4,521 research outputs found
Vacuum polarization by topological defects in de Sitter spacetime
In this paper we investigate the vacuum polarization effects associated with
a massive quantum scalar field in de Sitter spacetime in the presence of
gravitational topological defects. Specifically we calculate the vacuum
expectation value of the field square, . Because this investigation
has been developed in a pure de Sitter space, here we are mainly interested on
the effects induced by the presence of the defects.Comment: Talk presented at the 1st. Mediterranean Conference on Classical and
Quantum Gravity (MCCQG
Solving Four Dimensional Field Theories with the Dirichlet Fivebrane
The realization of four dimensional super Yang-Mills theories in
terms of a single Dirichlet fivebrane in type IIB string theory is considered.
A classical brane computation reproduces the full quantum low energy effective
action. This result has a simple explanation in terms of mirror symmetry.Comment: Final version to appear in Phys. Rev.
Desenvolvimento de uma coleção nuclear temática de arroz para resistência à brusone.
Este trabalho tem por objetivo desenvolver uma Coleção Nuclear Temática de Arroz para Resistência à brusone com alta diversidade para resistência às raças do patógeno mais comuns em lavouras comerciais do Brasil
Vacuum Polarization of a Massless Scalar Field in the Background of a Global Monopole with Finite Core
In this paper we analyze the vacuum polarization effects of a massless scalar
field in the background of a global monopole considering a inner structure to
it. Specifically we investigate the effect of its structure on the vacuum
expectation value of the square of the field operator, ,
admitting a non-minimal coupling between the field with the geometry: $\xi
{\cal{R}}\hat{\Phi}^2$. Also we calculate the corrections on the vacuum
expectation value of the energy-momentum tensor, , due to
the inner structure of the monopole. In order to develop these analysis, we
calculate the Euclidean Green function associated with the system for points in
the region outside the core. As we shall see, for specific value of the
coupling parameter , the corrections caused by the inner structure of the
monopole can provide relevant contributions on these vacuum polarizations.Comment: Accepted for publication in Classical and Quantum Gravity. Added
references. 22 pages, 1 figur
On the dynamics of Extrasolar Planetary Systems under dissipation. Migration of planets
We study the dynamics of planetary systems with two planets moving in the
same plane, when frictional forces act on the two planets, in addition to the
gravitational forces. The model of the general three-body problem is used.
Different laws of friction are considered. The topology of the phase space is
essential in understanding the evolution of the system. The topology is
determined by the families of stable and unstable periodic orbits, both
symmetric and non symmetric. It is along the stable families, or close to them,
that the planets migrate when dissipative forces act. At the critical points
where the stability along the family changes, there is a bifurcation of a new
family of stable periodic orbits and the migration process changes route and
follows the new stable family up to large eccentricities or to a chaotic
region. We consider both resonant and non resonant planetary systems. The 2/1,
3/1 and 3/2 resonances are studied. The migration to larger or smaller
eccentricities depends on the particular law of friction. Also, in some cases
the semimajor axes increase and in other cases they are stabilized. For
particular laws of friction and for special values of the parameters of the
frictional forces, it is possible to have partially stationary solutions, where
the eccentricities and the semimajor axes are fixed.Comment: Accepted in Celestial Mechanics and Dynamical Astronom
Reflectance Fluctuations in an Absorbing Random Waveguide
We study the statistics of the reflectance (the ratio of reflected and
incident intensities) of an -mode disordered waveguide with weak absorption
per mean free path. Two distinct regimes are identified. The regime
shows universal fluctuations.
With increasing length of the waveguide, the variance of the reflectance
changes from the value , characteristic for universal conductance
fluctuations in disordered wires, to another value , characteristic
for chaotic cavities. The weak-localization correction to the average
reflectance performs a similar crossover from the value to . In
the regime , the large- distribution of the reflectance
becomes very wide and asymmetric, for .Comment: 7 pages, RevTeX, 2 postscript figure
Generalized Fokker-Planck Equation For Multichannel Disordered Quantum Conductors
The Dorokhov-Mello-Pereyra-Kumar (DMPK) equation, which describes the
distribution of transmission eigenvalues of multichannel disordered conductors,
has been enormously successful in describing a variety of detailed transport
properties of mesoscopic wires. However, it is limited to the regime of quasi
one dimension only. We derive a one parameter generalization of the DMPK
equation, which should broaden the scope of the equation beyond the limit of
quasi one dimension.Comment: 8 pages, abstract, introduction and summary rewritten for broader
readership. To be published in Phys. Rev. Let
Strong Effects of Weak Localization in Charge Density Wave/Normal Metal Hybrids
Collective transport through a multichannel disordered conductor in contact
with charge-density-wave electrodes is theoretically investigated. The
statistical distribution function of the threshold potential for charge-density
wave sliding is calculated by random matrix theory. In the diffusive regime
weak localization has a strong effect on the sliding motion.Comment: To be published in Physical Review
Bayesian factorial design as a tool in the identification of rice blast resistance sources.
Rice germplasm banks have many promising sources of resistance to pathogens. However, identification of resistant genotypes is often arduous, notably when the host-pathogen relationship is complex as in rice blast. In addition, selection of representative Magnaporthe oryzae isolates to adequately identify sources of broad-spectrum resistance is challenging. To overcome these obstacles, data from pathogenicity assays were analyzed as a factorial design, where the pairwise combination comprised rice genotypes and blast isolates. Using this methodology, we aimed to access information about host resistance
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