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113 results on '"Lee, Kyu-Joon"'

7. The effect of substitution of Mn for Ni on the magnetic and transport properties of CeNi0.8-xMnxBi2

Author

Kim, Soo-Whan, Lee, Kyu Joon, Adroja, D. T., Demmel, F., Taylor, J. W., and Jung, Myung-Hwa

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We report the results of Mn substitution for Ni in CeNi0.8Bi2, (i.e. CeNi0.8-xMnxBi2). All the samples have an antiferromagnetic ordered state below TN = 5.0 K due to localized 4f-magnetic moment on the Ce ions. Besides this antiferromagnetic ordering caused by Ce, the magnetic and transport properties are abruptly changed with increasing Mn contents at the boundary composition of x = 0.4. The magnetic state is changed into a ferromagnetic state around 200 K for x > 0.4, where the electrical resistivity is strongly suppressed to become simple metallic. These results of ferromagnetism and metallicity can be explained by the double-exchange mechanism. The mixed valence states of Ni and Mn ions are confirmed by X-ray photoelectron spectroscopy (XPS). For x <= 0.4, the initial Ni3+ state gradually changes to the Ni2+ state with increasing x up to 0.4. On further increase of x > 0.4, the Ni2+ state is substituted for the Mn2+ state, which gradually changes to the final Mn3+ state. We also present an inelastic neutron scattering (INS) measurements on CeNi0.8Bi2 (i.e. x=0) between 1.2 and 12 K. The high energy INS study reveals the presence of two well defined crystal electric field (CEF) excitations near 9 meV and 19 meV at 1.2 K and 6 K, while the low energy INS study reveals the presence of quasi-elastic scattering above 4 K. We will discuss our INS results of CeNi0.8Bi2 based on the crystal electric field model., Comment: 21 pages, 12 figures

Published
2014
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8. The role of temperature and drive current in skyrmion dynamics

Author

Litzius, Kai, Leliaert, Jonathan, Bassirian, Pedram, Rodrigues, Davi, Kromin, Sascha, Lemesh, Ivan, Zazvorka, Jakub, Lee, Kyu-Joon, Mulkers, Jeroen, Kerber, Nico, Heinze, Daniel, Keil, Niklas, Reeve, Robert M., Weigand, Markus, Van Waeyenberge, Bartel, Schütz, Gisela, Everschor-Sitte, Karin, Beach, Geoffrey S. D., and Kläui, Mathias

Published
2020
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10. Hole mediated ferromagnetism in Cu-doped ZnO thin films

Author

Singh, Abhinav Pratap, Park, B. -G., Lee, Ik-Jae, Lee, Kyu Joon, Jung, Myung-Hwa, Kim, Jinhee, and Kim, J. -Y.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We report the successful synthesis of ZnO:Cu thin films doped with holes, resulting in room temperature ferromagnetism. Hole doping is achieved by As-diffusion from the GaAs substrate into ZnO films, assisted by thermal annealing. The As-diffusion is probed with the help of x-ray absorption spectra collected at the As K-edge which show enhanced signature of diffusion in the annealed samples. Introduction of holes, due to the As doping, in ZnO films is further evidenced by the Cu L3,2-edge spectra. XMCD and magnetic measurements show that the ferromagnetic interaction between doped Cu ions is enhanced after hole doping., Comment: 14 pages, 3 figures

Published
2011

11. Small anisotropy of the lower critical field and $s_\pm$-wave two-gap feature in single crystal LiFeAs

Author

Song, Yoo Jang, Ghim, Jin Soo, Yoon, Jae Hyun, Lee, Kyu Joon, Jung, Myung Hwa, Ji, Hyo-Seok, Shim, Ji Hoon, and Kwon, Yong Seung

Subjects
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Abstract

The in- and out-of-plane lower critical fields and magnetic penetration depths for LiFeAs were examined. The anisotropy ratio $\gamma_{H_{c1}}(0)$ is smaller than the expected theoretical value, and increased slightly with increasing temperature from 0.6$T_c$ to $T_c$. This small degree of anisotropy was numerically confirmed by considering electron correlation effect. The temperature dependence of the penetration depths followed a power law($\sim$$T^n$) below 0.3$T_c$, with $n$$>$3.5 for both $\lambda_{ab}$ and $\lambda_c$. Based on theoretical studies of iron-based superconductors, these results suggest that the superconductivity of LiFeAs can be represented by an extended $s_\pm$-wave due to weak impurity scattering effect. And the magnitudes of the two gaps were also evaluted by fitting the superfluid density for both the in- and out-of-plane to the two-gap model. The estimated values for the two gaps are consistent with the results of angle resolved photoemission spectroscopy and specific heat experiments., Comment: 10 pages, 5 figures

Published
2010
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13. Defect Engineering of Metal Halide Perovskite Nanocrystals via Spontaneous Diffusion of Ag Nanocrystals

Author

Jeon, Sanghyun, primary, Ahn, Junhyuk, additional, Jung, Myung‐Chul, additional, Woo, Ho Kun, additional, Bang, Junsung, additional, Jung, Byung Ku, additional, Oh, Seongkeun, additional, Lee, Sang Yeop, additional, Lee, Kyu Joon, additional, Paik, Taejong, additional, Ha, Don‐Hyung, additional, Ahn, Jae‐Pyoung, additional, Jeong, Sohee, additional, Kim, Dong Hoe, additional, Noh, Jun Hong, additional, Jang, Ho Seong, additional, Han, Myung Joon, additional, and Oh, Soong Ju, additional

Published
2023
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26. Molecular Mechanisms of Beta-Arrestin-1 Dependent Regulation of LIMK and Cofilin

Author

Lee, Kyu Joon

Subjects
Biochemistry, Molecular biology
Abstract

Beta-arrestins are adaptor proteins that can scaffold a number of signaling proteins to promote localized activity within the cell. Downstream of some GPCRs, β-arrestins can promote activation of the actin filament severing protein, cofilin, through two mechanisms: one involving inhibition of LIM Kinase (LIMK) which negatively regulates cofilin activity through phosphorylation on serine 3. The mechanism by which β-arrestin-1 regulates LIMK activity has not been elucidated; however, it has been shown to be important for cell migration downstream of protease-activate-receptor-2 (PAR-2), dendritic spine formation and opioid receptor function. Here my work demonstrate that β-arrestin-1 directly binds both cofilin and LIMK, and inhibits LIMK activity directly and investigate the mechanism by which inhibition of kinase activity occurs. Using serial truncations and site-directed mutagenesis, I identify crucial residues for cofilin and LIMK interaction within amino acids 1-99 of β-arrestin-1 and show that charged residues at 50 and 51 are crucial for binding to LIMK and R51 is required for LIMK inhibition, PAR2 stimulated cofilin dephosphorylation and cell migration. Additionally, our work reveals that amino acids 1-99 aminos of β-arrestin-1 bind both cofilin and LIMK with a higher apparent affinity than the full length and blocks PAR2-stimulated cofilin dephosphorylaton in HEK293 cells, suggesting it functions as a selective dominant negative β-arrestin-1, inhibiting specifically the cofilin pathway. Thus, residues in the N-terminus of β-arrestin-1 are involved in LIMK inhibition and cofilin activation and this, in turn, is important for cell migration downstream of PAR-2.

Published
2015

28. Additional file 2 of The CRK2-CYC13 complex functions as an S-phase cyclin-dependent kinase to promote DNA replication in Trypanosoma brucei

Author

Lee, Kyu Joon and Li, Ziyin

Abstract

Additional file 2: Figure S7. Full western blots used for Fig. 1e, f. Figure S8. Full western blots used for Fig. 2. Figure S9. Full western blots used for Fig. 4b, c. Figure S10. Full western blots used for Fig. 5c. Figure S11. Full western blots used for Fig. 6a-e. Figure S12. Full western blots used for Figure S2. Figure S13. Full western blots used for Figure S5. Figure S14. Full western blots used for Figure S6.

Published
2021
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29. Giant Dzyaloshinskii-Moriya Interaction and Room-Temperature Nanoscale Skyrmions in CoFeB/MgO Heterostructures

Author

Chen, Runze, primary, Wang, Xinran, additional, Cheng, Houyi, additional, Lee, Kyu-Joon, additional, Xiong, Danrong, additional, Kim, Jun-Young, additional, Li, Sai, additional, Yang, Hongxin, additional, Zhang, Hongchao, additional, Cao, Kaihua, additional, Peng, Shouzhong, additional, Kläui, Mathias, additional, and Zhao, Weisheng, additional

Published
2021
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35. Synthesis and Characterization of Nano-Ilmenite FeTiO

Author

Raghavender, A.D., Hoa Hong, Nguyen, Jung, Myung-Hwa, Lee, Kyu Joon, Skoko, Željko, Cerquieira, M. F., Samantelle, A. P., and Nikola Radić, Slobodan Milošević

Subjects
Nano-ilmenie FeTiO3, sol-gel, semiconductor, antiferromagnetic, XRD
Abstract

Ilmenite FeTiO3 is one of the most common minerals in the Earth crust. FeTiO3 is an interesting wide bandgap (2.6-2.9 eV) antiferromagnetic semiconductor with potential applications in spintronics, optoelectronics, high temperature integrated circuits, chemical catalysts, photocatalysts etc. Most of the efforts on designing ferromagnetic semiconductors operating at room temperature concentrate on homogeneous doping of semiconductors with magnetic impurities. General route of synthesis of ilmenite FeTiO3 is by solid-state reaction at very high pressure and high temperature. The Fe2+ ions are not stable, so the synthesis is quite challenging. In this work nano-ileminite FeTiO3 was synthesized by the sol-gel method at very low temperature, with an average particle size of 20 nm. Structural, optical and magnetic characterizations were performed on the samples. The bandgap of FeTiO3 was determined to be 2.8 eV . The FeTiO3 nanoparticles exhibit weak magnetic properties at and below room temperature. The blocking temperature (TB) observed from low temperature magnetization data seems not to change with the increasing applied magnetic field. The observed results indicate that nanocrystalline FeTiO3 have different properties in comparison to the bulk FeTiO3.

Published
2012

39. Magnetic properties of Mn and Co doped PbPdO2

Author

Lee, Kyu Joon, Choo, Sung Min, Saiga, Yuta, Takabatake, Toshiro, Jung, Myung-Hwa, Lee, Kyu Joon, Choo, Sung Min, Saiga, Yuta, Takabatake, Toshiro, and Jung, Myung-Hwa

Abstract

type:text, We report the dramatic change of gapless semiconductor properties by different chemical doping elements of Co and Mn into PbPdO_2. The metal-insulatorlike transition temperature T_ = 100 K for PbPdO_2 shifts to a higher temperature of 150 K by the Co doping and to a lower temperature of 70 K by the Mn doping. Because of the anisotropic band structure with the majority of heavy holes and the minority of light electrons, the transport and magnetic properties are significantly changed by the chemical doping elements. At low temperatures, the Co doping enhances ferromagnetic interactions, whereas the Mn doping favors antiferromagnetic interactions. These results are of great interests because you can control the magnetic ordering as well as manipulate the carrier density by changing the doping elements. These materials could be a good candidate for spintronics applications.

Published
2011

48. Magnetic properties of Mn and Co doped PbPdO2

Author

Lee, Kyu Joon, Choo, Sung Min, Saiga, Yuta, Takabatake, Toshiro, Jung, Myung-Hwa, Lee, Kyu Joon, Choo, Sung Min, Saiga, Yuta, Takabatake, Toshiro, and Jung, Myung-Hwa

Abstract

We report the dramatic change of gapless semiconductor properties by different chemical doping elements of Co and Mn into PbPdO_2. The metal-insulatorlike transition temperature T_ = 100 K for PbPdO_2 shifts to a higher temperature of 150 K by the Co doping and to a lower temperature of 70 K by the Mn doping. Because of the anisotropic band structure with the majority of heavy holes and the minority of light electrons, the transport and magnetic properties are significantly changed by the chemical doping elements. At low temperatures, the Co doping enhances ferromagnetic interactions, whereas the Mn doping favors antiferromagnetic interactions. These results are of great interests because you can control the magnetic ordering as well as manipulate the carrier density by changing the doping elements. These materials could be a good candidate for spintronics applications.

49. Proximity Interactions among Basal Body Components in Trypanosoma bruceiIdentify Novel Regulators of Basal Body Biogenesis and Inheritance

Author

Dang, Hung Quang, Zhou, Qing, Rowlett, Veronica W., Hu, Huiqing, Lee, Kyu Joon, Margolin, William, and Li, Ziyin

Abstract

ABSTRACTThe basal body shares similar architecture with centrioles in animals and is involved in nucleating flagellar axonemal microtubules in flagellated eukaryotes. The early-branching Trypanosoma bruceipossesses a motile flagellum nucleated from the basal body that consists of a mature basal body and an adjacent pro-basal body. Little is known about the basal body proteome and its roles in basal body biogenesis and flagellar axoneme assembly in T. brucei. Here, we report the identification of 14 conserved centriole/basal body protein homologs and 25 trypanosome-specific basal body proteins. These proteins localize to distinct subdomains of the basal body, and several of them form a ring-like structure surrounding the basal body barrel. Functional characterization of representative basal body proteins revealed distinct roles in basal body duplication/separation and flagellar axoneme assembly. Overall, this work identified novel proteins required for basal body duplication and separation and uncovered new functions of conserved basal body proteins in basal body duplication and separation, highlighting an unusual mechanism of basal body biogenesis and inheritance in this early divergent eukaryote.IMPORTANCEThe basal body in the early-branching protozoan Trypanosoma bruceinucleates flagellum assembly and also regulates organelle segregation, cell morphogenesis, and cell division. However, the molecular composition and the assembly process of the basal body remain poorly understood. Here, we identify 14 conserved basal body proteins and 25 trypanosome-specific basal body proteins via bioinformatics, localization-based screening, and proximity-dependent biotin identification. We further localized these proteins to distinct subdomains of the basal body by using fluorescence microscopy and superresolution microscopy, discovered novel regulators of basal body duplication and separation, and uncovered new functions of conserved basal body proteins in basal body duplication and separation. This work lays the foundation for dissecting the mechanisms underlying basal body biogenesis and inheritance in T. brucei.

Published
2017
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50. Evaluating the anticancer potential of Polygonum multiflorum root-derived stilbenes against H2452 malignant pleural mesothelioma cells.

Author

Ngo, Trung Huy, Lee, Yoon-Jin, Choi, Hyukjae, Song, Kyung-Sik, Lee, Kyu Joon, and Nam, Joo-Won

Subjects
*PLANT roots, *PLANT extracts, *MEDICINAL plants
Abstract

A naturally occurring stilbene, resveratrol, shows promising effects in the treatment of malignant pleural mesothelioma (MPM) both as a single agent and in combination with chemotherapeutic drugs. To discover new anticancer agents targeting MPM, stilbene-targeted isolation was performed on the roots of Polygonum multiflorum Thunb., an herbal medicine rich in stilbene compounds. In this study, seven stilbene glycosides (1 – 7) were isolated, along with four non-stilbenes (8 – 11), of which compounds 4 and 9 – 11 have not previously been isolated from this species. Stiquinoside A (1) is a previously undescribed stilbene glycoside, and its structure was elucidated as (E)-2,3,5,4′-tetrahydroxystilbene 2- O - β - d -quinovopyranoside based on 1D and 2D-NMR, HR-ESI-MS, and acid hydrolysis experiments. Compounds 1 , 4 , 6 , and 8 significantly inhibit the growth of MPM cancer cells H2452. These results demonstrate the potential utility of stilbenes in new strategies for the treatment of MPM. [Display omitted] • A new (1) and six reported (2 – 7) stilbenes were obtained from Polygonum multiflorum. • Three non-stilbenes (9 – 11) were isolated from P. multiflorum for the first time. • Stilbenes 1 , 4 , and 6 showed significant inhibitory effects on H2452 cells. • Emodin (8), an anthraquinone, significantly inhibited H2452 cells. [ABSTRACT FROM AUTHOR]

Published
2024
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