1,459 research outputs found
Optimal generalization of power filters for gravitational wave bursts, from single to multiple detectors
Searches for gravitational wave signals which do not have a precise model
describing the shape of their waveforms are often performed using power
detectors based on a quadratic form of the data. A new, optimal method of
generalizing these power detectors so that they operate coherently over a
network of interferometers is presented. Such a mode of operation is useful in
obtaining better detection efficiencies, and better estimates of the position
of the source of the gravitational wave signal. Numerical simulations based on
a realistic, computationally efficient hierarchical implementation of the
method are used to characterize its efficiency, for detection and for position
estimation. The method is shown to be more efficient at detecting signals than
an incoherent approach based on coincidences between lists of events. It is
also shown to be capable of locating the position of the source.Comment: 16 pages, 5 figure
Time-frequency detection algorithm for gravitational wave bursts
An efficient algorithm is presented for the identification of short bursts of
gravitational radiation in the data from broad-band interferometric detectors.
The algorithm consists of three steps: pixels of the time-frequency
representation of the data that have power above a fixed threshold are first
identified. Clusters of such pixels that conform to a set of rules on their
size and their proximity to other clusters are formed, and a final threshold is
applied on the power integrated over all pixels in such clusters. Formal
arguments are given to support the conjecture that this algorithm is very
efficient for a wide class of signals. A precise model for the false alarm rate
of this algorithm is presented, and it is shown using a number of
representative numerical simulations to be accurate at the 1% level for most
values of the parameters, with maximal error around 10%.Comment: 26 pages, 15 figures, to appear in PR
Overview of the BlockNormal Event Trigger Generator
In the search for unmodeled gravitational wave bursts, there are a variety of
methods that have been proposed to generate candidate events from time series
data. Block Normal is a method of identifying candidate events by searching for
places in the data stream where the characteristic statistics of the data
change. These change-points divide the data into blocks in which the
characteristics of the block are stationary. Blocks in which these
characteristics are inconsistent with the long term characteristic statistics
are marked as Event-Triggers which can then be investigated by a more
computationally demanding multi-detector analysis.Comment: GWDAW-8 proceedings, 6 pages, 2 figure
Etude de la filière viande de chèvre au Zimbabwe
Cet article présente une étude du secteur caprin au Zimbabwe, et plus particulièrement dans la province de Masvingo, basée sur l'utilisation du concept de filière comme outil d'analyse. Après une brève justification du choix analytique et une présentation des outils méthodologiques retenus, deux représentations de la filière sont proposées. Le deuxième modèle, plus puissant, est ensuite commenté au vu des données comptables. En conclusion, ce type d'analyse permet d'identifier des interlocuteurs privilégiés pour la mise en place d'actions de développement visant au renforcement des circuits de commercialisation de la viande de chèvre et à l'amélioration des revenus des petits producteurs
Joint searches between gravitational-wave interferometers and high-energy neutrino telescopes: science reach and analysis strategies
Many of the astrophysical sources and violent phenomena observed in our
Universe are potential emitters of gravitational waves (GWs) and high-energy
neutrinos (HENs). A network of GW detectors such as LIGO and Virgo can
determine the direction/time of GW bursts while the IceCube and ANTARES
neutrino telescopes can also provide accurate directional information for HEN
events. Requiring the consistency between both, totally independent, detection
channels shall enable new searches for cosmic events arriving from potential
common sources, of which many extra-galactic objects.Comment: 4 pages. To appear in the Proceedings of the 2d Heidelberg Workshop:
"High-Energy Gamma-rays and Neutrinos from Extra-Galactic Sources",
Heidelberg (Germany), January 13-16, 200
Virological outcomes in ARV-naïve patients switching or not from a first successful boosted PI-regimen to efavirenz, nevirapine or abacavir regimens
International audiencen.
Testing the performance of a blind burst statistic
In this work we estimate the performance of a method for the detection of
burst events in the data produced by interferometric gravitational wave
detectors. We compute the receiver operating characteristics in the specific
case of a simulated noise having the spectral density expected for Virgo, using
test signals taken from a library of possible waveforms emitted during the
collapse of the core of Type II Supernovae.Comment: 8 pages, 6 figures, Talk given at the GWDAW2002 worksho
Outcome after failure of allogeneic hematopoietic stem cell transplantation in children with acute leukemia: a study by the Société Francophone de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC)
Allogeneic hematopoietic stem cell transplantation (SCT) contributes to improved outcome in childhood acute leukemia (AL). However, therapeutic options are poorly defined in case of post-transplantation relapse. We aimed to compare treatment strategies in 334 consecutive children with acute leukemia relapse or progression after SCT in a recent ten-year period. Data could be analyzed in 288 patients (157 ALL, 123 AML and 8 biphenotypic AL) with a median age of 8.16 years at transplantation. The median delay from first SCT to relapse or progression was 182 days. The treatment consisted in chemotherapy alone (n=108), chemotherapy followed by second SCT (n=70), supportive/palliative care (n=67), combination of chemotherapy and DLI (n=30), or isolated reinfusion of donor lymphocytes (DLI) (n=13). The median OS duration after relapse was 164 days and differed according to therapy: DLI after chemotherapy = 385 d, second allograft = 391d, chemotherapy = 174d, DLI alone = 140d, palliative care = 43d. A second SCT or a combination of chemotherapy and donor lymphocytes infusion yielded similar outcome (HR=0.85, p=0.53) unlike chemotherapy alone (HR 1.43 p=0.04), palliative care (HR=4.24, p<0.0001) or isolated DLI (HR=1,94, p<0.04). Despite limitations in this retrospective setting, strategies including immunointervention appear superior to other approaches, mostly in AML
Noise parametric identification and whitening for LIGO 40-meter interferometer data
We report the analysis we made on data taken by Caltech 40-meter prototype
interferometer to identify the noise power spectral density and to whiten the
sequence of noise. We concentrate our study on data taken in November 1994, in
particular we analyzed two frames of data: the 18nov94.2.frame and the
19nov94.2.frame.
We show that it is possible to whiten these data, to a good degree of
whiteness, using a high order whitening filter. Moreover we can choose to
whiten only restricted band of frequencies around the region we are interested
in, obtaining a higher level of whiteness.Comment: 11 pages, 15 figures, accepted for publication by Physical Review
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