102,455 research outputs found
Speed selection for coupled wave equations
No full textWe discuss models for coupled wave equations describing interacting fields, focusing on the speed of travelling wave solutions. In particular, we propose a general mechanism for selecting and tuning the speed of the corresponding (multi-component) travelling wave solutions under certain physical conditions. A number of physical models (molecular chains, coupled Josephson junctions, propagation of kinks in chains of adsorbed atoms and domain walls) are considered as examples
L'“ékphrasis” oltre l'“ékphrasis”: due ragionamenti sul saggismo di Roberto Longhi
No full textIl presente contributo sul saggismo di Roberto Longhi, nonostante l’evidente divaricazione tra le due parti di cui si compone, possiede un carattere profondamente unitario. L’idea centrale che sta alla base delle sue due sezioni è che l’ékphrasis longhiana travalichi i limiti e le forme consuete di questo genere di scrittura, pur
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senza stravolgerne del tutto statuti e finalità.The idea of the paper is that Roberto Longhi’s ékphrasis goes beyond the usual limits and forms of this kind of writing, but without altering the statutes and all purposes. This need originates from a basic problem: the unbridgeable gap between image and word that describes it
Size and timescale of epidemics in the SIR framework
No full textThe most important features to assess the severity of an epidemic are its size and its timescale. We discuss these features in a systematic way in the context of SIR and SIR-type models. We investigate in detail how the size and timescale of the epidemic can be changed by acting on the parameters characterizing the model. Using these results and having as guideline the COVID-19 epidemic in Italy, we compare the efficiency of different containment strategies for contrasting an epidemic diffusion such as social distancing, lockdown, tracing, early detection and isolation
Solitons in a double pendulums chain model, and DNA roto-torsional dynamics
No full textIt was first suggested by Englander et al to model the nonlinear dynamics of DNA relevant to the transcription process in terms of a chain of coupled pendulums. In a related paper [4] we argued for the advantages of an extension of this approach based on considering a chain of double pendulums with certain characteristics. Here we study a simplified model of this kind, focusing on its general features and nonlinear travelling wave excitations; in particular, we show that some of the degrees of freedom are actually slaved to others, allowing for an effective reduction of the relevant equations
Near-horizon limit of the charged BTZ black hole and AdS(2) quantum gravity
No full textWe show that the 3D charged Banados-Teitelboim-Zanelli (BTZ) black hole
solution interpolates between two different 2D AdS spacetimes: a near-extremal, nearhorizon
AdS2 geometry with constant dilaton and U(1) field and an asymptotic AdS2
geometry with a linear dilaton. Thus, the charged BTZ black hole can be considered as
interpolating between the two different formulations proposed until now for AdS2 quantum
gravity. In both cases the theory is the chiral half of a 2D CFT and describes, respectively,
Brown-Hennaux-like boundary deformations and near-horizon excitations. The central
charge cas of the asymptotic CFT is determined by 3D Newton constant G and the AdS
length l, cas = 3l/G, whereas that of the near-horizon CFT also depends on the U(1)
charge Q, cnh ∝ lQ/√G
A composite model for DNA torsion dynamics
No full textDNA torsion dynamics is essential in the transcription process; a simple model for it, in reasonable agreement with experimental observations, has been proposed by Yakushevich (Y) and developed by several authors;
in this, the nucleotides (the DNA subunits made of a sugar-phosphate group and the attached nitrogen base) are described by a single degree of freedom. In this paper we propose and investigate, both analytically
and numerically, a “composite” version of the Y model, in which the sugar-phosphate group and the base are described by separate degrees of freedom. The model proposed here contains as a particular case the Y model and shares with it many features and results, but represents an improvement from both the conceptual and the
phenomenological point of view. It provides a more realistic description of DNA and possibly a justification for the use of models which consider the DNA chain as uniform. It shows that the existence of solitons is a generic
feature of the underlying nonlinear dynamics and is to a large extent independent of the detailed modeling of DNA. The model we consider supports solitonic solutions, qualitatively and quantitatively very similar to the
Y solitons, in a fully realistic range of all the physical parameters characterizing the DNA
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