Vegetation patterns and diversity along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of northern Oman   总被引：1，自引：0，他引：1  

Katja Brinkmann  Annette Patzelt  Uta Dickhoefer  Eva Schlecht  Andreas Buerkert 《Journal of Arid Environments》2009,73(11):1035-1045

Little is known about the effects of grazing on vegetation composition on the Arabian Peninsula. The aim of this study therefore was to analyse the vegetation response to environmental conditions of open woodlands along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of Oman. The species composition, vegetation structure, grazing damage and several environmental variables were investigated for 62 samples using a nested plot design. Classification analysis and a Canonical Variate Analysis (CVA) were used to define vegetation types and to identify underlying environmental gradients. The relationship between environmental variables and diversity was analysed using correlation coefficients and a main-effects ANOVA. The plant species richness followed a unimodal distribution along the altitudinal gradient with the highest number of species at the intermediate altitudinal belt. The cluster analysis led to five vegetation groups: The Sideroxylon mascatense–Dodonaea viscosa group on grazed and the Olea europaea–Fingerhuthia africana group on ungrazed plateau sites at 2000 m a.s.l., the Ziziphus spina-christi–Nerium oleander group at wadi sites and the Moringa peregrina–Pteropyrum scoparium group at 1200 m a.s.l, and the Acacia gerrardii–Leucas inflata group at 1700 m a.s.l. The CVA indicated a clear distinction of the groups obtained by the agglomerative cluster analysis. The landform, altitude and grazing intensity were found to be the most important variables distinguishing between clusters. Overgrazing of the studied rangeland is an increasing environmental problem, whereas the plant composition at ungrazed sites pointed to a relatively fast and high regeneration potential of the local vegetation.  相似文献   

Seismic fragility curves for greek bridges: methodology and case studies   总被引：2，自引：1，他引：1  

Ioannis F. Moschonas  Andreas J. Kappos  Panagiotis Panetsos  Vissarion Papadopoulos  Triantafyllos Makarios  Pavlos Thanopoulos 《Bulletin of Earthquake Engineering》2009,7(2):439-468

This study focusses on the estimation of seismic fragility curves for all common bridge types found in modern greek motorways. At first a classification scheme is developed in order to classify the existing bridges into a sufficient number of classes. A total of 11 representative bridge classes resulted, based on the type of piers, deck, and pier-to-deck connection. Then an analytical methodology for deriving fragility curves is proposed and applied to the representative bridge models. This procedure is based on pushover analysis of the entire bridge and definition of damage states in terms of parameters of the bridge pushover curves. The procedure differentiates the way of defining damage according to the seismic energy dissipation mechanism in each bridge, i.e. bridges with yielding piers of the column type and bridges with bearings (with or without seismic links) and non-yielding piers of the wall type. The activation of the abutment-backfill system due to closure of the gap between the deck and the abutments is also taken into account. The derived fragility curves are subjected to a first calibration against empirical curves based on damage data from the US and Japan.  相似文献   

Dating of Late Pleistocene terrace deposits of the River Rhine using Uranium series and luminescence methods: Potential and limitations     

Stphane Kock  Jan D. Kramers  Frank Preusser  Andreas Wetzel 《Quaternary Geochronology》2009,4(5):363-373

Uranium-series dating of pedogenic carbonate crusts from fluvial gravels is tested using Optically Stimulated Luminescence (OSL) ages as references. OSL dating yielded ages of 30–15 ka and 13–11 ka, which correlate with the cold periods of the Last Glacial Maximum and the Younger Dryas. These ages are internally coherent and consistent with the geological background and are thus regarded as reliable. Most of the U/Th results scatter widely in the ²³⁰Th/²³²Th vs. ²³⁴U/²³²Th isochron diagram, making regression unrealistic. Semiquantitative age estimates from the data were found to be mostly older than the OSL ages and the geological context. It is suggested that a heterogeneous initial ²³⁰Th input, not relatable to a detrital component, is responsible for the observed discrepancies. This input may be due to bacterial activities and Th transport on organic colloids. It appears necessary to avoid samples where bacteria could have contributed to carbonate precipitation. Further, the relative importance of this problem decreases with sample age, so that U/Th dating of sinters is expected to be more reliable in the >100 ka age range.  相似文献   

Multistage Variscan magmatism in the central Tauern Window (Austria) unveiled by U/Pb SHRIMP zircon data   总被引：2，自引：0，他引：2  

Roland Eichhorn  Georg Loth  Rudolf Höll  Fritz Finger  Andreas Schermaier  Allen Kennedy 《Contributions to Mineralogy and Petrology》2000,139(4):418-435

U/Pb SHRIMP ages of nine Variscan leucocratic orthogneisses from the central Tauern Window (Austria) reveal three distinct pulses of magmatism in Early Carboniferous (Visean), Late Carboniferous (Stephanian) and Early Permian, each involving granitoid intrusions and a contemporaneous opening of volcano-sedimentary basins. A similar relationship has been reported for the Carboniferous parts of the basement of the Alps further to the west, e.g. the “External massifs” in Switzerland. After the intrusion of subduction-related, volcanic-arc granitoids (374?±?10?Ma; Zwölferkogel gneiss), collisional intrusive-granitic, anatectic and extrusive-rhyolitic/dacitic rocks were produced over a short interval at ca. 340?Ma (Augengneiss of Felbertauern: 340?±?4?Ma, Hochweißenfeld gneiss: 342?± 5?Ma, Falkenbachlappen gneiss: 343?±?6?Ma). This Early Carboniferous magmatism, which produced relatively small volumes of melt, can be attributed to the amalgamation of the Gondwana-derived “Tauern Window” terrane with Laurussia–Avalonia. Probably due to the oblique nature of the collision, transtensional phenomena (i.e. volcano-sedimentary troughs and high-level intrusives) and transpressional regimes (i.e. regional metamorphism and stacked nappes with anatexis next to thrust planes) evolved contemporaneously. The magmas are mainly of the high-K I-type and may have been generated during a short phase of decompressional melting of lithospheric mantle and lower crustal sources. In the Late Carboniferous, a second pulse of magmatism occurred, producing batholiths of calc-alkaline I-type granitoids (e.g. Venediger tonalite: 296?±?4?Ma) and minor coeval bodies of felsic and intermediate volcanics (Heuschartenkopf gneiss: 299?±?4?Ma, Peitingalm gneiss: 300?±?5?Ma). Prior to this magmatism, several kilometres of upper crust must have been eroded, because volcano-sedimentary sequences hosting the Heu- schartenkopf and Peitingalm gneisses rest unconformably on 340-Ma-old granitoids. The youngest (Permian) period of magma generation contains the intrusion of the S-type Granatspitz Central Gneiss at 271?±?4?Ma and the extrusion of the rhyolitic Schönbachwald gneiss protolith at 279?±?9?Ma. These magmatic rocks may have been associated with local extension along continental wrench zones through the Variscan orogenic crust or with a Permian rifting event. The Permian and the above-mentioned Late Carboniferous volcano-sedimentary sequences were probably deposited in intra-continental graben structures, which survived post-Variscan uplift and Alpine compressional tectonics.  相似文献   

Methane exchange between coal-bearing basins and the atmosphere: the Ruhr Basin and the Lower Rhine Embayment, Germany   总被引：1，自引：0，他引：1  

Thomas Thielemann  Andreas Lücke  Gerhard H. Schleser  Ralf Littke   《Organic Geochemistry》2000,31(12):121

A precise knowledge of methane exchange processes is required to fully understand the recent rise of atmospheric methane concentration. Three of these processes take place at the lithosphere/atmosphere boundary: bacterial consumption of methane and emission of bacterial or thermogenic methane. This study was initiated to quantify these processes on a regional scale in the Ruhr Basin and the Lower Rhine Embayment. Since these areas are subject to bituminous coal and lignite mining, natural and anthropogenically-induced methane exchange processes could be studied. The methane emission and consumption rates and their carbon isotope signal were measured at the lithosphere/atmosphere boundary using flux chambers. On most of the soils studied, methane consumption by bacteria was identified. Thermogenic methane was released only at some of the natural faults examined. In active and abandoned bituminous coal mining areas methane emissions were restricted to small areas, where high emission rates were measured. The carbon isotope composition of methane at natural faults and in mining subsidence troughs was typical of thermogenic methane (−45 to −32 ‰ δ¹³C). Methane exchange balancing revealed that natural methane emissions from these two basins represent no source of atmospheric importance. However, methane release by upcast mining shafts dominates the methane exchange processes and is by about two orders of magnitude greater than methane consumption by bacterial oxidation in the soils.  相似文献   

A Concise History of Dutch River Floods     

Richard S. J. Tol  Andreas Langen 《Climatic change》2000,46(3):357-369

Based on a brief account of 1,000 years of river floods and flood management in the Dutch Rhine delta, it is argued that vulnerability to river floods depends on the complex interaction of economics, institutions, politics and, to a limited extent, climate. Response functions and thresholds for climate change impacts should take this complexity into account rather than assuming society to be constant or evolving in a straightforward manner.  相似文献   

German research in transport geography: Life in the space between objective analysis and political advice1     

Andreas Kagermeier 《GeoJournal》2000,50(1):17-24

Transportation has been a bone of public contention for decades, the discussion ranging from traffic-calming measures in individual streets to the continual growth of global transport movements. In the last 20 years transport topics have also received increased attention within the discipline of geography, be it academic, professional or in schools, but the topics addressed by today's transport geography have almost nothing in common with the roots of the field. This means that transport geography is a handed-down, hyphenated sub-branch of geography in name only. In fact, the name refers to a field of geography that is experiencing not only all the birthing pains and uncertainties of a discipline in the process of defining a new direction for itself, but also the sense of excitement and thrill of the new. This paper sets out to show both the role transport geography plays as part of human geography with its concepts and paradigms, and also the role it plays within the political debate on transport. An appeal is made to geographers to become more involved in this branch of our science.  相似文献   

How can we model subsurface stormflow at the catchment scale if we cannot measure it?     

Peter Chifflard  Theresa Blume  Katja Maerker  Luisa Hopp  Ilja van Meerveld  Thomas Graef  Oliver Gronz  Andreas Hartmann  Bernhard Kohl  Edoardo Martini  Christian Reinhardt‐Imjela  Martin Reiss  Michael Rinderer  Stefan Achleitner 《水文研究》2019,33(9):1378-1385

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Performance of the Nuclear Compton Telescope     

Steven Boggs  Mark Bandstra  Jason Bowen  Wayne Coburn  Robert Lin  Cornelia Wunderer  Andreas Zoglauer  Mark Amman  Paul Luke  Pierre Jean  Peter von Ballmoos 《Experimental Astronomy》2005,20(1-3):387-394

On 1 June 2005, the prototype Nuclear Compton Telescope (NCT) flew on a high altitude balloon from Fort Sumner, New Mexico. NCT is a balloon-borne soft γ-ray (0.2–10 MeV) telescope for studying astrophysical sources of nuclear line emission and γ-ray polarization. Our program is designed to develop and test technologies and analysis techniques crucial for the Advanced Compton Telescope; however, our detector design and configuration is also well matched to the focal plane requirements for focusing Laue lenses. The NCT prototype utilizes two, 3D imaging germanium detectors (GeDs) in a novel, ultra-compact design optimized for nuclear line emission in the 0.5–2 MeV range. Our prototype flight provides a critical test of the novel detector technologies, analysis techniques, and background rejection procedures developed for high resolution Compton telescopes.  相似文献   

Book reviews     

T. Littmann  Rudolf Brázdil  Manfred Domrös  Mohammed A. Kishk  A. Wallner  Radan Květ  Andreas Grotewold 《GeoJournal》1992,26(4):547-549

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