Depth profiling the thermal reflection coefficient of an opaque solid via an inverse thermal wave scattering theory based on the Method of Images

A new formulation of the inverse problem of depth profiling the thermal properties of an opaque solid based on one-dimensional photo-generated thermal waves is presented. The inverse problem as posed is linear in a set of lumped thermal reflection coefficients which account for the return of energy to the surface by all significant heat conduction channels. An analysis based on the Method of Images relates these coefficients to individual values of the interface thermal reflection coefficients in the material. No weak backscattering assumption is invoked to linearize the problem. The method yields a unique solution subject to a given condition of regularization. Solutions recovered by the method are stable at experimentally feasible error levels. Received: 27 September 1999 / Published online: 16 June 2000     

Spatial Filters on Demand Based on Aperiodic Photonic Crystals

Photonic Crystal spatial filters, apart from stand‐alone spatial filtering function, can also suppress multi‐transverse‐mode operation in laser resonators. Here it is shown that such photonic crystals can be designed by solving the inverse problem: for a given spatial filtering profile. Optimized Photonic Crystal filters were fabricated in photosensitive glass. Experiments have shown that such filters provide a more pronounced filtering effect for total and partial transmissivity conditions.     

On the existence of longitudinal or flexural waves in rods at nonlinear higher harmonics

This article theoretically studies the conditions for existence of longitudinal or flexural waves in nonlinear, isotropic rods and presents numerical simulations corroborating the theoretical results. It has been known that the existence of guided waves at nonlinearity induced double harmonics is subject to constraints which arise from the potential of power flux transfer from the primary generating mode to the generated higher order modes. The knowledge about the behavior of waves in rods at harmonics higher than double is still limited. This gap was addressed here by the method of perturbation coupled with wavemode orthogonality and forced response. This reduces the nonlinear problem to a forced linear problem which was subsequently investigated to formulate an angular order-based constraint as the condition of existence/nonexistence of nonlinearity-driven higher harmonics of longitudinal and flexural waves in rods.     

基于压缩感知理论的非线性γ谱分析方法

γ谱分析是一种重要的放射性核素定量分析方法. 弱峰的检测和重叠峰的分解是γ 谱分析中的难点. 为了解决这两个问题, 基于压缩感知理论, 提出了一种新的γ 谱分析方法. 这一方法从谱仪对γ 谱调制的物理机理出发, 通过数学建模, 将γ 谱分析转化为一个以真实γ 谱为解的求逆问题, 并在压缩感知理论框架下, 运用γ 谱特征峰的稀疏性, 进行逆问题的求解, 直接获得γ 谱的估计结果. 数值模拟结果和蒙特卡洛模拟结果表明: 该方法能在降低统计涨落的同时, 有效减小谱仪调制带来的能谱展宽, 从而提高γ 谱分析精度. 关键词： γ谱分析')" href="#">γ谱分析 压缩感知 非线性 逆问题     

Energy streamlines for qualitative inverse scattering in fluids and solids

In time-harmonic acoustic fields, energy streamlines are defined as the integral curves of the power-flux density vector, averaged over a period. They provide a tool to visualize the details of propagation of energy. After reviewing the role of energy streamlines in the linear sampling method for acoustic inverse scattering, this work formulates a physical interpretation of the same qualitative method in the case of an isotropic homogeneous solid matrix. Specifically, it is shown that the linear sampling method results from conservation of energy along streamline tubes of energy flow associated with elastic waves.     

等离子体平衡逆问题的一种数值解法

本文借助离散化算子,把滤波方法推广到非圆截面,对具有非圆截面的等离子体平衡逆问题建立了一个稳定的显式逆推滤波算法;给出了部分非圆截面的计算结果;对圆截面情形的数值解与解析解作了比较。     

Conservation laws of nonconservative nonholonomic system based on Herglotz variational problem

The generalized variational principle of Herglotz type provides a variational method for describing nonconservative or dissipative processes. The purpose of this letter is to extend this variational principle to a first order linear nonholonomic system and study the conservation laws of the nonconservative nonholonomic system based on Herglotz variational problem. A new differential variational principle of the nonconservative nonholonomic system is proposed, which is based on Herglotz variational problem. And the differential equations of motion of the system are also obtained. Then, according to the condition for the invariance of the differential variational principle, the conservation theorem based on Herglotz variational problem for the nonconservative nonholonomic system are obtained. The theorem contains the conservation theorem of the nonconservative holonomic system as its special case, which can be reduced to the first Noether's theorem based on Herglotz variational problem under proper conditions. The inverse theorem of the conservation theorem is also provided and proved. An example is given to illustrate the application at the end of this letter.     

Numerical strategies for filtering partially observed stiff stochastic differential equations

In this paper, we present a fast numerical strategy for filtering stochastic differential equations with multiscale features. This method is designed such that it does not violate the practical linear observability condition and, more importantly, it does not require the computationally expensive cross correlation statistics between multiscale variables that are typically needed in standard filtering approach. The proposed filtering algorithm comprises of a “macro-filter” that borrows ideas from the Heterogeneous Multiscale Methods and a “micro-filter” that reinitializes the fast microscopic variables to statistically reflect the unbiased slow macroscopic estimate obtained from the macro-filter and macroscopic observations at asynchronous times. We will show that the proposed micro-filter is equivalent to solving an inverse problem for parameterizing differential equations. Numerically, we will show that this microscopic reinitialization is an important novel feature for accurate filtered solutions, especially when the microscopic dynamics is not mixing at all.     

Inverse problem of a statistical estimation of scatterer characteristics and model examples

The inverse scattering problem involving experimental data with errors is considered in its statistical formulation. An algorithm for retrieving regularized estimates of the characteristics of spatially distributed scatterers (the phase velocity and absorption inhomogeneities) is developed. The algorithm takes into account the multiple scattering and generalizes the Wiener filtering to the nonlinear case. For weak scatterers, this nonlinear generalization is reduced to the linear Wiener filtering. The performance of the algorithm is verified by model examples simulating the operation of active acoustic tomography systems against various noise levels. The necessity of taking into account the multiple scattering and the fundamental role of the nonlinear filtering in the regularization procedure is demonstrated. It is remarkable that the noise robustness achieved in the reconstruction of strong scatterers with the optimal regularization algorithm is only slightly inferior to that achieved in the case of weak scatterers.     

用多项式近似逆滤波函数实现场曲修正

根据光电成像系统传递函数,确定逆滤波函数对获得图像进行反降质恢复.将连续逆滤波函数按泰勒级数展开,用多项式近似表示.对逆滤波函数的多项式作反傅里叶变换,得到图像恢复在空间域中的近似运算表达,即图像信号及其各阶导数的线性组合,而不是复杂的反卷积操作.该方法特别适合空间移变系统的图像恢复.详细分析了这种方法的原理,推导了运算公式,并给出了对场曲图像处理的结果.     

A robust spatial filtering technique for multisource localization and geoacoustic inversion

Geoacoustic inversion and source localization using beamformed data from a ship of opportunity has been demonstrated with a bottom-mounted array. An alternative approach, which lies within a class referred to as spatial filtering, transforms element level data into beam data, applies a bearing filter, and transforms back to element level data prior to performing inversions. Automation of this filtering approach is facilitated for broadband applications by restricting the inverse transform to the degrees of freedom of the array, i.e., the effective number of elements, for frequencies near or below the design frequency. A procedure is described for nonuniformly spaced elements that guarantees filter stability well above the design frequency. Monitoring energy conservation with respect to filter output confirms filter stability. Filter performance with both uniformly spaced and nonuniformly spaced array elements is discussed. Vertical (range and depth) and horizontal (range and bearing) ambiguity surfaces are constructed to examine filter performance. Examples that demonstrate this filtering technique with both synthetic data and real data are presented along with comparisons to inversion results using beamformed data. Examinations of cost functions calculated within a simulated annealing algorithm reveal the efficacy of the approach.     

零点约束矩阵滤波设计

为解决在空域预滤波阶段抑制强噪声的问题,提出了零点约束矩阵滤波设计方法,并给出了解的表达式。通过设计凸规划问题,在严格约束阻带响应等于零的情况下,使通带误差最小。将凸规划问题转换为线性约束二阶最优化问题,构造Lagrange函数并得到最优解,重排后得出滤波矩阵。仿真可知,本方法可设计出强干扰离散分布或处于某扇面的预滤波器,可用于解决常规波束形成算法受强干扰影响方位估计性能的问题。      

Measuring short impulse responses with inverse filtered maximum-length sequences

Most loudspeakers have a non-flat frequency response which produces a long oscillating impulse response. An inverse filtering approach may be used to calculate the driving waveform necessary to equalize the response of the loudspeaker in order to radiate shorter acoustic pulses. When combined with the MLS technique, inverse filtering may be used to pre-emphasize the driving signal so that a shorter impulse response, with a prescribed waveform, is measured. This technique is described and illustrated by applying it to a distributed mode loudspeaker. Originally, this loudspeaker has a rather irregular response in a wide band. When the MLS signal is pre-emphasized with the proper inverse filter, a shorter impulse response is measured with a zero-phase cosine-magnitude spectrum.     

Voice source characteristics in Mongolian "throat singing" studied with high-speed imaging technique, acoustic spectra, and inverse filtering.

Mongolian "throat singing" can be performed in different modes. In Mongolia, the bass-type is called Kargyraa. The voice source in bass-type throat singing was studied in one male singer. The subject alternated between modal voice and the throat singing mode. Vocal fold vibrations were observed with high-speed photography, using a computerized recording system. The spectral characteristics of the sound signal were analyzed. Kymographic image data were compared to the sound signal and flow inverse filtering data from the same singer were obtained on a separate occasion. It was found that the vocal folds vibrated at the same frequency throughout both modes of singing. During throat singing the ventricular folds vibrated with complete but short closures at half the frequency of the true vocal folds, covering every second vocal fold closure. Kymographic data confirmed the findings. The spectrum contained added subharmonics compared to modal voice. In the inverse filtered signal the amplitude of every second airflow pulse was considerably lowered. The ventricular folds appeared to modulate the sound by reducing the glottal flow of every other vocal fold vibratory cycle.     

利用辐射场诊断模式成分的病态特性

 根据辐射场测量并确定已知尺寸和工作频率的波导内可能存在的模式(即模式诊断)是一个电磁逆问题。针对该逆问题,利用电磁分析软件计算过模圆波导馈电圆锥喇叭天线的远区辐射场,通过比较多种模式以不同比例组合馈电产生的总辐射场之间的差异,研究模式诊断逆问题的病态程度。结果表明该逆问题病态严重,模式成分比例变化很大,但某些位置上辐射场变化较小甚至没有区别,即辐射场对各模式比例变化不敏感。如果在这些位置上测量则很难判断出各模式的成分,只有通过增加信息量才能缓解病态的严重程度,得到较准确的结果。通过分析,给出了对各模式组合比例变化敏感的测量位置。     

水平阵信号压缩感知用于简正波分离

针对水平阵信号简正波分离过程中常规波束形成分辨率低以及warping模态滤波不适用于复杂声信号的问题,提出水平阵信号压缩感知用于简正波分离的方法。利用压缩感知在方位估计中的高分辨特性,通过估计水平阵接收信号在频率方位角上的二维分布,分离得到各阶简正波的方位谱,并逆Fourier变换得到时域波形。仿真孔径1 km、阵元间隔10 m水平阵接收20~200 Hz伪随机声信号和脉冲声信号,所提方法分离出的各阶简正波与理论波形的相关系数在0.97~1.0。对2011年北黄海声学实验中的海底28元水平阵接收的气枪信号,在合成至1 km孔径后使用压缩感知方法分离简正波,其与warping模态滤波分离得的前5阶简正波相关系数在0.82~0.93。仿真与实验都说明了水平阵信号压缩感知简正波分离方法的有效性。      

线性瞬态涡流电磁场定解问题解的唯一性和稳定性

线性瞬态涡流电磁场定解问题的主要特点是边界条件使用磁感应强度的法向分量边界条件代替了电场强度的切向分量边界条件，约束方程中忽略了位移电流.这种具有特殊性的定解问题的解是否唯一和稳定对于求解瞬态涡流电磁场而言是一个基本问题.本文在非涡流区引入标量位函数，证明了在推导过程中起重要作用的辅助函数的存在性.通过推导线性瞬态涡流电磁场定解问题的能量估计式，证明了该定解问题的解是唯一的，并且关于初始条件和外源项是稳定的.本结果对于线性瞬态涡流电磁场的求解有一定的指导意义.作为应用，给出了通有单脉冲电流的单匝圆环线圈与球形导体共轴的涡流问题的解析解. 关键词： 瞬态涡流电磁场 能量估计式 唯一性 稳定性     

Voice Source Characteristics in Mongolian “Throat Singing” Studied with High-Speed Imaging Technique, Acoustic Spectra, and Inverse Filtering

Mongolian “throat singing” can be performed in different modes. In Mongolia, the bass-type is called Kargyraa. The voice source in bass-type throat singing was studied in one male singer. The subject alternated between modal voice and the throat singing mode. Vocal fold vibrations were observed with high-speed photography, using a computerized recording system. The spectral characteristics of the sound signal were analyzed. Kymographic image data were compared to the sound signal and flow inverse filtering data from the same singer were obtained on a separate occasion. It was found that the vocal folds vibrated at the same frequency throughout both modes of singing. During throat singing the ventricular folds vibrated with complete but short closures at half the frequency of the true vocal folds, covering every second vocal fold closure. Kymographic data confirmed the findings. The spectrum contained added subharmonics compared to modal voice. In the inverse filtered signal the amplitude of every second airflow pulse was considerably lowered. The ventricular folds appeared to modulate the sound by reducing the glottal flow of every other vocal fold vibratory cycle.     

Probing Nuclear Symmetry Energy with Giant Dipole Resonances in Finite Nuclei

The relationship between the centroid energies of the isovector giant dipole resonance of finite nuclei and the symmetry energy has been studied.It is found the excitation energies of the dipole resonance in finite nuclei are correlated linearly with the symmetry energy at and below the saturation density.This linear correlation leads to the symmetry energy at the saturation density at the interval 33.0 MeV ≤ S(ρ_0) ≤ 37.0 MeV,and the symmetry energy at ρ=0.1 fm~(-3) at the interval 21.2-22.5 MeV.It is proposed that a precise measurement of the dipole mode in nuclei could set up an important constraint on the equation of state for nuclear matter.