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In 2018 a collaborative project between Politecnico di Milano (PoliMI) and Regione Lombardia (RL) was launched to join forces and expertise toward the improvement of the regional transport infrastructures maintenance management. One of the project goals was the development of regional guidelines aimed to support the design and implementation of monitoring systems for bridges. The focus of this paper is on the illustration of the Monitoring Regional (MoRe) guidelines and of their implementation on nine pilot monitoring systems designed and deployed within the project. The (MoRe) guidelines tackle the entire monitoring process from the analyses of the monitoring goals and the preliminary investigations needed to the identification of the phenomena and relevant indicators to monitor, up to the selection of monitoring devices and the presentation of results. A short illustration of the permanent monitoring systems installed on nine exemplary bridges in the Lombardia region concludes the paper. [ABSTRACT FROM AUTHOR]

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Nowadays, designing and adopting sustainable and greener transport systems is of upmost interest. The European Commission and different EU countries are developing plans and programs—but also delivering resources—aimed at the decarbonization of cities and transport by 2030. In this paper, the case study of the city of Brescia, a city of about 200,000 inhabitants located in northern Italy, is addressed. Specifically, a preliminary operational and financial feasibility study is performed assuming the replacement of the entire compressed natural gas (CNG) powered bus fleet of a specific line; the two alternatives considered are battery electric buses (BEBs) and fuel cell electric buses (FCEBs). For the comparison and evaluation of the two alternatives, specific economic parameters of the three alternatives (BEB, FCEB and the current solution CNGB) were considered: CAPEX (CAPital EXpenditure) and OPEX (OPerational EXpenditure). This allowed us to determine the TCO (total cost of ownership) and TCRO (total cost and revenues of ownership) along three annuities (2022, 2025 and 2030). For the BEB alternative, the TCO and TCRO values are between EUR 0.58/km and EUR 0.91/km. In the case of the FCEB solution, the values of TCO and TCRO are between EUR 1.75/km and EUR 2.15/km. Considering the current CNGB solution, the TCO and TCRO values range between EUR 1.43/km and EUR 1.51/km. [ABSTRACT FROM AUTHOR]

In the framework of direct Structural Health Monitoring approaches, this paper presents a low frequency range analysis performed on a steel truss bridge designed in 1946 and built up in Northern Italy. The bridge is instrumented with a permanent structural health monitoring system, that guarantees a continuous flux of data and information from a heterogeneous set of sensors. In this analysis, static and quasistatic bridge responses are considered. These experimental data are merged with the analogous outputs obtained from numerical simulations, performed on FE models representative of the actual bridge, with the purpose of identifying damage‐sensitive indexes. Simulations are performed considering the healthy structure and modelling different damage scenarios. The static analysis consists in the construction of a regressive model able to estimate sensor output responses starting from environmental measurements, with the primary purpose to reduce the effect of temperature over measured static response. This procedure allows to relate the damages simulated by means of a numerical model with the real data, so that the monitoring rules can effectively defined. [ABSTRACT FROM AUTHOR]

Structural health monitoring of civil infrastructure, such as bridges and buildings, has become a trending topic in the last few years. The key factor is the technological push given by new technologies that permit the acquisition, storage, processing and visualisation of data in real time, thus assessing a structure's health condition. However, data related to anomaly conditions are difficult to retrieve, and, by the time those conditions are met, in general, it is too late. For this reason, the problem becomes unsupervised, since no labelled data are available, and anomaly detection algorithms are usually adopted in this context. This research proposes a novel algorithm that transforms the intrinsically unsupervised problem into a supervised one for condition monitoring purposes. Considering a bridge equipped with N sensors, which measure static structural quantities (rotations of the piers) and environmental parameters, exploiting the relationships between different physical variables and determining how these relationships change over time can indicate the bridge's health status. In particular, this algorithm involves the training of N models, each of them able to estimate the quantity measured via a sensor by using the others' N − 1 measurements. Hence, the system can be represented by the ensemble of the N models. In this way, for each sensor, it is possible to compare the real measurement with the predicted one and evaluate the residual between the two; this difference can be addressed as a symptom of changes in the structure with respect to the condition regarded as nominal. This approach is applied to a real test case, i.e., Candia Bridge in Italy, and it is compared with a state-of-the-art anomaly detector (namely an autoencoder) in order to validate its robustness. [ABSTRACT FROM AUTHOR]

Rail corrugation is a degradation phenomenon that manifests as a quasi-periodic irregularity on the running surface of the rail. It is a critical problem for urban railway lines because it induces ground-borne vibrations transmitted to the buildings near the infrastructure, causing complaints from the inhabitants. A typical treatment to mitigate the rail corrugation problem is the periodic grinding of the rails, performed by dedicated vehicles. The scheduling of rail maintenance is particularly critical because it can be performed only when the service is interrupted. A procedure for the continuous monitoring of rail corrugation is proposed, based on axlebox acceleration measurements. The rail irregularity is estimated from the measured acceleration by means of a frequency domain model of vertical dynamics of the wheel–rail interaction. The results obtained by using two different methods (a state-of-the-art method and a new one) are compared. Finally, the study of the evolution of the power content of the rail irregularity enables the identification of the track sections where corrugation is developing and rail grinding is necessary. [ABSTRACT FROM AUTHOR]

High refractive index glasses are preferred in integrated photonics applications to realize higher integration scale of passive devices. With a refractive index that can be tuned between SiO2 (1.45) and a-SiC (3.2), silicon oxycarbide SiOC offers this flexibility. In the present work, silicon oxycarbide thin films from 0.1 – 2.0 μm thickness are synthesized by reactive radio frequency magnetron sputtering a silicon carbide SiC target in a controlled argon and oxygen environment. The refractive index n and material extinction coefficient k of the silicon oxycarbide films are acquired with variable angle spectroscopic ellipsometry over the UV-Vis-NIR wavelength range. Keeping argon and oxygen gases in the constant ratio, the refractive index n is found in the range from 1.41 to 1.93 at 600 nm which is almost linearly dependent on RF power of sputtering. The material extinction coefficient k has been estimated to be less than 10-4 for the deposited silicon oxycarbide films in the visible and near-infrared wavelength regions. Morphological and structural characterizations with SEM and XRD confirms the amorphous phase of the SiOC films.

Large overpressures can be produced when a high-speed train enters and crosses a railway tunnel. Predicting them is important since, in critical conditions, pressure variations may be dangerous for train structures and for passengers' health and comfort. European regulations impose pressure thresholds which trains must comply with in order to be homologated for travelling through tunnels. Currently, full-scale tests are required to demonstrate respect of these prescriptions. In this work, a procedure for calculating the pressure variations inside the tunnel based on 3 D steady CFD simulations and a 1 D compressible fluid-dynamics model is proposed, to be used both as a design tool and for virtual homologation of new rolling stock. Results of a large experimental campaign performed on the Italian high-speed line are used to set-up the proposed methodology and to validate it. Different train geometries, tunnel crossing speeds and tunnel initial air conditions are considered. [ABSTRACT FROM AUTHOR]

We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nano-disks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion EA = 1:31±0:15 eV, a diffusivity prefactor of D0=0.53(×2:1±1) cm2 s-1 that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III ad-atoms on III-V crystal surfaces and the fabrication of designable nanostructures. [ABSTRACT FROM AUTHOR]

Featured Application: Experimental data presented in this work can be taken into consideration both to perform numerical simulations of trains crossing tunnels and to update the reference standards. This works focuses on a series of experimental tests carried out to investigate overpressures in tunnels due to train crossings. Although the above-mentioned topic is well known and also defined in European standards, in the literature full-scale data are lacking, which are useful to validate the numerical codes required in the certification process and are used in train structural dimensioning. In this respect, an extensive full-scale experimental campaign was planned for observing as many test conditions as possible, such as single passages of different trains, two train crossing, different tests speed, and different tunnel characteristics. In detail, the understanding of the pressure wave generation and transmission is deeply enhanced by studying the pressure evolution both on board and at trackside, considering both single train passages or two trains crossings and having the possibility to compare aerodynamic loads on sealed and unsealed trains. Furthermore, the position of sensors, the speed of the train, and the initial conditions within the tunnel have been proven to be fundamental parameters for properly estimating the pressure loads on trains. [ABSTRACT FROM AUTHOR]

The fabrication and characterization of an infrared photodetector based on GaAs droplet epitaxy quantum dots embedded in Al0.3Ga0.7As barrier is reported. The high control over dot electronic properties and the high achievable number density allowed by droplet epitaxy technique permitted us to realize a device using a single dot layer in the active region. Moreover, thanks to the independent control over dot height and width, we were able to obtain a very sharp absorption peak in the thermal infrared region (3–8 μm). Low temperature photocurrent spectrum was measured by Fourier spectroscopy, showing a narrow peak at 198 meV (∼6.3 μm) with a full width at half maximum of 25 meV. The observed absorption is in agreement with theoretical prediction based on effective mass approximation of the dot electronic transition. [ABSTRACT FROM AUTHOR]

In this article we present silicon oxycarbide (SiOC) as a potential dielectric platform for integrated photonic applications. By controlling the amount of carbon and oxygen in the composition of SiOC films, which in this work are deposited by using a reactive RF magnetron sputtering process, the refractive index of the material can be widely tuned from less than that of silica 1.40 to almost that of silicon carbide (3.0), while keeping high transparency in the near-infrared wavelength range. An in-depth analysis of the structural, morphological and optical properties of the deposited SiOC thin films is reported, pointing out the relationship between the change in the film composition and the tuneability of the refractive index. Single mode optical waveguides with a refractive index contrast of up to 28% and propagation loss as low as 2 dB/cm at 1550 nm are demonstrated. An integrated Mach-Zehnder interferometer is presented as a first example of PIC realized on high refractive index SiOC platform. Results show that SiOC is a promising alternative to conventional dielectric platforms for the realization of PICs. [ABSTRACT FROM AUTHOR]

The resistance to motion of trains is an essential requisite especially while designing high-speed trains and high-capacity railway lines. The optimisation of friction effects and aerodynamic performance can be done during the design stage of a new train but the actual value of the running resistance can be inferred only by means of full-scale tests during the operation of a train. A CEN standard (EN 14067-4) describes the methodologies for the assessment of the running resistance of railway vehicles starting from full-scale test measurements. According to this standard, the speeddependent terms of the resistance force have to be determined by means of coasting tests on railway lines, whose characteristics must be well known. Since this is not always possible and small errors on the gradient could lead to major uncertainties in the evaluation of the resistance force, a new method for the estimation of the running resistance coefficients, irrespective of the characteristics of the track is proposed in this paper. The reliability of the method is verified by comparing the results with those obtained from the procedure proposed in the CEN standard. The comparison shows that the new methodology is able to evaluate the resistance coefficients with an accuracy equivalent to that of the other methods but with fewer tests and with a more robust procedure relying on a lesser number of parameters. [ABSTRACT FROM AUTHOR]

In GaAs nanowires grown along the cubic [111]c direction, zinc blende and wurtzite arrangements have been observed in their stacking sequence, since the energetic barriers for nucleation are typically of similar order of magnitude. It is known that the interplanar spacing of the (111)c Ga (or As) planes in the zinc blende polytype varies slightly from the wurtzite polytype. However, different values have been reported in the literature. Here, the ratio of the interplanar spacing of these polytypes is extracted based on X-ray diffraction measurements for thin GaAs nanowires with a mean diameter of 18-25 nm. The measurements are performed with a nano-focused beam which facilitates the separation of the scattering of nanowires and of parasitic growth. The interplanar spacing of the (111)c Ga (or As) planes in the wurtzite arrangement in GaAs nanowires is observed to be 0.66% ± 0.02% larger than in the zinc blende arrangement. [ABSTRACT FROM AUTHOR]

Wepresent a novel approach for the growth of GaAs nanowires (NWs) withcontrollable number density and diameter, which consists of the combinationbetween droplet epitaxy (DE) and self-assisted NW growth. In our method,GaAs islands are initially formed on Si(111) by DE and, subsequently,GaAs NWs are selectively grown on their top facet, which acts as anucleation site. By DE, we can successfully tailor the number densityand diameter of the template of initial GaAs islands and the samedegree of control is transferred to the final GaAs NWs. We show how,by a suitable choice of V/III flux ratio, a single NW can be accommodatedon top of each GaAs base island. By transmission electron microscopy,as well as cathodo- and photoluminescence spectroscopy, we confirmedthe high structural and optical quality of GaAs NWs grown by our method.We believe that this combined approach can be more generally appliedto the fabrication of different homo- or heteroepitaxial NWs, nucleatedon the top of predefined islands obtained by DE. [ABSTRACT FROM AUTHOR]

What makes three dimensional semiconductor quantum nanostructures so attractive is the possibility to tune their electronic properties by careful design of their size and composition. These parameters set the confinement potential of electrons and holes, thus determining the electronic and optical properties of the nanostructure. An often overlooked parameter, which has an even more relevant effect on the electronic properties of the nanostructure, is shape. Gaining a strong control over the electronic properties via shape tuning is the key to access subtle electronic design possibilities. The Pulsed Dropled Epitaxy is an innovative growth method for the fabrication of quantum nanostructures with highly designable shapes and complex morphologies. With Pulsed Dropled Epitaxy it is possible to combine different nanostructures, namely quantum dots, quantum rings and quantum disks, with tunable sizes and densities, into a single multi-function nanostructure, thus allowing an unprecedented control over electronic properties. [ABSTRACT FROM AUTHOR]

The goal of this work is to apply the idea of the city in 15 min to railway stations that can become the starting point of the analysis as they represent the "gateway", where users start their last mile of travel after getting off the train. Within the research, 11 railway stations located in the Lombardy Region in Italy were identified and analyzed. To perform the analysis, an analytical index was implemented and determined for each station: this index summarizes the main features of the station itself in relation to the territory in which it is located. The adopted approach is comparative: it is not important the absolute value of the index of each station, but the comparison between the different indices. In this way it is possible on the one hand to classify the stations and on the other hand to identify and propose possible interventions to improve the role of a railway station in a territory. The proposed model is expandable and replicable: it is possible to add other useful indicators for the calculation of the index of each station and it is also possible to perform the analysis in different territorial contexts. In fact, it is a decision support tool able to provide indications and information for the planning and programming of the railway system and of the city; among the potential users of the proposed model there are railway station managers and administrations. [ABSTRACT FROM AUTHOR]

We used spatially resolved photoluminescence (PL) and resonant Raman spectroscopy to study the electronic structure of single GaAs nanowires (NWs) consisting of zinc-blende (ZB) and wurtzite (WZ) segments. For narrow ZB segments and stacking faults the energy range of the observed PL peak positions is found to deviate from that of the maxima in resonance Raman profiles. These different energy ranges reflect the fact that the PL recombination is dominated by spatially indirect transitions whereas the resonance enhancement of Raman scattering is caused by direct transitions. Our results provide evidence for the type II band alignment between ZB and WZ GaAs and a coherent picture of all near-band-gap transition energies in GaAs NWs. [ABSTRACT FROM AUTHOR]

In III-V nanowires the energetic barriers for nucleation in the zinc blende or wurtzite arrangement are typically of a similar order of magnitude. As a result, both arrangements can occur in a single wire. Here, we investigate the evolution of this polytypism in self-catalyzed GaAs nanowires on Si(lll) grown by molecular beam epitaxy with time-resolved in situ x-ray diffraction. We interpret our data in the framework of a height dependent Markov model for the stacking in the nanowires. In this way, we extract the mean sizes of faultless wurtzite and zinc blende segments--a key parameter of polytypic nanowires--and their temporal evolution during growth. Thereby, we infer quantitative information on the differences of the nucleation barriers including their evolution without requiring a model of the nucleus. [ABSTRACT FROM AUTHOR]

We present a unified model of compound semiconductor growth based on kinetic Monte Carlo simulations in tandem with experimental results that can describe and predict the mechanisms for the formation of various types of nanostructures observed during droplet epitaxy. The crucial features of the model include the explicit and independent representation of atoms with different species and the ability to treat solid and liquid phases independently. Using this model, we examine nanostructural evolution in droplet epitaxy. The model faithfully captures several of the experimentally observed structures, including compact islands and nanorings. Moreover, simulations show the presence of Ga/GaAs core-shell structures that we validate experimentally. A fully analytical model of droplet epitaxy that explains the relationship between growth conditions and the resulting nanostructures is presented, yielding key insight into the mechanisms of droplet epitaxy. [ABSTRACT FROM AUTHOR]