48,591 research outputs found
Taxes and Unmarried Fathers’ Participation in the Underground Economy
In this paper we employ data from the Fragile Families and Child Well-Being Study in order to estimate a model of underground labor supply developed by Lemieux et al. (1994). We focus specifically on the underground labor supply of unmarried fathers, a group that is likely to have significant involvement in the underground economy. We also extend the empirical analysis of Lemieux et al. by taking into account exogenous state and local variation in marginal tax rates, as well as sociodemographic variables related to the likelihood of participation in the underground. In accordance with expectations, we find that a significant proportion of unmarried fathers report participation in the underground. However, although the theoretical model predicts a positive relationship between the tax rate and underground hours of work (under certain conditions), we find that the effect of the tax rate on hours is statistically indistinguishable from zero, even after including exogenous variation in tax rates. We also fail to find a positive and statistically significant effect of the tax rate on participation in the underground. Within the context of the model, these results have specific implications for the magnitudes of the probability of detection and the penalty on evaded tax. Therefore, we conclude that additional empirical information is needed regarding these parameters. Future research might also employ other datasets in the estimation of the theoretical model outlined by Lemieux et al., as well as investigate the applicability of other models of underground labor supply.
The evolution of HI and CIV quasar absorption line systems at 1.9 < z < 3.2
We have investigated the distribution and evolution of ~3100 intergalactic HI
absorbers with HI column densities log N(HI) = [12.75, 17.0] at 1.9 < z < 3.2,
using 18 high resolution, high S/N quasar spectra obtained from the ESO
VLT/UVES archive. We used two sets of Voigt profile fitting analysis, one
including all the available high-order Lyman lines to obtain reliable HI column
densities of saturated lines, and another using only the Ly-alpha lines. There
is no significant difference between the results from the two fits. Combining
our results with literature data, the mean number density at 0 < z < 4 is not
well described by a single power law and strongly suggests that its evolution
slows down at z < 1.5 at the high and low column density ranges. We also
divided our entire HI absorbers at 1.9 < z < 3.2 into two samples, the
unenriched forest and the CIV-enriched forest, depending on whether HI lines
are associated with CIV at log N(CIV) > 12.2 within a given velocity range. The
entire HI column density distribution function (CDDF) can be described as the
combination of these two well-characterised populations which overlap at log
N(HI) ~ 15. At log N(HI) < 15, the unenriched forest dominates, showing a
similar power-law distribution to the entire forest. The CIV-enriched forest
dominates at log N(HI) > 15, with its distribution function proportional to
N(HI)^(-1.45). However, it starts to flatten out at lower N(HI), since the
enriched forest fraction decreases with decreasing N(HI). The deviation from
the power law at log N(HI) = [14, 17] shown in the CDDF for the entire HI
sample is a result of combining two different HI populations with a different
CDDF shape. The total HI mass density relative to the critical density is
Omega(HI) ~ 1.6 x 10^(-6) h^(-1), where the enriched forest accounts for ~40%
of Omega(HI).Comment: 26 pages, 20 figures, accepted for AA, in pres
The phosphoinositide 3-kinase-dependent activation of Btk is required for optimal eicosanoid production and generation of reactive oxygen species in antigen-stimulated mast cells
Activated mast cells are a major source of the eicosanoids PGD(2) and leukotriene C(4) (LTC(4)), which contribute to allergic responses. These eicosanoids are produced following the ERK1/2-dependent activation of cytosolic phospholipase A(2), thus liberating arachidonic acid, which is subsequently metabolized by the actions of 5-lipoxygenase and cyclooxygenase to form LTC(4) and PGD(2), respectively. These pathways also generate reactive oxygen species (ROS), which have been proposed to contribute to FcepsilonRI-mediated signaling in mast cells. In this study, we demonstrate that, in addition to ERK1/2-dependent pathways, ERK1/2-independent pathways also regulate FcepsilonRI-mediated eicosanoid and ROS production in mast cells. A role for the Tec kinase Btk in the ERK1/2-independent regulatory pathway was revealed by the significantly attenuated FcepsilonRI-dependent PGD(2), LTC(4), and ROS production in bone marrow-derived mast cells of Btk(-/-) mice. The FcepsilonRI-dependent activation of Btk and eicosanoid and ROS generation in bone marrow-derived mast cells and human mast cells were similarly blocked by the PI3K inhibitors, Wortmannin and LY294002, indicating that Btk-regulated eicosanoid and ROS production occurs downstream of PI3K. In contrast to ERK1/2, the PI3K/Btk pathway does not regulate cytosolic phospholipase A(2) phosphorylation but rather appears to regulate the generation of ROS, LTC(4), and PGD(2) by contributing to the necessary Ca(2+) signal for the production of these molecules. These data demonstrate that strategies to decrease mast cell production of ROS and eicosanoids would have to target both ERK1/2- and PI3K/Btk-dependent pathways
The Distribution of Column Densities and b Values in the Lyman-Alpha Forest
We describe the properties of the Ly forest in the column density
range \nhi \geq 2\times10^{12} cm based on 1056 lines in the
wavelength range 4300--5100\AA measured in extremely high S/N,
spectra of four quasars. The column density distribution is well described by a
-1.5 power law to cm, below which limit confusion
becomes too severe to measure a spectrum of individual clouds. The distribution
of values shows a well-defined lower envelope with a cutoff at b=20\kms
corresponding to a cloud temperature of 24,000 K. There is only a very small
fraction (less than 1%) of narrow line clouds which cannot be identified with
metal-lines. From modeling the Ly absorption lines as complexes of
clouds each with thermal broadening corresponding to we find the
distribution can be understood if there is a mean of 3.25 clouds per absorption
line with a spread in velocity centroids characterized by a dispersion of
10.75\kms.Comment: 17 pages + 3 tables of text as 1 LaTeX file (uses aastex version 4
style macros: aaspp4.sty, flushrt) plus 1 uuencoded compressed tar file of 7
PostScript figures. Appendix tables and figures [complete spectra and line
lists (~1.6 Mb uncompressed)] are available by anonymous ftp at
ftp://hubble.ifa.hawaii.edu/pub/preprints. To appear in the October 1995
Astronomical Journa
Large Deviation Function of the Partially Asymmetric Exclusion Process
The large deviation function obtained recently by Derrida and Lebowitz for
the totally asymmetric exclusion process is generalized to the partially
asymmetric case in the scaling limit. The asymmetry parameter rescales the
scaling variable in a simple way. The finite-size corrections to the universal
scaling function and the universal cumulant ratio are also obtained to the
leading order.Comment: 10 pages, 2 eps figures, minor changes, submitted to PR
Spectacular X-ray tails, intracluster star formation and ULXs in A3627
We present the discovery of spectacular double X-ray tails associated with
ESO137-001 and a possibly heated X-ray tail associated with ESO137-002, both
late-type galaxies in the closest rich cluster Abell 3627. A deep Chandra
observation of ESO137-001 allows us for the first time to examine the spatial
and spectral properties of such X-ray tails in detail. Besides the known bright
tail that extends to ~ 80 kpc from ESO137-001, a fainter and narrower secondary
tail with a similar length was surprisingly revealed. There is little
temperature variation along both tails. We also identified six X-ray point
sources as candidates of intracluster ULXs with L(0.3-10 keV) of up to
2.5x10^40 erg s^-1. Gemini spectra of intracluster HII regions downstream of
ESO137-001 are also presented, as well as the velocity map of these HII regions
that shows the imprint of ESO137-001's disk rotation. For the first time, we
unambiguously know that active star formation can happen in the cold ISM
stripped by ICM ram pressure and it may contribute a significant amount of the
intracluster light. We also report the discovery of a 40 kpc X-ray tail of
another late-type galaxy in A3627, ESO137-002. Its X-ray tail seems hot, ~ 2
keV (compared to ~ 0.8 keV for ESO137-001's tails). We conclude that the high
pressure environment around these two galaxies is important for their bright
X-ray tails and the intracluster star formation.Comment: ApJ in press, January 2010, v708, only several minor word changes,
emulateapj5.sty, 24 pages, 11 color + 5 B/W figures (figure quality degraded)
and 4 tables. The abstract has been abbreviated. A high-resolution PDF is
available at: http://www.astro.virginia.edu/~ms4ar/eso137_p3.pd
Maximizing Welfare in Social Networks under a Utility Driven Influence Diffusion Model
Motivated by applications such as viral marketing, the problem of influence
maximization (IM) has been extensively studied in the literature. The goal is
to select a small number of users to adopt an item such that it results in a
large cascade of adoptions by others. Existing works have three key
limitations. (1) They do not account for economic considerations of a user in
buying/adopting items. (2) Most studies on multiple items focus on competition,
with complementary items receiving limited attention. (3) For the network
owner, maximizing social welfare is important to ensure customer loyalty, which
is not addressed in prior work in the IM literature. In this paper, we address
all three limitations and propose a novel model called UIC that combines
utility-driven item adoption with influence propagation over networks. Focusing
on the mutually complementary setting, we formulate the problem of social
welfare maximization in this novel setting. We show that while the objective
function is neither submodular nor supermodular, surprisingly a simple greedy
allocation algorithm achieves a factor of of the optimum
expected social welfare. We develop \textsf{bundleGRD}, a scalable version of
this approximation algorithm, and demonstrate, with comprehensive experiments
on real and synthetic datasets, that it significantly outperforms all
baselines.Comment: 33 page
Triple-ionised carbon associated with the low-density neutral hydrogen gas at 1.7 < z < 3.3: the integrated N(HI)-N(CIV) relation
From the Voigt profile fitting analysis of 183 intervening CIV systems at 1.7
< z < 3.3 in 23 high-quality UVES/VLT and HIRES/Keck QSO spectra, we find that
a majority of CIV systems (~75%) display a well-characterised scaling relation
between integrated column densities of HI and CIV with a negligible redshift
evolution, when column densities of all the HI and CIV components are
integrated within a given (-150, +150) km/sec range centred at the CIV flux
minimum. The integrated CIV column density N(CIV, sys) increases with N(HI,
sys) at log N(HI, sys) = 14.0--15.5 and log N(CIV, sys) = 11.8--14.0, then
becomes almost independent of N(HI, sys) at log N(HI, sys) > 16, with a large
scatter: at log N(HI, sys) = 14--22, log N(CIV, sys) = C1 / (log(NHI, sys) +
C2) + C3, with C1 = -1.90+0.55, C2 = -14.11+0.19 and C3 = 14.76+0.17,
respectively. The steep (flat) part is dominated by SiIV-free (SiIV-enriched)
CIV systems. Extrapolating the N(HI, sys)-N(CIV, sys) relation implies that
most absorbers with log N(HI) < 14 are virtually CIV-free. The N(HI,
sys)-N(CIV, sys) relation does not hold for individual components, clumps or
the integration velocity range less than +-100 km/sec. It is expected if the
line-of-sight extent of CIV is smaller than HI and N(CIV, sys) decreases more
rapidly than N(HI, sys) at the larger impact parameter, regardless of the
location of the HI+CIV gas in the IGM filaments or in the intervening galactic
halos.Comment: Accepted for publication on MNRAS, 26 pages, 20 figures, 4 tables.
On-line materials are found in the submitted civ.tar.gz file: complete Table
2, complete Table 3, complete Table 4, velocity plots civ1.pdf, civ2.pdf,
civ3.pdf, civ4.pdf and civ5.pd
Effect of Long-Range Interactions in the Conserved Kardar-Parisi-Zhang Equation
The conserved Kardar-Parisi-Zhang equation in the presence of long-range
nonlinear interactions is studied by the dynamic renormalization group method.
The long-range effect produces new fixed points with continuously varying
exponents and gives distinct phase transitions, depending on both the
long-range interaction strength and the substrate dimension . The long-range
interaction makes the surface width less rough than that of the short-range
interaction. In particular, the surface becomes a smooth one with a negative
roughness exponent at the physical dimension d=2.Comment: 4 pages(LaTex), 1 figure(Postscript
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