Doctor of Philosophy

dissertationHigh Performance Computing (HPC) on-node parallelism is of extreme importance to guarantee and maintain scalability across large clusters of hundreds of thousands of multicore nodes. HPC programming is dominated by the hybrid model "MPI + X", with MPI to exploit the parallelism across the nodes, and "X" as some shared memory parallel programming model to accomplish multicore parallelism across CPUs or GPUs. OpenMP has become the "X" standard de-facto in HPC to exploit the multicore architectures of modern CPUs. Data races are one of the most common and insidious of concurrent errors in shared memory programming models and OpenMP programs are not immune to them. The OpenMP-provided ease of use to parallelizing programs can often make it error-prone to data races which become hard to find in large applications with thousands lines of code. Unfortunately, prior tools are unable to impact practice owing to their poor coverage or poor scalability. In this work, we develop several new approaches for low overhead data race detection. Our approaches aim to guarantee high precision and accuracy of race checking while maintaining a low runtime and memory overhead. We present two race checkers for C/C++ OpenMP programs that target two different classes of programs. The first, ARCHER, is fast but requires large amount of memory, so it ideally targets applications that require only a small portion of the available on-node memory. On the other hand, SWORD strikes a balance between fast zero memory overhead data collection followed by offline analysis that can take a long time, but it often report most races quickly. Given that race checking was impossible for large OpenMP applications, our contributions are the best available advances in what is known to be a difficult NP-complete problem. We performed an extensive evaluation of the tools on existing OpenMP programs and HPC benchmarks. Results show that both tools guarantee to identify all the races of a program in a given run without reporting any false alarms. The tools are user-friendly, hence serve as an important instrument for the daily work of programmers to help them identify data races early during development and production testing. Furthermore, our demonstrated success on real-world applications puts these tools on the top list of debugging tools for scientists at large

Previsioni demografiche. Alcune note metodologiche e una applicazione al caso dei comuni della Sardegna

Le previsioni demografiche rappresentano un importante strumento analitico e programmatico, in particolare in periodi come questo in cui si rivela crescente l’attenzione verso sistemi territoriali che non rientrano nelle aggregazioni amministrative canoniche, comunque ricchi di peculiarità e sufficientemente omogenei sotto il profilo economico, sociale e geografico. Proprio per questo motivo essi risultano destinatari di misure politiche di medio periodo mirate e specifiche, per le quali è utile disporre di possibili scenari futuri. Il progetto di ricerca del quale questo saggio rappresenta una tappa si inserisce in tale quadro di riferimento. In particolare, il suo carattere innovativo risiede nel livello di disaggregazione utilizzato, quello comunale. Ma per fare ciò occorreva proporre alcuni strumenti metodologici relativamente alle tecniche di previsione della popolazione. Il modello previsivo da noi messo a punto si basa su un algoritmo matematico che, partendo dai tassi di fertilità specifici comunali territorialmente ponderati e seguendo taluni ipotetici andamenti della fertilità stessa, della mortalità e del fenomeno migratorio, fornisce la popolazione prevista per sesso e classi di età per ognuno dei 375 comuni sardi. L’arco temporale nel quale si opera va dal 1995 (periodo osservato) al 2010, procedendo per successivi quinquenni. Come corollario dell’apparato metodologico abbiamo intentato un esercizio applicativo riguardante i comuni della Sardegna. I principali risultati ottenuti sono così sintetizzabili: in primo luogo, la Sardegna dovrebbe sostanzialmente stabilizzarsi sulle cifre dell’anno base, con saggi di variazione sempre abbastanza contenuti. Considerando le dinamiche comunali, si dovrebbe assistere all’approfondimento di taluni fenomeni del recente passato, con la crescita delle aree costiere, fra cui spiccano le Baronie e l’Ogliastra, l’hinterland cagliaritano ed il bacino urbano che ha come fulcro Sassari, e la prosecuzione sul sentiero di spopolamento di alcuni sistemi interni quali le Barbage, il Sulcis ed i comuni dell’oristanese non collegati al sistema campidanese. I dati disaggregati per classi di età farebbero registrare, infine, un ulteriore ispessimento delle classi di età avanzate, confermato da un incremento costante dei principali indicatori demografici sintetici

Symmetric polarization insensitive directional couplers fabricated by femtosecond laser waveguide writing

We study analytically the polarization behaviour of directional couplers composed of birefringent waveguides, showing that they can induce polarization transformations that depend on the specific input-output path considered. On the basis of this study, we propose and demonstrate experimentally, by femtosecond laser writing, directional couplers that are free from this problem and also yield a polarization independent power-splitting ratio. More in detail, we devise two different approaches to realize such devices: the first one is based on local birefringence engineering, while the second one exploits ultra-low birefringence waveguides obtained by thermal annealing

L'Econometria per le indagini territoriali: appunti metodologici e un'applicazione alla Sardegna

Il recente interesse scientifico per la new economic geography ha favorito il sorgere e il consolidarsi di un filone di ricerca di economia applicata che mira alla formalizzazione e misurazione delle relazioni spaziali fra fenomeni economici. Questa attività di ricerca, dapprima relegata in una nicchia accademica, oggi trova progressivamente applicazione nei corsi universitari, segno di una disciplina che suscita interesse per l’approccio innovativo all’indagine delle dinamiche sociali ed economiche. L’econometria spaziale nasce come branca dell’econometria tradizionale con la finalità di affrontare le problematiche connesse all’impiego di dati georeferenziati, cioè collegati ad entità geografiche. Fra i vari temi assumono rilevanza particolare l’interdipendenza (o autocorrelazione) e l’eterogeneità (o eteroschedasticità) spaziale. Per essi, troppo spesso, gli elementi forniti dalla econometria tradizionale appaiono insufficienti. Questo lavoro si propone di rendere esplicite le peculiarità proprie delle tecniche dell’econometria spaziale insieme ad alcune istruzioni d’uso per le loro applicazioni concrete

La disponibilità a pagare e le preferenze dei turisti per i siti del Parco Geominerario della Sardegna: il caso di Porto Flavia

Questo lavoro presenta alcuni risultati di uno studio di valutazione contingente, condotto al fine di stimare il valore turistico di Porto Flavia: un sito fra i più interessanti del Parco Geominerario recentemente istituito in Sardegna sotto il patrocinio dell’UNESCO. Dopo aver discusso il ruolo che adeguate politiche di gestione dei beni culturali ed ambientali possono assumere per garantire uno sviluppo turistico sostenibile, descriviamo le principali caratteristiche del metodo, la struttura dell’indagine ed i dati ottenuti. L’analisi dei dati si concentra sulla stima della disponibilità a pagare e del flusso turistico potenziale. Sono identificati possibili obiettivi d’intervento per la valorizzazione del percorso esistente ed una gamma di prezzi per diverse opzioni di offerta turistica

Thermal phase shifters for femtosecond laser written photonic integrated circuits

Photonic integrated circuits (PICs) are today acknowledged as an effective solution to fulfill the demanding requirements of many practical applications in both classical and quantum optics. Phase shifters integrated in the photonic circuit offer the possibility to dynamically reconfigure its properties in order to fine tune its operation or to produce adaptive circuits, thus greatly extending the quality and the applicability of these devices. In this paper, we provide a thorough discussion of the main problems that one can encounter when using thermal shifters to reconfigure photonic circuits. We then show how all these issues can be solved by a careful design of the thermal shifters and by choosing the most appropriate way to drive them. Such performance improvement is demonstrated by manufacturing thermal phase shifters in femtosecond laser written PICs (FLW-PICs), and by characterizing their operation in detail. The unprecedented results in terms of power dissipation, miniaturization and stability, enable the scalable implementation of reconfigurable FLW-PICs that can be easily calibrated and exploited in the applications

Integrated sources of entangled photons at telecom wavelength in femtosecond-laser-written circuits

Photon entanglement is an important state of light that is at the basis of many protocols in photonic quantum technologies, from quantum computing, to simulation and sensing. The capability to generate entangled photons in integrated waveguide sources is particularly advantageous due to the enhanced stability and more efficient light-crystal interaction. Here we realize an integrated optical source of entangled degenerate photons at telecom wavelength, based on the hybrid interfacing of photonic circuits in different materials, all inscribed by femtosecond laser pulses. We show that our source, based on spontaneous parametric down-conversion, gives access to different classes of output states, allowing to switch from path-entangled to polarization-entangled states with net visibilities above 0.92 for all selected combinations of integrated devices

An integrated approach to the assessment of balance and functional mobility in individuals with history of severe traumatic brain injury

Individuals who experienced severe Traumatic Brain Injury (sTBI) are often characterized by relevant motor dysfunctions which are likely to negatively affect activities of daily living and quality of life and often persist for years. However, detailed objective information about their magnitude are scarce. The aim of this study was to quantitatively assess the extent of motor deficits in terms of postural control effectiveness under static and dynamic conditions and to investigate the existence of possible correlations between the results of clinical tests and instrumental measures. Postural sway and functional mobility (i.e., instrumented Timed Up and Go test, iTUG) were objectively measured in 18 individuals with sTBI and 18 healthy controls using a pressure plate and a wearable inertial sensor. Additionally, participants with history of sTBI completed the Rivermead Mobility Index (RMI). One-way ANOVA and Spearman's rank correlation analysis were employed to examine differences between the two groups and determine potential correlations between the instrumental tests and clinical scales. The results show that people with sTBI were characterized by larger sway area and longer iTUG walking sub-phase. Significant correlations were also detected between RMI scores and iTUG total duration, as well as the walking phase. Taken together, these findings suggest that, even years after the initial injury, individuals with sTBI appear characterized by impaired postural control and functional mobility, which appears correlated with the RMI score. The integration of instrumental measures with clinical scales in the routine assessment and treatment of individuals with sTBI would result in more comprehensive, objective, and sensitive evaluations, thus improving precision in treatment planning, enabling ongoing progress monitoring, and highlighting the presence of motor deficits even years after the initial injury. Such integration is of importance for enhancing the long-term quality of life for individuals with sTBI