1,120 research outputs found
Transport in a Levy ratchet: Group velocity and distribution spread
We consider the motion of an overdamped particle in a periodic potential
lacking spatial symmetry under the influence of symmetric L\'evy noise, being a
minimal setup for a ``L\'evy ratchet.'' Due to the non-thermal character of the
L\'evy noise, the particle exhibits a motion with a preferred direction even in
the absence of whatever additional time-dependent forces. The examination of
the L\'evy ratchet has to be based on the characteristics of directionality
which are different from typically used measures like mean current and the
dispersion of particles' positions, since these get inappropriate when the
moments of the noise diverge. To overcome this problem, we discuss robust
measures of directionality of transport like the position of the median of the
particles displacements' distribution characterizing the group velocity, and
the interquantile distance giving the measure of the distributions' width.
Moreover, we analyze the behavior of splitting probabilities for leaving an
interval of a given length unveiling qualitative differences between the noises
with L\'evy indices below and above unity. Finally, we inspect the problem of
the first escape from an interval of given length revealing independence of
exit times on the structure of the potential.Comment: 9 pages, 12 figure
Stationary states in Langevin dynamics under asymmetric L\'evy noises
Properties of systems driven by white non-Gaussian noises can be very
different from these systems driven by the white Gaussian noise. We investigate
stationary probability densities for systems driven by -stable L\'evy
type noises, which provide natural extension to the Gaussian noise having
however a new property mainly a possibility of being asymmetric. Stationary
probability densities are examined for a particle moving in parabolic, quartic
and in generic double well potential models subjected to the action of
-stable noises. Relevant solutions are constructed by methods of
stochastic dynamics. In situations where analytical results are known they are
compared with numerical results. Furthermore, the problem of estimation of the
parameters of stationary densities is investigated.Comment: 9 pages, 9 figures, 3 table
Bimodality and hysteresis in systems driven by confined L\'evy flights
We demonstrate occurrence of bimodality and dynamical hysteresis in a system
describing an overdamped quartic oscillator perturbed by additive white and
asymmetric L\'evy noise. Investigated estimators of the stationary probability
density profiles display not only a turnover from unimodal to bimodal character
but also a change in a relative stability of stationary states that depends on
the asymmetry parameter of the underlying noise term. When varying the
asymmetry parameter cyclically, the system exhibits a hysteresis in the
occupation of a chosen stationary state.Comment: 4 pages, 5 figures, 30 reference
Stationary states for underdamped anharmonic oscillators driven by Cauchy noise
Using methods of stochastic dynamics, we have studied stationary states in
the underdamped anharmonic stochastic oscillators driven by Cauchy noise. Shape
of stationary states depend both on the potential type and the damping. If the
damping is strong enough, for potential wells which in the overdamped regime
produce multimodal stationary states, stationary states in the underdamped
regime can be multimodal with the same number of modes like in the overdamped
regime. For the parabolic potential, the stationary density is always unimodal
and it is given by the two dimensional -stable density. For the mixture
of quartic and parabolic single-well potentials the stationary density can be
bimodal. Nevertheless, the parabolic addition, which is strong enough, can
destroy bimodlity of the stationary state.Comment: 9 page
Paradoxical diffusion: Discriminating between normal and anomalous random walks
Commonly, normal diffusive behavior is characterized by a linear dependence
of the second central moment on time, , while anomalous
behavior is expected to show a different time dependence, with for
superdiffusive motions. Here we demonstrate that this kind of qualification, if
applied straightforwardly, may be misleading: There are anomalous transport
motions revealing perfectly "normal" diffusive character (), yet being non-Markov and non-Gaussian in nature. We use recently developed
framework \cite[Phys. Rev. E \textbf{75}, 056702 (2007)]{magdziarz2007b} of
Monte Carlo simulations which incorporates anomalous diffusion statistics in
time and space and creates trajectories of such an extended random walk. For
special choice of stability indices describing statistics of waiting times and
jump lengths, the ensemble analysis of paradoxical diffusion is shown to hide
temporal memory effects which can be properly detected only by examination of
formal criteria of Markovianity (fulfillment of the Chapman-Kolmogorov
equation).Comment: 8 pages, 7 figure
Dynamic Thermal Analysis of a Power Amplifier
This paper presents dynamic thermal analyses of a power amplifier. All the
investigations are based on the transient junction temperature measurements
performed during the circuit cooling process. The presented results include the
cooling curves, the structure functions, the thermal time constant distribution
and the Nyquist plot of the thermal impedance. The experiments carried out
demonstrated the influence of the contact resistance and the position of the
entire cooling assembly on the obtained results.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
EFFECT OF MODE OF LOAD CARRIAGE ON POSTURAL SWAY
People commonly carry external loads for sport and recreational purposes; recently the safety of such practice has come into question. The purpose of this study was to evaluate balance under different load carriage conditions. Fifteen college-age individuals completed three blocks of quiet standing trials: unloaded, wearing a backpack, and wearing a shoulder bag. A-P sway amplitude was greater under the backpack condition than the unloaded condition (P = 0.013); however, A-P sway amplitude did not differ between the backpack and shoulder bag condition, nor did it differ between the unloaded and shoulder bag condition. M-L sway amplitude, sway area, peak sway velocity, and stance width were not dependent on load condition. This evidence suggests a backpack and shoulder bag are equally safe means of load carriage in college-age individuals
Two Algebraic Process Semantics for Contextual Nets
We show that the so-called 'Petri nets are monoids' approach initiated by Meseguer and Montanari can be extended from ordinary place/transition Petri nets to contextual nets by considering suitable non-free monoids of places. The algebraic characterizations of net concurrent computations we provide cover both the collective and the individual token philosophy, uniformly along the two interpretations, and coincide with the classical proposals for place/transition Petri nets in the absence of read-arcs
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