3499 research outputs found
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Modelling and analyzing adaptive self-assembling strategies with Maude
No full textBuilding adaptive systems with predictable emergent behavior is a challenging task and it is becoming a critical need. The research community has accepted the challenge by introducing approaches of various nature: from software architectures, to programming paradigms, to analysis techniques. We recently proposed a conceptual framework for adaptation centered around the role of control data. In this paper we show that it can be naturally realized in a reflective logical language like Maude by using the Reflective Russian Dolls model. Moreover, we exploit this model to specify, validate and analyse a prominent example of adaptive system: robot swarms equipped with self-assembly strategies. The analysis exploits the statistical model checker PVeStA
Systemic risk and banking regulation: some facts on the new regulatory framework
No full textThe recent financial crisis highlighted the relevant role of the systemic effects of banks’ defaults on the stability of the whole financial system. In this work we draw an organic picture of the current regulations, moving from the definitions of systemic risk to the issues concerning data availability. We show how a more detailed flow of data on traded deals might shed light on some systemic risk features
taken into account only partially in the past. In particular, we analyse how the new regulatory framework allows regulators to describe OTC derivatives markets according to more detailed partitions, thus depicting a more realistic picture of the system. Finally, we suggest to study submarkets illiquidity conditions to consider possible spill over effects which might lead to a worsening
for the entire system
Robust local–global SOM-based ACM
No full textA novel active contour model (ACM) for image segmentation, driven by both local and global image-intensity information encoded by a self-organising map (SOM), is proposed. Experimental results demonstrate the robustness of the proposed model to the contour initialisation and to the additive noise, when compared with the state-of-the-art local and global ACMs. They also demonstrate its robustness to scene changes
CaSPiS: a calculus of sessions, pipelines and services
No full textService-oriented computing is calling for novel computational models and languages with well-disciplined primitives for client–server interaction, structured orchestration and unexpected events handling. We present CaSPiS, a process calculus where the conceptual abstractions of sessioning and pipelining play a central role for modelling service-oriented systems. CaSPiS sessions are two-sided, uniquely named and can be nested. CaSPiS pipelines permit orchestrating the flow of data produced by different sessions. The calculus is also equipped with operators for handling (unexpected) termination of the partner's side of a session. Several examples are presented to provide evidence of the flexibility of the chosen set of primitives. One key contribution is a fully abstract encoding of Misra et al.'s orchestration language Orc. Another main result shows that in CaSPiS it is possible to program a ‘graceful termination’ of nested sessions, which guarantees that no session is forced to hang forever after the loss of its partner
Archivi d'impresa a Genova
No full textOltre tre secoli di storia della città di Genova sopravvivono tra le seppiate carte e testimonianze di cento e più archivi d’impresa.
Il volume, esito di un articolato lavoro di studio e ricerca sul campo, propone il censimento di 112 aziende storiche del capoluogo ligure fondate tra il Seicento e il Novecento e operanti nei diversi settori produttivi e merceologici, offrendo uno spaccato unico ed esemplare di una stagione di vivace fermento culturale ed imprenditoriale.
Corredano ed arricchiscono l’opera un denso repertorio iconografico e un ricco apparato bibliografico
Longevity assets and pre-retirement consumption/portfolio decisions
No full textWe derive a closed form solution for the optimal consumption/investment problem of an agent whose force of mortality is stochastic and whose financial horizon coincides with a fixed retirement date. The investment set includes a longevity asset, as a derivative on the force of mortality. We explore the optimal choices of a representative agent having Hyperbolic Absolute Risk Aversion preferences on both consumption and final
wealth. Our numerical analysis shows that individuals optimally invest a large fraction of their wealth in the longevity asset. In our base scenario, calibrated on real world data, a 60-year old male retiring after 5 years should invest around 88% of his wealth in the longevity asset. Such a percentage decreases as time to retirement decreases. We explore sensitivity of our results to market and individual characteristics
Robust model predictive control for discrete-time fractional-order systems
No full textIn this paper we propose a tube-based robust model predictive control scheme for fractional-order discrete-time systems of the Grunwald-Letnikov type with state and input constraints. We first approximate the infinite-dimensional
fractional-order system by a finite-dimensional linear system
and we show that the actual dynamics can be approximated
arbitrarily tight. We use the approximate dynamics to design
a tube-based model predictive controller which endows to the
controlled closed-loop system robust stability properties
Revisiting bisimilarity and its modal logic for nondeterministic and probabilistic processes
No full textThe logic PML is a probabilistic version of Hennessy–Milner logic introduced by Larsen and Skou to characterize bisimilarity over probabilistic processes without internal nondeterminism. In this paper, two alternative interpretations of PML over nondeterministic and probabilistic processes as models are considered, and two new bisimulation-based equivalences that are in full agreement with those interpretations are provided. The new equivalences include as coarsest congruences the two bisimilarities for nondeterministic and probabilistic processes proposed by Segala and Lynch. The latter equivalences are instead known to agree with two versions of Hennessy–Milner logic extended with an additional probabilistic operator interpreted over state distributions in place of individual states. The new interpretations of PML and the corresponding new bisimilarities are thus the first ones to offer a uniform framework for reasoning on processes that are purely nondeterministic or reactive probabilistic or that mix nondeterminism and probability in an alternating/nonalternating way
Auxetic anti-tetrachiral materials: equivalent elastic properties and frequency band-gaps
No full textA comprehensive characterization of the novel class of anti-tetrachiral cellular solids, both considering the static and the dynamic response, is provided in the paper. The heterogeneous material is characterized by a periodic microstructure made of equi-spaced rings each interconnected by four ligaments. In the most general case, rings and ligaments are surrounded by a softer matrix and the rings can be filled by a different material. First, the first order linear elastic homogenized constitutive response is estimated resorting to two different microstructural models: a discrete model, in which the ligaments are modeled as beams and the presence of the matrix is neglected and the equivalent elastic properties are evaluated through a simplified analytical approach, and a more detailed continuous model, where the actual properties of matrix, ligaments and rings, varying in the 2D domain, are considered and the first order computational homogenization is adopted. Special attention is given to the dependence of the 2D overall Cauchy-type elastic constants on the mechanical and geometrical parameters characterizing the microstructure. The results, indeed, show the existence of large variations in the linear elastic constants and degree of anisotropy. A comparison with available experimental results confirms the validity of the analytical and numerical approaches adopted. Finally, the rigorous Floquet–Bloch approach is applied to the periodic cell of the cellular solid to evaluate the dispersion of propagation waves along the orthotropic axes in the framework of elasticity and to detect band gaps characterizing the material. A numerical approach, based on the first order computational homogenization, is also adopted and the rigorous and approximate solutions are compared
On Expressiveness and Behavioural Theory of Attribute-based Communication
No full textAttribute-based communication is an interesting alternative to broadcast and binary communication when providing abstract models for the so called Collective Adaptive Systems which consist of a large number of interacting components that dynamically adjust and combine their behavior to achieve specifc goals. A basic process calculus, named AbC, is introduced whose primary
primitive for interaction is attribute-based communication. An AbC system consists of a set of parallel components each of which is equipped with a set of attributes. Communication takes place in an implicit multicast fashion, and interactions among components are dynamically established by taking into account\connections" as determined by predicates over the attributes
exposed by components. First, the syntax and the semantics of AbC are presented, then expressiveness and effectiveness of the calculus are demonstrated both in terms of the ability to model scenarios featuring collaboration, reconfiguration, and adaptation
and of the possibility of encoding a process calculus for broadcasting channel-based communication and other communication
paradigms. Behavioral equivalences for AbC are introduced for establishing formal relationships between different descriptions
of the same system