196,837 research outputs found
In margine all'attività di Polidoro pittore di facciate
No full textIl saggio analizza l'attività di Polidoro da Caravaggio pittore di facciate a Roma in rapporto alla cultura dell'Italia settentrionale con particolare riferimento al territorio della Lomellina.The essay analyzes the activity of Polidoro da Caravaggio, painter of Roman facades, in relationship with the culture of Northern Italy with particular reference to the Lomellina area
L’equazione di Laplace: Una riflessione storico-epistemologica
No full textL’equazione oggi detta “di Laplace” raggiunse una notevole visibilità grazie
alla pubblicazione della famosa opera di Pierre-Simon Laplace “Traité de
Mécanique Céleste” (1799). Laplace ebbe il merito di mettere a punto una teoria
analitica per trattare problemi dell’astronomia intesa come “meccanica celeste”. In
quel contesto, l’equazione modellizza il problema dell’attrazione gravitazionale che
uno sferoide esercita su un punto materiale generico. Tuttavia, l’equazione era già
nota a Leonhard Euler, che l’aveva ottenuta nel 1752 in un lavoro nel quale descrive
il moto di un fluido incomprimibile. Adottando una prospettiva epistemologica e
mettendo a confronto i contributi di Euler e di Laplace, si discute di seguito la
questione se sia corretto associare solamente il nome di Laplace all’equazione che
stiamo considerando.The equation that at present time is known as “Laplace’s equation”
achieved considerable visibility thanks to the publication of the famous work of
Pierre-Simon Laplace “Traité de Mécanique Céleste” (1799). Laplace is
acknowledged as the developer of an analytical theory to deal with problems of
astronomy understood as “celestial mechanics”. In this context, the equation models
the problem of gravitational attraction that a spheroid exerts on a generic material
point. However, the equation was already known to Leonhard Euler, who had
obtained it in 1752 in a work in which he describes the motion of an incompressible
fluid. Adopting an epistemological perspective and comparing the contributions of
Euler and Laplace, in this article we discuss the question of whether it is correct to
associate only Laplace’s name with the equation we are considering
Asymptotic decay for some differential system with fading memory
No full textWe study the large time behavior of the solution u to an initial andboundary value problem related to an integro-differential equationwith a damping term. We prove that the solution u exponentially decays only if the relaxation kernel does
Fundamental solutions for Kolmogorov-Fokker-Planck operators with time-depending measurable coefficients
No full textWe consider a Kolmogorov-Fokker-Planck operator of the kind: (equation presented) where n ai j (t) oq i; j=1 is a symmetric uniformly positive matrix on Rq, q ≤ N, of bounded measurable coefficients defined for t 2 R and the matrix B = n bi j oN i; j=1 satisfies a structural assumption which makes the corresponding operator with constant ai j hypoelliptic. We construct an explicit fundamental solution Γ for L, study its properties, show a comparison result between Γ and the fundamental solution of some model operators with constant ai j, and show the unique solvability of the Cauchy problem for L under various assumptions on the initial datum
Harnack inequality for hypoelliptic ultraparabolic equations with a singular lower order term
No full textWe prove a Harnack inequality for the positive solutions of ultraparabolic equations of the type L u + V u = 0;where L is a linear second order hypoelliptic differential operator and V belongs to a class of functions of Stummel-Kato type. We also obtain the existence of a Green function and an uniqueness result for the Cauchy-Dirichlet problem
A Green function and regularity results for an ultraparabolic equation with a singular potential
No full textWe prove a Harnack inequality for the positive solutions ofa Schroedinger type equationL_0 u + V u = 0;where L_0 is an operator satisfying the Hoermander's condition and V belongs to a class of functions of Stummel-Kato type. We also obtain the existence of a Green function and an uniqueness result for the Cauchy-Dirichlet problem
Hölder regularity for solutions of an ultraparabolic equations in divergence form
No full textWe prove the Holder regularity for the solutions to Kolmogorov Partial Differential Equations in divergence form. The coefficients of the second order part of the operator is assumed in the Vanishing Mean Oscillation space
Il ruolo dell’attività sportiva nella prevenzione dell’osteoporosi: evidenze scientifiche a confronto
No full textKolmogorov-Fokker-Planck Equations : comparison Principles near Lipschitz type Boundaries
No full textWe prove several new results concerning the boundary behavior of non-negative solutions to the equation \Ku=0 where \begin{eqnarray*}%\label{kolsim} \K:= \sum_{i=1}^m\partial_{x_i x_i}+\sum_{i=1}^m x_i\partial_{y_{i}}-\partial_t.\end{eqnarray*} Our results are established near the non-characteristic part of the boundary of certain local \MLip-domains where the latter is a class of local Lipschitz type domains adapted to the geometry of \K. Generalizations to more general operators of Kolmogorov-Fokker-Planck type are also discussed
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