Numerical analysis and passive control of a car side window buffeting noise based on Scale-Adaptive Simulation

Flow over an open side window in a car exhibits similar characteristics as the flow over an open cavity. Computational Fluid Dynamics (CFD) simulation over a cavity was done as a benchmark. The unsteady flow simulation was carried out using Scale Adaptive Simulation (SAS) turbulence model. The benchmark results, frequency and sound pressure levels of feedback and resonance modes, all well matched with the experimental data. Then, with the right rear window, for example, the mechanism of the side window buffeting was investigated. The simulation results show that side window buffeting noise is generated by large scale vortices and in low frequency. Furthermore, buffeting noise characteristics under several patterns of side windows opening were also numerically investigated. As a result, rear window buffeting noise is more severe than that of front window when one window open, and combination pattern of side windows open can reduce buffeting noise. To decrease the interior noise and improve car ride comfort, four suppression measures through adding a side window weather deflector at the A-pillars, constructing a cavity at the B-pillars, combination of the front and rear windows and installing a row of square cylinder deflector at the B-pillars were also studied, respectively. In conclusion, certain noise reduction can be achieved through four passive control methods.     

二进制偏移载波调制的零相关窗水声同步技术研究

针对线性调频信号同步相关的旁瓣、m序列扩频同步的序列自噪声和二进制相移键控调制信号在主瓣周围一个码片范围内存在较强烈的旁瓣三个问题,提出了一种基于二进制偏移载波(BOC)调制信号的无干扰窗水声同步方式.利用互补序列的非周期自相关函数之和为零的特殊性质,实现了在主瓣周围一个码片范围外,零相关窗范围内的无干扰窗.使用BOC(1,1)方式对信号进行亚载波调制,以减少主瓣周围一个码片范围内的旁瓣.对单通道信号和双通道信号的零相关窗形式都进行了设计,通过仿真和实验验证了BOC零相关窗方法在水声系统的同步、信道测量和估计中的有效性.     

Electronic Transport through a Waveguide in the Presence of a Magnetic Obstacle

By means of the transfer matrix technique, the electronic transport through a quantum waveguide in the presence of a magnetic obstacle is investigated theoretically. By comparing the calculated conductance spectra of the opposite spin electrons, we find that there exists a notable spin filtering window in the low energy region. Dependences of such a spin filtering window on the size, position and potential strength of the magnetic obstacle are studied in detail.     

基于心音窗函数的心音图形化处理方法的研究

心音分析与识别目前主要局限在一维信号处理方面, 为了获得心音信号更直观特征表现形式, 提高分类识别效果, 拓展心音识别研究领域, 提出了一种将心音与图像处理技术相结合、基于心音窗函数的心音纹理图特征提取与识别算法. 本文首先给出心音的模型, 定义心音时频图和心音纹理图, 然后讨论如何利用心音窗函数和短时傅里叶变换获取二维心音时频图, 并且针对心音的特点, 重点研究了心音窗函数的构造原则和实现方法, 最后通过改进的脉冲耦合神经网络模型实现了对心音纹理图的特征提取与身份识别. 仿真实验表明, 心音窗函数与传统窗函数相比较, 所获得的心音时频图具有第一、第二心音纹理更加清晰, 噪声纹理得到较好抑制的优点, 并且改进的脉冲耦合神经网络模型具有更低的计算成本, 与3种典型识别方法相比较, 呈现更高的识别率, 因而基于图像处理技术对心音进行特征提取与身份识别是一种行之有效的方法.     

水平层状各向异性介质中电磁场并矢Green函数的一种高效算法

利用高阶窗函数结合连分式展开等技术研究并建立一种水平层状各向异性介质中电磁场并矢Green函数的快速有效算法. 首先借助于高阶窗函数将构成并矢Green函数的Sommerfeld积分转化成广义快速下降路径上积分,并给出高阶窗函数Hankel变换的一种新的更高阶幂级数展开式以及严格的Lommel函数表达式,以满足在全空间上高精度计算并矢Green函数的要求. 在此基础上,用Bessel函数的零点将积分路径划分成一系列小区间并通过改进的自适应Gauss求积公式确定各个小区间上的积分值,然后引入连分式展开法对各个区间上的积分值求和,从而使整个积分的收敛效率得到大大提高. 最后通过数值结果验证本方法的有效性. 关键词： 高阶窗函数 连分式展开 并矢Green函数 层状各向异性介质     

Optimization of optical communication window mesh through full-wave analysis of periodic mesh

In order to develop an optical communication window mesh with good optical transmittance and shielding effectiveness at the same time, models were established for the shielding effectiveness and optical transmittance of optical communication window mesh, verified through experiments, and used to run full-wave analyses. The effect of period and linewidth of mesh on the shielding effectiveness and optical transmittance of optical communication window mesh was investigated through simulation. Simulation results indicated that better optical transmittance can be achieved using optical communication window mesh with high porosity and finer linewidth while the given shielding effectiveness requirement is satisfied.     

Influence of a skull cranial window on the measurement of haemoglobin concentration in cortical tissue by multi-spectral imaging analysis

The simplified cranial window, which is transparent thinned skull, has been used for the optical imaging of cortical tissue of small animals to measure the concentration change in haemoglobin as an intrinsic signal of brain activation. The multi-spectral images of the cortical tissue of guinea pigs through the skull cranial window were compared with those of the exposed cortex to evaluate the influence of the scattering and absorption properties of the skull on the measurement of the concentration change in haemoglobin. Although skull thickness affects the sensitivity of the optical signal due to a decrease in mean optical path length in the cortical tissue, the influence of the skull cranial window on the wavelength dependence of optical path length can be ignored when the skull thickness is less than approximately 100 mm. Accurate concentration changes in oxygenated and deoxygenated haemoglobins can be calculated from the optical signal measured through a skull cranial window and the wavelength dependence of optical path length for the exposed cortex.     

基于变分辨率的自适应窗口目标跟踪方法研究

针对视觉跟踪中运动目标的大小也随之改变这一问题,提出一种基于变分辨率的自适应窗口目标跟踪方法。在最大后验概率视觉跟踪算法基础上,分析了运动目标窗口内外框上的后验概率贡献指标,建立了自适应窗口调整目标尺度的数学模型。当运动目标尺寸变化时,其分辨率也相应变化,为了保证跟踪的实时性和效率,采用变分辨率的特征统计采样方法。在对运动目标实现自适应窗口的跟踪时,特征统计的分辨率也随之改变,对尺寸越大的运动目标尺度赋予更低的分辨率,从而实现基于变分辨率的自适应窗口目标跟踪。     

Insertion loss of sound waves through composite acoustic window materials

This study evaluated the insertion loss of sound waves through composite acoustic window materials for sonar dome applications, and examined the influence of dome shape on the sonar performance. The insertion loss of sound waves through acoustic window materials was experimentally measured as a function of frequency at normal incidence. The insertion loss was also theoretically estimated with three- and four-medium layer models. The theoretical estimation of insertion loss showed good agreement with the experimental measurements. The insertion loss was also measured as a function of angle of incidence. The characteristics of longitudinal and converted shear waves were observed at various angles of incidence. This study will be useful to select acoustic window materials with the appropriate acoustic characteristics for practical sonar dome applications.     

强火光中图像拍摄技术研究

对串联战斗部一级战斗部装药燃烧的火光进行近紫外波段光谱分析,选取了310 nm～320 nm作为高速摄像机拍摄窗口,并采用窄带滤波器过滤掉拍摄窗口之外的其他光谱,使用激光辅助照明设备对火光中的物体在320 nm处进行照明,较为清晰地拍摄到了强火光中的物体图像,并进一步通过串联战斗部穿靶试验,验证了系统的科学和有效性。     

Two different effects of Na on Cu2ZnSnS4 thin-film solar cells

Among the many factors that affect the characteristics of Cu₂ZnSnS₄ thin-film solar cells, the effects of Na were examined. Because Na passivates the grain boundaries (GBs) in absorber layers, the GBs increase the minority carrier collection by providing a current pathway through which the minority carriers can reach the buffer and window layer and be collected. However, excess Na remains in the absorber layer and diffuses into the buffer and window layers, where it acts as an impurity and traps the minority carriers, thus decreasing the solar cell characteristics. By applying an annealing process after the deposition of the buffer and window layers, the Na content could be decreased. By improving the solar cell characteristics, a power conversion efficiency of 6.43% was achieved.     

Study on the optical path difference of aero-optical window

To study the optical path difference (OPD) of optical widow in which light beams transmit under the aerodynamic thermal environment, a grid model is introduced. Based on it, the aero-optical effect of the side-mounted window is analyzed in detail combining the optical transmission theory and the numerical simulation method. Firstly, the temperature and stress of the window are simulated, and then the OPD is obtained through the refractive index. To demonstrate it, temperature field, deformation field and stress field of the window are calculated and analyzed. The influences of thermal shock and atmosphere pressure on the OPD are discussed.     

Influence of surface roughness on superhydrophobicity

Superhydrophobic surfaces, with a liquid contact angle theta greater than 150 degrees , have important practical applications ranging from self-cleaning window glasses, paints, and fabrics to low-friction surfaces. Many biological surfaces, such as the lotus leaf, have a hierarchically structured surface roughness which is optimized for superhydrophobicity through natural selection. Here we present a molecular dynamics study of liquid droplets in contact with self-affine fractal surfaces. Our results indicate that the contact angle for nanodroplets depends strongly on the root-mean-square surface roughness amplitude but is nearly independent of the fractal dimension D(f) of the surface.     

An adaptive window object tracking algorithm based on variable resolution

This paper presents an adaptive window object tracking method based on variable resolution. It copes with the change in size of the object during visual tracking. On the basis of the visual tracking algorithm, based on maximum posterior probability, we analyze the posterior probability index on the inside and outside panes of the object window, then build a mathematical model for adjusting object size with an adaptive window. Since the resolution changes according to the size of the object, this thesis uses a statistical sampling method of the feature by variable resolution. The resolution of the statistical feature is correspondingly changed in object tracking with an adaptive window. The resolution of a larger object is decreased, which realizes an object tracking method with adaptive window based on variable resolution.     

HL-2A装置ECRH系统传输效率的测量研究

介绍了HL-2A装置ECRH系统传输效率的测量方法。通过对MOU、回旋管输出窗口及真空密封窗口吸收功率的测量,得到HL-2A电子回旋系统的传输效率为90％左右。提出了除由MOU处测量微波功率外,可以由传输线的其他部位确定功率的方法。     

一种利用十字窗口识别红外弱小目标的新方法

为有效地识别红外图像中的弱小目标,在分析传统识别方法的基础上,提出了一种利用十字窗口识别红外弱小目标的新方法.该方法在待识别点上、下、左、右四个方向以目标大小选取四个参考点构造十字形识别窗口,根据待识别点与参考点之间的灰度梯度识别该像素点是否为目标像素.该方法无需预测背景,可以在低信噪比、强度变化剧烈的图像中获得较高的识别率与较低的虚警率.实验结果表明了该算法的有效性.     

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介绍了HL-2A装置ECRH系统传输效率的测量方法。通过对MOU、回旋管输出窗口及真空密封窗口吸收功率的测量,得到HL-2A电子回旋系统的传输效率为90％左右。提出了除由MOU处测量微波功率外,可以由传输线的其他部位确定功率的方法。     

Mean Shift跟踪算法中核函数参数的评估与分析

Mean Shift是一种基于特征的对目标实现快速跟踪的算法,传统的Mean Shift算法由于跟踪中物体的尺度变化会使跟踪偏离目标乃至跟踪失败,并且原有的自适应地对跟踪窗宽的调整,是基于对核窗宽的改变来得到的。在＂固定跟踪窗宽—改变核窗宽＂的基础上对目标进行跟踪,对目标空间定位精度进行了评估与分析,通过实验结果表明改变核函数参数能改善目标跟踪的精度。     

A study of the interplay between the structure variation and fluctuations of the Shanghai stock market

The intricate interplay between the variation of the stock network structure and fluctuations of that stock market is increasingly becoming a hot topic. In this work, employing a moving window to scan through every stock price time series over a period from 2 January 2001 to 7 December 2010, we use mutual information to measure the statistical interdependence between stock prices, and we construct a corresponding network for 501 Shanghai stocks in every given window. Then we address the time-varying relationships between the structure variation and fluctuations for the Shanghai stock market. All the results obtained here indicate that at turning points the growing independence of stocks causes the scalefreeness of the degree distribution to be disrupted, and that the Shanghai stock index has little volatility clustering. In contrast, under normality of the market, the stock networks have characteristics of scalefree degree distribution. Furthermore, the degree of volatility clustering is a little higher.