1,174 research outputs found
Interplay of frequency-synchronization with noise: current resonances, giant diffusion and diffusion-crests
We elucidate how the presence of noise may significantly interact with the
synchronization mechanism of systems exhibiting frequency-locking. The response
of these systems exhibits a rich variety of behaviors, such as resonances and
anti-resonances which can be controlled by the intensity of noise. The
transition between different locked regimes provokes the development of a
multiple enhancement of the effective diffusion. This diffusion behavior is
accompanied by a crest-like peak-splitting cascade when the distribution of the
lockings is self-similar, as it occurs in periodic systems that are able to
exhibit a Devil's staircase sequence of frequency-lockings.Comment: 7 pages, 6 figures, epl.cls. Accepted for publication in Europhysics
Letter
Viral self-assembly as a thermodynamic process
The protein shells, or capsids, of all sphere-like viruses adopt icosahedral
symmetry. In the present paper we propose a statistical thermodynamic model for
viral self-assembly. We find that icosahedral symmetry is not expected for
viral capsids constructed from structurally identical protein subunits and that
this symmetry requires (at least) two internal "switching" configurations of
the protein. Our results indicate that icosahedral symmetry is not a generic
consequence of free energy minimization but requires optimization of internal
structural parameters of the capsid proteins.Comment: pdf file, 13 pages, three figure
Entropic stochastic resonance: the constructive role of the unevenness
We demonstrate the existence of stochastic resonance (SR) in confined systems
arising from entropy variations associated to the presence of irregular
boundaries. When the motion of a Brownian particle is constrained to a region
with uneven boundaries, the presence of a periodic input may give rise to a
peak in the spectral amplification factor and therefore to the appearance of
the SR phenomenon. We have proved that the amplification factor depends on the
shape of the region through which the particle moves and that by adjusting its
characteristic geometric parameters one may optimize the response of the
system. The situation in which the appearance of such entropic stochastic
resonance (ESR) occurs is common for small-scale systems in which confinement
and noise play an prominent role. The novel mechanism found could thus
constitute an important tool for the characterization of these systems and can
put to use for controlling their basic properties.Comment: 8 pages, 8 figure
Biased diffusion in confined media: Test of the Fick-Jacobs approximation and validity criteria
We study biased, diffusive transport of Brownian particles through narrow,
spatially periodic structures in which the motion is constrained in lateral
directions. The problem is analyzed under the perspective of the Fick-Jacobs
equation which accounts for the effect of the lateral confinement by
introducing an entropic barrier in a one dimensional diffusion. The validity of
this approximation, being based on the assumption of an instantaneous
equilibration of the particle distribution in the cross-section of the
structure, is analyzed by comparing the different time scales that characterize
the problem. A validity criterion is established in terms of the shape of the
structure and of the applied force. It is analytically corroborated and
verified by numerical simulations that the critical value of the force up to
which this description holds true scales as the square of the periodicity of
the structure. The criterion can be visualized by means of a diagram
representing the regions where the Fick-Jacobs description becomes inaccurate
in terms of the scaled force versus the periodicity of the structure.Comment: 20 pages, 7 figure
Kinetic Equations for Diffusion in the Presence of Entropic Barriers
We use the mesoscopic nonequilibrium thermodynamics theory to derive the
general kinetic equation of a system in the presence of potential barriers. The
result is applied to the description of the evolution of systems whose dynamics
is influenced by entropic barriers. We analyze in detail the case of diffusion
in a domain of irregular geometry in which the presence of the boundaries
induces an entropy barrier when approaching the exact dynamics by a coarsening
of the description. The corresponding kinetic equation, named Fick-Jacobs
equation, is obtained, and its validity is generalized through the formulation
of a scaling law for the diffusion coefficient which depends on the shape of
the boundaries. The method we propose can be useful to analyze the dynamics of
systems at the nanoscale where the presence of entropy barriers is a common
feature.Comment: 16 pages, 5 figures. Accepted for publication in Phys. Rev.
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