Korean Institute for Advanced Study

Korean, South Korea

Korean Institute for Advanced Study

Korean, South Korea
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Hoppe J.,Korean Institute for Advanced Study | Hoppe J.,KTH Royal Institute of Technology | Hoppe J.,Sogang University
Journal of Physics A: Mathematical and Theoretical | Year: 2013

The classical dynamics of M-dimensional extended objects arising from stationary points of the world volume swept out in space time is discussed from various points of view. A introduction to the Hamiltonian mechanics of bosonic compact M(em)branes is given, emphasing the diversity of the different formulations and gauge choices. For moving hypersurfaces, a graph description-including its nonlinear realization of Lorentz invariance-and hydrodynamic formulations (in light-cone coordinates as well as when choosing the time coordinate of a Lorentz observer as the dependent variable) are presented. A matrix regularization for M = 2 (existing for all topologies) is explained in detail for the 2-sphere, as well as multilinear formulations for M > 2. The recently found dynamical symmetry that exists for all M and related reconstruction algebras are covered, just as some explicit solutions of the level-set equations. © 2013 IOP Publishing Ltd.

Lee J.-U.,Sogang University | Seck N.M.,Sogang University | Yoon D.,Sogang University | Yoon D.,University of Cambridge | And 3 more authors.
Carbon | Year: 2014

The polarization dependence of the double resonant Raman scattering (2D) band in bilayer graphene (BLG) is studied as a function of the excitation laser energy. It has been known that the complex shape of the 2D band of BLG can be decomposed into four Lorentzian peaks with different Raman frequency shifts attributable to four individual scattering paths in the energy-momentum space. From our polarization dependence study, however, we reveal that each of the four different peaks is actually doubly degenerate in its scattering channels, i.e., two different scattering paths with similar Raman frequency shifts for each peak. We find theoretically that one of these two paths, ignored for a long time, has a small contribution to their scattering intensities but are critical in understanding their polarization dependences. Because of this, the maximum-to-minimum intensity ratios of the four peaks show a strong dependence on the excitation energy, unlike the case of single-layer graphene (SLG). Our findings thus reveal another interesting aspect of electron-phonon interactions in graphitic systems. © 2014 Elsevier Ltd. All rights reserved.

Hibon P.,Aix - Marseille University | Hibon P.,Korean Institute for Advanced Study | Cuby J.-G.,Aix - Marseille University | Willis J.,European Southern Observatory | And 8 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. The Lyα luminosity function (LF) of high-redshift Lyα emitters (LAEs) is one of the few observables of the re-ionization epoch accessible with 8-10 m class telescopes. The evolution of the LAE LF with redshift is dependent upon the physical evolution of LAEs and the ionisation state of the Universe towards the end of the Dark Ages. Methods. We performed a narrow-band imaging program at 1.06 μm using CFHT/WIRCam. The observations target Lyα emitters at redshift z ∼ 7.7 in the CFHT-LS D1 field. From these observations we derived a photometric sample of 7 LAE candidates at z ∼ 7.7. Results. We derive luminosity functions for the full sample of seven objects and for subsamples of four objects. Assuming the brightest objects in our sample are real, we find that the resulting luminosity function is not consistent with previous work at lower redshifts. More definitive conclusions will require spectroscopic confirmation. © 2010 ESO.

Lee J.-U.,Sogang University | Park J.,Sogang University | Son Y.-W.,Korean Institute for Advanced Study | Cheong H.,Sogang University
Nanoscale | Year: 2015

The resonance effects on the Raman spectra from 5 to 900 cm-1 of few-layered MoS2 thin films up to 14-layers were investigated by using six excitation energies. For the main first-order Raman peaks, the intensity maximum occurs at ∼2.8 eV for single layered and at ∼2.5 eV for few-layered MoS2, which correspond to the band-gap energy. At the excitation energy of 1.96 eV, several anomalous behaviors are observed. Many second-order peaks are anomalously enhanced even though the main first-order peaks are not enhanced. In the low-frequency region (<100 cm-1), a broad peak centered at ∼38 cm-1 and its second order peak at 76 cm-1 appear for the excitation energy of 1.96 eV. These anomalous resonance effects are interpreted as occuring due to the strong resonance with excitons or exciton-polaritons. © 2015 The Royal Society of Chemistry.

Schneider D.P.,Pennsylvania State University | Richards G.T.,Drexel University | Hall P.B.,York University | Strauss M.A.,Princeton University | And 48 more authors.
Astronomical Journal | Year: 2010

We present the fifth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog, which is based upon the SDSS Seventh Data Release. The catalog, which contains 105,783 spectroscopically confirmed quasars, represents the conclusion of the SDSS-I and SDSS-II quasar survey. The catalog consists of the SDSS objects that have luminosities larger than Mi = -22.0 (in a cosmology with H 0 = 70kms-1Mpc-1, ΩM = 0.3, and ΩΛ = 0.7), have at least one emission line with FWHM larger than 1000kms-1 or have interesting/complex absorption features, are fainter than i 15.0, and have highly reliable redshifts. The catalog covers an area of ≈ 9380 deg2. The quasar redshifts range from 0.065 to 5.46, with a median value of 1.49; the catalog includes 1248 quasars at redshifts greater than 4, of which 56 are at redshifts greater than 5. The catalog contains 9210 quasars with i < 18; slightly over half of the entries have i < 19. For each object the catalog presents positions accurate to better than 01rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200 at a spectral resolution of ≃ 2000; the spectra can be retrieved from the SDSS public database using the information provided in the catalog. Over 96% of the objects in the catalog were discovered by the SDSS. We also include a supplemental list of an additional 207 quasars with SDSS spectra whose archive photometric information is incomplete. © 2010. The American Astronomical Society. All rights reserved.

Geller M.J.,Harvard - Smithsonian Center for Astrophysics | Hwang H.S.,Korean Institute for Advanced Study
Astronomische Nachrichten | Year: 2015

During the last three decades progress in mapping the Universe from an age of 400 000 years to the present has been stunning. Instrument/telescope combinations have naturally determined the sampling of various redshift ranges. Here we outline the impact of the Hectospec on the MMT on exploration of the Universe in the redshift range 0.2 ≲ z ≲ 0.8. We focus on dense redshift surveys, SHELS and HectoMAP. SHELS is a complete magnitude limited survey covering 8 square degrees. The HectoMAP survey combines a red-selected dense redshift survey and a weak lensing map covering 50 square degrees. Combining the dense redshift survey with a Subaru HyperSuprimeCam (HSC) weak lensing map will provide a powerful probe of the way galaxies trace the distribution of dark matter on a wide range of physical scales. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim). Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Chang S.H.,Pukyong National University | Lee J.S.,Korean Institute for Advanced Study
Journal of the Korean Physical Society | Year: 2016

The switching-type transition induced by external parameters, e.g., the thermal conductance and the temperature, has been intensively investigated by using the thermal random circuit breaker (RCB) network model. Recently, some researchers argued that the thermal RCB network model was not able to predict the switching-type transition induced by a new parameter, i.e., the compliance current. However, we demonstrate that the compliance current-induced transition can be explained by using the thermal RCB network model. This work clearly demonstrates that the basic mechanism of unipolar resistance switching is closely related to the formation and the rupture of conducting filaments due to the bias voltage and thermal effects. © 2016, The Korean Physical Society.

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