Constitutive relations and Schroedinger's formulation of nonlinear electromagnetic theories

We present a systematic study of nonlinear and higher derivatives extensions of electromagnetism. We clarify when action functionals S[F] can be explicitly obtained from arbitrary (not necessarily self-dual) nonlinear equations of motion. We show that the "Deformed twisted self-duality condition" proposal originated in the context of supergravity counterterms is actually the general framework needed to discuss self-dual theories starting from a variational principle. We generalize to nonlinear and higher derivatives theories Schroedinger formulation of Born-Infeld theory, and for the latter, and more in general for nonlinear theories, we derive a closed form expression of the corresponding deformed twisted self-duality conditions. This implies that the hypergeometric expression entering these duality conditions and leading to Born-Infeld theory satisfies a hidden quartic equation.Comment: Revised version with: integrability conditions on equations of motion; equivalence between deformed twisted self-duality conditions and equations of motion from action functionals S[F] (Section 2.5); stressed universality of the quartic equation. References added. 31 pages. To appear in JHE

Duality Rotations in Nonlinear Electrodynamics and in Extended Supergravity

We review the general theory of duality rotations which, in four dimensions, exchange electric with magnetic fields. Necessary and sufficient conditions in order for a theory to have duality symmetry are established. A nontrivial example is Born-Infeld theory with n abelian gauge fields and with Sp(2n,R) self-duality. We then review duality symmetry in supergravity theories. In the case of N=2 supergravity duality rotations are in general not a symmetry of the theory but a key ingredient in order to formulate the theory itself. This is due to the beautiful relation between the geometry of special Kaehler manifolds and duality rotations.Comment: Invited contribution to Rivista del Nuovo Cimento in occasion of the 2005 Enrico Fermi Prize of the Italian Physical Society. 96 pages, corrected typo

The size of BDDs and other data structures in temporal logics model checking

Temporal Logic Model Checking is a verification method in which we describe a system, the model, and then we verify whether important properties, expressed in a temporal logic formula, hold in the system. Many Model Checking tools employ BDDs or some other data structure to represent sets of states. It has been empirically observed that the BDDs used in these algorithms may grow exponentially as the model and formula increase in size. We formally prove that no kind of data structure of polynomial size can represent the set of valid initial states for all models and all formulae. This result holds for all data structures where a state can be checked in polynomial time. Therefore, it holds not only for all types of BDDs regardless of variable ordering, but also for more powerful data structures, such as RBCs, MTBDDs, ADDs and SDDs. Thus, the size explosion of BDDs is not a limit of these specific data representation structures, but is unavoidable: every formalism used in the same way would lead to an exponential size blow up

Analisi CFD di fenomeni di mescolamento e di scambio termico alla parete all’interno di reattori nucleari

Il presente è diviso in 2 parti: nella prima, utilizzando un codice CFD commerciale, si studiano i fenomeni di scambio termico convettivo in moto turbolento relativi al mescolamento di sodio liquido a diverse temperature all’interno di una giunzione a T; avendo scelto un caso per il quale sono disponibili dei dati sperimentali, è stato possibile quantificare meglio l’errore commesso dal codice, evidenziando, in particolare pregi e difetti dei vari modelli di turbolenza utilizzati. I modelli RANS più raffinati si rivelano efficaci per lo studio del flusso medio, ma non riescono a valutare correttamente la forma e la posizione della zona di mescolamento all’interno del tubo principale; i modelli LES, invece, sono migliori nella valutazione dei fenomeni di mescolamento, ma i valori di temperatura calcolati sono ancora distanti dai dati sperimentali. Nella seconda parte si è implementata la metodologia ideata dai ricercatori del DIMNP (Dip. di Ing. Nucleare, Meccanica e della Produzione) per svolgere l’analisi completa del comportamento del vessel di un impianto nucleare, in seguito ad un incidente ipotizzato, che possa condurre a condizioni di PTS (Pressurized Thermal Shock). L’allievo ha svolto questa attività in collaborazione col GRNSPG (Gruppo di Ricerca Nucleare di San Piero a Grado), occupandosi di vari aspetti inerenti al problema considerato: • la simulazione CFD del flusso all’interno del down-comer, durante il transitorio relativo all’incidente nucleare ipotizzato; • l’analisi termica all’interno dello spessore solido del vessel; • la correlazione tra i vari codici di calcolo. La metodologia è stata testa sull’impianto nucleare ATUCHA II, in Argentina, ipotizzando un transitorio incidentale di tipo LOCA (Loss of Coolant Accident), verificando sia l’integrità del vessel, sia l’efficienza e la validità della metodologia stessa

Looking at the Global Transformations: Why an Integrated Perspective is Still Required

In this article, the authors offer an introduction to the Sophia Global Studies center, its methodology and framework, and offer some reflections on the ways in which this center can respond to the complex issues facing humanity in an increasingly globalized world. They argue that the recent appearance of isolationist trends in various parts of the world only confirms the relevance of this center of global studies

Robust motion control of a robot manipulator via Integral Suboptimal Second Order Sliding modes

This paper deals with the formulation of an Integral Suboptimal Second Order Sliding Mode control algorithm oriented to solve motion control problems for robot manipulators, taking into account the presence of unavoidable modelling uncertainties and external disturbances affecting the systems. The proposed algorithm is designed so that the so-called reaching phase, normally present in the evolution of a system controlled via a Sliding Mode controller, is reduced to a minimum. Moreover, since the relative degree of the relevant system output is suitably augmented through the use of an integrator, the control action affecting the robotic system is continuous, with a significant benefit, in terms of chattering alleviation, for the overall controlled electromechanical system. The verification and validation of our proposal have been performed by simulating the motion control scheme relying on a model of the considered robot, i.e. a COMAU SMART3-S2 anthropomorphic industrial robot manipulator, identified on the basis of real data. © 2013 IEEE

Robust motion control of a robot manipulator via Integral Suboptimal Second Order Sliding modes

This paper deals with the formulation of an Integral Suboptimal Second Order Sliding Mode control algorithm oriented to solve motion control problems for robot manipulators, taking into account the presence of unavoidable modelling uncertainties and external disturbances affecting the systems. The proposed algorithm is designed so that the so-called reaching phase, normally present in the evolution of a system controlled via a Sliding Mode controller, is reduced to a minimum. Moreover, since the relative degree of the relevant system output is suitably augmented through the use of an integrator, the control action affecting the robotic system is continuous, with a significant benefit, in terms of chattering alleviation, for the overall controlled electromechanical system. The verification and validation of our proposal have been performed by simulating the motion control scheme relying on a model of the considered robot, i.e. a COMAU SMART3-S2 anthropomorphic industrial robot manipulator, identified on the basis of real data. © 2013 IEEE

Design of an Integral Suboptimal Second-Order Sliding Mode Controller for the Robust Motion Control of Robot Manipulators

The formulation of an integral suboptimal second-order sliding mode ((ISSOSM) control algorithm, oriented to solve motion control problems for robot manipulators, is presented in this paper. The proposed algorithm is designed so that the so-called reaching phase, normally present in the evolution of a system controlled via the sliding mode approach, is reduced to a minimum. This fact makes the algorithm more suitable to be applied to a real industrial robot, since it enhances its robustness, by extending it also to time intervals during which the classical sliding mode is not enforced. Moreover, since the algorithm generates second-order sliding modes, while the model of the controlled electromechanical system has a relative degree equal to one, the control action actually fed into the plant is continuous, which provides a positive chattering alleviation effect. The assessment of the proposal has been carried out by experimentally testing it on a COMAU SMART3-S2 anthropomorphic industrial robot manipulator. The satisfactory experimental results, also compared with those obtained with a standard proportional-derivative controller and with the original suboptimal algorithm, confirm that the new algorithm can actually be used in an industrial context

Guidance of quadrotor unmanned aerial vehicles via adaptive multiple-surface sliding mode control

In many application domains, navigation of unmanned aerial vehicles (UAVs) requires a planar flight to move along a desired path or to track a moving object under uncertain conditions. In this paper, we propose a robust control approach for quadrotor UAVs performing a nonholonomic-like navigation with a predefined velocity based guidance law. Specifically, the quadrotor model is first recast in the framework of nonholonomic systems, and then an adaptive multiple-surface sliding mode approach, with suboptimal second order sliding mode control, is applied. The robustness features of the proposed approach are discussed and assessed in simulation