2,618 research outputs found
Discrimination in the Workplace: Evidence from a Civil War in Peru
Few events give the opportunity to observe the full range of human behavior as wars do. In the case of civil wars in ethnically-mixed societies, the distribution of violence across various segments of the population can provide evidence on the extent and nature of discrimination. As in the case of markets, identifying discrimination in the warplace is challenging. There is uncertainty on the reconstruction of events as well as the rationale behind the violence. We use a unique data set collected by the Peruvian Truth and Reconciliation Commission on war crimes during the 1980's to show that there is evidence of taste-based discrimination by agents of the state towards ethnic minorities and women. The evidence is robust to different assumptions on the logic of repression and missing data problems. Working Paper 07-3
Use Permits: A Hedonistic Approach Applied to Farmland in the Southeastern US
In the State of Georgia, any agricultural producer who wishes to pump more than 100,000 gallons of water a day for crop irrigation is required to have an irrigation permit. The permit stays with the land and in the event of sale the permit is transferred with the property. Until recently, permits were essentially granted freely to all applicants in the Flint River water basin, without limit. In 1999, however, with increasing demand for water from growing urban Atlanta and several years of drought in the Southeast, the state of Georgia placed a moratorium on the issuance of agricultural water permits in the Flint River basin. This research exploits this policy change within a hedonic pricing framework to estimate the value of irrigation rights in the Southeast US. While the value of irrigation rights has been studied extensively in the western US, differences in property rights and legal regimes, as well as a lack of established water-rights markets in the East, leave us with little information regarding the value of irrigation rights in this setting. Working Paper 06-4
Pattern-based phylogenetic distance estimation and tree reconstruction
We have developed an alignment-free method that calculates phylogenetic
distances using a maximum likelihood approach for a model of sequence change on
patterns that are discovered in unaligned sequences. To evaluate the
phylogenetic accuracy of our method, and to conduct a comprehensive comparison
of existing alignment-free methods (freely available as Python package decaf+py
at http://www.bioinformatics.org.au), we have created a dataset of reference
trees covering a wide range of phylogenetic distances. Amino acid sequences
were evolved along the trees and input to the tested methods; from their
calculated distances we infered trees whose topologies we compared to the
reference trees.
We find our pattern-based method statistically superior to all other tested
alignment-free methods on this dataset. We also demonstrate the general
advantage of alignment-free methods over an approach based on automated
alignments when sequences violate the assumption of collinearity. Similarly, we
compare methods on empirical data from an existing alignment benchmark set that
we used to derive reference distances and trees. Our pattern-based approach
yields distances that show a linear relationship to reference distances over a
substantially longer range than other alignment-free methods. The pattern-based
approach outperforms alignment-free methods and its phylogenetic accuracy is
statistically indistinguishable from alignment-based distances.Comment: 21 pages, 3 figures, 2 table
Detection of Structure in Infrared-Dark Clouds with Spitzer: Characterizing Star Formation in the Molecular Ring
We have conducted a survey of a sample of infrared-dark clouds (IRDCs) with
the Spitzer Space Telescope in order to explore their mass distribution. We
present a method for tracing mass using dust absorption against the bright
Galactic background at 8 microns. The IRDCs in this sample are comprised of
tens of clumps, ranging in sizes from 0.02 to 0.3 pc in diameter and masses
from 0.5 to a few 10 Msun, the broadest dynamic range in any clump mass
spectrum study to date. Structure with this range in scales confirms that IRDCs
are the the precursors to stellar clusters in an early phase of fragmentation.
Young stars are distributed in the vicinity of the IRDCs, but the clumps are
typically not associated with stars and appear pre-stellar in nature. We find
an IRDC clump mass spectrum with a slope of 1.76 +/- 0.05 for masses from 30 to
3000 Msun. This slope is consistent with numerous studies, culled from a
variety of observational techniques, of massive star formation regions and is
close to the mass function of Galactic stellar clusters and star clusters in
other galaxies. We assert that the shape of the mass function is an intrinsic
and universal feature of massive star formation regions, that are the birth
sites of stellar clusters. As these clouds evolve and their constituent clumps
fragment, the mass spectrum will steepen and eventually assume the form of the
core mass function that is observed locally.Comment: Accepted to ApJ. 37 pages, 24 figures. Full-resolution versions of
the figures are available at
http://www.astro.lsa.umich.edu/~seragan/ftp/irdc_figs
A model for estimating time-variant rainfall infiltration as a function of antecedent surface moisture and hydrologic soil type
Recent research indicates that the use of remote sensing techniques for the measurement of near surface soil moisture could be practical in the not too distant future. Other research shows that infiltration rates, especially for average or frequent rainfall events, are extremely sensitive to the proper definition and consideration of the role of the soil moisture at the beginning of the rainfall. Thus, it is important that an easy to use, but theoretically sound, rainfall infiltration model be available if the anticipated remotely sensed soil moisture data is to be optimally utilized for hydrologic simulation. A series of numerical experiments with the Richards' equation for an array of conditions anticipated in watershed hydrology were used to develop functional relationships that describe temporal infiltration rates as a function of soil type and initial moisture conditions
An evaluation of DNA-damage response and cell-cycle pathways for breast cancer classification
Accurate subtyping or classification of breast cancer is important for
ensuring proper treatment of patients and also for understanding the molecular
mechanisms driving this disease. While there have been several gene signatures
proposed in the literature to classify breast tumours, these signatures show
very low overlaps, different classification performance, and not much relevance
to the underlying biology of these tumours. Here we evaluate DNA-damage
response (DDR) and cell cycle pathways, which are critical pathways implicated
in a considerable proportion of breast tumours, for their usefulness and
ability in breast tumour subtyping. We think that subtyping breast tumours
based on these two pathways could lead to vital insights into molecular
mechanisms driving these tumours. Here, we performed a systematic evaluation of
DDR and cell-cycle pathways for subtyping of breast tumours into the five known
intrinsic subtypes. Homologous Recombination (HR) pathway showed the best
performance in subtyping breast tumours, indicating that HR genes are strongly
involved in all breast tumours. Comparisons of pathway based signatures and two
standard gene signatures supported the use of known pathways for breast tumour
subtyping. Further, the evaluation of these standard gene signatures showed
that breast tumour subtyping, prognosis and survival estimation are all closely
related. Finally, we constructed an all-inclusive super-signature by combining
(union of) all genes and performing a stringent feature selection, and found it
to be reasonably accurate and robust in classification as well as prognostic
value. Adopting DDR and cell cycle pathways for breast tumour subtyping
achieved robust and accurate breast tumour subtyping, and constructing a
super-signature which contains feature selected mix of genes from these
molecular pathways as well as clinical aspects is valuable in clinical
practice.Comment: 28 pages, 7 figures, 6 table
Nonlithographic epitaxial Sn_xGe_(1–x) dense nanowire arrays grown on Ge(001)
We have grown 1-µm-thick Sn_xGe_(1–x)/Ge(001) epitaxial films with 0 < x < 0.085 by molecular-beam epitaxy. These films evolve during growth into a dense array of Sn_xGe_(1–x) nanowires oriented along [001], as confirmed by composition contrast observed in scanning transmission electron microscopy in planar view. The Sn-rich regions in these films dominate optical absorption at low energy; phase-separated Sn_xGe_(1–x) alloys have a lower-energy band gap than homogeneous alloys with the same average Sn composition
A two-phase approach for detecting recombination in nucleotide sequences
Genetic recombination can produce heterogeneous phylogenetic histories within
a set of homologous genes. Delineating recombination events is important in the
study of molecular evolution, as inference of such events provides a clearer
picture of the phylogenetic relationships among different gene sequences or
genomes. Nevertheless, detecting recombination events can be a daunting task,
as the performance of different recombinationdetecting approaches can vary,
depending on evolutionary events that take place after recombination. We
recently evaluated the effects of postrecombination events on the prediction
accuracy of recombination-detecting approaches using simulated nucleotide
sequence data. The main conclusion, supported by other studies, is that one
should not depend on a single method when searching for recombination events.
In this paper, we introduce a two-phase strategy, applying three statistical
measures to detect the occurrence of recombination events, and a Bayesian
phylogenetic approach in delineating breakpoints of such events in nucleotide
sequences. We evaluate the performance of these approaches using simulated
data, and demonstrate the applicability of this strategy to empirical data. The
two-phase strategy proves to be time-efficient when applied to large datasets,
and yields high-confidence results.Comment: 5 pages, 3 figures. Chan CX, Beiko RG and Ragan MA (2007). A
two-phase approach for detecting recombination in nucleotide sequences. In
Hazelhurst S and Ramsay M (Eds) Proceedings of the First Southern African
Bioinformatics Workshop, 28-30 January, Johannesburg, 9-1
Dual-Career Couples in Academia : Does Wage Growth Suffer When One’s Partner Works for the Same University?
Extending the literature on monopsony in academic labor markets, we find that faculty pay is inversely related to seniority in both cross-sectional and longitudinal data sets for a large public university in the United States. Fixed-effects results indicate that the negative relationship cannot be explained by lower quality of senior faculty. Arguing that mobility costs are higher when both partners work for the same university, we allow monopsony power to vary by employment status of partner. We find that pay of male faculty is negatively and significantly related to the number of years the partner has been employed by the university and that the penalty is greater when couples are hired together.Monopsony, academic labor market
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