Comparing the expressiveness of downward fragments of the relation algebra with transitive closure on trees

Motivated by the continuing interest in the tree data model, we study the expressive power of downward navigational query languages on trees and chains. Basic navigational queries are built from the identity relation and edge relations using composition and union. We study the effects on relative expressiveness when we add transitive closure, projections, coprojections, intersection, and difference; this for Boolean queries and path queries on labeled and unlabeled structures. In all cases, we present the complete Hasse diagram. In particular, we establish, for each query language fragment that we study on trees, whether it is closed under difference and intersection.     

模糊聚类分析和排序在研究生招生中的应用

模糊聚类分析按一定要求和规律对模糊性问题加以处理,通常先建立模糊相似关系而后按实际要求进行分类。文中针对研究生招生工作,组建模糊数学模型,在用传递闭包法求得聚类顺序的基础上,根据"物以类聚"的思想,提出了基于模糊聚类的两种多指标综合排序方法,为以后解决同类问题提供了新思路。     

Robustly chain transitive sets with orbital shadowing diffeomorphisms

Let f be a diffeomorphism of a closed C ^∞ manifold M, and let Λ???M be a closed f-invariant set. We show that if f?|_Λ is robustly chain transitive with orbital shadowing property, then Λ is a basic set.     

群作用轨道及其应用

运用群作用与同态刻划了群作用之轨道，轨道数与群阶数之间的关系，群与它可迁作用正规子群共轭子群之关系及其作用。     

The efficiency of systematic sampling in stereology — reconsidered

In the present paper, we summarize and further develop recent research in the estimation of the variance of stereological estimators based on systematic sampling. In particular, it is emphasized that the relevant estimation procedure depends on the sampling density. The validity of the variance estimation is examined in a collection of data sets, obtained by systematic sampling. Practical recommendations are also provided in a separate section.     

Transitive filtration of Lie superalgebras

0　ＩＮＴＲＯＤＵＣＴＩＯＮＷｅｋｎｏｗｔｈａｔｆｉｌｔｒａｔｉｏｎｐｌａｙｓａｎｅｍｉｎｅｎｔｒｏｌｅｉｎｔｈｅｓｔｕｄｙｏｆＬｉｅａｌｇｅｂｒａｓａｎｄＬｉｅｓｕｐｅｒａｌｇｅｂｒａｓ .Ｍｏｒｅｏｖｅｒ,ｆｉｌｔｒａｔｉｏｎｉｓａｌｓｏａｋｉｎｄｏｆｅｆｆｅｃｔｉｖｅｍｅｔｈｏｄｓｆｏｒｓｏｌｖｉｎｇｐｒｏｂｌｅｍｓ .Ｆｏｒｅｘａｍｐｌｅ ,ｗｅｓｔｕｄｉｅｄＵ(Ｌ)ｂｙｍｅａｎｓｏｆｉｔｓｃａｎｏｎｉｃａｌｆｉｌｔｒａｔｉｏｎ(ｓｅｅＲｅｆ.[1]) .Ｔｈｅｃｌａｓｓｉｆｉｃａｔｉｏｎｏｆｔｈｅｎｏｎ…     

体育教学中应用迁移规律的探讨

根据体育教学中影响和产生迁移规律的因素,以及体育教学中迁移的形式,提出迁移在体育教学中的应用,促进教学质量的提高.     

大学评价的Fuzzy聚类方法

在对教学、科研两方面分别进行综合评价的基础上，按教育部对学科门的划分及大学各学科门的比例对高校进行分类，再利用模糊聚类方法计算出模糊关系矩阵和传递闭包，逐步降低阈值从而得到分型的截矩阵，然后根据每个学校的类和教学、科研两方面的型给出其类型结果.     

Development of Vibrating Monitoring for Hydro Power Turbines under Operating Condition

Units and components of the powerful power equipment are exposed to the big static and dynamic load. An example of such equipments is turbines hydraulic power plant and, especially, hydroelectric pumped storage power plant. Existing techniques of control of a vibrating condition do not consider： very wide frequency range of vibrating processes, difficult character of such processes in the form of the sum multiharmonic, random and close to shock processes. Such techniques usually do not consider intervals of start-up and stop, and also work on transitive modes when loadings on a construction are maximum. Available techniques of an estimation of admissible level of vibrating influence and tests for vibration durability are not harmonized enough among themselves. Various known interpretations of communication of vibrating characteristics and durability estimations on mechanical pressure at broadband vibrating influence yield ambiguous result. On the basis of the analysis of the published information, we attempt to formulate the requirement to system of vibrating monitoring of the hydraulic turbine and power motor pumps. System should provide data acquisition and the analysis of the data on a vibrating condition taking into account accumulation of vibrating influences and long term of operation on the basis of estimation methods as low-cycle, and high-cycle （gigacycle） fatigue is made.     

Comments on the shortcomings of predicting the precision of Cavalieri volume estimates based upon assumed measurement functions

It is well known that the estimation of an object's volume by means of serial cross-sections, the so-called Cavalieri method, yields an unbiased estimate. But by itself it provides no means by which to estimate how precise this estimate is unless the shape of the volume is fully known beforehand. This knowledge can only be partially determined from the serial section information that is collected. Methods have been developed that claim to surmount this difficulty by using the serial section data to create a mathematical model of the volume's shape properties. The model then is used to estimate (predict) the precision of the volume estimate (its CE) from the single set of data available. Unfortunately, the theory underlying the model is flawed and so the model itself amounts to no more than an unsubstantiated guess about the shape of the volume. Therefore, the precision of the volume estimates that one obtains from the method is only as good as the model and this cannot be ascertained from the single set of acquired data. In this letter I explain the inadequacies of the modelling method. I suggest that it be used only with caution, if at all. Instead I suggest two alternative ways to predict the CE, one that is based upon a rule-of-thumb approach to the object's shape, and another that is based upon spectral analysis of the measurement function and that is easy to implement with available computer software.