关键词： cardiac hypertrophy   actin assembly   phosphoinositide   mechano-transduction   CapZ tentacle  

摘要： Mechanical stress causes filament remodeling leading to myocyte hypertrophy and heart failure. The actin capping protein Z (CapZ) tightly binds to the barbed end of actin filaments, thus regulating actin assembly. The hypothesis is that the binding between CapZ and the actin filament is modulated through phosphatidylinositol 4,5-bisphosphate (PIP2) and how the COOH-terminus of CapZ beta 1 regulates this binding. Primary neonatal rat ventricular myocytes (NRVMs) were strained at 10% amplitude and 1-Hz frequency. Dot blotting measured the PIP2 amount, and affinity precipitation assay assessed the direct interaction between PIP2 and CapZ beta 1. Fluorescence recovery after photobleaching of green fluorescent protein-CapZ beta 1 and actin-green fluorescent protein after 1 h of strain shows the dynamics significantly increased above the unstrained group. The increases in CapZ and actin dynamics were blunted by neomycin, suggesting PIP2 signaling is involved. The amount of PIP2 dramatically increased in NRVMs strained for 1 h. With a ROCK or RhoA inhibitor, changes were markedly reduced. Subcellular fractionation and antibody localization showed PIP2 distributed to the sarcomeres. More PIP2-bound CapZ beta 1 was found in strained NRVMs. Less PIP2 bound to the CapZ beta 1 with its COOH-terminus intact than in the COOH-terminal mutant of CapZ beta 1, suggesting some inhibitory role for the COOH-terminus. Myocyte hypertrophy normally induced by 48 h of cyclic strain was blunted by dominant negative RhoA or neomycin. This suggests that after many hours of cyclic strain, a possible mechanism for cell hypertrophy is the accumulation of thin filament assembly triggered partially by the increased PIP2 level and its binding to CapZ.

关键词： GAUGE field theory   LATTICE field theory   FINITE size scaling (Statistical physics)   CHIRALITY   FIELD theory (Physics)  

摘要： We investigate the chiral properties of SU(2)C gauge theory with six flavors, i.e., six light Dirac fermions in the fundamental representations by lattice simulation, and point out that the spontaneous breakdown of chiral symmetry does not occur in this system. The quark mass dependence of the mesonic spectrum provides evidence for such a possibility. The decay constant tends to be increased by the finite size effect, which is opposite to the behavior predicted by chiral perturbation theory and indicates that the long distance dynamics in the six-flavor theory could be different from the theory with chiral symmetry breaking. The subtracted chiral condensate, whose utility is demonstrated by the simulation of two-flavor theory, is shown to vanish in the chiral limit within the precision of available data.

关键词： 管道施工机械手   虚拟样机建模   动力学仿真  

摘要： 管道施工机械手用于铺设地下大型水泥管道。为了能够准确模拟机械手的工作过程,为物理样机的设计和制造提供参数依据,采用Solidworks、Adams建立机械手虚拟样机的联合建模方法。为了能够实现仿真过程与实际工作状态的高度一致,保证仿真结果准确反映实际工况,在虚拟样机的运动副中添加外力等效摩擦力,对油缸铰接销轴柔性处理,以及添加过渡轴解决冗余约束等。对机械手虚拟样机进行了管道对接过程的动力学仿真,提取了相关仿真数据,并与实验样机的实验数据进行了对比。结果表明:仿真模型基本与实验样机相符,仿真数据基本准确、可靠。

关键词： 多体动力学   逆动力学模型   数值仿真  

摘要： 考虑到移动串联机械手不能很好地满足高速、大负载、准确作业的性能要求,提出了一种新颖的轮式悬架移动并联机械手构型。为实现建模的通用性与完备性,基于多体动力学,在笛卡尔坐标下构建了系统逆动力学模型,并据此分别对移动串联机械手和移动并联机械手进行了逆动力学数值仿真,以验证建模方法的正确性和新构型移动机械手的动力学性能。仿真结果的比较、分析表明,与串联构型相比,移动并联机械手的系统刚度有所提高,且不必增大能耗为代价;电机驱动力矩有所降低,有利于电机的选型和控制策略的制定。

关键词： (110.4500) Optical coherence tomography   (170.2655) Functional monitoring and imaging  

摘要： Pulmonary alveoli have been studied for many years, yet no unifying hypothesis exists for their dynamic mechanics during respiration due to their miniature size (100-300 mu m dimater in humans) and constant motion, which prevent standard imaging techniques from visualizing four-dimensional dynamics of individual alveoli in vivo. Here we report a new platform to image the first layer of air-filled subpleural alveoli through the use of a lightweight optical frequency domain imaging (OFDI) probe that can be placed upon the pleura to move with the lung over the complete range of respiratory motion. This device enables in-vivo acquisition of four-dimensional microscopic images of alveolar airspaces (alveoli and ducts), within the same field of view, during continuous ventilation without restricting the motion or modifying the structure of the alveoli. Results from an exploratory study including three live swine suggest that subpleural alveolar air spaces are best fit with a uniform expansion (r(2) = 0.98) over a recruitment model (r(2) = 0.72). Simultaneously, however, the percentage change in volume shows heterogeneous alveolar expansion within just a 1 mm x 1 mm field of view. These results signify the importance of four-dimensional imaging tools, such as the device presented here. Quantification of the dynamic response of the lung during ventilation may help create more accurate modeling techniques and move toward a more complete understanding of alveolar mechanics. (C) 2013 Optical Society of America

关键词： Cross linking   Elastic constants   Glass transition temperature   Molecular dynamics   Self-healing materials   Urea-formaldehyde  

摘要： Urea-formaldehyde polymers, which are utilized in the adhesives industry, have recently been shown to be suitable materials for synthesizing micro/nanocapsules for use in self-healing (nano)composites. In this study, molecular dynamics was employed to simulate the process in which urea and formaldehyde are cross-linked via methylene and ether cross linkers, and to study the structure and mechanical/thermal properties of simulated poly(urea-formaldehyde)s (PUFs). The elastic stiffness constants of the simulated materials were calculated using the constant-strain (static) method. A temperature cycle was applied to the cross-linked PUFs, and the glass transition behavior of each material was investigated through the mean squared displacement (MSD) and temperature evolution of the energy and the specific volume of the polymer. The simulation results confirmed that there was considerable improvement in the properties of the poly(UF) materials upon cross linking. The radial distribution function was also used to study the local structures of the polymers, and this revealed that increasing the temperature and cross linking density results in a significant drop in hydrogen bonding intensity in the cross-linked PUF systems.

关键词： Particulate nanocomposites   Size effects   Mechanical behaviour   Micromechanical models   Molecular Dynamics  

摘要： This paper aims at developing a method to account for a particle size effect on the mechanical behaviour of particulate nanocomposites. An introduction of specific information at the atomic scale, through Molecular Dynamics (MD) simulations, into homogenisation models of the overall mechanical behaviour of heterogeneous materials (micromechanical approaches) is proposed here. By studying virtual nanocomposites, which consist of silica inclusions embedded in a polymer matrix, MD simulations have shown the existence of an interphase of disturbed matrix surrounding the inclusions, whose thickness depends neither on the inclusion size nor on the volume fraction of inclusions. By considering this interphase of fixed thickness, a particle size effect is then deduced from a dilute micromechanical model which derives from the classical Eshelby's inhomogeneity problem. Effective elastic moduli of the composite strongly vary with the particle size for a fixed volume fraction of particles. Nevertheless, opposite trends are observed relative to the interphase behaviour. Whereas effective moduli increase with the particle size for an interphase softer than the matrix, they decrease in the reverse case. The confrontation between MD and micromechanical approaches and the characterisation of the interphase elastic moduli by an inverse method allow the stiffening effects observed by MD to be explained in the case of an interphase softer than the pure matrix. (C) 2013 Elsevier B. V. All rights reserved.

关键词： NdFeB alloy   Reaction milling in hydrogen   Disproportionation   Reaction kinetics  

摘要： The process of solid gas reaction milling in hydrogen was applied to achieve full disproportionation and microstructure nanocrystallization of NdFeB alloy. The NdFeB alloy was disproportionated by room-temperature reactive ball milling in hydrogen, with the mechanical energy serving as the driving force. The reaction progress during milling was examined by hydrogen absorption measurement, and the corresponding microstructure change was characterized by X-ray diffraction (XRD). The mechanism of mechanically activated hydrogenation disproportionation reaction of NdFeB alloy was investigated. The disproportionation kinetics of an as-cast Nd16Fe76B8 (atomic ratio) alloy during reaction milling was experimentally studied by in-situ monitoring of the hydrogen absorbed by the alloy in the vial. On the assumption that the impact energy to activate the reaction plays a role analogous to that of the thermal energy for the conventional thermally activated process, a theoretical model for the kinetics of the mechanically assisted disproportionation was proposed. By fitting the experimental data with the theoretical model, the kinetic equation and the energy utilization efficiency under different milling conditions were obtained. The effect of milling parameters and hydrogen pressure on the disproportionation kinetics was evaluated and the underlying mechanisms were discussed by referring to the mechanical energy input intensity and the Gibbs free energy change for the reaction. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

标准号: LY/T 2231-2013

摘要： 本标准规定了以汽油机为动力的手扶步进式割灌机(以下简称割灌机)的术语、定义、技术要求、试验方法、检验规则、标志、使用说明书、包装、运输和贮存。本标准适用于以汽油机为动力的手扶步进式割灌机,以其他内燃机为动力的割灌机亦可参照使用。

标准号: LY/T 1609-2013

摘要： 本标准规定了以汽油机为动力的随进式起草皮机的术语和定义、型号编制方法、基本参数、技术要求、试验方法、检验规则、标志、包装、使用说明书、运输和贮存。本标准适用于以汽油机为动力的随进式起草皮机(以下简称起草皮机)。