期刊文献+
共找到135,398篇文章
< 1 2 250 >
每页显示 20 50 100
log-normal脆弱模型下集群失效时间数据的非参数估计方法与应用
1
作者 赵雅梅 黄希芬 潘东东 《中国卫生统计》 北大核心 2025年第4期566-569,579,共5页
目的 构建适用于集群失效时间数据的log-normal脆弱模型的非参数极大似然估计方法。方法 采用基于MM(minorization-maximization)算法原理的非参数极大似然估计方法,建立适用于集群失效时间数据的log-normal脆弱模型的非参数估计算法框... 目的 构建适用于集群失效时间数据的log-normal脆弱模型的非参数极大似然估计方法。方法 采用基于MM(minorization-maximization)算法原理的非参数极大似然估计方法,建立适用于集群失效时间数据的log-normal脆弱模型的非参数估计算法框架。结果 log-normal脆弱模型既考虑了集群内失效时间的相依性,又考虑了不同个体间的异质性。模拟结果显示,该方法可以用来分析具有高维协变量的集群失效时间数据,且具有良好的效果。将log-normal脆弱模型应用到慢性肉芽肿患者反复感染的数据集,客观评价了慢性肉芽肿患者反复感染的影响因素。结论 log-normal脆弱模型的MM非参数估计算法对集群失效时间数据具有良好的估计效果。本研究对医学领域处理高维集群失效时间数据具有重要意义。 展开更多
关键词 log-normal脆弱模型 MM算法 集群失效时间数据
在线阅读 下载PDF
Strong Laws of Large Numbers for Sequences of Blockwise m-Dependent and Sub-Orthogonal Random Variables under Sublinear Expectations 被引量:1
2
作者 Jialiang FU 《Journal of Mathematical Research with Applications》 2026年第1期103-118,共16页
In this paper,we establish some strong laws of large numbers,which are for nonindependent random variables under the framework of sublinear expectations.One of our main results is for blockwise m-dependent random vari... In this paper,we establish some strong laws of large numbers,which are for nonindependent random variables under the framework of sublinear expectations.One of our main results is for blockwise m-dependent random variables,and another is for sub-orthogonal random variables.Both extend the strong law of large numbers for independent random variables under sublinear expectations to the non-independent case. 展开更多
关键词 sublinear expectations strong law of large numbers blockwise m-dependent suborthogonal random variables
原文传递
The mechanism of international law empowering international standardization and China’s response
3
作者 Diao Zixuan Duan Yue +1 位作者 Li Ruihan Wang Quanzhi 《China Standardization》 2026年第1期60-62,共3页
As a crucial aspect of international governance,international standardization requires legitimacy grounded in the principles and frameworks established by international law.Building upon an understanding of the common... As a crucial aspect of international governance,international standardization requires legitimacy grounded in the principles and frameworks established by international law.Building upon an understanding of the commonalities between international law and international standardization,this paper explores the mechanism through which international law centered on treaties empowers international standardization. 展开更多
关键词 international law international standardization MECHANISM
原文传递
Geometric perspective of reciprocal transformations induced by conservation laws in integrable systems
4
作者 Faren Wang Senyue Lou Man Jia 《Communications in Theoretical Physics》 2026年第2期1-8,共8页
This paper presents a geometric perspective that connects reciprocal transformations with multidimensional integrable deformations.By interpreting conservation laws as closed 1-forms,we formalize reciprocal transforma... This paper presents a geometric perspective that connects reciprocal transformations with multidimensional integrable deformations.By interpreting conservation laws as closed 1-forms,we formalize reciprocal transformations as induced local diffeomorphisms on the jet bundle.This allows us to characterize higher-dimensional deformations as systematic fiber bundle extensions,where fiber coordinates are generated by potential functions of the conservation laws.This perspective provides an interpretation for the covariant lifting of Lax pairs to higher dimensions and reveals that auto-Backlund transformations are composite diffeomorphisms.These results are applied to several classical integrable models. 展开更多
关键词 integrable systems reciprocal transformation conservation laws fiber bundle Lax pairs Backlund transformation
原文传递
Capturability distinction analysis of continuous and pulsed guidance laws
5
作者 Yuting LU Qinglei HU +2 位作者 Yang YU Tuo HAN Jianying ZHENG 《Chinese Journal of Aeronautics》 2026年第1期472-484,共13页
The capture zones of the continuous and pulsed guidance laws in the pursuit-evasion game are analytically discussed in this paper to provide deep insights into the capturability distinction between the continuous guid... The capture zones of the continuous and pulsed guidance laws in the pursuit-evasion game are analytically discussed in this paper to provide deep insights into the capturability distinction between the continuous guidance law and the pulsed guidance law.Specifically,first,in the pursuit-evasion game,various capture cases are defined regarding the Zero-Effort Miss distance(ZEM)to facilitate the capturability analysis.Then,for both the evader and the pursuer,the Linear-Quadratic Differential Game(LQDG)guidance laws concerning the continuous acceleration and the pulsed acceleration are converted into a unified form.In each capture case,the optimal solution existence conditions are derived,and the corresponding capture zones are formulated.The discussion on the capture zones shows that if the optimal solution exists,the distinction between the pulsed guidance law and the continuous guidance law can be neglected under small guidance effort weight.However,the capture zone of the continuous guidance law is larger than that of the pulsed guidance law with large pursuer guidance effort weight,but smaller with large evader guidance effort weight.Finally,various simulations are conducted to illustrate the distinction of the continuous and pulsed guidance laws,as well as the impact of the acceleration ratio and the time constant ratio on the capturability. 展开更多
关键词 Differential game theory Linear-quadratic differential game Pulsed guidance law Capturability Capture zone
原文传递
Impact of the Law on the Protection of Minors on the Denial of Tobacco Sales to Minors in China
6
作者 Qingqing Xu Xinying Zeng +7 位作者 Yongfu Yan Xinbo Di Huiyu Xie Zida Meng Mingxin Qi Jidong Huang Lin Xiao Shiwei Liu 《Biomedical and Environmental Sciences》 2026年第3期375-383,共9页
Adolescents who abuse tobacco are more vulnerable to long-term nicotine dependence,and more than 75%of current smokers started smoking during puberty[1].This early initiation is particularly concerning because the pre... Adolescents who abuse tobacco are more vulnerable to long-term nicotine dependence,and more than 75%of current smokers started smoking during puberty[1].This early initiation is particularly concerning because the prefrontal cortex,which governs executive functions and complex behavior,is not fully mature until age 25,making it especially susceptible to the neurotoxic effects of smoking[2].The smoking rate among Chinese secondary school students decreased from 5.9%in 2019 to 4.2%in 2023[3].However,easy access to cigarettes remains a critical obstacle to further reducing the smoking rate[4].China’s tobacco control strategy goes beyond general population measures to include specific policies protecting minors,such as the Tobacco Monopoly Law(1991)and the Law on the Protection of Minors(2006),which explicitly prohibit tobacco sales to minors.A 2020 revision of the Law on the Protection of Minors,which came into effect in June 2021,introduced specific penalties for noncompliance and significantly enhanced the enforceability of the legislation[5]. 展开更多
关键词 smoking initiation tobacco sales prefrontal cortex prefrontal cortexwhich nicotine dependence law enforcement tobacco control China
在线阅读 下载PDF
Log-normal湍流信道中超奈奎斯特传输系统的误码性能 被引量:13
7
作者 曹明华 武鑫 +1 位作者 杨顺信 贾科军 《光学精密工程》 EI CAS CSCD 北大核心 2020年第2期465-473,共9页
超奈奎斯特传输理论与调制技术相结合,可有效提高系统的频谱效率。本文将超奈奎斯特理论引入大气激光通信系统,构建了一种适合于log-normal湍流信道的超奈奎斯特光传输系统,推导了QPSK调制方式下超奈奎斯特大气光传输系统平均误码率的... 超奈奎斯特传输理论与调制技术相结合,可有效提高系统的频谱效率。本文将超奈奎斯特理论引入大气激光通信系统,构建了一种适合于log-normal湍流信道的超奈奎斯特光传输系统,推导了QPSK调制方式下超奈奎斯特大气光传输系统平均误码率的表达式,利用蒙特卡洛仿真进一步分析了该系统的误码性能及频谱效率。结果表明:采用超奈奎斯特技术方案可以较大幅度提升大气光传输系统的频谱效率,当SNR为18 dB,S.I.为0.4时其频谱效率可以达到1.7 Baud/Hz,而未采用超奈奎斯特技术时只有1.56 Baud/Hz。另一方面,大气湍流对超奈奎斯特系统误码性能的影响较明显,当S.I.为0.4,BER为3.8×10^-3时,信噪比恶化了约1 dB。相对于频谱效率的提升,误码性能的恶化是能够接受的。因此,可以将FTN技术引入大气光传输系统来提高系统的频谱效率。 展开更多
关键词 超奈奎斯特 log-normal湍流信道 大气激光通信 误码率性能 频谱效率
在线阅读 下载PDF
Poisson Log-normal回归模型的影响评价(英文)
8
作者 李泽慧 赵为华 谢晓方 《昆明理工大学学报(自然科学版)》 CAS 北大核心 2013年第4期102-108,共7页
本文利用EM算法研究了来自于Lognormal分布权重的混合Poisson模型,即Poisson Lognormal回归模型,从而利用基于完全数据似然函数的条件期望进行影响评价.基于数据删除模型和局部影响分析方法,分别得到了广义Cook距离、Q距离和三种不同扰... 本文利用EM算法研究了来自于Lognormal分布权重的混合Poisson模型,即Poisson Lognormal回归模型,从而利用基于完全数据似然函数的条件期望进行影响评价.基于数据删除模型和局部影响分析方法,分别得到了广义Cook距离、Q距离和三种不同扰动模型下的正则曲率度量等诊断统计量. 展开更多
关键词 POISSON log-normal回归 EM算法 局部影响分析 数据删除 Gauss—Hermite积分
在线阅读 下载PDF
变环境不同阶段下Log-normal分布缺失数据的可靠性估计
9
作者 李丽 胡尧 邓春霞 《中外企业家》 2015年第5期69-70,73,共3页
本文研究了变环境不同阶段Log-normal分布下,观测数据中包含缺失数据的情形下的可靠性估计问题。通过EM算法估计参数以及可靠性,最后通过模拟研究验证了本文方法的可行性。
关键词 变环境 不同阶段 log-normal分布 缺失数据
在线阅读 下载PDF
情绪健康的测量:Wong和Law情绪智力量表的修订及其信效度评价
10
作者 肖蓉 吕夏 《南方医科大学学报》 北大核心 2025年第10期2191-2198,共8页
目的对Wong和Law情绪智力量表(WLEIS)中文版进行修订并评价其测量学性能。方法对Wong和Law情绪智力量表(WLEIS)中文版的11个条目内容表述进行了修改,形成了Wong和Law情绪智力量表中文修订版(WLEIS-CR),使用广泛性焦虑障碍量表(GAD-7)、... 目的对Wong和Law情绪智力量表(WLEIS)中文版进行修订并评价其测量学性能。方法对Wong和Law情绪智力量表(WLEIS)中文版的11个条目内容表述进行了修改,形成了Wong和Law情绪智力量表中文修订版(WLEIS-CR),使用广泛性焦虑障碍量表(GAD-7)、9条目病人健康问卷(PHQ-9)和心盛量表(FS)为效标对1546名成年被试进行施测,对192名大学生被试进行重测,用所得数据对WLEIS-CR进行项目分析、验证性因素分析、信度、效度检验和等值性检验。结果WLEIS-CR的16个项目鉴别力指数均在0.4以上(r=0.570~0.764,P<0.001);验证性因素分析所得结构方程模型具有良好的拟合度(χ^(2)/df=4.610,GFI=0.965,PGFI=0.674,RMR=0.028,NFI=0.975,CFI=0.980,RMSEA=0.048)。WLEIS-CR与FS、GAD-7,PHQ-9的效标相关分别为0.674、-0.347、-0.368(P<0.001)。WLEIS-CR总量表α系数为0.913,各分量表的α系数在0.867~0.916之间,总量表的分半信度为0.956,各分量表的分半信度在0.865~0.924之间。总量表的重测信度为0.701,各因子的重测信度在0.610~0.684之间。制定并检验了WLEIS-CR结果解释标准,情绪智力为低水平者占7.6%、较低水平者占19.3%、中等水平占22.3%、较高水平占34.3%、很高水平占16.5%。WLEIS-CR具有跨性别、跨年龄和跨身份的等值性。结论WLEIS-CR具有良好的信、效度和测量等值性,适用于对中国成年人的情绪智力进行评估,测量他们的情绪健康状况。 展开更多
关键词 情绪健康 情绪智力 Wong和law情绪智力量表 信度 效度 测量等值
在线阅读 下载PDF
一种估算三参数log-normal分布参数的近似方法 被引量:1
11
作者 王立君 《数理统计与管理》 CSSCI 北大核心 1999年第2期40-43,共4页
三参数(log-normal)分布在可靠性工程中有广泛应用,但其分布参数的估计较为困难。为解决这一问题,本文将极大似然法引入其概率图。
关键词 log-normal分布 参数估计 近似法 估算 可靠性
在线阅读 下载PDF
A new car-following model yielding log-normal type headways distributions 被引量:1
12
作者 李力 王法 +2 位作者 姜锐 胡坚明 吉岩 《Chinese Physics B》 SCIE EI CAS CSCD 2010年第2期180-185,共6页
Modeling time headways between vehicles has attracted increasing interest in the traffic flow research field recently, because the corresponding statistics help to reveal the intrinsic interactions governing the vehic... Modeling time headways between vehicles has attracted increasing interest in the traffic flow research field recently, because the corresponding statistics help to reveal the intrinsic interactions governing the vehicle dynamics. However, most previous micro-simulation models cannot yield the observed log-normal distributed headways. This paper designs a new car-following model inspired by the Galton board to reproduce the observed time-headway distributions as well as the complex traffic phenomena. The consistency between the empirical data and the simulation results indicates that this new car-following model provides a reasonable description of the car-following behaviours. 展开更多
关键词 traffic flow CAR-FOLLOWING log-normal distribution
原文传递
Efficient Mean Estimation in Log-normal Linear Models with First-order Correlated Errors
13
作者 Zhang Song Wang De-hui 《Communications in Mathematical Research》 CSCD 2013年第3期271-279,共9页
In this paper, we propose a log-normal linear model whose errors are first-order correlated, and suggest a two-stage method for the efficient estimation of the conditional mean of the response variable at the original... In this paper, we propose a log-normal linear model whose errors are first-order correlated, and suggest a two-stage method for the efficient estimation of the conditional mean of the response variable at the original scale. We obtain two estimators which minimize the asymptotic mean squared error (MM) and the asymptotic bias (MB), respectively. Both the estimators are very easy to implement, and simulation studies show that they are perform better. 展开更多
关键词 log-normal first-order correlated maximum likelihood two-stage estimation mean squared error
在线阅读 下载PDF
Linear Maximum Likelihood Regression Analysis for Untransformed Log-Normally Distributed Data
14
作者 Sara M. Gustavsson Sandra Johannesson +1 位作者 Gerd Sallsten Eva M. Andersson 《Open Journal of Statistics》 2012年第4期389-400,共12页
Medical research data are often skewed and heteroscedastic. It has therefore become practice to log-transform data in regression analysis, in order to stabilize the variance. Regression analysis on log-transformed dat... Medical research data are often skewed and heteroscedastic. It has therefore become practice to log-transform data in regression analysis, in order to stabilize the variance. Regression analysis on log-transformed data estimates the relative effect, whereas it is often the absolute effect of a predictor that is of interest. We propose a maximum likelihood (ML)-based approach to estimate a linear regression model on log-normal, heteroscedastic data. The new method was evaluated with a large simulation study. Log-normal observations were generated according to the simulation models and parameters were estimated using the new ML method, ordinary least-squares regression (LS) and weighed least-squares regression (WLS). All three methods produced unbiased estimates of parameters and expected response, and ML and WLS yielded smaller standard errors than LS. The approximate normality of the Wald statistic, used for tests of the ML estimates, in most situations produced correct type I error risk. Only ML and WLS produced correct confidence intervals for the estimated expected value. ML had the highest power for tests regarding β1. 展开更多
关键词 HETEROSCEDASTICITY MAXIMUM LIKELIHOOD Estimation LINEAR Regression Model log-normal Distribution Weighed LEAST-SQUARES Regression
暂未订购
Suppression of Log-Normal Distributed Weather Clutter Observed by an S-Band Radar
15
作者 Shuji Sayama Seishiro Ishii 《Wireless Engineering and Technology》 2013年第3期125-133,共9页
We have observed weather clutter containing targets (ships) using an S-band radar with a frequency 3.05 GHz, a beam width 1.8°, and a pulsewidth 0.5 μs. To investigate the weather clutter amplitude statistics, w... We have observed weather clutter containing targets (ships) using an S-band radar with a frequency 3.05 GHz, a beam width 1.8°, and a pulsewidth 0.5 μs. To investigate the weather clutter amplitude statistics, we introduce the Akaike Information Criterion (AIC). We have found that the weather clutter amplitudes obey the log-normal, Weibull, and log-Weibull distributions with the shape parameters of 0.308 to 0.470, 4.42 to 4.51, and 15.91 to 16.44, respectively, for small data within the beam width of an antenna. We have proposed the log-normal/CFAR circuit modified a Cell-Averaging (CA) LOG/CFAR circuit. It is found that weather clutter is suppressed with improvement of 51.58 dB by log-normal/CFAR. As a result, we have showed that weather clutter observed by S-band radar does not obey the Rayleigh distribution and our log-normal/CFAR circuit has an effect on suppression of clutter and detection of target, while conventional LOG/CFAR circuit does not. In addition, if our circuit can be realized, we will have an advantage economically. 展开更多
关键词 CFAR S-BAND RADAR WEATHER CLUTTER log-normal Distribution
暂未订购
基于Laws特征增强的多聚焦图像融合方法
16
作者 董晨鹏 郭政义 +2 位作者 马怡冉 颜超 章秀华 《武汉工程大学学报》 2025年第6期658-663,682,共7页
针对细节丢失和块效应等影响融合图像质量的问题,提出了一种基于Laws特征增强的多聚焦图像融合方法。首先,利用Laws滤波提取多聚焦图像的Laws特征,得到Laws特征图;用改进的均值滤波方法对Laws特征图进行增强处理,得到特征增强图,并对特... 针对细节丢失和块效应等影响融合图像质量的问题,提出了一种基于Laws特征增强的多聚焦图像融合方法。首先,利用Laws滤波提取多聚焦图像的Laws特征,得到Laws特征图;用改进的均值滤波方法对Laws特征图进行增强处理,得到特征增强图,并对特征增强图采用极值策略提取决策图:最后,将源图像与决策图进行加权融合,得到融合结果。使用该方法对大量图像进行实验处理,结果表明:与其他融合方法相比,基于归一化互信息度量值最大提升32.87%,基于多尺度方案图像融合度量值增加26.57%。该图像融合方法显著提高视觉效果,具有较强的鲁棒性,适用于光场相机的全景深成像。 展开更多
关键词 多聚焦图像 图像融合 laws特征增强 极值策略
在线阅读 下载PDF
Integrating Factors and Conservation Laws of Herglotz Type for Birkhoffian Systems 被引量:1
17
作者 WANG Wenjing ZHANG Yi 《Wuhan University Journal of Natural Sciences》 2025年第1期49-56,共8页
The method of integrating factors is used to study the conservation laws of the Herglotz type Birkhoffian systems in this paper.Firstly,the definition of the integrating factors of the Herglotz type Birkhoffian system... The method of integrating factors is used to study the conservation laws of the Herglotz type Birkhoffian systems in this paper.Firstly,the definition of the integrating factors of the Herglotz type Birkhoffian systems is given.Secondly,the relationship between the integrating factors and conservation laws is studied,and the conservation theorems of Herglotz type Birkhoff's equations and their inverse theorems are established.Thirdly,two types of generalized Killing equations for calculating integrating factors are given.Finally,as an example,a linear damped oscillator is taken.This example can be transformed into a Herglotz type Birkhoffian system.The resulting conservation theorems are used to find the conserved quantities for this example. 展开更多
关键词 Birkhoffian system Herglotz's variational principle integrating factors conservation law
原文传递
Conservation Laws and Particular Solutions for a Keller-Segel Model
18
作者 Luyun Chen Jie Lou 《Advances in Pure Mathematics》 2025年第2期107-118,共12页
This work focuses on a Keller-Segel chemotaxis model, with an emphasis on its conservation laws. Through a new approach combined with the multiplier method, called the mixed method, we obtain conservation vectors that... This work focuses on a Keller-Segel chemotaxis model, with an emphasis on its conservation laws. Through a new approach combined with the multiplier method, called the mixed method, we obtain conservation vectors that are related and unrelated to symmetric information. In addition, some exact solutions with particular forms are obtained according to the method of conservation laws. These particular solutions are different from the group-invariant solutions. 展开更多
关键词 Keller-Segel Model Conservation laws Mixed Method Exact Solutions
在线阅读 下载PDF
Good Faith as a Compromise between Civil Law and Common Law Jurisdictions in the Legislative History of the CISG
19
作者 Jingchi Wen 《Proceedings of Business and Economic Studies》 2025年第4期19-24,共6页
There is a wide recognition that encompassing an obligation of good faith in every commercial contract is one of the most important advances in contract law in the twentieth century^([1]).Despite the fact that this co... There is a wide recognition that encompassing an obligation of good faith in every commercial contract is one of the most important advances in contract law in the twentieth century^([1]).Despite the fact that this concept has been incorporated in the vast majority of national legal systems,its precise scope and application may vary from one to another,depending on the commercial traditions and customs of each legal system^([2]).The fact that good faith has been treated differently in different national legal systems has also been reflected on the international level through its inclusion in international legal instruments,one of which is the United Nations Convention on Contracts for the International Sale of Goods(hereafter CISG).In this article,the legislative history of the CISG will be closely examined with the purpose of finding out how a compromise was reached between the common law countries,which expressly objected to the imposition of a duty of good faith,and the civil law countries,which explicitly endorse its incorporation.A logical result flowing from this historical examination,as will be submitted,is that the conceptual ambiguity of good faith is the underlying reasoning behind their fundamentally different attitudes towards the incorporation of this notion in the international commercial context. 展开更多
关键词 CISG International economic law Commercial law Good faith
在线阅读 下载PDF
Thermodynamic Energy-Laws Presuppose Time Orientation Subject to Principle of Least Action
20
作者 Helmut Tributsch 《Journal of Modern Physics》 2025年第2期310-327,共18页
It is shown that time asymmetry is essential for deriving thermodynamic law and arises from the turnover of energy while reducing its information content and driving entropy increase. A dynamically interpreted princip... It is shown that time asymmetry is essential for deriving thermodynamic law and arises from the turnover of energy while reducing its information content and driving entropy increase. A dynamically interpreted principle of least action enables time asymmetry and time flow as a generation of action and redefines useful energy as an information system which implements a form of acting information. This is demonstrated using a basic formula, originally applied for time symmetry/energy conservation considerations, relating time asymmetry (which is conventionally denied but here expressly allowed), to energy behaviour. The results derived then explained that a dynamic energy is driving time asymmetry. It is doing it by decreasing the information content of useful energy, thus generating action and entropy increase, explaining action-time as an information phenomenon. Thermodynamic laws follow directly. The formalism derived readily explains what energy is, why it is conserved (1st law of thermodynamics), why entropy increases (2nd law) and that maximum entropy production within the restraints of the system controls self-organized processes of non-linear irreversible thermodynamics. The general significance of the principle of least action arises from its role of controlling the action generating oriented time of nature. These results contrast with present understanding of time neutrality and clock-time, which are here considered a source of paradoxes, intellectual contradictions and dead-end roads in models explaining nature and the universe. 展开更多
关键词 Thermodynamic laws Newton’s Time Nature’s Time Entropy Increase IRREVERSIBILITY SELF-ORGANIZATION Least Action
在线阅读 下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部