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S. Nechaev

Publications and source records attributed to S. Nechaev.

33 records · Page 2Linked to original sources
arXiv2010

KPZ scaling in topological mixing

In the spirit of recent works on topological chaos generated by sequential rotation of infinitely thin stirrers placed in a viscous liquid, we consider the statistical properties of braiding exponent which quantitatively characterizes the chaotic behavior of advected particles in two-dimensional flows. We pay a special attention to the random stirring protocol and study the time-dependent behavior of the variance of the braiding exponent. We show that this behavior belongs to the Kardar-Parisi-Zhang universality class typical for models of nonstationary growth. Using the matrix (Magnus) representation of the braid group generators, we relate the random stirring protocol with the growth of random heap generated by a ballistic deposition.

cond-mat.stat-mech↗
arXiv2006

Random patterns generated by random permutations of natural numbers

We survey recent results on some one- and two-dimensional patterns generated by random permutations of natural numbers. In the first part, we discuss properties of random walks, evolving on a one-dimensional regular lattice in discrete time $n$, whose moves to the right or to the left are induced by the rise-and-descent sequence associated with a given random permutation. We determine exactly the probability of finding the trajectory of such a permutation-generated random walk at site $X$ at time $n$, obtain the probability measure of different excursions and define the asymptotic distribution of the number of "U-turns" of the trajectories - permutation "peaks" and "through". In the second part, we focus on some statistical properties of surfaces obtained by randomly placing natural numbers $1,2,3, >...,L$ on sites of a 1d or 2d square lattices containing $L$ sites. We calculate the distribution function of the number of local "peaks" - sites the number at which is larger than the numbers appearing at nearest-neighboring sites - and discuss some surprising collective behavior emerging in this model.

cond-mat.stat-mech↗
arXiv2006

On the distribution of surface extrema in several one- and two-dimensional random landscapes

We study here a standard next-nearest-neighbor (NNN) model of ballistic growth on one- and two-dimensional substrates focusing our analysis on the probability distribution function $P(M,L)$ of the number $M$ of maximal points (i.e., local ``peaks'') of growing surfaces. Our analysis is based on two central results: (i) the proof (presented here) of the fact that uniform one--dimensional ballistic growth process in the steady state can be mapped onto ''rise-and-descent'' sequences in the ensemble of random permutation matrices; and (ii) the fact, established in Ref. \cite{ov}, that different characteristics of ``rise-and-descent'' patterns in random permutations can be interpreted in terms of a certain continuous--space Hammersley--type process. For one--dimensional system we compute $P(M,L)$ exactly and also present explicit results for the correlation function characterizing the enveloping surface. For surfaces grown on 2d substrates, we pursue similar approach considering the ensemble of permutation matrices with long--ranged correlations. Determining exactly the first three cumulants of the corresponding distribution function, we define it in the scaling limit using an expansion in the Edgeworth series, and show that it converges to a Gaussian function as $L \to \infty$.

cond-mat.stat-mech↗
arXiv2006

How long does it take to pull an ideal polymer into a small hole?

We present scaling estimates for characteristic times $τ_{\rm lin}$ and $τ_{\rm br}$ of pulling ideal linear and randomly branched polymers of $N$ monomers into a small hole by a force $f$. We show that the absorbtion process develops as sequential straightening of folds of the initial polymer configuration. By estimating the typical size of the fold involved into the motion, we arrive at the following predictions: $τ_{\rm lin}(N) \sim N^{3/2}/f$ and $τ_{\rm br}(N) \sim N^{5/4}/f$, and we also confirm them by the molecular dynamics experiment.

cond-mat.stat-mech↗
arXiv2005

Whether the mean-field two-length scale theory of hydrophobic effect can be microscopically approved?

We discuss the simple microscopic derivation of a hydrophobic effect. Our approach is based on the standard functional representation of the partition function of interacting classical particles and subsequent passage to collective variables (local densities of the solvent). We get an expression for the solvation free energy of solute molecule of any arbitrary shape and derive the nonlinear equation for the mean solvent density surrounding the solvated object. We pay a special attention to some inconsistencies between the microscopic consideration and the two-length scale mean-field theory of hydrophobic effect.

cond-mat.stat-mech↗
arXiv2005

Application of a two-length scale field theory to the solvation of charged molecules: I. Hydrophobic effect revisited

On a basis of a two-length scale description of hydrophobic interactions we develop a continuous self-consistent theory of solute-water interactions which allows to determine a hydrophobic layer of a solute molecules of any geometry with explicit account of solvent structure described by its correlation function. We compute the mean solvent density profile n(r) surrounding the spherical solute molecule as well as its solvation free energy. We compare the two-length scale theory to the numerical data of Monte-Carlo simulations found in the literature and discuss the possibility of a self-consistent adjustment of the free parameters of the theory. In the frameworks of the discussed approach we compute also the solvation free energies of alkane molecules and the free energy of interaction of two spheres separated by some distance. We describe the general setting of a self-consistent account of electrostatic interactions in the frameworks of the model where the water is considered not as a continuous media, but as a gas of dipoles. We analyze the limiting cases where the proposed theory coincides with the electrostatics of a continuous media.

cond-mat.soft↗
arXiv2001

Multifractality of entangled random walks and non-uniform hyperbolic spaces

Multifractal properties of the distribution of topological invariants for a model of trajectories randomly entangled with a nonsymmetric lattice of obstacles are investigated. Using the equivalence of the model to random walks on a locally nonsymmetric tree, statistical properties of topological invariants, such as drift and return probabilities, have been studied by means of a renormalization group (RG) technique. The comparison of the analytical RG--results with numerical simulations as well as with the rigorous results of P.Gerl and W.Woess demonstrates clearly the validity of our approach. It is shown explicitly by direct counting for the discrete version of the model and by conformal methods for the continuous version that multifractality occurs when local uniformity of the phase space (which has an exponentially large number of states) has been broken.

cond-mat.stat-mech↗
arXiv2000

Adsorption of a random heteropolymer at a potential well revisited: location of transition point and design of sequences

The adsorption of an ideal heteropolymer loop at a potential point well is investigated within the frameworks of a standard random matrix theory. On the basis of semi-analytical/semi-numerical approach the histogram of transition points for the ensemble of quenched heteropolymer structures with bimodal symmetric distribution of types of chain's links is constructed. It is shown that the sequences having the transition points in the tail of the histogram display the correlations between nearest-neighbor monomers.

cond-mat.dis-nn↗
arXiv2000

Topological relaxation of entangled flux lattices: Single vs collective line dynamics

A symbolic language allowing to solve statistical problems for the systems with nonabelian braid-like topology in 2+1 dimensions is developed. The approach is based on the similarity between growing braid and "heap of colored pieces". As an application, the problem of a vortex glass transition in high-T_c superconductors is re-examined on microscopic level

cond-mat.mes-hall↗
arXiv2000

Multifractality in uniform hyperbolic lattices and in quasi-classical Liouville field theory

We introduce a deterministic model defined on a two dimensional hyperbolic lattice. This model provides an example of a non random system whose multifractal behaviour has a number theoretic origin. We determine the multifractal exponents, discuss the termination of multifractality and conjecture the geometric origin of the multifractal behavior in Liouville quasi--classical field theory.

cond-mat.stat-mech↗
arXiv1999

Anchoring of polymers by traps randomly placed on a line

We study dynamics of a Rouse polymer chain, which diffuses in a three-dimensional space under the constraint that one of its ends, referred to as the slip-link, may move only along a one-dimensional line containing randomly placed, immobile, perfect traps. For such a model we compute exactly the time evolution of the probability $P_{sl}(t)$ that the chain slip-link will not encounter any of the traps until time $t$ and consequently, that until this time the chain will remain mobile.

cond-mat.stat-mech↗
arXiv1998

Kinetics of Anchoring of Polymer Chains on Substrates with Chemically Active Sites

We consider dynamics of an isolated polymer chain with a chemically active end-bead on a 2D solid substrate containing immobile, randomly placed chemically active sites (traps). For a particular situation when the end-bead can be irreversibly trapped by any of these sites, which results in a complete anchoring of the whole chain, we calculate the time evolution of the probability $P_{ch}(t)$ that the initially non-anchored chain remains mobile until time $t$. We find that for relatively short chains $P_{ch}(t)$ follows at intermediate times a standard-form 2D Smoluchowski-type decay law $ln P_{ch}(t) \sim - t/ln(t)$, which crosses over at very large times to the fluctuation-induced dependence $ln P_{ch}(t) \sim - t^{1/2}$, associated with fluctuations in the spatial distribution of traps. We show next that for long chains the kinetic behavior is quite different; here the intermediate-time decay is of the form $ln P_{ch}(t) \sim - t^{1/2}$, which is the Smoluchowski-type law associated with subdiffusive motion of the end-bead, while the long-time fluctuation-induced decay is described by the dependence $ln P_{ch}(t) \sim - t^{1/4}$, stemming out of the interplay between fluctuations in traps distribution and internal relaxations of the chain.

cond-mat.soft↗