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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Measurement of metastable N/+/1S/ 5755-A emission in the twilight thermosphere

Measurements are reported of the 5755-A emission arising from the transition N(+)(1D-1S) made at Sutherland, South Africa (32.4 deg S, 20.8 deg E). The surface brightness of the emission in mid-November 1977 decayed from approximately 5 R at 10 solar depression angle (SDA) to approximately 1 R at 15 deg SDA. By the use of these data, it has been determined that less than 5% of all N2 ionizations result in the production of N(+) ions in the 1S state. Quenching of N(+)(1S) by neutral constituents and electrons is found to be negligible above 220 km in the twilight thermosphere in November and December 1977. Measurements of the 5755-A emission therefore potentially provide a ground based means of measuring the N2 density in the twilight thermosphere.

Torr, D. G.↗
NASA NTRS1981

Analysis of the photo voltage decay /PVD/ method for measuring minority carrier lifetimes in P-N junction solar cells

The photo voltage decay (PVD) method for the measurement of minority carrier lifetimes in P-N junction solar cells with cell thickness comparable to or even less than the minority carrier diffusion length is examined. The method involves the generation of free carriers in the quasi-neutral bulk material by flashes of light and the monitoring of the subsequent decay of the induced open-circuit voltages as the carriers recombine, which is dependent on minority carrier recombination lifetime. It is shown that the voltage versus time curve for an ordinary solar cell (N(+)-P junction) is proportional to the inverse minority carrier lifetime plus a factor expressing the ratio of diffusion length to cell thickness. In the case of an ideal back-surface-field cell (N(+)-P-P(+) junction) however, the slope is directly proportional to the inverse minority carrier lifetime. It is noted that since most BSF cells are not ideal, possessing a sizable back surface recombination velocity, the PVD measurements must be treated with caution and supplemented with other nonstationary methods.

Von Roos, O.↗
NASA NTRS1981

Evaluation of TIROS-N and NOAA-6 satellite data: Comparisons of colocated soundings and analyses for a January case

An early January 1980 synoptic situation was used in evaluating the performance of TIROS-N and NOAA-6 operational temperature soundings. Visual and statistical comparisons of temperature and thickness fields were employed to determine the effects of manual screening of the satellite soundings and measure the accuracy of both the satellite soundings and analyses derived from them. Comparisons between the performance of TIROS-N and NOAA-6 were emphasized. Both satellites were able to correctly position the major troughs and ridges. Gradients were underestimated though, with troughs markedly too warm and ridges slightly too cold. The poorest data occurred near the surface and tropopause as reflected by larger standard deviations in those layers. The performance of TIROS-N was slightly superior to that of NOAA-6.

Schmidt, B. D.↗
NASA NTRS1981

A numerical evaluation of TIROS-N and NOAA-6 analyses in a high resolution limited area model

Vertical temperature profiles derived from TIROS-N and NOAA-6 radiance measurements were used to create separate analyses for the period 0000 GMT 6 January to 0000 GMT 7 January 1980. The 0000 GMT 6 January satellite analyses and a conventional analysis were used to initialize and run the University of Wisconsin's version of the Australian Region Primitive Equations model. Forecasts based on conventional analyses were used to evaluate the forecasts based only on satellite upper air data. The forecasts based only on TIROS-N or NOAA-6 data did reasonably well in locating the main trough and ridge positions. The satellite initial analyses and forecasts revealed errors correlated to the synoptic situation. The trough in both TIROS-N and NOAA-6 forecasts which was initially too warm remained too warm as it propagated eastward during the forecast period. Thus, it is unlikely that the operational satellite data will improve forecasts in a data dense region. However, in regions of poor data coverage, the satellite data should have a beneficial effect on numerical forecasts.

Derber, J. C.↗
NASA NTRS1982

The ultraviolet spectra of R and N type stars

Low dispersion long wave radiation spectra of three early N-type carbon stars (BL Orionis, TX Piscium and T Indi) obtained with the IUE are discussed. N-star spectra were compared with IUE observations of late M-type stars and several differences were noted. The Mg II and C II chromospheric emission lines reported are the first convincing detection of a 10,000-20,000 K chromosphere in the N stars.

Obrien, G. T.↗
NASA NTRS1981

The isotropic composition of cosmic ray B, C, N, and O nuclei

High resolution measurements are presented for the elemental and isotopic composition of galactic cosmic ray B, C, N, and O nuclei with about 30-130 MeV/nucleon. The isotopes are separately resolved, and the resulting abundances are limited by statistical rather than systematic uncertainties. N is found to be significantly depleted in the cosmic ray source with respect to the solar system and local interstellar medium, and it is concluded that the N-14/O-16 limit is inconsistent with models in which a majority of cosmic rays are accelerated interstellar material.

Mewaldt, R. A.↗
NASA NTRS1982

Radiative lifetime of the 5S2 metastable state of N/+/

The radiative lifetime of metastable N(+)(5S2) has been measured to be 4.2 + or - 0.6 msec, a value generally in agreement with theory, by direct monitoring of the spontaneous emission from approximately 1,000,000 ions stored in a radio-frequency ion trap. Additional measurements were made of the quenching rate coefficient (2.5 x 10 to the -9th cu cm/sec) and the production cross section (greater than or equal to 10 to the -18th sq cm) of N(+)(5S2) in N2. This work supports the interpretation of the 2145-A feature in the spectrum of aurorae as being due to N(+)(5S2) emission.

Knight, R. D.↗
NASA NTRS1982

Theoretical oscillator strengths for 21 spin-forbidden lines of C, N, O, Al, and Si

Detailed calculations are reported of the oscillator strengths of 21 spin-forbidden lines of C II, C III, N I, N II, N III, O I, O II, Al II, and Si III, including 10 lines arising from seven ground levels. All 21 lines lie in the region from 1160 to 2670 A, and the oscillator strengths probably are accurate typically to + or - 50%. These weak lines are particularly important in determining accurate elemental abundances in the interstellar gas.

Cowan, R. D.↗
NASA NTRS1981

A theory of the n-i-p silicon solar cell

A computer model has been developed, based on an analytical theory of the high base resistivity BSF n(+)(pi)p(+) or p(+)(nu)n(+) silicon solar cell. The model makes very few assumptions and accounts for nonuniform optical generation, generation and recombination in the junction space charge region, and bandgap narrowing in the heavily doped regions. The paper presents calculated results based on this model and compares them to available experimental data. Also discussed is radiation damage in high base resistivity n(+)(pi)p(+) space solar cells.

Goradia, C.↗
NASA NTRS1983

Dynamic Mechanical Properties of N-Phenylnadimide Modified PMR Polyimide Composites

The rheological behavior of newly developd Celion 6000/N-phenylnadimide modified PMR polyimide and PMR-15 composites was investigated. The dynamic mechanical properties were correlated with the structure of N-phenylnadimide modified PMR polyimides. The storage modulus (G'), loss modulus (G''), and loss tangent (tan delta) of four composite systems were measured over a temperature range from -150 to 400 C. Three well defined peaks were seen in the regions of 360, 100, and -120 C, corresponding to the alpha, beta, and gamma relaxations, respectively, of the matrix resins. The activation energies of the alpha, beta, and gamma relaxations were estimated to be 232, 60, and 14 kcal/mole, respectively, for PMR-15. Addition of N-phenylnadimide to the PMR-15 composition lowered the glass transition temperature and the activation energies of PMR-15 polyimide. The dynamic mechanical data appear to be consistent with the formation of a copolymer from N-phenylnadimide and a PMR-15 prepolymer.

Pater, R. H.↗
NASA NTRS1984

Effect of reabsorbed recombination radiation on the saturation current of direct gap p-n junctions

The application of the radiative transfer theory for semiconductors to p-n homojunctions subject to low level injection conditions is discussed. By virtue of the interaction of the radiation field with free carriers across the depletion layer, the saturation current density in Shockley's expression for the diode current is reduced at high doping levels. The reduction, due to self-induced photon generation, is noticeable for n-type material owing to the small electron effective mass in direct band-gap III-V compounds. The effect is insignificant in p-type material. At an equilibrium electron concentration of 2 x 10 to the 18th/cu cm in GaAs, a reduction of the saturation current density by 15 percent is predicted. It is concluded that realistic GaAs p-n junctions possess a finite thickness.

Von Roos, O.↗
NASA NTRS1984

On Bowen enhancement of the N III spectrum under solar and nebular conditions

Expected enhancement of the N III emission-line spectrum by the Bowen He II to O III to N III resonant photoexcitation process is computed using a six-configuration model. Preliminary comparisons with available solar and nebular observations indicate that the process may play only a small role, although photoexcitation quenching of the N III and O III far-infrared fine-structure lines is noted as a possibly important mechanism. Some features are discussed in connection with the nebular emission at 1750 A, which is suggested as an indicator of excitation class for planetary nebulae.

Kastner, S. O.↗
NASA NTRS1985

On the production of N(+) by energetic electrons

Calculations of the ratio of N(+) to total N2 ion production for auroral electrons which give a value of 0.16 compared to the value of 0.22 that has been assumed in a recent publication is presented. The corresponding ratio for photoelectron production is 0.05, which makes photoelectron production of N(+) negligible compared to photodissociative production. The ratio of 3914-A to total ion production is found to be 0.07 for auroral electrons and a similar 0.06 for photoelectrons. The 3371-A ratio to total N2 ion production is 0.09. This calculation also reveals that the secondary electrons in auroras, with energies less than 100 eV, produce only about one third of the total number of ions produced. Only one quarter of the N(+) ions are created by secondary electrons.

Richards, P. G.↗
NASA NTRS1986

N-ROSS: The dynamics and control issues

The Navy Remote Ocean Sensing System (N-ROSS) Dynamic Stability Study team concluded that the frozen April 1985 design was viable and contained no show stoppers, although it was also clear from the study results that the configuration required further optimization. While the frozen N-ROSS configuration used has since been superceded, and the vehicle is now under competitive procurement, several other results remain from the study that will have lasting value to the N-ROSS program. The importance of constructing an integrated simulation, to serve as a design and verification aid, has been clearly established. The two team approach to the study afforded the Navy a higher degree of confidence in the results than could have been accomplished by a single simulation, and the approach led to results that highlighted subtleties in the model and simulation development that surely would have been overlookded without the benefit of an independent companion simulation with which to compare it.

Lindberg, Robert E.↗
NASA NTRS1987

Development of a P-I-N HgCdTe photomixer for laser heterodyne spectrometry

An improved HgCdTe photomixer technology was demonstrated employing a p-i-n photodiode structure. The i-region was near intrinsic n-type HgCdTe; the n-region was formed by B+ ion implantation; and the p-region was formed either by a shallow Au diffusion or by a Pt Schottky barrier. Experimental devices in a back-side illuminated mesa diode configuration were fabricated, tested, and delivered. The best photomixer was packaged in a 24-hour LN2 dewar along with a cooled GaAs FET preamplifier. Testing was performed by mixing black-body radiation with a CO2 laser beam and measuring the IF signal, noise, and signal-to-noise ratio in the GHz frequency range. Signal bandwidth for this photomixer was 1.3 GHz. The heterodyne NEP was 4.4 x 10 to the -20 W/Hz out to 1 GHz increasing to 8.6 x 10 to the -10 W/Hz at 2 GHz. Other photomixers delivered on this program had heterodyne NEPs at 1 GHz ranging from 8 x 10 to the -20 to 4.4 x 10 to the -19 W/Hz and NEP bandwidths from 2 to 4 GHz.

Bratt, Peter R.↗
NASA NTRS1986

Dissociative excitation of the N(+)(5S) state by electron impact on N2 - Excitation function and quenching

Metastable N(+)(5S) ions were produced in the laboratory by dissociative excitation of N2 with energetic electrons. The resulting radiative decay of the N(+)(5S) state was observed with sufficient resolution to completely resolve the doublet from the nearby N2 molecular radiation. The excitation function was measured from threshold to 500 eV. The cross section peaks at a high electron energy and also exhibits a high threshold energy both of which are typical of dissociative excitation-ionization processes. This finding complicates the explanation of electron impact on N2 as the mechanism for the source of the 2145 A 'auroral mystery feature' by further increasing the required peak cross section. It is suggested that the apparent N(+)(5S) quenching in auroras may be an artifact due to the softening of the electron energy spectrum in the auroral E region.

Erdman, P. W.↗
NASA NTRS1988

Vertical column abundance measurements of atmospheric hydroxyl from 26 deg, 40 deg, and 65 deg N

The vertical column abundance of atmospheric hydroxyl was measured with Pepsios spectrometers from Boca Raton, Florida (26.4 N); Fritz Peak, Colorado (40 deg N); and Poker Flat, Alaska (65 deg N). The data show a global solar zenith angle dependence for the OH abundances, with the general features common in measurements from all three locations since 1980. However, while theoretical models agree well with the pre-1980 abundances, the post-1980 data do not. It appears that a significant change in the atmospheric photochemistry needs to be introduced.

Burnett, Clyde R.↗
NASA NTRS1988

High temperature transport properties of air - N-O interaction energies and collision integrals

Potential curves for the higher-lying states of NO are used together with a general scattering code to compute accurate values of transport collision integrals for N(4S/0/)-O(3P) interactions. It is found that the major contribution to the collision integrals comes from these higher-lying states of NO. New values of the collision integrals for N(4S/0/)-N(4S/0/) and O(3P)-O(3P) interactions are computed as well. The tabulations of the collision integrals cover a broad range of temperatures from 250 to 100,000 K and can be used to determine transport properties such as viscosity, thermal conductivity, and the diffusion coefficient to the second order.

Levin, E.↗