关键词： 准连续型机械臂   动力学   牛顿欧拉法   置信域算法  

摘要： 针对一种具有17个自由度的准连续型机械臂开展动力学研究,利用牛顿欧拉法建立动力学模型,并借助Matlab对机械臂进行动力学仿真,得到机械臂运动过程中,每个关节转动所需要的力矩,进而将力矩转换为驱动绳拉力。同时,针对关节力矩与驱动绳拉力之间的转换,优化了最优化模型中的目标函数,采用置信域算法解决了驱动绳拉力值曲线不光滑的问题,并通过降元进一步缩减了计算时间。

关键词： 农业机械化   城乡收入差距   农村劳动力转移  

摘要： 在数理经济模型分析基础上,实证分析了农业机械化、农村劳动力转移、城乡收入差距之间的关系及其作用机制,研究发现:农业机械化可以缩小城乡收入差距,农村劳动力转移在农业机械化缩小城乡收入差距过程中发挥着中介作用。具体作用机制是,农业机械化会直接增加农村居民的农业生产经营收入,还能通过促进农村劳动力转移使农村居民的工资性收入增加,在二者共同作用之下,农村居民收入显著提高,城乡收入差距得以缩小。

关键词： PtS2 monolayer   Mechanical property   Tensile strain   Rectangular defects  

摘要： Using the classical molecular dynamics simulations, the mechanical properties of the PtS2 monolayer with rectangular defects have been investigated. Particularly, a counterintuitive defect enlargement method to recover from defect-induced mechanical degradation has been explored. As the rectangular defects are enlarged along the zigzag direction, the uniaxial tension has been firstly applied in the same direction. It's found that the Young's modulus (Y-s) increases slightly with the size of the defects. However, both the fracture strain and stress are increased obviously as the length of the rectangular defect increasing, indicating the recovery of the mechanical properties for the defective PtS2 monolayer. And this degradation recovery could be attributed to the higher degree of geometric asymmetry when the defect being lengthened. Then, the mechanical properties of the defective PtS2 monolayer under uniaxial tension in the armchair direction have also been studied. The calculations show that the Y-s, fracture strain and stress decrease significantly as the rectangular defect enlarging. These results suggest even though the defect itself can induce the mechanical degradation, enlargement of the defect along a direction may promote the mechanical recovery in the same direction.

关键词： Nickel-based superalloys   High-temperature oxidation   Breakaway   Gradient of microstructure and properties   Microtensile testing  

摘要： The oxidation behavior of a nickel-based superalloy was investigated from 650 to 1,000 degrees C for up to 1,000 h in air. Samples with thicknesses ranging from 20 to 500 mu m were used to document the evolutions of microstructure and oxide scale. Oxidation products and subsurface evolution of the metal microstructure were characterized by XRD and EDS analyses. Local breakaway was observed after 600 h at 800 degrees C and after 100 h at 900 degrees C due to the full consumption of Cr from the alloy. Room temperature tensile tests were performed on aged and pre-oxidized specimens with thicknesses ranging from 20 mu m to 500 mu m, at 800 degrees C. The results were compared to tensile tests performed on the as-received metallurgical state. Both size effects due to sample thickness reduction and to sample thickness/pre-oxidation width ratio were examined onto the mechanical behavior. Interestingly, the formation of TCP phases, the oxide layer and the subsequent Cr-depleted subsurface region from either aging or oxidation treatments impairs the mechanical integrity. Bulk and subsurface regions are impacted, especially for tens-of-micrometer thin samples.

关键词： 动力机械   电子控制   研究  

ISBN: (纸本)9787568071369

摘要： 本书为华中科技大学能源与动力工程学院动力机械工程系“动力机械电子控制技术”主讲教材，是顺应目前车辆动力系统电动化、智能化、网联化的发展趋势，以培养适应时代变化、兼具动力机械与电子控制技术的复合型和研究型人才为目标，总结近年来的教学改革与实践，参照当前有关国内外文献资料编写而成的。全书内容共分为6章，分别介绍了动力机械电子控制技术所涉及的控制理论与控制方法，电控系统开发及测试，汽油机电子控制技术，柴油机电子控制技术，电动汽车的电池、电机与电控技术，智能驾驶与智能网联汽车等。 本书具有鲜明的学科交叉性、时代性和综合性，可作为汽车工程、动力机械及工程、新能源汽车等专业的大学本专科课程教材，也可供相关工程技术人员参考。

关键词： Biopreservation   Bacteriocins   Diffusion   Permeability   Mechanical properties  

摘要： Films were prepared by casting 2% w/v apple pectin, 0.5% w/v low-acyl gellan and 2.2% w/v glycerol as plasticizer. Bioactive film (BF, films with 3912 International Units (IU) nisin/cm(2)) and control films (CF, films without nisin) were elaborated. The objective was to analyze the release kinetics of nisin from films to a food model, to determine the period of film bioactivity and potential use as antimicrobial packaging. The release of nisin from BF to a food model was determined at 5 degrees C and 30 degrees C. The release kinetics of nisin was fitted to the analytical solution of the Fick's second law for an infinite plate. The diffusion coefficients of nisin (D) were 5.22 x 10(-14)and 7.36 x 10(-14)m(2)/s for 5 degrees C and 30 degrees C, respectively. Besides, both films were characterized in their mechanical properties and gas permeabilities [oxygen (PO2) and water vapour permeability (WVP)]. The mechanical properties were reduced by the nisin incorporation, whereas PO(2)was increased, and no significant effect on WVP was observed.

关键词： CuxP/g-C3N4   Photo-Fenton reaction   Wastewater treatment   Anti-interference   Catalytic mechanism  

摘要： Metal-based Fenton-like catalysts usually activate H2O2 to produce free radicals ((OH)-O-center dot and O-2(center dot)) for the degradation of organic pollutants. However, a catalytic reaction dominated by free radicals is easily interfered with by various inorganic anions and water matrices. Herein, g-C3N4-wrapped copper phosphide (CuxP), as a highly efficient Fenton-like catalyst, was successfully synthesized by a simple low-temperature phosphidation method. The CuxP/g-C3N4 catalyst exhibited excellent catalytic ability for the removal of various organic contaminants over a wide pH range of 3-11. In addition, the catalyst exhibited strong anti-interference ability toward various inorganic anions (Cl-, SO42-, NO3-, F-, H2PO4-, HCO3- and CO32-) and water matrices (lake water, river water, tap water and simulated water matrix). The reasons for this performance were analyzed by verifying the mechanism of the catalytic reaction. Compared to the pure CuxP catalyst, the CuxP/g-C3N4 composite possessed good catalytic stability. The enhanced and deactivated mechanisms of the CuxP/g-C3N4 catalyst were systematically analyzed by a series of characterization techniques. A possible reaction mechanism was also proposed based on the experimental results. This work provides new insights into designing highly efficient metal-based Fenton-like catalysts with strong anti-interference ability to practically treat wastewater. (C) 2021 Elsevier Inc. All rights reserved.

关键词： Chemo-mechanical modelling   Hydrogels   Poroelastic effects   Crosslinking kinetics   Finite element simulations  

摘要： Hydrogels are mechanically stabilized through the action of external agents which induce the formation of crosslinks in the polymer network as a consequence of transport and reactive mechanisms. Crosslinking increases the stiffness of the construct, produces inelastic deforma-tions in the polymer network and interacts with the swelling capacity of hydrogels. The control of this process is hence crucial for fulfilling functional criteria in several technological fields, like drug-delivery or bioprinting. Nevertheless, experimental approaches for monitoring the crosslinking kinetics with the required resolution are currently missing. The development of new computational models in the field might open the way to novel investigation tools. This paper presents a thermodynamically consistent chemo-mechanical model in large deformation for reactive-diffusive mechanisms occurring during crosslinking in alginate hydrogels. The system accounts for shrinking and swelling effects, fluid movements, as well as the reaction kinetics of calcium-induced crosslinking. Crosslinks alter mechanical and diffusive properties in the hydrogel. Moreover, on the basis of thermodynamic arguments, internal stresses directly affect the crosslinking kinetics, revealing a two-way coupling between mechanics and chemistry. The model is implemented in a finite element framework, considering a monolithic coupling between chemical transport and mechanics. The computational framework allows characterizing the (experimentally inaccessible) heterogeneous distribution of mechano-chemical quantities and properties in the hydrogel. Parametric campaigns of simulations are presented to investigate hydrogels' behaviour and compare numerical outcomes with available experimental evidence.

关键词： Subcooled flow boiling   Bubble sliding   Wall heat flux partitioning model   Bubble dynamics  

摘要： This paper aimed to develop a mechanistic model for wall heat flux partitioning based on bubble dynamics in horizontal subcooled flow boiling. The model was established from two dimensions of space and time. In the space dimension, the heating surface was divided into three regions based on the motion characteristics of bubbles, including bubble nucleation region, bubble sliding region, and non-boiling region. In the time dimension, the heat transfer mechanism on the heating surface of the bubble nucleation region and bubble sliding region could be divided into evaporation, condensation, and transient heat transfer. An evaporation model for subcooled boiling was developed based on condensation at the top of the bubble. A transient quench heat transfer model for subcooled flow boiling was modified. The heat flux of each region was obtained by the sum of the time-averaged heat fluxes of these heat transfer mechanisms during a bubble periodic time. The total wall heat flux was obtained by the sum of the area weights of the heat fluxes in these three regions. The new wall heat flux partitioning model and the RPI model were used to predict the experimental values at a variety of flow conditions. The results showed that the new model could well predict the experimental values and the deviation between the predicted heat flux and the experimental results was within 25%. The study also found that it was necessary to consider the condensation at the top of the bubble and the heat transfer mechanism caused by bubble sliding. (C) 2021 Elsevier Ltd. All rights reserved.

关键词： Hydrogen charging kinetics   Mg-10 wt% Fe2O3   Rate-determining steps   Dissociative chemisorption   Hydrogen diffusion  

摘要： The rate-determining steps in the hydrogen charging of Mg-10Fe(2)O(3), prepared by mechanical milling in hydrogen (MgH2-forming mechanical milling), were analyzed by comparing dependences of hydrogen charging rate on hydrogen pressure and temperature with those of previously established theoretical rate equations. Hydrogen charging of the activated Mg-10Fe(2)O(3) can be classified into dissociative chemisorption of hydrogen molecules on particle surfaces, diffusion of hydrogen atoms through a thickening Mg hydride layer, and chemical reaction of Mg with hydrogen at the interface. The dependences of the initial hydrogen charging rates on hydrogen pressure (linear) and temperature (Arrhenius equation / T-1/2) showed that the rate-determining step of the hydrogen charging of Mg-10Fe(2)O(3) was the dissociative chemisorption of hydrogen molecules on the surfaces of Mg and/or Fe in the initial hydrogen charging stage. In the later stage, the diffusion of hydrogen atoms through the thickening Mg hydride layer determined the hydrogen charging rate of Mg-10Fe(2)O(3).