关键词： 最优激励轨迹   参数辨识   RRR机械臂   条件数  

摘要： 机器人动力学参数的精确辨识是对机器人进行精确控制的前提,参数辨识的精度与所采用的标定轨迹直接相关.以RRR机械臂为研究对象,建立该机械臂的动力学模型.在动力学参数辨识时,选择有穷傅里叶级数做为最优激励轨迹的表达式,通过最小化退化矩阵的条件数来获得最优激励轨迹中的参数,同时把各关节位置、速度和加速度的物理约束与激励轨迹结合起来,使获得的最优激励轨迹在物理意义上是可行的.通过在激励轨迹中指定频率范围来避免激励机器人的柔性特性,利用最小二乘法来辨识动力学参数.最后仿真验证了该辨识方法的有效性.

关键词： 汽/气动力机械泵   凝结水回收装置   凝结水回收成套装置  

摘要： 阐述了在杠杆浮球式疏水阀基础上发展起来的汽/气动力机械泵以及以汽/气动力机械泵为主机的高温凝结水回收成套装置系统的特点和用途。分析了以汽/气动力机械泵为主机的开式(闭式)高温凝结水回收成套装置系统在设计或工程中应用选型。高温凝结水回收成套装置和大排量浮球式疏水阀等可配套使用,通过大量实际应用的效果表明,该成套装置系统既具有广泛的适应性,又需与现场情况紧密结合。

关键词： 擒纵机构   动力学分析   碰撞  

摘要： 擒纵机构是机械手表中的关键部件之一,由于受到周期性受迫振荡而使其运动十分复杂。基于此,研究了瑞士叉瓦式擒纵机构的动力学问题,将擒纵机构的半周期分成4个部分,采用冲击微分方程理论,建立动力学模型,并用Matlab软件对其进行了动力学仿真计算。以Seiko7009a为实例,根据摆轮与时间、摆角与摆幅等关系,揭示了瑞士叉瓦式擒纵机构动力学特性,并分析了影响走时准确性的关键因素。结论表明:提出的数学模型在描述和预测动力学上具有较高的精度。

关键词： SUGINO动力头   孔加工   速技能  

摘要： MC记者：您能给我们介绍一下速技能在海内外市场的发展情况吗？ 林总：速技能是一家日本本土企业,产品主要是自动加工的动力头,主要应用于汽车、摩托车零部件的孔加工生产。除了在日本本土的发展以外,20多年来速技能在海外市场发展很迅速,共有七个子公司。

关键词： GEODYNAMICS   ROCK deformation   STRUCTURAL geology   EARTH'S mantle  

摘要： Comprehensive analysis of the parameters characterizing contemporary and neotectonic deformations of the Earth's crust and upper mantle developed in the Mongolia-Siberia area is presented. The orientation of the axes of horizontal deformation in the geodetic network from the data of GPS geodesy is accepted as an indicator of current deformations at the Earth's surface. At the level of the middle crust, this is the orientation of the principal axes of the stress-tensors calculated from the mechanisms of earthquake sources. The orientation of the axes of stress-tensors reconstructed on the basis of structural data is accepted as an indicator of Late Cenozoic deformations in the upper crust. Data on seismic anisotropy of the upper mantle derived from published sources on the results of splitting of shear waves from remote earthquakes serve as indicators of deformation in the mantle. It is shown that the direction of extension (minimum compression) in the studied region coincides with the direction of anisotropy of the upper mantle, the median value of which is 310-320 degrees NW. Seismic anisotropy is interpreted as the ordered orientation of olivine crystals induced by strong deformation owing to the flow of mantle matter. The observed mechanical coupling of the crust and upper mantle of the Mongolia-Siberia mobile area shows that the lithospheric mantle participated in the formation of neotectonic structural elements and makes it possible to ascertain the main processes determining the Late Cenozoic tectogenesis in this territory. One of the main mechanisms driving neotectonic and contemporary deformations in the eastern part of the Mongolia-Siberia area is the long-living and large-scale flow of the upper mantle matter from the northwest to the southeast, which induces both the movement of the northern part of the continent as a whole and the divergence of North Eurasia and the Amur Plate with the formation of the Baikal Rift System. In the western part of the regio

关键词： Collagen   Steered molecular dynamics   Elastic modulus   Mechanical behavior   Size effect  

摘要： Collagen is a fibrous protein that is responsible for structural integrity of various connective tissues such as bone, tendon, and skin. The mechanical properties of these hierarchical tissue structures are greatly influenced by presence of long and slender (similar to 300 long and similar to 1.5 nm in diameter) collagen molecules that impart strength and elasticity. The current molecular dynamics studies of collagen are limited to the use of short collagen molecules that are approximately 8.5 nm in length. This study investigates the mechanical behavior of the full-length collagen molecule and the short collagen by using steered molecular dynamics. The simulations were carried out at various loading conditions corresponding to different rates of pulling and springs of different stiffness were used to pull collagen molecules. The underlying mechanisms with respect to unfolding of collagen molecules differ significantly between short and full-length molecules when stretched in molecular dynamics simulations. These differences affect the mechanical properties of the short and full-length collagen molecules. In addition, the elastic modulus values are also affected by the pulling rate and the stiffness of the spring used by varying amounts for small and full-length collagen molecules. From this study, one may decipher the nuances of mechanical response of collagen in greater detail and recognize the similarities and differences in deformation mechanism of short and long collagen. (C) 2011 American Society of Civil Engineers.

关键词： Cell cycle and cell division   Imaginal discs   Mechanical tension   Notch signaling   Cloning   Drosophila melanogaster   Relaxation (physics)   Cytoskeleton  

摘要： Shaping the primordia during development relies on forces and mechanisms able to control cell segregation. In the imaginal discs of Drosophila the cellular populations that will give rise to the dorsal and ventral parts on the wing blade are segregated and do not intermingle. A cellular population that becomes specified by the boundary of the dorsal and ventral cellular domains, the so-called organizer, controls this process. In this paper we study the dynamics and stability of the dorsal-ventral organizer of the wing imaginal disc of Drosophila as cell proliferation advances. Our approach is based on a vertex model to perform in silico experiments that are fully dynamical and take into account the available experimental data such as: cell packing properties, orientation of the cellular divisions, response upon membrane ablation, and robustness to mechanical perturbations induced by fast growing clones. Our results shed light on the complex interplay between the cytoskeleton mechanics, the cell cycle, the cell growth, and the cellular interactions in order to shape the dorsal-ventral organizer as a robust source of positional information and a lineage controller. Specifically, we elucidate the necessary and sufficient ingredients that enforce its functionality: distinctive mechanical properties, including increased tension, longer cell cycle duration, and a cleavage criterion that satisfies the Hertwig rule. Our results provide novel insights into the developmental mechanisms that drive the dynamics of the DV organizer and set a definition of the so-called Notch fence model in quantitative terms.

关键词： ERRORS  

摘要： A correction to the article 'Kinetics and Mechanistic Aspects of the Heck Reaction Promoted by a CN-Palladacycle' that was published in the 2005 issue is presented.

关键词： Anisotropy   Basic-Leucine Zipper Transcription Factors/chemistry   Kinetics   Optical Tweezers   Protein Folding   Protein Structure, Secondary   Protein Structure, Tertiary   Saccharomyces cerevisiae/chemistry   Saccharomyces cerevisiae Proteins/chemistry   Stress, Mechanical   Thermodynamics  

摘要： Coiled coils are one of the most abundant protein structural motifs and widely mediate protein interactions and force transduction or sensation. They are thus model systems for protein engineering and folding studies, particularly the GCN4 coiled coil. Major single-molecule methods have also been applied to this protein and revealed its folding kinetics at various spatiotemporal scales. Nevertheless, the folding energy and the kinetics of a single GCN4 coiled coil domain have not been well determined at a single-molecule level. Here we used high-resolution optical tweezers to characterize the folding and unfolding reactions of a single GCN4 coiled coil domain and their dependence on the pulling direction. In one axial and two transverse pulling directions, we observed reversible, two-state transitions of the coiled coil in real time. The transitions equilibrate at pulling forces ranging from 6 to 12 pN, showing different stabilities of the coiled coil in regard to pulling direction. Furthermore, the transition rates vary with both the magnitude and the direction of the pulling force by greater than 1000 folds, indicating a highly anisotropic and topology-dependent energy landscape for protein transitions under mechanical tension. We developed a new analytical theory to extract energy and kinetics of the protein transition at zero force. The derived folding energy does not depend on the pulling direction and is consistent with the measurement in bulk, which further confirms the applicability of the single-molecule manipulation approach for energy measurement. The highly anisotropic thermodynamics of proteins under tension should play important roles in their biological functions.

关键词： Coupled physical-biogeochemical model   Mechanistic process model   Osmotic stress   Senegal River Estuary  

摘要： This paper presents the outline of an estuary modeling study encompassing a study of the biogeochemical model on its own. It includes a preliminary validation of the new mechanistic features using mesocosm data, and a study of a coupled physical and biogeochemical model of the Senegal River Estuary (SRE) from flood to low-water conditions. The originality of this work is that it distinguishes the marine and freshwater origins of some of the organisms modeled and includes additional mortality terms owing to the osmotic stress experienced by the freshwater organisms. The mechanistic model implemented in the Eco3M modelling tool, and partially designed for this study, succeeded in representing the dynamics of the planktonic food web in two mesocosm experiments and in the SRE under very different conditions using a single set of model parameters. Among the important results, it reveals that distinguishing between marine and freshwater origins provides substantial additional information on the distribution of organisms along the estuary. Finally, failure to take account of the osmotic stress and the origin of the organisms can give rise to substantial errors in the calculation of the biomass in the SRE. (C) 2011 Elsevier B.V. All rights reserved.