标准号: LY/T 2401-2014

摘要： 本标准规定了以汽油机为动力的手推式草坪修边机(以下简称修边机)的术语和定义、型号编制方法、基本参数、技术要求及试验方法、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、配备刚性切割装置的手推式草坪修边机,不适用于便携手持式修边机,也不适用于柔性切割装置的修边机。

关键词： Chain composition effect   Molecular dynamics simulation   Mechanical property of polymer gel  

摘要： Polymer gels, defined either from the structural point of view (structural gel) or by their mechanical properties (mechanical gel), are ubiquitous in our daily life. In our previous work U. Phys. Chem. B, 2011, 115, 11345), we reported that, the mechanical gel formed by strong solvophobic ABA block copolymers with fixed chain compositions shows a strong mechanical response, which meant the formed gel had a high modulus. In this work, we focus on the effect of chain composition on the relationship between structural gel and mechanical gel, where the chain length of block copolymer is lower than its entanglement chain length for simplicity. Our results show that the chain composition has a great effect on the mechanical response of the ABA copolymer solutions with a strong solvophobicity. On the other hand, for the structural gel formed by weak solvophobic block polymers, we do not find any strong mechanical responses even we change the chain composition in a wide range. Moreover, we find three typical gelation processes, companied with three kinds of different mechanical responses. These results may provide us an effective method to control the mechanical property of a polymer gel as expected. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Nanostructures   Mechanical testing   Molecular dynamics   Mechanical properties  

摘要： Calcium silicate hydrate (C-S-H) is the most important binding phase of cement paste and can determine the mechanical properties of cementitious material. The multi-scale nature of C-S-H gel brings about challenges in interpreting the mechanical properties of C-S-H. C-S-H models at the nano scales are commonly formulated by the aggregation of colloids that consist of layered molecular structures. In this study, the mechanical properties of C-S-H were investigated at the molecular level (similar to 5 nm). Uniaxial tension testing in the x, y, z directions was applied to the layered structure of C-S-H. The structural difference in the layer leads to heterogeneous mechanical properties in three directions. Particularly in the z direction, the C-S-H layer connected by H-bonds and Ca2+, has the weakest tensile strength. Resulting from the investigation, it can be concluded that the simulation can provide molecular insights into the linkage between molecular and larger scale structures. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Silica   Doping   Internal friction   Elastic moduli   Molecular dynamics  

摘要： Gravitational wave detectors and other precision measurement devices are limited by the thermal noise in the oxide coatings on the mirrors of such devices. We have investigated the mechanical loss in amorphous oxides by calculating the internal friction using classical, atomistic molecular dynamics simulations. We have implemented the trajectory bisection method and the non-local ridge method in the DL-POLY molecular dynamics simulation software to carry out those calculations. These methods have been used to locate the local potential energy minima that a system visits during a molecular dynamics trajectory and the transition state between any two consecutive minima. Using the numerically calculated barrier height distributions, barrier asymmetry distributions, relaxation times, and deformation potentials, we have calculated the internal friction of pure amorphous silica and silica mixed with other oxides. The results for silica compare well with experiment. Finally, we use the numerical calculations to comment on the validity of previously used theoretical assumptions. (C) 2014 AIP Publishing LLC.

关键词： Catalytic Domain   Crystallography, X-Ray   Dimethylallyltranstransferase/chemistry   Dimethylallyltranstransferase/physiology   Magnesium/chemistry   Magnesium/metabolism   Molecular Dynamics Simulation   Novobiocin/analogs & derivatives   Novobiocin/chemistry   Phenylpyruvic Acids/chemistry   Phenylpyruvic Acids/chemistry   Prenylation/physiology   Quantum Theory   Signal Transduction   Static Electricity   Static Electricity  

摘要： Understanding the mechanism of prenyltransferases is important to the design of engineered proteins capable of synthesizing derivatives of naturally occurring therapeutic agents. CloQ is a Me-independent aromatic prenyltransferase (APTase) that transfers a dimethylallyl group to 4-hydroxyphenylpyruvate in the biosynthetic pathway for clorobiocin. APTases consist of a common ABBA fold that defines a beta-barrel containing the reaction cavity. Positively charged basic residues line the inside of the beta-barrel of CloQ to activate the pyrophosphate leaving group to replace the function of the Mg2+ cofactor in other APTases. Classical molecular dynamics simulations of CloQ, its E281G and F68S mutants, and the related NovQ were used to explore the binding of the 4-hydroxyphenylpyruvate (4HPP) and dimethylallyl diphosphate substrates in the reactive cavity and the role of various conserved residues. Hybrid quantum mechanics/molecular mechanics potential of mean force (PMF) calculations show that the effect of the replacement of the Mg2+ cofactor with basic residues yields a similar activation barrier for prenylation to Me-dependent APTases like NphB. The topology of the binding pocket for 4HPP is important for selective prenylation at the ortho position of the ring. Methylation at this position alters the conformation of the substrate for O-prenylation at the phenol group. Further, a two-dimensional PMF scan shows that a "reverse" prenylation product may be a possible target for protein engineering.

关键词： QUANTUM mechanics   DENSITY matrices   RENORMALIZATION group   GAUSSIAN distribution   CONDENSED matter  

摘要： We discuss the semiclassical and classical character of the dynamics of a single spin 1/2 coupled to a bath of noninteracting spins 1/2. On the semiclassical level, we extend our previous approach presented in D. Stanek, C. Raas, and G. S. Uhrig, Phys. Rev. B 88, 155305 (2013) by the explicit consideration of the conservation of the total spin. On the classical level, we compare the results of the classical equations of motions in absence and presence of an external field to the full quantum result obtained by density-matrix renormalization (DMRG). We show that for large bath sizes and not too low magnetic field the classical dynamics, averaged over Gaussian distributed initial spin vectors, agrees quantitatively with the quantum-mechanical one. This observation paves the way for an efficient approach for certain parameter regimes.

关键词： ACTIN   RHEOLOGY (Biology)   GOLGI apparatus   IN vitro studies   CELL membranes   OPTICAL tweezers   MUSCLE contraction   CORRELATION (Statistics)  

摘要： Background: In vitro studies have shown that physical parameters, such as membrane curvature, tension, and composition, influence the budding and fission of transport intermediates. Endocytosis in living cells also appears to be regulated by the mechanical load experienced by the plasma membrane. In contrast, how these parameters affect intracellular membrane trafficking in living cells is not known. To address this question, we investigate here the impact of a mechanical stress on the organization of the Golgi complex and on the formation of transport intermediates from the Golgi complex. Results: Using confocal microscopy, we visualize the deformation of Rab6-positive Golgi membranes applied by an internalized microsphere trapped in optical tweezers and simultaneously measure the corresponding forces. Our results show that the force necessary to deform Golgi membranes drops when actin dynamics is altered and correlates with myosin II activity. We also show that the applied stress has a long-range effect on Golgi membranes, perturbs the dynamics of Golgi-associated actin, and induces a sharp decrease in the formation of Rab6-positive vesicles from the Golgi complex as well as tubulation of Golgi membranes. Conclusions: We suggest that acto-myosin contractility strongly contributes to the local rigidity of the Golgi complex and regulates the mechanics of the Golgi complex to control intracellular membrane trafficking.

关键词： 多级行星传动   模块化   动力学响应  

摘要： 多级行星传动系统的动力学研究多采用整体式建模方法,此种方法不便于通过动态性能分析快速选取传动方案,而且模型不具有通用性,传动形式改变,需要重建系统动力学模型。为克服整体式建模方法的缺点,提出了模块化思想,将多级行星传动系统划分为4个分级子模块,综合考虑啮合刚度、阻尼和行星轮支撑刚度等因素,建立了各级子模块的动力学模型,通过各级模块的集成,得到了多级行星传动系统非线性动力学方程。以空间机械臂关节用多级行星传动系统为例,通过调用各级模块,形成4级行星传动系统动力学微分方程组,对其进行数值求解,得到了系统的时域及频域响应特性。通过与整体式建模方法所得响应结果进行对比,验证了模块化建模方法的同一性和有效性。

关键词： 自动处理装置   半自动化   工程机械   中石化   猫道   石油   机械手臂   自动化程度  

摘要： 动力猫道装置是指在钻井、修井过程中,将井场钻具自动送上和放下钻台的装置。动力猫道可与钻杆自动处理装置、二层台钻具自动排放装置、铁钻工、气动卡瓦等联合使用,实现井口钻杆操作全自动化或半自动化,大大提高钻井工作效率,增强施工的安全性。目前,国外的动力猫道主要有固定式、举升式、机械手臂等3种。固定式动力猫道适用于低钻台或小型钻机,如修井机和2 000m以下的小钻机,缺点是钻具与V形槽之间的摩擦大,对钻具的保护不够。举升式动力猫道比较适用于我国陆地大型钻机,但国外设计的尺寸比较大，不符合我国对运输尺寸的要求。机械手臂的优点是处理能力强、速度快、自动化程度高，缺点是不易维修、成本高、安装复杂、不宜频繁拆装和运输。为此，中石化石油工程机械有限公司研制了适合国内移动运输的自动化动力猫道装置。

关键词： 振动与波   变频动力吸振器   振动分析   飞轮振动   机械变频  

摘要： 为拓宽动力吸振器的工作频带,以满足卫星飞轮振动控制的需求,提出了一种新型的基于机械变频技术的动力吸振器结构,对该变型结构的工作原理进行理论分析和实验研究后表明,机械变频装置的引入,可以有效地将动力吸振器的工作频带拓宽到20 Hz。由此,能够有效抑制飞轮安装板的对于飞轮振动的响应幅值,频率调节范围增大;而且结构紧凑,可靠性高。这一改进的动力吸振技术为卫星飞轮振动控制提供了新的研究方法。