6,196 research outputs found
Analytic Torsion on Hyperbolic Manifolds and the Semiclassical Approximation for Chern-Simons Theory
The invariant integration method for Chern-Simons theory for gauge group
SU(2) and manifold \Gamma\H^3 is verified in the semiclassical approximation.
The semiclassical limit for the partition function associated with a connected
sum of hyperbolic 3-manifolds is presented. We discuss briefly L^2 - analytical
and topological torsions of a manifold with boundary.Comment: 12 pages, LaTeX fil
On Useful Conformal Tranformations In General Relativity
Local conformal transformations are known as a useful tool in various
applications of the gravitational theory, especially in cosmology. We describe
some new aspects of these transformations, in particular using them for
derivation of Einstein equations for the cosmological and Schwarzschild
metrics. Furthermore, the conformal transformation is applied for the
dimensional reduction of the Gauss-Bonnet topological invariant in to the
spaces of lower dimensions.Comment: 17 pages, LaTeX. The paper is intended mainly for pedagogical
purposes and represents a collection of exercises concerning local conformal
transformations and dimensional reduction. To be published in "Gravitation
and Cosmology
Forms on Vector Bundles Over Compact Real Hyperbolic Manifolds
We study gauge theories based on abelian forms on real compact
hyperbolic manifolds. The tensor kernel trace formula and the spectral
functions associated with free generalized gauge fields are analyzed.Comment: Int. Journ. Modern Physics A, vol. 18 (2003), 2041-205
Dynamo in the Intra-Cluster Medium: Simulation of CGL-MHD Turbulent Dynamo
The standard magnetohydrodynamic (MHD) description of the plasma in the hot,
magnetized gas of the intra-cluster (ICM) medium is not adequate because it is
weakly collisional. In such collisionless magnetized gas, the microscopic
velocity distribution of the particles is not isotropic, giving rise to kinetic
effects on the dynamical scales. These kinetic effects could be important in
understanding the turbulence, as so as the amplification and maintenance of the
magnetic fields in the ICM. It is possible to formulate fluid models for
collisonless or weakly collisional gas by introducing modifications in the MHD
equations. These models are often referred as kinetic MHD (KMHD). Using a KMHD
model based on the CGL-closure, which allows the adiabatic evolution of the two
components of the pressure tensor (the parallel and perpendicular components
with respect to the local magnetic field), we performed 3D numerical
simulations of forced turbulence in order to study the amplification of an
initially weak seed magnetic field. We found that the growth rate of the
magnetic energy is comparable to that of the ordinary MHD turbulent dynamo, but
the magnetic energy saturates in a level smaller than of the MHD case. We also
found that a necessary condition for the dynamo works is to impose limits to
the anisotropy of the pressure.Comment: 3 pages, 1 figure, 274 IAU Symposium: Advances in Plasma Astrophysic
Efeito do nĂșmero de nĂłs sobre o crescimento inicial de plantas de crajiru (Arrabidaea chica (Humb. & Bonpl.) B. Verl.).
O objetivo deste trabalho foi avaliar tipos de estacas e o efeito do nĂșmero de brotaçÔes sobre o crescimento e produção de folhas de crajiru.bitstream/CPAF-RO-2010/12384/1/ct-99-crajiru.pd
Features of collisionless turbulence in the intracluster medium from simulated Faraday Rotation maps
Observations of the intracluster medium (ICM) in galaxy clusters suggest for
the presence of turbulence and the magnetic fields existence has been proved
through observations of Faraday Rotation and synchrotron emission. The ICM is
also known to be filled by a rarefied weakly collisional plasma. In this work
we study the possible signatures left on Faraday Rotation maps by collisionless
instabilities. For this purpose we use a numerical approach to investigate the
dynamics of the turbulence in collisionless plasmas based on an
magnetohydrodynamical (MHD) formalism taking into account different levels of
pressure anisotropy. We consider models covering the sub/super-Alfv\'enic and
trans/supersonic regimes, one of them representing the fiducial conditions
corresponding to the ICM. From the simulated models we compute Faraday Rotation
maps and analyze several statistical indicators in order to characterize the
magnetic field structure and compare the results obtained with the
collisionless model to those obtained using standard collisional MHD framework.
We find that important imprints of the pressure anisotropy prevails in the
magnetic field and also manifest in the associated Faraday Rotation maps which
evidence smaller correlation lengths in the collisionless MHD case. These
points are remarkably noticeable for the case mimicking the conditions
prevailing in ICM. Nevertheless, in this study we have neglected the decrease
of pressure anisotropy due to the feedback of the instabilities that naturally
arise in collisionless plasmas at small scales. This decrease may not affect
the statistical imprint differences described above, but should be examined
elsewhere.Comment: 24 pages, 15 figures, MNRAS accepte
Bootstrap inference in the presence of bias
We consider bootstrap inference for estimators which are (asymptotically)
biased. We show that, even when the bias term cannot be consistently estimated,
valid inference can be obtained by proper implementations of the bootstrap.
Specifically, we show that the prepivoting approach of Beran (1987, 1988),
originally proposed to deliver higher-order refinements, restores bootstrap
validity by transforming the original bootstrap p-value into an asymptotically
uniform random variable. We propose two different implementations of
prepivoting (plug-in and double bootstrap), and provide general high-level
conditions that imply validity of bootstrap inference. To illustrate the
practical relevance and implementation of our results, we discuss five
applications: (i) a simple location model for i.i.d. data, possibly with
infinite variance; (ii) regression models with omitted controls; (iii)
inference on a target parameter based on model averaging; (iv) ridge-type
regularized estimators; and (v) dynamic panel data models
Compostagem laminar - uma alternativa para o manejo de resĂduos orgĂąnicos.
COMPOSTAGEM LAMINAR - UMA ALTERNATIVA PARA O APROVEITAMENTO DE RESĂDUOS ORGĂNICOS: A compostagem laminar foi inspirada nos processos naturais, mais propriamente a degradação da serrapilheira nas matas. Como o material Ă© depositado sobre o solo, todos os processos fermentativos sĂŁo aerĂłbicos, sendo criado um ambiente propĂcio para o desenvovimento da fauna edĂĄfica, como minhocas, colĂȘmbolos, ĂĄcaros, insetos diversos e principalmente microvida como fungos, bactĂ©rias e actinomicetos, que tem a capacidade de degradar a matĂ©ria orgĂąnica retirando nitrogĂȘnio do ar, o qual ficarĂĄ disponĂvel para as plantas.bitstream/item/31321/1/comunicado-169.pd
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