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.

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 Al₂O₃/CeO₂/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.

Population genetic structure of the Korean Pacific abalone Haliotis diversicolor supertexta inferred from microsatellite marker analysis

An, H.S.,Lee, J.W.,Hong, S.W. Pergamon Press ; Elsevier Science Ltd 2013 Biochemical systematics and ecology Vol.48 No.-

The Pacific abalone Haliotis diversicolor supertexta, of the family Haliotidae, is one of the most important shellfish species in eastern Asia. In Korea, it is intensively caught in Jeju Island, where it is highly appreciated as seafood. However, its natural population has declined drastically in the past several decades. To investigate its genetic characteristics for conservation and management purposes, the genetic variation in four populations from Jeju Island, Korea was analyzed using 20 microsatellite loci. All populations showed very high genetic diversity and a deficit of heterozygotes. The minor but significant genetic differentiations (both F<SUB>ST</SUB> and R<SUB>ST</SUB>) observed were mainly due to genetic differences between populations from Pyoson and other localities, suggesting that abalone may not be panmictic. The Pyoson abalone population showed a significant difference in allelic richness that could be related to harvesting intensity and stock enhancement activity. This result was also corroborated by an analysis of molecular variance (AMOVA). Overall, this report presents novel observations of the wild genetic population structure in H. diversicolor supertexta from Korea using microsatellite markers and provides critical information for supporting conservation strategies for this species, namely that the Pyoson abalone population should have a higher conservation priority due to its unique genetic characteristics.

Influence of laser wavelength on the laser induced breakdown spectroscopy measurement of thin CuIn_1-xGa_xSe₂ solar cell films

Kim, C.K.,In, J.H.,Lee, S.H.,Jeong, S. Pergamon Press ; Elsevier Science Ltd 2013 Spectrochimica acta. Part B, Atomic spectroscopy Vol.88 No.-

Laser induced breakdown spectroscopy (LIBS) measurement of thin CuIn<SUB>x</SUB>Ga<SUB>1-x</SUB>Se<SUB>2</SUB> (CIGS) films (1.2-1.9μm) with varying Ga to In ratios was carried out using the fundamental (1064nm) and second harmonic (532nm) wavelength Nd:YAG lasers (τ=5ns, spot diameter=150μm, top-hat profile) in air. The concentration ratios of Ga to In, x<SUB>Ga</SUB>=Ga/(Ga+In), of the CIGS samples ranged from 0.027 to 0.74 for which the band gap varied nearly proportionally to x<SUB>Ga</SUB> from 0.96 to 1.42. It was found that the LIBS signal of 1064nm (1.17eV) wavelength laser was significantly influenced by x<SUB>Ga</SUB>, whereas that of the 532nm (2.34eV) laser was consistent for all values of x<SUB>Ga</SUB>. The observed dependency of the LIBS signal intensity on the laser wavelength was attributed to the large difference of photon energy of the two wavelengths that changed the absorption of incident laser energy by the film. The 532nm wavelength was found to be advantageous for multi-shot analysis that enabled depth profile analysis of the thin CIGS films and for improving measurement precision by averaging the multi-shot LIBS spectra.

Nanomaterial-based biosensor as an emerging tool for biomedical applications.

Lee, Sang Hun,Sung, Jong Hwan,Park, Tai Hyun Pergamon Press [etc.] 2012 Annals of biomedical engineering Vol.40 No.6

<P>The combination of nanomaterials and biological sensing elements to selectively recognize chemical or biological molecules has resulted in the development of novel nanobiosensors. Nanobiosensors offer several important advantages over conventional biological procedures, and could have a significant impact on humankind. Hence, the momentum toward building miniaturized, reliable, sensitive, and selective sensing instruments has focused on combining nanomaterials with biomolecules for detection of a wide range of analytes. In this article, we present an overview of the various nanomaterial-based biosensors that utilize different biological recognition elements for biomedical applications. In this review, several types of nanomaterial-based biosensors along with their applications are discussed, including the latest developments in the field of nanobiosensors for biomedical applications.</P>

Gating of NMDA receptor-mediated hippocampal spike timing-dependent potentiation by mGluR5

Kwag, Jeehyun,Paulsen, Ole Pergamon Press 2012 NEUROPHARMACOLOGY - Vol.63 No.4

<P>Hippocampal long-term potentiation (LTP) is believed to be important for learning and memory. Experimentally, the pairing of precisely timed pre- and postsynaptic spikes within a time window of ∼10 ms can induce timing-dependent LTP (tLTP), but the requirements for induction of tLTP change with development: in young rodents single postsynaptic spikes are sufficient to induce tLTP, whereas postsynaptic burst firing appears to be required in the adult. However, hippocampal neurons <I>in vivo</I> show theta-modulated single spike activities also in older hippocampus. Here we investigated the conditions for single spike pairing to induce tLTP at older CA3–CA1 synapses. We found that the pairing of single pre- and postsynaptic spikes could induce tLTP in older hippocampus when the postsynaptic neuronal membrane was depolarized and the pairing frequency exceeded ∼4 Hz. The spike frequency requirement is postsynaptic, as tLTP could still be induced with presynaptic stimulation at 1 Hz as long as the postsynaptic spike frequency exceeded ∼4 Hz, suggesting that postsynaptic theta-frequency activity is required for the successful induction of tLTP at older CA3–CA1 synapses. The induction of tLTP was blocked by an NMDA receptor antagonist and by the selective mGluR5 blockers, MPEP and MTEP, whereas activation of mGluR1 and mGluR5 by DHPG relieved the postsynaptic spike frequency requirement for tLTP induction. These results suggest that activation of mGluR5 during single-spike pairing at older CA3–CA1 synapses gates NMDA receptor-dependent tLTP.</P>

New delay-partitioning approaches to stability criteria for uncertain neutral systems with time-varying delays

Kwon, O.M.,Park, M.J.,Park, J.H.,Lee, S.M.,Cha, E.J. Pergamon Press [etc.] 2012 Journal of the Franklin Institute Vol.349 No.9

In this paper, the problem of stability analysis for uncertain neutral systems with time-varying delays is considered. The parameter uncertainties are assumed to be norm-bounded. By use of new augmented Lyapunov functional and delay-partitioning techniques, delay-dependent stability criteria to guarantee the asymptotic stability are established in terms of linear matrix inequalities (LMIs), which can be solved easily by various efficient convex optimization algorithms. Four numerical examples are given to show the superiority of the proposed methods.

Use of electrosprayed Sophora flavescens natural-product nanoparticles for antimicrobial air filtration

Jung, J.H.,Lee, J.E.,Bae, G.N. Pergamon Press ; Elsevier Science Ltd 2013 Journal of aerosol science Vol.57 No.-

Previously, we demonstrated that electrospraying, driven by high-intensity electric fields, can be used to generate stable antimicrobial nanoparticles continuously from ethanolic extracts of natural plant products. In this study, we evaluated the performance of antimicrobial air filters made by these electrosprayed natural-product nanoparticles. As a natural antimicrobial suspension, an ethanolic extract of Sophora flavescens Ait. was sprayed in steady cone-jet mode using our specially designed electrospray system (Jung et al., 2011b). Natural-product nanoparticles with a bimodal size distribution were electrosprayed and deposited continuously onto the surfaces of air filters at various concentrations. The physical (filtration efficiency, pressure drop, and fiber morphology) and biological (antimicrobial efficacy against airborne Staphylococcus epidermidis) characteristics were evaluated. Consequently, although the filter pressure drop increased with the amount of nanoparticles on the filter, the antimicrobial activity was enhanced. Compared with the conventional nebulization process, the filters generated by electrospraying S. flavescens natural-product nanoparticles resulted in more effective removal of S. epidermidis bioaerosols. These results will facilitate the implementation of this new technology to control air quality and protect against hazardous airborne microorganisms.

Stability and stabilization for discrete-time systems with time-varying delays via augmented Lyapunov-Krasovskii functional

Kwon, O.M.,Park, M.J.,Park, J.H.,Lee, S.M.,Cha, E.J. Pergamon Press [etc.] 2013 Journal of the Franklin Institute Vol.350 No.3

This paper is concerned with the stability and stabilization problems for discrete-time systems with interval time-varying delays. By construction of an augmented Lyapunov-Krasovskii functional and utilization of zero equalities, improved delay-dependent criteria for asymptotic stability of the systems are derived in terms of linear matrix inequalities (LMIs). Based on the proposed stability criteria, a sufficient condition for designing feedback gains of time-delayed controllers which guarantee the stability of the concerned system is presented. Through three numerical examples, the effectiveness to enhance the feasible region of the proposed criteria is demonstrated.