1,720,963 research outputs found
Darboux–Weinstein theorem for locally conformally symplectic manifolds
No full textA locally conformally symplectic (LCS) form is an almost symplectic form ω such that a closed one-form θ exists with dω=θ∧ω. We present a version of the well-known result of Darboux and Weinstein in the LCS setting and give an application concerning Lagrangian submanifolds
De Rham and twisted cohomology of Oeljeklaus-Toma manifolds
Get PDFOeljeklaus–Toma (OT) manifolds are complex non-Kähler manifolds whose construction arises from specific number fields. In this note, we compute their de Rham cohomology in terms of invariants associated to the background number field. This is done by two distinct approaches, one by averaging over a certain compact group, and the other one using the Leray–Serre spectral sequence. In addition, we compute also their twisted cohomology. As an application, we show that the low degree Chern classes of any complex vector bundle on an OT mani- fold vanish in the real cohomology. Other applications concern the OT manifolds admitting locally conformally Kähler (LCK) metrics: we show that there is only one possible Lee class of an LCK metric, and we determine all the possible twisted classes of an LCK metric, which implies the nondegeneracy of certain Lefschetz maps in cohomology
Variational problems in conformal geometry
Get PDFWe study the Euler-Lagrange equation for several natural functionals defined
on a conformal class of almost Hermitian metrics, whose expression involves the
Lee form of the metric. We show that the Gauduchon metrics are the
unique extremal metrics of the functional corresponding to the norm of the
codifferential of the Lee form. We prove that on compact complex surfaces, in
every conformal class there exists a unique metric, up to multiplication by a
constant, which is extremal for the functional given by the -norm of
, where denotes the complex structure. These extremal metrics are
not the Gauduchon metrics in general, hence we extend their definition to any
dimension and show that they give unique representatives, up to constant
multiples, of any conformal class of almost Hermitian metrics
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
On a class of Kato manifolds
No full textIn this talk we describe Kato manifolds, also known as manifolds with global spherical shell. We revisit Brunellaâ s proof of the fact that Katosurfaces admit locally conformally K\"ahler metrics, and we show that it holdsfor a large class of higher dimensional complex manifolds containing a globalspherical shell. On the other hand, we construct manifolds containing a globalspherical shell which admit no locally conformally K\"ahler metric. We then con-sider a specific class, which can be seen as a higher dimensional analogue of Inoue-Hirzebruch surfaces, and study several of their analytical properties. Inparticular, we give new examples, in any complex dimension , of com-pact non-exact locally conformally K\"ahler manifolds with algebraic dimension , algebraic reduction bimeromorphic to \C\Proj^{n-2} and admitting non-trivialholomorphic vector fields. These results are joint work with Nicolina Istrati(University of Tel Aviv) and Massimiliano Pontecorvo (Roma Tre University).Non UBCUnreviewedAuthor affiliation: Università Roma TrePostdoctora
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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