Submitted by Maria Eneide de Souza Araujo (mearaujo@ipen.br) on 2015-02-24T17:23:36Z No. of bitstreams: 0 / Made available in DSpace on 2015-02-24T17:23:36Z (GMT). No. of bitstreams: 0 / Os efeitos da atmosfera de sinterização e do tamanho inicial das partículas na sinterização da céria contendo 10% em mol de gadolínia (GdO1,5) foram sistematicamente estudados neste trabalho. Materiais de partida com três valores para a área de superfície específica foram utilizados, 210 m2/g, 36,2 m2/g e 7,4 m2/g. Diferentes cinéticas de sinterização foram verificadas. Quanto menor o tamanho inicial das partículas, menor é a temperatura para o início da sinterização e mais acelerada a densificação do material. Curvas mestres de sinterização foram construídas para cada um dos materiais analisados. Um programa computacional foi especialmente desenvolvido para este propósito. Diferenças significativas entre as energias de ativação para densificação foram verificadas. Para este trabalho foi determinado que, quanto menor o tamanho inicial de partícula, menores as energias de ativação. A evolução das distribuições de tamanhos de cristalitos foi investigada para os materiais de maior área superficial específica. Foi determinado que a eliminação e migração de poros (pore drag) é o mecanismo predominante para o crescimento de grãos durante o início da sinterização da céria gadolínia. Os efeitos da atmosfera de sinterização no desvio de estequiometria, na densificação, na evolução microestrutural e na condutividade elétrica da céria-gadolínia foram analisados. Atmosferas redutoras, oxidantes e inertes foram usadas para este propósito. Desvios na estequiometria da céria foram verificados no volume do material, sendo este dependente da área de superfície específica e da atmosfera utilizada. Quanto maior o potencial de redução da atmosfera utilizada, maior a concentração de Ce3+ no material. Com o aumento da concentração de Ce3+ um aumento no tamanho médio de grãos foi verificado. Uma diminuição na condutividade elétrica total, intra e intergranular foram determinadas para as amostras sinterizadas em atmosferas redutoras. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Cette thèse traite de la modélisation multi-échelle de composites particulaires fortement chargés. La méthode d’estimation, qualifiée d’“Approche Morphologique” (A.M.), repose sur une double schématisation géométrique et cinématique du composite permettant de fournir la réponse aux deux échelles. Afin d’évaluer les capacités prédictives de l’A.M. en élasticité linéaire avec évolution de l’endommagement, l’A.M. est testée vis-à-vis de ses aptitudes à rendre compte des effets de taille et d’interaction de particules sur la chronologie de décohésion. Pour cela, différentes microstructures périodiques simples, aléatoires monomodales et bimodale générées numériquement sont considérées. Les résultats obtenus sont cohérents avec les données de la littérature : la décohésion des grosses particules précède celle des plus petites et est d’autant plus précoce que le taux de charges est important. Puis, l’objectif est de coupler deux non-linéarités traitées séparément dans deux versions antérieures de l’A.M : l’endommagement par décohésion charges/matrice et les grandes déformations. La formulation du problème de localisation-homogénéisation est reprise à la source de manière analytique. Le critère de nucléation de défauts est étendu en transformations finies. Le problème obtenu, fortement non-linéaire, est résolu numériquement via un algorithme de Newton-Raphson. Les étapes sous-jacentes à la résolution (calcul de la matrice tangente, codage en langage Python®) sont explicitées. Des évaluations progressives (matériaux sain et endommagé)permettent de valider la mise en oeuvre numérique. Les effets de taille et d’interaction sont alors restitués en transformations finies. / This study is devoted to multi-scale modeling of highly-filled particulate composites.This method, the “Morphological Approach” (M.A.), is based on a geometrical and kinematicalschematization which allows the access to both local fields and homogenized response. In order toevaluate the predictive capacities of the M.A. considering a linear elastic behavior for the constituentsand evolution of damage, analysis is performed regarding the ability of the M.A. to accountfor particle size and interaction effects on debonding chronology. For that purpose, simple periodic,random monomodal and bimodal microstructures are considered. The results are consistent withliterature data : debonding of large particles occurs before the one of smaller particles and thehigher the particle volume fraction, the sooner the debonding. Finally, the objective is to operatethe coupling of two non linearities which were separately studied in previous versions of the M.A. :debonding between particles and matrix, and finite strains. The whole analytical background of theapproach is reconsidered in order to define the localization-homogenization problem. The nucleationcriterion is extended to the finite strains context. The final problem, strongly non linear, is numericallysolved through a Newton-Raphson algorithm. The different solving steps (jacobian matrix,coding with Python®) are developed. Progressive evaluations (sound and damage materials) allowthe validation of numerical implementation. Then, size and interaction effects are reproduced infinite strains.

Doctor of Philosophy / Department of Grain Science and Industry / X. Susan Sun / Poly(lactic acid) (PLA), a synthetic biopolymer, is a promising substitute of some petroleum-based polymers due to its mechanical and biodegradable properties. But, because of the high cost of PLA (compared to those petroleum plastics for disposable application), starch has been incorporated into PLA to reduce cost and accelerate the biodegradability rate of the composites. But, the addition of starch as filler to PLA decreased mechanical performance of the composite. The addition of methylenediphenyl diisocyanate (MDI) into PLA/starch blends improved drastically the mechanical properties of the composite. Results from thermal-degradation analysis showed that PLA had the highest Arrhenius activation energy and strongest thermal endurance of all samples, followed by PLA/starch/MDI and PLA/starch. Aged samples exposed to fluctuating humidity storage conditions significantly decreased their performance. But, storing the samples in plastic bags could minimize degradation of properties. PLA and its composites with starch would not significantly affect application function when they are stored in controlled environment. PLA and PLA/starch based composites sealed in plastic bags can be stored in fluctuating humidity conditions (30-90% RH) for up to 30 days. Tensile strength, elongation, and damping increased with average particle size of starch granules (APS). But, declination of these properties was detected with APS larger than 45 mm. Crystallinity increased as the APS decreased. Young’s modulus, storage modulus, and moisture absorption were not significantly affected by the starch APS. The use of MDI as a coupling agent altered the role of starch APS on those properties of poly(lactic acid)/starch composite. The oxidation of the primary alcohol group on C6 of starch molecules up to 10% degree of substitution did not significantly affect the mechanical properties of PLA/starch/MDI, but the composites showed a reduced inelastic deformation (tensile curve) and significant increase in storage modulus and damping. Results suggest that a substitution of hydroxyl group on C6 of starch molecules for carboxyl group (up to 10%) increased the strengthening effect of MDI enough to reduce inelastic deformation of the composites upon load, but not enough to enhance mechanical properties.

Please read the abstract in the section 00front of this document / Thesis (PhD)--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / PhD / Unrestricted

Metal additive manufacturing (AM) can produce complex parts that were once considered impossible or too costly to fabricate using conventional machining techniques, making AM machines an exceptional tool for rapid prototyping, one-off parts, and labor-intensive geometries. Due to the growing popularity of this technology, especially in the defense and medical industries, more researchers are looking into the physics and mechanics behind the AM process. Many factors and parameters contribute to the overall quality of a part, one of them being the powder bed itself. So far, little investigation has been dedicated to the behavior of the powder in the powder bed during the lasering process. A powder spreading machine that simulates the powder bed fusion process without the laser was designed by Lawrence Livermore National Laboratory and was built as a platform to observe powder characteristics. The focus for this project was surface roughness and particle size distribution (PSD), and how dose rate and coating speed affect the results. Images of the 316L stainless steel powder on the spreading device at multiple layers were taken and processed and analyzed in MATLAB to access surface quality of each region. Powder from nine regions of the build plate were also sampled and counted to determine regional particle size distribution. As a comparison, a simulation was developed to mimic the adhesive behavior of the powder, and to observe how powder distributes powder when spread.

Die Charakterisierung von Nanopartikeln erfordert eine Messung des Dispersitätszustandes bei allen Schritten der Herstellung - von der Synthese bis zum fertigen Produkt. Dafür ist eine leistungsfähige Partikelmesstechnik notwendig, deren Methoden bei der Beschreibung des komplexen Materialverhaltens helfen können. Die Ultraschalldämpfungsspektroskopie ist eine Messmethode, die zur prozessbegleitenden Charakterisierung hochdisperser Pulver und Suspensionen geeignet ist. Mit Vergleichen von Messungen und Modellrechungen wurde festgestellt, dass für die Ultraschalldämpfungs-Modellierung in Dispersionen homogener Partikel ein auf dem Phänomen der elastischen Streuung basierendes Modell praktisch relevant ist. Dies betrifft sowohl die Anwendung zur Messung in Suspensionen als auch in Emulsionen homogener Partikel. Bei einem Vergleich von Modellrechungen und Messungen für ein System poröser Partikel bzw. Aggregate wurde das Modell der Streuung an poroelastischen Kugeln als geeignet zur Beschreibung der Dämpfung disperser Systeme identifiziert. Bei Vorhandensein grober Partikel in Suspensionen nanoskaliger Systeme ist somit eine korrekte Auswertung der Partikelgröße möglich; der bislang übliche Messbereich wurde erweitert. Sekundärer Schwerpunkt der Arbeit ist die Diskussion der numerischen Modellanwendung. Es werden weiterhin Lösungsmöglichkeiten zur Dämpfungsberechnung und zur Berechnung der Größenverteilungen beschrieben. Des Weiteren wurden Anregungen für Entwickler von Ultraschallspektrometern abgeleitet.

Stale bread contributes to the biggest volume of food waste in Sweden. Current method on recovering bread waste is by producing biogas or bioethanol. Despite advantages in the energy sector, the bread which still has relatively high quality could be recovered into new products with higher value, such as food for human consumption. Development of a product, termed ‘fungal cake’ by solid state fermentation on bread waste using Neurospora intermedia in small scale petri dishes have previously been successfully conducted. This study aims to scale up the production of fungal cake into bench scale production. Two systems using different bioreactors were used in this study. The first system operated in batch mode using a tray bioreactor, in which the effect of particle size, mixing, and bread loading were evaluated. The fermentation was conducted during 5 days. Bread crumb with a larger particle size of 2 mm resulted in similar outcomes as bread crumb with a smaller particle size of 0.5 mm in terms of CO2 evolution rate, cumulative CO2 production, starch, and protein content of the final product. However, larger particle size resulted in a more homogeneous growth of the fungus throughout the product, which is preferred. The presence of daily mixing had no significant effect compared to static condition for all measured variables. Thus, mixing could be introduced to promote product homogeneity. Likewise, bread loading had no significant effect on the measured variables, which implies that a higher productivity can be achieved using a higher bread loading. The second system operated in continuous mode using a newly developed continuous tubular bioreactor with product recycle. Two experiments, in which the residence time (48h and 24h) and recycle ratio (10/65 and 20/55) were conducted. Both experiments yielded product with stable starch and protein content, indicated by a stable CO2 evolution rate over time. The performance using continuous tubular bioreactor was compared to batch fermentation in tray bioreactor using the same ratio of inoculum and both system yielded product with the same starch and protein content. Successful operation in continuous bioreactor certainly improved the productivity of fungal cake production.

Les systèmes agroforestiers stockent du carbone dans la biomasse des arbres. Cependant leur intérêt ne se limite pas à ce carbone stocké sous forme de bois. En effet, les arbres produisent de grandes quantités de litières, et apportent également du carbone dans les horizons profonds du sol par la mortalité et l’exsudation racinaire. Or, les sols agricoles, ayant de très faibles teneurs en matière organique, ont un potentiel de stockage en carbone bien plus important que les sols forestiers. A ce jour, il n’existe pratiquement pas de travaux permettant d’avoir une estimation de l’impact des arbres agroforestiers sur le carbone du sol. La plupart des études sont en effet menées sur le stockage de carbone dans la biomasse aérienne des arbres. Une étude a ainsi estimé qu’en climat tempéré et pour des densités comprises entre 50 et 100 arbres/ha, le stockage de carbone serait compris entre 1.5 et 4 tC/ha/an, ce qui est très important comparé au potentiel de stockage d’autres systèmes de culture. On se propose donc dans ce travail de contribuer significativement à la connaissance sur les possibilités de stockage de C dans les sols en agroforesterie. Tout d’abord, nous quantifierons les stocks de C dans les parcelles agroforestières et les comparerons aux témoins agricoles. Nous étudierons également l’hétérogénéité spatiale de ces stocks, sous la ligne d’arbres ou sous la culture intercalaire, et ce à différentes profondeurs. Dans un deuxième temps, nous étudierons les entrées de carbone au sol, notamment via la mortalité racinaire des arbres. Puis, nous étudierons les processus liés à la stabilisation de ce carbone dans les horizons profonds du sol. Enfin, nous chercherons à savoir si l’apport de carbone frais dans les horizons du sol ne pourrait pas entraîner une minéralisation d’une partie du carbone stable du sol, phénomène connu sous le nom du priming effect, et qui pourrait jouer un rôle non négligeable dans le bilan de carbone de ces systèmes. La modélisation sera utilisée afin d’estimer le stockage de carbone sur le long terme. L’étude sera menée dans un contexte de système de culture méditerranéen, sur un site expérimental d’exception. L’analyse mécaniste fournira le cadre conceptuel pour la compréhension de la dynamique du C dans d’autres systèmes agroforestiers à l’avenir. / Agroforestry is a land use type where trees are associated with crops and/or animals within the same field. This agroecosystem could help mitigating climate change, and also contribute to its adaptation. The goal of this thesis was to evaluate the potential of soil organic carbon storage under agroforestry systems. This study was performped at the oldest experimental site in France, a trial supervised by INRA since 1995, but also at farmers' fields. Soil organic carbon stocks were compared between agroforestry and agricultural plots, down to 2 m soil depth. All organic inputs to the soil were quantified (tree roots, leaf litter, crop roots and residues). The stability of additionnal stored carbon was caracterised with soil organic matter fractionation, and soil incubations. A model of soil organic carbon dynamic was described in order to better undrestand this dynamic in agroforestry, especially in deep soil layers. This study revealed the interest and the potential of agroforestry systems in increasing soil organic carbon stocks, with accumulation rates of 0.09 to 0.46 t C ha -1 yr -1. It also reveals the role of tree rows in this storage, and the importance of carbon inputs from root mortality. However, it raises concerns about the stability of this storage.

The master´s thesis deals with the volume changes of concrete during its concrete glow. These volume changes are generally more susceptible to high-strength concretes – HSC, which contain a bigger dose of binder. The theoretical section describes the possible reduction volume change especially in HSC, which are focused on the composition of concrete, especially on the type and particle size distribution of aggregate. Then attention is also paid to the different types of cements and their possible substitution. The part of the theoretical work describes the types of volume changes that may occur. In the experimental part are suggested the HSC by to secure informations. Different kinds of aggregates are used and a continuous or discontinuous grain curve and a different maximum grain size. Part of the sample was made only from CEM I 42,5 R and the second part of the sample from CEM I 42,5 R with the addition of very finely ground limestone. In terms of the part of the work were monitored volume changes of concrete with different composition and also their mechanical properties after 7, 28 and 90 days. Specifically, compressive strength, tensile strength, strength of the surface layers of concrete, water absorption and water-permeability test concrete. In conclusion, are listed all the results of tests.

Living shorelines are designed to address coastal erosion and their use is encouraged over that of hard structures such as sea walls and bulkheads because they provide habitat, improve water quality and stabilize shorelines. Objectives of this study were to: (i) Compare soil Nitrogen [N], Phosphorus [P], Organic Carbon [OC], organic matter (SOM) and soil bulk density between living, hardened and natural shoreline to determine if soil present within living shorelines is comprised of higher SOM and lower bulk density, that encourage marsh growth, as compared to hardened shorelines. (ii) Use an experimental mesocosm to test the effect of shoreline substrate types (living vs hardened vs natural) and nitrogen loading (at four concentration 0, 12, 24, 36 ml) on the growth of Spartina alterniflora. No previous study has documented the growth of Spartina in response to inorganic N loading at various shoreline substrate types. My results show living shoreline has significantly lower soil bulk density [F 2, 138 = 10.79, p <0.01] and higher SOM content than hardened shoreline [F 2, 138 = 10.26, p <0.01]. Combinations of N addition decreased plant’s root-shoot ratio and resulted in increased dry shoot weight. These results indicate that living shoreline is capable of trapping sediments within the nearshore environment, contributing to vertical marsh accretion by accumulation of organic matter, in the face of sea level rise. Findings from this research provide insights to local government, planners, developers and consultants on the benefits of living shoreline structures for the purpose of best shoreline management practice.