1,720,957 research outputs found
On homogeneous CR manifolds and their CR algebras
No full textIn this paper we show some results on homogeneous CR manifolds, proved by introducing their associated CR algebras. In particular, we give different notions of nondegeneracy (generalizing the usual notion for the Levi form) which correspond to geometrical properties for the corresponding manifolds. We also give distinguished equivariant CR fibrations for homogeneous CR manifolds. In the second part of the paper we apply these results to minimal orbits for the action of a real form of a semisimple Lie group G on a flag manifold G/Q
A characterization of CR quadrics with a symmetry property
No full textpeer reviewedWe study CR quadrics satisfying a symmetry property (S~)
which is slightly weaker than the symmetry property (S), recently introduced by W. Kaup, which requires the existence of an automorphism reversing the gradation of the Lie algebra of infinitesimal automorphisms of the quadric.
We characterize quadrics satisfying the (S~)
property in terms of their Levi–Tanaka algebras. In many cases the (S~)
property implies the (S) property; this holds in particular for compact quadrics.
We also give a new example of a quadric such that the dimension of the algebra of positive-degree infinitesimal automorphisms is larger than the dimension of the quadric
The CR structure of minimal orbits in complex flag manifolds
No full textLet be a real form of a complex semisimple Lie group Gˆ, P⊂Gˆ a parabolic subgroup and V=Gˆ/P the corresponding flag manifold of Gˆ. As was shown by J. A. Wolf in [Bull. Amer. Math. Soc. 75 (1969), 1121--1237; MR0251246 (40 #4477)], there exists exactly one G-orbit M on V that is closed (and hence compact) in V. This orbit is connected, of minimal dimension amongst the G-orbits and it is naturally endowed with a G-invariant CR structure, namely the one induced by the Gˆ-invariant complex structure of V. Let us call a homogeneous CR manifold which occurs as a closed orbit of this kind a minimal parabolic orbit. Observe that any minimal parabolic orbit M is (up to equivalences) uniquely determined just by a pair (G,P), where G is a real form of a complex semisimple Lie group Gˆ and P is a parabolic subgroup of Gˆ.
The authors single out a set of properties satisfied by the pairs of Lie algebras (\germ g={\rm Lie}(G),\germ p={\rm Lie}(P))(g=Lie(G),p=Lie(P)) associated with minimal parabolic orbits and prove that, conversely, any pair satisfying such properties (called an effective minimal parabolic CR algebra) is associated with a minimal parabolic orbit in some flag manifold.
After this, they show that for a fixed real semisimple Lie algebra \germ gg, the effective minimal parabolic CR algebras of the form (\germ g,\germ p)(g,p) are in one-to-one correspondence with a special class of cross-markings of the Satake diagram of \germ gg. Then, they study some topological properties of the homogeneous CR manifolds associated with effective minimal parabolic CR algebras and give complete characterizations of those, whose associated minimal parabolic orbits satisfy some special conditions on their CR structure. Such characterizations determine immediately new families of examples of CR manifolds that are either CR separable or of finite type or that satisfy nondegeneracy conditions of various kinds
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
On the topology of minimal orbits in complex flag manifolds
No full textWe compute the Euler-Poincare characteristic of the homogeneous compact manifolds that can be described as minimal orbits for the action of a real form in a complex flag manifold
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
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