52,157 research outputs found

    Fluid mechanics mechanisms in the stall process of helicopters

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    Recent experimental results from airfoils in the Mach number, Reynolds number, or reduced frequency ranges typical of helicopter rotor blades have identified the most influential flow mechanisms in the dynamic stall process. The importance of secondary shed vortices, downstream wake action, and the flow in the separated region is generally acknowledged but poorly understood. By means of surface pressure cross-correlations and flow field measurements in static stall, several new hypotheses have been generated. It is proposed that vortex shedding may be caused by acoustic disturbances propagating forward in the lower (pressure) surface boundary layer, that wake closure is a misnomer, and that the shed vortex leaves a trail of vorticity that forms a turbulent free shear layer. The known dynamic stall flow mechanisms are reviewed and the potential importance of recently proposed and hypothetical flow phenomena with respect to helicopter blade aeroelastic response are assessed

    Research and development of materials for use as lubricants in a liquid hydrogen environment Final report, Jul. 1964 - Nov. 1965

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    Lubricant materials for rolling contact bearings operating in liquid hydrogen environmen

    Skeletal stressing method and apparatus Patent

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    Method and apparatus for applying compressional forces to skeletal structure of subject to simulate force during ambulatory condition

    Weight simulator

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    Device applies compressive force to bone to minimize loss of bone calcium during weightlessness or bedrest. Force is applied through weights, or hydraulic, pneumatic or electrically actuated devices. Device is lightweight and easy to maintain and operate

    Programmable physiological infusion

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    A programmable physiological infusion device and method are provided wherein a program source, such as a paper tape, is used to actuate an infusion pump in accordance with a desired program. The system is particularly applicable for dispensing calcium in a variety of waveforms

    Programmed physiological infusion system

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    Infusion system delivers incremental volumes from a reservoir with a piston pump at a rate that varies in time and follows the envelope of a preprogrammed curve

    Hawking temperature from scattering off the charged 2D black hole

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    The charged 2D black hole is visualized as presenting an potential barrier VOUT(r∗)V^{OUT}(r^*) to on-coming tachyon wave. Since this takes the complicated form, an approximate form VAPP(r∗)V^{APP}(r^*) is used for scattering analysis. We calculate the reflection and transmission coefficients for scattering of tachyon off the charged 2D black hole. The Hawking temperature is also derived from the reflection coefficient by Bogoliubov transformation. In the limit of Q→0Q \to 0, we recover the Hawking temperature of the 2D dilaton black hole.Comment: 12 pages 3 figures, RevTeX, to obtain figures contact author ([email protected]
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