Recent Advances in Understanding Particle Acceleration Processes in Solar Flares

We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional magnetic field configurations (e.g., current sheets, collapsing traps, separatrix regions) and stochastic acceleration in a turbulent environment. Fluid, test-particle, and particle-in-cell approaches are used and results compared. While these studies show considerable promise in accounting for the various observational manifestations of solar flares, they are limited by a number of factors, mostly relating to available computational power. Not the least of these issues is the need to explicitly incorporate the electrodynamic feedback of the accelerated particles themselves on the environment in which they are accelerated. A brief prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011

Modelagem de um condicionador de ar de alta precisão para uso em processamento agrícola Modeling of a high precision air conditioner for use in agricultural processing

Apresenta-se neste trabalho, estudo detalhado sobre a modelagem de um condicionador de ar com controle acurado de temperatura e umidade relativa. Desenvolveu-se um programa de computador que permite predizer o comportamento do sistema sob diferentes condições psicrométricas e de vazão do ar de entrada. O modelo global físico-matemático inclui equações de balanço de massa e de energia para três diferentes volumes de controle que compõem o condicionador. Modelaram-se os processos de mistura, evaporação (ou condensação) simultânea de uma superfície d'água e de uma gota e o aquecimento de corrente de ar, separadamente. Propõem-se expressões semi-empíricas simples para os coeficientes de transferência de calor e massa inerentes ao processo de evaporação sobre uma superfície d'água e um modelo simplificado para o sistema de spray. Construiu-se um condicionador de ar no qual foram feitos testes experimentais para o ajuste das constantes que aparecem nas expressões para os coeficientes de transferência. Os dados obtidos validaram o modelo global, com precisão aceitável para projetos de engenharia.<br>In this work, a detailed procedure for the analysis of an accurately controlled air conditioner is presented. A computer program, that allows predicting the behavior of the system under different psychrometric conditions and different input air mass flow rates, was developed. The global physical-mathematical model includes mass and energy conservation equations for three different control volumes that compose the conditioner. Thus, the processes of mixture of air, simultaneous evaporation (or condensation) from a water surface and from a drop, and the air-stream heating are modeled separately. Simple semi-empiric expressions for heat and mass coefficients inherent to the evaporation process on a water surface are proposed as well a simplified model for the spray system. Experimental tests made on an air-conditioner allowed to obtain the constants that appear in the expressions for the heat and mass transfer coefficients and to validate the global model, within an engineering acceptable precision level

Twenty-year experience with stentless biological aortic valve and root replacement: Informing patients of risks and benefits

OBJECTIVES: The aim of this study was to provide predictive data on the performance of the Freestyle stentless bioprosthesis that can be used to support and improve the shared decision-making process of prosthetic valve choice for aortic valve replacement. METHODS: Between 1993 and 2014, 604 patients received the Freestyle stentless bioprosthesis (143 subcoronary, 58 root inclusion and 403 full-root replacement). Perioperative data were collected retrospectively, and follow-up data were collected prospectively from 2015. Follow-up was 96% complete (median 4.3 years), with 114 (19%) patients having a follow-up period exceeding 10 years. A competing risks regression model was developed to predict the probability of mortality, structural valve deterioration (SVD) and reoperation for other causes than SVD. RESULTS: The median age of patients was 64 years, 91 (15%) patients had undergone previous aortic valve replacement and 351 (58%) underwent concomitant procedures. The 15-year probability of SVD, reoperation for other causes and death were 16.9%, 8.1% and 47.7%, respectively. Linearized occurrence rates for prosthesis endocarditis, thromboembolic events and bleeding were 0.5%, 0.9% and 0.1% per patient-year, respectively. The constructed predictive model, including age, renal function and implantation technique as significant covariates, had good to fair predictive performance up to 19 years. CONCLUSIONS: The Freestyle stentless bioprosthesis is an efficient prosthesis for aortic valve replacement or root replacement, with low incidences of SVD and valve-related events at long-term follow-up. The predictive model designed in this study can be used to fully inform patients about their expected individual trajectory after implantation of this prosthesis. This improves the shared decision-making process between patients and clinicians