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At least 613 records · Page 34

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NASA NTRS1979

The grabens of Canyonlands National Park, Utah - Geometry, mechanics, and kinematics

Results are reported for three years of field and analytical study of a system of young and very well exposed grabens in southeastern Utah. A kinematic and mechanical model is developed for these specific grabens with the hope that this will aid in interpreting graben systems elsewhere on the earth and other planets. Because studies on other planets must be based entirely on photo analysis, an attempt is made to determine to what extent three-dimensional geometry could be inferred from photographs alone. An equation based on the model of graben geometry and kinematics relates thickness of faulted plates to graben parameters measurable on photographs. The initial width of a nascent graben is a simple function of the dip of the faults bounding the graben and of the thickness of the faulted brittle plate. The uniform spacing of the grabens is a natural result of the geometry of the system.

Mcgill, G. E.↗

NASA NTRS1979

Stellar evolution from the zero-age main sequence

A consistent set of 247 evolutionary sequences extending from the ZAMS to the red-giant branch is presented for Y from 0.10 to 0.40, Z from 0.00001 to 0.10, and masses of 0.55 to 6.90 solar masses. Each sequence is started from a homogeneous ZAMS model, and almost all are evolved to the base of the red-giant branch. It is shown that: (1) the relative position of the main sequence can be determined as a function of composition; (2) theoretical luminosity functions can be derived from the relative evolutionary time scales; (3) a dip in luminosity sometimes occurs at the base of the red-giant branch and is most pronounced at larger Z values; (4) metal-poor stars evolve farther up along the main sequence before turning off toward the red-giant branch; and (5) the onset of helium burning halts the evolution across the Hertzsprung gap for the most massive and most metal-poor models, so that the star remains blue during its phase of core-helium burning.

Mengel, J. G.↗

NASA NTRS1980

Process modifications for improved carbon fiber composites: Alleviation of the electrical hazards problem

Attempts to alleviate carbon-fiber-composite electrical hazards during airplane crash fires through fiber gasification are described. Thermogravimetric and differential scanning calorimetric experiments found several catalysts that caused fibers to combust when composites were exposed to test fires. Composites were tested in the 'Burn-Bang' apparatus and in high voltage electrical detection grid apparatus. In a standard three minute burn test modified composites released no fibers, while state-of-the-art composites released several hundred fiber fragments. Expected service life with and without catalytic modification was studied and electron microscopy and X-ray microanalysis furnished physical appearance and chemical composition data. An acrylic acid polymer fiber coating was developed that wet the carbon fiber surface uniformly with the catalyst, providing a marked contrast with the uneven coats obtained by solution-dipping.

Ramohalli, K.↗

NASA NTRS1979

Equatorial electrojet control on the low latitude ionospheric total electron content

Faraday rotation measurements at 140 MHz were made at a number of locations (covering dip latitudes 3 deg N to 27 deg N) in India, during the period October 1975 to July 1976, when the geosynchronous satellite ATS-6 was positioned at 35 deg E. The ionospheric total electron content (TEC) derived from these measurements shows a semi-annual variation with maxima in equinoxes at all the stations. It is observed that the mean peak electron content is more in April than in October, for the stations situated to the north (poleward) of the crest of the equatorial anomaly whereas for the stations situated to the south (equatorward) of the crest of the equatorial anomaly, a peak larger in October than in April is observed. The equatorial electrojet in this period is found to be stronger in April than in October and can be considered as contributing to this asymmetry in the semi-annual variation of the ionospheric TEC.

Sethia, G.↗

NASA NTRS1979

The equatorial total electron content and shape factor

The diurnal variations of electron content and shape factor observed at an equatorial station during sunspot minimum are shown to be consistent with the electron density profiles observed at Jicamarca during sunspot minimum. The rapid increase in electron content and the shape factor at sunrise results from the EUV production of ionization in the E and F regions. Day-to-day variations in daytime electron content are observed to be quite small at the equator. The evening decrease in the shape factor results from an upward drift of the F region at sunset and the evening decay of the E and bottomside F regions. The nighttime peak or plateau in the shape factor is produced by the slow downward drift of the electron density profile. The deep predawn dip in the shape factor is caused by the main peak of the F layer reaching low altitudes where high loss rates cause a large reduction in ionization below 300 km and very flat electron density profile.

Donnelly, R. F.↗

NASA NTRS1980

On ultracold molecular gas toward the galactic center

Several positions near the galactic center (Sgr A) in the J=1-0 rotational transitions of (C-12)O, (C-13)O, and C(O-18) were observed in order to better understand the nature of the 'very cold' molecular gas whose existence was first stressed by Liszt and his colleagues (1975, 1977). It is established that several dips in the (C-12)O spectra are due to optically thick clouds of foreground CO with relatively low excitation temperatures (T sub ex). T sub ex is found to be greater than about 5.3 K for all such (C-12)O clouds in all five observed directions. Such clouds fall at the extreme low end of the measured range of T sub ex for nearby dark clouds, but would, nonetheless, generally be detected in sensitive emission surveys of galactic CO.

Zuckerman, B.↗

NASA NTRS1980

The behavior of the O/+/-H/+/ transition level at solar maximum

An examination of the transition level at which the ionospheric ions O(+) and H(+) are equal in concentration has been carried out by using the retarding potential analyzer data from the OGO 6 satellite. Between dip latitudes of 0 and 50 deg the transition level shows a much more pronounced latitude dependence during solar maximum than during solar minimum. The longitude dependence of the transition level features indicates the roles that zonal and meridional F region winds might play in the distribution of O(+) and H(+) in the low- and mid-latitude ionosphere.

Kutiev, I.↗

NASA NTRS1980

Recombination spectrum and reddening in NGC 1068

Measurements of the emission-line intensities of NGC 1068 have been made over the wavelength range extending from rest wavelengths equal to 1216 A to 1.875 micron. The data, plus other available emission-line data, can be explained in terms of a simple model where the emission lines are formed in an H II region, and the line ratios are consistent with those predicted by standard radiative recombination theory and reddening corresponding to 0.4 mag. The continuum flux is seen to consist of a galaxy component plus a nonstellar component which dominates the observed flux in the ultraviolet. The observed ultraviolet continuum does not show an absorption dip caused by the intertellar 2200 A feature nor does it contain enough energy to power the observed infrared flux.

Neugebauer, G.↗

NASA NTRS1980

Rocket observations of energetic ions in the nighttime equatorial precipitation zone

The paper deals with the first direct measurements of energetic particles at low altitudes in the equatorial zone. The measurements were carried out at Chilca, Peru (magnetic dip = -0.7 degrees) during the NASA launch operation Antarqui. The results illustrate how the incident energetic particle intensity, energy spectrum, and pitch-angle distribution vary with altitude in the presence of a horizontal magnetic field.

Voss, H. D.↗

NASA NTRS1980

Implications of the high-state iron-line feature and soft X-ray emission of Hercules X-1

The interpretation that the soft X-ray emission of Her X-1 is due to reprocessing of the primary hard X-rays intercepted by a plasma layer in the Alfven surface imposes quite a stringent - but not an unreasonable - constraint on its parameters. By using the Alfven shell parameters constrained by this interpretation, the degree of ionization of the Alfven shell is calculated. Because the flux of hard X-ray from the neutron star is greatly attenuated inside the Alfven shell, except for a skin depth from its inner surface, the degree of ionization is determined by photoionization due to soft X-rays produced within the Alfven shell. On one hand, the large soft X-ray luminosity, which is about the same as the hard X-ray luminosity, indicates that a substantial fraction of primary hard X-rays is absorbed by the Alfven shell. On the other hand, the fact that the hard X-ray spectrum of Her X-1 observed during the high state shows neither a significant absorption feature down to about 3 keV nor an iron K-absorption dip tells us that the hard X-rays observed at the earth are mostly not reprocessed. This apparent conflict is resolved if the Alfven shell is clumpy (i.e., made of streams or blobs). The observed iron-line feature around 6.5 keV (E.W. about 300 keV) is explained by fluorescent iron K photons produced as a by-product of reprocessing of the hard X-rays by the Alfven shell; for this a large enhancement of the iron abundance with respect to the solar value is not required.

Bai, T.↗

NASA NTRS1980

On sound transmission into a stiffened cylindrical shell with rings and stringers treated as discrete elements

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model is presented for the transmission of an oblique plane sound wave into a finite cylindrical shell stiffened by stringers and ring frames. The rings and stringers are modeled as discrete structural elements. The numerical case studied was typical of a narrow-bodied jet transport fuselage. The numerical results show that the ring-frequency dip in the transmission loss curve that is present for a monocoque shell is still present in the case of a stiffened shell. The ring frequency effect is a result of the cylindrical geometry of the shell. Below the ring frequency, stiffening does not appear to have any significant effect on transmission loss, but above the ring frequency, stiffeners can enhance the transmission loss of a cylindrical shell.

Koval, L. R.↗

NASA NTRS1980

The discovery of an 81 minute modulation of the X-ray flux from 2A0311-227

The X-ray flux from 2A0311-227 was modulated at the 81 min orbital period of its optical counterpart. An absorption dip with N sub H equivalent to 5 x 10 to the 22nd power H atoms per square cm was observed at magnetic phase 0.42. It was interpreted as the accretion column of a magnetic white dwarf passing in front of the X-ray source. The spectrum was thermal with a temperature of 18 keV and a 300 eV equivalent width iron line at 6.6 keV.

White, N. E.↗

NASA NTRS1980

Anti-reflection coatings on large area glass sheets

Antireflective coatings which may be suitable for use on the covers of photovoltaic solar modules can be easily produced by a dipping process. The coatings are applied to glass by drawing sheets of glass vertically out of dilute aqueous sodium silicate solutions at a constant speed, allowing the adherent liquid film to dry, then exposing the dried film to concentrated sulfuric acid, followed by a water rinse and dry. The process produces coatings of good optical performance (96.7 percent peak transmission at 0.540 mu M wavelength) combined with excellent stain and soil resistance, and good resistance to abrasion. The process is reproduceable and easily controlled.

Pastirik, E.↗

NASA NTRS1980

Fine-scale characteristics of interplanetary sector

The structure of the interplanetary sector boundaries observed by Helios 1 within sector transition regions was studied. Such regions consist of intermediate (nonspiral) average field orientations in some cases, as well as a number of large angle directional discontinuities (DD's) on the fine scale (time scales 1 hour). Such DD's are found to be more similar to tangential than rotational discontinuities, to be oriented on average more nearly perpendicular than parallel to the ecliptic plane to be accompanied usually by a large dip ( 80%) in B and, with a most probable thickness of 3 x 10 to the 4th power km, significantly thicker previously studied. It is hypothesized that the observed structures represent multiple traversals of the global heliospheric current sheet due to local fluctuations in the position of the sheet. There is evidence that such fluctuations are sometimes produced by wavelike motions or surface corrugations of scale length 0.05 - 0.1 AU superimposed on the large scale structure.

Behannon, K. W.↗

NASA NTRS1981

Transonic flutter study of a wind-tunnel model of an arrow-wing supersonic transport

A 1/20-size, low-speed flutter model of the SCAT-15F complete airplane was tested on cables to simulate a near free-flying condition. Only the model wing and fuselage were flexible. Flutter boundaries were measured for a nominal configuration and a configuration with wing fins removed at Mach numbers M from 0.76 to 1.2. For both configurations, the transonic dip in the wing flutter dynamic pressure q boundary was relatively small and the minimum flutter q occurred near M = 0.92. Removing the wing fins increased the flutter q about 14 percent and changed the flutter mode from symmetric to antisymmetric. Vibration and flutter analyses were made using a finite-element structural representation and subsonic kernel-function aerodynamics. For the nominal configuration, the analysis (using calculated modal data) predicted the experimental flutter q levels within 10 percent but did not predict the correct flutter mode at the higher M. For the configuration without wing fins, the analysis predicted 16 to 36 percent unconservative (higher than experimental) flutter q levels and showed extreme sensitivity to mass representation details that affected wing tip mode shapes. For high subsonic M, empennage aerodynamics had a significant effect on the predicted flutter boundaries of several symmetric modes.

Ruhlin, C. L.↗

NASA NTRS1981

A Module Experimental Process System Development Unit (MEPSDU)

The technical readiness of a cost effective process sequence that has the potential for the production of flat plate photovoltaic modules which met the price goal in 1986 of $.70 or less per Watt peak was demonstrated. The proposed process sequence was reviewed and laboratory verification experiments were conducted. The preliminary process includes the following features: semicrystalline silicon (10 cm by 10 cm) as the silicon input material; spray on dopant diffusion source; Al paste BSF formation; spray on AR coating; electroless Ni plate solder dip metallization; laser scribe edges; K & S tabbing and stringing machine; and laminated EVA modules.

Source record↗

NASA NTRS1980

Ion temperature troughs induced by a meridional neutral air wind in the night-time equatorial topside ionosphere

A mathematical model was constructed to calculate O(+) and H(+) concentrations, field-aligned velocities, and electron temperatures in the night-time equatorial topside ionosphere. The model is used to establish the ability of F-region neutral air winds to produce observed ion temperature distributions, and to study the properties of ion temperature troughs as functions of altitude, latitude, and ionospheric composition. The O(+) - H (+) transition height represents an altitude limit above which the ion cooling from adiabatic expansion of the plasma is very small; the northern and southern edges of the ion temperature troughs are restricted to the limiting dip altitudes determined by magnetic field line geometry and by the functional form of the F-region neutral wind velocity.

Bailey, G. J.↗

NASA NTRS1980

The energetic charged particle absorption signature of Mimas

In the present paper, the average long-term effect of Saturn's satellite Mimas on the distribution of trapped radiation (macrosignature) is examined, along with a microsignature of satellite absorption, specifically, a brief dip in charged particle intensities observed on the inbound pass of Pioneer 11 as it passed through the orbital range of Mimas. It is hypothesized that it is indeed the shadow of Mimas, in the sense that the observations reveal the effect of this satellite on a distribution of particles which interacted with it in the recent past and then drifted in longitude to the observational location. The hypothesis led to a characterization of the electron energy spectrum in Saturn's inner magnetosphere and to an estimate of the radial diffusion coefficient for such electrons.

Van Allen, J. A.↗