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Lasaridi, Konstadia Ekaterini. "Compost stability : a comparative evaluation of respirometric techniques." Thesis, University of Leeds, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368055.
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Skubała, Anna. "Evolution of compost stability tu real time : PhD thesis summary." Rozprawa doktorska, [s.n.], 2018. http://dlibra.tu.koszalin.pl/Content/1093.
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Oliveira, Raquel Varagilal de. "Testes de maturação aplicados a matrizes bioestabilizadas." Master's thesis, ISA, 2010. http://hdl.handle.net/10400.5/3363.
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Mestrado em Engenharia do Ambiente - Instituto Superior de AgronomiaThe Municipal Solid Waste Organic Fraction (MSWOF) and sludge from wastewater treatment plants have, among the agricultural waste with interest, the greatest concern because of their potential on organic and inorganic contaminants and also due the large quantities produced. However, products obtained after their treatment can have agricultural interest since they fulfill the quality standards. Two nitrogen sources (sodium caseinate and soy beans) and a carbon source (starch, cellulose or sucrose) were added to composts from different sources. Mixtures were maintained in Dewar flasks during 10 days. Stability was evaluated using the following parameters: maximum temperature reached, respiratory activity (AT4) and Solvita®. The fastest increase of temperature was observed for composts with starch addition, which indicates higher microbial activity, so the application of stabilized composts to soils during the incorporation of biodegradable materials (with starch) can promote their biodegradability. Dewar test was more sensitive for the stability assessment. Results of Solvita® test at 24 hours were similar to Dewar test results. AT4 test gave different stability levels for composts with addition of carbon sources, but similar for the initial composts.
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Pinapati, Kishore. "VARIATION OF GEOTECHNICAL STRENGTH PROPERTIES WITH AGE OF LANDFILLS ACCEPTING BIOSOLIDS." Master's thesis, University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3992.
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The solid portion of waste disposal, known as Municipal Solid Waste (MSW) can be landfilled. Landfilling has proved to be a safe, sanitary and economical method of disposal. A by-product from wastewater treatment plants called biosolids is sometimes co-disposed along with MSW in landfills. Recent work at the University of Central Florida has focused on the behavior of the mixture of MSW and biosolids. As an increased amount of waste accumulates in these landfills, it creates a new problem – the geotechnical stability of landfills. In current literature, classical geotechnical testing methods have been followed to find the strength properties of these landfill materials. Furthermore, geotechnical methods of slope stability analyses have been employed to determine the stability of landfill slopes. As these materials have a high organic content, their strength properties may potentially change with time because of the decay of the organic materials. In the present work, an attempt is made to monitor the change in the geotechnical strength properties of the landfill materials as a function of time. Direct shear tests used for soil testing, with some modifications, were performed on cured compost samples of MSW mixed with biosolids. Geotechnical strength properties of these cured samples were compared to those of an artificially prepared mixture of MSW and biosolids, from the published literature. In addition, direct shear tests are also performed to find the interface properties of a geonet with the cured samples to check the role of a geonet in reinforcing the landfill slopes. A slope stability analysis software SLOPE/W is used to analyze the stability of the landfills. Cohesion is observed to decrease with time while the friction angle increases with time. Stability (the factor of safety against failure) of landfill slopes increases with time due to increased effective stresses and increased friction angle, as the organic material decays. This may result in additional subsidence but an increase in the effective shear strength with time. Based on the interface test results and subsequent slope stability analyses, it is found that the inclusion of a geonet improves the slope stability of a landfill. This could be a potential benefit to the landfill as reinforcement if properly placed. Based on the slope stability analysis on landfills with different slopes, it is concluded that the slope stability of a landfill is improved by keeping the slopes less steep.M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering
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Raut, Desai Aditya Babu. "Use of compost filter bermsfor sediment trapping: primary focus on water quality and structural stability." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/1299.
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Runoff from road construction and maintenance sites is responsible for erosion and deposition of sediments in the receiving water bodies. In addition to soil particles from erosion, runoff also transports other pollutants such as rubber, toxic metals, automobile fluids, car exhausts (which settle with the rain), pesticides, fertilizers, and other debris. Compost has been used effectively as a valuable soil amendment to aid plant growth. Berms (mounds) of compost placed at the top or bottom of steep slopes can be used to slow the velocity of water and provide additional protection for receiving waters. However, a downside of the application of composted organic material is the potential degradation of runoff water quality. Overloading with nitrogen and phosphorus causes eutrophication, which reduces the suitability of waterways for beneficial uses. A field testing of the berms coupled with a laboratory analysis of the testing water will provide a basis for the impact of the compost berms on the runoff water quality. The study of the impact of compost on the runoff water quality was investigated. The objective of this study was to evaluate the performance of berms made from various materials such as dairy manure compost, yard waste compost and composted bio-solids mixed with wood chips in a ratio of 50:50 on the runoff water quality, as well as, the sediment removal efficiencies. Field tests were performed on the berms to simulate conventional rainfall runoff and the tested water was collected as time-weighted samples and analyzed in the laboratory. Several variables were investigated during this study. Results of this investigation demonstrated that the effectiveness of this application was hampered by the structural instability of the berm. A 100% failure rate was observed in the berms tested. Optimum performance was observed in yard waste compost berms, which introduced the least amount of contaminants into the water. However, some masking effect could be present due to berm failures. In fact, the actual sediment removal by the berms could not be determined. The study of compost filter berms showed some evidence of the existence of first flush effect.
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Faverial, Julie. "Compostage et vermicompostage des effluents d'elevage : une alternative durable pour le recyclage des dechets d'origine animale." Thesis, Antilles, 2016. http://www.theses.fr/2016ANTI0047/document.
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En Guadeloupe, l'utilisation de composts se heurte à de nombreux freins, aussi bien en termes de leur qualité qu’en termes d’un manque de plateformes de compostage à grande échelle et de proximité. Des études récentes ont montré que la qualité des composts locaux était plus faible qu’en milieu tempéré, ce qui constituerait un verrou majeur à l’adoption de la pratique et l’utilisation des composts industriels locaux. Pourtant, les objectifs de valorisation des déchets organiques fixés par les instances publiques sont ambitieux et le gisement local, bien que diffus et actuellement mal géré ou négligé, présenterait un réel intérêt pour la profession agricole à être orienté vers la valorisation biologique telle que le compostage. Dans ce contexte, l’objectif de ce travail était d'évaluer la qualité des composts élaborés en milieu tropical et d'apporter des éléments factuels pour son amélioration et, plus spécifiquement, d’apporter de l’information sur les potentialités agronomiques du compostage des effluents d’élevage en Guadeloupe, présentant ainsi le compostage comme une alternative durable pour le recyclage des déchets d’origine animale.Une méta-analyse de 442 composts d'origine diverse, la première réalisée sur le sujet, nous a permis de démontrer que les composts produits en milieu tropical présentent des teneurs en carbone, azote, potassium et fraction soluble de la matière organique plus faibles que celles des composts produits en milieu tempéré, et que cela pourrait notamment être dû à l’influence des conditions climatiques lors du compostage. En revanche, nous avons pu mettre en évidence que certaines matières premières permettaient l’obtention de composts de meilleure qualité quelque soit le climat considéré, il s’agissait entre autres des effluents d’élevage.Les résultats issus d'une série d’expérimentations menée sur la production de composts d’effluents d’élevage avec co-compostage et vermicompostage ont été traités avec une approche méthodologique innovante dans ce domaine, les Réseaux Bayésiens. L’évaluation réalisée sur le co-compostage effluents/déchets verts nous a permis d’identifier l’"effet de concentration" du carbone et de la lignine, comme celui qui définit la qualité des composts en termes de quantité et de stabilité de la matière organique. En revanche, dans le cas des nutriments, seule la qualité des matières premières a été identifiée comme le facteur déterminant de la qualité des produits finaux. Ces résultats nous ont amené à considérer les effluents d’élevage de bovin comme la matière première la plus efficace pour produire des co-composts de qualité satisfaisante, répondant à la problématique d’usure de la matière organique des sols guadeloupéens et permettant de satisfaire les attentes de la profession agricole.De plus des expérimentations réalisées sur les composts domestiques ont montré que la gamme analysée présentait une variabilité trop importante pour être considérée comme acceptable par la profession agricole. Le compostage domestique peut permettre de produire des composts de bonne qualité agronomique à utiliser à la petite échelle des jardins particuliers et des jardins créolesIn Guadeloupe, the practice of composting faces many obstacles and preconceptions both in terms of quality and in terms of lack of large-scale composting plants as well as local composting facilities. Recent studies have shown that the quality of local composts was lower compared to those from temperate regions. This constitutes an important constraint for the adoption of the former by farmers. However, organic waste recovery targets set by the government are ambitious and local resources, although diffused and currently poorly managed or neglected would be of real interest for the farming profession by being directed towards organic recycling such as composting. In this context, the aim of this thesis was to evaluate the quality of compost produced in the tropics, provide factual elements for improvement and, more specifically, to provide information on the agronomic potential of composting livestock manure in Guadeloupe, presenting composting as a sustainable alternative for the recycling of animal waste.A meta-analysis of 442 composts from various sources, the first one to be conducted on the subject enabled us to demonstrate that composts produced in the tropics present lower contents of carbon, nitrogen, potassium and soluble fraction of organic matter than those produced in temperate environments. This could especially be due to the influence of climatic conditions during composting. However, we were able to show that some raw materials allow better quality composts whatever the considered climate, especially the case of livestock manure.A series of experiments conducted on the production of livestock manure composts with co-composting and vermicomposting were treated with an innovative methodological approach in this field, the Bayesian Networks. The evaluation carried out on co-composting has allowed us to identify that the "concentration effect" was the main factor affecting compost quality in terms of amount and stability of organic matter. While in the case of nutrients, only the quality of raw materials has been identified as the determining factor affecting the quality of the end products. These results led us to consider manure, mainly cattle manure, as the most efficient feedstock for producing satisfactory quality composts, meeting the needs of loss of soil organic matter in Guadeloupe and the needs of the farming profession.Further experiments performed on household composts showed that their quality exhibited a too important variability to be considered acceptable by farmers. Our results indicate that household composts could be suitable for use in small-scale private gardens and Creole gardens
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Sequeira, Liliana Lopes. "Compostagem de resíduos sólidos urbanos e avaliação da qualidade dos produtos obtidos - caso de estudo Amarsul S.A." Master's thesis, ISA, 2013. http://hdl.handle.net/10400.5/6130.
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Mestrado em Engenharia do Ambiente - Tecnologias Ambientais - Instituto Superior de AgronomiaThe composting has proven a good alternative in the management, treatment and valorization of municipal solid waste. Depending on the raw materials used for its production, the product may be considered organic fertilizer/corrective to be used in agriculture activities. The present work was developed aiming the evaluation of the MSW composting evolution, by the determination of physical, physical-chemical and biological parameters, in biomass collected along the process, as well as the assessment of stability/maturation degree of the final compost. For each collected sample it was also introduced two different types of biodegradable/compostable plastics, each sample corresponding to a particular phase of stability/curing of composting process in order to evaluate the influence of these plastics in the samples that was obtained and the possible occurrence of biodegradation of plastics in the several phases analyzed. The results showed that the parameters fulfilled the existing literature, allowing the compound the designation of matured/stabilized. The biological characterization of the final compost showed that it presents phytotoxicity, which fact is related to the presence of ammoniacal nitrogen and high electrical conductivity. The introduction of biodegradable plastics in the process didn’t affect any parameter analyzed, showing increasing degree of biodegradability over the course of analysis.
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Ben, Sassi Meriem. "Impacts d’apports de composts de déchets urbains sur la résistance et la résilience de la microflore du sol à des évènements de type canicule/sécheresse." Thesis, Avignon, 2012. http://www.theses.fr/2012AVIG0639/document.
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Face aux changements climatiques actuels et à l'augmentation des populations, la vulnérabilité du sol et des services écosystémiques qu’il rend s’accroît. En particulier dans les zones climatiques méditerranéennes, les modèles météorologiques prévoient une augmentation des sécheresses estivales et une augmentation des températures accompagnées par l’apparition plus fréquente d’évènements extrêmes de type canicule et sécheresse. Ces événements, leur intensité, leur durée et la soudaineté avec laquelle ils arrivent, sont de nature à affecter la structure et la fonction des écosystèmes avec des conséquences principalement négatives sur leur biodiversité et leurs fonctions et services. Par ailleurs, l’apport de compost au sol pourrait constituer une solution pour prévenir et atténuer les effets des sécheresses et des canicules dans les agrosystèmes méditerranéens. Les objectifs de ce travail étaient de caractériser les effets à court et à long-terme de perturbations de type canicule et/ou sécheresse appliquées à un sol méditerranéen agricole (structures et fonctions des communautés microbiennes édaphiques) et d’étudier les impacts d’épandage préalable de composts sur la réponse à court et à long-terme de ces communautés microbiennes (structures et fonctions) vis-à-vis d’un événement extrême de canicule-sécheresse. Nos travaux nous ont permis d’évaluer l’influence de chacun des facteurs température élevée et sécheresse dans la perturbation canicule et sécheresse associées sur les paramètres microbiologiques et physico-chimiques du sol. Les effets de cette combinaison des deux perturbations a induit des réponses similaires à l’une ou l’autre des perturbations appliquées individuellement en bénéficiant des effets positifs et négatifs sur la communauté microbienne de chaque type de perturbation. Nous avons mis en évidence une durée seuil de la perturbation canicule-sécheresse sur la résistance de la communauté microbienne induisant un changement de structure taxonomique et fonctionnelle. Cette déstructuration de la communauté microbienne est durable et n’a pas permis de résilience. L’ajout préalable de composts de différents types au champ a amélioré la structure physico-chimique et stimulé les microorganismes indigènes du sol. Cependant, face à des perturbations de type canicule-sécheresse (telles que nous les avons testées), il semble que l’apport préalable de compost n’ait pas d’effets majeurs sur l’amélioration de la qualité du sol en terme de stabilité microbienne, mais que l’historique saisonnier influencerait cette stabilitéCurrent climate change and increasing populations’ growth enhance soil and ecosystem services vulnerability. Meteorological models predicted an increase in summer drought and higher air temperature with more frequent occurrence of extreme events like heat-waves and drought. Intensity and duration of these events may affect structure and functions of ecosystems and thereby the biodiversity and the functions of soil. The amendment of soils with composts could be an alternative to prevent and mitigate the effects of drought and heat waves in the Mediterranean agroecosystems. The objectives of this work were to characterize the effects of short and long-term high temperature and/or drought perturbation on soil Mediterranean microbial communities (structures and functions) and to study the impacts of compost amendment on short and long-term functional and taxonomic responses of microbial communities subjected to drought and high temperature. Our work allowed us to evaluate the influence of each factor (drought or high temperature) within the combined perturbation (drought and high temperature) on microbiological and physico-chemical soil properties. The effects of this combined perturbation induced similar or different responses of each of perturbations applied individually involving positive and negative effects on the microbial community. This work had shown threshold resistance duration inducing a change in taxonomic and functional microbial community structure after high temperature and drought perturbation. This abrupt shift in the community response did not allow resilience. Compost amendments improved the physico-chemical soil structure and stimulated indigenous soil microorganisms. However, it seemed that seasonal soil variations history rather than compost amendment influences soil microbial stability
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Oliveira, Dayane Carvalho Ramos Salles de 1987. "Color stability of direct esthetic restorations = Estabilidade da cor de restaurações estéticas diretas." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/290398.
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Orientador: Luis Alexandre Maffei Sartini PaulilloTexto em português e inglês
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
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Resumo: O objetivo deste estudo foi avaliar através de espectrometria FT-IR e espectrofotometria de refletância, a estabilidade da cor de restaurações estéticas em resinas compostas após envelhecimento artificial acelerado (EAA). Para tanto, foram utilizados os sistemas adesivos: convencional de 3 passos - Adper ScotchBond Multi-Purpose (3M/ESPE), convencional de 2 passos - Tetric N Bond (Ivoclar Vivadent), autocondicionante de 2 passos - ClearFill SE Bond (Kuraray) e resinas compostas na cor EA1: nanoparticulada Filtek Z350 XT Supreme (3M/ESPE) e microhíbrida IPS Empress Direct (Ivoclar Vivadent). Espécimes simulando restaurações diretas (n=10) foram confeccionadas, com auxilio de matriz padronizada (4x4x1 mm) sobre substrato dentinário. Restaurações sem sistema adesivo foram utilizadas como controle. As avaliações de cor foram mensuradas com espectrofotômetro (EasyShade Advanced, Vita Zahnfabrik) em duas regiões distintas da restauração: na superfície da resina composta e na interface adesiva, em dois períodos de tempo: 48 h após acabamento e polimento da restauração e após 300 h de EAA com ciclos de 50oC alternados de 4 h de condensação e 4 h de exposição com luz UV. Os espécimes foram aferidos sob fonte de luz padronizada com irradiância espectral relativa D65 (Gti MiniMatcher, Gti Graphic Technology Inc.). Os dados do sistema CIE L*a*b* foram utilizados para o cálculo do ?E, ?L, ?a e ?b pela diferença de cada coordenada final pela inicial. Para análise do grau de conversão (GC) das resinas compostas utilizadas, espécimes com 4 mm de diâmetro (n=10) foram confeccionados e após 48 h analisados em espectrômetro FT-IR Spectrum 100 (Perkin Elmer). Os resultados obtidos foram analisados pela análise de variância a dois fatores e teste de Tukey (?=0,05). Os sistemas adesivos não interferiram na alteração de cor (?E) do corpo da restauração (?=0,90) ou da interface de união (?=0,78). Por outro lado, o fator resina composta foi significativo para a estabilidade de cor (?E) e para os valores das coordenadas isoladas (?<0,001). Em relação ao GC, a resina IPS Empress Direct apresentou resultados superiores (67%) frente a Z350XT (61%) com diferença estatisticamente significante (?<0,001). Desta forma, concluiu-se que o sistema adesivo não foi capaz de alterar a cor final de restaurações estéticas diretas. Entretanto, em relação para o fator resina composta foi encontrada diferença quanto à estabilidade da cor pelo EEA e ao GC, no qual a IPS Empress Direct apresentou resultados superiores
Abstract: The aim of this study was tm po evaluate the color stability and degree of conversion of esthetic composite resin restorations after accelerated artificial aging (AAA) by FT-IR and reflectance spectrometry. Thus, two etch and rinse adhesive systems - Adper ScotchBond Multi-Purpose (3M/ESPE) and Tetric N Bond (Ivoclar Vivadent) and one two-step self-etching bond system - ClearFill SE Bond (Kuraray) were used with two EA1 shade composite resins: Filtek Z350 XT nanofilled (3M/ESPE) and IPS Empress Direct microhybrid (Ivoclar Vivadent). The restored specimens (n=10) were made with standardized dimensions using a silicon mold under dentin substrate (4x4x1mm). The color were measured with a spectrophotometer (EasyShade Advanced, Vita Zahnfabrik) on composite resin surface and bond interface: 48 hours after finishing and polishing procedures; after 300 hours of AAA with 50oC cycles with 4 hours of condensation and 4 hours of UV exposure. Specimens were measured in a color-assessment cabinet (Gti MiniMatcher, Gti Graphic Technology Inc.) with a light source simulating the spectral relative irradiance of CIE standard illuminant D65. The CIE L*a*b* data were used to calculate the ?E, ?L, ?a and ?b by the difference between each final and initial coordinate. The degree of conversion (DC) of the composite resins used was measured using 4x4x1 mm samples (n=10). The DC analysis was performed using a FT-IR spectrometer Spectrum 100 (Perkin Elmer) after 48 hours. Data were submitted to two-way ANOVA and Tukey test (?=0.05). As the results, the adhesive systems had no significant influence on the color stability (?E) of the restoration surface (?=0.90) or the bonding interface (?=0.78). Moreover, the composite resin factor was significant and influenced the color as measured by ?E and isolated coordinates (?<0.001). As for the DC, IPS Empress Direct resin showed better results (67%) compared to Z350XT (61%) with statistically significant differences (?<0.001). Therefore, the adhesive system could not affect the final color of direct esthetic restorations. On the other hand, IPS Empress Direct showed better results of DC and color stability after EEA
Mestrado
Dentística
Mestra em Clínica Odontológica
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Pigalle, Florence. "Etude de la stabilité du cisplatine en solution aqueuse : proposition et évaluation de protocoles de conservation." Paris 5, 1991. http://www.theses.fr/1991PA05P029.
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Benigni, Alexis. "Projet CLEAR : Horloge composite numérique polyvalente : Asservissement en fréquence multisources." Thesis, Bourgogne Franche-Comté, 2018. http://www.theses.fr/2018UBFCD044/document.
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L'objectif de la thèse est de concevoir et développer un système numérique de combinaison de signaux d'horloges hétérogènes (PPS, horloges atomiques, quartz, ...). Le signal résultant possède une meilleure stabilité que chacune des entrée quelque soit la durée d'intégration et il peut détecter des défaillances chez une des entréesThe goal of the PhD is to design and build a numerical system capable of combining clock signals from various sources (PPS, atomic clocks, quartz, ...). The output signal will have a better stability at each integration time than any single input signal and it could detect failures in input sources
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Alsunbul, Hanan. "Fundamental aspects of dental resin-composite stability." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/fundamental-aspects-of-dental-resincomposite-stability(e4b0a8d2-f474-442a-ad74-e58ddc31dc70).html.
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Dental resin-composite is a material made of inorganic filler phase and organic matrix phase with a coupling agent that bonds the filler to the matrix. These materials became popular in dentistry for their improved aesthetic and clinical performance. The indications of these materials had expanded to involve restoration of anterior and posterior teeth including the more extensive restorations. The introduction of Bulk fill materials made their clinical applications less time consuming especially with their claimed improved clinical performance such as less shrinking ability, less water sorption and more stability in the oral environment. In this research we aimed to study the general stability of a wide group of resin-composite materials with regard of their polymerisation shrinkage, the effect of solvents storage on their mass and volume, their sorption and solubility and the effect of the solvents storage on the diametral strength and surface hardness of these materials. Bonded disk method was used to assess the polymerisation shrinkage strain and its rate was then obtained using a numerical differentiation method. For the polymerisation stress, Bio-man instrument was used. Modulus of elasticity was then calculated from the measured stress and strain at 60 min. The results demonstrated different shrinkage behaviour that is strongly related to the different monomer systems of the materials. The nature of the monomer system determines the amount of the bulk contraction that occurs during polymerization and the resultant stress. Higher values of shrinkage strain and stress were demonstrated by the investigated flowable materials. The bulk fill materials showed comparable result when compared to traditional resin-composites. The effect of three different solvents was investigated in which the materials were stored for a total storage time of 180d. Generally the materials were most greatly affected by MEK storage compared to the other two solvents. However, the glass-fibre-reinforced material (EVX) was mostly affected by water immersion. The pattern of change/recovery behaviour of the materials, during solvent challenge, was similar to the pattern of viscoelastic creep/recovery behaviour of resin-composite materials. The surface micro-hardness of the material and the diametral strength were studied after a period of solvents storage. The storage time and the type of solvent have a significant influence on these properties. In general, MEK showed more drastic reduction in the material micro-hardness with an exception of G-aenial universal flo (GA-F) which showed similar results in water/ethanol and MEK. The bulk-fill materials showed no superior results compared with the other materials. The significant decrease in the surface micro-hardness of the investigated materials makes their long-term stability open to question. For the bulk-fill materials that are designed to be used as a base, their penetration by the solvents may be shielded.
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Flanagan, Ronan. "The dimensional stability of composite laminates and structures." Thesis, Queen's University Belfast, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263396.
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Chandiramani, Naresh K. "Dynamic stability of shear deformable viscoelastic composite plates." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/70917.
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Linear viscoelasticity theory is used to analyze the dynamic stability of composite, viscoelastic flat plates subjected to in-plane, biaxial edge loads. In deriving the associated governing equations, a hereditary constitutive law is assumed. In addition, having in view that composite-type structures exhibit weak rigidity in transverse shear, the associated governing equations account for the transverse shear deformations, as well as the transverse normal stress effect. The integro-differential equations governing the stability are solved for simply-supported boundary conditions by using the Laplace transform technique, thus yielding the characteristic equation of the system.
In order to predict the effective time-dependent properties of the orthotropic plate, an elastic behavior is assumed for tile fiber, whereas the matrix is considered as linearly viscoelastic.
In order to evaluate the nine independent properties of the orthotropic viscoelastic material in terms of its isotropic constituents, the micromechanical relations developed by Aboudi [24] are considered in conjunction with the correspondence principle for linear viscoelasticity. The stability behavior analyzed here concerns the determination of the critical in-plane normal edge loads yielding asymptotic stability of the plate. The problem is studied as an eigenvalue problem.
The general dynamic stability solutions are compared with their quasi-static counterparts. Comparisons of the various solutions obtained in the framework of the Third Order Transverse Shear Deformation Theory (TTSD) are made with its first order counterpart. Several special cases are considered and pertinent numerical results are compared with the very few ones available in the field literature.Master of Science
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Tawfik, Samer Anwar. "Stability and morphing characteristics of bistable composite laminates." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24702.
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Thesis (Ph.D.)--Aerospace Engineering, Georgia Institute of Technology, 2009.Committee Chair: Erian Armanios; Committee Member: D. Stefan Dancila; Committee Member: Juan R. Cruz; Committee Member: Massimo Ruzzene; Committee Member: Rami Haj-Ali
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Bailey, Robert. "The stability characteristics of laminated composite panels with cutouts." Thesis, University of the West of Scotland, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265937.
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Herein is contained details of a comprehensive finite element survey and experimental investigation into the buckling and postbuckling characteristics of thin laminated square Carbon-Epoxy panels with various cutout geometries, subjected to uniaxial compression. The plate edges are considered to be fully fixed with constant edge displacement loading. The panels were quasi isotropic in nature with a stacking sequence of (0/90/±45)2,. Square, circular and elliptical centrally located cutouts were considered with cutout dimension/panel widths ranging from 0.1 to 0.7 in increments of 0.1. Eccentrically located circular and square cutouts were considered for cutout dimension/panel width ratios ranging from 0.1 to 0.4 with vertical and horizontal eccentricity varying from 0 to 20% of the panels width. Multiple circular cutouts with cutout dimension/panel width ranging from 0 to 0.3 with separation distance/panel width ratios ranging from 0.2 to 0.65. A finite element eigenvalue analysis was adopted to determine the critical buckling loads and buckle mode shapes for the panels. The postbuckling response of the panels were investigated by adopting a non-linear finite element analysis approach using an Incremental Newton-Raphson Iterative solution scheme. A limited experimental test programme was undertaken to act as verification to the finite element solutions. A purpose built buckling rig was designed and manufactured for the purposes of the tests. It has been confirmed that the critical buckling loads for centrally located circular and square cutouts initially reduces as the cutout size increases. After reaching a minimum value it thereafter increases with large cutout sizes, the exact changeover point being dependant upon the shape of the cutout. The orientation of ellipse major axis significantly affects the critical buckling load of a panel. A horizontally aligned ellipse exhibits similar behaviour as that to a circular or square cutout. However when the major axis is rotated relative to the horizontal axis its buckling capacity reduces monotonically till it has a buckling load less than that for an unperforated panel when vertical aligned. It has been shown when a circular cutout is eccentrically placed in a panel, for small cutout sizes the buckling load reduces with horizontal eccentricity while a small increase is experienced for vertical eccentricity. Multiple circular cutouts significantly reduce the buckling capacity of the panel for all cutout sizes and separation distances. Initial geometric imperfection in the panel does not affect the critical buckling load significantly. The postbuckled response of such panels are also insensitive to the magnitude of imperfection. Panels with circular, square and elliptical cutouts exhibit substantial postbuckled strength. The post buckling response of such panels are insensitive to cutout geometry shape.
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Allen, Aaron Andrew. "Stability results for damped multilayer composite beams and plates." [Ames, Iowa : Iowa State University], 2009.
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Düvelmeyer, Dana. "Some stability results of parameter identification in a jump diffusion model." Universitätsbibliothek Chemnitz, 2005. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200501234.
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In this paper we discuss the stable solvability of the inverse problem of parameter identification in a jump diffusion model. Therefore we introduce the forward
operator of this inverse problem and analyze its properties. We show continuity of
the forward operator and stability of the inverse problem provided that the domain
is restricted in a specific manner such that techniques of compact sets can be exploited. Furthermore, we show that there is an asymptotical non-injectivity which
causes instability problems whenever the jump intensity increases and the jump
heights decay simultaneously.
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Attaf, Brahim. "Vibration and stability analyses of unstiffened and stiffened composite plates." Thesis, University of Surrey, 1990. http://epubs.surrey.ac.uk/842974/.
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Vibration and stability studies have been undertaken on glass fibre reinforced polymer composite unstiffened and stiffened plates to optimise their dynamic properties. Boundary conditions, stiffeners and orthotropy of the material add to the complexity of a mathematical solution and to overcome this problem experimental and analytical studies were undertaken. The former method was carried out by impact hammer and an FFT digital signal analyser and the latter method was undertaken using finite element computer software. The current research concentrated upon the procedures and possible techniques available to optimise the dynamic properties of the plate without introducing weight penalty with the object of achieving an efficient structural performance coupled with an economic design. It has been shown that most of the increase in frequency and critical buckling load was directly related to the increase in stiffness of the stiffener and its position on the plate structure. The mode shapes have provided information regarding the most advantageous position for the setting of the stiffeners; they must be positioned away from nodal lines. The effect of the stiffener was significant for the fully clamped and clamped/free plates where only bending modes of vibration are present. However, for the completely free plates, where both bending and torsional modes of vibration could occur, the effect that the stiffeners have on the torsional modes was minimal. To locate precisely the position of the stiffener may be difficult when the plates are subjected to in-plane compressive loads, because higher order mode shapes may interchange. The mass-saving advantage which has been obtained in this research has shown that the stiffened plates with top-hat stiffeners were seen to have higher natural frequencies, within a specific vibration mode, compared to stiffened plates with rectangular stiffeners (blade).
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Shashikumar, Bangalore M. "Effect of leachate on the stability of landfill composite liners." Ohio : Ohio University, 1992. http://www.ohiolink.edu/etd/view.cgi?ohiou1173217012.
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RODRIGUES, ANSELMO BARBOSA. "VOLTAGE STABILITY PROBABILISTIC ASSESSMENT IN COMPOSITE GENERATION AND TRANSMISSION SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14870@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Em alguns países, os sistemas de energia elétrica estão operando próximos aos seus limites devido à falta de investimentos para expansão da transmissão e crescimento natural da demanda de energia elétrica. Esta condição de operação também pode ocorrer em sistemas de potência nos quais a expansão da transmissão é realizada de forma adequada. Neste caso, o carregamento excessivo da rede de transmissão é geralmente originado pela perda de interligações que transportam grandes blocos de energia. Os dois cenários de operação descritos acima têm causado problemas de Estabilidade de Tensão em sistemas de energia elétrica. Os estados de instabilidade de tensão são caracterizados principalmente pela presença de dois mecanismos: a insolubilidade das equações de fluxo de potência e a perda de controlabilidade. Os distúrbios que originam estes dois mecanismos são de natureza aleatória. Conseqüentemente, os índices de estabilidade de tensão, usados para analisar a perda de controlabilidade e a insolubilidade, são variáveis aleatórias. Desta forma, a análise de estabilidade de tensão deveria reconhecer incertezas associadas com parâmetros da rede elétrica, tais como: flutuações de carga e disponibilidade dos equipamentos. Geralmente, a modelagem de incertezas na análise de estabilidade de tensão é realizada usando os seguintes métodos probabilísticos: a Simulação Monte Carlo e a Enumeração de Estados. O principal índice estimado por estes métodos é o risco de instabilidade de tensão. Entretanto, o cálculo do risco de instabilidade de tensão é geralmente realizado contabilizando apenas um dos mecanismos causadores dos cenários de instabilidade de tensão. Além disso, a severidade dos estados de instabilidade de tensão não tem sido devidamente investigada. O objetivo desta tese é desenvolver um método para realizar uma análise probabilística da estabilidade de tensão que contabilize os dois mecanismos causadores da instabilidade de tensão no cálculo do seu risco. Serão também propostos índices probabilísticos, baseados na Análise de Robustez, para expressar a severidade dos estados de instabilidade de tensão. O método proposto se baseia na combinação das seguintes técnicas: Enumeração de Estados, Simulação Monte Carlo, Método da Matriz D’ e Fluxo de Potência Ótimo Não-Linear. Os métodos de Enumeração de Estados e Simulação Monte Carlo são usados para selecionar os estados do sistema resultantes de falhas nos equipamentos e erros de previsão de carga. A identificação da perda de controlabilidade e a restauração da solubilidade dos estados selecionados são realizadas pelo Método da Matriz D’ e pelo Fluxo de Potência Ótimo, respectivamente. A combinação dos métodos citados acima foi usada para obter os seguintes índices probabilísticos: risco de instabilidade de tensão, valores esperados da margem de estabilidade de tensão para as barras, e probabilidades dos estados de robustez. Os resultados dos testes com o método proposto revelaram que as probabilidades de estados instáveis, associados aos dois mecanismos causadores da instabilidade de tensão, são bastante significativas. Adicionalmente, a Análise de Robustez permitiu identificar a causa raiz e a severidade dos problemas de instabilidade de tensão.
In some countries, the electric power systems are operating near to their limits due to the absence of investments in the transmission network expansion and natural growth of the electricity demand. This operation condition can also occur in electric power systems in which the transmission expansion is carried out in appropriate way. In this case, the excessive loading of the transmission network is usually originated by the loss of interconnections that transport large energy blocks. The two operation scenarios described above have caused Voltage Stability problems in the electric power systems. The voltage instability states are mainly characterized by the presence of two mechanisms: the unsolvability of the power flow equations and the controllability loss. The disturbances that originate these two mechanisms are of stochastic nature. Consequently, the voltage instability indices, used to analyze the unsolvability and controllability loss, are random variables. In this way, the voltage stability assessment would recognize the uncertainties associated with the parameters of the electric network, for example: load fluctuations and equipment availability. Generally, the uncertainties modeling in the voltage stability is carried out using the following probabilistic methods: the Monte Carlo Simulation and the State Enumeration. The main index estimated by these methods is the voltage instability risk. However, the voltage instability risk evaluation is usually carried out considering only one of the mechanisms that cause voltage instability scenarios. Furthermore, the severity of the unstable states has not been properly investigated. The aim of this thesis is to develop a method to carry out a probabilistic assessment of the voltage stability that take into account the two mechanisms that cause the voltage instability in the evaluation of its risk. Probabilistic indices, based on Well-Being Analysis, are also proposed to express the severity of the voltage instability states. The proposed method is based on the combination of the following techniques: State Enumeration Method, Monte Carlo Simulation, D’ Matrix Method and Nonlinear Optimal Power Flow. The State Enumeration and Monte Carlo Simulation Methods are used to select the system states resulting of equipment failures and load forecast errors. The identification of the controllability loss and the solvability restoration of the power flow equations for the selected states are carried out by the D’ Matrix Method and by the Nonlinear Optimal Power Flow, respectively. The combination of the methods cited above was used to obtain the following probabilistic indices: voltage instability risk, expected value of the voltage instability margin for the buses, and Well-Being states probabilities. The results of the tests with the proposed method revealed that the probabilities of unstable states, associated with the two voltage instability mechanism, are very significant. Additionally, the Well-Being Analysis was able to identify the root cause and the severity of the voltage instability problems.
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Rantis, Theofanis D. "Probability-based stability analysis of a laminated composite plate under combined in-plane loads." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07292009-090358/.
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Klimeš, Pavel. "Ocelová konstrukce heliportu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-265365.
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The diploma thesis concerns with the design and static analysis of the heliport steel construction, which has the height of 20 m. The heliport is situated in Prague, Na Františku as a part of the hospital. The technical report and drawings are included in the thesis as well. The thesis consists of the determination of the heliport total load (including permanent, live and climate loads) and, its implementation in the SCIA Engineer 2015.3 computer software. The stress analysis of selected rods and, joints was consequently carried out by means of the manual calculation.
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Greenwood, Jacob Ryan. "Enabling Compact Devices Through Origami and Developable Mechanisms." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7764.
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This thesis provides resources that enable the design of novel and compact mechanical devices by providing terminology, engineering models, and design methods in the fields of developable mechanisms and origami-based engineering.The first part of this work presents engineering models to aid in the design of cylindrical developable mechanisms. These models take into account the added spatial restrictions imposed by the developable surface. Equations are provided for the kinematic analysis of cylindrical developable mechanisms. A new classification for developable mechanisms is also presented (intramobile, extramobile, and transmobile) and two graphical methods are provided for determining this classification for single-DOF planar cylindrical developable mechanisms. Characteristics specific to four-bar cylindrical developable mechanisms are also discussed. The second part addresses a key challenge in origami design: how to achieve stability while maintaining the desired folding motion. The origami stability integration method (OSIM) provides an approach for graphically combining various techniques to achieve stability. This thesis presents improvements and additions to the OSIM that allow it to be applied to many different scenarios. Existing stability techniques are also categorized into four groups based on whether they are intrinsic or extrinsic to the origami pattern and whether they exhibit gradual or non-gradual energy storage behaviors. These categorizations can help designers select appropriate techniques for their application. Four case studies are presented which use the OSIM and the technique categorization to conceptualize stability in origami-based devices.
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Flintham, T. P. "Flow resistance in ploughed upland drains : narrow channels with uniform or composite roughness." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/34807.
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Ploughed upland drains are straight prismatic channels of low aspect ratio. The drains are either uniformly or compositely roughened. In compositely roughened drains the bed and side-walls are differentially roughened although each roughness type is homogeneous. Upland catchments, containing extensive ploughed drainage networks, are particularly prone to flash flooding and increased sediment yield. However, the basic hydraulic data necessary to route flow through the drainage network and improve the engineering design of stable drainage channels are currently unavailable. A logarithmic flow resistance equation is developed for low aspect ratio channels, where the effective Nikuradse equivalent grain size is known. Testing against field data indicates that the relationship successfully predicts the resistance to uniform flow through upland drains. The performance of eight composite roughness formulae to predict the mean velocity in differentially roughened channels is compared. The composite roughness equations involve dividing the cross-sectional flow area into a number of sub-areas. The different methods of cross-sectional area division are considered and their effect on mean velocity prediction examined. Preferences are indicated concerning composite roughness equations which predict the mean velocity in channels of simple cross-sectional shape. Empirical equations are derived to determine the mean bed and side-wall shear stresses in straight symmetrical trapezoidal and rectangular open channels, with uniform or composite roughness. The model proposed is appropriate for stable sub-critical and super-critical flows. The equations are based on data collected from laboratory channels and should be cautiously applied to larger scale channels. Using the mean shear stress model, a design procedure is proposed to improve drainage channel stability.
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Cintra, Daniele Campos. "Interação genótipos-ambientes e parâmetros de adaptabilidade e estabilidade para características de crescimento em bovinos de corte compostos no Brasil." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/74/74131/tde-18052007-133705/.
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Dados de 111.101 pesos a desmama ajustado aos 205 dias de idade (PES205), 50.860 pesos ajustados aos 390 dias (PES390) e 47.462 ganhos de peso até 185 dias após a desmama (GP185) foram analisados para avaliar a interação genótipos-ambientes e estimar parâmetros de adaptabilidade para sete combinações genotípicas de bovinos cruzados para corte, criados em três diferentes ambientes do Brasil. A interação genótipos-ambientes foi fonte de variação significativa (P<0,01) para todas as características avaliadas. As decomposições das somas de quadrados das interações genótipos-ambientes, para cada variável estudada, foram realizadas pelo método de regressão. Foram verificados por meios dos coeficientes angulares que, para PES205, os animais de composição genotípica 7 foram considerados como de adaptabilidade ampla. Os genótipos 2, 3 e 6 foram considerados de adaptabilidade específica a ambientes favoráveis e as composições genotípicas 1, 4 e 5 foram classificadas como de adaptabilidades específicas a ambientes desfavoráveis. Para PES390, os animais considerados como de adaptabilidade ampla foram os de composições genotípicas 1 e 3. Os de combinações genotípicas 2, 6 e 7 foram considerados de adaptabilidade específica a ambientes favoráveis e os genótipos 4 e 5 foram classificados como animais com adaptabilidade específica a ambientes desfavoráveis. Para GP185, verificou-se que os animais considerados como de adaptabilidade ampla foram os de composição genotípica 4 e 5, enquanto que as combinações genotípicas 1, 2 e 3 foram considerados de adaptabilidade específica a ambientes favoráveis e as composições genotípicas 6 e 7 foram classificados como de adaptabilidades específicas a ambientes desfavoráveis.Data from 111,101 weaning weight adjusted to 205 days (WW), 50,860 yearling weight adjusted to 390 days (YW) and 47,462 weight gain from weaning to yearling (WG) were analyzed to evaluated the genotype-environmental interactions and estimates adaptability parameters for seven genotype combinations of crossbreed beef cattle, raised in three environment of the Brazil.. The genotypeenvironmental interation effect was significative (P<0.01) for all de traits analyzed. The sum squares decompositions of genotype-environmental interations, were accomplishment by regression method for each trait analyzed. Were verified, through the slopes of the regression lines that, for WW, the animals considered as wide adaptability were genotype composition 7. The genotype compositions 2, 3 and 6 were considered of specific adaptability for favorable environments, and genotype compositions 1, 4 and 5 were classified as combinations with specific adaptability for unfavorable environments. For YW, the animals considered as wide adaptability were genotypes compositions 1 and 3. The genotype compositions 2, 6 and 7 were considered of specific adaptability for favorable environments and genotype compositions 4 and 5 were classified as combinations with specific adaptability for unfavorable environments. For WG, the animals with genotype composition 4 and 5 were considered as wide adaptability, while the genotype compositions 1, 2 and 3 were considered of specific adaptability for favorable environments and genotype compositions 6 and 7 were classified as combinations with specific adaptability for unfavorable environments.
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Shang, Xiaoyang. "Aeroelastic stability of composite hingeless rotors with finite-state unsteady aerodynamics." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/12543.
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Amy, John Victor. "Composite system stability methods applied to advanced shipboard electric power systems." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/10945/23576.
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CIVINSLarge increases in the complexity of shipboard electric loads as well as development of electric drive, integrated electric drive and pulsed power systems make manifest the present and future importance of naval electric power systems. The most crucial attribute of these systems is their ability to fulfill their function in the presence of "large-signal" perturbations. Fundamental differences between shipboard and commercial electric power systems make all but the most general nonlinear, "large-signal" stability analyses inappropriate for the design and assessment of naval electric power systems. The tightly coupled and compact nature of shipboard systems are best accommodated by composite system stability analyses. Composite system methods, based upon Lyapunov's direct method, require that each component's stability be represented by a Lyapunov function. A new Lyapunov function which is based upon coenergy is developed for 3-phase synchronous machines. This use of coenergy is generalizable to all electromechanical energy conversion devices. The coenergy-based Lyapunov function is implemented as a "stability organ" which generates waveforms at information teirninals of a "device object" in the object oriented simulation environment of WAVESIM. Single generator simulation results are used to acquire a measure of the "over sufficiency" of the coenergy-based Lyapunov function. Some means of combining the components' Lyapunov functions is necessary with composite system stability criterions. To provide the largest stability region in a Lyapunov function convective derivative space, thereby reducing "over sufficiency", a "timevariant weighted-sum" composite system criterion is developed. This criterion is implemented as a "stability demon" "device object" within the WAVESIM environment. The "stability demon" is tested through RLC circuit simulations and a two-generator simulation. The output of the "stability demon" is suitable for use within an overall system stabilising controller.
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Martin, Sophie. "Le composant des granules de stress G3BP : caractérisation phénotypique de souris KO, et identification de son interactome ribonucléoprotéique dans le cerveau de souris." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20247.
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Les protéines capables de lier des ARNs sont essentielles pour les différentes étapes de maturation de l'ARN messager (ARNm), en dirigeant leur localisation et leur devenir dans la cellule, et en formant avec les ARNs des particules ribonucléoprotéiques (mRNPs). Les mRNPS peuvent former des structures cellulaires dynamiques qui sont adressées vers des fonctions spécifiques. Ces granules, tels que les granules de stress formés suite à un stress cellulaire, contiennent des ARNm dont la traduction est inhibée et qui sont stockés transitoirement. Ma thèse a consisté en la caractérisation fonctionnelle de G3BP (RasGAP SH3 binding protein), une RBP exprimée de façon ubiquitaire chez l'homme et la souris, et impliquée dans l'assemblage des granules de stress. Par recombinaison homologue classique, des souris knock-out pour G3BP ont été générées. Ces souris ont une espérance de vie faible et des défauts du comportement associés au Système Nerveux Central, en particulier un phénotype de type ataxie. Des expériences d'électrophysiologie ont aussi montré une altération de la plasticité synaptique dans l'hippocampe des souris KO. J'ai donc réalisé des expériences d'immunoprécipitation après cross-link (Cross-Linking and Immunoprecipitation, CLIP) pour purifier à partir de cerveau de souris un complexe stable contenant G3BP, et les ARNs associés ont été identifiés par séquençage haut débit (High-Throughput Sequencing, HITS-CLIP). De façon surprenante, la plupart des cibles de G3BP correspondent à des transcrits codants mais qui contiennent des séquences introniques, et des ARNs non codants. De plus, mes résultats ont montré que l'absence de G3BP1 affecte la stabilité de ces transcrits pré-matures spécifiquement dans le cervelet, ce qui peut être corrélé au phénotype d'ataxie des souris KO G3BP1. Cela suggère un nouveau mécanisme de régulation qui passe par la stabilisation de transcrits pré-matures, qui pourraient être convertis en transcrits matures par exemple lors d'un stress et de la séquestration de G3BP dans les granulesRNA binding proteins (RBPs) are essential in the different steps of processing of the messenger RNAs (mRNAs), directing their localization and fate within the cell, and forming with them the ribonucleoprotein particles (mRNPs). mRNPs can assemble into dynamic cellular structures in which they are routed towards specific functions. RNA granules such as stress granules (SGs) contain translationally silenced mRNPs storing transiently repressed mRNAs.My thesis work consisted in the functional characterization of G3BP (RasGAP SH3 binding protein), an RBP that is expressed ubiquitously in both humans and mice and is involved in the assembly of SGs. Using classical homozygous recombination, viable G3BP1 knock out mice were generated that demonstrated short lifespan.and behavioral defects linked to the Central Nervous System (CNS), notably an ataxia phenotype. Electrophysiology experiments showed an alteration of synaptic plasticity in the hippocampus of KO mice. Therefore, I used Cross-Linking and Immunoprecipitation (CLIP) to purify from mouse brain a stable complex containing G3BP, and performed High-Throughput Sequencing (HITS-CLIP) to identify associated RNAs. Strikingly, most of the G3BP targets correspond to intron sequence-retaining transcripts and non-coding RNAs. My results also showed that G3BP1 depletion influences the stability of these premature transcripts in the cerebellum, which can be correlated to the ataxia phenotype of the G3BP1 KO mice. This comprehensive analysis suggests a new mechanism of gene regulation based on stabilization of silenced premature transcripts which might be converted to mature transcripts under stress condition and sequestration of G3BP in SGs
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ALEMAN, ROMAN AUGUSTO ARCINIEGA. "STABILITY ANALYSIS OF LAMINATED COMPOSITE CYLINDRICAL SHELLS AND PANELSSTABILITY ANALYSIS OF LAMINATED COMPOSITE CYLINDRICAL SHELLS AND PANELS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1946@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOREste trabalho apresenta um estudo do comportamento não- linear e instabilidade de cascas e painéis cilíndricos laminados de materiais compósitos. Com esta finalidade é desenvolvida uma formulação de alta ordem de deformação cisalhante que leva en conta estes efeitos nas relações deformação-deslocamento. O comportamento da casca é descrito por uma consistente teoria não-linear para cascas laminadas que considera pequenas deformações e rotações moderadas e incorpora automaticamente o efeito das deformações cisalhantes. O modelo de bifurcação clássico é utilizado para estudar a estabilidade da casca compósita. O comportamento pós-crítico é examinado a partir de uma solução modal obtida com técnicas de perturbação. Em ambos os casos aplica-se o método de Rayleigh-Ritz para discretizar o sistema de equações diferenciais de equilíbrio em um sistema de equações algébricas. O método de Newton-Raphson é empregado na resolução das equações não- lineares de equilíbrio do caminho pós-crítico e na obtenção do caminho fundamental da estrutura imperfeita. A implementação numérica (em álgebra simbólica) é feita utilizando a linguagem de programação Maple V release 3. É então desenvolvido um estudo paramétrico com o objetivo de determinar a influência dos parâmetros geométricos e das características próprias do laminado (número de lâminas e orientação das fibras) na resposta crítica e pós-crítica da casca compósita para dois tipos de carregamento, a saber: pressão lateral e compressão axial. É analisado, também, o grau de sensibilidade às imperfeições geométricas destas estruturas. São apresentadas comparações dos resultados teóricos aqui obtidos com outros existentes na literatura com o objetivo de demonstrar a confiabilidade da formulação e metodologia numérica aqui desenvolvidas.
The purpose of the present work is to study the non-linear behaviour and instability of laminated composite cylindrical shells and panels under axial and pressure loading. The analysis is performed within a refined non- linear theory for composite laminated shells incorporating the effects of transverse shear and the geometric imperfections. The classical bifurcation theory is used to analyze the critical behavior of the shell. To examine the post-critical behavior of the shell, a modal solution based on the basic ideas of Koiter`s theory is deduced and the Rayleigh-Ritz method together with the Newton-Raphson strategy are used to solve the non-linear equilibrium problem and plot either the post-critical path or the non- linear equilibrium path of the imperfect shell. The analytical and numerical procedures were performed by the use of the symbolic algebra package Maple V release 3. The influence played by the geometrical parametrs of the shell and physical parameters of the composite laminate, such as stacking sequences and fiber orientation in each lamina, on the critical and post-critical behavior of the shell is examined and a series of conclusions are outlined. The imperfection sensitivity of these shells is also analyzed. Comparisons of the present results with those obtained by other theories and experiments are found to be satisfactory and show the validity of the present methodology.
Este trabajo presenta un estudio de la inestabilidad y comportamiento no lineal y la inestabilidad de cortezas y paneles cilíndricos laminados de materiales compuestos. Con esta finalidad se desarrolla una formulación de alta orden de deformación cisallante que considera estos hechos en las relaciones deformación desplazamiento. EL comportamiento de la corteza se describe a través de una consistente teoría no lineal para cascas laminadas. Esta teoría considera pequeñas deformaciones y rotaciones moderadas e incorpora automáticamente las deformaciones cisallantes. El modelo de bifurcación clásico se utiliza para estudiar la estabilidad de la corteza. El comportamiento poscrítico se examina a partir de una solución modal obtenida con técnicas de perturbación. En ambos casos se aplica el método de Rayleigh Ritz para discretizar el sistema de ecuaciones diferenciales de equilibrio en un sistema de ecuaciones algébraicas. El método de Newton Raphson es utilizado en la resolución de las ecuaciones no lineares de equilibrio del camino postcrítico y en la obtención del camino fundamental de la extructura imperfecta. La implementación numérica (en álgebra simbólica) se realiza utilizando el lenguaje de programación Maple V release 3. Con el objetivo de determinar la influencia de los parámetros geométricos y de las características proprias del laminado en la respuesta crítica y postcrítica de la casca compósita, se realiza un estudio paramétrico para para dos tipos de carga: presión lateral y compresión axial. Se analiza también, el grado de sensibilidad a las imperfeiciones geométricas de estas extructuras. Finalmente, y con el objetivo de demostrar la confiabilidad de la formulación y la metodología numérica aqui desarrolladas, se comparan los resultados teóricos obtenidos con los reportados en la literatura.
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Jilani, Adel Benhaj. "Deformations of Piezoceramic-Composite Actuators." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/29540.
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In the past few years a new class of layered piezoceramic and piezoceramic-composite actuators, known as RAINBOW and GRAPHBOW, respectively, that are capable of achieving 100 times greater out-of-plane displacements than previously available has been developed. Prior to the development of RAINBOW and GRAPHBOW, large stacks of piezoelectric actuators, requiring complicated electronic drive circuits, were necessary to achieve the displacement now possible through the use of a single RAINBOW actuator. The major issues with both RAINBOW and GRAPHBOW are the prediction of their room-temperature shapes after processing, and their deformation response under application of electric field.
In this research, a methodology for predicting the manufactured shapes of rectangular and disk-style RAINBOW and GRAPHBOW is developed. All of the predictive analyses developed are based on finding approximate displacement responses that minimize the total potential energy of the devices through the use of variational methods and the Rayleigh-Ritz technique. These analyses are based on classical layered plate theory and assumed the various layers exhibited linear elastic, temperature-independent behavior. Geometric nonlinearities are important and are included in the strain-displacement relations. Stability of the predicted shapes is determined by examining the second variation of the total potential energy. These models are easily modified to account for the deformations induced by actuation of the piezoceramic.
The results indicate that for a given set of material properties, rectangular RAINBOW can have critical values of sidelength-to-thickness ratio (Lx/H or Ly/H) below which RAINBOW exhibits unique, or single-valued, spherical or domed shapes when cooled from the processing temperature to room temperature. For values of sidelength-to-thickness ratio greater than the critical value, RAINBOW exhibits multiple room-temperature shapes. Two of the shapes are stable and are, in general, near-cylindrical. The third shape is spherical and is unstable. Similarly, disk-style RAINBOW can have critical values of radius-to-thickness ratios (R/H) below which RAINBOW exhibits axisymmetric room-temperature shapes. For values of R/H greater than the critical value, disk-style RAINBOW exhibits two stable near-cylindrical shapes and one unstable axisymmetric shape. Moreover, it is found that for the set of material properties used in this study, the optimal reduced layer thickness would be at 55%, since the maximum change in curvature is achieved under the application of an electric field, while the relationship between the change in curvatures and the electric field is kept very close to being linear. In general, good agreement is found for comparisons between the predicted and manufactured shapes of RAINBOW. A multi-step thermoelastic analysis is developed to model the addition of the fiber-reinforced composite layer to RAINBOW to make GRAPHBOW. Results obtained for rectangular RAINBOW indicate that if the bifurcation temperature in the temperature-curvature relation is lower than the composite cure temperature, then a unique stable GRAPHBOW shape can be obtained. If the RAINBOW bifurcation temperature is above the composite cure temperature, multiple room-temperature GRAPHBOW shapes are obtained and saddle-node bifurcations can be encountered during the cooling to room temperature of [0°/RAINBOW], [RAINBOW/0o], and [0o2/RAINBOW]. Rectangular [RAINBOW/0o/90o] seems to be less likely to encounter saddle-node bifurcations. Furthermore, the unstable spherical RAINBOW configuration is converted to a stable near-cylindrical configuration. For the case considered of disk-style GRAPHBOW, three stable room-temperature shapes are obtained and the unstable axisymmetric RAINBOW configuration is also converted to a stable near-cylindrical configuration. For both rectangular and disk-style GRAPHBOW, the relationship between the major curvature and the electric field is shown to be very close to being linear. This characteristic would aid any dynamic analysis of RAINBOW or GRAPHBOW.Ph. D.
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Ricchiuto, Mario. "Construction and analysis of compact residual discretizations for conservation laws on unstructured meshes." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211035.
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This thesis presents the construction, the analysis and the verication of compact residual discretizations for the solution of conservation laws on unstructured meshes. The schemes considered belong to the class of residual distribution (RD) or fluctuation splitting (FS) schemes.
The methodology presented relies on three main elements: design of compact linear first-order stable schemes for linear hyperbolic PDEs, a positivity preserving procedure mapping stable first-order linear schemes onto nonlinear second-order schemes with non-oscillatory shock capturing capabilities, and a conservative formulation enabling to extend the schemes to nonlinear CLs. These three design steps, and the underlying theoretical tools, are discussed in depth. The nonlinear RD schemes resulting from this construction are tested on a large set of problems involving the solution of scalar models, and systems of CLs. This extensive verification fills the gaps left open, where no theoretical analysis is possible.
Numerical results are presented on the Euler equations of a perfect gas, on a two-phase flow model with highly nonlinear thermodynamics, and on the shallow-water equations.
On irregular grids, the schemes proposed yield quite accurate and stable solutions even on very difficult computations. Direct comparisone show that these results are more accurate than the ones given by FV and WENO schemes. Moreover, our schemes have a compact nearest-neighbor stencil. This encourages to further develop our approach, toward the design of very high-order schemes, which would represent a very appealing alternative, both in terms of accuracy and efficiency, to now classical FV and ENO/WENO discretizations. These schemes might also be very competitive with respect to very high-order DG schemes.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
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Murphy, Mary Catherine. "A study of the structural stability of an unbalanced sandwich composite configuration." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA272496.
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Morton, Sean (Sean C. ). "Diffusional stability studies of a T91/12Cr-2Si-Fe functionally graded composite." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/106724.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.MIT Institute Archives copy: incomplete; ends at page 7.
Includes bibliographical references (leaf 16 ).
by Sean Morton.
S.B.
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Wu, Dongzhu. "SUBSTRATE DESIGN AND MEMBRANE STABILITY OF MULTILAYER COMPOSITE MEMBRANE FOR CO2 SEPARATION." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1510429230811329.
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Alhakami, Arwa Ali. "Effect of time and temperature on the color stability of dental composite." Thesis, University of Iowa, 2019. https://ir.uiowa.edu/etd/6907.
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OBJECTIVE: To evaluate the effects of different times and temperatures of coffee exposures on the color stability of three types of dental composites (DC).
METHODS: Three types of DC were used to fabricate standardized discs (n=288; n=96/DC): microfill (Durafill VS), microhybrid (Z100TM), and nanofill (Estelite OMEGA) of shade A2. Each disc was 2mm in thickness and 9mm in diameter. After being light cured with a Quarts tungsten halogen (QTH) unit at the energy level recommended for each DC, discs were polished using sand paper under water irrigation. All samples were initially stored in an incubator in distilled water for 24-hours at 37 65ºC and each DC group was further divided into 6 subgroups (n=16/per group): 65ºC coffee, 37ºC coffee, 4ºC coffee, 65ºC distilled water, 37ºC distilled water, 4ºC distilled water (control group with water media). Baseline color was measured by spectrophotometer (Easy VITA shade compact) with color changes (ΔE*) recorded after 1-day, 3.5-days, and 7-days. The statistical analysis revealed no interactions between DC, temperature, and time of incubation and the main effects were examined using one-way ANOVA followed by the post-hoc Tukey’s HSD test or a Bonferroni adjustment (alpha=0.05).
RESULTS: Mean (ΔE*) observed with coffee exposures for the microfill DC (11.58±6.37) was statistically significant higher than for the nanofill DC (10.64±6.77; p<0.001), and mean (ΔE*) for the nanofill DC was significantly higher than for the microhybrid DC (9.26±5.83; p<0.001). For all DC, mean (ΔE*) observed with coffee exposure at 65ºC (18.33±4.32) was significantly higher than at 37°C (7.03±2.05; p<0.001), and mean (ΔE*) at 37ºC was significantly higher than at 4ºC (6.11±2.67; p<0.001). Mean (ΔE*) after coffee exposure for 1 day (8.64±5.35) was significantly lower than for 3.5-days (11.07±6.50; p<0.001) and 7-days (11.76±6.84; p<0.001); while no difference was observed between 3.5-days and 7-days of incubation (p=0.0769).
CONCLUSION: The findings of this study indicated that exposure time, temperature, and composite type affect the color stability of DC, with higher temperature affecting the color stability more than lower temperatures. Also, color stability was affected more by increasing the exposure time.
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Galdeano, David. "Contribution à la commande corps-complet des robots humanoïdes : du concept à l'implémentation temps-réel." Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20070/document.
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Les robots humanoïdes sont en passe d'être commercialisés pour le public à grande échelle, mais pour réussir cet objectif il est nécessaire de rendre ces robots fiables, fonctionnels et sécurisés. Ceci implique de nombreuses améliorations par rapport à de l'état de l'art, pour permettre un produit fini. Un des domaines à améliorer est la commande corps-complet des robots humanoïdes. Les objectifs de cette thèse sont de proposer une architecture de commande permettant de générer des mouvements corps-complet bio-inspirés. L'idée principale étant de s'inspirer de la marche humaine afin de reproduire ces mouvements sur un robot humanoïde. La solution de commande proposée utilise le principe de tâches pour quatre objectifs cinématiques: (i) la pose relative des pieds, (ii) la position du CoM, (iii) l'orientation du buste, et (iv) l'évitement des butées articulaires. La stabilité est renforcée en modifiant la position du CoM désirée à l'aide d'un stabilisateur basé sur la régulation non linéaire du ZMP. L'approche résultante est appelée architecture de commande hybride cinématique/dynamique. Cette approche a été validée expérimentalement sur deux prototypes de robots humanoïdes pour différentes tâches telles que le squat et la marcheHumanoid robots are a rising trend, and are about to be sold to the public on a large scale, but for this to be possible it is necessary to make them reliable, secure and functional. This implies many improvements over the prior state of the art. A domain of improvement is the full-body control of humanoid robots. The objective of this thesis is to propose a control architecture for generating a bio-inspired full-body control. The main idea is to learn from human walking to replicate these movements on a humanoid robot. The proposed control solution uses the principle of kinematics task for four objectives: (i) the relative pose of the feet, (ii) the position of the Centre de masse (CoM), (iii) the orientation of the upper-body, and (iv) the joints' limits avoidance. Stability is enhanced by modifiying the CoM position by using a stabilizer based on nonlinear regulation of the Zero Moment Point (ZMP). The resulting approach is called hybrid kinematic / dynamic control architecture. This approach has been validated experimentally on two prototypes of humanoid robots for tasks such as squat and walking
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Gojuri, Arun. "Stability of End Notched Flexure Specimen." Thesis, Högskolan i Skövde, Institutionen för teknik och samhälle, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-4487.
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This paper deals with two-dimensional Finite Element Analysis of the End Notched Flexure (ENF) specimen. The specimen is known to be unstable if the crack length is shorter than some critical crack length acr. A geometric linear two-dimensional Finite Element (FE) analysis of the ENF specimen is performed to evaluate acr for isotropic and orthotropic elastic materials, respectively. Moreover, the Mode II Energy Release Rate (ERR) JII and the compliance of the specimen are calculated. The influence of anisotropy is studied. Comparisons are made with the results from beam theory. This work is an extension of previous work.
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Kayatin, Matthew Jay Davis Virginia A. "Rheology, structure, and stability of carbon nanotube-unstaturated polyester resin dispersions." Auburn, Ala, 2008. http://hdl.handle.net/10415/1421.
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Lange, David. "Risk and performance based fire safety design of steel and composite structures." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/3159.
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For the development of performance based design on a proper scientific basis the use of the concept of risk is inevitable. However, the application of this concept to actual structural design is not simple because of the large ranges of probability and consequences of events which exist. This is compounded by a plethora of different actions that can be taken to reduce the probabilities of the events and also the magnitude of the consequences. It is the reduction in the magnitude of these consequences which is essentially the goal of design. This work aims to address the challenges posed by the application of the concepts of performance based design for structures in fire. Simple methodologies have been developed for the assessment of the consequences of an extreme event. These methodologies are based upon fundamental behaviour of structures in fire. A methodology has been developed which can be used to assess the capacity/deflection behaviour through the complete thermal deflection of floor slabs. This takes into account positive effects on the capacity of floor slabs of the membrane stress at the slabs boundaries at low deflections as well as the final capacity provided by the tensile membrane action of the reinforcement mesh at high deflections. For vertical stability of structures in fire, analytical equations to describe the behaviour of floor systems at the perimeter of a building are developed. From these equations, the resulting pull-in forces on external columns can be calculated as well as the resulting horizontal load applied to the column. From this, a simple stability assessment is proposed which can be used to assess the consequences of multiple floor fires on tall buildings. These analytical methodologies are brought together in a risk based frame- work for structural design which can be used to identify areas in a building or structural components which pose a high residual risk. These elements can be qualitatively ’ranked’ according to their relative risk and appropriate measures taken to reduce the risk to an acceptable level. The framework is illustrated via 2 case studies. The first is of a typical small office building, and the second is of a prestige office development.
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Román, Carla Cecília Alandia. "Análise da estabilidade de cor e rugosidade de superfície de compósitos submetidos à fumaça de cigarro." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/58/58131/tde-15122011-094523/.
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O objetivo deste estudo foi avaliar a estabilidade de cor e rugosidade de superfície de 3 compósitos odontológicos com partículas diferentes: nanohíbrido (Tetric N-Ceram - Ivoclar Vivadent), híbrido (Z250 - 3M ESPE) e microhíbrido com matriz silorano (Filtek P90 3M - ESPE), submetidos à fumaça de cigarro. Para isso, foram obtidos 60 corpos-de-prova (8mm de diâmetro X 2mm de espessura), 20 para cada tipo de material restaurador utilizado, dos quais 10 receberam polimento com lixas dágua em abrasividades decrescentes (Grupo1) e a outra metade não foi submetida a nenhum tipo de acabamento/polimento ficando sob efeito apenas de uma matriz de poliéster (Grupo 2). Após armazenamento dos corpos de prova em água destilada a 37°C por 24 horas, foram realizadas as primeiras leituras de cor (Colorímetro Vita Easy Shade) na escala de cor CIEL*a*b* e rugosidade superficial (Rugosímetro Surfcorder SE 1700 - Kosakalab). Em seguida, as amostras foram expostas à fumaça de 20 cigarros por um período de 10 minutos cada, (Marlboro - Philip Morris), sendo que entre um cigarro e outro as amostras foram submetidas à escovação em dispositivo padronizado e lavagem em água corrente. Após ação do número total de cigarros, foram realizadas leituras finais de cor e rugosidade. Os valores de ΔE, ΔL, Δa e Δb foram analisados estatisticamente utilizando 2 way ANOVA e Teste de Bonferroni (p<0.05) e os valores de rugosidade média (Ra) foram analisados isoladamente para cada tipo de material (teste t Student, p < 0.05). Verificou-se que o compósito Tetric N apresentou maior alteração de cor, em níveis clinicamente inaceitáveis (ΔE>3,3) e de rugosidade de superfície em relação aos demais compósitos quando utilizada a tira de poliéster como acabamento. Concluiu-se que a ausência de polimento aumenta a capacidade manchadora do cigarro sobre todos os compósitos e a rugosidade de superfície dos materiais, com exceção de P90.The purpose of this study was to evaluate the color stability and surface roughness of three dental composites with different type of fillers: Nanohybrid (Tetric N-Ceram), Hybrid (Filtek Z250-3M ESPE) and Microhybrid silorane based composite (Filtek P90- 3M ESPE), exposed to cigarette smoke. 20 specimens (8mm diameter X 2mm thickness) of each material were prepared and separated into two groups (n=10) according to the surface treatment : Group 1- polymerization through a polyester film strip and polishing with water sandpaper in decreasing abrasiveness (600, 800 e 1200); and Group 2- polymerization through a polyester film strip, without any polishing. After immersion in destilled water 37° for 24 hours, baseline color of all specimens was measured using reflectance spectrophotometer (Easy Shade - Vita) with CIEL*a*b* system, surface roughness was also measured using a rugosimeter (SJ-201P Mitutoyo, Tokyo, Japan). After base line measurements, the specimens were exposed to smoke from 20 cigarettes in 10 minutes each, (Marlboro - Philip Morris), between one cigarette and other, the specimens were submitted to brushing in a standardized device and washed with water. After the action of the total number of cigarettes, final measurements of color and surface roughness were performed. Values of ΔE, ΔL, Δa e Δb were statistically analyzed using 2 way ANOVA e Teste de Bonferroni (p<0.05) and values of average surface roughness (Ra) were analyzed separately for each type of material (teste t Student, p < 0.05). It was found that the composite Tetric N-Ceram showed increased of surface roughness and greater color change in clinically unacceptable levels (ΔE>3,3), in comparison with the other composites when used the polyester strip without polishing. It was concluded that the absence of polishing increases the cigarette staining and surface roughness on all composites except for Filtek P90.
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Pekárková, Jana. "Ověření termodynamické stability ettringitu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-240041.
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The thesis deals with possibilities of FBC fly ash utilization for composite cements. It focuses on thermodynamic stability of ettringite, which is produced during composite cements hydration. Specific tasks are dedicated to observation of influence of outdoor environment and influence of calciumhydrosilicate environment to stability of ettringite.
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Pudhota, Madhuri. "THERMAL STABILITY OF PHENOLIC BASED BINDERS AND FRICTIONAL PERFORMANCE OF BRAKE COMPOSITE MATERIALS." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1652.
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To enhance frictional performance, wear and to obtain improved thermal stability with a reduction of noise, vibration, and harshness (NVH) and provide environment friendly brakes for the increasing needs of the population's comfort and safety requirements this study was initiated. The thermal stability of two different phenolic resins as binder on the frictional performance of brake composite material was studied. The two phenolic resins used are Durite phenolic resin and Bakelite phenolic resins. They were tested for friction, wear, thermal stability and degradation. This was executed by using a universal friction tester (UFT) for testing friction and wear, then on thermo gravimetric analysis (TGA) and the TGA results indicate more mass loss of NB samples contrary to test results. When individual materials were heated, Bakelite lost less mass compared to Durite. The friction test indicates more friction when used the NB samples but they had less wear and more stability nevertheless this could vary for other compositions and conditions.
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Nabinejad, Omid. "Mechanical Performance and Thermal Stability of Natural Fiber Composite Using Palm Oil Biomass." Thesis, Ph.D, 2017. http://hdl.handle.net/20.500.11937/57464.
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This Thesis demonstrates an experimental study on the development of thermoset-based natural fiber particle-reinforced composite. The overall objective was to improve the mechanical properties and investigate the thermal stability of the composite. It addresses, the effect of various chemical treatment of filler types, filler size, filler percentage and matrix type on the mechanical properties and thermal stability of the composite. To improve the mechanical performance, a hybrid composite containing carbon nanotubes was also synthesized.
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Chung, Chang-Bum. "Compressive behavior of thick composite shells : benchmark solutions for loss of stabilty and hygroscopic effects." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/13406.
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Lagarde, Lauriane. "Structure et stabilité des réseaux lamellaires gélifiés." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAE031.
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Cette thèse apporte une nouvelle vision de la structure des réseaux lamellaires gélifiés. Les systèmes étudiés, choisis pour des applications cosmétiques, sont basés sur des mélanges d’alcools cétéaryliques, de tensioactifs esters de phosphate et d’eau. À l’aide de nombreuses méthodes analytiques, nous avons prouvé que la formation d’une structure lamellaire est possible à des forces ioniques allant jusqu’à 2.2 mol∙L-1. Pour la première fois, un comportement de percolation élastiqueest rapporté en fonction de la concentration en alcools gras et tensioactifs. Le seuil au-dessus duquel un réseau percolé apparaît est ici à 3 % et est indépendant de la force ionique et de la présence de longues chaînes d’oxyde de polyéthylène ancrées dans les bicouches. Au-dessus de 3 %, les systèmes passent de structures vésiculaires unilamellaires à des paquets plans de lamelles, qui forment un réseau tridimensionnel pouvant contenir d’importantes quantités de solution aqueuse. L’impact de la force ionique, de la présence d’oxyde de polyéthylène et de la nature des contre-ions sur lespropriétés rhéologiques et sur la stabilité de la formulation est ensuite étudié. Une augmentation inhabituelle du module élastique et de l’énergie de cohésion est observée lorsque la force ionique est accrue. L’addition d’oxyde de polyéthylène, à l’inverse, diminue d’un ordre de magnitude les valeurs du module élastique du réseau. Les systèmes étudiés sont stables à l'échelle macroscopique et on peut distinguer dans le gel, selon sa mobilité : l’eau fixée entre lamelles, l’eau restreinte en troisdimensions et l’eau libre, extractible par ultracentrifugationThis Ph.D. brings new insights into the structure of lamellar gel networks. The systems studied are relevant for cosmetic applications and based on a mixture of cetearyl alcohols, phosphates esters surfactants and water. Using several analytical methods, we show that the formation of a lamellar gel structure is possible up to the ionic strength of 2.2 mol∙L-1. For the first time for such systems, an elastic percolation behavior as a function of the concentration of fatty alcohols and surfactants isreported. The threshold above which a percolated network is formed is found here at 3 % and appears to be independent of the ionic strength and of the presence of long polyethylene oxide chains between the bilayers. Above 3 %, the systems transform from unilamellar vesicle-like structures towards planar stacks of lamellae, connected together in a three dimensional network,that can hold large amounts of aqueous solution. The impact of the ionic strength, of polyethylene oxide chains and of the nature of the counterions on the rheological properties and on the stability of the formulation is then investigated. When the ionic strength is raised, an unusual increase of the elastic modulus and of the cohesive energy of the network is observed. At the opposite, the addition of polyethylene oxide chains decreases of one order of magnitude the values of the elastic modulus,leading to much softer networks. All systems studied are macroscopically stable and one finds in the gel, according to water mobility: interlamellar fixed water, water restricted in three dimensions and free water, drainable by ultracentrifugation
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Parveen, Tania. "Composite load model decomposition : induction motor contribution." Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/31301/1/Tania_Parveen_Thesis.pdf.
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In this thesis, a new technique has been developed for determining the composition of a collection of loads including induction motors. The application would be to provide a representation of the dynamic electrical load of Brisbane so that the ability of the power system to survive a given fault can be predicted. Most of the work on load modelling to date has been on post disturbance analysis, not on continuous on-line models for loads. The post disturbance methods are unsuitable for load modelling where the aim is to determine the control action or a safety margin for a specific disturbance. This thesis is based on on-line load models. Dr. Tania Parveen considers 10 induction motors with different power ratings, inertia and torque damping constants to validate the approach, and their composite models are developed with different percentage contributions for each motor. This thesis also shows how measurements of a composite load respond to normal power system variations and this information can be used to continuously decompose the load continuously and to characterize regarding the load into different sizes and amounts of motor loads.
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Kiša, Daniel. "Matematické modelování kráčejících robotů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417089.
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Tato diplomová práce se zabývá matematickými modely kráčejících robotů. Dva z těchto modelů jsou vybrány a analyzovány. Pasivní model "rimless wheel" , který slouží jako základ pro další, složitější modely, je podrobně analyzován. "Compass gait" model dvounohého robota je v práci analyzován a numericky simulován v programovacím jazyce Python. Metoda pro nalezení podmínek pro pasivní chůzi robota je rovněž implementována.
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Dubau-Assibat, Nathalie. "Influence de la nature de substituants sur la stabilité relative des dérivés diazoi͏̈ques et de leurs isomères structuraux." Toulouse 3, 1995. http://www.theses.fr/1995TOU30117.
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L'etude des derives diazoiques et de leurs isomeres structuraux constitue l'un des axes de recherche de notre laboratoire. Dans un premier chapitre, une etude bibliographique nous a permis de faire le point sur les principales proprietes de trois familles d'explosifs poly-azotes: les derives diazoiques, les azotures et les tetrazoles. Le deuxieme chapitre traite des reactions de cycloaddition (3+2) d'une serie de dipoles 1,3 (nitrilimines, derives diazoiques, nitrones), avec un dipolarophile original: le reactif de lawesson. La reactivite du dipole nitrilimines etant tres influencee par la nature des substituants, l'etude comparee de nitrilimines electrophiles et nucleophiles est presentee dans le troisieme chapitre ainsi que les premieres caracteristiques spectroscopiques et chimiques d'une isodiazirine. Dans le quatrieme chapitre, nous montrerons que l'addition oxydante d'une quinone sur deux diazophosphines induit des reactions de rearrangement originales: derive diazoiques-nitrilimine-isodiazirine derive diazoique-diazocumulene enfin, dans le dernier chapitre, nous etudions l'influence de l'acidite de l'atome de bore sur la stabilite des nitrilimines n-borees
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Schejn, Aleksandra Maria. "Synthesis and catalytic activity of ZIF-8 and doped-ZIF-8 crystals : stability and cytotoxicity evaluation." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0212/document.
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Depuis plusieurs années, les MOFs (Metal Organic Frameworks) suscitent une grande attention pour leurs applications potentielles en catalyse hétérogène. Ces matériaux sont également étudiés dans les domaines de la séparation, du stockage de gaz, de la libération contrôlée ou comme systèmes de vectorisation de médicaments. Leur structure complexe étant formée par des centres de coordination métalliques unis par des ligands polydentates, les MOFs disposent de nombreux sites acido-basiques de Lewis ou de Brönsted qui sont cruciaux pour l'activité des matériaux et la sélectivité des produits lors des réactions catalysées par les MOFs. Dans ce travail, nous nous sommes tout particulièrement intéressés à une classe de MOFs appelée « zéolithic imidazolate frameworks » (ZIF-8). Les ZIF-8 présentent de nombreuses propriétés intéressantes, notamment une grande surface spécifique, une faible densité, une forte porosité ainsi qu’une excellente stabilité chimique et thermique. Dans une première partie, la préparation de matériaux ZIF-8 et d’hétérostructures à base ZIF-8 a été développée afin de conférer à ces matériaux des propriétés adaptées à l'application souhaitée. La mise en forme de ces catalyseurs a également été étudiée afin d’obtenir la forme optimale pour une utilisation industrielle de ces matériaux. En variant le précurseur d’ions Zn2+ utilisé pour la synthèse, nous avons démontré que les propriétés (taille, porosité, ...) de ZIF-8 cristaux pouvaient être contrôlées en fonction de l’application catalytique recherchée. Ces ZIF-8 cristaux ont été utilisés avec succès en tant que catalyseurs hétérogènes dans les réactions de Knoevenagel et Friedländer. Nous avons développé de nouveaux matériaux ZIF-8 dopés par des ions Cu2+. Les particules Cu/ZIF-8 se sont montrés être des catalyseurs efficaces dans la réaction de Combes et la cycloaddition de Huisgen. La recyclabilité du matériau a été évaluée et il a notamment été montré que les particules ZIF-8 pouvaient être réutilisées jusqu'à dix fois sans perte d'activité catalytique. Nous avons également fonctionnalisé les cristaux ZIF-8 avec des particules magnétiques Fe3O4. L’hétérostructure hybride Fe3O4@ZIF-8 peut facilement être récupérée par séparation magnétique après les expériences de catalyse. Afin d’étendre le champ d’application des catalyseurs ZIF-8, le matériau a également utilisé pour la conversion du dioxyde de carbone en carbonates cycliques en utilisant un réacteur du Parr. Comme la réaction est d’un grand intérêt industriel, le catalyseur a été mis en forme par compression. Dans la dernière partie de ce mémoire, la toxicité des particules ZIF-8 et ZIF-8 dopé par Cu ou Fe a été évaluée en utilisant des cellules alvéolaires A549 et de la peau IHK comme modèles. La stabilité des particules a été déterminée à l’aide de milieux mimant la digestion des particules in vivo. Les résultats obtenus montrent que les particules sont très sensibles aux variations de pH ainsi qu’aux sels présents dans les différents milieuxMetal organic frameworks (MOFs) have gained considerable attention as heterogeneous catalytic systems and also have been studied in the area of separation, gas storage, controlled release or as drug delivery systems. According to their complex structure formed by metal centers coordinated with polydentate linkers, MOFs expose abundance of Lewis and/or Brönsted acid-base sites that are crucial for the materials catalytic activity and selectivity towards specific reactions. Moreover, these materials have many other attractive properties, including a large surface area, a low density and a high porosity. In this work, we focused on the zeolithic imidazolate framework (ZIF-8) material – a MOF exhibiting high porosity and stability and which can also be used as a template for further functionalization and modification. Firstly, we focused on the preparation of ZIF-8 crystals and ZIF-8 heterostructures with properties adapted to the desired application, and then shaping of the catalyst to obtain the best form of material for industrial scale-up utilization. By varying Zn2+ precursors used for the synthesis, we demonstrated that the properties (size, porosity,…) of ZIF-8 crystals can be controlled and tuned depending on the applications. These ZIF-8 crystals were successfully applied as heterogeneous catalysts in Knoevenagel and Friedländer reactions. Next, we developed protocols for the synthesis of Cu2+-doped ZIF-8 crystals. The use of these crystals could be extended to Cu-mediated reactions, like the Combes condensation and the Huisgen cycloaddition. We evaluated recyclability and we showed that the nanomaterials could be reused up to ten times without any loss of catalytic activity. Moreover, we functionalized ZIF-8 crystals with magnetic Fe3O4 nanoparticles. The hybrid Fe3O4@ZIF-8 heterostructures could be easily recovered by magnetic separation after catalytic experiments. To show multiple benefits originating from the ZIF-8 structure and properties, we also used this material for the conversion of CO2 into cyclic carbonates using a Parr reactor. As the reaction could be scale-up at the industrial level, we shaped the powder in the form of pellets and use it under the same conditions. In the last chapter, we evaluated the toxicity and the stability in biological media of ZIF-8, Cu- and Fe-doped ZIF-8 particles using A549 alveolar cells, IHK skin cells as models and in vitro ingestion under fed conditions. These models were chosen according to the most probable first contact entering gates for nanoparticles inside human body, skin, lungs and digestive tract. Outcomes from these preliminary studies motivated us to conduct extended stability tests of the particles in different media. We showed that the particles are altered by pH changes and medium complexity