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  • Articles  (63)
  • Wiley  (63)
  • 2015-2019  (63)
  • 1990-1994
  • 2019  (63)
  • Physics  (63)
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  • Articles  (63)
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Publisher
Years
  • 2015-2019  (63)
  • 1990-1994
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  • 1
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    Combining Numerical and Statistical Models to Predict Storm‐Induced Dune Erosion (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Dune erosion is an important aspect to consider when assessing coastal flood risk, as dune elevation loss makes the protected areas more susceptible to flooding. However, most advanced dune erosion numerical models are computationally expensive, which hinders their application in early‐warning systems. Based on a combination of probabilistic and process‐based numerical modeling, we develop an efficient statistical tool to predict dune erosion during storms. The analysis focuses on Dauphin Island, AL, in the northern Gulf of Mexico, where we combine synthetic sea storms with a calibrated and validated XBeach model to develop and test a range of different surrogate models for their ability to predict barrier island geometric parameters under storm conditions. Surrogate models are developed by combining the oceanographic forcing from 100 optimally sampled sea storm events covering the entire multivariate parameter space (used as XBeach input) and associated changes in the dune system (XBeach output). We test four surrogate models using a k‐fold approach for validation. All models perform well in predicting changes in dune elevation, barrier island area, and width but are less accurate in predicting alterations in the cross‐shore locations of dune morphological features. Multivariate adaptive regression splines is identified as the best surrogate model based on its fast development and good performance, attaining a modified Mielke index of 0.81 for dune crest height. As demonstrated at Dauphin Island, our approach shows potential to be used in an operational framework to predict dune response (in particular crest elevation change) when water level and wave forecasts are available.
    Print ISSN: 2169-9003
    Electronic ISSN: 2169-9011
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Warm white light emitting from single composition SrGa12O19:Dy3+ phosphors for AC‐LED (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Making illumination light sources become comfortable to the human eye is a long‐term effort, which justifies the current research on warm white‐light‐emitting diodes (w‐LEDs). In this work, a novel phosphor for w‐LEDs, namely SrGa12O19: Dy3+(SGO: Dy3+), with a low‐color temperature (CT) was designed and synthesized. The crystal structure, the luminescence properties, the thermoluminescence properties and the stability of SGO: Dy3+ were investigated. We demonstrate outstanding luminescent characteristics and excellent stabilities. The intensity of emission light keep remained when excited by a flickering light source with a chopping speed or off‐time of a few seconds, which indicates that the SGO: Dy3+ phosphor has anti‐flicker properties that will be useful for potential applications, as LEDs driven by alternating current (AC‐LED). The chromaticity coordinates and the correlated color temperature (CCT) of SGO: Dy3+ phosphors with different Dy3+ concentrations are close with an optimal doping at 4.00 mol% Dy3+ for chromaticity coordinate (0.4269, 0.4348) and a lowest CCT of 3361 K. The perfect weatherability of this phosphor was also confirmed since the phosphorescence intensity and the color were stable at high temperature and in a high humidity environment. The performance obtained shows that SGO: Dy3+ is a suitable candidate for illumination sources that are beneficial to human health.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 3
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    New high‐temperature‐dependence‐of‐magnetic‐susceptibility‐based climofunction for quantifying paleoprecipitation from Chinese loess (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The ferrimagnetic properties of soils are used to quantitatively reconstruct paleomonsoon precipitation from Chinese loess. Numerous magneto‐climofunctions have been established based on the magnetic proxies that are selectively sensitive to neoformation of fine‐grained superparamagnetic (SP) or single‐domain (SD) ferrimagnetic particles. Accumulating evidence has indicated that maghemite is the final product of the ferrimagnetic phases during pedogenesis in loessic soils. Quantitative estimates of abundance of maghemite of both SP and SD grains is therefore still required in developing magneto‐climofunctions. Here, we present detailed measurements on a suite of modern soil samples from the Chinese Loess Plateau to determine pedogenic ferrimagnetic mineralogy and to develop a new magneto‐climofunction based on a new parameter derived from the high‐temperature‐dependent magnetic susceptibility. Particle‐size fractionation processes combined with magnetic measurements indicate that fine‐grained SP and SD maghemite is the dominant pedogenic ferrimagnetic phases. High‐temperature dependent susceptibility measurements show that the thermally‐induced susceptibility drops between ~230°C and ~400°C during heating mainly result from the conversion of maghemite to hematite. We proposed a new parameter quantifying changes in the temperature dependence of magnetic susceptibility between 230‐400°C, "χtd ", that captures the concentration of pedogenically formed maghemite. Results show that χtd has a strong correlation with known quantities of maghemite in synthetic standard samples, and that χtd of modern soils correlates with modern mean annual precipitation (MAP) quite well (R2=0.82, n=24). The established χtd‐MAP climofunction provides a new approach to reconstructing paleorainfall during past warm interglacials from paleosols in Chinese loess.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Ebullition of oxygen from seagrasses under supersaturated conditions (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Gas ebullition from aquatic systems to the atmosphere represents a potentially important fraction of primary production that goes unquantified by measurements of dissolved gas concentrations. Although gas ebullition from photosynthetic surfaces has often been observed, it is rarely quantified. The resulting underestimation of photosynthetic activity may significantly bias the determination of ecosystem trophic status and estimated rates of biogeochemical cycling from in situ measures of dissolved oxygen. Here, we quantified gas ebullition rates in Zostera marina meadows in Virginia, U.S.A. using simple funnel traps and analyzed the oxygen concentration and isotopic composition of the captured gas. Maximum hourly rates of oxygen ebullition (3.0 mmol oxygen m−2 h−1) were observed during the coincidence of high irradiance and low tides, particularly in the afternoon when oxygen and temperature maxima occurred. The daily ebullition fluxes (up to 11 mmol oxygen m−2 d−1) were roughly equivalent to net primary production rates determined from dissolved oxygen measurements indicating that bubble ebullition can represent a major component of primary production that is not commonly included in ecosystem‐scale estimates. Oxygen content comprised 20–40% of the captured bubble gas volume and correlated negatively with its δ18O values, consistent with a predominance of mixing between the higher δ18O of atmospheric oxygen in equilibrium with seawater and the lower δ18O of oxygen derived from photosynthesis. Thus, future studies interested in the metabolism of highly productive, shallow water ecosystems, and particularly those measuring in situ oxygen flux, should not ignore the bubble formation and ebullition processes described here.
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
    Published by Wiley on behalf of The Association for the Sciences of Limnology and Oceanography (ASLO).
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  • 5
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    Modeling the Impacts of Urbanization and Open Water Surface on Heavy Convective Rainfall: A Case Study over the Emerging Xiong'an City, China (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract In this study, we examine the impacts of urbanization and open water surface on heavy convective rainfall based on numerical modeling experiments using the Weather Research and Forecasting model. We focus on a severe storm event over the emerging Xiong'an City in northern China. The storm event consists of two episodes and features intense moisture transport and strong large‐scale forcing. A set of Weather Research and Forecasting simulations were implemented to examine the sensitivity of spatiotemporal rainfall variability in and around the urban area to different land use scenarios. Modeling results highlight contrasting roles of open water and urban surface in dictating space‐time organizations of convective rainfall under strong large‐scale forcing. Dynamic perturbation to atmospheric forcing dominates the impacts of open water and urban surface on spatial rainfall distribution during the second storm episode, while urban surface promotes early initiation of convection during the first storm episode through enhanced buoyant energy. Open water surface contributes to convective inhibition through evaporative cooling but can enhance moist convection when the impact of urban surface is also considered. The synergistic effect of open water and urban surface leads to rainfall enhancement both over and in the downwind urban area. Changes in rainfall accumulation with different spatial extents of urban coverage highlight strong dependence of urban‐induced rainfall anomalies on urbanization stages. Our results provide improved understandings on hydrometeorological impacts due to emerging cities in complex physiographic settings and emphasize the importance of atmospheric forcing in urban rainfall modification studies.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Climate Response to Pulse Versus Sustained Stratospheric Aerosol Forcing (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Solar geoengineering has been suggested as a potential means to counteract anthropogenic warming. Major volcanic eruptions have been used as natural analogues to large‐scale deployments of stratospheric aerosol geoengineering, yet difference in climate responses to these forcings remains unclear. Using the National Center for Atmospheric Research Community Earth System Model, we compare climate responses to two highly idealized stratospheric aerosol forcings that have different durations: a short‐term pulse representative of volcanic eruptions and a long‐term sustained forcing representative of geoengineering. For the same amount of global mean cooling, decreases in land temperature, precipitation, and runoff in the pulse case are much larger than that in the sustained case. The spatial pattern changes differ substantially between these two cases. Thus, direct extrapolations from volcanic eruption observations provide limited insight into impacts of potential stratospheric aerosol geoengineering. However, simulations of volcanic eruptions can be useful to test process representations in models that are used to simulate geoengineering deployments.
    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
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    Optical and Judd‐Ofelt spectroscopic study of Er3+‐doped strontium gadolinium gallium garnet single‐crystal (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Er3+‐doped strontium gadolinium gallium garnet (SrGdGa3O7) single‐crystal was grown by Czochralski method. The Er3+ concentration in the crystal was determined as 4.2 × 1021 ions/cm3 by inductively coupled plasma atomic absorption spectroscopy. Refractive index of the crystal was measured at the wavelengths of 633, 1311 and 1553 nm by prism coupling technique. The results show that the crystal is a positive uniaxial crystal with a birefringence of ~0.01, and the Sellmeier equation reported previously for the crystal doped with Nd3+ is also valid for the one doped with Er3+. Unpolarized absorption spectrum of the crystal was measured at room temperature and the Er3+ absorption cross‐section spectrum was calibrated from it. The Er3+ spectroscopic properties were studied by Judd‐Ofelt theory. Some fundamental spectroscopic parameters were obtained that include absorption coefficient and cross‐section spectral distributions, electronic transition oscillator strength, Judd‐Ofelt parameters, fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 8
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    Silica foams with ultra‐large specific surface area structured by hollow mesoporous silica spheres (2019)
    Wiley
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    Publication Date: 2019
    Description: Hollow mesoporous silica spheres assembled foam material with uniform macro‐pore structure and ultra‐high specific surface area, prepared from HMSSs stabilized colloidal foams Abstract Ceramic foams with multi‐scale pores and large specific surface area have received extensive attention due to their unique structure and superior properties. Considering that there are still challenges to synthesize porous ceramics with large specific surface area, a novel ceramic foam material with ultra‐large specific surface area has been prepared using hollow silica mesoporous spheres (HMSSs) as building block in this work. These building blocks were made weakly hydrophobic in order to produce HMSS particle stabilized foams. The foams exhibit a uniform primary macropore structure, which is composed of a three dimensional HMSS‐assembled network, via HMSS‐stabilized foams. The influence of sintering temperature on the microstructure and properties of HMSS foams is investigated. The HMSS foams exhibit highest specific surface area of 1733 m2/g, attributed to the radial mesopores in HMSS shell, when sintered at between 500°C and 800°C. This specific surface area is much higher than that of existing ceramic materials. The uniform pore structure and ultra‐large specific surface area make it a promising lightweight material in potential application fields, including catalyst, adsorption, fire‐resistant thermal insulation, and load and control release system.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 9
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    Optical and thermal properties of TiO2‐doped Y2O3 transparent ceramics synthesized by hot isostatic pressing (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Highly transparent Y2O3 ceramics using TiO2 as an additive were synthesized by presintering and hot isostatic pressing (HIP). The effects of TiO2 contents and sintering conditions on the optical properties of the final transparent ceramics were investigated. A small amount (0.04‐0.16 wt%) may decrease the densification temperature by about 200°C. The Y2O3 ceramics doped with 0.16 wt% TiO2 revealed a transparency of 82% in the wavelength range 1‐6 μm. The thermal conductivity of the samples is about 11.8 W/m K at 25°C, which is close to that of the undoped Y2O3 ceramics.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 10
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    Computational modeling of grain boundary electrostatic effect in polycrystalline SrTiO3 thin film (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Understanding the leakage current caused by charge transport and local accumulation in dielectric oxides is critical for predicting and extending the lifetime of dielectric‐based electronic devices. The internal interfaces such as grain boundaries (GBs) inside a dielectric induce local strain and charge segregation and thus further influence the charge transport behavior. In this work, we employ computational modeling based on the Schottky barrier model and nonlinear Nernst‐Planck transport equation is used to study the oxygen vacancy transport and leakage current evolution in a SrTiO3 thin film under a DC bias with planar electrodes. It is found that in polycrystalline SrTiO3, the GB‐bounded donors create an electric potential barrier and a local depletion region near the GBs, impeding the oxygen vacancy transport and suppressing the leakage current increase compared to a single crystal SrTiO3 thin film. The effects of temperature, the magnitude of an applied field, the number density of GBs, the GB‐bounded donor concentration, and the depletion layer width on the leakage current evolution are systematically investigated. The simulation results are compared with the analytical solutions, as well as with existing theoretical and experimental reports. This work thus helps shed light to the grain‐structure dependent electrostatic behaviors in dielectric thin films under different intrinsic and extrinsic conditions.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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