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1.
Ian Cartwright Uwe Morgenstern William Howcroft Harald Hofmann Robin Armit Michael Stewart Chad Burton Dylan Irvine 《水文研究》2020,34(21):4034-4048
Determining mean transit times in headwater catchments is critical for understanding catchment functioning and understanding their responses to changes in landuse or climate. Determining whether mean transit times (MTTs) correlate with drainage density, slope angle, area, or land cover permits a better understanding of the controls on water flow through catchments and allows first-order predictions of MTTs in other catchments to be made. This study assesses whether there are identifiable controls on MTTs determined using 3H in headwater catchments of southeast Australia. Despite MTTs at baseflow varying from a few years to >100 years, it was difficult to predict MTTs using single or groups of readily-measured catchment attributes. The lack of readily-identifiable correlations hampers the prediction of MTTs in adjacent catchments even where these have similar geology, land use, and topography. The long MTTs of the Australian headwater catchments are probably in part due to the catchments having high storage volumes in deeply-weathered regolith, combined with low recharge rates due to high evapotranspiration. However, the difficulty in estimating storage volumes at the catchment scale hampers the use of this parameter to estimate MTTs. The runoff coefficient (the fraction of rainfall exported via the stream) is probably also controlled by evapotranspiration and recharge rates. Correlations between the runoff coefficient and MTTs in individual catchments allow predictions of MTTs in nearby catchments to be made. MTTs are shorter in high rainfall periods as the catchments wet up and shallow water stores are mobilized. Despite the contribution of younger water, the major ion geochemistry in individual catchments commonly does not correlate with MTTs, probably reflecting heterogeneous reactions and varying degrees of evapotranspiration. Documenting MTTs in catchments with high storage volumes and/or low recharge rates elsewhere is important for understanding MTTs in diverse environments. 相似文献
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Monometamorphic metasediments of Paleozoic or Mesozoic age constituting Schneeberg and Radenthein Complex experienced coherent deformation and metamorphism during Late Cretaceous times. Both complexes are part of the Eoalpine high-pressure wedge that formed an intracontinental suture and occur between the polymetamorphosed Ötztal–Bundschuh nappe system on top and the Texel–Millstatt Complex below. During Eoalpine orogeny Schneeberg and Radenthein Complexes were south-dipping and they experienced a common tectonometamorphic history from ca. 115 Ma onwards until unroofing of the Tauern Window in Miocene times. This evolution is subdivided into four distinct tectonometamorphic phases. Deformation stage D1 is characterized by WNW-directed shearing at high temperature conditions (550–600°C) and related to the initial exhumation of the high-pressure wedge. D2 and D3 are largely coaxial and evolved during high- to medium-temperature conditions (ca. 450 to ≥550°C). These stages are related to advanced exhumation and associated with large-scale folding of the high-pressure wedge including the Ötztal-Bundschuh nappe system above and the Texel–Millstatt Complex below. For the area west of the Tauern Window, F2/F3 fold interference results in the formation of large-scale sheath-folds in the frontal part of the nappe stack (formerly called “Schlingentektonik” by previous authors). Earlier thrusts were reactivated during Late Cretaceous normal faulting at the base of the Ötztal–Bundschuh nappe system and its cover. Deformation stage D4 is of Oligo-Miocene age and accounted for tilting of individual basement blocks along large-scale strike-slip shear zones. This tilting phase resulted from indentation of the Southern Alps accompanied by the formation of the Tauern Window. 相似文献
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Novel information and communication technologies have created new possibilities for transferring information and knowledge over distance. Although this might open up broad options for economic interaction, knowledge regarding the effects of these changes on the geographies of production and innovation is still incomplete. Under these circumstances, permanent co-location and face-to-face (F2F) interaction may be efficient in some contexts but not in others. Support by computer-mediated communication (CMC), temporary, and virtual interaction is increasingly becoming the basis for establishing trans-local production networks. By combining results from social psychology with economic geography, it is argued that there is no generally superior spatial fix for economic interaction. Different spatial configurations can be advantageous in different production and innovation contexts, even over large distances without permanent or even regular F2F contact. This paper systematically investigates the effects of new communication technologies and different organisational forms for economic interaction by emphasizing the potential of combining CMC with forms of temporary and permanent F2F interaction. 相似文献
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Nils Rune Sandstå Brian Robins Harald Furnes Maarten de Wit 《Contributions to Mineralogy and Petrology》2011,162(2):365-377
Exceptionally well-preserved pillowed and massive phenocryst-free metabasaltic lava flows in the uppermost part of the Palaeoarchaean
Hooggenoeg Complex of the Barberton Greenstone Belt exhibit both flow banding and large leucocratic varioles. The flow banding
is defined by blebs and bands of pale and dark green metabasalt and was the result of mingling of two types of basalt (Robins
et al. in Bull Volcanol 72:579–592, 2010a). Varioles occur exclusively in the dark chlorite-, MgO- and FeO-rich metabasalt. Varioles are absent in the outermost rinds
of pillows and increase in both abundance and size towards the centres of pillows. In the central parts of some pillows, they
impinge to form homogeneous pale patches, bands or almost homogenous cores. Individual varioles consist essentially of radially
orientated or outwardly branching dendritic crystals of albite. Many varioles exhibit concentric zones and finer-grained rims.
Some varioles seem to have grown around tiny vesicles and vesicles appear to have been trapped in others between a core and
a finer-grained rim. The matrix surrounding the ocelli contains acicular pseudomorphs of actinolite and chlorite after chain-like,
skeletal Ca-rich pyroxenes that are partly overgrown by the margins of varioles. Varioles are enriched in the chemical constituents
of feldspar but contain concentrations of immobile TiO2, Cr, Zr and REE that are similar to the host metabasalts. The shape, distribution, texture and composition of the varioles
exclude liquid immiscibility and support an origin by spherulitic crystallisation of plagioclase from severely undercooled
basalt melt and glass. Nucleation of plagioclase was strongly inhibited and took place on vesicles, on the bases of drainage
cavities and along early fractures. Eruption in deep water and retention of relatively high concentrations of volatiles in
the melt may be the principal cause of spherulitic crystallisation in the interiors of pillows rather than only in their margins
as in younger submarine flows. 相似文献
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The IVS Intensive sessions are single-baseline, 1-h VLBI sessions carried out everyday in order to determine Universal Time
(UT1). We investigate different possibilities to improve the results of such sessions. We do this investigation by extracting
2-h single-baseline sessions from the CONT08 data set. These are analysed like normal Intensives, and the results are compared
to the results of the analysis of the full CONT08 data set. We find that tropospheric asymmetry is the major error source
for the single-baseline sessions. It is possible to improve the accuracy of the estimated UT1 either by using accurate a priori
tropospheric gradients or by estimating gradients in the data analysis. 相似文献
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