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  • 1
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    Three-dimensional textural and quantitative analyses of orogenic gold at the nanoscale (2016)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2016-08-23
    Description: Ore textures provide direct clues for tracking ore-forming processes. In this regard, most of our knowledge is generally based on two-dimensional (2-D) image analyses, leaving a considerable gap in comprehending three-dimensional (3-D) in-situ textural settings. Recent advances in lab-based and synchrotron radiation–based X-ray computed microtomography and nanotomography have made it possible to visualize and quantify rock volumes in a 3-D space. In this study, we first analyzed microscale textures in oriented drill cores from the world-class Suurikuusikko orogenic gold deposit of northern Finland using lab-based X-ray computed microtomography. The technique revealed a kinematic history and a number of in-situ 3-D quantitative aspects including size, shape, spatial distribution, and geometrical orientation of arsenopyrite and pyrite in a highly altered host-rock matrix. For 3-D nanotomography, the experimental procedure known as holotomography was adopted. Individual arsenopyrite crystals were separated and scanned with voxel sizes ranging from 50 nm to 150 nm using the X-ray nanoprobe beamline (ID16B) at the European Synchrotron Radiation Facility, France. This ultrahigh-resolution technique illustrated the 3-D distribution of micron- to nanoscale gold inclusions, mostly associated with primary rutile or along secondary microfractures inside arsenopyrite. The workflow, from micro- to nanotomography, outlined in this study offers an indispensable new technique in quantifying and characterizing 3-D textural settings of ores, which is otherwise impossible with conventional 2-D imaging devices. The method can also be highly useful in evaluating the amenability of ores to treatment with different processing options.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 2
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    Design of an {alpha}-L-transfucosidase for the synthesis of fucosylated HMOs (2016)
    Oxford University Press
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    Publication Date: 2016-02-03
    Description: Human milk oligosaccharides (HMOs) are recognized as benefiting breast-fed infants in multiple ways. As a result, there is growing interest in the synthesis of HMOs mimicking their natural diversity. Most HMOs are fucosylated oligosaccharides. α- l -Fucosidases catalyze the hydrolysis of α- l -fucose from the non-reducing end of a glucan. They fall into the glycoside hydrolase GH29 and GH95 families. The GH29 family fucosidases display a classic retaining mechanism and are good candidates for transfucosidase activity. We recently demonstrated that the α- l -fucosidase from Thermotoga maritima ( Tm αFuc) from the GH29 family can be evolved into an efficient transfucosidase by directed evolution ( Osanjo et al. 2007 ). In this work, we developed semi-rational approaches to design an α- l -transfucosidase starting with the α- l -fucosidase from commensal bacteria Bifidobacterium longum subsp. infantis ( Bi AfcB, Blon_2336). Efficient fucosylation was obtained with enzyme mutants (L321P- Bi AfcB and F34I/L321P- Bi AfcB) enabling in vitro synthesis of lactodifucotetraose, lacto- N -fucopentaose II, lacto- N -fucopentaose III and lacto- N -difucohexaose I. The enzymes also generated more complex HMOs like fucosylated para -lacto- N -neohexaose (F- p -LNnH) and mono- or difucosylated lacto- N -neohexaose (F-LNnH-I, F-LNnH-II and DF-LNnH). It is worth noting that mutation at these two positions did not result in a strong decrease in the overall activity of the enzyme, which makes these variants interesting candidates for large-scale transfucosylation reactions. For the first time, this work provides an efficient enzymatic method to synthesize the majority of fucosylated HMOs.
    Print ISSN: 0959-6658
    Electronic ISSN: 1460-2423
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 3
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    Spatial variability in specific discharge and streamwater chemistry during low flows: results from snapshot sampling campaigns in eleven Swiss catchments (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Catchments consist of distinct landforms that affect the storage and release of subsurface water. Certain landforms may be the main contributors to streamflow during extended dry periods and these may vary for different catchments in a given region. We present a unique dataset from snapshot field campaigns during low‐flow conditions in eleven catchments across Switzerland to illustrate this. The catchments differed in size (10 to 110 km2), varied from predominantly agricultural lowlands to Alpine areas, and covered a range of physical characteristics. During each snapshot campaign, we jointly measured streamflow and collected water samples for the analysis of major ions and stable water isotopes. For every sampling location (basin), we determined several landscape characteristics from national geo‐datasets, including drainage area, elevation, slope, flowpath length, dominant land use, and geological and geomorphological characteristics, such as the lithology and fraction of Quaternary deposits. The results demonstrate very large spatial variability in specific low‐flow discharge and water chemistry: neighboring sampling locations could differ significantly in their specific discharge, isotopic composition and ion concentrations, indicating that different sources contribute to streamflow during extended dry periods. However, none of the landscape characteristics that we analyzed could explain the spatial variability in specific discharge or stream water chemistry in multiple catchments. This suggests that local features determine the spatial differences in discharge and water chemistry during low‐flow conditions and that this variability cannot be assessed a priori from available geodata and statistical relations to landscape characteristics. The results furthermore suggest that measurements at the catchment outlet during low‐flow conditions do not reflect the heterogeneity of the different source areas in the catchment that contribute to streamflow.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 4
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    A probabilistic sediment cascade model of sediment transfer in the Illgraben (2014)
    Wiley
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    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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  • 5
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    On basal-prismatic twinning interfaces in magnesium (2014)
    Institute of Physics (IOP)
    Details
    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
    Published by Institute of Physics (IOP)
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  • 6
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    Jack oliver (1923-2011) (2011)
    Nature Publishing Group (NPG)
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    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
    Published by Nature Publishing Group (NPG)
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  • 7
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    Kinematics of the Pamir and Hindu Kush regions from GPS geodesy (2013)
    Wiley
    Details
    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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  • 8
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    Erosional power in the Swiss Alps: characterization of slope failure in the Illgraben (2012)
    Wiley
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    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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  • 9
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    Combined Flow Abstraction and Climate Change Impacts on an Aggrading Alpine River (2017)
    Wiley
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    Publication Date: 2017-12-29
    Description: Recent climatic warming and associated glacial retreat may have a large impact on sediment release and transfer in Alpine river basins. Concurrently, the sediment transport capacity of many European Alpine streams is affected by hydropower exploitation, notably where flow is abstracted but the sediment supply downstream is maintained. Here, we investigate the combined effects of climate change and flow abstraction on morphodynamics and sediment transfer in the Borgne River, Switzerland. From photogrammetrically derived historical Digital Elevation Models (DEMs) we find considerable net aggradation of the braided river bed (up to 5 meters) since the onset of flow abstraction in 1963. Reaches responded through bed level steepening which was strongest in the upper most reach. Widespread aggradation however did not commence until the onset of glacier retreat in the late 1980s and the dry and warm years of the early 1990s. Upstream flow intake data shows that this aggradation coincided with an increase in sediment supply, although aggradation accounts for no more than 25% of supplied material. The remainder was transferred through the studied reaches. Estimations of bed load transport capacity indicate that flow abstraction reduces transport capacity by 1-2 orders of magnitude. Whilst residual transport rates vary with morphological evolution, they are in the same order of magnitude as the sediment supply rates, which is why significant transport remains. However, the reduction in transport capacity makes the system more sensitive to short-term (annual) changes in climate-driven hydrological variability and climate-induced changes in intake management and sediment delivery rates.
    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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  • 10
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    Ecomorphodynamics of rivers with converging boundaries (2014)
    Wiley
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    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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