253 research outputs found
Dynamic effect of overhangs and islands at the depinning transition in two-dimensional magnets
With the Monte Carlo methods, we systematically investigate the short-time
dynamics of domain-wall motion in the two-dimensional random-field Ising model
with a driving field ?DRFIM?. We accurately determine the depinning transition
field and critical exponents. Through two different definitions of the domain
interface, we examine the dynamics of overhangs and islands. At the depinning
transition, the dynamic effect of overhangs and islands reaches maximum. We
argue that this should be an important mechanism leading the DRFIM model to a
different universality class from the Edwards-Wilkinson equation with quenched
disorderComment: 9 pages, 6 figure
The depinning transition of a driven interface in the random-field Ising model around the upper critical dimension
We investigate the depinning transition for driven interfaces in the
random-field Ising model for various dimensions. We consider the order
parameter as a function of the control parameter (driving field) and examine
the effect of thermal fluctuations. Although thermal fluctuations drive the
system away from criticality the order parameter obeys a certain scaling law
for sufficiently low temperatures and the corresponding exponents are
determined. Our results suggest that the so-called upper critical dimension of
the depinning transition is five and that the systems belongs to the
universality class of the quenched Edward-Wilkinson equation.Comment: accepted for publication in Phys. Rev.
Monte Carlo Dynamics of driven Flux Lines in Disordered Media
We show that the common local Monte Carlo rules used to simulate the motion
of driven flux lines in disordered media cannot capture the interplay between
elasticity and disorder which lies at the heart of these systems. We therefore
discuss a class of generalized Monte Carlo algorithms where an arbitrary number
of line elements may move at the same time. We prove that all these dynamical
rules have the same value of the critical force and possess phase spaces made
up of a single ergodic component. A variant Monte Carlo algorithm allows to
compute the critical force of a sample in a single pass through the system. We
establish dynamical scaling properties and obtain precise values for the
critical force, which is finite even for an unbounded distribution of the
disorder. Extensions to higher dimensions are outlined.Comment: 4 pages, 3 figure
1) Design of new Ti-based biomaterials by using ab-initio simulations, FEM, and experiments 2) Detailed analysis of an indent
Motivation Theoretical methods Experimental methods Results Conclusion
Critical behavior of a traffic flow model
The Nagel-Schreckenberg traffic flow model shows a transition from a free
flow regime to a jammed regime for increasing car density. The measurement of
the dynamical structure factor offers the chance to observe the evolution of
jams without the necessity to define a car to be jammed or not. Above the
jamming transition the dynamical structure factor exhibits for a given k-value
two maxima corresponding to the separation of the system into the free flow
phase and jammed phase. We obtain from a finite-size scaling analysis of the
smallest jam mode that approaching the transition long range correlations of
the jams occur.Comment: 5 pages, 7 figures, accepted for publication in Physical Review
Stochastic boundary conditions in the deterministic Nagel-Schreckenberg traffic model
We consider open systems where cars move according to the deterministic
Nagel-Schreckenberg rules and with maximum velocity , what is an
extension of the Asymmetric Exclusion Process (ASEP). It turns out that the
behaviour of the system is dominated by two features: a) the competition
between the left and the right boundary b) the development of so-called
"buffers" due to the hindrance an injected car feels from the front car at the
beginning of the system. As a consequence, there is a first-order phase
transition between the free flow and the congested phase accompanied by the
collapse of the buffers and the phase diagram essentially differs from that of
(ASEP).Comment: 29 pages, 26 figure
Hysteretic dynamics of domain walls at finite temperatures
Theory of domain wall motion in a random medium is extended to the case when
the driving field is below the zero-temperature depinning threshold and the
creep of the domain wall is induced by thermal fluctuations. Subject to an ac
drive, the domain wall starts to move when the driving force exceeds an
effective threshold which is temperature and frequency-dependent. Similarly to
the case of zero-temperature, the hysteresis loop displays three dynamical
phase transitions at increasing ac field amplitude . The phase diagram in
the 3-d space of temperature, driving force amplitude and frequency is
investigated.Comment: 4 pages, 2 figure
Depinning transition and thermal fluctuations in the random-field Ising model
We analyze the depinning transition of a driven interface in the 3d
random-field Ising model (RFIM) with quenched disorder by means of Monte Carlo
simulations. The interface initially built into the system is perpendicular to
the [111]-direction of a simple cubic lattice. We introduce an algorithm which
is capable of simulating such an interface independent of the considered
dimension and time scale. This algorithm is applied to the 3d-RFIM to study
both the depinning transition and the influence of thermal fluctuations on this
transition. It turns out that in the RFIM characteristics of the depinning
transition depend crucially on the existence of overhangs. Our analysis yields
critical exponents of the interface velocity, the correlation length, and the
thermal rounding of the transition. We find numerical evidence for a scaling
relation for these exponents and the dimension d of the system.Comment: 6 pages, including 9 figures, submitted for publicatio
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