1,103 research outputs found
Quasi locality of the GGE in interacting-to-free quenches in relativistic field theories
We study the quench dynamics in continuous relativistic quantum field theory,
more specifically the locality properties of the large time stationary state.
After a quantum quench in a one-dimensional integrable model, the expectation
values of local observables are expected to relax to a Generalized Gibbs
Ensemble (GGE), constructed out of the conserved charges of the model.
Quenching to a free bosonic theory, it has been shown that the system indeed
relaxes to a GGE described by the momentum mode occupation numbers. We first
address the question whether the latter can be written directly in terms of
local charges and we find that, in contrast to the lattice case, this is not
possible in continuous field theories. We then investigate the less stringent
requirement of the existence of a sequence of truncated local GGEs that
converges to the correct steady state, in the sense of the expectation values
of the local observables. While we show that such a sequence indeed exists, in
order to unequivocally determine the so-defined GGE, we find that information
about the expectation value of the recently discovered quasi-local charges is
in the end necessary, the latter being the suitable generalization of the local
charges while passing from the lattice to the continuum. Lastly, we study the
locality properties of the GGE and show that the latter is completely
determined by the knowledge of the expectation value of a countable set of
suitably defined quasi-local charges
Non-Equilibrium Steady State generated by a moving defect: the supersonic threshold
We consider the dynamics of a system of free fermions on a 1D lattice in the
presence of a defect moving at constant velocity. The defect has the form of a
localized time-dependent variation of the chemical potential and induces at
long times a Non-Equilibrium Steady State (NESS), which spreads around the
defect. We present a general formulation which allows recasting the
time-dependent protocol in a scattering problem on a static potential. We
obtain a complete characterization of the NESS. In particular, we show a strong
dependence on the defect velocity and the existence of a sharp threshold when
such velocity exceeds the speed of sound. Beyond this value, the NESS is not
produced and remarkably the defect travels without significantly perturbing the
system. We present an exact solution for a like defect traveling with
an arbitrary velocity and we develop a semiclassical approximation which
provides accurate results for smooth defects.Comment: 18 pages, 13 figure
A Partition-Based Implementation of the Relaxed ADMM for Distributed Convex Optimization over Lossy Networks
In this paper we propose a distributed implementation of the relaxed
Alternating Direction Method of Multipliers algorithm (R-ADMM) for optimization
of a separable convex cost function, whose terms are stored by a set of
interacting agents, one for each agent. Specifically the local cost stored by
each node is in general a function of both the state of the node and the states
of its neighbors, a framework that we refer to as `partition-based'
optimization. This framework presents a great flexibility and can be adapted to
a large number of different applications. We show that the partition-based
R-ADMM algorithm we introduce is linked to the relaxed Peaceman-Rachford
Splitting (R-PRS) operator which, historically, has been introduced in the
literature to find the zeros of sum of functions. Interestingly, making use of
non expansive operator theory, the proposed algorithm is shown to be provably
robust against random packet losses that might occur in the communication
between neighboring nodes. Finally, the effectiveness of the proposed algorithm
is confirmed by a set of compelling numerical simulations run over random
geometric graphs subject to i.i.d. random packet losses.Comment: Full version of the paper to be presented at Conference on Decision
and Control (CDC) 201
Asynchronous Distributed Optimization over Lossy Networks via Relaxed ADMM: Stability and Linear Convergence
In this work we focus on the problem of minimizing the sum of convex cost
functions in a distributed fashion over a peer-to-peer network. In particular,
we are interested in the case in which communications between nodes are prone
to failures and the agents are not synchronized among themselves. We address
the problem proposing a modified version of the relaxed ADMM, which corresponds
to the Peaceman-Rachford splitting method applied to the dual. By exploiting
results from operator theory, we are able to prove the almost sure convergence
of the proposed algorithm under general assumptions on the distribution of
communication loss and node activation events. By further assuming the cost
functions to be strongly convex, we prove the linear convergence of the
algorithm in mean to a neighborhood of the optimal solution, and provide an
upper bound to the convergence rate. Finally, we present numerical results
testing the proposed method in different scenarios.Comment: To appear in IEEE Transactions on Automatic Contro
Generalized hydrodynamics of classical integrable field theory: the sinh-Gordon model
Using generalized hydrodynamics (GHD), we develop the Euler hydrodynamics of
classical integrable field theory. Classical field GHD is based on a known
formalism for Gibbs ensembles of classical fields, that resembles the
thermodynamic Bethe ansatz of quantum models, which we extend to generalized
Gibbs ensembles (GGEs). In general, GHD must take into account both solitonic
and radiative modes of classical fields. We observe that the quasi-particle
formulation of GHD remains valid for radiative modes, even though these do not
display particle-like properties in their precise dynamics. We point out that
because of a UV catastrophe similar to that of black body radiation, radiative
modes suffer from divergences that restrict the set of finite-average
observables; this set is larger for GGEs with higher conserved charges. We
concentrate on the sinh-Gordon model, which only has radiative modes, and study
transport in the domain-wall initial problem as well as Euler-scale
correlations in GGEs. We confirm a variety of exact GHD predictions, including
those coming from hydrodynamic projection theory, by comparing with Metropolis
numerical evaluations.Comment: 41 pages, 9 figure
Lack of thermalization for integrability-breaking impurities
We investigate the effects of localized integrability-breaking perturbations
on the large times dynamics of thermodynamic quantum and classical systems. In
particular, we suddenly activate an impurity which breaks the integrability of
an otherwise homogeneous system. We focus on the large times dynamics and on
the thermalization properties of the impurity, which is shown to have mere
perturbative effects even at infinite times, thus preventing thermalization.
This is in clear contrast with homogeneous integrability-breaking terms, which
display the prethermalization paradigm and are expected to eventually cause
thermalization, no matter the weakness of the integrability-breaking term.
Analytic quantitative results are obtained in the case where the bulk
Hamiltonian is free and the impurity interacting.Comment: 21 pages, 6 figure
Multi-Sensoriality In Language Acquisition: The Relationship Between Selective Visual Attention Towards The Adultâs Face And Language Skills
Introduzione Le componenti uditive e visive del linguaggio offrono al bambino informazioni cruciali per il processamento del parlato. LâabilitĂ del bambino di integrare informazioni da diverse fonti multimodali (audio e visive) e di focalizzare lâattenzione sui segnali rilevanti presenti nellâambiente circostante (selective visual attention) sono aspetti importanti che influenzano le prime fasi di acquisizione di una lingua. Alcuni recenti studi hanno ipotizzato e testato la relazione tra attenzione selettiva visiva verso specifiche aree del volto parlante (occhi o bocca) e le abilitĂ linguistiche di bambini nei primi anni di vita. Molti ricercatori hanno speculato su come questa relazione potesse essere mediata dal livello di expetise del bambino, a livello linguistico (language expertise hypothesis), ma nessuno studio, fin ad ora, ha cercato di approfondire questa ipotesi, andando ad investigare le abilitĂ linguistiche dei bambini usando misure di linguaggio spontaneo. Altri studi, hanno cercato di esplorare come diversi comportamenti attentivi verso specifiche aree del volto (occhi o bocca) fossero correlati alle abilitĂ linguistiche concomitanti o longitudinali dei partecipanti. In molti casi, i risultati di questi studi hanno confermato lâesistenza di relazioni significative tra attenzione visiva selettiva e abilitĂ linguistiche al tempo dellâesperimento o qualche mese dopo. Obiettivi Lâobiettivo generale di questa tesi è quello di esaminare il fenomeno dellâattenzione selettiva visiva verso il volto e la sua relazione con lo sviluppo del linguaggio sia in un setting di laboratorio sia in un contesto naturalistico. In particolare, tre sono gli obiettivi specifici: - il primo obiettivo specifico è quello di sintetizzare e analizzare i fattori individuati dalla letteratura di riferimento che possono determinare diversi patterns di attenzione selettiva visiva nei bambini durante un compito audiovisivo. Ed in particolare, descrivere come la letteratura spiega questi patterns in relazione agli aspetti dello sviluppo del linguaggio; 8 - il secondo obiettivo specifico è quello di analizzare sperimentalmente lâattenzione selettiva visiva del bambino verso specifiche aree del volto (occhi e bocca) durante un compito di esposizione audiovisivo. In particolare, lo studio è volto ad indagare due aspetti. Il primo aspetto riguarda lâetĂ e la condizione linguistica (esposizione ad una lingua nativa vs una lingua non nativa) dei partecipanti e come queste influenzano lâattenzione selettiva visiva verso specifiche aree del volto. Il secondo aspetto riguarda lâesplorazione dellâesistenza di una correlazione tra comportamento attentivo dei bambini la produzione vocale al tempo dellâesperimento e allâampiezza del vocabolario tre mesi dopo; - il terzo obiettivo specifico è quello di capire se lâattenzione a volti o altre parti della scena visiva (oggetto, altre parti della stanza) è influenzato o spigato dalle abilitĂ vocali del bambino al tempo del task e se gli episodi di fissazione al volto adulto possono essere predetti da specifiche proprietĂ fonologiche e semantiche del parlato del bambino. Metodo Per quanto concerne il primo studio, una rassegna sistematica della letteratura è stata condotta esplorando quattro fonti bibliografiche e usando specifici criteri di inclusione per selezionare la letteratura scientifica di interesse. Per quanto riguarda il secondo studio, i movimenti oculari verso un volto parlante la lingua nativa (Italiano) e non-nativa (Inglese) di 26 bambini tra i 6 e i 14 mesi sono stati tracciati usando lâeye tracker. Due gruppi sono stati creati sulla base dellâetĂ (G1, M = 7 mesi, N = 15 bambini; G2, M = 12 mesi, N = 11 bambini). Ogni competenza linguistica del bambino è stata valutata due volte, al tempo dellâesperimento, attraverso lâosservazione diretta e tre mesi dopo, attraverso il MB-CDI. Due gruppi sono stati creati sulla base della produzione vocale dei bambini (vocalizzi pre-canonici, babbling, parole) attraverso un latent class cluster analysis: una classe vocale âaltaâ (percentuale di babbling e parole piĂš alta) e una classe vocale âbassaâ (percentuale maggiore di produzioni pre-canoniche). Per quanto concerne il terzo studio, il comportamento attentivo di 29 bambini tra i 12 e i 19 mesi è stato esplorato utilizzando sia una videocamera stazionaria 9 (posizionata di fronte alla diade) e una go-pro (posizionata sulla fronte del caregiver di riferimento) durante un semplice task linguistico (single object task). Durante il task i bambini sono stati esposti ad un set di stimoli audiovisivi, parole vere e non parole, scelte sulla base dei report dei genitori e sulle risposte al MB-CDI. Il comportamento attentivo dei bambini è stato codificato offline, secondo per secondo per un totale di 116 sessioni. La codifica ha riguardato specifiche aree di interesse (il volto, lâoggetto, o altre parti della stanza). La produzione vocale per ogni bambino è stata quantificata usando LENA e le produzioni del bambino (vocalizzi pre-canonici, babbling, parole) durante un periodo di gioco con la mamma sono state trascritte foneticamente. Risultati La rassegna sistematica della letteratura (Capitolo 2) ha portato allâidentificazione di 19 articoli. Alcuni dei quali volti a chiarire il ruolo giocato da diversi fattori nel spiegare diversi patterns attentivi. Altri interessati ad indagare la correlazione tra lâattenzione selettiva visiva verso specifiche aree del volto alle competenze linguistiche o sociali dei partecipanti, aprendo le porte a diverse linee interpretative. Il primo studio empirico (Capitolo 3) ha messo in luce che i bambini italiani con etĂ superiore ai 12 mesi, mostrano maggiore interesse verso lâarea della bocca, specialmente quando esposti alla lingua nativa. Questo è in accordo con la recente letteratura, ma contrasta con la language expertise hypotesis (secondo la quale bambini attorno allâanno di etĂ dovrebbero spostare il focus attentivo dalla bocca agli occhi). Il secondo risultato emerso in questo lavoro empirico riguarda lâinteresse verso lâarea della bocca per i bambini che hanno maggiori livelli di produzione in termini di babbling e parole al tempo dellâesperimento. Il terzo risultato riguarda lâassociazione positiva tra il comportamento attentivo verso la bocca ed il vocabolario espressivo dei bambini misurato tramite questionario (MB-CDI) tre mesi dopo lâesperimento. Dal secondo studio empirico (Capitolo 4) emerge una differenza significativa in termini di tempo attentivo verso il volto adulto tra i bambini del gruppo linguistico âaltoâ e âbassoâ durante un task condotto in un contesto naturalistico. 10 In particolare, da questo studio emergono due risultati interessanti: il primo è che i bambini che producono forme vocaliche piĂš avanzate (babbling e parole) guardano di piĂš verso il volto adulto, specialmente quando esposti alle non-parole. Il secondo riguarda lâesistenza di una relazione significativa tra gli episodi di fissazione al volto e le abilitĂ vocaliche del bambino al tempo del task (vocalizzi pre-canonici, babbling e parole). In particolare, emerge che la quantitĂ di babbling prodotto ha un ruolo nel predire gli episodi di fissazione al volto durante il task, sia per le parole sia per le non parole. Conclusioni Diverse ipotesi linguistiche e sociali sono state avanzate per spiegare le differenze emerse dalla rassegna della letteratura in relazione al fenomeno dellâattenzione selettiva visiva. Gli studi empirici presentati in questa tesi hanno portato due contributi originali in questâambito di ricerca. Da un lato, i nostri risultati confermano lâidea che la bocca e, piĂš in generale, il volto forniscono segnali visivi cruciali nelle prime fasi di acquisizione del linguaggio. Dallâaltro lato, i risultati hanno messo in luce che la conoscenza linguistica e le abilitĂ linguistiche dei partecipanti aiutano a spiegare diversi comportamenti attentivi. In altre parole, è possibile dire che lâattenzione selettiva ai volti, o a specifiche aree di questi, è spiegata dalle conoscenze e abilitĂ linguistiche attuali dei partecipanti.Introduction Speech is the result of multimodal or multi-sensorial processes. The auditory and visual components of language provide the child with information crucial to the processing of speech. The language acquisition process is influenced by the childâs ability to integrate information from multimodal (audio and visual) sources and to focus attention on the relevant cues in the environment; this is selective visual attention. This dissertation will explore the relationship between childrenâs selective visual attention and their early language skills. Several recent studies with infant populations have hypothesised or tested the relationship between childrenâs selective visual attention towards specific regions of the talking face (i.e., the eyes or the mouth) and their language skills. These studies have tried to show how concomitant or longitudinal language skills can explain looking behaviours. In most cases, these studies have speculated on how this relationship is mediated by the childâs level of language expertise (this is known as the language expertise hypothesis). However, no studies until now, to the best of our knowledge, have investigated the childâs linguistic skills using spontaneous language measures. Aims The dissertation has one broad aim, within which there are three particular aims. The broad aim is to examine the phenomenon of selective visual attention toward the face in both a laboratory and a naturalistic setting, and its relationship with language development. The three particular aims are as follows. The first aim is to synthesise and analyse the factors that might determine different looking patterns in infants during audiovisual tasks using dynamic faces; it describes how the literature explains these patterns in relation to aspects of language development. The second aim is to experimentally investigate the childâs selective visual attention towards a specific region of the adultâs face (the eyes and the mouth) in a task using the eye-tracking method. In particular, the study will explore two 12 questions: First, how do age and language condition (exposure to native vs non-native speech) affect looking behaviour in children? Second, are a childâs looking behaviours related to vocal production at the time of the experiment and to vocabulary rates three months later, and if so, how? The third aim is to understand whether selective attention towards the face or other parts of the visual scene (i.e. the object or elsewhere) is influenced or explained by the childâs vocal skills at the time of the task. And can the episodes of fixation towards the adultâs face be predicted by specific phonological and semantic properties (i.e., pre-canonical vocalisations, babbling, words) of the childâs speech? Method For the first study, a systematic review of the literature was conducted, exploring four bibliographic databases and using specific inclusion criteria to select the records. For the second study, eye movements towards a dynamic face (on a screen), speaking in the childâs native language (Italian) and a non-native language (English), were tracked using an eye-tracker in 26 infants between 6 and 14 months. Two groups were created based on age (G1, M = 7 months, N = 15 infants; G2, M = 12 months, N = 11 infants). Each childâs language skill was assessed twice: at the time of the experiment (through direct observation, Time 1) and three months later (through MB-CDI, Time 2). Two groups were created, based on the childâs vocal production (Time 1, latent class cluster analysis): a high class (higher percentage of babbling and words) vs a low class (higher percentage of pre-canonical vocalisations). For the third study, the looking behaviour of the same 29 children between 12 and 19 months was tracked, using both a stationary video camera and a head-mounted camera on the motherâs head during a single object task. During the task, children were exposed to a set of audiovisual stimuli, real words and non-words, chosen based on the parentsâ reports and their MB-CDI answers. The childâs looking behaviour was coded offline second-by-second for a total of 116 sessions. The coding relates to specific areas of interest, i.e., the face, the object or 13 elsewhere. The vocal production of each child was quantified using a LENA device, and their speech during a play period with their mothers was transcribed phonetically. Results The systematic search of the literature (Chapter 2) identified 19 papers. Some tried to clarify the role played by audiovisual factors in support of speech perception (provided by looking towards the eyes or the mouth of a talking face). Others related selective visual attention towards specific areas of the adultâs face to the childâs competence in terms of linguistic or social skills, this leads to correspondingly different lines of interpretation. The first empirical study (Chapter 3) shows that Italian children older than 12 months displayed a greater interest in the mouth area, especially when they were exposed to their native language. This accords with the more recent literature but contrasts with the language expertise hypothesis. The second significant result of Chapter 3 is that children who had a higher level of production in terms of babbling and words at the time of the experiment looked more towards the mouth area. The study reported in Chapter 3 also demonstrated a positive association between the childâs looking to the mouth and their expressive vocabulary as measured (using the MB-CDI) three months after the experiment The second empirical study (Chapter 4) shows a significant difference in the looking time towards the adultâs face between children with low- and high-vocal production in a naturalistic setting. More specifically, from this study, we find two things. Firstly, we found that the children who produced more advanced vocal forms (higher amount of babbling and word production) looked more towards the adultâs face, especially when exposed to non-words. Secondly, that a significant relationship exists between the episodes of fixation towards the adultâs face and the childâs vocal skills (i.e., pre-canonical vocalisations, babbling, words); babbling productions predicted the episodes of face fixation in the task as a whole, for both words and non-words. 14 Conclusion Linguistic and social-based hypotheses attempting to explain the differences in the selective visual attention phenomenon emerged from the literature review. The empirical studies presented in this thesis bring two original contributions to this research field. First, our findings reinforce the idea that the mouth and, more generally the face, provide crucial visual cues when acquiring a language. Secondly, our results demonstrate that language knowledge and language skills at the time the child was observed significantly help to explain different looking behaviours. In other words, we can conclude that each childâs attention to faces is shaped by their own linguistic characteristics
Sound Generation using GAN Models
openIn recent years, there has been a noticeable increase in the use of artificial intelligence for the generation of audio files. This master thesis presents a comprehensive approach to sound generation, incorporating the utilization of multiple GAN models and post-processing techniques to generate diverse samples of different duration.
In particular, some of the GAN models used include SpecGAN, Catch-A-Waveform (CAW) and UNAGAN. The proposed pipeline consists of the following components:
- SpecGAN, employed to generate one-second inharmonic samples.
- UNAGAN, used to generate variable-length harmonic samples.
- Post-processing, applied to minimize the amount of noise in the generated samples.
- Post-processing and the utilization of CAW for concatenating and inpainting multiple samples generated with SpecGAN or UNAGAN.
- CAW, which, starting from a single reference sample, is used to generate longer and cleaner samples.
Experiments were conducted using both harmonic and inharmonic sound datasets.
The results demonstrated that this pipeline allows for the generation of variable-length sounds, both harmonic and inharmonic, with quality comparable to that of real samples.In recent years, there has been a noticeable increase in the use of artificial intelligence for the generation of audio files. This master thesis presents a comprehensive approach to sound generation, incorporating the utilization of multiple GAN models and post-processing techniques to generate diverse samples of different duration.
In particular, some of the GAN models used include SpecGAN, Catch-A-Waveform (CAW) and UNAGAN. The proposed pipeline consists of the following components:
- SpecGAN, employed to generate one-second inharmonic samples.
- UNAGAN, used to generate variable-length harmonic samples.
- Post-processing, applied to minimize the amount of noise in the generated samples.
- Post-processing and the utilization of CAW for concatenating and inpainting multiple samples generated with SpecGAN or UNAGAN.
- CAW, which, starting from a single reference sample, is used to generate longer and cleaner samples.
Experiments were conducted using both harmonic and inharmonic sound datasets.
The results demonstrated that this pipeline allows for the generation of variable-length sounds, both harmonic and inharmonic, with quality comparable to that of real samples
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