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Simulation of Sintering for the Complex Ceramic Bodies by NASTRAN
Lee, Sang-Ki,Kim, Hyung-Jong,Lee, June-Gunn The Korean Ceramic Society 1999 The Korean journal of ceramics Vol.5 No.3
In a ceramic green body, some degree of nonuniformity in density always presents. These differences in green density will appear as nonuniform shrinkage after sintering takes place. For the complex ceramic bodies with various curves and angles, therefore, it is quite difficult to foresee the final dimensions precisely after sintering. This simulation study shows that, considering the sintering process as a thermal shrinkage phenomenon, the use of NASTRAN enables to predict the precise shape of a sintered body. Based on this result, 'the reverse engineering technique' has been developed that can unfold the exact dimensions of a green body to have the desired shape after sintering. This approach will provide a simple and useful tool for ceramic engineers to fabricate complicate bodies with tight dimensional tolerances.
Lee, Boeun,Lee, Hae Ri,Yim, Taeeun,Kim, Jong Hak,Lee, June Gunn,Chung, Kyung Yoon,Cho, Byung Won,Oh, Si Hyoung The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.6
<P>Herein, we evaluate the detailed insertion mechanism of aluminum ions into the Mo6S8 Chevrel phase in the 1-ethyl-3-methylimidazolium tetrachloroaluminate ionic liquid through combined structural and electrochemical characterization. This involves two-step two-phase insertion reactions, where the first and the second step account for 3/4 and 1/4 of the total reversible capacity, respectively. During the first step, aluminum ions occupy the inner ring sites in the Chevrel phase, forming AlMo6S8 with a higher activation energy for cation diffusion. Subsequently, Al4/3Mo6S8 emerges as a discharge product during the second step, where one aluminum ion fills one outer ring site in every three AlMo6S8 units. The diffusion coefficient for aluminum ions through the Chevrel phase was found much lower than that of lithium or magnesium ions, reflecting the difficulties in redistributing trivalent charge carried by each aluminum ion. (C) 2016 The Electrochemical Society. All rights reserved.</P>
Trends in Computational Materials Science Based on Density Functional Theory
Lee, June Gunn The Korean Ceramic Society 2016 한국세라믹학회지 Vol.53 No.2
This review deals with computational treatments of subatomic levels of matter based on density functional theory (DFT), and tries to identify several current trends, which are largely consequences of the ever-increasing power of computers, which has substantially extended the performance of conventional DFT beyond its original scope. This review mainly focuses on the conceptual outline, rather than on lines of equations, highlighting several examples of calculations for each topic. It should be noted that these issues are hardly new to leading groups in the field, but certainly are for materials people in general. It should also be noted that the on-going efforts will continue and lead to a larger system size, a longer time scale, a higher accuracy, and a better efficiency of calculation for years to come.
Enhancement of electrocatalytic activity of gold nanoparticles by sonochemical treatment
Lee, Yang-Hee,Kim, Gunn,Joe, Minwoong,Jang, Ji-Hoon,Kim, Juyeong,Lee, Kwang-Ryeol,Kwon, Young-Uk Royal Society of Chemistry 2010 Chemical communications Vol.46 No.31
<P>We demonstrate that gold nanoparticles can become catalytically active for the electrochemical hydrogen oxidation reaction by a sonication treatment. Experimental data and theoretical calculations indicate that the activity arises from the supercooled molten state of gold nanoparticles which are enriched with coordinatively unsaturated gold atoms.</P> <P>Graphic Abstract</P><P>Gold nanoparticles can become an active electrocatalyst for the oxidation of hydrogen by sonochemical treatment. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cc00950d'> </P>
1.5 V Sub-mW CMOS Interface Circuit for Capacitive Sensor Applications in Ubiquitous Sensor Networks
Sungsik Lee,Ahra Lee,Chang-Han Je,Myung-Lae Lee,Gunn Hwang,Chang-Auck Choi 한국전자통신연구원 2008 ETRI Journal Vol.30 No.5
In this paper, a low-power CMOS interface circuit is designed and demonstrated for capacitive sensor applications, which is implemented using a standard 0.35-μm CMOS logic technology. To achieve low-power performance, the low-voltage capacitance-to-pulse-width converter based on a self-reset operation at a supply voltage of 1.5 V is designed and incorporated into a new interface circuit. Moreover, the external pulse signal for the reset operation is made unnecessary by the employment of the self-reset operation. At a low supply voltage of 1.5 V, the new circuit requires a total power consumption of 0.47 mW with ultra-low power dissipation of 157 μW of the interfacecircuit core. These results demonstrate that the new interface circuit with self-reset operation successfully reduces power consumption. In addition, a prototype wireless sensor-module with the proposed circuit is successfully implemented for practical applications. Consequently, the new CMOS interface circuit can be used for the sensor applications in ubiquitous sensor networks, where low-power performance is essential.
Kim, Gunn,Lee, Sang Bong,Lee, Hoonkyung,Ihm, Jisoon IOP Pub 2007 Journal of Physics, Condensed Matter Vol.19 No.2
<P>Using the tight-binding method and the Landauer–Büttiker conductance formalism, we demonstrate that a multiply connected armchair carbon nanotube with mirror-reflection symmetry can sustain an electron current of the π-bonding orbital while suppressing that of the π-antibonding orbital over a certain energy range. Accordingly, the system behaves like an electron orbital valve and it may be used as a scanning tunnelling microscope to probe pairing symmetry in d-wave superconductors or even orbital ordering in solids which is believed to occur in some transition-metal oxides. </P>
Hyunsuk Lee,Sang Hyub Lee,Gunn Huh,Yeji Kim,허세범,Moonhaeng Hur,Minwoo Lee,Byeongyun Ahn 대한소화기내시경학회 2022 Clinical Endoscopy Vol.55 No.2
Common bile duct (CBD) stones are prevalent in 11% to 21% of patients with gallstones and can cause various clinicalmanifestations, from biliary colic to biliary sepsis. The treatment of choice is endoscopic retrograde cholangiopancreatography,but approximately 5% to 10% of CBD stones are difficult to remove using these conventional endoscopic methods. Althoughpercutaneous transhepatic cholangioscopy and lithotripsy can be used as an alternative, it can be technically demanding and riskyif the intrahepatic duct is not dilated. We report a case of a large CBD stone that was successfully removed using percutaneoustranscholecystic cholangioscopy.
Enhanced stability and activity of Pt–Y alloy catalysts for electrocatalytic oxygen reduction
Jong Yoo, Sung,Kim, Soo-Kil,Jeon, Tae-Yeol,Jun Hwang, Seung,Lee, June-Gunn,Lee, Seung-Cheol,Lee, Kug-Seung,Cho, Yong-Hun,Sung, Yung-Eun,Lim, Tae-Hoon Royal Society of Chemistry 2011 Chemical communications Vol.47 No.41
<P>We report Pt-based alloys with early transition metals. Significant electrocatalysis occurs during oxygen reduction reaction (ORR) at the Pt–Y alloy electrodes, and the extent depends on the alloy composition. The Pt–Y alloy electrode activity is related to the d-band center position, and the lattice strain and stability for oxygen reduction reaction.</P> <P>Graphic Abstract</P><P>The Pt–Y alloy electrode activity is related to the <I>d</I>-band center position/the lattice strain, and the stability is interpreted with correlation between the <I>d</I>-band fillings and heat of alloy formation. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1cc12448j'> </P>