A dark matter disc in three cosmological simulations of Milky Way mass galaxies     

J. I. Read  L. Mayer  A. M. Brooks  F. Governato  G. Lake 《Monthly notices of the Royal Astronomical Society》2009,397(1):44-51

Making robust predictions for the phase-space distribution of dark matter at the solar neighbourhood is vital for dark matter direct-detection experiments. To date, almost all such predictions have been based on simulations that model the dark matter alone. Here, we use three cosmological hydrodynamic simulations of bright, disc-dominated galaxies to include the effects of baryonic matter self-consistently for the first time. We find that the addition of baryonic physics drastically alters the dark matter profile in the vicinity of the solar neighbourhood. A stellar/gas disc, already in place at high redshift, causes merging satellites to be dragged preferentially towards the disc plane where they are torn apart by tides. This results in an accreted dark matter disc that contributes ∼0.25–1.5 times the non-rotating halo density at the solar position. The dark disc, unlike dark matter streams, is an equilibrium structure that must exist in disc galaxies that form in a hierarchical cosmology. Its low rotation lag with respect to the Earth significantly boosts Weakly Interacting Massive Particle (WIMP) capture in the Earth and Sun, boosts the annual modulation signal and leads to distinct variations in the flux as a function of recoil energy that allow the WIMP mass to be determined.  相似文献   

Large-scale galactic turbulence: can self-gravity drive the observed H i velocity dispersions?     

Oscar Agertz  George Lake  Romain Teyssier  Ben Moore  Lucio Mayer  Alessandro B. Romeo 《Monthly notices of the Royal Astronomical Society》2009,392(1):294-308

Observations of turbulent velocity dispersions in the H  i component of galactic discs show a characteristic floor in galaxies with low star formation rates and within individual galaxies the dispersion profiles decline with radius. We carry out several high-resolution adaptive mesh simulations of gaseous discs embedded within dark matter haloes to explore the roles of cooling, star formation, feedback, shearing motions and baryon fraction in driving turbulent motions. In all simulations the disc slowly cools until gravitational and thermal instabilities give rise to a multiphase medium in which a large population of dense self-gravitating cold clouds are embedded within a warm gaseous phase that forms through shock heating. The diffuse gas is highly turbulent and is an outcome of large-scale driving of global non-axisymmetric modes as well as cloud–cloud tidal interactions and merging. At low star formation rates these processes alone can explain the observed H  i velocity dispersion profiles and the characteristic value of  ∼10 km s⁻¹  observed within a wide range of disc galaxies. Supernovae feedback creates a significant hot gaseous phase and is an important driver of turbulence in galaxies with a star formation rate per unit area  ≳10⁻³ M_⊙ yr⁻¹ kpc⁻²  .  相似文献   

Postscript: planning urban geographies and the contested rationalities of city-making     

Robert W. Lake 《Urban geography》2017,38(2):239-242

Urban space is produced through material enactments performed by situated actors whose practices follow a determinative logic – a rationality – that links specific means to specific ends. The three papers in this special issue explore the divergent, contested, contingent, and relational character of rationalities through which urban geographies are produced on the ground.  相似文献   

2018年总目次     

《湖泊科学》 《湖泊科学》2018,30(6):I-VII

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Use of otolith-shape analysis for stock discrimination of Boops boops along the Algerian coast (southwestern Mediterranean Sea)     

D Ider  Z Ramdane  K Mahé  JL Duffour  M Bacha 《African Journal of Marine Science》2017,39(3):251-258

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High-Resolution Records of the Holocene Paleoenvironmental Variation Reflected by Carbonate and Its Isotopic Compositions in Bosten Lake and Response to Glacial Activities   总被引：1，自引：0，他引：1  

ZHANG Chengjun  ZHENG Mianping  Alexander PROKOPENKO  Steffen MISCHKE  GOU Xiaohui  YANG Qili  ZHANG Wanyi  FENG Zhaodong 《《地质学报》英文版》2009,83(6):1101-1115

Abstract: The Early Holocene paleoclimate in Bosten Lake on the northern margin of the Tarim Basin, southern Xinjiang, is reconstructed through an analysis of a 953 cm long core (BSTC2000) taken from Bosten Lake. Multiple proxies of this core, including the mineral components of carbonate, carbonate content, stable isotopic compositions of carbonate, Ca/Sr, TOC and C/N and C/S of organic matter, are used to reconstruct the climatic change since 8500 a B.P. The chronology model is made by nine AMS 14C ages of leaves, seeds and organic matter contained in two parallel cores. The climate was cold and wet during 8500 to 8100 a B.P. Temperature increased from 8100 to 6400 a B.P., the climate was warm and humid, and the lake expanded. The lake level was highest during this stage. Then from 6400 to 5100 a B.P., the climate became cold and the lake level decreased slightly. During the late mid-Holocene, the climate was hot and dry from 5100 to 3100 a B.P., but there was a short cold period during 4400 to 3800 a B.P. At this temporal interval, a mass of ice and snow melting water supplied the lake at the early time and made the lake level rise. The second highest lake level stage occurred during 5200 to 3800 a B.P. The climate was cool and wet during 3100 to 2200 a B.P., when the lake expanded with decreasing evaporation. The lake had the last short-term high level during 3100 to 2800 a B.P. After this short high lake level period, the lake shrank because of the long-term lower temperature and reduced water supply. From 2200 to 1200 a B.P., the climate was hot and dry, and the lake shrank greatly. Although the temperature decreased somewhat from 1200 a B.P. to the present, the climate was warm and dry. The lake level began to rise a little again, but it did not reach the river bed altitude of the Konqi River, an outflow river of the Bosten Lake.  相似文献   

Climate variability recorded by n-alkanes of paleolake sediment in Qaidam Basin on the northeast Tibetan Plateau in late MIS3   总被引：1，自引：0，他引：1  

PU Yang    ZHANG HuCai  LEI GuoLiang  CHANG FengQin  YANG MingSheng  ZHANG WenXiang  LEI YanBin  YANG LunQing  & PANG YouZhi  State Key Laboratory of Lake Science  Environment  Nanjing Institute of Geography  Limnology  Chinese Academy of Sciences  Nanjing  China  Graduate University of Chinese Academy of Sciences  Beijing  Key Laboratory of Boyang Lake  MOE  School of Environmental  Chemical Engineering  Nanchang University  Nanchang 《中国科学:地球科学(英文版)》2010,(6)

Here we combine n-alkanes preserved in a shell bar section from Qarhan paleolake, Qaidam Basin with the other sedimentary proxies to elucidate the lake evolution process during the period 39.7 to 17.5 14C ka BP (calibrated age ranges from 43.5 to 22.4 cal. ka BP). In different stages, the n-alkane homologues exhibited different distribution modes indicative of variations in the surrounding vegetation and the hydrologic condition of the lake. The n-alkanes proxies (CPIh, ACLh, Paq) have the same trends as th...  相似文献   

Integrated Interpretation of Interwell Connectivity Using Injection and Production Fluctuations   总被引：1，自引：1，他引：0  

Ali A. Yousef  Jerry L. Jensen  Larry W. Lake 《Mathematical Geosciences》2009,41(1):81-102

A method to characterize reservoirs, based on matching temporal fluctuations in injection and production rates, has recently been developed. The method produces two coefficients for each injector–producer pair; one parameter, λ, quantifies the connectivity and the other, τ, quantifies the fluid storage in the vicinity of the pair. Previous analyses used λ and τ separately to infer the presence of transmissibility barriers and conduits in the reservoir, but several common conditions could not be easily distinguished. This paper describes how λ and τ can be jointly interpreted to enhance inference about preferential transmissibility trends and barriers. Two different combinations are useful: one is a plot of log (λ) versus log (τ) for a producer and nearby injectors, and the second is a Lorenz-style flow capacity (F) versus storativity (C) plot. These techniques were tested against the results of a numerical simulator and applied to data from the North Buck Draw field. Using the simulated data, we find that the F–C plots and the λ–τ plots are capable of identifying whether the connectivity of an injector–producer well pair is through fractures, a high-permeability layer, multiple-layers or through partially completed wells. Analysis of data from the North Buck Draw field shows a reasonable correspondence between τ and the tracer breakthrough times. Of two possible geological models for Buck Draw, the F–C and λ–τ plots support the model that has less connectivity in the field. The wells in fluvial deposits show better communication than those wells in more estuarine-dominated regions.  相似文献   

中缅毗邻区金腊Pb-Zn-Ag多金属矿田花岗岩锆石U-Pb定年与地球化学特征   总被引：4，自引：0，他引：4       下载免费PDF全文

陈永清  黄静宁  卢映祥  程志中  李建荣 《地学前缘》2009,16(1):344

位于中缅毗邻区的金腊铅锌银多金属矿田大地构造上处于保山—掸泰地块东缘,勐统—耿马—西盟元古宙—古生代被动大陆边缘活动带南段。与矿化有关的花岗岩(简称金腊花岗岩)包括老厂似斑状角闪二长花岗岩、勐林山似斑状黑云二长花岗岩和南腊碱长花岗斑岩。文中系统研究了上述岩石的主量元素、稀土元素、微量元素、成矿元素和锆石U-Pb同位素年龄等特征,从构造岩浆演化的角度,探讨上述岩体之间内在联系、成因演化以及与成矿的关系:(1)在金腊花岗岩三种岩石类型中,老厂似斑状角闪二长花岗岩和勐林山似斑状黑云二长花岗岩的锆石同位素U-Pb年龄皆为(45±1)Ma,形成于岩浆结晶分异早期阶段的深成环境,而南腊碱长花岗斑岩的锆石同位素U-Pb年龄为(43.41±0.78)Ma,形成于岩浆结晶分异晚期阶段的浅成环境。(2)主量元素和微量元素(稀土元素和某些微量元素(Zr/Hf、Nb/Ta、Rb/Sr、Rb/Ba、K/Rb、(Rb/Yb)N、Sr*、K*和Zr*)),结合U-Pb同位素定年研究表明,本区花岗岩形成于喜马拉雅同碰撞造山成矿作用末期局部拉张构造环境,并分别代表了构造岩浆演化过程中不同演化阶段岩浆分异结晶的产物。(3)上述三类花岗岩样品皆位于S型花岗岩区,但从老厂似斑状角闪二长花岗岩,勐林山似斑状黑云二长花岗岩,到南腊碱长花岗斑岩,样品分布逐渐远离"I"型花岗岩和"S"型花岗岩的分界线,这表明自老厂似斑状角闪二长花岗岩至勐林山似斑状黑云二长花岗岩,到南腊碱长花岗斑岩幔源组分逐渐减少。(4)相对中国花岗岩,南腊碱长花岗斑岩不仅更富集W、Cu、Bi、Sb、Mo、Sn、Ag、Pb和Au等成矿元素,而且还强烈富集F、B和As等矿化剂元素,因此,碱长花岗斑岩是最有成矿远景的岩体。  相似文献   

Using GIS and large-scale digital data to implement hedonic pricing studies     

Iain R. Lake  Andrew A. Lovett  Ian J. Bateman  Brett Day 《International journal of geographical information science》2013,27(6):521-541

This paper describes how a standard GIS package can be used to convert large-scale vector digital data (point, line and annotation features) into polygons using standardised and replicable methods. Building area, garden and land use polygons are all derived from such data (Ordnance Survey LandLine.Plus). These entities are then combined with further sources of digital data to derive more refined information such as property types. Finally, complex DEMs are developed for use in visibility studies. The variables calculated are subsequently employed in a property valuation study where many are found to be significant determinants of property price. The main exception is variables relating to viewsheds, although it is argued that this does not invalidate the techniques used in their deviation but highlights the difficulties involved in modelling a large number of variables in a property price analysis.  相似文献