Zipf's law for randomly generated frequencies: explicit tests for the goodness-of-fit

The question, whether Zipf's law arises only in consequence of interactions in a complex system or if it is also valid for random structures, has been controversially discussed in the literature over several decades. We show by means of simulations that the frequency distributions of simple random sequences usually obey this regularity. For tens of thousands of cases the goodness-of-fit is explicitly demonstrated by estimating the parameter and calculating the corresponding chi-square value. From the study it becomes clear that some existing results in the literature should be revised, and some ideas concerning the explanation of Zipf's law are provided.     

Sensitivity analysis approaches to high-dimensional screening problems at low sample size

Sensitivity analysis is an essential tool in the development of robust models for engineering, physical sciences, economics and policy-making, but typically requires running the model a large number of times in order to estimate sensitivity measures. While statistical emulators allow sensitivity analysis even on complex models, they only perform well with a moderately low number of model inputs: in higher dimensional problems they tend to require a restrictively high number of model runs unless the model is relatively linear. Therefore, an open question is how to tackle sensitivity problems in higher dimensionalities, at very low sample sizes. This article examines the relative performance of four sampling-based measures which can be used in such high-dimensional nonlinear problems. The measures tested are the Sobol' total sensitivity indices, the absolute mean of elementary effects, a derivative-based global sensitivity measure, and a modified derivative-based measure. Performance is assessed in a ‘screening’ context, by assessing the ability of each measure to identify influential and non-influential inputs on a wide variety of test functions at different dimensionalities. The results show that the best-performing measure in the screening context is dependent on the model or function, but derivative-based measures have a significant potential at low sample sizes that is currently not widely recognised.     

基于Logistic序列的数字图像加密技术研究

Logistic映射是一个离散动力学系统．具有简单的数学模型,对其产生的混沌序列进行变换就很容易得到混沌数字序列,对初值和结构参数的改变具有极端的敏感性．并且产生的混沌序列具有类白噪声统计特性等特点．本文基于以上特性提出了新的基于Logistic序列的数字图像加密技术．仿真实验结果证明该算法实现简单,计算量小且有效可行。具有较好的安全性．     

The CUSUM statistics of change-point models based on dependent sequences

In this paper, we investigate the mean change-point models based on associated sequences. Under some weak conditions, we obtain a limit distribution of CUSUM statistic which can be used to judge the mean change-mount δn is satisfied or dissatisfied n1/2δn=o(1). We also study the consistency of sample covariances and change-point location statistics. Based on Normality and Lognormality data, some simulations such as empirical sizes, empirical powers and convergence are presented to test our results. As an important application, we use CUSUM statistics to do the mean change-point analysis for a financial series.     

A Resampling Algorithm for Chaotic Time Series

In the field of chaotic time series analysis, there is a lack of a distributional theory for the main quantities used to characterize the underlying data generating process (DGP). In this paper a method for resampling time series generated by a chaotic dynamical system is proposed. The basic idea is to develop an algorithm for building trajectories which lie on the same attractor of the true DGP, that is with the same dynamical and geometrical properties of the original data. We performed some numerical experiments on some short noise-free and high-noise series confirming that we are able to correctly reproduce the distribution of the largest finite-time Lyapunov exponent and of the correlation dimension.     

国际期刊论文引言语篇的情态序列与推销策略分析

研究选取语言学类国际期刊的论文引言语篇作为语料，在Swales的CARS模型下分析情态序列在引言各语步和语阶中的分布及体现的话语策略。分析发现，情态序列主要出现在“文献综述”和“研究发现”这两个语阶中。情态序列在“文献综述”中的使用体现作者对该领域的熟悉程度和对前人研究所持有的态度，表明当前研究的必要性。“研究发现”部分中情态动词后动词及副词的共现带有正面、积极的语义趋向。无灵主语与情态动词的共现及被动态的高频共现使论文保持了客观的文体风格，使研究成果更为可信。     

一种适于作A-CDMA系统扩频码的混沌序列

提出了用分段线性化映射和不可逆变换来产生Ａ－ＣＤＭＡ的混沌扩频码的理论。理论分析表明,该混沌序列具有较理想的Ａ－ＣＤＭＡ扩频码性能。实验研究分析了实际应用中的有限精度效应和处理增益长度给混沌扩频码性能带来的影响,得出了混沌扩频序列的性能略比ｍ序列好,以及符合Ａ－ＣＤＭＡ要求的混沌扩频序列数多于对应的ｍ序列扩频码数的结论,证实了这类混沌序列作为Ａ－ＣＤＭＡ扩频码的可行性。     

Local convergency rate of MSE in density estimation using the second-order modulus of smoothness

In this article, the local convergence rate of the mean square error (MSE) corresponding to a delta sequence-based density estimators is investigated by using second-order modulus of continuity type majorants. We look at the rate of convergency of the MSE of estimator for densities belonging to the class of functions which are defined by the second-order finite differences. The main contribution of this study is to obtain stronger convergence rate of a MSE by relaxing the second-order differentiation condition when compared with the class of density functions defined by the first-order finite differences.     

公式化语言在心理词汇中在线处理的研究综述

公式化语言是语言的重要组成成分,目前从心理语言学和二语习得方面对其研究还较少,尤在国内更少。文章主要从心理语言学角度对现有的公式化语言相关研究及其研究方法进行综述,讨论这些研究的结果以及其局限,分析现有研究对今后公式化语言在心理语言学和二语习得方面研究方向的启示。     

基于语料库的情态语义类型和中国EFL学习者英语水平相关性研究

长期以来,情态一直被认为是人类语言与思维最难把握但同时却又最基本的范畴之一,当然对于研究者而言也是一个既复杂又棘手的问题。选择WECCL2.0作为被观察的语料库,LOC-NESS作为参照语料库,分析中国EFL学习者中初级组和高级组在义务类情态序列和认识类情态序列的使用是否存在显著性差异。研究发现,中国EFL学习者中水平越低越倾向于使用义务类情态序列,认识情态的使用能力则随着语言水平的提高而提高,因此在实际的英语教学中应该重视情态序列特别是认识类情态序列的教学。