1,302 research outputs found

    The First Comparison Between Swarm-C Accelerometer-Derived Thermospheric Densities and Physical and Empirical Model Estimates

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    The first systematic comparison between Swarm-C accelerometer-derived thermospheric density and both empirical and physics-based model results using multiple model performance metrics is presented. This comparison is performed at the satellite's high temporal 10-s resolution, which provides a meaningful evaluation of the models' fidelity for orbit prediction and other space weather forecasting applications. The comparison against the physical model is influenced by the specification of the lower atmospheric forcing, the high-latitude ionospheric plasma convection, and solar activity. Some insights into the model response to thermosphere-driving mechanisms are obtained through a machine learning exercise. The results of this analysis show that the short-timescale variations observed by Swarm-C during periods of high solar and geomagnetic activity were better captured by the physics-based model than the empirical models. It is concluded that Swarm-C data agree well with the climatologies inherent within the models and are, therefore, a useful data set for further model validation and scientific research.Comment: https://goo.gl/n4QvU

    Defending Renaissance Italy: The Innovative Culture of Italian Military Engineers

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    The cultural and social effect of the Renaissance Italian military engineer is profiled within this thesis. It encompasses their vocational careers concerning the fluctuations in individuality, print censorship, and uneasiness attached to patronage and marketability. Their work and reputation directly coincided with the demand for trace italienne from numerous Italian city-states and entities throughout the cinquecento. As knowledge spread throughout the Italian peninsula, the individualistic demand for military engineers diminished, integrating their discipline with other professions. As the demand for patronage intensified, fears of fraudulence and plagiarism existed among printers and fellow engineers. This apprehension directly contributed to a lack of printed fortification treatises throughout the cinquecento and was escalated by foreign interventions (Sack of Rome, 1527). This thesis aims to tackle these issues met by Italian military engineers

    Faramir and the Heroic Ideal of the Twentieth Century; or, How Aragorn Died at the Somme

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    After Frodo, Faramir perhaps best represents Tolkien’s thinking on war and processing of his World War I experiences. Carter reveals Faramir to be a far more modern warrior than any of his compatriots, particularly in contrast to Aragorn and Boromir, who are representative of much older and rapidly obsolescing models of heroism and methods of warfare

    Real-Time Planning with Multi-Fidelity Models for Agile Flights in Unknown Environments

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    Autonomous navigation through unknown environments is a challenging task that entails real-time localization, perception, planning, and control. UAVs with this capability have begun to emerge in the literature with advances in lightweight sensing and computing. Although the planning methodologies vary from platform to platform, many algorithms adopt a hierarchical planning architecture where a slow, low-fidelity global planner guides a fast, high-fidelity local planner. However, in unknown environments, this approach can lead to erratic or unstable behavior due to the interaction between the global planner, whose solution is changing constantly, and the local planner; a consequence of not capturing higher-order dynamics in the global plan. This work proposes a planning framework in which multi-fidelity models are used to reduce the discrepancy between the local and global planner. Our approach uses high-, medium-, and low-fidelity models to compose a path that captures higher-order dynamics while remaining computationally tractable. In addition, we address the interaction between a fast planner and a slower mapper by considering the sensor data not yet fused into the map during the collision check. This novel mapping and planning framework for agile flights is validated in simulation and hardware experiments, showing replanning times of 5-40 ms in cluttered environments.Comment: ICRA 201
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