Identification and data-driven model reduction of state-space representations of lossless and dissipative systems from noise-free data

We illustrate procedures to identify a state-space representation of a lossless or dissipative system from a given noise-free trajectory; important special cases are passive systems and bounded-real systems. Computing a rank-revealing factorization of a Gramian-like matrix constructed from the data, a state sequence can be obtained; the state-space equations are then computed by solving a system of linear equations. This idea is also applied to perform model reduction by obtaining a balanced realization directly from data and truncating it to obtain a reduced-order model.     

基于并行相关的实时时差估计器设计与实现

从相关时差估计的基本原理出发,提出了一种并行时域相关结构,基于这种并行结构设计实现了一种简单高效的时差估计器.与传统频域相关时差估计器相比,这种时差估计器的主要优点是提高了运算效率,运算周期大为缩短,可以满足实时高精度时差估计的需求,同时结构简单,硬件资源开销小,易于设计实现.实际测试结果验证了上述结论.     

一种JPEG图像的DCT域隐写分析方法

提出了一种基于JPEG图像DCT系数差分矩阵统计特征的隐写分析方法。该算法保留了以往算法选用的DCT系数水平和竖直方向的差分矩阵相关特征,通过增加其主副对角线方向上差分矩阵来提取和计算特征向量,进而利用SVM分类器进行分类。实验结果表明,该方法能够有效地对JPEG图像进行检测,并且具有较高的检测正确率。     

135MW机组一次调频功能优化

介绍云浮发电厂#4机组一次调频功能的基本原理。通过试验,发现一次调频功能存在问题,经过分析,对控制逻辑和参数进行修改,解决了存在问题,并使DCS侧的一次调频功能与DEH侧的功能很好地配合,在不影响机组稳定运行下完全有能力参与一次调频。     

对象间差异度的限制非对称相似关系模型

经典Rough集理论主要是利用了不可分辨关系对完备信息系统进行分析的。对现有粗糙集模型进行扩充后,才可以应用于不完备信息系统。容差关系、非对称相似关系、基于对象间完备度的限制容差关系、限制非对称相似关系等是现有的扩充模型。通过分析其优点和不足之处,提出一种新的模型——对象间差异度的限制非对称相似关系模型,在该模型中,给出的知识粒度更精确,更符合实际。实例结果也证明新模型可以从不完备信息系统获取更加精确的知识粒度。     

An explicit predictor-corrector solver with application to seismic wave modelling

Wave-equation-based forward modelling using explicit finite-difference methods is a standard technique for calculating synthetic seismograms. The stability criterion restricts the size of the time step. In this paper a predictor–corrector method for solving the wave equation is described which allows the use of a larger time step. A stability analysis of the method is also carried out. Parallel implementation of the algorithm is described for a distributed computing environment which makes use of MPI and PVM message passing calls for communication between processors.     

Efficient algorithms for segmentation of item-set time series

We propose a special type of time series, which we call an item-set time series, to facilitate the temporal analysis of software version histories, email logs, stock market data, etc. In an item-set time series, each observed data value is a set of discrete items. We formalize the concept of an item-set time series and present efficient algorithms for segmenting a given item-set time series. Segmentation of a time series partitions the time series into a sequence of segments where each segment is constructed by combining consecutive time points of the time series. Each segment is associated with an item set that is computed from the item sets of the time points in that segment, using a function which we call a measure function. We then define a concept called the segment difference, which measures the difference between the item set of a segment and the item sets of the time points in that segment. The segment difference values are required to construct an optimal segmentation of the time series. We describe novel and efficient algorithms to compute segment difference values for each of the measure functions described in the paper. We outline a dynamic programming based scheme to construct an optimal segmentation of the given item-set time series. We use the item-set time series segmentation techniques to analyze the temporal content of three different data sets–Enron email, stock market data, and a synthetic data set. The experimental results show that an optimal segmentation of item-set time series data captures much more temporal content than a segmentation constructed based on the number of time points in each segment, without examining the item set data at the time points, and can be used to analyze different types of temporal data.     

The application of a proportional difference type iterative learning control in active vibration control

Active vibration control is used to instead passive solutions in order to increase the performance at low frequencies, in a variety of different engineering systems. This method has improved the performance specifically. The paper will propose a proportional difference type iterative learning control algorithm to deal with the periodic sources and to investigate the active solution as the three degrees of freedom ＂mass spring damping＂ mount. Simulation shows that this method could get a better tracking performance, also the displacement could converge to zero with a fast speed.     

The periodic nature of the positive solutions of a nonlinear fuzzy max-difference equation

We investigate the periodic nature of the positive solutions of the fuzzy difference equation , where k, m are positive integers, A₀, A₁, are positive fuzzy numbers and the initial values x_i, i = −d, −d + 1, … , −1, d = max{k, m}, are positive fuzzy numbers. In addition, we give conditions so that the solutions of this equation are unbounded.     

高雷诺数流动的平均化差分格式

本文在N—S方程涡量一流函数形式的经典ADI格式和SOR松驰迭代公式的基础上,对其“外来项”进行平均化处理,构造出了平均化差分格式及迭代求解程序。对雷诺数Re=100,1000,10000的空腔流动分别进行了数值计算,并与各数值方法的结果及实验资料进行了比较,结果令人满意。