898 research outputs found
Free-energy bounds for hierarchical spin models
In this paper we study two non-mean-field spin models built on a hierarchical
lattice: The hierarchical Edward-Anderson model (HEA) of a spin glass, and
Dyson's hierarchical model (DHM) of a ferromagnet. For the HEA, we prove the
existence of the thermodynamic limit of the free energy and the
replica-symmetry-breaking (RSB) free-energy bounds previously derived for the
Sherrington-Kirkpatrick model of a spin glass. These RSB mean-field bounds are
exact only if the order-parameter fluctuations (OPF) vanish: Given that such
fluctuations are not negligible in non-mean-field models, we develop a novel
strategy to tackle part of OPF in hierarchical models. The method is based on
absorbing part of OPF of a block of spins into an effective Hamiltonian of the
underlying spin blocks. We illustrate this method for DHM and show that,
compared to the mean-field bound for the free energy, it provides a tighter
non-mean-field bound, with a critical temperature closer to the exact one. To
extend this method to the HEA model, a suitable generalization of Griffith's
correlation inequalities for Ising ferromagnets is needed: Since correlation
inequalities for spin glasses are still an open topic, we leave the extension
of this method to hierarchical spin glasses as a future perspective
Chacun sa citation
La citabilità del testo filmico pone – seppure in misura differente – rilevanti problemi di metodo sia al cineasta che allo studioso. Per queste ragioni è importante restringere il raggio d'azione della citazione ed attenersi, per lo meno in ambito cinematografico, alla classificazione proposta da Genette (1982). Attraverso l'analisi di alcuni film presenti nell'opera collettiva Chacun son cinéma (2007) – nello specifico i film di Hou Hsiao-Hsien, Abbas Kiarostami, Jean-Pierre e Luc Dardenne, Atom Egoyan – si sviluppa una proposta di studio su alcune delle possibilità di citazione al cinema.The quotability of films entails – albeit in different ways – relevant methodological problems both for directors and for scholars. For these reasons, it is important to restrict the range of action of quotations. Moreover, as far as cinema is concerned, it would be suitable to follow Genette's classification (1982). Through the analysis of some movies from the collective opera Chacun son cinéma (2007) and, specifically, through the examination of films shot by Hou Hsiao-Hsien, Abbas Kiarostami, Jean-Pierre and Luc Dardenne, and Atom Egoyan – this article offers a proposal for the study of some possibilities of quotation in movies
Le contrôle de l’Univers: la dialettica del potere nelle Histoire(s) du cinéma di Jean-Luc Godard
Con le sue Histoire(s) du cinéma Jean-Luc Godard lega definitivamente la sua esistenza di essere umano alla storia del cinema, inteso come irrefrenabile flusso di immagini, come sistema di schermi e specchi rispetto ai quali la nostra esperienza è produttrice e prodotto allo stesso tempo. L’immagine è la negazione del niente – dice Godard – ma anche lo sguardo del niente su di noi. Attraverso una scrittura cinematografica onnivora, attraverso lo sfruttamento delle potenzialità citazioniste del film – possibili solo per un regista –, Godard allestisce un meccanismo dialettico di potere visivo che mette in luce la resistenza dell’individuo nei confronti delle immagini e la resistenza delle immagini nei confronti dell’individuo. All’incrocio tra un film-archivio e un film-museo, Godard manipola le immagini fino a svelarci la struttura del loro segreto potere.In Histoire(s) du cinéma, Jean-Luc Godard finally connects his human being’s existence with history of cinema as uncontrollable stream of images, as a system of screens and mirrors that our experience produces and from which it is produced. The image is the nothing’s negation – Godard says – but also the nothing’s gaze on us. Through an omnivorous cinematographic writing, through the exploitation of quotation’s potentiality of movies – made possible only for a director –, Godard prepares a dialectic mechanism of visual power that points out the individual’s endurance versus images and images’ endurance versus the individual. Between film-archive and film-museum, Godard manipulates images until to reveal us their secret power structure
Lo sguardo smarrito: riflessioni intorno a Il grido di Michelangelo Antonioni.
L’articolo intende dimostrare il ruolo centrale che Il grido ha nell’evoluzione stilistica del cinema di Antonioni. La prima parte si sofferma sul tema del viaggio di Aldo che si lega saldamente ad una destrutturazione del paesaggio tale da impedire ai personaggi – e allo spettatore – di orientarsi al suo interno. Il tema dell’indebolimento della visione, dello sguardo sia dei personaggi che dello spettatore viene poi, nella seconda parte, analizzato sistematicamente con riferimento ad alcune sequenze del film.This paper aims to emphasize the crucial role played by Il grido in the development of Antonioni’s filmstyle. The first part is focused on Aldo’s absurd journey throughout the Po Valley, strictly tied to adeconstruction of the landscape. This narrative and stylistic choice prevents characters – and viewersas well – from orienting themselves within such a landscape and journey. This lack of vision and gaze,both related to characters and viewers, is systematically analyzed in the second part of the paper,referring to some sequences from the movie
How can cells count? Robustness in self-assembly pathways
Cells are characterised by different kinds of structures, organelles, each of them with a specific function. In some cases, in order to perform its task, an organelle needs to have some precise features, lika a location, or shape, size and requires to be present in an exact number. Some of these features can't be directly encoded in DNA itself and they are controlled by other means.
The present work addresses the poorly understood problem of how cells can count. More precisely, what mechanisms are used by the cell in order to control and constrain the number of structures it needs. In order to do so, this thesis starts by considering the flagellum, a structure that allows the cell to move in its environment, and analyses its self-assembly pathway traying to figure out what the purpose of each step of the process is in making the "counting mechanism" robust to initial resources number variations and stochastic fluctuations.ope
Miracle: the multi-interface cross-layer extension of ns2
We present Miracle, a novel framework which extends ns2 to facilitate the simulation and the design of beyond 4G networks. Miracle enhances ns2 by providing an efficient and embedded engine for handling cross-layer messages and, at the same time, enabling the coexistence of multiple modules within each layer of the protocol stack. We also present a novel framework developed as an extension of Miracle called Miracle PHY and MAC. This framework facilitates the development of more realistic Channel, PHY and MAC modules, considering features currently lacking in most state-of-the-art simulators, while at the same time giving a strong emphasis on code modularity, interoperability and reusability. Finally, we provide an overview of the wireless technologies implemented in Miracle, discussing in particular the models for the IEEE 802.11, UMTS and WiMAX standards and for Underwater Acoustic Networks. We observe that, thanks to Miracle and its extensions, it is possible to carefully simulate complex network architectures at all the OSI layers, from the physical reception model to standard applications and system management schemes. This allows to have a comprehensive view of all the interactions among network components, which play an important role in many research areas, such as cognitive networking and cross-layer design
Probabilistic load forecasting with Reservoir Computing
Some applications of deep learning require not only to provide accurate
results but also to quantify the amount of confidence in their prediction. The
management of an electric power grid is one of these cases: to avoid risky
scenarios, decision-makers need both precise and reliable forecasts of, for
example, power loads. For this reason, point forecasts are not enough hence it
is necessary to adopt methods that provide an uncertainty quantification.
This work focuses on reservoir computing as the core time series forecasting
method, due to its computational efficiency and effectiveness in predicting
time series. While the RC literature mostly focused on point forecasting, this
work explores the compatibility of some popular uncertainty quantification
methods with the reservoir setting. Both Bayesian and deterministic approaches
to uncertainty assessment are evaluated and compared in terms of their
prediction accuracy, computational resource efficiency and reliability of the
estimated uncertainty, based on a set of carefully chosen performance metrics
Explainability in subgraphs-enhanced Graph Neural Networks
Recently, subgraphs-enhanced Graph Neural Networks (SGNNs) have been
introduced to enhance the expressive power of Graph Neural Networks (GNNs),
which was proved to be not higher than the 1-dimensional Weisfeiler-Leman
isomorphism test. The new paradigm suggests using subgraphs extracted from the
input graph to improve the model's expressiveness, but the additional
complexity exacerbates an already challenging problem in GNNs: explaining their
predictions. In this work, we adapt PGExplainer, one of the most recent
explainers for GNNs, to SGNNs. The proposed explainer accounts for the
contribution of all the different subgraphs and can produce a meaningful
explanation that humans can interpret. The experiments that we performed both
on real and synthetic datasets show that our framework is successful in
explaining the decision process of an SGNN on graph classification tasks
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