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GaN Quantum Dots: Physics and Applications
Le si Dang,B. Daudin,C. Adelmann,E. Martinez,E. Monroy,G. Fishman,H. Mariette,J. Simon,J. L. Rouviere,N. Pelekanos,조용훈 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.III
Recent works by our group on hexagonal and cubic GaN/AlN quantum dots grown by molecular beam epitaxy are reviewed. It is shown that the growth of GaN on AlN can occur either in a layer-by-layer mode to form quantum wells or in the Stranski-Krastanow mode to form self-assembled quantum dots. High resolution transmission electron microscopy reveals that quantum dots are truncated pyramids (typically 3 nm high and 15 nm wide), nucleating on top of a wetting layer. The existence of internal electric fields of 7 MV/cm in hexagonal quantum dots is evidenced by observations of various physical effects related to the quantum confined Stark effect, {\it e.g.} energy redshift of the interband transition, decrease of its oscillator strength, or enhancement of the exciton interaction with LO phonons. Prospects for UV and near-IR applications, using interband and intersubband transitions of GaN/AlN quantum dots, respectively, will be discussed also in this presentation.
CO and CO2 Methanation Over Supported Cobalt Catalysts
Le, T. A.,Kim, M. S.,Lee, S. H.,Park, E. D. Baltzer Science Publishers 2017 Topics in catalysis Vol.60 No.9
<P>CO and CO2 methanation was investigated over cobalt catalysts supported on different supports such as gamma-Al2O3, SiO2, TiO2, CeO2, and ZrO2. Among them, the cobalt catalyst supported on the high-surface-area CeO2 was determined to be the most active for both CO and CO2 methanation. These catalytic activities increased with increasing surface area of CeO2. To increase the specific catalytic activity for CO and CO2 methanation, various Co-CeO2 catalysts with different cobalt contents were prepared with co-precipitation method. The optimum cobalt content was determined for both reactions. The prepared catalysts were characterized with N-2 physisorption, temperature-programmed reduction with H-2, pulsed-chemisorption of CO2, temperature-programmed desorption of CO2, and X-ray diffraction. The high cobalt dispersion and strong CO2 adsorption appeared to be responsible for the high catalytic activity for CO and CO2 methanation, respectively. This Co-CeO2 also showed the stable catalytic activity even after an exposure to high-temperature reaction conditions.</P>
Jang, H. H.,Ryu, S. H.,Le, T. K.,Doan, T. T.,Nguyen, T. H.,Park, K. D.,Yim, D. E.,Kim, D. H.,Kang, C. K.,Ahn, T. Springer Science + Business Media 2017 Biotechnology letters Vol.39 No.1
<P>A highly efficient synthesis of 5'-OH omeprazole sulfide was developed using CYP102A1 from Bacillus megaterium as a biocatalyst.</P>
SVCT-2 in breast cancer acts as an indicator for L-ascorbate treatment
Hong, S-W,Lee, S-H,Moon, J-H,Hwang, J J,Kim, D E,Ko, E,Kim, H-S,Cho, I J,Kang, J S,Kim, D J,Kim, J-E,Shin, J-S,Jung, D-J,Jeong, Y-J,Cho, B-J,Kim, T-W,Lee, J S,Kang, J-S,Hwang, Y-I,Noh, D-Y,Jin, D-H,Le Macmillan Publishers Limited 2013 Oncogene Vol.32 No.12
L-ascorbate (L-ascorbic acid, vitamin C) clearly has an inhibitory effect on cancer cells. However, the mechanism underlying differential sensitivity of cancer cells from same tissue to L-ascorbate is yet to be clarified. Here, we demonstrate that L-ascorbate has a selective killing effect, which is influenced by sodium-dependent vitamin C transporter 2 (SVCT-2) in human breast cancer cells. Treatment of human breast cancer cells with L-ascorbate differentially induced cell death, dependent on the SVCT-2 protein level. Moreover, knockdown of endogenous SVCT-2 via RNA interference in breast cancer cells expressing high levels of the protein induced resistance to L-ascorbate treatment, whereas transfection with SVCT-2 expression plasmids led to enhanced L-ascorbate chemosensitivity. Surprisingly, tumor regression by L-ascorbate administration in mice bearing tumor cell xenograft also corresponded to the SVCT-2 protein level. Interestingly, SVCT-2 expression was absent or weak in normal tissues, but strongly detected in tumor samples obtained from breast cancer patients. In addition, enhanced chemosensitivity to L-ascorbate occurred as a result of caspase-independent autophagy, which was mediated by beclin-1 and LC3 II. In addition, treatment with N-acetyl-L-cysteine, a reactive oxygen species (ROS) scavenger, suppressed the induction of beclin-1 and LC3 II, implying that the differential SVCT-2 protein-dependent L-ascorbate uptake was attributable to intracellular ROS induced by L-ascorbate, subsequently leading to autophagy. These results suggest that functional SVCT-2 sensitizes breast cancer cells to autophagic damage by increasing the L-ascorbate concentration and intracellular ROS production and furthermore, SVCT-2 in breast cancer may act as an indicator for commencing L-ascorbate treatment.
H. Ashassi-Sorkhabi,E. Asghari, P. La’le Badakhshan 한국물리학회 2014 Current Applied Physics Vol.14 No.2
Nanostructured manganese oxide was produced by potentiostatic and cyclic voltammetric deposition techniques from aqueous KMnO4 solutions. Scanning electron microscopy (SEM) and X-ray diffraction were used to study the morphology and crystal structure of the deposited films. The electrochemical properties of deposited films, that obtained by two techniques, were investigated via performing the cyclic voltammetric tests. The results showed the higher specific capacitances of the nanostructured manganese oxide electrodes which have been produced via cyclic voltammetric deposition. The good retention was obtained for all synthesized electrode materials.
Inhibitor effects on molecular beacon-based mercury assays for tuning of detection range
Le, V.S.,Jeong, J.E.,Kim, B.,Lee, J.,Kyhm, K.,Woo, H.Y. Elsevier Sequoia 2017 Sensors and actuators. B Chemical Vol.240 No.-
A series of inhibitors were incorporated to modulate the detection range of mercury assay. A single-strand DNA-based mercury probe (ssDNA-Hg) containing 5 thymine (T) bases at both termini, which forms a hairpin structure in the presence of mercuric (Hg<SUP>2+</SUP>) ions via the T...Hg<SUP>2+</SUP>...T interaction, was designed. Although many previous studies focused on mercury detection to improve the sensitivity and selectivity, few studies have been reported to tune the detection range to cover a wide range of target concentrations in different environments. In the present study, a new Hg<SUP>2+</SUP> detection scheme was designed to extend, narrow and shift the range of mercury detection using inhibitors. The complementary DNA (ssDNA-C) and cationic conjugated polyelectrolyte (CPE) induced a shift or broadening of the spectral response range by functioning as an allosteric inhibitor. Iodide and cyanide ions worked as efficient depletants, adjusting the binding constant of ssDNA-Hg and Hg<SUP>2+</SUP> (1.1x10<SUP>7</SUP>M<SUP>-1</SUP>) by ~10 times (up to ~1.4x10<SUP>6</SUP>M<SUP>-1</SUP>) in the presence of I<SUP>-</SUP> or CN<SUP>-</SUP> ions, resulting in a large shift in the detection range according to [I<SUP>-</SUP>] or [CN<SUP>-</SUP>] with a sharp titration curve via a sequestration mechanism. Similar Hg<SUP>2+</SUP> detection range shift was successfully demonstrated using same series of inhibitors in real samples such as Han River and tap water. This study suggests that the binding affinity of probe can be tuned toward a target and the resulting detection response range can be controlled using a range of inhibitors.
Vu, H.C.,Dwivedi, A.D.,Le, T.T.,Seo, S.H.,Kim, E.J.,Chang, Y.S. Elsevier 2017 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.307 No.-
Graphene oxide has been utilized effectively for the adsorption of heavy metals. Incorporation of graphene oxide with magnetite nanoparticles through co-precipitation enhances separation of a newly designed magnetite graphene oxide by a magnetic field. Considering the instability of magnetite graphene oxide under different water chemistry conditions, we designed encapsulated magnetite graphene oxide inside a non-toxic alginate bead as a high-performance green chemical for the uptake of Cr(VI) and As(V) in water treatment applications (mGO/bead). The alginate, itself revealed low contribution for metal ions uptake, however this could potentially inhibit the aggregation of magnetite graphene oxide powder showing enhanced performance to extract metals from water. Material capacity minimally altered over a range of pH values for As(V), while Cr(VI) uptake varied with pH changes, which were explained by a local pH-controlled mechanism. Induced hydrolysis was facilitated by the release of Fe<SUP>3+</SUP> from Fe<SUP>3+</SUP>-crosslinked mGO/beads, thus enhancing the removal of Cr(VI). For a complex mixture of heavy metals, influence of the presence of co-occurring ions in a mixed contaminant system (Cr(VI), As(V), Cu(II), Cd(II)) revealed an excellent performance (~80-100% removal) by the composite material. The mGO/bead maintained its activity in wastewater and exhibited greater adsorption efficiency for both Cr(VI) and As(V) compared with activated carbon and carbon nanotube. The mGO/beads could be collected and reused for at least 5 cycles without the leaching of core mineral contents. The results indicate the advantages of mGO/beads over the popular adsorbents that can be developed as a versatile material for water treatment.