1,720,979 research outputs found
Discrete Chi-Square method for detecting many signals
No full text Unambiguous detection of signals superimposed on unknown trend is difficult for unevenly spaced data. Here, we formulate the Discrete Chi-square Method (DCM) that can determine the best model for many signals superimposed on arbitrary polynomial trends. DCM minimizes the Chi-square for the data in the multi-dimensional tested frequency space. The required number of tested frequency combinations remains manageable, because the method test statistic is symmetric in this tested frequency space. With our known tested constant frequency grid values, the non-linear DCM model becomes linear, and all results become unambiguous. We test DCM with simulated data containing different mixtures of signals and trends. DCM gives unambiguous results, if the signal frequencies are not too close to each other, and none of the signals is too weak. It relies on brute computational force, because all possible free parameter combinations for all reasonable linear models are tested. DCM works like winning a lottery by buying all lottery tickets. Anyone can reproduce all our results with the DCM computer code.</p
Discrete Chi-square Method for Detecting Many Signals
Get PDFUnambiguous detection of signals superimposed on unknown trends is difficult for unevenly spaced data. Here, we formulate the Discrete Chi-square Method (DCM) that can determine the best model for many signals superimposed on arbitrary polynomial trends. DCM minimizes the Chi-square for the data in the multi-dimensional tested frequency space. The required number of tested frequency combinations remains manageable, because the method test statistic is symmetric in this tested frequency space. With our known tested constant frequency grid values, the non-linear DCM model becomes linear, and all results become unambiguous. We test DCM with simulated data containing different mixtures of signals and trends. DCM gives unambiguous results, if the signal frequencies are not too close to each other, and none of the signals is too weak. It relies on brute computational force, because all possible free parameter combinations for all reasonable linear models are tested. DCM works like winning a lottery by buying all lottery tickets. Anyone can reproduce all our results with the DCM computer code. All files, variables and other program code related items are printed in magenta colour. Our Appendix gives detailed instructions for using this http URL. We also present one preliminary real use case, where DCM is applied to the observed (O) minus the computed (C) eclipse epochs of a binary star, XZ And. This DCM analysis reveals evidence for the possible presence of a third and a fourth body in this system. One recent study of a very large sample of binary stars indicated that the probability for detecting a fourth body from the O-C data of eclipsing binaries is only about 0.00005.Peer reviewe
Sunspot cycles are connected to the Earth and Jupiter
Get PDFThe sunspot number record covers over three centuries.These numbers measure
the activity of the Sun. This activity follows the solar cycle of about eleven
years. In the dynamo-theory, the interaction between differential rotation and
convection produces the solar magnetic field. On the surface of Sun, this field
concentrates to the sunspots. The dynamo-theory predicts that the period, the
amplitude and the phase of the solar cycle are stochastic. Here we show that
the solar cycle is deterministic, and connected to the orbital motions of the
Earth and Jupiter. This planetary-influence theory allows us to model the whole
sunspot record, as well as the near past and the near future of sunspot
numbers. We may never be able to predict the exact times of exceptionally
strong solar flares, like the catastrophic Carrington event in September 1859,
but we can estimate when such events are more probable. Our results also
indicate that during the next decades the Sun will no longer help us to cope
with the climate change. The inability to find predictability in some
phenomenon does not prove that this phenomenon itself is stochastic.Comment: 40 pages, 15 figures, 21 table
Say Hello to Algol's New Companion Candidates
Get PDFConstant orbital period ephemerides of eclipsing binaries give the computed eclipse epochs (C). These ephemerides based on the old data cannot accurately predict the observed future eclipse epochs (O). Predictability can be improved by removing linear or quadratic trends from the O − C data. Additional companions in an eclipsing binary system cause light-time travel effects that are observed as strictly periodic O − C changes. Recently, Hajdu et al. estimated that the probability of detecting the periods of two new companions from the O − C data is only 0.00005. We apply the new discrete chi-square method to 236 yr of O − C data of the eclipsing binary Algol (β Persei). We detect the tentative signals of at least five companion candidates having periods between 1.863 and 219.0 yr. The weakest one of these five signals does not reveal a “new” companion candidate, because its 680.4 ± 0.4 day signal period differs only 1.4σ from the well-known 679.85 ± 0.04 day orbital period of Algol C. We detect these same signals also from the first 226.2 yr of data, and they give an excellent prediction for the last 9.2 yr of our data. The orbital planes of Algol C and the new companion candidates are probably coplanar because no changes have been observed in Algol’s eclipses. The 2.867 day orbital period has been constant since it was determined by Goodricke.Constant orbital period ephemerides of eclipsing binaries give the computed eclipse epochs (C). These ephemerides based on the old data cannot accurately predict the observed future eclipse epochs (O). Predictability can be improved by removing linear or quadratic trends from the O - C data. Additional companions in an eclipsing binary system cause light-time travel effects that are observed as strictly periodic O - C changes. Recently, Hajdu et al. estimated that the probability of detecting the periods of two new companions from the O - C data is only 0.00005. We apply the new discrete chi-square method to 236 yr of O - C data of the eclipsing binary Algol (beta Persei). We detect the tentative signals of at least five companion candidates having periods between 1.863 and 219.0 yr. The weakest one of these five signals does not reveal a "new" companion candidate, because its 680.4 +/- 0.4 day signal period differs only 1.4 sigma from the well-known 679.85 +/- 0.04 day orbital period of Algol C. We detect these same signals also from the first 226.2 yr of data, and they give an excellent prediction for the last 9.2 yr of our data. The orbital planes of Algol C and the new companion candidates are probably coplanar because no changes have been observed in Algol's eclipses. The 2.867 day orbital period has been constant since it was determined by Goodricke.Peer reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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