1,721,811 research outputs found
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
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
Finite-Time stabilization of linear systems with unknown control direction via Extremum Seeking
No full textIn this paper the finite-time stabilization problem is solved for a linear time-varying system with unknown control direction by exploiting a modified version of the classical extremum seeking algorithm. We propose to use a suitable oscillatory input to modify the system dynamics, at least in an average sense, so as to satisfy a Differential Linear Matrix Inequality (DLMI) condition which in turns guarantees that the system's state remains inside a prescribed time varying hyper-ellipsoid in the state space. The finite-time stability (FTS) of the averaged dynamics implies the FTS of the original system, as the distance between the original and the averaged dynamics can be made arbitrarily small by choosing a sufficiently high value of the dithering frequency used by the extremum seeking algorithm. The main advantage of the proposed approach resides in that it is capable of dealing with systems with unknown control direction, and/or with a control direction that changes over time. Being FTS a quantitative approach, the paper also gives an estimate of the necessary minimum dithering/mixing frequency, and the effectiveness of the proposed finite-time stabilization approach is anal
An Efficient Approach for Online Diagnosis of Discrete Event Systems
No full textA novel approach to fault diagnosis of discrete event systems is presented in this paper. The standard approach is based on the offline computation of the set of fault events that may have occurred at each reachable state, providing a fast online diagnosis at a price of excessive memory requirements. A different approach is here adopted, which is based on the online computation of the set of possible fault events required to explain the last observed event. This is efficiently achieved by modelling the plant by Petri nets, since their mathematical representation permits to formulate the fault diagnosis problems in terms of mathematical programming, which is a standard tool. Moreover, the graphical representation of the net allows the diagnoser agent to compute off-line reduced portions of the net in order to improve the efficiency of the online computation, without a big increase in terms of memory requirement
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