Treballs Finals de Grau (TFG) - Física

URI permanent per a aquesta col·leccióhttps://hdl.handle.net/2445/59725

Treballs Finals del Grau de Física de la Facultat de Físca de la Universitat de Barcelona.

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Convolutional Neural Networks for Structured Illumination Microscopy
(2026-06) López Martínez, Lucas; Maluenda Niubó, David
Optical super-resolution, the ability to exceed the Abbe diffraction limit, has revolutionized microscopy during the last decades. At the same time, machine learning models, and in particular neural networks, are being created for performing more and more complex tasks. In this work, we set out to developing a convolutional neural network for the reconstruction of images from structured illumination microscopy, one of the leading super-resolution techniques. To achieve this, we designed the model’s architecture and implemented it with the Python library PyTorch, we prepared an artificial dataset with a preexisting microscope simulator, we trained the model with these images, and we tested it with new ones to assess its generalizability. We find that, under the conditions simulated, our model recreates the original images with a high level of detail, surpassing the resolution of a classical reconstruction method, the joint Richardson-Lucy algorithm, by approximately 35 %, and obtaining better scores in different similarity indices
Fluid front pinning in a microchannel under constant pressure
(2026-06) López Gómez, Mar; Benavent Claró, Andreu
Fluid transport at the microscale is fundamentally governed by interfacial phenomena, and geometric irregularities strongly influence flow behavior. Specifically, the sudden pinning of liquid fronts at channel roughness plays a crucial role in the design and operation of microfluidic systems. However, the kinematic dynamics of the interface during the pinning and detachment phases remain poorly understood under constant pressure conditions. In this work, we show that the sudden velocity increase after fluid detachment depends exclusively on the system’s geometry. Using optical microscopy to track an advancing meniscus over a controlled roughness, we demonstrate a universal geometric deformation independent of fluid viscosity or applied pressure. This geometric defect forces the interface to deform, leading to an accumulation of surface potential energy. Upon detachment, this energy is abruptly released, producing the observed kinematic acceleration
Non-linear effects on thin YIG films
(2026-06) López-Arenas Rovira, Carles; Costache, Marius V.
This work investigates the non-linear magnetization dynamics in thin Yttrium Iron Garnet (YIG) films under high microwave rf magnetic fields at different powers. Through out-ofplane ferromagnetic resonance (FMR) and power sweep measurements, we characterize the resonance frequencies across samples of varying thicknesses. We successfully observe two distinct non-linear regimes and highlight the importance of the radiative damping term, αrad, which governs the onset of these non-linear effects.
Calorimetric Investigation of Magnetic Phase Transitions and Magnetocaloric Effects in Terbium
(2026-06) Llort Mas, Aleix; Mendive Tapia, Eduardo; Stern Taulats, Enric
This work presents a calorimetric study of the magnetic phase transitions in terbium under different temperatures and applied magnetic fields. From these measurements, transition temperatures have been obtained at TC = 222 K and at TN = 230 K. We report the magnetic phase diagram by tracking the change of these transitions driven by the application of a magnetic field. In addition, the transition entropy changes were obtained. The results reproduce the expected ferromagnetic, helical antiferromagnetic and paramagnetic phases and show thermal hysteresis between cooling and heating processes. The entropy associated with the phase transition decreases with increasing magnetic field, which is consistent with the progressive alignment of the magnetic moments. Although the experimental data agrees with previous studies, it is insufficient to confirm the existence of a fan or conical phase previously suggested.
Vortex dynamics in Bose-Einstein condensates
(2026-06) Lin, Yixue; Juliá-Díaz, Bruno; Briongos-Merino, Héctor
The theoretical framework used to understand the Bose-Einstein condensate (BEC) phenomenon is presented, with emphasis on the case with strong interactions, the so-called Thomas-Fermi regime. Superfluidity, a consequence of BEC important for the understanding of liquid helium, is characterized by the presence of quantized vortices. A heuristic ansatz for quantized vortices is presented, aiming to study them in a simulation, where the numerical implementation is based on the split-step Fourier method. Imaginary-time evolution is performed for the free vortex and one displaced vortex case. With the objective of studying the dynamics of the latter, real time evolution is performed. Finally, the results are briefly discussed
Spatial characterization of thickness in thin films deposited by thermal evaporation
(2026-06) Lara Rodríguez, Raül; Galceran Vercher, Regina
This work analyzes the spatial thickness distribution of aluminum thin films deposited onto a glass substrate via thermal evaporation. A methodology combining a gridded lift-off mask with optical mapping enabled precise large-area topographic characterization. The experimental data were fitted to the Knudsen cosine law (R2 = 0.92), confirming a radial thickness decay with a maximum central thickness of d0 = (93.0 ± 0.5) nm. The empirical beaming parameter (n = 0.9 ± 0.3) is highly consistent with an ideal planar surface source (n = 1). This demonstrates that the crucible used distributes the atomic flux predictably, acting as a flat emitting area without inducing severe collimation. Finally, the preservation of this distinct directional profile is attributed to the high-vacuum regime, which prevents the intermolecular flux dispersion typical of higher working pressures.
Weak Interactions as a mechanism against Gravitational Collapse in Primordial Baryonic Stars
(2026-06) Lampurlanés Rosell, Joan; Espriu, D. (Domènec)
This work investigates whether weak interactions mediated by Z-boson exchange can provide a stabilising pressure against gravitational collapse (GC) in primordial baryonic stars. Building on previous works, we completed the equation of state by incorporating the degeneracy pressure of an ultra-relativistic fermionic gas. A crossover density 𝑛* ≈ 9 · 1010 fm−3 is identified, marking the transition between weak-interaction-dominated and degeneracy-dominated regimes. The Tolman-Oppenheimer-Volkoff equation is solved numerically with a boundary condition derived from the thermal radiation pressure of the primordial plasma, yielding a universal stellar radius of approximately 15 meters. Stability analysis via the turning point theorem reveals that all stable configurations have central densities well below the crossover density, demonstrating that weak interactions do not play a relevant structural role in these compact objects.
The role of pH in the light-harvesting properties of PC645
(2026-06) Lafuente Puig, Jia Laura; Franzese, Giancarlo; Curutchet Barat, Carles E.
The PC645 is a pigment-protein complex that plays a key role in light harvesting algae by absorbing photons and facilitating energy transfer within the photosynthetic apparatus. In this work, we investigate the relation between pH and the light harvesting mechanisms of PC645. We perform classical molecular dynamics (MD) simulations combined with quantum/molecular mechanical polarizable (QM/MMPol) models to derive the exciton Hamiltonian of the system. Using this Hamiltonian, we compute the absorption spectrum of the complex and simulate the energy transfer dynamics between pigments. Our results reveal two effects of acidic pH: a decrease in the site energy of one of the pigments of the complex and a slower Electronic Energy Transfer (EET) rate, a parameter which quantifies how quickly energy is transferred between pigments. This preliminary work establishes the basis for future research, suggesting avenues for improvement and more advanced simulations to be performed.
Phase transition and evolutionary mechanisms in a grand canonical minority game
(2026-06) Jordà i Coll, Enrique; Montero Torralbo, Miquel
We consider the grand canonical minority game as a model for financial markets. We first characterise the phase transition of the standard minority game and the grand canonical variant between a symmetric, unpredictable phase and an asymmetric, predictable phase and identify the critical point. Then we look at two evolutionary mechanisms: competitive selection and cooperation through imitation. Through overcrowding, competition destroys the asymmetric phase. Limited imitation recovers the asymmetric phase and reduces volatility relative to competitive selection. These results suggest that, in this model, coordination is not maximised by selecting the most successful agents but by preserving sufficient strategic heterogeneity
Construction of a Regge Model for ππ Scattering Total Cross Sections
(2026-06) Hornas Cuadros, Berta; Mathieu, Vincent
A model for high-energy ππ scattering based on Regge residues is developed using the dominant ρ and f trajectories together with the Pomeron contribution. The mesonic residues are determined from hadronic couplings extracted from the decay widths of the ρ(770) and f2(1270) mesons. The resulting total cross sections are compared with the available experimental data and show a reasonable agreement in the high-energy region
Micromagnetic study of spin-wave dispersion engineering and magnon confinement in YIG magnonic crystals
(2026-06) Homar Genovart, Antoni; Costache, Marius V.
This work investigates magnonic crystals based on nanostructured Yttrium Iron Garnet (YIG) waveguides through micromagnetic simulations performed with mumax3. Two main objectives are addressed: engineering controllable spin-wave band structures and spatially confining magnons in a cavity. The structures consist of a YIG waveguide patterned with a one-dimensional periodic array of holes of varying geometry. For rectangular holes, a lower flat band emerges whose frequency decreases with increasing hole width, providing a geometric tuning knob; this tunability is exploited to design a magnon cavity that confines magnons at a defect site via a quadratic taper. Concave and elliptical geometries yield quasi-gapless, thin-film-like dispersions, identified as the most suitable candidates for magnon Rayleigh–Jeans condensation, which preliminary parametric-pumping simulations did not yet achieve.
Modelling the epidemiological impact of diagnostic performance on malaria transmission: a multi-scale approach
(2026-06) Hernàndez Arnal, Violeta; López Codina, Daniel; Prats i Soler, Clara; Ibañes Miguez, Marta
Malaria is one of the leading causes of preventable death worldwide, yet the epidemiological impact of diagnostic performance on the transmission dynamics is poorly understood. Three models of increasing complexity are studied: a single-strain model, a two-strain model and a spatially distributed model in order to quantify how the choice of the diagnostic method and the geographical distribution of healthcare centers affect the prevalence of the disease. The results of the study show that Rapid Diagnosis Tests (RDT) present a blind spot that allows the mutated variant to circulate silently at high prevalence levels, a phenomenon suppressed when changing the diagnostic method to microscopy. The spatial analysis demonstrates that diagnostic quality has a stronger influence on endemic prevalence rather than the size of the healthcare network.
Non-minimal coupling and the gyromagnetic factor of spin-1 and higher-spin fields
(2026-06) Guillamet i Forment, Joan Sebastià; Soto Riera, Joan
This thesis investigates non-minimal electromagnetic couplings for spin s = 1 and higherspin fields, focusing on the universality of the gyromagnetic factor (g). From the non-relativistic limit of the non-minimal Proca equation up to O(1/m2), where m is the particle’s mass, we derive an effective Hamiltonian, identifying the g-factor (M1), Darwin, spin-orbit, and electric quadrupole (E2) corrections. We show that a generic spin-1 field has g = 1 + a/q, where q is its electric charge and a is the anomalous moment coupling constant, whereas g = 2 arises from the non-Abelian structure of electroweak W± bosons, countering Belinfante’s conjecture (g = 1/s). New physics or internal substructures are parameterized via a dimension-4, E1-generating operator, and dimension-6 operators that modify the electric corrections and generate their magnetic duals, including M2. Finally, dimensional analysis reveals that an arbitrary, anomalous, renormalizable coupling is allowed for elementary bosons in Minkowski space, rendering g arbitrary rather than fixed at 2
Testing the BB84 Quantum Protocol Under Intercept-Resend Attacks
(2026-06) Gudel Pérez, Nora; Salvadó Serra, Jordi
This study evaluates the cryptographic resilience of the BB84 quantum key distribution protocol against intercept-resend attacks under realistic noise conditions. Utilizing Qiskitbased simulations, the work models eavesdropper detection through a binomial statistical framework across three experiments, transitioning from deterministic parameter evaluation to continuous, unpredictable adversarial scenarios. The results demonstrate that detection probability is inextricably linked to the interception fraction (p) and the evaluated qubit block size (n). Receiver Operating Characteristic (ROC) analysis and confusion matrices quantitatively reveal that small qubit blocks suffer from high statistical variance, allowing weak attacks to evade detection. Conversely, increasing the block size effectively mitigates false negatives and drastically improves diagnostic sensitivity. Ultimately, the analysis confirms that the BB84 protocol ensures reliable eavesdropper detection if the sample size is large enough to isolate quantum disturbances from background noise.
Studying the nature of the astrophysical transient AT2025zjx
(2026-06) González Navarra, Joan Miquel; Blagorodnova Mujortova, Nadejda
Intermediate-Luminosity Red Transients (ILRTs) are a class of gap transients situated between the two extremes of classical novae and core-collapse supernovae in terms of their peak luminosity. In this work, a photometric and spectroscopic study of the transient event AT2025zjx is presented, making use of observations carried out at a dozen observatories around the world. The transient took place in the interacting galactic system NGC 520 and presents a light curve with a single maximum with an absolute magnitude of Mr = −14.27 ± 0.15. The event exhibits a slow cooling with a mild reddening of the continuum, accompanied by narrow Balmer, Ca II, and [Ca II] lines in its spectra, as well as a decrease of the Na I D absorption line due to the interaction with the dense surrounding material. The evolution of the Balmer decrement (Hα/Hβ) suggests possible dust formation in late phases. The event AT2025zjx is classified as a fast-decaying ILRT, whose properties likely represent the final explosion of a dust-enshrouded super-AGB star.
Complex systems and statistical physics in housing markets
(2026-06) Gómez Plaza, Ivan; Perelló, Josep, 1974-
Complex systems far from thermodynamic equilibrium feature emergent behaviours that classical models cannot describe. Housing markets are an example, driving systemic financial risk and socia ly price indices analysed present heavy tails, confirming a high probability of crises. Mean squared displacement scaling reveals a short-term superdiffusive regime that transitions to subdiffusion, uncovering a finite market memory. Escape times display a strong temporal asymmetry, reaching upward barriers six times faster than downward ones. Using random matrix theory, we identify a dominant market mode alongside a secondary group mode in heterogeneous regions. These results introduce statistical physics into the understudied housing market, providing a framework directly applicable to systemic risk monitoring.
Machine learning algorithms for single-atom reconstruction in a quantum-gas microscope
(2026-06) Gómez Montañez, Pablo; Rubio Abadal, Antonio; Gas Ferrer, Carlos; Tarruell Pellegrin, Leticia
A quantum-gas microscope is a device that enables the detection of individual ultracold atoms in optical lattices with single-site resolution. In this context, the strontium quantum-gas microscope developed at ICFO is a promising platform for studying strongly correlated many-body states in the Fermi-Hubbard model with high spatial resolution. This work explores the use of a convolutional neural network (CNN) as a non-linear method to reconstruct the single-site occupation of the optical lattice. The neural network is based on unsupervised autoencoders, which learn a compact latent representation associated with lattice occupation while capturing the optical response of the imaging system. The comparison between the experimentally measured point spread function (PSF) and the learned PSF reveals excellent agreement, showing that the network captur the fundamental imaging response. Finally, the measured pinning fidelity, defined from the overlap between two consecutive occupation images, demonstrates that atoms remain trapped at the same site with high probability during imaging, while hopping and loss remain sufficiently suppressed.
Neutrino Propagation in the Sun: A Study of the MSW Effect
(2026-06) Giral López, Marta; Salvadó Serra, Jordi
The discovery of neutrino oscillations solved the solar neutrino problem but contradicts the Standard Model by having non-zero mass neutrinos, hinting at new physics beyond the SM. In this work, the impact of the Mikheyev-Smirnov-Wolfenstein (MSW) or matter effect in twoneutrino oscillations is studied via numerical simulation and results are compared with the adiabatic approximation (the analytical approach) and latest experimental data from neutrino detectors. The numerical resolution also allows to incorporate Non-Standard Interactions parametrized by a scalar ε, weighted in respect to the matter potential. Results show that numerical values are in agreement with the adiabatic approximation and the Standard and Non-Standard Interactions for the studied range of ε, not constrained by experimental data.
Neural networks for hadron resonance extraction
(2026-06) Garcia Clapés, Guim; Gonzalez-Solis De La Fuente, Sergi; Montaña Faiget, Glòria
We present a neural network approach to resonance parameter extraction and model classification applied to the pion vector form factor. Five theoretical parametrizations of the ρ(770) resonance of increasing sophistication are considered, ranging from simple Breit-Wigner models to fully analytic implementations derived from Chiral Perturbation Theory. Trained exclusively on synthetic spectra, the networks recover the physical pole parameters with precision comparable to traditional χ2 fits in a single inference step. Extended to simultaneous parameter extraction and model classification, a multitask network consistently identifies the parametrization that best describes the experimental data, in agreement with traditional fitting results, while extracting the model parameters with comparable precision. The resulting fast, single-step inference framework opens the door to future applications in hadronic physics
Group and Field Galaxy Catalogs in TNG100: Assembly Bias and Gas Depletion
(2026-06) García-Cardoso, Judith; Manrique Oliva, Alberto; Perea Duarte, Jaime D.; Solanes, José M. (José María)
We investigate the impact of the group environment on galaxy properties using the TNG100-1 simulation at z = 0. Analyzing 4,424 galaxies in 544 groups and 6,561 field galaxies (9.0 ≤log10(M⋆/M⊙) ≤ 12.0), we find that the Galaxy Stellar Mass Function (GSMF) is best described by a double-Schechter model across environments. Group members exhibit a higher mass than field counterparts, indicating environmental suppression of intermediate-mass satellites. Merger history analysis shows that single Brightest Group Galaxies (BGGs) experience twice as many mergers as BGGs in groups with multiple or no distinct centrals. While merger counts correlate with group richness and BGG stellar mass, they show no significant relationship with the r-band magnitude gap (Δm21). This implies that Δm21 encodes complementary information on halo assembly history, consistent with assembly bias. Finally, group satellites exhibit a mass-independent neutral hydrogen (H i) deficit of ∼ 0.4 dex relative to the field, which increases to ∼ 1.0 dex for BGGs with M⋆ >∼1010.5M⊙.

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