DECEA - Artigos publicados em periódicos

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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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    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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    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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    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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    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.
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    Problemas e soluções no desenvolvimento de um SIG móvel para aplicações urbanas.
    (2008) Martins, Waister Silva; Rocha, Mauro Nacif; Monteiro, Bruno Rabello; Lisboa Filho, Jugurta
    Este artigo apresenta a experiência do desenvolvimento do SIG-Pocket, um Sistema de Informação Geográfica Móvel (SIG Móvel) para dispositivo PDA (Personal Digital Assistant). O sistema tem como origem de consulta dados geo-espaciais da base cartográfica municipal, que é exibida na forma de um mapa digital urbano. A comunicação dispositivoservidor é feita usando Web Services. Os resultados obtidos indicam a viabilidade de se desenvolver aplicações de SIG em dispositivos PDAs para uso na administração pública, considerando todas as limitações referentes ao desempenho no desenho dos mapas e ao volume de dados que o dispositivo cliente consegue armazenar.
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    On the equivalence between implicit regularization and constrained differential renormalization.
    (2008) Pontes, Carlos Renato; Scarpelli, Antônio Paulo Baêta; Sampaio, Marcos Donizeti Rodrigues; Fernandes, José Luiz Acebal; Nemes, Maria Carolina
    Constrained differential renormalization (CDR) and the constrained version of implicit regularization are two regularization independent techniques that do not rely on dimensional continuation of the space-time. These two methods, which have rather distinct bases, have been successfully applied to several calculations, which show that they can be trusted as practical, symmetry invariant frameworks (gauge and supersymmetry included) in perturbative computations even beyond one-loop order. In this paper, we show the equivalence between these two methods at one-loop order. We show that the configuration space rules of CDR can be mapped into the momentum-space procedures of implicit regularization, the major principle behind this equivalence being the extension of the properties of regular distributions to regularized ones.
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    Pragmatismo e cognição : self, mente, mundo e verdade na teoria pragmática do conhecimento.
    (2010) Bouyer, Gilbert Cardoso
    O presente artigo discute os fundamentos e pressuposições pragmáticas frequentemente usados para compreensão dos fenômenos cognitivos. Discutindo os conceitos de self, mente mundo e verdade, marcos teórico-epistemológicos das ciências cognitivas, o texto aponta implicações de tais conceitos de acordo com uma teoria pragmática do conhecimento. A abordagem do pragmatismo pode ser vista como uma espécie de pluralismo antes que um monismo ou um dualismo (como cognitivismo) porque há muitos caminhos emergentes no qual as coisas são definidas ou constituídas como úteis em diferentes situações. Um tema comum ligando diferentes abordagens pragmáticas à cognição é a mudança no modo como a relação pessoa/ambiente é concebida. Ao invés da pessoa estar inserida em um ambiente, as atividades da pessoa e do ambiente são vistas como partes de um todo mutuamente construído. Simplesmente, a relação dentro/fora entre pessoa e ambiente é substituída pela relação parte/todo. Vista desta forma, a cognição não mais é o espelho do mundo, mas sim parte de um processo natural envolvendo hábitos evolucionários bem sucedidos e capacidades. Cognição e mundo são mutuamente moldados.
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    Development of a method to determine Ni and Cd in biodiesel by graphite furnace atomic absorption spectrometry.
    (2011) Lobo, Fabiana Aparecida; Goveia, Danielle; Oliveira, Adriana Paiva de; Romão, Luciane Pimenta Cruz; Fraceto, Leonardo Fernandes; Dias Filho, Newton Luiz; Rosa, André Henrique
    This paper proposes a low cost, simple, fast method for determining Ni and Cd in biodiesel samples by graphitefurnaceatomicabsorptionspectrometry (GFAAS). The method was evaluated in biodiesel from different sources. Tungsten was used as a permanent modifier and the samples were prepared in the form of microemulsions, by mixing about 0.5 g of biodiesel with 5 g of surfactant (Triton X-100) in volumetric flasks and completing the volume with HNO3 1% (v/v). The detection limits obtained for Ni and Cd in microemulsions were ≤0.9 and 0.1 μg L−1, respectively. The relative standard deviation (% R.S.D., n = 12) was ≤8.20% for Ni (washed animal fat sample) and ≤4.71% for Cd (sunflower oil sample). Accuracy was checked based on addition and recovery experiments, which yielded recovery rates varying from 93% to 108% for Ni and from 98% to 116% for Cd. Sample preparation is rapid and easy, and the use of an inorganic standard for calibration makes this sample preparation procedure suitable for routine applications.
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    Effects of ozone exposure on ‘golden’ papaya fruit by photoacoustic phase-resolved method : physiological changes associated with carbon dioxide and ethylene emission rates during ripening.
    (2011) Corrêa, Savio Figueira; Mota, Leonardo; Paiva, Luisa Brito; Couto, Flávio Mota do; Silva, Marcelo Gomes da; Oliveira, Jurandi Gonçalves de; Sthel, Marcelo Silva; Vargas, Helion; Miklós, András
    This work addresses the effects of ozone activity on the physiology of ‘Golden’ papaya fruit. Depth profile analysis of double-layer biological samples was accomplished using the phase-resolved photoacoustic spectroscopy. The feasibility of the method was demonstrated by singling out the spectra of the cuticle and the pigment layers of papaya fruit. The same approach was used to monitor changes occurring on the fruit during ripening when exposed to ozone. In addition, one has performed real time studies of fluorescence parameters and the emission rates of carbon dioxide and ethylene. Finally, the amount of pigments and the changes in waxy cuticle have been monitored. Results indicate that a fruit deliberately subjected to ozone at a level of 6 ppmv underwent ripening sooner (at least 24-48 h) than a fruit stored at ambient conditions. Moreover, ozone caused a reduction in the maximum quantum yield of photosynthetic apparatus located within the skin of papaya fruit. VC 2011 American Institute of Physics.
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    Fast placement and routing by extending coarse-grained reconfigurable arrays with Omega Networks.
    (2011) Ferreira, Ricardo dos Santos; Cardoso, João Manuel Paiva; Assis, Alex Damiany; Vendramini, Júlio; Teixeira, Tiago
    Reconfigurable computing architectures are commonly used for accelerating applications and/or for achieving energy savings. However, most reconfigurable computing architectures suffer from computationally demanding placement and routing (P&R) steps. This problem may disable their use in systems requiring dynamic compilation (e.g., to guarantee application portability in embedded systems). Bearing in mind the simplification of P&R steps, this paper presents and analyzes a coarse-grained reconfigurable array (CGRA) extended with global multistage interconnect networks, specifically Omega Networks. We show that integrating one or two Omega Networks in a CGRA permits to simplify the P&R stage resulting in both low hardware resource overhead and low performance degradation (18% for an 8 _ 8 array). We compare the proposed CGRA, which integrates one or two Omega Networks, with a CGRA based on a grid of processing elements with reach neighbor interconnections and with a torus topology. The execution time needed to perform the P&R stage for the two array architectures shows that the array using two Omega Networks needs a far simpler and faster P&R. The P&R stage in our approach completed on average in about 16_ less time for the 17 benchmarks used. Similar fast approaches needed CGRAs with more complex interconnect resources in order to allow most of the benchmarks used to be successfully placed and routed.