Batch Experiments for the Determination of the Ti(IV,III) Couple Formal Potential in 1 mol⋅dm<Superscript>−3</Superscript> HCl, 2 mol⋅dm<Superscript>−3</Superscript> NaCl Medium at 25 °C

The determination of the Ti(IV,III) redox couple formal potential in 1 mol⋅dm⁻³ HCl, 2 mol⋅dm⁻³ NaCl medium at 25 °C through batch experiments involving the preparation of Ti(IV) and Ti(III) mixtures via the reaction of Ti(IV) with zinc amalgam, has been carried out with Emf measurements in order to verify the correctness of the previous value that the authors obtained by a coulometric-potentiometric investigation in the same conditions. The results from the two independent methods are in good agreement: (9±1) mV by the first method and (9±2) mV by the average batch result.     

Electrochemical polarisation and galvanic couple behaviour of the primary phase of 55% Al–Zn coating investigated using band microelectrodes (BME) and band microelectrode arrays

Electrochemical polarisation experiments have shown that anodic dissolution processes on Al–40% Zn alloys are significantly enhanced in chloride compared to sulfate-based electrolytes. The aluminium content of the alloys allowed passive behaviour to be observed in sulfate electrolyte even in the presence of zinc-rich precipitates on the surface. Electrolyte pH affected cathodic processes, which was attributed to the rate of proton reduction and the passivity of the surface. Monitoring the OCP of the alloy band during polarisation of neighbouring zinc electrodes in band microelectrode (BME) arrays showed that generation of alkaline pH at the zinc electrodes affected the OCP of the alloy when the inter-electrode spacing was 10, 50, and 200 μm. Where elements of a BME array were close enough to interact via mass transport, the overall galvanic behaviour of the cell was found to be anodic or cathodic, whereas the alloy was consistently cathodic with respect to zinc in galvanic cells at larger separations. Dedicated to the 80th birthday of Keith B. Oldham.     

2-2型PMNT/NFO复合磁电效应模拟

利用弹性力学模型,基于铁电相与铁磁相的本构方程,建立磁电复合材料的本构方程,推导2-2型非理想耦合的磁电双层、三层复合薄膜的纵向、横向磁电(ME)电压系数.研究铁磁相材料铁酸镍(NFO)和铁电相材料铌镁酸铅-钛酸铅(PMNT)复合的磁电效应,分析复合材料的磁电电压系数与PMNT体积分数、界面耦合参数、两相体积比及复合总层数的关系.结果表明两相材料的性能、体积分数以及耦合系数、复合层数都影响磁电电压系数.     

Effects of size-dependent elasticity on stability of nanotweezers

It is well-recognized that the electromechanical response of a nanostructure is affected by its element size. In the present article, the size dependent stability behavior and nanotweezers fabricated from nanowires are investigated by modified couple stress elasticity （MCSE）. The governing equation of the nanotweezers is obtained by taking into account the presence of Coulomb and intermolecular attractions. To solve the equation, four techniques, i.e., the modified variational iteration method （MVIM）, the monotonic iteration method （MIM）, the MAPLE numerical solver, and a lumped model, are used. The variations of the arm displacement of the tweezers versus direct current （DC） voltage are obtained. The instability parameters, i.e., pull-in voltage and deflection of the system, are computed. The results show that size-dependency will affect the stability of the nanotweezers significantly if the diameter of the nanowire is of the order of the length scale. The impact of intermolecular attraction on the size-dependent stability of the system is discussed.     

Dynamic analysis and design of electrically actuated viscoelastic microbeams considering the scale effect

Viscoelastic phenomena widely exist in MEMS materials, which may have certain effects on quasi-static behaviors and transition mechanism of nonlinear jumping phenomena. The static and dynamic behaviors of a doubly clamped viscoelastic microbeam actuated by one sided electrode are investigated in detail, based on a modified couple stress theory. The governing equation of motion is introduced here, which is essentially nonlinear due to its midplane stretching effect and electrostatic force. Through quasi-static analysis, the equilibrium position, pull-in voltage and pull-in location of the system are obtained with differential quadrature method and finite element method. The equivalent geometric nonlinear parameter is presented to explain the influence of the scale effect on the pull-in location. Different from elastic material, there are two kinds of pull-in voltages called as instantaneous pull-in voltage and the durable pull-in voltage in viscoelastic system. Then, Galerkin discretization and the method of multiple scales are applied to determine the response and stability of the system for small vibration amplitude. A new perturbation method to deal with viscoelastic term is presented. Theoretical expressions about the parameter spaces of linear-like vibration, hardening-type vibration and softening-type vibration are then deduced. The influence of viscoelasticity and scale effect on nonlinear dynamic behavior is studied. Results show that the viscoelasticity can reduce the effective elastic modulus and make the system tend to softening-type vibration; the scale effect can increase effective elastic modulus and make the system tend to hardening-type vibration. And most of all, simulation results of case studies are used to realize parameter optimization. Then parameter conditions of linear-like vibration, which is desired for many applications, are obtained. In this paper, the results of multi-physical field coupling simulation are used to verify the theoretical analysis.     

Flow of couple stress fluid with variable thermal conductivity

The steady flow and heat transfer of a couple stress fluid due to an inclined stretching cylinder are analyzed. The thermal conductivity is assumed to be temperature dependent. The governing equations for the flow and heat transfer are transformed into ordinary differential equations. Series solutions of the resulting problem are computed. The effects of various interested parameters, e.g., the couple stress parameter, the angle of inclination, the mixed convection parameter, the Prandtl number, the Reynolds number, the radiation parameter, and the variable thermal conductivity parameter, are illustrated. The skin friction coefficient and the local Nusselt number are computed and analyzed. It is observed that the heat transfer rate at the surface increases while the velocity and the shear stress decrease when the couple stress parameter and the Reynolds number increase. The temperature increases when the Reynolds number increases.     

Elastic stress fields caused by a dislocation in Ge x Si1−x /Si film-substrate system

The elastic stress fields caused by a dislocation in Ge_xSi_(1-x) epitaxial layer on Si substrate are investigated in this work. Based on the previous results in an anisotropic bimaterial system,the image method is further developed to determine the stress field of a dislocation in the film-substrate system under coupled condition. The film-substrate system is firstly transformed into a bimaterial system by distributing image dislocation densities on the position of the free surface. Then,the unknown image dislocation densities are solved by using boundary conditions,i.e.,traction free conditions on the free surface. Numerical simulation focuses on the Ge0.1Si0.9/Si film-substrate system. The effects of layer thickness,position of the dislocation and crystallographic orientation on the stress fields are discussed. Results reveal that both the stresses σxx,σxz at the free surface and the stress σxy,σyy,σyz on the interface are influenced by the layer thickness,but the former is stronger. In contrast to the weak dependence of stress field on the crystallographic orientation the stress field was strongly affected by dislocation position. The stress fields both in the film-substrate system and bimaterial system are plotted.     

异质神经元的排列对环形耦合神经元网络频率同步的影响

以一维环形耦合的非全同FitzHugh-Nagumo神经元网络为研究对象,讨论这种异质神经元在环上的不同排列对其频率同步的影响.研究结果显示,异质神经元的排列不同,对应的神经元网络达到频率同步所需的临界耦合强度也不完全相同.在平均意义下,异质性较小的神经元在环上的距离越近,神经元网络达到频率同步所需的临界耦合强度越大;相反,异质性较大的神经元在环上的距离越近,神经元网络达到同步所需的临界耦合强度越小.通过对频率同步过程的分析,进一步给出了产生这一现象的动力学机理.     

DAIP树脂及其复合材料的性能研究

加入热固性丁苯树脂可降低DAIP树脂的酯键密度,提高其耐水性,在该体系中加入适量的偶联剂,可改善树脂与玻璃纤维的界面,提高复合材料的耐水性和介电性能。     

非对称的非局部塑性理论

从非局部连续场论出发，假定形变与局部转动均属微小，当存在体力矩出现非对称应力场时，设对称应力的能量函数和非对称应力的能量函数可以独立计算。基于热力学原理和屈服面的概念，建立了一种新的非对称－非局部弹塑性力学理论。