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We attempt to consider a biological structure as an open nonequilibrium system the properties of which can be described on the basis of kinetic approach with the help of appropriate kinetic equations. This approach allows us to evaluate in principle scales of sizes and to connect these values to the inner characteristics of the processes of kinetic interaction and advection. One can compare the results with some empirical data concerning these characteristics for bio-systems, in particular mammals, and also for some parts of the systems, say sizes of green leaves. A sense of the nonequilibrium entropy as a measure of complexity of bio-organisms is discussed. Besides the estimations of bio-systems on a global scale, possible methods to describe restricted regions (associated e.g. with living cells) as nonequilibrium open structure with specific boundaries are also discussed. A new boundary 1D problem is formulated and solved for kinetic equations with the membrane-like boundaries conditions. Non-classical transport properties in the system are found. [ABSTRACT FROM AUTHOR]

Some new problems with nonequlibrium boundary conditions are formulated and solved. So-called nonuniform relaxation problem with nonequilibrium conditions on a free boundary for supersonic and subsonic cases are considered. Classical 1D heat transfer problem but with nonequilibrium boundary condition on one surface is also studied. Possible nonequilibrium flows with anomalous transport of momentum and heat are observed and discussed. [ABSTRACT FROM AUTHOR]

A two-dimensional unsteady flow past a rectangular cylinder has been investigated numerically using the Boltzmann equation. The effect of cylinder aspect ratio varying from 1 to 10 and the flow Reynolds number from 10 to 400 on flow pattern has been analyzed. Results are presented in terms of drag, lift and pressure coefficients and Strouhal number of vortex shedding. Flow visualization images in the wake of the cylinder are shown and discussed. It was found that the shape and size of the recirculation bubble downstream of the cylinder are strong functions of its aspect ratio. Drag, lift, pressure coefficients and Strouhal number strongly depend on Re in steady regime while a dependence becomes weaker in unsteady flow regime. The flow configuration over a cylinder also varies with the aspect ratio. In addition, the present predictions are compared with numerical and experimental results from other works and a good agreement is reached. [ABSTRACT FROM AUTHOR]

The present paper is devoted to simulating the compressible turbulent flows at the new level. The principal importance of the kinetic approach for description of turbulence is discussed. An explicit-implicit numerical scheme in the framework of the direct approach for the Boltzmann kinetic equation is examined. Numerical investigation of supersonic jets and the supersonic turbulent separated flow in the vicinity of backward/forward-facing step with leeward-face angle equals to 8°, 25°, 45° and 90° and Ma ≈ 3 for a model 2D case is made. At lower Knudsen number values (starting from 0.001) instabilities in the jet flow is observed. The comparison with available experimental and numerical results is performed in terms of the pressure and skin friction distributions over the body surface and the distribution of heat-transfer coefficient. A good agreement with the experimental heat-transfer coefficient is observed. [ABSTRACT FROM AUTHOR]

The aim of present work is to investigate the feasibility of applying a kinetic approach to the problem of modeling turbulent or unstable flows. We perform three-dimensional direct numerical simulations of the Taylor Green (TG) type conditions and decay of isotropic turbulence in periodic compressible flow. The simulation is based on the direct numerical solving the Boltzmann kinetic equation. For the regular initial condition the results show the fragmentation of the large initial eddies and subsequently the full damping energy of the system. Dependence of the kinetic energy on the wave number is obtained by means of the Fourier expansion of the velocity components. The decay exponent of the kinetic energy spectrum for both problems close to the value '-5/3'. [ABSTRACT FROM AUTHOR]

The chaotic processes in time and space are investigated explicitly by means of solving the initial-boundary problem for the discrete kinetic equation. The Carleman model is studied. The physical interpretation of this kinetic system is presented. Numerical solutions show series of bifurcations when decreasing the Knudsen number. That leads to the period-doublings and then to the chaotic regimes with the positive senior Lyapunov exponential. The spatial oscillating profiles with the average solutions which differ from the steady profiles are observed. The chaotic character of the oscillations with intermittence is studied. This introduces a basic model for kinetic description of complicated physical processes. [ABSTRACT FROM AUTHOR]

GPU-accelerated computing of the Boltzmann collision integral is studied using deterministic method with piecewise approximation of the velocity distribution function and analytical integration over collision impact parameters. The acceleration of 40 times is achieved compared to CPU calculations for a 3D problem of collisional relaxation of bi-Maxwellian velocity distribution. [ABSTRACT FROM AUTHOR]

With increasing of X-ray energy an interesting situation appears when due to different dependence of refraction and absorption on X-ray energy a sample becomes transparent but still produces refraction. So such samples become unvisible for usual absorption methods but could be analyzed with various phase contrast methodes. The situation becomes more actual for higher X-ray energy especially for range20-100keV. F. Polack and D. Joyeux described an extension of an interferential differential phase contrast to scanning X-ray microscopy. The principle is to illuminate two points of an object with coherent radiation and detect the fringe shift induced by small phase differences. Fresnel mirrors have been suggested to split a X-ray beam in two coherent ones. In this paper it is proposed instead to use bifocal (multi-focal) lenses. Design and fabrication process of the lenses are described. [ABSTRACT FROM AUTHOR]

X-rays refractive optics has made a real success in a hard radiation domain promising for many applications. An analysis made of refractive materials properties, which are most suitable for this new kind of X-ray focusing optics shows that in silicon refraction effects prevail on attenuation. A wide variety of technologies dedicated to microstructure formation on Si make it as most suitable one. Using electron beam lithography and deep plasma etching planar parabolic profiles are produced with the focal distance 1 m on 17.4 keV radiation. They are tested on synchrotron radiation at beamline X47 SRPING-8. Experiments carried out open the way to construct kinoform refracting profiles, which exceed simple parabolas in gain and aperture. A number of kinoform profiles on silicon is created for energies up to 50 keV, which at apertures 2mm have calculated gain up to 5000. Some focusing properties of such planar refracting profiles are discussed. [ABSTRACT FROM AUTHOR]

Focusing of 20 keV x-ray radiation using elliptical diffraction zones fabricated inside a silicon crystal have been observed successfully for the first time. These are the lenses with the first and third diffraction orders. An alignment of focusing elements was made with a 10 micron resolution x-ray imaging system. Focusing quality of the lenses have been investigated by using x-ray sensitive high resolution film and observing, under the light microscope, the shape of the registered focal spot first. And finally by scanning focal plane with pinhole and analysing three dimensional image. Experiments were made in a monochromatic beam. The signal/noise ratio of 300 have been obtained. These experiments open quite wide perspectives in focusing “hard” x-ray radiation up to 100 keV. Authors are hoping that this kind of focusing elements will find there real applications in microdiffraction experiments with energy about 20 kev and higher, in microfluorescence analysis experiments, near edge absorption experiments with micron spacial resolution. A new scheme to focus “hard” x-ray radiation have been suggested. Real geometry parameters for lens with elliptical diffraction zones was calculated for energy 60 keV. [ABSTRACT FROM AUTHOR]