基于最大似然的单通道交叠激光微多普勒信号参数分离估计

利用激光对目标微弱振动进行探测有利于获得明显的微多普勒效应,这为精确估计目标微动特征参数,实现对目标的分类和精细识别提供了可能.但对于多散射点或多目标激光探测,信号为单通道多分量微动混合的形式,而且补偿目标主体运动后,数值上相近的微动参数还会导致信号在时频域存在严重的交叠.为从这类混合信号中精确估计各分量的微动参数,本文提出了基于最大似然框架的参数分离估计方法.利用精细化扫描的奇异值比谱法从混合信号中获得目标微动频率,并得到各分量的幅值比信息.推导了微动参数最大似然估计的解析表达形式,根据激光微多普勒信号的特点从频谱能量分布的角度重新设计了似然函数,解决了传统似然函数在激光微动信号中出现的高度非线性问题,降低了初始化的要求,提高了抗噪性能,并采用马尔可夫-蒙特卡罗方法具体实现了参数的估计.在微动参数得到估计的基础上给出了信号的幅值和初相的估计方法.用本文方法对仿真和实验数据进行处理,得到了接近克拉美罗下界的估计结果,验证了方法的有效性.与传统非参数化估计方法的对比结果体现了所提方法对混合微动参数精确估计上的优势.     

厄尔尼诺和南方涛动海气耦合模型中参数估计的变分方法

提出一种基于变分原理估计厄尔尼诺和南方涛动海气耦合模型中未知参数的方法. 首先将所研究的非线性海气耦合动力方程引入到目标泛函中; 接着利用变分方法导出伴随方程和待辨识参数泛函梯度的公式; 然后设计了估计未知参数的算法.数值试验结果表明变分方法是一 种能有效估计海气耦合非线性系统未知参数的方法.     

基于变分方法的混沌系统参数估计

提出一种基于变分原理的估计混沌系统未知参数的方法,对以x= F(x,θ) 为控制方程的所有混沌系统具有普适性.首先将混沌系统方程引入到目标泛函中;接着利用变分原理导出了混沌系统的伴随方程和待辨识参数泛函梯度的通用公式;然后设计了估计混沌系统未知参数的算法;最后对典型的Lorenz混沌系统和超混沌Chen系统的未知参数进行了估计.数值仿真结果表明该方法是一种非常有效的估计混沌系统未知参数的方法. 关键词： 混沌系统 参数估计 变分方法 伴随方程     

采用邻域近似算法估计环境参数不确定性

根据贝叶斯理论,逆问题的解可以用后验概率密度来表征,它包含了模型参数先验知识和观测数据信息,反映了反演参数的不确定性.一种快速吉布斯采样算法已经被用于后验概率密度的多维积分运算,但其需要调用大量的声场前向模型,在多个频率或水平变化的匹配场参数反演中,计算量仍然很大.基于邻域近似算法,提出一种比快速吉布斯采样算法更快的参数不确定性估计方法.对低维参数反演问题,邻域算法可以很好地逼近真实的后验概率密度;而对高维问题及其敏感参数,在模型参数样本量有限的条件下,邻域算法很难精确地估计后验概率密度.为了克服以上缺点,并完整地得到反演参数的不确定性信息,设计了一种多步估计方案.数值仿真和实测数据分析表明,多步邻域算法采用较少的计算代价,可获得与快速吉布斯方法相似的估计精度.     

连续能量共轭加权蒙特卡罗动态参数计算

本文开展基于连续能量共轭加权蒙特卡罗的堆芯动态参数计算研究,这些参数主要包括缓发中子有效份额、瞬发中子代时间和瞬发中子衰减常数,在目前普遍采用的迭代裂变概率（IFP）的基础上,扩展原有IFP方法中共轭通量的选择,比较径迹长度估计、碰撞估计、吸收估计和tally记数估计的差别,及协方差和方差权重计算.同时,给出多个概率区间的动态参数分布范围,对迭代裂变概率法进行深入的研究,对比并给出下一代事件估计计数和不同中间代迭代裂变概率估计计数对计算结果的影响,从中得出合适的迭代代数.相关程序在计算完成后自动输出各种粒子分布状况统计.     

基于长电偶极子和大磁圆环的新型电磁矢量传感器双基地多输入多输出雷达角度和极化参数联合估计

针对常规双基地电磁矢量传感器多输入多输出(multiple-input multiple-output,MIMO)雷达中短电偶极子(L/λ<0.1)和小磁环(2π(R/λ)<0.1)辐射效率不足问题,本文根据实际应用中电磁矢量传感器的有效长度来设计新型的发射电磁矢量传感器阵列和接收电磁矢量传感器阵列.首先,通过平行因子算法来实现对双基地MIMO雷达阵列接收数据空时特性的充分利用.这种处理过程能够实现发射俯仰角和接收俯仰角的自动参数配对.然后,针对归一化坡印亭矢量估计器在长电偶极子和大磁圆环约束下无法实现角度和极化参数有效测量的问题,对于利用平行因子算法得到的发射和接收加载矩阵采用新的盲估计算法来实现对角度参数和极化参数的高精度估计.所提出的盲估计算法在不需要电偶极子长度和磁环周长的先验信息的情况下能够有效地实现发射四维参数和接收四维参数的精确估计,且该算法估计得到的八维参数满足自动参数配对特性.最后,详细推导了长电偶极子和大磁圆环约束下双基地MIMO雷达中角度和极化参数估计性能的克拉美罗界.仿真实验表明,对于实际中长电偶极子和大磁圆环组成的新型电磁矢量传感器,本文所提算法具有良好的参数估计性能.通过理论分析和仿真实验结果可以发现,本文的研究工作能够进一步促进电磁矢量传感器在双基地MIMO雷达中的应用.     

MPEG-4视频中运动背景下的目标检测算法

针对由运动摄像机捕获的MPEG-4视频流中的运动目标检测问题,提出了一种直接利用压缩视频码流进行全局运动估计的新算法.算法从全局运动估计的基础出发,利用背景宏块运动相似性的特点快速建立背景宏块集合并采用常用的四参数全局运动估计模型估计运动参数.最后,计算运动矢量残差,通过对运动矢量残差的筛选检测运动日标.算法利用MPEG-4码流中蕴含的运动信息.不需要对压缩流完全解码,较大地提高了检测效率;进一步改善了检测效果.实验验证了提出的全局运动估计算法的检测效率和检测效果.     

求解α本征值的k-α迭代方法误差估计

分析求解α本征值的k-α迭代方法,指出迭代法中参数的选择影响使用标准差的平均值估计出来的α误差.如果参数选取不当,实际估计误差可能和真实估计误差相差很大.MCNP4C程序中使用的参数给出的误差估计通常和真实估计误差有一定的偏差.本文给出一个新的参数选择办法,能够让实际估计误差几乎等于真实估计误差,并用数值实验进行验证.     

基于统计推断的油滴实验数据处理

基于统计推断中对总体参数的区间估计,由对应样本的电荷测得值求得油滴带电量对单元电荷整倍数的总平均偏离量的区间估计.同时讨论了教学实验中样本容量的选取问题.给出由样本观察值对单元电荷量值的估计.     

联合简正波水波和底波频散特性的贝叶斯地声参数反演

大多数基于浅海简正波模态频散数据的地声参数反演方法无法对深层底质声学参数进行可靠估计,究其原因是仅利用了简正波水波频散特征,忽略了与深层底质声学参数密切相关的底波频散特征,因此,本文在分析了包含水波和底波的浅海宽带数据的基础上,结合底波频散特征对深层底质声学参数变化更加敏感的物理特性,实现了基于完整简正波频散特性的贝叶斯地声参数反演,并针对简正波宽带声场模型计算复杂度较高的现实问题,利用变分贝叶斯蒙特卡罗方法的推断优势,完成了未知参数的可靠估计和快速后验分析.仿真和海上实验结果表明:联合简正波水波和底波频散特征数据的贝叶斯地声参数反演,不仅可以有效估计深层底质声学参数,而且降低了其他相关环境参数的估计不确定性.     

量子密码通信中量子比特率理论分析

在量子密钥分配中,量子比特率是一个重要的系统参数。通过引入测量因子和筛选因子,建立了基于理想单光子源和泊松分布单光子源的量子比特率理论模型,给出了量子比特率的表达式,并对两种单光子源进行了比较分析。结果表明,当平均光子数大于1时,泊松分布单光子源能被优化。在发射机脉冲重复率一定的条件下,采用泊松分布单光子源无法达到理想单光子源的量子比特率,这是为保密通信所必须付出的代价。     

On the Grüneisen parameter for crystals and glasses

Additional data confirming the close relation between the Grüneisen parameter and the Poisson ratio are obtained. The estimate of the Grüneisen parameter based on the Leont’ev formula using the data on density, bulk compression modulus, and velocity of sound is in conformity with the results of calculations based on the Grüneisen and Belomestnykh-Tesleva equations.     

Transition curves for the variance of the nearest neighbor spacing distribution for Poisson to Gaussian orthogonal and unitary ensemble transitions

Using an appropriate 2x2 random matrix ensemble, transition curves for the variance of the nearest neighbor spacing distribution are constructed for the Poisson to Gaussian orthogonal and unitary ensemble transitions in terms of an easily identifiable transition parameter.     

Sub-poissonian statistics of fluorescence from a single atom driven by a continuous wave laser field

Statistics of fluorescence photons emitted by a single two-level atom interacting with a continuous wave laser field are analyzed. The photon-counting distribution is calculated for the so-called intermediate fluorescence photons, i.e., those counted during the time interval between instants at which photons are emitted. The result is a sub-Poissonian (narrower than Poisson) distribution, which agrees with experimental observations. This intermediate-photon distribution is used to calculate the average number of fluorescence photons, the second factorial moment of the photon-counting distribution, and Mandel’s Q parameter commonly used to evaluate the deviation of photon statistics from the Poisson distribution. The theoretical expressions obtained for moments of the intermediate-photon distribution are different from well-known Mandel’s formulas.     

Detection of radionuclides from weak and poorly resolved spectra using Lasso and subsampling techniques

We consider a problem of identification of nuclides from weak and poorly resolved spectra. A two stage algorithm is proposed and tested based on the principle of majority voting. The idea is to model gamma-ray counts as Poisson processes. Then, the average part is taken to be the model and the difference between the observed gamma-ray counts and the average is considered as random noise. In the linear part, the unknown coefficients correspond to if isotopes of interest are present or absent. Lasso types of algorithms are applied to find non-vanishing coefficients. Since Lasso or any prediction error based algorithm is inconsistent with variable selection for finite data length, an estimate of parameter distribution based on subsampling techniques is added in addition to Lasso. Simulation examples are provided in which the traditional peak detection algorithms fail to work and the proposed two stage algorithm performs well in terms of both the False Negative and False Positive errors.     

Theoretical Study of Quantum Bit Rate in Free-Space Quantum Cryptography

The quantum bit rate is an important operating parameter in free-space quantum key distribution. We introduce the measuring factor and the sifting factor, and present the expressions of the quantum bit rate based on the ideal single-photon sources and the single-photon sources with Poisson distribution. The quantum bit rate is studied in the numerical simulation for the laser links between a ground station and a satellite in a low earth orbit. The results show that it is feasible to implement quantum key distribution between a ground station and a satellite in a low earth orbit.     

Temporal and spatial evolution of electron bunching in a one-dimensional pulse

A generalized form of bunching parameter for a one-dimensional electron pulse is defined and the formula is simplified into a symmetric form by considering completely elastic one-dimensional collisions. Using a two-parameter Poisson distribution, for electrons arrival times at the undulator beginning and for their initial positions within the pulse, the temporal and spatial evolution of mean value of bunching parameter are evaluated. For the special case, where the distribution parameters, t and x, are set to zero the generalized bunching parameter is reduced to the similar form used in previous free electron laser studies.     

A New First-Order Integer-Valued Autoregressive Model with Bell Innovations

A Poisson distribution is commonly used as the innovation distribution for integer-valued autoregressive models, but its mean is equal to its variance, which limits flexibility, so a flexible, one-parameter, infinitely divisible Bell distribution may be a good alternative. In addition, for a parameter with a small value, the Bell distribution approaches the Poisson distribution. In this paper, we introduce a new first-order, non-negative, integer-valued autoregressive model with Bell innovations based on the binomial thinning operator. Compared with other models, the new model is not only simple but also particularly suitable for time series of counts exhibiting overdispersion. Some properties of the model are established here, such as the mean, variance, joint distribution functions, and multi-step-ahead conditional measures. Conditional least squares, Yule–Walker, and conditional maximum likelihood are used for estimating the parameters. Some simulation results are presented to access these estimates’ performances. Real data examples are provided.     

Estimating the intensity of Poisson flows of events by observation of the origins of busy periods

We estimate the intensities of Poisson flows of events and the mean service time by sampling the time intervals between the origins of busy periods with an arbitrary service-time distribution. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 30–36, April, 1998.     

On the flexibility of agglomeration based physical space discontinuous Galerkin discretizations

In this work we show that the flexibility of the discontinuous Galerkin (dG) discretization can be fruitfully exploited to implement numerical solution strategies based on the use of elements with very general shapes. Thanks to the freedom in defining the mesh topology, we propose a new h-adaptive technique based on agglomeration coarsening of a fine mesh. The possibility to enhance the error distribution over the computational domain is investigated on a Poisson problem with the goal of obtaining a mesh independent discretization.The main building block of our dG method consists of defining discrete polynomial spaces directly on physical frame elements. For this purpose we orthonormalize with respect to the L²-product a set of monomials relocated in a specific element frame and we introduce an easy way to reduce the cost related to numerical integration on agglomerated meshes. To complete the dG formulation for second order problems, two extensions of the BR2 scheme to arbitrary polyhedral grids, including an estimate of the stabilization parameter ensuring the coercivity property, are here proposed.