1,005 research outputs found
A search for gravitational lensing in 38 X-ray selected clusters of galaxies
We present the results of a CCD imaging survey for gravitational lensing in a
sample of 38 X-ray-selected clusters of galaxies. Our sample consists of the
most X-ray luminous (Lx>= 2x10^{44} erg s^{-1}) clusters selected from the
Einstein Observatory Extended Medium Sensitivity Survey (EMSS) that are
observable from Mauna Kea (dec > -40deg). The sample spans a redshift range of
0.15 0.5. CCD images of the
clusters were obtained in excellent seeing. There is evidence of strong
gravitational lensing in the form of giant arcs (length l > 8'', axis ratio l/w
> 10) in 8 of the 38 clusters. Two additional clusters contain shorter arclets,
and 6 more clusters contain candidate arcs that require follow-up observations
to confirm their lensing origin. Since the survey does not have a uniform
surface brightness limit we do not draw any conclusion based on the statistics
of the arcs found. We note, however, that 60% (3 of 5) of the clusters with Lx
> 10^{45} erg s^{-1}, and none of the 15 clusters with Lx < 4x10^{44} erg
s^{-1} contain giant arcs, thereby confirming that high X-ray luminosity does
identify the most massive systems, and thus X-ray selection is the preferred
method for finding true, rich clusters at intermediate and high redshifts. The
observed geometry of the arcs, most of which are thin, have large axis ratios
(l/w > 10), and are aligned orthogonal to the optical major axes of the
clusters, indicate the cluster core mass density profiles must be compact
(steeper than isothermal). In several cases, however, there is also some
evidence, in the form of possible radial arcs, for density profiles with finite
core radii.Comment: Latex file, 17 pages, 7 jpeg figures, to be published in Astronomy
and Astrophysics Supplement
Galactic Punctuated Equilibrium: How to Undermine Carter's Anthropic Argument in Astrobiology
We investigate a new strategy which can defeat the (in)famous Carter's
"anthropic" argument against extraterrestrial life and intelligence. In
contrast to those already considered by Wilson, Livio, and others, the present
approach is based on relaxing hidden uniformitarian assumptions, considering
instead a dynamical succession of evolutionary regimes governed by both global
(Galaxy-wide) and local (planet- or planetary system-limited) regulation
mechanisms. This is in accordance with recent developments in both astrophysics
and evolutionary biology. Notably, our increased understanding of the nature of
supernovae and gamma-ray bursts, as well as of strong coupling between the
Solar System and the Galaxy on one hand, and the theories of "punctuated
equilibria" of Eldredge and Gould and "macroevolutionary regimes" of Jablonski,
Valentine, et al. on the other, are in full accordance with the regulation-
mechanism picture. The application of this particular strategy highlights the
limits of application of Carter's argument, and indicates that in the real
universe its applicability conditions are not satisfied. We conclude that
drawing far-reaching conclusions about the scarcity of extraterrestrial
intelligence and the prospects of our efforts to detect it on the basis of this
argument is unwarranted.Comment: 3 figures, 26 page
PCV104 Timely Use Of Ace Inhibitors And Arbs After Newly Diagnosed Diabetes Among Older Adults With Hypertension In The U.S
Developing Learning-based Instagram Media on Derivative
This study aims to develop learning media using Instagram and determine its feasibility. This research method used Research and Development (R&D) with the ADDIE development model through 5 stages, namely Analysis, Design, Development, Implementation, and Evaluation. The research was conducted at SMA N 1 Ngemplak. The data collection technique used a validation questionnaire conducted by two teachers and one lecturer and students response questionnaire. The data analysis techniques were descriptive qualitative and quantitative. The result of this research was a derivative learning media in the form of videos presented through Instagram. The feasibility test results showed that the learning media had met three eligibility criteria for learning media. The assessment of media and material experts showed that learning-based Instagram media was in the good category. Based on students' assessment, learning media's feasibility based on Instagram social media was good to use. The correlation between the students response questionnaire and the learning outcome test also showed a unidirectional and significant correlation. It indicated that there was a correspondence between the questionnaire scores and the learning outcome test scores. Based on these results, learning media through Instagram social media is suitable for the learning process
The Dust Content of Galaxy Clusters
We report on the detection of reddening toward z ~ 0.2 galaxy clusters. This
is measured by correlating the Sloan Digital Sky Survey cluster and quasar
catalogs and by comparing the photometric and spectroscopic properties of
quasars behind the clusters to those in the field. We find mean E(B-V) values
of a few times 10^-3 mag for sight lines passing ~Mpc from the clusters'
center. The reddening curve is typical of dust but cannot be used to
distinguish between different dust types. The radial dependence of the
extinction is shallow near the cluster center suggesting that most of the
detected dust lies at the outskirts of the clusters. Gravitational
magnification of background z ~ 1.7 sources seen on Mpc (projected) scales
around the clusters is found to be of order a few per cent, in qualitative
agreement with theoretical predictions. Contamination by different spectral
properties of the lensed quasar population is unlikely but cannot be excluded.Comment: 4 pages, 3 figure
Pengembangan Youtube Bahan Belajar Dari Rumah Untuk Materi Persamaan Linear Satu Variabel Tingkat SMP
Penelitian ini bertujuan untuk mengembangkan Youtube bahan belajar dari rumah yang dapat digunakan dalam pembelajaran persamaan linear satu variabel dan untuk mengetahui kelayakan Youtube bahan belajar dari rumah. Penelitian ini merupakan Research and Development (R&D) model ADDIE, terdiri dari 5 tahapan yaitu : (1) Analysis; (2) Design; (3) Development; (4) Implementation; (5) Evaluation. Instrumen yang digunakan adalah angket validasi, angket respon peserta didik, dan tes hasil belajar. Data dianalisis secara deskriptif, kualitatif dan kuantitatif. Hasil pada tahap analisis adalah mengetahui permasalahan dari hasil wawancara, observasi dan analisis materi kemudian peneliti memberikan solusi berupa pengembangan Youtube bahan belajar dari rumah. Tahap desain menghasilkan perencanaan isi materi, pemilihan software, perancangan isi angket dan pembuatan channel Youtube. Tahap pengembangan menghasilkan pembuatan video Youtube dan penilaian dari validator yang mencapai rata-rata 4,61 (sangat valid). Tahap implementasi memperoleh skor rata-rata dari angket respon peserta didik yaitu 4,31 (baik). Tahap evaluasi memperoleh hasil korelasi angket respon peserta didik dengan tes hasil belajar sebesar r = 0,719. Hasil penelitian ini berupa video Youtube bahan belajar dari rumah dengan channel “Cinta Matematika Kuy” untuk materi persamaan linear satu variabel. Video ini telah melalui uji kelayakan, dan dinyatakan layak digunakan subagai bahan belajar dari rumah
Limits on Dust in Rich Clusters of Galaxies from the Color of Background Quasars
I measure the V-I color distribution of two samples of radio-selected
quasars. Quasars from one sample are projected on the sky within 1 degree of a
rich foreground Abell cluster of galaxies, while quasars from the other sample
are more than 3 degrees from any such cluster . There is no significant
difference between the color distributions of the two samples. The 90\% upper
limit on the relative reddening between the two samples is E(B-V)=0.05 mag.
This result limits the allowed quantity of smoothly distributed dust in rich
clusters, and contradicts previous indications for the existence of such a
component.Comment: Submitted to ApJ Letters. 14 pages incl. 2 figures, uuencoded,
compressed postscript. Also available by anonymous ftp to
ftp://wise3.tau.ac.il/pub/dani/dust.ps.
Anomaly Detection for Diagnosing Failures in a Centrifugal Compressor Train
Predicting machine failures is of the utmost importance in industrial systems as it can turn expensive crashes and repair costs into affordable maintenance costs. To this end, this paper presents preliminary work for detecting failures in a centrifugal compressor train based on sensorial data. We show the detection capabilities of a two-step process consisting of: (1) a preprocessing step to reduce the dimensionality of the input data using Principal Component Analysis, and (2) an anomaly detection step using the Mahalanobis distance to detect anomalous observations on the sensors' data. The experiments using real-world data demonstrate the feasibility of our approach and the ability of the method to detect the failures eight days in advance
Ce(OH)2Cl and lanthanide-substituted variants as precursors to redox-active CeO2 materials
The cerium(III) hydroxide chloride Ce(OH)2Cl crystallises directly as a polycrystalline powder from a solution of CeCl3·7H2O in poly(ethylene) glycol (Mn = 400) heated at 240 °C and is found to be isostructural with La(OH)2Cl, as determined from high-resolution synchrotron powder X-ray diffraction (P21/m, a = 6.2868(2) Å, b = 3.94950(3) Å, c = 6.8740(3) Å, β = 113.5120(5)°). Replacement of a proportion of the cerium chloride in synthesis by a second lanthanide chloride yields a set of materials Ce1−xLnx(OH)2Cl for Ln = La, Pr, Gd, Tb. For La the maximum value of x is 0.2, with an isotropic expansion of the unit cell, but for the other lanthanides a wider composition range is possible, and the lattice parameters show an isotropic contraction with increasing x. Thermal decomposition of the hydroxide chlorides at 700 °C yields mixed-oxides Ce1−xLnxO2−δ that all have cubic fluorite structures with either expanded (Ln = La, Gd) or contracted (Ln = Pr, Tb) unit cells compared to CeO2. Scanning electron microscopy shows a shape memory effect in crystal morphology upon decomposition, with clusters of anisotropic sub-micron crystallites being seen in the precursor and oxide products. The Pr- and Tb-substituted oxides contain the substituent in a mixture of +3 and +4 oxidation states, as seen by X-ray absorption near edge structure spectroscopy at the lanthanide LIII edges. The mixed oxide materials are examined using temperature programmed reduction in 10%H2 in N2, which reveals redox properties suitable for heterogeneous catalysis, with the Pr-substituted materials showing the greatest reducibility at lower temperature
SDSS-RASS: Next Generation of Cluster-Finding Algorithms
We outline here the next generation of cluster-finding algorithms. We show
how advances in Computer Science and Statistics have helped develop robust,
fast algorithms for finding clusters of galaxies in large multi-dimensional
astronomical databases like the Sloan Digital Sky Survey (SDSS). Specifically,
this paper presents four new advances: (1) A new semi-parametric algorithm -
nicknamed ``C4'' - for jointly finding clusters of galaxies in the SDSS and
ROSAT All-Sky Survey databases; (2) The introduction of the False Discovery
Rate into Astronomy; (3) The role of kernel shape in optimizing cluster
detection; (4) A new determination of the X-ray Cluster Luminosity Function
which has bearing on the existence of a ``deficit'' of high redshift, high
luminosity clusters. This research is part of our ``Computational
AstroStatistics'' collaboration (see Nichol et al. 2000) and the algorithms and
techniques discussed herein will form part of the ``Virtual Observatory''
analysis toolkit.Comment: To appear in Proceedings of MPA/MPE/ESO Conference "Mining the Sky",
July 31 - August 4, 2000, Garching, German
- …