https://repositorio.ufu.br/handle/123456789/19114 2026-10-09T15:29:56Z https://repositorio.ufu.br/handle/123456789/50558 Title: Análise tomográfica de redes neurais aplicada a problemas quânticos de muitos corpos Abstract: The use of artificial neural networks to represent many-body quantum states has spar- ked great interest in recent years, offering a promising approach to addressing complex problems arising in this context. In this work, we propose a tomography of the weights of a neural network applied to the problem to obtain the ground state of 1D spin chains with neighbor interaction. One of the objectives is to understand how unsupervised machine learning methods can identify regimes in 1D spin chains, such as ferromagnetic, antifer- romagnetic, and frustrated regimes. Our work seeks to contribute to the understanding of how neural networks incorporate physical characteristics of physical models, such as entanglement, into their synaptic weights. 2026-02-05T00:00:00Z https://repositorio.ufu.br/handle/123456789/50283 Title: Termometria óptica em vidros fosfatos dopados com Sm3+ e Ho3+: transferência de energia e modelo LIR de múltiplos processos Abstract: This study investigated the spectroscopic and thermo-optical properties of phosphate glas ses belonging to the PAN10K system (40P2O5−15Al2O3−35Na2O−10K2O), doped with Sm3+ ions and co-doped with Ho3+, with a focus on understanding energy transfer mecha nisms and their application in optical thermometry. The samples were prepared via the melt-quenching method and characterized using optical absorption spectroscopy, pho toluminescence (including temperature-dependent lifetime measurements), and Raman spectroscopy. Absorption spectra demonstrated the e cient incorporation of rare-earth ions into the glass matrix, while Raman spectra allowed for correlating the phosphate network structure with the observed optical processes. Analysis of Sm3+ emissions revea led the inuence of dopant concentration on concentration quenching phenomena and on the dynamics of radiative and non-radiative processes. In samples doped with Sm3+ and co-doped with Ho3+, the Ho3+ ion was observed to modulate the Sm3+ electronic energy level structure, thereby facilitating energy transfer mechanisms and altering the system’s thermal response. The temperature dependence of luminescence intensity was descri bed using a modi ed Arrhenius model involving multiple thermally activated processes, enabling the determination of activation energies associated with non-radiative deactiva tion and radiative activation mechanisms. Based on these results, a multi-process optical thermometry model grounded in the luminescence intensity ratio (LIR) was developed; this model is capable of accurately describing the thermal response of the samples under various doping conditions. The sample containing 0.5% Sm3+ and 3% Ho3+ exhibited the highest relative sensitivity, reaching 1.90% K−1 at 300 K. The results demonstrate that the thermometric response of co-doped systems cannot be described exclusively by the simpli ed model of coupled thermal populations, since energy transfer and non-radiative relaxation processes can play a signi cant role in the population dynamics of the emitting levels. Thus, this work contributes to a more comprehensive understanding of the physical mechanisms involved in luminescence-based optical thermometry. 2026-07-27T00:00:00Z https://repositorio.ufu.br/handle/123456789/49581 Title: Estudo de geração de vapor de água mediado por folhas de grafeno oxidado e grafeno oxidado reduzido Abstract: This work investigates photothermal conversion and steam generation in nanofluids based on graphene oxide (GO) and reduced graphene oxide (rGO), obtained via reduction with L-ascorbic acid (ALA) and palladium chloride (PdCl2). The study focused on the correlation between modifications in the material's electronic and morphological structure and its thermal transport and optical absorption properties. Characterization via electron microscopy, Raman spectroscopy, and UV–Vis indicated that PdCl2 promotes the restoration of the graphitic lattice and sheet stacking, whereas ALA tends to keep the sheets more separated, resulting in a less compact morphology. Thermal Lens measurements revealed non-monotonic behavior of thermal diffusivity regarding the dispersed phase concentration: a reduction in diffusivity was observed at low concentrations relative to the base fluid, followed by an increase at higher concentrations. Although the exact causes of this behavior require further investigation, the data suggest a complex interaction between heat transport in the solvent and the presence of the nanostructures. In evaporation tests, the highest efficiencies (up to ∼70%) were not associated solely with the highest degree of structural ordering, but rather with hybrid samples combining high optical absorption with moderate thermal diffusivity, which favors the localization of thermal energy at the liquid-vapor interface. The results demonstrate that controlling aggregation and optical properties is crucial for optimizing solar-thermal energy conversion systems. 2026-02-19T00:00:00Z https://repositorio.ufu.br/handle/123456789/49576 Title: Permeabilidade seletiva de água e metanol através de filmes ultrafinos de rGO/Polímero: uma investigação computacional Abstract: The search for clean and sustainable energy sources, driven by the growing energy demand and the problems caused by the use of fossil fuels, poses the challenge of developing technologies capable of replacing the polluting energy matrix (1). In this context, the Direct Methanol Fuel Cell (DMFC) stands out as an alternative, non-intermittent, and portable energy source, with low 𝐶𝑂2 emissions, no release of other polluting gases, and the ability to operate under conditions close to room temperature (2). Reduced graphene oxide (rGO) wrapped with poly(styrene sulfonate) (PSS) leads to the formation of a stable hybrid material (GPSS). This composite enables the fabrication of ultrathin films with promising barrier properties for DMFC applications, aiming to prevent methanol crossover poisoning, one of the major challenges of this technology (3). Experimental evidence shows that polymer electrolyte membranes of DMFCs coated with ultrathin GPSS-based films exhibit a significant reduction in methanol permeation and an increase in the cell’s power density. In this context, the objective of this work was to study the mechanism behind the methanol barrier provided by GPSS, which still allows the permeation of water and protons (4). To that end, classical Molecular Dynamics simulations were employed to investigate the structural and dynamic properties of GPSS at different polymer ionization fractions in a solvent composed of water, methanol, and hydronium. Regarding structural properties, the influence of the sulfonation fraction on the self-assembly of the layered film was discussed, including its effect on the PSS conformation and the distribution of rGO sheets, as well as the nature of the PSS–rGO interactions. As for the dynamic properties, the impact of GPSS structure on solvent diffusion was analyzed, and the mechanisms leading to the selective diffusion of methanol were elucidated. 2025-10-01T00:00:00Z