1,420 research outputs found
Resonantly suppressed transmission and anomalously enhanced light absorption in ultrathin metal films
We study light diffraction in the periodically modulated ultrathin metal
films both analytically and numerically. Without modulation these films are
almost transparent. The periodicity results in the anomalous effects, such as
suppression of the transmittance accompanied by a strong enhancement of the
absorptivity and specular reflectivity, due to excitation of the surface
plasmon polaritons. These phenomena are opposite to the widely known enhanced
transparency of periodically modulated optically thick metal films. Our
theoretical analysis can be a starting point for the experimental investigation
of these intriguing phenomena.Comment: 4 pages, 5 figure
Warm turbulence in the Boltzmann equation
We study the single-particle distributions of three-dimensional hard sphere
gas described by the Boltzmann equation. We focus on the steady homogeneous
isotropic solutions in thermodynamically open conditions, i.e. in the presence
of forcing and dissipation. We observe nonequilibrium steady state solution
characterized by a warm turbulence, that is an energy and particle cascade
superimposed on the Maxwell-Boltzmann distribution. We use a dimensional
analysis approach to relate the thermodynamic quantities of the steady state
with the characteristics of the forcing and dissipation terms. In particular,
we present an analytical prediction for the temperature of the system which we
show to be dependent only on the forcing and dissipative scales. Numerical
simulations of the Boltzmann equation support our analytical predictions.Comment: 4 pages, 5 figure
Size-independence of statistics for boundary collisions of random walks and its implications for spin-polarized gases
A bounded random walk exhibits strong correlations between collisions with a
boundary. For an one-dimensional walk, we obtain the full statistical
distribution of the number of such collisions in a time t. In the large t
limit, the fluctuations in the number of collisions are found to be
size-independent (independent of the distance between boundaries). This occurs
for any inter-boundary distance, including less and greater than the
mean-free-path, and means that this boundary effect does not decay with
increasing system-size. As an application, we consider spin-polarized gases,
such as 3-Helium, in the three-dimensional diffusive regime. The above results
mean that the depolarizing effect of rare magnetic-impurities in the container
walls is orders of magnitude larger than a Smoluchowski assumption (to neglect
correlations) would imply. This could explain why depolarization is so
sensitive to the container's treatment with magnetic fields prior to its use.Comment: 5 page manuscript with extra details in appendices (additional 3
pages
Casimir forces in modulated systems
For the first time we present analytical results for the contribution of
electromagnetic fluctuations into thermodynamic properties of modulated
systems, like cholesteric or smectic liquid crystalline films. In the case of
small dielectric anisotropy we have derived explicit analytical expressions for
the chemical potential of such systems. Two limiting cases were specifically
considered: (i) the Van der Waals (VdW) limit, i.e., in the case when the
retardation of the electromagnetic interactions can be neglected; and (ii) the
Casimir limit, i.e. when the effects of retardation becomes considerable. It
was shown that in the Casimir limit, the film chemical potential oscillates
with the thickness of the film. This non-monotonic dependence of the chemical
potential on the film thickness can lead to step-wise wetting phenomena,
surface anchoring reorientation and other important effects. Applications of
the results may concern the various systems in soft matter or condensed matter
physics with multilayer or modulated structures.Comment: 13 page
Dynamics of nearly spherical vesicles in an external flow
We analytically derive an equation describing vesicle evolution in a fluid
where some stationary flow is excited regarding that the vesicle shape is close
to a sphere. A character of the evolution is governed by two dimensionless
parameters, and , depending on the vesicle excess area, viscosity
contrast, membrane viscosity, strength of the flow, bending module, and ratio
of the elongation and rotation components of the flow. We establish the ``phase
diagram'' of the system on the plane: we find curves corresponding
to the tank-treading to tumbling transition (described by the saddle-node
bifurcation) and to the tank-treading to trembling transition (described by the
Hopf bifurcation).Comment: 4 pages, 1 figur
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