Saturn S-2 Automatic Software System /SASS/

SATURN S-2 Automatic Software System /SASS/ was designed and implemented to aid SATURN S-2 program development and to increase the overall operating efficiency within the S-2 data laboratory. This program is written in FORTRAN 2 for SDS 920 computers

The Generation of Magnetic Fields Through Driven Turbulence

We have tested the ability of driven turbulence to generate magnetic field structure from a weak uniform field using three dimensional numerical simulations of incompressible turbulence. We used a pseudo-spectral code with a numerical resolution of up to $144^3$ collocation points. We find that the magnetic fields are amplified through field line stretching at a rate proportional to the difference between the velocity and the magnetic field strength times a constant. Equipartition between the kinetic and magnetic energy densities occurs at a scale somewhat smaller than the kinetic energy peak. Above the equipartition scale the velocity structure is, as expected, nearly isotropic. The magnetic field structure at these scales is uncertain, but the field correlation function is very weak. At the equipartition scale the magnetic fields show only a moderate degree of anisotropy, so that the typical radius of curvature of field lines is comparable to the typical perpendicular scale for field reversal. In other words, there are few field reversals within eddies at the equipartition scale, and no fine-grained series of reversals at smaller scales. At scales below the equipartition scale, both velocity and magnetic structures are anisotropic; the eddies are stretched along the local magnetic field lines, and the magnetic energy dominates the kinetic energy on the same scale by a factor which increases at higher wavenumbers. We do not show a scale-free inertial range, but the power spectra are a function of resolution and/or the imposed viscosity and resistivity. Our results are consistent with the emergence of a scale-free inertial range at higher Reynolds numbers.Comment: 14 pages (8 NEW figures), ApJ, in press (July 20, 2000?

Apollo experience report. Guidance and control systems: Orbital rate drive electronics for the Apollo command module and lunar module

A brief record of the development and use of the orbital-rate-drive assembly in the Apollo Program is presented. This device was procured as government-furnished equipment and was used on both the lunar module and the command module. Reviews of design, development, procurement, and flight experience are included

Turbulent magnetic dynamo excitation at low magnetic Prandtl number

Planetary and stellar dynamos likely result from turbulent motions in magnetofluids with kinematic viscosities that are small compared to their magnetic diffusivities. Laboratory experiments are in progress to produce similar dynamos in liquid metals. This work reviews recent computations of thresholds in critical magnetic Reynolds number above which dynamo amplification can be expected for mechanically-forced turbulence (helical and non-helical, short wavelength and long wavelength) as a function of the magnetic Prandtl number $P_M$. New results for helical forcing are discussed, for which a dynamo is obtained at $P_M=5\times10^{-3}$. The fact that the kinetic turbulent spectrum is much broader in wavenumber space than the magnetic spectrum leads to numerical difficulties which are bridged by a combination of overlapping direct numerical simulations and subgrid models of magnetohydrodynamic turbulence. Typically, the critical magnetic Reynolds number increases steeply as the magnetic Prandtl number decreases, and then reaches an asymptotic plateau at values of at most a few hundred. In the turbulent regime and for magnetic Reynolds numbers large enough, both small and large scale magnetic fields are excited. The interactions between different scales in the flow are also discussed.Comment: 8 pages, 8 figures, to appear in Physics of Plasma

In situ apparatus for the study of clathrate hydrates relevant to solar system bodies using synchrotron X-ray diffraction and Raman spectroscopy

Clathrate hydrates are believed to play a significant role in various solar system environments, e.g. comets, and the surfaces and interiors of icy satellites, however the structural factors governing their formation and dissociation are poorly understood. We demonstrate the use of a high pressure gas cell, combined with variable temperature cooling and time-resolved data collection, to the in situ study of clathrate hydrates under conditions relevant to solar system environments. Clathrates formed and processed within the cell are monitored in situ using synchrotron X-ray powder diffraction and Raman spectroscopy. X-ray diffraction allows the formation of clathrate hydrates to be observed as CO2 gas is applied to ice formed within the cell. Complete conversion is obtained by annealing at temperatures just below the ice melting point. A subsequent rise in the quantity of clathrate is observed as the cell is thermally cycled. Four regions between 100-5000cm-1 are present in the Raman spectra that carry features characteristic of both ice and clathrate formation. This novel experimental arrangement is well suited to studying clathrate hydrates over a range of temperature (80-500K) and pressure (1-100bar) conditions and can be used with a variety of different gases and starting aqueous compositions. We propose the increase in clathrate formation observed during thermal cycling may be due to the formation of a quasi liquid-like phase that forms at temperatures below the ice melting point, but which allows easier formation of new clathrate cages, or the retention and delocalisation of previously formed clathrate structures, possibly as amorphous clathrate. The structural similarities between hexagonal ice, the quasi liquid-like phase, and crystalline CO2 hydrate mean that differences in the Raman spectrum are subtle; however, all features out to 5000cm-1 are diagnostic of clathrate structure.Comment: Astronomy & Astrophysics, in press. 6 page

Carbonate Formation in Non-Aqueous Environments by Solid-Gas Carbonation of Silicates

We have produced synthetic analogues of cosmic silicates using the Sol Gel method, producing amorphous silicates of composition Mg(x)Ca(1-x)SiO3. Using synchrotron X-ray powder diffraction on Beamline I11 at the Diamond Light Source, together with a newly-commissioned gas cell, real-time powder diffraction scans have been taken of a range of silicates exposed to CO2 under non-ambient conditions. The SXPD is complemented by other techniques including Raman and Infrared Spectroscopy and SEM imaging.Comment: 5 pages, 3 figures. Contribution to the Proceedings of the First European Conference on Laboratory Astrophysics (ECLA

Evaluation of CBS 600 carburized steel as a gear material

Gear endurance tests were conducted with one lot of consumable-electrode vacuum-melted (CVM) AISI 9310 gears and one lot of air-melt CBS 600 gears. The gears were 8 pitch with a pitch diameter of 8.89 centimeters (3.5 in.). Bench-type rolling-element fatigue tests were also conducted with one lot of CVM AISI 9310, three lots of CVM CBS 600, and one of air-melt CBS 600 material. The rolling-element bars were 0.952 centimeter (0.375 in.) in diameter. The CBS 600 material exhibited pitting fatigue lives in both rolling-element specimens and gears at least equivalent to that of CVM AISI 9310. Tooth fracture failure occurred with the CBS 600 gears after overrunning a fatigue spall, but it did not occur with the CVM AISI 9310 gears. Tooth fracture in the CBS 600 was attributed to excessive carbon content in the case, excessive case depth, and a higher than normal core hardness

Spatial curvature effects on molecular transport by diffusion

For a substance diffusing on a curved surface, we obtain an explicit relation valid for very small values of the time, between the local concentration, the diffusion coefficient, the intrinsic spatial curvature and the time. We recover the known solution of Fick's law of diffusion in the flat space limit. In the biological context, this result would be useful in understanding the variations in the diffusion rates of integral proteins and other molecules on membranes.Comment: 10 page

Spin glass behavior in an interacting gamma-Fe2O3 nanoparticle system

In this paper we investigate the superspin glass behavior of a concentrated assembly of interacting maghemite nanoparticles and compare it to that of canonical atomic spin glass systems. ac versus temperature and frequency measurements show evidence of a superspin glass transition taking place at low temperature. In order to fully characterize the superspin glass phase, the aging behavior of both the thermo-remanent magnetization (TRM) and ac susceptibility has been investigated. It is shown that the scaling laws obeyed by superspin glasses and atomic spin glasses are essentially the same, after subtraction of a superparamagnetic contribution from the superspin glass response functions. Finally, we discuss a possible origin of this superparamagnetic contribution in terms of dilute spin glass models