National Nuclear Energy Commission

About: National Nuclear Energy Commission is a government organization based out in Rio de Janeiro, Brazil. It is known for research contribution in the topics: Dosimetry & Laser. The organization has 3816 authors who have published 4694 publications receiving 59951 citations.

Recovery of uranium from acid mine drainage waters by ion exchange

Abstract: Of the many applications involving the use of ion exchange, the removal of contaminants in effluents ranks as one that has aroused considerable attention. In the present study, this process was used to remove and recover uranium from acid mine waters at Caldas Uranium Mining and Extraction Plant, in the southeast of Brazil. Studies of sorption and NaCl elution to recovery uranium as a commercial product, are presented. Lime precipitation tests with the effluent from the resin revealed an overall uranium decontamination level of 94% in the sludge when compared with the actual lime precipitation treatment of acid mine water.

Determination of dental decay rates with optical coherence tomography

Abstract: We report the use of optical coherence tomography (OCT) to detect and quantify demineralization process induced by S. mutans biofilm in third molars human teeth. Artificial lesions were induced by a S. mutans microbiological culture and the samples (N = 50) were divided into groups according to the demineralization time: 3, 5, 7, 9, and 11 days. The OCT system was implemented using a light source delivering an average power of 96 μW in the sample arm, and spectral characteristics allowing 23 μm of axial resolution. The images were produced with lateral scans step of 10 μm and analyzed individually. As a result of the evaluation of theses images, lesion depth was calculated as function of demineralization time. The depth of the lesion in the root dentine increased from 70 μm to 230 μm (corrected by the enamel refraction index, 1.62 @ 856 nm), depending of exposure time. The lesion depth in root dentine was correlated to demineralization time, showing that it follows a geometrical progression like a bacteria growth law.

On a new instability in electron-positron storage rings (The head-tail effect)

Abstract: It is shown that a bunched electron or positron beam of a storage ring can become unstable because of an effect not previously considered; the instability is due to the regenerative effect introduced by synchrotron oscillations, which enhances the action on the beam of rapidly decaying electromagnetic signals excited by the beam itself on its surrounding media. The results obtained show that the effect can produce instabilities for small beam currents (in the milliampere range), and that it can be influenced and reduced by properly choosing some parameters of the storage ring.

A stabilized finite element procedure for turbulent fluid–structure interaction using adaptive time–space refinement

Abstract: This paper presents our effort to addressing fluid–structure interaction (FSI) problems by means of computational mechanics. A stabilized finite element formulation is used to solve the incompressible Navier–Stokes equations written in primitive variables. The structure is modelled using rigid-body dynamic equations solved using a Runge–Kutta method. The distinctive feature of our approach is the combination of large eddy simulation (LES)—based on implicit turbulence modelling—with time–space adaptive techniques in arbitrary Lagrangian Eulerian co-ordinates (ALE). Three representative numerical examples are presented. The first one is the simulation of turbulent vortex shedding around a fixed obstacle, comparing our two-dimensional (2D) LES results with experiments and more refined three-dimensional (3D) numerical solutions. The second example presents an ALE computation with moving boundaries, where we were able to detect the lock-in phenomenon for an oscillating cylinder driven by periodic vortex shedding. Our final example is the FSI problem associated to the flow around a dominant central span section of the Rio-Niteroi bridge, where we compare our results with experiments performed in a wind tunnel. Copyright © 2004 John Wiley & Sons, Ltd.