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Search Results: 1 - 10 of 471665 matches for " S. N. Dorogovtsev "
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Avalanche mixing of granular solids in a rotating 2D drum: diffusion and fractionality
S. N. Dorogovtsev
Physics , 1998,
Abstract: The dynamics of the avalanche mixing in a slowly rotated 2D upright drum is studied in the situation where the difference $\delta$ between the angle of marginal stability and the angle of repose of the granular material is finite. An analytical solution of the problem is found for a half filled drum, that is the most interesting case. The mixing is described by a simple linear difference equation. We show that the mixing looks like linear diffusion of fractions under consideration with the diffusion coefficient vanishing when $\delta$ is an integer part of $\pi$. The characteristic mixing time tends to infinity in these points. A full dependence of the mixing time on $\delta$ is calculated and predictions for an experiment are made.
Avalanche mixing of granular solids in a rotating 2D drum and discrete mapping
S. N. Dorogovtsev
Physics , 1998,
Abstract: Evolution of mixing of granular solids in a slowly rotated 2D drum is considered as a discrete mapping. The rotation is around the axis of the upright drum which is filled partially, and the mixing occurs only at a free surface of a material. The most simple cases that demonstrate clearly the essence of such a type of mixing are studied analytically. We calculate the characteristic time of the mixing and the distribution of the mixed material over the drum.
Nonlinear nonlocal diffusion of magnetic flux in thin type-II superconductors and Josephson junction arrays: Exact solutions
S. N. Dorogovtsev
Physics , 1998,
Abstract: An exact solution of the nonlinear nonlocal diffusion problem is obtained that describes the evolution of the magnetic flux injected into a soft or hard type-II superconductor film or a two-dimensional Josephson junction array. (The magnetic field in vortices is assumed to be perpendicular to the film; the electric field induced by the vortex motion is proportional to the local magnetic induction; flux creep in the hard superconductors under consideration is described by the logarithmic U(j) dependence.) Self-similar flux distributions with sharp square-root fronts are found. The fronts are shown to expand with power law time-dependence. A sharp peak in the middle of the distribution appears in the hard superconductor case.
Clustering of correlated networks
S. N. Dorogovtsev
Physics , 2003, DOI: 10.1103/PhysRevE.69.027104
Abstract: We obtain the clustering coefficient, the degree-dependent local clustering, and the mean clustering of networks with arbitrary correlations between the degrees of the nearest-neighbor vertices. The resulting formulas allow one to determine the nature of the clustering of a network.
Networks with desired correlations
S. N. Dorogovtsev
Physics , 2003,
Abstract: We discuss a simple method of constructing correlated random networks, which was recently proposed by M. Bogu~n'a and R. Pastor-Satorras (cond-mat/0306072). The result of this construction procedure is a sparse network whose degree--degree distribution asymptotically approaches a given function at large degrees. We argue that this convergence is possible if the desired function is sufficiently slowly decreasing.
Renormalization group for evolving networks
S. N. Dorogovtsev
Physics , 2003, DOI: 10.1103/PhysRevE.67.045102
Abstract: We propose a renormalization group treatment of stochastically growing networks. As an example, we study percolation on growing scale-free networks in the framework of a real-space renormalization group approach. As a result, we find that the critical behavior of percolation on the growing networks differs from that in uncorrelated nets.
Avalanche Mixing of Granular Solids
S. N. Dorogovtsev
Physics , 1997, DOI: 10.1209/epl/i1998-00106-9
Abstract: Mixing of two fractions of a granular material in a slowly rotating two-dimensional drum is considered. The rotation is around the axis of the upright drum. The drum is filled partially, and mixing occurs only at a free surface of the material. We propose a simple theory of the mixing process which describes a real experiment surprisingly well. A geometrical approach without appealing to ideas of self-organized criticality is used. The dependence of the mixing time on the drum filling is calculated. The mixing time is infinite in the case of the half-filled drum. We describe singular behaviour of the mixing near this critical point.
Gyrotropic Percolation
S. N. Dorogovtsev
Physics , 1997,
Abstract: Spiral (gyrotropic) percolation which is related to the behavior of an electron system in strong magnetic fields is studied. It is shown that the scaling behavior area near the percolation threshold is anomalously narrow. The percolation threshold is higher than in a system with usual isotropic percolation (i.e., it is at higher concentrations of undamaged structure elements). Our old value of the critical exponent of the correlation length is corrected.
Mesoscopics and fluctuations in networks
S. N. Dorogovtsev,A. N. Samukhin
Physics , 2002, DOI: 10.1103/PhysRevE.67.037103
Abstract: We describe fluctuations in finite-size networks with a complex distribution of connections, $P(k)$. We show that the spectrum of fluctuations of the number of vertices with a given degree is Poissonian. These mesoscopic fluctuations are strong in the large-degree region, where $P(k) \lesssim 1/N$ ($N$ is the total number of vertices in a network), and are important in networks with fat-tailed degree distributions.
Phase Transition with the Berezinskii--Kosterlitz--Thouless Singularity in the Ising Model on a Growing Network
M. Bauer,S. Coulomb,S. N. Dorogovtsev
Statistics , 2005, DOI: 10.1103/PhysRevLett.94.200602
Abstract: We consider the ferromagnetic Ising model on a highly inhomogeneous network created by a growth process. We find that the phase transition in this system is characterised by the Berezinskii--Kosterlitz--Thouless singularity, although critical fluctuations are absent, and the mean-field description is exact. Below this infinite order transition, the magnetization behaves as $exp(-const/\sqrt{T_c-T})$. We show that the critical point separates the phase with the power-law distribution of the linear response to a local field and the phase where this distribution rapidly decreases. We suggest that this phase transition occurs in a wide range of cooperative models with a strong infinite-range inhomogeneity. {\em Note added}.--After this paper had been published, we have learnt that the infinite order phase transition in the effective model we arrived at was discovered by O. Costin, R.D. Costin and C.P. Grunfeld in 1990. This phase transition was considered in the papers: [1] O. Costin, R.D. Costin and C.P. Grunfeld, J. Stat. Phys. 59, 1531 (1990); [2] O. Costin and R.D. Costin, J. Stat. Phys. 64, 193 (1991); [3] M. Bundaru and C.P. Grunfeld, J. Phys. A 32, 875 (1999); [4] S. Romano, Mod. Phys. Lett. B 9, 1447 (1995). We would like to note that Costin, Costin and Grunfeld treated this model as a one-dimensional inhomogeneous system. We have arrived at the same model as a one-replica ansatz for a random growing network where expected to find a phase transition of this sort based on earlier results for random networks (see the text). We have also obtained the distribution of the linear response to a local field, which characterises correlations in this system. We thank O. Costin and S. Romano for indicating these publications of 90s.
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