Wall-Pressure Fluctuations Inside Attached Cavitation

This study experimentally investigates the statistics of wall-pressure fluctuations and their source inside attached cavitation under different cavity regimes. Experiments were conducted in the divergent section of a convergent-divergent channel at a constant Reynolds number of Re = 7.8 × 105 based on throat height, and different cavitation numbers σ = 1.18, 0.92, 0.82 and 0.78. Four high-frequency unsteady pressure transducers were flushed-mounted in the divergent section downstream the throat where cavitation develops to sample the unsteady pressure signals induced by cavity behaviors. Flow visualization and wall-pressure measurement in high frequency on the order of MHz were employed using a synchronizing sampling technique. Results are presented for sheet/cloud cavitating flows. Specifically, sheet cavitation with both inception shear layer and fully cavitated shear layer and cloud cavitation under re-entrant jet dominated shedding and shock wave dominated shedding are studied. Compared with re-entrant jet, the interactions between shock wave and cavity could induce pressure peaks with high magnitude within cavity, which will collapse the local vapor along its propagating path and reduce local void fraction. Furthermore, statistics analysis shows that within the cavity, wall-pressure fluctuations increase with the distance to cavity leading edge increase in the first half of cavity length, and the moments of the probability density distribution skewness and kurtosis factor decrease, indicating the asymmetry and intermittency of wall-pressure fluctuation signals decrease. In shock wave dominated cavity shedding condition, the skewness and kurtosis factor increase. These results can provide data to improve the accuracy of turbulence modeling in numerical simulation of turbulent cavitating flow.

Testing Conditional Asset Pricing in Pakistan: The Role of Value-at-risk and Illiquidity Factors

This article investigates performance of conditional and unconditional Capital Asset Pricing Model and Fama–French model augmented with a downside risk, that is, the value-at-risk (VaR) factor and an illiquidity factor as additional risk factors using the discount factor methodology of Cochrane (1996). Using monthly portfolio data as test assets from the Pakistani stock market from January 1993 to January 2013 we provide empirical evidence on the efficacy of the VaR and illiquidity factors in asset pricing. We find that these factors improve the efficacy of the Fama–French model and including these factors reduces the explanatory power of co-kurtosis factor.

Comparación in vitro del efecto del pulido en la morfología superficial de tres resinas compuestas

Objetivos: El objetivo del presente estudio fue evaluar la morfología de las superficie de tres resinas compuestas de restauración directa Filtek Z 250 (3M), TetricCeram (Ivoclar-Vivadent) y Te Econom (Ivoclar-Vivadent) pulidas con el sistema de pulido Astropol (Ivoclar-Vivadent), dada la importancia de obtener superficies altamente estéticas y adecuadamente lisas que dificulten el acúmulo de placa bacteriana, la tinción de la restauración que pueda afectar el color y la salud bucal del paciente. Material y Métodos: Se evaluaron 15 especímenes, cinco de cada resina compuesta las cuales fueron pulidas con el sistema Astropol® para posteriormente obtener las medidas con el microscopio confocal de superficie y tras procesar los datos con el programa ArRUGa 2.0 y utilizar los parámetros utilizados fueron el Ra, RMS, Skewness, Kurtosis, factor de Wenzel y dimensión fractal. Los resultados fueron analizados con las pruebas de ANOVA de una sola vía y de Sheffe con un nivel de confianza del 0.05, los cuales indicaron que había una diferencia estadísticamente significativa en los parámetros de rugosidad de las tres resinas. Resultados: En el presente estudio se encontró que la superficie más lisa fue la obtenida utilizando la resina Z-250-3M y el sistema de pulido Astropol-IvoclarVivadent. Conclusiones: La utilización de los parámetros de rugosidad de forma y un instrumento como el microscopio confocal nos da mayor información del comportamiento de las rugosidades.

Fault Diagnosis Method Based on Embedded Acquisition Equipment and SVM

Fault diagnosis method based on embedded acquisition equipment and SVM is proposed in the paper.The function of the module mainly includes data acquisition, data processing and data storage.SVM is trained by the features and the five states of rolling bearing. The structure of diagnostic model by SVM is defined as 5 input nodes and 5 output nodes,among which 5 input nodes are the features including peak factor,waveform factor,impulse factor,margin factor and kurtosis factor and 5 output nodes are the five states of rolling bearing include normal state, housing washer failure, retainer failure, rolling element failure and inner ring failure.The experimental results show that the diagnostic performance of SVM is effective.