Developing and characterizing bulk metallic glasses for extreme applications

Metallic glasses have typically been treated as a “one size fits all” type of material. Every alloy is considered to have high strength, high hardness, large elastic limits, corrosion resistance, etc. However, similar to traditional crystalline materials, properties are strongly dependent upon the constituent elements, how it was processed, and the conditions under which it will be used. An important distinction which can be made is between metallic glasses and their composites. Charpy impact toughness measurements are performed to determine the effect processing and microstructure have on bulk metallic glass matrix composites (BMGMCs). Samples are suction cast, machined from commercial plates, and semi-solidly forged (SSF). The SSF specimens have been found to have the highest impact toughness due to the coarsening of the dendrites, which occurs during the semi-solid processing stages. Ductile to brittle transition (DTBT) temperatures are measured for a BMGMC. While at room temperature the BMGMC is highly toughened compared to a fully glassy alloy, it undergoes a DTBT by 250 K. At this point, its impact toughness mirrors that of the constituent glassy matrix. In the following chapter, BMGMCs are shown to have the capability of being capacitively welded to form single, monolithic structures. Shear measurements are performed across welded samples, and, at sufficient weld energies, are found to retain the strength of the parent alloy. Cross-sections are inspected via SEM and no visible crystallization of the matrix occurs.

Next, metallic glasses and BMGMCs are formed into sheets and eggbox structures are tested in hypervelocity impacts. Metallic glasses are ideal candidates for protection against micrometeorite orbital debris due to their high hardness and relatively low density. A flat single layer, flat BMG is compared to a BMGMC eggbox and the latter creates a more diffuse projectile cloud after penetration. A three tiered eggbox structure is also tested by firing a 3.17 mm aluminum sphere at 2.7 km/s at it. The projectile penetrates the first two layers, but is successfully contained by the third.

A large series of metallic glass alloys are created and their wear loss is measured in a pin on disk test. Wear is found to vary dramatically among different metallic glasses, with some considerably outperforming the current state-of-the-art crystalline material (most notably Cu₄₃Zr₄₃Al₇Be₇). Others, on the other hand, suffered extensive wear loss. Commercially available Vitreloy 1 lost nearly three times as much mass in wear as alloy prepared in a laboratory setting. No conclusive correlations can be found between any set of mechanical properties (hardness, density, elastic, bulk, or shear modulus, Poisson’s ratio, frictional force, and run in time) and wear loss. Heat treatments are performed on Vitreloy 1 and Cu₄₃Zr₄₃Al₇Be₇. Anneals near the glass transition temperature are found to increase hardness slightly, but decrease wear loss significantly. Crystallization of both alloys leads to dramatic increases in wear resistance. Finally, wear tests under vacuum are performed on the two alloys above. Vitreloy 1 experiences a dramatic decrease in wear loss, while Cu₄₃Zr₄₃Al₇Be₇ has a moderate increase. Meanwhile, gears are fabricated through three techniques: electrical discharge machining of 1 cm by 3 mm cylinders, semisolid forging, and copper mold suction casting. Initial testing finds the pin on disk test to be an accurate predictor of wear performance in gears.

The final chapter explores an exciting technique in the field of additive manufacturing. Laser engineered net shaping (LENS) is a method whereby small amounts of metallic powders are melted by a laser such that shapes and designs can be built layer by layer into a final part. The technique is extended to mixing different powders during melting, so that compositional gradients can be created across a manufactured part. Two compositional gradients are fabricated and characterized. Ti 6Al¬ 4V to pure vanadium was chosen for its combination of high strength and light weight on one end, and high melting point on the other. It was inspected by cross-sectional x-ray diffraction, and only the anticipated phases were present. 304L stainless steel to Invar 36 was created in both pillar and as a radial gradient. It combines strength and weldability along with a zero coefficient of thermal expansion material. Only the austenite phase is found to be present via x-ray diffraction. Coefficient of thermal expansion is measured for four compositions, and it is found to be tunable depending on composition.

Continuous stochastic processes

A general review of stochastic processes is given in the introduction; definitions, properties and a rough classification are presented together with the position and scope of the author's work as it fits into the general scheme.

The first section presents a brief summary of the pertinent analytical properties of continuous stochastic processes and their probability-theoretic foundations which are used in the sequel.

The remaining two sections (II and III), comprising the body of the work, are the author's contribution to the theory. It turns out that a very inclusive class of continuous stochastic processes are characterized by a fundamental partial differential equation and its adjoint (the Fokker-Planck equations). The coefficients appearing in those equations assimilate, in a most concise way, all the salient properties of the process, freed from boundary value considerations. The writer’s work consists in characterizing the processes through these coefficients without recourse to solving the partial differential equations.

First, a class of coefficients leading to a unique, continuous process is presented, and several facts are proven to show why this class is restricted. Then, in terms of the coefficients, the unconditional statistics are deduced, these being the mean, variance and covariance. The most general class of coefficients leading to the Gaussian distribution is deduced, and a complete characterization of these processes is presented. By specializing the coefficients, all the known stochastic processes may be readily studied, and some examples of these are presented; viz. the Einstein process, Bachelier process, Ornstein-Uhlenbeck process, etc. The calculations are effectively reduced down to ordinary first order differential equations, and in addition to giving a comprehensive characterization, the derivations are materially simplified over the solution to the original partial differential equations.

In the last section the properties of the integral process are presented. After an expository section on the definition, meaning, and importance of the integral process, a particular example is carried through starting from basic definition. This illustrates the fundamental properties, and an inherent paradox. Next the basic coefficients of the integral process are studied in terms of the original coefficients, and the integral process is uniquely characterized. It is shown that the integral process, with a slight modification, is a continuous Markoff process.

The elementary statistics of the integral process are deduced: means, variances, and covariances, in terms of the original coefficients. It is shown that an integral process is never temporally homogeneous in a non-degenerate process.

Finally, in terms of the original class of admissible coefficients, the statistics of the integral process are explicitly presented, and the integral process of all known continuous processes are specified.

A study of the proposed Diamond Creek Reservoir

Politically the Colorado river is an interstate as well as an international stream. Physically the basin divides itself distinctly into three sections. The upper section from head waters to the mouth of San Juan comprises about 40 percent of the total of the basin and affords about 87 percent of the total runoff, or an average of about 15 000 000 acre feet per annum. High mountains and cold weather are found in this section. The middle section from the mouth of San Juan to the mouth of the Williams comprises about 35 percent of the total area of the basin and supplies about 7 percent of the annual runoff. Narrow canyons and mild weather prevail in this section. The lower third of the basin is composed of mainly hot arid plains of low altitude. It comprises some 25 percent of the total area of the basin and furnishes about 6 percent of the average annual runoff.

The proposed Diamond Creek reservoir is located in the middle section and is wholly within the boundary of Arizona. The site is at the mouth of Diamond Creek and is only 16 m. from Beach Spring, a station on the Santa Fe railroad. It is solely a power project with a limited storage capacity. The dam which creats the reservoir is of the gravity type to be constructed across the river. The walls and foundation are of granite. For a dam of 290 feet in height, the back water will be about 25 m. up the river.

The power house will be placed right below the dam perpendicular to the axis of the river. It is entirely a concrete structure. The power installation would consist of eighteen 37 500 H.P. vertical, variable head turbines, directly connected to 28 000 kwa. 110 000 v. 3 phase, 60 cycle generators with necessary switching and auxiliary apparatus. Each unit is to be fed by a separate penstock wholly embedded into the masonry.

Concerning the power market, the main electric transmission lines would extend to Prescott, Phoenix, Mesa, Florence etc. The mining regions of the mountains of Arizona would be the most adequate market. The demand of power in the above named places might not be large at present. It will, from the observation of the writer, rapidly increase with the wonderful advancement of all kinds of industrial development.

All these things being comparatively feasible, there is one difficult problem: that is the silt. At the Diamond Creek dam site the average annual silt discharge is about 82 650 acre feet. The geographical conditions, however, will not permit silt deposites right in the reservoir. So this design will be made under the assumption given in Section 4.

The silt condition and the change of lower course of the Colorado are much like those of the Yellow River in China. But one thing is different. On the Colorado most of the canyon walls are of granite, while those on the Yellow are of alluvial loess: so it is very hard, if not impossible, to get a favorable dam site on the lower part. As a visitor to this country, I should like to see the full development of the Colorado: but how about THE YELLOW!

Argumentação na mídia impressa: textos opinativos dO Globo na década de 1940 e na atualidade

A tese tem por objetivo uma análise da argumentação em colunas de opinião, fazendo um paralelo entre dois momentos de um tradicional jornal brasileiro, O Globo. Dessa forma, analisamos textos opinativos dos períodos de 1947 e 2007 um intervalo, portanto, de 60 anos. Realizamos uma comparação entre esses dois períodos, a fim de estabelecer semelhanças e contrastes no que diz respeito à construção do texto argumentativo. Ao todo, foram selecionados para esse estudo comparativo um total de cinqüenta textos vinte e cinco de 1947 e vinte e cinco de 2007. Foram elencados para essa análise três elementos a fim de verificar a argumentação do jornal nas duas épocas, a saber: a seleção vocabular a serviço da argumentação, o uso dos tempos verbais e a pontuação. Após uma análise quantitativa e qualitativa desses três elementos, também apresentamos algumas considerações acerca do ensino da argumentação na escola, com algumas sugestões de atividades para os professores de Língua Portuguesa

Enhancement of three-photon absorption cross-sections in a novel class of symmetrical charge transfer fluorene-based molecules

The three-photon absorption effect (3PA) of two novel symmetrical charge transfer fluorene-based molecules (abbreviated as BASF and BMOSF) has been determined by using a Q-switched Nd:YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 84 x 10(-78) and 114 x 10(-78) cm(6) s(2), respectively. The geometries and electronic excitations of these two molecules are systematically studied by PM3 and ZINDO/S methods. The relationships between 3PA cross-sections and intramolecular charge transfer are discussed micromechanically. The experimental and theoretical results have shown that the larger intramolecular charge transfer, which was characterized by the charge density difference between the ground state (SO) and the first excited state (S-I), the greater enhancement of the 3PA cross-sections. (c) 2005 Elsevier B.V. All rights reserved.

Os neologismos na coluna Gente Boa: um estudo lexicográfico

Este trabalho traça um resumido perfil do colunismo social no Brasil, aborda a linguagem característica dessas colunas, conceitua neologismo/neologia através das obras lexicográficas brasileiras e se encerra com o glossário. O ponto que pretende desenvolver focaliza o inventário lexical produzido pelos escritores de colunas sociais, especificamente os textos da coluna Gente Boa, assinada por Joaquim Ferreira dos Santos e publicada diariamente no jornal O Globo, o que se associa a aspectos semânticos, discursivos, gramaticais e estilísticos da língua portuguesa. Para isso, utiliza como corpus adequado para o levantamento lexicográfico desse registro os textos escritos publicados na imprensa, que se destinam a retratar uma realidade social bastante cobiçada.

A survey of river habitats on the River Lune

A survey of the River Lune using River Habitat Survey (RHS) was carried out at 103 sections in February/March 99, to which were added 37 sites surveyed between 1994 -1996. Summary statistics were produced on the distribution and extent of flow features (e.g. riffles, pools, rapids etc.), substrate types, tree and associated features and bank profiles. Information on land-use and management was also included in the analyses. A Habitat Modification Score (HMS) describing the level of habitat modification was derived for each site and compared to the whole reference network and to rivers of similar types in Britain. The HMS shows that more than 70% of the sites on the catchment are predominantly unmodified and very few sites are significantly modified. Highly modified sites are concentrated in the urban areas and on the tributaries.

Do humor da crônica à crônica de humor

Com base no pressuposto de que o humor é um fenômeno regularmente presente em crônicas, esta tese pretende investigar as origens dessa relação. Por que motivo leitores diversos, estudiosos das Letras e do Jornalismo são categóricos nessa associação? Além disso, se o humor constitui traço marcante do gênero, como se caracterizam as estratégias que o possibilitam? Para que essas questões sejam respondidas, apresentamos a trajetória do fenômeno humorístico nas crônicas anteriores e posteriores à chegada da imprensa no Brasil. Ademais, com corpus oriundo do jornal O Globo, trabalhamos com a teoria semiolinguística do discurso, especificamente com o contrato de comunicação e com os modos de organização do texto. Nosso objetivo geral, em suma, é verificar até que ponto procedimentos discursivos vários podem explicar o funcionamento do humor em crônicas jornalísticas contemporâneas, contribuindo para que elas se tornem um ícone de sedução dos cadernos dos jornais, transmutando-se em colunas de entretenimento

Enquadrando a esfera pública: a controvèrsia das cotas raciais na imprensa

As investigações em torno da atuação política da imprensa costumam partir de duas posturas teóricas opostas. De um lado, alguns analistas enfatizam a importância da imprensa para a constituição de uma esfera pública nas democracias modernas. Desse prisma, ela seria encarregada de viabilizar o debate público e submeter ao escrutínio da sociedade as decisões estatais. Do outro lado, uma perspectiva mais cética defende que a imprensa não pode ser tomada como um pilar da esfera pública. Suas rotinas e estruturas a tornariam uma instância de manipulação retórica incompatível com o ideal moderno de um público deliberativo. Contudo, para além dessas oposições é importante notar que o ideal de uma deliberação pública mediada pela imprensa tem funcionado historicamente como um discurso de legitimação para a própria imprensa. Partindo da premissa de que a ideia de esfera pública é uma categoria política, esta pesquisa pretende entender de que modo alguns jornais se servem de uma dada concepção de esfera pública para se autolegitimarem enquanto pilares do debate público democrático. Através do estudo da maneira como a grande imprensa brasileira lidou com o tema das ações afirmativas raciais no ensino superior, este trabalho mostra como determinados enquadramentos midiáticos serviram para que a imprensa reivindicasse para si o status de esfera pública de debate do tema. A pesquisa se baseou numa análise de todos os textos sobre as ações afirmativas raciais no ensino superior publicados entre 2001 e 2009 nos dois principais jornais brasileiros: O Globo e Folha de S. Paulo. No total, 1.831 textos de diferentes tipos (reportagens, artigos, colunas, editoriais, cartas de leitores etc.) foram compilados e analisados a partir de Programas Computacionais de Codificação Assistida de Dados Qualitativos (CAQDAS, na sigla anglófona). A análise indica que ambos os jornais promoveram uma dramatização pública da controvérsia ao organizarem as discussões em torno das ações afirmativas raciais de acordo com determinados modelos de esfera pública. Tal dramatização não somente possibilitou que a imprensa influenciasse os destinos das ações afirmativas raciais no país, apresentando-as como medidas essencialmente polêmicas, mas também limitou a cobertura a estruturas narrativas padronizadas

Avaliação de ligações entre vigas de perfil I ou H e colunas em perfis tubulares circulares.

Considerando uma nova realidade com o incremento do uso de perfis tubulares, este trabalho apresenta uma análise de ligações soldadas tipo T com perfis tubulares circulares (CHS) para a coluna e perfil I ou H para a viga com flexão no plano, efetuado com base nas normas EC3, CIDECT e a NBR 16239 comparando com o critério de deformação limite, proposto por Lu et al., através de um modelo em elementos finitos desenvolvido no programa Ansys versão 12.0. A não-linearidade geométrica foi introduzida no modelo através da Formulação de Lagrange Atualizado. Com base nos resultados numéricos avaliados foram traçadas curvas momento-rotação para cada modelo com o objetivo de obter o momento resistente de cada ligação bem como a classificação da ligação quanto a capacidade de rotação, a influência dos parâmetros geométricos em cada modelo e o modo de falha que controlará o dimensionamento da ligação.