53,387 research outputs found
Preliminary investigation of the electrodynamics of a conducting tether
An introductory study of the properties of an electrically conducting tether flown from the shuttle is presented. Only a single configuration is considered: a vertical conductor moving normally across the Earth's field, connecting the shuttle to a large conducting balloon that passively extracts electrons from the ionosphere. The distortions in the plasma at maximum current collection are described, as are the local and distant wakes. Numerical values are given
Variable stars in the globular cluster NGC 3201. I. Multimode SX Phe-type variables
We report on the discovery of eleven multimode SX Phoenicis--type blue
stragglers in the field of the southern globular cluster NGC 3201. In these
variables both radial and non-radial modes are excited. For three variables the
derived period ratio is close to that observed in SX Phoenicis itself,
suggesting that these stars are pulsating in the fundamental and the
first-overtone radial modes. Using the McNamara (1997) period-luminosity
relation we have estimated the apparent distance modulus to NGC 3201 to be
14.08mag.Comment: 10 pages, requires mn2e.cls,contact the first author at
[email protected] for high-resolution figure
3D Reconstruction of a Rotating Erupting Prominence
A bright prominence associated with a coronal mass ejection (CME) was seen
erupting from the Sun on 9 April 2008. This prominence was tracked by both the
Solar Terrestrial Relations Observatory (STEREO) EUVI and COR1 telescopes, and
was seen to rotate about the line of sight as it erupted; therefore, the event
has been nicknamed the "Cartwheel CME." The threads of the prominence in the
core of the CME quite clearly indicate the structure of a weakly to moderately
twisted flux rope throughout the field of view, up to heliocentric heights of 4
solar radii. Although the STEREO separation was 48 degrees, it was possible to
match some sharp features in the later part of the eruption as seen in the 304
{\AA} line in EUVI and in the H\alpha-sensitive bandpass of COR1 by both STEREO
Ahead and Behind. These features could then be traced out in three-dimensional
space, and reprojected into a view in which the eruption is directed towards
the observer. The reconstructed view shows that the alignment of the prominence
to the vertical axis rotates as it rises up to a leading-edge height of \approx
2.5 solar radii, and then remains approximately constant. The alignment at 2.5
solar radii differs by about 115 degrees from the original filament orientation
inferred from H{\alpha} and EUV data, and the height profile of the rotation,
obtained here for the first time, shows that two thirds of the total rotation
is reached within \approx 0.5 solar radii above the photosphere. These features
are well reproduced by numerical simulations of an unstable moderately twisted
flux rope embedded in external flux with a relatively strong shear field
component.Comment: published in Solar Physics (Online First
Advanced propulsion for LEO-Moon transport. 2: Tether configurations in the LEO-Moon system
This brief work discusses a possible application of a tether as a dynamical element in a low Earth orbit (LEO)-Moon transport system, and is a part of the Cal Space study of that transport system. To be specific, that study concentrated on the downward transport of O2 from the Moon to LEO, where it is stored for use as a rocket propellant, thus reducing Earth liftoff mass requirements by a factor of about 8. Moreover, in order to display clearly the role of advanced technology, only one novel technology was introduced at a single node in the transport system, the rest being 'conventional' rocket transport. Tethers were found useful in several different roles: hanging from platforms in lunar orbits, as supports for elevators, spinning in LEO, or spinning in a tether transport orbit, an elliptical orbit with perigee at approximately 600 km. This last use is considered here. Presented are the usefulness of the tether, nature of the tether system, the apparatus needed to support, deploy, and control it, and a discussion of needed developments
Experimental and analytical dynamic flow characteristics of an axial-flow fan from an air cushion landing system model
An investigation was conducted to compare the steady-state and dynamic flow characteristics of an axial-flow fan which had been used previously as the air supply fan for some model air cushion landing system studies. Steady-state flow characteristics were determined in the standard manner by using differential orifice pressures for the flow regime from free flow to zero flow. In this same regime, a correlative technique was established so that fan inlet and outlet pressures could be used to measure dynamic flow as created by a rotating damper. Dynamic tests at damper frequencies up to 5 Hz showed very different flow characteristics when compared with steady-state flow, particularly with respect to peak pressures and the pressure-flow relationship at fan stall and unstall. A generalized, rational mathematical fan model was developed based on physical fan parameters and a steady-state flow characteristic. The model showed good correlation with experimental tests at damper frequencies up to 5 Hz
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