Wave scattering by a strongly elongated irregularity

We consider the problem of single scattering by a strongly elongated irregularity which is located in the near zone with respect to the coordinate along its major axis and in the far zone with respect to the transverse coordinates. Expressions describing the scattered-wave field are obtained by applying the stationary-phase method for integration over the longitudinal coordinate in the formula for single scattering. We present some results of modeling of the scattered-wave intensity based on the obtained formula as applied to meteor-burst propagation of radio waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 12, pp. 1057–1065, December, 2004.     

Diffraction by a strongly elongated body of revolution

A high-frequency acoustic field in a penumbra domain on the surface of a strongly elongated body is investigated. A new asymptotic formula expressing the field in the form of inverse Mellin transform of an expression containing Whittaker functions is derived. Presented numerical results show that the increase of the transverse curvature of the body increases field attenuation on a hard surface and decreases it on an acoustically soft surface. This effect agrees to previous results.     

Calculation of diffraction by strongly elongated bodies of revolution

An approach to construct approximations for the diffracted field on the surface of strongly elongated bodies is suggested. The approach is based on high-frequency asymptotic decomposition which is constructed under the supposition that transverse curvature of the surface is asymptotically large. Leading order terms of asymptotic decompositions for the fields diffracted by spheroid, one-sheeted and two-sheeted hyperboloids and on narrow cone are derived.     

Coherent Brillouin spectroscopy in a strongly scattering liquid by picosecond ultrasonics

In a modification of a picosecond ultrasonic technique, a short acoustic pulse is launched into a liquid sample by a laser pulse absorbed in a semitransparent transducer film and is detected via coherent Brillouin scattering of a time-delayed probe pulse. With both excitation and probing performed from the transducer side, the arrangement is suitable for in vivo study of biological tissues. The signal is collected from a micrometer-thick layer next to the transducer and is not affected by the diffuse scattering of probe light deeper in the sample. The setup, utilizing a 33 nm thick single crystal SrRuO(3) transducer film, is tested on a full fat milk sample, with 11 GHz acoustic frequency recorded.     

Sound scattering by a body in a planar layered waveguide

In the framework of the theory of integral equations, the problem of sound diffraction by pressure-release and acoustically stiff inhomogeneities of an oceanic waveguide is considered. The iteration method is used to obtain recurrent relations for the surface currents. The relations describe the diffraction process as a sequence of interactions between the body and the waveguide boundaries (multiple reflections). The validity condition for the zero-order approximation, which ignores multiple reflections, is formulated and physically justified.     

Anisotropic diffusion of light in a strongly scattering material

Light transport in a strongly scattering, strongly anisotropic material is studied experimentally using both static and time-resolved techniques. Both the static and the dynamic results are well characterized by a diffusion equation with an anisotropic diffusion tensor and a scalar absorption term. Light diffuses 4.0 times faster along the uniaxial axis of the material compared with diffusion in the orthogonal directions.     

Sonoluminescent tomography of strongly scattering media

A novel optical imaging technique called sonoluminescent tomography was developed for cross-sectional imaging of strongly scattering media noninvasively. Sonoluminescence, which was generated internally in the medium by cw ultrasound, was used to produce a two-dimensional image of an object embedded in a scattering medium by means of raster scanning the medium. The image had a high contrast and good spatial resolution. The spatial resolution was limited by the focal-spot size of the ultrasound, and one could improve the resolution by tightening the focus. This inexpensive imaging technique has potential applications in medicine and other fields related to scattering media.     

Diffraction of a plane wave incident at a small angle to the axis of a strongly elongated spheroid

The high-frequency acoustic field in the half-shadow region on the surface of a strongly elongated body of rotation is studied. The asymptotic formulas obtained earlier for axial incidence of a plane wave are generalized to the case of incidence of a wave at a small angle to the body axis. The results of calculations are presented. Analysis has been performed on how the angle of incidence and the parameter describing the degree of elongation of the body affect the character of the field distribution over the surface.     

Dispersion of photon density waves in a strongly scattering medium

In the approximation of the radiation transfer equation, the damping decrement and the velocity of photon density waves propagating in a strongly scattering medium are studied as functions of the increasing modulation frequency of the source of radiation up to the microwave frequency range. The results obtained for microwave frequencies are found to be in qualitative agreement with those derived from the Bethe-Salpeter equation.     

Study of the scattering of nonlinearly interacting plane acoustic waves by an elongated spheroid

The scattering of nonlinearly interacting plane acoustic waves on a rigid elongated spheroid is considered. The foci of the spheroid coincide with foci of the spheroidal coordinate system. The method of successive approximations is used to obtain the solutions to the inhomogeneous wave equation in the first and second approximations. Asymptotic expressions are offered for the components of the total acoustic pressure of the difference frequency wave, and the scattering diagrams for these components are presented.     

Numerical models of a far turbulent wake of an elongated body of revolution

The work presents a comparison of numerical models of a far turbulent wake of a towed elongated body of revolution in a homogeneous fluid: model based on the direct numerical simulation, and two semi-empirical models involving the equation of the turbulence energy balance. Computational results demonstrate the self-similarity of the decay and agree with known experimental data.     

High-frequency ultrasound scattering from microspheres and single cells

Assessing the proportion of biological cells in a volume of interest undergoing structural changes, such as cell death, using high-frequency ultrasound (20-100 MHz), requires the development of a theoretical model of scattering by any arbitrary cell ensemble. A prerequisite to building such a model is to know the scattering by a single cell in different states. In this paper, a simple model for the high-frequency acoustic scattering by one cell is proposed. A method for deducing the backscatter transfer function from a single, subresolution scatterer is also devised. Using this method, experimental measurements of backscatter from homogeneous, subresolution polystyrene microspheres and single, viable eukaryotic cells, acquired across a broad, continuous range of frequencies were compared with elastic scattering theory and the proposed cell scattering model, respectively. The resonant features observed in the backscatter transfer function of microspheres were found to correspond accurately to theoretical predictions. Using the spacing of the major spectral peaks in the transfer functions obtained experimentally, it is possible to predict microsphere diameters with less than 4% error. Such good agreement was not seen between the cell model and the measured backscatter from cells. Possible reasons for this discrepancy are discussed.     

Coherence-gated wave-front sensing in strongly scattering samples

We show that, by coherence-gate rejection of out-of-focus light, wave-front distortions can be measured in the presence of a scattering background that is dominant by several orders of magnitude. Applications are expected for multiphoton and confocal laser-scanning microscopy.     

Spectral and scattering theory for a class of strongly oscillating potentials

Following a recent investigation by Pearson [23] on scattering theory for some class of oscillating potentials, we consider the Schrödinger operator inL ²(IR ⁿ ) given by:H =-e ^?U?·e ^2U ?e ^?U +e ^?2U (F + (?·Q)). HereU andF are real functions ofx, andQ is a IR ⁿ -valued function ofx, such that:

1. U is bounded, and the local singularities ofF andQ ² are controlled in a suitable sense by the kinetic energy,
2. U, Q, andF tend to zero at infinity faster than ‖x‖^?1. We defineH by a method of quadratic forms and derive the usual results of scattering theory, namely: the absolutely continuous spectrum is [0, ∞) and the singular continuous spectrum is empty, the wave operators exist and are asymptotically complete. This enlarges the class of already studied strongly oscillating potentials that give rise to the scattering and spectral properties mentioned above.

     

Propagation and scattering of waves in a strongly nonuniform nonabsorbing medium

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 3, pp. 307–313, March, 1989.     

Detecting the amplitude mode of strongly interacting lattice bosons by Bragg scattering

We report the first detection of the Higgs-type amplitude mode using Bragg spectroscopy in a strongly interacting condensate of ultracold atoms in an optical lattice. By the comparison of our experimental data with a spatially resolved, time-dependent bosonic Gutzwiller calculation, we obtain good quantitative agreement. This allows for a clear identification of the amplitude mode, showing that it can be detected with full momentum resolution by going beyond the linear response regime. A systematic shift of the sound and amplitude modes' resonance frequencies due to the finite Bragg beam intensity is observed.