72 research outputs found
Noise Estimate of Pendular Fabry-Perot through Reflectivity Change
A key issue in developing pendular Fabry-Perot interferometers as very
accurate displacement measurement devices, is the noise level. The Fabry-Perot
pendulums are the most promising device to detect gravitational waves, and
therefore the background and the internal noise should be accurately measured
and reduced. In fact terminal masses generates additional internal noise mainly
due to thermal fluctuations and vibrations. We propose to exploit the
reflectivity change, that occurs in some special points, to monitor the
pendulums free oscillations and possibly estimate the noise level. We find that
in spite of long transients, it is an effective method for noise estimate. We
also prove that to only retain the sequence of escapes, rather than the whole
time dependent dynamics, entails the main characteristics of the phenomenon.
Escape times could also be relevant for future gravitational wave detector
developments.Comment: PREPRINT Metrology for Aerospace (MetroAeroSpace), 2014 IEEE
Publication Year: 2014, Page(s): 468 - 47
Characterization of escape times of Josephson Junctions for signal detection
The measurement of the escape time of a Josephson junction might be used to
detect the presence of a sinusoidal signal embedded in noise when standard
signal processing tools can be prohibitive. We show that the prescriptions for
the experimental set-up and some physical behaviors depend on the detection
strategy. More specifically, by exploiting the sample mean of escape times to
perform detection, two resonant regions are identified. At low frequencies
there is a stochastic resonance/activation phenomenon, while near the plasma
frequency a geometric resonance appears. The naive sample mean detector is
outperformed, in terms of error probability, by the optimal likelihood ratio
test. The latter exhibits only geometric resonance, showing monotonically
increasing performance as the bias current approaches the junction critical
current. In this regime the escape times are vanishingly small and therefore
performance are essentially limited by measurement electronics. The behavior of
the likelihood ratio and sample mean detector for different values of incoming
signal to noise ratio are discussed, and a relationship with the error
probability is found. The likelihood ratio test based detectors could be
employed also to estimate unknown parameters in the applied input signal. As a
prototypical example we study the phase estimation problem of a sinusoidal
current, that is accomplished by using the filter bank approach. Finally we
show that for a physically feasible detector the performances are found to be
very close to the Cramer- Rao theoretical bound. Applications might be found
for example in some astronomical detection problems or to analyze weak signals
in the sub-terahertz range.Comment: 22 pages, 14 figure
Spatio-temporal resolution enhancement for cloudy thermal sequences
Many applications require remotely sensed brightness temperature (BT) data acquired with high temporal and spatial resolutions. In this regard, a viable strategy to overtake the physical limitations of space-borne sensors to achieve these data relies on fusing low temporal but high spatial resolution (HSR) data with high temporal but low spatial resolution data. The most promising methods rely on the fusion of spatially interpolated high temporal resolution data with temporally interpolated HSR data. However, the unavoidable presence of cloud masses in the acquired image sequences is often neglected, compromising the functionality and/or the effectiveness of the most of these fusion algorithms. To overcome this problem, a framework combining techniques of temporal smoothing and spatial enhancement is proposed to estimate surface BTs with high spatial and high temporal resolutions even when cloud masses corrupt the scene. Numerical results using real thermal data acquired by the SEVIRI sensor show the ability of the proposed approach to reach better performance than techniques based on either only interpolation or only spatial sharpening, even dealing with missing data due to the presence of cloud masses
Resolution Enhancement of Hyperspectral Data Exploiting Real Multi-Platform Data
Multi-platform data introduce new possibilities in the context of data fusion, as they allow to exploit several remotely sensed images acquired by different combinations of sensors. This scenario is particularly interesting for the sharpening of hyperspectral (HS) images, due to the limited availability of high-resolution (HR) sensors mounted onboard of the same platform as that of the HS device. However, the differences in the acquisition geometry and the nonsimultaneity of this kind of observations introduce further difficulties whose effects have to be taken into account in the design of data fusion algorithms. In this study, we present the most widespread HS image sharpening techniques and assess their performances by testing them over real acquisitions taken by the Earth Observing-1 (EO-1) and the WorldView-3 (WV3) satellites. We also highlight the difficulties arising from the use of multi-platform data and, at the same time, the benefits achievable through this approach
Search for gravitational waves associated with the InterPlanetary Network short gamma ray bursts
We outline the scientific motivation behind a search for gravitational waves
associated with short gamma ray bursts detected by the InterPlanetary Network
(IPN) during LIGO's fifth science run and Virgo's first science run. The IPN
localisation of short gamma ray bursts is limited to extended error boxes of
different shapes and sizes and a search on these error boxes poses a series of
challenges for data analysis. We will discuss these challenges and outline the
methods to optimise the search over these error boxes.Comment: Methods paper; Proceedings for Eduardo Amaldi 9 Conference on
Gravitational Waves, July 2011, Cardiff, U
Swift follow-up observations of candidate gravitational-wave transient events
We present the first multi-wavelength follow-up observations of two candidate
gravitational-wave (GW) transient events recorded by LIGO and Virgo in their
2009-2010 science run. The events were selected with low latency by the network
of GW detectors and their candidate sky locations were observed by the Swift
observatory. Image transient detection was used to analyze the collected
electromagnetic data, which were found to be consistent with background.
Off-line analysis of the GW data alone has also established that the selected
GW events show no evidence of an astrophysical origin; one of them is
consistent with background and the other one was a test, part of a "blind
injection challenge". With this work we demonstrate the feasibility of rapid
follow-ups of GW transients and establish the sensitivity improvement joint
electromagnetic and GW observations could bring. This is a first step toward an
electromagnetic follow-up program in the regime of routine detections with the
advanced GW instruments expected within this decade. In that regime
multi-wavelength observations will play a significant role in completing the
astrophysical identification of GW sources. We present the methods and results
from this first combined analysis and discuss its implications in terms of
sensitivity for the present and future instruments.Comment: Submitted for publication 2012 May 25, accepted 2012 October 25,
published 2012 November 21, in ApJS, 203, 28 (
http://stacks.iop.org/0067-0049/203/28 ); 14 pages, 3 figures, 6 tables;
LIGO-P1100038; Science summary at
http://www.ligo.org/science/Publication-S6LVSwift/index.php ; Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p110003
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
Tests of General Relativity with GW170817
The recent discovery by Advanced LIGO and Advanced Virgo of a gravitational wave signal from a binary
neutron star inspiral has enabled tests of general relativity (GR) with this new type of source. This source, for
the first time, permits tests of strong-field dynamics of compact binaries in the presence of matter. In this
Letter, we place constraints on the dipole radiation and possible deviations from GR in the post-Newtonian
coefficients that govern the inspiral regime. Bounds on modified dispersion of gravitational waves are
obtained; in combination with information from the observed electromagnetic counterpart we can also
constrain effects due to large extra dimensions. Finally, the polarization content of the gravitational wave
signal is studied. The results of all tests performed here show good agreement with GR.The authors gratefully acknowledge the support of the
United States National Science Foundation (NSF) for
the construction and operation of the LIGO Laboratory
and Advanced LIGO as well as the Science and Technology
Facilities Council (STFC) of the United Kingdom,
the Max-Planck-Society (MPS), and the State of
Niedersachsen/Germany for support of the construction
of Advanced LIGO and construction and operation of the
GEO600 detector. Additional support for Advanced LIGO
was provided by the Australian Research Council
Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)
This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands
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