Analysis and optimization of stress wave propagation in two-dimensional granular crystals with defects

Granular crystals are compact periodic assemblies of elastic particles in Hertzian contact whose dynamic response can be tuned from strongly nonlinear to linear by the addition of a static precompression force. This unique feature allows for a wide range of studies that include the investigation of new fundamental nonlinear phenomena in discrete systems such as solitary waves, shock waves, discrete breathers and other defect modes. In the absence of precompression, a particularly interesting property of these systems is their ability to support the formation and propagation of spatially localized soliton-like waves with highly tunable properties. The wealth of parameters one can modify (particle size, geometry and material properties, periodicity of the crystal, presence of a static force, type of excitation, etc.) makes them ideal candidates for the design of new materials for practical applications. This thesis describes several ways to optimally control and tailor the propagation of stress waves in granular crystals through the use of heterogeneities (interstitial defect particles and material heterogeneities) in otherwise perfectly ordered systems. We focus on uncompressed two-dimensional granular crystals with interstitial spherical intruders and composite hexagonal packings and study their dynamic response using a combination of experimental, numerical and analytical techniques. We first investigate the interaction of defect particles with a solitary wave and utilize this fundamental knowledge in the optimal design of novel composite wave guides, shock or vibration absorbers obtained using gradient-based optimization methods.

Collective behavior of asperities as a model for friction and adhesion

Understanding friction and adhesion in static and sliding contact of surfaces is important in numerous physical phenomena and technological applications. Most surfaces are rough at the microscale, and thus the real area of contact is only a fraction of the nominal area. The macroscopic frictional and adhesive response is determined by the collective behavior of the population of evolving and interacting microscopic contacts. This collective behavior can be very different from the behavior of individual contacts. It is thus important to understand how the macroscopic response emerges from the microscopic one. In this thesis, we develop a theoretical and computational framework to study the collective behavior. Our philosophy is to assume a simple behavior of a single asperity and study the collective response of an ensemble. Our work bridges the existing well-developed studies of single asperities with phenomenological laws that describe macroscopic rate-and-state behavior of frictional interfaces. We find that many aspects of the macroscopic behavior are robust with respect to the microscopic response. This explains why qualitatively similar frictional features are seen for a diverse range of materials. We first show that the collective response of an ensemble of one-dimensional independent viscoelastic elements interacting through a mean field reproduces many qualitative features of static and sliding friction evolution. The resulting macroscopic behavior is different from the microscopic one: for example, even if each contact is velocity-strengthening, the macroscopic behavior can be velocity-weakening. The framework is then extended to incorporate three-dimensional rough surfaces, long- range elastic interactions between contacts, and time-dependent material behaviors such as viscoelasticity and viscoplasticity. Interestingly, the mean field behavior dominates and the elastic interactions, though important from a quantitative perspective, do not change the qualitative macroscopic response. Finally, we examine the effect of adhesion on the frictional response as well as develop a force threshold model for adhesion and mode I interfacial cracks.

Topological strings, double affine Hecke algebras, and exceptional knot homology

In this thesis, we consider two main subjects: refined, composite invariants and exceptional knot homologies of torus knots. The main technical tools are double affine Hecke algebras ("DAHA") and various insights from topological string theory.

In particular, we define and study the composite DAHA-superpolynomials of torus knots, which depend on pairs of Young diagrams and generalize the composite HOMFLY-PT polynomials from the full HOMFLY-PT skein of the annulus. We also describe a rich structure of differentials that act on homological knot invariants for exceptional groups. These follow from the physics of BPS states and the adjacencies/spectra of singularities associated with Landau-Ginzburg potentials. At the end, we construct two DAHA-hyperpolynomials which are closely related to the Deligne-Gross exceptional series of root systems.

In addition to these main themes, we also provide new results connecting DAHA-Jones polynomials to quantum torus knot invariants for Cartan types A and D, as well as the first appearance of quantum E6 knot invariants in the literature.

O livro didático de alfabetização na era do letramento: uma análise crítica

Essa pesquisa insere-se em um contexto de muitas discussões acerca da qualidade da educação no Brasil, motivadas principalmente pelos maus resultados atingidos pelo país em exames internacionais. Os constantes debates têm dado margem, inclusive, a movimentos que, culpando os PCNs pelo fracasso generalizado na alfabetização, clamam pela volta de um ensino tradicional. De fato, apesar das imensas contribuições trazidas pelos estudos que embasam os PCNs, apenas a sua institucionalização não garantiu a ocorrência de mudanças efetivas na educação. Principalmente no campo da alfabetização, interpretações equivocadas levaram, por exemplo, ao desencadeamento de um processo de desmetodização do ensino, caracterizado pela exclusão total, nos últimos anos, das questões de ordem metodológica das pautas de discussões. Tal fenômeno, denominado por Soares (2004) de desinvenção da alfabetização, e também abordado por outros pesquisadores (cf. MORAIS, 2006; FRADE, 2003; CARVALHO, 2007), obviamente, acabou se refletindo nos novos livros didáticos, avaliados e recomendados pelo MEC. O problema é que os novos livros parecem não estar satisfazendo às necessidades dos docentes. Estudos recentes têm revelado tanto uma insatisfação desses profissionais em relação a tais materiais quanto a manutenção de práticas didáticas preconizadas pelos métodos tradicionais (Cf. BRITO et al., 2007; SILVA 2008; e MORAIS E ALBURQUERQUE, 2008). Considerando-se que: (a) hoje já se reconhece que os processos de alfabetização e letramento são complementares e indissociáveis (SOARES, 2004); (b) na realidade brasileira os livros didáticos ainda são recursos centrais no trabalho em sala de aula; (c) as obras são avaliadas a partir de rígidos critérios, alinhados às mais recentes teorias; e (d), a disponibilização gratuita desses materiais demanda um alto investimento do governo, o objetivo deste estudo foi analisar criticamente um dos livros didáticos de alfabetização do PNLD/2010 (L.E.R., Leitura, escrita e reflexão 1 ano, FTD), na tentativa de levantar pistas sobre os possíveis motivos dessa não-adesão dos docentes aos novos livros. Para tanto, foi realizada uma análise documental crítica, de abordagem qualitativa, que observou na obra os seguintes aspectos: o espaço dedicado ao ensino do sistema de escrita alfabética; a existência de articulação desse trabalho com o de letramento; a coerência entre a orientação pedagógica declarada e as atividades propostas; e a clareza e objetividade das instruções e sugestões fornecidas ao docente. As análises realizadas mostram, entre os dados mais relevantes, que o livro estudado ainda dedica um espaço muito reduzido às atividades de ensino do sistema de escrita e não apresenta uma articulação satisfatória entre essas atividades e àquelas voltadas ao letramento, corroborando dados de outros estudos, aqui já mencionados. Esses resultados podem ser indicativos de que os critérios estipulados para a avaliação desses livros precisariam ser revistos de forma que atendessem mais equilibradamente tanto aos objetivos da alfabetização e do letramento quanto às necessidades da prática docente. Para um maior aprofundamento deste estudo considero que, futuramente, seus dados podem ser complementados por análises dos próprios docentes sobre o livro estudado, ou até mesmo por pesquisas sobre seu uso efetivo em sala de aula

Brincadeira e arte: patrimônio, formação cultural e samba de coco em Pernambuco

Esta proposta de estudo aborda questões relativas a políticas públicas de cultura. Tem por referente o samba de coco nas comunidades afrodescendentes de Castainho e Atoleiros, situadas nos municípios de Garanhuns e Caetés, do agreste de Pernambuco, região que se constitui parcela de território do antigo quilombo dos Palmares, um dos principais focos de resistência dos escravos negros do Brasil colonial, que se manteve incólume durante quase um século. Na região atribuída à existência do antigo quilombo estão vários grupos autointitulados remanescentes, que fazem dos ideais de força e resistência quilombola sua própria vida. O título do estudo é Brincadeira e arte: patrimônio, formação cultural e samba de coco em Pernambuco. O objetivo geral é relacionar o processo de criação em manifestações artísticas populares com as políticas institucionais empreendidas, numa perspectiva intercultural e transdisciplinar, tomando como referencial empírico a brincadeira de samba de coco nos municípios de Garanhuns e Caetés, em Pernambuco, respectivamente nas comunidades Sítio Castainho e Sítio Atoleiros, através da Banda Folclore Verde do Castainho e do Samba de Coco Santa Luzia. A ideia é viabilizar um estudo que se reporta ao conceito de patrimônio cultural étnico brasileiro, percebendo cultura como uma construção histórica da humanidade e compreendendo a manifestação artística como patrimônio imaterial. Trata-se de uma análise sobre grupos brincantes do chamado samba de coco como manifestação plural, de características diversificadas, que ambiciona influenciar políticas públicas destinadas a artistas populares ligados à música, ao canto, à dança e à literatura popular, encarnada em letras de canções, cujo conteúdo é repassado às novas gerações através da oralidade ou por ações de formação cultural, como iniciativas do poder público. Políticas públicas de cultura, patrimônio e formação cultural para preservação são as palavras-chave para identificação das condições atuais da relação entre artistas e gestão pública, considerando a perspectiva de educação não formal, no sentido atribuído pela UNESCO, referenciando-se em depoimentos como principal fonte. Conhecer algumas dimensões do imaginário mítico-simbólico que envolve produtores e gestores, é fundamento para o estudo, que se constitui a partir do levantamento, caracterização e análise da relação entre artistas e instituições de cultura, em diversas instâncias, considerando ideais de modernidade, permanências e transformações observadas no exercício, difusão e gestão da brincadeira. Os produtores do Povoado Atoleiros são criadores do samba de coco, brincadeira de adultos que se traduz em espaço de confraternização e comunhão e recebe interferência do poder público municipal, em Caetés, um dos municípios do entorno de Garanhuns, na periferia do qual está também o Sítio Castainho. Este, a partir de formas diversas de articulação, é contemplado por ações das gestões públicas municipal, estadual e federal, especificamente dentro do Festival de Inverno de Garanhuns FIG. A abordagem contempla a situação das duas comunidades, mas não elimina o reconhecimento de outros locais para a brincadeira do samba de coco e ações de preservação a ela direcionadas, como partes de um processo cultural que é também e necessariamente educativo e, em suas possibilidades de rupturas e continuidades, forma gerações.

Uma memória ímpar: a trajetória de Arthur Napoleão na sociabilidade musical de dois continentes (1843-1925)

Essa tese tem como objetivo primordial estudar a trajetória musical do pianista português Arthur Napoleão (1843-1925), desde a sua iniciação musical na cidade natal do Porto, até o falecimento no Rio de Janeiro em 1925. Discute-se aqui a relevância da inserção do pianista e de sua música nos meio sócios-culturais dos países da Europa e Américas, em cujas cidades se apresentou durante os primeiros quinze anos de sua carreira. Do mesmo modo, estuda-se também as circunstâncias da permanência do notável intérprete no Brasil, como imigrante radicado, desde 1868, bem como se deu a consolidação da sua nova perspectiva laboral no campo da música, como empreendedor e mediador cultural. E ainda por meio da organização de estabelecimentos comerciais voltados para a venda de pianos e partituras musicais, que se tornaram importantes espaços de sociabilidade musical na Corte, depois capital federal da República, ao longo de sua vida. As numerosas e variadas fontes aqui utilizadas são caudatárias do texto autobiográfico legado por Arthur Napoleão, de 1907. Essas "Memórias", ao mesmo tempo fonte de informação e objeto de estudo, possibilitam traçar, pelo exame vis-à-vis com a documentação restante, a trajetória artística de Arthur Napoleão, desde Portugal até o Brasil, no universo sócio-cultural em transformação, da segunda metade do século XIX ao primeiro quarto do XX.

Soft Flesh in Sablefish, Anoplopoma fimbria, of Southeastern Alaska: Relationships with Depth, Season, and Biochemistry

The condition of soft-textured flesh in commercially harvested sablefish, Anoplopoma fimbria, from southeastern Alaska was investigated by National Marine Fisheries Service (NMFS) scientists from the Alaska Fisheries Science Center’s Auke Bay Laboratories (ABL) in Alaska and the Northwest Fisheries Science Center in Seattle, Wash. Sablefish were sampled by longline, pot, and trawl at five sites around Chichagof Island at depths of 259–988 m in the summer of 1985 and at depths of 259–913 m in the winter of 1986. At the time of capture and data collection, sablefish were categorized as being “firm” or “soft” by visual and tactile examination, individually weighed, measured for length, and sexed. Subsamples of the fish were analyzed and linear regressions and analyses of variance were performed on both the summer (n = 242) and winter (n = 439) data for combinations of chemical and physical analyses, depth of capture, weight vs. length, flesh condition, gonad condition, and sex. We successfully identified and selected sablefish with firm- and soft-textured flesh by tactile and visual methods. Abundance of firm fish in catches varied by season: 67% in winter and 40% in summer. Winter catches may give a higher yield than summer catches. Abundance of firm fish catches also varied with depth. Firm fish were routinely found shallower than soft fish. The highest percentage of firm fish were found at depths less than 365 m in summer and at 365–730 m in winter, whereas soft fish were usually more abundant at depths greater than 731 m. Catches of firm fish declined with increasing depth. More than 80% of the fish caught during winter at depths between 365 and 730 m had firm flesh, but this declined to 48% at these depths in summer. Longlines and pots caught similar proportions of firm and soft fish with both gears catching more firm than soft fish. Trawls caught a higher proportion of soft fish compared to longlines and pots in winter. Chemical composition of “firm” and “soft” fish differed. On average “soft” fish had 14% less protein, 12% more lipid, and 3% less ash than firm fish. Cooked yields from sablefish with soft-textured flesh were 31% less than cooked yields from firm fish. Sablefish flesh quality (firmness) related significantly to the biochemistry of white muscle with respect to 11 variables. Summer fish of all flesh conditions averaged 6% heavier than winter fish. Regulating depth of fishing could increase the yield from catches, but the feasibility and benefits from this action will require further evaluation and study. Results of this study provide a basis for reducing the harvest of sablefish with soft flesh and may stimulate further research into the cause and effect relationship of the sablefish soft-flesh phenomenon.

The use of spatial impulse responses to characterise flexible forming processes with mobile tools

A novel test method for the characterisation of flexible forming processes is proposed and applied to four flexible forming processes: Incremental Sheet Forming (ISF), conventional spinning, the English wheel and power hammer. The proposed method is developed in analogy with time-domain control engineering, where a system is characterised by its impulse response. The spatial impulse response is used to characterise the change in workpiece deformation created by a process, but has also been applied with a strain spectrogram, as a novel way to characterise a process and the physical effect it has on the workpiece. Physical and numerical trials to study the effects of process and material parameters on spatial impulse response lead to three main conclusions. Incremental sheet forming is particularly sensitive to process parameters. The English wheel and power hammer are strongly similar and largely insensitive to both process and material parameters. Spinning develops in two stages and is sensitive to most process parameters, but insensitive to prior deformation. Finally, the proposed method could be applied to modelling, classification of existing and novel processes, product-process matching and closed-loop control of flexible forming processes. © 2012 Elsevier B.V.

Identifying cancer subtypes in glioblastoma by combining genomic, transcriptomic and epigenomic data

We present a nonparametric Bayesian method for disease subtype discovery in multi-dimensional cancer data. Our method can simultaneously analyse a wide range of data types, allowing for both agreement and disagreement between their underlying clustering structure. It includes feature selection and infers the most likely number of disease subtypes, given the data. We apply the method to 277 glioblastoma samples from The Cancer Genome Atlas, for which there are gene expression, copy number variation, methylation and microRNA data. We identify 8 distinct consensus subtypes and study their prognostic value for death, new tumour events, progression and recurrence. The consensus subtypes are prognostic of tumour recurrence (log-rank p-value of $3.6 \times 10^{-4}$ after correction for multiple hypothesis tests). This is driven principally by the methylation data (log-rank p-value of $2.0 \times 10^{-3}$) but the effect is strengthened by the other 3 data types, demonstrating the value of integrating multiple data types. Of particular note is a subtype of 47 patients characterised by very low levels of methylation. This subtype has very low rates of tumour recurrence and no new events in 10 years of follow up. We also identify a small gene expression subtype of 6 patients that shows particularly poor survival outcomes. Additionally, we note a consensus subtype that showly a highly distinctive data signature and suggest that it is therefore a biologically distinct subtype of glioblastoma. The code is available from https://sites.google.com/site/multipledatafusion/

Time-optimal control of a 3-level quantum system and its generalization to an n-level system

We solve the problem of steering a three-level quantum system from one eigen-state to another in minimum time and study its possible extension to the time-optimal control problem for a general n-level quantum system. For the three-level system we find all optimal controls by finding two types of symmetry in the problem: ℤ2 × S3 discrete symmetry and S1 continuous symmetry, and exploiting them to solve the problem through discrete reduction and symplectic reduction. We then study the geometry, in the same framework, which occurs in the time-optimal control of a general n-level quantum system. © 2007 IEEE.

Time-optimal control of a 3-level quantum system and its generalization

We solve the problem of steering a three-level quantum system from one eigen-state to another in minimum time and study its possible extension to the time-optimal control problem for a general n-level quantum system. For the three-level system we find all optimal controls by finding two types of symmetry in the problems: ℤ × S3 discrete symmetry and 51 continuous symmetry, and exploiting them to solve the problem through discrete reduction and symplectic reduction. We then study the geometry, in the same framework, which occurs in the time-optimal control of a general n-level quantum system. Copyright ©2007 Watam Press.

Tool-path design for metal spinning

Toolpath design in spinning is an open ended problem, with a large number of solutions, and remains an art acquired by practice. To be able to specify a toolpath without the need for experimental trials, further understanding of the process mechanics Is required. At the moment, the mechanics of the process Is not completely understood, due to the complex deformation and because long solution times required for accurate numerical modelling of the process Inhibit detailed study. This paper proposes and applies a new approach to modelling the process and aims to contribute to the understanding of process mechanics, In particular with respect to the mechanisms of failure and and to apply this understanding for toolpath design In spinning. A new approach to numerical modelling Is proposed and applied to Investigate the process. The findings suggest that there are two different causes and two different modes of wrinkling In spinning, depending on the stage In the process and direction of roller movement. A simple test Is performed to estimate the limits of wrinkling and provide a guideline for toolpath design In a typical spinning process. The results show that the required toolpath geometry in the early stages of the process is different from that In later stages. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA. Weinheim.

Nitrogen defects and ferromagnetism in Cr-doped dilute magnetic semiconductor AlN from first principles

High Curie temperature of 900 K has been reported in Cr-doped AlN diluted magnetic semiconductors prepared by various methods, which is exciting for spintronic applications. It is believed that N defects play important roles in achieving the high-temperature ferromagnetism in good samples. Motivated by these experimental advances, we use a full-potential density-functional-theory method and supercell approach to investigate N defects and their effects on ferromagnetism of (Al,Cr)N with N vacancies (V-N). We investigate the structural and electronic properties of V-N, single Cr atom, Cr-Cr atom pairs, Cr-V-N pairs, and so on. In each case, the most stable structure is obtained by comparing different atomic configurations optimized in terms of the total energy and the force on every atom, and then it is used to calculate the defect formation energy and study the electronic structures. Our total-energy calculations show that the nearest substitutional Cr-Cr pair with the two spins in parallel is the most favorable and the nearest Cr-V-N pair makes a stable complex. Our formation energies indicate that V-N regions can be formed spontaneously under N-poor condition because the minimal V-N formation energy equals -0.23 eV or Cr-doped regions with high enough concentrations can be formed under N-rich condition because the Cr formation energy equals 0.04 eV, and hence real Cr-doped AlN samples are formed by forming some Cr-doped regions and separated V-N regions and through subsequent atomic relaxation during annealing. Both of the single Cr atom and the N vacancy create filled electronic states in the semiconductor gap of AlN. N vacancies enhance the ferromagnetism by adding mu(B) to the Cr moment each but reduce the ferromagnetic exchange constants between the spins in the nearest Cr-Cr pairs. These calculated results are in agreement with experimental observations and facts of real Cr-doped AlN samples and their synthesis. Our first-principles results are useful to elucidate the mechanism for the ferromagnetism and to explore high-performance Cr-doped AlN diluted magnetic semiconductors.

Structure and photoluminescence studies of Pr-implanted GaN

The structure and photoluminscence (PL) properties of Pr-implanted GaN thin films have been studied. RBS/channeling technique was used to explore the damage recovery at high annealing temperature and study the dependence of the radiation damage with ion implantation direction. A complete recovery of the ion implantation damage cannot be achieved at annealing temperatures up to 1050degreesC. It is found that the channeling implantation results in the decrease of the damage. The PL experimental results indicate that the PL efficiency increases exponentially with annealing temperature up to the maximum temperature of 1050degreesC. Moreover, the PL intensity is also seriously affected by ion implantation geometries. The PL intensity for the sample implanted along channeled direction is nearly 2 times more intense than that observed from the sample implanted along random direction. The thermal quenching of PL intensity from 10 to 300K for sample annealed at 1050degreesC is only 30%. (C) 2004 Elsevier B.V. All rights reserved.