NASA Scientific and Technical Aerospace Reports

Biological and Physical Space Research Laboratory 2002 Science Review; December 2003, pp. 5; In English; See also
20040073490; No Copyright; Abstract Only; Available from CASI only as part of the entire parent document
There have been numerous studies of glasses indicating that low-gravity processing enhances glass formation. NASA PI
s are investigating the effect of low-g processing on the nucleation and crystal growth rates. Dr. Ethridge is investigating a
potential mechanism for glass crystallization involving shear thinning of liquids in 1-g. For shear thinning liquids, low-g (low
convection) processing will enhance glass formation. The study of the viscosity of glass forming substances at low shear rates
is important to understand these new crystallization mechanisms. The temperature dependence of the viscosity of undercooled
liquids is also very important for NASA s containerless processing studies. In general, the viscosity of undercooled liquids is
not known, yet knowledge of viscosity is required for crystallization calculations. Many researchers have used the Turnbull
equation in error. Subsequent nucleation and crystallization calculations can be in error by many orders of magnitude. This
demonstrates the requirement for better methods for interpolating and extrapolating the viscosity of undercooled liquids. This
is also true for undercooled water. Since amorphous water ice is the predominant form of water in the universe, astrophysicists
have modeled the crystallization of amorphous water ice with viscosity relations that may be in error by five orders-ofmagnitude.
Author
Crystal Growth; Glass; Crystallization; Temperature Dependence; Microgravity; Viscosity
20040073528 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
Chaos in the Solar System
Lecar, Myron; Franklin, Fred A.; Holman, Matthew J.; Murray, Norman J.; Annual review of Astronomy and Astrophysics;
2001; Volume 39, pp. 581-631; In English
Contract(s)/Grant(s): NAG5-10365; Copyright; Avail: Other Sources; Abstract Only
The physical basis of chaos in the solar system is now better understood: In all cases investigated so far, chaotic orbits
result from overlapping resonances. Perhaps the clearest examples are found in the asteroid belt. Overlapping resonances
account for its kirkwood gaps and were used to predict and find evidence for very narrow gaps in the outer belt. Further afield,
about one new "short-peroid" comet is discovered each year. They are believed to come from the "Kuiper
Belt" (at 40 AU or more) via chaotic orbits produced by mean-motion and secular resonances with Neptune. Finally, the
planetary system itself is not immune from chaos. In the inner solar system, overlapping secular resonances have been
identified as the possible source of chaos. For example, Mercury in 1012 years, may suffer a close encounter with Venus or
plunge into the Sun. In the outer solar system, three-body resonances have been identified as a source of chaos, but on an even
longer time scale of 109 times the age of the solar system. On the human time scale, the planets do follow their orbits in a
stately procession, and we can predict their trajectories for hundreds of thousands of years. That is because the mavericks, with
shorter instability times, have long since been ejected. The solar system is not stable; it is just old!
Author
Chaos; Solar System; Gas Giant Planets; Astrophysics
20040073612 Naval Research Lab., Washington, DC
SKA Hybrids Involving the US LNSD COncept
Lazio, Joseph; Apr. 5, 2004; 12 pp.; In English
Report No.(s): AD-A422485; NRL/MR/7210--04-8768; No Copyright; Avail: CASI; A03, Hardcopy
The likely Key Projects for the SKA demand both a large frequency range (potentially 0.06-24 GHz) and a large range
of fields of view (potentially less than 1 deg(2) at higher frequencies to as much as 200 deg(2) below 1 GHz). The US SKA
Consortium has proposed the Large Number/Small-Diameter (LNSD) concept, which generally covers the frequency ranges
and fields of view required by the Key Projects. Opportunities do exist, however, to enhance the design of this concept and
provide access to larger ranges of frequency and field of view. We describe a number of "hybrid" arrays, involving
the LNSD concept, that are designed to increase the probability that most of the SKA Key Projects can be conducted. There
are two broad classes of hybrids, those that combine concepts and those that combine technological aspects from the different
international groups. We consider how the US LNSD concept could form the basis of both kinds of hydrids. We focus on two
"strawman hybrids." The first is an SKA composed of high- and low-frequency sub-arrays, with the LNSD concept
forming the high-frequency sub-array.
DTIC
Interferometry; Radio Astronomy
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