1,721,019 research outputs found
Reversibility, coarse graining and the chaoticity principle
No full textWe describe a way of interpreting the chaotic
principle of {\rm [GC1]} more extensively than it was meant in the
original works. Mathematically the analysis is based on the dynamical
notions of Axiom A and Axiom B and on the notion of Axiom C, that we
introduce arguing that it is suggested by the results of an experiment
([BGG]) on chaotic motions. Physically we interpret a breakdown of the
Anosov property of a time reversible attractor (replaced, as a control
parameter changes, by an Axiom A property) as a spontaneous breakdown
of the time reversal symmetry: the relation between time reversal and
the symmetry that remains after the breakdown is analogous to the
breakdown of -invariance while still holds
Critical indices for the Yukawa(2) quantum field theory
No full textThe understanding of the Yukawa(2) quantum field theory is still incomplete if the fermionic mass is much smaller than the coupling. We analyze the Schwinger functions for small coupling uniformly in the mass and we find that the asymptotic behavior of the two-point Schwinger function is anomalous and described by two critical indices, related to the renormalization of the mass and of the wave function. The indices are explicitly computed by convergent series in the coupling. (C) 1997 Published by Elsevier Science B.V
Critical indices in a d=1 filled-band Fermi system
No full textBy renormalization-group methods we obtain nonperturbative results about a d=1 system of interacting spinless fermions in a periodic potential when the conduction band is filled. Both the strength of the interaction and the amplitude of the periodic potential are assumed to be small. We determine that the large-distance asymptotic behavior of the two-point Schwinger function is anomalous and described by two critical indices, explicitly computed by convergent series, related to the renormalization of the spectral gap and of the discontinuity at the Fermi surface
Retinoblastoma protein family in cell cycle and cancer: a review
No full textTwo genes, p707 and Rb2/p130, are strictly related to RE, the most investigated tumor suppressor gene, responsible for susceptibility to retinoblastoma. The products of these three genes, namely pRb, p107, and pRb2/p130 are characterized by a peculiar steric conformation, called ''pocket,'' responsible for most of the functional interactions characterizing the activity of these proteins in the homeostasis of the cell cycle. The interest in these genes and proteins springs from their ability to regulate cell cycle processes negatively, being able, for example, to dramatically slow down neoplastic growth. So far, among these genes, only RE is firmly established to act as a tumor suppressor, because its lack-of-function is clearly involved in tumor onset and progression. It has been found deleted or mutated in most retinoblastomas and sarcomas, but its inactivation is likely to play a crucial role in other types of human cancers. The two other members of the family have been discovered more recently and are currently under extensive investigation. We review analogies and differences among the pocket protein family members, in an attempt to understand their functions in normal and cancer cells. (C) 1996 Wiley-Liss, Inc
Beta function and anomaly of the Fermi surface for a d=1 system of interacting fermions in a periodic potential
No full textWe derive a perturbation theory, based on the renormalization group, for the Fermi surface of a one dimensional system of fermions in a periodic potential interacting via a short range, spin independent potential. The infrared problem is studied by writing the Schwinger functions in terms of running couplings. Their flow is described by a Beta function, whose existence and analyticity as a function of the running couplings is proved. If the fermions are spinless we prove that the Beta function is vanishing and the renormalization flow is bounded for any small interaction. If the fermions are spinning the Beta function is not vanishing but, if the conduction band is not filled or half filled and the interaction is repulsive, it is possible again to control the flow proving the partial asymptotic freedom of the theory. This is done showing that the Beta function is partially vanishing using the exact solution of the Mattis model, which is the spin analogue of the Luttinger model. In both these cases Schwinger functions are anomalous so that the system is a ''Lutttinger liquid.'' Our results extend the work in [B.G.P.S], where neither spin nor periodic potential were considered; an explicit proof of some technical results used but not explicitly proved there is also provided
The October 2000 flooding in Valle d'Aosta (Italy): Event description and land planning measures for the risk mitigation
Full text linkOn October 13-16th, 2000 heavy rainfalls in the Northwestern Italian Alps caused huge flooding and landslides with significant damages to houses and infrastructures and several life losses. In this paper a description of the main events that affected Valle d’Aosta’s region and the subsequent land planning measures adopted for the risk mitigation are presented. After a first meteorological and hydrological framing, based on the data of the regional monitoring system (that pointed out rainfalls up to 236 mm in 24 h also in high‐altitude zones, because of the rise of the isotherm 0°C around 3000 m above sea level), the main effects of the event (extensive flooding, landslides, soil slips and debris flows) in the regional catchment of the Dora Baltea river are described. Through aerial and direct surveys those effects have been transferred into a thematic cartography within two months from the event, in order to have detailed elements for the technical, administrative and political land planning decisions, and, on this basis, a new regional directive containing detailed measures for the hydro‐geological risk mitigation and land safety has been adopted. © 2003 by Taylor nad Francis Group, LLC
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
Quasi Linear Flows on Tori: Regularity of Their Linearization
No full text. Under suitable conditions a flow on a torus C (p) --close, with p large enough, to a quasi periodic diophantine rotation is shown to be conjugated to the quasi periodic rotation by a map that is analytic in the perturbation size. This result is parallel to Moser's theorem stating conjugability in class C (p 0 ) for some p 0 ! p. The extra conditions restrict the class of perturbations that are allowed. 1. Introduction 1.1. The perturbation of the Hamiltonian of a system of ` harmonic oscillators with frequencies 1 2ß (! 01 ; : : : ; ! 0` ) is described by the Hamiltonian H 0 (A; ff) = ! 0 \Delta A+ "A \Delta f (ff) + " A \Delta F (A; ff) A ; (1:1) where A; ff 2 IR ` \Theta TT ` are the action--angle variables of the oscillators, \Delta denotes the scalar product, f is a vector and F a matrix that describe the perturbation structure and " is the intensity of the perturbation. The Hamiltonian system (1.1) is not integrable in general (see for instance (4.10) in [G3]). N..
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