关键词： 月球探索   柔性取样器   柔性动力学   模态分析  

摘要： 针对月球表取任务,本文提出一种由三个刚性臂和一个柔性臂组合、结构新颖的月壤取样器。该取样器具有收缩体积小、工作空间大和重量轻的优点。重点描述了柔性臂的驱动机构设计。采用虚功原理建立了柔性臂的柔性动力学模型,并采用Wilson-theta的数值计算方法分析了取样器的动力学特性。通过动力学响应确定了取样器的工作极限。最后通过仿真和实验验证了该柔性动力学分析的正确性。

关键词： 机械通气   休克   Vigileo监测  

摘要： 目的探讨Vigileo监测在老年机械通气休克患者容量复苏中的应用。方法将进行机械通气的老年休克患者30例分为常规组和Vigileo组各15例,常规组根据临床症状、生命体征、尿量、中心静脉压(CVP)指导容量复苏,Vigileo组根据每搏量变异度(SVV)指导容量复苏。比较两组患者在复苏前后心率、平均动脉压(MAP)、氧合指数、复苏时间、机械通气时间及Vigileo组复苏前后血流动力学参数的变化。结果 Vigileo组复苏后SVV等指标较复苏前改善(P<0.05)。复苏后两组心率、MAP、氧合指数均较复苏前下降(P<0.05);复苏后Vigileo组氧合指数升高较常规组更明显(P<0.05)。Vigileo组复苏时间、机械通气时间短于常规组(P<0.05)。结论 Vigileo监测可以及时预测患者的容量反应性,更快、更有效地指导容量复苏,优于传统监测指标。

关键词： high-yield fiber materials   chemical-mechanical pulp   kinetics   bleaching   correlations  

摘要： A comparative kinetic analysis of the effect of bleaching pretreatment and temperature increase on the thermal ageing of high-yield fiber material derived from poplar wood is presented. Comparative investigations have been carried out with pulp chips not subjected to preliminary bleaching. The temperature values studied were the following: 90 degrees C, 105 degrees C and 120 degrees C. Brightness reversion was observed within the interval from 6 to 36 hours. It has been found that the ageing process is best described by an exponential kinetic equation valid for processes taking place on uniformly inhomogeneous surfaces. The values of the activation energy and the preexponential factor in the Arrhenius equation applied increased simultaneously in the course of the process for the bleached and the unbleached samples. The correlation between them indicating a compensation effect leads to the conclusion that the mechanism of the thermal ageing process is identical. It is not affected by the temperature, the treatment duration and the bleaching applied.

关键词： String   Hammers   Wire   Compression   Dynamic models   Springs   Equations of motion  

摘要： The theoretical framework for constructing a fully mechanistic multibody dynamic model of a vertical piano action is described, and its general validity is established. Equations of motion are derived symbolically using a graph-theoretic formulation. Model fidelity is increased by introducing several novel features: (i) a new contact model for representing the compression of the felt-lined interfaces between interacting parts, capable of capturing the intermittent loading and unloading of these contacts occurring through the key stroke, as well as providing smooth transitions between these states;(ii) models for two important components that are unique to the vertical action, the bridle strap and the butt spring;(iii) a sophisticated key pivot model that captures both the rotational motion and the vertical translation of the key as it can lift off the balance rail under some conditions;(iv) flexible beam models for backcheck wire and hammer shank so as to predict observed vibrations in the response accurately;and (v) coupling of the mechanism model to a flexible stiff string model for realistic hammer impact. For simulation, parameters were obtained by experimental testing and measurement of a physical prototype vertical action. Techniques are described for the virtual regulation of the model to ensure that initial conditions and pseudostatic response accurately represent the precise configuration and desired relationships between the parts during the key stroke. Two input force profiles were used for simulations, a forte pressed (hard) and piano pressed touch (soft), typical of those measured at the key surface when activated by a pianist. Simulated response to these quite different inputs is described, and compared to experimental observations obtained from a physical prototype.

关键词： Mechanical systems   Forward and inverse dynamics   Fundamental equations of constrained motion   Nonholonomic constraints   Underactuation equivalence principle  

摘要： This paper deals with the forward and the inverse dynamic problems of mechanical systems subjected to nonholonomic constraints. The intrinsically dual nature of these two problems is identified and utilised to develop a systematic approach to formulate and solve them according to an unified framework. The proposed methodology is based on the fundamental equations of constrained motion which derive from Gauss's principle of least constraint. The main advantage arising from using the fundamental equations of constrained motion is that they represent an effective method capable to derive the generalised acceleration of a mechanical system, constrained in general by a set of nonholonomic constraints, together with the generalized constraint forces (forward dynamics). When the constraint equations are used to represent the desired behaviour of the mechanical system under study, the generalised constraint forces deriving from the fundamental equations of constrained motion provide the control actions which reproduce the specified motion for the system (inverse dynamics). This approach is systematically extended to underactuated mechanical systems introducing a new method named underactuation equivalence principle. The underactuation equivalence principle is founded on the key idea that the underactuation property of a mechanical system can be mathematically represented using a particular set of nonholonomic constraint equations. Two simple case-studies are reported to exemplify the proposed methodology. In the first case-study the computation of the generalised constraint forces relative to the revolute joint constraints of a physical pendulum is illustrated. In the second case-study the calculation of the control action which solves the swing-up problem for an inverted pendulum is described.

关键词： Revolute joint clearance   contact forces   multibody dynamics   Kriging metamodel   genetic algorithms  

摘要： Over the past two decades, extensive work has been conducted on the dynamic effect of joint clearances in multibody mechanical systems. In contrast, little work has been devoted to optimizing the performance of these systems. In this study, the analysis of revolute joint clearance is formulated in terms of a Hertzian-based contact force model. For illustration, the classical slider-crank mechanism with a revolute clearance joint at the piston pin is presented and a simulation model is developed using the analysis/design software MSC. ADAMS. The clearance is modeled as a pin-in-a-hole surface-to-surface dry contact, with an appropriate contact force model between the joint and bearing surfaces. Different simulations are performed to demonstrate the influence of the joint clearance size and the input crank speed on the dynamic behavior of the system with the joint clearance. In the modeling and simulation of the experimental setup and in the followed parametric study with a slightly revised system, both the Hertzian normal contact force model and a Coulomb-type friction force model were utilized. The kinetic coefficient of friction was chosen as constant throughout the study. An innovative design-of-experiment (DOE)-based method for optimizing the performance of a mechanical system with the revolute joint clearance for different ranges of design parameters is then proposed. Based on the simulation model results from sample points, which are selected by a Latin hypercube sampling (LHS) method, a polynomial function Kriging meta-model is established instead of the actual simulation model. The reason for the development and use of the meta-model is to bypass computationally intensive simulations of a computer model for different design parameter values in place of a more efficient and cost-effective mathematical model. Finally, numerical results obtained from two application examples with different design parameters, including the joint clearance size, crank speed, and c

关键词： Molecular Dynamic Simulation   Hepatic Encephalopathy   Glutamine Synthetase   Glutamine Synthetase Activity   Mutant R324C  

关键词： Nucleation   High resolution X-ray diffraction   Growth from solutions   Organic compounds   Dielectric materials  

摘要： Single crystals of brucinium 2-carboxy-6-nitrophLhalate clihydraLe (B2C6ND) have been grown by the slow evaporation solution technique at room temperature using water-ethanol (1:1) mixed solvent. The metastable zone width and induction period have been experimentally determined for the growth conditions. Nucleation kinetics and fundamental growth parameters such as surface free energy, critical radius and critical free energy change are also evaluated according to the experimental data. The crystal system and the lattice parameters have been confirmed by single crystal X-ray diffraction. The crystalline perfection of the grown B2C6ND crystals has been characterized by HRXRD method. Optical band gap and Urbach tail width of the sample have been studied employing UV-Vis absorption spectroscopy. The Vickers microhardness number (11,), yield strength (cu) and stiffness constant (C-11) of the grown crystal have been evaluated. The dielectric permittivity and dielectric loss of the grown B2C6ND crystal have been investigated as a function of frequency in the temperature range 313-353 K. The laser damage threshold value of B2C6ND crystal was estimated to be 2.8 GW/cm(2) using a NcLYAG laser. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Amorphous metals   Copper   Nickel   Glass transitions   Activation energies  

摘要： The dynamics of the Johari-Goldstein (JG) beta relaxation and the alpha relaxation in bulk metallic glasses (MGs) has been investigated by using mechanical spectroscopy combined with the Coupling Model. The beta relaxations of MGs exhibit different behaviors such as peaks, humps, and excess wings due to the different fluctuations of the chemical interactions among the constituting atoms. A universal correlation between the beta relaxation and the alpha relaxation is generally found by their activation energies and relaxation times as well as the non-exponentiality parameter of the alpha relaxation, which can be predicted quantitatively from the Coupling Model. Based on the quasi-point defects theory, a correlation factor chi shows a broad peak along with the beta relaxation, suggesting that the concentration and the correlation degree of the string-like configurations involved in the beta relaxation vary with increasing temperature, which challenges the previous view that the system is in an iso-configuration state below T-g and may shed new light on the nature of the JG beta relaxation in metallic glasses. (C) 2014 AIP Publishing LLC.

关键词： 农业机械总动力   灰色预测   背景值  

摘要： 随着现代科技的不断发展，农业机械化程度不断提高，而农业机械总动力是衡量一个国家农业现代化程度的重要指标。传统的灰色预测方法无法更加准确地进行预测，因此，提出了基于背景值优化的GM（1，1）模型预测，并用2003～2012年的数据对模型进行验证对比，解释了此方法相比单纯的灰色预测精度有所提高，可以预测我国未来数年内农业机械总动力的拥有量，便于国家对农机发展的宏观调控。