Gaussian mixture model clustering with completed likelihood minimum message length criterion

An improved Gaussian mixture model （GMM）- based clustering method is proposed for the difficult case where the true distribution of data is against the assumed GMM. First, an improved model selection criterion, the completed likelihood minimum message length criterion, is derived. It can measure both the goodness-of-fit of the candidate GMM to the data and the goodness-of-partition of the data. Secondly, by utilizing the proposed criterion as the clustering objective function, an improved expectation- maximization （EM） algorithm is developed, which can avoid poor local optimal solutions compared to the standard EM algorithm for estimating the model parameters. The experimental results demonstrate that the proposed method can rectify the over-fitting tendency of representative GMM-based clustering approaches and can robustly provide more accurate clustering results.

Robustness of Minimum Norm Quadratic Unbiased Estimator of Variance Under the General Linear Model

Necessary and sufficient conditions for equalities between a 2 y′(I-P Xx)y and minimum norm quadratic unbiased estimator of variance under the general linear model, where a 2 is a known positive number, are derived. Further, when the Gauss? Markov estimators and the ordinary least squares estimator are identical, a relative simply equivalent condition is obtained. At last, this condition is applied to an interesting example.

Recursive weighted least squares estimation algorithm based on minimum model error principle

Kalman filter is commonly used in data filtering and parameters estimation of nonlinear system,such as projectile's trajectory estimation and control.While there is a drawback that the prior error covariance matrix and filter parameters are difficult to be determined,which may result in filtering divergence.As to the problem that the accuracy of state estimation for nonlinear ballistic model strongly depends on its mathematical model,we improve the weighted least squares method(WLSM)with minimum model error principle.Invariant embedding method is adopted to solve the cost function including the model error.With the knowledge of measurement data and measurement error covariance matrix,we use gradient descent algorithm to determine the weighting matrix of model error.The uncertainty and linearization error of model are recursively estimated by the proposed method,thus achieving an online filtering estimation of the observations.Simulation results indicate that the proposed recursive estimation algorithm is insensitive to initial conditions and of good robustness.

Estimation on principal component of multi-collinearity Gauss-Markov model based on minimum description length

Gauss-Markov model is frequently used in data analysis; the analysis and estimation of its parameters is always a hot issue. Based on the information theory and from the viewpoint of optimal information on description—minimum description length, this paper discusses a case: where there is multi-collinearity in the coefficient matrix, principal component estimation is used to estimate and select the original parameters, so as to reduce its multi-collinearity and improve its credibility. From the viewpoint of minimum description length, this paper discusses the approach of selecting principal components and uses this approach to solve a practical problem.

Minimum Description Length Methods in Bayesian Model Selection: Some Applications

Computations involved in Bayesian approach to practical model selection problems are usually very difficult. Computational simplifications are sometimes possible, but are not generally applicable. There is a large literature available on a methodology based on information theory called Minimum Description Length (MDL). It is described here how many of these techniques are either directly Bayesian in nature, or are very good objective approximations to Bayesian solutions. First, connections between the Bayesian approach and MDL are theoretically explored;thereafter a few illustrations are provided to describe how MDL can give useful computational simplifications.

Determination of the Minimum Wave Speed for the Modelling of Ventilated Cavitation

Ventilated cavitation plays an important role on the drag reduction of underwater vehicles and surface ships. For the modelling of ventilated cavitation, the minimum speed of the pressure wave is a crucial parameter for the closure of the pressure-density coupling relationship. In this study, the minimum wave speed is determined based on a theoretical model coupling the wave equation and the bubble interface motion equation. The influences of several paramount parameters （e.g., frequency, bubble radius and void fraction） on the minimum wave speed are quantitatively demonstrated and discussed. Compared with the minimum wave speed in the traditional cavitation, values for the ventilated cavitation are much higher. The physical mechanisms for the above difference are briefly discussed with the suggestions on the usage of the present findings.

Impacts of the Minimum Purchase Price Policy for Grain on the Planting Area of Rice in Hubei Province Based on a Mixed Linear Model

Impacts of the minimum purchase price policy for grain on the planting area of rice in Hubei Province were analyzed based on a mixed linear model.After the indicator system containing the minimum purchase price policy and other factors influencing the planting area of rice was constructed,principal component analysis of the system was conducted,and then a mixed linear model where the planting area of rice was as the dependent variable was established.The results show that after the exclusion of the interference from other factors,the minimum purchase price policy for grain had a positive impact on the planting area of rice in Hubei Province.That is,the minimum purchase price policy significantly stimulated the growth of rice planting area in Hubei Province.

Calculation and Evaluation of Ecological Flow of Hydropower Station Based on Fuzzy Evaluation Model

The reasonable determination of ecological flow is of great significance for the efforts to promote the transformation of water ecological environmental protection from pollution management to synergistic management of water resources,water ecology and water environment,and to promote them in an integrated manner.This paper analyzed and calculated the ecological flow process of the Bangsha River diversion power station using the minimum ecological flow method,the annual spreading method,the improved annual spreading method,the NGPRP method,and the month-by-month frequency method,and evaluated the reasonableness of the process and results of the ecological flow calculations by using the fuzzy evaluation model established.The study showed that the minimum ecological flow rate determined by improving the coupling of the spreading method and the NGPRP method was the best,and the suitable ecological flow rate determined by the month-by-month frequency method was the best;the minimum ecological flow rate of the Bangsha River diversion power station was at 0.43-4.21 m 3/s,and the suitable ecological flow rate was at 0.56-4.94 m 3/s,and the trend of its change showed the trend of first increasing and then decreasing,and the trend of change from January to July showed the trend of first increasing and then decreasing.Its trend of change showed an increasing and then decreasing trend,from January to July showed a gradually increasing trend,from August to December showed a gradually decreasing trend.It aimed to provide a theoretical basis for the reasonable determination of the ecological flow of the river hydropower station.

最低刑龄制度应对未成年人犯罪的困境与出路——由“邯郸13岁男孩被害案”引发的思考

2024年3月10日河北省邯郸市发生一起3名未满14周岁的未成年人故意杀人案件,引发了社会各界的广泛关注和强烈反响。舆论焦点从传统的“未龄不责”,逐渐转向了“低龄轻责”和“未龄免死”等问题。对舆论意见体现出的在最低刑龄制度应对未成年人犯罪时存在的价值冲突,需要在理论层面进行深入探讨,也需要考虑我国特有的历史文化传统。在理论层面,首先,刑事责任年龄的设定是一种对身份的法律拟制,必然引发同一性和差异性的矛盾;其次,公众对于“未龄轻责”和“未龄免死”的不满,很大程度上源于报应心理。然而,报应主义与未成年人特殊保护原则之间存在着天然的矛盾。此外,网络舆论导向的修法可能会引发刑法谦抑性危机。如何通过制度设计来维持刑罚量配置的均衡,以保证刑法的谦抑性,即是刑事责任年龄制度所面临的难题。在我国历史上,“恤幼”思想源远流长,影响着我国古代的立法,即使在重刑时代,其也优先于报应主义的思想。在制度设计上,从汉代开始,我国古代传统法中对刑事责任年龄的规定就体现出了相对弹性的模式,这种立法模式能够在一定程度上弥补法律拟制的缺陷。此外,自唐代起开始适用的“列举罪名+划定法定刑”罪行分级模式具有体系化和精确化的优势,也能够为最低刑龄制度的完善方向提供参考。从实践层面看,构建最低刑龄制度的路径可以从以下几个方面展开:第一,需要从过于刚性的“唯年龄论”转变为更加相对弹性的立法模式,以弥补法律拟制所导致的立法空缺。第二,现在立法中存在对相似案件处罚不均衡的情况,对此,应当缩小因年龄差异而导致的处罚差距,尽可能确保罪罚均衡。同时,还应当坚定对未成年人特殊保护的立场,放宽对未成年人减刑的限制,进一步完善专门矫治教育制度,与刑法形成良好的衔接。第三,采用系统化的罪行分级方式,以法定最高刑为罪行分级的界限标准,建立更为严密的法网,防止处罚范围的过度扩张。

基于组合赋权与灰云模型的综合能源系统需求响应效益评价

考虑到当前综合能源系统研究缺乏完善的需求响应量化评估方案,难以在优化运行层面综合评估需求响应效益这一问题,提出了一种基于改进AHP群决策—CRITIC组合赋权与灰云模型的综合能源系统需求响应效益评价方法。首先,从综合能效性、社会经济性和需求侧互动性三个维度构建了需求响应效益评价指标体系。其次,采用一致性和权重拟合性更优的指数标度法构造判断矩阵,降低赋值误差,并通过AHP群决策法确定主观权重,从而削弱主观极值偏差对权重的影响;在由CRITIC法确定客观权重后,基于最小欧氏距离建立组合权重模型,并通过非线性规划求取最优组合权重;针对评价等级信息的模糊性与隶属等级的随机性,采用正态灰云白化权模型确定指标分类等级与场景评分。最后,以北方某综合能源系统为例,根据用户参与需求响应方式设置了4种运行场景,分析了不同需求响应对系统运行的影响与作用,算例结果表明所提指标体系与评价方法科学有效。

考虑边界约束影响的充填挡墙厚度确定方法及应力分布规律研究

不合理的边界加固方式会导致充填过程中挡墙边缘抗弯能力弱化进而影响采场安全。基于此,为了确定合理的充填挡墙厚度,探讨边界约束对充填挡墙稳定性的影响,将挡墙结构简化为4类薄板模型。以第一强度准则为判断依据,提出了不同边界约束模式下充填挡墙厚度确定方法。结合大冶铁矿工程实际,探讨了不同边界约束模式下充填挡墙应力分布规律,并通过解析几何和数值模拟对本文理论模型进行了验证。研究结果表明:①挡墙最小厚度与充填高度、充填料浆容重呈正相关关系,与挡墙抗拉强度呈负相关关系,增加挡墙抗拉强度有利于挡墙稳定性;②挡墙内外侧拉伸应力分布存在明显差异,外侧呈X型分布,内侧呈O型分布,边界抗弯能力弱化会导致拉伸区域拓展,增加挡墙边界弯矩可以有效防止挡墙破坏;③数值模拟获取的应力分布规律与解析几何分析结果高度一致,进一步验证了本文充填挡墙厚度确定方法的可靠性,结果可为类似采场充填挡墙参数优化提供参考。

基于生态网络的黄河上游(四川段)水源涵养生态安全格局构建

在对黄河上游四川段水源涵养功能及修复潜力评估的基础上,利用形态学空间格局分析法(MSPA)识别黄河上游四川段生态源地,运用最小累积阻力模型识别生态廊道.结果表明:整个研究区水源涵养能力由南至北逐渐降低,水源涵养修复潜力等级高的区域主要分布在研究区域北部;MSPA识别的核心区主要位于若尔盖县和石渠县,占总面积的44.04%,形成由3个等级的生态源地和3个等级的生态廊道组成的黄河上游四川段生态安全格局;整个生态网络均集中于研究区中北部,东西部和南部生态网络分布较少.基于生态网络进行生态安全格局的构建,可为黄河上游四川段水源涵养生态修复布局提供重要依据.

基于生态安全格局的资源枯竭型城市生态保护修复关键区识别:以徐州市贾汪区为例

科学构建生态安全格局、识别生态保护修复关键区是系统推进生态修复目标,实现资源枯竭型城市绿色转型发展和生态安全的基本保障与重要途径。本文以东部典型资源枯竭型城市徐州市贾汪区为例,通过定量评估土壤保持、碳存储、生境质量、产水量和固碳释氧五种生态系统服务功能变化,分析了绿色转型中的贾汪区生态修复治理成效。在此基础上,基于热点分析、最小累计阻力模型和电路理论等方法,识别了生态源地、生态廊道、生态“夹点”、障碍区等生态安全格局要素,分析了2000—2020年生态安全格局及其动态变化,并识别生态保护修复关键区域。研究结果表明:①2000—2020年贾汪区生态系统服务总体呈增加趋势,生态环境逐步得到改善,生态源地斑块数量逐渐减少但总面积持续增加,廊道分布由“西多东少”转变为“较为均衡”的格局。②确定生态保护修复关键区包括重要生态源地10处,重要生态廊道39处,障碍修复关键区5.53 km^(2),廊道保护关键区1.70 km^(2),多位于主城区西南部和潘安湖南部生态流动强度高且廊道狭窄处,应加强重点修复和保护。③根据生态保护修复关键区覆被类型,建议重要生态源地树立红线观念、加强生态用地和非生态用地有效连接、拓宽生态廊道范围、增加廊道沿线植被恢复等保护修复策略。研究结果可为资源枯竭型城市的生态修复规划确定优先修复事项提供有效技术支撑。

内啮合同曲率圆柱密封面泄漏评估方法

针对高压介质的金属密封问题,利用有限元分析方法得到圆柱面分析模型,以密封面接触应力、理论接触面积为输入参数,得到不同过盈量下密封面的真实接触面积,结合修正后的微观泄漏计算模型,研究不同曲率圆柱密封面泄漏规律。研究表明:随着圆环过盈量增加到0.04 mm,密封面产生稳定接触,泄漏量不再随着过盈量而发生变化,密封性能满足最小密封比压要求。该预测方法以密封面平均接触压力为唯一变量,可以对不同啮合方式的任意尺寸圆柱密封面泄漏量进行预测,计算泄漏率与实验数据,验证了模型的准确性,对金属高压密封设计和评估具有重要意义。

煤矿井下金属结构等效储能模型耦合电磁波能量安全性分析

煤矿井下无线通信设备发射的电磁波能量可以被周围金属结构耦合吸收,这种现象存在点燃矿井内爆炸性气体的危险。现有针对井下金属结构耦合电磁波安全性研究只是对金属结构等效阻性模型耦合电磁波能量进行分析,缺乏对金属结构耦合电磁波能量在时间上积累的储能过程研究。针对上述问题,提出一种适用于金属结构耦合−积累−释放电磁波能量研究的等效储能结构模型,即金属结构等效容性储能模型与金属结构等效感性储能模型。首先通过低衰减度传输线模型,推导出发射天线输出功率、发射天线与金属结构之间距离与接收端感应电压之间的关系。然后建立金属结构等效储能模型,推导出接收端参数与放电火花能量之间的数学关系式,分析了接收端参数对放电火花能量的影响。最后通过接收端感应电压与感应电压有效值的关系,推导出发射天线输出功率、发射天线与金属结构之间距离与放电火花能量之间的数学关系式,分析了发射天线输出功率、发射天线与金属结构之间距离对放电火花能量的影响,并给出在其他参数确定情况下2种金属结构等效储能模型各自的理论参考安全点。仿真结果表明:①对于金属结构等效容性储能模型,放电火花能量随着等效储能电容、接收端感应电压有效值增大而增大,安全点向左偏移,对等效储能电容、接收端感应电压有效值的安全要求变得严苛。②放电火花能量随着发射天线功率增大而增大,随着发射天线与金属结构之间距离增大而减小,得到金属结构等效容性储能模型理论参考安全点。③对于金属结构等效感性储能模型,放电火花能量随着等效储能电感、接收端感应电压有效值增大而增大,安全点向左偏移,对等效储能电感、接收端感应电压有效值的安全要求变得严苛。④放电火花能量随着发射天线功率增大而增大,随着发射天线与金属结构之间距离增大而减小,得到金属结构等效感性储能模型理论参考安全点。⑤对比2种金属结构储能模型理论参考安全点,得到金属结构等效容性储能模型的危险性远大于金属结构等效感性储能模型的结论。

基于综合赋权与云熵优化的园区综合能源系统评价

综合能源系统(integrated energy system,IES)作为能源转型中的重要环节已得到越来越多国家的广泛关注。构建一套匹配中国国情的综合能源系统评价体系和评价方法不仅能够为综合能源系统规划后评价打下基础,以此对规划方案进行优劣排序;还能够提高综合能源系统项目的管理水平,在制定统一、完整的综合能源系统综合评价标准时提供参考。为此,首先结合园区IES基本特征以及运行特性,构建包含经济性、可靠性、环保性以及智能友好性4个方面的综合评价指标体系;然后为解决IES在运行中的不确定性问题,对基于传统云物元模型的综合评价体系提出云熵优化,即考虑不同评价者对模糊性的可接受程度;为解决单一赋权方法可能导致的评价结果过于主观或过于客观的问题,选择基于最小鉴别信息原理将决策实验室法与熵权法相结合的综合赋权法,并采用变权法进一步完善综合评价指标;最后通过算例分析,验证所提综合评价体系的科学正确性。

原油价格不确定性测度及其对宏观经济的非对称影响研究

有效测度原油价格不确定性并研究其对我国宏观经济的影响,具有重要的理论和现实意义。本文基于最小生成树模型,从全局视角衡量原油多元定价机制中195个影响因素的相对重要程度,并采用高维因子非预期条件波动率模型测度国际原油价格的不确定性。基于收敛交叉映射模型,本文对原油价格不确定性与宏观经济间的非线性因果关系进行识别,研究发现仅存在原油价格不确定性对固定资产投资、产出增速的单向因果关系。进一步地,在厘清原油价格不确定性对宏观经济影响机制的基础上,利用包含马尔可夫区制转移特征的向量自回归模型考察原油价格不确定性对我国宏观经济的影响,理论与实证结果均表明原油价格不确定性对我国宏观经济具有显著负向影响;在不同经济状态下,原油价格不确定性对投资、产出增速的影响具有非对称性。本研究为有效防范原油市场风险、保障能源安全和推动经济稳定增长提供了理论支持。

砂-粉混合料颗粒接触状态的临界条件确定

砂-粉混合料被广泛应用于高速铁路路基、人工筑岛及海底沉管隧道垫层等重大工程,如何科学地表征砂-粉混合料复杂的颗粒接触状态及连续演变的力学行为特征,并深入揭示其对混合料静/动力学特性的影响已是一项紧迫的基础性科学研究任务。本文基于代表性砂-粉混合料的基本物理性能指标及力学特性指标试验数据,验证Rahman等提出的区分“细粒填充砂粒”和“砂粒悬浮细粒”的阈值细粒含量FCth半经验公式预测能力。基于理想二元介质材料的理论最小孔隙比计算方法,提出确定中间性态土颗粒接触状态临界条件参量FC_(in-min)和FC_(in-max)的方法,分析各参数对FC_(in-min)和FC_(in-max)的影响规律,建立基于基本物理性能指标的FC_(in-min)和FC_(in-max)预测方法,最终提出全FC范围(FC=0~100%)的砂-粉混合料各颗粒接触状态临界条件参量的有效评价方法。

基于组合基元法的非理想模型装配偏差预测算法研究

基于模型定义(model-based definition,MBD)体系的装配偏差算法适用于赛博空间中理想数模的装配场景,但不适用于物理空间中非理想状态的装配场景,导致现场产生大量修配工作。针对这一问题,文章模拟真实的装配场景,基于零件的非理想状态,并将配合特征之间的拓扑关系考虑在内,对装配偏差的传递与累积过程展开研究,给出一种装配偏差预测算法。首先,针对孔轴配合与槽轴配合,将装配约束转化为定位点约束,依据最大实体原则,构造柱面点云的最小包围圆,确定接触状态,给出串行装配偏差算法,并将以上两种配合定义为两种基元,对应的装配偏差算法定义为两种独立基元算法。其次,基于平面贴合、孔轴配合与槽轴配合给出并行装配偏差算法,并将其定义为组合基元算法。最后,基于非理想模拟数据进行实例验证,达到了准确预测装配偏差的目标,为后续在赛博空间基于实测数据的装配偏差计算提供理论依据,以促进高精度装配。

基于米特-霍恩模型破解城市最低生活保障政策执行困境

城市最低生活保障制度作为保障基本民生的一项基础性制度安排,在治理城市贫困的进程中发挥关键作用。文章基于米特-霍恩模型分析框架对我国城市低保政策执行进行系统分析,研究发现城市低保政策执行过程存在着政策目标瞄准偏差、目标功能异化、标准偏低、资源投入不足、组织间沟通与执行方式欠缺、执行机构力量薄弱、环境条件不充分以及执行者偏好不同等现实困境,据此从重新审视标准与目标、促进组织间交流与执行方式转型创新、增强执行机构力量与部门衔接、营造政策执行的良好环境、引导政策执行者价值取向等方面提出完善城市低保政策执行的优化路径。