关键词： 柔性机械臂   模态分析   Kane方程   动力学特性  

摘要： 根据假设模态法,对刚-柔性机械臂系统进行了位形表达及运动学分析.基于Kane方程,建立了刚-柔性机械臂系统的动力学模型.数值仿真结果表明,截取前二阶模态即可满足刚-柔性机械臂系统的精度要求;分析了柔性机械臂的结构参数、材料参数和驱动力矩对其动力学特性的影响.研究结果表明:通过采用矩形截面,采用较大弹性模量的材料,减小外部施加的驱动力矩,避免驱动力矩产生突变,可以有效地提高刚-柔性机械臂系统的动力学性能.

关键词： 刚-柔混合动力学   机械臂   动态响应  

摘要： 建立了刚-柔混合两杆机械臂的动力学方程,并进行了数值仿真,分别讨论了在大范围运动已知条件下和大范围运动未知条件下,刚-柔混合机械臂的动力学响应。在大范围运动未知条件下,又讨论了刚性机械臂和柔性机械臂的运动对系统动态响应的影响。

关键词： 灌装   机械手   运动学仿真   动力学仿真  

摘要： 首先利用平面几何关系,建立了灌装机械手的运动学方程,再通过MATLAB计算了各关节的位移曲线、速度曲线以及加速度曲线,在此基础上进行了动力学仿真,得到了各关节的扭矩曲线。结果表明:各关节运动较平稳,所选的电机的额定扭矩大于所需的最大扭矩,满足使用要求,为灌装机械手的设计提供了理论依据。

关键词： 粮食作物   农业机械化   系统动力学模型   仿真  

摘要： 分析了中国粮食作物机械化生产系统结构组成,构建了因果分析图和系统动力学流图。在此基础上,进行了系统动力学模型构建与仿真分析。结果表明:经济发展水平、土地经营规模、农业劳动力转移是影响粮食作物机械化生产系统的主要因素。只有通过提高粮食作物生产规模化程度和专业化程度并配合产业发展规律,才能从根本上提高机械化生产的效率和生产能力。

关键词： Rare-earth minerals   Mechanical activation   Tumbling mill   Kinetics   Leaching   Zinc ferrite  

摘要： Synthetic indium-bearing zinc ferrite (IBZF) was mechanically activated by a tumbling mill. Subsequently, the behavior and kinetics of leaching zinc and indium from the initial IBZF and activated IBZF in sulfuric acid solution were investigated. The results demonstrate that the tumbling ball milling enhances the leaching reactivity of IBZF and increases the zinc and indium extractions. The reaction temperature and H2SO4 concentration have an important effect on leaching zinc and indium from the initial IBZF and activated IBZF. The kinetic model -ln(1-x) = kt was used to describe the kinetics of leaching zinc and indium from the initial IBZF and activated IBZF and to calculate the kinetic parameters. The tumbling ball milling causes a decrease in activation energy and reaction order, which indicates that the dissolution of IBZF after mechanical activation by a tumbling mill becomes less sensitive to temperature and H2SO4 concentration. For the zinc leaching, the activation energy decreases from 73.9 to 70.3 kJ/mol and the reaction order decreases from 0.72 to 0.70. For indium leaching, the activation energy decreases from 78.1 to 73.5 kJ/mol and the reaction order decreases from 0.82 to 0.69. It is found that the dissolution rates of the initial IBZF and activated IBZF are controlled by surface chemical reactions. Minerals & Metallurgical Processing, 2013, Vol. 30, No. 1, pp. 45-52. An official publication of the Society for Mining, Metallurgy, and Exploration, Inc.

关键词： Epoxy nanocomposites   Dynamic cure kinetics   KAS method   SB (m, n) model   Thermal stability   Elastic moduli, microhardness  

摘要： Nanocomposites, based on tetrabromo-bisphenol-A epoxy and aniline formaldehyde condensates, containing 5 and 10 % organically modified montmorillonite (O-MMT), were prepared. The morphologies of these nanocomposites were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of O-MMT on the dynamic cure kinetics, thermal stability, and mechanical properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and non-destructive ultrasonic testing techniques. The XRD and SEM results indicated a good dispersion of O-MMT within the epoxy matrix. The relation between the activation energy, E (a), and the degree of cure, alpha, for the examined systems was obtained by applying model-free isoconversional Kissinger-Akahira-Sunose method. As alpha increases, E (a) increases gradually, almost independent of the amount of O-MMT. The dynamic cure kinetics of the neat epoxy system as well as its nanocomposites were described by estA k-Berggren, [SB (m, n)], autocatalytic model. The O-MMT enhances the thermal stability of the examined epoxy system. The results of the mechanical properties indicated that the addition of O-MMT enhances the Young's and shear elastic modulus and microhardness. The values of these parameters increase with increasing O-MMT loading.

关键词： Poly(vinylidene fluoride)   Carbon nanotube   Molecular dynamics   Mechanical properties  

摘要： Molecular dynamics simulations and geometry optimizations based on the Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force field were performed to understand the effect of Single Wall Carbon Nanotubes (SWCNTs) on the mechanical properties of Poly(vinylidene fluoride) (PVDF). In particular, the Young's modulus, bulk and shear modulus, pullout energy, pullout force, interfacial shear stress and interfacial bonding energy were calculated. The presence of the SWCNTs can increase the Young's modulus of the systems studied here by 1 GPa in the direction of the SWCNT axis, although this depends on the distance between neighboring SWCNTs. The calculated interfacial shear stress was between 100 and 129 MPa, which is in agreement with results obtained for other SWCNT-polymer systems. The results, and in particular those obtained for the bulk and shear modulus, show that SWCNTs do not have a significant effect on the bulk mechanical properties. Functionalizing the SWCNTs may yield stronger adhesion between the nanotube and the polymer, thereby achieving improved mechanical properties. (C) 2012 Elsevier B.V. All rights reserved.

关键词： stacking fault energy   high manganese steel   TWIP   TRIP   shape memory alloys  

摘要： The thermodynamic properties of the Fe-Mn-C system were investigated by using an analytical model constructed by a CALPHAD approach. The stacking fault energy (SFE) of the fcc structure with respect to the hcp phase was always constant at T-0, independent of the composition and temperature when other related parameters were assumed to be constant. Experimental limits for the thermal hcp formation and the mechanical (deformation-induced) hcp formation were separated by the SFE at T-0. The driving force for the fcc to hcp transition, defined as a dimensionless value -dG(m)/(RT), was determined in the presence of Fe-rich and Mn-rich composition sets in each phase. Carbon tended to partition to the Mn-rich phase rather than to the Fe-rich phase for the compositions studied. The results obtained revealed a thermo-mechanical correlation with empirical yield strength, maximum true stress and maximum true strain. The proportionality between thermodynamics and mechanical properties is discussed.

关键词： mechanical stability   non-B DNA   proteins   single-molecule laser tweezers   transition dynamics  

摘要： With the firm demonstration of the in vivo presence and biological functions of many non-B DNA structures, it is of great significance to understand their physiological roles from the perspective of structural conformation, stability, and transition kinetics. Although relatively simple in primary sequences compared to proteins, non-B DNA species show rather versatile conformations and dynamic transitions. As the most-studied non-B DNA species, the G-quadruplex displays a myriad of conformations that can interconvert between each other in different solutions. These features impose challenges for ensemble-average techniques, such as X-ray crystallography, NMR spectroscopy, and circular dichroism (CD), but leave room for single-molecular approaches to illustrate the structure, stability, and transition kinetics of individual non-B DNA species in a solution mixture. Deconvolution of the mixture can be further facilitated by statistical data treatment, such as iPoDNano (integrated population deconvolution with nanometer resolution), which resolves populations with subnanometer size differences. This Personal Account summarizes current mechanical unfolding and refolding methods to interrogate single non-B DNA species, with an emphasis on DNA G-quadruplexes and i-motifs. These single-molecule studies start to demonstrate that structures and transitions in non-B DNA species can approach the complexity of those in RNA or proteins, which provides solid justification for the biological functions carried out by non-B DNA species. DOI 10.1002/tcr.201200021

关键词： Molecular Dynamics Simulation   Pyridines/chemistry   Solutions   Spectrum Analysis, Raman   Temperature  

摘要： The in situ observation of geometrical and electronic structural dynamics of a single molecule junction is critically important in order to further progress in molecular electronics. Observations of single molecular junctions are difficult, however, because of sensitivity limits. Here, we report surface-enhanced Raman scattering (SEAS) of a single 4,4'-bipyridine molecule under conditions of in situ current flow in a nanogap, by using nano-fabricated, mechanically controllable break junction (MCBJ) electrodes. When adsorbed at room temperature on metal nanoelectrodes in solution to form a single molecule junction, statistical analysis showed that nontotally symmetric b(1) and b(2) modes of 4,4'-bipyridine were strongly enhanced relative to observations of the same modes in solid or aqueous solutions. Significant changes in SERS intensity, energy (wavenumber), and selectivity of Raman vibrational bands that are coincident with current fluctuations provide information on distinct states of electronic and geometrical structure of the single molecule junction, even under large thermal fluctuations occurring at room temperature. We observed the dynamics of 4,4'-bipyridine motion between vertical and tilting configurations in the Au nanogap via b(1) and b(2) mode switching. A slight increase in the tilting angle of the molecule was also observed by noting the increase in the energies of Raman modes and the decrease in conductance of the molecular junction.