13,382 research outputs found
Rectification of spatial disorder
We demonstrate that a large ensemble of noiseless globally coupled-pinned
oscillators is capable of rectifying spatial disorder with spontaneous current
activated through a dynamical phase transition mechanism, either of first or
second order, depending on the profile of the pinning potential. In the
presence of an external weak drive, the same collective mechanism can result in
an absolute negative mobility, which, though not immediately related to
symmetry breaking, is most prominent at the phase transition
Phase synchronization and noise-induced resonance in systems of coupled oscillators
We study synchronization and noise-induced resonance phenomena in systems of
globally coupled oscillators, each possessing finite inertia. The behavior of
the order parameter, which measures collective synchronization of the system,
is investigated as the noise level and the coupling strength are varied, and
hysteretic behavior is manifested. The power spectrum of the phase velocity is
also examined and the quality factor as well as the response function is
obtained to reveal noise-induced resonance behavior.Comment: to be published in Phys. Rev.
Resonant effects in a voltage-activated channel gating
The non-selective voltage activated cation channel from the human red cells,
which is activated at depolarizing potentials, has been shown to exhibit
counter-clockwise gating hysteresis. We have analyzed the phenomenon with the
simplest possible phenomenological models by assuming discrete
states, i.e. two normal open/closed states with two different states of ``gate
tension.'' Rates of transitions between the two branches of the hysteresis
curve have been modeled with single-barrier kinetics by introducing a
real-valued ``reaction coordinate'' parameterizing the protein's conformational
change. When described in terms of the effective potential with cyclic
variations of the control parameter (an activating voltage), this model
exhibits typical ``resonant effects'': synchronization, resonant activation and
stochastic resonance. Occurrence of the phenomena is investigated by running
the stochastic dynamics of the model and analyzing statistical properties of
gating trajectories.Comment: 12 pages, 9 figure
Scale-free networks in complex systems
In the past few years, several studies have explored the topology of
interactions in different complex systems. Areas of investigation span from
biology to engineering, physics and the social sciences. Although having
different microscopic dynamics, the results demonstrate that most systems under
consideration tend to self-organize into structures that share common features.
In particular, the networks of interaction are characterized by a power law
distribution, , in the number of connections per node,
, over several orders of magnitude. Networks that fulfill this propriety of
scale-invariance are referred to as ``scale-free''. In the present work we
explore the implication of scale-free topologies in the antiferromagnetic (AF)
Ising model and in a stochastic model of opinion formation. In the first case
we show that the implicit disorder and frustration lead to a spin-glass phase
transition not observed for the AF Ising model on standard lattices. We further
illustrate that the opinion formation model produces a coherent, turbulent-like
dynamics for a certain range of parameters. The influence, of random or
targeted exclusion of nodes is studied.Comment: 9 pages, 4 figures. Proceeding to "SPIE International Symposium
Microelectronics, MEMS, and Nanotechnology", 11-15 December 2005, Brisbane,
Australi
Stochastic Resonance in Underdamped, Bistable Systems
We carry out a detailed numerical investigation of stochastic resonance in
underdamped systems in the non-perturbative regime. We point out that an
important distinction between stochastic resonance in overdamped and
underdamped systems lies in the lack of dependence of the amplitude of the
noise-averaged trajectory on the noise strength, in the latter case. We provide
qualitative explanations for the observed behavior and show that signatures
such as the initial decay and long-time oscillatory behaviour of the temporal
correlation function and peaks in the noise and phase averaged power spectral
density, clearly indicate the manifestation of resonant behaviour in noisy,
underdamped bistable systems in the weak to moderate noise regime.Comment: Revtex; (10+8)pp including 8 figure
Stochastic Modeling of Expression Kinetics Identifies Messenger Half-Lives and Reveals Sequential Waves of Co-ordinated Transcription and Decay
The transcriptome in a cell is finely regulated by a large number of molecular mechanisms able to control the balance between mRNA production and degradation. Recent experimental findings have evidenced that fine and specific regulation of degradation is needed for proper orchestration of a global cell response to environmental conditions. We developed a computational technique based on stochastic modeling, to infer condition-specific individual mRNA half-lives directly from gene expression time-courses. Predictions from our method were validated by experimentally measured mRNA decay rates during the intraerythrocytic developmental cycle of Plasmodium falciparum. We then applied our methodology to publicly available data on the reproductive and metabolic cycle of budding yeast. Strikingly, our analysis revealed, in all cases, the presence of periodic changes in decay rates of sequentially induced genes and co-ordination strategies between transcription and degradation, thus suggesting a general principle for the proper coordination of transcription and degradation machinery in response to internal and/or external stimuli. Citation: Cacace F, Paci P, Cusimano V, Germani A, Farina L (2012) Stochastic Modeling of Expression Kinetics Identifies Messenger Half-Lives and Reveals Sequential Waves of Co-ordinated Transcription and Decay. PLoS Comput Biol 8(11): e1002772. doi:10.1371/journal.pcbi.100277
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