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        • Mitral Loop Cerclage Annuloplasty for Secondary Mitral Regurgitation

          Park, Y.H.,Chon, M.K.,Lederman, R.J.,Sung, S.C.,Je, H.G.,Choo, K.S.,Lee, S.H.,Shin, E.S.,Kim, J.S.,Hwang, K.W.,Lee, S.Y.,Chun, K.J.,Kim, C.M.,Kim, J.H. Elsevier 2017 JACC. Cardiovascular interventions Vol.10 No.6

          <P>OBJECTIVES This is an early feasibility clinical test of mitral loop cerclage annuloplasty to treat secondary mitral valve regurgitation. BACKGROUND Secondary mitral regurgitation is characterized by cardiomyopathy, mitral annular enlargement, and leaflet traction contributing to malcoaptation. Transcatheter mitral loop cerclage applies circumferential compression to the mitral annulus by creating a loop through the coronary sinus across the interventricular septum, protecting entrapped coronary arteries from compression, and interactive annular reduction under echocardiographic guidance. This is the first human test of mitral loop annuloplasty. METHODS Five subjects with severe symptomatic secondary mitral regurgitation underwent mitral loop cerclage, with echocardiographic and computed tomography follow-up over 6 months. RESULTS Mitral loop cerclage was successful in 4 of 5 subjects and aborted in 1 of the 5 because of unsuitable septal coronary vein anatomy. Immediately and over 6 months, measures of both mitral valve regurgitation (effective orifice area and regurgitation fraction) and chamber dimensions (left atrial and left ventricular volumes) were reduced progressively and ejection fractions increased. Two with persistent and permanent atrial fibrillation spontaneously reverted to sinus rhythm during follow-up. One subject experienced a small myocardial infarction from an unrecognized small branch coronary occlusion. Another, experiencing cardiogenic shock at baseline, died of intractable heart failure after 6 weeks. CONCLUSIONS In this first human test, mitral loop cerclage annuloplasty was successful in 4 of 5 attempts, caused reverse remodeling (reduction in secondary mitral regurgitation and heart chamber volumes), and suggested electrical remodeling (reversion of atrial fibrillation). Further evaluation is warranted. (C) 2017 by the American College of Cardiology Foundation. Published by Elsevier. All rights reserved.</P>

        • Orbital hybridization mechanism for the enhanced photoluminescence in edge-functionalized sp<sup>2</sup> carbon clusters

          Kang, B.,Choi, Y.,Kim, B.S.,Youn, I.S.,Lee, G. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.109 No.-

          <P>Using the first principles methods, we performed systematic study on the effect of edge-functional groups on the electronic energy levels and the optical properties of sp(2) carbon clusters. It is found that the intrinsic pi and pi* orbitals are weakly altered by oxygen-bearing functional groups, but it is significantly disrupted by pyrrolic groups. Thereby the oscillator strength of the lowest-energy transition is found to be much stronger for the pyrrolic group functionalized cluster than for the carboxyl group. From our results being consistent with the experimental reports, we suggest that the photoluminescence enhancement is caused by a perturbation of the intrinsic, frontier molecular orbitals by edge groups. (C) 2016 Elsevier. Ltd. All rights reserved.</P>

        • KCI등재SCIESCOPUS

          Domain engineering in BiFeO<sub>3</sub> thin films

          Baek, Seung-Hyub,Choi, Seokhoon,Kim, Taemin Ludvic,Jang, Ho Won ELSEVIER 2017 CURRENT APPLIED PHYSICS Vol.17 No.5

          <P>Recent advances in synthesizing complex oxide epitaxial heterostructures with precise control in atomic scale have opened a new era of materials science and engineering research, enabling discoveries of novel physical phenomena even from materials that have been studied for a long time. The exquisite control of high-quality thin films through composition, defects, strain, and microstructure allows us to clearly distinguish intrinsic and extrinsic properties that were obscured by the limitation of sample quality. This is vividly exemplified by the recent research on bismuth ferrite (BiFeO3). Due to the moderately low symmetry of BiFeO3 with a rhombohedral structure, domain engineering, controlling the configuration of domains and domain walls, plays a critical role not only in understanding fundamental physics of electrical and magnetic properties, but also in inducing novel functionalities such as photovoltaic and photocatalysis. In this review, various ways to control domain structures of BiFeO3 will be described with the consequent modification in the physical properties of BiFeO3. This methodology can be expanded to other low-symmetric thin film materials for designing new functionalities. (C) 2017 Elsevier B.V. All rights reserved.</P>

        • Effect of number of cross-linkable sites on proton conducting, pore-filling membranes

          Kang, Hyeon-gu,Lee, Mi-Soon,Sim, Woo-Jong,Yang, Tae-Hyun,Shin, Kyung-Hee,Shul, Yong-Gun,Choi, Young-Woo Elsevier 2014 Journal of membrane science Vol.460 No.-

          Highly cross-linked membranes were prepared using a pore-filling technique for application in polymer electrolyte fuel cells (PEFCs). The electrolyte that fills the porous substrate should have a higher ion exchange capacity (IEC) than membranes prepared by a casting method. Hence, a cross-linking agent is employed to prevent the polymer electrolyte from dissolving in water. The goal of this study is to improve the chemical, mechanical, and electrochemical stability in membranes without decreasing the IEC. We evaluated the membrane characteristics using two different types of cross-linking agents-1,3,5-triacryloylhexahydro-1,3,5-triazine (C1) with three cross-linkable sites and N,N'-ethylene bisacrylamide (C2) with two cross-linkable sites. The membranes with Cl improved the chemical and electrochemical properties without a remarkable decrease in the IEC and proton conductivity compared to the membranes created with C2. Moreover, the Cl membrane also demonstrated an improvement in the electrochemical durability during the accelerated lifetime test. (C) 2014 Elsevier B.V. All rights reserved

        • Sulfonated poly(arylene sulfone) multiblock copolymers for proton exchange membrane fuel cells

          Jung, Myung Su,Kim, Tae-Ho,Yoon, Young Jun,Kang, Chan Gu,Yu, Duk Man,Lee, Jang Yong,Kim, Hyung-Joong,Hong, Young Taik Elsevier 2014 Journal of membrane science Vol.459 No.-

          We report herein aromatic multiblock copolymers (sPAS-A/Bs) consisting of sulfonated hydrophilic poly (arylene sulfone) blocks combined with hydrophobic poly(arylene ether sulfone) blocks. The synthesis involved polycondensation reactions of sulfonated and non-sulfonated oligomers, coupling reactions between these oligomers to produce the precursor copolymers based on sulfonated poly(arylene thioether sulfone)s (sPTS-A/Bs), followed by their oxidation to the corresponding sPAS-A/Bs. Thus, the sulfonated poly(arylene sulfone) blocks were chosen as the hydrophilic part due to their high chain stiffness, strong acidity, and resistance against desulfonation. The SPAS-A/B membranes showed well-connected hydrophilic nanophase domains, an increased thermal and oxidative stability, and decreased water uptake compared to the corresponding sPTS-A/B membranes. At 80 degrees C and 50% relative humidity (RH), SPAS-A/B membranes showed a high proton conductivity of 0.028 S/cm, which was comparable to that of Nation 212 and far exceeded those of the parent sPTS-A/B membranes. Moreover, the sPAS-A/B membranes showed high cell performance of 826 mA/cm(2) at low humidity (@0.6 V. 70 degrees C, 50% RH) and great durability over 1200 h in open circuit voltage hold test (80 degrees C. 10% RH). Because of their superior transport and stability properties, the sPAS-A/B membranes hold tremendous potential to fulfill the demands of proton exchange membrane fuel cells. (C) 2014 Elsevier B.V. All rights reserved.

        • SCIESCOPUS

          Streamline approach to die design and investigation of material flow during the vortex extrusion process

          Shahbaz, M.,Ebrahimi, R.,Kim, H.S. Elsevier Science Ltd 2016 Applied mathematical modelling Vol.40 No.5

          <P>In this study, a streamline approach based on a cubic Bezier formulation is used to investigate the material flow during vortex extrusion (VE). The velocity field and upper bound terms are calculated based on the proposed mathematical model in order to estimate the process load. The VE dies designed according to the proposed mathematical model are used for finite element analyses of the VE process in order to investigate the effect of various processing parameters on the strain distribution and process load. Comparisons of the simulated results with those obtained from the upper bound analysis demonstrate that the load increases in the VE process as the twist angle increases. Furthermore, we demonstrate that reducing the twist zone length and increasing the friction improve the material twisting during the VE process. (C) 2015 Elsevier Inc. All rights reserved.</P>

        • Heat, heat waves, and out-of-hospital cardiac arrest

          Kang, S.H.,Oh, I.Y.,Heo, J.,Lee, H.,Kim, J.,Lim, W.H.,Cho, Y.,Choi, E.K.,Yi, S.M.,Sang, D.S.,Kim, H.,Youn, T.J.,Chae, I.H.,Oh, S. Elsevier/North-Holland Biomedical Press 2016 INTERNATIONAL JOURNAL OF CARDIOLOGY Vol.221 No.-

          <P>Objective: Cardiac arrest is one of the common presentations of cardiovascular disorders and a leading cause of death. There are limited data on the relationship between out-of-hospital cardiac arrest (OHCA) and ambient temperatures, specifically extreme heat. This study investigated how heat and heat waves affect the occurrence of OHCA. Methods: Seven major cities in Korea with more than 1 million residents were included in this study. A heat wave was defined as a daily mean temperature above the 98th percentile of the yearly distribution for at least two consecutive days. Results: A total of 50,318 OHCAs of presumed cardiac origin were identified from the nationwide emergency medical service database between 2006 and 2013. Ambient temperature and OHCA had a J-shaped relationship with a trough at 28 degrees C. Heat waves were shown to be associated with a 14-% increase in the risk of OHCA. Adverse effects were apparent from the beginning of each heat wave period and slightly increased during its continuation. Excess OHCA events during heat waves occurred between 3 PM and 5 PM. Subgroup analysis showed that those 65 years or older were significantly more susceptible to heat waves. Conclusions: Ambient temperature and OHCA had a J-shaped relationship. The risk of OHCA was significantly increased with heat waves. Excess OHCA events primarily occurred during the afternoon when the temperature was high. We found that the elderly were more susceptible to the deleterious effects of heat waves. (C) 2016 Elsevier Ireland Ltd. All rights reserved.</P>

        • KCI등재SCIESCOPUS

          Oxygen electrocatalysis in chemical energy conversion and storage technologies

          Lee, J.,Jeong, B.,Ocon, J.D. Elsevier 2013 CURRENT APPLIED PHYSICS Vol.13 No.2

          <P>Oxygen electrocatalysis that we first defined is considered as the most important phenomenon in almost all electrochemical industries because it is the most sluggish reaction that governs the overall reaction rate in electrochemical cells. In this review, we cover two main areas of oxygen-water electrocatalysis, oxygen reduction to water and oxygen evolution from water. In particular, it aims to provide the readers with an understanding of the critical scientific challenges facing the development of oxygen electro-catalysts, various unique attributes of recent novel catalysts, the latest developments in electrode construction and the outlook for future generation of oxygen electrocatalysts. This review will be of value to both electrochemists and other applied scientists interested in this field of electrocatalysis. (c) 2012 Elsevier B.V. All rights reserved.</P>

        • Stress relaxation and transitions in optical bandgap of yttrium doped zinc oxide (YZO) thin films

          Kaur, N.,Sharma, S.K.,Young kim, D. Elsevier 2016 Current applied physics Vol.16 No.3

          <P>The stress relaxation and its effect on the bandgap of Y-doped ZnO (YZO) thin films were investigated by thermal annealing. YZO thin films were prepared on quartz glass by spin coating and subsequent annealed in vacuum. All the annealed YZO films showed a preferred (002) orientation. Photoluminescence (PL) provides the direct evidence of shifting the bandgap owing to stress release phenomena. The shifting in bandgap by increasing the annealing temperature can be attributed to the stress relaxation of YZO thin films. The bandgap of annealed films was initially decreased due to increase in magnitude of compressive stress and then increased as the tensile stress induced in the films. Therefore, these results may suggest the way to tune the band gap of YZO thin films by varying the residual stress through annealing. (C) 2015 Elsevier B.V. All rights reserved.</P>

        • CNT branching of three-dimensional steam-activated graphene hybrid frameworks for excellent rate and cyclic capabilities to store lithium ions

          Park, Sul Ki,Choi, Kwangrok,Lee, Si-Hwa,Oh, Il-Kwon,Park, Sungjin,Park, Ho Seok Elsevier 2017 Carbon Vol.116 No.-

          <P>The hierarchically architectured graphene-based materials are considered as a promising active or supporting material for the lithium ion batteries (LIBs). However, it faces critical challenges of the limited stored capacity, the mechanical brittleness, and the contact resistance. Herein, we demonstrate the unique hierarchical structures, where carbon nanotubes (CNTs) are branched onto the modified surfaces of three-dimensional (3D), steam-activated reduced graphene oxide (sRG-O) frameworks, prepared by self-assembly, steam activation, and microwave methods. The surface sites of 3D sRG-O are critical for controlling crystalline structure and deposition density of Fe3O4 nanoparticles through a microwave induced synthesis, as well as for providing a large surface area and conducting pathway. Simultaneously, the bamboo-like CNT branches are grown on the Fe3O4 nanoparticles acting as catalysts to stabilize and conductively connect 3D sRG-O/Fe interparticles for the enhanced rate and cyclic performances of LIB. Such a unique structure consisting of 1D nanostructure branched on the activated surface of 3D macroporous structure with decoration of OD nanoparticles provides high specific capacity of 1757 mAh g(-1) at 50 mA g(-1), good rate capability of 73.31% at 1000 mA g(-1), and gradual increase from 1490 to 2890 mAh g(-1) after 100 cycles. (C) 2017 Elsevier Ltd. All rights reserved.</P>

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