Organic electrochemical transistors based on a dielectrophoretically aligned nanowire array

Choi, WooSeok,An, Taechang,Lim, Geunbae Springer 2011 Nanoscale research letters Vol.6 No.1

<P>In this study, we synthesized an organic electrochemical transistor (OECT) using dielectrophoresis of a carbon nanotube-Nafion (CNT-Nafion) suspension. Dielectrophoretically aligned nanowires formed a one-dimensional submicron bundle between triangular electrodes. The CNT-Nafion composite nanowire bundles showed p-type semiconductor characteristics. The drain-source current decreased with increasing gate voltage. The nanowire bundles showed potential as pH sensor because the drain-source current ratio varied linearly according to the gate voltage in pH buffers.</P>

Electrospinning onto Insulating Substrates by Controlling Surface Wettability and Humidity

Choi, WooSeok,Kim, Geon Hwee,Shin, Jung Hwal,Lim, Geunbae,An, Taechang Springer US 2017 NANOSCALE RESEARCH LETTERS Vol.12 No.1

<P>We report a simple method for electrospinning polymers onto flexible, insulating substrates by controlling the wettability of the substrate surface. Water molecules were adsorbed onto the surface of a hydrophilic polymer substrate by increasing the local humidity around the substrate. The adsorbed water was used as the ground electrode for electrospinning. The electrospun fibers were deposited only onto hydrophilic areas of the substrate, allowing for patterning through wettability control. Direct writing of polymer fiber was also possible through near-field electrospinning onto a hydrophilic surface.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (10.1186/s11671-017-2380-6) contains supplementary material, which is available to authorized users.</P>

ENHANCEMENT OF THE PRODUCTION OF EICOSAPENTAENOIC ACID (EPA) AND FATTY ACID FROM MARINE GREEN MICROALGAE CULTURED IN F/2 MEDIA WITH THE DIFFERENT CONCENTRATIONS

Wooseok Choi,Taeho Kim,Seon-Mi Jeon,Areumi Park,Hyeon Yong Lee,Do-Hyung Kang 한국수산과학회 양식분과 2015 한국수산과학회 양식분과 학술대회 Vol.2015 No.5

OPTIMIZATION OF CULTURE CONDITION FOR BIOMASS PRODUCTION OF SALINE Tetraselmis sp. WITH ENHANCING FATTY ACIDS CONCENTRATION

Wooseok Choi,Taeho Kim,Hyeon Yong Lee,Do-Hyung Kang 한국수산과학회 양식분과 2015 한국수산과학회 양식분과 학술대회 Vol.2015 No.5

Excess Compensation: Agency Cost or Performance Motivator? Perspectives from Governance Structures in Korea

Wooseok Choi,Eunsuh Lee 한국회계정보학회 2012 한국회계정보학회 학술대회발표집 Vol.2012 No.1

In this study, we investigate whether govemance structures are associated with excess cash compensation, which is defined as observed cash compensation determinants. Six measures of governance structures are examined in this study: (1) the owner-managers; (2) block-holders; (3) foreign shareholders; (4) institutional investors; (5) financial institutions; and (6) chaebols. Based on 6,823 observations in Korea from 2000 to 2009, the results indicate that governance structures are significantly related to excess cash compensation. Specifically, ownership by block-holders and the magnitude of debts from financial institutions are negatively related to excess cash compensation, whereas ownership by owner-managers and foreign shareholders, and chaebols are positively related to excess cash compensation. An additional test suggests that excess cash compensation is positively associated with current accounting performance of firms. The findings of this study imply that excess cash compensation can be used as a motivator for directors to improve financial performance of firms consistent with Fama (1980), while it can also represent an agency cost consistent with Core et al. (1999) under certain circumstances.

Highly sensitive and accurate estimation of bloodstain age using smartphone

Choi, Wooseok,Shin, Joonchul,Hyun, Kyung-A,Song, Jaewoo,Jung, Hyo-Il Elsevier 2019 Biosensors & Bioelectronics Vol.130 No.-

<P><B>Abstract</B></P> <P>The estimation of bloodstain age is an important factor in forensic analysis. Previously, we have reported a smartphone-based colorimetric system for age estimation of bloodstain, in which Whole blood and EDTA whole blood were dropped on 4 different materials (700 μL) and captured using a smartphone for 72 h. In order to enhance sensitivity and accuracy of the previous system, the current work is dedicated towards the application of pattern recognition and classification of bloodstain images based on a smartphone. Three detection methods (blood pool, crack ratio, and colorimetric analysis) in terms of 6 steps of drying process of the bloodstain (coagulation, gelation, edge desiccation, center desiccation, crack propagation, and final desiccation) were applied to estimate age of the bloodstain accurately. Three parameters from the bloodstain images were then classified as comparing to those of stored reference images with similar trends in database. The bloodstain age was successfully determined by 9 h, 18 h, and 48 h with respect to the three detection methods mentioned above, respectively. The differences in bloodstain images were clearly distinguished every hour by using smartphone-based pattern recognition analysis. Therefore, our system is expected to shed a light on the field of forensic science by estimating bloodstain age in real time.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A smartphone-based pattern recognition was introduced to estimate bloodstain age. </LI> <LI> Blood pool, crack ratio, and brightness values of the images were successfully measured. </LI> <LI> The proposed methods was designed for enhancing accuracy in the early time zone. </LI> <LI> A low detection limit of 1 h toward age estimation of bloodstains could be achieved. </LI> </UL> </P>

Excess Compensation and Corporate Governance

Wooseok Choi(최우석),Eunsuh Lee(이은서),Maria A. Leach-Lopez 한국국제회계학회 2019 국제회계연구 Vol.0 No.86

본 연구는 유가증권 상장법인과 코스닥 기업을 대상으로 기업지배구조가 초도임원보수(超度任員報酬; Excess Compensation)에 미치는 영향을 분석하였다. 기업지배구조는 소유경영자, 최대주주, 외국인 투자자, 금융기관, 그리고 재벌을 이용해 측정하였으며, 예상보수를 초과해 지급한 임원보수를 의미하는 초도임원보수는 임원 보수모형의 잔차를 사용해 측정하였다. 초도임원보수가 기업에 미치는 영향과 관련해서는 두 가지 상반된 견해가 있다. 먼저, 초도임원보수가 기업의 성과를 향상시킬 수 있다는 긍정적 시각이다(Fama 1980). 만약 초도임원보수가 기업의 성과를 향상시키는 경향이 있다면, 기업지배구조와 초도임원보수는 유의한 양(+)의 관계를 예상할 수 있다. 반대로, 초도임원보수가 대리인비용의 결과라는 부정적 견해도 존재한다(Core et al. 1999). 만약 초도임원보수가 대리인 비용을 나타내는 것이라면 기업 지배구조와 초도임원보수는 유의한 음(-)의 관계를 가질 것으로 예상할 수 있다. 본 연구의 분석결과는 다음과 같다. 금융기관변수와 초도임원보수사이에는 유의한 음(-)의 관계가 있는 것으로 나타났다. 이러한 분석결과는 금융기관은 기업이 지급하는 초도임원보수를 대리인 비용으로 생각하는 경향이 있음을 보여준다. 반면, 소유경영자, 외국인 투자자, 그리고 재벌은 초도임원보수와 유의한 양(+)의 관계가 있는 것으로 나타났다. 이와 같은 실증결과는 소유경영자, 외국인 투자자, 그리고 재벌은 초도임원보수가 기업의 성과를 향상시키는데 도움을 주는 요인 중 하나라고 생각하는 경향이 있음을 나타낸 것이다. 본 연구는 초도임원보수를 도출하여 실증분석을 시도하였다는 점에서 의의가 있다. 또한 초도임원보수가 기업 지배구조에 의해서 영향을 받는다는 결과를 보임으로써, 임원보상의 결정변수에 관한 기존 연구를 확장하였다는 점에서 그 공헌점이 있다. Excess compensation of CEOs does not by itself impose a significant problem. However, a serious business ethical violation would occur if excess compensation is related to a large extraction of rent. In this study, we investigate how governance structures are associated with excess cash compensation, which is defined as observed cash compensation less expected cash compensation derived from the standard economic determinants. Five measures of governance structures are examined in this study as follows: (1) owner-managers; (2) block-holders; (3) foreign shareholders; (4) financial institutions; and (5) chaebols, business conglomerates in Korea controlled by family. Based on 6,823 observations in Korea obtained over a 10-year period, the results indicate that governance structures differentially affect excess cash compensation depending on the views of the role of excess cash compensation. Specifically, financial institutions are negatively related to excess cash compensation, implying that they consider excess cash compensation as an agency cost. By contrast, owner-managers, foreign shareholders, and chaebols are positively related to excess cash compensation, implying that they consider excess cash compensation as a performance motivator.

Enhancement of skin anti-inflammatory activities of <i>Scutellaria baicalensis</i> extract using a nanoencapsulation process

Choi, Wooseok,No, Ra Hwan,Kwon, Hee-Souk,Lee, Hyeon Yong Informa Healthcare 2014 Journal of cosmetic and laser therapy Vol.16 No.6

<P>In this study, we sought to increase the anti-inflammatory activity of <I>Scutellaria baicalensis</I> extracts using a nanoencapsulation process. The ethanol extract of <I>Scutellaria baicalensis</I> was encapsulated with lecithin and two other extracts as follows: aqueous extraction at 100°C for 24 h (AE), 70% ethanol extracts at 80°C for 24 h (EE), which were also compared as controls. The ethanol extract of <I>S. baicalensis</I> with lecithin was estimated to be 94.3 nm while the encapsulation efficiency of the nanoparticles was measured as 61.4% higher than other encapsulation processes. Antioxidant activity was also observed as 60% inhibition of DPPH radical scavenging activity, and nitric oxide production by RAW264.7 cells was also reduced by 5.1 μM after the addition of 0.5 mg/mL nanoparticles. Only 743.7 pg/mL of PGE<SUB>2</SUB> was produced by RAW 264.7 macrophages after the addition of 0.5 mg/mL of nanoparticles, as compared to 1105.6 pg/mL and 962.3 pg/mL of PGE<SUB>2</SUB> production after the addition of 1.0 mg/mL of aqueous and ethanol extracts, respectively. This is the first report, to our knowledge, of real-time penetration of nanoparticles into human fibroblasts using a confocal scanning microscope.</P>

드론을 이용한 시각장애인 보행 유도에 관한 연구

최우석(Wooseok Choi),조재식(Jaesik Cho),김상우(Sangwoo Kim),정연모(Yunmo Chung) 대한전자공학회 2015 대한전자공학회 학술대회 Vol.2015 No.6

다짐에너지에 따른 바텀애시의 파쇄특성 및 입도특성의 변화

최우석 ( Wooseok Choi ),박재성 ( Jaesung Park ),노수각 ( Sookack Noh ),봉태호 ( Taeho Bong ),손영환 ( Younghwan Son ) 한국농공학회 2012 한국농공학회 학술대회초록집 Vol.2012 No.-

바텀애시는 전체 석탄회 발생량의 약 20%로 대부분 재활용되지 못하고 회사장에 매립되고 있는 실정이다. 그러나 적치, 매립장의 규모증가와 처리 비용 증대와 같은 경제적 손실로 인하여 바텀애시의 재활용에 관한 연구와 재활용시 현장 기준에 대한 연구가 필요하다. 특히 다공성 재료인 바텀애시는 다짐 시 다짐에너지로 인한 입자 파쇄가 일어나 이에 따른 입도 및 다짐특성의 변화가 발생할 수 있다. 본 연구에서는 바텀애시의 다짐 방법에 따른 파쇄특성을 알아보기 위해 영흥 화력발전소의 바텀애시에 대하여 다짐시험, 입도분석을 실시하였다. 시험은 표준A다짐에서 구한 다짐곡선을 기준으로 건조 측, 최적함수비, 습윤 측에 해당하는 함수비의 시료에 대하여 다짐에너지에 따른 다짐시험 전후의 입도분석을 실시하였다. 시험 결과 다짐에너지가 증가하면서 세립분 함유량이 증가함이 나타났으며 입경별 함유량의 변화가 다짐 함수비의 영향을 받는 것으로 나타났다. 건설재료로써 바텀애시를 재활용할 경우 이러한 다짐방법에 따른 파쇄특성의 분석을 통하여 입도나 다짐함수비에 대한 현장기준을 제시할 수 있을 것으로 판단된다.