关键词： Bioreactor   Mixing   Gas hold-up   Numerical modeling   Gas-liquid pseudophase system  

摘要： The paper presents the results of numerical simulations of hydrodynamics in a gas-liquid pseudophase system (sucrose solution with yeast suspension). The simulations were performed in a bioreactor with a working volume of 0.02m(3), equipped with a Rushton turbine or Smith turbine stirrers. The results of the study were developed in the form of vectors of liquid velocity and the contours of the analyzed magnitudes. Also, the local values of the gas hold-up phi in the gas-liquid pseudophase system were presented. The results of numerical simulations of the gas hold-up were compared to the results of my own experimental study.

关键词： Laminated composites  

摘要： Nowadays, glass reinforced epoxy (GRE) pipes are industrially manufactured by the filament winding process using internal heating technology. This study deals with the comprehensive evaluation of a strategy aimed to improve the plant productivity by means of physical experiments, mechanical tests, and numerical simulations of the curing process. The reactive system is composed by diglycidyl ether of bisphenol A (DGEBA), methyltetrahydrophtalic anhydride (MTHPA), and benzyltriethyl ammonium chloride (BTEAC) used as initiator. An increase in BTEAC concentration in system formulation leads to a reduction in curing times of GRE pipes. The processing problems associated with this increment are proposed to be solved by the incorporation of a reactive diluent (RD) together with the optimization of the curing cycle. The effects that different amounts of 1,4-butanedioldiglycidyl ether (DGEBD) added as RD exerts on system viscosity, copolymerization kinetics mechanism, curing process and properties of matrix, laminated composites and GRE pipes are deeply analyzed. Results demonstrate that if a 10 wt% RD is used, not only the strategy turns out to be feasible but also GRE pipes performance is improved. POLYM. ENG. SCI., 59:344-354, 2019. (c) 2018 Society of Plastics Engineers

关键词： MECHANICAL behavior of materials   SILICON   DEFORMATIONS (Mechanics)   SILICON films   MOLECULAR dynamics   PLASTICITY  

摘要： The mechanical properties and deformation behaviors of monocrystalline silicon coated by an amorphous SiO2 film with different thicknesses are explored by nanoindentation process with molecular dynamics (MD) simulation. The results indicate that the calculated indentation modulus increases with the growing indentation depth for monocrystalline silicon with and without amorphous SiO2 film, while the modulus decreases with increasing film thickness at the same indentation depth. The derived hardness during indentation process, which is more sensitive to amorphous SiO2 film thickness, is complex due to the plastic deformation of SiO2 film, illustrating a deformation-induced softening behavior. The plastic deformation of amorphous SiO2 film exhibits four periods during whole indentation process, namely densification, densification-rupture transition, rupture during loading and elastic recovery during unloading, which are reasonably verified by CN number of silicon atoms and Si-O bond number within SiO2 film as a function of indentation depth. It is concluded that the SiO2 film acts as a medium to dissipate the energy and to transmit the stress from indenter to underlying silicon substrate. The MD results show that the differences of phase distribution between silicon with and without SiO2 film at the same penetration depth are driven by the stress.

关键词： Tungsten alloys   Mechanical activation   Spark plasma sintering   Diffusion   Grain boundaries   Strength  

摘要： This paper is a study of sintering mechanisms, structure, and mechanical properties of ultrafine-grained 95W-Ni-Fe tungsten heavy alloys. Powder particle sizes were controlled by mechanical activation (MA) of original coarse-grained components and by addition of ultrafine particles. W-Ni-Fe alloys were obtained by sintering in hydrogen and Spark Plasma Sintering (SPS) in a vacuum. The dependence of ultrafine-grained (UFG) alloy density on sintering temperatures has been found to be non-monotonic with a maximum corresponding to the optimal sintering temperature. It has been demonstrated that the sintering activation energy of UFG alloys is significantly lower than that of coarse-grained alloys. It has been shown that the optimal SPS temperature for mechanically activated nanopowders goes down by 350-400 degrees C in comparison with the optimal sintering temperature in hydrogen for coarse-grained 95W-Ni-Fe powder composition. The reason for a lower optimal sintering temperature lies in a decreased activation energy of grain-boundary diffusion and formation of a non-equilibrium solid solution of nickel and iron in the surface layer of tungsten ci-W particles during high-energy MA. High-energy MA and SPS were used to obtain samples of UFG tungsten alloys with high mechanical properties: macro-elastic limit - up to 2250 MPa, yield stress - up to 2500 MPa. (C) 2018 Elsevier B.V. All rights reserved.

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。