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  • Articles  (10,861)
  • Wiley  (10,861)
  • American Chemical Society
  • 2015-2019  (10,861)
  • Journal of the American Ceramic Society  (3,142)
  • Water Resources Research  (2,430)
  • Earth Surface Processes and Landforms  (929)
  • 1922
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  • Articles  (10,861)
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  • 1
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    Microwave Dielectric Properties, Crystal Structure, and Microstructure of the Bi3Nb1−xTaxO7 Solid Solution (2015)
    Wiley
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    Publication Date: 2015-08-11
    Description: New, commensurate members of the fluorite-related Bi 3 Nb 1− x Ta x O 7 family were synthesized and their crystal structures, microstructures, and microwave (MW) dielectric properties were characterized. The incorporation of Ta into the tetragonal Bi 3 Nb 1− x Ta x O 7 solid solution was found to gradually affect the density and the MW dielectric properties. The materials sintered at 870°C exhibited relative permittivities in the range k ′ = 86–72, Q  ×  f values from 793 to 1189 GHz and a positive temperature coefficient of resonant frequency from 88 to 12 ppm/K. The formation of the members of the fluorite-related solid solution along the Bi 3 Nb 1− x Ta x O 7 composition depends on a phase transition, and thus their properties are compared within the compositional range. The correlations between their MW dielectric properties, compositions, crystal structures, and processing parameters were discussed in detail. Optimization of MW properties can be achieved by utilizing the ability of the Bi 3 Nb 1− x Ta x O 7 solid solution that it undergoes a phase transformation from cubic to tetragonal structure which are both characterized by unique properties, under certain synthesis conditions.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
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    Optical Thermometry Based on Up-Conversion Luminescence Behavior of Er3+ -Doped Transparent Sr2YbF7 Glass-Ceramics (2015)
    Wiley
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    Publication Date: 2015-08-11
    Description: Transparent novel glass-ceramics containing Sr 2 YbF 7 :Er 3+ nanocrystals were successfully fabricated by melt-quenching technique. Their structural and up-conversion luminescent properties were systemically investigated by XRD, HRTEM, and a series of spectroscopy methods. The temperature-dependent up-conversion spectra prove that 2 H 11/2 and 4 S 3/2 levels of Er 3+ are thermally coupled energy levels (TCEL). Consequently, the 2 H 11/2 4 I 15/2 and 4 S 3/2 4 I 15/2 emissions of Er 3+ in Sr 2 YbF 7 :Er 3+ glass-ceramics can be used as optical thermometry based on fluorescence intensity ratio (FIR) technique. Combined with low phonon energy and high thermal stability, Er 3+ ions in Sr 2 YbF 7 glass-ceramics present broad operating temperature range (300–500 K), large energy gap of TCEL (786 cm −1 ) and high theoretical maximum value of relative sensitivity (62.14 × 10 −4  K −1 at 560 K), which suggests that Sr 2 YbF 7 :Er 3+ glass-ceramics may be excellent candidates for optical temperature sensors.
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    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
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    Influence of injection mode on transport properties in kilometer-scale three-dimensional discrete fracture networks (2015)
    Wiley
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    Publication Date: 2015-08-08
    Description: We investigate how the choice of injection mode impacts transport properties in kilometer-scale three-dimensional discrete fracture networks (DFN). The choice of injection mode, resident or flux-weighted, is designed to mimic different physical phenomena. It has been hypothesized that solute plumes injected under resident conditions evolve to behave similarly to solutes injected under flux-weighted conditions. Previously, computational limitations have prohibited the large scale simulations required to investigate this hypothesis. We investigate this hypothesis by using a high performance DFN suite, dfnWorks , to simulate flow in kilometer-scale three-dimensional DFNs based on fractured granite at the Forsmark site in Sweden, and adopt a Lagrangian approach to simulate transport therein. Results show that after traveling through a pre-equilibrium region both injection methods exhibit linear scaling of the first moment of travel time and power law scaling of the breakthrough curve with similar exponents, slightly larger than two. The physical mechanisms behind this evolution appear to be the combination of in-network channeling of mass into larger fractures, which offer reduced resistance to flow, and in-fracture channeling, which results from the topology of the DFN. This article is protected by copyright. All rights reserved.
    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
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    Multivariate postprocessing techniques for probabilistic hydrological forecasting (2015)
    Wiley
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    Publication Date: 2015-08-08
    Description: Hydrologic ensemble forecasts driven by atmospheric ensemble prediction systems need statistical post-processing in order to account for systematic errors in terms of both location and spread. Runoff is an inherently multivariate process with typical events lasting from hours in case of floods to weeks or even months in case of droughts. This calls for multivariate post-processing techniques that yield well calibrated forecasts in univariate terms and ensure a realistic temporal dependence structure at the same time. To this end, the univariate ensemble model output statistics (EMOS) post-processing method is combined with two different copula approaches that ensure multivariate calibration throughout the entire forecast horizon. The domain of this study covers three sub-catchments of the river Rhine that represent different sizes and hydrological regimes: the Upper Rhine up to the gauge Maxau, the river Moselle up to the gauge Trier, and the river Lahn up to the gauge Kalkofen. In this study the two approaches to model the temporal dependence structure are ensemble copula coupling (ECC), which preserves the dependence structure of the raw ensemble, and a Gaussian copula approach (GCA), which estimates the temporal correlations from training observations. The results indicate that both methods are suitable for modelling the temporal dependencies of probabilistic hydrologic forecasts. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 5
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    Semianalytical solutions for transport in aquifer and fractured clay matrix system (2015)
    Wiley
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    Publication Date: 2015-08-08
    Description: A three-dimensional mathematical model that describes transport of contaminant in a horizontal aquifer with simultaneous diffusion into a fractured clay formation is proposed. A group of semi-analytical solutions is derived based on specific initial and boundary conditions as well as various source functions. The analytical model solutions are evaluated by numerical Laplace inverse transformation and analytical Fourier inverse transformation. The model solutions can be used to study the fate and transport in a three-dimensional spatial domain in which a non-aqueous phase liquid exists as a pool atop a fractured low permeability clay layer. The non-aqueous phase liquid gradually dissolves into the groundwater flowing past the pool, while simultaneously diffusing into the fractured clay formation below the aquifer. Mass transfer of the contaminant into the clay formation is demonstrated to be significantly enhanced by the existence of the fractures, even though the volume of fractures is relatively small compared to the volume of the clay matrix. The model solution is a useful tool in assessing contaminant attenuation processes in a confined aquifer underlain by a fractured clay formation. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 6
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    A well-balanced FV scheme for compound channels with complex geometry and movable bed (2015)
    Wiley
    Details
    Publication Date: 2015-07-29
    Description: This work focuses on the implementation of a Shallow Water-Exner model for compound natural channels with complex geometry and movable bed within the finite volume framework. The model is devised for compound channels modeling: cross-section overbanks are treated with fixed bed conditions, while the main channel is left free to modify its morphology. A capacitive approach is used for bedload transport modeling, in which the solid flow rates are estimated with bedload transport formulas. The model equations pose some numerical issues in the case of natural channels, where bedload transport may occur for both subcritical and supercritical flows and geometry varies in space. An explicit path-conservative scheme, designed to overcome all these issues, is presented in the paper. The scheme solves liquid and solid phases dynamics in a coupled manner, in order to correctly model near critical currents/channel interactions and is well-balanced, that is able to properly reproduce steady states. The Roe and Osher Riemann solvers are implemented, so as to take into account the spatial geometry variations of natural channels. The scheme reaches up to 2 nd order accuracy. Validation is performed with fixed and movable bed test cases whose analytical solution is known, and with flume experimental data. An application of the model to a real case study is also shown. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 7
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    The effect of lateral confinement on gravel bed river morphology (2015)
    Wiley
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    Publication Date: 2015-08-05
    Description: In this paper we use a physical modelling approach to explore the effect of lateral confinement on gravel bed river planform style, bed morphology, and sediment transport processes. A set of 27 runs was performed in a large flume (25 m long, 2.9 m wide), with constant longitudinal slope (0.01) and uniform grain size (1 mm), changing the water discharge (1.5 to 2.5 l/s) and the channel width (0.15 m to 1.5 m) to model a wide range of channel configurations, from narrow, straight, embanked channels to wide braided networks. The outcomes of each run were characterized by a detailed digital elevation model describing channel morphology, a map of dry areas and areas actively transporting sediment within the channel, and continuous monitoring of the amount of sediment transported through the flume outlet. Analysis reveals strong relationships between unit stream power and parameters describing the channel morphology. In particular, a smooth transition is observed between narrow channels with an almost rectangular cross section profile (with sediment transport occurring across the entire channel width) and complex braided networks where only a limited proportion (30%) of the bed is active. This transition is captured by descriptors of the bed elevation frequency distribution, e.g. standard deviation, skewness and kurtosis. These summary statistics represent potentially useful indicators of bed morphology that are compared with other commonly used summary indicators such as the braiding index and the type and number of bars. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 8
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    Ab initio Molecular Dynamics Simulations of the Hydroxylation of Nanoporous Silica (2015)
    Wiley
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    Publication Date: 2015-08-08
    Description: Accurate information on the interactions between water and silica is critical to the understanding of its properties including mechanical strength under stress and long-term chemical durability of silica and silicate glasses. In this study, interactions between water and nanoporous amorphous silica models were investigated using density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations which accurately describe bond breakage and formation as well as chemical reactions. AIMD simulations up to 30 ps were performed for systems containing water and nanoporous silica with a wide range of porosities (31%–67%). Partial removal of defects, such as two-membered rings, was observed during the AIMD runs whereas more reactive coordination defects were removed during the initial geometry optimization. The limited two-membered ring removal can be attributed to restricted water-defect movement or the increased stability of rings located on concave surfaces. Two-membered ring removal mechanisms included the formation of an overcoordinated silicon (Si 5 ) intermediate defect from the dynamic simulations. Si 5 defects continued to develop throughout the simulations, indicating a thermodynamic drive for two-membered ring removal which is kinetically limited. Changes in the electronic structures, such as atomic charges, and bond length-bond angle correlation functions were monitored during the hydroxylation process.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 9
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    Influence of Particle Size and Soaking Conditions on Rheology and Microstructure of Amorphous Calcium Polyphosphate Hydrogel (2015)
    Wiley
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    Publication Date: 2015-08-08
    Description: Amorphous calcium polyphosphate (ACPP), an inorganic polymer ceramic, has shown promise as a drug delivery matrix following a repeat gelling protocol. This study described a simple method of preparing ACPP hydrogel in the presence of an excess volume of water. The increased water availability accelerates water molecule ingress and microstructural transformation of ACPP hydrogels. The impact of some experimental settings (soaking time, temperature, stirring, and ACPP particle size) on the physiochemical and rheological natures of ACPP hydrogel were investigated and from which possible hydrogel formation mechanisms were inferred. We believe that the formation of ACPP hydrogel is through the mechanisms of intermolecular ionic interaction and entanglement of polyphosphate chains. The potential application of ACPP hydrogel as a ceramic matrix for sustained drug release warrants further investigation.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
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    Hybrid Sol–Gel Glasses with Glass-Transition Temperatures Below Room Temperature (2015)
    Wiley
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    Publication Date: 2015-08-08
    Description: Melting gels are hybrid gels that have the ability to soften and flow at around 100°C for some combinations of mono- and di-substituted alkoxysiloxanes, where substitutions are either all aromatic or all aliphatic. In this study, melting gels were prepared using phenyltriethoxysilane (PhTES) and dimethyldiethoxysilane (DMDES), meaning both an aromatic and aliphatic substitution. Differential scanning calorimetry was performed to identify glass-transition temperatures, and thermal gravimetric analysis coupled with differential thermal analysis (TGA-DTA) was performed to measure weight loss. The glass-transition temperatures ( T g ) ranged from −61°C to +5.6°C, which are between the values in the methyl only system, where all T g values are less than 0°C, and those values in the phenyl only system, where T g values are greater than 0°C. The T g decreased with an increase in the DMDES fraction. Below 450°C, the gels lost little weight, but around 600°C there was a drop in weight. This temperature is lower than the temperature for gels prepared with only aromatic substitutions, but higher than that for gels prepared with only aliphatic substitutions. Final heat treatment was carried out at 150°C for the gel with 80%PhTES-20%DMDES (in mol%), and the consolidation temperature increased with increasing DMDES content to 205°C for the gel with 50%PhTES-50%DMDES. After this heat treatment, the melting gels no longer soften.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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