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At least 505 records · Page 28

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NASA NTRS1987

Flutter study of an advanced composite wing with external stores

A flutter test using a scaled model of an advanced composite wing for a Navy attack aircraft has been conducted in the NASA Langley Research Center Transonic Dynamics Tunnel. The model was a wall-mounted half-span wing with a semi-span of 6.63 ft. The wing had an aspect ratio of 5.31, taper ratio of 0.312, and quarter-chord sweep of 25 degrees. The model was supported in a manner that simulated the load path in the carry-through structure of the aircraft and the symmetric boundary condition at the fuselage centerline. The model was capable of carrying external stores from three pylon locations on the wing. Flutter tests were conducted for the wing with and without external stores. No flutter was encountered for the clean wing at test conditions which simulated the scaled airplane operating envelope. Flutter boundaries were obtained for several external store configurations. The flutter boundaries for the fuel tanks were nearly Mach number independent (occurring at constant dynamic pressure). To study the aerodynamic effect of the fuel tank stores, pencil stores (slender cylindrical rods) which had the same mass and pitch and yaw inertia as the fuel tanks were tested on the model. These pencil store configurations exhibited a transonic dip in the flutter dynamic pressure, indicating that the aerodynamic effect of the actual fuel tanks on flutter was significant. Several flutter analyses methods were used in an attempt to predict the flutter phenomenon exhibited during the wind-tunnel test. The analysis gave satisfactory predictions of flutter for the pencil store configurations, but unsatisfactory correlation for the actual fuel tank configurations.

Cole, Stanley R.↗

NASA NTRS1987

Electric fields and double layers in plasmas

Various mechanisms for driving double layers (DLs) in plasmas are described, including applied potential drops, currents, contact potentials, and plasma expansions. Somne dynamic features of the DLs are discussed; and it is demonstrated that DLs and the currents through them undergo slow oscillations, determined by the ion transit time across an effective length of the system in which the DLs form. It is shown that a localized potential dip forms at the low potential end of a DL, which interrupts the electron current through it according to the Langmuir criterion whenever the ion flux into the DL is disrupted. Also considered is the generation of electric fields perpendicular to the ambient magnetic field by contact potentials.

Singh, Nagendra↗

NASA NTRS1988

Protective Coating For Laser Drilling Of Silicon

Sodium silicate prevents spattered silicon from fusing with surrounding material. Sodium silicate solution applied to wafer by dipping and draining or by spinning; application by spraying also works. When dried in oven, solution leaves thin coating of sodium silicate glass.

Shlichta, Paul J.↗

NASA NTRS1987

Static aeroelastic effects on the flutter of a supercritical wing

The results of an effort to calculate the effects of angle of attack and the associated aeroelastic deformation on the flutter of a highly swept supercritical wing by use of the modified strip analysis employed in previous studies of this wing are discussed. The spanwise distributions of steady state section lift-curve slope and aerodynamic center required as input for these calculations were obtained from static aeroelastic calculations for the wing by use of the FLO22 transonic code and an assumed dynamic pressure. The process is iterative so that flutter can be obtained at the same dynamic pressure as that used to calculate the statistically deformed shape and loading about which the flutter oscillation occurs (matched conditions). The results of this investigation show that the unconventional backward turn of the transonic dip in the experimental flutter boundary for angles of attack greater than zero is caused by variations in mass ratio and not by static aeroelastic deformation, although inclusion of the latter appears to be required for quantitative accuracy in the calculations.

Yates, E. Carson, Jr.↗

NASA NTRS1988

Variable spectra of active galaxies

The analysis of EXOSAT spectra of active galaxies are presented. The objects examined for X-ray spectral variability were MR 2251-178 and 3C 120. The results of these investigations are described, as well as additional results on X-ray spectral variability related to EXOSAT observations of active galaxies. Additionally, the dipping X-ray source 4U1624-49 was also investigated.

Halpern, Jules P.↗

NASA NTRS1988

Cascade model of gamma-ray bursts: Power-law and annihilation-line components

If, in a neutron star magnetosphere, an electron is accelerated to an energy of 10 to the 11th or 12th power eV by an electric field parallel to the magnetic field, motion of the electron along the curved field line leads to a cascade of gamma rays and electron-positron pairs. This process is believed to occur in radio pulsars and gamma ray burst sources. Results are presented from numerical simulations of the radiation and photon annihilation pair production processes, using a computer code previously developed for the study of radio pulsars. A range of values of initial energy of a primary electron was considered along with initial injection position, and magnetic dipole moment of the neutron star. The resulting spectra was found to exhibit complex forms that are typically power law over a substantial range of photon energy, and typically include a dip in the spectrum near the electron gyro-frequency at the injection point. The results of a number of models are compared with data for the 5 Mar., 1979 gamma ray burst. A good fit was found to the gamma ray part of the spectrum, including the equivalent width of the annihilation line.

Harding, A. K.↗

NASA NTRS1987

Source parameters for 11 earthquakes in the Tien Shan, central Asia, determined by P and SH waveform inversion

The style and the distribution of faulting occurring today in the Tien Shan region were studied, by digitizing long-period World-Wide Standard Seismograph Network P and SH waveforms of 11 of the largest Tien Shan earthquakes between 1965 and 1982 and then using a least squares inversion routine to constrain their fault plane solutions and depths. The results of the examination indicate that north-south shortening is presently occurring in the Tien Shan, with the formation of basement uplifts flanked by moderately dipping thrust faults. The present-day tectonics of the Tien Shan seem to be analogous to those of the Rocky Mountains in Colorado, Wyoming, and Utah during the Laramide orogeny in Late Cretaceous and Early Tertiary time.

Nelson, Michael R.↗

NASA NTRS1987

Calculated nighttime eastward plasma drift velocities at low latitudes and their solar cycle dependence

After calculating ambient electron densities as a function of altitude, latitude and local time, a simplified expression is used to calculate F-region eastward plasma drifts given a zonal neutral wind model. The derived eastward plasma drift on a magnetic flux tube is examined as a function of the flux tube apex height. If the neutral wind is assumed to be independent of latitude the plasma drift maximizes along the flux tube which intercepts the F-region peak concentration at the Appleton anomaly. Above this altitude the velocity decreases to reflect a decrease in the flux tube integrated F-region Pedersen conductivity. For a latitude dependent wind the plasma drift tends to maximize along the flux tube which intercepts the F-peak at the dip equator. Above this altitude the drift decreases to reflect the latitude distribution of the wind.

Anderson, D. N.↗

NASA NTRS1987

A high-resolution local network study of the Nazca plate Wadati-Benioff zone under western Argentina

Seismic data, recorded by INPRES telemetered network located above one of the subhorizontal segments of the subducted Nazca plate Wadati-Benioff zone beneath western Argentina, were analyzed to determine the zone's fine structure. The depth of the center and the thickness of the subhorizontal Wadati-Benioff zone beneath the network were calculated to be about 107 km and about 20 km, respectively, with most of the seismogenic zone concentrated in a region about 12 km thick. The Nazca plate is interpreted to be in a state of down-dip tension and to be decoupled from the overriding South American plate by a weak zone of asthenospheric or shear-heated material. The South American plate is estimated to be 80 km thick, based on the location of the subducted Nazca plate and an inferred decoupling zone between the plates.

Smalley, Robert F., Jr.↗

NASA NTRS1988

Atmospheric neutrons at 8.5-GV cutoff in the Southern Hemisphere

Measurements of the altitude, latitude, angle, and energy distributions of 5-80-MeV neutrons at 29 deg S geomagnetic latitude and 8.5-GV cutoff, obtained with the University of California neutron double-scatter telescope on a flight from Alice Springs, Australia, on November 10, 1981, are reported. The data are presented in extensive tables and graphs and characterized in detail. The altitude distribution of upward-moving and downward moving neutrons is found to peak at 100 g/sq cm (as reported for 41 deg N geomagnetic latitude by Preszler et al., 1974), while the angular distributions exhibit dips at 60 and 130 deg and the energy distribution has a flat region at about 20 MeV. The escape current of 0.059 + or - 0.008 neutrons/sq cm sec is consistent with theoretical models for the injection of energetic protons into the earth radiation belt (Merker, 1972 and 1975).

Ait-Ouamer, Farid↗

NASA NTRS1988

Effect of bulges on the stability of boundary layers

The instability of flows around hump and dip imperfections is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for viscous/inviscid interaction and separation bubbles. Then, the two-dimensional linear stability of this flow is analyzed, and the amplification factors are computed. Results are obtained for several height/width ratios and locations. The theoretical results have been used to correlate the experimental results of Walker and Greening (1942). The observed transition locations are found to correspond to amplification factors varying between 7.4 and 10.0, consistent with previous results for flat plates. The method accounts for both viscous and shear-layer instabilities. Separation is found to increase significantly the amplification factor.

Nayfeh, Ali H.↗

NASA NTRS1988

Ultraviolet spectroscopy of R Coronae Borealis

Observations of the hydrogen-deficient supergiant R CrB were obtained with the IUE over an interval of 54 days in order to study the nature of this star's irregular, small-amplitude variations in light. By chance, the series of observations coincided with a dip in the light intermediate between the normal fluctuations and the deep declines associated with the formation of an obscuring dust cloud. High-resolution spectra have been used to search for radial velocity variations, while low-resolution spectra yield ultraviolet light curves down to 1810 A. Both types of spectra have been analyzed for indications of temperature changes. It is found that a combination of photospheric temperature variation and variable extinction is necessary to account for the details of the observations. A simple, ad hoc, periodic model is presented in which the amount of obscuring dust varies in proportion to the drop in temperature, but at a later time, reproduces the wavelength dependence of both the amplitudes and phase shifts of the light curves. The radial velocities are consistent with pulsation being responsible for the temperature variation.

Holm, A. V.↗

NASA NTRS1988

The dwarf nova dippers

Previous papers have shown that the dwarf nova OY Car has an extensive vertical disk structure during its superoutbursts. This structure is analogous to that seen in the low mass X-ray binaries (LMXBs), in that the whole disk flares toward its edge, and there is a bulge or 'dark spot' where the mass transfer stream meets the disk edge. The paper presents evidence suggesting that two more dwarf novae may have such a stream impact bulge, which manifests itself as a dip in the UV light curve, analogous to those seen in the X-ray light curves of the LMXB dippers.

Naylor, T.↗

NASA NTRS1988

The virtual cathode as a transient double sheath

The two-dimensional plasma potential measurements are given of a space-charge dominated double sheath near a hot cathode. Laboratory data show that a virtual cathode is a self-consistent solution only for a transient cathode-plasma system. Slow charge exchange ions get trapped in the potential dip that forms the virtual cathode and eventually destroy it.

Intrator, T.↗

NASA NTRS1988

Asymmetry in zeta Auriage chromospheres

Asymmetry in the ultraviolet spectra of zeta-Aur, similar to that reported in optical observations, was studied using IUE data. A plot of the integrated flux of zeta Aurigae from 1625 to 1675 A as a function of absolute phase shows no significant difference between the ingress and egress phases. A plot of the integrated flux from 1625 to 1675 A for 22 Vul as a function of absolute phase for both ingress and egress confirms that the atmospheric eclipse is asymmetric in 22 Vul. The eclipse in 22 Vul begins symmetrically but departs from symmetry at a phase greater than 0.05. The pronounced dip at ingress suggests a feature in the chromosphere.

Ahmad, I. A.↗

NASA NTRS1988

Heat Flow and Magnetization in the Oceanic Lithosphere

Two aspects of the processing and interpretation of satellite measurements of the geomagnetic field are described. One deals with the extraction of the part of the geomagnetic field that originates from sources in the earth's atmosphere. The other investigates the possibility of using the thermal state of the oceanic lithosphere to further constrain modelling and interpretation of magnetic anomalies. It is shown that some of the magnetic signal in crustal anomaly maps can be an artifact of the mathematical algorithms that have been used to separate the crustal field from the observed data. Strong magnetic anomalies can be distorted but are probably real, but weak magnetic anomalies can arise from leakage of power from short wavelengths, and will also appear in anomaly maps as repetitions of the strong crustal anomaly. The distortion and the ghost anomalies follow the magnetic dip lines in a way that is similar to actual MAGSAT anomaly fields. This phenomenon will also affect the lower degree spherical harmonic terms in the power spectrum of the crustal field. A model of the magnetic properties of the oceanic crust that has been derived from direct measurements of the rock magnetic properties of oceanic rocks is presented. The average intensity of magnetization in the oceanic crust is not strong enough to explain magnetic anomalies observed over oceanic areas. This is the case for both near surface observations (ship and aeromagnetic data) and satellite altitude observations. It is shown that magnetic sources in the part of the upper mantle that is situated above the Curie isotherm, if sufficiently strong, can produce satellite magnetic anomalies that are comparable to MAGSAT data. The method developed for the study of depth to the Curie isotherm and magnetic anomalies can also be used in inverse modelling of satellite magnetic anomalies when the model is to be adjusted with an annihilator.

Hayling, Kjell Lennart↗

NASA NTRS1988

Proterozoic Bushveld-Vredefort catastrophe: Possible causes and consequences

Bushveld Complex and Vredefort Dome are unique features, formed in close proximity during the same time interval, approximately 2 Ga. Both show evidence of catastrophic events in the shallow marine environment of the otherwise stable Kaapvaal Craton. Explanation by multiple impacts of an asteroid, brecciated by an inter-asteroidal collision and disintegrating in Earth's gravity field is supported by pseudotachylite, shatter cones, coesite, and stishovite at Vredefort but these shock phenomena were not found in the Bushveld Complex. The Bushveld Complex was formerly interpreted as a lopolith, a view incompatible with gravity, electrical resistivity, magnetic, and seismic-reflection data. It is outlined by five inward-dipping lobes of layered ultramafic-mafic plutonic rocks that partly coalesce to form a basin-like feature 400 km in diameter and 65,000 sq. km. in area, equivalent to a small lunar mare. The Bushveld Complex is orders of magnitudes larger than other proposed terrestrial impact structures and differs from them in important ways. Its principal members, in order of age, are Rooiberg Felsite, RLS, and Lebowa Granite. The Bushveld-Vredefort events occurred during the interval from neutral or reducing atmosphere to oxidizing atmosphere. This transition is usually related to the evolution of photosynthesizing organisms. If the impact hypothesis for Bushveld-Vredefort can be confirmed, it may represent a global catastrophe sufficient to contribute to environmental changes favoring aerobic photosynthesizing eukaryotes over anaerobic prokaryotes.

Elston, W. E.↗

NASA NTRS1988

Gneiss-charnockite transformation at Kottavattam, Southern Kerala (India)

At Kottavattam, leucocratic granitic garnet-biotite gneisses (age less than 2 Ga) were partially transformed to coarse-grained charnockite along a system of conjugate fractures (N70E and N20W) and the foliation planes (N60 to 80W; dip 80 to 90 SW) about 550 m.y. ago. To examine and quantify changes in fabric, mineralogy, pore fluids and chemical composition associated with this process, large rock specimens showing gneiss-charnockite transition were studied in detail. The results of the present study corroborate the concept that charnockite formation at Kottavattam is an internally-generated phenomenon and was not triggered by the influx of carbonic fluids from a deep-seated source. It is suggested that charnockitization was caused by the following mechanism: (1) near-isothermal decompression during uplift of the gneiss complex led to an increase of the pore fluid pressure (P sub fluid greater than P sub lith) which - in a regime of anisotropic stress - triggered or at least promoted the development of conjugate fractures; (2) the simultaneous release of pore fluids from bursting fluid inclusions and their escape into the developing fracture system resulted in a drop of fluid pressure; and (3) the internal generation and buffering of the fluids and their, probably, limited migration in an entirely granitic rock system explains the absence of any significant metasomatic mass transfer.

Raith, M.↗