https://repositorio.ufba.br/handle/ufba/498 Sun, 03 May 2026 16:59:42 GMT 2026-05-03T16:59:42Z http://repositorio.ufba.br:80/retrieve/eae096b5-d14a-4091-8e9f-325fb3a6ebbe/Logo politécnica.PNG https://repositorio.ufba.br/handle/ufba/498 https://repositorio.ufba.br/handle/ri/44434 Título: Avaliação das propriedades físico-mecânicas e reológicas de compósitos de cimento de fosfato de magnésio com adição de fibras de aço, de sisal (agave sisalana) e de pva Autor(es): Lima, Danilo Carvalho de Primeiro Orientador: Ribeiro, Daniel Véras Abstract: Magnesium phosphate cement (MPC) is an acid-base binder with superior physical mechanical properties compared to conventional hydraulic cements, yet it still presents many gaps, aiming at its development and wider application. This study evaluates the physical, mechanical, and rheological performance of MPC composites reinforced with PVA, sisal, and steel fibers in different proportions, aiming to reduce the brittleness and low deformability of the cementitious matrix. The MPC raw materials (calcined MgO, ammonium dihydrogen monophosphate - ADP, sodium tripolyphosphate – STP, and boric acid), sand, and steel (metallic), polymeric (PVA), and sisal (vegetable) fibers were characterized in terms of physical, chemical, and mineralogical aspects to optimize the formulation and allow evaluations of the composites in the fresh and hardened states. In the fresh state, setting time, pH, calorimetry, and rheological analysis tests were performed on the reference matrix and samples with different fiber contents. After molding and curing, the samples were subjected to phase formation analysis by XRD and thermogravimetry (TG/DTA), in addition to physical-mechanical analysis (specific mass, apparent porosity, capillary absorption, dimensional stability, axial compressive strength, and flexural tensile strength). The results showed that the addition of steel fibers to the CFM promoted significant gains in flexural tensile strength and compressive strength, with emphasis on the increase in toughness, evaluated by the I10 factor, indicating a more ductile post-cracking behavior and an efficient redistribution of stresses. While the addition of natural fibers to the composites resulted in a loss of mechanical performance, contributing to reduced strength values and increased variability in results, possibly due to high water absorption and low interfacial adhesion with the matrix, the chemical acetylation treatment showed promise in improving the mechanical properties of CFM composites with sisal fibers. The insertion of PVA fibers into the CFM matrix provided a modest improvement in mechanical strength compared to the reference matrix and superior performance to that of composites containing natural sisal fibers. Editora / Evento / Instituição: UNIVERSIDADE FEDERAL DA BAHIA Tipo: Dissertação Tue, 03 Mar 2026 00:00:00 GMT https://repositorio.ufba.br/handle/ri/44434 2026-03-03T00:00:00Z https://repositorio.ufba.br/handle/ri/44432 Título: Modificação da fibra da luffa cylindrica (l. aegyptiacal) com ácidos graxos para aplicação como biossorvente de óleo diesel Autor(es): Melo, Luciana Lima Primeiro Orientador: Vidal, Rosangela Regia Lima Abstract: The high demand for and widespread use of petroleum and its derivatives, such as diesel oil, across various economic sectors have caused significant impacts on the environment and human health. In the environment, these compounds have become major pollutants, primarily due to spills. In this context, sorption processes emerge as a promising alternative for removing oily pollutants from water, underscoring the need for biodegradable, low-cost, and highly efficient materials. Luffa cylindrica fiber (vegetable sponge) shows potential as a biosorbent due to its porous structure and mechanical stability. However, its sorptive capacity still requires improvement. Thus, this work proposes the surface modification of Luffa cylindrica fiber with fatty acids (lauric, palmitic, stearic, oleic, and linoleic acids) to increase its affinity for oily compounds. The main objective was to evaluate the effect of these modifications on the sorption capacity of diesel oil. Sample characterization was performed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Sorption studies were conducted by varying sorbent mass, process time, agitation speed, and temperature. Batch experiments were carried out using reference systems (diesel oil, distilled water, or saline water) and systems containing diesel oil spilled into distilled or saline water. The results indicated that oleic acid modification provided the most significant increase in diesel oil sorption capacity among the evaluated systems. The pseudo-second-order model showed the best fit to the kinetic data, indicating that the process is controlled by surface interactions. The predominant mechanism is driven primarily by hydrophobic interactions and van der Waals forces, reflecting the nonpolar affinity between diesel oil and the modified fiber surface. It is concluded that modifying Luffa cylindrica fiber with oleic acid increases its hydrophobicity and sorption efficiency, highlighting the material's potential for oil spill remediation. Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Dissertação Mon, 27 Feb 0002 00:00:00 GMT https://repositorio.ufba.br/handle/ri/44432 0002-02-27T00:00:00Z https://repositorio.ufba.br/handle/ri/44431 Título: Avaliação em massa de imóveis urbanos através de modelagem de regressão espacial Autor(es): Gonçalves, Waltério de Oliveira Primeiro Orientador: Alixandrini Junior, Mauro José Abstract: With the increasing demand for efficiency in municipal revenue collection, real estate appraisal has gained even more relevance due to the fundamental role of the Property and Territorial Urban Tax (IPTU). Since the implementation of Complementary Law No. 101 of May 4, 2000, known as the Fiscal Responsibility Law (LRF), municipalities have faced an urgent need for more robust methods to calculate the market value of properties, driven by the pursuit of tax equity. Detailed and precise planning is essential to ensure that the values assigned to properties fairly reflect their characteristics and location. This study modeled parameters for the appraisal of urban properties, promoting fair proportionality in the generation of Generic Value Maps (PVG). The research was conducted in Camaçari, a municipality in the Metropolitan Region of Salvador (BA), which has over 300,000 inhabitants and stands out as one of Brazil's main industrial hubs, hosting the Camaçari Industrial Pole. The study covered areas in the neighborhoods of Arembepe, Barra de Jacuípe, Boa Esperança, Genipabu, and Vale do Landirana, using a sample of 124 land plots for modeling and 12 for validation. The methodology compared the Ordinary Least Squares (OLS) regression with the global spatial model Conditional Auto Regressive (CAR) and the local Geographically Weighted Regression (GWR) model. The models were evaluated based on quality indicators such as the Akaike Information Criterion (AIC), Log Likelihood (LIK), coefficient of determination ($R^2$), and Root Mean Square Error (RMSE), in addition to specific metrics for mass appraisal, such as Median Ratio (Med R), Coefficient of Dispersion (COD), and Price Related Differential (PRD), according to the International Association of Assessing Officers (IAAO) criteria. The results indicated that GWR was able to significantly reduce spatial effects, outperforming the other models in most quality and performance criteria. The methodology was combined with Ordinary Kriging to generate unit value surfaces. The semivariogram adjusted to the Gaussian model allowed the kriging of predicted values, and the surface generated by the GWR predicted values achieved the lowest RMSE and better performance indicators, close to the limits recommended by the IAAO. It is concluded that GWR modeling was the most effective in representing spatial variations in real estate values in the studied area, and the proposed methodology for PVG generation demonstrated great potential for application by municipalities in the mass appraisal of urban properties, contributing to fairer and more precise tax collection, especially for taxes such as IPTU and the Real Estate Transfer Tax (ITBI). Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Dissertação Fri, 28 Mar 2025 00:00:00 GMT https://repositorio.ufba.br/handle/ri/44431 2025-03-28T00:00:00Z https://repositorio.ufba.br/handle/ri/44369 Título: Técnicas de modulação vetorial baseadas na distribuição da energia de modo comum para atenuação da corrente de fuga em inversores fotovoltaicos de três níveis Autor(es): Mendonça, Luan Aleixo Canário Primeiro Orientador: Bahia, Filipe Antônio da Costa Abstract: Transformerless photovoltaic inverters are susceptible to leakage current, predominantly caused by the common-mode voltage. Modulation strategies typically focus on reducing the amplitude of this voltage, while its frequency spectrum is often neglected. Since the leakage current flows through an RLC loop formed by the output filter and the parasitic capacitance of the photovoltaic modules, the distribution of the common-mode voltage frequency spectrum relative to the circuit resonance frequency has a direct impact on its magnitude. Therefore, shifting the energy of its frequency components away from the resonance region constitutes an effective leakage current mitigation strategy. Based on this premise, this work introduces a modulation approach grounded in the spectral distribution of common-mode energy. To validate this approach, two modulation techniques are proposed. The first concentrates most of the energy around the switching frequency, making it more suitable when the resonance frequency is significantly higher. The second redistributes part of the energy to higher-order harmonics, making it more advantageous when the resonance frequency is close to or lower than the switching frequency. The proposed techniques operate over the entire modulation index range, enable DC-link capacitor voltage balancing, and exhibit low harmonic distortion and switching losses, as confirmed by both simulation and experimental results. In addition, the analysis of leakage current as a function of the modulation index reveals an optimal operating region in which the leakage current is minimized. Editora / Evento / Instituição: Universidade Federal da Bahia Tipo: Tese Fri, 10 Apr 2026 00:00:00 GMT https://repositorio.ufba.br/handle/ri/44369 2026-04-10T00:00:00Z