Strategie di caratterizzazione e controllo degli aspetti termici dei dispositivi elettronici di potenza in ambito automotive

L’attività di ricerca svolta nei tre anni del corso di dottorato si è articolata in due tematiche generali. La prima ha riguardato lo studio delle problematiche di natura termica di dispositivi e assemblaggi elettronici, mentre la seconda è consistita nella progettazione, simulazione, realizzazione e testing di sistemi di elettronica di potenza per la regolazione AC delle tensioni prodotte da generatori a magneti permanenti. Nell’ambito della prima tematica è stato sviluppato a livello teorico ed implementato tramite relativo software un nuovo codice per la simulazione termica in regime stazionario di dispositivi e sistemi di potenza. Tale codice, denominato DJOSER, si basa sulla risoluzione analitica diretta delle equazioni di trasporto del calore in un solido multistrato, ed è candidato a sostituire i più complessi ed onerosi programmi di calcolo agli elementi finiti a parità di accuratezza. Come ulteriore attività connessa a questo tema vanno inclusi sia l’attività di validazione teorica (confronto con gli elementi finiti) e sperimentale (verifica dei risultati mediante tecniche di misura della temperatura per via elettrica e termografica), sia le numerose applicazioni su sistemi reali suggeriti dal rapporto con industrie del settore. In ultimo la tecnica di simulazione termica è stata applicata con successo, in congiunzione con un risolutore elettrico dedicato, ad uno studio sul comportamento elettrotermico di transistori cellulari bipolari, evidenziando in particolare il fenomeno dell’Hot-Spot e consentendo di proporre delle efficaci contromisure. Sempre nell’ambito della prima tematica generale, durante i tre anni di dottorato è stato allestito un sistema di misura dinamica della temperatura di dispositivi elettronici con il metodo ottico ‘senza-contatto’ della termoriflessione, che sfrutta la dipendenza dalla temperatura del coefficiente di riflessione di semiconduttori e metalli. Con l’apparato di misura allestito e l’elettronica di controllo progettata, sono stati rilevati dei transitorî su campioni opportunamente costruiti, sui quali è stato possibile misurare la resistenza termica con risoluzione spaziale con il metodo TRAIT, il cui valore è stato confermato da una analisi della struttura effettuata con il programma DJOSER. Nell’ambito della ricerca sui sistemi di elettronica di potenza, è stato progettato e realizzato in duplice versione un nuovo tipo di regolatore AC da applicare a generatori a magneti permanenti, specifico per motoveicoli senza batteria e per i sistemi per la produzione eolica dell'energia di piccola taglia. L’aspetto innovativo del progetto in questione è il tipo di regolazione, serie anziché parallelo (gli interruttori sono posti in serie al generatore), il che evita la cortocircuitazione dell'alternatore con la conseguente erogazione di forti correnti e produzione di coppie frenanti. L’interruzione del circuito avviene solo in determinati istanti in cui la corrente nel carico si annulla, al fine di evitare spike di tensione. Il progetto è stato realizzato e testato sperimentalmente su un alternatore, in una prima versione con la parte di controllo realizzata in elettronica analogica con componenti discreti e integrati, e in una seconda in cui la gestione del controllo è stata totalmente demandata da un microcontrollore. Il progetto è stato oggetto di un brevetto in ambito italiano ed è attualmente in attesa di approvazione come brevetto internazionale (PCT)

Two-Way Optical Frequency Comparisons Over 100km Telecommunication Network Fibers

By using two-way frequency transfer, we demonstrate ultra-high resolution comparison of optical frequencies over a telecommunication fiber link of 100 km operating simultaneously digital data transfer. We first propose and experiment a bi-directional scheme using a single fiber. We show that the relative stability at 1 s integration time is 7 10^18 and scales down to 5 10^21. The same level of performance is reached when an optical link is implemented with an active compensation of the fiber noise. We also implement a real-time two-way frequency comparison over a uni-directional telecommunication network using a pair of parallel fibers. The relative frequency stability is 10^15 at 1 s integration time and reaches 2 10^17 at 40 000 s. The fractional uncertainty of the frequency comparisons was evaluated for the best case to 2 10^20. These results open the way to accurate and high resolution frequency comparison of optical clocks over intercontinental fiber networks

LST-R: A method for assessing land surface temperature reduction in urban, hot and semi-arid Global South

Over the next 30 years, temperatures are expected to increase in hot semi-arid zones. Despite increasing studies on urban heat, cooling measures suitable for this climate zone remain poorly investigated. The proposed method is innovative because it focuses on significant landscape metrics for determining the land surface temperature (LST) and evaluating cooling measures. Recurrence of warm spells was identified analysing the daily air temperatures. Daytime and night-time LST data acquired from space were correlated with landscape metrics extracted from very high-resolution satellite imagery. Stepwise linear regression was used to identify the significant metrics that affected it. Cooling measures were selected considering implementation leeway; performance of existing measures; strengths, weaknesses, opportunities, and threats, equity analyses. Although the method was tested in Niamey, Niger, it can be applied to any city or town in hot semi-arid Global South, requiring decision-making support on cooling policies. • Landscape metrics are consistent with development standard and general requirements • Evaluation of measures to reduce land surface temperature includes experts’ advice • Equity of measures to reduce land surface temperature is considere

Measuring the Virgo area tilt noise with a laser gyroscope

We report on the measurements of tilt noise performed at the Virgo site with a ring laser gyroscope. The apparatus is a He-Ne laser operating in a square cavity mounted on a vertical plane perpendicular to the north-south arm of the inteferometer. We discuss the possibility of using the ring laser signal to improve the performances of the control system of the Virgo seismic suspensions. The comparison between the ring laser signal and the control signals for the longitudinal translations of the inverted pendulum (IP) shows remarkable coherence in the frequency range 20-200 mHz.Comment: 4 pages, Proceedings of 46th Rencontres de Morion

Tackling the Limits of Optical Fiber Links

International audienceWe theoretically and experimentally investigate relevant noise processes arising in optical fiber links, which fundamentally limit their relative stability. We derive the unsuppressed delay noise for three configurations of optical links: two-way method, Sagnac interferometry, and actively compensated link, respectively designed for frequency comparison, rotation sensing, and frequency transfer. We also consider an alternative two-way setup allowing real-time frequency comparison and demonstrate its effectiveness on a proof-of-principle experiment with a 25-km fiber spool. For these three configurations, we analyze the noise arising from uncommon fiber paths in the interferometric ensemble and design optimized interferometers. We demonstrate interferometers with very low temperature sensitivity of respectively -2.2, -0.03 and 1 fs/K. We use one of these optimized interferometers on a long haul compensated fiber link of 540 km. We obtain a relative frequency stability of 3x10^-20 after 10,000 s of integration time

Super-resolved FRET imaging by confocal fluorescence-lifetime single-molecule localization microscopy

FRET-based approaches are a unique tool for sensing the immediate surroundings and interactions of (bio)molecules. FRET imaging and FLIM (Fluorescence Lifetime Imaging Microscopy) enable the visualization of the spatial distribution of molecular interactions and functional states. However, conventional FLIM and FRET imaging provide average information over an ensemble of molecules within a diffraction-limited volume, which limits the spatial information, accuracy, and dynamic range of the observed signals. Here, we demonstrate an approach to obtain super-resolved FRET imaging based on single-molecule localization microscopy using an early prototype of a commercial time-resolved confocal microscope. DNA Points Accumulation for Imaging in Nanoscale Topography (DNA-PAINT) with fluorogenic probes provides a suitable combination of background reduction and blinking kinetics compatible with the scanning speed of usual confocal microscopes. A single laser is used to excite the donor, a broad detection band is employed to retrieve both donor and acceptor emission, and FRET events are detected from lifetime information

Horizontal rotation signals detected by "G-Pisa" ring laser for the Mw=9.0, March 2011, Japan earthquake

We report the observation of the ground rotation induced by the Mw=9.0, 11th of March 2011, Japan earthquake. The rotation measurements have been conducted with a ring laser gyroscope operating in a vertical plane, thus detecting rotations around the horizontal axis. Comparison of ground rotations with vertical accelerations from a co-located force-balance accelerometer shows excellent ring laser coupling at periods longer than 100s. Under the plane wave assumption, we derive a theoretical relationship between horizontal rotation and vertical acceleration for Rayleigh waves. Due to the oblique mounting of the gyroscope with respect to the wave direction-of-arrival, apparent velocities derived from the acceleration / rotation rate ratio are expected to be always larger than, or equal to the true wave propagation velocity. This hypothesis is confirmed through comparison with fundamental-mode, Rayleigh wave phase velocities predicted for a standard Earth model.Comment: Accepted for publication in Journal of Seismolog

Spatial analysis of demersal food webs through integration of eDNA metabarcoding with fishing activities

The evaluation of the status of marine communities, and especially the monitoring of those heavily exploited by fisheries, is a key, challenging task in marine sciences. Fishing activities are a major source of disruption to marine food webs, both directly, by selectively removing components at specific trophic levels (TL), and indirectly, by altering habitats and production cycles. Food web analysis can be very useful in the context of an Ecosystem Approach to Fisheries, but food web reconstructions demand large and expensive data sets, which are typically available only for a small fraction of marine ecosystems. Recently, new technologies have been developed to easily, quickly and cost-effectively collect environmental DNA (eDNA) during fishing activities. By generating large, multi-marker metabarcoding data from eDNA samples obtained from commercial trawlers, it is possible to produce exhaustive taxonomic inventories for the exploited ecosystems, which are suitable for food-web reconstructions. Here, we integrate and re-analyse the data of a recent study in which the α diversity was investigated using the eDNA opportunistically collected during fishing operations. Indeed, we collect highly resolved information on species feeding relationships to reconstruct the food webs at different sites in the Strait of Sicily (Mediterranean Sea) from eDNA and catch data. After observing that the trophic networks obtained from eDNA metabarcoding data are more consistent with the available knowledge, a set of food web indicators (species richness, number of links, direct connectance and generality) is computed and analysed to unravel differences in food webs structure through different areas (spatial variations). Species richness, number of links and generality (positively) and direct connectance (negatively) are correlated with increasing distance from the coast and fishing effort intensity. The combined effects of environmental gradients and fishing effort on food web structure at different study sites are then examined and modelled. Taken together, these findings indicate the suitability of eDNA metabarcoding to assist and food web analysis, obtain several food web-related ecological indicators, and tease out the effect of fishing intensity from the environmental gradients of marine ecosystems

Fiber laser strain sensor device

We present a fiber laser strain sensor (FLSS) with noise-equivalent sensitivity equal to or better than 80?p?rms?(Hz)?1/2 at very low frequencies, from 100?mHz to several hundreds of hertz. The strain affects the fiber laser emission wavelength, and an imbalanced Mach?Zender interferometer (MZI) converts wavelength variations into phase-amplitude variations. The sensor has been also tested in the time domain by applying sinusoidal strain bursts: the device also shows a good signal-to-noise ratio at the lowest burst frequencies