Numerical taxonomy and the principle of maximum entropy

The standard procedure in numerical classification and identification of micro-organisms based on binary features is given a justification based on the principle of maximum entropy. This principle also strongly supports the assumption that all characteristics upon which the classification is based are equally important and the use of polythetic taxa. The relevance of the principle of maximum entropy in connection with taxonomic structures based on clustering and maximal predictivity is discussed. A result on asymptotic separateness of maximum entropy distributions has implications for minimizing identification errors.The work was partially supported by the Bank of Sweden Tercentenary Foundation, The Swedish Council for Forestry and Agricultural Research, The Carl Trygger Foundation, and the Swedish Cancer Foundation.     

On the null distribution of distance between two groups,using mixed continuous and categorical variables

The location model is a useful tool in parametric analysis of mixed continuous and categorical variables. In this model, the continuous variables are assumed to follow different multivariate normal distributions for each possible combination of categorical variable values. Using this model, a distance between two populations involving mixed variables can be defined. To date, however, no distributional results have been available, against which to assess the outcomes of practical applications of this distance. The null distribution of estimated distance is therefore considered in this paper, for a range of possible situations. No explicit analytical expressions are derived for this distribution, but easily implementable Monte Carlo schemes are described. These are then applied to previously cited examples.     

铝液阴极法生产铝钙合金的研究

研究了在实验室条件下电解温度、阴极电流密度、电解时间和极距对熔盐电解法制取铝钙合金的电流效率的影响。当电解温度为690～710℃,阴极电流密度为0.8～0.9安/厘米~2时电流效率出现最大值,电解时间延长,电流效率降低,极距增加到一定值后电流效率变化不大。     

一种求解k-Median问题的遗传算法

k-Median问题在理论和实际中都有重要的应用。提出一种遗传算法,针对交叉和变异操作,采用不同的选择策略,并在一般距离空间和Metric距离空间的各实例上,通过与局部搜索等算法进行比较,验证了算法的求解性能。     

试析现代远程教育条件下的教师角色

现代远程教育是以计算机通信技术为依托,实现异地、多点、双向交互式与协作式的教学过程。在整个学习过程中,学生占据主体地位。但一些已习惯于充当教学主体的教师,在远程教学过程中,仍采用传统的教学方法;在学生与教师分离的条件下,不知如何发挥自身的作用。因此,本文结合作者在远程教学工作中的经验,讨论了教师要更新观念,转换角色,以适应现代远程教育、教学的要求。     

低压线路允许长度和电压损失的估算方法

根据线路的允许电压损失和导线的允许电流，得出了不同截面导线所允许的输电距离的估算方法，并按此方法计算了不同截面常用导线的允许输电距离。     

Partial dissimilarities with application to clustering

We consider dissimilarities which are defined only on some pairs of items. Such situations may occur in some problems like unfolding or merging, or can be encountered as an intermediate step of a more general transformation. We give necessary and sufficient conditions for the existence of extensions with good properties and characterize the family of such extensions. Using partial dissimilarities we construct a dissimilarity-into-distance transformation family.The author thanks the editor and two anonymous referees for their suggestions and their helpful comments.     

最小二乘估计中的Cook距离与相关系数

对于影响度量Cook距离,本文建立了它与简单相关系数及复相关系数之间的精确关系,并找到了它与广义相关系数之间的不等式关系。     

液相指纹图谱结合欧氏距离对野菊花质量控制的研究

利用高效液相色谱建立了野菊花的色谱指纹图谱。采用反相C18柱,流动相为水∶甲醇,线性梯度,检测波长320nm,流速1ml/min进行试验。利用欧氏方法,对3省11个产地的样品进行了分析,为中药野菊花的质量控制提供了较为全面的信息基础,是一种简易可行的分析方法。     

使用模糊加权距离的模糊K—近邻算法

本文用自定义的模糊加权距离代替K—近邻分类器中的明氏距离,这种替代突出了每一样本中占有优势的特征分量对距离的贡献。仿真实验及实用结果表明这种替换可进一步改善分类器的性能。