Search results for " diffusion"

Anisotropic skyrmion diffusion controlled by magnetic-field-induced symmetry breaking

2021

The diffusion of particles has wide repercussions, ranging from particle-based soft-matter systems to solid-state systems with particular electronic properties. Recently, in the field of magnetism, the diffusion of magnetic skyrmions, topologically stabilized quasiparticles, has been demonstrated. Here, we show that, by applying a magnetic in-plane field, and therefore, breaking the symmetry of the system, skyrmion diffusion becomes anisotropic, with faster diffusion parallel to the field axis and slower diffusion perpendicular to it. We furthermore show that the absolute value of the applied magnetic in-plane field controls the absolute values of the diffusion coefficients, so that one can…

Diffusion in Flashing Periodic Potentials

2005

The one-dimensional overdamped Brownian motion in a symmetric periodic potential modulated by external time-reversible noise is analyzed. The calculation of the effective diffusion coefficient is reduced to the mean first passage time problem. We derive general equations to calculate the effective diffusion coefficient of Brownian particles moving in arbitrary supersymmetric potential modulated: (i) by external white Gaussian noise and (ii) by Markovian dichotomous noise. For both cases the exact expressions for the effective diffusion coefficient are derived. We obtain acceleration of diffusion in comparison with the free diffusion case for fast fluctuating potentials with arbitrary profil…

Applications and Implications of Fractional Dynamics for Dielectric Relaxation

2012

This article summarizes briefly the presentation given by the author at the NATO Advanced Research Workshop on “Broadband Dielectric Spectroscopy and its Advanced Technological Applications”, held in Perpignan, France, in September 2011. The purpose of the invited presentation at the workshop was to review and summarize the basic theory of fractional dynamics (Hilfer, Phys Rev E 48:2466, 1993; Hilfer and Anton, Phys Rev E Rapid Commun 51:R848, 1995; Hilfer, Fractals 3(1):211, 1995; Hilfer, Chaos Solitons Fractals 5:1475, 1995; Hilfer, Fractals 3:549, 1995; Hilfer, Physica A 221:89, 1995; Hilfer, On fractional diffusion and its relation with continuous time random walks. In: Pekalski et al. …

One-Dimensional Diffusion

2009

Kerr effect as a tool for the investigation of dynamic heterogeneities

2006

We propose a dynamic Kerr effect experiment for the distinction between dynamic heterogeneous and homogeneous relaxation in glassy systems. The possibility of this distinction is due to the inherent nonlinearity of the Kerr effect signal. We model the slow reorientational molecular motion in supercooled liquids in terms of non-inertial rotational diffusion. The Kerr effect response, consisting of two terms, is calculated for heterogeneous and for homogeneous variants of the stochastic model. It turns out that the experiment is able to distinguish between the two scenarios. We furthermore show that exchange between relatively 'slow' and 'fast' environments does not affect the possibility of …

The effective diffusion coefficient in a one-dimensional discrete lattice with the inclusions

2015

Abstract The expression for the effective diffusion coefficient in one-dimensional discrete lattice model of random walks in matrix with inclusions and unequal hopping lengths is derived. This allowed us to suggest a physical interpretation to the concentration jump – ad hoc parameter commonly used in extended effective medium theory for accounting particle partial reflection on the boundary matrix–inclusion. The analytical results obtained are in excellent agreement with computer simulations.

Role of spin diffusion in current-induced domain wall motion for disordered ferromagnets

2015

Current-induced spin transfer torque and magnetization dynamics in the presence of spin diffusion in disordered magnetic textures is studied theoretically. We demonstrate using tight-binding calculations that weak, spinconserving impurity scattering dramatically enhances the nonadiabaticity. To further explore this mechanism, a phenomenological drift-diffusion model for incoherent spin transport is investigated. We show that incoherent spin diffusion indeed produces an additional spatially dependent torque of the form ∼∇ 2 [m × (u · ∇)m] + ξ ∇ 2 [(u · ∇)m], where m is the local magnetization direction, u is the direction of injected current, and ξ is a parameter characterizing the spin dyna…

Multiscale Computer Simulations in Physics, Chemistry, and Biology: The Example Of Silica

2002

We show to what extent molecular dynamics simulations (MD) can explore struc-tural and dynamic properties of atomic systems whereby the system under consideration is amorphous silica (SiO2). Two studies are presented: (i) a large scale simulation of the dynam-ics of a SiO2 melt and (ii) the investigation of free silica surfaces where a mixture of a classical MD and a Car-Parrinello molecular dynamics is used.

Electron dynamical response in InP semiconductors driven by fluctuating electric fields

2015

Abstract The complexity of electron dynamics in low-doped n-type InP crystals operating under fluctuating electric fields is deeply explored and discussed. In this study, we employ a multi-particle Monte Carlo approach to simulate the non-linear transport of electrons inside the semiconductor bulk. All possible scattering events of hot electrons in the medium, the main details of the band structure, as well as the heating effects, are taken into account. The results presented in this study derive from numerical simulations of the electron dynamical response to the application of a sub-Thz electric field, fluctuating for the superimposition of an external source of Gaussian correlated noise.…

Dynamics of Polymer Chains Confined in Slit-Like Pores

1996

Monte Carlo simulations of an off-lattice bead spring model of polymer chains are presented, confining the chains between two repulsive parallel planes a distance D apart. Varying the chain length N from N = 16 to N = 128, we show that under good solvent conditions the chains behave like two-dimensional self-avoiding walks, their mean square gyration radius scales as (R g 2 ) N 2v with v = 3/4. The density profile across the slit is independent of N and maximal in the center of the slit. The dynamical properties of the chains are found to be in full agreement with the Rouse model with excluded volume in d = 2 dimensions, the relaxation times vary like τ N Z with z = 2v +1 = 5/2, the diffusi…