https://repositorio.ufba.br/handle/ri/10581 Sun, 03 May 2026 15:49:51 GMT 2026-05-03T15:49:51Z https://repositorio.ufba.br/handle/ri/44227 Título: Standard perturbation theory (SPT) for models with interaction in the dark sector Autor(es): Mello, Matheus Monteiro Wolney Primeiro Orientador: Von Marttens, Rodrigo Abstract: This dissertation investigates the formation and nonlinear evolution of cosmic structures in cosmological models with an interacting dark sector (IDS), extending the standard ΛCDM framework. Starting from the fluid and perturbation equations governing the density and velocity fields, a fully time-dependent perturbative formalism is developed, going beyond the Einstein–de Sitter (EdS) approximation. Evolution equations for second-, third-, and arbitrary-order perturbative kernels are derived, explicitly incorporating the effects of interactions between dark matter and dark energy. A central result of this work is the critical assessment of the commonly employed approximation in which the ratio between the matter density parameter, Ωm, and the square of the perturbation growth rate, f 2 , is assumed to be approximately unity. In the ΛCDM model, this approximation is motivated by the empirical relation f ≈ Ω 0.55 m , which implies that Ωm/f 2 remains close to unity over a significant fraction of cosmic history. This near equality allows the separation of temporal and spatial dependencies in the perturbative equations, rendering nonlinear kernels approximately time-independent and substantially simplifying analytical and numerical calculations. For this reason, the approximation based on the Einstein–de Sitter limit is frequently employed even in cosmologies where it is not strictly valid. It is nevertheless shown that, within the ΛCDM framework, this approximation remains valid even at low redshifts, since deviations from unity remain small in the late Universe. In interacting dark sector models, however, such deviations become significantly larger at late times, indicating that assumptions based on the Einstein–de Sitter limit are no longer reliable when dark sector interactions are present. Using the numerical code SPTIDS, developed and implemented by the author as part of this work, the matter power spectrum at one-loop level and the reduced bispectrum are computed for IDS cosmologies. The results show that dark sector interactions enhance the growth of matter perturbations and amplify higher-order correlations relative to the ΛCDM model, providing distinctive nonlinear signatures. These results demonstrate the necessity of a fully time-dependent perturbative treatment for precision modeling of large-scale structure in interacting dark sector scenarios, while also pointing to possible observational deviations from the standard cosmological model. Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Dissertação Tue, 10 Feb 2026 00:00:00 GMT https://repositorio.ufba.br/handle/ri/44227 2026-02-10T00:00:00Z https://repositorio.ufba.br/handle/ri/43365 Título: Complex approaches to handedness and brain lateralization Autor(es): Silva, Yago Emanoel Ramos Primeiro Orientador: Miranda, José Garcia Vivas Abstract: The evolutionary history of the human species reveals a marked progression in brain and upper limb lateralization within the Homo genus. Particularly for tool use and fire control, Homo sapiens evolved with increasingly refined motor abilities, culminating in a strong preference for a dominant hand. Contrary to the common belief that asymmetry may indicate inefficiency or inadaptability, manual lateralization in humans reflects a form of specialization—similar to patterns observed in apex predators—where specialization often confers adaptive advantages. The experience of left-handed individuals in predominantly right-handed societies underscores the need to better understand motor behavior and the mechanisms underlying hand dominance. This experimental study employs a combination of biomechanical metrics and EEG(Eletroencefalografy)-based measurements to analyze general motor behavior during fine motor tasks performed with both hands, specifically handwriting. It further explores how these behaviors evolve over time, with a focus on the emergent dynamics given by permutation entropy measures. Our findings reveal that right-handed exhibit more optimized and stable motor strategies across hands, whereas left-handers and ambidextrous individuals display greater variability and less consistent dominance patterns. However, temporal analyses using permutation entropy of motor behavior revealed similar lateralization profiles between left- and right-handed groups, suggesting functional equivalence in hand use. EEG analyses indicated that right-handers individuals show more distributed and temporally non-linear brain behavior, potentially due to reduced experience or training with the non-dominant hand in daily tasks. We conclude that human lateralization supports a variety of neuromotor configurations and those behavioral patterns are shaped more by usage habits and experience than by intrinsic differences between handedness groups. These findings highlight the evolutionary and functional relevance of motor lateralization in Homo sapiens. Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Dissertação Mon, 11 Aug 2025 00:00:00 GMT https://repositorio.ufba.br/handle/ri/43365 2025-08-11T00:00:00Z https://repositorio.ufba.br/handle/ri/43269 Título: Proposta de Instrumentação para caracterização de cordas de guitarra elétrica e estudo de cordas vibrantes. Autor(es): Simões, André Jackson Ramos Primeiro Orientador: Pepe, Iuri Muniz Abstract: The electric guitar is a musical instrument based on string vibration, that is well known by physics. This work presents the development of an experimental setup capable of verifying the vibrating string equation for electric guitar strings, by building an electric guitar prototype as well as a digital dynamometer prototype to measure guitar string tension. With the developed apparatus, it was possible to verify the relationship between vibrating string frequency and physical quantities such as length, tension, linear density and number of the harmonic associated with the string. Beyond the verification of the vibrating string equation, it was possible to characterize the guitar strings, as well as measure the differences between brands and types of strings. The methods were shown to be useful for academic study and can be applied in educational scenarios, or even in the musical instruments industry. Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Dissertação Mon, 10 Mar 2025 00:00:00 GMT https://repositorio.ufba.br/handle/ri/43269 2025-03-10T00:00:00Z https://repositorio.ufba.br/handle/ri/28664 Título: Sobre algumas características da entropia de Shannon para sistemas atômicos confinados Autor(es): Nascimento, Wallas Santos Abstract: A entropia de Shannon, que no âmbito da Teoria da Informação fornece uma medida de incerteza de uma dada distribuição de probabilidade, tem sido empregada no estudo de sistemas atômicos e moleculares livres para, entre outras, analisar a qualidade da função de onda. Entretanto, poucos estudos têm sido feitos para sistemas quânticos confinados espacialmente. Estes sistemas, em particular, têm suas propriedades físico-químicas alteradas em relação ao sistema livre. O presente trabalho tem como objetivo analisar a entropia de Shannon para sistemas quânticos confinados. Com esse intuito foram estudados o oscilador harmônico unidimensional confinado, bem como alguns sistemas atômicos com um e dois elétrons. Os sistemas de um elétron escolhidos foram: o átomo de hidrogênio confinado e alguns de seus íons isoeletrônicos confinados como o átomo de hélio ionizado e o átomo de lítio duplamente ionizado. Para o estudo de sistemas com dois elétrons foram escolhidos o átomo de hélio confinado e um de seus íons isoeletrônicos confinados, o átomo de lítio ionizado. Para esses sistemas, em seu estado fundamental, foram calculas as entropias de Shannon no espaço das posições e no espaço dos momentos, bem como a soma entrópica St. Com esse procedimento foi possível apontar as tendências do comportamento das entropias de Shannon, testar o cumprimento da relação de incerteza entrópica e, por fim, analisar a conjectura de Gadre. Os cálculos foram implementados no pacote computacional Maple13.; ABSTRACT - The Shannon entropy, which in the context of Information Theory provides a measure of uncertainty of a given probability distribution have been used in the study of free atomic and molecular systems for, among others, to analyze the quality of the wave function. However, few studies have been done to spatially confined quantum systems. These systems, in particular, have their physical-chemical properties changed compared to free system. This paper aims to analyze the Shannon entropy for quantum confined systems. With this purpose we studied the one-dimensional harmonic oscillator confined as well as some atomic systems with one and two electrons. An electron systems were chosen: the hydrogen atom confined and some of its isoelectronic ions confined as ionized helium atom (He+) and doubly ionized lithium atom (Li2+). For the study of systems with two electrons were chosen the confined helium atom (He) and their isoelectronic ions confined atom lithium ion (Li+). For those systems in their ground state were calculas the Shannon entropy of the positions in space of time and space as well as the sum of entropy St. With this procedure it was possible to identify trends in the behavior of the Shannon entropy test the performance of entropic uncertainty relation, and finally analyze the conjecture Gadre. The calculations have been implemented in the computational package M aple13 Tipo: Dissertação Wed, 20 Feb 2019 00:00:00 GMT https://repositorio.ufba.br/handle/ri/28664 2019-02-20T00:00:00Z