关键词： 机械设计制造   工程学院   科技   重庆   机械电子工程   石油装备   本科专业   动力工程  

关键词： rumen passage rate   ruminal particle dynamics   modeling  

摘要： A mechanistic and dynamic model was developed to represent physiological aspects of particle dynamics in the reticulo-rumen (RR) and to predict rate of passage out of the RR (Kp) of forage particles quantitatively. The model consists of 2 conceptual pools with 3 spatial compartments of particles;the compartment the particle enters is based on functional specific gravity (FSG). The model assumes 2 major pressure gradient-driven flows of particles out of the RR through the reticuloomasal orifice between 2 consecutive primary reticular contractions. One is associated with the second phase of primary reticular contraction and involves propulsion of particles in the vicinity of the honeycomb structure of the reticulum from the RR. The second flow involves movement of particles in the reticulum without selection by size. Particle outflow rate was assumed to be proportional to liquid outflow rate. The passage coefficient, defined as the ratio of particle to liquid outflow rate, was estimated for each particle group by an equation derived from the probability of passage based on FSG and particle size. Particles retained on a 1.18-mm screen were defined as large particles. When the model was evaluated with 41 observations in an independent database, it explained 66% of the variation in observed Kp of forage particles with a root mean square prediction error of 0.009. With 16 observations that also included measurements of liquid passage rate, the model explained 81 and 86% of the variation in observed Kp liquid and Kp forage, respectively. An analysis of model predictions using a database with 455 observations indicated that the assumptions underlying the model seemed to be appropriate to describe the dynamics of forage particle flow out of the RR. Sensitivity analysis showed that probability of a particle being in the pool likely to escape is most critical in the passage of large forage particles, whereas the probability of being in the reticulum as well as in the likely to

关键词： POLYETHYLENE   NANOFIBERS   POLYMERS -- Mechanical properties   MOLECULAR dynamics   SIMULATION methods & models   ELASTICITY   TEMPERATURE effect   AMORPHOUS substances  

摘要： The extent to which the intrinsic mechanical properties of polymer fibers depend on physical size has been a matter of dispute that is relevant to most nanofiber applications. Here, we report the elastic and plastic properties determined from molecular dynamics simulations of amorphous, glassy polymer nanofibers with diameter ranging from 3.7 to 17.7 nm. We find that, for a given temperature, the Young's elastic modulus E decreases with Fiber radius and can be as much as 52% lower than that of the corresponding bulk material. Poisson's ratio nu of the polymer comprising these nanofibers was found to decrease from a value of 0.3 to 0.1 with decreasing fiber radius. Our findings also indicate that a small but finite stress exists on the simulated nanofibers prior to elongation, attributable to surface tension. When strained uniaxially tip to a tensile strain of epsilon = 0.2 over the range of strain rates and temperatures considered, the nanofibers exhibit a yield stress ay between 40 and 72 MPa, which is not strongly dependent oil fiber radius;this yield stress is approximately half that of the same polyethylene simulated in the amorphous bulk.

关键词： 集团公司   动力机械   江苏省   董事长   总经理   林海   高级工程师   人大常委  

摘要： 男，61岁，教授级高级工程师，1984年任现职。1960年9月至1965年7月在江苏省泰州中学学习，1973年5月至1984年11月在林业部泰州林机厂工作，1994年6月至今任江苏林海动力机械集团公司董事长、总经理，1998年以来被选举为江苏省第九、十、十一届人大常委委员。

关键词： dielectric losses   dielectric relaxation   friction   glass transition   polymer melts  

摘要： In this paper, low-frequency mechanical spectroscopy has been used to study poly(methyl methacrylate) (PMMA) melt around the glass transition temperature T-g for shedding light on its unique relaxation behaviors. The mechanical spectra show an asymmetrical broad structure with a maximum peak on the high-temperature side and a shoulder peak on the low-temperature side. The shoulder peak corresponds to the alpha relaxation due to the local segmental motion;while the maximum peak is assigned to the alpha(') relaxation due to the slow motion of longer chain segments or chains. The alpha relaxation mode has a stronger temperature dependence of relaxation time than the alpha(') mode, causing the alpha(') mode to merge with the alpha mode with decreasing temperature toward T-g. Time-temperature superposition (TTS) breaks down in the entire temperature range due to the different friction coefficients of the alpha and alpha(') relaxations. For only the alpha(') process, TTS is found to hold for PMMA melt, where the high-frequency decay of the mechanical loss decreases like a power law of the frequency with an exponent of -1/3. Moreover, compared with the dielectric results, the relaxation times of beta and alpha relaxations from mechanical measurements are about one order of magnitude slower than those from dielectric experiments.

关键词： 机械手   动力分析   机器人设计   相互作用   连接链   几何学   操纵器   反向  

摘要： 机械手是通过接头相互作用的可动连接链，其一端固定在基座上，另一端的手或受动器可以在空间自由活动。本书开始介绍了文章主题一机械手，接着详细地描述了连续机械手的正向和反向分析，从常见的工业机器人设计（相对简单的几何学）到非常复杂的连续连接情况，大部分内容适用于广泛机械手操纵器的几何闭型解，特色在于对6R-P、7R机理的详细分析。

关键词： Frictional-impact oscillator   Non-smooth dynamics   Time-varying system   Stick-slip  

摘要： We analyze the dynamics of a two-dimensional system constituted by two masses subjected to elastic, gravitational and viscous forces and constrained by a moving frictional mono-lateral surface. The model exhibits a time-varying dynamics capable of reproducing the hopping phenomenon, an unwanted phenomenon observed in many applications such as the motion of a robotic arm on a surface or that of a wiper on a windscreen. The system dynamics, besides being affected by geometrical non-linearities, has a non-smooth nature due to the impact and friction laws involved in the model. The complexity of the resulting equations and of the transition conditions require the problem to be solved numerically. Various periodic motions are found and the effect of varying the system parameters, in particular the friction coefficient, is investigated. Finally, simulations are used to gain some insight the behavior of the windscreen wiper. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： cytoskeleton   elasticity   viscosity   atomic force microscopy   laser scanning confocal microscopy  

摘要： Dynamic mechanical properties of cells are becoming recognized as indicators and regulators of physiological processes such as differentiation, malignant phenotypes and mitosis. A key process in development and homeostasis is apoptosis and whilst the molecular control over this pathway is well Studied, little is known about the mechanical consequences of cell death. Here, we study the caspase-dependent mechanical kinetics of single cells during early apoptosis initiated with the general protein-kinase inhibitor staurosporine. This results in internal remodelling of the cytoskeleton and nucleus which is reflected in dynamic changes in the mechanical properties of the cell. Utilizing simultaneous confocal and atomic force microscopy (AFM), we measured distinct mechanical dynamics in the instantaneous cellular Young's Modulus and longer timescale viscous deformation. This allowed us to visualize time-dependent nuclear and cytoskeletal control of force dissipation with fluorescent fusion proteins throughout the cell. This work reveals that the cell death program not only orchestrates biochemical dynamics but also controls the mechanical breakdown of the cell. Importantly, the consequences of mechanical disregulation during apoptosis may be a contributing factor to several human pathologies through the poorly timed release of dead cells and cell debris. Cell Motil. Cytoskeleton 66: 409-422, 2009. (C) 2009 Witey-Liss. Inc.

关键词： 事故预防   农用设备   农业机械   农业安全性   附件   收集器   定义   设计   尺寸规格   人类工效学   园艺机具   操纵   收获机械   危害   维护   作标记   职业安全性   操作   动力传动系统   保护措施   安全性   安全性工程   安全性措施   安全性要求   技术文献   工作地点   工作场所安全性  

标准号: BS ISO 21628-2008