Thesis for defense agenda
Reading date: 03/05/2024
- AVTZI, STYLIANI: Hybrid diffuse optics methods to assess the emergence of dementia in older adultsAuthor: AVTZI, STYLIANI
Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
Programme: DOCTORAL DEGREE IN PHOTONICS
Department: Institute of Photonic Sciences (ICFO)
Mode: Normal
Deposit date: 25/01/2024
Reading date: 03/05/2024
Reading time: 10:00
Reading place: ICFO, Mediterranean Technology Park, Avinguda Carl Friedrich Gauss, 3, 08860 Castelldefels, Barcelona
Thesis director: DURDURAN, TURGUT
Committee:
PRESIDENT: BUSQUETS FACIABÉN, ALBERT
SECRETARI: ARTIGAS GARCIA, DAVID
VOCAL: ARMENDOLA, CATERINA
Thesis abstract: Hybrid diffuse optical devices offer a non-invasive and continuous and cost-effective method for monitoring cerebral blood flow and metabolism on the bedside use and realistic simulation applications. The incorporation of diffuse correlation spectroscopy (DCS) and near-infrared spectroscopy (NIRS) in these devices extends their versatility. This PhD project focused on utilizing diffuse optics to assess brain activity during functional and stress tests in older populations.Ageing is the primary risk factor for various brain conditions such as stroke, cognitive disorders, and mobility issues. As the population becomes increasingly older, these age-related pathologies are becoming a significant social and economic burden. The underlying assumption is that microvascular damage and changes in brain blood flow regulation contribute significantly to an increased risk of cerebrovascular diseases, cognitive and mobility disorders. This underscores the importance of creating a widely accessible monitoring system and associated protocols able to detect these changes early on, ultimately leading to personalised interventions. Two multi-disciplinary studies were performed during my doctorate studies to identify alterations in the haemodynamic parameters of older adults in response to existing pathologies.Microvascular cerebral blood flow (CBF) in a cohort of younger and older adults (>65 y.o.) with and without mild cognitive impairment (MCI) in overall good health was monitored during functional and stress tests. It was observed that CBF of older adults with MCI could not recover to baseline conditions compared to younger participants indicating possible autoregulation and vasoreactivity problems similar to those previously observed in chronic sleep apnea and chronic carotid stenosis patients. CBF measurements during functional cognitive tasks revealed gender differences. For a given test MCI participants presented a statistically higher response than normocognitive (NC) subjects. The combination of these results favour the "inefficiency hypothesis" that suggests that older adults activate the brain networks as NC individuals to cope with behavioural demands but with increased activity. A new hybrid diffuse optics device was developed combining a custom-made fast-DCS with a commercial NIRS device along with external devices for physiological signal recordings in the second study. The project aimed to measure changes in cerebral haemodynamics in older adults with Motoric Risk Syndrome (MCR) during functional cognitive and motor tasks protocols to evaluate the pre-post impact at 3 and 6 months of physical exercise alone or combined with transcranial direct current stimulation (tDC). Results revealed higher CBF but not oxy-haemoglobin (HbO2) responses in dual tasks (DT) compared to single (ST). There were no differences between groups at baseline and 3 months but statistically different responses in CBF were observed at 6 months for both intervention groups compared to the control group but not in HbO2 response, indicating that intervention affects CBF response possibly due to improvements of vascular health, highlighting the importance of physical activity and transcranial stimulation on the maintenance of vascular health. A big part of my research focused on the development of new algorithms for de-contaminating the measured data from extracerebral signal to develop an optimal model to minimise the effect for both studies. In summary this study proves the capability of hybrid optics to capture the evoked haemodynamic responses in the pre-frontal cortex and offers insights into the use of techniques to assess cognitive function in older adults, specifically those with MCI and MCR. The findings highlight the complex relationship between blood flow responses and cognitive activities suggesting that compensatory mechanisms may play a role in individuals facing cognitive challenges. Future research in these areas holds promise, for enhanc
- NESTOROV, ANNA MARIA: Optimizing serverless architectures for data-intensive analytics workloadsAuthor: NESTOROV, ANNA MARIA
Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
Programme: DOCTORAL DEGREE IN COMPUTER ARCHITECTURE
Department: (DAC)
Mode: Normal
Deposit date: 25/03/2024
Reading date: 03/05/2024
Reading time: 10:00
Reading place: Sala C6-E101 - Facultat d'Informàtica de Barcelona (FIB)
Thesis director: CARRERA PÉREZ, DAVID | BERRAL GARCÍA, JOSEP LLUÍS
Committee:
PRESIDENT: SANCHEZ ARTIGAS, MARC
SECRETARI: GUITART FERNANDEZ, JORDI
VOCAL: TAHERKORDI, AMIRHOSEIN
Thesis abstract: Recently, serverless computing has garnered attention from academia and industry due to its on-demand resource provisioning, allowing users to focus solely on their core business logic by breaking down tasks into small stateless functions.Serverless offers benefits like a 'pay-per-use' cost model, greater flexibility, and transparent elastic resource auto-scaling.Researchers in academia and industry are increasingly exploring serverless computing's potential in complex, data-intensive analytics. These tasks, resource-heavy and highly parallel, involve significant inter-function communications. However, this shift presents challenges, requiring alignment with the specific needs and constraints of such applications. This research area is currently considered one of the most compelling areas of study. This thesis shows that it is possible to efficiently execute modern data-intensive analytics workloads, traditionally deployed in managed cloud clusters, within serverless computing environments using direct data inter-function communication and optimized performance-cost efficient resource allocation policies. To demonstrate this thesis, we first build a performance model for serverless workloads, considering data sharing, volume, and communication technologies. The model, with a relative error of 5.52%, evaluates the performance of a representative workload in serverless, analyzing task granularity and concurrency, data locality, resource allocation, and scheduling policies. Our results indicate that the performance of data-intensive analytics workloads in serverless can be up to 4.32x faster depending on how these are deployed. Furthermore, this characterization highlights inefficiencies in centralized object storage and stresses the primary importance of efficient resource use.We then introduce Floki, a data forwarding system that tackles the centralized object storage bottleneck. It enables direct communication between producer-consumer function pairs using fixed-size communication methods. Floki establishes point-to-point data channels for intra- and inter-node data transmission, allowing transparent data transfer and reducing network data copying. This workflow-oriented approach boosts performance and minimize resource requirements without restricting function placement.Our experimental evaluation, performed on the principal communication patterns in distributed systems, shows that Floki reduces the end-to-end time up to 74.95x, decreasing the most extensive data sharing time from 12.55 to 4.33 minutes, saving almost two-thirds of time. Additionally, Floki achieves up to 50,738x of resource-saving, equivalent to a memory allocation of approximately 1.9MB instead of an object storage allocation of 96GB.Finally, we investigates how to achieve efficient resource utilization in modern serverless environments and proposes Dexter, a novel resource allocation manager, leveraging serverless computing elasticity. Dexter continuously monitors application execution, dynamically allocating resources at a fine-grained level combining predictive and reactive strategies to ensure performance-cost efficiency (optimizing total runtime cost). Unlike black-box Machine Learning (ML) models, Dexter reaches a sufficiently good solution, prioritizing simplicity, generality, and ease of understanding. The proposed experimental evaluation demonstrates that our solution achieves a significant cost reduction of up to 4.65x, while improving resource efficiency up to 3.50x, when compared with the default serverless Spark resource allocation that dynamically requests exponentially more executors to accommodate pending tasks. Dexter also enables substantial resource savings, demanding up to 5.71x fewer resources. Dexter is a robust solution to new, unseen workloads, achieving up to 2.72x higher performance-cost efficiency thanks to its conservative resource scaling approach.
Reading date: 06/05/2024
- BAS CALOPA, PAU: Partial discharges in low-pressure atmosphere: an experimental approach to improving electrical protectionAuthor: BAS CALOPA, PAU
Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
Programme: DOCTORAL DEGREE IN ELECTRICAL ENGINEERING
Department: (DEE)
Mode: Article-based thesis
Deposit date: 21/03/2024
Reading date: 06/05/2024
Reading time: 11:00
Reading place: Edifici TR5, sala conferències, ESEIAAT-UPC
Thesis director: RIBA RUIZ, JORDI ROGER | MORENO EGUILAZ, JUAN MANUEL
Committee:
PRESIDENT: MONTAÑA PUIG, JUAN
SECRETARI: ABOMAILEK RUBIO, BASEL CARLOS
VOCAL: URRESTY BETANCOURT, JULIO CÉSAR
Thesis abstract: This thesis contributes to the field of partial discharges in low-pressure environments, aiming to improve electrical wire interconnecting systems (EWIS) protection in aerospace applications. A series of experimental studies have been conducted to evaluate the potential of corona and surface discharges as indicators of electrical insulation degradation. To this end, the influence of variables such as pressure, pressure drop, frequency, and geometry on corona discharge behaviour has been examined. Furthermore, the performance of various sensors, including CMOS image sensors, photoelectric UV sensors, and acoustic cameras, in detecting corona discharges has been investigated and compared. Additionally, by employing RGB image processing techniques, this thesis presents a novel method for the quantification of corona discharges. This method allowed studying the correlation between the light intensity of electrical discharges and the dissipated electrical energy, with a particular focus on how pressure and frequency variation impacts on this relationship. The feasibility of utilizing corona and surface discharges as an indicator for the degradation of wire insulation has also been explored, providing foundational knowledge for the future development of electrical protection tools aimed at predictive maintenance. The findings from this research contribute to the advancement of predictive maintenance strategies, offering potential for early detection of insulation failures, thereby enhancing the safety and reliability of aerospace electrical systems.
- JOHANSSON, LINH HA HUONG LOVISA: 3D-printed biomimetic bone grafts: Clinical validation and improvement strategiesAuthor: JOHANSSON, LINH HA HUONG LOVISA
Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
Programme: DOCTORAL DEGREE IN MATERIALS SCIENCE AND ENGINEERING
Department: (CEM)
Mode: Normal
Deposit date: 26/03/2024
Reading date: 06/05/2024
Reading time: 10:00
Reading place: EEBE (Escola d'Enginyeria Barcelona Est), Aula A0.02, Edifici A, planta 0, Campus Diagonal-Besòs.
Thesis director: GINEBRA MOLINS, MARIA PAU | RAYMOND LLORENS, SANTIAGO
Committee:
PRESIDENT: MONTERO MARTÍN, JAVIER
SECRETARI: DÍEZ ESCUDERO, ANNA
VOCAL: OLDE DAMINK, LEON
Thesis abstract: Bone defects pose a major clinical and socio-economic burden and there is a clear need for new bone grafting strategies that take into account the physical-chemical properties of the native bone, to help treat bone defects in a time- and cost-effective way.Autografts are considered the gold standard due to their biological performance, however, additional surgical procedures for bone harvesting poses drawbacks. For this reason, the industrial- and scientific communities have focused on the development of synthetic bone grafting solutions. The present PhD thesis advances in the development of biomimetic personalised bone grafting solutions, including the clinical validation and the development of new material formulations with improved mechanical performance. Chapter 1: Gives an insight into the general context of bone regeneration and the materials used as bone substitutes, emphasising the need for innovative personalised synthetic bone grafts. This chapter offers an overview of additive manufacturing techniques and frequently employed ceramics in bone tissue engineering and their consolidation strategies. Further, a global presentation is given on their clinical translation, especially emphasising calcium phosphates and MimetikOss® 3D. Chapter 2: Focuses on evaluating the clinical performance of the 3D-printed bone graft MimetikOss® 3D in a horizontal vestibular augmentation. The ridge in the anterior maxilla is reconstructed with a synthetic patient-specific bone graft with a staged approach for dental implant placement. 3D-printed bone grafts permit a perfect fit in the surgical site without any additional shaping, which reduces surgery time compared with other bone augmentation techniques (e.g., guided bone regeneration, standard blocks). The bone graft is completely osseointegrated and its macropores colonised by newly formed bone at 10-months post-surgery without signs of encapsulation. A stable bone gain is achieved, resulting in a fully restored bone width. Dental implants were placed without the need for regrafting and stayed stable at 1- year post-loading, demonstrating the clinical relevance of these bone grafts in vestibular bone augmentations. Chapter 3: Encompasses two routes for incorporating PLGA, as a binder or as a coating, to 3D-printed self-setting scaffolds, taking advantage of their low-temperature hardening, to enhance their mechanical performance. The addition of PLGA increases the capacity for plastic deformation, which significantly improves their toughness (by a 2.6-fold and 4.2-fold change in flexion for PLGA as a binder and as a coating, respectively; and by an 8-fold and 1.6-fold change in compression, respectively), while preserving the in vitro cell viability of MimetikOss® 3D (with MG-63 and hMSC cells). The configuration with PLGA as binder is the better option regarding the enhancement in mechanical performance and osteogenic differentiation (2-fold and 1.5-fold change increase for ALPL and RUNX2 expressions, respectively). Screwability tests demonstrate that the enhanced mechanical properties increase the fixability of the scaffolds in a complex fixation indication in the jaw. Chapter 4: Discusses the impact, limitations, and challenges of 3D-printed biomimetic bone grafts and emphasises the steps remaining before transferring the new technology to the market. It is shown that the developments made in this PhD thesis can be beneficial for the patients and have a positive impact on society. Composite patient-specific bone grafts have an impact on cost, time and performance of the future bone grafting solutions, and they strive towards added value in personalised medicine. This will help treat complex and large bone defects in a way that benefits both the clinician and the patient and encourages sustainable healthcare based on synthetic biomaterials. This technology was protected by a filed patent application, however, there is still work left before it can be translated to the market.
Reading date: 07/05/2024
- DÍEZ MÉRIDA, JAIME: Probing Magic-Angle Twisted Bilayer Graphene with Gate Defined homo-JunctionsAuthor: DÍEZ MÉRIDA, JAIME
Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
Programme: DOCTORAL DEGREE IN PHOTONICS
Department: Institute of Photonic Sciences (ICFO)
Mode: Normal
Deposit date: 09/04/2024
Reading date: pending
Reading time: pending
Reading place: pending
Thesis director: EFETOV, DMITRI | LEWENSTEIN, MACIEJ
Committee:
PRESIDENT: WEITZ, THOMAS
SECRETARI: RUBIO VERDÚ, CARMEN
VOCAL: RIBEIRO PALAU, REBECA LISSETTE
Thesis abstract: In 2018, following a theoretical prediction from 2011, it was found that stacking two layers of graphene with a relative twist angle of 1.1° between them leads to multiple new properties. At this so-called magic angle, the electronic band structure of the material reconstructs, creating a narrow flat band at the Fermi level. The formation of a flat band enhances electron-electron interactions, resulting in the emergence of states of matter not present in the original graphene layers, including correlated insulators, superconductivity, ferromagnetism and non-trivial topological states. The understanding of the origin of these correlated states could help unravel the physics of highly correlated flat band systems which could potentially provide key technological developments. The main objective of this thesis is to study magic-angle twisted bilayer graphene (MATBG) by creating monolithic gate-defined Josephson junctions. By exploiting the rich phase space of the material, we can create a Josephson junction by independently tuning the superconductor and the weak link state. Studying the Josephson effect is a first step towards understanding fundamental properties of a superconductor, such as its order parameter. First, we have optimized the fabrication of these gate-defined junctions made of all van der Waals materials. We have made double-graphite-gated hBN encapsulated MATBG devices where the top gate is split into two parts via nanolithography techniques. This configuration allows to independently control the three regions of the Josephson junction (superconductor, weak-link and superconductor). Then, we have studied the gate-defined Josephson junctions via low-temperature transport measurements. After demonstrating the Josephson effect in the fabricated devices, we focus on the behavior of one of these junctions in great detail. In particular, we have observed an unconventional behavior when the weak link of the junction is set close to the correlated insulator at half-filling of the hole-side flatband. We have observed a phase shifted Fraunhofer pattern with a pronounced magnetic hysteresis, characteristic of magnetic Josephson junctions. To understand the origin of the signals, we have performed a critical current distribution Fourier analysis as well as a tight binding calculation of a MATBG Josephson junction. Our theoretical calculations with a valley polarized state as the weak link can explain the key signatures observed in the experiment. Lastly, the combination of magnetization and its current-induced magnetization switching has allowed us to realize a programmable zero-field superconducting diode.Finally, we have shown the flexibility of these devices by studying a MATBG p-n junction under light illumination. We have studied the relaxation dynamics of hot electrons using time and frequency-resolved photovoltage measurements. The measurements have revealed an ultrafast cooling in MATBG compared to Bernal-bilayer from room temperature down to 5 K. The enhanced cooling in MATBG can be explained by the presence of the moiré pattern and corresponding mini-Brillouin zone. In summary, we have demonstrated that by integrating various MATBG states within a single device, we can gain a deeper insight into the system's properties and can engineer innovative, complex hybrid structures, such as magnetic Josephson junctions and superconducting diodes.