Experimental Investigation of Damping Coefficient for Compressor Reed Valves

Reed valve dynamics has a major role on the performance and reliability of compressors and has been the subject of many studies over the years. In terms of mathematical modeling, most of these studies describe valve dynamics through a mass-spring-damper system, in which a damping coefficient has to be empirically adjusted. This is a consequence of little knowledge about the effect of different parameters on valve damping. For instance, in spite of great effort to understand viscous effects on the pressure distribution acting on the valve surface, very few works have addressed such effects on valve damping, especially for valve geometries found in compressors. The present study aims to experimentally quantify valve damping under controlled conditions, considering the effects of clamping geometry, clamping force, gasket thickness and the presence of fluid around the valve. Finally, experimental data of damping coefficients are used to predict valve dynamics and compressor efficiency. We found that the damping coefficients of typical valves adopted in small reciprocating compressors have negligible effect on compressor efficiency and valve bending stress, but can change by up to17% the valve impact velocity against the seat

Microsurgical Testicular Denervation for the Treatment of Chronic Testicular Pain – Initial Results

INTRODUCTION: Chronic testicular pain remains an important challenge for urologists. Currently, the treatment plan is primarily empirical, with the first approach consisting of clinical measures. However, some patients remain in pain despite a conservative treatment protocol and, for them, it is possible to perform a surgical procedure that involves severing the scrotal and spermatic branches of the genitofemoral and ilioinguinal nerve fibers. METHODS: In our institution, 60 patients were evaluated and treated for idiopathic chronic testicular pain between January 2003 and July 2007. Priority was give to clinical treatment, which evolved from simple to more complex measures. Microsurgical treatment was performed on those who experienced no considerable pain relief (10 individuals in our study). RESULTS: Over a twenty-four-month follow-up period, 70% of patients showed complete remission and 20% exhibited partial relief from pain

Competências essenciais nos serviços de informática: analise das percepções entre profissionais, gestores e professores de graduação.

O estudo analisa as competências essenciais para os profissionais de computação, verificando a existência de um gap entre a percepção de três grupos de indivíduos: profissionais, gestores e professores. Verifica, ainda, o grau de relevância e as divergências das competências, segundo a percepção de cada grupo; e o gap existente entre as competências demandadas e ofertadas. A pesquisa é exploratória e descritiva, qualitativa e quantitativa e faz uma revisão da literatura sobre o tema. O marco teórico está fundamentado no Modelo de Competências de Le Boterf (2003) e no Modelo de Análise do Gap da Qualidade de Parasuraman, Zeithaml e Berry (1985), articulado com a Qualidade em Instituições de Ensino de Sirvanci (1996). A partir dos modelos referenciais, aplicou-se o Teste T para teste das hipóteses. Os resultados revelaram a existência de gaps entre os diferentes grupos pesquisados.

Reporting an experience : recovering and recording residues of teaching laboratories of Chemical Institute of the Federal University of Rio Grande do Sul.

An experience aiming to promote a residue interchange and recovery between the teaching laboratories of the Chemistry Institute of this University is described. At the present, several residues interchange have already appeared as advantageous. To make the work easier, a software has been developed in order to keep a record of all the residues generated by the teaching laboratories. Standard labels have been developed for the residues in order to organize them. The software and the label design are described

NONLINEAR DYNAMICS OF A VIBRATION-BASED ENERGY HARVESTING SYSTEM USING PIEZOELECTRIC AND SHAPE MEMORY ALLOY ELEMENTS

Energy harvesting is the conversion of available mechanical vibration energy into electrical energy that can be employed for different purposes. Several works have investigated the development of linear vibration energy harvesters that are efficient in a very narrow bandwidth around the fundamental resonance frequency. Nowadays, many researches have included different kinds of nonlinearities to expand the bandwidth of the energy harvesters. This paper deals with the use of smart materials for energy harvesting purposes. Basically, piezoelectric and shape memory elements are combined to build an energy harvesting system. The analysis is developed considering a one-degree of freedom mechanical system where the equation of motion is formulated by assuming the electromechanical coupling provided by a piezoelectric element and the restitution force provided by shape memory element described using a polynomial constitutive model. Numerical results indicate that the inclusion of the SMA element can dramatically change system dynamics, showing different kinds of responses including periodic and chaotic regimes