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Choy, Seunghwan,Oh, Dongyeop X.,Lee, Seungwon,Lam, Do Van,You, Gihoon,Ahn, Jin-Soo,Lee, Seung-Woo,Jun, Sang-Ho,Lee, Seung-Mo,Hwang, Dong Soo American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.10
<P>Although biodegradable membranes are essential for effective bone repair, severe loss of mechanical stability because of rapid biodegradation, soft tissue invasion, and excessive immune response remain intrinsically problematic. Inspired by the exoskeleton-reinforcing strategy found in nature, we have produced a Ti-infiltrated chitin nanofibrous membrane. The membrane employs vapor-phase infiltration of metals, which often occurs during metal oxide atomic layer deposition (ALD) on organic substrates. This metal infiltration manifests anomalous mechanical improvement and stable integration with chitin without cytotoxicity and immunogenicity. The membrane exhibits both impressive toughness (∼13.3 MJ·m<SUP>-3</SUP>) and high tensile strength (∼55.6 MPa), properties that are often mutually exclusive. More importantly, the membrane demonstrates notably enhanced resistance to biodegradation, remaining intact over the course of 12 weeks. It exhibits excellent osteointegrative performance and suppresses the immune response to pathogen-associated molecular pattern molecules indicated by IL-1β, IL-6, and granulocyte-macrophage colony-stimulating factor expression. We believe the excellent chemico-biological properties achieved with ALD treatment can provide insight for synergistic utilization of the polymers and ALD in medical applications.</P> [FIG OMISSION]</BR>
Choy, Seunghwan,Lam, Do Van,Lee, Seung-Mo,Hwang, Dong Soo American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.42
<P>Collagen, one of the most popular biomedical materials, exhibits rapid biodegradation accompanied by a notable decrease of mechanical stability in the human body. This is a key challenge for its use in large-sized tissue regeneration, which takes a long time. In order to resolve this problem, we introduced vapor-phase titanium (Ti) derivatives into the interchain regions in collagen via TiO<SUB>2</SUB> atomic layer deposition (ALD), which has been widely used for thin-film deposition. The introduced Ti simultaneously enhanced both the tensile strength (∼384.45 MPa) and Young’s modulus (∼1.56 GPa) by approximately 29 and 26% compared to the pristine commercial collagen membrane. In vitro tests demonstrated that approximately 31% of Ti-infiltrated collagen is retained after 4 weeks, whereas the pristine commercial collagen rapidly degrades by up to 90% within 1 week. The in vivo biodegradation rate was greatly improved and inversely proportional to the number of TiO<SUB>2</SUB> ALD cycles. Moreover, bone mineralization, which is observed during the late stage of bone healing, appeared only in the Ti-infiltrated collagen. We believe that our simple vapor-phase treatment method could be widely used with xenograft materials, which typically require adequate biodegradation rates and stable mechanical properties.</P> [FIG OMISSION]</BR>
배터리 차량에 사용되는 IPMSM의 최대 효율 제어기법
정승환(SeungHwan Jung),최익(Ick Choy),김권호(KwonHo Kim) 전력전자학회 2009 전력전자학술대회 논문집 Vol.2009 No.1
Currently, IPMSM is used to minicars having a special purpose and an electric automobile. These vehicles drive works generally to a battery. and control methods to raise efficiency of a IPMSM was studied very much. This paper proposes convenient maximum efficiency control algorithm applying various type of IPMSMs. and compares simulation results of existing efficiency control method.
상태평준화 방법을 이용한 태양광발전시스템에서의 벅컨버터 해석
정승환(Seunghwan Jung),최익(Ick Choy),임지훈(Jihoon Im),송승호(Seungho Song),최주엽(Juyeop Choi),이동하(Dongha Lee),안진웅(Jinung An) 한국태양에너지학회 2010 한국태양에너지학회 학술대회논문집 Vol.2010 No.11
현재, 개발되고 있는 신재생에너지분야 가운데 태양광발전시스템은 그 활용범위가 장난감에서부터 인공위성에 이르기까지 널리 쓰이고 있다. 하지만 기존의 제어기는 단순히 전력변환장치의 제어를 목적으로 설계되어, 태양광전지를 입력으로 받는 부분은 고려되어 있지 않다. 그 중에서도 벅 컨버터는 태양광 전지를 고려하여 모델링 하였을 때 비선형적인 특성이 나타나게 되고, 이를 선형제어기를 사용하여 제어하기는 쉽지 않다. 본 논문에서는 태양광발전시스템에서 사용되고 있는 벅 컨버터를 상태공간평준화 방법을 사용하여 모델링하고, 정상상태 해석을 통하여 벅 컨버터의 특성을 밝힌다.
청소차에서 쓰이는 IPMSM의 제어기 보드의 개발과 제어기법 연구
정승환(Seunghwan Jung),최익(Ick Choy),김권호(Kwonho Kim) 전력전자학회 2008 전력전자학술대회 논문집 Vol.- No.-
본 논문은 청소차에 쓰이는 IPMSM을 위한 적절한 제어기법을 연구하고, 이를 위한 제어기 보드를 개발하였다. 청소차에 쓰이는 전동기는 주행용, 브러쉬용, 흡입용이 있으며, 용도에 따라 최대 토크 제어 기법과 최적 효율 제어기법을 적용함으로서 목적에 맞는 효과를 기대할 수 있다. 또한 이러한 제어 기법을 적용할 수 있는 제어기 보드를 제작하였다.
Enhancement of nanofluid stability and critical heat flux in pool boiling with nanocellulose
Hwang, Won-Ki,Choy, Seunghwan,Song, Sub Lee,Lee, Jaeyoung,Hwang, Dong Soo,Lee, Kwon-Yeong Applied Science Publishers 2019 Carbohydrate polymers Vol.213 No.-
<P><B>Abstract</B></P> <P>A nanofluid, which is an aqueous fluid with nanoparticles, is an attractive medium for enhancing critical heat flux (CHF); however, its instability over a long period of time due to sedimentation and aggregation has impeded its successful application in industry. In this study, lightweight negatively charged TEMPO-oxidized cellulose nanofibers (CNFs) were utilized as a nano-sized substance in water and examined to enhance both the CHF performance and thermal stability of nanofluids. Owing to low density of the CNFs and long range repulsion between negatively charged CNFs, there were no aggregation and sedimentation of CNFs with multiple boiling/cooling cycles. In addition, with CNF concentrations of 0.01, 0.03, 0.05, and 0.10 wt%, CHF enhancement increases of 40.7%, 45.1%, 54.9%, and 69.4%, respectively, were achieved over that of pure water. The present results demonstrated the great potential of CNFs as eco-friendly and cost-effective nano-substances that can overcome the instability of nanofluids.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanofluid containing cellulose nanofibers (CNFs) enhanced critical heat flux (CHF). </LI> <LI> Chemical inertness and self-repulsiveness of CNFs manifested stable pool boiling. </LI> <LI> Nanofibrous structure was beneficial for CHF enhancement. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Alternative nanofluid containing carboxylated nanocellulose exhibits enhanced critical heat flux (CHF) and stable dispersion during pool boiling.</P> <P>[DISPLAY OMISSION]</P>