959 research outputs found
Gas levitator having fixed levitation node for containerless processing
A method and apparatus is disclosed for levitating a specimen of material in a containerless environment at a stable nodal position independent of gravity. An elongated levitation tube has a contoured interior in the form of convergent section, constriction, and a divergent section in which the levitation node is created. A gas flow control means prevents separation of flow from the interior walls in the region of a specimen. The apparatus provides for levitating and heating the specimen simultaneously by combustion of a suitable gas mixture combined with an inert gas
Preliminary assessment of the vacuum environment in the wake of large space vehicles
The vacuum environment in the wake region of presently planned large space vehicles is calculated using simplified models of the particle fluxes from the various sources. The fluxes which are calculated come directly from the ambient, are due to ambient particles backscattered from spacecraft emissions, and are due to self scattering of spacecraft emissions. Using nominal values for the surface emissions, the flux density environment behind a large unmanned craft at 550 km altitude is calculated. Calculations indicate that the flux density on a wake vacuum experiment conducted in the vicinity of the shuttle is substantially greater than that behind unmanned craft
Method and apparatus for shaping and enhancing acoustical levitation forces
A method and apparatus for enhancing and shaping acoustical levitation forces in a single-axis acoustic resonance system wherein specially shaped drivers and reflectors are utilized to enhance to levitation force and better contain fluid substance by means of field shaping is described
Proceedings of workshops to define engineering requirements for a space vacuum research facility
The construction of a molecular wake shield for the shuttle orbiter is presented as well as a collision model with a program depicting emitted molecular density around the spacecraft giving estimates of backscattered flux and other collisional processes
Preliminary characterization of a one-axis acoustic system
The acoustic fields and levitation forces produced along the axis of a single-axis resonance system were measured. The system consisted of a St. Clair generator and a planar reflector. The levitation force was measured for bodies of various sizes and geometries (i.e., spheres, cylinders, and discs). The force was found to be roughly proportional to the volume of the body until the characteristic body radius reaches approximately 2/k (k = wave number). The acoustic pressures along the axis were modeled using Huygens principle and a method of imaging to approximate multiple reflections. The modeled pressures were found to be in reasonable agreement with those measured with a calibrated microphone
Postflight analysis of the single-axis acoustic system on SPAR VI and recommendations for future flights
The single axis acoustic levitator that was flown on SPAR VI malfunctioned. The results of a series of tests, analyses, and investigation of hypotheses that were undertaken to determine the probable cause of failure are presented, together with recommendations for future flights of the apparatus. The most probable causes of the SPAR VI failure were lower than expected sound intensity due to mechanical degradation of the sound source, and an unexpected external force that caused the experiment sample to move radially and eventually be lost from the acoustic energy well
Jet-Induced Explosions of Core Collapse Supernovae
We numerically studied the explosion of a supernova caused by supersonic jets
present in its center. The jets are assumed to be generated by a
magneto-rotational mechanism when a stellar core collapses into a neutron star.
We simulated the process of the jet propagation through the star, jet
breakthrough, and the ejection of the supernova envelope by the lateral shocks
generated during jet propagation. The end result of the interaction is a highly
nonspherical supernova explosion with two high-velocity jets of material moving
in polar directions, and a slower moving, oblate, highly distorted ejecta
containing most of the supernova material. The jet-induced explosion is
entirely due to the action of the jets on the surrounding star and does not
depend on neutrino transport or re-acceleration of a stalled shock. The jet
mechanism can explain the observed high polarization of Type Ib,c and Type II
supernovae, pulsar kicks, very high velocity material observed in supernova
remnants, indications that radioactive material was carried to the
hydrogen-rich layers in SN1987A, and some others observations that are very
difficult or impossible to explain by the neutrino energy deposition mechanism.
The breakout of the jet from a compact, hydrogen- deficient core may account
for the gamma-ray bursts and radio outburst associated with SN1998bw/GRB980425.Comment: 14 pages, LaTeX, aaspp4.sty, epsf.sty, submitted to ApJ Let
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