4,355 research outputs found
Inertial forces in the Casimir effect with two moving plates
We combine linear response theory and dimensional regularization in order to
derive the dynamical Casimir force in the low frequency regime. We consider two
parallel plates moving along the normal direction in dimensional space. We
assume the free-space values for the mass of each plate to be known, and obtain
finite, separation-dependent mass corrections resulting from the combined
effect of the two plates. The global mass correction is proportional to the
static Casimir energy, in agreement with Einstein's law of equivalence between
mass and energy for stressed rigid bodies.Comment: 9 pages, 1 figure; title and abstract changed; to appear in Physical
Review
Particle Creation by a Moving Boundary with Robin Boundary Condition
We consider a massless scalar field in 1+1 dimensions satisfying a Robin
boundary condition (BC) at a non-relativistic moving boundary. We derive a
Bogoliubov transformation between input and output bosonic field operators,
which allows us to calculate the spectral distribution of created particles.
The cases of Dirichlet and Neumann BC may be obtained from our result as
limiting cases. These two limits yield the same spectrum, which turns out to be
an upper bound for the spectra derived for Robin BC. We show that the particle
emission effect can be considerably reduced (with respect to the
Dirichlet/Neumann case) by selecting a particular value for the oscillation
frequency of the boundary position
Quantum radiation pressure on a moving mirror at finite temperature
We compute the radiation pressure force on a moving mirror, in the
nonrelativistic approximation, assuming the field to be at temperature At
high temperature, the force has a dissipative component proportional to the
mirror velocity, which results from Doppler shift of the reflected thermal
photons. In the case of a scalar field, the force has also a dispersive
component associated to a mass correction. In the electromagnetic case, the
separate contributions to the mass correction from the two polarizations
cancel. We also derive explicit results in the low temperature regime, and
present numerical results for the general case. As an application, we compute
the dissipation and decoherence rates for a mirror in a harmonic potential
well.Comment: Figure 3 replaced, changes mainly in Sections IV and V, new appendix
introduced. To appear in Physical Review
Correlation Function of Galaxy Groups
We use the Updated Zwicky Catalog of galaxies (Falco et al. 1999) to generate
a catalog of groups, by means of a friend-of-friend algorithm. The correlation
length of the total sample is well fitted with a power law with parameters and for values of . Three subsamples defined by
the range of group virial masses were used to have their clustering
properties examined throughout the autocorrelation function. We find an
increase of the amplitude of the correlation function according to the group
masses which extends the results of the relation for galaxy systems
at small . For completeness we have also analyzed a sample of groups
obtained from the Southern Sky Redshift Survey (da Costa et al.1998) in the
range of virial masses to compare the results with those obtained from
GUZC.Comment: 9 figures, accepted for publication in Ap
Quantum radiation in a plane cavity with moving mirrors
We consider the electromagnetic vacuum field inside a perfect plane cavity
with moving mirrors, in the nonrelativistic approximation. We show that low
frequency photons are generated in pairs that satisfy simple properties
associated to the plane geometry. We calculate the photon generation rates for
each polarization as functions of the mechanical frequency by two independent
methods: on one hand from the analysis of the boundary conditions for moving
mirrors and with the aid of Green functions; and on the other hand by an
effective Hamiltonian approach. The angular and frequency spectra are discrete,
and emission rates for each allowed angular direction are obtained. We discuss
the dependence of the generation rates on the cavity length and show that the
effect is enhanced for short cavity lengths. We also compute the dissipative
force on the moving mirrors and show that it is related to the total radiated
energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review
Casimir torque between corrugated metallic plates
We consider two parallel corrugated plates and show that a Casimir torque
arises when the corrugation directions are not aligned. We follow the
scattering approach and calculate the Casimir energy up to second order in the
corrugation amplitudes, taking into account nonspecular reflections,
polarization mixing and the finite conductivity of the metals. We compare our
results with the proximity force approximation, which overestimates the torque
by a factor 2 when taking the conditions that optimize the effect. We argue
that the Casimir torque could be measured for separation distances as large as
1 Comment: 7 pages, 3 figures, contribution to QFEXT07 proceeding
The Seyfert Population in the Local Universe
The magnitude-limited catalog of the Southern Sky Redshift Survey (SSRS2), is
used to characterize the properties of galaxies hosting Active Galactic Nuclei.
Using emission-line ratios, we identify a total of 162 (3%) Seyfert galaxies
out of the parent sample with 5399 galaxies. The sample contains 121 Seyfert 2
galaxies and 41 Seyfert 1. The SSRS2 Seyfert galaxies are predominantly in
spirals of types Sb and earlier, or in galaxies with perturbed appearance as
the result of strong interactions or mergers. Seyfert galaxies in this sample
are twice as common in barred hosts than the non-Seyferts. By assigning
galaxies to groups using a percolation algorithm we find that the Seyfert
galaxies in the SSRS2 are more likely to be found in binary systems, when
compared to galaxies in the SSRS2 parent sample. However, there is no
statistically significant difference between the Seyfert and SSRS2 parent
sample when systems with more than 2 galaxies are considered. The analysis of
the present sample suggests that there is a stronger correlation between the
presence of the AGN phenomenon with internal properties of galaxies
(morphology, presence of bar, luminosity) than with environmental effects
(local galaxy density, group velocity dispersion, nearest neighbor distance).Comment: 35 pages, 13 figures, Accepted to be publised in Astronomical Journa
Reserva legal florestal: uma leitura sob a ótica da economia ecológica.
A legislação ambiental brasileira que trata da reserva legal florestal é alvo de intensa polêmica, pois põe em confronto interesses públicos e privados. Os debates têm se acirrado em torno da proposta do "novo" Código Florestal, que revoga a lei 4.771/1965. Desde o início, o Código Florestal brasileiro vem sofrendo inúmeras alterações, por meio de leis, decretos e medidas provisórias o que demonstra a dificuldade dos legisladores em conciliar os interesses dos diversos atores envolvidos no assunto e em considerar as diferenças regionais que marcam o território nacional. O presente trabalho analisa a evolução da legislação da reserva legal e discorre sobre aspectos polêmicos a ela relacionados. Busca fazer a leitura desse instrumento de política ambiental à luz da estrutura analítica central da Economia Ecológica quanto à utilização dos bens e serviços ambientais: i) determinação de uma escala de uso sustentável; ii) definição de uma distribuição justa; e iii) alocação eficiente dos mesmos. Propõe critérios para a implementação de políticas que permitam uma distribuição mais equitativa dos custos da conservação ambiental entre toda a sociedade, bem como a importância de ajustes locacionais das reservas legais, na busca de um melhor equilíbrio entre a conservação da biodiversidade e o custo de oportunidade das terras.ENANPPAS 2010
Disorder in quantum vacuum: Casimir-induced localization of matter waves
Disordered geometrical boundaries such as rough surfaces induce important
modifications to the mode spectrum of the electromagnetic quantum vacuum. In
analogy to Anderson localization of waves induced by a random potential, here
we show that the Casimir-Polder interaction between a cold atomic sample and a
rough surface also produces localization phenomena. These effects, that
represent a macroscopic manifestation of disorder in quantum vacuum, should be
observable with Bose-Einstein condensates expanding in proximity of rough
surfaces
Lateral Casimir-Polder force with corrugated surfaces
We derive the lateral Casimir-Polder force on a ground state atom on top of a
corrugated surface, up to first order in the corrugation amplitude. Our
calculation is based on the scattering approach, which takes into account
nonspecular reflections and polarization mixing for electromagnetic quantum
fluctuations impinging on real materials. We compare our first order exact
result with two commonly used approximation methods. We show that the proximity
force approximation (large corrugation wavelengths) overestimates the lateral
force, while the pairwise summation approach underestimates it due to the
non-additivity of dispersion forces. We argue that a frequency shift
measurement for the dipolar lateral oscillations of cold atoms could provide a
striking demonstration of nontrivial geometrical effects on the quantum vacuum.Comment: 12 pages, 6 figures, contribution to QFEXT07 proceeding
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