Dipòsit Digital de la Universitat de Barcelona

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El Dipòsit Digital de la Universitat de Barcelona és el repositori institucional que conté en format digital els materials derivats de l'activitat docent, investigadora i institucional de la comunitat universitària.

Enviaments recents

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