3,927 research outputs found
Do Maternal Investments in Human Capital Affect Childrens' Academic Achievement?
Children of educated mothers fare better on a variety of educational outcomes. However, little research has been done on the effects of human capital investments undertaken by mothers with children at home. Such investments have a theoretically ambiguous effect on child outcomes, since human capital investment reduces time spent with children but may have positive spillover effects on child investment. Using childand sibling-fixed effects models to deal with unobserved heterogeneity, we find that cumulative maternal schooling undertaken during a child's lifetime has significant positive effects on child outcomes, and that negative time allocation effects are minimal.
Making History Visible: Ireland’s National Famine Way Told Through Models and Interactive Digital Narratives
The National Famine Way is a trail along Ireland’s Royal Canal that traces the remarkable trek of the 1,490 tenants who were evicted by their landlord, Denis Mahon, from his estate in Strokestown, County Roscommon, in the Republic of Ireland, during ‘Black ’47,’ the worst year of the Great Irish Famine (Irish: An Gorta Mór, the Great Hunger of 1847). The evictees were ‘escorted’ from their homes to vessels that awaited them in Dublin. They were then taken to Liverpool, where they were placed on four so-called ‘coffin ships’ bound for Canada. The path along the Royal Canal is 165 kilometres, or approximately one hundred miles. Today it is shared by hikers, bikers, ‘boat people,’ site-seekers, commemorators, and self-identified famine ‘pilgrims.’ For some of the latter, the signposts of children’s shoes erected along the path have acquired an iconic or even mythic significance. This article begins by applying a model that approaches the Way as a five-pronged cultural heritage complex. The article expands the model by considering how the National Famine Way’s cultural heritage is being approached from the lenses of transmedia
‘at the altar of memory’: Great Irish Famine Memorials in Words and Images
After discussing some of the most important facts and figures pertaining to An Gorta Mór (the Great Irish Famine of 1845-1852), this article turns to some of the images of monuments, crosses, stones and sculptures erected in commemoration of those who succumbed during the period. Alongside the images are travelers\u27 statements, many of which were captured by the author while journeying to \u27dark pilgrimage\u27 sites in Ireland, Canada and the United States
Novel Families of Fractional Quantum Hall States: Pairing of Composite Fermions
Fractional quantum Hall (FQH) states have recently been observed at
unexpected values of the filling factor nu. Here we interpret these states as a
novel family of FQH states involving pairing correlations rather than Laughlin
correlations among the quasiparticles (QP's). The correlations depend upon the
behavior of the QP-QP pseudopotential V_QP(L'), the interaction energy of a
pair as a function of the pair angular momentum L'. This behavior, known from
numerical studies of small systems, is used to demonstrate that pairing
correlations give rise to FQH states at the experimentally observed values of
nu.Comment: to appear in Physics Letters
Dark Matter Halos within Clusters
We examine the properties of dark matter halos within a rich galaxy cluster
using a high resolution simulation that captures the cosmological context of a
cold dark matter universe. The mass and force resolution permit the resolution
of 150 halos with circular velocities larger than 80 kms within the cluster's
virial radius of 2 Mpc. This enables an unprecedented study of the statistical
properties of a large sample of dark matter halos evolving in a dense
environment. The cumulative fraction of mass attached to these halos varies
from 0% at 200 kpc, to 13% at the virial radius. Even at this resolution the
overmerging problem persists; halos that pass within 200 kpc of the cluster
center are tidally disrupted. Additional substructure is lost at earlier epochs
within the massive progenitor halos. The median ratio of apocentric to
pericentric radii is 6:1; the orbital distribution is close to isotropic,
circular orbits are rare, radial orbits are common. The orbits of halos are
unbiased with respect to both position within the cluster and with the orbits
of the smooth dark matter background and no velocity bias is detected. The
tidal radii of surviving halos are generally well-fit using the simple analytic
prediction applied to their orbital pericenters. Halos within clusters have
higher concentrations than those in the field. Within the cluster, halo density
profiles can be modified by tidal forces and individual encounters with other
halos that cause significant mass loss - ``galaxy harassment''. Mergers between
halos do not occur inside the clusters virial radius.Comment: LaTeX MN style, 20 pages, 30 figures included + 1 colour plo
Resolving the Structure of Cold Dark Matter Halos
We examine the effects of mass resolution and force softening on the density
profiles of cold dark matter halos that form within cosmological N-body
simulations. As we increase the mass and force resolution, we resolve
progenitor halos that collapse at higher redshifts and have very high
densities. At our highest resolution we have nearly 3 million particles within
the virial radius, several orders of magnitude more than previously used and we
can resolve more than one thousand surviving dark matter halos within this
single virialised system. The halo profiles become steeper in the central
regions and we may not have achieved convergence to a unique slope within the
inner 10% of the virialised region. Results from two very high resolution halo
simulations yield steep inner density profiles, . The
abundance and properties of arcs formed within this potential will be different
from calculations based on lower resolution simulations. The kinematics of
disks within such a steep potential may prove problematic for the CDM model
when compared with the observed properties of halos on galactic scales.Comment: Final version, to be published in the ApJLetter
Fractional quantum Hall effect and electron correlations in partially filled first excited Landau level
We present a quantitative study of most prominent incompressible quantum Hall
states in the partially filled first excited Landau level (LL1) which have been
recently studied experimentally by Choi et al. The pseudopotential describing
the electron - electron interaction in LL1 is harmonic at short range. It
produces a series of incompressible states which is different from its LL0
counterpart. The numerical data indicate that the most prominent states
, 7/3, and 8/3 are not produced by Laughlin correlated electrons,
but result from a tendency of electrons to form pairs or larger clusters which
eventually become Laughlin correlated. States with smaller gaps at filling
factors 14/5, 16/7, 11/5, 19/7 are Laughlin correlated electron or hole states
and fit Jain's sequence of filled levels.Comment: 4 pages, 7 figure
Cold collapse and the core catastrophe
We show that a universe dominated by cold dark matter fails to reproduce the
rotation curves of dark matter dominated galaxies, one of the key problems that
it was designed to resolve. We perform numerical simulations of the formation
of dark matter halos, each containing \gsim 10^6 particles and resolved to
0.003 times the virial radius, allowing an accurate comparison with rotation
curve data. A good fit to both galactic and cluster sized halos can be achieved
using the density profile rho(r) \propto [(r/r_s)^1.5(1+(r/r_s)^1.5)]^-1, where
r_s is a scale radius. This profile has a steeper asymptotic slope, rho(r)
\propto r^-1.5, and a sharper turnover than found by lower resolution studies.
The central structure of relaxed halos that form within a hierarchical universe
has a remarkably small scatter (unrelaxed halos would not host disks). We
compare the results with a sample of dark matter dominated, low surface
brightness (LSB) galaxies with circular velocities in the range 100-300 km/s.
The rotation curves of disks within cold dark matter halos rise too steeply to
match these data which require a constant mass density in the central regions.
The same conclusion is reached if we compare the scale free shape of observed
rotation curves with the simulation data. It is important to confirm these
results using stellar rather than HI rotation curves for LSB galaxies. We test
the effects of introducing a cut-off in the power spectrum that may occur in a
universe dominated by warm dark matter. In this case halos form by a monolithic
collapse but the final density profile hardly changes, demonstrating that the
merger history does not play a role in determining the halo structure.Comment: Latex 13 pages, 4 figures. Submitted to MNRAS. High resolution colour
version of figure 4 and other N-body images here:
http://star-www.dur.ac.uk:80/~moore/images
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