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At least 1,459 records · Page 81

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NASA NTRS1986

Plasma boundaries in the inner magnetosphere

Based principally on data collected aboard the DE 1 and 2 spacecraft during the October 7 to December 1, 1981 period, plasma boundaries in the inner magnetosphere are studied. Results indicate that in the evening sector, the low-energy ion transition and the 100-eV inner edge of the electron plasma sheet are coincident with each other, with the field lines threading the 100-eV equatorward edge of the auroral electron precipitation, and with variations in magnetic activity. A characteristic energy dispersion, observed in the plasma sheet inner edges at 100 eV, 1 keV and 10 keV, with the lower energy boundaries located earthward of the higher energy boundaries, is shown to increase from the midnight sector toward dusk, and to decrease with increasing magnetic activity. In the evening sector, these boundaries are shown to be accurate signatures of the boundary between closed and open convection trajectories, and the characteristic electron energy sheet dispersion is found to be similarly governed by the convection pattern such that the inner edges may be seen as the Alfven layers at those energies.

Horwitz, J. L.↗

NASA NTRS1986

An optical imaging and polarimetric study of the Lynds 723 and Barnard 335 molecular outflow regions

Optical polarization measurements are reported for a sample of stars viewed through the periphery of two dense molecular clouds, Barnard 335 and Lynds 723. These observations suggest that the direction of the magnetic field threading these clouds lies along position angle 111 + or - 4 deg for B335 and 90 + or - 8 deg for L723. In each case, the deduced field direction is approximately parallel to the direction defined by a collimated bipolar molecular outflow driven by a highly obscured FIR source. R, I, and H-alpha CCD images of these regions reveal knots of optical emission apparently associated with the molecular outflows. In the case of L723, two emission features are found within the blueshifted wing of the molecular outflow; along with the FIR source, these knots define a position angle nearly identical to that of the molecular flow. For B335, the observed emission knot lies in the redshifted wing of the molecular outflow along a position angle approximately equal to that of the flow.

Vrba, F. J.↗

NASA NTRS1986

The equivalent angle-of-attack concept for engineering analysis

An account is given of methods for the estimation of a wing-body-tail missile configuration's aerodynamic performance by means of the 'component buildup' method, in which the overall aerodynamic loads for an airframe are built up from the assumed characteristics of isolated airframe components and then subjected to additional loads generated by component interference. Attention is given to the cases of missile airframes in steady flow at arbitrary angles of attack and bank; the unifying thread of the present treatment is slender body theory, together with its nonlinear extensions through the equivalent angle-of-attack concept. The estimation of the forces and moments acting on each of the fins is emphasized, so that control cross-coupling effects as well as longitudinal and lateral directional effects can be determined.

Hemsch, M. J.↗

NASA NTRS1987

Latitudinal motions of the aurora during substorms

Sequences of auroral images obtained with Dynamics Explorer 1 are used to investigate latitudinal motions of the aurora in substorms. Average speeds of poleward motion are about 230 m/s near local midnight for two isolated, small substorms and about 1000 m/s during an intensification within a previously active auroral oval. The speed of poleward expansion measured at about 6-min temporal resolution can differ greatly from the average speed because of the episodic development of substorms. Recovery of the high-latitude boundary of the aurora to presubstorm latitudes is first observed in the postmidnight sector. In the premidnight sector the discrete aurora can become stationary for a period of time or even continue further poleward before a retreat to lower latitudes begins. During the recovery phase, a prominent decrease in luminosities is first observed at intermediate latitudes within the auroral distribution. This region is bounded at higher latitudes by the discrete aurora and at lower latitudes by bright diffuse aurora. Given that magnetic field lines threading these auroral distributions map to the plasma sheet boundary layer and to the central plasma sheet, respectively, magnetic field lines at the intermediate auroral latitudes then map to the plasma sheet at distances of more than about 22 earth radii.

Craven, J. D.↗

NASA NTRS1987

Mass outflows associated with young stellar objects

Properties of optical and molecular outflows associated with young stellar objects are discussed with emphasis placed on new results concerning outflow energetics, collimating structures, and the relationship between the outflow properties and the magnetic field geometry characterizing the host molecular clouds. Particular consideration is given to the IRAS observations of YSO mass outflows, which reveal extended far-IR emission associated with high-velocity molecular gas and in which a number of disk-like structures associated with YSO outflow sources were resolved. The disk axes appeared to lie along the direction of molecular outflows or stellar jets. The mass outflows showed a remarkable tendency to align along the direction of the magnetic fields which thread their host molecular clouds, suggesting that the cloud magnetic field must play an important role in determining the flattening (and perhaps the rotation) of protostellar structures.

Strom, Stephen E.↗

NASA NTRS1988

Heavy-Duty Rescue Straps For Coveralls

New type of strap on coveralls helps rescuers lift victims of industrial accidents. Made of heavy twill. New material, 1 in. wide and has breaking strength of 600 lb, sewn to coveralls with polyester thread in box "X" stitching. Reinforcing nylon webbing, 1 3/4 in. wide sewn with strap at attachment points.

Waddell, Henry M.↗

NASA NTRS1988

Hydrogen/Air-Ignition Torch

Torch is simple, reliable, and economical. Airflow cools inner tube prior to flowing through openings in inner tube and mixing with gaseous hydrogen. Spark plug connected to constant-duty simple ignition transformer threaded into side of torch and into inner tube. Transformer used to excite spark plug for period long enough to ignite gas. Transformer is turned off.

Repas, George A.↗

NASA NTRS1988

Semiautomatic Probe-And-Drogue Attachment Mechanism

Spring-loaded pawls provide quick coupling. As probe enters drogue during coupling, three spring-loaded pawls in probe latch probe in drogue, preventing accidental uncoupling. Then worm-gear mechanism turned by standard 0.25-in. (6.35-mm) tool transfers motion to central threaded shaft, extending cap at tip of probe until all play taken up. This centers probe in drogue and renders coupling pawls to extend again. New mechanism useful for coupling modular components in other applications where ease and security of attachment, precise final alignment, and ease of removal important and where stresses and bending reasonably low.

Wanagas, John D.↗

NASA NTRS1988

High-temperature properties of ceramic fibers and insulations for thermal protection of atmospheric entry and hypersonic cruise vehicles

Multilayer insulations (MIs) which will operate in the 500 to 1000 C temperature range are being considered for possible applications on aerospace vehicles subject to convective and radiative heating during atmospheric entry. The insulations described consist of ceramic fibers, insulations, and metal foils quilted together with ceramic thread. As these types of insulations have highly anisotropic properties, the total heat transfer characteristics must be determined. Data are presented on the thermal diffusivity and thermal conductivity of four types of MIs and are compared to the baseline Advanced Flexible Reusable Surface Insulation currently used on the Space Shuttle Orbiter. In addition, the high temperature properties of the fibers used in these MIs are discussed. The fibers investigated included silica and three types of aluminoborosilicate (ABS). Static tension tests were performed at temperatures up to 1200 C and the ultimate strain, tensile strength, and tensile modulus of single fibers were determined.

Kourtides, Demetrius A.↗

NASA NTRS1987

A boundary layer model for magnetospheric substorms

An alternative framework for understanding magnetospheric substorm activity is presented. It is argued that observations of magnetic field and plasma flow variations in the magnetotail can be explained in terms of the passage of the plasma sheet boundary layer over the satellite detecting the tail signatures. It is shown that field-aligned currents and particle acceleration processes on magnetic field lines threading the ionospheric Harang discontinuity lead to the distinctive particle and field signatures observed in the magnetotail during substorms. It is demonstrated that edge effects of field-aligned currents associated with the westward traveling surge can lead to the negative B(z) perturbations observed in the tail that are presently attributed to observations made on the anti-earthward side of a near-earth neutral line. Finally, it is shown that the model can provide a physical explanation of both the driven system and the loading-unloading system whose combined effects provide the observed substorm perturbation pattern in the magnetosphere and ionosphere.

Rostoker, Gordon↗

NASA NTRS1987

Ionospheric convection signatures and magnetic field topology

A statistical study of signatures of the high-latitude ionospheric convection pattern and the simultaneously observed energetic electron precipitation is presented. Most often found are convection cells in which the sunward flowing region contains auroral particle precipitation but the antisunward flowing region does not. However, observations also show the frequent occurrence of convection cells in which neither the antisunward nor the sunward flowing plasma region contains auroral particle precipitation. These findings may appear within the dawnside or duskside convection pattern and strongly suggest that such convection cells may be associated with open magnetic field lines that thread the magnetotail lobes.

Coley, W. R.↗

NASA NTRS1987

Microscopy of epitaxially grown beta-SiC on 001-plane silicon

Various defects occurring in epitaxially grown layers of beta-SiC are characterized by TEM, and the mechanisms of growth and defect formation are discussed. In particular, attention is given to the following types of defects: misfit dislocations, interfacial twins, antiphase boundaries, threading dislocations, and wide stacking faults. Details of the experimental procedure are given.

Pirouz, P.↗

NASA NTRS1988

Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

Mii, Y. J.↗

NASA NTRS1988

Observations of electron beam structure in space experiments

Observations of a 100-mA, 1-keV electron beam were made with a low light level TV system and other instruments aboard the space shuttle STS 3 in March 1982. When fired at a moderate pitch angle with respect to the magnetic field, the beam electrons initially moved outward along a classical helical trajectory. Within a short distance, however, the beam electrons were deflected away from the helical trajectory into paths parallel to magnetic field lines threading the primary helix. This resulted in the formation of a thin-walled, cylindrical electron beam structure having a radius equal to the primary beam gyroradius. This structure, which is consistent with earlier laboratory vacuum chamber observations and recent two-dimensional computer electrostatic plasma simulations, has important implications for determining the extent to which pulsed electron beams can radiate electromagnetic energy in the ionosphere.

Banks, Peter M.↗

NASA NTRS1988

High temperature properties of ceramic fibers and insulations for thermal protection of atmospheric entry and hypersonic cruise vehicles

Kourtides, Demetrius A.↗

NASA NTRS1987

Magnetic configuration of the distant plasma sheet - ISEE 3 observations

The influence of the IMF orientation and magnitude and substorm activity on the magnetic configuration of the central plasma sheet at 20-240 earth radii down the geomagnetic tail is investigated on the basis of ISEE-3 data. The results are presented graphically, and high-speed antisolar bulk flows threaded by southward magnetic fields are shown to be present in the distant plasma sheet after periods of substorm activity and southward IMF Bz. The effective dayside reconnection efficiency is estimated as 25 + or - 4 percent, in good agreement with theoretical models.

Slavin, J. A.↗

NASA NTRS1989

Inflatable-Seal Assembly For Cryogenic Fluids

Connector for cryogenic fluid lines quickly joined or separated, seals tightly, and reduces transfer of heat to fluid. Features redundant sealing rings inflated after joining so they wedge tightly against connector base, preventing leakage. Cylinder of FEP inflatable. Pair of threaded stainless-steel rings - one at each end of cylinder - secure cylinder in quick-disconnect assembly.

Buehler, Kurt↗

NASA NTRS1986

Visualization design and verification of Ada tasking using timing diagrams

The use of timing diagrams is recommended in the design and testing of multi-task Ada programs. By displaying the task states vs. time, timing diagrams can portray the simultaneous threads of data flow and control which characterize tasking programs. This description of the system's dynamic behavior from conception to testing is a necessary adjunct to other graphical techniques, such as structure charts, which essentially give a static view of the system. A series of steps is recommended which incorporates timing diagrams into the design process. Finally, a description is provided of a prototype Ada Execution Analyzer (AEA) which automates the production of timing diagrams from VAX/Ada debugger output.

Vidale, R. F.↗