32,222 research outputs found

    Application of theory to propeller design

    Get PDF
    The various theories concerning propeller design are discussed. The use of digital computers to obtain specific blade shapes to meet appropriate flow conditions is emphasized. The development of lifting-line and lifting surface configurations is analyzed. Ship propulsive performance and basic propeller design considerations are investigated. The characteristics of supercavitating propellers are compared with those of subcavitating propellers

    Cross-Border Issues in the Regulation of Charities: Experiences from the UK and Ireland

    Get PDF
    Drawing on the specific experiences of the three authors across the jurisdictions of England and Wales, Scotland, Northern Ireland, the Republic of Ireland, this article outlines the new legal-regulatory framework for charities in each jurisdiction, providing an overview of their respective treatments of external charities (i.e. non-domestic charities operating in a host jurisdcition) before assessing the operational challenges posted by these regimes for such cross-border charities. It shows that the treatment of external charities across the four jurisdictions in not the product of a fully coordinated and coherent joint approach by the four sets of legislators. The article concludeds by offering some preliminary recommendations intended to address the burdens caused by these overlapping regulatory systems

    Development of Ground-testable Phase Fresnel Lenses in Silicon

    Full text link
    Diffractive/refractive optics, such as Phase Fresnel Lenses (PFL's), offer the potential to achieve excellent imaging performance in the x-ray and gamma-ray photon regimes. In principle, the angular resolution obtained with these devices can be diffraction limited. Furthermore, improvements in signal sensitivity can be achieved as virtually the entire flux incident on a lens can be concentrated onto a small detector area. In order to verify experimentally the imaging performance, we have fabricated PFL's in silicon using gray-scale lithography to produce the required Fresnel profile. These devices are to be evaluated in the recently constructed 600-meter x-ray interferometry testbed at NASA/GSFC. Profile measurements of the Fresnel structures in fabricated PFL's have been performed and have been used to obtain initial characterization of the expected PFL imaging efficiencies.Comment: Presented at GammaWave05: "Focusing Telescopes in Nuclear Astrophysics", Bonifacio, Corsica, September 2005, to be published in Experimental Astronomy, 8 pages, 3 figure

    Unpowered Aerodynamic Characteristics of a 15-Percent Scale Model of a Twin-Engine Commuter Aircraft

    Get PDF
    An experimental investigation was conducted in the Ames 12-Foot Pressure Wind Tunnel to determine the unpowered aerodynamic characteristics of a 15-percent-scale model of a twin-engine commuter aircraft. Model longitudinal aerodynamic characteristics were examined at discrete flap deflections for various angle-of-attack and wind-tunnel-velocity ranges with the empennage on and off. Data are presented for the basic model configuration consisting of the fuselage, wing, basic wing leading edge, double slotted flaps, midengine nacelles, and empennage. Other configurations tested include a particle-span drooped leading edge (dropped outboard of the engine nacelles), a full-span drooped leading edge, low- and high-mounted engine nacelles, and a single-slotted flap. An evaluation was made of the model mounting system by comparing data obtained with the model mounted conventionally on the wind-tunnel model-support struts and the model inverted
    • …
    corecore