Biomedical subjects

T Elperin

Publications and source records attributed to T Elperin.

16 recordsLinked to original sources

PubMed2003

Peculiarities of first-order phase transitions in the presence of an electric field.

In this study, we developed a variational approach for thermodynamic systems with nondistributed parameters in the presence of the external electrostatic field. Using the obtained general relations, we analyzed some characteristic features of the first-order phase transitions in the presence of electric field. We determined the range of the thermodynamic parameters where both phases are stable (hysteresis), and the range of the parameters whereby both phases are metastable. In the range where both phases are metastable, we considered kinetics of formation of a new phase and determined the dependencies of the concentrations of phases in the region of their metastability on the amplitude of the external electric field. The obtained results imply the feasibility to control phase composition in the system by varying the amplitude of the external electrostatic field.

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PubMed2001

Thermophoretic and ponderomotive forces in a linear cluster of particles.

We investigate amplification of thermophoretic and ponderomotive forces caused by renormalization of static fields in linear clusters of particles with scale separation. We found analytically the dependence of the forces acting on the particles in a cluster as a function of the number of particles in a cluster and material characteristics of the particles and the surrounding fluid. We analytically determined the velocity of stationary motion of particles, velocity distribution in a surrounding viscous fluid, and the thermophoretic force when the particles remain stationary due to the applied constraint forces.

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PubMed2001

Mean-field theory for a passive scalar advected by a turbulent velocity field with a random renewal time.

Mean-field theory for turbulent transport of a passive scalar (e.g., particles and gases) is discussed. Equations for the mean number density of particles advected by a random velocity field, with a finite correlation time, are derived. Mean-field equations for a passive scalar comprise spatial derivatives of high orders due to the nonlocal nature of passive scalar transport in a random velocity field with a finite correlation time. A turbulent velocity field with a random renewal time is considered. This model is more realistic than that with a constant renewal time used by Elperin et al. [Phys. Rev. E 61, 2617 (2000)], and employs two characteristic times: the correlation time of a random velocity field tau(c), and a mean renewal time tau. It is demonstrated that the turbulent diffusion coefficient is determined by the minimum of the times tau(c) and tau. The mean-field equation for a passive scalar was derived for different ratios of tau/tau(c). The important role of the statistics of the field of Lagrangian trajectories in turbulent transport of a passive scalar, in a random velocity field with a finite correlation time, is demonstrated. It is shown that in the case tau(c)<<tau<<tau(N) the form of the mean-field equation for a passive scalar is independent of the statistics of the velocity field, where tau(N) is the characteristic time of variations of a mean passive scalar field.

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PubMed2001

Strange behavior of a passive scalar in a linear velocity field.

Damping (or growth) rates of a typical realization, mean-field and high-order correlation functions of a passive scalar (e.g., a number density of particles) advected by a linear velocity fields are estimated. It is shown that all statistical moments higher than the first moment and a typical realization of a passive scalar without an external pumping decay for both laminar and random incompressible linear velocity fields. Strong compressibility of a laminar linear velocity field can result in a growth of a typical realization and the high-order moments of a passive scalar. It is demonstrated that for a laminar compressible linear velocity field the flux of particles from the infinity does not vanish and the total number of particles is not conserved. For a random compressible linear velocity field a typical realization decays whereas the high-order moments of a passive scalar can grow. Comparison of the obtained results with those for dynamics of a passive scalar advected by a homogeneous isotropic and compressible turbulent flow with a given longitudinal two-point correlation function F=1-r(2) is performed (where r is the distance between two points measured in the units of the maximum scale of turbulent motions).

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PubMed2000

Amplification of a magnetic field in systems with a finite electric conductivity

In this study we investigated the kinematics of electromagnetic fields with various configurations of the magnetic and electric fields in systems with spherical and cylindrical symmetry using the exact solutions to the diffusion equation for the electromagnetic field in systems with moving boundaries. In the class of self-similar solutions we determined analytically conditions for the amplification of the electromagnetic field as functions of material velocity and electric conductivity. We investigated also the effects of the amplification of an electromagnetic field during propagation of a spherical shock wave in a dielectric material whereby the shock wave causes transformation of a material into a conductor.

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PubMed2000

Granular flow in a three-dimensional rotating container

We considered a flow of a cohesionless granular material in a partially filled three-dimensional rotating container. A model is suggested to describe a density of the surface flow and the profile of the free surface of the granular material. It is shown that when the container has an ellipsoidal shape the obtained system of partial differential equations can be reduced to a set of two ordinary differential equations.

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PubMed1999

Mechanism of the onset of axial segregation in a rotating cylindrical drum filled with binary granular mixtures.

A phenomenon of axial band formation in a long rotating cylindrical drum filled with a binary granular mixture is described as a two-stage process. At the first stage, due to different mobility of the large and small particles, a central core occupied by a small-size fraction is formed along the axis of the drum. The axial segregation, i.e., transverse band formation, is found to be associated with the instability of the radially segregated state caused by an asymmetry of the free surface of the granular material. This instability is caused by the difference in the repose angles of two granular fractions and deviation of the filling level of the drum from 0.5.

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PubMed1996