Empirical likelihood for spatial cross-sectional data models with matrix exponential spatial specification

In this paper,we study spatial cross-sectional data models in the form of matrix exponential spatial specification(MESS),where MESS appears in both dependent and error terms.The empirical likelihood(EL)ratio statistics are established for the parameters of the MESS model.It is shown that the limiting distributions of EL ratio statistics follow chi-square distributions,which are used to construct the confidence regions of model parameters.Simulation experiments are conducted to compare the performances of confidence regions based on EL method and normal approximation method.

Beamspace maximum likelihood algorithm based on sum and difference beams for elevation estimation

Beamspace super-resolution methods for elevation estimation in multipath environment has attracted significant attention, especially the beamspace maximum likelihood(BML)algorithm. However, the difference beam is rarely used in superresolution methods, especially in low elevation estimation. The target airspace information in the difference beam is different from the target airspace information in the sum beam. And the use of difference beams does not significantly increase the complexity of the system and algorithms. Thus, this paper applies the difference beam to the beamformer to improve the elevation estimation performance of BML algorithm. And the direction and number of beams can be adjusted according to the actual needs. The theoretical target elevation angle root means square error(RMSE) and the computational complexity of the proposed algorithms are analyzed. Finally, computer simulations and real data processing results demonstrate the effectiveness of the proposed algorithms.

A Likelihood-Based Multiple Change Point Algorithm for Count Data with Allowance for Over-Dispersion

Count data is almost always over-dispersed where the variance exceeds the mean. Several count data models have been proposed by researchers but the problem of over-dispersion still remains unresolved, more so in the context of change point analysis. This study develops a likelihood-based algorithm that detects and estimates multiple change points in a set of count data assumed to follow the Negative Binomial distribution. Discrete change point procedures discussed in literature work well for equi-dispersed data. The new algorithm produces reliable estimates of change points in cases of both equi-dispersed and over-dispersed count data;hence its advantage over other count data change point techniques. The Negative Binomial Multiple Change Point Algorithm was tested using simulated data for different sample sizes and varying positions of change. Changes in the distribution parameters were detected and estimated by conducting a likelihood ratio test on several partitions of data obtained through step-wise recursive binary segmentation. Critical values for the likelihood ratio test were developed and used to check for significance of the maximum likelihood estimates of the change points. The change point algorithm was found to work best for large datasets, though it also works well for small and medium-sized datasets with little to no error in the location of change points. The algorithm correctly detects changes when present and fails to detect changes when change is absent in actual sense. Power analysis of the likelihood ratio test for change was performed through Monte-Carlo simulation in the single change point setting. Sensitivity analysis of the test power showed that likelihood ratio test is the most powerful when the simulated change points are located mid-way through the sample data as opposed to when changes were located in the periphery. Further, the test is more powerful when the change was located three-quarter-way through the sample data compared to when the change point is closer (quarter-way) to the first observation.

Vulnerable brain regions in adolescent major depressive disorder:A resting-state functional magnetic resonance imaging activation likelihood estimation meta-analysis

BACKGROUND Adolescent major depressive disorder(MDD)is a significant mental health concern that often leads to recurrent depression in adulthood.Resting-state functional magnetic resonance imaging(rs-fMRI)offers unique insights into the neural mechanisms underlying this condition.However,despite previous research,the specific vulnerable brain regions affected in adolescent MDD patients have not been fully elucidated.AIM To identify consistent vulnerable brain regions in adolescent MDD patients using rs-fMRI and activation likelihood estimation(ALE)meta-analysis.METHODS We performed a comprehensive literature search through July 12,2023,for studies investigating brain functional changes in adolescent MDD patients.We utilized regional homogeneity(ReHo),amplitude of low-frequency fluctuations(ALFF)and fractional ALFF(fALFF)analyses.We compared the regions of aberrant spontaneous neural activity in adolescents with MDD vs healthy controls(HCs)using ALE.RESULTS Ten studies(369 adolescent MDD patients and 313 HCs)were included.Combining the ReHo and ALFF/fALFF data,the results revealed that the activity in the right cuneus and left precuneus was lower in the adolescent MDD patients than in the HCs(voxel size:648 mm3,P<0.05),and no brain region exhibited increased activity.Based on the ALFF data,we found decreased activity in the right cuneus and left precuneus in adolescent MDD patients(voxel size:736 mm3,P<0.05),with no regions exhibiting increased activity.CONCLUSION Through ALE meta-analysis,we consistently identified the right cuneus and left precuneus as vulnerable brain regions in adolescent MDD patients,increasing our understanding of the neuropathology of affected adolescents.

Multimodal abnormalities of brain structures in adolescents and young adults with major depressive disorder:An activation likelihood estimation meta-analysis

BACKGROUND Major depressive disorder(MDD)in adolescents and young adults contributes significantly to global morbidity,with inconsistent findings on brain structural changes from structural magnetic resonance imaging studies.Activation likeli-hood estimation(ALE)offers a method to synthesize these diverse findings and identify consistent brain anomalies.METHODS We performed a comprehensive literature search in PubMed,Web of Science,Embase,and Chinese National Knowledge Infrastructure databases for neuroi-maging studies on MDD among adolescents and young adults published up to November 19,2023.Two independent researchers performed the study selection,quality assessment,and data extraction.The ALE technique was employed to synthesize findings on localized brain function anomalies in MDD patients,which was supplemented by sensitivity analyses.RESULTS Twenty-two studies comprising fourteen diffusion tensor imaging(DTI)studies and eight voxel-based morphome-try(VBM)studies,and involving 451 MDD patients and 465 healthy controls(HCs)for DTI and 664 MDD patients and 946 HCs for VBM,were included.DTI-based ALE demonstrated significant reductions in fractional anisotropy(FA)values in the right caudate head,right insula,and right lentiform nucleus putamen in adolescents and young adults with MDD compared to HCs,with no regions exhibiting increased FA values.VBM-based ALE did not demonstrate significant alterations in gray matter volume.Sensitivity analyses highlighted consistent findings in the right caudate head(11 of 14 analyses),right insula(10 of 14 analyses),and right lentiform nucleus putamen(11 of 14 analyses).CONCLUSION Structural alterations in the right caudate head,right insula,and right lentiform nucleus putamen in young MDD patients may contribute to its recurrent nature,offering insights for targeted therapies.

Optimization of Generator Based on Gaussian Process Regression Model with Conditional Likelihood Lower Bound Search

The noise that comes from finite element simulation often causes the model to fall into the local optimal solution and over fitting during optimization of generator.Thus,this paper proposes a Gaussian Process Regression(GPR)model based on Conditional Likelihood Lower Bound Search(CLLBS)to optimize the design of the generator,which can filter the noise in the data and search for global optimization by combining the Conditional Likelihood Lower Bound Search method.Taking the efficiency optimization of 15 kW Permanent Magnet Synchronous Motor as an example.Firstly,this method uses the elementary effect analysis to choose the sensitive variables,combining the evolutionary algorithm to design the super Latin cube sampling plan;Then the generator-converter system is simulated by establishing a co-simulation platform to obtain data.A Gaussian process regression model combing the method of the conditional likelihood lower bound search is established,which combined the chi-square test to optimize the accuracy of the model globally.Secondly,after the model reaches the accuracy,the Pareto frontier is obtained through the NSGA-II algorithm by considering the maximum output torque as a constraint.Last,the constrained optimization is transformed into an unconstrained optimizing problem by introducing maximum constrained improvement expectation(CEI)optimization method based on the re-interpolation model,which cross-validated the optimization results of the Gaussian process regression model.The above method increase the efficiency of generator by 0.76%and 0.5%respectively;And this method can be used for rapid modeling and multi-objective optimization of generator systems.

The study of a neutron spectrum unfolding method based on particle swarm optimization combined with maximum likelihood expectation maximization

The neutron spectrum unfolding by Bonner sphere spectrometer(BSS) is considered a complex multidimensional model,which requires complex mathematical methods to solve the first kind of Fredholm integral equation. In order to solve the problem of the maximum likelihood expectation maximization(MLEM) algorithm which is easy to suffer the pitfalls of local optima and the particle swarm optimization(PSO) algorithm which is easy to get unreasonable flight direction and step length of particles, which leads to the invalid iteration and affect efficiency and accuracy, an improved PSO-MLEM algorithm, combined of PSO and MLEM algorithm, is proposed for neutron spectrum unfolding. The dynamic acceleration factor is used to balance the ability of global and local search, and improves the convergence speed and accuracy of the algorithm. Firstly, the Monte Carlo method was used to simulated the BSS to obtain the response function and count rates of BSS. In the simulation of count rate, four reference spectra from the IAEA Technical Report Series No. 403 were used as input parameters of the Monte Carlo method. The PSO-MLEM algorithm was used to unfold the neutron spectrum of the simulated data and was verified by the difference of the unfolded spectrum to the reference spectrum. Finally, the 252Cf neutron source was measured by BSS, and the PSO-MLEM algorithm was used to unfold the experimental neutron spectrum.Compared with maximum entropy deconvolution(MAXED), PSO and MLEM algorithm, the PSO-MLEM algorithm has fewer parameters and automatically adjusts the dynamic acceleration factor to solve the problem of local optima. The convergence speed of the PSO-MLEM algorithm is 1.4 times and 3.1 times that of the MLEM and PSO algorithms. Compared with PSO, MLEM and MAXED, the correlation coefficients of PSO-MLEM algorithm are increased by 33.1%, 33.5% and 1.9%, and the relative mean errors are decreased by 98.2%, 97.8% and 67.4%.

Weighted Maximum Likelihood Technique for Logistic Regression

In this paper, a weighted maximum likelihood technique (WMLT) for the logistic regression model is presented. This method depended on a weight function that is continuously adaptable using Mahalanobis distances for predictor variables. Under the model, the asymptotic consistency of the suggested estimator is demonstrated and properties of finite-sample are also investigated via simulation. In simulation studies and real data sets, it is observed that the newly proposed technique demonstrated the greatest performance among all estimators compared.

Heuristic techniques for maximum likelihood localization of radioactive sources via a sensor network

Maximum likelihood estimation(MLE)is an effective method for localizing radioactive sources in a given area.However,it requires an exhaustive search for parameter estimation,which is time-consuming.In this study,heuristic techniques were employed to search for radiation source parameters that provide the maximum likelihood by using a network of sensors.Hence,the time consumption of MLE would be effectively reduced.First,the radiation source was detected using the k-sigma method.Subsequently,the MLE was applied for parameter estimation using the readings and positions of the detectors that have detected the radiation source.A comparative study was performed in which the estimation accuracy and time consump-tion of the MLE were evaluated for traditional methods and heuristic techniques.The traditional MLE was performed via a grid search method using fixed and multiple resolutions.Additionally,four commonly used heuristic algorithms were applied:the firefly algorithm(FFA),particle swarm optimization(PSO),ant colony optimization(ACO),and artificial bee colony(ABC).The experiment was conducted using real data collected by the Low Scatter Irradiator facility at the Savannah River National Laboratory as part of the Intelligent Radiation Sensing System program.The comparative study showed that the estimation time was 3.27 s using fixed resolution MLE and 0.59 s using multi-resolution MLE.The time consumption for the heuristic-based MLE was 0.75,0.03,0.02,and 0.059 s for FFA,PSO,ACO,and ABC,respectively.The location estimation error was approximately 0.4 m using either the grid search-based MLE or the heuristic-based MLE.Hence,heuristic-based MLE can provide comparable estimation accuracy through a less time-consuming process than traditional MLE.

Joint polarization and DOA estimation based on improved maximum likelihood estimator and performance analysis for conformal array

The conformal array can make full use of the aperture,save space,meet the requirements of aerodynamics,and is sensitive to polarization information.It has broad application prospects in military,aerospace,and communication fields.The joint polarization and direction-of-arrival(DOA)estimation based on the conformal array and the theoretical analysis of its parameter estimation performance are the key factors to promote the engineering application of the conformal array.To solve these problems,this paper establishes the wave field signal model of the conformal array.Then,for the case of a single target,the cost function of the maximum likelihood(ML)estimator is rewritten with Rayleigh quotient from a problem of maximizing the ratio of quadratic forms into those of minimizing quadratic forms.On this basis,rapid parameter estimation is achieved with the idea of manifold separation technology(MST).Compared with the modified variable projection(MVP)algorithm,it reduces the computational complexity and improves the parameter estimation performance.Meanwhile,the MST is used to solve the partial derivative of the steering vector.Then,the theoretical performance of ML,the multiple signal classification(MUSIC)estimator and Cramer-Rao bound(CRB)based on the conformal array are derived respectively,which provides theoretical foundation for the engineering application of the conformal array.Finally,the simulation experiment verifies the effectiveness of the proposed method.

Smoothed Empirical Likelihood Inference for Nonlinear Quantile Regression Models with Missing Response

In this paper, three smoothed empirical log-likelihood ratio functions for the parameters of nonlinear models with missing response are suggested. Under some regular conditions, the corresponding Wilks phenomena are obtained and the confidence regions for the parameter can be constructed easily.

Empirical Likelihood Statistical Inference for Compound Poisson Vector Processes under Infinite Covariance Matrix

The paper discusses the statistical inference problem of the compound Poisson vector process(CPVP)in the domain of attraction of normal law but with infinite covariance matrix.The empirical likelihood(EL)method to construct confidence regions for the mean vector has been proposed.It is a generalization from the finite second-order moments to the infinite second-order moments in the domain of attraction of normal law.The log-empirical likelihood ratio statistic for the average number of the CPVP converges to F distribution in distribution when the population is in the domain of attraction of normal law but has infinite covariance matrix.Some simulation results are proposed to illustrate the method of the paper.

电商直播中消费者购买意愿影响因素研究——基于双路径模型视角

随着电商直播步入新的风口,其蕴藏的巨大商业潜力受到越来越广泛的关注,消费者购买意愿成为影响电商直播可持续发展的重要因素。研究运用双路径模型(ELM),基于中枢路径和边缘路径构建消费者购买意愿的影响因素,实证分析在电商直播中产品因素与主播特征对消费者购买意愿的影响。研究发现,产品质量、价格优惠性、主播吸引力和主播交互性对购买意愿有显著正向影响,但主播专业性对购买意愿的影响并不显著;在中枢路径下,产品质量和价格优惠性通过实用价值影响消费者购买意愿;在边缘路径下,主播专业性、主播吸引力和主播交互性通过享乐价值影响消费者购买意愿。

时间效应下的健康信息说服机制研究--基于精细加工可能性模型的实证

通过健康信息传播和教育说服公众形成健康行为意愿是一个现实课题。本文以精细加工可能性模型(elabo‐ration likelihood model,ELM)为理论基础,将说服路径分为中心路径和外围路径,同时引入短期的时间纵向数据追踪。本文实施了10天左右持续使用健康信息的日记报告实验,基于30名大学生提交的377条健康信息日记数据,建立个体层面与信息线索、时间层面的多层线性回归模型(hierarchical linear modeling,HLM),探究健康信息对个体健康行为意愿的说服机制。研究结果表明,健康行为意愿的说服过程主要是信息质量和来源可信度的混合式说服路径;在7天周期内,健康信息说服效果逐渐增强,其中信息质量的说服效果更为稳定,来源可信度的说服效果则随着时间推移逐渐被抵消;健康信息说服路径随个体特征和接触时机而变;健康意识调节来源可信度和信息热度对说服效果的影响,且具有时间效应;卷入度调节信息质量和来源可信度对信息说服效果的影响,但不存在时间效应。本文的研究结果有助于深入理解健康信息对健康行为意愿改变的说服机制,为建立“以人为本”的个性化健康信息传播和健康教育方案提供了参考。

写给物理学家的生成模型

科学研究的本质在于创造。生成式人工智能为更有创意的科学探索打开了无尽的想象空间。作为生成式人工智能的核心,生成模型学习数据样本背后的概率分布,并据此随机采样生成新的样本。生成模型和统计物理在本质上是同一枚硬币的两面。文章从物理的视角介绍扩散模型、自回归模型、流模型、变分自编码器等现代生成模型。生成模型在原子尺度物质结构的生成与设计中展现出巨大的潜力。不仅如此,基于和统计物理的内在联系,生成模型对于优化“大自然的损失函数”——变分自由能具有独特的优势,这为求解困难的统计物理和量子多体问题提供了新的可能。同时,物理学的洞察也在推动生成模型的发展和创新。通过借鉴物理学原理和方法,还可以设计出更加高效、更加统一的生成模型,以应对人工智能领域中的挑战。

基于ML估计的高动态GNSS信号快速捕获检测方法

针对高动态环境下GNSS因频域带宽增加导致捕获难度增大的问题,分析了接收端数字中频采样信号的传输特性及复基带信号经FFT模块处理后的相关峰的检测,提出了基于极大似然(ML)估计的高动态GNSS信号快速捕获检测方法。首先,根据随机信号的统计理论建立二元假设检验条件,构建了奈曼-皮尔逊准则下的GNSS信号捕获判决门限模型;其次,通过判决量的统计特性对等效高斯白噪声方差进行ML估计,根据其估计值计算捕获判决门限,其中通过虚警率的量化放大处理,解决了判决量样本值的增加带来的估计偏差问题;最后,对不同高动态条件下北斗B3I信号进行了捕获检测仿真实验。结果表明采用ML估计方法确定捕获判决门限从而提高高动态GNSS信号捕获的检测方法对高动态适应范围较宽,其频移捕获精度与SINS信息辅助捕获相当,比序贯检测算法提高约28%以上,相同条件下具有更快的平均捕获检测速度。

泰勒展开与交替投影最大似然结合的离网格DOA估计算法

针对最大似然DOA估计算法需要多维搜索、计算量大且面临着在网格估计的问题,该文提出一种基于泰勒展开的离网格交替投影最大似然算法。该方法首先利用交替投影将多维搜索转化为多个1维搜索,获得对应预设大网格的粗估计结果;再利用矩阵求导理论将1维代价函数在粗估计结果处进行2阶泰勒展开;最后通过对2阶泰勒展开求偏导并令导数等于零,求得离网参数的闭式解。与交替投影最大似然算法相比,该方法突破了搜索网格大小的限制,在保证算法精度的同时,有效减少了算法的在网格计算点数,提升了运算效率。仿真结果证明了该算法的有效性。

一种动平台MIMO雷达对海广域探测波束锐化方法

为解决动平台相控阵雷达前视成像方位分辨率低的问题,文中利用多输入多输出(Multiple Input Multiple Output,MIMO)雷达角度分辨力的优势,给出了一种适用于广域宽角扫描的机载MIMO雷达波束锐化方法。首先,根据MIMO雷达虚拟阵列原理,在宽发窄收和同时多波束探测模式下,建立了子阵级MIMO雷达前视成像回波模型;然后,在贝叶斯准则下,结合噪声统计先验信息,给出了基于最大似然估计的波束锐化方法。仿真和数据分析发现,该方法在较宽的角域内均可以获得良好的波束锐化性能,同时又极大节省了时间资源,具有一定的工程应用价值。

多元广义线性模型经验似然方法分析

针对多元广义线性模型,基于估计相关阵、广义估计方程和经验似然方法,本文构造出经验似然比统计量,此统计量能克服“工作相关阵”方法的误设定问题.在一定的条件下,本文也获得了经验似然比统计量渐近Wilks性质,该结果可用作未知参数向量置信域的构造.最后,通过数值模拟对所提方法的有效性进行验证.

联合RIS子块与接收天线的索引调制方案性能分析

利用大量无源反射器件设计的可重构智能表面(RIS),具有拓展无线通信覆盖范围、降低系统成本/功耗和提升未来通信系统性能的优势;而索引调制(IM),通过激活通信资源的子集可实现信息的隐性传输,有望为无线通信带来更高的频谱效率和能量效率,因此,为进一步提升未来无线通信系统的性能,该论文融合RIS与IM技术,提出一种联合RIS子块与接收天线的IM方案。在该方案中,按照相邻原则,将RIS反射元件分割为若干子块,进而利用RIS子块索引与接收天线索引同时实现附加信息传递,即对待传输比特序列,将其分割为三部分,其中第一部比特被调制为星座符号,第二部分用于指示RIS子块划分,第三部分用于指示接收天线索引;在此基础上,根据最大似然(ML)检测的成对错误概率(PEP)解析形式,分四种情况,从理论上推导出对应的矩母函数(MGF),得到无条件PEP的解析表达式,最后得到该方案ML检测的平均误码率(ABER)性能上界。仿真结果表明,与现有RIS辅助的IM方案相比,无须增加额外频谱资源,所提方案的系统可达速率和系统差错性能方面均具有一定优势;同时,验证了ML检测的ABER上界具备严格一致性。