3,421 research outputs found
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 --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 .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 algorithms. The classical algorithms are modified by
the use of 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 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, ; then, the average over
walkers is performed. It is observed that the error goes as .
However, if the number of walkers increases above a certain critical value
, 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
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 , 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 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
sigma model). In particular, our analysis shows that the so-called
sausages define an attracting manifold in the -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
field theory and a certain -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
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