738 research outputs found
Statistical mechanics of red blood cell aggregation: The distribution of rouleaux in thermal equilibrium
When placed in suspension red blood cells adhere face-to-face and form long, cylindrical, and sometimes branched structures called rouleaux. We use methods developed in statistical mechanics to compute various statistical properties describing the size and shape of rouleaux in thermodynamic equilibrium. This leads to analytical expressions for (1) the average number of rouleaux consisting ofn cells and havingm branch points; (2) the average number of cells per rouleau; (3) the average number of branch points per rouleau; and (4) the number of rouleaux withn cells in a system containing a total ofN cells. We also derive asymptotic formulas that simplify these analytic expressions, and present numerical comparisons of the exact and asymptotic results
Path Integral Approach to the Non-Relativistic Electron Charge Transfer
A path integral approach has been generalized for the non-relativistic
electron charge transfer processes. The charge transfer - the capture of an
electron by an ion passing another atom or more generally the problem of
rearrangement collisions is formulated in terms of influence functionals. It
has been shown that the electron charge transfer process can be treated either
as electron transition problem or as elastic scattering of ion and atom in the
some effective potential field. The first-order Born approximation for the
electron charge transfer cross section has been reproduced to prove the
adequacy of the path integral approach for this problem.Comment: 19 pages, 1 figure, to appear in Journal of Physics B: Atomic,
Molecular & Optical, vol.34, 200
Why is the DNA Denaturation Transition First Order?
We study a model for the denaturation transition of DNA in which the
molecules are considered as composed of a sequence of alternating bound
segments and denaturated loops. We take into account the excluded-volume
interactions between denaturated loops and the rest of the chain by exploiting
recent results on scaling properties of polymer networks of arbitrary topology.
The phase transition is found to be first order in d=2 dimensions and above, in
agreement with experiments and at variance with previous theoretical results,
in which only excluded-volume interactions within denaturated loops were taken
into account. Our results agree with recent numerical simulations.Comment: Revised version. To appear in Phys. Rev. Let
Brownian Motion and Polymer Statistics on Certain Curved Manifolds
We have calculated the probability distribution function G(R,L|R',0) of the
end-to-end vector R-R' and the mean-square end-to-end distance (R-R')^2 of a
Gaussian polymer chain embedded on a sphere S^(D-1) in D dimensions and on a
cylinder, a cone and a curved torus in 3-D.
We showed that: surface curvature induces a geometrical localization area; at
short length the polymer is locally "flat" and (R-R')^2 = L l in all cases; at
large scales, (R-R')^2 is constant for the sphere, it is linear in L for the
cylinder and reaches different constant values for the torus. The cone vertex
induces (function of opening angle and R') contraction of the chain for all
lengths. Explicit crossover formulas are derived.Comment: 9 pages, 4 figures, RevTex, uses amssymb.sty and multicol.sty, to
appear in Phys. Rev
Diffusion of Inhomogeneous Vortex Tangle and Decay of Superfluid Turbulence
The theory describing the evolution of inhomogeneous vortex tangle at zero
temperature is developed on the bases of kinetics of merging and splitting
vortex loops. Vortex loops composing the vortex tangle can move as a whole with
some drift velocity depending on their structure and their length. The flux of
length, energy, momentum etc. executed by the moving vortex loops takes a
place. Situation here is exactly the same as in usual classical kinetic theory
with the difference that the "carriers" of various physical quantities are not
the point particles, but extended objects (vortex loops), which possess an
infinite number of degrees of freedom with very involved dynamics. We offer to
fulfill investigation basing on supposition that vortex loops have a Brownian
structure with the only degree of freedom, namely, lengths of loops . This
conception allows us to study dynamics of the vortex tangle on the basis of the
kinetic equation for the distribution function of the density of a
loop in the space of their lengths. Imposing the coordinate dependence on the
distribution function n(l,\mathbf{% r},t) and modifying the "kinetic"
equation with regard to inhomogeneous situation, we are able to investigate
various problem on the transport processes in superfluid turbulence. In this
paper we derive relation for the flux of the vortex line density
. The correspoding evolution of quantity
obeys the diffusion type equation as it can be expected from dimensional
analysis. The according diffusion coefficient is evaluated from calculation of
the (size dependent) free path of the vortex loops. We use this equation to
describe the decay of the vortex tangle at very low temperature. We compare
that solution with recent experiments on decay of the superfluid turbulence.Comment: 7 pages, 6 figure
Thermalkalibacillus uzonensis gen. nov. sp. nov, a novel aerobic alkali-tolerant thermophilic bacterium isolated from a hot spring in Uzon Caldera, Kamchatka
A novel thermophilic, alkali-tolerant, and CO-tolerant strain JW/WZ-YB58T was isolated from green mat samples obtained from the Zarvarzin II hot spring in the Uzon Caldera, Kamchatka (Far East Russia). Cells were Gram-type and Gram stain-positive, strictly aerobic, 0.7-0.8 μm in width and 5.5-12 μm in length and produced terminal spherical spores of 1.2-1.6 μm in diameter with the mother cell swelling around 2 μm in diameter (drumstick-type morphology). Cells grew optimally at pH25°C 8.2-8.4 and temperature 50-52°C and tolerated maximally 6% (w/v) NaCl. They were strict heterotrophs and could not use either CO or CO2 (both with or without H2) as sole carbon source, but tolerated up to 90% (v/v) CO in the headspace. The isolate grew on various complex substrates such as yeast extract, on carbohydrates, and organic acids, which included starch, d-galactose, d-mannose, glutamate, fumarate and acetate. Catalase reaction was negative. The membrane polar lipids were dominated by branched saturated fatty acids, which included iso-15:0 (24.5%), anteiso-15:0 (18.3%), iso-16:0 (9.9%), iso-17:0 (17.5%) and anteiso-17:0 (9.7%) as major constituents. The DNA G+C content of the strain is 45 mol%. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain JW/WZ-YB58T is distantly (\u3c93% similarity) related to members of Bacillaceae. On the basis of 16S rRNA gene sequence, physiological and phenotypic characteristics, the isolate JW/WZ-YB58T (ATCC BAA-1258; DSM 17740) is proposed to be the type strain for the type species of the new taxa within the family Bacillaceae, Thermalkalibacillus uzoniensis gen. nov. sp. nov. The Genbank accession number for the 16S rRNA gene sequence is DQ221694. © Springer-Verlag 2006
Entangled Polymer Rings in 2D and Confinement
The statistical mechanics of polymer loops entangled in the two-dimensional
array of randomly distributed obstacles of infinite length is discussed. The
area of the loop projected to the plane perpendicular to the obstacles is used
as a collective variable in order to re-express a (mean field) effective theory
for the polymer conformation. It is explicitly shown that the loop undergoes a
collapse transition to a randomly branched polymer with .Comment: 17 pages of Latex, 1 ps figure now available upon request, accepted
for J.Phys.A:Math.Ge
Entropy, time irreversibility and Schroedinger equation in a primarily discrete space-time
In this paper we show that the existence of a primarily discrete space-time
may be a fruitful assumption from which we may develop a new approach of
statistical thermodynamics in pre-relativistic conditions. The discreetness of
space-time structure is determined by a condition that mimics the Heisenberg
uncertainty relations and the motion in this space-time model is chosen as
simple as possible. From these two assumptions we define a path-entropy that
measures the number of closed paths associated with a given energy of the
system preparation. This entropy has a dynamical character and depends on the
time interval on which we count the paths. We show that it exists an
like-equilibrium condition for which the path-entropy corresponds exactly to
the usual thermodynamic entropy and, more generally, the usual statistical
thermodynamics is reobtained. This result derived without using the Gibbs
ensemble method shows that the standard thermodynamics is consistent with a
motion that is time-irreversible at a microscopic level. From this change of
paradigm it becomes easy to derive a . A comparison with the
traditional Boltzmann approach is presented. We also show how our approach can
be implemented in order to describe reversible processes. By considering a
process defined simultaneously by initial and final conditions a well defined
stochastic process is introduced and we are able to derive a Schroedinger
equation, an example of time reversible equation.Comment: latex versio
Onsager-Machlup theory and work fluctuation theorem for a harmonically driven Brownian particle
We extend Tooru-Cohen analysis for nonequilirium steady state(NSS) of a
Brownian particle to nonequilibrium oscillatory state (NOS) of Brownian
particle by considering time dependent external drive protocol. We consider an
unbounded charged Brownian particle in the presence of an oscillating electric
field and prove work fluctuation theorem, which is valid for any initial
distribution and at all times. For harmonically bounded and constantly dragged
Brownian particle considered by Tooru and Cohen, work fluctuation theorem is
valid for any initial condition(also NSS), but only in large time limit. We use
Onsager-Machlup Lagrangian with a constraint to obtain frequency dependent work
distribution function, and describe entropy production rate and properties of
dissipation functions for the present system using Onsager-Machlup functional.Comment: 6 pages, 1 figur
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