Reasoning about Knowledge and Strategies: Epistemic Strategy Logic

In this paper we introduce Epistemic Strategy Logic (ESL), an extension of Strategy Logic with modal operators for individual knowledge. This enhanced framework allows us to represent explicitly and to reason about the knowledge agents have of their own and other agents' strategies. We provide a semantics to ESL in terms of epistemic concurrent game models, and consider the corresponding model checking problem. We show that the complexity of model checking ESL is not worse than (non-epistemic) Strategy LogicComment: In Proceedings SR 2014, arXiv:1404.041

Interaction Pressure Tensor for a class of Multicomponent Lattice Boltzmann models

We present a theory to obtain the pressure tensor for a class of non-ideal multicomponent lattice Boltzmann models, thus extending the theory presented by Shan (X. Shan, Phys. Rev. E 77, 066702 (2008)) for single component fluids. We obtain the correct form of the pressure tensor directly on the lattice and the resulting equilibrium properties are shown to agree very well with those measured from numerical simulations. Results are compared with those of alternative theories.Comment: 7 Pages, 5 figure

The Numerical Sausage

The renormalization group equation describing the evolution of the metric of the non linear sigma models poses some nice mathematical problems involving functional analysis, differential geometry and numerical analysis. We describe the techniques which allow a numerical study of the solutions in the case of a two-dimensional target space (deformation of the $O(3)\; \sigma$--model. Our analysis shows that the so-called sausages define an attracting manifold in the U(1) symmetric case, at one-loop level. The paper describes i) the known analytical solutions, ii) the spectral method which realizes the numerical integrator and allows to estimate the spectrum of zero--modes, iii) the solution of variational equations around the solutions, and finally iv) the algorithms which reconstruct the surface as embedded in $R^3$.Comment: 15 pages, uuencoded postscript fil

Verification of Agent-Based Artifact Systems

Artifact systems are a novel paradigm for specifying and implementing business processes described in terms of interacting modules called artifacts. Artifacts consist of data and lifecycles, accounting respectively for the relational structure of the artifacts' states and their possible evolutions over time. In this paper we put forward artifact-centric multi-agent systems, a novel formalisation of artifact systems in the context of multi-agent systems operating on them. Differently from the usual process-based models of services, the semantics we give explicitly accounts for the data structures on which artifact systems are defined. We study the model checking problem for artifact-centric multi-agent systems against specifications written in a quantified version of temporal-epistemic logic expressing the knowledge of the agents in the exchange. We begin by noting that the problem is undecidable in general. We then identify two noteworthy restrictions, one syntactical and one semantical, that enable us to find bisimilar finite abstractions and therefore reduce the model checking problem to the instance on finite models. Under these assumptions we show that the model checking problem for these systems is EXPSPACE-complete. We then introduce artifact-centric programs, compact and declarative representations of the programs governing both the artifact system and the agents. We show that, while these in principle generate infinite-state systems, under natural conditions their verification problem can be solved on finite abstractions that can be effectively computed from the programs. Finally we exemplify the theoretical results of the paper through a mainstream procurement scenario from the artifact systems literature

On the non-convergence of the Wang-Landau algorithms with multiple random walkers

This paper discusses some convergence properties in the entropic sampling Monte Carlo methods with multiple random walkers, particularly in the Wang-Landau (WL) and $1/t$ algorithms. The classical algorithms are modified by the use of $m$ independent random walkers in the energy landscape to calculate the density of states (DOS). The Ising model is used to show the convergence properties in the calculation of the DOS, as well as the critical temperature, while the calculation of the number $\pi$ by multiple dimensional integration is used in the continuum approximation. In each case, the error is obtained separately for each walker at a fixed time, $t$; then, the average over $m$ walkers is performed. It is observed that the error goes as $1/\sqrt{m}$. However, if the number of walkers increases above a certain critical value $m>m_x$, the error reaches a constant value (i.e. it saturates). This occurs for both algorithms; however, it is shown that for a given system, the $1/t$ algorithm is more efficient and accurate than the similar version of the WL algorithm. It follows that it makes no sense to increase the number of walkers above a critical value $m_x$, since it does not reduces the error in the calculation. Therefore, the number of walkers does not guarantee convergence.Comment: 10 pages, 12 figures, Regular Articl

Lattice Boltzmann Simulations of Droplet formation in confined Channels with Thermocapillary flows

Based on mesoscale lattice Boltzmann simulations with the "Shan-Chen" model, we explore the influence of thermocapillarity on the break-up properties of fluid threads in a microfluidic T-junction, where a dispersed phase is injected perpendicularly into a main channel containing a continuous phase, and the latter induces periodic break-up of droplets due to the cross-flowing. Temperature effects are investigated by switching on/off both positive/negative temperature gradients along the main channel direction, thus promoting a different thread dynamics with anticipated/delayed break-up. Numerical simulations are performed at changing the flow-rates of both the continuous and dispersed phases, as well as the relative importance of viscous forces, surface tension forces and thermocapillary stresses. The range of parameters is broad enough to characterize the effects of thermocapillarity on different mechanisms of break-up in the confined T-junction, including the so-called "squeezing" and "dripping" regimes, previously identified in the literature. Some simple scaling arguments are proposed to rationalize the observed behaviour, and to provide quantitative guidelines on how to predict the droplet size after break-up.Comment: 18 pages, 9 figure

PROCEDURE FAULT TOLERANT PER LA STIMA DEI DATI ARIA DALLE MISURE DI UNA SONDA MULTI-PRESSIONE

Questo lavoro riguarda lo sviluppo di algoritmi fault tolerant per la determinazione di dati aria quali velocità, pressione statica, angolo di attacco e angolo di derapata basati su misure provenienti da una sonda multi-pressione. In studi precedenti il Dipartimento di Ingegneria Aerospaziale dell'Università di Pisa ha sviluppato la configurazione geometrica di una sonda non intrusiva di tipo multi-foro per la misurazione delle pressioni locali, atta a garantire la stabilità del flusso nelle varie condizioni di volo. La sonda è costituita da un corpo assial-simmetrico con una parte cilindrica, lunga 100 mm, collegata ad un supporto che ne permette l'installazione sul velivolo. Alle estremità, due tronchi di cono terminano con degli elementi emisferici di raggio 10 mm. L'emisfera frontale è provvista di fori per la determinazione delle misure di pressione. l'architettura descritta deriva da studi condotti sui Flush Air Data Systems, FADSs, costituiti da gruppi di prese di pressione poste direttamente sulla fusoliera del velivolo. La configurazione geometrica è stata realizzata con l'obiettivo di utilizzare trasduttori di pressione di tipo Micro Electro Mechanical System (MEMS). La tecnologia dei MEMS permette di ridurre i costi, la dimensione delle sonde e di realizzare un elevato numero di fori aumentando il livello di ridondanza. Dopo la definizione della forma geometrica è stato caratterizzato il campo aerodinamico attorno la sonda nelle varie condizioni operative. L'analisi CFD (Computational fluid dynamics) ha permesso di scegliere la collocazione delle prese di pressione e la definizione di un database preliminare che verrà usato nella calibrazione degli algoritmi per la ricostruzione dei dati aria. Era stata valutata la realizzabilità della ricostruzione dei dati aria attraverso la reti neurali artificiali a partire da cinque misure di pressione differenti. In questo lavoro il numero di fori è aumentato fino a 21 per garantire un adeguato livello di affidabilità. L'architettura che ne è risultata è volta a garantire il calcolo dei parametri di volo anche in presenza di due avarie (two fail operative system). Il modello è costituito da tre unità di calcolo che lavorano in parallelo, ognuna delle quali è costituita da tre reti neurali che calcolano rispettivamente l'angolo di attacco, l'angolo di derapata e la velocità. Inoltre questo lavoro descrive lo sviluppo degli algoritmi di monitoring in grado di individuare possibili avarie e a provvedere alla riconfigurazione del sistema. La gestione delle avarie è una delle più importanti caratteristiche delle sonde multi-foro perchè in condizione di avaria (alcuni sensori o fori potrebbero essere bloccati o altri strumenti di acquisizione dati potrebbero avere problemi) i parametri di volo potrebbero essere calcolati in maniera erronea corrispondente agli errati valori di pressione. Lo sviluppo dello schema di monitoring prevede un confronto tra un predefinito numero di differenze di pressione e un intervallo di riferimento dipendente dall'angolo d'incidenza, di derapata e dal numero di Mach. Quando ci si trova in condizione di avaria alcune delle differenze di pressione escono dall'intervallo di riferimento permettendone l'identificazione. Il lavoro mostra la metodologia usata per la scelta delle differenze di pressione appropriate insieme con i relativi intervalli di riferimento, i quali sono usati nell'algoritmo di monitoring per identificare i trasduttori in avaria sulla base della conoscenza delle differenze di pressione

A numerical study of the RG equation for the deformed O(3)O(3) nonlinear sigma model

The Renormalization Group equation describing the evolution of the metric of the nonlinear sigma model poses some nice mathematical problems involving functional analysis, differential geometry and numerical analysis. In this article we briefly report some results obtained from the numerical study of the solutions in the case of a two dimensional target space (deformation of the $O(3)$ sigma model). In particular, our analysis shows that the so-called sausages define an attracting manifold in the $U(1)$-symmetric case, at one-loop level. Moreover, data from two-loop evolution are used to test the association put forward in Nucl. Phys., B406 (1993) 521 between the so-called $SSM_{\nu}$ field theory and a certain $U(1)$-symmetric, factorized scattering theory (FST).Comment: LaTex (RevTex style), 16 pages, 6 uuencoded figures. Minor technical changes

Attending to Motion: an object-based approach

Visual attention is the biological mechanism allowing to turn mere sensing into conscious perception. In this process, object-based modulation of attention provides a further layer between low-level space/feature-based region selection and full object recognition. In this context, motion is a very powerful feature, naturally attracting our gaze and yielding rapid and effective shape distinction. Moving from a pixel-based account of attention to the definition of proto-objects as perceptual units labelled with a single saliency value, we present a framework for the selection of moving objects within cluttered scenes. Through segmentation of motion energy features, the system extracts coherently moving proto-objects defining them as consistently moving blobs and produces an object saliency map, by evaluating bottom-up distinctiveness of each object candidate with respect to its surroundings, in a center-surround fashion