The (3+1)‐dimensional dust‐acoustic waves in multi‐components magneto‐plasmas

A three‐dimensional four components magneto‐plasma system consists of super‐thermal κ‐distributed electrons and positrons, Maxwellian ions, and inertial massive negatively charged dust grains is considered to examine the modulational instability (MI) of the dust‐acoustic waves (DAWs), which propagates in such a magneto‐plasma system. The reductive perturbation method, which is valid for small but finite amplitude DAWs, is employed to derive the (3 + 1)‐dimensional non‐linear Schrödinger equation (NLSE). The NLSE leads to the MI of DAWs as well as the formation of dust‐acoustic rogue waves (DARWs) which are formed due to the effects of non‐linearity in the propagation of the DAWs. It is found that the basic features (viz. amplitude and width) of the DAWs and DARWs (which is formed in the unstable region) are significantly modified by the various plasma parameters such as κ‐distributed electrons and positrons, temperatures, and number densities of plasma species, and so on. The application of the results in both space and laboratory magneto‐plasma systems is briefly discussed.     

Effective charge of a macroparticle in a non‐isothermal plasma within the Poisson–Boltzmann model

The electrostatic potential distribution around a charged, spherical, finite‐size macroparticle in a non‐isothermal plasma‐like medium is studied numerically within the Poisson–Boltzmann model. It is assumed that plasma consists of electrons and one species of singly charged ions. The effective charge of a macroparticle is calculated and its dependence on the electron to ion temperature ratio as well as on the particle radius and bare charge is considered. Numerical results for the effective charge in an isothermal plasma are compared with known analytical expressions.     

Hénon混沌系统的自适应广义预测控制快速算法

提出了一种带有约束矩阵的Hénon 混沌系统的广义预测控制快速算法,首先用带有遗忘因子的递推最小二乘参数辨识法来逼近混沌系统,然后该算法引入了一种约束矩阵,约束矩阵的引入避免了矩阵求逆的计算,占用内存小,计算速度快,并且具有较强的跟踪给定信号和抑制系统参数摄动和随机噪声的能力.仿真结果验证了该方法的有效性. 关键词： 广义预测控制 约束矩阵 Hénon混沌系统 参数辨识     

Hénon混沌系统的自适应预测函数控制快速算法

提出了一种带有预测函数的Hénon 混沌系统的广义预测控制快速算法.首先用时变遗忘因子的递推最小二乘方法辨识混沌系统,然后在广义预测控制的基础上引入了预测函数控制方法,并充分利用了预测信息的补偿作用.这种算法克服了广义预测控制中求解逆矩阵的缺点,提高了系统响应的速度,并且具有较强的跟踪给定信号、抑制系统参数摄动和随机噪声的能力.仿真结果验证了该方法的有效性. 关键词： 广义预测控制 预测函数 Hénon 混沌系统 参数辨识     

Fe84Zr3.5Nb3.5B8Cu1薄带的动态磁化过程

由于铁磁性样品的交流磁化率虚部χ″随磁场强度H的变化是非线性的，在低场(0～12 mT)有一个与铁磁共振信号强度相当的低场非共振信号. 利用ESR谱仪测量交流磁化率虚部χ″对磁场强度H的一次微分随磁场强度的变化dχ″/dH～H，研究Fe₈₄Zr_3.5Nb_3.5B₈Cu₁合金薄带的动态磁化特性. 合金薄带样品是各向异性的，易磁化轴（易轴）在薄带的横向方向，外加磁场H在易轴方向. 样品在可逆磁化区域(0～2.0 mT)和趋近饱和的磁化区域(9.0 mT以上)，dχ″/dH=0；在不可逆畴壁移动过程中，当H为4.2 mT 时, χ″(H)达到最大值χ_max；在磁畴转动过程中，χ″(H)正比于H²（瑞利区）；而实验中却发现，在某些区域交流磁化率虚部χ″(H) 与磁场强度H的n次方即Hⁿ(n≥3)有关；而且发现，在一定区域，有三段不可逆畴壁移动和磁畴转动交替出现的现象. 在这一过程中，dχ″/dH为常数的磁场范围分别为4.8～5.2mT, 5.8～6.4 mT, 8.0～8.5 mT, 其常数相对值分别为1：0.85：0.60. 样品的交流磁化率虚部χ″对磁场H的微分dχ″/dH随磁场H的这一变化规律反映了不可逆畴壁移动和磁畴转动交替发生的微观过程.     

Eu3+掺杂硅酸盐玻璃的变温发射光谱特性

研究了从77K到670K不同基质、不同掺杂浓度下硅酸盐玻璃中Eu^3 离子在488nm激光激发下的变温荧光发射特性。发现有些样品荧光发射强度先随温度升高而增强而后又随温度升高而减弱;而有些样品的荧光发射强度在观察温度区域内随温度升高一直增强。本文用热激后、声子辅助吸收过程和无辐射能量传递过程造成的温度猝灭相互关系的机制解释了样品荧光发射强度随温度的变化关系,用同一公式拟合了这些样品的变温曲线。比较了不同激发通道的数量关系,计算了样品的温度猝灭值。     

一类逻辑环站点双态转移的研究

本对于容量有限和具有优先队列的逻辑环随机运作系统,研究其站点双态转移的有关问题,转移规律的探讨,零转移和非零转移的判断及其数目函数的推导;中还提出若干相关的新概念。章有别于以往寻求传统的工作特性参数表达式的思路,从另一个侧面揭示该类系统的数学特征。     

On nice equivalence relations on <Superscript>λ</Superscript>2

Let E be an equivalence relation on the powerset of an uncountable set, which is reasonably definable. We assume that any two subsets with symmetric difference of size exactly 1 are not equivalent. We investigate whether for E there are many pairwise non equivalent sets. I would like to thank Alice Leonhardt for the beautiful typing.This research was supported by The Israel Science Foundation. Publication 724. Mathematics Subject Classification (2000): 03E47, 03E35; 20K20, 20K35     

Global and blow‐up solutions for non‐linear degenerate parabolic systems

In this paper the degenerate parabolic system u_t=u(u_xx+av). vt=v(v_xx+bu) with Dirichlet boundary condition is studied. For , the global existence and the asymptotic behaviour (α₁=α₂) of solution are analysed. For , the blow‐up time, blow‐up rate and blow‐up set of blow‐up solution are estimated and the asymptotic behaviour of solution near the blow‐up time is discussed by using the ‘energy’ method. Copyright © 2003 John Wiley & Sons, Ltd.