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Effects of flux on the luminescence of MgGa<sub>2</sub>O<sub>4</sub>:Mn<sup>2+</sup> phosphors
Ahn, Wonsik,Im, Minhyuk,Kim, Young Jin Pergamon Press 2017 Materials research bulletin Vol.96 No.3
<P><B>Abstract</B></P> <P>The effects of H<SUB>3</SUB>BO<SUB>3</SUB> and MgF<SUB>2</SUB> fluxes on the crystal structure and photoluminescence (PL) of MgGa<SUB>2</SUB>O<SUB>4</SUB>:Mn<SUP>2+</SUP> phosphors were investigated. The PL excitation spectra of the powders consisted of intensive broad bands (∼290nm), and sharp peaks at longer wavelengths. The former could be attributed to charge transfer between the Mn<SUP>2+</SUP> and O<SUP>2−</SUP> ions, referred to as charge transfer band (CTB), while the latter was attributed to the <I>d–d</I> transitions of Mn<SUP>2+</SUP> ions. Under CTB excitation, the PL spectra exhibited green emission peaks at 505nm, assignable to the <SUP>4</SUP>T<SUB>1</SUB>(<SUP>4</SUP>G) → <SUP>6</SUP>A<SUB>1</SUB>(<SUP>6</SUP>S) transition of Mn<SUP>2+</SUP> ions in tetrahedral sites. Compared to MgF<SUB>2</SUB>, H<SUB>3</SUB>BO<SUB>3</SUB> was more favorable for phase formation, higher crystallinity, and particle size enlargement, thus resulting in a significant enhancement in the emission intensity. The Mn<SUP>2+</SUP> concentration affected the CTB and the crystal structure; the strongest emission intensity was observed for a high Mn<SUP>2+</SUP> concentration of 0.5mol%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of H<SUB>2</SUB>BO<SUB>3</SUB> and MgF<SUB>2</SUB> fluxes on the luminescence of MgGa<SUB>2</SUB>O<SUB>4</SUB>:Mn<SUP>2+</SUP> were studied. </LI> <LI> Flux effects were explained considering the crystallinity and particle size. </LI> <LI> H<SUB>2</SUB>BO<SUB>3</SUB> significantly enhanced the emission intensity, whereas MgF<SUB>2</SUB> did not. </LI> <LI> Mn<SUP>2+</SUP> concentration affected the charge transfer band and the emission intensity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Ahn, Wonsik,Kim, Young Jin The Korean Ceramic Society 2016 한국세라믹학회지 Vol.53 No.4
$Si^{4+}-N^{3-}$ was incorporated into $Ce^{3+}-doped$ lutetium aluminum garnet ($Lu_{2.965}Ce_{0.035}Al_5O_{12}$, $LuAG:Ce^{3+}$) lattices, resulting in the formation of $Lu_{2.965}Ce_{0.035}Al_{5-x}Si_xO_{12-x}N_x$ [(Lu,Ce)AG:xSN]. For x = 0-0.25, the synthesized powders consisted of the LuAG single phase, and the lattice constant decreased owing to the smaller $Si^{4+}$ ions. However, for x > 0.25, a small amount of unknown impurity phases was observed, and the lattice constant increased. Under 450 nm excitation, the PL spectrum of $LuAG:Ce^{3+}$ exhibited the green band, peaking at 505 nm. The incorporation of $Si^{4+}-N^{3-}$ into the $Al^{3+}-O^{2-}$ sites of $LuAG:Ce^{3+}$ led to a red-shift of the emission peak wavelength from 505 to 570 nm with increasing x. Corresponding CIE chromaticity coordinates varied from the green to yellow regions. These behaviors were discussed based on the modification of the $5d^1$ split levels and crystal field surroundings of $Ce^{3+}$, which arose from the Ce-(O,N)8 bonds.
초과로 부터 Amotsaokonal A-C, Benzaldehyde, Cycloterpenal의 성분분리
WonSik Jeong,Seong Su Hong,Changon Seo,Jin Gwan Kwon,Eun Kyung Ahn,Ju Hyeong Park,Hana Cho,Joa Sub Oh 한국약용작물학회 2016 한국약용작물학술대회 발표집 Vol.2016 No.10
Background : Amomum tsao-ko (Zingiberaceae) is widely distributed among several countries in Asia. It’s dried fruit is widely used in Korea for medical plant, China and Japan for the treatment of dyspepsia, eliminates, vomiting, abdominal pain, phlegm, warms the spleen, and malaria. In this study, we describe the structural determination of the new compounds and the inhibitory activities of isolated compounds against LPS-induced NO production in RAW264.7 cells. Methods and Results : The fruits of A. tsao-ko were extracted with 80% EtOH two times at room temperature. The EtOH extract was suspended in distilled water and partitioned with solvent to give CH2Cl2, EtOAc and n-BuOH. The CH2Cl2 was suspended in n-hexane and partitioned with solvent to give 50%, 70% and 90% MeOH. The purification of each fraction by column chromatography separation and HPLC analysis. Consequently, one new benzaldehyde (1) and two new cycloterpenals (2 and 3) along with five known compounds (4 –8) have been isolated from the fruits of A. tsao-ko. The structure and relative stereochemistry were determined from HRMS, 1D and extensive 2D NMR techniques as well as by comparison of their data with the published values. Conclusion : These compounds were identified as Amotsaokonal A (1), Amotsaokonal B (2), Amotsaokonal C (3), methyl linolenate (4), trans-nerolidol (5), (2E)-dodecenyl acetate (6), (2E)-dodecenyl acetate (7), and pyrrole-2-carboxylic acid (8). All isolates were tested for their inhibitory activities on LPS-induced nitric oxide production in RAW264.7 cells.
Analysis of a Clutch Damper Using a Discrete Model
Kukhyun Ahn,Jang Moo Lee,Wonsik Lim,Yeong-il Park 대한기계학회 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.11
It is important to have a precise model for the clutch damper in order to simulate the entire powertrain of a vehicle and predict the responses of the system. In this research, we developed a new model in which the spring used in the clutch damper is divided into a finite number of elements. The model takes many unique properties of arc-shaped springs into consideration and is anticipated to be more precise than conventional simple models. With the model, two meaningful results were presented which can be utilized afterwards. One is a simulation concerning the peak torque transmitted via the clutch damper. The other is a simulation that shows the hysteretic characteristics of the clutch damper.<br/>
안현선(Ahn, Hyun Seon),김원식(Kim, Wonsik),이지수(Lee, Jeesoo) 학습자중심교과교육학회 2020 학습자중심교과교육연구 Vol.20 No.11
많은 대학이 대학생들의 학습성과의 구성요소 및 학습성과에 영향을 미치는 요인 규명 등에 관심을 기울이며 학습성과 향상을 위한 지원 방안에 대한 의견 수렴과 교육제도개편에 힘써 왔다. 이러한 흐름에 따라, 이 연구에서는 수도권 소재 대학의 재학생 596명을 대상으로 학습참여와 학습성과 간의 관계를 규명하고, 이러한 관계가 학생이 지각하는 전공만족도 수준에 따라 어떻게 달라지는지를 살펴보고자 하였다. 상관분석 결과, 학습참여와 학업성취도, 그리고 전공만족도 간에 정적으로 유의한 관계가 나타났다. 이러한 관계는 학습참여의 하위측면에 따라 상이하였고, 특히 학습전략과 능동협동학습이 학업성취도와 상대적으로 강한 상관을 보였다. 이어, 다중회귀분석을 통해 전공만족도 상·하 집단별로 학업성취도에 대한 학습참여의 하위측면의 상대적 예측력을 검증하였다. 그 결과, 대학생이 지각하는 전공만족도 수준에 따라 학업성취도에 대한 학습참여의 각 하위측면은 서로 다른 예측력을 나타냈다. 학습전략은 전공만족도 수준에 상관없이 모든 학생에게 학업성취도를 높이는 주요요인으로 나타난 반면, 교수-학생 상호작용과 지원적 환경은 학생들의 전공만족도 수준에 따라 그 예측력에 차이가 있었다. 이러한 결과를 바탕으로, 다양한 교수법과 학생수준을 고려한 맞춤형 수업, 그리고 조직화된 수업활동 제시 등 대학생의 학습성과와 학습참여 증진을 위한 방법 재고 필요성에 대한 논의를 제시하였다. The purpose of this study is to investigate the relationships among student engagement, academic achievement, and college major satisfaction among undergraduates. Based on the database collected from 596 students enrolled in a university in urban areas, the present study examined a) the relations between specific aspects of student engagement and academic achievement, and b) whether these relations would differ depending on the degree of students’ perceptions of their satisfaction with college majors. Correlational analyses revealed that there were significantly positive associations between student engagement, academic achievement, and college major satisfaction. Among the specific aspects of student engagement, learning strategies and active-collaborative learning showed relatively strong relations to academic achievement. Multiple regression analyses demonstrated that specific aspects of student engagement showed different utility in predicting academic achievement depending on the levels (i.e., high vs. low) of college satisfaction major perceived by students. While learning strategies significantly predicted academic achievement for the whole student sample, teacher-student interaction and supportive environment showed different predictive powers depending on the levels of college major satisfaction. The need for considering various student factors to improve teaching effectiveness and student engagement was discussed.