最小相关系数的多元校正波长选择算法

在近红外光谱的定量分析中,由于仪器的精密程度越来越高,采集的光谱数据通常具有很高的维度.因此,波长选择对于剔除噪声及冗余变量,简化模型,提高模型的预测性能是必不可少的.近红外光谱特征波长选择方法众多,但变量间的多重共线性问题仍是导致模型效果较差的一个关键问题.变量间共线性可以通过相关系数进行分析,当相关系数高于0.8,...     

An Adaptive Rank Aggregation-Based Ensemble Multi-Filter Feature Selection Method in Software Defect Prediction

Feature selection is known to be an applicable solution to address the problem of high dimensionality in software defect prediction (SDP). However, choosing an appropriate filter feature selection (FFS) method that will generate and guarantee optimal features in SDP is an open research issue, known as the filter rank selection problem. As a solution, the combination of multiple filter methods can alleviate the filter rank selection problem. In this study, a novel adaptive rank aggregation-based ensemble multi-filter feature selection (AREMFFS) method is proposed to resolve high dimensionality and filter rank selection problems in SDP. Specifically, the proposed AREMFFS method is based on assessing and combining the strengths of individual FFS methods by aggregating multiple rank lists in the generation and subsequent selection of top-ranked features to be used in the SDP process. The efficacy of the proposed AREMFFS method is evaluated with decision tree (DT) and naïve Bayes (NB) models on defect datasets from different repositories with diverse defect granularities. Findings from the experimental results indicated the superiority of AREMFFS over other baseline FFS methods that were evaluated, existing rank aggregation based multi-filter FS methods, and variants of AREMFFS as developed in this study. That is, the proposed AREMFFS method not only had a superior effect on prediction performances of SDP models but also outperformed baseline FS methods and existing rank aggregation based multi-filter FS methods. Therefore, this study recommends the combination of multiple FFS methods to utilize the strength of respective FFS methods and take advantage of filter–filter relationships in selecting optimal features for SDP processes.     

一类基于通量分裂的二阶精度TVD差分格式

基于通量分裂和逆风特性,选取单元交界面上的正、负数值通量,并结合高阶Runge-Kutta TVD时间离散方法,构造了一维非线性双曲型守恒律的一类二阶精度的差分格式,证明了差分格式的TVD特性。按分量形式推广到方程组。通过几个典型的数值算例验证了格式的有效性。     

采用NND方法计算三维喷管气流场

本文运用NND显式差分格式,计算了三维喷管气流场。气流场计算的基本方程为一般贴体坐标系下三维守恒型的欧拉方程。采用了时间分裂法和Steger-Warming矢通量分裂技术。在喷管内沿周向的每个由轴线和壁面构成的子午面上根据泊松方程生成贴体网格。本文运用三维程序计算了轴对称JPL喷管,同时与实验结果和前人采用轴对称二维程序所计算的结果做了对比。最后,本文还计算了三维矢量喷管,计算结果与现有的实验结果一致。通过轴对称JPL喷管和三维矢量喷管的计算考核,表明建立的算法和编写的计算程序是正确的。文中提出了采用子午面形式的贴体网格时奇性轴的处理方法。计算结果表明在喷管壁面处,马赫数与压强的计算结果与实验值吻合较好,而在喷管轴线处,只有当网格较密时,才能得出与实验结果接近的计算结果。     

Convergence and error bound analysis for the space‐time CESE method

In this work, we study the convergence behavior of a recently developed space‐time conservation element and solution element method for solving conservation laws. In particular, we apply the method to a one‐dimensional time‐dependent convection‐diffusion equation possibly with high Peclet number. We prove that the scheme converges and we obtain an error bound. This method performs well even for strong convection dominance over diffusion with good long‐time accuracy. Numerical simulations are performed to verify the results. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17: 64–78, 2001     

On a higher‐order bounded discretization scheme

This paper presents a new higher‐order bounded scheme, weighted‐average coefficient ensuring boundedness (WACEB), for approximating the convective fluxes in solving transport equations with the finite volume difference method (FVDM). The weighted‐average formulation is used for interpolating the variables at cell faces and the weighted‐average coefficient is determined from normalized variable formulation and total variation diminishing (TVD) constraints to ensure the boundedness of solution. The new scheme is tested by solving three problems: (1) a pure convection of a box‐shaped step profile in an oblique velocity field, (2) a sudden expansion of an oblique velocity field in a cavity, and (3) a laminar flow over a fence. The results obtained by the present WACEB are compared with the UPWIND and the QUICK schemes and it is shown that this scheme has at least second‐order accuracy, while ensuring boundedness of solutions. Moreover, it is demonstrated that this scheme produces results that better agree with the experimental data in comparison with other schemes. Copyright © 2000 John Wiley & Sons, Ltd.     

Optical Channel Selection Avoiding DIPP in DSB-RFoF Fronthaul Interface

The paper presents a method of selecting an optical channel for transporting the double-sideband radio-frequency-over-fiber (DSB-RFoF) radio signal over the optical fronthaul path, avoiding the dispersion-induced power penalty (DIPP) phenomenon. The presented method complements the possibilities of a short-range optical network working in the flexible dense wavelength division multiplexing (DWDM) format, where chromatic dispersion compensation is not applied. As part of the study, calculations were made that indicate the limitations of the proposed method and allow for the development of an algorithm for effective optical channel selection in the presence of the DIPP phenomenon experienced in the optical link working in the intensity modulation–direct detection (IM-DD) technique. Calculations were made for three types of single-mode optical fibers and for selected microwave radio carriers that are used in current systems or will be used in next-generation wireless communication systems. In order to verify the calculations and theoretical considerations, a computer simulation was performed for two types of optical fibers and for two selected radio carriers. In the modulated radio signal, the cyclic-prefix orthogonal frequency division multiplexing (CP-OFDM) format and the 5G numerology were used.     

修正的Bakhvalov-Shishkin网格上奇异摄动问题的一致收敛性

研究具有两个边界层的奇异摄动两点边界值问题，为了提高其数值解的精度，构造了修正的Bakhvalov—Shishkin网格及相应的离散差分格式，并且利用Green函数证明了该差分格式具有O(N^-2)，一致于撮动参数ε的收敛阶，从而本质上改进了在Shishkin网格上得到的结果，即相应的差分格式具有关于ε一致的收敛阶O(N^-2 ln^2 N)，其中N为网格结点数．最后用数值例子说明该方法的可行性．     

Selectivity of DNA Replication: The Importance of Base-Pair Geometry over Hydrogen Bonding

The polymerase enzyme hardly differentiates between thymine and difluorotoluene nucleotides with respect to the replication selectivity. X-ray structure analysis show the importance of the Watson–Crick geometry for the replication fidelity; base selection is determined by the spatial prerequisite of the substrate pocket and directed protein interactions in the minor groove (schematically shown on the right).     

Modelling of pipeline integrity taking into account the fluid–structure interaction

Two mechanical models have been presented in this paper for structural failure prediction of piping systems conveying liquids subjected to pressure transients. One model takes into account the axial fluid–structure interaction (FSI) phenomenon between fluid and pipe motion, whereas the other refers to an extension of the well-known waterhammer formulation. Both models are described by a system of non-linear hyperbolic equations which are solved by using a numerical procedure based upon the operator splitting technique and Glimm's scheme. To implement Glimm's method, it is presented the solution of a 4×4 Riemann problem with discontinuous coefficients. Numerical predictions of both models are presented and compared, so that the influence of the FSI term on the failure analysis is focused on. © 1998 John Wiley & Sons, Ltd.