检索结果-南通市图书馆

Research in Astronomy and Astrophysics 2014年第4期14卷 401-410页

作者： xin-fa deng School of Science Nanchang University

Using the LOWZ and CMASS samples of the ninth data release （DR9） from the SDSS-III Baryon Oscillation Spectroscopic Survey （BOSS）, I investigate properties of star forming galaxies and active galactic nuclei （AGNs）. The CMASS sample seriously suffers from the radial selection effect, even within the redshift 0.44 〈 z 〈 0.6, which will likely lead to statistical conclusions in the CMASS sample being less robust. In the LOWZ sample, the fraction of star-forming galaxies is nearly constant from the least dense regime to the densest regime; the AGN fraction is also insensitive to the local environment. In addition, I note that in the LOWZ sample, the distributions of stellar mass and stellar velocity dispersion for star forming galaxies and AGNs are nearly the same.

关键词： galaxies: active- galaxies: statistics

The environmental dependence of different colors in the CMASS sample of the SDSS DR9

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2014年第5期14卷 553-564页

作者： xin-fa deng School of Science Nanchang University

I investigate the environmental dependence of galaxy colors in the CMASS sample of the Sloan Digital Sky Survey Data Release 9 （SDSS DR9）. To decrease the radial selection effect, I divide the CMASS sample into subsamples with a redshift binning size of △z = 0.01 and analyze the environmental dependence of the u - r, u - g, g - r, r - i and i - z colors for these subsamples in each redshift bin. Statistical analysis shows that all five colors weakly correlate with the local environment, which may mean that the environmental processes responsible for a galaxy＇s properties pro- ceed slowly over cosmic time.

关键词： galaxies fundamental parameters -- galaxies statistics

A tool for the morphological classification of galaxies: the concentration index

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2013年第6期13卷 651-661页

作者： xin-fa deng School of Science Nanchang University

Using galaxy data from the Sloan Digital Sky Survey Data Release 8, I ex- plore whether the concentration index is a good morphological classification tool and find that a reasonable sample of pure late-type galaxies can be constructed with the choice of the r-band concentration index ci=2.85. The opposite is not true, however, due to the fairly high contamination of an early-type sample by late-type galaxies. In such an analysis, the influence of selection effects is less important. To disentangle correlations of the morphology and concentration index with stellar mass, star forma- tion rate （SFR）, specific star formation rate （SSFR） and active galactic nucleus （AGN） activity, I investigate correlations of the concentration index with these properties at a fixed morphology and correlations of the morphology with these properties at a fixed concentration index. It is found that at a fixed morphology, high-concentration galaxies are preferentially more massive and have a lower SFR and SSFR than low- concentration galaxies, whereas at a fixed concentration index, elliptical galaxies are preferentially more massive and have a lower SFR and SSFR than spiral galaxies. This result shows that the stellar mass, SFR and SSFR of a galaxy are correlated with its concentration index as well as its morphology. In addition, I note that AGNs are pref- erentially found in more concentrated galaxies only in the sample of spiral galaxies.

关键词： galaxies: fundamental parameters -- galaxies: statistics

Super-Large-Scale Structures in the Sloan Digital Sky Survey

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2006年第1期6卷 35-42页

作者： xin-fa deng Yi-Qing Chen Qun Zhang Ji-Zhou He Mathematics and Physics College Nanchang University Jiangxi 330047 Management Collegel Nanchang University Nanchang 330047

We study the super-large-scale structures in the Sloan Digital Sky Survey by cluster analysis, and examine the geometry and the properties of the member galaxies. Two subsamples are selected from the SDSS, Subsample 1 at the celestial equator and Subsample 2 further north. In Subsample 1 we discover two compact super-large-scale structures： the Sloan Great Wall and the Cfa Great Wall. The Sloan Great Wall, located at a median redshift of z= 0.07804, has a total length of about 433 Mpc and a mean galaxy density of about six times that of the whole sample. Most of its member galaxies are of medium size and brightness. The Cfa Great Wall, located at a median redshift of z = 0.03058, has a total length of about 251 Mpc and includes large percentages of faint and small galaxies and relatively fewer early-type galaxies.

关键词： galaxy: distances and redshifts - large-scale structure of universe

Local Environmental Dependence of Galaxy Properties in a Volume-Limited Sample of Main Galaxies

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2007年第5期7卷 639-648页

作者： xin-fa deng Ji-Zhou He Qun Zhang Xiao-Xia Qian Peng Jiang Yong xin School of Science Nanchang University Nanchang 330031

Using a volume-limited sample of Main Galaxies from SDSS Data Release 5, we investigate the dependence of galaxy properties on local environment. For each galaxy, a local three-dimensional density is calculated. We find that the galaxy morphological type depends strongly on the local environment; galaxies in dense environments have predominantly early type morphologies. Galaxy colors have only a weak dependence on the environment. This puts an important constraint on the process of galaxy formation.

关键词： galaxy distances and redshifts -- galaxies statistics

Isolated Main Galaxy Pairs from the SDSS Data Release 4

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2006年第4期6卷 411-420页

作者： xin-fa deng Yi-Qing Chen Ping Wu Cheng-Hong Luo Ji-Zhou He Mathematics and Physics College Nanchang University Nanchang 330047 Management College Nanchang UniversityNanchang330047

From the Main galaxy data of the SDSS Data Release 4 （SDSS4）, we have identiffed close galaxy pairs at neighbourhood radius R = 100 kpc by three-dimensional cluster analysis. Using the criterion that an ＂isolated galaxy pair＂ must be separated from its ＂nearest neighbor＂ by more than 500 kpc, we constructed an isolated galaxy pair sample of 1158 pairs. We also constructed a random pair sample by randomly selecting 1158 galaxy pairs from the Main galaxy sample, which has the same redshift distribution as the isolated galaxy pair sample, and in which the two components of any pair have the same redshifts. Comparative studies of luminosity and size between the members of the galaxy pairs are performed. We find and further confirm there is no tendency for paired galaxies to have similar luminosities or sizes. From the isolated pair sample we also selected a subsample with the magnitude limit of the primary raised by 2 magnitudes, so as to include pairs in which the secondary is 2 magnitudes fainter than the primary. This subsample contains 82 pairs. A random pair sample is similarly constructed.

关键词： galaxy: fundamental parameters- galaxies: interactions

多层RAM涂层对任意入射角电磁波的反射特性分析

在线全文

学校读者我要写书评

暂无评论

上海航天 2002年第4期19卷 18-21页

作者：夏新仁邓发升空军工程大学导弹学院陕西三原713800

为了解决结构型吸波材料的分析和设计中所遇到的反射系数计算问题 ,从电磁场理论出发 ,导出了电磁波以任意角入射时多层雷达吸波材料 (RAM)涂层的反射系数公式。此法简单易行 ,为结构型吸波材料的计算机辅助分析和设计提供了基础。同时... 详细信息

为了解决结构型吸波材料的分析和设计中所遇到的反射系数计算问题 ,从电磁场理论出发 ,导出了电磁波以任意角入射时多层雷达吸波材料 (RAM)涂层的反射系数公式。此法简单易行 ,为结构型吸波材料的计算机辅助分析和设计提供了基础。同时给出了计算曲线的例子 ,通过实例计算分析了电磁波的入射角。

关键词：多层RAM涂层任意入射角电磁波反射特性雷达吸波材料隐身

再入飞行器总体方案评估中模糊多属性决策的应用

在线全文

学校读者我要写书评

暂无评论

现代防御技术 2004年第4期32卷 32-36页

作者：陈新发邓克文蒲永飞中国工程物理研究院结构力学研究所四川绵阳621900

再入飞行器总体设计时,总体方案的决策是研制工作的重要环节。介绍了一种模糊多属性决策方法,在从多个方面考虑和评价一个再入体的总体设计方案的同时兼顾了语言变量和权重系数的模糊性,为决策部门作出正确决定提供更加客观的决策依据。

关键词：再入飞行器总体设计模糊多属性决策

A comparative study of piezoelectric unimorph and multilayer actuators as stiffness sensors via contact resonance

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2016年第4期32卷 633-639页

作者： Ji Fu fa-xin Li State Key Laboratory for Turbulence and Complex System College of Engineering Peking University

Piezoelectric bar-shaped resonators were proposed to act as hardness sensors in the 1960 s and stiffness sensors in the 1990 s based on the contact impedance *** this work, we point out that both multilayer and unimorph（or bimorph） piezoelectric actuators could act as stiffness/modulus sensors based on the principle of mechanical contact resonance. First, the practical design and the performance of a piezoelectric unimorph actuator–based stiffness sensor were presented. Then the working principle of piezoelectric multilayer actuator–based stiffness sensors was given and verified by numerical investigation. It was found that for these two types of resonance-based sensors, the shift of the resonance frequency due to contact is always positive, which is different from that of the contact impedance method. Further comparative sensitivity study indicated that the unimorph actuator–based stiffness sensor is very suitable for measurement on soft materials, whereas the multilayer actuator–based sensor is more suitable for hard materials.

关键词： piezoelectric stiffness multilayer actuator modulus hardness impedance shaped diamond verified

Numerical Simulation of Macrosegregation Caused by Thermal–Solutal Convection and Solidification Shrinkage Using ALE Model

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2019年第11期32卷 1396-1406页

作者： Kang-xin Chen Hou-fa Shen Key Laboratory for Advanced Materials Processing Technology Ministry of Education School of Materials Science and Engineering Tsinghua University

Solidifi cation shrinkage has been recognized as an important factor for macrosegregation formation. An arbitrary Lagrangian–Eulerian(ALE) model is constructed to predict the macrosegregation caused by thermal–solutal convection and solidi-fi cation shrinkage. A novel mesh update algorithm is developed to account for the domain change induced by solidifi cation shrinkage. The velocity–pressure coupling between the non-homogenous mass conservation equation and momentum equation is addressed by a modifi ed pressure correction method. The governing equations are solved by the streamline-upwind/Petrov–Galerkin-stabilized fi nite element algorithm. The application of the model to the Pb-19.2 wt%Sn alloy solidifi cation problem is considered. The inverse segregation is successfully predicted, and reasonable agreement with the literature results is obtained. Thus, the ALE model is established to be a highly effective tool for predicting the macrosegregation caused by solidifi cation shrinkage and thermal–solutal convection. Finally, the effect of solidifi cation shrinkage is analyzed. The results demonstrate that solidifi cation shrinkage delays the advance of the solidifi cation front and intensifi es the segregation.

关键词： Macrosegregation Solidification shrinkage Finite element method Arbitrary Lagrangian–Eulerian(ALE)