光在超声速湍流边界层中的传输

采用数值方法分析超声速边界层流场对光传输的影响,并根据光波的变化对流场特征进行分析.用法福尔质量加权平均N-S方程及两方程湍流模型求解三维超声速平板湍流边界层流动;光在流场中的传输采用傍轴近似光波传输方程描述,用相屏法和快速傅里叶变换(FFT)技术求解.利用穿越流场的光波光强和相位的改变,直观分析光波畸变和流场的部分特征信息.     

Hydromagnetic Instabilities in a Nonuniformly Rotating Layer of an Electrically Conducting Nanofluid

Journal of Experimental and Theoretical Physics - The stability of magnetized flows of a nonuniformly rotating layer of an electrically conducting nanofluid is investigated with regard to the...     

Light Propagation through Weakly Absorbing Layers of Dielectric Cube-Shaped Particles

Light propagation through ensembles of dielectric particles with various packing density is studied by the method of physical modeling in the SHF range. Monolayers and multilayers of weakly absorbing cube-shaped particles with the refractive index n = 1.5 are investigated. Particle dimensions are comparable to the incident radiation wavelength. Dependences of the transmittance T and the scattering efficiency factor Q on the diffraction parameter are obtained for ensembles of particles with various overlap factors . For monolayers of particles, the effect of an enhanced transmittance with increasing packing density of particles is observed. Conditions are specified at which the monolayer transmittance is equal to zero. It is shown that the Mie formulas, derived for spherical particles, can be used to calculate the optical characteristics of an ensemble of particles with chaotic orientation of particle sides, if the diameter of an equivalent sphere is set equal to the cube edge length multiplied by a correction factor of 1.15. Transition to an ordered orientation of cube-shaped particle sides leads to increase in the scattering efficiency factor for > 2.     

Propagation of Perturbations in a Boundary Layer under Strong Hypersonic Interaction

Doklady Physics - Nonstationary processes in a hypersonic boundary layer are studied. A phase shift by propagation of perturbations upstream was found caused by a finite upstream propagation...     

Finite-Difference Time-Domain Analysis of Wave Propagation in a Thin Plasma Layer

The propagation property of an electromagnetic wave in with the finite-difference time-domain method. The effects a thin plasma layer at high pressure is investigated of the non-uniformity of plasma distribution, and the frequency of incident wave on the propagation property of the electromagnetic wave are discussed. Numerical results indicate that the phase shift and the reflectivity of wave are sensitive to plasma density distribution, and reflectivity is lower at the middle band of frequency for different plasma distributions.     

Propagation of gaseous detonation across inert layers

In rotating detonation engines and explosion accidents, detonation may propagate in an inhomogeneous mixture with inert layers. This study focuses on detonation propagation in a stoichiometric H₂/O₂/N₂ mixture with multiple inert layers normal to the detonation propagation direction. One- and two-dimensional simulations considering detailed chemistry are conducted. The emphasis is placed on assessing the effects of inert layer on detonation reinitiation/failure, detonation propagation speed, detonation cell structure and cell size. Specifically, the inert layer thickness and the spacing between two consecutive inert layers are varied. Either detonation reinitiation or failure across the inert layers is observed. It is found that successful detonation reinitiation occurs only at relatively small values of the inert layer thickness and spacing. For each given value of the inert layer spacing, there is a critical inert layer thickness above which detonation fails after crossing the inert layers. This critical inert layer thickness is found to decrease as the inert layer spacing increases. The detailed process of detonation reinitiation across the inert layers is analyzed. The interaction between the transverse shock waves is shown to induce local autoignition/explosion and eventually over-driven detonation development in the reactive layer. The averaged detonation propagation speed in the inhomogeneous mixture is compared to the CJ speed and very good agreement is achieved. This indicates that the inert layer does not affect the detonation propagation speed once successful detonation reinitiation happens. Unlike the detonation speed, the detonation cell structure and cell size are greatly affected by the inert layer results. For the first time, large cellular structure with size linearly proportional to the inert layer spacing is observed for detonation propagation across inert layers. Besides, a double cellular structure is observed for relatively large spacing between inert layers. The formation of double cellular structure is interpreted.     

Propagation of radio waves across a velocity discontinuity in a zero temperature plasma

A non-relativistic treatment of the investigated effect is given. It is shown that a transverse wave incident on the interface of a velocity discontinuity generates reflected and transmitted waves. The intensities of reflected and transmitted electric fields are calculated.The author's thanks are due to Mrs. E. Dosoudilová for executing the numerical computations.     

超声速湍流边界层中激光传输的积分法

采用Born近似的Maxwell方程组积分解形式较少应用于气动光学数值计算, 其困难在于对该方程组的离散化数值计算.而结合GCV-FFT(Generalized convolution by fast Fourier transform)方法, 在自由空间传播的Rayleigh-Sommerfeld衍射方程数值计算可以达到比较高的精度.通过对Green函数及采样系数的修正, 积分方法可以用于气动光学现象的数值模拟.通过在超声速湍流边界层中光束传输的数值计算, 可以看到一些气动光学效应, 如光束偏移破碎等, 可以用修正GCV-FFT+数值积分的方法得到良好的模拟.现有的方法可以给出更接近物理本质的定量结果.      

Influence of Magnetic-Field and Plasma-Density Inhomogeneities on the Propagation and Amplification of Radio Waves in the Solar Corona

We analyze the maser generation of millisecond spikes of the solar radio emission at the cyclotron resonance of a fast extraordinary wave in an inhomogeneous medium. It is shown that the magnetic-field inhomogeneity with parameters typical of the solar corona drastically reduces the time of electromagnetic-wave amplification, which is explained by the fact that these waves leave the resonance region in the wave-vector space. As a result, an unstable electron distribution can be formed. The efficient generation of radiation becomes possible only in such local regions where the influence of the magnetic-field inhomogeneity is compensated by small-scale inhomogeneities of the plasma density with typical scales ranging from tens to hundreds of kilometers. Taking the effect of inhomogeneous medium into account allows us to explain spatial and temporal characteristics of the spikes.     

大气对流边界层光传输的实验室模似

利用湍流池模拟大气对流边界层的光传输 ,同时测量了到达角起伏和光路上的温度脉动。结果表明 ,在混合层的上部 ,对数温度谱偏陡 ,和大气中的观测结果一致 ,到达角起伏谱也偏陡 ,但到达角起伏谱曲线反映了湍流在小尺度范围内具有各向同性的特征 ,此时利用温度脉动方法得到的折射率结构常数小 ;当边界层顶部逆温层消失 ,发展为完全对流状态时 ,温度谱幂率等于“ - 5 3” ,到达角起伏谱幂率等于“ - 8 3” ,两种方法测量得到的折射率结构常数一致。     

Influence of Coating Layer on Acoustic Wave Propagation in a Random Complex Medium with Resonant Scatterers

We investigate the influence of coating layer on acoustic wave propagation in a dispersed random medium consisting of coa.ted fibers.In the strong-scattering regime, the characteristics of wave scattering resonances are found to evolve regularly with the properties of the coating layer.By theoretical calculation,frequency gaps are found in acoustic excitation spectra in a random medium.The scattering cross section results present the evolution of scattering resonances with the properties of the coating layer,which offers a good explanation for the change of the frequency gaps.The velocity of the propagation quasi-mode is also shown to depend on the filling fraction of the coating layer.We use the generalized coherent potential-approximation approach to solve acoustic wave dispersion relations in a complicated random medium consisting of coating-structure scatterers.It is shown that our model reveals subtle changes in the behavior of the acoustic wave propagating quasi-modes.     

Reflection of Light by a Hyperbolic Metamaterial Layer in a Case of Propagation of Special Inhomogeneous Waves in It

Optics and Spectroscopy - The boundary problem of reflection of electromagnetic waves by a hyperbolic metamaterial layer under conditions of total reflection from the boundary with this layer in...     

Diffusion in a Weakly Random Hamiltonian Flow

We consider the motion of a particle governed by a weakly random Hamiltonian flow. We identify temporal and spatial scales on which the particle trajectory converges to a spatial Brownian motion. The main technical issue in the proof is to obtain error estimates for the convergence of the solution of the stochastic acceleration problem to a momentum diffusion. We also apply our results to the system of random geometric acoustics equations and show that the energy density of the acoustic waves undergoes a spatial diffusion.     

Random Walk Weakly Attracted to a Wall

We consider a random walk X _n in ℤ₊, starting at X ₀=x≥0, with transition probabilities

Weakly singular perturbations of a discrete spectrum

We consider weakly singular perturbations ¦x¦^–(0<<2) of an even restoring potential. We compute the matrix elements of the perturbation together with the additional point potential associated with the perturbation. It is shown that even for unperturbed wave functions, the matrix elements exist when 0 < < 3/2. The series for the Rayleigh-Schrödinger coefficients converge in all orders for the same interval in , regardless of the form of the restoring potential. For odd states, the matrix elements of the perturbation exist when 0 < < 3, while estimates for the Rayleigh-Schrödinger coefficients give the boundary = 2.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 14–18, June, 1989.     

An Analysis of Deformations during Wave Propagation through the Contact Layer of Elastic Media

Russian Physics Journal - The stress-strain state at the interface between elastic media, which represents a contact layer characterized by the size and a set of physical-mechanical parameters, is...     

Anomalies of Radiation Absorption and Superluminal Propagation of light: II. A Layer of a Periodic Medium with a Helical Structure

The features of superluminal propagation of light through a layer of a helical periodic medium (HPM) are investigated and the group velocity is calculated. Multilayer systems with a layer of an HPM that provide superluminal propagation of light over large distances with compensation of losses upon light transmission through the system are considered. The features of radiation absorption in a layer of an HPM are considered. Effects of anomalously high and anomalously low absorption are found. It is shown that these effects are caused by an increase (decrease) in the density of light energy in the layer and by changes in the group velocity. The possibility of experimental observation of the effects discovered is discussed.     

Search for a Magnetic-Field Dependence of the Interaction of the Nuclear Quadrupole Moment with the Electric-Field Gradient

It is argued that the nuclear quadrupole–electric field gradient (EFG) interaction is, in principle, dependent on the presence of a magnetic fieldB. A rough estimate of the size of this effect yields 10⁻⁴in fields up to 10 T. However, if the site symmetry of the nucleus in question includes time-reversal symmetry, the linear dependence of the EFG onBvanishes. In diamagnetic compounds, time-reversal symmetry is violated only by the presence of nuclear spins. In such compounds, the dominant dependence of the EFG onBshould be quadratic and should be described by a fourth-rank tensor. In ferro- and antiferromagnetic compounds time-reversal symmetry is strongly violated and a linear dependence of the EFG onB, described by a third-rank tensor, is expected. A search for a magnetic field dependence of the EFG was carried out by measuring the quadrupole coupling constants (QCCs) of the²⁷Al and¹⁴N nuclei in corundum and sodium nitroprusside (SNP) by pure NQR, and by NMR in fields of 6.3 and 11 T. These diamagnetic compounds were selected because previous measurements, done in different fields, yielded differing results for the QCCs. A new technique for measuring QCCs by NMR is introduced that circumvents the necessity of precisely orienting the sample crystals. For the QCCs of both the²⁷Al and¹⁴N nuclei in corundum and SNP, respectively, a precision of distinctly better than 10⁻⁴is reached. The results obtained in 0, 6.3, and 11 T fields fully agree with each other which means that, in fields up to 11 T, any possible field dependence of the QCCs is smaller than 10⁻⁴. These results confirm that in diamagnetic compounds a linear dependence of QCCs onBis largely suppressed.     

Weibel Mechanism of Magnetic-Field Generation in the Process of Expansion of a Collisionless-Plasma Bunch with Hot Electrons

Radiophysics and Quantum Electronics - We perform qualitative physical analysis and particle-in-cell two-dimensional numerical simulation of the Weibel mechanism of magnetic-field generation due to...