Doctoral School

Reading date: 06/05/2024

• BAS CALOPA, PAU: Partial discharges in low-pressure atmosphere: an experimental approach to improving electrical protection
  
  Author: 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 strategies
  
  Author: 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-Junctions
  
  Author: 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.
  

• NÚÑEZ CORBACHO, MARC: Aerodynamic shape optimization under uncertainties using embedded methods and adjoint techniques
  
  Author: NÚÑEZ CORBACHO, MARC
  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 CIVIL ENGINEERING
  Department: Barcelona School of Civil Engineering (ETSECCPB)
  Mode: Normal
  Deposit date: 09/04/2024
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: ROSSI BERNECOLI, RICCARDO | BAIGES AZNAR, JOAN
  Committee:
       PRESIDENT: LEHMKUHL BARBA, ORIOL
       SECRETARI: MARTINEZ FRUTOS, JESUS
       VOCAL: RICCHIUTO, MARIO
  Thesis abstract: This thesis develops a framework to perform shape optimization under uncertainties for a body under the action of aerodynamic forces. The solution of the flow is performed with finite elements using the full potential equation with an embedded approach, where the object of study is defined implicitly with a level set function. The optimization problem is solved by combining different software packages to perform the solution of the flow, advance in the optimization loop and perform uncertainty quantification. The first contribution of the thesis is the development of a full embedded approach for the solution of the full potential equation. Due to the inviscid hypothesis of potential solvers, these require the definition of a gap in the computational mesh in order to generate lift, known as the wake. Based on previous works where the wake is defined implicitly with an embedded approach, this work also considers the geometry as an embedded body. Mesh refinement and numerical terms are employed to improve the definition of the geometry in the mesh and ensure the definition of the Kutta condition. The solver is validated for two and three dimensions for subsonic and transonic flows with different reference data. Another contribution of the thesis is the development of the adjoint analysis for the subsonic full potential equation with embedded geometries in two dimensions. Each coordinate of the object of study is considered a design parameter in the adjoint analysis, where the effect of the level set function is considered. The sensitivities of the objective function with respect to the design parameters are validated by comparing them to the sensitivities obtained by using a finite differences approach. A shape optimization problem where the lift coefficient is maximized with geometrical constraints is solved as an example of application of the adjoint sensitivities. The embedded shape optimization problem is extended to consider uncertainties in the inlet condition. The optimization problem is reformulated by choosing a risk measure, the Conditional Value-at-risk, which is minimized. The adjoint sensitivities are adapted for the stochastic case, considering the selected risk measure. The estimation of the risk measure is performed thanks to an external uncertainty quantification library, by applying a novel approach which uses Monte Carlo methods to estimate the Conditional Value-at-risk. The stochastic case is solved in a distributed environment, where each optimization step deploys a Monte Carlo hierarchy to estimate the objective function and its gradients.
  

• ZHANG, ZHIHUI: Linking architecture and emotions: sensory dynamics and methodological innovations
  
  Author: ZHANG, ZHIHUI
  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 ARCHITECTURAL, CIVIL AND URBAN HERITAGE AND REFURBISHMENT OF EXISTING BUILDINGS
  Department: (RA)
  Mode: Article-based thesis
  Deposit date: 25/03/2024
  Reading date: 07/05/2024
  Reading time: 11:30
  Reading place: Sala de Graus ETSAB. Planta Baixa (E.T.S. Arquitectura de Barcelona)
  Thesis director: FORT MIR, JOSEP MARIA | GIMÉNEZ MATEU, LUIS
  Committee:
       PRESIDENT: FONSECA ESCUDERO, DAVID
       SECRETARI: NAVARRO DELGADO, ISIDRO
       VOCAL: VENTURA RODÀ, ORIOL
  Thesis abstract: This study delves deeply into the complex relationship between the field of architecture and human emotions, aiming to fill a significant gap in existing research. It extensively explores the profound impact of architectural design elements, such as lighting, colour schemes, and the integration of natural landscapes, on emotional responses. This research goes beyond traditional focuses on aesthetics and sustainability, striving to innovate methods for assessing the emotional impact of architectural spaces.In this study, we adopted a technological pathway from the laboratory to virtual reality, and finally to AI, combining theoretical analysis with practical experiments and case studies. The main research includes examining the effects of lighting and spatial dimension variations on people's emotions, as well as the application of facial emotion recognition technology in virtual reality architectural environments, exploring AI's perceptual capabilities as a tool in architectural design. These studies aim to narrow the gap between theoretical research and practical application, providing new perspectives and empirical data for the field of architectural design.The study concludes with a reflection on the methodologies used and their broader implications for architectural design practice. It offers specific strategies for architects and designers, aimed at creating spaces that resonate emotionally and add substantial value to human experiences. By prioritizing emotional factors in the design process, this research seeks to enhance overall quality of life and promote well-being in thoughtfully designed architectural spaces.