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At least 721 records · Page 40
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NASA NTRS1982

Incompressible Navier-Stokes and parabolized Navier-Stokes solution procedures and computational techniques

Recent developments with finite-difference techniques are emphasized. The quotation marks reflect the fact that any finite discretization procedure can be included in this category. Many so-called finite element collocation and galerkin methods can be reproduced by appropriate forms of the differential equations and discretization formulas. Many of the difficulties encountered in early Navier-Stokes calculations were inherent not only in the choice of the different equations (accuracy), but also in the method of solution or choice of algorithm (convergence and stability, in the manner in which the dependent variables or discretized equations are related (coupling), in the manner that boundary conditions are applied, in the manner that the coordinate mesh is specified (grid generation), and finally, in recognizing that for many high Reynolds number flows not all contributions to the Navier-Stokes equations are necessarily of equal importance (parabolization, preferred direction, pressure interaction, asymptotic and mathematical character). It is these elements that are reviewed. Several Navier-Stokes and parabolized Navier-Stokes formulations are also presented.

Rubin, S. G.↗
NASA NTRS1982

Microchondrule-bearing clast in the Piancaldoli LL3 meteorite - A new kind of type 3 chondrite and its relevance to the history of chondrules

Electron microprobe, scanning electron microscope, and petrographic analyses of the microchondritic clast of the Piancaldoli LL3 chondrite are reported and compared with other type three chondrites. The clast, like other type three chondrites, has a fine-grained Fe-rich opaque silicate matrix, sharply defined chondrules, abundant low-Ca clinopyroxene and minor troilite and Si and Cr-bearing metallic Fe, Ni. However, the very high model matrix abundance, unique characteristics of the chondrules, and absence of microscopically observable olivine indicate that the clast is a new type of type three chondrite. It is concluded that the microchondrules were formed by the same process that formed normal-sized chondrules in type three chondrites: melting of preexisting dustballs. It is suggested that dust grains were mineralogically sorted in the nebula before aggregating into dustballs.

Rubin, A. E.↗
NASA NTRS1983

Modeling of G333.6-0.2 as a spherical H II region

The radio and IR observations of the H II region G333.6-0.2 are matched with a detailed spherical model with a density distribution which has a uniform-density core of radius 0.05 pc, a power-law intermediate zone, and a uniform-density halo. A stellar radiation field is required that is somewhat different from those predicted by available model atmospheres. Of the stellar models of Kurucz, the Teff = 34,000 K and log g = 3.5 model best fits the observed ratio of helium to hydrogen recombination lines. A good fit to all the observations in obtained with an S(2+) ionizing flux which is a factor of 20 times less than predicted by the Kurucz atmosphere. Current model atmospheres may not be appropriate because a single stable star with Teff = 34,000 K fails by at least an order of magnitude to produce the ionizing luminosity. The small radius of the constant-density core implies a short dynamical lifetime of approximately 5000 years for this spherical model; this may indicate that a nonspherical blister geometry is more appropriate for this H II region.

Rubin, R. H.↗
NASA NTRS1983

Nature of the H chondrite parent body regolith - Evidence from the Dimmitt breccia

Meteorite regolith breccias are clastic rocks which formed by lithification of fragmental regolith material that once resided at the surface of a meteorite parent body. A study is reported of the matrix and 21 clasts of various sizes (0.2-24 mm) in the Dimmitt H chondrite regolith breccia using petrographic and electron microprobe techniques. In addition, oxygen isotope studies of three clasts and instrumental neutron activation analysis (INAA) and Ar-39/Ar-40 age dating of one clast are reported. The Dimmitt meteorite was found about 1942 near Dimmitt, Texas. Attention is given to analytical procedures, the clastic matrix, equilibrated clasts, poikilitic melt-rock clast, clasts of different chondrite groups, graphite-magnetite aggregates, the origin of exotic clasts, and the complexity of parent body surfaces processes.

Rubin, A. E.↗
NASA NTRS1983

Mineralogy and petrology of the Abee enstatite chondrite breccia and its dark inclusions

A model is proposed for the petrogenesis of the Abee E4 enstatite chondrite breccia, which consists of clasts, dark inclusions and matrix, and whose dark inclusions are an unusual kind of enstatite chondritic material. When the maximum metamorphic temperature of the breccia parent material was greater than 840 C, euhedral enstatite crystals in metallic Fe, Ni, and sulfide-rich areas grew into pliable metal and sulfide. Breccia parent material was impact-excavated, admixed with dark inclusions, and rapidly cooled. During this cooling, the clast and matrix material acquired thermal remanent magnetization. A subsequent ambient magnetic field imparted a uniform net magnetic orientation to the matrix and caused the magnetic orientation of the clasts to be less random. The Abee breccia was later consolidated by shock or by shallow burial and long period, low temperature metamorphism.

Rubin, A. E.↗
NASA NTRS1983

Calculation of afterbody flows with a composite velocity formulation

A recently developed technique for numerical solution of the Navier-Stokes equations for subsonic, laminar flows is investigated. It is extended here to allow for the computation of transonic and turbulent flows. The basic approach involves a multiplicative composite of the appropriate velocity representations for the inviscid and viscous flow regions. The resulting equations are structured so that far from the surface of the body the momentum equations lead to the Bernoulli equation for the pressure, while the continuity equation reduces to the familiar potential equation. Close to the body surface, the governing equations and solution techniques are characteristic of those describing interacting boundary layers. The velocity components are computed with a coupled strongly implicity procedure. For transonic flows the artificial compressibility method is used to treat supersonic regions. Calculations are made for both laminar and turbulent flows over axisymmetric afterbody configurations. Present results compare favorably with other numerical solutions and/or experimental data.

Swanson, R. C.↗
NASA NTRS1985

Error Correction for Tandem Data-Transmission Paths

Mathematical analysis for digital data transmission calculates optimum number of binary error-correcting repeaters to install in given number of wideband channel links. Asymptotic results compared to computed numerical results.

Posner, E. C.↗
NASA NTRS1983

Static versus dynamic loads as an influence on bone remodelling

Bone remodelling activity in the avian ulna was assessed under conditions of disuse alone, disuse with a superimposed continuous compressive load, and disuse interrupted by a short daily period of intermittent loading. The ulna preparation is made by two submetaphyseal osteotomies, the cut ends of the bone being covered with stainless steel caps which, together with the bone they enclosed, are pierced by pins emerging transcutaneously on the dorsal and ventral surfaces of the wing. The 110 mm long undisturbed section of the bone shaft can be protected from functional loading, loaded continuously in compression by joining the pins with springs, or loaded intermittently in compression by engaging the pins in an Instron machine. Similar loads (525 n) were used in both static and dynamic cases engendering similar peak strains at the bone's midshaft (-2000 x 10-6). The intermitent load was applied at a frequency of 1 Hz during a single 100 second period per day as a ramped square wave, with a rate of change of strain during the ramp of 0.01 per second.

Lanyon, L. E.↗
NASA NTRS1984

Control of bone remodelling by applied dynamic loads

The data showing the relationship between bone mass and peak strain magnitude prepared and submitted for publication. The data from experiments relating remodelling activity with static or dynamic loads were prepared and submitted for publication. Development of programs to relate the location of remodelling activity with he natural and artificial dynamic strain distributions continued. Experiments on the effect of different strain rates on the remodelling response continued.

Lanyon, L. E.↗
NASA NTRS1983

The effect of heavy element opacity on the structure of H II regions

In the modeling of H II regions, there generally has been universal dismissal of opacity due to elements other than H and He. It is found that in certain cases, the trace elements do contribute substantially to the opacity, modifying the ionization equilibrium directly and having feedback on the thermal structure. When important, this effect will reduce the volume where some lines from high ionization states are produced and will decouple transition zones that have traditionally been assumed to be coextensive. The possible reconciliation of some recent problems where observations and theory appeared to be inconsistent with one another are discussed.

Rubin, R. H.↗
NASA NTRS1983

Fragmental breccias and the collisional evolution of ordinary chondrite parent bodies

The present investigation is concerned with the results of a survey of gas-poor, melt-rock, or exotic clast-bearing fragmental breccias among the ordinary chondrite groups. It is found that such breccias constitute 5 percent, 22 percent, and 23 percent of H, L, LL chondrites respectively. Four melt-rock-clast-bearing fragmental breccias were selected for more detailed study to determine petrologic relationships between blasts and hosts. Attention is given to the abundances of melt-rock or exotic clast-bearing fragmental breccias, the formation of fragmental breccias, and the implications of breccia abundances in different chondrite groups.

Rubin, A. E.↗
NASA NTRS1983

Lithification opf gas-rich chondrite regolith breccias by grain boundary and localized shock melting

The fine-grained matrices (less than 150 microns) of 14 gas-rich ordinary chondrile regolith breccias were studied in an attempt to decipher the nature of the lithification process that converted loose regolith material into consolidated breccias. It is found that there is a continuouos gradation in matrix textures from nearly completely clastic (class A) to highly cemented (class C) breccias in which the remining clasts are completely surrounded by interstitial, shock-melted material. It is concluded that this interstitial material is formed by shock melting in the porous regolith. In general, the abundances of solar-wind-implanted He-4 and Ne-20 are inversely correlated with the abundance of intenstitial, shock-melted, feldspathic material. Chondrites with the highest abundance of interstitial, melted material (class C) experienced the highest shock pressures and temperatures and suffered the most extensive degassing. It is this interstitial, feldspathic melt that lithifies and cements the breccias together; those breccias with very little interstitial melt (class A) are the most porous and least consolidated.

Bischoff, A.↗
NASA NTRS1984

Digital SAR processing using a fast polynomial transform

A new digital processing algorithm based on the fast polynomial transform is developed for producing images from Synthetic Aperture Radar data. This algorithm enables the computation of the two dimensional cyclic correlation of the raw echo data with the impulse response of a point target, thereby reducing distortions inherent in one dimensional transforms. This SAR processing technique was evaluated on a general-purpose computer and an actual Seasat SAR image was produced. However, regular production runs will require a dedicated facility. It is expected that such a new SAR processing algorithm could provide the basis for a real-time SAR correlator implementation in the Deep Space Network. Previously announced in STAR as N82-11295

Truong, T. K.↗
NASA NTRS1984

Holocene eruptive activity of El Chichon volcano, Chiapas, Mexico

Geologic and radiometric-age data indicate that El Chichon was frequently and violently active during the Holocene, including eruptive episodes about 600, 1250, and 1700 years ago and several undated, older eruptions. These episodes, involving explosive eruptions of sulfur-rich magma and associated domegrowth processes, were apparently separated by intervals of approximately 350 to 650 years. Some of El Chichon's eruptions may correlate with unusual atmospheric phenomena around A.D. 1300 and possibly A.D. 623.

Tilling, R. I.↗
NASA NTRS1984

Models of four highly obscured compact H II regions

Models are constructed for three stars in order to determine their properties and elemental abundances through comparisons of model predictions and observations. By comparing predicted line fluxes with those observed, it is noted that oxygen is apparently enhanced by a factor of 2 in W3A, and of 4 in G75.84 + 0.40A and G29.9 - 0.0. The first two cases are based on the premise that the O(++)-emitting regions are as clumped as those of S(++). The H II regions all need more than one main sequence star or one unusually large star to provide the observed radio luminosity.

Simpson, J. P.↗
NASA NTRS1984

First known EL5 chondrite - Evidence for dual genetic sequence for enstatite chondrites

The compositionally distinct EH and EL groups together with four (3-6) petrologic types which constitute the enstatite chondrites represent increasing degrees of metamorphic alteration. Although bulk composition variations preclude a simple conversion of EH4 into EL6 material, complex models which involve simultaneous bulk composition and petrologic type variations may be implied by other classification schemes in common use. Attention is presently given to the discovery of the first EL5 chondrite, which breaks the EH3,4-EH5-EL6 sequence and indicates that the enstatite chondrites constitute the two discrete, isochemical metamorphic sequences EH3-5 and EL5-6.

Sears, D. W. G.↗