10 research outputs found
Mesoscopic non-equilibrium thermodynamics approach to the dynamics of polymers
We present a general formalism able to derive the kinetic equations of
polymer dynamics. It is based on the application of nonequilibrium
thermodynamics to analyze the irreversible processes taking place in the
conformational space of the macromolecules. The Smoluchowski equation results
from the analysis of the underlying diffusion process in that space within the
scheme of nonequilibrium thermodynamics. We apply the method to different
situations, concerning flexible, semiflexible and rod-like polymers and to the
case of more concentrated solutions in which interactions become important.Comment: 13 pages (RevTex). To be published in Physica
A Mesoscopic Approach to the ``Negative'' Viscosity Effect in Ferrofluids
We present a mesoscopic approach to analyze the dynamics of a single magnetic
dipole under the influence of an oscillating magnetic field, based on the
formulation of a Fokker-Planck equation. The dissipated power and the viscosity
of a suspension of such magnetic dipoles are calculated from non-equilibrium
thermodynamics of magnetized systems. By means of this method we have found a
non-monotonous behaviour of the viscosity as a function of the frequency of the
field which has been referred to as the ``negative'' viscosity effect.
Moreover, we have shown that the viscosity depends on the vorticity field thus
exhibiting non-Newtonian behaviour. Our analysis is complemented with numerical
simulations which reproduce the behaviour of the viscosity we have found and
extend the scope of our analytical approach to higher values of the magnetic
field.Comment: 9 pages, 2 eps figures, simulations have been adde
Simultaneous Brownian Motion of N Particles in a Temperature Gradient
A system of N Brownian particles suspended in a nonuniform heat bath is
treated as a thermodynamic system whith internal degrees of freedom, in this
case their velocities and coordinates. Applying the scheme of non-equilibrium
thermodynamics, one then easily obtains the Fokker-Planck equation for
simultaneous Brownian motion of N particles in a temperature gradient. This
equation accounts for couplings in the motion as a result of hydrodynamic
interactions between particles.Comment: 9 pages, RevTe
Shot noise as a tool to probe an electron energy distribution
We discuss the possibility to employ the shot-noise measurements for the
analysis of the energy resolved ballistic currents. Coulomb interactions play
an essential role in this technique, since they lead to the
shot-noise-suppression level which depends on the details of the energy
profile.Comment: 7 pages, 2 figs; contribution to the Proceedings of EP2DS-14, Prague,
2001; to appear in Physica
Stochastic model for the dynamics of interacting Brownian particles
Using the scheme of mesoscopic nonequilibrium thermodynamics, we construct
the one- and two- particle Fokker-Planck equations for a system of interacting
Brownian particles. By means of these equations we derive the corresponding
balance equations. We obtain expressions for the heat flux and the pressure
tensor which enable one to describe the kinetic and potential energy
interchange of the particles with the heat bath. Through the momentum balance
we analyze in particular the diffusion regime to obtain the collective
diffusion coefficient in terms of the hydrodynamic and the effective forces
acting on the Brownian particles.Comment: latex fil
Nonequilibrium thermodynamics versus model grain growth: derivation and some physical implications
Nonequilibrium thermodynamics formalism is proposed to derive the flux of
grainy (bubbles-containing) matter, emerging in a nucleation growth process.
Some power and non-power limits, due to the applied potential as well as owing
to basic correlations in such systems, have been discussed. Some encouragement
for such a discussion comes from the fact that the nucleation and growth
processes studied, and their kinetics, are frequently reported in literature as
self-similar (characteristic of algebraic correlations and laws) both in basic
entity (grain; bubble) size as well as time scales.Comment: 8 pages, 1 figur
On temperature- and space-dimension dependent matter agglomeration in a mature growing stage
Model matter agglomerations, with temperature as leading control parameter,
have been considered, and some of their characteristics have been studied. The
primary interest has been focused on the grain volume fluctuations, the
magnitude of which readily differentiates between two commonly encountered
types of matter agglomeration/aggregation processes, observed roughly for high-
and low-density matter organizations. The two distinguished types of matter
arrangements have been described through the (entropic) potential driving
system. The impact of the potential type on the character of matter
agglomeration has been studied, preferentially for (low density) matter
agglomeration for which a logarithmic measure of its speed has been proposed. A
common diffusion as well as mechanical relaxation picture, emerging during the
mature growing stage, has been drawn using a phenomenological line of
argumentation. Applications, mostly towards obtaining soft agglomerates of
so-called jammed materials, have been mentioned
On the origin of plankton patchiness
Plankton is the productive base of aquatic ecosystems and plays a major role
in the global control of atmospheric carbon dioxide. Nevertheless, after
intensive study, the factors that drive its spatial distribution are still far
from being clear. The models proposed so far show very limited agreement with
actual data as many of their results are not consistent with field
observations. Here we show that fluctuations and turbulent diffusion in
standard prey-predator models are able to accurately and consistently explain
plankton field observations at mesoscales (1-100 km). This includes not only
the spatial pattern but also its temporal evolution. We explicitly elucidate
the interplay between physical and biological factors, suggesting that the form
in which small scale biotic fluctuations are transferred to larger scales may
constitute one of the key elements in determining the spatial distribution of
plankton in the sea.Comment: 16 pages, 3 figure