Quasar-galaxy and AGN-galaxy cross-correlations

We compute quasar-galaxy and AGN-galaxy cross-correlation functions for samples taken from the \cite{VCV98} catalog of quasars and active galaxies, using tracer galaxies taken from the Edinburgh/Durham Southern Catalog. The sample of active galaxy targets shows positive correlation at projected separations $r_p < 6 h^{-1} Mpc$ consistent with the usual power-law. On the other hand, we do not find a statistically significant positive quasar-galaxy correlation signal except in the range $3 h^{-1} Mpc < r_p < 6 h^{-1} Mpc$ where we find similar AGN-galaxy and quasar-galaxy correlation amplitudes. At separations $r_p<3 h^{-1} Mpc$ a strong decline of quasar-galaxy correlations is observed, suggesting a significant local influence of quasars in galaxy formation. In an attempt to reproduce the observed cross-correlation between quasars and galaxies, we have performed CDM cosmological hydrodynamical simulations and tested the viability of a scenario based on the model developed by \cite{silkrees98}. In this scheme a fraction of the energy released by quasars is considered to be transferred into the baryonic component of the intergalactic medium in the form of winds. The results of the simulations suggest that the shape of the observed quasar-galaxy cross-correlation function could be understood in a scenario where a substantial amount of energy is transferred to the medium at the redshift of maximum quasar activity.Comment: 11 pages, 9 figures. Accepted for publication in Ap

Policy Driven Management for Distributed Systems

Separating management policy from the automated managers which interpret the policy facilitates the dynamic change of behavior of a distributed management system. This permits it to adapt to evolutionary changes in the system being managed and to new application requirements. Changing the behavior of automated managers can be achieved by changing the policy without having to reimplement them—this permits the reuse of the managers in different environments. It is also useful to have a clear specification of the policy applying to human managers in an enterprise. This paper describes the work on policy which has come out of two related ESPRIT funded projects, SysMan and IDSM. Two classes of policy are elaborated—authorization policies define what a manager is permitted to do and obligation policies define what a manager must do. Policies are specified as objects which define a relationship between subjects (managers) and targets (managed objects). Domains are used to group the objects to which a policy applies. Policy objects also have attributes specifying the action to be performed and constraints limiting the applicability of the policy. We show how a number of example policies can be modeled using these objects and briefly mention issues relating to policy hierarchy and conflicts between overlapping policies. © 1994, Plenum Publishing Corporation. All rights reserved.Accepted versio

The ROSAT All-Sky Survey: a Catalog of Clusters of Galaxies in a Region of 1 Ster around the South Galactic Pole

A field of 1.013 ster in the ROSAT all-sky survey (RASS), centered on the south galactic pole (SGP), has been searched in a systematic, objective manner for clusters of galaxies. The procedure relied on a correlation of the X-ray positions and properties of ROSAT sources with the distribution of galaxies in the COSMOS digitised data base, which was obtained by scanning the plates of the UK Schmidt IIIa-J optical southern sky survey. The study used the second ROSAT survey data base (RASS-2) and included several optical observing campaigns to measure redshifts. The search, a precursor to the larger REFLEX survey of the whole southern sky, reached the detection limits of the RASS and the COSMOS data, and yielded a catalog of 186 clusters in which the lowest flux is 1.5e-12 erg/cm2/s in the 0.1-2.4 keV band. Of these 157 have measured redshifts. Using a limit of 3.0e-12 erg/cm2/s a complete subset of 112 clusters was obtained, of which 110 have measured redshifts. The spatial distribution of the X-ray clusters out to z = 0.15 shows an extension of the Local Supercluster to the Pisces-Cetus supercluster (z<~0.07), and a more distant orthogonal structure at 0.07<z<0.15.Comment: To be published in ApJ Supplements in February 2002: 53 pages: 18 figure

The Aquarius Superclusters - I. Identification of Clusters and Superclusters

We study the distribution of galaxies and galaxy clusters in a 10^deg x 6^deg field in the Aquarius region. In addition to 63 clusters in the literature, we have found 39 new candidate clusters using a matched-filter technique and a counts-in-cells analysis. From redshift measurements of galaxies in the direction of these cluster candidates, we present new mean redshifts for 31 previously unobserved clusters, while improved mean redshifts are presented for 35 other systems. About 45% of the projected density enhancements are due to the superposition of clusters and/or groups of galaxies along the line of sight, but we could confirm for 72% of the cases that the candidates are real physical associations similar to the ones classified as rich galaxy clusters. On the other hand, the contamination due to galaxies not belonging to any concentration or located only in small groups along the line of sight is ~ 10%. Using a percolation radius of 10 h^{-1} Mpc (spatial density contrast of about 10), we detect two superclusters of galaxies in Aquarius, at z = 0.086 and at z = 0.112, respectively with 5 and 14 clusters. The latter supercluster may represent a space overdensity of about 160 times the average cluster density as measured from the Abell et al. (1989) cluster catalog, and is possibly connected to a 40 h^{-1} Mpc filament from z ~ 0.11 to 0.14.Comment: LateX text (21 pages) and 12 (ps/eps/gif) figures; figures 5a, 5b and 6 are not included in the main LateX text; to be published in the Astronomical Journal, March issu

A Flux-limited Sample of Bright Clusters of Galaxies from the Southern Part of the ROSAT All-Sky Survey: the Catalog and the LogN-LogS

We describe the selection of an X-ray flux-limited sample of bright clusters of galaxies in the southern hemisphere, based on the first analysis of the ROSAT All-Sky Survey data (RASS1). The sample is constructed starting from an identification of candidate clusters in RASS1, and their X-ray fluxes are remeasured using the Steepness Ratio Technique. This method is better suited than the RASS1 standard algorithm for measuring flux from extended sources. The final sample is count-rate-limited in the ROSAT hard band (0.5-2.0 keV), so that due to the distribution of NH, its effective flux limit varies between about 3-4 x 10**-12 ergs cm**-2 s**-1 over the selected area. This covers the Decl<2.5 deg part of the south Galactic cap region (b<-20 deg) - with the exclusion of patches of low RASS1 exposure time and of the Magellanic Clouds area - for a total of 8235 deg**2. 130 candidate sources fulfill our selection criteria for bonafide clusters of galaxies in this area. Of these, 101 are Abell/ACO clusters, while 29 do not have a counterpart in these catalogs. Of these clusters, 126 (97%) clusters have a redshift and for these we compute an X-ray luminosity. 20% of the cluster redshifts come from new observations, as part of the ESO Key Program REFLEX Cluster Survey that is under completion. Considering the intrinsic biases and incompletenesses introduced by the flux selection and source identification processes, we estimate the overall completeness to be better than 90%. The observed number count distribution, LogN-LogS, is well fitted by a power law with slope alpha = 1.34 +/- 0.15 and normalization A = 11.87 +/- 1.04 sr**-1 (10**-11 ergs cm**-2 s**-1)**alpha, in good agreement with other measurements.Comment: 27 pages, 8 figures and 3 tables included, LaTex, emulateapj.sty and epsf.sty, accepted for publication in ApJ: scheduled for the March 20, 1999, Vol.514. The cluster catalog is available at http://www.merate.mi.astro.it/~degrand

Conquering Language: Using NLP on a Massive Scale to Build High Dimensional Language Models from the Web

International audienceDictionaries only contain some of the information we need to know about a language. The growth of the Web, the maturation of linguistic process-ing tools, and the decline in price of memory storage allow us to envision de-scriptions of languages that are much larger than before. We can conceive of building a complete language model for a language using all the text that is found on the Web for this language. This article describes our current project to do just that

The Nearby Optical Galaxy Sample: The Local Galaxy Luminosity Function

In this paper we derive the galaxy luminosity function from the Nearby Optical Galaxy (NOG) sample, which is a nearly complete, magnitude-limited (B<14 mag), all-sky sample of nearby optical galaxies (~6400 galaxies with cz<5500 km/s). For this local sample, we use galaxy distance estimates based on different peculiar velocity models. Therefore, the derivation of the luminosity function is carried out using the locations of field and grouped galaxies in real distance space. The local field galaxy luminosity function in the B system is well described by a Schechter function. The exact values of the Schechter parameters slightly depend on the adopted peculiar velocity field models. The shape of the luminosity function of spiral galaxies does not differ significantly from that of E-S0 galaxies. On the other hand, the late-type spirals and irregulars have a very steeply rising luminosity function towards the faint end, whereas the ellipticals appreciably decrease in number towards low luminosities. The presence of galaxy systems in the NOG sample does not affect significantly the field galaxy luminosity function, since environmental effects on the total luminosity function appear to be marginal.Comment: 35 pages including 7 figures and 4 tables. Accepted for publication in Ap

Training Pre-Service Early Childhood Educators in Physical Activity (TEACH): Protocol for a Quasi-Experimental Study

Background: Early childhood educators (ECEs) influence young children’s early uptake of positive health behaviours in childcare settings and serve as important daytime role models. As such, it is imperative that post-secondary early childhood education programs provide students with the foundational knowledge and professional training required to confidently facilitate quality active play opportunities for young children. The primary objective of the Training pre-service EArly CHildhood educators in physical activity (TEACH) study is to develop and implement an e-Learning course in physical activity and sedentary behaviour to facilitate improvements in: pre-service ECEs’ self-efficacy and knowledge to lead physical activity and outdoor play opportunities and minimize sedentary behaviours in childcare. This study will also explore pre-service ECEs’ behavioural intention and perceived control to promote physical activity and outdoor play, and minimize sedentary behaviour in childcare, and the implementation of the e-Learning course. Methods/Design: A mixed-methods quasi-experimental design with three data collection time points (baseline, post-course completion, 3-month follow-up) will be employed to test the e-Learning course in early childhood education programs (n = 18; 9 experimental, 9 comparison) across Canada. Pre-service ECEs enrolled in colleges/universities assigned to the experimental group will be required to complete a 4-module e-Learning course, while programs in the comparison group will maintain their typical curriculum. Pre-service ECEs’ self-efficacy, knowledge, as well as behavioural intention and perceived behavioural control will be assessed via online surveys and module completion rates will be documented using website metrics. Group differences across timepoints will be assessed using linear mixed effects modelling and common themes will be identified through thematic analysis. Discussion: The TEACH study represents a novel, evidence-informed approach to address the existing gap in physical activity and sedentary behaviour-related education in Canadian post-secondary early childhood education programs. Moreover, e-Learning platforms, can be employed as an innovative, standardized, and scalable way to provide ECEs with consistent training across jurisdictions

Implementation of an e-Learning course in physical activity and sedentary behavior for pre- and in-service early childhood educators: Evaluation of the TEACH pilot study

Background: Childcare-based physical activity (PA) and sedentary behavior (SB) interventions have traditionally used in-person training to supplement early childhood educators’ (ECEs) knowledge and confidence to facilitate physically active programming for the children in their care. However, this method of delivery is resource-intensive and unable to reach a high number of ECEs. The purpose of the Training pre-service EArly CHildhood educators in PA (TEACH) pilot study was to test the implementation (e.g., fidelity, feasibility, acceptability) of an e-Learning course targeting PA and SB among a sample of pre-service (i.e., post-secondary students) and in-service (i.e., practicing) ECEs in Canada. Methods: A pre-/post-study design was adopted for this pilot study, and implementation outcomes were assessed cross-sectionally at post-intervention. Pre-service ECEs were purposefully recruited from three Canadian colleges and in-service ECEs were recruited via social media. Upon completing the e-Learning course, process evaluation surveys (n = 32 pre-service and 121 in-service ECEs) and interviews (n = 3 pre-service and 8 in-service ECEs) were completed to gather ECEs’ perspectives on the e-Learning course. Fidelity was measured via e-Learning course metrics retrieved from the web platform. Descriptive statistics were calculated for quantitative data, and thematic analysis was conducted to analyze qualitative data. Results: Moderate-to-high fidelity to the TEACH study e-Learning course was exhibited by pre-service (68%) and in-service (63%) ECEs. Participants reported that the course was highly acceptable, compatible, effective, feasible, and appropriate in complexity; however, some ECEs experienced technical difficulties with the e-Learning platform and noted a longer than anticipated course duration. The most enjoyed content for pre- and in-service ECEs focused on outdoor play (87.5% and 91.7%, respectively) and risky play (84.4% and 88.4%, respectively). Conclusions: These findings demonstrate the value of e-Learning for professional development interventions for ECEs. Participant feedback will be used to make improvements to the TEACH e-Learning course to improve scalability of this training