Single-test determination of the friction coefficient and stress-strain curve for application in metal-forming analyses

The compression test of a ring is customarily used to determine the friction coefficient in metal-forming problems. The aim of this paper is to describe a procedure to obtain, for metals in the large deformation range, the stress-strain curve and friction coefficient through the same test. The friction coefficient is evaluated by comparing curves obtained by a finite element code with the experimental curves. The stress-strain curve is obtained by inverting an analytical solution, calculated by a lower-upper-bound approach. Good results in terms of accuracy are obtained.     

Methodological considerations in the study of genetic discrimination

The potential significance and dimensions of genetic discrimination have been described extensively in published literature, but epidemiological and verified case data are limited. Obtaining unbiased data from individuals about discrimination which has been based on erroneous or unjustifiable assumptions about their genetic predispositions poses unique challenges. Through review and discussion of research literature, we identify methodological considerations for collecting valid epidemiological data on genetic discrimination from individuals in the community; in particular, we consider issues which relate to sampling, selection and response. We identify issues to promote sound study design, with particular attention to verification of genetic discrimination, and highlight the importance of clinical and genetic knowledge of complex genotype-phenotype relationships.     

Finite element implementation and numerical issues of strain gradient plasticity with application to metal matrix composites

A framework of finite element equations for strain gradient plasticity is presented. The theoretical framework requires plastic strain degrees of freedom in addition to displacements and a plane strain version is implemented into a commercial finite element code. A couple of different elements of quadrilateral type are examined and a few numerical issues are addressed related to these elements as well as to strain gradient plasticity theories in general. Numerical results are presented for an idealized cell model of a metal matrix composite under shear loading. It is shown that strengthening due to fiber size is captured but strengthening due to fiber shape is not. A few modelling aspects of this problem are discussed as well. An analytic solution is also presented which illustrates similarities to other theories.     

EVOLUTIONARY DYNAMIC MODEL OF POPULATION WITH NICHE CONSTRUCTION AND ITS APPLICATION RESEARCH

Based on the theories and approaches in biomechanics, the mechanism and pattern of niche construction were discussed systematically. Through establishing the spatial pattern of niche and its measuring-fitness formula, and the dynamic system models of single- and two-population with niche construction, including corresponding theoretical analysis and numerical simulation on their evolutionary dynamics of population and the mechanism of competitive coexistence, the co-evolutionary relationship between organisms and their environments was revealed. The results indicate that population dynamics is governed by positive feedback between primary ecological factors and resource content. Niche construction generates an evolutionary effect in system by influencing the fitness of population. A threshold effect exists in single population dynamic system. In dynamic system of two competitive populations, niche construction can lead to alternative competitive consequences, which may be a potential mechanism to explain the competitive coexistence of species.     

DNA on loan: issues to consider when carrying out genetic research with aboriginal families and communities

In the current research milieu where genetic etiology is considered a critical component in the discovery of pathogenesis, aboriginal families and communities affected with genetic conditions may be considered as research participants. However, because of concerns about the impact of genetic information and historical harmful research practices, some aboriginal communities have considerable unease when faced with this prospect. Therefore, in the circumstance that genetics is considered an important part of research inquiry by aboriginal families and communities, there needs to be assurance that the research will be carried out according to mutual expectations. A research relationship that respects aboriginal individuals and communities within their culture and is in keeping with their values is essential. This respect extends to the use of biological samples, considering the DNA to be 'on loan' to the researcher for the purpose of the research for which consent was obtained. This paper will explore practical ways of maintaining a respectful research relationship when genetics research with aboriginal people is undertaken.     

Some problems and issues in geophysical turbulence

Velocity fluctuations in the large scales of the atmosphere's meso-scale have turbulent characteristics of random fluctuations and a scale-size distribution near k^−5/3 (Gage, 1979. J. Atmos. Sci. 36, 1950–1954; Lilly, 1983. J. Atmos. Sci. 40, 749–761; Lilly et al., 1998. Theoret. Comput. Fluid Dyn. 11, 139–153). Explanations of this motion field have ranged from inverse cascading quasi-geostrophic (i.e. quasi-two-dimensional) turbulence, to gravity waves (VanZandt, 1982. Geophys. Res. Lett. 9, 575–578). We describe efforts to relate observational spectra to various theories ranging from quasi-geostrophic turbulence to gravity waves. We note that at the larger scales quasi-geostrophic theory may suffice, but at smaller scales, a quasi-geostrophic explanation becomes untenable because the importance of rotation becomes progressively weaker as scales of the flow becomes smaller (the Rossby number approaches unity). We then discuss numerical simulations designed to discriminate between alternative explanations of the flow. Several simulations are reviewed, starting with those of Herring and Métais (1989. J. Fluid Mech. 202, 97–115), and finally those described by Lilly et al. (1998. Theoret. Comput. Fluid Dyn. 11, 139–153).     

方法论在材料力学课程教学中的应用

将科学方法论中的一些方法引入到材料力学课程教学之中. 经过对几届学生的教学实践表明：学生们不仅能够掌握该课程的内容,而且还能学到科学方法. 掌握了方法论的方法,这对学生今后学习新知识、新技能和培养学生独立思考解决问题以及创新能力很有益处.     

Legal and policy issues in genetics and insurance

Genetic screening and testing techniques provide a powerful diagnostic tool for the acquisition of predictive information. The potential value of such diagnostic techniques cannot be overstated. However, commercial organisations such as insurance companies and employers are also highly interested in the acquisition and use of genetic information. Concerns about the potential abuse of genetic information have stimulated a counter-current of public pressure for restrictions on the use which can be made of genetic diagnostic information. In a number of countries this pressure has generated enough concern to stimulate legislatures to enact laws which curtail the use and acquisition of genetic information. This pattern has clearly emerged in the United States of America and there are indications that similar trends are developing in Europe. This paper examines the law and policy issues arising from the interface between genetics and insurance.     

射影平面在结构几何组成分析中的应用

针对欧氏几何中平行线无交点等几何现象,引入了欧氏空间中射影平面的模型,使中心射影的对应完备化,使无穷远点、无穷远直线等抽象的几何概念在结构分析中直观化．从而,完善了平面结构几何组成规则中的一些结论．     

An application of enhanced heating surface with mini-reentrant cavities for flow boiling research in minichannels

The paper presents the results of flow boiling heat transfer in a minichannel 1.0 mm deep and 40 mm wide, vertically oriented. The heating element for the working fluid (FC-72) that flows along the vertical minichannel is thin, single-sided enhanced alloy foil. In the selected area or on the entire enhanced side of the heating foil mini-reentrant cavities distributed unevenly were formed. Liquid crystal thermography has been used for measuring the two-dimensional temperature distribution on the plain side of the heating foil. Simultaneously, the observations of the flow structures have been carried out on the enhanced side of the heating foil contacting fluid in a minichannel. The results are presented as void fraction dependence along the minichannel length for the selected cross-sections. Exemplary boiling curves obtained from initial increasing and subsequent decreasing the heat flux supplied to the foil are also presented.     

An analytical model of a matrix heat exchanger with longitudinal heat conduction in the matrix in application for the exchanger dynamics research

The paper presents an analytical method for the solution of the problem of a fixed matrix heat exchanger with axial heat conduction within the matrix. The small parameter method and Laplace transform have been applied. A general solution has been obtained for the unsteady state in the form of function series, using single and double convolutions of functions, as well as a particular solution for both the uniform and non-uniform initial temperature of the matrix and for an arbitrary function of the fluid temperature at the inlet. Particular solutions have been used in the study of the matrix dynamics in determining dynamic characteristics for the standard input signals in the form of: Dirac pulse, Heaviside function and the function of sinusoidal variable temperature of the fluid at the inlet. The results obtained both illustrate and enable the assessment of the effect of axial heat conduction in the matrix on the dynamic properties of the heat exchanger.

---

Investigation of the damage variable basic issues in continuum damage and healing mechanics

Consistent mathematics and mechanics are used here to properly interpret the damage variable within the confines of the concept of reduced area due to damage. In this work basic issues are investigated for the damage variable in conjunction with continuum damage and healing mechanics. First, the issue of the additive decomposition of the damage variable into damage due to voids and damage due to cracks in continuum damage mechanics is discussed. The accurate decomposition is shown to be non-additive and involves a term due to the interaction of cracks and voids. It is shown also that the additive decomposition can only be used for the special case of small damage. Furthermore, a new decomposition is derived for the evolution of the damage variable. The second issue to be discussed is the new concept of independent and dependent damage processes. For this purpose, exact expressions for the two types of damage processes are presented. The third issue addressed is the concept of healing processes occurring in series and in parallel. In this regard, systematically and consistently, the equations of healing processes occurring either consecutively or simultaneously are discussed. This is followed by introducing the new concept of small healing in damaged materials. Simplified equations that apply when healing effects are small are shown. Finally, some interesting and special damage processes using a systematic and original formulation are presented.     

Modeling and numerical issues in hyperelasto-plasticity with anisotropy

In the paper we discuss modeling and numerical issues that arise in conjunction with anisotropic hyperelastic–plastic response. Both elastic and plastic anisotropy are included. A particular kinematic hardening rule is proposed and its predictive capability is investigated. From the numerical viewpoint, we are concerned with the algorithmic consequences of the loss of coaxiality that arises from anisotropy. The numerical investigation shows that significant truncation errors are introduced if commonly used linearizations of the (classical) exponential Backward Euler rule are utilized in the presence of non-coaxiality.     

曲线公路隧道交通风力非稳态模拟研究

为分析小半径曲线隧道对交通风力的影响,采用移动网格和滑移交界面技术对半径600 m的曲线隧道和直线隧道进行三维非稳态数值计算.结果表明,采用动网格技术进行直线隧道交通风力计算结果与实验吻合;曲线隧道中,隧道断面风速分布表现出极不对称性,外侧风速较大,内侧较小;曲线隧道交通风力较直线隧道明显增大,汽车内车道行驶交通风力大于外车道行驶;曲线隧道中,汽车头部侧面出现了负压峰值,与直线隧道相比,该值较低,车身侧面压力沿纵向逐渐增大,汽车尾部背风面存在较低的负压区.     

Methodological improvement of an intrusive four-sensor probe for the multi-dimensional two-phase flow measurement

This paper aimed to improve the four-sensor probe methodology for the multi-dimensional two-phase flow measurement. We theoretically derived the interfacial measurement theorem relating the local instantaneous interfacial velocity to local measurable velocities of the multi-sensor probe in the improvement. Based on this theorem, theoretical measurement methods for the local instantaneous interfacial normal direction and the local time-averaged interfacial area concentration (IAC) using the four-sensor probe were presented. An interface-pairing signal-processing scheme was proposed to identify the same interfaces from the sequential signals detected by different sensors. The practical application of the improved IAC methodology to the two-phase flow in a vertical large diameter pipe showed that the four-sensor probes (together with the interface-pairing signal-processing scheme) could effectively measure the local time-averaged IACs with high effective interface percentages not only in the one-dimensional two-phase flow but also in the multi-dimensional two-phase flow. The measurement error analysis indicated that the errors from the bubble deformation and velocity variation due to the sensor piecing were negligible if we only applied the multi-sensor probe to the two-phase flow with the bubbles having much larger size than the sensor diameter. The total error from both the escaped and missing bubbles in the void fraction and IAC measurements was estimated at about 15.75% in the two-phase flow in a pool.     

A survey of some recent results in the stability and instability analyses of time-varying systems

After formulating the problem of stability and instability of linear and non-linear time varying feedback systems, we give a concise survey of a few known stability results for non-linear time invariant and time varying systems. This serves as motivation for the establishment of general frequency domain stability and instability criteria for time varying linear and non-linear feedback systems. All the details are omitted in an attempt to give an overall view. Finally some comments are made on the stability analysis of systems governed by partial differential equations.