https://repositorio.ufu.br/handle/123456789/19114 Sun, 05 Apr 2026 15:17:26 GMT 2026-04-05T15:17:26Z https://repositorio.ufu.br/handle/123456789/48507 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. Wed, 18 Feb 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/48507 2026-02-18T00:00:00Z https://repositorio.ufu.br/handle/123456789/47639 Title: Transições de fase quânticas dinâmicas do modelo de Creutz com hopping de longo alcance Abstract: In this dissertation, we investigate dynamical quantum phase transitions (DQPTs) in the Creutz model with hopping of range D, decaying according to a power-law with exponent ν. We obtain the exact solution of a generic two-band model, of which the Creutz model is a particular case. We derive analytical expressions for dynamical quantities which are relevant to the study of DQPTs, such as the Loschmidt amplitude and the dynamical free energy of the system. This allows us to analytically determine the Yang-Lee-Fisher (YLF) zeros associated with the Loschmidt amplitude. Consequently, we identify the critical times at which non-analyticities in the dynamical free energy occur in the Creutz model with long-range hopping. Our results indicate that the number of YLF zeros increases with increasing D and decreasing ν. In particular, our findings suggest that in the limit D → ∞ e ν → 0, the dynamical free energy becomes non-analytic at almost all times. A similar consequence, when considering these limits, has already been observed in the case of the Su-Schrieffer-Heeger (SSH) model with long-range hopping. Fri, 01 Aug 2025 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/47639 2025-08-01T00:00:00Z https://repositorio.ufu.br/handle/123456789/47519 Title: Uso de espectroscopia de emissão ótica com plasma induzido por laser (LIBS) associada à aprendizagem de máquinas para análise de resíduos de disparos de armas de fogo (GSR) Abstract: In a situation involving an accident or assault with a firearm, it is possible to identify the person responsible for the shots using chemical markers. This is done by identifying elements already catalogued in conventional ammunition, such as Ba - barium, Pb - lead and Sb - antimony. However, ammunition such as NTA (non-toxic ammunition) does not have chemical markers as clear as conventional ammunition, requiring alternative methods to identify a possible shooter. Therefore, this work proposes an experimental protocol capable of providing such chemical markers, while still providing a margin of accuracy in identification and avoiding false positives. To this end, laser-induced breakdown spec- troscopy (LIBS) is used to provide the elemental signature of the samples, which in turn serves as information for training the Random Forest(RF) classification model, which is based on statistical information metrics. With this supervised machine learning method, it is possible to analyze which parameters are used to distinguish a shooter from a non- shooter, making it explainable. The samples were collected at a shooting range, under protocols established by SENASP (National Secretariat for Public Security), consisting of 2, 6 and 8 shots with NTA ammunition, and 1 and 6 shots with conventional ammu- nition. For comparison, samples were taken from 0 shots (samples from the hand of an individual who did not come into contact with the firearm). The results show chemical markers identified from Cu I, Cu II, Ti I and Mo I atomic transitions, the classification model was able to achieve an accuracy of over 90% and has a generalization power high enough to distinguish a shooter from a non-shooter regardless of the type of ammunition, conventional or NTA. Tue, 25 Feb 2025 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/47519 2025-02-25T00:00:00Z https://repositorio.ufu.br/handle/123456789/46802 Title: Formulação de um modelo de transições eletrônicas e estudo da agregação em oligômeros conjugados a base de tiofeno-benzeno-tiofeno Abstract: Organic semiconducting and luminescent materials have a fundamental role in technological advances in the fields of electronics, optics, and communications. Therefore, understanding the optical properties of these materials is essential for the development of efficient devices. In this work, the photophysical properties of thiophene–benzene–thiophene (TBT) oligomers were investigated, aiming to understand the type of aggregate formed in these systems. Optical absorption and photoluminescence (PL) experiments were carried out to elucidate the emission mechanisms as a function of concentration and excitation power. Fluorescence lifetime measurements were also performed to determine how long the generated exciton remains in the excited state before recombining. The system’s reversibility after irradiation was analyzed to assess whether the observed aggregates were reversible or permanent. Finally, a computational analysis of the photoluminescence spectra was conducted to extract parameters related to the electronic transition energy and the electron vibrational mode coupling, using a two emissive species model. At the end of the study, a model for the electronic transitions of the analyzed oligomers was proposed, along with the identification of the aggregate type, characterized as an exciplex. Fri, 25 Jul 2025 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/46802 2025-07-25T00:00:00Z