1,056 research outputs found
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
Phase Transitions in Lyotropic Nematic Gels
In this paper, we discuss the equilibrium phases and collapse transitions of
a lyotropic nematic gel immersed in an isotropic solvent. A nematic gel
consists of a cross-linked polymer network with rod-like molecules embedded in
it. Upon decreasing the quality of the solvent, we find that a lyotropic
nematic gel undergoes a discontinuous volume change accompanied by an
isotropic-nematic transition. We also present phase diagrams that these systems
may exhibit. In particular, we show that coexistence of two isotropic phases,
of two nematic phases, or of an isotropic and a nematic phase can occur.Comment: 13 pages Revtex, 10 figures, submitted to EPJ
Non-equilibrium fluctuations and mechanochemical couplings of a molecular motor
We investigate theoretically the violations of Einstein and Onsager
relations, and the efficiency for a single processive motor operating far from
equilibrium using an extension of the two-state model introduced by Kafri {\em
et al.} [Biophys. J. {\bf 86}, 3373 (2004)]. With the aid of the Fluctuation
Theorem, we analyze the general features of these violations and this
efficiency and link them to mechanochemical couplings of motors. In particular,
an analysis of the experimental data of kinesin using our framework leads to
interesting predictions that may serve as a guide for future experiments.Comment: 4 pages, 4 figures, accepted to Phys. Rev. Let
Transport Mean Free Path for Magneto-Transverse Light Diffusion
We derive an expression for the transport mean free path
associated with magneto-transverse light diffusion for a random collection of
Faraday-active
Mie scatterers. This expression relates the magneto-transverse diffusion in
multiple scattering directly to the magneto-transverse scattering of a single
scatterer.Comment: 5 pages, 1 figure, Latex, accepted for publication in Europhysics
Letter
Photonic Hall Effect in ferrofluids: Theory and Experiments
An experimental and theoretical study on the Photonic Hall Effect (PHE) in
liquid and gelled samples of ferrofluids is presented. The ferrofluids are
aqueous colloidal suspensions of Fe(_{2})CoO(_{4}) particles, which can be
considered as anisotropic and absorbing Rayleigh scatterers.
The PHE is found to be produced by the orientation of the magnetic moments of
the particles, as is also the case for the Faraday effect. The dependence of
the PHE with respect to the concentration of the scatterers, the magnetic field
and the polarization of the incident light is measured in liquid and in gelled
samples and is compared to a simple model based on the use of a scattering
matrix and the single scattering approximation.Comment: 20 pages, 11 figures, submitte
Coherent Backscattering of light in a magnetic field
This paper describes how coherent backscattering is altered by an external
magnetic field. In the theory presented, magneto-optical effects occur inside
Mie scatterers embedded in a non-magnetic medium. Unlike previous theories
based on point-like scatterers, the decrease of coherent backscattering is
obtained in leading order of the magnetic field using rigorous Mie theory. This
decrease is strongly enhanced in the proximity of resonances, which cause the
path length of the wave inside a scatterer to be increased. Also presented is a
novel analysis of the shape of the backscattering cone in a magnetic field.Comment: 27 pages, 5 figures, Revtex, to appear in Phys. Rev.
Energy versus information based estimations of dissipation using a pair of magnetic colloidal particles
Using the framework of stochastic thermodynamics, we present an experimental
study of a doublet of magnetic colloidal particles which is manipulated by a
time-dependent magnetic field. Due to hydrodynamic interactions, each bead
experiences a state-dependent friction, which we characterize using a
hydrodynamic model. In this work, we compare two estimates of the dissipation
in this system: the first one is energy based since it relies on the measured
interaction potential, while the second one is information based since it uses
only the information content of the trajectories. While the latter only offers
a lower bound of the former, we find it to be simple to implement and of
general applicability to more complex systems.Comment: Main text: 5 pages, 4 figures. Supplementary material: 5 pages, 5
figure
Gallavotti-Cohen-Type symmetry related to cycle decompositions for Markov chains and biochemical applications
We slightly extend the fluctuation theorem obtained in \cite{LS} for sums of
generators, considering continuous-time Markov chains on a finite state space
whose underlying graph has multiple edges and no loop. This extended frame is
suited when analyzing chemical systems. As simple corollary we derive in a
different method the fluctuation theorem of D. Andrieux and P. Gaspard for the
fluxes along the chords associated to a fundamental set of oriented cycles
\cite{AG2}.
We associate to each random trajectory an oriented cycle on the graph and we
decompose it in terms of a basis of oriented cycles. We prove a fluctuation
theorem for the coefficients in this decomposition. The resulting fluctuation
theorem involves the cycle affinities, which in many real systems correspond to
the macroscopic forces. In addition, the above decomposition is useful when
analyzing the large deviations of additive functionals of the Markov chain. As
example of application, in a very general context we derive a fluctuation
relation for the mechanical and chemical currents of a molecular motor moving
along a periodic filament.Comment: 23 pages, 5 figures. Correction
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