58 research outputs found
A Decision Model to Predict the Optimal Size of the Diversified Management Industry from the View of Profit Maximization and Coordination of Industrial Scale
To avoid the risk of single and homogeneous development, China’s coal enterprises have explored a diversified development model and are actively developing coal-based industries such as electric power, coal chemical, coal equipment manufacturing, logistics, and building materials. In previous studies of the diversification strategy, the focus has been placed on the motivation for diversification, the measurement of diversification, and the relationship between diversification and enterprise performance. From an enterprise strategic decision, we predicted the optimal size of each industry by considering the limited enterprise capital, human resources, the synergetic relationship among industrial clusters (mainly the scale coordination), and policy factors. The optimal decision model for diversified industrial management was constructed using linear programming methods. The decision target was to maximize the enterprise’s profit, but to also consider the social and environmental benefits. One of the largest listed coal enterprises in China, China Coal Energy (also a typical diversified enterprise), was selected as a case for analysis. Data were collected from surveys and annual reports from 2010 to 2014. The optimal scales of coal, electric power, chemical, and equipment manufacturing were predicted, and could be used as a reference for future enterprise production decisions. Furthermore, this decision model can be used as a reference for other diversified enterprises
Photometry of Variable Stars from Dome A, Antarctica
Dome A on the Antarctic plateau is likely one of the best observing sites on
Earth thanks to the excellent atmospheric conditions present at the site during
the long polar winter night. We present high-cadence time-series aperture
photometry of 10,000 stars with i<14.5 mag located in a 23 square-degree region
centered on the south celestial pole. The photometry was obtained with one of
the CSTAR telescopes during 128 days of the 2008 Antarctic winter.
We used this photometric data set to derive site statistics for Dome A and to
search for variable stars. Thanks to the nearly-uninterrupted synoptic
coverage, we find 6 times as many variables as previous surveys with similar
magnitude limits. We detected 157 variable stars, of which 55% are
unclassified, 27% are likely binaries and 17% are likely pulsating stars. The
latter category includes delta Scuti, gamma Doradus and RR Lyrae variables. One
variable may be a transiting exoplanet.Comment: Accepted for publication in the Astronomical Journal. PDF version
with high-resolution figures available at
http://faculty.physics.tamu.edu/lmacri/papers/wang11.pd
The First Release of the CSTAR Point Source Catalog from Dome A, Antarctica
In 2008 January the 24th Chinese expedition team successfully deployed the
Chinese Small Telescope ARray (CSTAR) to DomeA, the highest point on the
Antarctic plateau. CSTAR consists of four 14.5cm optical telescopes, each with
a different filter (g, r, i and open) and has a 4.5degree x 4.5degree field of
view (FOV). It operates robotically as part of the Plateau Observatory, PLATO,
with each telescope taking an image every 30 seconds throughout the year
whenever it is dark. During 2008, CSTAR #1 performed almost flawlessly,
acquiring more than 0.3 million i-band images for a total integration time of
1728 hours during 158 days of observations. For each image taken under good sky
conditions, more than 10,000 sources down to 16 mag could be detected. We
performed aperture photometry on all the sources in the field to create the
catalog described herein. Since CSTAR has a fixed pointing centered on the
South Celestial Pole (Dec =-90 degree), all the sources within the FOV of CSTAR
were monitored continuously for several months. The photometric catalog can be
used for studying any variability in these sources, and for the discovery of
transient sources such as supernovae, gamma-ray bursts and minor planets.Comment: 1 latex file and 9 figures The paper is accepted by PAS
The sky brightness and transparency in i-band at Dome A, Antarctica
The i-band observing conditions at Dome A on the Antarctic plateau have been
investigated using data acquired during 2008 with the Chinese Small Telescope
ARray. The sky brightness, variations in atmospheric transparency, cloud cover,
and the presence of aurorae are obtained from these images. The median sky
brightness of moonless clear nights is 20.5 mag arcsec^{-2} in the SDSS
band at the South Celestial Pole (which includes a contribution of about 0.06
mag from diffuse Galactic light). The median over all Moon phases in the
Antarctic winter is about 19.8 mag arcsec^{-2}. There were no thick clouds in
2008. We model contributions of the Sun and the Moon to the sky background to
obtain the relationship between the sky brightness and transparency. Aurorae
are identified by comparing the observed sky brightness to the sky brightness
expected from this model. About 2% of the images are affected by relatively
strong aurorae.Comment: There are 1 Latex file and 14 figures accepted by A
Data Release of the AST3-2 Automatic Survey from Dome A, Antarctica
AST3-2 is the second of the three Antarctic Survey Telescopes, aimed at
wide-field time-domain optical astronomy. It is located at Dome A, Antarctica,
which is by many measures the best optical astronomy site on the Earth's
surface. Here we present the data from the AST3-2 automatic survey in 2016 and
the photometry results. The median 5 limiting magnitude in -band is
17.8 mag and the light curve precision is 4 mmag for bright stars. The data
release includes photometry for over 7~million stars, from which over 3,500
variable stars were detected, with 70 of them newly discovered. We classify
these new variables into different types by combining their light curve
features with stellar properties from surveys such as StarHorse.Comment: 16 pages, 20 figures, accepted for publication in MNRA
PHOTOMETRY OF VARIABLE STARS FROM DOME A, ANTARCTICA: RESULTS FROM THE 2010 OBSERVING SEASON
We present results from a season of observations with the Chinese Small
Telescope ARray (CSTAR), obtained over 183 days of the 2010 Antarctic winter.
We carried out high-cadence time-series aperture photometry of 20,000 stars
with i<15.3 mag located in a 23 square-degree region centered on the south
celestial pole.
We identified 188 variable stars, including 67 new objects relative to our
2008 observations, thanks to broader synoptic coverage, a deeper magnitude
limit and a larger field of view.
We used the photometric data set to derive site statistics from Dome A. Based
on two years of observations, we find that extinction due to clouds at this
site is less than 0.1 and 0.4 mag during 45% and 75% of the dark time,
respectively.Comment: Accepted for publication in the Astronomical Journal. Light curves
and finding charts of all variable stars will be made available at
http://casdc.china-vo.org/data/csta
STELLAR VARIABILITY AND FLARE RATES FROM DOME A, ANTARCTICA, USING 2009 AND 2010 CSTAR OBSERVATIONS
The Chinese Small Telescope ARray (CSTAR) carried out high-cadence
time-series observations of 20.1 square degrees centered on the South Celestial
Pole during the 2008, 2009 & 2010 winter seasons from Dome A in Antarctica. The
nearly-continuous 6 months of dark conditions during each observing season
allowed for >10^6 images to be collected through gri and clear filters,
resulting in the detection of >10^4 sources over the course of 3 years of
operation. The nearly space-like conditions in the Antarctic plateau are an
ideal testbed for the suitability of very small-aperture (<20 cm) telescopes to
detect transient events, variable stars and stellar flares. We present the
results of a robust search for such objects using difference image analysis of
the data obtained during the 2009 & 2010 winter seasons. While no transients
were found, we detected 29 flaring events and find a normalized flaring rate of
5+\-4x10^-7 flare/hour for late-K dwarfs, 1+\-1x10^-6 flare/hour for M dwarfs
and 7+\-1x10^-7 flare/hour for all other stars in our sample. We suggest future
small-aperture telescopes planned for deployment at Dome A would benefit from a
tracking mechanism, to help alleviate effects from ghosting, and a finer pixel
scale, to increase the telescope's sensitivity to faint objects. We find that
the light curves of non-transient sources have excellent photometric qualities
once corrected for systematics, and are limited only by photon noise and
atmospheric scintillation.Comment: Accepted for Publication in the Astronomical Journal, 14 pages, 12
figures and 2 table
Exoplanets in the Antarctic Sky I. The first data release of AST3-II (CHESPA) and new found variables within the southern CVZ of TESS
Located at Dome A, the highest point of the Antarctic plateau, the Chinese Kunlun station is considered to be one of the best ground-based photometric sites because of its extremely cold, dry, and stable atmosphere. A target can be monitored from there for over 40 days without diurnal interruption during a polar winter. This makes Kunlun station a perfect site to search for short-period transiting exoplanets. Since 2008, an observatory has existed at Kunlun station, and three telescopes are working there. Using these telescopes, the AST3 project has been carried out over the last 6 yr with a search for transiting exoplanets as one of its key programs (CHESPA). In the austral winters of 2016 and 2017, a set of target fields in the southern continuous viewing zone (CVZ) of TESS were monitored by the AST3-II telescope. In this paper, we introduce the CHESPA and present the first data release containing photometry of 26,578 bright stars (m(i) <= 15). The best photometric precision at the optimum magnitude for the survey is around 2 mmag. To demonstrate the data quality, we also present a catalog of 221 variables with a brightness variation greater than 5 mmag from the 2016 data. Among these variables, 179 are newly identified periodic variables not listed in the AAVSO database (https://www.aavso.org/), and 67 are listed in the Candidate Target List. These variables will require careful attention to avoid false-positive signals when searching for transiting exoplanets. Dozens of new transiting exoplanet candidates will be released in a subsequent paper
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