The Politecnico di Torino is an engineering public university based in Turin, Italy. Established in 1859, Politecnico di Torino is Italy’s oldest technical university. The university offers several courses in the fields of Engineering, Architecture and Industrial Design. Wikipedia.
Taricco G.,Polytechnic University of Turin
IEEE Journal on Selected Topics in Signal Processing | Year: 2011
Spectrum sensing is the key to coordinate the secondary users in a cognitive radio network by limiting the probability of interference with the primary users. Linear cooperative spectrum sensing consists of comparing the linear combination of the secondary users' recordings against a given threshold in order to assess the presence of the primary user signal. Simplicity is traded off for a slight suboptimality with respect to the likelihood-ratio test. Tuning the performance of linear cooperative radio sensing is complicated by the fact that optimization of the linear combining vector is required. This is accomplished by solving a nonconvex optimization problem, which is the main focus of this work. The global optimum is found by an explicit algorithm based on the solution of a polynomial equation in one scalar variable. Numerical results are reported for validation purposes and to analyze the effects of the system parameters on the complementary receiver operating characteristic. It is shown that the optimum probability of missed detection for a system with constant local signal-to-noise ratios (SNRs) and constant channel gain correlation coefficients can be expressed in closed form by a simple expression. Simulation results are also included to validate the accuracy of the Gaussian approximation. These results illustrate how large the number of sampling intervals must be in order that the Gaussian approximation holds. © 2011 IEEE.
Lucia U.,Polytechnic University of Turin
Renewable and Sustainable Energy Reviews | Year: 2013
Exergy and entropy generation analysis of the open systems allows to obtain a measure of how far the open real systems deviate from equilibrium with their environment. A link between entropy generation maximum principle and the exergy analysis of engineering and natural systems is suggested in order to use the exergy and entropy approach to improve the renewable energy systems. © 2012 Elsevier Ltd.
Calafiore G.C.,Polytechnic University of Turin
SIAM Journal on Optimization | Year: 2010
Random convex programs (RCPs) are convex optimization problems subject to a finite number N of random constraints. The optimal objective value J* of an RCP is thus a random variable. We study the probability with which J* is no longer optimal if a further random constraint is added to the problem (violation probability V *). It turns out that this probability rapidly concentrates near zero as N increases. We first develop a theory for RCPs leading to explicit bounds on the upper tail probability of V *. Then we extend the setup to the case of RCPs with r a posteriori violated constraints (RCPVs): a paradigm that permits us to improve the optimal objective value while maintaining the violation probability under control. Explicit and nonasymptotic bounds are derived also in this case: the upper tail probability of V * is upper bounded by a multiple of a beta distribution irrespective of the distribution on the random constraints. All results are derived under no feasibility assumptions on the problem. Further the relation between RCPVs and chanceconstrained problems (CCP) is explored showing that the optimal objective J* of an RCPV with the generic constraint removal rule provides with arbitrarily high probability an upper bound on the optimal objective of a corresponding CCP. Moreover whenever an optimal constraint removal rule is used in the RCPVs then appropriate choices of N and r exist such that J* approximates arbitrarily well the objective of the CCP. © 2010 Society for Industrial and Applied Mathematics.
Dolcini F.,Polytechnic University of Turin
Physical Review B - Condensed Matter and Materials Physics | Year: 2011
We investigate electron interferometry of edge states in topological insulators. We show that when interboundary coupling is induced at two quantum point contacts of a four terminal setup, both Fabry-Pérot-like and Aharonov-Bohm-like loop processes arise. These underlying interference effects lead to a full electrically controllable system, where the magnitude of charge and spin linear conductances can be tuned by gate voltages, without applying magnetic fields. In particular we find that, under appropriate conditions, interboundary coupling can lead to negative values of the conductance. Furthermore, the setup also allows to selectively generate pure charge or pure spin currents by choosing the voltage bias configuration. © 2011 American Physical Society.
Frasca P.,Polytechnic University of Turin
Systems and Control Letters | Year: 2012
This note studies a network of agents having continuous-time dynamics with quantized interactions and time-varying directed topology. Due to the discontinuity of the dynamics, solutions of the resulting ODE systems are intended in the sense of Krasovskii. A limit connectivity graph is defined, which encodes persistent interactions between nodes: if such graph has a globally reachable node, Krasovskii solutions reach consensus (up to the quantizer precision) after a finite time. Under the additional assumption of a time-invariant topology, the convergence time is upper bounded by a quantity which depends on the network size and the quantizer precision. It is observed that the convergence time can be very large for solutions which stay on a discontinuity surface. © 2011 Elsevier B.V. All rights reserved.