Showing papers by "Polytechnic University of Turin published in 2005"

Uncertain convex programs: randomized solutions and confidence levels

Abstract: Many engineering problems can be cast as optimization problems subject to convex constraints that are parameterized by an uncertainty or ‘instance’ parameter. Two main approaches are generally available to tackle constrained optimization problems in presence of uncertainty: robust optimization and chance-constrained optimization. Robust optimization is a deterministic paradigm where one seeks a solution which simultaneously satisfies all possible constraint instances. In chance-constrained optimization a probability distribution is instead assumed on the uncertain parameters, and the constraints are enforced up to a pre-specified level of probability. Unfortunately however, both approaches lead to computationally intractable problem formulations. In this paper, we consider an alternative ‘randomized’ or ‘scenario’ approach for dealing with uncertainty in optimization, based on constraint sampling. In particular, we study the constrained optimization problem resulting by taking into account only a finite set of N constraints, chosen at random among the possible constraint instances of the uncertain problem. We show that the resulting randomized solution fails to satisfy only a small portion of the original constraints, provided that a sufficient number of samples is drawn. Our key result is to provide an efficient and explicit bound on the measure (probability or volume) of the original constraints that are possibly violated by the randomized solution. This volume rapidly decreases to zero as N is increased.

Battery choice and management for new-generation electric vehicles

Abstract: Different types of electric vehicles (EVs) have been recently designed with the aim of solving pollution problems caused by the emission of gasoline-powered engines. Environmental problems promote the adoption of new-generation electric vehicles for urban transportation. As it is well known, one of the weakest points of electric vehicles is the battery system. Vehicle autonomy and, therefore, accurate detection of battery state of charge (SoC) together with battery expected life, i.e., battery state of health, are among the major drawbacks that prevent the introduction of electric vehicles in the consumer market. The electric scooter may provide the most feasible opportunity among EVs. They may be a replacement product for the primary-use vehicle, especially in Europe and Asia, provided that drive performance, safety, and cost issues are similar to actual engine scooters. The battery system choice is a crucial item, and thanks to an increasing emphasis on vehicle range and performance, the Li-ion battery could become a viable candidate. This paper deals with the design of a battery pack based on Li-ion technology for a prototype electric scooter with high performance and autonomy. The adopted battery system is composed of a suitable number of cells series connected, featuring a high voltage level. Therefore, cell equalization and monitoring need to be provided. Due to manufacturing asymmetries, charge and discharge cycles lead to cell unbalancing, reducing battery capacity and, depending on cell type, causing safety troubles or strongly limiting the storage capacity of the full pack. No solution is available on the market at a cheap price, because of the required voltage level and performance, therefore, a dedicated battery management system was designed, that also includes a battery SoC monitoring. The proposed solution features a high capability of energy storing in braking conditions, charge equalization, overvoltage and undervoltage protection and, obviously, SoC information in order to optimize autonomy instead of performance or vice-versa.

Evidence for a kaon-bound state K(-)pp produced in K(-) absorption reactions at rest.

Abstract: We have searched for a deeply bound kaonic state by using the FINUDA spectrometer installed at the e{sup +}e{sup -} collider DA{phi}NE. Almost monochromatic K{sup -}'s produced through the decay of {phi}(1020) mesons are used to observe K{sup -} absorption reactions stopped on very thin nuclear targets. Taking this unique advantage, we have succeeded to detect a kaon-bound state K{sup -}pp through its two-body decay into a {lambda} hyperon and a proton. The binding energy and the decay width are determined from the invariant-mass distribution as 115{sub -5}{sup +6}(stat){sub -4}{sup +3}(syst) MeV and 67{sub -11}{sup +14}(stat){sub -3}{sup +2}(syst) MeV, respectively.

Quantifying signals with power-law correlations: a comparative study of detrended fluctuation analysis and detrended moving average techniques.

Abstract: Detrended fluctuation analysis (DFA) and detrended moving average (DMA) are two scaling analysis methods designed to quantify correlations in noisy nonstationary signals. We systematically study the performance of different variants of the DMA method when applied to artificially generated long-range power-law correlated signals with an a priori known scaling exponent alpha(0) and compare them with the DFA method. We find that the scaling results obtained from different variants of the DMA method strongly depend on the type of the moving average filter. Further, we investigate the optimal scaling regime where the DFA and DMA methods accurately quantify the scaling exponent alpha(0) , and how this regime depends on the correlations in the signal. Finally, we develop a three-dimensional representation to determine how the stability of the scaling curves obtained from the DFA and DMA methods depends on the scale of analysis, the order of detrending, and the order of the moving average we use, as well as on the type of correlations in the signal.

Magnetic charges in local field theory

Abstract: Novel lagrangians are discussed in which (non-abelian) electric and magnetic gauge fields appear on a par. To ensure that these lagrangians describe the correct number of degrees of freedom, tensor gauge fields are included with corresponding gauge symmetries. Non-abelian gauge symmetries that involve both the electric and the magnetic gauge fields can then be realized at the level of a single gauge invariant Lagrangian, without the need of performing duality transformations prior to introducing the gauge couplings. The approach adopted, which was initially developed for gaugings of maximal supergravity, is particularly suited for the study of flux compactifications

Mechanistic analytical models for long-distance seed dispersal by wind.

Abstract: We introduce an analytical model, the Wald analytical long‐distance dispersal (WALD) model, for estimating dispersal kernels of wind‐dispersed seeds and their escape probability from the canopy. The model is based on simplifications to well‐established three‐dimensional Lagrangian stochastic approaches for turbulent scalar transport resulting in a two‐parameter Wald (or inverse Gaussian) distribution. Unlike commonly used phenomenological models, WALD’s parameters can be estimated from the key factors affecting wind dispersal—wind statistics, seed release height, and seed terminal velocity—determined independently of dispersal data. WALD’s asymptotic power‐law tail has an exponent of −3/2, a limiting value verified by a meta‐analysis for a wide variety of measured dispersal kernels and larger than the exponent of the bivariate Student t‐test (2Dt). We tested WALD using three dispersal data sets on forest trees, heathland shrubs, and grassland forbs and compared WALD’s performance with that of ot...

On the Optimal Design of Triple Modular Redundancy Logic for SRAM-based FPGAs

Abstract: Triple modular redundancy (TMR) is a suitable fault tolerant technique for SRAM-based FPGA However, one of the main challenges in achieving 100% robustness in designs protected by TMR running on programmable platforms is to prevent upsets in the routing from provoking undesirable connections between signals from distinct redundant logic parts, which can generate an error in the output This paper investigates the optimal design of the TMR logic (eg, by cleverly inserting voters) to ensure robustness Four different versions of a TMR digital filter were analyzed by fault injection Faults were randomly inserted straight into the bitstream of the FPGA The experimental results presented in this paper demonstrate that the number and placement of voters in the TMR design can directly affect the fault tolerance, ranging from 403% to 098% the number of upsets in the routing able to cause an error in the TMR circuit

Singular limits in liouville-type equations

Abstract: We consider the boundary value problem $ \Delta u + \varepsilon ^{2} k{\left( x \right)}e^{u} = 0$ in a bounded, smooth domain $\Omega$ in $ \mathbb{R}^{{\text{2}}} $ with homogeneous Dirichlet boundary conditions. Here $$ \varepsilon > 0,k(x) $$ is a non-negative, not identically zero function. We find conditions under which there exists a solution $ u_{\varepsilon } $ which blows up at exactly m points as $ \varepsilon \to 0 $ and satisfies $ \varepsilon ^{2} {\int_\Omega {ke^{{u_{\varepsilon } }} \to 8m\pi } }% $ . In particular, we find that if $k\in C^2(\bar\Omega)$ , $ \inf _{\Omega } k > 0 $ and $\Omega$ is not simply connected then such a solution exists for any given $m \ge 1$

Space-time decoding with imperfect channel estimation

Abstract: Under the assumption of a frequency-flat slow Rayleigh fading channel with multiple transmit and receive antennas, we examine the effects of imperfect estimation of the channel parameters on error probability when known pilot symbols are transmitted among information data. Three different receivers are considered. The first one derives an estimate of the channel [by using either a maximum-likelihood (ML) or a minimum mean square error (MMSE) criterion], and then uses this estimate in the same metric that would be applied if the channel were perfectly known. The second receiver derives again an estimate of the channel, but uses the ML metric conditioned on the channel estimate. Our last receiver simultaneously processes the pilot and data symbols received. Simulation results are exhibited, showing that only a relatively small percentage of the transmitted frame need be allocated to pilot symbols in order to experience an acceptable degradation of error probability due to imperfect channel knowledge. Algorithms for the recursive calculation of the decision metric of the last two receivers are also developed for application to sequential decoding of trellis space-time codes.

Friction Compensation in Robotics: an Overview

Abstract: Friction effects are particularly critical for industrial robots, since they can induce large positioning errors, stick-slip motions, and limit cycles. This paper offers a reasoned overview of the main friction compensation techniques that have been developed in the last years, regrouping them according to the adopted kind of control strategy. Some experimental results are reported, to show how the control performances can be affected not only by the chosen method, but also by the characteristics of the available robotic architecture and of the executed task.

Information and Willingness to Pay in a Contingent Valuation Study: The Value of S. Erasmo in the Lagoon of Venice

Abstract: This paper reports on a contingent valuation (CV) study eliciting willingness to pay (WTP) for a public program for the preservation of lagoon, beach and infrastructure in the island of S. Erasmo in the Lagoon of Venice, Italy. We use split samples to investigate the effect of providing a summary of reasons for voting in favor and against the program before the referendum valuation question. Reminding respondents of the reasons for voting for or against the program increases WTP among less highly educated respondents, and decreases WTP among more highly educated respondents.

On the use of Saint Venant equations to simulate the spreading of a granular mass

Abstract: [1] Cliff collapse is an active geomorphological process acting at the surface of the Earth and telluric planets. Recent laboratory studies have investigated the collapse of an initially cylindrical granular mass along a rough horizontal plane for different initial aspect ratios a = Hi/Ri, where Hi and Ri are the initial height and radius, respectively. A numerical simulation of these experiments is performed using a minimal depth-integrated model based on a long-wave approximation. A dimensional analysis of the equations shows that such a model exhibits the scaling laws observed experimentally. Generic solutions are independent of gravity and depend only on the initial aspect ratio a and an effective friction angle. In terms of dynamics, the numerical simulations are consistent with the experiments for a ≤ 1. The experimentally observed saturation of the final height of the deposit, when normalized with respect to the initial radius of the cylinder, is accurately reproduced numerically. Analysis of the results sheds light on the correlation between the area overrun by the granular mass and its initial potential energy. The extent of the deposit, the final height, and the arrest time of the front can be directly estimated from the “generic solution” of the model for terrestrial and extraterrestrial avalanches. The effective friction, a parameter classically used to describe the mobility of gravitational flows, is shown to depend on the initial aspect ratio a. This dependence should be taken into account when interpreting the high mobility of large volume events.

Design and optimization of a MEMS electret-based capacitive energy scavenger

Abstract: In this paper, a method for the design and optimization of an electret-based vibration-to-electric microconverter is presented, using a nonlinear dynamical model of the device. The dynamics of the converter is analyzed in detail, showing the importance of properly accounting for the nonlinearity in the optimization process. A procedure to determine a set of optimization parameters is finally presented.

Magnetization Switching and Microwave Oscillations in Nanomagnets Driven by Spin-Polarized Currents

Abstract: A novel theoretical approach to magnetization dynamics driven by spin-polarized currents is presented. Complete stability diagrams are obtained for the case where spin torques and external magnetic fields are simultaneously present. Quantitative predictions are made for the critical currents and fields inducing magnetization switching, for the amplitude and frequency of magnetization self-oscillations, and for the conditions leading to hysteretic transitions between self-oscillations and stationary states.

Are scaling laws on strength of solids related to mechanics or to geometry

Abstract: One of the largest controversial issues of the materials science community is the interpretation of scaling laws on material strength. In spite of the prevailing view, which considers mechanics as the real cause of such effects, here, we propose a different argument, purely based on geometry. Thus, as happened for relativity, geometry could again hold an unexpected and fundamental role.

Advanced Testing and Characterization of Interlayer Shear Resistance

Abstract: The performance of multilayered pavement systems depends strongly on interlayer bonding. To guarantee good bonding, tack coats (also called bond coats) are usually applied at various interfaces during pavement construction or overlay. The effectiveness of the tack coat can be assessed with the use of several devices arranged by different laboratories to evaluate interlayer shear resistance. This paper shows how interlayer shear resistance may be evaluated through the Ancona shear testing research and analysis (ASTRA) device. ASTRA results, expressed in units of maximum interlayer shear stress (τpeak) highlight the effects of various influence parameters such as type of interface treatment, curing time, procedure of specimen preparation, temperature, and applied normal load. Moreover, this paper compares the τpeak results obtained by two different shear test devices: the ASTRA tester designed and developed in the Polytechnic University of Marche (Italy) and the layer-parallel direct shear tester created by...

Two-parameter deformations of logarithm, exponential, and entropy: A consistent framework for generalized statistical mechanics

Abstract: A consistent generalization of statistical mechanics is obtained by applying the maximum entropy principle to a trace-form entropy and by requiring that physically motivated mathematical properties are preserved. The emerging differential-functional equation yields a two-parameter class of generalized logarithms, from which entropies and power-law distributions follow: these distributions could be relevant in many anomalous systems. Within the specified range of parameters, these entropies possess positivity, continuity, symmetry, expansibility, decisivity, maximality, concavity, and are Lesche stable. The Boltzmann-Shannon entropy and some one-parameter generalized entropies already known belong to this class. These entropies and their distribution functions are compared, and the corresponding deformed algebras are discussed.

Variable temperature infrared spectroscopy: A convenient tool for studying the thermodynamics of weak solid–gas interactions

Abstract: This tutorial review describes the use of variable temperature infrared spectroscopy of adsorbed species (VTIR), a recent method for studying the thermodynamics of weak solid–gas interactions. Examples show how a fundamental relationship of thermodynamics (the van't Hoff equation, used long since in several fields of physical chemistry) can describe equilibrium processes at the solid–gas interface. The VTIR method is fully exploited by measuring absorbance of an IR band, temperature and pressure over a wide temperature range: an estimation of the interaction energy is, however, possible even ignoring the equilibrium pressure. Precise thermodynamic characterization of solid–gas interactions is required in several fields: on the applied side, gas sensing, separation and storage, which involve such areas as work-place security, air pollution control and the energy sector; regarding fundamental knowledge, weak solid–gas interactions are relevant to a number of fields, including hydrogen bonding, coordination chemistry and surface phenomena in a broad sense.Infrared (IR) spectroscopy of (gas) molecules adsorbed on a solid is frequently used to characterize both, the adsorbed species and the adsorbing centres at the solid surface. The potential of the technique can be greatly enhanced by obtaining IR spectra over a temperature range, and simultaneously measuring IR absorbance, temperature and equilibrium pressure. When this is done, variable temperature infrared (VTIR) spectroscopy can be used not only for a more detailed surface characterization, but also for precise studies on the thermodynamics of solid–gas interactions. Furthermore, when weak interactions are concerned, the technique shows favourable features compared to adsorption calorimetry, or to other classical methods. The potential of the VTIR method is highlighted by reviewing recently reported studies on dihydrogen, dinitrogen and carbon monoxide adsorption on zeolites. To facilitate understanding, an outline of the basis of the method is also given, together with an appraisal of the critical points involved in its practical use.