19,296 research outputs found
Resonant activation: a strategy against bacterial persistence
A bacterial colony may develop a small number of cells genetically identical
to, but phenotypically different from other normally growing bacteria. These
so-called persister cells keep themselves in a dormant state and thus are
insensitive to antibiotic treatment, resulting in serious problems of drug
resistance. In this paper, we proposed a novel strategy to "kill" persister
cells by triggering them to switch, in a fast and synchronized way, into
normally growing cells that are susceptible to antibiotics. The strategy is
based on resonant activation (RA), a well-studied phenomenon in physics where
the internal noise of a system can constructively facilitate fast and
synchronized barrier crossings. Through stochastic Gilliespie simulation with a
generic toggle switch model, we demonstrated that RA exists in the phenotypic
switching of a single bacterium. Further, by coupling single cell level and
population level simulations, we showed that with RA, one can greatly reduce
the time and total amount of antibiotics needed to sterilize a bacterial
population. We suggest that resonant activation is a general phenomenon in
phenotypic transition, and can find other applications such as cancer therapy.Comment: 21 pages, 12 figures, submitte
Quantum dynamics in strong fluctuating fields
A large number of multifaceted quantum transport processes in molecular
systems and physical nanosystems can be treated in terms of quantum relaxation
processes which couple to one or several fluctuating environments. A thermal
equilibrium environment can conveniently be modelled by a thermal bath of
harmonic oscillators. An archetype situation provides a two-state dissipative
quantum dynamics, commonly known under the label of a spin-boson dynamics. An
interesting and nontrivial physical situation emerges, however, when the
quantum dynamics evolves far away from thermal equilibrium. This occurs, for
example, when a charge transferring medium possesses nonequilibrium degrees of
freedom, or when a strong time-dependent control field is applied externally.
Accordingly, certain parameters of underlying quantum subsystem acquire
stochastic character. Herein, we review the general theoretical framework which
is based on the method of projector operators, yielding the quantum master
equations for systems that are exposed to strong external fields. This allows
one to investigate on a common basis the influence of nonequilibrium
fluctuations and periodic electrical fields on quantum transport processes.
Most importantly, such strong fluctuating fields induce a whole variety of
nonlinear and nonequilibrium phenomena. A characteristic feature of such
dynamics is the absence of thermal (quantum) detailed balance.Comment: review article, Advances in Physics (2005), in pres
Restoring the encoding properties of a stochastic neuron model by an exogenous noise
Here we evaluate the possibility of improving the encoding properties of an impaired neuronal system by superimposing an exogenous noise to an external electric stimulation signal. The approach is based on the use of mathematical neuron models consisting of stochastic HH-like circuit, where the impairment of the endogenous presynaptic inputs is described as a subthreshold injected current and the exogenous stimulation signal is a sinusoidal voltage perturbation across the membrane. Our results indicate that a correlated Gaussian noise, added to the sinusoidal signal can significantly increase the encoding properties of the impaired system, through the Stochastic Resonance (SR) phenomenon. These results suggest that an exogenous noise, suitably tailored, could improve the efficacy of those stimulation techniques used in neuronal systems, where the presynaptic sensory neurons are impaired and have to be artificially bypassed
Resonance phenomena in discrete systems with bichromatic input signal
We undertake a detailed numerical study of the twin phenomena of stochastic
and vibrational resonance in a discrete model system in the presence of
bichromatic input signal. A two parameter cubic map is used as the model that
combines the features of both bistable and threshold settings. Our analysis
brings out several interesting results, such as, the existence of a cross over
behaviour from vibrational to stochastic resonance and the possibility of using
stochastic resonance as a filter for the selective detection/transmission of
the component frequencies in a composite signal. The study also reveals a
fundamental difference between the bistable and threshold mechanisms with
respect to amplification of a multi signal input.Comment: 17 pages, 16 figures, submitted to European Physical Journa
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