750 research outputs found
Sparling two-forms, the conformal factor and the gravitational energy density of the teleparallel equivalent of general relativity
It has been shown recently that within the framework of the teleparallel
equivalent of general relativity (TEGR) it is possible to define the energy
density of the gravitational field. The TEGR amounts to an alternative
formulation of Einstein's general relativity, not to an alternative gravity
theory. The localizability of the gravitational energy has been investigated in
a number of space-times with distinct topologies, and the outcome of these
analises agree with previously known results regarding the exact expression of
the gravitational energy, and/or with the specific properties of the space-time
manifold. In this article we establish a relationship between the expression
for the gravitational energy density of the TEGR and the Sparling two-forms,
which are known to be closely connected with the gravitational energy. We also
show that our expression of energy yields the correct value of gravitational
mass contained in the conformal factor of the metric field.Comment: 12 pages, Latex file, no figures, to be published in Gen. Rel. Gra
The Casimir effect for the scalar and Elko fields in a Lifshitz-like field theory
In this work, we obtain the Casimir energy for the real scalar field and the
Elko neutral spinor field in a field theory at a Lifshitz fixed point (LP). We
analyze the massless and the massive case for both fields using dimensional
regularization. We obtain the Casimir energy in terms of the dimensional
parameter and the LP parameter. Particularizing our result, we can recover the
usual results without LP parameter in (3+1) dimensions presented in the
literature. Moreover, we compute the effects of the LP parameter in the thermal
corrections for the massless scalar field.Comment: 20 pages, 2 figures, some results have been modified and other
changes to the text have been made to match the accepted version in Eur.
Phys. J.
Gravity localization on hybrid branes
This work deals with gravity localization on codimension-1 brane worlds
engendered by compacton-like kinks, the so-called hybrid branes. In such
scenarios, the thin brane behaviour is manifested when the extra dimension is
outside the compact domain, where the energy density is non-trivial, instead of
asymptotically as in the usual thick brane models. The zero mode is trapped in
the brane, as required. The massive modes, although are not localized in the
brane, have important phenomenological implications such as corrections to the
Newton's law. We study such corrections in the usual thick domain wall and in
the hybrid brane scenarios. By means of suitable numerical methods, we attain
the mass spectrum for the graviton and the corresponding wavefunctions. The
spectra possess the usual linearly increasing behaviour from the Kaluza-Klein
theories. Further, we show that the 4D gravitational force is slightly
increased at short distances. The first eigenstate contributes highly for the
correction to the Newton's law. The subsequent normalized solutions have
diminishing contributions. Moreover, we find out that the phenomenology of the
hybrid brane is not different from the usual thick domain wall. The use of
numerical techniques for solving the equations of the massive modes is useful
for matching possible phenomenological measurements in the gravitational law as
a probe to warped extra dimensions.Comment: 15 pages, 11 figure
The Teleparallel Lagrangian and Hamilton-Jacobi Formalism
We analyze the Teleparallel Equivalent of General Relativity (TEGR) from the
point of view of Hamilton-Jacobi approach for singular systemsComment: 11 pages, no figures, to appear in GR
Energy of general 4-dimensional stationary axisymmetric spacetime in the teleparallel geometry
The field equation with the cosmological constant term is derived and the
energy of the general 4-dimensional stationary axisymmetric spacetime is
studied in the context of the hamiltonian formulation of the teleparallel
equivalent of general relativity (TEGR). We find that, by means of the integral
form of the constraints equations of the formalism naturally without any
restriction on the metric parameters, the energy for the asymptotically flat/de
Sitter/Anti-de Sitter stationary spacetimes in the Boyer-Lindquist coordinate
can be expressed as . It is surprised to learn that the
energy expression is relevant to the metric components ,
and only. As examples, by using this formula
we calculate the energies of the Kerr-Newman (KN), Kerr-Newman Anti-de Sitter
(KN-AdS), Kaluza-Klein, and Cveti\v{c}-Youm spacetimes.Comment: 12 page
Space-time defects and teleparallelism
We consider the class of space-time defects investigated by Puntigam and
Soleng. These defects describe space-time dislocations and disclinations
(cosmic strings), and are in close correspondence to the actual defects that
arise in crystals and metals. It is known that in such materials dislocations
and disclinations require a small and large amount of energy, respectively, to
be created. The present analysis is carried out in the context of the
teleparallel equivalent of general relativity (TEGR). We evaluate the
gravitational energy of these space-time defects in the framework of the TEGR
and find that there is an analogy between defects in space-time and in
continuum material systems: the total gravitational energy of space-time
dislocations and disclinations (considered as idealized defects) is zero and
infinit, respectively.Comment: 22 pages, no figures, to appear in the Class. Quantum Gravit
Lost in Cloud
Cloud computing can reduce cost significantly because businesses can share computing resources. In recent years Small and Medium Businesses (SMB) have used Cloud effectively for cost saving and for sharing IT expenses. With the success of SMBs, many perceive that the larger enterprises ought to move into Cloud environment as well. Government agency s stove-piped environments are being considered as candidates for potential use of Cloud either as an enterprise entity or pockets of small communities. Cloud Computing is the delivery of computing as a service rather than as a product, whereby shared resources, software, and information are provided to computers and other devices as a utility over a network. Underneath the offered services, there exists a modern infrastructure cost of which is often spread across its services or its investors. As NASA is considered as an Enterprise class organization, like other enterprises, a shift has been occurring in perceiving its IT services as candidates for Cloud services. This paper discusses market trends in cloud computing from an enterprise angle and then addresses the topic of Cloud Computing for NASA in two possible forms. First, in the form of a public Cloud to support it as an enterprise, as well as to share it with the commercial and public at large. Second, as a private Cloud wherein the infrastructure is operated solely for NASA, whether managed internally or by a third-party and hosted internally or externally. The paper addresses the strengths and weaknesses of both paradigms of public and private Clouds, in both internally and externally operated settings. The content of the paper is from a NASA perspective but is applicable to any large enterprise with thousands of employees and contractors
Seleção de genes endógenos para análise de qRT-PCR em sementes de café.
A técnica quantitativa de PCR em tempo real, qRT-PCR, permite analisar a expressão de genes alvo em diferentes condições experimentais. No entanto, a análise precisa dos resultados gerados pela qRT-PCR está diretamente relacionada ao gene normalizador utilizado, o qual deve apresentar expressão constitutiva semelhante para as diferentes amostras/tratamentos avaliados no experimento. Os genes normalizadores escolhidos para as análises em sementes podem diferir daqueles utilizados para as raÃzes e folhas. Este trabalho teve como objetivo a avaliação de genes normalizadores úteis ao estudo de expressão gênica em sementes. O experimento englobou sementes mantidas nos frutos, sementes desmuciladas mecanicamente ou por meio da fermentação. Essas sementes e frutos foram em seguida, secados à sombra ou em secador até atingirem os teores de água de 12% ou 35%, foram acondicionados em embalagens herméticas e mantidos em câmara fria (10ºC/ 40%UR) por um perÃodo de até 12 meses. Foram avaliados 11 genes candidatos a normalizadores, os quais foram escolhidos, previamente, em um estudo de microarranjos. As expressões e estabilidade destes genes foram avaliadas por meio dos softwares geNorm, NormFinder, Delta Ct e BestKeeper. Pela análise conjunta dos resultados obtidos a partir destes softwares, observou-se que a estabilidade de um gene normalizador é variável em função do fator experimental considerado. O gene da actina é indicado como normalizador nas análises de expressão gênica em sementes de café quando forem considerados todos os três fatores avaliados neste estudo, ou seja, processamento, secagem e armazenamento
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