Bifurcation phenomena and control for magnetohydrodynamic flows in a smooth expanded channel

This work reports the effects of magnetic field on an electrically conducting fluid with low electrical conductivity flowing in a smooth expanded channel. The governing nonlinear magnetohydrodynamic （MHD） equations in induction- free situations are derived in the framework of MHD approximations and solved numerically using the finite-difference technique. The critical values of Reynolds number （based on upstream mean velocity and channel height） for symmetry breaking bifurcation for a sudden expansion channel （1：4） is about 36, whereas the value in the case of the smooth expansion geometry used in this work is obtained as 298, approximately （non-magnetic case）. The flow of an electrically conducting fluid in the presence of an externally applied constant magnetic field perpendicular to the plane of the flow is reduced significantly depending on the magnetic parameter （M）. It is expansion （1：4） is about 475 for the magnetic parameter M found that the critical value of Reynolds number for smooth = 2. The separating regions developed behind the smooth symmetric expansion are decreased in length for increasing values of the magnetic parameter. The bifurcation diagram is shown for a symmetric smoothly expanding channel. It is noted that the critical values of Reynolds number increase with increasing magnetic field strength.     

激光可远程识别爆炸物

正激光能识别数百米之外的化学粉末,例如爆炸物或肥料,研究者将这一发现发表于近日的美国《国家科学院院刊》上。并未参与新研究的瑞士日内瓦大学物理学家Jerome Kasparian说:"这是之前从未有过的新方法。"研究者开发出一种名为拉曼光谱学的探测技术,利用光束使分子处于震动、扭曲或摇摆的     

Ferromagnetic resonance frequency shift model of laminated magnetoelectric structure tuned by electric field

Based on Smith-Beljers theory and classical laminate theory, an explicit model is proposed for the ferromagnetic resonance （FMR） frequency shift of a stress-mediumed laminated magnetoelectric structure tuned by an electric field. This model can effectively predict the experimental phenomenon that the FMR frequency increases under a parallel magnetic field and decreases under a perpendicular magnetic field when the electric field ranges from - 10 kV/m to 10 kV/m. Besides, this theory further shows that the FMR frequency increases monotonically as the angle between the direction of the external magnetic field and the outside normal direction of the laminated structure increases, and the frequency will increase as great as 7 GHz. In addition, when the angle reaches a certain critical value, the external electric field fails to tune the FMR frequency. When the angle is above the critical value, the increase of the electric field induces the FMR frequency to increase, and the opposite scenario happens when it is below the critical value. When the angle is 90~ （parallel magnetic field）, the FMR frequency is the most sensitive to the change of the electric field.     

辐射超声速扩散传输产生条件的研究

 利用1维辐射扩散方程的解析理论,在外加辐射源为恒温源的条件下,对能够产生辐射超声速扩散传输的条件进行了研究,可以解析地得出在固定物质密度下能够产生超声速扩散流的参数区域。分析得出：对于一个固定的恒温外源,随着时间的增加,热波波头位置是随时间的平方根增长的,光学厚度正比于波头位置,也是随时间而逐渐增加的;而马赫数是按时间平方根倒数减少的。并推导出在不同密度下恰好产生超声速扩散时,辐射源温度和辐射热波波头位置满足的临界值条件,它们是关于介质密度的函数关系式。最后以SiO₂泡沫为算例,对这些结果的物理图像做了简要的阐述,对它们的应用进行了具体的说明和分析。     

On a critical Neumann problem with a perturbation of lower order

We investigate the solvability of the Neumann problem （1.1） involving the critical Sobolev nonlinearity and a term of lower order. We allow a coefficient of u in equation （1.1） to be unbounded. We prove the existence of a solution in a weighted Sobolev space.     

不完全序值信息下考虑主体心理行为的匹配决策

针对不完全序值信息下的双边匹配问题,从主体心理行为的角度进行研究,具有现实意义,但相关研究非常少见。鉴于此,本文提出了一种决策方法。描述了不完全序值信息下考虑主体心理行为的双边匹配问题;以每个主体给出的临界值作为其参照点,计算了每个主体给出的序值相对于参照点的收益或损失;考虑到主体损失规避的心理行为特征,依据TODIM思想计算每个主体对另一方主体的益损值的感知价值;在此基础上,构建了求解该双边匹配问题的双目标优化模型,使用线性加权法将双目标优化模型转化为单目标优化模型,通过求解该单目标优化模型获得匹配结果;技术服务外包中的供给方与需求方匹配实例分析说明了所提方法比传统方法效果更显著。     

铜对水稻的影响及迁移积累规律的研究

通过盆栽试验,探讨了在吉林省砂壤水稻土中铜对水稻的毒性效应以及在水稻各器官的分布,累积,迁移规律,并确定了铜在该土壤中对水稻毒性临界值。     

具有破产约束的最优投资决策模型

本文给出了追求目标行为的投资决策模型,将投资目标系统化为这个扩散过程的两个吸收壁(Barriers),而文[1]的模型没有考虑破产,仅有一个吸收壁.在投资目标行为设定中,不仅要考虑目标完成水平,而且也要考虑破产,因为不破产是完成目标水平的前提条件,所以不应该被忽略.根据现有文献的实证结果导出投资回报率满足的扩散过程.本文首先描述所要解决的实际问题,设置在计划时间内要达到的目标,最后给出这个事件的概率解析表达式.     

数理统计学在多阶段库存管理模型中的研究综述

多阶段库存问题是供应链管理的重要课题,基于数理统计学在临界值策略方面、需求分布函数估计方面、优化算法方面介绍了国内外多阶段库存管理模型模型的研究进展和现状.     

关联测度广义可压缩性

In this paper the amalgamation of (I+1)×J tables under consistent significance is considered and the sufficient condition is obtained. The sufficient and necessary conditions are given to avoid the famous paradoxes "YAP" and "YRP". A practical algorithm is given to compute the critical value when pooling tables with odds ratio less than 1.