445 research outputs found

    Combining local regularity estimation and total variation optimization for scale-free texture segmentation

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    Texture segmentation constitutes a standard image processing task, crucial to many applications. The present contribution focuses on the particular subset of scale-free textures and its originality resides in the combination of three key ingredients: First, texture characterization relies on the concept of local regularity ; Second, estimation of local regularity is based on new multiscale quantities referred to as wavelet leaders ; Third, segmentation from local regularity faces a fundamental bias variance trade-off: In nature, local regularity estimation shows high variability that impairs the detection of changes, while a posteriori smoothing of regularity estimates precludes from locating correctly changes. Instead, the present contribution proposes several variational problem formulations based on total variation and proximal resolutions that effectively circumvent this trade-off. Estimation and segmentation performance for the proposed procedures are quantified and compared on synthetic as well as on real-world textures

    The Mechanical Properties of Single Fibrin Fibers

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    Background: Blood clots perform the mechanical task of stemming the flow of blood. Objectives: To advance understanding and realistic modeling of blood clot behavior we determined the mechanical properties of the major structural component of blood clots, fibrin fibers. Methods: We used a combined atomic force microscopy (AFM)/fluorescence microscopy technique to determine key mechanical properties of single crosslinked and uncrosslinked fibrin fibers. Results and conclusions: Overall, full crosslinking renders fibers less extensible, stiffer, and less elastic than their uncrosslinked counterparts. All fibers showed stress relaxation behavior (time-dependent weakening) with a fast and a slow relaxation time, 2 and 52 s. In detail, crosslinked and uncrosslinked fibrin fibers can be stretched to 2.5 and 3.3 times their original length before rupturing. Crosslinking increased the stiffness of fibers by a factor of 2, as the total elastic modulus, E0, increased from 3.9 to 8.0 MPa and the relaxed, elastic modulus, E∞, increased from 1.9 to 4.0 MPa upon crosslinking. Moreover, fibers stiffened with increasing strain (strain hardening), as E0 increased by a factor of 1.9 (crosslinked) and 3.0 (uncrosslinked) at strains ε \u3e 110%. At low strains, the portion of dissipated energy per stretch cycle was small (\u3c 10%) for uncrosslinked fibers, but significant (approximately 40%) for crosslinked fibers. At strains \u3e 100%, all fiber types dissipated about 70% of the input energy. We propose a molecular model to explain our data. Our single fiber data can now also be used to construct a realistic, mechanical model of a fibrin network

    Modeling Reactive Hyperemia to Better Understand and Assess Microvascular Function: A Review of Techniques

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    Reactive hyperemia is a well-established technique for the non-invasive evaluation of the peripheral microcirculatory function, measured as the magnitude of limb re-perfusion after a brief period of ischemia. Despite widespread adoption by researchers and clinicians alike, many uncertainties remain surrounding interpretation, compounded by patient-specific confounding factors (such as blood pressure or the metabolic rate of the ischemic limb). Mathematical modeling can accelerate our understanding of the physiology underlying the reactive hyperemia response and guide in the estimation of quantities which are difficult to measure experimentally. In this work, we aim to provide a comprehensive guide for mathematical modeling techniques that can be used for describing the key phenomena involved in the reactive hyperemia response, alongside their limitations and advantages. The reported methodologies can be used for investigating specific reactive hyperemia aspects alone, or can be combined into a computational framework to be used in (pre-)clinical settings

    Segmentation d'Images solaires en Extrême Ultraviolet par une Approche Classification floue Multispectrale

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    L'étude de la variabilité de la couronne solaire et le suivi de régions caractéristiques à sa surface (régions actives, trous coronaux) sont d'une importance capitale en astrophysique et pour le développement de la météorologie de l'espace. Dans ce cadre, nous proposons un algorithme de segmentation multispectrale d'images du Soleil acquises en extrême ultraviolet, utilisant un algorithme de classification flou spatialement contraint. L'utilisation de la logique floue permet de prendre en compte les imprécisions et les incertitudes inhérentes à la définition des différentes régions d'intérêt dans l'image. La méthode est appliquée sur des images prises par le téléscope EIT du satellite SoHO, depuis janvier 1997 jusque mai 2005, couvrant ainsi presque l'intégralité d'un cycle solaire. Les résultats en terme de caractérisation géométrique et radiométrique des régions actives et des trous coronaux sont en accord avec d'autres observations menées par ailleurs. La méthode met de plus en évidence des périodes dans la série temporelle étudiée, reliées à des phénomènes de physique solaire connus

    CRISPR-Based DNA Imaging in Living Cells Reveals Cell Cycle-Dependent Chromosome Dynamics [preprint]

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    In contrast to the well-studied condensation and folding of chromosomes during mitosis, their dynamics in interphase are less understood. We developed a sensitive, multicolor system, CRISPR-Sirius, allowing the real-time tracking of the dynamics of chromosomal loci. We tracked loci kilobases to megabases apart and found significant variation in the inter-locus distances of each pair, indicating differing degrees of DNA contortion. We resolved two distinct modes of dynamics of loci: saltatory local movements as well as translational movements of the domain. The magnitude of both of these modes of movements increased from early to late G1, whereas the translational movements were reduced in early S. The local fluctuations decreased slightly in early S and more markedly in mid-late S. These newly observed movements and their cell cycle-dependence are indicative of a hitherto unrecognized compaction-relaxation dynamic of the chromosomal fiber operating concurrently with changes in the extent of observed genomic domain movements

    Review on Applications of X-ray computed tomography for coal characterization : recent progress and perspectives

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    This research was funded by the National Natural Science Foundation of China (grant nos. 42130806, 41830427, 41922016 and 42102227).Peer reviewedPostprin
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