431 research outputs found
Sifting the gravitational-wave universe via multimessenger astronomy: forthcoming prospects for continuous-wave detection
No full textThe upgrade of worldwide gravitational-wave detector network has led to the first transient gravitational-wave detection, which has started to hone the comprehension we have about our Universe and some of its constituents. A broader picture would be however provided by the detection of continuous-wave signals, which could be more easily achieved by exploiting the synergy with multimessenger Astronomy. Thanks to electromagnetic observations we may indeed be able to know, with enough accuracy, the sky location, rotational and/or orbital parameters of a broad class of rapidly-rotating neutron stars. This would allow us to perform a multitude of targeted and directed continuous-wave searches, and would facilitate narrow-band searches for the same class of signals. We will describe the prospects for detecting continuous gravitational waves, by especially employing novel strategies for neutron stars in binary systems directed to sources whose parameters have been electromagnetically estimated. Employing those methods to analyze data from the ever-more-sensitive advanced detectors will remarkably increase the chances of a continuous-wave detection
Searching for continuous gravitational wave signals using LIGO and Virgo detectors
No full textDirect and unequivocal detection of gravitational waves represents a great challenge of contemporary physics and astrophysics. A worldwide effort is currently operating towards this direction, building ever sensitive detectors, improving the modelling of gravitational wave sources and employing ever more sophisticated and powerful data analysis techniques. In this paper we review the current status of LIGO and Virgo ground based interferometric detectors and some data analysis tools used in the continuous wave searches to extract the faint gravitational signals from the interferometric noise data. Moreover we discuss also relevant results from recent continuous wave searches
Optical fiber multichannel local area networks
No full textThe throughput and average delay for a fiber-optic multichannel local area network (LAN) is derived. This system, which can be seen as an extension of the classical single-channel local area networks, provides fault tolerance and reliability as well as better capacity and throughput characteristics than single-channel networks. The average system delay is smaller only at high load and larger at low load. Expressnet and Fasnet, two round-robin protocols specifically designed for unidirectional systems, are considered in detail for nongated sequential service (NGSS). The developed analysis is easily extended to any round-robin protoco
Directed searches for continuous gravitational waves from binary systems: Parameter-space metrics and optimal Scorpius X-1 sensitivity
No full textWe derive simple analytic expressions for the (coherent and semi-coherent) phase metrics of continuous-wave sources in low-eccentricity binary systems, both for the long-segment and short- segment regimes (compared to the orbital period). The resulting expressions correct and extend previous results found in the literature. We present results of extensive Monte-Carlo studies comparing metric mismatch predictions against the measured loss of detection statistic for binary parameter offsets. The agreement is generally found to be within ~ 10%-30%. As an application of the metric template expressions, we estimate the optimal achievable sensitivity of an Einstein@Home directed search for Scorpius X-1, under the assumption of sufficiently small spin wandering. We find that such a search, using data from the upcoming advanced detectors, would be able to beat the torque- balance level [1,2] up to a frequency of ~ 500 - 600 Hz, if orbital eccentricity is well-constrained, and up to a frequency of ~ 160 - 200 Hz for more conservative assumptions about the uncertainty on orbital eccentricity
New prospects for continuous gravitational wave detection from binary systems in the advanced detector era
No full textGravitational wave detection is eagerly expected as one of the major discoveries of the next decade. A worldwide effort is currently underway, building ever-more-sensitive detectors and developing more powerful data-analysis tools. Continuous gravitational waves (CWs) are a promising class of signals for advanced detectors, and a particularly interesting type of CW sources are neutron stars in low-mass X-ray binaries, with Scorpius X-1 being the most remarkable representative. We describe the details of a project aimed to perform directed searches for CWs from binary systems. We use a search algorithm based on coherently computing a maximum likelihood statistic for a bank of signal templates, and then incoherently summing this statistic over the segments in which the entire data set has been previously split. The current strategy strongly relies on the derivation of precise analytic expressions for the (coherent and semicoherent) phase metrics of CW sources in low-eccentricity binary systems, for the two regimes of long and short segments compared to the orbital period. As an application of the metric template expressions, we estimate the optimal achievable sensitivity of an Einstein@Home directed search for Scorpius X-1, under the assumption of sufficiently small spin wandering, and using data from the upcoming advanced detectors. We find that such a search would be able to beat the torque-balance level up to a frequency of 500-600 Hz, if orbital eccentricity is well-constrained, and up to a frequency of ∼160-200 Hz for more conservative assumptions about the uncertainty on orbital eccentricity
Design of wideband acoustic detectors of gravitational waves equipped with displacement concentrators
No full textWe present the concept design of a new class of acoustic detectors of gravitational waves (GWs), which feature a wideband sensitivity. The main novelty relies in the geometry of the test mass, which is equipped with integrated whips. This tapering provides more resonant modes with favorable cross-section to GWs to achieve a large bandwidth. Moreover, the whips act as displacement concentrators and ensure a high mechanical gain at the sensing surfaces. The resulting decrease in mechanical stiffness allows us to achieve the noise matching condition with reasonable operating parameters of the displacement transducer. The performances of the detector are modeled taking into account the quantum and thermal noise sources in the case of a capacitive transducer with a SQUID amplifier. This class of detectors can be designed to target GWs in the frequency range above 1 kHz at a sensitivity comparable to that predicted for future long baseline interferometric detectors. After showing how to scale the design for different constructing materials and target frequencies, we discuss the predicted sensitivity to specific astrophysical signal waveforms
Corneal thickness mapping by 3D swept-source anterior segment optical coherence tomography
No full text{PURPOSE:} To assess accuracy and repeatability of central corneal thickness ({CCT)} measurements obtained by swept-source anterior segment optical coherence tomography ({AS-OCT)}, spectral-domain retinal {OCT} with corneal module and ultrasound pachymetry ({USP)}, and to assess repeatability of pachymetric mapping with {AS-OCT.} {METHODS:} 50 healthy volunteers were recruited. A single, experienced operator analysed the right eye of each participant twice in the same session with {AS-OCT} ('corneal map' routine), retinal {OCT} and {USP.} {CCT} measurements were compared using repeated-measures analysis of variance, Bonferroni test, Pearson correlation and Bland-Altman plots. Repeatability of thickness maps and {CCT} measurements were assessed using Alpha of Cronbach, intraclass correlation coefficient ({ICC)} and coefficient of repeatability. {RESULTS:} Mean {CCT±SD} was 540±28.9 μm for {AS-OCT}, 544±29.5 μm for retinal {OCT} and 549.3±31.7 μm for {USP;} the differences were statistically significant (p{\textless}0.01). {CCT} measurements obtained with the three instruments were highly correlated: r was 0.965 for {AS-OCT/USP}, 0.962 for retinal {OCT/USP} and 0.984 for {AS-OCT/retinal} {OCT} comparison. The repeatability of {CCT} measurements was higher for {AS-OCT} than for the other devices (p{\textless}0.001). Repeatability of pachymetric maps was excellent ({ICC=0.999).} {CONCLUSIONS:} Pachymetric maps by swept-source {AS-OCT} showed excellent repeatability. {CCT} measurements obtained by {AS-OCT}, {USP} and retinal {OCT} were highly correlated although not identical
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