DECEA - Departamento de Ciências Exatas e Aplicadas

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    Symmetrisation in the semiclassical theory of Coulomb excitation.
    (1997) Sargeant, Adam James; Johnson, R. C.; Tostevin, J. A.
    Corrections to the Alder and Winther semiclassical cross section for first order Coulomb excitation are considered through the Sukumar and Brink systematic expansion of the propagator in inverse powers of Sommerfeld's parameter, r/. The zeroth order term is that provided by unsymmetrised Alder-Winther theory and it is shown that to order 1/~7 the only type of correction is one corresponding to energy symmetrisation.
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    Saturation of the width of the strength function
    (2000) Sargeant, Adam James; Hussein, Mahir Saleh; Pato, Mauricio Porto; Ueda, Masahito
    The strength function of a single state ud& is studied using the deformed Gaussian orthogonal ensemble. In particular we study the dependence of the spreading width of ud& on the degree of mixing.
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    Effective astrophysical S factor for nonresonant reactions.
    (2000) Ueda, Masahito; Sargeant, Adam James; Pato, Mauricio Porto; Hussein, Mahir Saleh
    We have made an asymptotic expansion of the effective S factor, Seff , for nonresonant reactions of charged particles. The resulting analytic formulas can generate approximations to Seff which contain derivatives, with respect to the center of mass energy E, of the astrophysical S factor, S(E), up to any desired order. Thus our approximation incorporates better the center-of-mass energy dependence in S(E) than previous approximations which included only the first or second derivatives. The range of applicability of the method is discussed. We numerically investigate our expressions for the reaction 7Be(p,g )8B.
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    Attenuation of the intensity within a superdeformed band.
    (2001) Sargeant, Adam James; Hussein, Mahir Saleh; Pato, Mauricio Porto; Takigawa, Noboru; Ueda, Masahito
    The attenuation of the intra-band intensity of a superdeformed band which results from mixing with normally deformed configurations is calculated using reaction theory. It is found that the sharp increase of the attenuation is mostly due to the tunnelling through a spin dependent barrier and not to the chaotic nature of the normally deformed states.
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    Evaluation of effective astrophysical S factor for non-resonant reactions.
    (2001) Ueda, Masahito; Sargeant, Adam James; Pato, Mauricio Porto; Hussein, Mahir Saleh
    We derived analytic formulas of the effective astrophysical S factor, Seff, for a non- resonant reaction of charged particles using a Taylor expansion of the astrophysical S factor, S(E), and a uniform approximation. The formulas will be able to generate more accurate approximations to Seff than previous ones.
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    Energy averages and fluctuations in the decay out of superdeformed bands.
    (2002) Sargeant, Adam James; Hussein, Mahir Saleh; Pato, Mauricio Porto; Ueda, Masahito
    We derive analytic formulas for the energy average including the energy average of the fluctuation contribution! and variance of the intraband decay intensity of a superdeformed band. Our results may be expressed in terms of three dimensionless variables: G#/GS , GN /d, and GN /(GS1G#). Here G# is the spreading width for the mixing of a superdeformed ~SD! state u0& with the normally deformed ~ND! states uQ& whose spin is the same as u0&’s. The uQ& have mean lever spacing d and mean electromagnetic decay width GN whilst u0& has electromagnetic decay width GS. The average decay intensity may be expressed solely in terms of the variables G#/GS and GN /d or, analogously to statistical nuclear reaction theory, in terms of the transmission coefficients T0(E) and TN describing transmission from the uQ& to the SD band via u0& and to lower ND states. The variance of the decay intensity, in analogy with Ericson’s theory of cross section fluctuations, depends on an additional variable, the correlation length GN /(GS1G#)5(d/2p)TN /(GS1G#). This suggests that analysis of an experimentally determined variance could yield the mean level spacing d as does analysis of the cross section autocorrelation function in compound nucleus reactions. We compare our results with those of Gu and Weidenmu¨ller.
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    Experiências com Ssimulated Annealing e Busca Tabu na resolução do problema de alocação de salas.
    (2002) Souza, Marcone Jamilson Freitas; Martins, Alexandre Xavier; Araújo, Cássio Roberto de
    Este trabalho trata do problema de alocação de salas. Uma vez que este problema é NP-difícil, muitos métodos heurísticos têm sido propostos para resolvê-lo. Simulated Annealing (SA) e Busca Tabu (BT) são exemplos de tais métodos que têm sido aplicados com sucesso na resolução deste problema. Esta classe de heurísticas encontra uma boa solução melhorando uma alocação inicial através de técnicas de pesquisa em vizinhança. Contrariamente às heurísticas convencionais, SA e BT permitem movimentos de piora como forma de escapar de ótimos locais. Neste artigo relata-se uma experiência com a utilização destas técnicas e propõe-se uma técnica híbrida SA+TS, a qual combina as características mais apropriadas de SA e BT de forma a obter um procedimento mais eficaz. A eficiência dessa combinação é avaliada comparando-a com as versões puras dos métodos envolvidos.
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    Resonances and thermonuclear reaction rates for charged particle collisions.
    (2004) Sargeant, Adam James; Pato, Mauricio Porto; Hussein, Mahir Saleh
    We derive an approximate analytic expression for thermonuclear reaction rate for charged particles for the case that the cross section contains a single narrow or broad resonance described by a Breit-Wigner shape. An asymptotic series is obtained by making a Taylor series expansion which is exact at both the effective energy of the Gamow window and at the resonance energy. The resulting expression is uniformly valid as the effective energy and resonance energy coalesce or separate and as the resonance width is varied from narrow to broad. This is not true of conventional analytic approximations. We compare our uniform approximation with the exact reaction rate numerically and find it to be accurate over a large parameter range. We use our expressions to calculate the reaction rate for 12Csp,gd13N.
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    Addendum : attenuation of the intensity within a superdeformed band.
    (2004) Sargeant, Adam James; Hussein, Mahir Saleh; Pato, Mauricio Porto; Takigawa, Noboru; Ueda, Masahito
    We investigate a random matrix model [Phys. Rev. C 65, 024302 (2002)] for the decay-out of a superdeformed band as a function of the parameters: G# /GS, GN/D, GS /D, and D/D. Here G# is the spreading width for the mixing of a superdeformed (SD) state u0l with a normally deformed (ND) doorway state udl, GS and GN are the electromagnetic widths of the SD and ND states, respectively, D is the mean level spacing of the compound ND states and D is the energy difference between u0l and udl. The maximum possible effect of a transition from ordered to chaotic states is inferred from analytical and numerical calculations of the decay intensity in the limiting cases for which the ND states obey Poisson and GOE statistics. Our results show that the sharp attenuation of the decay intensity cannot be explained solely by a transition from ordered to chaotic states.
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    Resonances and the thermonuclear reaction rate.
    (2004) Hussein, Mahir Saleh; Ueda, Masahito; Sargeant, Adam James; Pato, Mauricio Porto
    We present an approximate analytic expression for thermonuclear reaction rate of charged particles when the cross section contains a single narrow or wide resonance described by a Breit-Wigner shape. The resulting expression is uniformly valid as the effective energy and resonance energy coalesce. We use our expressions to calculate the reaction rate for 12C(p,γ)13N.
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    Variance of the decay intensity of superdeformed bands.
    (2004) Hussein, Mahir Saleh; Sargeant, Adam James; Pato, Mauricio Porto; Ueda, Masahito
    We present analytic formulae for the energy average and variance of the intraband decay intensity of a superdeformed band.
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    Level density for deformations of the Gaussian orthogonal ensemble.
    (2005) Bertuola, Alberto Carlos; Carvalho, Josué Xavier de; Hussein, Mahir Saleh; Pato, Mauricio Porto; Sargeant, Adam James
    Formulas are derived for the average level density of deformed, or transition, Gaussian orthogonal random matrix ensembles. After some general considerations about Gaussian ensembles, we derive formulas for the average level density for sid the transition from the Gaussian orthogonal ensemble sGOEd to the Poisson ensemble and siid the transition from the GOE to m GOEs.
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    Uma ferramenta didática para aprendizagem de redes sem fio.
    (2005) Silva, Leandro Fernandes da; Barbosa, Carlos Henrique Nogueira de Resende; Andrade, Alessandro Vivas; Castro, Cristiano Leite de
    Redes sem fio são formadas por nós dotados de algum poder de processamento computacional, com liberdade para se movimentarem em direções arbitrárias e com a capacidade de estabelecerem conexões temporárias entre si para a transmissão de dados. Este trabalho tem por objetivo apresentar uma ferramenta de código aberto, desenvolvida para propósitos de aprendizagem dos conceitos básicos relacionados às redes sem fio.
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    Novas formulações para o problema da árvore geradora mínima capacitada em níveis.
    (2005) Martins, Alexandre Xavier; Souza, Marcone Jamilson Freitas; Souza, Maurício Cardoso de
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    How large is the spreading width of a superdeformed band?
    (2005) Wilson, Andrew Norman; Sargeant, Adam James; Davidson, Peter Michael; Hussein, Mahir Saleh
    Recent models of the decay out of superdeformed (SD) bands can broadly be divided into two categories. One approach is based on the similarity between the tunneling process involved in the decay and that involved in the fusion of heavy ions, and it builds on the formalism of nuclear reaction theory. The other arises from an analogy between the superdeformed decay and transport between coupled quantum dots. These models suggest conflicting values for the spreading width of the decaying superdeformed states. In this paper, the decay of superdeformed bands in the five even-even nuclei in which the SD excitation energies have been determined experimentally is considered in the framework of both approaches, and the significance of the difference in the resulting spreading widths is considered. The results of the two models are also compared to tunneling widths estimated from previous barrier height predictions and a parabolic approximation to the barrier shape.
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    Combining an evolutionary algorithm with data mining to solve a single-vehicle routing problem.
    (2006) Santos, Haroldo Gambini; Ochi, Luiz Satoru; Marinho, Euler Horta; Drummond, Lúcia Maria de Assumpção
    The aim of this work is to present some alternatives to improve the performance of an evolutionary algorithm applied to the problem known as the oil collecting vehicle routing problem. Some proposals based on the insertion of local search and data mining (DM) modules in a genetic algorithm (GA) are presented. Four algorithms were developed: a GA, a GA with a local search procedure, a GA including a DM module and a GA including local search and DM. Experimental results demonstrate that the incorporation of DM and local search modules in GA can improve the solution quality produced by this method.
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    UFVBeerGame : intermediando o aprendizado em cadeias de fornecimento com simulação e jogos empresariais.
    (2006) Ambrósio, Bernardo Giori; Braga, José Luís; Pereira, Mariane de Oliveira
    Apresenta-se nesse trabalho uma implementação do BeerGame, um jogo de empresas desenvolvido no Massachusetts Institute of Technology com o objetivo de ser uma ferramenta de apoio ao ensino na área de cadeias de fornecimento, permitindo o desenvolvimento do pensamento sistêmico. O UFVBeerGame estende o jogo original, adotando um modelo de cadeia de produção e distribuição mais realista, contendo os papéis Fábrica, Distribuidor, Atacadista e Varejista. Cada sessão pode ser acompanhada pelo instrutor via o módulo de gerenciamento, que exibe gráficos comparativos em cada instante do jogo. O sistema foi testado em sala de aula com turmas de diferentes cursos, e está disponível para uso como software livre.
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    Symmetry-breaking study with deformed ensembles.
    (2007) Carvalho, Josué Xavier de; Hussein, Mahir Saleh; Pato, Mauricio Porto; Sargeant, Adam James
    A random matrix model to describe the coupling of m-fold symmetry is constructed. The particular threefold case is used to analyze data on eigenfrequencies of elastomechanical vibration of an anisotropic quartz block. It is suggested that such an experimental and theoretical study may supply a powerful means to discern the intrinsic symmetry of physical systems.
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    Implicit regularization beyond one-loop order : scalar field theories.
    (2007) Pontes, Carlos Renato; Scarpelli, Antônio Paulo Baêta; Sampaio, Marcos Donizeti Rodrigues; Nemes, Maria Carolina
    Implicit regularization (IR) has been shown as a useful momentum space tool for perturbative calculations in dimension-specific theories, such as chiral gauge, topological and supersymmetric quantum field theoretical models at one-loop level. In this paper, we aim at generalizing systematically IR to be applicable beyond one-loop order. We use a scalar field theory as an example and pave the way for the extension to quantum field theories which are richer from the symmetry content viewpoint. Particularly, we show that a natural (minimal) renormalization scheme emerges, in which the infinities displayed in terms of integrals in one internal momentum are subtracted, whereas infrared and ultraviolet modes do not mix and therefore leave no room for ambiguities. A systematic cancellation of the infrared divergences at any loop order takes place between the ultraviolet finite and divergent parts of the amplitude for non-exceptional momenta leaving, as a by-product, a renormalization group scale.
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    Perturbation treatment of symmetry breaking within random matrix theory.
    (2008) Carvalho, Josué Xavier de; Hussein, Mahir Saleh; Pato, Mauricio Porto; Sargeant, Adam James
    We discuss the applicability, within the random matrix theory, of perturbative treatment of symmetry breaking to the experimental data on the flip symmetry breaking in quartz crystal. We found that the values of the parameter that measures this breaking are different for the spacing distribution as compared to those for the spectral rigidity. We consider both two-fold and three-fold symmetries. The latter was found to account better for the spectral rigidity than the former. Both cases, however, underestimate the experimental spectral rigidity at large L. This discrepancy can be resolved if an appropriate number of eigenfrequencies is considered to be missing in the sample. Our findings are relevant for symmetry violation studies in general.