1,721,203 research outputs found
Analisi di sistemi ibridi e progetto di controllori ibridi
No full textI sistemi ibridi possono essere utilizzati per modellare processi continui, come quelli descritti da equazioni differenziali, e processi discreti, come quelli descritti da relazioni di transizione. Circuiti elettrici composti da parti analogiche e digitali, sistemi con impatti, computer operanti con vincoli di real-time sono esempi di sistemi definibili mediante la modellazione come sistema ibrido delle loro parti continue e discrete e della relativa interazione.
Molte definizioni di sistema ibrido possono essere trovate in letteratura. In generale, la modellazione del comportamento di un sistema ibrido e l'interazione delle parti discrete e continue è basata sulla nozione centrale di stato. In questa tesi si considera una definizione di sistema ibrido molto generale, che sussume le altre definizioni presenti in letteratura. Utilizzando questa definizione generale, nella tesi vengono studiati due problemi classici per la teoria del controllo e per l'informatica: problemi di stabilità e problemi di verifica formale, entrambi generalizzati su sistemi ibridi.
Il problema della stabilità di sistemi ibridi è studiato per una particolare classe di sistemi ibridi detti homogenei. Si segue un approccio prossimo alla teoria di Lyapunov e sono proposti degli algoritmi basati sulla decomposizione di polinomi in somme dei quadrati (sum of squares problems). Il problema della verifica formale di sistemi ibridi è studiato attraverso la generalizzazione della semantica della logica temporale TCTL su sistemi ibridi. Si propone poi un metodo per ridurre formule TCTL a espressioni di punto fisso.
Nella tesi sono trattati anche problemi di sintesi di controllori, nell'ambito classico della teoria del controllo. Sono proposti controllori continui per sistemi con saturazioni in input. Sono poi proposti controllori ibridi per problemi di passività di sistemi e di definizione di politiche di trasmissione dati su modelli semplificati di reti.Hybrid systems define a common mathematical framework for
combining continuous and discrete processes, like the
case of processes defined by differential equations and by
transition relations, respectively.
Electrical circuits with both analog and
digital components, models of impacts, computing devices running real-time
applications, are all examples of processes defined by a combination
of differential equations and transition relations. Thus,
they can be modeled and studied as hybrid systems.
Hybrid systems have been studied in the last twenty years both by the
computer science community and by the control community, and
a lot of different definitions and results have been developed.
Common to all of these definitions is the mathematical
characterization of the evolution and of the interaction
of continuous and discrete processes by way of the crucial notion of
state. In this thesis, we consider a quite general definition
of hybrid systems that, to the best of the knowledge of the candidate,
subsumes classical definitions of a hybrid system in both computer
science and control theory. Based on this general definition
of a hybrid system, we study two classical problems:
stability problems of control theory and
verification problems of computer science, both generalized
to hybrid systems. Indeed, in the first part of the thesis,
we propose Lyapunov-like tools for the stability problem of a
peculiar class of hybrid systems, and we propose a
specific temporal logic, and a method for rewriting the formulas of
this logic as fixpoint expressions, for the verification problem of
hybrid systems.
The synthesis problem on hybrid systems, namely the problem
of synthesizing a hybrid system for achieving some
predetermined goal, is a forward consequence of
the studies on analysis of hybrid systems.
In the second part of the thesis,
we consider the framework of dynamical control systems,
proposing non-hybrid controllers
on continuous systems with bounds on the inputs, and hybrid controllers that,
by virtue of their discrete dynamics, guarantee suitable properties of the
closed loop. Is worth mentioning that the combination of a classical
continuous process and of a hybrid controller results in a hybrid system
that can be studied with the analysis tools developed in the first part of
the thesis
Laboratorio dei Diritti Fondamentali: il diritto alla salute e il rispetto della dignità della persona. Analisi delle criticità esistenti in due realtà territoriali Italiane alla luce della normativa e dell’elaborazione culturale europea
No full textIn vitro absorption of drugs using the Sartorius apparatus according to Stricker: salicylic acid. II
No full textLaboratorio dei Diritti Fondamentali: il diritto alla salute e il rispetto della dignità della persona. Analisi delle criticità esistenti in due realtà territoriali Italiane alla luce della normativa e dell’elaborazione culturale europea
No full textGain-scheduled, model-based anti-windup for LPV systems
Full text linkpeer reviewedThe aim of this paper is to show that a recently proposed technique for anti-windup control of exponentially unstable plants can be easily extended to solve the corresponding robust anti-windup problem for linear parameter varying systems, for which the time varying parameters are measured online. The proposed technique is minimally conservative with respect to the size of the resulting operating region (which coincides, up to an arbitrarily small quantity, with the largest set on which asymptotic stability can be guaranteed for the considered plant with the given saturation level and uncertainty characteristics), and is not limited to plants having only small uncertainties or being open-loop stable.MIUR under PRIN project
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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