22,526 research outputs found
Steering the potential barriers: entropic to energetic
We propose a new mechanism to alter the nature of the potential barriers when
a biased Brownian particle under goes a constrained motion in narrow, periodic
channel. By changing the angle of the external bias, the nature of the
potential barriers changes from purely entropic to energetic which in turn
effects the diffusion process in the system. At an optimum angle of the bias,
the nonlinear mobility exhibits a striking bell-shaped behavior. Moreover, the
enhancement of the scaled effective diffusion coefficient can be efficiently
controlled by the angle of the bias. This mechanism enables the proper design
of channel structures for transport of molecules and small particles. The
approximative analytical predictions have been verified by precise Brownian
dynamic simulations.Comment: (6 pages, 7 figures) Submitted to PR
On the Melting of Bosonic Stripes
We use quantum Monte Carlo simulations to determine the finite temperature
phase diagram and to investigate the thermal and quantum melting of stripe
phases in a two-dimensional hard-core boson model. At half filling and low
temperatures the stripes melt at a first order transition. In the doped system,
the melting transitions of the smectic phase at high temperatures and the
superfluid smectic (supersolid) phase at low temperatures are either very
weakly first order, or of second order with no clear indications for an
intermediate nematic phase.Comment: 4 pages, 5 figure
Spontaneous spiking in an autaptic Hodgkin-Huxley set up
The effect of intrinsic channel noise is investigated for the dynamic
response of a neuronal cell with a delayed feedback loop. The loop is based on
the so-called autapse phenomenon in which dendrites establish not only
connections to neighboring cells but as well to its own axon. The biophysical
modeling is achieved in terms of a stochastic Hodgkin-Huxley model containing
such a built in delayed feedback. The fluctuations stem from intrinsic channel
noise, being caused by the stochastic nature of the gating dynamics of ion
channels. The influence of the delayed stimulus is systematically analyzed with
respect to the coupling parameter and the delay time in terms of the interspike
interval histograms and the average interspike interval. The delayed feedback
manifests itself in the occurrence of bursting and a rich multimodal interspike
interval distribution, exhibiting a delay-induced reduction of the spontaneous
spiking activity at characteristic frequencies. Moreover, a specific
frequency-locking mechanism is detected for the mean interspike interval.Comment: 8 pages, 10 figure
Controlling diffusive transport in confined geometries
We analyze the diffusive transport of Brownian particles in narrow channels
with periodically varying cross-section. The geometrical confinements lead to
entropic barriers, the particle has to overcome in order to proceed in
transport direction. The transport characteristics exhibit peculiar behaviors
which are in contrast to what is observed for the transport in potentials with
purely energetic barriers. By adjusting the geometric parameters of the channel
one can effectively tune the transport and diffusion properties. A prominent
example is the maximized enhancement of diffusion for particular channel
parameters. The understanding of the role of channel-shape provides the
possibility for a design of stylized channels wherein the quality of the
transport can be efficiently optimized.Comment: accepted for publication in Acta Physica Polonica
Double Entropic Stochastic Resonance
We demonstrate the appearance of a purely entropic stochastic resonance (ESR)
occurring in a geometrically confined system, where the irregular boundaries
cause entropic barriers. The interplay between a periodic input signal, a
constant bias and intrinsic thermal noise leads to a resonant ESR-phenomenon in
which feeble signals become amplified. This new phenomenon is characterized by
the presence of two peaks in the spectral amplification at corresponding
optimal values of the noise strength. The main peak is associated with the
manifest stochastic resonance synchronization mechanism involving the
inter-well noise-activated dynamics while a second peak relates to a regime of
optimal sensitivity for intra-well dynamics. The nature of ESR, occurring when
the origin of the barrier is entropic rather than energetic, offers new
perspectives for novel investigations and potential applications. ESR by itself
presents yet another case where one constructively can harvest noise in driven
nonequilibrium systems.Comment: 6 pages, 7 figures ; Europhys. Lett., in press (2009
The future of employment relations:goodbye ‘flexicurity’ - welcome back transitional labour markets?
The future of employment relations:goodbye ‘flexicurity’ - welcome back transitional labour markets?
On the arithmetic of Krull monoids with infinite cyclic class group
Let be a Krull monoid with infinite cyclic class group and let denote the set of classes containing prime divisors. We study under
which conditions on some of the main finiteness properties of
factorization theory--such as local tameness, the finiteness and rationality of
the elasticity, the structure theorem for sets of lengths, the finiteness of
the catenary degree, and the existence of monotone and of near monotone chains
of factorizations--hold in . In many cases, we derive explicit
characterizations
- …