1,332 research outputs found
Thermodynamic bounds on equilibrium fluctuations of a global or local order parameter
We analyze thermodynamic bounds on equilibrium fluctuations of an order
parameter, which are analogous to relations, which have been derived recently
in the context of non-equilibrium fluctuations of currents. We discuss the case
of {\it global} fluctuations when the order parameter is measured in the full
system of interest, and {\it local} fluctuations, when the order parameter is
evaluated only in a sub-part of the system. Using isometric fluctuation
theorems, we derive thermodynamic bounds on the fluctuations of the order
parameter in both cases. These bounds could be used to infer the value of
symmetry breaking field or the relative size of the observed sub-system to the
full system from {\it local} fluctuations.Comment: 8 pages, 6 figures, in press for Europhys. Let
Isometric fluctuation relations for equilibrium states with broken symmetry
We derive a set of isometric fluctuation relations, which constrain the order
parameter fluctuations in finite-size systems at equilibrium and in the
presence of a broken symmetry. These relations are exact and should apply
generally to many condensed-matter physics systems. Here, we establish these
relations for magnetic systems and nematic liquid crystals in a
symmetry-breaking external field, and we illustrate them on the Curie-Weiss and
the models. Our relations also have implications for spontaneous symmetry
breaking, which are discussed.Comment: 9 pages, 4 figures, in press for Phys. Rev. Lett. to appear there in
Dec. 201
A Poisson-Boltzmann approach for a lipid membrane in an electric field
The behavior of a non-conductive quasi-planar lipid membrane in an
electrolyte and in a static (DC) electric field is investigated theoretically
in the nonlinear (Poisson-Boltzmann) regime. Electrostatic effects due to
charges in the membrane lipids and in the double layers lead to corrections to
the membrane elastic moduli which are analyzed here. We show that, especially
in the low salt limit, i) the electrostatic contribution to the membrane's
surface tension due to the Debye layers crosses over from a quadratic behavior
in the externally applied voltage to a linear voltage regime. ii) the
contribution to the membrane's bending modulus due to the Debye layers
saturates for high voltages. Nevertheless, the membrane undulation instability
due to an effectively negative surface tension as predicted by linear
Debye-H\"uckel theory is shown to persist in the nonlinear, high voltage
regime.Comment: 15 pages, 4 figure
Phase transitions in optimal strategies for betting
Kelly's criterion is a betting strategy that maximizes the long term growth
rate, but which is known to be risky. Here, we find optimal betting strategies
that gives the highest capital growth rate while keeping a certain low value of
risky fluctuations. We then analyze the trade-off between the average and the
fluctuations of the growth rate, in models of horse races, first for two horses
then for an arbitrary number of horses, and for uncorrelated or correlated
races. We find an analog of a phase transition with a coexistence between two
optimal strategies, where one has risk and the other one does not. The above
trade-off is also embodied in a general bound on the average growth rate,
similar to thermodynamic uncertainty relations. We also prove mathematically
the absence of other phase transitions between Kelly's point and the risk free
strategy.Comment: 23 pages, 5 figure
Stokes parameters for light scattering from a Faraday-active sphere
We present an exact calculation for the scattering of light from a single
sphere made of Faraday-active material, to first order in the external magnetic
field. We use a recent expression for the T-matrix of a Mie scatterer in a
magnetic field to compute the Stokes parameters in single scattering that
describe completely flux and polarization of the scattered light.Comment: 17 pages, 5 figures, Latex, accepted for publication in JQSR
Thermal expansion within a chain of magnetic colloidal particles
We study the thermal expansion of chains formed by self-assembly of magnetic
colloidal particles in a magnetic field. Using video-microscopy, complete
positional data of all the particles of the chains is obtained. By changing the
ionic strength of the solution and the applied magnetic field, the interaction
potential can be tuned. We analyze the thermal expansion of the chain using a
simple model of a one dimensional anharmonic crystal of finite size.Comment: 5 pages and 3 figure
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