5,560 research outputs found

    Generalized Formulation of Weighted Optimal Guidance Laws with Impact Angle Constraint

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    The purpose of this paper is to investigate the generalized formulation of weighted optimal guidance laws with impact angle constraint. From the generalized formulation, we explicitly find the feasible set of weighting functions that lead to analytical forms of weighted optimal guidance laws. This result has potential significance because it can provide additional degrees of freedom in designing a guidance law that accomplishes the specified guidance objective.Comment: This work has been accepted for publication in IEEE Transactions on Aerospace and Electronic Systems (in press

    Fracture Toughness of Silicate Glasses: Insights from Molecular Dynamics Simulations

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    Understanding, predicting and eventually improving the resistance to fracture of silicate materials is of primary importance to design new glasses that would be tougher, while retaining their transparency. However, the atomic mechanism of the fracture in amorphous silicate materials is still a topic of debate. In particular, there is some controversy about the existence of ductility at the nano-scale during the crack propagation. Here, we present simulations of the fracture of three archetypical silicate glasses using molecular dynamics. We show that the methodology that is used provide realistic values of fracture energy and toughness. In addition, the simulations clearly suggest that silicate glasses can show different degrees of ductility, depending on their composition.Comment: arXiv admin note: text overlap with arXiv:1410.291

    Predicting blunt cerebrovascular injury in pediatric trauma: Validation of the Utah Score

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    Risk factors for blunt cerebrovascular injury (BCVI) may differ between children and adults, suggesting that children at low risk for BCVI after trauma receive unnecessary computed tomography angiography (CTA) and high-dose radiation. We previously developed a score for predicting pediatric BCVI based on retrospective cohort analysis. Our objective is to externally validate this prediction score with a retrospective multi-institutional cohort. We included patients who underwent CTA for traumatic cranial injury at four pediatric Level I trauma centers. Each patient in the validation cohort was scored using the “Utah Score” and classified as high or low risk. Before analysis, we defined a misclassification rate <25% as validating the Utah Score. Six hundred forty-five patients (mean age 8.6 ± 5.4 years; 63.4% males) underwent screening for BCVI via CTA. The validation cohort was 411 patients from three sites compared with the training cohort of 234 patients. Twenty-two BCVIs (5.4%) were identified in the validation cohort. The Utah Score was significantly associated with BCVIs in the validation cohort (odds ratio 8.1 [3.3, 19.8], p < 0.001) and discriminated well in the validation cohort (area under the curve 72%). When the Utah Score was applied to the validation cohort, the sensitivity was 59%, specificity was 85%, positive predictive value was 18%, and negative predictive value was 97%. The Utah Score misclassified 16.6% of patients in the validation cohort. The Utah Score for predicting BCVI in pediatric trauma patients was validated with a low misclassification rate using a large, independent, multicenter cohort. Its implementation in the clinical setting may reduce the use of CTA in low-risk patients

    The Minimum Backlog Problem

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    We study the minimum backlog problem (MBP). This online problem arises, e.g., in the context of sensor networks. We focus on two main variants of MBP. The discrete MBP is a 2-person game played on a graph G=(V,E)G=(V,E). The player is initially located at a vertex of the graph. In each time step, the adversary pours a total of one unit of water into cups that are located on the vertices of the graph, arbitrarily distributing the water among the cups. The player then moves from her current vertex to an adjacent vertex and empties the cup at that vertex. The player's objective is to minimize the backlog, i.e., the maximum amount of water in any cup at any time. The geometric MBP is a continuous-time version of the MBP: the cups are points in the two-dimensional plane, the adversary pours water continuously at a constant rate, and the player moves in the plane with unit speed. Again, the player's objective is to minimize the backlog. We show that the competitive ratio of any algorithm for the MBP has a lower bound of Ω(D)\Omega(D), where DD is the diameter of the graph (for the discrete MBP) or the diameter of the point set (for the geometric MBP). Therefore we focus on determining a strategy for the player that guarantees a uniform upper bound on the absolute value of the backlog. For the absolute value of the backlog there is a trivial lower bound of Ω(D)\Omega(D), and the deamortization analysis of Dietz and Sleator gives an upper bound of O(DlogN)O(D\log N) for NN cups. Our main result is a tight upper bound for the geometric MBP: we show that there is a strategy for the player that guarantees a backlog of O(D)O(D), independently of the number of cups.Comment: 1+16 pages, 3 figure

    Hope for a New Us/Earth via E-Co-Aectivity and Jeong (정 情)

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    In E-Co-Affectivity, Marjolein Oele explores the deep connectivity and relational entanglements of plants, animals, humans, and the soil as elemental components of a co-affective community. Her deconstructive reading of the Aristotelian conception of degrees of three souls, with such hierarchy of humans-animals-vegetables via what she calls categorical contamination,” is a brilliant example of how re-reading the western canon can cast important interpretive light upon contemporary ethico-political questions. Oele’s work shows how it is crucial to foreground (eco)feminist re-interpretations of the writings of major figures in the western philosophical traditions. It is reconstruction and construction of feminist hermeneutics so that it is not a mere interpretation, but a transformation of old traditions into planetary cosmo-centric new-becomings. Through my reading of E-Co-Affectivity, I focus on the coherence of the crucial themes of the middle voice, precarity, and e-co-affectivity, from my comparative ecofeminist perspective. The Korean concept of jeong, which can be a healing mechanism in the midst of our planetary crises, I will suggest, resonates profoundly with e-co-affectivity
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