1,720,961 research outputs found
On the horizontal cohomology with general coefficients
Get PDFsummary:[For the entire collection see Zbl 0699.00032.] \par A new cohomology theory suitable for understanding of nonlinear partial differential equations is presented. This paper is a continuation of the following paper of the author [Differ. geometry and its appl., Proc. Conf., Brno/Czech. 1986, Commun., 235-244 (1987; Zbl 0629.58033)]
On Integrable Nets in General and Concordant Chebyshev Nets in Particular
No full textWe consider general integrable curve nets in Euclidean space as a particular integrable geometry invariant with respect to rigid motions and net-preserving reparameterisations. For their description, we first give an overview of the most important second-order invariants and relations among them. As a particular integrable example, we reinterpret the result of I.S. Krasil'shchik and M. Marvan (see Section 2, Case 2 in [Acta Appl. Math. 56 (1999), 217-230]) as a curve net satisfying an ℝ-linear relation between the Schief curvature of the net and the Gauss curvature of the supporting surface. In the special case when the curvatures are proportional (concordant nets), we find a correspondence to pairs of pseudospherical surfaces of equal negative constant Gaussian curvatures. Conversely, we also show that two generic pseudospherical surfaces of equal negative constant Gaussian curvatures induce a concordant Chebyshev net. The construction generalises the well-known correspondence between pairs of curves and translation surfaces.This research received support from MŠMT under RVO 47813059. The author is grateful to Evgeny Ferapontov and Jan Cieśliński for the introduction to integrable surfaces and thought-provoking discussions that inspired this particular research
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
Yang-Baxter sigma models and their Lax Pairs
No full textIntegrabilitu nelineárních ?-modelů lze chápat ve smyslu existence 1-parametrické Laxovy formulace příslušných polních rovnic. V práci [4] se ukázalo, že Yang-Baxterovy ?-modely jsou integrabilní. Na základě obecného výsledku nalezneme Laxův pár Yang-Baxterova SU(2) modelu. Laxovy páry zobecněného principálního chirálního modelu jsou definovány pomocí Sochenových rovnic. Tyto rovnice řešíme pro případ Lieovy grupy SU(2). V této práci také diskutujeme důležitou vlastnost Laxových párů týkající se Bianchiho identit.The integrability of nonlinear ?-models can be considered as the existence of 1-parametric Lax formulation of the field equations. There has been shown in paper [4] that Yang-Baxter ?-models are integrable. Considering the general result we find Lax pair for Yang-Baxter SU(2) model. The Sochen equations that define the Lax pairs for generalized principal chiral models are given. We solve these equations for the case of Lie group SU(2). The important property of Lax pairs relating to Bianchi identities is discussed as well.katedra fyzik
Matching van Stockum dust to Papapetrou vacuum
Get PDFAddressing a long-standing problem, we show that every van Stockum dust can
be matched to a 1-parametric family of non-static Papapetrou vacuum metrics,
and the converse. The boundary, if existing, is determined by vanishing of
certain first-order invariant on the vacuum side. Moreover, we establish a
relation to Ehlers and Kramer--Neugebauer transformations, which allows us to
look for dust clouds with a prescribed boundary. Explicit examples include the
Bonnor metric and a new vacuum exterior to the Lanczos--van Stockum dust
metric, as well as dust clouds with nontrivial topology.Comment: 13 pages, 1 figure. New in version 2: Sections 4, 8, 9, 1
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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