An information-theoretic approach to the gravitational-wave burst detection problem

The observational era of gravitational-wave astronomy began in the Fall of 2015 with the detection of GW150914. One potential type of detectable gravitational wave is short-duration gravitational-wave bursts, whose waveforms can be difficult to predict. We present the framework for a new detection algorithm for such burst events -- \textit{oLIB} -- that can be used in low-latency to identify gravitational-wave transients independently of other search algorithms. This algorithm consists of 1) an excess-power event generator based on the Q-transform -- \textit{Omicron} --, 2) coincidence of these events across a detector network, and 3) an analysis of the coincident events using a Markov chain Monte Carlo Bayesian evidence calculator -- \textit{LALInferenceBurst}. These steps compress the full data streams into a set of Bayes factors for each event; through this process, we use elements from information theory to minimize the amount of information regarding the signal-versus-noise hypothesis that is lost. We optimally extract this information using a likelihood-ratio test to estimate a detection significance for each event. Using representative archival LIGO data, we show that the algorithm can detect gravitational-wave burst events of astrophysical strength in realistic instrumental noise across different burst waveform morphologies. We also demonstrate that the combination of Bayes factors by means of a likelihood-ratio test can improve the detection efficiency of a gravitational-wave burst search. Finally, we show that oLIB's performance is robust against the choice of gravitational-wave populations used to model the likelihood-ratio test likelihoods

On the background estimation by time slides in a network of gravitational wave detectors

Time shifting the outputs of Gravitational Wave detectors operating in coincidence is a convenient way to estimate the background in a search for short duration signals. However this procedure is limited as increasing indefinitely the number of time shifts does not provide better estimates. We show that the false alarm rate estimation error saturates with the number of time shifts. In particular, for detectors with very different trigger rates this error saturates at a large value. Explicit computations are done for 2 detectors, and for 3 detectors where the detection statistic relies on the logical ``OR'' of the coincidences of the 3 couples in the network.Comment: accepted for publication in CQ

Gravitational waves: search results, data analysis and parameter estimation

The Amaldi 10 Parallel Session C2 on gravitational wave (GW) search results, data analysis and parameter estimation included three lively sessions of lectures by 13 presenters, and 34 posters. The talks and posters covered a huge range of material, including results and analysis techniques for ground-based GW detectors, targeting anticipated signals from different astrophysical sources: compact binary inspiral, merger and ringdown; GW bursts from intermediate mass binary black hole mergers, cosmic string cusps, core-collapse supernovae, and other unmodeled sources; continuous waves from spinning neutron stars; and a stochastic GW background. There was considerable emphasis on Bayesian techniques for estimating the parameters of coalescing compact binary systems from the gravitational waveforms extracted from the data from the advanced detector network. This included methods to distinguish deviations of the signals from what is expected in the context of General Relativity

Performance of Pyridylthiourea-Polyethylenimine Polyplex for siRNA-Mediated Liver Cancer Therapy in Cell Monolayer, Spheroid, and Tumor Xenograft Models

Medical application of siRNAs relies on methods for delivering nucleic acids into the cytosol. Synthetic carriers, which assemble with nucleic acids into delivery systems, show promises for cancer therapy but efficiency remains to be improved. In here, the effectiveness of pyridylthiourea‐polyethylenimine (πPEI), a siRNA carrier that favors both polyplex disassembly and endosome rupture upon sensing the acidic endosomal environment, in 3 experimental models of hepatocellular cancer is tested. The πPEI‐assisted delivery of a siRNA targeting the polo‐like kinase 1 into Huh‐7 monolayer produces a 90% cell death via a demonstrated RNA interference mechanism. Incubation of polyplex with Huh‐7 spheroids leads to siRNA delivery into the superficial first cell layer and a 60% reduction in spheroid growth compared to untreated controls. Administration of polyplexes into mice bearing subcutaneous implanted Huh‐7Luc tumors results in a reduced tumor progression, similar to the one observed in the spheroid model. Altogether, these results support the in vivo use of synthetic and dedicated polymers for increasing siRNA‐mediated gene knockdown, and their clinical promise in cancer therapeutics

New measurement of ΔG/G\Delta G/G at COMPASS from open charm events

The gluon polarization, $\Delta g/g$, in the nucleon was measured using COMPASS data taken between 2002 and 2006. The analysis relies on the search for open-charm events with the production of $D$-mesons in order to isolate photon-gluon fusion processes. This method is characterized by the absence of physical backgrounds, oering a very clean extraction of $\Delta g/g$. It is however statistically limited, that is why a weighted method was developed to minimize the statistical error. The preliminary result is : $\langle\frac{\Delta g}{g}\rangle= -$0.49 $\pm$ 0.27 $\pm$ 0.11(syst.)

Mesure de la polarisation des gluons dans le nucléon par la muo-production de mésons charmés à COMPASS

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Experimental Study of Cavitation in Laminar Flow

International audienceAn experimental setup has been especially developed in order to observe cavitation in laminar flows. Experiments have been carried out with a silicon oil of viscosity υ = 100cSt passing through a Venturi-type geometry with 18°/8° convergent/divergent angles respectively. The range of Reynolds numbers at the inlet section is between 350 and 1000. Two dynamic regimes are identified. They are characterized by two critical Reynolds numbers, induced by major hydrodynamic changes in the flow, in addition to a hysteresis effect between the inception and the disappearance of cavitation

Searches for continuous gravitational waves from Scorpius X-1 and XTE J1751-305 in LIGO’s sixth science run

International audienceScorpius X-1 (Sco X-1) and x-ray transient XTE J1751-305 are low-mass x-ray binaries (LMXBs) that may emit continuous gravitational waves detectable in the band of ground-based interferometric observatories. Neutron stars in LMXBs could reach a torque-balance steady-state equilibrium in which angular momentum addition from infalling matter from the binary companion is balanced by angular momentum loss, conceivably due to gravitational-wave emission. Torque balance predicts a scale for detectable gravitational-wave strain based on observed x-ray flux. This paper describes a search for Sco X-1 and XTE J1751-305 in LIGO science run 6 data using the TwoSpect algorithm, based on searching for orbital modulations in the frequency domain. While no detections are claimed, upper limits on continuous gravitational-wave emission from Sco X-1 are obtained, spanning gravitational-wave frequencies from 40 to 2040 Hz and projected semimajor axes from 0.90 to 1.98 light-seconds. These upper limits are injection validated, equal any previous set in initial LIGO data, and extend over a broader parameter range. At optimal strain sensitivity, achieved at 165 Hz, the 95% confidence level random-polarization upper limit on dimensionless strain h0 is approximately 1.8×10-24. The closest approach to the torque-balance limit, within a factor of 27, is also at 165 Hz. Upper limits are set in particular narrow frequency bands of interest for J1751-305. These are the first upper limits known to date on r-mode emission from this XTE source. The TwoSpect method will be used in upcoming searches of Advanced LIGO and Virgo data

Attached cavitation in laminar separations within a transition to unsteadiness

Attached sheet cavitation is usually observed in turbulent water flows within small laminar separation bubbles which can provide favorable conditions for inception and attachment of cavities. In the present study, viscous silicone oils are used within a small scale Venturi geometry to investigate attached cavitation into laminar separated flows for Reynolds numbers from 346 to 2188. Numerical simulations about single phase flows are performed with steady simulations for a Reynolds number range Re > [50; 1400] and with unsteady simulations for Re > [1000; 2000]. They reveal the emergence of two large laminar boundary layer separations downstream of the Venturi throat in addition to low pressure zones which can possibly induce both degassing or cavitation features. Experiments are performed with high-speed photography, and several multiphase dynamics are observed in these viscous flows, which are considered as quasisteady flows at low Reynolds numbers Re B 1400. Degassing phenomenon with air bubble recirculation has been first observed at pressures far above liquid vapor pressure whereas typical attached cavities have been identified for low pressure conditions as “band” and “tadpole” cavities into the different separations of the laminar flows. For higher Reynolds numbers, a flow regime transition can be noticed in the wake of well-developed gas structures, characterized by wake instabilities, causing vortex cavitation above a critical Reynolds number associated with the bubble width Rebc 616. This regime transition can possibly occur either quasicontinuously in the wake of an attached “band” vapor cavity or intermittently behind a recirculating air bubble generated with degassing. This last phenomenon is associated in our study to classical “patch” cavitation