19,610 research outputs found

    Lead telluride bonding and segmentation study Semiannual phase report, 1 Feb. - 31 Jul. 1969

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    Thermoelectric system of Cd-Si-Ge, and tungsten diffusion bonded lead tellurid

    Molecular Weight Dependence of Polymersome Membrane Elasticity and Stability

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    Vesicles prepared in water from a series of diblock copolymers and termed "polymersomes" are physically characterized. With increasing molecular weight Mˉn\bar{M}_n, the hydrophobic core thickness dd for the self-assembled bilayers of polyethyleneoxide - polybutadiene (PEO-PBD) increases up to 20 nmnm - considerably greater than any previously studied lipid system. The mechanical responses of these membranes, specifically, the area elastic modulus KaK_a and maximal areal strain αc\alpha_c are measured by micromanipulation. As expected for interface-dominated elasticity, KaK_a (\simeq 100 pN/nmpN/nm) is found to be independent of Mˉn\bar{M}_n. Related mean-field ideas also predict a limiting value for αc\alpha_c which is universal and about 10-fold above that typical of lipids. Experiments indeed show αc\alpha_c generally increases with Mˉn\bar{M}_n, coming close to the theoretical limit before stress relaxation is opposed by what might be chain entanglements at the highest Mˉn\bar{M}_n. The results highlight the interfacial limits of self-assemblies at the nano-scale.Comment: 16 pages, 5 figures, and 1 tabl

    A review of human factors principles for the design and implementation of medication safety alerts in clinical information systems.

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    The objective of this review is to describe the implementation of human factors principles for the design of alerts in clinical information systems. First, we conduct a review of alarm systems to identify human factors principles that are employed in the design and implementation of alerts. Second, we review the medical informatics literature to provide examples of the implementation of human factors principles in current clinical information systems using alerts to provide medication decision support. Last, we suggest actionable recommendations for delivering effective clinical decision support using alerts. A review of studies from the medical informatics literature suggests that many basic human factors principles are not followed, possibly contributing to the lack of acceptance of alerts in clinical information systems. We evaluate the limitations of current alerting philosophies and provide recommendations for improving acceptance of alerts by incorporating human factors principles in their design

    Endothelial Progenitors Exist within the Kidney and Lung Mesenchyme

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    The renal endothelium has been debated as arising from resident hemangioblast precursors that transdifferentiate from the nephrogenic mesenchyme (vasculogenesis) and/or from invading vessels (angiogenesis). While the Foxd1-positive renal cortical stroma has been shown to differentiate into cells that support the vasculature in the kidney (including vascular smooth muscle and pericytes) it has not been considered as a source of endothelial cell progenitors. In addition, it is unclear if Foxd1-positive mesenchymal cells in other organs such as the lung have the potential to form endothelium. This study examines the potential for Foxd1-positive cells of the kidney and lung to give rise to endothelial progenitors. We utilized immunofluorescence (IF) and fluorescence-activated cell sorting (FACS) to co-label Foxd1-expressing cells (including permanently lineage-tagged cells) with endothelial markers in embryonic and postnatal mice. We also cultured FACsorted Foxd1-positive cells, performed in vitro endothelial cell tubulogenesis assays and examined for endocytosis of acetylated low-density lipoprotein (Ac-LDL), a functional assay for endothelial cells. Immunofluorescence and FACS revealed that a subset of Foxd1-positive cells from kidney and lung co-expressed endothelial cell markers throughout embryogenesis. In vitro, cultured embryonic Foxd1-positive cells were able to differentiate into tubular networks that expressed endothelial cell markers and were able to endocytose Ac-LDL. IF and FACS in both the kidney and lung revealed that lineage-tagged Foxd1-positive cells gave rise to a significant portion of the endothelium in postnatal mice. In the kidney, the stromal-derived cells gave rise to a portion of the peritubular capillary endothelium, but not of the glomerular or large vessel endothelium. These findings reveal the heterogeneity of endothelial cell lineages; moreover, Foxd1-positive mesenchymal cells of the developing kidney and lung are a source of endothelial progenitors that are likely critical to patterning the vasculature. © 2013 Sims-Lucas et al

    The unfulfilled gene is required for the development of mushroom body neuropil in Drosophila

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    <p>Abstract</p> <p>Background</p> <p>The mushroom bodies (MBs) of <it>Drosophila </it>are required for complex behaviors and consist of three types of neurons, γ, α'/β' and α/β. Previously, roles for transcription factors in MB neuronal differentiation have only been described for a subset of MB neurons. We are investigating the roles of <it>unfulfilled </it>(<it>unf</it>; <it>HR51</it>, CG16801) in MB development. <it>unf </it>encodes a nuclear receptor that is orthologous to the nuclear receptors fasciculation of axons defective 1 (FAX-1) of the nematode and photoreceptor specific nuclear receptor (PNR) of mammals. Based on our previous observations that <it>unf </it>transcripts accumulate in MB neurons at all developmental stages and the presence of axon pathfinding defects in <it>fax-1 </it>mutants, we hypothesized that <it>unf </it>regulates MB axon growth and pathfinding.</p> <p>Results</p> <p>We show that <it>unf </it>mutants exhibit a range of highly penetrant axon stalling phenotypes affecting all neurons of the larval and adult MBs. Phenotypic analysis of <it>unf</it><sup><it>X1 </it></sup>mutants revealed that α'/β' and α/β neurons initially project axons but stall prior to the formation of medial or dorsal MB lobes. <it>unf</it><sup><it>Z0001 </it></sup>mutants form medial lobes, although these axons fail to branch, which results in a failure to form the α or α' dorsal lobes. In either mutant background, γ neurons fail to develop larval-specific dorsal projections. These mutant γ neurons undergo normal pruning, but fail to re-extend axons medially during pupal development. <it>unf</it><sup><it>RNAi </it></sup>animals displayed phenotypes similar to those seen in <it>unf</it><sup><it>Z0001 </it></sup>mutants. Unique asymmetrical phenotypes were observed in <it>unf</it><sup><it>X1</it></sup>/<it>unf</it><sup><it>Z0001 </it></sup>compound heterozygotes. Expression of <it>UAS-unf </it>transgenes in MB neurons rescues the larval and adult <it>unf </it>mutant phenotypes.</p> <p>Conclusions</p> <p>These data support the hypothesis that <it>unf </it>plays a common role in the development of all types of MB neurons. Our data indicate that <it>unf </it>is necessary for MB axon extension and branching and that the formation of dorsal collaterals is more sensitive to the loss of <it>unf </it>function than medial projections. The asymmetrical phenotypes observed in compound heterozygotes support the hypothesis that the earliest MB axons may serve as pioneers for the later-born MB neurons, providing evidence for pioneer MB axon guidance in post-embryonic development.</p

    Strong-Segregation Theory of Bicontinuous Phases in Block Copolymers

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    We compute phase diagrams for AnBmA_nB_m starblock copolymers in the strong-segregation regime as a function of volume fraction ϕ\phi, including bicontinuous phases related to minimal surfaces (G, D, and P surfaces) as candidate structures. We present the details of a general method to compute free energies in the strong segregation limit, and demonstrate that the gyroid G phase is the most nearly stable among the bicontinuous phases considered. We explore some effects of conformational asymmetry on the topology of the phase diagram.Comment: 14 pages, latex, 21 figures, to appear in Macromolecule

    Multi-objective evolutionary–fuzzy augmented flight control for an F16 aircraft

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    In this article, the multi-objective design of a fuzzy logic augmented flight controller for a high performance fighter jet (the Lockheed-Martin F16) is described. A fuzzy logic controller is designed and its membership functions tuned by genetic algorithms in order to design a roll, pitch, and yaw flight controller with enhanced manoeuverability which still retains safety critical operation when combined with a standard inner-loop stabilizing controller. The controller is assessed in terms of pilot effort and thus reduction of pilot fatigue. The controller is incorporated into a six degree of freedom motion base real-time flight simulator, and flight tested by a qualified pilot instructor

    Longtime behavior of nonlocal Cahn-Hilliard equations

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    Here we consider the nonlocal Cahn-Hilliard equation with constant mobility in a bounded domain. We prove that the associated dynamical system has an exponential attractor, provided that the potential is regular. In order to do that a crucial step is showing the eventual boundedness of the order parameter uniformly with respect to the initial datum. This is obtained through an Alikakos-Moser type argument. We establish a similar result for the viscous nonlocal Cahn-Hilliard equation with singular (e.g., logarithmic) potential. In this case the validity of the so-called separation property is crucial. We also discuss the convergence of a solution to a single stationary state. The separation property in the nonviscous case is known to hold when the mobility degenerates at the pure phases in a proper way and the potential is of logarithmic type. Thus, the existence of an exponential attractor can be proven in this case as well

    Nonlinear dynamics in gene regulation promote robustness and evolvability of gene expression levels

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    Cellular phenotypes underpinned by regulatory networks need to respond to evolutionary pressures to allow adaptation, but at the same time be robust to perturbations. This creates a conflict in which mutations affecting regulatory networks must both generate variance but also be tolerated at the phenotype level. Here, we perform mathematical analyses and simulations of regulatory networks to better understand the potential trade-off between robustness and evolvability. Examining the phenotypic effects of mutations, we find an inverse correlation between robustness and evolvability that breaks only with nonlinearity in the network dynamics, through the creation of regions presenting sudden changes in phenotype with small changes in genotype. For genotypes embedding low levels of nonlinearity, robustness and evolvability correlate negatively and almost perfectly. By contrast, genotypes embedding nonlinear dynamics allow expression levels to be robust to small perturbations, while generating high diversity (evolvability) under larger perturbations. Thus, nonlinearity breaks the robustness-evolvability trade-off in gene expression levels by allowing disparate responses to different mutations. Using analytical derivations of robustness and system sensitivity, we show that these findings extend to a large class of gene regulatory network architectures and also hold for experimentally observed parameter regimes. Further, the effect of nonlinearity on the robustness-evolvability trade-off is ensured as long as key parameters of the system display specific relations irrespective of their absolute values. We find that within this parameter regime genotypes display low and noisy expression levels. Examining the phenotypic effects of mutations, we find an inverse correlation between robustness and evolvability that breaks only with nonlinearity in the network dynamics. Our results provide a possible solution to the robustness-evolvability trade-off, suggest an explanation for the ubiquity of nonlinear dynamics in gene expression networks, and generate useful guidelines for the design of synthetic gene circuits
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