Intra Cluster Research Articles

Multiple Parameter Based Clustering (MPC): Prospective Analysis for Effective Clustering in Wireless Sensor Network (WSN) Using K-Means Algorithm

In wireless sensor network cluster architecture is useful because of its inherent suitability for data fusion. In this paper we represent a new approach called Multiple Parameter based Clustering (MPC) embedded with the traditional k-means algorithm which takes different parameters (Node energy level, Euclidian distance from the base station, RSSI, Latency of data to reach base station) into consideration to form clusters. Then the effectiveness of the clusters is evaluated based on the uniformity of the node distribution, Node range per cluster, Intra and Inter cluster distance and required energy level of each centroid. Our result shows that by varying multiple parameters we can create clusters with more uniformly distributed nodes, minimize intra and maximize inter cluster distance and elect less power consuming centroid.

Genetic divergence in grain amaranth (Amaranthus hypochondriacus L.)

Extent and magnitude of genetic divergence for 14 characters among 98 genotypes of grain amaranth (Amaranthus hypochondriacus L.) were determined for the purpose of identifying more diverse parents which are expected to engender maximum variability. Based on genetic divergence D2 statistics, genotypes were grouped into 18 clusters in which cluster I contained maximum number of genotypes (42), Cluster II (11), Cluster III (7), Cluster IV and V (5 in each case) and Cluster VI has 4 genotypes. Cluster VII, VIII, IX, X have (3 in each), cluster XI, XII, XIII, XIV (2 in each) and clusters XV, XVI, XVII and XVIII (1in each case). The clustering pattern revealed that there was no relationship between genetic divergence and eco-geographical region. Intra cluster values ranged from 0.00 to 141.86 and cluster XI is most diverse group. The inter cluster values ranged from 133.08 to 1214.59. Maximum divergence was noticed between clusters VIII and XI (1214.59) followed by clusters XI and XV (982.16) and clusters II and XI (938.89). The diverse clusters derived could be used in hybridization programme to generate wide range of transgressive segregants in population to develop high yielding grain amaranth varieties.

The evolution of cool-core clusters

Cool-core clusters are characterized by strong surface brightness peaks in the X-ray emission from the Intra Cluster Medium (ICM). This phenomenon is associated with complex physics in the ICM and has been a subject of intense debate and investigation in recent years. In order to quantify the evolution in the cool-core cluster population, we robustly measure the cool-core strength in a local, representative cluster sample, and in the largest sample of high-redshift clusters available to date. We use high-resolution Chandra data of three representative cluster samples spanning different redshift ranges: (i) the local sample from the 400 SD survey with median z = 0.08, (ii) the high redshift sample from the 400 SD Survey with median z=0.59, and (iii) 15 clusters drawn from the RDCS and the WARPS, with median z = 0.83. Our analysis is based on the measurement of the surface brightness concentration, c_SB, which allows us to characterize the cool-core strength in low signal-to-noise data. We also obtain gas density profiles to derive cluster central cooling times and entropy. In addition to the X-ray analysis, we search for radio counterparts associated with the cluster cores. We find a statistically significant difference in the c_SB distributions of the two high-z samples, pointing towards a lack of concentrated clusters in the 400 SD high-z sample. Taking this into account, we confirm a negative evolution in the fraction of cool-core clusters with redshift, in particular for very strong cool-cores. This result is validated by the central entropy and central cooling time, which show strong anti-correlations with c_SB. However, the amount of evolution is significantly smaller than previously claimed, leaving room for a large population of well formed cool-cores at z~1.

Integrating gene expression and GO classification for PCA by preclustering

BackgroundGene expression data can be analyzed by summarizing groups of individual gene expression profiles based on GO annotation information. The mean expression profile per group can then be used to identify interesting GO categories in relation to the experimental settings. However, the expression profiles present in GO classes are often heterogeneous, i.e., there are several different expression profiles within one class. As a result, important experimental findings can be obscured because the summarizing profile does not seem to be of interest. We propose to tackle this problem by finding homogeneous subclasses within GO categories: preclustering.ResultsTwo microarray datasets are analyzed. First, a selection of genes from a well-known Saccharomyces cerevisiae dataset is used. The GO class "cell wall organization and biogenesis" is shown as a specific example. After preclustering, this term can be associated with different phases in the cell cycle, where it could not be associated with a specific phase previously. Second, a dataset of differentiation of human Mesenchymal Stem Cells (MSC) into osteoblasts is used. For this dataset results are shown in which the GO term "skeletal development" is a specific example of a heterogeneous GO class for which better associations can be made after preclustering. The Intra Cluster Correlation (ICC), a measure of cluster tightness, is applied to identify relevant clusters.ConclusionsWe show that this method leads to an improved interpretability of results in Principal Component Analysis.

Inter and Intra Cluster Scheduling for Performance Analysis of Coexistence Heterogeneous Networks

In ubiquitous networking environments, we generally need two or more heterogeneous communication systems coexisting in a single place. Especially, wireless local area networks (WLANs) based on IEEE 802.11b specifications and wireless personal area networks (WPANs) based on IEEE 802.15.4 specifications need to coexist in the same Industrial, Science and Medial (ISM) band. If the WPAN communication coverage is expanded using a cluster-tree network topology, then the 802.15.4 network is more susceptible to interference from neighboring WLANs. In this paper, we propose an adaptive transmission power aware cluster scheduling algorithm using multiple channels in a WPAN in the presence of WLAN interference. The algorithm includes node identification, channel allocation, clustering and time scheduling. To evaluate the performance of the proposed algorithm, the performance metrics such as Bit error, Throughput, Average End-End Delay and Average Jitter is measured through Qualnet simulation. The measurement result shows that the proposed algorithm is effective in an IEEE 802.15.4 cluster-tree network in the presence of multiple IEEE 802.11 interferers.

Intra cluster medium properties and AGN distribution in high-zRCS clusters

Context. The study of the thermodynamical and chemical properties of the intra cluster medium (ICM) in high redshift clusters of galaxies is a powerful tool for investigating the formation and evolution of large scale structures. Here we discuss the X-ray properties of clusters of galaxies optically selected in the red-sequence cluster survey (RCS) observed with the Chandra satellite, at redshifts 0.6 1. Finally, we find the significant excess of medium and low luminosity AGN close to the centroid of the X-ray emission. Their X-ray emission is not dominating the ICM, but their presence may be relevant for studying the interaction between AGN and ICM.

A PHOTOMETRIC SEARCH FOR TRANSIENTS IN GALAXY CLUSTERS

We have begun a program to search for supernovae and other transients in the fields of galaxy clusters with the 2.3 m Bok Telescope on Kitt Peak. We present our automated photometric methods for data reduction, efficiency characterization, and initial spectroscopy. With this program, we aim to ultimately identify ∼25–35 cluster Type Ia supernovae (SNe Ia) (∼10 of which will be intracluster, hostless events) and constrain the SN Ia rate associated with old, passive stellar populations. With these measurements we will constrain the relative contribution of hostless and hosted SNe Ia to the metal enrichment of the intracluster medium. In the current work, we have identified a central excess of transient events within 1.25r200 in our cluster fields after statistically subtracting out the "background" transient rate taken from an off-cluster CCD chip. Based on the published rate of SNe Ia for cluster populations we estimate that ∼20% of the excess cluster transients are due to cluster SNe Ia, a comparable fraction to core collapse (CC) supernovae and the remaining are likely to be active galactic nuclei. Interestingly, we have identified three intracluster SN candidates, all of which lay beyond R > r200. These events, if truly associated with the cluster, indicate a large deficit of intracluster (IC) SNe at smaller radii, and may be associated with the IC stars of infalling groups or indicate that the intracluster light (ICL) in the cluster outskirts is actively forming stars which contribute CC SNe or prompt SNe Ia.

Warming rays in cluster cool cores

Context. Cosmic rays are confined in the atmospheres of galaxy clusters and, therefore, they can play a crucial role in the heating of their cool cores. Aims. We discuss here the thermal and non-thermal features of a model of cosmic ray heating of cluster cores that can provide a solution to the cooling-flow problems. To this aim, we generalize a model originally proposed by Colafrancesco, Dar & DeRujula (2004) and we show that our model predicts specific correlations between the thermal and non-thermal properties of galaxy clusters and enables various observational tests. Methods. The model reproduces the observed temperature distribution in clusters by using an energy balance condition in which the X-ray energy emitted by clusters is supplied, in a quasi-steady state, by the hadronic cosmic rays, which act as “warming rays” (WRs). The temperature profile of the intracluster (IC) gas is strictly correlated with the pressure distribution of the WRs and, consequently, with the non-thermal emission (radio, hard X-ray and gamma-ray) induced by the interaction of the WRs with the IC gas and the IC magnetic field. Results. The temperature distribution of the IC gas in both cool-core and non cool-core clusters is successfully predicted from the measured IC plasma density distribution. Under this contraint, the WR model is also able to reproduce the thermal and non-thermal pressure distribution in clusters, as well as their radial entropy distribution, as shown by the analysis of three clusters studied in detail: Perseus, A2199 and Hydra. The WR model provides other observable features of galaxy clusters: a correlation of the pressure ratio (WRs to thermal IC gas) with the inner cluster temperature $(P_{\rm WR}/P_{\rm th}) \sim (kT_{\rm inner})^{-2/3}$, a correlation of the gamma-ray luminosity with the inner cluster temperature $L_{\gamma} \sim (kT_{\rm inner})^{4/3}$, a substantial number of cool-core clusters observable with the GLAST-LAT experiment, a surface brightness of radio halos in cool-core clusters that recovers the observed one, a hard X-ray ICS emission from cool-core clusters that is systematically lower than the observed limits and yet observable with the next generation high-sensitivity and spatial resolution HXR experiments like Simbol-X. Conclusions. The specific theoretical properties and the multi-frequency distribution of the e.m. signals predicted in the WR model render it quite different from the other models so far proposed for the heating of clusters' cool-cores. Such differences make it possible to prove or disprove our model as an explanation for the cooling-flow problems on the basis of multi-frequency observations of galaxy clusters.

H I imaging of galaxies in X-ray bright groups

ABSTRACT Environment plays an important role in the evolution of the gas contents of galaxies. Gasdeficiency of cluster spirals and the role of the hot intraclu ster medium (ICM) in strippinggas from these galaxies is a well studied subject. Loose groups with diffuse X-ray emmisionfrom the intragroup medium (IGM) offer an intermediate environment between clusters andgroups without a hot IGM. These X-ray bright groups have smaller velocity dispersion andlower temperature than clusters, but higher IGM density than loose groups without diffuseX-ray emission. A single dish comparative study of loose groups with and without diffuseX-ray emission from the IGM, showed that the galaxies in X-ray bright groups have lost moregas on average than the galaxies in non X-ray bright groups. In this paper we present GMRTHobservations of 13 galaxies from 4 X-ray bright groups: NGC5044, NGC720, NGC1550and IC1459. The aim of this work is to study the morphology of Hin these galaxies andto see if the hot IGM has in any way affected their Hcontent or distribution. In addition todisturbed Hmorphology,we find that most galaxies have shrunken H disks compared to thefield spirals. This indicates that IGM assisted stripping pr ocesses like ram pressure may havestripped gas from the outer edges of the galaxies.Key words: galaxies:evolution-galaxies:interactions-radiolines:galaxies-X-rays:galaxies

Globular clusters and dwarf galaxies in Fornax

We acquired radial velocities of a significant number of globular clusters (GCs) on wide fields between galaxies in the nearby Fornax cluster of galaxies, in order to derive their velocity dispersion radial profile and to probe the dynamics of the cluster. We used FLAMES on the VLT to obtain accurate velocities for 149 GCs, within a ~500x150 kpc strip centered on NGC 1399, the Fornax central galaxy. These objects are at the very bright tail (M_V < -9.5) of the GC luminosity function, overlapping the so-called ``ultra-compact dwarfs'' magnitude range. Eight of the brightest FLAMES-confirmed members indeed show hints of resolution in the subarcsecond pre-imaging data we used for selecting the ~500 targets for FLAMES spectroscopy. Ignoring the GCs around galaxies by applying 3d_25 diameter masks, we find 61 GCs of 20.0 < V < 22.2 lying in the intra-cluster (IC) medium. The velocity dispersion of the population of ICGCs is 200 km/s at ~150 kpc from the central NGC 1399 and rises to nearly 400 km/s at 200 kpc, a value which compares with the velocity dispersion of the population of dwarf galaxies, thought to be infalling from the surroundings of the cluster.

Chemical enrichment of galaxy clusters from hydrodynamical simulations

We have developed in GADGET-2 a feature–rich and highly flexible code for modeling the stellar evolution and the chemical enrichment. Simulating clusters, we find a very good agreement in reproducing both the radial abundance profiles and the enrichment history of the Intra–Cluster medium.

The Survival of Planetary Nebulae in the Intracluster Medium

The stellar population stripped from galaxies in clusters evolves under the extreme conditions imposed by the intracluster (IC) medium. Intracluster stars generally suffer very high systemic velocities moving through a rarefied and extremely hot IC medium. We present numerical simulations that aim to explore the evolution and survival of IC asymptotic giant branch (AGB) envelopes and planetary nebula (PN) shells. Our models reflect the evolution of a low-mass star under the observed conditions in the Virgo IC medium. We find that the integrated hydrogen-recombination line emission of a PN is dominated by the inner dense shell, whose evolution is unaffected by the environment. Ram pressure stripping mainly affects the outermost IC PN shell, which hardly influences the emission when the PN is observed as a point source. More importantly, we find that a PN with progenitor mass of 1 M☉ fades to ~30% and ~10% of its maximum emission in 5000 and 10,000 yr, respectively, disclosing an actual PN lifetime (tPN) several times shorter than what is usually adopted (25,000 yr). This result affects the theoretical calculation of the luminosity-specific density of IC PNe, which scales with tPN. For tPN = 10,000 yr, our more conservative estimate, we obtain that the luminosity-specific density of PNe is in fair agreement with the value obtained from red giants. With our more realistic PN lifetime, we infer a fraction of IC starlight in the Virgo core of above 15%, which is higher than current estimates.

Simulating galaxy clusters - III. Properties of the intracluster stars

Cosmological (� -cold dark matter) TREESPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metallicity-dependent radiative cooling, strong starburst, and (optionally) active galactic nuclei, driven galactic superwinds, effects of a metagalactic ultraviolet field and thermal conduction. Results for two clusters, one Virgo-like (T � 3k eV) and one (sub-) Coma-like (T � 6k eV), are presented. At z = 0 the stellar con- tents of both clusters consist of a central dominant (cD) galaxy surrounded by cluster galaxies and intracluster (IC) stars. The IC stars are found to contribute 20-40 per cent of the total cluster B-band luminosity at z = 0 and to form at a mean redshiftf ∼ 3, which is on average approximately 0.5 Gyr older than the stars in cluster galaxies. UBVRIJHK surface brightness profiles of the IC star populations are presented; the profile of the larger cluster matches the observed V-band profile of the cD in Abell 1413 (T � 8k eV) quite well. The typical colour of the IC stellar population is B − R = 1.4-1.5, comparable to the colour of sub-L ∗ E and S0 galaxies. The mean iron abundance of the IC stars is approximately solar in the central part of the cluster (r ∼ 100 kpc) decreasing to approximately half solar at the virial radius. The IC stars are α-element enhanced with a weak trend of (O/Fe) increasing with r and an overall (O/Fe) ∼ 0.4 dex, indicative of dominant enrichment from Type II supernovae. The IC stars are kinematically significantly colder than the cluster galaxies: the velocity dispersions of the IC stars are in the inner parts of the clusters (r ∼ 100-500 kpc) only approximately half of those of the cluster galaxies, increasing slightly outward to approximately 70 per cent at r = 1-2 Mpc. The typical projected velocity dispersion in the Virgo-like cluster at R 50 kpc is 300-600 km s −1 , depending on orientation and projected distance from the cluster centre. Rotation is found to be dynamically insignificant for the IC stars. The velocity distributions of IC stars and clusters galaxies are highly radially anisotropic in one cluster and in the other close to being isotropic. Ke yw ords: galaxies: clusters: general - galaxies: evolution - galaxies: formation - cosmology: theory.

Cosmic rays, cooling flows and non-thermal processes in galaxy clusters

Abstract Bremsstrahlung cooling of the intracluster (IC) plasma in galaxy clusters can be quenched by the energy supplied to the plasma by hadronic cosmic rays (CRs). This solution requires an energy deposition more intense and more distributed than in conventional CR models, but this alternative model is also successful in describing the origin of CRs. The model also provides a simple explanation of other puzzling features of galaxy clusters, among which we discuss here the non-thermal tail of their X-ray emission spectrum.

Thermal and non-thermal plasmas in the galaxy cluster 3C 129

We describe new Chandra spectroscopy data of the cluster which harbors the prototypical head radio galaxy 3C 129 and the weaker radio galaxy 3C 129.1. We combined the Chandra data with Very Large Array (VLA) radio data taken at 0.33, 5, and 8 GHz (archival data) and 1.4 GHz (new data). We also obtained new HI observations at the Dominion Radio Astrophysical Observatory (DRAO) to measure the neutral Hydrogen column density the direction of the cluster with arcminute angular resolution. The Chandra observation reveals extended X-ray emission from the radio galaxy 3C 129.1 with a total luminosity of 1.5E+41 erg/s. The X-ray excess is resolved into an extended central source of ~2 arcsec (1 kpc) diameter and several point sources with an individual luminosity up to 2.1E+40 erg/s. In the case of the radio galaxy 3C 129, the Chandra observation shows, addition to core and jet X-ray emission reported an earlier paper, some evidence for extended, diffuse X-ray emission from a region east of the radio core. The 12 arcsec x 36 arcsec (6 kpc x 17 kpc) region lies in front of the radio core, the same direction into which the radio galaxy is moving. We use the radio and X-ray data to study detail the pressure balance between the non-thermal radio plasma and the thermal Intra Cluster Medium (ICM) along the tail of 3C 129 which extends over 15 arcmin (427 kpc). Depending on the assumed lower energy cutoff of the electron energy spectrum, the minimum pressure of the radio plasma lies a factor of between 10 and 40 below the ICM pressure for a large part of the tail. We discuss several possibilities to explain the apparent pressure mismatch.

Neutralinos and the Origin of Radio Halos in Clusters of Galaxies

We assume that the supersymmetric lightest neutralino is a good candidate for the cold dark matter in the galaxy halo and explore the possibility to produce extended diffuse radio emission from high-energy electrons arising from the neutralino annihilation in galaxy clusters whose intracluster medium is filled with a large-scale magnetic field. We show that these electrons fit the population of seed relativistic electrons that is postulated in many models for the origin of cluster radio halos. For a uniform magnetic field of ≈1-3 μG the population of seed relativistic electrons from neutralino annihilation can fit the radio halo spectra of two well-studied clusters: Coma and 1E 0657-56. In the case of a magnetic field that is radially decreasing from the cluster center, central values ≈8 μG (for Coma) and ≈50 μG (for 1E 0657-56) are required to fit the data. The radio halo data strongly favor a centrally peaked dark matter density profile (like a Navarro, Frenk, & White [NFW97] density profile). The shape and the frequency extension of the radio halo spectra are connected with the mass and physical composition of the neutralino. A pure gaugino neutralino with mass Mχ ≥ 80 GeV can reasonably fit the radio halo spectra of both Coma and 1E 0657-56. The model we present here provides a number of extra predictions that make it definitely testable. On the one hand, it agrees quite well with the observations that (1) the radio halo is centered on the cluster dynamical center, usually coincident with the center of its X-ray emission; (2) the radio halo surface brightness is similar to the X-ray one; and (3) the monochromatic radio luminosity at 1.4 GHz correlates strongly with the intracluster (IC) gas temperature. On the other hand, the same model predicts that radio halos should be present in every cluster, which is not presently observed, although the predicted radio halo luminosities can change (decrease) by factors of up to ~102-106, depending on the amplitude and the structure of the IC magnetic field. In addition, neutral pions arising from neutralino annihilation should give rise to substantial amounts of diffuse gamma-ray emission, up to energies of order Mχ, that could be tested by the next-generation gamma-ray experiments.

High energy phenomena in clusters of galaxies

Several phenomena in high energy astrophysics have been recently related to clusters of galaxies and to cosmic ray interactions occurring inside these structures. In many of these phenomena the observable effects depend on the energy density of cosmic rays confined in the Intra Cluster (IC) medium, which is a poorly known quantity. We propose here that useful indications about this quantity can be obtained from present and future observations in the radio and hard X-ray frequency ranges.

Measurement of the Hubble Constant from X‐Ray and 2.1 Millimeter Observations of Abell 2163

We report 2.1 mm observations of the Sunyaev-Zeldovich (S-Z) effect; these observations confirm our previous detection of a decrement in the cosmic microwave background intensity toward the cluster Abell 2163. The S-Z data are analyzed using the relativistically correct expression for the Comptonization. We begin by assuming the intracluster (IC) gas to be isothermal at the emission-weighted average temperature determined by a combined analysis of the ASCA and Ginga X-ray satellite observations. The results of ROSAT/PSPC observations are used to determine an isothermal model for the S-Z surface brightness. Fitting to this model, we determine the peak Comptonization to be y0 = 3.73+ 0.47−0.61×10−4. The uncertainty includes contributions due to statistical uncertainty in the detection, instrumental baseline, calibration, and density model. Combining the X-ray and S-Z measurements, we determine the Hubble constant to be H0(q0=½)=60+ 40−23 km s-1 Mpc-1, where the uncertainty is dominated by the systematic difference in the ASCA- and Ginga-determined IC gas temperatures. ASCA observations suggest the presence of a significant thermal gradient in the IC gas. We determine H0 as a function of the assumed IC gas thermal structure. Using the ASCA-determined thermal structure and keeping the emission-weighted average temperature the same as in the isothermal case, we find H0(q0 = ½) = 78+ 54−28 km s-1 Mpc-1. Including additional uncertainties due to cluster asphericity, peculiar velocity, IC gas clumping, and astrophysical confusion, we find H0(q0=½)=78+ 60−40 km s-1 Mpc-1.

Multimass Models for Clusters of Galaxies

It is now a widely spread opinion that a ratio of 10:1 between dark and luminous matter exists. Supported by the existence of flat rotation curves at large radii for spirals, this fact reinforces cosmological scenarios with, for instance, massive neutrinos. This content of dark matter is often estimated from the dynamical analysis of clusters of galaxies based essentially on the application of the Virial theorem or the monomassive Emden sphere or deduced from numerical simulations. However, a careful examination shows crucial failures in such approaches1, at least the lack of a mass spectrum and/or of a dynamically influent Intra Cluster Medium. This has been included in simple models1 together with other realistic features such as temperature gradient, isovelocity and/or isothermicity of the gravitational plasma. Our aim is thus to account simultaneously for all the available data concerning both galaxies and ICM; namely, the Nonisothermal Multimass Models1 allow us to fit jointly the numerical density profiles of galaxies, the luminosity function, the velocity dispersion profiles versus magnitude or radius, the luminosity segregation2, the X-ray temperature, luminosity and surface brightness profiles.

The distribution and mass of iron in the intracluster space of rich clusters of galaxies

view Abstract Citations (37) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The distribution and mass of iron in the intracluster space of rich clusters of galaxies. Rephaeli, Y. Abstract It is shown that intracluster (IC) iron, whose presence is deduced from observations of an X-ray emission feature in the spectra of some X-ray clusters, could not have sedimented in the cluster core in a Hubble time. It is therefore concluded that the iron and gas are likely to be similarly distributed. Estimates of the total IC iron mass are given, and the possibility that the iron has been convected to the IC space by galactic winds from the visible cluster galaxies is briefly considered. Publication: The Astrophysical Journal Pub Date: October 1978 DOI: 10.1086/156495 Bibcode: 1978ApJ...225..335R Keywords: Galactic Clusters; Intergalactic Media; Iron; X Ray Astronomy; Cosmic Gases; Interstellar Magnetic Fields; Spatial Distribution; Astrophysics; Clusters of Galaxies:X-Ray Spectra; Intergalactic Matter:Iron full text sources ADS |