26 research outputs found
Evaluation and Analysis of Distributed Graph-Parallel Processing Frameworks
A number of graph-parallel processing frameworks have been proposed to address the needs of processing complex and large-scale graph structured datasets in recent years. Although significant performance improvement made by those frameworks were reported, comparative advantages of each of these frameworks over the others have not been fully studied, which impedes the best utilization of those frameworks for a specific graph computing task and setting. In this work, we conducted a comparison study on parallel processing systems for large-scale graph computations in a systematic manner, aiming to reveal the characteristics of those systems in performing common graph algorithms with real-world datasets on the same ground. We selected three popular graph-parallel processing frameworks (Giraph, GPS and GraphLab) for the study and also include a representative general data-parallel computing systemâ Sparkâin the comparison in order to understand how well a general data-parallel system can run graph problems. We applied basic performance metrics measuring speed, resource utilization, and scalability to answer a basic question of which graph-parallel processing platform is better suited for what applications and datasets. Three widely-used graph algorithmsâ clustering coefficient, shortest path length, and PageRank scoreâwere used for benchmarking on the targeted computing systems.We ran those algorithms against three real world network datasets with diverse characteristics and scales on a research cluster and have obtained a number of interesting observations. For instance, all evaluated systems showed poor scalability (i.e., the runtime increases with more computing nodes) with small datasets likely due to communication overhead. Further, out of the evaluated graphparallel computing platforms, PowerGraph consistently exhibits better performance than others
Multicolor photometry of the galaxies in the central region of Abell 2634
An optical photometric observation with the BATC multicolor system is carried
out for the central 56' x 56' region of the nearby cluster of galaxies, Abell
2634. We achieved the spectral energy distributions (SEDs) of 5572 sources
detected down to mag, including 178 previously known galaxies, with
fourteen filters covering a wavelength range from 3600 \AA\ to 10000 \AA. After
excluding the foreground and background galaxies, a sample of 124 known members
is formed for an investigation of the SED properties. Based on the knowledge of
SED properties of member galaxies, we performed the selection of faint galaxies
belonging to Abell 2634. The color-color diagrams are powerful in the
star/galaxy separation, and 359 faint galaxies are selected by their color
features. The technique of photometric redshift and color-magnitude correlation
for the early-type galaxies are applied for these faint galaxies, and a list of
74 faint member galaxies is achieved. Basis on the enlarged sample of member
galaxies, the spatial distribution and color-magnitude relation of the galaxies
in core region of Abell 2634 are discussed. We find a tendency that the color
index dispersion of the early-type members is larger for the outer region,
which might reflect some clues about the environmental effect on the evolution
of galaxies in a cluster.Comment: 35 pages, 21 Postscript figures and tables, LaTeX, using aasms4.st
Photometric Redshift Determination with the BATC Multicolor System
In this paper, we present the methodology of photometric redshift
determination with the BATC 15-color system by using hyperz program. Both
simulated galaxies and real galaxies with known redshifts were used to estimate
the accuracy of redshifts inferred from the multicolor photometry. From the
test with simulated galaxies, the uncertainty in the inferred redshifts is
about for a given range of photometric uncertainty of . The results with the 27 real galaxies are in good agreement with the
simulated ones. The advantage of using BATC intermediate-band system to derive
redshift is clear through the comparison with the UBVRI broad-band system. The
accuracy in redshift determination with BATC system is mainly affected by the
selection of filters and the photometric uncertainties in the observation. When
we take the limiting magnitudes of the 15 filters into account, we find that
redshift can be determined with good accuracy for galaxies with redshifts less
than 0.5, using only filters with central wavelengths shorter than 6000 A.Comment: 22 pages, accepted for publishing by PAS
15 colour photometry of Landolt SA95 standard star field
In this paper, we present a set of photometric observations in 15 colors of
stars in the Landolt covered by the system range from 300 nm to 1000 nm. Visual
magnitudes of the stars being studied in the field are from 10th to 20th mag.
The observational methodology and the data reduction procedures are described.
The relationships between the BATC intermediate-band system and the Landolt
UBVRI broad band system are obtained. A catalogue of the photometry has been
produced which contains the SEDs of 3613 stars. The electronic form of this
catalogue can be accessed at the CDS via anonymous ftp to cdsarc.u-strasbg.fr.Comment: 21 pages, accepted for publishing by A&
Chandra X-ray Analysis of Galaxy Cluster A168
We present Chandra X-ray observations of galaxy cluster A168 (z=0.045). Two
X-ray peaks with a projected distance of 676 kpc are found to be located close
to two dominant galaxies, respectively. Both peaks are significantly offset
from the peak of the number density distribution of galaxies. This suggests
that A168 consists of two subclusters, a northern subcluster (A168N) and a
southern subcluster (A168S). Further X-ray imaging analysis reveals that (1)
the X-ray isophotes surrounding the two X-ray peaks are heavily distorted, (2)
an elongated and ontinuous filament connects the two X-ray peaks. These suggest
that strong interactions have occurred between the two subclusters. Spectral
analysis shows that A168 has a mean temperature of 2.53 +/- 0.09 keV and a mean
metallicity of 0.31 +/- 0.04 Z_{solar}. The metallicity is roughly a constant
across the cluster but the temperature shows some systematic variations. Most
X-ray, optical and radio properties of A168 are consistent with it being an
off-axis merger several Gyrs after a core passage, although detailed numerical
simulations are required to see whether the observed properties, in particular
the significant offset between the optical and X-ray centers, can be reproduced
in such a scenario.Comment: 17 pages, 7 figures, to be published in ApJ. When this paper was
being refereed, Eric Hallman and Maxim Markevitch carried out a similar work
(astro-ph/0406322); our results are in broad agreemen
Strong [O III] {\lambda}5007 Compact Galaxies Identified from SDSS DR16 and Their Scaling Relations
Green pea galaxies are a special class of star-forming compact galaxies with
strong [O III]{\lambda}5007 and considered as analogs of high-redshift
Ly{\alpha}-emitting galaxies and potential sources for cosmic reionization. In
this paper, we identify 76 strong [O III]{\lambda}5007 compact galaxies at z <
0.35 from DR1613 of the Sloan Digital Sky Survey. These galaxies present
relatively low stellar mass, high star formation rate, and low metallicity.
Both star-forming main sequence relation (SFMS) and mass-metallicity relation
(MZR) are investigated and compared with green pea and blueberry galaxies
collected from literature. It is found that our strong [O III] {\lambda}5007
compact galaxies share common properties with those compact galaxies with
extreme star formation and show distinct scaling relations in respect to those
of normal star-forming galaxies at the same redshift. The slope of SFMS is
higher, indicates that strong [O III]{\lambda}5007 compact galaxies might grow
faster in stellar mass. The lower MZR implies that they may be less chemically
evolved and hence on the early stage of star formation. A further environmental
investigation confirms that they inhabit relatively low-density regions. Future
largescale spectroscopic surveys will provide more details on their physical
origin and evolution.Comment: 12 pages, 8 figures, 1 table. Published in A