The significance and determination by image analysis of microcrack density in hard chromium plating

It is well known that the microcrack density is a fundamental parameter in hard chromium electroplating. The chemical and mechanical properties of this coating are widely dependent on its microcrack density. In this paper a simple image analysis procedure to determine microcrack density is presented in order to demonstrate it as a fundamental tool to estimate the fatigue, corrosion and wear behavior, as well as the residual stress field of a coated component. For this purpose, the image analysis procedure was carried out on two kinds of hard chromium plating - one called accelerated (high velocity of deposition and fluoride-free) and the other conventional (with fluoride). The coatings were applied on samples of AISI 4340 aeronautical steel, which is widely used in aircraft landing gear components. To characterize the practical significance of this study, the microcrack density results were related to the fatigue, wear and corrosion behavior from previous study and to the residual stress field in the coatings.

Estratégias adaptativas da locomoção na ultrapassagem de obstáculo móvel

Pós-graduação em Ciências da Motricidade - IBRC

Modelagem sísmica via métodos das diferenças finitas: caso da bacia do Amazonas

Este trabalho tem por objetivo apresentar os resultados da modelagem sísmica em meios com fortes descontinuidades de propriedades físicas, com ênfase na existência de difrações e múltiplas reflexões, tendo a Bacia do Amazonas como referência à modelagem. As condições de estabilidade e de fronteiras utilizadas no cálculo do campo de ondas sísmicas foram analisadas numericamente pelo método das diferenças finitas, visando melhor compreensão e controle da interpretação de dados sísmicos. A geologia da Bacia do Amazonas é constituída por rochas sedimentares depositadas desde o Ordoviciano até o Recente que atingem espessuras da ordem de 5 km. Os corpos de diabásio, presentes entre os sedimentos paleozóicos, estão dispostos na forma de soleiras, alcançam espessuras de centenas de metros e perfazem um volume total de aproximadamente 90000 Km³. A ocorrência de tais estruturas é responsável pela existência de reflexões múltiplas durante a propagação da onda sísmica o que impossibilita melhor interpretação dos horizontes refletores que se encontram abaixo destas soleiras. Para representar situações geológicas desse tipo foram usados um modelo (sintético) acústico de velocidades e um código computacional elaborado via método das diferenças finitas com aproximação de quarta ordem no espaço e no tempo da equação da onda. A aplicação dos métodos de diferenças finitas para o estudo de propagação de ondas sísmicas melhorou a compreensão sobre a propagação em meios onde existem heterogeneidades significativas, tendo como resultado boa resolução na interpretação dos eventos de reflexão sísmica em áreas de interesse. Como resultado dos experimentos numéricos realizados em meio de geologia complexa, foi observada a influência significativa das reflexões múltiplas devido à camada de alta velocidade, isto provocou maior perda de energia e dificultou a interpretação dos alvos. Por esta razão recomenda-se a integração de dados de superfície com os de poço, com o objetivo de obter melhor imagem dos alvos abaixo das soleiras de diabásio.

Comportamento mecânico do aço AISI 4340 revestido com WC-CrCNi; WC-10Ni; Ni-20Cr; Ni-Cr-B-Si-Fe; Cr3C2-NiCr pelo processo HVOF

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Modelagem sísmica por diferenças finitas em meios bidimensionais com difratores

Este trabalho tem por objetivo a modelagem sísmica em meios com fortes descontinuidades de propriedades físicas, com ênfase na existência de difrações. Como parte deste estudo foi feita a análise numérica visando as condições de estabilidade e de fronteiras utilizadas no cálculo do campo de ondas sísmicas. Para a validação do programa de diferenças finitas foi feita a comparação cinemática com a Teoria do Raio para um modelo simples. O motivo deste estudo é ter uma melhor compreensão e controle sobre os problemas de modelagem, visando contribuir para a solução de problemas na interpretação de dados sísmicos. Segundo vários autores na literatura geológica, Derby (1877), Evans (1906), Paiva (1929) e Moura (1938). A Bacia do Amazonas é constituída por rochas sedimentares depositadas desde o Ordoviciano até o recente, atingindo espessuras da ordem de 5 km. Os corpos de diabásio, presentes entre os sedimentos paleozóicos, estão dispostos na forma de soleiras, alcançando espessuras de centenas de metros, perfazendo um volume total de 90.000 quilômetros cúbicos. A ocorrência de tais estruturas é responsável pela existência de reflexões múltiplas durante a propagação da onda sísmica, impossibilitando uma melhor interpretação dos horizontes refletores que se encontram abaixo das soleiras. Para representar situações geológicas desse tipo foi usado um modelo acústico de velocidades. Para o cálculo dos sismogramas foi utilizado um programa de diferenças finitas com aproximação de quarta ordem da equação da onda acústica no espaço e no tempo. As aplicações dos métodos de diferenças finitas para o estudo de propagação de ondas sísmicas têm melhorado a compreensão sobre a propagação em meios onde existem heterogeneidades significativas, tendo como resultado boa resolução na interpretação dos eventos de reflexão sísmica em áreas de interesse. Como resultado dos experimentos numéricos realizados em meio de geologia complexa, foi observado a influência significativa das múltiplas devido a camada de alta velocidade, o que faz com que haja maior perda de energia dificultando a interpretação dos alvos. Por esta razão recomendo a integração de dados de superfície com os dados de poço, com o objetivo de se obter uma melhor imagem dos alvos abaixo das soleiras de diabásio.

Estudo da resistência ao desgaste e à corrosão de revestimentos metálico-cerâmicos aplicados na liga AA7050 mediante aspersão térmica oxicombustível de alta velocidade (HVOF)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Inibição da divisão celular em Xanthomonas citri subsp. citri e Bacillus subtilis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Caracterização do aço inoxidável ASTM A743 CA6NM e do seu revestimento de WC-10Co-4Cr aspergido termicamente por HVOF

Pós-graduação em Engenharia Mecânica - FEG

Evolução tectônica e estratigráfica das bacias da margem continental do Uruguai

Pós-graduação em Geociências e Meio Ambiente - IGCE

Impactos causados por vibrações mecânicas em chapas de alumínio no processo de laminação a frio

This paper purpose is to analyze one of the main problems faced by cold rolling industry of the current time, the mechanical vibration. Factors such as strips with high velocity in order to increase the productivity and thickness becoming thinner and thinner cause the vibrations to be present at all times during rolling. These market requirements also drive the industry for technology development and thus bring the challenges that the operation of a new modern equipment and more powerful. The initial purpose is to analyze the forces that cause vibration in a rolling mill type four high with two stands, where is desirable to identify the origins of these vibrational forces to make possible dismiss them or at least control its intensity, in order to prevent damage in the rolling mill and ensure product quality to the customer. For it, will be used instruments to record and store the vibrations that occur during the lamination process. With this data will be able to analyze the characteristics of the vibrations and act at your elimination. At the end of the work is expected to demonstrate how important the critical view of the engineer in the analysis of graphics combined with the calculations of the natural vibration frequency and engagement of key parts of the laminator. With these two tools at hand, will be possible to increase the productivity of the rolling mill and act preventively in maintenance, thereby reducing your downtime and increasing its performance and efficiency

Impactos causados por vibrações mecânicas em chapas de alumínio no processo de laminação a frio

This paper purpose is to analyze one of the main problems faced by cold rolling industry of the current time, the mechanical vibration. Factors such as strips with high velocity in order to increase the productivity and thickness becoming thinner and thinner cause the vibrations to be present at all times during rolling. These market requirements also drive the industry for technology development and thus bring the challenges that the operation of a new modern equipment and more powerful. The initial purpose is to analyze the forces that cause vibration in a rolling mill type four high with two stands, where is desirable to identify the origins of these vibrational forces to make possible dismiss them or at least control its intensity, in order to prevent damage in the rolling mill and ensure product quality to the customer. For it, will be used instruments to record and store the vibrations that occur during the lamination process. With this data will be able to analyze the characteristics of the vibrations and act at your elimination. At the end of the work is expected to demonstrate how important the critical view of the engineer in the analysis of graphics combined with the calculations of the natural vibration frequency and engagement of key parts of the laminator. With these two tools at hand, will be possible to increase the productivity of the rolling mill and act preventively in maintenance, thereby reducing your downtime and increasing its performance and efficiency

Type Ia Supernovae : Homogeneity and Diversity

The use of type Ia supernovae as distance estimators has shown that about 75% of the energy content of the universe has a negative equation of state parameter and thus, drives the acceleration of the universe. Constraining the exact nature of this energy is one of the main goals in cosmology. As the statistics of observed high-redshift supernovae increases, systematic effects become the limiting factor to pursue such investigations, thus deeper understanding of the physical properties of SNe is of great importance. In this thesis we investigate spectral homogeneity and diversity of local and high redshift supernovae. Special emphasis has been given to the analysis of optical spectra of local peculiar supernovae 1999aa and 1999ac. The study of the spectra of SN 1999aa pointed out that this SN could be a link between the extreme peculiar SN 1991T and normal SNe. Moreover, the identification of a high velocity component of Ca II and possibly of a low velocity component of C III suggests some degree of asphericity in the ejecta of this supernova. Evidence for a deflagration of a C+O white dwarf was found in the early spectra of SN 1999ac. The spectral proprieties of a vast sample of local SNe are also studied by means of newly introduced spectral indicators. These were used to possibly improve the intrinsic spread of SN peak magnitudes to 0.15 mag, independently of light curve parameters. The first quantitative comparison between local and high redshift supernova is carried out. No evidence for extreme peculiar sub-luminous SNe was found in our data set including 13 SNe with redshift range z=0.279-0.912. Furthermore, SN2002fd (z=0.279) was found to show spectral characteristics similar to SN 1991T/SN 1999aa-like supernovae. We also present a feasibility study of the Hubble diagram in rest frame I-band up to z~0.5, and show the possibility to probe the presence of intergalactic dust, which could possibly mimic the effect of dark energy in the Hubble diagram.

Mesoscale dynamics and boundary-layer structure in topographically forced low-level jets

Two types of mesoscale wind-speed jet and their effects on boundary-layer structure were studied. The first is a coastal jet off the northern California coast, and the second is a katabatic jet over Vatnajökull, Iceland. Coastal regions are highly populated, and studies of coastal meteorology are of general interest for environmental protection, fishing industry, and for air and sea transportation. Not so many people live in direct contact with glaciers but properties of katabatic flows are important for understanding glacier response to climatic changes. Hence, the two jets can potentially influence a vast number of people. Flow response to terrain forcing, transient behavior in time and space, and adherence to simplified theoretical models were examined. The turbulence structure in these stably stratified boundary layers was also investigated. Numerical modeling is the main tool in this thesis; observations are used primarily to ensure a realistic model behavior. Simple shallow-water theory provides a useful framework for analyzing high-velocity flows along mountainous coastlines, but for an unexpected reason. Waves are trapped in the inversion by the curvature of the wind-speed profile, rather than by an infinite stability in the inversion separating two neutral layers, as assumed in the theory. In the absence of blocking terrain, observations of steady-state supercritical flows are not likely, due to the diurnal variation of flow criticality. In many simplified models, non-local processes are neglected. In the flows studied here, we showed that this is not always a valid approximation. Discrepancies between simulated katabatic flow and that predicted by an analytical model are hypothesized to be due to non-local effects, such as surface inhomogeneity and slope geometry, neglected in the theory. On a different scale, a reason for variations in the shape of local similarity scaling functions between studies is suggested to be differences in non-local contributions to the velocity variance budgets.

Accretion disk winds in active galactic nuclei: an X-ray view

This Thesis focuses on the X-ray study of the inner regions of Active Galactic Nuclei, in particular on the formation of high velocity winds by the accretion disk itself. Constraining AGN winds physical parameters is of paramount importance both for understanding the physics of the accretion/ejection flow onto supermassive black holes, and for quantifying the amount of feedback between the SMBH and its environment across the cosmic time. The sources selected for the present study are BAL, mini-BAL, and NAL QSOs, known to host high-velocity winds associated to the AGN nuclear regions. Observationally, a three-fold strategy has been adopted: - substantial samples of distant sources have been analyzed through spectral, photometric, and statistical techniques, to gain insights into their mean properties as a population; - a moderately sized sample of bright sources has been studied through detailed X-ray spectral analysis, to give a first flavor of the general spectral properties of these sources, also from a temporally resolved point of view; - the best nearby candidate has been thoroughly studied using the most sophisticated spectral analysis techniques applied to a large dataset with a high S/N ratio, to understand the details of the physics of its accretion/ejection flow. There are three main channels through which this Thesis has been developed: - [Archival Studies]: the XMM-Newton public archival data has been extensively used to analyze both a large sample of distant BAL QSOs, and several individual bright sources, either BAL, mini-BAL, or NAL QSOs. - [New Observational Campaign]: I proposed and was awarded with new X-ray pointings of the mini-BAL QSOs PG 1126-041 and PG 1351+640 during the XMM-Newton AO-7 and AO-8. These produced the biggest X-ray observational campaign ever made on a mini-BAL QSO (PG 1126-041), including the longest exposure so far. Thanks to the exceptional dataset, a whealth of informations have been obtained on both the intrinsic continuum and on the complex reprocessing media that happen to be in the inner regions of this AGN. Furthermore, the temporally resolved X-ray spectral analysis field has been finally opened for mini-BAL QSOs. - [Theoretical Studies]: some issues about the connection between theories and observations of AGN accretion disk winds have been investigated, through theoretical arguments and synthetic absorption line profiles studies.

Three dimensional seismic imaging and earthquake locations in a complex, segmented fault region in Southern Apennines (Italy)

The southern Apennines of Italy have been experienced several destructive earthquakes both in historic and recent times. The present day seismicity, characterized by small-to-moderate magnitude earthquakes, was used like a probe to obatin a deeper knowledge of the fault structures where the largest earthquakes occurred in the past. With the aim to infer a three dimensional seismic image both the problem of data quality and the selection of a reliable and robust tomographic inversion strategy have been faced. The data quality has been obtained to develop optimized procedures for the measurements of P- and S-wave arrival times, through the use of polarization filtering and to the application of a refined re-picking technique based on cross-correlation of waveforms. A technique of iterative tomographic inversion, linearized, damped combined with a strategy of multiscale inversion type has been adopted. The retrieved P-wave velocity model indicates the presence of a strong velocity variation along a direction orthogonal to the Apenninic chain. This variation defines two domains which are characterized by a relatively low and high velocity values. From the comparison between the inferred P-wave velocity model with a portion of a structural section available in literature, the high velocity body was correlated with the Apulia carbonatic platforms whereas the low velocity bodies was associated to the basinal deposits. The deduced Vp/Vs ratio shows that the ratio is lower than 1.8 in the shallower part of the model, while for depths ranging between 5 km and 12 km the ratio increases up to 2.1 in correspondence to the area of higher seismicity. This confirms that areas characterized by higher values are more prone to generate earthquakes as a response to the presence of fluids and higher pore-pressures.