1,177 research outputs found

    On Semantic Word Cloud Representation

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    We study the problem of computing semantic-preserving word clouds in which semantically related words are close to each other. While several heuristic approaches have been described in the literature, we formalize the underlying geometric algorithm problem: Word Rectangle Adjacency Contact (WRAC). In this model each word is associated with rectangle with fixed dimensions, and the goal is to represent semantically related words by ensuring that the two corresponding rectangles touch. We design and analyze efficient polynomial-time algorithms for some variants of the WRAC problem, show that several general variants are NP-hard, and describe a number of approximation algorithms. Finally, we experimentally demonstrate that our theoretically-sound algorithms outperform the early heuristics

    Analysis of geometrical and topological attitude for proteinprotein interaction

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    Protein-protein interaction takes usually place on an extended area of the external molecules surfaces that are morphologically fitting. Geometric and topological congruence (i.e. concavity and convexity correspondences) is required to support the neighboring interaction of surface patches belonging to the two protein molecules. It is therefore important to adopt representations and data structures that can facilitate the analysis and the implementation of techniques for the evaluation of geometric and topological properties on extended surfaces. These areas of activity are usually roughly “planar” but with local concavity and complexity that must match each other for interacting. To this purpose we are suggesting a solution different from the one of ligand-protein interaction in which are involved a pocket and a small molecule. The solution here suggested is based on the concavity tree representation. Starting from the convex hull of the protein molecule a recursive process leads to a series of concavity and meta-concavity that allows reaching the detail level required. The consequence of the recursive process is obviously a hierarchical data structure (a tree) which at each level supports a complete description of a surface. Each node of the tree contains an array of features that support the geometrical, topological and biochemical properties of the correspondent surface patch

    Cognitive evaluation of computer-drawn sketches

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    CISRG discussion paper ; 1

    Perceptually Motivated Shape Context Which Uses Shape Interiors

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    In this paper, we identify some of the limitations of current-day shape matching techniques. We provide examples of how contour-based shape matching techniques cannot provide a good match for certain visually similar shapes. To overcome this limitation, we propose a perceptually motivated variant of the well-known shape context descriptor. We identify that the interior properties of the shape play an important role in object recognition and develop a descriptor that captures these interior properties. We show that our method can easily be augmented with any other shape matching algorithm. We also show from our experiments that the use of our descriptor can significantly improve the retrieval rates

    StrokeStyles: Stroke-based Segmentation and Stylization of Fonts

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    We develop a method to automatically segment a font’s glyphs into a set of overlapping and intersecting strokes with the aim of generating artistic stylizations. The segmentation method relies on a geometric analysis of the glyph’s outline, its interior, and the surrounding areas and is grounded in perceptually informed principles and measures. Our method does not require training data or templates and applies to glyphs in a large variety of input languages, writing systems, and styles. It uses the medial axis, curvilinear shape features that specify convex and concave outline parts, links that connect concavities, and seven junction types. We show that the resulting decomposition in strokes can be used to create variations, stylizations, and animations in different artistic or design-oriented styles while remaining recognizably similar to the input font

    Rotation independent hierarchical representation for Open and Closed Curves and its Applications

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    The algorithm used for the segmentation of an image,and scheme used for the representation of the segmentationresult are mostly selected based on the final image analysis orinterpretation objective. The boundary based imagesegmentation and representation system developed by Naborssegments and stores the result as a graph-tree hierarchicalstructure that is capable of supporting diverse applications. Thispaper shows that Nabors’ hierarchical representation of curves isnot invariant to rotation, and proposes an enhancedrepresentation which retains its structure and remains invariantunder rotation. The curve matching algorithm which matchestwo curves based on their hierarchical representation makes iteasy to determine if a curve is a section of a larger curve. Thepotential of the representation is illustrated by developing imageregistration and image stitching methods based on the newrepresentation

    Osteoblasts infill irregular pores under curvature and porosity controls: A hypothesis-testing analysis of cell behaviours

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    The geometric control of bone tissue growth plays a significant role in bone remodelling, age-related bone loss, and tissue engineering. However, how exactly geometry influences the behaviour of bone-forming cells remains elusive. Geometry modulates cell populations collectively through the evolving space available to the cells, but it may also modulate the individual behaviours of cells. To factor out the collective influence of geometry and gain access to the geometric regulation of individual cell behaviours, we develop a mathematical model of the infilling of cortical bone pores and use it with available experimental data on cortical infilling rates. Testing different possible modes of geometric controls of individual cell behaviours consistent with the experimental data, we find that efficient smoothing of irregular pores only occurs when cell secretory rate is controlled by porosity rather than curvature. This porosity control suggests the convergence of a large scale of intercellular signalling to single bone-forming cells, consistent with that provided by the osteocyte network in response to mechanical stimulus. After validating the mathematical model with the histological record of a real cortical pore infilling, we explore the infilling of a population of randomly generated initial pore shapes. We find that amongst all the geometric regulations considered, the collective influence of curvature on cell crowding is a dominant factor for how fast cortical bone pores infill, and we suggest that the irregularity of cement lines thereby explains some of the variability in double labelling data as well as the overall speed of osteon infilling.Comment: 14 pages, 11 figures, Appendi

    Structural engineering of nanoporous anodic alumina and applications

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    En esta tesis doctoral se utilizan diversas estrategias de ingeniería estructural para desarrollar nuevas nanoestructuras basadas en alúmina nanoporosa. Dichas nanoestructuras o moldes son posteriormente utilizados para desarrollar otras nanoestructuras innovadoras basadas en ciertos materiales tales como polímeros, metales magnéticos y semiconductores, interesantes desde el punto de vista de futuras aplicaciones. Las nanoestructuras replicadas a partir de los moldes de alúmina porosa pueden ser integradas en varios tipos de nanodispositivos (nanoelectrodos para deposición directa de nanopartículas desde una corriente de gas, precipitadores electrostáticos, células solares con heterouniones volumétricas, dispositivos ópticos unidimensionales, nanofiltros, etc.).En primer lugar, se fabrican cuatro tipos tradicionales de alúmina porosa autoordenada utilizando la anodización blanda en dos pasos. Los ácidos utilizados para fabricar dichos tipos de alúmina porosa son sulfúrico, oxálico y fosfórico. Los voltajes de anodización aplicados son 20, 40 y 160-195 V, respectivamente. El diámetro del poro varia entre 20 y 250 nm, siendo la distancia entre poros 55, 100 y 400-500 nm, respectivamente. Posteriormente, se fabrica alúmina porosa autoordenada utilizando la anodización dura en un paso utilizando ácido oxálico. También se emplea la anodización dura en dos pasos para fabricar moldes de alúmina porosa ordenada sin capa protectiva, la cuál es característica de un proceso de anodización dura en un paso. Además, siguiendo una técnica de re-anodización, se elimina la capa barrera de óxido de la parte posterior de los moldes de alúmina sin eliminar el sustrato de aluminio ni desprender el molde de alúmina del sustrato. Después, por medio de un proceso de anodización asimétrico en el cuál se modifican las condiciones de anodización (voltaje de anodinado, tipo y concentración de ácido), se fabrican moldes de alúmina jerarquizados con múltiples configuraciones. También se producen moldes de alúmina porosa bicapa combinando anodizado duro y blando. Posteriormente, se emplea un molde de nitruro de silicio para fabricar moldes de alúmina porosa perfectamente ordenados mediante la técnica de nanoimpresión. Además, utilizando esta misma técnica y seleccionando las condiciones de anodización adecuadas, es posible fabricar moldes de alúmina porosa perfectamente ordenados con un ordenamiento de poros extraordinario. Finalmente, se fabrican nanoembudos basados en alúmina porosa intercalando consecutivamente pasos de anodizado y ampliación de diámetro de poro. Dichas nanoestructuras son diseñadas con un alto grado de precisión mediante dos procesos de calibración sistemáticos. Además, se desarrolla un modelo teórico que predice el crecimiento del poro durante el proceso de anodización. Este modelo es experimentalmente validado.A partir de dichas nanoestructuras basadas en moldes de alúmina porosa se estudian varias aplicaciones. En primer lugar, se sinterizan nanopilares magnéticos ordenados sobre sustratos de aluminio mediante deposición electroquímica. Estos se caracterizan por varias técnicas (ESEM, EDXS y XRD). Por sus propiedades magnéticas, dichos nanopilares podrían ser empleados como nanoelectrodos para deposición directa de nanopartículas desde una corriente de gas o como precipitadores electrostáticos. En segundo lugar, se fabrican estructuras poliméricas compuestas de nanopilares sobre un sustrato nanoestructurado basado en el mismo polímero. Para ello, se emplean moldes de alúmina porosa jerarquizados. Además, nanopilares del mismo polímero son transferidos sobre sustratos de ITO/vidrio. La nanoestructura resultante es caracterizada por ESEM, TEM, XRD, CS-AFM y se demuestra que ésta puede ser óptima para integrarse en celdas solares orgánicas con heterouniones volumétricas de alto rendimiento. En tercer lugar, se presenta la primera etapa en la fabricación de mosaicos de nanohilos y nanotubos de níquel. Además, dichas nanoestructuras se utilizan para llevar a cabo un estudio sistemático sobre cómo la re-organización de los poros durante el cambio de régimen de anodización de blando a duro en moldes de alúmina porosa bicapa. Estos mosaicos de nanoestructuras magnéticas podrían ser empleados para desarrollar nuevas plataformas de almacenamiento de datos. Finalmente, se fabrican cadenas de nanoesferas de silicio por infiltración bajo vacío a través de nanoembudos basados en alúmina porosa. Dichas nanoestructuras podrían ser integradas en dispositivos ópticos de tamaño nanométrico.In this PhD thesis, several structural engineering strategies are applied to develop innovative templates based on nanoporous anodic alumina. These templates are subsequently used to develop other nanostructures based on certain materials with multiple applications such as polymers, magnetic metals and semiconductors. These replicated nanostructures could be integrated in various types of nanodevices (e.g. nanoelectrodes for direct deposition of nanoparticles from a gas draught, bulk-heterojunction solar cells, one-dimensional optoelectronic devices, nanofilters and so on). It is expected that the results presented will become a starting point to develop new nanodevices and applications in a wide range of research fields
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