1,608 research outputs found
Casimir torque between nanostructured plates
We investigate in detail the Casimir torque induced by quantum vacuum
fluctuations between two nanostructured plates. Our calculations are based on
the scattering approach and take into account the coupling between different
modes induced by the shape of the surface which are neglected in any sort of
proximity approximation or effective medium approach. We then present an
experimental setup aiming at measuring this torque.Comment: 7 pages, 7 figure
Casimir torque between corrugated metallic plates
We consider two parallel corrugated plates and show that a Casimir torque
arises when the corrugation directions are not aligned. We follow the
scattering approach and calculate the Casimir energy up to second order in the
corrugation amplitudes, taking into account nonspecular reflections,
polarization mixing and the finite conductivity of the metals. We compare our
results with the proximity force approximation, which overestimates the torque
by a factor 2 when taking the conditions that optimize the effect. We argue
that the Casimir torque could be measured for separation distances as large as
1 Comment: 7 pages, 3 figures, contribution to QFEXT07 proceeding
Thermal Casimir Effect in the Plane-Sphere Geometry
The thermal Casimir force between two metallic plates is known to depend on
the description of material properties. For large separations the dissipative
Drude model leads to a force a factor of 2 smaller than the lossless plasma
model. Here we show that the plane-sphere geometry, in which current experiment
are performed, decreases this ratio to a factor of 3/2, as revealed by exact
numerical and large distance analytical calculations. For perfect reflectors,
we find a repulsive contribution of thermal photons to the force and negative
entropy values at intermediate distances.Comment: 4 pages, 3 figure
Casimir energy and geometry : beyond the Proximity Force Approximation
We review the relation between Casimir effect and geometry, emphasizing
deviations from the commonly used Proximity Force Approximation (PFA). We use
to this aim the scattering formalism which is nowadays the best tool available
for accurate and reliable theory-experiment comparisons. We first recall the
main lines of this formalism when the mirrors can be considered to obey
specular reflection. We then discuss the more general case where non planar
mirrors give rise to non-specular reflection with wavevectors and field
polarisations mixed. The general formalism has already been fruitfully used for
evaluating the effect of roughness on the Casimir force as well as the lateral
Casimir force or Casimir torque appearing between corrugated surfaces. In this
short review, we focus our attention on the case of the lateral force which
should make possible in the future an experimental demonstration of the
nontrivial (i.e. beyond PFA) interplay of geometry and Casimir effect.Comment: corrected typos, added references, QFEXT'07 special issue in J. Phys.
Orbital frustration at the origin of the magnetic behavior in LiNiO2
We report on the ESR, magnetization and magnetic susceptibility measurements
performed over a large temperature range, from 1.5 to 750 K, on high-quality
stoichiometric LiNiO2. We find that this compound displays two distinct
temperature regions where its magnetic behavior is anomalous. With the help of
a statistical model based on the Kugel'-Khomskii Hamiltonian, we show that
below T_of ~ 400 K, an orbitally-frustrated state characteristic of the
triangular lattice is established. This then gives a solution to the
long-standing controversial problem of the magnetic behavior in LiNiO2.Comment: 5 pages, 5 figures, RevTex, accepted in PR
Atypical characteristics in the longnosed skate Dipturus oxyrinchus (Linnaeus, 1758) from the coast of Syria (Eastern Mediterranean)
EnA specimen of sharpnosed skate Dipturus oxyrinchus (Linnaeus, 1758) presenting snout and tail abnormalities was captured off the Syrian coast. It is an adult female with a shortened and rounded snout, lack of second dorsal fin and a reduced and rounded caudal fin. This abnormal specimen is described in the present note, and it appears that both snout and tail abnormalities did not affect their development and they reached similar parameters and swimming activities than the normal ones
Casimir energies with finite-width mirrors
We use a functional approach to the Casimir effect in order to evaluate the
exact vacuum energy for a real scalar field in dimensions, in the
presence of backgrounds that, in a particular limit, impose Dirichlet boundary
conditions on one or two parallel surfaces. Outside of that limit, the
background may be thought of as describing finite-width mirrors with
frequency-dependent transmission and reflection coefficients. We provide new
explicit results for the Casimir energy in some particular backgroundsComment: 18 pages, no figures. Version to appear in Phys. Rev.
Quantum noise in ideal operational amplifiers
We consider a model of quantum measurement built on an ideal operational
amplifier operating in the limit of infinite gain, infinite input impedance and
null output impedance and with a feddback loop. We evaluate the intensity and
voltage noises which have to be added to the classical amplification equations
in order to fulfill the requirements of quantum mechanics. We give a
description of this measurement device as a quantum network scattering quantum
fluctuations from input to output ports.Comment: 4 pages, 2 figures, RevTe
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