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14 results on '"Jo, D.S."'

2. Comparison of Urban Air Quality Simulations During the KORUS‐AQ Campaign With Regionally Refined Versus Global Uniform Grids in the Multi‐Scale Infrastructure for Chemistry and Aerosols (MUSICA) Version 0

Author

Jo, D.S., Emmons, L.K., Callaghan, P., Tilmes, S., Woo, J.‐H., Kim, Y., Kim, J., Granier, C., Soulié, A., Doumbia, T., Darras, S., Buchholz, R.R., Simpson, I.J., Blake, D.R., Wisthaler, A., Schroeder, J.R., Fried, A., Kanaya, Y., Jo, D.S., Emmons, L.K., Callaghan, P., Tilmes, S., Woo, J.‐H., Kim, Y., Kim, J., Granier, C., Soulié, A., Doumbia, T., Darras, S., Buchholz, R.R., Simpson, I.J., Blake, D.R., Wisthaler, A., Schroeder, J.R., Fried, A., and Kanaya, Y.

Abstract

Model intercomparison studies often report a large spread in simulation results, but quantifying the causes of these differences is hindered by the fact that several processes contribute to the model spread simultaneously. Here we use the Multi-Scale Infrastructure for Chemistry and Aerosols (MUSICA) version 0 to investigate the model resolution dependencies of simulated chemical species, with a focus on the differences between global uniform grid and regional refinement grid simulations with the same modeling framework. We construct two global (ne30 [∼112 km] and ne60 [∼56 km]) and two regional refinement grids over Korea (ne30x8 [∼14 km] and ne30x16 [∼7 km]). The grid resolution can change chemical concentrations by an order of magnitude in the boundary layer, and the importance increases as the species' reactivity increases (e.g., up to 50% and 1,000% changes for ethane and xylenes, respectively). The diurnal cycle of oxidants (OH, O3, and NO3) also varies with the grid resolution, which leads to different oxidation pathways of volatile organic compounds (e.g., the fraction of monoterpenes reacting with NO3 in Seoul around midnight is 90% for ne30, but 65% for ne30x16). The models with high-resolution grids usually do a better job at reproducing aircraft observations during the KORUS-AQ campaign, but not always, implying compensating errors in the coarse grid simulations. For example, ozone is better reproduced by the coarse grid due to the artificial mixing of NOx. When developing new chemical mechanisms and evaluating models over urban areas, the uncertainties associated with model resolution should be considered. © 2023 The Authors. Journal of Advances in Modeling Earth Systems published by Wiley Periodicals LLC on behalf of American Geophysical Union.

Published
2023
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3. A Scheme for Representing Aromatic Secondary Organic Aerosols in Chemical Transport Models: Application to Source Attribution of Organic Aerosols Over South Korea During the KORUS-AQ Campaign

Author

Brewer, J.F., Jacob, D.J., Jathar, S.H., He, Y., Akherati, A., Zhai, Shixian, Jo, D.S., Hodzic, A., Nault, B.A., Campuzano-Jost, P., Jimenez, J.L., Park, R.J., Oak, Y.J., Liao, H., Brewer, J.F., Jacob, D.J., Jathar, S.H., He, Y., Akherati, A., Zhai, Shixian, Jo, D.S., Hodzic, A., Nault, B.A., Campuzano-Jost, P., Jimenez, J.L., Park, R.J., Oak, Y.J., and Liao, H.

Abstract

We present a new volatility basis set (VBS) representation of aromatic secondary organic aerosol (SOA) for atmospheric chemistry models by fitting a statistical oxidation model with aerosol microphysics (SOM-TOMAS) to results from laboratory chamber experiments. The resulting SOM-VBS scheme also including previous work on SOA formation from semi- and intermediate volatile organic compounds (S/IVOCs) is implemented in the GEOS-Chem chemical transport model and applied to simulation of observations from the Korea-United States Air Quality Study (KORUS-AQ) field campaign over South Korea in May–June 2016. Our SOM-VBS scheme can simulate the KORUS-AQ organic aerosol (OA) observations from aircraft and surface sites better than the default schemes used in GEOS-Chem including for vertical profiles, diurnal cycle, and partitioning between hydrocarbon-like OA and oxidized OA. Our results confirm the important contributions of oxidized primary OA and aromatic SOA found in previous analyses of the KORUS-AQ data and further show a large contribution from S/IVOCs. Model source attribution of OA in surface air over South Korea indicates one third from domestic anthropogenic emissions, with a large contribution from toluene and xylenes, one third from external anthropogenic emissions, and one third from natural emissions. © 2023. American Geophysical Union. All Rights Reserved.

Published
2023

9. Application of hot forming quenching on patchwork blank using two-stage refilled friction stir spot welding

Author

Jo D.S., Kim J.H., Ko D.C., and Kim B.M.

Subjects
Engineering (General). Civil engineering (General), TA1-2040
Abstract

The purpose of this study is to apply Hot Forming Quenching (HFQ) on Patchwork Blank of AA6061 using Two-stage refilled Friction Stir Spot Welding (TFSSW). TFSSW is a developed joining method to improve joint strength of conventional Friction Stir Spot Welding (FSSW) and it consists of two stages. The first stage is a conventional FSSW process and second stage is a refilling process for refilling keyhole. The Design of Experiment (DOE) was used to optimize the TFSSW process parameters. A hat shape forming test was performed using a patchwork blank manufactured with the optimal process parameters to investigate validity of applying HFQ. Formed hat shape part was sequentially heat treated with artificial aging (T6) condition. The hardness of the weld zone was measured to confirm a drop of mechanical property in comparison with the conventional cold forming, which shows the validity of HFQ application to patchwork blank using TFSSW.

Published
2018
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12. Synthesis and photoluminescence properties of YAG:Ce3+ phosphor using a liquid-phase precursor method.

Author

Chen, W.Q., Jo, D.S., Song, Y.H., Masaki, T., and Yoon, D.H.

Subjects
*PHOTOLUMINESCENCE, *PHOSPHORS, *CHEMICAL synthesis, *CERIUM, *DOPING agents (Chemistry), *COPRECIPITATION (Chemistry), *SOLID state physics
Abstract

Abstract: Trivalent cerium Ce3+-doped YAG (Y2.94Ce0.06Al5O12) phosphors were synthesized by solid-state reaction, liquid-phase precursor, co-precipitation, and drying methods. The specimen obtained by the LPP method showed the highest emission intensity among the four methods and fired at 1400°C firing, and the intensity was approximately 180% higher compared with a commercial product. The phosphors obtained by the LPP method showed more homogeneous, agglomerate-free, nearly spherical particles. [Copyright &y& Elsevier]

Published
2014
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13. Synthesis of high efficient Ca2SiO4:Eu2+ green emitting phosphor by a liquid phase precursor method

Author

Luo, Y.Y., Jo, D.S., Senthil, K., Tezuka, S., Kakihana, M., Toda, K., Masaki, T., and Yoon, D.H.

Subjects
*SILICON oxide, *LIQUID phase epitaxy, *INORGANIC synthesis, *SOLID state chemistry, *LUMINESCENCE spectroscopy, *LIGHT emitting diodes, *PHOSPHORS
Abstract

Abstract: Green emitting Eu2+-doped Ca2SiO4 phosphors were synthesized by three different methods (a conventional solid state reaction (SSR) method, a novel liquid phase precursor approach using SiO2 sol (LPP-SiO2(sol)) and water-soluble silicon compound (LPP-WSS)). The obtained phosphors exhibited a broad excitation spectrum ranging from 225 to 450nm and a strong green emission peak at 502nm due to the 4f 65d 1→4f 7(8S7/2) transition of Eu2+. The highest luminescent intensity was obtained for the samples fired at 1100°C. The dependence of luminescence properties on Eu2+ concentration for the phosphors synthesized using LPP-WSS method was also examined from 0.1 to 5.0mol% and the maximum emission intensity was observed at 3.0mol% Eu2+. A detailed analysis using various characterizations revealed that phosphors produced by the LPP-WSS process exhibited more homogenous phase distribution and higher luminescence intensity than those from the other two processes, which suggested the potential application of Ca2SiO4:Eu2+ in white light-emitting diodes and fluorescence lamps. [Copyright &y& Elsevier]

Published
2012
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14. Enhancement of photoluminescence properties of CaAl2Si2O8:Eu2+ by SiO2 addition

Author

Kim, B.S., Song, Y.H., Jo, D.S., Abe, T., Senthil, K., Masaki, T., Toda, K., and Yoon, D.H.

Subjects
*PHOTOLUMINESCENCE, *CALCIUM compounds, *SILICA, *LIQUID phase epitaxy, *CRYSTAL structure, *PHOSPHORS, *WAVELENGTHS
Abstract

Abstract: SiO2 added phosphors, CaAl2Si2O8:Eu2+ + xSiO2 (x =0, 1, 2, 3, 4, 5, 6 and 13mol) were synthesized by a novel liquid phase precursor (LPP) method. The photoluminescence properties of phosphor added by 5mol of SiO2 showed 110% enhancement in the emission intensity compared to the CaAl2Si2O8:Eu2+ phosphor. A broad emission and excitation wavelength was observed approximately from 400nm to 600nm centered at 430nm and from 280nm to 400nm centered at 365nm, respectively. Photoluminescence intensity of the phosphors increased continuously by SiO2 addition up to x =5mol and then it decreased with further addition of SiO2. The observed photoluminescence properties of the phosphors were discussed related to their crystalline structure and morphology. [Copyright &y& Elsevier]

Published
2012
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