Turbulence simulation and multiple scale subgrid models

 The problem of modelling turbulence in CFD is due to the wide range of length scales present in a turbulent flow. The physics of these scales is examined, and the need for models of the small scale motions is made clear. A review is given of methods of turbulence modelling. These methods can be divided into two classes: Reynolds averaged Navier–Stokes (RANS) models, and large eddy simulation (LES). The Reproducing Kernel Particle method (RKPM) is then presented and proposed as a class of filters for LES of inhomogeneous turbulent flows. Important properties of the method are discussed, including the effectiveness of the RKPM reproduction as a low-pass filter. The commutation of the filtering operation with differentiation is demonstrated, showing that the commutation error can be made arbitrarily small. A one-dimensional non-linear example problem is solved using a Galerkin method in which a bi-scale constitutive model is used for the subgrid scale terms. The extension of the method to the three-dimensional equations of fluid dynamics is then outlined, where the method is used as a filter in a dynamic subgrid stress model. Emphasis is placed on the multi-scale properties of RKPM, which allow the reproduction of different scales of the solution using the same set of nodal parameters.     

Estimating reproduction numbers for adults and children from case data

We present a method for estimating reproduction numbers for adults and children from daily onset data, using pandemic influenza A(H1N1) data as a case study. We investigate the impact of different underlying transmission assumptions on our estimates, and identify that asymmetric reproduction matrices are often appropriate. Under-reporting of cases can bias estimates of the reproduction numbers if reporting rates are not equal across the two age groups. However, we demonstrate that the estimate of the higher reproduction number is robust to disproportionate data-thinning. Applying the method to 2009 pandemic influenza H1N1 data from Japan, we demonstrate that the reproduction number for children was considerably higher than that of adults, and that our estimates are insensitive to our choice of reproduction matrix.     

Quantitative Analysis of Colour Rendering in Graphic Arts with Three-Colour Printing by Way of Various Photographic Techniques

Various methods of reproduction usual in the graphic arts industry are compared as to their colour-rendering qualities. The methods of reproduction examined differ according to the nature and the number of their intermediate photographic steps. Colour rendering results were obtained by a combination of experimental methods and calculation. The reproduction methods are compared for the case of a perfect grey reproduction, wherein use is made of a definite set of three-colour printing inks.     

同态滤波耦合后处理优化的图像增强算法

目的为了提高图像增强算法中的亮度分布,抑制伪光晕与噪声现象,改善增强图像的细节与亮度。方法提出一种同态滤波耦合后处理优化的图像增强方案。首先,利用引导滤波器估计输入图像的照度,利用YCb Cr色彩空间中平滑的Y通道为导向图像,以有效捕捉真实场景的亮度,准确计算图像照度。其次,根据得到的照度估计,提取图像景物的反射率,为了同时提供动态范围压缩和色调再现,设计一种多尺度Retinex和色彩修复算子,利用3个不同尺度的Gaussian滤波加权组合,进行彩色图像增强。最后,为了实现多尺度Retinex与色彩修复算子的最优性能,通过非线性拉伸和参数优化组成的自动后处理方法,构建一种学习策略,利用量子行为粒子优化机制(QDPSO)自适应地确定每个输入图像的最佳参数,从而有效考虑了景物的照度与反射率的关系,避免了色彩失真。结果实验数据表明,与当前常用的增强算法对比,所提算法得到增强图像清晰度和细节更优,更符合视觉的感知特性,且效率更高,耗时约为0.7 s左右。结论所提算法具有良好的增强效果,在图像信息处理领域具有一定的借鉴作用。     

The Study of Colour Reproduction by Computation and Experiment

Colour reproduction changes caused by changes in the elements of a colour photographic system can be predicted by computational methods. Typical computations are outlined with the aid of a simple model of a colour photographic system. Colour preference information is required to predict correctly the desirability of a computed change in colour reproduction. The preferred reproduction of an object colour depends on the viewer’s adaptation. It is believed that, by a combination of adaptation measurements and colour preference measurements, the optimum reproduction of several important colours can be specified. An experiment in which adaptation measurements were used to determine the preferred reproduction of flesh colour is described.     

多光谱颜色重建在植物病虫害检测中的应用

为了克服传统RGB三基色相机图像颜色重建的缺点，论文提出用多光谱相机捕获植物光谱图像的方法，根据图像捕获位置和观测位置照明光源的情况重建出植物病虫害的真实色彩。实验利用16个窄带滤光片和黑白面阵CCD摄像机获得植物病虫害的多光谱信息，通过多项式插值拟合出观测目标的光谱曲线。并和PR-715光谱辐射度计进行比较，对重建结果做出分析。试验结果表明16个通道的多光谱图像能够重建出植物病虫害的颜色。     

Bayesian state and parameter estimation of uncertain dynamical systems

The focus of this paper is Bayesian state and parameter estimation using nonlinear models. A recently developed method, the particle filter, is studied that is based on stochastic simulation. Unlike the well-known extended Kalman filter, the particle filter is applicable to highly nonlinear models with non-Gaussian uncertainties. Recently developed techniques that improve the convergence of the particle filter simulations are introduced and discussed. Comparisons between the particle filter and the extended Kalman filter are made using several numerical examples of nonlinear systems. The results indicate that the particle filter provides consistent state and parameter estimates for highly nonlinear models, while the extended Kalman filter does not.     

Design and implementation of microwave multi-band/multi-level filters using equal-length transmission lines and Yule?Walker scheme

A new method to design microwave filter with multiple-band/multiple-level response is proposed. The modified Yule?Walker equation is used to define the frequency-domain response of filter in the Z domain. To implement a filter having transfer function in the Z domain, an equal-length transmission-line configuration is employed to emulate the filter. A band-pass filter a dual-band band-pass filter and a dual-level band-pass filter are implemented and their frequency responses are measured to illustrate the validity of this design method.     

基于实验室重现噪声的高速列车车厢主动降噪实验研究

为降低高速列车运行时的车厢内低频噪声,研究了车厢内大范围区域的噪声主动控制问题。针对高速列车运行实测噪声频谱与目标降噪区域尺寸（1.8 m×2.5 m×1.3 m）,设计48通道的前馈主动控制系统。按照比较匀称的排列方式,次级声源布放在车厢内除底部的其余5个面上,误差点分布在目标区域。通过测量各声学路径传递函数,离线计算和控制滤波器工作状态。在半消声室内进行一节车厢布局的降噪实验,使用车外声场重现系统播放4种车速工况下的初级噪声,测量主动控制系统的降噪性能并分析不同车速下噪声和不同参考信号下系统性能的异同。结果表明,对于不同车速的噪声,使用车厢窗户的振动信号为参考信号,在目标区域48个测量点可获得3.1～4.7 dB（A）的平均降噪量,验证了主动控制系统在大范围区域实现降噪的可行性。     

图像重建中滤波算子的一种优化方法

目的　在图像重建过程中 ,通过滤波算子的优化 ,降低投影噪声对重建结果的影响 .方法　对“滤波 -重建 -滤波”的图像重建形式 ,用矩阵理论、最优化理论等数学方法两个滤波算子进行优化 .结果与结论　得到了其优化算子的矩阵表达式     

水下机动目标跟踪技术研究

水下目标跟踪是海洋国土监视、反潜战等环境下的关键技术。以往的跟踪滤波算法主要基于卡尔曼滤波、扩展卡尔曼滤波等算法,这些方法实现比较复杂,滤波精度不高。最近出现了不敏卡尔曼滤波、粒子滤波、转换瑞利滤波、双多基地跟踪算法等,需要研究这些算法在水下目标跟踪中的性能。总结对比了国内外学者在此领域的研究成果,得出了这些滤波算法在水下目标跟踪中的优缺点。重点论述了纯角度跟踪和非线性滤波算法的发展、在水下目标跟踪中的应用以及多基地声纳跟踪水下目标技术的发展,回顾了机动目标跟踪和多目标数据互联算法。研究表明,非卡尔曼滤波算法能够更高精度地跟踪水下目标,双多基地声纳是今后发展的重点。为今后的研究提供参考。     

Performance of minimum-mean-square-error filters for spatially nonoverlapping target and input-scene noise

Using computer simulations, we investigate the performance of a minimum-mean-square-error filter for input-scene noise that is spatially nonoverlapping (disjoint) with a target for a limited set of images. Different input-scene-noise statistics are used to test the filter performance. We show that in the presence of spatially nonoverlapping target and input-scene noise, the output of the minimummean- square-error filter has a well-defined correlation peak, small sidelobes, and a high peak-to-correlationenergy ratio compared with other widely used filters such as the classical matched filter, the phase-only filter, and the inverse filter. We also test the robustness of the minimum-mean-square-error filter to errors in noise statistics used in the filter design. We show that, for the images tested here, the performance of the minimum-mean-square-error filter is not sensitive to errors in noise statistics and the filter can detect the target even if a considerable error exists. The discrimination capability and the illumination sensitivity of the minimum-mean-square-error filter are also tested.     

State primary standard of the unit of relative permittivity and unit of relative permeability in the frequency range 1 MHz – 18 GHz

The composition and generalized block diagram of the State Primary Standard of the unit of relative permittivity and unit of relative permeability in the frequency range 1 MHz – 18 GHz and methods of reproduction and transfer of the unit are considered. Measurement equations for all the standard devices and a brief analysis of the errors that arise in reproduction of the unit are presented.     

Comparison of reproduction performance of a single pole head and a ring head

The reproduction pulse amplitude of a single pole head from double-layer perpendicular media has been analyzed. We derived an analytic expression to relate the pulse amplitude to the head and medium parameters. Experimental data are also presented to verify the calculated results. The reproduction performances of a single pole head and a ring head are theoretically compared and found to be comparable when both are normalized to the same head inductance.     

Adaptive IIR filter design for single sensor applications

The goal of this research was to investigate the theoretical design and physical implementation of a digital adaptive IIR filter to serve as an enhancement to the traditional active RC or passive RLC anti-aliasing filter. This all-digital filter will reside directly on the DSP engine. As explained in the paper, the adaptive IIR filter is designed to process an oversampled signal coming from a single sensor to reject noise in an acquisition system. Differentiation between the noise and the signal is obtained by exploiting the different auto-correlation functions of the two signals. In contrast to oversampling techniques employed in sampled data systems that are designed to relax the requirements of an analog anti-aliasing filter, this filter will track a signal in the frequency domain. Several power spectral density plots are given to illustrate the performance of the new filter. The results also indicate that the new filter performs well as compared to the Wiener filter in the stationary case     

基于网点结构形态的印刷色彩再现研究

以调幅网点和同心圆网点作为主要研究对象,分析了网点结构对网点呈色特性的影响,应用Clapper-Yule颜色预测模型和Lambert-Beer法则,解释了同心圆网点高饱和度色彩再现的机理,并通过实验对理论分析进行了验证。结果表明:网点内部结构的差异会影响色彩再现质量,同心圆网点环形内部结构是影响其印刷呈色的重要因素;同心圆网点的色彩表现力优于调幅网点,特别是在饱和度再现上优势明显。     

A Filtering Technique for Three-Phase Power Systems

A novel filter for use in three-phase power systems is introduced. When the input to the filter is a balanced three-phase set of signals, the filter suppresses noise and distortions and extracts a smooth three-phase fundamental component. When the input signal to the filter is unbalanced, it extracts the fundamental positive-sequence component of the input signal. The filter also estimates the magnitude, phase angle, and frequency of the signal and adaptively follows the variations in all these three variables. The characteristics of the filter, including its mathematical equations, stability analysis, steady state, and dynamic responses, are discussed in this paper. The filter highly attenuates the harmonics, unknown interharmonics, and distortions. However, an extension of the filter for full removal of harmonics and unknown interharmonics is also presented, and its operating principles are discussed. The structural simplicity and robustness of the filter make it desirable for power system applications. In addition to the wide applications in power systems, it can specifically be used as an adaptive antialiasing filter for three-phase applications.     

A Technique for Synthesizing Digital Filters

In designing digital systems, one often faces the task of replacing a given analog filter by an equivalent digital filter. This paper proposes a method for synthesizing such digital filters in the time domain. It is assumed that the pulsed transfer function of the digital filter is a ratio of two rational polynomials. The coefficients are then determined by least-square fitting the digital filter to the analog filter's sampled input and output data. The resulting equations for computing the coefficients are linear. It is shown that the digital filter is essentially related to the analog filter, the sampling time, and the power spectrum of the signal being processed. If the signal is band-limited and the sampling frequency is sufficiently high, the digital filter can then be simply approximated by the Z transform of the analog filter multiplied by the sampling period.     

斜变滤波器频域加窗对图像重建的影响

斜变滤波器的性能对图像重建有重要的影响,频域加窗设计法是其主要的设计方法。设计了4种经典的加窗滤波器：RL滤波器、SL滤波器、Hamming窗滤波器和指数窗滤波器。从单位冲激响应和频率响应2个方面分析了这4种滤波器的特性;从频率响应和旁瓣衰减速度2个方面比较了这4种滤波器。理论分析与仿真结果表明：指数窗滤波器的震荡噪声最小;SL滤波器整体最优。     

一类具有时滞的HIV感染模型的动力学性态

研究一类具有胞内时滞和饱和发生率的HIV感染动力学模型,通过计算得到了病毒感染的基本再生率。进而,通过分析特征方程根的分布,讨论了系统可行平衡点的局部渐近稳定性。根据构造的Lyapunov泛函,证明了当基本再生率小于1时,病毒未感染平衡点是全局渐近稳定的。利用无穷维动力系统的持续生存理论证明了当基本再生率大于1时,系统是一致持续生存的。最后,采用比较原理和单调迭代技巧,给出了病毒感染平衡点全局吸引的充分条件。