3,163 research outputs found
Blazar properties: an update from recent results
After a brief critical overview of the main properties of blazars and their
classification, some significant results from recent multiwavelength
observations are summarized, in the context of the jet physics.Comment: 5 pages, 2 figures. Invited talk at the 2nd Heidelberg workshop:
"High-Energy Gamma-rays and Neutrinos from Extra-Galactic Sources", January
13-16, 2009, to be published in Int. J. Mod. Phys. D. Updated reference
Degenerate Kolmogorov equations and ergodicity for the stochastic Allen–Cahn equation with logarithmic potential
Random separation property for stochastic Allen-Cahn-type equations
We study a large class of stochastic p-Laplace Allen-Cahn equations with singular potential. Under suitable assumptions on the (multiplicative-type) noise we first prove existence, uniqueness, and regularity of variational solutions. Then, we show that a random separation property holds, i.e. almost every trajectory is strictly separated in space and time from the potential barriers. The threshold of separation is random, and we further provide exponential estimates on the probability of separation from the barriers. Eventually, we exhibit a convergence-in-probability result for the random separation threshold towards the deterministic one, as the noise vanishes, and we obtain an estimate of the convergence rate
A Cahn–Hilliard system with forward-backward dynamic boundary condition and non-smooth potentials
A system with equation and dynamic boundary condition of Cahn–Hilliard type is considered.
This system comes from a derivation performed in Liu–Wu (Arch. Ration. Mech. Anal., 233:167–247,
2019) via an energetic variational approach. Actually, the related problem can be seen as a transmission
problem for the phase variable in the bulk and the corresponding variable on the boundary. The asymptotic
behavior as the coefficient of the surface diffusion acting on the boundary phase variable goes to 0 is
investigated. By this analysis we obtain a forward-backward dynamic boundary condition at the limit.
We can deal with a general class of potentials having a double-well structure, including the non-smooth
double-obstacle potential. We illustrate that the limit problem is well-posed by also proving a continuous
dependence estimate. Moreover, in the case when the two graphs, in the bulk and on the boundary, exhibit
the same growth, we show that the solution of the limit problem is more regular and we prove an error
estimate for a suitable order of the diffusion parameter
Splitting the solar radiation in direct and diffuse components; Insights and constrains on the clearness-diffuse fraction representation
open3noIn many engineering applications, it is mandatory to know separately the solar radiation diffuse and direct components. Examples regard the assessment of the energy potentially exploitable by a system of solar thermal or photovoltaic panels and, in general, all the cases where it is necessary to calculate the radiative solar power collected by a surface. In fact, radiation components will differently project on the surface of interest and will weigh in a different manner, depending on the surface orientation, in the computation of the effective incident radiation. To perform this decomposition starting from data relative to a horizontal plane, two non-dimensional quantities, namely, the diffuse fraction, kd, and the clearness, kt, are usually put in mutual relation by correlating experimental data on a graphical ground rather than using physical considerations. In the present study, some insights are given on the shape of this correlation starting from geometric and physical considerations. It is shown that many results and graphs presented in literature have not physical meaning; rather they are simply artifacts due to geometrical or other constraints. These evidences open the way to a new approach to solar radiation decomposition founded on physical-based correlations.openScarpa, F.*; Marchitto, A.; Tagliafico, L.A.Scarpa, F.; Marchitto, A.; Tagliafico, L. A
Hemisphere Mixing: a Fully Data-Driven Model of QCD Multijet Backgrounds for LHC Searches
A novel method is proposed here to precisely model the multi-dimensional
features of QCD multi-jet events in hadron collisions. The method relies on the
schematization of high-pT QCD processes as 2->2 reactions made complex by
sub-leading effects. The construction of libraries of hemispheres from
experimental data and the definition of a suitable nearest-neighbor-based
association map allow for the generation of artificial events that reproduce
with surprising accuracy the kinematics of the QCD component of original data,
while remaining insensitive to small signal contaminations. The method is
succinctly described and its performance is tested in the case of the search
for the hh->bbbb process at the LHC.Comment: 4 pages plus header, 1 figure, proceedings of EPS 2017 Venic
An alternative proof of well-posedness of stochastic evolution equations in the variational setting
We present a new proof of well-posedness of stochastic evolution equations in variational form, relying solely on a (nonlinear) infinite-dimensional approximation procedure rather than on classical finite-dimensional projection arguments of Galerkin type
Jets from Sub-Parsec to Kiloparsec Scales: A Physical Connection
The Chandra discovery of bright X-ray emission from kpc-scale jets allows
insight into the physical parameters of the jet flow at large scale. At the
opposite extreme, extensive studies of the inner relativistic jets in Blazars
with multiwavelength observations, yield comparable information on sub-parsec
scales. In the framework of simple radiation models for the emission regions we
compare the physical parameters of jets on these two very different scales in
the only two well studied Blazars for which large-scale emission has been
resolved by Chandra. Notably, we find that the relativistic Doppler factors and
powers derived independently at the two scales are consistent, suggesting that
the jet does not suffer severe deceleration or dissipation. Moreover the
internal equipartition pressures in the inner jet and in the external X-ray
bright knots scale inversely with the jet cross section as expected in the
simple picture of a freely expanding jet in equipartition.Comment: 4 figures, accepted by Ap
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