Young Sun Lee

University of Texas at Austin, Austin, Texas, United States

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Publications (154)548.91 Total impact

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    ABSTRACT: The tension between the Hipparcos parallax of the Pleiades and other independent distance estimates continues even after the new reduction of the Hipparcos astrometric data and the development of a new geometric distance measurement for the cluster. A short Pleiades distance from the Hipparcos parallax predicts a number of stars in the solar neighborhood that are sub-luminous at a given photospheric abundance. We test this hypothesis using spectroscopic abundances for a subset of stars in the Hipparcos catalog, which occupy the same region as the Pleiades in the color-magnitude diagram. We derive stellar parameters for 170 nearby G and K type field dwarfs in the Hipparcos catalog based on high-resolution spectra obtained using KPNO 4-m echelle spectrograph. Our analysis shows that, when the Hipparcos parallaxes are adopted, most of our sample stars follow empirical color-magnitude relations. A small fraction of stars are too faint compared to main-sequence fitting relations by $\Delta M_V \geq 0.3$ mag, but the differences are marginal at a $2\sigma$ level partly due to relatively large parallax errors. On the other hand, we find that photometric distances of stars showing signatures of youth as determined from lithium absorption line strengths and $R'_{\rm HK}$ chromospheric activity indices are consistent with the Hipparcos parallaxes. Our result is contradictory to a suggestion that the Pleiades distance from main-sequence fitting is significantly altered by stellar activity and/or the young age of its stars, and provides an additional supporting evidence for the long distance scale of the Pleiades.
    No preview · Article · Jan 2016
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    ABSTRACT: We describe an application of the SEGUE Stellar Parameter Pipeline (SSPP) to medium-resolution stellar spectra obtained by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), in order to determine estimates of the stellar atmospheric parameters (Teff, log g, and [Fe/H]) and the abundance ratios ([α/Fe] and [C/Fe]). By performing a coordinate match with the LAMOST stellar database, we selected stars with LAMOST spectra in common with stars having available spectroscopy from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), the RAdial Velocity Experiment (RAVE), and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We ran the selected LAMOST stellar spectra from each survey through SSPP, and compared the stellar parameters down to signal-to-noise ratio (S/N) of 10 and chemical abundances down to S/N = 20 derived by SSPP with those determined by the APOGEE, RAVE, and SEGUE software pipelines. Our results show that the derived stellar parameters generally agree quite well, even though there exist some small systematic offsets with small scatter in Teff, , and [Fe/H], due to the use of different temperature scales, abundance scales, and calibrations adopted by each survey. Comparison of the [α/Fe] determinations for LAMOST spectra suggests no sign of significant systematic offsets (<-0.04 dex), with a small scatter (<0.08 dex) relative to stars in common with APOGEE and SEGUE. The [C/Fe] estimates determined for the LAMOST spectra also exhibit good agreement, with a very small offset (∼0.01 dex) and scatter (∼0.12 dex) relative to the SEGUE stars, while there exists about a -0.19 dex offset, with a small scatter of ∼0.13 dex, for the APOGEE sample. Due to the existence of small offsets in the stellar parameters and abundances among difference data sets, optimal results when combining the different data sets will be obtained by removing the offsets. Once accomplished, the stellar parameters and chemical abundances estimated by SSPP from the LAMOST stellar spectra should provide a reliable database for studies of the Galactic disk and halo systems. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Dec 2015 · The Astronomical Journal
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    ABSTRACT: In a pioneering effort, Preston et al. reported that the colors of blue horizontal-branch (BHB) stars in the halo of the Galaxy shift with distance, from regions near the Galactic center to about 12 kpc away, and interpreted this as a correlated variation in the ages of halo stars, from older to younger, spanning a range of a few Gyrs. We have applied this approach to a sample of some 4700 spectroscopically confirmed BHB stars selected from the Sloan Digital Sky Survey to produce the first "chronographic map" of the halo of the Galaxy. We demonstrate that the mean de-reddened g$-$r color, <(g$-$r)o>, increases outward in the Galaxy from $-$0.22 to $-$0.08 (over a color window spanning [$-$0.3:0.0]) from regions close to the Galactic center to ~40 kpc, independent of the metallicity of the stars. Models of the expected shift in the color of the field BHB stars based on modern stellar evolutionary codes confirm that this color gradient can be associated with an age difference of roughly 2-2.5 Gyrs, with the oldest stars concentrated in the central ~15 kpc of the Galaxy. Within this central region, the age difference spans a mean color range of about 0.05 mag (~0.8 Gyrs). Furthermore, we show that chronographic maps can be used to identify individual substructures, such as the Sagittarius Stream, and overdensities in the direction of Virgo and Monoceros, based on the observed contrast in their mean BHB colors with respect to the foreground/background field population.
    Full-text · Article · Oct 2015
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    ABSTRACT: We obtain a new determination of the metallicity distribution function (MDF) of stars within $\sim5$-$10$ kpc of the Sun, based on recently improved co-adds of $ugriz$ photometry for Stripe 82 from the Sloan Digital Sky Survey. Our new estimate uses the methodology developed previously by An et al. to study in situ halo stars, but is based on a factor of two larger sample than available before, with much-improved photometric errors and zero-points. The newly obtained MDF can be divided into multiple populations of halo stars, with peak metallicities at [Fe/H] $\approx -1.4$ and $-1.9$, which we associate with the inner-halo and outer-halo populations of the Milky Way, respectively. We find that the kinematics of these stars (based on proper-motion measurements at high Galactic latitude) supports the proposed dichotomy of the halo, as stars with retrograde motions in the rest frame of the Galaxy are generally more metal-poor than stars with prograde motions, consistent with previous claims. In addition, we generate mock catalogs of stars from a simulated Milk Way halo system, and demonstrate for the first time that the chemically- and kinematically-distinct properties of the inner- and outer-halo populations are qualitatively in agreement with our observations. The decomposition of the observed MDF and our comparison with the mock catalog results suggest that the outer-halo population contributes on the order of $\sim35\%$-$55\%$ of halo stars in the local volume.
    No preview · Article · Oct 2015
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    ABSTRACT: Objective: To determine whether visually stratified CT findings and pulmonary function variables are helpful in predicting mortality in patients with combined pulmonary fibrosis and emphysema (CPFE). Methods: We retrospectively identified 113 patients with CPFE who underwent high-resolution CT between January 2004 and December 2009. The extent of emphysema and fibrosis on CT was visually assessed using a six- and five-point scale, respectively. Univariate and multivariate Cox proportional hazards regression analyses were performed to determine the prognostic value of visually stratified CT findings and pulmonary function variables in CPFE patients. Differences in 5-year survival rates in CPFE patients according to the extent of honeycombing were calculated using Kaplan-Meier analysis. Results: An increase in the extent of visually stratified honeycombing on CT (hazard ratio [HR] 1.95, P = 0.018, 95% confidence interval [CI] 1.12 to 3.39) and reduced diffusing capacity of lung for carbon monoxide (DLCO) (HR 0.97, P = 0.017, 95% CI 0.94 to 0.99) were independently associated with increased mortality. In CPFE patients, the 5-year survival was 78.5% for < 5% honeycombing, 55.7% for 6 - 25% honeycombing, 32% for 26 - 50% honeycombing, and 33.3% for > 50% honeycombing on CT. Conclusion: The > 50% honeycombing on CT and reduced DLCO are important prognostic factors in CPFE. Advances in Knowledge: Visual estimation of honeycombing extent on CT can help in the prediction of prognosis in CPFE.
    No preview · Article · Sep 2015 · The British journal of radiology
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    ABSTRACT: We report the discovery of one extremely metal-poor (EMP; [Fe/H]<-3) and one ultra metal-poor (UMP; [Fe/H]<-4) star selected from the SDSS/SEGUE survey. These stars were identified as EMP candidates based on their medium-resolution (R~2,000) spectra, and were followed-up with high-resolution (R~35,000) spectroscopy with the Magellan-Clay Telescope. Their derived chemical abundances exhibit good agreement with those of stars with similar metallicities. We also provide new insights on the formation of the UMP stars, based on comparison with a new set of theoretical models of supernovae nucleosynthesis. The models were matched with 20 UMP stars found in the literature, together with one of the program stars (SDSS J1204+1201), with [Fe/H]=-4.34. From fitting their abundances, we find that the supernovae progenitors, for stars where carbon and nitrogen are measured, had masses ranging from 20.5 M_sun to 28 M_sun and explosion energies from 0.3 to 0.9x10^51 erg. These results are highly sensitive to the carbon and nitrogen abundance determinations, which is one of the main drivers for future high-resolution follow-up of UMP candidates. In addition, we are able to reproduce the different CNO abundance patterns found in UMP stars with a single progenitor type, by varying its mass and explosion energy.
    Preview · Article · Jul 2015 · The Astrophysical Journal
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    ABSTRACT: The relationship between protein arginine methyltransferases (PRMTs) and insulin synthesis in β-cells is not yet well understood. In this study, we showed that /PRMT4 expression was increased in INS-1 and HIT-T15 pancreatic β-cells under high glucose conditions. In addition, asymmetric dimethylation of Arg17 in histone H3 was significantly increased in both cell lines in the presence of glucose. Inhibition or knockdown of PRMT4 suppressed glucose-induced insulin gene expression in INS-1 cells by 81.6% and 79%, respectively. Additionally, overexpression of a mutant PRMT4 also significantly repressed insulin gene expression. Consistently, insulin secretion induced in response to high glucose was decreased by both PRMT4 inhibition and knockdown. Moreover, inhibition of PRMT4 blocked high glucose-induced insulin gene expression and insulin secretion in primary pancreatic islets. These results suggest that PRMT4 might be a key regulator of high glucose-induced insulin secretion from pancreatic β-cells via H3R17 methylation.
    No preview · Article · Apr 2015 · Journal of Molecular Endocrinology
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    ABSTRACT: We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125 kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey's SEGUE project. We use a position-velocity clustering estimator (the 4distance) and a smooth stellar halo model to quantify the amount of substructure in the halo. Overall, we find that the halo as a whole is highly structured, and confirm earlier work using BHB stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius. In addition, we find that the amount of substructure in the halo increases with increasing metallicity, and that the K giant sample shows significantly stronger substructure than the BHB stars, which only sample the most metal poor stars. Using a friends-of-friends algorithm to identify groups, we find that a large fraction ($\sim 33\%$) of the stars in groups in our sample are associated with Sgr. We also identify stars belonging to other halo star streams, including the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. However, a large fraction of stars in our sample (more than 50\%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity.
    Preview · Article · Mar 2015 · The Astrophysical Journal

  • No preview · Article · Mar 2015
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    ABSTRACT: We aimed to estimate the prevalence of combined pulmonary fibrosis and emphysema (CPFE) and describe the follow-up CT results of CPFE in asymptomatic smokers. This study was retrospective, and approved by an institutional review board. CT images of 2,016 current or previous male smokers who underwent low-dose chest CT at our healthcare centre were reviewed. Quantitative CT analysis was used to assess the extent of emphysema, and two radiologists visually analyzed the extent of fibrosis. Changes in fibrosis (no change, improvement, or progression) were evaluated on follow-up CT imaging (n = 42). Kaplan-Meier survival analysis, multivariate logistic regression and its ROC curve were used for survival and progression analysis. The prevalence of CPFE among asymptomatic male smokers was 3.1 % (63/2,016). The median follow-up period was 50.4 months, and 72.7 % (16/22) of continued smoker had progressing fibrosis on follow-up CT. CPFE progressed more rapidly in continuous smokers than in former smokers (p = 0.002). The 3.5-year follow-up period after initial CPFE diagnosis maximized the sum of sensitivity and specificity of CPFE progression prediction in continuous smokers. The prevalence of CPFE turned out not to be inconsiderable in asymptomatic male smokers, but serial CT follow-up would be helpful in recognizing disease progression. • The prevalence of CPFE in asymptomatic smokers is 3.1 % (63/2,016). • Progression of CPFE is associated with smoking status. • 3.5 years of follow-up period would be needed to identify CPFE progression.
    No preview · Article · Feb 2015 · European Radiology
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    ABSTRACT: We present carbon abundances of red giants in Milky Way globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC 2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax, Ursa Minor, and Draco. This sample doubles the number of dSph stars with measurements of [C/Fe]. The [C/Fe] ratio in the clusters decreases with increasing luminosity above log(L/L_sun) ~= 1.6, which can be explained by deep mixing in evolved giants. The same decrease is observed in dSphs, but the initial [C/Fe] of the dSph giants is not uniform. Stars in dSphs at lower metallicities have larger [C/Fe] ratios. We hypothesize that [C/Fe] (corrected to the initial carbon abundance) declines with increasing [Fe/H] due to the metallicity dependence of the carbon yield of asymptotic giant branch stars and due to the increasing importance of Type Ia supernovae at higher metallicities. We also identified 11 very carbon-rich giants (8 previously known) in three dSphs. However, our selection biases preclude a detailed comparison to the carbon-enhanced fraction of the Milky Way stellar halo. Nonetheless, the stars with [C/Fe] < +1 in dSphs follow a different [C/Fe] track with [Fe/H] than the halo stars. Specifically, [C/Fe] in dSphs begins to decline at lower [Fe/H] than in the halo. The difference in the metallicity of the [C/Fe] "knee" adds to the evidence from [alpha/Fe] distributions that the progenitors of the halo had a shorter timescale for chemical enrichment than the surviving dSphs.
    Preview · Article · Jan 2015 · The Astrophysical Journal
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    ABSTRACT: We have developed a procedure that estimates distances to stars using measured spectroscopic and photometric quantities. It employs a Bayesian approach to build the probability distribution function over stellar evolutionary models given the data, delivering estimates of expected distance for each star individually. Our method provides several alternative distance estimates for each star in the output, along with their associated uncertainties. The code was first tested on simulations, successfully recovering input distances to mock stars with errors that scale with the uncertainties in the adopted spectro-photometric parameters, as expected. The code was then validated by comparing our distance estimates to parallax measurements from the Hipparcos mission for nearby stars (< 60 pc), to asteroseismic distances of CoRoT red giant stars, and to known distances of well-studied open and globular clusters. The photometric data of these reference samples cover both the optical and near infra-red wavelengths. The spectroscopic parameters are also based on spectra taken at various wavelengths, with varying spectral coverage and resolution: the Radial Velocity Experiment, the Sloan Digital Sky Survey programs SEGUE and APOGEE, and the ESO HARPS instrument. For Hipparcos and CoRoT samples, the typical random distance scatter is 20% or less, both for the nearby and farther data. There is a trend towards underestimating the distances by < 10%. The comparison to star clusters from SEGUE and APOGEE has led to systematic differences < 5% for most cluster stars although with significant scatter. Finally, we tested our distances against those previously determined for a high quality sample of giant stars from the RAVE survey, again finding a reasonable agreement, with only a small systematic trend. Efforts are underway to provide our code to the community by running it on a public server.
    Full-text · Article · Jan 2015
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    ABSTRACT: We present an analysis of a new, large sample of field blue-straggler stars (BSSs) in the thick disk and halo system of the Galaxy, based on stellar spectra obtained during the Sloan Digital Sky Survey (SDSS) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Using estimates of stellar atmospheric parameters obtained from application of the SEGUE Stellar Parameter Pipeline, we obtain a sample of some 8000 BSSs, which are considered along with a previously selected sample of some 4800 blue horizontal-branch (BHB) stars. We derive the ratio of BSSs to BHB stars, F$_{\rm BSS/BHB}$, as a function of Galactocentric distance and distance from the Galactic plane. The maximum value found for F$_{\rm BSS/BHB}$ is $\sim~$4.0 in the thick disk (at 3 kpc $<$ $|$Z$|$ $<$ 4 kpc), declining to on the order of $\sim~1.5-2.0$ in the inner-halo region; this ratio continues to decline to $\sim~$1.0 in the outer-halo region. We associate a minority of field BSSs with a likely extragalactic origin; at least 5$\%$ of the BSS sample exhibit radial velocities, positions, and distances commensurate with membership in the Sagittarius Stream.
    Full-text · Article · Jan 2015 · The Astrophysical Journal
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    ABSTRACT: A new porphyrin-based Co-MOF, [Co(DpyDtolP)](6)center dot 12H(2)O (I), composed of DpyDtolP (5,15-di(4-pyridyl)-10,20-di(4-methylphenyl)porphyrin) was prepared in a high yield and structurally characterized by X-ray crystallography. DpyDtolP is a ditopic N-donor ligand with a large space or gap between the two pyridyl groups at the 5- and 15-positions of the porphyrin backbone. Unlike the pyridyl groups, the 4-tolyl groups in DpyDtolP could not be involved in coordination toward the metal ion. Nevertheless, the presence of these two 4-tolyl groups led to a new infinite three-dimensional framework: Co-MOF (I) with exceptionally high thermal stability at elevated temperature. The single crystals of I maintained their crystallinity even after vacuum drying at 250 degrees C. The resulting dried single crystals diffracted X-ray to give the same structural solution as the as-prepared crystals. The robust framework of I contained micropores that were periodically arranged in a hexagonal symmetry. While the evacuated I moderately sorbed N-2 at 77 K, it sorbed 142.8 cm(3) g(-1) (6.37 mmol g(-1)) of CO2 at 196 K. The CO2 sorption isotherms exhibited a very clear step in both the adsorption and desorption branches. A slight hysteretic behavior was observed between the two branches. Furthermore, the crystal structure of CO2-captured I (I_CO2) revealed that the linear arrangement of the CO2 molecules occupied the inside of micropores, thereby indicating the effective CO2 capture by evacuated I. The evacuated I was also found to be ideal for the encapsulation of iodine molecules in cyclohexane to provide iodine-captured I (I_I-2), which was also characterized by X-ray crystallography. The linear arrangement of polyiodine chains in the micropores was observed, and a single crystal of I_I-2 exhibited electrically conducting behavior. The encapsulation amount of iodine was dependent on the crystal sizes of I. Additionally, the separately prepared microscale sample, micro-I, with a much reduced particle dimension than the bulk I exhibited an enhanced uptake of iodine under the same conditions.
    No preview · Article · Jan 2015 · Crystal Growth & Design
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    ABSTRACT: The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrograph, and a novel optical interferometer. All the data from SDSS-III are now made public. In particular, this paper describes Data Release 11 (DR11) including all data acquired through 2013 July, and Data Release 12 (DR12) adding data acquired through 2014 July (including all data included in previous data releases), marking the end of SDSS-III observing. Relative to our previous public release (DR10), DR12 adds one million new spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic Survey (BOSS) over an additional 3000 sq. deg of sky, more than triples the number of H-band spectra of stars as part of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial velocity measurements of 5500 stars from the Multi-Object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include measured abundances of 15 different elements for each star. In total, SDSS-III added 5200 sq. deg of ugriz imaging; 155,520 spectra of 138,099 stars as part of the Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey; 2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216 stars over 9376 sq. deg; 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5,513 stars. Since its first light in 1998, SDSS has imaged over 1/3 the Celestial sphere in five bands and obtained over five million astronomical spectra.
    Full-text · Article · Jan 2015 · The Astrophysical Journal Supplement Series
  • Jung Yeon Park · Matthew S. Johnson · Young Sun Lee

    No preview · Article · Jan 2015
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    ABSTRACT: Pseudomonas syringae pv. actinidiae is the causal agent of bacterial canker in kiwifruit (genus Actinidia). Multilocus sequence analysis of seven housekeeping and 11 type III effector genes differentiated the virulent P. syringae pv. actinidiae isolates worldwide into three groups designated as Psa1-Psa3. In this work, a total of 12 P. syringae pv. Actinidiae strains, including three Psa1, three Psa2, three Psa3 strains isolated from Korea and three Psa3 strains from Italy, were compared based on their phenotypic properties. Strains with different geographic origins had unique growth patterns as demonstrated by growth rate at several temperatures; all tested strains exhibited maximum growth at temperatures below 22°, while the growth of Psa3 strains was completely inhibited above 30°. Psa3 strains isolated from Korea had longer lag phases than the Psa3 strains from Italy. The Psa2 strains were different from Psa1 and Psa3 strains in the API 20NE test, in which the Psa2 strains could not utilize potassium gluconate, capric acid and trisodium citrate. Psa3 strains isolated from Korea could hydrolyze esculin. The API ZYM test showed that β-glucosidase activity was detected only from Psa3 strains. The strains belonging to the three Psa groups differed with regard to their susceptibility to ampicillin, novobiocin, and oleandomycin.
    No preview · Article · Sep 2014 · Korean Journal of Microbiology
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    Hyo Jin Song · Jong Hun Jun · Dong Guk Cha · Young Sun Lee
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    ABSTRACT: Postoperative visual loss (POVL) after non-ophthalmic surgery is rare, with a reported incidence ranging from 0.013 to 0.2%. Most perioperative visual loss is associated with spine operations and cardiac bypass procedures. The most common cause of POVL is ischemic optic neuropathy. However, there are no previous reports of postoperative visual loss after laparoscopic appendectomy. A 43-year-old female with no underlying disease underwent laparoscopic appendectomy; the operation was completed in one hour and her blood pressure was stable during the perioperative period. In the post-anesthetic care unit, the patient complained of nausea and headache, but she did not complain of any unusual visual symptoms. Approximately one hour after arriving at the ward, the patient complained of visual disturbance. Neurologic examination revealed left homonymous hemianopsia, and subarachnoid hemorrhage and intracerebral hemorrhage were found in the occipital area on brain MRI.
    Preview · Article · Sep 2014 · Korean journal of anesthesiology
  • Qihao Ji · Young Sun Lee
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    ABSTRACT: Built upon prior comparative studies of 3D and 2D films, the current project investigates the effects of 2D and 3D on viewers’ perception of enjoyment, narrative engagement, presence, involvement, and flow across three movie genres (Action/fantasy vs. Drama vs. Documentary). Through a 2 by 3 mixed factorial design, participants (n = 102) were separated into two viewing conditions (2D and 3D) and watched three 15-min film segments. Result suggested both visual production methods are equally efficient in terms of eliciting people’s enjoyment, narrative engagement, involvement, flow and presence, no effects of visual production method was found. In addition, through examining the genre effects in both 3D and 2D conditions, we found that 3D works better for action movies than documentaries in terms of eliciting viewers’ perception of enjoyment and presence, similarly, it improves views’ narrative engagement for documentaries than dramas substantially. Implications and limitations are discussed in detail.
    No preview · Article · Sep 2014 · 3D Research
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    ABSTRACT: A new set of very high signal-to-noise (S/N > 100/1), medium-resolution (R~3000) optical spectra have been obtained for 302 of the candidate "weak-metal" stars selected by Bidelman & MacConnell. We use these data to calibrate the recently developed generalization of the SEGUE Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (Teff, log g , and [Fe/H]) for these non-SDSS/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series. The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the stars with metallicities -1.8 < [Fe/H] <= -0.8 exhibit orbital eccentricities e < 0.4, yet are clearly separated from members of the inner-halo population with similar metallicities by their location in a Lindblad energy vs. angular momentum diagram. A comparison is made with recent results for a similar-size sample of RAVE stars from Ruchti et al. We conclude, based on both of these samples, that the MWTD is real, and must be accounted for in discussions of the formation and evolution of the disk system of the Milky Way.
    Full-text · Article · Aug 2014 · The Astrophysical Journal

Publication Stats

8k Citations
548.91 Total Impact Points


  • 2015
    • University of Texas at Austin
      Austin, Texas, United States
    • Gachon University
      • Lee Gil Ya Cancer and Diabetes Institute
      Sŏngnam, Gyeonggi-do, South Korea
  • 2014-2015
    • Chungnam National University
      • Department of Astronomy and Space Science
      Daiden, Daejeon, South Korea
    • Macquarie University
      • Department of Physics and Astronomy
      Sydney, New South Wales, Australia
    • Hanyang University Medical Center
      Sŏul, Seoul, South Korea
    • Florida State University
      • School of Communication
      Tallahassee, Florida, United States
  • 2012-2015
    • New Mexico State University
      • Department of Astronomy
      Las Cruces, New Mexico, United States
    • University of California Observatories
      Santa Cruz, California, United States
    • Case Western Reserve University
      • Department of Astronomy
      Cleveland, Ohio, United States
    • Universität Heidelberg
      • Centre for Astronomy (ZAH)
      Heidelburg, Baden-Württemberg, Germany
  • 2010-2015
    • Korea University
      • • Department of Chemistry
      • • Department of Psychology
      • • Department of Internal Medicine
      Sŏul, Seoul, South Korea
    • Gyeongsang National University
      Shinshū, Gyeongsangnam-do, South Korea
  • 2008-2015
    • Chonbuk National University Hospital
      Sŏul, Seoul, South Korea
    • Chonbuk National University
      Tsiuentcheou, Jeollabuk-do, South Korea
  • 2009-2014
    • Sunchon National University
      • Department of Biology
      Junten, South Jeolla, South Korea
  • 2013
    • Columbia University
      • Teachers College
      New York, New York, United States
    • University of Utah
      • Department of Physics and Astronomy
      Salt Lake City, Utah, United States
    • Korea Food and Drug Administration
      Seishō-gun, Gyeongsangbuk-do, South Korea
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
  • 2011-2013
    • Catholic University of Korea
      Sŏul, Seoul, South Korea
    • Kosin University
      • College of Medicine
      Tsau-liang-hai, Busan, South Korea
    • LG Household & healthcare
      Sŏul, Seoul, South Korea
    • Seoul Medical Center
      Sŏul, Seoul, South Korea
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, California, United States
  • 2011-2012
    • CUNY Graduate Center
      New York, New York, United States
    • The Ohio State University
      • Department of Astronomy
      Columbus, Ohio, United States
  • 2005-2012
    • Michigan State University
      • Department of Physics and Astronomy
      East Lansing, Michigan, United States
    • RMIT University
      • Department of Chinese Medicine
      Melbourne, Victoria, Australia
    • Chosun University
      Gwangju, Gwangju, South Korea
  • 1988-2009
    • Seoul National University
      • Research Institute of Pharmaceutical Sciences
      Sŏul, Seoul, South Korea
  • 2004-2008
    • Daegu Haany University
      Daikyū, Daegu, South Korea
  • 1987-2007
    • Yonsei University
      • Department of Economics
      Sŏul, Seoul, South Korea
  • 2003
    • Daegu University
      • College of Oriental Medicine
      Daikyū, Daegu, South Korea