872 research outputs found
A Conley-type decomposition of the strong chain recurrent set
For a continuous flow on a compact metric space, the aim of this paper is to
prove a Conley-type decomposition of the strong chain recurrent set. We first
discuss in details the main properties of strong chain recurrent sets. We then
introduce the notion of strongly stable set as an invariant set which is the
intersection of the -limits of a specific family of nested and
definitively invariant neighborhoods of itself. This notion strengthens the one
of stable set; moreover, any attractor results strongly stable. We then show
that strongly stable sets play the role of attractors in the decomposition of
the strong chain recurrent set; indeed, we prove that the strong chain
recurrent set coincides with the intersection of all strongly stable sets and
their complementaries
The generalized recurrent set, explosions and Lyapunov functions
We consider explosions in the generalized recurrent set for homeomorphisms on
a compact metric space. We provide multiple examples to show that such
explosions can occur, in contrast to the case for the chain recurrent set. We
give sufficient conditions to avoid explosions and discuss their necessity.
Moreover, we explain the relations between explosions and cycles for the
generalized recurrent set. In particular, for a compact topological manifold
with dimension greater or equal , we characterize explosion phenomena in
terms of existence of cycles. We apply our results to give sufficient
conditions for stability, under perturbations, of the property
of admitting a continuous Lyapunov function which is not a first integral
Tax systems and tax reforms in Latin America: country studies
This paper is part of a wider research concerning taxation systems an reforms carried on ar the Departemnt of Pubic economics of the Uiversity of Pavia -I taly. These country studies refer to Argentina, Brazil, Chile, Costa Rica, Colombia, Mexico, Paraguay and Uruguay and are due to eminent native esperts. The papers depict and discuss the tax systems ad reforms in the aforementioned countries since the early 1990 to 2006.Tax Systems; Tas reofoerms; Latin American countries
The Role of Environment on the Formation of Early-Type Galaxies
(Abridged) We present a detailed study of the stellar populations of a
volume-limited sample of early-type galaxies from SDSS, across a range of
environments -- defined as the mass of the host dark matter halo. The stellar
populations are explored through the SDSS spectra, via projection onto a set of
two spectral vectors determined from Principal Component Analysis. We find the
velocity dispersion of the galaxy to be the main driver behind the different
star formation histories of early-type galaxies. However, environmental effects
are seen to play a role (although minor). Galaxies populating the lowest mass
halos have stellar populations on average ~1Gyr younger than the rest of the
sample. The fraction of galaxies with small amounts of recent star formation is
also seen to be truncated when occupying halos more massive than 3E13Msun. The
sample is split into satellite and central galaxies for a further analysis of
environment. Satellites are younger than central galaxies of the same stellar
mass. The younger satellite galaxies in 6E12Msun halos have stellar populations
consistent with the central galaxies found in the lowest mass halos of our
sample (i.e. 1E12Msun). This result is indicative of galaxies in lower mass
halos being accreted into larger halos.Comment: 11 pages, 10 figures. Accepted for publication in MNRA
The generalized recurrent set, explosions and Lyapunov functions
We consider explosions in the generalized recurrent set for homeomorphisms on a compact metric space. We provide multiple examples to show that such explosions can occur, in contrast to the case for the chain recurrent set. We give sufficient conditions to avoid explosions and discuss their necessity. Moreover, we explain the relations between explosions and cycles for the generalized recurrent set. In particular, for a compact topological manifold with dimension greater or equal 2, we characterize explosion phenomena in terms of existence of cycles. We apply our results to give sufficient conditions for stability, under C 0 perturbations, of the property of admitting a continuous Lyapunov function which is not a first integral
BC2L-C N-Terminal Lectin Domain Complexed with Histo Blood Group Oligosaccharides Provides New Structural Information
International audienceLectins mediate adhesion of pathogens to host tissues, filling in a key role in the first steps of infection. Belonging to the opportunistic pathogen Burkholderia cenocepacia, BC2L-C is a superlectin with dual carbohydrate specificity, believed to mediate cross-linking between bacteria and host cells. Its C-terminal domain binds to bacterial mannosides while its N-terminal domain (BCL2-CN) recognizes fucosylated human epitopes. BC2L-CN presents a tumor necrosis factor alpha (TNF-α) fold previously unseen in lectins with a novel fucose binding mode. We report, here, the production of a novel recombinant form of BC2L-CN (rBC2L-CN2), which allowed better protein stability and unprecedented co-crystallization with oligosaccharides. Isothermal calorimetry measurements showed no detrimental effect on ligand binding and data were obtained on the binding of Globo H hexasaccharide and l-galactose. Crystal structures of rBC2L-CN2 were solved in complex with two blood group antigens: H-type 1 and H-type 3 (Globo H) by X-ray crystallography. They provide new structural information on the binding site, of importance for the structural-based design of glycodrugs as new antimicrobials with antiadhesive properties
Birkhoff attractors of dissipative billiards
We study the dynamics of dissipative billiard maps within planar convex
domains. Such maps have a global attractor. We are interested in the
topological and dynamical complexity of the attractor, in terms both of the
geometry of the billiard table and of the strength of the dissipation. We focus
on the study of an invariant subset of the attractor, the so-called Birkhoff
attractor. On the one hand, we show that for a generic convex table with
"pinched" curvature, the Birkhoff attractor is a normally contracted manifold
when the dissipation is strong. On the other hand, for a mild dissipation, we
prove that generically the Birkhoff attractor is complicated, both from the
topological and the dynamical point of view.Comment: 48 pages, 10 figure
La conoscenza di architettura, città e paesaggio: "Il Progetto Logico di Rilievo" in una sperimentazione metodologica
Non si parla come si pensa, ma si pensa come si parla: ciò induce a dire che come il flusso del pensiero segue la sintassi della lingua madre, così il pensiero formale, sia esso interpretativo o propositivo, segue l'impianto geometrico. La Geometria è di fatto un sistema assiomatico che, se modernamente lo si è compreso come puramente formale, nella realtà dei comuni mortali nasce e rimane materiale: un vero "a priori" kantiano. Ora, le ragioni del "volere geometrico" che pervade la vita delle civiltà può avere svariate ragioni che scomodano svariate discipline: a noi può bastare la duplice considerazione che vede la Geometria tanto come mezzo per giustificare scelte formali attraverso sicure relazioni tra entità, quanto il filo logico che rende comprensibile e comunicabile una idea anche di pura fantasia. Il nostro contributo intende dimostrare, quanto sia utile ancora e sempre, dalla tradizione alla contemporaneità, la conoscenza della Geometria nelle sue varie forme. You do not speak as you think, but you think as you speak: this means that as the flow of thought follows our language syntax, so the formal thinking, whether purposeful or interpretational, follows the geometric layout. Geometry is an axiomatic system that, if modernly it is purely formal, in ordinary life remains material: a true Kantian "a priori". Geometry pervades the civilized people's life; we can take into consideration two aspects: firstly, the Geometry justify formal choices through fixed relationships between entities; secondly, Geometry makes understandable and communicable ideas. Our contribution aims to demonstrate how Geometry, from tradition to modernity, is still useful in its various form
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