Critical behaviour and ultrametricity of Ising spin-glass with long-range interactions

Ising spin-glass systems with long-range interactions ($J(r)\sim r^{-\sigma}$) are considered. A numerical study of the critical behaviour is presented in the non-mean-field region together with an analysis of the probability distribution of the overlaps and of the ultrametric structure of the space of the equilibrium configurations in the frozen phase. Also in presence of diverging thermodynamical fluctuations at the critical point the behaviour of the model is shown to be of the Replica Simmetry Breaking type and there are hints of a non-trivial ultrametric structure. The parallel tempering algorithm has been used to simulate the dynamical approach to equilibrium of such systems.Comment: 15 pages and 12 figure

Re-enacting Early Video Art as a Research Tool for Media Art Histories

This paper will discuss re-enactment as a relevant tool for practice-based research to investigate pioneering video performances and video artworks from the 1970s and 1980s from a theoretical, art-historical and curatorial point of view. Since the early 2000s, the re-enactment of artists’ performance has been growing as an art practice internationally and has been investigated in several studies and exhibitions. In this paper, I will pro- pose that the re-enactment of early video artworks can open up critical analysis on the original work—its nature, form and content—as well as on collective and personal memory and mediation. Re-enactment becomes a research tool that investigates the nature of video which was at the time a relatively new medium. Re-enactment informs the research into the original piece, its documentation, the relationships between the artist and the body, the work and the viewer. It investigates the effects of analogue video on the viewer and the artist in comparison with the digital video employed in the re-enactment and its documentation. The paper will analyse case studies from the research projects REWIND, REWINDItalia and EWVA (European Women’s Video Art in the 70s and 80s)

Interventions, Productions and Collaborations:the relationship between RAI and visual artists

On 17 May 1952, before RAI Radiotelevisione Italiana Studios began their regular broadcast from Milan, the Spatialist painter and sculptor Lucio Fontana broadcast his own experimental 'artwork' on Italian television, beginning a fruitful relationship between RAI and visual artists. For some, such as the painter Mario Sasso and the Arte Povera artist Pino Pascali, it provided careers as designers and art directors. For others, such as Carlo Quartucci and Gianni Toti, who were given unique access to RAI's television apparatus, it was an opportunity to explore their own artistic experimentations with an expensive and exclusive medium. RAI also hosted seminal artists' performances on-screen including John Cage and Fabio Mauri. This article, based on documents and interviews collected during the Arts and Humanities Research Council-funded project REWINDItalia, discusses these and other seminal cases as well as tracing and assessing the history of this fruitful and complex exchange between RAI and visual artists

First Order Phase Transition and Phase Coexistence in a Spin-Glass Model

We study the mean-field static solution of the Blume-Emery-Griffiths-Capel model with quenched disorder, an Ising-spin lattice gas with quenched random magnetic interaction. The thermodynamics is worked out in the Full Replica Symmetry Breaking scheme. The model exhibits a high temperature/low density paramagnetic phase. When the temperature is decreased or the density increased, the system undergoes a phase transition to a Full Replica Symmetry Breaking spin-glass phase. The nature of the transition can be either of the second order (like in the Sherrington-Kirkpatrick model) or, at temperature below a given critical value (tricritical point), of the first order in the Ehrenfest sense, with a discontinuous jump of the order parameter and a latent heat. In this last case coexistence of phases occurs.Comment: 4 pages, 8 figure

A simple spin model for three steps relaxation and secondary proccesses in glass formers

A number of general trends are known to occur in systems displaying secondary processes in glasses and glass formers. Universal features can be identified as components of large and small cooperativeness whose competition leads to excess wings or apart peaks in the susceptibility spectrum. To the aim of understanding such rich and complex phenomenology we analyze the behavior of a model combining two apart glassy components with a tunable different cooperativeness. The model salient feature is, indeed, based on the competition of the energetic contribution of groups of dynamically relevant variables, e.g., density fluctuations, interacting in small and large sets. We investigate how the model is able to reproduce the secondary processes physics without further ad hoc ingredients, displaying known trends and properties under cooling or pressing.Comment: 11 Pages, 11 Figure

Complexity of waves in nonlinear disordered media

The statistical properties of the phases of several modes nonlinearly coupled in a random system are investigated by means of a Hamiltonian model with disordered couplings. The regime in which the modes have a stationary distribution of their energies and the phases are coupled is studied for arbitrary degrees of randomness and energy. The complexity versus temperature and strength of nonlinearity is calculated. A phase diagram is derived in terms of the stored energy and amount of disorder. Implications in random lasing, nonlinear wave propagation and finite temperature Bose-Einstein condensation are discussed.Comment: 20 pages, 11 Figure

Reply to Comment on ``Spherical 2+p spin-glass model: an analytically solvable model with a glass-to-glass transition''

In his Comment, Krakoviack [Phys. Rev. B (2007)] finds that the phase behavior of the s+p spin-glass model is different from what proposed by Crisanti and Leuzzi [Phys. Rev. B 73, 014412 (2006)] if s and p are larger than two and are separated well enough. He proposes a trial picture, based on a one step replica symmetry breaking solution, displaying a mode-coupling-like glass-to-glass transition line ending in a A3 singularity. However, actually, the physics of these systems changes when p-s is large, the instability of which the one step replica symmetry breaking glassy phase suffers turns out to be so wide ranging that the whole scenario proposed by Krakoviack must be seriously reconsidered.Comment: 4 pages, 5 figure; reply to arXiv:0705.3187. To be published in Phys Rev B 76 (2007

The K-sat problem in a simple limit

We compute the thermodynamic properties of the 3-satisfiability problem in the infinite connectivity limit. In this limit the computations can be strongly simplified and the thermodynamical properties can be obtained with an high accuracy. We find evidence for a continuous replica symmetry breaking in the region of high number of clauses, $\alpha > \alpha_c$.Comment: 9 pages, 6 figures. To appear in J. Stat. Phys. Minor change

The disordered Backgammon model

In this paper we consider an exactly solvable model which displays glassy behavior at zero temperature due to entropic barriers. The new ingredient of the model is the existence of different energy scales or modes associated to different relaxational time-scales. Low-temperature relaxation takes place by partial equilibration of successive lower energy modes. An adiabatic scaling solution, defined in terms of a threshold energy scale \eps^*, is proposed. For such a solution, modes with energy \eps\gg\eps^* are equilibrated at the bath temperature, modes with \eps\ll\eps^* remain out of equilibrium and relaxation occurs in the neighborhood of the threshold \eps\sim \eps^*. The model is presented as a toy example to investigate conditions related to the existence of an effective temperature in glassy systems and its possible dependence on the energy sector probed by the corresponding observable.Comment: 24 pages, 11 figure