Development of bulk heterojunction morphology by the difference of intermolecular interaction behaviors

Cha, H.,Baek, J.Y.,An, T.K.,Kim, S.O.,Kwon, S.K.,Kim, Y.H.,Park, C.E. Elsevier Science 2014 ORGANIC ELECTRONICS Vol.15 No.12

The morphology of a bulk heterojunction can be controlled by adding a processing additive in order to improve its power conversion efficiency (PCE) in photovoltaic devices. The phase-separated morphologies of blends of PONTBT or P3HT with fullerene derivatives are systematically examined in the presence of processing additives that possess various alkane alkyl chain lengths or end-group electronegativities. We determined the morphologies of the bulk heterojunction layers by using atomic force microscopy (AFM) and grazing incidence wide angle X-ray scattering (GIWAXS). The photocurrent-voltage characteristics of the bulk heterojunction solar cells were found to be strongly dependent on the intermolecular interactions between the conjugated polymers, the fullerene derivatives, and the processing additives in the photoactive layer. The optimal PONTBT:fullerene derivative blend morphology was obtained with a processing additive, 1,3-diiodopropane (1,3-DIP), that possesses a short alkyl chain and an end group with weak electronegativity, and was found to exhibit a high fill factor (FF) and a high current density (J<SUB>SC</SUB>). In contrast, in blends of P3HT with the fullerene derivative, PCEs with higher FF and J<SUB>SC</SUB> values were achieved by incorporating the processing additive, 1,8-dibromooctane (1,8-DBrO), which has a long alkyl chain and a strong electronegative end group. Thus the selection of the processing additive with the aim of enhancing photovoltaic performance needs to take into account the intermolecular interaction of the conjugated polymer.

An inkjet printing method: Drop and Synthesis (DAS). Application to the synthesis of ZnS:Mn nano-phosphor with a pattern

Cha, H.,Ahn, S.I.,Choi, K.C. Elsevier 2010 CURRENT APPLIED PHYSICS Vol.10 No.4

An inkjet printing method was introduced to synthesize materials with a pattern, which have been very difficult to print by normal inkjet printers. Based on the proposed method, ZnS:Mn nano-phosphor was synthesized with a pattern by a chemical reaction with two different reactive inks. The nano-phosphor had mostly hexagonal-type structures with an average size of 20 nm. Photoluminescence and cathodoluminescence spectra showed an intensity resonance between peaks at 441 nm and 597 nm depending on a capping agent, which means that the Mn<SUP>2+</SUP> ion was incorporated into the vacancy sites of ZnS lattice after the formation of vacancies in ZnS.

Nitrogen-doped open pore channeled graphene facilitating electrochemical performance of TiO2 nanoparticles as an anode material for sodium ion batteries

Cha, H.,Jeong, H.,Kang, J. Royal Society of Chemistry 2014 Journal of Materials Chemistry A Vol.2 No.15

We report that titanium dioxide nanoparticles anchored on nitrogen-doped open pore channeled graphene exhibit high performance as anode materials for sodium ion batteries with a high reversible capacity of 405 mA h g(-1) at a current density of 50 mA g(-1), excellent cycle stability with a capacity of 250 mA h g(-1) over 100 charge-discharge cycles at a current density of 100 mA g(-1), and superior rate capability. Also, it shows that high electrochemical performance is attributed to the facilitated ion diffusion by their open pore channels, in addition to the promoted electron transfer in electrochemical reactions by nitrogen-doping.

Life History and Taxonomy of Aglaothamnion oosumiense Itono(Ceramiaceae, Rhodophyta)

Chah,Ok Kyong,Kim, Gwang Hoon 公州大學校 基礎科學硏究所 1998 自然科學硏究 Vol.7 No.-

Life history and post-fertilization process of Aglaothamnion oosumiense from Korea were studied in culture. This species showed a Polysiphonia-type life history with dioecious gametophyte as well as asexual reproduction via parasporangium on male plants. The occurrence of parasporangium plants was not affected by environmental factors nor inherited strictly to the next generation. Most (>95%) of the paraspores developed into male plants, while less than 5% of paraspores became parasporangiate male plants again. Bisexual plants were also observed. Each carpogonial branch had two auxiliary cells, which divided distally to produce the primary gonimoblast initials, respectively, before the foot cells were cut off proximately from it by intercalary divisions. Two carposporophytes resulted from a successful fertilization. Morphologically, Aglaothamnion posumiense resembled Aglaothamnion callophyllidicola(Yamada) Boo, Lee, Rueness et Yoshida, and the taxonomic characters separating them were found to be unstable. The taxonomic relationship between the two species, therefore, should be critically reassessed with a thorough reexamination including their type specimens.

A Study on the Relative Perceived Importance of Leadership Attributes in the U.S. and Korea

Chah,Dong Ok 成均館大學校 韓國産業硏究所 1995 韓國經濟 Vol.21 No.2

최근 사회인지이론이 조직행동론 분야에서 광범위하게 사용되고 또 조직에 대한 국가문화의 영향에 관하여 국제적인 토론이 빈번해지고 있다. 본 논문에서는 이러한 두가지 흐름을 리더쉽 연구에 받아들여 한국과 미국의 중간관리자들은 효과적인 최고경영자가 갖추어야 할 여러 리더쉽 특질들에 대해 어떻게 생각하고 있는가?를 조사하였다. 본 연구의 결과를 종합해 볼 때 리더의 유효성을 설명하는 리더쉽 특질은 두 문화간에 큰 차이가 없었다. 이는 본 연구에서 제시된 '수렴(convergence)' 가정에 근거한「리더쉽 모델」의 일반화를 뒷받침하는 한 증거가 될 수 있다 하겠다.

CONSUMPTION BEHAVIOR AND LIQUIDITY CONSTRAINTS

CHAH, EUN YOUNG 한국경제학회 1995 The Korean Economic Review Vol.11 No.1

ADJUSTMENT COSTS, DURABLES AND INTERTEMPORAL SUBSTITUTION

CHAH, EUN YOUNG 梨花女子大學校 法政大學 1995 社會科學論集 Vol.15 No.-

Efficacy of ketamine in the treatment of migraines and other unspecified primary headache disorders compared to placebo and other interventions: a systematic review

Chah, Neysan,Jones, Mike,Milord, Steve,Al-Eryani, Kamal,Enciso, Reyes The Korean Dental Society of Anesthsiology 2021 Journal of Dental Anesthesia and Pain Medicine Vol.21 No.5

Background: Migraine headaches are the second leading cause of disability worldwide and are responsible for significant morbidity, reduction in the quality of life, and loss of productivity on a global scale. The purpose of this systematic review and meta-analysis was to evaluate the efficacy of ketamine on migraines and other primary headache disorders compared to placebo and other active interventions, such as midazolam, metoclopramide/diphenhydramine, and prochlorperazine/diphenhydramine. Methods: An electronic search of databases published up to February 2021, including Medline via PubMed, EMBASE, Web of Science, and Cochrane Library, a hand search of the bibliographies of the included studies, as well as literature and systematic reviews found through the search was conducted to identify randomized controlled trials (RCTs) investigating ketamine in the treatment of migraine/headache disorders compared to the placebo. The authors assessed the risk of bias according to the Cochrane Handbook guidelines. Results: The initial search strategy yielded 398 unduplicated references, which were independently assessed by three review authors. After evaluation, this number was reduced to five RCTs (two unclear risk of bias and three high risk of bias). The total number of patients in all the studies was 193. Due to the high risk of bias, small sample size, heterogeneity of the outcomes reported, and heterogeneity of the comparison groups, the quality of the evidence was very low. One RCT reported that intranasal ketamine was superior to intranasal midazolam in improving the aura attack severity, but not duration, while another reported that intranasal ketamine was not superior to metoclopramide and diphenhydramine in reducing the headache severity. In one trial, subcutaneous ketamine was superior to saline in migraine severity reduction; however, intravenous (I.V.) ketamine was inferior to I.V. prochlorperazine and diphenhydramine in another study. Conclusion: Further double-blind controlled studies are needed to assess the efficacy of ketamine in treating acute and chronic refractory migraines and other primary headaches using intranasal and subcutaneous routes. These studies should include a long-term follow-up and different ketamine dosages in diagnosed patients following international standards for diagnosing headache/migraine.

변혁적 리더십이 변화대처행동 및 혁신행동에 미치는 영향 : 인지된 변화타당성의 매개효과와 리더-구성원 가치일치의 조절효과

차동옥(Chah Dongok),문명(Moon Myung),최순주(Choi Sunju),최중락(Choe Joonglark) 한국인사관리학회 2020 조직과 인사관리연구 Vol.44 No.4

변혁적 리더십은 조직변화 과정에서 긍정적인 영향을 미친다. 그런데 어떤 과정을 거쳐 변혁적 리더 십이 구성원들의 행동에 영향을 미치는 가에 대한 연구는 많지 않다. 그리고 변혁적 리더십과 구성원들 의 변화대처행동 간의 관계에 관한 실증연구도 부족하다. 본 연구에서는 변혁적 리더십이 구성원들의 인지된 변화타당성에 미치는 영향을 규명하고, 또한 구성원들이 인지하는 변화타당성이 구성원들의 변 화대처행동과 혁신행동에 어떤 영향을 미치는가를 살펴보았다. 연구가설을 검증하기 위해 기업에서 근무하는 구성원들을 대상으로 서울 및 수도권 지역의 16개 기업에서 총 303부의 설문지를 수거하여 실증분석에 활용하였다. 연구결과를 살펴보면 변혁적 리더십 이 구성원들의 변화타당성 인식에 정(+)의 영향을 미치고 있는 것을 확인하였다. 그리고 변혁적 리더십 은 인지된 변화타당성을 통해 구성원들의 변화대처행동과 혁신행동에 유의미한 간접효과를 가지고 있 는 것으로 나타났다. 본 연구에서는 변혁적 리더십이 구성원들의 인지된 변화타당성을 높이고 이를 통해 구성원들의 변화대처행동과 혁신행동을 증가시키며, 특히 리더-구성원 가치일치가 높을 경우에 이러한 관계가 더욱 강하게 작용한다는 것을 확인하였다. 본 연구는 성공적인 조직변화를 위해서는 리더가 구성원들에게 변화타당성을 설득하고 리더-구성원 가치를 일치의 정도를 높이기 위해 노력해 야 한다는 실무적 시사점을 제시한다. In our study, we examined the effects of transformational leadership on coping behavior and innovative behavior via perceived appropriateness of change and leader-member value congruence. We collected data from 303 employees working in Seoul Metropolitan area. The results of our study are as follows. First, transformational leadership has the direct effect on employees perceived appropriateness of change. Second, We verified that transformational leadership has the indirect effect on employees coping behavior and innovative behavior through employees perceived appropriateness of change. Finally, we identified the moderated mediation effects of leader-member value congruence. The theoretical and practical implications of our study are presented.

포용적 리더십이 부하의 역할내 성과와 발언행동에 미치는 영향에 관한 연구

차동옥(Chah, Dong-Ok),김상수(Kim, Sang-Soo),이정훈(Lee, Jung-Hun),방호진(Bang, Ho-Jin),문지영(Moon, Jee-Young) 대한경영학회 2013 大韓經營學會誌 Vol.26 No.8