6,198 research outputs found
On the variational modeling of non-associative plasticity
No full textsponsorship: R. Alessi acknowledges the Italian Ministry of Education, University and Research (MIUR) under the PRIN 2017 20177TTP3S grant. (Italian Ministry of Education, University and Research (MIUR) under the PRIN 2017|20177TTP3S)status: Publishe
The maze of languages in Aosta Valley (Italy)
No full textThe article analyses linguistic rights in Aosta Valley, abandoning the already well-trodden path of pure legal description of legal safeguards to highlight the concrete effectiveness and limits of the measures hitherto provided for by the legal system, by means of a multidisciplinary approach. Accordingly, after a description of the constitutional-legal framework, which provides for an Italian French bilingual system and for a weaker protec- tion of other languages, legal categories are compared with concrete reality of language practice, showing the existing cleavage between them. The paper then focuses on the causes of the current situation and their consequences on social representation of languages, high- lighting the role played by the political ethnic discourse. Finally, some suggestions are drawn in order to find a way out of what can be rightly defined as a maze
Audiomobiles, Sculptures and Conundrums
No full textRoberto Gerhard was a pioneer of electronic music in England creating a number of substantial concert, theatre and radio works from as early as 1954. Gerhard’s electronic music is one of the richest repositories for understanding the development of the composer’s late compositional technique. Apart from the Symphony no.3, ‘Collages’, none of Gerhard’s electronic music is published. This paper will discuss aspects of Gerhard’s electronic music, focusing on Audiomobiles (1958-59) and Sculptures (1963)
Energetic formulation for rate-independent processes: remarks on discontinuous evolutions with a simple example
No full textAnalysis of localization phenomena in Shape Memory Alloys bars by a variational approach
No full textLocalization of the phase transformations in Shape Memory Alloys (SMA) wires are well known. Several experimental and theoretical studies appeared in the last years. In this work the problem is addressed by means of a variational approach within the framework of the modeling of rate-independent materials by the specification of a non-local free energy and a dissipation function, focusing attention on the basic case of isothermal conditions. General expressions are given for a rather broad class of models, whereas a simple model is studied in detail. A full stability analysis of both homogeneous and non-homogeneous solutions is carried out analytically, showing that stable non-homogeneous solutions have necessarily to occur if the bar is longer than an internal length determined by the constitutive parameters. The analysis also shows that snap-back phenomena may occur both in the nucleation and the coalescence phase, depending on another material length which is also function of the number of transformation fronts. This helps to explain why the second stress drop associated to coalescence is much more difficult to observe experimentally. Closed form expressions are given for the phase fraction profiles of both single and multiple localizations as well as nucleation and propagation stresses. A comparison between the prediction of the model with experimental data finally shows a good agreement both in terms of global response and in the spatio-temporal evolution of the transformation domains
Roberto Gerhard’s Sound Compositions: A Historical-Philological Perspective. Archive, Process, Intent and reenactment
No full textThis research advances the current state of knowledge in the field of early tape music both empirically and methodologically. The purpose of this study is to evaluate the impact that the electronic medium exerted in the musical thinking of Roberto Gerhard, one of the most outspoken, prolific and influential composers in the Spanish diaspora whose musical legacy, for the most part unknown, is a major landmark in the early history of electroacoustic music. Gerhard’s personal tape collection, one of the largest historical archives of its kind reported in the literature, is exceptional for both its antiquity (50+-year-old tapes) and its abundance of production materials. Through the digitisation and analysis of the composer’s tape collection this research argues that the empirical study of audio documents sets out a basis for a broader understanding of textual processes. More specifically, the research demonstrates that the reconstruction of works based on magnetic tape sketches is a powerful method to advance the understanding of early tape music. This research also examines Gerhard’s sound compositions in relation to the post-war context in which they were composed. Finally, this research presents performance documentation that proposes an approach to the electroacoustic music repertoire in which creativity is not at odds with rigor and critical discernment demonstrating that archival study can be closely aligned to the concept of re-enactment
Anatomy of a Sovereign Debt Crisis: CDS Spreads and Real-Time Macroeconomic Data
No full textWe construct a unique and comprehensive data set of 19 real-time daily macroeconomic indicators for 11 Eurozone countries, for the 5/11/2009{4/25/2013 period. We use this new data set to characterize the time-varying dependence of the cross-section of sovereign credit default swap (CDS) spreads on country-specific macro indicators. We employ daily Fama-MacBeth type cross-sectional regressions to produce time-series of macro-sensitivities, which are then used to identify risk regimes and forecast future equity market volatility. We document pronounced time-variation in the macro-sensitivities, consistent with the notion that market participants focused on very different macro indicators at the different times of the crisis. Second, we identify three distinct crisis risk regimes, based on the general level of CDS spreads, the macro-sensitivities, and the GIPSI connotation. Third, we document the predictive power of the macro-sensitivities for future option-implied equity market volatility, consistent with the notion that expected future risk aversion is an important driver of how CDS spreads impound macro information
Filologia editoriale, Roberto Calasso in dialogo con Paola Italia e Francisco Rico
No full textPaola Italia e Francisco Rico intervengono sul libro di Roberto Calasso, presidente e fondatore di Adelphi Edizioni, L'impronta dell'editore, e discutono di problemi di filologia delle forme editoriali, dal punto di vista dell'autore, del lettore e dell'editore.Paola Italia and Francisco Ricos interview Roberto Calasso, Publisher, Writer, and Founder of Adelphi Edizioni, about his book: L'impronta dell'editore, talking about philology, publishing and editing, from the author, the reader and the publisher's point of view
Variational Approach to Fracture Mechanics with Plasticity
No full textIn the framework of rate-independent systems, an elastic-plastic-damage model, aimed at the description of ductile fracture processes, is proposed and investigated through a variational formulation.
A cohesive, or ductile, crack occurs when the displacement field suffers a discontinuity whilst still being associated to a non-vanishing tensile stress.
To predict and effectively describe ductile fracture phenomena is a crucial task for many engineering materials (metals, polymers, ...), as testified by the great interest of the scientific community on the subject.
Gradient damage models have been fruitfully used for the description of brittle fractures: in such cases, once the damage level reaches its maximum value, a crack is created where the traction between the two opposite lips immediately drops to zero. On the other hand, the perfect plasticity model could describe the formation of plastic slips at constant stress level.
Hence, in order to describe the typical effects of a cohesive fracture, the main idea is to couple, through a variational approach, the perfect plasticity model and a softening gradient damage model.
The use of a variational approach results in a weak and derivative-free formulation, gives effective means to deal with the concepts of bifurcation and stability, is intrinsically discrete and indicates a natural and rational way to define efficient numerical algorithms.
Embedding damage effects in a plasticity model is not a new idea. Nevertheless the proposed model presents many original aspects as the coupling between plasticity and damage and the way the governing equations of the variables are found. The variational approach relies simply on three concepts: the irreversibility condition, a global, local or differential stability condition and the energy balance.
The resulting model possesses a great flexibility in the possible coupled responses, depending on the constitutive parameters.
These various responses are first considered by investigating in a one-dimensional quasi-static traction bar test a homogeneous evolution which highlights the main features of the model. The discussion about the stability of the homogeneous solutions leads to the existence of a critical bar length which in turn depends on the characteristic internal material length. For bars that are longer than this critical value the homogeneous response is proven to become unstable and a localization must appear.
A construction of localization is then proposed which explicitly takes into account the irreversibility condition on the damage field. This allows the non-homogeneous evolution and the global response to be investigated.
It turns out that in general a cohesive crack appears at the center of the damage zone before the complete rupture.
At this point the plastic strain localises as a Dirac measure which becomes responsible for this cohesive crack.
The associated cohesive law is obtained in a closed form in terms of the parameters of the model and it recovers the cohesive fracture law postulated by Barenblatt.
Finally, a numeric resolution scheme is proposed, which is based on an alternate minimization algorithm, and implemented through a finite element library only for the one-dimensional traction bar test. Although the adopted finite element spaces do not embed discontinuities, the numeric results agree perfectly with the analytic solutions. This is due to a kind of numeric regularisation. Nevertheless, future developments aim to extend the simulations in a two/three-dimensional setting and test a generalized finite element method.Bando Vinc
A phenomenological approach to fatigue with a variational phase-field model: The one-dimensional case
No full textWe propose a new variational fatigue phase-field model. The basic idea of the model is to let the fracture energy decrease as a suitably defined accumulated strain measure increases, which is obtained by introducing a dissipation potential which explicitly depends on the strain history. This amounts to a phenomenological description of a multitude of microscopic material degradation mechanisms, that are responsible for the macroscopic evidence of fatigue effects. In this first step of a longer term project, the analysis is limited to the simplest possible setting, namely: linear elasticity, brittle material behavior, symmetric response in tension and compression. However, in this variational framework, the extension to include additional material phenomena, such as plasticity, is straightforward. We show the results of numerical simulations based on a solution strategy devised from the variational approach. Already with the choice of simple constitutive functions, based on few key constitutive parameters, the present model is capable to describe typical σ-N (Wöhler) curves, to recover the known trends in the description of the mean-stress effects and to account for generic loads in a straightforward manner
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