7,033 research outputs found
Security policy refinement using data integration: a position paper.
In spite of the wide adoption of policy-based approaches for security management, and many existing treatments of policy verification and analysis, relatively little attention has been paid to policy refinement: the problem of deriving lower-level, runnable policies from higher-level policies, policy goals, and specifications. In this paper we present our initial ideas on this task, using and adapting concepts from data integration. We take a view of policies as governing the performance of an action on a target by a subject, possibly with certain conditions. Transformation rules are applied to these components of a policy in a structured way, in order to translate the policy into more refined terms; the transformation rules we use are similar to those of global-as-view database schema mappings, or to extensions thereof. We illustrate our ideas with an example. Copyright 2009 ACM
Errors on the inverse problem solution for a noisy spherical gravitational wave antenna
A single spherical antenna is capable of measuring the direction and
polarization of a gravitational wave. It is possible to solve the inverse
problem using only linear algebra even in the presence of noise. The simplicity
of this solution enables one to explore the error on the solution using
standard techniques. In this paper we derive the error on the direction and
polarization measurements of a gravitational wave. We show that the solid angle
error and the uncertainty on the wave amplitude are direction independent. We
also discuss the possibility of determining the polarization amplitudes with
isotropic sensitivity for any given gravitational wave source.Comment: 13 pages, 4 figures, LaTeX2e, IOP style, submitted to CQ
A general class of braneworld wormholes
The brane cosmology scenario is based on the idea that our Universe is a
3-brane embedded in a five-dimensional bulk. In this work, a general class of
braneworld wormholes is explored with , where is the four
dimensional Ricci scalar, and specific solutions are further analyzed. A
fundamental ingredient of traversable wormholes is the violation of the null
energy condition (NEC). However, it is the effective total stress energy tensor
that violates the latter, and in this work, the stress energy tensor confined
on the brane, threading the wormhole, is imposed to satisfy the NEC. It is also
shown that in addition to the local high-energy bulk effects, nonlocal
corrections from the Weyl curvature in the bulk may induce a NEC violating
signature on the brane. Thus, braneworld gravity seems to provide a natural
scenario for the existence of traversable wormholes.Comment: 6 pages, Revtex4. V2: comments and references added, to appear in
Phys. Rev.
Evolving wormhole geometries within nonlinear electrodynamics
In this work, we explore the possibility of evolving (2+1) and
(3+1)-dimensional wormhole spacetimes, conformally related to the respective
static geometries, within the context of nonlinear electrodynamics. For the
(3+1)-dimensional spacetime, it is found that the Einstein field equation
imposes a contracting wormhole solution and the obedience of the weak energy
condition. Nevertheless, in the presence of an electric field, the latter
presents a singularity at the throat, however, for a pure magnetic field the
solution is regular. For the (2+1)-dimensional case, it is also found that the
physical fields are singular at the throat. Thus, taking into account the
principle of finiteness, which states that a satisfactory theory should avoid
physical quantities becoming infinite, one may rule out evolving
(3+1)-dimensional wormhole solutions, in the presence of an electric field, and
the (2+1)-dimensional case coupled to nonlinear electrodynamics.Comment: 17 pages, 1 figure; to appear in Classical and Quantum Gravity. V2:
minor corrections, including a referenc
Melhoramento genético como ferramenta para o crescimento e o desenvolvimento da ovinocultura de corte.
Resumo: Dentre as ações relacionadas à promoção do crescimento e do desenvolvimento de uma atividade pecuária, o melhoramento genético é uma das que mais merece atenção. Para que a ovinocultura de corte no Brasil possa se desenvolver, são necessárias a seleção e a multiplicação de genótipos apropriados aos diversos ecossistemas encontrados no país. Com a finalidade de aperfeiçoar a capacidade de produção dos animais, as ferramentas básicas do melhoramento genético são a seleção e os métodos de acasalamento. Neste trabalho são apresentadas algumas definições fundamentais do melhoramento genético e discutidas formas de sua contribuição para o crescimento da ovinocultura de corte. [Animal breeding as a tool for upgrowth and development of meat sheep sector]. Abstract: Among the actions to promote the growing and the development of an animal breeding activity, the genetic improvement is one of that more attention deserve. Selection and multiplication of genotypes appropriated to several ecossystems found in the country are necessary to the development of meat sheep sector in Brazil. To optimize the production ability of the animals, the basic tools of animal breeding are the selection and the mating methods. In this paper fundamental definitions of animal breeding are presented and forms of its contribution for the upgrowth of meat sheep sector are discussed.Palestra apresentada no XVII Congresso Brasileiro de Reprodução Animal, 31 de maio a 02 de junho de 2007, Curitiba, PR
Deconvolving the information from an imperfect spherical gravitational wave antenna
We have studied the effects of imperfections in spherical gravitational wave
antenna on our ability to properly interpret the data it will produce. The
results of a numerical simulation are reported that quantitatively describe the
systematic errors resulting from imperfections in various components of the
antenna. In addition, the results of measurements on a room-temperature
prototype are presented that verify it is possible to accurately deconvolve the
data in practice.Comment: 5 pages, 2 figures, to be published in Europhysics Letter
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