101,945 research outputs found
Measurement uncertainty in pulsar timing array experiments
No full textVerbiest J, Shaifullah GM. Measurement uncertainty in pulsar timing array experiments. CLASSICAL AND QUANTUM GRAVITY. 2018;35(13): 52.Highly precise monitoring of arrival times of pulses from pulsars will allow for gravitational-wave detection in the nano-Hertz regime in the near future. Due to the complex nature of such pulsar-timing experiments and to the large number of effects that can affect these data (starting with magnetospheric effects at the pulsars themselves but extending across the entire signal path down to the final gravitational-wave detection algorithm), any treatment of the measurement uncertainties relevant to such a gravitational-wave detection has been lacking and incomplete so far. In this review, we provide an exhaustive description of the currently known influences on measurement precision in pulsar-timing experiments in general and in gravitational-wave detection through pulsar-timing specifically. While some of these effects remain poorly understood and largely unquantified at present, we discuss both analytic and observational quantifications where available
Timing and Properties of Recycled Pulsars
No full textShaifullah G. Timing and properties of recycled pulsars. Bielefeld: Universität Bielefeld; 2017.Recycled pulsars are old pulsars which have been spun up to very high rotational frequencies through the transfer of angular momentum by stellar material accreted from a companion via Roche-lobe overflow. These pulsars consist of matter at extreme densities, subject to some of the strongest electromagnetic fields and while the study of these objects has remained a challenging task, recycled pulsars are also extremely sensitive probes for studying fundamental physics. In this thesis I present results from three investigations related to the observation of recycled pulsars. I present an overview of the most significant artifacts that affect digital data recording systems for pulsar observations. I show that for the special case of a coherent dedispersion pulsar backend, the action of the dedispersion filter is non-linear in phase and therefore the resultant signal cannot be reconstructed perfectly by an analysis-synthesis filterbank which is built using simple digital filters, if the channel bandwidths are very high. I review a least-mean-squares based filter optimisation algorithm with the aim of addressing this issue. I then present an updated pulsar timing solution for PSR J20510827, which was the second black-widow pulsar to be discovered. For the first time for this system, we are able to detect a decrease in the dispersion measure of . The extended timing also results in the most precise measurements to date of the mean proper motion () and the 2-D transverse velocity () of this system. Secular variations in the orbital period are recovered for more than one complete cycle and we detect previously unknown short-term variations, on timescales of days. The 21-year dataset results in a weighted timing residual of of , which is comparable to that of sources already in PTAs suggesting some black-widow pulsars _may_ indeed be useful PTA sources. Finally, I measure the spectral indices of 12 recycled pulsars for 11 of which flux densities at less than two frequency bands were known, using multi-epoch flux density measurements at three frequency bands carried out with the Arecibo Radio Observatory. We add rederived spectral indices for 43 recycled pulsars which had preexisting spectral index measurements by adding flux density measurements at other frequency bands and 19 recycled pulsars for which only flux densities were available in literature to increase the sample size to 74, which is almost two-thirds of the known Galactic population of 195. The measured spectral indices suggest that while no obvious difference exists between isolated recycled pulsars and those in binaries, redback systems appear to have steeper spectral indices. Recycled pulsars which are also visible in the -ray regime appear to have a steeper spectral index than those which are visible only radio frequencies. This may be the reason why targeted searches for such sources at high radio frequencies have been less successful compared to concurrent searches at lower frequencies. The two-tailed Kolmogorov-Smirnov test shows that the spectral index distribution of recycled pulsars is similar to that of classical pulsars, as well
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
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3346: Samuel G. Freedman, author, 2013
No full textPhotograph of author Samuel G. Freedman, at NT Daily Slash meeting in the Mayborn School of Journalism at UNT
The Right to Strike under the United States Constitution: Theory, Practice, and Possible Implications for Canada
No full textAnswering critics of the Canadian Supreme Court's judgment in B.C. Health, the author argues that the Court laid the foundation for a principled and durable doctrine protecting constitutional labour rights, one that goes directly to the heart of the matter — the inequality of workers’ power in the employment relation. In the author’s view, two paths could lead from B.C. Health to the recognition of Charter protec- tion for a right to strike: one that treats the right as an accessory to col- lective bargaining, and one that upholds the right directly on the basis of the Charter values of equality and participation. The author supports the latter approach, contending that constitutional rights should be defined in relation to fundamental values, in a way that is not contingent on time-bound or fact-sensitive assessments about the role of strikes within a particular collective bargaining regime. Although a Charter right to strike may involve the courts in difficult choices about when to defer to legislative policy decisions, and courts may lack the institutional capac- ity to deal effectively with labour law issues, the author points out that judges can look to ILO standards for expert guidance. Noting that the U.S. experience in this area might be of considerable use to Canadians, the author concludes by providing an overview of American case law concerning a constitutional right to strike.Peer reviewe
Effect of matching algorithm and profile shape on pulsar pulse time of arrival uncertainties
No full textWang J, Verbiest J, Shaifullah G, Yuan J. Effect of matching algorithm and profile shape on pulsar pulse time of arrival uncertainties. Research in Astronomy and Astrophysics. 2023.For high-precision pulsar timing analysis and low-frequency gravitational wave detection, it is essential to accurately determine pulsar pulse times of arrival (ToAs) and associated uncertainties. To measure the ToAs and their uncertainties, various cross-correlation-based techniques can be employed. We develop methodologies to investigate the impact of the template-matching method, profile shape, signal-to-noise ratio (S/N) of both template and observation on ToA uncertainties. These methodologies are then applied to data from the International Pulsar Timing Array. We demonstrate that the Fourier domain Markov chain Monte Carlo method is generally superior to other methods, while the Gaussian interpolation shift method outperforms other methods in certain cases, such as profiles with large duty cycles or smooth profiles without sharp features. However, it is important to note that our study focuses solely on ToA uncertainty, and the optimal method for determining both ToA and ToA uncertainty may differ
G-Rank: Unsupervised Continuous Learn-to-Rank for Edge Devices in a P2P Network
No full textRanking algorithms in traditional search engines are powered by enormous training data sets that are meticulously engineered and curated by a centralized entity. Decentralized peer-to-peer (p2p) networks such as torrenting applications and Web3 protocols deliberately eschew centralized databases and computational architectures when designing services and features. As such, robust search-and-rank algorithms designed for such domains must be engineered specifically for decentralized networks, and must be lightweight enough to operate on consumer-grade personal devices such as a smartphone or laptop computer. We introduce G-Rank, an unsupervised ranking algorithm designed exclusively for decentralized networks. We demonstrate that accurate, relevant ranking results can be achieved in fully decentralized networks without any centralized data aggregation, feature engineering, or model training. Furthermore, we show that such results are obtainable with minimal data preprocessing and computational overhead, and can still return highly relevant results even when a user’s device is disconnected from the network. G-Rank is highly modular in design, is not limited to categorical data, and can be implemented in a variety of domains with minimal modification. The results herein show that unsupervised ranking models designed for decentralized p2p networks are not only viable, but worthy of further research.https://github.com/awrgold/G-RankComputer Scienc
Author inscription in The Chinese slave-girl: a story of woman's life in China
No full textThis edition includes a gift inscription by author Rev. J.A. Davis, "To Rev. A. G. Russell with the warmest regards of the author J.A. Davis."Davis, John Agnell, 1839-1897
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