Damped Lyα systems at high redshift and models of protogalactic discs     

Karsten Jedamzik  & Jason X. Prochaska 《Monthly notices of the Royal Astronomical Society》1998,296(2):430-436

We employ observationally determined intrinsic velocity widths and column densities of damped Lyman alpha (Lyα) systems at high redshift to investigate the distribution of baryons in protogalaxies within the context of a standard cold dark matter (CDM) model. We proceed under the assumption that damped Lyα systems represent a population of cold, rotationally supported, protogalactic discs, and that the abundance of dark matter haloes is well approximated by a CDM model with critical density and vanishing cosmological constant. Using conditional cross-sections to observe a damped system with a given velocity width and column density, we compare observationally inferred velocity width and column density distributions to the corresponding theoretically determined distributions for a variety of disc parameters and CDM normalizations. In general, we find that the observations cannot be reproduced by the models for most disc parameters and CDM normalizations. Whereas the column density distribution favours small discs with large neutral gas fraction, the velocity width distribution favours large and thick discs with small neutral gas fraction. The possible resolutions of this problem in the context of this CDM model may be (1) an increased contribution of rapidly rotating discs within massive dark matter haloes to damped Lyα absorption, or (2) the abandoning of simple disc models within this CDM model for damped Lyα systems at high redshift. Here the first possibility may be achieved by supposing that damped Lyα system formation occurs only in haloes with fairly large circular velocities, and the second possibility may result from a large contribution of mergers and double discs to damped Lyα absorption at high redshift.  相似文献   

The petrogenesis of Tertiary cone-sheets in Ardnamurchan, NW Scotland: petrological and geochemical constraints on crustal contamination and partial melting     

Jörg Geldmacher  Karsten M. Haase  Colin W. Devey  C. Dieter Garbe-Schönberg 《Contributions to Mineralogy and Petrology》1998,131(2-3):196-209

Abundant cone sheets form one of the last magmatic stages in the Tertiary central complex on the Scottish peninsula of Ardnamurchan and can be grouped into a younger inner and an older outer suite relative to a gabbro intrusion. Most of the cone-sheets consist of tholeiitic to transitional basalt with MgO contents between 7.5% and 4%, although more evolved rocks also occur (to 0.5% MgO). The mafic samples are slightly enriched in the light rare earth elements (Chondrite-normalized La/Sm ∼1.1), the enrichment increases in the more evolved rocks. The compositional variation of the basaltic rocks is mainly due to crystal fractionation of olivine and clinopyroxene at depths of ∼10 km but trace elements show simultaneous assimilation of Archean Lewisian granulite crust. The andesitic to rhyolitic lavas formed by fractional crystallization from the contaminated basaltic magma coupled with assimilation of Proterozoic Moine metasediments at uppermost crustal levels. The occurrence of composite cone-sheets with basaltic and rhyolitic parts and mixtures between these magmas implies that the melts ascended successively but within a short period of time. The parental magmas of the Ardnamurchan cone-sheets must have formed at relatively shallow depths in the mantle and are comparable to the youngest tholeiitic lavas from the neighbouring island of Mull. Received: 5 June 1997 / Accepted: 12 November 1997  相似文献   

Turbulent mixing in the Northern North Sea: a numerical model study     

Karsten Bolding  Hans Burchard  Thomas Pohlmann  Adolf Stips 《Continental Shelf Research》2002,22(18-19)

The aim of this study is to intervalidate observations and numerical simulation results for the turbulent dissipation rate under strong wind conditions in the Northern North Sea during one week in October 1998. The observations were obtained by spatially and temporally averaging measurements of small-scale shear with a free-falling shear probe. The 1D numerical model used for this study is based on a state-of-the-art two-equation k− turbulence model with an algebraic second-moment closure scheme. It is discussed by means of annual and seasonal model simulations how the influence of heat and salt advection and internal waves can be accounted for. After these precautions, the agreement between observations and simulations of the turbulent dissipation rate are fairly good. Remaining differences cannot only be explained by problems such as undersampling and noise level, but also by idealising model assumptions.  相似文献   

On the feasibility of seafloor magnetotelluric soundings in the North Sea     

Karsten Bahr 《Ocean Dynamics》1988,41(3-6):277-281

  相似文献   

An overview of the Lagrangian experiments undertaken during the North Atlantic regional Aerosol Characterisation Experiment (ACE‐2)     

Doug W. Johnson  Simon Osborne  Robert Wood  Karsten Suhre  Randy Johnson  Steven Businger  Patricia K. Quinn  Alfred Wiedensohler  Philip A. Durkee  Lynn M. Russell  Meinrat O. Andreae  Colin O'Dowd  Kevin J. Noone  Brian Bandy  J. Rudolph  Spyros Rapsomanikis 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):290-320

  相似文献   

Preliminary Mapping and Characterisation of Soils in the Pirin Mountains (Bulgaria)     

Maika LBiger  Jrg Seheithauer  Karsten Grunewald 《山地科学学报》2008,5(2)

Soft types, humus types and vegetation as well as their hypsometric variation were analysed in terms of sequences in the northern part of the high mountains of the Pirin National Park at altitudes between 1000 and 2400 m a.s.l. The study area is characterised by a large variety of natural parameters like petrology (mainly marble and granite), morphology (different slope deposits, exposition) and the orographic climate gradient. Statistical analyses using these parameters provided a basis for the soil group classification of the sites. Based on a Digital Terrain Model (DTM) and a geological map of the Pirin National Park, the results of these statistical analyses were used to generate a "map of potential soft groups" (regionalisation using GIS). Six potential soil groups could be determined. The resulting map exhibits a confidence level of 68% on 74.4% of the covered area. Rendzic Leptosols, in combination with Folio Histosols and Histi-lithic Leptosols occur in the alpine and subalpine regions on calcareous substrates. With decreasing altitude they are replaced by a mosaic of Rendzic Leptosols, Phaeozems and an increasing occurrence of Cambic Umbrisols. Umbrisols found on silicatic substrates in the alpine region are replaced by Cambic Umbrisols with decreasing altitude as well. Hence, pedogenesis is characterised by increasing browning and depth of the soil profiles with decreasing altitude. The pH-level is slightly acidic to neutral in lower zones and on calcareous rocky bases. Acidification increases in the subalpine zone. Soft pH decreases down to 4 on silicate subtrates. Typical humic values in mineral topsoils are 10 to 12%, and in organic layers of the softs above 2000 m a.s.l, they are even more. The C:N ratio closely ranges around 20 (median).  相似文献   

New Olivine Reference Material for In Situ Microanalysis     

Valentina G. Batanova  Jay M. Thompson  Leonid V. Danyushevsky  Maxim V. Portnyagin  Dieter Garbe‐Schnberg  Erik Hauri  Jun‐Ichi Kimura  Qing Chang  Ryoko Senda  Karsten Goemann  Catherine Chauvel  Sylvain Campillo  Dmitri A. Ionov  Alexander V. Sobolev 《Geostandards and Geoanalytical Research》2019,43(3):453-473

A new olivine reference material – MongOL Sh11‐2 – for in situ analysis has been prepared from the central portion of a large (20 × 20 × 10 cm) mantle peridotite xenolith from a ~ 0.5 My old basaltic breccia at Shavaryn‐Tsaram, Tariat region, central Mongolia. The xenolith is a fertile mantle lherzolite with minimal signs of alteration. Approximately 10 g of 0.5–2 mm gem quality olivine fragments were separated under binocular microscope and analysed by EPMA, LA‐ICP‐MS, SIMS and bulk analytical methods (ID‐ICP‐MS for Mg and Fe, XRF, ICP‐MS) for major, minor and trace elements at six institutions world‐wide. The results show that the olivine fragments are sufficiently homogeneous with respect to major (Mg, Fe, Si), minor and trace elements. Significant inhomogeneity was revealed only for phosphorus (homogeneity index of 12.4), whereas Li, Na, Al, Sc, Ti and Cr show minor inhomogeneity (homogeneity index of 1–2). The presence of some mineral and fluid‐melt micro‐inclusions may be responsible for the inconsistency in mass fractions obtained by in situ and bulk analytical methods for Al, Cu, Sr, Zr, Ga, Dy and Ho. Here we report reference and information values for twenty‐seven major, minor and trace elements.  相似文献   

Modeling the impact of wind and waves on suspended particulate matter fluxes in the East Frisian Wadden Sea (southern North Sea)   总被引：3，自引：1，他引：2  

Karsten A. Lettmann  Jörg-Olaf Wolff  Thomas H. Badewien 《Ocean Dynamics》2009,59(2):239-262

Suspended particulate matter (SPM) fluxes and dynamics are investigated in the East Frisian Wadden Sea using a coupled modeling system based on a hydrodynamical model [the General Estuarine Transport Model (GETM)], a third-generation wave model [Simulating Waves Nearshore (SWAN)], and a SPM module attached to GETM. Sedimentological observations document that, over longer time periods, finer sediment fractions disappear from the Wadden Sea Region. In order to understand this phenomenon, a series of numerical scenarios were formulated to discriminate possible influences such as tidal currents, wind-enhanced currents, and wind-generated surface waves. Starting with a simple tidal forcing, the considered scenarios are designed to increase the realism step by step to include moderate and strong winds and waves and, finally, to encompass the full effects of one of the strongest storm surges affecting the region in the last hundred years (Storm Britta in November 2006). The results presented here indicate that moderate weather conditions with wind speeds up to 7.5 m/s and small waves lead to a net import of SPM into the East Frisian Wadden Sea. Waves play only a negligible role during these conditions. However, for stronger wind conditions with speeds above 13 m/s, wind-generated surface waves have a significant impact on SPM dynamics. Under storm conditions, the numerical results demonstrate that sediments are eroded in front of the barrier islands by enhanced wave action and are transported into the back-barrier basins by the currents. Furthermore, sediment erosion due to waves is significantly enhanced on the tidal flats. Finally, fine sediments are flushed out of the tidal basins due to the combined effect of strong erosion by wind-generated waves and a longer residence time in the water column because of their smaller settling velocities compared to coarser sediments.

Karsten A. LettmannEmail:

  相似文献   

Mining-Induced Stress Transfer and Its Relation to a \text{M}_w 1.9 Seismic Event in an Ultra-deep South African Gold Mine     

Moritz Ziegler  Karsten Reiter  Oliver Heidbach  Arno Zang  Grzegorz Kwiatek  Dietrich Stromeyer  Torsten Dahm  Georg Dresen  Gerhard Hofmann 《Pure and Applied Geophysics》2015,172(10):2557-2570

  相似文献   

Simulating the temporal and spatial dynamics of the North Sea using the new model GETM (general estuarine transport model)     

Adolf?StipsEmail author  Karsten?Bolding  Thomas?Pohlmann  Hans?Burchard 《Ocean Dynamics》2004,54(2):266-283

Here we present results of a 1-year realistic North Sea simulation from the new model GETM (general estuarine transport model) and assess the capabilities of this model by comparing them to model results from the well-known HAMSOM (Hamburg shelf sea and ocean model) model, in situ data from the North Sea project and satellite-derived sea-surface temperature data. The annual cycle and the spatial variability of stratification and mixing in the North Sea is simulated. It is shown that the new model is successful in reproducing the general temporal and spatial dynamics of the North Sea. The major advantages of GETM for achieving improved results in this simulation are the implementation of general vertical coordinates, of a state-of-the-art turbulence model and of higher-order advection schemes. By exploiting the full capabilities of these features a more realistic simulation could be achieved. We found that the greatest differences in the model results are produced by applying advection schemes of different complexity. Here we are able to demonstrate that better advection schemes lead to stronger horizontal gradients and stronger vertical stratification during summer. When comparing these results to measurements from the North Sea project and to satellite data, we find that these stronger gradients are more realistic. Therefore, we consider it as essential to use such high-order advection schemes if the spatial variability of estuarine or shelf seas like the North Sea is to be resolved adequately. The advanced turbulence closure scheme also contributed to more realistic simulation of the vertical stratification. Finally, general vertical coordinates better resolve the shallow regions, but are also useful for the deeper regions, as they allow a better estimation of sea-surface temperature compared to traditional coordinates.Responsible Editor: Phil Dyke  相似文献