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Showing 1 to 6 of 6 (0.029 seconds)Spelling suggestions: "subject:"dgps""
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Cosmological Results and Implications in Effective DGPChow, Lik-Neng Nathan January 2009 (has links)
We study a simple extension of the decoupling limit of boundary effctive actions for the Dvali-Gabadadze-Porrati model, by covariantizing the π lagrangian and coupling to gravity in the usual way. This extension agrees with DGP to leading order in Mpl^−1 , and simplifies the cosmological analysis. It is also shown to softly break the shift symmetry, while still being consistent with solar system observations. The generally covariant equations of motion for π and the metric are derived, then the cosmology is developed under the Cosmological Principle. Three analytic solutions are found and their stability is studied. Interesting DGP phenomenology is reproduced, and we consider one of the stable solutions. The cosmological analogue of the Vainshtein effect is reproduced and the effective equation of state, w_π, is shown to be
bounded by −1 from above. This solution is additionally shown to be an attractor
solution in an expanding universe. We evolve π numerically and reproduce these properties, and show that the universe will go through a contraction phase, due to this π field. We then place a constraint on r_c
≥ 10^29 cm, given recent WMAP5 data. This lower bound on r_c gives an upper bound on the anomalous perihelion precession of the moon ∼ 1 × 10^−13, 2 orders of magnitude below current experimental precision.
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| 2 |
Cosmological Results and Implications in Effective DGPChow, Lik-Neng Nathan January 2009 (has links)
We study a simple extension of the decoupling limit of boundary effctive actions for the Dvali-Gabadadze-Porrati model, by covariantizing the π lagrangian and coupling to gravity in the usual way. This extension agrees with DGP to leading order in Mpl^−1 , and simplifies the cosmological analysis. It is also shown to softly break the shift symmetry, while still being consistent with solar system observations. The generally covariant equations of motion for π and the metric are derived, then the cosmology is developed under the Cosmological Principle. Three analytic solutions are found and their stability is studied. Interesting DGP phenomenology is reproduced, and we consider one of the stable solutions. The cosmological analogue of the Vainshtein effect is reproduced and the effective equation of state, w_π, is shown to be
bounded by −1 from above. This solution is additionally shown to be an attractor
solution in an expanding universe. We evolve π numerically and reproduce these properties, and show that the universe will go through a contraction phase, due to this π field. We then place a constraint on r_c
≥ 10^29 cm, given recent WMAP5 data. This lower bound on r_c gives an upper bound on the anomalous perihelion precession of the moon ∼ 1 × 10^−13, 2 orders of magnitude below current experimental precision.
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| 3 |
Diretório dos grupos de pesquisa do CNPq - como ferramenta de análise de redes : um estudo de caso do CDS/UnBAlvarenga, Gisele Carneiro de Lemos Palmeirão 10 March 2014 (has links)
Dissertação (mestrado)—Universidade de Brasília, Centro de Desenvolvimento Sustentável, Programa de Pós-Graduação em Desenvolvimento Sustentável, 2014. / Submitted by Ana Cristina Barbosa da Silva (annabds@hotmail.com) on 2015-02-06T16:20:32Z
No. of bitstreams: 1
2014_GiseleCarneirodeLemosPalmeiraodeAlvarenga.pdf: 3738115 bytes, checksum: 0a5fa360f5c1cb1cff9cbd1da1865105 (MD5) / Approved for entry into archive by Ruthléa Nascimento(ruthleanascimento@bce.unb.br) on 2015-02-13T14:36:08Z (GMT) No. of bitstreams: 1
2014_GiseleCarneirodeLemosPalmeiraodeAlvarenga.pdf: 3738115 bytes, checksum: 0a5fa360f5c1cb1cff9cbd1da1865105 (MD5) / Made available in DSpace on 2015-02-13T14:36:08Z (GMT). No. of bitstreams: 1
2014_GiseleCarneirodeLemosPalmeiraodeAlvarenga.pdf: 3738115 bytes, checksum: 0a5fa360f5c1cb1cff9cbd1da1865105 (MD5) / O objetivo deste estudo foi identificar as redes de pesquisa existentes no Centro de Desenvolvimento Sustentável da Universidade de Brasília - CDS/UnB utilizando os dados registrados no Diretório dos Grupos de Pesquisa – DGP, com vistas a contribuir para melhorar o acesso às informações coletadas e oferecer sugestões que aprimorem o funcionamento do Diretório. A pesquisa evidenciou desconhecimento de uma parte substancial da comunidade científica quanto ao potencial que o Diretório comporta. Isso foi reconhecido pelos próprios respondentes, que sugeriram dentre outras ações, uma maior divulgação sobre os benefícios que este banco de dados pode oferecer, tornando o seu manuseio mais abrangente. Revelou, ainda, a real percepção dos dirigentes de pesquisa sobre o funcionamento do Diretório, o que facilitará sua utilização pela comunidade científica. Também, observou-se que muitas das sugestões propostas já vêm sendo incorporadas, tais como: o registro dos egressos, a inclusão de titulação dos membros do grupo e a possibilidade de inserir instituições parceiras no desenvolvimento da pesquisa. Tais iniciativas bem como a realização desta pesquisa contribuem para tornar o DGP mais conhecido e acessível à sociedade. ________________________________________________________________________________ ABSTRACT / The aim of this study was to identify existing networks of research at the Centre for Sustainable Development at the University of Brasilia - CDS/UnB using the data registered in the Directory of Research Groups – DGP, in order to contribute to improving access to information collected and offer suggestions that will improve the operation of the Directory. The research showed lack of knowledge of a substantial part of the scientific community about the Directory potential’s. This was acknowledged by the respondents themselves, which suggested among other things, greater disclosure about the benefits that this database can provide, making handling more comprehensive. Also brought up the real perception of the managers about the operation of the directory, which will make easier its use by the scientific community. Also, it was observed that many of the proposed suggestions have already been incorporated, such as the registration of graduates, including titration of group members and the possibility of inserting partner institutions in the research. Such initiatives as well as the realization of this research contribute to make the Directory best known and accessible to society.
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An?lise em conjunta de testes cosmol?gicosGimenes, Humberto Scalco 01 April 2013 (has links)
Made available in DSpace on 2014-12-17T15:15:02Z (GMT). No. of bitstreams: 1
HumbertoSG_DISSERT.pdf: 1623099 bytes, checksum: 9db2624a800c722b68b561bc7a9bc747 (MD5)
Previous issue date: 2013-04-01 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Nesta disserta??o, uma revis?o sobre tr?s modelos cosmol?gicos n?o-padr?o do tipo
Friedmann-Robertson-Walker s?o apresentados. O modelo !CDM, o g?s de Chaplygin
generalizado e o modelo de brana de Dvali-Gabadadze-Porrati (DGP). Apresentamos
tamb?m, tr?s testes estat?sticos utilizados em Cosmologia, cada um envolvendo uma
vela padr?o diferente. Estes testes t?m como objetivo, vincular os diferentes par?metros
de cada modelo e assim compar?-los com os dados observacionais mais atuais.
Efetuamos o teste do m?dulo de dist?ncia de Supernovas do tipo Ia, atrav?s de 580
Supernovas do Union Compilation 2.1 (2011) [1]. A Fra??o de massa de aglomerados
de gal?xias, onde utilizamos um conjunto de 52 aglomerados observados pelo CHANDRA
(2009) [2] e a raz?o CMB/BAO, onde foram utilizados um conjunto de 6 picos de
BAO do WiggleZ Dark Energy Survey (2011) [3]. Esses testes foram aplicados para cada
um dos modelos apresentados. Verificamos que individualmente, os testes cosmol?gicos
n?o s?o bons o suficiente para vincular modelos, criando espa?os param?tricos
degenerados, necessitando de uma an?lise em conjunta dos testes para vincular os par?metros.
OBS: N?o foi poss?vel efetuar a descri??o integral do resumo, devido o fato do sistema utilizado n?o aceitar os s?mbolos existentes. Desse modo, solicitamos que a visualiza??o desse elemento seja efetuada no arquivo da disserta??o.
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Temporal Variations in the Compliance of Gas Hydrate FormationsRoach, Lisa Aretha Nyala 20 March 2014 (has links)
Seafloor compliance is a non-intrusive geophysical method sensitive to the shear modulus of the sediments below the seafloor. A compliance analysis requires the computation of the frequency dependent transfer function between the vertical stress, produced at the seafloor by the ultra low frequency passive source-infra-gravity waves, and the resulting displacement, related to velocity through the frequency. The displacement of the ocean floor is dependent on the elastic structure of the sediments and the compliance function is tuned to different depths, i.e., a change in the elastic parameters at a given depth is sensed by the compliance function at a particular frequency. In a gas hydrate system, the magnitude of the stiffness is a measure of the quantity of gas hydrates present. Gas hydrates contain immense stores of greenhouse gases making them relevant to climate change science, and represent an important potential alternative source of energy. Bullseye Vent is a gas hydrate system located in an area that has been intensively studied for over 2 decades and research results suggest that this system is evolving over time.
A partnership with NEPTUNE Canada allowed for the investigation of this possible evolution. This thesis describes a compliance experiment configured for NEPTUNE Canada’s seafloor observatory and its failure. It also describes the use of 203 days of simultaneously logged pressure and velocity time-series data, measured by a Scripps differential pressure gauge, and a Güralp CMG-1T broadband seismometer on NEPTUNE Canada’s seismic station, respectively, to evaluate variations in sediment stiffness near Bullseye. The evaluation resulted in a (- 4.49 x10-3± 3.52 x 10-3) % change of the transfer function of 3rd October, 2010 and represents a 2.88% decrease in the stiffness of the sediments over the period. This thesis also outlines a new algorithm for calculating the static compliance of isotropic layered sediments.
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| 6 |
Temporal Variations in the Compliance of Gas Hydrate FormationsRoach, Lisa Aretha Nyala 20 March 2014 (has links)
Seafloor compliance is a non-intrusive geophysical method sensitive to the shear modulus of the sediments below the seafloor. A compliance analysis requires the computation of the frequency dependent transfer function between the vertical stress, produced at the seafloor by the ultra low frequency passive source-infra-gravity waves, and the resulting displacement, related to velocity through the frequency. The displacement of the ocean floor is dependent on the elastic structure of the sediments and the compliance function is tuned to different depths, i.e., a change in the elastic parameters at a given depth is sensed by the compliance function at a particular frequency. In a gas hydrate system, the magnitude of the stiffness is a measure of the quantity of gas hydrates present. Gas hydrates contain immense stores of greenhouse gases making them relevant to climate change science, and represent an important potential alternative source of energy. Bullseye Vent is a gas hydrate system located in an area that has been intensively studied for over 2 decades and research results suggest that this system is evolving over time.
A partnership with NEPTUNE Canada allowed for the investigation of this possible evolution. This thesis describes a compliance experiment configured for NEPTUNE Canada’s seafloor observatory and its failure. It also describes the use of 203 days of simultaneously logged pressure and velocity time-series data, measured by a Scripps differential pressure gauge, and a Güralp CMG-1T broadband seismometer on NEPTUNE Canada’s seismic station, respectively, to evaluate variations in sediment stiffness near Bullseye. The evaluation resulted in a (- 4.49 x10-3± 3.52 x 10-3) % change of the transfer function of 3rd October, 2010 and represents a 2.88% decrease in the stiffness of the sediments over the period. This thesis also outlines a new algorithm for calculating the static compliance of isotropic layered sediments.
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