18,930 research outputs found
On the low detection efficiency of disk water megamasers in Seyfert 2 AGN
Disk megamasers are a unique tool to study active galactic nuclei (AGN)
sub-pc environment, and precisely measure some of their fundamental parameters.
While the majority of disk megamasers are hosted in heavily obscured (i.e.,
Seyfert 2, Sy2) AGN, the converse is not true, and disk megamasers are very
rarely found even in obscured AGN. The very low detection rate of such systems
in Sy2 AGN could be due to the geometry of the maser beaming, which requires a
strict edge-on condition. We explore some other fundamental factors which could
play a role in a volume-limited survey of disk megamasers in Sy2 galaxies, most
importantly the radio luminosity.Comment: 2 pages, 2 figures. To appear in the Proceedings IAU Symposium No.
336, 2017 "Astrophysical Masers: Unlocking the Mysteries of the Universe
Nash estimates and upper bounds for non-homogeneous Kolmogorov equations
We prove a Gaussian upper bound for the fundamental solutions of a class of
ultra-parabolic equations in divergence form. The bound is independent on the
smoothness of the coefficients and generalizes some classical results by Nash,
Aronson and Davies. The class considered has relevant applications in the
theory of stochastic processes, in physics and in mathematical finance.Comment: 21 page
Towards a Maude tool for model checking temporal graph properties
We present our prototypical tool for the verification of graph transformation systems. The major novelty of our tool is that it provides a model checker for temporal graph properties based on counterpart semantics for quantified m-calculi. Our tool can be considered as an instantiation of our approach to counterpart semantics which allows for a neat handling of creation, deletion and merging in systems
with dynamic structure. Our implementation is based on the object-based machinery of Maude, which provides the basics to deal with attributed graphs. Graph transformation
systems are specified with term rewrite rules. The model checker evaluates logical formulae of second-order modal m-calculus in the automatically generated CounterpartModel (a sort of unfolded graph transition system) of the graph transformation system under study. The result of evaluating a formula is a set of assignments for each state, associating node variables to actual nodes
Fluid-fluid demixing curves for colloid-polymer mixtures in a random colloidal matrix
We study fluid-fluid phase separation in a colloid-polymer mixture adsorbed
in a colloidal porous matrix close to the \theta -point. For this purpose we
consider the Asakura-Oosawa model in the presence of a quenched matrix of
colloidal hard spheres. We study the dependence of the demixing curve on the
parameters that characterize the quenched matrix, fixing the polymer-to-colloid
size ratio to 0.8. We find that, to a large extent, demixing curves depend only
on a single parameter f, which represents the volume fraction which is
unavailable to the colloids. We perform Monte Carlo simulations for volume
fractions f equal to 40% and 70%, finding that the binodal curves in the
polymer and colloid packing-fraction plane have a small dependence on disorder.
The critical point instead changes significantly: for instance, the colloid
packing fraction at criticality increases with increasing f. Finally, we
observe for some values of the parameters capillary condensation of the
colloids: a bulk colloid-poor phase is in chemical equilibrium with a
colloid-rich phase in the matrix.Comment: 26 pages, 8 figures. In publication in Molecular Physics, special
volume dedicated to Luciano Reatto for his 70th birthda
Framed sheaves on projective space and Quot schemes
We prove that, given integers , and , the moduli
space of torsion free sheaves on with Chern character
that are trivial along a hyperplane
is isomorphic to the Quot scheme of -dimensional length quotients of the free sheaf
on .Comment: Minor improvement
How log-normal is your country? An analysis of the statistical distribution of the exported volumes of products
We have considered the statistical distributions of the volumes of the
different products exported by 148 countries. We have found that the form of
these distributions is not unique but heavily depends on the level of
development of the nation, as expressed by macroeconomic indicators like GDP,
GDP per capita, total export and a recently introduced measure for countries'
economic complexity called fitness. We have identified three major classes: a)
an incomplete log-normal shape, truncated on the left side, for the less
developed countries, b) a complete log-normal, with a wider range of volumes,
for nations characterized by intermediate economy, and c) a strongly asymmetric
shape for countries with a high degree of development. The ranking curves of
the exported volumes from each country seldom cross each other, showing a clear
hierarchy of export volumes. Finally, the log-normality hypothesis has been
checked for the distributions of all the 148 countries through different tests,
Kolmogorov-Smirnov and Cramer-Von Mises, confirming that it cannot be rejected
only for the countries of intermediate economy.Comment: 10 pages, 5 figures, submitted to IWcee15 conferenc
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