11,448 research outputs found
Finite quotients of the algebraic fundamental group of projective curves in positive characteristic
Let X be a smooth connected projective curve defined over an algebraically closed field k of characteristic p >0. Let G be a finite group whose order is divisible by p. Suppose that G has a normal p-Sylow subgroup. We give a necessary and sufficient condition for G to be a quotient of the algebraic fundamental group pi(1)(X) of X
Modified Renormalization Strategy for Sandpile Models
Following the Renormalization Group scheme recently developed by Pietronero
{\it et al}, we introduce a simplifying strategy for the renormalization of the
relaxation dynamics of sandpile models. In our scheme, five sub-cells at a
generic scale form the renormalized cell at the next larger scale. Now the
fixed point has a unique nonzero dynamical component that allows for a great
simplification in the computation of the critical exponent . The values
obtained are in good agreement with both numerical and theoretical results
previously reported.Comment: APS style, 9 pages and 3 figures. To be published in Phys. Rev.
Evolution of Supermassive Black Holes from Cosmological Simulations
The correlations between the mass of supermassive black holes and properties
of their host galaxies are investigated through cosmological simulations. Black
holes grow from seeds of 100 solar masses inserted into density peaks present
in the redshift range 12-15. Seeds grow essentially by accreting matter from a
nuclear disk and also by coalescences resulting from merger episodes. At z=0,
our simulations reproduce the black hole mass function and the correlations of
the black hole mass both with stellar velocity dispersion and host dark halo
mass. Moreover, the evolution of the black hole mass density derived from the
present simulations agrees with that derived from the bolometric luminosity
function of quasars, indicating that the average accretion history of seeds is
adequately reproduced . However, our simulations are unable to form black holes
with masses above at , whose existence is inferred
from the bright quasars detected by the Sloan survey in this redshift range.Comment: Talk given at the International Workshop on Astronomy and
Relativistic Astrophysics (IWARA 2009), Maresias, Brazil. to be published in
the International Journal of Modern Physics
Epidemic model on a network: analysis and applications to COVID-19
We analyze an epidemic model on a network consisting of
susceptible-infected-recovered equations at the nodes coupled by diffusion
using a graph Laplacian. We introduce an epidemic criterion and examine
different vaccination/containment strategies: we prove that it is most
effective to vaccinate a node of highest degree. The model is also useful to
evaluate deconfinement scenarios and prevent a so-called second wave. The model
has few parameters enabling fitting to the data and the essential ingredient of
importation of infected; these features are particularly important for the
current COVID-19 epidemic
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