1,266 research outputs found
Quantum Gowdy Model: Schrodinger Representation with Unitary Dynamics
The linearly polarized Gowdy model is paradigmatic for studying
technical and conceptual issues in the quest for a quantum theory of gravity
since, after a suitable and almost complete gauge fixing, it becomes an exactly
soluble midisuperspace model. Recently, a new quantization of the model,
possessing desired features such as a unitary implementation of the gauge group
and of the time evolution, has been put forward and proven to be essentially
unique. An appropriate setting for making contact with other approaches to
canonical quantum gravity is provided by the Schr\"odinger representation,
where states are functionals on the configuration space of the theory. Here we
construct this functional description, analyze the time evolution in this
context and show that it is also unitary when restricted to physical states,
i.e. states which are solutions to the remaining constraint of the theory.Comment: 21 pages, version accepted for publication in Physical Review
Regression with Linear Factored Functions
Many applications that use empirically estimated functions face a curse of
dimensionality, because the integrals over most function classes must be
approximated by sampling. This paper introduces a novel regression-algorithm
that learns linear factored functions (LFF). This class of functions has
structural properties that allow to analytically solve certain integrals and to
calculate point-wise products. Applications like belief propagation and
reinforcement learning can exploit these properties to break the curse and
speed up computation. We derive a regularized greedy optimization scheme, that
learns factored basis functions during training. The novel regression algorithm
performs competitively to Gaussian processes on benchmark tasks, and the
learned LFF functions are with 4-9 factored basis functions on average very
compact.Comment: Under review as conference paper at ECML/PKDD 201
Dinâmica e variabilidade espacial de plantas daninhas em sistemas de mobilização do solo em sorgo forrageiro.
A study of atmospheric neutrinos with the IMB detector
A sample of 401 contained neutrino interactions collected in the 3300 metric ton fiducial mass IMB detector was used to study neutrino oscillations, geomagnetic modulation of the flux and to search for point sources. The majority of these events are attributed to neutrino interactions. For the most part, these neutrinos are believed to originate as tertiary products of cosmic ray interactions in the atmosphere. The neutrinos are a mixture of v sub e and v sub micron
On the General Analytical Solution of the Kinematic Cosserat Equations
Based on a Lie symmetry analysis, we construct a closed form solution to the
kinematic part of the (partial differential) Cosserat equations describing the
mechanical behavior of elastic rods. The solution depends on two arbitrary
analytical vector functions and is analytical everywhere except a certain
domain of the independent variables in which one of the arbitrary vector
functions satisfies a simple explicitly given algebraic relation. As our main
theoretical result, in addition to the construction of the solution, we proof
its generality. Based on this observation, a hybrid semi-analytical solver for
highly viscous two-way coupled fluid-rod problems is developed which allows for
the interactive high-fidelity simulations of flagellated microswimmers as a
result of a substantial reduction of the numerical stiffness.Comment: 14 pages, 3 figure
Quantum Gowdy model: A unitary description
The quantization of the family of linearly polarized Gowdy spacetimes
is discussed in detail, starting with a canonical analysis in which the true
degrees of freedom are described by a scalar field that satisfies a
Klein-Gordon type equation in a fiducial time dependent background. A time
dependent canonical transformation, which amounts to a change of the basic
(scalar) field of the model, brings the system to a description in terms of a
Klein-Gordon equation on a background that is now static, although subject to a
time dependent potential. The system is quantized by means of a natural choice
of annihilation and creation operators. The quantum time evolution is
considered and shown to be unitary, allowing both the Schr\"odinger and
Heisenberg pictures to be consistently constructed. This has to be contrasted
with previous treatments for which time evolution failed to be implementable as
a unitary transformation. Possible implications for both canonical quantum
gravity and quantum field theory in curved spacetime are commented
Localization of a 64-kDa phosphoprotein in the lumen between the outer and inner envelopes of pea chloroplasts
The identification and localization of a marker protein for the intermembrane space between the outer and inner chloroplast envelopes is described. This 64-kDa protein is very rapidly labeled by [γ-32P]ATP at very low (30 nM) ATP concentrations and the phosphoryl group exhibits a high turnover rate. It was possible to establish the presence of the 64-kDa protein in this plastid compartment by using different chloroplast envelope separation and isolation techniques. In addition comparison of labeling kinetics by intact and hypotonically lysed pea chloroplasts support the localization of the 64-kDa protein in the intermembrane space. The 64-kDa protein was present and could be labeled in mixed envelope membranes isolated from hypotonically lysed plastids. Mixed envelope membranes incorporated high amounts of 32P from [γ-32P]ATP into the 64-kDa protein, whereas separated outer and inner envelope membranes did not show significant phosphorylation of this protein. Water/Triton X-114 phase partitioning demonstrated that the 64-kDa protein is a hydrophilic polypeptide. These findings suggest that the 64-kDa protein is a soluble protein trapped in the space between the inner and outer envelope membranes. After sonication of mixed envelope membranes, the 64-kDa protein was no longer present in the membrane fraction, but could be found in the supernatant after a 110000 × g centrifugation
Holography in asymptotically flat space-times and the BMS group
In a previous paper (hep-th/0306142) we have started to explore the
holographic principle in the case of asymptotically flat space-times and
analyzed in particular different aspects of the Bondi-Metzner-Sachs (BMS)
group, namely the asymptotic symmetry group of any asymptotically flat
space-time. We continue this investigation in this paper. Having in mind a
S-matrix approach with future and past null infinity playing the role of
holographic screens on which the BMS group acts, we connect the IR sectors of
the gravitational field with the representation theory of the BMS group. We
analyze the (complicated) mapping between bulk and boundary symmetries pointing
out differences with respect to the AdS/CFT set up. Finally we construct a BMS
phase space and a free hamiltonian for fields transforming w.r.t BMS
representations. The last step is supposed to be an explorative investigation
of the boundary data living on the degenerate null manifold at infinity.Comment: 31 pages, several changes in section 3 and 7 and references update
Análise de agrupamento de municípios do entorno do Lago de Sobradinho, utilizando atributos físicos do solo.
Objetivou-se avaliar os atributos físicos do solo dos municípios localizados no entorno do lago de Sobradinho utilizando a análise de agrupamento. Foram coletadas amostras de solo nas camadas de 0-0,10 m, com três repetições em cada propriedade, sendo o uso do solo a caatinga e a agricultura nos municípios de Sobradinho em quatro propriedades, Casa Nova com oito propriedades, Sento Sé com oito propriedades e Remanso com quatro propriedades no Estado da Bahia. Os atributos analisadas foram: diâmetro médio ponderado (DMP), diâmetro médio geométrico (DMG), densidade do solo (Ds), porosidade total do solo (Pt), argila, silte, areia, grau de floculação (GF) e argila dispersa em água (ADA), sendo analisados pela análise de agrupamento utilizando o método de Ward e a distância Euclidiana, após a estatística descritiva e o teste de normalidade. Verificou-se a formação clara de dois grandes grupos: no qual GI engloba Casa Nova e Remanso e o GII formado por Sento Sé e Sobradinho. Dentro do GII podem diferir outros dois subgrupos tendo Casa Nova e Remanso em um deles e isoladamente Sobradinho. A formação do GII pode ser atribuída aos maiores valores de argila e consequentemente do grau de floculação. De modo geral, não se verifica diferença entre o uso da agricultura e a Caatinga, em todos os grupos, com bases nos atributos físicos do solo
Análise multivariada da qualidade química de um Latossolo sob sistemas de manejo do solo.
Os sistemas de manejo podem influenciar atributos químicos do solo, sendo importante a busca de aplicação de novas técnicas para a compreensão dos efeitos ocasionados. Objetivou-se avaliar atributos químicos de um Latossolo Vermelho distroférrico sob sistemas de manejo por meio da estatística multivariada. Os tratamentos consistiram dos seguintes sistemas de manejo do solo: plantio direto, plantio direto escarificado, plantio direto escarificado cruzado, preparo convencional, preparo reduzido e preparo conservacionista. O trabalho foi conduzido com delineamento em blocos ao acaso com quatro repetições, sendo as amostras coletadas nas camadas de 0,00-0,10 e 0,10-0,20 m. Os atributos analisados foram: pH em água; matéria orgânica; cálcio, magnésio, potássio e alumínio trocáveis; fósforo e acidez potencial, com posterior cálculo da soma de bases, da capacidade de troca de cátions a pH 7,0 e da saturação por bases. Os dados foram analisados por meio de agrupamentos e componentes principais. Verificou-se que o sistema de preparo convencional e plantio direto na camada de 0,00 - 0,10 m apresentaram similaridade, e que preparo reduzido e plantio direto escarificado cruzado comparado aos demais sistemas, concentraram o maior número de atributos químicos e foram influenciados pelos valores de cálcio, magnésio, soma de base, capacidade de troca de cátions e saturação por base. Na camada de 0,10-0,20 m, os subgrupos plantio direto escarificado cruzado, preparo convencional, preparo reduzido e plantio direito concentraram grande parte dos atributos químicos, sendo influenciado pelos valores de potássio, soma de base, magnésio, capacidade de troca de cátions, saturação por base, matéria orgânica e pH
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