomyoma, the cephalad component showed atypical degeneration with an irregular contour. Malignant degeneration of a leiomyoma was confirmed by operative and histologic examination. We conclude that malignant degeneration should be considered on MR images of any degenerated leiomyoma showing an irregular contour.     

Modeling and acoustic analysis of irregular sound enclosure by using Chebyshev-variational method

A modeling method for irregular sound enclosures was proposed based on the Chebyshev-variational theory. A rectangular space was first assumed to bound the irregular sound space and the sound pressure in the rectangular space expressed as a triple-Chebyshev series. Next, a coordinate transformation was performed and the Lagrangian functional of the irregular sound space obtained. Finally, the Lagrangian functional was solved under the Ritz method framework, and the enclosure's acoustic characteristic equation deduced and the eigenpairs obtained. The accuracy of the present method was validated according to agreement between the present results and finite element results for an enclosure with a curved surface.Furthermore, the acoustic characteristics of a trapezoidal enclosure and an enclosure with an inner groove were investigated. The results showed that the mode shapes of the trapezoidal sound space changed with increased inclination angle and the natural frequencies, except the first order, of the sound space with a rectangular inner groove decreased with increased groove depth.     

Two-frequency mutual coherence function for electromagnetic pulse propagation over rough surfaces

The propagation of a transient electromagnetic pulse over irregular terrain is considered. We model the wave propagation using the parabolic wave equation, which is valid for near-horizontal propagation. We model the effect of scattering from the rough terrain by introducing a surface-flattening coordinate transform. This coordinate transform simplifies the boundary condition of our problem, and introduces an effective refractive index into our wave equation. As a result, the problem of propagation over an irregular surface becomes equivalent to the problem of propagation through random media. The parabolic equation is solved analytically using the path integral method. Both vertically polarized and horizontally polarized signals are treated. Cumulant expansion is introduced to obtain an approximate expression for the two-frequency mutual coherence function. From the mutual coherence function, spatial and temporal dependence of the propagating signal can be determined. It can be shown that scattering from the irregular surface can cause broadening of the transient signal. This can have a significant impact on the performance of radio communication systems.     

Self-sustained oscillations in systems with delay under irregularly varying excitation conditions

A mathematical model of a system consisting of two coupled chaotic delay subsystems is presented. Instead of constant initial conditions in the form of a single impetus to excite the subsystems, continuous irregular oscillations are used that simulate intrinsic noise and continue acting on self-sustained oscillations after their excitation. An equation of an autonomous subsystem with regard to feedback variation is derived. It is shown that, when an autonomous subsystem is excited by irregular oscillations, chaotic motions become stochastic. In this case, the intensity of oscillations simulating intrinsic noise increases, suppressing self-sustained oscillations and providing the regenerative amplification of irregular oscillations. Interaction of coupled oscillations for identical and nonidentical subsystems is considered for the case of different noiselike initial conditions. It is found that interacting oscillations are not completely identical even if the parameters of the subsystems are the same.     

The effect of cross-channel synchrony on the perception of temporal regularity

Temporal models of pitch are based on the assumption that the auditory system measures the time intervals between neural events, and that pitch corresponds to the most common time interval. The current experiments were designed to test whether time intervals are analyzed independently in each peripheral channel, or whether the time-interval analysis in one channel is affected by synchronous activity in other channels. Regular and irregular click trains were filtered into narrow frequency bands to produce target and flanker stimuli. The threshold for discriminating a regular target from an irregular distracter click train was measured in the presence of an irregular masker click train in the target band, as a function of the frequency separation between the target band and a flanker band. The flanker click train was either regular or irregular. The threshold for detecting the regular target was 5-7 dB lower when the flanker was regular. The data indicate that the detection of temporal regularity (and thus, pitch) involves cross-channel processes that can operate over widely separated channels. Model simulations suggest that these cross-channel processes occur after the time-interval extraction stage and that they depend on the similarity, or consistency, of the time-interval patterns in the relevant channels.     

Statistical and receiver operating characteristic analysis of empirical spike-count distributions: quantifying the ability of cochlear nucleus units to signal intensity changes

Analytical methods from signal detection theory were applied in an effort to quantify the ability of cochlear nucleus (CN) units to signal changes in intensity. Of particular interest was the relation between this ability and the different patterns of discharge that characterize auditory neurons. Single-unit responses to best-frequency (BF) tone bursts were recorded from neurons in the gerbil cochlear nucleus, and empirical spike-count distributions were generated. The mean-to-variance ratios for regular units were generally larger than those of irregular units. Receiver operating characteristic (ROC) curves were generated from empirical spike-count distributions. The area under the ROC curve [P(A)] was computed and used to define the performance of an observer detecting whether or not a change in firing rate has occurred, thus signaling a change in intensity. For a given change in mean spike count, units characterized by regular interspike-interval (ISI) histograms typically gave larger P(A) values than did units characterized by irregular ISI histograms. In addition, onset units gave larger values of P(A) than did irregular units for a given change in mean spike count. These results suggest that regular and onset units are better able to signal intensity changes than are irregular units.     

DDA simulations of light scattering by small irregular particles with various structure

We present DDA investigations of light scattering by irregular particles whose size is comparable with wavelength. We consider four types of randomly irregular particles: strongly damaged spheres, rough-surface spheres, pocked spheres, and agglomerated debris particles. Each type of particle is generated with a well defined algorithm producing an ensemble of stochastically different particles that have a common origin. The different types of irregular particles produce different angular dependencies of intensity and linear polarization degree. Transformation of phase curves of intensity and polarization with changing size parameter for irregular particles tends to be more monotonic, unlike spheres. We find that the magnitude of the negative polarization branch (NPB) tends to shrink as particle absorption increases; whereas, the maximal value and position of the positive polarization branch tends to increase. The most frequently observed shape of the negative polarization at small phase angles is asymmetric with a shift of the minimum position towards the angle of polarization sign inversion. All types of considered irregular particles reveal such asymmetry at x<10. Symmetric negative polarization branches occur seldom. The necessary conditions for their appearance are a relatively large size parameter x?10 to 12 and low absorption.     

静电磁场不规则区域问题的小波插值Galerkin算法

讨论了用小波插值Galerkin方法(WIGM)求解椭圆型偏微分方程,特别是求解区域不规则时的问题.在归纳出WIGM一般形式的基础上,推导出该方法在Sobolev空间范数下的误差界限为C2-m.提出了一种解决不规则区域中静电磁场场分析问题的数值算法,其中选用对称插值尺度函数为基函数,它的对称性及其与平均插值尺度函数的关系可以在一定程度上降低数值求解的计算量.最后通过计算实例说明该算法的有效性.     

Theory of simple fluids near a structured surface

Convenient theoretical methods for calculating structure and thermodynamic properties of fluids near an irregular hard wall are developed. Using the diagrammatic expansion, we prove that: Firstly, a fluid system in contact with an irregular surface can be treated as two coupling fluids. The first one is defined by the studied fluid interacting with a planar hard wall. It is called the reference system. The second, which is referred to as the fictitious system, is confined to the surface cavities. Secondly, these developments can be used to find a self-consistent approximation.     

Rayleigh wave attenuation due to the scattering by two-dimensional irregularities of the walls of an empty borehole

Attenuation of the Rayleigh waves propagating along an irregular surface of an empty borehole is investigated. This problem generalizes the problem on the attenuation of Rayleigh waves by an irregular boundary of a half-space. The technique used to evaluate the attenuation coefficient is based on the perturbation method and the mean field method. As a result, an expression is obtained that relates the partial attenuation coefficients of the surface Rayleigh wave to the scattering by the irregular surface of an empty borehole into the bulk longitudinal and transverse waves (the R → P and R → S processes) and into the surface Rayleigh waves (the R → R processes). The frequency-dependent behavior of the partial attenuation coefficients is analyzed for different correlation functions of irregularities.