关键词： nanotechnology   scanning probe microscopy   single-molecule analysis   virus mechanics  

摘要： In this study we test the hypothesis that mechanically elastic regions in a virus particle (or large biomolecular complex) must coincide with conformationally dynamic regions, because both properties are intrinsically correlated. Hypothesis-derived predictions were subjected to verification by using 19 variants of the minute virus of mice capsid. The structural modifications in these variants reduced, preserved, or restored the conformational dynamism of regions surrounding capsid pores that are involved in molecular translocation events required for virus infectivity. The mechanical elasticity of the modified capsids was analyzed by atomic force microscopy, and the results corroborated every prediction tested: Any mutation (or chemical cross-linking) that impaired a conformational rearrangement of the pore regions increased their mechanical stiffness. On the contrary, any mutation that preserved the dynamics of the pore regions also preserved their elasticity. Moreover, any pseudo-reversion that restored the dynamics of the pore regions (lost through previous mutation) also restored their elasticity. Finally, no correlation was observed between dynamics of the pore regions and mechanical elasticity of other capsid regions. This study (i) corroborates the hypothesis that local mechanical elasticity and conformational dynamics in a viral particle are intrinsically correlated;(ii) proposes that determination by atomic force microscopy of local mechanical elasticity, combined with mutational analysis, may be used to identify and study conformationally dynamic regions in virus particles and large biomolecular complexes;(iii) supports a connection between mechanical properties and biological function in a virus;(iv) shows that viral capsids can be greatly stiffened by protein engineering for nanotechnological applications.

关键词： friction   Force   MACROSCOPIC   Theoretical Study   Mechanical Vibration   geometry   external drives   Equations of motion   WELLS   PHENOMENON  

摘要： The suppression of friction between sliding objects, modulated or enhanced by mechanical vibrations, is well established. However, the precise conditions of occurrence of these phenomena are not well understood. Here we address these questions focusing on a simple spring-block model, which is relevant to investigate friction both at the atomistic as well as the macroscopic scale. This allows us to investigate the influence on friction of the properties of the external drive, of the geometry of the surfaces over which the block moves, and of the confining force. Via numerical simulations and a theoretical study of the equations of motion, we identify the conditions under which friction is suppressed and/or recovered, and we evidence the critical role played by surface modulations and by the properties of the confining force.

关键词： free radicals   liquid structure   liquid theory   molecular dynamics method   organic compounds   polarisability   solutions   solvation  

摘要： An efficient methodology is presented to improve the QM description of solute-solvent interactions in condensed systems within the quantum mechanical/molecular mechanical (QM/MM) framework. It is based on the recently developed new treatment of the adaptive multiscale QM/MM-MD method, i.e., the number-adaptive multiscale method that includes the close solvent molecules around the solute into QM region and enables them to flow across the boundary between the QM and MM regions. We have applied it to zwitterionic (ZW) glycine molecule in aqueous solution, and investigated the hydration structures and charge distributions, which are compared with those by the standard (SD) method that only a solute glycine molecule is treated quantum mechanically. It is shown that the total energy and temperature are satisfactorily conserved, providing reasonable hydration numbers and induced polarization of ZW glycine molecule in aqueous solution. In contrast, the SD method is found overestimated the hydration numbers in comparison to the experimental ones due to the inappropriate expression of the electron distribution. In conclusion, the present method should become quite useful as the quantitative statistical sampling method to study various chemical phenomena in condensed systems. (C) 2012 American Institute of Physics. [http://***/10.1063/1.4732307]

关键词： Transition metal carbides   elastic properties   lattice dynamical properties   first-principles   AgC   AuC  

摘要： Based on density functional theory, we have studied the structural stability, elastic, mechanical and lattice dynamical properties of AgC and AuC compounds for various structures: NaCl (B1), CsCl (B2), ZnS (B3), wurtzite (B4), WC (B-h), NiAs (B8(1)) and CdTe. Generalized gradient approximation has been used for modeling exchange-correlation effects. The second-order elastic constants and related polycrystalline properties (bulk modulus, shear modulus, Young's modulus, Poisson's ratio, Debye temperature and sound velocities) have been calculated and discussed. We have also calculated phonon dispersion and phonon density of states of these compounds in all considered structures. According to the results, we found that, AgC compound is mechanically and dynamically stable in B8(1), B1 and B4 structures. Our results indicate that B81 and B3 are the candidate stable structures energetically, mechanically and dynamically for AgC and AuC compounds, respectively.

关键词： 空气动力   动力机械   项目投资管理   销售服务   新能源   高科技   集团化   进出口  

摘要： 祥天科立泰空气动力机械有限公司是一家专业从事高科技新能源，以“空气能源”为核心，“空气动力”机械高端制造，研发生产销售服务，项目投资管理，货物技术进出口等集团化综合性的企业。

关键词： 中国航天科工集团   机械测试   内蒙   固体火箭发动机   试验基地   研究院  

摘要： 中国航天科工集团第六研究院六0一所（又名内蒙航天动力机械测试所）创建于1965年，是我国第一座大型固体火箭发动机地面试验基地。

关键词： 课程教学   热能动力机械测控技术   MATLAB软件  

摘要： 文章主要是针对我校热能与动力工程专业学生学习测控技术课程过程中遇到的问题进行了探讨。结合MATLAB软件数值计算和图形处理功能,不断改进教学方法和手段。将MATLAB软件应用于热能动力机械测控技术课程理论与实践教学,不仅提高了学生学习主动性和积极性,而且培养了学生的创新能力,逻辑思维能力,以及工程应用能力。

关键词： Lipids   Interfaces   QM/MM   Molecules   Membranes  

摘要： Biomolecular dynamics studies using a QM/MM approach have been largely used especially to study enzymatic reactions. However, to the best of our knowledge, the very same approach has not been used to study the water/membrane interface using a quantum mechanical treatment for the lipids. Since a plethora of biochemical processes take place in this region, we believe that it is of primary importance to understand, at the level of molecular orbitals, the behavior of a drug in such an odd environment. In this work, we take advantage of an integration of the CPMD and the GROMACS code, using the Car- Parrinello method, to treat the benzocaine local anesthetic as well as two of the membrane lipids and the GROMOS force field to treat the remaining lipids and the water molecules.

关键词： Aluminium alloys   Amorphous   Crystallization kinetics   Mechanical properties  

摘要： The crystallization kinetics and mechanical properties of Al86Ni6Y4.5Co2La1.5 metallic glass powder have been investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and nanoindentation. The first crystallization stage of the Al86Ni6Y4.5Co2La1.5 glass powder is identified to be a surface nucleation and one-dimensional growth process while the second and third crystallization stages are characterized by volume nucleation but followed by one-dimensional growth and two-dimensional growth, respectively. The hardness and elastic modulus show opposite trends on crystallization;they are both sensitive to the precipitation of fcc-Al, growth of fcc-Al and precipitation of complex intermetallic phases. The changes of hardness and elastic modulus of the Al86Ni6Y4.5Co2La1.5 metallic glass powder with crystallization are discussed. (C) 2012 Elsevier B.V. All rights reserved.

关键词： IAPP   Aggregation   Sequence analysis   Molecular dynamics   Fibril   Type II diabetes  

摘要： A collective approach of sequence analysis, phylogenetic tree and in silico prediction of amyloidogenecity using bioinformatics tools have been used to correlate the observed species-specific variations in IAPP sequences with the amyloid forming propensity. Observed substitution patterns indicate that probable changes in local hydrophobicity are instrumental in altering the aggregation propensity of the peptide. In particular, residues at 17th, 22nd and 23rd positions of the IAPP peptide are found to be crucial for amyloid formation. Proline25 primarily dictates the observed non-amyloidogenecity in rodents. Furthermore, extensive molecular dynamics simulation of 0.24 mu s have been carried out with human IAPP (hIAPP) fragment 19-27, the portion showing maximum sequence variation across different species, to understand the native folding characteristic of this region. Principal component analysis in combination with free energy landscape analysis illustrates a four residue turn spanning from residue 22 to 25. The results provide a structural insight into the intramolecular beta-sheet structure of amylin which probably is the template for nucleation of fibril formation and growth, a pathogenic feature of type II diabetes. (c) 2012 Elsevier B.V. All rights reserved.