Tesis Doctorals - Facultat - Física

URI permanent per a aquesta col·leccióhttps://hdl.handle.net/2445/41381

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Advanced Transition Metal Oxide Nanomaterials for Energy Technologies
(Universitat de Barcelona, 2025-02-10) Yang, Linlin; Cabot i Codina, Andreu; Martinez Alanis, Paulina R.; Universitat de Barcelona. Facultat de Física
[eng] Transition metal oxides (TMOs) are compounds formed from transition metals and oxygen, known for their complex and versatile structures, including diverse crystal forms and multiple oxidation states. This versatility gives TMOs unique electronic, magnetic, optical, and thermal properties, making them valuable in advanced technological applications. The ability of TMOs to engage in redox reactions, coupled with their stability abundant availability, and cost-effectiveness, makes them ideal for applications such as electrochromic devices, catalysis, and batteries. Electrochromic smart windows (ESWs) offer an attractive option for regulating indoor lighting conditions. Electrochromic materials based on ion insertion/desertion mechanisms also present the possibility for energy storage, thereby increasing overall energy efficiency and adding value to the system. However, current electrochromic electrodes suffer from performance degradation, long response time, and low coloration efficiency (CE). In Chapter 2, I detail the synthesis mechanism of defect-engineered brookite titanium dioxide (TiO2) nanorods (NRs) with different lengths and investigate their electrochromic performance as potential energy storage materials. The controllable synthesis of TiO2 NRs with inherent defects, along with smaller impedance and higher carrier concentrations, significantly enhanced their electrochromic performance, including improved resistance to degradation, shorter response times, and enhanced CE. The electrochromic performance of TiO2 NRs, particularly longer ones, is characterized by fast switching speeds (20 s for coloration and 12 s for bleaching), high CE (84.96 cm2 C−1 at a 600 nm wavelength), and good stability, highlighting their potential for advanced electrochromic smart window applications based on Li+ ion intercalation. This work was published in Small in 2023. Direct urea fuel cells (DUFCs), generating electric power from the electrooxidation of urea have great potential as a cost-effective technology to simultaneously treat urea-containing wastewater and produce electricity. DUFCs release only gaseous products, not generating new waste, and they are characterized by a relatively high theoretically open circuit voltage (OCV) of 1.147 V, similar to that of hydrogen fuel cells. However, the relatively low OCVs and peak power densities realized so far have hindered their commercialization. Therefore, improving the OCVs and peak power densities of DUFCs using low-cost and abundant transition oxide nanoparticles as catalysts is required to ensure practical significance. In Chapter 3, I detail the production of self-supported electrodes consisting of NiO nanosheets vertically grown on CuO nanowires and use them to realize the urea oxidation reaction (UOR). Such electrodes show excellent UOR performance requiring 1.39 V vs. reversible hydrogen electrode (RHE) to achieve 100 mA cm-2. Besides, DUFCs provide OCV and power densities up to 0.88 V and 11.35 mW cm-2. Electrochemical characterization and Raman spectroscopy prove the formation of NiOOH to enable the UOR. Mott-Schottky analysis and ultraviolet photoelectron spectroscopy show the NiO/CuO p-p heterostructure to facilitate the charge transfer from CuO nanowires to NiO nanosheets. Besides, at a local level, density functional theory calculations show that the presence of CuO modulates the electronic states of Ni at the very NiOOH/CuO interface, which results in stretched Ni-O bonds and a uniquely elongated N-H bond of urea that favor its oxidation. This work was published in Nano Energy in 2023. Rechargeable aqueous zinc-air batteries (ZABs) have emerged as a promising candidate technology for energy storage applications owing to their high energy density, safety, and environmental friendliness. However, ZABs are limited by the sluggish kinetics of the multiple electron-proton coupling processes involved in the oxygen evolution reaction (OER) that takes place at the air cathode during ZAB charging. Therefore, the development of transition oxide nanoparticles as highly efficient, low- cost, and durable OER catalysts is crucial for the realization of high-performance ZABs, among other electrochemical technologies. Beyond optimizing electronic energy levels, the modulation of the electronic spin configuration is an effective strategy, often overlooked, to boost activity and selectivity in a range of catalytic reactions, including the OER. This electronic spin modulation is frequently accomplished using external magnetic fields, which makes it impractical for real applications. In Chapter 4, I detail the synthesis of Ni/MnFe2O4 heterojunctions and apply them in OER. I investigate the spin modulations of the reconstrued NiOOH/MnFeOOH during the OER by the heterojunctions without an external magnetic field. NiOOH/MnFeOOH shows a high spin state of Ni, which regulates the OH− and O2 adsorption energy and enables spin alignment of oxygen intermediates. As a result, NiOOH/MnFeOOH electrocatalysts provide excellent OER performance with an overpotential of 261 mV at 10 mA cm−2. Besides, rechargeable ZABs based on Ni/MnFe2O4 show a high OCV of 1.56 V and excellent stability for more than 1000 cycles. This outstanding performance is rationalized using density functional theory calculations, which show that the optimal spin state of both Ni active sites and oxygen intermediates facilitates spin-selected charge transport, optimizes the reaction kinetics, and decreases the energy barrier to the evolution of oxygen. This work was published in Adv. Mater. in 2024. The main conclusions of this thesis and some perspectives for future work are presented in the last
Few Interacting Particles in Low-Dimensional Quantum Systems: From Harmonic Oscillators to Fractal Lattices
(Universitat de Barcelona, 2025-02-21) Rojo Francàs, Abel; Juliá-Díaz, Bruno; Universitat de Barcelona. Facultat de Física
[eng] Quantum mechanics is a fascinating field to explore, where its effects are usually non- trivial and counterintuitive. In this Thesis, we focus on systems with a small number of particles in low dimensions, where the quantum effects are enhanced. We consider experimentally realistic systems, considering either an external harmonic confinement or a lattice potential. These systems can be created nowadays in ultracold atom laboratories worldwide, where they can control the dimensionality, the external potential, as well as the number of particles and the interactions. Our goal is to understand the static and dynamic properties of different systems involving few particles and a wide range of interactions. In particular, we focus on the one-dimensional harmonic trap, fractal lattices, and one-dimensional three-site lattices. In each system, we consider a contact interaction potential defined by a delta function in the continuum space or an on-site interaction for the lattices. In addition, we compute different properties, such as energy spectra, densities, pair correlations, mean square displacement, and population of each site, in both static and time-dependent cases. We combine analytical and numerical techniques to study the different systems. In particular, the numerical part is mostly done using exact diagonalization techniques. With this approach, we can only examine systems with few particles due to the intrinsic limitations of the method, although it provides the capacity to obtain any property needed. The case of the harmonic oscillator trap includes an additional limitation due to the exact diagonalization method, as the basis must be truncated, resulting in upper-bound energies. We show how to correct this error and obtain a better estimate of the energy and the density by using the analytical solution of the two-particle system. We demonstrate that this correction works for a larger number of particles by computing results for up to eight particles. For the systems with harmonic oscillator confinement, we compute the energy spectrum as a function of the interaction strength, the density for different interaction values, and pair correlations. We present the results for the symmetric SU (N ) case and then study systems with broken interaction symmetry. We present different interaction configurations, and we explore the ground state structure, where the correlations play an important role. We also consider the impurity case, where one particle interacts with all the bath particles but the bath particles do not interact with each other. We show that the impurity system can be mapped to an effective one particle in a double-well model, showing two phases: the miscible and the immiscible. Afterwards, we study fractal lattice systems, where the sites and the tunneling connections are configured in a non-standard scheme creating an effective finite representation of a fractal structure. Under this situation, we explore the effect on the transport of a single-particle obtaining the diffusion exponent and relating it to spectral properties. We demonstrate that the fractal slows down the motion of the particle and that this effect is robust against a random potential. Using the slower dynamics, we show how the fractal system can preserve information about the initial phase of the wavefunction for much longer times than a regular lattice. We also explore the entanglement of a two-particle system and how the interactions affect entanglement creation. Finally, we study a three-site lattice where each site has a different energy and the couplings are time-dependent. We implement the spatial adiabatic passage protocol, that transfers a single particle from the first to the third site, and generalize it for a few particle systems with interactions. Due to the interactions, the adiabaticity of the protocol is lost, but we demonstrate that it is possible to populate the third state for certain interaction strength values. As a result, since the final state populates the most energetic site of the system, we propose this setup as a quantum battery model.
Enhanced Optical Response in Arrays of Multifunctional Plasmonic Nanostructures
(Universitat de Barcelona, 2025-04-11) Rodríguez Álvarez, Javier; Fraile Rodríguez, Arantxa; Labarta, Amílcar; Universitat de Barcelona. Facultat de Física
[eng] This thesis is devoted to the study of two plasmonic nanostructures that present a 3-fold symmetry, namely, inverted honeycomb lattices of bars and twisted stacks of triskelion nanostructures. These systems are particularly interesting due to the inherent geometric frustration originated by the mis- match between dipolar excitations, and the odd parity associated with the 3-fold symmetry. The combination of FDTD simulations with the fabrica- tion and subsequent far-field and near-field optical characterization of such structures allows for a multifaceted description of the system. In this thesis, a remarkable agreement between experiments and simulation is achieved, demonstrating the effectiveness of this combined approach in elucidating the response of plasmonic systems. This thesis begins with a fundamental overview of the field, laying the groundwork for the essential concepts necessary for understanding the main findings presented in subsequent sections. These results are discussed in detail through the publications derived from this research. Furthermore, simulation methodologies, nanofabrication techniques, and characterization methods are introduced, as they form the core of the research presented herein. Publications I and II are devoted to the study of inverted honeycomb plas- monic lattices. Here we prove the potential of such structures as refractive index sensors, taking advantage of the sharp SLR and the well-defined spec- tral dependence with the refractive index. The general sensing capabilities of this SLR can easily be expanded due to the out-of-plane electric field of hot spots spanning hundreds of nanometers away from the structure surface, providing a huge potential sensing volume. From a fundamental point of view, we have successfully characterized the plasmonic response of this system through state-of-the-art EELS experiments and FDTD simulations. By using EELS, both bright and dark modes can be detected. In particular, we present the first observation of resonances with an anti-ferroelectric arrangement of the dipolar excitations of the slits in the honeycomb lattice that occur with such spatial periodicity so that their unit cell has twice the area of the honeycomb lattice. The samples presented in this part have been fabricated by EBL and specially dedicated FIB milling using Au ions to avoid contamination of the sample. Publications III and IV focus on the study of two stacked triskelia nanostruc- tures, and their response as a function of the geometry of the structure, in particular, the twist angle between them. The triskelion motif is character- ized by its 3-fold symmetry and inherent two-dimensional chirality in 2D. This system holds two coupled plasmonic resonances tunable by control- ling the angle between both triskelia. We have demonstrated that a simple bonding-antibonding model is insufficient to fully elucidate the behavior of these two resonances. Instead, we have observed a continuous evolution of the excited modes as a function of the angle between the elements. Further insight into the combination of such resonances with SLR is proposed. The fabrication of this structure by successive EBL over large areas and high degree of alignment are also detailed.
Directed cell migration: forces, shapes, and fluctuations in tissues. From active hydrodynamics to experiments
(Universitat de Barcelona, 2025-03-21) Pi Jaumà, Irina; Casademunt i Viader, Jaume; Universitat de Barcelona. Facultat de Física
[eng] This thesis investigates collective cell migration in epithelial tissues, under the framework of active soft matter physics. We model epithelial tissues as active polar fluids, since their components, the cells, have an internal source of energy and align, polarizing, in order to generate movement. Despite the myriad of extremely complex chemical interactions and signaling cascades within cells, ultimately motion must be governed by the most basic laws of physics. The focus of this thesis, therefore, is to use a simple and phenomenological model, encoding all these complex interactions in terms of the physical forces and mechanical parameters of the tissue. This allows us, in a very simplified but effective way, to have a generic model to model several relevant scenarios in collective cell migration. One of the main focuses of the thesis is the collective durotaxi, a phenomenon by which the migration of cellular aggregates is directed by the rigidity of the extracellular environment. Comparing the model with in vitro experiments, we identify the existence of an optimal stiffness of the substrate that maximizes the migration speed, and we observe that the wetting properties of the aggregates are closely linked to it. In addition, in the same way that the tensile forces made by cells are influenced by the stiffness of the substrate or the environment, we also study the inverse feedback mechanism, that is, how these forces can modify the rigidity of the environment. We find that their stiffening can be a mechanism to induce a jump to a much higher state of traction and trigger the spreading of the tissue. Durotaxi could have implications in fundamental biological processes where there is directed movement of cells, such as in embryonic development or cancerous metastasis. Apart from durotaxis, other factors that contribute to targeted migration are examined, such as the influence of tissue shape and fluctuations. We experimentally demonstrate that an asymmetry in shape can induce spontaneous tissue movement, without requiring global polarization, and we classify different modes of migration according to the parameters of the model. By carrying out epithelial tissue migration experiments, where we control their initial shape, we corroborate some of these predictions, especially the distinction between an anisotropic and an isotropic expansion. Finally, to incorporate the inherent variability of biological systems, we introduce stochastic noise into the model and study the consequences of different noise sources. The noise can be internal in the dynamics of polarity, or external in a coupling parameter between the cells and the substrate, related to the adhesion kinetics of the ligands. Although the model captures well some aspects of the fluctuations of the tensile forces in the experiments, such as their magnitude with the distance from the center of the fabric or the temporal correlations, other aspects remain to be explored in more depth, such as the spatial correlations and the diffusion coefficients of the center of mass of the fabric. In conclusion, this work provides a framework to decipher the physical mechanisms underlying collective cell migration, thus contributing to the knowledge of various biological processes, such as tissue regeneration, wound closure or tumor progression. The development of simple but effective theoretical models can also inspire new experimental designs, allowing a fruitful integration between theory and experiments in our quest to explain nature.
Development of a Neurovascular Microfluidic Model with an Endothelial Barrier-Integrity Sensor for Pharmaceutical Innovation in Neurodegenerative Diseases
(Universitat de Barcelona, 2025-03-14) Palma Florez, Sujey; Mir Llorente, Mònica; Lagunas Targarona, Anna; Universitat de Barcelona. Facultat de Física
[eng] Neurodegenerative diseases represent a significant health challenge, as no cure is currently available. The unique anatomy of the blood-brain barrier, which limits drug delivery to the brain, as well as the lack of predictive pre-clinical models, contribute to delays in the drug discovery process. This research presents the development of two distinct 3D models aimed at advancing pharmaceutical innovation for neurodegenerative diseases. We designed a blood-brain barrier-on-a-chip device that incorporates trans-endothelial electrical resistance electrodes for real-time assessment of barrier integrity. The 3D microfluidic design involves the co-culture of brain endothelial cells, pericytes, and astrocytes, before being fully characterized to verify the proper development of the blood-brain barrier. The developed platform was then utilized to evaluate the permeability and toxicity of novel nanotherapeutic agents for neurodegenerative diseases. Furthermore, a more advanced in vitro model for drug discovery of neurodegenerative diseases was assembled. This model incorporated human induced-neurons along with other cell types to create a neurovascular-unit in vitro. Specifically, we co-cultured human induced neurons with oligodendrocytes, astrocytes, pericytes, and endothelial cells within a microfluidic device. Finally, we monitored the release of neurofilament light, a potential biomarker of neuronal degeneration, in response to exposure to two different neurotoxic agents. Quantifying neurofilament light release enables assessment of neurodegenerative progression and evaluation of potential therapeutic interventions to mitigate disease advancement. The blood-brain barrier-on-a-chip and neurovascular-unit-on-a-chip models represent a versatile and scalable platform that offers a cost-effective, human-relevant alternative to traditional animal models. These platforms facilitate drug screening and accelerate the discovery of treatments for neurodegenerative diseases.
High Entropy Materials as Air Cathodes for Robust Zinc-Air Batteries
(Universitat de Barcelona, 2025-02-10) He, Ren; Cabot i Codina, Andreu; Universitat de Barcelona. Facultat de Física
[eng] This thesis focuses on the development of high-entropy materials (HEMs) as advanced bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The study systematically investigates the synthesis methods, structural properties, and catalytic performance of these materials, with particular emphasis on their application in zinc-air batteries (ZABs). Through the incorporation of transition metals and experiencing surface reconstruction processes, these materials exhibit remarkable catalytic efficiencies and stability. Density functional theory (DFT) calculations provide further insights into the active sites and mechanisms driving the enhanced catalytic activity. This research highlights the potential of high entropy alloys (HEAs) and high-entropy phosphides (HEPs) as next-generation catalysts, paving the way for future advancements in energy storage and conversion technologies. In Chapter 2, I detail the development a low-temperature colloidal method to synthesize CrMnFeCoNi and CuMnFeCoNi HEAs, along with quaternary and ternary alloys. CrMnFeCoNi displays superior bifunctional catalytic performance for both OER and ORR, outperforming CuMnFeCoNi, quaternary alloys, and commercial catalysts like RuO2 and Pt/C. DFT calculations reveal that the incorporation of Cr into the MnFeCoNi matrix lowered the energy barriers for OER and optimized ORR intermediate steps. This material exhibits high power density, specific capacity, and excellent long-term cycling stability when applied as a bifunctional catalyst in ZABs, underscoring its potential for energy storage applications. This work was published in Energy Storage Materials in 2023. Chapter 3 presents the synthesis of FeCoNiMoW HEA by incorporating 4d Mo and 5d W into a 3d FeCoNi matrix using a low-temperature solution-based method. The resulting alloy demonstrates a highly distorted lattice and strong electronic coupling effects. The FeCoNiMoW HEA exhibits excellent catalytic performance for OER with low overpotentials and great bifunctional properties, surpassing commercial catalysts like Pt/C and RuO2. DFT calculations identify Ni as the active site for OER, with Mo and W enhancing oxygen intermediate interactions. The FeCoNiMoW-based ZABs show high power density, specific capacity, and exceptional long-term stability, even 1 in flexible applications, making them a promising candidate for wearable energy devices. This work was published in Advanced Materials in 2023. In Chapter 4, I detail the synthesis of FeCoNiPdWP HEPs via a mild colloidal method, resulting in a homogeneous nanostructure. These HEPs demonstrate exceptional bifunctional catalytic performance for both OER and ORR, with a low overpotential of 227 mV for OER and a half-wave potential of 0.81 V for ORR. The outstanding OER performance is attributed to the reconstructed FeCoNiPdWOOH surface, enriched with high-oxidation-state Fe, Co, and Ni. Pd facilitates OH⁻ adsorption, while W modulates the electronic structure for better oxygen intermediate adsorption. For ORR, surface reconstruction into FeCoNiPdWPOH further enhances performance, with Pd and W maintaining their phosphide environments and Pd as the main active site for ORR. The small energy gap between OER and ORR enables FeCoNiPdWP HEPs to achieve over 700 h of stable operation in ZABs, showcasing their potential for long-term and highly efficient bifunctional catalysis. This work was published in Energy & Environmental Science in 2024. The main conclusions of this thesis and some perspectives for future work are presented in the last.
A multidisciplinary approach to rheological blood characterisation and angiogenesis modelling using microfluidics
(Universitat de Barcelona, 2025-01-24) Ferré Torres, Josep; Hernández Machado, Aurora; Universitat de Barcelona. Facultat de Física
[eng] Blood viscosity plays a critical role in cardiovascular health, influencing hemodynamic processes and disease states. Accurate and rapid measurement of blood rheological properties is essential for diagnostic and therapeutic interventions. Concurrently, understanding the mechanisms of endothelial cell migration is fundamental to elucidating angiogenesis and developing treatments for vascular diseases. This thesis presents a comprehensive study encompassing the design and industrialisation of a novel medical device for blood viscosity measurements alongside the mathematical modelling of collective chemotactic endothelial cell migration. A microfluidic system employing fluid front rheology was developed, featuring a microchannel equipped with electrodes to facilitate efficient and rapid analysis of blood samples within five minutes. This innovative methodology requires minimal sample volumes and provides reliable rheological data, demonstrating significant potential for integration into routine clinical workflows. The device’s capability for high-throughput screening addresses the need for timely diagnostic and therapeutic decision-making in clinical settings. The analysis of plasma viscosity revealed greater variability than anticipated, yet plasma samples predominantly exhibited Newtonian behaviour, aligning with established theoretical models. Factors such as protein concentration, red blood cell lysis, and overall plasma composition contribute to this variability. Blood viscosity measurements indicated substantial variability across different samples, underscoring the complexity arising from the non-Newtonian, shear-thinning nature of blood. Individual differences in haematocrit levels, red blood cell deformability, and aggregation tendencies further complicate the utilisation of blood viscosity as a standalone diagnostic marker. These findings emphasise the necessity for comprehensive patient profiling, including age, sex, medical history, lifestyle habits, and concurrent medications, to enhance the diagnostic accuracy of rheological assessments. The considerable overlap in viscosity profiles between healthy and non-healthy individuals suggests that blood viscosity measurements should be integrated with other clinical data and biomarkers to improve understanding of a patient’s haemodynamic status. Personalised diagnostic approaches are recommended to optimise patient outcomes through targeted interventions. In parallel, the thesis addresses the computational challenges of modelling chemotactic endothelial cell migration on moving and deformable domains. A phase-field method was employed to solve equations governing the dynamics of growing capillaries and the extracellular matrix using a fixed mesh framework. An energy functional accounting for local chemoattraction at the cell membrane was proposed, effectively reproducing actin behaviour observed in experimental studies. A finite difference numerical method was developed, proving efficient, accurate, and robust, facilitating the investigation of cell migration in two-dimensional environments. Simulations demonstrated that migration on flat substrates leads to stationary states of motion, consistent with experimental observations. Introducing obstacles enabled the reproduction of complex migratory behaviours, highlighting the cells’ ability to exploit microenvironment geometry for effective migration. The inclusion of extracellular matrix degradation mechanisms allowed tip cells to navigate towards maximum chemotactic gradients by creating their pathways, simulating the action of matrix metalloproteases. This modelling provides valuable insights into the autonomy of tip cells in directing migration and the interplay between cellular activities and extracellular matrix modifications. This simulation approach offers a new framework for understanding cell migration dynamics within complex environments, emphasising the intricate relationships between cellular behaviour, environmental structure, and matrix remodelling. The model simulates migrating cells and their chemotactic interaction with their surroundings by accurately capturing stationary motion, obstacle navigation, and matrix degradation mechanisms. These insights extend beyond theoretical validation, providing a predictive tool to explore how cells navigate diverse extracellular landscapes. These could inform therapeutic strategies targeting cell migration in tissue regeneration, cancer metastasis, and angiogenesis. Furthermore, this type of modelisation allows state-of-the-art deep learning models to build upon and create systems that would inform the biomaterial engineers of the necessary properties of the surroundings to generate an optimal vasculature network.
Effective field theory methods at high temperature and chemical potential
(Universitat de Barcelona, 2025-03-31) Comadran, Marc; Manuel Hidalgo, Cristina; Universitat de Barcelona. Facultat de Física
[eng] This thesis applies and develops effective field theory methods for the study of plasmas at high temperature and/or density. In the 90s, the theoretical frameworks necessary to study quantum electrodynamics (QED) and quantum chromodynamics (QCD) in these extreme conditions were developed. The tools developed assumed that the mass of the plasma constituents could be neglected. In a first stage of the thesis, we investigate the effects of incorporating small masses associated with the fermionic constituents of the plasma in perturbative calculations, relevant when they are not extremely small compared to the temperature and/or chemical potential that characterizes the plasma. Our study provides a first step to address this impact, calculating small massive corrections to both the photon and gluon polarization tensor, under the hard thermal loop approach. To evaluate these mass corrections, we show the usefulness of effective field theories, in particular, the on-shell effective field theory (OSEFT) for fermions. Next, we analyze the impact of mass corrections in the context of energy loss due to collision of a highly massive and energetic fermion, which passes through a plasma at high temperature and/or density. Let us consider the following two cases: when the constituents of the plasma are electrons, positrons and photons, and also when these are quarks, antiquarks and gluons. Using dimensional regularization, we effectively manage the new divergences arising from the expansion by small masses and demonstrate a consistent cancellation of divergences between hard and soft contributions, obtaining a finite result. Mass corrections for energy loss are determined in the first order with logarithmic precision, extending the foundational work of Braaten and Thoma for massless fermions. In a second stage of the thesis, we develop a new effective field theory, the OSEFT for abelian gauge fields. The final Lagrangian can be formulated in terms of a gauge-invariant vector field without the need to introduce a gauge fixation term. We prove the invariance under reparameterization (RI) of the theory, which means that the Lorentz symmetry is respected. By exploiting RI symmetry, we provide a derivation from early principles of the side-jump effect for photons. We also present applications of photon OSEFT in the context of electron and positron plasmas, for example, in quantum kinetic theory and in perturbative quantum field theory calculations. In addition, we show that when considering small purely quantum effects, the classical definition of polarization ratios, given in terms of the Stokes parameters, loses its Lorentz invariance. We therefore propose a new definition of polarization ratios, which is Lorentz invariant when these small quantum effects are present, relevant in reference systems that are not at rest with respect to the medium and with possible applications in astrophysics and cosmology, where these conditions are common. Finally, we construct a quantum kinetic theory for photons in the presence of a background of axions, at the so-called collision-free limit, from the complete theory of quantum electrodynamics. We show that, in the classical regime, kinetic equations exhibit well-known features of electrodynamics with axions. The formalism we present allows us to systematically calculate how the classical limit is corrected due to small quantum effects. In addition, we address the impact of the axion background on the collective modes of photons that occur in electron and positron plasmas in thermal equilibrium. Notably, the axion background breaks the degeneration of the transverse collective modes, while the longitudinal collective mode, called plasmon, is not affected.
Salt dependent DNA translocation dynamics across nanopores
(Universitat de Barcelona, 2025-04-25) Colchero Truniger, Alejandro; Ritort Farran, Fèlix; Pastor del Campo, Isabel; Universitat de Barcelona. Facultat de Física
[eng] This thesis uses two complementary single-molecule techniques, nanopipette microscopy and optical tweezers, to investigate the impact of various monovalent salts at high concentrations in DNA. The thesis begins by characterizing the conductance and noise properties of nanopipettes in a wide range of concentrations. Once the nanopipettes have been characterized, they are used to conduct DNA translocation experiments to examine how different cations influence their translocation parameters. These experiments also allow us to explore the effects of applied voltage and salt concentration on DNA folding configurations during translocation. In addition, we explore why compact DNA folding configurations have lower dwell times compared to longer folding configurations. Finally, optical tweezers are used to carry out stretching experiments on a DNA fork, providing information on DNA stability under conditions of high ionic strength related to DNA translocation experiments. The thesis is divided into six parts. Part I provides an introduction to the experimental techniques used throughout this work, along with the theoretical frameworks and concepts that will be needed for Parts II, III and IV. This part is divided into three chapters. Chapter 1 is an introduction to the nanofear field. The chapter describes the setup and basic concepts required to perform electrical measurements with nanopipettes and discusses the limits of resolution of the technique. The main sources of noise when experiments with nanopores are carried out are also described. Also, some relevant nanofluidic phenomena are introduced when working at the nanoscale, along with some theoretical foundations on the regulation of surface load. Finally, some previous results of DNA translocation through nanopores are shown. Chapter 2 introduces the optical trap and mini-tweezers configuration that was used to perform the experiments in this thesis. Chapter 3 introduces the basic components and structure of nucleic acids, focusing on DNA, which will be the biomolecule studied throughout the thesis. The chapter concludes by presenting the theoretical foundations of two elastic models used to describe the elastic properties of polynucleotides. Part II contains results of experiments with nanopipettes. It begins with chapter 4, where the conductance of nanopipettes for different salt concentrations is studied, comparing the contributions of conductance in volume and surface area and the effect of pH on surface loading. In addition, two conductivity models are compared to model the conductance of nanopipettes with concentration. In addition, the blinking noise of the nanopipettes is analyzed, exploring how the parameters that describe the noise change with concentration and tension. Chapter 5 presents λ-DNA translocation experiments in different monovalent salts. This chapter investigates the effect of concentration and cation type on translocation parameters such as residence time, electric current blocking, and charge blocking of λ-DNA translocations. The chapter focuses on how the cation-DNA interaction changes with the size of the cation. Chapter 6 studies the different folding configurations that occur during DNA translocation and how they depend on salt tension and concentration. To do this, an analysis of the different levels that occur during λ-DNA translocation and the residence time of the different levels is carried out. The analysis also allows us to extract general data on DNA translocation through nanopipettes. Finally, the causes of the lower dispersion of the dwell time of the more compact folding configurations compared to the longer folding configurations are explored. Part III includes experiments with optical tweezers. In Chapter 7, optical tweezers are used to conduct stretching experiments of long DNA forks at high ionic concentrations of various monovalent salts. The average opening force and the effect of concentration on fork stability are investigated. The chapter concludes with a joint discussion of the results of translocation experiments and optical tweezers at high salt concentrations. Part IV contains the results of a one-month international stay. Chapter 8 includes a brief introduction to the SPRNT (Single-molecule picometer resolution nanopore tweezers) technique, which was used to perform experiments with the Hel308 helicase. In addition, some preliminary experiments of the with the gp41 helicase using SPRNT are presented. Part V contains the final conclusions of the thesis and the future perspectives of the work. Part VI consists of all the Appendices. Appendices E and C complement the results of some of the chapters, while Appendices A, B, F, and D describe in detail the most important experimental protocols and MATLAB codes used in the development of the thesis.
New experimental techniques for axion searches in the RADES and BabyIAXO experiments
(Universitat de Barcelona, 2025-02-20) Cogollos Triviño, Cristian; Picatoste Olloqui, Eduardo; Doebrich, Babette; Universitat de Barcelona. Facultat de Física
[eng] Initially proposed as part of the solution to the strong CP problem of the Standard Model of particle physics, axions and axion-like particles appear on several Beyond Standard Model extensions. These pseudoscalar pseudo-Nambu-Goldstone bosons could also be the answer to one of the most puzzling questions on cosmology, the Dark Matter problem. For decades, searches have been performed for finding these elusive particles. The most promising of which deals with the conversion of axions into photons and their observation. Depending on the origin of these axions we can distinguish between two main kind of experiments, haloscopes (for dark matter axions) and helioscopes (for solar axions). In this document we compile three different contributions to axion searches within the same framework that have been inside the scope of the thesis work during the last years. The first comprises the work developed in a proposal that paves the path for haloscope searches at BabyIAXO, in particular a set of 5 meter long cavities are proposed for covering the structures already used at CAST for axion searches. In the second part we expose the characterization and optimization of the radioactive background of the acquisition electronics for the BabyIAXO helioscope. In the last part a general framework for treating multicavity resonators is presented as an extension of the theory developed for the first RADES prototype, based on this idea two new prototypes were designed, manufactured and characterized.
Optimization and degradation of supercapacitors in aqueous and super-concentrated “water-in-salt” electrolytes
(Universitat de Barcelona, 2025-01-22) Delgado Galindo, José Miguel; Morante i Lleonart, Joan Ramon; Jacas Biendicho, Jordi; Universitat de Barcelona. Facultat de Física
[eng] Supercapacitors are electrochemical energy storage devices. Its energy comes from the electrostatic accumulation of ionic charge on the surface of an electrode, compensated by an opposite electrical charge on the inner surface of the electrode, for this reason they are also called electrochemical double layer capacitors. Since no chemical reactions are involved, these devices can be charged and discharged rapidly. This makes them ideal for high-power applications such as powering camera flashes, starting engines, or managing power peaks in electrical grids. They are also used for energy recovery in regenerative braking systems of trains or electric vehicles. Although capacitors provide great power, their energy density is an order of magnitude lower than that of batteries, which limits their extensive use. One of the objectives of this thesis is to increase the energy, power, and energy efficiency of capacitors based on activated carbon electrodes in aqueous electrolytes. To this end, different strategies have been addressed to increase capacitance and voltage, which are directly related to the increase in energy, as well as to reduce resistance, which is related to performance and lifespan. Using the aqueous electrolyte 1 M KOH, the following aspects have been studied: 1) optimizing the mass balance between the positive and negative electrodes to improve energy efficiency and cycle life, 2) thermally treating the electrodes at temperatures below the melting point of the binder to increase energy, 3) investigating the impact of two membranes, fibreglass, and polypropylene, on rate-capacitance performance. Optimizations conducted in Chapter 3 using YP50 as electrode show that the positive to negative mass ratio should be adjusted to 0.6, the thermal treatment should be set to 240 ºC, and fibreglass membranes should be used to achieve a better capacitor response. In Chapter 4, we used super-concentrated aqueous solutions based on potassium acetate, called “water-in-salt” electrolytes, to increase the voltage of the devices. Concentrations from 1 m to 32 m (mol/Kg) have been studied, verifying an increase in the potential window up to 1.8 V and finding a compromise between capacitance, rate capability, cycle life, and cost for the 27 m KAc electrolyte. The use of the 27 m KAc electrolyte showed a capacitance of 26.3 F/g and 19.6 F/g when increasing the scan rate from 5 to 100 mV/s, with a retention of 74.5%, a capacitance of 13 F/g over 10,000 charge cycles at 1 A/g, and the estimated electrolyte cost was €4.42 to produce 1,000 cells. In chapter 6 we prepared hybrid capacitors, composed of a capacitive activated carbon electrode and a faradaic electrode using lithium oxides. Lithium titanium oxide (LTO), commonly used as anode for its well-defined phase transition around 1.6 V vs Li/Li+, was used as the negative electrode and YP50 as the positive. Lithium iron phosphate (LFP), commonly used as cathode for its well-defined phase transition around 3.5 V vs Li/Li+, was used as the positive electrode and YP50 as the negative. The YP50/LTO capacitor with the 1 M LiPF6 organic electrolyte showed a high capacitance of 30.2 F/g at a low rate of 0.6 mV/s and 7.7 F/g at a medium rate of 20 mV/s in a potential window of 2 V. The LFP/YP50 capacitor showed with the organic electrolyte 1 M LiPF6 a capacitance of 20.9 F/g at a low rate of 0.1 mV/s and 8.7 F/g at a medium rate of 20 mV/s in a potential window of 2.9 V and with the super-concentrated water-in-salt electrolyte 32 m KAc + 6 m LiAc it showed a very high capacitance of 52.4 F/g at 0.1 mV/s and 13.3 F/g at 10 mV/s in a potential window of 1.8 V. The other objective of this thesis, discussed in chapter 5, is the study of degradation mechanisms involving irreversible reactions in aqueous capacitor components, which reduce its performance. These mechanisms are accelerated by operating conditions such as temperature, humidity, and working potential window. We studied the degradation mechanism of activated carbon capacitors in two aqueous electrolytes: super-concentrated "water-in-salt" 27 m KAc and dilute 1 M KOH. To accelerate their degradation, we have performed an electrochemical characterization of the cells by means of a series of 10,000 charge and discharge cycles at 1 A/g in a potential window of 2 V, which, being larger than the stability window of the electrolytes, ensures a rapid degradation. Once the cells were degraded, we proceeded to disassemble and study with SEM, EDS, FTIR, XRD and XPS methods. A reassembly of the cells with 27 m KAc was also performed after degradation, changing the electrolyte and the membrane and maintaining the electrodes and current collectors, cycled again and studied with the method of failure mode and effects analysis (FMEA) to identify and evaluate the potential failure modes, analyse their causes and its severity and create strategies to mitigate them. The main failure modes analysed are related to the decomposition of the electrolytes, leading to water splitting and the generation of hydrogen and oxygen. Oxygen would oxidize the current collectors and the electrodes, increasing the resistance and reducing the electrical conductivity and capacitance. The oxidation of the activated carbon electrodes would generate CO2, which together with O2 and H2 would block the pores of the electrodes, making electrical contact difficult and reducing capacitance. The decomposition of the electrolytes would limit their stability and cause their precipitation on the electrodes, as well as decomposition of the electrode binder with loss of cohesion.
Nanocrystals boost electrochemical oxidation of biomass-derived compounds
(Universitat de Barcelona, 2025-01-24) Montaña Mora, Guillem; Cabot i Codina, Andreu; Güell Vilà, Frank; Universitat de Barcelona. Facultat de Física
[eng] The global energy situation coupled with the indiscriminate use of fossil fuels is currently a major problem for both human health and the prosperity of the planet. Biomass represents a highly promising renewable resource, and electrochemical processes can serve as an efficient technology for energy conversion and the sustainable generation of a wide variety of high-value products. However, the main current challenge is the development of competitive, efficient, and cost-effective catalysts. Nanostructured materials are highly valuable in this field due to their large surface area and the ability to modulate their properties through structural, compositional, and morphological changes, providing them versatility across a wide range of application fields. Historically, noble metals such as Pt or Pd have been the primary choice as catalysts due to their remarkable electrochemical properties despite their high cost, limited availability, and susceptibility to contamination with CO. In this context, in the different chapters of the thesis, I detail the work I have undertaken to produce and optimize different catalysts for application in electrochemical systems, either for electricity generation or for the valorization of compounds extracted from biomass. Among the four types of materials produced, two are based on Pd alloys modified to enhance both activity and stability. In the other two catalysts, I have replaced noble metals with more cost-effective and abundant transition metals. In Chapter 2, the development of a bimetallic electrocatalyst based on cobalt-iron oxyhydroxide derived from cobalt-iron phosphide nanorods is detailed. This material is used in high-performance anodes for the OER at high current densities, exceeding 1 A cm-2. Under alkaline conditions and anodic polarization, phosphorous depletion and a morphological transition occur, converting the initial CoFeP nanorods to CoFe oxyhydroxide nanoplates with a high ECSA. This procedure enables the preservation of the metal homogeneous distribution on the support, achieving a high density of active sites. In Chapter 3, the application of the compound PdH0.58@C2N as a catalyst in the FOR reaction is studied. The introduction of hydrogen modifies the electronic energy levels, increasing the specific activity to achieve a current density of up to 5.6 A·mgPd−1, which is 5.2 times higher than that of Pd/C. Additionally, the introduction of hydrogen reduces the onset potential and enhances stability, as it exhibits the slowest current decay compared to the reference 16 electrocatalysts. Analysing the results using DFT, it is observed that the d-band of the PdH0.58@C2N surface is downshifted, weakening the adsorbate binding and thus accelerating the rate-limiting step of the FOR. In Chapter 4, the synthesis of the ternary compound Pd2Sn0.8P and the effect of phosphorus incorporation into the Pd-Sn alloy on the electrocatalytic response for formate oxidation are detailed. As a result, Pd2Sn0.8P exhibits very high catalytic activity, with record mass current densities of up to 10.0 A·mgPd−1. Additionally, compared to Pd1.6Sn, not only is the activity improved, but the stability of the catalyst is also enhanced. To understand how phosphorus affects the reaction mechanism, the system was studied using DFT calculations, which confirm that the presence of phosphorus favours the desorption of CO2, thus reducing the energy barrier of the rate-limiting step. In Chapter 5, I detail the effect of introducing an oxophilic element into Ni nanoparticles used as catalysts in the oxidation of glucose. We observed that incorporating Sn not only enhances the reaction kinetics but also that NiSn0.6 achieves excellent current densities and a Faradaic efficiency of 93% towards formic acid. A DFT study shows that Sn facilitates the adsorption of glucose on the Ni surface and promotes the formation of catalytically active Ni³⁺ species. At low concentrations and potentials, formic acid overoxidation to carbonates reduces the total Faradaic efficiency, while at high concentrations, the non-Faradaic glucose degradation pathway is promoted, increasing selectivity towards fructose, acetic acid, and lactic acid production.
Dissipation in active matter systems: self-organization and transport
(Universitat de Barcelona, 2025-03-14) Torrenegra-Rico, Juan David; Rubí Capaceti, José Miguel; Universitat de Barcelona. Facultat de Física
[eng] This thesis delves into the study of catalytic Janus particles (AP) that convert chemical energy into mechanical motion, resulting in energy dissipation. Understanding this dissipation is challenging due to the complex interplay between chemical and mechanical processes. Traditional thermodynamic models often fail to fully capture the dynamics of the system, as they tend to treat active Brownian particles as minimally interactive with their environement and overlook entropy production and energy dissipation in non-equilibrium conditions. To address this gap, the thesis introduces a new model that considers thermodynamic constraints related to dissipation and entropy production, providing a deeper understanding of energy dissipation in active systems. Expanding on this framework, the research investigates how assemblies of Janus particles behave when exposed to varying concentrations of fuel in an inhomogeneous medium. The study reveals a non-linear relationship between energy dissipation and the fraction of particles that assemble, leading to a new thermodynamic criterion for self-assembly based on the behavior of chemical potentials. This offers a clearer understanding of how microscopic interactions drive larger-scale self-organization. Environmental factors such as concentration gradients and fluid flows significantly affect the formation and stability of these active matter structures. Hydrodynamic interactions (HI) increase the mobility of catalytic Janus particle aggregates, enabling the formation of more complex structures. However, while these interactions can reduce the efficiency of energy conversion, they create feedback loops between particle activity and the surround-ing medium. In these loops, changes in substrate consumption and fluid flow affect both the speed of chemical reactions and the resulting structural configurations of the particles. Managing these interactions is crucial for optimizing the performance and assembly of the particles. In confined environments, active particles have various applications, such as drug delivery, in situ cancer treatments, and environmental cleanup. However, effective particle transport in these settings remains challenging. Studies on particle transport in porous media show that oscillating forces in channels with exible walls can boost transport efficiency through enhanced stochastic resonance. Further optimization occurs when channel oscillations are synchronized with transverse forces, improving the particles' ability to navigate complex biological and environmental settings. A notable phenomenon identified in this research is the presence of a stochastic resonance regime for active particles under confinement. In this regime, periodically adding substrate improves transport efficiency at specific noise levels, enabling the particles to travel longer distances while consuming less fuel. This has practical implications for medical applications, such as transporting particles through cell membranes and tissues, and for environmental applications like soil remediation. In summary, this thesis develops a comprehensive framework that integrates entropy production, energy dissipation, chemical reactions, hydrodynamic interactions, and concen- tration gradients in non-equilibrium systems. It addresses gaps in current thermodynamic models, which typically focus on isolated aspects of these processes. Through its investiga- tion of the self-assembly and transport of catalytic active particles, this research uncovers key mechanisms that govern particle behavior, structure, and transport efficiency. The findings provide valuable insights for the design of advanced materials and devices that require controlled self-assembly and transport properties.
A Comprehensive Validation of Global Precipitation Measurement Satellite Products Over a Western Mediterranean Region
(Universitat de Barcelona, 2025-01-16) Peinó Calero, Eric; Bech, Joan; Udina Sistach, Mireia; Universitat de Barcelona. Facultat de Física
[eng] Precipitation estimation is essential for understanding atmospheric processes, water resource management, and climate modeling. Advances in remote sensing, particularly the Global Precipitation Measurement (GPM) mission, have improved global precipitation coverage, especially in regions where traditional methods are insufficient. Since its launch in 2014, GPM has become one of the most comprehensive efforts to quantify precipitation globally, with continuous updates to its products. The complex Mediterranean climate, characterized by high variability and uncertainty in precipitation projections, highlights the importance of validating these products. This thesis focuses on validating GPM precipitation estimates over a Western Mediterranean region. The thesis is structured into three parts, based on three scientific publications and a preprint. It begins with the validation of Integrated Multi-satellite Retrievals for GPM (IMERG) products across multiple temporal scales, particularly their performance in detecting intense rainfall in the Mediterranean. The impact of cloud top phase on satellite retrievals is also examined through 18 case studies, along with a comparison to Support to Operational Hydrology and Water Management (H SAF) products. Finally, rain estimates and drop size distributions from the GPM Dual-frequency Precipitation Radar (DPR) are validated. Many GPM validation studies lack evaluations at sub-daily scales or in mountainous regions. This thesis addresses these gaps by assessing IMERG Early, Late, and Final runs at different temporal scales in Catalonia, using ground stations from 2015 to 2020. While IMERG Final reduces errors at all scales, it underestimates precipitation in areas like the Pyrenees, and both Early and Late runs tend to overestimate rainfall. IMERG also shows high bias and low correlation at sub-daily scales, indicating challenges in estimating precipitation at high temporal resolution. Very heavy rainfall is significantly underestimated, by more than 80%. The second part of the study focuses on extreme precipitation events, using IMERG Early and Late products to assess retrievals’ performance. Stratified results based on the microphysical properties of clouds show a general underestimation of precipitation, which worsens with increased rainfall intensity and temporal resolution. Passive microwave (PMW) sensors showed less bias than infrared (IR) sensors, although including IR increased errors. IMERG performed better in ice-phase clouds compared to warm and mixed-phase clouds. This analysis was extended to compare IMERG with H SAF products in 18 extreme rainfall cases, using a pixel-to-point approach to reduce discrepancies between satellite and ground data. H64 performed best at daily scales, and H68 at hourly detection, although accuracy decreased with increasing rainfall intensity. Despite biases, the IMERG Late product was the most effective at detecting extreme precipitation events. The final part of the thesis evaluates the GPM Core satellite’s Dual-frequency Precipitation Radar (DPR), focusing on seven disdrometers in various topographic regions from 2014 to 2023. Radar reflectivity, drop size distributions, and precipitation intensity were compared. GPM DPR captured variability in observed drop size distributions but overestimated the mass-weighted mean diameter and underestimated the intercept parameter. Errors were highest for rainfall rate and the intercept parameter, but lowest for radar reflectivity and the mass-weighted mean diameter. The classification of stratiform and convective rainfall by GPM DPR also showed an overestimation of stratiform cases. This research is one of the first in the Iberian Peninsula to validate IMERG products with a detailed focus on orographic, climatic, and precipitation intensity factors at high temporal resolution. By comparing GPM and H SAF products and evaluating updates to DPR version 7, this study provides valuable insights into satellite precipitation estimation and lays the foundation for future research.
Orígens del concepte d’indistingibilitat quàntica en l’estadística de Fermi-Dirac
(Universitat de Barcelona, 2025-01-15) Ibáñez Solé, Joana; Pérez Canals, Enric; Universitat de Barcelona. Facultat de Física
[cat] Entre el 1924 i el 1927 a través de la mecànica quàntica va començar a entreveure’s la idea de que alguns sistemes estaven formats pel que avui dia anomenem “partícules indistingibles”. Aquesta nova percepció de la identitat de les partícules, capgiraria la manera de concebre la naturalesa i la interacció en els sistemes formats per elements idèntics. Amb el naixement de la mecànica quàntica i els diferents descobriments de la física a l’inici del segle XX, l’estadística de Maxwell-Boltzmann ja no respon totes les preguntes que planteja la física. Al llarg dels diferents capítols veurem com neix l’estadística quàntica de Fermi-Dirac i, amb ella, la percepció de la idea d’indistingibilitat i també com evoluciona aquest concepte. Es vol entendre quin és el context científic amb el que s’arriba als anys 1924-1927, per tal d’explicar què va portar a Fermi a desenvolupar una nova estadística quàntica, anomenada actualment estadística de Fermi-Dirac, diferent a la que havien desenvolupat Bose i Einstein dos anys abans i amb un mètode totalment diferenciat (tot i que paral·lel en el temps) al que farà anar Dirac. Estudiarem també els treballs que publica Heisenberg durant aquells anys i analitzarem quin paper van jugar en el desenvolupament de les estadístiques quàntiques. Addicionalment, veurem que el mètode de Dirac, per la seva banda, vindrà marcat per la formulació, entre el 1925 i el 1926, de la nova mecànica quàntica o mecànica matricial per part de Born, Heisenberg i Jordan.
The Onset of Geometry in Complex Networks - From Stuctural Properties to Dynamical Processes
(Universitat de Barcelona, 2024-12-05) Kolk, Jasper Eibertus van der; Boguñá, Marián; Serrano Moral, Ma. Ángeles (María Ángeles); Universitat de Barcelona. Facultat de Física
[eng] Over the past few decades, the use of complex networks to describe the properties of systems of many interacting particles has become widespread in many fields of science. Surprisingly, networks from disparate disciplines share a wide range of basic properties, such as small worldness, high levels of clustering and broad degree distributions. One of the most promising frameworks to explain this observation is that of network geometry, where nodes are assumed to live in some underlying metric space that conditions their connectivity. The fact that this approach can reproduce all the basic network properties and symmetries as well as produce strong results in practical tasks such as community detection and link prediction has led many to wonder if there is a way to determine if real networks are indeed geometric in nature. However, these studies do not contemplate the fact that the transition between non-geometric and geometric networks might not be sharp. In this thesis we study the effect the effect of the underlying metric space on the complex network for different geometric coupling strengths. We show that three different regimes can be identified: In the non-geometric regime, where the coupling is extremely weak, results are similar to those of the configuration model, which is explicitly non-geometric. Increasing the coupling slightly leads us to the quasi-geometric regime, where the scaling of the clustering coefficient with the system size is extremely slow, leading to significant levels of this quantity for finite systems. Additionally, we show that, here, geometric information can be extracted from the topology alone through network embedding, and that it is essential for obtaining self-similar network replicas through geometric renormalization. Finally, we study a large number of empirical networks and show that they are best described in the quasi-geometric regime. Increasing the coupling further leads us the geometric region. This is the regime typically studied past works where the effects of the underlying metric space are strong and where clustering remains finite in the thermodynamic limit. Motivated by these results for single-layer graphs we also study geometric multiplexes. We introduce the mutual network, which is made up of all edges that are shared by all layers. This object allows us to obtain rigorous results on edge overlap as well as mutual clustering. We show that the geometric region can be extended in the mutual case when the coupling of the individual layers to their underlying metric space are of similar strengths. Having extensively investigated the structural properties at various coupling strengths, we lastly turn to dynamical processes running of top of the network. Specifically, we show that the underlying metric space reveals periodic Turing patterns, both in the quasi- and strongly geometric regimes as well as in empirical networks. All these results show that the underlying geometry is essential for understanding complex networks, both from a structural as well as dynamical point of view.
Overcoming antiapoptotic adaptations to enhance non-small cell lung cancer treatment
(Universitat de Barcelona, 2024-11-29) Martín Silva, Fernando; Montero Boronat, Joan; Universitat de Barcelona. Facultat de Física
[eng] The treatment of lung cancer has substantially progressed due to the development of targeted therapies against driver oncogenes. However, this type of cancer is still the leading cause of cancer-related mortality, requiring new strategies and treatments. In this context, genomic-based precision medicine has revolutionized the management of lung cancer, especially for non-small cell lung cancer (NSCLC). Nevertheless, these therapies are not always effective and often present limited clinical outcome. Thus, we believe that functional assays could be an excellent complement to genomic assays, as they can predict drug efficacy directly in patient-derived cancer cells. We initially evaluated the predictive capacity of the functional assay dynamic BH3 profiling (DBP) in a representative panel of NSCLC cell lines and targeted therapies. Our results confirmed that DBP was an excellent binary predictor in this subset of cells. Precision medicine aims to assign the right therapy to the right patient and is becoming key for improving the survival of cancer patients. However, resistance is common through mutations and other genomic alterations, but other factors can also contribute to the potential relapse of patients, including the evasion of apoptotic cell death. In this study, we seek to better understand and overcome antiapoptotic adaptations to boost NSCLC treatment. We initially explored antiapoptotic adaptations in response to ALK inhibitors in cell lines and patient-derived tumor cells. All of these cell models showed a significant decrease in the expression of the sensitizer protein NOXA in response to ALK inhibitors, leading to an antiapoptotic MCL-1 dependence. In some instances, the antiapoptotic BCL-xL protein could also contribute to the evasion of apoptosis, requiring a case-by-case analysis to identify the antiapoptotic protein(s) involved in cell death protection. Importantly, these antiapoptotic adaptations could be overcome with BH3 mimetics or alternative approaches, enhancing the effectiveness of ALK inhibitors. Finally, we demonstrated that the reactivation of downstream PI3K/AKT and MAPK signaling pathways reduced the effectiveness of the third-generation ALK inhibitor lorlatinib, which could be overcome with specific inhibitors of these pathways. The impairment of the mitochondrial apoptotic pathway is commonly associated with early adaptations to treatment. Nevertheless, the evasion of apoptosis can also contribute to other resistance mechanisms that appear after longer exposure to treatment, including cellular senescence. This cellular phenotype involves cell cycle arrest in response to stress signals such as chemotherapeutic agents, radiotherapy or cell cycle inhibitors. However, the impact of targeted therapies on senescence induction 2 is still unclear. In this study, we also demonstrated that the long-term treatment with the third-generation EGFR inhibitor osimertinib increased the expression of senescence markers. Furthermore, osimertinib-induced senescent cells acquired resistance to apoptosis through different molecular mechanisms that again converged in antiapoptotic MCL-1 and BCL-xL dependencies. Finally, the treatment with BH3 mimetics eliminated the majority of senescent cells, and we demonstrate their excellent senolytic efficacy in this context. In conclusion, we proposed novel therapeutic combinations to enhance the efficacy of targeted therapies in NSCLC, which could have a significant impact in the clinical setting in the future.
Direct CP measurement of Lambda b0->pkGamma decay and photon reconstruction optimization for Run III conditions
(Universitat de Barcelona, 2024-11-27) García Moreno, Paula; Garrido Beltrán, Lluís; Vázquez Gómez, Ricardo; Universitat de Barcelona. Facultat de Física
[eng] This thesis focuses on conducting a CP measurement of the rare radiative b-baryon decay Lambda b0 -> pkgamma using proton-proton collisions collected by the LHCb experiment during both the entire Run I and Run II periods. Two distinct approaches were employed for this purpose. The first approach involved measuring CP asymmetry of the signal mode for both Run I and Run II. This was achieved by employing previously determined production and detection asymmetry values for Run I, and then deriving the corresponding asymmetries for Run II using the available information from both Run I and Run II. The second approach served as a crosscheck and aimed to calculate the difference between CP asymmetry between a control mode that shares the same final state hadrons and mother particle (Lambda b0 -> pK J\Psi). This choice allowed the production and detection asymmetries of both the signal and control modes to ideally cancel out in the first approximation. Another method to derive the CP asymmetry difference without assuming asymmetry cancellation is to obtain them using Monte Carlo (MC) simulations. Moreover, this thesis is also covering a study in order to optimize the cluster shape used for reconstructing calorimetric objects. With the start of Run III data taking period, LHCb operates at an increased luminosity five times greater than in preceding years, which translates into a higher overlap between electromagnetic showers and higher pile-up effects. This study explores two new, smaller cluster shapes with the goal of determining if they can provide better resolution than larger cluster shapes - 3x3 used in the previous runs. The two shapes under consideration are the 2x2 mask, where only the 2x2 zone with the highest energy out of the nine cells of a 3x3 cluster are retained, and the Swiss Cross mask, which removes the corner cells from a 3x3 cluster. This study employs a particle gun MC simulation generating photons with energies spanning from 1 GeV to 168 GeV, originating from the primary vertex. This MC setup ensures that each event contains only one photon, eliminating overlap and pile-up effects. Consequently, a comprehensive assessment of necessary energy and position corrections is facilitated, isolating pure geometric factors.
Developing a 3D full-thickness skin model based on thiol-norbornene chemistry
(Universitat de Barcelona, 2024-10-28) Cirulli, Angela; Martínez Fraiz, Elena; Universitat de Barcelona. Facultat de Física
[eng] Collagen-based gels are widely used as the standard for in vitro skin tissue models due to their biocompatibility and structural similarity to natural skin. However, they have notable drawbacks, such as batch-to-batch variability and gel contraction, which can affect the consistency and reliability of experimental results. To address these issues, various alternatives have been proposed. However, developing a 3D model capable of mimicking the morphology and physiology of the in vivo tissue still represents a challenge. In this thesis, we focused on developing a 3D full-thickness skin model using photocrosslinking gels based on thiol-norbornene chemistry to overcome these limitations. Our initial approach involved creating RGD-functionalized norbornene-pullulan-based gels. The incorporation of the RGD peptide, which is known for enhancing cell adhesion, was aimed at improving cell-matrix interactions to support the development of a functional epithelial layer. The results were promising, as the epithelized-dermal skin models formed successfully, indicating that the norbornene-pullulan gels provided an adequate substrate for skin cell attachment and proliferation. This success laid the groundwork for developing more complex and physiologically relevant skin models. To further refine our model, we investigated single (SN) and interpenetrating network (IPN) systems, based on norbornene dextran (+/- agarose) resulting in robust full-thickness skin models. The norbornene dextran-based gels provided a stable and supportive dermal compartment, where a well-differentiated epidermis on top was observed. A key advantage of our norbornene-based gel systems is their ability to be finely tuned and customized through photocrosslinking. This method allows for precise control over gel properties such as stiffness, which is critical for replicating the mechanical environment of skin tissue. Additionally, the thiol-norbornene chemistry used in our gels is known for its rapid and efficient crosslinking, minimizing the potential for cytotoxicity and preserving cell viability during the gelation process. One of the most significant outcomes of our research was demonstrating the potential to vascularize these gel systems. Vascularization is crucial for in vitro skin models as it facilitates nutrient and oxygen delivery to the tissue, promoting cell survival and function. By incorporating endothelial cells, we successfully induced the formation of capillary-like structures within the gel matrix. This advancement not only enhances the physiological relevance of our skin model but also opens new possibilities for studying skin-related diseases and drug testing in a more realistic in vitro environment. Finally, we also developed a method for the creation of hydrogels with gradients of stiffness, for strategically favoring the incorporation of different cell types depending on the matrix’s stiffness. In conclusion, this thesis presents a significant advancement in developing in vitro skin tissue models. By using photocrosslinking gels based on thiol-norbornene chemistry, we addressed key limitations associated with traditional collagen-based gels. The RGD-functionalized norbornene-pullulan gels supported the formation of epithelized-dermal skin models, while the norbornene dextran-based IPN systems provided robust and more reliable full-thickness skin models with a well-differentiated epidermis. Furthermore, the ability to vascularize these gels enhances their potential for in vitro applications, making our model a competitive alternative for studying skin biology, disease mechanisms, and drug testing. Our findings underscore the importance of developing customizable and valid gel systems for tissue engineering applications. The versatility and tunability of thiol-norbornene-based gels make them a promising platform for creating various tissue models beyond the skin, potentially advancing the field of regenerative medicine and in vitro testing. Future research should focus on further optimizing these gels and exploring their applications in other tissue types, paving the way for more accurate and functional in vitro models.
Synthesis of value-added Nitrogen-based products through advanced electrocatalytic systems
(Universitat de Barcelona, 2024-10-28) Chávez Blanco, Marcelo Eduardo; Murcia López, Sebastián; Morante i Lleonart, Joan Ramon; Universitat de Barcelona. Facultat de Física
[eng] The transition towards a sustainable and carbon-neutral economy is crucial due to the escalating concerns over excessive greenhouse gas emissions, climate change, and the need for effective utilization of renewable energy sources. The continued reliance on fossil fuels has led to a significant increase in CO2 and other greenhouse gases, contributing to global warming and severe climate change impacts. To mitigate these effects, it is imperative to develop sustainable energy systems that can harness and store renewable energy efficiently. This thesis explores the synthesis of value-added nitrogen-based products, particularly ammonia, through advanced electrocatalytic systems, addressing the urgent need for sustainable ammonia production pivotal for agriculture, industry, and as a potential energy carrier. The Power-to-X concept involves converting renewable electricity into carbon-neutral synthetic fuels and chemicals, such as hydrogen, synthetic natural gas, liquid fuels, and ammonia, which can be stored and utilized as energy carriers. Electrocatalysis contributes to Power-to-X technologies by enabling the efficient conversion of electrical energy into chemical bonds, thus providing a sustainable method to store and transport renewable energy. Electrochemical processes are particularly advantageous due to their low environmental impact, mild operational conditions, and compatibility with renewable energy sources. Chapter 3 investigates the synergistic effects of combining Cu and Ti-based materials as electrocatalysts for the electrochemical reduction of nitrate to ammonia. The study demonstrates that the integration of Cu2O-Cu nanocubes on Ti substrates significantly enhances catalytic performance, leading to higher yields and selectivity of NH3. Detailed kinetic insights reveal that the improved activity is due to better adsorption and activation of nitrate ions, facilitated by efficient electron transfer and intermediate stabilization. Chapter 4 evaluates the energy efficiency and scalability of flow-cell configurations in ammonia electrogeneration. By optimizing the flow-cell design and operational parameters, the research demonstrates substantial improvements in energy efficiency, with the tandem system combining Cu-based and TiO2-based catalysts achieving high faradaic efficiency and selectivity. Energy efficiency calculations indicate that the optimized configuration is economically viable for large-scale applications. The feasibility of large-scale implementation of these flow-cell systems presents a promising pathway for integrating sustainable ammonia production into industrial processes. Chapter 5 explores the impact of lithium enrichment on hydrogen evolution reactions during nitrate electroreduction. The incorporation of lithium into mixed nickel oxide and tin oxide catalysts effectively limits the evolution of hydrogen, enhancing the selectivity towards nitrate conversion, and providing insights about catalyst doping for future works. Overall, this thesis contributes to the field of sustainable chemistry by presenting innovative electrocatalytic strategies for ammonia synthesis. The research findings highlight the potential of Cu and Ti-based catalysts, the advantages of flow-cell configurations, and the beneficial effects of lithium enrichment, paving the way for more efficient and environmentally friendly ammonia synthesis technologies.

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