Biomedical subjects

M Urbakh

Publications and source records attributed to M Urbakh.

At least 19 recordsLinked to original sources

PubMed2006

The escape of a particle from a driven harmonic potential to an attractive surface.

We investigate theoretically the dynamics of a colloidal particle, trapped by optical tweezers, which gradually approaches an attractive surface with a constant velocity until it escapes the trap and jumps to the surface. We find that the height of the energy barrier in such a colloid-surface system follows the scaling DeltaE proportional, variant(z(0)(t)-const)(32) when the trap approaches the surface, z(0)(t) being the trap surface distance. Using this scaling we derive equations for the probability density function of the jump lengths, for the velocity dependence of its mean and most probable values, and for the variance. These can be used to extract the parameters of the particle-surface interaction from experimental data.

Journal Article↗

PubMed2005

Tuning diffusion and friction in microscopic contacts by mechanical excitations.

We demonstrate that lateral vibrations of a substrate can dramatically increase surface diffusivity and mobility and reduce friction at the nanoscale. Dilatancy is shown to play an essential role in the dynamics of a nanometer-size tip which interacts with a vibrating surface. We find an abrupt dilatancy transition from the state with a small tip-surface separation to the state with a large separation as the vibration frequency increases. Atomic force microscopy experiments are suggested which can test the predicted effects.

Journal Article↗

PubMed2004

From deterministic dynamics to kinetic phenomena.

We investigate a one-dimensional Hamiltonian system that describes a system of particles interacting through short-range repulsive potentials. Depending on the particle mean energy epsilon the system demonstrates a spectrum of kinetic regimes, characterized by their transport properties ranging from ballistic motion to localized oscillations through anomalous diffusion regimes. We establish relationships between the observed kinetic regimes and the "thermodynamic" states of the system. The nature of heat conduction in the proposed model is discussed.

Journal Article↗

PubMed2004

Friction through dynamical formation and rupture of molecular bonds.

We introduce a model for friction in a system of two rigid plates connected by bonds (springs) and experiencing an external drive. The macroscopic frictional properties of the system are shown to be directly related to the rupture and formation dynamics of the microscopic bonds. Different regimes of motion are characterized by different rates of rupture and formation relative to the driving velocity. In particular, the stick-slip regime is shown to correspond to a cooperative rupture of the bonds. Moreover, the notion of static friction is shown to be dependent on the experimental conditions and time scales. The overall behavior can be described in terms of two Deborah numbers.

Journal Article↗

PubMed2004

Directed molecular transport in an oscillating symmetric channel.

A mechanism responsible for the directed transport and molecular separation in a symmetric channel is proposed. We found that under the action of spatial harmonic oscillations of the channel, the system exhibits a directed transport in either direction, presenting multiple current reversals as the amplitude and/or frequency of the oscillations are varied. The particles of different masses may be forced to move with different velocities in the same or in the opposite directions by properly adjusting driving parameters. The directed transport can be produced in both directions even in the absence of thermal noise; the latter can speed up or slow down the transport depending on the system parameters.

Biological Clocks↗

PubMed2003

Dynamical heat channels.

We consider heat conduction in a 1D dynamical channel. The channel consists of an ensemble of noninteracting particles, which move between two heat baths according to some dynamical process. We show that the essential thermodynamic properties of the heat channel can be obtained from the diffusion properties of the underlying particles. Emphasis is put on the conduction under anomalous diffusion conditions.

Journal Article↗

PubMed2003

Beyond the conventional description of dynamic force spectroscopy of adhesion bonds.

Dynamic force spectroscopy of single molecules is described by a model that predicts a distribution of rupture forces, the corresponding mean rupture force, and variance, which are all amenable to experimental tests. The distribution has a pronounced asymmetry, which has recently been observed experimentally. The mean rupture force follows a (lnV)2/3 dependence on the pulling velocity, V, and differs from earlier predictions. Interestingly, at low pulling velocities, a rebinding process is obtained whose signature is an intermittent behavior of the spring force, which delays the rupture. An extension to include conformational changes of the adhesion complex is proposed, which leads to the possibility of bimodal distributions of rupture forces.

Spectrum Analysis↗

PubMed2002

Ballistic flights and random diffusion as building blocks for Hamiltonian kinetics.

We propose a kinetic approach to transport in Hamiltonian systems with a mixed phase space. The approach is based on the decomposition of the dynamical picture into two contributions: (a) ballistic flights, and (b) random diffusion. The kinetic scheme leads to a stochastic process with statistical properties which are similar to those produced by the original Hamiltonian. We show that our approach helps in obtaining an insight into several properties of Hamiltonian kinetics such as anomalous diffusion, chaos-assisted population exchange, and current rectification. In particular, the chaos-assisted exchange offers a classical counterpart for the recently reported chaos-assisted tunneling.

Journal Article↗

PubMed2002

Manipulation of dynamical systems by symmetry breaking.

We propose an approach to manipulate and control transport in Hamiltonian systems which are characterized by a mixed phase space. The approach is based on symmetry breaking of the phase space structure by applying a zero-mean periodic force for a finite duration of time. This induces time and space reversal asymmetry, which modifies the internal dynamics of the system and leads to directed transport. It is shown that our strategy allows to perform manipulations both with individual particles and with statistical ensembles of particles.

Journal Article↗

PubMed2001

Confined molecules under shear: from a microscopic description to phenomenology.

A coarse grained two-state model is derived starting from a molecular dynamics description of a molecular system under shear. This model captures the main features of the response of a confined system under shear, and generalizes the phenomenological Tomlinson model for the response of a driven system. The derivation is based on the solution of coupled microscopic equations using a mean field approximation. The two-state model agrees well with the direct numerical solution and offers a practical approach to investigate the response of sheared systems under a broad range of parameters.

Journal Article↗

PubMed2000

Molecular motor that never steps backwards.

We investigate the dynamics of a classical particle in a one-dimensional two-wave potential composed of two periodic potentials that are time independent and of the same amplitude and periodicity. One of the periodic potentials is externally driven and performs a translational motion with respect to the other. It is shown that, if one of the potentials is of the ratchet type, translation of the potential in a given direction leads to motion of the particle in the same direction, whereas translation in the opposite direction leaves the particle localized at its original location. Moreover, even if the translation is random, but still has a finite velocity, an efficient directed transport of the particle occurs.

Journal Article↗

PubMed2000

Atomic scale engines: cars and wheels.

We introduce a new approach to build microscopic engines on the atomic scale that move translationally or rotationally and can perform useful functions such as the pulling of a cargo. Characteristic of these engines is the possibility to determine dynamically the directionality of the motion. The approach is based on the transformation of the fed energy to directed motion through a dynamical competition between the intrinsic lengths of the moving object and the supporting carrier.

Journal Article↗

PubMed1996