关键词： continental collision   India-Asia orogen   Tibetan Plateau   underthrusting   three-dimensional finite element modeling   crustal viscosity  

摘要： The impact of mechanical layering and the strength of the Indian lower crust on the dynamics of the modern India-Asia collisional system are studied using 3-D thermomechanical modeling. The model includes an Indian oceanic domain, Indian continental domain, and an Asian continental domain. Each domain consists of four layers: upper/lower crust, and upper/lower lithospheric mantle. The Tarim and Sichuan Basins are modeled as effectively rigid blocks and the Quetta-Chaman and Sagaing strike-slip faults as vertical weak zones. The geometry, densities, and viscosities are constrained by geophysical data sets (CRUST2.0, gravity, and seismology). Both static (no horizontal movement of model boundaries) and dynamic scenarios (indentation) are modeled. It is demonstrated that 3-D viscosity distributions resulting from typical creep flow laws and temperature fields generate realistic surface velocities. Lateral variations in the gravitational potential energy cause locally significant tectonic overpressure (i.e., difference between pressure and lithostatic pressure) in a mechanically strong Indian lower crust (up to similar to 500MPa for the static scenario and similar to 800MPa for the dynamic scenario). Different density distributions in the lithosphere as well as different viscosities (3 orders of magnitude) in the Indian lower crust cause only minor differences in the surface velocity field. This result suggests that surface velocities alone are insufficient to infer the state of mechanical coupling of the lithosphere. Model results are in agreement with GPS velocities for Indian lower crustal viscosities of 10(21)-10(24)Pas, for a strong Quetta-Chaman Fault (10(22)Pas) and a weak Sagaing Fault (10(20)Pas).

关键词： Platelet activation   Platelet lysis   Thromboembolism   Anticoagulation   PIV   Hypertension   Blood pressure  

摘要： We hypothesize that the formation of the closing vortex and subsequent b-datum regurgitation jet in bileaflet mechanical heart valves is governed by the magnitude of the driving mean aortic pressure (MAP), and that this sensitivity does impact the blood damage index (BDI) corresponding to platelet activation and lysis. High spatial resolution time resolved (1 kHz) as well as phase locked particle image velocimetry techniques captured the dynamic leaflet closure and regurgitation jet of a model 25 mm St. Jude Medical BMHV. Cell trajectories were estimated using Lagrangian particle tracking analysis while the leaflet kinematics was quantified by tracking the leaflet tip-position throughout closure. The non-principal as well as principal shear stress loading histories along each cell trajectory revealed BDI for platelet activation and lysis as a function of cell initial position, release time-point, and blood pressure. Results show that the leaflet closing time reduces by roughly 10 ms, in response to an increase in MAP by 40 mmHg. We report that higher MAP leads to a stronger b-datum vortex and jet formation. Platelet activation BDI lowers with a higher MAP due to reduction in exposure times despite an increase in principal shear stress experienced. Platelet lysis BDI however increases with higher MAP. Maximum BDI may occur for cells initially in the b-datum zone during the onset of leaflet closure. Our results provide a better understanding of BDI of the regurgitant b-datum jet and sheds light on the potential importance of blood damage testing under hypertensive conditions.

关键词： CAD技术的概念   发展趋势   机械制造业   企业运用  

摘要： 随着现代科学技术和计算机技术的发展,我们的生活已经迈入来了一个高效、科学、以及数字化的进程,我们的计算机技术的发展是我们社会共同进步的原因,也是我们发展的必经阶段和必要过程。计算机技术的应用有很多种,但在我们现在的机械制造企业对策方面,我们对CAD技术的研究和发展更加的步入了一个深层次的地步。这更加与我们的现代计算机技术的发展息息相关,计算机技术的发展奠定了我们CAD技术的发展基础,同时也是我们在发展的过程中需要重点把握的内容,CAD技术的发展应用在许多方面,但现在,一个比较重要的一方面就是我们CAD技术在我们的机械制造方面的企业运用,本文主要讲述的也就是关于CAD技术的发展趋势和在机械制造中的应用,企业是如何运用CAD技术这方面的内容。

关键词： Robotic arms  

摘要： Grasping objects by continuum arms or fingers is a new field of interest in robotics. Continuum manipulators have the advantages of high adaptation and compatibility with respect to the object shape. However, due to their extremely nonlinear behavior and infinite degrees of freedom, continuum arms cannot be easily modeled. In fact, dynamics modeling of continuum robotic manipulators is state-of-the-art. Using the exact modeling approaches, such as theory of Cosserat rod, the resulting models are either too much time-taking for computation or numerically unstable. Thus, such models are not suitable for applications such as real-time control. However, based on realistic assumptions and using some approximations, these systems can be modeled with reasonable computational efforts. In this paper, a planar continuum robotic arm is modeled, considering its backbone as two circular arcs. In order to simulate finger grasping, the continuum arm experiences a point-force along its body. Finally, the results are validated using obtained experimental data.

关键词： 玻璃机械和设备   玻璃制品   推动力   环境问题  

摘要： 玻璃制品在我国的出现时间，最早可以追溯到公元前三、四世纪，距今已经有着几千年的历史。随着国民经济的快速发展，不同行业对于玻璃制品的使用也是越来越广泛，对我国整体的玻璃产业的发展起到了极大的促进作用。玻璃制品因其不可替代性，在我国整体社会发展中，所发挥的作用也将会越来越大。随着玻璃机械和设备的不断完善，对于推动玻璃产业技术变革和加工工艺革新起着重要的作用。可以说，在新时代、新形势下已经成为玻璃产业主要的推动力。

关键词： CHEMICAL kinetics   SYNTHESIS (Chemistry)   AMINO ketones   SUCROSE   CATALYSTS   RATE determining steps (Chemistry)  

摘要： For the first time, in a green protocol, an investigation of the kinetics and mechanism of the reaction between benzaldehyde 1, 4-chloroanilinne 2, and acetophenone 3 compounds in the presence of saccharose as a catalyst was performed for generating beta-aminoketone. For determining the kinetic parameters, the reaction was monitored by using the UV/Vis spectrophotometry technique. The second order rate constant (K-1) was automatically calculated by the standard equations contained within the program. In the studied temperature range, the second order rate constant (lnK(1),lnK(1)/T)depended on reciprocal temperature that was in good consistent with Arrhenius and Eyring equations, respectively. These data provided the suitable plots for calculating the activation energy and parameters (Ea, Delta G(double dagger,) Delta S-double dagger Delta H-double dagger) of the reaction. Furthermore, useful information was obtained from studying the effects of solvent, concentration, and catalyst on the reaction mechanism. The results showed that the first step of the reaction mechanism is a rate determining step (RDS). The obtained experimental data and also the steady state assumption confirmed the proposed mechanism.

关键词： 铁路   机械动力设备   检修   维护  

摘要： 当前,随着我国国民经济快速发展,我国的交通运输事业也发生了了翻天覆地的变化,铁路作为交通运输行业的一个重要组成部分,也发挥着越来越重要的作用。但是,维持铁路事业正常发展的机械动力设备却面临着越来越大的压力,因为这些机械动力设备承担着过重的任务,却往往得不到及时的检修与维护,这就使得我国铁路事业的发展面临困境,所以,必须重视对铁路机械动力设备的检修与维护,并及时进行设备的更新换代,在分析铁路机械动力设备检修策略的同时,就大力发展铁路机械设备的维护问题展开研究。

关键词： 柔性机械臂   轨迹规划   残余振动抑制   粒子群优化算法   绝对节点坐标法   自然坐标法  

摘要： 随着21世纪航天事业的迅速发展以及航天应用需求的日益增加，未来的空间任务越来越多，例如空间站的建设和运营、航天员舱外运动等，这些空间任务都需要空间机械臂来完成。空间机械臂是我国载人航天三期工程的重大关键技术之一，是深入开展载人航天活动必不可少的工具，是支持空间站建设和运营的关键设备，也是空间站四个关键技术攻关项目之一。在空间应用中，由于发射成本的限制、空间能源的限制以及空间操作的要求，轻质量、高载重/自重比、低能耗、操作灵活以及响应快速的多自由度柔性机械臂得到了世界各航天强国的高度重视，应用也越来越广泛。 空间柔性机械臂本质上属于多体系统动力学的范畴，而柔性多体系统动力学的研究也一直是该研究领域的热点和难点之一。基于小变形、小转动假设的柔性多体系统动力学，已经无法满足轻质航天器的精确动力学建模需求，其原因是无法精确描述柔性构件的大变形。将能够精确描述柔性构件大变形的绝对节点坐标法（ANCF）以及描述刚体体的自然坐标法（NCF）结合起来，可以形成研究刚-柔耦合多体系统动力学的绝对坐标（ACB）方法，该方法可以满足轻质航天器的高精度建模需求。空间柔性机械臂的制造多采用柔性关节和柔性臂杆，这两方面柔性因素，将不同程度地引起机械臂的振动问题。同时，机械臂在执行任务之前，轨迹规划都是必须的。如果能将机械臂轨迹规划研究和振动抑制研究有效地结合起来，将具有十分重要的意义，称之为柔性机械臂轨迹规划振动抑制研究。 本文以绝对坐标方法作为柔性机械臂动力学建模的基础，以柔性机械臂的轨迹规划、振动抑制以及控制作为导向，主要做了如下工作： 1)提出了在自然坐标法刚体单元上施加轴向扭矩的简洁公式，该公式可直接应用于基于自然坐标法建模的机械臂关节上施加驱动力矩;对自然坐标法逆动力学进行了分析，阐述了单元固有约束、单元之间约束副等的物理意义，提出了通过旋转副连接的自然坐标法刚体单元之间产生相对运动所需驱动力矩的计算方法，该公式可直接应用于机械臂逆运动学中计算驱动力矩。 2)基于连续介质力学理论和有限元方法，并运用矩阵分析理论，详细推导了绝对节点坐标法三维二节点梁单元的弹性力及其雅可比矩阵，该推导思路可拓展到其它绝对节点坐标法单元的推导。 3)基于实验室自行开发研制的航天结构刚度测试设备，对一定数量的机械臂柔性关节的扭转刚度进行测试，并对测试数据进行了拟合，通过数据拟合结果，提炼出三种典型的柔性关节刚度模型，分别为：线性刚度模型、非线性刚度模型以及含间隙的非线性刚度模型。 4)针对机械臂关节空间“点到点”、“静止到静止”的运动，提出了基于傅里叶余弦级数的轨迹规划函数，该规划函数具有一个冗余系数可供设计，通过设计该系数，可以非常有效地抑制柔性关节机械臂的残余振动;在此基础上，引入粒子群优化算法来优化该系数，可以更加有效地抑制柔性关节机械臂的残余振动。 5)对冗余自由度机械臂的正运动学和逆运动学进行了分析，并着重讨论了逆运动学的算法，以平面三连杆机械臂为例，验证了本文中逆运动学算法的正确性以及高精度性;利用机械臂的冗余自由度，结合粒子群优化算法，通过优化机械臂的自运动，可以保证机械臂末端沿设计轨迹运动的同时，最小化机械臂末端的残余振动。 6)对某空间七自由度机械臂的正运动学和逆运动学进行了详细推导，包括齐次变换矩阵以及雅可比矩阵等，分析了机械臂末端执行器的两种典型运动：直线运动和圆弧运动，并具体给出了末端轨迹规划方法，通过算例验证了该规划方法的有效性，计算得到的关节轨迹、速度以及加速度都非常光滑连续。

关键词： Molecular dynamics  

摘要： The mechanical properties of polyglycolic acid (PGA) of different water weight fractions (1.7%, 2.9%, and 5%) were investigated by molecular dynamics (MD) simulation through a tensile test. The variation in the degree of crystallinity with water content was also investigated using XRD profiles. The Young's modulus, mechanical strength, and fracture mechanism of all PGA-water systems were drawn from the corresponding stress-strain profiles. Furthermore, water diffusion behavior within the PGA matrix both before and after the tension test was also studied. The water diffusion coefficients were derived from the mean square displacements of all water molecules within the PGA matrix.

关键词： Mechanical stability  

摘要： Green fluorescent protein (GFP) is used as a biosensor for protein-protein interactions, co-translational folding and localization of different structures in cells, in which the mechanical stability and thermal conductivity of the beta-barrels play a vital role. In this work, we first explore themechanical and thermal properties of beta-barrels in GFP by using the molecular dynamics simulations. Our results show that the beta-barrel is destabilized once one strand is detached. Moreover, we also observe that the temperature relaxation processes of an unfolded state and the native state are nearly the same. Our dynamics simulations improve the understanding of mechanical stability of beta-barrels and help to find nanoscale mechanism controlling energy transport in biomolecules.