Doctoral School

Reading date: 20/01/2025

• AKHTER, MOHAMMAD NAYEEM: Non-Hermitian mode management in optical fibers and waveguides
  
  Author: AKHTER, MOHAMMAD NAYEEM
  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 COMPUTATIONAL AND APPLIED PHYSICS
  Department: Department of Physics (FIS)
  Mode: Normal
  Deposit date: 29/11/2024
  Reading date: 20/01/2025
  Reading time: 11:00
  Reading place: Sala de Conferencies de l'edifici TR5, C/ Colom 9, Campus de Terrassa - UPC / https://meet.google.com/xyg-wpcb-xsf
  Thesis director: STALIUNAS, KESTUTIS | BOTEY CUMELLA, MURIEL
  Committee:
       PRESIDENT: MUSSOT, ARNAUD
       SECRETARI: PONS RIVERO, ANTONIO JAVIER
       VOCAL: TASOLAMPROU, ANNA
  Thesis abstract: This thesis uncovers a novel approach to tailoring optical beam transformations in GRaded INdex (GRIN) MultiMode Fibers (MMFs) through non-Hermitian mode management. Recently, MMFs have gained a resurgence of interest due to their demand in optical communications, high-power lasers, and dynamic fields of optical sensing and imaging. MMFs exhibit rich and complex spatiotemporal phenomena, and one of their main drawbacks is the poor quality of the propagated beam. Any beam injected in such fibers spontaneously evolves towards a multimode configuration generating speckle formation at the output. This randomness results from the different values of propagation constants of the fiber modes causing random mode phase shifts during propagation. This issue persists even in parabolic GRIN MMFs designed to have equidistant propagation constants, theoretically resulting in periodic self-imaging phenomenon. However, minor imperfections disrupt this mode equidistance, generally leading to randomness. Several approaches to tackling dephasing and randomization challenges include adaptive phase adjustment of the input beam and dissipative beam cleanup as the most common techniques. Recently, beam self-cleaning has been introduced as a novel approach to mitigate randomness effects, which relies on nonlinear mode coupling and, therefore, requires a high input beam power. Moreover, while self-cleaning redistributes energy among the modes, it maintains the integral properties of the beam, such as second-order moments in both real and wave number spaces, and the beam quality factor. Generally, conventional methods such as modulating the refractive index, dispersion, or nonlinearity along optical fibers, which may induce mode coupling, and parametric or Faraday modulational instability, do not efficiently reduce turbulence, since they generally broaden the angular spectra. This thesis presents a potentially transformative approach that enables an effective mode-cleaning while reducing turbulence. The proposal is based on the introduction of a periodic non-Hermitian modulation, by simultaneously engineering the refractive index and the gain/loss coefficient along the fibers or waveguides, allowing a precise control the mode coupling. Indeed, the field of non-Hermitian Photonics has recently become an ideal platform to uncover novel exotic physical phenomena such as breaking spatial symmetry and causality, with specific applications in dynamic periodic systems to improve laser performance or to condense optical turbulence, for instance. Thus, this thesis aims to control the mode coupling within MMFs and waveguides, using the concept of unidirectionality induced by periodic non-Hermitian potentials. Such unidirectional coupling among transverse modes, either towards lower-order modes or towards higher-order modes, is mainly governed by the spatial shift between the real and imaginary parts of the complex potential. This scheme leads to mode-cleaning in linear and active nonlinear fibers, as a main potential application. Moreover, we also explore the controlled generation of higher-order modes in parabolic GRIN MMF. Finally, we show it is also possible to tailor the beam profile in active non-Hermitian nonlinear GRIN MMFs. In addition, the proposed scheme leads to an effective all-optical mode-cleaning and thus reduces the second-order moments in both real and angular spaces. Importantly, these techniques no longer require high-power or manual adjustment of the input beam. We predict these effects analytically based on either a simplified Gaussian beam model or the standard mode expansion technique. The predictions are then numerically proven by solving the wave propagation equation introducing the longitudinal periodic non-Hermitian potential. The robustness and effectiveness of the proposed scheme have been discussed. We also estimate the conditions and parameters for the experimental realisation of predicted phenomena.
  

• ENCALADA LÓPEZ, DAVID ALEJANDRO: Soil Deterioration and Crack Formation during Drying. Mitigation Strategies
  
  Author: ENCALADA LÓPEZ, DAVID ALEJANDRO
  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 GEOTECHNICAL ENGINEERING
  Department: Department of Civil and Environmental Engineering (DECA)
  Mode: Normal
  Deposit date: 29/11/2024
  Reading date: 20/01/2025
  Reading time: 11:00
  Reading place: ETSECCPB. UPC, Campus Nord Building C1. Classroom: 002 C/Jordi Girona, 1-3 08034 Barcelona
  Thesis director: LEDESMA VILLALBA, ALBERTO | PRAT CATALAN, PERE
  Committee:
       PRESIDENT: GALLIPOLI, DOMENICO
       SECRETARI: ROMERO MORALES, ENRIQUE EDGAR
       VOCAL: MENDES, JOAO
  Thesis abstract: This thesis investigates the cracking behaviour of deformable soils undergoing moisture exchange with the environment. The research combines experimental approaches, evaluates proposed models, and includes the evaluation of numerical modelling to understand the properties controlling soil cracking during desiccation.The experimental work encompasses four main areas: soil deformation measurement, suction measurement, soil-atmosphere interaction evaluation, and soil cracking assessment.Three methodologies were employed to assess soil deformation: direct measurement, volume displacement, and digital image analysis (DIA). DIA proved particularly effective, offering simplicity and rapidity in acquiring soil shrinkage curves (SSC) while providing additional information on soil colour changes due to water content variations. The collected data validated a proposed model capable of capturing various curve shapes, including J-shaped and S-shaped, with physically meaningful parameters.Suction measurements employed multiple techniques, including high-capacity tensiometers (HCTs), conventional tensiometers, water potential sensors, hygrometers, and filter paper. HCTs stood out for their extensive range and good overlap with methods estimating suction from relative humidity. These measurements facilitated the construction of soil water retention curves (SWRC) for different soil specimens.The volumetric and suction measurements at unconfined conditions, through SSC and SWRC, allowed the construction of part of the state surface (e-s-p). This data improves current constitutive models for unsaturated soils by considering the non-linear behaviour of suction-induced stiffness. An analytical solution for the e-s curve was derived from the proposed model, which aims to extend to confined conditions and link soil deformational behaviour with constrained swelling and swelling pressure.Soil-atmosphere interaction tests were conducted in an open atmosphere, environmental chamber, and large-scale field settings. These experiments evaluated soil evaporation stages and tested a model considering diffusion resistance and relative humidity at the soil surface. The impact of these factors varied with soil type: diffusion resistance significantly affected granular soils, relative humidity influenced high-plasticity clay, and low-plasticity soil was affected by both. A capillary barrier using a geosynthetic layer was evaluated as a mitigation strategy, demonstrating effectiveness in reducing evaporation and preventing cracking below the barrier.Soil cracking was assessed using two approaches: surface evaluation with DIA and X-ray computed tomography (CT) for depth analysis. Results showed good agreement with SSC, revealing that cracking represented a percentage of volume changes during induced shrinkage, depending on soil type and initial water content. X-ray CT revealed the influence of pre-existing flaws on crack formation and demonstrated incomplete crack sealing during wetting cycles.Fibre addition was tested as a crack reduction method, showing effectiveness in the first drying cycle but reduced efficacy in subsequent cycles. X-ray CT observations highlighted the persistence of sealed cracks as weak points, leading to crack reopening along previous paths.Finally, numerical modelling focused on simulating soil deformation in selected soil-atmosphere interaction tests. The models emphasised the importance of boundary conditions, particularly mass and heat transfer coefficients, in representing soil-atmosphere interaction. The simulations corroborated the capillary barrier effect of geosynthetics as an effective strategy for moisture preservation and crack prevention.
  

Reading date: 21/01/2025

• PUY CONTRERAS, ANDREU: Dynamic social patterns and information transfer in schooling fish
  
  Author: PUY CONTRERAS, ANDREU
  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 COMPUTATIONAL AND APPLIED PHYSICS
  Department: Department of Physics (FIS)
  Mode: Normal
  Deposit date: 26/11/2024
  Reading date: 21/01/2025
  Reading time: 11:00
  Reading place: Sala d'actes Manuel Martí Recobert, Edfici B6 - planta 0, C/ Jordi Girona 1-3 Barcelona, Campus Nord UPC. https://meet.google.com/ors-abxa-idx
  Thesis director: PASTOR SATORRAS, ROMUALDO
  Committee:
       PRESIDENT: ZAPPERI, STEFANO
       SECRETARI: ALONSO MUÑOZ, SERGIO
       VOCAL: REINA, ANDREAGIOVANNI
  Thesis abstract: Moving animal groups, such as flocks of birds, schools of fish, insect swarms, herds of mammals, and human crowds, exhibit intricate and highly coordinated behaviors. This thesis explores the underlying mechanisms of collective behavior by analyzing extensive, high-resolution experimental data of trajectories of schooling fish in a controlled environment.We first introduce a force map technique to investigate the alignment forces experienced by individual fish. After validating the method with an agent-based model, we apply it to experimental data and find evidence of effective alignment with faster neighbors, alongside an unexpected anti-alignment with slower ones. Instead of interpreting this as explicit anti-alignment behavior, we suggest it arises from a selective attention mechanism, where fish are less attentive to slower neighbors. This implies the existence of temporal leadership dynamics based on relative speeds, a hypothesis we support through both agent-based modeling and analysis of leader-follower relationships in the experimental data.Next, we examine how variations in perceived risk influence the behavior and interactions of fish within a group. By merging two subgroups of fish, each with different habituation levels to the experimental tank, we observe that individuals with higher perceived risk tend to occupy more central positions and show increased group cohesion, aligning with the selfish herd hypothesis. Beyond spatial positioning, we note behavioral adjustments in coordination, leader-follower dynamics, and burst-and-coast movement patterns. To further validate these findings, we develop a machine learning tool capable of identifying the subgroup identity of individual fish based on their behavior.We also investigate spontaneous behavioral cascades in schooling fish, focusing on turning avalanches, where large directional shifts are propagated through the group. Using tools from condensed matter physics and seismology, we analyze various avalanche metrics and reveal scale-free behaviour through power-law distributions, data collapses and scaling relationships. This confirms a necessary condition for criticality in fish schools. We also explore the biological role of turning avalanches, linking them to collective decision-making processes that govern changes in the school’s direction. Boundary effects from interactions with the tank walls, as well as the influential roles of boundary individuals, are also identified. Furthermore, by applying the nearest-neighbor declustering method from seismology, which is based on identifying main events and aftershocks, we uncover spatiotemporal correlations in avalanche events and an Omori-Utsu law with a faster decay rate compared to typical earthquake dynamics.Finally, we explore and extend the nearest-neighbor declustering technique for analyzing aftershock correlations in point processes. Using earthquake catalogs, we show that this method can in some cases produce spurious Omori-Utsu and productivity relationships in the absence of true correlations. However, by assessing the robustness of these results under variations in newly introduced parameters, we demonstrate that the method can reliably distinguish genuine aftershocks.Overall, this thesis provides novel insights into the mechanisms driving collective behavior in animal groups, emphasizing the role of selective social interactions and critical dynamics. Our empirical, data-driven approach highlights the complexity of animal collectives and lays a foundation for future studies on collective decision-making, leadership, and information transfer in biological systems.
  

Reading date: 22/01/2025

• BERTOL GROS, ANA: Between rigor and imagination. Creativity in structures education
  
  Author: BERTOL GROS, ANA
  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 ENGINEERING, SCIENCES AND TECHNOLOGY EDUCATION
  Department: Institute of Education Sciences (ICE)
  Mode: Normal
  Deposit date: 13/12/2024
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: LÓPEZ ÁLVAREZ, DAVID | BARDÍ MILÀ, BERTA
  Committee:
       PRESIDENT: COUSO LAGARÓN, DIGNA
       SECRETARI: ALIER FORMENT, MARC
       VOCAL: LLORENS LARGO, FARAÓN
  Thesis abstract: Creativity has been defined as a 21st century competence.In engineering, creativity is a vital component for the success and advancement of the profession. It enables engineers to view challenges from new perspectives, generate original and practical ideas, pose novel questions, and devise solutions to complex problems. This competence fosters interdisciplinarity, allowing professionals to collaborate within various fields to develop comprehensive projects that adhere to regulations and standards without sacrificing functionality or aesthetics. Teaching creativity to engineers is essential, as it equips them to devise innovative solutions, adapt to emerging technologies, enhance sustainability, and excel in a competitive job market.Traditionally, engineering education has been structured with methodologies centered on theoretical lectures and exercises with single answers. These studies, organized in silos with rigorous curricula, leave little room for exploration. Therefore, to promote creativity, educational methodologies must be adapted to the cognitive processes of university students and to the real demands of the profession and society.This doctoral thesis focuses on the field of structures, positioned at the intersection of engineering and architecture. This unique context presents an opportunity to explore creativity and contribute innovative ideas to enhance engineering education. The objective of this work is to analyze the theories, perspectives, and methodologies used in teaching structure courses to improve creativity in engineering education. By concentrating efforts in this area, the doctoral thesis aims to achieve reproducible and applicable results that can advance the field of engineering education.This work, based on a qualitative research paradigm, is structured on three pillars. The first is a literature review defining this thesis’s theoretical framework, synthesizing results from five areas relevant to creativity. Results show that, in higher education, effective creativity combines this innate skill with specific field knowledge. In engineering, this involves explaining the creative process to solve real problems. Research shows everyone has creative potential, but it must be fostered through education.The second pillar examines professional perspectives on creativity in engineering. Interviews with experts in structures reveal their opinions on integrating creativity in higher education. While there is agreement on general aspects of creativity, opinions diverge in the field of structures. Some professors question the need for creativity in their field, often due to time constraints that prevent the exploration of new teaching methodologies.The third pillar comprises field experiences. To understand the study environment, three research stays were conducted at European universities. In addition, two teaching innovation projects were carried out at the home institution. The results show that improving the design of the engineering curriculum requires collaboration and diverse teaching methodologies, the most recommended being thinking with your hands.Throughout this research, it has been discovered that there is a crucial need to provide accessible and adapted guidelines that can be applied by all educators in the discipline, regardless of their experience in creativity. The results of this research converge in the creation of nine practical guidelines to guide the development of creativity in structures. By implementing these results, engineering education can reshape the perception of creativity and demonstrate its tangible value in engineering practice. Creativity should not be seen as a separate entity but integrated throughout the curriculum, permeating all aspects of the student's educational itinerary. This requires a concerted effort by all staff involved in these teachings, where each person must play a fundamental role in fostering a culture of creativity.
  

• ORTEGA CASTILLO, IVÁN: Protocol d'anàlisi del sòl urbà consolidat en l'àmbit de la regeneració urbana: el cas de Ca n'Anglada - Terrassa (Barcelona)
  
  Author: ORTEGA CASTILLO, IVÁN
  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, BUILDING CONSTRUCTION AND URBANISM TECHNOLOGY
  Department: Department of Architectural Technology (TA)
  Mode: Normal
  Deposit date: 05/12/2024
  Reading date: 22/01/2025
  Reading time: 15:00
  Reading place: Videoconferencia + Presencialmente :Aula Sala de Actos- EPSEB / meet.google.com/aup-xctk-zrx
  Thesis director: LACASTA PALACIO, ANA MARIA | GIRALDO FORERO, MARIA DEL PILAR
  Committee:
       PRESIDENT: MARTÍNEZ DURAN, ANNA
       SECRETARI: MARTI CASANOVAS, MIQUEL
       VOCAL NO PRESENCIAL: RIVERA ROGEL, CARMEN ALICIA
  Thesis abstract: The main purpose of this thesis is to develop an analysis protocol for consolidated urban areas using territorial indicators as the main part of the methodology. It examines contemporary urban architecture through numerical factors that relate to the transversal themes of the territories, in order to facilitate proposals for interventions in urban regeneration.Since the mid-20th century, urban settlements have experienced significant demographic growth due to increased migratory movements from rural areas to cities. This has led to territorial expansion, causing many areas to develop rapidly without specific urban planning regulations, resulting in serious structural deficiencies. One of these areas is the neighborhood of Ca n'Anglada, located in the municipality of Terrassa. It is a representative example of a consolidated urban area with strong interdisciplinary issues, and has been the subject of various public administration interventions without success. To understand the current issues, a preliminary analysis is presented that addresses interdisciplinary factors through the sociological, territorial and urban perspectives, tracing the development of the area from its origins to the present day, marked by a society and a territory that are strongly divided.Currently, urban regeneration operations in consolidated urban lands involve a great previous analysis work, which in many cases implies a great search for data that is found in various sources, which makes it difficult to get an idea of the globality of the problems of the territories. For this reason, subsequently through a systematic review of existing bibliographic references and their evaluation based on the content and background of each document, the main territorial indicators in urban planning are selected to analyze the neighborhood of Ca n'Anglada from a completely objective point of view. The bibliographic references deemed valid for developing the protocol also help define a set of optimal values and result ranges for each territorial indicator, determining the most favorable values for the territories in the analyzed aspects and categories. The study proposes processing this large volume of data from various sources to calculate each of the indicators using a database system with a structured language. This approach enables more efficient and straightforward management of the numerical values and allows for the subsequent representation of the results using geolocation software.This protocol is presented with clearly differentiated phases according to their temporal space, from an objective point of view. The first phase analyzes the current state of the neighborhood, presenting aspects reflected by the territorial indicators. The second phase assesses the results of the territorial indicators selected in the study of major urban planning operations in urban regeneration that have been carried out so far and may have significantly impacted the area. The final phase presents proposals for urban regeneration, considering both the pre-existing conditions and the current state. By applying the defined protocol, we obtain a precise image of the area’s problems and its opportunities for action to address themThus, with the development of this protocol for the analysis of consolidated urban areas, using the Ca n’Anglada neighborhood as an example, a set of analysis methodologies is created to automate current processes and enable greater agility in the workflows of technical drafters of urban planning modifications. This protocol facilities the phases of situational analysis and the development of urban planning, as well as monitoring the evolution of the actions.