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Park, Heetaek,Jung, Keeyoung,Nezafati, Marjan,Kim, Chang-Soo,Kang, Byoungwoo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.41
<P>The Na superionic conductor (aka Nasicon, Na1+xZr2SixP3-xO12, where 0 <= x <= 3) is one of the promising solid electrolyte materials used in advanced molten Na-based secondary batteries that typically operate at high temperature (over similar to 270 degrees C). Nasicon provides a 3D diffusion network allowing the transport of the active Na-ion species (i.e., ionic conductor) while blocking the conduction of electrons (i.e., electronic insulator) between the anode and cathode compartments of cells. In this work, the standard Nasicon (Na3Zr2Si2PO12, bare sample) and 10 at% Na-excess Nasicon (Na3.3Zr2Si2PO12, Na-excess sample) solid electrolytes were synthesized using a solid-state sintering technique to elucidate the Na diffusion mechanism (i.e., grain diffusion or grain boundary diffusion) and the impacts of adding excess Na at relatively low and high temperatures. The structural, thermal, and ionic transport characterizations were conducted using various experimental tools including X-ray diffraction ()MD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). In addition, an ab initio atomistic modeling study was carried out to computationally examine the detailed microstructures of Nasicon materials, as well as to support the experimental observations. Through this combination work comprising experimental and computational investigations, we show that the predominant mechanisms of Na-ion transport in the Nasicon structure are the grain boundary and the grain diffusion at low and high temperatures,, respectively. Also, it was found that adding 10 at% excess Na could give rise to a substantial increase in the total conductivity (e.g., 1.2 X 10(-4) S/cm at 300 degrees C) of Nasicon electrolytes resulting from the enlargement of the bottleneck areas in the Na diffusion channels of polycrystalline grains.</P>
Park, Heetaek,Kim, Minkyung,Kang, ShinYoung,Kang, Byoungwoo The Royal Society of Chemistry 2019 Journal of materials chemistry. A, Materials for e Vol.7 No.21
<P>Tavorite LiVPO4F has great potential as a cathode material due to its high energy density, superior thermal stability and fast kinetics. It has been controversial whether the redox reaction pathway of LiVPO4F is symmetric or not, but the origin of such symmetric/asymmetric redox reaction pathways has not been clearly understood. By combining <I>ab initio</I> calculations with experiments, we found that oxygen defects on fluorine sites, OF<SUP>−</SUP>, can be a key factor that affects the symmetry of the redox pathway of LiVPO4F1−δOδ (<I>δ</I> < 1). The computational results indicate that (1) the thermodynamically metastable ‘triclinic’ polymorph of VPO4F1−δOδ, which maintains the structural symmetry of LiVPO4F, can be kinetically stabilized considering its marginally higher energy than the stable ‘monoclinic’ phase; and (2) the OF<SUP>−</SUP> defects slightly destabilize the intermediate phase (<I>x</I> = 0.667) (Li0.667VPO4F <I>versus</I> Li0.667VPO4F0.917O0.083), inferring that the presence of OF<SUP>−</SUP> defects can induce the asymmetric redox pathway of LiVPO4F1−δOδ. We also experimentally found that the concentration of OF<SUP>−</SUP> defects is critically affected by the synthesis process of LiVPO4F, and VPO4F with lower OF<SUP>−</SUP> concentration can support the possible presence of the metastable (triclinic) phase, leading to the redox pathway being prone to being symmetric. Therefore, controlling oxygen defects by a synthesis processes can affect electrochemical performance <I>via</I> different redox reaction pathways of LiVPO4F. This understanding provides further possibilities for improving the electrochemical performance.</P>
Park, Heetaek,Kang, Minseok,Park, Yoon-Cheol,Jung, Keeyoung,Kang, Byoungwoo Elsevier 2018 Journal of Power Sources Vol.399 No.-
<P><B>Abstract</B></P> <P>Molten sodium (Na) anode high temperature batteries, such as Na-NiCl<SUB>2</SUB> and Na-S, draw attentions to be used in stationary electricity storage applications. Recent efforts are exerted to lower their operating temperatures down to below 200 °C in order to adopt ultra-low cost cell production, establish easier maintenance, pursue enhanced safety, and more. One of main challenges in lowering the operation temperature is radical decrease in ionic conductivity of their solid electrolytes. Na<SUB>3</SUB>Zr<SUB>2</SUB>Si<SUB>2</SUB>PO<SUB>12</SUB> (Nasicon) is considered as a solid electrolyte for the lower temperature operation. Here we report Na ionic conductivity of Nasicon at 150 °C increases by adding Ge element. The ionic conductivity of Ge-added sample (Na<SUB>3</SUB>[Zr<SUB>2-δ</SUB>Ge<SUB>δ</SUB>]Si<SUB>2</SUB>PO<SUB>12</SUB>, δ = 0.1, 0.2) is measured as high as 1.4 × 10<SUP>−2</SUP> S cm<SUP>-1</SUP> at 150 °C which is about two times higher than those of the bare Nasicon. The phase transition temperature of the Ge-added samples is lowered, thereby the volume fraction of the rhombohedral phase, which is stable at higher temperatures and exhibits higher Na ion conductivities, increases. This finding provides a useful guideline to further increase the ionic conductivity of Nasicon solid electrolytes, which can advance materialization of lower temperature operating Na batteries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Na<SUP>+</SUP> ion conductivity at intermediate temperatures improves by adding Ge to Nasicon. </LI> <LI> Reduction of the phase transition temperature by adding Ge has been verified. </LI> <LI> Modifying phase transition behavior can enhance Na<SUP>+</SUP> ion conductivity of Nasicon. </LI> </UL> </P>
활동성 폐결핵으로 인해 초기에 장결핵으로 오진된 크론병 1예
박수민 ( Sumin Park ),이태영 ( Taeyeong Lee ),임원 ( Won Lim ),박상규 ( Sangkyu Park ),박호준 ( Hojun Park ),윤정희 ( Jeonghui Yun ),김도형 ( Dohyeong Kim ),최수룡 ( Sooryong Choi ),오희택 ( Heetaek Oh ),송철수 ( Chulsoo Song ) 대한소화기학회 2021 대한소화기학회지 Vol.77 No.1
Differentiating Crohn’s disease (CD) from intestinal tuberculosis (TB) is a challenge. In patients suspected of having CD or intestinal TB compounded with active pulmonary TB in its early stages, clinicians often lean towards a diagnosis of intestinal TB. A 14-year-old female patient was admitted with symptoms of abdominal pain and diarrhea with hematochezia. Colonoscopy revealed a stricture of the ileocecal valve and scattered longitudinal ulcers. Initial chest radiography showed consolidation in the left lower lobe of the lung. Chest CT revealed branching nodular opacities and consolidation. The TB PCR of the bronchial washing fluid was positive. The patient was diagnosed with pulmonary and intestinal TB. The colonoscopy findings favored CD. Despite this, anti-tubercular therapy was initiated based on the radiology findings and PCR test. After treatment with anti-tubercular therapy, the patient’s diarrhea and abdominal pain worsened despite the improvement observed on her chest radiography. Follow-up colonoscopy revealed aggravation of her ulcers. The patient was diagnosed with CD and treated with prednisolone and mesalazine. Her clinical condition improved, and follow-up colonoscopy showed significant improvement of the ulcers. This case highlights the need for caution in diagnosis and suggests that clinicians consider reevaluation in similar cases. (Korean J Gastroenterol 2021;77:30-34)
LID 개념 적용으로 인한 유출 감소 특성 가능성 분석 및 바이모달 트램 전용노선에서의 적용성 검토
박준호(Junho Park),박영곤(Youngkon Park),윤희택(Heetaek Yoon),유용구(Yonggu Yoo),김종건(Jonggun Kim),박윤식(Younshik Park),임경재(Kyoung Jae Lim) 한국철도학회 2008 한국철도학회 학술발표대회논문집 Vol.- No.-
Changes in land uses at urbanizing areas are causing flooding, increase in NPS pollutants. Thus, Low Impact Development (LID) concept is now being employed in urban planning for sustainable development. Compared with the conventional BMPs, the LID is a new concept in urban planning to minimize the impacts of urbanization for site-specific LID IMPs. The objective of this study is to analyze the efficiency of LID adoption in study watershed in peak rate runoff and runoff volume reduction perspectives. The analysis revealed that the peak rate runoff and runoff volume decreased significantly with the LID adoption. This indicates that the Bimodal tram route with grass installed at the center of the road will contribute reduction in surface runoff and peak rate runoff, and also in NPS pollutant generation from the Bimodal tram route.
바이모달 트램 재해관리 시스템 입력자료 구축을 위한 AV2SWMM 모듈 개발
김종건(Jonggun Kim),박영곤(Youngkon Park),윤희택(Heetaek Yoon),박윤식(Younshik Park),장원석(Wonseok Jang),박준호(Junho Park),임경재(Kyoung Jae Lim) 한국철도학회 2008 한국철도학회 학술발표대회논문집 Vol.- No.-
With unexpected torrential rainfall, flash flooding is occurring frequently and its impacts are tremendous. Thus proper natural disaster management plans are required. The disaster management system of the Bimodal tram utilizes the SWMM as a core engine to simulate runoff and urban sewer networks for flooding simulation. To develop the efficient Bimodal tram disaster management system, very detailed subcatchment boundaries and flow networks have to be developed in a GIS data format. Thus the objective of this study is to develop ArcView GIS based module (AV2SWMM) for easy preparation of model input for the tram disaster management system. With the AV2SWMM module, very detailed subcatchment boundaries and flow networks can be developed for accurate simulation of flash flooding at the study site, which were not/hardly possible with SWMM 5.0 interface. The AV2SWMM can be used in developing accurate model input for other regions where the Bimodal tram system is expected to be introduced.
공공건설사업의 최적 발주방식 선정을 위한 의사결정지원모델
박희택,박찬식,Park, Heetaek,Park, Chansik 한국건설관리학회 2016 건설관리 : 한국건설관리학회 학회지 Vol.17 No.5
현재 국내 공공건설사업의 발주제도는 입 낙찰제도와 뚜렷한 구분이 없이 혼용되고 있으며, 선정할 수 있는 기준 자체도 단순히 사업예산이나 추정금액에 의해 정해지고 있다. 발주방식은 본래 사업의 특성이나 유형, 목적 등 다양한 요인들의 특성을 적절히 반영하여 결정해야 함에도 불구하고, 주어진 예산이나 기간, 획일적인 법 규정으로 인해 탄력적으로 운영되지 못하고 있어, 이에 대한 근본적인 해결방안을 마련해야 할 필요성이 지속적으로 제기되고 있다. 이를 위해, 본 연구는 최적 발주방식을 선정할 수 있는 의사결정지원모델을 제안하였다. 이를 위해 문헌고찰과 설문 및 면담조사, 통계적 분석기법을 활용하여 영향요인을 발굴하고, 최종 발주방식 유형별 의사결정지원모델을 제안하여, 실무 적용타당성을 검증하였다. 그 결과 의사결정지원모델은 향후 발주방식을 선정하는데 기초자료로 유용하게 활용함으로써 기존 업무관행을 개선할 수 있을 것으로 기대한다. The Project Delivery System (PDS) is used in mixed way without clear classification from tendering system and the standard itself that can be selected is set with project budget or estimated cost only. Essentially, the PDS should consider and reflect project characteristics and types, internal and external factors for the purpose of improving the lives of citizens and their welfare. However, the current status is not operated flexibly due to the given budget, period and uniform laws and regulations. In order to solve this problem, this study suggests a Decision Support Model to select the optimal PDS for public construction projects. The current problem of the PDS for public construction projects were identified and the application of a decision support model was proposed. Subsequently a decision-making model was suggested for each PDS using the identified factors and linear discriminant function of discriminant analysis. An additional questionnaire survey and actual practical case analysis were carried out to verify the effectiveness and applicability of the model to actual work. It can be used by adjusting the decision support model and detailed factors according to the specific characteristics of public organization, ability of person in charge and project type.