Volnei Borges
Universidade Federal do Rio Grande do Sul
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Publication
Featured researches published by Volnei Borges.
Annals of Nuclear Energy | 1999
Cláudia Helena F. Batistela; Marco T. Vilhena; Volnei Borges
Abstract The aim of this work is to present a new approach based upon the application of the LTSN method to solve the eigenvalue problem in a slab, namely the problem of criticality. This procedure leads to the solution of a transcendental equation for the effective multiplication factor. We report numerical simulations considering the SN multigroup problem in heterogeneous slab.
Kerntechnik | 2006
Bárbara Denicol do Amaral Rodriguez; M.T. de Vilhena; Volnei Borges
Abstract In this paper an exposure build-up factor formulation is reported by solving the photon transport equation in a heterogeneous slab by the LTSN method, assuming the Klein-Nishina scattering kernel as the scattering differential cross section as well as the multigroup model in the wavelength variable. Numerical simulations and comparisons with available results in the literature are presented for different compositions containing water, iron and lead.
Nuclear Technology | 1995
Volnei Borges; Marco T. Vilhena
Recent advances in the study of a fluidized-bed nuclear reactor’s stability, due to short and long time transients, are discussed. The point-kinetic model, which considers flux variation in the axi...
International Journal of Nuclear Energy Science and Technology | 2010
Bárbara Denicol do Amaral Rodriguez; Marco T. Vilhena; Volnei Borges
In the first part of this paper, we describe a review in the Laplace transform technique applied to SN two-dimensional transport equation in a rectangular domain considering Compton scattering. In Compton scattering the incident photon interacts with an electron of the irradiated medium, giving the electron kinetic energy, and also producing a scattered photon. In order to track that electron, in the second part of this paper, we apply the PN approximation to X,Y-geometry electron transport problems. In this derivation, the energy deposited by the free electron is taken into account. To reach this objective we solve two model problems: the first one for the transport of photons, assuming the Klein-Nishina scattering kernel as the scattering differential cross-section as well as the multigroup model in the energy variable; and the second one for the transport of free electrons considering the screened Rutherford scattering kernel. The results are presented under absorbed energy form in several points of interest. We report numerical simulations and comparisons with results obtained by using the Geant4 version 9.1 program which applies the Monte Carlos technique to low energy libraries for both two-dimensional problems.
International Journal of Low Radiation | 2007
Bárbara Denicol do Amaral Rodriguez; Marco T. Vilhena; Volnei Borges; Carlos Malamut
In this paper, we report a formulation for the exposure buildup factor by solving the one-dimensional photon transport equation in a heterogeneous slab by the LTSN method, assuming the Klein-Nishina scattering kernel as the scattering differential cross-section as well as the multigroup model in the wavelength variable. We present numerical simulations and comparisons with available results in the literature for a multilayered slab composed of water, iron and lead. We also report an analytical solution to the exposure buildup factor by solving the photon transport equation in a rectangle applying the LTSN nodal method.
Applied Mathematics and Computation | 2017
Vinicius G. Ribeiro; Jorge G. Zabadal; Cíntia O. Monticelli; Volnei Borges
In this work, a new approach to estimate heat transfer coefficients for solidgas interfaces is proposed. The new formulation takes into account that the photon transfer process between solid walls and gases is not instantaneous, but involves electronic transitions, even when low frequency radiation is exchanged. The delay required to electron cloud transitions, called relaxation time, which plays a crucial role in the heat transfer process, is evaluated using the LandauTeller model.
Radiologia Brasileira | 2008
Fernanda do Amarante; Simara Santos de Souza; Volnei Borges; Carlos Jader Feldman
OBJECTIVE: To evaluate the bone mineral density variability in patients with systemic lupus erythematosus, before the beginning and at 30 and 60 days from the beginning of glucocorticoid therapy. MATERIALS AND METHODS: Fifteen premenopausal women with systemic lupus erythematosus were referred for bone densitometry before being submitted to glucocorticoid therapy. RESULTS: It was demonstrated that the bone mineral density in g/cm2 in the lumbar spine presented a significant decrease in the span between the first analysis previously to the beginning of the glucocorticoid therapy and the third analysis after 60 days under therapy. On the other hand no significant difference was found in the femoral neck. CONCLUSION: The authors conclude that, at short term, rather than only at long term as previously reported by other authors, corticotherapy in patients with systemic lupus erythematosus results in a decrease in the bone mineral density in the lumbar spine.
Journal of Nuclear Science and Technology | 1997
Cláudia Helena F. Batistela; Marco T. Vilhena; Volnei Borges
World Journal of Nuclear Science and Technology | 2013
J. C. L. Fernandes; Marco T. Vilhena; B. E. J. Bodmann; Volnei Borges
World Journal of Nuclear Science and Technology | 2012
Volnei Borges; J. C. L. Fernandes; Bardo Ernest Bodmann; Marco T. Vilhena; Bárbara Denicol do Amaral Rodriguez
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Bárbara Denicol do Amaral Rodriguez
Universidade Federal do Rio Grande do Sul
View shared research outputsNational Council for Scientific and Technological Development
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