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  • 1
    Publication Date: 2014-06-17
    Description: ABSTRACT Many rivers worldwide show converging sections where a characteristic limiting front for vegetation establishment on gravel bars is observed. An important conceptual model was advanced by Gurnell and Petts (2006), who demonstrated that for the convergent section of the Tagliamento River, the downstream front of vegetation establishment can be explained by unit stream power. We introduce a theoretical framework based on 1-D ecomorphodynamic equations modified to account for the biological dynamics of vegetation. We obtain the first analytical result explaining the position and river width where vegetation density is expected to vanish in relation to a characteristic streamflow magnitude and both hydraulic and biologic parameters. We apply our model to a controlled experiment within a convergent flume channel with growing seedlings perturbed by periodic floods. For a range of timescales where hydrological and biological processes interact, we observe the formation of a front in the convergent section beyond which vegetation cannot survive, the location of which is explained by flow magnitude. This experiment confirms that the timescales of the involved processes and the unit stream power determine the existence and the position of the front within convergent river reaches, respectively. Copyright © 2014 John Wiley & Sons, Ltd.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley
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  • 2
    Publication Date: 2014-08-09
    Description: The existence of basal-prismatic interfaces and their roles in twinning of hexagonal materials have recently attracted appreciable attention of scientific community. In this paper, we utilize molecular statics to investigate the formation of basal-prismatic facets in the ##IMG## [http://ej.iop.org/images/1757-899X/63/1/012134/mse14_63_012034.jpg] {10bar12} twin boundary of magnesium. This interface is shown to be the consequence of a collective motion and interaction of twinning disconnections. By analyzing volume deformations caused by the migration of a single basal-prismatic interface, we show that the passage of this interface distorts the material equivalently to twinning shear.
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
    Publication Date: 2014-01-23
    Description: We present a probabilistic sediment cascade model to simulate sediment transfer in a mountain basin (Illgraben, Switzerland) where sediment is produced by hillslope landslides and rockfalls and exported out of the basin by debris flows and floods. The model conceptualizes the fluvial system as a spatially lumped cascade of connected reservoirs representing hillslope and channel storages where sediment goes through cycles of storage and remobilization by surface runoff. The model includes all relevant hydrological processes that lead to runoff formation in an Alpine basin, such as precipitation, snow accumulation, snow melt, evapotranspiration, and soil water storage. Although the processes of sediment transfer and debris flow generation are described in a simplified manner, the model produces complex sediment discharge behavior which is driven by the availability of sediment and antecedent wetness conditions (system memory) as well as the triggering potential (climatic forcing). The observed probability distribution of debris flow volumes and their seasonality in 2000-2009 are reproduced. The stochasticity of hillslope sediment input is important for reproducing realistic sediment storage variability, although many details of the hillslope landslide triggering procedures are filtered out by the sediment transfer system. The model allows us to explicitly quantify the division into transport and supply-limited sediment discharge events. We show that debris flows may be generated for a wide range of rainfall intensities because of variable antecedent basin wetness and snowmelt contribution to runoff, which helps to understand the limitations of methods based on a single rainfall threshold for debris flow initiation in Alpine basins.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2013-08-07
    Description: The thorniest problem in comparative neurobiology is the identification of the particular brain region of birds and reptiles that corresponds to the mammalian neocortex [Butler AB, Reiner A, Karten HJ (2011) Ann N Y Acad Sci 1225:14–27; Wang Y, Brzozowska-Prechtl A, Karten HJ (2010) Proc Natl Acad Sci USA 107(28):12676–12681]....
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 5
    Publication Date: 2012-04-22
    Description: ABSTRACT Landslides and rockfalls are key geomorphic processes in mountain basins. Their quantification and characterization are critical for understanding the processes of slope failure and their contributions to erosion and landscape evolution. We used digital photogrammetry to produce a multi-temporal record of erosion (1963 – 2005) of a rock slope at the head of the Illgraben, a very active catchment prone to debris flows in Switzerland. Slope failures affect 70% of the study slope and erode the slope at an average rate of 0.39 ± 0.03 m yr¯¹. The analysis of individual slope failures yielded an inventory of ~2500 failures ranging over 6 orders of magnitude in volume, despite the small slope area and short study period. The slope failures form a characteristic magnitude-frequency distribution with a rollover and a power-law tail between ~200 m³ and 1.6x10⁶ m³ with an exponent of 1.65. Slope failure volume scales with area as a power law with an exponent of 1.1. Both values are low for studies of bedrock landslides and rockfall and result from the highly fractured and weathered state of the quartzitic bedrock. Our data suggest that the magnitude-frequency distribution is the result of two separate slope failure processes. Type (1) failures are frequent, small slides and slumps within the weathered layer of highly fractured rock and loose sediment, and make up the rollover. Type (2) failures are less frequent and larger rockslides and rockfalls within the internal bedded and fractured slope along pre-determined potential failure surfaces, and make up the power-law tail. Rockslides and rockfalls of high magnitude and relatively low frequency make up 99% of the total failure volume and are thus responsible for the high erosion rate. They are also significant in the context of landscape evolution as they occur on slopes above 45° and limit the relief of the slope. Copyright © 2012 John Wiley & Sons, Ltd.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
    Published by Wiley
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  • 6
    Publication Date: 2013-04-12
    Description: [1]  GPS velocities measured in the Pamir and surrounding regions show a total of ~30 mm/yrof northward relative motion between stable Pakistan and Eurasia. The convergence budget is partitioned into10–15 mm/yr of localized shortening across theTrans-Alai Thrust, which bounds the Pamir on the north, consistent with southward subduction of intact lithosphere. Another 10–15 mm/yr of shortening is distributed across the Chitral Himalaya and Hindu Kush, suggesting that Hindu Kush seismicity might be related to northward subduction of Indian lithosphere. Modest shortening at 〈5 mm/yr occurs north of the Trans-Alai Thrust, across the South Tien Shan and between the Ferghana Valley and Eurasia. Negligible north–south shortening occurs within the high Pamir, but as much as5 mm/yr, and perhaps 10 mm/yr, of east–west extension occurs within this region. This extension is matched by a comparable amount of east–west shortening in the Tajik Depression.The localization of shortening to the margins of the Pamir combined with observations of distributed internal extension implies that theeast-west vertically averaged, horizontal compressive normal stress is smaller than the north–south compressive stress.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Nature Publishing Group (NPG)
    Publication Date: 2011-02-11
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Molnar, Peter -- England -- Nature. 2011 Feb 10;470(7333):176. doi: 10.1038/470176a.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geological Sciences at the University of Colorado in Boulder, Colorado 80309, USA. peter.molnar@colorado.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21307924" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 8
    Publication Date: 2014-11-28
    Type: paper
    Format: application/pdf
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  • 9
    Publication Date: 2014-03-15
    Description: Pleistocene drainage basin integration led to progressive excavation of Tertiary–Quaternary sedimentary basins along the Yellow River in the northeastern Tibetan Plateau. Cosmogenic burial dating of ancestral river deposits and basin fill from two key watershed divides confirms a fluvial connection between basins at 0.5–1.2 Ma, prior to excavation by the Yellow River. Preservation of the relict depositional surface that represents the maximum height of basin fill allows reconstruction of the volume of eroded material across a broad region. We quantify the isostatic response to this erosional unloading using a two-dimensional flexural model. Calculated maximum vertical displacements for different effective elastic thicknesses vary from ~160 m to ~260 m near the Pleistocene spillway from the Qinghai paleo-lake. We suggest that the isostatic response to fluvial excavation along the Yellow River defeated local tributaries, isolated Lake Qinghai, and led to the development of an internally drained basin in the past 0.5–1.2 m.y.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 10
    Publication Date: 2013-03-30
    Description: We determined vertical components of slip rates of 0.22 ± 0.03 mm a –1 for the Jiayuguan fault and 0.11 ± 0.03 mm a –1 for the Jintanan Shan fault, which lie along the northeastern edge of the Tibetan Plateau and in the western Hexi Corridor (Northern Qilian Shan, China). We used structural investigations, air-photo imagery analysis, topographic profiling, optically stimulated luminescence (OSL) dating, and 10 Be exposure dating. To quantify the slip rates along the faults, we identified and surveyed the well-preserved fault scarps, and we sampled quartz-rich pebbles and cobbles on fan surfaces and within ~2-m-deep pits to determine surface exposure ages and pre-depositional inheritance. Our slip rates pertain to the past ~115 ka. They are consistent with previous geological and GPS constraints that suggest that NNE–SSW shortening across the northeastern Tibetan Plateau has been distributed onto several active faults and that shortening is partitioned into low slip rates of ≤1 mm a –1 on each fault. We infer that the decreasing slip rate from 95°E eastward to the eastern end of the Altyn Tagh fault and the low slip rates of these thrust faults are related. The total shortening in the direction parallel to the Altyn Tagh fault in the Yumen Basin of 0.90–1.43 mm a –1 attests that left-lateral strike slip at the eastern end of the fault has indeed been absorbed by deformation within the Yumen Basin. We infer that the Tibetan Plateau continues to grow northeastward by thrust faulting at low rates and by folding on the northeastern edge of the Hexi Corridor basin.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
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