Engineering topics

Gabriel, Stephen B.

Publications and source records attributed to Gabriel, Stephen B..

8 records

NASA NTRS1992

Dielectric-Particle Injector For Processing Of Materials

Device generates electrically charged particles of solid, or droplets of liquid, fabricated from dielectric material and projects them electrostatically, possibly injecting them into electrostatic-levitation chamber for containerless processing. Dielectric-particle or -droplet injector charges dielectric particles or droplets on zinc plate with photo-electrons generated by ultraviolet illumination, then ejects charged particles or droplets electrostatically from plate.

Leung, Philip L.↗

NASA NTRS1992

Lightweight, High-Yield Photocathode

Layer of Astroquartz (or equivalent) cloth woven from quartz thread multiplies electron current emitted by aluminum photocathode sensitive to ultraviolet light when placed in external steady-state electric field. Desirable in applications where low power consumption required.

Leung, Philip L.↗

NASA NTRS1990

Period and phase of the 88-year solar cycle and the Maunder minimum - Evidence for a chaotic sun

The problem of whether the solar dynamo is quasi-periodic or chaotic is addressed by examining 1500 years of sunspot, geomagnetic, and auroral activity cycles. Sub-harmonics were found of the fundamental solar cycle period during the years preceding the Maunder minimum and loss of phase of the subharmonic on emergence from it. These phenomena are indicative of chaos. They indicate that the solar dynamo is chaotic and is operating in a region close to the transition between period doubling and chaos. Since Maunder-type minima reoccur irregularly for millennia, it appears that the sun remains close to this transition to and from chaos. This is postulated to be a universal characteristic of solar type stars caused by feedback in the dynamo number.

Feynman, J.↗

NASA NTRS1990

A new model for the calculation and prediction of solar proton fluences

A new predictive engineering model for the energy greater than 10 MeV and greater than 30 MeV solar proton environment at earth is reviewed. The data used are from observations made from 1956 through 1985. In this data set, the distinction between 'ordinary events' and 'anomalously large events' that was required in earlier models disappeared. This permitted the use of statistical analysis methods developed for ordinary events on the entire data set. The greater than 10-MeV fluences with the new model are about twice those expected on the basis of earlier models. At energies greater than 30 MeV, the old and new models agree.

Feynman, Joan↗

NASA NTRS1990

Environmental interactions on Space Station

This paper describes the key environment/system interactions associated with the Space Station and its companion polar platform and defines the range of test environments that will need to be simulated. These environments include the neutral atmosphere, the ionospheric plasma, natural and man-made particulates, the ambient magnetic field, the South Atlantic Anomaly, and the ram/wake environment. The system/environment interactions include glow, oxygen erosion, drag, radiation effects, induced electric fields, high-voltage solar-array effects, and EMC/EMI associated with plasma/neutral gas operations. The Space Station and its associated systems pose unique demands on the ability to simulate these effects; synergistic effects require multiple environments to be simulated simultaneously, and the long life requirements require proper scaling of the exposure time. The analysis of specific effects and the calibration or improvement of ground test techniques will likely require in situ evaluation. Qualification and acceptance testing, because of cost and the impractically of extensive on-orbit analysis/modification, will likely remain ground test objectives except in very rare cases.

Garrett, Henry B.↗

NASA NTRS1989

Mandrels For Microtextured Small-Vessel Implants

Research shows artificial blood-vessel and heart-valve implants made more compatible with their biological environments by use of regularly microtextured surfaces. In new manufacturing process, ion beam etches patterned array of small pillars on mandrel used to mold tubular plastic implant. Pillars create tiny regularly spaced holes in inner surface of tube. Holes expected to provide sites for attachment of healthy lining. Polytetrafluoroethylene (PTFE) used as mandrel material because it can be etched by ion beam.

Deininger, William D.↗

NASA NTRS1988

Luminal surface fabrication for cardiovascular prostheses

A method is provided for forming a mold surface with microscopic upstanding pillars for molding the inside surface of a vascular prostheses (synthetic blood vessel). The mold article is formed from a quantity of Teflon (polytetrafluoroethylene) which has a polished, flat surface on which a gold film has been sputter deposited. A photoresist layer, which cannot adhere directly to Teflon, adheres to the gold. The photoresist is exposed and developed leaving a sputter resistant mask defining the desired pillar locations, and the resulting workpiece is ion etched to form the pillars in the Teflon. A synthetic blood vessel material is cast against the Teflon mold to form blind recesses on the inside of the synthetic blood vessel, with the recesses being of predetermined uniform cross section and present in a predetermined uniform pattern.

Deininger, William D.↗

NASA NTRS1987

Luminal surface fabrication for cardiovascular prostheses

Methodology used for the production of highly ordered surfaces on polytetrafluoroethylene (PTFE) Teflon, for use of this material as a surface layer in small-diameter vascular prostheses, is described. Directed argon-ion beam sputter etching is used to produce highly ordered specific surface morphologies, and photolithographic techniques are used for pattern definition. The methodology also includes surface polishing of the samples, sputter deposition of the intermediary layer of gold to enhance photoresist adhesion and improve pattern resolution, and rotating of the sample to minimize the effects of ion-beam nonuniformity and asymmetry. Use of these techniques resulted in the formation of regular arrays of sharply defined hexagonal pillars with smooth vertical walls and large relief.

Deininger, William D.↗