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1
Content available Monte Carlo based angular analysis of multiple scattered photons for underwater optical imaging
Li S., Wang R., Chen G.
Optica Applicata
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2018
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Vol. 48, nr 2
237--247
EN
Image contrast and visibility associated with underwater optical imaging systems are usually degraded by the absorbing and scattering effects of turbid waters. To improve the image contrast, laser-range-gate has been widely applied to underwater optical imaging systems. The work of Katsev et al. (Appl.Opt. 38(33), 1999, pp. 6849–6858) shows that the contrast of a shadow image is greater than that of the object image. The present paper outlines a Monte Carlo based simulation method of image formation for underwater optical imaging. It is found that the contrast of a shadow image varies with gate starting depths. The angular distribution of multiply scattered photons is obtained via semi-analytical models (Shengfu Li et al., Opt.Commun. 381, 2016, pp. 43–47). The simulated results show that increasing the gate starting depth can reduce the highly backscattered photons, thus can improve the image contrast.
2
Content available remote Surface effects on the wave propagation in composites with random dispersive parallel cylindrical nanofibers
Kong Z., Qiang F. W., Wei P. J., Tang Q.
Archives of Mechanics
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2015
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Vol. 67, nr 5
355--370
EN
The propagation of elastic waves in composites with randomly distributed parallel cylindrical nanofibers is studied. The non-classical boundary conditions on the surface of nanofibers are derived by using the surface elasticity theory. The scattering waves from an individual nanofiber are obtained by the plane-wave expansion method. These scattering waves from all nanofibers are summed up to obtain the multiple-scattering waves. The effective propagation constants (speed and attenuation) of coherent waves and the associated effective dynamical moduli of composites are evaluated numerically. Based on these numerical results, the influences of the surface effects on the effective dynamical properties of composites are discussed.
3
Content available Analytical description of frc subjected to transient loads
Weber W., Zastrau B. W.
Journal of Theoretical and Applied Mechanics
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2013
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Vol. 51 nr 1
183--194
EN
In many real-world applications, such as in civil engineering, non-periodic composite materials are used, whose dynamical behaviour is still not deeply understood, especially concerning its wave scattering properties. In this paper, the scattering of a transient non-plane elastic SH wave by an arbitrary arrangement of identical multi-layered and thus inhomogeneous obstacles is investigated. The obstacles are embedded in a homogeneous, isotropic, and linear elastic matrix of infinite extent. The solution procedure is analytical and will then be evaluated numerically for investigating a small material clipping of a real-world problem.
PL
W rzeczywistych obiektach, np. w inżynierii lądowej, zastosowanie znajdują materiały kompozytowe o strukturze nieperiodycznej. Dynamika takich elementów nadal pozostaje niedostatecznie rozpoznana, zwłaszcza w kontekście właściwości rozpraszania fal. W prezentowanej pracy omówiono problem rozpraszania przejściowych, niepłaskich fal sprężystości spolaryzowanych poziomo (typu SH) w dowolnym układzie identycznych, wielowarstwowych, i przez to niejednorodnych, ekranów tłumiących. Założono, że ekrany te zostały wbudowane w jednorodną, izotropową, liniowo-sprężystą osnowę o nieskończenie wielkich rozmiarach. Zaproponowano analityczne rozwiązanie problemu, które posłuży symulacjom numerycznym efektu słabego obcinania fali w materiale wybranego obiektu rzeczywistego.
4
Content available remote Random Lasers: Characteristics, Applications and Some Research Results
Van Hoang D., Thi Phuong N., Van Phu N.
Computational Methods in Science and Technology
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2010
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Vol. spec. iss. (2)
48-51
EN
The random laser differs from other types of laser in that its cavity is formed not by mirrors but by multiple scattering in a disordered gain medium. Over the course of ten years, random lasers have been attentive by many researchers in the world because their characteristics can lead to unique applications. This report presents the mechanism of random laser operation, classification, characteristics and prediction of different applications. Some research results of authors about random laser have also been noted in report.
5
Content available remote Ultrasonic scattering from compressible cylinders including multiple scattering and thermoviscous effects
Hasheminejad S. M., Alibakhshi M. A.
Archives of Acoustics
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2006
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Vol. 31, No. 2
243-263
EN
This paper presents a study of acoustic scattering by a pair of parallel circular thermoviscous fluid cylinders submerged in an unbounded viscous thermally conducting medium. The translational addition theorem for cylindrical wave functions, the appropriate wave field expansions and the pertinent boundary conditions are employed to develop a closed-form solution in the form of infinite series. The analytical results are illustrated with a numerical example in which two identical thermoviscous fluid cylinders are insonified by a nearby parallel acoustic line source at broadside/end-fire incidence. The backscattered pressure amplitude is numerically evaluated and discussed for representative values of the parameters characterizing the system. The effects of source position, transmission frequency and proximity of the two cylinders are examined. Particular attention has been focused on multiple scattering interactions as well as thermoviscous effects. The imperative influence of thermoviscosity on the analysed phenomena is revealed by notable reduction of backscattering amplitude at intermediate and high frequencies. The numerical results also show that the multiple scattering interaction effects are of great (moderate) consequence for end-fire (broadside) incidence at small separations of the cylinders. A limiting case involving a pair of ideal compressible fluid cylinders is considered and a fair agreement with preceding solutions is established.
6
Content available remote Range dependent radiation leakage from thin scattering columns due to multiple small angle scatter
Kravtsov Y. A., Apresyan L. A., Asatryan A. A., Chrzanowski J., Kirkiewicz J.
Optica Applicata
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2003
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Vol. 33, nr 2-3
293-305
EN
The phenomenon of range dependent radiation leakage from thin random columns caused by small angle multiple scatter is analysed. On the basis of modified Born approximation (Ishimaru, 1978; Apresyan and Kravtsov, 1996), it is shown that extinction coefficient, describing energy leakage due to multiple scatter on large (as compared to wavelength) inhomogeneities, first increases proportionally to distance z1/2 and then saturates on the level which might significantly exceed conventional extinction coefficient, connected with large angle light scatter on small inhomogeneities. The effect might be observed in many physical systems, for example, in a tube filled with water emulsion or suspension, containing small and large particles. The phenomenon may be helpful in distinguishing the contribution of small and large inhomogeneities to total extinction
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