45,029 research outputs found
The numerical analysis of the rotational theory for the formation of lunar globules
The morphology of lunar globules is studied through the application of a numerical analysis of their rotation in space during cooling. It is assumed that molten rock is shot from the surface of the moon, solidifies in space above the moon and then falls back to the surface. The rotational theory studied makes the following assumptions: the volume of the molten rock does not change during cooling; the angular momentum is conserved; there are no internal motions because of the high viscosity of the molten rock, i.e., in equilibrium the globule is rotating as a rigid body; finally, the kinetic reaction of the globule to the forces is fast relative to the rate of cooling, i.e., the globule reaches equilibrium at constant energy. These assumptions are subjected to numerical analysis yielding good agreement between the actual globule shapes and the numerical results, but leaving some doubt as to the validity of the rotational theory due to the failure to establish the existence of true local minima and an incomplete understanding of the thermokentics
Condensation, Partial Melting and Evaporation Processes Influence the Bulk Compositions of Spinel-Cored Spherules in the CO3.1 Chondrite Miller Range 90019
Here we focus on spinel-cored spherule calcium-aluminum rich inclusions (CAI), dominantly ~75-80 microns in diameter in the CO3.1 chondrite Miller Range 90019, which make up ~ 12 % of the fine-grained CAIs in one thin section. Their mineralogical content ranges from rare grossite- and hibonite-bearing varieties, through perovskite-melilitebearing, to fassaite-bearing and finally anorthitebearing. Non-spherical CAIs have been divided into 4 other groups, defined based on mineralogical abundances. We also characterized a group of AOAs from this sample. No glass has been recognized in any inclusions. Some relatively evolved members (anorthite-, spinel- + fassaite-bearing) among the spherules are found engulfed in AOAs. We characterized the bulk compositions of ~145 CAIs and AOAs in this meteorite, derived from EDS-x-ray mapping of the inclusions. We determined bulk compositions both with and without Wark-Lovering rims (when present), which are largely composed of diopside forsterite. The balance of the inclusions appear to have not been melted or partially melted, but rather they have textures that indicate they are condensates, often modified by extensive reaction with nebular gases. This presents the opportunity to examine effects on the bulk compositions of spherules resulting potentially from melting plus evaporation. Other aspects of this suite of refractory inclusions have been discussed in these abstracts. Oxygen isotope variations in one spherule were presented in [4]. The latter study showed a complex history of reaction with nebular gases possessing a variety of Oisotope compositions. Additional O isotopic studies of inclusions in this work are included in Mane et al
A numerical simulation of the NFAC (National Full-scale Aerodynamics Complex) open-return wind tunnel inlet flow
The flow into an open return wind tunnel inlet was simulated using Euler equations. An explicit predictor-corrector method was employed to solve the system. The calculation is time-accurate and was performed to achieve a steady-state solution. The predictions are in reasonable agreement with the experimental data. Wall pressures are accurately predicted except in a region of recirculating flow. Flow-field surveys agree qualitatively with laser velocimeter measurements. The method can be used in the design process for open return wind tunnels
Motion of buoyant particles and coarsening of solid-liquid mixtures in a random acceleration field
Flow induced by a random acceleration field (g-jitter) is considered in two
related situations that are of interest for microgravity fluid experiments: the
random motion of an isolated buoyant particle and coarsening of a solid-liquid
mixture. We start by analyzing in detail actual accelerometer data gathered
during a recent microgravity mission, and obtain the values of the parameters
defining a previously introduced stochastic model of this acceleration field.
We then study the motion of a solid particle suspended in an incompressible
fluid that is subjected to such random accelerations. The displacement of the
particle is shown to have a diffusive component if the correlation time of the
stochastic acceleration is finite or zero, and mean squared velocities and
effective diffusion coefficients are obtained explicitly. Finally, the effect
of g-jitter on coarsening of a solid-liquid mixture is considered. Corrections
due to the induced fluid motion are calculated, and estimates are given for
coarsening of Sn-rich particles in a Sn-Pb eutectic fluid, experiment to be
conducted in microgravity in the near future.Comment: 25 pages, 4 figures (included). Also at
http://www.scri.fsu.edu/~vinals/ross2.p
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