Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

20000067648 NASA Marshall Space Flight Center, Huntsville, AL USA
Mechanisms for the Crystallization of ZBLAN
Ethridge, Edwin C., NASA Marshall Space Flight Center, USA; Tucker, Dennis S., NASA Marshall Space Flight Center, USA;
[2000]; 1p; In English; Microgravity Materials, 8 Jun. 2000, Huntsville, AL, USA; Sponsored by NASA, USA; No Copyright;
Avail: Issuing Activity; Abstract Only
A number of research teams have observed that glass forming melts that are solidified in low-g exhibit enhanced glass formation.
This project will examine one of these glasses, the heavy metal fluoride glass ZBLAN. A four year ground based research
program has been approved to examine the crystallization of ZBLAN glasses with the purpose of testing a theory for the crystallization
of ZBLAN glass. The theory could explain the general observations of enhanced glass formation of other glasses melted
and solidified in low-g. Fluid flow in 1-g results from buoyancy forces and surface tension driven convection. This fluid flow can
introduce shear in undercooled liquids in 1-g. In low-g it is known that fluid flows are greatly reduced so that the shear rate in
fluids in low-g are extremely low. It is believed that fluids may have some weak structure in the absence of flow. Even very small
shear rates could cause this structure to collapse in response to the shear. A general result would be shear thinning of the fluid.
The hypothesis of this research is that: Shear thinning in undercooled liquids increases the rate of nucleation and crystallization
of glass forming melts. Shear of the melt can be reduced in low-g enhancing undercooling and glass formation. Samples will be
melted and quenched in 1-g under quiescent conditions at a number of controlled cooling rates to determine times and temperatures
of crystallization and heated at controlled heating rates to determine kinetic crystallization parameters. Experiments will also be
performed on the materials while under controlled vibration conditions and compared with the quiescent experiments in order
to evaluate the effect of shear in the liquid on crystallization kinetics. After the experimental parameters are well known, experiments
will be repeated under low-g (and 2-g) conditions on the KC-135 aircraft during low-g parabolic maneuvers. The results
will determine the effects of shear on crystallization. Our experimental setups will be designed with low-g experiments in mind
and will be tested as breadboard low-g experiments. It is very likely that the thermal analysis instrumentation can be adapted to
be run in the microgravity glovebox facilities. Critical space experiments may result to test the theory at longer low-g time experiments
in space.
Author
Crystallization; Glass; Metal Fluorides; Melts (Crystal Growth)
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PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
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20000062449 Forschungszentrum Rossendorf e.V., Dresden, Germany
Kaons in nuclear matter
Kolomeitsev, E. E.; Feb. 28, 1997; 170p; In German; In English
Report No.(s): DE99-715823; FZR-167; No Copyright; Avail: Department of Energy Information Bridge
The subject of the doctoral thesis is examination of the properties of kaons in nuclear matter. A specific method is explained
that has been developed for the scientific objectives of the thesis and permits description of the kaon- nucleon interactions and
kaon-nucleon scattering in a vacuum. The main challenge involved was to find approaches that would enable application of the
derived relations out of the kaon mass shell, connected with the second objective, namely to possibly find methods which are independent
of models. The way chosen to achieve this goal relied on application of reduction formulas as well as current algebra
relations and the PCAC hypothesis.
NTIS
Kaons; Matter (Physics); Nucleons
20000062715 Joint Inst. for Nuclear Research, Bogolyubov Lab. of Theoretical Physics, Dubna, USSR
Is the Casimir effect relevant to sonoluminescence
Nesterenko, V. V.; Pirozhenko, I.; Dec. 31, 1998; 12p; In English
Report No.(s): DE99-607974; JINR-E-2-98-40; No Copyright; Avail: Department of Energy Information Bridge
The Casimir energy of a solid ball (or cavity in an infinite medium) is calculated by a direct frequency summation using the
contour integration. The dispersion is taken into account, and the divergences are removed by making use of the zeta function
technique. The Casimir energy of a dielectric ball (or cavity) turns out to be positive, it being increased when the radius of the
ball decreases. The latter eliminates completely the possibility of explaining, via the Casimir effect, the sonoluminescence for
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