4,366 research outputs found
Improved and Quality-assessed Emission and Absorption Line measurements in Sloan Digital Sky Survey galaxies
We present a new database of absorption and emission-line measurements based
on the entire spectral atlas from the Sloan Digital Sky Survey (SDSS) 7th data
release of galaxies within a redshift of 0.2. Our work makes use of the
publicly available penalized pixel-fitting(pPXF) and gas and absorption line
fitting (gandalf) IDL codes, aiming to improve the existing measurements for
stellar kinematics, the strength of various absorption-line features, and the
flux and width of the emissions from different species of ionised gas. Our fit
to the stellar continuum uses both standard stellar population models and
empirical templates obtained by combining a large number of stellar spectra in
order to fit a subsample of high-quality SDSS spectra for quiescent galaxies.
Furthermore, our fit to the nebular spectrum includes an exhaustive list of
both recombination and forbidden lines. Foreground Galactic extinction is
implicitly treated in our models, whereas reddening in the SDSS galaxies is
included in the form of a simple dust screen component affecting the entire
spectrum that is accompanied by a second reddening component affecting only the
ionised gas emission. In order to check for systematic departures, we provide a
quality assessment for our fit to the SDSS spectra in our sample. This quality
assessment also allows the identification of objects with either problematic
data or peculiar features. For example, based on the quality assessment,
approximately 1% of the SDSS spectra classified as "galaxies" by the SDSS
pipeline do in fact require additional broad lines to be matched, even though
they do not show a strong continuum from an active nucleus, as do the SDSS
objects classified as "quasars". Finally, we provide new spectral templates for
galaxies of different Hubble types, obtained by combining the results of our
spectral fit for a subsample of 452 morphologically selected objects.Comment: Accepted for publication in ApJS. 23 pages, 14 figures, 4 tables. A
version with high-resolution figures is available at
http://gem.yonsei.ac.kr/~ksoh/ossy/arXiv/Oh_11_OSSY.pd
Evolution of green shipping research: themes and methods
Over the past 30 years, there have been growing concerns on theenvironmental impacts of maritime transportation, which have attractedgreat attention from both academia and practitioners. Understandingdevelopments in this area can help guide future research. We conducteda comprehensive review of green shipping research, comprising 213papers published in transportation journals in SSCI of 2017 over theperiod 1988–2017. We find that research on green shipping hasincreased greatly since 2012, accounting for 77.5% of the reviewedpapers. The main focus today on green shipping was on air pollution,and the classification of green shipping practice, such as technical measures,operational options, market-based measures, and recycling andreusing, is becoming clear. According to the existing studies, futureresearch on green shipping must strengthen technology research tonot only solve practical problems, but also to establish a theoreticalgreen shipping system. Moreover, researchers from different countriescould cooperate with each other to give effective suggestions on settingstandards and laws of green shipping. Finally, we identify the futureresearch themes will focus on setting up green shipping system andlegislation and policy
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