Search NASA⌕ Search

SEARCH · Search NASA

Results for “Field stability”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The role of CO2 in weathering reactions and the presence of S2 on Venus: Implications for the pyrite stability field

The stability of pyrite has become the focal point of study, since regions of low radio thermal emissivity were detected during the Pioneer Venus and Magellan radar mapping missions of Venus. Thermodynamic calculations and experimental studies have been performed assuming CO2 is a major contributor to the weathering of sulfides, as CO2 is the major gas species in the Venusian atmosphere. The purpose of the present study, however, is to demonstrate that CO2 is a non-reactive gas and that a minor species, S2, is the most important gas in determining whether pyrite is stable in the high radar reflectivity regions.

Straub, Darcy W.↗
NASA NTRS1991

Mapping the stability field of Jupiter Trojans

Jupiter Trojans are a remnant of outer solar system planetesimals captured into stable or quasistable libration about the 1:1 resonance with the mean motion of Jupiter. The observed swarms of Trojans may provide insight into the original mass of condensed solids in the zone from which the Jovian planets accumulated, provided that the mechanisms of capture can be understood. As the first step toward this understanding, the stability field of Trojans were mapped in the coordinate proper eccentricity, e(sub p), and libration amplitude, D. To accomplish this mapping, the orbits of 100 particles with e(sub p) in the range of 0 to 0.8 and D in the range 0 to 140 deg were numerically integrated. Orbits of the Sun, the four Jovian planets, and the massless particles were integrated as a full N-body system, in a barycentric frame using fourth order symplectic scheme.

Levison, H. F.↗
NASA NTRS1961

Note on Hydromagnetic Propagation and Geomagnetic Field Stability

In the adjoining letter, Dessler [1961] argues that the interface between the solar wind and the geomagnetic field is stable and cannot, therefore, generate hydromagnetic waves. According to our interpretation, his argument may be paraphrased as follows: He observes that, for many sudden commencement geomagnetic storms, surface magnetograms show no marked change in the level of disturbances from the period before the sudden commencement until well into the initial phase of the storm. He applies the attenuation factors calculated by Francis and Karplus [1960] to the measurements of the 1 cps component of the magnetic disturbances obtained at the surface. From this calculation, he concludes that, during the initial phase of these geomagnetic storms, the amplitudes of hydromagnetic disturbances above the ionosphere are less than 1. Assuming that the sudden commencement indicates the presence of a solar wind, he further concludes that hydromagnetie disturbances are not generated in the region between the geomagnetic field and the solar wind and that this interface is, therefore, inherently stable. He subsequently accounts for the hydromagnetie disturbances which are frequently observed at the earth as having been produced by fluctuations in the energy density of the impinging solar wind.

Coleman, P. J., Jr.↗
NASA NTRS1989

d.c. electric field stabilization of plasma fluctuations due to a velocity shear in the parallel ion flow

Consideration is given to the suggestion by Basu and Coppi (1988, 1989) that the DE-2 observations of broadband turbulence associated with sheared ion flows can be explained by electrostatic waves driven by a sheared ion flow along the magnetic field. It is pointed out that such a theory ignores the stronger shear in the ion flow transverse to the magnetic field, and that, when this shear is taken into account, the modes described by Basu and Coppi are easily destabilized. The theory of Basu and Coppi is shown to break down even when the shear in the parallel flow exceeds the shear in the transverse flow.

Ganguli, G.↗
NASA NTRS1981

Retrieval and use of high-resolution moisture and stability fields from Nimbus 6 HIRS radiances in pre-convective situations

A moisture-temperature retrieval scheme was developed for lower-tropospheric analysis and forecasting parameters from the Nimbus 6 High-resolution Infrared Radiation Sounder, in a study of convective development on the Great Plains of the U.S. on four case study days in August 1975. Dew points and temperatures, along with such secondary parameters as total precipitate water and static stability indices, were derived and analyzed at a horizontal resolution of up to 30 km on the four days. Convective development beginning 2.0-2.5 hours after the satellite pass at local noon was found to correlate well with local moisture and instability maxima seen in the satellite-derived analyses. A statistical structure analysis of the satellite-derived parameters gave the highest signal-to-noise values for the moisture and stability parameters, while the temperature parameters showed much lower signal-to-noise content.

Hillger, D. W.↗
NASA NTRS1993

Partially Grooved Domain Stabilization Structures for Vertical Bloch Line Memory

Bias field stability ranges were measured and numerically simulated for magnetic domains ingarnets stabilized by partially grooved rectangular and ring grooves. Simulation results agreefavorably with experimental results when finite slope effects of the groove walls are included. Asbias fields increase, rectangular and ring domains both destabilize through stripe head recession. Asbias fields decrease, destabilization in rectangular domains occurs by runout, while destabilization inring domains occurs by midstripe domain buckling. While ring domains are stable at lower biasfields than rectangular domains, bias field stability ranges are approximately equal. Hence, for thesame partial grooving depth, rectangular domains are preferred because they offer higher storagedensity potential in Vertical Block Line (VBL) storage arrays as long as bit propagation margins atstripe ends are sufficient.

Katti, R. R.↗
NASA NTRS1982

The effects on the MHD stability of field line tying to the end faces of a cylindrical magnetic loop

The ideal MHD energy equation is used to derive a stability equation for a specific class of perturbations, in an examination of magnetic loop MHD stability which takes field line tying at its root points into account. It is found that the field line tying effect is negligible to the m=1 kink mode, but important to the localized modes, in the case of a loop of aspect ratio greater than 10. The stability criterion for high-m value localized modes is derived, and compared with the Suydam criterion, to show that there are two field line tying effects for the perturbation of the class studied: (1) a field line bending effect, which is always stabilizing, and (2) a shear effect which is stabilizing or destabilizing depending on the sign of the gradient of the potential magnetic field. The net effect of field line tying is determined by the sum of these two effects.

An, C. Y.↗
NASA NTRS1977

Phase relations in the Fe-Ni-Cr-S system and the sulfidation of an austenitic stainless steel

The stability fields of various sulfide phases that form on Fe-Cr, Fe-Ni, Ni-Cr and Fe-Cr-Ni alloys were developed as a function of temperature and the partial pressure of sulfur. The calculated stability fields in the ternary system were displayed on plots of log P sub S sub 2 versus the conjugate extensive variable which provides a better framework for following the sulfidation of Fe-Cr-Ni alloys at high temperatures. Experimental and estimated thermodynamic data were used in developing the sulfur potential diagrams. Current models and correlations were employed to estimate the unknown thermodynamic behavior of solid solutions of sulfides and to supplement the incomplete phase diagram data of geophysical literature. These constructed stability field diagrams were in excellent agreement with the sulfide phases and compositions determined during a sulfidation experiment.

Jacob, K. T.↗