349 research outputs found
Chaotic Waveguide-Based Resonators for Microlasers
We propose the construction of highly directional emission microlasers using
two-dimensional high-index semiconductor waveguides as {\it open} resonators.
The prototype waveguide is formed by two collinear leads connected to a cavity
of certain shape. The proposed lasing mechanism requires that the shape of the
cavity yield mixed chaotic ray dynamics so as to have the appropiate (phase
space) resonance islands. These islands allow, via Heisenberg's uncertainty
principle, the appearance of quasi bound states (QBS) which, in turn,
propitiate the lasing mechanism. The energy values of the QBS are found through
the solution of the Helmholtz equation. We use classical ray dynamics to
predict the direction and intensity of the lasing produced by such open
resonators for typical values of the index of refraction.Comment: 5 pages, 5 figure
Various series expansions for a Heisenberg antiferromagnet model for SrCu(BO)
We use a variety of series expansion methods at both zero and finite
temperature to study an antiferromagnetic Heisenberg spin model proposed
recently by Miyahara and Ueda for the quasi two-dimensional material
SrCu(BO). We confirm that this model exhibits a first-order quantum
phase transition at T=0 between a gapped dimer phase and a gapless N\'eel phase
when the ratio of nearest and next-nearest neighbour interactions is
varied, and locate the transition at . Using longer series we are
able to give more accurate estimates of the model parameters by fitting to the
high temperature susceptibility data.Comment: RevTeX, 13 figure
Field dependent thermodynamics and Quantum Critical Phenomena in the dimerized spin system Cu2(C5H12N2)2Cl4
Experimental data for the uniform susceptibility, magnetization and specific
heat for the material Cu2(C5H12N2)2Cl4 (abbreviated CuHpCl) as a function of
temperature and external field are compared with those of three different
dimerized spin models: alternating spin-chains, spin-ladders and the bilayer
Heisenberg model. It is shown that because this material consists of weakly
coupled spin-dimers, much of the data is insensitive to how the dimers are
coupled together and what the effective dimensionality of the system is. When
such a system is tuned to the quantum critical point by application of a field,
the dimensionality shows up in the power-law dependences of thermodynamic
quantities on temperature. We discuss the temperature window for such a quantum
critical behavior in CuHpCl.Comment: Revtex, 5 pages, 4 figures (postscript
A Role for Timp3 in Microbiota-Driven Hepatic Steatosis and Metabolic Dysfunction
The effect of gut microbiota on obesity and insulin resistance is now recognized, but the underlying host-dependent mechanisms remain poorly undefined. We find that tissue inhibitor of metalloproteinase 3 knockout (Timp3(-/-)) mice fed a high-fat diet exhibit gut microbiota dysbiosis, an increase in branched chain and aromatic (BCAA) metabolites, liver steatosis, and an increase in circulating soluble IL-6 receptors (sIL6Rs). sIL6Rs can then activate inflammatory cells, such as CD11c(+) cells, which drive metabolic inflammation. Depleting the microbiota through antibiotic treatment significantly improves glucose tolerance, hepatic steatosis, and systemic inflammation, and neutralizing sIL6R signaling reduces inflammation, but only mildly impacts glucose tolerance. Collectively, our results suggest that gut microbiota is the primary driver of the observed metabolic dysfunction, which is mediated, in part, through IL-6 signaling. Our findings also identify an important role for Timp3 in mediating the effect of the microbiota in metabolic diseases
Blazars in the Fermi Era: The OVRO 40-m Telescope Monitoring Program
The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope
provides an unprecedented opportunity to study gamma-ray blazars. To capitalize
on this opportunity, beginning in late 2007, about a year before the start of
LAT science operations, we began a large-scale, fast-cadence 15 GHz radio
monitoring program with the 40-m telescope at the Owens Valley Radio
Observatory (OVRO). This program began with the 1158 northern (declination>-20
deg) sources from the Candidate Gamma-ray Blazar Survey (CGRaBS) and now
encompasses over 1500 sources, each observed twice per week with a ~4 mJy
(minimum) and 3% (typical) uncertainty. Here, we describe this monitoring
program and our methods, and present radio light curves from the first two
years (2008 and 2009). As a first application, we combine these data with a
novel measure of light curve variability amplitude, the intrinsic modulation
index, through a likelihood analysis to examine the variability properties of
subpopulations of our sample. We demonstrate that, with high significance
(7-sigma), gamma-ray-loud blazars detected by the LAT during its first 11
months of operation vary with about a factor of two greater amplitude than do
the gamma-ray-quiet blazars in our sample. We also find a significant (3-sigma)
difference between variability amplitude in BL Lacertae objects and
flat-spectrum radio quasars (FSRQs), with the former exhibiting larger
variability amplitudes. Finally, low-redshift (z<1) FSRQs are found to vary
more strongly than high-redshift FSRQs, with 3-sigma significance. These
findings represent an important step toward understanding why some blazars emit
gamma-rays while others, with apparently similar properties, remain silent.Comment: 23 pages, 24 figures. Submitted to ApJ
Le transcodage de l’axe II : une avancée utile
International audienceLa première table de correspondance établie en 2007 entre la CFTMEA et la CIM-10 était loin d'être exhaustive et ne concernait que l'Axe I. La Révision 2010 de la CFTMEA, qui permet un transcodage terme à terme, rend les deux classifications compatibles dans la pratique quotidienne et propose également un transcodage à l'Axe II
Small Corrections to the Tunneling Phase Time Formulation
After reexamining the above barrier diffusion problem where we notice that
the wave packet collision implies the existence of {\em multiple} reflected and
transmitted wave packets, we analyze the way of obtaining phase times for
tunneling/reflecting particles in a particular colliding configuration where
the idea of multiple peak decomposition is recovered. To partially overcome the
analytical incongruities which frequently rise up when the stationary phase
method is adopted for computing the (tunneling) phase time expressions, we
present a theoretical exercise involving a symmetrical collision between two
identical wave packets and a unidimensional squared potential barrier where the
scattered wave packets can be recomposed by summing the amplitudes of
simultaneously reflected and transmitted wave components so that the conditions
for applying the stationary phase principle are totally recovered. Lessons
concerning the use of the stationary phase method are drawn.Comment: 14 pages, 3 figure
Epidemic space
The aim of this article is to highlight the importance of 'spatiality' in understanding the materialization of risk society and cultivation of risk sensibilities. More specifically it provides a cultural analysis of pathogen virulence (as a social phenomenon) by means of tracing and mapping the spatial flows that operate in the uncharted zones between the microphysics of infection and the macrophysics of epidemics. It will be argued that epidemic space consists of three types of forces: the vector, the index and the vortex. It will draw on Latour's Actor Network Theory to argue that epidemic space is geared towards instability when the vortex (of expanding associations and concerns) displaces the index (of finding a single cause)
A first estimate of triply heavy baryon masses from the pNRQCD perturbative static potential
Within pNRQCD we compute the masses of spin-averaged triply heavy baryons
using the now-available NNLO pNRQCD potentials and three-body variational
approach. We focus in particular on the role of the purely three-body
interaction in perturbation theory. This we find to be reasonably small and of
the order 25 MeV Our prediction for the Omega_ccc baryon mass is 4900(250) in
keeping with other approaches. We propose to search for this hitherto
unobserved state at B factories by examining the end point of the recoil
spectrum against triple charm.Comment: 18 figures, 21 page
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