基于子网划分的电网关键节点识别

结合电网拓扑结构和潮流追踪技术,提出一种基于子网划分的电网关键节点识别方法。首先,根据发电机节点的邻域信息和功率将发电机节点划分为不同的子集,然后根据电网的系数分配矩阵将负荷节点划分到为其提供最大功率的发电机节点子集中,完成子网划分。接着采用多属性决策法对每个子网的节点进行排序,进一步改进并计算每个子网的结构系数,作为衡量子网重要性的指标。根据子网重要性,从每个子网中提取特定比例的候选关键节点,对这些候选节点依据多属性决策法重新排序,得到关键节点的最终排序。以IEEE14、IEEE57和IEEE118三种节点系统为例进行分析,得到各个系统的子网划分结果和各个标准网络的重要节点排序结果。采用本文方法、PageRank法和多属性决策法分别进行关键节点排序,并对排序靠前的关键节点进行级联故障性能实验和网络效能实验。实验表明,本文算法选择的关键节点对整个网络的传播性能影响最大,优于其他两种关键节点识别方法。     

The growth of mixed alkaline-earth fluorides for laser host applications

A comprehensive analysis is implemented concerning the growth, properties, and applications of doped-co-doped single and mixed alkali earth fluoride systems. Calcium-strontium fluoride solid solutions with a Sr content proportion varying widely between 0.007 and 0.675 mol.% are obtained as a batch of axis-symmetrical boules grown by a Bridgman-Stockbarger (BS) method. The crystallization front (CF) can be controlled to retain a convex CF-shape that is favourable for normal growth of single crystals. This achieved using a broad adiabatic furnace zone (AdZ) independently of the boules’ composition. The influence of the thermal field distribution on the CF and the real crystallization rate (CR), which are both critically decisive in controlling crystal quality, were originally assessed using empirically derived formulas. The optical characteristics of the grown boules were monitored by measuring the external transmittance t and calculating the total losses following light irradiation of optical windows that were prepared from sections of the boules that had been cut parallel to one another. The t-measurements were performed by two different techniques and the comparative analysis of the results reliably indicates any inhomogeneity in the grown boules. A simple supercooling criterion proved to closely relate the morphological stability of the CF enabling one to set up the optimum growth conditions. Thus the normal growth criterion outlines the concentration bounds where the isotropic growth mechanism is replaced by cellular anisotropic growth. A procedure has been established for provisioning researchers with optical quality calcium-strontium fluoride crystals with widely varying composition grown under practically identical conditions. As a consequence one can explore possible reasons that can affect the growth mechanism for this or any other systems with a fluoride structure and so provide scope aimed at the future improvement of the crystal quality thereby enlarging the field of mixed fluoride systems’ applications.     

一种新的激光车辙深度测量方法研究

车辙深度测量通常使用共梁式多路激光测距传感器测量路面多个离散点,由多个测量点组成的断面信息计算车辙深度,因横向采样点间距宽,导致测量误差较大。提出了一种新的激光车辙深度测量方法,采用线激光器和三维(3D)相机组合集成测量路面3D断面,通过3D断面解算车辙深度。3D相机以一定夹角采集激光器投射在路面的线结构光图像,获取路面的3D断面数据,对断面数据通过拉依达准则进行异常值剔除,再进行旋转、平移和模型识别,最终计算路面左右轮迹和最大车辙深度。实际证明,数据重复性和相关性都达到98%以上,与传统方法相比较,该方法采样间距小、测量精度高、成本低、通用性强,具有广阔的使用推广价值。     

Raman spectroscopy utilizing Fisher‐based feature selection combined with Support Vector Machines for the characterization of breast cell lines

Raman spectroscopy has the potential to significantly aid in the research and diagnosis of cancer. The information dense, complex spectra generate massive datasets in which subtle correlations may provide critical clues for biological analysis and pathological classification. Therefore, implementing advanced data mining techniques is imperative for complete, rapid and accurate spectral processing. Numerous recent studies have employed various data methods to Raman spectra for classification and biochemical analysis. Although, as Raman datasets from biological specimens are often characterized by high dimensionality and low sample numbers, many of these classification models are subject to overfitting. Furthermore, attempts to reduce dimensionality result in transformed feature spaces making the biological evaluation of significant and discriminative spectral features problematic. We have developed a novel data mining framework optimized for Raman datasets, called Fisher‐based Feature Selection Support Vector Machines (FFS‐SVM). This framework provides simultaneous supervised classification and user‐defined Fisher criterion‐based feature selection, reducing overfitting and directly yielding significant wavenumbers from the original feature space. Herein, we investigate five cancerous and non‐cancerous breast cell lines using Raman microspectroscopy and our unique FFS‐SVM framework. Our framework classification performance is then compared to several other frequently employed classification methods on four classification tasks. The four tasks were constructed by an unsupervised clustering method yielding the four different categories of cell line groupings (e.g. cancer vs non‐cancer) studied. FFS‐SVM achieves both high classification accuracies and the extraction of biologically significant features. The top ten most discriminative features are discussed in terms of cell‐type specific biological relevance. Our framework provides comprehensive cellular level characterization and could potentially lead to the discovery of cancer biomarker‐type information, which we have informally termed ‘Raman‐based spectral biomarkers’. The FFS‐SVM framework along with Raman spectroscopy will be used in future studies to investigate in‐situ dynamic biological phenomena. Copyright © 2013 John Wiley & Sons, Ltd.     

Failure waves in glass under dynamic compression

Abstract

Plate impact (I-d strain) and bar impact (I-d stress) experiments were performed on soda lime glass and pyrex glass. Embedded manganin gauges were used to monitor stress-time profiles in both types of experiments. In the plate impact experiments we found that glass not only fails through inelastic (or densification) deformation, but also through a unique failure process which gives rise to a failure wave first observed by Kanel et al. in the Soviet Union in 1990. In the present work three independent observations were made that support the existence of failure wave in glass: (i) the spall strength below and above the HEL is zero behind the failure wave, (ii) a small recompression is present in the longitudinal gauge (embedded between glass and PMMA) profile due to the reflections of release waves from the advancing failure wave, and (iii) transverse stress (measured by transverse gauge) increases on the arrival of the failure wave. The transverse stress increases because the glass loses its shear strength as a result of the arrival of the failure wave. The speed of the failure wave is about 1.5–2mm/μs. In the experiments on pyrex bars we used high speed Imacon framing camera to monitor the speed of the failure front. We found that pyrex bars fail through a failure front propagating across the cross section of the bar. The speed of the failure front is a function of the impactor (pyrex bar or steel plate) velocity. The speed increases from 2.3 mm/μs, corresponding to impact velocity of 125 m/s, to 5.2mm/μs for impact velocity of 330 m/s.     

Finite-element modeling of stresses and strains in a diamond anvil cell device: case of a diamond-coated rhenium gasket

The stresses and strains in a diamond anvil cell device were investigated using a finite-element code NIKE2D for the case of an ultra-hard composite gasket material. The pressure distribution in a diamond-coated rhenium gasket was measured by the energy dispersive diffraction technique to 213 GPa and compared with the finite-element modeling results. We examine various models for the mechanical properties of diamond-coated rhenium gasket as well as for diamond failure for shear stresses exceeding 100 GPa. The elastic and plastic properties of gasket were varied such that a good agreement between the experimentally measured pressure distribution and the computational pressure profiles were obtained. As a result, we obtained the effective Young’s modulus, Poisson’s ratio, yield stress for indented gasket, linear hardening modulus, and hardening parameter value for this layered ultra-hard composite gasket material. Future diamond design strategies for attainment of extreme high pressures using ultra-hard gasket materials are also discussed.     

Room vs. temperature studies of model composites: modes of failure of carbon fibre/epoxy interfaces

Laser Raman spectroscopy (LRS), transmission polarised optical microscopy (TPOM) and scanning electron microscopy (SEM) have been used to characterise the interface of model single-fibre composites. The composites consisted of single-carbon fibres embedded in epoxy resin. Local stress measurements as a function of applied strain were performed using LRS at both room temperature (RT) and 60?°C. Consecutively, the coupons were strained to failure and field emission SEM was used to study the fracture surfaces. In a parallel study, identical systems were subjected to incremental tension and fracture events were recorded as a function of applied strain. At RT, TPOM was used to provide additional insight in the local stress transfer. The stress transfer was found to depend on the combined effect of interfacial chemistry and thermal stresses. Thus, in the case of sized fibres, there is a distinct change in the interfacial failure mode at high temperature, whereas in the case of unsized fibres, the stress transfer is dominated by thermal stresses: at high temperature it is weak, due to the relief of the thermal stress field.     

基于脉冲宽度调制的滑模变结构控制的一阶H桥逆变器的分岔和混沌行为研究

滑模变结构控制是一种在宽工作范围具有快速响应和高稳定性的鲁棒控制, 因而被广泛地应用于逆变器控制中. 滑模控制的逆变器本质上是一种由非线性控制方式控制的时变非线性系统, 具有复杂的动力学行为. 本文以基于脉冲宽度调制的滑模变结构控制的一阶H桥逆变器为例, 首先观察不同滑模变结构控制器参数下系统的输出波形, 发现了一种多种倍数的倍周期同时存在的新型分岔现象; 其次, 使用频闪映射方法建立系统的离散迭代模型, 并利用折叠图法分析输出波形. 通过分析可知系统不能以这种新型分岔为道路通向混沌. 此外, 在工程应用中十分关心系统稳定性, 但是由于滑模变结构控制器的非线性特性, 常规解析方法都已不再适用于对系统进行分析, 而图解法又难以满足精度要求. 因此, 本文提出了一种新的适用于滑模变结构控制的逆变器的快变尺度稳定性的判断依据, 经验证该判据可以准确地判断系统是否处于稳定运行状态, 进而为滑模变结构控制器的参数设计提供可靠依据. 关键词： H桥逆变器 滑模变结构控制 新型分岔 稳定性判据