14,011 research outputs found
A Stress/Displacement Virtual Element Method for Plane Elasticity Problems
The numerical approximation of 2D elasticity problems is considered, in the
framework of the small strain theory and in connection with the mixed
Hellinger-Reissner variational formulation. A low-order Virtual Element Method
(VEM) with a-priori symmetric stresses is proposed. Several numerical tests are
provided, along with a rigorous stability and convergence analysis
Collapse of Primordial Clouds
We present here studies of collapse of purely baryonic Population III objects
with masses ranging from to . A spherical Lagrangian
hydrodynamic code has been written to study the formation and evolution of the
primordial clouds, from the beginning of the recombination era () until the redshift when the collapse occurs. All the relevant processes
are included in the calculations, as well as, the expansion of the Universe. As
initial condition we take different values for the Hubble constant and for the
baryonic density parameter (considering however a purely baryonic Universe), as
well as different density perturbation spectra, in order to see their influence
on the behavior of the Population III objects evolution. We find, for example,
that the first mass that collapses is for ,
and with the mass scale . For
we obtain for the first
mass that collapses. The cooling-heating and photon drag processes have a key
role in the collapse of the clouds and in their thermal history. Our results
show, for example, that when we disregard the Compton cooling-heating, the
collapse of the objects with masses occurs earlier. On
the other hand, disregarding the photon drag process, the collapse occurs at a
higher redshift.Comment: 10 pages, MN plain TeX macros v1.6 file, 9 PS figures. Also available
at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES").
MNRAS in pres
Collapse of Primordial Clouds II. The Role of Dark Matter
In this article we extend the study performed in our previous article on the
collapse of primordial objects. We here analyze the behavior of the physical
parameters for clouds ranging from to . We
studied the dynamical evolution of these clouds in two ways: purely baryonic
clouds and clouds with non-baryonic dark matter included. We start the
calculations at the beginning of the recombination era, following the evolution
of the structure until the collapse (that we defined as the time when the
density contrast of the baryonic matter is greater than ). We analyze the
behavior of the several physical parameters of the clouds (as, e.g., the
density contrast and the velocities of the baryonic matter and the dark matter)
as a function of time and radial position in the cloud. In this study all
physical processes that are relevant to the dynamical evolution of the
primordial clouds, as for example photon-drag (due to the cosmic background
radiation), hydrogen molecular production, besides the expansion of the
Universe, are included in the calculations. In particular we find that the
clouds, with dark matter, collapse at higher redshift when we compare the
results with the purely baryonic models. As a general result we find that the
distribution of the non-baryonic dark matter is more concentrated than the
baryonic one. It is important to stress that we do not take into account the
putative virialization of the non-baryonic dark matter, we just follow the time
and spatial evolution of the cloud solving its hydrodynamical equations. We
studied also the role of the cooling-heating processes in the purely baryonic
clouds.Comment: 8 pages, MN plain TeX macros v1.6 file, 13 PS figures. Also available
at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES").
MNRAS in pres
Multipartite Entanglement Signature of Quantum Phase Transitions
We derive a general relation between the non-analyticities of the ground
state energy and those of a subclass of the multipartite generalized global
entanglement (GGE) measure defined by T. R. de Oliveira et al. [Phys. Rev. A
73, 010305(R) (2006)] for many-particle systems. We show that GGE signals both
a critical point location and the order of a quantum phase transition (QPT). We
also show that GGE allows us to study the relation between multipartite
entanglement and QPTs, suggesting that multipartite but not bipartite
entanglement is favored at the critical point. Finally, using GGE we were able,
at a second order QPT, to define a diverging entanglement length (EL) in terms
of the usual correlation length. We exemplify this with the XY spin-1/2 chain
and show that the EL is half the correlation length.Comment: Published version. Incorporates correction made in erratu
Some Classes of Point Processes.
We dene four classes of point processes which we call A, B, *A, *B. Although we study point processes on R; these classes are suitable for generalizations for point processes on Rm and other measure metric spaces. The main result is the equivalence of classes *A and *B for point processes on R: As a matter of fact, we prove that A B A = B S; where S is the class of simple processes. We also relate these classes and the class of Poisson processes.We dene four classes of point processes which we call A, B, *A, *B. Although we study point processes on R; these classes are suitable for generalizations for point processes on Rm and other measure metric spaces. The main result is the equivalence of classes *A and *B for point processes on R: As a matter of fact, we prove that A B A = B S; where S is the class of simple processes. We also relate these classes and the class of Poisson processes
Scalar Spectrum from a Dynamical Gravity/Gauge model
We show that a Dynamical AdS/QCD model is able to reproduce the linear Regge
trajectories for the light-flavor sector of mesons with high spin and also for
the scalar and pseudoscalar ones. In addition the model has confinement by the
Wilson loop criteria and a mass gap. We also calculate the decay amplitude of
scalars into two pion in good agreement to the available experimental data.Comment: Presented in the 4th International Workshop on Astronomy and
Relativistic Astrophysic
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