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San Carlos de Bariloche, Argentina

Guozden T.M.,Instituto Balseiro | Clausse A.,National University of Central Buenos Aires
International Journal of Heat and Mass Transfer

Species separation can be produced by imposing a pressure gradient in gaseous mixtures, which induces different molecular velocities depending on the molar weight. Pressure gradients can be achieved by centrifugal forces brought about by the passage of the gas through a curved nozzle at supersonic velocity. The efficiency of this process depends on the geometry of the nozzle as well as the flow operating conditions. The numerical solver Fluent was used in order to produce a model of the aerodynamics and the oxygen diffusion of a steady-state flow of air in a curved nozzle. The development of the pressure and O2 concentration profiles along the nozzle were analyzed for different pressure boundary conditions at the inlet and the exit, testing several nozzle sizes. Optimum values of the cut and the inlet pressure were found which maximize the separation efficiency. The effect of the exit pressure was associated with the axial pressure distribution along the inner wall of the nozzle. The results were compared with measurements showing good agreement. © 2016 Elsevier Ltd. All rights reserved. Source

Alessi M.,Instituto Balseiro | Alessi M.,Bariloche Atomic Center | Otranto S.,CONICET | Focke P.,Bariloche Atomic Center
Physical Review A - Atomic, Molecular, and Optical Physics

In this work we have measured single-electron capture in collisions of He32+ projectiles incident on a helium target for energies of 13.3-100 keV/amu with the cold-target recoil-ion momentum spectroscopy setup implemented at the Centro Atómico Bariloche. State-selective single-capture cross sections were measured as a function of the impact energy. They were found to agree with previous existing data from the Frankfurt group, starting at the impact energy of 60 keV/amu; as well as with recent data, at 7.5 keV/amu, from the Lanzhou group. The present experimental results are also contrasted to the classical trajectory Monte Carlo method with dynamical screening. © 2011 American Physical Society. Source

Leiva J.S.,Instituto Balseiro | Blanco P.J.,Laboratorio Nacional Of Computacao Cientifica | Buscaglia G.C.,University of Sao Paulo
International Journal for Numerical Methods in Engineering

In this article we address decomposition strategies especially tailored to perform strong coupling of dimensionally heterogeneous models, under the hypothesis that one wants to solve each submodel separately and implement the interaction between subdomains by boundary conditions alone. The novel methodology takes full advantage of the small number of interface unknowns in this kind of problems. Existing algorithms can be viewed as variants of the 'natural' staggered algorithm in which each domain transfers function values to the other, and receives fluxes (or forces), and vice versa. This natural algorithm is known as Dirichlet-to-Neumann in the Domain Decomposition literature. Essentially, we propose a framework in which this algorithm is equivalent to applying Gauss-Seidel iterations to a suitably defined (linear or nonlinear) system of equations. It is then immediate to switch to other iterative solvers such as GMRES or other Krylov-based method, which we assess through numerical experiments showing the significant gain that can be achieved. Indeed, the benefit is that an extremely flexible, automatic coupling strategy can be developed, which in addition leads to iterative procedures that are parameter-free and rapidly converging. Further, in linear problems they have the finite termination property. © 2009 John Wiley & Sons, Ltd. Source

Gennari F.C.,CONICET | Gennari F.C.,Instituto Balseiro | Gennari F.C.,Bariloche Atomic Center
International Journal of Hydrogen Energy

In the present study, the synthesis of two different LiBH 4-Y(BH4)3 and LiBH4-YH3 composites was performed by mechanochemical processing of the 4LiBH 4-YCl3 mixture and as-milled 4LiBH4-YCl 3 plus 3LiH. It was found that Y(BH4)3 and YH3 formed in situ during milling are effective to promote LiBH 4 destabilization but differ substantially from each other in terms of the dehydrogenation pathway. During LiBH4-Y(BH4) 3 dehydriding, Y(BH4)3 decomposes first generating in situ freshly YH3 and subsequently, it destabilizes LiBH4 with the formation of minor amounts of YB4. About 20% of the theoretical hydrogen storage was obtained via the rehydriding of YB4-4LiH-3LiCl at 400 °C and 6.5 MPa. As a novel result, a compound containing (B12H12)2- group was identified during dehydriding of Y(BH4)3. In the case of 4LiBH4-YH3 dehydrogenation, the increase of the hydrogen back pressure favors the formation of crystalline YB4, whereas a reduction to ≤0.1 MPa induces the formation of minor amounts of Li 2B12H12. Although for hydrogen pressures ≤0.1 MPa direct LiBH4 decomposition can occur, the main dehydriding pathway of 4LiBH4-YH3 composite yields YB 4 and LiH. The nanostructured composite obtained by mechanochemical processing gives good hydrogen storage reversibility (about 80%) regardless of the hydrogen back pressure. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

Bubach D.,Bariloche Atomic Center | Perez Catan S.,Bariloche Atomic Center | Arribere M.,Bariloche Atomic Center | Arribere M.,Instituto Balseiro | Guevara S.R.,Bariloche Atomic Center

The emission of volatile pollutants from the volcanic eruption of the Puyehue-Cordón Caulle complex (North Patagonia Andean Range) that started in June 4th, 2011, was investigated by bioindication means with the epyphytic fruticose lichen Usnea sp. The elemental composition of pooled samples made up with 10 lichen thalli were analysed by Instrumental Neutron Activation Analysis. Eleven sampling sites were selected within the impacted region at different distance from the volcanic source. Five sites were selected as they were already sampled in a previous study prior to the eruption. Two other new sampling sites were selected from outside the impacted zone to provide non-impacted baseline sites.The elements associated with the lichen incorporation of particulate matter (PM) of geological origin were identified by linear correlation with a geochemical tracer (Sm concentrations). The elements associated with PM uptake were Ce, Eu, Fe, Hf, La, Lu, Na, Nd, Sb, Sc, Se, Ta, Tb, Th, U, and Yb. Arsenic and Cs concentrations showed contributions exceeding the PM fraction in sites near the volcanic centre, also higher than the baseline concentrations, which could be associated with permanent emissions from the geothermal system of the Puyehue-Cordón Caulle complex. The lichen concentrations of Ba, Ca, Co, Hg, K, Rb, Sr, and Zn were not associated with the PM, not showing higher concentrations in the sites nearby the volcanic source or respect to the baseline values either. Therefore, there is no indication of the emission of volatile forms of these elements in the lichen records. The lichen records only identified Br volatile emissions associated with the Puyehue-Cordón Caulle complex eruption in 2011. © 2012 Elsevier Ltd. Source

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