Radiation Pressure as a Source of Decoherence

We consider the interaction of an harmonic oscillator with the quantum field via radiation pressure. We show that a `Schrodinger cat' state decoheres in a time scale that depends on the degree of `classicality' of the state components, and which may be much shorter than the relaxation time scale associated to the dynamical Casimir effect. We also show that decoherence is a consequence of the entanglement between the quantum states of the oscillator and field two-photon states. With the help of the fluctuation-dissipation theorem, we derive a relation between decoherence and damping rates valid for arbitrary values of the temperature of the field. Coherent states are selected by the interaction as pointer states.Comment: 14 pages, 3 figures, RevTex fil

Decoherence via Dynamical Casimir Effect

We derive a master equation for a mirror interacting with the vacuum field via radiation pressure. The dynamical Casimir effect leads to decoherence of a 'Schroedinger cat' state in a time scale that depends on the degree of 'macroscopicity' of the state components, and which may be much shorter than the relaxation time scale. Coherent states are selected by the interaction as pointer states.Comment: 4 pages, 2 figure

Fluctuation induced quantum interactions between compact objects and a plane mirror

The interaction of compact objects with an infinitely extended mirror plane due to quantum fluctuations of a scalar or electromagnetic field that scatters off the objects is studied. The mirror plane is assumed to obey either Dirichlet or Neumann boundary conditions or to be perfectly reflecting. Using the method of images, we generalize a recently developed approach for compact objects in unbounded space [1,2] to show that the Casimir interaction between the objects and the mirror plane can be accurately obtained over a wide range of separations in terms of charge and current fluctuations of the objects and their images. Our general result for the interaction depends only on the scattering matrices of the compact objects. It applies to scalar fields with arbitrary boundary conditions and to the electromagnetic field coupled to dielectric objects. For the experimentally important electromagnetic Casimir interaction between a perfectly conducting sphere and a plane mirror we present the first results that apply at all separations. We obtain both an asymptotic large distance expansion and the two lowest order correction terms to the proximity force approximation. The asymptotic Casimir-Polder potential for an atom and a mirror is generalized to describe the interaction between a dielectric sphere and a mirror, involving higher order multipole polarizabilities that are important at sub-asymptotic distances.Comment: 19 pages, 7 figure

Typology of cattle production in Brazil at the municipality level.

Brazil is one of largest beef producers in the world. Data from the Brazilian Agricultural Census 2006, carried out by the Brazilian Institute of Geography and Statistics (IBGE), has shown that approximately 2.7 million farms had bovine cattle, i.e. more than half of the farms in the country, raising 176.1 million head. In the last three decades, the expansion of beef production has relied strongly on increasing stocking rates and animal productivity rather than expansion of pasture area. Still, there is high variability in productivity levels and technology adoption throughout the territory. Identifying and characterizing such variations is essential to allow improving the estimates of greenhouse gases flows, and to better evaluate mitigation and adaptation options besides other issues related to technology adoption and public policies

Tipificação de municípios produtores de bovinos no Brasil.

Resumo: Num país com as dimensões do Brasil é muito acentuada a variabilidade dos sistemas de produção agropecuária praticados pelos produtores. Conhecer esta diferenciação é fundamental para propor linhas de pesquisa, desenvolvimento, transferência de tecnologia e políticas públicas apropriadas. Dados do Censo Agropecuário brasileiro de 2006, realizado pelo Instituto Brasileiro de Geografia e Estatística (IBGE), mostram que mais da metade dos estabelecimentos agropecuários do país possuíam pelo menos um bovino, correspondendo a 2,7 milhões de estabelecimentos e 176,1 milhões de cabeças. Este trabalho trata da classificação e caracterização dos municípios produtores de bovinos no Brasil, empregando técnicas de análise multivariada (análise fatorial e de cluster). Foram empregadas 47 variáveis oriundas de tabulações especiais de dados do Censo Agropecuário 2006. Os dados foram filtrados para estabelecimentos com bovinos e agregados por município (5.517 municípios). As variáveis reuniram informações socioeconômicas e tecnológicas dos estabelecimentos, tais como uso da terra, tamanho do rebanho, área de pastagens (naturais e plantadas), principal finalidade da produção de bovinos, produtividade, taxa de lotação, manejo das pastagens, uso de insumos, origem da renda do produtor, produção familiar ou não-familiar. As análises identificaram dez grupos de municípios produtores de bovinos, destacando: 1) a grande variabilidade que constitui a bovinocultura brasileira; 2) os evidentes padrões de produção e tecnificação no território. Os resultados foram discutidos com pesquisadores especialistas em bovinocultura, sendo considerados aderentes à realidade brasileira.bitstream/item/140888/1/BolPesq33-Fasiaben.pd

Evaluation of the Pinus taeda quality using ultrasound.

IUS2-PB1-1

Motion-Induced Radiation from a Dynamically Deforming Mirror

A path integral formulation is developed to study the spectrum of radiation from a perfectly reflecting (conducting) surface. It allows us to study arbitrary deformations in space and time. The spectrum is calculated to second order in the height function. For a harmonic traveling wave on the surface, we find many different regimes in which the radiation is restricted to certain directions. It is shown that high frequency photons are emitted in a beam with relatively low angular dispersion whose direction can be controlled by the mechanical deformations of the plate.Comment: 4 pages, 2 eps figues included, final version as appeared in PR

Trembling cavities in the canonical approach

We present a canonical formalism facilitating investigations of the dynamical Casimir effect by means of a response theory approach. We consider a massless scalar field confined inside of an arbitaray domain $G(t)$, which undergoes small displacements for a certain period of time. Under rather general conditions a formula for the number of created particles per mode is derived. The pertubative approach reveals the occurance of two generic processes contributing to the particle production: the squeezing of the vacuum by changing the shape and an acceleration effect due to motion af the boundaries. The method is applied to the configuration of moving mirror(s). Some properties as well as the relation to local Green function methods are discussed. PACS-numbers: 12.20; 42.50; 03.70.+k; 42.65.Vh Keywords: Dynamical Casimir effect; Moving mirrors; Cavity quantum field theory; Vibrating boundary