关键词： 六自由度机械臂   建模   仿真分析   扭矩  

摘要： 随着工业自动化的不断发展,机械臂在自动化生产车间的应用日趋广泛。本文通过对一种六自由度机械臂的结构分析,了解其工作及传动原理。利用计算机辅助设计软件对其进行三维建模,并在动力学分析软件中进行扭矩仿真分析,为其结构设计及关节处电机选型提供参考。

关键词： 2F2R宏微机械臂   动力学模型   弹性振动   尺度效应  

摘要： 柔性宏刚性微机械臂是一类典型的刚柔混合机械臂系统。采用有限元法,以2F2R宏微机械臂为研究对象,通过分析,详细推导和建立具有普遍意义的动力学模型。基于给定关节空间运动轨迹,对2F2R宏微机械臂的结构参量、截面参量、材质、集中质量分布等与系统弹性振动尺度效应之间关系与变化规律进行分析。在此基础上,针对操作空间运动轨迹,采用宏微空间分解方法,进一步分析上述设计参量与系统弹性振动尺度效应之间关系。通过上述两方面研究工作,获得许多有参考价值的研究成果,这对于该类宏微机械臂的设计与控制都将具有重要意义。

关键词： catheter ablation   heart failure   intra-aortic balloon pump   percutaneous left ventricular assist device   ventricular tachycardia  

摘要： Introduction: There is a paucity of data in favor of mechanical support during catheter ablation of ventricular tachycardia (VT). This study investigated the outcomes of VT ablation associated with mechanical support using percutaneous ventricular assist device (PVAD) versus intra-aortic balloon pump (IABP). Methods and results: We retrospectively examined the outcomes of patients who underwent VT ablation associated with PVAD versus IABP from 2010 to 2013, captured by the Medicare Inpatient Standard Analytic File database. Data from 345 patients (PVAD = 230, IABP = 115) were examined. On admission, the incidence of heart failure was higher in PVAD(84.3% vs. 73.0%;P = 0.01) with similar rates of renal failure in PVAD versus IABP (33.0% vs. 37.4%;P = 0.42). However, PVAD was associated with reduced in-hospital cardiogenic shock (9.1% vs. 23.5%;P < 0.001), renal failure (11.7% vs. 21.7%;P = 0.01), and length of stay (8.4 +/- 7.9 vs. 10.6 +/- 7.5;P < 0.001), but with greater hospital discharges to home/self-care (66.0% vs. 51.6%;P = 0.02). Index mortality (6.5% vs. 19.1%;P = 0.001) and mortality in patients with cardiogenic shock (18.2% vs. 41.2%;P = 0.03) were significantly lower with PVAD versus IABP. Furthermore, PVAD was associated with lower all-cause (27.0% vs. 38.7%;P = 0.04) and heart failure-related (21.4% vs. 33.3%;P = 0.03) 30-day hospital readmissions, but with similar redo-VT ablation rates at 1 year (10.2% vs. 14.0%;P = 0.34). Conclusion: Among the cases captured by the Medicare database, catheter ablation of VT associated with mechanical support using PVAD was associated with reduced in-hospital cardiogenic shock, renal failure, length of stay, hospital readmissions and mortality, but no difference in redo-VT ablation at 1 year.

关键词： binding energy   mechanical activation process   molecular dynamics   uniformity  

摘要： Herein, molecular dynamics simulations and experiments were carried to select solvent for the mechanical activation process. The interaction between solvent and each component of the Al-PTFE mechanical activated energy composites has been studied by means of molecular dynamics. Then, the status of Al and PTFE in solvent was analyzed, and the microstructure of the composite was also studied combined with experiment. At last, the mechanical activated energy composites were prepared with n-hexane as the solvent. The results show that the adsorption of PTFE, toluene, and hexane on the (0 0 1), (0 1 0), and (100) surface of Al2O3 is stable. Al2O3 (0 0 1) surface and Al2O3 (0 1 0) surface interact with 3 substances mainly via the electrostatic force. Al2O3 (1 0 0) surface interacts with 3 substances mainly via the van der Waals force. The binding energies of toluene-Al2O3 and hexane-Al2O3 are larger than PTFE-Al2O3. PTFE cannot adsorb on the surface of aluminum in the existence of n-hexane and toluene. n-Hexane can make PTFE disperse uniformly, and a considerable part of these PTFE will be coated on the surface of Al after n-hexane is removed. The uniformity of Al/PTFE mechanical activated energetic composites prepared in n-hexane is good, and it increases with the milling time.

关键词： Hydrogen reduction   Magnetite   Mechanical activation   Reduction kinetics   Nucleation and growth  

摘要： The effect of mechanical activation on the reduction kinetics of magnetite concentrate by hydrogen was studied. The magnetite concentrate was milled for 8 h in a planetary ball mill. After 8 h of milling, the average particle size was reduced from 14 to 4.4 A mu m, resulting in a lattice microstrain of 0.3. Isothermal reduction experiments were conducted by thermogravimetry to focus on the chemical reaction as the rate-controlling factor by eliminating external mass transfer effects and using a thin layer of particles to remove interstitial diffusion resistance. Thus, about 2 mg of magnetite powder was reduced at different temperatures under a sufficient flow of hydrogen. The magnetite concentrate and reduction products were analyzed by SEM and XRD. It was found that the onset reduction temperature decreased from 587 to 500 K (314-227 A degrees C) due to the mechanical activation. The activation energy for hydrogen reduction of the activated concentrate decreased about 10% compared with the as-received concentrate. In view of the results, a reaction rate expression was established based on the nucleation and growth model with an Avrami parameter n = 2.5.

关键词： Wrist watch   Mechanical regulator   Compliant hinge   Isochronism   Quality factor   FE   CFD   Multi-body  

摘要： This paper presents a new mechanical regulator for wrist watches, highlighting the methodology used to set up a comprehensive model of the device. The mechanical regulator, which is characterized by a high frequency monolithic oscillator made of monocrystalline silicon coupled to a deadbeat escapement, has been designed to provide a high quality factor, a condition necessary to guarantee enhanced chronometric performances compared to traditional mechanical regulators. The chronometric performances and the isochronism of the oscillating system have been assessed by means of a multi-body model whose parameters have been evaluated by FE and CFD simulations. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： gaseous   adsorption   fixed-bed   diffusion kinetics   modeling  

摘要： Adsorption is a complex physicochemical process involving interparticle transport, interphase mass-transfer, intraparticle diffusion, and surface reactions. Although the exact description of the adsorption process will inevitably vary from system to system, it will always be governed by those primary mechanisms. Therefore, by devising a model framework that can inherently include those mechanisms, it would be possible to create a modeling platform on which many different adsorption problems could be solved numerically. To accomplish this task, a generalized 1-D conservation law model was created to include the necessary mechanisms of adsorption on several different geometrical domains. Specific model applications for adsorption were developed under that framework and validated using experimental data available in literature or obtained in this work. This modeling platform makes it easier to model various adsorption problems and develop new adsorption models because of the common treatment of the mathematics governing the physical processes. (c) 2017 American Institute of Chemical Engineers

关键词： Clay   Epoxy resin   Exfoliated   Intercalated   Interphase   Molecular dynamics simulations  

摘要： Polymer/clay nanocomposites (PCNs) are multi-functional materials that have superior mechanical and thermal properties than polymer-based materials while maintaining their characteristic properties of lightweight and optical clarity. These materials are obtained by adding small amounts of clay nanofillers to a polymer matrix. In this work, we proposed a molecular model to investigate the morphology and thermomechanical properties of thermosetting clay nanocomposites. The epoxy matrix was composed of several representative cross-linked epoxy units, and different structures of PCNs, which correspond to intercalated or exfoliated status, were considered by varying the amount of polymer phase in the interlayer space. Molecular dynamics simulations of different nanocomposite structures were used to provide atomistic insights into the arrangement of the constitutive components of PCNs, the molecular interactions occurring in the interphase zone, and the influence of silicate layer on the thermodynamic and elastic properties of these multi-functional materials. (C) 2017 Elsevier B.V. All rights reserved.

关键词： MECHANICAL behavior of materials   TISSUE scaffolds   POROUS materials   COMPOSITE materials   DEGRADATION of plastics   DIGITAL image processing  

摘要： Tissue engineering combines artificial scaffolds and living cells in order to reconstruct damaged tissues and organs. The biodegradable scaffolds should maintain their mechanical properties during first stages of the regeneration. The aim of this study was to investigate the extent the degradation affects the mechanical stability of novel biodegradable composite scaffolds in relation to their composition. The scaffolds were made using fused deposition modeling. They were composed of ternary composites containing poly(epsilon-caprolactone) (PCL), 5 wt% of tricalcium phosphate (TCP) and 5, 15, and 25 wt% of poly(lactide-co-glycolide) (PLGA). Scaffolds made of pristine PCL and binary composite PCL-TCP were tested as reference samples. The degradation experiment was carried out in simulated body fluid at 37 degrees C for 12 weeks. Mechanical tests were carried out in a mechanical tester. Strain was measured using digital image correlation and crossbar displacement. Chemical composition had a significant effect on initial mechanical properties and their changes during degradation. The initial apparent Young's modulus of ternary composite scaffolds was two times higher than that of PCL-TCP. Higher PLGA concentration yielded faster decrease of the mechanical properties. At the end of the experiment, there were no significant differences of the modulus among all tested materials although degradation of the ternary composite scaffolds was significantly advanced. (C) 2015 Society of Plastics Engineers

关键词： Kevlar (R)   Aramid fibers   Molecular dynamics   Reactive potentials   Rate-dependence   Temperature-dependence   Fracture  

摘要： Molecular dynamic simulations are used to quantify how the mechanical behavior of PPTA crystallites, the fundamental building blocks of aramid fibers such as Kevlar (R), depend on strain-rate, temperature, and crystallite size. The (axial) crystallite elastic modulus is found to be independent of strain-rate and decreases with increasing temperature. The crystallite failure strain increases with increasing strain rate and decreases with increasing temperature and crystallite size. These observations are consistent with crystallite failure being driven by stress-assisted thermal fluctuations of bonds within PPTA crystallites and the concepts of the kinetic theory of fracture. Appealing to reliability theory, a model is proposed that predicts the onset of both primary and secondary bond failure within a crystallite as of function of strain rate, temperature, and crystallite size. The model is parameterized using bond failure data from constant strain-rate molecular dynamic strain-to-failure simulations and is used to compute the activation volume, activation energy, and frequency for both primary and secondary bond ruptures. (C) 2017 Published by Elsevier Ltd.