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        • SCISCIESCOPUS

          The effect of microstructural inhomogeneity on the growth paths of surface-cracks in copper processed by equal channel angular pressing

          Goto, M.,Ando, Y.,Han, S.Z.,Kim, S.S.,Kawagoishi, N.,Euh, K. Pergamon Press ; Elsevier Science Ltd 2010 Engineering fracture mechanics Vol.77 No.11

          The growth behavior of cracks is monitored on specimens of ultrafine grained copper produced by equal channel angular pressing. Temporary retardation of crack growth under low stress amplitudes occurs when the crack length reaches about 0.1mm, but there is no similar retardation at high stress amplitudes. Dependent on stress amplitude, different crack growth path morphologies develop. Analysis of the fracture surfaces is conducted by scanning electron microscopy, showing planer, granular and striated surfaces. The physical background of growth path and fracture surface formation is discussed by considering crack growth mechanism and microstructural inhomogeneity.

        • SCISCIESCOPUS

          An efficient decal transfer method using a roll-press to fabricate membrane electrode assemblies for direct methanol fuel cells

          Mehmood, A.,Ha, H.Y. Pergamon Press ; Elsevier Science Ltd 2012 International journal of hydrogen energy Vol.37 No.23

          This study has focused on the development of a roll-press based decal transfer method to fabricate membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs). This method exhibits an outstanding transfer rate of catalyst layers from substrates to the membrane, despite hot-pressing at a considerably lower pressure and for a much shorter duration than the flat-press based conventional decal method. The MEA produced by a roll-press (R-MEA) delivers an excellent single-cell performance with power densities more than 30% higher than that fabricated using a flat-press (F-MEA). The new method considerably improves catalyst active sites in both electrodes and renders a high cathode porosity. The superior pore structure of the cathode makes the R-MEA more efficient in terms of performance and operation stability under lower air stoichiometries. Moreover, MEAs can be prepared in a continuous mode using this new method due to the unique design of the roll-press. All these advantages demonstrate the superiority of this method over the conventional flat-press decal method and make it suitable for use in the commercial manufacturing of MEAs for direct methanol fuel cells.

        • Fabrications and evaluations of hydrogen permeation on Al<sub>2</sub>O<sub>3</sub>/CeO<sub>2</sub>/graphene (ACG) composites membrane by Hot Press Sintering (HPS)

          Lee, N.R.,Lee, S.S.,Kim, K.I.,Kim, W.G.,Ju, H.,Kim, D.M.,Hong, T.W. Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.18

          Ceramic membrane has high permeation rate of hydrogen and chemical stability. Al<SUB>2</SUB>O<SUB>3</SUB> indicates stable at high temperature and a relatively large surface area. In addition, Al<SUB>2</SUB>O<SUB>3</SUB> of porous is used as hydrogen separation membranes support, because of the high hydrogen permeability based on Knudsen diffusion mechanism. In this work, metal alkoxides as starting materials was used Aluminum isopropoxide powder. Then CeO<SUB>2</SUB> as catalyst at the partial oxidation and Graphene Oxide as electrical conductivity are added, Al<SUB>2</SUB>O<SUB>3</SUB>-CeO<SUB>2</SUB>-Graphene oxide (ACG) composites are synthesized by sol-gel process. ACG membrane was fabricated type of disk by Hot Press Sintering. A synthesized ACG composite material was characterized by EDS, SEM, TG/DTA, XRD, BET. The hydrogen permeation property of ACG membrane was measured by Sievert's type hydrogen permeation membrane equipment. The hydrogen permeability of ACG membranes was examined at RT-673 K under increasing pressure. Results, hydrogen permeability was obtained to 2.62 x 10<SUP>-7</SUP> mol/ms Pa<SUP>½</SUP> at 673 K under 0.3 MPa.

        • Flexible photoanodes of TiO<sub>2</sub> particles and metallic single-walled carbon nanotubes for flexible dye-sensitized solar cells

          Lee, J.,Kang, H.,Hwang, J.Y.,Kim, S.W.,Baik, S. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.79 No.-

          Recent advance in flexible electronics demands development of flexible energy sources. Of particular interests are flexible dye-sensitized solar cells (DSCs). However, a brittle nature of TiO<SUB>2</SUB> materials is one of hurdles to realize flexible DSCs. Here we synthesized flexible photoanodes of TiO<SUB>2</SUB> particles and single-walled carbon nanotubes (SWNTs). Metallic SWNTs provided a greater photovoltaic conversion efficiency than semiconducting SWNTs due to the more efficient electron transport. The metallic SWNTs also constructed effective mechanical network among TiO<SUB>2</SUB> particles providing flexibility and durability. The photoanode was transferred on an indium tin oxide (ITO)-coated polyethylene terephthalate film and characterized for front-illuminated DSCs under the AM 1.5 simulated sunlight. There was only a small decrease in photovoltaic conversion efficiency with bending which was primarily caused by cracking of the ITO layer. Due to this limitation, the TiO<SUB>2</SUB>-metallic SWNT photoanode was transferred on a Ti foil and went through up to 1000 bending cycles. The cycled photoanode was assembled for back-illuminated DSCs due to the non-transparent Ti foil. There was no decrease in photovoltaic conversion efficiency even after 1000 bending cycles demonstrating excellent flexibility and durability.

        • SCISCIESCOPUS

          Hydrogen-rich syngas production through coal and charcoal gasification using microwave steam and air plasma torch

          Yoon, S.J.,Lee, J.G. Pergamon Press ; Elsevier Science Ltd 2012 International journal of hydrogen energy Vol.37 No.22

          In the present study, microwave plasma gasification of two kinds of coal and one kind of charcoal was performed with various O<SUB>2</SUB>/fuel ratios of 0-0.544. Plasma-forming gases used under 5 kW microwave plasma power were steam and air. The changes in the syngas composition and gasification efficiency in relation to the location of the coal supply to the reactor were also compared. As the O<SUB>2</SUB>/fuel ratio was increased, the H<SUB>2</SUB> and CH<SUB>4</SUB> contents in the syngas decreased, and CO and CO<SUB>2</SUB> increased. When steam plasma was used to gasify the fuel with the O<SUB>2</SUB>/fuel ratio being zero, it was possible to produce syngas with a high content of hydrogen in excess of 60% with an H<SUB>2</SUB>/CO ratio greater than 3. Depending on the O<SUB>2</SUB>/fuel ratio, the composition of the syngas varied widely, and the H<SUB>2</SUB>/CO ratio necessary for using the syngas to produce synthetic fuel could be adjusted by changing the O<SUB>2</SUB>/fuel ratio alone. Carbon conversion increased as the O<SUB>2</SUB>/fuel ratio was increased, and cold gas efficiency was maximized when the O<SUB>2</SUB>/fuel ratio was 0.272. Charcoal with high carbon and fixed carbon content had a lower carbon conversion and cold gas efficiency than the coals used in this study.

        • Stand-off laser-induced breakdown spectroscopy of aluminum and geochemical reference materials at pressure below 1torr

          Lee, K.J.,Choi, S.J.,Yoh, J.J. Pergamon Press ; Elsevier Science Ltd 2014 Spectrochimica acta. Part B, Atomic spectroscopy Vol.101 No.-

          Laser-induced breakdown spectroscopy (LIBS) is an atomic emission spectroscopy that utilizes a highly irradiated pulse laser focused on the target surface to produce plasma. We obtain spectroscopic information from the microplasma and determine the chemical composition of the sample based on its elemental and molecular emission peaks. We develop a stand-off LIBS system to analyze the effect of the remote sensing of aluminum and various geochemical reference materials at pressures below 1torr. Using a commercial 4 inch refracting telescope, our stand-off LIBS system is configured at a distance of 7.2m from the four United States Geological Survey (USGS) geochemical samples that include granodiorite, quartz latite, shale-cody, and diabase, which are selected for planetary exploration. Prepared samples were mixed with a paraffin binder containing only hydrogen and carbon, and were pelletized for experimental convenience. The aluminum plate sample is considered as a reference prior to using the geochemical samples in order to understand the influence of a low pressure condition on the resulting LIBS signal. A Q-switched Nd:YAG laser operating at 1064nm and pulsed at 10Hz with 21.7 to 48.5mJ/pulse was used to obtain signals, which showed that the geochemical samples were successfully detected by the present stand-off detection scheme. A low pressure condition generally results in a decrease of the signal intensity, while the signal to noise ratio can vary according to the samples and elements of various types. We successfully identified the signals at below 1torr with stand-off detection by a tightly focused light detection and by using a relatively larger aperture telescope. The stand-off LIBS detection at low pressure is promising for potential detection of the minor elements at pressures below 1torr.

        • Vinylene carbonate and tris(trimethylsilyl) phosphite hybrid additives to improve the electrochemical performance of spinel lithium manganese oxide/graphite cells at 60<sup>o</sup>C

          Koo, B.,Lee, J.,Lee, Y.,Kim, J.K.,Choi, N.S. Pergamon Press 2015 ELECTROCHIMICA ACTA Vol.173 No.-

          The organophosphorus compounds tris(trimethylsilyl) phosphite (TMSP) and vinylene carbonate (VC) have been considered for use as functional additives to improve the electrochemical performance of Li<SUB>1.1</SUB>Mn<SUB>1.86</SUB>Mg<SUB>0.04</SUB>O<SUB>4</SUB> (LMO)/graphite full cells. Our investigation reveals that the combination of VC and TMSP as additives enhances the cycling properties and storage performance of full cells at 60<SUP>o</SUP>C. The unique functions of the TMSP additive in the VC electrolyte are investigated via ex situ X-ray photoelectron spectroscopy (XPS) and <SUP>19</SUP>F nuclear magnetic resonance (NMR) measurements. The TMSP additive effectively eliminates trace water and hydrogen fluoride (HF) and produces a protective film on the LMO cathode that alleviates manganese dissolution at 60<SUP>o</SUP>C.

        • Optimization of hybrid-type instrumentation for Pu accountancy of U/TRU ingot in pyroprocessing

          Seo, H.,Won, B.H.,Ahn, S.K.,Lee, S.K.,Park, S.H.,Park, G.I.,Menlove, S.H. Pergamon Press 2016 Applied radiation and isotopes Vol.108 No.-

          One of the final products of pyroprocessing for spent nuclear fuel recycling is a U/TRU ingot consisting of rare earth (RE), uranium (U), and transuranic (TRU) elements. The amounts of nuclear materials in a U/TRU ingot must be measured as precisely as possible in order to secure the safeguardability of a pyroprocessing facility, as it contains the most amount of Pu among spent nuclear fuels. In this paper, we propose a new nuclear material accountancy method for measurement of Pu mass in a U/TRU ingot. This is a hybrid system combining two techniques, based on measurement of neutrons from both (1) fast- and (2) thermal-neutron-induced fission events. In technique #1, the change in the average neutron energy is a signature that is determined using the so-called ring ratio method, according to which two detector rings are positioned close to and far from the sample, respectively, to measure the increase of the average neutron energy due to the increased number of fast-neutron-induced fission events and, in turn, the Pu mass in the ingot. We call this technique, fast-neutron energy multiplication (FNEM). In technique #2, which is well known as Passive Neutron Albedo Reactivity (PNAR), a neutron population's changes resulting from thermal-neutron-induced fission events due to the presence or absence of a cadmium (Cd) liner in the sample's cavity wall, and reflected in the Cd ratio, is the signature that is measured. In the present study, it was considered that the use of a hybrid, FNEMxPNAR technique would significantly enhance the signature of a Pu mass. Therefore, the performance of such a system was investigated for different detector parameters in order to determine the optimal geometry. The performance was additionally evaluated by MCNP6 Monte Carlo simulations for different U/TRU compositions reflecting different burnups (BU), initial enrichments (IE), and cooling times (CT) to estimate its performance in real situations.

        • SCISCIESCOPUS

          Mechanics of stretchable electronics on balloon catheter under extreme deformation

          Su, Y.,Liu, Z.,Wang, S.,Ghaffari, R.,Kim, D.H.,Hwang, K.C.,Rogers, J.A.,Huang, Y. Pergamon Press ; Elsevier Science Ltd 2014 International journal of solids and structures Vol.51 No.7

          Stretchable electronics has been applied to balloon catheters for high-efficacy ablation, with tactile sensing integrated on the surface, to establish full and conformal contact with the endocardial surface for elimination of the heart sink caused by blood flow around their surfaces. The balloon of the catheter folds into uniform 'clover' patterns driven by the pressure mismatch inside (~vacuum) and outside of the balloon (pressure ~1atm). The balloon catheter, on which microelectrodes and interconnects are printed, undergoes extreme mechanical deformation during its inflation and deflation. An analytic solution is obtained for balloon catheter inflation and deflation, which gives analytically the distribution of curvatures and the maximum strain in the microelectrodes and interconnects. The analytic solution is validated by the finite element analysis. It also accounts for the effect of inflated radius, and is very useful to the optimal design of balloon catheter.

        • SCISCIESCOPUS

          Enhanced degradation of n-MOSFETs with high-k/metal gate stacks under channel hot-carrier/gate-induced drain leakage alternating stress

          Kim, D.,Lee, S.,Kim, C.,Lee, C.,Park, J.,Kang, B. Pergamon Press 2012 Microelectronics and reliability Vol.52 No.9

          Enhanced degradation of n-MOSFETs with high-k/metal gate stacks under CHC/GIDL alternating stress is investigated. CHC stress generates negative oxide charges while GIDL stress generates positive oxide charges in the gate oxide near drain region. Theses oxide charges degrade device reliability, and degradation is enhanced when CHC stress and GIDL stress are applied alternatively. The degradation under CHC/GIDL alternating stress is due to the neutral traps and interface traps, and increases with the increase in frequency.

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