关键词： 农用动力机械   模糊控制策略   液压悬挂系统   优化技术   车辆工程   转向系统   履带车辆   传递特性  

摘要： 20091053 浅谈车辆工程CAE中拓扑优化技术的应用；20091054 拖拉机电控液压悬挂系统的耕深模糊控制策略；20091055 橡胶履带车辆差速转向系统的研究；20091056 柴油机燃烧噪声的传递特性；20091057 KM496BZL型柴油机的研制……

摘要： A technique of analysis of dynamics of mechanisms with symmetry elements is given. One of possible schemes of such analysis is considered by example of the tooth wheel mechanism.

摘要： 1521-Pos

关键词： Hammett correlation   steric effects   substituent effects   kinetics   Combes quinoline synthesis   trifluoromethyl-1,3-diketones  

摘要： A comprehensive product regioselectivity and kinetics study of the modified Combes quinoline synthesis shown below has been undertaken: [GRAPHICS] This is the first reported investigation of the Combes condensation employing 19F NMR spectroscopy to monitor intermediate consumption and product formation rates. The reaction was found to be first order in both the diketone and aniline. Product regioselectivity and reaction rates were found to be influenced by substituents on the diketones and anilines with rates varying as much as five fold. The consumption rate of key imine and enamine intermediates mirrored quinoline formation rates, in accord with rate determining annulation. A rho of -0.32 was determined for this cyclization. While the sign of the reaction constant is consistent with rate limiting electrophilic aromatic substitution (EAS), the magnitude is likely a composite value, resulting from opposing substituent effects in the nucleophilic addition and EAS steps. Mechanistic details and reaction pathways supporting these findings are proposed. Copyright (c) 2008 John Wiley & Sons, Ltd.

关键词： integro-differential equations   plasma instability   plasma nonlinear waves   plasma oscillations  

摘要： The universal integrodifferential model equation derived by Berk [Phys. Rev. Lett. 76, 1256 (1996)] for studying the nonlinear evolution of unstable modes driven by kinetic wave particle resonances near the instability threshold is reduced to a differential equation and next as a further simplification to a nonlinear oscillator equation. This mechanical analogy properly reproduces most of the essential physics of the system and allows an understanding of the qualitative features of the theory of Berk.

关键词： European pine sawfly   Bayesian inference   Hidden variable   Scale discrepancy   Spatio-temporal model   Two-regime assumption  

摘要： Knowledge about large-scale and long-term dynamics of (natural) populations is required to assess the efficiency of control strategies, the potential for long-term persistence, and the adaptability to global changes such as habitat fragmentation and global warming. For most natural populations, such as pest populations, large-scale and long-term surveys cannot be carried out at a high resolution. For instance, for population dynamics characterized by irregular abundance explosions, i.e., outbreaks, it is common to report detected outbreaks rather than measuring the population density at every location and time event. Here, we propose a mechanical-statistical model for analyzing such outbreak occurrence data and making inference about population dynamics. This spatio-temporal model contains the main mechanisms of the dynamics and describes the observation process. This construction enables us to account for the discrepancy between the phenomenon scale and the sampling scale. We propose the Bayesian method to estimate model parameters, pest densities and hidden factors, i.e., variables involved in the dynamics but not observed. The model was specified and used to learn about the dynamics of the European pine sawfly (Neodiprion sertifer Geoffr., an insect causing major defoliation of pines in northern Europe) based on Finnish sawfly data covering the years 1961-1990. In this application, a dynamical Beverton-Holt model including a hidden regime variable was incorporated into the model to deal with large variations in the population densities. Our results gave support to the idea that pine sawfly dynamics should be studied as metapopulations with alternative equilibria. The results confirmed the importance of extreme minimum winter temperatures for the occurrence of European pine sawfly outbreaks. The strong positive connection between the ratio of lake area over total area and outbreaks was quantified for the first time.

关键词： Plastics magnet   Vibration force field   Tri-screw extruder   Mixing   Morphology  

摘要： The vibration force field employed during polymer-based composite mixing has been proved of great effect on the morphology and the performance of product. Here the ferromagnet/PVC compound is firstly mixed via a self-devised vibrating tri-screw extruder and then molded into dumbbell samples which are afterwards pulse magnetized to make plastics magnet. After that, the effects of vibration force field on the mechanical properties and magnetic performance of plastics magnet is experimentally investigated. The results indicate that both the quality targets of the specimens change significantly with the employing of vibration force field. Compared with those prepared under stable status (non-vibration), the tensile strength and the elongation at break of the specimens elevate, respectively by 17.1 and 37.7% at most, while the maximum increase of remanence, coercive force, intrinsic coercive force and magnetic energy product are 8, 5, 5 and 11%, respectively. The morphologies of specimens have also been studied with SEM in order to search the proof for the change of the product performance. The results of microstructure analysis show that vibration force field improves the blending effectively, which are consistent with the change of the mechanical properties and magnetic performance of plastics magnet under vibration force field. (C) 2008 Elsevier B.V. All rights reserved.

关键词： ecosystem dynamics   terrestrial biosphere model   net ecosystem productivity (NEP)   eastern United States   ecosystem structure  

摘要： Insights into how terrestrial ecosystems affect the Earth's response to changes in climate and rising atmospheric CO2 levels rely heavily on the predictions of terrestrial biosphere models (TBMs). These models contain detailed mechanistic representations of biological processes affecting terrestrial ecosystems;however, their ability to simultaneously predict field-based measurements of terrestrial vegetation dynamics and carbon fluxes has remained largely untested. In this study, we address this issue by developing a constrained implementation of a new structured TBM, the Ecosystem Demography model version 2 (ED2), which explicitly tracks the dynamics of fine-scale ecosystem structure and function. Carbon and water flux measurements from an eddy-flux tower are used in conjunction with forest inventory measurements of tree growth and mortality at Harvard Forest (42.5 degrees N, 72.1 degrees W) to estimate a number of important but weakly constrained model parameters. Evaluation against a decade of tower flux and forest dynamics measurements shows that the constrained ED2 model yields greatly improved predictions of annual net ecosystem productivity, carbon partitioning, and growth and mortality dynamics of both hardwood and conifer trees. The generality of the model formulation is then evaluated by comparing the model's predictions against measurements from two other eddy-flux towers and forest inventories of the northeastern United States and Quebec. Despite the markedly different composition throughout this region, the optimized model realistically predicts observed patterns of carbon fluxes and tree growth. These results demonstrate how TBMs parameterized with field-based measurements can provide quantitative insight into the underlying biological processes governing ecosystem composition, structure, and function at larger scales.

关键词： coupled cluster calculations   density functional theory   electronic structure   infrared spectra   liquid theory   molecular dynamics method   permittivity   polarisability   ultraviolet spectra   visible spectra   water  

摘要： The dynamic polarizability and optical absorption spectrum of liquid water in the 6-15 eV energy range are investigated by a sequential molecular dynamics (MD)/quantum mechanical approach. The MD simulations are based on a polarizable model for liquid water. Calculation of electronic properties relies on time-dependent density functional and equation-of-motion coupled-cluster theories. Results for the dynamic polarizability, Cauchy moments, S(-2), S(-4), S(-6), and dielectric properties of liquid water are reported. The theoretical predictions for the optical absorption spectrum of liquid water are in good agreement with experimental information.

关键词： 机械臂   动力学仿真   虚拟样机   计算机动画  

摘要： 基于多刚体动力学的原理,在分析机械臂的运动学和拉格朗日动力学方程的基础上求解其雅可比矩阵,并采用虚拟样机技术建立了机械臂的三维仿真模型,进行了动力学分析,获得了机械臂的动态特性。通过将获得的动态特性还原到模型中,建立了基于可视化技术的机械臂运动姿态的计算机动画,逼真地模拟了机械臂的整个运动过程,检验了机械臂动力学模型的相关性能。