IMT Institutional Repository: No conditions. Results ordered -Date Deposited.
2020-02-25T07:33:24Z
EPrints
http://eprints.imtlucca.it/images/logowhite.png
http://eprints.imtlucca.it/
2018-03-28T13:20:52Z
2018-03-28T13:20:52Z
http://eprints.imtlucca.it/id/eprint/4065
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4065
2018-03-28T13:20:52Z
Partitioned coupling of advection–diffusion–reaction systems and Brinkman flows
We present a partitioned algorithm aimed at extending the capabilities of existing solvers for the simulation of coupled advection–diffusion–reaction systems and incompressible, viscous flow. The space discretisation of the governing equations is based on mixed finite element methods defined on unstructured meshes, whereas the time integration hinges on an operator splitting strategy that exploits the differences in scales between the reaction, advection, and diffusion processes, considering the global system as a number of sequentially linked sets of partial differential, and algebraic equations. The flow solver presents the advantage that all unknowns in the system (here vorticity, velocity, and pressure) can be fully decoupled and thus turn the overall scheme very attractive from the computational perspective. The robustness of the proposed method is illustrated with a series of numerical tests in 2D and 3D, relevant in the modelling of bacterial bioconvection and Boussinesq systems.
Pietro Lenarda
Marco Paggi
marco.paggi@imtlucca.it
R. Ruiz Baier
2018-03-28T13:15:58Z
2018-03-28T13:15:58Z
http://eprints.imtlucca.it/id/eprint/4064
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4064
2018-03-28T13:15:58Z
A 3D finite strain model for intralayer and interlayer crack simulation coupling the phase field approach and cohesive zone model
In this study, a new 3D finite element formulation which enables simulating the interaction between brittle crack propagation and interface delamination in heterogeneous materials is presented. The Phase Field (PF) model for brittle fracture has been coupled with the Cohesive Zone Model (CZM) within the framework of the large deformation analysis. These numerical techniques have been implemented within a 8-node locking-free solid shell element, relying on the enhanced assumed strain concept, and a 8-node interface finite element, respectively. The predictive capabilities of the proposed formulation have been assessed through the simulation of cracking in flat and curved geometries under in-plane and out-ofplane loading conditions. The results show the ability of the model to predict complex crack paths where intralayer crack propagation and delamination occur simultaneously and interact. The proposed formulation provides a powerful modeling tool for the simulation of fracture phenomena in heterogeneous materials and laminate structures, which are characterized by the existence of numerous interfaces, such as in photovoltaic laminates.
Valerio Carollo
valerio.carollo@imtlucca.it
José Reinoso
Marco Paggi
marco.paggi@imtlucca.it
2018-03-28T13:09:05Z
2018-03-28T13:09:05Z
http://eprints.imtlucca.it/id/eprint/4062
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4062
2018-03-28T13:09:05Z
Inkjet printed 2D-crystal based strain gauges on paper
We present an investigation of inkjet printed strain gauges based on two-dimensional (2D) materials. The technology leverages water-based and biocompatible inks to fabricate strain measurement devices on flexible substrates such as paper. We demonstrate that the device performance and sensitivity are strongly dependent on the printing parameter (i.e., drop-spacing, number of printing passes, etc.). We show that values of the Gauge Factor up to 125 can be obtained, with large sensitivity (>20) even when small strains (0.3) are applied. Furthermore, we provide preliminary examples of heterostructure-based strain sensors, enabled by the inkjet printing technology.
C. Casiraghi
M. Macucci
K. Parvez
R. Worsley
Y. Shin
F. Bronte
Claudia Borri
claudia.borri@imtlucca.it
Marco Paggi
marco.paggi@imtlucca.it
G. Fiori
2018-03-28T13:00:53Z
2018-03-28T13:00:53Z
http://eprints.imtlucca.it/id/eprint/4061
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4061
2018-03-28T13:00:53Z
Long-term EVA degradation simulation: Climatic zones comparison and possible revision of accelerated tests
The increasing demand of photovoltaics installations, also in harsh climatic conditions, requires the accurate comprehension of module lifetime and durability. Accelerated environmental tests (damp heat, thermal cycling, and humidity freeze) are performed as pass/fail criteria to determine whether modules are suitable for sale, while do not accurate predict durability in all possible climates. Recently, we proposed a computational model to study the thermo-oxidative degradation of EVA encapsulant. This model was suitable to describe effects of temperature fluctuations on degradation, while neglecting dramatic changes of outdoor exposure in different climatic zones. To investigate the correlation between climatic zones and EVA degradation, we completed the existing degradation model by adding the UV exposure dependency. This model, for the first time, simulates EVA thermo-photo-oxidation in accelerated and environmental conditions. We compared results of simulated standard accelerated tests and outdoor exposure, observing a significant mismatch of results. The low prediction capability of standard tests pushed us to analyze modified accelerated tests, by adding an internal UV source. Modified test simulations show a better matching with outdoor long-term weathering. The modified setup will enable novel accelerated tests with predictive behavior of long-term EVA degradation and a more accurate PV module lifetime.
Mariacristina Gagliardi
mariacristina.gagliardi@imtlucca.it
Marco Paggi
marco.paggi@imtlucca.it
2018-03-12T11:03:10Z
2018-03-12T11:03:10Z
http://eprints.imtlucca.it/id/eprint/4004
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4004
2018-03-12T11:03:10Z
A Periodic Tracking MPC that is Locally Equivalent to Periodic Economic MPC
Stability for economic Model Predictive Control (MPC) is in general difficult to establish. In contrast, tracking MPC has well-established stability guarantees, but can yield poor closed-loop performance in terms of the selected economic criterion. In Zanon et al. (2016), a formal procedure to design a tracking MPC scheme so as to locally approximate the behaviour of economic MPC was proposed for the case of optimal steady-state operation. In this paper, we extend that result to the periodic case and provide a procedure to compute the tracking stage cost numerically. We illustrate our developments in a simulated example.
Mario Zanon
mario.zanon@imtlucca.it
Sébastien Gros
Moritz Diehl
2018-03-12T11:01:45Z
2018-03-12T11:01:45Z
http://eprints.imtlucca.it/id/eprint/4017
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4017
2018-03-12T11:01:45Z
Regulation of Differential Drive Robots using Continuous Time MPC without Stabilizing Constraints or Costs
In this paper, model predictive control (MPC) of differential drive robots is considered. Here, we solve the set point stabilization problem without incorporating stabilizing constraints and/or costs in the MPC scheme. In particular, we extend recent results obtained in a discrete time setting to the continuous time domain. To this end, so called swaps and replacements are introduced in order to validate a growth condition on the value function and, thus, to rigorously prove asymptotic stability of the MPC closed loop for nonholonomic robots.
Karl Worthmann
Mohamed W. Mehrez
Mario Zanon
mario.zanon@imtlucca.it
George K.I. Mann
Raymond G. Gosine
Moritz Diehl
2018-03-12T10:59:23Z
2018-03-12T10:59:23Z
http://eprints.imtlucca.it/id/eprint/4029
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4029
2018-03-12T10:59:23Z
Airborne Wind Energy: Airfoil-Airmass Interaction
The Airborne Wind Energy paradigm proposes to generate energy by flying a tethered airfoil across the wind flow at a high velocity. While Airborne Wind Energy enables flight in higher-altitude, stronger wind layers, the extra drag generated by the tether motion imposes a significant limit to the overall system efficiency. To address this issue, two airfoils with a shared tether can reduce overall system drag. A study proposed in Zanon et al. (2013) confirms this claim by showing that, in the considered scenario, the dual-airfoil system is more advantageous than the single-airfoil one. The results computed in Zanon et al. (2013) however, do not model the interaction between the airfoils and the airmass. In this paper, the impact of the airfoil-airmass interaction on the extracted power is studied. As this phenomenon is complex to model, a blade element-momentum approach is proposed and the problem is solved by means of optimal control techniques.
Mario Zanon
mario.zanon@imtlucca.it
Sébastien Gros
Johan Meyers
Moritz Diehl
2018-03-12T10:57:31Z
2018-03-12T10:57:31Z
http://eprints.imtlucca.it/id/eprint/4031
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4031
2018-03-12T10:57:31Z
Orbit control for a power generating airfoil based on nonlinear MPC
The Airborne Wind Energy paradigm proposes to generate energy by flying a tethered airfoil across the wind flow. An essential problem posed by Airborne Wind Energy is the control of the tethered airfoil trajectory during power generation. Tethered flight is a fast, strongly nonlinear, unstable and constrained process, motivating control approaches based on fast Nonlinear Model Predictive Control. In this paper, a computationally efficient 6-DOF control model for a high performance, large-scale, rigid airfoil is proposed. A control scheme based on receding-horizon Nonlinear Model Predictive Control to track reference trajectories is applied to the proposed model. In order to make a real-time application of Nonlinear Model Predictive Control possible, a Real-Time Iteration scheme is proposed and its performance investigated.
Sébastien Gros
Mario Zanon
mario.zanon@imtlucca.it
Moritz Diehl
2018-03-12T10:55:17Z
2018-03-12T10:55:17Z
http://eprints.imtlucca.it/id/eprint/4027
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4027
2018-03-12T10:55:17Z
Nonlinear MPC and MHE for Mechanical Multi-Body Systems with Application to Fast Tethered Airplanes
Mechanical applications often require a high control frequency to cope with fast dynamics. The control frequency of a nonlinear model predictive controller depends strongly on the symbolic complexity of the equations modeling the system. The symbolic complexity of the model equations for multi-body mechanical systems can often be dramatically reduced by using representations based on non-minimal coordinates, which result in index-3 differential-algebraic equations (DAEs). This paper proposes a general procedure to efficiently treat multi-body mechanical systems in the context of MHE & NMPC using non-minimal coordinate representations, and provides the resulting computational times that can be achieved on a tethered airplane system using code generation.
Sébastien Gros
Mario Zanon
mario.zanon@imtlucca.it
Milan Vukov
Moritz Diehl
2018-03-12T10:52:20Z
2018-03-12T10:52:20Z
http://eprints.imtlucca.it/id/eprint/4024
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4024
2018-03-12T10:52:20Z
An Experimental Test Setup for Advanced Estimation and Control of an AirborneWind Energy System
This chapter gives a detailed description of a test setup developed at KU Leuven for the launch and recovery of unpropelled tethered airplanes. The airplanes are launched by bringing them up to flying speed while attached by a tether to the end of a rotating arm. In the development of the setup, particular care was taken to allow experimental validation of advanced estimation and control techniques such as moving horizon estimation and model predictive control. A detailed overview of the hardware, sensors and software used on this setup is given in this chapter. The applied estimation and control techniques are outlined in this chapter as well, and an analysis of the closed loop performance is given.
Kurt Geebelen
Milan Vukov
Mario Zanon
mario.zanon@imtlucca.it
Sébastien Gros
Andrew Wagner
Moritz Diehl
Dirk Vandepitte
Jan Swevers
Hammad Ahmad
2018-03-12T10:50:31Z
2018-03-12T10:50:31Z
http://eprints.imtlucca.it/id/eprint/4025
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4025
2018-03-12T10:50:31Z
Airborne Wind Energy Based on Dual Airfoils
The airborne wind energy (AWE) paradigm proposes to generate energy by flying a tethered airfoil across the wind flow at a high velocity. Although AWE enables flight in higher altitude and stronger wind layers, the extra drag generated by the tether motion imposes a significant limit to the overall system efficiency. To address this issue, two airfoils with a shared tether can reduce overall system drag. Although this technique may improve the efficiency of AWE systems, such improvement can only be achieved through properly balancing the system trajectories and parameters. This brief tackles that problem using optimal control. A generic procedure for modeling multiple-airfoil systems with equations of minimal complexity is proposed. A parametric study shows that at small and medium scales, dual-airfoil systems are significantly more efficient than single-airfoil systems, but they are less advantageous at very large scales.
Mario Zanon
mario.zanon@imtlucca.it
Sebastien Gros
Joel Andersson
Moritz Diehl
2018-03-12T10:47:52Z
2018-03-12T10:47:52Z
http://eprints.imtlucca.it/id/eprint/4026
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4026
2018-03-12T10:47:52Z
A Lyapunov function for periodic economic optimizing Model Predictive Control
Model Predictive Control (MPC) schemes are commonly using reference-tracking cost functions, which have attractive properties in terms of stability and numerical implementation. However, many control applications have clear economic objectives that can be used directly as the NMPC cost function. Such NMPC schemes are labelled Economic NMPC. Unfortunately, Economic NMPC schemes suffer from some drawbacks. In particular, stability results for economic NMPC are still very sparse. A Lyapunov function for Economic NMPC was first proposed in [1] for problems having a steady-state optimum. The present paper develops a further generalization and clarification of these results for periodic systems.
Mario Zanon
mario.zanon@imtlucca.it
Sebastien Gros
Moritz Diehl
2018-03-12T10:45:32Z
2018-03-12T10:45:32Z
http://eprints.imtlucca.it/id/eprint/4023
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4023
2018-03-12T10:45:32Z
Model Predictive Control of Rigid-Airfoil Airborne Wind Energy Systems
In order to allow for a reliable and lasting operation of Airborne Wind Energy systems, several problems need to be addressed. One of the most important challenges regards the control of the tethered airfoil during power generation. Tethered flight of rigid airfoils is a fast, strongly nonlinear, unstable and constrained process, and one promising way to address the control challenge is the use of Nonlinear Model Predictive Control (NMPC) together with online parameter and state estimation based on Moving Horizon Estimation (MHE). In this paper, these techniques are introduced and their performance demonstrated in simulations of a 30 m wingspan tethered airplane with power generation in pumping mode.
Mario Zanon
mario.zanon@imtlucca.it
Sébastien Gros
Moritz Diehl
2018-03-12T10:30:55Z
2018-03-12T10:44:22Z
http://eprints.imtlucca.it/id/eprint/4020
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4020
2018-03-12T10:30:55Z
Control of Dual-Airfoil Airborne Wind Energy systems based on nonlinear MPC and MHE
Airborne Wind Energy (AWE) systems generate energy by flying a tethered airfoil across the wind flow at a high velocity. Tethered flight is a fast, strongly nonlinear, unstable and constrained process, motivating control approaches based on fast Nonlinear Model Predictive Control (NMPC) and state estimation approaches based on Moving Horizon Estimation (MHE). Dual-Airfoil AWE systems, i.e. systems with two airfoils attached to a Y-shaped tether have been shown to be more effective than systems based on a single airfoil. This paper proposes a control scheme for a dual-airfoil AWE system based on NMPC and MHE and studies its performance in a realistic scenario based on state-of-the-art turbulence models.
Mario Zanon
mario.zanon@imtlucca.it
Greg Horn
Sebastien Gros
Moritz Diehl
2018-03-12T10:30:32Z
2018-03-12T10:30:32Z
http://eprints.imtlucca.it/id/eprint/4021
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4021
2018-03-12T10:30:32Z
Model Predictive Control of Autonomous Vehicles
The control of autonomous vehicles is a challenging task that requires advanced control schemes. Nonlinear Model Predictive Control (NMPC) and Moving Horizon Estimation (MHE) are optimization-based control and estimation techniques that are able to deal with highly nonlinear, constrained, unstable and fast dynamic systems. In this chapter, these techniques are detailed, a descriptive nonlinear model is derived and the performance of the proposed control scheme is demonstrated in simulations of an obstacle avoidance scenario on a low-fricion icy road.
Mario Zanon
mario.zanon@imtlucca.it
Janick V. Frasch
Milan Vukov
Sebastian Sager
Moritz Diehl
2018-03-12T10:28:15Z
2018-03-12T10:28:15Z
http://eprints.imtlucca.it/id/eprint/4022
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4022
2018-03-12T10:28:15Z
Towards time-optimal race car driving using nonlinear MPC in real-time
This paper addresses the real-time control of autonomous vehicles under a minimum traveling time objective. Control inputs for the vehicle are computed from a nonlinear model predictive control (MPC) scheme. The time-optimal objective is reformulated such that it can be tackled by existing efficient algorithms for real-time nonlinear MPC that build on the generalized Gauss-Newton method. We numerically validate our approach in simulations and present a real-world hardware setup of miniature race cars that is used for an experimental comparison of different approaches.
Robin Verschueren
Stijn De Bruyne
Mario Zanon
mario.zanon@imtlucca.it
Janick V. Frasch
Moritz Diehl
2018-03-12T09:30:24Z
2018-03-12T09:30:24Z
http://eprints.imtlucca.it/id/eprint/4018
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4018
2018-03-12T09:30:24Z
Indefinite linear MPC and approximated economic MPC for nonlinear systems
The stability proof for economic model predictive control (MPC) relies on strict dissipativity, which is in general hard to check. In this contribution, we will first analyze the linear quadratic case with possibly indefinite cost. The conditions for stability will be recalled and it will be shown that every stabilizing LQR/MPC has an equivalent positive definite LQR/MPC which yields the same open loop and closed loop behavior. This analysis will then be used to formulate an approximated nonlinear economic MPC scheme, which has stability guarantees. An example will be used to illustrate the proposed technique and show its potential in terms of performance.
Mario Zanon
mario.zanon@imtlucca.it
Sébastien Gros
Moritz Diehl
2018-03-12T09:27:54Z
2018-03-12T09:27:54Z
http://eprints.imtlucca.it/id/eprint/4019
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4019
2018-03-12T09:27:54Z
Local properties of economic NMPC, dissipativity and dynamic programming
Classical model predictive control (MPC) implementations rely on a quadratic, positive definite cost function. In economic MPC on the contrary, the stage cost can be any generic function. Recent research has focused on establishing the conditions for stability of economic MPC where strict dissipativity has been shown to play an important role. In this paper, starting from the linear quadratic case and successively extending the analysis to the nonlinear case, we attempt at clarifying the relationship between strict dissipativity and the properties of the MPC optimal control problem.
Mario Zanon
mario.zanon@imtlucca.it
Sebastien Gros
Moritz Diehl
2018-03-12T09:25:10Z
2018-03-12T09:25:10Z
http://eprints.imtlucca.it/id/eprint/4014
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4014
2018-03-12T09:25:10Z
A compression algorithm for real-time distributed nonlinear MPC
Model Predictive Control (MPC) requires the online solution of an Optimal Control Problem (OCP) at each sampling time. Efficient online algorithms such as the Real-Time Iteration (RTI) scheme have been developed for real-time MPC implementations even for fast nonlinear dynamic systems. The RTI framework is based on direct Multiple Shooting (MS) for centralized systems. Distributed Multiple Shooting (DMS) is an MS-based OCP discretization strategy for distributed systems. Many fast dynamic systems can be described as connected subsystems and in order to exploit this structure, a DMS based RTI scheme has been developed and implemented in ACADO code generation. A novel technique called compression is proposed to reduce the dimensions of the convex subproblem, while exploiting the coupling structure. The performance of the presented scheme is illustrated on a nontrivial example from the literature, where a speedup of factor 11 in simulation time and factor 6 in the total computation time can be shown over the classical RTI scheme.
Rien Quirynen
Mario Zanon
mario.zanon@imtlucca.it
Attila Kozma
Moritz Diehl
2018-03-12T09:23:35Z
2018-03-12T09:23:35Z
http://eprints.imtlucca.it/id/eprint/4015
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4015
2018-03-12T09:23:35Z
Baumgarte stabilisation over the SO(3) rotation group for control
Representations of the SO(3) rotation group are crucial for airborne and aerospace applications. Euler angles is a popular representation in many applications, but yield models having singular dynamics. This issue is addressed via non-singular representations, operating in dimensions higher than 3. Unit quaternions and the Direction Cosine Matrix are the best known non-singular representations, and favoured in challenging aeronautic and aerospace applications. All nonsingular representations yield invariants in the model dynamics, i.e. a set of nonlinear algebraic conditions that must be fulfilled by the model initial conditions, and that remain fulfilled over time. However, due to numerical integration errors, these conditions tend to become violated when using standard integrators, making the model inconsistent with the physical reality. This issue poses some challenges when non-singular representations are deployed in optimal control. In this paper, we propose a simple technique to address the issue for classical integration schemes, establish formally its properties, and illustrate it on the optimal control of a satellite.
Sebastien Gros
Mario Zanon
mario.zanon@imtlucca.it
Moritz Diehl
2018-03-12T09:21:29Z
2018-03-12T09:21:29Z
http://eprints.imtlucca.it/id/eprint/4016
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4016
2018-03-12T09:21:29Z
Autogenerating microsecond solvers for nonlinear MPC: A tutorial using ACADO integrators
Nonlinear model predictive control (NMPC) allows one to explicitly treat nonlinear dynamics and constraints. To apply NMPC in real time on embedded hardware, online algorithms as well as efficient code implementations are crucial. A tutorial-style approach is adopted in this article to present such algorithmic ideas and to show how they can efficiently be implemented based on the ACADO Toolkit from MATLAB (MathWorks, Natick, MA, USA). Using its code generation tool, one can export tailored Runge–Kutta methods—explicit and implicit ones—with efficient propagation of their sensitivities. The article summarizes recent research results on autogenerated integrators for NMPC and shows how they allow to formulate and solve practically relevant problems in only a few tens of microseconds. Several common NMPC formulations can be treated by these methods, including those with stiff ordinary differential equations, fully implicit differential algebraic equations, linear input and output models, and continuous output independent of the integration grid. One of the new algorithmic contributions is an efficient implementation of infinite horizon closed-loop costing. As a guiding example, a full swing-up of an inverted pendulum is considered. Copyright © 2014 John Wiley & Sons, Ltd.
Rien Quirynen
M. Vukov
Mario Zanon
mario.zanon@imtlucca.it
Moritz Diehl
2018-03-12T09:20:18Z
2018-03-12T09:20:18Z
http://eprints.imtlucca.it/id/eprint/4013
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4013
2018-03-12T09:20:18Z
Estimation of uncertain ARX models with ellipsoidal parameter variability
Adeleh Mohammadi
Moritz Diehl
Mario Zanon
mario.zanon@imtlucca.it
2018-03-12T09:18:45Z
2018-03-12T09:18:45Z
http://eprints.imtlucca.it/id/eprint/4009
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4009
2018-03-12T09:18:45Z
Direct Optimal Control and Model Predictive Control
Mario Zanon
mario.zanon@imtlucca.it
Andrea Boccia
Vryan Gil S. Palma
Sonja Parenti
Ilaria Xausa
2018-03-12T09:16:28Z
2018-03-12T09:16:28Z
http://eprints.imtlucca.it/id/eprint/4042
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4042
2018-03-12T09:16:28Z
A relaxation strategy for the optimization of Airborne Wind Energy systems
Sébastien Gros
Mario Zanon
mario.zanon@imtlucca.it
Moritz Diehl
2018-03-12T09:13:16Z
2018-03-12T09:13:16Z
http://eprints.imtlucca.it/id/eprint/4043
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4043
2018-03-12T09:13:16Z
Nonlinear Moving Horizon Estimation for combined state and friction coefficient estimation in autonomous driving
Real-time autonomous driving requires a precise knowledge of the state and the ground parameters, especially in dangerous situations. In this paper, an accurate yet computationally efficient nonlinear multi-body vehicle model is developed, featuring a detailed Pacejka tire model, and a Moving Horizon Estimation (MHE) scheme is formulated. To meet the real-time requirements, an efficient algorithm based on the Real Time Iteration (RTI) scheme for the Direct Multiple Shooting method is exported through automatic C code generation. The exported plain C-code is tailored to the model dynamics, resulting in computation times in the range of a few milliseconds. In addition to state estimates, MHE provides friction coefficient estimates, allowing the controller to adapt to varying road conditions. Simulation results from an obstacle avoidance scenario on a low friction road are presented.
Mario Zanon
mario.zanon@imtlucca.it
J. V. Frasch
Moritz Diehl
2018-03-12T09:11:30Z
2018-03-12T09:11:30Z
http://eprints.imtlucca.it/id/eprint/4044
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4044
2018-03-12T09:11:30Z
Rotational start-up of tethered airplanes based on nonlinear MPC and MHE
The idea of Airborne Wind Energy (AWE) is to generate power by flying a tethered airfoil across the windflow. Tethered flight is a fast, strongly nonlinear, unstable and constrained process, motivating control approaches based on fast Nonlinear Model Predictive Control (NMPC) and state estimation approaches based on Moving Horizon Estimation (MHE). In particular, the start-up phase of AWE systems is an involved procedure, and starting and landing using NMPC has not been investigated yet. In this paper, a control strategy for starting-up AWE systems is proposed, based on a rotating carousel that is currently built at the KU Leuven. A computationally efficient 6-DOF control model for a small-scale, rigid airfoil is presented. We present and investigate a control scheme based on receding-horizon Nonlinear Model Predictive Control to track reference trajectories and Moving Horizon Estimation to estimate the actual system state and parameters. The MHE shceme is able to estimate also the wind speed, given no direct wind measurement.
Mario Zanon
mario.zanon@imtlucca.it
Sébastien Gros
Moritz Diehl
2018-03-12T09:04:11Z
2018-03-12T09:04:11Z
http://eprints.imtlucca.it/id/eprint/4045
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4045
2018-03-12T09:04:11Z
Control of Airborne Wind Energy systems based on Nonlinear Model Predictive Control amp; Moving Horizon Estimation
Among the several problems arising in the Airborne Wind Energy paradigm, an essential one is the control of the tethered airfoil trajectory during power generation. Tethered flight is a fast, strongly nonlinear, unstable and constrained process, motivating control approaches based on fast Non-linear Model Predictive Control. In this paper, a computationally efficient model is proposed, based on Differential-Algebraic equations. A control scheme based on Nonlinear Model Predictive Control (NMPC) and an estimator based on Moving Horizon Estimation (MHE) is proposed to handle the wind turbulences. In order to make a real-time application of Non-linear Model Predictive Control possible, a Real-Time Iteration scheme is proposed
S. Gros
Mario Zanon
mario.zanon@imtlucca.it
M. Diehl
2018-03-12T09:02:09Z
2018-03-12T09:02:09Z
http://eprints.imtlucca.it/id/eprint/4046
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4046
2018-03-12T09:02:09Z
An auto-generated nonlinear MPC algorithm for real-time obstacle avoidance of ground vehicles
We address the problem of real-time obstacle avoidance on low-friction road surfaces using spatial Nonlinear Model Predictive Control (NMPC). We use a nonlinear four-wheel vehicle dynamics model that includes load transfer. To overcome the computational difficulties we propose to use the ACADO Code Generation tool which generates NMPC algorithms based on the real-time iteration scheme for dynamic optimization. The exported plain C code is tailored to the model dynamics, resulting in faster run-times in effort for real-time feasibility. The advantages of the proposed method are shown through simulation.
J. V. Frasch
A. Gray
Mario Zanon
mario.zanon@imtlucca.it
H. J. Ferreau
S. Sager
F. Borrelli
M. Diehl
2018-03-12T08:59:04Z
2018-03-12T08:59:04Z
http://eprints.imtlucca.it/id/eprint/4012
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4012
2018-03-12T08:59:04Z
Model Predictive Control of Nonholonomic Mobile Robots Without Stabilizing Constraints and Costs
The problem of steering a nonholonomic mobile robot to a desired position and orientation is considered. In this paper, a model predictive control (MPC) scheme based on tailored nonquadratic stage cost is proposed to fulfill this control task. We rigorously prove asymptotic stability while neither stabilizing constraints nor costs are used. To this end, we first design suitable maneuvers to construct bounds on the value function. Second, these bounds are exploited to determine a prediction horizon length such that the asymptotic stability of the MPC closed loop is guaranteed. Finally, numerical simulations are conducted to explain the necessity of having nonquadratic running costs.
Karl Worthmann
Mohamed W. Mehrez
Mario Zanon
mario.zanon@imtlucca.it
George K. I. Mann
Raymond G. Gosine
Moritz Diehl
2018-03-12T08:57:17Z
2018-03-12T08:57:17Z
http://eprints.imtlucca.it/id/eprint/4047
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4047
2018-03-12T08:57:17Z
Efficient Nonlinear Model Predictive Control Formulations for Economic Objectives with Aerospace and Automotive Applications
This thesis is concerned with optimal control techniques for optimal trajectory planning and real-time control and estimation. The framework of optimal control is a powerful tool which enjoys increasing popularity due to its applicability to a wide class of problems and its ability to deliver solutions to very complicated problems which cannot be intuitively solved.
The downside of optimal control is the computational burden required to compute the optimal solution. Due to recent algorithmic developments and increases in the computational power, this burden has been significantly reduced over the last decades. In order to guarantee effectiveness and reliability of the solver, three main components are necessary: fast and robust algorithms, a good problem formulation, and a mathematical model tailored to optimisation. Indeed, both the model and the optimal control problem can usually be formulated in many different ways, some of which are better suited for optimisation. In this thesis we are concerned with all three components, with a focus on the last two.
Concerning the problem formulation, we propose practical approaches for formulating optimal control, MPC and MHE problems in an optimisation- friendly fashion. Moreover, we analyse the stability properties of various MPC formulations, with a focus on so-called economic MPC, for which the stability theory is still developing.
On the algorithmic level, we review the literature on optimisation and optimal control and we prove that it is possible to tune tracking MPC formulations in order to locally obtain the same behaviour as economic MPC. The main advantages of tuned tracking MPC over economic MPC consist in easier to guarantee closed-loop stability and applicability of efficient real-time algorithms.
On the modelling side, we propose an approach for deriving models of reduced complexity and reduced nonlinearity for multibody mechanical systems. The use of nonminimal coordinates and DAE models enlarges the range of modelling possibilities and allows the control engineer to derive models which are better suited for optimisation. In order to provide an easy framework for the model derivation, we extend the Euler-Lagrange approach and we demonstrate how to implement the proposed approach in practice.
In order to demonstrate the effectiveness of the proposed techniques, we deploy them for two applications: tethered airplanes and autonomous vehicles. Both examples are characterised by fast nonlinear constrained dynamics for which simple controllers cannot be deployed.
Tethered airplanes are of particular interest because they are an emerging technology for wind energy production. In this thesis, we use optimal control to design trajectories which extract maximum energy from the airmass and compare single and dual-airfoil configurations. We moreover demonstrate the effectiveness of MPC and MHE for controlling the system in real time and apply the new tuning procedure for tracking MPC to show its ability to locally approximate economic MPC.
Mario Zanon
mario.zanon@imtlucca.it
2018-03-09T14:21:54Z
2018-03-09T14:21:54Z
http://eprints.imtlucca.it/id/eprint/4010
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4010
2018-03-09T14:21:54Z
Primal decomposition of the optimal coordination of vehicles at traffic intersections
Robert Hult
Mario Zanon
Sebastien Gros
Paolo Falcone
2018-03-09T14:17:27Z
2018-03-09T14:17:27Z
http://eprints.imtlucca.it/id/eprint/4011
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4011
2018-03-09T14:17:27Z
A tracking MPC formulation that is locally equivalent to economic MPC
The stability proof for economic Model Predictive Control (MPC) is in general difficult to establish. In contrast, tracking MPC has well-established and practically applicable stability guarantees, but can yield poor closed-loop performance in terms of the selected economic criterion. In this paper, we derive a formal procedure to design a tracking MPC scheme so as to locally approximate the behaviour of economic MPC. Given an economic stage cost, the desired tracking stage cost can therefore be computed automatically. Because tracking MPC guarantees stability of the closed-loop system, our procedure succeeds if and only if economic MPC is locally stabilising. This fact can be used to certify whether economic MPC is not stabilising. We illustrate the theoretical developments in a simulated example.
Mario Zanon
mario.zanon@imtlucca.it
Sébastien Gros
Moritz Diehl
2018-03-09T14:15:46Z
2018-03-09T14:15:46Z
http://eprints.imtlucca.it/id/eprint/4007
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4007
2018-03-09T14:15:46Z
Time-optimal race car driving using an online exact hessian based nonlinear MPC algorithm
This work presents an embedded nonlinear model predictive control (NMPC) strategy for autonomous vehicles under a minimum time objective. The time-optimal control problem is stated in a path-parametric formulation such that existing reliable numerical methods for real-time nonlinear MPC can be used. Building on previous work on timeoptimal driving, we present an approach based on a sequential quadratic programming type algorithm with online propagation of second order derivatives. As an illustration of our method, we provide closed-loop simulation results based on a vehicle model identified for small-scale electric race cars.
Robin Verschueren
Mario Zanon
mario.zanon@imtlucca.it
Rien Quirynen
Moritz Diehl
2018-03-09T14:12:55Z
2018-03-09T14:12:55Z
http://eprints.imtlucca.it/id/eprint/4008
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4008
2018-03-09T14:12:55Z
A Sparsity Preserving Convexification Procedure for Indefinite Quadratic Programs Arising in Direct Optimal Control
Quadratic programs (QP) with an indefinite Hessian matrix arise naturally in some direct optimal control methods, e.g., as subproblems in a sequential quadratic programming scheme. Typically, the Hessian is approximated with a positive definite matrix to ensure having a unique solution; such a procedure is called regularization. We present a novel regularization method tailored for QPs with optimal control structure. Our approach exhibits three main advantages. First, when the QP satisfies a second order sufficient condition for optimality, the primal solution of the original and the regularized problem are equal. In addition, the algorithm recovers the dual solution in a convenient way. Second, and more importantly, the regularized Hessian bears the same sparsity structure as the original one. This allows for the use of efficient structure-exploiting QP solvers. As a third advantage, the regularization can be performed with a computational complexity that scales linearly in the length of the control horizon. We showcase the properties of our regularization algorithm on a numerical example for nonlinear optimal control. The results are compared to other sparsity preserving regularization methods.
Read More: https://epubs.siam.org/doi/10.1137/16M1081543
Robin Verschueren
Mario Zanon
mario.zanon@imtlucca.it
Rien Quirynen
Moritz Diehl
2018-03-09T14:11:50Z
2018-03-09T14:11:50Z
http://eprints.imtlucca.it/id/eprint/4005
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4005
2018-03-09T14:11:50Z
Distributed Algorithm for Optimal Vehicle Coordination at Traffic Intersections
Automated vehicle coordination can be used to control vehicles across traffic intersections safely and efficiently. This paper proposes a novel parallelizable algorithm, which solves the coordination problem at traffic intersections under a given precedence order by using a tailored variant of the augmented Lagrangian based alternating direction inexact Newton method (ALADIN). Here, each vehicle solves its own optimal control problem and exchanges information about arrivial and departure times at the intersection with its neighbors such that collisions are avoided. We illustrate the performance of ALADIN by analyzing two scenarios, one during rush hour and one at low-traffic conditions.
Yuning Jiang
Mario Zanon
mario.zanon@imtlucca.it
Robert Hult
Boris Houska
2018-03-09T14:09:34Z
2018-03-09T14:09:34Z
http://eprints.imtlucca.it/id/eprint/4006
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4006
2018-03-09T14:09:34Z
Periodic Optimal Control, Dissipativity and MPC
Recent research has established the importance of (strict) dissipativity for proving stability of economic MPC in the case of an optimal steady state. In many cases, though, steady-state operation is not economically optimal and periodic operation of the system yields a better performance. In this technical note, we propose ways of extending the notion of (strict) dissipativity for periodic systems. We prove that optimal P-periodic operation and MPC stability directly follow, similarly to the steady-state case, which can be seen as a special case of the proposed framework. Finally, we illustrate the theoretical results with several simple examples.
Mario Zanon
mario.zanon@imtlucca.it
Lars Grune
Moritz Diehl
2018-03-09T14:07:48Z
2018-03-09T14:07:48Z
http://eprints.imtlucca.it/id/eprint/4001
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4001
2018-03-09T14:07:48Z
Numerical Optimal Control with Periodicity Constraints in the Presence of Invariants
Periodic optimal control problems (POCPs) based on dynamic models holding invariants are often problematic to treat using standard numerical methods. The difficulty stems from a failure of standard constraint qualifications and typically hinders the convergence of the numerical solver, or even defeats it. Optimisation problems having weak constraint qualifications can be treated using dedicated solvers, at the price of a more involved algorithmic. In this paper, we analyse the constraint qualification of POCPs holding invariants, and propose three simple and computationally inexpensive modifications of the formulation that allow for a recovery of Linear Independence Constraint Qualification (LICQ), while not affecting the Second-Order Sufficient Conditions (SOSC) for optimality. Hence, the resulting POCP can be tackled via standard solvers, without special treatment. The application of these approaches is detailed for the case of POCPs holding index-reduced Differential-Algebraic Equations and representations of the SO(3) Lie group.
Sebastien Gros
Mario Zanon
mario.zanon@imtlucca.it
2018-03-09T14:06:33Z
2018-03-09T14:06:33Z
http://eprints.imtlucca.it/id/eprint/4002
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4002
2018-03-09T14:06:33Z
Penalty Functions for Handling Large Deviation of Quadrature States in NMPC
Sebastien Gros
Mario Zanon
mario.zanon@imtlucca.it
2018-03-09T14:05:19Z
2018-03-09T14:05:19Z
http://eprints.imtlucca.it/id/eprint/4000
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4000
2018-03-09T14:05:19Z
Day-ahead scheduling and real-time Economic MPC of CHP unit in Microgrid with Smart buildings
This paper presents a model for day-ahead scheduling of the CHP heat and electric energy production for a residential Microgrid taking into account the economic factors in a liberalized electricity markets, the technical factors in the safety/quality of supply, and the consumer preferences. This day-ahead scheduling model is complemented with a real-time economic MPC model for a subsequent control with respect to the outcomes of the day-ahead scheduling. This combined scheduling and economic MPC provides a general set-up capable of overcoming several major difficulties encountered with a typical scheduling + tracking MPC set-up, e.g. the problems of connecting the economic objectives with different temporal resolution and different requirements in terms of delivery.
Josip Vasilj
Sebastien Gros
Damir Jakus
Mario Zanon
mario.zanon@imtlucca.it
2018-03-09T14:01:44Z
2018-03-09T14:03:11Z
http://eprints.imtlucca.it/id/eprint/4003
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4003
2018-03-09T14:01:44Z
An Asynchronous Algorithm for Optimal Vehicle Coordination at Traffic Intersections
Mario Zanon
mario.zanon@imtlucca.it
Sébastien Gros
Henk Wymeersch
Paolo Falcone
2018-03-08T09:25:39Z
2018-03-08T09:25:39Z
http://eprints.imtlucca.it/id/eprint/3969
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3969
2018-03-08T09:25:39Z
Benefiting Colleagues but not the City: Localized
Effects from the Relocation of Superstar Inventors
In this paper I examine episodes in which superstar inventors relocate to a new city. In particular,
in order to assess whether the beneficial effects of physical proximity to a superstar have a restricted
network dimension or a wider spatial breadth (spillovers), I estimate changes in patterns of patenting
activity following these events for two different groups of inventors: the superstar’s close collaborators,
and all the other inventors in a given urban area, for both the locality where the superstar moves
to and for the one that is left behind. In the case of collaborators, I restrict the attention to patents
realized independently from the superstar. The results from the event study register a large and persistent
positive effect on the collaborators in the city of destination, as well as a simultaneous negative
trend affecting those still residing in the previous location. In the long run, these effects translate
into an increased difference between the two groups of about 0.16 patents per inventor. Conversely,
no city-wide spillover effect can be attested, offering little support to place-based policies aimed at
inducing a positive influx of top innovators in urban areas.
Paolo Zacchia
paolo.zacchia@imtlucca.it
2017-09-26T07:59:20Z
2017-09-26T07:59:20Z
http://eprints.imtlucca.it/id/eprint/3798
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3798
2017-09-26T07:59:20Z
Revisiting the problem of a crack impinging on an interface: a modeling framework for the interaction between the phase field approach for brittle fracture and the interface cohesive zone model
The problem of a crack impinging on an interface has been thoroughly investigated in the last three decades due to its important role in the mechanics and physics of solids. In the current investigation, this problem is revisited in view of the recent progresses on the phase field approach of brittle fracture. In this concern, a novel formulation combining the phase field approach for modeling
brittle fracture in the bulk and a cohesive zone model for pre-existing adhesive interfaces is herein proposed to investigate the competition between crack penetration and deflection at an interface. The model, implemented within the finite element method framework using a monolithic fully implicit solution strategy, is applied to provide a further insight into the understanding of the role of model parameters on the above competition. In particular, in this study, the role of the fracture toughness ratio between the interface and the adjoining bulks and of the characteristic fracture-length scales of the dissipative models is analyzed. In the case of a brittle interface, the asymptotic predictions based on linear elastic fracture mechanics criteria for crack penetration, single
deflection or double deflection are fully captured by the present method. Moreover, by increasing the size of the process zone along the interface, or by varying the internal length scale of the phase field model, new complex phenomena are emerging, such as simultaneous crack penetration and deflection and the transition from single crack penetration to deflection and penetration with
subsequent branching into the bulk. The obtained computational trends are in very good agreement with previous experimental observations and the theoretical considerations on the competition and interplay between both fracture mechanics models open new research perspectives for the simulation and understanding of complex fracture patterns.
Marco Paggi
marco.paggi@imtlucca.it
José Reinoso
2017-09-26T07:55:57Z
2017-09-26T07:55:57Z
http://eprints.imtlucca.it/id/eprint/3800
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3800
2017-09-26T07:55:57Z
Strength prediction of notched thin ply laminates using finite fracture mechanics and the phase field approach
Thin ply laminates are a new class of composite materials with great potential for application in the design of thinner and highly optimized components, resulting in potential weight savings and improved mechanical performance. These new composites can stir the development of lighter structures, overcoming current design limitations as well as notably reducing the onset and development of matrix cracking and delamination events. This paper presents the application of two recent modeling methods for the failure analysis and strength prediction of open-hole thin ply laminates under tensile loading,
which exhibit a brittle response upon failure: (i) the analytical coupled energy-stress Finite Fracture Mechanics (FFMs) technique, and (ii) the FE-based Phase Field (PF) approach for fracture that is incorporated into an enhanced assumed solid shell element. The predictions obtained using both strategies are compared with experimental data. These correlations exhibit a very satisfactory level of agreement, proving the robustness and reliability of both methods under consideration.
José Reinoso
A. Arterio
Marco Paggi
marco.paggi@imtlucca.it
P.P. Camanho
2017-09-26T07:53:06Z
2017-09-26T07:53:06Z
http://eprints.imtlucca.it/id/eprint/3801
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3801
2017-09-26T07:53:06Z
A new analytical critical thrust force model for delamination analysis of laminated composites during drilling operation
Fibre reinforced polymer (FRP) composite laminates are employed in many industrial applications due to
their attractive mechanical and structural properties. Machining operation, such as drilling of FRP
laminates, plays a significant role in the assembly of parts in aircraft and spacecraft production. Among
other production bottlenecks, drilling-induced delamination remains a major defect which adversely
affects the quality of assembly parts. An efficient strategy in preventing this problem is the calculation of
the critical thrust force above which delamination is initiated. Therefore, in this study, a new analytical
model is proposed to predict the critical thrust force for delamination. Unlike the general models in the
literature which derived only mode I strain energy release rate based on the assumption of classical
laminate plate theory (CLPT) combined with linear elastic fracture mechanics (LEFM) mode I considerations
in the elliptic delamination zone, the proposed analytical model is derived based on first-order
shear deformation theory (FSDT) and accounts for mode I and mode II strain energy release rates in
the delamination zone. This strategy allows to activate mixed mode criteria for delamination initiation
which is a valid assumption for laminates with layers of different orientations. The present model is
partly derived for general laminates subject to distributed loading and further extended to cross-ply
laminate sequence subject to a mixed load condition. The results show that the effect of shear deformation
in the prediction of the critical thrust force is influential with increasing ply thickness and the
effect of chisel edge on shear deformation is more profound in the distributed load regime.
Saheed Olalekan Ojo
saheed.ojo@imtlucca.it
S.O. Ismail
Marco Paggi
marco.paggi@imtlucca.it
H.N. Dhakal
2017-09-18T12:42:34Z
2017-09-18T12:42:34Z
http://eprints.imtlucca.it/id/eprint/3790
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3790
2017-09-18T12:42:34Z
A lumped mass beam model for the wave propagation in anti-tetrachiral periodic lattices
The engineered class of periodic anti-tetrachiral materials is mainly characterized by
the unusual macroscopic property of a negative Poisson’s ratio. The auxetic behavior of the material
depends on the geometric and elastic features of the microstructure. In particular, the material symmetries
of the periodic cell govern the quadratic or orthotropic symmetry of the first-order elastic
tensor (i.e. auxetic quadratic or auxetic orthotropy). Under the assumption of uniform mass density
and elastic properties, one or the other case can be realized by a square or rectangular microstructure,
respectively. A beam lattice model with lumped masses is employed to analyse the effects
of different, usually small-valued, geometric and elastic parameters of the high- and low-frequency
dispersion curves and band gaps characterizing the free wave propagation.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Marco Lepidi
2017-09-18T12:26:07Z
2017-09-18T12:26:07Z
http://eprints.imtlucca.it/id/eprint/3789
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3789
2017-09-18T12:26:07Z
Passive control of wave propagation in periodic anti-tetrachiral meta-materials
Periodic anti-tetrachiral materials are strongly characterized by a marked auxeticity,
the unusual and fascinating mechanical property mathematically expressed by negative values
of the Poisson’s ratio. The auxetic behavior is primarily provided by pervasive rolling-up mechanisms
developed by the doubly-symmetric micro-structure of the periodic cell, composed by a
regular pattern of rigid rings connected by tangent flexible ligaments. Adopting a beam-lattice
model to describe the linear free dynamics of the elementary cell, the planar wave propagation
along the bi-dimensional material domain can be studied according to the Floquet-Bloch
theory. Parametric analyses of the dispersion curves, carried out with numerical or asymptotic
tools, typically reveal a highly-dense spectrum, with persistent absence of total band-gaps in the
low-frequency range. The paper analyses the wave propagation in the meta-material developed
by introducing rigid massive inserts, locally housed by all the rings and working as undamped
linear oscillators with assigned inertia and/or stiffness properties. The elastic coupling between
the cell microstructure and the oscillators, if properly tuned (inertial resonators), is found to
significantly modify the Floquet-Bloch spectrum of the material. The effects of the resonator
parameters (tuning frequency and mass ratio) on the low-frequency band structure of the metamaterial
are discussed, with focus on the valuable possibility to (i) open total band gaps, by
either the widening of an existing partial band gap or the avoidance of a crossing point between
adjacent dispersion curves, (ii) finely control the total band-gap amplification, in order to assess
the maximum achievable performance of the meta-material against the vibration propagation
Marco Lepidi
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
2017-09-18T10:54:34Z
2017-09-18T10:54:34Z
http://eprints.imtlucca.it/id/eprint/3787
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3787
2017-09-18T10:54:34Z
Asymptotic approximation of the band structure for tetrachiral metamaterials
Tetrachiral materials are characterized by a cellular microstructure made by a periodic pattern of stiff rings and flexible ligaments. Their mechanical behaviour can be described by a planar lattice of rigid massive bodies and elastic massless beams. Therefore, the periodic cell dynamics is governed by a monoatomic structural model, conveniently reduced to the only active degrees-of-freedom. The paper presents an explicit parametric description of the Floquet-Bloch spectrum (or band structure) governing the propagation of elastic waves through the tetrachiral material. By virtue of multiparametric perturbation techniques, an analytical asymptotic approximation is achieved for the dispersion surfaces in the Brillouin zone. Since different optimization strategies tend to fail in opening low-frequency band gaps in the material spectrum, this specific design purpose is commonly pursued by introducing interring inertial resonators. The paper demonstrates that multiparametric perturbation methods can efficiently deal with the consequent enlargement of the parameter space, necessary to describe the resulting inertial metamaterial. Indeed, paying due attention to the doubling of internal resonance conditions, an accurate parametric approximations of the enriched band structure can be achieved. From the applicative perspective, the research findings furnish suited analytical tools for the optimal design of pass and stop bands.
Marco Lepidi
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
2017-09-18T09:41:05Z
2017-09-18T09:41:05Z
http://eprints.imtlucca.it/id/eprint/3785
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3785
2017-09-18T09:41:05Z
On the Statics of the Dome of the Basilica of S. Maria Assunta in Carignano, Genoa
The paper deals with the dome of the Basilica of S. Maria Assunta in Carignano in Genoa, designed by Galeazzo Alessi and built in the sixteenth century, for which meridian cracking, rather common in masonry domes, requires the assessment of the dome. In order to set a general procedure for the assessment this structures, limit analysis approaches are here discussed and compared. On the basis of classic limit analysis, local (dome only) and global (dome-drum system) collapse mechanisms are considered considering the different behaviour of several structural elements (lantern, shells of the dome, drum, colonnade). A static (safe theorem) and a kinematic approach are applied to the structure by means of equilibrium limit conditions and kinematically admissible collapse mechanisms. Comparisons between the obtained results are carried out so as to: (i) discuss a general approach to the assessment of dome-drum systems based on both numerical tools and standard limit analyses approaches; (ii) provide a first glance in the assessment of the dome.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Antonio Brencich
Luigi Gambarotta
2017-09-18T08:51:48Z
2017-09-18T08:51:48Z
http://eprints.imtlucca.it/id/eprint/3784
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3784
2017-09-18T08:51:48Z
Simplified modelling of chiral lattice materials with local resonators
A simplified model of periodic chiral beam-lattices containing local resonators has been formulated to obtain a better understanding of the influence of the chirality and of the dynamic characteristics of the local resonators on the acoustic behaviour. The beam-lattice models are made up of a periodic array of rigid heavy rings, each one connected to the others through elastic slender massless ligaments and containing an internal resonator made of a rigid disk in a soft elastic annulus. The band structure and the occurrence of low frequency band-gaps are analysed through a discrete Lagrangian model. For both the hexa- and the tetrachiral lattice, two acoustic modes and four optical modes are identified and the influence of the dynamic characteristics of the resonator on those branches is analysed together with some properties of the band structure. By approximating the ring displacements of the discrete Lagrangian model as a continuum field and through an application of the generalized macro-homogeneity condition, a generalized micropolar equivalent continuum has been derived, together with the overall equation of motion and the constitutive equation given in closed form. The validity limits of the dispersion functions provided by the micropolar model are assessed by a comparison with those obtained by the discrete model.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Luigi Gambarotta
2017-08-04T10:51:15Z
2017-08-04T10:51:15Z
http://eprints.imtlucca.it/id/eprint/3752
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3752
2017-08-04T10:51:15Z
The scientific impact of nations on scientific and technological development
Determining how scientific achievements influence the subsequent process of knowledge creation is a fundamental step in order to build a unified ecosystem for studying the dynamics of innovation and competitiveness. Yet, relying separately on data about scientific production on one side, through bibliometric indicators, and about technological advancements on the other side, through patents statistics, gives only a limited insight on the key interplay between science and technology which, as a matter of fact, move forward together within the innovation space. In this paper, using citation data of both scientific papers and patents, we quantify the direct impact of the scientific outputs of nations on further advancements in science and on the introduction of new technologies. Our analysis highlights the presence of geo-cultural clusters of nations with similar innovation system features, and unveils the heterogeneous coupled dynamics of scientific and technological success. This study represents a first step in the buildup of a comprehensive framework for knowledge creation and innovation.
Aurelio Patelli
Giulio Cimini
giulio.cimini@imtlucca.it
Emanuele Pugliese
Andrea Gabrielli
2017-08-04T10:42:24Z
2017-08-04T10:42:24Z
http://eprints.imtlucca.it/id/eprint/3750
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3750
2017-08-04T10:42:24Z
Unfolding the innovation system for the development of countries: co-evolution of Science, Technology and Production
We show that the space in which scientific, technological and economic developments interplay with each other can be mathematically shaped using pioneering multilayer network and complexity techniques. We build the tri-layered network of human activities (scientific production, patenting, and industrial production) and study the interactions among them, also taking into account the possible time delays. Within this construction we can identify which capabilities and prerequisites are needed to be competitive in a given activity, and even measure how much time is needed to transform, for instance, the technological know-how into economic wealth and scientific innovation, being able to make predictions with a very long time horizon. Quite unexpectedly, we find empirical evidence that the naive knowledge flow from science, to patents, to products is not supported by data, being instead technology the best predictor for industrial and scientific production for the next decades.
Emanuele Pugliese
Giulio Cimini
giulio.cimini@imtlucca.it
Aurelio Patelli
Andrea Zaccaria
Luciano Pietronero
Andrea Gabrielli
2017-08-04T10:05:21Z
2017-08-04T10:05:21Z
http://eprints.imtlucca.it/id/eprint/3743
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3743
2017-08-04T10:05:21Z
Multi-field asymptotic homogenization of thermo-piezoelectric materials with periodic microstructure
Abstract This study proposes a multi-field asymptotic homogenization for the analysis of thermo-piezoelectric materials with periodic microstructures. The effect of the microstructural heterogeneity is taken into account by means of periodic perturbation functions, which derive from the solution of nonhomogeneous recursive cell problems defined over the unit periodic cell. A strong coupling is present between the microdisplacement field and the microelectric potential field, since the mechanical and the electric problems are fully coupled in the asymptotically expanded microscale field equations. The microdisplacement, the electric potential, and the relative temperature fields have been related to the macroscopic quantities and to their gradients in the derived down-scaling relations. Average field equations of infinite order have been obtained and the closed form of the overall constitutive tensors has been determined for the equivalent first-order homogenized continuum. A formal solution of such equations has been derived by means of an asymptotic expansion of the macrofields. The accuracy of the proposed formulation is assessed in relation to illustrative examples of a bi-material periodic microstructure subjected to harmonic body forces, free charge densities, and heat sources, whose periodicity is much greater than the characteristic microstructural size. The good agreement obtained between the solution of the homogenized model and the finite element solution of the original heterogeneous material problem confirms the validity of the proposed formulation.
Francesca Fantoni
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Marco Paggi
marco.paggi@imtlucca.it
2017-08-04T10:04:05Z
2017-08-04T10:04:05Z
http://eprints.imtlucca.it/id/eprint/3742
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3742
2017-08-04T10:04:05Z
Dispersive wave propagation in two-dimensional rigid periodic blocky materials with elastic interfaces
Abstract Dispersive waves in two-dimensional blocky materials with periodic microstructure made up of equal rigid units, having polygonal centro-symmetric shape with mass and gyroscopic inertia, connected with each other through homogeneous linear interfaces, have been analyzed. The acoustic behavior of the resulting discrete Lagrangian model has been obtained through a Floquet–Bloch approach. From the resulting eigenproblem derived by the Euler–Lagrange equations for harmonic wave propagation, two acoustic branches and an optical branch are obtained in the frequency spectrum. A micropolar continuum model to approximate the Lagrangian model has been derived based on a second-order Taylor expansion of the generalized macro-displacement field. The constitutive equations of the equivalent micropolar continuum have been obtained, with the peculiarity that the positive definiteness of the second-order symmetric tensor associated to the curvature vector is not guaranteed and depends both on the ratio between the local tangent and normal stiffness and on the block shape. The same results have been obtained through an extended Hamiltonian derivation of the equations of motion for the equivalent continuum that is related to the Hill-Mandel macro homogeneity condition. Moreover, it is shown that the hermitian matrix governing the eigenproblem of harmonic wave propagation in the micropolar model is exact up to the second order in the norm of the wave vector with respect to the same matrix from the discrete model. To appreciate the acoustic behavior of some relevant blocky materials and to understand the reliability and the validity limits of the micropolar continuum model, some blocky patterns have been analyzed: rhombic and hexagonal assemblages and running bond masonry. From the results obtained in the examples, the obtained micropolar model turns out to be particularly accurate to describe dispersive functions for wavelengths greater than 3-4 times the characteristic dimension of the block. Finally, in consideration that the positive definiteness of the second order elastic tensor of the micropolar model is not guaranteed, the hyperbolicity of the equation of motion has been investigated by considering the Legendre–Hadamard ellipticity conditions requiring real values for the wave velocity.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Luigi Gambarotta
2017-08-04T09:59:14Z
2017-08-04T09:59:14Z
http://eprints.imtlucca.it/id/eprint/3741
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3741
2017-08-04T09:59:14Z
Multi-parametric sensitivity analysis of the band structure for tetrachiral inertial metamaterials
Tetrachiral materials are characterized by a cellular microstructure made by a periodic pattern of stiff rings and flexible ligaments. Their mechanical behaviour can be described by a planar lattice of rigid massive bodies and elastic massless beams. The periodic cell dynamics is governed by a monoatomic structural model, conveniently reduced to the only active degrees-of-freedom. The paper presents an explicit parametric description of the band structure governing the free propagation of elastic waves. By virtue of multiparametric perturbation techniques, sensitivity analyses are performed to achieve analytical asymptotic approximation of the dispersion functions. The parametric conditions for the existence of full band gaps in the low-frequency range are established. Furthermore, the band gap amplitude is analytically assessed in the admissible parameter range. In inertial tetrachiral metamaterials, stop bands can be opened by the introduction of intra-ring resonators. Perturbation methods can efficiently deal with the consequent enlargement of the mechanical parameter space. Indeed high-accuracy parametric approximations are achieved for the band structure, enriched by the new optical branches related to the resonator frequencies. In particular, target stop bands in the metamaterial spectrum are analytically designed through the asymptotic solution of inverse spectral problems.
Subjects: Materials Science (cond-mat.mtrl-sci)
Cite as: arXiv:1706.08754 [cond-mat.mtrl-sci]
(or arXiv:1706.08754v1 [cond-mat.mtrl-sci] for this version)
Marco Lepidi
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
2017-08-04T09:55:23Z
2017-08-04T09:55:23Z
http://eprints.imtlucca.it/id/eprint/3740
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3740
2017-08-04T09:55:23Z
Identification of higher-order continua equivalent to a Cauchy elastic composite
A heterogeneous Cauchy elastic material may display micromechanical effects that can be modeled in a homogeneous equivalent material through the introduction of higher-order elastic continua. Asymptotic homogenization techniques provide an elegant and rigorous route to the evaluation of equivalent higher-order materials, but are often of difficult and awkward practical implementation. On the other hand, identification techniques, though relying on simplifying assumptions, are of straightforward use. A novel strategy for the identification of equivalent second-gradient Mindlin solids is proposed in an attempt to combine the accuracy of asymptotic techniques with the simplicity of identification approaches. Following the asymptotic homogenization scheme, the overall behaviour is defined via perturbation functions, which (differently from the asymptotic scheme) are evaluated on a finite domain obtained as the periodic repetition of cells and subject to quadratic displacement boundary conditions. As a consequence, the periodicity of the perturbation function is satisfied only in an approximate sense, nevertheless results from the proposed identification algorithm are shown to be reasonably accurate.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Marco Paggi
marco.paggi@imtlucca.it
F. Dal Corso
D. Bigoni
2017-03-21T14:13:22Z
2017-03-21T14:13:22Z
http://eprints.imtlucca.it/id/eprint/3680
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3680
2017-03-21T14:13:22Z
A nonlinear finite thickness cohesive interface element for modeling delamination in fibre-reinforced composite laminates
Abstract Delamination events are major issues which notably affect the integrity of composite structures. To minimize the experimental efforts, there is an increasing demand for developing reliable numerical tools that can accurately simulate delamination initiation and propagation under mixed-mode loading conditions. The current investigation is concerned with the formulation and the finite element (FE) implementation of a new nonlinear finite thickness cohesive interface model for delamination analysis of fibre-reinforced composite laminates relying on the solid shell concept. The incorporation of geometrically nonlinear effects into the proposed interface formulation is motivated by the recent trend of producing composite structures that can experience large displacements prior to failure, as is the case of postbuckling in stiffened panels. The inelastic material behavior of the interface is modeled using two standard nonlinear decohesion laws: (i) an exponential-based, and (ii) a polynomial-based interface laws. Finally, the performance of the proposed interface element is demonstrated by means of several examples focusing on double cantilever beam (DCB) and rib-stiffened specimens. A excellent level of accuracy is achieved when comparing the numerical predictions and the available experimental data.
José Reinoso
Marco Paggi
marco.paggi@imtlucca.it
A. Blázquez
2017-03-21T14:01:17Z
2017-03-21T14:01:17Z
http://eprints.imtlucca.it/id/eprint/3679
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3679
2017-03-21T14:01:17Z
Revisiting the problem of a crack impinging on an interface: a modeling framework for the interaction between the phase field approach for brittle fracture and the interface cohesive zone model
The problem of a crack impinging on an interface has been thoroughly investigated in the last three decades due to its important role in the mechanics and physics of solids. In this investigation, this problem is revisited in view of the recent progresses on the phase field approach to brittle fracture. In this concern, a novel formulation combining the phase field approach for modeling brittle fracture in the bulk and a cohesive zone model for pre-existing adhesive interfaces is herein proposed to investigate the competition between crack penetration and deflection at an interface. The model, implemented within the finite element method framework using a monolithic fully implicit solution strategy, is applied to provide a further insight into the understanding of the role of model parameters on the above competition. In particular, in this study, the role of the fracture toughness ratio between the interface and the adjoining bulks and the characteristic fracture-length scales of the dissipative models are analyzed. In the case of a brittle interface, the asymptotic predictions based on linear elastic fracture mechanics criteria for crack penetration, single deflection or double deflection are fully captured by the present method. Moreover, by increasing the size of the process zone along the interface, or by varying the internal length scale of the phase field model, new complex phenomena are emerging, such as simultaneous crack penetration and deflection and the transition from single crack penetration to deflection and penetration with subsequent branching into the bulk.
Marco Paggi
marco.paggi@imtlucca.it
José Reinoso
2017-03-21T12:24:42Z
2017-09-18T09:30:16Z
http://eprints.imtlucca.it/id/eprint/3675
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3675
2017-03-21T12:24:42Z
Auxetic behavior and acoustic properties of microstructured piezoelectric strain sensors
The use of multifunctional composite materials adopting piezo-electric periodic cellular lattice structures with auxetic elastic behavior is a recent and promising solution in the design of piezoelectric sensors. In the present work, periodic anti-tetrachiral auxetic lattice structures, characterized by different geometries, are taken into account and the mechanical and piezoelectrical response are investigated. The equivalent piezoelectric properties are obtained adopting a first order computational homogenization approach, generalized to the case of electro-mechanical coupling, and various polarization directions are adopted. Two examples of in-plane and out-of-plane strain sensors are proposed as design concepts. Moreover, a piezo-elasto-dynamic dispersion analysis adopting the Floquet–Bloch decomposition is performed. The acoustic behavior of the periodic piezoelectric material with auxetic topology is studied and possible band gaps are detected.
Maria Laura De Bellis
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
2017-03-21T12:19:26Z
2017-03-21T12:19:26Z
http://eprints.imtlucca.it/id/eprint/3674
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3674
2017-03-21T12:19:26Z
Multi-field asymptotic homogenization of thermo-piezoelectric materials with periodic microstructure
This study proposes a multi-field asymptotic homogenization for the analysis of thermo-piezoelectric materials with periodic microstructures. The effect of the microstructural heterogeneity is taken into account by means of periodic perturbation functions, which derive from the solution of non homogeneous recursive cell problems defined over the unit periodic cell. A strong coupling is present between the micro displacement field and the micro electric potential field, since the mechanical and the electric problems are fully coupled in the asymptotically expanded microscale field equations. The micro displacement, the electric potential, and the relative temperature fields have been related to the macroscopic quantities and to their gradients in the derived down-scaling relations. Average field equations of infinite order have been obtained and the closed form of the overall constitutive tensors has been determined for the equivalent first-order homogenized continuum. A formal solution of such equations has been derived by means of an asymptotic expansion of the macro fields. The accuracy of the proposed formulation is assessed in relation to illustrative examples of a bi-material periodic microstructure subjected to harmonic body forces, free charge densities, and heat sources, whose periodicity is much greater than the characteristic microstructural size. The good agreement obtained between the solution of the homogenized model and the finite element solution of the original heterogeneous material problem confirms the validity of the proposed formulation.
Francesca Fantoni
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Marco Paggi
marco.paggi@imtlucca.it
2017-03-21T12:16:36Z
2017-03-21T12:16:36Z
http://eprints.imtlucca.it/id/eprint/3673
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3673
2017-03-21T12:16:36Z
Parametric design of the band structure for lattice materials
Lattice materials are often investigated to determine how small parameter variations in the periodic microstructrure can influence the elastic wave propagation. A general hierarchical scheme, based on asymptotic perturbation techniques, is outlined to analytically assess the parametric sensitivity of the material band structure to a generic multi-parametric perturbation (direct problem). Modeling refinements, parameters updates, microstructural damages and manufacturing irregularities can be treated indifferently and simultaneously. According to a converse strategy, based on the inversion of the sensitivity problem, a hierarchical scheme is sketched to identify the parameter combinations which realize a design band structure (inverse problem). The direct and inverse problem are applied to the sensitivity analysis and band structure design of the anti-tetrachiral lattice material. Despite the high spectral density and the high-dimensional parameter space, the multi-parameter perturbation technique demonstrates its suitability in, first, analytically---although asymptotically---describe the material spectrum and, second, designing the material microstructure to obtain the desired spectral components. The inverse problem solution is discussed in terms of existence, uniqueness, asymptotic consistency and physical admissibility.
Marco Lepidi
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
2017-03-21T12:12:26Z
2017-03-21T12:12:26Z
http://eprints.imtlucca.it/id/eprint/3672
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3672
2017-03-21T12:12:26Z
Overall thermomechanical properties of layered materials for energy devices applications
This paper is concerned with the analysis of effective thermomechanical properties of multi-layered materials of interest for solid oxide fuel cells (SOFC) and lithium ions batteries fabrication. The recently developed asymptotic homogenization procedure is applied in order to express the overall thermoelastic constants of the first order equivalent continuum in terms of microfluctuations functions, and these functions are obtained by the solution of the corresponding recursive cell problems. The effects of thermal stresses on periodic multi-layered thermoelastic composite reproducing the characteristics of solid oxide fuel cells (SOFC-like) are studied assuming periodic body forces and heat sources, and the solution derived by means of the asymptotic homogenization approach is compared with the results obtained by finite elements analysis of the associate heterogeneous material.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Lorenzo Morini
Amdrea Piccolroaz
2017-03-21T12:04:34Z
2017-09-21T14:58:45Z
http://eprints.imtlucca.it/id/eprint/3670
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3670
2017-03-21T12:04:34Z
Wave propagation in non-centrosymmetric beam-lattices with lumped masses: discrete and micropolar modelling
The in-plane acoustic behavior of non-centrosymmetric lattices having nodes endowed with mass and rotational inertia and connected by massless ligaments with asymmetric elastic properties has been analyzed through a discrete model and a continuum micropolar model. In the first case the propagation of harmonic waves and the dispersion functions have been obtained by the discrete Floquet–Bloch approach. It is shown that the optical branch departs from a critical point with vanishing group velocity and is decreasing for increasing the norm of the wave vector. A micropolar continuum model has been derived through a continualization method based on a down-scaling law from a second-order Taylor expansion of the generalized macro-displacement field. It is worth noting that the second order elasticity tensor coupling curvatures and micro-couples turns out to be negative-definite also in the general case of non-centrosymmetric lattice. The eigenvalue problem governing the harmonic propagation in the micropolar non-centrosymmetric continuum results in general characterized by a hermitian full matrix that is exact up to the second order in the wave vector.
Examples concerning square and equilateral triangular lattices have been analyzed and their acoustic properties have been derived with the discrete and continuum models. The dependence of the Floquet–Bloch spectra on the lattice non-centrosymmetry is shown together with validity limits of the micropolar model. Finally, in consideration of the negative definiteness of the second order elastic tensor of the micropolar model, the loss of strong hyperbolicity of the equation of motion has been investigated.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Luigi Gambarotta
2017-03-21T12:00:57Z
2017-03-21T12:00:57Z
http://eprints.imtlucca.it/id/eprint/3669
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3669
2017-03-21T12:00:57Z
Dispersive wave propagation in two-dimensional rigid periodic blocky materials with elastic interfaces
Dispersive waves in two-dimensional blocky materials with periodic microstructure made up of equal rigid units having polygonal centro-symmetric shape with mass and gyroscopic inertia, connected each other through homogeneous linear interfaces, have been analysed. The acoustic behavior of the resulting discrete Lagrangian model has been obtained through a Floquet-Bloch approach. From the resulting eigenproblem derived by the Euler-Lagrange equations for harmonic wave propagation, two acoustic branches and an optical branch are obtained in the frequency spectrum. A micropolar continuum model to approximate the Lagrangian model has been derived based on a second-order Taylor expansion of the generalized macro-displacement field. The constitutive equations of the equivalent micropolar continuum have been obtained, with the peculiarity that the positive definiteness of the second-order symmetric tensor associated to the curvature vector is not guaranteed and depends both on the ratio between the local tangent and normal stiffness and on the block shape. The same results has been obtained through an extended Hamiltonian derivation of the equations of motion for the equivalent continuum that is related to the Hill-Mandel macro homogeneity condition. Moreover, it is shown that the hermitian matrix governing the eigenproblem of harmonic wave propagation in the micropolar model is exact up to the second order in the norm of the wave vector with respect to the same matrix from the discrete model. To appreciate the acoustic behavior of some relevant blocky materials and to understand the reliability and the validity limits of the micropolar continuum model, some blocky patterns have been analysed: rhombic and hexagonal assemblages and running bond masonry.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Luigi Gambarotta
2017-03-21T11:56:47Z
2017-03-21T11:56:47Z
http://eprints.imtlucca.it/id/eprint/3668
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3668
2017-03-21T11:56:47Z
High-frequency parametric approximation of the Floquet-Bloch spectrum for anti-tetrachiral materials
The class of anti-tetrachiral cellular materials is phenomenologically characterized by a strong auxeticity of the elastic macroscopic response. The auxetic behavior is activated by rolling-up deformation mechanisms developed by the material microstructure, composed by a periodic pattern of stiff rings connected by flexible ligaments. A linear beam lattice model is formulated to describe the free dynamic response of the periodic cell, in the absence of a soft matrix. After a static condensation of the passive degrees-of-freedom, a general procedure is applied to analyze the wave propagation in the low-dimensional space of the active degrees-of-freedom. The exact dispersion functions are compared with explicit – although approximate – dispersion relations, obtained from asymptotic perturbation solutions of the eigenproblem governing the Floquet–Bloch theory. A general hierarchical scheme is outlined to formulate and solve the perturbation equations, taking into account the dimension of the perturbation vector. Original recursive formulas are presented to achieve any desired order of asymptotic approximation. For the anti-tetrachiral material, the fourth-order asymptotic solutions are found to approximate the dispersion curves with fine agreement over wide regions of the parameter space. The asymptotic eigensolutions allow an accurate sensitivity analysis of the material spectrum under variation of the key physical parameters, including the cell aspect ratio, the ligament slenderness and the spatial ring density. Finally, the explicit dependence of the dispersion functions on the mechanical parameters may facilitate the custom design of specific spectral properties, such as the wave velocities and band gap amplitudes.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Marco Lepidi
2017-03-21T11:05:10Z
2017-09-21T14:56:38Z
http://eprints.imtlucca.it/id/eprint/3666
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3666
2017-03-21T11:05:10Z
Optimal design of low-frequency band gaps in anti-tetrachiral lattice meta-materials
The elastic wave propagation is investigated in a beam lattice material characterized by a square periodic cell with anti-tetrachiral microstructure. With reference to the Floquet-Bloch spectrum, focus is made on the band structure enrichments and modifications which can be achieved by equipping the cellular microstructure with tunable local resonators. By virtue of its composite mechanical nature, the so-built inertial meta-material gains enhanced capacities of passive frequency-band filtering. Indeed the number, placement and properties of the inertial resonators can be designed to open, shift and enlarge the band gaps between one or more pairs of consecutive branches in the frequency spectrum. In order to improve the meta-material performance, several nonlinear optimization problems are formulated. The largest among the band gap amplitudes in the low-frequency range is selected as suited objective function. Proper inequality constraints are introduced to restrict the admissible solutions within a compact set of mechanical and geometric parameters, including only physically realistic properties of both the lattice and the resonators. The optimization problems related to full and partial band gaps are solved by using a globally convergent version of the numerical method of moving asymptotes, combined with a quasi-Monte Carlo multi-start technique. The optimal solutions are numerically computed, discussed and compared from the qualitative and quantitative viewpoints, bringing to light the limits and potential of the meta-material performance. The clearest trends emerging from the numerical analyses are pointed out and interpreted from the physical viewpoint. Finally, some specific recommendations about the microstructural design of the meta-material are synthesized.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Giorgio Gnecco
giorgio.gnecco@imtlucca.it
Marco Lepidi
Luigi Gambarotta
2017-02-01T08:49:17Z
2017-02-01T08:49:17Z
http://eprints.imtlucca.it/id/eprint/3652
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3652
2017-02-01T08:49:17Z
Statistical shape modeling of the left ventricle: myocardial infarct classification challenge
Statistical shape modeling is a powerful tool for visualizing and quantifying geometric and functional patterns of the heart. After myocardial infarction (MI), the left ventricle typically remodels in response to physiological challenges. Several methods have been proposed in the literature to describe statistical shape changes. Which method best characterizes left ventricular remodeling after MI is an open research question. A better descriptor of remodeling is expected to provide a more accurate evaluation of disease status in MI patients. We therefore designed a challenge to test shape characterization in MI given a set of three-dimensional left ventricular surface points. The training set comprised 100 MI patients, and 100 asymptomatic volunteers (AV). The challenge was initiated in 2015 at the Statistical Atlases and Computational Models of the Heart workshop, in conjunction with the MICCAI conference. The training set with labels was provided to participants, who were asked to submit the likelihood of MI from a different (validation) set of 200 cases (100 AV and 100 MI). Sensitivity, specificity, accuracy and area under the receiver operating characteristic curve were used as the outcome measures. The goals of this challenge were to (1) establish a common dataset for evaluating statistical shape modeling algorithms in MI, and (2) test whether statistical shape modeling provides additional information characterizing MI patients over standard clinical measures. Eleven groups with a wide variety of classification and feature extraction approaches participated in this challenge. All methods achieved excellent classification results with accuracy ranges from 0.83 to 0.98. The areas under the receiver operating characteristic curves were all above 0.90. Four methods showed significantly higher performance than standard clinical measures. The dataset and software for evaluation are available from the Cardiac Atlas Project website1.
A. Suinesiaputra
P. Ablin
X. Alba
M. Alessandrini
J. Allen
W. Bai
S. Cimen
P. Claes
B. R. Cowan
J. D'hooge
N. Duchateau
J. Ehrhardt
A. F. Frangi
A. Gooya
V. Grau
K. Lekadir
A. Lu
A. Mukhopadhyay
Ilkay Oksuz
ilkay.oksuz@imtlucca.it
X. Pennec
M. Pereanez
C. Pinto
P. Piras
M. M. Rohe
D. Rueckert
M. Sermesant
K. Siddiqi
M. Tabassian
L. Teresi
S. A. Tsaftaris
M. Wilms
A. A. Young
X. Zhang
P. Medrano-Gracia
2017-02-01T08:36:30Z
2017-02-01T08:36:30Z
http://eprints.imtlucca.it/id/eprint/3651
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3651
2017-02-01T08:36:30Z
MRI-TRUS Image Synthesis with Application to Image-Guided Prostate Intervention
Accurate and robust fusion of pre-procedure magnetic resonance imaging (MRI) to intra-procedure trans-rectal ultrasound (TRUS) imaging is necessary for image-guided prostate cancer biopsy procedures. The current clinical standard for image fusion relies on non-rigid surface-based registration between semi-automatically segmented prostate surfaces in both the MRI and TRUS. This surface-based registration method does not take advantage of internal anatomical prostate structures, which have the potential to provide useful information for image registration. However, non-rigid, multi-modal intensity-based MRI-TRUS registration is challenging due to highly non-linear intensities relationships between MRI and TRUS. In this paper, we present preliminary work using image synthesis to cast this problem into a mono-modal registration task by using a large database of over 100 clinical MRI-TRUS image pairs to learn a joint model of MR-TRUS appearance. Thus, given an MRI, we use this learned joint appearance model to synthesize the patient’s corresponding TRUS image appearance with which we could potentially perform mono-modal intensity-based registration. We present preliminary results of this approach.
John A. Onofrey
Ilkay Oksuz
ilkay.oksuz@imtlucca.it
Saradwata Sarkar
Rajesh Venkataraman
Lawrence H. Staib
Xenophon Papademetris
2017-01-30T10:33:52Z
2017-01-30T11:33:18Z
http://eprints.imtlucca.it/id/eprint/3647
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3647
2017-01-30T10:33:52Z
Lattice orientation and crack size effect on the mechanical properties of Graphene
The effect of lattice orientation and crack length on the mechanical properties of Graphene are studied based on molecular dynamics simulations. Bond breaking and crack initiation in an initial edge crack model with 13 different crack lengths, in 10 different lattice orientations of Graphene are examined. In all the lattice orientations, three recurrent fracture patterns are reported. The influence of the lattice orientation and crack length on yield stress and yield strain of Graphene is also investigated. The arm-chair fracture pattern is observed to possess the lowest yield properties. A sudden decrease in yield stress and yield strain can be noticed for crack sizes <10 nm. However, for larger crack sizes, a linear decrease in yield stress is observed, whereas a constant yield strain of ≈≈0.05 is noticed. Therefore, the yield strain of ≈≈0.05 can be considered as a critical strain value below which Graphene does not show failure. This information can be utilized as a lower bound for the design of nano-devices for various strain sensor applications. Furthermore, the yield data will be useful while developing the Graphene coating on Silicon surface in order to enhance the mechanical and electrical characteristics of solar cells and to arrest the growth of micro-cracks in Silicon cells.
Pattabhi R. Budarapu
pattabhi.budarapu@imtlucca.it
B. Javvaji
V. K. Sutrakar
D. Roy Mahapatra
Marco Paggi
marco.paggi@imtlucca.it
G. Zi
T. Rabczuk
2017-01-26T14:29:19Z
2017-01-26T14:29:19Z
http://eprints.imtlucca.it/id/eprint/3642
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3642
2017-01-26T14:29:19Z
Solving Mixed-Integer Quadratic Programs via Nonnegative Least Squares
This paper proposes a new algorithm for solving Mixed-Integer Quadratic Programming (MIQP) problems. The algorithm is particularly tailored to solving small-scale MIQPs such as those that arise in embedded hybrid Model Predictive Control (MPC) applications. The approach combines branch and bound (B&B) with nonnegative least squares (NNLS), that are used to solve Quadratic Programming (QP) relaxations. The QP algorithm extends a method recently proposed by the author for solving strictly convex QP's, by (i) handling equality and bilateral inequality constraints, (ii) warm starting, and (iii) exploiting easy-to-compute lower bounds on the optimal cost to reduce the number of QP iterations required to solve the relaxed problems. The proposed MIQP algorithm has a speed of execution that is comparable to state- of-the-art commercial MIQP solvers and is relatively simple to code, as it requires only basic arithmetic operations to solve least-square problems.
Alberto Bemporad
alberto.bemporad@imtlucca.it
2016-11-14T11:24:12Z
2016-11-14T11:24:12Z
http://eprints.imtlucca.it/id/eprint/3595
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3595
2016-11-14T11:24:12Z
Whole Image Synthesis Using a Deep Encoder-Decoder Network
The synthesis of medical images is an intensity transformation of a given modality in a way that represents an acquisition with a different modality (in the context of MRI this represents the synthesis of images originating from different MR sequences). Most methods follow a patch-based approach, which is computationally inefficient during synthesis and requires some sort of ‘fusion’ to synthesize a whole image from patch-level results. In this paper, we present a whole image synthesis approach that relies on deep neural networks. Our architecture resembles those of encoder-decoder networks, which aims to synthesize a source MRI modality to an other target MRI modality. The proposed method is computationally fast, it doesn’t require extensive amounts of memory, and produces comparable results to recent patch-based approaches.
Vasileios Sevetlidis
Mario Valerio Giuffrida
valerio.giuffrida@imtlucca.it
Sotirios A. Tsaftaris
2016-11-14T11:18:52Z
2016-11-14T11:18:52Z
http://eprints.imtlucca.it/id/eprint/3594
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3594
2016-11-14T11:18:52Z
Rotation-Invariant Restricted Boltzmann Machine Using Shared Gradient Filters
Finding suitable features has been an essential problem in computer vision. We focus on Restricted Boltzmann Machines (RBMs), which, despite their versatility, cannot accommodate transformations that may occur in the scene. As a result, several approaches have been proposed that consider a set of transformations, which are used to either augment the training set or transform the actual learned filters. In this paper, we propose the Explicit Rotation-Invariant Restricted Boltzmann Machine, which exploits prior information coming from the dominant orientation of images. Our model extends the standard RBM, by adding a suitable number of weight matrices, associated with each dominant gradient. We show that our approach is able to learn rotation-invariant features, comparing it with the classic formulation of RBM on the MNIST benchmark dataset. Overall, requiring less hidden units, our method learns compact features, which are robust to rotations.
Mario Valerio Giuffrida
valerio.giuffrida@imtlucca.it
Sotirios A. Tsaftaris
2016-05-11T11:02:48Z
2016-09-13T09:42:41Z
http://eprints.imtlucca.it/id/eprint/3485
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3485
2016-05-11T11:02:48Z
Human and Robot Hands: Sensorimotor Synergies to Bridge the Gap Between Neuroscience and Robotics
The control of the many degrees of freedom of the hand through functional modules (hand synergies) has been proposed as a potentially useful model to describe how the hand can maintain postures while being able to rapidly change its configuration to accomplish a wide range of tasks. However, whether and to what extent synergies are actually encoded in motor cortical areas is still debated. A direct encoding of hand synergies is suggested by electrophysiological studies in nonhuman primates, but the evidence in humans resulted, so far, partial and indirect. In this chapter, we review the organization of the brain network that controls hand posture in humans and present preliminary results of a functional Magnetic Resonance Imaging (fMRI) on the encoding of synergies at a cortical level to control hand posture in humans.
Andrea Leo
Giacomo Handjaras
Hamal Marino
Matteo Bianchi
Pietro Pietrini
pietro.pietrini@imtlucca.it
Emiliano Ricciardi
emiliano.ricciardi@imtlucca.it
2016-04-27T07:56:32Z
2016-04-27T07:56:32Z
http://eprints.imtlucca.it/id/eprint/3474
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3474
2016-04-27T07:56:32Z
A probabilistic interpretation of set-membership filtering: application to polynomial systems through polytopic bounding
Set-membership estimation is usually formulated in the context of set-valued calculus and no probabilistic calculations are necessary. In this paper, we show that set-membership estimation can be equivalently formulated in the probabilistic setting by employing sets of probability measures. Inference in set-membership estimation is thus carried out by computing expectations with respect to the updated set of probability measures PP as in the probabilistic case. In particular, it is shown that inference can be performed by solving a particular semi-infinite linear programming problem, which is a special case of the truncated moment problem in which only the zeroth order moment is known (i.e., the support). By writing the dual of the above semi-infinite linear programming problem, it is shown that, if the nonlinearities in the measurement and process equations are polynomial and if the bounding sets for initial state, process and measurement noises are described by polynomial inequalities, then an approximation of this semi-infinite linear programming problem can efficiently be obtained by using the theory of sum-of-squares polynomial optimization. We then derive a smart greedy procedure to compute a polytopic outer-approximation of the true membership-set, by computing the minimum-volume polytope that outer-bounds the set that includes all the means computed with respect to P.
Alessio Benavoli
Dario Piga
dario.piga@imtlucca.it
2016-04-27T07:52:54Z
2016-04-27T07:52:54Z
http://eprints.imtlucca.it/id/eprint/3472
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3472
2016-04-27T07:52:54Z
Sparse optimization for automated energy end use disaggregation
Retrieving the household electricity consumption at individual appliance level is an essential requirement to assess the contribution of different end uses to the total household consumption, and thus to design energy saving policies and user-tailored feedback for reducing household electricity usage. This has led to the development of nonintrusive appliance load monitoring (NIALM), or energy disaggregation, algorithms, which aim to decompose the aggregate energy consumption data collected from a single measurement point into device-level consumption estimations. Existing NIALM algorithms are able to provide accurate estimate of the fraction of energy consumed by each appliance. Yet, in the authors' experience, they provide poor performance in reconstructing the power consumption trajectories overtime. In this brief, a new NIALM algorithm is presented, which, besides providing very accurate estimates of the aggregated consumption by appliance, also accurately characterizes the appliance power consumption profiles overtime. The proposed algorithm is based on the assumption that the unknown appliance power consumption profiles are piecewise constant overtime (as it is typical for power use patterns of household appliances) and it exploits the information on the time-of-day probability in which a specific appliance might be used. The disaggregation problem is formulated as a least-square error minimization problem, with an additional (convex) penalty term aiming at enforcing the disaggregate signals to be piecewise constant overtime. Testing on household electricity data available in the literature is reported.
Dario Piga
dario.piga@imtlucca.it
Andrea Cominola
Matteo Giuliani
Andrea Castelletti
Andrea Emilio Rizzoli
2016-03-15T10:05:20Z
2016-03-15T10:05:20Z
http://eprints.imtlucca.it/id/eprint/3236
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3236
2016-03-15T10:05:20Z
Dynamic energy release rate in couple-stress elasticity
This paper is concerned with energy release rate for dynamic steady state crack problems in elastic materials with microstructures. A Mode III semi-infinite crack subject to loading applied on the crack surfaces is considered. The micropolar behaviour of the material is described by the theory of couple-stress elasticity developed by Koiter. A general expression for the dynamic J-integral including both traslational and micro-rotational inertial contributions is derived, and the conservation of this integral on a path surrounding the crack tip is demonstrated.
Lorenzo Morini
lorenzo.morini@imtlucca.it
Amdrea Piccolroaz
Gennady Mishuris
2016-03-15T10:00:03Z
2016-03-15T10:08:29Z
http://eprints.imtlucca.it/id/eprint/3235
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3235
2016-03-15T10:00:03Z
Analysis of interfacial crack propagation under asymmetric loading in anisotropic materials
This paper considers a steady-state crack propagating along an interface between dissimilar orthotropic materials under an asymmetric load. Although most of the known results so far deal with symmetric loading, it has been shown recently that a significant asymmetry in the applied loading may lead to a pronounced effect in terms of the values of the SIFs. The aim of the paper is to extend these results from the static case to a moving crack. In particular, we show the significance of the asymmetry of the loading for computing the energy release rate.
Lewis Pryce
Lorenzo Morini
lorenzo.morini@imtlucca.it
Gennady Mishuris
2016-03-15T09:31:37Z
2016-03-15T09:31:37Z
http://eprints.imtlucca.it/id/eprint/3234
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3234
2016-03-15T09:31:37Z
Interfacial Cracks in Piezoelectric Bimaterials: an approach based on Weight Functions and Boundary Integral Equations
The focus of this paper is on the analysis of a semi-infinite crack lying along a perfect interface in a piezoelectric bimaterial with arbitrary loading on the crack faces. Making use of the extended Stroh formalism for piezoelectric materials combined with Riemann-Hilbert formulation, general expressions are obtained for both symmetric and skew-symmetric weight functions associate with plane crack problems at the interface between dissimilar anisotropic piezoelectric media. The effect of the coupled electrical fields is incorporated in the derived original expressions for the weight function matrices. These matrices are used together with Betti's reciprocity identity in order to obtain singular integral equations relating the extended displacement and traction fields to the loading acting on the crack faces. In order to study the variation of the piezoelectric effect, two different poling directions are considered. Examples are shown for both poling directions with a number of mechanical and electrical loadings applied to the crack faces.
Lewis Pryce
Lorenzo Morini
lorenzo.morini@imtlucca.it
D. Andreeva
A. Zagnetko
2016-03-15T09:17:00Z
2016-03-15T09:17:00Z
http://eprints.imtlucca.it/id/eprint/3233
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3233
2016-03-15T09:17:00Z
Analysis of the validity of the asymptotic techniques in the lower hybrid wave equation solution for reactor applications
Knowing that the lower hybrid (LH) wave propagation in tokamak plasmas can be correctly described with a full wave approach only, based on fully numerical techniques or on semianalytical approaches, in this paper, the LH wave equation is asymptotically solved via the Wentzel-Kramers-Brillouin (WKB) method for the first two orders of the expansion parameter, obtaining governing equations for the phase at the lowest and for the amplitude at the next order. The nonlinear partial differential equation(PDE) for the phase is solved in a pseudotoroidal geometry (circular and concentric magnetic surfaces) by the method of characteristics. The associated system of ordinary differential equations for the position and the wavenumber is obtained and analytically solved by choosing an appropriate expansion parameter. The quasilinear PDE for the WKB amplitude is also solved analytically, allowing us to reconstruct the wave electric field inside the plasma. The solution is also obtained numerically and compared with the analytical solution. A discussion of the validity limits of the WKB method is also given on the basis of the obtained results.
A. Cardinali
Lorenzo Morini
lorenzo.morini@imtlucca.it
C. Castaldo
R. Cesario
F. Zonca
2016-03-15T08:52:08Z
2016-03-18T11:01:35Z
http://eprints.imtlucca.it/id/eprint/3232
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3232
2016-03-15T08:52:08Z
Contribution of Tore Supra in preparation of ITER
Tore Supra routinely addresses the physics and technology of very long-duration plasma discharges, thus bringing precious information on critical issues of long pulse operation of ITER. A new ITER relevant lower hybrid current drive (LHCD) launcher has allowed coupling to the plasma a power level of 2.7 MW for 78 s, corresponding to a power density close to the design value foreseen for an ITER LHCD system. In accordance with the expectations, long distance (10 cm) power coupling has been obtained. Successive stationary states of the plasma current profile have been controlled in real-time featuring (i) control of sawteeth with varying plasma parameters, (ii) obtaining and sustaining a 'hot core' plasma regime, (iii) recovery from a voluntarily triggered deleterious magnetohydrodynamic regime. The scrape-off layer (SOL) parameters and power deposition have been documented during L-mode ramp-up phase, a crucial point for ITER before the X-point formation. Disruption mitigation studies have been conducted with massive gas injection, evidencing the difference between He and Ar and the possible role of the q = 2 surface in limiting the gas penetration. ICRF assisted wall conditioning in the presence of magnetic field has been investigated, culminating in the demonstration that this conditioning scheme allows one to recover normal operation after disruptions. The effect of the magnetic field ripple on the intrinsic plasma rotation has been studied, showing the competition between turbulent transport processes and ripple toroidal friction. During dedicated dimensionless experiments, the effect of varying the collisionality on turbulence wavenumber spectra has been documented, giving new insight into the turbulence mechanism. Turbulence measurements have also allowed quantitatively comparing experimental results with predictions by 5D gyrokinetic codes: numerical results simultaneously match the magnitude of effective heat diffusivity, rms values of density fluctuations and wavenumber spectra. A clear correlation between electron temperature gradient and impurity transport in the very core of the plasma has been observed, strongly suggesting the existence of a threshold above which transport is dominated by turbulent electron modes. Dynamics of edge turbulent fluctuations has been studied by correlating data from fast imaging cameras and Langmuir probes, yielding a coherent picture of transport processes involved in the SOL. Corrections were made to this article on 6 January 2012. Some of the letters in the text were missing.
B. Saoutic
J. Abiteboul
L. Allegretti
S. Allfrey
J.M. Ané
T. Aniel
A. Argouarch
J.F. Artaud
M.H. Aumenier
S. Balme
V. Basiuk
O. Baulaigue
P. Bayetti
A. Bécoulet
M. Bécoulet
M.S. Benkadda
F. Benoit
G. Berger-by
J.M. Bernard
B. Bertrand
P. Beyer
A. Bigand
J. Blum
D. Boilson
G. Bonhomme
H. Bottollier-Curtet
C. Bouchand
F. Bouquey
C. Bourdelle
S. Bourmaud
C. Brault
S. Brémond
C. Brosset
J. Bucalossi
Y. Buravand
P. Cara
V. Catherine-Dumont
A. Casati
M. Chantant
M. Chatelier
G. Chevet
D. Ciazynski
G. Ciraolo
F. Clairet
M. Coatanea-Gouachet
L. Colas
L. Commin
E. Corbel
Y. Corre
X. Courtois
R. Dachicourt
M. Dapena Febrer
M. Davi Joanny
R. Daviot
H. De Esch
Joan Decker
P. Decool
P. Delaporte
E. Delchambre
E. Delmas
L. Delpech
C. Desgranges
P. Devynck
T. Dittmar
L. Doceul
D. Douai
H. Dougnac
J.L. Duchateau
B. Dugué
N. Dumas
R. Dumont
A. Durocher
F.X. Duthoit
A. Ekedahl
D. Elbeze
M. El Khaldi
F. Escourbiac
F. Faisse
G. Falchetto
M. Farge
J.L. Farjon
M. Faury
N. Fedorczak
C. Fenzi-Bonizec
M. Firdaouss
Y. Frauel
X. Garbet
J. Garcia
J.L. Gardarein
L. Gargiulo
P. Garibaldi
E. Gauthier
O. Gaye
A. Géraud
M. Geynet
P. Ghendrih
I. Giacalone
S. Gibert
C. Gil
G. Giruzzi
M. Goniche
V. Grandgirard
C. Grisolia
G. Gros
A. Grosman
R. Guigon
D. Guilhem
B. Guillerminet
R. Guirlet
J. Gunn
O. Gurcan
S. Hacquin
J.C. Hatchressian
P. Hennequin
C. Hernandez
P. Hertout
S. Heuraux
J. Hillairet
G.T. Hoang
C. Honore
M. Houry
T. Hutter
P. Huynh
G. Huysmans
F. Imbeaux
E. Joffrin
J. Johner
L. Jourd'Heuil
Y.S. Katharria
D. Keller
S.H. Kim
M. Kocan
M. Kubic
B. Lacroix
V. Lamaison
G. Latu
Y. Lausenaz
C. Laviron
F. Leroux
L. Letellier
M. Lipa
X. Litaudon
T. Loarer
P. Lotte
S. Madeleine
P. Magaud
P. Maget
R. Magne
L. Manenc
Y. Marandet
G. Marbach
J.L. Maréchal
L. Marfisi
C. Martin
G. Martin
V. Martin
A. Martinez
J.P. Martins
R. Masset
D. Mazon
N. Mellet
L. Mercadier
A. Merle
D. Meshcheriakov
O. Meyer
L. Million
M. Missirlian
P. Mollard
V. Moncada
P. Monier-Garbet
D. Moreau
P. Moreau
Lorenzo Morini
lorenzo.morini@imtlucca.it
M. Nannini
M. Naiim Habib
E. Nardon
H. Nehme
C. Nguyen
S. Nicollet
R. Nouilletas
T. Ohsako
M. Ottaviani
S. Pamela
H. Parrat
P. Pastor
A.L. Pecquet
B. Pégourié
Y. Peysson
I. Porchy
C. Portafaix
M. Preynas
M. Prou
J.M. Raharijaona
N. Ravenel
C. Reux
P. Reynaud
M. Richou
H. Roche
P. Roubin
R. Sabot
F. Saint-Laurent
S. Salasca
F. Samaille
A. Santagiustina
Y. Sarazin
A. Semerok
J. Schlosser
M. Schneider
M. Schubert
F. Schwander
J.L. Ségui
G. Selig
P. Sharma
J. Signoret
A. Simonin
S. Song
E. Sonnendruker
F. Sourbier
P. Spuig
P. Tamain
M. Tena
J.M. Theis
D. Thouvenin
A. Torre
J.M. Travère
E. Tsitrone
J.C. Vallet
E. Van Der Plas
A. Vatry
J.M. Verger
L. Vermare
F. Villecroze
D. Villegas
R. Volpe
K. Vulliez
J. Wagrez
T. Wauters
L. Zani
D. Zarzoso
X.L. Zou
2016-03-15T08:47:07Z
2016-03-15T08:47:07Z
http://eprints.imtlucca.it/id/eprint/3231
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3231
2016-03-15T08:47:07Z
RF current drive and plasma fluctuations
The role played by electron density fluctuations near the plasma edge on rf current drive in tokamaks is assessed quantitatively. For this purpose, a general framework for incorporating density fluctuations in existing modelling tools has been developed. It is valid when rf power absorption takes place far from the fluctuating region of the plasma. The ray-tracing formalism is modified in order to take into account time-dependent perturbations of the density, while the Fokker–Planck solver remains unchanged. The evolution of the electron distribution function in time and space under the competing effects of collisions and quasilinear diffusion by rf waves is determined consistently with the time scale of fluctuations described as a statistical process. Using the ray-tracing code C3PO and the 3D linearized relativistic bounce-averaged Fokker–Planck solver LUKE, the effect of electron density fluctuations on the current driven by the lower hybrid (LH) and the electron cyclotron (EC) waves is estimated quantitatively. A thin fluctuating layer characterized by electron drift wave turbulence at the plasma edge is considered. The effect of fluctuations on the LH wave propagation is equivalent to a random scattering process with a broadening of the poloidal mode spectrum proportional to the level of the perturbation. However, in the multipass regime, the LH current density profile remains sensitive to the ray chaotic behaviour, which is not averaged by fluctuations. The effect of large amplitude fluctuations on the EC driven current is found to be similar to an anomalous radial transport of the fast electrons. The resulting lower current drive efficiency and broader current profile are in
Yves Peysson
Joan Decker
Lorenzo Morini
lorenzo.morini@imtlucca.it
S. Coda
2016-03-15T08:44:33Z
2016-03-18T10:58:52Z
http://eprints.imtlucca.it/id/eprint/3230
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3230
2016-03-15T08:44:33Z
A versatile ray-tracing code for studying rf wave propagation in toroidal magnetized plasmas
A new ray-tracing code named C 3 PO has been developed to study the propagation of arbitrary electromagnetic radio-frequency (rf) waves in magnetized toroidal plasmas. Its structure is designed for maximum flexibility regarding the choice of coordinate system and dielectric model. The versatility of this code makes it particularly suitable for integrated modeling systems. Using a coordinate system that reflects the nested structure of magnetic flux surfaces in tokamaks, fast and accurate calculations inside the plasma separatrix can be performed using analytical derivatives of a spline-Fourier interpolation of the axisymmetric toroidal MHD equilibrium. Applications to reverse field pinch magnetic configuration are also included. The effects of 3D perturbations of the axisymmetric toroidal MHD equilibrium, due to the discreteness of the magnetic coil system or plasma fluctuations in an original quasi-optical approach, are also studied. Using a Runge–Kutta–Fehlberg method for solving the set of ordinary differential equations, the ray-tracing code is extensively benchmarked against analytical models and other codes for lower hybrid and electron cyclotron waves.
Y. Peysson
Joan Decker
Lorenzo Morini
lorenzo.morini@imtlucca.it
2016-03-14T14:23:16Z
2016-03-14T14:23:16Z
http://eprints.imtlucca.it/id/eprint/3229
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3229
2016-03-14T14:23:16Z
Stroh formalism in analysis of skew-symmetric and symmetric weight functions for interfacial cracks
The focus of the article is on analysis of skew-symmetric weight matrix functions for interfacial cracks in two dimensional anisotropic solids. It is shown that the Stroh formalism proves to be an efficient approach to this challenging task. Conventionally, the weight functions, both symmetric and skew-symmetric, can be identified as a non-trivial singular solutions of the homogeneous boundary value problem for a solid with a crack. For a semi-infinite crack, the problem can be reduced to solving a matrix Wiener-Hopf functional equation. Instead, the Stroh matrix representation of displacements and tractions, combined with a Riemann-Hilbert formulation, is used to obtain an algebraic eigenvalue problem, that is solved in a closed form. The proposed general method is applied to the case of a quasi-static semi-infinite crack propagation between two dissimilar orthotropic media: explicit expressions for the weight matrix functions are evaluated and then used in the computation of complex stress intensity factor corresponding to an asymmetric load acting on the crack faces.
Lorenzo Morini
lorenzo.morini@imtlucca.it
Enrico Radi
Alexander Movchan
Natalia Movchan
2016-03-14T14:17:09Z
2016-03-14T14:17:09Z
http://eprints.imtlucca.it/id/eprint/3227
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3227
2016-03-14T14:17:09Z
Integral identities for a semi-infinite interfacial crack in anisotropic elastic bimaterials
The focus of the article is on the analysis of a semi-infinite crack at the interface between two dissimilar anisotropic elastic materials, loaded by a general asymmetrical system of forces acting on the crack faces. Recently derived symmetric and skew-symmetric weight function matrices are introduced for both plane strain and antiplane shear cracks, and used together with the fundamental reciprocal identity (Betti formula) in order to formulate the elastic fracture problem in terms of singular integral equations relating the applied loading and the resulting crack opening. The proposed compact formulation can be used to solve many problems in linear elastic fracture mechanics (for example various classic crack problems in homogeneous and heterogeneous anisotropic media, as piezoceramics or composite materials). This formulation is also fundamental in many multifield theories, where the elastic problem is coupled with other concurrent physical phenomena.
Lorenzo Morini
lorenzo.morini@imtlucca.it
Amdrea Piccolroaz
Gennady Mishuris
Enrico Radi
2016-03-11T12:45:11Z
2016-03-11T12:45:11Z
http://eprints.imtlucca.it/id/eprint/3219
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3219
2016-03-11T12:45:11Z
Weight function approach to study a crack propagating along a bimaterial interface under asymmetric loading in anisotropic solids
The focus of this paper is the study of the dynamic steady-state propagation of interfacial cracks in anisotropic bimaterials under general, nonsymmetric loading conditions. Symmetric and skew-symmetric weight functions, defined as singular nontrivial solutions of a homogeneous traction-free crack problem, have been recently derived for a quasistatic semiinfinite crack at the interface between two dissimilar anisotropic materials. In this paper, the expressions for the weight functions are generalized to the case of a dynamic steady-state crack between two anisotropic media. A functional matrix equation, through which it is possible to evaluate the stress intensity factors and the energy release rate at the crack tip, is obtained. A general method for calculating the asymptotic coefficients of the displacement and traction fields, without any restrictions regarding the loading applied on the crack faces, is developed. The proposed approach is applied for the computing stress intensity factors and higher-order asymptotic terms corresponding to two different example loading configurations acting on the crack faces in an orthotropic bimaterial.
Lewis Pryce
Lorenzo Morini
lorenzo.morini@imtlucca.it
Gennady Mishuris
2016-03-11T12:26:37Z
2016-04-06T09:07:16Z
http://eprints.imtlucca.it/id/eprint/3217
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3217
2016-03-11T12:26:37Z
Remarks on the energy release rate for an antiplane moving crack in couple stress elasticity
This paper is concerned with the steady-state propagation of an antiplane semi-infinite crack in couple stress elastic materials. A distributed loading applied at the crack faces and moving with the same velocity of the crack tip is considered, and the influence of the loading profile variations and microstructural effects on the dynamic energy release rate is investigated. The behavior of both energy release rate and maximum total shear stress when the crack tip speed approaches the critical speed (either that of the shear waves or that of the localized surface waves) is studied. The limit case corresponding to vanishing characteristic scale lengths is addressed both numerically and analytically by means of a comparison with classical elasticity results.
Lorenzo Morini
lorenzo.morini@imtlucca.it
Amdrea Piccolroaz
Gennady Mishuris
2016-03-11T12:10:25Z
2016-05-04T09:55:02Z
http://eprints.imtlucca.it/id/eprint/3214
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3214
2016-03-11T12:10:25Z
Conservation integrals for two circular holes kept at different temperatures in a thermoelastic solid
Abstract An explicit analytic solution for thermal stresses in an infinite thermoelastic medium with two circular cylindrical holes of different sizes kept at different constant temperatures, under steady-state heat flux is presented. The solution is obtained by using the most general representation of a biharmonic function in bipolar coordinates. The stress field is decomposed into the sum of a particular stress field induced by the steady-state temperature distribution and an auxiliary isothermal stress field required to satisfy the boundary conditions on the holes. The variations of the stress concentration factor on the surface of the holes are determined for varying geometry of the holes. The concept of the conservation integrals Jk, M and L is extended to steady state thermoelasticity and the integrals are proved to be path-independent. These integrals are calculated on closed contours encircling one or both holes. The geometries of a hole in a half-space and an eccentric annular cylinder are considered as particular cases.
Enrico Radi
Lorenzo Morini
lorenzo.morini@imtlucca.it
I. Sevostianov
2016-03-11T12:02:01Z
2016-05-04T09:53:37Z
http://eprints.imtlucca.it/id/eprint/3212
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3212
2016-03-11T12:02:01Z
Multiscale asymptotic homogenization analysis of thermo-diffusive composite materials
In this paper an asymptotic homogenization method for the analysis of composite materials with periodic microstructure in presence of thermodiffusion is described. Appropriate down-scaling relations correlating the microscopic fields to the macroscopic displacements, temperature and chemical potential are introduced. The effects of the material inhomogeneities are described by perturbation functions derived from the solution of recursive cell problems. Exact expressions for the overall elastic and thermodiffusive constants of the equivalent first order thermodiffusive continuum are derived. The proposed approach is applied to the case of a two-dimensional bi-phase orthotropic layered material, where the effective elastic and thermodiffusive properties can be determined analytically. Considering this illustrative example and assuming periodic body forces, heat and mass sources acting on the medium, the solution performed by the first order homogenization approach is compared with the numerical results obtained by the heterogeneous model.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Lorenzo Morini
lorenzo.morini@imtlucca.it
Amdrea Piccolroaz
2016-02-29T08:59:31Z
2016-02-29T08:59:31Z
http://eprints.imtlucca.it/id/eprint/3151
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3151
2016-02-29T08:59:31Z
Direct learning ofLPVcontrollers from data
In many control applications, it is attractive to describe nonlinear (NL) and time-varying (TV) plants by linear parametervarying (LPV) models and design controllers based on such representations to regulate the behaviour of the system. The LPV system class offers the representation of NL and TV phenomena as a linear dynamic relationship between input and output signals, which relationship is dependent on some measurable signals, e.g., operating conditions, often called as scheduling variables. For such models, powerful control synthesis tools are available, but the way how to systematically convert available first principles models to LPV descriptions of the plant, to efficiently identify LPV models for control from data and to understand how modeling errors affect the control performance are still subject of undergoing research. Therefore, it is attractive to synthesize the controller directly from data without the need of modeling the plant and addressing the underlying difficulties. Hence, in this paper, a novel data-driven synthesis scheme is proposed in a stochastic framework to provide a practically applicable solution for synthesizing LPV controllers directly from data. Both the cases of fixed order controller tuning and controller structure learning are discussed and two different design approaches are provided. The effectiveness of the proposed methods is also illustrated by means of an academic example and a real application based simulation case study.
Simone Formentin
Dario Piga
dario.piga@imtlucca.it
Roland Tóth
Sergio M. Savaresi
2016-02-29T08:58:00Z
2016-02-29T08:58:00Z
http://eprints.imtlucca.it/id/eprint/3150
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3150
2016-02-29T08:58:00Z
Computation of the Structured Singular Value via Moment LMI Relaxations
The Structured Singular Value (SSV) provides a powerful tool to test robust stability and performance of feedback systems subject to structured uncertainties. Unfortunately, computing the SSV is an NP-hard problem, and the polynomial-time algorithms available in the literature are only able to provide, except for some special cases, upper and lower bounds on the exact value of the SSV. In this work, we present a new algorithm to compute an upper bound on the SSV in case of mixed real/complex uncertainties. The underlying idea of the developed approach is to formulate the SSV computation as a (nonconvex) polynomial optimization problem, which is relaxed into a sequence of convex optimization problems through moment-based relaxation techniques. Two heuristics to compute a lower bound on the SSV are also discussed. The analyzed numerical examples show that the developed approach provides tighter bounds than the ones computed by the algorithms implemented in the Robust Control Toolbox in Matlab, and it provides, in most of the cases, coincident lower and upper bounds on the structured singular value.
Dario Piga
dario.piga@imtlucca.it
2016-02-26T12:55:26Z
2016-02-26T12:55:26Z
http://eprints.imtlucca.it/id/eprint/3125
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3125
2016-02-26T12:55:26Z
On the Relationship between Variational Level Set-Based and SOM-Based Active Contours
Most Active Contour Models (ACMs) deal with the image segmentation problem as a functional optimization problem, as they work on dividing an image into several regions by optimizing a suitable functional. Among ACMs, variational level set methods have been used to build an active contour with the aim of modeling arbitrarily complex shapes. Moreover, they can handle also topological changes of the contours. Self-Organizing Maps (SOMs) have attracted the attention of many computer vision scientists, particularly in modeling an active contour based on the idea of utilizing the prototypes (weights) of a SOM to control the evolution of the contour. SOM-based models have been proposed in general with the aim of exploiting the specific ability of SOMs to learn the edge-map information via their topology preservation property and overcoming some drawbacks of other ACMs, such as trapping into local minima of the image energy functional to be minimized in such models. In this survey, we illustrate the main concepts of variational level set-based ACMs, SOM-based ACMs, and their relationship and review in a comprehensive fashion the development of their state-of-the-art models from a machine learning perspective, with a focus on their strengths and weaknesses.
Mohammed Abdelsamea
mohammed.abdelsamea@imtlucca.it
Giorgio Gnecco
giorgio.gnecco@imtlucca.it
Mohamed Medhat Gaber
Eyad Elyan
2016-02-26T12:26:43Z
2017-03-21T10:32:36Z
http://eprints.imtlucca.it/id/eprint/3122
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3122
2016-02-26T12:26:43Z
Optimal design of auxetic hexachiral metamaterials with local resonators
A parametric beam lattice model is formulated to analyse the propagation properties of elastic in-plane waves in an auxetic material based on a hexachiral topology of the periodic cell, equipped with inertial local resonators. The Floquet-Bloch boundary conditions are imposed on a reduced order linear model in the only dynamically active degrees-offreedom. Since the resonators can be designed to open and shift band gaps, an optimal design, focused on the largest possible gap in the low-frequency range, is achieved by solving a maximization problem in the bounded space of the significant geometrical and mechanical parameters. A local optimized solution, for a the lowest pair of consecutive dispersion curves, is found by employing the globally convergent version of the Method of Moving asymptotes, combined with Monte Carlo and quasi-Monte Carlo multi-start techniques.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Marco Lepidi
Giorgio Gnecco
giorgio.gnecco@imtlucca.it
Luigi Gambarotta
2016-02-22T11:06:25Z
2016-09-13T10:01:54Z
http://eprints.imtlucca.it/id/eprint/3105
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3105
2016-02-22T11:06:25Z
Functional Exploration Studies of Supramodal Organization in the Human Extrastriate Cortex
In the context of the Touch-Hapsys project, our group investigated whether the two main components of the cortical visual systems, i.e., the ventral ”what” pathway and the dorsal ”where” pathways, are devoted merely to the processing of visual information or rather they are organized in a supramodal fashion, that is, they are able to process information independently from the sensory modality through which such an information reaches the brain. Sighted and congenitally blind individuals underwent fMRI scan examinations while performing distinct visual and/or tactile experimental tasks involving object recognition, movement detection and spatial localization. These functional studies revealed that both sighted subjects and individuals with no previous visual experience rely on these supramodal brain areas of the ventral and dorsal extrastriate cortex to acquire normal knowledge about objects and interact effectively with the surrounding world.
Emiliano Ricciardi
emiliano.ricciardi@imtlucca.it
Daniela Bonino
Lorenzo Sani
Pietro Pietrini
pietro.pietrini@imtlucca.it
2016-02-22T10:41:48Z
2016-09-13T09:56:48Z
http://eprints.imtlucca.it/id/eprint/3100
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3100
2016-02-22T10:41:48Z
Sensing Glove for Brain Studies: Design and Assessment of Its Compatibility for fMRI With a Robust Test
In this paper, we describe a biomimetic-fabric-based sensing glove that can be used to monitor hand posture and gesture. Our device is made of a distributed sensor network of piezoresistive conductive elastomers integrated into an elastic fabric. This solution does not affect natural movement and hand gestures, and can be worn for a long time with no discomfort. The glove could be fruitfully employed in behavioral and functional studies with functional MRI (fMRI) during specific tactile or motor tasks. To assess MR compatibility of the system, a statistical test on phantoms is introduced. This test can also be used for testing the compatibility of mechatronic devices designed to produce different stimuli inside the MR environment. We propose a statistical test to evaluate changes in SNR and time-domain standard deviations between image sequences acquired under different experimental conditions. fMRI experiments on subjects wearing the glove are reported. The reproducibility of fMRI results obtained with and without the glove was estimated. A good similarity between the activated regions was found in the two conditions.
Nicola Vanello
Valentina Hartwig
Mario Tesconi
Emiliano Ricciardi
emiliano.ricciardi@imtlucca.it
Alessandro Tognetti
Giuseppe Zupone
Roger Gassert
Dominique Chapuis
Nicola Sgambelluri
Enzo Pasquale Scilingo
Giulio Giovannetti
Vincenzo Positano
Maria Filomena Santarelli
Antonio Bicchi
Pietro Pietrini
pietro.pietrini@imtlucca.it
Danilo De Rossi
Luigi Landini
2016-02-18T11:22:34Z
2016-02-18T11:22:34Z
http://eprints.imtlucca.it/id/eprint/3071
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3071
2016-02-18T11:22:34Z
La macchina della verità alla luce delle recenti acquisizioni delle neuroscienze
Pietro Pietrini
pietro.pietrini@imtlucca.it
2016-02-18T11:13:14Z
2016-02-18T11:16:02Z
http://eprints.imtlucca.it/id/eprint/3070
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3070
2016-02-18T11:13:14Z
(a cura di) Manuale di tecniche diagnostiche ed esami di laboratorio / Wilson Denise
Il Manuale di Tecniche Diagnostiche ed Esami di Laboratorio di McGraw-Hill illustra in maniera specifica tutto ciò che è necessario conoscere sulla corretta indicazione all'utilizzo e all'interpretazione degli esami diagnostici.
Affronta inoltre il tema della preparazione del paziente nelle fasi di esecuzione e che precedono e seguono l'esame, allo scopo di fornirgli un'assistenza scrupolosa e attenta alle diverse normative relative alla sicurezza.
Il Manuale, di agile formato e facile consultazione, rappresenta l'unico testo interamente pensato e costruito a partire dalle linee guida della pratica professionale basate sulle evidenze scientifiche, un valido motivo in più per utilizzarlo con successo nella pratica clinica quotidiana.
Pietro Pietrini
pietro.pietrini@imtlucca.it
Silvia Pellegrini
2016-02-12T11:52:51Z
2016-02-12T12:08:13Z
http://eprints.imtlucca.it/id/eprint/3061
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3061
2016-02-12T11:52:51Z
Modelling and analyzing adaptive self-assembly strategies with Maude
Building adaptive systems with predictable emergent behavior is a difficult task and it is becoming a critical need. The research community has accepted the challenge by introducing approaches of various nature: from software architectures to programming paradigms and analysis techniques. Our white-box conceptual approach to adaptive systems based on the notion of control data promotes a clear distinction between the application and the adaptation logic. In this paper we propose a concrete instance of our approach based on (i) a neat identification of control data; (ii) a hierarchical architecture that provides the basic structure to separate the adaptation and application logics; (iii) computational reflection as the main mechanism to realize the adaptation logic; (iv) probabilistic rule-based specifications and quantitative verification techniques to specify and analyze the adaptation logic. We show that our solution can be naturally realized in Maude, a Rewriting Logic based framework, and illustrate our approach by specifying, validating and analyzing a prominent example of adaptive systems: robot swarms equipped with self-assembly strategies.
Roberto Bruni
Andrea Corradini
Fabio Gadducci
Alberto Lluch Lafuente
Andrea Vandin
andrea.vandin@imtlucca.it
2016-01-20T10:27:26Z
2016-04-06T10:06:49Z
http://eprints.imtlucca.it/id/eprint/3025
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3025
2016-01-20T10:27:26Z
Supervised Learning of Functional Maps for Infarct Classification
Our submission to the STACOM Challenge at MICCAI 2015 is based on the supervised learning of functional map representation between End Systole (ES) and End Diastole (ED) phases of Left Ventricle (LV), for classifying infarcted LV from the healthy ones. The Laplace-Beltrami eigen-spectrum of the LV surfaces at ES and ED, represented by their triangular meshes, are used to compute the functional maps. Multi-scale distortions induced by the mapping, are further calculated by singular value decomposition of the functional map. During training, the information of whether an LV surface is healthy or diseased is known, and this information is used to train an SVM classifier for the singular values at multiple scales corresponding to the distorted areas augmented with surface area difference of epicardium and endocardium meshes. At testing similar augmented features are calculated and fed to the SVM model for classification. Promising results are obtained on both cross validation of training data as well as on testing data, which encourages us in believing that this algorithm will perform favourably in comparison to state of the art methods.
Anirban Mukhopadhyay
Ilkay Oksuz
ilkay.oksuz@imtlucca.it
Sotirios A. Tsaftaris
sotirios.tsaftaris@imtlucca.it
2016-01-20T10:15:32Z
2016-04-06T07:35:14Z
http://eprints.imtlucca.it/id/eprint/3024
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3024
2016-01-20T10:15:32Z
Reconstruction of DSC-MRI Data from Sparse Data Exploiting Temporal Redundancy and Contrast Localization
In order to asses brain perfusion, one of the available methods is the estimation of parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) from Dynamic Susceptibility Contrast-MRI (DSC-MRI). This estimation requires both high temporal resolution to capture the rapid tracer kinetic, and high spatial resolution to detect small impairments and reliably discriminate boundaries.With this inmind, we propose a compressed sensing approach to decrease the acquisition time without sacrificing the reconstruction, especially in the region affected by tracer passage. To this end we propose the utilization of an available TVL1- L2 minimization scheme with a novel additional term that introduce the information on the volume at baseline (no tracer). We show on simulated data the benefit of such a scheme, that is able to achieve an accurate reconstruction even at high acceleration (x16), with a RMSE of 2.8, 10 times lower than the error obtained with the original reconstruction.
Davide Boschetto
davide.boschetto@imtlucca.it
M. Castellaro
P. Di Prima
A. Bertoldo
Enrico Grisan
2016-01-19T15:59:42Z
2016-04-06T07:39:00Z
http://eprints.imtlucca.it/id/eprint/3018
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3018
2016-01-19T15:59:42Z
Semiautomatic detection of villi in confocal endoscopy for the evaluation of celiac disease
Celiac Disease (CD) is an immune-mediated enteropathy, diagnosed in the clinical practice by intestinal biopsy and the concomitant presence of a positive celiac serology. Confocal Laser Endomicroscopy (CLE) allows skilled and trained experts to potentially perform in vivo virtual histology of small-bowel mucosa. In particular, it allows the qualitative evaluation of mucosa alteration such as a decrease in goblet cells density, presence of villous atrophy or crypt hypertrophy. We present a semi-automatic method for villi detection from confocal endoscopy images, whose appearance change in case of villous atrophy. Starting from a set of manual seeds, a first rough segmentation of the villi is obtained by means of mathematical morphology operations. A merge and split procedure is then performed, to ensure that each seed originates a different region in the final segmentation. A border refinement process is finally performed, evolving the shape of each region according to local gradient intensities. Mean and median Dice coefficients for 290 villi originating from 66 images when compared to manually obtained ground truth are 80.71 and 87.96 respectively.
Davide Boschetto
davide.boschetto@imtlucca.it
H. Mirzaei
R.W.L. Leong
Giacomo Tarroni
Enrico Grisan
2016-01-19T15:31:34Z
2016-04-06T07:34:52Z
http://eprints.imtlucca.it/id/eprint/3017
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3017
2016-01-19T15:31:34Z
Detection and density estimation of goblet cells in confocal endoscopy for the evaluation of celiac disease
Celiac Disease (CD) is an immune-mediated enteropathy, diagnosed in the clinical practice by intestinal biopsy and the concomitant presence of a positive celiac serology. Confocal Laser Endomicroscopy (CLE) allows skilled and trained experts to potentially perform in vivo virtual histology of small-bowel mucosa. In particular, it allows the qualitative evaluation of mucosa alteration such as a decrease in goblet cells density, presence of villous atrophy or crypt hypertrophy. We present a semi-automatic computer-based method for the detection of goblet cells from confocal endoscopy images, whose density changes in case of pathological tissue. After a manual selection of a suitable region of interest, the candidate columnar and goblet cells' centers are first detected and the cellular architecture is estimated from their position using a Voronoi diagram. The region within each Voronoi cell is then analyzed and classified as goblet cell or other. The results suggest that our method is able to detect and label goblet cells immersed in a columnar epithelium in a fast, reliable and automatic way. Accepting 0.44 false positives per image, we obtain a sensitivity value of 90.3. Furthermore, estimated and real goblet cell densities are comparable (error: 9.7 ± 16.9, correlation: 87.2, R2 = 76).
Davide Boschetto
davide.boschetto@imtlucca.it
H. Mirzaei
R.W.L. Leong
Enrico Grisan
2016-01-19T15:25:22Z
2016-04-06T07:36:06Z
http://eprints.imtlucca.it/id/eprint/3016
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3016
2016-01-19T15:25:22Z
Baseline constrained reconstruction of DSC-MRI tracer kinetics from sparse fourier data
In order to assess brain perfusion, one of the available methods is the estimation of parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) from Dynamic Susceptibility Contrast MRI (DSC-MRI). This estimation requires both high temporal and spatial resolution to capture the rapid tracer kinetic and detect small impairments and reliably discriminate boundaries. With this in mind, we propose a compressed sensing approach to decrease the acquisition time without sacrificing the reconstruction, especially in the region affected by the tracer. Within the framework of a TV-L1-L2 minimization for solving the reconstruction from partial Fourier data, we introduce a novel baseline-constraining term weighting the difference of the reconstructed volume from the baseline in all regions where no perfusion is apparent. We show that the proposed reconstruction scheme is able to provide accurate estimation of the tracer kinetics (the necessary step for estimating CBF, CBV and MTT) in the volume even at high acceleration (x16), with a RMSE of 11, a third of what achievable without the baseline constraint.
Davide Boschetto
davide.boschetto@imtlucca.it
P. Di Prima
M. Castellaro
A. Bertoldo
Enrico Grisan
2015-12-04T08:57:09Z
2015-12-04T09:00:42Z
http://eprints.imtlucca.it/id/eprint/2967
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2967
2015-12-04T08:57:09Z
Il Futuro della Cyber Security in Italia. Un libro bianco per raccontare le principali sfide che il nostro Paese dovrà affrontare nei prossimi cinque anni
Roberto Baldoni
Rocco De Nicola
r.denicola@imtlucca.it
2015-11-30T12:56:35Z
2015-11-30T12:56:35Z
http://eprints.imtlucca.it/id/eprint/2937
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2937
2015-11-30T12:56:35Z
Introduction to “Rigorous Engineering of Autonomic Ensembles”– Track Introduction
Today’s software systems are becoming increasingly distributed and decentralized and have to adapt autonomously to dynamically changing, open-ended environments. Often their nodes partake in complex interactions with other nodes or with humans. We call these kinds of distributed, complex systems operating in openended and changing environments, ensembles.
Martin Wirsing
Rocco De Nicola
r.denicola@imtlucca.it
Matthias Hölzl
2015-11-30T12:37:23Z
2016-04-06T07:56:18Z
http://eprints.imtlucca.it/id/eprint/2936
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2936
2015-11-30T12:37:23Z
A Life Cycle for the Development of Autonomic Systems: The E-mobility Showcase
Component ensembles are a promising way of building self-aware autonomic adaptive systems. This approach has been promoted by the EU project ASCENS, which develops the core idea of ensembles by providing rigorous semantics as well as models and methods for the whole development life cycle of an ensemble-based system. These methods specifically address adaptation, self-awareness, self-optimization, and continuous system evolution. In this paper, we demonstrate the key concepts and benefits of the ASCENS approach in the context of intelligent navigation of electric vehicles (e-Mobility), which itself is one of the three key case studies of the project.
Tomáš Bureš
Rocco De Nicola
r.denicola@imtlucca.it
Ilias Gerostathopoulos
Nicklas Hoch
Michal Kit
Nora Koch
Giacoma Valentina Monreale
Ugo Montanari
Rosario Pugliese
Nikola Serbedzija
Martin Wirsing
Franco Zambonelli
2015-11-24T15:47:03Z
2015-11-24T15:47:03Z
http://eprints.imtlucca.it/id/eprint/2930
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2930
2015-11-24T15:47:03Z
Robust model predictive control for discrete-time fractional-order systems
In this paper we propose a tube-based robust model predictive control scheme for fractional-order discrete-time systems of the Grunwald-Letnikov type with state and input constraints. We first approximate the infinite-dimensional
fractional-order system by a finite-dimensional linear system
and we show that the actual dynamics can be approximated
arbitrarily tight. We use the approximate dynamics to design
a tube-based model predictive controller which endows to the
controlled closed-loop system robust stability properties.
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Sotiris Ntouskas
Haralambos Sarimveis
2015-11-18T11:03:28Z
2016-09-13T09:51:45Z
http://eprints.imtlucca.it/id/eprint/2919
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2919
2015-11-18T11:03:28Z
FMRI Compatible Sensing Glove for Hand Gesture Monitoring
Here we describe and validate a fabric sensing glove for hand finger movement monitoring. After a quick calibration procedure, and by suitably processing of the outputs of the glove, it is possible to estimate hand joint angles in real time. Moreover, we tested the fMRI compatibility of the glove and ran a pilot fMRI experiment on the neural correlates of handshaking during human-to-human and human-to-robot interactions. Here we describe how the glove can be used to monitor correct task execution and to improve modeling of the expected hemodynamic responses during fMRI experimental paradigms.
Nicola Vanello
Valentina Hartwig
Enzo Pasquale Scilingo
Daniela Bonino
Emiliano Ricciardi
emiliano.ricciardi@imtlucca.it
Alessandro Tognetti
Pietro Pietrini
pietro.pietrini@imtlucca.it
Danilo De Rossi
Luigi Landini
Antonio Bicchi
2015-11-02T14:43:10Z
2015-11-02T14:43:10Z
http://eprints.imtlucca.it/id/eprint/2803
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2803
2015-11-02T14:43:10Z
An Accurate Thermoviscoelastic Rheological Model for Ethylene Vinyl Acetate Based on Fractional Calculus
The thermoviscoelastic rheological properties of ethylene vinyl acetate (EVA) used to embed solar cells have to be accurately described to assess the deformation and the stress state of photovoltaic (PV) modules and their durability. In the present work, considering the stress as dependent on a noninteger derivative of the strain, a two-parameter model is proposed to approximate the power-law relation between the relaxation modulus and time for a given temperature level. Experimental validation with EVA uniaxial relaxation data at different constant temperatures proves the great advantage of the proposed approach over classical rheological models based on exponential solutions.
Marco Paggi
marco.paggi@imtlucca.it
Alberto Sapora
2015-11-02T14:37:29Z
2017-03-27T14:28:03Z
http://eprints.imtlucca.it/id/eprint/2802
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2802
2015-11-02T14:37:29Z
Topological characterization of antireflective and hydrophobic rough surfaces: are random process theory and fractal modeling applicable?
The random process theory (RPT) has been widely applied to predict the joint probability distribution functions (PDFs) of asperity heights and curvatures of rough surfaces. A check of the predictions of RPT against the actual statistics of numerically generated random fractal surfaces and of real rough surfaces has been only partially undertaken. The present experimental and numerical study provides a deep critical comparison on this matter, providing some insight into the capabilities and limitations in applying RPT and fractal modeling to antireflective and hydrophobic rough surfaces, two important types of textured surfaces. A multi-resolution experimental campaign using a confocal profilometer with different lenses is carried out and a comprehensive software for the statistical description of rough surfaces is developed. It is found that the topology of the analyzed textured surfaces cannot be fully described according to RPT and fractal modeling. The following complexities emerge: ( i ) the presence of cut-offs or bi-fractality in the power-law power-spectral density (PSD) functions; ( ii ) a more pronounced shift of the PSD by changing resolution as compared to what was expected from fractal modeling; ( iii ) inaccuracy of the RPT in describing the joint PDFs of asperity heights and curvatures of textured surfaces; ( iv ) lack of resolution-invariance of joint PDFs of textured surfaces in case of special surface treatments, not accounted for by fractal modeling.
Claudia Borri
claudia.borri@imtlucca.it
Marco Paggi
marco.paggi@imtlucca.it
2015-10-26T12:20:25Z
2015-10-29T14:19:05Z
http://eprints.imtlucca.it/id/eprint/2782
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2782
2015-10-26T12:20:25Z
Benefits and challenges of using smart meters for advancing residential water demand modeling and management: a review
Over the last two decades, water smart metering programs have been launched in a number of medium to large cities worldwide to nearly continuously monitor water consumption at the single household level. The availability of data at such very high spatial and temporal resolution advanced the ability in characterizing, modeling, and, ultimately, designing user-oriented residential water demand management strategies. Research to date has been focusing on one or more of these aspects but with limited integration between the specialized methodologies developed so far. This manuscript is the first comprehensive review of the literature in this quickly evolving water research domain. The paper contributes a general framework for the classification of residential water demand modeling studies, which allows revising consolidated approaches, describing emerging trends, and identifying potential future developments. In particular, the future challenges posed by growing population demands, constrained sources of water supply and climate change impacts are expected to require more and more integrated procedures for effectively supporting residential water demand modeling and management in several countries across the world.
Andrea Cominola
Matteo Giuliani
Dario Piga
dario.piga@imtlucca.it
Andrea Castelletti
Andrea Emilio Rizzoli
2015-10-22T13:41:13Z
2015-10-22T13:41:13Z
http://eprints.imtlucca.it/id/eprint/2779
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2779
2015-10-22T13:41:13Z
Distributed solution of stochastic optimal control problems on GPUs
Stochastic optimal control problems arise in many applications and are, in principle, large-scale involving up to millions of decision variables. Their applicability in control applications is often limited by the availability of algorithms that can solve them efficiently and within the sampling time of the controlled system.
In this paper we propose a dual accelerated proximal gradient algorithm which is amenable to parallelization and demonstrate that its GPU implementation affords high speed-up values (with respect to a CPU implementation) and greatly outperforms well-established commercial optimizers such as Gurobi.
Ajay Kumar Sampathirao
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Alberto Bemporad
alberto.bemporad@imtlucca.it
Panagiotis Patrinos
panagiotis.patrinos@imtlucca.it
2015-10-22T13:39:05Z
2016-05-04T10:15:53Z
http://eprints.imtlucca.it/id/eprint/2780
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2780
2015-10-22T13:39:05Z
Scenario-Based Model Predictive Operation Control of Islanded Microgrids
We propose a model predictive control (MPC) approach for the operation of islanded microgrids that takes into account the stochasticity of wind and load forecasts. In comparison to worst case approaches, the probability distribution of the prediction is used to optimize the operation of the microgrid, leading to less conservative solutions. Suitable models for time series forecast are derived and employed to create scenarios. These scenarios and the system measurements are used as inputs for a stochastic MPC, wherein a mixed-integer problem is solved to derive the optimal controls. In the provided case study, the stochastic MPC yields an increase of wind power generation and decrease of conventional generation.
Christian Hans
hans@control.tu-berlin.de
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Alberto Bemporad
alberto.bemporad@imtlucca.it
Raisch Jörg
raisch@control.tu-berlin.de
Carsten Reincke-Collon
2015-10-19T10:16:18Z
2016-02-26T11:47:36Z
http://eprints.imtlucca.it/id/eprint/2778
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2778
2015-10-19T10:16:18Z
Supervised and semi-supervised classifiers for the detection of flood-prone areas
Supervised and semi-supervised machine-learning techniques are applied and compared for the recognition of the flood hazard. The learning goal consists in distinguishing between flood-exposed and marginal-risk areas. Kernel-based binary classifiers using six quantitative morphological features, derived from data stored in digital elevation models, are trained to model the relationship between morphology and the flood hazard. According to the experimental outcomes, such classifiers are appropriate tools when one is interested in performing an initial low-cost detection of flood-exposed areas, to be possibly refined in successive steps by more time-consuming and costly investigations by experts. The use of these automatic classification techniques is valuable, e.g., in insurance applications, where one is interested in estimating the flood hazard of areas for which limited labeled information is available. The proposed machine-learning techniques are applied to the basin of the Italian Tanaro River. The experimental results show that for this case study, semi-supervised methods outperform supervised ones when—the number of labeled examples being the same for the two cases—only a few labeled examples are used, together with a much larger number of unsupervised ones.
Giorgio Gnecco
giorgio.gnecco@imtlucca.it
Rita Morisi
rita.morisi@imtlucca.it
Giorgio Roth
Marcello Sanguineti
Angela Celeste Taramasso
2015-10-19T09:51:47Z
2016-04-05T12:19:09Z
http://eprints.imtlucca.it/id/eprint/2777
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2777
2015-10-19T09:51:47Z
Supervised Learning Modelization and Segmentation of Cardiac Scar in Delayed Enhanced MRI
Delayed Enhancement Magnetic Resonance Imaging can be used to non-invasively differentiate viable from non-viable myocardium within the Left Ventricle in patients suffering from myocardial diseases. Automated segmentation of scarified tissue can be used to accurately quantify the percentage of myocardium affected. This paper presents a method for cardiac scar detection and segmentation based on supervised learning and level set segmentation. First, a model of the appearance of scar tissue is trained using a Support Vector Machines classifier on image-derived descriptors. Based on the areas detected by the classifier, an accurate segmentation is performed using a segmentation method based on level sets.
Laura Lara
Sergio Vera
Frederic Perez
Nico Lanconelli
Rita Morisi
rita.morisi@imtlucca.it
Bruno Donini
Dario Turco
Cristiana Corsi
Claudio Lamberti
Giovana Gavidia
Maurizio Bordone
Eduardo Soudah
Nick Curzen
James Rosengarten
John Morgan
Javier Herrero
Miguel A. González Ballester
2015-10-19T09:40:53Z
2016-04-06T08:50:40Z
http://eprints.imtlucca.it/id/eprint/2776
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2776
2015-10-19T09:40:53Z
Binary and Multi-class Parkinsonian Disorders Classification Using Support Vector Machines
This paper presents a method for an automated Parkinsonian disorders classification using Support Vector Machines (SVMs). Magnetic Resonance quantitative markers are used as features to train SVMs with the aim of automatically diagnosing patients with different Parkinsonian disorders. Binary and multi–class classification problems are investigated and applied with the aim of automatically distinguishing the subjects with different forms of disorders. A ranking feature selection method is also used as a preprocessing step in order to asses the significance of the different features in diagnosing Parkinsonian disorders. In particular, it turns out that the features selected as the most meaningful ones reflect the opinions of the clinicians as the most important markers in the diagnosis of these disorders. Concerning the results achieved in the classification phase, they are promising; in the two multi–class classification problems investigated, an average accuracy of 81% and 90% is obtained, while in the binary scenarios taken in consideration, the accuracy is never less than 88%.
Rita Morisi
rita.morisi@imtlucca.it
Giorgio Gnecco
giorgio.gnecco@imtlucca.it
Nico Lanconelli
Stefano Zanigni
David Neil Manners
Claudia Testa
Stefania Evangelisti
LauraLudovica Gramegna
Claudio Bianchini
Pietro Cortelli
Caterina Tonon
Raffaele Lodi
2015-10-19T09:31:34Z
2015-10-19T09:31:34Z
http://eprints.imtlucca.it/id/eprint/2775
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2775
2015-10-19T09:31:34Z
Semi-automated scar detection in delayed enhanced cardiac magnetic resonance images
Late enhancement cardiac magnetic resonance images (MRI) has the ability to precisely delineate myocardial scars. We present a semi-automated method for detecting scars in cardiac MRI. This model has the potential to improve routine clinical practice since quantification is not currently offered due to time constraints. A first segmentation step was developed for extracting the target regions for potential scar and determining pre-candidate objects. Pattern recognition methods are then applied to the segmented images in order to detect the position of the myocardial scar. The database of late gadolinium enhancement (LE) cardiac MR images consists of 111 blocks of images acquired from 63 patients at the University Hospital Southampton NHS Foundation Trust (UK). At least one scar was present for each patient, and all the scars were manually annotated by an expert. A group of images (around one third of the entire set) was used for training the system which was subsequently tested on all the remaining images. Four different classifiers were trained (Support Vector Machine (SVM), k-nearest neighbor (KNN), Bayesian and feed-forward neural network) and their performance was evaluated by using Free response Receiver Operating Characteristic (FROC) analysis. Feature selection was implemented for analyzing the importance of the various features. The segmentation method proposed allowed the region affected by the scar to be extracted correctly in 96% of the blocks of images. The SVM was shown to be the best classifier for our task, and our system reached an overall sensitivity of 80% with less than 7 false positives per patient. The method we present provides an effective tool for detection of scars on cardiac MRI. This may be of value in clinical practice by permitting routine reporting of scar quantification.
Rita Morisi
rita.morisi@imtlucca.it
Bruno Donini
Nico Lanconelli
James Rosengarden
John Morgan
Stephen Harden
Nick Curzen
2015-10-19T09:22:53Z
2015-10-19T09:22:53Z
http://eprints.imtlucca.it/id/eprint/2774
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2774
2015-10-19T09:22:53Z
Sparse Solutions to the Average Consensus Problem via Various Regularizations of the Fastest Mixing Markov-Chain Problem
In the consensus problem on multi-agent systems, in which the states of the agents represent opinions, the agents aim at reaching a common opinion (or consensus state) through local exchange of information. An important design problem is to choose the degree of interconnection of the subsystems to achieve a good trade-off between a small number of interconnections and a fast convergence to the consensus state, which is the average of the initial opinions under mild conditions. This paper addresses this problem through l₁ -norm and l₀ -“pseudo-norm” regularized versions of the well-known Fastest Mixing Markov-Chain (FMMC) problem. We show that such versions can be interpreted as robust forms of the FMMC problem and provide results to guide the choice of the regularization parameter.
Giorgio Gnecco
giorgio.gnecco@imtlucca.it
Rita Morisi
rita.morisi@imtlucca.it
Alberto Bemporad
alberto.bemporad@imtlucca.it
2015-06-29T14:12:27Z
2015-06-29T14:12:27Z
http://eprints.imtlucca.it/id/eprint/2724
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2724
2015-06-29T14:12:27Z
Auxetic anti-tetrachiral materials: equivalent elastic properties and frequency band-gaps
A comprehensive characterization of the novel class of anti-tetrachiral cellular solids, both considering the static and the dynamic response, is provided in the paper. The heterogeneous material is characterized by a periodic microstructure made of equi-spaced rings each interconnected by four ligaments. In the most general case, rings and ligaments are surrounded by a softer matrix and the rings can be filled by a different material. First, the first order linear elastic homogenized constitutive response is estimated resorting to two different microstructural models: a discrete model, in which the ligaments are modeled as beams and the presence of the matrix is neglected and the equivalent elastic properties are evaluated through a simplified analytical approach, and a more detailed continuous model, where the actual properties of matrix, ligaments and rings, varying in the 2D domain, are considered and the first order computational homogenization is adopted. Special attention is given to the dependence of the 2D overall Cauchy-type elastic constants on the mechanical and geometrical parameters characterizing the microstructure. The results, indeed, show the existence of large variations in the linear elastic constants and degree of anisotropy. A comparison with available experimental results confirms the validity of the analytical and numerical approaches adopted. Finally, the rigorous Floquet–Bloch approach is applied to the periodic cell of the cellular solid to evaluate the dispersion of propagation waves along the orthotropic axes in the framework of elasticity and to detect band gaps characterizing the material. A numerical approach, based on the first order computational homogenization, is also adopted and the rigorous and approximate solutions are compared.
Andrea Bacigalupo
andrea.bacigalupo@imtlucca.it
Maria Laura De Bellis
2015-05-29T08:09:32Z
2015-05-29T08:09:32Z
http://eprints.imtlucca.it/id/eprint/2700
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2700
2015-05-29T08:09:32Z
Dictionary learning for unsupervised identification of ischemic territories in CP-BOLD Cardiac MRI at rest
Marco Bevilacqua
marco.bevilacqua@imtlucca.it
Cristian Rusu
Rohan Dharmakumar
Sotirios A. Tsaftaris
sotirios.tsaftaris@imtlucca.it
2015-05-29T08:04:45Z
2015-05-29T08:04:45Z
http://eprints.imtlucca.it/id/eprint/2699
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2699
2015-05-29T08:04:45Z
Whole-heart, free-breathing, three-dimensional myocardial BOLD MRI at 3T with simultaneous 13N-ammonia PET in canines
Hsin-Jung Yang
Damini Dey
Jane Sykes
John Butler
Avinash Kali
Ivan Cokic
Behzad Sharif
Debiao Li
Sotirios A. Tsaftaris
sotirios.tsaftaris@imtlucca.it
Piotr Slomka
Frank S. Prato
Rohan Dharmakumar
2015-05-21T09:00:30Z
2015-05-21T09:00:30Z
http://eprints.imtlucca.it/id/eprint/2695
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2695
2015-05-21T09:00:30Z
An agent based approach for the development of EV fleet Charging Strategies in Smart Cities
In the present paper an agent based approach, addressed to simulate the behaviour of a Plug-in Electric Vehicles (PEV) fleet into a Smart City, is presented. Considering the traffic data-set available from mobility plans, a spatial and time model, representing the evolution of travel patterns, can be developed considering each vehicle as an agent. The following statistical analysis in space and time of the agent behaviours is used to plan the PEV charging infrastructure of municipalities. The proposed planning methodology has been tested on an European city in order to evaluate the effectiveness of the proposed procedure. Such charging infrastructure, defined according to the mobility needs, has been tested and used to evaluate the customer satisfaction of PEV users in term of charging demand. The proposed charging system has been implemented to estimate the average daily energy profiles for charging the smart city PEV fleet during a typical workday. This has been finally used as one day ahead energy reference profile to develop a market-oriented EV charging strategies. The performance of the proposed smart charging strategies has been finally simulated and compared.
Mario Mureddu
Alfonso Damiano
M. Musio
Guido Caldarelli
guido.caldarelli@imtlucca.it
Alessandro Chessa
alessandro.chessa@imtlucca.it
Antonio Scala
2015-05-21T08:52:50Z
2015-11-02T09:56:19Z
http://eprints.imtlucca.it/id/eprint/2694
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2694
2015-05-21T08:52:50Z
Integrating the electric grid and the commuter
network through a “Vehicle to Grid” concept: a Complex Networks Theory approach
The new opportunities in the energy production,
storage and distribution, raise new systemic challenges in the
coordination and integration of each element in the infras-
tructural networks, considering also the unavoidable environ-
mental constraints. In this ’multi-network’ scenario an exciting
prospective is to develop the so-called vehicle-to-grid concept to
introduce a positive coupling between the electric grid and the
commuter network. The present research will use concepts and
tools borrowed from the scientific field of Complex Networks, to
understand the infrastructures’ interplay in the perspective of
modeling, simulating and possibly controlling the systemic risk.
Alessandro Chessa
alessandro.chessa@imtlucca.it
Guido Caldarelli
guido.caldarelli@imtlucca.it
Alfonso Damiano
Antonio Scala
2015-05-19T11:12:43Z
2015-05-19T11:12:43Z
http://eprints.imtlucca.it/id/eprint/2686
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2686
2015-05-19T11:12:43Z
Green power grids: how energy from renewable sources affects network and markets
The increasing attention to environmental issues is forcing the implementation of novel energy models based on renewable sources, fundamentally changing the configuration of energy management and introducing new criticalities that are only partly understood. In particular, renewable energies introduce fluctuations causing an increased request of conventional energy sources oriented to balance energy requests on short notices. In order to develop an effective usage of low-carbon sources, such fluctuations must be understood and tamed. In this paper we present a microscopic model for the description and the forecast of short time fluctuations related to renewable sources and to their effects on the electricity market. To account for the inter-dependencies among the energy market and the physical power dispatch network, we use a statistical mechanics approach to sample stochastic perturbations on the power system and an agent based approach for the prediction of the market players behavior. Our model is a data-driven; it builds on one day ahead real market transactions to train agents behaviour and allows to infer the market share of different energy sources. We benchmark our approach on the Italian market finding a good accordance with real data.
Mario Mureddu
Guido Caldarelli
guido.caldarelli@imtlucca.it
Alessandro Chessa
alessandro.chessa@imtlucca.it
Antonio Scala
Alfonso Damiano
2015-05-19T09:35:54Z
2015-10-28T14:47:41Z
http://eprints.imtlucca.it/id/eprint/2681
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2681
2015-05-19T09:35:54Z
Model Predictive Control for Linear Impulsive Systems
Linear impulsive control systems have been extensively studied with respect to their equilibrium points which, in most cases, are no other than the origin. However, the trajectory of an impulsive system cannot be stabilized to arbitrary desired points hindering their utilization in a great many applications. In this paper, we study the equilibrium of linear impulsive systems with respect to target-sets. We properly extend the notion of invariance and design stabilizing model predictive controllers (MPC). Finally, we apply the proposed methodology to control the intravenous bolus administration of Lithium.
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Panagiotis Patrinos
panagiotis.patrinos@imtlucca.it
Haralambos Sarimveis
Alberto Bemporad
alberto.bemporad@imtlucca.it
2015-05-18T14:51:11Z
2015-05-18T14:51:11Z
http://eprints.imtlucca.it/id/eprint/2679
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2679
2015-05-18T14:51:11Z
Decentralised hierarchical multi-rate control of large-scale drinking water networks
Ajay Kumar Sampathirao
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Alberto Bemporad
alberto.bemporad@imtlucca.it
2015-05-12T10:26:46Z
2017-01-26T14:22:08Z
http://eprints.imtlucca.it/id/eprint/2674
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2674
2015-05-12T10:26:46Z
A Hybrid Model Predictive Control Approach to Attitude Control with Minimum-Impulse-Bit Thrusters
This paper studies an important aspect of attitude control for a launcher's upper stage: the minimum impulse bit (MIB), that is, the minimum torque that can be exerted by the thrusters. We model this effect using principles of hybrid systems theory and we design a hybrid model predictive control scheme for the attitude control of a launcher during its long coasting period, aiming at minimizing the number of thrusters' actuations. We apply the proposed methodology to a nonlinear model of a typical upper stage with multi-payload capability.
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Daniele Bernardini
daniele.bernardini@imtlucca.it
Hans Strauch
Samir Bennani
Alberto Bemporad
alberto.bemporad@imtlucca.it
2015-05-12T10:23:59Z
2015-05-12T10:23:59Z
http://eprints.imtlucca.it/id/eprint/2673
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2673
2015-05-12T10:23:59Z
Sloshing-aware attitude control of impulsively actuated spacecraft
Upper stages of launchers sometimes drift, with the main engine switched-off, for a longer period of time until re-ignition and subsequent payload release. During this period a large amount of propellant is still in the tank and the motion of the fluid (sloshing) has an impact on the attitude of the stage. For the flight phase the classical spring/damper or pendulum models cannot be applied. A more elaborate sloshing-aware model is described in the paper involving a time-varying inertia tensor.
Using principles of hybrid systems theory we model the minimum impulse bit (MIB) effect, that is, the minimum torque that can be exerted by the thrusters. We design a hybrid model predictive control scheme for the attitude control of a launcher during its long coasting period, aiming at minimising the actuation count of the thrusters.
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Daniele Bernardini
daniele.bernardini@imtlucca.it
Hans Strauch
Samir Bennani
Alberto Bemporad
alberto.bemporad@imtlucca.it
2015-05-04T15:19:39Z
2015-05-04T15:36:21Z
http://eprints.imtlucca.it/id/eprint/2664
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2664
2015-05-04T15:19:39Z
Causal-Consistent Reversibility in a Tuple-Based Language
Causal-consistent reversibility is a natural way of undoing concurrent computations. We study causal-consistent reversibility in the context of µKlaim, a formal coordination language based on distributed tuple spaces. We consider both uncontrolled reversibility, suitable to study the basic properties of the reversibility mechanism, and controlled reversibility based on a rollback operator, more suitable for programming applications. The causality structure of the language, and thus the definition of its reversible semantics, differs from all the reversible languages in the literature because of its generative communication paradigm. In particular, the reversible behavior of µKlaim read primitive, reading a tuple without consuming it, cannot be matched using channel-based communication. We illustrate the reversible extensions of µKlaim on a simple, but realistic, application scenario.
Elena Giachino
Ivan Lanese
Claudio Antares Mezzina
claudio.mezzina@imtlucca.it
Francesco Tiezzi
2015-03-26T11:47:08Z
2016-06-30T12:29:59Z
http://eprints.imtlucca.it/id/eprint/2637
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2637
2015-03-26T11:47:08Z
An Instrumental Least Squares Support Vector Machine for Nonlinear System Identification
Least-Squares Support Vector Machines (LS-SVMs), originating from Statistical Learning and Reproducing Kernel Hilbert Space (RKHS) theories, represent a promising approach to identify nonlinear systems via nonparametric estimation of the involved nonlinearities in a computationally and stochastically attractive way. However, application of LS-SVMs and other RKHS variants in the identification context is formulated as a regularized linear regression aiming at the minimization of the l2-loss of the prediction error. This formulation corresponds to the assumption of an auto-regressive noise structure, which is often found to be too restrictive in practical applications. In this paper, Instrumental Variable (IV) based estimation is integrated into the LS-SVM approach, providing, under minor conditions, consistent identification of nonlinear systems regarding the noise modeling error. It is shown how the cost function of the LS-SVM is modified to achieve an IV-based solution. Although, a practically well applicable choice of the instrumental variable is proposed for the derived approach, optimal choice of this instrument in terms of the estimates associated variance still remains to be an open problem. The effectiveness of the proposed IV based LS-SVM scheme is also demonstrated by a Monte Carlo study based simulation example.
Vincent Laurain
Roland Tóth
Dario Piga
dario.piga@imtlucca.it
Wei Xing Zheng
2015-02-09T08:41:42Z
2015-02-09T08:41:42Z
http://eprints.imtlucca.it/id/eprint/2571
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2571
2015-02-09T08:41:42Z
LPV system identification under noise corrupted scheduling and
output signal observations
Most of the approaches available in the literature for the identification of Linear Parameter-Varying (LPV) systems rely on the assumption that only the measurements of the output signal are corrupted by the noise, while the observations of the scheduling variable are considered to be noise free. However, in practice, this turns out to be an unrealistic assumption in most of the cases, as the scheduling variable is often related to a measured signal and, thus, it is inherently affected by a measurement noise. In this paper, it is shown that neglecting the noise on the scheduling signal, which corresponds to an error-invariables
problem, can lead to a significant bias on the estimated parameters. Consequently, in order to overcome this corruptive phenomenon affecting practical use of data-driven LPV modeling, we present an identification scheme to compute a consistent estimate of LPV Input/Output (IO) models from noisy output and scheduling signal observations. A simulation example is provided to prove the effectiveness
of the proposed methodology.
Dario Piga
dario.piga@imtlucca.it
Pepijn Cox
p.b.cox@tue.nl
Roland Tóth
r.toth@tue.nl
Vincent Laurain
vincent.laurain@univ-lorraine.fr
2015-01-08T14:09:38Z
2015-01-08T14:09:38Z
http://eprints.imtlucca.it/id/eprint/2438
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2438
2015-01-08T14:09:38Z
Control as a key technology for a radical innovation in wind energy generation
This paper is concerned with an innovative technology, denoted as Kitenergy, for the conversion of high-altitude wind energy into electricity. The research activities carried out in the last five years, including theoretical analyses, numerical simulations and experimental tests, indicate that Kitenergy could bring forth a revolution in wind energy generation, providing renewable energy in large quantities at lower cost than fossil energy. After an overview of the main features of the technology, this work investigates three important aspects: the evaluation of the performance achieved by the employed control law, the optimization of the generator operating cycle and the possibility to generate continuously a constant and maximal power output. These issues are tackled through the combined use of advanced modeling, control and optimization methods, which results to be key technologies for a significant breakthrough in renewable energy generation.
Mario Milanese
Lorenzo Fagiano
Dario Piga
dario.piga@imtlucca.it
2015-01-08T13:49:05Z
2015-01-08T13:49:05Z
http://eprints.imtlucca.it/id/eprint/2437
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2437
2015-01-08T13:49:05Z
Kitenergy: a radical innovation in wind energy generation
This paper presents an innovative technology of high-altitude wind power generation, indicated as Kitenergy, which exploits the automatic flight of tethered airfoils (e.g. power kites) to extract energy from wind blowing between 200 and 800 meters above the ground. The key points of such a technology are described and the design of large scale plants is investigated here, in order to show that Kitenergy technology has the potential to provide large quantities of renewable energy with competitive cost with respect to fossil sources. Such claims are supported by the results obtained so far in the research activities undergoing at Politecnico di Torino, Italy, including numerical simulations, prototype experiments and wind data analyses.
Lorenzo Fagiano
Mario Milanese
Dario Piga
dario.piga@imtlucca.it
2014-09-02T09:44:03Z
2014-09-02T09:44:03Z
http://eprints.imtlucca.it/id/eprint/2273
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2273
2014-09-02T09:44:03Z
Douglas-Rachford splitting: complexity estimates and accelerated variants
We propose a new approach for analyzing convergence of the Douglas-Rachford splitting method for solving convex composite optimization problems. The approach is based on a continuously differentiable function, the Douglas-Rachford Envelope (DRE), whose stationary points correspond to the solutions of the original (possibly nonsmooth) problem. The Douglas-Rachford splitting method is shown to be equivalent to a scaled gradient method on the DRE, and so results from smooth unconstrained optimization are employed to analyze its convergence and optimally choose parameter {\gamma} and to derive an accelerated variant of Douglas-Rachford splitting.
Panagiotis Patrinos
panagiotis.patrinos@imtlucca.it
Lorenzo Stella
lorenzo.stella@imtlucca.it
Alberto Bemporad
alberto.bemporad@imtlucca.it
2014-08-08T10:44:40Z
2014-08-08T10:44:40Z
http://eprints.imtlucca.it/id/eprint/2270
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2270
2014-08-08T10:44:40Z
Annotated image datasets of rosette plants
While image-based approaches to plant phenotyping are gaining momentum, benchmark data focusing on typical imaging situations and tasks in plant phenotyping are still lacking, making it difficult to compare existing methodologies. This report describes a benchmark dataset of raw and annotated images of plants. We describe the plant material, environmental conditions, and imaging setup and procedures, as well as the datasets where this image selection stems from. We also describe the annotation process, since all of these images have been manually segmented by experts, such that each leaf has its own label. Color images in the dataset show top-down views on young rosette plants. Two datasets show different genotypes of Arabidopsis while another dataset shows tobacco (Nicoticana tobacum) under different treatments. A version of the dataset, described also in this report, is in the public domain at http://www.plant-phenotyping.org/CVPPP2014-dataset and can be used for the purpose of plant/leaf segmentation from background, with accompanying evaluation scripts. This version was used in the Leaf Segmentation Challenge (LSC) of the Computer Vision Problems in Plant Phenotyping (CVPPP 2014) workshop organized in conjunction with the 13th European Conference on Computer Vision (ECCV), in Zürich, Switzerland. We hope with the release of this, and future, dataset(s) to invigorate the study of computer vision problems and the development of algorithms in the context of plant phenotyping. We also aim to provide to the computer vision community another interesting dataset on which new algorithmic developments can be evaluated.
Hanno Scharr
Massimo Minervini
massimo.minervini@imtlucca.it
Andreas Fischbach
Sotirios A. Tsaftaris
sotirios.tsaftaris@imtlucca.it
2014-03-03T14:22:13Z
2014-03-03T14:22:13Z
http://eprints.imtlucca.it/id/eprint/2171
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2171
2014-03-03T14:22:13Z
Separation of particles from suspensions using transverse force field: a mass transport analysis
We report the calculation of the efficiency for particle separation processes occurring in suspension under transverse force field in a circular duct. The calculation has been performed for a laminar fluid flow directed toward the duct vertical axis. The force field acting on the suspended particles only, is orthogonal to the duct. In the dimensionless calculations occurs a dimensionless group, Ca, which provides a tool for the dimensioning of the purification section.
Alessandro Lavacchi
Ugo Bardi
Claudia Borri
claudia.borri@imtlucca.it
M. Orfei
Alexander Tolstogouzov
2014-03-03T14:13:47Z
2014-03-03T14:17:25Z
http://eprints.imtlucca.it/id/eprint/2169
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2169
2014-03-03T14:13:47Z
Purification of liquid indium by electric current-induced impurity migration in a static transverse magnetic field
We have developed an original method for indium purification. Our approach is based on the directional transfer of impurities by applying crossed electric and magnetic fields to the melting volume. The method reduced the concentration of nickel and tin by a factor of 10 while copper was reduced by a factor of 3. A simple hydrodynamic mass transport model describing the process was also derived.
Ugo Bardi
Claudia Borri
claudia.borri@imtlucca.it
Alessandro Lavacchi
Alexander Tolstogouzov
E.B. Trunin
O.E Trunina
2014-03-03T14:05:58Z
2014-03-03T14:05:58Z
http://eprints.imtlucca.it/id/eprint/2168
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2168
2014-03-03T14:05:58Z
Isothermal oxidation resistance comparison between air plasma sprayed, vacuum plasma sprayed and high velocity oxygen fuel sprayed CoNiCrAlY bond coats
Commercial CoNiCrAlY powders with the same chemical composition were sprayed by vacuum plasma spraying (VPS), air plasma spraying (APS) and high velocity oxygen fuel (HVOF) onto Hastelloy X superalloy substrates obtaining coatings of comparable thickness. After coating, samples were maintained at 1273 K in air for different periods up to 3000 h. Morphological, microstructural and compositional analyses were performed in order to assess the high temperature oxidation resistance provided by the different spraying systems. HVOF technique provided bond coats with higher oxidation resistance compared to APS and VPS.
Martina Di Ferdinando
Alessio Fossati
Alessandro Lavacchi
Ugo Bardi
Francesca Borgioli
Claudia Borri
claudia.borri@imtlucca.it
Carlo Giolli
Andrea Scrivani
2013-10-25T08:43:32Z
2013-10-25T08:43:32Z
http://eprints.imtlucca.it/id/eprint/1847
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1847
2013-10-25T08:43:32Z
Environmental Risk Assessment using the QSPR-Thesaurus Web tool
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Igor V. Tetko
Prakash Kunwar
Stefan Brandmaier
Sergii Novoratskyi
Larisa Charochkina
Volodymyr Prokopenko
Willie J.G.M. Peijnenburg
2013-10-25T08:37:29Z
2013-10-25T08:37:29Z
http://eprints.imtlucca.it/id/eprint/1846
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1846
2013-10-25T08:37:29Z
JAQPOT RESTful Web Services: An Implementation of the OpenTox Application Programming Interface for On-line Prediction of Toxicological Properties
Pantelis Sopasakis
pantelis.sopasakis@imtlucca.it
Haralambos Sarimveis
2012-11-30T08:34:15Z
2012-11-30T08:34:15Z
http://eprints.imtlucca.it/id/eprint/1441
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1441
2012-11-30T08:34:15Z
Simulation-optimization under uncertainty through metamodeling and bootstrapping
Most methods in simulation-optimization assume known environments, whereas this research accounts for uncertain environments combining Taguchi's world view with either regression or Kriging (Gaussian Process) metamodels (response surfaces). These metamodels are combined with Non-Linear Mathematical Programming (NLMP) to find a robust optimal solution. Varying the constraint values in the NLMP model gives an estimated Pareto frontier. To account for the variability of the estimated Pareto frontier, this research uses bootstrapping which gives confidence regions for the robust optimal solution. This methodology is illustrated through the Economic Order Quantity (EOQ) inventory-management model, accounting for the uncertainties in the demand rate and the cost coefficients.
Gabriella Dellino
gabriella.dellino@imtlucca.it
Jack P.C. Kleijnen
Carlo Meloni
2012-04-04T09:18:53Z
2012-04-04T09:18:53Z
http://eprints.imtlucca.it/id/eprint/1256
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1256
2012-04-04T09:18:53Z
An upper Riemann-Stieltjes approach to stochastic design problems
In this paper we study a class of stochastic design problems formulated in terms of general inequality conditions on expectations. These inequalities can be used to express various mean square or almost sure stabilization conditions for stochastic systems. In contrast with existing probabilistic methods that only solve such problems with a certain probability (degree of confidence), we propose a novel method that provides a full guarantee that the constructed solution truly solves the original problem. The main idea of our method is based on overapproximating the expectations by suitably constructed upper Riemann-Stieltjes sums and imposing the inequalities on these sums instead. Next to the full guarantee on the constructed solution, the method offers three other advantages. First, it applies to arbitrary probability distributions. Second, under rather mild conditions we can derive a #x201C;converse theorem #x201D; that states that if the original problem is solvable, our method will find a solution by sufficiently refining the upper Riemann-Stieltjes sums. Finally, we will show that convexity of the function used in the expectation can be exploited to obtain convex design conditions in our approach.
W.P.M.H. Heemels
Alberto Bemporad
alberto.bemporad@imtlucca.it
2011-08-09T13:38:06Z
2013-03-05T15:50:07Z
http://eprints.imtlucca.it/id/eprint/785
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/785
2011-08-09T13:38:06Z
Digital watermarking for the copyright protection of compressed video
In this chapter, a new technique for the watermarking of MPEG-1 and MPEG-2 compressed video streams is proposed. The watermarking scheme operates directly in the domain of MPEG-1 system streams and MPEG-2 program streams (multiplexed streams). Perceptual models are used during the embedding process in order to preserve video quality. The watermark is embedded in the compressed domain and is detected without the use of the original video sequence. Experimental evaluation demonstrates that the proposed scheme is able to withstand a variety of attacks. The resulting watermarking system is very fast and reliable, and is suitable for the copyright protection of video content.
Dimitrios Simitopoulos
Sotirios A. Tsaftaris
sotirios.tsaftaris@imtlucca.it
Nikolaos Boulgouris
Georgios Triantafyllidis
Michael Strintzis
2011-08-01T13:34:28Z
2011-08-08T08:38:45Z
http://eprints.imtlucca.it/id/eprint/755
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/755
2011-08-01T13:34:28Z
A rollout algorithmic approach for complex parallel machine scheduling in healthcare operations
Michele Ciavotta
Gabriella Dellino
gabriella.dellino@imtlucca.it
Carlo Meloni
Marco Pranzo
2011-08-01T10:52:00Z
2011-08-04T07:30:21Z
http://eprints.imtlucca.it/id/eprint/749
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/749
2011-08-01T10:52:00Z
Enhanced evolutionary algorithms for multidisciplinary design optimization: a control engineering perspective
This chapter deals with the application of hybrid evolutionary methods to design optimization issues in which approximation techniques and model management strategies can be used to guide the decision making process in a multidisciplinary context. An enhanced evolutionary algorithmic scheme devoted to design optimization is proposed, and its use in real applications is illustrated in the framework of the multidisciplinary design optimization (MDO). At this aim, a case study is discussed. It relies to the field of automotive engineering in which the design optimization of a system is carried out considering simultaneously both mechanical and control requirements. The studied system is the regulator of the injection pressure of an innovative common rail system for compressed natural gas (CNG) engines, whose engineering design optimization includes several practical and numerical difficulties. To tackle such a situation, a multiobjective optimization formulation of the problem is proposed. The adopted optimization strategy pursues the Pareto optimality on the basis of fitness functions that capture domain specific design aspects as well as static and dynamic objectives. The computational experiments show the ability of the proposed method for finding a satisfactory set of efficient solutions.
Gabriella Dellino
gabriella.dellino@imtlucca.it
Paolo Lino
Carlo Meloni
Alessandro Rizzo
2011-07-27T09:19:44Z
2014-07-16T14:00:50Z
http://eprints.imtlucca.it/id/eprint/601
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/601
2011-07-27T09:19:44Z
Predictive control via set-membership state estimation for constrained linear systems with disturbances
Alberto Bemporad
Andrea Garulli
2011-07-27T09:02:50Z
2011-08-04T07:29:08Z
http://eprints.imtlucca.it/id/eprint/502
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/502
2011-07-27T09:02:50Z
A SAT-based hybrid solver for optimal control of hybrid systems
Combinatorial optimization over continuous and integer variables was proposed recently as a useful tool for solving complex optimal control problems for linear hybrid dynamical systems formulated in discrete-time. Current approaches are based on mixed-integer linear or quadratic programming (MIP), which provides the solution after solving a sequence of relaxed standard linear (or quadratic) programs (LP, QP). An MIP formulation has the drawback of requiring conversion of the discrete/logic part of the hybrid problem into mixed-integer inequalities. Although this operation can be done automatically, most of the original discrete structure of the problem is lost during the conversion. Moreover, the efficiency of the MIP solver mainly relies upon the tightness of the continuous LP/QP relaxations. In this paper we attempt to overcome such difficulties by combining MIP and techniques for solving constraint satisfaction problems into a “hybrid” solver, taking advantage of SAT solvers for dealing efficiently with satisfiability of logic constraints. We detail how to model the hybrid dynamics so that the optimal control problem can be solved by the hybrid MIP+SAT solver, and show that the achieved performance is superior to the one achieved by commercial MIP solvers.
Alberto Bemporad
alberto.bemporad@imtlucca.it
Nicolò Giorgetti
2011-07-27T08:53:24Z
2011-08-04T07:29:08Z
http://eprints.imtlucca.it/id/eprint/462
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/462
2011-07-27T08:53:24Z
Anti-windup synthesis via sampled-data piecewise affine optimal control
Discrete-time receding horizon optimal control is employed in model-based anti-windup augmentation. The optimal control formulation enables designs that minimize the mismatch between the unconstrained closed-loop response with a given controller and the constrained closed-loop response with anti-windup augmentation. Recently developed techniques for off-line computation of the constrained linear regulator's solution, which is piecewise affine, facilitate implementation. The resulting sampled-data, anti-windup closed-loop system's properties are established and its performance is demonstrated on a simulation example.
Alberto Bemporad
alberto.bemporad@imtlucca.it
Andrew R. Teel
Luca Zaccarian
2011-07-27T08:47:33Z
2014-03-05T13:44:24Z
http://eprints.imtlucca.it/id/eprint/567
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/567
2011-07-27T08:47:33Z
Event-driven optimal control of continuous Petri nets
Optimally controlling a hybrid system is a challenging problem for which mainly continuous-time and discrete-time methods have been suggested. In this paper, the problem of optimal control is addressed in the framework of continuous Petri nets, a kind of hybrid systems whose state evolution is piecewise linear. The proposed approach consists of transforming the continuous Petri net into an equivalent hybrid system whose evolution is described by means of discrete-event steps. In particular, each step coincides with the occurrence of an event in the continuous Petri net. Thus, the number of steps required to know the behavior of the Petri net is minimum, while the accuracy is completely preserved. It is shown how to design a mixed integer linear programming problem in order to compute the optimal control solution of different performance criteria.
Jorge Júlvez
Alberto Bemporad
alberto.bemporad@imtlucca.it
Laura Recalde
Manuel Silva
2011-06-30T14:28:11Z
2011-10-07T08:27:21Z
http://eprints.imtlucca.it/id/eprint/629
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/629
2011-06-30T14:28:11Z
Technological change and network dynamics: Lessons from the pharmaceutical industry
In this paper, we investigate how underlying relevant technological conditions induce distinguishable patterns of change in industry structure and evolution. A mapping is detected between the specific nature of problem decompositions and research techniques at the micro level of knowledge bases, and patterns of structural evolution at the macro level of the industry network. The graph-theoretic techniques we introduce map major technological discontinuities on changes observed at the level of dominant organization forms. They might have applications in other domains, whenever the identification of structural breaks and homological relationships between technological and industrial spaces are important issues.
Fabio Pammolli
f.pammolli@imtlucca.it
Luigi Orsenigo
Massimo Riccaboni
massimo.riccaboni@imtlucca.it
2011-06-30T14:25:35Z
2011-08-31T14:40:39Z
http://eprints.imtlucca.it/id/eprint/652
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/652
2011-06-30T14:25:35Z
Technological Competencies in Networks of Innovators
Fabio Pammolli
f.pammolli@imtlucca.it
Massimo Riccaboni
massimo.riccaboni@imtlucca.it
2011-06-30T14:25:07Z
2011-08-31T14:40:39Z
http://eprints.imtlucca.it/id/eprint/659
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/659
2011-06-30T14:25:07Z
Intellectual Property, Technological Regimes and Market Dynamics
Fabio Pammolli
f.pammolli@imtlucca.it
Maria Alessandra Rossi
2011-06-30T14:24:45Z
2011-08-31T14:40:39Z
http://eprints.imtlucca.it/id/eprint/662
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/662
2011-06-30T14:24:45Z
Technological Paradigms and the Evolution of Networks: Lessons from the Pharmaceutical Industry
Fabio Pammolli
f.pammolli@imtlucca.it
Massimo Riccaboni
massimo.riccaboni@imtlucca.it
2011-06-30T14:24:24Z
2011-08-31T14:40:39Z
http://eprints.imtlucca.it/id/eprint/664
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/664
2011-06-30T14:24:24Z
Technological regimes and the evolution of networks of innovators. Lessons from biotechnology and pharmaceuticals
In this paper, we analyse the relationships between technological regimes, regimes of local interaction, and the global structure of an industrial network. Given the complexity of the task, we follow a semi-inductivist approach, combining quantitative empirical analyses and simulative exercises. We show that the topological properties of the R&D network in pharmaceuticals are the result of neither a purely random nor of a cumulative process of growth. Instead, they emerge from a mixture of the two generative processes, under a regime of intense and stable entry. This paper should be considered only as a first step towards the understanding of some general determinants of industry networks growth. Despite its limitations, it provides a parsimonious and general framework to reverse engineer the growth of networks in different industries. Some of the current limitations of our analysis could be overcome, in the future, based on a higher availability of data on real systems and, in particular, of detailed topological and economic information on real-world networks. While currently such data are rare, the increasing interest in industrial networks should soon lead to the development of suitable data sets, offering further guidance for modelling and interpreting the growth of these complex and important economic systems.
Fabio Pammolli
f.pammolli@imtlucca.it
Massimo Riccaboni
massimo.riccaboni@imtlucca.it
2011-06-30T14:24:14Z
2011-08-31T14:40:39Z
http://eprints.imtlucca.it/id/eprint/665
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/665
2011-06-30T14:24:14Z
The Nature and the Extent of Markets for Technology
Fabio Pammolli
f.pammolli@imtlucca.it
Ashish Arora
Alfonso Gambardella
Massimo Riccaboni
massimo.riccaboni@imtlucca.it
2011-06-30T14:24:03Z
2011-08-31T14:40:39Z
http://eprints.imtlucca.it/id/eprint/666
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/666
2011-06-30T14:24:03Z
Europe and the United States: The Power of Networks. Lessons from Technology Transfer
Fabio Pammolli
f.pammolli@imtlucca.it
Massimo Riccaboni
massimo.riccaboni@imtlucca.it
Jason Owen-Smith
Walter W. Powell
2011-06-30T14:23:48Z
2011-08-31T14:40:39Z
http://eprints.imtlucca.it/id/eprint/668
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/668
2011-06-30T14:23:48Z
Technological Regimes and the Growth of Networks: An Empirical Analysis
This paper shows how specific technological
and relational regimes have shaped the growth of the network
of R&D collaborative agreements in pharmaceuticals in the
1990s. Our analysis reveals the existence of a complex set of
regimes of firm growth within the network, providing additional
evidence supporting prediction that both growth and
innovative activities of large and small firms respond, even
within a given industry, to considerably different technological
and economic factors. Moreover, the paper shows, in the
context of a specific industry and by means of a series of
preliminary and explorative empirical analyses, that information
on the topological properties of a given industrial settings
and on roles/positions of organizations within it can be used
to disentangle some fundamental generative processes underlying
observed processes of growth. This result contributes
to the “old” stochastic approach to firm growth, in the
direction of building parsimonious and, at the same time, more
realistic, representations of processes of industrial growth.
Fabio Pammolli
f.pammolli@imtlucca.it
Massimo Riccaboni
massimo.riccaboni@imtlucca.it
2011-02-22T16:11:10Z
2011-07-11T14:25:31Z
http://eprints.imtlucca.it/id/eprint/90
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/90
2011-02-22T16:11:10Z
Assessing the Impact of E-Voting Technologies on Electoral Outcomes: an Analysis of Buenos Aires’ 2005 Congressional Election
Using data from an e-voting experiment conducted in the 2005
Congressional Election in Argentina, we estimate the effect of different e-voting
technologies on the likelihood that citizens cast their vote for different parties for
the National Congress and the Legislature of Buenos Aires. Our results indicate
that voters are extremely receptive to the information cues provided by the
different voting technologies and associated ballot designs, and that particular
voting devices have a significant impact on voter choice, systematically favouring
some parties to the detriment of others. We conclude that the choice of alternative
electronic voting devices might have considerable effect on electoral outcomes in
multi-party electoral systems.
Gabriel Katz
g.katz@imtlucca.it
R. Michael Alvarez
Ernesto Calvo
Marcelo Escolar
Julia Pomares
2011-02-22T15:54:05Z
2011-07-11T14:25:31Z
http://eprints.imtlucca.it/id/eprint/85
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/85
2011-02-22T15:54:05Z
Assessing Voters’ Attitudes towards Electronic Voting in Latin America: Evidence from Colombia’s 2007 E-Voting Pilot
Electronic voting could increase citizens’ electoral participation and trust in countries characterized by fragile democratic institutions and public discredit of the political system such as those in Latin America. This paper examines attitudes towards e-voting among participants in a large scale pilot project conducted in Colombia in 2007, focusing on the perceived reliability and usability of different automated voting technologies. Using a multivariate probit model, we determine the effect of socio-demographic, geographic and technical factors on users’ evaluations of electronic voting vis a vis the traditional paper ballot system. Our results show that users find e-voting not only easier than the current voting system, but also substantially more reliable. While voters’ opinions on usability are driven by technical issues, their trust in the new technologies is strongly affected by individual characteristics. We conclude that e-voting entails a promising opportunity to empower voters and increase confidence in elections in Colombia.
R. Michael Alvarez
Gabriel Katz
g.katz@imtlucca.it
Ricardo Llamosa
Hugo E. Martinez
2011-02-22T14:56:25Z
2011-07-11T14:25:31Z
http://eprints.imtlucca.it/id/eprint/82
This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/82
2011-02-22T14:56:25Z
Assessing the Impact of Alternative Voting Technologies on Multi-Party Elections: Design Features, Heuristic Processing and Voter Choice
This paper analyzes the influence of alternative voting technologies on electoral outcomes in multi-party systems. Using data from a field experiment conducted during the 2005 legislative election in Argentina, we examine the role of information effects associated with alternative voting devices on the support for the competing parties. We find that differences in the type of information displayed and how it was presented across devices favored some parties to the detriment of others. The impact of voting technologies was found to be larger than in two-party systems, and could lead to changes in election results. We conclude that authorities in countries moving to adopt new voting systems should carefully take the potential partisan advantages induced by different technologies into account when evaluating their implementation.
Gabriel Katz
g.katz@imtlucca.it
R. Michael Alvarez
Ernesto Calvo
Marcelo Escolar
Julia Pomares