300 BC-1900 AD无定河流域城镇时空格局演变

通过分析和整理从战国中晚期（约300 BC）至清末（约1900 AD）无定河流域历代县级及以上城址的位置、兴废年代数据,结合行政区划沿革、经济社会发展、政权更迭等资料,分析流域城镇格局的时空演变过程。研究表明：① 受气候周期性波动影响,无定河流域城镇的兴起与衰废具有明显的周期性特征,城镇几何中心的移动轨迹具有明显的“西北—东南”向潮汐性运动特征;② 城址存续年限普遍较短,具有明显的阶段性特征,流域内曾存在过4个阶段性中心城镇,中心城镇移动的方向和过程与城镇几何中心的潮汐性移动过程趋势一致;③ 流域城镇空间格局可分为3种类型,即秦汉与隋唐时期的沿河流谷地分布,宋、明两代的沿边境线与长城分布,以及元、清两代集中于流域下游分布。流域城镇未来的发展布局应重视气候变化对城镇分布的长期影响,关注区域环境的脆弱性,合理安排城镇体系发展规模与布局。     

乌兰布和沙漠典型植物群落土壤风蚀可蚀性研究

为探明植被恢复对乌兰布和沙漠土壤风蚀可蚀性的影响，以乌兰布和沙漠内不同沙地固 定阶段的 8 种典型植物群落及群落内表土作为研究对象，对土壤物理因子（可蚀性颗粒含量、土壤 含水量、有机质含量）、土壤结皮因子、植被因子 3 类土壤风蚀可蚀性因子指标进行监测，分析土壤 风蚀可蚀性因子在不同植物群落类型间、沙地固定阶段间的差异。结果表明：（1）在乌兰布和沙漠 典型植物群落中，沙蓬、沙生针茅、盐爪爪等草本植物群落的土壤风蚀可蚀性最强，白刺、梭梭、沙 冬青等灌木植物群落土壤风蚀可蚀性弱于草本植物群落，说明灌木林能显著降低土壤风蚀作用。 （2）随着沙地的不断固定，土壤结构不断发育，土壤可蚀性不断降低，土壤风蚀可蚀性强弱表现为 固定沙地<半固定沙地<流动沙地。（3）土壤可蚀性颗粒含量、土壤有机质含量、土壤含水量、土壤结 皮、植被因子与植被类型及沙地固定阶段具有显著相关关系。因此，在沙区生态建设工程中，为了 减少土壤风蚀量，不仅要考虑物种的选择，还要促进人工生态系统的演替和恢复，从而有效降低土 壤风蚀可蚀性。研究结果可为乌兰布和沙区植被生态系统服务功能的科学评价、防沙治沙工程的 建设与管理提供一定参考。     

RECENT TECTONIC DEFORMATION ANOMALY AND EARTHQUAKES IN GANSU-NINGXIA-QINGHAI AREA

1　IntroductionAccordingtogeologicalstructure ,theGansu Ningxia Qinghaiareabelongstothenortheastmar ginofQinghai Tibetblock .Thisareahasbeenpaidmuchattentionby geo specialistsinChinaandabroadbecauseofitssignificanttectonicmovement,itsintensiveseismicity ,anditsimportanceinearth quakehazardmitigation .IntheDevelopmentPro gramonNationalKeyBasicResearchesundertheProject“MechanismandPredictionofContinentalStrongEarthquakes”,themechanismsofcontinen talstrongearthquakesarestudied ,usinghypo…     

Influence of the Choice of Core-Envelope Transition Point on the Binary Merger of Two Main-sequence Components

We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, qmix, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as qmix< 0.8, none of the     

Age and early metamorphic history of the Sanbagawa belt: Lu–Hf and P–T constraints from the Western Iratsu eclogite

Two distinct age estimates for eclogite-facies metamorphism in the Sanbagawa belt have been proposed: (i) c.  120–110 Ma based on a zircon SHRIMP age for the Western Iratsu unit and (ii) c.  88–89 Ma based on a garnet–omphacite Lu–Hf isochron age from the Seba and Kotsu eclogite units. Despite the contrasting estimates of formation ages, petrological studies suggest the formation conditions of the Western Iratsu unit are indistinguishable from those of the other two units—all ∼20 kbar and 600–650 °C. Studies of the associated geological structures suggest the Seba and Western Iratsu units are parts of a larger semi-continuous eclogite unit. A combination of geochronological and petrological studies for the Western Iratsu eclogite offers a resolution to this discrepancy in age estimates. New Lu–Hf dating for the Western Iratsu eclogite yields an age of 115.9 ± 0.5 Ma that is compatible with the zircon SHRIMP age. However, petrological studies show that there was significant garnet growth in the Western Iratsu eclogite before eclogite facies metamorphism, and the early core growth is associated with a strong concentration of Lu. Pre-eclogite facies garnet (Grt1) includes epidote–amphibolite facies parageneses equilibrated at 550–650 °C and ∼10 kbar, and this is overgrown by prograde eclogite facies garnet (Grt2). The Lu–Hf age of c.  116 Ma is strongly skewed to the isotopic composition of Grt1 and is interpreted to reflect the age of the pre-eclogite phase. The considerable time gap ( c.  27 Myr) between the two Lu–Hf ages suggests they may be related to separate tectonic events or distinct phases in the evolution of the Sanbagawa subduction zone.     

GIS支持下长江口南支河道百年来的演变

利用长江口南支河道1900—2001年的5幅海图资料,在GIS的支持下,建立了百年来长江口南支河道的水下数字高程模型(DEM),在此基础上对其演变特征进行了计算和分析。结果表明:(1)1900—2001年间南支河道表现为微冲,不同时段的冲淤状况不同。(2)南支河道的冲淤演变主要表现为5个水道和4个成形沙体的冲淤变化,各水道的最大水深和成形沙体的总面积和总体积都呈不断增大趋势。(3)南支河道各主要断面以复式河槽为主,主槽位于南岸,且最大水深不断增大。位于南支河道入口处和出口处断面的变化比中段断面的变化剧烈。(4)南支河道的演变是自然演变和人工控制共同作用的结果。     

Disk galaxy evolution: from the Milky Way to high-redshift disks

We develop a detailed model of the Milky Way (a `prototypical' disk galaxy) and extend it to other disks with the help of some simple scaling relations, obtained in the framework of Cold Dark Matter models. This phenomenological (`hybrid') approach to the study of disk galaxy evolution allows us to reproduce successfully a large number of observed properties of disk galaxies in the local Universe and up to redshift z ∼ 1. The important conclusion is that, on average, massive disks have formed the bulk of their stars earlier than their lower mass counterparts: the `star formation hierarchy' has been apparently opposite to the `dark matter assembly' hierarchy. It is not yet clear whether `feedback' (as used in semi-analytical models of galaxy evolution) can explain that discrepancy. This revised version was published online in August 2006 with corrections to the Cover Date.