1,721,871 research outputs found
An algebraic characterization of language-based opacity in labeled Petri nets
No full textOpacity is a property of discrete event systems (DES) that is related to the possibility of hiding a secret to external observers (the intruders). The secret can be either a system state, or a sequence of events executed by the system itself. When the latter type of secrets is considered, the opacity property is referred to as language-based opacity (LBO). This paper deals with LBO when the DES is modeled by a labeled Petri net. One necessary and sufficient condition to check LBO by solving Integer Linear Programming problems is given; such a condition exploits the algebraic representation of Petri nets. A sufficient condition is then derived, which is less demanding from the computational point of view. The effectiveness of the proposed approach is shown by means of examples
Assessment of Bisimulation Non-Interference in Discrete Event Systems Modelled with Bounded Petri Nets
No full textNon-interference in discrete event systems deals with the possibility by an intruder to infer the occurrences of private and non observable events, the so called high-level ones, by interacting with the system at a user level, i.e., by observing the occurrence of the so called low-level ones. When bisimulation non-interference is considered, the security objective is not only to avoid the detection of high-level event occurrences, but also to avoid the detection of their non occurrences; i.e., the secret includes also the non occurrences of some events. This letter deals with such a more restrictive security property in the framework of discrete event systems modelled as Petri nets. A necessary and sufficient condition is given to assess bisimulation non-interference in bounded Petri nets. Such a condition requires the solution of integer linear programming optimization problems, whose solution can be used also to statically enforce bisimulation non-interference when this condition is not satisfied by the original system
Assessment of multilevel intransitive non-interference for Discrete Event Systems
No full textPrivacy of distributed cyber-physical systems can be compromised by the presence of information leaks which permit to external intruders to infer the state of the system itself. These systems are built using several off-the-shelf components with communication capabilities that provide a significant level of control, and lower operational costs in comparison to the traditional vendor-specific proprietary and closed-source systems. However, these components expose the control systems to more vulnerabilities and threats. This work focuses on the multi-level intransitive non-interference, a property particularly suitable to tackle privacy problems of control systems under attack. The property is characterized and verified using Petri net models and mathematical programming
Materiali, tecniche e tecnologie costruttive nel complesso “Duca degli Abruzzi” in Bari tra tradizione ed innovazione
No full textPlasma Magnetic Control in Tokamak Devices
No full textIn tokamak experimental reactors, the magnetic control system is one of the main plasma control systems that is required, together with the density control, since the very beginning, even before first operations. Indeed, the magnetic control drives the current in the external poloidal circuits in order to first achieve the breakdown conditions and, after plasma formation, to track the desired plasma current, shape and position. Furthermore, when the plasma poloidal cross-section is vertically elongated, the magnetic control takes also care of the vertical stabilization of the plasma column, and therefore it is an essential system for operation. This chapter introduces a reference architecture for plasma magnetic control in tokamaks. Given the proposed architecture, the techniques to design all the required control algorithms is also presented. Experimental results obtained on the JET and EAST tokamaks and simulations for machines currently under construction are shown to prove the effectiveness of the proposed architecture and control algorithms
La pietra artificiale nell’edilizia all’inizio del XX secolo: processi di degrado di un materiale “innovativo”
No full textFinite-Time Stabilizability, Detectability, and Dynamic Output Feedback Finite-Time Stabilization of Linear Systems
No full textIn this note, we deal with linear systems and we extend to the finite-time setting the concepts of stabilizability and detectability. It will be shown that, similarly to what happens in the classical Lyapunov framework, even in the finite-time context, stabilizability and detectability play a role into the existence of
stabilizing dynamical controllers. We prove that a dynamic output feedback controller, which finite-time stabilizes the overall closed-loop system, exists if and only if the open-loop system is finite-time detectable and stabilizable plus a further linear matrix inequality coupling condition. We also show that, in the finite-time context, the equivalence between stabilizability via output feedback and stabilizability via observer-based controllers is no longer true
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
Assessment of initial-state-opacity in live and bounded labeled Petri net systems via optimization techniques
Full text linkOpacity is a property of discrete event systems (DES) that is related to the possibility of hiding a secret to external observers, the so called intruders. If the secret is the system initial state, then the related opacity problem is referred to as Initial State Opacity (ISO). This paper gives a necessary and sufficient condition to check ISO in DES modeled as bounded and live labeled Petri nets (PNs). The proposed approach relies on both the algebraic representation of labeled PNs dynamic, and on their structural representation in terms of minimal support T-invariants. The proposed necessary and sufficient condition enables ISO assessment by means of the solution of Integer Linear Programming problems, which can be efficiently solved nowadays by means of off-the-shelf optimization tools
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