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At least 883 records · Page 49

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NASA NTRS1986

Spatial greenstone-gneiss relationships: Evidence from mafic-ultramafic xenolith distribution patterns

The distribution patterns of mafic-ultramafic xenoliths within Archaean orthogneiss terrain furnish an essential key for the elucidation of granite-greenstone relations. Most greenstone belts constitute mega-xenoliths rather than primary basin structures. Transition along strike and across strike between stratigraphically low greenstone sequences and xenolith chains demonstrate their contemporaneity. These terrains represent least deformed cratonic islands within an otherwise penetratively foliated deformed gneiss-greenstone crust. Whereas early greenstone sequences are invariably intruded by tonalitic/trondhjemitic/granodioritic gneisses, stratigraphically higher successions may locally overlap older gneiss terrains and their entrained xenoliths unconformably. The contiguity of xenolith patterns suggests their derivation as relics of regional mafic-ultramafic volcanic crustal units and places limits on horizontal movements between individual crustal blocks.

Glikson, A. Y.↗

NASA NTRS1986

A palaeomagnetic perspective of Precambrian tectonic styles

The considerable success derived from palaeomagnetic studies of Phanerozoic rocks with respect to the tectonic styles of continental drift and plate tectonics, etc., have not been repeated by the many palaeomagnetic studies of Precambrian rocks. There are 30 years of research with results covering the major continents for Precambrian times that overlap considerably yet there is no concensus. There is good evidence that the usual assumptions employed by palaeomagnetism are valid for the Precambrian. The exisence of magnetic reversals during the Precambrian, for instance, is difficult to explain except in terms of a geomagnetic field that was predominantly dipolar in nature. It is a small concession to extend this notion of the Precambrian geomagnetic field to include its alignment with the Earth's spin axis and the other virtues of an axial geocentric dipole that characterize the recent geomagnetic field. In terms of greenstone terranes it is obvious that tectonic models postulated to explain these observations are paramount in understanding Precambrian geology. What relevance the current geographical relationships of continents have with their Precambrian relationships remains a paradox, but it would seem that the ensialic model for the development of greenstone terranes is favored by the Precambrian palaeomagnetic data.

Schmidt, P. W.↗

NASA NTRS1986

Mission analysis flow sequencing optimization

This investigation is an extension of a project dealing with the problem of optimal use of ground resources for future space missions. This problem was formulated as a linear programming problem using an indirect approach. Instead of minimizing the inventory level of needed ground resources, the overlapping periods during which the same types of resources are used by various flights are minimized. The model was built upon the assumption that during the time interval under consideration, the costs of various needed resources remain constant. Under other assumptions concerning costs of resources, the objective function, in general, assumes a non-linear form. In this study, one case where the form of the objective function turns out to be quadratic is considered. Also, disadvantages and limitations of the approach used are briefly discussed.

Scott, M.↗

NASA NTRS1985

To catch a comet: Technical overview of CAN DO G-324

The primary photographing of aboard STS 61-E. INTRODUCTION objective of the C.E. Williams Middle School Get Away Special "CAN DO" is the Comet Halley. As it is currently scheduled, G-324 will fly in March of 1986 The project will involve middle school students, grades 6 through 8, in the study and interpretation of astronomical photographs and techniques. -The-objectives of these studies are detailed in another paper to be presented at this symposium. 6-324 is contained in a 5 cubic foot G.A.S. Canister with an opening door and pyrex window for photography. It will be pressurized with one atmosphere of dry nitrogen. Three 35mm still cameras with 250 exposure film backs and different focal length lenses will be fired by a combination of automatic timer and an active comet detector. A lightweight 35mm movie camera will shoot single exposures at about 4 minute intervals to give an overlapping "skymap" of the mission. The fifth camera is a solid state television camera specially constructed for detection of the comet by the microprocessor. In addition to the photographic goals of CAN DO, the canister also contains a separate package of middle school student designed passive experiments. These-projects will be described in detail in the accompanying paper on educational goals.

Thomas J. O'Brien↗

NASA NTRS1986

Planning for the utilization of the PCDS in studying the interaction of clouds (ISCCP-C data) and the Earth radiation budget (ERBE data)

The Pilot Climate Data System (PCDS) affords an opportunity to analyze data from different but highly complementary data sets. Two of these highly complementary data sets supported by the PCDS are the International Satellite Cloud Climatology Project (ISCCP) and the Earth Radiation Budget Experiment (ERBE). Both data set sponsors are aware of the utility of one data set to the other, and both projects utilize gridded data on a 2.5 deg by 2.5 deg grid. The ISCCP data have been collected since July 1983, and the NOAA-9 data for ERBE have been collected for more than a year. Therefore, there is a good chance to use these temporally overlapping data sets to investigate hypothesized relationships. Changes in cloudiness affect both cloud albedo feedback (shortwave) and the greenhouse effect (longwave). The relative importance of the effects of clouds on albedo versus outgoing longwave radiation (OLR) in determining the radiation balance has long been a matter of controversy. Now, however, changes in cloud amount as observed by the ISCCPO can be correlated to corresponding changes in the albedo and changes in the OLR from ERBE. Monthly means can be utilized in all instances.

Jacobowitz, H.↗

NASA NTRS1985

Pulsed excimer laser processing

The status of pulsed excimer laser processing of PV cells is presented. The cost effective feasibility of fabricating high efficiency solar cells on Czochralski wafers using a pulsed excimer laser for junction formation, surface passivation, and front metallization. Laser annealing results were promising with the best AR coated cell having an efficiency of 16.1%. Better results would be expected with larger laser spot size because there was some degradation in open circuit voltage caused by laser spot overlap and edge effects. Surface heating and photolytic decomposition by the laser was used to deposit tungsten from the reaction of tungsten hexafluoride and hydrogen. The line widths were 5 to 10 mils, and the depositions passed the tape adhesion test. Thinner lines are practical using an optimized optical system.

Wong, D.↗

NASA NTRS1986

Shoulder and hip joints for hard space suits and the like

For use in hard space suits and the like, a joint between the torso covering and the upper arm covering (i.e., shoulder) or between the torso covering and upper leg covering (i.e., hip) is disclosed. Each joint has an outer covering and a inner covering. The outer covering has plural perferably truncated toroidal sections decreasing in size proceeding outwardly. In one embodiment at each joint there are two bearings, the first larger than the second. The outer race of the larger bearing is attached to the outer edge of the smaller end of each section and the inner race of the larger bearing is attached to the end wall. The inner race of the smaller bearing is attached to the end wall. The outer race of the smaller bearing is attached to the larger end of the next section. Each bearing hask appropriate seals. Between each section is a rubber ring for the comfort of the wearer. Such rubber rings have radial flanges attached to the inner races of two adjacent bearings. Matching semicircular grooves are formed in the abutting overlapping surfaces. Bellows-like inner walls are also provided for each section fixed at one end to an inner cylindrical flange and, at the opposite end, to an end wall. Each outer section may rotate 360 deg relative to the next outer section, whereas the bellows sections do not rotate, but rather expand or contract locally as the rigid sections rotate relative to each other.

Vykukal, H. C.↗

NASA NTRS1985

Thermal history of a metamorphic core complex

Fission track (FT) thermochronology studies of lower plate rocks of the Ruby Mountains-East Humbolt Range metamorphic core complex provide important constraints on the timing an nature of major middle Tertiary extension of northeast Nevada. Rocks analyzed include several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison Pass pluton was also studied. The minerals dated include apatite, zircon, and sphene and were obtained from the same rocks that have been previously studied. FT ages are concordant and range in age from 26.4 Ma to 23.8 Ma, with all showing overlap at 1 sigma between 25.4 to 23.4 Ma. Concordancy of all FT ages from all structural levels indicates that the lower plate cooled rapidly from temperatures above approx. 285 C (assumed sphene closure temperature (2)) to below approx. 150 C (assumed apatite closure temperature) near the beginning of the Miocene. This suggests that the lower plate cooled at a rate of at least approx. 36 deg C/Ma during this event. Rapid cooling of the region is considered to reflect large-scale tectonic denudation (intracrustal thinning), the vertical complement to intense crustal extension. FT data firmly establish the upper limit on the timing of mylonitization during detachment faulting and also coincide with the age of extensive landscape disruption.

Dokka, R. K.↗

NASA NTRS1985

The evolution of rifting process in the tectonic history of the Earth

The continental rifting is the response of the lithosphere to the oriented tension. The distribution of viscosity in the lithosphere plays an essential role during all stages of the rifting. The viscosity is a function of the temperature, the lithostatic pressure, the rock composition, the deformation rate and other factors. The temperature is the most important factor. The vertical section of continental lithosphere of the rift zone may be divided into the following layers: the upper crust, in which brittle deformation prevails; the medialcrust, in which the role of plastic deformation increases; the lower crust, in which plastic deformation prevails; and the uppermost plastic part of the mantle overlapping asthenosphere. The depth of the boundaries in the crust layers are mainly controlled by the temperature.

Milanovsky, E. E.↗

NASA NTRS1986

The Astro-1 mission

The Astro-1 mission was to be launched in March 1986 for an effective duration of 7 days, chosen to overlap spacecraft encounters with Halley's Comet, i.e., Vega-2 (on 9 March) and Giotto (on 13/14 March). The ultraviolet instrument complement while not designed with cometary research as the prime objective, was well suited to the study of comets. The opportunity of an extended mission during the time of the spacecraft encounters of Halley's Comet offered an extraordinary opportunity for a synergistic interaction between the intercept spacecraft, the Earth-orbital Astro-1 mission, and ground-based observations. The addition of visual-wavelength, wide-field cameras would enhance the scientific return of the mission. Loss of Challenger cancelled the mission.

Brandt, J. C.↗

NASA NTRS1985

Measurement of ultrasonic velocity using phase-slope and cross-correlation methods

Computer implemented phase-slope and cross-correlation methods are introduced for measuring time delays between pairs of broadband ultrasonic pulse-echo signals for determining velocity in engineering materials. The phase-slope and cross-correlation methods are compared with the overlap method which is currently in wide use. Comparison of digital versions of the three methods shows similar results for most materials having low ultrasonic attenuation. However, the cross-correlation method is preferred for highly attenuating materials. An analytical basis for the cross-correlation method is presented. Examples are given for the three methods investigated to measure velocity in representative materials in the magahertz range.

Hull, D. R.↗

NASA NTRS1985

Inversion of chalcogen defect levels in silicon - An MNDO study

MNDO (modified neglect of diatomic overlap) calculations have been carried out for substitutional oxygen and sulfur impurities in silicon. The calculations of the gap levels reveal a reversal of trend with atomic ionization energies in agreement with self-consistent Green function results, and analysis of the MNDO charge distribution supports the view that the electronegativity difference between oxygen and sulfur gives rise to this shallower energy level.

Singh, R. K.↗

NASA NTRS1985

Moments of catchment storm area

The portion of a catchment covered by a stationary rainstorm is modeled by the common area of two overlapping circles. Given that rain occurs within the catchment and conditioned by fixed storm and catchment sizes, the first two moments of the distribution of the common area are derived from purely geometrical considerations. The variance of the wetted fraction is shown to peak when the catchment size is equal to the size of the predominant storm. The conditioning on storm size is removed by assuming a probability distribution based upon the observed fractal behavior of cloud and rainstorm areas.

Eagleson, P. S.↗

NASA NTRS1985

On an algorithm for analysis of the radiation patterns of dual reflector and segmented reflector antennas

An algorithm has been developed to calculate the radiation patterns of a large reflector antenna for space applications. The algorithm treats each panel in the reflector array as an analytic surface having n-sided polygonal boundaries. The radiation fields for individual panels are computed and stored separately, and then added to yield a uniform radiation pattern for the entire reflector. Numerical methods developed to reduce the overlap of the aperture fields of adjacent panels are described in detail. Calculations of the tangential field components of the aperture plane are carried out based on the principles of geometric optics (GO). Some radiation patterns calculated with the algorithm are compared with patterns produced by other methods, together with measured data for a classical Cassegrain antenna and the calculated patterns are illustrated.

Christodoulou, C. G.↗

NASA NTRS1986

Optical technique to characterize heavy rain

A technique to measure the size and velocity of raindrops is presented and experimental and numerical results discussed. The technique bases the droplet size on the absolute intensity of the light scattered when the droplets cross a laser-based probe volume. The velocity is obtained from the Doppler frequency. A size range of 0.1 mm to 9 mm was covered with overlapping ranges. Experiments were conducted with simulated rain sprays except that the local LWC was much larger than the values encountered in natural rain. The accuracy of the size measurement was not strongly affected by spray interference, but it showed a clear dependence with the droplet shape. A simple numerical model based on the light reflected from ellipsoids attempts to explain the relationship between droplet shape and absolute scattered light.

Hess, C. F.↗

NASA NTRS1985

Stability of interfaces with mesh refinement

A study is conducted of the stability of mesh refinement in space and time for several different interface equations and finite-difference approximations. First, a root condition which implies stability for the initial-boundary value problem for this type of interface is derived. From the root condition, the stability of several interface equations is proved, using the maximum principle. In some cases, the final verification steps can be done analytically; in other cases, a simple computer program has been written to check the condition for values of a parameter along the boundary of the unit circle. Using this method, stability for Lax-Wendroff with all the interface conditions considered, and for Leapfrog with interpolation interface conditions when the fine and coarse grids overlap is proved.

Berger, M. J.↗

NASA NTRS1985

Bonding and nondestructive evaluation of graphite/PEEK composite and titanium adherends with thermoplastic adhesives

Bonded single overlap shear specimens were fabricated from Graphite/PEEK (Polyetheretherketone) composite adherends and titanium adherends. Six advanced thermoplastic adhesives were used for the bonding. The specimens were bonded by an electromagnetic induction technique producing high heating rates and high-strength bonds in a few minutes. This contrasts with conventionally heated presses or autoclaves that take hours to process comparable quality bonds. The Graphite/PEEK composites were highly resistant to delamination during the testing. This allowed the specimen to fail exclusively through the bondline, even at very high shear loads. Nondestructive evaluation of bonded specimens was performed ultrasonically by energizing the entire thickness of the material through the bondline and measuring acoustic impedance parameters. Destructive testing confirmed the unique ultrasonic profiles of strong and weak bonds, establishing a standard for predicting relative bond strength in subsequent specimens.

Hodges, W. T.↗

NASA NTRS1985

To speak or not to speak - A multiple resource perspective

The desirability of employing speech response in a dynamic dual task situation was discussed from a multiple resource perspective. A secondary task technique was employed to examine the time-sharing performance of five dual tasks with various degrees of resource overlap according to the structure-specific resource model of Wickens (1980). The primary task was a visual/manual tracking task which required spatial processing. The secondary task was either another tracking task or a spatial transformation task with one of four input (visual or auditory) and output (manual or speech) configurations. The results show that the dual task performance was best when the primary tracking task was paired with the visual/speech transformation task. This finding was explained by an interaction of the stimulus-central processing-response compatibility of the transformation task and the degree of resource competition between the time-shared tasks. Implications on the utility of speech response were discussed.

Tsang, P. S.↗