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Biomedical subjects

Fabio Marchesoni

Publications and source records attributed to Fabio Marchesoni.

9 recordsLinked to original sources
PubMed2006

Subdiffusion and long-time anticorrelations in a stochastic single file.

The subdiffusion of a stochastic single file is interpreted as a jumping process. Contrary to the current continuous time random walk models, its statistics is characterized by finite averages of the jumping times and square displacements. Subdiffusion is then related to a persistent anticorrelation of the jump sequences. In continuous time representation, this corresponds to negative power-law velocity autocorrelations, attributable to the restricted geometry of the file diffusion.

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PubMed2006

Diffusion of interacting Brownian particles: Jamming and anomalous diffusion.

The free self-diffusion of an assembly of interacting particles confined on a quasi-one-dimensional ring is investigated both numerically and analytically. The interparticle pairwise interaction can be either attractive or repulsive and the energy barrier opposing thermal hopping of two particles one past the other is finite. Thus, for sufficiently long times, self-diffusion becomes normal or conventional diffusion. However, depending on the particle density, subdiffusive transients with exponent 12 and suppression of normal diffusion are observed. Above a certain density threshold, a sudden drop to zero of the diffusion coefficient for attractive particles signals the transition to a jammed phase. Furthermore, a Gaussian cluster of attractive particles condenses, by shrinking in size, for densities larger than such density threshold; lower density clusters spread out, regardless of the interaction sign, through a diffusion mechanism that is anomalous at short times, and normal for sufficiently long times. These effects could be observed in systems with colloidal particles, vortices, electrons, among other interacting particle systems.

Journal Article↗
PubMed2006

Achieving optimal rectification using underdamped rocked ratchets.

An underdamped rocked ratchet operated at very low temperatures and damping is shown: (i) to be capable of rectifying the ac input signal more efficiently than in the overdamped regime; (ii) to be insensitive to the initial conditions, at variance with noiseless, or deterministic, ratchets; and (iii) to be characterized by a wide damping "window," where its efficiency is appreciable also for weak input amplitudes. All these properties are rather robust, irrespective of the wave form of the drive and the ratchet potential. Our results relate to recent experiments on current-biased annular Josephson junctions and also on rectifiers of magnetic flux quanta in superconductors.

Journal Article↗
PubMed2006

Single-file diffusion on a periodic substrate.

An assembly of "nonpassing" particles diffusing on a one-dimensional periodic substrate is shown to undergo single-file diffusion for both noiseless (ballistic) and stochastic dynamics. The dependence of the corresponding diffusion coefficients on the density and temperature of the particles and on the substrate parameters is determined by means of numerical simulations and analytically interpreted within the formalism of standard Brownian motion.

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PubMed2005

Interacting particles on a rocked ratchet: rectification by condensation.

The transport of interacting particles subject to an external low-frequency ac force on a ratchetlike asymmetric substrate is studied via a nonlinear Fokker-Planck equation as well as via numerical simulations. With increasing the particle density, the ratchet current can either increase or decrease depending on the temperature, the drive amplitude, and the nature of the interparticle interaction. At low temperatures, attracting particles can condense randomly at some potential minima, thus breaking the discrete translational symmetry of the substrate. Depending on the drive amplitude, condensation results either in a drop to zero or in the saturation of the net particle velocity at densities above the condensation density-the latter case producing a very efficient rectification mechanism.

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PubMed2004

Stochastic transport of interacting particles in periodically driven ratchets.

An open system of overdamped, interacting Brownian particles diffusing on a periodic substrate potential U(x+l)=U(x) is studied in terms of an infinite set of coupled partial differential equations describing the time evolution of the relevant many-particle distribution functions. In the mean-field approximation, this hierarchy of equations can be replaced by a nonlinear integro-differential Fokker-Planck equation. This is applicable when the distance a between particles is much less than the interaction length lambda , i.e., a particle interacts with many others, resulting in averaging out fluctuations. The equation obtained in the mean-field approximation is applied to an ensemble of locally (a<<lambda<<l) interacting (either repelling or attracting) particles placed in an asymmetric one-dimensional substrate potential, either with an oscillating temperature (temperature rachet) or driven by an ac force (rocked ratchet). In both cases we focus on the high-frequency limit. For the temperature ratchet, we find that the net current is typically suppressed (or can even be inverted) with increasing density of the repelling particles. In contrast, the net current through a rocked ratchet can be enhanced by increasing the density of the repelling particles. In the case of attracting particles, our perturbation technique is valid up to a critical value of the particle density, above which a finite fraction of the particles starts condensing in a liquidlike state near the substrate minima. The dependence of the net transport current on the particle density and the interparticle potential is analyzed in detail for different values of the ratchet parameters.

Computer Simulation↗
PubMed2004

Transport via nonlinear signal mixing in ratchet devices.

The nonlinear signal mixing of two driving forces is used to control transport in overdamped ratchet devices. The interplay between the relative phase and the frequency ratio of the two driving forces is sufficient to generate an intriguing transport action that can be put to work to optimize shuttling and separation of particles in a variety of physical and technological applications. Analytic results for a striking multiple current reversal behavior including prominent, spikelike current features are obtained for doubly rocked and rocked-pulsated Brownian ratchets. This tunable signal mixing is readily implementable and exhibits even richer behaviors than those realized by the hard-to-implement modifiable-ratchet profiles.

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PubMed2004

Manipulating small particles in mixtures far from equilibrium.

The motion of two interacting species of small particles, coupled differently to their environment, is studied both analytically and via numerical simulations. We find three ways of controlling the particle motion of one (passive) B species by means of another (active) A species: (i) dragging the target particles B by driving the auxiliary particles A, (ii) rectifying the motion of the B species on the asymmetric potential created by the A-B interactions, and (iii) dynamically modifying (pulsating) this potential by controlling the motion of the A particles. This allows easy control of the magnitude and direction of the velocity of the target particles by changing the ac drive(s).

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