Showing papers by "Polytechnic University of Milan published in 2009"
TL;DR: A classification of a number of decentralized, distributed and hierarchical control architectures for large scale systems is proposed and attention is focused on the design approaches based on Model Predictive Control.
1,234 citations
TL;DR: Novel dynamical phenomena with no counterpart in ordinary lattices, such as nonreciprocal Bloch oscillations related to violation of the Friedel's law of Bragg scattering in complex potentials, are highlighted.
Abstract: Bloch oscillations in complex lattices with PT symmetry are theoretically investigated with specific reference to optical Bloch oscillations in photonic lattices with gain or loss regions. Novel dynamical phenomena with no counterpart in ordinary lattices, such as nonreciprocal Bloch oscillations related to violation of the Friedel's law of Bragg scattering in complex potentials, are highlighted.
666 citations
TL;DR: In this article, the linear absorption spectrum of regioregular poly(3-hexylthiophene) films was analyzed to probe directly the film microstructure and how it depends on processing conditions.
Abstract: We analyze the linear absorption spectrum of regioregular poly(3-hexylthiophene) films spun from a variety of solvents to probe directly the film microstructure and how it depends on processing conditions. We estimate the exciton bandwidth and the percentage of the film composed of aggregates quantitatively using a weakly interacting H-aggregate model. This provides a description of the degree and quality of crystallites within the film and is in turn correlated with thin-film field-effect transistor characteristics.
510 citations
TL;DR: In this article, benchmark configurations for quantitative validation and comparison of incompressible interfacial flow codes, which model two-dimensional bubbles rising in liquid columns, are proposed, and the benchmark quantities: circularity, center of mass, and mean rise velocity are defined and measured to monitor convergence toward a reference solution.
Abstract: Benchmark configurations for quantitative validation and comparison of incompressible interfacial flow codes, which model two-dimensional bubbles rising in liquid columns, are proposed. The benchmark quantities: circularity, center of mass, and mean rise velocity are defined and measured to monitor convergence toward a reference solution. Comprehensive studies are undertaken by three independent research groups, two representing Eulerian level set finite-element codes and one representing an arbitrary Lagrangian-Eulerian moving grid approach.
486 citations
TL;DR: In this article, the main concepts behind the structural rules for Fibre Reinforced Concrete structural design are briefly explained, and a New fib Model Code that aims to update the previous CEB-FIP Model Code 90, published in 1993, is presented.
Abstract: Although the use of Fibre Reinforced Concrete (FRC) for structural applications is continuously increasing, it is still limited with respect to its potentials, mainly due to the lack of International Building Codes for FRC structural elements. Within fib (Federation Internationale du Beton), the Special Activity Group 5 is preparing a New fib Model Code that aims to update the previous CEB-FIP Model Code 90, published in 1993, that can be considered as the reference document for Eurocode 2. The New Model Code includes several innovations and addresses among other topics, new materials for structural design. In this respect, FRC will be introduced. The Technical Groups fib TG 8.3 “Fibre reinforced concrete” and fib TG 8.6 “Ultra high performance FRC” are preparing some sections of the New Model Code, including regular and high performance FRC. This paper aims to briefly explain the main concepts behind the structural rules for FRC structural design.
433 citations
TL;DR: In this article, the authors study the organizational drivers of internal audit effectiveness in the light of recent changes in the "mission" of internal auditing and its central role in corporate governance.
Abstract: This study attempts to understand the organizational drivers of internal audit effectiveness in the light of recent changes in the ‘mission’ of internal auditing and its central role in corporate governance. On the basis of data from 153 Italian companies, our survey shows that the effectiveness of internal auditing is influenced by: (1) the characteristics of the internal audit team, (2) the audit processes and activities, and (3) the organizational links. Internal audit effectiveness increases in particular when the ratio between the number of internal auditors and employees grows, the Chief Audit Executive is affiliated to the Institute of Internal Auditors, the company adopts control risk self-assessment techniques, and the audit committee is involved in the activities of the internal auditors.
344 citations
TL;DR: In this paper, the physical mechanisms underlying the refractive index modification and the different laser systems used to induce such modification are discussed, and a thorough review of the photonic devices demonstrated with the femtosecond laser microfabrication technique is presented.
Abstract: In this paper we review the micromachining of photonic devices in several materials by means of ultrashort laser pulses. The physical mechanisms underlying the refractive index modification and the different laser systems used to induce such modification are discussed. A thorough review of the photonic devices demonstrated with the femtosecond laser microfabrication technique is presented. In particular, this paper is focused on photonic devices based on optical waveguides. The devices are organized into two categories: passive and active devices. In the former category power splitters, directional couplers, interferometers and Bragg gratings are reviewed, while in the latter amplifiers and lasers are discussed. Finally, conclusions and future perspectives of femtosecond laser micromachining in photonics are provided.
343 citations
TL;DR: A waste generation and composition analysis is described and a comprehensive review of municipal solid waste management (MSWM) in Pudong is provided and the current situation will be evaluated, and its problems will be identified.
339 citations
TL;DR: In this article, the authors present a study of the energy and environmental balances for electric vehicles using batteries or fuel cells, through the methodology of the well to wheel (WTW) analysis, applied to ECE-EUDC driving cycle simulations.
288 citations
TL;DR: In this paper, a parametric analysis was performed in progressive steps, by running the models of a virtual Test Cell and of a sample building, to calculate the associated achievable energy savings, and it was found that thermal inertia effects are enhanced if it is coupled with other energy saving measures and an efficient building use.
286 citations
16 May 2009
TL;DR: An approach is discussed that addresses models that deal with non-functional properties, such as reliability and performance by keeping models alive at run time and feeding a Bayesian estimator with data collected from the running system, which produces updated parameters.
Abstract: Models can help software engineers to reason about design-time decisions before implementing a system. This paper focuses on models that deal with non-functional properties, such as reliability and performance. To build such models, one must rely on numerical estimates of various parameters provided by domain experts or extracted by other similar systems. Unfortunately, estimates are seldom correct. In addition, in dynamic environments, the value of parameters may change over time. We discuss an approach that addresses these issues by keeping models alive at run time and feeding a Bayesian estimator with data collected from the running system, which produces updated parameters. The updated model provides an increasingly better representation of the system. By analyzing the updated model at run time, it is possible to detect or predict if a desired property is, or will be, violated by the running implementation. Requirement violations may trigger automatic reconfigurations or recovery actions aimed at guaranteeing the desired goals. We illustrate a working framework supporting our methodology and apply it to an example in which a Web service orchestrated composition is modeled through a Discrete Time Markov Chain. Numerical simulations show the effectiveness of the approach.
10 May 2009
TL;DR: This paper proposes an approach to determine optimal leader-follower strategies for a mobile robot patrolling an environment that can be applied to environments with arbitrary topologies.
Abstract: Game theoretic approaches to patrolling have become a topic of increasing interest in the very last years. They mainly refer to a patrolling mobile robot that preserves an environment from intrusions. These approaches allow for the development of patrolling strategies that consider the possible actions of the intruder in deciding where the robot should move. Usually, it is supposed that the intruder can hide and observe the actions of the patroller before intervening. This leads to the adoption of a leader-follower solution concept. In this paper, mostly theoretical in its nature, we propose an approach to determine optimal leader-follower strategies for a mobile robot patrolling an environment. Differently from previous works in literature, our approach can be applied to environments with arbitrary topologies.
20 Apr 2009
TL;DR: C-SPARQL is an extension of SPARQL to support continuous queries, registered and continuously executed over RDF data streams, considering windows of such streams, and is presented by means of examples in Urban Computing.
Abstract: C-SPARQL is an extension of SPARQL to support continuous queries, registered and continuously executed over RDF data streams, considering windows of such streams. Supporting streams in RDF format guarantees interoperability and opens up important applications, in which reasoners can deal with knowledge that evolves over time. We present C-SPARQL by means of examples in Urban Computing.
TL;DR: It is shown that a well-known class of organic salts, bis(trimethylammonium) alkane diiodides, can reversibly encapsulate α,ω-diiodoperfluoroalkanes (DIPFAs) through intermolecular interactions between the host's I– anions and the guest's terminal iodine substituents.
Abstract: Halogen bonding has increasingly facilitated the assembly of diverse host-guest solids. Here, we show that a well-known class of organic salts, bis(trimethylammonium) alkane diiodides, can reversibly encapsulate α,ω-diiodoperfluoroalkanes (DIPFAs) through intermolecular interactions between the host9s I– anions and the guest9s terminal iodine substituents. The process is highly selective for the fluorocarbon that forms an I–···I(CF2)mI···I– superanion that is matched in length to the chosen dication. DIPFAs that are 2 to 12 carbons in length (common industrial intermediates) can thereby be isolated from mixtures by means of crystallization from solution upon addition of the dissolved size-matched ionic salt. The solid-state salts can also selectively capture the DIPFAs from the vapor phase, yielding the same product formed from solution despite a lack of porosity of the starting lattice structure. Heating liberates the DIPFAs and regenerates the original salt lattice, highlighting the practical potential for the system in separation applications.
TL;DR: These results are based on extensive investigations of the electronic properties and of the orbital structure of the interface using x-ray absorption spectroscopy and find that the degeneracy of the Ti 3d states is fully removed and that theTi 3d xy levels become the first available states for conducting electrons.
Abstract: In 2004, Ohtomo and Hwang discovered that an electron gas is created at the interface between insulating LaAlO3 and SrTiO3 compounds. Here we show that the generation of a conducting electron gas is related to an orbital reconstruction occurring at the LaAlO3/SrTiO3 interface. Our results are based on extensive investigations of the electronic properties and of the orbital structure of the interface using x-ray absorption spectroscopy. In particular, we find that the degeneracy of the Ti 3d states is fully removed and that the Ti 3dxy levels become the first available states for conducting electrons
TL;DR: In this article, the experimental response of three 1 : 3 scale unbonded, post-tensioned cantilever bridge piers, subjected to quasi-static and pseudo-dynamic loading protocols, are compared with an equivalently reinforced monolithic benchmark.
Abstract: It has been well documented that following a major earthquake a substantial percentage of economic loss results from downtime of essential lifelines in and out of major urban centres. This has thus led to an improvement of both performance-based seismic design philosophies and to the development of cost-effective seismic structural systems capable of guaranteeing a high level of protection, low structural damage and reduced downtime after a design-level seismic event. An example of such technology is the development of unbonded post-tensioned techniques in combination with rocking–dissipating connections.
In this contribution, further advances in the development of high-performance seismic-resistant bridge piers are achieved through the experimental validation of unbonded post-tensioned bridge piers with external, fully replaceable, mild steel hysteretic dissipaters.
The experimental response of three 1 : 3 scale unbonded, post-tensioned cantilever bridge piers, subjected to quasi-static and pseudo-dynamic loading protocols, are presented and compared with an equivalently reinforced monolithic benchmark. Minimal physical damage is observed for the post-tensioned systems, which exhibit very stable energy dissipation and re-centring properties. Furthermore, the external dissipaters can be easily replaced if severely damaged under a major (higher than expected) earthquake event. Thus, negligible residual deformations, limited repair costs and downtime can be achieved for critical lifeline components. Satisfactory analytical–experimental comparisons are also presented as a further confirmation of the reliability of the design procedure and of the modelling techniques. Copyright © 2008 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors consider sinusoidal waves of spanwise velocity which vary in time and are modulated in space along the streamwise direction, so that the phase speed may be null, positive or negative, and the waves may be either stationary or travelling forward or backward in the direction of the mean flow.
Abstract: Waves of spanwise velocity imposed at the walls of a plane turbulent channel flow are studied by direct numerical simulations. We consider sinusoidal waves of spanwise velocity which vary in time and are modulated in space along the streamwise direction. The phase speed may be null, positive or negative, so that the waves may be either stationary or travelling forward or backward in the direction of the mean flow. Such a forcing includes as particular cases two known techniques for reducing friction drag: the oscillating wall technique (a travelling wave with infinite phase speed) and the recently proposed steady distribution of spanwise velocity (a wave with zero phase speed). The travelling waves alter the friction drag significantly. Waves which slowly travel forward produce a large reduction of drag that can relaminarize the flow at low values of the Reynolds number. Faster waves yield a totally different outcome, i.e. drag increase (DI). Even faster waves produce a drag reduction (DR) effect again. Backward-travelling waves instead lead to DR at any speed. The travelling waves, when they reduce drag, operate in similar fashion to the oscillating wall, with an improved energetic efficiency. DI is observed when the waves travel at a speed comparable with that of the convecting near-wall turbulence structures. A diagram illustrating the different flow behaviours is presented.
TL;DR: In this article, the importance of shot peening process to obtain nanocrystal surface is presented with an inclusive clarification of actual state of the art, and the available microstructural characteristics of thin layers obtained with different processes are depicted.
Abstract: The importance of application of shot peening process to obtain nanocrystal surface is presented with an inclusive clarification of actual state of the art. Description of different shot peening methods which have proved to be able to create nanocrystallised layers is presented. Then the available microstructural characteristics of nanocrystal thin layers obtained with different processes are depicted. In addition, the influence of the process is reviewed on material behaviour under different loading conditions. On this basis, some possible addresses for future research in this field are drawn and underlined.
25 Mar 2009
TL;DR: The Java Modelling Tools (JMT) suite is presented, an integrated framework of Java tools for performance evaluation of computer systems using queueing models that offers a rich user interface that simplifies the definition of performance models by means of wizard dialogs and of a graphical design workspace.
Abstract: We present the Java Modelling Tools (JMT) suite, an integrated framework of Java tools for performance evaluation of computer systems using queueing models. The suite offers a rich user interface that simplifies the definition of performance models by means of wizard dialogs and of a graphical design workspace.The performance evaluation features of JMT span a wide range of state-of-the-art methodologies including discrete-event simulation, mean value analysis of product-form networks, analytical identification of bottleneck resources in multiclass environments, and workload characterization with fuzzy clustering. The discrete-event simulator supports several advanced modeling features such as finite capacity regions, load-dependent service times, bursty processes, fork-and-join nodes, and implements spectral estimation for analysis of simulative results. The suite is open-source, released under the GNU general public license (GPL), and it is available for free download at: http://jmt.sourceforge.net.
20 Oct 2009
TL;DR: In this paper, an aging model based on the concept of accumulated charge throughput was developed to estimate battery life under "real world" driving cycles (custom driving cycles based on driving statistics) to determine the "damage" on the life related to each driving pattern to determine equivalent miles/years.
Abstract: This paper deals with life estimation of lithium batteries for plug-in hybrid electric vehicles (PHEVs). An aging model, based on the concept of accumulated charge throughput, has been developed to estimate battery life under “real world” driving cycles (custom driving cycles based on driving statistics). The objective is to determine the “damage” on the life related to each driving pattern to determine equivalent miles/years. Results indicates that Lithium-ion batteries appear to be 10 year/150,000 mile capable, provided that they are not overcharged, nor consistently operated at high temperatures, nor in charge sustaining mode at a very low state of charge.
TL;DR: In this paper, the exciton size and diffusion length of single-walled carbon nanotubes were determined using sub-15'fs near-infrared pulses to measure the nascent bleach of the lowest exciton resonance.
Abstract: Knowledge of excited-state dynamics in carbon nanotubes is determinant for their prospective use in optoelectronic applications. It is known that primary photoexcitations are quasi-one-dimensional excitons, the electron–hole correlation length (‘exciton size’) of which corresponds to a finite volume in the phase space. This volume can be directly measured by nonlinear spectroscopy provided the time resolution is short enough for probing before population relaxation. Here, we report on the experimental determination of exciton size and mobility in (6, 5) carbon nanotubes. The samples are sodium cholate suspensions of nanotubes (produced by the CoMoCat method) obtained by density-gradient ultracentrifugation. By using sub-15 fs near-infrared pulses to measure the nascent bleach of the lowest exciton resonance, we estimate the exciton size to be 2.0±0.7 nm. Exciton–exciton annihilation in our samples is found to be rather inefficient so that many excitons can coexist on a single nanotube. An accurate determination of the size and diffusion length of excitons generated with single-walled nanotubes supports the Wannier–Mott picture of their behaviour, and improves the outlook for the use of nanotubes in optoelectronics and biosensing applications.
TL;DR: The paper presents both a descriptive analysis and a thematic analysis in order to provide a state‐of‐art of international literature about disaster management within the period 1980‐2006.
Abstract: Purpose – The paper aims to discuss a systematic review of the literature about disaster management within the period 1980‐2006.Design/methodology/approach – The research protocol is based on the methodology that is commonly used in healthcare for analysing the literature and provides a state‐of‐art medical discipline. The paper presents both a descriptive analysis and a thematic analysis in order to provide a state‐of‐art of international literature. The research protocol is provided in order to make transparent the review process.Findings – The descriptive analysis highlights the peculiarities of the literature in terms of attention paid during the years, country of provenience and clusters of content of the selected papers. The thematic analysis deepens the content of the papers formalising the state of art.Research limitations/implications – The review considered only academic journals and peer‐reviewed published papers, excluding working papers and books.Practical implications – Through both the anal...
TL;DR: In this paper, the authors proposed a policy for an efficient use of energy-hungry sensors in wireless sensor networks, which is based on the assumption that data acquisition consumes significantly less energy than data transmission.
Abstract: The energy problem in wireless sensor networks remains one of the major barriers preventing the complete exploitation of this technology. Sensor nodes are typically powered by batteries with a limited lifetime, and even when additional energy can be harvested from the external environment, it remains a limited resource to be consumed judiciously. Efficient energy management is thus a key requirement, with most strategies assuming that data acquisition consumes significantly less energy than data transmission. When this assumption does not hold, effective energy management strategies should include policies for an efficient use of energy-hungry sensors.
TL;DR: This study shows that the quantification of helical blood flow in vivo is feasible, and it might allow detection of anomalies in the expected physiological development of helicals flow in aorta and accordingly, could be used in a diagnostic/prognostic index for clinical practice.
Abstract: The mechanics of blood flow in arteries plays a key role in the health of individuals. In this framework, the role played by the presence of helical flow in the human aorta is still not clear in its relation to physiology and pathology. We report here a method for quantifying helical flow in vivo employing time-resolved cine phase contrast magnetic resonance imaging to obtain the complete spatio-temporal description of the three-dimensional pulsatile blood flow patterns in aorta. The method is applied to data of one healthy volunteer. Particle traces were calculated from velocity data: to them we applied a Lagrangian-based method for helical flow quantification, the Helical Flow Index, which has been developed and evaluated in silico in order to reveal global organization of blood flow. Our results: (i) put in evidence that the systolic hemodynamics in aorta is characterized by an evolving helical flow (we quantified a 24% difference in terms of the content of helicity in the streaming blood, between mid and early systole); (ii) indicate that in the first part of the systole helicity is ascrivable mainly to the asymmetry of blood flow in the left ventricle, joined with the laterality of the aorta. In conclusion, this study shows that the quantification of helical blood flow in vivo is feasible, and it might allow detection of anomalies in the expected physiological development of helical flow in aorta and accordingly, could be used in a diagnostic/prognostic index for clinical practice.
TL;DR: In this paper, a comprehensive investigation of random telegraph noise (RTN) in deca-nanometer Flash memories, considering both the nor and the nand architecture, is presented, evidencing that the slope of its exponential tails is the critical parameter determining the scaling trend for RTN.
Abstract: This paper presents a comprehensive investigation of random telegraph noise (RTN) in deca-nanometer Flash memories, considering both the nor and the nand architecture. The statistical distribution of the threshold voltage instability is analyzed in detail, evidencing that the slope of its exponential tails is the critical parameter determining the scaling trend for RTN. By means of 3-D TCAD simulations, the slope is shown to be the result of cell geometry, atomistic substrate doping, and random placement of traps over the cell active area. Finally, the slope dependence on cell geometry (width, length, and oxide thickness), doping, and bias conditions is summarized in a powerful formula that is able to predict the RTN instabilities in deca-nanometer Flash memories.
TL;DR: Despite the post-operative reduction of RV performance along the long axis suggested by TAPSE and PSV, the absence of a decrease in 3D RVEF leads to caution in the interpretation of these 2D and Doppler parameters after cardiac surgery, supporting the hypothesis of geometrical rather than functional changes in the right ventricle.
Abstract: Aims A reduction in tricuspid annular plane systolic excursion (TAPSE) and peak systolic velocity (PSV) of tricuspid annulus after cardiac surgery is a well-known phenomenon, even though its origin is not well established. Recently, a new three-dimensional (3D) echocardiographic software adapted for right ventricular (RV) analysis has been validated. Aims of this study were to evaluate RV function in patients with mitral valve prolapse undergoing surgical valvular repair and to compare and correlate 3D RV ejection fraction (RVEF) with TAPSE and PSV before and after surgery. Methods and results Forty patients were studied by transthoracic 2D and 3D echocardiography pre- and 3, 6, and 12 months post-surgery. TAPSE (15.5+3, 16.5+3, and 18.5+4 mm at 3, 6, and 12 months, respectively) and PSV (11.9+2, 12+2, and 12.8+3 cm/s at 3, 6, and 12 months, respectively) were significantly (P , 0.001) lower after surgery in comparison with pre-surgical values (TAPSE: 25.3+ 4 mm; PSV: 17.8+4 cm/s). On the contrary, pre-operative RVEF (58.4+4%) did not change after surgery (56.9+5, 59.5+5, and 58.5+5% at each step). Conclusion Despite the post-operative reduction of RV performance along the long axis suggested by TAPSE and PSV, the absence of a decrease in 3D RVEF leads to caution in the interpretation of these 2D and Doppler parameters after cardiac surgery, supporting the hypothesis of geometrical rather than functional changes in the right ventricle.
TL;DR: The cross antenna is able to convert propagating fields of any polarization state into correspondingly polarized, localized, and enhanced fields and vice versa and opens the road towards the control of light-matter interactions based on polarized light as well as the analysis of polarized fields on the nanometer scale.
Abstract: We propose a novel cross resonant optical antenna consisting of two perpendicular nanosized gold dipole antennas with a common feed gap. We demonstrate that the cross antenna is able to convert propagating fields of any polarization state into correspondingly polarized, localized, and enhanced fields and vice versa. The cross antenna structure therefore opens the road towards the control of light-matter interactions based on polarized light as well as the analysis of polarized fields on the nanometer scale.
TL;DR: In this paper, the effect of aminic and carboxylic groups on carbon steel rebar in an alkaline environment was investigated through electrochemical potentiodynamic polarisation tests in simulating concrete pore solution in the presence of chlorides.
TL;DR: In this paper, a multi-resolution and multi-sensor approach was developed for the accurate and detailed 3D modeling of the entire Roman Forum in Pompei, Italy, which contains more than 350 finds spread all over the forum as well as larger mural structures of previous buildings and temples.
Abstract: This article reports on a multi-resolution and multi-sensor approach developed for the accurate and detailed 3D modeling of the entire Roman Forum in Pompei, Italy. The archaeological area, approximately 150 × 80 m, contains more than 350 finds spread all over the forum as well as larger mural structures of previous buildings and temples. The interdisciplinary 3D modeling work consists of a multi-scale image- and range-based digital documentation method developed to fulfill all the surveying and archaeological needs and exploit all the intrinsic potentialities of the actual 3D modeling techniques. The data resolution spans from a few decimeters down to few millimeters. The employed surveying methodologies have pros and cons which will be addressed and discussed. The results of the integration of the different 3D data in seamlessly textured 3D model are finally presented and discussed.
23 Jun 2009
TL;DR: An introduction to HOTs and a survey of the several application cases where their use is relevant are provided and a number of possible future applications of HOTs is also proposed.
Abstract: The level of maturity that has been reached by model transformation technologies is proved by the growing literature on transformation libraries that address an increasingly wide spectrum of applications.
With the success of the modeling and transformation paradigm, the need arises to address more complex applications that require a direct manipulation of model transformations.
The uniformity and flexibility of the model-driven paradigm allows this class of applications to make use of the same transformation infrastructure. This is possible because transformations can be translated into transformation models and given as objects to a different class of model transformations, called Higher-Order Transformations (HOT).
This paper provides an introduction to HOTs and a survey of the several application cases where their use is relevant. A number of possible future applications of HOTs is also proposed.