8,135 research outputs found
Statistical physics of adaptive correlation of agents in a market
Recent results and interpretations are presented for the thermal minority
game, concentrating on deriving and justifying the fundamental stochastic
differential equation for the microdynamics.Comment: Invited talk presented at the Conference: Disordered and Complex
Systems, King's College London, July 200
Stochastic Gross-Pitaevsky Equation for BEC via Coarse-Grained Effective Action
We sketch the major steps in a functional integral derivation of a new set of
Stochastic Gross-Pitaevsky equations (GPE) for a Bose-Einstein condensate (BEC)
confined to a trap at zero temperature with the averaged effects of
non-condensate modes incorporated as stochastic sources. The closed-time-path
(CTP) coarse-grained effective action (CGEA) or the equivalent influence
functional method is particularly suitable because it can account for the full
back-reaction of the noncondensate modes on the condensate dynamics
self-consistently. The Langevin equations derived here containing nonlocal
dissipation together with colored and multiplicative noises are useful for a
stochastic (as distinguished from say, a kinetic) description of the
nonequilibrium dynamics of a BEC. This short paper contains original research
results not yet published anywhere.Comment: 6 page
Quantum optimal control of photoelectron spectra and angular distributions
Photoelectron spectra and photoelectron angular distributions obtained in
photoionization reveal important information on e.g. charge transfer or hole
coherence in the parent ion. Here we show that optimal control of the
underlying quantum dynamics can be used to enhance desired features in the
photoelectron spectra and angular distributions. To this end, we combine
Krotov's method for optimal control theory with the time-dependent
configuration interaction singles formalism and a splitting approach to
calculate photoelectron spectra and angular distributions. The optimization
target can account for specific desired properties in the photoelectron angular
distribution alone, in the photoelectron spectrum, or in both. We demonstrate
the method for hydrogen and then apply it to argon under strong XUV radiation,
maximizing the difference of emission into the upper and lower hemispheres, in
order to realize directed electron emission in the XUV regime
Semiclassical Asymptotics for the Maxwell - Dirac System
We study the coupled system of Maxwell and Dirac equations from a
semiclassical point of view. A rigorous nonlinear WKB-analysis, locally in
time, for solutions of (critical) order is performed,
where the small semiclassical parameter denotes the
microscopic/macroscopic scale ratio
Journal Staff
Electrical properties and strain gauge factor of Cr/SiOx cermet films with compositions 50/50 and 70/30 wt% were investigated in order to evaluate their use in strain gauge devices. The films were deposited by flash evaporation. The microstructures and resulting phases were characterized by electron diffraction and electron microscopy. The influence of the thickness and deposition rate on the sheet resistance, the temperature coefficient of resistance and the gauge factor were investigated. The results are consistent with a mixed conduction mechanism with metallic and a thermally activated tunneling components, between interconnected and discrete conductive phases, respectively.Se investigaron las propiedades eléctricas y el factor extensométrico de películas del cermet- Cr/SiOx en composiciones 50/50 y 70/30 % en peso, para evaluar su uso en dispositivos "strain gauge". Las películas fueron depositadas por evaporación "flash". Las estructuras y fases resultantes fueron caracterizadas por microscopía y difracción de electrones. Se estudió la influencia del espesor y la velocidad del depósito sobre la resistencia laminar, el coeficiente térmico de resistencia y el factor extensométrico. Los resultados son consistentes con un mecanismo de conducción mixto, con una componente metálica y otra por efecto túnel térmicamente activado, entre fases conductoras interconectadas y discretas, respectivamente
An infrared study of galactic OH/IR stars. I. An optical/near-IR atlas of the Arecibo sample
In this paper we present optical and near-infrared finding charts, accurate
astrometry (~1") and single-epoch near-infrared photometry for 371 IRAS
sources, 96% of those included in the so-called Arecibo sample of OH/IR stars
(Eder et al. 1988; Lewis et al. 1990a; Chengalur et al. 1993). The main
photometric properties of the stars in the sample are presented and discussed
as well as the problems found during the process of identification of the
optical/near-infrared counterparts. In addition, we also identify suitable
reference stars in each field to be used for differential photometry purposes
in the future.
We find that 39% of the sources (144 in number) have no optical counterpart,
8 of them being invisible even at near infrared wavelengths. The relative
distribution of sources with and without optical counterpart in the IRAS
two-colour diagram and their characteristic near infrared colours are
interpreted as the consequence of the increasing thickness of their
circumstellar shells. Among the objects not detected at near infrared
wavelengths four non-variable sources are proposed to be heavily obscured
post-AGB stars which have just very recently left the AGB. Eight additional
objects with unusually bright and/or blue near-infrared colours are identified
as candidate post-AGB stars and/or proto-planetary nebulae.Comment: 28 pages, 9 figures, for associated finding charts see:
http://www.edpsciences.org/articles/aa/full/2005/08/aa1709/FINDING_CHARTS/are
cibo_index.htm
Harvesting Excitons Through Plasmonic Strong Coupling
Exciton harvesting is demonstrated in an ensemble of quantum emitters coupled
to localized surface plasmons. When the interaction between emitters and the
dipole mode of a metallic nanosphere reaches the strong coupling regime, the
exciton conductance is greatly increased. The spatial map of the conductance
matches the plasmon field intensity profile, which indicates that transport
properties can be tuned by adequately tailoring the field of the plasmonic
resonance. Under strong coupling, we find that pure dephasing can have
detrimental or beneficial effects on the conductance, depending on the
effective number of participating emitters. Finally, we show that the exciton
transport in the strong coupling regime occurs on an ultrafast timescale given
by the inverse Rabi splitting (fs), orders of magnitude faster than
transport through direct hopping between the emitters.Comment: 5 pages, 3 figure
On Higgs and sphaleron effects during the leptogenesis era
We discuss the effects of various processes that can be active during the
leptogenesis era, and present the Boltzmann equations that take them into
account appropriately. A non-vanishing Higgs number asymmetry is always
present, enhancing the washout of the lepton asymmetry. This is the main new
effect when leptogenesis takes place at GeV, reducing the final
baryon asymmetry and tightening the leptogenesis bound on the neutrino masses.
If leptogenesis occurs at lower temperatures, electroweak sphalerons partially
transfer the lepton asymmetry to a baryonic one, while Yukawa interactions and
QCD sphalerons partially transfer the asymmetries of the left-handed fields to
the right-handed ones, suppressing the washout processes. Depending on the
specific temperature range in which leptogenesis occurs, the final baryon
asymmetry can be enhanced or suppressed by factors of order 20%--40% with
respect to the case when these effects are altogether ignored.Comment: one reference adde
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