Diffusing-wave spectroscopy in randomly inhomogeneous media with spatially localized scatterer flows

Multiple scattering of laser radiation in a randomly inhomogeneous turbid medium with a spatially localized flow of particles is studied. The time autocorrelation function of backscattered light is calculated for the case of a laminar flow of scatterers in a cylindrical capillary embedded in the medium. A new method is proposed and tested experimentally for determining the position of the dynamic region and the dominant form and characteristic velocity of the particle motion there. Zh. éksp. Teor. Fiz. 113, 1213–1222 (April 1998)     

Horseshoe vortices in inhomogeneous flows

The formation of a horseshoe-shaped vortex from an initial straight cylindrical vortex occurring in the viscous layer of a retarding fluid flow in a channel with a nonuniform cross section is studied experimentally. The spatial bends of the vortex filament and the effect of the ambient fluid pressure first form an arch with supports at the bottom of the channel, then a horseshoe-shaped vortex, and finally a circular vortex with the destruction of the supports.     

Diffusion in inhomogeneous media

The problem is to establish the correct diffusion equation in a medium that is inhomogeneous and whose temperature also varies in space. As a special model we study particles whose phase space distribution obeys Kramers' equation with a generalized collision operator. In the usual limit of strong collisions a diffusion equation is obtained. This equation contains additional drift terms, which depend on the form of the collision operator. They cannot be expressed as a mobility and a diffusion coefficient, unless the decay law of the velocity happens to be linear. Conclusion: no universal form of the diffusion equation exists, but each system has to be studied individually.Dedicated to Professor Harry Thomas on the occasion of his 60th birthday     

Radio-wave tomography of inhomogeneous media

Results of experimental investigations on radar sensing of inhomogeneous media and objects with the use of both superbroadband (from 0.5 to 17 GHz) multifrequency scanning and supershort nanosecond and subnanosecond radar pulses are considered. It is demonstrated that addition of angular and spatial scanning and subsequent synthesis of a large aperture allow a three-dimensional tomography of low-contrast inhomogeneities to be realized with a spatial resolution of about 1 cm. Examples are presented that confirm a high efficiency of the method for contactless tomography of the forest structure and detection and visualization of infantry mines below a rough sand surface. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 20–25, September, 2006.     

Optical properties of inhomogeneous media

A theory is presented for the optical properties of inhomogeneous media consisting of small particles in a continuous dielectric host. In contrast to the commonly used Maxwell-Garnett approach, our theory includes the dipole-dipole coupling between the randomly distributed particles. The pronounced disorder-induced broadening explains the large width of typical experimental absorption lines and thus resolved the long-standing discrepancy between measured spectra and the predictions of the Maxwell-Garnett model.     

Alfven-wave scattering in inhomogeneous media

Alfven-wave scattering by inhomogeneities of the permittivity tensor (r) is examined. The scattering index , phase velocity v*, and group velocity c* are calculated over the entire wavelength range. Asymptotic formulas for , v*, and c* are derived for long (as compared with scatterer size), short, and ultrashort wavelengths.Moscow Institute of Electronic Engineering. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 5, pp. 421–432, May, 1992.     

Surface-induced optical anisotropy of inhomogeneous media

We demonstrate that the presence of interfaces induces anisotropy in the optical properties of thin inhomogeneous layers. Several mechanisms are discussed that can control the properties of this surface-induced anisotropy. We found that the effective refractive indices for s- and p-polarized fields are different and depend on the thickness of the layer, concentration and optical properties of inclusions in the layer, and the angle of incidence.     

Sound amplification in inhomogeneous flows of nonequilibrium gas

The conditions of the acoustic instability of flows of thermodynamically nonequilibrium gas are determined. It is shown that the growth increments of the velocity, temperature, pressure, and density disturbances are different. When the Mach numbers are small, only the velocity and temperature disturbances grow along the flow.     

Oscillatory waves in inhomogeneous neural media

In this Letter we show that an inhomogeneous input can induce wave propagation failure in an excitatory neural network due to the pinning of a stationary front or pulse solution. A subsequent reduction in the strength of the input can lead to a Hopf instability of the stationary solution resulting in breatherlike oscillatory waves.     

Soliton control in inhomogeneous nonlocal media

In this paper, we have addressed a new way to achieve soliton control, such as compression (or broadening) and fission. More concretely, nonlocality management technique has been adopted, and different control purposes can be realized by controlling corresponding nonlocal parameter. Essentially, nonlocality management should be classified into nonlinearity management.     

Spatiotemporal solitons in inhomogeneous nonlinear media

We investigate the possibility of forming spatiotemporal solitons (optical bullets) in inhomogeneous, dispersive nonlinear media using a graded-index Kerr medium as an example. We use a variational approach to solve the multidimensional, inhomogeneous, nonlinear Schrödinger equation and show that spatiotemporal solitons can be stabilized under certain conditions. We verify their existence by means of a full numerical analysis and show that such solitons should be observable experimentally.     

Radiative transfer in stochastically inhomogeneous media

New radiative transfer theory is developed for stochastically inhomogeneous scattering media. The three-dimensional shapes and large scale (compared to the mean free path) structures of the media are modeled by stochastic interfaces separating regions of different scattering properties. The small scale fluctuations are characterized by a pair-correlation function. The radiative transfer equation is extended to include individual scattering and propagation probabilities of a ray for each subregion as well as the probability for a ray to cross the interface between two subregions. The propagation probability is found to depend on the entire preceding path of the ray; the present formulation accounts for the two previous scatterings. A new adding/doubling algorithm is developed to solve this problem numerically. Transmission through a cloud layer and backward scattering seem to be particularly sensitive to inhomogeneities.