6,765 research outputs found

    Vibration and Instability of Plate-Assemblies including Shear and Anisotropy (VIPASA) user's guide, addendum

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    Extensions developed at Langley Research Center to the VIPASA computer program are described including a procedure for simple thermal stress analysis and options for graphical display of output. Input requirements for operation of the modified program are given in detail

    A Calculus of Bounded Capacities

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    Resource control has attracted increasing interest in foundational research on distributed systems. This paper focuses on space control and develops an analysis of space usage in the context of an ambient-like calculus with bounded capacities and weighed processes, where migration and activation require space. A type system complements the dynamics of the calculus by providing static guarantees that the intended capacity bounds are preserved throughout the computation

    Nature’s Eden? The Production and Effects of ‘Pristine’ Nature in the Galápagos Islands

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    Best known for inspiring Charles Darwin's theory of evolution, the Galápagos Islands are often referred to as an “evolutionary Eden” and celebrated as one of the world’s few remaining bastions of “pristine” nature. However, recent concerns of a crisis of over-development prompted UNESCO to put the Galápagos on its list of World Heritage Sites “In Danger.” In this paper, we interrogate the conception of pristine nature which undergirds the recent crisis discourse and argue that such understandings of nature are not in fact natural, but are social productions that reflect particular ways of understanding island space. We then explore the material and political effects of understandings of “pristine” nature by showing how they work to structure the tourism industry and investment in public infrastructure in ways that have created social inequalities as well as negative environmental impacts. We then briefly discuss measures taken so far to address the crisis situation, arguing that they would benefit from critical attention to the complexity of social-environmental relations in the Galápagos and a re-thinking of the nature of the islands

    Self-tuned quantum dot gain in photonic crystal lasers

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    We demonstrate that very few (1 to 3) quantum dots as a gain medium are sufficient to realize a photonic crystal laser based on a high-quality nanocavity. Photon correlation measurements show a transition from a thermal to a coherent light state proving that lasing action occurs at ultra-low thresholds. Observation of lasing is unexpected since the cavity mode is in general not resonant with the discrete quantum dot states and emission at those frequencies is suppressed. In this situation, the quasi-continuous quantum dot states become crucial since they provide an energy-transfer channel into the lasing mode, effectively leading to a self-tuned resonance for the gain medium.Comment: 4 pages, 4 figures, submitted to Phys. Re

    A Flexible and Modular Framework for Implementing Infrastructures for Global Computing

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    We present a Java software framework for building infrastructures to support the development of applications for systems where mobility and network awareness are key issues. The framework is particularly useful to develop run-time support for languages oriented towards global computing. It enables platform designers to customize communication protocols and network architectures and guarantees transparency of name management and code mobility in distributed environments. The key features are illustrated by means of a couple of simple case studies

    Effects of Training Intensity on Locomotor Performance in Individuals With Chronic Spinal Cord Injury: A Randomized Crossover Study

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    Background. Many physical interventions can improve locomotor function in individuals with motor incomplete spinal cord injury (iSCI), although the training parameters that maximize recovery are not clear. Previous studies in individuals with other neurologic injuries suggest the intensity of locomotor training (LT) may positively influence walking outcomes. However, the effects of intensity during training of individuals with iSCI have not been tested. Objective. The purpose of this pilot, blinded-assessor randomized trial was to evaluate the effects of LT intensity on walking outcomes in individuals with iSCI. Methods. Using a crossover design, ambulatory participants with iSCI \u3e1 year duration performed either high- or low-intensity LT for ≀20 sessions over 4 to 6 weeks. Four weeks following completion, the training interventions were alternated. Targeted intensities focused on achieving specific ranges of heart rate (HR) or ratings of perceived exertion (RPE), with intensity manipulated by increasing speeds or applying loads. Results. Significantly greater increases in peak treadmill speeds (0.18 vs 0.02 m/s) and secondary measures of metabolic function and overground speed were observed following high- versus low-intensity training, with no effects of intervention order. Moderate to high correlations were observed between differences in walking speed or distances and differences in HRs or RPEs during high- versus low-intensity training. Conclusion. This pilot study provides the first evidence that the intensity of stepping practice may be an important determinant of LT outcomes in individuals with iSCI. Whether such training is feasible in larger patient populations and contributes to improved locomotor outcomes deserves further consideration
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