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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.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Ultra-stable oscillator with complementary transistors

A high frequency oscillator, having both good short and long term stability, is formed by including a piezoelectric crystal in the base circuit of a first bi-polar transistor circuit, the bi-polar transistor itself operated below its transitional frequency and having its emitter load chosen so that the input impedance, looking into the base thereof, exhibits a negative resistance in parallel with a capacitive reactance. Combined with this basic circuit is an auxiliary, complementary, second bi-polar transistor circuit of the same form with the piezoelectric crystal being common to both circuits. By this configuration small changes in quiescent current are substantially cancelled by opposite variations in the second bi-polar transistor circuit, thereby achieving from the oscillator a signal having its frequency of oscillation stable over long time periods as well as short time periods.

Kleinberg, L. L.↗
NASA NTRS1973

Development of thermally stable phosphonitrile elastomers for advanced aerospace structures

Both high and low molecular weight, curable poly(fluoroalkoxy phosphazene) terpolymers were prepared. These terpolymers resulted from reaction of (Cl2PNn) polymer with alkoxides derived from CF3CH2OH and C3F7CH2OH, and an alkoxide derived from CH3CH(OH)C2H4OH. The terpolymers were crosslinked with polyisocyanates at room temperature. High molecular weight materials were converted into isocyanate prepolymers which as films underwent moisture cures at room temperature. Prepolymer solutions were stable for several days, and showed good adhesion. Also the effects of polymerization of (Cl2PN)3 were studied. Purified octachlorophosphazene, thiocyanate salts, or hydrogen chloride were employed in attempts to decrease molecular weight. Hydrogen chloride was found to be a good agent for preparation of low molecular weight poly(dichloro phosphazene).

Reynard, K. A.↗
NASA NTRS1973

A highly stable explicit integration technique for computational continuum mechanics

A user-oriented subroutine package is built around a highly stable explicit integration algorithm for solution of large order systems of ordinary differential equations, as result from discretization of initial-boundary value problems in continuum mechanics. Fast and accurate solutions, for problems in laminar and turbulent, two and three-dimensional viscous flow fields and multi-dimensional transient heat transfer, are presented using this algorithm, as embodied within a general purpose finite element computer program.

Baker, A. J.↗
NASA NTRS1974

On the marginally stable saturation spectrum of unstable type I equatorial electrojet irregularities

Formulation of a self-consistent convective nonlinear theory of type I irregularities in the equatorial electrojet. It is found that a combination of three mechanisms - convective amplification, quasi-linear polarization electric field reduction, and nonlinear particle orbit diffusion damping - accounts for radar backscatter observations of a ubiquitous marginally stable (or 'constant ion-acoustic Doppler shift') saturation spectrum better than any of the three mechanisms treated separately. In particular, no spatially homogeneous theory without wave refraction can account for the observations. Wave refraction alone or with quasi-linear polarization electric field reduction is also inadequate. Wave refraction, quasi-linear polarization reduction, and particle orbit diffusion theory appear to account for type I observations at radar elevation angles less than 60 deg. Vertical type I backscatter cannot be explained without modifying the present laminar electrojet model.

Lee, K.↗
NASA NTRS1974

Vibrationally excited nitrogen in stable auroral red arcs and its effect on ionospheric recombination

The time-dependent continuity equations, including diffusion, were solved for the first six energy levels of molecular nitrogen for conditions in the thermosphere corresponding to stable auroral red (SAR) arcs. The results show that molecular nitrogen is excited vibrationally to the degree that the rate constant for the ionospheric loss process, O(+) + N2 yields NO(+) + N, is increased by as much as a factor of 7.6 at F2 region altitudes. It was found that deviations from the energetically equivalent Boltzmann distribution were large, causing the rate constant to be as much as 1.6 times the rate constant calculated for the Boltzmann distribution. These results indicate that SAR arc intensities as small as 58 R can produce noticeable increases in the ionosphere ion-atom interchange reaction rate and hence in the rate of loss of ionospheric electrons. It is suggested that the observed decrease of electron density in the F2 region in SAR arcs can probably be explained by enhanced reaction rates for ion-atom interchange between O(+) and N2 caused by vibrational excitation of molecular nitrogen by electron impact.

Newton, G. P.↗
NASA NTRS1974

A stable, linear frequency-modulated oscillator, part 1

The development of a push-pull frequency-modulated oscillator employing field-effect transistors is described. The advantages of field-effect transistors for use in a frequency-stable oscillator are presented. Linearization of the frequency deviation was accomplished by utilizing the square-law characteristic of an FET used as a modulating amplifier. The push-pull oscillator model produced a linear frequency deviation of more than 10 MHz at a center frequency of approximately 100 MHz. Output power is within 0.6 db of a nominal +8.5 dBm over the desired frequency range, and the modulation bandwidth is dc to 10 MHz. Frequency variation with temperature after compensation with a negative-temperature-coefficient capacitor is within + or - 0.05% from 0 to 60 C.

Honnell, M. A.↗
NASA NTRS1974

Development of space stable thermal control coatings for use on large space vehicles

The development of a large scale manufacturing method for the production of a stable zinc orthotitanate pigment is discussed. Major emphasis was placed on the evaluation of ultraviolet radiation stability tests of pigments derived from coprecipitated and individually precipitated oxalates. Emphasis was also placed on an investigation of the conditions (time and temperature) leading to high reflectance and high optical stability. Paints were formulated in OI-650 and in OI-650G vehicles from pigments which were prepared at various temperatures. Analyses of ultraviolet irradiation test data were conducted regarding optimum pigment preparation parameters and treatment conditions.

Gilligan, J. E.↗
NASA NTRS1974

Development of space stable thermal control coatings for use on large space vehicles

The development of a large scale manufacturing method for the production of a stable zinc orthotitanate pigment is discussed. Major emphasis was placed on the evaluation of the radiation stability of Tektronix, Inc. pigments and of the conditions (time and temperature) leading to high reflection and high optical stability. Paints were formulated in OI-650 and in OI-650G vehicles from pigments which were prepared at various temperatures, some of which were chemically treated to remove ZnO. Ultraviolet irradiation tests of these paints were performed, and observations made regarding optimum pigment preparation parameters.

Gilligan, J. E.↗
NASA NTRS1975

Development of space stable thermal control coatings for use on large space vehicles

The development of a large scale manufacturing method for the production of a stable zinc orthotitanate pigment is studied, with emphasis placed on the comprehensive analysis of the properties and environmental stability of oxalate precursor zinc orthotitanate pigments and of the preparative conditions (time and temperature) leading to optimum properties and optical stability.

Gilligan, J. E.↗
NASA NTRS1974

ENDOR and ESR studies of a stable radical in irradiated cytidine

A model is proposed for a stable radical species formed by X-irradiation in a single crystal of cytidine and studied by electron nuclear double resonance (ENDOR) and electron spin resonance (ESR) techniques at room temperature. ENDOR and ESR spectra are analyzed to obtain the principal values of the spectroscopic splitting factor and the spectroscopic and hyperfine splitting tensors. The results show hyperfine coupling of an unpaired electron to one hydrogen nucleus and two slightly different geometric forms of the radical with small differences in hyperfine couplings. It is proposed that this radical is formed in the ribose sugar group with a hydrogen atom in a beta position coupling with respect to a carbon-centered unpaired electron and a spin density of approximately 0.2 on a carbon atom.

Allison, D. L.↗
NASA NTRS1976

Polymeric foams stable at high temperatures

Crosslinked poly(N-arylenebenzimidazoles) are stable up to 370 C. Polymers are made by mixing appropriate stoichiometric amounts of tetramine and aromatic dicarboxylic acid anhydride with phenol or alkyl-substituted phenol.

Riccitiello, S. R.↗
NASA NTRS1974

Development of space stable thermal control coatings for use on large space vehicles

The development of a large scale manufacturing method for the production of a stable zinc orthotitanate pigment by means of an oxalate co-precipitation method is examined. Pigments were prepared at various temperatures, and major emphasis was placed on the determination of the important parameters of post-precipitation firing and treatment. A large-scale process for the modification of a glass resin binder was developed and paints were formulated using the binder.

Gilligan, J. E.↗
NASA NTRS1976

Development of a protective decorative fire resistant low smoke emitting, thermally stable coating material

The development of suitable electrocoatings and subsequent application to nonconductive substrates are discussed. Substrates investigated were plastics or resin-treated materials such as FX-resin (phenolic-type resin) impregnated fiberglass mat, polyphenylene sulfide, polyether sulfone and polyimide-impregnated unidirectional fiberglass. Efforts were aimed at formulating a fire-resistant, low smoke emitting, thermally stable, easily cleaned coating material. The coating is to be used for covering substrate panels, such as aluminum, silicate foam, polymeric structural entities, etc., all of which are applied in the aircraft cabin interior and thus subject to the spillages, scuffing, spotting and the general contaminants which prevail in aircraft passenger compartments.

Source record↗
NASA NTRS1976

Simultaneous observations of the proton ring current and stable auroral red arcs

Explorer 45 observed the equatorial proton ring current in the plasmapause region and Fritz Peak Observatory observed stable auroral red (SAR) arcs on Dec. 17, 1971 during a geomagnetic storm. An estimate of energy lost from the ring current was obtained by using Explorer 45 observations of pitch angle distribution transitions which are probably due to pitch angle diffusion-driven resonant interactions with ion cyclotron waves. Estimates of the equatorial loss rate yield values greater than the required SAR arc energy input rate, and the location of the peaks in these loss rates agrees with the observed location of the arcs. It is thus concluded that this energy loss is sufficient to sustain the SAR arcs.

Williams, D. J.↗
NASA NTRS1976

Laws of effluent dispersion in the steady-state atmospheric surface layer in stable and unstable conditions

The two-dimensional diffusion equation has been solved by an integral method to obtain the distribution of ground-level concentration of an inert effluent emitted from a semi-infinite area source in a steady-state and horizontally homogeneous atmospheric surface layer. Mean wind velocity and eddy diffusivity profiles derived from empirically determined flux-profile relations of Businger et al. (1971) for stable and unstable surface layers were used. It is found that concentration as a function of downwind distance can be described by a simple formula over distances of practical interest in surface layer dispersion. Corresponding results for a cross-wind infinite line source are obtained by simple differentiation. The concentration distribution is completely determined by the friction velocity, the Monin-Obukhov length, the roughness length, and the effluent source strength. The generalization of the integral method needed to obtain accurate solutions of the diffusion equation with the given wind velocity and diffusivity profiles is discussed in an appendix.

Lebedeff, S. A.↗
NASA NTRS1977

The design of hydraulic pressure regulators that are stable without the use of sensing line restrictors or frictional dampers

Parameters controlled in design determine the stability of hydraulic pressure regulators in service. The non-linear sensing line restrictor can provide stability, but degrades the transient response. Linear damping is not always physically realizable and is sensitive to clearance and viscosity. Design relationships are analytically derived through which regulators can be made to be stable without the use of either of these damping means. The analytical distinctions between the parameters derived and those in prior literature are discussed. An analytically derived circuit component that stabilizes an otherwise unstable regulator and its experimental verification is described.

Gold, H.↗
NASA NTRS1978

Synthesis of thermally stable polymers

The reaction of bis triazo linediones with divinyl esters and substituted styrenes was investigated. Twenty new polymers were derived via reaction of two previously synthesized bis triazol linediones and four new bis atriazol linediones with eight styrenes. The structure and polymer properties of these thermally stable polymers was examined. The reaction of triazo linediones with enol esters was also considered.

Butler, G. B.↗