充分发展湍流场中Pr数对被动标量输运的影响

采用直接数值模拟方法,研究壁湍流中分子Pr数对湍流被动标量输运的影响.发现在槽道湍流的外层,湍流雷诺平均普朗特数PrT与分子普朗特数的倒数呈线性关系;湍流亚格子普朗特数PrT与分子普朗特数的关系较为复杂,在分子普朗特数为1附近时,湍流亚格子Prt数出现极小值.     

Vibrational Dynamics of a Centrifuged Fluid Layer

The dynamics of a low-viscosity fluid layer inside a rotating cylinder under transverse translational vibration relative to the rotation axis is investigated experimentally. A novel vibrational effect, the generation of intense azimuthal fluid flows with velocities comparable with the cavity rotation velocity, is revealed. The structure and intensity of the vibrational flows and the flow transformation with variation of the determining dimensionless parameters (frequency and vibrational acceleration) are studied.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 147–156.Original Russian Text Copyright © 2005 by Ivanova, Kozlov, and Polezhaev.     

Thermal Convection in a Plane Layer Rotating About a Horizontal Axis

The thermal convection of a fluid in a plane vertical layer with a cylindrical lateral boundary, which rotates uniformly about a horizontal symmetry axis, is investigated experimentally. The structure and excitation limit of the convective flows are studied as functions of the rotation frequency, the temperature difference between the layer boundaries, and the layer thickness. The determining dimensionless parameters are found. It is shown that the period-average gravity action produces convection in the form of hexagonally distributed cells stationary in the reference system tied to the cavity.     

多重分形降趋波动分析法和移动平均法的分形谱算法对比分析

多重分形降趋波动分析法(MFDFA)和多重分形降趋移动平均法(MFDMA)是用来估算一维随机分形信号多重分形谱的两种算法, 已被拓展应用于二维和高维分形信号的分析. 本文简要介绍了MFDFA和MFDMA算法及其在一维时间序列中的应用. 首次系统地从算法模型、计算统计精度、样本量的敏感性、无标度区选取的敏感性、矩选择的敏感性和计算量这六个方面对两种算法进行了对比分析, 以典型多重分形信号BMC信号为例, 分析两种算法的适用性和优劣性. 为实际应用中, 针对具体信号如何选用MFDFA或MFDMA算法, 以及两种算法的参数设置提供了有价值的参考.     

A mean value theorem for metric spaces

We present a form of the Mean Value Theorem (MVT) for a continuous function f between metric spaces, connecting it with the possibility to choose the relation of f in a homeomorphic way. We also compare our formulation of the MVT with the classic one when the metric spaces are open subsets of Banach spaces. As a consequence, we derive a version of the Mean Value Propriety for measure spaces that also possesses a compatible metric structure.     

Profile monitoring of reflow process using approximations of mixture second‐order polynomials

Lately, profile monitoring has received considerable attention in the statistical process control research field. This paper proposes a novel monitoring framework for the reflow process data, which uses two goodness‐of‐fit criteria to select the change points in the mixture polynomial model. Among change points, the mixture second‐order polynomials are utilized to piecewisely approximate the nonlinear profile data of the reflow process. The well‐known Hotelling T² and proposed EWMA₄ control charts are then employed to monitor the parameter estimates. The experimental results demonstrate that the proposed monitoring framework presents better performances in detecting outlying profiles than the conventional methods in phase I. In phase II, the performance of the proposed framework is assessed in terms of the out‐of‐control average run length. Copyright © 2014 John Wiley & Sons, Ltd.     

Complete q-Moment Convergence of Moving Average Processes under ψ-mixing Assumption

In this paper,we study the complete q-moment convergence of moving average processes under ψ-mixing assumption.The results obtained not only extend some previous known results,but also improve them.     

基于ARIMA与神经网络集成的GDP时间序列预测研究

本文深入分析了单整自回归移动平均(ARIMA)模型与神经网络(NN)模型的预测特性和优劣,并在此基础上建立了由ARIMA模型和NN模型集成的GDP时间序列预测模型与算法。其基本思想是充分发挥两种模型在线性空间和非线性空间的预测优势,据此将GDP时间序列的数据结构分解为线性自相关主体和非线性残差两部分,首先用ARIMA模型预测序列的线性主体,然后用NN模型对其非线性残差进行估计,最终集成为整个序列的预测结果。仿真实验表明:集成模型的预测准确率显著高于单一模型的预测准确率,从而证实了集成模型用于GDP预测的有效性。     

混合分数布朗运动下亚式期权定价

运用混合分数布朗运动的Ito公式,将几何平均亚式期权定价化成一个偏微分方程求解问题,通过偏微分方程求解获得了几何平均型亚式看涨期权的定价公式.     

Hypergraph list coloring and Euclidean Ramsey theory

A hypergraph is simple if it has no two edges sharing more than a single vertex. It is s‐list colorable (or s‐choosable) if for any assignment of a list of s colors to each of its vertices, there is a vertex coloring assigning to each vertex a color from its list, so that no edge is monochromatic. We prove that for every positive integer r, there is a function d_r(s) such that no r‐uniform simple hypergraph with average degree at least d_r(s) is s‐list‐colorable. This extends a similar result for graphs, due to the first author, but does not give as good estimates of d_r(s) as are known for d₂(s), since our proof only shows that for each fixed r ≥ 2, d_r(s) ≤ 2 We use the result to prove that for any finite set of points X in the plane, and for any finite integer s, one can assign a list of s distinct colors to each point of the plane so that any coloring of the plane that colors each point by a color from its list contains a monochromatic isometric copy of X. © 2011 Wiley Periodicals, Inc. Random Struct. Alg., 2011