733 research outputs found
C-Terminus of Progranulin Interacts with the Beta-Propeller Region of Sortilin to Regulate Progranulin Trafficking
Progranulin haplo-insufficiency is a main cause of frontotemporal lobar degeneration (FTLD) with TDP-43 aggregates. Previous studies have shown that sortilin regulates progranulin trafficking and is a main determinant of progranulin level in the brain. In this study, we mapped the binding site between progranulin and sortilin. Progranulin binds to the beta-propeller region of sortilin through its C-terminal tail. The C-terminal progranulin fragment is fully sufficient for sortilin binding and progranulin C-terminal peptide displaces progranulin binding to sortilin. Deletion of the last 3 residues of progranulin (QLL) abolishes its binding to sortilin and also sortilin dependent regulation of progranulin trafficking. Since progranulin haplo-insufficiency results in FTLD, these results may provide important insights into future studies of progranulin trafficking and signaling and progranulin based therapy for FTLD
Searching for Gravitational Waves from the Inspiral of Precessing Binary Systems: New Hierarchical Scheme using "Spiky" Templates
In a recent investigation of the effects of precession on the anticipated
detection of gravitational-wave inspiral signals from compact object binaries
with moderate total masses, we found that (i) if precession is ignored, the
inspiral detection rate can decrease by almost a factor of 10, and (ii)
previously proposed ``mimic'' templates cannot improve the detection rate
significantly (by more than a factor of 2). In this paper we propose a new
family of templates that can improve the detection rate by factors of 5--6 in
cases where precession is most important. Our proposed method for these new
``mimic'' templates involves a hierarchical scheme of efficient, two-parameter
template searches that can account for a sequence of spikes that appear in the
residual inspiral phase, after one corrects for the any oscillatory
modification in the phase. We present our results for two cases of compact
object masses (10 and 1.4 solar masses and 7 and 3 solar masses) as a function
of spin properties. Although further work is needed to fully assess the
computational efficiency of this newly proposed template family, we conclude
that these ``spiky templates'' are good candidates for a family of precession
templates used in realistic searches, that can improve detection rates of
inspiral events.Comment: 17 pages, 22 figures, version accepted by PRD. Minor revision
Data analysis of gravitational-wave signals from spinning neutron stars. IV. An all-sky search
We develop a set of data analysis tools for a realistic all-sky search for
continuous gravitational-wave signals. The methods that we present apply to
data from both the resonant bar detectors that are currently in operation and
the laser interferometric detectors that are in the final stages of
construction and commissioning. We show that with our techniques we shall be
able to perform an all-sky 2-day long coherent search of the narrow-band data
from the resonant bar EXPLORER with no loss of signals with the dimensionless
amplitude greater than .Comment: REVTeX, 26 pages, 1 figure, submitted to Phys. Rev.
Matching of the continuous gravitational wave in an all sky search
We investigate the matching of continuous gravitational wave (CGW) signals in
an all sky search with reference to Earth based laser interferometric
detectors. We consider the source location as the parameters of the signal
manifold and templates corresponding to different source locations. It has been
found that the matching of signals from locations in the sky that differ in
their co-latitude and longitude by radians decreases with source
frequency. We have also made an analysis with the other parameters affecting
the symmetries. We observe that it may not be relevant to take care of the
symmetries in the sky locations for the search of CGW from the output of
LIGO-I, GEO600 and TAMA detectors.Comment: 16 pages, 7 figures, 3 Tables, To appear in Int. J. Mod. Phys.
FAR and NEAR Target Dynamic Visual Acuity: A Functional Assessment of Canal and Otolith Performance
Upon their return to earth, astronauts experience the effects of vestibular adaptation to microgravity. The postflight changes in vestibular information processing can affect postural and locomotor stability and may lead to oscillopsia during activities of daily living. However, it is likely that time spent in microgravity affects canal and otolith function differently. As a result, the isolated rotational stimuli used in traditional tests of canal function may fail to identify vestibular deficits after spaceflight. Also, the functional consequences of deficits that are identified often remain unknown. In a gaze control task, the relative contributions of the canal and otolith organs are modulated with viewing distance. The ability to stabilize gaze during a perturbation, on visual targets placed at different distances from the head may therefore provide independent insight into the function of this systems. Our goal was to develop a functional measure of gaze control that can also offer independent information about the function of the canal and otolith organs
Data analysis of gravitational-wave signals from spinning neutron stars. III. Detection statistics and computational requirements
We develop the analytic and numerical tools for data analysis of the
gravitational-wave signals from spinning neutron stars for ground-based laser
interferometric detectors. We study in detail the statistical properties of the
optimum functional that need to be calculated in order to detect the
gravitational-wave signal from a spinning neutron star and estimate its
parameters. We derive formulae for false alarm and detection probabilities both
for the optimal and the suboptimal filters. We assess the computational
requirements needed to do the signal search. We compare a number of criteria to
build sufficiently accurate templates for our data analysis scheme. We verify
the validity of our concepts and formulae by means of the Monte Carlo
simulations. We present algorithms by which one can estimate the parameters of
the continuous signals accurately.Comment: LaTeX, 45 pages, 13 figures, submitted to Phys. Rev.
Searching for Gravitational Waves from Binary Inspirals with LIGO
We describe the current status of the search for gravitational waves from
inspiralling compact binary systems in LIGO data. We review the result from the
first scientific run of LIGO (S1). We present the goals of the search of data
taken in the second scientific run (S2) and describe the differences between
the methods used in S1 and S2.Comment: 9 pages, 2 figures. Published in proceedings of the 8th Gravitational
Wave Data Analysis Workshop, Milwaukee, WI, USA, 17-20 December 200
Searching for periodic sources with LIGO. II: Hierarchical searches
The detection of quasi-periodic sources of gravitational waves requires the
accumulation of signal-to-noise over long observation times. If not removed,
Earth-motion induced Doppler modulations, and intrinsic variations of the
gravitational-wave frequency make the signals impossible to detect. These
effects can be corrected (removed) using a parameterized model for the
frequency evolution. We compute the number of independent corrections
required for incoherent search strategies which use stacked
power spectra---a demodulated time series is divided into segments of
length , each segment is FFTed, the power is computed, and the
spectra are summed up. We estimate that the sensitivity of an all-sky search
that uses incoherent stacks is a factor of 2--4 better than would be achieved
using coherent Fourier transforms; incoherent methods are computationally
efficient at exploring large parameter spaces. A two-stage hierarchical search
which yields another 20--60% improvement in sensitivity in all-sky searches for
old (>= 1000 yr) slow (= 40 yr) fast (<=
1000 Hz) pulsars. Assuming 10^{12} flops of effective computing power for data
analysis, enhanced LIGO interferometers should be sensitive to: (i) Galactic
core pulsars with gravitational ellipticities of \epsilon\agt5\times 10^{-6}
at 200 Hz, (ii) Gravitational waves emitted by the unstable r-modes of newborn
neutron stars out to distances of ~8 Mpc, and (iii) neutron stars in LMXB's
with x-ray fluxes which exceed . Moreover,
gravitational waves from the neutron star in Sco X-1 should be detectable is
the interferometer is operated in a signal-recycled, narrow-band configuration.Comment: 22 Pages, 13 Figure
Observational Limit on Gravitational Waves from Binary Neutron Stars in the Galaxy
Using optimal matched filtering, we search 25 hours of data from the LIGO
40-meter prototype laser interferometric gravitational-wave detector for
gravitational-wave chirps emitted by coalescing binary systems within our
Galaxy. This is the first test of this filtering technique on real
interferometric data. An upper limit on the rate R of neutron star binary
inspirals in our Galaxy is obtained: with 90% confidence, R< 0.5/hour. Similar
experiments with LIGO interferometers will provide constraints on the
population of tight binary neutron star systems in the Universe.Comment: RevTeX, minor revisions, exactly as published in PRL 83 (1999) p1498,
4 pages, 2 figures include
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