2,254 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
Impediments to plant health in table grape production in southeastern France
At the La Tapy Experimental Station in southeastern France, a plot of table grapes is managed according to the principles of organic farming in order to study potential technical impediments of this growing system compared to another plot that is managed according to the principles of sustainable agriculture. Muscat de Hambourg, the variety common to these two plots, is used as a reference for the different observations. Results are primarily related to the impact of pest management efficiency on vine quality. The qualitative requirement that powdery mildew be absent on table grapes is difficult to fulfil in the case of organic farming, even with several different treatments and frequent applications. Botrytis management is related to climatic conditions; disease prevention is therefore essential. Small populations of grapeberry moths (Lobesia botrana) and the absence of grape bud moths (Eupoecilia ambiguella) on those plots, as well as the efficacy of specific treatments, even in the context of biological control, using products containing Bacillus thuringiensis, led to either none or negligible damage on the two observed plots. Monitoring of grape leaf hopper populations (Empoasca vitis) revealed that there was no increase in the larva population. The stable level of auxiliaries on this plot partially explains the low incidence of Empoasca vitis
Calibrated Stochastic Dynamic Models for Resource Management
In this paper we develop a positive calibrated approach to stochastic dynamic programming. Risk aversion, discount rate, and intertemporal substitution preferences of the decision-maker are calibrated by a procedure that minimizes the mean squared error from data on past decisions. We apply this framework to managing stochastic water supplies from Oroville Reservoir, located in Northern California. The calibrated positive SDP closely reproduces the historical storage and releases from the dam and shows sensitivity of optimal decisions to a decision-maker's risk aversion and intertemporal preferences. The calibrated model has average prediction errors that are substantially lower than those from the model with an expected net present value objective.Resource /Energy Economics and Policy,
Renormalon disappearance in Borel sum of the 1/N expansion of the Gross-Neveu model mass gap
The exact mass gap of the O(N) Gross-Neveu model is known, for arbitrary ,
from non-perturbative methods. However, a "naive" perturbative expansion of the
pole mass exhibits an infinite set of infrared renormalons at order 1/N,
formally similar to the QCD heavy quark pole mass renormalons, potentially
leading to large perturbative ambiguities. We examine the
precise vanishing mechanism of such infrared renormalons, which avoids this
(only apparent)contradiction, and operates without need of (Borel) summation
contour prescription, usually preventing unambiguous separation of perturbative
contributions. As a consequence we stress the direct Borel summability of the
(1/N) perturbative expansion of the mass gap. We briefly speculate on a
possible similar behaviour of analogous non-perturbative QCD quantities.Comment: 16 pp., 1 figure. v2: a few paragraphs and one appendix added, title
and abstract slightly changed, essential results unchange
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
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
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.
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
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