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Imperfections are unavoidable in production processes of real devices. Despite this, and despite the fact that real devices usually operate in regimes far from ideality, they still work. This is related to the fact that imperfections give rise to hidden dynamics, which, opportunely excited, have an overall positive effect on the device. In this paper, we focus on a complex and imperfect electromechanical structure which can be considered as a paradigm for imperfect systems. The electrical and mechanical interactions within the structure generate complex patterns of vibration which may prevent the system to reach the correct working conditions. A control strategy to ensure the optimal working conditions based on the excitation of the hidden dynamics induced by imperfections is discussed, characterizing its effect with respect to the control signal properties and to the power provided to the structure.

The relevance of odd, and in particular loss-less, frequency transformations is well established in analog filter design. A loss-less frequency transformation s ← F ( s ) , in fact, allows to design multi-bandpass multi-bandstop filters as transformed systems G ( s ) = G ( F ( s ) ) from an original prototype lowpass filter G ( s ) , by properly selecting F ( s ) . In this paper the invariance of the shape of the Nyquist plot for linear time-invariant continuous-time systems under a class of odd frequency transformations is proved. This result allows to determine closed-loop stability conditions for this class of transformed systems on the basis of the Nyquist’s criterion referred to the original, lower order, system.

Complex patterns can be often retrieved in spatially-extended systems formed by coupled nonlinear dynamical units. In particular, Turing patterns have been extensively studied investigating mathematical models related to different contexts, such as chemistry, physics, biology, and also mechanics and electronics. In this paper, we focus on the emergence of Turing patterns in a circuit architecture formed by coupled units in which a mernrsitive element is considered. Furthermore, the unit is formed by only two elements, namely a capacitor and a memristor. The analytical conditions for which Turing patterns can be obtained in the proposed architecture are discussed in order to inform the design of the circuit parameters. Moreover, the characterization of the different types of patterns is performed with respect to the strength of the diffusion occurring between the units. Finally, it is worth to note that the proposed architecture can be considered as the simplest electronic circuit able to undergo Turing instability and give rise to pattern formation.

GPUSPH is an implementation of Weakly-Compressible Smoothed Particle Hydrodynamics with an explicit predictor–corrector integration scheme, that takes advantage of the parallel nature of the method to run on Graphic Processing Units (GPUs). Despite the massive speed-up granted by the use of GPUs, the application of GPUSPH to the simulation of highly viscous fluids is still problematic, due to the severe time-stepping restrictions imposed by the explicit integration scheme when the viscous term becomes dominant. This is an issue in the simulation of lava flows, where the thermal-dependent rheology can lead to kinematic viscosities in the order of 10 4 m 2 s − 1 or more at low temperatures. To overcome this limitation, we introduce a semi-implicit integration scheme, where only the viscous part of the momentum equation is solved implicitly. Here we show the significant advantages of our approach in terms of simulation run times as well as better quality of the results over the fully explicit scheme.

Numerical simulation is a fundamental aspect of modern volcanology, providing tools for the forecasting of lava flows behavior, so as to assist in the design of mitigation actions for volcanic risk. In addition to the prediction of the emplacement topology, numerical simulation can be useful to study the possible outcomes of the interaction between a lava flow and a building. This kind of information can help to estimate the vulnerability of buildings so as to produce more accurate risk evaluations. Smoothed Particle Hydrodynamics (SPH) is a particle-based numerical method, particularly suited for the simulation of fluids with a high level of complexity, that can intrinsically deal with all of the physical properties of lava. GPUSPH is a simulation engine based on the SPH method that has been developed in order to take into account the challenging aspects of lava simulations and has been successfully applied to the simulation of lava-related benchmark tests. Here we use the SPH method, coupled within the framework of GPUSPH with a rigid body mechanics solver provided by the Project Chrono engine, for the realistic study of lava-buildings interaction. The resulting coupled model is able to simulate masonry with a brick-level accurate description, providing insights on any damages happening to the structure. We will show the simulation of a lava flow interacting with an elementary masonry piece, where a total collapse of the structure is induced by the action of the lava.

The realization of integrated devices determines unavoidable imperfections which are linked to the manufacturing process, thus making them imperfect systems. Imperfection is not always detrimental, as it can lead to unexpected complex and organized behaviors. In this paper we explore the possibility of designing imperfect electronic circuits producing a chaotic flow with bandwidth up to the order to several megahertz thanks to the hidden dynamics induced by construction imperfections, and whose characteristics can be tuned by means of a single variable resistor, acting as bifurcation parameter. Moreover, a strategy to estimate the parameters of the hidden dynamics is devised and the synchronization of imperfect chaotic circuits is shown. The paper further remarks that imperfection can play an important role in the realization of robust chaos generators based on simple circuits.

Lossless positive-real systems have been widely studied in the literature. They are systems in which the energy is entirely transferred between input and output. In this paper, new aspects related to the linear quadratic gaussian (LQG) control of lossless positive-real systems are reported including both the continuous-time and the discrete-time cases. Direct formulas for the calculation of the optimal gains will be introduced and the properties of the different structures of the LQG compensator obtained for the continuous-time and the discrete-time cases will be emphasized, also in view of designing positive-real LQG compensators. Numerical examples related to low-damped structures are also discussed to verify the possibility to design the LQG compensator on the basis of a lossless approximation.