1,108 research outputs found
Search for long-lived gravitational-wave transients coincident with long gamma-ray bursts
Long gamma-ray bursts (GRBs) have been linked to extreme core-collapse supernovae from massive stars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of long-lived (similar to 10-1000 s) GW emission associated with the accretion disk of a collapsed star or with its protoneutron star remnant. Using data from LIGO\u27s fifth science run, and GRB triggers from the Swift experiment, we perform a search for unmodeled long-lived GW transients. Finding no evidence of GW emission, we place 90% confidence-level upper limits on the GW fluence at Earth from long GRBs for three waveforms inspired by a model of GWs from accretion disk instabilities. These limits range from F \u3c 3.5 ergs cm(-2) to F \u3c 1200 ergs cm(-2), depending on the GRB and on the model, allowing us to probe optimistic scenarios of GW production out to distances as far as approximate to 33 Mpc. Advanced detectors are expected to achieve strain sensitivities 10X better than initial LIGO, potentially allowing us to probe the engines of the nearest long GRBs
The effects of LIGO detector noise on a 15-dimensional Markov-chain Monte-Carlo analysis of gravitational-wave signals
Gravitational-wave signals from inspirals of binary compact objects (black
holes and neutron stars) are primary targets of the ongoing searches by
ground-based gravitational-wave (GW) interferometers (LIGO, Virgo, and
GEO-600). We present parameter-estimation results from our Markov-chain
Monte-Carlo code SPINspiral on signals from binaries with precessing spins. Two
data sets are created by injecting simulated GW signals into either synthetic
Gaussian noise or into LIGO detector data. We compute the 15-dimensional
probability-density functions (PDFs) for both data sets, as well as for a data
set containing LIGO data with a known, loud artefact ("glitch"). We show that
the analysis of the signal in detector noise yields accuracies similar to those
obtained using simulated Gaussian noise. We also find that while the Markov
chains from the glitch do not converge, the PDFs would look consistent with a
GW signal present in the data. While our parameter-estimation results are
encouraging, further investigations into how to differentiate an actual GW
signal from noise are necessary.Comment: 11 pages, 2 figures, NRDA09 proceeding
The Critical Coupling Likelihood Method: A new approach for seamless integration of environmental and operating conditions of gravitational wave detectors into gravitational wave searches
Any search effort for gravitational waves (GW) using interferometric
detectors like LIGO needs to be able to identify if and when noise is coupling
into the detector's output signal. The Critical Coupling Likelihood (CCL)
method has been developed to characterize potential noise coupling and in the
future aid GW search efforts. By testing two hypotheses about pairs of
channels, CCL is able to identify undesirable coupled instrumental noise from
potential GW candidates. Our preliminary results show that CCL can associate up
to of observed artifacts with , to local noise sources,
while reducing the duty cycle of the instrument by . An approach
like CCL will become increasingly important as GW research moves into the
Advanced LIGO era, going from the first GW detection to GW astronomy.Comment: submitted CQ
Synthesis and Properties of Peroxy Oligomers Obtained by Telomerization Effects of the Presence of Bases
New bifunctional oligomers bearing peroxy groups have been synthesized by telomerization in one step reaction. For obtaining oligoperoxides (PO) by telomerization method, epoxide compounds will react with substances containing labile hydrogen atom. Using the principle of stochiometric imbalance between diepoxy compounds and substances with mobile hydrogen atoms and employing a functional peroxide as telogen, the synthesis of PO was studied. 2,2–Di[4–(2,3–epoxy–1-propoxy)phenyl]–propane (diglycidyl ether of diphenylol propane - DGEDPP), 1,2–Di (2,3–epoxy–1-propoxy) ethane (diglycidyl ether of ethylene glycol -DGEEG) and 1,2–Epoxy–3–tert–butylperoxypropane (EP) have been synthesized by methods reported in the literature. Chemical structures have been confirmed by NMR and FTIR, number-average molecular weights Mn of POs by cryoscopy, active oxygen content [O]act. for POs was determined by iodometry and epoxy number (e.n.) for POs was measured via direct titration of PO samples. A 50% solution of potassium or sodium isopropylates in 2-propanol is used to catalyze the telomerisation. Different parameters such as ratio of components, temperature, reaction time have been optimized in vu to get well defined peroxy oligomers. The presence of peroxy groups in synthesized POs allows us to employ these compounds as curing agents for polymers containing unsaturated double bonds and may be used to improve performance of unsaturated polyester GFR systems
Quantile Models with Endogeneity
In this article, we review quantile models with endogeneity. We focus on models that achieve identification through the use of instrumental variables and discuss conditions under which partial and point identification are obtained. We discuss key conditions, which include monotonicity and full-rank-type conditions, in detail. In providing this review, we update the identification results of Chernozhukov & Hansen (2005). We illustrate the modeling assumptions through economically motivated examples. We also briefly review the literature on estimation and inference
A 15-month survey of Dimethylsulfoniopropionate and Dimethylsulfoxide content in Posidonia oceanica
Posidonia oceanica is the only reported seagrass to produce significant amount of
dimethylsulfoniopropionate (DMSP). It is also the largest known producer of DMSP
among coastal and inter-tidal higher plants. Here, we studied (i) the weekly to seasonal
variability and the depth variability of DMSP and its related compound dimethylsulfoxide
(DMSO) in P. oceanica leaves of a non-disturbed meadow in Corsica, France, (ii) the
weekly to seasonal variability and the depth variability of DMSP to DMSO concentration
to assess the potential of the DMSP:DMSO ratio as indicator of stress, and (iii)
the relationships between DMSP, DMSO, and the DMSP:DMSO ratio with potential
explanatory variables such as light, temperature, photosynthetic activity (effective
quantum yield of photosystem II), and leaf size. The overall average concentrations of
organosulfured compounds in P. oceanica leaves were 130 ± 39 µmol.g−1
fw for DMSP
and 4.9 ± 2.1 µmol.g−1
fw for DMSO. Concentrations of DMSP and DMSO in P. oceanica
were overall distinctly higher and exhibited a wider range of variations than other marine
primary producers such as Spartina alterniflora, phytoplankton communities, epilithic
Cyanobacteria and macroalgae. Concentrations of both DMSP and DMSO in P. oceanica
leaves decreased from a maximum in autumn to a minimum in summer; they changed
little with depth. Potential explanatory variables except the leaf size, i.e., the leaf age
were little or not related to measured concentrations. To explain the seasonal pattern
of decreasing concentrations with leaf aging, we hypothesized two putative protection
functions of DMSP in young leaves: antioxidant against reactive oxygen species and
predator-deterrent. The similar variation of the two molecule concentrations over time
and with depth suggested that DMSO content in P. oceanica leaves results from oxidation
of DMSP. The DMSP:DMSO ratio remained constant around a mean value of 29.2 ± 9.0
µmol:µmol for the non-disturbed harvested meadow regardless of the time of the
year, the depth or the leaf size. As suggested for the salt march plant S. alterniflora, we hypothesized the DMSP:DMSO ratio could be considered as indicator of stress in
seagrasses exposed to environmental or anthropogenic stressors. More research would
now be needed to confirm the functions of DMSP and DMSO in seagrasses and how
the DMSP:DMSO ratio will vary under various disturbances.FCT: 57/2016, UID/Multi/04326/2019.info:eu-repo/semantics/publishedVersio
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