6,954 research outputs found
Cognitive performance in multiple system atrophy
The cognitive performance of a group of patients with multiple system atrophy (MSA) of striato-nigral predominance was compared with that of age and IQ matched control subjects, using three tests sensitive to frontal lobe dysfunction and a battery sensitive to memory and learning deficits in Parkinson's disease and dementia of the Alzheimer type. The MSA group showed significant deficits in all three of the tests previously shown to be sensitive to frontal lobe dysfunction. Thus, a significant proportion of patients from the MSA group failed an attentional set-shifting test, specifically at the stage when an extra-dimensional shift was required. They were also impaired in a subject-ordered test of spatial working memory. The MSA group showed deficits mostly confined to measures of speed of thinking, rather than accuracy, on the Tower of London task. These deficits were seen in the absence of consistent impairments in language or visual perception. Moreover, the MSA group showed no significant deficits in tests of spatial and pattern recognition previously shown to be sensitive to patients early in the course of probable Alzheimer's disease and only a few patients exhibited impairment on the Warrington Recognition Memory Test. There were impairments on other tests of visual memory and learning relative to matched controls, but these could not easily be related to fundamental deficits of memory or learning. Thus, on a matching-to-sample task the patients were impaired at simultaneous but not delayed matching to sample, whereas difficulties in a pattern-location learning task were more evident at its initial, easier stages. The MSA group showed no consistent evidence of intellectual deterioration as assessed from their performance on subtests of the Wechsler Adult Intelligence Scale (WAIS) and the National Adult Reading Test (NART). Consideration of individual cases showed that there was some heterogeneity in the pattern of deficits in the MSA group, with one patient showing no impairment, even in the face of considerable physical disability. The results show a distinctive pattern of cognitive deficits, unlike those previously seen using the same tests in patients with Parkinson's and Alzheimer's diseases, and suggesting a prominent frontal-lobe-like component. The implications for concepts of 'subcortical' dementia and 'fronto-striatal' cognitive dysfunction are considered
Fronto-striatal cognitive deficits at different stages of Parkinson's disease
Groups of patients with idiopathic Parkinson's disease, either medicated or unmedicated, were compared with matched groups of normal controls on a computerized battery previously shown to be sensitive to frontal lobe dysfunction, including tests of planning, spatial working memory and attentional set-shifting. In a series of problems based on the 'Tower of London' test, medicated patients with Parkinson's disease were shown to be impaired in the amount of time spent thinking about (planning) the solution to each problem. Additionally, an impairment in terms of the accuracy of the solution produced on this test was only evident in those patients with more severe clinical symptoms and was accompanied by deficits in an associated test of spatial short-term memory. Medicated patients with both mild and severe clinical symptoms were also impaired on a related test of spatial working memory. In contrast, a group of patients who were unmedicated and 'early in the course' of the disease were unimpaired in all three of these tests. However, all three Parkinson's disease groups were impaired in the test of attentional set-shifting ability, although unimpaired in a test of pattern recognition which is insensitive to frontal lobe damage. These data are compared with those previously published from a group of young neurosurgical patients with localized excisions of the frontal lobes and are discussed in terms of the specific nature of the cognitive deficit at different stages of Parkinson's disease
Environmental Policy Aid Under Uncertainty
Recent emphasis on uncertainty in environmental decision making reflects numerous changes in environmental science and policy making over the past few decades. Firstly, environmental policy problems increasingly involve large, interconnected and complex social choices. For example, climate change, ozone depletion, biodiversity loss, genetically-engineered crops, environment-related diseases and health risks involve large scale, long-term impacts, whose precise causes and consequences are often poorly understood. Given these uncertainties and the risk of irreversible environmental changes, different perspectives about the nature, policy implications, or even the existence of a problem, are inevitable (Rittel and Webber, 1973; Sarewitz, 2004)
Star Formation in Sculptor Group Dwarf Irregular Galaxies and the Nature of "Transition" Galaxies
We present new H-alpha narrow band imaging of the HII regions in eight
Sculptor Group dwarf irregular (dI) galaxies. Comparing the Sculptor Group dIs
to the Local Group dIs, we find that the Sculptor Group dIs have, on average,
lower values of SFR when normalized to either galaxy luminosity or gas mass
(although there is considerable overlap between the two samples). The
properties of ``transition'' (dSph/dIrr) galaxies in Sculptor and the Local
Group are also compared and found to be similar. The transition galaxies are
typically among the lowest luminosities of the gas rich dwarf galaxies.
Relative to the dwarf irregular galaxies, the transition galaxies are found
preferentially nearer to spiral galaxies, and are found nearer to the center of
the mass distribution in the local cloud. While most of these systems are
consistent with normal dI galaxies which currently exhibit temporarily
interrupted star formation, the observed density-morphology relationship (which
is weaker than that observed for the dwarf spheroidal galaxies) indicates that
environmental processes such as ``tidal stirring'' may play a role in causing
their lower SFRs.Comment: 35 pages, 10 figures, accepted for Feb 2003 AJ, companion to
astro-ph/021117
Perturbative evolution of particle orbits around Kerr black holes: time domain calculation
Treating the Teukolsky perturbation equation numerically as a 2+1 PDE and
smearing the singularities in the particle source term by the use of narrow
Gaussian distributions, we have been able to reproduce earlier results for
equatorial circular orbits that were computed using the frequency domain
formalism. A time domain prescription for a more general evolution of nearly
geodesic orbits under the effects of radiation reaction is presented. This
approach can be useful when tackling the more realistic problem of a
stellar-mass black hole moving on a generic orbit around a supermassive black
hole under the influence of radiation reaction forces.Comment: 8 pages, 5 figures, problems with references and double-printing
fixe
Lava channel formation during the 2001 eruption on Mount Etna: evidence for mechanical erosion
We report the direct observation of a peculiar lava channel that was formed
near the base of a parasitic cone during the 2001 eruption on Mount Etna.
Erosive processes by flowing lava are commonly attributed to thermal erosion.
However, field evidence strongly suggests that models of thermal erosion cannot
explain the formation of this channel. Here, we put forward the idea that the
essential erosion mechanism was abrasive wear. By applying a simple model from
tribology we demonstrate that the available data agree favorably with our
hypothesis. Consequently, we propose that erosional processes resembling the
wear phenomena in glacial erosion are possible in a volcanic environment.Comment: accepted for publication in Physical Review Letter
HAT-P-32b and HAT-P-33b: Two Highly Inflated Hot Jupiters Transiting High-jitter Stars
We report the discovery of two exoplanets transiting high-jitter stars. HAT-P-32b orbits the bright V = 11.289 late-F-early-G dwarf star GSC 3281-00800, with a period P = 2.150008 Âą 0.000001 d. The stellar and planetary masses and radii depend on the eccentricity of the system, which is poorly constrained due to the high-velocity jitter (~80 m s^(â1)). Assuming a circular orbit, the star has a mass of 1.16 Âą 0.04 M_â and radius of 1.22 Âą 0.02 R_â, while the planet has a mass of 0.860 Âą 0.164 M_J and a radius of 1.789 Âą 0.025 R_J. The second planet, HAT-P-33b, orbits the bright V = 11.188 late-F dwarf star GSC 2461-00988, with a period P = 3.474474 Âą 0.000001 d. As for HAT-P-32, the stellar and planetary masses and radii of HAT-P-33 depend on the eccentricity, which is poorly constrained due to the high jitter (~50 m s^(â1)). In this case, spectral line bisector spans (BSs) are significantly anti-correlated with the radial velocity residuals, and we are able to use this correlation to reduce the residual rms to ~35 m s^(â1). We find that the star has a mass of 1.38 Âą 0.04 M_â and a radius of 1.64 Âą 0.03 R_â while the planet has a mass of 0.762 Âą 0.101 M_J and a radius of 1.686 Âą 0.045 R_J for an assumed circular orbit. Due to the large BS variations exhibited by both stars we rely on detailed modeling of the photometric light curves to rule out blend scenarios. Both planets are among the largest radii transiting planets discovered to date
HAT-P-47b AND HAT-P-48b: Two Low Density Sub-Saturn-Mass Transiting Planets on the Edge of the Period--Mass Desert
We report the discovery of two new transiting extrasolar planets orbiting
moderately bright (V = 10.7 and 12.2 mag) F stars (masses of 1.39 Msun and 1.10
Msun, respectively). The planets have periods of P = 4.7322 d and 4.4087 d, and
masses of 0.21 MJ and 0.17 MJ which are almost half-way between those of
Neptune and Saturn. With radii of 1.31 RJ and 1.13 RJ, these very low density
planets are the two lowest mass planets with radii in excess that of Jupiter.
Comparing with other recent planet discoveries, we find that sub-Saturns
(0.18MJ < Mp < 0.3MJ) and super-Neptunes (0.05MJ < Mp < 0.18MJ) exhibit a wide
range of radii, and their radii exhibit a weaker correlation with irradiation
than higher mass planets. The two planets are both suitable for measuring the
Rossiter-McLaughlin effect and for atmospheric characterization. Measuring the
former effect would allow an interesting test of the theory that star-planet
tidal interactions are responsible for the tendency of close-in giant planets
around convective envelope stars to be on low obliquity orbits. Both planets
fall on the edge of the short period Neptunian desert in the semi-major
axis-mass plane.Comment: Submitted to AAS Journal
Confirmation of SBS 1150+599A As An Extremely Metal-Poor Planetary Nebula
SBS 1150+599A is a blue stellar object at high galactic latitude discovered
in the Second Byurakan Survey. New high-resolution images of SBS 1150+599A are
presented, demonstrating that it is very likely to be an old planetary nebula
in the galactic halo, as suggested by Tovmassian et al (2001). An H-alpha image
taken with the WIYN 3.5-m telescope and its "tip/tilt" module reveals the
diameter of the nebula to be 9.2", comparable to that estimated from spectra by
Tovmassian et al. Lower limits to the central star temperature were derived
using the Zanstra hydrogen and helium methods to determine that the star's
effective temperature must be > 68,000K and that the nebula is optically thin.
New spectra from the MMT and FLWO telescopes are presented, revealing the
presence of strong [Ne V] lambda 3425, indicating that the central star
temperature must be > 100,000K. With the revised diameter, new central star
temperature, and an improved central star luminosity, we can constrain
photoionization models for the nebula significantly better than before. Because
the emission-line data set is sparse, the models are still not conclusive.
Nevertheless, we confirm that this nebula is an extremely metal-poor planetary
nebula, having a value for O/H that is less than 1/100 solar, and possibly as
low as 1/500 solar.Comment: 19 pages, 6 figures. Accepted for publication in the Astronomical
Journa
Self-interacting Dark Matter and Invisibly Decaying Higgs
Self-interacting dark matter has been suggested in order to overcome the
difficulties of the Cold Dark Matter model on galactic scales. We argue that a
scalar gauge singlet coupled to the Higgs boson, which could lead to an
invisibly decaying Higgs, is an interesting candidate for this self-interacting
dark matter particle. We also present estimates on the abundance of these
particles today as well as consequences to non-Newtonian forces.Comment: 4 pages, Revte
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