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At least 289 records · Page 16

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NASA NTRS1988

OFMspert - Inference of operator intentions in supervisory control using a blackboard architecture

The authors proposes an architecture for an expert system that can function as an operator's associate in the supervisory control of a complex dynamic system. Called OFMspert (operator function model (OFM) expert system), the architecture uses the operator function modeling methodology as the basis for the design. The authors put emphasis on the understanding capabilities, i.e., the intent referencing property, of an operator's associate. The authors define the generic structure of OFMspert, particularly those features that support intent inferencing. They also describe the implementation and validation of OFMspert in GT-MSOCC (Georgia Tech-Multisatellite Operations Control Center), a laboratory domain designed to support research in human-computer interaction and decision aiding in complex, dynamic systems.

Jones, Patricia S.↗

NASA NTRS1988

ALH85085 - A unique volatile-poor carbonaceous chondrite with possible implications for nebular fractionation processes

The characteristics and possible origin of the chondrite ALH85085 are discussed. It is found that the metal silicate, and sulfide compositions of ALH85085 are similar to those in CM-CO and Al Rais-Renazzo chondrites. High siderophile abundances and volatile depletion are observed. It is found that ALH85085 agglomerated when temperatures in the nebula were near 1000 K, in the same region where Renazzo, Al Rais, and the CI chondrites formed. It is suggested that ALH85085 was annealed and lightly shocked after agglomeration. C1 and other clasts were subsequently incorporated during late-stage brecciation.

Grossman, Jeffrey N.↗

NASA NTRS1989

Chondrules in the Sharps H3 chondrite - Evidence for intergroup compositional differences among ordinary chondrite chondrules

Bulk compositions of 19 chondrules and one matrix-rich sample from H3.4 Sharps were determined by instrumental neutron activation analysis. Samples were characterized petrographically, and mineral compositions were determined by electron microprobe analysis. There is constancy among ordinary chondrite (OC) groups in the compositional interrelationships of different chondrule types; e.g., in H3 as well as L3 and LL3 chondrites, porphyritic chondrules are more refractory than nonporphyritic chondrules. Precursor components of H3 chondrules are closely related to those of LL3 chondrules. The mean Ir/Ni, Ir/Co, and Ir/Au ratios of H3 chondrules differ from the corresponding ratios of LL3 chondrules at the 99, 90, and 79 percent confidence levels, respectively. The ratios in H3 chondrules exceed those in LL3 chondrules by amounts similar to those by which H whole-rocks exceed LL whole-rocks. These data suggest that there are primary systematic differences in bulk composition between H and LL chondrules. These differences support the inference that chondrule formation occurred after major nebular fractionation events had established the observed bulk compositional differences among OC groups.

Rubin, Alan E.↗

NASA NTRS1988

Shock effects in meteorites

The impacts that can occur between objects on intersecting solar system orbits can generate shock-induced deformations and transformations, creating new mineral phases or melting old ones. These shock-metamorphic effects affect not only the petrography but the chemical and isotopic properties and the ages of primordial meteoritic materials. A fuller understanding of shock metamorphism and breccia formation in meteorites will be essential not only in the study of early accretion, differentiation, and regolith-evolution processes, but in the characterization of the primordial composition of the accreted material itself.

Stoeffler, D.↗

NASA NTRS1988

Oxidation state in chondrites

An evaluation is made of extant data on chondrite oxidation states and intrinsic O fugacities. A variety of oxidation states are exhibited by the chondritic meteorites; petrologic and chemical data may be used to arrange the major chondrite groups in order of oxidation state. The intrinsic O fugacity measurements on chondrite whole-rock samples are noted to display a corresponding ordering of oxidation states. Metamorphosed chondrites and igneous meteorites that were substantially altered by metamorphic reactions, outgassing, and igneous processes may preserve information on the oxidation state and size of their parent bodies.

Rubin, Alan E.↗

NASA NTRS1988

Properties of chondrules

Chondrules contain a record of many essential characteristics of the primordial solar nebula, whose high-temperature chondrule-generating events have spanned nearly 10 million years. As chondrules cooled, they became magnetized by nebular fields; chondrule rims show that dust was present in the vicinity of chondrule formation, and that multiple melting events were possible. The chondrule precursors included many large grains, showed variable degrees of Fe-oxidation, and encompassed many isotopic reservoirs. The properties of these nebular materials systematically changed from the enstatite, to ordinary, and finally to carbonaceous chondrite formation regions.

Grossman, Jeffrey N.↗

NASA NTRS1989

3-D composite velocity solutions for subsonic/transonic flows

A composite velocity procedure for the three-dimensional reduced Navier-Stokes equations is developed. In the spirit of matched asymptotic expansions, the velocity components are written as a combination multiplicative and additive composite of viscouslike velocities and pseudopotential or inviscid velocities. The solution procedure is then consistent with both asymptotic inviscid flow and boundary layer theory. For transonic flow cases, the Enquist-Osher flux biasing scheme developed for the full potential equation is used. A quasi-conservation form of the governing equations is used in the shock region to capture the correct rotational shock with the standard nonconservation form of the equations used in nonshock regions. The consistent coupled strongly implicit procedure coupled with a plane relaxation procedure is used to solve the discretized equations.

Gordnier, R. E.↗

NASA NTRS1988

Formation of ureilites by impact-melting of cabonaceous chondritic material

Ureilites are modeled as impact-melt products of CV-chondrite-like material. This model is consistent with the brecciated nature and cumulate textures of ureilites, O-isotopic constraints (which indicate ureilite derivation from an isotopically heterogeneous body like the CV-chondrite parent), the high abundance of planetary-type noble gases, and the relatively high concentrations of siderophile and chalcophile elements (indicating incomplete separation of metal-sulfide from silicate). Each ureilite may have been derived from a separate cratering event.

Rubin, Alan E.↗

NASA NTRS1989

Elasto-plastic finite element analyses of two-dimensional rolling and sliding contact deformation of bearing steel

An elastoplastic finite element analysis of repeated rolling-plus-sliding contact is presented for the elastic-linear-kinematic hardening-plastic properties of hardened bearing steel at room temperature. Contacts in the absence of frictional heating are found to produce peak cyclic strain ranges and residual stresses that are similar to the values obtained for pure rolling. For the cases considered, the energy dissipated as heat by plastic deformation is found to be 3-15 percent of the energy dissipated at the surface by friction.

Kumar, A. M.↗

NASA NTRS1989

The effect of density variations on elemental abundance ratios in gaseous nebulae

Using numerical analysis it is demonstrated that when there are changes in gas density within a nebulae various empirical methods for determining the electron density can give different results. Eleven different species are considered which have line pair ratios that are well-known electron density (Ne) diagnostic tools. In the presence of varying density, there is a progression in inferred values of Ne from N+ (122/204 microns) at the lowest to C(2+) (1906/1909 A) at the highest. For many of the 11 species there is a fixed order in the inferred density, while for others the order can change somewhat for different mixes of densities. When there are nonconstant density conditions, it is shown that systematic biases may occur in the empirical determination of chemical abundance ratios. Tabular material is presented that delineates the maximum bias that can occur in the determination of a particular abundance ratio in a two-component model.

Rubin, R. H.↗

NASA NTRS1989

3-D composite velocity solutions for subsonic/transonic flow over afterbodies

A composite velocity procedure for the three-dimensional reduced Navier-Stokes equations is developed. The velocity components are written as a combined multiplicative and additive composite of viscous like velocities and pseudo-potential or inviscid velocities. The solution procedure is then consistent with both asymptotic inviscid flow and boundary layer theory. For transonic flow cases, the Enquist-Osher flux biasing scheme developed for the full potential equation is used. A quasi-conservation form of the governing equations is used in the shock region to capture the correct rotational behavior. The composite velocity procedure is applied for the solution of three-dimensional afterbody problems.

Gornier, Raymond E.↗

NASA NTRS1990

Rolling-Contact Spalling In Bearings

Report describes experimental and theoretical studies of effects of thermal and mechanical contact stresses and attendant plastic deformations responsible for rolling-contact spalling of the 440C-steel bearings in high-pressure-oxygen turbopump.

Kumar, A. M.↗

NASA NTRS1990

An engineering approach to automatic programming

An exploratory study of the automatic generation and optimization of symbolic programs using DECOM - a prototypical requirement specification model implemented in pure LISP was undertaken. It was concluded, on the basis of this study, that symbolic processing languages such as LISP can support a style of programming based upon formal transformation and dependent upon the expression of constraints in an object-oriented environment. Such languages can represent all aspects of the software generation process (including heuristic algorithms for effecting parallel search) as dynamic processes since data and program are represented in a uniform format.

Rubin, Stuart H.↗

NASA NTRS1989

Size-frequency distributions of chondrules in CO3 chondrites

The size-frequency distributions of chondrules were determined for eleven CO3 chondrites (including ALHA77003, ALHA77307, ALH82101, ALH85003, Colony, Felix, Isna, Kainsaz, Lance, Ornans, and Warrenton), using the results of petrographic analyses of thin sections. The mean proportion of different chondrule types in CO3 chondrites were estimated to be 69 percent POP, 18 percent PP, 8 percent PO, 2 percent BO, 2 percent RP, 1 percent C, and less than 0.1 percent GOP. These proportions are very different from those in ordinary or EH and CV chondrites, with the smaller proportion of nonporphyritic chondrules than EH chondrites, but a larger proportion than CV chondrites. Relative proportions of chondrule types vary with size interval; thus, with decreasing chondrule size, PO chondrules decrease fairly regularly in abundance, while RP chondrules are most abundant in the smallest size intervals.

Rubin, Alan E.↗

NASA NTRS1989

An olivine-microchondrule-bearing clast in the Krymka meteorite

A small (150 x 200-micron-size) clast consisting of 20 vol pct olivine microchondrules (with barred and granular textures) and 80 vol pct recrystallized silicate matrix material occurs in Krymka (LL3.1). This is the fourth microchondrule-bearing clast to be described. The chondrules are zoned in FeO with concentrations increasing toward the surface. The clast most closely resembles a previously described radial-pyroxene-microchondrule-bearing clast in Piancaldoli (LL3.4).

Rubin, Alan E.↗

NASA NTRS1990

Oxygen isotopes in chondrules and coarse-grained chondrule rims from the Allende meteorite

The relationship between the porphyritic chondrules and coase-grained chondrule rims of the Allende CV chondrite are examined. The oxygen isotopic compositions of seven chondrule-rim pairs and a large rimless refractory chondrule from Allende are determined. The results suggest that, to account for the O-isotopic compositions of the CV chondrules and rims, three solid precursor components are required: a high-temperature, refractory-, alkali, and (O-16)-rich component; a low-temperature, FeO-rich, refractory, and (O-16)-poor component, and an additional component to explain the composition of BO chondrules.

Rubin, Alan E.↗

NASA NTRS1990

A flux-split solution procedure for unsteady inlet flows

The unstart and restart of an axisymmetric inlet is investigated using a flux-split procedure applied to the Euler and Reduced Navier Stokes (RNS) equations. A time consistent direct sparse matrix solver is applied to compute the transient flow field both internal and external to the inlet. Time varying oblique and normal shocks are captured. The code is quite general and is applicable for subsonic, transonic and supersonic free streams. The current analysis is concerned with supersonic flight conditions.

Pordal, H. S.↗

NASA NTRS1989

Attention in dichoptic and binocular vision

The ability of human subjected to mobilize attention and cope with task requirements under dichoptic and binocular viewing was investigated in an experiment employing a target search task. Subjects were required to search for a target at either the global level, the local level, or at both levels of a compound stimulus. The tasks were performed in a focused attention condition in which subjects had to attend to the stimulus presented to one eye/field (under dichoptic and binocular viewings, respectively) and to ignore the stimulus presented to the irrelevant eye/field, and in a divided attention condition in which subjects had to attend to the stimuli presented to both eyes/fields. Subjects' performance was affected mainly by attention conditions which interacted with task requirements, rather than by viewing situation. An interesting effect of viewing was found for the local-directed search task in which the cost of dividing attention was higher under binocular than under dichoptic viewing.

Kimchi, Ruth↗