572 research outputs found
Union Threat Effects and Nonunion Industry Wage Differentials
We investigate the impact of union strength on changes in nonunion wages and employment. The prevailing model in this area is the threat model, which predicts that increases in union strength cause increases in nonunion wages and decreases in nonunion employment. In testing the threat model, we are also testing two alternatives, the crowding and complements models. In contrast to the prediction of the threat model, decreases in the percent organized (reflecting a declining union threat) are associated with increases in the nonunion wage. Furthermore, increases in union wages appear to decrease, rather than to increase, nonunion wages. Evidence on the determinants of intra-industry variation in nonunion wage premia is somewhat more consistent with the crowding model and is strikingly consistent with the complements model of union and nonunion wage determination. Further evidence on the determinants of intra-industry variation in nonunion employment is consistent with the complements model and the threat model; movements in nonunion industry employment are negatively related to changes in proxies for union strength. Thus, the combined evidence supports the complements model, but neither the threat model nor the crowding model.
Postponement and recuperation of Belgian fertility: how are they related to rising female educational attainment?
Fertility trends in Europe after 1970 are routinely referred to in terms of the postponement of fertility. The shortening of the effective reproductive lifespan and its association with post-materialist values have raised questions as to whether fertility can or will be recuperated. Decomposition of cohort fertility in Belgium by level of education shows that the postponement of fertility after 1970 is closely related to the expansion of education: compared with cohorts born in 1946-1950, 40 to 50 per cent of the difference in cumulated fertility at age 25 in the 1951-1975 birth cohorts is attributable to rising educational levels. Educational differentials also prove relevant with regard to the recuperation of fertility at older ages as the tempo and quantum of order-specific fertility have responded differently to variations in the economic and policy context, depending on the educational level considered. Differential fertility trends by level of education have thus attenuated the relationship between female educational attainment and completed fertility in recent cohorts.
A generalized model of mutation-selection balance with applications to aging
A probability model is presented for the dynamics of mutation-selection
balance in a haploid infinite-population infinite-sites setting sufficiently
general to cover mutation-driven changes in full age-specific demographic
schedules. The model accommodates epistatic as well as additive selective
costs. Closed form characterizations are obtained for solutions in finite time,
along with proofs of convergence to stationary distributions and a proof of the
uniqueness of solutions in a restricted case. Examples are given of
applications to the biodemography of aging, including instabilities in current
formulations of mutation accumulation.Comment: 20 pages Updated to include more historical comment and references to
the literature, as well as to make clear how our non-linear, non-Markovian
model differs from previous linear, Markovian particle system and
measure-valued diffusion models. Further updated to take into account
referee's comment
The Age-Specific Force of Natural Selection and Walls of Death
W. D. Hamilton's celebrated formula for the age-specific force of natural
selection furnishes predictions for senescent mortality due to mutation
accumulation, at the price of reliance on a linear approximation. Applying to
Hamilton's setting the full non-linear demographic model for mutation
accumulation of Evans et al. (2007), we find surprising differences. Non-linear
interactions cause the collapse of Hamilton-style predictions in the most
commonly studied case, refine predictions in other cases, and allow Walls of
Death at ages before the end of reproduction. Haldane's Principle for genetic
load has an exact but unfamiliar generalization.Comment: 27 page
The WIRED Survey. IV. New Dust Disks from the McCook & Sion White Dwarf Catalog
We have compiled photometric data from the Wide-field Infrared Survey
Explorer All Sky Survey and other archival sources for the more than 2200
objects in the original McCook & Sion Catalog of Spectroscopically Identified
White Dwarfs. We applied color-selection criteria to identify 28 targets whose
infrared spectral energy distributions depart from the expectation for the
white dwarf photosphere alone. Seven of these are previously known white dwarfs
with circumstellar dust disks, five are known central stars of planetary
nebulae, and six were excluded for being known binaries or having possible
contamination of their infrared photometry. We fit white dwarf models to the
spectral energy distributions of the remaining ten targets, and find seven new
candidates with infrared excess suggesting the presence of a circumstellar dust
disk. We compare the model dust disk properties for these new candidates with a
comprehensive compilation of previously published parameters for known white
dwarfs with dust disks. It is possible that the current census of white dwarfs
with dust disks that produce an excess detectable at K-band and shorter
wavelengths is close to complete for the entire sample of known WDs to the
detection limits of existing near-IR all-sky surveys. The white dwarf dust disk
candidates now being found using longer wavelength infrared data are drawn from
a previously underrepresented region of parameter space, in which the dust
disks are overall cooler, narrower in radial extent, and/or contain fewer
emitting grains.Comment: accepted for publication in The Astrophysical Journal; 34 pages, 5
figures, 5 tables; added missing reference in Section 2 (p. 7
A Mid-Infrared Counterpart to the Magnetar 1E 2259+586
We report the discovery of a 4.5 um counterpart to the anomalous X-ray pulsar
(magnetar) 1E 2259+586 with the Spitzer Space Telescope. The mid-infrared flux
density is 6.3+/-1.0 uJy at 4.5 um and <20 uJy (at 95% confidence) at 8 um, or
0.02% of the 2-10 keV X-ray flux (corrected for extinction). Combining our
Spitzer measurements with previously published near-infrared data, we show that
the overall infrared emission from 1E 2259+586 is qualitatively similar to that
from the magnetar 4U 0142+61. Therefore the passive X-ray-heated dust disk
model originally developed for 4U 0142+61 might also apply to 1E 2259+586.
However, the IR data from this source can also be fitted by a simple power-law
spectrum as might be expected from magnetospheric emission.Comment: Accepted for publication in ApJ. 6 pages, 4 figures, uses emulateap
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