Y S Lee

Kyungpook National University Hospital, Sŏul, Seoul, South Korea

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Publications (670)1335.43 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: We report a direct measurement of the low-frequency optical conductivity of large-area single-crystal herbertsmithite, a promising spin-liquid candidate material, by means of terahertz time-domain spectroscopy. In the spectral range below 1.4 THz, we observe a contribution to the real part of the in-plane conductivity σ_{ab}(ω) from the spin degree of freedom. This spin-induced conductivity exhibits a power-law dependence on frequency σ_{ab}(ω)∼ω^{β} with β≈1.4. Our observation is consistent with the theoretically predicted low-frequency conductivity arising from an emergent gauge field of a gapless U(1) Dirac spin liquid.
    Physical Review Letters 09/2013; 111(12):127401. · 7.94 Impact Factor
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    ABSTRACT: We investigated the structural and optical properties of Cu-poor CuGaSe2 (CGSe) films depending on the use of different substrates: indium-doped tin oxide (ITO) coated soda-lime glass (SLG) and fluorine-doped tin oxide (FTO) coated SLG as back contacts, widely used Mo-coated SLG, and pure SLG. The Cu-poor phase is chosen as a counterpart of Cu-poor Cu(In,Ga)Se2 to show the highest efficiency in this class of materials, and also give a test board for parasitic phases which might influence on device properties. Although the Cu-poor CGSe thin-films were deposited on the four substrates at the same time in an identical condition, they showed differences in the morphology and grain size due to different CGSe/substrate interfaces and growth mechanisms depending on the substrates. These surface properties of the CGSe films were identified clearly by atomic force microscopy (AFM) measurements. X-ray diffraction (XRD) measurement also supported the result of the AFM analysis and showed that the preferred orientation of CGSe is (112), independent of the substrates. The existence of parasitic phases was examined by Raman and photoluminescence spectroscopic techniques. While defect compounds such as CuGa3Se5 and CuGa5Se8 were identified for all films, the signals related to these parasitic phases are strongest for the films on the pure SLG substrate. Furthermore, the absorption property was investigated by spectroscopic ellipsometry in a photon energy range of 0.7–5 eV. We found that the absorption coefficient values for the CGSe films are about 104–105 cm−1 in the visible region. The absorption coefficient is also changed according to the use of different substrates. This difference comes from the parasitic phase formation, which leads to an increase of the bandgap and suppression of the optical absorption strength. Our systematic study suggests clearly that the difference in distribution of parasitic phases in the CGSe films could originate primarily from the different substrates used for the film deposition.
    Current Applied Physics 07/2013; 13(5):907–912. · 1.81 Impact Factor
  • Value in Health 05/2013; 16(3):A297. · 2.19 Impact Factor
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    ABSTRACT: We use low temperature spectroscopic scanning tunneling microscopy to study topological materials in which the surface states are protected by time reversal symmetry. We image the local density of states around a variety of single-atom impurities in the presence of a magnetic field. On a subset of these impurities, we observe broad peaks in the local density of states at energies around the Dirac point. Furthermore, we use Landau level spectroscopy and quasiparticle scattering to discuss the interplay between impurities and the surface states.
    03/2013;
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    Dataset: Matan 2011
  • Entomological Research 01/2013; 43(3):162-170.
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    ABSTRACT: The Korean mussel Mytilus coruscus, an endemic marine bivalve mollusk, is economically important. Its population is currently decreasing due to overexploitation and invasion of a more competitive species, Mytilus galloprovincialis. In this study, microsatellite markers for M. coruscus were developed using a cost-effective pyrosequencing technique. Among the 33,859 dinucleotide microsatellite sequences identified, 176 loci that contained more than 8 CA, CT, or AT repeats were selected for primer synthesis. Sixty-four (36.4%) primer sets were produced from the 100- to 200-bp polymerase chain reaction products obtained from 2 M. coruscus individuals. Twenty of these were chosen to amplify DNA from 82 M. coruscus individuals, and 18 polymorphic loci and 2 monomorphic loci were selected as microsatellite markers. The number of alleles and the allele richness of the polymorphic loci ranged from 2 to 22 and from 2.0 to 19.7 with means of 10.8 and 10.1, respectively. Null alleles were detected for all but three loci, which resulted in an observed heterozygosity lower than the expected heterozygosity and therefore an excess of homozygotes. In a cross-species transfer analysis of these markers using 7 Mytilidae species, the locus Mc65 was amplified from all species tested and was found to be polymorphic in all of them. Among the species, M. galloprovincialis, Lithophaga curta, and Hormomya mutabilis showed the same transferability of 25%, but the five amplified loci were polymorphic only in M. galloprovincialis and H. mutabilis. These microsatellite markers may be useful for future resource management and artificial production of juveniles for aquaculture.
    Genetics and molecular research: GMR 01/2013; 12(3):4009-4017. · 0.99 Impact Factor
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    ABSTRACT: To evaluate the correlation between immunohistochemical expression of synuclein-gamma, glucose transporter-1, and survival outcomes in endometrioid endometrial carcinoma. A tissue microarray was constructed using formalinfixed, paraffin-embedded tissue that included 23 early and 18 advanced cases. The intensity and area of the immunohistochemical reactions were evaluated using the semi-quantitative scoring system. Synuclein-y expression was higher in the advanced stage, although it was not statistically significant (p = 0.51). Glucose transporter-1 was overexpressed in the advanced stage (p = 0.01). Synuclein-gamma (score = 0 vs > 0) and glucose transporter-1 (score < or = 7 vs > 7) did not show any differences in overall survival (p = 0.54, p = 0.48) and disease-free survival (p = 0.61, p = 0.14). In this study the expression of synuclein-y and glucose transporter-1 were not considered to be a prognostic factor and were not related with survival outcomes in endometrioid endometrial carcinoma.
    European journal of gynaecological oncology 01/2013; 34(2):128-31. · 0.58 Impact Factor
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    ABSTRACT: A series of (Y2 − xLix)Ti2O7 − x samples abbreviated as YLT-2L were prepared by the addition of 2x moles of LiO0.5 self-flux into the parent compound, where x = 0.040 to 0.110. Preparation temperatures were either 1300 or 1350 °C, depending on the amount of flux addition. However, the Y2Ti2O7 had no LiO0.5 co-existence; it was prepared at the highest temperature, 1600 °C. Relative densities of all the YLT-2L samples were larger than 97%, but for the Y2Ti2O7, it was 94.3(2)% only. By the addition of flux, preparation temperature reduced for more than 250 °C. Among all the YLT-2L samples, the one with x = 0.070 had the highest total electrical conductivity (2.90(2) × 10− 4 S·cm− 1 at 700 °C) and the lowest total activation energy (0.99(1) eV). By doping Li ion into the Y-site, oxygen vacancies were created, although YLT-2L samples had flux co-existence, electrical conductivity was still comparable to the parent compound reported by Yamaguchi et al. (1998) and Kobayashi et al. (2002). At 500, 600 and 700 °C, the ionic transference numbers (ti) found for the YLT-2L samples were 1.00(2), 0.96(2) and 0.90(3), respectively, and did not vary with the amount of substitution and the flux addition. Contribution of the electronic conductivity was due to the presence of a small amount of the Ti3 + ions in the samples investigated by the Ti K-edge XANES spectra.
    Solid State Ionics 01/2013; 253:227–233. · 2.05 Impact Factor
  • D K Singh, Y S Lee
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    ABSTRACT: We report on the study of unusual spin glass properties in the geometrically frustrated pyrochlore Tb_{2}Mo_{2}O_{7}, T_{g}≃24 K. The analysis of the nonlinear part of dc and complex susceptibilities, near the glass transition regime, suggests the existence of a statistical distribution of relaxation times in short-range ordered ferromagnetic clusters. In addition, the magnetic spins are not sufficiently frozen below the glass transition temperature, which is apparently responsible for the nonequilibrium scaling behavior of the static critical exponents of nonlinear susceptibilities. Our report is expected to shed new light in understanding the freezing properties of frustrated pyrochlores with short-range ferromagnetic interactions.
    Physical Review Letters 12/2012; 109(24):247201. · 7.94 Impact Factor
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    ABSTRACT: Sinomenine is an alkaloid compound and a prominent anti-inflammatory agent found in the root of the climbing plant Sinomenium acutum. However, its effects on the mechanism of human mast cell line (HMC)-1-mediated inflammation remained unknown. To provide insight into the biological effects of sinomenine, we examined its influence on the pro-inflammatory cytokine production in HMC-1 cells stimulated by phorbol 12-myristate-13-acetate (PMA) plus A23187 by evaluating the stimulated cells in the presence or absence of sinomenine. In the present study, the pro-inflammatory cytokine production was measured using ELISA, Reverse Transcription-polymerase chain reaction (RT-PCR) and nuclear factor (NF)-kappaB, mitogen-activated protein kinases (MAPKs) pathway activation, as determined by Western blot analysis. Also, cyclooxygenase (COX)-2 expression was measured through Western blot and RT-PCR analysis. Sinomenine inhibited the pro-inflammatory cytokine production induced by PMA plus A23187 in a dose-dependent manner. Furthermore, sinomenine inhibited the phosphorylations of extracellular signal-regulated kinase (ERK) and p38 MAPKs as well as the translocation of NF-kappaB p65 through reduced IkappaBalpha degradation. In addition, sinomenine suppressed COX-2 protein and mRNA expression dose-dependently. Taken together, the results of this study indicate that the anti-inflammatory effects of sinomenine may occur via the inhibition of pro-inflammatory cytokine and COX-2 production through the inhibition of MAPKs and NF-kappaB pathway activation by PMA plus A23187 stimulation in HMC-1 cells.
    European review for medical and pharmacological sciences 09/2012; 16(9):1184-91. · 1.09 Impact Factor
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    ABSTRACT: We perform time- and angle-resolved photoemission spectroscopy of a prototypical topological insulator Bi$_2$Se$_3$ to study the ultrafast dynamics of surface and bulk electrons after photo-excitation. By analyzing the evolution of surface states and bulk band spectra, we obtain their electronic temperature and chemical potential relaxation dynamics separately. These dynamics reveal strong phonon-assisted surface-bulk coupling at high lattice temperature and total suppression of inelastic scattering between the surface and the bulk at low lattice temperature. In this low temperature regime, the unique cooling of Dirac fermions in TI by acoustic phonons is manifested through a power law dependence of the surface temperature decay rate on carrier density.
    Physical Review Letters 08/2012; 109(12). · 7.94 Impact Factor
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    ABSTRACT: We develop a theoretical model that describes the second harmonic generation of light from the surface of the topological insulator Bi2Se3 and experimentally demonstrate that the technique is sensitive to the surface electrons. By performing a crystal symmetry analysis of Bi2Se3(111) we determine the nonlinear electric susceptibility tensor elements that give rise to second harmonic generation. Using these results, we present a phenomenological model that shows that the relative magnitudes of these tensor elements can be determined by measuring the polarization and intensity of the radiated second harmonic light as a function of the in-plane crystal orientation and incident laser polarization. We describe optical techniques capable of isolating second harmonic light and, using these techniques, we measure the first-order linear optical and second-order nonlinear optical responses as a function of crystal orientation and laser polarization on bulk single crystals of Bi2Se3(111). The experimental results are consistent with our theoretical description. By comparing the data to our theoretical model we determine that a portion of the measured second harmonic light originates from the accumulation region of Bi2Se3(111), which we confirm by performing surface doping-dependent studies. Our results show that second harmonic generation is a promising tool for spectroscopic studies of topological surfaces and buried interfaces.
    Physical review. B, Condensed matter 07/2012; 86(3).
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    ABSTRACT: Methicillin-resistant Staphylococcus aureus (MRSA) infections are a rapidly growing health problem around the globe. Recently, there has been considerable interest in the use of plant materials as an alternative method to control pathogenic microorganisms. In this study we evaluated the antibacterial activity of bark of Alnus pendula against MRSA. The MIC determination was done using the microdilution broth method and bacterial growth was determined by measuring optical density using spectrophotometer. Alnus pendula bark EtOH extract and fractions (F-1, -2, -3 and -4) were investigated against MRSA. The most active fractions (F-3 and F-4) led to the isolation of oregonin (ORE) and hirsutanone (HIR). These compounds were active against MRSA strains with minimum inhibitory concentrations (MICs) ranging from 31.25 to 250 microg/ml MIC and 2 MIC of HIR completely inhibited the growth of MRSA. The bark EtOH extract of Alnus Pendula has potent antibacterial activity against MRSA.
    European review for medical and pharmacological sciences 07/2012; 16(7):853-9. · 1.09 Impact Factor
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    ABSTRACT: Gapless surface states on topological insulators are protected from elastic scattering on nonmagnetic impurities which makes them promising candidates for low-power electronic applications. However, for widespread applications, these states should have to remain coherent at ambient temperatures. Here, we studied temperature dependence of the electronic structure and the scattering rates on the surface of a model topological insulator, Bi2Se3, by high-resolution angle-resolved photoemission spectroscopy. We found an extremely weak broadening of the topological surface state with temperature and no anomalies in the state's dispersion, indicating exceptionally weak electron-phonon coupling. Our results demonstrate that the topological surface state is protected not only from elastic scattering on impurities, but also from scattering on low-energy phonons, suggesting that topological insulators could serve as a basis for room-temperature electronic devices.
    Physical Review Letters 05/2012; 108(18):187001. · 7.94 Impact Factor
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    ABSTRACT: Heavily electron-doped surfaces of Bi$_2$Se$_3$ have been studied by spin and angle resolved photoemission spectroscopy. Upon doping, electrons occupy a series of {\bf k}-split pairs of states above the topological surface state. The {\bf k}-splitting originates from the large spin-orbit coupling and results in a Rashba-type behavior, unequivocally demonstrated here via the spin analysis. The spin helicities of the lowest laying Rashba doublet and the adjacent topological surface state alternate in a left-right-left sequence. This spin configuration sets constraints to inter-band scattering channels opened by electron doping. A detailed analysis of the scattering rates suggests that intra-band scattering dominates with the largest effect coming from warping of the Fermi surface.
    04/2012;
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    ABSTRACT: Dirac-like surface states on surfaces of topological insulators have a chiral spin structure that suppresses backscattering and protects the coherence of these states in the presence of nonmagnetic scatterers. In contrast, magnetic scatterers should open the backscattering channel via the spin-flip processes and degrade the state's coherence. We present angle-resolved photoemission spectroscopy studies of the electronic structure and the scattering rates upon the adsorption of various magnetic and nonmagnetic impurities on the surface of Bi2Se3, a model topological insulator. We reveal a remarkable insensitivity of the topological surface state to both nonmagnetic and magnetic impurities in the low impurity concentration regime. Scattering channels open up with the emergence of hexagonal warping in the high-doping regime, irrespective of the impurity's magnetic moment.
    Physical Review Letters 03/2012; 108(11):117601. · 7.94 Impact Factor
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    ABSTRACT: We have performed high-field multifrequency electron spin resonance (ESR) and high-field magnetization measurements in magnetic fields H of up to 53 T on single crystals of the kagome-lattice antiferromagnet KFe3(OH)6(SO4)2. We have analyzed the magnetization curve and the ESR excitation modes for H∥c by using two kinds of anisotropy origins, the Dzyaloshinsky-Moriya (DM) interactions and the single-ion anisotropy, the former of which is inevitable in a kagome-lattice antiferromagnet. We obtained good agreement between experiment and calculation for the case of the DM interactions. In addition, we have clarified the origin of a field-induced metamagnetic transition observed in the magnetization curve and determined the intraplane and interplane exchanges and the DM interaction parameters.
    Physical review. B, Condensed matter 03/2012; 85(9).

Publication Stats

4k Citations
1,335.43 Total Impact Points

Institutions

  • 2009–2013
    • Kyungpook National University Hospital
      • Department of Obstetrics and Gynecology
      Sŏul, Seoul, South Korea
    • Korea University
      Sŏul, Seoul, South Korea
    • Pontificia Universidad Católica de Valparaíso
      Ciudad de Valparaíso, Valparaíso, Chile
  • 2006–2013
    • Soongsil University
      • Department of Physics
      Sŏul, Seoul, South Korea
    • Dong-A University
      • Department of Biotechnology
      Pusan, Busan, South Korea
    • Korea Centers for Disease Control and Prevention
      Daiden, Daejeon, South Korea
  • 1996–2013
    • Massachusetts Institute of Technology
      • • Department of Physics
      • • Department of Materials Science and Engineering
      Cambridge, Massachusetts, United States
  • 2010–2012
    • Wonkwang University
      • College of Pharmacy
      Iksan, North Jeolla, South Korea
    • Kyungnam University
      Changnyeong, South Gyeongsang, South Korea
    • Chosun University
      • Department of Information and Communication Engineering
      Gwangju, Gwangju, South Korea
  • 2011
    • Brookhaven National Laboratory
      • Condensed Matter Physics & Materials Science Department
      New York City, NY, United States
    • Korea Advanced Institute of Science and Technology
      • Department of Physics
      Sŏul, Seoul, South Korea
  • 1997–2011
    • Catholic University of Korea
      • • Department of Obstetrics and Gynecology
      • • Department of Internal Medicine
      • • Department of Radiology
      Seoul, Seoul, South Korea
    • Korea Institute of Science and Technology
      Sŏul, Seoul, South Korea
    • RURAL DEVELOPMENT ADMINISTRATION
      Seikan-ri, South Chungcheong, South Korea
  • 1996–2011
    • Hanyang University
      • • College of Medicine
      • • Department of Chemistry
      • • Department of Physics
      Ansan, Gyeonggi, South Korea
  • 2007–2010
    • Chonbuk National University
      • Semiconductor Physics Research Center
      Seoul, Seoul, South Korea
    • Korea Institute of Machinery and Materials
      Sŏul, Seoul, South Korea
  • 2000–2010
    • Sungkyunkwan University
      • • Samsung Medical Center
      • • Department of Molecular and Cell Biology
      Sŏul, Seoul, South Korea
    • National Veterinary Research Quarantine Service
      Sŏul, Seoul, South Korea
    • National Institutes of Health
      • Laboratory of Membrane Biochemistry and Biophysics
      Bethesda, MD, United States
  • 1996–2010
    • Seoul National University
      • • Department of Physics and Astronomy
      • • Research Institute of Pharmaceutical Sciences
      • • College of Veterinary Medicine
      • • Department of Chemistry
      • • Institute of Molecular Biology and Genetics
      • • Department of Microbiology and Immunology
      Seoul, Seoul, South Korea
  • 1994–2010
    • Gyeongsang National University
      • Division of Applied Life Science
      Chinju, South Gyeongsang, South Korea
  • 2006–2009
    • Chungnam National University
      • • Department of Mechanical Design Engineering
      • • Department of Applied Biology
      Seongnam, Gyeonggi, South Korea
  • 2008
    • Chonnam National University
      • School of Applied Chemical Engineering
      Gwangju, Gwangju, South Korea
    • Korea Institute of Materials Science
      Sŏngnam, Gyeonggi Province, South Korea
  • 2006–2008
    • Korea Institute of Radiological & Medical Sciences
      Sŏul, Seoul, South Korea
  • 2003–2008
    • Hanbat National University
      • Department of Information and Communication Engineering
      Taiden, Daejeon, South Korea
    • Kanagawa University
      Yokohama, Kanagawa, Japan
    • University of Toronto
      • Department of Physics
      Toronto, Ontario, Canada
    • Pohang Accelerator Laboratory
      Urusan, Ulsan, South Korea
  • 1995–2007
    • Kyungpook National University
      • • Department of Physics
      • • Center for High Energy Physics
      • • College of Natural Sciences
      Sangju, North Gyeongsang, South Korea
  • 2001–2003
    • National Institute of Standards and Technology
      • NIST Center for Neutron Research
      Gaithersburg, MD, United States
    • Keimyung University
      • Department of Microbiology
      Seoul, Seoul, South Korea
    • Saga University
      • Department of Chemistry and Applied Chemistry
      Сага Япония, Saga, Japan
    • National Institute of Health Sciences, Japan
      • Division of Cellular and Molecular Toxicology
      Edo, Tōkyō, Japan
  • 1990–2003
    • Asan Medical Center
      Sŏul, Seoul, South Korea
  • 1999–2002
    • Kwandong University
      • College of Medicine
      Gangneung, Gangwon, South Korea
    • Seoul Women's University
      Sŏul, Seoul, South Korea
  • 1998–2002
    • Yeungnam University
      • College of Pharmacy
      Asan, South Chungcheong, South Korea
  • 1996–2001
    • Ulsan University Hospital
      Urusan, Ulsan, South Korea
  • 1992–2001
    • National Cancer Center Korea
      Kōyō, Gyeonggi Province, South Korea
  • 1990–2001
    • Seoul National University Hospital
      • • Department of Radiology
      • • Department of Dermatology
      Seoul, Seoul, South Korea
  • 1999–2000
    • Chungbuk National University
      • • Division of Life Sciences
      • • Department of Biochemistry
      Tyundyu, North Chungcheong, South Korea
  • 1994–1999
    • Seoul Medical Center
      Sŏul, Seoul, South Korea
  • 1993–1999
    • Yonsei University
      • Department of Physics
      Seoul, Seoul, South Korea
    • Chung-Ang University Hospital
      Sŏul, Seoul, South Korea
  • 1994–1997
    • University of Ulsan
      • • Department of Pharmacology
      • • Department of Internal Medicine
      Ulsan, Ulsan, South Korea