https://repositorio.ufu.br/handle/123456789/20564 2026-07-17T17:11:10Z https://repositorio.ufu.br/handle/123456789/48828 Title: Estudo do uso de nanopartículas metálicas (NPM) e filmes finos metálicos em amostras de grãos para o aprimoramento da performance analítica da técnica de Espectroscopia de Emissão Óptica Induzida por Laser (LIBS) Abstract: The agricultural sector is responsible for nearly ¼ of Brazil’s GDP, and consolidates the country as one of the largest producers of food globally. Given this scenario, the need for analysis techniques regarding the composition, which envisions the quality control of grains, is proving to be more and more necessary. Between all of the analytic techniques, the LIBS (Laser Induced Breakdown Spectroscopy) technique has proven to be relevant because of its versatility, ease of application, robustness, multi-element analysis capability, among other benefits. Despite all of the advantages of this technique, there are still many efforts in improving the sensibility of the technique. Improvements, such as double-pulsed LIBS (DP-LIBS), femtosecond LIBS (fs-LIBS), or the use of metallic nanoparticles (NELIBS), have been studied for optimizing, among other parameters, the limit of detection (LOD). The use of metallic nanoparticles, in particular, associated to LIBS (NELIBS) has shown relevant results for the enhancement of the technique. While most of the work in the literature has been focused on metallic, vitreous or ceramics, samples, this work is focused on the use (or incorporation) of metallic nanoparticles, as well as thin metallic films, in grain samples (coffee, corn, sorghum, soy) for the analytic enhancement of LIBS. The best results were achieved using thin gold (Au) films deposited on the surface of the grain samples. Expressive gains in intensity of the atomic lines were observed, in the order of 200% for coffee, 600% for corn, 1500% for sorghum, 600% for soy in selected atomic lines of iron (Fe). This work aims to measure the gain in intensity of the most relevant atomic lines present in the spectrum, and to analyze the possible mechanism that led to this phenomenon, through the investigation of the plasma’s temperature and electron density. The results show an indicative increase in both temperature and plasma density for the samples with deposited nanoparticles, as well as, the ones coated with thin films. 2026-03-17T00:00:00Z https://repositorio.ufu.br/handle/123456789/48605 Title: Eletrodinâmica Quântica de Cavidades na Faixa de Micro-ondas em Chips Semicondutores com Pontos Quânticos Definidos Eletrostaticamente Abstract: This work presents a theoretical and computational study of light-matter interaction in circuit quantum electrodynamics (cQED) architectures based on semiconductor quantum dots. Using the density matrix formalism and the theory of open quantum systems, we employ the Lindblad master equation to model dissipative mechanisms, including energy relaxation (T1) and decoherence (T2). The theoretical framework starts from the quantization of the electromagnetic field and the Jaynes-Cummings model within the rotating-wave approximation (RWA), and is extended to the dispersive regime via the Schrieffer-Wolff transformation, yielding effective Hamiltonians and dispersive shifts. We then perform numerical simulations to characterize coherent dynamics under microwave control and to compare the obtained results with experimental benchmarks reported in the literature, with emphasis on reproducing Rabi oscillations and Ramsey interferometry. Finally, we examine the limits of validity of the RWA at stronger coupling and demonstrate the controlled preparation of dark states (decoherence-free subspaces) in the two-qubit Tavis-Cummings model. 2026-02-28T00:00:00Z https://repositorio.ufu.br/handle/123456789/48360 Title: O Efeito Bumerangue Quântico 2024-04-26T00:00:00Z https://repositorio.ufu.br/handle/123456789/47784 Title: Modelos efetivos e fatores giromagnéticos via DFT2kp e funcionais híbridos Abstract: The Density Functional Theory (DFT) and the k · p method are two important techniques for calculating the electronic band structures of crystalline materials, which is fundamental for studying their electronic, optical, and transport properties. The DFT2kp package inte- grates DFT and the k·p method by implementing computational routines for the automatic construction of effective k · p models from ab initio data generated by DFT calculations. In this work, we investigated how the hybrid functional Heyd–Scuseria–Ernzerhof 2006 (HSE06) influences the values of the parameters (effective mass, g-factors, and Dresselhaus constant) extracted from effective k · p models for GaAs. To this end, DFT calculations were performed using both the semilocal Perdew–Burke–Ernzerhof Generalized Gradient Approximation (PBE-GGA) functional and the hybrid HSE06 functional in various config- urations. The results show that the HSE06 functional yields band gaps and k · p model parameters that are more accurate than those obtained with the semilocal functional. It was also observed that these parameters are sensitive to adjustments of the tunable HSE06 parameters. Finally, an analysis of the variation of the k · p parameters as a function of the band gap was carried out, demonstrating that applying a scissor-shift to PBE-GGA calculations can produce results similar to those obtained with HSE06, suggesting that in applications tolerating some inaccuracy, the high computational cost of HSE06 may not be justified. 2025-09-23T00:00:00Z