一种基于单色测量的迷彩色光谱反射比测量计算方法

提出一种基于单色测量的迷彩色光谱反射比的测量计算方法。这种方法根据单色光通量的计算方法推导得出,以单色块反射比的测量为基础,根据单色块光谱反射比和各单色在迷彩样品中所占面积,可计算出迷彩样品的光谱反射比。通过实地测量实验进行对比验证,证明了此计算方法具有一定的可行性。     

旋转不变的非局域均值算法在磁共振图像去噪中的应用

磁共振成像（MRI）实验时常采用多次扫描累加平均提高图像信噪比（SNR）,但当扫描过程中运动引起图像变形时,简单地累加平均就无法奏效.为此,本研究组曾提出一种匹配加权平均方法（MWA）提高图像的信噪比.在此基础上,该文提出一种旋转不变的非局域均值算法（RINLM）,即选取圆形邻域区域并将其划分为一系列以中心像素为圆心的等面积圆环,再计算模式的相似性.RINLM算法可以更好地利用图像中旋转的冗余信息、找到更多的相似结构,提高算法的去噪性能.我们把该方法应用于低信噪比图像序列的平均和去噪中,可以更好地处理旋转的局部运动.与非局域均值算法（NLM）相比,RINLM算法可以进一步提高图像的信噪比;与MWA方法相比,其与RINLM算法的结合可以进一步提高磁共振图像序列信噪比,更好的保持图像边缘信息.     

Placement and dimension optimization of shunted piezoelectric patches for vibration reduction

Passive structural vibration reduction by means of shunted piezoelectric patches is addressed in this paper. We present a strategy to optimize, in terms of damping efficiency, the geometry of piezoelectric patches as well as their placement on the host elastic structure. This procedure is based on the maximization of the modal electro-mechanical coupling factor (MEMCF) of the mechanical vibration mode to which the shunt is tuned. To illustrate the method, a general analytical model of a laminated beam is proposed. Two particular configurations are investigated: (i) a beam with two collocated piezoelectric patches connected in series or in parallel to the shunt and (ii) a cantilever beam with one patch. After a modal expansion, original closed-form solutions of the MEMCF are exhibited, which enables to compute optimal values for the placement, length and thickness of the piezoelectric patches that maximize the MEMCF. A dimensionless model is used so that this study can be used to design any smart beam, whatever be its dimensions. More general results about the coupling mechanisms between the piezoelectric patches and the host structure are also raised. In particular, it is found that the patches thickness is an essential parameter and that several configurations are possible, depending on the considered vibration mode. Experiments are also proposed to validate the model.     

三维光滑接触界面上的分配参数滑移面算法

针对三维滑移界面上的分配参数滑移算法,提出一种三维滑移面光滑目的 ,仅根据单元面顶点的坐标和法向等局部信息,构造出曲面片边界G¹连续(切平面连续),曲面片内C¹连续的三维光滑曲面,此目的 为实际的滑移面提供一个准确的几何表达.在此光滑曲面上构建了具有C¹连续的法向压力场和质量面密度场.然后在光滑滑移界面上通过Newton-Raphson迭代计算接触点,依据分配参数滑移算法施加接触约束和接触计算.数值算例显示光滑的接触滑移面可以减少滑移节点的振动,提高计算的收敛性.     

The generalized product partition of unity for the meshless methods

The partition of unity is an essential ingredient for meshless methods named by GFEM, PUFEM (partition of unity FEM), XFEM (extended FEM), RKPM (reproducing kernel particle method), RPPM (reproducing polynomial particle method), the method of hp clouds in the literature. There are two popular choices for partition of unity: a piecewise linear FEM mesh and the Shepard-type partition of unity. However, the partition of unity (PU) by a FEM mesh leads to the singular (or nearly singular) matrices and non-smooth approximation functions. The Shepard-type partition of unity requires lengthy computing time and its implementation is difficult. In order to alleviate these difficulties, Oh et al. introduced the smooth piecewise polynomial PU functions with flat-top, that lead to small matrix condition numbers, and almost everywhere partition of unity, that can handle essential boundary conditions. Nevertheless, we could not have the smooth closed form PU functions with flat-top for general polygonal patches (2D) and general polyhedral patches (3D). In this paper, we introduce one of the most simple and efficient partition of unity, called the (generalized) product partition of unity. The product PU functions constructed by this method are the closed form smooth piecewise polynomials with flat-top and could handle background meshes (general polygonal patches as well as general polyhedral patches) arising in practical applications of meshless methods.     

Segmentation algorithm for non-stationary compound Poisson processes

We introduce an algorithm for the segmentation of a class of regime switching processes. The segmentation algorithm is a non parametric statistical method able to identify the regimes (patches) of a time series. The process is composed of consecutive patches of variable length. In each patch the process is described by a stationary compound Poisson process, i.e. a Poisson process where each count is associated with a fluctuating signal. The parameters of the process are different in each patch and therefore the time series is non-stationary. Our method is a generalization of the algorithm introduced by Bernaola-Galván, et al. [Phys. Rev. Lett. 87, 168105 (2001)]. We show that the new algorithm outperforms the original one for regime switching models of compound Poisson processes. As an application we use the algorithm to segment the time series of the inventory of market members of the London Stock Exchange and we observe that our method finds almost three times more patches than the original one.     

Prediction of the sound field above a patchwork of absorbing materials

The aim of this paper is to investigate the acoustic performance of sound absorbing materials through a numerical wave based prediction technique. The final goal of this work is to get insight into the acoustic behavior of a combination of sound absorbing patches. In order to address a wide frequency range, a model based on the Trefftz approach is adopted. In this approach, the dynamic field variables are expressed in terms of global wave function expansions that satisfy the governing dynamic equations exactly. Therefore, approximation errors are associated only with the boundary conditions of the considered problem. This results in a computationally efficient technique. The main advantage of this method is the fact that the sound absorbing patches do not have to be locally reacting. In this article, the wave based method is described and experimentally validated for the case of normal incidence sound absorption identification in a standing wave tube. Afterwards, the method is applied to simulate some interesting setups of absorbing materials.     

Frequency Selective Surfaces with Anisotropic Dielectric Superstrates

A full wave analysis is developed for frequency selective surfaces composed of rectangular patches mounted on a dielectric anisotropic substrate and covered with a uniaxial anisotropic superstrate. The moment method is used in combination with the spectral domain immittance approach to determine the FSS structure reflection and transmission coefficients.     

Band gap structure analysis of phononic crystal rods with hybrid shunted piezoelectric patches

The band gap structures by arranging hybrid shunted piezoelectric materialswith resistance inductive(RL) circuit and negative impedance converter(NIC) closely and at intervals are presented.The theoretical model is built using transfer matrix method.Then the MATLAB computing language is utilized to simulate the band gap structures.Meanwhile,the effects of the resistance,inductance and capacitance on the local resonant gap are studied.By comparing different combinations of resistance,inductance and capacitance as well as different arrangement of circuits,a 13 kHz band gap is reached under the effect of arranging hybrid periodic shunted piezoelectric patches at intervals and the stability of the system is also analyzed.It is proved that utilizing hybrid shunted piezoelectric patches would have a clear impact on the band gap structure of phononic crystal rods.Moreover,the band gap would be clearly enlarged by arranging hybrid piezoelectric patches at intervals.     

混合压电分流电路作用下声子晶体杆振动带隙结构分析

对于电阻电感(RL)及负阻抗变换器(NIC)混合压电分流电路分别采用紧密及间隔排列方式进行带隙结构计算,并且针对分流电路中电阻、电感及电容对于局域共振带隙的影响进行研究。采用传递矩阵法建立了压电分流电路作用下声子晶体杆带隙分析的理论模型,并运用MATLAB语言对带隙结构进行编程仿真计算。通过电阻、电感、电容参数的匹配及电路不同排列方式的对比,最终得到了在混合间隔压电分流电路作用下宽度为13 kHz的带隙,并对振动控制系统稳定性进行了分析。研究结果表明:采用混合压电分流电路会对杆件带隙结果产生影响,且采用压电片间隔排列的方式会使带隙宽度明显扩大。      

Sparse representation-based image restoration via nonlocal supervised coding

Sparse representation (SR) and nonlocal technique (NLT) have shown great potential in low-level image processing. However, due to the degradation of the observed image, SR and NLT may not be accurate enough to obtain a faithful restoration results when they are used independently. To improve the performance, in this paper, a nonlocal supervised coding strategy-based NLT for image restoration is proposed. The novel method has three main contributions. First, to exploit the useful nonlocal patches, a nonnegative sparse representation is introduced, whose coefficients can be utilized as the supervised weights among patches. Second, a novel objective function is proposed, which integrated the supervised weights learning and the nonlocal sparse coding to guarantee a more promising solution. Finally, to make the minimization tractable and convergence, a numerical scheme based on iterative shrinkage thresholding is developed to solve the above underdetermined inverse problem. The extensive experiments validate the effectiveness of the proposed method.     

Removing harmonic distortion of measurements of a defocusing three-step phase-shifting digital fringe projection system

Binary defocusing method was adopted in 3D profilometry as it allows real-time measurement and does not need to handle the luminance nonlinearity of a projector. Current patch-based binary fringe patterns are periodic and carry strong harmonic distortion as compared with the ideal sinusoidal fringe patterns, which affects the measuring performance remarkably. In this paper, we propose a framework for generating aperiodic fringe patterns based on optimized patches. The produced fringe patterns can significantly lower the noise floor and suppress the harmonic distortion in the constructed phase map. Accordingly, the achieved depth measuring performance can be significantly improved. Special care is also taken during the optimization of the patches in our framework such that the depth measuring performance is robust to fringe period and defocusing extent.     

基于主成分分析的光谱重建训练样本选择方法研究

训练样本构成是影响光谱重建精度的一个重要因素,针对学习型光谱重建算法中训练样本选择问题,提出了一种基于主成分分析的训练样本选择方法。为了保证训练样本与重建样本的相似度,首先根据欧式距离最小原则从待选样本集中选择与重建样本相机响应值相似的样本,并去掉其中的重复样本;然后进行主成分分析;设定阈值筛选各主成分系数较大的样本作为训练样本,最后得到与主成分个数相同的训练样本子集。为验证该方法的有效性,通过在镜头前加载宽带滤色片搭建多通道图像获取系统采集多通道图像信息,将得到的各样本子集用作训练样本,利用伪逆法重建光谱信息,最后将重建的光谱精度与常用的训练样本及训练样本选择方法得到的重建光谱精度进行比较。实验结果表明：提出的方法显著提高了光谱重建的色度精度和光谱精度,优于常用的样本选择方法,能较大程度满足高精度颜色复制要求。     

Planar infrared binary phase reflectarray

A reflective, binary phase reflectarray is demonstrated in the infrared, at a wavelength of 10.6 microm. The unique aspect of this work, at this frequency band, is that the specific desired phase shift is achieved using an array of subwavelength metallic patches on top of a ground-plane-backed dielectric stand-off layer. This is an alternative to the usual method of constructing a reflective Fresnel zone plate by means of a given thickness of dielectric. This initial demonstration of the reflectarray approach at infrared is significant in that there is inherent flexibility to create a range of phase shifts by varying the dimensions of the patches. This will allow for a multilevel phase distribution, or even a continuous variation of phase, across an optical surface with only two-dimensional lithography, avoiding the need for dielectric height variations.     

Theoretical study of the normal-incidence reflective spectra for determining the thickness and refractive index of dielectric film

We theoretically study and propose the design concept of a new non-contact measurement method of the thickness and refractive index of dielectric film. The needed measurement set-up includes a probe, an optical detection head and a spectrometer. The probe is composed of two patches of dielectric substrates, and the optical detection head is used to detect the reflective spectra. After depositing a testing dielectric film on the two patches, the coating film thickness and refractive index can be determined by analyzing the normal-incidence reflective spectra of the two dielectric substrates. This method has two requirements. First, the coating dielectric films on the two substrates must be the same. Second, the two dielectric substrates respectively have higher and lower refractive indices than the testing dielectric film.     

Population persistence in weakly-coupled sinks

We consider a single species population obeying a saturated growth model with spatial diffusion taken into account explicitly. Strong spatial heterogeneity is considered, represented by a position dependent reproduction rate. The geometry of the problem is that of two patches where the reproductive rate is positive, surrounded by unfavorable patches where it is negative. We focus on the particular case where the population would not persist in the single patches (sinks). We find by means of an analytical derivation, supplemented by a numerical calculation, the conditions for the persistence of the population in the compound system of weakly connected patches. We show that persistence is possible even if each individual patch is a sink where the population would go extinct. The results are of particular relevance for ecological management at the landscape level, showing that small patches may harbor populations as long as the connectivity with adjacent patches is maintained. Microcosmos experiences with bacteria could be performed for experimental verification of the predictions.     

Excitation of a periodic cylindrical microstrip <Emphasis Type="Italic">N</Emphasis>-element antenna array

We consider the problem of excitation of a periodic cylindrical microstrip antenna array which consists of N elements placed periodically in the azimuthal plane on the surface of a dielectric substrate. Each element is an array of M patches having the rectangular-cylindrical shape. Each patch is fed by a rod which is approximately modeled by a charged filament of finite length. An integral equation for the surface current on the patches is formulated and solved by the method of moments in the spatial domain. Far-field patterns of the antenna are calculated for different values of N and M at the resonant frequencies. It is shown that a two-frequency N-lobe antenna having two different far-field patterns at two different resonant frequencies can be developed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 2, pp. 134–146, February 2007.     

The Multi-Focus-Image-Fusion Method Based on Convolutional Neural Network and Sparse Representation

Multi-focus-image-fusion is a crucial embranchment of image processing. Many methods have been developed from different perspectives to solve this problem. Among them, the sparse representation (SR)-based and convolutional neural network (CNN)-based fusion methods have been widely used. Fusing the source image patches, the SR-based model is essentially a local method with a nonlinear fusion rule. On the other hand, the direct mapping between the source images follows the decision map which is learned via CNN. The fusion is a global one with a linear fusion rule. Combining the advantages of the above two methods, a novel fusion method that applies CNN to assist SR is proposed for the purpose of gaining a fused image with more precise and abundant information. In the proposed method, source image patches were fused based on SR and the new weight obtained by CNN. Experimental results demonstrate that the proposed method clearly outperforms existing state-of-the-art methods in addition to SR and CNN in terms of both visual perception and objective evaluation metrics, and the computational complexity is greatly reduced. Experimental results demonstrate that the proposed method not only clearly outperforms the SR and CNN methods in terms of visual perception and objective evaluation indicators, but is also significantly better than other state-of-the-art methods since our computational complexity is greatly reduced.     

Percolation theory for the distribution and abundance of species

We develop and test new models that unify the mathematical relationships among the abundance of a species, the spatial dispersion of the species, the number of patches occupied by the species, the edge length of the occupied patches, and the scale on which the distribution of species is mapped. The models predict that species distributions will exhibit percolation critical thresholds, i.e., critical population abundances at which the fragmented patches (as measured by the number of patches and edge length) start to coalesce to form large patches.