关键词： 六连杆机构   运动学分析   静力学   动力学  

摘要： 提出了一种新型的单自由度六连杆机械压力机机构,为了实现机构的动态静力学以及动力学分析,采用复数矢量法建立了机构的运动学模型,基于达朗贝尔原理建立了机构的动态静力学方程,利用拉格朗日法建立了机构的动力学方程;分别利用MATLAB理论计算与ADAMS虚拟样机仿真得到压力机机构中滑块的位置曲线、速度曲线、加速度曲线,以及曲柄的平衡力矩和驱动力矩变化曲线。研究不仅为六连杆压力机运动学分析、平衡力矩和驱动力矩的求解和结构设计提供了理论依据,也为其他压力机机构的静力学和动力学分析提供了有效方法。

关键词： Atrial   KCNA5 mutations   Electromechanical coupling   Atrial contraction   Computer simulation  

摘要： A recent study has identified six novel genetic variations (D322H, E48G, A305T, D469E, Y155C, P488S) in KCNA5 (encoding Kv1.5 which carries the atrial-specific ultra-rapid delayed rectifier current, I-Kur) in patients with early onset of lone atrial fibrillation. These mutations are distinctive, resulting in either gain-of-function (D322H, E48G, A305T) or loss-of-function (D469E, Y155C, P488S) of Ikur channels. Though affecting potassium channels, they may modulate the cellular active force and therefore atrial mechanical functions, which remains to be elucidated. The present study aimed to assess the inotropic effects of the identified six KCNA5 mutations on the human atria. Multiscale electromechanical models of the human atria were used to investigate the impact of the six KCNA5 mutations on atrial contractile functions. It was shown that the gain-of-function mutations reduced active contractile force primarily through decreasing the calcium transient (CaT) via a reduction in the L-type calcium current (I-CaL) as a secondary effect of modulated action potential, whereas the loss-of-function mutations mediated positive inotropic effects by increased CaT via enhancing the reverse mode of the Na+/Ca2+ exchanger. The 3D atrial electromechanical coupled model predicted different functional impacts of the KCN5A mutation variants on atrial mechanical contraction by either reducing or increasing atrial output, which is associated with the gain-of-function mutations or loss-of-function mutations in KCNA5, respectively. This study adds insights to the functional impact of KCNA5 mutations in modulating atrial contractile functions. (C) 2017 The Authors. Published by Elsevier Ltd.

关键词： Ni   Boriding   Powder pack   Boride layer   Hardness  

摘要： Kinetics of boride layer growth and tensile behaviour in bonded commercial-purity nickel was investigated. Bonding was carried out in a solid medium consisting of Ekabor-II powders at 1173, 1223 and 1273 K for periods of 3, 5 and 8 h. Scanning electron microscopy (SEM) and optical microscopy showed column morphology in the boride layer. X-ray diffraction (XRD) analyses indicated that the boride layer formed on the surface consisted mainly of Ni2B, with precipitates of Ni6Si2B. A parabolic relationship between layer thickness and processing temperature was observed. The obtained results showed that although the boride layer thickness increased with increasing boriding temperature and time, boriding parameters had no significant effect on the hardness of the boride layer or the matrix. Tensile properties were negatively influenced by the bonding treatment;both yield and tensile strength values decreased due to the presence of the hard yet brittle surface coating. In addition, the growth kinetics of boride layers was also analysed. The results showed a nearly parabolic relationship between the layer thickness and the process temperature, with activation energy of 47.3 kJ mol(-1).

关键词： Yield stress  

摘要： Using molecular dynamics simulation, tension and bending tests of a Fe nanopillar are carried out to obtain its Young's modulus and yield strength. Then the comparative study of Young's modulus and yield strength of a Fe nanopillar under bending and tension are carried out varying its diameter in the range of diameter 1-15nm. We find out the reasons why bending Young's modulus and yield strength of a Fe nanopillar are higher than those of tension Young's modulus and yield strength of a Fe nanopillar. Using the mobility parameters of bulk Fe from the experimental study [N. Urabe and J. Weertman, Materials Science and Engineering 18, 41 (1975)], its temperature dependent stress-strain relationship, yield strength and strain hardening modulus are obtained from the dislocation dynamics simulations. Strain rate dependent yield strength and strain hardening modulus of bulk Fe pillars under tension are studied. Temperature dependent creep behaviors of bulk Fe pillars under tension are also studied. To verify the soundness of the present dislocation dynamics studies of the mechanical properties of bulk Fe pillars under tension, the stress vs. strain relationship and dislocation density vs. strain of bulk Fe pillars obtained by us are compared with the published results obtained by S. Queyreau, G. Monnet, and B. Devincre, International Journal of Plasticity 25, 361 (2009). (C) 2017Author(s).

关键词： CL-20/TNTcocrystal explosive   Molecular dynamics   Mechanical properties Sensitivity   Binding energy   Detonation performance  

摘要： To investigate and compare the differences of structures and properties of CL-20/TNT cocrystal and composite explosives, the CL-20/TNT cocrystal and composite models were established. Molecular dynamics simulations were performed to investigate the structures, mechanical properties, sensitivity, stabilities and detonation performance of cocrystal and composite models with COMPASS force field in NPT ensemble. The lattice parameters, mechanical properties, binding energies, interaction energy of trigger bond, cohesive energy density and detonation parameters were determined and compared. The results show that, compared with pure CL-20, the rigidity and stiffness of cocrystal and composite models decreased, while plastic properties and ductility increased, so mechanical properties can be effectively improved by adding TNT into CL-20 and the cocrystal model has better mechanical properties. The interaction energy of the trigger bond and the cohesive energy density is in the order of CL-20/ TNT cocrystal > CL-20/TNT composite > pure CL-20, i.e., cocrystal model is less sensitive than CL-20 and the composite model, and has the best safety parameters. Binding energies show that the cocrystal model has higher intermolecular interaction energy values than the composite model, thus illustrating the better stability of the cocrystal model. Detonation parameters vary as CL-20 > cocrystal > composite, namely, the energy density and power of cocrystal and composite model are weakened;however, the CL-20/TNT cocrystal explosive still has desirable energy density and detonation performance. This results presented in this paper help offer some helpful guidance to better understand the mechanism of CL-20/TNT cocrystal explosives and provide some theoretical assistance for cocrystal explosive design.

关键词： Advanced oxidation processes   Congo red   Langmuir-Hinshelwood   N-TiO2   Photocatalysis  

摘要： In this study, the photocatalytic degradation of Congo red has been investigated in N-doped TiO2 (N-TiO2) aqueous suspensions under visible light irradiation. Visible light-active N-TiO2 was successfully prepared at three different weight contents (2.5, 5, and 7%) employing sol-gel method. It was able to harvest the visible irradiation with wavelength suitable for activation. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometer, diffused reflectance UV-Vis spectroscopy, nitrogen adsorption Brunauer-Emmert-Teller, Raman spectroscopy, photoluminescence and X-ray photoelectron spectrometer were used to characterize the doped catalyst. The samples had a relatively large specific Brunauer-Emmert-Teller surface areas of about 42 m(2) g(-1) with average X-ray diffraction crystalline size of 52 nm and showed visible light photocatalytic activity at about 408 nm. The impacts of several operating parameters on the Congo red photodegradation process were examined. Langmuir-Hinshelwood model exhibited pseudo-first-order degradation kinetics. N-TiO2-assisted plausible photodegradation mechanism has been suggested based on the qualitatively detected intermediate compounds.

关键词： Arsenic   Biosorption   Kinetic   Mechanistic   Thermodynamic   Modelling  

摘要： In the present study, TW/MnFe2O4 composite (MTW) was synthesized and estimated as an effective biosorbent for removing As (III) and As(V) from wastewater. Physicochemical analysis of composite was performed through SEM-EDX. 86.615 and 83.478% removal efficiency were obtained by composite dosage of 2 g/L at contact time 120 min at temperature 30 degrees C and pH 7.0 and 4.0 for As(III) and As(V), respectively. Kinetic results study showed that Brouers-Weron-Sotolongo and Ritchie second-order for As(III) and Brouers-Weron-Sotolongo model for As(V) were capable to describe an accurate explanation of adsorption kinetic. Applicability of mechanistic models in the current study exposed that the rate-controlling step in the biosorption of both As(III) and As(V) on the surface of composite was film diffusion rather than intraparticle diffusion. The estimated thermodynamic parameters Delta G degrees, Delta H degrees and Delta S degrees revealed that the biosorption of both As(III) and As(V) on the composite was feasible, spontaneous and exothermic.

关键词： Foot   Mechanical energetics   Kinetics   Multi-segment foot model   Walking  

摘要： Introduction/aim: Foot structure has been implicated as a risk factor of numerous overuse injuries, however, the mechanism linking foot structure and the development of soft-tissue overuse injuries are not well understood. The aim of this study was to identify factors that could predict foot function during walking. Methods: A total of eleven variables (including measures of foot structure, anthropometry and spatiotemporal gait characteristics) were investigated for their predictive ability on identifying kinematic, kinetic and energetic components of the foot. Three-dimensional motion capture and force data were collected at preferred walking speed on an instrumented treadmill. Mechanical measures were subsequently assessed using a custom multi-segment foot model in Opensim. Factors with significant univariate associations were entered into multiple linear regression models to identify a group of factors independently associated with the mechanical measures. Results: Although no model could be created for any of the kinematic measures analysed, approximately 46% and 37% of the variance in the kinetic and energetic measures were associated with three or two factors respectively. Arch-height ratio, foot length and step width were associated with peak subtalar joint (STJ) moment, while greater STJ negative work was correlated to a low arch-height ratio and greater foot mobility. Conclusion: The models presented in this study suggest that the soft-tissue structures of a flat-arched, mobile foot are at a greater risk of injury as they have greater requirements to absorb energy and generate larger forces. However, as these associations are only moderate, other measures may also have an influence.

摘要： This study reports the synthesis of nanocrystalline undoped and europium doped BaWO4:Eu3+ nanophosphors by a mechanical activation process using high energy ball mill (HEBM) technique. The prepared nanophosphors were characterized systematically by Rietveld analysis of the X-ray powder diffraction (XRD) data, Raman spectroscopy, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The synthesized nanophosphors were found to possess spherical morphology and small particle sizes similar to 25 nm. To explore this material for application in luminescence, detailed time resolved photoluminescence studies were carried out. It was observed that it is a rare breed of phosphor material that exhibits exceptional luminescence properties such as the capability to give high emission output till 5.0 mol% without undergoing quenching and unique property to get excited by mid ultraviolet (MUV) light, near ultraviolet (NUV) light, as well as by visible light such as blue and green. It was also observed that energy transfer primarily takes place from tungstate group of host to Eu3+. In fact energy transfer from the host to Eu3+ becomes more and more efficient with the increasing concentration of Eu3+ ions. Two lifetime values are observed for all europium ion (Eu3+) concentrations, one of the order of 465-650 mu s (T-S, short lifetime) and the other of the order of 1050-1320 ms (T-L, longer lifetime). This reflects the fact that Eu3+ ions occupy two sites;regular symmetric Ba2+ site (S-1) and asymmetric site (S-2), which will be closer to charge compensating defects. Calculation of Judd-Ofelt parameter illustrated that at all europium concentrations, the local surrounding around it lacked inversion symmetry (asymmetric environment), and the exact point group symmetry around europium ion was found to be C-6v. The red purity (intense D-5(0)-F-7(2)) and high quantum efficiency (78%) of BaWO4:Eu3+ projects it as a new red ph