Stability of the Dispersed Band in a Shallow Layer Settler

The present study is aimed at shallow-layer settlers, involving pilot plant data collecting about the thickness of the dispersion band at different points along its length and its use in simulation work. At steady state, after step inputs in the agitation power, the length of the dispersed band varied in time, and didnt return to its initial condition. Although clean, pure fluids were used, crud formation was observed and acquired relevance especially for long period experiments. This behavior brought out the fact that crud formed during the experimentation disturbed the stability of the dispersed band. Crud analysis, performed by fluorescence microscopy, suggested the presence of bacteria. This bacterial nature of the crud was confirmed and biocide utilization seemed to be adequate for its minimization

Avaliação de quarta geração: uma análise das potencialidades e limitações baseada na experiência de avaliação do Programa Água para Todos

The present empiric theoretical essay was developed with the objective of analyzing the potentialities and limitations of the Fourth Generation Evaluation (FGE), a model proposed by Guba and Lincoln (1989), with a social-constructivist basis. The analysis was based on the consideration of several studies that used or analyzed the model in question and the experience of using the FGE by the authors when carrying out evaluative research on the Water for All Program in the municipality of Bonito de Minas, state of Minas Gerais. As a result, the FGE is adequate to the demands of evaluating public policies in the contemporary world, in a hegemonically democratic context, where participation in decisions of public interest is an expensive value for public management and for society. Although there is a predominance of the use of AV4G for the evaluation of public health policies, this evaluation model is also suitable for evaluating policies in other areas, especially when combined with other models.El presente ensayo teórico fue desarrollado con el objetivo de analizar las potencialidades y limitaciones de la evaluación de cuarta generación (AV4G), modelo propuesto por Guba y Lincoln (1989), de base social-constructivista. El análisis se dio a partir de la consideración de diversos estudios que utilizaron o analizaron el modelo en cuestión y de la experiencia de utilización de la AV4G por los autores, cuando de la realización de investigación evaluativa acerca del Programa Agua para Todos, en el municipio de Bonito de Minas, estado de Minas Gerais. Como resultado, se tiene que la AV4G se muestra adecuada a las demandas de evaluación de políticas públicas en la contemporaneidad, en un contexto hegemónicamente democrático, donde la participación en las decisiones de interés público es un valor caro para la gestión pública y para la sociedad. Aunque existe el predominio del uso de la AV4G para la evaluación de políticas públicas de salud, este modelo de evaluación también se muestra adecuado para la evaluación de políticas en otras áreas, especialmente cuando se combina con otros modelos.O presente ensaio teórico-empírico foi desenvolvido com o objetivo de analisar as potencialidades e limitações da avaliação de quarta geração (AV4G), modelo proposto por Guba e Lincoln (1989), de base social-construtivista. A análise se deu a partir da consideração de diversos estudos que utilizaram ou analisaram o modelo em questão e da experiência de utilização da AV4G pelos autores, quando da realização de pesquisa avaliativa acerca do Programa Água para Todos, no município de Bonito de Minas, estado de Minas Gerais. Como resultado, tem-se que a AV4G se mostra adequada às demandas de avaliação de políticas públicas na contemporaneidade, em um contexto hegemonicamente democrático, onde a participação nas decisões de interesse público é um valor caro para a gestão pública e para a sociedade. Embora haja o predomínio do uso da AV4G para avaliação de políticas públicas de saúde, esse modelo de avaliação também se mostra adequado para avaliação de políticas em outras áreas, especialmente quando combinado com outros modelos

Laser-Plasma Interactions Enabled by Emerging Technologies

An overview from the past and an outlook for the future of fundamental laser-plasma interactions research enabled by emerging laser systems

Optimization of plasma amplifiers

Plasma amplifiers offer a route to side-step limitations on chirped pulse amplification and generate laser pulses at the power frontier. They compress long pulses by transferring energy to a shorter pulse via the Raman or Brillouin instabilities. We present an extensive kinetic numerical study of the three-dimensional parameter space for the Raman case. Further particle-in-cell simulations find the optimal seed pulse parameters for experimentally relevant constraints. The high-efficiency self-similar behavior is observed only for seeds shorter than the linear Raman growth time. A test case similar to an upcoming experiment at the Laboratory for Laser Energetics is found to maintain good transverse coherence and high-energy efficiency. Effective compression of a 10 kJ , nanosecond-long driver pulse is also demonstrated in a 15-cm-long amplifier

Demonstration of laser pulse amplification by stimulated Brillouin scattering

The energy transfer by stimulated Brillouin backscatter from a long pump pulse (15 ps) to a short seed pulse (1 ps) has been investigated in a proof-of-principle demonstration experiment. The two pulses were both amplified in different beamlines of a Nd:glass laser system, had a central wavelength of 1054 nm and a spectral bandwidth of 2 nm, and crossed each other in an underdense plasma in a counter-propagating geometry, off-set by 10∘. It is shown that the energy transfer and the wavelength of the generated Brillouin peak depend on the plasma density, the intensity of the laser pulses, and the competition between two-plasmon decay and stimulated Raman scatter instabilities. The highest obtained energy transfer from pump to probe pulse is 2.5%, at a plasma density of 0.17ncr, and this energy transfer increases significantly with plasma density. Therefore, our results suggest that much higher efficiencies can be obtained when higher densities (above 0.25ncr) are used

A robust plasma-based laser amplifier via stimulated Brillouin scattering

Brillouin amplification in plasma is more resilient to fluctuations in the laser and plasma parameters than Raman amplification, making it an attractive alternative to Raman amplification. In this work, we focus on high plasma densities, n0>ncr/4 , where stimulated Raman scattering is not possible and laser beam filamentation is the dominant competing process. Through analytic theory and multi-dimensional particle-in-cell simulations, we identify a parameter regime for which Brillouin amplification can be efficient while maintaining filamentation of the probe at a controlled level. We demonstrate pump-to-probe compression ratios of up to 72 and peak amplified probe fluences over 1 kJ cm−2 with ≃50% efficiency. High pulse quality is maintained through control of parasitic filamentation, enabling operation at large beam diameters. Provided the pump and probe pulse diameters can be increased to 1 mm, our results suggest that Brillouin amplification can be used to produce sub-picosecond pulses of petawatt power