1,720,976 research outputs found
Banach-valued multilinear singular integrals with modulation invariance
Get PDFWe prove that the class of trilinear multiplier forms with singularity over a one-dimensional subspace, including the bilinear Hilbert transform, admits bounded L-p-extension to triples of intermediate UMD spaces. No other assumption, for instance of Rademacher maximal function type, is made on the triple of UMD spaces. Among the novelties in our analysis is an extension of the phase-space projection technique to the UMD-valued setting. This is then employed to obtain appropriate single-tree estimates by appealing to the UMD-valued bound for bilinear Calderon-Zygmund operators recently obtained by the same authors.Peer reviewe
Singular integrals along variable codimension one subspaces
Get PDFThis article deals with maximal operators on formed by taking
arbitrary rotations of tensor products of a -dimensional H\"ormander--Mihlin
multiplier with the identity in coordinates, in the particular
codimension 1 case . These maximal operators are naturally connected to
differentiation problems and maximally modulated singular integrals such as
Sj\"olin's generalization of Carleson's maximal operator. Our main result, a
weak-type -estimate on band-limited functions, leads to
several corollaries. The first is a sharp estimate for the
maximal operator restricted to a finite set of rotations in terms of the
cardinality of the finite set. The second is a version of the
Carleson--Sj\"olin theorem. In addition, we obtain that functions in the Besov
space , , may be recovered from their
averages along a measurable choice of codimension subspaces, a form of
Zygmund's conjecture in general dimension .Comment: Published version on Ars Inveniendi Analytic
Navier–Stokes–Voigt Equations with Memory in 3D Lacking Instantaneous Kinematic Viscosity
Get PDFWe consider a Navier–Stokes–Voigt fluid model where the instantaneous kinematic viscosity has been completely replaced by a memory term incorporating hereditary effects, in presence of Ekman damping. Unlike the classical Navier–Stokes–Voigt system, the energy balance involves the spatial gradient of the past history of the velocity rather than providing an instantaneous control on the high modes. In spite of this difficulty, we show that our system is dissipative in the dynamical systems sense and even possesses regular global and exponential attractors of finite fractal dimension. Such features of asymptotic well-posedness in absence of instantaneous high modes dissipation appear to be unique within the realm of dynamical systems arising from fluid models
Directional square functions
Get PDFQuantitative formulations of Fefferman's counterexample for the ball
multiplier are naturally linked to square function estimates for conical and
directional multipliers. In this article we develop a novel framework for these
square function estimates, based on a directional embedding theorem for
Carleson sequences and multi-parameter time-frequency analysis techniques. As
applications we prove sharp or quantified bounds for Rubio de Francia type
square functions of conical multipliers and of multipliers adapted to
rectangles pointing along directions. A suitable combination of these
estimates yields a new and currently best-known logarithmic bound for the
Fourier restriction to an -gon, improving on previous results of A. Cordoba.
Our directional Carleson embedding extends to the weighted setting, yielding
previously unknown weighted estimates for directional maximal functions and
singular integrals.Comment: 49 pages, 4 figures. Final version to appear in Analysis&PDE. arXiv
admin note: text overlap with arXiv:1902.0364
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
- …
