Stochastic Quantization and Casimir Forces: Pistons of Arbitrary Cross Section

Recently, a method based on stochastic quantization has been proposed to compute the Casimir force and its fluctuations in arbitrary geometries. It relies on the spectral decomposition of the Laplacian operator in the given geometry. Both quantum and thermal fluctuations are considered. Here we use such method to compute the Casimir force on the plates of a finite piston of arbitrary cross section. Asymptotic expressions valid at low and high temperatures and short and long distances are obtained. The case of a piston with triangular cross section is analysed in detail. The regularization of the divergent stress tensor is described.Comment: 10 pages and 4 figures. Accepted for publication in the Proceedings of the tenth conference on Quantum Field Theory under the influence of external conditions - QFEXT'1

Design of one-dimensional Lambertian diffusers of light

We describe a method for designing a one-dimensional random surface that acts as a Lambertian diffuser. The method is tested by means of rigorous computer simulations and is shown to yield the desired scattering pattern.Comment: 6 pages, 2 figure

Social roles and aging from a life-span perspective

Este trabalho investigou os papéis sociais e as tarefas evolutivas desempenhados por adultos. O local escolhido para investigação foi um assentamento de famílias de baixa renda do Distrito Federal criado em 1989. Utilizou-se um questionário contendo 17 questões abertas e 15 questões fechadas, preenchido pela primeira autora durante uma visita domiciliar. Participaram 98 respondentes (73 F e 25 M), sendo 51 entre 50 e 59 anos e 47 a partir de 60 anos. Os resultados apontaram que este grupo é heterogêneo e que seus papéis sociais são influenciados pelas variáveis demográficas (idade, sexo, escolaridade, ocupação, naturalidade e estado civil) e também pelas variáveis relativas à moradia atual. Concluiu-se também que as expectativas sociais, o suporte social e a escolarização são fatores de suma importância para oferecer recursos para a otimização e compensação necessárias a um envelhecimento bem sucedido. __________________________________________________________________________________________________________ ABSTRACTThis study investigated the social roles and developmental tasks of adults. The study took place in a settlement of low-income families, created in The Federal District in 1989. Data were collected through a questionnaire composed of 17 open and 15 closed questions, administered by the first author during a home visit. There were 98 respondents, 73 female and 25 male, being 51 between 50 to 59 years old and 47 elders above the age of 60. The result indicated that this group is heterogeneous and that its social roles are influenced by the demographic variables - age, sex, educational level, work, place of the birth and marital status, as well for the relative variables to current residence. The data allow the conclusion that social expectations, social support and the educational level are important resources for the optimization and necessary compensation to successful aging

Quantum Chaos of Bogoliubov Waves for a Bose-Einstein Condensate in Stadium Billiards

We investigate the possibility of quantum (or wave) chaos for the Bogoliubov excitations of a Bose-Einstein condensate in billiards. Because of the mean field interaction in the condensate, the Bogoliubov excitations are very different from the single particle excitations in a non-interacting system. Nevertheless, we predict that the statistical distribution of level spacings is unchanged by mapping the non-Hermitian Bogoliubov operator to a real symmetric matrix. We numerically test our prediction by using a phase shift method for calculating the excitation energies.Comment: minor change, 4 pages, 4 figures, to appear in Phys. Rev. Let

Chaotic Scattering in the Regime of Weakly Overlapping Resonances

We measure the transmission and reflection amplitudes of microwaves in a resonator coupled to two antennas at room temperature in the regime of weakly overlapping resonances and in a frequency range of 3 to 16 GHz. Below 10.1 GHz the resonator simulates a chaotic quantum system. The distribution of the elements of the scattering matrix S is not Gaussian. The Fourier coefficients of S are used for a best fit of the autocorrelation function if S to a theoretical expression based on random--matrix theory. We find very good agreement below but not above 10.1 GHz

Level density of a Fermi gas: average growth and fluctuations

We compute the level density of a two--component Fermi gas as a function of the number of particles, angular momentum and excitation energy. The result includes smooth low--energy corrections to the leading Bethe term (connected to a generalization of the partition problem and Hardy--Ramanujan formula) plus oscillatory corrections that describe shell effects. When applied to nuclear level densities, the theory provides a unified formulation valid from low--lying states up to levels entering the continuum. The comparison with experimental data from neutron resonances gives excellent results.Comment: 4 pages, 1 figur

Conceptual mechanization studies for a horizon definition spacecraft electrical power subsystem

Solar cell-battery electrical power subsystem for horizon definition spacecraf

Discrete Symmetries in the Weyl Expansion for Quantum Billiards

We consider two and three-dimensional quantum billiards with discrete symmetries. We derive the first terms of the Weyl expansion for the level density projected onto the irreducible representations of the symmetry group. As an illustration the method is applied to the icosahedral billiard. The paper was published in J. Phys. A /27/ (1994) 4317-4323Comment: 8 printed pages Latex fil

Average ground-state energy of finite Fermi systems

Semiclassical theories like the Thomas-Fermi and Wigner-Kirkwood methods give a good description of the smooth average part of the total energy of a Fermi gas in some external potential when the chemical potential is varied. However, in systems with a fixed number of particles N, these methods overbind the actual average of the quantum energy as N is varied. We describe a theory that accounts for this effect. Numerical illustrations are discussed for fermions trapped in a harmonic oscillator potential and in a hard wall cavity, and for self-consistent calculations of atomic nuclei. In the latter case, the influence of deformations on the average behavior of the energy is also considered.Comment: 10 pages, 8 figure