3,746 research outputs found
Nonextensive diffusion as nonlinear response
The porous media equation has been proposed as a phenomenological
``non-extensive'' generalization of classical diffusion. Here, we show that a
very similar equation can be derived, in a systematic manner, for a classical
fluid by assuming nonlinear response, i.e. that the diffusive flux depends on
gradients of a power of the concentration. The present equation distinguishes
from the porous media equation in that it describes \emph{% generalized
classical} diffusion, i.e. with scaling, but with a generalized
Einstein relation, and with power-law probability distributions typical of
nonextensive statistical mechanics
Lattice gas with ``interaction potential''
We present an extension of a simple automaton model to incorporate non-local
interactions extending over a spatial range in lattice gases. {}From the
viewpoint of Statistical Mechanics, the lattice gas with interaction range may
serve as a prototype for non-ideal gas behavior. {}From the density
fluctuations correlation function, we obtain a quantity which is identified as
a potential of mean force. Equilibrium and transport properties are computed
theoretically and by numerical simulations to establish the validity of the
model at macroscopic scale.Comment: 12 pages LaTeX, figures available on demand ([email protected]
Questioning the validity of non-extensive thermodynamics for classical Hamiltonian systems
We examine the non-extensive approach to the statistical mechanics of
Hamiltonian systems with where is the classical kinetic energy. Our
analysis starts from the basics of the formalism by applying the standard
variational method for maximizing the entropy subject to the average energy and
normalization constraints. The analytical results show (i) that the
non-extensive thermodynamics formalism should be called into question to
explain experimental results described by extended exponential distributions
exhibiting long tails, i.e. -exponentials with , and (ii) that in the
thermodynamic limit the theory is only consistent in the range
where the distribution has finite support, thus implying that configurations
with e.g. energy above some limit have zero probability, which is at variance
with the physics of systems in contact with a heat reservoir. We also discuss
the (-dependent) thermodynamic temperature and the generalized specific
heat.Comment: To appear in EuroPhysics Letter
Is the Tsallis entropy stable?
The question of whether the Tsallis entropy is Lesche-stable is revisited. It
is argued that when physical averages are computed with the escort
probabilities, the correct application of the concept of Lesche-stability
requires use of the escort probabilities. As a consequence, as shown here, the
Tsallis entropy is unstable but the thermodynamic averages are stable. We
further show that Lesche stability as well as thermodynamic stability can be
obtained if the homogeneous entropy is used as the basis of the formulation of
non-extensive thermodynamics. In this approach, the escort distribution arises
naturally as a secondary structure.Comment: 6 page
"Blue energy" from ion adsorption and electrode charging in sea- and river water
A huge amount of entropy is produced at places where fresh water and seawater
mix, for example at river mouths. This mixing process is a potentially enormous
source of sustainable energy, provided it is harnessed properly, for instance
by a cyclic charging and discharging process of porous electrodes immersed in
salt and fresh water, respectively [D. Brogioli, Phys. Rev. Lett. 103, 058501
(2009)]. Here we employ a modified Poisson-Boltzmann free-energy density
functional to calculate the ionic adsorption and desorption onto and from the
charged electrodes, from which the electric work of a cycle is deduced. We
propose optimal (most efficient) cycles for two given salt baths involving two
canonical and two grand-canonical (dis)charging paths, in analogy to the
well-known Carnot cycle for heat-to-work conversion from two heat baths
involving two isothermal and two adiabatic paths. We also suggest a slightly
modified cycle which can be applied in cases that the stream of fresh water is
limited.Comment: 7 Figure
A repulsive reference potential reproducing the dynamics of a liquid with attractions
A well-known result of liquid state theory is that the structure of dense
fluids is mainly determined by repulsive forces. The WCA potential, which cuts
intermolecular potentials at their minima, is therefore often used as a
reference. However, this reference gives quite wrong results for the viscous
dynamics of the Kob-Andersen binary Lennard-Jones liquid [Berthier and Tarjus,
Phys. Rev. Lett. 103, 170601 (2009)]. We show that repulsive inverse-power law
potentials provide a useful reference for this liquid by reproducing its
structure, dynamics, and isochoric heat capacity
Breakdown of Hydrodynamic Transport Theory in the Ordered Phase of Helimagnets
It is shown that strong fluctuations preclude a hydrodynamic description of
transport phenomena in helimagnets, such as MnSi, at T>0. This breakdown of
hydrodynamics is analogous to the one in chiral liquid crystals. Mode-mode
coupling effects lead to infinite renormalizations of various transport
coefficients, and the actual macroscopic description is nonlocal. At T=0 these
effects are weakened due to the fluctuation-dissipation theorem, and the
renormalizations remain finite. Observable consequences of these results, as
manifested in the neutron scattering cross-section, are discussedComment: 4pp., 1 eps figur
The RES complex is required for efficient transformation of the precatalytic B spliceosome into an activated Bact complex.
The precise function of the trimeric retention and splicing (RES) complex in pre-mRNA splicing remains unclear. Here we dissected the role of RES during the assembly and activation of yeast spliceosomes. The efficiency of pre-mRNA splicing was significantly lower in the absence of the RES protein Snu17, and the recruitment of its binding partners, Pml1 (pre-mRNA leakage protein 1) and Bud13 (bud site selection protein 13), to the spliceosome was either abolished or substantially reduced. RES was not required for the assembly of spliceosomal B complexes, but its absence hindered efficient Bact complex formation. ΔRES spliceosomes were no longer strictly dependent on Prp2 activity for their catalytic activation, suggesting that they are structurally compromised. Addition of Prp2, Spp2, and UTP to affinity-purified ΔRES B or a mixture of B/Bact complexes formed on wild-type pre-mRNA led to their disassembly. However, no substantial disassembly was observed with ΔRES spliceosomes formed on a truncated pre-mRNA that allows Prp2 binding but blocks its activity. Thus, in the absence of RES, Prp2 appears to bind prematurely, leading to the disassembly of the ΔRES B complexes to which it binds. Our data suggest that Prp2 can dismantle B complexes with an aberrant protein composition, suggesting that it may proofread the spliceosome's RNP structure prior to activation
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