三维燃烧介质和壁面温度的非接触联合重建研究

温度分布在线实时测量对于燃烧过程优化和污染物控制具有重要意义, 针对以往非接触三维温度分布重建过程的耗时性问题和忽略壁面辐射的不足, 本文提出了一种新的离散重建模型, 用于三维吸收、 发射和散射性高温燃烧介质以及壁面温度的快速联合非接触测量. 该模型以四个CCD(Charge Coupled Device) 为测量传感器, 通过构建辐射逆问题求解方程, 从CCD输出的辐射投影图像重建温度分布. 介质中不同投影方向内的辐射传递过程通过离散传递法来描述, 介质的散射和壁面反射则通过离散坐标法来近似. 离散后计算局部辐射强度的病态方程通过最小二乘余量法来求解, 论文对其计算速度进行了优化. 通过非对称温度分布测量算例分析了该模型的有效性, 讨论了测量噪音、 介质和壁面辐射特性对重建精度的影响, 并与其他方法对比分析了模型的重建速度. 计算结果表明本文提出的离散模型可以有效地用于大型高温燃烧介质和壁面温度分布的联合非接触测量. 即使在有噪声的情况下, 该模型也能获得准确的测量结果, 与其他计算方法相比, 采用改进的最小二乘余量法, 能有效地提高温度分布的重建计算速度.     

A new method for reconstructing medium inhomogeneities using Rayleigh waves: Case studies

The problem of reconstructing local low-contrast inhomogeneities in the Earth’s surface layers by means of coherent Rayleigh surface waves is considered. It is shown that analysis of the frequency characteristics of shear projections in this wave on the surface allows construction of the function of inhomogeneity distribution in a specified depth range. The results from seismoacoustic reconstruction of inhomogeneities correlate with data obtained using standard geophysical methods and are confirmed by direct observations.     

心脏磁场分布电流源重构及其精度分析

用测量到的心脏磁场信号重构其电流源是一种无创揭示心脏电活动的方法. 心脏电活动的时空信息可视化, 将有助于心脏功能的研究和心脏疾病诊断. 本文通过仿真实验研究了一种减时窗波束形成器对分布时变电流源的重构能力, 以及源重构结果与心室兴奋传播的关系. 采用元胞自动机模拟心室的兴奋传播, 产生分布随时间变化的电流源, 并用边界元法构建了一个心脏-躯干模型, 模拟体电导的作用. 仿真结果表明, 这种减时窗波束形成器能够重构分布时变电流源, 并达到较好的精度. 将该方法和无穷大均匀介质导联矩阵用于一例正常人的心脏磁场信号分析, 其结果可以反映心室兴奋传播的基本特征. 关键词： 心磁图 源重构 边界元 波束形成器     

Causal dynamic MRI reconstruction via nuclear norm minimization

This work addresses the problem of online reconstruction of dynamic magnetic resonance images (MRI). The proposed method reconstructs the difference between the images of previous and current time frames. This difference image is modeled as a rank deficient matrix and is solved from the partially sampled k-space data via nuclear norm minimization. Our proposed method has been compared against state-of-the-art offline and online reconstruction methods. Our method has similar reconstruction accuracy as the offline method and significantly higher accuracy compared to the online technique. It is about an order of magnitude faster than the online technique compared against. Our experimental data consisted of dynamic MRI data that were collected at 6 to 7 frames per second and having resolutions of 128×128 and 256×256 pixels per frame. Experimental evaluation indicates that our proposed method is capable of reconstructing 128×128 images at the rate of 4 frames per second and 256×256 images at the rate of 2 frames per second. The previous online method requires about 3.75 s for reconstructing each image. The improvement in reconstruction speed is clearly discernible. Moreover, our method has a reconstruction error that is about half that of the previous online method.     

Estimating thermal transport in deep X-ray lithography with an inversion method

This study proposes a general methodology for estimating the depth profile of the heat source of the thermal transport system during deep X-ray lithography. The exposure process in a lithography system is considered as an inverse heat conduction problem with an unknown heat source. The conjugate gradient method is used to solve the inverse problem. Numerical results confirm that the method proposed herein can accurately estimate the heat source even involving the inevitable measurement errors. Furthermore, this methodology can also be applied to estimate the local distribution of temperatures when using scanning thermal microscopy (SThM) to microthermally machine materials and will contribute to increase the quality of microthermally machined products. In addition, a thermomechanical data-storage system, which utilizes a resistively heated atomic-force-microscopy (AFM) cantilever tip to read and write data bits, can also adopt this inverse methodology to control the temperature of a polymer substrate.     

Method of reconstructing wavefront aberrations from the intensity measurement

A method for reconstructing wavefront aberrations from intensity measurements in the focal plane of a focusing optic is presented. This reconstruction method is simple, fast, and accurate in reconstructing wavefront aberrations because it uses the inverse Fourier transform of an intensity distribution in the focal plane with a reference electric field. The validity of the reconstruction method is demonstrated by computing a wavefront aberration from the intensity distributions in the focal plane.     

热图法测量激光强度时空分布的重构理论研究

为了把量热法应用于远场激光强度时空分布测量,研究了基于热像仪靶面温度测量反演入射激光强度时空分布的重构理论。针对背光面两种不同边界条件(对流-辐射热流边界和恒定温度边界)推导出了由靶面温度分布反演激光束时空分布的重构表达式。获得的分析表达式对广泛的材料具有适用性。通过引入广义参量F0=α/L2,分别就F0》1和F0《1情况给出了重构近似表达式,并对满足F0》1条件的回推算法进行了数值模拟验证。数值结果表明,两种背光面边界条件下回推得到的激光束时空分布与原始激光束达到了很好的一致,但存在一与靶材傅里叶数相关的最小起始回推时间τ0。成果可用于强激光远场参量测量设备的研制。     

Comparison of the efficiencies of Fourier and wavelet expansions in passive acoustic thermal tomography

A comparison of the accuracy achieved in temperature-distribution reconstruction by the Fourier and wavelet expansions in passive acoustic tomography is carried out. Since the use of focused ultrasound in hyperthermia leads to local heating of the tissue, the wavelet representation of such temperature distributions with local fluctuations is more compact than their Fourier representation. It is demonstrated that the compactness of the wavelet representation provides an opportunity to reduce considerably the number of unknown quantities in solving the inverse problem of acoustic thermal tomography and to increase the accuracy of the temperature-distribution reconstruction in comparison with the case of using the Fourier representation. A method for choosing a compact wavelet basis for temperature distributions obtained in the hyperthermia process is proposed.     

基于相机rawRGB通过加权多项式和维纳估计方法重建光谱反射率

基于相机RGB预测物体光谱反射率的研究一直备受研究者们的关注。传统方法都是通过单一光源下的信息进行光谱反射率恢复。最近,Zhang等在Color Research & Application报道了一种基于单光源相机RGB信息预测物体光谱反射率的两步方法。首先基于单个光源下的相机响应RGB值,挑选出一定量的训练数据,采用多项式模型和伪逆的方法预测出不同光源下的CIE XYZ值;然后根据预测的多光源下的CIE XYZ值及整体训练数据预估光谱反射率,再通过预估的光谱反射率挑选一定量训练样本,通过伪逆方法预测出物体光谱反射率。尽管仍然基于一个光源下的相机响应RGB,但通过映射到多光源下的色度值XYZ,提高输入信息的维度来优化光谱反射率的重建精度。受Zhang等工作的启发,提出新的基于单一光源下相机的raw RGB响应信息,通过三阶多项式模型扩展的加权最小二乘方法对多光源下的CIE XYZ值进行预测,然后根据预测出的多光源下的CIE XYZ值再通过维纳估计的方法进行光谱反射率重建,通过这样的两步方法实现从相机响应RGB到光谱反射率的重构。该新方法,采用全体训练数据,应用十分方便,避免了Zhang等的方法需要挑选一定量的局部训练样本的问题。同时Zhang等的方法挑选出的局部训练样本同等重要,而该方法在第1步中,根据训练样本与给定的测试样本的接近程度,赋予训练样本不同的权重,以提高预测精度。通过采用140色色卡作为训练样本,24色色卡和自制的44色印刷品样本进行测试,以判断预测和实测反射率接近程度的均方根误差（RMSE）和人感知色差为评价标准进行比较,结果表明,该方法明显优于Zhang等的方法,而且预测精度随着光源数量的增加而提高,当光源个数达到6时,表现最佳。     

The effect of perfusion on the temperature distribution during thermotherapy: Study on perfused porcine kidneys

The effect of perfusion on the temperature distribution during radio-frequency hyperthermia and laser-induced thermotherapy was investigated with the perfused porcine kidney model. The phase shift-based proton resonance frequency shift method was used to map the temperature distribution. In experiments with modulated perfusion rates it was demonstrated that perfusion dissipates a significant amount of the absorbed energy and, therefore, the resulting heat distribution is strongly dependent on the perfusion rate. The measured time course of the temperature distribution was used to estimate the thermal conductivity, local perfusivity and heat absorption rate of the tissue. These parameters were in a good agreement with literature data. This approach can also be extended to measure heat absorption and heat transfer parameters in vivo, which can significantly improve the accuracy of thermotherapy session planning.     

On the choice of expansion functions in the Helmholtz equation least-squares method

This paper examines the performance of Helmholtz equation least-squares (HELS) method in reconstructing acoustic radiation from an arbitrary source by using three different expansions, namely, localized spherical waves (LSW), distributed spherical waves (DSW), and distributed point sources (DPS), under the same set of measurements. The reconstructed acoustic pressures are validated against the benchmark data measured at the same locations as reconstruction points for frequencies up to 3275 Hz. Reconstruction is obtained by using Tikhonov regularization or its modification with the regularization parameter selected by error-free parameter-choice methods. The impact of the number of measurement points on the resultant reconstruction accuracy under different expansion functions is investigated. Results demonstrate that DSW leads to a better-conditioned transfer matrix, yields more accurate reconstruction than both LSW and DPS, and is not affected as much by the change in measurement points. Also, it is possible to obtain optimal locations of the auxiliary sources for DSW, LSW, and DPS by taking an independent layer of measurements. Use of these auxiliary sources and an optimal combination of regularization and error-free parameter choice methods can yield a satisfactory reconstruction of acoustic quantities on the source surfaces as well as in the field in the most cost-effective manner.     

Analysis of Digital Lateral Shearing Interferometer

A new method is proposed for reconstructing wavefront from discretely sampled interferogram data obtained by a digital lateral shearing interferometer. Assumptions applied in the conventional methods are not used and reconstruction error caused by the difference between the amount of shear and the sampling interval can be removed. System error and the influence of the discrete sampling, which limit accuracy of the tested results of the lateral shearing interferometer, are analyzed.     

Algebraic tomographic reconstruction of two-dimensional gas temperature based on tunable diode laser absorption spectroscopy

Based on tunable diode laser absorption spectroscopy, the combustion gas temperature distribution was reconstructed using the algebraic iterative reconstruction technique. The effects of the projected angle and number of rays on the temperature reconstruction results for both fan beam and parallel beam were investigated. The flow field information was shown in detail. The reconstruction quality increased with increased ray number for both parallel- and fan-beam projections. The trend tended to be smooth when the total number of beams exceeded 100. A virtual ray method combined with the reconstruction algorithms was proposed. The virtual ray method is effective to improve the accuracy of reconstruction results for the symmetric and non-axisymmetric temperature distributions. Moreover, the temperature reconstruction of an infrared gas-field furnace is demonstrated, showing the virtual ray method can be applied to the combustion diagnostics.     

Hybrid near-field acoustic holography

Hybrid near-field acoustical holography (NAH) is developed for reconstructing acoustic radiation from an arbitrary object in a cost-effective manner. This hybrid NAH is derived from a modified Helmholtz equation least squares (HELS) formula that expands the acoustic pressure in terms of outgoing and incoming waves. The expansion coefficients are determined by solving an overdetermined linear system of equations obtained by matching the assumed-form solution to measured acoustic pressures through the least squares. Measurements are taken over a conformal surface around a source at close range so that the evanescent waves can be captured. Next, the modified HELS is utilized to regenerate as much acoustic pressures on the conformal surface as necessary and take them as input to the Helmholtz integral formulation implemented numerically by boundary element method (BEM). The acoustic pressures and normal velocities on the source surface are reconstructed by using a modified Tikhnov regularization (TR) with its regularization parameter determined by generalized cross validation (GCV) method. Results demonstrate that this hybrid NAH combines the advantages of HELS and inverse BEM. This is because a majority of the input data are regenerated but not measured, thus the efficiency of reconstruction is greatly enhanced. Meanwhile, the accuracy of reconstruction is ensured by the Helmholtz integral theory and modified TR together with GCV method, provided that HELS converges fast enough on the measurement surface. Numerical examples of reconstructing acoustic quantities on the surface of a simplified engine block are demonstrated. [Work supported by NSF.]     

积分球光源分布温度对宽波段光学遥感器绝对辐射定标的影响及其校正

实测了积分球输出光谱辐亮度分布曲线,并得到积分球光源的分布温度。从理论上分析了积分球光源分布温度影响宽波段光学遥感器绝对辐射定标精度的原因和机理,并仿真计算了包括积分球和太阳在内的几种不同分布温度光源定标某宽波段光学遥感器时得到的定标系数。仿真结果表明,不同分布温度间的定标系数最大差别大于2%。在此基础上提出了积分球光源分布温度影响绝对辐射定标系数的校正方法,为提高宽波段遥感器的辐射定标精度和遥感图像辐射校正提供了思路和依据。     

一种考虑声线弯曲的温度场重建算法

声波在非均匀温度场中传播时会由于声波的折射而产生声线弯曲现象。为提高非均匀温度场声学CT (Computer Tomography)重建精度,提出一种考虑声线弯曲的重建算法。首先用最小二乘法获得一个不考虑声线弯曲的重建温度场,然后用打靶-插值法确定本征声线出射角,用三角形前向展开法追踪声线,获得此温度场中声波发射/接收器间的本征声线,建立本征声线上声波传播时间与温度分布间的关系,进而实现考虑声线弯曲的最小二乘法温度场重建。单峰、双峰温度场仿真重建结果表明:所采用的本征声线追踪法计算简单运行速度快;考虑声线弯曲后,可明显提高温度场重建精度。因此所提重建算法能更好地适应实际温度场重建需求。      

精密热处理过程温度测量多模态重构方法

为了增大惯性约束聚变玻璃靶丸的磁悬浮力,通过热处理工艺对其表面金属氧化物涂层进行晶态调控从而增强磁性能的方法对热处理温度控制精度要求极高,需要从多方面对温度进行把控。目前基于圆图记录仪的温度测量手段已经不能满足惯性约束聚变对热处理温度开展实时多模态数据分析的要求。提出一种针对精密热处理过程温度测量的多模态重构方法,首先将精密热处理过程的温度数据进行数字化传输与存储,然后在计算机中进行多模态解析与重构,最后基于空间拓扑关系与特征参数标定结果,利用Corexy机构实现热处理温度的多模态重构。结果表明所提方法可以实现对温度调控过程的单一化模态分离与多模态重构,实现误差一般小于5%。     

红外无损探测中多宗量多热源反演问题的研究

为研究红外无损探测稳态多热源反演逆问题, 建立不同形状的均质与非均质稳态热传导模型, 其中内热源个数、位置、强度、面积均为未知项. 基于数值算法中有限元算法对模型进行离散分析, 化简有限元矩阵方程, 最终转化为对Ax = b高度欠定方程的求解. 首次利用分段多项式谱截断奇异值分解法处理内热源逆问题, 并对算法进行改进, 有效改善了该算法在处理多热源反演时存在的严重的热源叠加效应. 根据反演出的内热源信息, 利用有限元算法计算重构出整个模型内所有节点的温度分布. 运用数值仿真Comsol软件和具体实物实验对算法进行有效性评估, 并验证算法在不同热传导模型中的表现. 结果表明, 算法能够准确反演出多热源各参量信息, 在非均质材料模型中仍能准确地反演出热源项, 并有效重构出模型内温度场. 该算法可应用于材料无损检测及人体红外医学成像等领域.     

基于同态信号处理的数字全息广义线性重建算法研究

为了提高数字全息图的重建速度和精度,本文提出了一种基于同态信号处理的数字全息广义线性重建算法. 首先利用预放大数字全息显微系统并结合同态信号处理原理进行了理论分析,得到了广义线性重建算法的实现条件及重建步骤,并对该算法的优点进行了分析;然后利用计算机模拟和实验相结合的方法对理论分析进行了验证. 结果表明：数字全息广义线性重建算法不仅可以有效的消除全息图频谱中零级项的干扰,实现高精度再现,而且由于采用一个完整象限的固定区域滤波,避免了常规线性算法的手动滤波操作,极大地提高了重建速度,同时最大限度地保留了原始像中的高频成分,实现全息图的高分辨重建. 关键词： 数字全息显微术 同态信号处理 傅里叶变换 分辨率     

Research on Temperature Field Reconstruction Based on RBF Approximation with Polynomial Reproduction Considering the Refraction Effect of Sound Wave Paths

The temperature field distribution directly reflects the combustion condition in a furnace．In this paper, acoustic thermometry to reconstruct temperature distribution is investigated. A method based on radial basis function approximation with polynomial reproduction (RBF-PR) is proposed in order to improve the accuracy and stability of the method based on RBF approximation. In addition, the refraction effect of sound wave paths is considered in the process of reconstruction. The curved lines with refraction effect are numerically calculated by solving differential equations, which show that sonic waves curve towards the zones of higher temperature. The reconstructed performance is validated via numerical simulation using four temperature distribution models. Results and analysis show that the proposed method has much greater accuracy than the method based on RBF approximation, and when considering the effect of refraction, our method can reconstruct more excellent reconstruction performance than others, which do not take into account the refraction effect of sound wave paths.