2,090 research outputs found
Dynamic Normalization for Compact Binary Coalescence Searches in Non-Stationary Noise
The output of gravitational-wave interferometers, such as LIGO and Virgo, can be highly non-stationary. Broadband detector noise can affect the detector sensitivity on the order of tens of seconds. Gravitational-wave transient searches, such as those for colliding black holes, estimate this noise in order to identify gravitational-wave events. During times of non-stationarity we see a higher rate of false events being reported. To accurately separate signal from noise, it is imperative to incorporate the changing detector state into gravitational-wave searches. We develop a new statistic which estimates the variation of the interferometric detector noise. We use this statistic to re-rank candidate events identified during LIGO-Virgo's second observing run by the PyCBC search pipeline. This results in a 7% improvement in the sensitivity volume for low mass binaries, particularly binary neutron stars mergers
Improving the Sensitivity of Advanced LIGO Using Noise Subtraction
This paper presents an adaptable, parallelizable method for subtracting
linearly coupled noise from Advanced LIGO data. We explain the features
developed to ensure that the process is robust enough to handle the variability
present in Advanced LIGO data. In this work, we target subtraction of noise due
to beam jitter, detector calibration lines, and mains power lines. We
demonstrate noise subtraction over the entirety of the second observing run,
resulting in increases in sensitivity comparable to those reported in previous
targeted efforts. Over the course of the second observing run, we see a 30%
increase in Advanced LIGO sensitivity to gravitational waves from a broad range
of compact binary systems. We expect the use of this method to result in a
higher rate of detected gravitational-wave signals in Advanced LIGO data.Comment: 15 pages, 6 figure
The Issues of Mismodelling Gravitational-Wave Data for Parameter Estimation
Bayesian inference is used to extract unknown parameters from gravitational
wave signals. Detector noise is typically modelled as stationary, although data
from the LIGO and Virgo detectors is not stationary. We demonstrate that the
posterior of estimated waveform parameters is no longer valid under the
assumption of stationarity. We show that while the posterior is unbiased, the
errors will be under- or overestimated compared to the true posterior. A
formalism was developed to measure the effect of the mismodelling, and found
the effect of any form of non-stationarity has an effect on the results, but
are not significant in certain circumstances. We demonstrate the effect of
short-duration Gaussian noise bursts and persistent oscillatory modulation of
the noise on binary-black-hole-like signals. In the case of short signals,
non-stationarity in the data does not have a large effect on the parameter
estimation, but the errors from non-stationary data containing signals lasting
tens of seconds or longer will be several times worse than if the noise was
stationary. Accounting for this limiting factor in parameter sensitivity could
be very important for achieving accurate astronomical results, including an
estimation of the Hubble parameter. This methodology for handling the
non-stationarity will also be invaluable for analysis of waveforms that last
minutes or longer, such as those we expect to see with the Einstein Telescope.Comment: 15 pages, 5 figures. Comments welcom
The c-terminal extension of a hybrid immunoglobulin A/G heavy chain is responsible for its Golgi-mediated sorting to the vacuole
We have assessed the ability of the plant secretory pathway to handle the expression of complex heterologous proteins by investigating the fate of a hybrid immunoglobulin A/G in tobacco cells. Although plant cells can express large amounts of the antibody, a relevant proportion is normally lost to vacuolar sorting and degradation. Here we show that the synthesis of high amounts of IgA/G does not impose stress on the plant secretory pathway. Plant cells can assemble antibody chains with high efficiency and vacuolar transport occurs only after the assembled immunoglobulins have traveled through the Golgi complex. We prove that vacuolar delivery of IgA/G depends on the presence of a cryptic sorting signal in the tailpiece of the IgA/G heavy chain. We also show that unassembled light chains are efficiently secreted as monomers by the plant secretory pathway
Pade approximants for functions with branch points - strong asymptotics of Nuttall-Stahl polynomials
Let f be a germ of an analytic function at infinity that can be analytically
continued along any path in the complex plane deprived of a finite set of
points, f \in\mathcal{A}(\bar{\C} \setminus A), \sharp A <\infty. J. Nuttall
has put forward the important relation between the maximal domain of f where
the function has a single-valued branch and the domain of convergence of the
diagonal Pade approximants for f. The Pade approximants, which are rational
functions and thus single-valued, approximate a holomorphic branch of f in the
domain of their convergence. At the same time most of their poles tend to the
boundary of the domain of convergence and the support of their limiting
distribution models the system of cuts that makes the function f single-valued.
Nuttall has conjectured (and proved for many important special cases) that this
system of cuts has minimal logarithmic capacity among all other systems
converting the function f to a single-valued branch. Thus the domain of
convergence corresponds to the maximal (in the sense of minimal boundary)
domain of single-valued holomorphy for the analytic function f
\in\mathcal{A}(\bar{\C} \setminus A). The complete proof of Nuttall's
conjecture (even in a more general setting where the set A has logarithmic
capacity zero) was obtained by H. Stahl. In this work, we derive strong
asymptotics for the denominators of the diagonal Pade approximants for this
problem in a rather general setting. We assume that A is a finite set of branch
points of f which have the algebraic character and which are placed in a
generic position. The last restriction means that we exclude from our
consideration some degenerated "constellations" of the branch points.Comment: 47 pages, 8 figure
Statistical Communication Theory
Contains research objectives and reports on three research projects
Electromagnetic follow-up of gravitational wave transient signal candidates
Pioneering efforts aiming at the development of multi-messenger gravitational
wave and electromagnetic astronomy have been made. An electromagnetic
observation follow-up program of candidate gravitational wave events has been
performed (Dec 17 2009 to Jan 8 2010 and Sep 4 to Oct 20 2010) during the
recent runs of the LIGO and Virgo gravitational wave detectors. It involved
ground-based and space electromagnetic facilities observing the sky at optical,
X-ray and radio wavelengths. The joint gravitational wave and electromagnetic
observation study requires the development of specific image analysis
procedures able to discriminate the possible electromagnetic counterpart of
gravitational wave triggers from contaminant/background events. The paper
presents an overview of the electromagnetic follow-up program and the image
analysis procedures.Comment: Proceedings of the 12th International Conference on "Topics in
Astroparticle and Underground Physics" (TAUP 2011), Munich, September 2011
(to appear in IoP Journal of Physics: Conference Series
GEO 600 and the GEO-HF upgrade program: successes and challenges
The German-British laser-interferometric gravitational wave detector GEO 600
is in its 14th year of operation since its first lock in 2001. After GEO 600
participated in science runs with other first-generation detectors, a program
known as GEO-HF began in 2009. The goal was to improve the detector sensitivity
at high frequencies, around 1 kHz and above, with technologically advanced yet
minimally invasive upgrades. Simultaneously, the detector would record science
quality data in between commissioning activities. As of early 2014, all of the
planned upgrades have been carried out and sensitivity improvements of up to a
factor of four at the high-frequency end of the observation band have been
achieved. Besides science data collection, an experimental program is ongoing
with the goal to further improve the sensitivity and evaluate future detector
technologies. We summarize the results of the GEO-HF program to date and
discuss its successes and challenges
Cost-benefit analysis for commissioning decisions in GEO600
Gravitational wave interferometers are complex instruments, requiring years
of commissioning to achieve the required sensitivities for the detection of
gravitational waves, of order 10^-21 in dimensionless detector strain, in the
tens of Hz to several kHz frequency band. Investigations carried out by the
GEO600 detector characterisation group have shown that detector
characterisation techniques are useful when planning for commissioning work. At
the time of writing, GEO600 is the only large scale laser interferometer
currently in operation running with a high duty factor, 70%, limited chiefly by
the time spent commissioning the detector. The number of observable
gravitational wave sources scales as the product of the volume of space to
which the detector is sensitive and the observation time, so the goal of
commissioning is to improve the detector sensitivity with the least possible
detector down time. We demonstrate a method for increasing the number of
sources observable by such a detector, by assessing the severity of
non-astrophysical noise contaminations to efficiently guide commissioning. This
method will be particularly useful in the early stages and during the initial
science runs of the aLIGO and adVirgo detectors, as they are brought up to
design performance.Comment: 17 pages, 17 figures, 2 table
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