arXiv subjects

A. B. Kukushkin

Publications and source records attributed to A. B. Kukushkin.

At least 19 recordsLinked to original sources

arXiv2025

Generalization of the viscous stress tensor to the case of non-small gradients of hydrodynamic velocity: a path to numerical modeling of turbulence non-locality

Generalization of the Chapman-Enskog method to the case of large gradients of hydrodynamic velocity allowed us to obtain an integral (over spatial coordinates) representation of the viscous stress tensor in the Navier-Stokes equation. In the case of small path lengths of the medium disturbance, the tensor goes over to the standard form, which, as is known, is difficult to apply to the description of tangential discontinuities and separated flows. The obtained expression can allow numerical modeling of the nonlocality of turbulence, expressed by the empirical Richardson t^3 law for pair correlations in a turbulent medium.

physics.flu-dyn↗

arXiv2021

Analysis of deviation from neoclassical ion equilibrium against electron and ion temperature profiles in T-10 tokamak

The results of the analysis of the deviation of the force equilibrium for ions from the neoclassical theory prediction, calculated using the direct measurements of the radial electric field, in the view of its possible local and nonlocal correlation with the profiles of electron, Te, and ion, Ti, temperatures in the T-10 tokamak are presented. Local correlations are analyzed by means of the Pearson's correlation. Nonlocal correlations are treated with an inverse problem under the assumption of an integral equation relationship between the deviation and Te and Ti profiles. The discharges with zero, weak and strong auxiliary heating (electron cyclotron resonance heating) are analyzed. It is found that the electrons substantially (not less than ions) contribute to the deviation of the ion equilibrium from the neoclassical theory prediction both in the local and nonlocal models.

physics.plasm-ph↗

arXiv2020

Optimization identification of superdiffusion processes in biology: an algorithm for processing observational data and a self-similar solution of the kinetic equation

This work is an attempt to transfer to biology the methods developed in physics for formulating and solving the kinetic equations in which the kernel of the integral operator in spatial coordinates is slowly decreasing with increasing distance and belongs to the class of Levy distributions. An algorithm is proposed for the reconstruction of the step-length probability density function (PDF) on a moderate number of trajectories of biological objects (migrants) and for the derivation of the Green's function of the corresponding integro-differential kinetic equation for the density of migrants in the entire space-time range, including the construction of an approximate self-similar solution. A wide class of time-dependent superdiffusion processes with a model power-law step-length PDF is considered, which corresponds to "Levy walks with rests" for given values of the migrant's constant velocity and the average time T of the migrant's stay between runs. The algorithm is tested within the framework of a synthetic diagnostics, consisting in the generation of artificial experimental data for trajectories of migrants and the subsequent reconstruction of the parameters of the step-length PDF and T. For different volumes of synthetic data, to obtain a general idea of the distributions under study (non-parametric case) and to evaluate the accuracy of recovering the parameters of the PDF (in the case of a parametric representation), the method of balanced identification is used. The approximate self-similar solution for the parameters of step-length PDF and T is shown to provide reasonable accuracy of the space-time evolution of migrant's density.

q-bio.QM↗

arXiv2019

Recovery of parameters of fast nonlocal heat transport in magnetic fusion plasmas: testing a model of waves with high internal reflections

Our analysis of the model [J. Phys.: Conf. Ser. 941 (2017) 012008] elaborated for interpreting the initial stage of the fast nonlocal transport events, which exhibit immediate response, in the heat diffusion time scale, of the spatial profile of electron temperature to its local perturbation, shows that the nonlocal transport by electromagnetic (EM) waves needs too high reflectivity of vacuum vessel walls to describe the experimental data. Here we try another model, which assumes high internal reflections and is compatible with the "wild cable" transport of TEM waves along magnetically-bound skeletal nanostructures. An inverse problem for recovery of the source and sink of waves, and internal reflectivity, is formulated and solved. Preliminary results of analyzing the data from tokamaks JET and TFTR, and stellarator LHD are presented.

physics.plasm-ph↗

arXiv2018

Automodel solutions for superdiffusive transport by the Lévy walks

The method of approximate automodel solution for the Green's function of the time-dependent superdiffusive (nonlocal) transport equations (J. Phys. A: Math. Theor. 49 (2016) 255002) is extended to the case of a finite velocity of carriers. This corresponds to extension from the Lévy flights-based transport to the transport of the type, which belongs to the class of "Lévy walk + rests", to allow for the retardation effects in the Lévy flights. This problem covers the cases of the transport by the resonant photons in astrophysical gases and plasmas, heat transport by electromagnetic waves in plasmas, migration of predators, and other applications. We treat a model case of one-dimensional transport on a uniform background with a simple power-law step-length probability distribution function (PDF). A solution for arbitrary superdiffusive PDF is suggested, and the verification of solution for a particular power law PDF, which corresponds, e.g., to the Lorentzian wings of atomic spectral line shape for emission of photons, is carried out using the computation of the exact solution.

cond-mat.stat-mech↗

arXiv2018

Contribution of the Hall effect to radial electric field and spontaneous/intrinsic rotation in tokamak core plasmas

The Hall effect, defined as the separation of electric charges of opposite sign when they move in a magnetic field, is suggested to contribute substantially to the observed negative radial electric field Er in the core plasma in tokamaks and, respectively, to the spontaneous/intrinsic rotation of plasma. A simple way to evaluate the Hall effect contribution to the Er value, using the independently measured space distributions of magnetic field and plasma rotation velocity, is suggested. The estimates of the effect for experimental data from the TM-4 and T-10 tokamaks suggest that the above phenomena in tokamaks should be described in the framework of the two-fluid magnetohydrodynamics.

physics.plasm-ph↗

arXiv2015

Automodel solutions for Lévy flight-based transport on a uniform background

A wide class of non-stationary superdiffusive transport on a uniform background with a power-law decay, at large distances, of the step-length probability distribution function (PDF) is shown to possess an automodel solution. The solution for Green function is constructed using the scaling laws for the propagation front (relevant-to-superdiffusion average displacement) and asymptotic solutions far beyond and far in advance of the propagation front. These scaling laws are determined essentially by the long-free-path carriers (Lévy flights). The validity of the suggested automodel solution is proved by its comparison with numerical solutions in the one-dimensional (1D) case of the transport equation with a simple long-tailed PDF with various power-law exponents and in the 3D case of the Biberman-Holstein equation of the resonance radiation transfer for various (Doppler, Lorentz, Voight and Holtsmark) spectral line shapes.

physics.data-an↗

arXiv2014

A method for diffraction-based identification of annealing-produced restructuring of amorphous fullerene

A method is suggested for estimation of structural properties of amorphous fullerene and its derivatives produced by vacuum annealing. The method is based on the fitting of the neutron or x-ray powder diffraction patterns for scattering wave vector's modulus in the range from few units to several tens of inverse nanometers. The respective inverse problem assumes that the structured component of a sample can be described with a limited number, Nstr, of candidate sp2 carbon structures (fullerenes, flat and curved flakes with graphene-like atom arrangement) of a limited number of atoms, Natom. These structures are packed heterogeneously, in the domains with various average density of atoms and various degree of ordering of structures, using the Rigid Body Molecular Dynamics with variable parameter of pair interaction of atoms in the neighboring rigid-body nanostructures. The method is applied to interpreting the data of neutron diffraction by an amorphous fullerene annealed at temperatures 600, 800, 850, 900 and 1000 C. The results for Nstr equal to 36 and Natom in the range from 14 to 285 enabled us to quantify structural properties of the samples in terms of the average size and curvature of the sp2 carbon structures, and analyze sensitivity of results to the layout of these structures in the domains (mixture of various structures in each domain vs. mixture of domains of identical structures).

cond-mat.mtrl-sci↗

arXiv2013

Algorithm of Amorphous Carbonaceous Nanomaterial Structure Identification with a Joint X-Ray and Neutron Diffraction Data Analysis

An algorithm is developed for structure identification of amorphous carbonaceous nanomaterials with a joint x-ray and neutron diffraction data analysis, using the data on the chemical composition of the sample from other diagnostics. The algorithm is an extension of one formerly developed for the x-ray diffraction diagnostics of similar nanomaterials ([1] Chem. Phys. Lett., 506, 265-268 (2011)). The algorithm is tested on the example of processing the computed data for a sample which models a fragment of hydrocarbon films analyzed in [1]. The algorithm is of interest for structure diagnostics of materials with comparable atomic fractions of carbon and hydrogen.

cond-mat.mtrl-sci↗

arXiv2011

Numerical Modeling of Electrodynamic Aggregation of Magnetized Nanodust

The recent results of applying the parallel numerical code SELFAS-3 to modelling of electrodynamic aggregation of magnetized nanodust are presented. The modelling describes evolution of a many-body system of basic blocks which are taken as strongly magnetized thin rods (i.e., one-dimensional static magnetic dipoles), with electric conductivity and static electric charge, screened with its own plasma sheath. The code provides continuous modelling of the following stages of evolution: (i) alignments of randomly situated solitary basic blocks in an external magnetic field and formation of stable filaments, (ii) percolation of electric conductivity in a random filamentary system, and electric short-circuiting in the presence of an external electric field, (iii) evolution of electric current profile in a filamentary network with a trend towards a fractal skeletal structuring.

physics.comp-ph↗

arXiv2010

Numerical code SELFAS-3 and electrodynamic aggregation of magnetized nanodust

The principles of the parallel numerical code SELFAS-3 are presented. The code modifies previous version of the code to enable parallel computations of electrodynamic aggregation in a many-body system of basic blocks which are taken as strongly magnetized thin rods (i.e., one-dimensional static magnetic dipoles), with electric conductivity and static electric charge, screened with its own static plasma sheath. The aggregation modelling includes the electric current dynamics in a complicated evolving network to describe the processes of external and internal electric short-circuiting. The code enables the continuous modelling of a transition between the following states: randomly situated ensemble of solitary basic blocks; electric current-carrying filamentary system; restructured filamentary network with a trend towards a fractal skeletal structuring. The latter trend is illustrated with generation of a bigger magnetic dipole in (i) homogeneous random ensemble between the biased electrodes in the presence of a plasma electric current filament and (ii) random ensemble around a straight linear nanodust filament with inhomogeneous distribution of the trapped magnetic flux along the filament.

physics.comp-ph↗

arXiv2009

Dynamic percolation of electric conductivity and a trend towards fractal skeletal structuring in a random ensemble of magnetized nanodust

Numerical modeling of electrodynamic aggregation is carried out for a random ensemble of magnetized nanodust taken as a many body system of strongly magnetized thin rods (i.e., one-dimensional static magnetic dipoles), which possess electric conductivity and static electric charge, screened with its own static plasma sheath. The self-assembling of quasi-linear filaments from an ensemble of randomly situated basic blocks and the electric short-circuiting between biased electrodes are shown to be supported by the alignment of blocks in an external magnetic field. Statistical analysis of short-circuiting time allows tracing the dynamic percolation of electric conductivity and shows a decrease of percolation threshold for volume fraction, as compared with the observed percolation of carbon nanotubes in liquids and polymer composites. Modeling of short-circuiting stage of evolution is continued with tracing the dynamics of pinching of electric current filaments to show the interplay of all the magnetic and electric mechanisms of filaments networking. A trend towards a fractal skeletal structuring (namely, repeat of original basic block at a larger length scale) is illustrated with the evidence for generation of a bigger magnetic dipole.

physics.comp-ph↗

arXiv2005

Evidences for and the models of self-similar skeletal structures in fusion devices, severe weather phenomena and space

The paper briefly reviews (i) the evidences for self-similar structures of a skeletal form (namely, tubules and cartwheels, and their simplest combinations), called the Universal Skeletal Structures (USS), observed in the range 10-5 cm - 1023 cm. in the high-current electric discharges in various fusion devices, severe weather phenomena, and space, (ii) the models for interpreting the phenomenon of skeletal structures, including the hypothesis for a fractal condensed matter (FCM), assembled from nanotubular dust, and (iii) probable role of FCM, which might be responsible for the USS phenomenon, in tornado, ball lightning, and waterspout.

physics.plasm-ph↗

arXiv2005

Simple model of skeletal matter composed of magnetized electrically conducting thin rods

A simple electrodynamic model for describing the behavior of a skeletal matter composed of magnetized, electrically conducting thin rods (1D magnetic dipoles) is proposed. It is aimed at modeling the self-assembling of a skeletal matter from carbon nanotubes (or similar nanodust), as suggested for interpreting the experimental data on the long-lived filamentary structures in the high-current electric discharges. Here the capability of the model is illustrated with the example of how a straight tubular skeleton, which is composed of ~300 dipoles and carry circular electric current in its wall, may be wrapped up by a distant pulsed electric current to make a toroid-like structure.

physics.comp-ph↗

arXiv2004

Evidences for skeletal structures in tornado and the probable role of nanotubular dust in the origin of tornado

The results are presented of an analysis, with the help of the method of multilevel dynamical contrasting of the images, of available databases of the images of tornado. This analysis extends some preliminary results on identification of skeletal structures in tornadoes (Phys. Lett. A 306 (2002) 175) and enables us to apply to the case of tornado our former hypothesis for the probable role of nanotubular dust in the origin and stability/longevity of filamentary structures of a skeletal form in electric discharges. A hypothesis for the contribution of nanotubular dust to initiation of tornadoes is suggested, in which a key role is delivered to ability of the hypothetical skeleton inside the thundercloud to provide fast long-range transport of electricity. Thus, initiation of tornado is suggested to be an electrostatic instability caused exclusively by the presence and special structuring of a nanodust.

physics.ao-ph↗

arXiv2004

Similarity of skeletal structures in laboratory and space and the probable role of self-assembling of a fractal dust in fusion devices

This papers briefly reviews the progress in studying the long-lived filamentary structures of a skeletal form (namely, tubules and cartwheels, and their simple combinations) in electric discharges in various fusion devices. These include fast Z-pinch, tokamak and laser produced plasmas. We also report on the results of a search for the phenomenon of skeletal structures -- formerly revealed in laboratory data from fusion devices -- at larger and much larger length scales, including the powerful electromagnetic phenomena in the Earth atmosphere and cosmic space. It is found that the similarity of, and a trend toward self-similarity in, the observed skeletal structures more or less uniformly covers the range 10^{-5} cm - 10^{23} cm. These evidences suggest all these skeletal structures, similarly to skeletons in the particles of dust and hail, to possess a fractal condensed matter of particular topology of the fractal. The probable role of the phenomenon of self-assembling of a fractal dust in fusion devices and outside the fusion is discussed briefly.

physics.plasm-ph↗

arXiv2002

Similarity of structuring in the range 10^{-5} cm to 10^23 cm hints at a baryonic cold dark skeleton of the Universe

The presence of skeletal structures of the same distinctive topology (cartwheels, tubules, etc.), in the range 10^{-5} - 10^23 cm, and a trend toward self-similarity of these structures are found. These evidences come from the electron micrography of dust deposits in tokamak (10^{-6} - 10^{-3}cm), the images of plasma taken in laboratory electric discharges -- tokamaks, Z-pinches, plasma focus and vacuum spark (10^{-2} - 10 cm), hail particles (1-10 cm), the images of tornado (10^3 - 10^5 cm), the Hubble Space Telescope and Chandra X-Ray Observatory public archives' images (up to 10^23 cm). The redshift surveys of galaxies and quasars suggests the possibility to draw the above similarity farther, up to 10^26 cm. The above similarity hints at the presence of a baryonic cold dark skeleton (BCDS) of the Universe, which -- in the entire range 10^{-5} - 10^26 cm -- may contain ordinary matter in a fractal condensed form like that in the above-mentioned dust skeletons and hail particles. The probable compatibility of the BCDS with the major cosmological facts (Hubble's expansion and cosmic microwave background) is suggested. Our former hypotheses (and the respective proof-of-concept studies) for the probable microscopic mechanisms of skeleton's assembling, chemical composition, and survivability in ambient hot plasmas are discussed briefly. The respective major cosmological implication is that the purely gravitational description of the large-scale structure of the Universe is likely to be appended with a contribution of quantum electromagnetism, presumably in the form of a skeleton self-assembled from tubular nanostructures (carbon nanotubes or similar nanostructures of other chemical elements).

astro-ph↗

arXiv2002

"Wild Cables" in Fusion Plasmas and their Diagnostics with Spectral Line Stark Broadening

We discuss the opportunities of diagnosing the parameters of hypothetical "wild cables" in fusion plasmas via analyzing the Stark broadening of hydrogen spectral lines. The "wild cables" concept have suggested the observed long-lived skeletal structures in tokamaks and Z-pinches to be caused by a microdust-assembled skeleton. We present the results of calculating the widths of vacuum channels produced by the pressure of on-skeleton high-frequency (HF) electromagnetic waves of the TEM type, which thus might protect the skeletons from ambient high-temperature plasma. The values of amplitude of such wave appear to be compatible with the measurements of those in-plasma HF electric fields in tokamak T-10 and a gaseous Z-pinch which give observable Stark broadening of hydrogen spectral lines.

physics.plasm-ph↗