15,140 research outputs found
Postnatal depression and reproductive success in modern, low-fertility contexts
Background and objectives: Postnatal depression (PND) presents a puzzling phenomenon to evolutionary
anthropologists as it is highly prevalent and yet detrimental to child development and maternal
health. Adaptive explanations have been proposed, but have not been tested with data that directly link
PND to female fertility.
Methodology: A survey was designed to gather complete reproductive histories and retrospective measures
of PND to measure the effects of PND on fitness. Respondents were born between 1930 and 1967,
with the majority based in the UK during their childrearing years. The hypothesis that PND is detrimental
to fitness is assessed using Mann–Whitney U tests on completed fertility. Binary logistic regression
modelling is used to test the hypothesis that PND reduces the likelihood of parity progression.
Results: Women experiencing PND at their first or second birth have lower completed fertility, with PND
at the first birth leading to lowered fertility. Logistic regression analyses show that this is the result of
reductions in the likelihood of parity progression to a third birth when PND is experienced at the first
birth or when repeat bouts occur.
Conclusions and implications: Our results call into question adaptationist arguments, contribute to the
growing understanding of the importance of emotional wellbeing to fertility decision making, and given
the economic consequences of markedly below replacement fertility, highlight a potential new source of
financial incentive to invest in screening and preventative measures to ensure good maternal mental
health
How Hot is the Wind from TW Hydrae?
It has recently been suggested that the winds from Classical T Tauri stars in
general, and the wind from TW Hya in particular, reaches temperatures of at
least 300,000 K while maintaing a mass loss rate of \Msol
yr or larger. If confirmed, this would place strong new requirements on
wind launching and heating models. We therefore re-examine spectra from the
Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and
spectra from the Far Ultraviolet Spectroscopic Explorer satellite in an effort
to better constrain the maximum temperature in the wind of TW Hya. We find
clear evidence for a wind in the \ion{C}{2} doublet at 1037 \AA and in the
\ion{C}{2} multiplet at 1335 \AA. We find no wind absorption in the \ion{C}{4}
1550 \AA doublet observed at the same time as the \ion{C}{2} 1335 \AA line or
in observations of \ion{O}{6} observed simultaneously with the \ion{C}{2} 1037
\AA line. The presence or absence of \ion{C}{3} wind absorption is ambiguous.
The clear lack of a wind in the \ion{C}{4} line argues that the wind from TW
Hya does not reach the 100,000 K characteristic formation temperature of this
line. We therefore argue that the available evidence suggests that the wind
from TW Hya, and probably all classical T Tauri stars, reaches a maximum
temperature in the range of 10,000 -- 30,000 K.Comment: 17 pages, 3 figures, Figure 1 in 2nd version fixes a small velocity
scaling error and new revision adds a reference to an additional paper
recently foun
Gear drive automatically indexes rotary table
Combination indexer and drive unit drills equally spaced circular hole patterns on rotary tables. It automatically rotates the table a distance exactly equal to one hole spacing for each revolution of a special idler gear
Children in J.D. Salinger: an isolated world
This study attempts to analyze one of the most noticeable aspects of the fiction of J.D.Salinger - his consistent use of children
Calculating risk change with management actions using Bayesian networks for the South River, Virginia, USA
Ecological managers often implement one or more management options to manage risk without the direct integration of a quantitative risk assessment and evaluation of management alternatives. Throughout the decision making process a manager should consider multiple stressors as well as stressor interactions and the resulting effects. In my study, I used Bayesian networks in a relative risk assessment model framework (BN-RRM) to integrate two management options into existing risk assessment models for biotic endpoints and water quality endpoints in the mercury contaminated site, South River, VA. The two management options assessed were agricultural best management practices (BMPs) and bank stabilization. The primary management goal expressed by managers is no regrets. In other words, managers do not want to make the site worse in any way, such as reducing mercury levels at the detriment of habitat, loss of other species, degradation of water quality, or other environmental parameters. The Bayesian networks represent the expected effects of a management option and the potential for unintended consequences. Agricultural BMPs did not change the skew of the risk distributions, but aligns with the no regrets management focus because risk did not increase. Bank stabilization management shifted the risk distribution for smallmouth bass so that there was greater likelihood of zero risk. The risk distribution for the water quality-fishing endpoint changed because likelihood of medium and high risk increased. If bank stabilization is implemented without consideration of Belted Kingfisher nests, there was 100% likelihood of high risk to the Kingfisher. My research provides South River managers with a tool that describes how management options are expected to change risk to biotic and water quality endpoints. Adaptive management for the South River is a long-term process. The BN-RRM models can be updated with new monitoring data to inform future management decisions
Constraints on the disk geometry of the T Tauri star AA Tau from linear polarimetry
We have simultaneously monitored the photometric and polarimetric variations
of the Classical T Tauri star AA Tau during the fall of 2002. We combine these
data with previously published polarimetric data covering two earlier epochs.
The phase coverage is complete, although not contiguous. AA Tau clearly shows
cyclic variations coupled with the rotation of the system. The star-disk system
produces a repeatable polarisation curve where the polarisation increases with
decreasing brightness. The data fit well with the model put forward by Bouvier
et al. (1999) where AA Tau is viewed almost edge-on and its disk is actively
dumping material onto the central star via magnetospheric accretion. The inner
edge of the disk is deformed by its interaction with the tilted magnetosphere,
producing eclipses as it rotates and occults the photosphere periodically. From
the shape of the polarisation curve in the QU-Plane we confirm that the
accretion disk is seen at a large inclination, almost edge-on, and predict that
its position angle is PA~90 deg., i.e., that the disk's major axis is oriented
in the East-West direction.Comment: Astron. Astrophys., in pres
The Origins of Fluorescent H_2 Emission From T Tauri Stars
We survey fluorescent H_2 emission in HST STIS spectra of the classical T Tauri stars (CTTSs) TW Hya, DF Tau, RU Lupi, T Tau, and DG Tau, and the weak-lined T Tauri star (WTTS) V836 Tau. From each of those sources we detect between 41 and 209 narrow H_2 emission lines, most of which are pumped by strong Lyα emission. H_2 emission is not detected from the WTTS V410 Tau. The fluorescent H_2 emission appears to be common to circumstellar environments around all CTTSs, but high spectral and spatial resolution STIS observations reveal diverse phenomenon. Blueshifted H_2 emission detected from RU Lupi, T Tau, and DG Tau is consistent with an origin in an outflow. The H_2 emission from TW Hya, DF Tau, and V836 Tau is centered at the radial velocity of the star and is consistent with an origin in a warm disk surface. The H_2 lines from RU Lupi, DF Tau, and T Tau also have excess blueshifted H_2 emission that extends to as much as -100 km s^(-1). The strength of this blueshifted component from DF Tau and T Tau depends on the upper level of the transition. In all cases, the small aperture and attenuation of H_2 emission by stellar winds restricts the H_2 emission to be formed close to the star. In the observation of RU Lupi, the Lyα emission and the H_2 emission that is blueshifted by 15 km s^(-1) are extended to the SW by ~0".07, although the faster H_2 gas that extends to ~100 km s^(-1) is not spatially extended. We also find a small reservoir of H_2 emission from TW Hya and DF Tau consistent with an excitation temperature of ~2.5 × 10^4 K
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