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Sunghyun Yoon,Chang Sun Yoon,Byung Ho Kim 한국자기학회 2005 Journal of Magnetics Vol.10 No.1
The crystallographic and magnetic properties of a series of substitutions in nickel ferrite where the Fe³+ is replaced with In³+ have been investigated using X-ray diffraction (XRD) and Mossbauer spectroscopy. Information on the exact crystalline structure, lattice parameters, bond lengths and bond angles were obtained by refining their XRD profiles by a Rietveld method. All the crystal structures were found to be cubic with the space group Fd/3m. The lattice constants increased with In³+ concentration. The expansion of the tetrahedron was outstanding, indicative of the tetrahedral (A) site preference of larger indium ion. The Mossbauer spectra showed two sets of sextuplet originating from ferric ions occupying the tetrahedral sites and the octahedral (B) sites under the Neel temperature T_N. Regardless of the composition x, the electric quadrupole splitting was zero within the experimental error. At x = 0.2, the magnetic hyperfine fields increased slightly, which meant that the nonmagnetic indium ions occupied preferentially the A-site. At the same time, the intensity of the B-site subspectra decreased markedly at the elevated temperature, indicating that the occupation of the A site by indium induced a considerable perturbation on the B site.
Crystallographic, Magnetic and Mössbauer Study of Phase Transition in LaVO₃
Sunghyun Yoon 한국자기학회 2007 Journal of Magnetics Vol.12 No.3
Nature of phase transition in LaVO₃ has been studied using X-ray diffraction, SQUID magnetometer, and Mossbauer spectroscopy with 1% of <SUP>57</SUP>Fe doped sample. The crystal structure was orthorhombic with space group Pnma. Antiferromagnetic phase transition temperature TN was 140 K, below which a weak ferromagnetic trace has been found. Mossbauer spectra below TN were single set of hyperfine sextet, which enabled us to discard the possibility of two inequivalent magnetic sites or uncompensated antiferromagnetism. Hyperfine magnetic field abruptly disappeared as low as about 90 K, much below TN.
Yoon Sunghyun,Chung Yongchul G. 대한화학회 2021 Bulletin of the Korean Chemical Society Vol.42 No.11
There has been a recent report regarding the existence of solid-like H2 adsorption in nanoporous materials. Herein, we employed grand canonical Monte Carlo (GCMC) simulations on a series of metal–organic frameworks with 1D and 3D channels to investigate the limitation of a model-based approach in estimating the H2 adsorption capacities. The excess hydrogen uptakes of several structures with pore sizes ranging from 5 to 37 Å were computationally predicted. The pore volume and the density of adsorbed H2 were obtained by fitting the Toth equa- tion to the excess H2 isotherm data from the simulation. The results were compared with the data obtained from direct simulation. Sensitivity analyses show that the pore volume and the density of adsorbed H2, predicted from modelbased fitting, are not accurate enough to estimate the adsorbed H2 density and the pore volume, especially for the materials with 1D channels
Yoon, Sunghyun,Lee, Young Ju 대한수의학회 2022 Journal of Veterinary Science Vol.23 No.3
Background: Avian pathogenic Escherichia coli (APEC) causes colibacillosis, resulting in significant economic losses in the poultry industry. Objectives: In this study, the molecular characteristics of two extended-spectrum beta-lactamase (ESBL)-producing APEC isolates were compared with previously reported ESBL-producing E. coli isolates. Methods: The molecular characteristics of E. coli isolates and the genetic environments of the ESBL genes were investigated using whole genome sequencing. Results: The two ESBL-producing APEC were classified into the phylogenetic groups C and B1 and ST410 and ST162, respectively. Moreover, the ESBL genes of the two isolates were harbored in different Inc plasmids. The EC1809182 strain, harboring the bla<sub>CTX-M-55</sub> gene on the plasmid, exhibited extensive homology to IncFIB (98.4%) and IncFIC(FII) (95.8%). The EC1809191 strain, harboring the bla<sub>CTX-M-1</sub> gene, was homologous to IncI1-I (Gamma) (99.3%). All chromosomes carried the multidrug transporter, mdf(A) gene. Mobile genetic elements, adjacent to CTX-M genes, facilitated the dissemination of genes in the two isolates, analogous to other ESBL-producing E. coli isolates. Conclusions: This study clarifies the transmission dynamics of CTX-M genes and supports strengthened surveillance to prevent the transmission of the antimicrobial-resistant genes to humans via the food chain.
Mössbauer Study of Two Discernable Fe Sites in CaFe₂O₄
Sunghyun Yoon 한국자기학회 2009 Journal of Magnetics Vol.14 No.2
Structural and magnetic properties of polycrystalline CaFe₂O₄ prepared by the solid state reaction method were studied using powder X-ray diffraction (XRD) and Mossbauer spectroscopy. The structure of CaFe₂O₄ belongs to an orthorhombic system (space group: Pnma) with the lattice parameters a = 9.2373 A, b = 3.0237 A, and c = 10.7124 A. Results of structural refinement indicate, however, that there are two slightly different iron sites in the sample. The Mossbauer spectrum at 4.2 K shows a hyperfine sextet with a hyperfine magnetic field and an isomer shift of 47.3 T and 0.36 ㎜/s, respectively. An examination of the spectrum revealed that the line widths of the spectral lines were not uniform. The degree of asymmetric line broadening decreases with increasing temperature, suggesting that the difference in the degree of crystalline distortions between two FeO? octahedra is eliminated as the temperature rises.
Sunghyun Yoon,Jai Kyoung Sim,Young-Ho Cho IEEE 2016 Journal of microelectromechanical systems Vol.25 No.2
<P>A piezoelectric pulsewave energy harvester composed of flexible three-layers generates electrical power from human arterial pulsewaves. We present the simple structure and novel fabrication process of the flexible three-layers, having a silver inter-electrode layer between a P(VDF-TrFE) piezoelectric layer and a polyimide support layer. The triple functions and the purposes of the silver inter-electrode layer are designed, acting as an electrode for piezoelectric poling, an electrode for piezoelectric energy harvesting, as well as an etch stop barrier for window patterning on the polyimide support layer. We also developed special processes for the window patterning on the polyimide support layer with the polyimide residue removal on the silver electrode, thereby increasing the piezoelectric energy generation efficiency and support flexibility, as well as achieving an electric contact to the silver electrode through the patterned window. The fabricated energy harvester generates 0.2 similar to 1.9 mu W from the human pulsewave in the range of 50 similar to 220 BPM, where the effect of window formation is demonstrated to increase energy efficiency and flexibility in the amount of 45% and 8%, respectively. The flexible energy harvester is capable to integrate additional physiological sensors for the applications to the multi-functional self-powered skin patches. [2015-0194]</P>