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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
131

ESTUDO FARMACOGNÓSTICO DE Pithecoctenium echinatum (Jacq.) Baill / STUDY OF PHARMACOGNOSY Pithecoctenium echinatum (Jacq.) Baill

Casoti, Rosana 28 March 2012 (has links)
Fundação de Amparo a Pesquisa do Estado de São Paulo / Pithecoctenium echinatum belongs to the family Bignoniaceae, popularly known as comb monkey used in folk medicine for inflammations, rheumatism, skin infections, headaches, cleanses the blood and calming. The objective of this study was to characterize morphological and anatomical fruit of P. echinatum; to determine the physico-chemical quality of the plant drug, isolating chemical compounds of secondary metabolism, as well as to investigate antimicrobial, antioxidant and anti-inflammatory, and analyzing biochemical parameters of liver and kidney toxicity in the crude extract (CE) of seeds of P. echinatum. This species has bicarpelar ovary with the presence of trichomes, crystals and emergencies. It has parietal placentation. The rudiment seminal anatropous, unitegmic and tenuinucellate. The ring nectary has stomatal complexes and trichomes. The epicarp has cutin with the presence of lenticels, estomatíferos and complex emergencies. The outer mesocarp has parenchyma cells, stone cells, sclerified cells and crystals. The endocarp is represented by a single cell layer is not sclerified. The seed is winged and exotestal. The endothelium and the endosperm are the membranaceous embryo. The mesophyll has chemical compounds such as alkaloids, fixed oils, volatile oils, scarce presence of starch and consists of pectic walls. In physico-chemical characterization, using pharmacopoeia tests was used dried vegetable drug, noting that no significant variation of the samples collected in different locations. The hydroethanolic extract 70% seeds of P. echinatum presented secondary metabolic compounds such as steroids and/or triterpenes, flavonoids, alkaloids, anthraquinones, tannins, catechin, phenolic hydroxyl heterosides cardiotonic and volatile oils. Assay polyphenols, flavonoids and tannins were determined by spectroscopic in the CE and fractions. P. echinatum showed antioxidant potential (IC50 131.84 mg/ml) in acetate fraction by the DPPH method and antimicrobial activity to P. aeruginosa, P. zophii and C. albicans by the microdilution method (MIC). From the CE the seeds of P. echinatum we performed the isolation and identification of hesperetin and diometin. These flavonoids were isolated from P. echinatum first. The compounds were determined and analyzed by HPLC / MS and NMR and their spectra compared with the literature. The anti-inflammatory activity of the CE was assayed by the induction of inflammation for cotton rolls and serum taken from rats submitted to the bioassay, in which were administered orally by 300mg/kg/day of CE for 6 consecutive days and compared to nimesulide (5mg/kg/day) and negative control (propylene glycol 20% v/v). The results showed that the CE of P. echinatum showed significant inhibition of inflammation of 24.7%, similar to the inhibition obtained by the group of animals treated with nimesulide 21.4% compared to controls. The hematological parameters showed an increase in the number of leukocytes and decreased of corpuscular medium volume, while AST, ALT and creatinine showed no significant difference in the use of CE compared with the control group propylene glycol. Therefore, the physico-chemical parameters established for P. echinatum enable quality control of drugs of this kind, and this presented antimicrobial, antioxidant and anti-inflammatory activities. Furthermore, no evidence of a hepatotocidade and nephrotoxicity in the experimental conditions tested. / Pithecoctenium echinatum pertence à família Bignoniaceae, conhecida popularmente como pente-de-macaco e é utilizada na medicina popular para inflamações, reumatismo, infecções cutâneas, dor de cabeça, depurativo do sangue e calmante. O objetivo deste trabalho foi realizar a caracterização morfo-anatômica do fruto de P. echinatum; determinar parâmetros físico-químicos de qualidade da droga vegetal; isolar compostos químicos do metabolismo secundário, bem como investigar atividade antimicrobiana, antioxidante e anti-inflamatória, além de analisar parâmetros bioquímicos de toxicidade hepática e renal no extrato bruto das sementes de P. echinatum. Esta espécie possui ovário bicarpelar com presença de tricomas, emergências e cristais. Possui placentação parietal. O rudimento seminal é anátropo, unitegumentado e tenuinucelado. O anel nectarífero possui complexos estomáticos e tricomas. O epicarpo é cutinizado com presença de lenticelas, emergências e complexos estomatíferos. O mesocarpo externo possui células parenquimáticas, células pétreas, células esclerificadas e cristais. A semente é alada e exotestal. O endotélio e o endosperma constituem o envoltório membranáceo do embrião. O mesofilo cotiledonar possui compostos químicos como alcaloides, óleos fixos e voláteis, presença escassa de amido e é constituído de paredes pécticas. Na caracterização físico-química, por meio de testes farmacopeicos foi utilizado droga vegetal seca, constatando que não houve variação significativa das amostras coletadas em locais diferentes. O extrato hidroetanólico 70% (EB) das sementes de P. echinatum apresentou compostos do metabolismo secundário como esteróides e/ou triterpenos, flavonoides, alcaloides, antraquinonas, taninos catéquicos, oxidrila fenólica e heterosídeos cardiotônicos e óleos voláteis. Por doseamento espectroscópico foram determinados polifenóis, flavonoides e taninos no EB e frações. P. echinatum apresentou potencial antioxidante (CE50 131,84 μg/ml) na fração acetato pelo método do DPPH e atividade antimicrobiana à P. aeruginosa, P. zophii e C. albicans pelo método de microdiluição em caldo (CIM). A partir do EB das sementes de P. echinatum foi realizado o isolamento e a identificação de dois flavonoides diometina e hesperitina, agliconas flavona e flavanona, respectivamente. Estes flavonoides foram isolados de P. echinatum pela primeira vez. Os compostos foram determinados e analisados por CLAE/MS e RMN e seus espectros comparados com a literatura. A atividade anti-inflamatória do EB foi avaliada pelo método da indução da inflamação por cilindros de algodão, e realizadas dosagens séricas dos ratos submetidos ao bioensaio, nos quais foram administrados a três grupos de ratos, por via oral, 300mg/kg/dia do extrato bruto, 5mg/kg/dia de nimesulida e propilenoglicol 20% v/v, por 6 dias. Os resultados obtidos mostraram que o extrato bruto de P. echinatum apresentou inibição da inflamação significativa de 24,7%, semelhante à inibição obtida pelo grupo de animais tratados com nimesulida de 21,4%, em relação ao grupo controle. Os parâmetros hematológicos mostraram que houve aumento no número de leucócitos e diminuição no volume corpuscular médio (VCM), enquanto que AST, ALT e creatinina não apresentaram diferença significativa no uso do extrato de P. echinatum, quando comparados com o grupo controle propilenoglicol. Portanto, os parâmetros físico-químicos estabelecidos para P. echinatum possibilitam controle de qualidade da droga dessa espécie, e esta, apresentou atividades antimicrobiana, antioxidante e antiinflamatória. Além disso, não foram observados sinais de hepatotocidade e nefrotoxicidade nas condições experimentais testadas.
132

Land use practices and their impact on the water quality of the Upper Kuils River (Western Cape Province, South Africa)

Mwangi, François Ngera January 2014 (has links)
>Magister Scientiae - MSc / The water quality in many Cape Town Rivers and streams is a major challenge. Kuils River is subject to multiple land use impacts from upstream to downstream because of rapid urbanization in its catchment area. The main pollution sources are urban and industrial, organic matter from litter under the road-bridge, and golf course. However no systematic efforts have been made to evaluate and improve the health of the river in term of management. To assess impacts on water quality, this study was conducted from 4th September to 27th November 2012 in 5 selected sites in the upper reach of the Kuils river. The main aim was to compare the health of the river in 2012 with that found in 2005 using physical and chemical characteristics and the South Africa Scoring System (SASS). The statistical analysis showed a significant difference between and within sites. The water temperature, pH, dissolved oxygen concentration, total dissolved solids (TDS), and salinity were collected in situ by YSI 30 meter. To evaluate nutrient (nitrate and phosphorus) concentrations water samples were analyzed at UWC laboratory using spectrophotometer. In addition human activities, basic conditions (7.13 to 8.76), high total dissolved solids (416 to to 916.5 mg L¯¹) and salinity (0.31 to 0.71 mg L¯¹) concentrations were influenced by Malmesbury shales. Nitrate (0.1 to 3.1 mg L¯¹) and phosphorus (0.11 to 5.27 mg L¯¹) concentrations and the decrease in dissolved oxygen in November 2012 showed eutrophic conditions of the river. In the tributary site phosphorus (1.32 to 3.62 mg L¯¹) concentrations revealed hypertrophic condition compared to South Africa guideline. Macroinvertebrates sampled showed a total of 28 taxa grouped in 11 orders were sampled. Poor habitat diversity and water quality degradation were principal causes of low species diversity. The South Africa Score System version 5 (SASS5) and Average Score per Taxon (ASPT) indicated that the river is seriously impacted in 2012 compared to 2005 where water quality was in poor condition. The SASS and the ASPT scores were less than 50 and 4.2 at all sampling sites in most part of sampling period.
133

Développement de mélanges chargés en poudres d'aluminure de titane pour moulage par injection et applications aéronautiques / Development of mixtures of polymers loaded whith titanium aluminide alloys - Injection molding and aerospace

Tourneroche, Paul 22 March 2016 (has links)
La réduction de l’impact des activités humaines sur l’environnement est au sujet de nombreux programmes de recherche. Ainsi, dans le domaine du transport aérien a été créé le projet Clean-Sky, regroupant les thèmes de recherche associés. La thèse, partie de ce dernier, a pour objectif de réduire l’impact environnemental de la production de composants en alliages avancés à base de Titane. La production actuelle ayant une empreinte écologique non négligeable, un procédé de fabrication alternatif est étudié, il s’agit du moulage par injection de poudres métalliques. La première partie de cette consiste donc en la recherche d’une formulation de mélange optimale parmi les solutions classiques et innovantes. Elles sont triées en fonction de leurs aptitudes, déterminées par caractérisations physico-chimiques, à assurer le bon déroulement de chaque étape du procédé. Un nombre réduit de solution étant ainsi dégagé, il s’agit de passer aux étapes d’injection, de déliantage et de frittage. Plusieurs géométries de pièces sont testées dans chacun de ces cas, afin de valider l’adaptation aux différentes contraintes imposées. Lors de ces trois phases, des analyses physico-chimiques complètes permettent de mettre en avant la ou les formulations les plus aptes à permettre la production de ces composants. Une fois la solution fixée, chaque étape du procédé est optimisées, afin de faciliter le transfert industriel et d’assurer la rentabilité du nouveau processus de fabrication. Ces travaux de doctorat ont permis de mettre en avant deux formulations, répondant aux critères définis en début de thèse. Les étapes de mélange, injection, déliantage et frittage ont été optimisées et le transfert industriel est possible. / Reducing the ecological footprint of human activities is, today, the aim of most of the research programs. In Europe, the « Clean Sky » project funds research activities to make air transport « greener ». This PhD, being part of it, is about improving production of Titanium Aluminide based components. Nowadays production having a strong environmental impact, an alternative way has been investigated: metal injection molding. The first step of this work was focused on a bibliographic study, to select relevant, common and innovative mixtures to be used in the process. Throughout the process, these mixtures have been tested, physically and chemically analyzed, to get data about the optimal mixture. Several components geometries have been tested, during injection, debinding, and sintering steps. Once the mixture(s) chosen, process’ parameters have been optimized to make industrial transfer easier, and lower its overall cost. The developments achieved during this PhD led to two qualified mixtures, and optimized mixing, molding, debinding and sintering steps.
134

Caractérisation des transformations physico-chimiques intervenant lors de la thermodégradation du bois. Influence de l'intensité de traitement, de l'essence et de l'atmosphère / Characterization of physical and chemical changes occurring during wood thermal degradation. Influence of treatment intensity, wood species and inert atmosphere

Candelier, Kévin 06 December 2013 (has links)
Le traitement thermique est basé sur la modification chimique des biopolymères par thermodégradation, en évitant l'ajout de produits chimiques. Ce traitement améliore la stabilité dimensionnelle et la durabilité fongique du bois. Ces améliorations se font au détriment des propriétés mécaniques qui ont tendance à s'affaiblir. Aujourd'hui, plusieurs types de procédés sont utilisés. Ils se distinguent entre autre par la nature du milieu dans lequelle se déroule le traitement. La durabilité de ce nouveau matériau bois est liée au degré de thermodégradation, dépendant des conditions et de l'intensité du traitement. Un pilote de traitement par conduction, travaillant sous vide ou sous azote, mesurant la masse en dynamique est utilisé afin de mieux comprendre l'influence de l'atmosphère. Les résultats obtenus montrent que l'utilisation du vide permet d'éliminer, de l'enceinte de traitement, les produits volatils formées au cours du traitement conduisant à des taux de lignine de Klason plus faibles du fait de la non recondensation des produits de dégradation. Cette limitation de recondensation des produits volatiles engendre des pertes de masse, pour une même intensité de traitement plus faibles, confirmés par des taux de polysaccharides plus élevés pour un traitement sous vide. Des études de cinétiques des réactions de thermodégradation ont confirmé la plus grande sensibilité des feuillus vis-à-vis de la thermodégradation (comparé aux résineux). De plus, ces analyses ont permis d'identifier les principaux produits de thermodégradation du bois qui varient en fonction de l'intensité du traitement et a permis de montrer une thermosensibilité plus importante de la lignine que de l'holocelluloses pour la gamme de températures utilisée. Le fruit de ces travaux est donc une progression significative des connaissances de bases sur les mécanismes de thermodégradation et leurs relations avec les paramètres de traitement / Thermal treatment is based on biopolymer chemical degradation by heat transfer, without additional chemical products impregnation. This process improves the dimensional stability and the decay resistance of wood. These improvements come at the expense of wood mechanical properties of wood which weak. Several types of heating processes exist currently differing mainly by the nature of the inert atmosphere used during treatment. The durability of this new wood material is correlated to the degree of polymers thermal degradation depending on the conditions and the treatment intensity. A conducting heat treatment pilot using nitrogen or vacuum and allowing dynamic record of mass loss is used to understand better the atmosphere influence. The results show that utilization of vacuum permit the elimination of volatile products formed during heat treatment and accumulated in oven, leading to lower extractives and Klason lignin contents due to the non recondensation of thermal degradation products. Limitation of the formation of recondensation products generates a lower mass loss for same treatment intensity and explains the lower polysaccharides degradation during a vacuum process. Fine chemical analyses and the study about thermal degradation reaction kinetics have allowed confirming the higher sensibility of hardwood than softwood to thermal degradation. In addition, these analyses have permitted the volatile thermal degradation products identification related to the treatment intensity. Subsequently, results have shown a higher thermal sensibility of lignin than holocelluloses for temperatures below 230°C. This work is a significant increase in basic knowledge about the mechanisms of wood thermal degradation and their relations with the processing parameters
135

Qualidade do leite de vacas em torneios leiteiros / Milk quality in dairy cows tournaments / Qualidade do leite de vacas em torneios leiteiros

ROSA, Poliana P. S. G. 25 February 2015 (has links)
Submitted by biblioteca unifenas (biblioteca@unifenas.br) on 2016-09-28T13:54:49Z No. of bitstreams: 1 Poliana Silvia Garcia Rosa Dissertacao.pdf: 823674 bytes, checksum: 729179eaf82075941fd1280b8b99f1e2 (MD5) / Made available in DSpace on 2016-09-28T13:54:49Z (GMT). No. of bitstreams: 1 Poliana Silvia Garcia Rosa Dissertacao.pdf: 823674 bytes, checksum: 729179eaf82075941fd1280b8b99f1e2 (MD5) Previous issue date: 2015-02-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The objective of this research was to evaluate the physicochemical characteristics of the Dutch and crossbred cows milk originating from dairy tournaments, in the southern region of Minas Gerais, in the period from March to October 2012, using the nonparametric data for protein, fat, lactose, total solids, nonfat dry extract and somatic cell count variables. Normative Instruction 62 establishes maximum levels of somatic cell count of 500,000 cells / ml of milk, minimum fat content of 3.0%, total solids 11.4%, 2.9% protein, dry extract 8.4%. The somatic cell count reflects the health of the mammary gland of the animal. Of the 108 samples of milk collected from cows participants on the last day of the milk match, after complete milking and weighing of milk, 24% of the animals showed somatic cell counts that do not fit the parameters established by the Normative Instruction 62. The other parameters evaluated as lactose, fat, total solids and nonfat dry extract showed significant differences by comparing the milk with high somatic cell count, milk with low somatic cell count. The level of milk protein with high somatic cell count remained in the Normative Instruction 62 standard, because of the increase of plasma proteins in milk as a result of the inflammatory response. Most milk samples from dairy tournaments did not fit in Instruction 62, as the increase in somatic cells interfered in the chemical physical quality. / Objetivou-se nesta pesquisa avaliar as características físico-químicas do leite de vacas holandesas e mestiças oriundas de torneios leiteiros na região do Sul de Minas Gerais, no período de março a outubro de 2012, sendo utilizados os dados não paramétricos para as variáveis de proteína, gordura, lactose, sólidos totais, extrato seco desengordurado e contagem de células somáticas. A Instrução Normativa 62 estabelece níveis máximo de contagem de células somáticas de 500.000 células/mL de leite, teores mínimos de gordura de 3,0%, sólidos totais de 11,4%, proteína 2,9%, extrato seco desengordurado 8,4%. A contagem de células somáticas reflete na saúde da glândula mamária do animal. Das108 amostras de leite coletadas das vacas participantes no último dia do torneio leiteiro, após a ordenha completa e pesagem do leite, 24% dos animais apresentaram contagem de células somáticas que não se enquadram nos parâmetros estabelecidos pela Instrução Normativa 62. Os demais parâmetros avaliados como lactose, gordura, sólidos totais e extrato seco desengordurado não apresentaram diferenças significativas, comparando o leite com contagem de células somáticas altas, com leite com contagem de células somáticas baixas. O nível de proteína em leite com contagem de células somáticas altas se mantiveram no padrão da Instrução Normativa 62, pois houve um aumento das proteínas plasmáticas no leite em decorrência da resposta inflamatória. Conclui-se que a maioria das amostras de leite coletadas em torneios leiteiro não se enquadraram na Instrução Normativa 62.
136

Evaluation of physicochemical properties of a new epoxy resinbased root canal sealer / Avaliação das propriedades físico-químicas de um novo cimento obturador de canais radiculares à base de resina epóxica

Vertuan, Gislene Cristina 10 July 2018 (has links)
Introduction: The aim of this study was to evaluate some of the physico-chemical properties of a new root canal sealer. Methodology: The sealers tested were Sealer Plus (MKLife, Porto Alegre, Rio Grande do Sul, Brazil), compared as AH Plus (Dentsply, DeTrey GmbH, Konstanz, Alemanha). For the radiopacity, flow, solubility and fabrication of test specimens relative to setting times the ANSI/ADA No. 57 (2000) and ISO 6876 (2012) specifications were followed. To measure the initial and final setting times the ASTM C266/2008 standard was used. pH was evaluated in the time intervals of 3, 24, 72 and 168 hours). Statistical tests were applied to the results obtained at a level of significance of 5%. Results: The results demonstrated that the Sealer Plus sealer showed a lower radiopacity value than AH Plus sealer (p<0.05), however, this was higher than the minimum value recommended by the specifications; that is 3 mm Al. Relative to flow, the value for Sealer Plus was 19.19 mm and for AH Plus, 19.81 mm (p>0.05). Sealer plus presented initial and final setting times of 138 min. and 210 min., respectively, while the values for AH Plus were 437 min. and 849 min., respectively, (p<0.05). Relative to solubility, Sealer Plus presented 0.21% and AH Plus, 0.27% (p>0.05). None of the sealers showed a significant increase in pH (p>0.05). Conclusion: Sealer Plus sealer presented physico-chemical properties in accordance with ANSI/ADA (2000) No.57 and ISO 6876 (2012) specifications. / Introdução: Este estudo objetivou avaliar algumas propriedades físico-químicas de um novo cimento obturador de canais radiculares. Metodologia: Para os testes de radiopacidade, escoamento, solubilidade e confecção dos corpos de prova para os tempos de presa foram seguidas as especificações nº57 da ANSI/ADA (2000) e ISO 6876 (2012). Para a medição dos tempos de presa, inicial e final, foi empregada a norma ASTM C266/2008. O pH foi avaliado nos períodos de 3, 24, 72 e 168 horas. Sobre os resultados foram aplicados testes estatísticos com nível de significância de 5%. Resultados: Os resultados demonstraram que o cimento Sealer Plus apresentou menor radiopacidade do que o cimento AH Plus (p<0.05), porém, superior ao mínimo recomendado pelas especificações, ou seja, de 3 mm de Al. Com relação ao escoamento, o do Sealer Plus foi 19,19 mm e do AH Plus 19,81 mm (p>0.05). O Sealer Plus apresentou tempos de presa inicial e final de 138 min. e 210 min., respectivamente, enquanto o AH Plus, 437 min. e 849 min., respectivamente, (p<0.05). Em relação à solubilidade, o Sealer Plus apresentou 0,21% e o AH Plus 0,27% (p>0.05). Nenhum dos cimentos apresentou aumento significativo do pH (p>0.05). Conclusão: O cimento Sealer Plus apresentou propriedades físico-químicas de acordo com as especificações nº 57 da ANSI/ADA (2000) e ISO 6876 (2012).
137

Potencial antimicrobiano e biocompatibilidade de óleos essenciais em associação a biomateriais à base de silicato tricálcico /

Castro Núñez, Gabriela Mariana. January 2020 (has links)
Orientador: Juliane Maria Guerreiro Tanomaru / Resumo: Os cimentos reparadores endodônticos à base de silicato de cálcio apresentam biocompatibilidade e bioatividade. Porém, sua ação antimicrobiana é limitada. O acréscimo de óleos essencias pode favorecer as propriedades antimicrobianas de materiais. Os óleos essenciais são substâncias de origem vegetal com propriedades antimicrobiana, antiviral, antifúngica, antitoxigênica, antiparasitária e inseticida. Este estudo teve como objetivo avaliar a associação de diferentes óleos essenciais nas propriedades físico-químicas, citocompatibilida, potencial bioativo e atividade antibiofilme dos cimentos reparadores à base de silicato de cálcio, MTA Repair HP (MTA HP) e Biodentine (BIO). Publicação 1: avaliou a associação de 1,5% de Farnesol (FAR). Publicação 2: analisou o acréscimo de 1% de Thyme Essential Oil (TEO). Publicação 3: associou 1% de lemongrass oil (LEO). As propriedades físico-químicas de tempo de presa, solubilidade após 7 dias de imersão em água destilada e pH em 1, 3, 7, 14 e 21 dias foram avaliadas. A citocompatibilidade foi avaliada por meio dos testes de methyltetrazolium (MTT) e Vermelho Neutro (VN) após exposição das células Saos-2 às diferentes diluições dos eluídos dos materiais por 24h. A bioatividade foi avaliada pela atividade enzimática da fosfatase alcalina (ALP) nos períodos de 1, 3 e 7 dias. Nódulos de mineralização foram também quantificados após 21 dias pela coloração com vermelho de Alizarina (ARS). A capacidade de inibição de Metaloproteinase de Matriz (MM... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor
138

[en] INFLUENCE OF THE INCORPORATION OF IRON ORE TAILINGS ON THE CHEMICAL, PHYSICAL AND MECHANICAL PROPERTIES OF CONCRETE / [pt] INFLUÊNCIA DA INCORPORAÇÃO DO REJEITO DE MINÉRIO DE FERRO NAS PROPRIEDADES QUÍMICAS, FÍSICAS E MECÂNICAS DO CONCRETO

FERNANDO NOBREGA MENDES PROTASIO 25 January 2021 (has links)
[pt] O presente trabalho tem como objetivo investigar a influência da substituição de frações de areia por rejeito de minério de ferro (RMF) no concreto. Estudaram-se a reatividade do rejeito com o cimento, as variações de porosidade, a trabalhabilidade e o efeito filler do material. Para isso uma série de ensaios químicos, físicos, mecânicos e térmicos foram conduzidos. O RMF foi caracterizado quanto à composição química, granulometria e massa específica. Constatou-se que o material é formado por sílica e hematita e possui massa específica muito próxima à da areia, embora seja uma ordem de grandeza mais fino. Para avaliar a reatividade do RMF confrontou-se os resultados de diversos experimentos. Foram realizados ensaios de compressão axial em pastas de cimento com substituição de 10 por cento, 20 por cento e 30 por cento de cimento por RMF, em diferentes idades. O RMF foi ensaiado quimicamente pelo método Chapelle modificado e o índice de atividade pozolânica foi determinado. Além disso, fragmentos de concreto com RMF, aos 28 e 90 dias, foram ensaiados por termogravimetria e os produtos de hidratação comparados à amostra de referência. O grau de cristalinidade do RMF foi determinado por difração de raios-X. Todas as evidências indicam que o material é inerte. O efeito do RMF na trabalhabilidade do concreto e da pasta de cimento foi avaliado por ensaio de abatimento (slump test) e espalhamento (flow table), respectivamente, e detectou-se um aumento da trabalhabilidade com o aumento da fração de RMF. A porosidade foi avaliada por ensaio de imersão em água no concreto com diferentes frações de RMF, e por ensaio de microtomografia computadorizada, na qual foi determinada a distribuição dos poros. De modo geral, detectou-se tendência de redução da porosidade com o acréscimo do RMF. A resistência mecânica do concreto foi avaliada para substituições de 10 por cento, 20 por cento e 30 por cento de areia por RMF e os resultados foram comparados à substituição das mesmas frações de areia por material inerte, na granulometria do RMF. O efeito filler causou um aumento da resistência, tendo o melhor resultado sido obtido com a fração de 20 por cento de RMF. Também foi avaliado o comportamento à flexão em prismas de concreto com adição de fibras de aço na fração de 30 kg/m cúbicos e 20 por cento de substituição de areia por RMF. Os resultados de cargas máximas, tensões residuais e tenacidade foram, em média, muito próximos nas amostras com RMF e de referência. / [en] The present work aims to investigate the influence of the replacement of sand fractions by iron ore tailings (IOT) on concrete. The reactivity of tailings in the presence of cement, the variation of porosity and workability, and the filler effect of the material were studied. For this purpose, a series of chemical, physical, mechanical and thermal tests were conducted. The IOT was characterized by its chemical composition, particle size and specific weight. It is found that the material is formed by silica and hematite and has a specific weight similar to that of sand, although its grains are ten times smaller. To evaluate the reactivity of the IOT, the results of several experiments were compared. Axial compression tests were performed on cement pastes with replacement of 10 percent, 20 percent and 30 percent cement by IOT at different ages. The IOT was chemically tested by the modified Chapelle test and the pozzolanic activity index was determined. In addition, IOT concrete fragments at 28 and 90 days were tested by thermogravimetry and the hydration products were compared to the reference sample. The degree of crystallinity of the IOT was determined by X-ray diffraction. All evidence indicates that the material is inert. The effect of IOT on the workability of concrete and cement paste was tested by slump test and flow table, respectively, and an increase in workability was detected by increasing the IOT fraction. Porosity was evaluated by the water immersion test on concretes with different IOT fractions, and by computed tomography, which determined the pore distribution. In general, a tendency to reduce porosity was observed as IOT fraction increased. The mechanical strength of the concrete was evaluated for 10 percent, 20 percent and 30 percent sand replacements by IOT and the results were compared to the replacement of the same sand fractions by inert material, in the IOT granulometry. The filler effect caused an increase in resistance, with the best result being the 20 percent IOT fraction. It was also evaluated the flexural behavior in prismatic concrete specimens with addition of steel fibers in the fraction of 30 kg/m cubic and 20 percent of sand substitution by IOT. The results of maximum loads, residual stresses and toughness were on average very similar in the IOT and reference samples.
139

Lanthanum-Doped Hafnium Oxide: A Robust Ferroelectric Material

Schroeder, Uwe, Richter, Claudia, Park, Min Hyuk, Schenk, Tony, Pesič, Milan, Hoffmann, Michael, Fengler, Franz P. G., Pohl, Darius, Rellinghaus, Bernd, Zhou, Chuanzhen, Chung, Ching-Chang, Jones, Jacob L., Mikolajick, Thomas 04 October 2022 (has links)
Recently simulation groups have reported the lanthanide series elements as the dopants that have the strongest effect on the stabilization of the ferroelectric non-centrosymmetric orthorhombic phase in hafnium oxide. This finding confirms experimental results for lanthanum and gadolinium showing the highest remanent polarization values of all hafnia-based ferroelectric films until now. However, no comprehensive overview that links structural properties to the electrical performance of the films in detail is available for lanthanide-doped hafnia. La:HfO₂ appears to be a material with a broad window of process parameters, and accordingly, by optimization of the La content in the layer, it is possible to improve the performance of the material significantly. Variations of the La concentration leads to changes in the crystallographic structure in the bulk of the films and at the interfaces to the electrode materials, which impacts the spontaneous polarization, internal bias fields, and with this the field cycling behavior of the capacitor structure. Characterization results are compared to other dopants like Si, Al, and Gd to validate the advantages of the material in applications such as semiconductor memory devices.
140

Luminescent sp²-Carbon-Linked 2D Conjugated Polymers with High Photostability

Xu, Shunqi, Li, Yungui, Biswal, Bishnu P., Addicoat, Matthew A., Paasch, Silvia, Imbrasas, Paulius, Park, SangWook, Shi, Huanhuan, Brunner, Eike, Richter, Marcus, Lenk, Simone, Reineke, Sebastian, Feng, Xinliang 28 September 2021 (has links)
Luminescent organic materials with high photostability are essential in optoelectronics, sensor, and photocatalysis applications. However, small organic molecules are generally sensitive to UV irradiation, giving rise to chemical decompositions. In this work, we demonstrate two novel CN-substituted two-dimensional sp²-carbon-linked conjugated polymers (2D CCPs) containing a chromophore triphenylene unit. The Knoevenagel polymerization between 2,3,6,7,10,11-hexakis(4-formylphenyl)triphenylene (HFPTP) and 1,4-phenylenediacetonitrile (PDAN) or 2,2’-(biphenyl-4,4’-diyl)diacetonitrile (BDAN), provides the crystalline 2D CCP-HFPTP-PDAN (2D CCP-1) and 2D CCP-HFPTP-BDAN (2D CCP-2) with dual pore structures, respectively. 2D CCP-1 and 2D CCP-2 exhibit the photoluminescence quantum yield (PLQY) up to 24.9% and 32.3%, which are the highest values among the reported 2D conjugated polymers and π-conjugated 2D covalent organic frameworks. Furthermore, compared with the well-known emissive small molecule tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), both 2D CCPs show superior photostability under UV irradiation for two hours, profiting from the twisted and rigid structures of the CN-substituted vinylene linkages. The present work will trigger the further explorations of novel organic emitters embedded in 2D CCPs with high PLQY and photostability, which can be useful for optoelectronic devices.

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