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Competition in Two-sided Platform Markets with Direct Network Effect
Jungsik Hyun 서울대학교 경제연구소 2016 Seoul journal of economics Vol.29 No.3
In light of recent trends in social networking services that encourage users of platforms to “share,” “recommend,” and “do activities” with others, this work analyzes platform competition in two-sided markets that exhibit direct (or within-) network effect in addition to conventional cross-network effect. Introduction of direct network effect to one group (buyer-side) in a two-sided market generates two counteracting effects: demand-augmenting effect and demand-sensitizing effect. The former allows platforms to raise buyer-side price, thereby increasing the sum of prices charged to buyers and sellers, whereas the latter causes platforms to lower them. I show that demand-augmenting effect dominates demand-sensitizing effect under the monopoly platform, whereas introducing competition between platforms under sufficient direct network effect relatively strengthens the demandsensitizing effect, which lowers the price charged to buyers.
Can Urinary Cotinine Predict Nicotine Dependence Level in Smokers?
Jung, Hyun-Suk,Kim, Yeol,Son, Jungsik,Jeon, Young-Jee,Seo, Hong-Gwan,Park, So-Hee,Huh, Bong Ryul Asian Pacific Journal of Cancer Prevention 2012 Asian Pacific journal of cancer prevention Vol.13 No.11
Background: Although nicotine dependence plays a role as a main barrier for smoking cessation, there is still a lack of solid evidence on the validity of biomarkers to determine nicotine dependence in clinical settings. This study aimed to investigate whether urinary cotinine levels could reflect the severity of nicotine dependence in active smokers. Materials and Methods: Data regarding general characteristics and smoking status was collected using a self-administered smoking questionnaire. The Fagerstr$\ddot{o}$m test for nicotine dependence (FTND) was used to determine nicotine dependence of the participants, and a total of 381 participants were classified into 3 groups of nicotine dependence: low (n=205, 53.8%), moderate (n=127, 33.3%), and high dependence groups (n=49, 12.9%). Stepwise multiple linear regression model and receiver operating characteristic (ROC) curves analyses were used to determine the validity of urinary cotinine for high nicotine dependence. Results: In correlation analysis, urinary cotinine levels increased with FTND score (r=0.567, P<0.001). ROC curves analysis showed that urinary cotinine levels predicted the high-dependence group with reasonable accuracy (optimal cut-off value=1,000 ng/mL; AUC=0.82; P<0.001; sensitivity=71.4%; specificity=74.4%). In stepwise multiple regression analysis, the total smoking period (${\beta}$=0.042, P=0.001) and urinary cotinine levels (${\beta}$=0.234, P<0.001) were positively associated with nicotine dependence, whereas an inverse association was observed between highest education levels (>16 years) and nicotine dependence (${\beta}$=-0.573, P=0.034). Conclusions: The results of this study support the validity of using urinary cotinine levels for assessment of nicotine dependence in active smokers.
Ahn, Sung Soo,Hwang, Sang Hyun,Jung, Seung Min,Lee, Sang-Won,Park, Yong-Beom,Yun, Mijin,Song, Jason Jungsik Williams & Wilkins Co 2017 Medicine Vol.96 No.34
<P><B>Abstract</B></P><P>The aim of the study was to evaluate splenic glucose metabolism in macrophage activation syndrome (MAS), characterized by overwhelming systemic inflammation. Splenic <SUP>18</SUP>F-fluorodeoxyglucose (FDG) uptake was compared in patients with MAS and sepsis using positron emission tomography/computed tomography (PET/CT).</P><P>Clinical and FDG-PET/CT findings from patients with MAS and those with culture-proven sepsis were evaluated. The standardized uptake value (SUV) for the spleen and liver were measured. The maximum of the spleen to liver SUV ratio (SLR<SUB>max</SUB>) was calculated as spleen SUV<SUB>max</SUB>/liver SUV<SUB>mean</SUB>. The radiological splenic volume was also measured, and splenic metabolic volume (MV) was defined as the total splenic volume with an SLR<SUB>mean</SUB> > 1.14. The association between clinical features, laboratory variables, and SLR<SUB>max</SUB> was analyzed.</P><P>The median SLR<SUB>max</SUB> and splenic MV were significantly higher in patients with MAS (n = 38) than they were in those with sepsis (n = 15) (SLR<SUB>max</SUB>: 1.51 vs 1.09, <I>P</I> = .001; MV: 346.0 vs 154.0, <I>P</I> = .015). Multivariate analyses revealed that SLR<SUB>max</SUB> > 1.31 was useful for discriminating between MAS and sepsis. SLR<SUB>max</SUB> positively correlated with ferritin and lactate dehydrogenase level in MAS. Furthermore, MAS patients with high splenic FDG uptake (SLR<SUB>max</SUB> > 1.72) had higher in-hospital mortality compared to those with moderate to low splenic FDG uptake (<I>P</I> = .013).</P><P>This study was the first to demonstrate that splenic FDG uptake is significantly elevated in patients with MAS compared to those with sepsis. This may be useful to differentiate between MAS and sepsis, and to predict poor prognosis in patients with MAS.</P>
햅틱을 이용한 자동차 네비게이션 지원 시스템과 UI 개발 및 평가
정경미(Kyungmi Chung),현진실(Jinshil Hyun),황중식(Jungsik Hwang),조광수(Kwangsu Cho) 한국HCI학회 2012 한국HCI학회 학술대회 Vol.2012 No.1
이 연구에서는 운전자의 주의 집중을 저해할 수 있는 위험한 상황에서 진동 촉각 단서의 제시 간격과 시각적 표적의 제시 위치 일치 여부에 따라 나타날 수 있는 촉진효과와 억제효과의 가능성과 함께 회귀억제 현상이 일어날 경우 눈의 움직임엔 어떠한 변화가 있는지를 살펴보고자 하였다. 운전 중 촉각으로 공간정보를 전달하기 위해 5×5 배열의 진동단자로 구성한 진동시스템을 운전자 시트의 등에 부착하였으며, Flicker paradigm 을 사용하여 시각적 변화를 탐색하는 실험을 실시하였다. 두 독립변인으로는 유효성(유효, 비유효, 통제조건)과 자극제시간격(pre 1440ms, pre 2160ms, pre 2880ms)을 설정하였고, 바뀐 시각자극을 찾는데 걸린 시간과 4 분면 안에서 바뀐 물체의 위치를 올바르게 찾을 수 있는지의 여부를 종속변인으로 측정하였다. This study investigated that the possibility of the facilitation and inhibition effects resulting from the SOAs of the vibrotactile cue and whether the location of the presented visual target corresponds to that of the cue, observing the changes in eye movement when IOR appears. To convey spatial haptic cue-based information while driving, we installed the haptic interface using vibrotactile signals with 5-by-5 tactor array on the back of the driver's seat and conducted a visual search experiment based on flicker paradigm. The two independent variables were validity (valid, invalid, no cueing) and the interval between the onset of the cue and onset of the target (pre 1440ms, pre 2160ms, pre 2880ms), and reaction times (RTs) for correct responded trials were measured as dependent variables.
차범하(Bermha Cha),장진만(Jin Man Jang),서정식(Jungsik Seo),고세현(Se-Hyun Ko),손성호(Seong Ho Son),이원식(Wonsik Lee),유우경(Woo Kyung You),이재성(Jai-Sung Lee) 한국생산제조학회 2011 한국생산제조시스템학회 학술발표대회 논문집 Vol.2011 No.4
재활용된 티타늄 수소화물 분말을 사용하여 피드스톡을 제조하고, 이를 이용하여 사출성형공정 조건을 최적화 하였다. 원료분말은 Ti chip의 재활용 공정을 통해 제조된 평균 350nm 크기의 분말을 사용하였으며, 피드스톡 제조 시 최적 분말 고상율은 68%였다. 제조된 피드스톡은 2000Pa.s 이하의 점도를 나타냈으며, 최적의 사출조건으로 미세한 부분까지 건전하게 성형된 사출체를 제조하였다. 또한 피드스톡의 열분석 결과를 이용하여 탈지 및 탈수소화 공정의 최적화를 이루었으며, 고진공하에서 소결 시 완전치밀화를 얻을 수 있었다.