Hong-Ro Lee

Synthesis and optical property of water-soluble ZnS:Cu quantum dots by use of thioglycolic acid

For additional use in industry and biomedicine, water-soluble Cu2+-doped ZnS quantum dots (QDs) (ZnS:Cu) were synthesized with thioglycolic acid (TGA) as the stabilizer in aqueous solutions in air. The products were characterized by x-ray diffraction, ultraviolet–visible spectroscopy, transmission electron microscopy, and photoluminescence. The effect of Cu2+ doping concentration and TGA/(Zn+Cu) molar ratio on crystal structures and the luminescent intensity of ZnS:Cu QDs have been investigated. As a result, The as-prepared ZnS:Cu QDs had diameters of 10–12 nm and a sphere monodisperse form that consists of ZnS:Cu nanoparticles of approximately 2 nm. The optimum Cu2+ doping concentration and TGA/(Zn+Cu) molar ratio were obtained when the photoluminescent emission showed a maximum value.

Precipitation hardening and microstructures of rapidly solidified Mg−Zn−Ca−X alloys

Two quaternary magnesium alloys based on ternary Mg-5wt.%Zn-4wt.%Ca containing either Co(2wt.%) or Zr(0.5wt.%) were rapidly solidified using melt spinning. The nano-scale second phase distribution and thermal stability were studied using TEM, STEM and EDS system. Microhardness measurements conducted in the aged condition have identified that the Mg−Ca−Zn−Co alloy presented a peak value at 150°C followed by a hardness decrease. The Mg−Ca−Zn−Co alloy showed refined quaternary precipitates distributed along the cell boundary and a refined grain structure, yielding higher hardness values than the Mg−Ca−Zn−Zr alloy at all aging temperatures.

Synthesis and luminescence properties of Zn(Cu0.01Cd0.02Mg0.02)S phosphor

To improve the luminescence properties of ZnS : Cu, a multi-doped method was used to prepare Zn(Cu(0.01) Cd(0.02) Mg(0.02))S in this paper. As a new designed semiconductor compound, particular properties of Zn(Cu(0.01) Cd(0.02) Mg(0.02))S were investigated, especially luminescence intensity and lifetime. Structure and compositions of Zn(Cu(0.01) Cd(0.02) Mg(0.02))S phosphor were analyzed by XRD and TEM respectively. Luminescence intensity and luminescence lifetime of the prepared Zn(Cu(0.01) Cd(0.02) Mg(0.02))S phosphor were investigated by luminescence spectrometry. As a result, compared with pure ZnS or doped ZnS phosphors, Zn(Cu(0.01) Cd(0.02) Mg(0.02))S showed remarkably improved luminescence properties. The optimum ratio of three dopants was obtained for solving luminescence problems.

Fast protein structure alignment algorithm based on local geometric similarity

This paper proposes a novel fast protein structure alignment algorithm and its application. Because it is known that the functions of protein are derived from its structure, the method of measuring the structural similarities between two proteins can be used to infer their functional closeness. In this paper, we propose a 3D chain code representation for fast measuring the local geometric similarity of protein and introduce a backtracking algorithm for joining a similar local substructure efficiently. A 3D chain code, which is a sequence of the directional vectors between the atoms in a protein, represents a local similarity of protein. After constructing a pair of similar substructures by referencing local similarity, we perform the protein alignment by joining the similar substructure pair through a backtracking algorithm. This method has particular advantages over all previous approaches; our 3D chain code representation is more intuitive and our experiments prove that the backtracking algorithm is faster than dynamic programming in general case. We have designed and implemented a protein structure alignment system based on our protein visualization software (MoleView). These experiments show rapid alignment with precise results.

Hierarchical Land-Use Classification Using Optical Imagery and LiDAR Data

It is difficult to apply the statistical classification of optical imagery with spectral information to identify and distinguish the land-use information because the input data is highly correlated to each other even though labeled information to characterize the class distributions is typically sparse. The advent of LiDAR data with very accurate elevation information to identify and distinguish 3-dimensional informative features has given tremendous interest in the remote sensing community. In this paper, we propose new classification approach designed to integrate optical imagery and LiDAR data. The proposed method mixes the point-based classification for the LiDAR data and the statistical classification for the optical imagery. Clustering generates several class features from the elevation information of LiDAR data. The class features are used to define discriminant functions for a land class, a building class, and a tree class combined with the input data. Statistical classification generates several class features, such as the grass classes, the soil classes, the water classes, and the road classes from the spectral information of optical imagery. The class features from the LiDAR data and the optical imagery are hierarchically combined to characterize land-use information.

Luminescence Properties of Ba 3 Si 6 O 12 N 2 :Eu 2+ Green Phosphor

Department of Advanced Materials Engineering, Chungnam National University, Daejeon 305-764, Korea(Received October 12, 2015 ; revised October 21, 2015 ; accepted October 28, 2015)AbstractTo fabricate white LED having a high color rendering index value, red color phosphor mixed with thegreen color phosphor together in the blue chip, namely the blue chips with RG phosphors packaging is mostfavorable for high power white LEDs. In our previous papers, we reported on successful syntheses of Sr

Poly(MAA-Mn) for Triple-Layer Structure Synthesis of ZnS/ZnS:Mn/SiO2 Phosphors

Methacrylic acid (MAA) was used as a manganese carrier to prepare ZnS/MAA-Mn particles, and ZnS/ZnS:Mn phosphors were formed from ZnS/MAA-Mn by ion substitution through heat treatment. After silica coating on surface by chemical precipitation method with tetraethyl orthosilicate (TEOS), ZnS/ZnS:Mn/SiO2 phosphors were prepared successfully as a new core/shell structure compound. The thickness of layers was controlled by adjusting concentrations of manganese (II) acetate (Mn(CH3COO)2) and TEOS. Structure, morphology, and composition of prepared phosphors were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Photoluminescence (PL) properties of ZnS with different Mn2+ content were analyzed by PL spectrometer. PL emission intensity and PL stability were analyzed for evaluating effects of silica coating and Mn2+ activator doping. As a result, the structure of two layers could be observed, and optimum composition of ZnS/ZnS:Mn/SiO2 structure was also obtained.