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Scale effects on non-cavitation hydrodynamics and noise of highly-skewed propeller in wake flow 被引量:1
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作者 杨琼方 王永生 张明敏 《Journal of Southeast University(English Edition)》 EI CAS 2013年第2期162-169,共8页
Regarding the scale effects on propeller's noncavitation hydrodynamics and hydroacoustics, three similar 7bladed highly-skewed propellers in the wake flow are addressed with diameters of 250, 500 and 1 000 mm, respec... Regarding the scale effects on propeller's noncavitation hydrodynamics and hydroacoustics, three similar 7bladed highly-skewed propellers in the wake flow are addressed with diameters of 250, 500 and 1 000 mm, respectively. The discrete line-spectrum noise and its standardized spectrum level scaling law, together with the total sound pressure level are analyzed. The non-cavitation noise predictions are completed by both the frequency domain method and the time domain method. As a fluctuated noise source, the time-dependent fluctuated pressure and normal velocity distribution on propeller blades are obtained by the unsteady Reynolds-averaged Navier-Stokes ( URANS ) simulation. Results show that the pressure coefficient distribution of three propellers on the 0.7R section is nearly superposed under the same advance ratio. The periodic thrust fluctuation of three propellers can exactly reflect the tonal components of the axial passing frequency (APF) and the blade passing frequency (BPF), and the fluctuation enhancement from the small to the middle propeller at the BPF is greater than that from the middle to the big one. By the two noise prediction methods, the increment of the total sound pressure level from the small to the big propeller differs by 2.49 dB. Following the standardized scaling law, the spectrum curves of the middle and big propellers are nearly the same while significantly differing from the small one. The increment of both the line-spectrum level and the total sound pressure increases with the increase in diameter. It is suggested that the model scale of the propeller should be as large as possible in engineering to reduce the prediction error of the empirical scalin~ law and weaken the scale effects. 展开更多
关键词 highly skewed propeller non-cavitation noise scale effects frequency domain time domain
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投资组合行业配置的动态VaR研究——基于时变Copula-GJR-Skewed-t模型
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作者 刘澄 张玲 《金融理论与实践》 CSSCI 北大核心 2013年第9期7-11,共5页
用时变Copula-GJR-Skewed-t模型研究了深证22个行业分类指数中任意两个投资组合的动态VaR,并与静态VaR比较。实证结果表明,时变t-Copula函数在众多Copula函数中对行业投资组合的拟合效果最优,给出了模型估计出的VaR最大和最小的5对行业... 用时变Copula-GJR-Skewed-t模型研究了深证22个行业分类指数中任意两个投资组合的动态VaR,并与静态VaR比较。实证结果表明,时变t-Copula函数在众多Copula函数中对行业投资组合的拟合效果最优,给出了模型估计出的VaR最大和最小的5对行业组合,不同行业组合的动态VaR在股市周期各阶段关系相对稳定,同一行业组合的动态VaR和静态VaR关系相对稳定,且略高于静态VaR。 展开更多
关键词 时变COPULA 动态VAR 行业组合 GJR—skewed—t
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基于Skewed-t分布的FIGARCH模型与VaR的度量 被引量:6
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作者 黄炎龙 《应用概率统计》 CSCD 北大核心 2012年第2期189-202,共14页
金融资产收益率序列的波动具有典型的尖峰厚尾和非对称性特征,描述这种特性需以合适的概率分布函数为基础.因此,寻求更好的概率分布函数对风险度量、VaR的计算有着十分重要的意义.有鉴于此引入Skewed-t分布度量VaR,并比较分析了RiskMetr... 金融资产收益率序列的波动具有典型的尖峰厚尾和非对称性特征,描述这种特性需以合适的概率分布函数为基础.因此,寻求更好的概率分布函数对风险度量、VaR的计算有着十分重要的意义.有鉴于此引入Skewed-t分布度量VaR,并比较分析了RiskMetrics及FIGARCH类模型度量VaR值的准确程度,本文同时分析了多头头寸和空头头寸情况下的VaR.结果表明,在两种头寸情况下,Skewed-t分布在空头和多头情形对资产厚尾特性以及非对称性的拟合效果均要比正态分布好;在两种头寸中不同的置信水平下,FIAGARCH(CHUNG)模型预测的VaR值改进了使用传统模型的精确性,高估或低估风险的程度较轻. 展开更多
关键词 VAR FIGARCH模型 skewed-t分布 动态分位数测试
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Performance-based seismic assessment of skewed bridges with and without considering soil-foundation interaction effects for various site classes 被引量:5
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作者 Abdoul R.Ghotbi 《Earthquake Engineering and Engineering Vibration》 SCIE EI CSCD 2014年第3期357-373,共17页
The seismic behavior of skewed bridges has not been well studied compared to straight bridges. Skewed bridges have shown extensive damage, especially due to deck rotation, shear keys failure, abutment unseating and co... The seismic behavior of skewed bridges has not been well studied compared to straight bridges. Skewed bridges have shown extensive damage, especially due to deck rotation, shear keys failure, abutment unseating and column- bent drift. This research, therefore, aims to study the behavior of skewed and straight highway overpass bridges both with and without taking into account the effects of Soil-Structure Interaction (SSI) due to near-fault ground motions. Due to several sources of uncertainty associated with the ground motions, soil and structure, a probabilistic approach is needed. Thus, a probabilistic methodology similar to the one developed by the Pacific Earthquake Engineering Research Center (PEER) has been utilized to assess the probability of damage due to various levels of shaking using appropriate intensity measures with minimum dispersions. The probabilistic analyses were performed for various bridge configurations and site conditions, including sand ranging from loose to dense and clay ranging from soft to stiff, in order to evaluate the effects. The results proved a considerable susceptibility of skewed bridges to deck rotation and shear keys displacement. It was also found that SSI had a decreasing effect on the damage probability for various demands compared to the fixed-base model without including SSI. However, deck rotation for all types of the soil and also abutment unseating for very loose sand and soft clay showed an increase in damage probability compared to the fixed-base model. The damage probability for various demands has also been found to decrease with an increase of soil strength for both sandy and clayey sites. With respect to the variations in the skew angle, an increase in skew angle has had an increasing effect on the amplitude of the seismic response for various demands. Deck rotation has been very sensitive to the increase in the skew angle; therefore, as the skew angle increased, the deck rotation responded accordingly. Furthermore, abutment unseating showed an increasing trend due to an increase in skew angle for both fixed-base and SSI models. 展开更多
关键词 skewed bridges SSI demand model probabilistic assessment damage probability
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Mobile bed thickness in skewed asymmetric oscillatory sheet flows 被引量:6
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作者 Xin Chen Yong Li Fujun Wang 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2018年第2期257-265,共9页
A new instantaneous mobile bed thickness model is presented for sediment transport in skewed asymmetric oscillatory sheet flows. The proposed model includes a basic bed load part and a suspended load part related to t... A new instantaneous mobile bed thickness model is presented for sediment transport in skewed asymmetric oscillatory sheet flows. The proposed model includes a basic bed load part and a suspended load part related to the Shields parameter, and takes into account the effects of mass conservation, phase-lag, and asymmetric boundary layer development, which are important in skewed asymmetric flows but usually absent in classical models. The proposed model is validated by erosion depth and sheet flow layer thickness data in both steady and unsteady flows, and applied to a new instantaneous sediment transport rate formula. With higher accuracy than classical empirical models in steady flows, the new formula can also be used for instantaneous sediment transport rate prediction in skewed asymmetric oscillatory sheet flows. 展开更多
关键词 Mobile bed thickness PHASE-LAG Sediment transport Sheet flow skewed asymmetric oscillatory flow
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Seismic response of skewed RC box-girder bridges 被引量:4
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作者 Ahmed Abdel-Mohti Gokhan Pekcan 《Earthquake Engineering and Engineering Vibration》 SCIE EI CSCD 2008年第4期415-426,共12页
It is critical to ensure the functionality of highway bridges after earthquakes to provide access to important facilities. Since the 1971 San Fernando earthquake, there has been a better understanding of the seismic p... It is critical to ensure the functionality of highway bridges after earthquakes to provide access to important facilities. Since the 1971 San Fernando earthquake, there has been a better understanding of the seismic performance of bridges. Nonetheless, there are no detailed guidelines addressing the performance of skewed highway bridges. Several parameters affect the response of skewed highway bridges under both service and seismic loads which makes their behavior complex. Therefore, there is a need for more research to study the effect of skew angle and other related factors on the performance of highway bridges. This paper examines the seismic performance of a three-span continuous concrete box girder bridge with skew angles from 0 to 60 degrees, analytically. Finite element (FE) and simplified beam-stick (BS) models of the bridge were developed using SAP2000. Different types of analysis were considered on both models such as: nonlinear static pushover, and linear and nonlinear time history analyses. A comparison was conducted between FE and BS, different skew angles, abutment support conditions, and time history and pushover analysis. It is shown that the BS model has the capability to capture the coupling due to skew and the significant modes for moderate skew angles. Boundary conditions and pushover load profile are determined to have a major effect on pushover analysis. Pushover analysis may be used to predict the maximum deformation and hinge formation adequately. 展开更多
关键词 skew bridge seismic response pushover analysis time history analysis MODELING
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The effect of different intensity measures and earthquake directions on the seismic assessment of skewed highway bridges 被引量:3
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作者 M.Bayat F.Daneshjoo N.Nistico 《Earthquake Engineering and Engineering Vibration》 SCIE EI CSCD 2017年第1期165-179,共15页
In this study the probable seismic behavior of skewed bridges with continuous decks under earthquake excitations from different directions is investigated. A 45° skewed bridge is studied. A suite of 20 records is... In this study the probable seismic behavior of skewed bridges with continuous decks under earthquake excitations from different directions is investigated. A 45° skewed bridge is studied. A suite of 20 records is used to perform an Incremental Dynamic Analysis (IDA) for fragility curves. Four different earthquake directions have been considered: -45°, 0°, 22.5, 45°. A sensitivity analysis on different spectral intensity measures is presented; efficiency and practicality of different intensity measures have been studied. The fragility curves obtained indicate that the critical direction for skewed bridges is the skew direction as well as the longitudinal direction. The study shows the importance of finding the most critical earthquake in understanding and predicting the behavior of skewed bridges. 展开更多
关键词 skewed highway bridge earthquake direction spectral intensity measure analytical fragility curve
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Improving MapReduce Performance by Balancing Skewed Loads 被引量:4
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作者 FAN Yuanquan WU Weiguo XU Yunlong CHEN Heng 《China Communications》 SCIE CSCD 2014年第8期85-108,共24页
MapReduce has emerged as a popular computing model used in datacenters to process large amount of datasets.In the map phase,hash partitioning is employed to distribute data that sharing the same key across data center... MapReduce has emerged as a popular computing model used in datacenters to process large amount of datasets.In the map phase,hash partitioning is employed to distribute data that sharing the same key across data center-scale cluster nodes.However,we observe that this approach can lead to uneven data distribution,which can result in skewed loads among reduce tasks,thus hamper performance of MapReduce systems.Moreover,worker nodes in MapReduce systems may differ in computing capability due to(1) multiple generations of hardware in non-virtualized data centers,or(2) co-location of virtual machines in virtualized data centers.The heterogeneity among cluster nodes exacerbates the negative effects of uneven data distribution.To improve MapReduce performance in heterogeneous clusters,we propose a novel load balancing approach in the reduce phase.This approach consists of two components:(1) performance prediction for reducers that run on heterogeneous nodes based on support vector machines models,and(2) heterogeneity-aware partitioning(HAP),which balances skewed data for reduce tasks.We implement this approach as a plug-in in current MapReduce system.Experimental results demonstrate that our proposed approach distributes work evenly among reduce tasks,and improves MapReduce performance with little overhead. 展开更多
关键词 MAPREDUCE cloud computing skewed loads performance prediction supportvector machines
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SKEWED SYMMETRY DETECTION OF QUADRIC SURFACE SOLIDS UNDER ORTHOGRAPHIC PROJECTION
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作者 王翔 丁运亮 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI 2009年第3期212-218,共7页
The skewed symmetry detection plays an improtant role in three-dimensional(3-D) reconstruction. The skewed symmetry depicts a real symmetry viewed from some unknown viewing directions. And the skewed symmetry detect... The skewed symmetry detection plays an improtant role in three-dimensional(3-D) reconstruction. The skewed symmetry depicts a real symmetry viewed from some unknown viewing directions. And the skewed symmetry detection can decrease the geometric constrains and the complexity of 3-D reconstruction. The detection technique for the quadric curve ellipse proposed by Sugimoto is improved to further cover quadric curves including hyperbola and parabola. With the parametric detection, the 3-D quadric curve projection matching is automatical- ly accomplished. Finally, the skewed symmetry surface of the quadric surface solid is obtained. Several examples are used to verify the feasibility of the algorithm and satisfying results can be obtained. 展开更多
关键词 three-dimensional computer graphics face reconstruction skewed symmetry detection quadric surface solid
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Genomic Instability in Cancer I: DNA-Repair Triggering Primitive Hereditary 4n-Skewed, Amitotic Division-System, the Culprit in EMT/MET/Metaplasia Cancer-Concepts 被引量:3
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作者 Kirsten H. Walen 《Journal of Cancer Therapy》 2018年第12期974-997,共24页
The objective was to gain proof of genome damage-repair induced mitotic slippage process (MSP) to 4n-diplochromosome skewed division-system, earlier suggested to have “cancer-deciding” consequences. Our damage-model... The objective was to gain proof of genome damage-repair induced mitotic slippage process (MSP) to 4n-diplochromosome skewed division-system, earlier suggested to have “cancer-deciding” consequences. Our damage-model showed two succeeding phases: molecular mutations for initiation of fitness-gained cells, and large chromosomal changes to aneuploidy from inherited DNA-breakage-repair inaccuracies. The mutations were gained while DNA-repair and DNA-replication, co-existed in the route to tetraploidy, a phenomenon also expressed for some existing unicellular organisms. These organisms also showed genome reductive, amitotic, meioticlike division, and was the origin of human genome conserved, self-inflicted 90° reorientation of the 4n nucleus relative to the cytoskeleton axis. In the in vitro DNA-damage model, this remarkable 4n-event deciding “flat-upright” cell-growth characteristics showed several consequences, for example, cancer-important, E-cadherin-β-catenin cell-to-cell adherence destruction, which gave diploid progeny cells, mobility freedom from cell contact inhibition, likely in renewal tissues. This 4n-skewed division-system with inheritance in progeny cells for repeat occurrences as mentioned for flat-up-right growth patterns is similar to claimed concepts of metaplasia-EMT/MET embryogenesis events in cancer evolution. A scrutiny of this literature, proof-wise invalidated this embryological concept by tetraploid 8C cells occurring in MET events and, was noted for small cell occurrence, i.e., diploidy from 4n-8C reductive division, an also event for tumor relapse cells, derived from genome damaging therapy agents. Pre-cancer hyperplasia reported MSP, cadherincatenin destruction and 90° perpendicularity to basal cell membrane. The DNA-damage-repair model can weed-out therapy-agents triggering 4n-skewed division. Cancer-control, beginning-information, is likely from mutational identity of the 4n derived fitness-gained cells. 展开更多
关键词 CANCER Evolution DNA-Damage-Repair Mitotic Slippage HEREDITARY PRIMITIVE Tetraploidy 90° Amitotic skewed DIVISION Fitness-Gain Embryogenesis-Type EMT/MET Human Cell Conservation
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A numerical study for boundary layer current and sheet flow transport induced by a skewed asymmetric wave 被引量:1
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作者 CHEN Xin ZHANG Zichao WANG Fujun 《Acta Oceanologica Sinica》 SCIE CAS CSCD 2018年第9期82-89,共8页
An analytical model with essential parameters given by a two-phase numerical model is utilized to study the net boundary layer current and sediment transport under skewed asymmetric oscillatory sheet flows. The analyt... An analytical model with essential parameters given by a two-phase numerical model is utilized to study the net boundary layer current and sediment transport under skewed asymmetric oscillatory sheet flows. The analytical model is the first instantaneous type model that can consider phase-lag and asymmetric boundary layer development. The two-phase model supplies the essential phase-lead, instantaneous erosion depth and boundary layer development for the analytical model to enhance the understanding of velocity skewness and acceleration skewness in sediment flux and transport rate. The sediment transport difference between onshore and offshore stages caused by velocity skewness or acceleration skewness is shown to illustrate the determination of net sediment transport by the analytical model. In previous studies about sediment transport in skewed asymmetric sheet flows, the generation of net sediment transport is mainly concluded to the phase-lag effect.However, the phase-lag effect is shown important but not enough for the net sediment transport, while the skewed asymmetric boundary layer development generated net boundary layer current and mobile bed effect are key important in the transport process. 展开更多
关键词 analytical model boundary layer current sediment transport sheet flow skewed asymmetric wave
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Influence of active constrained layer damping on the coupled vibration response of functionally graded magneto-electro-elastic plates with skewed edges 被引量:3
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作者 M.Vinyas D.Harursampath T.Nguyen-Thoi 《Defence Technology(防务技术)》 SCIE EI CAS CSCD 2020年第5期1019-1038,共20页
This article makes the first attempt in assessing the influence of active constrained layer damping(ACLD)treatment towards precise control of frequency responses of functionally graded skew-magneto-electroelastic(FGSM... This article makes the first attempt in assessing the influence of active constrained layer damping(ACLD)treatment towards precise control of frequency responses of functionally graded skew-magneto-electroelastic(FGSMEE)plates by employing finite element methods.The materials are functionally graded across the thickness of the plate in terms of modest power-law distributions.The principal equations of motion of FGSMEE are derived via Hamilton’s principle and solved using condensation technique.The effect of ACLD patches are modelled by following the complex modulus approach(CMA).Additionally,distinctive emphasis is laid to evaluate the influence of geometrical skewness on the attenuation capabilities of the plate.The accuracy of the current analysis is corroborated with comparison of previous researches of similar kind.Additionally,a complete parametric study is directed to understand the combined impacts of various factors like coupling fields,patch location,fiber orientation of piezoelectric patch in association with skew angle and power-law index. 展开更多
关键词 Vibration control Functionally graded MEE plates skew angle Active constrained layer damping(ACLD) PATCHES
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Prediction of Skewed Bridge Behaviors with Arbitrary Boundary Conditions—— Theoretical Approach and Its Design Application
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作者 Pang-jo Chun Gongkang Fu 《Journal of Civil Engineering and Architecture》 2012年第6期639-650,共12页
In this paper, we report on an analytical solution for beam-type skewed highway bridges subjected to truck loading. To confirm the analysis derivation and the solution obtained, the moment and shear responses to the d... In this paper, we report on an analytical solution for beam-type skewed highway bridges subjected to truck loading. To confirm the analysis derivation and the solution obtained, the moment and shear responses to the design truck load are acquired using the analytical method for a number of typical US highway bridges and compared with those from numerical finite element method (FEM) analysis. In addition, the lateral distribution factors for moment and shear used in routine design are investigated based on comparison of the analytical approach and FEM. The analytical solution is shown in good agreement with the FEM result. Furthermore, the relevant provisions in the American Association of State Highway Transportation Officials' (AASHTO's) LRFD Bridge Design Specifications are also discussed here for comparison, particularly with respect to design application. It is observed that the design code specified load distribution factor may not predict well, especially for shear and/or severe skew. 展开更多
关键词 skewed plates thick plates skewed bridges truck loading analytical solution.
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Diophantine equations and Fermat's last theorem for multivariate(skew-)polynomials
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作者 PAN Jie JIA Yu-ming LI Fang 《Applied Mathematics(A Journal of Chinese Universities)》 SCIE CSCD 2024年第1期159-173,共15页
Fermat’s Last Theorem is a famous theorem in number theory which is difficult to prove.However,it is known that the version of polynomials with one variable of Fermat’s Last Theorem over C can be proved very concisely... Fermat’s Last Theorem is a famous theorem in number theory which is difficult to prove.However,it is known that the version of polynomials with one variable of Fermat’s Last Theorem over C can be proved very concisely.The aim of this paper is to study the similar problems about Fermat’s Last Theorem for multivariate(skew)-polynomials with any characteristic. 展开更多
关键词 Fermat's last theorem polynomial ring skew polynomial ring
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一种新型Skew Tent映射的混沌混合优化算法 被引量:16
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作者 江善和 王其申 江巨浪 《控制理论与应用》 EI CAS CSCD 北大核心 2007年第2期269-273,共5页
针对已有的混沌优化算法几乎都是利用Logistic映射作为混沌序列发生器,而该混沌序列的概率密度函数呈两头多、中间少的切比雪夫型的分布性质,不利于搜索的效率和能力,为此,首先构造一种新型混沌映射序列发生器—Skew Tent映射并结合迭... 针对已有的混沌优化算法几乎都是利用Logistic映射作为混沌序列发生器,而该混沌序列的概率密度函数呈两头多、中间少的切比雪夫型的分布性质,不利于搜索的效率和能力,为此,首先构造一种新型混沌映射序列发生器—Skew Tent映射并结合迭代优化特点加以改进,然后分析了它的混沌特性.其次,将改进的混沌映射与Alopex启发算法相结合,充分发挥Alopex算法的快速搜索能力和混沌优化全局寻优的特性,提出一种混沌混合优化算法,提高了算法的收敛速度和有效搜索全局最优解.最后,仿真算例验证了该算法的有效性和Skew Tent混沌映射的应用前景. 展开更多
关键词 LOGISTIC映射 skew TENT映射 ALOPEX算法 混沌混合优化 全局最优
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改进分段Skew Tent映射及其在扩频通信中应用 被引量:6
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作者 王保平 李文康 +2 位作者 吴成茂 张薇 谢红梅 《红外与激光工程》 EI CSCD 北大核心 2013年第10期2772-2777,共6页
混沌序列用作扩频系统扩频码,具有码元丰富、保密性好等优点。针对传统Skew Tent映射所产生随机序列的混沌特性较弱,特别是其随机性、相关性等指标较差等不足,将Skew Tent映射进行分段对偶扩展获得一种改进分段Skew Tent映射构造方法,... 混沌序列用作扩频系统扩频码,具有码元丰富、保密性好等优点。针对传统Skew Tent映射所产生随机序列的混沌特性较弱,特别是其随机性、相关性等指标较差等不足,将Skew Tent映射进行分段对偶扩展获得一种改进分段Skew Tent映射构造方法,并将其所产生的随机序列用于构造扩频通信系统的扩频码。通过扩频通信系统仿真测试验证了改进分段Skew Tent映射相比Skew Tent映射具有更加良好的混沌特性,以及所产生随机序列作为扩频系统地址码在降低系统的误码率方面有了较大的改善。改进分段Skew Tent映射作为加密算法用于图像通信系统中,有效提高了图像信息的传输质量和安全性。混沌映射进行分段对偶扩展是一种行之有效的改进方法,混沌特性更好的迭代映射更利于扩频通信在军民领域的广泛应用。 展开更多
关键词 skewTent映射 混沌性能 扩频系统 图像加密
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一类半环的skew-环同余的刻画 被引量:2
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作者 徐慧 冯军庆 《纺织高校基础科学学报》 CAS 2008年第1期14-16,共3页
利用半环的满的、自共轭的闭的理想给出了加法是正则半群的半环上的skew-环同余的一种刻画.类似于环中理想和同余的对应关系理论,给出了加法正则半环的skwe-环同余和一类特殊理想的一一对应关系;另外,借助于半环的一个逆序给出了skew-... 利用半环的满的、自共轭的闭的理想给出了加法是正则半群的半环上的skew-环同余的一种刻画.类似于环中理想和同余的对应关系理论,给出了加法正则半环的skwe-环同余和一类特殊理想的一一对应关系;另外,借助于半环的一个逆序给出了skew-环同余类的一种表示. 展开更多
关键词 半环 同余 skew-环 理想
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具有TARCH-Skew-t误差项时序的ADF单位根检验 被引量:3
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作者 蔺富明 王莉莉 彭作祥 《西南师范大学学报(自然科学版)》 CAS CSCD 北大核心 2006年第1期48-51,共4页
随机模拟了有限样本情况下具有TARCH-Skew-t误差项时间序列的ADF单位根检验.在数据生成过程为AR(1)-TARCH-Skew-t时,分析了样本容量、条件分布中参数的变化和反映信息非对称性参数的变动对临界值的影响.结果显示,只能直接使用zt统计量的... 随机模拟了有限样本情况下具有TARCH-Skew-t误差项时间序列的ADF单位根检验.在数据生成过程为AR(1)-TARCH-Skew-t时,分析了样本容量、条件分布中参数的变化和反映信息非对称性参数的变动对临界值的影响.结果显示,只能直接使用zt统计量的Fuller临界值表. 展开更多
关键词 单位根过程 偏T分布 杠杆效应 临界值
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基于Skewness纹理的北京城市化区域提取
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作者 李熙 关泽群 沈体雁 《安徽农业科学》 CAS 北大核心 2008年第17期7407-7409,7412,共4页
北京地区部分农作物和城市化区域的光谱属性接近,仅仅利用光谱信息无法有效地提取北京的城市化区域。提出了利用Skewness纹理区分农作物和城市化区域,结合光谱和高程信息可以有效提取城市化区域。经过大量的样本检验表明,引入Skewness... 北京地区部分农作物和城市化区域的光谱属性接近,仅仅利用光谱信息无法有效地提取北京的城市化区域。提出了利用Skewness纹理区分农作物和城市化区域,结合光谱和高程信息可以有效提取城市化区域。经过大量的样本检验表明,引入Skewness特征能够大幅度提高分类精度。 展开更多
关键词 ETM+ 遥感 纹理 建成区 skewNESS
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具有GARCH-skew-t误差项的时序的单位根检验 被引量:4
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作者 彭作祥 庞皓 《数理统计与管理》 CSSCI 北大核心 2005年第6期49-54,共6页
本文通过随机模拟,分析条件分布为偏t分布、具有自回归条件异方差误差项的时间序列的ADF单位根检验的临界值、检验的有效性和实际显著水平的扭曲分析。结果显示,随着波动持久性的增强,已不能直接使用Fu ller的临界值表。
关键词 ADF单位根检验 自回归条件异方差 偏T分布 波动
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