19,912 research outputs found
Test program to demonstrate the stability of hydrazine in propellant tanks
A 24-month coupon test program to evaluate the decomposition of propellant tanks is reported. The propellant fuel evaluated was monopropellant-grade hydrazine (N2H4), which is normally a colorless, fuming, corrosive, strongly reducing liquid. The degree of hydrazine decomposition was determined by means of chemical analyses of the liquid and evolved gases at the end of the test program. The experimental rates of hydrazine decomposition were determined to be within acceptable limits. The propellant tank materials and material combinations were not degraded by a 2-year exposure to hydrazine propellant. This was verified using change-of-weight determinations and microscopic examination of the specimen surface before and after exposure, and by posttest chemical analyses of hydrazine liquid for residual metal content
Sealed containers in Z
Physical means of securing information, such as sealed envelopes and scratch cards, can be used to achieve cryptographic objectives. Reasoning about this has so far been informal.
We give a model of distinguishable sealed envelopes in Z, exploring design decisions and further analysis and development of such models
50 nm GaAs mHEMTs and MMICs for ultra-low power distributed sensor network applications
We report well-scaled 50 nm GaAs metamorphic HEMTs (mHEMTs) with DC power consumption in the range
1-150 ΜW/Μ demonstrating f<sub>T</sub> of 30-400 GHz. These metrics enable the realisation of ultra-low power (<500
ΜW) radio transceivers for autonomous distributed sensor network applications
A Pseudorandom Binary Noise Ultrasonic System
The random noise ultrasonic system represents the state-of-the-art in terms of sensitivity and resolution for ultrasonic NDE systems. The principle impediment to its use in the field is the lack of real-time inspection capability. If a pair of pseudorandom binary noise sources are substituted for the white noise source in the random noise system, a real-time capability is achieved. An instrument using such sources will be demonstrated and its capabilities will be discussed
SMA Imaging of the Maser Emission from the H30 Radio Recombination Line in MWC349A
We used the Submillimeter Array to map the angular distribution of the
H30 recombination line (231.9 GHz) in the circumstellar region of the
peculiar star MWC349A. The resolution was 1\farcs2, but because of high
signal-to-noise ratio we measured the positions of all maser components to
accuracies better than 0\farcs01, at a velocity resolution of . The
two strongest maser components (called high velocity components) at velocities
near -14 and are separated by 0\farcs048 \pm 0\farcs001 (60 AU)
along a position angle of 102 \pm 1\arcdeg. The distribution of maser
emission at velocities between and beyond these two strongest components were
also provided. The continuum emission lies at the center of the maser
distribution to within 10 mas. The masers appear to trace a nearly edge-on
rotating disk structure, reminiscent of the water masers in Keplerian rotation
in the nuclear accretion disk of the galaxy NGC4258. However, the maser
components in MWC349A do not follow a simple Keplerian kinematic prescription
with , but have a larger power law index. We explore the
possibility that the high velocity masers trace spiral density or shock waves.
We also emphasize caution in the interpretation of relative centroid maser
positions where the maser is not clearly resolved in position or velocity, and
we present simulations that illustrate the range of applicability of the
centroiding method.Comment: 23 pages with 9 figures (two of these figures are vertically aligned
as Figure 4) submitted to the Astrophysical Journa
The Submillimeter Array
The Submillimeter Array (SMA), a collaborative project of the Smithsonian
Astrophysical Observatory (SAO) and the Academia Sinica Institute of Astronomy
and Astrophysics (ASIAA), has begun operation on Mauna Kea in Hawaii. A total
of eight 6-m telescopes comprise the array, which will cover the frequency
range of 180-900 GHz. All eight telescopes have been deployed and are
operational. First scientific results utilizing the three receiver bands at
230, 345, and 690 GHz have been obtained and are presented in the accompanying
papers.Comment: 10 pages, 4 figure
Temporal and dimensional effects in evolutionary graph theory
The spread in time of a mutation through a population is studied analytically
and computationally in fully-connected networks and on spatial lattices. The
time, t_*, for a favourable mutation to dominate scales with population size N
as N^{(D+1)/D} in D-dimensional hypercubic lattices and as N ln N in
fully-connected graphs. It is shown that the surface of the interface between
mutants and non-mutants is crucial in predicting the dynamics of the system.
Network topology has a significant effect on the equilibrium fitness of a
simple population model incorporating multiple mutations and sexual
reproduction. Includes supplementary information.Comment: 6 pages, 4 figures Replaced after final round of peer revie
Very high performance 50 nm T-gate III-V HEMTs enabled by robust nanofabrication technologies
In this paper, we review a range of nanofabrication techniques which enable the realization of uniform, high yield, high performance 50 nm T-gate III-V high electron mobility transistors (HEMTs). These technologies have been applied in the fabrication of a range of lattice matched and pseudomorphic InP HEMTs and GaAs metamorphic HEMTs with functional yields in excess of 95%, threshold voltage uniformity of 5 mV, DC transconductance of up to 1600 mS/mm and f/sub T/ of up to 480 GHz. These technologies and device demonstrators are key to enabling a wide range of millimeter-wave imaging and sensing applications beyond 100 GHz, particularly where array-based multi-channel solutions are required
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