Measurements of armour layer roughness geometry function and porosity     

Jochen Aberle 《Acta Geophysica》2007,55(1):23-32

The roughness geometry function of the interfacial sublayer of a gravel-bed armour layer was measured directly by filling water stepwise into a laboratory flume and indirectly from a digital elevation model (DEM) of the surface. The results of both methods are compared and show that the DEM can be used to reliably estimate the roughness density function for a wide range of the interfacial sublayer. The direct measurements revealed an absolute minimum of porosity at the level of the roughness trough which is significantly smaller than porosity in the undisturbed subsurface and porosity estimates obtained from relationships found in the literature. The significance of the results for hydraulic engineering and ecological applications is highlighted.  相似文献   

Portales Valley: Petrology of a metallic‐melt meteorite breccia     

Alex Ruzicka  Marvin Killgore  David W. Mittlefehldt  Marc D. Fries 《Meteoritics & planetary science》2005,40(2):261-295

Abstract— Portales Valley (PV) is an unusual metal‐veined meteorite that has been classified as an H6 chondrite. It has been regarded either as an annealed impact melt breccia, as a primitive achondrite, or as a meteorite with affinities to silicated iron meteorites. We studied the petrology of PV using a variety of geochemical‐mineralogical techniques. Our results suggest that PV is the first well‐documented metallic‐melt meteorite breccia. Mineral‐chemical and other data suggest that the protolith to PV was an H chondrite. The composition of FeNi metal in PV is somewhat fractionated compared to H chondrites and varies between coarse vein and silicate‐rich portions. It is best modeled as having formed by partial melting at temperatures of ?940–1150 °C, with incomplete separation of solid from liquid metal. Solid metal concentrated in the coarse vein areas and S‐bearing liquid metal concentrated in the silicate‐rich areas, possibly as a result of a surface energy effect. Both carbon and phosphorus must have been scavenged from large volumes and concentrated in metallic liquid. Graphite nodules formed by crystallization from this liquid, whereas phosphate formed by reaction between P‐bearing metal and clinopyroxene components, depleting clinopyroxene throughout much of the meteorite and growing coarse phosphate at metal‐silicate interfaces. Some phosphate probably crystallized from P‐bearing liquids, but most probably formed by solid‐state reaction at ?975‐725 °C. Phosphate‐forming and FeO‐reduction reactions were widespread in PV and entailed a change in the mineralogy of the stony portion on a large scale. Portales Valley experienced protracted annealing from supersolidus to subsolidus temperatures, probably by cooling at depth within its parent body, but the main differences between PV and H chondrites arose because maximum temperatures were higher in PV. A combination of a relatively weak shock event and elevated pre‐shock temperatures probably produced the vein‐and‐breccia texture, with endogenic heating being the main heat source for melting, and with stress waves from an impact event being an essential trigger for mobilizing metal. Portales Valley is best classified as an H7 metallic‐melt breccia of shock stage S1. The meteorite is transitional between more primitive (chondritic) and evolved (achondrite, iron) meteorite types and offers clues as to how differentiation could have occurred in some asteroidal bodies.  相似文献   

Proper motion measurements in various young stellar object jets in Taurus     

Jochen Eislöffel  Reinhard Mundt 《Astrophysics and Space Science》1995,233(1-2):55-58

We present proper motion measurements for a number of knots in the jets and bow shocks of the outflows from DG Tau, DG Tau B, T Tau, CoKu Tau 1, FS Tau, and FS Tau B in the nearby Taurus-Auriga star forming region. From these measurements and the available radial velocity data we derive tangential velocities, spatial velocities, angles of the outflows with respect to the plane of the sky, and in a couple of cases the pattern motions of the knots relative to the flow speed.  相似文献   

Automatic regional moment tensor inversion in the European-Mediterranean region   总被引：4，自引：0，他引：4  

Fabrizio Bernardi  Jochen Braunmiller  Urs Kradolfer  Domenico Giardini 《Geophysical Journal International》2004,157(2):703-716

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Southernmost outcrops of marine lower Tertiary carbonate rocks in NE-Africa (Gebel Abyad,Sudan)     

Dr. Nabil Barazi  Dr. Jochen Kuss 《International Journal of Earth Sciences》1987,76(2):529-537

Early Tertiary carbonates (Gebel Abyad Formation) are described from an isolated limestone plateau from the northwestern Sudan. They represent the southernmost outskirts of marine, Tertiary sediments in northeast Africa, which can be connected with transgressive/regressive cycles of the Tethys onto the African craton. Microfacies studies of the carbonates yielded exclusively shallow marine sediments which dried up temporarily, and with changing rates of terrigenous input. They contain a low diverse fauna and flora, poor in individuals. The paleogeographic reconstruction of this isolated occurrence was possible by comparing sediments from southern Egypt.

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Zusammenfassung Aus dem nordwestlichen Sudan werden alttertiäre Karbonate (Gebel Abyad Formation) beschrieben, die ein isoliertes Vorkommen darstellen. Diese repräsentieren die südlichsten marinen tertiären Ablagerungen in Nordost-Afrika, die mit transgressiv/regressiven Zyklen der Tethys auf den afrikanischen Kraton in Verbindung gebracht werden können. Die mikrofaziell bearbeiteten Kalke stellen ausschlie\lich flachmarine Ablagerungen dar, mit Anzeichen für zeitweiliges Trockenfallen, und wechselnden Anteilen terrigener Zufuhr. Sie enthalten eine gering-diverse, individuenarme Fauna und Flora. Faziell vergleichbare Ablagerungen in Südägypten lassen eine Rekonstruktion dieses isolierten Kalkvorkommens zu einem paläogeographischen Modell zu.

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Résumé Cette note décrit des roches carbonatées d'âge tertiaire inférieur (formation du Jebel Abyad) qui font partie d'un plateau isolé dans le nord-ouest du Soudan. Elles représentent l'extension méridionale maximale de la sédimentation marine tertiaire dans le nord-est de l'Afrique, sédimentation qui peut Être reliée aux cycles de transgressionsrégressions de la Téthys sur le bloc continental africain. L'étude des microfacies amène à les identifier comme des dépÔts marins de faible profondeur, temporairement asséchés et mÊlés d'apports terrigènes en quantité variable. Ils renferment une flore et une faune pauvres en espèces et en individus. La comparaison avec des sédiments du Sud égyptien permet de les intégrer dans un modèle paléogéographique.

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The role of fluids in partitioning brittle deformation and ductile creep in auriferous shear zones between 500 and 700 °C     

Jochen Kolb   《Tectonophysics》2008,446(1-4):1-15

The fabric, mineralogy, geochemistry, and stable isotope systematics of auriferous shear zones in various hydrothermal gold deposits were studied in order to discuss the role of fluids in rock deformation at temperatures between 500 °C and 700 °C. The strong hydrothermal alteration and gold mineralization indicates that effective permeability development goes ahead with high-temperature rock deformation. The economic gold enrichment is often hosted by breccias and quartz veins in the ductile shear zones, which either formed at fast strain rates or by low strain continuous deformation at slow strain rates. Both processes require (1) a close-to lithostatic to supralithostatic fluid pressure and/or (2) a strong rheology contrast of the deformed lithologies that is often developed during progressive hydrothermal alteration. Compartments of high fluid pressure are sealed from the rest of the shear zones by high-temperature deformation mechanisms, e.g. intracrystalline plasticity and diffusion creep, and compaction. In contrast, in mylonites with heterogeneous crystal plastic and brittle deformation mechanisms for the various minerals, an interconnected network of a grain-scale porosity forms an effective fluid conduit, which hampers fluid pressure build-up and the formation of veins.The auriferous shear zones of the various gold mines represent fluid conduits in the deeper crust, 100 m along strike and up to 1000 m down-dip. The hydrothermal fluids infiltrated may be responsible for low magnitude earthquakes in the Earth's lower crust, which otherwise deforms viscously.  相似文献   

Geo-ontology Tools: The Missing Link   总被引：1，自引：0，他引：1  

Jochen Albrecht  Brandon Derman  Laxmi Ramasubramanian 《Transactions in GIS》2008,12(4):409-424

Numerous authors have presented ontology building tools that have all been developed as part of academic projects and that are usually adaptations of more generic tools for geo-spatial applications. While we trust that these tools do their job for the special purpose they have been built, the GIScience user community is still a long way away from off-the-shelf ontology builders that can be used by GIS project managers. In this article, we present a comparative study of ontology building tools described in some twenty peer-reviewed GIScience journal articles. We analyze them from the perspective of two application domains, crime analysis and transportation/land use. For the latter, we developed a database schema, which is substantially different from the three main templates commonly used. The crime analysis application uses a rule base for an agent-based model that had no precursor. In both cases, the currently available set of tools cannot replace manual coding of ontologies for use with ESRI-based application software. Based on these experiences, we outline a requirements list of what the tools described in the first part of the article are missing to make them practical from an applications perspective. The result is an R&D agenda for this important aspect of GIScience.  相似文献   

An efficient geosciences workflow on multi-core processors and GPUs: a case study for aerosol optical depth retrieval from MODIS satellite data     

Jia Liu  Dustin Feld  Jochen Garcke  Thomas Soddemann  Peiyuan Pan 《International Journal of Digital Earth》2016,9(8):748-765

Quantitative remote sensing retrieval algorithms help understanding the dynamic aspects of Digital Earth. However, the Big Data and complex models in Digital Earth pose grand challenges for computation infrastructures. In this article, taking the aerosol optical depth (AOD) retrieval as a study case, we exploit parallel computing methods for high efficient geophysical parameter retrieval. We present an efficient geocomputation workflow for the AOD calculation from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. According to their individual potential for parallelization, several procedures were adapted and implemented for a successful parallel execution on multi-core processors and Graphics Processing Units (GPUs). The benchmarks in this paper validate the high parallel performance of the retrieval workflow with speedups of up to 5.x on a multi-core processor with 8 threads and 43.x on a GPU. To specifically address the time-consuming model retrieval part, hybrid parallel patterns which combine the multi-core processor’s and the GPU’s compute power were implemented with static and dynamic workload distributions and evaluated on two systems with different CPU–GPU configurations. It is shown that only the dynamic hybrid implementation leads to a greatly enhanced overall exploitation of the heterogeneous hardware environment in varying circumstances.  相似文献   

Spatial variations of sea-level rise and impacts: An application of DIVA   总被引：1，自引：0，他引：1  

Sally?BrownEmail author  Robert?J?Nicholls  Jason?A?Lowe  Jochen?Hinkel 《Climatic change》2016,134(3):403-416

Due to complexities of creating sea-level rise scenarios, impacts of climate-induced sea-level rise are often produced from a limited number of models assuming a global uniform rise in sea level. A greater number of models, including those with a pattern reflecting regional variations would help to assure reliability and a range of projections, indicating where models agree and disagree. This paper determines how nine new patterned-scaled sea-level rise scenarios (plus the uniform and patterned ensemble mean rises) influence global and regional coastal impacts (wetland loss, dry land loss due to erosion and the expected number of people flooded per year by extreme sea levels). The DIVA coastal impacts model was used under an A1B scenario, and assumed defences were not upgraded as conditions evolved. For seven out of nine climate models, impacts occurred at a proportional rate to global sea-level rise. For the remaining two models, higher than average rise in sea level was projected in northern latitudes or around populated coasts thus skewing global impact projections compared with the ensemble global mean. Regional variability in impacts were compared using the ensemble mean uniform and patterned scenarios: The largest relative difference in impacts occurred around the Mediterranean coast, and the largest absolute differences around low-lying populated coasts, such as south, south-east and east Asia. Uniform projections of sea-level rise impacts remain a useful method to determine global impacts, but improved regional scale models of sea-level rise, particularly around semi-enclosed seas and densely populated low-lying coasts will provide improved regional impact projections and a characterisation of their uncertainties.  相似文献   

3+1 formulation of non-ideal hydrodynamics     

Jochen Peitz  & Stefan Appl 《Monthly notices of the Royal Astronomical Society》1998,296(2):231-244

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