4,701 research outputs found
Labor supply models: unobserved heterogeneity, nonparticipation and dynamics
This chapter is concerned with the identification and estimation of models of labor supply. The focus is on the key issues that arise from unobserved heterogeneity, nonparticipation and dynamics. We examine the simple ‘static’ labor supply model with proportional taxes and highlight the problems surrounding nonparticipation and missing wages. The difference in differences
approach to estimation and identification is developed within the context of the labour supply model. We also consider the impact of incorporating nonlinear taxation and welfare programme participation. Family labor supply is looked at from botht e unitary and collective persepctives.
Finally we consider intertemporal models focusing on the difficulties that arise with participation and heterogeneity
Collective labor supply with children
We extend the collective model of household behavior to allow for the existence of public consumption. We show how this model allows the analysis of welfare consequences of policies aimed at changing the distribution of power within the household. Our setting provides a conceptual framework for addressing issues linked to the "targeting" of specific benefits or taxes. We also show that the observation of the labor supplies and the household demand for the public good allow one to identify individual welfare and the decision process. This requires either a separability assumption or the presence of a distribution factor
Detection of a relic X-ray jet in Cygnus A
We present a 200 ks Chandra ACIS-I image of Cygnus A, and discuss a long
linear feature seen in its counterlobe. This feature has a non-thermal spectrum
and lies on the line connecting the brighter hotspot on the approaching side
and the nucleus. We therefore conclude that this feature is (or was) a jet.
However, the outer part of this X-ray jet does not trace the current counterjet
observed in radio. No X-ray counterpart is observed on the jet side. Using
light-travel time effects we conclude that this X-ray 50 kpc linear feature is
a relic jet that contains enough low-energy plasma (gamma ~ 10^3) to
inverse-Compton scatter cosmic microwave background photons, producing emission
in the X-rays.Comment: 4 pages. Proceedings of "High Energy Phenomena in Relativistic
Outflows", held in Dublin, Ireland, September 24-28, 200
Multiwavelength study of Cygnus A IV. Proper motion and location of the nucleus
Context. Cygnus A, as the nearest powerful FR II radio galaxy, plays an
important role in understanding jets and their impact on the surrounding
intracluster medium. Aims. To explain why the nucleus is observed superposed
onto the eastern lobe rather than in between the two lobes, and why the jet and
counterjet are non-colinear. Methods. We made a comparative study of the radio
images at different frequencies of Cygnus A, in combination with the published
results on the radial velocities in the Cygnus A cluster. Results. From the
morphology of the inner lobes we conclude that the lobes are not interacting
with one another, but are well separated, even at low radio frequencies. We
explain the location of the nucleus as the result of the proper motion of the
galaxy through the cluster. The required proper motion is of the same order of
magnitude as the radial velocity offset of Cygnus A with the sub-cluster it
belongs to. The proper motion of the galaxy through the cluster likely also
explains the non-co-linearity of the jet and counterjet.Comment: Accepted for publication in A&A, 8 pages, 4 figure
Catchment-scale vulnerability assessment of groundwater pollution from diffuse sources using the DRASTIC method : a case study
The catchment-scale groundwater vulnerability assessment that delineates zones representing different
levels of groundwater susceptibility to contaminants from diffuse agricultural sources has become an important
element in groundwater pollution prevention for the implementation of the EUWater Framework Directive (WFD).
This paper evaluates the DRASTIC method using an ArcGIS platform for assessing groundwater vulnerability in
the Upper Bann catchment, Northern Ireland. Groundwater vulnerability maps of both general pollutants and
pesticides in the study area were generated by using data on the factors depth to water, net recharge, aquifer media,
soil media, topography, impact of vadose zone, and hydraulic conductivity, as defined in DRASTIC. The mountain
areas in the study area have “high” (in 4.5% of the study area) or “moderate” (in 25.5%) vulnerability for general
pollutants due to high rainfall, net recharge and soil permeability. However, by considering the diffuse agricultural
sources, the mountain areas are actually at low groundwater pollution risk. The results of overlaying the maps of
land use and the groundwater vulnerability are closer to the reality. This study shows that the DRASTIC method is
helpful for guiding the prevention practices of groundwater pollution at the catchment scale in the UK
The Compton-thick quasar at the heart of the high-redshift giant radio galaxy 6C 0905+39
Our XMM-Newton spectrum of the giant, high-redshift (z=1.88) radio galaxy 6C
0905+39 shows that it contains one of the most powerful, high-redshift,
Compton-thick quasars known. Its spectrum is very hard above 2 keV. The steep
XMM spectrum below that energy is shown to be due to extended emission from the
radio bridge using Chandra data. The nucleus of 6C 0905+39 has a column density
of 3.5 (+1.4,-0.4) X 10^24 cm^-2 and absorption-corrected X-ray luminosity of
1.7 (+0.9,-0.1) X 10^45 erg/s in the 2-10 keV band. A lower redshift active
galaxy in the same field, SDSS J090808.36+394313.6, may also be Compton-thick.Comment: 5 pages, 5 figures, accepted to MNRA
Evaluating the employment impact of a mandatory job search program
This paper exploits area-based piloting and age-related eligibility rules to identify treatment effects of a labor market program—the New Deal for Young People in the U.K. A central focus is on substitution/displacement effects and on equilibrium wage effects. The program includes extensive job assistance and wage subsidies to employers. We find that the impact of the program significantly raised transitions to employment by about 5 percentage points. The impact is robust to a wide variety of nonexperimental estimators. However, we present some evidence that this effect may not be as large in the longer run
The radio luminosity function of radio-loud quasars from the 7C Redshift Survey
We present a complete sample of 24 radio-loud quasars (RLQs) from the new 7C
Redshift Survey. Every quasar with a low-frequency (151 MHz) radio flux-density
S_151 > 0.5 Jy in two regions of the sky covering 0.013 sr is included; 23 of
these have sufficient extended flux to meet the selection criteria, 18 of these
have steep radio spectra (hereafter denoted as SSQs). The key advantage of this
sample over most samples of RLQs is the lack of an optical magnitude limit. By
combining the 7C and 3CRR samples, we have investigated the properties of RLQs
as a function of redshift z and radio luminosity L_151.
We derive the radio luminosity function (RLF) of RLQs and find that the data
are well fitted by a single power-law with slope alpha_1=1.9. We find that
there must be a break in the RLQ RLF at log_10(L_151 / W Hz^-1 sr^-1) < 27, in
order for the models to be consistent with the 7C and 6C source counts. The
z-dependence of the RLF follows a one-tailed gaussian which peaks at z=1.7. We
find no evidence for a decline in the co-moving space density of RLQs at higher
redshifts.
A positive correlation between the radio and optical luminosities of SSQs is
observed, confirming a result of Serjeant et al. (1998). We are able to rule
out this correlation being due to selection effects or biases in our combined
sample. The radio-optical correlation and best-fit model RLF enable us to
estimate the distribution of optical magnitudes of quasars in samples selected
at low radio frequencies. We conclude that for samples with S_151 < 1 Jy one
must use optical data significantly deeper than the POSS-I limit (R approx 20),
in order to avoid severe incompleteness.Comment: 28 pages with 13 figures. To appear in MNRA
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