https://repositorio.ufba.br/handle/ufba/514 Fri, 17 Apr 2026 08:02:13 GMT 2026-04-17T08:02:13Z http://repositorio.ufba.br:80/xmlui/bitstream/id/4d25f89d-a4b7-4958-87b3-fc1f8b866a1e/logo fisica.PNG https://repositorio.ufba.br/handle/ufba/514 https://repositorio.ufba.br/handle/ri/44227 Standard perturbation theory (SPT) for models with interaction in the dark sector Mello, Matheus Monteiro Wolney Von Marttens, Rodrigo 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. Universidade Federal da Bahia 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 Complex approaches to handedness and brain lateralization Silva, Yago Emanoel Ramos Miranda, José Garcia Vivas 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. Universidade Federal da Bahia 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 Proposta de Instrumentação para caracterização de cordas de guitarra elétrica e estudo de cordas vibrantes. Simões, André Jackson Ramos Pepe, Iuri Muniz 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. Universidade Federal da Bahia 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/42843 Utilização de bases de dados para a vigilância epidemiológica combinando conceitos e técnicas de sistemas dinâmicos, inteligência artificial e ciência de rede. Borges, Dérick Gabriel Fernandes Andrade, Roberto Fernandes Silva This study explores the application of dynamical systems, statistical approaches, artificial intelligence and network science in the context of epidemiological surveillance, with an emphasis on syndromic surveillance of respiratory infections. A first study was carried out using primary health care data from 27 immediate geographic regions, corresponding to the capitals of the states of Brazil. The integration of artificial intelligence and dynamical systems resulted in the creation of the Mixed Model of Artificial Intelligence and Next Generation, which combines different methods to improve the early detection of outbreaks from time series. Then, a second study was carried out, applying a metapopulation model and concepts from network science. Using mobility information and primary health care data from one of the largest states in Brazil, Bahia, the spatial dissemination of potential respiratory diseases was investigated by identifying propagation hubs, based on a sentinel index. This work directly contributes to the project Alert-Early System for Outbreaks with Pandemic Potential (AESOP), demonstrating the potential of new tools to mitigate the impact of emerging and re-emerging diseases in Brazil. Universidade Federal da Bahia Tese Tue, 22 Jul 2025 00:00:00 GMT https://repositorio.ufba.br/handle/ri/42843 2025-07-22T00:00:00Z