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    Evaluation of alternative feed ingredients and phytase supplementation for broiler chickens
    (Universidade Federal de Viçosa, 2026-06-26) Borges, Samuel Oliveira; Calderano, Arele Arlindo; http://lattes.cnpq.br/1727142251318507
    Modern poultry production requires nutritional strategies capable of improving productive efficiency, reducing feed costs, and promoting the sustainable use of available resources. In this context, the evaluation of alternative feed ingredients and the use of exogenous enzymes have emerged as relevant tools for optimizing broiler nutrition. Accordingly, this thesis was developed to contribute to the nutritional management of broiler chickens through two complementary approaches: the determination of the nutritional value and metabolizable energy values of alternative feed ingredients and the evaluation of phytase supplementation in diets with planned nutritional reductions. The first study aimed to determine the apparent metabolizable energy (AME) and nitrogen-corrected apparent metabolizable energy (AMEn) values of alternative feed ingredients used in broiler diets. Eight ingredients were evaluated: whole annatto seed meal, spray-dried porcine plasma, poultry viscera meal, three sources of soybean acid oil, distillers corn oil, and degummed rice bran oil. The determined AME and AMEn values were, respectively, 7,023 and 6,841 kcal/kg, 7,743 and 7,466 kcal/kg, and 8,318 and 7,913 kcal/kg for the three soybean acid oil sources; 8,554 and 8,457 kcal/kg for distillers corn oil; 8,273 and 7,910 kcal/kg for degummed rice bran oil; 999 and 975 kcal/kg for whole annatto seed meal; 3,388 and 2,753 kcal/kg for spray-dried porcine plasma; and 3,691 and 3,216 kcal/kg for poultry viscera meal. These findings demonstrated substantial variation among the evaluated ingredients, reinforcing the importance of the specific nutritional characterization of each feedstuff to improve the precision of diet formulation. The second study evaluated the effects of phytase supplementation in nutritionally deficient diets on growth performance, blood biochemical parameters, bone characteristics, and body composition of broiler chickens. Phytase supplementation restored body weight gain, feed conversion ratio, bone mineralization, serum calcium and phosphorus concentrations, as well as lean tissue and bone deposition, achieving results comparable to those obtained with nutritionally adequate diets, even under reductions in available phosphorus, calcium, sodium, metabolizable energy, crude protein, and digestible amino acids. Overall, the results demonstrate that nutritional efficiency in broiler production can be enhanced through the combination of accurate nutritional evaluation of alternative feed ingredients and the use of technologies that improve nutrient utilization. The use of alternative feed ingredients increases formulation flexibility and may reduce dependence on conventional feedstuffs, whereas phytase supplementation enhances nutrient availability and sustains productive performance in more cost-effective feeding programs. Keywords: agro-industrial coproducts; exogenous enzymes; metabolizable energy
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    Exogenous enzyme strategies in broiler diets: impacts on performance, nutrient utilisation and metabolic efficiency
    (Universidade Federal de Viçosa, 2026-03-27) Léo, Rosa Aparecida Reis de; Hannas, Melissa Izabel; http://lattes.cnpq.br/3577720934216190
    This thesis investigated the effects of different exogenous enzyme supplementation strategies on the nutritional and metabolic efficiency of broiler chickens. Two complementary studies were conducted to evaluate phytase superdosing and multi- enzyme supplementation in nutritionally reduced diets containing plant- and animal- derived ingredients. In the first study, the effects of phytase superdosing were evaluated in diets formulated with corn, soybean meal, and meat and bone meal. Increasing phytase inclusion levels improved feed conversion ratio and enhanced bone mineralisation, with linear increases observed in metabolisable energy and nutrient metabolizability coefficients. Supplementation with 2000 and 2500 FTU/kg resulted in greater calcium and phosphorus deposition in bones, increased nutrient utilization by up to 29%, and reduced phosphorus excretion by more than 30%, demonstrating that phytase superdosing remains effective even in diets containing mixed phosphorus sources. The second study evaluated exogenous enzyme supplementation in nutritionally reduced diets, focusing on growth performance, metabolisable energy, and amino acid digestibility. Enzyme inclusion promoted nutritional recovery, increased metabolisable energy values, and improved amino acid digestibility, demonstrating that enzymatic strategies can mitigate the effects of dietary nutrient reduction without compromising bird performance. Collectively, the results demonstrate that exogenous enzyme supplementation, whether through phytase superdosing or multi-enzyme complexes, improves nutrient utilization, metabolic efficiency, and sustainability in broiler production systems. These findings reinforce the role of enzyme technology as a multifunctional nutritional tool capable of optimizing feed efficiency and reducing the environmental impact of modern poultry production. Keywords: exogenous enzymes; phytase; broiler chickens; nutrient utilization; metabolisable energy; amino acid digestibility; bone mineralisation; sustainability
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    Mecanismos moleculares de formação de complexos biomacromolécula-surfactante: abordagem cinética e termodinâmica
    (Universidade Federal de Viçosa, 2025-12-19) Marques, Isabela Araujo; Silva, Luis Henrique Mendes da; http://lattes.cnpq.br/5866809240745442
    A compreensão das interações entre biomacromoléculas e surfactantes é fundamental para o avanço de diversas áreas tecnológicas, desde a formulação de alimentos e cosméticos até o desenvolvimento de sistemas avançados de liberação de fármacos. Alinhada a esse cenário, esta tese aborda a análise integrada da termodinâmica e cinética de sistemas supramoleculares, focando nos complexos formados entre biomacromoléculas e surfactantes. Para tanto, investigaram-se os sistemas -ciclodextrina (CD)-dodecilbenzeno sulfonato de sódio (SDBS) e caseína micelar (CM)-surfactantes Brij, empregando a ressonância plasmônica de superfície (RPS). No sistema CD-SDBS, as análises revelaram constantes cinéticas de associação (ka) de 102 M-1 s-1, de dissociação (kd) de 10-1 s-1 e de equilíbrio (Kb) de 103 L mol-1. A dependência térmica dessas constantes indicou um mecanismo envolvendo reorganizações conformacionais da cadeia alquílica do SDBS na cavidade da CD durante a dissociação. Adicionalmente, o líquido iônico cloreto de 1- butil-3-metilimidazólio reduziu a estabilidade do complexo, mas favoreceu a inserção da cadeia hidrofóbica na cavidade. No sistema CM-Brij, a RPS descreveu de forma integrada os mecanismos de interação. Para o complexo CM-Brij 58, obtiveram-se ka de 104 M-1 s-1, kd de 10-2 s-1 e Kb da ordem de 104 L mol-1. Os resultados evidenciaram um mecanismo em duas etapas: ancoragem inicial por ligações de hidrogênio entre o segmento PEG do surfactante e as -caseínas superficiais, seguida pela inserção da cauda hidrofóbica em canais do nanoagregado proteico. A comparação entre os surfactantes Brij 56, 58 e 78 demonstrou que pequenas modificações estruturais alteram significativamente as barreiras energéticas para formação dos complexos. Em conjunto, os resultados elucidam como interações hidrofóbicas, ligações de hidrogênio e efeitos de solvatação governam o reconhecimento molecular nesses sistemas, fornecendo bases para o planejamento de sistemas coloidais, encapsulamento e materiais funcionais auto-organizados. Palavras-chave: química supramolecular; ciclodextrina; caseína micelar; álcool graxo etoxilado; dodecil benzeno sulfonato de sódio; termodinâmica; cinética; ressonância plasmônica de superfície
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    Defusing the bomb: a large-scale analysis and machine learning approach to review bombing in video games on Steam
    (Universidade Federal de Viçosa, 2026-07-09) Ribeiro, Marcus Vinicius Guerra; Melo, Philipe de Freitas; http://lattes.cnpq.br/5964940449181622
    Steam is currently the largest digital distribution platform for PC games and hosts one of the most extensive publicly accessible ecosystems of user reviews. In this context, Review Bombing (RB) has emerged as an orchestrated form of collective action in which large volumes of reviews are posted within short periods of time with the intent of influencing a game's public evaluation. Despite its relevance, large scale empirical analyses of RB remain limited. In this work, we present a comprehensive longitudinal study of RB on Steam based on a dataset comprising 157,825 games and more than 103 million user reviews, validated against 89 RB incidents and 11,800,720 RB reviews identified by Steam's official moderation pipeline and subsequently confirmed through manual review. We analyze temporal patterns, user participation, and textual characteristics of RB incidents, as well as the thematic content of reviews through topic modeling. Our findings demonstrate that RB constitutes a distinct and empirically observable phenomenon, characterized by recurring temporal, behavioral, and linguistic patterns that significantly differentiate it from the organic flow of user reviews. We further show that these incidents are predominantly driven by established and highly engaged users and are frequently used as vehicles for expressing geopolitical, cultural, and ideological grievances, often framed through consumer oriented language such as refund requests and allegations of fraudulent practices. Moreover, we show that RB can be instrumentalized both to promote and to challenge hate speech, highlighting important tensions between consumer expression and platform governance. Finally, we develop and evaluate a machine learning approach for detecting RB incidents based on temporal, semantic, and behavioral features, achieving an F1 score of 0.67 using XGBoost. Our results indicate that semantic shifts in review content, temporal variations in reviewing activity, and the concentration of negative reviews are the most predictive signals for identifying RB incidents. Keywords: review bombing; hate speech; Steam; natural language processing; topic modeling; gaming culture
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    Impacto da forma de defeitos padronizados e direção do campo magnético em diodos supercondutores
    (Universidade Federal de Viçosa, 2026-06-11) Melo Junior, Eloi Benicio de; Araujo, Clodoaldo Irineu Levartoski de; http://lattes.cnpq.br/0834006212434045
    Investigamos o Efeito Diodo Supercondutor (SDE) em dispositivos com defeitos padronizados por meio de duas análises complementares. A primeira análise concentrou-se na influência do campo magnético perpendicular ao plano (Hz), revelando uma forte dependência do SDE com a geometria dos defeitos. Identificamos dois mecanismos principais que governam a corrente crítica (Ic) nesses dispositivos: a coexistência da aglomeração de corrente (current crowding) e da corrente de blindagem de Meissner para campos magnéticos inferiores a Hstop, e o aprisionamento de fluxo no volume (bulk pinning) para campos superiores a Hstop. A segunda análise investigou a dependência angular da eficiência do SDE (). Verificamos que a eficiência do SDE é fortemente influenciada tanto pelo campo magnético no plano (Hin) quanto pela geometria dos defeitos padronizados. Em particular, a eficiência do SDE atinge seu valor máximo quando Hin está orientado perpendicularmente à corrente aplicada. Esse comportamento é explicado pela interação entre a corrente de blindagem de Meissner induzida pelo campo magnético no plano e a aglomeração de corrente. Nossos resultados demonstram a versatilidade desses diodos supercondutores, cujo desempenho pode ser controlado por Hin, Hz ou pela aplicação simultânea de ambos os campos. Além de fornecer uma compreensão abrangente do SDE na presença de um campo magnético no plano, esses resultados abrem novas perspectivas para futuras pesquisas sobre diodos supercondutores. Palavras-chave: supercondutividade; efeito diodo; dispositivos