球状星团的金属丰度特征与其恒星形成史     

张枚  马駬 《中国天文和天体物理学报》1992,(4)

本文根据球状星团所特有的金属丰度特征,利用星族综合方法,探讨了球状星团诸恒星的形成史。研究表明,这些恒星不可能通过恒星形成率和初始质量函数均不随时间变化的单一恒星形成模式产生。原初云通过恒星演化而得到金属丰度污染的过程和多数恒星的形成过程必须分为两个不同的阶段。 球状星团得到金属丰度污染的过程中,若恒星形成具有通常的初始质量函数,则其恒星形成率必须较低,且初始质量函数不能太陡,从而使污染过程中只形成数量较少的低质量恒星,以保证单个球状星团内金属丰度的均匀性。另一种可能性是污染阶段有非常特殊的初始质量函数,只形成大质量的恒星,从而除提供适量污染外不留下任何痕迹。 多数恒星应是在原初云不同部位得到适当污染后通过局域的短暂的爆发性恒星形成(星暴过程)产生。本文进一步探讨了在Fan和Rees球状星团形成模型的框架下,两相介质中温云块相互碰撞造成星暴过程的可能性。  相似文献   

Geophysical Images of the North Anatolian Fault Zone in the Erzincan Basin, Eastern Turkey, and their Tectonic Implications     

Ümİt Avşar  Erşan Türkoğlu  Martyn Unsworth  İlyas Çağlar  Bülent Kaypak 《Pure and Applied Geophysics》2013,170(3):409-431

The collision between the Arabian and Eurasian plates in eastern Turkey causes the Anatolian block to move westward. The North Anatolian Fault (NAF) is a major strike-slip fault that forms the northern boundary of the Anatolian block, and the Erzincan Basin is the largest sedimentary basin on the NAF. In the last century, two large earthquakes have ruptured the NAF within the Erzincan Basin and caused major damage (M _s = 8.0 in 1939 and M _s = 6.8 in 1992). The seismic hazard in Erzincan from future earthquakes on the NAF is significant because the unconsolidated sedimentary basin can amplify the ground motion during an earthquake. The amount of amplification depends on the thickness and geometry of the basin. Geophysical constraints can be used to image basin depth and predict the amount of seismic amplification. In this study, the basin geometry and fault zone structure were investigated using broadband magnetotelluric (MT) data collected on two profiles crossing the Erzincan Basin. A total of 24 broadband MT stations were acquired with 1–2 km spacing in 2005. Inversion of the MT data with 1D, 2D and 3D algorithms showed that the maximum thickness of the unconsolidated sediments is ~3 km in the Erzincan Basin. The MT resistivity models show that the northern flanks of the basin have a steeper dip than the southern flanks, and the basin deepens towards the east where it has a depth of 3.5 km. The MT models also show that the structure of the NAF may vary from east to west along the Erzincan Basin.  相似文献   

Erosion rates of different land uses and sediment sources in a watershed using the <Superscript>137</Superscript>Cs tracing method: field studies in the Loess Plateau of China     

Mian Li  Wenyi Yao  Zhenzhou Shen  Jishan Yang  Er Yang 《Environmental Earth Sciences》2016,75(7):591

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高红移星系特征与星系环境     

马駬  陈时 《中国天文和天体物理学报》1993,(1)

本文在星系有偏袒形成的冷暗物质模型框架下,假定星系都在红移～5时形成,研究了星系群和星系团的形成对星系演化的影响。由示冷暗物质模型中各种不同尺度扰动的幅度相近,星系群和星系团的维里化与星系的维里化在时间上比较接近,在星系群或星系团的维里化过程中获得巨大维里速度的星系仍然富有气体,因此,当它们因为频繁的互相碰撞,或者因为进入星系团中心区的稠密星系际介质受到巨大冲压,或者是被附近射电星系的喷流所产生的高压茧状体所包容,都可能激发活动性,造成恒星的爆发性形成.高红移星系团中观测到的B-O效应和高红移射电星系的光学像与射电喷流同轴向现象都可以据此得到解释.  相似文献   

Biodiversity of free-living marine nematodes in the southern Yellow Sea,China     

Xiaoshou Liu  Man Xu  Er Hua  Zhinan Zhang 《中国海洋大学学报(英文版)》2016,15(1):1-10

Biodiversity patterns of free-living marine nematodes were studied using specific,taxonomic and phylogenetic diversity measures in the southern Yellow Sea,China.The results showed that the average of Shannon-Wiener diversity index(H′) in the study area was 3.17.The higher values were distributed in the east part of Shandong coastal waters and north part of Jiangsu coastal waters,while the lower values were distributed in the southern Yellow Sea Cold Water Mass(YSCWM).The average of taxonomic diversity(Δ) was 62.09 in the study region.The higher values were distributed in the transitional areas between the coastal areas and the southern YSCWM,while the lower values were distributed near the north part of Jiangsu coastal waters and the YSCWM.Results of correlation analysis of species diversity and taxonomic diversity showed that some of the two kinds of diversity index were independent,which suggested that combining the two kinds of diversity indices can reflect the ecological characteristics better.A test for 95% probability funnels of average taxonomic distinctness and variation in taxonomic distinctness suggested that Station 8794(in the YSCWM) was outside of the 95% probability funnels,which may be due to the environmental stress.Results of correlation analysis between marine nematodes biodiversity and environmental variables showed that the sediment characteristics(Md? and Silt-clay fraction) and phaeophorbide a(Pha-a) were the most important factors to determine the biodiversity patterns of marine nematodes.  相似文献