检索结果-南通市图书馆

An optimal rigidity theorem for complete submanifolds in a sphere

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics(A Journal of Chinese Universities) 2008年第2期23卷 219-226页

作者： xu hong-wei ZHU Jiao-feng Center of Math. Sci. Zhejiang Univ. Hangzhou 310027 China

It is proved that if M^n is an n-dimensional complete submanifold with parallel mean curvature vector and flat normal bundle in S^n＋p（1）, and if supM S 〈 α（n, H）, where α（n,H）=n＋n^3/2（n-1）H^2-n（n-2）/n（n-1）√n^2H^4＋4（n-1）H^2,then M^n must be the totally urnbilical sphere S^n（1/√1＋H^2）.An example to show that the pinching constant α（n, H） appears optimal is given.

关键词： submanifold rigidity flat normal bundle mean curvature.

Weakly stable constant mean curvature hypersurfaces

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics(A Journal of Chinese Universities) 2009年第1期24卷 119-126页

作者： FU Hai-ping xu hong-wei Center of Math. Sci. Zhejiang Univ. Hangzhou 310027 China Dept. of Math. Nanchang Univ. Nanchang 330047 China

Let M^n be an n-dimensional complete noncompact oriented weakly stable constant mean curvature hypersurface in an （n ＋ 1）-dimensional Riemannian manifold N^n＋1 whose （n - 1）th Ricci curvature satisfying Ric^N（n-1）（n - 1）c. Denote by H and φ the mean curvature and the trace-free second fundamental form of M respectively. If ｜φ｜^2 - （n- 2）√n（n- 1）｜H｜｜φ｜＋ n（2n - 1）（H^2＋ c）〉 0, then M does not admit nonconstant bounded harmonic functions with finite Dirichlet integral. In particular, if N has bounded geometry and c ＋ H^2 〉 0, then M must have only one end.

关键词： constant mean curvature weakly stable hypersurface ends

Rigidity of closed submanifolds in a locally symmetric Riemannian manifold

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics(A Journal of Chinese Universities) 2016年第2期31卷 237-252页

作者： GU Juan-ru LENG Yan xu hong-wei Department of Applied Mathematics Zhejiang University of Technology Hangzhou 310023 China Center of Mathematical Sciences Zhejiang University Hangzhou 310027 China

Let Mn（n ≥ 4） be an oriented closed submanifold with parallel mean curvature in an （n ＋ p）-dimensional locally symmetric Riemannian manifold Nn＋p. We prove that if the sectional curvature of N is positively pinched in [5, 1], and the Ricci curvature of M satisfies a pinching condition, then M is either a totally umbilical submanifold, or δ= 1, and N is of constant curvature. This result generalizes the geometric rigidity theorem due to xu and Gu [15].

关键词： Submanifold Ejiri rigidity theorem Ricci curvature Mean curvature.

Effect of Chromium on CCT Diagrams of Novel Air-Cooled Bainite Steels Analyzed by Neural Network

在线全文

学校读者我要写书评

暂无评论

Journal of Iron and Steel Research International 2007年第4期14卷 39-42页

作者： YOU wei xu wei-hong LIU Ya-xiu BAI Bing-zhe FANG hong-sheng Department of Mechanical and Electrical Engineering North China Institute of Science and Technology Beijing 101601 China Department of Electronics and Information Engineering North China Institute of Science and Technology Beijing 101601 China Department of Materials Science and Engineering Tsinghua University Beijing 100084 China

The quantitative effects of chromium content on continuous cooling transformation （CCT） diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the c... 详细信息

关键词： novel air-cooled bainite steel CCT diagram artificial neural network chromium content quantitative effect

Electrochemical behavior of different shelled microcapsule composite copper coatings

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 2011年第3期18卷 377-384页

作者： Xiu-qing xu Yan-hong Guo wei-ping Li Li-qun Zhu School of Materials Science and Engineering Beihang University Beijing 100191 China

Copper/liquid microcapsule composite coatings with polyvinyl alcohol （PVA）, gelatin or methyl cellulose （MC） as shell materials were prepared by electrodeposition. The influence of shell materials on the corrosion resistance of the composite coatings in 0.1 M H2SO4 was investigated by means of electrochemical techniques, scanning electron microscopy （SEM）, and energy dispersion spectrometry （EDS）. The results show that the participation of microcapsules can enhance the corrosion resistance of the composite coatings compared with the traditional copper layer. Based on the analysis of electrochemical test results, the release ways of microcapsules were deduced. Gelatin and MC as the shell materials of microcapsules are easy to release quickly in the composite coating. On the contrary, the releasing speed of PVA microcapsules is relatively slow due to their characteristics.

关键词： composite coatings shell materials copper microcapsules electrochemical properties corrosion resistance electrodeposition

NDVI-Based Lacunarity Texture for Improving Identification of Torreya Using Object-Oriented Method

在线全文

学校读者我要写书评

暂无评论

Agricultural Sciences in China 2011年第9期10卷 1431-1444页

作者： HAN Ning WU Jing Amir Reza Shah Tahmassebi xu hong-wei WANG Ke Institute of Remote Sensing and Information System Application College of Environment and Resource Science Zhejiang University Hangzhou 310029 P.R. China School of Environment and Resource Zhejiang Agriculture and Forestry University Hangzhou 311300 P.R.China

Normalized Difference Vegetation Index （NDVI） is a very useful feature for differentiating vegetation and non-vegetation in remote sensed imagery. In the light of the function of NDVI and the spatial patterns of the vegetation landscapes, we proposed the lacunarity texture derived from NDVI to characterize the spatial patterns of vegetation landscapes concerning the ＂gappiness＂ or ＂emptiness＂ characteristics. The NDVI-based lacunarity texture was incorporated into object-oriented classification for improving the identification of vegetation categories, especially Torreya which was the targeted tree species in the present research. A three-level hierarchical network of image objects was defined and the proposed texture was integrated as potential sources of information in the rules base. A knowledge base of rules created by classifier C5.0 indicated that the texture could potentially be applied in object-oriented classification. It was found that the addition of such texture improved the identification of every vegetation category. The results demonstrated that the texture could characterize the spatial patterns of vegetation structures, which could be a promising approach for vegetation identification.

关键词： Torreya NDVI lacunarity class hierarchy object-oriented method decision tree spatial pattern

生物炭与绿色木霉配施对黄瓜养分吸收和光合特性的影响研究

在线全文

学校读者我要写书评

暂无评论

吉林师范大学学报(自然科学版) 2025年第1期46卷 86-94页

作者：未晓巍董佳伟张菊孙铭悦张劭涵孟津好苏闰申徐洪伟吉林师范大学吉林省植物资源科学与绿色生产重点实验室吉林四平136000 吉林师范大学生命科学学院吉林四平136000

黄瓜作为一种重要的设施蔬菜作物,在全球范围内广泛种植.设施黄瓜的种植受连作障碍的影响,使得黄瓜生长受到土壤养分、水分和日照条件的多重限制.生物炭是一种土壤改良剂,被认为是一种具有潜力的提高蔬菜作物产量的手段.然而,生物炭与... 详细信息

黄瓜作为一种重要的设施蔬菜作物,在全球范围内广泛种植.设施黄瓜的种植受连作障碍的影响,使得黄瓜生长受到土壤养分、水分和日照条件的多重限制.生物炭是一种土壤改良剂,被认为是一种具有潜力的提高蔬菜作物产量的手段.然而,生物炭与木霉菌的联合施用对黄瓜植株光合特性及养分变化的具体影响尚不明确.因此,本文旨在通过考察植物对氮、磷等养分的吸收,叶片光合色素含量及气体交换参数,探讨生物炭与绿色木霉联合施用对黄瓜光合作用及养分吸收的影响.本文采用3种生物炭水平(C0、C50和C80)及2种绿色木霉施用量(T0和T1)进行温室实验.结果表明,与C0相比,C50T1处理显著提高了黄瓜植株的氮吸收(增加80.8%)和磷吸收(增加85.13%),C80T1也呈增加趋势,并显著增强了叶片光合特性,包括净光合速率、气孔导度、蒸腾速率以及叶绿素含量.研究还发现,光合速率与黄瓜植株的总氮磷积累量及光合特性呈显著相关关系.这些结果加深了对生物炭与绿色木霉联合施用对黄瓜植株光合作用和养分吸收影响的理解,对于设施蔬菜的农业管理具有重要指导意义.

关键词：生物炭绿色木霉光合特性黄瓜土壤养分

Estimations of Net Primary Productivity and Evapotranspiration Based on HJ-1A/B Data in Jinggangshan City, China

在线全文

学校读者我要写书评

暂无评论

Journal of Mountain Science 2013年第5期10卷 777-789页

作者： ZHANG Rong-hua SUN Rui DU Jun-ping ZHANG Ting-long TANG Yao xu hong-wei YANG Sheng-tian JIANG wei-guo State Key Laboratory of Remote Sensing Science Jointly Sponsored by Beijing Normal University and the Institute of Remote Sensing Applications of Chinese Academy of Sciences School of Geography and Remote Sensing Sciences Beijing Normal University Beijing Key Laboratory of Environmental Remote Sensing and City Digitalization College of Resources and Environment Northwest Agricultural and Forestry University The Academy of Disaster Reduction and Emergency Management Ministry of Civil Affairs and Ministry of Education Beijing Normal University

Net primary productivity （NPP） and evapotranspiration （ET） are two key variables in the carbon and water cycles of terrestrial ecosystems. In this study, to test a newly developed NPP algorithm designed for H J-1 A/B data and to evaluate the usage of HJ-1 A/B data in the quantitative assessment of environments, NPP and ET in Jinggangshan city, Jiangxi province, are calculated using H J-1 A/B data. The results illustrate the following：（1） The NPP and ET in Jinggangshan city in 2olo both show obvious seasonal variation, with the highest values in summer and the lowest values in winter, and relatively higher values were observed in autumn than in spring. （2） The spatial pattern indicates that the annual NPP is high in the southern area in Jinggangshan city and low in the northern area. Additionally, high NPP is distributed in forests located in areas with high elevation, and low NPP is found in croplands at low elevations. ET has no significant north-south difference, with high values in the southeast and northwest and low values in the southwest, and high ET is distributed in forests at low elevations in contrast to low ET in forests in high-elevation areas and in cropland and shrub grassland in low-elevation areas. （3） Compared to the MODIS product, the range of H J-1 NPP is larger, and the spatial pattern is more coincident with the topography. The range of H J-1 ET is smaller than that of the MODIS product, and ET is underestimated to some extent but can reflect the effect of topography. This study suggests that the algorithm can be used to estimate NPP and ET in a subtropical monsoon climate if remotely sensed images with high spatial resolution are available.

关键词： Net primary productivity Remotesensing Evapotranspiration HJ-~A/B data

Coefficients of earth pressure at rest in thick and deep soils

在线全文

学校读者我要写书评

暂无评论

Mining Science and Technology 2009年第2期19卷 252-255页

作者： TIAN Qiu-hong xu Zhi-wei ZHOU Guo-qing ZHAO Xiao-dong HU Kun State Key Laboratory for Geomechanics ＆ Deep Underground Engineering School of Architecture and Civil Engineering China University of Mining ＆ Technology Xuzhou Jiangsu 221008 China

The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest, K0, was investigated under high pressures. The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0. Moreover, K0 increases during the loading process becoming greater at high pressures. In the unloading process, however, K0 increases only at the initial stage but decreases thereafter. In addition, the incremental magnitude definition, K0=dσ3/dσ1, gives higher values than the total magnitude definition, K0=σ3/σ1, under loading. This is also true during initial stages of unloading. The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures. It is necessary to choose the appropriate Kn to avoid some accidents.

关键词： experimental research earth pressure at rest loading and unloading paths thick and deep soils