7,168 research outputs found
Characterising large-scale structure with the REFLEX II cluster survey
We study the large-scale structure with superclusters from the REFLEX X-ray
cluster survey together with cosmological N-body simulations. It is important
to construct superclusters with criteria such that they are homogeneous in
their properties. We lay out our theoretical concept considering future
evolution of superclusters in their definition, and show that the X-ray
luminosity and halo mass functions of clusters in superclusters are found to be
top-heavy, different from those of clusters in the field. We also show a
promising aspect of using superclusters to study the local cluster bias and
mass scaling relation with simulations.Comment: Proceedings of IAU Symposium 308 "The Zeldovich Universe: Genesis and
Growth of the Cosmic Web", 23-28 June 2014, Tallinn, Estoni
Finding kernel function for stock market prediction with support vector regression
Stock market prediction is one of the fascinating issues of stock market research. Accurate stock prediction becomes the biggest challenge in investment industry because the distribution of stock data is changing over the time. Time series forcasting, Neural Network (NN) and Support Vector Machine (SVM) are once commonly used for prediction on stock price. In this study, the data mining operation called time series forecasting is implemented. The large amount of stock data collected from Kuala Lumpur Stock Exchange is used for the experiment to test the validity of SVMs regression. SVM is a new machine learning technique with principle of structural minimization risk, which have greater generalization ability and proved success in time series prediction. Two kernel functions namely Radial Basis Function and polynomial are compared for finding the accurate prediction values. Besides that, backpropagation neural network are also used to compare the predictions performance. Several experiments are conducted and some analyses on the experimental results are done. The results show that SVM with polynomial kernels provide a promising alternative tool in KLSE stock market prediction
Cluster science from ROSAT to eROSITA
Galaxy clusters are one of the important cosmological probes to test the
consistency of the observable structure and evolution of our Universe with the
predictions of specific cosmological models. We use results from our analysis
of the X-ray flux-limited REFLEX cluster sample from the ROSAT All-Sky Survey
to illustrate the constraints on cosmological parameters that can be achieved
with this approach. The upcoming eROSITA project of the Spektrum-Roentgen-Gamma
mission will increase these capabilities by two orders of magnitude and
importantly also increase the redshift range of such studies. We use the
projected instrument performance to make predictions on the scope of the
eROSITA survey and the potential of its exploitation.Comment: 5 pages, 8 figures, accepted for publication in Astronomische
Nachrichten; the proceedings of the XMM-Newton Science Workshop: "Galaxy
Clusters as Giant Cosmic Laboratories" at ESAC, Madrid, Spain, 21-23 May 201
Disturbed galaxy clusters are more abundant in an X-ray volume-limited sample
We present first strong observational evidence that the X-ray cool-core bias
or the apparent bias in the abundance of relaxed clusters is absent in our
REFLEX volume-limited sample (ReVols). We show that these previously observed
biases are due to the survey selection method such as for an flux-limited
survey, and are not due to the inherent nature of X-ray selection. We also find
that the X-ray luminosity distributions of clusters for the relaxed and for the
disturbed clusters are distinct and a displacement of approximately 60 per cent
is required to match two distributions. Our results suggest that to achieve
more precise scaling relation one may need to take the morphology of clusters
and their fractional abundance into account.Comment: A&A, 606, L4, 4 pages, 3 figure
Witnessing a merging bullet being stripped in the galaxy cluster, RXCJ2359.3-6042
We report the discovery of the merging cluster, RXCJ2359.3-6042, from the
REFLEX II cluster survey and present our results from all three detectors
combined in the imaging and spectral analysis of the XMM-Newton data. Also
known as Abell 4067, this is a unique system, where a compact bullet penetrates
an extended, low density cluster at redshift z=0.099 clearly seen from our
follow-up XMM-Newton observation. The bullet goes right through the central
region of the cluster without being disrupted and we can clearly watch the
process how the bullet component is stripped of its layers outside the core.
There is an indication of a shock heated region in the East of the cluster with
a higher temperature. The bulk temperature of the cluster is about 3.12 keV
implying a lower mass system. Spearheading the bullet is a cool core centred by
a massive early type galaxy. The temperatures and metallicities of a few
regions in the cluster derived from the spectral analysis supports our
conjecture based on the surface brightness image that a much colder compact
component at 1.55 keV with large metallicity (0.75 Zsol) penetrates the main
cluster, where the core of the infalling component survived the merger leaving
stripped gas behind at the centre of the main cluster. We also give an estimate
of the total mass within r500, which is about 2e14Msol from the deprojected
spherical-beta modelling of the cluster in good agreement with other mass
estimates from the M--Tx and M-sigma_v relations.Comment: 5 pages, 4 figures, A&A in press. Images with better resolution will
be available through the journa
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