关键词： 关节位移极限   冗余机械臂   延迟反馈法   混沌控制  

摘要： 考虑关节位移极限指标,研究冗余机械臂系统动力学特性及延迟反馈法对系统混沌运动控制。以平面3自由度机械臂为研究对象,利用Jacobian矩阵伪逆法得到平面机械臂系统的动力学模型。基于关节位移极限指标,建立冗余机械臂系统的混沌动力学状态方程,采用龙格库塔法对模型求解,利用相图、Poincaré图及Lyapunov指数图等进行分析。结果表明基于关节位移极限的冗余机械臂的自运动表现出混沌现象。在此基础上,利用延迟反馈法进行混沌控制,得到在合适的扰动权重参数条件下,延迟反馈控制能使冗余机械臂的混沌运动稳定在周期轨道上,且发现在混沌吸引子内存在除1倍周期以外的2倍周期以及3倍周期窗口,通过选取不同的扰动权重能使系统稳定在不同的周期轨道上。

关键词： 多体系统   动力学方程   关节润滑机械系统   动力学模型  

摘要： 基于多体动力学方程,全面分析了关节润滑机械系统的动力学模型。只考虑间隙的接触属于干接触,利用接触力学模型创建间隙关节元素的接触力,使用工修正摩擦力对关节摩擦力进行计算。全面考虑关节润滑,通过多体系统动力学理论对流体的压力进行全面计算,然后利用多体系统动力学方程创建全面考虑润滑的机械系统动力学模型。在平面曲柄滑块结构进行实验,利用数值的计算对比间隙之间关节在润滑时候的动态特点。从实验的结果可以看出,对关节润滑进行全面考虑之后的动力学模型与理想的状态更加的接近。

关键词： Palladium(II)   Organic disulfides   Kinetics   UV-Vis   Redox reactions  

摘要： Kinetics and mechanisms of a disulfide bond disproportionation in DL-homocystine (H(2)HCysS) and 3,3'-dithiodipropionic acid (H(2)DTDPA) induced by Pd(II) species were investigated spectrophotometrically in strong hydrochloric acidic media. The products of the disproportionation are thiolate and sulfinate complexes. The reaction of Pd(II) with H(2)DTDPA is autocatalytic with contributions from both catalytic and non-catalytic pathways. The reaction of Pd(II) with H(2)HCysS is irreversible and of the first order. For both ligands, a rate-determining step is the formation of a S,S'-binuclear complex species prior to the disproportionation. A subsequent electrophile-assisted disproportionation of a disulfide bond is caused by a nucleophilic attack of a water molecule. Both reactions proceed through an associative mechanism by a solvolytic pathway. The difference in the mechanisms for two ligands is explained in terms of steric availability of a disulfide bond. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： 机械设计制造   学院   三峡大学   能源与动力工程   机械电子工程   材料成型   控制工程   本科专业  

摘要： 2014年1月原机械与材料学院更名为机械与动力学院,学院现设有机械设计制造及其自动化、机械电子工程、材料成型及控制工程、工业工程、能源与动力工程、核工程与核技术六个本科专业,其中机械设计制造及其自动化为国家特色专业、第二批卓越工程师教育培养计划专业和省本科品牌专业,材料成型及控制工程为第三批卓越工程师教育培养计划专业。

关键词： porous electrode   pressure sensitivity   self-powered sensors   mechanical impact  

摘要： Microsystems with limited power supplies, such as electronic skin and smart fuzes, have a strong demand for self-powered pressure and impact sensors. In recent years, new self-powered mechanical sensors based on the piezoresistive characteristics of porous electrodes have been rapidly developed, and have unique advantages compared to conventional piezoelectric sensors. In this paper, in order to optimize the mechanical sensitivity of porous electrodes, a material preparation process that can enhance the piezoresistive characteristics is proposed. A flexible porous electrode with superior piezoresistive characteristics and elasticity was prepared by modifying the microstructure of the porous electrode material and adding an elastic rubber component. Furthermore, based on the porous electrode, a self-powered pressure sensor and an impact sensor were fabricated. Through experimental results, the response signals of the sensors present a voltage peak under such mechanical effects and the sensitive signal has less clutter, making it easy to identify the features of the mechanical effects.

关键词： dissolution   dissolution model(s)   in vitro model(s)   precipitation   bioavailability   oral absorption   pharmacokinetics   astroPlus modeling   solubility   simulation(s)  

摘要： Solubility, dissolution, and precipitation in the gastrointestinal tract can be critical for the oral bioavailability of weakly basic drugs. To understand the dissolution and precipitation during the transfer out of the stomach into the intestine, a multicompartment transfer system was developed by modifying a conventional dissolution system. This transfer system included gastric, intestinal, sink and supersaturation, and reservoir compartments. Simulated gastric fluid and fasted state simulated intestinal fluid were used in the gastric and intestinal compartment, respectively, to mimic fasted condition. The new transfer system was evaluated based on 2 model weak bases, dipyridamole and ketoconazole. Traditional 2-stage dissolution using 250 mL of simulated gastric fluid media, followed by 250 mL of fasted state simulated intestinal fluid, was used as a reference methodology to compare dissolution and precipitation results. An in silico model was built using R software suite to simulate the in vitro time-dependent dissolution and precipitation process when formulations were tested using the transfer system. The precipitation rate estimated from the in vitro data was then used as the input for absorption and pharmacokinetic predictions using GastroPlus. The resultant simulated plasma concentration profiles were generally in good agreement with the observed clinical data, supporting the translatability of the transfer system in vitro precipitation kinetics to in vivo. (C) 2019 American Pharmacists Association (R). Published by Elsevier Inc. All rights reserved.

关键词： Sit-to-stand   Cerebral palsy   Mechanical energy   Kinematics   Kinetics   Children  

摘要： Background: Sit-to-stand (STS) is one of the most common fundamental activity in daily life. The pathology of the neuromuscular control system in children with spastic diplegic cerebral palsy (SDCP) could contribute to atypical movement patterns leading to the inefficiency performance including the STS task. However, there was also a lack of evidence about kinematics, kinetics, and especially mechanical work during the STS task in children with SDCP aged 7-12 years old. Research question: What were the differences in mechanical work, kinematics and kinetics during STS task between children with SDCP and typically developing (TD) children? Methods: Eleven children with SDCP (GMFCS I-II) and eleven age and gender-matched control TD children with an age range of 7-12 years were enrolled. Motion analysis and force plate systems were used to collect data. All participants performed the STS task from an adjustable chair. Independent sample t-test and two-way analysis of variance were used in this study. Results: The children with SDCP took a longer time and used more mechanical work during STS than TD children. M the beginning of the STS task, children with SDCP showed more trunk flexion and posterior pelvic tilting;in addition, during the STS task they also presented more trunk, hip, and knee flexion than TD children. However, the children with SDCP showed less ankle dorsiflexion compared with TD children. For the kinetic variables, asymmetry was found in children with SDCP. The maximum hip and knee extension moment, plantar flexion moment, and peak vertical ground reaction force (GRF) of the non-dominant leg were higher than the values of the dominant leg in these children. Significance: Even though, children with SDCP who are able to independently STS. They were also a mechanically less efficient performance during STS task. Therefore, this task still needs to be trained during rehabilitation sessions.

关键词： Molecular dynamics simulation   Nanocomposites   Graphene oxide   Finite element analysis  

摘要： The mechanical behavior of oxygen functionalized single layer graphene (graphene oxide, GO)/polyethylene (PE) nanocomposites is studied by all atom-based molecular dynamics (MD) simulation and finite element analysis (FEA). To account for the effect of the oxygen functional group, both pristine and 15 hydroxyl functionalized graphene embedded into the transversely isotropic nanocomposites unit cell models are considered. Using the classical ensemble simulations at 200K and at atmospheric pressure, the transversely isotropic elastic constants of the nanocomposites molecular unit cell structures are determined from uniaxial tension and shear tests. To evaluate the effect of the addressed oxygen functional groups on elastic constants of the nanocomposites, periodic FEA models with the perfect interface condition between the graphene and PP matrix are constructed. Due to the degradation of the graphene by the oxidation, the longitudinal Young's modulus and the in-plane shear modulus of the nanocomposites determined from the MD simulation and FEA are found to be degraded by the oxygen functional groups. According to the MD simulation results, however, the longitudinal shear modulus of the nanocomposites is improved by the oxygen functional groups compared with the pristine graphene. On the other hand, FEA analysis of the longitudinal shear modulus is overestimated unless the oxygen functional group-dependent cohesive interface law between the graphene and PP matrix is addressed.

关键词： MDS   mechanical polishing   nanofinishing   diamond  

摘要： Mechanical polishing is one of the essential attributes of nanofinishing. To maintain precision during nanofinishing process, the mechanical polishing needs to be studied and analyzed at nanometric scale. In view of this, a set of molecular dynamics simulation has been carried out to analyze the process behavior and its effects on abrasive particles. After simulation, it is observed that the finishing force and velocity damage the abrasive particle by changing its phase from diamond cubic to graphite. Thus, the abrasive particles need replacement in a scheduled time-bound manner. In addition, a strategy has been proposed for efficient and economic polishing.

关键词： H-2 activation   Metal catalysis   Statistical modelling   Temperature dependent kinetics  

摘要： The temperature dependencies of the reactions MnO+ + H-2/D-2 from 150 to 600 K are measured in a selected- ion flow tube apparatus. The reactions are approximately 15% efficient at room temperature with rate constants (k = 2.7 +/- 0.7 x 10(-10) cm(3) s(-1) for H-2 and 1.5 +/- 0.4 x 10(-10) cm(3) s(-1) for D-2 at 300 K) that vary as T-1.1 +/- 0.2 and T-1.3 +/- 0.2, respectively. Both Mn+ and MnOH+/D+ products are observed, with Mn+ being the minority product in the H-2 reaction, but the majority product in the D-2 reaction. Reaction coordinates are explored using a variety of density functional methods, with quantitative but not qualitative differences in the results. Unlike the analogous FeO+ + H-2 reaction, no evidence for spin inversion prior to the rate-limiting transition state is found. A crossing between septet and quintet potential energy surfaces in the product well exists, and the possibility of spin inversion on the way to products is discussed. The reaction coordinates inform a statistical treatment of the reaction, which well reproduces all kinetic results, including the product branching inversion observed due to isotope substitution. Published by Elsevier B.V.