4,303 research outputs found
Early diffusion evidence of retrograde transsynaptic degeneration in the human visual system
We investigated whether diffusion tensor imaging (DTI) indices of white matter integrity would offer early markers of retrograde transsynaptic degeneration (RTD) in the visual system after stroke
Objective: We investigated whether diffusion tensor imaging (DTI) indices of white matter integrity
would offer early markers of retrograde transsynaptic degeneration (RTD) in the visual system
after stroke.
Methods: We performed a prospective longitudinal analysis of the sensitivity of DTI markers of
optic tract health in 12 patients with postsynaptic visual pathway stroke, 12 stroke controls,
and 28 healthy controls. We examined group differences in (1) optic tract fractional anisotropy
(FA-asymmetry), (2) perimetric measures of visual impairment, and (3) the relationship between
FA-asymmetry and perimetric assessment.
Results: FA-asymmetry was higher in patients with visual pathway lesions than in control groups.
These differences were evident 3 months from the time of injury and did not change significantly
at 12 months. Perimetric measures showed evidence of impairment in participants with visual
pathway stroke but not in control groups. A significant association was observed between
FA-asymmetry and perimetric measures at 3 months, which persisted at 12 months.
Conclusions: DTI markers of RTD are apparent 3 months from the time of injury. This represents
the earliest noninvasive evidence of RTD in any species. Furthermore, these measures associate
with measures of visual impairment. DTI measures offer a reproducible, noninvasive, and sensitive
method of investigating RTD and its role in visual impairment
Development of Athletes Conceptions of Sport Officials Authority
This study examined baseball players\u27 conceptions of umpires\u27 authority. Eighty male players, ages 6-22 years, completed an abbreviated Inventory of Piaget\u27s Developmental Tasks (Furth, 1970), which was used to measure cognitive development. They then heard recorded scenarios describing conflicts with an umpire and a parent. Players indicated if they would argue with the authorities, why they obey the authorities (obedience), and why the authorities get to make decisions (legitimacy). Obedience and legitimacy responses were categorized into Damon\u27s (1977) three levels. Measures of arguing, obedience, and legitimacy were analyzed for four age levels and three levels of cognitive development. Older and more cognitively developed players were more likely to argue with authorities. Conceptions of obedience and legitimacy were positively associated with age, though they were not related to scores of cognitive development. The positive relationship between age and authority conceptions and the absence of a relationship between cognitive development and authority conceptions are both consistent with Damon\u27s position
Enforcement is central to the evolution of cooperation.
Cooperation occurs at all levels of life, from genomes, complex cells and multicellular organisms to societies and mutualisms between species. A major question for evolutionary biology is what these diverse systems have in common. Here, we review the full breadth of cooperative systems and find that they frequently rely on enforcement mechanisms that suppress selfish behaviour. We discuss many examples, including the suppression of transposable elements, uniparental inheritance of mitochondria and plastids, anti-cancer mechanisms, reciprocation and punishment in humans and other vertebrates, policing in eusocial insects and partner choice in mutualisms between species. To address a lack of accompanying theory, we develop a series of evolutionary models that show that the enforcement of cooperation is widely predicted. We argue that enforcement is an underappreciated, and often critical, ingredient for cooperation across all scales of biological organization
Reply to: Broad definitions of enforcement are unhelpful for understanding evolutionary mechanisms of cooperation.
The SDSS-2MASS-WISE Ten Dimensional Stellar Color Locus
We present the fiducial main sequence stellar locus traced by 10 photometric
colors observed by SDSS, 2MASS, and WISE. Median colors are determined using
1,052,793 stars with r-band extinction less than 0.125. We use this locus to
measure the dust extinction curve relative to the r-band, which is consistent
with previous measurements in the SDSS and 2MASS bands. The WISE band
extinction coefficients are larger than predicted by standard extinction
models. Using 13 lines of sight, we find variations in the extinction curve in
H, Ks, and WISE bandpasses. Relative extinction decreases towards Galactic
anti-center, in agreement with prior studies. Relative extinction increases
with Galactic latitude, in contrast to previous observations. This indicates a
universal mid-IR extinction law does not exist due to variations in dust grain
size and chemistry with Galactocentric position. A preliminary search for
outliers due to warm circumstellar dust is also presented, using stars with
high signal-to-noise in the W3-band. We find 199 such outliers, identified by
excess emission in Ks-W3. Inspection of SDSS images for these outliers reveals
a large number of contaminants due to nearby galaxies. Six sources appear to be
genuine dust candidates, yielding a fraction of systems with infrared excess of
0.120.05%.Comment: 11 pages, 10 figures, MNRAS Accepted. Tables 1 and 2 available
online: https://github.com/jradavenport/wise_locu
Optical Sky Brightness at Cerro Tololo Inter-American Observatory from 1992 to 2006
We present optical UBVRI sky brightness measures from 1992 through 2006. The
data are based on CCD imagery obtained with the CTIO 0.9-m, 1.3-m, and 1.5-m
telescopes. The B- and V-band data are in reasonable agreement with
measurements previously made at Mauna Kea, though on the basis of a small
number of images per year there are discrepancies for the years 1992 through
1994. Our CCD-based data are not significantly different than values obtained
at Cerro Paranal. We find that the yearly averages of V-band sky brightness are
best correlated with the 10.7-cm solar flux taken 5 days prior to the sky
brightness measures. This implies an average speed of 350 km/sec for the solar
wind. While we can measure an enhancement of the night sky levels over La
Serena 10 degrees above the horizon, at elevation angles above 45 degrees we
find no evidence that the night sky brightness at Cerro Tololo is affected by
artificial light of nearby towns and cities.Comment: 24 pages, 5 figures, to be published in the June, 2007, issue of the
Publications of the Astron. Society of the Pacifi
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