Doctoral School

Reading date: 17/04/2026

• PERA I FERRERUELA, JORDI: Itinerant ferromagnetism and polarons in SU(N) Fermi gases
  
  Author: PERA I FERRERUELA, JORDI
  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: 13/03/2026
  Reading date: 17/04/2026
  Reading time: 11:00
  Reading place: Aula Graus, Edifici C4, Planta baixa, Campus Nord - UPC
  Thesis director: CASULLERAS AMBROS, JOAQUIN | BORONAT MEDICO, JORDI
  Thesis abstract: This thesis presents an in-depth study of the magnetic properties of repulsive Fermi gases in the continuum. Once a purely academic subject, Fermi gases can now be realized experimentally in ultracold atom laboratories, making a theoretical understanding of their behavior both timely and necessary. Our analysis focuses primarily on whether such systems favor a transition to a ferromagnetic state or remain paramagnetic. As technique, we use a perturbative approach that systematically includes the effects of higher-order terms, temperature, and mass imbalance. In the final part of the thesis, we also study the Fermi polaron problem. First, we examine a simple case: a Fermi gas with equal masses at zero temperature up to second order in perturbation theory. As this chapter can be considered an introduction to the magnetic phenomenology of Fermi gases, we compare the outcome of our second order analysis with the well-known scenario of the Stoner model, which is the first-order model. In both cases, a ferromagnetic transition always occurs. Moving from the Stoner model to the second-order one, there are two differences to point out: the continuous phase transition observed at S=1/2 becomes discontinuous, and the ferromagnetic phase arises at lower densities. The next step is to improve the description of the potential interaction. We do so by going up to third order in perturbation theory. However, this improvement comes with a cost; as we now have more information about the potential, the complexity of the problem is higher. We split the analysis into two parts. We first consider a hard-sphere potential without p-wave intra-particle interaction. We observe the same tendencies that we encounter when we move from first order to second order, but, more importantly, we recover the continuous phase transition for S=1/2. Having now at hand the third-order energies, we explore a wide range of different potentials. Surprisingly, for each spin S we observe a richness of scenarios: continuous transitions, discontinuous ones, combinations of the other two, stairs-like cases, and even, no transition at all. Next, we introduce another variable to our problem: the temperature. Thermal effects do not eliminate the ferromagnetic phase for any potential, but they clearly go against it: either they force the system to remain paramagnetic or make the transition to occur at higher densities, which probably hinders the ferromagnetic phase. Nevertheless, larger spins better resist these thermal effects. Additionally, temperature reduces the diversity of magnetic behavior, leading to more universal patterns: continuous transitions for S=1/2 and discontinuous ones for larger spins. Up to this point, we assumed that all the particles have the same mass. The next step is to consider different relations of masses. Adding another variable increases even more the complexity of the problem and, hence, we only inspect it at second order and at zero temperature. As we have commented above, at second order there is always a ferromagnetic transition. Now, this is also the case, but with some nuances. The massive particles are always the promoted ones, even at low densities. For S=1/2, this is the end of the story. But for larger spins, as we can have many mass relations, we can obtain lots of configurations, which may give us more tunability. Finally, we move beyond magnetic properties to study the Fermi polaron problem: an impurity immersed in a Fermi sea. We focus on how impurities affect our system. We examine the main properties of the Fermi polaron at third order and the effects of mass. Specifically, the massive polaron works just fine, but the light polaron is unstable. Altogether, this work offers a detailed and thorough exploration of Fermi gases, providing both qualitative insight and quantitative predictions relevant to experimental efforts.
  

Reading date: 20/04/2026

• BORGES CAVALCANTI, DANILO: Finite Element Method with Embedded Strong Discontinuities for Coupled Hydro-Mechanical Problems
  
  Author: BORGES CAVALCANTI, DANILO
  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 STRUCTURAL ANALYSIS
  Department: Department of Civil and Environmental Engineering (DECA)
  Mode: Change of supervisor + Article-based thesis
  Deposit date: 09/03/2026
  Reading date: 20/04/2026
  Reading time: 14:00
  Reading place: Sala Zienkiewich (CIMNE) Building C1, UPC - Campus North Gran Capitan S/N 08034 Barcelona
  Thesis director: DE POUPLANA SARDÀ, IGNASI | CAMPOS RAMOS MARTHA, LUIZ FERNANDO | DE MESQUITA ROEHL, DEANE
  Thesis abstract: Coupled hydro–mechanical (HM) processes in fractured porous media govern the performance and safety of several subsurface engineering applications, where pressure-driven changes in stress and permeability can control injectivity, leakage pathways, and fault reactivation potential. This thesis develops a robust and versatile finite element formulation for transient HM problems in the presence of pre-existing strong discontinuities that remains practical for integration into standard finite element workflows. The proposed approach is formulated within the Embedded Finite Element Method (E-FEM) and grounded on the Strong Discontinuity Approach (SDA), enabling an implicit representation of fractures and faults while circumventing mesh conformity constraints. A unified description is introduced to model discontinuities acting either as preferential flow paths or as hydraulic barriers, capturing the longitudinal flow along the discontinuity and the transversal exchange with the porous matrix in steady-state and transient settings. The formulation is systematically verified against discrete fracture models with interface elements and applied to benchmark problems representative of fractured-reservoir conditions, including a coupled fault reactivation scenario. In addition, the thesis investigates the occurrence of spurious oscillations in cohesive traction fields along embedded discontinuities and demonstrates that the choice of an SDA-based embedded formulation can markedly improve traction smoothness. These improvements strengthen the use of E-FEM for HM assessments involving pre-existing fractures and faults.
  

• FORERO QUINTERO, JOSE FERNANDO: Flexibility Management System with Distributed Energy Resources
  
  Author: FORERO QUINTERO, JOSE FERNANDO
  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: Department of Electrical Engineering (DEE)
  Mode: Article-based thesis
  Deposit date: 19/02/2026
  Reading date: 20/04/2026
  Reading time: 12:00
  Reading place: Aula 28.8 Sala de Conferències. ETSEIB-UPC
  Thesis director: VILLAFÁFILA ROBLES, ROBERTO | MONTESINOS MIRACLE, DANIEL
  Thesis abstract: The challenge of climate change is ever demanding more technological and political efforts to respond adequately to its adverse effects, which could put life on the planet at risk. Diverse plans have been proposed to incorporate more renewable generation and digitalize the power system in a decarbonizing energy transition framework. However, such plans are either not being accomplished or are insufficient according to the Paris Agreement. At the same time, emerging technologies such as artificial intelligence, high-performance sensing and automation, and real-time information and communication systems, among others, are transforming electrical networks into smart grids, aggregating more complexity.This thesis, based on a papers compendium, first surveys the existing energy management systems with distributed energy resources, delving into their configuration, energy and flexibility sources, information and communication systems, profitability analysis and indicators, and flexibility services. After reviewing the state of the art, this thesis focuses on boosting management systems towards the real-time horizon, proposing a flexibility management system. This system is a hierarchical three-level management system based on an adaptive autoregression algorithm, cost-benefits analysis, and redispatching and unit recommitment submodules to control and manage the power, and short-term flexibility requests.To validate the proposed system, not only several simulations and sensitivity analyses are carried out, but real-world energy assets are addressed in PVZEN microgrid lab in Torino, Italy. The results demonstrate that proposed system can reduce the cost overruns of real-time power deviations of the distributed resources, leverage the excess of renewable energy, and generate profits providing flexibility services to the grid. Chapters 2, 3, and 4 show the papers related to this thesis, starting with reviewing the art status, passing through the simulations and analysis, and finishing with the essays on real-world energy assets. Main conclusions and future work are depicted at the end of the document.
  

• NAVARRO GRANADOS, JORDI: Theoretical and Experimental Study on Cold-Formed Elements for Steel Framing in Seismic Areas
  
  Author: NAVARRO GRANADOS, JORDI
  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 EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS
  Department: Department of Civil and Environmental Engineering (DECA)
  Mode: Normal
  Deposit date: 20/03/2026
  Reading date: pending
  Reading time: pending
  Reading place: pending
  Thesis director: CASAFONT RIBERA, MIQUEL | BOVÉ TOUS, ORIOL
  Thesis abstract: This Thesis presents a theoretical and experimental study on cold-formed elements for seismic-resistant steel framing systems. The focus is on evaluating the feasibility of using low- and mid-rise buildings based on cold-formed steel framing with flat strap bracings as diagonal members, and built-up steel profiles or concrete-filled steel sections as boundary (chord) studs, to resist seismic actions in moderate to high seismicity areas. Three representative prototype residential buildings with five, seven, and ten storeys, located in areas with peak ground accelerations (PGA) of 0.2 g, 0.3 g, and 0.4 g have been considered.This Thesis consists of six chapters; the first is an introduction, the second describes the current state of the art, and the last presents conclusions and future research. Chapters 3, 4, and 5 constitute the main body of this Thesis, and their content is described below.Chapter 3 presents a theoretical investigation into the compressive performance of single Cold-Formed Steel (CFS) members with Cee-shaped cross-sections, as well as various built-up sections (back-to-back, toe-to-toe, nested and a stud pack 4) derived from Cee profiles. The initial assessment of compressive performance is conducted using closed-form hand expressions. These results are subsequently complemented by design based on the Finite Strip Method (FSM) and further refined through simulations employing the Generalised Beam Theory (GBT). Detailed results for the compressive performance of the studied sections, considering a range of parameters including section thicknesses, steel grades, and buckling lengths considered, are also provided. Chapter 4 describes the performed experimental investigation into the compressive performance of steel-only and concrete-filled cold-formed steel built-up sections. The study encompasses the design and preparation of the test specimens, the experimental results, the predicted compressive resistance, and a comparative analysis between the predicted and observed values. Particular attention is given to the increasing of the effective area resulting from concrete infill; which is theoretically and experimentally validated through modifications to existing design approaches. Additionally, Chapter 4 analyses the compressive resistance of two CFS built-up sections filled with concrete -referred to as 4-pack Concrete-Filled Cold-Formed Steel (CF CFS) and 6-pack Concrete-Filled Cold-Formed Steel (CF CFS)-, across a range of concrete strength classes, from C20/25 to C50/60.Chapter 5 develops the design of three representative prototype steel framing buildings, 5-, 7-, and 10-storey, in regions of moderate (PGA 0.2 g) and high seismicity (PGA 0.3 g and 0.4 g) areas, by means of a Finite Element Method software, complemented with hand calculations. The main goal is obtained the internal forces in the most critical members of the buildings (namely the chord studs and the diagonal bracings of the wall panels). As described in detail in Chapter 5, the spectral ordinates, the base shear forces, and their distribution along the height of the buildings have been determined by hand calculations in accordance with the provisions of the second-generation Eurocode, since these provisions are not yet implemented in the FEM software. The results of the seismic analyses for each prototype building and seismicity level are presented, as well as a sizing proposal of the chord studs based on both the internal forces and the compressive performance of the concrete-filled in Chapters 3 and 4.
  

• ROGNON, PAUL JORIS DENIS: Improving variable selection properties by leveraging external data.
  
  Author: ROGNON, PAUL JORIS DENIS
  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 STATISTICS AND OPERATIONS RESEARCH
  Department: Department of Statistics and Operations Research (EIO)
  Mode: Normal
  Deposit date: 09/03/2026
  Reading date: 20/04/2026
  Reading time: 14:00
  Reading place: Sala d'actes de la FMECampus Diagonal Sud, Edifici U. C. Pau Gargallo, 14 08028 Barcelona
  Thesis director: ROSSELL RIBERA, DAVID | ZWIERNIK, PÌOTR
  Thesis abstract: Sparse high-dimensional signal recovery is only possible under certain conditions on the number of parameters, sample size, signal strength, and underlying sparsity. I show that leveraging external information, as possible with data integration or transfer learning, allows pushing these mathematical limits. Specifically, I consider external information-dependent l0 penalties and Bayesian variable selection methods, show that they attain model selection consistency under milder conditions than standard methods, and that they also attain faster model recovery rates. First, I obtain results for oracle-based penalties and prior inclusion probabilities that have access to perfect sparsity and signal strength information. Those results provide an understanding of how and when external information helps variable selection. They also provide a theoretical benchmark to evaluate practical non-oracle selection methods using external information. Subsequently, I propose data-based procedures grounded in empirical Bayes methods that leverage external information to ease variable selection and do not require an oracle. I derive their properties in the particular case where external information partitions the set of variables in blocks with potentially distinct characteristics. Finally, I discuss a computational framework for the incorporation of external information in Bayesian variable selection through empirical Bayes in the general case.