关键词： 大型运输机   机械操纵系统   动力学建模   飞行品质   性能验证  

摘要： 为提高大型运输机长跨度软式操纵系统(MMFCS)设计时的操纵性能,而得到优化的机械飞行操纵系统,采用软式操纵回路等效刚度的计算方法,引入钢索等效弹性模量的计算公式,得到软式操纵回路的等效刚度计算新方法.用多自由度刚体动力学的方法研究了整个软式操纵系统的建模问题,在一个软件平台上建立了整个操纵系统动力学模型,为操纵系统性能的综合性能仿真和品质评定提供了一种新思路.通过数字仿真结果与机械操纵系统物理实验报告的比较,证明了操纵系统回路刚度计算以及系统操纵性能仿真具有工程设计的参考意义,验证了该方法的有效性.

关键词： 微机械   动力学   尺度效应   纳米机械  

摘要： 介绍了微机械产生的背景、微机械动力学的主要研究内容以及微机械动力学研究的意义。在此基础上,回顾和总结了近年来国内外在多学科耦合大规模动力学模拟、动力学尺度效应分析、纳米机械的动力学模拟等微机械动力学方面的研究进展,并分析了微机械动力学研究不同于宏观机械的方面。最后指出了微机械动力学研究的不足以及有待解决的关键问题。

关键词： 木工机械   电主轴   设计   动力学分析  

摘要： 简要介绍了高速加工的优点和木材高速切削的特点和要求,据此分析了木工机械用高速电主轴的关键技术,然后对木工机械用电主轴进行了结构设计,最后基于传递矩阵法利用MATLAB对所设计的木工机械用高速电主轴进行动力学分析。

关键词： Actin dynamics   Wiskostatin   Dictyostelium discoideum  

摘要： Many essential functions in eukaryotic cells like phagocytosis, division, and motility rely on the dynamical properties of the actin cytoskeleton. A central player in the actin system is the Arp2/3 complex. Its activity is controlled by members of the WASP (Wiskott-Aldrich syndrome protein) family. In this work, we investigated the effect of the carbazole derivative wiskostatin, a recently identified N-WASP inhibitor, on actin-driven processes in motile cells of the social ameba . Drug-treated cells exhibited an altered morphology and strongly reduced pseudopod formation. However, TIRF microscopy images revealed that the overall cortical network structure remained intact. We probed the mechanical stability of wiskostatin-treated cells using a microfluidic device. While the total amount of F-actin in the cells remained constant, their stiffness was strongly reduced. Furthermore, wiskostatin treatment enhanced the resistance to fluid shear stress, while spontaneous motility as well as chemotactic motion in gradients of cAMP were reduced. Our results suggest that wiskostatin affects the mechanical integrity of the actin cortex so that its rigidity is reduced and actin-driven force generation is impaired.

关键词： DYNAMICS   CHAOS theory   MATHEMATICAL models   ENERGY dissipation   PHASE transformations (Physics)   PARAMETER estimation  

摘要： In second part of the paper both classical and novel scenarios of transition from regular to chaotic dynamics of dissipative continuous mechanical systems are studied. A detailed analysis allowed us to detect the already known classical scenarios of transition from periodic to chaotic dynamics, and in particular the Feigenbaum scenario. The Feigenbaum constant was computed for all continuous mechanical objects studied in the first part of the paper. In addition, we illustrate and discuss different and novel scenarios of transition of the analysed systems from regular to chaotic dynamics, and we show that the type of scenario depends essentially on excitation parameters. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Twinning   Molecular dynamics   Modeling   Dislocation   Plastic deformation  

摘要： An overview is given of the deformation mechanisms in nanotwinned copper, as studied by recent molecular dynamics, dislocation mechanics and crystal plasticity modeling. We highlight the unique role of nanoscale twin lamellae in producing the hard and soft modes of dislocation glide, as well as how the coherent twin boundaries affect slip transfer, dislocation nucleation, twinning and detwinning. These twin boundary-mediated deformation mechanisms have been mechanistically linked to the mechanical properties of strength, ductility, strain hardening, activation volume, rate sensitivity, size-dependent strengthening and softening in nanotwinned metals. Finally, discussions are dedicated to identifying important unresolved issues for future research. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： Molecular dynamics simulation   mechanical properties   Mg2Si  

摘要： This paper reports a study of the mechanical behavior of single-crystal bulk Mg2Si by the molecular dynamics method in view of the effect of temperature and strain rate. A modified Morse potential energy function in which the bond-angle deformation has been taken into account is developed and employed to describe the atomic interactions to shed light on the mechanical properties. The stress-strain response of single-crystal bulk Mg2Si under uniaxial tensile loading is investigated at different temperatures (300 K to 1200 K) and different strain rates, respectively. Through comparison of the mechanical properties of single-crystal bulk Mg2Si at different temperatures and strain rates, it is found that the elastic modulus gradually decreases with increasing temperature, while the strain rate seems to have little effect on the mechanical properties of single-crystal bulk Mg2Si. Moreover, in contrast to conventional polycrystalline bulk Mg2Si, single-crystal bulk Mg2Si exhibits much better mechanical performance.

关键词： Allometric Trophic Network model   community ecology   food web   multi-trophic dynamics   seasonal plankton succession  

摘要： Mechanistic understanding of consumer-resource dynamics is critical to predicting the effects of global change on ecosystem structure, function and services. Such understanding is severely limited by mechanistic models inability to reproduce the dynamics of multiple populations interacting in the field. We surpass this limitation here by extending general consumer-resource network theory to the complex dynamics of a specific ecosystem comprised by the seasonal biomass and production patterns in a pelagic food web of a large, well-studied lake. We parameterised our allometric trophic network model of 24 guilds and 107 feeding relationships using the lakes food web structure, initial spring biomasses and body-masses. Adding activity respiration, the detrital loop, minimal abiotic forcing, prey resistance and several empirically observed rates substantially increased the model's fit to the observed seasonal dynamics and the size-abundance distribution. This process illuminates a promising approach towards improving food-web theory and dynamic models of specific habitats.

关键词： Molecular dynamics   mechanical properties   vacancy effect   temperature effect   beta-Zn4Sb3  

摘要： The molecular dynamics method is employed to study the mechanical properties of single-crystal bulk -Zn4Sb3. According to the interatomic potential obtained from first-principles calculation and fitting to the ground-state physical equations, the stress-strain curves of single-crystal bulk -Zn4Sb3 under different conditions, which include Zn atom vacancy and temperature effects, are presented. From the stress-strain responses, single-crystal bulk -Zn4Sb3 exhibits typical nonlinear elastic brittleness of thermoelectric materials. With increasing Zn atom vacancy proportion, the mechanical properties of single-crystal bulk -Zn4Sb3 gradually degrade. When the Zn atom vacancy proportion reaches 10% in the vacancy model, the elastic modulus and the ultimate stress are found to decrease by 30% and 50% compared with the full-occupancy model. With increasing temperature from 300 K to 700 K, the crystal structure of the vacancy model of -Zn4Sb3 maintains stability, and the mechanical properties are degraded slowly. The mechanical properties along the [001] axis are better than along the [010] axis.

关键词： Cell mechanics   Subcellular   Live-imaging   Vesicle tracking   Drosophila   Aplysia  

摘要： Growing experimental evidence suggests that mechanical tension plays a significant role in determining the growth, guidance, and function of neurons. Mechanical tension in axons contributes to neurotransmitter clustering at the neuromuscular junction (NMJ) and is actively regulated by neurons both and . In this work, we applied mechanical strain on neurons and neurons and studied their vesicle dynamics by live-imaging. Our experiments show that mechanical stretch modulates the dynamics of vesicles in two different model systems: (1) The global accumulation of synaptic vesicles (SV) at the NMJ and (2) the local motion of individual large dense core vesicles (LDCV) in neurites. Specifically, a sustained stretch results in enhanced SV accumulation in the NMJ. This increased SV accumulation occurs in the absence of extracellular Ca2+, plateaus after approximately 50 min, and persists for at least 30 min after stretch is reduced. On the other hand, mechanical compression in neurites immediately disrupts LDCV motion, leading to decreased range and processivity. This impairment of LDCV motion persists for at least 15 min after tension is restored. These results show that mechanical stretch modulates both local and global vesicle dynamics and strengthens the notion that tension serves a role in regulating neuronal function.