1,720,960 research outputs found
On the porosity of the set of 𝜔-nonexpansive mappings without fixed points
No full textLet
C
C
be a nonempty closed convex bounded subset of a Banach space
E
E
. Let
M
\mathcal {M}
denote the family of all multivalued mappings from
C
C
into
E
E
which are nonempty weakly compact convex valued,
ω
\omega
-nonexpansive and weakly-weakly u.s.c., endowed with the metric of uniform convergence. Let
M
0
{\mathcal {M}_0}
be the set of all
F
∈
M
F \in \mathcal {M}
for which the fixed point problem is well posed. It is proved that the set
M
∖
M
0
\mathcal {M}\backslash {\mathcal {M}_0}
is
σ
\sigma
-porous (in particular meager). A similar result is given for weak properness.</p
On the geodesical connectedness for a class of Semi-Riemannian manifolds
No full textAbstractWe prove a variational principle for geodesics on a semi-Riemannian manifold M of arbitrary index k and possessing k linearly independent Killing vector fields that generate a timelike distribution on M. Using such a principle and a suitable completeness condition for M, we prove some existence and multiplicity results for geodesics joining two fixed points of M
Stationary solutions to a hybrid viscous hydrodynamic model with classical boundaries
Get PDFIn this paper we present a quantum-classical hybrid model based on the hydrodynamic equations in steady state form. The approach presented here, which has already been proposed in previous works, consists in considering an intrinsically hybrid version of the Bohm potential, which acts only in the region of the domain where quantum effects play an important role, while it disappears where the quantum contribution is essentially negligible and the operation of the device can be well described by using a classical model. Compared to previous results from the same line of research, here we assume that the device at the boundaries of the domain behaves classically, while quantum effects are localised in the central part of it. This is the case of greatest scientific interest, since, in real devices, quantum effects are generally localized in a small area within the device itself. The well posedness of the problem is ensured by adding a viscous term necessary for the convergence of the hybrid limit to an appropriate weak solution. Some numerical tests are also performed for different values of the viscous coefficient, in order to evaluate the effects of the viscosity, especially on the boundaries of the device
EXISTENCE AND UNIQUENESS FOR A STATIONARY HYBRID QUANTUM HYDRODYNAMICAL MODEL WITH GENERAL PRESSURE FUNCTIONAL*
No full textIn this paper we generalize the results obtained in [F. Di Michele, M. Mei, B. Rubino, and R. Sampalmieri, Int. J. Numer. Anal. Model., 13:898–925, 2016], where a hybrid model for semiconductor devices has been presented. In particular we consider a more general pressure function, which allows us to account also for the isotropic case. General Dirichlet boundary conditions are also included. In this case we need a different and more restrictive subsonic condition which directly involves the first derivative of the quantum function Q(x). The existence of solutions is obtained by regularizing the problem and performing a suitable vanishing viscosity limit. Also the zero-charge-space limit is discussed and our results are tested on a simple toy model
Existence of solutions for a viscous hybrid quantum system for arbitrary large current density
No full text In this paper, we continue to analyse the properties of the hybrid model introduced in the works by Chiarelli et al. and Di Michele et al. In particular, we consider a quantum hybrid model with a special viscous functional, as introduced in the work by Gamba and Jüngel, for the quantum hydrodynamical model in its standard form (QHD). We show that the hybrid QHD (H-QHD) model admits weak solutions also for arbitrary large value of the current density J under a suitable pressure function. </jats:p
Light rays having extreme points with the same spatial coordinates
No full textAbstractIn this paper we deal with lightlike geodesics in Lorentzian manifolds which are closed with respect to the spatial coordinates. We consider the case where the initial point is fixed or moves on a level of a given time function. The case where the initial point is free is also considered, under a periodicity condition on the metric
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
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