尾缘凹陷轴流风轮内流特性分析与降噪研究

为减少空调室外机用低压轴流风轮叶片的颤振,改善音质,降低噪音和电机功率。本文设计了尾缘凹陷新型三叶轴流风轮,同时除对前缘局部加厚处理外,对叶片其他区域整体减薄。文中采用Navier-Stokes方程对新风轮和原风轮的内流及气动特性进行了三维数值模拟,同时对两者的流量压力曲线和噪音频谱进行了实验研究。研究表明:对轴流风轮叶片尾缘进行凹陷设计,对前缘以外的区域减薄设计,能够减轻风轮重量,降低电机负荷同时减弱转子尾迹;对叶轮前缘进行局部加厚处理可以减小叶尖颤振,降低叶片旋转频率峰值噪音,从整体上降低噪音,改善音质。     

Morphology and magnetic properties of FeCo nanocrystalline powder produced by modified mechanochemical procedure

Properties of FeCo nanocrystalline intermetallic powders prepared by salt-matrix hydrogen reduction of a milled Fe₂O₃-Co₃O₄ mixture were investigated. The product of 72 ks ball-milling at 350 rpm was CoFe₂O₄ nanopowder. Reduction of this powder for 3.6 ks by hydrogen at 750 °C resulted in the formation of Fe_0.67Co_0.33 stoichiometric compound. Scanning electron microscopy, electron dispersive spectrometry, X-ray diffraction and vibrating sample magnetometry were used to characterize the nanopowder. Using a salt-matrix (NaCl as a dispersion medium) resulted in the decrease of the reduction temperature and improvement of the morphology and magnetic properties of the nanopowder. Dispersion of the ball-milled product in Hexan resulted in further improvements of the magnetic properties.     

Affine Weyl group symmetries of Frobenius Painlevé equations

In this paper, we introduce a Frobenius Painlevé IV equation and the corresponding Hamilton system, and we give the symmetric form of the Frobenius Painlevé IV equation. Then, we construct the Lax pair of the Frobenius Painlevé IV equation. Furthermore, we recall the Frobenius modified KP hierarchy and the Frobenius KP hierarchy by bilinear equations, then we show how to get Frobenius Painlevé IV equation from the Frobenius modified KP hierarchy. In order to study the different aspects of the Frobenius Painlevé IV equation, we give the similarity reduction and affine Weyl group symmetry of the equation. Similarly, we introduce a Frobenius Painlevé II equation and show the connection between the Frobenius modified KP hierarchy and the Frobenius Painlevé II equation.     

New algorithms for discrete vector optimization based on the Graef-Younes method and cone-monotone sorting functions

Abstract

The well-known Jahn-Graef-Younes algorithm, proposed by Jahn in 2006, generates all minimal elements of a finite set with respect to an ordering cone. It consists of two Graef-Younes procedures, namely the forward iteration, which eliminates a part of the non-minimal elements, followed by the backward iteration, which is applied to the reduced set generated by the previous iteration. Without using the backward iteration, we develop new algorithms that also compute all minimal elements of the initial set, by combining the forward iteration with certain sorting procedures based on cone-monotone functions. In particular, when the ordering cone is polyhedral, computational results obtained in MATLAB allow us to compare our algorithms with the Jahn-Graef-Younes algorithm, within a bi-objective optimization problem.     

Conjugate processes: Theory and application to risk forecasting

Many dynamical phenomena display a cyclic behavior, in the sense that time can be partitioned into units within which distributional aspects of a process are homogeneous. In this paper, we introduce a class of models – called conjugate processes – allowing the sequence of marginal distributions of a cyclic, continuous-time process to evolve stochastically in time. The connection between the two processes is given by a fundamental compatibility equation. Key results include Laws of Large Numbers in the presented framework. We provide a constructive example which illustrates the theory, and give a statistical implementation to risk forecasting in financial data.     

Existence of the solutions of a reaction cross-diffusion model for two species

In this paper, we investigate a two-cooperative species model with reaction cross-diffusion under the Dirichlet boundary value condition. By applying Lyapunov–Schmidt reduction method and some important formulas, we obtain the existence of coexistence solutions under some given conditions.     

基于粗糙集的突发事件属性约简方法

针对突发事件不完备信息系统中的原始数据存在大量属性冗余的问题,提出一种基于粗糙集的不完备信息系统属性约简方法,以剔除冗余属性,提高知识清晰度。首先对缺失、冗余、噪声以及连续型数据进行预处理;然后进行属性分类,将属性分为条件属性与决策属性,进而建立决策表;最后根据决策表的特征,结合有序加权平均算子的思想,提出一种基于属性重要度的启发式属性约简算法。文末,通过实例验证了方法的正确性与有效性,并利用该方法实现了火灾数据的属性约简。