关键词： 混合动力   节能减排   电驱动   液压挖掘机   能量回收  

摘要： 介绍混合动力在工程机械中的应用,说明混合动力节能减排的途径、混合动力的基本形式、混合动力的特点、具体实例及其技术上存在的问题。

关键词： 空间机械臂   关节   动力学   建模  

摘要： 空间机械臂的机械部分是一个由关节和臂杆等结构、机构部件组成,在空间零重力环境下运行的多体系统。关节是空间机械臂的核心部件,在机械臂动力学特性中起着重要的作用。准确全面地了解关节的动力学特性,是正确分析与模拟机械臂系统空间运动特性的关键,而建立精确的关节动力学模型,是机械臂系统设计、分析和控制的基础。文章结合空间应用的特殊性,对机械臂关节动力学建模方法的发展过程和研究成果进行了总结;并讨论了关节模型的求解算法;最后,对空间机械臂关节动力学建模与分析方面有待进一步研究的问题进行了展望。

关键词： Cropping system   Weed dynamics   Model   Mechanical weeding   Grassland   Integrated crop protection  

摘要： Because of environmental and health safety issues. it is necessary to develop strategies that do not rely on herbicides to manage weeds. Introducing temporary grassland into annual crop rotations and mechanical weeding are the two main features that are frequently used in integrated and organic cropping systems for this purpose. To evaluate the contribution of these two factors in interaction with other cropping system components and environmental conditions, the present study updated an existing biophysical model (i.e. ALOMYSYS) that quantifies the effects of cropping system oil weed dynamics. Based oil previous experiments, new sub-models were built to describe the effects on plant survival and growth reduction of mechanical weeding resulting from weed seedling uprooting and covering by soil, and those of grassland mowing resulting from tiller destruction. Additional modifications described the effect of the multiyear crop canopy of grassland on weed survival, growth, development and seed return to the soil. The improved model was used to evaluate the weed dynamics over 27 years in the conventional herbicide-based cropping system most frequently observed in farm Surveys (i.e. oilseed rape/winter wheat/winter barley rotation with Superficial tillage) and then to test prospective non-chemical scenarios. Preliminary simulations tested a large range of mechanical weeding and mowing strategies, varying operation frequencies, dates and, in the case of mechanical weeding, characteristics (i.e. tool, working depth, tractor speed). For mechanical weeding soon after sowing, harrowing was better than hoeing for controlling weed seed production. The later the operation, the more efficient the hoeing and the less efficient the harrowing. Tractor speed had little influence. Increasing tilling depth increased plant mortality but increased weed seed production because of additional seed germination triggering by the weeding tool. Decreasing the interrow width for hoeing was nefar

关键词： Thermo-mechanical properties   Molecular dynamics simulation   Bismuth telluride  

摘要： Molecular dynamics method is explored to investigate the effects of temperature on the mechanical and thermal properties of single crystal bismuth telluride from 0 K to 600 K, with potentials developed by Huang et al. The structural properties, lattice constants, linear thermal expansion coefficients, independent elastic constants were all calculated. The lattice constants were estimated by the size of box from the NPT simulation. The thermal expansion coefficient was calculated by a differential operation of the temperature dependence of the lattice constants. The tension and shear simulations have been conducted to calculate the elastic constants. The six independent elastic constants were calculated as a function of temperature from the stress-strain relations obtained from the NVT ensemble. All the calculated results are in good agreement with previous experimental and theoretical results. These agreements confirm the reliability of the present potential functions. The simulation results enable us to predict the mechanical and thermal properties of Bi2Te3 as an effective thermoelectric material in the whole range of its working temperature, and the data will be helpful for the practical manufacture and manipulation of Bi2Te3 thermoelectric devices. (C) 2010 Elsevier B.V. All rights reserved.

关键词： adsorption   kinetics   semiconductor surfaces   modelling   sensors  

摘要： A quantum mechanical model of co-adsorption on semiconductor surfaces is developed and successfully adopted towards exposure to several gases. It is related to nanofilms and thus allows the application of electric fields altering the electronic surface properties of adsorption centres (electro-adsorptive effect, EAE). The model is matched against experimental data with O(2), NO(2) and CO measurements under the hypothesis of no direct interaction among the species. However the sequence of adsorption plays an important role where the adsorption of one gas species is opening up other sites that are filled by another sort of impinging molecules. Quantum mechanical modelling of co-adsorption: (a) NO(2) and CO present at the SnO(2) surface. (b) Simplified model. (c) Probability of adsorption. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

关键词： Indium   Zinc ferrite   Mechanical activation   Kinetics   Sulphuric acid leaching  

摘要： The synthetic indium-bearing zinc ferrite (IBZF) was mechanically activated by a stirring ball mill and subsequently studied for the leaching behavior and kinetics of extracting indium from IBZF. The effect of the change in crystalline phase, lattice distortion, particle size, specific surface area and morphology introduced by mechanical activation (MA) was also investigated. The activated IBZF showed different physicochemical characteristics and was found to be easier to dissolve in sulphuric acid than the unmilled sample. MA enhanced the leaching reactivity of IBZF. When IBZF was mechanically activated for 30 and 60 min, the activation energy decreased from 68.8 kJ/mol to 54.4 and 44.7 kJ/mol, respectively. The leaching process of unmilled IBZF was controlled by chemical reaction, but became the hybrid controlled process after MA. The reaction orders of the unmilled, activated for 30 and 60 min IBZF dissolution with respect to H2SO4 concentration were 0.69, 0.58, and 0.54. respectively. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Thickness   Monomers   Monolayers   Compression   Solvents  

摘要： We present and discuss the results of discontinuous molecular dynamics simulations of mechanically assembled polymer layers chemically attached to flexible substrates under poor solvent conditions. Square-well chains of lengths comprising 20 to 100 units end-grafted to a hard surface at lose density are compressed laterally at varying rates. Brush thickness depends on the interplay between solvent quality and the substrate compression rate. Brushes formed in poor solvents at fast compression rates are thinner and exhibit more heterogeneity in coverage than brushes formed in good solvents at slow compression rates. End-monomer trapping increases with increasing compression rate and/or decreasing solvent quality. By varying relaxation/compression rate, we can modify the effects of brush thickness hysteresis. Finally, we suggest a general blueprint for efficient formation of defect-free monolayers that might be followed by experimenters.

关键词： Condensed matter: structural   mechanical & thermal Nanoscale science and low-D systems  

摘要： Molecular dynamics simulations have been performed to study the mechanical properties of methyl (CH3) functionalized graphene. It is found that the mechanical properties of functionalized graphene greatly depend on the location, distribution and coverage of CH3 radicals on graphene. Surface functionalization exhibits a much stronger influence on the mechanical properties than edge functionalization. For patterned functionalization on graphene surfaces, the radicals arranged in lines perpendicular to the tensile direction lead to larger strength deterioration than those parallel to the tensile direction. For random functionalization, the elastic modulus of graphene decreases gradually with increasing CH3 coverage, while both the strength and fracture strain show a sharp drop at low coverage. When CH3 coverage reaches saturation, the elastic modulus, strength and fracture strain of graphene drop by as much as 18%, 43% and 47%, respectively.

关键词： Medical physics Biological physics  

摘要： Peptide nanostructures present a wide range of opportunities for applications in biomedicine and bionanotechnology;hence experimental and theoretical studies aiming at determination of thermo-mechanical stability of peptide-based nanostructures are critical for the design and development of their technological applications. Here, we present a homogeneous deformation method combined with the finite elasticity theory and molecular dynamics simulations (MD) for the calculation of second-order anisotropic elastic constants for a membrane model made up of self-assembled cyclic peptide nanotubes. We have computed the values of all anisotropic elastic constants at 300 K. The value of the engineering Young's modulus (in the z direction) is 19.6 GPa. We observed a yield behavior in the z direction for a strain value of 6%. Furthermore, we also report calculated heat capacity, thermal expansion coefficient and isothermal compressibility of the system under study.

关键词： chemical mechanical polishing   elemental semiconductors   indentation   molecular dynamics method   nanotechnology   particle size   silicon   wear  

摘要： Molecular dynamics simulations of nanoscratching processes were used to study the atomic-scale removal mechanism of single crystalline silicon in chemical mechanical polishing (CMP) process and particular attention was paid to the effect of scratching depth. The simulation results under a scratching depth of 1 nm showed that a thick layer of silicon material was removed by chip formation and an amorphous layer was formed on the silicon surface after nanoscratching. By contrast, the simulation results with a depth of 0.1 nm indicated that just one monoatomic layer of workpiece was removed and a well ordered crystalline surface was obtained, which is quite consistent with previous CMP experimental results. Therefore, monoatomic layer removal mechanism was presented, by which it is considered that during CMP process the material was removed by one monoatomic layer after another, and the mechanism could provide a reasonable understanding on how the high precision surface was obtained. Also, the effects of the silica particle size and scratching velocity on the removal mechanism were investigated;the wear regimes and interatomic forces between silica particle and workpiece were studied to account for the different removal mechanisms with indentation depths of 0.1 and 1 nm.