소결 분위기가 $(1-x)CaTiO_3-xLaAlO_3$계의 마이크로파 유전특성에 미치는 영향

여동훈,김현재,문종하 한국세라믹학회 1997 한국세라믹학회지 Vol.34 No.5

The effects of sintering atmospheres(air, O2, N2) on the sintering and microwave dielectric properties of (1-x)CaTiO3-xLaAlO3 system was investigated. The sintered density of (1-x)CaTiO3-xLaAlO3 under air atmosphere increased linearly with increasing x, but it decreased in the range of x>0.5 under O2 atmosphere and x>0.6 under N2 atmosphere in spite of the increament of the smaller La(1.06$\AA$) and Al(0.5 $\AA$) ion than Ca(0.99$\AA$) and Ti(0.6$\AA$). In case of the air sintering atmosphere of (1-x)CaTiO3-xLaAlO3 the two phases of orthorhombic and rhombohedral crystal system were coexisting, and the XRD peak of rhombohedral crystalsystem was to be higher with increasing x. However, the sintering atmosphere of O2 and N2 made the monophasic crystal system of orthorhombic keep up by x=0.5 and x=0.6, respectively, and it transformed to pseudo-cubic crystal system in x>0.5 and x>0.6. The XRD peak intensity of (1-x)CaTiO3-xLaAlO3 was to be gradually higher with increasing x under the air atmosphere of sintering. Whereas, its XRD peak intensity increased till x=0.6 but decreased with increasing x in the range of x>0.6 under O2 and N2 atmosphere. The relative dielectric constant of (1-x)CaTiO3-xLaAlO3 sintered under air atmosphere decreased linearly and the Q.f0 value increased according as x increased. On the other hand, the relative dielectric constant of (1-x)CaTiO3-xLaAlO3 under O2 and N2 atmosphere decreased in the range of x$\leq$0.5 with increasing x, but increased rapidly in the range of x$\geq$0.6. And the Q.f0 value increased till x=0.6 but decreased in the range of x>0.6 with increasing x. The temperature coefficient of resonant frequency had no relation to sintering atmosphere.

고속도로 건설사업의 재정/민자 발주선택 의사결정 지원모델

여동훈,정우용,한승헌,이영천,Yeo, Donghoon,Jeong, Wooyong,Han, Seung Heon,Lee, Young Cheon 대한토목학회 2009 대한토목학회논문집 D Vol.29 No.3D

2007년 기준으로 정부는 18.4조원을 사회기반시설에 투자하고 있으며, 이 중 16.3%에 해당되는 3조원을 민간투자 사업에 집행하고 있다. 이는 인프라 시설에 대한 국민적인 요구를 충족시킴과 동시에 재정부담을 경감하고 사업 추진시 위험을 축소시키기 위한 것이다. 하지만 현재 국가 인프라 사업은 기획단계에서 재정사업 또는 민자사업으로 결정하는 체계적인 기준이나 지침이 없이 주로 재정 상태를 고려한 주무관청의 자체판단에 따라 사업추진 방식이 결정되고 있다. 또한 초기에 재정 사업으로 추진되는 경우에도, 사업타당성 조사를 실시하는 과정에서 민자사업으로서의 가능성은제대로 평가되지 않는 상황이다. 따라서 본 연구는 국가 인프라사업에 대하여 재정사업과 민자사업을 선택하는 합리적인 발주기준을 제시하는 것을 목표로 한다. 이를 위하여 고속도로 사업을 중심으로 재정 민자 의사결정 기준을 경제성, 정책성, 사업관리 항목으로 나누고 이를 바탕으로 재정 민자 의사결정 모델을 제시하였다. 본 연구에서는 의사결정 모델을 구축하기 위해 30건의 재정 및 민자사업 실제 사례를 분석하고 102건의 전문가 설문을 실시하였다. 본 모델은 크게 두 단계로 구분되는데, 첫째 경제성 평가는 평균 및 표준편차 분석을 통해 민자불가, 재정민자 양측가능 및 재정불가 구간을 제시하였으며, 둘째 정책성 평가와 사업관리 평가는 로지스틱 회귀분석을 실시함으로써 재정 또는 민자사업의 추진여부를 구분 짓는 예측식을 도출하였다. 본 연구의 결과를 통해 고속도로 사업의 기획단계에 참여하는 의사결정자는 고려중인 사업의 재정 민자사업 결정시 보다 체계적이고 합리적인 사업발주방식을 결정할 수 있을 것으로 사료된다. Korean government is investing 1.8 billion won on infrastructure and investment on PPP projects constitutes 16.3%. This phenomenon is to promote private investment as well as lessening government burdens of public budgeting. However, the only criterion to be considered is government financial status in selecting public or private highway investment projects. So systematic decision support model is required in choosing public or private highway investment projects. So, this paper suggests a systematic decision support model for deciding public or private highway investment at the early stage of project planning. Furthermore, this paper identifies key decision variables with respect to economic, politic, project management criterions based on the related literatures and feedbacks from experts. This paper analyzed 30 cases of government investment and PPP projects and got the survey result from highway specialists. As a result, this paper presents an interval with respect to economic criteria using mean and standard deviation and a logistic regression equation which can predict the possibility of PPP project. Through this study, decision maker of central or local government can decide public or PPP highway project more systematically and reasonably.

참여자별 수익성을 고려한 민간투자사업 성과예측 모델

여동훈,유기원,이강욱,한승헌,Yeo, Dong Hoon,Yu, Giwon,Lee, Kang-Wook,Han, Seung-Heon 대한토목학회 2015 대한토목학회논문집 Vol.35 No.2

민간투자사업에 대한 부정적인 시각으로 인해 민간투자사업 시장은 축소되었으나, 최근 국내 재정사업의 축소로 인해 민간투자사업에 대한 필요성이 다시금 제기되고 있다. 민간투자사업은 건설사, special purpose company (SPC), 재무투자자 등 다양한 참여자들 간의 이해관계가 복잡하여 사업의 성과를 판단하기 위해서는 참여자 간 관점 차이에 대한 고려가 필요하나, 기존의 연구는 재무적 관점의 수익성 예측, 또는 리스크 식별을 통한 수익성 예측을 중심으로 수행되었다. 이러한 점을 고려하여 본 연구에서는 민간투자사업 주요 참여자별 특성에 따른 민간투자사업 성과예측 모델을 개발하였다. 이를 위해 첫째, 다양한 분야의 문헌고찰을 통해 민간투자사업의 조직구조를 분석하였으며, 건설사, SPC, 재무투자자의 관점에서 민간투자사업 수익성 영향요인을 도출하였다. 둘째, 도출된 수익성 영향인자들을 바탕으로 민간투자사업 관련 전문가 설문조사 및 인터뷰를 실시하였다. 셋째, 구조방정식 모델(structural equation model)을 통해 민간투자사업의 구성개념들 간에 직접효과와 간접효과를 분석하여 민간투자사업의 수익성 및 수익안정성 측면에서의 성과를 거시적으로 이해할 수 있는 모델을 개발하였다. 넷째, 모델을 통해 도출된 결과를 바탕으로 민간투자사업의 재도약을 위한 발전방안을 제시하였다. 향후 본 모델을 통해 수익성과 수익안정성 측면에서 건설사, 재무투자자, SPC 운영사의 사업성과 예측이 가능하며, 이에 따른 대응전략을 모색하는데 활용 가능할 것으로 기대된다. The market of public-private partnership (PPP) projects has reduced from 9.4 trillion won in 2007 to 4.5 trillion won in 2012. However, the need of PPP projects is brought up by a massive down scale of government financial business. Previous studies regarding PPP projects mostly evaluate profitability from the financial perspective or analyze risk factors as a whole. Although PPP projects generally have complex structure involving diverse stakeholders, such as contractor, financial investor, and special purpose company (SPC) operators, existing studies have rarely considered the different viewpoints of PPP project stakeholders. Therefore, purpose of this study is to develop a structural equation model (SEM) considering the diverse stakeholders of PPP projects. To this end, the authors first reviewed the organizational structure of PPP projects. Next, the identification of the factors affecting project profitability are done via comprehensive literature reviews. After that, we conducted in-depth interviews and questionnaire surveys to reflect stakeholders' perspectives (contractors, financial investors, and SPC operators). As a result, a SEM model is developed to analyze direct and indirect effect on the PPP project performances. Finally, using the analysis results, relevant implications and directions for improvements are discussed. The prediction of the business performance of contractor, financial investor, and SPC operator is expect to be possible through the model developed and supports the strategy deduction that is appropriate for the participants.

Spatiotemporal Analysis of Event-related Current Density Reveals Dissociable Effects of Arousal and Valence on Emotional Picture Processing

여동훈,김현,허성진,최정우,차광수,김경환 대한의학회 2019 Journal of Korean medical science Vol.34 No.20

Background: The processing of emotional visual stimulation involves the processing of emotional and visuoperceptual information. It is not completely revealed how the valence and arousal affect these two aspects. The objective was to investigate the effects of valence and arousal on spatiotemporal characteristics of cortical information processing using distributed source imaging of event-related current density (ERCD). Methods: Electroencephalograms (64 channels) were recorded from 19 healthy men while presenting affective pictures. Distributed source localization analysis was adopted to obtain the spatiotemporal pattern of ERCD on cortical surface in response to emotional visual stimulation. A nonparametric cluster-based permutation test was used to find meaningful time and space without prior knowledge. Results: Significant changes of ERCD in 400–800 ms among positive, negative, and neutral emotional conditions were found in left posterior cingulate cortex (PCC) and right inferior temporal cortex (ITC). In the PCC, the stimuli with higher arousal levels showed more negative ERCD than neutral stimuli. In the ITC, the ERCD for negative stimuli was significantly more negative than those of positive and neutral ones. Conclusion: Arousal and valence had strong influence on memory encoding and visual analysis at late period. The location and time showing significant change in neural activity according to arousal and valence would provide valuable information for understanding the changes of cortical function by neuropsychiatric disorders.

Mg₂SiO₄/Glass Composite계 세라믹스를 이용한 음이온 발생용 후막형 클러스터

여동훈,신효순,홍연우,Yeo, Dong-Hun,Shin, Hyo-Soon,Hong, Youn-Woo 한국전기전자재료학회 2010 전기전자재료학회논문지 Vol.23 No.2

The eco-friendly technologies have been extended as matter of international concern due to various diseases and syndromes according to an environmental pollution. In this study, we have manufactured a ceramic cluster with thick film type for anion generation equipment which is maximized anion but minimized ozone contents generated. To develop the formulation of ceramic cluster, we conducted the $Mg_2SiO_4$ powders doped with 10 vol% glass frits as Na-Zn-B-O system and sintered at $1050^{\circ}C$ for 2 hours in air for starting materials and investigated the matching properties between the Ag-Pd electrode and the starting materials. The sintered sample for the composition of cluster has 6.7 of dielectric constant and 32 kV/mm of withstand voltage. The yield of anions was measured according to an electrode pattering, discharge gap between electrode, and thickness of electrode protective layer in the cluster of thick film type. We have manufactured the ceramic clusters with optimized thick film structure that have an anion over a hundred particles and the ozone of 0.6 ppb generated.

마그네슘 합금 판재를 이용한 후드 개발

여동훈,정용희,이영선,최상운,이목영 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

In order to get mass reduction, magnesium alloys have been used for many automotive applications such as steering wheel, seat frame, cam cover and so on. Those parts are manufactured by die casting but the use of magnesium sheets is limited. This limited application is due to its low room-temperature formability. Magnesium is a hexagonal lattice structure metal and so has only few slip systems at room temperature but it has good formability at elevated temperature, over 200℃. Therefore, in this study, magnesium hood was manufactured by warm forming (forming at elevated temperature, > 200℃) and its stiffness & weight reduction rate was also evaluated. The weight of Mg hood records 54% of steel hood and the stiffness is better than steel hood. And, through this study, technologies and basic studies that need to be overcome in order to enlarge the use of Mg sheets were drawn. The lessons drawn are as follows ; when designing die, thermal expansion/contraction of die material and magnesium sheets should be considered as an important factor and cooling condition of formed panel should be investigated cautiously in order to make sound panels.

차세대 세라믹 패키징 재료 개발 동향

여동훈,신효순,홍연우,Yeo, Dong-Hun,Sin, Hyo-Sun,Hong, Yeon-U 한국전기전자재료학회 2009 전기전자재료 Vol.22 No.12

Computer Vision 활용한 금융혁신 연구 사례

여동훈 대한산업공학회 2022 대한산업공학회 춘계학술대회논문집 Vol.2022 No.6

긍정, 부정 감정 유발 시각자극에 의한 감마-대역 신경동기화 증가

여동훈,최정우,김경환,Yeo, Donghoon,Choi, Jeong Woo,Kim, Kyung Hwan 대한의용생체공학회 2018 의공학회지 Vol.39 No.2

It is known that gamma-band activity (GBA) and phase synchrony (GBPS) are induced by emotional visual stimuli. However, the characteristics of GBA and GBPS according to different emotional states have not been identified. The purpose of this study is to investigate the changes in gamma-band neuronal synchronization induced by positive and negative emotional visual stimuli using electroencephalograms (EEGs). Thirteen healthy male subjects have participated in the experiment. The induced spectral power in gamma-band was the highest for negative stimuli, and the lowest for neutral stimuli in 300-2,000 ms after the stimulus onset. The inter-regional phase synchronization in gamma-band was increased in 500-2,000 ms, mainly between the bilateral frontal regions and the parieto-occipital regions. Larger number of significant connections were found by negative stimuli compared to positive ones. Judging from temporal and spatial characteristics of the gamma-band activity and phase synchrony increases, the results may imply that affective visual stimuli cause stronger memory encoding than non-emotional stimuli, and this effect is more significant for negative emotional stimuli than positive ones.

급속응고된 Fe - 4wt% C - Si 계 합금분말 압출재의 기계적 성질에 관한 연구

여동훈,김동익,나형용 대한금속재료학회 1989 대한금속재료학회 학술대회 개요집 Vol.1989 No.0