https://repositorio.ufu.br/handle/123456789/5166 2026-04-05T16:35:58Z 2026-04-05T16:35:58Z https://repositorio.ufu.br/handle/123456789/48549 2026-03-19T06:20:28Z 2026-02-24T00:00:00Z

Title: Um lugar para cada coisa e cada coisa em seu lugar: ensino, pesquisa e extensão - uma trajetória musical

2026-02-24T00:00:00Z https://repositorio.ufu.br/handle/123456789/48521 2026-03-07T06:30:42Z 2026-02-02T00:00:00Z

Title: Estudo optoestrutural de perovskitas de iodeto de césio e chumbo em vidro borossilicato: efeitos da dopagem com terras raras e nióbio Abstract: In this work, the structural and optical properties of CsPbI3 perovskites embedded in a borosilicate glass matrix, doped with rare-earth ions (Nd3+, Er3+, Sm3+, and Ho3+) and co-doped with Nb⁵⁺, were investigated. The results show that increasing the Nb5+ concentration favors its incorporation into the glass matrix and promotes the formation of the cubic perovskite phase. The addition of rare-earth ions also contributes to the stabilization of this phase, although no dominant element could be identified. Raman spectroscopy confirmed the presence of vibrational modes associated with the SNAB glass matrix and the role of Nb5+ as a network modifier. Temperature-dependent photoluminescence spectra exhibited emission bands attributed to CsPbI3, with a maximum at ~720 nm (1.72 eV) at 77 K, shifting to ~700 nm (1.78 eV) with increasing temperature, accompanied by spectral broadening and thermal quenching. Among the investigated samples, the Er3+-doped compositions are the most promising, due to the effective stabilization of the cubic phase and their potential application as optical thermometers, exhibiting a relative sensitivity of 4.3% K-1. These results demonstrate that co-doping with Nb5+ and rare-earth ions is an efficient strategy to control the structural stability and optical properties of CsPbI3 perovskites embedded in glass matrices.

2026-02-02T00:00:00Z https://repositorio.ufu.br/handle/123456789/48507 2026-03-07T06:30:24Z 2026-02-18T00:00:00Z

Title: Análise da deflexão gravitacional da luz em ocultações estelares Abstract: This dissertation investigates the astrometric effects of the gravitational deflection of light during stellar occultations, with emphasis on the simultaneous contribution of multiple bodies in the Solar System. The main objective is to evaluate how these effects contribute to the apparent position of the occulting body under different occultation geometries and to what extent they may affect high-precision astrometric measurements. To this end, the relativistic model of Klioner, with microarcsecond-level accuracy, is employed, from which numerical routines are implemented to compute the deflection vectors associated with different massive bodies. The methodology combines theoretical analysis of the gravitational effect, computational implementation supported by the SORA package, and real case studies. Initially, the fundamental concepts of stellar occultations are presented, including how astrometric positions are determined and which factors constrain their accuracy, such as observation quality, number of chords, and temporal coverage of the event. The Klioner light-deflection model is then described, with emphasis on the specific expressions and approximations used in this work. Based on this, a computational approach is developed to adapt the model to the context of stellar occultations, allowing the evaluation of angular separations, deflection angles, and offsets in right ascension and declination, as well as the combined contribution of each massive body. Validation is carried out through a case study of the stellar occultation by Ganymede on 21 December 2020, which is used as a reference to analyze the behavior of the corrections arising from the proximity of the Sun, Jupiter, and Saturn at that moment. The results show that, although the gravitational deflection due to multiple bodies often remains below the positional uncertainties of many events, its magnitude is comparable to the precision achieved in the best recorded occultations, becoming significant when angular separations are small or when the event has a high signal-to-noise ratio. The analysis demonstrates that the event geometry, the alignment between the star, observer, and deflecting bodies, and the uncertainties in the ephemerides are decisive in determining the final magnitude of the correction. It is concluded that the systematic consideration of gravitational light deflection by multiple bodies improves the astrometric consistency of stellar occultations and may contribute to the refinement of reference frames, especially in future observational scenarios with higher instrumental precision.

2026-02-18T00:00:00Z https://repositorio.ufu.br/handle/123456789/48360 2026-02-24T06:20:42Z 2024-04-26T00:00:00Z

Title: O Efeito Bumerangue Quântico

2024-04-26T00:00:00Z