用马尔可夫调制的泊松过程近似多分形突发流量研究

研究了用马尔可夫调制的泊松过程(MMPP)对Internet多分形流量突发行为进行近似建模的能力. MMPP可用于描述适当时间尺度范围内流量的变化以及相关性, 而且它可作为排队系统输入过程得到分析结果. 描述了刻画突发流量行为的重要统计量, 在此基础上给出了一个基于矩的MMPP参数估计方法. 除了对MMPP进行拟合优度检测以外, 本文通过将MMPP的样本过程和实际流量记录输入到排队系统模型中比较其输出结果来研究MMPP对排队性能的预测能力. 数值和仿真实验表明, MMPP能够较好地用于对多分形流量近似建模, 即可以准确地预测网络结点的排队性能.     

调查中零频数过多的统计分析方法

无论是在自然科学领域还是在人文社会科学领域,我们会遇到各种各样的计数数据.对于社会生活、生产、管理中的一些计数数据通常是用泊松分布以及泊松过程来描述具有非常好的拟合效果.然而实际环境中,由于受各种因素影响与制约,出现了很多频数为零的数据.此时对含零特别多的计数数据,我们仍用泊松回归模型拟合就有些不合适了[1],因此人们开始构造新的模型,其中对于这种数据拟合效果比较好的一种模型就是零过多泊松分布模型(Zero-Inflated Poisson Distribution)[3,5].     

Converse result on Szász-type operators

Szasz-type operators can be constructed by a Poisson process. The purpose of this paper is to derive the converse result in connection with Szasz-type operators by Steckin-Marchaud-type inequalities and new Ditzian modulus of continuity. The degree of approximation on deterministic signals is also given.     

The evolution of patent pools and patent application behavior against the

在技术标准大量引用技术专利的背景下,标准联盟以专利池运营其拥有的技术专利,专利池在标准创立及产业化中扮演着日益重要的角色。以典型专利池为研究样本,定量分析专利池中的专利数量变化与专利申请行为;研究表明,专利池创立前后是专利申请的高峰期,这些专利绝大部分为专利池的发起人所控制。对专利引用进行泊松回归,揭示出专利池中的专利质量随时间推移逐步降低,在专利池演进过程中,发起人存在策略性的专利申请行为,倾向于将低价值专利＂塞入＂专利池中。     

Updating a Classic: “The Poisson Distribution and the Supreme Court” Revisited

W.A. Wallis studied vacancies in the US Supreme Court over a 96‐year period (1837–1932) and found that the distribution of the number of vacancies per year could be characterized by a Poisson model. This note updates this classic study.     

Snippets of physics

It is well known in Newtonian gravity that a spherically symmetric density distribution produces a force outside it which falls as the square of the distance. Surprisingly, the converse is not true! Just be cause the force falls as inverse square outside a density distribution, you cannot conclude that it must be spherically symmetric. This article, first in a new series, explores this and related issues. This is based on an article originally published by the author in Physics Education, Vol 22, No. 4, p.263, 2006. T Padmanabhan works at IUCAA, Pune and is interested in all areas of theoretical physics, especially those which have something to do with gravity.     

多重网格法在地球物理正反演应用研究中的进展

现阶段地球物理三维勘探面临越来越复杂的问题,其要求更精细的三维网格剖分,现有的一些方法随着网格节点的增加其收敛速度相应减慢。对于应用中更复杂实际模型、更细密网格剖分以及更快收敛速度要求,难于有进一步提高。要有所突破,需借助计算数学最新进展,引入新的高效算法。多重网格法是近二十年迅速发展的一种求解微分方程近乎最优的新算法。本文首先简单介绍了多重网格法基本原理和运算格式,着重介绍了当前国内外多重网格法在地球物理正反演中的应用成果和发展现状。此外,对多重网格法在地球物理正反演中的应用前景及发展趋势进行了展望。     

技术标准背景下的专利池演进及专利申请行为

在技术标准大量引用技术专利的背景下,标准联盟以专利池运营其拥有的技术专利,专利池在标准创立及产业化中扮演着日益重要的角色。以典型专利池为研究样本,定量分析专利池中的专利数量变化与专利申请行为;研究表明,专利池创立前后是专利申请的高峰期,这些专利绝大部分为专利池的发起人所控制。对专利引用进行泊松回归,揭示出专利池中的专利质量随时间推移逐步降低,在专利池演进过程中,发起人存在策略性的专利申请行为,倾向于将低价值专利"塞入"专利池中。     

A regression analysis of researchers’ social network metrics on their citation performance in a college of engineering

Previous research shows that researchers’ social network metrics obtained from a collaborative output network (e.g., joint publications or co-authorship network) impact their performance determined by g-index. We use a richer dataset to show that a scholar's performance should be considered with respect to position in multiple networks. Previous research using only the network of researchers’ joint publications shows that a researcher's distinct connections to other researchers, a researcher's number of repeated collaborative outputs, and a researchers’ redundant connections to a group of researchers who are themselves well-connected has a positive impact on the researchers’ performance, while a researcher's tendency to connect with other researchers who are themselves well-connected (i.e., eigenvector centrality) had a negative impact on the researchers’ performance. Our findings are similar except that we find that eigenvector centrality has a positive impact on the performance of scholars. Moreover, our results demonstrate that a researcher's tendency toward dense local neighborhoods and the researchers’ demographic attributes such as gender should also be considered when investigating the impact of the social network metrics on the performance of researchers.     

How to consider fractional counting and field normalization in the statistical modeling of bibliometric data: A multilevel Poisson regression approach

The numerical-algorithmic procedures of fractional counting and field normalization are often mentioned as indispensable requirements for bibliometric analyses. Against the background of the increasing importance of statistics in bibliometrics, a multilevel Poisson regression model (level 1: publication, level 2: author) shows possible ways to consider fractional counting and field normalization in a statistical model (fractional counting I). However, due to the assumption of duplicate publications in the data set, the approach is not quite optimal. Therefore, a more advanced approach, a multilevel multiple membership model, is proposed that no longer provides for duplicates (fractional counting II). It is assumed that the citation impact can essentially be attributed to time-stable dispositions of researchers as authors who contribute with different fractions to the success of a publication’s citation. The two approaches are applied to bibliometric data for 254 scientists working in social science methodology. A major advantage of fractional counting II is that the results no longer depend on the type of fractional counting (e.g., equal weighting). Differences between authors in rankings are reproduced more clearly than on the basis of percentiles. In addition, the strong importance of field normalization is demonstrated; 60% of the citation variance is explained by field normalization.