12,424 research outputs found
On Effective Spacetime Dimension in the Ho\v{r}ava-Lifshitz Gravity
In this manuscript we explicitly compute the effective dimension of spacetime
in some backgrounds of Ho\v{r}ava-Lifshitz (H-L) gravity. For all the cases
considered, the results are compatible with a dimensional reduction of the
spacetime to , at high energies (ultraviolet limit), which is confirmed
by other quantum gravity approaches, as well as to , at low energies
(infrared limit). This is obtained by computing the free energy of massless
scalar and gauge fields. We find that the only effect of the background is to
change the proportionality constant between the internal energy and
temperature. Firstly, we consider both the non-perturbative and perturbative
models involving the matter action, without gravitational sources but with
manifest time and space symmetry breaking, in order to calculate modifications
in the Stephan-Boltzmann law. When gravity is taken into account, we assume a
scenario in which there is a spherical source with mass and radius in
thermal equilibrium with radiation, and consider the static and spherically
symmetric solution of the H-L theory found by Kehagias-Sfetsos (K-S), in the
weak and strong field approximations. As byproducts, for the weak field regime,
we used the current uncertainty of the solar radiance measurements to establish
a constraint on the free parameter of the K-S solution. We also
calculate the corrections, due to gravity, to the recently predicted attractive
force that black bodies exert on nearby neutral atoms and molecules.Comment: references adde
Spin-polarized transport in ferromagnetic multilayered semiconductor nanostructures
The occurrence of inhomogeneous spin-density distribution in multilayered
ferromagnetic diluted magnetic semiconductor nanostructures leads to strong
dependence of the spin-polarized transport properties on these systems. The
spin-dependent mobility, conductivity and resistivity in
(Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a
function of temperature, scaled by the average magnetization of the diluted
magnetic semiconductor layers. An increase of the resistivity near the
transition temperature is obtained. We observed that the spin-polarized
transport properties changes strongly among the three materials.Comment: 3 pages, 4 figure
Complete high-precision entropic sampling
Monte Carlo simulations using entropic sampling to estimate the number of
configurations of a given energy are a valuable alternative to traditional
methods. We introduce {\it tomographic} entropic sampling, a scheme which uses
multiple studies, starting from different regions of configuration space, to
yield precise estimates of the number of configurations over the {\it full
range} of energies, {\it without} dividing the latter into subsets or windows.
Applied to the Ising model on the square lattice, the method yields the
critical temperature to an accuracy of about 0.01%, and critical exponents to
1% or better. Predictions for systems sizes L=10 - 160, for the temperature of
the specific heat maximum, and of the specific heat at the critical
temperature, are in very close agreement with exact results. For the Ising
model on the simple cubic lattice the critical temperature is given to within
0.003% of the best available estimate; the exponent ratios and
are given to within about 0.4% and 1%, respectively, of the
literature values. In both two and three dimensions, results for the {\it
antiferromagnetic} critical point are fully consistent with those of the
ferromagnetic transition. Application to the lattice gas with nearest-neighbor
exclusion on the square lattice again yields the critical chemical potential
and exponent ratios and to good precision.Comment: For a version with figures go to
http://www.fisica.ufmg.br/~dickman/transfers/preprints/entsamp2.pd
Recommended from our members
Prevention and non-pharmacological management of pain in newborns
Objective:
to describe the main non-pharmacological interventions for pain relief in newborns available in Neonatal Intensive Care Unit.
Method:
an exploratory search of the MedLine, Lilacs and Scielo online databases was conducted to retrieve references of studies published from 2004 to 2013.
Results:
several non-pharmacological interventions were shown to be effective, to represent low risk for neonates and to have a low operational cost. The ones most often discussed in the literature were: oral administration of glucose/sucrose, non-nutritive sucking, breastfeeding, skin-to-skin contact, facilitated tucking and swaddling.
Conclusion:
healthcare teams should be familiar with these methods and use them more effectively in Neonatal Intensive Care Unit daily routines, so as to ensure that newborns receive qualified and more human care
Dependence of the Black-body Force on Spacetime Geometry and Topology
In this paper we compute the corrections to the black-body force (BBF)
potential due to spacetime geometry and topology. This recently discovered
attractive force on neutral atoms is caused by the thermal radiation emitted
from black bodies and here we investigate it in relativistic gravitational
systems with spherical and cylindrical symmetries. For some astrophysical
objects we find that the corrected black-body potential is greater than the
flat case, showing that this kind of correction can be quite relevant when
curved spaces are considered. Then we consider four cases: The Schwarzschild
spacetime, the global monopole, the non-relativistic infinity cylinder and the
static cosmic string. For the spherically symmetric case of a massive body, we
find that two corrections appear: One due to the gravitational modification of
the temperature and the other due to the modification of the solid angle
subtended by the atom. We apply the found results to a typical neutron star and
to the Sun. For the global monopole, the modification in the black-body
potential is of topological nature and it is due to the central solid angle
deficit that occurs in the spacetime generated by that object. In the
cylindrical case, which is locally flat, no gravitational correction to the
temperature exists, as in the global monopole case. However, we find the
curious fact that the BBF depends on the topology of the spacetime through the
modification of the azimuthal angle and therefore of the solid angle. For the
static cosmic string we find that the force is null for the zero thickness
case.Comment: 8 pages, 5 figures. Revised versio
Avanços na transferência de embriões em caprinos e ovinos de corte no Brasil.
Atualmente, a caprino-ovinocultura apresenta-se em crescimento tecnológico e expansão numérica nas diversas regiões do Brasil. O incremento de sua produtividade interligada ao melhoramento genético está atrelado ao emprego de diversas biotecnologias de reprodução assistida, a exemplo da transferência de embriões (TE), a qual reúne uma série de metodologias para o cumprimento de todas as etapas de condução. A TE encontra-se em plena atividade de desenvolvimento e crescimento no aprimoramento de execução por muitos técnicos em nosso país. Representa uma capacidade exeqüível na rápida multiplicação de animais portadores de características zootécnicas desejáveis por meio do aproveitamento intensivo de uma fêmea em fase de vida reprodutiva
- …