3,892 research outputs found
Atmospheric considerations for the CTA site search
The Cherenkov Telescope Array (CTA) will be the next high-energy gamma-ray
observatory. Selection of the sites, one in each hemisphere, is not obvious
since several factors have to be taken into account. Among them, and probably
the most crucial, are the atmospheric conditions. Since July 2012, the site
working group has deployed automatic ground based instrumentation (ATMOSCOPE)
on all the candidate sites. Due to the limited time span available from ground
based data, long term weather forecast models become necessary tools for site
characterization. It is then of prime importance to validate the models by
comparing it to the ATMOSCOPE measurements. We will describe the sources of
data (ATMOSCOPE, weather forecasting model and satellite data) for the site
evaluation and how they will be used and combined.Comment: 4 pages. Proceedings of the Atmospheric Monitoring for High-Energy
Astroparticle Detectors (AtmoHEAD) Conference, Saclay (France), June 10-12,
201
On some Non Asymptotic Bounds for the Euler Scheme
We obtain non asymptotic bounds for the Monte Carlo algorithm associated to
the Euler discretization of some diffusion processes. The key tool is the
Gaussian concentration satisfied by the density of the discretization scheme.
This Gaussian concentration is derived from a Gaussian upper bound of the
density of the scheme and a modification of the so-called "Herbst argument"
used to prove Logarithmic Sobolev inequalities. We eventually establish a
Gaussian lower bound for the density of the scheme that emphasizes the
concentration is sharp.Comment: 26 page
Renormalization of the 2-point function of the Hubbard model at half-filling
We prove that the two dimensional Hubbard model at finite temperature T and
half-filling is analytic in the coupling constant in a radius at least . We also study the self-energy through a new two-particle irreducible
expansion and prove that this model is not a Fermi liquid, but a Luttinger
liquid with logarithmic corrections. The techniques used are borrowed from
constructive field theory so the result is mathematically rigorous and
completely non-perturbative.
Together with earlier results on the existence of two dimensional Fermi
liquids, this new result proves that the nature of interacting Fermi systems in
two dimensions depends on the shape of the Fermi surface.Comment: 45 pages, 28 figure
The Hubbard model at half-filling, part III: the lower bound on the self-energy
We complete the proof that the two-dimensional Hubbard model at half-filling
is not a Fermi liquid in the mathematically precise sense of Salmhofer, by
establishing a lower bound on a second derivative in momentum of the first
non-trivial self-energy graph.Comment: 31 pages, 4 figure
Double Scaling in Tensor Models with a Quartic Interaction
In this paper we identify and analyze in detail the subleading contributions
in the 1/N expansion of random tensors, in the simple case of a quartically
interacting model. The leading order for this 1/N expansion is made of graphs,
called melons, which are dual to particular triangulations of the D-dimensional
sphere, closely related to the "stacked" triangulations. For D<6 the subleading
behavior is governed by a larger family of graphs, hereafter called cherry
trees, which are also dual to the D-dimensional sphere. They can be resummed
explicitly through a double scaling limit. In sharp contrast with random matrix
models, this double scaling limit is stable. Apart from its unexpected upper
critical dimension 6, it displays a singularity at fixed distance from the
origin and is clearly the first step in a richer set of yet to be discovered
multi-scaling limits
Multi-epoch study of the gamma-ray emission within the M87 magnetosphere model
M87 is a nearby radio galaxy that has been detected at energies ranging from
radio to very high energy (VHE) gamma-rays. Its proximity and its jet,
misaligned from the line of sight allow detailed morphological studies. The
imaging atmospheric Cherenkov technique (from 100 GeV to 10 TeV) provides
insufficient angular resolution (few arc-minutes) to resolve the M87 emission
region. However, the short time scale variability observed by MAGIC, HESS and
VERITAS suggests the TeV emission is coming from a very small region, most
likely close to the core. We propose that the variable TeV emission may be
produced in a pair-starved region of the central black hole (BH) magnetosphere,
i.e. a region where the density of the electron-positron plasma is not
sufficient to completely screen the accelerating electric field. The funnel, a
low density and magnetically dominated region around the poles, appears as a
favourable site of low-density where a Blandford-Znajek process may explain the
main properties of the TeV -ray emission from M87. We produce a
broadband spectral energy distribution (SED) of the resulting radiation and
compare the model with the observed fluxes from the nucleus of M87, for both
low and high -ray activities. We finish with a brief discussion on the
connection between the accretion rate and the intermittence in the formation of
gaps in the magnetosphere.Comment: matches version accepted for publication in JCA
Nine Quick Tips for Analyzing Network Data
These tips provide a quick and concentrated guide for beginners in the
analysis of network data
High speed visualizations of the cavitating vortices of 2D mixing layer
The present study investigates experimentally vortex dynamics of a cavitating two-dimensional mixing layer at a high Reynolds number in order to determine the effect of growth and collapse of cavitation.
The dynamics and the topology of the vorticity regions corresponding to the low pressure area where cavitation effects take place are studied from the single phase state to highly cavitating conditions. LDV techniques are used in order to characterize the pattern of the turbulent single phase flow. Highspeed visualizations have been performed using a specific image processing of time series to highlight the behaviour and dynamics of the vapour phase. Visualizations, image processing and statistical analysis enable the estimation of the convective velocity and the shedding frequency of the cavitating KelvinâHelmholtz vortices. The measured visual vapour thickness grows linearly as the KelvinâHelmholtz instability develops and its expansion rate stays constant for the range of cavitation levels studied. The vortex pairing phenomenon is also analysed. Results show that the spatial development of the mixing area is slightly affected by the vapour phase allowing a self-similar behaviour of the mean motion
New cutaneous vaccine adjuvant that STINGs a little less
Cutaneous vaccination can be a challenge because the development of local skin inflammation is often unavoidable. Thus, it is important to identify and validate new vaccine adjuvants that enhance immunization without the burden of inflammation. Wang et al. now report on a cyclic GMP-AMP adjuvant, the natural stimulator of interferon genes agonist, providing evidence for potent immune responses without inflammation
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