Orbital hybridization mechanism for the enhanced photoluminescence in edge-functionalized sp² 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>

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.

Effects of the degree of polymerization on the structure of sodium silicate and aluminosilicate glasses and melts: An ¹⁷O NMR study

Lee, S.K.,Stebbins, J.F. Pergamon Press ; Elsevier Science Ltd 2009 Geochimica et cosmochimica acta Vol.73 No.4

Revealing the atomic structure and disorder in oxide glasses, including sodium silicates and aluminosilicates, with varying degrees of polymerization, is a challenging problem in high-temperature geochemistry as well as glass science. Here, we report <SUP>17</SUP>O MAS and 3QMAS NMR spectra for binary sodium silicate and ternary sodium aluminosilicate glasses with varying degrees of polymerization (Na<SUB>2</SUB>O/SiO<SUB>2</SUB> ratio and Na<SUB>2</SUB>O/Al<SUB>2</SUB>O<SUB>3</SUB> ratio), revealing in detail the extent of disorder (network connectivity and topological disorder) and variations of NMR parameters with the glass composition. In binary sodium silicate glasses [Na<SUB>2</SUB>O-k(SiO<SUB>2</SUB>)], the fraction of non-bridging oxygens (NBOs, Na-O-Si) increases with the Na<SUB>2</SUB>O/SiO<SUB>2</SUB> ratio (k), as predicted from the composition. The <SUP>17</SUP>O isotropic chemical shifts (<SUP>17</SUP>O δ<SUB>iso</SUB>) for both bridging oxygen (BO) and NBO increase by about 10-15ppm with the SiO<SUB>2</SUB> content (for k=1-3). The quadrupolar coupling products of BOs and NBOs also increase with the SiO<SUB>2</SUB> content. These trends suggest that both NBOs and BOs strongly interact with Na; therefore, the Na distributions around BOs and NBOs are likely to be relatively homogenous for the glass compositions studied here, placing some qualitative limits on the extent of segregation of alkali channels from silica-enriched regions as suggested by modified random-network models. The peak width (in the isotropic dimension) and thus bond angle and length distributions of Si-O-Si and Na-O-Si increase with the SiO<SUB>2</SUB> content, indicating an increase in the topological disorder with the degree of polymerization. In the ternary aluminosilicate glasses [Na<SUB>2</SUB>O]<SUB>x</SUB>[Al<SUB>2</SUB>O<SUB>3</SUB>]<SUB>1-x</SUB>SiO<SUB>2</SUB>, the NBO fraction decreases while the Al-O-Si and Al-O-Al fractions apparently increase with increasing Al<SUB>2</SUB>O<SUB>3</SUB> content. The variation of oxygen cluster populations suggests that deviation from ''Al avoidance'' is more apparent near the charge-balanced join (Na/Al=1). The Si-O-Si fraction, which is closely related to the activity coefficient of silica, would decrease with increasing Al<SUB>2</SUB>O<SUB>3</SUB> content at a constant mole fraction of SiO<SUB>2</SUB>. Therefore, the activity of silica may decrease from depolymerized binary silicates to fully polymerized sodium aluminosilicate glasses at a constant mole fraction of SiO<SUB>2</SUB>.

The present status and analysis of Science & Technology Information (STI) service policy in Korea

Yun-Seok, L.,jae-sung, K. JAI Press ; Elsevier Science Ltd 2009 Government information quarterly Vol.26 No.3

National Science & Technology Information (STI) infrastructure of Korea has been independently developed as a decentralized system within the government ministry. In order to effectively establish the national STI infrastructure, it is essential to create a networked and integrated system in the domestic and foreign information infrastructure. This study aims to analyze current national STI infrastructure and to suggest specific ways in which domestic and foreign STI infrastructure may be utilized.

Design and performance test of a multi-channel diffusion charger for real-time measurements of submicron aerosol particles having a unimodal log-normal size distribution

Park, K.-T.,Park, D.,Lee, S.-G.,Hwang, J. Pergamon Press ; Elsevier Science Ltd 2009 Journal of aerosol science Vol.40 No.10

It is important to develop a simple and fast method for measuring the sizes of submicron particles in both laboratories and fields. In our previous studies, Park, An, and Hwang [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430] and Park, Kim, An, and Hwang [(2007). Real-time measurement of submicron aerosol particles having a log-normal size distribution by simultaneously using unipolar diffusion charger and unipolar field charger. Journal of Aerosol Science, 38, 1240-245], we introduced methodologies that our lab made unipolar charger could lead to detection times of under 5s in conjunction with an electrometer and a condensation particle counter (CPC), and under 3s with two electrometers. However, both methodologies require an appropriate assumption of the geometric standard deviation of particle sizes. In this paper, we introduce a methodology for determining the geometric standard deviation of particle sizes as well as the geometric mean diameter and the total number concentration of particles. For this purpose, a diffusion charger that consisted of discharge zone, mixing and charging zone, and three flow channels for obtaining three different residence times and average charges of particles in the channels, was designed and tested. For determining the average particle charge, various methods including theoretical calculations and the tandem differential mobility analyzer (TDMA) method were used. The results obtained from the different methods agreed well with each other. To compare the size distribution with the data that were measured through a scanning mobility particle sizer (SMPS), sodium chloride (NaCl) particles were used. The estimated results by using a data inversion algorithm were less than those measured by SMPS by around 22% for the total number concentration and 10% for both the geometric mean diameter and the geometric standard deviation. Furthermore, the detection time was under 3s.

Real-time measurement of submicron aerosol particles having a log-normal size distribution by simultaneously using unipolar diffusion charger and unipolar field charger

Park, D.,Kim, S.,An, M.,Hwang, J. Pergamon Press ; Elsevier Science Ltd 2007 Journal of aerosol science Vol.38 No.12

Recently, Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430] have introduced a methodology for performing simple and fast measurements of submicron aerosol particles having a log-normal size distribution, using a unipolar diffusion charger, an electrometer, and a condensation particle counter (CPC). The methodology can be applied to particles of 30-700nm and requires an assumption of their geometric standard deviation in size. In this paper we propose a much cheaper but faster method which involves substituting a unipolar field charger and another electrometer for the CPC. With the data obtained using this dual-charger system, we developed a data inversion algorithm and estimated the particle size distribution by minimizing the differences between the measured aerosol currents and the calculated values. To compare the size distribution with the data measured using a scanning mobility particle sizer (SMPS), sodium chloride (NaCl) particles smaller than 0.1μm in diameter, and dioctyl sebacate (DOS) particles with a diameter of 0.1-0.7μm, were used. The estimated results for the NaCl and DOS particles were within 10% of the data measured with the SMPS, while a 33% deviation from the SMPS results was obtained in Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430]. Furthermore, the detection time obtained with the use of our dual-charger system was faster (<3s) than the 5s obtained by Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430].

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.

Properties of solid wood and laminated wood lumber manufactured by cold pressing and heat treatment

Kwon, J.H.,Shin, R.H.,Ayrilmis, N.,Han, T.H. Scientific and Technical Press ; Elsevier Science 2014 Materials & design Vol.62 No.-

Physical, mechanical, and morphological properties of solid wood lumbers which were cold pressed in a press and then heat treated in a kiln. Two different kinds of domestic thinning small-diameter softwood (Ginko biloba L.) and hardwood (Tilia amurensis Rupr.) were used in this study. First 50mm thick lumbers were cold pressed until 35mm (30% of control lumber) using a stopper for 5min. Then the cold pressed lumbers were heat treated in an electric kiln at 180<SUP>o</SUP>C for 6, 12, 24, or 48h. To increase the utilizability of woods, the LVLs were produced from 4mm thick veneers prepared from the heat treated lumbers using a veneer saw. Each LVL sample consisted of 5 layers which were subsequently 48h-, 24h-, 12h-, and 6h-treated veneers and untreated veneer (from top layer to bottom layer). The shrinkage rates of softwood and hardwood were considerably decreased with increasing temperature. The mechanical properties of heat treated samples were better than those of unpressed control samples. The bending strength and modulus of elasticity of the LVLs manufactured from cold pressed and then heat treated lumbers were slightly lower than those of untreated woods. The colour values obtained from the heat treated wood samples showed a clear effect of the temperature on the colour changes.

Genome-wide analysis and molecular characterization of heat shock transcription factor family in Glycine max.

Chung, Eunsook,Kim, Kyoung-Mi,Lee, Jai-Heon Science press ; Elsevier 2013 Journal of genetics and genomics Vol.40 No.3

<P>Heat shock transcription factors (Hsfs) play an essential role on the increased tolerance against heat stress by regulating the expression of heat-responsive genes. In this study, a genome-wide analysis was performed to identify all of the soybean (Glycine max) GmHsf genes based on the latest soybean genome sequence. Chromosomal location, protein domain, motif organization, and phylogenetic relationships of 26 non-redundant GmHsf genes were analyzed compared with AtHsfs (Arabidopsis thaliana Hsfs). According to their structural features, the predicted members were divided into the previously defined classes A-C, as described for AtHsfs. Transcript levels and subcellular localization of five GmHsfs responsive to abiotic stresses were analyzed by real-time RT-PCR. These results provide a fundamental clue for understanding the complexity of the soybean GmHsf gene family and cloning the functional genes in future studies.</P>

Production of transgenic Korean native cattle expressing enhanced green fluorescent protein using a FIV-based lentiviral vector injected into MII oocytes.

Xu, Yong-Nan,Uhm, Sang-Jun,Koo, Bon-Chul,Kwon, Mo-Sun,Roh, Ji-Yeol,Yang, Jung-Seok,Choi, Hyun-Yong,Heo, Young-Tae,Cui, Xiang-Shun,Yoon, Joon-Ho,Ko, Dae-Hwan,Kim, Teoan,Kim, Nam-Hyung Science press ; Elsevier 2013 Journal of genetics and genomics Vol.40 No.1

<P>The potential benefits of generating and using transgenic cattle range from improvements in agriculture to the production of large quantities of pharmaceutically relevant proteins. Previous studies have attempted to produce transgenic cattle and other livestock by pronuclear injection and somatic cell nuclear transfer, but these approaches have been largely ineffective; however, a third approach, lentivirus-mediated transgenesis, has successfully produced transgenic livestock. In this study, we generated transgenic (TG) Korean native cattle using perivitelline space injection of viral vectors, which expressed enhanced green fluorescent protein (EGFP) systemically. Two different types of lentiviral vectors derived from feline immunodeficiency virus (FIV) and human immunodeficiency virus (HIV) carrying EGFP were injected into the perivitelline space of MII oocytes. EGFP expression at 8-cell stage was significantly higher in the FIV group compared to the HIV group (47.5%2.2% v.s. 22.9%2.9%). Eight-cell embryos that expressed EGFP were cultured into blastocysts and then transferred into 40 heifers. Ten heifers were successfully impregnated and delivered 10 healthy calves. All of these calves expressed EGFP as detected by in?vivo imaging, PCR and Southern blotting. In addition, we established an EGFP-expressing cell line from TG calves, which was followed by nuclear transfer (NT). Recloned 8-cell embryos also expressed EGFP, and there were no differences in the rates of fusion, cleavage and development between cells derived from TG and non-TG calves, which were subsequently used for NT. These results illustrate that FIV-based lentiviruses are useful for the production of TG cattle. Moreover, our established EGFP cell line can be used for additional studies that involve induced pluripotent stem cells.</P>