湿骨内动态力——电性质的实验研究

本文设计了一种研究骨力─电性质的测试装置。它既用来测量骨的静态力─电性质，又可用来测量骨的动态力─电性质。利用本装置对湿骨试件进行了测试，发现湿骨中压电效应也起作用。从实验上证明了在动态载荷作用下湿骨中的力─电电位主要来源于压电效应。     

骨的力–电效应研究方法与进展

骨组织在受到应力作用(正常的生理活动)变形后在骨内产生电位的现象称为骨的力–电效应,它主要包括压电效应和动电效应.研究骨在动态过程中产生的电位幅值和分布特点,不仅是了解电刺激骨生长机理的必要步骤,也是实现骨治疗和重建的生理基础.它一方面是用数学方法来描述外力作用下其电位大小与应力、应变、应变率及加载速率的关系,另一方面是考察生理环境(pH值、离子浓度、温度、湿度等)对电位的影响.首先对力–电理论进行了简单的介绍,重点总结了其研究方法,包括理论模型和分离式霍普金生杆冲击、弯曲变形及缓冲液中的动态测试等实验方法.此外,对骨替代材料和牙本质领域的力–电效应研究也进行了一定的综述.     

加载速率对骨的流动电位的影响

骨受力变形时所引起的压力驱动骨内哈佛氏管或骨小管内的液体流动,是骨内出现流动电位的外部原因.由于人体经常受动态载荷作用,研究骨在动态加载过程中流动电位的变化,更有助于了解骨细胞周围电环境的性质.为此,设计了流动电位测试系统,在骨试样两端施加梯形压力波.实验测量了在不同加载速率下流动电位的变化波形.结果显示,加载速率越高,流动电位有减小的趋势.分析认为这是由于微管中局部产生的湍流引起的.     

磁头/盘界面超薄气膜挤压效应和动压效应研究

针对求解磁头/磁盘界面动态气膜力时出现的不易收敛和编程复杂的问题,本文提出了基于PDE工具求解气体润滑的瞬态和稳态雷诺方程的方法,计算了具有不同最小气膜厚度的Tri-pad正压型和Tri-pad负压型浮动块空气轴承在加载和卸载过程中的瞬态和稳态气膜压力分布,求解了作用面上的轴承力,并将2种状态下超薄气膜挤压效应和动压效应对轴承力的影响进行了对比.仿真结果表明:该方法具有足够的求解精度,且收敛速度快,为研究具有复杂磁头形貌特征的超薄气体润滑的动态特性提供了方便、准确的方法.     

液腔体中气体射流冲击压力的实验测量

对充液腔体中气体射流的冲击效应进行了实验研究. 测量结果表明了冲击压力的瞬态最 大值、稳态平均值和脉动值随喷管进口压比的增加而增加，冲击区是主要的噪声源和动态压 力承载部位. 通过充气与充水两种状态的对比实验，还揭示了腔体充水时气体射流冲击压力 出现一个上冲阶段，其瞬态最大值比充气值有显著的增加.     

用边界元法计算裂纹的瞬态和稳态问题

首先引入Ｎａｒｄｉｎｉ－Ｂｒｅｂｂｉａ解瞬态动力问题的边界元法，并推广应用于解稳态动力问题。然后采用两次映射奇异元计算了平面瞬态和稳态的动裂纹问题，计算结果与其他解比较效果很好。最后对一些问题进行了讨论     

外加极化电位对双相不锈钢在硫酸介质中腐蚀磨损行为及摩擦性能的影响

利用专门设计制造的腐蚀磨损试验机，对在不同极化电位下双相不锈钢于硫酸介质中的腐蚀磨损行为和摩擦性能进行了试验研究，并且借助于扫描电子显微镜等对试样的磨损表面作了观察与分析．结果表明：采用适当的阴极保护可以有效地降低双相不锈钢的腐蚀磨损率；在钝化电位下的腐蚀磨损率比在自然电位和阴极保护电位下的都高；外加极化电位在阴极保护电位区或与动态腐蚀电位相当时，摩擦系数比自然电位下的低；钝化区的摩擦系数比自然电位下的高，可见此时钝化膜的减摩性能差；在钝化电位下当载荷高于１１．７Ｎ时，双相不锈钢的表面钝化膜遭受严重破坏     

应用于高速轮轨滚动接触的蠕滑理论算法对比研究

运用多体动力学仿真软件UM建立了车辆-轨道多体动力学模型，并基于轮轨滚动蠕滑理论对比分析了FASTSIM算法与CONTACT算法两者在稳态和瞬态滚动状态中轮轨动态作用力之间的差异.计算结果表明:列车以稳态滚动状态行驶在直线轨道和曲线轨道上时通过FASTSIM算法计算得出的横、纵向轮轨蠕滑力与CONTACT算法的计算值存在的差异值较小，达到了10%~15%，而在瞬态滚动状态下尤其是在大蠕滑以及考虑风阻等比较恶劣的工况下行驶时计算得出的横、纵向蠕滑力与CONTACT算法的计算值存在较大的误差，差值达到了25%，并且随着车速的增加，最大差异值达到了30%，这表明CONTACT算法在瞬态滚动工况下进行蠕滑力计算上相比于FASTSIM算法更加精准，更适用于作出对列车运行时的安全性方面的评价.      

热-应力耦合结构灵敏度分析方法

研究稳态／瞬态热传导灵敏度分析、以及热与机械荷载同时作用的热结构应力灵敏度分析问题。考虑了温度场随设计变量的变化及其对应力的影响,提出温度场与结构热应力耦合问题的灵敏度计算方法。特别指出了热－应力耦合灵敏度分析中温度场导数的影响, 说明了在热－应力耦合结构灵敏度分析中必须考虑耦合灵敏度。在应用软件系统JIFEX中实现了所提出的方法,数值算例验证了灵敏度算法的精度。     

轴承非线性油膜力的一种变分近似解

基于自由边值理论和凸集上的变分方法，提出一种求解当轴颈大扰动时实际轴承瞬态油膜力的近似公式。公式中引入一个参数来模拟油膜破裂自由边界（雷诺边界条件），则凸集上的泛函极值问题就转换为求此参数的代数极值问题。对椭圆轴承在轴颈作大范围扰动情况下的计算结果表明，这一方法达到了很高的精度，可用于转子－轴承系统的非线性动力分析，能大量降低数值计算瞬态油膜力所需的计算量。     

Active manipulation of EM fields in open waveguides

The central question addressed in this paper is whether we can introduce an antenna array into a circular cylindrical waveguide to accurately control or determine the local field around the array with vanishingly small reflection from the boundary of the waveguide. We ask this question since we perceive the answer to be important to the applied community through its relevance for applications to electromagnetic shielding or slot antennas. We make use of the results presented in Onofrei (2014) for the scalar Helmholtz equation and show, by using the Debye representation in waveguides, how they apply to the current EM waveguide model. We prove the existence of a class of solutions and include a feasibility discussion for the antenna synthesis problem together with relevant simulations.     

Comments on a recent paper by W. Zijl

A recent paper by W. Zijl, which reformulated the Navier–Stokes and Boussinesq equations in terms of Clebsch potentials, has an error that greatly reduces the generality of the results. Some other recent efforts to use such potentials in fluid and plasma dynamics are briefly discussed.     

Second gradient electrodynamics: Green functions,wave propagation,regularization and self-force

In this work, the theory of second gradient electrodynamics, which is an important example of generalized electrodynamics, is proposed and investigated. Second gradient electrodynamics is a gradient field theory with up to second-order derivatives of the electromagnetic field strengths in the Lagrangian density. Second gradient electrodynamics possesses a weak nonlocality in space and time. In the framework of second gradient electrodynamics, the retarded Green functions, first-order derivatives of the retarded Green functions, retarded potentials, retarded electromagnetic field strengths, generalized Liénard–Wiechert potentials and the corresponding electromagnetic field strengths are derived for three, two and one spatial dimensions. The behaviour of the electromagnetic fields is investigated on the light cone. In particular, the retarded Green functions and their first-order derivatives show oscillations around the classical solutions inside the forward light cone and it is shown that they are singularity-free and regular on the light cone in three, two and one spatial dimensions. In second gradient electrodynamics, the self-force and the energy release rate are calculated and the equation of motion of a charged point particle, which is an integro-differential equation where the infamous third-order time-derivative of the position does not appear, is determined.     

摩擦诱发的事件相关电位认知成分特征研究

本研究旨在讨论人在探索物体表面时由物体表面摩擦属性的影响而引起的脑电变化.而事件相关电位技术是观测这一变化的理想手段.试验通过Neuroscan 64导事件相关电位采集系统来采集脑电信号,采用Oddball范式来诱发P300电位,并观察摩擦诱发的事件相关电位的认知成分P300的潜伏期和峰值特点.样本为摩擦系数不一样但其他属性基本一致的三种纸类.受试者通过手指主动触摸的方式判断物体表面摩擦力大小,观察此过程中的事件相关电位.试验发现,摩擦系数大样本诱发的P300的潜伏期小,峰值大.摩擦系数小的样本诱发的P300潜伏期大,峰值小.     

Repair of a Plate with a Circular Hole by Applying a Patch

The stressed state of a thin elastic infinite plate with a circular hole covered by a circular patch of a greater radius is considered. The center of the hole coincides with the center of the patch. The patch is attached to the plate along its entire boundary. Stresses are prescribed at infinity on the plate and at the hole boundary. Complex Muskhelishvili potentials are found by the method of power series, and the behavior of stresses on the patch–plate interface and at the hole boundary is studied.     

Active sound control in 3D bounded regions

We consider active sound control with the preservation of wanted sound in 3D bounded regions via numerical experiments. In contrast to some previous papers which are based on the difference potential method, our approach in the present work is based on surface potentials. In active sound control, some bounded domain is shielded from noise generated outside by situating additional sources at the perimeter of the domain to be protected. The method does not require knowledge of the source of noise (nature, location, and intensity). The approach allows the presence of wanted sound in the shielded domain, which is preserved, while the noise is canceled. To implement the method, the only required knowledge is the total acoustic field at the perimeter of the shielded domain. A number of test cases in different 3D bounded domain configurations are considered in the frequency domain. Furthermore, for the first time the effect of the number of secondary sources on the noise cancelation is studied. A significant level of volume noise cancelation is achieved at most parts of the shielded domain.     

On thermodynamically consistent constitutive equations for fiber-reinforced nonlinearly viscoelastic solids with application to biomechanics

In this paper, we are interested in developing thermodynamically consistent constitutive equations for fiber-reinforced nonlinearly viscoelastic bodies, in particular for transversely isotropic nonlinearly viscoelastic solids, in isothermal processes. It follows from results in the theory of algebraic invariants that constitutive equations for such materials can be expressed in terms of functions of 18 independent invariants associated with deformation and fiber orientation: 10 of them are isotropic invariants and 8 of them are associated with the deformation and the orientation of the fiber. Among the 8 anisotropic invariants just 6 are related to the viscoelastic response. The terms in the Cauchy stress tensor associated to these 6 invariants are analyzed with respect to thermodynamical consistency, and we obtain restrictions for the corresponding constitutive coefficients. This framework is applied to viscoelastic potentials within the context of biomaterials.     

Component assembling model and its application to quasi-brittle damage

Potential energy can be approximated by “pair-functional” potentials which is composed of pair potentials and embedding energy. Pair potentials are grouped according to discrete directions of atomic bonds such that each group is represented by an orientational component. Meanwhile, another kind of component, the volumetric one is derived from embedding energy. Damage and fracture are the changing and breaking of atomic bonds at the most fundamental level and have been reflected by the changing of these components’ properties. Therefore, material is treated as a component assembly, and its constitutive equations are formed by means of assembling these two kinds of components’ response functions. This material model is referred to as the component assembling model. Theoretical analysis and numerical computing indicate that the proposed model has the capacity of reproducing some results satisfactorily, with the advantages of physical explicitness and intrinsic induced anisotropy, etc.     

A unified treatment of the elastic elliptical inclusion under antiplane shear

Summary A generalized and unified treatment is presented for the antiplane problem of an elastic elliptical inclusion undergoing uniform eigenstrains and subjected to arbitrary loading in the surrounding matrix. The general solution to the problem is obtained through the use of conformal mapping technique and Laurent series expansion of the associated complex potentials. The resulting elastic fields are derived explicitly in both transformed and physical planes for the inclusion and the surrounding matrix. These relations are universal in the sense of being independent of any particular loading as well as the geometry of the matrix. The complete field solutions are provided for an elliptical inclusion under uniform loading at inifinity, and for a screw dislocation interacting with the elastic elliptical inclusion.