关键词： biocatalysis   formate dehydrogenase   cofactor regeneration   process modeling  

摘要： Formate dehydrogenase (FDH) from Candida boidinii is an important biocatalyst for the regeneration of the cofactor NADH in industrial enzyme-catalyzed reductions. The mathematical model that is currently applied to predict progress curves during (semi-)batch reactions has been derived from initial rate studies. Here, it is demonstrated that such extrapolation from initial reaction rates to performance during a complete batch leads to considerable prediction errors. This observation can be attributed to an invalid simplification during the development of the literature model. A novel mechanistic model that describes the course and performance of FDH-catalyzed NADH regeneration under industrially relevant process conditions is introduced and evaluated. Based on progress curve instead of initial reaction rate measurements, it was discriminated from a comprehensive set of mechanistic model candidates. For the prediction of reaction courses on long time horizons (>1 h), decomposition of NADH has to be considered. The model accurately describes the regeneration reaction under all conditions, even at high concentrations of the substrate formate and thus is clearly superior to the existing model. As a result, for the first time, course and performance of NADH regeneration in industrial enzyme-catalyzed reductions can be accurately predicted and used to optimize the cost efficiency of the respective processes. (C) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 26: 73-78, 2010

关键词： Atrial Septal Defect   Hemodynamic   Transcatheter Closure  

摘要： Objective. The secundum type of atrial septal defect (ASD) is a common congenital cardiac anomaly. Transcatheter closure of the defect is the preferable therapeutic approach to avoid potential future complications. This work extends the data collected so far regarding the electrocardiographic, morphologic, hemodynamic, and mechanical changes following the procedure. Design. From April 2002 to October 2003, 42 consecutive patients underwent successful transcatheter closure of secundum type ASD. They were sampled for different parameters by transthoracic echocardiography before the procedure and at three different points over the next 4 years, and analyzed in two age groups: children and adults. Results. The dimensions of the chambers normalized throughout the study period. Abnormal movement of the interventricular septum normalized mostly during the first month, but its thickness increased gradually to normal levels during the 4 years of the study. High elevated pulmonary artery pressure values began declining to near normal levels from the second month following the procedure. The stroke volume and the right bundle branch block pattern improved throughout the study period. Conclusions. Transcatheter ASD closure is followed by morphologic, conductive, and hemodynamic changes at different time intervals during the first years and results in normalization or near normalization of the heart's structure and function.

关键词： cams (mechanical)   engines   pneumatic systems   power transmission (mechanical)   springs (mechanical)   valves  

摘要： The paper presents a comparison of performance for a cam transmission of an engine valve train operating with a mechanical spring and with a return spring device that uses a pneumatic spring. Dynamic analysis of the cam mechanism is performed in the frequency and time domains employing a combined lumped-distributed parameter model capable of predicting the effects of the higher harmonics of the cam lift profile on system performance, in particular of the return spring device. Dynamic stiffness of the transmission in the frequency domain and time history of the contact force between cam and follower are evaluated. The limits of the traditional mechanical spring-closing system at high-speed camshaft operations are investigated, highlighting that they are mainly imposed by the internal resonances of the spring. The pneumatic spring is an improved replacement of the steel spring because of better dynamic behavior. Furthermore, the pneumatic return device allows preload tuning of the spring, which may increase transmission efficiency through proper control of the fluid pressure. Study of the pressure control circuit is also presented.

关键词： Hybrid system   Excavator   Wheel loader   Energy regeneration   Energy saving   Construction machinery  

摘要： Facing the environment problems, the improvement on the efficiency of the construction machinery such as the excavator and wheel loader is highly demanded. The hybrid power systems used in automobiles have been adapted into the construction machinery. This paper first analyzes the difference between the hybrid powered automobile vehicle and the hybrid powered construction machinery. The research and development of the hybrid power systems and energy regeneration systems of construction machinery are reviewed, and the applications of hybrid systems in construction machinery are presented. Finally, the challenges facing the researchers and the construction machinery manufacturers are discussed. (C) 2009 Elsevier B.V. All rights reserved.

关键词： 水平轴海流机   水动力性能   大涡模拟   滑移网格法   双转子   波浪海底边界层   空化  

摘要： 水平轴海流机是海流能发电机械的一种重要形式,目前还处于初期的研究阶段。本文首先采用线涡流函数面元法预测了海流机翼剖面的水动力特性,并结合叶素动量法对海流机水动力进行了校核；然后采用三维粘性流场数值计算方法预测了海流机单转子、串列布置双转子的水动力性能；研究了海底边界层速度分布、波浪对海流机水动力性能的影响；最后分析了海流机的空化性能。 对计算结果分析发现：线涡流函数面元法可以有效预测海流机翼剖面的水动力特性,结合叶素动量法可以对海流机性能进行初步的校核；对单转子海流机性能的预测发现,LES模型和SA模型都能够较好地预测海流机在设计工况下的水动力性能；对于本文中所研究的串列布置的双转子海流机,间距对水动力特性的影响较大,而初始相位角对水动力特性的影响较小,要保证串列布置的双转子海流机的输出性能,其间距需达到30倍的叶轮直径以上；海底边界层会引起海流机水动力特性周期性的变化,其频率特性与转动频率一致；波浪也会引起海流机周水动力特性期性的变化,其频率主要受波浪频率的影响,同时也受到转动频率的影响；数值预测的海流机的初生空化数为0.84与实验初生空化数接近,而且空泡的形态也与实验结果一致。 本文所发现的有关海流机水动力特性的规律,为海流机的优化设计和安全运行提供了新思路；采用三维粘性流场数值计算方法来预测海流机的性能,为海流机发电的进一步研究提供了参考。