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Análise de rota de beneficiamento para itabirito compacto da região de Serra Azul, Itatiaiuçu, Minas Gerais.
No full textPrograma de Pós-Graduação em Engenharia Mineral. Departamento de Engenharia de Minas, Escola de Minas, Universidade Federal de Ouro Preto.O esgotamento dos depósitos de minério de ferro friáveis (originados a partir de processos de enriquecimento supergênico dos itabiritos Cauê) têm sido o principal desafio das minas de Serra Azul, localizadas na porção noroeste do Quadrilátero Ferrífero, em Itatiaiuçu/MG. Com a escassez desse tipo de minério friável, se faz necessário o desenvolvimento de rotas de processo para o aproveitamento do itabirito compacto, rocha não alterada caracterizada pelo baixo teor de Fe, alto teor de SiO2 e por ser altamente competente. Desse modo, esse estudo objetivou testar rotas de cominuição e concentração a partir de uma amostra de itabirito compacto de Serra Azul, analisando a viabilidade do processo e identificando os principais desafios. Foram realizados os seguintes ensaios de caracterização tecnológica: caracterização física, química, mineralógica, WI de Bond, AI Bond, DWT, índice de abrasão. Além disso, ensaios em escala de bancada e piloto com rotas que envolveram operações de moagem primária, moagem secundária, separação magnética e flotação catiônica reversa foram executados. Os ensaios de caracterização mostraram que se trata de um minério de ferro de baixo teor de Fe (35,14%) e alto teor de SiO2 (49,32%), elevado WI (15,80 kWh/t) e altos índices de abrasão AI=0,938 e ta=0,35. Os resultados indicaram que o processamento da amostra deve demandar alto consumo de energia na moagem, alto custo com desgaste de corpos moedores (OPEX) e elevados custos de investimentos (CAPEX), além de grande volume de rejeitos gerados. Com relação a rota de beneficiamento, os ensaios de bancada e piloto comprovaram que a rota mais viável envolve britagem primária e secundária, moagem primária, separação magnética nas etapas rougher e scavenger para obtenção de um pré-concentrado. Em seguida, uma etapa de concentração via flotação catiônica reversa em estágios rougher, cleaner, e três scavenger. Por fim, o concentrado final apresentou teores de Fe (67,49%) e SiO2 (2,54%) e recuperação metalúrgica (80,22%), atendendo as premissas para a produção de pellet feed. Simulações em escala industrial (atendendo a demanda de produção de 4,5 Mtpa de pellet feed) mostraram que a adição de uma etapa de moagem HPGR, previamente a moagem I (moinho de bolas), e a substituição do moinho de bolas na moagem II, pelo moinho vertical (Vertimill), deverá gerar benefícios econômicos importantes.The depletion of friable iron ore deposits (originated from supergene enrichment processes in the Cauê itabirites) has been the main challenge for the Serra Azul mines, located in the eastern portion of the Quadrilátero Ferrífero, in Itatiaiuçu, Minas Gerais. Due to the scarcity of this friable ore, it is necessary to develop a process route for the utilization of compact itabirite, an unaltered rock characterized by low Fe content, high SiO2 content, and high compressive strength. Therefore, this study aimed to test comminution and concentration routes using a sample of compact itabirite from Serra Azul, analyzing the process feasibility and identifying the main challenges. The following technological characterization tests were performed: physical, chemical, and mineralogical characterization, Bond WI, Bond AI, DWT, and abrasion index. Furthermore, bench-scale and pilot tests were performed with routes involving primary grinding, secondary grinding, magnetic separation, and reverse cation flotation. The characterization tests revealed that the iron ore has a low Fe content (35.14%) and high SiO2 content (49.32%), high WI (15.80 kWh/t), and high abrasion indices (AI=0.938 and ta=0.35). The results indicated that processing the sample will require high energy consumption during grinding, high grinding media wear costs (OPEX) and high investment costs (CAPEX), in addition to a large volume of tailings generated. Regarding the beneficiation route, the bench and pilot tests confirmed that the most viable route involves primary and secondary crushing, primary grinding, magnetic separation in the rougher and scavenger stages to obtain a pre- concentrate. This is followed by a concentration step via reverse cation flotation in rougher, cleaner, and three scavenger stages. Finally, the final concentrate presented Fe (67.49%) and SiO2 (2.54%) contents and metallurgical recovery (80.22%), meeting the premises for pellet feed production. Industrial-scale simulations (meeting the production demand of 4.5 Mtpy of pellet feed) showed that the addition of an HPGR grinding stage, prior to grinding I (ball mill), and the replacement of the ball mill in grinding II, with the vertical mill (Vertimill), should generate significant economic benefits
3E analysis of a hybrid biomass / solar system for power generation and desalination.
No full textThe study addresses global energy challenges by proposing a hybrid biomass and solar energy system for power generation and water desalination. A model is applied to two cities in Northeast Brazil (Natal-RN and Fortaleza-CE), targeting urban centers with waste and sunny coastal regions. Key variables include residue composition, heating value, and quantity, essential for energy efficiency assessment. Energy, exergy, and economic (3E) analyses using Scilab software compare four configurations: the base Rankine cycle, Rankine with an external superheater (ESH), Rankine with concentrated solar power (CSP), and Rankine with CSP integrated with desalination. Results show that higher pressures and temperatures enhance efficiency, reducing solar field area by 16% when pressure and temperature increase from 4.5 MPa/400°C to 6.5 MPa/500°C. Fortaleza-CE, with higher solar irradiation, requires smaller solar fields than Natal-RN. Integrating desalination into CSP cycles increases Levelized Cost of Energy (LCOE) by up to 7.6% and solar field area due to higher energy demands but provides potable water, with water recovery rates around 10% of seawater input. The findings underscore the importance of optimizing operating conditions and leveraging local solar resources to maximize socio-economic benefits
How anxiety and depression mediate the link between sleep quality and health perception during crisis periods.
No full textDuring crisis periods, understanding the impact of sleep quality on self-rated health becomes crucial. However, the role of anxiety and depression as potential mediators in this relationship remains insufficiently explored. Therefore, this study aimed to assess the association of sleep quality with self-rated health, and mediation by anxiety and depression. This cross-sectional, population-based study was conducted with 1762 adults from October to December 2020 in the Iron Quadrilateral region of Brazil. The exposure variable was poor sleep quality, as measured by the PSQI. The outcome was self-rated health. The mediators tested were anxiety and depression, which were evaluated using symptoms, medical diagnoses, and the use of drugs. To test the mediators' factors, the Karlson-Holm-Breen method was used. The direct acyclic graph was used to select a minimal set of adjustments in multivariate analysis. There were 22.6% of people who rated their health as poor, 52.5% were poor sleepers, 35.1% had symptoms of anxiety and 24.7% had symptoms of depression. According to the multivariate analysis, individuals with poor sleep quality were 2.82 times more likely to self-assess their health as poor. The presence of symptoms of anxiety and depression explained 16.57% and 5.99% of the association between poor sleep quality and poor self-rated health, respectively, in the mediation analysis. During the COVID-19 pandemic, individuals who had poor sleep quality had lower self-rated health. Furthermore, symptoms of anxiety and depression explained a portion of the association. Our study emphasizes the importance of evaluating individuals' sleep quality and mental health during a crisis
Caracterização do debate online sobre cigarro eletrônico no Brasil : uma análise de tópicos de discussão no YouTube.
No full textO YouTube é uma das plataformas de compartilhamento de vídeo mais populares do Brasil, proporcionando um ambiente dinâmico para a disseminação de opiniões sobre questões de saúde pública, incluindo os cigarros eletrônicos. Neste contexto, este estudo tem como objetivo caracterizar o debate online sobre cigarros eletrônicos no Brasil, empregando técnicas de processamento de linguagem natural para a análise de tópicos nos comentários de vídeos do YouTube relacionados ao tema. A coleção de dados utilizada abrange mais de 285 mil comentários sobre o tema, cobrindo o período entre o início de 2018 e o fim de 2023. Nossos resultados identificam múltiplos tópicos de discussão, refletindo uma dinâmica diversificada ao longo dos anos. A discussão é polarizada, com predominância de tópicos favoráveis ao uso de cigarros eletrônicos, mas também revela fortes divergências sobre questões de saúde e regulamentação.YouTube is one of the most popular video-sharing platforms in Brazil, providing a dynamic environment for the dissemination of opinions on public health issues, including electronic cigarettes. In this context, this study aims to characterize the online debate about electronic cigarettes in Brazil by employing natural language processing techniques to perform topic analysis on comments from YouTube videos related to the subject. The dataset used includes over 285,000 comments on the topic, covering the period from early 2018 to the end of 2023. Our results identify multiple discussion topics, reflecting a diverse dynamic over the years. The discussion is polarized, with a predominance of topics favorable to the use of electronic cigarettes, but it also reveals strong disagreements on health and regulatory issues
Germinação e crescimento inicial de três espécies de leguminosas em substrato de área minerada : efeitos na alocação de biomassa e nodulação.
No full textThis study evaluated the germination, initial growth, biomass allocation, and association with nitrogen-fixing bacteria of three shrub legumes from rupestrian grassland, growing on bauxite mine substrates. The germinability of Senna reniformis, Chamaecrista mucronata and Centrosema coriaceum was evaluated in mine substrate after chemical and mechanical scarification. Plant survival and growth were evaluated on four substrates: mine substrate, mine substrate with the addition of 6.7% of topsoil from ferruginous rupestrian grassland, mine substrate with 3.3% of commercial substrate, and 1:1 mixture of mine and commercial substrate. Both scarification methods increased germinability of the three species. Inoculation of mine substrate with topsoil did not enhance plant nodulation. However, the moderate increase in the fertility, achieved by the adding 3.3% of commercial substrate, favored the nodulation. The 1:1 mixture of substrates increased the total plant biomass but reduced root biomass allocation and nodulation, which could reduce the success in the restoration of degraded areas.Neste estudo avaliou-se a germinação, crescimento inicial, alocação de biomassa e associação com bactérias fixadoras de nitrogênio em três leguminosas arbustivas nativas dos campos rupestres. A germinabilidade de Senna reniformis, Chamaecrista mucronata e Centrosema coriaceum foi avaliada após escarificação química e mecânica. A sobrevivência e crescimento das plantasforam avaliados em substrato de área minerada (MS), MS com a adição de 6,7% de solo superficial de campo rupestre ferruginoso, MS com adição de 3,3% de substrato comercial (CS) e mistura 1:1 de MS com CS.Ambos métodos de escarificação aumentaram a germinabilidade das três espécies. A inoculação do MS com solo superficial não contribuiu para a nodulação das plantas, porém, o aumento moderado da fertilidade pela adição de 3,3% de CS favoreceu a nodulação. A mistura de substratos (1:1) reduziu a alocação de biomassa nas raízes e as nodulações, o que pode reduzir o sucesso na restauração de áreas degradadas
Modelagem de fluxo não saturado em pilhas de rejeito : impactos dos níveis de compactação e da incerteza dos parâmetros hidráulicos do solo.
No full textPrograma de Pós-Graduação em Geotecnia. Núcleo de Geotecnia, Escola de Minas, Universidade Federal de Ouro Preto.Diante das alterações recentes na legislação brasileira de segurança de barragens, as pilhas de rejeitos filtrados surgem como alternativa ao modelo convencional de disposição de rejeitos. Contudo, a ausência de diretrizes técnicas específicas, somada à alta pluviometria do Brasil, apresenta desafios à sua adoção. Neste contexto, compreender o comportamento geomecânico e hidráulico dessas estruturas sob condições tropicais é essencial. Este estudo investigou o processo de infiltração em pilhas de rejeitos filtrados considerando diferentes índices de vazios e as incertezas associadas à calibração dos parâmetros hidráulicos não saturados. Por meio de simulações numéricas, avaliou-se a influência da variabilidade dos parâmetros no comportamento hidráulico ao longo do tempo, com foco na região próxima ao talude crítico e na recarga do dreno de fundo. Os resultados indicaram que as camadas superficiais são mais sensíveis às variações climáticas, apresentando rápidas oscilações nos teores de umidade e cargas de pressão devido à precipitação e evaporação diretas. No interior do dreno de fundo, predominou a saturação com cargas de pressão positivas e baixa variabilidade, tanto em relação às incertezas quanto aos índices de vazios, indicando menor influência desses fatores sob saturação. Na região intermediária, foi observado um gradiente de sucção entre as camadas, favorecendo a redistribuição descendente da umidade, especialmente no rejeito mais compactado, que exibiu maior sucção e menores teores de umidade ao longo das simulações — possivelmente devido à maior saturação e consequente aumento da condutividade hidráulica, considerando condutividades hidráulicas saturadas semelhantes para os diferentes índices de vazios. A saturação temporária do topo da pilha durante eventos intensos de chuva indicou escoamento superficial, destacando a necessidade de mecanismos de drenagem superficial e medidas de proteção contra erosão. A comparação entre métodos analíticos e numéricos mostrou coerência geral, embora ressaltando limitações do modelo bidimensional e a importância de aplicar fatores de segurança adequados no dimensionamento dos drenos. Por fim, constatou-se que o índice de vazios exerce maior influência no comportamento hidráulico que as incertezas dos parâmetros calibrados, evidenciando a compactação em campo como fator determinante do desempenho hidráulico. Ressalta-se a importância de calibração e validação dos modelos com dados reais para garantir a confiabilidade das análises.In light of recent changes in Brazilian dam safety legislation, filtered tailings stacks have emerged as an alternative to conventional tailings disposal methods. However, the lack of specific technical guidelines, combined with Brazil’s high rainfall, poses significant challenges to their implementation. In this context, understanding the geomechanical and hydraulic behavior of these structures under tropical conditions is essential. This study investigated the infiltration process in filtered tailings stacks considering different void ratios and uncertainties associated with the calibration of unsaturated hydraulic parameters. Numerical simulations were conducted to evaluate the influence of parameter variability on the hydraulic behavior over time, focusing on the region near the critical slope and the recharge of the bottom drainage system. Results indicated that the upper layers are more sensitive to climatic variations, exhibiting rapid fluctuations in moisture content and pressure heads due to direct rainfall and evaporation. Within the bottom drainage system, saturation prevailed, with positive pressure heads and low variability concerning both parameter uncertainties and void ratios, suggesting a reduced influence of these factors under saturated conditions. In the intermediate region, a suction gradient between layers was observed, promoting downward moisture redistribution, especially in the more compacted tailings, which exhibited higher suction and lower moisture content throughout the simulations—likely due to greater saturation and increased hydraulic conductivity, assuming similar saturated hydraulic conductivities among the different void ratios. Temporary saturation of the stack top surface during intense rainfall events indicated surface runoff, highlighting the need for surface drainage mechanisms and erosion protection measures. Comparison between analytical and numerical methods showed overall consistency, although limitations of the two-dimensional model and the importance of applying adequate factors of safety in drainage design were noted. Finally, it was found that the void ratio exerts a greater influence on hydraulic behavior than the uncertainties of calibrated parameters, underscoring field compaction as a key factor determining hydraulic performance. The study emphasizes the need for calibration and validation of models with field data to ensure reliable assessments
Exact geometric nonlinear analysis of frames modeled with nonprismatic shear-deformable elements defined by noncentroidal axes.
No full textThis paper provides an explicit closed-form expression for geometric-stiffness coefficients for nonprismatic frame elements defined by their noncentroidal axes. The proposed formulation uses the element’s exact elastic stiffness coefficients and exact Timoshenko’s shape functions. One advantage of working with exact stiffness values is the obvious quality of the resulting tangent stiffness matrix, which is expected to be highly accurate. In addition, adopting frame elements based on noncentroidal axes enables the modeling of complex nonprismatic frame elements using simple, straight-line segments. Hence, beams having cross sections that vary asymmetrically around their straight centerlines can be consistently modeled in a simplified process. The formulation takes into consideration the correct interaction between axial and flexural effects. To validate the formulation’s robustness, we evaluate the geometric nonlinear in-plane response of several metal frames possessing nonprismatic elements with variable thin-walled monosymmetric cross sections. We compare these results with highly accurate 3D responses obtained using the ANSYS software
A costura da narrativa bíblica em O evangelho segundo Jesus Cristo, de José Saramago.
No full textPrograma de Pós-Graduação em Letras. Departamento de Letras, Instituto de Ciências Humanas e Sociais, Universidade Federal de Ouro Preto.Este estudo analisa O Evangelho Segundo Jesus Cristo (1991), de José Saramago, à luz da crítica literária e da intertextualidade com os evangelhos canônicos, buscando compreender como o autor português reelabora a narrativa bíblica e a reinscreve em chave estética, histórica e política. Partindo da perspectiva de que a literatura pode questionar discursos fundantes sem destruí-los, a pesquisa examina a obra como gesto de paródia, no sentido proposto por Linda Hutcheon, isto é, uma repetição com diferença, que não anula o sagrado, mas o desloca e o reconfigura. A dissertação estrutura-se em quatro capítulos. O primeiro apresenta a fortuna crítica sobre Saramago e destaca a centralidade do narrador em sua poética. Ao mesmo tempo, a recusa da alienação entre autor e obra, lida à luz de Marx e tensionada por Žižek, revela como Saramago inscreve no romance um exercício de crítica social que denuncia as estruturas de poder veladas pela tradição religiosa. O segundo capítulo discute o mito, recuperando aportes de Eliade e, especialmente, Pierre Brunel, que reconhece Cristo como mito literário recorrente. A inserção de elementos não canônicos, a ironia e a fragmentação compõem estratégias narrativas que subvertem a narrativa bíblica e revelam sua historicidade, ao mesmo tempo em que instauram um quinto evangelho, profano e crítico. No terceiro capítulo, são analisados episódios centrais do romance: a Anunciação, o Nascimento, os milagres, as parábolas e a Crucificação, em confronto com os evangelhos canônicos. Cada passagem é lida como parte de um mosaico que, embora reconheça a fonte, a reorganiza a partir de uma perspectiva literária insurgente. O romance opera, assim, uma releitura que revela a humanidade das figuras sagradas e questiona a legitimidade da narrativa religiosa como única forma de verdade. Por fim, nas considerações finais, defende- se que a obra de Saramago não anula o mistério do sagrado, mas o desloca para o campo da literatura, onde pode ser interrogado, ironizado e reinventado. O Evangelho Segundo Jesus Cristo exemplifica a potência da literatura em reescrever mitos fundadores e problematizar as bases simbólicas da cultura ocidental. Nesse processo, o romance reafirma a literatura como espaço de crítica, memória e resistência, capaz de dar voz a sujeitos historicamente marginalizados e de propor novas formas de pertencimento e leitura do mundo.This study analyzes O Evangelho Segundo Jesus Cristo (1991), by José Saramago, in light of literary criticism and its intertextual dialogue with the canonical gospels, seeking to understand how the Portuguese author reworks the biblical narrative and reinscribes it within aesthetic, historical, and political dimensions. Based on the premise that literature can question foundational discourses without destroying them, the research examines the novel as an act of parody in the sense proposed by Linda Hutcheon, namely, a “repetition with difference” that does not annul the sacred but rather displaces and reconfigures it. The dissertation is organized into four chapters. The first presents the critical reception of Saramago’s work and highlights the centrality of the narrator in his poetics. At the same time, the refusal of alienation between author and text, interpreted through Marx and problematized by Žižek—reveals how Saramago inscribes within the novel a form of social critique that exposes structures of power concealed by religious tradition. The second chapter discusses the concept of myth, drawing on the contributions of Eliade and, especially, Pierre Brunel, who recognizes Christ as a recurring literary myth. The insertion of non- canonical elements, irony, and fragmentation constitute narrative strategies that subvert the biblical text and disclose its historicity, while simultaneously establishing a profane and critical “fifth gospel.”. The third chapter analyzes central episodes of the novel: the Annunciation, Nativity, miracles, parables, and Crucifixion,in dialogue with the canonical gospels. Each passage is read as part of a mosaic that, while acknowledging its sources, reorganizes them from an insurgent literary perspective. In this way, the novel enacts a rereading that reveals the humanity of sacred figures and questions the legitimacy of religious narrative as the sole form of truth. Finally, the conclusion argues that Saramago’s work does not eliminate the mystery of the sacred but relocates it within the field of literature, where it may be interrogated, ironized, and reinvented. O Evangelho Segundo Jesus Cristo exemplifies literature’s power to rewrite foundational myths and problematize the symbolic foundations of Western culture. In doing so, the novel reaffirms literature as a space of critique, memory, and resistance, capable of giving voice to historically marginalized subjects and of proposing new forms of belonging and of reading the world
Study on the recent changes in market structure in the mobile telephony sector in Brazil : an analysis based on indicators of industrial concentration.
No full textRecentemente a empresa de telecomunicações Oi decidiu vender seus ativos de telefonia móvel. Pela sua relevância mercadológica, este processo de venda pode ter modificado a estrutura de mercado que caracteriza este setor. Diante deste cenário, o presente estudo teve como objetivo avaliar a estrutura de mercado do setor de telefonia móvel no período de 2012 até o mês de abril de 2022, mês no qual os dados da Oi foram incorporados pelas três empresas Tim, Vivo e Claro. Para tal foram calculados os seguintes indicadores: o Índices de instabilidade, o Índice de Hirschman-Herfindahl e a Razão de Concentração (CR). Foi abordado o cenário segundo o critério do Conselho Administrativo de Defesa Econômica (CADE) e outro cenário balanceado, no qual buscou-se equilibrar as parcelas em cada região segundo o número de acessos disponíveis. Os resultados mostraram que já havia uma alta concentração do mercado em praticamente todas as regiões antes de se efetivar a venda, e que esta concentração aumentou. Demonstrou-se, também, que se trata de um setor no qual há pouca instabilidade na parcela de mercado das empresas. Tal estabilidade pode se originar das barreiras à entrada existentes neste setor.In June 2020, the telecommunications company Oi informs the market of its decision to sell its mobile telephony assets. This sales process may have modified the market structure that characterizes thiis setor. Given this scenario, the present study aimed to evaluate the market structure of the mobile telephony sector in the period from 2012 to April 2022, the month in which Oi's data were incorporated by the three companies Tim, Vivo and Claro. For this purpose, the following indicators were calculated: o Instability indices, the Hirschman-herfindahl Index and the Concentration Ratio (CR). The scenario was approached according to the criteria of the Adminis- trative Council for Economic Defense (Cade) and another balanced scenario, in which an attempt was made to balance the shares in each region according to the number of accesses available in April 2022. The results showed that there was already a high concentration of the market in practically all regions before the sale took place, and that this concentration increased. It was also demonstrated that this is a sector in which there is little instability in the market share of companies. Such stability may originate from the existing barriers to entry in this sector
Reduction of food insecurity over time : an unattainable reality for the poorest families?
No full textIntroduction: Food insecurity (FI), associated with inadequate access to food, reflects social inequality. Shifts in sociodemographic factors significantly impact household FI. This study initially hypothesized that the progression of the COVID-19 pandemic would exacerbate socioeconomic challenges, thereby influencing the trends and responses related to FI within the studied population. Objective: This study examines how social and demographic factors associated with FI change in an important population group during a health crisis, identifying vulnerable groups. Methods: This longitudinal study analyzed a random sample of students from public schools in two Brazilian municipalities. Data were collected at 9-month intervals at four time points (T0, T1, T2, and T3) between 2020 and 2022. FI was measured using the Brazilian Food Insecurity Scale (BFIS) and analyzed as a discrete numerical variable (BFIS score -0 to 14 points). Comparisons across time points were analyzed using the paired Wilcoxon test. A generalized linear mixed model assessed the relationship between BFIS score and social and demographic variables over time. Results: The average BFIS scores declined from 2.9 at T0 to 2.7 at T1; to 2.2 at T2 and T3, with significant differences between T0 and T2/T3 (P < 0.001), and T1 and T2/T3 (P = 0.017). Higher BFIS scores were associated with families earning less than or equal to half the minimum wage Rate Ratio (RR) =4.93 [95% CI: 3.81–6.36], enrolled in social programs RR =1.14 [95% CI: 1.02–3.81], receiving emergency aid RR =1.15 [95% CI: 1.04–1.28] or food baskets RR=1.30 [95% CI: 1.18–1.43]. Families headed by Black/Brown individuals and women had higher BFIS scores, as did those headed by single individuals and those with low educational attainment. Conclusion: There was no reduction in the average BFIS score for 2020 and 2022 for extremely poor families, despite improvements in other socioeconomic indicators. Families enrolled in social programs, beneficiaries of emergency aid, and households headed by women and black people experienced higher average BFIS scores, highlighting factors in the complex dynamics of FI during COVID-19 and a dynamically oscillating evolution in the sociodemographic landscape