Excel对学生成绩的频度分析的研究

数据频度分析是Excel的重要功能之一,Excel对学生成绩频度分析有四种方法：COUNTIF函数、COUNTIFS函数、FRE-QUENCY函数和数据透视表。四种方法均能方便快捷的完成对成绩数据的频度分析,完美高效地解决成绩统计问题。     

单纯形法中枢轴元素选取准则的改进

通过对线性规划的单纯形法的基变换的分析和认识,改进了确定枢轴元素的方法,使单纯形法的收敛速度得到了提高。并利用新的入基变量准则和与之相适应的单纯形作业法给出了例证。     

The development of pivot bearing with multiple degrees of freedom: 1st report: Prototype of pivot bearing with two degrees of freedom

This paper deals with the prototype of a new pivot bearing having two degrees of freedom. The idea of the pivot bearing is based on a continuous velocity joint (CVJ). The experimental axial stiffness and contact pressure are compared with those determined by theoretical analysis. Then, it is confirmed that the pivot bearing swings smoothly with a range of ±25°. Furthermore, the stiffness of the bearing increases as the swinging angle becomes larger. Therefore, this newly developed pivot bearing may be applied to a parallel mechanism, a joint of robot and so on.     

低扬程贯流式泵站启动扬程的计算

将泵站从启动至正常运行分为4个阶段,进行泵站启动扬程的分析计算。指出影响泵站启动扬程的主要因素有泵站启动时进水池和出水池的水位差、出水流道工作闸门的开启速度、出水流道的结构布置。通过对贯流式泵站启动过程进行分析,运用水力学原理,就泵站启动扬程的主要影响因素提出一种分析计算方法。以淮安第三抽水泵站为例进行泵站启动扬程分析及计算,所得结果与泵站的实际启动运行情况基本吻合。     

Local fill reduction techniques for sparse symmetric linear systems

Local algorithms for obtaining pivot orderings for sparse symmetric coefficient matrices are reviewed together with their mathematical background, appropriate data structures and details of efficient implementation. Heuristics that go beyond the classical Minimum Degree and Minimum Local Fill scoring functions are discussed, illustrated, improved and extensively tested on a test suite of matrices from various applications. Our tests indicate that the presented techniques have the potential of accelerating circuit simulation significantly.     

滑移装载机原地转向动力学分析

轮式滑移装载机是一种用于小空间的实用、高效、多功能的小型工程机械。其行走转向主要由两侧的液压马达带动车轮,通过两侧的速度差实现转向。通过对ZHL3210型滑移装载机的分析,并基于车辆地面力学研究,建立轮式滑移装载机原地转向模型,分析轮式滑移装载机原地转向的原理及系统的功率特性,同时建立原地转向过程中行走液压系统的数学模型。     

网络可观测性分析：以正交换法计算矩阵的秩

本文用正交换法计算矩阵的秩，以判断网络是否具有可观性。输入计算机的只是关联矩阵Ａ及回路矩阵Ｂ，与支路参数无关。算法快速简便。     

Characterisation of heavy petroleum fractions using modified molecular-type homologous series (MTHS) representation

The molecular characterisation of refinery feedstocks is a challenging task since, typically, a vast number of components are present in the mixture. Non-experimental approaches for characterisation of hydrocarbon streams fall into three categories: pseudo-component, compound class and average structural parameter methods. In this work, a new compound class approach is used to represent any hydrocarbon stream (with boiling range up 700 °C) via a modified molecular-type homologous series (MTHS) matrix. The fraction of each component/cut in the feedstock stream is estimated by minimising the discrepancies between the bulk physical properties and the ones reconstructed through our characterisation method. Mixture properties are calculated by applying Kay's mixing rule [Gases and vapors at high temperature and pressure—density of hydrocarbon. Ind Eng Chem 1936;28:1014–9], for each cut. The paraffinic, naphthenic and aromatic content of each cut of the analysed mixture can then be determined. To test the method, 15 olefin-free petroleum samples, from refineries all over the world, covering boiling ranges from 120 to 615 °C were characterised. The results show good agreement with the experimental data. A technique for integrating our characterisation approach with refinery lumped kinetic models is also presented. It is based on the pivot method [Kumar S, Ramkrishna D. On the solution of population balance equations by discretisation—I. A fixed pivot technique. Chem Eng Sci 1996;51:1311–32] appropriately modified to use the information provided by the characterisation procedure in order to obtain the necessary input for kinetic/reaction models, ensuring species mass conservation.     

A comparison of pivot selection techniques for permutation-based indexing

Recently, permutation based indexes have attracted interest in the area of similarity search. The basic idea of permutation based indexes is that data objects are represented as appropriately generated permutations of a set of pivots (or reference objects). Similarity queries are executed by searching for data objects whose permutation representation is similar to that of the query, following the assumption that similar objects are represented by similar permutations of the pivots. In the context of permutation-based indexing, most authors propose to select pivots randomly from the data set, given that traditional pivot selection techniques do not reveal better performance. However, to the best of our knowledge, no rigorous comparison has been performed yet. In this paper we compare five pivot selection techniques on three permutation-based similarity access methods. Among those, we propose a novel technique specifically designed for permutations. Two significant observations emerge from our tests. First, random selection is always outperformed by at least one of the tested techniques. Second, there is no technique that is universally the best for all permutation-based access methods; rather different techniques are optimal for different methods. This indicates that the pivot selection technique should be considered as an integrating and relevant part of any permutation-based access method.     

淮安芒硝资源开发现状与发展对策

介绍了淮安地区芒硝资源开发利用现状及国内国际市场芒硝产品的供需态势．对淮安地区芒硝产业的发展对策提出了相应的建议。