Compact Refrigeration System For Electronics Cooling Based on a Novel Two-Phase Jet Impingement Heat Sink

The performance of a compact vapor compression cooling system equipped with a R-134a small-scale oil-free compressor and a novel heat sink that integrates, into a single unit, the evaporator and the expansion device was experimentally evaluated. The expansion device can be a single orifice or an array of orifices responsible for the generation of a high-speed two-phase jet impinging on a heated surface. A comparison between the performance of the proposed refrigeration system operating with single and multiple jets is presented and the influence of the following parameters is quantified: (i) thermal load applied on the heat sink, (ii) number of orifices and (iii) geometrical arrangement of the orifices (jets). The analysis is based on thermodynamic performance metrics (coefficient of performance, second-law efficiency and second-law ratio) and steady-state heat transfer parameters (surface temperature and heat transfer coefficient) associated with the impinging jet(s) for single and multiple orifice tests. The two-phase jet heat sink was capable of dissipating cooling loads of up to 160 W and 200 W from a 6.36-cm2 surface for single and multiple orifice configurations, respectively. For these cases, the temperature of the impingement surface was kept below 40ºC and the heat transfer coefficient reached values between 14,000 and 16,000 W/(m2K). The proposed compact vapor compression cooling solution can be further developed for specific applications in thermal management of power electronics for a variety of stationary and mobile systems

A fault location method using Lamb waves and discrete wavelet transform

Non-destructive evaluation methods and signal process techniques are important steps in structural health monitoring systems to assess the structure integrity. This paper presents a method for fault location in aluminum beams based on time of flight of Lamb waves. The dynamic response signal captured from the structure was processed using the discrete wavelet transform. The information accuracy obtained from the processed signal depends on the correct choice of the mother wavelet. The best mother wavelet was selected using the Shannon's entropy criterion. Numerical results for a damage localized in different positions are presented using the spectral finite element method, and an experimental setup was used to assess the accuracy of the method. The results showed that the combination of the non-destructive evaluation technique based on Lamb waves with the discrete wavelet transform is effective in detecting and locating faults in aluminum beams whose results had errors less than 1%.51552

Design-Space Exploration of Stream Programs through Semantic-Preserving Transformations

Stream languages explicitly describe fork-join parallelism and pipelines, offering a powerful programming model for many-core Multi-Processor Systems on Chip (MPSoC). In an embedded resource-constrained system, adapting stream programs to fit memory requirements is particularly important. In this paper we present a design-space exploration technique to reduce the minimal memory required when running stream programs on MPSoC; this allows to target memory constrained systems and in some cases obtain better performance. Using a set of semantically preserving transformations, we explore a large number of equivalent program variants; we select the variant that minimizes a buffer evaluation metric. To cope efficiently with large program instances we propose and evaluate an heuristic for this method. We demonstrate the interest of our method on a panel of ten significant benchmarks. As an illustration, we measure the minimal memory required using a multi-core modulo scheduling. Our approach lowers considerably the minimal memory required for seven of the ten benchmarks

Reducing Memory Requirements of Stream Programs by Graph Transformations

International audienceStream languages explicitly describe fork-join parallelism and pipelines, offering a powerful programming model for many-core Multi-Processor Systems on Chip (MPSoC). In an embedded resource-constrained system, adapting stream programs to fit memory requirements is particularly important. In this paper we present a new approach to re- duce the memory footprint required to run stream programs on MPSoC. Through an exploration of equivalent program variants, the method selects parallel code minimizing mem- ory consumption. For large program instances, a heuristic accelerating the exploration phase is proposed and evalu- ated. We demonstrate the interest of our method on a panel of ten significant benchmarks. Using a multi-core modulo scheduling technique, our approach lowers considerably the minimal amount of memory required to run seven of these benchmarks while preserving throughput

Sovereign Rating, Macroeconomic Indicators and Firm Performance: Evidence from Latin America

macroeconomic indicators and the performance of non-financial listed companies based in five Latin America emerging countries, from 2010 to 2017. Using a sample of 1,424 non-financial listed firms, the authors employed a panel data regression. The Chow, Breusch-Pagan and Hausman tests confirmed the fixed effects hypothesis. Return on asset, return on equity and Tobin’s Q were used to measure firm performance. The evidence points that the sovereign rating quality increases return on assets and the market value of Latin American firms. Financial leverage, as well as gross domestic product, interest and inflation rates positively affect company performance, while corporate tax significantly decrease return on asset and Tobin’ Q. The study found significant differences of the effects of sovereign rating, gross domestic product and corporate tax between the performance of companies based in Brazil and their pairs based in Argentina, Chile, Colombia and Mexico. The study provides empirical evidence on the implications of the sovereign rating and macroeconomic policies on companies’ performance in Latin America, considering that few studies address these macroeconomic aspects in the corporate finance field. The empirical evidence has implications related to macroeconomic policies, as well as the consequences of the rating agencies report on managerial decisions Keywords: Sovereign Rating, Macroeconomic Indicators, Leverage, Performance, Latin America. DOI: 10.7176/RHSS/11-8-06 Publication date: April 30th 202