关键词： somitogenesis   segmentation   presomitic mesoderm   oscillations   excitable system   Yap   Notch   excitability   clock  

摘要： The periodic segmentation of the vertebrate body axis into somites, and later vertebrae, relies on a genetic oscillator (the segmentation clock) driving the rhythmic activity of signaling pathways in the presomitic mesoderm (PSM). To understand whether oscillations are an intrinsic property of individual cells or represent a population-level phenomenon, we established culture conditions for stable oscillations at the cellular level. This system was used to demonstrate that oscillations are a collective property of PSM cells that can be actively triggered in vitro by a dynamical quorum sensing signal involving Yap and Notch signaling. Manipulation of Yap-dependent mechanical cues is sufficient to predictably switch isolated PSM cells from a quiescent to an oscillatory state in vitro, a behavior reminiscent of excitability in other systems. Together, our work argues that the segmentation clock behaves as an excitable system, introducing a broader paradigm to study such dynamics in vertebrate morphogenesis.

关键词： Mechanical effects of light on material media   Optomechanics   Photonic crystals   Solitons   Nonperturbative methods   Semiclassical methods  

摘要： A Kuznetsov-Ma soliton that exhibits an unusual pulsating dynamics has attracted particular attention in hydrodynamics and plasma physics in the context of understanding nonlinear coherent phenomena. Here, we demonstrate theoretically the formation of a novel form of Kuznetsov-Ma soliton in a microfabricated optomechanical array, where both photonic and phononic evolutionary dynamics exhibit periodic structure and coherent localized behavior enabled by radiation-pressure coupling of optical fields and mechanical oscillations, which is a manifestation of the unique property of optomechanical systems. Numerical calculations of the optomechanical dynamics show an excellent agreement with this theory. In addition to providing insight into optomechanical nonlinearity, optomechanical Kuznetsov-Ma soliton dynamics fundamentally broadens the regime of cavity optomechanics and may find applications in on-chip manipulation of light propagation.

关键词： CHEMISTRY periodicals   RUTHENIUM   CATALYSIS   DYNAMICS  

摘要： The mechanism of the dimerization of terminal aryl alkynes promoted by [{RuCl(mu-Cl)(eta(6)-p-cymene)}(2)] (1)/AcOH, under cooperative transition metal/Bronsted acid catalysis, has been investigated with regard to (i) the activation of the dinuclear ruthenium complex and (ii) the catalytic formation of the trans-1,4-diaryl-1,3-enyne products, by a detailed kinetic investigation of both processes. Complex 1 is subject to a slow solvolytic process in neat acetic acid or is transformed rapidly in the presence of sodium acetate to form the monomeric ruthenium(II) acetato complex [RuCl(eta(6)-pcymene)(OAc)]. The latter is the active catalytic species promoting the alkyne dimerization process, via initial pi-alkyne coordination and intramolecular C-H abstraction by the acetate ligand, as key steps of the catalytic cycle. The presence of additive acetate salts allows for the reaction to proceed at room temperature with short reaction times and high trans/cis stereoselectivity, thus rendering this catalytic system among the most active and selective procedures for the dimerization of terminal alkynes in a protic medium. The linear coupling of three molecules of phenylacetylene affords an organometallic ruthenium complex featuring a butenynyl ligand which has been characterized by X-ray crystallography.

关键词： MECHANICAL behavior of materials   IONS   MOLECULAR physics   IONOMERS   MOLECULAR dynamics   POLYMERS  

摘要： Using coarse-grained molecular dynamics simulations, we study ionomers in equilibrium and under uniaxial tensile deformation. The spacing of ions along the chain is varied, allowing us to consider how different ionic aggregate morphologies, from percolated to discrete aggregates, impact the mechanical properties. From the equilibrium simulations, we calculate the stress-stress auto correlation function, showing a distinct deviation from the Rouse relaxation due to ionic associations that depends on ion content. We then quantify the morphology during strain, particularly the degree to which both chains and ionic aggregates tend to align. We also track the location of the ionomer peak in the anisotropic structure factor during strain. The length scale of aggregate order increases in the axial direction and decreases in the transverse direction, in qualitative agreement with prior experimental results. Published by AIP Publishing.

关键词： molecular dynamics   physicochemical interaction   oxygen atom   phosphatidylcholine   plasma medicine   AMBER   quantum mechanics  

摘要： Plasma medicine is one of the most attractive applications using atmospheric pressure nonequilibrium plasma. With respect to direct contact of the discharge plasma with a biological membrane, reactive oxygen species play an important role in induction of medical effects. However, complicated interactions between the plasma radicals and membrane have not been understood well. In the present work, we simulated elemental processes at the first stage of physicochemical interactions between oxygen atom and phosphatidylcholine using the quantum mechanical molecular dynamics code in a general software AMBER. The change in the above processes was classified according to the incident energy of oxygen atom. At an energy of 1 eV, the abstraction of a hydrogen atom and recombination to phosphatidylcholine were simultaneously occurred in chemical attachment of incident oxygen atom. The exothermal energy of the reaction was about 80% of estimated one based on the bond energies of ethane. An oxygen atom over 10 eV separated phosphatidylcholine partially. The behaviour became increasingly similar to physical sputtering. The reaction probability of oxygen atom was remarkably high in comparison with that of hydrogen peroxide. These results suggest that we can uniformly estimate various physicochemical dynamics of reactive oxygen species against membrane lipids.

关键词： 两挡变速器   电动汽车   机械式自动变速器   试验台   实时仿真  

摘要： 该文以实现动力不中断的高效动力传动系统为基本目标,对一种适用于电动汽车的动力保持型机械式自动两挡变速器进行了仿真与试验研究。该变速器主要由单排行星齿轮系统、膜片弹簧式离合器以及鼓式制动器构成,旨在解决换挡过程中的动力中断问题。该文建立了一个采用新型变速器的纯电动汽车前置前驱传动系统动力学模型。在MATLAB/Simulink环境下,搭建了一个纯电动车整车仿真模型。该模型用来进行分析、选定变速器的基本参数,研制出一台变速器功能样机。该仿真模型适合于实时仿真与试验,在试验过程中可以灵活地改变调整各种参数。根据新型变速器试验的需求,该文建立了一个变速器硬件在环仿真平台,搭建了一个变速器样机的试验台,进行实时仿真和台架试验。仿真和试验结果表明:该变速器解决了在换挡过程中存在的动力中断问题,使驱动电机工作在高效区间,提高了纯电动汽车的动力性和经济性。

关键词： 机械动力   自动绕障   教具小车   协调运动  

摘要： 为帮助工科大学生理解所学理论知识,提高大学生的工程实践能力及创新能力,设计了一种可依靠纯机械控制,自动完成多个"8"字轨迹的绕桩小车。此小车可以调节转向机构的转向角来适应桩距的改变,小车的总体结构设计主要包含五大方面:小车行走轨迹设计、能量转换机构的设计、传动机构设计、差速机构设计和转向机构设计。其效果是:结构简洁,启动性能好,行走平稳;精度很高;无碳、节能、环保;对提高实践教学效果发挥了重要作用。

关键词： 柔性机械臂   斜碰撞   动力学分析   柔性多体系统  

摘要： 对作大范围运动柔性机械臂系统,进行斜碰撞动力学分析.基于柔性多体系统刚柔耦合动力学理论,计入耦合变形项,全面考虑大范围刚体运动与弹性小变形运动的耦合,建立系统连续动力学方程.引入斜碰撞力学模型,将法向和切向碰撞力以广义力的形式加入动力学方程中,对系统进行斜碰撞动力学建模分析.法向碰撞模型选取基于连续接触力法的非线性弹簧阻尼模型,切向碰撞模型选取一种修正Coulomb摩擦模型,对切向摩擦力进行统一描述.给出接触、分离判据,实现不同状态的动力学模型转换与求解.对斜碰撞全局动力学进行了仿真验证,分析了柔性机械臂全局过程的动力学特性变化以及碰撞对大范围运动和小变形运动的作用,并对比了不同碰撞方向对大范围运动、变形、机械能、碰撞力等动力学参数的影响.

关键词： 空化   水动力学   水力机械   空泡流  

摘要： 空化现象是水利、船舶、交通及能源动力等工业界广泛存在的液体汽化现象,而水力机械的空化由于流道结构复杂、影响因素繁多,一直是困扰整个行业发展的关键难题。本文主要简单介绍近几年国内外以及作者课题组在空化水动力学基础研究方面的主要进展,主要内容包括:(1)三维云状空化流动结构及演变特性;以三维水翼空化云的准周期性脱落为例,阐明空化对水翼尾流区域的速度场、湍流强度以及涡量场的影响规律。(2)以扭曲水翼为对象,揭示U型云空化(马蹄形)向下游发展过程中演变规律及形成机制。(3)根据得到的空化云图和Q准则涡量图,对比扭曲水翼附着型空化绕流结构在不同攻角下的特点和演化过程。(4)基于理论分析和数值模拟,揭示了空化体积二阶导数为水力机械空化诱导低频水压脉动激振的根源,为深入理解水力机械、船舶推进器等的内部流动机理、工程中叶片区及流道表面的流动分离抑制提供了新的概念与方法。

关键词： 工程机械臂   系统结构   动力学   特性  

摘要： 随着科学技术的不断进步,机械产品在先进技术的引导下逐渐向环保、优质方向发展。工程机械臂作为重要元件应用于机械工程中,在实际应用中充分发挥动力学性能,这不仅会促进工作稳定进行,还会提高机械工程的经济效益。首先介绍了研究现状,然后分析了动力学特点。