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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Lubricating characteristics of polyimide bonded graphite fluoride and polyimide thin films

A friction and wear life study was conducted on the use of a polyimide (PI) varnish as a binder for the solid lubricant, graphite fluoride (CF(1.1))N. Also studied were the lubricating properties of PI thin films with no solid lubricant additives. For comparison, similar experiments on PI-bonded MoS2 and burnished films of MoS2 or (CF(li))N were conducted. The best results were obtained with the PI-bonded (CF(1.1))N films. The polyimide thin films (with no solid lubricant additives) did not lubricate well at 25 C; however, when heated to 100 C, low friction and long wear lives were obtained.

Fusaro, R. L.↗
NASA NTRS1972

Friction and wear life properties of polyimide thin films

A transition in the friction coefficient and wear life properties of Pyralin polyimide (PI) thin films was found to exist at a temperature between 25 deg and 100 deg C. Above this transition, PI thin films gave long wear lives and low friction coefficients. The presence of H2O in air improved the friction and wear life properties at 25 deg C; but at 100 deg C, H2O had a detrimental effect. At 100 deg C and above, a dry argon atmosphere gave lower friction coefficients and longer wear lives than did a dry air atmosphere.

Fusaro, R. L.↗
NASA NTRS1972

Superconducting properties of annealed Nb-Al-Ge thin films.

Discussion of the superconducting transition temperature and other superconducting properties of annealed Nb-Al-Ge thin films which were prepared by sputtering from a 3Nb-0.8Al-0.2Ge cathode. Annealing was performed in a high-vacuum environment maintained at 10 to the minus 9th torr or less, for times and temperatures near the optimum conditions for bulk Nb-Al-Ge. Films with transition temperatures from 12 to 16 K were annealed and in all cases a rise in transition temperature was observed, with the maximum value obtained thus far being 17.5 K. The current carrying capacity values, already substantially higher for unannealed thin films than for the bulk, were raised even further in the annealed samples, indicating that annealing has no detrimental effects on the flux pinning in these films.

Janocko, M. A.↗
NASA NTRS1972

The interpretation of total line intensities from optically thin gases. I, II, III.

Description of a general method for inferring, from the line emission of an optically thin medium, the physical state of a gas along the column in a line of sight. The method is devised for applications to astronomy, especially for studies of the solar corona, the chromosphere-corona transition region, planetary nebulae, and other optically thin sources. A unique specification is found in terms of a bivariate distribution function describing the partitioning of matter in a gas over density and temperature. It is shown that, given sufficient observational data, it is in principle possible to determine both this bivariate distribution function and the chemical composition. The formulation for a situation encountered in the solar corona illustrates the application of the method.

Jefferies, J. T.↗
NASA NTRS1972

Thin film fuel cell electrodes.

Earlier work shows that fuel cell electrodes prepared by sputtering thin films of platinum on porous vycor substrates avoid diffusion limitations even at high current densities. The presented study shows that the specific activity of sputtered platinum is not unusually high. Performance limitations are found to be controlled by physical processes, even at low loadings. Catalyst activity is strongly influenced by platinum sputtering parameters, which seemingly change the surface area of the catalyst layer. The use of porous nickel as a substrate shows that pore size of the substrate is an important parameter. It is noted that electrode performance increases with increasing loading for catalyst layers up to two microns thick, thus showing the physical properties of the sputtered layer to be different from platinum foil. Electrode performance is also sensitive to changing differential pressure across the electrode. The application of sputtered catalyst layers to fuel cell matrices for the purpose of obtaining thin total cells appears feasible.

Asher, W. J.↗
NASA NTRS1972

Transmission of sound in ducts with thin shear layers - Convergence to the uniform flow case.

The problem of the transmission of sound in a duct with very thin shear layers at the walls is treated by an inner expansion method. The results show that the formulation of the problem of the transmission of sound in a duct with a shear layer at the wall converges, in the case of a vanishingly thin shear layer, to the formulation of the same problem when uniform flow is assumed and the wall boundary condition is that of continuity of particle displacement.

Eversman, W.↗
NASA NTRS1973

Analysis of the dynamics of thin primary mirrors for large astronomical telescopes

The NASTRAN structural analysis program was used to investigate the dynamic properties of thin primary mirrors suitable for use in large orbiting astronomical telescopes. An analysis is included of the mode shapes and modal frequencies for several thin, homogeneous, isotropic mirrors. Typical cases include two different mirror diameters, two different diameter-to-thickness ratios, and both a mirror without and a mirror with a central hole that is 22 percent of the mirror diameter. The finite-element structural model is evaluated by comparing the NASTRAN generated results with theoretical values for a simply supported, flat, circular mirror. The same model is then used for evaluating the spherical mirrors. The mode shapes and frequencies of a 0.762-meter-diameter mirror with a 60-to-1 diameter-to-thickness ratio and a three-point rigid kinematic (not overconstrained) mount are calculated and plotted for comparison with results obtained previously from the SAMIS structural analysis program for this same mirror. A static analysis is also shown for comparison with experimentally obtained influence coefficients.

Ostroff, A. J.↗
NASA NTRS1973

Application of ERTS data to the detection of thin cirrus and clear air turbulence

The feasibility of detecting a thin cirrus and clear air turbulence from ERTS MSS data is explored. The result of analyses indicates that a thin cirrus not shown in conventional meteorological satellite picture can be revealed in ERTS MSS picture. It is also found that the core of jet stream can be located with high accuracy from ERTS pictures and the possible area of clear air turbulence can be predicted if the data of the quality of ERTS data are available in real time.

Tsuchiya, K.↗
NASA NTRS1973

A thin polymer insulator for Josephson tunneling applications

The use of an organic monolayer formed from a vapor as an insulating barrier for thin film Josephson junctions is considered, and the effect of an organic monolayer on the transition temperature of a thin film superconductor is investigated. Also analyzed are the geometric factors which influence Josephson junctions and Josephson junction interferometers.

Wilmsen, C. M.↗
NASA NTRS1973

Application of phase-change technique to thin sections with heating on both surfaces

A numerical digital computer program was developed to calculate the heat-transfer coefficients for both sides of a one-dimensional finite slab subject to the boundary conditions ascribed to the phase-change coating heat-transfer technique. In a typical tunnel test situation where a thin wing was exposed to heating on both sides, the data reduction procedures for a semi-infinite slab gave heat-transfer coefficients as much as 375 percent too high on the side with the lowest heating. The results from the one-dimensional finite-slab procedure are presented in the form of correction factors to the solution for a semi-infinite slab in terms of parameters normally used with the phase-change heat-transfer technique. These correlations are not restricted to slab thickness or thermophysical properties and are easily used to obtain accurate data on thin model sections.

Hunt, J. L.↗
NASA NTRS1972

Lubricating characteristics of polyimide bonded graphite fluoride and polyimide thin films.

A friction and wear life study was conducted on the use of a polyimide (PI) varnish as a binder for the solid lubricant, graphite fluoride (CF sub 1.1) sub n. Also studied were the lubricating properties of PI thin films with no solid lubricant additives. For comparison, similar experiments on PI-bonded MoS2 and burnished films of MoS2 or (CF sub 1.1) sub n were conducted. The best results were obtained with the PI-bonded (CF sub 1.1) sub n films. The polyimide thin films (with no solid lubricant additives) did not lubricate well at 25 C; however, when heated to 100 C, low friction and long wear lives were obtained.

Fusaro, R. L.↗
NASA NTRS1973

A thick-thin approximation for radiative transfer.

First- and second-order formulations of a thick-thin approximate technique for application to the solution of energy transport when nongray radiation is important are presented. The virtue of the technique is that it eliminates the cumbersome integral terms which usually appear. It is shown that the temperature distributions calculated with the technique agree well with the results of more rigorous calculations if a proper value of the critical optical depth, which separates the thick and thin regions of the spectrum, is used. The proper value of the critical optical depth is less than one and may be less than 0.5. It is also shown that the jump boundary conditions which are frequently employed with the Rosseland, or diffusion, approximation should incorporate the Planck mean absorption coefficient for a nongray gas. This is in contradiction to suggestions appearing in the literature.

Olstad, W. B.↗
NASA NTRS1973

Application of ERTS data to the detection of thin cirrus and clean air turbulence

The author has identified the following significant results. The feasibility of detecting a thin cirrus and clear air turbulence from ERTS-1 MSS data is explored. The result of analyses indicates that a thin cirrus not shown in a conventional meteorological satellite picture can be revealed in ERTS-1 MSS pictures. Is also found that the core of jet stream can be located with high accuracy from ERTS-1 pictures and the possible area of clear air turbulence can be predicted if the data of the quality of ERTS-1 data are available in real time.

Tsuchiya, K.↗
NASA NTRS1974

Radiation and scattering by thin-wire structures in the complex frequency domain

Piecewise-sinusoidal expansion functions and Galerkin's method are employed to formulate a solution for an arbitrary thin-wire configuration in a homogeneous conducting medium. The analysis is performed in the real or complex frequency domain. In antenna problems, the solution determines the current distribution, impedance, radiation efficiency, gain and far-field patterns. In scattering problems, the solution determines the absorption cross section, scattering cross section and the polarization scattering matrix. The electromagnetic theory is presented for thin wires and the forward-scattering theorem is developed for an arbitrary target in a homogeneous conducting medium.

Richmond, J. H.↗
NASA NTRS1974

QSO envelopes - Optically thin, low density, and normal abundances

Consideration of a family of photoionization models which are optically thin to the ionizing radiation, have low enough density that collisional de-excitation is unimportant, and have normal (cosmic) chemical abundances. The line ratios from all such models with a given form of the ionizing spectrum can be derived by means of a scaling law from a single numerical calculation and expressed as a function of one physical parameter. The value of the parameter is uniquely determined from the observed line ratios. The resulting model is in reasonably good agreement with the typical or composite QSO spectrum and with line intensities for two recently observed individual QSOs. It is therefore suggested that much of the emission may come from optically thin gas, although some of the observational evidence (especially the strength of Mg II 2800 A) indicates that thick gas may also be present in some objects.

Scargle, J. D.↗
NASA NTRS1975

Development of a high efficiency thin silicon solar cell

Progress is reported in an attempt to realize higher specific power output and radiation resistance from thin solar cells for space applications. The efforts applied to establishing the technological base for fabricating high efficiency thin solar cells are described. Progress is characterized by continuous improvements in all parameters of the space cell.

Lindmayer, J.↗
NASA NTRS1974

Examination of the influence of coatings on thin superalloy sections. Volume 2: Detailed procedures and data

The effects of an aluminide coating, Codep B-1, and of section thickness were investigated on two cast nickel base superalloys, Rene 80 and Rene 120. Cast section thicknesses ranged from 0.038 cm to 0.15 cm. Simulated engine exposures for 1000 hours at 899C or 982C in a jet fuel burner rig with cyclic air cooling were studied, as were the effects of surface machining before coating and re-machining and re-coating after exposures. The properties evaluated included tensile at room temperature., 871C and 982C, stress rupture at 760C, 871C, 982C and 1093C, high cycle mechanical fatigue at room temperature., and thermal fatigue with a 1093C peak temperature. Thin sections had tensile strengths similar to standard size bars up to 871C and lower strengths at 982C and above, with equivalent elongation, and stress rupture life was lower for thin sections at all test conditions. The aluminide coating lowered tensile and rupture strengths up to 871C, with greater effects on thinner specimens. Elevated temperature exposure lowered tensile and rupture strengths of thinner specimens at the lower test temperatures. Surface machining had little effect on properties, but re-machining after exposure reduced thickness and increased metallurgical changes enough to lower properties at most test conditions.

Kaufman, M.↗
NASA NTRS1974

Photomechanical vibration of thin crystals of polar semiconductors

It was found that thin crystals of polar (non-centrosymmetric) semiconductors constitute a new type of photosensitive system in which incident illumination is converted into mechanical energy: thus, illumination-induced elastic deformation (bending) was observed on thin (00.1) CdS and (111) GaAs crystals; furthermore, by employing chopped light the crystals were excited to their resonant vibration (photomechanical vibration); the dependence of the amplitude of this vibration on the energy of the incident radiation was found to be similar to the dependence of the surface photovoltage on the energy of the incident radiation (surface photovoltage spectrum). The present findings are consistent with a model based on light-induced modulation of the piezoelectric surface stresses.

Lagowski, J.↗