1,669 research outputs found
Public policies for the working poor: The earned income tax credit versus minimum wage legislation
This paper documents the declining relationship between low hourly wages and low household income over the last half-century and how this has reduced the share of minimum wage workers who live in poor households. It then compares recent and prospective increases in the earned income tax credit (EITC) and the minimum wage as methods of increasing the labor earnings of poor workers. Data from the Current Population Survey (CPS) are used to simulate the effects of both programs. Increases in the EITC between 1989 and 1992 delivered a much larger proportion of a given dollar of benefits to the poor than did increases in the minimum wage from 4.25. Scheduled increases in the EITC through 1996 will also do far more for the working poor than raising the minimum wage.
Dynamical evolution of globular cluster systems in clusters of galaxies I. The case of NGC 1404 in the Fornax cluster
We investigate, via numerical simulations, the tidal stripping and accretion
of globular clusters (GCs). In particular, we focus on creating models that
simulate the situation for the GC systems of NGC 1404 and NGC 1399 in the
Fornax cluster, which have poor (specific frequency 2) and
rich ( 10) GC systems respectively. We initially assign NGC
1404 in our simulation a typical ( 5) for cluster
ellipticals, and find that its GC system can only be reduced through stripping
to the presently observed value, if its orbit is highly eccentric (with orbital
eccentricity of 0.5) and if the initial scale length of the GCs system is
about twice as large as the effective radius of NGC 1404 itself. These stripped
GCs can be said to have formed a `tidal stream' of intracluster globular
clusters (ICGCs) orbiting the centre of Fornax cluster (many of which would be
assigned to NGC 1399 in an imaging study). The physical properties of these GCs
(e.g., number, radial distribution) depend on the orbit and initial
distribution of GCs in NGC 1404. Our simulations also predict a trend for
to rise with increasing clustercentric distance - a trend for which
there is some observational support in the Fornax cluster.Comment: 12 pages 12 figures, MNRAS in pres
Eridanus - A Supergroup in the Local Universe?
We examine a possible supergroup in the direction of the Eridanus
constellation using 6dF Galaxy Survey second data release (6dFGS DR2) positions
and velocities together with 2MASS and HyperLEDA photometry. We perform a
friends-of-friends analysis to determine which galaxies are associated with
each substructure before examining the properties of the constituent galaxies.
The structure is made up of three individual groups that are likely to merge to
form a cluster of mass 7x10^13 Msolar. We conclude that this structure is a
supergroup. We also examine the colours, morphologies and luminosities of the
galaxies in the region with respect to their local projected surface density.
We find that the colours of the galaxies redden with increasing density, the
median luminosities are brighter with increasing environmental density and the
morphologies of the galaxies show a strong morphology-density relation. The
colours and luminosities of the galaxies in the supergroup are already similar
to those of galaxies in clusters, however the supergroup contains more
late-type galaxies, consistent with its lower projected surface density. Due to
the velocity dispersion of the groups in the supergroup, which are lower than
those of clusters, we conclude that the properties of the constituent galaxies
are likely to be a result of merging or strangulation processes in groups
outlying this structure.Comment: Accepted for publication in MNRA
Poincare ball embeddings of the optical geometry
It is shown that optical geometry of the Reissner-Nordstrom exterior metric
can be embedded in a hyperbolic space all the way down to its outer horizon.
The adopted embedding procedure removes a breakdown of flat-space embeddings
which occurs outside the horizon, at and below the Buchdahl-Bondi limit
(R/M=9/4 in the Schwarzschild case). In particular, the horizon can be captured
in the optical geometry embedding diagram. Moreover, by using the compact
Poincare ball representation of the hyperbolic space, the embedding diagram can
cover the whole extent of radius from spatial infinity down to the horizon.
Attention is drawn to advantages of such embeddings in an appropriately curved
space: this approach gives compact embeddings and it distinguishes clearly the
case of an extremal black hole from a non-extremal one in terms of topology of
the embedded horizon.Comment: 16 pages, 8 figures; CQG accepte
A Richness Study of 14 Distant X-ray Clusters From the 160 Square Degree Survey
We have measured the surface density of galaxies toward 14 X-ray-selected
cluster candidates at redshifts greater than z=0.46, and we show that they are
associated with rich galaxy concentrations. We find that the clusters range
between Abell richness classes 0-2, and have a most probable richness class of
one. We compare the richness distribution of our distant clusters to those for
three samples of nearby clusters with similar X-ray luminosities. We find that
the nearby and distant samples have similar richness distributions, which shows
that clusters have apparently not evolved substantially in richness since
redshift z =0.5. We compare the distribution of distant X-ray clusters in the
L_x--richness plane to the distribution of optically-selected clusters from the
Palomar Distant Cluster Survey. The optically-selected clusters appear overly
rich for their X-ray luminosities when compared to X-ray-selected clusters.
Apparently, X-ray and optical surveys do not necessarily sample identical mass
concentrations at large redshifts. This may indicate the existence of a
population of optically rich clusters with anomalously low X-ray emission. More
likely, however, it reflects the tendency for optical surveys to select
unvirialized mass concentrations, as might be expected when peering along
large-scale filaments.Comment: The abstract has been abridged. Accepted for publication in the
Astrophysical Journa
Putting the Minimum Wage Debate in a Historical Context: Card and Krueger Meet George Stigler
Half a century ago George Stigler stated that evaluation of minimum wage policy should revolve around two questions: Does such legislation diminish poverty? Are there efficient alternatives? We argue that historically these were and continue to be appropriate questions to ask with respect to this policy. We then replicate and evaluate the analysis in Chapter 9 of Myth and Measurement: The New Economics of the Minimum Wage with regards to these questions. Given the evolution of the Earned Income Tax Credit we conclude that, aside from nostalgia, it is hard to explain the continued support for increasing the minimum wage by those interested in helping the working poor, and that Card and Krueger provide little new evidence to rekindle such support
Disentangling the Dynamical Mechanisms for Cluster Galaxy Evolution
The determination of the dynamical causes of the morphological Butcher-Oemler
(BO) effect, or the rapid transformation of a large population of late-type
galaxies to earlier Hubble types in the rich cluster environment between
intermediate redshifts and the local universe, has been an important unsolved
problem which is central to our understanding of the general problems of galaxy
formation and evolution. In this article, we survey the existing proposed
mechanisms for cluster galaxy transformation, and discuss their relevance and
limitations to the explanation of the morphological BO effect. A new infrared
diagnostic approach is devised to disentangle the relative importance of
several major physical mechanisms to account for the BO effect, and an example
of the first application of this procedure to a single rich, intermediate
redshift galaxy cluster is given to demonstrate the viability of this approach.
The preliminary result of this analysis favors the interaction-enhanced secular
evolution process as the major cause of the cluster-galaxy morphological
transformation. This conclusion is also supported by a wide range of other
published results which are assembled here to highlight their implications on a
coherent physical origin for the morphological BO effect.Comment: Accepted for publication in the PAS
Visualizing the Invisible: A Guide to Designing, Printing, and Incorporating Dynamic 3D Molecular Models to Teach StructureâFunction Relationships
Understanding the intricate relationship between macromolecular structure and function represents a central goal of undergraduate biology education (1â3). In teaching complex three-dimensional (3D) concepts, instructors typically depend on static two-dimensional (2D) textbook images or computer-based visualization software, which can lead to unintended misconceptions (4â6). While chemical and molecular kits exist, these models cannot handle the size and detail of macromolecules. Consequently, students may graduate in the life sciences without understanding how structure underlies function or acquiring skills to translate between 2D and 3D molecular models (5, 7)
Who Minimum Wage Increases Bite: An Analysis Using Monthly Data from the SIPP and CPS
In this paper we use an estimating equation from the research of leading proponents of the view that minimum wage increases do not cause employment losses. Rather than using annual data from the May Current Population Survey (CPS), we test this hypothesis using monthly data from both the Survey of Income and Program Participation (SIPP) and the CPS. We find the traditional result that neoclassical theory would predict: minimum wage increases create employment losses that are concentrated among less valued workers. Minimum wage increases have an insignificant effect on the employment of prime age workers (aged 25 to 61), but they have large and significant negative employment effects on teenagers, young high school dropouts, and young blacks. Hence, the very people minimum wage policies claim to help are most likely to be adversely affected
The Morphological Content of Ten EDisCS Clusters at 0.5 < z < 0.8
We describe Hubble Space Telescope (HST) imaging of 10 of the 20 ESO Distant
Cluster Survey (EDisCS) fields. Each ~40 square arcminute field was imaged in
the F814W filter with the Advanced Camera for Surveys Wide Field Camera. Based
on these data, we present visual morphological classifications for the ~920
sources per field that are brighter than I_auto=23 mag. We use these
classifications to quantify the morphological content of 10
intermediate-redshift (0.5 < z < 0.8) galaxy clusters within the HST survey
region. The EDisCS results, combined with previously published data from seven
higher redshift clusters, show no statistically significant evidence for
evolution in the mean fractions of elliptical, S0, and late-type (Sp+Irr)
galaxies in clusters over the redshift range 0.5 < z < 1.2. In contrast,
existing studies of lower redshift clusters have revealed a factor of ~2
increase in the typical S0 fraction between z=0.4 and z=0, accompanied by a
commensurate decrease in the Sp+Irr fraction and no evolution in the elliptical
fraction. The EDisCS clusters demonstrate that cluster morphological fractions
plateau beyond z ~ 0.4. They also exhibit a mild correlation between
morphological content and cluster velocity dispersion, highlighting the
importance of careful sample selection in evaluating evolution. We discuss
these findings in the context of a recently proposed scenario in which the
fractions of passive (E,S0) and star-forming (Sp,Irr) galaxies are determined
primarily by the growth history of clusters.Comment: 18 pages, 7 figures; To be published in ApJ; minor changes made to
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