1,721,029 research outputs found
Directed searches for continuous gravitational waves from binary systems: Parameter-space metrics and optimal Scorpius X-1 sensitivity
Full text linkWe 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
Full text linkGravitational 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
Statistical characterization of pulsar glitches and their potential impact on searches for continuous gravitational waves
Full text linkContinuous gravitational waves from neutron stars could provide an invaluable resource to learn about their interior physics. A common search method involves matched-filtering a modeled template against the noisy gravitational-wave data to find signals. This method suffers a mismatch (i.e. relative loss of signal-to-noise ratio) if the signal deviates from the template. One possible instance in which this may occur is if the neutron star undergoes a glitch, a sudden rapid increase in the rotation frequency seen in the timing of many radio pulsars. In this work, we use a statistical characterization of glitch rate and size in radio pulsars to estimate how often neutron star glitches would occur within the parameter space of continuous gravitational-wave searches, and how much mismatch putative signals would suffer in the search due to these glitches. We find that for many previous and potential future searches, continuous-wave signals have an elevated probability of undergoing one or more glitches, and that these glitches will often lead to a substantial fraction of the signal-to-noise ratio being lost. This could lead to a failure to identify candidate gravitational wave signals in the initial stages of a search, and also to the false dismissal of candidates in subsequent follow-up stages
Search for continuous gravitational waves: Improving robustness versus instrumental artifacts
Full text linkThe standard multi-detector F-statistic for continuous gravitational waves is susceptible to false alarms from instrumental artifacts, for example monochromatic sinusoidal disturbances (lines). This vulnerability to line artifacts arises because the F-statistic compares the signal hypothesis to a Gaussian-noise hypothesis, and hence is triggered by anything that resembles the signal hypothesis more than Gaussian noise. Various ad-hoc veto methods to deal with such line artifacts have been proposed and used in the past. Here we develop a Bayesian framework that includes an explicit alternative hypothesis to model disturbed data. We introduce a simple line model that defines lines as signal candidates appearing only in one detector. This allows us to explicitly compute the odds between the signal hypothesis and an extended noise hypothesis, resulting in a new detection statistic that is more robust to instrumental artifacts. We present and discuss results from Monte-Carlo tests on both simulated data and on detector data from the fifth LIGO science run. We find that the line-robust detection statistic retains the detection power of the standard F-statistic in Gaussian noise, while it can be substantially more sensitive in the presence of line artifacts. This new statistic also equals or surpasses the performance of the popular F-statistic consistency veto
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Search for continuous gravitational waves: metric of the multi-detector F-statistic
Full text linkWe derive the parameter-space metric of the multi-detector F-statistic, which is the optimal detection statistic for continuous gravitational waves in stationary Gaussian noise. We find that there is a family of F-statistic metrics, parametrized by the (unknown) amplitude parameters. We explicitly derive the maximal mismatch-range of this metric family, and we introduce a corresponding "average" F-metric. We show that the multi-detector metric consists of noise-weighted averages of single-detector contributions, which implies that the number of templates required to cover the parameter space does not scale with the number of detectors. Contrary to using a longer observation time, combining more detectors (of similar sensitivity) is therefore the computationally cheapest way to improve the sensitivity of a coherent wide-parameter search for continuous gravitational waves. We explicitly compute the F-statistic metric (family) for signals from isolated spinning neutron stars, and we evaluate the quality of different metric approximations in a Monte-Carlo study. We also compare the metric predictions to the measured mismatches and identify two regimes in which the metric is not a good description of the parameter-space structure.
Comment of the Author: Erratum-ibid. D75 (2007) 06990
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
