关键词： Molecular Dynamics   Tension   FCC Metals   Loading Rate Effects  

摘要： In this study, MD simulations of some face centred cubic (FCC) metals at nano-scale and under uniaxial tension were carried out. The effects of different loading rates of 5-200 m/s at constant temperature on the tensile behaviour and stress-strain curves were studied. The potential used in these simulations was Sutton-Chen many-body long-range potential. In addition, Velocity Verlet formulation of Nose-Hoover dynamic was applied in order to control the temperature fluctuations. Using periodic boundary conditions, the effects of loading rate on the mechanical-failure behaviour of Al, Ag, Cu and Ni were investigated. The maximum engineering stress, failure commencement strain and strain at the failure were evaluated at different loading rates. A correlation between the radius of local necking with the ductility, deformation and loading rate was established.

关键词： Aluminum alloys  

摘要： The aim of the present investigation was to study the effects of mechanical strain on the orthopedic biomaterial Ti-6Al-4V-osteoblast interface, using an in vitro model. Homogeneous strain was applied to Human Bone Marrow derived Osteoblasts (HBMDOs) cultured on Ti-6Al-4V, at levels which are considered physiological, by a four-point bending mechanostimulatory system. A simple model for the estimation of maximum hydrodynamic shear stresses developed on cell culture layer and induced by nutrient medium flow during mechanical loading, as a function of the geometry of the culture plate and the load characteristics, is proposed. Shear stresses were lower than those which can elicit cell response. Mechanical loading was found that contributes to the regulation of osteoblast differentiation by influencing the expression of the osteoblast-specific transcription factor Cbfa1, both at the mRNA and protein level, and also the osteocalcin expression, whereas osteopontin gene expression was unaffected by mechanical loading at all experimental conditions.

关键词： hydrogel   mechanical strength   poly(N-isopropylacrylamide)   simultaneous IPN   temperature sensitive  

摘要： In this study, a new IPN structure was designed and a simultaneous method was for the first time utilized to prepare temperature sensitive PNIPAAm IPN hydrogels by carrying out the radical polymerization and hydrolysis/condensation for two kinds of reaction at the same time. Due to the specific structures, the newly prepared simultaneous IPN gels displayed higher elastic modulus and faster shrinking rates than the conventional PNIPAAm gel.

关键词： cardiology   cellular biophysics   haemodynamics   prosthetics  

摘要： The hinge region of a mechanical bileaflet valve is implicated in blood damage and initiation of thrombus formation. Detailed fluid dynamic analysis in the complex geometry of the hinge region during the closing phase of the bileaflet valve is the focus of this study to understand the effect of fluid-induced stresses on the activation of platelets. A fixed-grid Cartesian mesh flow solver is used to simulate the blood flow through a two-dimensional geometry of the hinge region of a bileaflet mechanical valve. Use of local mesh refinement algorithm provides mesh adaptation based on the gradients of flow in the constricted geometry of the hinge. Leaflet motion is specified from the fluid-structure interaction analysis of the leaflet dynamics during the closing phase from a previous study, which focused on the fluid mechanics at the gap between the leaflet edges and the valve housing. A Lagrangian particle tracking method is used to model and track the platelets and to compute the magnitude of the shear stress on the platelets as they pass through the hinge region. Results show that there is a boundary layer separation in the gaps between the leaflet ear and the constricted hinge geometry. Separated shear layers roll up into vortical structures that lead to high residence times combined with exposure to high-shear stresses for particles in the hinge region. Particles are preferentially entrained into this recirculation zone, presenting the possibility of platelet activation, aggregation, and initiation of thrombi.

摘要： LL- and TT-type vibratory micromechanical gyroscopes (MMG) are considered with regard for nonlinear dependence of the suspension resistance forces and electrostatic forces on the displacement of the MMG sensitive elements. Nonlinear differential equations for a MMG operating in the measuring mode are obtained. These equations contain both analytical and nonanalytical nonlinearities. The effect of these nonlinearities on the dynamics and precision of vibratory MMGs is studied. The use of the method of averaging revealed stable steady-state modes of vibratory MMGs. The corresponding resonance curves are constructed. The results obtained may find application in the design of devices of the types considered.

关键词： 应用   平衡   离合器   消费者与供货者的关系   定义   设计   挠性联轴器   气体   煤气   汽油   工业   杠杆作用   负载物传送   厂商试验   机械驱动   矿物油   天然气   天然气工业   石油工业   定货人   石油   动力传输   动力传动工程   质量保证   质量控制   卖货商   联轴器   规范   技术数据单  

标准号: BS EN ISO 14691-2008

摘要： Petroleum technology, Mechanical transmission systems, Flexible couplings, Shaft couplings, Power transmission systems, Mechanical components, Petroleum, Natural gas, Rotation velocity, Design, Inspection, Performance testing, Quality control, Approval testing

关键词： Algorithms   Biomechanics   Capsid   Computer Simulation   Databases   Protein  

摘要： The mechanical properties of viral shells are crucial for viral assembly and infection. To study their distribution and heterogeneity on the viral surface, we performed atomistic force-probe molecular dynamics simulations of the complete shell of southern bean mosaic virus, a prototypical T = 3 virus, in explicit solvent. The simulation system comprised more than 4,500,000 atoms. To facilitate direct comparison with atomic-force microscopy (AFM) measurements, a Lennard-Jones sphere was used as a model of the AFM tip, and was pushed with different velocities toward the capsid protein at 19 different positions on the viral surface. A detailed picture of the spatial distribution of elastic constants and yielding forces was obtained that can explain corresponding heterogeneities observed in previous AFM experiments. Our simulations reveal three different deformation regimes: a prelinear regime of outer surface atom rearrangements, a linear regime of elastic capsid deformation, and a rearrangement regime that describes irreversible structural changes and the transition from elastic to plastic deformation. For both yielding forces and elastic constants, a logarithmic velocity dependency is evident over nearly two decades, the explanation for which requires including nonequilibrium effects within the established theory of enforced barrier crossing.

关键词： CHEMICAL kinetics   RADICALS (Chemistry)   QUARTZ   SIZE reduction of materials   SONICATION   SUSPENSIONS (Chemistry)  

摘要： The kinetics of radical formation during the mechanical activation of quartz by wet grinding or sonication was investigated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) as a scavenger. The consumption of DPPH during the sonication of quartz in an ethanol suspension is a zeroth-order process. A linear relationship between the rate constant of the DPPH consumption and the quartz concentration in the suspension indicates that radical formation under sonication increases with the growing total surface area of the quartz particles. Sonication leads to the formation of free radicals by the mechanical activation of the particle surface. The kinetics of the DPPH consumption during wet grinding of quartz in a stirred media mill is described successfully by a modified zeroth-order rate law taking the total surface area of the quartz particles into account. The surface-normalized rate constant of the DPPH consumption decreases from 1.8 x 10(-7) mol L-1 h(-1) m(-2) to 4.8 x 10(-8) mol L-1 h(-1) m(-2) if the specific surface area of the feed material increases from 0.5 to 84 m(2)/g. This finding indicates that the breakage of the quartz particles contributes much more to radical formation than does the mechanical activation of the particles in the mill because the breakage rate increases with growing particle diameter. Ethanol but not DPPH was found on the surface of the ground quartz particles. From this finding, it can be concluded that radicals on the surface of the quartz particles react with ethanol, leading to the formation of ethanol radicals and H radicals. DPPH reacts with the H radicals. As a side reaction, radicals can react with oxygen, leading to the formation of peroxides.

关键词： Osteogenic differentiation   Mechanotransduction   Fluid flow   Mesenchymal stem cell  

摘要： Many biochemical factors regulating progenitor cell differentiation have been examined in detail;however, the role of the local mechanical environment on stem cell fate has only recently been investigated. In this study, we examined whether oscillatory fluid flow, an exogenous mechanical signal within bone, regulates osteogenic, adipogenic or chondrogenic differentiation of C3H10T1/2 murine mesenchymal stem cells by measuring Runx2, PPAR gamma and SOX9 gene expression, respectively. Furthermore, we hypothesized that the small GTPase RhoA and isometric tension within the actin cytoskeleton are essential in flow-induced differentiation. We found that oscillatory fluid flow induces the upregulation of Runx2, Sox9 and PPAR gamma, indicating that it has the potential to regulate transcription factors involved in multiple unique lineage pathways. Furthermore, we demonstrate that the small GTPase RhoA and its effector protein ROCKII regulate fluid-flow-induced osteogenic differentiation. Additionally, activated RhoA and fluid flow have an additive effect on Runx2 expression. Finally, we show RhoA activation and actin tension are negative regulators of both adipogenic and chondrogenic differentiation. However, an intact, dynamic actin cytoskeleton under tension is necessary for flow-induced gene expression.

关键词： 传动系统设计   航空发动机   动力机械   集成平台   二期工程   平台建设   研究所   中国  

摘要： 经过数月的努力，中国航空动力机械研究所设计体系集成平台建设二期工程取得阶段性成果。在气动专业进行了实际应用验证，并已经扩大了基于天舟COMAN的设计体系集成平台的使用范围，进一步推进了结构、强度等专业的应用验证。航空动力机械研究所是我国唯一的集预先研究与型号研制于一体的中小航空发动机和直升机减速传动系统设计／试验研究所。