采用人工免疫算法的加速寿命试验分析方法

极大似然估计是加速寿命试验统计分析中常用的分析方法,但似然函数的优化问题是该方法广泛运用的主要障碍,常用的似然函数优化算法对初值要求高,而且容易陷入局部最优解.为了有效地解决上述问题,在似然函数的优化中引入了人工免疫算法,提出了一种采用人工免疫算法的步降应力加速寿命试验分析方法.利用人工免疫算法在解决多维复杂函数优化问题时强大的全局寻优能力,有效地解决了似然函数的优化问题.最后通过实例验证表明,采用人工免疫算法的步降应力加速寿命试验分析方法是有效的,而且在统计分析中避免了查统计用表,能够很方便的实现计算机编程计算,有较大的工程应用价值.     

等离子体中热阴极鞘层的结构

结合热阴极电子发射理论和等离子体鞘层流体方程研究了热阴极附近存在虚阴极结构时的等离子体鞘层问题,采用Sagdeev势的方法讨论了鞘层解和广义Bohm判据.结果表明,不同于普通的Bohm鞘,由于热阴极附近存在大量发射电子,影响整个等离子体鞘层结构,使得进入鞘层的离子临界Mach数不是独立的常数,而是与鞘层电位降等参数有关的物理量.临界Mach数随着鞘层电位降（从鞘边缘到虚阴极）先增大后降低,并且随着热阴极温度的升高单调增大.此外,在平板模型下有相当可观的残余热发射电子越过虚阴极鞘层进入等离子体. 关键词： 鞘层 热阴极发射 Bohm判据     

一种城市路灯合理排布的优化设计方法

文章借助于物理模型和数学计算分析，给出了一种优化的城市路灯排列的设计方法．利用该方法优化出的路灯排列方式（如三角型排列），与现在普遍采用的对称排列方式相比，可以在满足人们交通安全和正常工作生活的条件下，达到节省电力能源的效果；或者是在能源耗费相同的条件下，能提供更高、更均匀的照明度．     

Information and Distinguishability of Ensembles of Identical Quantum States

We consider a fixed quantum measurement performed over n identical copies of quantum states. Using a rigorous notion of distinguishability based on Shannon’s 12th theorem, we show that in the case of a single qubit, the number of distinguishable states is , where (α₁,α₂) is the angle interval from which the states are chosen. In the general case of an N-dimensional Hilbert space and an area Ω of the domain on the unit sphere from which the states are chosen, the number of distinguishable states is . The optimal distribution is uniform over the domain in Cartesian coordinates.     

无线传感器网络中分阶段的无需测距定位算法

为了提高无线传感器网络中基于无需测距算法定位精度,改进质心算法和DV-Hop算法,定位过程分为两个阶段:第一阶段在最佳通信半径与最佳阈值下,用基于阈值的优先质心算法定位部分节点;第二阶段在最佳通信半径与最佳指数值下用DV-Hop算法定位剩余节点。将算法应用在一种锚节点人工部署环境下,并与其他算法对比。MTLAB仿真结果表明,改进的算法在不增加泛洪次数、计算量和网络硬件成本下能提高定位精度,同时实现100%定位。     

二维Fisher准则函数在区域生长算法中的应用

本文针对传统区域生长算法中“种子”和“相似性准则”不能自适应获得的缺点,将二维Fisher准则函数算法[1]应用到区域生长算法中,根据图像特征,利用二维阈值,自动确定“种子”和“相似性准则”。实验表明,该算法不仅利用了二维Fisher准则函数算法的优点,而且也使区域生长算法具有自适应性,对荧光磁粉图像具有较好的分割效果。     

An exhaustive criterion for estimating quality of images in electrical impedance tomography with application to clinical imaging

This study proposes a versatile criterion for estimating quality of images in electrical impedance tomography. The point spread function (PSF) is calculated throughout the domain based on the scattering of energy as responses to a small anomaly spirally moved from the centre to the boundary. The proposed PSF is a measure of weighted spatial variance (WSV) of the conductivity over the whole domain. For each element, the weighting factor is a normalized multiplication of the area of that element by its square intensity. The WSV collectively incorporates all image attributes, i.e., spatial resolution, artifact, amplitude response, positioning error and shape deformation. The location of artifacts, which significantly influences reconstructed images in reality, is taken into account as well. The results illustrate that the proposed measure is more tolerant than existing criteria in evaluating performance of EIT systems in both theory and practice.     

A Criterion to Identify Maximally Entangled Four-QubitState

Paolo Facchi, et al. [Phys. Rev. A77 (2008) 060304(R)] presented a maximally multipartite entangled state (MMES). Here, we give a criterion for the identification of maximally entangled four-qubit states. Using this criterion, we not only identify some existing maximally entangled four-qubit states in the literature, but also find several new maximally entangled four-qubit states as well.     

Composition-dependent melting behaviour of NaxK55–x core–shell nanoalloys

Molecular dynamics simulations at constant temperature are performed to investigate melting-like transition in Na₁₃K₄₂, Na₁₉K₃₆ and Na₂₆K₂₉ nanoalloys using a second-moment-approximation tight-binding analytic potential to calculate the forces on the constituent atoms. A weighted histogram analysis method is employed to remove non-ergodicity issues due to the complex potential energy surface of these nanoalloys. The heat capacity shows three distinctive steps in melting for Na₁₃K₄₂, while Na₂₆K₂₉ and Na₁₉K₃₆ have two-step and one-step melting transition, respectively. The steepest descent method is used to quench the configurations in a given interval during the simulation and also study the isomerisation processes occurring at different temperatures. Analysing the configuration energies of quenched structures for the entire nanoalloy and the core atoms separately gives more details about the melting mechanism. The Lindemann parameter is also calculated at several temperatures during the simulation which shows a gradual increase for Na₁₃K₄₂ and Na₂₆K₂₉ while a sharp change is observed for Na₁₉K₃₆. These findings are in agreement with the multi-step nature of the phase transition in Na₁₃K₄₂ and Na₂₆K₂₉ and one-step melting of the Na₁₉K₃₆ magic composition.     

强磁场中相互作用费米气体的相对论稳定性

由单粒子的弱相互作用能谱及泊松公式,导出了强磁场中相互作用费米气体的相对论热力学势函数,求解了系统力学稳定性的判别式,分析了相互作用、磁场及相对论效应对系统稳定性的影响机理。结果表明,强磁场中弱相互作用费米气体的力学稳定性会受到弱相互作用的影响,强磁场对这种影响具有调节作用,而相对论效应对相互作用的影响基本没有调节作用。