关键词： Underwater vehicle   Underwater vehicle manipulator system   Underwater manipulation   Manipulation hydrodynamics  

摘要： Operations with Intervention Autonomous Underwater Vehicle (I-AUV) can not only realize automatic and accurate missions, but also save the pilots' endeavors and reduce their fatigues. However, the performance of a small sized I-AUV is easily affected by its own restoring forces and hydrodynamic effects. A novel small sized single body and streamlined I-AUV has been developed for autonomous cruising and manipulation through the schemes comparisons and analysis on the restoring forces and hydrodynamic performance. In order to investigate I-AUV manipulation hydrodynamic performance during manipulation, water channel experiments and computation fluid dynamics (CFD) have been made on various operation postures. Moreover, CFD simulations and analysis have been expanded from water channel domain to infinite domain to obtain I-AUV manipulation hydrodynamic performance during forward cruising.

关键词： h-BCN   Graphene   Mechanical properties   Molecular dynamics  

摘要： Using molecular dynamics (MD) simulations, we investigate the mechanical properties of hexagonal BCN monolayer, a newly synthesized two-dimensional material with an atom ratio of B/C/N = 1:1:1. The Tersoff potential is modified to get good agreement between predicted and measured fracture strengths of graphene. With this modified Tersoff potential, we perform extensive MD simulations to study the effect of temperature, strain rate and vacancy defect on the mechanical properties of h-BCN. It is found that h-BCN is a strong material with fracture strength of 81.4-93.5 GPa, albeit similar to 35% lower than that of graphene. Similar to graphene, temperature has strong effect on the mechanical properties of h-BCN. As the temperature increases from 10 K to 1300 K, the fracture strength and strain of h-BCN drops by 55% and 62%, respectively. The strain rate is found to have a moderate effect. When the strain rate increases from 0.00002 to 0.0125 ps(-1), the fracture strength and strain of h-BCN increases 6.1% and 12%, respectively. As for the atomic defect, a very small concentration (0.028%) of vacancy in h-BCN is able to cause a 28% reduction in fracture strength and a 35.5% reduction in fracture strain. These findings have significance for its future applications in nanodevices. (C) 2019 Elsevier B.V. All rights reserved.

关键词： Collagens   Detergents   Elastin   Blood vessels   Mechanical properties   Deoxyribonucleases   Extracellular matrix proteins   Scanning electron microscopy  

摘要： Decellularization of blood vessels is a promising approach to generate native biomaterials for replacement of diseased vessels. The decellularization process affects the mechanical properties of the vascular graft and thus can have a negative impact for in vivo functionality. The aim of this study was to determine how detergents under different fluid dynamics affects decellularization efficacy and mechanical properties of the vascular graft. We applied a protocol utilizing 1% TritonX, 1% Tributyl phosphate (TnBP) and DNase on porcine vena cava. The detergents were applied to the vessels under different conditions;static, agitation and perfusion with 3 different perfusion rates (25, 100 and 400 mL/min). The decellularized grafts were analyzed with histological, immunohistochemical and mechanical tests. We found that decellularization efficacy was equal in all groups, however the luminal ultrastructure of the static group showed remnant cell debris and the 400 mL/min perfusion group showed local damage and tearing of the luminal surface. The mechanical stiffness and maximum tensile strength were not influenced by the detergent application method. In conclusion, our results indicate that agitation or low-velocity perfusion with detergents are preferable methods for blood vessel decellularization.

关键词： 空间机械臂   动力学建模   驱动力矩  

摘要： 为了正确地掌握空间机械臂在轨服务过程的真实动力学特性,基于Lagrange方程,获得机械臂有/无气浮装置时关节驱动力矩的差值函数,然后利用带气浮装置的关节驱动力矩的地面实验数据减去理论差值,预测机械臂在轨服务时的真实驱动力矩。最后采用刚性较好的小型机械臂进行实验,验证了该方法的正确性。

关键词： 水性涂料   溶剂型涂料   水性涂装   环境保护法规   工程机械企业   涂料市场   环境友好型   标杆企业  

摘要： 随着环境保护意识的不断加强和环境保护法规的日益完善,作为环境友好型的一种涂一水性涂料具有VOCs含量低,对环境和人体伤害小等显著优势,因此水性涂料在国内持续升温。不少工程机械企业也开始尝试水性涂料,纷纷把水性涂装作为未来发展方向o但是,在工程机械涂料市场,溶剂型涂料仍然占据主导地位。

关键词： 医用机械臂   患者重心位置   动态特性   ADAMS  

摘要： 目的分析患者重心位置变化对医用机械臂的动力学特性的影响。方法由于不同肿瘤患者重心位置的差异引起医用机械臂动态特性的变化,利用SolidWorks建立医用机械臂三维模型,借助MATLAB robotic toolbox对其进行运动学模拟获取各关节驱动函数,利用ADMAS软件仿真不同重心位置的患者对医用机械臂动力学特性的影响,计算机械臂各关节的位移特征曲线及末端质心的位移偏差。结果验证了肿瘤患者在床板重心位置的不同存在位移偏差,得到医用机械臂末端质心的位移偏差和力矩曲线,marker9点加载下x、y、z三个方向位移偏差最大,分别为0.82、2.078和1.070 mm。结论研究结果可为后期医用机械臂运动控制和位置补偿提供依据。

关键词： Hardness  

摘要： The rapid corrosion of magnesium alloys in physiological environment constraints its applications to employ it as a biodegradable implant material. AZ31 and ZK60 alloys were executed to anodization in alkaline solution as a function of time and investigated their electrochemical and mechanical properties. The scanning electron microscopy reveals the compact passive film formation subsequently to anodization. The high-resolution spectra of x-ray photoelectron spectroscopy confirmed the existence of MgO, Mg(OH)(2) and traces of CO3-2 within the anodized layer. The quasi-static with displacement-controlled mode of indentation was performed to investigate the mechanical properties of the anodized films. Anodized ZK60 has an average hardness of similar to 0.49 GPa, greater than the hardness of anodized AZ31-Ano (0.35 GPa). Similarly, the stiffness and film elastic modulus for anodized ZK60 were higher when compared with anodized AZ31. The surface roughness of anodized ZK60 (473.54 +/- 51.61 nm) was higher than that of anodized AZ31 (112.11 +/- 11.31 nm). The potentiodynamic polarization scans for AZ31 showed corrosion current density of 4.46 mu A/cm(2) (untreated) and 394.8 e(-3) mu A/cm(2) (anodized), while in ZK60 corrosion current densities values shifted from 12.05 mu A/cm(2) (un-treated) to 714.8 e(-3) mu A/cm(2) (anodized). Similarly, electrochemical impedance spectroscopy indicated enhanced charge transfer resistance for anodized AZ31 (1.164 K Omega-cm(2)) and ZK60 (1.911 K Omega-cm(2)) when compared with untreated AZ31 (28.3 K Omega-cm(2)) and ZK60 (0.481 K Omega-cm(2)). Furthermore, MC3T3 preosteoblast cells on the anodized surfaces caused no adverse effects in regards to biocompatibility.

关键词： 农机具购置   购置补贴政策   农业机械化   农村劳动力转移   双重差分模型  

摘要： 农业机械化在县级层面的变动趋势及机械化发展的时空变化特征、农机具购置补贴政策与农机总动力、农机具购置补贴政策与农村劳动力转移之间的关系、农业机械化对农村劳动力转移的作用效果表明,农机总动力的发展对农村劳动力转移具有显著的正向影响。21世纪以来中国农业机械化发展呈现出明显的时空变化特征,具体表现为农业机械化在华北和黄淮海地区、东北地区和长江中下游地区得到长足发展,农业机械化覆盖面在西南和西北地区得以扩大。农机具购置补贴政策能够实现县级层面的农机总动力发展和农村劳动力转移。