恒星大气物理参数估计中的稀疏特征提取

随着斯隆数字巡天项目(SDSS)、欧空局GAIA和我国大天区面积多目标光纤光谱天文望远镜(LAMOST)等项目的相继实施,拥有的恒星光谱数据量急速增加,由此导致基于光谱的恒星大气物理参数自动测量方法的研究成为天文光谱分析的重要课题之一[1]。探讨了恒星光谱特征提取的方法(Haar+lasso),其基本思想是首先使用Haar小波包对原始光谱进行多尺度分解,去除高频系数,选取低频系数作为光谱信息的描述;再采用lasso算法提取最优的特征; 最后将最优特征输入非参数回归模型中对恒星大气参数进行自动测量。Haar小波可以较好地去除原始光谱信号中的高频噪声,对全频谱数据进行降维。lasso算法可以进一步剔除数据冗余, 提取与物理参数相关度较强的特征。Haar+lasso方法提高了物理参数自动测量的准确性和运行效率。我们采用本文方案对SLOAN发布的40 000个恒星子样本的物理参数进行测量,三个物理参数的平均绝对误差为： log Teff: 0.007 1 dex,log g: 0.225 2 dex和[Fe/H]: 0.199 6 dex。同现有相关文献的实验结果相比,该方案可以获得更准确的物理参数。     

基于Kramers-Kronig关系建立金属太赫兹色散模型

提出了一种基于测量反射率谱、使用Kramers-Kronig(KK)关系建立金属太赫兹色散模型的方法.结合合金铝和合金铜4—40 THz的测量反射率谱,通过反射系数振幅和相位的KK关系,采用高频端指数外推,低频端常数外推的方法,反演金属复折射率.以KK反演的复折射率作为实验值,以拟合复折射率和实验值误差最小为准则,使用遗传优化算法,拟合了合金铝和合金铜的Drude色散参数(等离子频率和碰撞频率).基于优化的Drude模型计算了0.1—40 THz材料的复折射率,与椭偏仪的实测结果符合,验证了模型的准确性.该方法理论与实验相互验证,以测量的复折射率作为实验定标,将远红外频段的色散信息拓展到太赫兹频域,确定了太赫兹频段金属的微观物理参数,提供了太赫兹频段色散和散射机理的研究依据.     

Simulation of the ultimate characteristics of thulium-doped fiber amplifiers

A completely spatially and spectrally resolved model of a thulium-doped fiber amplifier that, unlike existing models, takes into account the radiation mode structure is proposed. A genetic algorithm is used to optimize the pump scheme parameters in order to achieve the maximum gain or the minimum non-uniformity of the gain spectrum. The ultimate information characteristics of the amplifier are determined.     

Adaptive regularized filtering for BRDF model inversion and land surface albedo retrieval based on spectrum cutoff technique

A regularized inversion method is presented to invert the bidirectional reflectance distribution function (BRDF) model for albedo calculations. It is known as discrete ill-posed inverse problem. Essential issues that must be considered include solution existence, solution uniqueness, instability of the solution process, and geophysical meanings of solution. In order to robustly estimate BRDF models parameters, a spectrum cutoff technique is employed to suppress spurious oscillations due to poor angular distribution, sparse sample size, or both. We studied difficulties in estimating BRDF parameters and analyzed the cause of the instability in the solution, and then presented a novel algorithm. The proposed RSC (Regularized Spectrum Cutoff) method is based on improving the spectrum of the BRDF kernel matrix and can always find suitable BRDF parameters for sparse satellite observations. The algorithm is compared with the MODIS (Moderate Resolution Imaging Spectroradiometer) full retrieval (FR) algorithm, and it is tested to be suitable for the case of sufficient observations. Numerical experiments with POLDER (Polarization and Directionality of the Earth's Reflectances) BRDF datasets and MODIS images suggest that the developed spectrum cutoff method is adaptive and robust, and it is valuable for retrieving land surface BRDF and albedo.     

声场干涉结构相似度匹配的目标运动参数估计

针对水中运动声源定位问题,建立了一种基于声场干涉结构谱向量相似度匹配的目标运动参数估计方法。结合声场干涉结构水平纵向相关特性,利用目标辐射噪声LOFAR谱图中不同频率的谱值序列,基于两方位-两距离目标运动要素计算方法获取的目标距离解向量,构造声场干涉结构谱向量相似度匹配代价因子,实现目标运动参数估计。仿真数据与试验数据验证结果表明:在绘制的目标运动要素解算结果可视化分布图中可清晰呈现出目标初距、航向和速度结果。该算法实现过程简单、解算效率高,对目标方位误差有较好的鲁棒性。      

Image watermarking by using phase retrieval algorithm in gyrator transform domain

We propose an image watermarking scheme based on the phase retrieval algorithm in gyrator domain. The watermark is converted into a noise-like image by Arnold transform. The scrambled image is regarded as the amplitude of gyrator spectrum. The Gerchberg-Saxton algorithm is employed to obtain the unknown phase function in gyrator pair, in which the host image is the amplitude of input function. The phase information and the parameters of the two transforms serve as the key of watermarking algorithm. The numerical simulation has demonstrated the performance of the proposed algorithm.     

Wayside acoustic defective bearing detection based on improved Dopplerlet transform and Doppler transient matching

The diagnosis of train bearing defects plays a significant role in maintaining the safety of railway transport. However, the phenomenon of Doppler Effect in the acoustic signal recorded by the wayside Acoustic Defective Bearing Detector (ADBD) system leads to the difficulty for fault diagnosis of train bearings with a high moving speed. This paper proposes a double-searching solution based on improved Dopplerlet transform and Doppler transient matching to overcome the difficulty in wayside acoustic bearing diagnosis. In the solution, the first searching procedure is to extract necessary parameters of Doppler Effect under the situation with very low signal-to-noise ratio (SNR) based on an improved Dopplerlet transform. Using the obtained parameters, the Doppler Effect can be embedded into the constructed periodic Laplace wavelet transient models. Subsequently, the second searching procedure is conducted to search fault impact period of the defective bearing through an operation, called Doppler transient matching, which is to calculate the correlation coefficient between the Doppler transient model and the filtered raw signal with the Doppler Effect. The proposed double-searching algorithm can adapt to the real Doppler Effect situation and extract the exact fault impact period from the Doppler distorted signal, and thus shows powerful capability to analyze wayside acoustic signals from train bearings. The proposed wayside acoustic diagnostic scheme is verified by means of a simulated Doppler distorted signal with a very low SNR (−20 dB) and the experiments conducted on train bearings. The results indicate that the proposed algorithm is effective and has obvious advantages for ADBD system.     

封闭圆内开缝圆自然对流的非线性特性研究

本文通过数值计算对封闭圆内开缝圆自然对流的非线性特性进行了研究。数值计算以整个流场为计算区域,采用非稳态数学模型和具有QUICK差分格式的SIMPLE算法。计算结果表明,在不同参数下流动和换热存在稳态定常解、周期性振荡解、拟周期性振荡解和非周期性振荡解。稳态定常解的相图是一个点;周期性振荡解的相图是一个极限环,对应功率谱含一个基频及其谐波;拟周期性振荡解的相图为环面,对应功率谱含两个不相关的频率及它们的线性组合频率;非周期性振荡解的功率谱为无规则的宽带连续谱。     

Optical tomography reconstruction based on gradient tree

The adjoint differentiation scheme was first proposed by Alexander D. Klose for the reconstruction of optical tomography [J Q S R T 2002;72:715-32]. However, the scheme proposed there can only be employed for the computation of derivatives with respect to the optical parameters on the boundary, i.e. those derivatives with respect to the internal parameters cannot be obtained there, and as a result, the correct reconstructed result cannot be obtained with the gradient based optimization algorithms. In our paper, based on the adjoint differentiation scheme, a novel algorithm based on gradient tree is proposed for the computation of the derivatives with respect to both boundary and internal optical parameters. A scheme for approximate gradient calculation is also proposed for speeding up algorithm implementation. Experimental results show that the algorithm proposed performs well and good reconstruction results can be achieved.     

Reconstruction and interpretation of photon Doppler velocimetry spectrum for ejecta particles from shock-loaded sample in vacuum

The photon Doppler velocimetry(PDV) spectrum is investigated in an attempt to reveal the particle parameters of ejecta from shock-loaded samples in a vacuum. A GPU-accelerated Monte–Carlo algorithm, which considers the multiplescattering effects of light, is applied to reconstruct the light field of the ejecta and simulate the corresponding PDV spectrum.The influence of the velocity profile, total area mass, and particle size of the ejecta on the simulated spectra is discussed qualitatively. To facilitate a quantitative discussion, a novel theoretical optical model is proposed in which the singlescattering assumption is applied. With this model, the relationships between the particle parameters of ejecta and the peak information of the PDV spectrum are derived, enabling direct extraction of the particle parameters from the PDV spectrum.The values of the ejecta parameters estimated from the experimental spectrum are in good agreement with those measured by a piezoelectric probe.     

Cascaded Fresnel holographic image encryption scheme based on a constrained optimization algorithm and Henon map

We propose an image encryption scheme using chaotic phase masks and cascaded Fresnel transform holography based on a constrained optimization algorithm. In the proposed encryption scheme, the chaotic phase masks are generated by Henon map, and the initial conditions and parameters of Henon map serve as the main secret keys during the encryption and decryption process. With the help of multiple chaotic phase masks, the original image can be encrypted into the form of a hologram. The constrained optimization algorithm makes it possible to retrieve the original image from only single frame hologram. The use of chaotic phase masks makes the key management and transmission become very convenient. In addition, the geometric parameters of optical system serve as the additional keys, which can improve the security level of the proposed scheme. Comprehensive security analysis performed on the proposed encryption scheme demonstrates that the scheme has high resistance against various potential attacks. Moreover, the proposed encryption scheme can be used to encrypt video information. And simulations performed on a video in AVI format have also verified the feasibility of the scheme for video encryption.     

基于ERB尺度划分的多子带语声信号抗噪谱减算法

为了研究心理声学在语声增强方面的应用,本文提出了一种基于等效矩阵带宽(ERB)尺度划分的多子带语声信号抗噪谱减算法。此算法根据ERB尺度将带噪信号的频谱划分成多个子带,然后再根据每个子带的分段信噪比以及心理声学掩蔽原则分别计算每个子带的谱减参数,最后在每个子带中分别进行谱减算法处理。实验结果表明,应用新算法所获得的语声增强结果在信噪比、IS失真以及PESQ方面均优于之前提出的多子带语声信号抗噪谱减算法。     

遥感干涉超光谱图像压缩编码

基于卫星干涉超光谱成像光谱仪成像原理的分析,提出了一种新的遥感超光谱图像压缩方案，利用成像推扫平移特性提出一种低存储量，帧间小波域匹配的序列压缩，只需存储两帧图像，比起单帧处理提高图像PSNR 3-4dB.为了保护图像的光谱特征，系统采用了一种新的感兴趣区域（Region of interest, ROI） 编码技术，使系统的压缩比提高8倍以上.该感兴趣区域（ROI）编码采用率失真优化斜率提升，而不是比特平面移位，使图像在相同的光谱分辨率下拥有更好的空间分辨率.试验数据表明，算法大大保护了图像的光谱特性，在8倍压缩比情况时，满足卫星干涉超光谱遥感图像要求.     

一种新的恒星大气物理参数自动估计方案SVR(Haar)

提出了一种新的恒星大气物理参数自动估计的新方案,并称之为SVR(Haar)。由于观测光谱受到大量宇宙辐射、大气和观测设备等引起的噪声干扰,且这种噪声干扰往往是其中的频率较高成分。所以该方案的基本思想是首先使用Haar小波剔除高频噪声成份,以提高恒星大气物理参数估计的准确性;然后使用支持向量机回归方法(SVR)对恒星参数做出估计,该方法能通过ε不敏感域进一步提高对光谱微小畸变和干扰的容许能力,增强解决方案的鲁棒性。为了验证SVR(Haar)方案的有效性,针对相关研究中的权威模拟恒星光谱和SLOAN发布的实测光谱,以及文献中的典型处理方法,做了大量比较实验。实验结果表明,所提出的SVR(Haar)恒星参数估计方案比文献中常用的主成分分析和非参数回归模型均要好。     

Towards the proof of Kolmogorov hypotheses

A closure scheme for Kolmogorov spectrum at low and high frequencies is proposed. It allows us to validate second Kolmogorov hypothesis if expand the first one. The proposed closure scheme adds energy of turbulence to the list of controlling parameters and explains energy transfer over the spectrum by wave interaction between incompressible and adiabatic components of turbulence.     

Geant4在惯性约束聚变内爆物理中的应用

基于Geant4建立了内爆物理实验多种诊断设备的全三维仿真模型,包括中子成像系统、用于硬X射线诊断的滤波应光谱仪、楔形滤片质子能谱仪、化学气相沉积金刚石探测器(CVD)等。根据Geant4仿真模拟的数据,建立了合适的解谱及图像还原算法,优化了系统设计,从理论上预估了诊断设备的诊断能力。此外仿真数据亦用于设计实验方案,建立诊断设备的标定方法等。     

稀疏信道条件下正交多载波扩频水声通信无导频信道估计算法

提出了一种无导频信道估计算法,该算法首先利用水声信道的稀疏特性对扩频信号进行识别,再利用扩频信号识别结果对水声信道响应进行判决反馈估计,从而实现对稀疏水声信道响应的可靠重建。仿真和湖上试验结果证实:无导频信道估计算法可以在不降低通信质量的前提下,实现对水声通信信号的稳健均衡,提升水声通信速率。      

大孔径静态干涉光谱仪图像压缩技术

从图像压缩的角度分析了大孔径静态干涉成像光谱仪成像原理，并提出了一种新的遥感多光谱图像压缩方案。新方案利用大孔径静态干涉成像光谱仪推扫成像特点提出了一种低存储量，帧间小波域匹配的图像序列压缩方法，提高图像质量3～4dB。为了保证图像的光谱信息在8倍压缩比下有效应用，系统采用了一种新的感兴趣区域(ROD编码技术。感兴趣区域编码时，由于方案中采用率失真优化斜率提升，而不是比特平面移位，从而使图像在相同的光谱分辨率下拥有更好的空间分辨率。实验结果表明，算法大大保护了图像的光谱特性，在8倍压缩比下，满足了该类干涉多光谱遥感图像的质量要求。     

Quantum fluctuations of spatial dissipative solitons in a nonlinear interferometer

A quantum Langevin equation is derived that makes it possible to study the radiation field in a large-aperture nonlinear interferometer excited by external classical radiation. This equation is linearized in the vicinity of the solution for a stationary soliton. A mathematical formalism for obtaining a spectral representation of the solution to the linearized problem is constructed. It is shown that, in general, the excitation spectrum of a soliton consists of three branches, two of which belong to a continuous spectrum, while the third branch is discrete. The spectral representation obtained makes it possible to rigorously define the operator of soliton coordinate fluctuations, since, as is shown in the study, the traditional definition of this operator leads to a divergence in the vicinity of the solution. A new type of dissipative soliton is found, which is a natural generalization of a stationary soliton and takes into account its motion. A relation is found between this soliton and the contribution to the solution for field fluctuations from the discrete spectrum expansion. The mean squares of fluctuations of the soliton coordinate and momentum are calculated. A range of parameters is determined where the momentum of the soliton can always be measured with a spread smaller than the standard quantum limit. This possibility is related to the occurrence of states squeezed with respect to the soliton momentum. A scheme is proposed for the experimental observation of these states.     

Asymmetric multiple-image hiding using phase retrieval technique based on amplitude- and phase-truncation in fractional Fourier domain

We propose a multiple-image hiding scheme based on the amplitude- and phase-truncation approach, and phase retrieval iterative algorithm in the fractional Fourier domain. The proposed scheme offers multiple levels of security with asymmetric keys. Multiple input images multiplied with random phase masks are independently fractional Fourier transformed with different orders. The individual keys and common keys are generated by using phase and amplitude truncation of fractional spectrum. After using two fractional Fourier transform, the resultant encrypted image is hided in a host image with phase retrieval iterative algorithm. Using the correct universal keys, individual keys, and fractional orders, one can recover the original image successfully. Computer simulation results with four gray-scale images support the proposed method. To measure the validity of the scheme, we calculated the mean square error between the original and the decrypted images. In this scheme, the encryption process and generation of decryption keys are complicated and should be realized using computer. For decryption, an optoelectronic setup has been suggested.