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.

Characteristics of the East Asian summer monsoon in the South Sea of Korea during the Little Ice Age

Kong, G.S.,Kim, K.O.,Kim, S.P. Pergamon Press 2013 Quaternary international Vol.286 No.-

The sediment record of a drilled core, SSDP-103, and four AMS <SUP>14</SUP>C datings were used to generate oxygen and carbon isotope data over the last 2000 years of the benthic foraminifer Cibicides lobatulus in the South Sea of Korea. High sedimentation rates facilitated a decadal resolution throughout the study period. Significant periodicities of 316, 249, 144, and 88 years were observed in the δ<SUP>18</SUP>O record of the benthic foraminifera. Similar periodicities of 310, 220, 143, and 120 years were identified in the δ<SUP>13</SUP>C record. These periodicities were close to those of solar origin, which are related to changes in the oceanic and atmosphere circulation in East Asia. The three-point-smoothed δ<SUP>18</SUP>O curve of benthic foraminifera in the study area was closely correlated with the stalagmite δ<SUP>18</SUP>O record from Chinese caves for the last 2000 years, except during the dramatic cooling interval of the Little Ice Age (LIA). During the cooling period, the benthic foraminifera δ<SUP>18</SUP>O values significantly increased, while stalagmite δ<SUP>18</SUP>O values decreased. Such an inverse relationship during the LIA reflects synchronous strengthening of the East Asian summer monsoon (EASM) and weakening of the Indian summer monsoon (ISM). Under the present climatic system, an inverse relationship between these two Asian monsoons has frequently occurred when an El Nino event developed. The results suggest that late-Holocene cold events are associated with El Nino-like climatic patterns.

Increasing the thermoelectric power generated by composite films using chemically functionalized single-walled carbon nanotubes

Piao, M.,Na, J.,Choi, J.,Kim, J.,Kennedy, G.P.,Kim, G.,Roth, S.,Dettlaff-Weglikowska, U. Pergamon Press ; Elsevier Science Ltd 2013 Carbon Vol.62 No.-

We prepared and characterized flexible thermoelectric (TE) materials based on thin films of single-walled carbon nanotube (SWCNT) composites with polyvinylalcohol. While pristine SWCNTs incorporated in a polymer matrix generated a p-type TE material, chemical functionalization of SWCNTs by using polyethyleneimine produced an n-type TE material. TE modules made of both p- and n-type composite were fabricated to demonstrate TE voltage and power generation. A single p-n junction made of two composite strips containing 20wt.% of SWCNTs generated a high TE voltage of 92μV per 1K temperature gradient (ΔT). By combining five electrically connected p-n junctions an output voltage of 25mV was obtained upon the applying ΔT=50K. Furthermore, this module generated a power of 4.5nW when a load resistance matched the internal module resistance of 30kΩ. These promising results show the potential of TE energy conversion provided by the SWCNT composite films connected in scalable modules for applications that require light weight and mechanical flexibility.

Stability analysis of spatially interconnected discrete-time systems with random delays and structured uncertainties

Kim, B.-Y.,Kim, Y.-S.,Ahn, H.-S. Pergamon Press [etc.] 2013 Journal of the Franklin Institute Vol.350 No.7

In this paper, robust stability analysis of spatially interconnected systems with random delays as well as structured uncertainties in discrete-time domain is presented. The random delays are represented as a series of Markovian jumping parameters with some transition probability. A sufficient condition to guarantee well-posedness, stochastic stability, and H<SUB>~</SUB> performance of the spatially interconnected systems is established. Through numerical simulations, the validity of the proposed approach is illustrated.

Synthesis and magnetic characterization of a cubane-type Mn₄ cluster, housed in a sterically hindered carboxylate ligand pocket

Sivanesan, D.,Son, K.,Lee, H.J.,Park, K.T.,Jang, Z.,Suh, B.J.,Yoon, S. Pergamon Press 2013 Polyhedron Vol.50 No.1

The use of sterically hindered terphenyl-based carboxylate, <SUP>-</SUP>O<SUB>2</SUB>CAr<SUP>4F-Ph</SUP>, in manganese (II) chemistry has yielded a new cubane-type Mn<SUB>4</SUB> cluster, in which four Mn(II) sites have slightly distorted octahedral geometries with a distinctive O<SUB>6</SUB> donor atom sets. Based on the total energy calculations for magnetic states of the cluster using the LDA+U method, two kinds of magnetic exchange coupling interactions between Mn(II) sites are chosen to fit the measured magnetic properties, resulting in weak intra-molecular antiferromagnetic interactions (J=-1.91K, J'=-3.07K, and g=2.00).

Characterization of gaseous pollutants and PM_2.5 at fixed roadsides and along vehicle traveling routes in Bangkok Metropolitan Region

Kim Oanh, N.T.,Kongpran, J.,Hang, N.T.,Parkpian, P.,Hung, N.T.Q.,Lee, S.B.,Bae, G.N. Pergamon Press ; Elsevier [distribution] 2013 Atmospheric environment Vol.77 No.-

Traffic is a major source of air pollution in urban areas of developing countries that leads to high exposure risk of urban dwellers. This study comparatively investigated levels of fine particles (PM<SUB>2.5</SUB>), SO<SUB>2</SUB>, NO<SUB>2</SUB>, and BTEX (benzene, toluene, ethylbenzene and xylenes) at fixed roadsides and on traveling routes in congested urban and less congested suburban areas of Bangkok in 2010. The roadside air quality monitoring was done at two opposite sites across the selected roads. The traffic counting was made simultaneously in these roads and hourly flows of 8 different vehicle types were determined. Roadside PM<SUB>2.5</SUB> levels during dry season were high in both the city center and suburban area, significantly above the wet season, with 65-75% measurements exceeded 24 h Thailand ambient air quality standard of 50 μg m<SUP>-3</SUP>. Oppositely, roadside BTEX levels measured in the city center during wet season were higher than dry season and well above those in suburban area. Diurnal variations and the results of SPSS (Statistical Package for the Social Sciences) analysis showed associations between roadside pollutants levels and hourly traffic flows. The differences in pollution levels between 2 monitoring sites across a road were explained by road configurations and prevalent wind directions. On-route pollution levels were measured simultaneously both inside and outside selected vehicles (van, pickup), and on motorcycle. The on-route PM<SUB>2.5</SUB> levels along the urban route were higher during the dry season than wet season. PM<SUB>2.5</SUB> levels inside the vehicles were lower than outside whereas the opposite was observed for BTEX. BTEX were higher on more congested urban sub-routes with lower vehicle speeds. Higher pollution levels suggest a high risk of exposure.

Capillary oscillations at a circular orifice

Kim, H.J.,Fontelos, M.A.,Hwang, H.J. Pergamon Press ; Elsevier Science Ltd 2013 APPLIED MATHEMATICS LETTERS Vol.26 No.5

We compute the normal frequencies and normal modes for the oscillation of the free surface of a perfect incompressible fluid inside a semi-infinite container with a circular orifice. In doing that, a dual integral equation system involving the Bessel functions must be solved. We discuss the cases where the contact line between the free surface and the container is pinned as well as the case where it moves with a constant contact angle.

Effects of compression ratio on performance and emission characteristics of heavy-duty SI engine fuelled with HCNG

Lim, G.,Lee, S.,Park, C.,Choi, Y.,Kim, C. Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.11

The wide range of hydrogen's flammable limits enables ultra-lean combustion. A lean burn reduces the combustion temperature, increases thermal efficiency, and reduces knock, which is a serious problem in a spark ignition (SI) engine. The anti-knock improvement from hydrogen addition makes it feasible to increase the compression ratio (CR) and further improve the thermal efficiency. Herein, the effects of the CR on performance and emission characteristics were investigated using an 11-L heavy-duty SI engine fuelled with HCNG30 (CNG 70 vol%, hydrogen 30 vol%) and CNG. These fuels were used to operate an engine with CRs of 10.5 and 11.5. The results showed that thermal efficiency improved with an increased CR, which significantly decreased CO<SUB>2</SUB> emission. On the other hand, the NO<SUB>x</SUB> emission was largely increased. Nevertheless, for HCNG30, a CR of 11.5 improved thermal efficiency by 6.5% and decreased NO<SUB>x</SUB> emission by over 75%, as compared to a conventional CNG engine.