1,721,010 research outputs found
L'analisi geometrica delle equazioni alle derivate parziali e Bologna.
No full textLo scopo del lavoro e` duplice: da una parte illustrare in modo informale e divulgativo il campo di ricerca matematica che va sotto il nome di Analisi Geometrica delle Equazioni alle Derivate Parziali, e dall'altra ricordare l'amico, collega e maestro Cesare Parenti
Almost-Positivity Estimates of Pseudodifferential Operators
No full textIn this paper I will give a survey on a priori estimates such as the Gårding,
Sharp-Gårding, Melin, Hörmander and the Fefferman–Phong inequalities for pseu-
dodifferential operators, discuss some generalizations and open problems in some
directions. Finally, I will describe what is known at present in the case of systems
of pseudodifferential operators, the latter being a still largely open and unexplored
area
On the Stability of the -Hypoellipticity under Perturbations
No full textWe study the problem of perturbations of -hypoelliptic operators by lower order terms. After giving several examples which show many different possibilities, we then prove a stability result which shows that a hypoelliptic linear partial differential operator which loses finitely many derivatives and whose formal adjoint is still hypoelliptic (but with no assumption on the loss of derivatives) remains hypoelliptic with the same loss of derivatives after perturbation by a lower order linear partial differential operator (whose order depends on the loss of derivatives)
On the essential spectrum of certain non-commutative oscillators
No full textWe show here that the spectrum of the family of non-commutative harmonic oscillators Q_(α,β)(x, D) for α, β ∈ R+ in the range αβ = 1 is [0, + ∞) and is entirely essential spectrum. The previous existing results concern the case αβ > 1 (case in which Q_(α,β)(x, D) is globally elliptic with a discrete spectrum whose qualitative properties are being extensively studied), and ours therefore extend the picture to the range of parameters αβ ≥ 1
Wigner measures supported on weak KAM tori
No full textIn the setting of the Weyl quantization on the flat torus Tn , we exhibit a class of wave functions with uniquely associated Wigner probability measure, invariant under the Hamiltonian dynamics and with support contained in weak KAM tori in phase space. These sets are the graphs of Lipschitz-continuous weak KAM solutions of negative type of the stationary Hamilton-Jacobi equation. Such Wigner measures are, in fact, given by the Legendre transform of Mather’s minimal probability measures. The research that led to the present paper was partially supported by a grant of the group GNAMPA of INdAM
Global Gevrey hypoellipticity for the twisted Laplacian on forms
No full textWe study in this paper the global hypoellipticity property in the Gevrey category for the generalized twisted Laplacian on forms. Different from the 0-form case, where the twisted Laplacian is a scalar operator, this is a system of differential operators when acting on forms, each component operator being elliptic locally and degenerate globally. We obtain here the global hypoellipticity in anisotropic Gevrey space
On the local solvability of a class of degenerate second order operators with complex coefficients
Full text linkWe study the local solvability of a class of operators with multiple characteristics. The class considered here complements and extends the one previously studied in Federico and Parmeggiani (CPDEs 2016, Vol. 41), in that in this paper we consider some cases of operators with complex coefficients that were not present in Federico and Parmeggiani. The class of operators considered here ideally encompasses classes of degenerate parabolic and Schrodinger type operators. We will give local solvability theorems. In general, one has L-2 local solvability, but also cases of local solvability with better Sobolev regularity will be presented
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
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