关键词： Mg   Hydrogen storage materials   Hydrogen desorption   Kinetics   Dehydriding enthalpy   Mechanical alloying  

摘要： Mg95Sn3Zn2 alloy was prepared by mechanical alloying. The phase constituents and phase transition were analyzed by X-ray diffraction (XRD) method. The microstructure was characterized by scanning electron microscope (SEM). The hydrogen storage properties were evaluated in detail by the measurements of isothermal hydrogen absorption and desorption, and pressure-composition isotherms (PCI) using the Sieverts method. The addition of Zn benefits to extend the solubility of Sn in the Mg lattice, as a result supersaturated Mg(Sn, Zn) ternary solid solution was synthesized by mechanical alloying, which decomposed to MgH2, Sn and MgZn2 in the hydrogenating process. The in situ formed nanostructure Mg2Sn and MgZn2 have positive effects on the hydrogen absorption and desorption of Mg. Mg95Sn3Zn2 alloy showed significantly improved kinetics with lowered hydrogen absorption and desorption activation energies of 38.1 kJ/mol and 86.6 kJ/mol respectively, and exhibited a reduced dehydriding enthalpy of 67.0 +/- 1.9 kJ/(mol.H-2). (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Oligomers   Molecular mechanics   Organic compounds   Sodium   Lithium  

摘要： Salts of 12-hydroxystearate are important organogelators and grease thickeners, but a structural rationale for their rheological properties remains elusive. We use quantum mechanical calculations and molecular dynamics (MD) simulations to analyze aggregate structures for (1) (R)-12-hydroxystearic acid ((R)-12HSA), (2) lithium (R)-12-hydroxystearate ((R)-Li12HS), and (3) sodium (R)-12-hydroxystearate ((R)-Na12HS). First, quantum mechanical calculations were used to establish the structure and complexation energies of dimers of acetic acid, lithium acetate, and sodium acetate. The expected acetic acid dimer is predicted, and both the lithium acetate and sodium acetate dimer formed a C-2h-symmetric structure. All dimers were sufficiently stable to allow modeling them as pseudocovalent complexes in all-atom, explicit solvent MD. After microsecond-long MD, all systems produced strong ringlike ordered nuclei. The C-2h lithium salt molecules produced aggregates that had the most efficient packing at the head group and a higher frequency of hydroxyl hydrogen bonding compared to the sodium salt. This ordering propensity explains the high melting temperature of (R)-Li12HS. Also, the higher frequency of hydrogen bonding leads to fewer solvent-exposed hydrogen bond partners. This explains why lithium is a common counterion in high-temperature and water-resistant greases.

关键词： Molybdenite   Mechanical activation   Solid state reaction   Leaching  

摘要： The mechanical activation was applied as a pre-treatment method to improve molybdenite (MoS2) leaching. The effects of grinding ball size, ball to powder mass ratio, milling speed and time, molar ratio of mineral to oxidants, as well as the influence of solution pH, temperature and leaching time were investigated in detail. The results showed an extremely low Mo extraction (less than 2% at acidic and neutral conditions) for MoS2 activated alone. However, Mo extraction was increased significantly after co-grinding of MoS2 with NaClO2 and Na2CO3, e.g., more than 58% in any leaching solution applied. Prolonging the grinding time improved Mo extraction but the efficiency was declined gradually, giving rise to an optimum grinding efficiency at 4 h with a molar ratio of 1:3:5 for MoS2:NaClO2:Na2CO3. Distilled water was selected as the leaching solution since this gave similar Mo recovery to other lixiviants. Higher temperature and longer leaching time were beneficial to Mo extraction. However, it was also found that too large grinding balls and high ball to powder mass ratio adversely affected MoS2 extraction. The kinetics analysis indicated that the leaching of activated MoS2 followed a chemical reaction controlled mechanism. The XRD and SEM analyses indicated that mechanical activation not only reduced the particle size of MoS2 but also triggered solid state reaction to produce soluble Na2MoO4, thereby improving Mo extraction significantly.

关键词： Semicrystalline polyethylene   Coarse-grained molecular dynamics   Tie chains and entanglements  

摘要： Blending different molar mass fractions of polyethylene (PE) in order to obtain materials with higher fracture toughness has previously proven beneficial. Our approach has been to use coarse-grained (CG) molecular dynamics (MD) simulations to obtain semicrystalline polyethylene systems on a nanoscale, and then draw them in order to mimic tensile testing. The CG potentials were derived, validated and utilized to simulate melt equilibration, cooling, crystallization and mechanical deformation. Crystallinity, tie chain and entanglement concentrations were continuously monitored. During crystallization, the low molar mass fraction disentangled to a greater degree and ended up with a lower entanglement density than the high molar mass fraction, although the tie chain concentration was higher for the low molar mass fraction. The deformation behavior of semicrystalline PE above its glass transition temperature was then assessed in a uniaxial tensile deformation simulation. The low-strain mechanical properties (i.e. elastic modulus, yield stress and strain) were in accordance with the literature. The high-strain mechanical features and toughness were improved in bimodal systems. The presence of a high molar mass fraction in bimodal systems was shown to affect the crystallinity and tie chain concentration during the strain hardening, leading to tougher model systems. Finally, the bimodal system with equal shares of the molar mass fractions showed the highest toughness and the best ultimate mechanical properties while having a concentration of tie chains and entanglements intermediate between the values for the other systems. This was a clear sign of the non-exclusive role of tie chains and entanglements in the mechanical behavior of bimodal PE and more generally of semicrystalline polymers at high strains.

关键词： 舒芬太尼   芬太尼   机械通气   血流动力学   Meta分析  

摘要： 目的研究舒芬太尼(sufentanil)与芬太尼(fentanil)对重症患者机械通气血流动力学的影响。方法计算机检索PubMed、The Cochrane Library、CNKI、VIP及WanFang Data数据库,查找比较舒芬太尼与芬太尼对重症患者机械通气血流动力学影响的随机对照试验(RCT),检索时限为建库至2018年4月25日。同时手检纳入文献的参考文献。按纳入与排除标准由两人独立进行文献的筛选、资料提取和质量评价后,采用RevMan5.3软件进行Meta分析。结果共纳入11个研究,舒芬太尼组307例,芬太尼组302例。Meta分析结果显示:舒芬太尼组较对照组插管后收缩压低[MD=-10.51,95%CI (-20.50,-0.53), P=0.04];舒芬太尼组平均动脉压较对照组高[MD=7.86, 95%CI(5.37,10.34),P<0.01];舒芬太尼组插管后心率较对照组低[MD=-7.63, 95%CI (-14.25,-1.01),P=0.02];舒芬太尼组插管后心指数较对照组高[MD=7.76,95%CI (6.45, 9.06),P<0.01];舒芬太尼组插管各期的舒张压、呼吸频率及氧饱和度与对照组相比,差异均无统计学意义(P>0.05)。结论舒芬太尼组较芬太尼组对插管后危重患者的循环系统抑制更低,血流动力学更稳定,更好地保护机械通气患者的心肺功能。

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。