Showing papers by "Polytechnic University of Turin published in 2006"
TL;DR: A rich family of control problems which are in general hard to solve in a deterministically robust sense is therefore amenable to polynomial-time solution, if robustness is intended in the proposed risk-adjusted sense.
Abstract: This paper proposes a new probabilistic solution framework for robust control analysis and synthesis problems that can be expressed in the form of minimization of a linear objective subject to convex constraints parameterized by uncertainty terms. This includes the wide class of NP-hard control problems representable by means of parameter-dependent linear matrix inequalities (LMIs). It is shown in this paper that by appropriate sampling of the constraints one obtains a standard convex optimization problem (the scenario problem) whose solution is approximately feasible for the original (usually infinite) set of constraints, i.e., the measure of the set of original constraints that are violated by the scenario solution rapidly decreases to zero as the number of samples is increased. We provide an explicit and efficient bound on the number of samples required to attain a-priori specified levels of probabilistic guarantee of robustness. A rich family of control problems which are in general hard to solve in a deterministically robust sense is therefore amenable to polynomial-time solution, if robustness is intended in the proposed risk-adjusted sense.
1,122 citations
29 Sep 2006
TL;DR: VanetMobiSim mobility description is validated by illustrating how the interaction between featured macro- and micro-mobility is able to reproduce typical phenomena of vehicular traffic.
Abstract: In this paper, we present and describe VanetMobiSim, a generator of realistic vehicular movement traces for telecommunication networks simulators. VanetMobiSim mobility description is validated by illustrating how the interaction between featured macro- and micro-mobility is able to reproduce typical phenomena of vehicular traffic.
507 citations
TL;DR: Various techniques are discussed and compared able to reduce the size of the clustering input data set, in order to allow for storing a relatively small amount of data in the database of the distribution service provider for customer classification purposes.
Abstract: The recent evolution of the electricity business regulation has given new possibilities to the electricity providers for formulating dedicated tariff offers. A key aspect for building specific tariff structures is the identification of the consumption patterns of the customers, in order to form specific customer classes containing customers exhibiting similar patterns. This paper illustrates and compares the results obtained by using various unsupervised clustering algorithms (modified follow-the-leader, hierarchical clustering, K-means, fuzzy K-means) and the self-organizing maps to group together customers with similar electrical behavior. Furthermore, this paper discusses and compares various techniques-Sammon map, principal component analysis (PCA), and curvilinear component analysis (CCA)-able to reduce the size of the clustering input data set, in order to allow for storing a relatively small amount of data in the database of the distribution service provider for customer classification purposes. The effectiveness of the classifications obtained with the algorithms tested is compared in terms of a set of clustering validity indicators. Results obtained on a set of nonresidential customers are presented.
476 citations
TL;DR: It is shown that, for a wide class of probability distributions on the data, the probability constraints can be converted explicitly into convex second-order cone constraints; hence the probability-constrained linear program can be solved exactly with great efficiency.
Abstract: In this paper, we discuss linear programs in which the data that specify the constraints are subject to random uncertainty. A usual approach in this setting is to enforce the constraints up to a given level of probability. We show that, for a wide class of probability distributions (namely, radial distributions) on the data, the probability constraints can be converted explicitly into convex second-order cone constraints; hence, the probability-constrained linear program can be solved exactly with great efficiency. Next, we analyze the situation where the probability distribution of the data is not completely specified, but is only known to belong to a given class of distributions. In this case, we provide explicit convex conditions that guarantee the satisfaction of the probability constraints for any possible distribution belonging to the given class.
404 citations
TL;DR: In this article, the mechanism of thermal degradation of substituted polyhedral oligomeric silsesquioxanes (POSS) cages is studied in both inert atmosphere and in air, and the results show that Isobutyl and octyl substituted POSS undergo an almost complete evaporation when heated in inert atmosphere.
342 citations
TL;DR: An extension to continuous-valued variables of a verification method originated in the meteorological literature for the analysis of binary variables, based on the use of a suitable cost-loss function to evaluate the quality of the forecasts is proposed.
Abstract: . In the present paper we describe some methods for verifying and evaluating probabilistic forecasts of hydrological variables. We propose an extension to continuous-valued variables of a verification method originated in the meteorological literature for the analysis of binary variables, and based on the use of a suitable cost-loss function to evaluate the quality of the forecasts. We find that this procedure is useful and reliable when it is complemented with other verification tools, borrowed from the economic literature, which are addressed to verify the statistical correctness of the probabilistic forecast. We illustrate our findings with a detailed application to the evaluation of probabilistic and deterministic forecasts of hourly discharge values.
336 citations
18 Apr 2006
301 citations
TL;DR: A class of schemes of any desired order of accuracy which preserve the lake at rest perfectly are presented, which should have an impact for studying important classes of lake and ocean flows.
298 citations
TL;DR: In this article, an extension of the celebrated Paris law for crack propagation is given to take into account some of the deviations from the power-law regime in a simple manner using the Wohler SN curve of the material, suggesting a more general ''unified law''.
Abstract: An extension of the celebrated Paris law for crack propagation is given to take into account some of the deviations from the power-law regime in a simple manner using the Wohler SN curve of the material, suggesting a more general ''unified law''. In particular, using recent proposals by the first author, the stress intensity factor K(a) is replaced with a suitable mean over a material/structural parameter length scale Da, the ''fracture quantum''. In practice, for a Griffith crack, this is seen to correspond to increasing the effective crack length of Da, similarly to the Dugdale strip-yield models. However, instead of including explicitly information on cyclic plastic yield, short-crack behavior, crack closure, and all other detailed information needed to eventually explain the SN curve of the material, we include directly the SN curve constants as material property. The idea comes as a natural extension of the recent successful proposals by the first author to the static failure and to the infinite life envelopes. Here, we suggest a dependence of this fracture ''quantum'' on the applied stress range level such that the correct convergence towards the Wohler-like regime is obtained. Hence, the final law includes both Wohler's and Paris' material constants, and can be seen as either a generalized Wohler's SN curve law in the presence of a crack or a generalized Paris' law for cracks of any size. r 2006 Elsevier Ltd. All rights reserved.
290 citations
TL;DR: In this paper, the authors introduce a new failure criterion in the framework of finite fracture mechanics, which relies on the assumption that the finite distance is not a material constant but a structural parameter.
283 citations
TL;DR: An easy, quick and low cost hydrothermal synthesis was developed to prepare high surface area phospho-olivine LiFePO4 powders to be used as cathode material for Li-ion batteries as discussed by the authors.
TL;DR: A randomized arithmetic coding paradigm is introduced, which achieves encryption by inserting some randomization in the arithmetic coding procedure, and unlike previous works on encryption by arithmetic coding, this is done at no expense in terms of coding efficiency.
Abstract: We propose a novel multimedia security framework based on a modification of the arithmetic coder, which is used by most international image and video coding standards as entropy coding stage. In particular, we introduce a randomized arithmetic coding paradigm, which achieves encryption by inserting some randomization in the arithmetic coding procedure; notably, and unlike previous works on encryption by arithmetic coding, this is done at no expense in terms of coding efficiency. The proposed technique can be applied to any multimedia coder employing arithmetic coding; in this paper we describe an implementation tailored to the JPEG 2000 standard. The proposed approach turns out to be robust towards attempts to estimating the image or discovering the key, and allows very flexible protection procedures at the code-block level, allowing to perform total and selective encryption, as well as conditional access
TL;DR: Permanent-magnet-assisted synchronous reluctance motors are well suited to zero-speed sensorless control because of their inherently salient behavior but the cross-saturation effect can lead to large errors on the position estimate, which is based on the differential anisotropy.
Abstract: Permanent-magnet-assisted synchronous reluctance motors are well suited to zero-speed sensorless control because of their inherently salient behavior. However, the cross-saturation effect can lead to large errors on the position estimate, which is based on the differential anisotropy. These errors are quantified in this paper as a function of the working point. The errors that are calculated are then found to be in good accordance with the purposely obtained experimental measurements
TL;DR: A method for estimating the topology of a network based on the dynamical evolution supported on the network is suggested and can be also applied when disturbances and/or modeling errors are presented.
Abstract: We suggest a method for estimating the topology of a network based on the dynamical evolution supported on the network. Our method is robust and can be also applied when disturbances and/or modeling errors are presented. Several examples with networks of phase oscillators, pulse-coupled Hindmarch-Rose neurons, and Lorenz oscillators are provided to illustrate our approach.
TL;DR: In this article, the combustion properties of polypropylene (PP) composites were investigated. And the presence of Al-POSS leads to a decrease in combustion rate with respect to PP, resulting in a decrease of Heat Release Rate (−43% at 10-wt% POSS loading) as well as reduction in CO and CO2 production rates, whereas a negative effect on the above parameters is obtained with octaisobutyl POSS.
TL;DR: The introduction of discontinuous/non‐differentiable functions in the eXtended Finite‐Element Method allows to model discontinuities independent of the mesh structure, however, to compute the stiffness matrix of the elements intersected by the discontinuity, a subdivision of the element into quadrature subcells aligned with the discontinuit line is commonly adopted.
Abstract: The introduction of discontinuous/non-differentiable functions in the eXtended Finite-Element Method allows to model discontinuities independent of the mesh structure. However, to compute the stiffness matrix of the elements intersected by the discontinuity, a subdivision of the elements into quadrature subcells aligned with the discontinuity line is commonly adopted. In the paper, it is shown how standard Gauss quadrature can be used in the elements containing the discontinuity without splitting the elements into subcells or introducing any additional approximation. The technique is illustrated and developed in one, two and three dimensions for crack and material discontinuity problems
TL;DR: The achievable performance improvements of the proposed design procedure over Sky-Hook and clipped control laws are shown by means of simulation results obtained using a nonlinear half car model which proved to give an accurate description of the overall vertical dynamics of a vehicle equipped with continuous damping suspension systems.
Abstract: The problem considered in this paper is the design and analysis of a control strategy, for semi-active suspensions in road vehicles, based on model-predictive control (MPC) techniques. The optimal control law we compute using predictive techniques, aims to optimize the suspension performances by minimizing a quadratic cost function, while ensuring that the magnitude of the forces generated by the control law satisfies the physical constraints of passive damping. The online computation difficulties related to the predictive-control law are overcome by means of a "fast" implementation of the MPC algorithm. A performance comparison with well-established semi-active control strategies, such as Sky-Hook control and clipped control is presented. The achievable performance improvements of the proposed design procedure over Sky-Hook and clipped control laws are shown by means of simulation results obtained using a nonlinear half car model which proved to give an accurate description of the overall vertical dynamics of a vehicle equipped with continuous damping suspension systems
TL;DR: Boano et al. as mentioned in this paper used a physically-based morphodynamic model to predict the characteristics of the flow field in a meandering river and the temporal evolution of its planimetry.
Abstract: [1] A model for the evaluation of the intra-meander hyporheic exchange fluxes is presented. The method relies on a physically-based morphodynamic model to predict the characteristics of the flow field in a meandering river and the temporal evolution of its planimetry. The hyporheic fluxes induced at the meander scale by the river sinuosity can therefore be computed. The application of the model to a simulated case has shown the fundamental role of the river planimetry on the hyporheic exchange pattern at the meander scale, and its influence on the long-term evolution of the hyporheic exchange. Citation: Boano, F., C. Camporeale, R. Revelli, and L. Ridolfi (2006), Sinuositydriven hyporheic exchange in meandering rivers, Geophys. Res. Lett., 33, L18406, doi:10.1029/2006GL027630.
TL;DR: In this article, a spinel-type oxide catalysts AB 2 O 4 (where A = Co and Mn, and B = Cr and Fe) were used to remove soot and NO x from diesel exhaust in the temperature range of 350-450°C.
TL;DR: A minimalist probabilistic framework is used to analyze the emergence of statistically stable conditions favorable to tree‐grass coexistence in savannas and it is found that these conditions can be induced and stabilized by the stochastic fire regime.
Abstract: Fires play an important role in determining the composition and structure of vegetation in semiarid ecosystems. The study of the interactions between fire and vegetation requires a stochastic approach because of the random and unpredictable nature of fire occurrences. To this end, this article develops a minimalist probabilistic framework to investigate the impact of intermittent fire occurrences on the temporal dynamics of vegetation. This framework is used to analyze the emergence of statistically stable conditions favorable to tree‐grass coexistence in savannas. It is found that these conditions can be induced and stabilized by the stochastic fire regime. A decrease in fire frequency leads to bush encroachment, while more frequent and intense fires favor savanna‐to‐grassland conversions. The positive feedback between fires and vegetation can convert states of tree‐grass coexistence in semiarid savannas into bistable conditions, with both woodland and grassland as possible, though mutually exc...
TL;DR: In this paper, the role of turbulent mixing on particle formation in confined impinging jet reactors is investigated and computational fluid dynamics and simple precipitation models are used to derive scale-up criteria for the production of nanoparticles.
Abstract: In recent years there has been a growing interest in production on an industrial scale of particles with size in the sub-micron range (40-200 nm). This can be done by controlling particle formation in order to nucleate very small particles and by tailoring the particle surface in order to avoid particle aggregation and produce stable suspensions. In this work we focus on the role of turbulent mixing on particle formation in confined impinging jet reactors. In particular, we show how computational fluid dynamics and simple precipitation models could be used to derive scale-up criteria for the production of nanoparticles. © 2006 American Institute of Chemical Engineers AIChE J, 2006
TL;DR: A reliability-oriented place and route algorithm is presented that is able to effectively mitigate the effects of the considered faults and is demonstrated by extensive fault injection experiments showing that the capability of tolerating SEU effects in the FPGA's configuration memory increases up to 85 times with respect to a standard TMR design technique.
Abstract: The very high integration levels reached by VLSI technologies for SRAM-based field programmable gate arrays (FPGAs) lead to high occurrence-rate of transient faults induced by single event upsets (SEUs) in FPGAs' configuration memory. Since the configuration memory defines which circuit an SRAM-based FPGA implements, any modification induced by SEUs may dramatically change the implemented circuit. When such devices are used in safety-critical applications, fault-tolerant techniques are needed to mitigate the effects of SEUs in FPGAs' configuration memory. In this paper, we analyze the effects induced by the SEUs in the configuration memory of SRAM-based FPGAs. The reported analysis outlines that SEUs in the FPGA's configuration memory are particularly critical since they are able to escape well-known fault masking techniques such as triple modular redundancy (TMR). We then present a reliability-oriented place and route algorithm that, coupled with TMR, is able to effectively mitigate the effects of the considered faults. The effectiveness of the new reliability-oriented place and route algorithm is demonstrated by extensive fault injection experiments showing that the capability of tolerating SEU effects in the FPGA's configuration memory increases up to 85 times with respect to a standard TMR design technique
TL;DR: In this paper, a model of BC oxidation was developed based on Wagner's theory, which predicts a parabolic law for the growth of TGO scale, and the analysis of stress distribution in the system was performed.
TL;DR: In this article, a stochastic model of riparian vegetation ecosystem dynamics forced by random variations in river discharge is proposed, and the analytical expressions of the probability density function of the overall vegetation biomass and its first moments are obtained.
Abstract: [1] Riparian vegetation is part of one of the most diverse and fragile ecotones The key role played by river discharge on the dynamics of riparian vegetation has been widely studied and documented However, although randomness is a fundamental characteristic of river hydrology, very few quantitative vegetation studies take into account the random nature of river discharge Here we propose a stochastic model of riparian vegetation ecosystem dynamics forced by random variations in river discharge The model is solved, and the analytical expressions of the probability density function of the overall vegetation biomass and its first moments are obtained These theoretical results are used to investigate the effect of river hydrology on the distribution of vegetation along the riparian transect transverse to the river In particular, the influence of the type of riparian species and the statistical characteristics of discharge time series are discussed and compared with field observations
TL;DR: In this paper, a large number of Cu-based archaeological artefacts from the Mediterranean basin have been selected for investigation of their chemical composition, metallurgical features and corrosion products (i.e. the patina).
Abstract: A large number of Cu-based archaeological artefacts from the Mediterranean basin have been selected for investigation of their chemical composition, metallurgical features and corrosion products (i.e. the patina). The guidelines for the selection of the Cu-based artefacts have taken into account the representativeness of the Mediterranean archaeological context, the manufacturing technique, the degradation state and the expected chemical composition and structure of the objects. The results show wide variation of the chemical composition of the alloys that include all kinds of ancient Cu-based alloys such as low and high tin, and also leaded bronzes, copper and copper-iron alloys. The examination of the alloy matrix shows largely different metallurgical features thus indicating the use of different manufacturing techniques for producing the artefacts. The results of the micro-chemical investigation of the patina show the structures and the chemical composition of the stratified corrosion layers where copper or tin depletion phenomenon are commonly observed with a remarkably surface enrichment of some soil elements such as P, S, Ca, Si, Fe, Al and Cl. This information indicates the strict interaction between soil components and corrosion reactions and products. In particular, the ubiquitous and near constant presence of chlorine in the corrosion layers is observed in the patina of the archaeological Cu-based artefacts found in different contexts in Italy, Turkey, Jordan, Egypt, Spain and Tunisia. This latter occurrence is considered dangerous because it could induce a cyclic corrosion reaction of copper that could disfigure the artefact. The micro-chemical and micro-structural results also show that another source of degradation of the bronze archaeological artefacts, are their intrinsic metallurgical features whose formation is induced during the manufacturing of the objects, carried out in ancient times by repeated cycles of cold or hot mechanical work and thermal treatments. These combined treatments induce crystallisation and segregation phenomena of the impurities along the grain boundaries and could cause mechanical weakness and increase the extent of the inter-granular corrosion phenomena. [ABSTRACT FROM AUTHOR]
TL;DR: In this article, the authors present the advantages of dual-three phase induction motor drives over the conventional three-phase drives and the different applications reported in the literature, and briefly present their advantages over conventional 3-phase motor drives.
Abstract: The paper aims to perform an overview on the state-of-the-art in the control of multi-phase drives employing dual-three phase induction machines. In particular, the paper is focused on modeling aspects, Pulse-Width Modulation (PWM) techniques for Voltage Source Inverters (VSI), Field Oriented Control (FOC) and Direct Torque Control (DTC) strategies for dual-three phase induction machines. Furthermore, the paper briefly presents the advantages of dual-three phase induction motor drives over the conventional three-phase drives and the different applications reported in the literature.
TL;DR: In this article, the vertical distribution of plant roots in water controlled ecosystems was analyzed to determine the shape of the root profile. But the root profiles were not determined by the distribution of incoming rainfall pulses, and the root systems are deeper where the soils are coarse-textured and the evaporative demand slightly exceeds precipitation.
Abstract: [1] We propose an analytical model to relate the vertical distribution of plant roots in water controlled ecosystems to the local climatic and pedologic conditions. We find that the shape of the root profile is determined by the distribution of the incoming rainfall pulses, and that the rooting systems are deeper where the soils are coarse-textured and the evaporative demand slightly exceeds precipitation.
TL;DR: The TOPICA (TOrino Polytechnic Ion Cyclotron Antenna) code as mentioned in this paper was developed to handle the actual geometry of ICRF antennas (with curved, solid straps, a general shape housing, Faraday screen, etc).
Abstract: The demand for a predictive tool to help in designing ion-cyclotron radio frequency (ICRF) antenna systems for today's fusion experiments has driven the development of codes such as ICANT, RANT3D, and the early development of TOPICA (TOrino Polytechnic Ion Cyclotron Antenna) code. This paper describes the substantive evolution of TOPICA formulation and implementation that presently allow it to handle the actual geometry of ICRF antennas (with curved, solid straps, a general-shape housing, Faraday screen, etc) as well as an accurate plasma description, accounting for density and temperature profiles and finite Larmor radius effects. The antenna is assumed to be housed in a recess-like enclosure. Both goals have been attained by formally separating the problem into two parts: the vacuum region around the antenna and the plasma region inside the toroidal chamber. Field continuity and boundary conditions allow formulating of a set of two coupled integral equations for the unknown equivalent (current) sources; then the equations are reduced to a linear system by a method of moments solution scheme employing 2D finite elements defined over a 3D non-planar surface triangular-cell mesh. In the vacuum region calculations are done in the spatial (configuration) domain, whereas in the plasma region a spectral (wavenumber) representation of fields and currents is adopted, thus permitting a description of the plasma by a surface impedance matrix. Owing to this approach, any plasma model can be used in principle, and at present the FELICE code has been employed. The natural outcomes of TOPICA are the induced currents on the conductors (antenna, housing, etc) and the electric field in front of the plasma, whence the antenna circuit parameters (impedance/scattering matrices), the radiated power and the fields (at locations other than the chamber aperture) are then obtained. An accurate model of the feeding coaxial lines is also included. The theoretical model and its TOPICA implementation have been fully validated against measured data both in vacuo and in plasma-facing conditions for real-life structures.
06 Feb 2006
TL;DR: A current control scheme based on four digital current controllers in the stationary reference frame is proposed that provides operation with low values of low-order output voltage harmonics of a dual three-phase induction machine.
Abstract: Vector control of a dual three-phase induction machine, with two sets of three-phase stator windings spatially shifted by 30 electrical degrees, is elaborated in the paper. The stator windings are fed from a current-controlled PWM six-phase IGBT voltage source inverter (VSI). The main problem in realisation of such a drive is an adequate current control algorithm, which has to cope with the inherent asymmetries of the drive. Furthermore, the digital implementation has to ensure zero steady state current error for the whole frequency range of the drive. After reviewing the existing solutions, the paper proposes a current control scheme that is based on four digital current controllers in the stationary reference frame. A design procedure for the current controllers is presented and current controllers are implemented in a laboratory test rig, in conjunction with a previously developed PWM scheme that provides operation with low values of low-order output voltage harmonics. Experimental tests are conducted and the results are given for a direct rotor field oriented control (DRFOC) of a 10 kW dual three-phase induction motor drive prototype. The results confirm the validity of the control scheme.
11 Dec 2006
TL;DR: In this article, the authors deal with the endwinding cooling problems of Total Enclosed Fan Cooled (TEFC) induction motors and obtain information about the phenomena involved in the motor end space, three "ad hoc" prototypes have been built.
Abstract: The paper deals with the endwinding cooling problems of Total Enclosed Fan Cooled (TEFC) induction motors. In order to obtain information about the phenomena involved in the motor end space, three "ad hoc" prototypes have been build. The complete test bench set up together the followed test procedures are reported in detail. The measurement results have shown that all the motor part overtemperatures (winding, endwindings, stator lamination and external motor frame) decreasing with the inner air speed increasing. The measured motor overtemperatures and losses allow the thermal resistance identification of a simplified thermal model suitable to describe the thermal behaviors of the prototypes. By the thermal resistance between the endwinding and the motor frame, the related heat exchange coefficients have been evaluated as a function of the rotor speed. The proposed procedure allows separating the forced convection contribution by the other thermal exchange phenomena that occur in the end space regions. The obtained heat transfer coefficients are in agreement with the results reported in the past literature.