Biomedical subjects

Lev S Tsimring

Publications and source records attributed to Lev S Tsimring.

7 recordsLinked to original sources

PubMed2003

Order parameter description of stationary partially fluidized shear granular flows.

We carry out a detailed comparison of soft-particle molecular dynamics simulations with the theory of partially fluidized shear granular flows. We verify by direct simulations a constitutive relation based on the separation of the shear stress tensor into a fluid part proportional to the strain rate tensor, and a remaining solid part. The ratio of these two components is determined by the order parameter. Based on results of the simulations we construct the "free energy" function for the order parameter. We also present the simulations of the stationary deep 2D granular flows driven by an upper wall and compare it with the continuum theory.

Journal Article↗

PubMed2003

Model of coarsening and vortex formation in vibrated granular rods.

Neicu et al. observed experimentally spontaneous formation of the long-range orientational order and large-scale vortices in a system of vibrated macroscopic rods. We propose a phenomenological theory of this phenomenon based on a coupled system of equations for local rods density and tilt. The density evolution is described by the modified Cahn-Hilliard equation, while the tilt is described by the Ginzburg-Landau type equation. Our analysis shows that, in accordance with the Cahn-Hilliard dynamics, islands of the ordered phase appear spontaneously and grow due to coarsening. The generic vortex solutions of the Ginzburg-Landau equation for the tilt correspond to the vortical motion of the rods around the cores which are located near the centers of the islands.

Journal Article↗

PubMed2003

Using distributed nonlinear dynamics for public key encryption.

We introduce a new method for asymmetric (public key/private key) encryption exploiting properties of nonlinear dynamical systems. A high-dimensional dissipative nonlinear dynamical system is distributed between transmitter and receiver, so we call the method distributed dynamics encryption (DDE). The transmitter dynamics is public, and the receiver dynamics is hidden. A message is encoded by modulation of parameters of the transmitter, and this results in a shift of the overall system attractor. An unauthorized receiver does not know the hidden dynamics in the receiver and cannot decode the message. We present an example of DDE using a coupled map lattice.

Journal Article↗

PubMed2003

Dynamics-based sequential memory: winnerless competition of patterns.

We introduce a biologically motivated dynamical principle of sequential memory which is based on winnerless competition (WLC) of event images. This mechanism is implemented in a two-layer neural model of sequential spatial memory. We present the learning dynamics which leads to the formation of a WLC network. After learning, the system is capable of associative retrieval of prerecorded sequences of patterns.

Algorithms↗

PubMed2002

Contact tracing and epidemics control in social networks.

A generalization of the standard susceptible-infectious-removed stochastic model for epidemics in sparse random networks is introduced which incorporates contact tracing in addition to random screening. We propose a deterministic mean-field description that yields quantitative agreement with stochastic simulations on random graphs. Both the stochastic simulations and the mean-field equations show secondary epidemics if the contact tracing is not performed with sufficient strength. We also analyze the role of contact tracing in epidemics control in small-world networks and show that its effectiveness grows as the rewiring probability is reduced.

Journal Article↗

PubMed2002

Continuum theory of partially fluidized granular flows.

A continuum theory of partially fluidized granular flows is developed. The theory is based on a combination of the equations for the flow velocity and shear stresses coupled with the order-parameter equation which describes the transition between the flowing and static components of the granular system. We apply this theory to several important granular problems: avalanche flow in deep and shallow inclined layers, rotating drums, and shear granular flows between two plates. We carry out quantitative comparisons between the theory and experiment.

Journal Article↗

PubMed2002

Plasticity and learning in a network of coupled phase oscillators.

A generalized Kuramoto model of coupled phase oscillators with a slow varying coupling matrix is studied. The dynamics of the coupling coefficients is driven by the phase difference of pairs of oscillators in such a way that the coupling strengthens for synchronized oscillators and weakens for nonsynchronized pairs. The system possesses a family of stable solutions corresponding to synchronized clusters of different sizes. A particular cluster can be formed by applying external driving at a given frequency to a group of oscillators. Once established, the synchronized state is robust against noise and small variations in natural frequencies. The phase differences between oscillators within the synchronized cluster can be used for information storage and retrieval.

Artificial Intelligence↗