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  • 1
    Publication Date: 2016-12-23
    Description: The Connecticut River is a tidal salt wedge estuary, where advection of sharp salinity gradients through channel constrictions and over steeply sloping bathymetry leads to spatially heterogeneous stratification and mixing. A 3-d unstructured-grid finite-volume hydrodynamic model (FVCOM) was evaluated against shipboard and moored observations, and mixing by both the turbulent closure and numerical diffusion were calculated. Excessive numerical mixing in regions with strong velocities, sharp salinity gradients, and steep bathymetry reduced model skill for salinity. Model calibration was improved by optimizing both the bottom roughness ( z 0 ), based on comparison with the barotropic tidal propagation, and the mixing threshold in the turbulence closure (steady-state Richardson number, Ri st ), based on comparison with salinity. Whereas a large body of evidence supports a value of Ri st ∼ 0.25, model skill for salinity improved with Ri st ∼ 0.1. With Ri st = 0.25, numerical mixing contributed about 1/2 the total mixing, while with Ri st = 0.10 it accounted for ∼2/3, but salinity structure was more accurately reproduced. The combined contributions of numerical and turbulent mixing were quantitatively consistent with high-resolution measurements of turbulent mixing. A coarser grid had increased numerical mixing, requiring further reductions in turbulent mixing and greater bed friction to optimize skill. The optimal Ri st for the fine grid case was closer to 0.25 than for the coarse grid, suggesting that additional grid refinement might correspond with Ri st approaching the theoretical limit. Numerical mixing is rarely assessed in realistic models, but comparisons with high-resolution observations in this study suggest it is an important factor. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2017-05-17
    Description: Estuarine mixing is often intensified in regions where topographic forcing leads to hydraulic transitions. Observations in the salt-wedge estuary of the Connecticut River indicate that intense mixing occurs during the ebb tide in regions of supercritical flow that is accelerated by lateral expansion of the channel. The zones of mixing are readily identifiable based on echo-sounding images of large-amplitude shear instabilities. The gradient Richardson number (Ri) averaged across the mixing layer decreases to a value very close to 0.25 during most of the active mixing phase. The along-estuary variation in internal Froude number and interface elevation are roughly consistent with a steady, inviscid, two-layer hydraulic representation, and the fit is improved when a parameterization for interfacial stress is included. The analysis indicates that the mixing results from lateral straining of the shear layer, and that the rapid development of instabilities maintains the overall flow near the mixing threshold value of Ri=0.25, even with continuous, active mixing. The entrainment coefficient can be estimated from salt conservation within the interfacial layer, based on the finding that the mixing maintains Ri=0.25. This approach leads to a scaling estimate for the interfacial mixing coefficient based on the lateral spreading rate and the aspect ratio of the flow, yielding estimates of turbulent dissipation within the pycnocline that are consistent with estimates based on turbulence-resolving measurements.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2017-05-18
    Description: Although the existing body of empirical literature on the relation between corporate environmental performance (CEP) and corporate financial performance (CFP) is continuously growing, results are still inconclusive about this fundamental question in industrial ecology. Comparisons are difficult because of various estimation methods as well as the overall heterogeneous and complex interaction between the two constructs, but especially because of country-specific data sets. Consequently, we raise the question of whether regional differences are the driving force buried underneath the inconclusiveness. Therefore, the aim of this article is to explore this heterogeneity by aggregating 893 existing results from 142 empirical primary studies that are based on more than 750,000 firm-year observations. Our findings suggest a convex impact of a country's economic development on the magnitude of the CEP-CFP effect (i.e., the effect is positive in developing countries, disappears in emerging countries, and is again positive in highly developed countries). We also find that the overall positive relation strengthens for market-based CFP measures and diminishes for countries with civil law systems, firms from the service sector, reactive environmental activities, and process-based CEP measures. Further, several aspects of the examined data sample and the inclusion of relevant control variables explain heterogeneity in previous research results.
    Print ISSN: 1088-1980
    Electronic ISSN: 1530-9290
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Wiley
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  • 4
    Publication Date: 2017-05-04
    Description: Dykes at the Vicuña Pampa Volcanic Complex, which are mostly basaltic (trachy)-andesite and (trachy)-andesite, are exposed at the base and along the walls of a large depression resulting from intense degradation. Dykes intruding stiff layers (lavas, plugs and necks) are thin, mostly dip 〉60° and have coherent textures, whereas dykes intruding more compliant materials (breccias and conglomerates) tend to be thicker, have lower dips and have coherent, brecciated or mixed textures (coherent and brecciated textural domains in a single or compound dyke). Single dykes with brecciated and mixed textures are only found intruding near-surface units. Dykes with mixed textures always have sharp contacts between domains. Dykes with sinuous domain contacts and enclaves of one domain inside the other are interpreted as resulting from dyke arrest, partial cooling and reinjection of new magma. Dykes with straight domain contacts are considered to be compound dykes, with a new dyke intruding along the margins of an older, solidified one. This article is protected by copyright. All rights reserved.
    Print ISSN: 0954-4879
    Electronic ISSN: 1365-3121
    Topics: Geosciences
    Published by Wiley
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  • 5
    Publication Date: 2013-09-24
    Description: The plasma membrane protein CaRch1p of Candida albicans , homologous to the human solute carrier protein SLC10A7, is involved in the regulation of calcium homeostasis. C. albicans cells lacking CaRCH1 are hypersensitive to high extracellular Ca 2+ concentrations and show increased tolerance to ketoconazole (KCZ). We assume a higher basal Ca 2+ influx in the rch1/rch1 mutant strain at low extracellular Ca 2+ concentrations which is not detrimental to C. albicans cells but may be sufficient to activate calcineurin, finally resulting in an increased tolerance to KCZ. However, at 8 µg/ml KCZ plus 3 mM Ca 2+ the rch1/rch1 mutant and the wild type strains showed identical growth. By further increasing the Ca 2+ concentration to 30 mM this phenotype completely reversed and the rch1/rch1 mutant strain became extremely sensitive to 8 µg/ml KCZ, probably due to synergistic toxic effects of Ca 2+ and KCZ under these conditions. Furthermore, we aimed to clarify if CaRch1p interacts with the Cch1p component of the voltage-gated calcium influx channel Cch1p/Mid1p in C. albicans cells. As disruption of the two alleles of CCH1 in the rch1 / rch1 mutant strain did not alter its hypersensitivity to high extracellular Ca 2+ , and, as this phenotype was completely abolished by low amounts of Mg 2+ in the rch1/rch1 mutant as well as in the cch1/cch1 rch1/rch1 double mutant, we conclude that CaRch1p is a functional component of the low-affinity calcium uptake system (LACS) system and does not functionally interact with Cch1p. This article is protected by copyright. All rights reserved.
    Print ISSN: 0749-503X
    Electronic ISSN: 1097-0061
    Topics: Biology
    Published by Wiley
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  • 6
    Publication Date: 2013-10-06
    Description: [1]  Tropical Storms Irene and Lee in 2011 produced intense precipitation and flooding in the U.S. Northeast, including the Hudson River watershed. Sediment input to the Hudson River was approximately 2.7 Mt, about 5 times the long-term annual average. Rather than the common assumption that sediment is predominantly trapped in the estuary, observations and model results indicate that ~2/3 of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms, and only about 1/5 of the new sediment reaching the saline estuary. High sediment concentrations were observed in the estuary, but the model results suggest this was predominantly due to remobilization of bed sediment. Spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records. The results indicate that tidal rivers can intercept (at least temporarily) delivery of terrigenous sediment to the marine environment during major flow events.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2011-11-04
    Description: Well-developed karst aquifers consist of highly conductive conduits and a relatively low permeability fractured and/or porous rock matrix and therefore behave as a dual-hydraulic system. Groundwater flow within highly permeable strata is rapid and transient and depends on local flow conditions, i.e., pressurized or nonpressurized flow. The characterization of karst aquifers is a necessary and challenging task because information about hydraulic and spatial conduit properties is poorly defined or unknown. To investigate karst aquifers, hydraulic stresses such as large recharge events can be simulated with hybrid (coupled discrete continuum) models. Since existing hybrid models are simplifications of the system dynamics, a new karst model (ModBraC) is presented that accounts for unsteady and nonuniform discrete flow in variably saturated conduits employing the Saint-Venant equations. Model performance tests indicate that ModBraC is able to simulate (1) unsteady and nonuniform flow in variably filled conduits, (2) draining and refilling of conduits with stable transition between free-surface and pressurized flow and correct storage representation, (3) water exchange between matrix and variably filled conduits, and (4) discharge routing through branched and intermeshed conduit networks. Subsequently, ModBraC is applied to an idealized catchment to investigate the significance of free-surface flow representation. A parameter study is conducted with two different initial conditions: (1) pressurized flow and (2) free-surface flow. If free-surface flow prevails, the systems is characterized by (1) a time lag for signal transmission, (2) a typical spring discharge pattern representing the transition from pressurized to free-surface flow, and (3) a reduced conduit-matrix interaction during free-surface flow.
    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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  • 8
    Publication Date: 2014-12-11
    Description: Observations at the Columbia River plume show that wave breaking is an important source of turbulence at the offshore front, which may contribute to plume mixing. The lateral gradient of current associated with the plume front is sufficient to block (and break) shorter waves. The intense whitecaping that then occurs at the front is a significant source of turbulence, which diffuses downward from the surface according to a scaling determined by the wave height and the gradient of wave energy flux. This process is distinct from the shear-driven mixing that occurs at the interface of river water and ocean water. Observations with and without short waves are examined, especially two cases in which the background conditions (i.e., tidal flows and river discharge) are otherwise identical.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2017-08-12
    Description: This paper demonstrates two important aspects of regional dynamical downscaling of multi-decadal atmospheric re-analysis. First, that in this way skillful regional descriptions of multi-decadal climate variability may be constructed in regions with little or no local data. Secondly, that the concept of large-scale constraining allows global downscaling, so that global re-analyses may be completed by additions of consistent detail in all regions of the world. Global re-analyses suffer from inhomogeneities. However, their large-scale componenst are mostly homogeneous; Therefore, the concept of downscaling may be applied to homogeneously complement the large-scale state of the re-analyses with regional detail – wherever the condition of homogeneity of the description of large scales is fulfilled. Technically this can be done by dynamical downscaling using a regional or global climate model, which's large scales are constrained by spectral nudging. This approach has been developed and tested for the region of Europe, and a skillful representation of regional weather risks – in particular marine risks – was identified. We have run this system in regions with reduced or absent local data coverage, such as Central Siberia, the Bohai and Yellow Sea, Southwestern Africa and the South Atlantic. Also a global simulation was computed, which adds regional features to prescribed global dynamics. Our cases demonstrate that spatially detailed reconstructions of the climate state and its change in the recent three to six decades add useful supplementary information to existing observational data for mid-latitude and sub-tropical regions of the world.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2017-03-03
    Description: Recycling materials from end-of-life products has the potential to create environmental benefit by displacing more harmful primary material production. However, displacement is governed by market forces and is not guaranteed; if full displacement does not occur, the environmental benefits of recycling are reduced or eliminated. Therefore, quantifying the true “displacement rate” caused by recycling is essential to accurately assess environmental benefits and make optimal environmental management decisions. Our 2016 article proposed a market-based methodology to estimate actual displacement rates following an increase in recycling or reuse. The current article demonstrates the operation, utility, and challenges of that methodology in the context of the U.S. aluminum industry. Sensitivity analyses reveal that displacement estimates are sensitive to uncertainty in price elasticities. Results suggest that 100% displacement is unlikely immediately following a sustained supply-driven increase in aluminum recycling and even less likely in the long term. However, zero and even negative displacement are possible. A variant of the model revealed that demand-driven increases in recycling are less likely than supply-driven changes to result in full displacement. However, model limitations exist and challenges arose in the estimation process, the effects of which are discussed. We suggest implications for environmental assessment, present lessons learned from applying the estimation methodology, and highlight the need for further research in the market dynamics of recycling.
    Print ISSN: 1088-1980
    Electronic ISSN: 1530-9290
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Wiley
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