76,853 research outputs found
The Agricultural Research System of the Philippines: A Reconnaissance Report
Research and Development/Tech Change/Emerging Technologies,
Newly developed foam ceramic body shows promise as thermal insulation material at 3000 deg F
Optimized zirconia foam ceramic body shows promise for use as a thermal insulation material. The insulating media displays low density and thermal conductivity, good thermal shock resistance, high melting point, and mechanical strength
Similarity of the concentration field of gas-phase turbulent jets
This work is an experimental investigation of the turbulent concentration field formed when the nozzle gas from a round, momentum-driven, free turbulent jet mixes with gas entrained from a quiescent reservoir. The measurements, which were made with a non-intrusive laser-Rayleigh scattering diagnostic at Reynolds numbers of 5000, 16000, and 40000, cover the axial range from 20 to 90 jet exit diameters and resolve the full range of temporal and spatial concentration scales. Reynolds-number-independent and Reynolds-number-dependent similarities are investigated. The mean and r.m.s. values of the concentration are found to be consistent with jet similarity laws. Concentration fluctuation power spectra are found to be self-similar along rays emanating from the virtual origin of the jet. The probability density function for the concentration is also found to be self-similar along rays. Near the centreline of the jet, the scaled probability density function of jet fluid concentration is found to be nearly independent of the Reynolds number
GRBs and the 511 keV emission of the Galactic bulge
We consider the phenomenology of the 511 keV emission in the Galactic bulge,
as recently observed by INTEGRAL, and propose a model is which the positrons
are produced by gamma-ray bursts (GRB) associated with mini starbursts in the
central molecular zone (CMZ). We show that the positrons can easily diffuse
across the bulge on timescales of about 10^7 yr, and that their injection rate
by GRBs is compatible with the observed fluxes if the mean time between two
GRBs in the bulge is about 8 10^4 yr x E_GRB_51. We also explain the low
disk-to-bulge emission ratio by noting that positrons from GRBs in the Galactic
disk should annihilate on timescales of < 10^4 yr in the dense shell of the
underlying supernova remnant, after the radiative transition, while the
remnants of GRBs occurring in the hot, low-density medium produced by recurrent
starbursts in the CMZ become subsonic before they can form a radiative shell,
allowing the positrons to escape and fill the whole Galactic bulge. If the mean
time between GRBs is smaller than 10^4 E_51 yr, INTEGRAL should be able to
detect the (localized) 511 keV emission associated with one or a few GRB
explosions in the disk.Comment: 6 pages, accepted for publication in A&
Interim Service ISDN Satellite (ISIS) network model for advanced satellite designs and experiments
The Interim Service Integrated Services Digital Network (ISDN) Satellite (ISIS) Network Model for Advanced Satellite Designs and Experiments describes a model suitable for discrete event simulations. A top-down model design uses the Advanced Communications Technology Satellite (ACTS) as its basis. The ISDN modeling abstractions are added to permit the determination and performance for the NASA Satellite Communications Research (SCAR) Program
Development of alkali metal peroxide and superoxide blown ceramic foams Final report, 22 Jun. 1965 - 15 Mar. 1966
Alkali metal peroxide and superoxide blown ceramic foam bodies for thermal insulatio
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