5,320 research outputs found
Bone marrow transplantation alters the tremor phenotype in the murine model of globoid-cell leukodystrophy
Tremor is a prominent phenotype of the twitcher mouse, an authentic genetic model of Globoid-Cell Leukodystrophy (GLD, Krabbe’s disease). In the current study, the tremor was quantified using a force-plate actometer designed to accommodate low-weight mice. The actometer records the force oscillations caused by a mouse’s movements, and the rhythmic structure of the force variations can be revealed. Results showed that twitcher mice had significantly increased power across a broad band of higher frequencies compared to wildtype mice. Bone marrow transplantation (BMT), the only available therapy for GLD, worsened the tremor in the twitcher mice and induced a measureable alteration of movement phenotype in the wildtype mice. These data highlight the damaging effects of conditioning radiation and BMT in the neonatal period. The behavioral methodology used herein provides a quantitative approach for assessing the efficacy of potential therapeutic interventions for Krabbe’s disease
MECI: A Method for Eclipsing Component Identification
We describe an automated method for assigning the most probable physical
parameters to the components of an eclipsing binary, using only its photometric
light curve and combined colors. With traditional methods, one attempts to
optimize a multi-parameter model over many iterations, so as to minimize the
chi-squared value. We suggest an alternative method, where one selects pairs of
coeval stars from a set of theoretical stellar models, and compares their
simulated light curves and combined colors with the observations. This approach
greatly reduces the parameter space over which one needs to search, and allows
one to estimate the components' masses, radii and absolute magnitudes, without
spectroscopic data. We have implemented this method in an automated program
using published theoretical isochrones and limb-darkening coefficients. Since
it is easy to automate, this method lends itself to systematic analyses of
datasets consisting of photometric time series of large numbers of stars, such
as those produced by OGLE, MACHO, TrES, HAT, and many others surveys.Comment: 25 pages, 7 figures, accepted for publication in Ap
Radial migration in galactic disks caused by resonance overlap of multiple patterns: Self-consistent simulations
We have recently identified a new radial migration mechanism resulting from
the overlap of spiral and bar resonances in galactic disks. Here we confirm the
efficiency of this mechanism in fully self-consistent, Tree-SPH simulations, as
well as high-resolution pure N-body simulations. In all barred cases we clearly
identify the effect of spiral-bar resonance overlap by measuring a bimodality
in the changes of angular momentum in the disk, dL, whose maxima are near the
bar's corotation and outer Lindblad resonance. This contrasts with the smooth
distribution of dL for a simulation with no stable bar present, where strong
radial migration is induced by multiple spirals. The presence of a disk gaseous
component appears to increase the rate of angular momentum exchange by about
20%. The efficiency of this mechanism is such that galactic stellar disks can
extend to over 10 scale-lengths within 1-3 Gyr in both Milky Way size and
low-mass galaxies (circular velocity ~100 km/s). We also show that metallicity
gradients can flatten in less than 1 Gyr rendering mixing in barred galaxies an
order of magnitude more efficient than previously thought.Comment: replaced with accepted version: 5 pages, 5 figures (one new figure
added), minor change
Variable Stars in the Globular Cluster M5. Application of the Image Subtraction Method
We present -band light curves of 61 variables from the core of the
globular cluster M5 obtained using a newly developed image subtraction method
(ISM). Four of these variables were previously unknown. Only 26 variables were
found in the same field using photometry obtained with DoPHOT software. Fourier
parameters of the ISM light curves have relative errors up to 20 times smaller
than parameters measured from DoPHOT photometry. We conclude that the new
method is very promising for searching for variable stars in the cores of the
globular clusters and gives very accurate relative photometry with quality
comparable to photometry obtained by HST. We also show that the variable V104
is not an eclipsing star as has been suggested, but is an RRc star showing
non-radial pulsations.Comment: submitted to MNRAS, 9 pages, 4 figure
A small source in Q2237+0305 ?
Microlensing in Q2237+0305 between 1985 and 1995 (eg. Irwin et al. 1989;
Corrigan et al. 1991; Ostensen et al. 1996) has been interpreted in two
different ways; as microlensing by stellar mass objects of a continuum source
having dimensions significantly smaller than the microlens Einstein radius (ER)
(eg. Wambsganss, Paczynski & Schneider 1990; Rauch & Blandford 1991), and as
microlensing by very low mass objects of a source as large as 5 ER (Refsdal &
Stabell 1993; Haugan 1996). In this paper we present evidence in favour of a
small source. Limits on the source size (in units of ER) are obtained from the
combination of limits on the number of microlens Einstein radii crossed by the
source during the monitoring period with two separate light-curve features.
Firstly, recently published monitoring data (Wozniak et al. 2000; OGLE web
page) show large variations (~0.8-1.5 magnitudes) between image brightnesses
over a period of 700 days or ~15% of the monitoring period. Secondly, the 1988
peak in the image A light-curve had a duration that is a small fraction (<0.02)
of the monitoring period. Such rapid microlensing rises and short microlensing
peaks only occur for small sources. We find that the observed large-rapid
variation limits the source size to be <0.2 ER (95% confidence). The width of
the light-curve peak provides a stronger constraint of <0.02 ER (99%
confidence). The Einstein radius (projected into the source plane) of the
average microlens mass (m) in Q2237+0305 is ER ~ 10^{17}\sqrt{m} cm. The
interpretation that stars are responsible for microlensing in Q2237+0305
therefore results in limits on the continuum source size that are consistent
with current accretion disc theory.Comment: 8 pages, 3 figures, accepted for publication in M.N.R.A.
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