关键词： 机械动力学   力学模型   教学体系   教学方法  

摘要： 立足"机械动力学"课程的特点及教学过程中存在的问题,探索适合课程及学生知识结构特点的教学体系和教学方法。在教学体系中,注重实际问题与理论内容的结合,强调根据机械系统的物理模型建立力学模型能力的培养。在教学实践中,提出教师讲授与学生分组讨论相结合、教案与网络教学资源相结合、理论计算与软件分析相结合等多种教学方式,以提高学生学习的自觉性及参与度,提高"机械动力学"课程的教学质量。

关键词： 波度密封   空化   热传导   热效应  

摘要： 基于流体润滑理论,考虑润滑液膜空化现象和润滑液膜与密封环之间的热传导作用,建立波度端面机械密封三维流固热耦合模型,采用SUPG有限单元法求解广义雷诺方程、能量方程和热传导方程,计算端面液膜压力、开启力、泄漏率、摩擦因数等参数,对比分析密封热流体动力润滑(THD)和流体动力润滑(HD)密封特性。结果表明:随着转速、密封压力、波幅、波数的增加,开启力和泄漏率增加,摩擦因数减小;随着坝宽比、初始膜厚的增加,开启力和泄漏率减少,摩擦因数增加。热效应对密封性能影响显著,随着端面摩擦热升高,润滑液膜压力降低。

关键词： crystallization   mathematical modeling   Span 60   stearic acid   viscoelastic  

摘要： Modulation of crystallization of stearic acid and its derivatives is important for tuning the properties of stearate oleogels. The present study delineates the crystallization of stearic acid in stearate oleogels in the presence of Span 60. Microarchitecture analysis revealed that stearic acid crystals in the oleogels changed its shape from plate-like structure to a branched architecture in the presence of Span 60. Consequently, a significant variation in the mobility of the solute molecules inside the oleogel (Fluorescence recovery after photobleaching studies, FRAP analysis) was observed. Thermal analysis (gelation kinetics and DSC) revealed shortening of nucleation induction time and secondary crystallization with an increase in the Span 60 concentration. Furthermore, isosolid diagram suggested better physical stability of the formulations at higher proportions of Span 60. XRD analysis indicated that there was a decrease in the crystal size and the crystallinity of the stearic acid crystals with an increase in Span 60 concentration in the Span 60 containing oleogels. However, crystal growth orientation was unidirectional and found unaltered with Span 60 concentration (Avarmi analysis using DSC data). The mechanical study indicated a composition-dependent variation in the viscoelastic properties (instantaneous [(1)], intermediate [(2)], and delayed [(3)] relaxation times) of the formulations. In conclusion, Span 60 can be used to alter the kinetics of the crystallization, crystal habit and crystal structure of stearic acid. This study provides a number of clues that could be used further for developing oleogel based formulation.

关键词： sediment transport   morphodynamic evolution   wave base  

摘要： Using energetics-based formulations for wave-driven sediment transport, we develop a robust methodology for estimating the morphodynamic evolution of a cross-shore sandy coastal profile. In our approach, wave-driven cross-shore sediment flux depends on three components: two onshore-directed terms (wave asymmetry and wave streaming) and an offshore-directed slope term. In contrast with previous work, which applies shallow water wave assumptions across the transitional zone of the lower shoreface, we use linear Airy wave theory. The cross-shore sediment transport formulation defines a dynamic equilibrium profile and, by perturbing about this steady state profile, we present an advection-diffusion formula for profile evolution. Morphodynamic Peclet analysis suggests that the shoreface is diffusionally dominated. Using this depth-dependent characteristic diffusivity timescale, we distinguish a morphodynamic depth of closure for a given time envelope. Even though wave-driven sediment transport can (and will) occur at depths deeper than this morphodynamic closure depth, the rate of morphologic bed changes in response to shoreline change becomes asymptotically slow. Linear wave theory suggests a shallower shoreface depth of closure and much sharper break in processes than shallow water wave assumptions. Analyzing hindcasted wave data using a weighted frequency-magnitude approach, we determine representative wave conditions for selected sites along the U.S. coastline. Computed equilibrium profiles and depths of closure demonstrate reasonable similarities, except where inheritance is strong. The methodology espoused in this paper can be used to better understand the morphodynamics at the lower shoreface transition with relative ease across a variety of sites and with varied sediment transport equations.

关键词： hydrodynamic evaluation   mechanical flocculation   model of series of stirred tanks   outlet configuration   short-circuit   water treatment  

摘要： This paper focuses on hydrodynamic research aiming at the short-circuit evaluation of five different outlet configurations through the compartments of a mechanical flocculation unit of vertical shaft with mixing paddles at pilot scale. The tests were carried out with two, three and four compartments, variable and constant velocity gradients, including alternating senses of paddle rotation (clockwise in the first compartment, anticlockwise in the following one and so on). The research pointed out that the relevance of outlet configuration increases with the reduction of the number of compartments. In opposite, the velocity gradient and the sense of the paddle rotation seem less significant features. These results suggest the possibility of a viable increasing of performance, with low financial investments, mainly for flocculation units with three or two compartments installed in overloaded water treatment plants.

关键词： membrane transport   P-glycoprotein   permeability   micelle   thermodynamics   mathematical modeling   biophysical model   passive diffusion   transcellular transport  

摘要： An approach to characterizing P-glycoprotein (Pgp) interaction potential for sparingly water-soluble compounds was developed using bidirectional transport kinetics in MDR1-MDCK cell monolayers. Paclitaxel, solubilized in a dilute polysorbate 80 (PS80) micellar solution, was used as a practical example. Although the passage of paclitaxel across the cell monolayer was initially governed by the thermodynamic activity of the micelle-solubilized drug solution, Pgp inhibition was sustained by the thermodynamic activity (i.e., critical micelle concentration) of the PS80 micellar solution bathing the apical (ap) membrane. The mechanistic understanding of the experimental strategies and treatment of data was supported by a biophysical model expressed in the form of transport events occurring at the ap and basolateral (bl) membranes in series whereas the vectorial directions of the transcellular kinetics were accommodated. The derived equations permitted the stepwise quantitative delineation of the Pgp efflux activity (inhibited and uninhibited by PS80) and the passive permeability coefficient of the ap membrane, the passive permeability at the bl membrane and, finally, the distinct coupling of these with efflux pump activity to identify the rate-determining steps and mechanisms. The J(max)/K*(M) for paclitaxel was in the order of 10(-4) cm/s and the ap- and bl-membrane passive permeability coefficients were asymmetric, with bl-membrane permeability significantly greater than ap. (C) 2016 American Pharmacists Association (R). Published by Elsevier Inc. All rights reserved.

关键词： Desensitizing effect   Mechanical properties   Molecular dynamics   Polymer-bonded explosives (PBX)   TKX-50  

摘要： To improve the practicality and safety of a novel explosive dihydroxylamm onium 5,5'-bis (tetrazole)-1, 1'-diolate (TKX-50), polyvinylidene difluoride (PVDF) and polychlorotrifluoroe-thylene (PCTFE) were respectively added to the TKX-50, forming the polymer-bonded explosives (PBX). Interfacial and mechanical properties of PBX were investigated through molecular dynamics (MD) method, desensitizing mechanisms of fluorine-polymers for TKX-50 were researched by compression and bulk shear simulations. Results show that the binding energies (E-bind) between polymers (PVDF or PCTFE) and TKX-50 surfaces all rank in order of (011) > (100) > (010), shorter interatomic distance and the resulted higher potentials lead to higher E-bind on TKX-50/PVDF interfaces than that on PCTFE/TKX-50 interfaces. Compared with TKX-50, the ductility of PBX is improved due to the isotropic mechanical property and flexibility of fluorine-polymers especially the PCTFE. Desensitizing effect of fluorine-polymers for TKX-50 is found under loading condition, which is attributed to the enhanced compressibility and buffer capacity against external pressure in compression, as well as the improved lubricity to reduce the sliding potentials in bulk shear process.

关键词： Nano- and opto-mechanics   Parametric resonance   Quantum effects   Non-linear systems  

摘要： We investigate the behaviour of two non-linearly coupled flexural modes of a doubly clamped suspended beam (nanomechanical resonator). One of the modes is externally driven. We demonstrate that classically, the behavior of the non-driven mode is reminiscent of that of a parametrically driven linear oscillator: it exhibits a threshold behavior, with the amplitude of this mode below the threshold being exactly zero. Quantum-mechanically, we were able to access the dynamics of this mode below the classical parametric threshold. We show that whereas the mean displacement of this mode is still zero, the mean squared displacement is finite and at the threshold corresponds to the occupation number of 1/2. This finite displacement of the non-driven mode can serve as an experimentally verifiable quantum signature of quantum motion. (C) 2015 Elsevier B.V. All rights reserved.

关键词： BSCCO   Thermal properties   Avrami parameter   DTA/TG   Vickers microhardness  

摘要： This study deals with the effects of Ru-Bi partial substitutions on the thermal, structural and mechanical properties of Bi1.8-x Ru (x) Pb0.2Sr2CaCu2O10+delta (x = 0.0, 0.025, 0.050, 0.075) system, produced by using glass ceramics method. The effects of Ru-Bi partial substitutions on glass transition, nucleation and crystallization temperature were analyzed via differential thermal analyzer (DTA). Besides, microstructure and micromechanical properties of Ru-Bi partially substituted BSCCO glass ceramics were also investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers microhardness measurements. From the DTA results, nucleation kinetics were studied by using Ozawa, Augis-Bennett, Takhor and Kissinger equations. In addition to this, activation energies and Avrami parameters were also calculated. According to the results of the thermogravimetric analyses, the amount of oxidation was seen to be increased with increasing Ru concentration. Moreover, the lattice parameters, volume fractions and surface morphologies of our newly produced glass ceramics were investigated by XRD and SEM measurements, respectively. RISE behavior obtained from the microhardness measurements for all samples. Microhardness, elastic modulus, yield strength and fracture toughness values decreased with increasing Ru doping.

关键词： Polyethylene terephthalate   Silica   Glass transition temperature   Mechanical properties   Molecular dynamics simulation  

摘要： In this study, the glass transition behavior and mechanical properties of polyethylene terephthalate) (PET), PET/silica nanocomposite and PET/hydroxylated silica nanocomposite were studied through molecular dynamics (MD) simulations. It was found that the density and the specific volume of PET, PET/silica nanocomposite and PET/hydroxylated silica nanocomposite regularly changed along with the changes of temperature and the transition occurs at the Tg point, the simulation results show the addition of nanosilica decreased Tg of PET in PET/silica nanocomposite, but the addition of hydroxylated silica increased Tg of PET in PET/hydroxylated silica nanocomposite,and the underlying mechanism resulting in the change of the glass transition temperature of nanocomposite was discussed. Moreover, the thermal and mechanical properties of the systems were characterized, The MD simulations showed that the addition of silica, particle increases Young's modulus, bulk modulus, Poisson's ratio, lame constants and compressibility of PET/silica nanocomposite in comparison with those in the pure PET system. (C) 2015 Elsevier Ltd. All rights reserved.