Modeling the shape hierarchy for visually guided grasping

The monkey anterior intraparietal area (AIP) encodes visual information about three-dimensional object shape that is used to shape the hand for grasping. We modeled shape tuning in visual AIP neurons and its relationship with curvature and gradient information from the caudal intraparietal area (CIP). The main goal was to gain insight into the kinds of shape parameterizations that can account for AIP tuning and that are consistent with both the inputs to AIP and the role of AIP in grasping. We first experimented with superquadric shape parameters. We considered superquadrics because they occupy a role in robotics that is similar to AIP , in that superquadric fits are derived from visual input and used for grasp planning. We also experimented with an alternative shape parameterization that was based on an Isomap dimension reduction of spatial derivatives of depth (i.e., distance from the observer to the object surface). We considered an Isomap-based model because its parameters lacked discontinuities between similar shapes. When we matched the dimension of the Isomap to the number of superquadric parameters, the superquadric model fit the AIP data somewhat more closely. However, higher-dimensional Isomaps provided excellent fits. Also, we found that the Isomap parameters could be approximated much more accurately than superquadric parameters by feedforward neural networks with CIP-like inputs. We conclude that Isomaps, or perhaps alternative dimension reductions of visual inputs to AIP, provide a promising model of AIP electrophysiology data. Further work is needed to test whether such shape parameterizations actually provide an effective basis for grasp control.

A computational model of the anterior intraparietal area

The monkey anterior intraparietal area (AIP) encodes visual information about three-dimensional object shape that is used to shape the hand for grasping. In robotics a similar role has been played by modules that fit point cloud data to the superquadric family of shapes and its various extensions. We developed a model of shape tuning in AIP based on cosine tuning to superquadric parameters. However, the model did not fit the data well, and we also found that it was difficult to accurately reproduce these parameters using neural networks with the appropriate inputs (modelled on the caudal intraparietal area, CIP). The latter difficulty was related to the fact that there are large discontinuities in the superquadric parameters between very similar shapes. To address these limitations we adopted an alternative shape parameterization based on an Isomap nonlinear dimension reduction. The Isomap was built using gradients and curvatures of object surface depth. This alternative parameterization was low-dimensional (like superquadrics), but data-driven (similar to an alternative clustering approach that is also sometimes used in robotics) and lacked large discontinuities. Isomaps with 16 or more dimensions reproduced the AIP data fairly well. Moreover, we found that the Isomap parameters could be approximated from CIP-like input much more accurately than the superquadric parameters. We conclude that Isomaps, or perhaps alternative dimension reductions of CIP signals, provide a promising model of AIP tuning. We have now started to integrate our model with a robot hand, to explore the efficacy of Isomap shape reductions in grasp planning. Future work will consider dynamics of spike responses and integration with related visual and motor area models.

Design of a Semi-analytical Method to Describe Plasma-Wall Interactions

Electric probes are objects immersed in the plasma with sharp boundaries which collect of emit charged particles. Consequently, the nearby plasma evolves under abrupt imposed and/or naturally emerging conditions. There could be localized currents, different time scales for plasma species evolution, charge separation and absorbing-emitting walls. The traditional numerical schemes based on differences often transform these disparate boundary conditions into computational singularities. This is the case of models using advection-diffusion differential equations with source-sink terms (also called Fokker-Planck equations). These equations are used in both, fluid and kinetic descriptions, to obtain the distribution functions or the density for each plasma species close to the boundaries. We present a resolution method grounded on an integral advancing scheme by using approximate Green's functions, also called short-time propagators. All the integrals, as a path integration process, are numerically calculated, what states a robust grid-free computational integral method, which is unconditionally stable for any time step. Hence, the sharp boundary conditions, as the current emission from a wall, can be treated during the short-time regime providing solutions that works as if they were known for each time step analytically. The form of the propagator (typically a multivariate Gaussian) is not unique and it can be adjusted during the advancing scheme to preserve the conserved quantities of the problem. The effects of the electric or magnetic fields can be incorporated into the iterative algorithm. The method allows smooth transitions of the evolving solutions even when abrupt discontinuities are present. In this work it is proposed a procedure to incorporate, for the very first time, the boundary conditions in the numerical integral scheme. This numerical scheme is applied to model the plasma bulk interaction with a charge-emitting electrode, dealing with fluid diffusion equations combined with Poisson equation self-consistently. It has been checked the stability of this computational method under any number of iterations, even for advancing in time electrons and ions having different time scales. This work establishes the basis to deal in future work with problems related to plasma thrusters or emissive probes in electromagnetic fields.

Relationship between residual stresses and mechanical behavior in ceramic composites

En este trabajo, materiales de tipo alúmina/Y-TZP (ZrO2 tetragonal, estabilizada con 3 mol. % Y2O3), como sistema cerámico popular por sus mejoradas propiedades mecánicas en comparación con las cerámicas de alúmina puras, han sido estudiados en términos de propiedades mecánicas y tensiones residuales. El novedoso método de colado en cinta, consistente en el apilamiento de cintas de cerámica verde a temperatura ambiente y el uso de bajas presiones, se ha escogido para la presente investigación con el fin de poder aprovechar al máximo el futuro desarrollo de materiales laminados de alúmina-óxido de circonio. Se han determinado las propiedades de los materiales obtenidos por este nuevo método de procesamiento comparándolas con las de los materiales obtenidos por “slip casting”, con el fin de analizar si el método propuesto afecta a la microestructura y, por tanto, a las propiedades mecánicas y tensiones residuales propias de estos materiales. Para analizar la idoneidad del proceso de fabricación, utilizado para evitar la presencia de discontinuidades en las intercaras entre las láminas así como otros fenómenos que puedan interferir con las propiedades mecánicas, se estudiaron materiales cerámicos con la misma composición en cintas. Por otra parte también se analizó el efecto de la adición de óxido de circonio sobre la aparición de tensiónes residuales en cerámicas Al2O3/Y-TZP, teniendo en cuenta su notable influencia sobre las propiedades microestructurales y mecánicas de los materiales, así como el requisito de co-sinterización de capas con diferentes materiales compuestos en materiales laminados. La caracterización del material incluye la determinación de la densidad, el análisis de la microestructura, la obtención de las propiedades mecánicas (módulo de elasticidad, dureza, resistencia a la flexión y tenacidad de fractura) así como de las tensiones residuales. En combinación con otros métodos de medida tradicionales, la nanoindentación también se empleó como una técnica adicional para la medida del módulo de elasticidad y de la dureza. Por otro lado, diferentes técnicas de difracción con neutrones, tanto las basadas en longitud de onda constante (CW) como en tiempo de vuelo (TOF), han sido empleadas para la medición fiable de la deformación residual a través del grosor en muestras a granel. Las tensiones residuales fueron determinadas con elevada precisión, aplicando además métodos de análisis apropiados, como por ejemplo el refinamiento de Rietveld. Las diferentes fases en cerámicas sinterizadas, especialmente las de zirconia, se examinaron con detalle mediante el análisis de Rietveld, teniendo en cuenta el complicado polimorfismo del Óxido de Zirconio (ZrO2) así como las posibles transformaciones de fase durante el proceso de fabricación. Los efectos del contenido de Y-TZP en combinación con el nuevo método de procesamiento sobre la microestructura, el rendimiento mecánico y las tensiones residuales de los materiales estudiados (Al2O3/Y-TZP) se resumen en el presente trabajo. Finalmente, los mecanismos de endurecimiento, especialmente los relacionados con las tensiones residuales, son igualmente discutidos. In present work, Alumina/Y-TZP (tetragonal ZrO2 stabilized with 3 mol% Y2O3) materials, as an popular ceramic system with improved mechanical properties compared with the pure alumina ceramics, have been studied in terms of mechanical properties and residual stresses. The novel tape casting method, which involved the stacking of green ceramics tapes at room temperature and using low pressures, is selected for manufacturing and investigation, in order to take full advantage of the future development of alumina-zirconia laminated materials. Features of materials obtained by the new processing method are determined and compared with those of materials obtained by conventional slip casting in a plaster mold, in order to study whether the proposed method of processing affects microstructure and thereby the mechanical properties and residual stresses characteristics of materials. To analyse the adequacy of the manufacturing process used to avoid the presence of discontinuities at the interfaces between the sheets and other phenomena that interfere with the mechanical properties, ceramic materials with the same composition in tapes were investigated. Moreover, the effect of addition of zirconia on residual stress development of Al2O3/Y-TZP ceramics were taken into investigations, considering its significantly influence on the microstructure and mechanical properties of materials as well as the requirement of co-sintering of layers with different composites in laminated materials. The characterization includes density, microstructure, mechanical properties (elastic modulus, hardness, flexure strength and fracture toughness) and residual stresses. Except of the traditional measurement methods, nanoindentation technique was also used as an additional measurement of the elastic modulus and hardness. Neutron diffraction, both the constant-wavelength (CW) and time-of-flight (TOF) neutron diffraction techniques, has been used for reliable through-thickness residual strain measurement in bulk samples. Residual stresses were precisely determined combined with appropriate analysis methods, e.g. the Rietveld refinement. The phase compositions in sintered ceramics especially the ones of zirconia were accurately examined by Rietveld analysis, considering the complex polymorph of ZrO2 and the possible phase transformation during manufacturing process. Effects of Y-TZP content and the new processing method on the microstructure, mechanical performance and residual stresses were finally summarized in present studied Al2O3/Y-TZP materials. The toughening mechanisms, especially the residual stresses related toughening, were theoretically discussed.

Obtención de la función receptora en las estaciones sísmicas de banda ancha del Instituto Geográfico Nacional.

La estructura de velocidad en los primeros metros debajo de una estación sísmica produce un cierto efecto sobre el sismograma que ésta registra, dicho efecto se denomina función receptora. Si se conoce esta función, es posible, mediante modelización, obtener esa estructura de velocidad. La onda P que genera un telesismo, queda “atrapada” en los últimos kilómetros de su trayectoria en la estructura próxima a la estación que la registra, reverberando entre las discontinuidades de la misma y convirtiéndose, en algunas partes, en onda S. La diferencia de registro existente entre el sismograma del rayo no atrapado (componente vertical del registro) y el producido por este fenómeno (componente radial), sería la función receptora. En este proyecto, se pretende obtener mediante la técnica de Langston (1979),las funciones receptoras de las 55 estaciones que forman la Red Sísmica de banda ancha del Instituto Geográfico Nacional, con el fin de que en trabajos venideros, sea posible conocer de una manera más realista, la estructura de la corteza terrestre bajo el territorio español. Para la obtención de estas funciones, será necesario trabajar con un conjunto de sismogramas registrados por estaciones de banda ancha a partir de telesismos cuyos parámetros focales reúnan una serie de condiciones, definidas y detalladas ampliamente en esta memoria. Tras un proceso de selección, que será constante a lo largo de todo este trabajo,se van a emplear para el cálculo de las funciones receptoras, un total de 5231 sismogramas, generados por 186 telesismos. Para terminar, a modo de ejemplo y con el objetivo de mostrar la finalidad para la que se ha llevado a cabo este proyecto, se procederá a realizar la inversión de la función receptora obtenida para una de las estaciones sísmicas de la red, obteniendo así, un modelo de velocidades aproximado de la estructura de la litosfera existente bajo dicha estación. Abstract: The speed structure in the first layers under a seismic station produces an effect on the seismogram that is registered. This effect is known as receiver function. It is possible to obtain the speed structure if this function is detected through modelling. The P wave, which generates a teleseism, gets trapped in the final kilometres of its trajectory in the nearby station structure, reverberating among its discontinuities and turning into a S wave. The registered difference between the not caught ray seismogram (vertical component of the register) and the one that is produced by this phenomenon (radial component) would be known as receiver function. This project aims to obtain, through the Langston technique (1979), the receiver function of the 55 stations that make up the Broadband Seismic Network of the National Geography Institute to get to know, in a more realistic way, the structure of the Earth’s crust under the Spanish territory. In order to obtain these functions, it will be necessary to work with a number of seismograms registered by the broadband stations whose focal parameters meet the requirements that are well defined and detailed in the development of this memory. After selecting the appropriate data, that would be constant throughout the development of this project, we are going to apply a total of 5231 seismograms obtained by 186 teleseism to calculate the receivers functions. To conclude, and with the aim of demonstrating the purposes and uses that lie behind the development of this project, we will reverse the receiver function for one of the seismic stations, obtaining a approximate speeds’ model of the lithosphere structure that can be found under the previously mentioned station.

Juan Navarro Baldeweg : el dibujo de la mano como herramienta en el proceso creativo

Esta investigación es una incursión en el tránsito de Juan Navarro desde sus “habitaciones y horizontes”, las manifestaciones espontáneas de la mano y el proyectar, a la obra que nos devuelve a la experiencia física y corporal del mundo. Juan Navarro debe a sus manos gran parte de sus inquietudes y capacidades. Sus manos están presentes en su obra como materia –piezas de manos-, como herramienta -el dibujo por la mano- y como desencadenante en los procesos creativos de su obra de arquitectura. Las distintas obras remiten a una preocupación común: la de visualizar el espacio a través de un imaginario personal. Sin embargo, el proceso creativo en cada disciplina se desarrolla teniendo en cuenta la especificidad del medio y la experiencia que provoca en el espectador. La obra, como concreción del proceso creativo, se explica por las continuidades y discontinuidades entre las herramientas, mecanismos y estrategias utilizadas en los distintos medios. La tesis se estructura en dos partes, en la primera se estudia cómo se producen los procesos creativos, sus mecanismos en los distintos medios plásticos y el dibujo como herramienta transversal. Se identifican los conceptos y temas que dan lugar a la obra profundizando en el papel de la mano como presencia orgánica, biológica y responsable de una forma de representación personal. La segunda parte se articula en dos capítulos que, a través del dibujo, muestran la arquitectura como modelo e identifican los mecanismos utilizados en su forma de proyectar y su relación con la obra en distintos proyectos. El texto se estructura como una secuencia de ideas articuladas alrededor de un universo gráfico que nos conduce por múltiples itinerarios desde los que atisbar los procesos creativos de Juan Navarro. Estos caminos son hilos con los que se teje una visión personal de la relación entre las herramientas y mecanismos utilizados por Juan Navarro y su obra. La manera cómo se produce el proceso creativo, los mecanismos y las herramientas que los ponen en marcha constituyen una forma de abordar la obra, que hasta la fecha, se ha tratado aisladamente sin una intención de construir un cuerpo estructurado de conocimiento. En la arquitectura Juan Navarro existe un vacío de conocimiento teórico y gráfico sobre el propio proceso y su forma de proyectar. Se ha persistido en la explicación de la obra, sus referencias, temas abordados, relaciones y trasvases sin ahondar en la especificidad del medio. Estos vacíos establecen la necesidad y justificación de esta tesis doctoral. La investigación comienza descifrando una obra que desde sus inicios trabaja con la dualidad de lo gestual y lo conceptual. Plantea una forma de ordenación del mundo, de la sensación sometida a la medida en la que finalmente la obra se recibe como signo que desencadena sentimientos y te devuelve al mundo. Propone la recuperación de los sentidos a través de una arquitectura como vivencia no reductible al espacio geométrico. Identifica los mecanismos y herramientas que se establecen en este proceso y termina concluyendo que el dibujo es la herramienta doblemente transversal porque atiende de forma desigual a las distintas disciplinas y a los dos extremos en que se presenta la actividad creatividad en el trabajo de Juan Navarro. Estos extremos se corresponden con un conocimiento corporal inconsciente y un trabajo constante guiado por la motivación, la predeterminación y la conceptualización. El dibujo por la mano es el espacio de encuentro entre lo que representa la mano y la posibilidad de expresión proyectual codificada. Se produce en un territorio que se extiende desde lo analógico subyacente –que se nutre de imágenes complejas- y el dominio simbólico construido. Abstract. This research is a foray into Juan Navarro’s transition from his "Rooms and Horizons", -spontaneous demonstrations of the hand-, to the project, -the work that brings us back to experiencing the physical world-. Juan Navarro owes his hands much of his capacities and inquisitiveness. His hands are present in his work as the subject –“Hand Pieces”-, as a tool -through hand-drawing - and as a trigger in the creative processes of his work of architecture. The various works refer to a common theme: the viewing space through a personal imagery. However, the creative process in each discipline develops taking into account the specificity of the medium and the experience that arouses in the observer. The work, as completion of the creative process, is explained by the continuities and discontinuities between the tools, mechanisms and strategies used in the different media. The thesis is structured in two parts, the first studies how the creative processes are iniciated, their mechanisms in the different plastic art media, as well as drawing as a transversal tool. In this section the investigation identifies the concepts and themes that give rise to the art work, exploring the role of the hand as the organic, biological presence responsible for a way of personal representation. The second part is divided into two chapters, which, via the drawing, show the architecture as a model and identify the mechanisms used in the his way of projecting form of the project and its the relationship of hand-drawing to with his work ilustrated with different projects. The text is structured as a sequence of ideas, articulated around a graphic universe that leads us by multiple paths, letting us glimpse into the creative processes of Juan Navarro. These paths are threads that weave a personal vision of the relationship between the tools and mechanisms used by Juan Navarro in his work. The way the creative process takes place, the mechanisms and tools that set it in action, constitutes a way of dealing with the work, that, hithergo, has been treated in isolation without an intention to build a structured body of knowledge. In Navarro Baldeweg’s architecture there is a vacuum of theoretical and graphic knowledge of the process itself and his way of projecting. So far, emphasis has been placed mainly on his work’s explanation, its references, the subjects covered, connections and transfers, without delving into the specificity of each medium. These academic gaps justify the need for this doctoral thesis. The investigation begins deciphering a work that, since its very beginning, deals with the duality of the gesture and the concept. It poses a way of managing the world and the sensations which are submitted until it finally detects the work as a sign that triggers feelings and returns the observer to the real world. It proposes the recovery of the senses through an architecture that is sensed as an experience and not merely reduced to geometric space. It identifies the mechanisms and tools that are set out in this process and concludes that drawing is a core tool working in two directions, because it caters unevenly to the various disciplines and to both ends of the creative activity presented in the work of Juan Navarro. These ends correspond with an unconscious physical knowledge and a continuous work guided by motivation, predetermination and conceptualization. Hand-drawing is the meeting space between what the hand represents, and the possibility of an encoded, projectual expression. Thus, hand-drawing takes place in a territory that covers the underlying analogue - which feeds on complex images - to the symbolic built domain.

Specific cleavage of chromosomal and plasmid DNA strands in gram-positive and gram-negative bacteria can be detected with nucleotide resolution

A sensitive and precise in vitro technique for detecting DNA strand discontinuities produced in vivo has been developed. The procedure, a form of runoff DNA synthesis on molecules released from lysed bacterial cells, mapped precisely the position of cleavage of the plasmid pMV158 leading strand origin in Streptococcus pneumoniae and the site of strand scission, nic, at the transfer origins of F and the F-like plasmid R1 in Escherichia coli. When high frequency of recombination strains of E. coli were examined, DNA strand discontinuities at the nic positions of the chromosomally integrated fertility factors were also observed. Detection of DNA strand scission at the nic position of F DNA in the high frequency of recombination strains, as well as in the episomal factors, was dependent on sexual expression from the transmissable element, but was independent of mating. These results imply that not only the transfer origins of extrachromosomal F and F-like fertility factors, but also the origins of stably integrated copies of these plasmids, are subject to an equilibrium of cleavage and ligation in vivo in the absence of DNA transfer.

Tight frames of k-plane ridgelets and the problem of representing objects that are smooth away from d-dimensional singularities in Rn

For each pair (n, k) with 1 ≤ k < n, we construct a tight frame (ρλ : λ ∈ Λ) for L2 (Rn), which we call a frame of k-plane ridgelets. The intent is to efficiently represent functions that are smooth away from singularities along k-planes in Rn. We also develop tools to help decide whether k-plane ridgelets provide the desired efficient representation. We first construct a wavelet-like tight frame on the X-ray bundle χn,k—the fiber bundle having the Grassman manifold Gn,k of k-planes in Rn for base space, and for fibers the orthocomplements of those planes. This wavelet-like tight frame is the pushout to χn,k, via the smooth local coordinates of Gn,k, of an orthonormal basis of tensor Meyer wavelets on Euclidean space Rk(n−k) × Rn−k. We then use the X-ray isometry [Solmon, D. C. (1976) J. Math. Anal. Appl. 56, 61–83] to map this tight frame isometrically to a tight frame for L2(Rn)—the k-plane ridgelets. This construction makes analysis of a function f ∈ L2(Rn) by k-plane ridgelets identical to the analysis of the k-plane X-ray transform of f by an appropriate wavelet-like system for χn,k. As wavelets are typically effective at representing point singularities, it may be expected that these new systems will be effective at representing objects whose k-plane X-ray transform has a point singularity. Objects with discontinuities across hyperplanes are of this form, for k = n − 1.

Multiple modes of cellular activation and virus transmission in HIV infection: A role for chronically and latently infected cells in sustaining viral replication

CD4+ T cell activation, required for virus replication in these cells, occurs in local microenvironmental domains in transient bursts. Thus, although most HIV originates from short-lived virus-producing cells, it is unlikely that chronic infection is generally sustained in rapid continuous cycles of productive infection as has been proposed. Such continuity of productive infection cycles would depend on efficient long-range transmission of HIV from one set of domains to another, in turn requiring the maintenance of sufficiently high concentrations of cell-free virus across lymphoid tissues at all times. By contrast, long-lived cellular sources of HIV maintain the capacity to infect newly activated cells at close range despite the temporal and spatial discontinuities of activation events. Such proximal activation and transmission (PAT) involving chronically and latently infected cells may be responsible for sustained infection, particularly when viral loads are low. Once CD4 cells are productively infected through PAT, they can infect other activated cells in their immediate vicinity. Such events propagate locally but generally do not spread systemically, unlike in the acute phase of the infection, because of the early establishment of protective anergy. Importantly, antiretroviral drug treatment is likely to differentially impact long-range transmission and PAT.

The copper transporter CTR1 provides an essential function in mammalian embryonic development

Copper serves as an essential cofactor for a variety of proteins in all living organisms. Previously, we described a human gene (CTR1;SLC31A1) that encodes a high-affinity copper-uptake protein and hypothesized that this protein is required for copper delivery to mammalian cells. Here, we test this hypothesis by inactivating the Ctr1 gene in mice by targeted mutagenesis. We observe early embryonic lethality in homozygous mutant embryos and a deficiency in copper uptake in the brains of heterozygous animals. Ctr1−/− embryos can be recovered at E8.5 but are severely developmentally retarded and morphologically abnormal. Histological analysis reveals discontinuities and variable thickness in the basement membrane of the embryonic region and an imperfect Reichert's membrane, features that are likely due to lack of activity in the collagen cross-linking cupro-enzyme lysyl oxidase. A collapsed embryonic cavity, the absence of an allantois, retarded mesodermal migration, and increased cell death are also apparent. In the brains of heterozygous adult mice, which at 16 months are phenotypically normal, copper is reduced to approximately half compared with control littermates, implicating CTR1 as the required port for copper entry into at least this organ. A study of the spatial and temporal expression pattern of Ctr1 during mouse development and adulthood further shows that CTR1 is ubiquitously transcribed with highest expression observed in the specialized epithelia of the choroid plexus and renal tubules and in connective tissues of the eye, ovary, and testes. We conclude that CTR1 is the primary avenue for copper uptake in mammalian cells.

Flightless brown kiwis of New Zealand possess extremely subdivided population structure and cryptic species like small mammals.

Using allozymes and mtDNA sequences from the cytochrome b gene, we report that the brown kiwi has the highest levels of genetic structuring observed in birds. Moreover, the mtDNA sequences are, with two minor exceptions, diagnostic genetic markers for each population investigated, even though they are among the more slowly evolving coding regions in this genome. A major unexpected finding was the concordant split in molecular phylogenies between brown kiwis in the southern South Island and elsewhere in New Zealand. This basic phylogeographic boundary halfway down the South Island coincides with a fixed allele difference in the Hb nuclear locus and strongly suggests that two morphologically cryptic species are currently merged under one polytypic species. This is another striking example of how molecular genetic assays can detect phylogenetic discontinuities that are not reflected in traditional morphologically based taxonomies. However, reanalysis of the morphological characters by using phylogenetic methods revealed that the reason for this discordance is that most are primitive and thus are phylogenetically uninformative. Shared-derived morphological characters support the same relationships evident in the molecular phylogenies and, in concert with the molecular data, suggest that as brown kiwis colonized northward from the southern South Island, they retained many primitive characters that confounded earlier systematists. Strong subdivided population structure and cryptic species in brown kiwis seem to have evolved relatively recently as a consequence of Pleistocene range disjunctions, low dispersal power, and genetic drift in small populations.

Um modelo multiescala concorrente para representar o processo de fissuração do concreto.

Este trabalho propõe uma técnica de modelagem multiescala concorrente do concreto considerando duas escalas distintas: a mesoescala, onde o concreto é modelado como um material heterogêneo, e a macroescala, na qual o concreto é tratado como um material homogêneo. A heterogeneidade da estrutura mesoscópica do concreto é idealizada considerando três fases distintas, compostas pelos agregados graúdos e argamassa (matriz), estes considerados materiais homogêneos, e zona de transição interfacial (ZTI), tratada como a parte mais fraca entre as três fases. O agregado graúdo é gerado a partir de uma curva granulométrica e posicionado na matriz de forma aleatória. Seu comportamento mecânico é descrito por um modelo constitutivo elástico-linear, devido a sua maior resistência quando comparado com as outras duas fases do concreto. Elementos finitos contínuos com alta relação de aspecto em conjunto com um modelo constitutivo de dano são usados para representar o comportamento não linear do concreto, decorrente da iniciação de fissuras na ZTI e posterior propagação para a matriz, dando lugar à formação de macrofissuras. Os elementos finitos de interface com alta relação de aspecto são inseridos entre todos os elementos regulares da matriz e entre os da matriz e agregados, representando a ZTI, tornando-se potenciais caminhos de propagação de fissuras. No estado limite, quando a espessura do elemento de interface tende a zero (h ?0) e, consequentemente, a relação de aspecto tende a infinito, estes elementos apresentam a mesma cinemática da aproximação contínua de descontinuidades fortes (ACDF), sendo apropriados para representar a formação de descontinuidades associados a fissuras, similar aos modelos coesivos. Um modelo de dano à tração é proposto para representar o comportamento mecânico não linear das interfaces, associado à formação de fissuras, ou até mesmo ao eventual fechamento destas. A fim de contornar os problemas causados pela malha de elementos finitos de transição entre as malhas da macro e da mesoescala, que, em geral, apresentam diferenças expressivas 5 de refinamento, utiliza-se uma técnica recente de acoplamento de malhas não conformes. Esta técnica é baseada na definição de elementos finitos de acoplamento (EFAs), os quais são capazes de estabelecer a continuidade de deslocamento entre malhas geradas de forma completamente independentes, sem aumentar a quantidade total de graus de liberdade do problema, podendo ser utilizados tanto para acoplar malhas não sobrepostas quanto sobrepostas. Para tornar possível a análise em multiescala em casos nos quais a região de localização de deformações não pode ser definida a priori, propõe-se uma técnica multiescala adaptativa. Nesta abordagem, usa-se a distribuição de tensões da escala macroscópica como um indicador para alterar a modelagem das regiões críticas, substituindo-se a macroescala pela mesoescala durante a análise. Consequentemente, a malha macroscópica é automaticamente substituída por uma malha mesoscópica, onde o comportamento não linear está na iminência de ocorrer. Testes numéricos são desenvolvidos para mostrar a capacidade do modelo proposto de representar o processo de iniciação e propagação de fissuras na região tracionada do concreto. Os resultados numéricos são comparados com os resultados experimentais ou com aqueles obtidos através da simulação direta em mesoescala (SDM).

Contribuição ao estudo de instabilidade em túneis não revestidos da estrada de ferro Vitória-Minas através da teoria dos blocos-chave e caracterização da rocha através de ensaios laboratoriais e de campo.

No país existem inúmeras estruturas e obras civis que estão em operação a dezenas de anos e necessitam de monitoramento periódico devido a sua importância. Por este motivo, a dissertação apresenta um caso de um túnel antigo com problema de queda de bloco e visa instigar novas pesquisas e aumentar o conhecimento sobre o tema. Foram realizadas inspeções em campo em alguns túneis não revestidos da Estrada de Ferro Vitória-Minas (EFVM), bem como os ensaios em laboratório e in situ realizados nas amostras e no maciço rochoso para caracterizar o problema. Para o estudo foi escolhido o túnel Monte Seco Linha 1 e Linha 2 nos quais foram realizadas sondagens rotativas inclinadas e orientadas próximas ao eixo para investigação dos planos de descontinuidade. Os conceitos da Teoria dos Blocos-Chave foram aplicados às famílias de descontinuidades encontradas nos Túneis Monte Seco L1 e L2 para identificar os possíveis blocos instáveis formados pelas escavações. Para obtenção dos parâmetros geotécnicos de resistência e deformabilidade foram realizados ensaios de compressão uniaxial instrumentados com strain gages. A resistência a tração foi obtida através de Ensaio de Compressão Diametral (ECD). No ensaio de campo foi utilizado o Martelo de Schmidt para avaliação da rocha in situ. Através da análise dos dados foi possível distinguir setores cuja ocorrência de queda de blocos são maiores e a classe do maciço rochoso de acordo com a proposta de Bieniawski.

Corneal topography reinterpretation through separate analysis of the projected rings

Póster presentado en SPIE Photonics Europe, Brussels, 16-19 April 2012.

A new approach for semi-automatic rock mass joints recognition from 3D point clouds

Rock mass characterization requires a deep geometric understanding of the discontinuity sets affecting rock exposures. Recent advances in Light Detection and Ranging (LiDAR) instrumentation currently allow quick and accurate 3D data acquisition, yielding on the development of new methodologies for the automatic characterization of rock mass discontinuities. This paper presents a methodology for the identification and analysis of flat surfaces outcropping in a rocky slope using the 3D data obtained with LiDAR. This method identifies and defines the algebraic equations of the different planes of the rock slope surface by applying an analysis based on a neighbouring points coplanarity test, finding principal orientations by Kernel Density Estimation and identifying clusters by the Density-Based Scan Algorithm with Noise. Different sources of information —synthetic and 3D scanned data— were employed, performing a complete sensitivity analysis of the parameters in order to identify the optimal value of the variables of the proposed method. In addition, raw source files and obtained results are freely provided in order to allow to a more straightforward method comparison aiming to a more reproducible research.