关键词： 并购整合   机械行业   美国卡特彼勒公司   产品多元化   德国西门子公司   现跨越式发展   机械制造企业   工程机械  

摘要： 一、领先机械制造企业无不通过并购整合实现跨越式发展 美国卡特彼勒公司（Caterpillar），全球最大的工程机械、发动机厂商之一，自1908年起进行了一个多世纪的产品多元化和收购兼并，实现了从拖拉机到工程机械、发动机、金融，直至全面多元化的飞跃发展。德国西门子公司（Simens），全球最大的电气电子工程公司之一，上世纪伊始即开始多面混业兼并迅速多元化，近年并购整合步伐加快，飞速发展。

关键词： 并联机构   串联输入支链   逆动力学   弹性动力学方程   并联机械手  

摘要： 并联机构与串联机构相比具有承载能力强、定位精度高、动态性能好等特点，从而得到越来越广阔的应用。本文密切结合制造装备业对少自由度可重构并联机构的需求，拟以文献[1]中提出的含串联输入支链的并联机构2UPS-RPU为研究对象，对其展开相关的动力学分析研究工作。本文研究内容涉及机构结构分析、运动学分析，动力学分析及ADAMS仿真研究。主要研究内容如下：\n (1)分析2UPS-RPU并联机构的拓扑结构特征，利用Kutzbach-Grubler法计算了该机构的自由度。建立机构闭环位置约束方程，并由位置方程依次对时间求导可得到机构的速度及加速度方程，完成机构的逆运动学分析。\n (2)基于Newton-Euler法建立该机构刚体动力学逆解方程，该方法通过建立各个支链及动平台的力及力矩平衡方程，求解可得机构动力学逆解。同时利用虚功原理法建立机构的刚体动力学逆解模型。通过计算实例结果比较，可得两种方法建模计算结果是相同的，可证实所用方法建模的正确性。\n (3)利用有限元法及系统子结构法建立机构的弹性动力学方程，根据机构的结构特征，在一定的假设前提下，构建了杆单元的弹性位移方程，再由系统各个构件之间的约束关系，得到机构总体的弹性动力学模型。\n (4)以ADAMS动力学仿真软件为平台，对机构进行动力学特性仿真研究。得到了给定机构动平台载荷及其运动规律后，机构各个驱动副的驱动力及驱动力矩。并验证了刚体动力学理论计算结果的正确性。

关键词： Nano materials   Mechanical   Atomic structure  

摘要： The mechanical properties of graphite in the forms of single graphene layer and graphite flakes (containing several graphene layers) were investigated using molecular dynamics (MD) simulation. The in-plane properties, Young's modulus, Poisson's ratio, and shear modulus, were measured, respectively, by applying axial tensile stress and in-plane shear stress on the simulation box through the modified NPT ensemble. In order to validate the results, the conventional NVT ensemble with the applied uniform strain filed in the simulation box was adopted in the MD simulation. Results indicated that the modified NPT ensemble is capable of characterizing the material properties of atomistic structures with accuracy. In addition, it was found the graphene layers exhibit higher moduli than the graphite flakes: thus, it was suggested that the graphite flakes have to be expanded and exfoliated into numbers of single graphene layers in order to provide better reinforcement effect in nanocomposites. (C) 2009 Elsevier Ltd. All rights reserved.

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。