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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. Source


De Lima V.M.F.,Brazilian National Nuclear Energy Commission | Pereira A.,Sao 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. Source


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. Source


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. Source


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. Source

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