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Orientadores: Sergio Tonini Button, Mauro Moraes de Souza / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-11T13:19:22Z (GMT). No. of bitstreams: 1 SouzaFilho_Valterde_M.pdf: 4133313 bytes, checksum: a0db5181ce553fa4a0c17b20db4a876b (MD5) Previous issue date: 2008 / Resumo: A conformação a quente, especificamente em prensa horizontal, é um tema de pouco estudo no meio acadêmico, mas interessante pelo emprego da alta taxa de deformação que alcança 90s-1. A microestrutura resultante desse processo é influenciada por algumas variáveis como temperatura, taxa de deformação, tamanho de grão austenítico inicial e taxa de resfriamento. A proposta deste trabalho é prever o comportamento da microestrutura dos aços perante essa alta taxa de deformação com a utilização da simulação numérica. Para tanto, os materiais DIN 20NiCrMo8 MOD e DIN 16MnCr5 MOD foram ensaiados nessa taxa de deformação em um processo de conformação industrial. A comparação do tamanho de grão austenítico obtido da conformação industrial com o tamanho de grão austenítico obtido através da simulação numérica é demonstrada. A influência da taxa de resfriamento sobre a microestrutura para cada material também foi demonstrada. Concluiu-se que a previsão do tamanho de grão austenítico é adequada utilizando-se o software comercial MSC.Superform acrescido do cálculo para crescimento de grãos. A previsão do comportamento mecânico após o processo de conformação utilizando-se de equações da literatura foi insatisfatória, porém pode-se demonstrar a influência da variação da taxa de resfriamento na microestrutura das peças conformada a quente / Abstract: A conformação a quente, especificamente em prensa horizontal, é um tema de pouco estudo no meio acadêmico, mas interessante pelo emprego da alta taxa de deformação que alcança 90s-1. A microestrutura resultante desse processo é influenciada por algumas variáveis como temperatura, taxa de deformação, tamanho de grão austenítico inicial e taxa de resfriamento. A proposta deste trabalho é prever o comportamento da microestrutura dos aços perante essa alta taxa de deformação com a utilização da simulação numérica. Para tanto, os materiais DIN 20NiCrMo8 MOD e DIN 16MnCr5 MOD foram ensaiados nessa taxa de deformação em um processo de conformação industrial. A comparação do tamanho de grão austenítico obtido da conformação industrial com o tamanho de grão austenítico obtido através da simulação numérica é demonstrada. A influência da taxa de resfriamento sobre a microestrutura para cada material também foi demonstrada. Concluiu-se que a previsão do tamanho de grão austenítico é adequada utilizando-se o software comercial MSC.Superform acrescido do cálculo para crescimento de grãos. A previsão do comportamento mecânico após o processo de conformação utilizando-se de equações da literatura foi insatisfatória, porém pode-se demonstrar a influência da variação da taxa de resfriamento na microestrutura das peças conformada a quente / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Magister Scientiae - MSc / Natural radioactivity studies have been carried out to study the textural characteristics, heavy mineral composition, provenance, sediment transport, and depositional environment of beach placer deposits. The naturally occurring radionuclides such as 232Th, 238U and 40K are used as the tracers of the mineralogical properties of beach sands, which reflect the geological characteristics such as transport and sorting processes and the depositional environment. The present work focuses on the radiometric characteristics of beach sand deposits along the west coast of South Africa. Beach sands samples were collected at the Melkbosstrand (MBS) and Ouskip (OSK) beach. The activity concentrations of these radionuclides were determined by high-resolution gamma-ray spectrometry using a high-purity germanium (HPGe) detector in a low-background configuration.

Made available in DSpace on 2016-07-18T17:53:15Z (GMT). No. of bitstreams: 1 miriam ubida sales.pdf: 372296 bytes, checksum: f4ab27f8a6b466463d2c2ca5401a4ec3 (MD5) Previous issue date: 2015-03-26 / To evaluate the presence of pathogenic and apathogenic strains of Listeria spp in urban parks and squares in the city of Presidente Prudente, 117 soil samples from 57 different georeferenced locations were evaluated for pH and inoculated in Fraser Broth for selective enrichment of Listeria spp. After incubation at 30° C for 7 to 21 days, broth with evidence of growth were plated on ALOA chromogenic agar. Bacterial colonies compatible with the Listeria were classified by morphotinctorial and biochemical criteria and evaluated for antimicrobial susceptibility by disk diffusion method. Listeria was isolated in 37 squares / parks (64.9%) and 57 of 117 samples (47.8%) of soil, of which 5 were classified as L. monocytogenes and 2 as L. ivanovii. There was a predominance of acidic pH in the city soil (mean = 5.44). The average pH did not differ between positive and negative isolates samples with Listeria spp (p = 0.5523). Spatial modeling techniques revealed no link between points with positive isolates and variability of soil pH. The type of square / park (infant, sports, garden and rest) did not affect the percentage of isolation for Listeria spp. Sandy soils tended to have lower percentages of isolation than clay soils. The seven isolated pathogenic were resistant to four or more antibiotics, including ampicillin (3/7 = 42.9%) and sulfonamides (5/7 = 71.4%). Considering that no collection point received recent fertilization, we concluded that pathogenic and apathogenic Listeria species are dispersed in the soil of urban areas, even under unfavorable pH and the absence of organic fertilizer use. / Para avaliar a presença de linhagens patogênicas e apatogênicas de Listeria spp em parques e praças urbanos do município de Presidente Prudente, 117 amostras de solo de 57 diferentes locais georeferenciados, foram avaliadas quanto ao pH e inoculadas em caldo Fraser para enriquecimento seletivo de Listeria spp. Após incubação a 30ºC por sete a vinte e um dias, caldos com crescimento evidente foram plaqueados em ágar cromogênico ALOA. Colônias bacterianas compatíveis com o gênero Listeria foram classificadas por critérios morfotintoriais e bioquímicos e avaliadas quanto a sensibilidade microbiana pelo método de disco difusão. Listeria spp foi isolada de 37 praças/parques (64,9%) e de 56 das 117 amostras (47,8%) de solo, das quais cinco foram classificadas como L. monocytogenes e duas como L. ivanovii. Observou-se predomínio do pH ácido no solo do município (média=5,44). O pH médio não diferiu entre amostras com isolamentos positivos e negativos para Listeria spp (p=0,5523). Técnicas de modelagem espacial não revelaram relação entre pontos com isolamentos positivos e variabilidade do pH do solo. O tipo de praça/parque (infantil, esportivo, jardim e descanso) não influenciou nos percentuais de isolamento para Listeria spp. Solos arenosos tenderam a apresentar percentuais de isolamento inferiores aos solos argilosos. Os sete isolados patogênicos apresentaram resistência a quatro ou mais antimicrobianos, incluindo ampicilina (3/7=42,9%) e sulfonamidas (5/7=71,4%). Considerando-se que nenhum ponto de coleta recebeu adubação recente, conclui-se que espécies patogênicas e apatogênicas de Listeria estão dispersas no solo de aglomerados urbanos, mesmo sob pH desfavorável e a ausência do uso de adubo orgânico.

V poslední době je snahou nahradit klasickou komerční olovnatou piezoelektrickou keramiku bezolovnatou, z důvodu zvýšeného zájmu o ochranu životního prostředí a zdraví. Různé typy materiálů již byly navrženy, jako například (K, Na) NbO3 (KNN), (Bi, Na) TiO3 (BNT), (Bi, Na) TiO3 – BaTiO3 (BNT-BT), ale jejich piezoelektrické vlastnosti zatím nedosáhly takových hodnot jako u olovnatý chkeramik (např. olovnatý titanát olova ((Pb Zr)TiO3). Nejvíce se olovnatým materiálů blíží bezolovnatý systém na bázi (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 nebo (Ba, Ca) (Zr, Ti) O3 ((1-x)BZT-xBCT, BCZT) a to díky vysokým piezoelektrickým a dielektrickým parametrům. Nevýhodou tohoto prostředku je jeho velmi vysoká teplota slinování (1520 ° C) za účelem dosažení vysokých piezoelektrických vlastností (např. Piezoelektrické konstanty d33 > 600 pC / N). Tato práce se zabývá bezolovnatou keramikou na bázi BCZT, její výrobou a vylepšením piezoelektrických vlastností dopováním CeO2. Přidáním CeO2 (y wt.%) do (Ba0.85Ca0.15) (Zr0.1Ti0.9) O3 se výrazně snížila slinovací teplota a došlo ke zhutnění při 1350°C. U této kompozice se Curieova teplota pohybovala kolem TC~105°C a velikost zrn byla v rozmezí ~ 10-13 m. Fázový přechod z romboedrické struktury na tetragonální (R-T) byl zjištěn pomocí rentgenové spektroskopie u y = 0 - 0.1 wt.%, což koreluje s výsledky Ramanovy spektrální analýzy. Mikrostrukturní a strukturní charakteristiky byly detailně studovány v korelaci s dielektrickými, feroelektrickými a piezoelektrickými vlastnostmi. Nejlepší funkční vlastnosti byly dosaženy pro keramiku BCZT – 0.07 wt.% CeO2. Tato keramika vykazovala piezoelektrický nábojový koeficient d33 = 507±20pC/N, elektromechanický planární koeficient kp = 51.8 %, dielektrickou konstantu r = 4091±100, ztrátový činitel tan = 0.02, remanentní polarizaci Pr = 13.58C/cm2, intenzitu koercitivního pole EC = 2.13kV/cm při normovaném napětí, d33* nebo Smax/Emax = 840pm/V. Dvoustupňovou kalcinační technikou bylo docíleno homogenního růstu zrn s vysokou relativní hustotou (~ 99% teoretické hustoty). Tato kompozice BCZT- CeO2 vykazovala stálé feroelektrické, dielektrické a piezoelektrické vlastností i při velikosti zrn 10 µm. Bezolovnatá piezoelektrická keramika (Ba0.85Ca0.15-y Cey) (Zr0.1Ti0.9) O3 (BCCeZT) byla dále dopována CeO2 s cílem substituce Ce4+ v místě A krystalické mřížky. Posunutí rentgenových vrcholů k vyšším úhlům naznačuje kontrakce mřížky, což by mohlo způsobit obsazení iontů ceru v místech A této soustavy. Bylo zjištěno, že velikost zrn kolem 10 - 12 m je významná pro vysokou piezoaktivitu bezolovnaté BCCeZT keramiky. Nejvyšší piezoelektrické vlastnosti tato keramika vykazovala při y;Ce = 0.00135 a slinovaná na teplotě 1350°C/4h, kdy piezoelektrické parametry byly d33 = 501±10 pC/N, kp = 38.5±1.92 %, Pr = 12.19 C/cm2, TC = 108.1 °C a s maximální deformací S do 0.14 %. Pro další studium substituce v místě A, byly vyrobeny keramické materiály (Ba1-x-y Cax Cey) (Zr0.1 Ti0.9) O3 (x:Ca = 0.05, 0.10, 0.15, 0.20 a y;Ce = 0.00135). Opět se ukázalo, že pokud byla velikost zrn ~13um, tak keramika vykazovala vysoké piezoelektrické vlastnosti (d33 = 457pC/N) pro x = 0.15 % kalcinované na teplotě 1425 °C. Když se se velikost zrn zvýšila nad 16 um, piezoelektrický nábojový koeficient d33 klesl na 200 pC/N. Rentgenová analýza ukázala změnu fázové struktury z rombické na tetragonální při zvýšení obsahu vápníku.

This master's thesis deals with the effects of the cooling rate on the grain size of magnesium alloys based on Mg–Al (AZ91E) and Mg–Zr–RE (WE43B and Elektron21). The effects of the cooling rate are analyzed on samples of varying thickness for different cooling methods (forced–air–cooling, cooling into polymer, natural air cooling). We also evaluated the final microstructure, porosity, hardness, and mechanical properties for investment castings. Based on the evaluated grain sizes, we demonstrated a significant difference in the cooling rate influence on the grain size for the alloy AZ91E. Compared to Zirconium-based alloys (WE43B and Elektron21), for which the zirconium content influences grain size the most. For the alloys based on Mg–Zr–RE, it is possible to prefer casting conditions, without negative enlarging of the grain size.

In the Circum-Caribbean, long timescale paleoenvironmental records, which are used to establish important baseline data for climatological phenomena such as droughts, floods, and hurricanes, are rare. This project uses geological and geochemical proxies (X-Ray fluorescence core scanning data, grain-size analysis, loss on ignition) from a nine-meter-long sediment core from a coastal karst basin near Haiti’s southwestern peninsula to reconstruct Holocene environmental and climatic changes in a region that is both understudied and highly sensitive to the effects of storms, sea level change, tectonics, and anthropogenic impacts. The chronology of the core is established with 4 AMS dates from terrestrial organic matter and shows continuous sedimentation from ~8500 cal BP to the present, with an abrupt increase in sedimentation rate at ~2900 cal BP. High values of Ti and Ti/Ca are associated with finer sediments in the core and indicate relatively humid conditions at ~6500 cal BP, followed by a gradual drying trend. This is consistent with data from elsewhere in the Caribbean that reflects a southward migration of the ITCZ during the early Holocene. After 2500 cal BP, a series of large and abrupt increases in Ti and Ti/Ca are associated with an influx of finer, terrestrially-derived sediment into the bay due to enhanced discharge from the nearby Baradères River, possibly as a result of short-duration shifts to wetter climate conditions, hurricane-induced precipitation, and/or prehistoric-era human settlement. Variations in silicate input (e.g., K/Ti), marine productivity (e.g., Ca/Ti), and redox conditions (e.g., Mn/Fe) are linked to local climate changes and resulting changes in the depositional environment, while peaks in Rb/Sr and Ti/Ca could be signals for erosion related to events such as hurricanes and/or land use changes. Finally, high values of silt and clay, in conjunction with enhanced organics, Ti, Fe, K and P over the last couple centuries reflect historic-era deforestation and erosion. This study presents an excellent opportunity to further our understanding of the diverse relationships between ecosystem dymanics, climate, and anthropogenic forcings and adds to the growing inventory of paleoclimatological records in the Caribbean, improving the spatial distribution of such studies, and ultimately improving our understanding of the driving forces of both short- and long-term climate variability.

This work deals with the use of waste materials in the development of new industrial floors. The main task of this work is to choose a suitable waste materials, and design a new material using such materials, while achieving the required physico-mechanical properties. The aim of this work is also to verify the effects of process application, suitable microfiller and final coat and propose a suitable alternative industrial floors, which would not only be in terms of economic efficiency, but also in terms of ecological suitable replacement for commercial products.

Ce travail est une contribution à l'étude des conséquences mécaniques des transformations de phase à l'état solide dans les aciers, en particulier la plasticité de transformation (TRIP), en prenant en compte l'effet de la taille de grain austénitique (AGS). L'évolution de l'AGS a été étudiée sous différentes conditions d'austénitisation. Des essais de plasticité de transformation ont été conduits avec les mêmes conditions d'austénitisation afin d'observer l'évolution du TRIP avec l'AGS. Trois types de chargement mécanique sont considérés : la traction uniaxiale, la torsion uniaxiale et le cas biaxial de traction + torsion. Les résultats montrent que : i) le TRIP augmente avec l'AGS dans le cas de la traction ; ii) il est indépendant de l'AGS pour la torsion; iii) pour le cas du changement biaxial, le TRIP diminue légèrement. Ceci montre que les modèles décrivant le TRIP doivent être revus afin de prendre en compte l'AGS. / This work is a contribution to the study of mechanical consequences of solid-solid state phase transformations in steels, particularly the Transformation Induced Plasticity (TRIP), and the effect of the Austenite Grain Size (AGS). The evolution of AGS was studied taking into account different austenitization conditions. Then, TRIP tests were carried out with the same conditions to observe the evolution of TRIP with AGS. Three types of loading are considered: the uniaxial tension case, torsion case and biaxial tension and torsion case. The resuslts show that: i)the TRIP increase with AGS in the tensile case. ii) It is independant for the torsion case. iii) For the biaxial loading case, the TRIP decreases slightly. This shows that the micromechanical models describing the TRIP should be reviewed to take account of the AGS.