The Morphology and Mechanical Properties of Isotactic Polypropylene Injection-Molded Samples with the Presence of β-Nucleation Agent and Periodical Shear Field

The pressure vibration injection molding (PVIM) method was used to prepare β-nucleated isotactic polypropylene samples (PVIM β-iPP samples); a relatively low, periodical shear was imposed on the polymer melt in the mold at the filling and packing stages. The crystal structures and crystal orientation of the PVIM β-iPP samples were investigated by polarizing light microscopy (PLM), scanning electron microscopy (SEM), and synchrotron two-dimensional wide-angle X-ray diffraction (2D-WAXD). The PLM observations indicated that a cylindrite layer, rather than the transition layer, was found in PVIM β-iPP samples, which is different from the conventional injection-molded (CIM) samples. In addition, the thickness of the oriented layer of the PVIM samples was obviously greater than that of the CIM samples. The SEM observations demonstrated that a large amount of shish-kebab structures appeared in the shear layer of the PVIM β-iPP samples; at the same time, numerous β-spherulites were formed in the core layer. The 2D-WAXD data indicated that orientation homogeneity, to some degree, could be obtained by the periodical shear during PVIM. As a result, the above-mentioned morphology of the PVIM β-iPP samples leads to potentially useful prominent reinforcement and toughening of the material.     

The distribution of length of N random unit vectors for a von Mises population

Greenwood and Durand (1955) have expressed the distribution function (d.f.) of the length $\text{R}$ of N random unit vectors for a von Mises population as a double integral. This double integral is simplified herein by calculating analytically one of the integrals. Hence a numerical calculation for large parameter values now becomes possible.     

计算机技术与科技期刊的发展

论述了计算机技术与科技期刊的关系 ,着重叙述了计算机技术在科技期刊管理中的应用。开发并应用的管理软件 ,不但简化了科技期刊的编辑和管理工作 ,而且使科技期刊的编辑从时间和精力上更加对论文进行规范化的研究 ,将科技期刊办成精品 ,更好的发挥科技期刊科技情报的作用。     

对酒精-水小孔周期性泄流的实验与分析

介绍酒精-水周期性泄流实验的装置,阐述实验现象,记录实验数据并进行归纳整理,用计算机软件描绘图形,通过反复实验和分析,得出与以往盐水-水等不一样的酒精-水小孔周期性泄流的振荡规律.     

利用透射系数研究周期势的能带结构

利用一维方位势透射系数的递推公式研究了周期势的能带结构,文中考察了能 结构与垒宽、阱宽及位势个数的关系。     

周期调制结构平面薄膜电爆炸实验研究

在金属层表面引入微结构以实现对Z箍缩等离子体形成和发展过程中不稳定性的调控具有重要研究价值.在“强光一号”装置上(峰值电流~1.4 MA,上升时间~100 ns),开展了针对具有一维周期性凹槽调制结构的金属薄膜的电爆炸实验研究.实验负载采用外推型平面结构,基底为30μm厚铝膜,刻蚀周期为2 mm,刻蚀深度约为10μm.通过激光阴影成像、激光干涉成像和可见光自辐射成像等系统进行联合诊断.实验结果表明刻蚀结构对等离子体发展过程的不稳定性特征产生了明显调制作用,原本征波长也受到抑制,微结构周期对不稳定结构波长产生趋同效应;未刻蚀一侧边界层同样受刻蚀层结构的影响,在不稳定结构上表现出相似形貌,且内外侧不稳定性特征的耦合关联性增强;刻蚀凹槽处在爆炸过程中膨胀更为迅速,形成的表面等离子体结构与初始结构反相;在刻蚀结构的几何突变处会形成细长的等离子体喷流,在二分之一刻蚀波长处出现波谱特征峰.理论分析表明电流密度调制造成电热不稳定性分布改变是调控作用产生的重要原因.     

定期检修系统的可靠性建模与仿真

定期检修情况下冗余系统的可靠性建模是目前可靠性工程领域的难点之一。针对定期检修系统现有可靠性评价方法的不足,推导了考虑故障检测率、故障隔离率、修复率等参数的定期检修冗余系统的可靠度计算公式,并设计了一种基于仿真的方法,解决了定期检修冗余系统的可靠性评价工程问题。验证了仿真方法的正确性。最后应用MATLAB开发了定期检修冗余系统的可靠性仿真工具,并给出了一个实例。     

自全国各地100多位理事Road Machinery Branch of China Highway and Transportation Society He

In this paper, a three dimensional ratio-dependent chemostat model with periodically pulsed input is considered. By using the discrete dynamical system determined by the stroboscopic map and Floquet theorem, an exact periodic solution with positive concentrations of substrate and predator in the absence of prey is obtained. When β is less than some critical value the boundary periodic solution (xs(t), 0, zs(t)) is locally stable, and when β is larger than the critical value there are periodic oscillations in substrate, prey and predator. Increasing the impulsive period τ, the system undergoes a series of period-doubling bifurcation leading to chaos, which implies that the dynamical behaviors of the periodically pulsed ratio-dependent predator-prey ecosystem are very complex.