1,105 research outputs found
Skills, Capabilities and Inequalities at School Entry in a Disadvantaged Community
Socioeconomic inequalities in children’s skills and capabilities begin early in life and can have detrimental effects on future success in school. The present study examines the relationships between school readiness and sociodemographic inequalities using teacher reports of the Short Early Development Instrument in a disadvantaged urban area of Ireland. It specifically examines socioeconomic (SES) differences in skills within a low SES community in order to investigate the role of relative disadvantage on children’s development. Differences across multiple domains of school readiness are examined using Monte-Carlo permutation tests. The results show that child, family and environmental factors have an impact on children’s school readiness, with attendance in centre-based childcare having the most consistent relationship with readiness for school. In addition, the findings suggest that social class inequalities in children’s skills still exist within a disadvantaged community. These results are discussed in relation to future intervention programmes.School readiness, Socioeconomic inequalities, Monte-Carlo permutation tests
Differential parent and teacher reports of school readiness in a disadvantaged community
Differential ratings by multiple informants are an important issue in survey design. Although much research has focused on differential reports of child behaviour, discrepancies between parent and teacher reports of children’s school readiness are less explored.
What can we learn about quasars from alpha_OX measurements in galactic black hole binaries?
We draw a comparison between AGN and Galactic black hole binaries using a
uniform description of spectral energy distribution of these two classes of
accreting X-ray sources. We parametrize spectra of GBHs with an alpha_GBH
parameter which we define as a slope of a nominal power law function between 3
and 20 keV. We show that this parameter can be treated as an equivalent of the
X-ray loudness, alpha_OX, used to describe AGN spectra. We do not find linear
correlation between the alpha_GBH and disc flux (similar to that between
alpha_OX and optical/UV luminosity found in AGN). Instead, we show that
alpha_GBH follows a well defined pattern during a GBH outburst. We find that
alpha_GBH tend to cluster around 1, 1.5 and 2, which correspond to a hard, very
high/intermediate and soft spectral state, respectively. We conclude that
majority of the observed Type 1 radio quiet AGN are in a spectral state
corresponding to a very high/intermediate state of GBHs. The same conclusion is
valid for radio loud AGN. We also study variations of the spectral slopes
(alpha_GBH and the X-ray photon index, Gamma) as a function of disc and
Comptonization fluxes. We discuss these dependencies in the context of
correlations of alpha_OX and Gamma with the optical/UV and X-ray 2 keV fluxes
considered for AGN and quasars.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Fragmentation of a Circular Disc by Impact on a Frictionless Plate
The break-up of a two-dimensional circular disc by normal and oblique impact
on a hard frictionless plate is investigated by molecular dynamics simulations.
The disc is composed of numerous unbreakable randomly shaped convex polygons
connected together by simple elastic beams that break when bent or stretched
beyond a certain limit. It is found that for both normal and oblique impacts
the crack patterns are the same and depend solely on the normal component of
the impact velocity. Analysing the pattern of breakage, amount of damage,
fragment masses and velocities, we show the existence of a critical velocity
which separates two regimes of the impact process: below the critical point
only a damage cone is formed at the impact site (damage), cleaving of the
particle occurs at the critical point, while above the critical velocity the
disc breaks into several pieces (fragmentation). In the limit of very high
impact velocities the disc suffers complete disintegration (shattering) into
many small fragments. In agreement with experimental results, fragment masses
are found to follow the Gates-Gaudin-Schuhmann distribution (power law) with an
exponent independent of the velocity and angle of impact. The velocity
distribution of fragments exhibit an interesting anomalous scaling behavior
when changing the impact velocity and the size of the disc.Comment: submitted to J. Phys: Condensed Matter special issue on Granular
Medi
A study of the norcaradiene-cycloheptatriene equilibrium in a series of azulenones by NMR spectroscopy; the impact of substitution on the position of equilibrium
A systematic investigation of the influence of substitution at positions C-2 and C-3 on the azulenone skeleton, based on NMR characterisation, is discussed with particular focus on the impact of the steric and electronic characteristics of substituents on the position of the norcaradiene-cycloheptatriene (NCD-CHT) equilibrium. Variable temperature (VT) NMR studies, undertaken to enable the resolution of signals for the equilibrating valence tautomers revealed, in addition, interesting shifts in the equilibrium
Extreme AGN Feedback and Cool Core Destruction in the X-ray Luminous Galaxy Cluster MACS J1931.8-2634
We report on a deep, multiwavelength study of the galaxy cluster MACS
J1931.8-2634 using Chandra X-ray, Subaru optical, and VLA 1.4 GHz radio data.
This cluster (z=0.352) harbors one of the most X-ray luminous cool cores yet
discovered, with an equivalent mass cooling rate within the central 50 kpc is
approximately 700 solar masses/yr. Unique features observed in the central core
of MACSJ1931.8-2634 hint to a wealth of past activity that has greatly
disrupted the original cool core. We observe a spiral of relatively cool,
dense, X-ray emitting gas connected to the cool core, as well as highly
elongated intracluster light (ICL) surrounding the cD galaxy. Extended radio
emission is observed surrounding the central AGN, elongated in the east-west
direction, spatially coincident with X-ray cavities. The power input required
to inflate these `bubbles' is estimated from both the X-ray and radio emission
to reside between 4 and 14e45 erg/s, putting it among the most powerful jets
ever observed. This combination of a powerful AGN outburst and bulk motion of
the cool core have resulted in two X-ray bright ridges to form to the north and
south of the central AGN at a distance of approximately 25 kpc. The northern
ridge has spectral characteristics typical of cool cores and is consistent with
being a remnant of the cool core after it was disrupted by the AGN and bulk
motions. It is also the site of H-alpha filaments and young stars. The X-ray
spectroscopic cooling rate associated with this ridge is approximately 165
solar masses/yr, which agrees with the estimate of the star formation rate from
broad-band optical imaging (170 solar masses/yr). MACS J1931.8-2634 appears to
harbor one of most profoundly disrupted low entropy cores observed in a
cluster, and offers new insights into the survivability of cool cores in the
context of hierarchical structure formation.Comment: 19 pages, 15 figures, 5 tables. Accepted by MNRAS for publication
September 30 201
The Observed Growth of Massive Galaxy Clusters II: X-ray Scaling Relations
(Abridged) This is the second in a series of papers in which we derive
simultaneous constraints on cosmology and X-ray scaling relations using
observations of massive, X-ray flux-selected galaxy clusters. The data set
consists of 238 clusters drawn from the ROSAT All-Sky Survey with 0.1-2.4 keV
luminosities >2.5e44 erg/second, and incorporates extensive follow-up
observations using the Chandra X-ray Observatory. Our analysis accounts
self-consistently for all selection effects, covariances and systematic
uncertainties. Here we describe the reduction of the follow-up X-ray
observations, present results on the cluster scaling relations, and discuss
their implications. Our constraints on the luminosity-mass and temperature-mass
relations, measured within r_500, lead to three important results. First, the
data support the conclusion that excess heating of the intracluster medium has
altered its thermodynamic state from that expected in a simple, gravitationally
dominated system; however, this excess heating is primarily limited to the
central regions of clusters (r<0.15r_500). Second, the intrinsic scatter in the
center-excised luminosity-mass relation is remarkably small, being undetected
at the <10% level in current data; for the hot, massive clusters under
investigation, this scatter is smaller than in either the temperature-mass or
Y_X-mass relations (10-15%). Third, the evolution with redshift of the scaling
relations is consistent with the predictions of simple, self-similar models of
gravitational collapse, indicating that the mechanism responsible for heating
the central regions of clusters was in operation before redshift 0.5 (the limit
of our data) and that its effects on global cluster properties have not evolved
strongly since then.Comment: 25 pages, 7 figures, 14 tables. v3: final version (typographic
corrections). Results can be downloaded at
https://www.stanford.edu/group/xoc/papers/xlf2009.htm
X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters I: Number Counts and Spatial Distribution
We present an analysis of the X-ray bright point source population in 43
massive clusters of galaxies observed with the Chandra X-ray Observatory. We
have constructed a catalog of 4210 rigorously selected X-ray point sources in
these fields, which span a survey area of 4.2 square degrees. This catalog
reveals a clear excess of sources when compared to deep blank-field surveys,
which amounts to roughly 1 additional source per cluster, likely Active
Galactic Nuclei (AGN) associated with the clusters. The excess sources are
concentrated within the virial radii of the clusters, with the largest excess
observed near the cluster centers. The average radial profile of the excess
X-ray sources of the cluster are well described by a power law (N(r) ~ r^\beta)
with an index of \beta ~ -0.5. An initial analysis using literature results on
the mean profile of member galaxies in massive X-ray selected clusters
indicates that the fraction of galaxies hosting X-ray AGN rises with increasing
clustercentric radius, being approximately 5 to 10 times higher near the virial
radius than in the central regions. This trend is qualitatively similar to that
observed for star formation in cluster member galaxies.Comment: 18 Pages, 10 Figures, Submitted to MNRAS. Please contact Steven
Ehlert ([email protected]) for higher resolution figures. Updated to
reflect small changes requested by referee. This version has been accepted
into MNRA
Fundamental properties of Fanaroff-Riley II radio galaxies investigated via Monte Carlo simulations
[Abridged] Radio galaxies and quasars are among the largest and most powerful
single objects known and are believed to have had a significant impact on the
evolving Universe and its large scale structure. We explore the intrinsic and
extrinsic properties of the population of FRII objects (kinetic luminosities,
lifetimes, and the central densities of their environments). In particular, the
radio and kinetic luminosity functions of FRIIs are investigated using the
complete, flux limited radio catalogues of 3CRR and Best et al. We construct
multidimensional Monte Carlo simulations using semi-analytical models of FRII
radio source growth to create artificial samples of radio galaxies. Unlike
previous studies, we compare radio luminosity functions found with both the
observed and simulated data to explore the fundamental source parameters. We
allow the source physical properties to co-evolve with redshift, and we find
that all the investigated parameters most likely undergo cosmological
evolution. Strikingly, we find that the break in the kinetic luminosity
function must undergo redshift evolution of at least (1+z)^3. The fundamental
parameters are strongly degenerate, and independent constraints are necessary
to draw more precise conclusions. We use the estimated kinetic luminosity
functions to set constraints on the duty cycles of these powerful radio
sources. A comparison of the duty cycles of powerful FRIIs with those
determined from radiative luminosities of AGN of comparable black hole mass
suggests a transition in behaviour from high to low redshifts, corresponding to
either a drop in the typical black hole mass of powerful FRIIs at low
redshifts, or a transition to a kinetically-dominated, radiatively-inefficient
FRII population.Comment: Accepted to MNRAS. 30 pages, 18 figures, 4 tables + online material
(in appendix): 9 pages, 14 figure
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