检索结果-南通市图书馆

巴山山地退耕地植被自然恢复过程及物种多样性变化

在线全文

学校读者我要写书评

暂无评论

中国水土保持科学 2010年第2期8卷 99-104页

作者：魏振荣肖云丽李锐中国科学院水利部水土保持研究所西北农林科技大学陕西杨凌712100 中国科学院研究生院北京100049

巴山山地是我国南北方过渡地区,亦是长江重要的水源涵养区,探讨该地区退耕地植被自然恢复演替过程及其物种多样性的变化规律,对于指导该地区的人工植被建设具有重要的理论价值与实际意义。采用时空互代法对巴山山地退耕地植被自然恢复... 详细信息

巴山山地是我国南北方过渡地区,亦是长江重要的水源涵养区,探讨该地区退耕地植被自然恢复演替过程及其物种多样性的变化规律,对于指导该地区的人工植被建设具有重要的理论价值与实际意义。采用时空互代法对巴山山地退耕地植被自然恢复过程及其物种多样性变化进行研究,结果表明:1)巴山山地退耕地植被演替依次经过1年生植被草本群落、多年生草本群落、杂灌草群落及以栓皮栎、橿子栎或栓皮栎为建群种的阔叶林群落等不同阶段,形成地带性植物群落大致需要40～50 a;2)物种多样性会随立地环境的变化有所差异,阴坡的各物种多样性指标明显高于阳坡,但其变化规律基本一致。演替初期,植被群落的物种数、Shannon-wiener指数、Simpson指数和Pielou指数相对较低,随着植被群落演替的进行,各指标均呈波浪上升趋势;当植被恢复25 a时,各多样性指数均达到最大,分别为23、2.5、0.89和0.8;到地带性植物群落阶段时,其各物种多样性指标又略有降低并趋于稳定。该结论对于充分利用植被自然恢复进行生态改善,并根据植被演替进程采取相应的人工管理措施具有重要的指导意义。

关键词：植被自然恢复演替物种多样性退耕地巴山

Valuations on arithmetic surfaces

在线全文

学校读者我要写书评

暂无评论

Science china Mathematics 2009年第1期52卷 66-76页

作者： XU Ning Department of Mathematics, graduate school of chinese academy of sciences, beijing 100049, china Department of Mathematics Graduate School of Chinese Academy of Sciences Beijing 100049 China

In this paper, we give the definition of the height of a valuation and the definition of the big field ? p,G , where p is a prime and G ? ? is an additive subgroup containing 1. We conclude that ? p,G is a field and ? p,G is algebraically closed. Based on this the author obtains the complete classification of valuations on arithmetic surfaces. Furthermore, for any m ? p,G n ∈ ?, let V m,n be an ∝-vector space of dimension n - m + 1, whose coordinates are indexed from m to n. We generalize the definition of ? p,G , where p is a prime and G ? V m,n is an additive subgroup containing 1. We also conclude that ? p,G is a field if m ? 0 ? n.

关键词： valuation height rank totally ordered group big field transcendental number 14J10

Infrared Galaxies in the Nearby Universe

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2008年第6期8卷 643-652页

作者： Jian-Ling Wang 1 National Astronomical Observatories,chinese academy of sciences,beijing 100012,china 2 graduate school of chinese academy of sciences,beijing 100049,china National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China graduate school of chinese academy of sciences Beijing 100049 China

We used the Sloan Digital Sky Survey （SDSS） Data Release 5 （DR5） to study the morphological properties of 1137 nearby infrared （IR） galaxies, most of which are brighter than 15.9 mag in r-band. This sample was drawn from a cross-correlation of the Infra-Red Astronomical Satellite （IRAS） point source catalog redshift survey with DR5 at z ≤ 0.08. Based on this IR galaxy sample, we constructed five volume-limited sub-samples with IR luminosity ranging from 10^9.5 L⊙ to 10^12L⊙. By deriving the IR luminosity functions （LF） for different morphological types, we found that normal spiral galaxies are the dominant population below LIR ~ 8 ~ 10^10 L⊙; while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond LIR ≈ 5 × 10^10L⊙. As the IR luminosity decreases, the IR galaxies become more compact and have lower stellar masses. The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe, while, in contrast, the contribution from peculiar galaxies is only 39%.

关键词： galaxies evolution galaxies interactions galaxies starburst infrared galaxies galaxies luminosity function

H_2CO and H110α survey toward UCHII regions

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2011年第2期11卷 156-162页

作者： Xiao-Hong Han graduate University of chinese academy of sciences, beijing 100049, china National Astronomical Observatories / Urumqi Observatory Chinese Academy of Sciences Urumqi 830011 China graduate University of chinese academy of sciences Beijing 100049 China

We report results of the H2CO and H110α survey toward 281 UCHII regions using the Urumqi 25m radio *** obtained 37 new H2CO detections,and H110α was simultaneously detected in eight of *** H110α was detected in another UCHII *** calculated kinematic distances of nine UCHII regions with the detected H110α and resolved the kinematic distance ambiguity for six of *** detection rate of H2CO of our observation was 13.2%,which is low compared with one of the other *** possible reason is that the sensitivity of our telescope is relatively low.

关键词： ISM: HII regions -- ISM: molecules -- radio lines: ISM

Geometry of Broad Line Regions of Active Galactic Nuclei

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2008年第1期8卷 50-62页

作者： Xiao-Rong Lü1 Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, chinese academy of sciences, beijing 100049 2 graduate school of chinese academy of sciences, beijing 100049 Key Laboratory for Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 and graduate school of chinese academy of sciences Beijing 100049

It has long remained an open question as to the geometry of the broad line region （BLR） in active galactic nuclei （AGNs）. The reverberation mapping technique which measures the response of the broad emission lines to the ionizing continuum, when combined with multiwavelength continuum fitted by sophisticated accretion disks, provides a way of probing the BLR geometry. We analyze a sample of 35 AGNs, which have been monitored by the reverberation mapping campaign. In view of energy budget, the reverberation-based BH masses are found to be in agreement with those obtained by accretion disk models in two thirds of the present sample while the reverberation mapping methods underestimate the BH masses in about one third of objects, as also suggested by CoUin et al. in a recent work. We point out that there are obviously two kinds of BLR geometry, which are strongly dependent on the Eddington ratio, and separated by the value LBol/LEdd - 0.1. These results prefer a scenario of the disk and wind configuration of the BLR and identify the Eddington ratio as the physical driver regulating the wind in the BLR.

关键词： accretion, accretion disks - galaxies active - galaxies Seyfert - quasars general

Strong decays of N~*(1535) in an extended chiral quark model

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2009年第10期52卷 1452-1457页

作者： AN ChunSheng1,2,3 & ZOU BingSong1,2,3 1 Institute of High Energy Physics,chinese academy of sciences,beijing 100049,china 2 Theoretical Physics Center for Science Facilities,chinese academy of sciences,beijing 100049,china 3.graduate University of chinese academy of sciences,beijing 100049,china Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China Theoretical Physics Center for Science Facilities Chinese Academy of Sciences Beijing 100049 China graduate University of chinese academy of sciences Beijing 100049 China

The strong decays of the N*(1535) resonance are investigated in an extended chiral quark model by including the low-lying $ qqqq\bar q $ components in addition to the qqq component. The results show that these five-quark components in N*(1535) contribute significantly to the N*(1535) → Nπ and N*(1535) → Nη decays. The contributions to the Nη decay come from both the lowest energy and the next-tolowest energy five-quarks components, while the contributions to the Nπ decay come from only the latter one. Taking these contributions into account, the description for the strong decays of N*(1535) is improved, especially for the puzzling large ratio of the decays to Nη and Nπ.

关键词： N*(1535) strong decays five-quark components

Structure of augmentation quotients of finite homocyclic abelian groups

在线全文

学校读者我要写书评

暂无评论

Science china Mathematics 2007年第9期50卷 1280-1288页

作者： Guo-ping TANG school of Mathematical sciences,graduate University of chinese academy of sciences,beijing 100049,china 1. school of Mathematical sciences Graduate University of Chinese Academy of Sciences Beijing 100049 China

Let G be a finite abelian group and its Sylow p-subgroup a direct product of copies of a cyclic group of order p r , i.e., a finite homocyclic abelian group. Let Δ n (G) denote the n-th power of the augmentation ideal Δ(G) of the integral group ring ?G. The paper gives an explicit structure of the consecutive quotient group Q n (G) = Δ n (G)/Δ n+1(G) for any natural number n and as a consequence settles a problem of Karpilovsky for this particular class of finite abelian groups.

关键词： integral group ring augmentation ideal consecutive quotient of augmentation ideal 16S34 20C05

A Test on Different Types of the Time Curve of Hardness Ratio of Gamma-Ray Bursts based on the Curvature Effect

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2008年第4期8卷 451-464页

作者： Lan-Wei Jia National Astronomical Observatories/Yunnan Observatory,chinese academy of sciences,Kunming 650011,china graduate school of chinese academy of sciences,beijing 100049,china National Astronomical Observatories/ Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China and graduate school of chinese academy of sciences Beijing 100049 China

We analyzed a sample of 66 gamma-ray bursts （GRBs） and statistically confirmed the prediction on the time curve of the hardness ratio of GRBs made by Qin et al. based on the curvature effect. In their analysis, GRB pulses are divided into three types according to the shape of their raw hardness ratio （RHR） time curves, defined as to include the background counts to the signal counts, so as to make use of counts within small time intervals. Of the three types, very hard sources exhibit a perfect pulse-like profile （type 1）, hard bursts possess a pulse-like profile with a dip in the decay phase （type 2）, and soft bursts show no pulse-like profile but have only a dipped profile （type 3）. In terms of the conventional hardness ratio, type 3 sources are indeed generally softer than those of type 1 and type 2, in agreement with the prediction. We found that the minimum value of RHR is sensitive in distinguishing the different types. We propose that GRB pulses can be classified according to the minimum value of RHR and that the different type sources may be connected with different strengths of the shock or/and the magnetic field.

关键词： gamma-rays burst -- gamma-rays observations - methods statistical

水分胁迫及土壤质地对新银合欢幼苗根系生长的影响

在线全文

学校读者我要写书评

暂无评论

中国水土保持 2012年第6期 34-37,76页

作者：陈东王道杰郭灵辉陈晓艳中国科学院水利部成都山地灾害与环境研究所四川成都610041 中国科学院山地灾害与地表过程重点实验室四川成都610041 中国科学院研究生院北京100049

新银合欢是生物措施治理泥石流的重要树种,但在金沙江干热河谷的泥石流源区,干旱少雨和土壤砾石含量高已成为新银合欢生长的主要限制因子。为揭示新银合欢幼苗在生境中的抗逆特性,利用盆栽模拟试验,从水分胁迫和土壤质地的角度研究了非... 详细信息

新银合欢是生物措施治理泥石流的重要树种,但在金沙江干热河谷的泥石流源区,干旱少雨和土壤砾石含量高已成为新银合欢生长的主要限制因子。为揭示新银合欢幼苗在生境中的抗逆特性,利用盆栽模拟试验,从水分胁迫和土壤质地的角度研究了非生物因素对新银合欢幼苗根系生长的影响,结果表明:对根系生长的影响水分胁迫程度大于土壤质地状况;在相同土壤质地条件下,水分胁迫程度与根系长度、累积表面积及根尖数量均呈负相关;在相同土壤水分条件下,低砾石含量的土壤对根系生长的促进作用总体优于高砾石含量的,但在极端水分条件下这种差异不明显;低砾石组和高砾石组对根系生长构成限制条件的土壤水分含量分别在8.25%、11.46%以下。

关键词：新银合欢幼苗根系土壤质地水分胁迫