Search results for " mani"

Non-accumulation of critical points of the Poincaré time on hyperbolic polycycles

2007

We call Poincare time the time associated to the Poincar6 (or first return) map of a vector field. In this paper we prove the non-accumulation of isolated critical points of the Poincare time T on hyperbolic polycycles of polynomial vector fields. The result is obtained by proving that the Poincare time of a hyperbolic polycycle either has an unbounded principal part or is an almost regular function. The result relies heavily on the proof of Il'yashenko's theorem on non-accumulation of limit cycles on hyperbolic polycycles.

Minimal unit vector fields

2002

We compute the first variation of the functional that assigns each unit vector field the volume of its image in the unit tangent bundle. It is shown that critical points are exactly those vector fields that determine a minimal immersion. We also find a necessary and sufficient condition that a vector field, defined in an open manifold, must fulfill to be minimal, and obtain a simpler equivalent condition when the vector field is Killing. The condition is fulfilled, in particular, by the characteristic vector field of a Sasakian manifold and by Hopf vector fields on spheres.

Analysis of a slow–fast system near a cusp singularity

2016

This paper studies a slow fast system whose principal characteristic is that the slow manifold is given by the critical set of the cusp catastrophe. Our analysis consists of two main parts: first, we recall a formal normal form suitable for systems as the one studied here; afterwards, taking advantage of this normal form, we investigate the transition near the cusp singularity by means of the blow up technique. Our contribution relies heavily in the usage of normal form theory, allowing us to refine previous results. (C) 2015 Elsevier Inc. All rights reserved.

The CO2 output from the Sperchios Basin area (central Greece): the role of hidden degassing from streams

2018

The Sperchios Basin is an actively spreading rift area with deeply rooted extensional faults and also a site of quaternary volcanic activity. Such geologic conditions favoured the formation of many hydrothermal systems, whose surface expressions are among the biggest thermal springs of the whole Greece. Degassing of deeply derived geogenic CO2 is highlighted by strong bubbling within the main pools of the springs. Flux measurements were made in the Thermopyles spring with the floating chamber method and results showed that bubbling gases in the spring release about 1 ton/day of CO2. The outgoing stream has a flow of more than 250 l/s of water rich in CO2 (about 16 mmol/l). Although no bubbl…

Progettare con la luce

2015

el luglio del 2014 Filippo Maria Nicoletti, per gli amici Phil, si laurea in Disegno industriale (Università degli Studi di Palermo) presentando una Tesi su L’immagine progettata. Storia del rapporto tra fotografia e design, con la relazione di chi scrive e la correlazione del professore italo-americano Antonio Scontrino (Bowling Green State University). Un lavoro molto ben fatto, devo dire, che viene dunque editato, diventando un piccolo saggio che racchiude le informazioni essenziali di un tema piuttosto denso: il rapporto design-fotografia. Oltre a presentare una ricca e ragionata bibliografia, una serie d’interviste ben scelte (Roberto Bigano, Vincenzo Castellana, Giuseppe Castelli, Gio…

Improving operational performance in altered gravity

2022

Human motor adaptation is crucial to remain efficient when exposed to unfamiliar environments. In these contexts, the efficient strategies developed by the brain to optimise movement can prove deficient. Dexterous manual movement execution in space therefore require the learning of new coordinated motor actions. Traditionally, adaptation mechanisms are tested in laboratory using robotic devices that disturb the limb specifically involved in the task while the dynamics of the rest of the body remain unchanged. Although participants build a more accurate representation of the task over repetitions, these approaches are limiting as they do not reflect the ecological adjustment to globally modi…

Volumes of certain small geodesic balls and almost-Hermitian geometry

1984

Let D be the characteristic connection of an almost-Hermitian manifold, V D m (r) the volume of a small geodesic ball for the connection D and C C D 1 the first non-trivial term of the Taylor expansion of V D m (r). NK-manifolds are characterized in terms of C C D 1 and a family of Hermitian manifolds for which ∫ M C C D 1 dvol is a spectral invariant is given and one proves that C C D 1 and the spectrum of the complex Laplacian, together, determine the class in which a compact Hermitian manifold lines.

A topological obstruction to the geodesibility of a foliation of odd dimension

1981

Let M be a compact Riemannian manifold of dimension n, and let ℱ be a smooth foliation on M. A topological obstruction is obtained, similar to results of R. Bott and J. Pasternack, to the existence of a metric on M for which ℱ is totally geodesic. In this case, necessarily that portion of the Pontryagin algebra of the subbundle ℱ must vanish in degree n if ℱ is odd-dimensional. Using the same methods simple proofs of the theorems of Bott and Pasternack are given.

Dio nelle mani di chi fa

2006

Nota a Corte europea dei diritti dell'uomo 22 giugno 2021, Erkizia Almandoz c. Spagna, in tema di apologia del terrorismo e libertà di espressione.

2022

La sentenza in epigrafe si segnala all'attenzione perché con essa la Corte europea dei diritti dell'uomo torna a pronunciarsi sul delicato bilanciamento tra esigenze di sicurezza e libertà di espressione con particolare riferimento al c.d. «hate speech» terroristico. Nel caso di specie, il ricorrente, uomo politico di riferimento di una delle correnti indipendentiste dei Paesi Baschi (denominata «Izquierda Abertzale»), era stato ritenuto colpevole in via definitiva del delitto di apologia previsto e punito dall'art. 578 c.p. spagnolo. I giudici di Strasburgo ritengono incompatibile con l'art. 10 Cedu l'irrogazione della sanzione detentiva, non essendo il ricorrente organizzatore o promotore…