Brazilian National Nuclear Energy Commission
Sao Paulo, Brazil
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Pinto-Neto N.,Brazilian Center for Research in Physics (CBPF) | Falciano F.T.,Brazilian Center for Research in Physics (CBPF) | Pereira R.,Brazilian Center for Research in Physics (CBPF) | Santini E.S.,Brazilian Center for Research in Physics (CBPF) | Santini E.S.,Brazilian National Nuclear Energy Commission
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We study the Wheeler-DeWitt quantum cosmology of a spatially flat Friedmann cosmological model with a free massless scalar field. We compare the consistent histories approach with the deBroglie-Bohm theory when applied to this simple model under two different quantization schemes: the Schrödinger-like quantization, which essentially takes the square root of the resulting Klein-Gordon equation through the restriction to positive frequencies and their associated Newton-Wigner states, or the induced Klein-Gordon quantization, that allows both positive and negative frequencies together. We show that the consistent histories approach can give a precise answer to the question concerning the existence of a quantum bounce if and only if one takes the single frequency approach within a single family of histories; namely, a family containing histories concerning properties of the quantum system at only two specific moments of time: the infinity past and the infinity future. In that case, as shown by Craig and Singh, there is no quantum bounce. In any other situation, the question concerning the existence of a quantum bounce has no meaning in the consistent histories approach. On the contrary, we show that if one considers the deBroglie-Bohm theory, there are always states where quantum bounces occur in both quantization schemes. Hence, the assertion that the Wheeler-DeWitt quantization does not solve the singularity problem in cosmology is not precise. To address this question, one must specify not only the quantum interpretation adopted but also the quantization scheme chosen. © 2012 American Physical Society.

Klein E.L.,CPRM Geological Survey of Brazil | Fuzikawa K.,Brazilian National Nuclear Energy Commission
Ore Geology Reviews | Year: 2010

The Carará gold deposit, located in the Ipitinga Auriferous District, south-eastern portion of the Guiana Shield, northern Brazil, is a typical orogenic, greenstone-hosted, auriferous quartz vein. Mineralisation was post-metamorphic and syn-tectonic in relation to the host Palaeoproterozoic (ca. 2.03 Ga) shear zone developed close to the tectonic boundary between a Palaeoproterozoic continental arc and an Archaean block. The deposit style is very simple, consisting of a quartz vein and its hydrothermal envelope, which is composed of muscovite and tourmaline; sulphides are rare. Muscovite and tourmaline, in addition to gold, fill small fractures in the quartz vein. The fluid inclusion assemblage trapped in high- and low-grade portions of the Au-quartz vein is rather enigmatic, consisting of one-phase CO2 inclusions with no visible water at room or sub-zero temperatures, although small amounts of water have been detected by micro-Raman analysis. In this aspect Carará differs from the other gold showings in the same district, which are characterized by abundant aqueous-carbonic fluid inclusions. The carbonic fluid is composed predominantly of CO2 in addition to < 2 mol.% N2 and traces of CH4 and C2H6. The carbonic fluid show very variable densities, which is interpreted to result from post-entrapment re-equilibration. Inclusions in the high-grade quartz are the densest (0.89 to 1.07 g/cm3) and with less effects of re-equilibration. These inclusions approximate the physico-chemical characteristics of the parental fluid that started to be trapped at least around the amphibolite facies metamorphic conditions and then followed a retrograde path. Most of the inclusions appear to have been trapped and/or re-equilibrated at 350 to 475 °C and 1.8 to 3.6 kbar, which implies a 7 to 12 km depth of vein formation and gold mineralisation. Both phase separation of a carbonic-aqueous fluid (XCO2 > 0.8) and the existence of an originally CO2-dominated fluid could account for the observed fluid inclusion properties and the absence of H2O-bearing inclusions in the mineralised vein. The fluid inclusion characteristics, combined with published geological and isotopic information, indicate a deep-seated source for CO2 that could be mantle, magmatic or metamorphic in origin. We suggest that the likely sources are fluid produced by the 2.07 Ga-old charnockites that occur in the region and/or the coeval high grade metamorphism that is widespread in the Guiana Shield. © 2009 Elsevier B.V. All rights reserved.

De Lima V.M.F.,Brazilian National Nuclear Energy Commission | Pereira A.,São Paulo State University
Neural Plasticity | Year: 2016

Several explanations have been proposed to account for the mechanisms of neuroglial interactions involved in neural plasticity. We review experimental results addressing plastic nonlinear interactions between glial membranes and synaptic terminals. These results indicate the necessity of elaborating on a model based on the dynamics of hydroionic waves within the neuropil. These waves have been detected in a small scale experimental model of the central nervous system, the in vitro retina. We suggest that the brain, as the heart and kidney, is a system for which the state of water is functional. The use of nonlinear thermodynamics supports experiments at convenient biological spatiotemporal scales, while an understanding of the properties of ions and their interactions with water requires explanations based on quantum theories. In our approach, neural plasticity is seen as part of a larger process that encompasses higher brain functions; in this regard, hydroionic waves within the neuropil are considered to carry both physiological and cognitive functions. © 2016 Vera Maura Fernandes de Lima and Alfredo Pereira Jr.

Perez Guerrero J.S.,Brazilian National Nuclear Energy Commission | Skaggs T.H.,U.S. Department of Agriculture
Journal of Hydrology | Year: 2010

Mathematical models describing contaminant transport in heterogeneous porous media are often formulated as an advection-dispersion transport equation with distance-dependent transport coefficients. In this work, a general analytical solution is presented for the linear, one-dimensional advection-dispersion equation with distance-dependent coefficients. An integrating factor is employed to obtain a transport equation that has a self-adjoint differential operator, and a solution is found using the generalized integral transform technique (GITT). It is demonstrated that an analytical expression for the integrating factor exists for several transport equation formulations of practical importance in groundwater transport modeling. Unlike nearly all solutions available in the literature, the current solution is developed for a finite spatial domain. As an illustration, solutions for the particular case of a linearly increasing dispersivity are developed in detail and results are compared with solutions from the literature. Among other applications, the current analytical solution will be particularly useful for testing or benchmarking numerical transport codes because of the incorporation of a finite spatial domain. © 2010.

Deana A.M.,Nove de Julho University | Wetter N.U.,Brazilian National Nuclear Energy Commission
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

This work presents a mode-controlled quasi-CW resonator design based on an Nd:YLF crystal. Up to 47 % optical efficiency was obtained and, by passively Q-switching the laser, 209 kW of peak power at 1053 nm was obtained. The new resonator design is capable of delivering 2.3 mJ and 11 ns pulses in a very compact, simple and lightweight set-up. © 2012 SPIE.

Gomes L.,Brazilian National Nuclear Energy Commission | Jackson S.D.,University of Sydney
Journal of the Optical Society of America B: Optical Physics | Year: 2013

Excitation of the 2F7/2 → 2F 5/2 transition of the Yb3+ ion in Yb3+, Pr 3+-doped fluorozirconate glass at 974 nm results in efficient excitation of the 1G4 level of Pr3+ ion that in turn emits in the middle infrared at ∼3.6 μm. The energy transfer (ET) process Yb3+(2F5/2) → Pr 3+(1G4) is assisted by fast excitation migration among the Yb3+ ions. An upconversion process involving ET from the 2F5/2 level to the 1G4 excited state populates the 3P0 excited state that produces emission at 481, 521, 603, 636, and 717 nm. A study of the behavior of the fluorescence from the 1G4 level at 1325 nm and from the 3P0 level at 603 nm allowed the estimation of the ET rate constants for the processes involved after short-pulsed laser excitation at 974 nm. A rate-equation model was employed to evaluate the population inversion relating to the 1G4 → 3F4 transition of the Pr3+ ion at 3.6 μm under continuous wave pumping. © 2013 Optical Society of America.

Paixao L.,Brazilian National Nuclear Energy Commission
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2012

In prostate cancer treatment, there is an increasing interest in the permanent radioactive seeds implant technique. Currently, in Brazil, the seeds are imported with high prices, which prohibit their use in public hospitals. A ceramic matrix that can be used as a radioisotope carrier and radiographic marker was developed at our institution. The ceramic matrix is distinguished by the characteristic of maintaining the radioactive material uniformly distributed in its surface. In this work, Monte Carlo simulations were performed in order to assess the dose distributions generated by this prototype seed model, with the ceramic matrix encapsulated in titanium, in the same way as the commercial 6711 seed. The obtained data was assessed, as described in the TG-43U1 report by the American Association of Physicists in Medicine, for two seed models: (1) the most used model 6711 source - for validation and comparison, and (2) for the prototype model with the ceramic matrix. The dosimetric parameters dose rate constant, Λ, radial dose function, gL(r), and anisotropy function, F(r,θ), were derived from simulations by the Monte Carlo method using the MCNP5 code. A Λ 0.992 (± 2.33%) cGyh-1U-1 was found for the prototype model. In comparison with the 6711 model, a lower dose fall-off on transverse axis was found, as well as a lower dose anisotropy for the radius r = 0.25 cm. In general, for all distances, the prototype seed model presents a slightly larger anisotropy between 0° ≤ Θ < 50° and anisotropy similar to the 6711 model for Θ ≥ 50°. The dosimetric characteristics of the prototype model presented in this study suggest that its use is feasible. Because of the model's characteristics, seeds of lower specific activity iodine might be necessary which, on the other hand, would help to reduce costs. However, it has to be emphasized that the proposed source is a prototype, and the required (AAPM prerequisites) experimental study and tolerance manufacturer values are pending for future studies.

Perez Guerrero J.S.,Brazilian National Nuclear Energy Commission | Pimentel L.C.G.,Federal University of Rio de Janeiro | Skaggs T.H.,U.S. Department of Agriculture
International Journal of Heat and Mass Transfer | Year: 2013

The advection-dispersion transport equation with first-order decay was solved analytically for multi-layered media using the classic integral transform technique (CITT). The solution procedure used an associated non-self-adjoint advection-diffusion eigenvalue problem that had the same form and coefficients as the original problem. The generalized solution of the eigenvalue problem for any numbers of layers was developed using mathematical induction, establishing recurrence formulas and a transcendental equation for determining the eigenvalues. The orthogonality property of the eigenfunctions was found using an integrating factor that transformed the non-self-adjoint advection-diffusion eigenvalue problem into a purely diffusive, self-adjoint problem. The performance of the closed-form analytical solution was evaluated by solving the advection-dispersion transport equation for two- and five-layer media test cases which have been previously reported in the literature. Additionally, a solution featuring first-order decay was developed. The analytical solution reproduced results from the literature, and it was found that the rate of convergence for the current solution was superior to that of previously published solutions. © 2012 Elsevier Ltd. All rights reserved.

Deana A.M.,Nove de Julho University | Ranieri I.M.,Brazilian National Nuclear Energy Commission | Baldochi S.L.,Brazilian National Nuclear Energy Commission | Wetter N.U.,Brazilian National Nuclear Energy Commission
Applied Physics B: Lasers and Optics | Year: 2012

This work reports a diode-side-pumped and passively Q-switched Nd:YLiF 4 (YLF) laser operating at 1053 nm using a new laser resonator concept. Very stable pulses of 1 mJ energy with less than 10 ns pulse duration are obtained at 1 kHz repetition rate in a very simple, compact, and robust cavity that uses a double bounce configuration to achieve TEM 00 operation. © Springer-Verlag 2012.

Vieira R.J.R.,Brazilian Nuclear Energy Research Institute (IPEN) | Gomes L.,Brazilian Nuclear Energy Research Institute (IPEN) | Martinelli J.R.,Brazilian National Nuclear Energy Commission | Wetter N.U.,Brazilian Nuclear Energy Research Institute (IPEN)
Optics Express | Year: 2012

Random lasing in nanocrystalline Nd3+:YVO4 powder is demonstrated. A method that analyzes the decay kinetics after long-pulse excitation is used to determine the laser characteristics. This method permits to measure the fractional contribution of spontaneous and stimulated emission as well as upconversion as a function of the pump intensity. We observed that maximum linewidth narrowing is achieved when the stimulated emission reaches 50% of fractional contribution in the backscattering cone. © 2012 Optical Society of America.

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