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Worst-Case analysis of electrical and electronic equipment via affine arithmetic
No full textThis paper proposes to generate a smart tool that can inherently and effectively capture the results of parameter variations on the system responses of lumped and distributed electrical circuits. This methodology leverages the so-called affine arithmetic and represents parameter-dependent responses in terms of a multivariate polynomial. The affine representation is propagated from input parameters to circuit responses through a suitable redefinition of the basic operations, such as addition, multiplication or matrix inversion, that are involved in the circuit solution. The proposed framework is applied to the frequency-domain analysis of switching converters, and it turns out to be accurate and more efficient than traditional solutions based on Monte Carlo analysis
P- and S-wave velocity models from surface wave dispersion curves data transform
No full textThe inversion of surface wave dispersion curves is a well-established investigation approach to provide S-wave velocity models. Recent works have shown the possibility of exploiting the relation between surface wave wavelength and investigation depth to estimate directly the time-average S-wave velocity along a line or over an area. Moreover, the same relation is sensitive to Poisson's ratio and can be therefore used to retrieve also the time-average P-wave velocity model. Here we show that, starting from the estimated time average VS and VP models and using a Dix-like formula, we can estimate local VS and VP models. We use a synthetic 1D example to outline the method and then we show the results on a field dataset
Wireless Social Network. Design and management algorithms to improve reliability
No full textNowadays the most affordable means to bring wide band connectivity to rural areas is represented by wireless technology, which guarantees flexibility, scalability, ease of installation and low investments. Wireless technology in the unlicensed bands presents some disadvantages, when intended to cover large areas. Commercial operators indeed might deploy wireless networks in digital-divided areas exploiting licensed bands or hybrid configurations where the backhaul is realized by high performance licensed links. In the recent years, several Wireless Community Networks have been created and grown all over Europe, with some relevant cases represented by the deployments in Athens, Barcelona, Vienna. A Wireless Community Network is created by citizens interested to exchange knowledge, contacts and information on a transversal infrastructure, thanks to the use of wireless equipment working in the unlicensed frequency spectrum. As a matter of fact, such experiences must be started by skilled people, living in places characterized by dense urbanization. Wireless Community Networks could be regarded as a means to overcome the digital dived in countryside, but exporting a Wireless Community Network in rural areas is difficult because of lack of technical skills, and economic conditions not comparable to those found in a big city. In this contest, the research work has been dedicated to support the startup and consolidation of a social-based wireless network operator in a rural quasi-remote area. The idea is to realize network infrastructures capable to reduce the infrastructural digital divide, create technical skills and increase the digital culture of the population, with a low economic effort compared to what should be spent to commercial operators. Technologically speaking, the most efficient and affordable solution is represented by the exploitation of Wi-Fi technology. The latest version of the IEEE 802.11 standard offers exceptional possibilities in terms of throughput and latency, even if regulatory limitations and interferences may lower down the capabilities of the network, especially when it is intended to cover large areas. For this reason, a model for a managed deployment has been identified. The model has been realized following two major criteria. The first one is an efficient reuse of frequency channels and the protection from interferences in order to provide a good coverage of the territory taking into account the presence of self-generated and external noise. The second one is an efficient algorithm for channel access. Its goal is to avoid redundancy, minimize the latency and increase the throughput. This has been achieved through an hybrid system that accesses the channel with a combination of contention-free and contention-based protocols. The alternation between the two is based on the traffic load in the network. This model has been applied to a Wireless Community Network, that has been modified from an earlier version based in a single municipality (16 km2) where six base stations were mounting a total of 13 radios, to reach a dimension of 115 base stations with 346 radios, covering to 45 municipalities over 646 km2. The system alternates 11 channels offering consistent download and upload throughputs (12 Mbps and 8 Mbps respectively). This network is managed by an association for social promotion "Senza Fili Senza Confini", the first non-profit Internet Service Provider in Italy, which nowadays counts 2842 members, without any saturation or bottleneck. Senza Fili Senza Confini is a successful project, where the growth of the members' number has been statistically analyzed: it has been noticed that the subscription rate depends on the number of families of each village. Municipality counting less than 250 census families exhibit a 7% of the census families subscription at the first month and a constant subscription rate of 0.9% per month. Whereas, if the municipality counts more than 250 census families the subscriptions at first month are 4% of the census families and the average subscription rate is of 0.7% per month
Energy efficiency measures for buildings in Hebron city and their expected impacts in the distribution grid
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Integrating BIM and Bayesian networks to support the management of large building stocks
No full textUV-Cured Composite Films Containing ZnO Nanostructures: Effect of Filler Shape on Piezoelectric Response
No full textIn this work, a facile aqueous sol-gel approach was exploited for synthesizing different ZnO nanostructures; these latter were employed at 4 wt% loading in a UV-curable acrylic system. The piezoelectric behavior of the resulting UV-cured nanocomposite films (NCFs) at resonance and at low frequency (150 Hz, typical value of interest in energy harvesting applications) was thoroughly investigated and correlated to the structure and morphology of the utilized ZnO nanostructures. For this purpose, the NCFs were used as active material into cantilever-shaped energy harvesters obtained through standard microfabrication technology. Interesting piezoelectric behavior was found for all the prepared UV-cured nanostructured films; the piezoelectric response of the different nanofillers was compared in terms of RMS voltage measured as a function of the applied waveform and normalized to the maximum acceleration applied to the cantilever devices. The obtained results confirmed the promising energy harvesting capability of such ZnO nanostructured films. In particular, flower-like structures showed the best piezoelectric performance both at resonance and 150 Hz, gaining a maximum normalized RMS of 0.914 mV and a maximum peak-peak voltage of about 16.0 mVp-p corresponding to the application of 5.79 g acceleration
Microscopic and macroscopic models for the onset and progression of Alzheimer's disease
No full textIn the first part of this paper we review a mathematical model for the onset and progression of Alzheimer's disease (AD) that was developed in subsequent steps over several years. The model is meant to describe the evolution of AD in vivo. In [Y. Achdou et al., 2013] we treated the problem at a microscopic scale, where the typical length scale is a multiple of the size of the soma of a single neuron. Subsequently, in [M. Bertsch at al., 2016] we concentrated on the macroscopic scale, where brain neurons are regarded as a continuous medium, structured by their degree of malfunctioning. In the second part of the paper we consider the relation between the microscopic and the macroscopic models. In particular we show under which assumptions the kinetic transport equation, which in the macroscopic model governs the evolution of the probability measure for the degree of malfunctioning of neurons, can be derived from a particle-based setting. In the microscopic model we consider basically mechanism i), modelling it by a system of Smoluchowski equations for the amyloid concentration (describing the agglomeration phenomenon), with the addition of a diffusion term as well as of a source term on the neuronal membrane. At the macroscopic level instead we model processes i) and ii) by a system of Smoluchowski equations for the amyloid concentration, coupled to a kinetic-type transport equation for the distribution function of the degree of malfunctioning of the neurons. The second equation contains an integral term describing the random onset of the disease as a jump process localized in particularly sensitive areas of the brain. Even though we deliberately neglected many aspects of the complexity of the brain and the disease, numerical simulations are in both cases (microscopic and macroscopic) in good qualitative agreement with clinical data
Crack growth from internal defects and related size-effect in VHCF
No full textIt is well-known in the literature that fatigue cracks in VHCF originate from small internal defects. More than 95% of the total VHCF life is consumed in originating the so-called Fine Granular Area (FGA) around the small initial defect. Within the FGA, crack growth takes place even if the Stress Intensity Factor (SIF) is smaller than the threshold value for crack growth. Researchers proposed different explanations for this unexpected phenomenon but they unanimously accept that a weakening mechanism occurs around the initial defect, which permits crack growth below the SIF threshold. In the present paper, crack growth in the VHCF regime is innovatively modeled and a general expression for the fatigue limit is then obtained. The statistical distribution of the fatigue limit is also defined and a model for the fatigue limit as a function of the risk-volume is proposed. Finally, the proposed model is successfully applied to an experimental dataset
Effect of electroslag remelting on the VHCF response of an AISI H13 steel
No full textExperimental results have shown that high-strength steels can fail in the Very-High-Cycle Fatigue (VHCF) regime with cracks originating from internal defects. Material cleanliness thus plays a major role in the VHCF response of high-strength steels and refinement processes (eg, electroslag remelting [ESR] and vacuum arc remelting) could significantly enhance their performance. The present paper aims at investigating the effect of the ESR process on the VHCF behavior of an AISI H13 steel by carrying out fully reversed ultrasonic tension-compression tests on hourglass specimens manufactured with and without the ESR process. Size effect is also taken into account in the paper: the effectiveness in the prediction of the VHCF response of specimens with large risk-volumes from experimental data on specimens with small risk-volumes is discussed and experimentally validated