关键词： Cycling   Cadence   Mechanics   Electromechanical delay   Relative phase   EMG  

摘要： The purpose of this study was to examine the activation dynamics hypothesis, which states that, in cycling, the pattern between muscle activity and crank position shifts in regard to its angle in the crank cycle with increasing cadence to maintain invariant positioning of the mechanical output. We measured surface EMG of six muscles, and by means of force measurements at the crank and inverse dynamics calculated hip, knee, and ankle joint dynamics during cycling at five cadences (60-100 rpm) at 75% of maximal power in trained cyclists. The joint dynamics (net muscle moment and power) showed a consistent positive phase shift with increasing cadence. The phase shift in muscle activation patterns was highly variable amongst subjects and was, on average, close to zero. Our results are in contradiction with the activation dynamics hypothesis. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： MALDI   In-source decay   Post-source decay   Peptide dissociation   Basic residue effect   Dissociation efficiency   Dissociation kinetics and mechanism  

摘要： With matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry, total abundance of product ions formed by dissociation inside (in-source decay, ISD) and outside (post-source decay, PSD) the source was measured for peptide ions [Y (5) X + H](+), [XY (5) + H](+), [Y (2) XY (3) + H](+), and [XY (4) X + H](+) (X = tyrosine (Y), histidine (H), lysine (K), and arginine (R) with H for the ionizing proton). alpha-Cyano-4-hydroxycinammic acid was used as matrix. Product abundance became smaller in the presence of basic residues (H, K, and R), in the order Y > H a parts per thousand K > R. In particular, product abundances in ISD of peptide ions with R were smaller than those with H or K by an order of magnitude, which, in turn, were smaller than that for [Y (6) + H](+) by an order of magnitude. Product abundance was affected by the most basic residue when more than one basic residue was present. A kinetic explanation for the data was attempted under the assumption of quasi-thermal equilibrium for peptide ions in MALDI plume which undergoes expansion cooling. Dramatic disparity in product abundance was found to arise from small difference in critical energy and entropy. Results indicate similar transition structures regardless of basic residues present, where the ionizing proton keeps interacting with a basic site. Further implication of the results on the dissociation mechanism along b-y channels is discussed.

关键词： nickel hydroxide   carbon dioxide-bicarbonate conversion   reaction mechanism  

摘要： Carbon dioxide may react with free or metal-bound hydroxide to afford products containing bicarbonate or carbonate, often captured as ligands bridging two or three metal sites. We report the kinetics and probable mechanism of an extremely rapid fixation reaction mediated by a planar nickel complex [Ni-II(NNN)(OH)](1-) containing a tridentate 2,6-pyridinedicarboxamidate pincer ligand and a terminal hydroxide ligand. The minimal generalized reaction is M-OH + CO2 -> M-OCO2H;with variant M, previous rate constants are less than or similar to 10(3) M-1 s(-1) in aqueous solution. For the present bimolecular reaction, the (extrapolated) rate constant is 9.5 x 10(5) M-1 s(-1) in N, N'-dimethylformamide at 298 K, a value within the range of k(cat)/K-M approximate to 10(5)-10(8) M-1 s(-1) for carbonic anhydrase, the most efficient catalyst of CO2 fixation reactions. The enthalpy profile of the fixation reaction was calculated by density functional theory. The initial event is the formation of a weak precursor complex between the Ni-OH group and CO2, followed by insertion of a CO2 oxygen atom into the Ni-OH bond to generate a four center Ni(eta(2)-OCO2H) transition state similar to that at the zinc site in carbonic anhydrase. Thereafter, the Ni-OH bond detaches to afford the Nid.1-OCO2H_ fragment, after which the molecule passes through a second, lower energy transition state as the bicarbonate ligand rearranges to a conformation very similar to that in the crystalline product. Theoretical values of metric parameters and activation enthalpy are in good agreement with experimental values [.H 3.2d5_ kcal/ mol]. 3

关键词： Stream ecology   Community dynamics   Bayesian inference   Sensitivity analysis   Benthos   Invertebrates   Periphyton  

摘要： To evaluate the role of the benthic community within headwater stream ecosystems, it is crucial to understand the mechanisms of the processes dominating their turnover rates and temporal dynamics. To analyze the benthic community dynamics of an intermittent Mediterranean stream (Fuirosos, Spain), we developed a mechanistic model that describes the most important ecosystem components (five functional feeding groups of invertebrates, periphyton, and benthic organic matter) under consideration of important transformation processes. The model is an extension of that developed for application to the prealpine River Sihl (Switzerland). A combination of prior knowledge from the literature and information from field observations within a Bayesian framework is used to constrain plausible ranges of the estimated model parameters and to evaluate the uncertainty of the model outcome. The Bayesian inference resulted in a realistic description of most of the main features of the system, offered insights into the degree of information the data contains about model parameters, and also made it possible to quantify the dependence structure of the parameter estimates. Local and global sensitivity analyses revealed that rate parameters for growth and death of invertebrate functional feeding groups are most influential on the model results and additional information on these parameters would be most helpful to reduce output uncertainty. The study clearly points out the importance of organic matter dynamics, as allochthonous organic matter is the main energy source in this Mediterranean headwater stream. Hydrological disturbances of the system such as droughts and floods lead to complex colonization patterns which would require additional data to support a more detailed description by an extended model. Furthermore, the study shows that it is possible to deal with a complex ecological model with eight state variables and more than 60 parameters in a Bayesian framework. (C) 2010 Elsevier

关键词： Sintering   Activation energy   TMA   Kinetics   Nanocrystalline  

摘要： The paper details the results of sintering kinetics studies conducted on nanocrystalline Mo-30 wt.% W alloy powders prepared through mechanical alloying route. Both, constant rate of heating method as well as Stepwise Isothermal Dilatometry (SID) technique were used for studying the sintering kinetics. Measured step isothermal shrinkage data were analyzed by Mekipritti-Meng method. The shrinkage data was found to fit well with the rate equation proposed in this method and its validity was established for mechanically alloyed systems. Kinetic parameters were evaluated and sintering was found to occur through two major mechanisms operative successively, which are grain boundary diffusion and lattice diffusion with corresponding energies of activation as 230 kJ/mol and 480 kJ/mol, respectively. The results have been well supported by micro structural evaluation of specimens at different stages of sintering. (C) 2010 Elsevier B.V. All rights reserved.

关键词： 三自由度机械手   动力学分析   PD控制   无源重力补偿  

摘要： 设计一种在核环境下工作的螺栓拆卸机械手,该机械手末端执行器上装载了液压驱动的拆卸螺栓的扳手头,机械手可驱动扳手头在空间实现三自由度运动。建立、求解其动力学方程,并分析其动力学性能;通过Laplace变换建立机械手的传递函数模型,设计相应的补偿重力影响的PD控制系统。建立该螺栓拆卸机械手的联合仿真模型,进行动力学仿真。仿真结果为机构系统优化设计和样机制造提供参考。

关键词： 压力机   动力学分析   复数矢量法   三维模型  

摘要： 机械式压力机作为锻压机械的一个类别,广泛应用于石化、航空、军工、航天等行业,同时在民品制造领域中有广阔的用武之地。当转速不同,工作环境不同,压力机的受力和运动规律也会不同,这就要求压力机的传动系统的结构必须为最优结构。在设计过程中,锻压机械的动力学性能如何一直是设计过程中的一个难点,也是设计人员在设计过程中,必须解决的一个问题。尤其是对于多连杆机械式压力机,由于多连杆机械式压力机传动系统的结构更为复杂,因此对其进行动力学研究对于设计的成功性来说就显得尤为重要。\n 本文针对多连杆机械式压力机,根据复数矢量法采用模块化方法构建其传动机构数学模型,得到多连杆机械式压力机传动机构滑块的运动方程;根据运动方程,利用仿真软件Matlab得出滑块的位移、速度、加速度曲线,然后与曲柄连杆机构压力机滑块的位移、速度、加速度曲线进行比较,得到多连杆机械式压力机的优点;再根据动态静力学方法对传动机构进行动力学逆问题研究,建立其动态静力平衡方程;然后对多连杆机械式压力机进行动力学正问题研究,建立其等效动力学模型,并根据等效动力学模型建立其等效动力学方程;使用三维软件Soldworks构建传动机构的三维模型,应用动力学分析软件Adams对模型进行动力学正问题分析,对比两种动力学正问题研究方法,得出结论,为企业设计制造多连杆机械式压力机提供理论依据。

关键词： 旋转机械   滑动轴承   微小间隙   流体动力试验   Navier-Stokes方程   高阶有限差分法   数值求解  

摘要： 随着旋转机械向大型化和高参数方向发展,旋转机械微小间隙内流体激振力所产生的自激振动成为影响转子系统稳定性的重要因素之一。由滑动轴承间隙与密封间隙内流体产生的流体激振将直接影响设备运行的可靠性和安全性,成为影响大容量机组设备安全稳定运行的重大隐患。开展滑动轴承与密封间隙内流体动力特性理论与试验等方面研究,具有重要的理论意义和工程价值。\n Navier-Stokes方程是研究流体特性的理论基础,DQ方法等价于高阶有限差分法。本文应用局部DQ方法对流体力学方程进行了数值求解。首先以台阶流为求解模型,应用局部迎风DQ方法对原始变量的N-S方程进行了数值求解,建立了基于局部迎风DQ方法的复杂台阶流求解模型。在此研究基础上,提出了本质和自然边界条件的处理方法,分析了支持域大小、不同基函数、边界条件、迎风机制等因素对求解结果的影响。Reynolds方程是研究滑动轴承动力特性的理论基础,本文进一步将局部DO方法引入到滑动轴承动力特性求解模型中,应用局部DQ方法对滑动轴承静态压力及扰动压力的Reynolds进行了数值求解,建立了基于局部DQ方法的滑动轴承动力特性系数求解模型。\n 传统滑动轴承研究大多建立在Reynolds方程基础上,边界条件的选取对Reynolds方程的求解影响较大,且传统滑动轴承求解模型均为单相流模型。大量试验结果表明,滑动轴承负压区内油和气混合存在。因此为了更准确研究轴承特性,本文将CFD两相流数值计算应用到滑动轴承求解模型中,建立了滑动轴承两相流求解模型,该模型无需设定油膜破裂边界条件且更能准确模拟滑动轴承流场特性。为了求解滑动轴承动力特性系数,本文研究了CFD动网格技术,将CFD动网格技术应用于求解滑动轴承刚度、阻尼系数,建立了CFD两相流滑动轴承动力特性求解模型。本文分析了负压区内油膜气穴分布及汽化比例的影响因素,研究了两相流对滑动轴承静力及动力特性的影响。\n 本文研究了CFD旋转坐标系技术,应用旋转坐标系将非定常流动问题转化成定常问题,建立迷宫密封动力特性求解模型,对密封流场及密封动力特性系数进行求解研究。在CFD数值计算的基础上,分析了密封气流激振力的机理。研究表明,密封内流体的螺旋形流动效应是产生密封气流激振力的重要原因。传统密封型式均为轴向密封,因此气流激振问题难以得到根本解决。本文提出新型“径向环形密封”思想,与传统密封不同,密封的布置型式由轴向调整为径向,可以有效减小密封内气流的螺旋形效应,提高密封稳定性。数值计算结果表明,与传统密封相比,新型密封泄漏量少,气流力小。\n 本文设计搭建多功能密封试验台,可以对不同型式密封的静态及动态特性进行试验研究,利用密封试验台开展刷式密封泄流特性及磨损特性的静态性能及迷宫密封动态气流力识别的试验研究。传统密封气流力识别模型气缸只能做平动,一旦气缸出现偏摆则模型失效。本文提出了气缸任意运动状态下的密封气流力试验识别方法,引入转子动力学双平面平衡理论,将多级密封内的气流力等效到两个端面上,建立了多级密封气流力等效试验识别模型。通过气缸共振的方法放火气流力影响,提高识别精度,通过更换不同刚度的弹簧来实现多转速下的试验。本文所建立的密封动态气流力试验识别模型考虑了气缸偏摆等情况,是对传统识别方法的扩充。试验结果表明,随着进气压力增加,气流力增大,两者间近似为线性关系。升速过程中气流力的变化主要是由于振动变化所引起。随着振动的增加,气流力增大。气流力所作功量与气流力和振动之间的相位角差关系较大,相位差为90°时,作功量最大。

关键词： 农机产品   柴油机   轮式拖拉机   常州市   产品名单   江苏省   动力机械  

关键词： 劳动力转移   农业机械化   农业劳动生产率   农业生产   手工工具   科学技术   生产方式   自然力  

摘要： 农业生产中使用机器替代手工工具，用自然力来代替人力，以自觉运用科学技术来代替传统经验生产，克服了人的体力、器官的限制和经验的局限，必然大大提高劳动生产率。在改变劳动资料的同时必将改变劳动办法，即改革生产方式，这是提高农业劳动生产率的根本途径。