关键词： Amyloid beta-Peptides/chemistry   Amyloid beta-Peptides/drug effects   Amyloid beta-Peptides/genetics   Amyloid beta-Peptides/metabolism   Binding Sites/genetics   Humans   Ligands   Models, Biological   Models, Molecular   Molecular Dynamics Simulation   Mutagenesis, Site-Directed   Protein Binding/genetics   Protein Folding/drug effects   Protein Interaction Domains and Motifs/genetics   Protein Structure, Quaternary/genetics   Protein Structure, Secondary/drug effects   Protein Structure, Secondary/genetics  

摘要： Polymerization of the amyloid beta-peptide (A beta), a process which requires that the helical structure of A beta unfolds beforehand, is suspected to cause neurodegeneration in Alzheimer's disease. According to recent experimental studies, stabilization of the A beta central helix counteracts A beta polymerization into toxic assemblies. The effects of two ligands (Dec-DETA and Pep1b), which were designed to bind to and stabilize the A beta central helix, on unfolding of the A beta central helix were investigated by molecular dynamics simulations. It was quantitatively demonstrated that the stability of the A beta central helix is increased by both ligands, and more effectively by Pep1b than by Dec-DETA. In addition, it was shown that Dec-DETA forms parallel conformations with beta-strand-like A beta, whereas Pep1b does not and instead tends to bend unwound A beta. The molecular dynamics results correlate well with previous experiments for these ligands, which suggest that the simulation method should be useful in predicting the effectiveness of novel ligands in stabilizing the A beta central helix. Detailed A beta structural changes upon loss of helicity in the presence of the ligands are also revealed, which gives further insight into which ligand may lead to which path subsequent to unwinding of the A beta central helix.

关键词： QMCF MD   Stability of hydrogen peroxide   Hydrogen bonds   Radial distribution functions   Mean residence times   H-bond dynamics  

摘要： An ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation was performed on a single molecule of hydrogen peroxide immersed in water to investigate its stability in aqueous solution, since pure hydrogen peroxide is very unstable. The structural parameters such as radial distribution functions (RDFs), coordination number distributions (CNDs) and angular distribution functions (ADFs) indicate the existence of similar to 4 hydrogen bonds between hydrogen peroxide and water molecules, with both molecules acting as hydrogen bond donors and hydrogen bond acceptors. The overall hydration shell consists of similar to 6 water molecules surrounding the hydrogen peroxide molecule. The analysis of the hydrogen bond dynamics verified the presence of strong hydrogen bonds compared to pure water, thus confirming the stabilization of hydrogen peroxide in aqueous solution. (C) 2011 Elsevier B.V. All rights reserved.

关键词： aortic annulus   computed tomography   transcatheter aortic valve implantation  

摘要： Objectives The purpose of this study was to assess deformation dynamics and in vivo mechanical properties of the aortic annulus throughout the cardiac cycle. Background Understanding dynamic aspects of functional aortic valve anatomy is important for beating-heart transcatheter aortic valve implantation. Methods Thirty-five patients with aortic stenosis and 11 normal subjects underwent 256-slice computed tomography. The aortic annulus plane was reconstructed in 10% increments over the cardiac cycle. For each phase, minimum diameter, ellipticity index, cross-sectional area (CSA), and perimeter (Perim) were measured. In a subset of 10 patients, Young's elastic module was calculated from the stress-strain relationship of the annulus. Results In both subjects with normal and with calcified aortic valves, minimum diameter increased in systole (12.3 +/- 7.3% and 9.8 +/- 3.4%, respectively;p < 0.001), and ellipticity index decreased (12.7 +/- 8.8% and 10.3 +/- 2.7%, respectively;p < 0.001). The CSA increased by 11.2 +/- 5.4% and 6.2 +/- 4.8%, respectively (p < 0.001). Perim increase was negligible in patients with calcified valves (0.56 +/- 0.85%;p < 0.001) and small even in normal subjects (2.2 +/- 2.2%;p = 0.01). Accordingly, relative percentage differences between maximum and minimum values were significantly smallest for Perim compared with all other parameters. Young's modulus was calculated as 22.6 +/- 9.2 MPa in patients and 13.8 +/- 6.4 MPa in normal subjects. Conclusions The aortic annulus, generally elliptic, assumes a more round shape in systole, thus increasing CSA without substantial change in perimeter. Perimeter changes are negligible in patients with calcified valves, because tissue properties allow very little expansion. Aortic annulus perimeter appears therefore ideally suited for accurate sizing in transcatheter aortic valve implantation. (J Am Coll Cardiol 2012;59: 119-27) (C) 2012 by the American College of Cardiology Foundation

关键词： ELECTRONIC excitation   QUANTUM theory   MOLECULAR dynamics   COMPUTER simulation   FIELD theory (Physics)   ELECTRONIC structure   ENERGY transfer  

摘要： The ab initio quantum mechanical charge field molecular dynamics simulation technique was applied for the first time to an electronically excited system, namely hydrated Li(I). This approach does not only provide data for the influence of electronic excitation on structure and composition of the hydrate, but also leads to a spectrum for the excitation band including rotational, translational and vibrational energy transfers. The first excitation band for Li(I) in water peaks at 13.1 eV. The excitation leads to reduced coordination numbers of first and second hydration shell and stabilises the first and labilises the second shell. (C) 2011 Elsevier B. V. All rights reserved.

关键词： Nano-zinc oxide   EPDM   Cure kinetics   Morphology   Mechanical properties  

摘要： The morphology, cure behavior and mechanical properties of various ethylene-propylene-diene-monomer (EPDM) rubber containing zinc oxide nanoparticles (nZnO), were investigated comparing to those of EPDM with conventional zinc oxide (cZnO). The X-ray diffraction (XRD) analyses revealed that nZnO had lower grain sizes with respect to cZnO. The field-emission scanning electron microscopy (FESEM) studies showed that unlike the conventional system, the formation of large size ZnO agglomerates was discouraged for nZnO filled systems. The rheological characterization showed that replacing cZnO with lower content of nZnO in the recipes resulted in lower cure time and higher crosslinking density which further supported by Fourier transform infrared spectroscopy (FTIR) and swelling tests. The cure kinetic analysis showed that the activation energy of curing reaction was remarkably reduced upon the decrease of ZnO particle sizes. Therefore, we could interestingly show the improvement in cure characteristics particularly associated with the superior mechanical properties of nZnO-activated EDPM systems. (C) 2011 Elsevier B.V. All rights reserved.

关键词： 动力学模拟   机械负载   电动系统  

摘要： 针对基于电动系统的机械负载动力学模拟控制问题,给出了控制系统的总体结构,建立了驱动电机矢量控制的数学模型和负载模拟系统的动力学方程。采用带转矩反馈的控制算法对负载模拟电机进行控制。给出了驱动电机和负载模拟电机的参数,仿真实验中,分别对线性和非线性机械负载进行模拟,仿真结果表明负载模拟电机能够准确跟踪期望的转矩,证实了控制的有效性。

关键词： 机械手臂系统   动力学分析   摩擦补偿   精度控制  

摘要： 摩擦是大多数机械系统中不可避免的一种现象,由于摩擦会带来稳态误差,影响系统的动态特性以及系统精度的提高,摩擦问题已经成为当前研究的热点。在机械手臂系统中,关节摩擦严重影响了机械手臂系统性能的提高,使得手臂在运动过程中产生误差。低速时摩擦的非线性环节对机械手臂系统的影响尤为突出,因此必须采取合理的措施消除关节摩擦带来的影响。\n 本文将减小关节摩擦对机械系统的影响作为主要目的,首先对摩擦模型进行了讨论,并选定LuGre摩擦模型为研究重点;接着对磨削机械手臂的运动学,工作空间以及动力学进行了研究;分析了关节摩擦在机械系统中的影响,并采用自适应控制对关节摩擦进行补偿。并将该理论应用于机械手臂系统中,针对磨削机械手臂运动过程中的关节摩擦现象进行了自适应补偿研究,建立了机械手臂摩擦控制原型系统。\n 本文的主要研究内容如下:\n (1)结合摩擦学领域的最新成果,对几种重要的摩擦模型进行研究。对比分析不同摩擦模型的优点和缺点,选取LuGre摩擦模型作为文章的研究对象,并实现了LuGre摩擦模型在预滑阶段和滑动阶段的仿真。\n (2)推导了六自由度磨削机械手臂的运动学模型,并对其工作空间进行了求解;采用拉格朗日方法建立了磨削机械手臂的动力学模型,并重点分析了关节摩擦对磨削机械手臂的影响情况。\n (3)从理论上证明了LuGre摩擦的自适应摩擦补偿方法能够消除关节摩擦对机械手臂系统的影响,通过仿真实验对比分析了采用PID控制、采用自适应库仑摩擦补偿和采用自适应 LuGre摩擦补偿等方法对机械手臂的影响情况,验证了使用LuGre自适应摩擦补偿方法的实用性。\n (4)借助Visual C++、MATLAB、UG等软件完成了磨削机械手臂仿真原型系统的开发,实现了自动化建模,装配和仿真等功能,为机械手臂的设计提供了理论基础。

关键词： 风力机桨叶   机械动力学特性   风力发电机   覆冰厚度   评价指标  

摘要： 风力机桨叶是风力发电机组的关键部件,桨叶的结构设计是整个风力机组设计的基础。风力发电机组运行于大气中,风机的桨叶工作环境特别恶劣,受到气动载荷、重力载荷和惯性载荷的叠加作用,而且长期不停的工作,风力发电机的桨叶损坏率较高,桨叶损坏对风力发电造成了很大的经济损失。因此对风力机桨叶进行机械动力学特性测试和分析,对提高风力发电整体效率和节约风力发电成本,进一步促进风力发电是很有必要的。\n 本文采用理论计算和实验研究相结合的方法,以实验研究为主对风力机桨叶机械动力学特性进行研究分析,针对风力机桨叶进行了模态测试实验、静力测试实验和覆冰状态下的桨叶模态测试实验。\n 首先介绍了以风力机桨叶振动特性分析实验装置实验台待测桨叶为例,在Solidworks软件中建立风力机桨叶实体模型,应用有限元软件ANSYS对静止状态下的桨叶进行振动模态分析和静力分析,得出了风力机桨叶的固有频率和振型,并获得了风力机桨叶的主要承力部件,为后续的实验研究打下了重要的理论基础。\n 然后,利用实验室建成的风力机桨叶振动特性分析装置及其主要实验设备,分别设计了风力机桨叶模态测试和静力测试实验系统和实验方法,采用不测力法、测力法和共振法对风力机桨叶进行了实验模态测试,得出了风力机桨叶模态参数。利用液压加载装置对桨叶施加不同载荷,获得了桨叶在不同载荷作用下的形变特性,通过实验和有限元静力分析结果验证了叶根为风力机桨叶的主要承力部件。\n 最后,在模态测试和静力测试实验的基础上,搭建了用于风力机桨叶覆冰实验的实验台系统,在人工环境实验室中模拟大气结冰环境,监测不同覆冰厚度和温度下对桨叶覆冰机械动力学特性的影响,得出覆冰厚度和温度对桨叶固有特性的影响关系曲线。同时,建立了基于多传感器信息的覆冰厚度评价方法,获得了风力机桨叶覆冰厚度和评价指标之间定量关系,从而将覆冰厚度评价公式化、实用化。本文针对风力机桨叶机械动力学特性研究能够促进全面深入的了解风力机桨叶的结构特性,从而对我国风机制造的发展起到积极的作用。