地铁隧洞带水作业施工技术

以在建的北京地铁十号线双井一劲松区间暗挖隧道为例，通过分析北京特殊地层在带水条件下单洞结构单线隧道台阶法的施工工艺，洞悉浅埋暗挖正台阶法施工中超前预加固、开挖时空顺序、台阶长度等工艺对围岩稳定性的影响程度。     

湖泊水位资料与模型模拟恢复的6000年前全球湿润状况的对比研究

本项研究是ＰＭＩＰ（ＰａｌａｅｏｃｌｉｍａｔｅＭｏｄｅｌｉｎｇＩｎｔｅｒｃｏｍｐａｒｉｓｏｎＰｒｏｊｅｃｔ）国际合作项目中有关模型模拟与观测资料对比的一部分。模型试验对象是６０００ｙｒ．ＢＰ的全球湿润状况。模拟试验以检测太阳辐射变化对全球大尺度气候系统的影响为主要目的。观测资料是利用地质证据恢复的古湖泊水位变化,实际上是某一地区的有效降水（降水减蒸发）的变化。通过两者的比较发现,所有模拟试验均能重现６０００ｙｒ．ＢＰ在亚洲南部与非洲北部的湿润环境,从而证实了因太阳辐射变化导致的亚洲与非洲季风的增强。但模拟的季风增强无论是强度还是范围均小于地质记录。原因很可能是模拟试验中下垫面特征用“现代”的来处理。模拟试验对北半球夏季辐射增加造成的西风带北移及由此引起的中纬度地区的气候变化不够成功。绝大多数模拟对受洋流与海温影响较大的地区是失败的。主要原因可能是所有ＰＭＩＰ中的模拟试验都未考虑海洋的作用。     

Determination of predevelopment denudation rates of an agricultural watershed (Cayaguás River, Puerto Rico) using in-situ-produced Be in river-borne quartz

Accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities, to model global geochemical cycles, and to examine interactions among climate, weathering, and uplift. We present a simple approach to estimate predevelopment denudation rates using in-situ-produced cosmogenic ¹⁰Be in fluvial sediments. Denudation processes in an agricultural watershed (Cayaguás River Basin, Puerto Rico) and a matched undisturbed watershed (Icacos River Basin) were compared using ¹⁰Be concentrations in quartz for various size fractions of bed material. The coarse fractions in both watersheds bear the imprint of long subsurface residence times. Fine material from old shallow soils contributes little, however, to the present-day sediment output of the Cayaguás. This confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the Cayaguás Basin and suggests that pre-agricultural erosional conditions were comparable to those of the present-day Icacos.     

On the ultracompact nature of 4U 1822−000

We report the discovery of a periodic modulation in the optical lightcurve of the candidate ultracompact X-ray binary 4U 1822−000. Using time-resolved optical photometry taken with the William Herschel Telescope we find evidence for a sinusoidal modulation with a semi-amplitude of 8 per cent and a period of 191 min, which is most likely close to the true orbital period of the binary. Using the van Paradijs & McClintock relation for the absolute magnitude and the distance modulus allowing for interstellar reddening, we estimate the distance to 4U 1822−000 to be 6.3 kpc. The long orbital period casts severe doubts on the ultracompact nature of 4U 1822−000.     

Minimum Bedrock Exposure Ages and Their Implications: Larsemann Hills and Neighboring Bolingen Islands, East Antarctica

<正>Considerable controversy exists over whether or not extensive glaciation occurred during the global Last Glacial Maximum(LGM) in the Larsemann Hills.In this study we use the in situ produced cosmogenic nuclide ~(10)Be(half life 1.51 Ma) to provide minimum exposure ages for six bedrock samples and one erratic boulder in order to determine the last period of deglaciation in the Larsemann Hills and on the neighboring Bolingen Islands.Three bedrock samples taken from Friendship Mountain(the highest peak on the Mirror Peninsula,Larsemann Hills;～2 km from the ice sheet) have minimum exposure ages ranging from 40.0 to 44.7 ka.The erratic boulder from Peak 106(just at the edge of the ice sheet) has a younger minimum exposure age of only 8.8 ka.The minimum exposure ages for two bedrock samples from Blundell Peak(the highest peak on Stornes Peninsula,Larsemann Hills;～2 km from the ice sheet) are about 17 and 18 ka.On the Bolingen Islands(southwest to the Larsemann Hills;～10 km from the ice sheet),the minimum exposure age for one bedrock sample is similar to that at Friendship Mountain(i.e.,44 ka).Our results indicate that the bedrock exposure in the Larsemann Hills and on the neighboring Bolingen Islands commenced obviously before the global LGM(i.e.,20-22 ka),and the bedrock erosion rates at the Antarctic coast areas may be obviously higher than in the interior land.     

Periglacial climate at the 2.5 Ma onset of Northern Hemisphere glaciation inferred from the Whippoorwill Formation, northern Missouri, USA

The Whippoorwill Formation is a gleyed diamicton that is present locally within bedrock depressions beneath the oldest glacial till in northern Missouri, USA. Stratigraphy, paleomagnetism, and cosmogenic-nuclide burial ages show that it was deposited between the Matuyama-Gauss magnetostratigraphic boundary at 2.58 Ma and the first advance of the Laurentide ice sheet into Missouri at 2.47 ± 0.19 Ma. High cosmogenic-nuclide concentrations also show that the constituents of the Whippoorwill Formation experienced long exposure at a stable landscape surface with erosion rates of 1-2 m/Ma. However, cosmogenic-nuclide concentrations are invariant with depth below the Whippoorwill Formation surface, indicating active mixing of the soil profile shortly before burial by till. The Whippoorwill Formation retains numerous features indicative of cryoturbation. Therefore, we interpret it as a buried Gelisol, a soil formed under periglacial conditions in the presence of permafrost. At the onset of Northern Hemisphere glaciation, climate cooling established permafrost conditions and accelerated erosion by inducing landscape instability. Thus, weathered regolith materials were mobilized and redeposited by gelifluction shortly before the ice sheet overrode the landscape.     

山西吕梁山北段中生代构造特征及对成矿的制约

为进一步研究山西吕梁山北段中生代构造特征及对成矿的制约,利用数字化填图方法,在偏关县一带开展1:25万区域地质调查。发现几条中生代大型构造带,查明了这些大型构造带的空间展布、性质、断裂组合及运动学特征; 证实了中生代为该区重要的多金属成矿期,成矿作用尽管与中生代岩浆活动关系密切,但在空间上分布受NE向隐伏构造的制约; 大型挠褶构造是地壳强烈隆升的标志,区内大型构造带多数是在挠褶构造的基础上叠加断层而形成的。该研究对于探讨山西中—新生代构造的演化发展具有重要意义。     

中心地理论中市场原则的再讨论

本文指出中心地理论中k = 3系统由市场原则生成的几种传统说法的缺陷;提出所有相邻级别中心地,在满足以下两个条件：① 正三角形的中心地分布和中心地之正六边形市场区;② 较高级别中心地提供相应级别及比其等级低的货物,它们的市场区（或腹地）之大小应尽可能地接近,以尽最大可能地减少相邻级别中心地市场区之间的差距,进而降低所生成的中心地系统对要配置的商品或服务因其上限或下限范围之要求产生可能的排除,这即是市场原则之合理说法。本文的新提法能够调和克里斯塔勒自上而下和哈格特自下而上建构中心地系统所产生的规模等级及其解释之差异。从廖什的空间垄断竞争型中心地建模理念看,根据此提法建立的中心地系统尽可能地降低了厂商的空间垄断性,以减少厂商取得的超额利润,其符合正常市场理性原则。本文对中心地理论中k = 3市场原则内涵的修正能够提升中心地理论对现实世界的分析和实践指导作用。     

Erosions on the southern Tibetan Plateau: Evidence from in-situ cosmogenic nuclides 10Be and 26Al in fluvial sediments

Investigating topographic and climatic controls on erosion at variable spatial and temporal scales is essential to our understanding of the topographic evolution of the orogen.In this work,we quantified millennial-scale erosion rates deduced from cosmogenic 10Be and 26Al concentrations in 15 fluvial sediments from the mainstream and major tributaries of the Yarlung Zangbo River draining the southern Tibetan Plateau (TP).The measured ratios of 26Al/10Be range from 6.33 ± 0.29 to 8.96 ± 0.37,suggesting steady-state erosion processes.The resulted erosion rates vary from 20.60 ± 1.79 to 154.00 ± 13.60 m Myr-1,being spatially low in the upstream areas of the Gyaca knickpoint and high in the downstream areas.By examining the relationships between the erosion rate and topographic or climatic indices,we found that both topography and climate play significant roles in the erosion process for basins in the upstream areas of the Gyaca knickpoint.However,topography dominantly controls the erosion processes in the downstream areas of the Gyaca knickpoint,whereas variations in precipitation have only a second-order control.The marginal Himalayas and the Yarlung Zangbo River Basin (YZRB) yielded significantly higher erosion rates than the central plateau,which indicated that the landscape of the central plateau surface is remarkably stable and is being intensively consumed at its boundaries through river headward erosion.In addition,our 10Be erosion rates are comparable to present-day hydrologic erosion rates in most cases,suggesting either weak human activities or long-term steady-state erosion in this area.