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The Polytechnic University of Milan is the largest technical university in Italy, with about 40,000 students.It offers undergraduate, graduate and higher education courses in engineering, architecture and design.Founded in 1863, it is the oldest university in Milan.The Politecnico has two main campuses in Milan city, where the majority of the research and teaching activity are located, and other satellite campuses in five other cities across Lombardy and Emilia Romagna. The central offices and headquarters are located in the historical campus of Città Studi in Milan, which is also the largest, active since 1927.The university was ranked the best for Engineering and among the top big universities in Italy in the CENSIS-Repubblica Italian University rankings for 2011-2012 and is ranked as the 28th best technical university in the world according to the QS World University Rankings.Its notable alumni include Giulio Natta, Nobel laureate in chemistry in 1963. Wikipedia.

Franco D.,CNRS Astroparticle and Cosmology Lab | Consolati G.,Polytechnic of Milan | Trezzi D.,University of Milan
Physical Review C - Nuclear Physics | Year: 2011

Electron antineutrinos are commonly detected in liquid scintillator experiments via inverse β decay by looking at the coincidence between the reaction products: neutrons and positrons. Prior to positron annihilation, an electron-positron pair may form an orthopositronium (o-Ps) state, with a mean lifetime of a few nanoseconds. Even if the o-Ps decay is speeded up by spin-flip or pick-off effects, it may introduce distortions in the photon emission time distribution, crucial for position reconstruction and pulse shape discrimination algorithms in antineutrino experiments. Reversing the problem, the o-Ps-induced time distortion represents a new signature for tagging antineutrinos in liquid scintillator. In this article, we report the results of measurements of the o-Ps formation probability and lifetime for the most used solvents for organic liquid scintillators in neutrino physics (pseudocumene, linear alkyl benzene, phenylxylylethane, and dodecane). We characterize also a mixture of pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength shifter. In the second part of the article, we demonstrate that the o-Ps-induced distortion of the scintillation photon emission time distributions represent an optimal signature for tagging positrons on an event by event basis, potentially enhancing the antineutrino detection. © 2011 The American Physical Society.

Peroni M.,Polytechnic of Milan
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2011

Deformable Image Registration is a complex optimization algorithm with the goal of modeling a non-rigid transformation between two images. A crucial issue in this field is guaranteeing the user a robust but computationally reasonable algorithm. We rank the performances of four stopping criteria and six stopping value computation strategies for a log domain deformable registration. The stopping criteria we test are: (a) velocity field update magnitude, (b) vector field Jacobian, (c) mean squared error, and (d) harmonic energy. Experiments demonstrate that comparing the metric value over the last three iterations with the metric minimum of between four and six previous iterations is a robust and appropriate strategy. The harmonic energy and vector field update magnitude metrics give the best results in terms of robustness and speed of convergence.

Priimagi A.,Aalto University | Priimagi A.,Polytechnic of Milan | Barrett C.J.,McGill University | Shishido A.,Tokyo Institute of Technology
Journal of Materials Chemistry C | Year: 2014

The design of functional and stimuli-responsive materials is among the key goals of modern materials science. The structure and properties of such materials can be controlled via various stimuli, among which light is often times the most attractive choice. Light is ubiquitous and a gentle energy source and its properties can be optimized for a specific target remotely, with high spatial and temporal resolution. Light-control over molecular alignment has in recent years attracted particular interest, for potential applications such as reconfigurable photonic elements and optical-to-mechanical energy conversion. Herein, we bring forward some recent examples and emerging trends in this exciting field of research, focusing on liquid crystals, liquid-crystalline polymers and photochromic organic crystals, which we believe serve to highlight the immense potential of light-responsive materials to a wide variety of current and future high-tech applications in photonics, energy harvesting and conversion. This journal is © the Partner Organisations 2014.

Najafi H.,University of Alabama | Najafi B.,Polytechnic of Milan | Hoseinpoori P.,K. N. Toosi University of Technology
Applied Thermal Engineering | Year: 2011

In the present paper, a plate and fin heat exchanger is considered and air, as an ideal gas, is defined in both sides of the heat exchanger as the working fluid. Several geometric variables within the logical constraints are considered as optimization parameters. Two different objective functions including the total rate of heat transfer and the total annual cost of the system are defined. Since mentioned objectives are conflicting, no single solution can well-satisfy both objective functions simultaneously. In other words, any attempt to increase the value of the total rate of heat transfer leads to the higher total cost of the system which is certainly undesirable. Therefore, multi-objective optimization using genetic algorithm is utilized in order to achieve a set of optimal solutions, each of which is a trade-off between objectives and can satisfy both objective functions in an appropriate level. The main advantage of this work is providing a set of optimal solutions each of which can be selected by the designer based on the project's limits and the available investment. A sensitivity analysis is also presented in order to investigate the effect of some geometric parameters on each objective functions. © 2011 Elsevier Ltd. All rights reserved.

Bisagni C.,Polytechnic of Milan
Progress in Aerospace Sciences | Year: 2015

The results of an experimental investigation performed at the Politecnico di Milano inside the European project DAEDALOS on three composite cylindrical shells are here presented. At first, static buckling tests were performed under axial compression. Then, two types of dynamic tests were carried out: modal tests at different load levels before buckling and dynamic buckling tests applying an axial shortening of short duration. At the end, one shell was statically tested until final failure. The tests allow to understand the behavior of thin-walled cylindrical shells subjected to axial compression both in static and dynamic conditions. The results show the strength capacity of these structures to work in the post-buckling range with a capacity to sustain a load that is about 40% of the buckling load. The modal tests at different load levels allowed to observe that an increase of the load determines a reduction of the modal frequency and an increase of the damping. Large deformations are obtained before the final failure with out-of-plane displacements of almost 40. mm and a shortening equal to about 26 times the buckling shortening. © 2015 Elsevier Ltd.

Donno D.,Polytechnic of Milan | Donno D.,MINES ParisTech
Geophysics | Year: 2011

The suppression of multiple events is a crucial task in seismic data processing, and the adaptive subtraction of the predicted multiples is recognized as one of the main challenges for the success of the surface-related multiple elimination technique. The traditional least-squares matching approach can affect the primary events because the estimated multiples tend to adapt to the primaries under the minimum energy condition. We investigate two filtering techniques for improving the multiple removal results. In the first proposed method, we combine the advantages of the least-squares and pattern dip-based subtraction methods. Doing so, we exploit the separation of primaries and multiples in the dip domain, and then we apply the least-squares adaptive subtraction in each dip band before recomposing the data to obtain the final subtraction result. As a result of the dip decomposition, the primary-multiple interferences are reduced, allowing for a more reliable least-squares filtering. In the second method, we propose to replace the multiple subtraction step by a separation step using independent component analysis (ICA) methods. We employ the ICA method after least-squares adaptive filtering. Because of the non-Gaussian distributions of the involved signals, primaries and multiples can be separated by computing the optimal rotation between these two signals. We apply the ICA method in local 2D time-space windows to better compensate the space and time variant character of the data. Two-dimensional synthetic and field data examples demonstrate that the multiple subtraction results of both methods are indeed improved with respect to the classical least-squares method. © 2011 Society of Exploration Geophysicists.

Romano M.C.,Polytechnic of Milan
Chemical Engineering Science | Year: 2012

The calcium-looping process is a promising technique for CO 2 capture from coal-fired power plants and for reducing GHG emissions from the power generation sector. This paper presents a calculation model of the carbonator, the key reactor of the Ca-looping process, where CO 2 is captured as a result of its reaction with CaO. The model presented is based on the Kunii-Levenspiel theory for circulating fluidized bed and on the recent findings on the properties of CaO as a CO 2 sorbent, while taking into account the effects of coal ash and sulfur species.This model can be used for process optimization and for the prediction of the performance of power plants based on the Ca-looping process. Also presented in this paper are the results of a sensitivity analysis of the primary parameters that influence the performance of the carbonator. These results confirm the feasibility of the Ca-looping process with reactors of reasonable size for industrial applications and highlight the importance of the properties of the Ca-based sorbent as they highly affect the carbonator's performance. © 2011 Elsevier Ltd.

Bocchiola D.,Polytechnic of Milan | Diolaiuti G.,University of Milan
Theoretical and Applied Climatology | Year: 2013

We investigate here recent (1980-2009) climate variability in the upper Karakoram, Northern Pakistan, of particular interest given the peculiar glacier behavior during the last two decades. Differently from other glacierized regions in the Hindu Kush-Karakoram-Himalaya region, glaciers in the Karakoram display limited ice thinning, and in some cases advancing has been detected. Climate analysis is required to describe recent (i.e., last three decades) variability, to aid highlighting of the factors driving glacier evolution. Starting from monthly data, we analyze seasonal values of total precipitation, number of wet days, maximum (max) and minimum (min) air temperature, max precipitation in 24 h, and cloud cover for 17 weather stations in the upper Karakoram, clustered within three climatic regions as per use of principal components analysis. We detect possible nonstationarity in each of these regions by way of (1) linear regression, (2) moving window average, and (3) Mann-Kendall test, also in progressive form, to detect the onset date of possible trends. We then evaluate linear correlation coefficients between Northern Atlantic Oscillation (NAO) index and climate variables to assess effectiveness of teleconnections, claimed recently to affect climate in this area. Also, we compare temperature within the investigated zone against global temperature anomalies, to evidence enhanced warming within this area. We found mostly nonsignificant changes of total precipitation, unless for few stations displaying increase in Chitral-Hindu Kush region and Northwest Karakoram, or Gilgit area, and decrease in Western Himalaya, Kotli region. Max precipitation is mostly unchanged, unless for slight increase in Chitral and Gilgit areas, and slight decrease in Kotli region. Number of wet days is mostly increasing in Gilgit area, and decreasing in Chitral area, with no clear signal in Kotli region. Min temperatures increase always but during Summer, when decreasing values are detected, especially for Gilgit and Chitral regions. Max temperatures are found to increase everywhere. Cloud cover is significantly increasing in Gilgit area, but decreasing otherwise, especially in Kotli region. Max temperature regime is significantly positively correlated against global thermal anomaly, while min temperature regime is nonsignificantly negatively correlated. Max and min temperatures seem mostly negatively correlated to NAO. Some dependence of trend intensity for the considered variables against altitude is found, different for each region, suggesting that investigation of weather variables at the highest altitudes is warranted to discriminate further climate variability in the area. © 2012 Springer-Verlag Wien.

Bisagni C.,Polytechnic of Milan
Progress in Aerospace Sciences | Year: 2015

The "Dynamics in Aircraft Engineering Design and Analysis for Light Optimized Structures" (DAEDALOS) project aimed to develop methods and procedures to determine dynamic loads by considering the effects of dynamic buckling, material damping and mechanical hysteresis during aircraft service. Advanced analysis and design principles were assessed with the scope of partly removing the uncertainty and the conservatism of today's design and certification procedures. To reach these objectives a DAEDALOS aircraft model representing a mid-size business jet was developed. Analysis and in-depth investigation of the dynamic response were carried out on full finite element models and on hybrid models. Material damping was experimentally evaluated, and different methods for damping evaluation were developed, implemented in finite element codes and experimentally validated. They include a strain energy method, a quasi-linear viscoelastic material model, and a generalized Maxwell viscous material damping. Panels and shells representative of typical components of the DAEDALOS aircraft model were experimentally tested subjected to static as well as dynamic loads. Composite and metallic components of the aircraft model were investigated to evaluate the benefit in terms of weight saving. © 2015 Elsevier Ltd.

Leva S.,Polytechnic of Milan
Electric Power Systems Research | Year: 2011

A three-phase model of asynchronous machines operating at medium or high frequencies is presented. It can be used to study the propagation of surge waves along the stator windings of induction form wound machines. The model is derived from an analogy with a three-phase transmission line. The use of time-space Clarke vectors allows the introduction of mutual coupling between phases. The analytical expressions for voltage waves are derived by means of the Laplace approach to the solution of hyperbolic partial differential equations. Some applicative examples confirm the model validity and can underline some aspects of the project of three-phase windings. © 2010 Elsevier B.V.

Berzi D.,Polytechnic of Milan
Acta Mechanica | Year: 2014

We apply the extended kinetic theory (EKT) to the dense, simple shear flow of inelastic hard spheres. EKT is a phenomenological extension of kinetic theory which aims at incorporating in the simplest possible way the role of pre-collisional velocity correlations which are likely to occur at a concentration larger than the freezing point. The main effect of that correlation is the decrease in the rate at which fluctuating energy is dissipated in inelastic collisions. We use previously published results of numerical simulations performed using an event-driven algorithm to obtain analytical expressions for the radial distribution function at contact (which diverges at a concentration lower than the value at random close packing for sheared inelastic spheres) and the correlation length (i.e., the decreasing factor of the dissipation rate) at different values of the coefficient of restitution. With those, we show that when the diffusion of fluctuating energy of the particles is negligible, EKT implies that three branches of the analytical relation between the ratio of the shear stress to the pressure and the concentration (granular rheology) exist. Hence, for a certain value of the stress ratio, up to three corresponding values of the concentration are possible, with direct implications on the existence of multiple solutions to steady granular flows. © 2014 Springer-Verlag Wien.

Guadagnini A.,Polytechnic of Milan | Neuman S.P.,University of Arizona
Geophysical Research Letters | Year: 2011

Many earth and environmental variables appear to scale as multiplicative (multifractal) processes with spatial or temporal increments possessing Gaussian or heavy-tailed distributions. The behavior, characterized by power-law scaling, is typically limited to intermediate ranges of separation scales (lags) considered, in the case of fully developed turbulence, to be dominated by inertia. It has been established empirically that, in numerous cases (e.g. turbulence, diffusion-limited aggregates, natural images, kinetic surface roughening, fluvial turbulence, sand wave dynamics, Martian topography, river morphometry, gravel-bed mobility, barometric pressure, low-energy cosmic rays, cosmic microwave background radiation, metal-insulator transition, irregularities in human heartbeat time series, turbulence in edge magnetized plasma of fusion devices and turbulent boundary layers of the Earth's magnetosphere), this range of lags can be enlarged significantly, at both ends of the spectrum, via a procedure known as Extended Self-Similarity (ESS). We demonstrate numerically that a similar procedure extends the power-law scaling range over which additive (self-affine) signals exhibit apparent multifractality. We conclude that signals appearing to exhibit either standard or extended (such as those listed) multifractal scaling may potentially represent self-affine processes. Copyright 2011 by the American Geophysical Union.

Salicone S.,Polytechnic of Milan
IEEE Instrumentation and Measurement Magazine | Year: 2013

The concept of measurement uncertainty is quite new. It was proposed for the first time by the International Vocabulary of Metrology (VIM) [1] in its first edition in 1984, and it was then encompassed by the Guide to the Expression of Uncertainty in Measurements (GUM) in 1993, that represents the actual reference document [2]. © 1998-2012 IEEE.

MacChiarella G.,Polytechnic of Milan
IEEE Microwave and Wireless Components Letters | Year: 2013

This letter illustrates a new procedure for evaluating the characteristic polynomials associated to the prototype of a multiband microwave filter. This procedure is based on the Remez algorithm and allows an equiripple response in the assigned filter passbands and stopbands, once the number of poles in each passband and the number of imaginary transmission zeros in each stopband are assigned. Some examples and comparisons are reported to show the effectiveness of the new algorithm which has proved to be significantly faster than a similar one recently published in the literature. © 2001-2012 IEEE.

Longoni A.,Ramon Llull University | Golini R.,University of Bergamo | Cagliano R.,Polytechnic of Milan
International Journal of Production Economics | Year: 2014

This paper aims to study whether Human Resource Management and the organizational practices related to New Forms of Work Organization (NFWO) (e.g.; teamwork, training, and employee involvement) should be implemented to attain higher environmental and social sustainability performance. This potential connection is analyzed using the International Manufacturing Strategy Survey 2009 database containing data on the assembly industry. Several hierarchical regression models are used to study the direct impact of the considered practices on sustainability performance and their interactions with sustainability action programs. The results show that some of the practices related to NFWO are linked to sustainability performance. In particular, training has a direct positive effect on environmental and social sustainability performance and creates a positive interaction between social sustainability action programs and performance. Additionally, employee involvement and incentives have a direct positive impact on social sustainability performance. Finally, teamwork is a relevant practice for the successful implementation of environmental sustainability action programs. This paper contributes by empirically extending the knowledge on the role of organizational practices and the understanding of environmental and social sustainability achievement at the operational level. Moreover, we highlight the complexity of these relationships within different sustainability dimensions, showing the need for more qualitative studies about this topic. © 2013 Elsevier B.V.

Longhi S.,Polytechnic of Milan
Optics Letters | Year: 2010

Reflectionless transmission of light waves with unitary transmittance is shown to occur in a certain class of gain-grating structures and phase-conjugation mirrors in the unstable (above-threshold) regime. Such structures are synthesized by means of the Darboux method developed in the context of supersymmetric relativistic quantum mechanics. Transparency is associated to superluminal pulse transmission. © 2010 Optical Society of America.

Bellan D.,Polytechnic of Milan
Metrology and Measurement Systems | Year: 2015

This paper deals with the amplitude estimation in the frequency domain of low-level sine waves, i.e. sine waves spanning a small number of quantization steps of an analog-to-digital converter. This is a quite common condition for high-speed low-resolution converters. A digitized sine wave is transformed into the frequency domain through the discrete Fourier transform. The error in the amplitude estimate is treated as a random variable since the offset and the phase of the sine wave are usually unknown. Therefore, the estimate is characterized by its standard deviation. The proposed model evaluates properly such a standard deviation by treating the quantization with a Fourier series approach. On the other hand, it is shown that the conventional noise model of quantization would lead to a large underestimation of the error standard deviation. The effects of measurement parameters, such as the number of samples and a kind of the time window, are also investigated. Finally, a threshold for the additive noise is provided as the boundary for validity of the two quantization models. © 2015 Polish Academy of Sciences. All rights reserved.

Longhi S.,Polytechnic of Milan
Optics Letters | Year: 2010

A photonic realization of the Dirac oscillator (DO), i.e., of the relativistic extension of the quantum harmonic oscillator, is proposed for light propagation in fiber Bragg gratings. Transmission spectra clearly show the existence of electron and positron bound states of the DO, corresponding to resonance modes above and below the Bragg frequency, as well as the asymmetry of the energy spectrum for electron and positron branches. © 2010 Optical Society of America.

Salvadori G.,University of Salento | De Michele C.,Polytechnic of Milan | Durante F.,Free University of Bozen Bolzano
Hydrology and Earth System Sciences | Year: 2011

Calculating return periods and design quantiles in a multivariate environment is a difficult problem: this paper tries to make the issue clear. First, we outline a possible way to introduce a consistent theoretical framework for the calculation of the return period in a multi-dimensional environment, based on Copulas and the Kendall's measure. Secondly, we introduce several approaches for the identification of suitable design events: these latter quantities are of utmost importance in practical applications, but their calculation is yet limited, due to the lack of an adequate theoretical environment where to embed the problem. Throughout the paper, a case study involving the behavior of a dam is used to illustrate the new concepts outlined in this work. © Author(s) 2011. CC Attribution 3.0 License.

Longhi S.,Polytechnic of Milan
Optics Letters | Year: 2010

An optical analog of Zitterbewegung (ZB), i.e., of the trembling motion of Dirac electrons caused by the interference between positive and negative energy states, is proposed for spatial beam propagation in binary waveguide arrays. In this optical system the ZB is simply observable as a quiver spatial oscillatory motion of the beam center of mass around its mean trajectory. © 2010 Optical Society of America.

Kanyilmaz A.,Polytechnic of Milan
COMPDYN 2015 - 5th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering | Year: 2015

This paper presents a comparison between two different modeling approaches: Refined FE modeling using volumetric elements, and fiber modeling using beam elements with distributed plasticity. The numerical models calibrated with the experimental result from existing literature, reproduce the behavior of cold formed SHS40, and hot rolled DUPE100 steel elements under inelastic cyclic loading. The hysteresis loops obtained from two models show that the accuracy obtained by simpler fiber-element formulation is quite close to the more refined volumetric model. In terms of computation time, distributed plasticity model is much more efficient, and can be a good option to perform nonlinear analysis of multi-level buildings, which would be quite cumbersome with volumetric modeling approach. This study has been realized thanks to the research fund received from European commission with the contract MEAKADO RFSR-CT-2013-00022.

Bernuzzi C.,Polytechnic of Milan | Simoncelli M.,University of Pavia
Engineering Structures | Year: 2015

In this paper attention is focused on the uprights, i.e. vertical elements of the skeleton frames of steel storage rack systems. Their response is quite difficult to predict because of the significant influence of the interaction between local, distortional and overall buckling phenomena, owing to the presence of open mono-symmetric thin-walled cold-formed cross-sections. As a consequence, very high engineering competences are necessarily required to guarantee relevant load carrying capacities with structural systems of extremely limited weight and of very modest costs. Design provisions admit few alternatives, leading to different sizes and weight of the racks and, as consequence, to different degrees of economic competitiveness on the market. In the framework of a more general research project on steel storage rack structures, three options of designing the uprights in Europe have been investigated in the present paper. Several cases from practice have been selected, which comprise of uprights differing for cross-section geometry, slenderness and load conditions. A suitable finite element program for academic use characterized by a refined beam formulation capable of capturing key features of uprights has been used to model the elastic buckling interaction between the axial load and the bending moment. Non-negligible differences have been detected for what concerns the admitted design approaches in terms of beam-column load carrying capacity; furthermore, the direct comparison of the research outcomes offers practical indications for an optimal use of the material in accordance with the required safety standards. © 2015 Elsevier Ltd.

Gianinetto M.,Polytechnic of Milan
Photogrammetric Record | Year: 2012

In modern remote sensing applications the use of automatic image processing codes is becoming increasingly common. When dealing with satellite time series or multi-source data, image co-registration is a time-consuming, but necessary, pre-processing step. This study shows how a medium resolution satellite multitemporal dataset can be effectively processed using automatic data processing. Results on real and transformed ASTER data showed that, without human interaction, the automatic ground control points extraction (AGE) technique, developed at Politecnico di Milano, is able to obtain accuracies generally sufficient for practical applications and similar to those reported in other studies. © 2012 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd.

Longhi S.,Polytechnic of Milan
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

A general method for flexible control of the path of discretized light beams in homogeneous waveguide lattices, based on longitudinal modulation of the coupling constant, is theoretically proposed. As compared to beam steering and refraction achievable in graded-index waveguide arrays, the proposed approach enables the synthesis of rather arbitrary target paths. © 2011 American Physical Society.

Bombelli F.B.,University of East Anglia | Bombelli F.B.,Polytechnic of Milan | Webster C.A.,University of East Anglia | Moncrieff M.,Norwich University | Sherwood V.,University of East Anglia
The Lancet Oncology | Year: 2014

Metastatic melanoma is a highly aggressive malignancy that has traditionally been very difficult to treat. However, after decades of basic research into the signal transduction pathways that promote cancer cell survival, chemoresistance, growth, and crosstalk with the immune system, targeted therapies have now been developed that offer improved survival for patients with metastatic melanoma. Some of the most promising therapies that have been developed include ipilimumab, an anti-cytotoxic T lymphocyte antigen 4 antibody that enhances T-cell activity in the tumour, and selective BRAF inhibitors, such as vemurafenib that blocks tumour cell proliferation in patients with activating BRAF mutations. Although these treatments offer substantial hope for patients, they are not without their drawbacks, which include adverse side-effects, drug resistance, and eventual relapse. Nanotherapeutics holds significant promise to circumvent these shortcomings and has the additional advantage of potentially functioning as a diagnostic device. We will discuss the scope of the use of such multimodal nanoparticles for melanoma treatment and ask whether such particles can offer patients with metastatic melanoma improved prognoses for the future. © 2014 Elsevier Ltd.

Valente M.,Polytechnic of Milan
Applied Mechanics and Materials | Year: 2012

This study presents a displacement-based design procedure for seismic retrofitting of steel frames using buckling-restrained braces (BRB) to meet a given target displacement in the framework of the capacity spectrum method. The seismic performance of a six-storey steel frame equipped with BRB is investigated. Different storey-wise BRB distribution methods are proposed and the influence on the results of the design procedure is analyzed. Nonlinear dynamic analyses demonstrate the efficacy of the design procedure showing the improvements achieved by the retrofitting intervention using BRB. The maximum top displacement registered for the retrofitted frame under earthquake excitation coincides with the target displacement obtained in accordance with the design procedure. The introduction of buckling-restrained braces enhances the earthquake resistance of the steel frame, providing significant energy dissipation and the stiffness needed to satisfy structural drift limits. © (2012) Trans Tech Publications, Switzerland.

Limongelli M.P.,Polytechnic of Milan
Earthquake Engineering and Structural Dynamics | Year: 2014

In this paper, a new approach to structural damage localization is presented using as damage feature the interpolation error related to the use of a spline function in modeling the operational deformed shapes of the structure. Statistically significant variations of the interpolation error between the undamaged and the inspection phase indicate the onset of damage. A threshold value of the damage feature is defined in terms of the tolerable probability of false alarm to select variations of the interpolation error because of damage from those due to random sources. The method is successfully applied to a calibrated model of the factor building a real densely instrumented building at the University of California, Los Angeles. Results show that the method is effective for damage localization for both single and multiple locations of damage also in case of responses corrupted by noise. © 2014 John Wiley & Sons, Ltd.

Cucchiella F.,University of LAquila | D'Adamo I.,University of LAquila | Rosa P.,Polytechnic of Milan
Renewable and Sustainable Energy Reviews | Year: 2015

Abstract The photovoltaic (PV) industry has a relevant role in terms of energy systems sustainability. The economic and environmental benefits related to its application brought the PV sector to an overall installed power of about 138 GW in 2013 (+24% compared to 2012). The recent update of the European Waste Electrical and Electronic Equipment (WEEE) Directive classifies End-of-Life (EoL) PV panels as an electrical/electronic waste. Hence, it became mandatory to define alternative strategies to landfill [1]. The scientific literature presents different interesting technological solutions, together with related environmental benefits coming from the PV modules recycling. However, there is a clear fragmentation from an economic point of view [2]. The aim of this paper is to apply a financial methodology, like the Discounted Cash Flow (DCF) analysis, for the assessment of PV modules recycling process profitability. This method goes to evaluate two main indexes, as the Net Present Value (NPV) and the Discounted Payback Period (DPBT). The Italian context is selected as a reference case study for the definition of an optimal plant capacity size related to current and expected national market volumes. To this aim, two types (pilot and industrial) of plants are proposed by the authors. The obtained financial results are useful to support future strategic decisions about the PV recycling management. © 2015 Elsevier Ltd. All rights reserved.

Coronelli D.,Polytechnic of Milan
ACI Structural Journal | Year: 2010

A grid model is proposed for the nonlinear behavior of flat-slab structures. The inelastic response of the structure is concentrated in point hinges introduced into beam finite elements, modeling the response in bending, torsion, and shear. Both concentric punching and failures with unbalanced moments and shear are investigated. Static pushover analysis is used for the effects of gravity and lateral loads. The results are compared to experimental studies on interior, lateral, and corner slab-column connections. The effect of different types and arrangements of transverse reinforcement and the influence of the gravity load level on the drift capacity are shown. The formulation with internal moments, torque, and shear is synthetic and computationally light; three-dimensional (3-D) spatial configurations are considered. Copyright © 2010, American Concrete Institute. All rights reserved.

The expressive-sensorial dimension of materials is becoming increasingly important in the context of both theoretical and practical design. This has necessitated a corresponding and growing engagement in the field of design education as well: the topic must be included in didactic programs, and tools expressly designed with the aim of transmitting to students an awareness of the management of this important and subjective design dimension. During the educational process the future designer must acquire the skills required to select materials suitable for specific applications, which also implies the awareness that materials have both a technical profile with objective properties and a sensorial profile with subjective characteristics. This article provides an overview of current and past theoretical research, undertaken by the Design Faculty at The Politecnico di Milano, which aims to consider the evaluation of the expressive-sensorial dimension of materials in design education. Following a contextualization of the topic, we will explain the expressive-sensorial atlas of materials: the initial tool which was used to investigate theoretical aspects of the theme in greater depth and which led to further reflections. Then, we will describe the chromatic atlas of materials, a tool designed to examine the relationship between colour, material and process and to underline the significance of this topic in design education. Finally, our most recent research in the ambit of the expressive-sensorial dimension of materials will be illustrated. The two most important studies focus on; firstly, the development of thematic atlases dedicated to specific classes of materials, beginning with textiles; and secondly, further investigation of the relationship between the sensorial and emotional qualities of materials and sustainability.

Domaneschi M.,Polytechnic of Milan
Structural Control and Health Monitoring | Year: 2010

A benchmark model of a cable-stayed bridge has attracted in the last years the attention of the control community. In this paper robust feasible solutions are investigated. As a first step passive devices have been applied to the bridge numerical model between the deck and the piers. Further, an open-loop semi-active improvement of the passive control system is implemented, as suggested by the preliminary results. Finally, an innovative decentralized solution for a semi-active scheme in closed-loop configuration is introduced in the bridge model; the results are here compared, in terms of structural responses, with an active setting, defining an optimal target. The control algorithm adopted for the semi-active devices in the closed-loop setting is an on/off skyhook one with two force levels. The devices adopted in the numerical simulations have dissipative properties and, when managed in a semi-active arrangement, act as a 3D smart control system. The device force displacement relationship fits the results of laboratory tests during the characterization process of an electro-inductive device. The excitation considered in the benchmark problem is essentially the seismic one. A digression to the wind excitation is introduced in the numerical model so as to analyze the control system reaction. The aim of this study is to suggest control solutions for cable-stayed bridges with the common sense to research the best performance, though maintaining robustness, simplicity and feasibility. Copyright © 2009 John Wiley &Sons, Ltd.

Berzi D.,Polytechnic of Milan
Journal of Hydraulic Engineering | Year: 2013

The prediction of the transport of sediments in streams is of crucial importance for many geophysical and industrial applications. Most of the available formulas for sediment transport are empirical and apply to situations near initiation, where a few erratic particles are seen jumping and rolling over an immobile bed. However, they are commonly adopted for predicting massive transport of sediments, although more rigorous approaches exist. The latter make use of constitutive relations from kinetic theories of granular gases, but require the numerical integrations of complicated, nonlinear differential equations, hence discouraging their usage for practical purposes. A new, explicit formula for predicting intense sediment transport is proposed here, based on kinetic theories of granular gases and incorporating in a simple yet rigorous way the possibility of turbulent suspension of the particles. It is shown that this formula, unlike others, can quantitatively reproduce physical experiments on steady, uniform flows of natural and artificial particles and water over horizontal, movable beds taken from the literature. These findings suggest that granular physics is now mature enough to provide practical tools in fields that were so far mainly empirically oriented. © 2013 American Society of Civil Engineers.

This study returns to the topic of unauthorised development in the south of Italy. It starts by assessing the main positions that have informed the debate since the 1960s and evaluates the consequences of the condono edilizio (building amnesty) policy, in the light of the impact that illegal construction has had on the landscape, both urban, rural and coastal. A close observation of three case studies, unplanned settlements in Lazio, Campania and Sicily, suggests that the original energies and expectations behind their development have long since lost their momentum. Rather, the emergence of new evolutionary trends-hitherto underrepresented within the political debate-demand a different interpretative framework. Three design scenarios are outlined, based on recycling existing social and physical material: they translate into a future-oriented discourse those symptoms of change that are already appearing in an embryonic form throughout Italy's Mezzogiorno. © 2013 Urban Studies Journal Limited.

Ciarletta P.,CNRS Jean Le Rond dAlembert Institute | Ciarletta P.,Polytechnic of Milan
Journal of the Mechanics and Physics of Solids | Year: 2014

Soft materials can experience a mechanical instability when subjected to a finite compression, developing wrinkles which may eventually evolve into folds or creases. The possibility to control the wrinkling network morphology has recently found several applications in many developing fields, such as scaffolds for biomaterials, stretchable electronics and surface micro-fabrication. Albeit much is known of the pattern initiation at the linear stability order, the nonlinear effects driving the pattern selection in soft materials are still unknown. This work aims at investigating the nature of the elastic bifurcation undertaken by a growing soft layer subjected to a equi-biaxial strain. Considering a skin effect at the free surface, the instability thresholds are found to be controlled by a characteristic length, defined by the ratio between capillary energy and bulk elasticity. For the first time, a weakly nonlinear analysis of the wrinkling instability is performed here using the multiple-scale perturbation method applied to the incremental theory in finite elasticity. The Ginzburg-Landau equations are derived for different superposing linear modes. This study proves that a subcritical pitchfork bifurcation drives the observed wrinkle-to-fold transition in swelling gels experiments, favoring the emergence of hexagonal creased patterns, albeit quasi-hexagonal patterns might later emerge because of an expected symmetry break. Moreover, if the surface energy is somewhat comparable to the bulk elastic energy, it has the same stabilizing effect as for fluid instabilities, driving the formation of stable wrinkles, as observed in elastic bi-layered materials. © 2014 Elsevier Ltd.

Marcelli T.,Polytechnic of Milan | Hiemstra H.,University of Amsterdam
Synthesis | Year: 2010

This article reviews the applications of cinchona alkaloids as asymmetric catalysts. In the last few years, characterized by the resurgence of interest in asymmetric organocatalysis, cinchona derivatives have been shown to catalyze an outstanding array of chemical reactions, often with remarkable stereoselectivity. This work presents an overview of the transformations developed in the period from 2001 through 2009, highlighting applications in the synthesis of bioactive molecules and natural products. 1 Introduction 2 Additions to Carbonyls 3 Additions to Imines 4 Conjugate Additions 5 Additions to Olefins 6 Nucleophilic Substitutions 7 Electrophilic Halogenations 8 Opening of Cyclic Anhydrides 9 Acylations 10 Cycloadditions 11 Rearrangements 12 Decarboxylations 13 Miscellaneous 14 Conclusions and Outlook List of abbreviations: Alloc, allyloxycarbonyl; Boc, tert-butyloxy?carbonyl; Bs, benzenesulfonyl; BTTP, tert-butyliminotri(pyrrolidino)phosphorane; Cbz, benzyloxycarbonyl; DABCO, 1,4-diazabicyclo[2.2.2]octane; DBAD, dibenzyl azodicarboxylate; DBU, 1,8-diazabicycloundec-7-ene; DCE, 1,2-dichloroethane; DFT, density functional theory; DIPEA, N,N-diisopropylethyl?amine; DNP, 2,4-dinitrophenyl; DMB, 3,4-dimethoxybenzoyl; DPM, diphenylmethyl; DTAD, di-tert-butyl azodicarboxylate; EVE, ethyl vinyl ether; EWG, electron-withdrawing group; FBSM, 1-fluorobis(phenylsulfonyl)methane; HFiPA, 1,1,1,3,3,3-hexafluoro-2-propyl acrylate; LAH, lithium aluminum hydride; LG, leaving group; Moc, methyloxycarbonyl; MPEG, poly(ethylene glycol) monomethyl ether; MS, molecular sieves; MVK, methyl vinyl ketone; NFSI, N-fluorobenzenesulfonimide; NMR, nuclear magnetic resonance; Ns, p-nitrophenylsulfonyl; PEG, poly(ethylene glycol); PS, proton sponge [1,8-bis(dimethylamino)naphthalene]; rds, rate-determining step; TBAF, tetrabutylammonium fluoride; TCCA, trichloroisocyanuric acid; TFAA, trifluoroacetic anhydride; THF, tetrahydrofuran; TMAF, tetramethylammonium fluoride; TMS, trimethylsilyl; Ts, p-toluenesulfonyl; UNCA, urethane-protected -amino acid N-carboxyanhydrides. © Georg Thieme Verlag Stuttgart · New York.

Longhi S.,Polytechnic of Milan
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

An optical realization of the phenomenon of many-body coherent destruction of tunneling, recently predicted for interacting many-boson systems by Gong, Molina, and Hänggi [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103. 133002 103, 133002 (2009)], is proposed for light transport in engineered waveguide arrays. The optical system enables a direct visualization in Fock space of the many-body tunneling control process. © 2011 American Physical Society.

Longhi S.,Polytechnic of Milan
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

Light trapping in photonic lattices at a linear defect shows interesting nonclassical behavior when probed by maximally path-entangled N-photon states (NOON states). In particular, photon coincidences of localized light at the defect oscillate at a spatial frequency that is N times faster than the classical beating spatial frequency of the defect modes, resembling the λ/N oscillations of NOON states encountered in Mach-Zehnder interferometry. Analytical results of quantum interference are presented for an exactly solvable tight-binding waveguide array. © 2011 American Physical Society.

Fazzi D.,Italian Institute of Technology | Caironi M.,Italian Institute of Technology | Castiglioni. C.,Italian Institute of Technology | Castiglioni. C.,Polytechnic of Milan
Journal of the American Chemical Society | Year: 2011

Theoretical modeling has been applied to study the charge transport (CT) parameters of a high-electron-mobility (n-type) naphthalenetetracarboxydiimide copolymer that was recently synthesized and tested for organic field-effect transistor applications. To understand the physicochemical characteristics of such a material, the intra- and intermolecular CT properties of holes and electrons were investigated using different DFT functionals, evidencing the need of range-separated hybrid functionals to predict key parameters such as the hole and electron reorganization energies. Our calculations revealed clear differences between hole- and electron-charging processes, providing fundamental elements for the rationalization of their transport. © 2011 American Chemical Society.

Rulli M.C.,Polytechnic of Milan
Advances in Water Resources | Year: 2010

A new contour-based watershed partitioning method, relying on tracking flow lines moving from upslope to downslope, is presented. The model works by using only contour data and consists of three principal steps: 1) Ideal Drainage Network tracking; 2) hillslope and channel elements building; and 3) actual contour-based element network construction. It automatically detects and manages sinks, peaks and saddles and calculates element attributes taking into account the non-planar shape of the elements. Watershed, subwatershed and draining area at any point can be automatically detected by using network elements interconnectivity. It is also possible to determine the Actual Drainage Network.The model is able to manage point data set trough interpolation, according with specific procedures. Also grid datasets can be used as input, the model is in fact provided with an overlapping algorithm for matching grid datasets to elements.Comparisons with an existing contour-based element network construction method show a better and more physically based description of the element network particularly useful for hydrological and mass movements' analyses. © 2010 Elsevier Ltd.

Langfelder G.,Polytechnic of Milan
IEEE Transactions on Electron Devices | Year: 2013

This paper proposes a pixel topology for the joint capture of visible (VIS) and near-infrared (NIR) signals in a monolithic CMOS sensor, with neither optical nor IR-blocking filters, in a single shot and with the same sensor resolution for the VIS and NIR channels. The topology exploits the radiation absorption depth dependence on the wavelength and is based on the principle of the Transverse Field Detector. The device principle, finite element simulation, and design are presented with validation of the working principle through experimental tests on a prototype with an overall four-band passive pixel width of 6.4 μm. © 2013 IEEE.

Cordone R.,University of Milan | Piroddi L.,Polytechnic of Milan
IEEE Transactions on Systems, Man, and Cybernetics Part A:Systems and Humans | Year: 2013

Most approaches for deadlock prevention and liveness enforcement in Petri nets rely on siphon control methods or the theory of regions to derive monitor-based supervisors. These techniques raise methodological and computational issues, from the existence of feasible solutions to the hardness of guaranteeing maximal permissivity and optimality in the size and cost of the control subnet. Recently, the supervisor design problem has also been reformulated as a direct monitor optimization task based on integer linear programming, which can more effectively deal with the mentioned issues and objectives. This paper introduces an efficient branch-and-bound scheme for the exploration of the solution space of the direct monitor optimization problem. An extensive computational analysis on a set of benchmark instances demonstrates the efficiency of the approach. © 2013 IEEE.

Gal C.G.,University of Missouri | Grasselli M.,Polytechnic of Milan
Physica D: Nonlinear Phenomena | Year: 2011

We consider a model for the flow of a mixture of two viscous and incompressible fluids in a two or three dimensional channel-like domain. The model consists of the Navier-Stokes equations governing the fluid velocity coupled with a convective Cahn-Hilliard equation for the relative density of atoms of one of the fluids. We prove the instability of certain stationary solutions for such a system endowed with periodic boundary conditions on elongated domains (0,2πα0)×(0,2π) or (0,2πα0)×(0,2π)×(0,2πβ0) for a special class of periodic body forces, provided that α0 and β0 are small enough. As a consequence, we deduce a lower bound for the Hausdorff dimension of the global attractor. © 2010 Elsevier B.V. All rights reserved.

Longhi S.,Polytechnic of Milan
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2011

A classical realization of the two-site Bose-Hubbard Hamiltonian, based on light transport in engineered optical waveguide lattices, is theoretically proposed. The optical lattice enables a direct visualization of the Bose-Hubbard dynamics in Fock space. © 2011 IOP Publishing Ltd.

Lanzarone E.,CNR Institute for Applied Mathematics and Information Technologies | Matta A.,Polytechnic of Milan
Operations Research for Health Care | Year: 2014

Home Care (HC) providers are complex organizations that manage a large number of patients, different categories of operators, support staff and material resources in a context affected by high variability. Hence, robust resource planning is crucial for operations in HC organizations, in order to avoid process inefficiencies, treatment delays, and low quality of service. Under continuity of care, one of the main issues in HC planning is the assignment of a reference nurse to each assisted patient, because this decision has an impact on the workload assigned to the nurse for the entire patient's length of stay. In this paper, we derive an analytical structural policy for solving the nurse-to-patient assignment problem in the HC context under continuity of care. This policy accounts for randomness related to both the demands from patients already assigned to nurses and the demands from new patients who need assignments. The policy is compared to other previously developed approaches, and applied to a relevant real case. © 2014 Elsevier Ltd.

Frezzotti A.,Polytechnic of Milan
Physics of Fluids | Year: 2011

The paper aims at presenting a review of kinetic theory applications to evaporation condensation problems. The main results for monatomic and polyatomic gases and mixtures are described. The role of boundary conditions at the vapor-liquid interface is discussed and a description of molecular dynamics studies aimed at formulating vapor-liquid interaction models is given. © 2011 American Institute of Physics.

Chesi G.,University of Hong Kong | Colaneri P.,Polytechnic of Milan | Geromel J.C.,University of Campinas | Middleton R.,National University of Ireland, Maynooth | Shorten R.,National University of Ireland, Maynooth
IEEE Transactions on Automatic Control | Year: 2012

Ensuring stability of switched linear systems with a guaranteed dwell time is an important problem in control systems. Several methods have been proposed in the literature to address this problem, but unfortunately they provide sufficient conditions only. This technical note proposes the use of homogeneous polynomial Lyapunov functions in the non-restrictive case where all the subsystems are Hurwitz, showing that a sufficient condition can be provided in terms of an LMI feasibility test by exploiting a key representation of polynomials. Several properties are proved for this condition, in particular that it is also necessary for a sufficiently large degree of these functions. As a result, the proposed condition provides a sequence of upper bounds of the minimum dwell time that approximate it arbitrarily well. Some examples illustrate the proposed approach. © 2012 IEEE.

Orifici A.C.,RMIT University | Bisagni C.,Polytechnic of Milan
Composite Structures | Year: 2013

A numerical investigation was conducted into a perturbation-based analysis approach for assessing the imperfection sensitivity of composite cylindrical shells buckling under compression loading. The Single Perturbation Load Analysis (SPLA) approach was applied, which uses a single lateral load to introduce a realistic, worst-case and stimulating imperfection pattern. Finite element analysis was conducted for cylinders of both monolithic composite laminate and sandwich construction, with and without small and large cutouts. It was found that using a perturbation displacement equal to the shell thickness provides a suitable technique for estimating the reduction in buckling load caused by imperfections. Predictions of buckling knockdown factors using the SPLA approach showed advantages over the use of eigenmodes as the SPLA approach provides a clear design point and does not require experimental data for calibration. The effect of small and large cutouts was analogous to the effect of small and large perturbation loads. The location of the perturbation load influenced the buckling knockdown factors for both small and large cutouts, and worst-case locations were identified for both configurations. © 2013 Elsevier Ltd.

Rossi F.,Aix - Marseille University | Colaneri P.,Polytechnic of Milan | Shorten R.,National University of Ireland
IEEE Transactions on Automatic Control | Year: 2011

This technical note has been motivated by the need to assess the preservation of polyhedral Lyapunov functions for stable continuous-time linear systems under numerical discretization of the transition matrix. This problem arises when discretizing linear systems in such a manner as to preserve a certain type of stability of the discrete time approximation. Our main contribution is to show that a continuous-time system and its Padé discretization (of any order and sampling) always share at least one common piecewise linear (polyhedral) Lyapunov function. © 2011 IEEE.

Myers C.J.,University of Zurich | Celebrano M.,Polytechnic of Milan | Krishnan M.,University of Zurich
Nature Nanotechnology | Year: 2015

The binary switch is a basic component of digital information. From phase-change alloys to nanomechanical beams, molecules and atoms, new strategies for controlled bistability hold great interest for emerging technologies. We present a generic methodology for precise and parallel spatiotemporal control of nanometre-scale matter in a fluid, and demonstrate the ability to attain digital functionalities such as switching, gating and data storage in a single colloid, with further implications for signal amplification and logic operations. This fluid-phase bit can be arrayed at high densities, manipulated by either electrical or optical fields, supports low-energy, high-speed operation and marks a first step toward 'colloidal information'. The principle generalizes to any system where spatial perturbation of a particle elicits a differential response amenable to readout. © 2015 Macmillan Publishers Limited. All rights reserved.

Pianosi F.,Polytechnic of Milan | Raso L.,Technical University of Delft
Water Resources Research | Year: 2012

Uncertainty of hydrological forecasts represents valuable information for water managers and hydrologists. This explains the popularity of probabilistic models, which provide the entire distribution of the hydrological forecast. Nevertheless, many existing hydrological models are deterministic and provide point estimates of the variable of interest. Often, the model residual error is assumed to be homoscedastic; however, practical evidence shows that the hypothesis usually does not hold. In this paper we propose a simple and effective method to quantify predictive uncertainty of deterministic hydrological models affected by heteroscedastic residual errors. It considers the error variance as a hydrological process separate from that of the hydrological forecast and therefore predictable by an independent model. The variance model is built up using time series of model residuals, and under some conditions on the same residuals, it is applicable to any deterministic model. Tools for regression analysis applied to the time series of residual errors, or better their absolute values, combined with physical considerations of the hydrological features of the system can help to identify the most suitable input to the variance model and the most parsimonious model structure, including dynamic structure if needed. The approach has been called dynamic uncertainty modeling by regression on absolute errors and is demonstrated by application to two test cases, both affected by heteroscedasticity but with very different dynamics of uncertainty. Modeling results and comparison with other approaches, i.e., a constant, a cyclostationary, and a static model of the variance, confirm the validity of the proposed method. Copyright 2012 by the American Geophysical Union.

Maffezzoni P.,Polytechnic of Milan
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems | Year: 2010

This paper describes an original method to compute the synchronization regions of injection-locked oscillators that exhibit a strong nonlinear response, such as relaxation or ring architectures. The proposed method is based on the theory of controllably periodically forced oscillators and is implemented within the frame of the time-domain periodic steady-state analysis. The novel method is able to predict, in an accurate way, the conditions for which the correct frequency division occurs and can identify the transitions to more complex regimes that limit the exploitable synchronization region. © 2006 IEEE.

Limongelli M.P.,Polytechnic of Milan
Mechanical Systems and Signal Processing | Year: 2010

Damage detection can be carried out based on measured dynamic characteristics of the monitored structure. Several experimental investigations have shown that structural parameters are affected by environmental conditions. This circumstance can lead to erroneous conclusions if damage detection methods based on variations of global structural parameters are applied without properly taking into account this influence. In this paper the sensitivity to changing temperature of a new damage detection method, denoted as interpolation damage detection method (IDDM), is investigated with reference to an experimental example, widely studied by several researchers to check damage detection algorithms: the I40 bridge. Results show that, despite the changes of temperature, the IDDM provides a correct identification of damage location even for cases where the evolution of modal frequencies belies the actual damaged state of the structure. The sensitivity of the IDDM to the joint effect of gradient of temperature and noise in the recorded data is also investigated with reference to a numerical example. © 2010 Elsevier Ltd. All rights reserved.

Milani G.,Polytechnic of Milan | Tralli A.,University of Ferrara
Computers and Structures | Year: 2011

A simple homogenized model for the non linear analysis of masonry walls out-of-plane loaded is presented. In the model, the panels are assumed to behave as Kirchhoff-Love plates. A rectangular running bond elementary cell (RVE) is subdivided into several layers along the thickness and, for each layer, a discretization where bricks are meshed with plane-stress three-noded triangular elements and joints are reduced to interfaces is assumed. Non linearity is concentrated on brick-brick and joint interfaces, which exhibit a frictional behavior with limited tensile and compressive strength with softening. Finally, macroscopic curvature bending moment diagrams are obtained integrating along the thickness in-plane micro-stresses of each layer. Homogenized masonry flexural response is then implemented at a structural level in a FE non linear code based on a discretization with three-noded elements and elasto-damaging interfaces. Three different models of increasing accuracy are presented. The first (EPP) relies in assuming an elastic-perfectly plastic behavior for the interfaces. The incremental problem is solved at a structural level through a well known quadratic-programming approach. The second (ED) accounts in an approximate way for the softening behavior and consists in a preliminary homogenized limit analysis of the structure, which allows to identify the failure mechanism and in the subsequent FE non linear analysis of the whole structure assuming that all the non linearity is concentrated on the yield line defining the failure mechanism. The last (EPD) is a sequential quadratic programming approach. Here, deteriorating bending moment curvature curves obtained through homogenization are approximated through a linear piecewise constant discontinuous function. At each load step, all interfaces are assumed to behave as an elastic-perfectly plastic material and the discretized non linear problem is solved by means of the quadratic programming algorithm used for the EPP model. The two step model proposed is validated both a cell level and at a structural level comparing results provided with both experimental data and existing macroscopic numerical approaches available in the literature. © 2010 Elsevier Ltd. All rights reserved.

Gondoni P.,Polytechnic of Milan
Journal of visualized experiments : JoVE | Year: 2013

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (>80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

Longhi S.,Polytechnic of Milan
Applied Physics B: Lasers and Optics | Year: 2011

Spatial and/or temporal propagation of light waves in periodic optical structures offers a unique possibility to realize in a purely classical setting the optical analogues of a wide variety of quantum phenomena rooted in relativistic wave equations. In this work a brief overview of a few optical analogues of relativistic quantum phenomena, based either on spatial light transport in engineered photonic lattices or on temporal pulse propagation in Bragg grating structures, is presented. Examples include spatial and temporal photonic analogues of the Zitterbewegung of a relativistic electron, Klein tunneling, vacuum decay and pair production, the Dirac oscillator, the relativistic Kronig-Penney model, and optical realizations of non-Hermitian extensions of relativistic wave equations. © 2011 Springer-Verlag.

Capolongo S.,Polytechnic of Milan
Annali di igiene : medicina preventiva e di comunità | Year: 2012

In the last decades has been recorded, both nationally and internationally, a significant increase in disasters with a high number of deaths and injuries involved. The presence at the venue of the Advanced Medical Post (AMP) has improved the survival of the affected population. However, these temporary structures, not according to common standards relating to health hospital environments are devoid of design guidelines and technologies designed to hygiene and safety. Starting from the inquiry into the functioning and the structure of an Advanced Medical Post through interviews, questionnaires and joint activities with Italian organizations and structures, a number of measures have been established for the improvement of health standards. Through the survey and questionnaires developed for this purpose it was possible to determine the most hygienically critical areas and then several solutions were processed and evaluated (in synergy with associations previously interviewed). The most important priorities to satisfy were the hygiene improvement to be achieved through the use of specific materials (fabrics antimicrobial ...), the study of the articulation inside the operating room and intensive care of AMP (insulation and Zoning filter ...) and the definition of more efficient technological systems-plant (ventilation, aeration, lighting...). Therefore the solution proposed involves the use of a new layer fabric for mounting inside of curtains already supplied to the main associations and a series of technological devices and installations for limiting the spread of virus-bacteria. The introduction of this new unit for AMP modules could give a significant contribution to achieving high standards of hygiene during health care assistance in critical situations (maxi-emergencies and disasters) which, unfortunately, are actually becoming more frequent.

Milani G.,Polytechnic of Milan
Computers and Structures | Year: 2011

A simple homogenized model for the non-linear and limit analysis of masonry walls in-plane loaded is presented. A rectangular running bond elementary cell (RVE) is discretized by means of a few plane-stress three-noded triangular elements and interfaces. Non-linearity is concentrated on brick-brick interfaces and joints reduced to interface, exhibiting a frictional behavior with limited tensile and compressive strength with softening. Homogenized masonry behavior is then implemented at a structural level in a novel FE non-linear code relying on an assemblage of rigid infinitely resistant triangular elements and non-linear interfaces, exhibiting deterioration of the mechanical properties. Non-linear analyses are conducted on full scale walls - a deep beam and a windowed shear wall, for which experimental and numerical data are available in the literature - with a very limited computational effort. To circumvent some typical drawbacks of standard FE approaches, at each load step, all interfaces are assumed to behave as an elastic-perfectly plastic material and the discretized non-linear problem is solved by means of a standard sequential quadratic programming algorithm. © 2011 Elsevier Ltd. All rights reserved.

Ramponi R.,Polytechnic of Milan | Ramponi R.,TU Eindhoven | Blocken B.,TU Eindhoven
Building and Environment | Year: 2012

Accurate CFD simulation of coupled outdoor wind flow and indoor air flow is essential for the design and evaluation of natural cross-ventilation strategies for buildings. It is widely recognized that CFD simulations can be very sensitive to the large number of computational parameters that have to be set by the user. Therefore, detailed and generic sensitivity analyses of the impact of these parameters on the simulation results are important to provide guidance for the execution and evaluation of future CFD studies. A detailed review of the literature indicates that there is a lack of extensive generic sensitivity studies for CFD simulation of natural cross-ventilation. In order to provide such a study, this paper presents a series of coupled 3D steady RANS simulations for a generic isolated building. The CFD simulations are validated based on detailed wind tunnel experiments with Particle Image Velocimetry. The impact of a wide range of computational parameters is investigated, including the size of the computational domain, the resolution of the computational grid, the inlet turbulent kinetic energy profile of the atmospheric boundary layer, the turbulence model, the order of the discretization schemes and the iterative convergence criteria. Specific attention is given to the problem of oscillatory convergence that was observed during some of these coupled CFD simulations. Based on this analysis, the paper identifies the most important parameters. The intention is to contribute to improved accuracy, reliability and evaluation of coupled CFD simulations for cross-ventilation assessment. © 2012 Elsevier Ltd.

Bolzon G.,Polytechnic of Milan
Archives of Computational Methods in Engineering | Year: 2015

This paper summarizes the formulation of structural engineering problems concerned with inelastic phenomena that can be described in complementarity format. This mathematical construct can be transferred to the discretized version of the continuum problem by generalized variables. The evaluation of safety factors against collapse conditions, of primary deemed relevance for a safe and rational design in harmonized European Standards, can be performed in a consistent framework. The main features of these approaches and the relevant computational tools are revised. © 2015 CIMNE, Barcelona, Spain

Manenti F.,Polytechnic of Milan
ISA Transactions | Year: 2012

This manuscript highlights tangible benefits deriving from the dynamic simulation and control of operational transients of natural gas processing plants. Relevant improvements in safety, controllability, operability, and flexibility are obtained not only within the traditional applications, i.e. plant start-up and shutdown, but also in certain fields apparently time-independent such as the feasibility studies of gas processing plant layout and the process design of processes. Specifically, this paper enhances the myopic steady-state approach and its main shortcomings with respect to the more detailed studies that take into consideration the non-steady state behaviors. A portion of a gas processing facility is considered as case study. Process transients, design, and control solutions apparently more appealing from a steady-state approach are compared to the corresponding dynamic simulation solutions. © 2011 ISA. Published by Elsevier Ltd. All rights reserved.

Bolzon G.,Polytechnic of Milan | Buljak V.,University of Belgrade
Computational Mechanics | Year: 2011

Parametric studies and identification problems require to perform repeated analyses, where only a few input parameters are varied among those defining the problem of interest, often associated to complex numerical simulations. In fact, physical phenomena relevant to several practical applications involve coupled material and geometry non-linearities. In these situations, accurate but expensive computations, usually carried out by the finite element method, may be replaced by numerical procedures based on proper orthogonal decomposition combined with radial basis function interpolation. Besides drastically reducing computing times and costs, this approach is capable of retaining the essential features of the considered system responses while filtering most disturbances. These features are illustrated in this paper with specific reference to some elastic-plastic problems. The presented results can however be easily extended to other meaningful engineering situations. © 2011 Springer-Verlag.

Domaneschi M.,Polytechnic of Milan
Computers and Structures | Year: 2012

Phenomenological models are employed into composite structural systems for simulating passive devices aimed at vibration mitigation and the Bouc-Wen one subsists as a significant example. In recent years, the control systems progress has moved toward a more efficient and adaptable semi-active technology. Therefore the existent numerical procedures, which proved effective for the passive implementation, are expected to comprise such features as well. This paper deals with a method of controlling in real time the hysteresis component in simulated semi-active control systems through the Bouc-Wen model. An introductive discussion on the theoretical formulation of the original settlement allows to focus on a way for tuning the parameters which can be managed for hysteresis regulation. Proper algorithms, embedded into the analytical formulation of the model, are subsequently selected for implementing the semi-active characteristic. Finally, straightforward dynamic applications on a plane oscillator system point out the general capability of the proposed approach by seismic response simulation and mitigation of the induced structural effects. © 2012 Elsevier Ltd. All rights reserved.

Alfieri A.,Polytechnic University of Turin | Matta A.,Polytechnic of Milan
Journal of Intelligent Manufacturing | Year: 2012

Pull policies may perform quite differently depending on the particular manufacturing system they must control. Hence, it is clear the necessity of having efficient performance evaluation models to select the best control policy in a specific context. This paper proposes a mathematical programming representation of the main pull control policies applied to single-product serial manufacturing systems. The proposed models simulate the pull controlled system in the sense that, if instantiated with the same parameter values as in a simulation model, their solution gives the same event sequence of the simulation. The proposed mathematical representation is also used for a formal comparison of the considered pull control policies. The new models presented in this paper can represent a base to build new efficient optimization algorithms for the design of pull controlled production systems. © Springer Science+Business Media, LLC 2009.

Riverso S.,University of Pavia | Farina M.,Polytechnic of Milan | Ferrari-Trecate G.,University of Pavia
Automatica | Year: 2014

We consider the problem of designing decentralized controllers for large-scale linear constrained systems composed by a number of interacting subsystems. As in Riverso et al. (2013b), (i) the design of local controllers requires limited transmission of information from other subsystems and (ii) the addition/removal of a subsystem triggers the design of local controllers for child subsystems only. These properties enable Plug-and-Play (PnP) operations, and we show how to perform them while preserving global stability of the origin and constraint satisfaction. We improve several aspects of the PnP design procedure proposed in Riverso et al. (2013b) and, using recent results in the computation of Robust Control Invariant (RCI) sets, we show that all critical steps in the design of a local controller can be solved through Linear Programming (LP). Finally, an application of the proposed design procedure to a large-scale mechanical system is presented.

Grasselli M.,Polytechnic of Milan | Prazak D.,Charles University
Interfaces and Free Boundaries | Year: 2011

We consider a system which describes the behavior of a binary mixture of immiscible incompressible fluids with shear dependent viscosity by means of the diffuse interface approach. This system consists of Navier-Stokes type equations, characterized by a nonlinear stress-strain law, which are nonlinearly coupled with a convective Cahn-Hilliard equation for the order parameter. We analyze the corresponding dynamical system and, by means of the short trajectory method, we prove the existence of global and exponential attractors. We also discuss the dependence of an upper bound of the fractal dimension on the physical parameters of the system. © European Mathematical Society 2011.

Macchi A.,National Research Council Italy | Macchi A.,University of Pisa | Borghesi M.,Queens University of Belfast | Borghesi M.,ASCR Institute of Physics Prague | Passoni M.,Polytechnic of Milan
Reviews of Modern Physics | Year: 2013

Ion acceleration driven by superintense laser pulses is attracting an impressive and steadily increasing effort. Motivations can be found in the applicative potential and in the perspective to investigate novel regimes as available laser intensities will be increasing. Experiments have demonstrated, over a wide range of laser and target parameters, the generation of multi-MeV proton and ion beams with unique properties such as ultrashort duration, high brilliance, and low emittance. An overview is given of the state of the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives. The main features observed in the experiments, the observed scaling with laser and plasma parameters, and the main models used both to interpret experimental data and to suggest new research directions are described. © 2013 American Physical Society.

Masarati P.,Polytechnic of Milan
Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics | Year: 2011

This work discusses a simple means to add kinematic constraints to existing mechanical problems formulated in terms of ordinary differential equations. The constraints are expressed by algebraic relationships between the co-ordinates of the unconstrained problem. A solution projection approach ensures compliance of the solution with the derivatives of holonomic constraint equations up to second order within the desired accuracy. The structure of the unconstrained problem is not altered, resulting in a simple, little intrusive, yet effective means to enforce kinematic constraints into existing formulations and implementations originally intended to address differential problems, without the complexity of solving differential-algebraic problems or resorting to implicit numerical integration schemes and without altering the number and type of equations of the original unconstrained problem. The proposed formulation is compared with known approaches. Numerical applications of increasing complexity illustrate its distinguishing aspects.

Quadrio M.,Polytechnic of Milan
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

Drag-reduction techniques capable of reducing the level of turbulent friction through wall-parallel movement of the wall are described, with special emphasis placed on spanwise movement. The discussion is confined to active open-loop control strategies, although feedback control is briefly mentioned with regard to peculiarities of spanwise sensing and/or actuation. Theoretical considerations are first given to explain why spanwise motion is expected to be particularly effective in skin-friction drag reduction. A review of the spanwise oscillating-wall technique is given next, with discussion of recent results and prospects. Last, waves of spanwise velocity are addressed, either spanwise- or streamwise-travelling. The latter include the oscillating wall as a special case. The generalized Stokes layer-i.e. the laminar, transverse oscillating boundary layer that develops under the action of the streamwise-travelling waves-is described, and its importance in determining turbulent drag reduction discussed. Finally, open issues like energetic efficiency and its dependence on Reynolds number are addressed. © 2011 The Royal Society.

MacChiarella G.,Polytechnic of Milan
IEEE Microwave Magazine | Year: 2011

Several approaches employed for the synthesis of narrowband, star-junction multiplexers are presented. Synthesis techniques based on polynomial modeling allow for the evaluation of the expected response of the multiplexer without the need for defining a specific topology for the channel filters. When a specific topology for each filter is assigned, the synthesis of a low-pass prototype associated with the multiplexer can be carried out, still using the characteristic polynomials of the channel filters. The synthesis is performed with the filters detached from the multiplexer, by means of the usual techniques available. The denormalized parameters that characterize the designed multiplexer are computed and a first-order dimensioning of the structure can be carried out using well-established methods. The structure can then be built if suitable tuning elements are introduced for compensating for the approximations intrinsically associated with the polynomial characterization of microwave circuits.

Rampino L.,Polytechnic of Milan
International Journal of Design | Year: 2011

This paper presents an innovation pyramid that categorizes four different kinds of design-driven innovations in the product-design field. This pyramid is the final result of a long-term research process started at Politecnico di Milano in 2006 involving the three key disciplinary areas related to new product development: management, engineering and design. The disciplines were represented by the Indaco (Industrial Design, Art and COmunication) and Mechanical Engineering departments of the Politecnico di Milano, and the Business School of Bocconi University. The first step of the research project attempted to determine how to better demonstrate the contribution design makes to product innovation. In order to answer this, a phenomenological approach was used, i.e. observing product innovation as a phenomenon. From this approach, three possible levers of a design-driven innovation process emerged: form, mode of use, and technology. Additionally, four possible types of results of a design-driven process emerged: aesthetic, mode of use, meaning, and typological innovation. The levers and results are systematized here into an innovation pyramid, which helps to clarify both their similarities and their differences. © 2011 Rampino.

Iacchetti M.F.,Polytechnic of Milan
IEEE Transactions on Industrial Electronics | Year: 2011

This paper deals with the adaptive tuning of the stator inductance in a rotor-current-based Model Reference Adaptive System observer for the sensorless control of doubly fed induction machines. At first, the effect of mismatched parameters in this observer is discussed in order to show the considerable influence of the stator inductance on the accuracy of the estimated rotor position. Then, an adaptive tuning of the stator inductance is proposed and a small signal model is deduced in order to design the tuning loop. Moreover, a theoretical sensitivity and stability analysis is performed. Finally, the performances of the proposed scheme are experimentally investigated and validated. © 2011 IEEE.

Gatti D.,TU Darmstadt | Quadrio M.,Polytechnic of Milan
Physics of Fluids | Year: 2013

A fundamental problem in the field of turbulent skin-friction drag reduction is to determine the performance of the available control techniques at high values of the Reynolds number Re. We consider active, predetermined strategies based on spanwise forcing (oscillating wall and streamwise-traveling waves applied to a plane channel flow), and explore via Direct Numerical Simulations (DNS) up to Reτ = 2100 the rate at which their performance deteriorates as Re is increased. To be able to carry out a comprehensive parameter study, we limit the computational cost of the simulations by adjusting the size of the computational domain in the homogeneous directions, compromising between faster computations and the increased need of time-averaging the fluctuating space-mean wall shear-stress. Our results, corroborated by a few full-scale DNS, suggest a scenario where drag reduction degrades with Re at a rate that varies according to the parameters of the wall forcing. In agreement with already available information, keeping them at their low-Re optimal value produces a relatively quick decrease of drag reduction. However, at higher Re the optimal parameters shift towards other regions of the parameter space, and these regions turn out to be much less sensitive to Re. Once this shift is accounted for, drag reduction decreases with Re at a markedly slower rate. If the slightly favorable trend of the energy required to create the forcing is considered, a chance emerges for positive net energy savings also at large values of the Reynolds number. © 2013 AIP Publishing LLC.

Longhi S.,Polytechnic of Milan
Physical Review Letters | Year: 2010

Light propagation in distributed-feedback optical structures with gain or loss regions is shown to provide an accessible laboratory tool to visualize in optics the spectral properties of the one-dimensional Dirac equation with non-Hermitian interactions. Spectral singularities and PT symmetry breaking of the Dirac Hamiltonian are shown to correspond to simple observable physical quantities and are related to well-known physical phenomena such as resonance narrowing and laser oscillation. © 2010 The American Physical Society.

Iora P.,University of Brescia | Silva P.,Polytechnic of Milan
Applied Energy | Year: 2013

This paper presents a new CHP solution based on a double shaft intercooled gas cycle with external combustion (EFGT cycle). This configuration exploits the turbocharger technology widely diffused in the automotive industry, taking advantage of the capital cost reduction due to the economy of scale typical of the automotive market. Thermodynamic calculations based on actual turbochargers maps available from manufacturers data are carried out in order to evaluate the performances of the system. It is shown that the system results competitive both with natural gas fuelled solutions such as internal combustion engines and microturbines achieving conversion efficiency of 25-30%, as well as with low grade fuels like biomass. For a 50. kW biomass system with a grate combustor boiler and turbine inlet temperature of 750. °C, an electric efficiency of 21% is obtained, which is higher than the available state of the art solutions based on ORC technology for this size. A preliminary design of the system is performed, including the sizing of the boiler, showing its technical feasibility, while complete economic evaluations will be considered in future works. © 2012 Elsevier Ltd.

Felicetti R.,Polytechnic of Milan
Fire Technology | Year: 2013

The assessment of fire damage in concrete structures is a complex but intriguing task involving different areas of expertise, from Material Science to Structural Design, from Non-Destructive Testing to Fire Engineering. The problem grows to be even more challenging in the case of tunnels, as a consequence of the high fire severity and the operational difficulties implied by this type of infrastructure, but also because of the pressing time restrictions due to the high cost of traffic disruption during the assessment and repair works. A general overview on this subject is given in the paper, pointing out the different scales of observation, the relevant clues to be analysed at each scale and their appropriate inspection tools. These latter comprise a wide range of investigation techniques of different reliability and cost, but not many of them turn out to be viable and convenient to tackle the problem in question. In this perspective, some innovative assessment methods have been developed in recent years, having in common the ability to reveal the layered structure of fire damaged concrete, the relatively fast and easy implementation and the immediate availability of the results. A brief account on the features and the limitations of these methods is given also, as a tentative to trace some directions for future advances in this important and still open issue. © 2011 Springer Science+Business Media, LLC.

Alnaggar M.,Northwestern University | Cusatis G.,Northwestern University | Di Luzio G.,Polytechnic of Milan
Cement and Concrete Composites | Year: 2013

A large number of structures especially in high humidity environments are endangered by Alkali-Silica Reaction (ASR). ASR leads to the formation of an expansive gel that imbibes water over time. The gel expansion causes cracking and consequent deterioration of concrete mechanical behavior in the form of strength and stiffness reduction. In the recent past, many research efforts were directed towards evaluation, modeling and treatment of ASR effects on structures but a comprehensive computational model is still lacking. In this paper, the ASR effect is implemented within the framework of the Lattice Discrete Particle Model (LDPM), which simulates concrete heterogeneous character at the scale of coarse aggregate pieces. The proposed formulation, entitled ASR-LDPM, allows precise and unique modeling of volumetric expansion; expansion anisotropy under applied load; non-uniform cracking distribution; concrete strength and stiffness degradation; alkali ion concentration effect; and temperature effects of concrete subjected to ASR. In addition, a unique advantage of this formulation is its ability to distinguish between the expansion directly related to ASR gel expansion and the one associated with cracking. Simulation of experimental data gathered from the literature demonstrates the ability of ASR-LDPM to predict accurately ASR-induced concrete deterioration. © 2013 Elsevier Ltd. All rights reserved.

Vicenzo A.,Polytechnic of Milan
Journal of the Electrochemical Society | Year: 2013

Nickel-iron alloy coatings were produced by electrodeposition from an additive free electrolyte, at room temperature and current density in the range of 1 to 5 A dm-2, with Fe content up to 75 wt%. The structure and mechanical properties of the electrodeposited alloys are reported in the present work and analyzed focusing on structure-property relationships. In particular, the influence of the hydrogen evolution reaction is highlighted as a process factor affecting alloy phase structure, notably the composition limit of the γ-phase field. The variations of the mechanical properties with alloy composition are analyzed in the light of the concurrent modifications in phase structure and crystal size of the alloys. In particular, an assessment of the different factors influencing the hardness of γ phase alloys is proposed. Solid solution effects contribute significantly to the strength of γ phase alloys over a wide composition range, approximately from 5 to 25%, though a complex interplay between solid solution and Hall-Petch strengthening needs to be envisaged to account for the variations in hardness with composition over this range. Moreover, it is emphasized that with decreasing grain size, the increasing level of internal stresses and decreasing stiffness engender significant softening in nanocrystalline γ phase alloys with Fe content exceeding about 25%. © 2013 The Electrochemical Society. All rights reserved.

Cosmi F.,University of Trieste | Bernasconi A.,Polytechnic of Milan
Composites Science and Technology | Year: 2013

The development of predictive models for fatigue behavior of materials is closely related to a quantitative assessment of damage nucleation and propagation phenomena. Conventional methods used for this purpose, such as microscope observations, conventional radiographs, ultrasonography techniques, either are destructive or do not reach an adequate resolution. Imaging techniques using synchrotron radiation, and in particular X-ray micro-computed tomography (micro-CT), however, combine the advantages of a non-destructive technique with a high spatial resolution.In this paper, damage evolution in samples extracted from PA6.6GF35 specimens subjected to fatigue tests interrupted at different stages of fatigue life is investigated by means of synchrotron radiation micro-CT.Although preliminary, our results suggest that the application of this technique for micro-voids detection within the glass short fibre polyamide reinforced samples offers unique possibilities of investigating the micro-scale internal structure of the samples but, at the same time, presents several criticalities at different stages of the analyses, ranging from specimen size to set-up configuration and threshold selection. A frank discussion of the critical issues encountered during the analyses supplements the presentation in an effort to help defining general guidelines for future developments in this field. © 2013 Elsevier Ltd.

Dozio L.,Polytechnic of Milan
Composite Structures | Year: 2013

This paper deals with the formulation of advanced two-dimensional Ritz-based models for accurate prediction of natural frequencies of thin and thick sandwich plates with core made of functionally graded material (FGM). The formulation is rather general due to its invariant properties with respect to the underlying plate kinematic theory and the admissible set of Ritz functions. Convergence and accuracy of the method are investigated in this work using an entire family of higher-order layerwise and equivalent single-layer theories, whose corresponding displacement variables are approximated by series of Chebyshev polynomials multiplied by appropriate boundary functions. Results are presented for rectangular sandwich FGM plates with various thickness-to-length ratios and combinations of clamped, free and simply-supported edges. © 2012 Elsevier Ltd.

Di Sante D.,University of LAquila | Barone P.,CNR Institute of Neuroscience | Bertacco R.,Polytechnic of Milan | Picozzi S.,CNR Institute of Neuroscience
Advanced Materials | Year: 2013

Relativistic effects, including the Rashba effect, are increasingly seen as key ingredients in spintronics. A link between Rashba physics and the field of ferroelectrics is established by predicting giant Rashba spin-splitting in bulk GeTe (see the Figure showing the band-structure as well as in-plane and out- of-plane spin polarization for a constant energy cut). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Guatteri G.,Polytechnic of Milan
Systems and Control Letters | Year: 2011

In this paper we prove necessary conditions for optimality of a stochastic control problem for a class of stochastic partial differential equations that is controlled through the boundary. This kind of problem can be interpreted as a stochastic control problem for an evolution system in a Hilbert space. The regularity of the solution of the adjoint equation, that is a backward stochastic equation in infinite dimension, plays a crucial role in the formulation of the maximum principle. © 2010 Elsevier B.V.

Covarrubias M.,Polytechnic of Milan
Sensors (Basel, Switzerland) | Year: 2013

In this article, we present an approach that uses both two force sensitive handles (FSH) and a flexible capacitive touch sensor (FCTS) to drive a haptic-based immersive system. The immersive system has been developed as part of a multimodal interface for product design. The haptic interface consists of a strip that can be used by product designers to evaluate the quality of a 3D virtual shape by using touch, vision and hearing and, also, to interactively change the shape of the virtual object. Specifically, the user interacts with the FSH to move the virtual object and to appropriately position the haptic interface for retrieving the six degrees of freedom required for both manipulation and modification modalities. The FCTS allows the system to track the movement and position of the user's fingers on the strip, which is used for rendering visual and sound feedback. Two evaluation experiments are described, which involve both the evaluation and the modification of a 3D shape. Results show that the use of the haptic strip for the evaluation of aesthetic shapes is effective and supports product designers in the appreciation of the aesthetic qualities of the shape.

Altomare L.,Polytechnic of Milan
Biomatter | Year: 2014

Chitosan (CS) is a versatile biopolymer whose morphological and chemico-physical properties can be designed for a variety of biomedical applications. Taking advantage of its electrolytic nature, cathodic polarization allows CS deposition on electrically conductive substrates, resulting in thin porous structures with tunable morphology. Here we propose an easy method to obtain CS membranes with highly oriented micro-channels for tissue engineering applications, relying on simple control of process parameters and cathodic substrate geometry. Cathodic deposition was performed on two different aluminum grids in galvanostatic conditions at 6.25 mA cm(-2) from CS solution [1g L(-1)] in acetic acid (pH 3.5). Self-standing thin scaffolds were cross linked either with genipin or epichlorohydrin, weighted, and observed by optical and electron microscopy. Swelling properties at pH 5 and pH 7.4 have been also investigated and tensile tests performed on swollen samples at room temperature. Finally, direct and indirect assays have been performed to evaluate the cytotoxicity at 24 and 72 h. Thin scaffolds with two different oriented porosities (1000 µm and 500 µm) have been successfully fabricated by electrochemical techniques. Both cross-linking agents did not affected the mechanical properties and cytocompatibility of the resulting structures. Depending on the pH, these structures show interesting swelling properties that can be exploited for drug delivery systems. Moreover, thanks to the possibility of controlling the porosity and the micro-channel orientation, they should be used for the regeneration of tissues requiring a preferential cells orientation, e.g., cardiac patches or ligament regeneration.

Guilizzoni M.,Polytechnic of Milan
Journal of Colloid and Interface Science | Year: 2011

The shape and contact angles of drops on curved surfaces is experimentally investigated. Image processing, spline fitting and numerical integration are used to extract the drop contour in a number of cross-sections. The three-dimensional surfaces which describe the surface-air and drop-air interfaces can be visualized and a simple procedure to determine the equilibrium contact angle starting from measurements on curved surfaces is proposed. Contact angles on flat surfaces serve as a reference term and a procedure to measure them is proposed. Such procedure is not as accurate as the axisymmetric drop shape analysis algorithms, but it has the advantage of requiring only a side view of the drop-surface couple and no further information. It can therefore be used also for fluids with unknown surface tension and there is no need to measure the drop volume. Examples of application of the proposed techniques for distilled water drops on gemstones confirm that they can be useful for drop shape analysis and contact angle measurement on three-dimensional sculptured surfaces. © 2011 Elsevier Inc.

Pandolfi A.,Polytechnic of Milan | Weinberg K.,University of Siegen
Engineering Fracture Mechanics | Year: 2011

This study is motivated by the attempt to characterize failure modes of silicon chips commonly used in electronic industries. Previous experimental investigations provided the failure probability of dies made of a single-crystal and produced a large variety of crack patterns, but were not able to elucidate the link between defect distributions and crack initiation and propagation. To get some insight in the fracture activation and propagation mechanisms, we resort to finite element analyses and adopt an explicit methodology for crack tracking, based on the self-adaptive insertion of cohesive elements into a coherent mesh of solid elements. Finite kinematics material models with anisotropic features for both bulk and cohesive surfaces are employed to describe the behavior of single-crystal silicon plates undergoing a particular bending test up to failure. The cohesive model adopted in the calculation is fully anisotropic and newly formulated to accomplish the present study. Numerical simulations considering different material properties were able to ascertain the effects of particular flaws on failure modes of brittle silicon plates. © 2011 Elsevier Ltd.

Fiorini R.A.,Polytechnic of Milan
Fundamenta Informaticae | Year: 2014

Discrete Tomography (DT), differently from GT and CT, focuses on the case where only few specimen projections are known and the images contain a small number of different colours (e.g. black-and-white). A concise review on main contemporary physical and mathematical CT system problems is offered. Stochastic vs. Combinatorially Optimized Noise generation is compared and presented by two visual examples to emphasise a major double-bind problem at the core of contemporary most advanced instrumentation systems. Automatic tailoring denoising procedures to real dynamic system characteristics and performance can get closer to ideal self-registering and self-linearizing system to generate virtual uniform and robust probing field during its whole designed service life-cycle. The first attempt to develop basic principles for system background low-level noise source automatic characterization, profiling and identification by CICT, from discrete system parameter, is presented. As a matter of fact, CICT can supply us with cyclic numeric sequences perfectly tuned to their low-level multiplicative source generators, related to experimental high-level overall perturbation (according to high-level classic perturbation computational model under either additive or multiplicative perturbation hypothesis). Numeric examples are presented. Furthermore, a practical NTT example is given. Specifically, advanced CT system, HRO and Mission Critical Project (MCP) for very low Technological Risk (TR) and Crisis Management (CM) system will be highly benefitted mostly by CICT infocentric worldview. The presented framework, concepts and techniques can be used to boost the development of next generation algorithms and advanced applications quite conveniently.

Codecasa L.,Polytechnic of Milan
THERMINIC 2013 - 19th International Workshop on Thermal Investigations of ICs and Systems, Proceedings | Year: 2013

In this paper a novel approach is proposed for generating dynamic compact models of nonlinear heat diffusion problems for electronics components. The method is very efficient and leads to accurate approximations of the space-time distribution of temperature rise within the component for all waveforms of the injected powers. © 2013 IEEE.

Chen P.,Ecole Polytechnique Federale de Lausanne | Quarteroni A.,Ecole Polytechnique Federale de Lausanne | Quarteroni A.,Polytechnic of Milan
Computer Methods in Applied Mechanics and Engineering | Year: 2013

Several computational challenges arise when evaluating the failure probability of a given system in the context of risk prediction or reliability analysis. When the dimension of the uncertainties becomes high, well established direct numerical methods can not be employed because of the "curse-of-dimensionality". Many surrogate models have been proposed with the aim of reducing computational effort. However, most of them fail in computing an accurate failure probability when the limit state surface defined by the failure event in the probability space lacks smoothness. In addition, for a stochastic system modeled by partial differential equations (PDEs) with random input, only a limited number of the underlying PDEs (order of a few tens) are affordable to solve in practice due to the considerable computational effort, therefore preventing the application of many numerical methods especially for high dimensional random inputs. In this work we develop hybrid and goal-oriented adaptive reduced basis methods to tackle these challenges by accurately and efficiently computing the failure probability of a stochastic PDE. The curse-of-dimensionality is significantly alleviated by reduced basis approximation whose bases are constructed by goal-oriented adaptation. Moreover, an accurate evaluation of the failure probability for PDE system with solution of low regularity in probability space is guaranteed by the certified a posteriori error bound for the output approximation error. At the end of this paper we suitably extend our proposed method to deal with more general PDE models. Finally we perform several numerical experiments to illustrate its computational accuracy and efficiency. © 2013 Elsevier B.V.

Barazzetti L.,Polytechnic of Milan
Advanced Engineering Informatics | Year: 2016

This paper presents a novel semi-automated method for the generation of 3D parametric as-built models from point clouds. Laser scanning and photogrammetry have a primary role in the survey of existing facilities, especially for the generation of accurate and detailed as-built parametric models that reflect the true condition of a building. Various studies demonstrate that point clouds have a sporadic adoption in large and complex parametric modeling projects. The lack of advanced processing algorithms able to convert point clouds into parametric objects makes the generation of accurate as-built models a challenging task for irregular elements without predefined shape. The proposed semi-automated method allows the creation of parametric models from photogrammetric and laser scanning point clouds. The method is intended as a multi-step process where NURBS curves and surfaces are used to reconstruct complex and irregular objects, without excessive simplification of the information encapsulated into huge point clouds to avoid heavy models useless for practical purposes and productive work. Different case studies derived from actual BIM-based projects are illustrated and discussed to demonstrate advantages and limitations of the method. © 2016 Elsevier Ltd. All rights reserved.

Zunino P.,University of Pittsburgh | Zunino P.,Polytechnic of Milan
Computer Methods in Applied Mechanics and Engineering | Year: 2013

Numerical experiments performed by several authors repeatedly confirmed that the extended finite element method combined with classical time stepping schemes, such as backward Euler or Crank-Nicolson, provides optimal rates of convergence when applied to problems with moving interfaces. In spite of the rapid spread of this discretization approach, a complete space and time error analysis is not available yet. The objective of this work is to contribute to closing the gap between observations and rigorous analysis. More precisely, we preform a thorough space and time error analysis of different variants of the extended finite element method combined with backward Euler time advancing scheme when applied to problems with moving interfaces. Our results prove that the discretization error, measured in the natural norms, decreases with the expected rate, when space and time discretization steps are refined. We also show that the space and time approximation properties are fully decoupled. As a consequence, high order approximation schemes could be developed and analyzed within the theoretical framework proposed here. Numerical experiments are finally addressed for the verification of the algorithms. Besides the interest of providing rigorous error bounds, we believe that a general theoretical framework is extremely helpful as a guide for further developing and refining extended finite element methods for free interface problems. © 2013 Elsevier B.V.

Garatti S.,Polytechnic of Milan | Bitmead R.R.,University of California at San Diego
Automatica | Year: 2010

Linear System Identification yields a nominal model parameter, which minimizes a specific criterion based on the single input-output data set. Here we investigate the utility of various methods for estimating the probability distribution of this nominal parameter using only the data from this single experiment. The results are compared to the actual parameter distribution generated by many Monte Carlo runs of the data-collection experiment. The methods considered are collectively known as resampling schemes, which include Subsampling, the Jackknife, and the Bootstrap. The broad aim is to generate an empirical parameter distribution function via the construction of a large number of new data records from the original single set of data, based on an assumption that this data is representative of all possible data, and then to run the parameter estimator on each of these new records to develop the distribution function. The performance of these schemes is evaluated on a difficult, almost unidentifiable system, and compared to the standard results based on asymptotic normality. In addition to the exploration of this example as a means to evaluate the strengths and weaknesses of these resampling schemes, some new theoretical results are proven and demonstrated for Subsampling schemes. © 2010 Elsevier Ltd. All rights reserved.

Bolzon G.,Polytechnic of Milan
Engineering Structures | Year: 2010

A computationally effective numerical procedure is introduced to evaluate safety factors and collapse mechanisms of geometrically similar structures with dilatant frictional joints like concrete gravity dams. The envisaged methodology, alternative to the more traditional step-by-step integration of the governing rate equations, rests on the solution of a constrained minimization problem endowed with a closed-form algebraic formulation, under the hypothesis that damage evolves along structural joints while the bulk material remains linear elastic. © 2010 Elsevier Ltd.

Limongelli M.P.,Polytechnic of Milan
Journal of Sound and Vibration | Year: 2011

In this paper a new procedure, addressed as Interpolation Damage Detecting Method (IDDM), is investigated as a possible mean for early detection and location of light damage in a structure struck by an earthquake. Damage is defined in terms of the accuracy of a spline function in interpolating the operational mode shapes (ODS) of the structure. At a certain location a decrease (statistically meaningful) of accuracy, with respect to a reference configuration, points out a localized variation of the operational shapes thus revealing the existence of damage. In this paper, the proposed method is applied to a numerical model of a multistory frame, simulating a damaged condition through a reduction of the story stiffness. Several damage scenarios have been considered and the results indicate the effectiveness of the method to assess and localize damage for the case of concentrated damage and for low to medium levels of noise in the recorded signals. The main advantage of the proposed algorithm is that it does not require a numerical model of the structure as well as an intense data post-processing or user interaction. The ODS are calculated from Frequency Response Functions hence responses recorded on the structure can be directly used without the need of modal identification. Furthermore, the local character of the feature chosen to detect damage makes the IDDM less sensitive to noise and to environmental changes with respect to other damage detection methods. For these reasons the IDDM appears as a valid option for automated post-earthquake damage assessment, able to provide after an earthquake, reliable information about the location of damage. © 2011 Elsevier Ltd.

Maffezzoni P.,Polytechnic of Milan
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2010

This paper adopts a phase-domain macromodel based on perturbation projection vector to study the synchronization effects that take place between two weakly coupled oscillators. Original closed-form expressions for the locking region of the coupled oscillators and for the common locking frequency are derived. The route to synchronization is described analytically by predicting the oscillation frequency shifts, which are induced by mutual pulling as a function of the interaction strength. Under the assumption of a weak coupling, the proposed approach can be applied to a wide class of oscillator topologies. © 2010 IEEE.

Jenkins J.T.,Cornell University | Berzi D.,Polytechnic of Milan
Granular Matter | Year: 2010

Using the results of recent numerical simulations, we extend an existing kinetic theory for dense flows of identical, nearly elastic, frictionless spheres to identical, very dissipative, frictional spheres. The existing theory incorporates an additional length scale in the expression for the collisional rate of dissipation; this length scale is identified with the size of a cluster of correlated particles. Parameters of the theory for very dissipative, frictional spheres are set using the results of physical experiments on inclined flows of spheres over a rigid, bumpy base in the absence of sidewalls. The resulting theory is then tested against the results of physical experiments on flows of the same material over the surface of an erodible heap when frictional sidewalls are present. © Springer-Verlag 2010.

Dozio L.,Polytechnic of Milan | Carrera E.,Polytechnic University of Turin
Journal of Sound and Vibration | Year: 2011

A new variable kinematic Ritz method applied to free vibration analysis of arbitrary quadrilateral thin and thick isotropic plates is presented. Carrera's unified formulation and the versatile pb-2 Ritz method are properly combined to build a powerful yet simple modeling and solution framework. The proposed technique allows to generate arbitrarily accurate Ritz solutions from a large variety of refined two-dimensional plate theories by expanding so-called Ritz fundamental nuclei of the plate mass and stiffness matrices. Theoretical development of the present methodology is described in detail. Convergence and accuracy of the method are examined through several examples on thin, moderately thick, and very thick plates of rectangular, skew, trapezoidal and general quadrilateral shapes, with an arbitrary combination of clamped, free and simply supported edges. Present results are compared with existing three-dimensional solutions from open literature. Maximum and average differences of various higher-order plate theories and three-dimensional results are also presented with the aim of providing useful guidelines on the choice of appropriate plate theory to get a desired accuracy on frequency parameters. © 2011 Elsevier Ltd. All rights reserved.

Benedettini F.,University of LAquila | Gentile C.,Polytechnic of Milan
Engineering Structures | Year: 2011

The paper presents the results obtained from the application of different output-only modal identification techniques to ambient response data collected in two dynamic tests of a cable-stayed bridge and the subsequent finite element model correlation analysis. The first test, performed by using a traditional data acquisition system with servo-accelerometers, was aimed at investigating the vertical dynamic characteristics of the bridge. In the second test, an innovative radar vibrometer was used for non-contact measurement of deflection time series of the forestays and the identification of local natural frequencies of the stay cables.In the theoretical study, vibration modes were determined using a 3D Finite Element model of the bridge and the information obtained from the field tests, combined with a classic system identification technique, provided a linear elastic model, accurately fitting the modal parameters of the bridge in its present condition. © 2011 Elsevier Ltd.

Casadio R.,University of Bologna | Casadio R.,National Institute of Nuclear Physics, Italy | Micu O.,Romanian Space Science Institute | Scardigli F.,Polytechnic of Milan | Scardigli F.,Kyoto University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

We address the issue of (quantum) black hole formation by particle collision in quantum physics. We start by constructing the horizon wave-function for quantum mechanical states representing two highly boosted non-interacting particles that collide in flat one-dimensional space. From this wave-function, we then derive a probability that the system becomes a black hole as a function of the initial momenta and spatial separation between the particles. This probability allows us to extend the hoop conjecture to quantum mechanics and estimate corrections to its classical counterpart. © 2014 The Authors.

A comprehensive study on the use of a set of trigonometric functions, originally proposed by Beslin and Nicolas [Journal of Sound and Vibration 1997;202:63355], as admissible solutions in the Ritz method for general vibration analysis of rectangular orthotropic Kirchhoff plates is presented. The approach is denoted here as Trigonometric Ritz method (TRM). Since its introduction, application of TRM was limited to a very few plate problems. The aim of this work is to extend the potential of the method on predicting natural flexural frequencies of plates with various complicating factors, including in-plane loads, elastically restrained edges, rigid/elastic concentrated masses, intermediate line and point supports or their combinations. Computational efficiency, stability, convergence and accuracy of the method are discussed and supported by extensive analysis. TRM-based solutions are compared with many reference cases available in the literature obtained with other methods or Ritz functions. Numerical results indicate that TRM exhibits good to excellent accuracy for all cases considered. New solutions are also presented for future comparison purpose. © 2010 Elsevier Ltd.

Dozio L.,Polytechnic of Milan | Carrera E.,Polytechnic University of Turin
Composite Structures | Year: 2012

A variable-kinematic Ritz formulation based on two-dimensional higher-order layerwise and equivalent single-layer theories is described in this paper to accurately predict free vibration of thick and thin, rectangular and skew multilayered plates with clamped, free and simply-supported boundary conditions. The main result is the derivation at a layer level of so-called Ritz fundamental nuclei for the stiffness and mass matrices which are invariant with respect to both the assumed kinematic model and the type of Ritz functions. In this work, products of Chebyshev polynomials and boundary-compliant functions are chosen as admissible trial set. After studying the convergence of the method, its accuracy is evaluated, in terms of frequency parameters and through-the-thickness distribution of modal displacements, by comparison with some reference results available in the literature. Results for sandwich plates with soft core are given for the first time, which may serve as benchmark values for future research. © 2012 Elsevier Ltd.

Longhi S.,Polytechnic of Milan
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

A rectangular potential barrier for a Bloch particle in a tight-binding lattice is shown to become fully transparent by the application of a strong ac field with appropriate amplitude and frequency. Such a curious phenomenon bears some connection with the field-induced barrier transparency effect known for freely moving particles scattered by an ac-driven rectangular barrier; however, for a Bloch particle transparency is not related to a resonant tunneling process across the cycle-averaged oscillating potential barrier, as for the freely moving quantum particle. The phenomenon of field-induced transparency is specifically discussed here for photonic transport in waveguide arrays and demonstrated by full numerical simulations of the paraxial (Schrödinger) wave equation beyond the tight-binding approximation. © 2010 The American Physical Society.

Righetti P.G.,Polytechnic of Milan
Journal of Proteomics | Year: 2014

The review covers about fifty years of progress in "proteome" analysis, starting from primitive two-dimensional (2D) map attempts in the early sixties of last century. The polar star in 2D mapping arose in 1975 with the classic paper by O'Farrell in J Biol. Chem. It became the compass for all proteome navigators. Perfection came, though, only with the introduction of immobilized pH gradients, which fixed the polypeptide spots in the 2D plane. Great impetus in proteome analysis came with the introduction of informatic tools and creating databases, among which Swiss Prot remains the site of excellence. Towards the end of the nineties, 2D chromatography, epitomized by coupling strong cation exchangers with C18 resins, began to be a serious challenge to electrophoretic 2D mapping, although up to the present both techniques are still much in vogue and appear to give complementary results. Yet the migration of "proteomics" into the third millennium was made possible only by mass spectrometry (MS), which today represents the standard analytical tool in any lab dealing with proteomic analysis. Another major improvement has been the introduction of combinatorial peptide ligand libraries (CPLL), which, when properly used, enhance the visibility of low-abundance species by 3 to 4 orders of magnitude. Coupling MS to CPLLs permits the exploration of at least 8 orders of magnitude in dynamic range on any proteome. Biological significance: The present review is a personal recollection highlighting the developments that led to present-day proteomics on a long march that lasted about 50. years. It is meant to give to young scientists an overview on how science grows, which ones are the quantum jumps in science and which research is of particular significance in general and in the field of proteomics in particular. It also gives some real-life episodes of greater-than-life figures. As such, it can be viewed as a tutorial to stimulate the young generation to be creative (and use their imagination too!). This article is part of a Special Issue entitled: 20. years of Proteomics in memory of Viatliano Pallini. Guest Editors: Luca Bini, Juan J. Calvete, Natacha Turck, Denis Hochstrasser and Jean-Charles Sanchez. © 2013 Elsevier B.V.

Rossi F.,Polytechnic of Milan | Van Griensven M.,TU Munich
Tissue Engineering - Part A | Year: 2014

To address the increasing need for improved tissue substitutes, tissue engineering seeks to create synthetic, three-dimensional scaffolds made from polymeric materials, incorporating cells and growth factors to induce new tissue formation. Materials science, in conjunction with biotechnology, can satisfy these needs by developing artificial, synthetic substitutes and organ implants. Here, scaffold ability to promote cell growth and differentiation is a key point and, in this framework, orthogonal chemistry has led the field of biomaterial science into a new area of selective, versatile and biocompatible nature. In particular, the possibility to modify and functionalize scaffolds with compounds that are able to improve mechanical properties or cell viability and improve their differentiation in a tailorable manner opens new opportunities for researchers. In this review, we seek to emphasize the recent endeavors of exploiting this versatile chemistry toward the development of new cell culture scaffolds. © Mary Ann Liebert, Inc.

MacChiarella G.,Polytechnic of Milan | Tamiazzo S.,Andrew Telecommunication Products
IEEE Transactions on Microwave Theory and Techniques | Year: 2010

This paper illustrates a general approach to the synthesis of microwave multiplexers (RF combiners) presenting a star-junction topology (with a resonating junction). The channel filters composing the multiplexer can be arbitrarily specified; in particular, the attenuation characteristic may include transmission zeros (imaginary and/or complex). The synthesis procedure, developed in a low-pass frequency domain (suitably defined), is based on an iterative algorithm which evaluates the characteristic polynomials of both the overall multiplexer and the composing filters. Using these latter polynomials, the normalized coupling matrices of the filters can be computed using one of the methods available in the literature and the dimensioning of the channel filters is carried out through the usual de-normalized parameters (coupling coefficients and external Q). The detailed design steps illustrating the synthesis of a triplexer for base stations of mobile communications are presented. The designed device was then built, and the comparison between measurements and simulations has validated the new synthesis approach. © 2010 IEEE.

Giuffrida A.,Polytechnic of Milan
Applied Thermal Engineering | Year: 2016

A semi-empirical modeling procedure for twin-screw compressor performance simulation is proposed in this paper. In detail, the compression process is split into a number of stages, taking into account fluid leakages, heat transfers as well as heat and power losses. Compared to the simplified models reported in technical literature for other positive-displacement units, a different formulation for ambient heat loss is proposed, while mechanical power losses are modeled according to torque losses depending on both load and viscous friction effects. The proposed model applies to open-drive compressors, so three specific units for refrigeration applications with medium-high evaporation temperature are selected as the test cases for model tuning and validation, based on manufacturer's catalog data. After the identification of eight parameters, the model is able to compute the mass flow rate, the shaft power and the fluid discharge temperature, as well as volumetric and compressor efficiencies and ambient heat losses. Contrary to geometric models, the semi-empirical procedure proposed in this study does not take the presence of lubricating oil into account, as (i) oil injection with no external cooling results in a thermal neutral process; (ii) the compression work for the oil is negligible in comparison with the one required by the refrigerant fluid; and (iii) even injecting oil at a lower temperature, no considerable saving in refrigerant specific work can be achieved. Actually, this hypothesis does not significantly affect the output of the model. As a matter of fact, referring to the first test case with the larger displacement volume and to the identification of the eight model parameters based on eight convenient data points, the mass flow rate delivered by the compressor is predicted with a maximum error up to 2.44%, and the shaft power is predicted with an even limited error, except for few points with the lowest and highest pressure ratios, where the shaft power is under-estimated by 5%. Moreover, fluid temperature at the compressor exhaust is calculated with an error within ±1 K for pressure ratios up to 7.5. Similarly interesting results are achieved for the other two test case compressors, with absolute values of the errors in mass flow rate and shaft power predictions always less than 3% and 5% respectively. Finally, further considerations on the actual possibility of generalizing the model to semi-hermetic units are suggested. © 2015 Elsevier Ltd. All rights reserved.

MacChiarella G.,Polytechnic of Milan
IEEE Microwave and Wireless Components Letters | Year: 2010

In this letter, a simple solution is described for obtaining an accurate evaluation of the coupling matrix and the unloaded Q from the measured scattering parameters of a microwave lossy filter (assuming all the resonators with the same unloaded Q). The Cauchy method is applied in a predistorted frequency domain, where the measured (lossy) parameters refer to a lossless device. In this way, it becomes possible to synthesize a prototype low-pass network using well established techniques, once the topology of the filters has been assigned. With respect to the previous methods available in the literature, the one here proposed allows very accurate results even with filters exhibiting large insertion losses; moreover the computing time is extremely short allowing the use of the method in real time computer-aided tuning procedures for microwave filters. An example of application of the proposed method is reported in the letter for illustrative and validating purposes. © 2010 IEEE.

Napoli R.,Esion | Piroddi L.,Polytechnic of Milan
IEEE Transactions on Audio, Speech and Language Processing | Year: 2010

The extension of active noise control (ANC) techniques to deal with nonlinear effects such as distortion and saturation requires the introduction of suitable nonlinear model classes and adaptive algorithms. Large sized models are typically used, resulting in an increased computational load, delayed convergence (and sometimes even algorithm instability), and other unwanted dynamical effects due to overparametrization. This paper discusses the usage of polynomial Nonlinear AutoRegressive models with eXogenous variables (NARX) models and model selection techniques to reduce the model size and increase its robustness, for more efficient and reliable ANC. An offline procedure is devised to identify the controller model structure, and the controller parameters are successively updated with an adaptive algorithm based on the error gradient and on the residual noise. Simulation experiments show the effectiveness of the proposed approach. A brief analysis of the involved computational complexity is also provided. 1558-7916/$26.00 © 2009 IEEE.

Ciantia M.O.,Polytechnic of Milan | Hueckel T.,Duke University
Geotechnique | Year: 2013

Long portions of the Apulian coast are steep cliffs in carbonate soft rocks. These, especially the calcarenite, are affected by weathering processes that markedly alter their mechanical properties with time, potentially leading to instability of coastal geomorphological structures. Such alterations are mainly due to chemical reactions between the solid and fluid phases, and are driven by chemical variables, which are internal variables and hence uncontrollable. In a search for the variables that drive the process of rock weakening, recourse is made to the micro scale, at which most of the chemical processes are observed and quantified. Observations using scanning electron microsope, thin sections and X-ray computed tomography analyses appear to be crucial for the understanding, interpretation and definition of the degradation mechanisms of the material. A chemo-mechanical coupled model at the meso scale of the chemically reactive stressed porous system is presented and framed in the context of a multi-scale scenario of an array of coupled phenomena. An analogous model at the macro scale is developed in parallel together with upscaling and identification procedures for meso-scale and macro-scale material constants. The main outcome of the study is a tool for predicting the progress of time-dependent weathering phenomena, potentially allowing the stability of geological structures to be assessed as it evolves with a progressing chemical degradation in a specific configuration and under a specific set of loads.

Ponzini D.,Polytechnic of Milan | Rossi U.,University of Cagliari
Urban Studies | Year: 2010

This paper critically explores the 'politics of becoming' in a 'wannabe' creative city in the United States. It shows how, in Baltimore's policy sphere, Richard Florida's theory has served as an 'intellectual technology' aiming at the invention of a new macro-actor (the creative class), while related urban regeneration outcomes and prospects appear to be more problematic. In particular, at the city-wide level, the creative class policy has favoured the interests of local politicians and their closer institutional partners; while, in the described context of a socially deprived neighbourhood, the embraced culture-led policy, albeit successful in redesigning a more attractive urban realm and thus in attaining its stated goals, has proved to be concerned more with real estate revitalisation than with issues of social inclusion and life-chance provision. It is concluded that the prevailing institutional imperative of networking and collaboration, as observed in Baltimore's creative class initiative, overemphasises the importance of the politics of association in contemporary urban regeneration processes, while neglecting the relevance of classic goals of socio-spatial justice. © 2009 Urban Studies Journal Limited.

Bellucci M.C.,University of Milan | Volonterio A.,Polytechnic of Milan
European Journal of Organic Chemistry | Year: 2014

The development of efficient methods for the combinatorial synthesis of N-glycosyl conjugates is vital for many fields of modern synthetic organic chemistry. Herein, we report a multicomponent domino process for the regioselective synthesis of a large array N-glycosyl-Asp-urea conjugates, which could be further functionalized in a chemoselective way, starting from easily accessible reactants such as N-glycosylamines, fumaric acid monoesters, azides, and isocyanates. The process occurs under very mild conditions, does not require the use of strong bases/acids or high temperature, and is highly versatile, working efficiently with a range of protecting groups and substituents. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Longhi S.,Polytechnic of Milan
Physical Review Letters | Year: 2011

In recent works, the idea of time-reversed laser oscillation has been proposed and demonstrated to realize a two-channel coherent perfect absorber. Here the time reversal of optical parametric oscillation in a nonlinear χ(2) medium is considered and shown to realize a coherent perfect absorber for colored incident signal and idler fields. A detailed analysis is presented for the time-reversed process of mirrorless optical parametric oscillation in the full nonlinear regime. © 2011 American Physical Society.

Ciarletta P.,CNRS Jean Le Rond dAlembert Institute | Ciarletta P.,Polytechnic of Milan | Balbi V.,CNRS Jean Le Rond dAlembert Institute | Kuhl E.,Stanford University
Physical Review Letters | Year: 2014

Tubular organs display a wide variety of surface morphologies including circumferential and longitudinal folds, square and hexagonal undulations, and finger-type protrusions. Surface morphology is closely correlated to tissue function and serves as a clinical indicator for physiological and pathological conditions, but the regulators of surface morphology remain poorly understood. Here, we explore the role of geometry and elasticity on the formation of surface patterns. We establish morphological phase diagrams for patterns selection and show that increasing the thickness or stiffness ratio between the outer and inner tubular layers induces a gradual transition from circumferential to longitudinal folding. Our results suggest that physical forces act as regulators during organogenesis and give rise to the characteristic circular folds in the esophagus, the longitudinal folds in the valves of Kerckring, the surface networks in villi, and the crypts in the large intestine. © 2014 American Physical Society.

Pacciarini P.,Polytechnic of Milan | Rozza G.,International School for Advanced Studies | Rozza G.,Ecole Polytechnique Federale de Lausanne
Computer Methods in Applied Mechanics and Engineering | Year: 2014

In this work, we propose viable and efficient strategies for the stabilization of the reduced basis approximation of an advection dominated problem. In particular, we investigate the combination of a classic stabilization method (SUPG) with the Offline-Online structure of the RB method. We explain why the stabilization is needed in both stages and we identify, analytically and numerically, which are the drawbacks of a stabilization performed only during the construction of the reduced basis (i.e. only in the Offline stage). We carry out numerical tests to assess the performances of the "double" stabilization both in steady and unsteady problems, also related to heat transfer phenomena. © 2014 Elsevier B.V.

Buscarnera G.,Northwestern University | Buscarnera G.,Polytechnic of Milan | Whittle A.J.,Massachusetts Institute of Technology
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

This paper examines the influence of the initial state of sands on the potential for undrained instability. The main goal is to illustrate how advanced constitutive modeling of sand behavior can be used to evaluate the susceptibility for static liquefaction. The methodology is based on the concept of latent instability, in which the potential for collapse is contingent on particular boundary conditions. A generalized effective stress soil model, MIT-S1, is used to support the analysis and is combined with a theoretical approach for identifying loss of control owing to undrained shear perturbations. The theory is evaluated using experimental evidence available for Toyoura sand to point out the key role of void ratio and consolidation history and to provide experimental validation for the theory. Model predictions are then used to disclose the subtle role of drained preloading paths in promoting liquefaction instabilities. The ability of the constitutive model to reproduce the interplay between undrained kinematic constraints and material failure is fundamental in predicting potential instabilities arising from changes in drainage conditions. The examples shed light on the mechanics of static liquefaction and set a framework for applying the principles of material stability to the triggering analysis of flow slides induced by undrained shear perturbations. © 2013 American Society of Civil Engineers.

Gasparini S.,French Institute for Research in Computer Science and Automation | Caglioti V.,Polytechnic of Milan
International Journal of Computer Vision | Year: 2011

Indoor environments often contain several line segments. The 3D reconstruction of such environments can thus be reduced to the localization of lines in the 3D space. Multi-view reconstruction requires the solution of the correspondence problem. The use of a single image to localize space lines is attractive, since the correspondence problem can be avoided. However, using a central camera the line localization from single image is an ill-posed problem, because there are infinitely many lines sharing the same image. In this work we relaxed the constraint on single viewpoint imaging and considered a wide class of non-central catadioptric cameras, constituted by an axial symmetric mirror and a perspective camera placed at a generic relative position. In the paper we report the results of our study on line localization for such cameras, reporting the conditions that allow a line to be localized from a single image. We show how the analysis can be extended to other classes of non-central devices sharing a similar imaging model. We also present a brief overview of the main algorithms for line localization from single image that have been proposed. © 2011 Springer Science+Business Media, LLC.

Cantini L.,Ecole Normale Superieure de Paris | Sportiello A.,Polytechnic of Milan
Journal of Combinatorial Theory. Series A | Year: 2011

The Razumov-Stroganov conjecture relates the ground-state coefficients in the periodic even-length dense O(1) loop model to the enumeration of fully-packed loop configurations on the square, with alternating boundary conditions, refined according to the link pattern for the boundary points.Here we prove this conjecture, by means of purely combinatorial methods. The main ingredient is a generalization of the Wieland proof technique for the dihedral symmetry of these classes, based on the 'gyration' operation, whose full strength we will investigate in a companion paper. © 2011 Elsevier Inc.

Ignaccolo M.,Corecompete | De Michele C.,Polytechnic of Milan
Journal of Applied Meteorology and Climatology | Year: 2014

The authors test the adequacy of gamma distribution to describe the statistical variability of raindrop diameters in 1-min disdrometer data using the Kolmogorov-Smirnov goodness-of-fit test. The results do not support the use of this distribution, with a percentage of rejected cases that increases with the sample size. A different parameterization of the drop size distribution is proposed that does not require any particular functional form and is based on the adoption of statistical moments. The first three moments, namely the mean, standard deviation, and skewness, are sufficient to characterize the distribution of the drop diameter at the ground. These parameters, together with the drop count, form a 4-tuple, which fully describes the variability of the drop size distribution. The Cartesian product of this 4-tuple of parameters is the rainfall phase space. Using disdrometer data from 10 different locations, invariant, location-independent properties of rainfall are identified. © 2014 American Meteorological Society.

Dozio L.,Polytechnic of Milan
Mechanics Research Communications | Year: 2010

A Ritz method using a set of trigonometric functions is developed to obtain accurate in-plane modal properties of rectangular plates with arbitrary nonuniform elastic edge restraints. Reliability of the current approach is first assured by comparison against exact and analytical-type solutions for plates with classical boundary conditions and uniform elastic boundaries. For the first time to the author's knowledge, the problem of free in-plane vibration of plates having triangularly and parabolically varying elastic edge supports is then considered. Accurate upper-bound solutions are tabulated to provide valuable benchmark data against which the findings of other researchers can be compared in the future. Effects of nonuniform elastic spring stiffness on the in-plane natural frequencies and modal shapes are also presented. © 2010 Elsevier Ltd. All rights reserved.

Longhi S.,Polytechnic of Milan
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Defects in tight-binding lattices generally destroy the onset of Bloch oscillations (BOs) and the periodic self-imaging of the wave packet due to the lack of an equally spaced Wannier-Stark ladder spectrum. Here it is shown that localized and extended defects in the lattice can be engineered to be transparent for BOs. Such lattices are synthesized from the defect-free lattice by the technique of intertwining operators generally employed in supersymmetric quantum mechanics. The energy spectrum of the synthesized lattices differs from the Wannier-Stark ladder of the defect-free lattice because of the missing of pairs of resonances in the ladder, thus ensuring the persistence of BOs. © 2010 The American Physical Society.

Milani G.,Polytechnic of Milan
International Journal of Mechanical Sciences | Year: 2010

A heterogeneous full 3D limit analysis model for the evaluation of collapse loads of FRP-reinforced multi-layer masonry structures loaded in- and out-of-plane is presented. Four-noded rigid infinitely resistant tetrahedrons are used to model bricks, stones and filler. Three-noded rigid infinitely resistant triangles are used to model FRP strips. Plastic dissipation is allowed only at the interfaces between adjoining elements, i.e. on mortar joints reduced to interfaces, on brickbrick interfaces and on filler. A possible dissipation at the interfaces between FRP triangles and masonry wedges is also considered in order to take into account, in an approximate but effective way, the possible delamination of the strips from the supports. Italian code CNR-DT200 formulas are used as a reference to evaluate peak interface tangential strength. While the delamination from the support can be modeled only in an approximate way within limit analysis, the aim of the paper is to accurately reproduce the change in the failure mechanism observed in experiments due to the introduction of strengthening elements. A 3D approach to model masonry is used in order to take into account both the real texture of the panels along the thickness (i.e. multi-layer regular and irregular texture, presence of internal filler, etc.) and the presence of FRP strips either at the extrados or at the intrados of the structural elements. Two numerical examples are critically analyzed, consisting of a two leaf thick masonry wall simply supported at three edges, reinforced at the extrados and subjected to uniform lateral pressure and a complex three-layer tuff masonry shear wall with cavities filled with mortar and reinforced with horizontal and diagonal FRP strips at both faces. For the first example analyzed, full sensitivity analyses varying both FRP-brick peak strength and filler mechanical properties have been conducted in order to evaluate the capabilities of the model proposed when varying constituent materials mechanical properties. An additional FE simulation conducted with a standard code is also discussed to validate the model. When dealing with the second example, full comparisons with experimental data available are reported. Comparisons with experimental evidence and alternative FE procedures confirm that the limit analysis approach proposed may represent a valuable tool for predicting failure mechanisms and collapse loads of complex 3D multi-layer masonry structures reinforced with FRP strips. © 2010 Elsevier Ltd. All rights reserved.

Taliercio A.,Polytechnic of Milan
Mechanics Research Communications | Year: 2010

A hollow cylinder made of a linearly elastic isotropic micropolar material subjected to twist is analyzed. The complete analytical solution is obtained, including the case of a solid cylinder previously dealt with by other authors. The influence of the different material constants on the stress distribution and the torsional rigidity is illustrated. Alòso, the differences are pointed out between the obtained solution and that for a solid cylinder. © 2010 Elsevier B.V. All rights reserved.

Longhi S.,Polytechnic of Milan
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

A class of truncated tight-binding Hermitian and non-Hermitian lattices with commensurate energy levels, showing periodic reconstruction of the wave packet, is presented. Examples include exact Bloch oscillations on a finite lattice, periodic wave packet dynamics in non-Hermtian lattices with a complex linear site-energy gradient, and self-imaging in lattices with commensurate energy levels quadratically varying with the quantum number. © 2010 The American Physical Society.

Valoroso N.,Parthenope University of Naples | Fedele R.,Polytechnic of Milan
International Journal of Solids and Structures | Year: 2010

The identification of mode-I parameters of a cohesive-zone model for the analysis of adhesive joints is presented. It is based on an experimental-numerical methodology whereby the optimal parameters are obtained as the solution of a nonlinear programming problem. The data set for inverse analysis is provided either by local kinematic data, by global static data, or a combination of the two. Parameter sensitivities are computed via direct differentiation and identification exercises are discussed that show the effectiveness of the procedure and its stability with respect to noise and time-space sampling. © 2010 Elsevier Ltd. All rights reserved.

Sanchez P.,Technical University of Delft | Moutsouris K.,Athineum Refractive Center | Pandolfi A.,Polytechnic of Milan
Journal of Cataract and Refractive Surgery | Year: 2014

Purpose To evaluate numerically the biomechanical and optical behavior of human corneas and quantitatively estimate the changes in refractive power and stress caused by photorefractive keratectomy (PRK). Setting Athineum Refractive Center, Athens, Greece, and Politecnico di Milano, Milan, Italy. Design Retrospective comparative interventional cohort study. Methods Corneal topographies of 10 human eyes were taken with a scanning-slit corneal topographer (Orbscan II) before and after PRK. Ten patient-specific finite element models were created to estimate the strain and stress fields in the cornea in preoperative and postoperative configurations. The biomechanical response in postoperative eyes was computed by directly modeling the postoperative geometry from the topographer and by reproducing the corneal ablation planned for the PRK with a numerical reprofiling procedure. Results Postoperative corneas were more compliant than preoperative corneas. In the optical zone, corneal thinning decreased the mechanical stiffness, causing local resteepening and making the central refractive power more sensitive to variations in intraocular pressure (IOP). At physiologic IOP, the postoperative corneas had a mean 7% forward increase in apical displacement and a mean 20% increase in the stress components at the center of the anterior surface over the preoperative condition. Conclusion Patient-specific numerical models of the cornea can provide quantitative information on the changes in refractive power and in the stress field caused by refractive surgery. Financial Disclosures No author has a financial or proprietary interest in any material or method mentioned. © 2014 ASCRS and ESCRS.

Longhi S.,Polytechnic of Milan
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

A photonic analog of Klein tunneling for a relativistic electron across a potential step, based on spatial light propagation in an engineered binary waveguide array, is proposed. Klein tunneling can be simply visualized as optical beam refraction through a step-index interface, superimposed to the superlattice, and explained as an interband tunneling process between positive-energy (electron) and negative-energy (positron) minibands of the superlattice. Inhibition of Klein tunneling for a smooth potential step is also demonstrated. © 2010 The American Physical Society.

Langfelder G.,Polytechnic of Milan
Microelectronics Reliability | Year: 2010

The Transverse Field Detector (TFD) is a recently proposed CMOS pixel device for color imaging applications without the need of physical color filters. The color detection capability relies on the generation of a suitable electric field configuration in a depleted region of the Silicon active layer. In this paper a newly designed, structurally different version of the TFD is proposed, through which a three-color passive pixel can be implemented with a width reduced to 3 μm in a CMOS standard 90 nm technology. Experimental results on a prototypal device are also reported. © 2009 Elsevier Ltd. All rights reserved.

Ranci C.,Polytechnic of Milan
Urban Studies | Year: 2011

European cities are historically characterised by a strong association between social cohesion and competitiveness. However, in recent years, this stability has been affected by strains induced by rising new inequalities and increasing competition among cities. These facts have raised the need for a new understanding of the relationship between cohesion and competitiveness. This paper draws on a selection of social and economic indicators to explore this multifaceted relationship in 50 European cities, selected on the basis of their size and international role. The aims of the analysis are to assess the position of each European city, to identify clusters of cities and to suggest an interpretative hypothesis in order to characterise the particularities of this relationship in European cities. © 2011 Urban Studies Journal Limited.

Rinaldi S.,Polytechnic of Milan
Theoretical Population Biology | Year: 2012

A minimal model for the interactions of trees, insects, and their enemies suggests a simple formula for splitting all forests where insect outbreaks can occur into two categories: where outbreaks are periodic and endogenously generated and where outbreaks are triggered by exogenous factors and are, in general, recurrent but aperiodic. The formula is in full agreement with all field studies in which various phenomena triggering insect outbreaks have been identified. The observed consequences of introductions and removals of insects are also well predicted by the minimal model. But, even more surprisingly, the model allows a simple and explicit condition for the synchronization of outbreaks in spatially extended forests to be derived analytically. This condition is, in general, satisfied when the insect is a so-called pest, that is, when the outbreaks are extreme. The model also predicts the possibility of traveling waves of insect outbreaks. © 2011 Elsevier Inc.

Bocchiola D.,Polytechnic of Milan
Advances in Water Resources | Year: 2011

Data from a flume experiment were used to explore the modified hydraulic conditions and habitat suitability in streams where feeding of large woody debris (LWD) is present. Feeding of LWD was simulated by insertion of wood dowels with varying diameter and length. Two processes were mimicked, namely (i) lumped LWD load, and (ii) distributed LWD load. Lumped load may occur for wood coming either from upstream or from a tributary, and entering the stream of interest in one only section. Distributed load occurs for wood entering along the considered stream, in several sections. Distributed wood income resulted in homogeneously increased bed roughness, leading to increased flow depth and decreased velocity, whereas lumped input of wood from upstream resulted in larger local clustering and change of the flow properties, but with less influence on the distributed hydraulic properties. A method is proposed to predict bulk flow properties in presence of LWD. Then, a simple approach is used based upon the concept of wetter usable area WUA to investigate modified habitat conditions for fish species in presence of woody debris. An application to a real world case study from the literature is then shown, where increasing density of wood increases habitat availability for colonization by fish guilds. © 2011 Elsevier Ltd.

Franzoni C.,Polytechnic of Milan | Sauermann H.,Georgia Institute of Technology
Research Policy | Year: 2014

A growing amount of scientific research is done in an open collaborative fashion, in projects sometimes referred to as "crowd science", "citizen science", or "networked science". This paper seeks to gain a more systematic understanding of crowd science and to provide scholars with a conceptual framework and an agenda for future research. First, we briefly present three case examples that span different fields of science and illustrate the heterogeneity concerning what crowd science projects do and how they are organized. Second, we identify two fundamental elements that characterize crowd science projects - open participation and open sharing of intermediate inputs - and distinguish crowd science from other knowledge production regimes such as innovation contests or traditional "Mertonian" science. Third, we explore potential knowledge-related and motivational benefits that crowd science offers over alternative organizational modes, and potential challenges it is likely to face. Drawing on prior research on the organization of problem solving, we also consider for what kinds of tasks particular benefits or challenges are likely to be most pronounced. We conclude by outlining an agenda for future research and by discussing implications for funding agencies and policy makers. © 2013 Elsevier B.V. All rights reserved.

Raimondi M.T.,Polytechnic of Milan
Journal of applied biomaterials & functional materials | Year: 2012

Three-dimensional material microstructuring by femtosecond laser-induced two-photon polymerization is emerging as an important tool in biomedicine. During two-photon polymerization, a tightly focused femtosecond laser pulse induces a crosslinking photoreaction in the polymer confined within the focal volume. As a rapid-prototyping technique, two-photon polymerization enables the fabrication of truly arbitrary three-dimensional micro- and nano-structures directly from computer models, with a spatial resolution down to 100 nm. In this review, we discuss the fundamentals, experimental methods, and materials used for two-photon polymerization; in addition, we present some applications of this technology related to microfluidics and to biomaterial scaffolds for tissue engineering and regenerative medicine.

Taroni P.,Polytechnic of Milan | Taroni P.,CNR Institute for Photonics and Nanotechnologies
Photochemical and Photobiological Sciences | Year: 2012

Breast cancer is the most common cancer among women in industrialized countries. At present, X-ray mammography is the gold standard for breast imaging, but has limitations, especially when dense breasts are imaged, as typically occurs in young women. Optical imaging can non-invasively provide information on tissue composition, structure and physiology that can be beneficially exploited for breast lesion detection and identification. In the last few decades optical breast imaging has been investigated, using different geometries (projection imaging and tomography) and measurement techniques (continuous wave, frequency resolved and time resolved approaches). Also, data analysis and display varies significantly, ranging from intensity images to maps of the optical properties (absorption and scattering), tissue composition, and physiological parameters (typically blood volume and oxygenation). This paper outlines the historical evolution of optical imaging and spectroscopy of the breast, highlighting potentialities and limitations, and presents an overview of the main applications and perspectives of the field. © 2012 The Royal Society of Chemistry and Owner Societies.

Malerba P.G.,Polytechnic of Milan
Structure and Infrastructure Engineering | Year: 2014

The concept of life cycle applied to building structures is quite recent. In the past, constructions were built to be everlasting, and the number of massive buildings and bridges still in service apparently confirms the soundness of this approach. When reinforced concrete was introduced, new possibilities were open to engineers, in a time when the end of a structure's life was still considered as an extreme and very remote hypothesis. However, this belief was soon to be faced with the evidence of the deterioration of the concrete surfaces and with the corrosion of steel bars and strands, so that the concept of durability had to be introduced. It therefore became clear that the structures' constructions have to be monitored and periodically maintained, so as to extend their service life as much as possible. This paper gives an account of studies and rehabilitation works carried out on bridges located in the north of Italy, providing some remarks regarding the maintenance of structures of the past and the design of structure for the future. © 2013 Taylor & Francis.

Piazza R.,Polytechnic of Milan
Reports on Progress in Physics | Year: 2014

Colloid sedimentation has played a seminal role in the development of statistical physics thanks to the celebrated experiments by Perrin, which provided a concrete demonstration of molecular reality and gave strong support to Einstein's theory of Brownian motion. This review, which mostly focuses on settling at low Peclét number, where Brownian fluctuations are dominant, aims to show that a lot more can be learnt both from the sedimentation equilibrium and from the particle settling dynamics of a wide class of systems, ranging from simple colloids to mesogenic suspensions, from soft solids to active particles and living organisms. At the same time, the occurrence of unexpected and surprising effects brings about challenging questions in statistical and fluid mechanics that make sedimentation an exciting field of research. © 2014 IOP Publishing Ltd.

Dercole F.,Polytechnic of Milan
Theoretical Ecology | Year: 2016

A general procedure to formulate asexual (unstructured, deterministic) population dynamical models resulting from individual pairwise interactions is proposed. Individuals are characterized by a continuous strategy that is constant during life and represents their behavioral, morphological, and functional traits. Populations group conspecific individuals with identical strategy and are measured by densities in space. Species can be monomorphic, if only a single value of the strategy is present, or polymorphic otherwise. The procedure highlights the structural properties fulfilled by the population per-capita growth rates. In particular, the effect on the growth rate of jointly perturbing a set of similar strategies is proportional to the product of the corresponding densities, with a proportionality coefficient that can be density-dependent only through the sum of the densities. This generalizes the law of mass action, which traditionally refers to the case in which the per-capita growth rates are linearly density-dependent and insensitive to joint strategy perturbations. Being underpinned by individual strategies, the proposed procedure is most useful for evolutionary considerations, in the case strategies are inheritable. The developed body of theory is exemplified on a Holling-type-II many-prey-one-predator system and on a model of cannibalism. © 2016 Springer Science+Business Media Dordrecht

Zecca A.,Polytechnic of Milan
European Physical Journal Plus | Year: 2014

The Standard Cosmological Model with energy density ρ, pressure p and cosmological term λ is reconsidered. The interdependence among the cosmological equations in different equivalent forms is pointed out with λ possibly time dependent. For constant λ and for ρ, p expressed in terms of the scalar field φ of potential V(φ), the scheme is in fact equivalent to the coupling of Einstein and scalar field equations in the Robertson-Walker metric. A Lagrangian and the corresponding Hamiltonian H, that takes the zero value, are derived directly from the equations. The Wheeler-DeWitt (WDW) equation is obtained by canonical quantization of H that is performed in two non-equivalent ways. The WDW equations are transformed into Schrödinger-like eigenvalue problems with eigenvalue λ. The equations are separated for vanishing scalar potential. The φ-separated equation results in an eigenvalue problem in the separation constant λ1, that must be negative, and it is easily integrated. The R-separated equation, is again an eigenvalue problem with eigenvalue λ. It is solved, in the flat space-time case, by preliminary fixing λ1, in terms of the Bessel functions of the first kind and implies that λ can take all possible negative values. For fixed λ1, λ, the wave function of the Universe vanishes in correspondence with a big-bang situation and for large R. © 2014, Società Italiana di Fisica and Springer-Verlag Berlin Heidelberg.

Prati E.,CNR Institute for Microelectronics and Microsystems | Hori M.,Waseda University | Guagliardo F.,Polytechnic of Milan | Ferrari G.,Waseda University | Shinada T.,Japan National Institute of Advanced Industrial Science and Technology
Nature Nanotechnology | Year: 2012

Dopant atoms are used to control the properties of semiconductors in most electronic devices. Recent advances such as single-ion implantation have allowed the precise positioning of single dopants in semiconductors as well as the fabrication of single-atom transistors, representing steps forward in the realization of quantum circuits. However, the interactions between dopant atoms have only been studied in systems containing large numbers of dopants, so it has not been possible to explore fundamental phenomena such as the Anderson-Mott transition between conduction by sequential tunnelling through isolated dopant atoms, and conduction through thermally activated impurity Hubbard bands. Here, we observe the Anderson-Mott transition at low temperatures in silicon transistors containing arrays of two, four or six arsenic dopant atoms that have been deterministically implanted along the channel of the device. The transition is induced by controlling the spacing between dopant atoms. Furthermore, at the critical density between tunnelling and band transport regimes, we are able to change the phase of the electron system from a frozen Wigner-like phase to a Fermi glass by increasing the temperature. Our results open up new approaches for the investigation of coherent transport, band engineering and strongly correlated systems in condensed-matter physics. © 2012 Macmillan Publishers Limited.

Ardagna D.,Polytechnic of Milan | Panicucci B.,University of Modena and Reggio Emilia | Passacantando M.,University of Pisa
IEEE Transactions on Services Computing | Year: 2013

In recent years, the evolution and the widespread adoption of virtualization, service-oriented architectures, autonomic, and utility computing have converged letting a new paradigm to emerge: cloud computing. Clouds allow the on-demand delivering of software, hardware, and data as services. Currently, the cloud offer is becoming wider day by day because all the major IT companies and service providers, like Microsoft, Google, Amazon, HP, IBM, and VMWare, have started providing solutions involving this new technological paradigm. As cloud-based services are more numerous and dynamic, the development of efficient service provisioning policies becomes increasingly challenging. In this paper, we take the perspective of Software as a Service (SaaS) providers that host their applications at an Infrastructure as a Service (IaaS) provider. Each SaaS needs to comply with quality-of-service requirements, specified in service-level agreement (SLA) contracts with the end users, which determine the revenues and penalties on the basis of the achieved performance level. SaaS providers want to maximize their revenues from SLAs, while minimizing the cost of use of resources supplied by the IaaS provider. Moreover, SaaS providers compete and bid for the use of infrastructural resources. On the other hand, the IaaS wants to maximize the revenues obtained providing virtualized resources. In this paper, we model the service provisioning problem as a generalized Nash game and we show the existence of equilibria for such game. Moreover, we propose two solution methods based on the best-reply dynamics, and we prove their convergence in a finite number of iterations to a generalized Nash equilibrium. In particular, we develop an efficient distributed algorithm for the runtime allocation of IaaS resources among competing SaaS providers. We demonstrate the effectiveness of our approach by simulation and performing tests on a real prototype environment deployed on Amazon EC2. Results show that, compared to other state-of-the-art solutions, our model can improve the efficiency of the cloud system evaluated in terms of Price of Anarchy by 50-70 percent. © 2013 IEEE.

Fournier M.F.,Ecole Polytechnique Federale de Lausanne | Sauser R.,Ecole Polytechnique Federale de Lausanne | Ambrosi D.,Polytechnic of Milan | Meister J.-J.,Ecole Polytechnique Federale de Lausanne | Verkhovsky A.B.,Ecole Polytechnique Federale de Lausanne
Journal of Cell Biology | Year: 2010

During cell migration, forces generated by the actin cytoskeleton are transmitted through adhesion complexes to the substrate. To investigate the mechanism of force generation and transmission, we analyzed the relationship between actin network velocity and traction forces at the substrate in a model system of persistently migrating fish epidermal keratocytes. Front and lateral sides of the cell exhibited much stronger coupling between actin motion and traction forces than the trailing cell body. Further analysis of the traction - velocity relationship suggested that the force transmission mechanisms were different in different cell regions: at the front, traction was generated by a gripping of the actin network to the substrate, whereas at the sides and back, it was produced by the network's slipping over the substrate. Treatment with inhibitors of the actin - myosin system demonstrated that the cell body translocation could be powered by either of the two different processes, actomyosin contraction or actin assembly, with the former associated with significantly larger traction forces than the latter. © 2010 Fournier et al.

Chiappe C.,University of Pisa | Mele A.,Polytechnic of Milan
Topics in Current Chemistry | Year: 2010

Aiming to develop environmentally compatible chemical syntheses, the replacement of traditional organic solvents with ionic liquids (ILs) has attracted considerable attention. ILs are special molten salts with melting points below 100°C that are typically constituted of organic cations (imidazolium, pyridinium, sulfonium, phosphonium, etc.) and inorganic anions. Due to their ionic nature, they are endowed with high chemical and thermal stability, good solvent properties, and non-measurable vapor pressure. Although the recovery of unaltered ILs and recycling partly compensate their rather high cost, it is important to develop new synthetic approaches to less expensive and environmentally sustainable ILs based on renewable raw materials. In fact, most of these alternative solvents are still prepared starting from fossil feedstocks. Until now, only a limited number of ILs have been prepared from renewable sources. Surprisingly, the most available and inexpensive raw material, i.e., carbohydrates, has been hardly exploited in the synthesis of ILs. In 2003 imidazolium-based ILs were prepared from d-fructose and used as solvents in Mizoroki-Heck and Diels-Alder reactions. Later on, the first chiral ILs derived from sugars were prepared from methyl d-glucopyranoside. In the same year, a family of new chiral ILs, obtained from commercial isosorbide (dianhydro-d-glucitol), was described. A closely related approach was followed by other researchers to synthesize mono- and bis-ammonium ILs from isomannide (dianhydro-d-mannitol). Finally, a few ILs bearing a pentofuranose unit as the chiral moiety were prepared using sugar phosphates as glycosyl donors and 1-methylimidazole as the acceptor. © 2010 Springer-Verlag Berlin Heidelberg.

Longhi S.,Polytechnic of Milan
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

An optical realization of the tunneling dynamics of two interacting bosons in a double-well potential, based on light transport in a four-core microstructured fiber, is proposed. The optical setting enables one to visualize, in a purely classical system, the entire crossover from Rabi oscillations to correlated pair tunneling and to tunneling of a fragmented pair in the fermionization limit. © 2011 American Physical Society.

Mele A.,Polytechnic of Milan
Chimica Oggi | Year: 2010

The use of nuclear magnetic resonance (NMR) intermolecular nuclear Overhauser effect (NOE) represent one of the most effective investigation tool for the assessment of nanostructural organization in ionic liquids. Homo- and heteronuclear NOE provide, in principle, information on all the possible interactions within the liquid: cation-cation, cation-anion, anion-anion and, in case, solute solvent contacts. Some paradigmatic cases taken from the recent literature are exposed with the goal of outlining general approaches and strategies.

Longhi S.,Polytechnic of Milan
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

In recent works, it has been shown, rather generally, that the time-reversed process of lasing at threshold realizes a coherent perfect absorber (CPA). In a CPA, a lossy medium in an optical cavity with a specific degree of dissipation, equal in modulus to the gain of the lasing medium, can perfectly absorb coherent optical waves that are the time-reversed counterpart of the lasing field. Here, the time-reversed process of lasing is considered in detail for a homogeneously broadened two-level medium in an optical cavity and the conditions for CPA are derived. It is shown that, owing to the dispersive properties of the two-level medium, exact time-reversal symmetry is broken and the frequency of the field at which CPA occurs is generally different than the one of the lasing mode. Moreover, at a large cooperation parameter, the observation of CPA in the presence of bistability requires one to operate in the upper branch of the hysteresis cycle. © 2011 American Physical Society.

Arioli G.,Polytechnic of Milan | Koch H.,University of Texas at Austin
Archive for Rational Mechanics and Analysis | Year: 2010

We develop some computer-assisted techniques for the analysis of stationary solutions of dissipative partial differential equations, of their stability, and of their bifurcation diagrams. As a case study, these methods are applied to the Kuramoto-Sivashinski equation. This equation has been investigated extensively, and its bifurcation diagram is well known from a numerical point of view. Here, we rigorously describe the full graph of solutions branching off the trivial branch, complete with all secondary bifurcations, for parameter values between 0 and 80. We also determine the dimension of the unstable manifold for the flow at some stationary solution in each branch. © 2010 Springer-Verlag.

Annoni M.,Polytechnic of Milan
Measurement: Journal of the International Measurement Confederation | Year: 2012

The present work deals with the uncertainty evaluation in water jet velocity measurements carried out by means of a laser Doppler dual-incident-beam velocimeter in reference-beam configuration developed at the WJLab (Water Jet Laboratory of Dipartimento di Meccanica of Politecnico di Milano). The applied experimental procedure makes it possible to calculate the measurement uncertainty through the determination of its various components. Once uncertainty is known, the laser Doppler system is suitable for objective and significant velocity evaluations but also for improvements allowed by the knowledge of the most effective uncertainty sources. Such a subject is typically not considered by the specific water jet literature, but is becoming more and more important due to the evolution of water jet machining towards high precision applications. © 2012 Elsevier Ltd. All rights reserved.

Casolo S.,Polytechnic of Milan | Uva G.,Polytechnic of Bari
Earthquake Engineering and Structural Dynamics | Year: 2013

The paper proposes a systematic comparison between two methods of analysis that are well established in the field of earthquake engineering: nonlinear dynamic analysis and nonlinear static procedure (NSP), applied to the out-of-plane seismic response of two masonry façades representative of many ancient Italian churches. The comparison is based on extensive numerical analyses, which focus on the flexural and torsional mechanisms, while the in-plane damage mechanisms and the possible detachment between the façade and the lateral walls because of a poor connection have been presently disregarded. The computations, both in the static and in the dynamic field, are based on a rigid body and spring model specifically implemented for this issue, computationally efficient and equipped with a realistic model of damage and hysteresis at the mesoscale. An innovative aspect of this study is the heuristic modelling of three-wythe masonry, to include some typical texture effects on the macroscale nonlinear response. For each façade, two different masonry textures were considered, performing extensive dynamic analyses that offered a detailed overview about the performance under earthquakes of different intensities. In parallel, NSP and the classical N2-based seismic assessment were applied. A critical discussion and comparison of the results of the two methods is presented to rationally appraise limits and opportunities. In particular, flexural and twisting out-of-plane mechanisms were clearly appraised in the dynamic field, whereas NSPs were not always able to describe the collapse, because they missed the partial failures determined by higher vibration modes, as could be expected. © 2012 John Wiley & Sons, Ltd.

Pacella M.,University of Salento | Semeraro Q.,Polytechnic of Milan
Computers and Industrial Engineering | Year: 2011

In modern manufacturing, approaches for profile monitoring can be adopted to detect unnatural behaviors of production processes, i.e. to signal when the relationship used to represent the profiles changes with time. Most of the literature concerned with profile monitoring deals with the problem of model identification and multivariate charting of parameters vector. In this paper, a different approach, which is based on an unsupervised neural network, is presented for profile monitoring. The neural network allows a computer to automatically learn from data the relationship to represent in-control profiles. Then, the algorithm may produce a signal when an input profile does not fit to the prototype learned from the in-control ones. The neural network does not require an analytical model for the statistical description of profiles faced (model-free approach). A comparison study is provided in this paper, in which the Phase II performance of the neural network is compared to that of approaches representative of the industrial practice. Performance is assessed by computer simulation, with reference to a case study related to profiles measured on machined items subject to geometrical specification (roundness). The results indicate that the neural network may outperform usual control charts in signaling out-of-control conditions, due to spindle-motion errors in several production scenarios. The proposed approach can be considered a valuable option for profile monitoring in industrial applications. © 2010 Published by Elsevier Ltd. All rights reserved.

Bruggi M.,Polytechnic of Milan
Computer Methods in Applied Mechanics and Engineering | Year: 2016

Recently, new families of mixed finite elements have been proposed to address the analysis of linear elastic bodies on regular grids adopting a limited number of degrees of freedom per element. A two-dimensional mixed discretization is implemented to formulate an alternative topology optimization problem where stresses play the role of main variables and both compressible and incompressible materials can be dealt with. The structural compliance is computed through the evaluation of the complementary energy, whereas the enforcement of stress constraints is straightforward. Numerical simulations investigate the features of the proposed approach: comparisons with a conventional displacement-based scheme are provided for compressible materials; stress-constrained solutions for structures made of incompressible media are introduced. © 2016 Elsevier B.V.

Covarrubias M.,Polytechnic of Milan
International Journal of Advanced Robotic Systems | Year: 2013

This paper describes a desktop-mechatronic interface that has been conceived to support designers in the evaluation of aesthetic virtual shapes. This device allows a continuous and smooth free hand contact interaction on a real and developable plastic tape actuated by a servo-controlled mechanism. The objective in designing this device is to reproduce a virtual surface with a consistent physical rendering well adapted to designers' needs. The desktop-mechatronic interface consists in a servo-actuated plastic strip that has been devised and implemented using seven interpolation points. In fact, by using the MEC (Minimal Energy Curve) Spline approach, a developable real surface is rendered taking into account the CAD geometry of the virtual shapes. In this paper, we describe the working principles of the interface by using both absolute and relative approaches to control the position on each single control point on the MEC spline. Then, we describe the methodology that has been implemented, passing from the CAD geometry, linked to VisualNastran in order to maintain the parametric properties of the virtual shape. Then, we present the cosimulation between VisualNastran and MATLAB/Simulink used for achieving this goal and controlling the system and finally, we present the results of the subsequent testing session specifically carried out to evaluate the accuracy and the effectiveness of the mechatronic device. © 2013 Covarrubias et al.

Giustozzi F.,Polytechnic of Milan
Construction and Building Materials | Year: 2016

Pervious concrete is widely considered as an optimal material to manage storm waters in built environments as well as to provide several other environmental benefits. Despite the broad capabilities pervious concrete pavements have exhibited a high failure rate so far. Causes are mainly related to poor design, inadequate construction techniques including compaction, and heavy vehicular traffic. Performance of pervious concrete can be furthermore improved by modifying the cement matrix through polymer modifications, for instance. Polymers could indeed have the capability of improving mechanical performance, particularly flexural strength, without reducing drainability and void content. Four polymers have been tested in the present research and preliminary analyses on polymer-modified cement grouts and mortars were conducted during the first phase of the study; polymer-modified pervious concrete mixes were then prepared and further tested to evaluate the inclusion of polymers depending on the type and content. Results showed a delayed curing of polymer-modified mixes as well as an increased mechanical resistance and durability to raveling and freeze-thaw cycles; polyvinyl acetate polymer demonstrated to be a very good option. © 2016 Elsevier Ltd. All rights reserved.

Nair A.K.,Massachusetts Institute of Technology | Gautieri A.,Massachusetts Institute of Technology | Gautieri A.,Polytechnic of Milan | Chang S.-W.,Massachusetts Institute of Technology | Buehler M.J.,Massachusetts Institute of Technology
Nature Communications | Year: 2013

Bone is a natural composite of collagen protein and the mineral hydroxyapatite. The structure of bone is known to be important to its load-bearing characteristics, but relatively little is known about this structure or the mechanism that govern deformation at the molecular scale. Here we perform full-atomistic calculations of the three-dimensional molecular structure of a mineralized collagen protein matrix to try to better understand its mechanical characteristics under tensile loading at various mineral densities. We find that as the mineral density increases, the tensile modulus of the network increases monotonically and well beyond that of pure collagen fibrils. Our results suggest that the mineral crystals within this network bears up to four times the stress of the collagen fibrils, whereas the collagen is predominantly responsible for the material's deformation response. These findings reveal the mechanism by which bone is able to achieve superior energy dissipation and fracture resistance characteristics beyond its individual constituents. © 2013 Macmillan Publishers Limited. All rights reserved.

Celino I.,Polytechnic of Milan
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

The collection of volunteered geographic information (VGI) is a user-generated content practice to engage a large number of citizens to collectively create geospatial data. Based on the advent of Web 2.0 and the recent increasing popularity of crowdsourcing approaches, VGI has gained the interest of the geoscience community, because of its ability to complement the collection of geographic information coming from traditional sensing technologies. However, the involvement of a crowd of volunteers, potentially untrained or nonexperts, implies that VGI can be of varying quality. Tracing VGI provenance enables the recording of the collection activity; the information about who gathered what, where and when can then be employed to judge the VGI quality. In this paper, we focus on the adoption of a provenance-based Human Computation approach to aggregate and consolidate VGI. We discuss the representation, inference and publication of Human Computation VGI and its provenance. As more and more of those community-based data collection efforts happen on the Web, we propose the adoption of Semantic Web technologies, through employing an ontological formulation to capture provenance and by following Linked Data principles to publish provenance data on the Web. © 1980-2012 IEEE.

Ravazzani G.,Polytechnic of Milan
Computers and Geosciences | Year: 2013

This paper presents MOSAICO, a set of Fortran 90 Modules for facilitating development of raster based hydrological applications and stimulating adoption of netCDF as a common format for sharing and comparing data among hydrological community. MOSAICO include routines for high level operations for input output and manipulation of gridded dataset. A test program is presented in order to show basic MOSAICO capabilities. © 2012 Elsevier Ltd.

Natali D.,Italian Institute of Technology | Natali D.,Polytechnic of Milan | Caironi M.,Italian Institute of Technology
Advanced Materials | Year: 2012

A high-mobility organic semiconductor employed as the active material in a field-effect transistor does not guarantee per se that expectations of high performance are fulfilled. This is even truer if a downscaled, short channel is adopted. Only if contacts are able to provide the device with as much charge as it needs, with a negligible voltage drop across them, then high expectations can turn into high performances. It is a fact that this is not always the case in the field of organic electronics. In this review, we aim to offer a comprehensive overview on the subject of current injection in organic thin film transistors: physical principles concerning energy level (mis)alignment at interfaces, models describing charge injection, technologies for interface tuning, and techniques for characterizing devices. Finally, a survey of the most recent accomplishments in the field is given. Principles are described in general, but the technologies and survey emphasis is on solution processed transistors, because it is our opinion that scalable, roll-to-roll printing processing is one, if not the brightest, possible scenario for the future of organic electronics. With the exception of electrolyte-gated organic transistors, where impressively low width normalized resistances were reported (in the range of 10 Ω·cm), to date the lowest values reported for devices where the semiconductor is solution-processed and where the most common architectures are adopted, are ∼10 kΩ·cm for transistors with a field effect mobility in the 0.1-1 cm 2/Vs range. Although these values represent the best case, they still pose a severe limitation for downscaling the channel lengths below a few micrometers, necessary for increasing the device switching speed. Moreover, techniques to lower contact resistances have been often developed on a case-by-case basis, depending on the materials, architecture and processing techniques. The lack of a standard strategy has hampered the progress of the field for a long time. Only recently, as the understanding of the rather complex physical processes at the metal/semiconductor interfaces has improved, more general approaches, with a validity that extends to several materials, are being proposed and successfully tested in the literature. Only a combined scientific and technological effort, on the one side to fully understand contact phenomena and on the other to completely master the tailoring of interfaces, will enable the development of advanced organic electronics applications and their widespread adoption in low-cost, large-area printed circuits. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ciarletta P.,University Pierre and Marie Curie | Ambrosi D.,Polytechnic of Milan | Maugin G.A.,University Pierre and Marie Curie
Journal of the Mechanics and Physics of Solids | Year: 2012

In this work, we derive a novel thermo-mechanical theory for growth and remodeling of biological materials in morphogenetic processes. This second gradient hyperelastic theory is the first attempt to describe both volumetric growth and mass transport phenomena in a single-phase continuum model, where both stress- and shape-dependent growth regulations can be investigated. The diffusion of biochemical species (e.g. morphogens, growth factors, migration signals) inside the material is driven by configurational forces, enforced in the balance equations and in the set of constitutive relations. Mass transport is found to depend both on first- and on second-order material connections, possibly withstanding a chemotactic behavior with respect to diffusing molecules. We find that the driving forces of mass diffusion can be written in terms of covariant material derivatives reflecting, in a purely geometrical manner, the presence of a (first-order) torsion and a (second-order) curvature. Thermodynamical arguments show that the Eshelby stress and hyperstress tensors drive the rearrangement of the first- and second-order material inhomogeneities, respectively. In particular, an evolution law is proposed for the first-order transplant, extending a well-known result for inelastic materials. Moreover, we define the first stress-driven evolution law of the second-order transplant in function of the completely material Eshelby hyperstress. The theory is applied to two biomechanical examples, showing how an Eshelbian coupling can coordinate volumetric growth, mass transport and internal stress state, both in physiological and pathological conditions. Finally, possible applications of the proposed model are discussed for studying the unknown regulation mechanisms in morphogenetic processes, as well as for optimizing scaffold architecture in regenerative medicine and tissue engineering. © 2011 Elsevier Ltd. All rights reserved.

SH evaluation in Po Plain region is revisited with a view to: (a) updating available seismic source and ground motion attenuation models with recent data and testing the sensitivity of the results, (b) exploiting available non-stationary models to check their predictive performance at particular sites and, (c) handling the ground motion hazard generated by composite fault systems. Update of area source models and GMPEs does not strongly affect SH evaluated at representative sites, while usefulness of predictions derived from non-stationary models needs to be assessed on a site-by-site basis. A hybrid (deterministic-probabilistic) approach seems to be a promising tool for assessing site-specific hazard contributed by composite sources. © 2013 Springer Science+Business Media Dordrecht.

Fratesi U.,Polytechnic of Milan
Regional Studies | Year: 2015

Fratesi U. Regional knowledge flows and innovation policy: a dynamic representation, Regional Studies. This paper presents a tool to study ex-ante the effects of innovation policy on regional growth and income. It uses a dynamic evolutionary simulation approach and presents a model able to represent the flows of knowledge within and between regions. The model is unique but can be customized to represent different regional innovation modes. The model is calibrated with data of the average European Union NUTS-2 region, and is used to show the different impacts of various policy options, and the different impacts of the same policies in different regions, providing evidence in favour of regionally tailored, place-based approaches. Calibrating the model, through fieldwork, on an actual region will eventually allow ex-ante estimations of actual policy impacts to be produced. © 2015 Regional Studies Association.

Musso G.,Polytechnic University of Turin | Romero E.,Polytechnic University of Catalonia | della Vecchia G.,Polytechnic of Milan
Geotechnique | Year: 2013

This work presents an insight into double-structure effects on the coupled chemo-hydro-mechanical behaviour of a compacted active clay. In the first part, selected pore size distribution curves are introduced, to highlight the influence of solute concentration on the evolution of the microstructure of compacted samples. An aggregated structure with dual-pore network is induced by compaction even at relatively high water contents. This structural arrangement is enhanced by salinisation, and has a notable influence on transient volume change behaviour - that is, the occurrence of different stages of swelling upon pore water dilution and higher volume change rates upon salinisation. A coupled chemo-hydro-mechanical model, taking into consideration double-structural features from a chemo-mechanical viewpoint, is described and then used to interpret these behavioural responses and present complementary information on local transient processes. The model is designed to identify an intra-aggregate and an inter-aggregate domain, and assigns different values of hydraulic pressure and osmotic suction to each domain. Distinct constitutive laws for both domains are formulated, and the flow of salt and water between the two domains is accounted for by a physically based mass exchange term. The model is used to simulate salt diffusion tests run in an oedometer at constant vertical stress. Parameters used in the formulation are calibrated based on separate experimental evidence, both through direct test results and through back-analyses of laboratory experiments. © 2013 Thomas Telford Ltd.

Celebrano M.,Polytechnic of Milan | Rosman C.,University of Mainz | Sonnichsen C.,University of Mainz | Krishnan M.,University of Zurich
Nano Letters | Year: 2012

We demonstrate the ability to trap, levitate, and orient single anisometric nanoscale objects with high angular precision in a fluid. An electrostatic fluidic trap confines a spherical object at a spatial location defined by the minimum of the electrostatic system free energy. For an anisometric object and a potential well lacking angular symmetry, the system free energy can further strongly depend on the object's orientation in the trap. Engineering the morphology of the trap thus enables precise spatial and angular confinement of a single levitating nano-object, and the process can be massively parallelized. Since the physics of the trap depends strongly on the surface charge of the object, the method is insensitive to the object's dielectric function. Furthermore, levitation of the assembled objects renders them amenable to individual manipulation using externally applied optical, electrical, or hydrodynamic fields, raising prospects for reconfigurable chip-based nano-object assemblies. © 2012 American Chemical Society.

Lonati G.,Polytechnic of Milan | Zanoni F.,Airprotech srl
Waste Management | Year: 2013

The potential impact of the atmospheric emission of mercury from a new waste gasification plant is assessed by means of a probabilistic approach based on probability density functions for the description of the input data (namely, emission rate of mercury gaseous and particulate species) and the model parameters involved in the individual risk exposure assessment through the pathways of inhalation, soil ingestion, dermal contact, and diet. The use of probability functions allowed the uncertainty in the input data and model parameters to be accounted for; the uncertainty was propagated throughout the evaluation by Monte Carlo technique, resulting in the probability distributions for the ambient air and soil concentrations nearby the plant and for the subsequent individual risk, estimated in terms of hazard index for both an adult and a child receptor. The estimated median concentration levels in air and soil are respectively in the 1.6×10-3-2.2×10-2ngm-3 range and in the 3.5×10-4-1.7×10-2mgkg-1 range, that is at least two orders of magnitude lower than the current background concentration in the ambient air and one order of magnitude lower than the concentration locally measured in the soil. The diet pathway is responsible for the most part (>80%) of the daily mercury intake, which, however, is at least four (median estimated values) and three orders (estimates for a reasonable maximum exposure) lower than the reference dose in the most part of the modeling domain. According to the locally measured background mercury levels in air and soil the additional contribution of the plant emissions to the environmental mercury levels appears of small significance, with an almost negligible impact on the hazard index for the population living in the neighborhood of the plant. © 2012 Elsevier Ltd.

Fratesi U.,Polytechnic of Milan | Percoco M.,Bocconi University
Regional Studies | Year: 2014

Fratesi U. and Percoco M. Selective migration, regional growth and convergence: evidence from Italy, Regional Studies. This paper studies the link between regional disparities and migration flows, focusing on the skill content of migration. Disparities may lead to migration, which should reduce them; but at the same time if migration is skill-selective, it may have an opposite effect and reinforce the richest regions. The object of this empirical analysis is Italy, a country where unskilled interregional migration flows were a large and very well-known phenomenon during the 1950s and 1970s, whilst in recent years, after three decades of very low labour mobility, thousands of Southern graduates have been moving to Northern regions. What is the economic impact of those flows of selective migration? Using data covering the period 1980–2001, it is found that although a slight process of convergence occurred between Italian regions, the loss of human capital in the South was detrimental to regional growth. © 2013 Regional Studies Association.

Milani G.,Polytechnic of Milan
Journal of Mathematical Chemistry | Year: 2013

In this paper, the recently presented kinetic model proposed in Milani and Milani (J Math Chem 51(3):1116-1133, 2013) to interpret EPDM peroxide vulcanization is extensively revised and the resultant second order ODE is solved by means of an approximate but effective closed form analytical approach. The model has kinetic base and it is aimed at predicting, by means of a very refined approach, the vulcanization degree of rubber vulcanized with peroxides. Such a procedure takes contemporarily into consideration, albeit within a simplified scheme, the actual reactions occurring during peroxidic curing, namely initiation, H-abstraction, combination and addition, and supersedes the simplified approach used in practice, which assumes for peroxidic curing a single first order reaction. The main drawback of the overall procedure proposed in Milani and Milani (J Math Chem 51(3):1116-1133, 2013) is that the single second order non-linear differential equation obtained mathematically and representing the crosslink evolution with respect to time, was solved numerically by means of a Runge-Kutta approach. Such a limitation is here superseded and a major improvement is proposed allowing the utilization of an approximate but still effective closed form solution. After some simplifications applied on some parts of the solving function not allowing direct closed form integration, an analytical function is proposed. Kinetic parameters within the analytical model are evaluated through least squares where target data are represented by few experimental normalized rheometer curve values. In order to have an insight into the reliability of the numerical approach proposed, a case of technical interest of an EPDM with low unsaturation and crosslinked with three different peroxides at three increasing temperatures is critically discussed. © 2013 Springer Science+Business Media New York.

Milani G.,Polytechnic of Milan | Milani F.,CHEM.CO
Journal of Applied Polymer Science | Year: 2012

A simple numerical model for the interpretation of the reaction kinetics in ethylene-propylene-diene monomer (EPDM) vulcanized with accelerated sulfur is presented. The model is based on the assumption that during vulcanization, a number of partial reactions occurs, both in series and in parallel, which determine the formation of intermediate compounds, including activated and matured polymers. Once written a standard first-order differential equation (DIFF-EQ) for each partial reaction, an ordinary DIFF-EQ system (ODEs), was obtained and solved through Runge-Kutta algorithms. Alternatively and more efficiently, a single second-order nonhomogenous DIFF-EQ with constant coefficients was deduced, for which a closed-form solution was derived, provided that the nonhomogenous term was approximated with an exponential function. Kinetic constants were evaluated through experimental data fitting on standard rheometer tests. To assess model predictions, an experimental campaign at different temperatures on two EPDM compounds was performed. They exhibited moderate reversion at intermediate and high curing temperatures. A nonlinear least-squares fitting was performed to evaluate unknown constants entering into the DIFF-EQ model proposed. Scaled rheometer curves fit rather well, also in the presence of reversion. In addition, partial reaction kinetic constants were provided: this gave an interesting insight into the different reticulation processes occurring during vulcanization. © 2011 Wiley Periodicals, Inc.

Buscarnera G.,Northwestern University | Di Prisco C.,Polytechnic of Milan
Geotechnique | Year: 2013

This paper illustrates an application of the theory of material stability to the analysis of unsaturated slopes. The main goal is to contribute to the understanding of rainfall-induced flow slides. For this purpose, a coupled hydromechanical constitutive model is combined with a simplified approach for the analysis of infinite slopes. Simple shear-test simulations are used to evaluate triggering perturbations and investigate the role of both initial suction and stress anisotropy in the activation of slope failures. The numerical simulations clearly show that different mechanisms of activation can be originated. The onset of instability is detected by introducing appropriate stability indices for distinct modes of failure: localised shear failure, static liquefaction and wetting-induced collapse. Critical intervals of slope inclinations are identified, cautioning that the predicted failure mode may change dramatically depending on initial conditions, slope angle and material properties. The numerical simulations demonstrate that, in particular circumstances, saturation of the pore space can be the unexpected result of a volumetric instability. According to this interpretation, a rainfall-induced flow slide can originate from a complex chain process consisting of a sudden volume collapse, uncontrolled saturation of the pores and, eventually, catastrophic liquefaction of the deposit.

Milani G.,Polytechnic of Milan
Journal of Mathematical Chemistry | Year: 2013

A direct genetic algorithm (GA) approach with kinetic base, to provide effective numerical estimates of vulcanization level for EPDM cross-linked with accelerated sulphur is presented. The model requires a preliminary characterization of rubber through standard rheometer tests. A recently presented kinetic exponential model is used as starting point to develop the algorithm proposed. In such a model, three kinetic constants have to be determined by means of a non-linear least-squares curve fitting. The approach proposed circumvents a sometimes inefficient and not convergent non-linear data fitting, disregarding at a first attempt reversion and finding the local minimum of a suitable two-variable error function, to have an estimate of the first two kinetic constants. A comparison between present GA approach and traditional gradient based algorithms is discussed. The last constant, representing reversion is again evaluated through a minimization performed on a single variable error function. The applicability of the approach is immediate and makes the model extremely appealing when fast and reliable estimates of crosslinking density of cured EPDM are required. To show the capabilities of the approach proposed, a comprehensive comparison with both available experimental data and results obtained numerically with a least square exponential model for a real compound at different temperatures is provided. © 2012 Springer Science+Business Media New York.

Bruggi M.,Polytechnic of Milan
Computers and Structures | Year: 2016

A numerical method based on topology optimization is proposed to generate optimal strut-only models for structures made of plain concrete and optimal strut-and-tie models for concrete structures where fixed regions of reinforcement are prescribed. Assuming concrete as a hyper-elastic material carrying only compression, both the inherently nonlinear equilibrium equation and the energy-based topology optimization problem are solved within the same minimization procedure. Numerical simulations investigate load paths within the two-dimensional domain in case of conventional rebar cages. A stress diffusion problem is considered as well. © 2016 Elsevier Ltd. All rights reserved.

Berzi D.,Polytechnic of Milan | Fraccarollo L.,University of Trento
Physical Review Letters | Year: 2015

We reanalyze previous experimental measurements of solid volume fraction, mean velocity, and velocity fluctuations in collisional suspensions of plastic cylinders and water flowing over inclined, erodible beds. We show that the particle pressure scales with the granular temperature, as predicted by kinetic theory of granular gases. The assumption that the particle shear stress is also well predicted by kinetic theory permits us to determine the fluid shear stress and the effective fluid viscosity from the experiments. The fluid viscosity can be decomposed into turbulent and granularlike components: the turbulent viscosity can be modeled using a mixing length, which is a decreasing function of the local volume fraction and does not depend upon the distance from the bed; the granularlike viscosity, associated with the transfer of momentum due to the conjugate motion of the fluid mass added to the particles, can be modeled by replacing the particle density with the density of the added fluid mass in the viscosity of kinetic theory. © 2015 American Physical Society.

Ntalampiras S.,Polytechnic of Milan
Digital Signal Processing: A Review Journal | Year: 2014

Traffic congestion in modern cities is an increasing problem having significant consequences in our daily lives. This work proposes a non-intrusive, passive monitoring framework based on the acoustic modality which can be used either autonomously or as a part of a multimodal system and provide valuable information to an intelligent transportation system. We consider a large number of audio classes which are typically encountered in urban areas. We introduce a combination of a powerful audio representation mechanism based on time, frequency and wavelet domain features with universal background modeling which leads to higher recognition accuracies and detection rates (in terms of false alarm and miss probability rates) with respect to commonly employed methodologies. The basic advantage of a class-specific model derived using the universal background modeling logic is its tolerance to data which belong to other sound classes. Another important feature of the proposed system is its ability to detect crash incidents, which apart from their catastrophic impact on human life and property, have negative consequences on the traffic flow. Our experiments are based on the concurrent usage of professional sound effect collections which include audio recordings of high quality. We thoroughly examine the performance of the proposed system on isolated sound events as well as continuous audio streams using confusion matrices and detection error trade-off curves. © 2014 Elsevier Inc.

Marques G.D.,University of Lisbon | Iacchetti M.F.,Polytechnic of Milan
IEEE Transactions on Industrial Electronics | Year: 2014

Dispersed generation systems need several elements that should work together. One possible way to connect these elements is through a common dc link. This paper discusses a new control method for the doubly fed induction generator when connected to a dc link. Considerable benefits are obtained in this configuration, because a simple diode bridge can be used on the stator and only an ac/dc power electronic inverter is needed to control the rotor currents. As the ac mains do not impose the stator frequency, this should be regulated to get an appropriate operation of the induction machine. This paper proposes a method to regulate the stator frequency and control the torque based on adjustments of the $d-q$ rotor reference currents by using the field-oriented control. The analysis and synthesis of the control system based on a simplified model is discussed. Simulations and experimental results show that the proposed control exhibits good dynamics in the torque control and in frequency regulation. © 1982-2012 IEEE.

Masarati P.,Polytechnic of Milan
Multibody System Dynamics | Year: 2014

This work proposes the simultaneous solution of inverse kinematics and inverse dynamics of redundant manipulators for (nearly) real-time joint trajectory design and feedforward control torque computation using general-purpose multibody formulations and software tools based on redundant coordinate approaches. The proposed scheme consists of a staggered sequence of three inverse kinematics problems that compute positions, velocities, and accelerations, followed by an inverse dynamics problem that computes feedforward generalized driving forces. The soundness of the proposed scheme is illustrated by its application to several problems of increasing complexity. © 2013, Springer Science+Business Media Dordrecht.

Sassi R.,University of Milan | Mainardi L.T.,Polytechnic of Milan
IEEE Transactions on Biomedical Engineering | Year: 2011

Temporal heterogeneity of ventricular repolarization is a key quantity for the development of ventricular reentrant arrhythmia. In this paper, we introduce the V-index, a novel ECG-based estimator of the standard deviation of ventricular myocytes repolarization times SV. Differently from other ECG metrics of repolarization heterogeneity, the V-index was derived from the analysis of a biophysical model of the ECG, where repolarization is described by the dominant T-wave (DTW) paradigm. The model explains the shape of T-waves in each lead as a projection of a main waveform (the DTW) and its derivatives weighted by scalars, the lead factors. A mathematical formula is derived to link the heterogeneity of ventricular repolarization SV and the V-index. The formula was verified using synthetic 12-lead ECGs generated with a direct electrophysiological model for increasing values of SV (in the range 20-70 ms). A linear relationship between the V-index and SV was observed, V ≈ 0.675 sv + 1.8$ ms (R 2 = 0.9992$). Finally, 68 ECGs from the E-OTH-12-0068-010 database of the Telemetric and Holter ECG Warehouse were analyzed. The V-index coherently increased after sotalol administration, a drug known to have QT-prolonging potential (p ≈ 0.001). © 2011 IEEE.

Hernandez-Vargas E.A.,Helmholtz Center for Infection Research | Colaneri P.,Polytechnic of Milan | Middleton R.H.,University of Newcastle
Automatica | Year: 2013

This work is motivated by the drug therapy scheduling problem in HIV infection. Using simplified switched linear system models of HIV mutation and treatment with certain class of symmetry and finite horizon cost functions, we demonstrate that the optimal state and costate trajectories lie on a sliding surface where infinitely fast switching may occur. Results suggest that in the absence of other practical constraints, switching rapidly between therapies is relevant. Simulations show the potential benefits of a proactive switching strategy to minimize viral load and delay the emergence of resistant mutant viruses. © 2013 Elsevier Ltd. All rights reserved.

Manca D.,Polytechnic of Milan
Computers and Chemical Engineering | Year: 2016

The electrical energy (EE) price plays a significant role in the economic assessment of industrial processes. PSE/CAPE applications are often based on economic evaluations/optimizations where EE price and its possible dynamic evolution are important input data. Planning, scheduling, on-line optimization (dynamic) conceptual design, and feasibility studies are some of the applications where short-, medium-, and long-term predictions of EE quotations are involved. The paper discusses the main issues that contribute to EE quotations such as geographical, meteorological, seasonal, political, social, and financial terms. EE prices show a significant dependency on crude oil quotations with a time-delay of about a quarter/season. An econometric model comprising both linear and periodic components with an implicit stochastic term delivered by the reference component is first commented, then identified, and finally validated respect to real EE quotations. The paper provides also a discussion on how to forecast EE prices ranging from short- to long-term horizons. © 2015 Elsevier Ltd.

Berzi D.,Polytechnic of Milan
Journal of Hydraulic Engineering | Year: 2011

This work focuses on the sediment transport that is dominated by collisional exchange of momentum between particles and can be identified as the transition regime between bed-load and suspended-load transport. Idealizing the particles as inelastic frictional spheres and accounting for the role of the interstitial fluid on particle collisions, three regions characterize such flows: a diffuse collisional layer neighboring the free surface, in which a simple trapezium rule is employed to solve a boundary-value problem based on the kinetic theory; a dense, algebraic layer, in which there is an algebraic balance between production and dissipation of particle fluctuation energy, the concentration is approximately constant, and correlated motion between the particles exists; and a macroviscous layer, close to the erodible bed, in which the collisions are inelastic and the fluid viscous force dominates the momentum exchange. Using boundary conditions of no-slip and yielding at the erodible bed and vanishing of the particle stresses and energy flux at the top of the sediments, an analytical description of the flow field is obtained. After a sensitivity analysis of the approximate theoretical solution to the model parameters-only one of them has a phenomenological origin and cannot be directly measured-comparisons with experiments performed on sheet flows of water and plastic cylinders, sand, or gravel assess the validity of the theory. © 2011 American Society of Civil Engineers.

Periodic density functional theory calculations are here used to investigate polymorphism in poly(butylene-2,6-naphthalate) (PBN) and to understand the intra- and inter-molecular effects which are responsible for its behavior. Despite its similarity to poly(butylene terephthalate), the larger π-electron conjugation promoted by the presence of naphtyl rings generates peculiar intramolecular effects and stronger interchain packing interactions which cause some differences between the two polymers. This is particularly evident by comparing the structural and spectroscopic data predicted for the α and β crystals with respect to the respective one dimensional infinite chain models. Two different interpretations have been proposed in the previous literature to describe the structural transitions from the α to the β polymorph of PBN upon mechanical deformation or thermal treatments: from one hand, the setting on of a transplanar conformation on the methylene chains has been proposed while, on the other hand, a larger coplanarity of the ester groups and the naphtyl rings has been suggested. Our calculations reveal that both these effects are present in β-PBN and should be both taken into account to give an interpretation of the trends observed by IR spectroscopy and structural characterization. © 2014 Elsevier Ltd. All rights reserved.

Milani G.,Polytechnic of Milan
Construction and Building Materials | Year: 2011

A simple homogenized equilibrated and admissible model for the limit analysis of masonry walls in- and out-of-plane loaded is presented. A rectangular running bond elementary cell (RVE) is discretized by means of a few constant stress triangular elements (CST) and interfaces. Non linearity is concentrated on brick-brick interfaces and joints reduced to interface, exhibiting a frictional behavior with limited tensile and compressive strength. When dealing with the flexural behavior, a Kirchhoff-Love homogenized model is derived, subdividing the REV into several layers along the thickness and in discretizing each layer analogously to the in-plane case. When dealing with the in-plane behavior, a linear programming problem with very few variables is obtained, which can be handled even manually for some cases of technical interest. The lower bound model proposed is validated at a cell level through literature kinematic models, to show that the lower bound approach provides almost identical results with respect to upper bound approaches, meaning that the actual solution is well approximated. Homogenized masonry behavior is then implemented at a structural level in consolidated FE limit analysis codes for the evaluation of collapse loads and failure mechanisms of real scale masonry structures. © 2011 Elsevier Ltd. All rights reserved.

Ielmini D.,Polytechnic of Milan
IEEE Transactions on Electron Devices | Year: 2011

Resistive switching memory (RRAM) devices generally rely on the formation/dissolution of conductive filaments through insulating materials, such as metal oxides and chalcogenide glasses. Understanding the mechanisms for filament formation and disruption in resistive switching materials is a critical step toward the development of reliable and controllable RRAM for future-generation storage. In particular, the capability to control the filament resistance and the reset current through the compliance current during filament formation may provide a key signature to clarify the switching mechanism. This paper provides a physically based explanation for the universal resistance switching in bipolar RRAM devices. A numerical model of filament growth based on thermally activated ion migration accounts for the resistance switching characteristics. The same physical picture is extended to numerically model the reset transition. The impact of migration parameters and experimental setup on the set/reset characteristics is discussed through numerical simulations. © 2011 IEEE.

Ielmini D.,Polytechnic of Milan
Current Applied Physics | Year: 2011

Phase change memory (PCM) is attracting an increasing interest as next generation stand-alone and embedded memory technology. Quantitative predictions of PCM scaling require a thorough understanding of physical reliability mechanisms, such as current fluctuation, structural relaxation and crystallization in the amorphous phase. This work describes recent advances in the physical modeling of structure fluctuation, relaxation and crystallization for the amorphous chalcogenide in PCM cells, showing a unified interpretation of relaxation/crystallization kinetic. The statistical variability of crystallization in PCM arrays and potential limitations in memory downscaling are discussed. © 2011 Elsevier B.V. All rights reserved.

Milani G.,Polytechnic of Milan
International Journal of Solids and Structures | Year: 2011

A homogenization model for periodic masonry structures reinforced with continuous FRP grids is presented. Starting from the observation that a continuous grid preserves the periodicity of the internal masonry layer, rigid-plastic homogenization is applied directly on a multi-layer heterogeneous representative element of volume (REV) constituted by bricks, finite thickness mortar joints and external FRP grids. In particular, reinforced masonry homogenized failure surfaces are obtained by means of a compatible identification procedure, where each brick is supposed interacting with its six neighbors by means of finite thickness mortar joints and the FRP grid is applied on the external surfaces of the REV. In the framework of the kinematic theorem of limit analysis, a simple constrained minimization problem is obtained on the unit cell, suitable to estimate - with a very limited computational effort - reinforced masonry homogenized failure surfaces. A FE strategy is adopted at a cell level, modeling joints and bricks with six-noded wedge shaped elements and the FRP grid through rigid infinitely resistant truss elements connected node by node with bricks and mortar. A possible jump of velocities is assumed at the interfaces between contiguous wedge and truss elements, where plastic dissipation occurs. For mortar and bricks interfaces, a frictional behavior with possible limited tensile and compressive strength is assumed, whereas for FRP bars some formulas available in the literature are adopted to reproduce the delamination of the truss from the support. Two meaningful structural examples are considered to show the capabilities of the procedure proposed, namely a reinforced masonry deep beam (0°/90° continuous reinforcement) and a masonry beam in simple flexion for which experimental data are available. Good agreement is found between present model and alternative numerical approaches. © 2010 Elsevier Ltd. All rights reserved.

Floris C.,Polytechnic of Milan
Mechanics Research Communications | Year: 2011

This paper deals with the analysis of stability of a hinged-hinged viscoelastic column subjected to a non-zero mean stochastic axial force. The randomly variable part of this is described by a stationary Gaussian white noise process. The viscosity affects the curvature of the column, for which the classic Euler-Bernoulli's model is adopted. The viscosity is described by the linear Kelvin-Voigt's model. A dynamic stability analysis is performed. Normal modes are introduced in the integro-differential equation of motion so that uncoupled modal equations are retrieved. With reference to the first mode, by using an additional state variable, three Itô's ODE are obtained, from which the differential equations ruling the response statistical moment evolution are written by means of Itô's differential rule. The zero solution, that is undeformed straight column, corresponds to zero moments. If the column is perturbed, it is stable when the response moments tend to zero. A necessary and sufficient condition of stability in the moments of order r is that the matrix Ar of the coefficients of the ODE system ruling them has negative real eigenvalues and complex eigenvalues with negative real parts. Because of the linearity of the system the stability of the first two moments is the strongest condition of stability. If the mean axial force μP or the white noise intensity wP are increased, there exist critical values μPcr, wPcr for which almost an eigenvalue is positive. The critical mean axial force is found to be inversely proportional to the parameter φ∞, which measures the amount of viscous deformation. The search for the critical values of wP is made numerically, and several graphs are presented for a representative column. © 2010 Elsevier Ltd All rights reserved.

Airoldi A.,Polytechnic of Milan | Davila C.G.,NASA
Composite Structures | Year: 2012

Delamination processes often exhibit an increase in delamination resistance, or R-curve, with crack extension. It is shown that cohesive laws can represent the R-curves due to large-scale fibre bridging and that the shape of the cohesive laws can be derived from conventional experimental results. Two approaches are investigated for determining the shape parameters of cohesive laws. The first approach consists of extracting the cohesive parameters from experimental R-curves through the use of a new semi-analytical equation. The second approach consists of a numerical optimization procedure that identifies material parameters by reducing the error between a finite element model and the experimental load-deflection results. The second approach is advantageous when fibre bridging introduces inaccuracies in the experimental energy release rate measurements. In addition, the second approach can be extended to allow more complex approximations of cohesive laws. © 2012 Elsevier Ltd.

Valente M.,Polytechnic of Milan
Applied Mechanics and Materials | Year: 2012

This study investigates a displacement-based procedure for the seismic assessment and retrofitting of a six-storey RC structure, designed for gravity loads without specific earthquake-resistant provisions. The procedure is based on a simplified approach using nonlinear static pushover analyses and allows to compare alternative retrofitting strategies countering different structural deficiencies. Accurate numerical models were developed in order to provide reliable predictions of the behaviour of the building identifying the main structural deficiencies. Two retrofitting solutions based on alternative strategies were proposed for the RC structure. The introduction of concentric steel bracings decreased the displacement demand on the structure, thus reducing damage in structural members. A more uniform distribution of storey drift was observed throughout the height of the building. The application of FRP wrapping increased the deformation capacity of the columns and significantly enhanced the global ductility of the structure, without modifying the displacement demand. The validity of the simplified procedure and the effectiveness of the retrofitting interventions were assessed by nonlinear dynamic analyses. © (2012) Trans Tech Publications, Switzerland.

Pandolfi A.,Polytechnic of Milan | Vasta M.,University of Chieti Pescara
Mechanics of Materials | Year: 2012

In view of a more realistic description of the spatial distribution of the collagen fibers in soft biological tissues, for example the human cornea, we propose a material model alternative to the one based on generalized structure tensors, proposed by Gasser et al. (2006). We assume that the strain energy function depends on the mean value and on the variance of the pseudo-invariant I 4 of the distribution of the fibers. Indeed, the mean value was the only term considered in the original generalized structure tensor model. We derive the expression of the stress and of the consistent tangent stiffness of the new model and compare its mechanical response with the one of the original model for standard uniaxial, shear and biaxial tests. The comparisons are made with reference to the response of the exact fiber dispersed model, based on the direct integration of the contribution of the fibers. © 2011 Elsevier Ltd. All rights reserved.

Milani G.,Polytechnic of Milan | Lourenco P.B.,University of Minho
Journal of Engineering Mechanics | Year: 2013

The homogenized masonry nonlinear stress-strain curves obtained through the simple micromechanical model developed in the first part of the paper are here used for the analysis of strengthened masonry walls under various loading conditions. In particular, a deep beam and a shear wall strengthened with fiber-reinforced polymer (FRP) strips are analyzed for masonry loaded in-plane. Additionally, single and double curvature masonry structures strengthened in various ways, namely a circular arch with buttresses and a ribbed cross vault, are considered. For all the examples presented, both the nonstrengthened and FRPestrengthened cases are discussed. Additional nonlinear finite-element analyses are performed, modeling masonry through an equivalent macroscopic material with softening to assess the present model predictions. Detailed comparisons between the experimental data, where available, and numerical results are also presented. The examples show the efficiency of the homogenized technique with respect to (1) accuracy of the results; (2) low number of finite elements required; and (3) independence of the mesh at a structural level from the actual texture of masonry. © 2013 American Society of Civil Engineers.

Callegari S.,University of Bologna | Bizzarri F.,Polytechnic of Milan
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2013

The Noise Transfer Function (NTF) of ΔΣ modulators is typically designed after the features of the input signal. We suggest that in many applications, and notably those involving D/D and D/A conversion or actuation, the NTF should instead be shaped after the properties of the output/reconstruction filter. To this aim, we propose a framework for optimal design based on the Kalman-Yakubovich-Popov (KYP) lemma and semi-definite programming. Some examples illustrate how in practical cases the proposed strategy can outperform more standard approaches. © 2004-2012 IEEE.

Maffezzoni P.,Polytechnic of Milan
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2013

This paper describes an original nonlinear phase-domain macromodel of Injection-Locked Frequency Dividers which are driven by a nonlinear input device that produces heavy harmonic distortion. These non-harmonic frequency dividers can provide wide lock ranges, however their analysis is complicated by the strong nonlinear behavior for which the hypothesis of weak injection does not apply. The proposed approach consists in adopting a nonlinear model for the input section of the divider and in combining it with a Perturbation-Projection- Vector-based macromodel for the linear-time-varying section of the oscillator. The proposed macromodel is employed to predict the synchronization regions of an ILFD driven by several types of injected waveforms. In addition, closed-form expressions for the output phase-noise spectrum are also provided. © 2013 IEEE.

Rossella F.,University of Pavia | Soldano C.,University of Brescia | Bellani V.,University of Pavia | Tommasini M.,Polytechnic of Milan
Advanced Materials | Year: 2012

Metal-filled carbon nanotubes represent a novel class of photothermal nanomaterials: when illuminated by visible light they exhibit a strong enhancement of the temperature at the metal sites, due to the enhanced plasmonic light absorption at the metal surface, which behaves as a heat radiator. Potential applications include nanomedicine, heat-assisted magnetic recording, and light-activated thermal gradient-driven devices. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Jhawar R.,University of Milan | Piuri V.,University of Milan | Santambrogio M.,Polytechnic of Milan
IEEE Systems Journal | Year: 2013

The increasing popularity of Cloud computing as an attractive alternative to classic information processing systems has increased the importance of its correct and continuous operation even in the presence of faulty components. In this paper, we introduce an innovative, system-level, modular perspective on creating and managing fault tolerance in Clouds. We propose a comprehensive high-level approach to shading the implementation details of the fault tolerance techniques to application developers and users by means of a dedicated service layer. In particular, the service layer allows the user to specify and apply the desired level of fault tolerance, and does not require knowledge about the fault tolerance techniques that are available in the envisioned Cloud and their implementations. © 2007-2012 IEEE.

Valente M.,Polytechnic of Milan
Applied Mechanics and Materials | Year: 2012

This study investigates an innovative method based on low yield steel plate shear walls for seismic retrofitting of existing reinforced concrete (R/C) structures. A simplified numerical model of steel shear panels is developed for global analyses of multi-story R/C frames. The seismic performance of a non-ductile five-story R/C frame retrofitted with steel plate shear walls is evaluated in terms of drift control and energy dissipation capacity using nonlinear dynamic analyses. The results obtained by the application of two different story-wise distributions of steel plates are compared. In case of retrofitted frames a considerable decrease of the maximum top displacements is registered and the energy dissipated by the primary structural elements is significantly reduced for severe seismic actions. The energy dissipation concentrates in the steel panels, reducing the plastic demand on the structural members, along with the potential for structural damage. The different story-wise distributions of the steel panels change the damage distribution throughout the frame. The uniform arrangement of the steel panel thickness along the height of the frame causes a concentration of damage in the columns of the first story. In case of steel panel distribution proportional to story shear, the energy dissipation results more uniform over the height of the frame and a significant decrease of damage is registered for the columns of all the storeys. © (2012) Trans Tech Publications, Switzerland.

Valente M.,Polytechnic of Milan
Applied Mechanics and Materials | Year: 2012

This paper presents some results of a numerical study on the seismic performance and retrofitting of a R/C flat-slab prototype structure. The study was based on an experimental program carried out at the JRC ELSA Laboratory with the aim of assessing the seismic behaviour of flat-slab structures. Numerical models of the test structure were developed and nonlinear static and dynamic analyses were carried out. Two seismic retrofit techniques were numerically simulated to enhance the seismic performance of the structure. First the structure was rehabilitated by concrete jacketing of columns with added longitudinal and transverse reinforcement. The second intervention was based on confinement of column ends by using FRP wrapping. The results of this study provide information about the seismic performance of a common type of R/C structure not covered by the provisions of Eurocode 8, as well as the potential to mitigate the expected damage for varying earthquake intensity through retrofit. The comparison of the overall seismic response of the bare and rehabilitated structures showed the seismic performance improvements provided by the retrofitting interventions. © (2012) Trans Tech Publications, Switzerland.

Three masonry churches collapsed or severely injured during the 20-29 May 2012 earthquakes occurred in Emilia-Romagna, Italy are analyzed in detail from a numerical standpoint. A recently presented standalone 3D limit analysis code is utilized to evaluate failure mechanisms and horizontal acceleration causing the collapse. A comparison with the recent Italian Guidelines devoted to the safety assessment of monumental buildings is also provided. The horizontal acceleration associated to the first active failure mechanism is compared with that actually active during the 20-29 May shakes. A preliminary modal analysis is also conducted to evaluate vibration modes, to compare the numerical limit analysis acceleration with the spectral acceleration kept by the structures. © 2013 Elsevier Ltd.

Milani G.,Polytechnic of Milan | Tralli A.,University of Ferrara
International Journal of Solids and Structures | Year: 2012

A 3D model for the evaluation of the non-linear behavior of masonry double curvature structures is presented. In the model, the heterogeneous assemblage of blocks is substituted with a macroscopically equivalent homogeneous non-linear material. At the meso-scale, a curved running bond representative element of volume (REV) constituted by a central block interconnected with its six neighbors is discretized through of a few six-noded rigid wedge elements and rectangular interfaces. Non linearity is concentrated exclusively on joints reduced to interface, exhibiting a frictional behavior with limited tensile and compressive strength with softening. The macroscopic homogenous masonry behavior is then evaluated on the REV imposing separately increasing internal actions (in-plane membrane actions, meridian and parallel bending, torsion and out-of-plane shear). This simplified approach allows to estimate heuristically the macroscopic stress-strain behavior of masonry at the meso-scale. The non-linear behavior so obtained is then implemented at a structural level in a novel FE non-linear code, relying on an assemblage of rigid infinitely resistant six-noded wedge elements and non-linear interfaces, exhibiting deterioration of the mechanical properties. Several numerical examples are analyzed, consisting of two different typologies of masonry arches (a parabolic vault and an arch in a so-called "skew" disposition), a ribbed cross vault, a hemispherical dome and a cloister vault. To fully assess numerical results, additional non-linear FE analyses are presented. In particular, a simplified model is proposed, which relies in performing at a structural level a preliminary limit analysis - which allows to identify the failure mechanism - and subsequently in modeling masonry through elastic elements and non-linear interfaces placed only in correspondence or near the failure mechanism provided by limit analysis. Simulations performed through an equivalent macroscopic material with orthotropic behavior and possible softening are also presented, along with existing experimental evidences (where available), in order to have a full insight into the capabilities and limitations of the approach proposed. © 2011 Elsevier Ltd. All rights reserved.

Jenkins J.T.,Cornell University | Berzi D.,Polytechnic of Milan
Granular Matter | Year: 2012

We apply the continuum equations of a kinetic theory to predict the features of uniform, steady, inclined flows of identical, frictional, inelastic spheres over a rigid, bumpy base between vertical, frictional side walls. Numerical solutions of these equations over a range of mass flow rates exhibit features seen in physical experiments and numerical solutions in the absence of side walls. For the densest flows, we employ a phenomenological extension of kinetic theory that involves a length scale associated with particle correlations. When a dense flow is thick enough, an algebraic balance between the production and dissipation of fluctuation energy reproduces the relation between mass flow rate and mass hold-up obtained when solving the boundaryvalue problem of the extended theory. © Springer-Verlag 2012.

Fiasche M.,Polytechnic of Milan
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

This paper proposes a novel type of quantum-inspired evolutionary algorithm (QiEA) for numerical optimization inspired by the multiple universes principle of quantum computing, which is based on the concept and principles of quantum computing, such as a quantum bit and superposition of states. Numerical optimization problems are an important field of research with several applications in several areas: industrial plant optimization, data mining and many others, and although being successfully used for solving several optimization problems, evolutionary algorithms still present issues that can reduce their performances when faced with task where the evaluation function is computationally intensive. In order to address those issues the QiEA represent the most recent advance in the field of evolutionary computation. This work present some application about combinatorial and numerical optimization problems. © 2012 Springer-Verlag.

Butera F.M.,Polytechnic of Milan
Advances in Building Energy Research | Year: 2013

In the EU a Directive was adopted according to which after 31 December 2020 the construction of buildings that do not meet the requirement of being 'nearly zero (fossil) energy' will not be allowed. Today, only a few zero-energy buildings (ZEBs) exist, and they show that their design, construction and operation a dramatic challenge for many reasons. The first is that today's buildings require too much energy to work, and most of this energy is wasted because of their inappropriate architectural design. This means that architects have to change their design approach and find new ways of obtaining the same (or better) services with much lower energy need. Also mechanical engineers must change their approach, forgetting forever the practice of oversizing plants and systems, with a consequent unnecessary increase in costs and in energy consumption. Still, this is not enough: in order to design a ZEB a new professional must be added to the design team: the energy and comfort expert. This professional (actually a professional's team, given the complexity of the issue and the sophisticated simulation tools they have to manage) must be integrated right from the earliest phases of the design process. Moreover, the three professionals must work together in an interactive and iterative manner, making the definition of the concept design the most important phase of the entire design process. In other words, for ZEBs the so-called integrated design approach becomes a must. The challenge is not confined to the design phase, but extends to the operation: the best designed building may become an energy wasting one if it is not appropriately operated and if the occupants are not energy conscious. Finally, if we look with a wider perspective, not only Europe with its Directive, but also many other (probably all) countries will adopt the policy of ZEBs, and the number of these buildings will become significant, with a consequent impact on the electric system. In this framework, the issue of mismatch between instantaneous demand and supply of energy will be one of those issues that are crucial in the design, especially at the district scale. The above-mentioned issues are discussed and supported by examples of ZEBs. The design methodology and the technical solutions adopted will be described and the expected performances will be compared with the measured data after more than one year operation. © 2013 Copyright Taylor and Francis Group, LLC.

Cametti M.,Polytechnic of Milan | Rissanen K.,University of Jyvaskyla
Chemical Society Reviews | Year: 2013

The fluoride anion has recently gained well deserved attention among the scientific community for its importance in many fields of human activities, but also for concerns on its effect on health and the environment. Although surprisingly overlooked in systematic studies in the past, fluoride has nowadays become a topical target in the field of anion recognition. A multitude of scientific reports are published every year where the establishment of efficient and specific interaction with fluoride is sought in polar and aqueous media. Here, the emphasis is directed to a detailed description of the most interesting contemporary studies in the field, with a particular focus given to those published in the last few years. This journal is © The Royal Society of Chemistry.

Baeg K.-J.,Korea Electrotechnology Research Institute | Binda M.,Italian Institute of Technology | Natali D.,Italian Institute of Technology | Natali D.,Polytechnic of Milan | And 2 more authors.
Advanced Materials | Year: 2013

While organic electronics is mostly dominated by light-emitting diodes, photovoltaic cells and transistors, optoelectronics properties peculiar to organic semiconductors make them interesting candidates for the development of innovative and disruptive applications also in the field of light signal detection. In fact, organic-based photoactive media combine effective light absorption in the region of the spectrum from ultraviolet to near-infrared with good photogeneration yield and low-temperature processability over large areas and on virtually every substrate, which might enable innovative optoelectronic systems to be targeted for instance in the field of imaging, optical communications or biomedical sensing. In this review, after a brief resume of photogeneration basics and of devices operation mechanisms, we offer a broad overview of recent progress in the field, focusing on photodiodes and phototransistors. As to the former device category, very interesting values for figures of merit such as photoconversion efficiency, speed and minimum detectable signal level have been attained, and even though the simultaneous optimization of all these relevant parameters is demonstrated in a limited number of papers, real applications are within reach for this technology, as it is testified by the increasing number of realizations going beyond the single-device level and tackling more complex optoelectronic systems. As to phototransistors, a more recent subject of study in the framework of organic electronics, despite a broad distribution in the reported performances, best photoresponsivities outperform amorphous silicon-based devices. This suggests that organic phototransistors have a large potential to be used in a variety of optoelectronic peculiar applications, such as a photo-sensor, opto-isolator, image sensor, optically controlled phase shifter, and opto-electronic switch and memory. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Buffoli M.,Polytechnic of Milan
Annali di igiene : medicina preventiva e di comunità | Year: 2012

Hospitals are complex buildings because of their articulation, function, organization and technology equipment. Planning hospitals needs an interdisciplinary approach in order to organize efficiently the construction of qualitative and flexible units, that must be able to answer to all the requirements of different users and to the fast changes due to the research innovations. Human and care activities have a rapid progress, that creates a constant demand of modernizations of the hospitals and readjustment of the functional connections. Flexibility becomes the core of all the modifications depending on the progress of the medical science. The future challenge is to build structures that promote sustainable flexibility and also allow to achieve wellness in a synergic relation with complementary external activities. Therefore the research aims to identify lay-out models, technical and constructive solutions to guarantee different levels of flexibility. The research was made of different stages to define flexibility inside healthcare structures using strategies and technologies. The first step has followed the evolution of hospital structures during the centuries. It illustrates the most efficient methods and solutions used in last fifty years to achieve the flexibility. The second step was the analysis of the most important contemporaries healthcare structures. In that analysis, the hospitals will be compared through an evaluation matrix made by diferent flexibility levels that underlines the most efficient technologies and strategies used. At the end it was made a list of design indications focused on the definition of a new design approach that guarantees flexibility for these complex systems.

Langfelder G.,Polytechnic of Milan
Applied Optics | Year: 2012

The use of full color-sensitive photodetectors with three electrically tunable spectral responses allows the design of sensors that can be real-time reconfigured for different color acquisition modes. All the (physically identical) pixels can be biased in the same way, each giving the same set of RGB spectral responses: in this situation the conversion from the sensor color space to a reference color space can be implemented as usual, giving typical color errors ΔEa,b in the order of 2-3. Alternatively, pixels can be biased in two different ways (e.g., row by row), forming pairs: by joining the information from adjacent pixels, the sensor has six spectral responses, with a reduced resolution. By exploiting this plurality of spectral responses, color reproduction accuracy can be increased. In this work, an improved design of the Transverse Field Detector, a filterless and tunable three-color pixel, is used as the experimental device to propose a dual-color-mode reconfigurable sensor. © 2012 Optical Society of America.

Clark J.,University of Cambridge | Nelson T.,Los Alamos National Laboratory | Tretiak S.,Los Alamos National Laboratory | Cirmi G.,Massachusetts Institute of Technology | And 2 more authors.
Nature Physics | Year: 2012

Molecular conformational reorganization following photon absorption is a fundamental process driving reactions such as the cis-trans isomerization at the heart of the primary step of vision and can be exploited for switching in artificial systems using photochromics. In general, conformational change occurs on a timescale defined by the energy of the main vibrational mode and the rate of energy dissipation. Typically, for a conformational change such as a twist around the backbone of a conjugated molecule, this occurs on the tens of picoseconds timescale. However, here we demonstrate experimentally that in certain circumstances the molecule, in this case an oligofluorene, can change conformation over two orders of magnitude faster (that is sub-100 fs) in a manner analogous to inertial solvent reorganization demonstrated in the 1990s. Theoretical simulations demonstrate that non-adiabatic transitions during internal conversion can efficiently convert electronic potential energy into torsional kinetic energy, providing the 'kick' that prompts sub-100 fs torsional reorganization. © 2012 Macmillan Publishers Limited. All rights reserved.

Gibelli L.,Polytechnic of Milan
Physics of Fluids | Year: 2012

We present a kinetic theory derivation of higher-order slip boundary conditions. The situation studied is that of a pressure driven isothermal gas flowing through a plane microchannel. The distribution function is expanded in terms of half-range Hermite polynomials and the system of moment equations in the expansion coefficients is analytically solved. The velocity slip coefficients, as well as their Knudsen-layer corrections, are obtained by evaluating the solution in the near continuum limit. The proposed approach is accurate and easy to implement. The results are presented for the hard-sphere Boltzmann equation and Maxwell's diffuse-specular boundary conditions, but can be extended to arbitrary intermolecular interactions and more general scattering kernels. © 2012 American Institute of Physics.

Fabrizio M.,University of Bologna | Giorgi C.,University of Brescia | Pata V.,Polytechnic of Milan
Archive for Rational Mechanics and Analysis | Year: 2010

We discuss a novel approach to the mathematical analysis of equations with memory, based on a new notion of state. This is the initial configuration of the system at time t = 0 which can be unambiguously determined by the knowledge of the dynamics for positive times. As a model, for a nonincreasing convex function G: ℝ + → ℝ + such that we consider an abstract version of the evolution equation ∂ttu(x, t) - [G(0)u(x, t)+ ∫∞ 0 G′(S)u(x,t - s)ds] = 0 arising from linear viscoelasticity. © 2010 Springer-Verlag.

Adhikari R.S.,Polytechnic of Milan
Journal of Green Building | Year: 2012

The most suitable intervention for energy rehabilitation of historical buildings has to reach both the goal of the optimization of the energy saving and the preservation of the original characteristics of the building. The present work is related to refurbishment and energy rehabilitation of an historical building dating back to 15th century. The building complex under study is an ancient residential courtyard building located in Northern Italy near Verona. The strategies have been focused on the building envelope and energy supply systems respecting both the regulatory constraints imposed by preservation of historical buildings and, where possible, the current national legislation about the building energy efficiency. This result was achieved only through the identification of best solutions based on mutual compatibility and optimization of the performance of the building envelope and the HVAC systems. In the design phase, the thermal performance of the building for both winter and summer periods have been evaluated by dynamic computer simulations. It has been shown that adequate interventions focused on the building envelope and HVAC systems reduces the energy consumption in a significant way. Further, it has been shown through economical analysis that extra-costs for energy retrofit measures paid back quickly during the life span of the building. Historical buildings are characterized by unique and specific characters that could be preserved, also upgrading them to modern requirements. This study demonstrates how it is possible to intervene effectively (and correctly by the historical and architectural point of view) on the energy performance of ancient buildings. By applying innovative techniques and technologies, in fact, it is possible to achieve high energy efficiency levels, without affecting the original architectural appearance and value. The methodology presented can be an interesting case study for all those building interventions where energy, cultural and historical issues intersect.

Nardi P.,Polytechnic of Milan
Utilities Policy | Year: 2012

The European Commission's proposal to unbundle electricity transmission network encouraged a great debate among involved players. Mainstream economists suggest that unbundling of both the transmission network and the interconnections can be seen as a structural solution to the problem of low investments in the grid and consequent high concentration of markets in favour of incumbents (among others, Léautier, 2001). Other scholars point out that benefits have to be compared to costs of unbundling (Kwoka, 2002). Recent literature underlines that net effect is ambiguous; more empirical evidence is needed (Pollitt, 2008). This paper proposes an empirical analysis to evaluate whether, and to what extent, unbundling measures are related to the increase of grid investments, focussing on 14 UCTE countries between 2001 and 2010. Results are twisted: legal and ownership unbundling show higher investments in the network, although, only for ownerhip unbundling, a substantial lack of quality emerges, confirming the risks of diseconomies of coordination in ownership unbundled systems and the need of incentive regulation. © 2012 Elsevier Ltd.

Angelino G.,Polytechnic of Milan | Invernizzi C.M.,University of Brescia
Applied Thermal Engineering | Year: 2011

When using the cooling capacity of LNG several thermodynamic schemes are proposable employing conventional and non conventional conversion cycles. All conventional systems make use of organic working fluids such as methane or propane in series of Rankine cycles used in a cascading mode. A simpler system is available, using a single cycle and a single fluid in a Brayton cycle. However ordinary Brayton cycles exhibit a modest efficiency. Resorting to Brayton cycles with strong real gas effects (which is possible selecting the base parameters of pressure and temperature in the vicinity of the critical point) improves considerable cycle performance. Since the level of cold in a LNG flow is thermodynamically predetermined, working fluids must be selected with a critical point which fit the LNG thermal capacity, i.e. some 5-15 C higher than the usual LNG temperature which is around -160 °C. Nitrogen was found as the best fluid to exploit real gas effects with efficiencies above 63% while perfect gas cycles give efficiencies around 56%. However, in real gas cycles the cooling capacity of LNG is only partially exploited: a better exploitation is obtained from perfect gas cycles or for more complex cascading Rankine cycle. Selecting working fluids with a higher critical temperature than nitrogen, as for example argon, the efficiency decreases to 58% respect to 63% for nitrogen, but the utilization of the cold of LNG improves from 0.30 MW/(kg/s) to 0.75 MW/(kg/s). Obviously as heat rejection temperature increases a larger fraction of cold in the LNG flow can be utilized. Combined cycles making use of a gas turbine offer also a good performance. The merits of real gas effect Brayton cycles also in this case remains evident. Finally, it is theoretically possible to use real gas effect Brayton cycles at low temperatures, which are typical of waste heat (say 100-150 °C: in this case cycle efficiency remain good, but power obtainable from a unit flow of LNG is modest. © 2010 Elsevier Ltd. All rights reserved.

Lanzarone E.,CNR Institute for Applied Mathematics and Information Technologies | Matta A.,Polytechnic of Milan | Sahin E.,Ecole Centrale Paris
IEEE Transactions on Systems, Man, and Cybernetics Part A:Systems and Humans | Year: 2012

In recent years, home care (HC) service systems have been developed as alternatives to conventional hospitalization. Many resources are involved in delivering HC service, including different categories of human resources, support staff, and material resources. One of the main issues encountered while planning human HC resources is the patient assignment problem, i.e., deciding which operator(s) will take care of which admitted patient given some sets of constraints (e.g., the continuity of care). This paper addresses the resource assignment problem for HC systems. A set of mathematical programming models to balance the workloads of the operators within specific categories are proposed. The models consider several peculiarities of HC services, such as the continuity of care constraint, operators' skills, and the geographical areas which patients and operators belong to. Given the high variability of patient demands, models are developed under the assumption that patients' demands are either deterministic or stochastic. The analysis of the results obtained from a real case study demonstrates the applicability of the proposed models as well as the benefits that stem from applying them. Moreover, the obtained results show that an acceptable level of continuity of care cannot be obtained without modeling the continuity of care as a hard constraint. The analysis under continuity of care also shows the high value of information and the difficulties of fully balancing workloads with the application of standard techniques. © 2012 IEEE.

Simonov M.,Istituto Superiore Mario Boella | Simonov M.,Polytechnic of Milan
IEEE Transactions on Smart Grid | Year: 2014

An energy distribution network is a critical infrastructure that any compromise has an enormous impact on daily lives and the economy. The objective of this work is a computerized tool for distributed monitoring, dynamic re-configuration and control of DC distribution topology. This paper describes the double bar bus DC system exploiting the event-driven, service-oriented architecture, and real-time metering with nonuniform time sampling as an example of neighborhood optimization. We build a system with the capability to assess the resilience of and to rebuild better resilient grid partitions at run-time. The result is an intelligent system distributing loads between two buses dynamically in a way to keep self-sustainable and/or non-interruptible portion running at one bus by moving few other loads to the second bus. In standalone modality, the tool assesses the survivability of microgrid with high penetration of renewable energy. Running in cooperation with grid management tools, the same software can reconfigure optimally the local topology at run-time. © 2010-2012 IEEE.

Manca D.,Polytechnic of Milan
Computers and Chemical Engineering | Year: 2013

A feasibility study of a new plant or even of a revamped one bases the forecast of incomes and outcomes on a discounting back approach. This means that both prices and costs of commodities (i.e. raw materials and products) are assumed constant for long time-horizons. Commodities together with utilities play a major role in the economic assessment of OPEXs (operative expenditures). The paper tackles the "discounting back" problem that sees a coming apart between the dynamics of real market prices/costs (subject to fluctuations, volatility, and the "supply and demand" law) and the constant prices/costs assumed in conventional feasibility studies. The manuscript presents and discusses a methodology to model the time evolution of prices and costs of commodities for the feasibility-study framework of dynamic conceptual design. It also provides an improved methodology respect to direct Monte Carlo sampling of quotations over historical ranges, which is effective for repeated design optimization. © 2013 Elsevier Ltd.

Manca D.,Polytechnic of Milan
Computer Aided Chemical Engineering | Year: 2013

The Electric Energy (EE) price plays a significant role in the economic assessment of chemical and more in general of industrial processes. As far as both short-term and long-term economic predictions are required (such as in planning, scheduling, supply chain, on-line optimization, and conceptual design) the estimation of future prices of EE calls for a mathematical model capable of forecasting the price values according to the intrinsic features of the electric market. The paper presents and discusses a methodology to deploy a quantitative econometric model that describes the deterministic dynamic attributes of EE price. © 2013 Elsevier B.V.

Barazzetti L.,Polytechnic of Milan
Photogrammetric Engineering and Remote Sensing | Year: 2016

This paper presents a novel strategy for object-based change detection using very high spatial resolution (VHR) satellite images captured under variable off-nadir view angles. The variable off-nadir angle, along with weak absolute orientation, generates spurious slivers during the multitemporal comparison of classification results. The proposed solution for accurate object-to-object comparison is based on an intermediate registration of objectbased classification results with a piecewise affine transformation followed by robust, geometry-based techniques for sliver removal. Although different remote sensing applications require different strategies and methods for object-based change detection, the approach developed in this paper can overcome the overall limitation introduced by the slivers generated by weak geo-localization, variable off-nadir angles, and image segmentation. © 2015 American Society for Photogrammetry and Remote Sensing.

Mazzarella L.,Polytechnic of Milan
Energy and Buildings | Year: 2015

The building sector is one of the key consumers of energy in Europe; consequently, European Union has enacted several directives dealing, directly and indirectly, with energy efficiency in building aiming to reduce the buildings energy use. Those directives, while dealing with existing buildings, do not take care of the Architectural Heritage in a specific uniform way adopting the derogation regime: exceptions are available at the national level to exclude from their application buildings listed in the Architectural Heritage as historic buildings. Thus any country can adopt its own rules to include or exclude buildings from respecting the energy efficiency requirements for existing buildings. Consequently, up to now no general rules, codes and standards are available for energy retrofit of historical and architectural valuable buildings. On the other side, no international act, in the field Architectural Heritage conservation, deals with energy and energy retrofit. Furthermore, the European Union Treaty does not comprise the Cultural Heritage as matter of European legislation. Thus to cover this gap between historic/historical building and energy retrofit a lobbying action is needed, managed by the national Cultural Heritage authorities, which can steers EU policy in a more effective way towards energy retrofit of historic/historical buildings. © 2014 Elsevier B.V. All rights reserved.

Grillo S.,Polytechnic of Milan | Marinelli M.,University of Genoa | Massucco S.,University of Genoa | Silvestro F.,University of Genoa
IEEE Transactions on Smart Grid | Year: 2012

The paper proposes the modeling and the optimal management of a hot-temperature (sodium nickel chloride) battery system coupled with wind generators connected to a medium voltage grid. A discrete-time model of the storage device reproducing the battery main dynamics (i.e., state of charge, temperature, current, protection, and limitation systems) has been developed. The model has been validated through some experimental tests. An optimal management strategy has been implemented based on a forward dynamic programming algorithm, specifically developed to exploit the energy price arbitrage along the optimization time horizon (generation shifting). Taking advantage of this strategy wind generation performances can be enhanced and adapted to load demand, obtaining an increased economic gain measured by the difference between the economic revenue obtained with and without the proposed generation shifting policy. © 2012 IEEE.

Bianchini M.,Polytechnic of Milan | Glatzel P.,European Synchrotron Radiation Facility
Journal of Synchrotron Radiation | Year: 2012

A program that helps to plan experiments where the emitted X-rays are detected is presented. The tool is based on the standard formula for fluorescence-detected X-ray absorption spectroscopy and uses tabulated parameters to estimate count rates. The objective is to evaluate the feasibility of an experiment, estimate the influence of self-absorption on the spectral shape and investigate the possibility of range-extended EXAFS. The occurrence of negative edges, i.e. a decrease in the detected signal, is discussed. © 2012 International Union of Crystallography Printed in Singapore-all rights reserved.

Rulli M.C.,Polytechnic of Milan | D'Odorico P.,University of Virginia
Geophysical Research Letters | Year: 2013

The increasing global demand for food, fibers, and biofuels has made investments in agriculture a priority for some governments and corporations eager to expand their agricultural production while securing good profits. Here we calculate the water appropriation associated with land deals at different negotiation and implementation stages. Using estimates of actual and potential evapotranspiration for the crops planted in the acquired land, we calculate the green and blue water appropriated by land investors under a variety of irrigation scenarios. We also determine the grey water footprint as the amount of water required to dilute to allowable standards the pollution resulting from fertilizer applications. We found that about 380 × 109 m 3 yr-1 of rainwater is appropriated with the 43 million ha of reported contract area acquired by agri-investors (>240 × 10 9 m3 yr-1 in the 29 million ha of foreign acquisitions only). This water would be sufficient to feed ≈ 300-390 million people. Key Points Land and water grabbing are occurring at alarming rates. Grabbed water would be sufficient to improve food security in grabbed countries. Water grabbing is associated with water withdrawals increase ©2013. American Geophysical Union. All Rights Reserved.

Ghezzi C.,Polytechnic of Milan
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Software is constantly evolving. Evolution becomes necessary to respond to changes that may occur in the requirements and/or in the environment in which it is embedded. A consequence of changes is that several activities (such as analysis, verification, code generation, deployment) need to be redone, over and over. This paper focuses on verification. Incrementality comes into play because often changes are local to restricted parts. In order to save time, it would be beneficial if instead of redoing activities from scratch after each change, the results of previous processing may be reused and composed with the results of processing restricted portions of the changed software. Incrementality becomes even more necessary when changes occur at runtime and the software itself is responsible for reacting in a self-managed manner. In this setting, the processing that needs to be performed after each change is subject to severe time constraints. The paper is a position statement on incrementality in the context of self-adaptive systems. It starts by motivating the need for incrementality and then reviews three main approaches to incremental verification that have been proposed earlier, compares their potential, and outlines promising research directions. © 2012 Springer-Verlag.

Figini R.,ENEL S.p.A | Paolucci R.,Polytechnic of Milan | Chatzigogos C.,Geodynamique et Structure
Earthquake Engineering and Structural Dynamics | Year: 2012

In this paper, different formulations of a macro-element model for non-linear dynamic soil-structure interaction analyses of structures lying on shallow foundations are first reviewed, and secondly, a novel formulation is introduced, which combines some of the characteristics of previous approaches with several additional features. This macro-element allows one to model soil-footing geometric (uplift) and material (soil plasticity) non-linearities that are coupled through a stiffness degradation model. Footing uplift is introduced by a simple non-linear elastic model based on the concept of effective foundation width, whereas soil plasticity is treated by means of a bounding surface approach in which a vertical load mapping rule is implemented. This mapping is particularly suited for the seismic loading case for which the proposed model has been conceived. The new macro-element is subsequently validated using cyclic and dynamic large-scale laboratory tests of shallow foundations on dense sand, namely: the TRISEE cyclic tests, the Public Works Research Institute and CAMUS IV shaking table tests. Based on this comprehensive validation process against a set of independent experimental results, a unique set of macro-element parameters for shallow foundations on dense sand is proposed, which can be used to perform predictive analyses by means of the present model. © 2011 John Wiley & Sons, Ltd.

Ghezzi A.,Polytechnic of Milan
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Future Internet evolution requires innovative strategic stances and the design of original business models from actors involved in the ecosystem. The study focuses on Internet Carriers, recently striving to make their business sustainable, and proposes to enclose in a single reference framework all the critical levers, either consolidated or innovative, such actors can employ in order to design their value proposition, value network integration, and financial configuration. The framework grounds its findings on multiple case studies, and, by presenting an insightful list of business model parameters for Carriers, sheds light on key emerging strategic and tactical trends in the Internet interconnections market. © 2012 IFIP International Federation for Information Processing.

Maestri M.,Fritz Haber Institute | Maestri M.,Polytechnic of Milan | Reuter K.,Fritz Haber Institute | Reuter K.,TU Munich
Angewandte Chemie - International Edition | Year: 2011

A calculated approach: A significant improvement in the accuracy of UBI-QEP method has been achieved by using a modified parameterization procedure. The coverage dependence is now fully reproduced and the obtained activation barriers fall within 10a% for a range of reactions included in the data set (see example of OH dissociation on a Rh(111) surface; solid lines DFT reference, dashed lines UBI-QEP, dotted lines modified UBI-QEP, ML=monolayer). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cusimano G.,Polytechnic of Milan
Mechanism and Machine Theory | Year: 2013

This paper deals with the choice of motor and transmission with reference to the dynamic operating range of the motor and to the general case in which there is alternation of the power direction through the reducer. The paper proposes a method in which the resolving diagrams are obtained starting from the distinction between two different load torques, characterized by only direct and only inverse efficiency of the transmission respectively. In order to make the correct choice of the reducer to be coupled with a given motor, the paper also proposes a diagram that relates the transmission ratio and both the efficiencies. The guidelines for an automatized identification of all the admissible drive system-transmission couples are delineated and an industrial case study is discussed. © 2013 Elsevier Ltd.

Piccardi C.,Polytechnic of Milan
PLoS ONE | Year: 2011

Identifying communities (or clusters), namely groups of nodes with comparatively strong internal connectivity, is a fundamental task for deeply understanding the structure and function of a network. Yet, there is a lack of formal criteria for defining communities and for testing their significance. We propose a sharp definition that is based on a quality threshold. By means of a lumped Markov chain model of a random walker, a quality measure called "persistence probability" is associated to a cluster, which is then defined as an "α-community" if such a probability is not smaller than α. Consistently, a partition composed of α-communities is an "α-partition." These definitions turn out to be very effective for finding and testing communities. If a set of candidate partitions is available, setting the desired α-level allows one to immediately select the α-partition with the finest decomposition. Simultaneously, the persistence probabilities quantify the quality of each single community. Given its ability in individually assessing each single cluster, this approach can also disclose single well-defined communities even in networks that overall do not possess a definite clusterized structure. © 2011 Carlo Piccardi.

Bombarda P.,Polytechnic of Milan | Invernizzi C.M.,University of Brescia | Pietra C.,University of Brescia
Applied Thermal Engineering | Year: 2010

In the context of heat recovery for electric power generation, Kalina cycle (a thermodynamic cycle using as working fluid a mixture of water and ammonia) and Organic Rankine Cycle (ORC) represent two different eligible technologies. In this work a comparison between the thermodynamic performances of Kalina cycle and an ORC cycle, using hexamethyldisiloxane as working fluid, was conducted for the case of heat recovery from two Diesel engines, each one with an electrical power of 8900 kWe. The maximum net electric power that can be produced exploiting the heat source constituted by the exhaust gases mass flow (35 kg/s for both engines, at 346 °C) was calculated for the two thermodynamic cycles. Owing to the relatively low useful power, for the Kalina cycle a relatively simple plant layout was assumed. Supposing reasonable design parameters and a logarithmic mean temperature difference in the heat recovery exchanger of 50 °C, a net electric power of 1615 kW and of 1603 kW respectively for the Kalina and for the ORC cycle was calculated. Although the obtained useful powers are actually equal in value, the Kalina cycle requires a very high maximum pressure in order to obtain high thermodynamic performances (in our case, 100 bar against about 10 bar for the ORC cycle). So, the adoption of Kalina cycle, at least for low power level and medium-high temperature thermal sources, seems not to be justified because the gain in performance with respect to a properly optimized ORC is very small and must be obtained with a complicated plant scheme, large surface heat exchangers and particular high pressure resistant and no-corrosion materials. © 2009 Elsevier Ltd. All rights reserved.

Donati S.,University of Pavia | Donati S.,National Chung Hsing University | Norgia M.,Polytechnic of Milan
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2014

Self-mixing interferometry is a noncontact method well suited for measuring a variety of biological signals, like blood pressure wave at wrist and thorax (the optical stethoscope), blood velocity in vein and in external circulation, THz echoes from skin, ear drum vibration, and oculomotor reflex measurements. In this review, after presenting the underlying theory and the main developments of self-mixing, we analyze the applications to biosignal measurement reported so far, and illustrate potentialities and perspectives of the technique. © 2013 IEEE.

Capolongo S.,Polytechnic of Milan
Annali di igiene : medicina preventiva e di comunità | Year: 2013

This paper proposes an innovative and transparent methodology to support the "ASL Milano" (Local Health Agency) in the hygiene and health evaluation of construction projects, in order to highlight their positive and negative performance beyond the requirements imposed by the current laws and regulations regarding buildings' hygiene performance, which are too old and therefore unsuitable to ascertain the real quality of indoor environments. The compliance with laws or regulations, mostly out of date, and the assessment of performance involving only a part of the current emerging needs and problems, in fact, should be considered as a necessary, although not a sufficient step, to ensure high quality indoors. Consequently, it is necessary to identify and test an assessment tool which could provide an effective and flexible support for the development of hygiene and health statements regarding projects at building scale (new construction, conversion of the existing, rehabilitation, extension, change of use, etc). The assessment tool suggested by this paper is tailored for the metropolitan area of the city of Milan, but its evaluation framework could be developed and applied to other contexts.

In a previous paper [1], it was proved how total ignorance can be effectively represented, in Shafer's theory of evidence [2], by a rectangular possibility distribution. In addition, it was shown how this concept can be usefully employed to mathematically represent situations that are often met in the measurement practice, especially in the industrial world [3]. The aim of this new paper is to show how possibility distributions can be effectively used to represent any kind of knowledge, from total ignorance to total evidence, and combine different contributions, if necessary. © 1998-2012 IEEE.

Milani A.,Polytechnic of Milan
Journal of Physical Chemistry B | Year: 2015

Exploiting the very recent potentialities of state-of-the-art quantum chemical simulations of crystalline solids, unpolarized Raman spectra of α and γ polymorphs of Nylon-6 obtained through periodic density functional theory calculations are presented for the first time. The computed spectra are compared with the experimental spectra reported in the literature and allow a detailed interpretation to be proposed of the patterns observed, identifying unambiguous Raman marker bands of the different phases. The calculations of single crystal directional intensities gave the further possibility to predict the polarization properties of the Raman spectra of these polymorphs: considering in particular the α phase, polarized Raman spectra have been computed and showed a very good agreement with measurements previously reported for uniaxially oriented samples. © 2015 American Chemical Society.

Petti D.,Polytechnic of Milan
Nature Nanotechnology | Year: 2016

The search for novel tools to control magnetism at the nanoscale is crucial for the development of new paradigms in optics, electronics and spintronics. So far, the fabrication of magnetic nanostructures has been achieved mainly through irreversible structural or chemical modifications. Here, we propose a new concept for creating reconfigurable magnetic nanopatterns by crafting, at the nanoscale, the magnetic anisotropy landscape of a ferromagnetic layer exchange-coupled to an antiferromagnetic layer. By performing localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are reversibly patterned without modifying the film chemistry and topography. This opens unforeseen possibilities for the development of novel metamaterials with finely tuned magnetic properties, such as reconfigurable magneto-plasmonic and magnonic crystals. In this context, we experimentally demonstrate spatially controlled spin wave excitation and propagation in magnetic structures patterned with the proposed method. © 2016 Nature Publishing Group

Buscarnera G.,Northwestern University | di Prisco C.,Polytechnic of Milan
Geotechnique Letters | Year: 2011

This letter focuses on the mechanical conditions governing the initiation of landslides in unsaturated shallow slopes. The goal is to provide mathematical criteria for predicting the onset of slope instabilities and capturing the interplay between saturation conditions and shear failure. For this purpose, the standard scheme of infinite slope is used and the mechanical response of the deposit is represented through simple shear kinematics. This assumption enables the study of different perturbation scenarios using a modelling strategy that: (i) incorporates the constraints describing the interaction with the pore fluids into the control conditions and (ii) allows the analytical derivation of stability indices for each scenario. The theoretical results show that, in unsaturated slopes, the coupling between the solid skeleton and the pore fluid can exacerbate the tendency to undergo mechanical instabilities. This general aspect is clearly disclosed by the analytical expression of the stability index for water-undrained shearing. It is found that, because of hydro-mechanical coupling, the failure mode originated by these perturbations embodies some characteristics of both shear localisation and static liquefaction. As a result, depending on soil properties and initial conditions, the unstable response resulting from its activation can resemble either phenomena and predictive models are necessary to distinguish between the two scenarios.

Pagani M.,Comsol S.r.l | Perego U.,Polytechnic of Milan
Computer Methods in Applied Mechanics and Engineering | Year: 2015

The intentional or accidental cutting of thin shell structures by means of a sharp object is of interest in many engineering applications. The process of cutting involves several types of nonlinearities, such as large deformations, contact, crack propagation and, in the case of laminated shells, delamination. In addition to these, a special difficulty is represented by the blade sharpness, whose accurate geometric resolution would require meshes with characteristic size of the order of the blade curvature radius. A computational finite element approach for the simulation of blade cutting of thin shells is proposed and discussed. The approach is developed in an explicit dynamics framework. Solid-shell elements are used for the discretization, in view of possible future inclusion in the model of delamination processes. Since a sharp blade can interfere with the transmission of cohesive forces between the crack flanks in the cohesive process zone, standard cohesive interface elements are not suited for the simulation of this type of problems unless extremely fine meshes, with characteristic size comparable to the blade curvature radius, are used. To circumvent the problem, the use of a new type of directional cohesive interface element, previously proposed for the simulation of crack propagation in elastic shells, is further developed and reformulated for application to the cutting of elastoplastic thin structures, discretized by solid-shell elements. The proposed approach is validated by means of application to several cutting problems of engineering interest. © 2014 Elsevier B.V.

Casella F.,Polytechnic of Milan | Colonna P.,Technical University of Delft
Applied Thermal Engineering | Year: 2012

Integrated Gasification Combined Cycle (IGCC) power plants are an effective option to reduce emissions and implement carbon-dioxide sequestration. The combination of a very complex fuel-processing plant and a combined cycle power station leads to challenging problems as far as dynamic operation is concerned. Dynamic performance is extremely relevant because recent developments in the electricity market push toward an ever more flexible and varying operation of power plants. A dynamic model of the entire system and models of its sub-systems are indispensable tools in order to perform computer simulations aimed at process and control design. This paper presents the development of the lumped-parameters dynamic model of an entrained-flow gasifier, with special emphasis on the modeling approach. The model is implemented into software by means of the Modelica language and validated by comparison with one set of data related to the steady operation of the gasifier of the Buggenum power station in the Netherlands. Furthermore, in order to demonstrate the potential of the proposed modeling approach and the use of simulation for control design purposes, a complete model of an exemplary IGCC power plant, including its control system, has been developed, by re-using existing models of combined cycle plant components; the results of a load dispatch ramp simulation are presented and shortly discussed. © 2011 Elsevier Ltd. All rights reserved.

Martelli E.,Polytechnic of Milan | Nord L.O.,Norwegian University of Science and Technology | Bolland O.,Norwegian University of Science and Technology
Applied Energy | Year: 2012

One option for pre-combustion CO2 capture in power plants is the integrated reforming combined cycle (IRCC). IRCCs have previously been studied from multiple viewpoints: thermo-economic analysis, process optimization, environmental impact, and plant flexibility. This paper is focused on the design of the heat recovery steam cycle (HRSC), including the heat recovery steam generator (HRSG), and aims to define the optimal steam cycle configurations for plant efficiency and dual-fuel flexibility. A recently developed optimization algorithm was successfully applied to obtain a set of flexible and efficient designs for IRCCs. Results showed that the preferred designs consisted of a dual-pressure level HRSG with reheat and limited supplementary firing in duct burners, high-pressure evaporators and economizers in the syngas coolers, limited high-pressure level (140-154bar), and feedwater preheating. The most attractive optimized dual-pressure designs showed improvements of approximately 0.5% points in the net plant efficiency compared to the non-optimized base case. The resulting net plant efficiency was about 45.8% with a net power output of around 425MW for the best cases. © 2011 Elsevier Ltd.

Reguzzoni M.,Polytechnic of Milan | Sampietro D.,GReD s.r.l
International Journal of Applied Earth Observation and Geoinformation | Year: 2015

The boundary between Earth's crust and mantle is commonly modelled as a discontinuity surface, theso-called Moho. Although in some regions of the world this model may be too approximate or evenunrealistic, globally speaking it can provide a key to read several long wavelength geophysical signals. Recent research activities have shown the possibility to estimate the Moho discontinuity worldwide from global gravity field model, however usually the solution of this inverse problem requires strong unrealistic hypotheses. In this work a new procedure to relax some of these unrealistic hypotheses is devised and described indetails. Basically it allows to estimate the mean Moho depth even once the normal gravitational field isremoved if at least one seismic observation is available, to take into account the dependency of the crust density on the radial direction (usually neglected in Moho depth determination from gravity), to correctthe a-priori density model of the crystalline crust for scale factors again using seismic information andfinally to consider a Moho with a non-constant depth as reference surface in the inversion, thus reducing the linearization error. The new procedure is here applied to GOCE data to estimate a new crustal model. For this purpose additional external information has been used, such as topography, bathymetry and ice sheet modelsfrom ETOPO1, a recent 1° × 1° sediment global model and some prior hypotheses on crustal density. Inparticular the main geological provinces, each of them characterized by its own relation between densityand depth, have been considered. A model describing lateral density variations of the upper mantle isalso taken into account.The new crustal model is computed at a spatial resolution of 0.5°× 0.5°, its gravitational effect differs from GOCE observations of 49 mE and its Moho depth error standard deviation is globally of 3.4 km. Therefore the result seems to be an improvement in terms of resolution, consistency with the gravity field and accuracy not only with respect to previously released GEMMA models, but also with respect tothe current state-of-the-art global knowledge of the Earth crust. © 2014 Elsevier B.V.

Dozio L.,Polytechnic of Milan
Composite Structures | Year: 2011

This work presents accurate upper-bound solutions for free in-plane vibrations of single-layer and symmetrically laminated rectangular composite plates with an arbitrary combination of clamped and free boundary conditions. In-plane natural frequencies and modes shapes are calculated by the Ritz method with a simple, stable and computationally efficient set of trigonometric functions. Reliability of the method is assessed by comparison with known accurate solutions for isotropic plates and specially orthotropic single laminates. The extensive results presented here for the first time can be considered benchmark data against which other methods may be compared and validated in the future. Influence of fiber orientation, stacking sequence, degree of orthotropy, aspect ratio and boundary conditions upon the inplane vibration behavior are also discussed. © 2011 Elsevier Ltd.

Biondini F.,Polytechnic of Milan
Structure and Infrastructure Engineering | Year: 2015

A three-dimensional reinforced concrete (RC) deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion is presented in this study. The finite element formulation accounts for both material and geometrical nonlinearity. Damage modelling considers uniform and pitting corrosion and includes the reduction of cross-sectional area of corroded bars, the reduction of ductility of reinforcing steel and the deterioration of concrete strength due to splitting cracks, delamination and spalling of the concrete cover. The beam finite element is validated with reference to the results of experimental tests carried out on RC beams with corroded reinforcement. The application potentialities of the proposed formulation are shown through the finite element analysis of a statically indeterminate RC beam and a three-dimensional RC arch bridge under different damage scenarios and corrosion penetration levels. The results indicate that the design for durability of concrete structures exposed to corrosion needs to rely on structural analysis methods capable to account for the global effects of local damage phenomena on the overall system performance. © 2014, © 2014 Taylor & Francis.

Bruggi M.,Polytechnic of Milan
Structural and Multidisciplinary Optimization | Year: 2014

An alternative numerical approach is presented for the analysis of no–tension masonry–like solids. Whereas most of the strategies available in the literature resort to non–linear finite element techniques, the proposed approach re–formulates the problem within the framework of topology optimization. The equilibrium of a two–dimensional no–tension body is found searching for the distribution of an equivalent orthotropic material, in which tensile principal stresses are not allowed by prescribing negligible stiffness in the relevant direction, such that the potential energy of the solid is minimized. Unlike many conventional approaches that deal with the tough non–linearity of the problem through step–wise incremental analyses, the proposed method efficiently solves the effect of compatible loads through a one–shot energy–based optimization. Analytical and numerical benchmarks from the literature are investigated to assess the effectiveness of the proposed procedure and to discuss convergence features and possible applications inspired by the limit analysis of masonry–like structures. © 2014, Springer-Verlag Berlin Heidelberg.

Filippini M.,Polytechnic of Milan
Procedia Engineering | Year: 2011

The high temperature notched fatigue strength of the CMSX-4 single crystal superalloy has been experimentally investigated. Notched specimens with orientation <001> have been tested at 950°C in load control in the LCF life regime. SEM observations of the failed specimens has been made in order to associate the actual crack initiation location in the notch to the crystallographic orientation and to the critical location in the notch as given by suitable multiaxial fatigue parameters. In order to model the material behavior in the notch, stress-strain analysis of the notched specimens was performed by an elastic-plastic FEM procedure; the parameters describing the material behavior of the single crystal superalloy have been identified by comparison with experimentally determined stressstrain fatigue behavior of smooth specimens. A suitable model for the assessment of the fatigue life of single crystal materials is proposed for the purpose of application to the design of turbine engines components. © 2011 Published by Elsevier Ltd.

Maffezzoni P.,Polytechnic of Milan
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2012

This paper describes an original experimental procedure to extract the phase-sensitivity of oscillators to noise perturbations. The proposed method relies on measuring the width of the locking ranges over which the oscillator's response synchronizes with injected small-amplitude signals. It is shown that this sensitivity function can be employed to accurately predict how inner noise sources are transferred to output phase-noise and jitter. The extraction procedure is applied to a relaxation oscillator that exhibits a strongly nonlinear behavior. © 2011 IEEE.

Codecasa L.,Polytechnic of Milan
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2012

In this paper and in its companion, a novel cut-based decomposition for transfer functions of linear time-invariant circuits is introduced and an invariance property, with respect to the cut, is proven for the set of quantities introduced by this cut-based decomposition. These results naturally lead to a novel feedback theory of electric circuits which, unlike Bode's feedback theory, is based on the unambiguous decomposition of transfer functions. Such feedback theory provides a natural extension to the elementary model of feedback amplifiers based on block diagrams, from system theory to circuit theory, and a natural extension to Blackman's formula. © 2012 IEEE.

Codecasa L.,Polytechnic of Milan
IEEE Transactions on Circuits and Systems I: Regular Papers | Year: 2012

In this paper and in its companion, a novel cut-based decomposition for transfer functions of linear time-invariant circuits is introduce