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基于改进YOLOv7的交通信号灯检测
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作者 郑岚月 张玉洁 《系统仿真学报》 北大核心 2025年第4期993-1007,共15页
针对通用物体检测算法在信号灯检测方面存在着识别精度较低的问题,提出一种专门针对交通信号灯检测任务的改进的YOLOv7算法。去掉20×20检测尺度,添加160×160的检测尺度,在使模型轻量化的同时增加浅层特征;结合BiFormer中提出... 针对通用物体检测算法在信号灯检测方面存在着识别精度较低的问题,提出一种专门针对交通信号灯检测任务的改进的YOLOv7算法。去掉20×20检测尺度,添加160×160的检测尺度,在使模型轻量化的同时增加浅层特征;结合BiFormer中提出的BRA(bi-level routing attention)与坐标轴注意力,针对交通信号灯位置特点提出了ABRA(axially-guided BRA);针对IoU指标对物体尺寸敏感的问题,引入NWD(normalized wasserstein distance)度量,改进物体定位损失与置信度损失。实验结果表明:改进YOLOv7算法的mAP值达到了97.7%,比原始YOLOv7提高了11.4%,检测速度提升了90帧/s,计算复杂度降低了4.5%。 展开更多
关键词 交通信号灯检测 注意力机制 BiFormer NWD(normalized wasserstein distance) YOLOv7
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Normalized Solutions of Nonlinear Choquard Equations with Nonconstant Potential
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作者 LI Nan XU Liping 《应用数学》 北大核心 2025年第1期14-29,共16页
In this paper,we mainly focus on a type of nonlinear Choquard equations with nonconstant potential.Under appropriate hypotheses on potential function and nonlinear terms,we prove that the above Choquard equation with ... In this paper,we mainly focus on a type of nonlinear Choquard equations with nonconstant potential.Under appropriate hypotheses on potential function and nonlinear terms,we prove that the above Choquard equation with prescribed 2-norm has some normalized solutions by introducing variational methods. 展开更多
关键词 Nonlinear Choquard equation Potential function Variational method Normalized solution
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Normalized Positive Ground State Solutions for Nonhomogeneous Kirchhoff Equations
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作者 ZHANG Xiaocang XU Liping 《应用数学》 北大核心 2025年第3期711-720,共10页
This article studies a class of nonlinear Kirchhoff equations with exponential critical growth,trapping potential,and perturbation.Under appropriate assumptions about f and h,the article obtained the existence of norm... This article studies a class of nonlinear Kirchhoff equations with exponential critical growth,trapping potential,and perturbation.Under appropriate assumptions about f and h,the article obtained the existence of normalized positive solutions for this equation via the Trudinger-Moser inequality and variational methods.Moreover,these solutions are also ground state solutions.Additionally,the article also characterized the asymptotic behavior of solutions.The results of this article expand the research of relevant literature. 展开更多
关键词 Normalized positive ground state solution Nonhomogeneous Kirchhoff equation Variational method Exponential critical growth Trapping potential
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Study on Color Difference of Color Reproduction of 3D Objects
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作者 GU Chong DENG Yi-qiang 《印刷与数字媒体技术研究》 北大核心 2025年第4期33-38,69,共7页
To investigate the applicability of four commonly used color difference formulas(CIELAB,CIE94,CMC(1:1),and CIEDE2000)in the printing field on 3D objects,as well as the impact of four standard light sources(D65,D50,A,a... To investigate the applicability of four commonly used color difference formulas(CIELAB,CIE94,CMC(1:1),and CIEDE2000)in the printing field on 3D objects,as well as the impact of four standard light sources(D65,D50,A,and TL84)on 3D color difference evaluations,50 glossy spheres with a diameter of 2cm based on the Sailner J4003D color printing device were created.These spheres were centered around the five recommended colors(gray,red,yellow,green,and blue)by CIE.Color difference was calculated according to the four formulas,and 111 pairs of experimental samples meeting the CIELAB gray scale color difference requirements(1.0-14.0)were selected.Ten observers,aged between 22 and 27 with normal color vision,were participated in this study,using the gray scale method from psychophysical experiments to conduct color difference evaluations under the four light sources,with repeated experiments for each observer.The results indicated that the overall effect of the D65 light source on 3D objects color difference was minimal.In contrast,D50 and A light sources had a significant impact within the small color difference range,while the TL84 light source influenced both large and small color difference considerably.Among the four color difference formulas,CIEDE2000 demonstrated the best predictive performance for color difference in 3D objects,followed by CMC(1:1),CIE94,and CIELAB. 展开更多
关键词 Color difference formula 3D objects Light source Gray scale Normalized residual sum of squares
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Rate-frequency dependent shear behavior of rough rock joint experiencing normal load oscillations
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作者 DANG Wen-gang LI Xing-ling +1 位作者 TAO Kang FU Jin-yang 《Journal of Central South University》 2025年第5期1873-1886,共14页
Dynamic disturbances certainly reduce shear strength of rock joints,yet the mechanism needs deeper explanation.We investigate the shear behavior of a rough basalt joint by conducting laboratory shear experiments.Const... Dynamic disturbances certainly reduce shear strength of rock joints,yet the mechanism needs deeper explanation.We investigate the shear behavior of a rough basalt joint by conducting laboratory shear experiments.Constant and superimposed oscillating normal loads are applied at the upper block.Meanwhile,the bottom block moves at a constant shear rate.We investigate the shear behavior by:1)altering the normal load oscillation frequency with a same shear rate,2)altering the shear rate with a same normal load oscillation frequency,and 3)altering the normal load oscillation frequency and shear rate simultaneously with a constant ratio.The results show that the oscillating normal load reduces the coefficient of friction(COF).The reduce degree of COF increases with higher shear rate,decreases when increasing normal load oscillation frequency,and keeps constant if the special ratio,v/f(shear rate divided by normal oscillation frequency),is constant.Moreover,we identify a time lag between peak normal load and peak shear load.And the lagging proportion increases with higher shear rate,and decreases with larger static COF.Our results imply that a lower creep rate with a higher normal load oscillation frequency easily destabilizes the creeping fault zones. 展开更多
关键词 normal load oscillation shear rate oscillation frequency friction reduction time lag
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Nonparametric Estimation of the Trend Function for Stochastic Processes Driven by Fractional Brownian Motion of the Second Kind
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作者 WANG Yihan ZHANG Xuekang 《应用数学》 北大核心 2024年第4期885-892,共8页
The present paper deals with the problem of nonparametric kernel density estimation of the trend function for stochastic processes driven by fractional Brownian motion of the second kind.The consistency,the rate of co... The present paper deals with the problem of nonparametric kernel density estimation of the trend function for stochastic processes driven by fractional Brownian motion of the second kind.The consistency,the rate of convergence,and the asymptotic normality of the kernel-type estimator are discussed.Besides,we prove that the rate of convergence of the kernel-type estimator depends on the smoothness of the trend of the nonperturbed system. 展开更多
关键词 Nonparametric estimation Fractional Brownian motion Uniform consistency Asymptotic normality
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Schur Forms and Normal-Nilpotent Decompositions 被引量:1
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作者 LI Zhen 《应用数学和力学》 CSCD 北大核心 2024年第9期1200-1211,共12页
Real and complex Schur forms have been receiving increasing attention from the fluid mechanics community recently,especially related to vortices and turbulence.Several decompositions of the velocity gradient tensor,su... Real and complex Schur forms have been receiving increasing attention from the fluid mechanics community recently,especially related to vortices and turbulence.Several decompositions of the velocity gradient tensor,such as the triple decomposition of motion(TDM)and normal-nilpotent decomposition(NND),have been proposed to analyze the local motions of fluid elements.However,due to the existence of different types and non-uniqueness of Schur forms,as well as various possible definitions of NNDs,confusion has spread widely and is harming the research.This work aims to clean up this confusion.To this end,the complex and real Schur forms are derived constructively from the very basics,with special consideration for their non-uniqueness.Conditions of uniqueness are proposed.After a general discussion of normality and nilpotency,a complex NND and several real NNDs as well as normal-nonnormal decompositions are constructed,with a brief comparison of complex and real decompositions.Based on that,several confusing points are clarified,such as the distinction between NND and TDM,and the intrinsic gap between complex and real NNDs.Besides,the author proposes to extend the real block Schur form and its corresponding NNDs for the complex eigenvalue case to the real eigenvalue case.But their justification is left to further investigations. 展开更多
关键词 Schur form normal matrix nilpotent matrix tensor decomposition vortex identification
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Shear mechanical properties and frictional sliding responses of rough joint surfaces under dynamic normal displacement conditions 被引量:1
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作者 ZHU Qiang YIN Qian +9 位作者 TAO Zhi-gang HE Man-chao ZHENG Bo-wen JING Hong-wen REN Shu-lin ZHANG Qiang MENG Bo BAI Dong-feng WU Sai-sai WU Jiang-yu 《Journal of Central South University》 SCIE EI CAS CSCD 2024年第7期2393-2410,共18页
A comprehensive understanding of the dynamic frictional characteristics in rock joints under high normal load and strong confinement is essential for ensuring the safety of deep engineering construction and mitigating... A comprehensive understanding of the dynamic frictional characteristics in rock joints under high normal load and strong confinement is essential for ensuring the safety of deep engineering construction and mitigating geological disasters.This study conducted shear experiments on rough rock joints under displacement-controlled dynamic normal loads,investigating the shear behaviors of joints across varying initial normal loads,normal loading frequencies,and normal loading amplitudes.Experimental results showed that the peak/valley shear force values increased with initial normal loads and normal loading frequencies but showed an initial increase followed by a decrease with normal loading amplitudes.Dynamic normal loading can either increase or decrease shear strength,while this study demonstrates that higher frequencies lead to enhanced friction.Increased initial normal loading and normal loading frequency result in a gradual decrease in joint roughness coefficient(JRC)values of joint surfaces after shearing.Positive correlations existed between frictional energy dissipation and peak shear forces,while post-shear joint surface roughness exhibited a negative correlation with peak shear forces through linear regression analysis.This study contributes to a better understanding of the sliding responses and shear mechanical characteristics of rock joints under dynamic disturbances. 展开更多
关键词 dynamic normal displacement shear strength variations phase lag phenomenon STICK-SLIP
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基于Copula函数和风速正交分量的风矢量联合概率密度研究 被引量:1
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作者 程正兵 冀骁文 《计算力学学报》 CAS CSCD 北大核心 2024年第5期942-947,共6页
准确地表示风矢量联合概率密度对于风能的评估和风机结构设计具有重要意义,本文将围绕提升风矢量联合概率密度表示结果准确性展开研究。首先,将风矢量表示为风速正交分量,采用混合Normal分布分别对边缘概率密度进行表示,并提出了估计混... 准确地表示风矢量联合概率密度对于风能的评估和风机结构设计具有重要意义,本文将围绕提升风矢量联合概率密度表示结果准确性展开研究。首先,将风矢量表示为风速正交分量,采用混合Normal分布分别对边缘概率密度进行表示,并提出了估计混合Normal分布参数的方法。然后,基于Copula函数考虑风速正交分量间的相关性,从而得到二者的联合概率密度,其中Copula参数通过最小二乘法估计,紧接着通过雅可比变换得到风矢量联合概率密度。最后,采用印度风能研究所的测点S3和S7的每小时平均风速和风向数据,与以往基于Copula函数和风速、风向变量得到的风矢量联合概率密度结果进行对比。结果表明,与以往方法相比,所提方法得到的风矢量联合概率密度结果准确性有很大的提升,本文可为风能的开采和利用提供理论依据。 展开更多
关键词 COPULA函数 正交分解 风矢量 联合概率密度 混合Normal
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主动脉缩窄后远端扩张可能性的血流动力学分析
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作者 吴嘉慧 陈端端 鲁亦凡 《医用生物力学》 CAS CSCD 北大核心 2024年第S01期258-258,共1页
目的动脉缩窄后远端扩张(PSD)是指在主动脉缩窄(COA)下游区域发生的局部扩张。已有研究分析主动脉缩窄后远端扩张的形成机制。然而,血流动力学的变化如何作用于血管壁使得PSD发生还需要进一步的探讨。本研究的主要目的是利用一系列不同... 目的动脉缩窄后远端扩张(PSD)是指在主动脉缩窄(COA)下游区域发生的局部扩张。已有研究分析主动脉缩窄后远端扩张的形成机制。然而,血流动力学的变化如何作用于血管壁使得PSD发生还需要进一步的探讨。本研究的主要目的是利用一系列不同缩窄和扩张程度下的COA和PSD模型揭示主动脉缩窄后远端扩张处的血流动力学差异,评估PSD的发生可能性和破裂风险。方法计算机断层扫描重建正常人主动脉(Normal)。为了分析PSD形成后的血流动力学差异,修改缩窄或(和)扩张区域获得COA和PSD模型。进行血流动力学模拟,计算出动压、涡度、横向壁面剪切应力(Trans WSS)等血流动力学参数。通过修改最小缩窄径、缩窄长度、最大扩张径获得不同缩窄和扩张程度的COA和PSD模型,评估不同程度COA和PSD患者远端(再)扩张的风险。结果高动压、高涡度和高Trans WSS出现并聚集在COA缩窄段远端的凸侧,且在PSD中均有所缓解。动压、涡度、横向壁面剪切应力在远端的均值的顺序均为:COA>PSD>Normal。最小缩窄径越小,均值越大。而不同缩窄长度的均值相差不大。结论缩窄段远端的凸侧受异常血流动力学的影响最大,是扩张形成的主要区域,其受到的高动压、高涡度和高Trans WSS是远端(再)扩张的风险因素。最小缩窄径越小,远端(再)扩张的风险越大。 展开更多
关键词 作用于血管 主动脉缩窄 血流动力学参数 扩张程度 远端的 计算机断层扫描 壁面剪切应力 NORMAL
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Normal mouse serum alleviates radiation pneumonitis in mice by inhibiting the focal adhesion signaling pathway
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作者 YUAN Tong GUO Yuying +1 位作者 ZHANG Junling FAN Saijun 《南方医科大学学报》 CAS CSCD 北大核心 2024年第5期801-809,共9页
Objective To evaluate the therapeutic effect of normal mouse serum on radiation pneumonitis in mice and explore the possible mechanism.Methods Mouse models of radiation pneumonitis induced by thoracic radiation exposu... Objective To evaluate the therapeutic effect of normal mouse serum on radiation pneumonitis in mice and explore the possible mechanism.Methods Mouse models of radiation pneumonitis induced by thoracic radiation exposure were given intravenous injections of 100μL normal mouse serum or normal saline immediately after the exposure followed by injections once every other day for a total of 8 injections.On the 15th day after irradiation,histopathological changes of the lungs of the mice were examined using HE staining,the levels of TNF-α,TGF-β,IL-1αand IL-6 in the lung tissue and serum were detected using ELISA,and the percentages of lymphocytes in the lung tissue were analyzed with flow cytometry.High-throughput sequencing of exosome miRNA was carried out to explore the changes in the signaling pathways.The mRNA expression levels of the immune-related genes were detected by qRT-PCR,and the protein expressions of talin-1,tensin2,FAK,vinculin,α-actinin and paxillin in the focal adhesion signaling pathway were detected with Western blotting.Results In the mouse models of radiation pneumonitis,injections of normal mouse serum significantly decreased the lung organ coefficient,lowered the levels of TNF-α,TGF-β,IL-1αand IL-6 in the serum and lung tissues,and ameliorated infiltration of CD45^(+),CD4^(+)and Treg lymphocytes in the lung tissue(all P<0.05).The expression levels of Egfr and Pik3cd genes at both the mRNA and protein levels and the protein expressions of talin-1,tensin2,FAK,vinculin,α‑actinin and paxillin were all significantly down‑regulated in the mouse models after normal mouse serum treatment.Conclusion Normal mouse serum ameliorates radiation pneumonitis in mice by inhibiting the expressions of key proteins in the Focal adhesion signaling pathway. 展开更多
关键词 normal mouse serum radiation pneumonitis EXOSOMES focal adhesion pathway
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Exact MAX tests in genetic association analysis
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作者 Yi Li Jianan Tian +2 位作者 Chenliang Xu Yaning Yang Min Yuan 《中国科学技术大学学报》 CSCD 北大核心 2024年第12期33-38,I0005,I0009,共8页
The three common genetic models(or modes of inheritance)in association analysis are the dominant,additive,and recessive models.It is known that the Cochran-Armitage trend test(CATT)which correctly incorporates informa... The three common genetic models(or modes of inheritance)in association analysis are the dominant,additive,and recessive models.It is known that the Cochran-Armitage trend test(CATT)which correctly incorporates information from genetic models,is more powerful than the commonly used Pearson’s chi-square test.However,the true genetic model is usually unknown in practice,and the power of the CAT test could be substantially reduced with a wrongly specified genetic model.To achieve a power that is close to that of a correctly specified CAT test,it is natural to apply trend tests under different possible genetic models and to report the most significant test result.This results in a MAX-type testing procedure,and it was found that this test is usually more powerful than the Pearson’s chi-square test.Although the signi-ficance(i.e.,p value)of the MAX-type test can be accessed by either large sample approximation or permutation methods,requirements for sample size or simulation replicates are demanding with respect to accuracy and efficiency.This paper proposes an approach to calculate the exact p values of MAX-type tests based on the combinatorial counting method.The simulation results show that the exact method is more accurate than the large sample approximation methods and more computationally efficient than the permutation method,and our method can be readily applied to genome-wide association studies(GWASs).The proposed methodis built in an R package,MaXact,which is available at the https://github.com/Myuan 2019/MaXact/. 展开更多
关键词 exact test MAX test normal approximation PERMUTATION
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Improved Berry-Esseen Bound for Rademacher Sum
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作者 MA li YE Liu HAN Xin-Fang 《应用概率统计》 CSCD 北大核心 2024年第6期910-941,共32页
Let X=Σ_(i=1)^(n)a_(i)ξ_(i)be a Rademacher sum with Var(X)=1 and Z be a standard normal random variable.This paper concerns the upper bound of|P(X≤x)−P(Z≤x)|for any x∈R.Using the symmetric properties and R softwa... Let X=Σ_(i=1)^(n)a_(i)ξ_(i)be a Rademacher sum with Var(X)=1 and Z be a standard normal random variable.This paper concerns the upper bound of|P(X≤x)−P(Z≤x)|for any x∈R.Using the symmetric properties and R software,this paper gets the following improved Berry-Esseen type bound under some conditions,|P(X≤x)−P(Z≤x)|≤P(Z∈(0,a1)),∀x∈R,which is one of the modified conjecture proposed by Nathan K.and Ohad K. 展开更多
关键词 sum of i.i.d.random variables standard normal distribution QUANTILE Berry-Esseen upper bound
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Improvement of large-scale-region landslide susceptibility mapping accuracy by transfer learning
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作者 ZHANG Wen-gang LIU Song-lin +3 位作者 WANG Lu-qi SUN Wei-xin ZHANG Yan-mei NIE Wen 《Journal of Central South University》 CSCD 2024年第11期3823-3837,共15页
Machine-learning methodologies have increasingly been embraced in landslide susceptibility assessment.However,the considerable time and financial burdens of landslide inventories often result in persistent data scarci... Machine-learning methodologies have increasingly been embraced in landslide susceptibility assessment.However,the considerable time and financial burdens of landslide inventories often result in persistent data scarcity,which frequently impedes the generation of accurate and informative landslide susceptibility maps.Addressing this challenge,this study compiled a nationwide dataset and developed a transfer learning-based model to evaluate landslide susceptibility in the Chongqing region specifically.Notably,the proposed model,calibrated with the warmup-cosine annealing(WCA)learning rate strategy,demonstrated remarkable predictive capabilities,particularly in scenarios marked by data limitations and when training data were normalized using parameters from the source region.This is evidenced by the area under the receiver operating characteristic curve(AUC)values,which exhibited significant improvements of 51.00%,24.40%and 2.15%,respectively,compared to a deep learning model,in contexts where only 1%,5%and 10%of data from the target region were used for retraining.Simultaneously,there were reductions in loss of 16.12%,27.61%and 15.44%,respectively,in these instances. 展开更多
关键词 data-limited cases transfer learning landslide susceptibility machine learning normalization based on the parameters of the source domain
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基于分水岭变换和图论的图像分割方法 被引量:28
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作者 冯林 孙焘 +1 位作者 吴振宇 管慧娟 《仪器仪表学报》 EI CAS CSCD 北大核心 2008年第3期649-653,共5页
提出了一种融合分水岭变换和图论的图像分割方法。利用图像的局部灰度信息进行分水岭变换后,将图像分割成多个小区域,再结合各小区域的灰度和空间信息从全局角度用Normalized Cut方法在区域之间进行分割,产生最终的分割结果。实验结果表... 提出了一种融合分水岭变换和图论的图像分割方法。利用图像的局部灰度信息进行分水岭变换后,将图像分割成多个小区域,再结合各小区域的灰度和空间信息从全局角度用Normalized Cut方法在区域之间进行分割,产生最终的分割结果。实验结果表明,该方法可以消除分水岭变换后所产生的过分割现象,是一种有效的图像自动分割方法。 展开更多
关键词 图像分割 分水岭 图论 Normalized CUT
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考虑风电功率条件相关性的广义椭球不确定集合建模 被引量:17
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作者 吴巍 汪可友 +1 位作者 李国杰 葛延峰 《中国电机工程学报》 EI CSCD 北大核心 2017年第9期2500-2506,共7页
近年来,鲁棒优化在电力系统优化调度领域取得了优良的效果。鲁棒优化的一个关键问题是确定风电功率不确定集合,而现有方法难以依据最新风电功率预测信息更新不确定集合。针对这一问题,该文基于条件copula copula模型,构建考虑风电功率... 近年来,鲁棒优化在电力系统优化调度领域取得了优良的效果。鲁棒优化的一个关键问题是确定风电功率不确定集合,而现有方法难以依据最新风电功率预测信息更新不确定集合。针对这一问题,该文基于条件copula copula模型,构建考虑风电功率条件相关性的广义椭球不确定集合。该方法综合考虑了预测误差的时间相关性,非正态的边缘分布特性,以及与风电功率预测值的条件相关性。此外,提出了条件normal copula模型的解析表达式以及相应采样方法。该方法实现了依据最新预测信息更新不确定集合,提高了模型的准确性,降低了集合的保守度。对某风场历史数据进行仿真分析,结果验证了所提算法的有效性,以及预测误差统计特性对不确定集合拟合效果的影响。 展开更多
关键词 风电功率 NORMAL COPULA 条件分布 采样 自适应更新 不确定集合
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共反射面元叠加的应用理论——从共反射点到共反射面元 被引量:22
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作者 王华忠 杨锴 马在田 《地球物理学报》 SCIE EI CAS CSCD 北大核心 2004年第1期137-142,共6页
共反射面元 (CRS)叠加是目前认为最好的生成零炮检距剖面的方式 .共反射面元意指地下某一反射点邻近的一个反射弧段 ,该弧段在时空域内的走时响应称为CRS叠加面 ,该叠加面可视为反射弧段上各共反射点(CRP)的时空域内走时响应的组合 .在... 共反射面元 (CRS)叠加是目前认为最好的生成零炮检距剖面的方式 .共反射面元意指地下某一反射点邻近的一个反射弧段 ,该弧段在时空域内的走时响应称为CRS叠加面 ,该叠加面可视为反射弧段上各共反射点(CRP)的时空域内走时响应的组合 .在一般的共反射点走时关系基础上 ,引入两种特征波———Normal波和NormalIncidencePoint波 ,就可以在傍轴近似假设下 ,将CRP走时关系推广到反射点邻近的各反射点 ,将这些反射点的CRP走时关系加以组合就得到了关于该反射点的共反射面元的走时关系 .考察从共反射点 (CRP)到共反射面元 (CRS)的过渡 ,这一过程提供了CRS叠加的应用理论基础 . 展开更多
关键词 共反射面元 CRS 叠加 共反射点 Normal波 傍轴近似
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基于性能退化的卫星用光纤陀螺可靠性评估 被引量:16
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作者 晁代宏 马静 +1 位作者 陈淑英 张春熹 《红外与激光工程》 EI CSCD 北大核心 2011年第9期1763-1767,共5页
基于性能退化数据研究了卫星用光纤陀螺空间辐射环境下的可靠性评估方法。随着光纤陀螺技术水平的提高,其在卫星上的应用越来越广泛,其可靠性状况也愈发引起人们的关注。在对空间辐射环境下光纤陀螺失效机理分析的基础上,提出用Normal-P... 基于性能退化数据研究了卫星用光纤陀螺空间辐射环境下的可靠性评估方法。随着光纤陀螺技术水平的提高,其在卫星上的应用越来越广泛,其可靠性状况也愈发引起人们的关注。在对空间辐射环境下光纤陀螺失效机理分析的基础上,提出用Normal-Poisson复合随机过程模型对产品在空间辐射作用下的退化特性进行建模,基于所得模型,由光纤陀螺的性能退化信息估计模型中的参数进而评估得到光纤陀螺可靠性指标。该方法克服了传统可靠性分析方法依赖寿命数据的缺点,能够在没有寿命数据的情况下评估得到光纤陀螺的可靠性指标,从而可节约大量的试验经费和试验时间,在工程应用上具有重要的价值。 展开更多
关键词 光纤陀螺 可靠性 空间辐射环境 Normal.Poisson模型 性能退化数据
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锂离子电池正极材料LiNi_(1-x)Co_xO_2的合成及电化学性能研究 被引量:6
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作者 黄元乔 郭文勇 +2 位作者 李道聪 彭正合 周运鸿 《无机化学学报》 SCIE CAS CSCD 北大核心 2005年第5期736-740,共5页
LiNi1-xCoxO2 cathode materials for lithium ion batteries were synthesized by the co-precipitation and solid-state reaction methods with LiOH·H2O, Ni(NO3)2·6H2O and Co(NO3)2·6H2O as raw materials. The ma... LiNi1-xCoxO2 cathode materials for lithium ion batteries were synthesized by the co-precipitation and solid-state reaction methods with LiOH·H2O, Ni(NO3)2·6H2O and Co(NO3)2·6H2O as raw materials. The materials were characterized by XRD, SEM and electrochemical tests. The results showed that synthesized cathode materials were with layered structure similar to α-NaFeO2 and uniform morphology and nearly normal grain size distribution and better electrochemical performance when x was 0.18. The first charge and discharge capacity of the cathode material was 224.3 mAh·g-1 and 194.2 mAh·g-1, respectively. 88.5% of the first discharge capacity remained at the 20th cycle. 展开更多
关键词 锂离子电池 性能研究 正极材料 电化学 Ni(NO3)2 first 合成 NORMAL and with the The was for ion RAW XRD SEM
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基于分水岭算法和图论的图像分割 被引量:15
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作者 杨卫莉 郭雷 《计算机工程与应用》 CSCD 北大核心 2007年第7期28-30,44,共4页
提出一种新的基于分水岭算法和图论的图像分割方法FWTN(First Watershed Then Normalized cut),以克服传统的分水岭算法造成的图像过度分割。FWTN方法在分水岭算法之后,用Normalized Cut方法在区域之间进行分割,产生最终所分割的图像。F... 提出一种新的基于分水岭算法和图论的图像分割方法FWTN(First Watershed Then Normalized cut),以克服传统的分水岭算法造成的图像过度分割。FWTN方法在分水岭算法之后,用Normalized Cut方法在区域之间进行分割,产生最终所分割的图像。FWTN成功地解决了过分割问题,同时还对Normalized Cut方法中的NP-hard问题有所改进。实验结果表明该算法是一种切实可行的图像分割方法。 展开更多
关键词 图像分割 分水岭 Normalized CUT 图论
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