Uniqueness,loss of ellipticity and localization for the time‐discretized,rate‐dependent boundary value problem with softening

The discretization in time of the initial boundary value problem for rate‐dependent (elastic‐viscoplastic) solid materials in presence of softening is investigated in this paper. The emphasis is put on uniqueness, loss of ellipticity and localization. It is found that the time‐discretized problem resembles the incremental problem for rate‐independent materials and softening may lead to ill‐posedness (loss of ellipticity) if the time step is greater than a critical value. It is well established that the implication of loss of ellipticity for the numerical simulations after spatial discretization is the pathological mesh dependency of the computed results. We furnish a method to compute the critical time step and demonstrate its use for a simple example problem. Copyright © 2010 John Wiley & Sons, Ltd.     

关于可拓评价中几种关联函数的分析

绘制了几种可拓评价关联函数的曲线,讨论了它们的特点和应用场合,提出一个推论并进行了简要证明。指出了有关文献证明可拓学存在错误的不严谨性,分析了可变模糊方法和可拓方法的异同点,最后比较了关联函数和相对差异函数最大值点取在4个特殊位置时两种方法对福建省自然地理界线的划分情况。     

Thermomechanical vibration of curved functionally graded nanobeam based on nonlocal elasticity

In this article, thermal buckling and natural frequency of a curved functionally graded (FG) nanobeam in a thermal environment based on Eringen’s theory is investigated. Dimension of structure is in small scale, its geometric is curved, and properties of material vary in radial direction. In order to develop differential equation and boundary condition, Hamilton’s principle is adopted. Properties of material are a function of two variables of radial thickness and temperature. After developing equation of motion in thermal environment, analytical solution has been employed in order to obtain the amount of frequency and thermal buckling. Free vibration of a curved FG nanobeam subjected to in-plane thermal load may show zero frequency magnitude at a certain temperature, which specifies the existence of bifurcation type of instability. In numerical section, frequency responses have been studied one time based on temperature-dependent material property and another time based on temperature-independent material property and influences for parameters such as nonlocal parameter, power-law, mode number, temperature changes, and arc angle on natural frequency and critical temperature have been investigated. Results have shown that if properties of material are dependent on temperature, then expected frequency will be less than the case in which properties are independent of temperature. Performed validation certifies correctness of obtained results. Results indicate that critical temperature increasing the arc angle leads to a decrease in amount of dimensionless frequency, and this matter represents the importance of specification of critical temperature in curved structures.     

基于改进遗传算法的泊位岸桥协调调度优化

针对集装箱码头资源调度不合理造成资源浪费的问题,在考虑岸桥装卸成本的基础上,以在港集装箱船总的作业成本最小为优化目标,建立了基于非线性混合整数规划的泊位岸桥协调调度优化模型。为使模型更加接近码头操作的实际情况,模型假设船舶装卸时间依赖于为其分配的岸桥数。采用基于可拓关联函数的改进遗传算法对模型进行求解。改进算法强调了不可行解的重要性,用可拓关联度来衡量种群中不可行解的优劣程度,通过在种群迭代中始终保持一定数量的不可行解来维持种群多样性,从而克服传统算法局部搜索能力较差的缺陷。数值实验验证了模型和算法的可行性和有效性,与不考虑岸桥装卸成本的模型相比,能够有效减少港口资源的浪费。     

双非线性密度制约predator-prey系统的持久性

通过微分方程定性与稳定性理论和泛函分析中的Brouwer不动点定理.讨论了具有双非线性密度制约的Holling Ⅳ型功能反应的predator-prey非自治系统的一致持久性,并且当系统是周期系统时,得到该系统周期正解存在惟一且全局渐近稳定的充分条件.     

True stress control asymmetric cyclic plastic behavior in SA333 C–Mn steel

Asymmetric cyclic loading in the plastic region can leads to progressive accumulation of permanent strain. True stress controlled uniaxial asymmetric cycling on SA333 steel is conducted at various combinations of mean stress and stress amplitude in laboratory environment. It is investigated that fatigue life increases in the presence of mean stress. Plastic strain amplitude and hysteresis loop area are found to decrease with increasing mean stress. A huge difference of life and ratcheting strain accumulation is found in engineering and true stress controlled tests.     

Ⅱ型糖尿病大鼠不同病程期主动脉功能的改变

目的: 观察Ⅱ型糖尿病大鼠不同病程期血管对收缩剂的反应性及内皮依赖性血管舒张反应(EDVR)的改变。方法: 采用高能量饮食加小剂量腹腔注射链脲佐菌素(STZ)的方法,建立Ⅱ型糖尿病大鼠模型;观察注射STZ 后12 和20 周离体大鼠胸主动脉对苯肾上腺素(Phe)和氯化钾(KCl)引起收缩的反应性以及乙酰胆碱(Ach)引起的EDVR 反应的改变。结果: 注射STZ 后12 周,主动脉对Phe 的反应性增强,对KCl 的反应性不变,EDVR 轻度受损;注射STZ 后20 周,对Phe 的反应性进一步提高,对KCl的反应性显著增强,EDVR 明显受损。结论: Ⅱ型糖尿病大鼠大血管对血管收缩物质的反应性增强,而EDVR 则减弱,随着病程的发展这些改变进一步增加。     

Monitoring dependent process steps using robust cause‐selecting control charts

Cause‐selecting control charts are believed to be invaluable for monitoring and diagnosing multistage processes where the output quality of some stages is significantly impacted by the output quality of preceding stages. To establish a relationship between input and output variables, a standard procedure uses historical data, which are often prone to hold outliers. The presence of outliers tends to decrease the effectiveness of monitoring procedures because the regression model is distorted and the control limits become stretched. To dampen the negative repercussions of outliers, robust fitting techniques based on M‐estimators are implemented instead of the ordinary least‐squares method and two robust monitoring approaches are presented. An example is given to illustrate the application and performance of the proposed control charts. Furthermore, a simulation‐based study is included to investigate and compare the average run length of robust and non‐robust schemes. The results reveal that the robust procedure far outperforms the non‐robust counterpart due to its prompt detection of out‐of‐control conditions when outliers exist. Copyright © 2009 John Wiley & Sons, Ltd.     

语义特征造型中特征修改优先准则的研究

特征造型技术是新一代CAD系统的关键技术,是产品模型技术的核心。该文讨论了以细胞元模型为基础的语义特征造型技术。在语义特征造型中用特征依赖图（FDG）的数据模型来保存和维护设计中的各种特征信息及其之间的关系,在此基础上分析了依据特征依赖图中特征间的关系动态修改特征优先级的方法,确保了模型修改的有效性。最后给出了一个实例。     

Facile Hydrothermal Synthesis and Growth Kinetics of Fe-Based Magnetic Nanoparticles

The facile hydrothermal method was used to synthesize Fe3O4 nanoparticles with an average diameter of 11nm. The pure body-centered cubic (bcc)-Fe nanoparticles were prepared by reduction of Fe3O4 nanoparticles powder in H2 atmosphere. The structure, morphology and magnetic properties of the products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) and vibrating sample magnetometer (VSM). The results showed that the as-prepared Fe3O4 nanoparticles had a relatively homogeneous size. The particle diameters became bigger with the increase of reaction time. The growth kinetics of the Fe3O4 nanoparticles was also briefly discussed. The products exhibited superparamagnetic properties at room temperature and the specific saturation magnetization was dependent on the particle sizes.