三相供电线路的漏电流分布规律

面对安全用电的严峻形式 ,经国内外的实践证明 ,安装使用漏电保护开关对于防止触电身亡 ,避免设备接触地故障损坏和漏电引起火灾事故 ,及减少漏电引起的电能损耗 ,具有明显效果。然而对于漏电保护开关的跳闸临界值具有很大歧义 ,因此我们首先对漏电流进行分布拟合 ,将得出的参数值进行随机模拟 ,以此来制定漏电保护开关的跳闸临界值     

H1中(次)临界的复Ginzburg-Landau方程解的长时间行为

研究H1(Rn)中临界的复Ginzburg-Landau方程的初值问题,当空间维数n≥3时,讨论了它的解在空间C(0,oo;H1(Rn))∩ L2(0,∞;H1,2n/(n-2)(Rn))的长时间衰减行为.当空间维数n≥1时,对非线性项在H1(Rn)中具有次临界的增长阶的情形也有类似的结果.     

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.     

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     

小波自适应方法模拟二维涡旋演化

以涡量方程为控制方程,模拟初始状态涡量分布为高斯分布三个涡旋演化过程.提出一个关联实际流动的小波系数临界值,小波系数分为临界值以上及以下部分,进而涡量可分成尺度系数项、小波系数突出项和小波系数平凡项三部分.只采用尺度系数项和小波系数突出项近似涡量,既可以节约计算量,还可以自动追踪绝大部分的拟涡能.数值结果表明,用不到10%的小波系数,可控制99%以上的拟涡能.     

具有缺陷的不可压缩neo-Hookean球壳的动力学行为的定性分析

研究了一类具有缺陷的不可压缩超弹性材料球壳的径向对称运动问题,该类材料可以看作是带有径向摄动的均匀各向同性不可压缩的neo-Hookean材料．得到了描述球壳内表面运动的二阶非线性常微分方程,并给出了方程的首次积分．通过对微分方程的解的动力学行为的分析,讨论了材料的缺陷参数和球壳变形前的内外半径的比值对解的定性性质的影响,并给出了相应的数值算例．特别地,对于一些给定的参数,证明了存在一个正的临界值,当内压与外压之差小于临界值时,球壳内表面随时间的演化是非线性周期振动;当内压与外压之差大于临界值时,球壳的内表面半径随时间的演化将无限增大,即球壳最终将被破坏．     

Critical Number of Fermion Flavors at Finite Chemical Potential in QED3

We propose a new method for calculating the dressed fermion propagator at finite chemical potential in QED3 under the rainbow approximation of Dyson-Schwinger equation. In the above approximation, we show that the dressed fermion propagator at finite chemical potential # has the form S（p） = iγ.p^-A（p^-2） ＋ B（ p^-2） with p^-μ= （p^-1p3 ＋ iμ）. Using this form of fermion propagator at nonzero chemical potential, we investigate the Dyson-Schwinger equation for the dressed fermion propagator at finite chemical potential and study the effects of the chemical potential on the critical number of the fermion flavors.     

重金属污染水稻的冠层反射光谱特征研究

利用野外光谱仪获取矿区农田重金属污染水稻的冠层反射光谱,通过曲线模拟和统计分析提取了与水稻冠层叶片重金属含量变化极显著相关的光谱敏感波段(Pb, 460 nm;Zn, 560 nm;Cu, 660 nm;As, 1 100 nm)、归一化植被指数(Pb, NDVI_{(510, 810)};Zn, NDVI_{(510, 870)};Cu, NDVI_{(660, 870)};As, NDVI_{(510, 810)})和“红边”位置等水稻冠层反射光谱特征。表明水稻重金属污染可以被地面遥感传感器快速检测,其浓度变化与所提取的光谱特征之间存在极显著相关,归一化植被指数与“红边”位置对光谱信息的表达要优于敏感波段。归一化植被指数以及“红边”位置可以作为水稻重金属污染遥感监测模型的光谱特征参数选择参考。同时,文章提出了利用遥感技术监测水稻重金属污染的“光谱临界值”概念, 并计算出研究中各重金属对应的“光谱临界值”。     

A hyperbolic Lindstedt–Poincaré method for homoclinic motion of a kind of strongly nonlinear autonomous oscillators

A hyperbolic Lindstedt-Poincare method is presented to determine the homoclinic solutions of a kind of nonlinear oscillators, in which critical value of the homoclinic bifurcation parameter can be determined. The generalized Lienard oscillator is studied in detail, and the present method＇s predictions are compared with those of Runge-Kutta method to illustrate its accuracy.