• Title/Summary/Keyword: Hwang Doyeon

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Synthesis of the Ni-doped ternary compound Ba(Fe1-xNix)2Se3

  • Park, Hyeon Beom;Shin, Soohyeon;Jung, Soon-Gil;Hwang, Doyeon;Lee, Hyoyoung;Park, Tuson
    • Progress in Superconductivity and Cryogenics
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    • v.17 no.4
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    • pp.30-33
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    • 2015
  • We report the synthesis of Ni-doped $BaFe_2Se_3$ single crystals by using a flux method. X-ray diffraction (XRD) of $Ba(Fe_{1-x}Ni_x)_2Se_3$ shows a gradual peak shift with an increase in the nominal Ni-doping rate, x = 0, 0.05, and 0.10, due to a decrease in unit-cell volume. All samples show a spin glass transition, and temperature dependence of magnetic susceptibility shows a negligible change in the spin-glass transition temperature ($T_g$) with Ni concentration x. The temperature dependence of electrical resistivity for $BaFe_2Se_3$ shows an insulating behavior, and the resistivity value at 295 K and the activation energy ($E_a$) obtained from the Arrhenius plot decrease with increasing x. These results suggest that the Ni doping can be effectively worked as a dopant for electron charge carriers, but is less efficient in controlling the magnetic property, such as spin glass transition, in the $BaFe_2Se_3$ compound.

Reaction Characteristics of New Oxygen Carrier for 0.5 MWth Chemical Looping Combustion System at High Temperature and High Pressure Conditions (0.5 MWth 케미컬루핑 연소 시스템 적용을 위한 신규 산소전달입자의 고온·고압 반응 특성)

  • KIM, JUNGHWAN;LEE, DOYEON;NAM, HYUNGSEOK;JO, SUNG-HO;HWANG, BYUNG WOOK;BAEK, JEOM-IN;RYU, HO-JUNG
    • Transactions of the Korean hydrogen and new energy society
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    • v.29 no.5
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    • pp.473-482
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    • 2018
  • To check applicability of recently developed new oxygen carrier for 0.5 MWth chemical looping combustion system, reactivity tests were carried out at high temperature and high pressure conditions. Pressure, temperature, gas velocity, $CH_4$ flow rate, and solid height were considered as operating variables. The new oxygen carrier (N016-R4) showed not only high fuel conversion but also high $CO_2$ selectivity within all the operating conditions in this study. The reactivity of N016-R4 particle was compared with previous oxygen carriers. The N016-R4 particle represented outstanding reactivity among 10 oxygen carriers in terms of fuel conversion and $CO_2$ selectivity.

Hydrodynamics and Solid Circulation Characteristics of Oxygen Carrier for 0.5 MWth Chemical Looping Combustion System (0.5 MWth 케미컬루핑 연소시스템 적용을 위한 산소전달입자의 수력학 특성 및 고체순환 특성)

  • RYU, HO-JUNG;KIM, JUNGHWAN;HWANG, BYUNG WOOK;NAM, HYUNGSEOK;LEE, DOYEON;JO, SUNG-HO;BAEK, JEOM-IN
    • Transactions of the Korean hydrogen and new energy society
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    • v.29 no.6
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    • pp.635-641
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    • 2018
  • To select the operating condition of 0.5 MWth chemical looping combustion system, minimum fluidization velocity, transition velocity to fast fluidization and solid circulation rate were measured using mass produced new oxygen carrier (N016-R4) which produced by spray drying method for 0.5 MWth chemical looping combustion system. A minimum fluidization velocity decreased as the pressure increased. The measured transition velocity to fast fluidization was 2.0 m/s at ambient temperature and pressure. The measured solid circulation rate increased as the solid control valve opening increased. We could control the solid circulation rate from 26 to $93kg/m^2s$. Based on the measured minimum fluidization velocity and transition velocity to fast fluidization, we choose appropriate operating conditions and demonstrated continuous solid circulation at high pressure condition (5 bar-abs) up to 24 hours.

Effect of Loop Seal Geometry on Solid Circulation in a Gas-Solid Fluidized Bed (기체-고체 유동층에서 루프실의 형상이 고체순환에 미치는 영향)

  • RYU, HO-JUNG;JO, SUNG-HO;LEE, SEUNG-YONG;LEE, DOYEON;NAM, HYUNGSEOK;HWANG, BYUNG WOOK;KIM, HANA;WON, YOO SEOB;KIM, JUNGHWAN;BAEK, JEOM-IN
    • Transactions of the Korean hydrogen and new energy society
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    • v.30 no.4
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    • pp.312-319
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    • 2019
  • Effect of loop seal geometry on solid circulation characteristics was investigated with two different types of upper loop seals and lower loop seals in a gas-solid fluidized bed system. Upper loop seal which has a wide gap between solid intake and outlet parts requires more fluidization gas to maintain smooth solid circulation. Moreover, the lower loop seal which has a wide gap requires more fluidization gas to achieve the same solid circulation rate. These results can be explained by results of minimum fluidization velocity in the lower loop seals. Consequently, if a loop seal has a wide gap between solid intake and outlet parts, more fluidization gases should be fed to ensure enough solid circulation rate and smooth solid circulation.

The Effect of Locally Administered Fibrinolytic Drugs Following Aneurysmal Subarachnoid Hemorrhage : A Meta-Analysis with Eight Randomized Controlled Studies

  • Jang, Kyoung Min;Choi, Hyun Ho;Nam, Taek Kyun;Park, Yong Sook;Kwon, Jeong Taik;Byun, Jun Soo;Hwang, Doyeon
    • Journal of Korean Neurosurgical Society
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    • v.64 no.2
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    • pp.207-216
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    • 2021
  • Objective : Rapid dissolution of blood clots reduces vasospasm and hydrocephalus after subarachnoid hemorrhage (SAH), and locally administered fibrinolytic drugs (LAFDs) could facilitate the dissolution. However, the efficacy of LAFDs remains controversial. The aim of this meta-analysis was to determine the efficacy of LAFDs for vasospasm and hydrocephalus and in clinical outcomes. Methods : From PubMed, EMBASE, and Cochrane database, data were extracted by two authors. Meta-analysis was performed using a random effect model. Inclusion criteria were patients who had LAFDs with urokinase-type or recombinant tissue-plasminogen activator after SAH in comparison with medically untreated patients with fibrinolytic drugs. We only included randomized controlled trials (RCTs) in this analysis. The outcomes of interest were vasospasm, hydrocephalus, mortality, and 90-day unfavorable functional outcome. Results : Data from eight RCTs with 550 patients were included. Pooled-analysis revealed that the LAFDs were significantly associated with lower rates of vasospasm (LAFDs group vs. control group, 26.5% vs. 39.2%; odds ratio [OR], 0.48; 95% confidence interval [CI], 0.32-0.73); hydrocephalus (LAFDs group vs. control group, 26.0% vs. 31.6%; OR, 0.54; 95% CI, 0.32-0.91); and mortality (LAFDs group vs. control group, 10.5% vs. 15.7%; OR, 0.58; 95% CI, 0.34-0.99). The proportion of 90-day unfavorable outcomes was lower in the LAFDs group (LAFDs group vs. control group, 32.7% vs. 43.5%; OR, 0.55; 95% CI, 0.37-0.80). Conclusion : This meta-analysis with eight RCTs indicated that LAFDs were significantly associated with lower rates of vasospasm and hydrocephalus after SAH. Thus, LAFDs could consequently reduce mortality and improve clinical outcome after SAH.

Estimation of PM10 and PM2.5 inhalation dose by travel time and respiratory volume in common transport microenvironments in Seoul, Korea (서울지역 교통수단별 이동시간과 호흡량을 고려한 미세먼지 흡입량 추정에 관한 연구)

  • Lee, Yong-Il;Jung, Wonseck;Hwang, Doyeon;Kim, Taesung;Park, Duckshin
    • Particle and aerosol research
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    • v.14 no.4
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    • pp.97-105
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    • 2018
  • Recently, people's interest in particulate matter (PM) has been increasing, due to its hazardous health effects. The purpose of this study was to investigate the concentrations and as well as the inhaled weight of PM, correlated with person's heart rate in subway, bus, vehicle and bicycle in the major public transportation (Sadang - Jamsil and Nowon - Dongdaemun) in Seoul. The concentration of $PM_{10}$ and $PM_{2.5}$ were measured from each of transportation means and calculated the average concentrations which were 87.2 and $57.8{\mu}g/m^3$ for subway, 62.8 and $42.5{\mu}g/m^3$ for vehicle, 61.5 and $36.8{\mu}g/m^3$ for bus and 53.0 and $29.4{\mu}g/m^3$ for bicycle in $PM_{10}$ and $PM_{2.5}$ respectively. Inhalation dose for $PM_{10}$ and $PM_{2.5}$ were estimated at 248.1 and $139.4{\mu}g$ for bicycle, 56.7 and $39.3{\mu}g$ for vehicle, 49.4 and $29.9{\mu}g$ for bus and 44.3 and $29.1{\mu}g$ for subway, respectively. Even though subway had the highest concentration, the highest inhalation dose was the bicycle. It was due to the long travel time-exposure and breathing rate which leads to maximum of $PM_{10}$ 5.6 and $PM_{2.5}$ with 4.8 times inhalation dose comparing with other modes of transportation. With regards to future studies, the amount of inhalation in each transportation means should be considered in risk assessments of PM.