关键词： 柔性机械臂   逆动力学   近似方法   RBF神经网络   数值仿真  

摘要： 本文以单柔性机械臂为例,利用拉格朗日方程和Rayleigh-Ritz方法进行简单的逆运动学分析,分别采用近似法和RBF神经网络方法对模型进行了数值仿真分析。通过分析可以看出,相较于近似方法,利用RBF神经网络方法得到的轨迹更接近实际轨迹,为后续解决柔性杆件运动过程中的控制问题提供了较好的解决办法。

关键词： 农业劳动力老龄化   小麦   地形   机械投入   技术效率  

摘要： 为厘清农业劳动力老龄化与小麦生产的关系,基于全国农村固定观察点2010年调研数据,从生产方式(机械化)和生产技术效率2个方面考察了不同地形下农业劳动力老龄化对小麦生产的影响。结果表明:农业劳动力老龄化促进了小麦机械要素的投入,且对丘陵山地地区的促进作用更大;此外,农业劳动力老龄化对平原地区小麦生产的技术效率有显著的负向影响,而对丘陵与山地地区小麦生产的技术效率则产生了显著的正向影响。因此,为应对农业劳动力老龄化,提高小麦生产技术效率,应结合不同地区地形地貌的特点,进一步提高机械对劳动的替代程度以及机械作业效率,加大农业机械的创新和研发力度,同时创建农机跨区作业市场。

关键词： 动力机械   人工自愈   振动   靶向抑制  

摘要： 人工自愈是在故障机理和风险分析的基础上,通过仿生设计赋予机器自发作用的维持健康状态的能力,从而使机器储存、补充和调动自愈力以维持机体的健康状态。透平压缩机、发电机组和航空发动机等动力机械是工业和国防的心脏设备,一旦发生故障将导致事故和巨大损失,在运行中通过自监测、自诊断和主动控制来抑制故障的发生以实现自愈化,是机器向高级智能阶段发展研究中的一个重要方向。本文总结了北京化工大学诊断与自愈工程(DSE)研究中心在人工自愈与动力机械振动故障靶向抑制方面的主要研究工作及成果,并以转子轴系不平衡和压缩机转子失稳振动为例,证明了靶向抑制方法的有效性。以上成果可为自主开发具有自愈功能的智能动力机械提供科学依据。

关键词： 轨道工程车车辆   柴油机组   静音箱  

摘要： 简要介绍了某种AC25 kV及柴油机双动力轨道工程车机械间及柴油机组通风系统设计。通过采用合理的机械间、静音箱内部结构及进出风口设计,使机械间、柴油机静音箱内部实现合理散热。

关键词： Particulate matter   Particle size   Erosion   Wear   Particle collisions   Flow (Dynamics)  

摘要： Aircraft engines are subject to deterioration due to solid particle erosion. The environmental particulates encountered in service often feature broad particle size distributions and a generally large scatter of particle properties. In order to numerically calculate the erosive change of shape of the components, experimentally calibrated erosion models are required. Due to aerodynamic and mechanical particle size effects, erosion tests with different particle size distributions have to be calibrated individually. In this study, erosion experiments under high-pressure compressor conditions are conducted using a sandblast type erosion rig. Flat plates out of Ti6Al4V were eroded at different impingement angles. The erodent used was quartz sand with size distributions corresponding to standardized Arizona Road Dust (ARD) grades A2, A3, and A4. The particle impact conditions were investigated using a high-speed shadowgraphy technique in combination with computational fluid dynamics (CFD) computations. Dimensional analyses were carried out in respect to the particle transport process and the material removal process. A nondimensional erosion model is derived. The experimental shadowgraphy results are corrected using numerically calibrated similarity parameters for the particle impact conditions. Thus, the influence of the aerodynamic particle size effect was eliminated by correcting the impact conditions. The isolated mechanical particle size effect is demonstrated. It is shown that wear increases and that the modeled erosion rate maximum shifts toward larger impact angles when using coarser particle size distributions.

关键词： molecular dynamics simulation   nanoporous materials   network   three-fold node   mechanical behavior  

摘要： Structurally, nanoporous (NP) materials can be regarded as a network of interconnected nanowires. In this study, molecular dynamics simulations are employed to investigate the deformation behavior of individual ligaments and isolated three-fold nodes, which are the two main structural components in NP materials. The shear strain tensor analysis is used to quantitatively differentiate deformation mechanisms accommodating strain among structures and capture onset of necking during stretching. Ligaments and nodes behave differently in both elastic regime and plastic regime. Our results suggest that node structure is brittle with low stiffness and yield strength, similar to NP structure, while ligament structure is ductile and exhibits high stiffness and yield strength. In isolated three-fold nodes and NP network structure, we observed similar deformation behavior exists;formation of pyramidal shape defects consisted of twinning partials and Shockley partials on different {111} planes at node region. The similarity of mechanical properties and deformation behavior between node structure and NP structure indicates that the role of node components is substantially significant in controlling structure-property relationships of NP materials. Enhancing node components is proposed as a potential method for improving mechanical properties of NP materials.

关键词： ACTIVATION (Chemistry)   MECHANICAL alloying   COPPER oxide   THERMIT   PARAMETER estimation   NITRATION  

摘要： The general aspects of the mechanical activation (MA) of Al/CuO thermite compositions based on micron-sized particles and nanopowders of the starting components have been analyzed using X-ray diffraction and hydrogen titration. The latter method has been employed to evaluate the amount of residual oxygen in CuO and Cu2O from the weight loss during heating in H-2. The reactivity of the activated mixtures was assessed using DSC and TG in combination with mass spectrometric analysis. In addition, we have measured the ignition temperature, burning velocity, and brightness temperature of the reaction products. The results demonstrate that mechanical activation leads to the fragmentation of the components, mixture homogenization, and the formation of a composite, producing "weakly bound" oxygen in CuOn and causing partial reaction between the components. The total exothermic heat effect in DSC scans, burning velocity, and brightness temperature as functions of specific milling dose (D) have an extremum. The highest reactivity is observed near D = 2 kJ/g, where a sufficient defect density in the components and good mixture homogenization are ensured, but the degree of MA-induced conversion does not exceed 10%. The burning velocity then reaches 400-700 m/s, and the brightness temperature is 3400-3800 degrees C. The milling dose dependence of the self-ignition temperature has no extremum. The self-ignition temperature steadily decreases with increasing milling dose, even though the ignition knock "power" falls off. The use of nanoparticulate starting components does not appear reasonable.

关键词： mechanical properties   uniaxial tension   molecular dynamics   microstructure   nanoporous gold  

摘要： The present paper aims to investigate the microstructural differences of models used in nanoporous metals and research on the mechanical response of various morphological architectures, including cube, gyroid, diamond and stochastic bicontinuous structures. By using molecular dynamics simulations, the influential parameters of architectural morphology, relative density and ligament diameter on the mechanical properties of nanoporous gold under uniaxial tension are presented and further compared with current constitutive theory and experimental results of the literature. The differences among those structures are critically demonstrated and addressed. Results present that the Young's modulus as a function of relative density and the yield strength as a function of ligament diameter both display power-law relation but the scaling exponents vary with the microstructures. The modulus of stochastic bicontinuous structures is in better agreement with the experimental results. The relationship between yield stress and relative density is approximately linear, indicating the yielding behavior may be dominated by the yielding of ligaments in the process of deformation. These results promise much for the design of nanoporous structures with tunable, desirable mechanical properties stemming from various microstructures.

关键词： Acetylcholinesterase   Butyrylcholinesterase   Neolignan   Tyrosinase   alpha-Glucosidase  

摘要： Neolignans are a large group of polyphenols found in plants and exhibit a wide range of bioactivities including cytotoxicity, apoptosis inducer, antimalarial and antifungal effects, acetylcholinesterase, tyrosinase, and alpha-glucosidase inhibition. In this study we tested acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), tyrosinase, and alpha-glucosidase inhibitory effects of a rare neolignan, (-)-4-O-methyldehydrodiconiferyl alcohol 9'-O-beta-glucopyranoside (1) in search for its new pharmaceutical effects. This compound exhibited good tyrosinase inhibition with an IC50 value of 44.62 +/- 3.99 mu g/mL. Enzyme kinetics and molecular modelling studies were performed to provide insights into its tyrosinase inhibition mechanism.

关键词： Geopolymers   Reaction kinetics   Chemical bonding   Mechanical properties   Porosity  

摘要： The reaction kinetics of red mud-class F fly ash based geopolymer (RFFG) was investigated through understanding the influence of curing temperature on the formation of geopolymer gel, porosity, and the development of mechanical properties. Chemical bonding, mineralogy, mechanical properties and porosity of RFFG during a curing period of up to 120 days were assessed with Fourier transform infrared spectroscopy, X-ray diffractometer, unconfined compression tests, and micro-CT and N-2-BJH techniques, respectively. The geopolymer gels were found to develop via a three-stage process: dissolution-Al-rich gels (I), Al-rich gels-Si-rich gels (II) and Si-rich gels-tectosilicate networks (III). The mechanical strength is largely governed by the development of geopolymer gels and affected by porosity, both of which are influenced by curing temperature. The early mechanical strength of RFFG is enhanced by elevated curing temperatures, but the long-term strength can be compromised by higher porosity resulted from an excessively high curing temperature.