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At least 811 records · Page 45
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NASA NTRS1989

0714 - 2914 (M4-1) - Another Seyfert galaxy with aligned radio continuum and optical emission-line morphologies

Direct imaging and long-slit spectroscopic mapping of the emission-line gas in the Seyfert 2 galaxy 0714 - 2914 (M4-1, MCG - 5-18-2) are reported. The nuclear regions contain an extended (1 kpc size), high-excitation nebulosity that is well aligned with the jet-like nonthermal radio source. The profiles of Forbidden O III 5007A are asymmetric, with extended red wings to the north and west of the nucleus and extended blue wings to the south and east. This switch in the sense of asymmetry is accounted for in terms of a combination of normal rotational motions in the galaxy disk and high-velocity outflow or infall associated with the Seyfert activity.

Wilson, A. S.↗
NASA NTRS1989

Morphological study of the innervation pattern of the rabbit sinoatrial node

The pattern of sinoatrial (SA) node innervations in rabbit was elucidated using a newly developed highly reproducible cholinesterase/silver impregnation staining procedure which made it possible to delineate large nerves, fine processes, and ganglion cells. The SA node and dominant pacemaker sites were identified by microelectrode recording. A generalized pattern of innnervation was recognized, which includes a large ganglionic complex inferior to the SA node; two or more moderately large nerves traversing the SA node parallel to the crista terminalis; nerves entering the intercaval region from the septum, the superior vena cava, and the inferior vena cava to impinge on the SA node; and a fine network of nerve processes, which was particularly dense in the SA node. From the location and distribution of the nerves and ganglionic branches, it can be inferred that the neural network in the intercaval region is capable of performing complex modulatory and integrative functions among the structures within this region.

Roberts, L. A.↗
NASA NTRS1990

Long-wave morphological instabilities in the directional solidification of a dilute binary mixture

Long-wave instabilities in a directionally-solidified binary mixture may occur in several limits. Sivashinsky (1983) identified a small-segregation-coefficient limit and obtained a weakly nonlinear evolution equation governing subcritical two-dimensional bifurcation. Brattkus and Davis (1988) identified a near-absolute-stability limit and obtained a strongly nonlinear evolution equation governing supercritical two-dimensional bifurcation. The present investigation identifies a third strongly nonlinear evolution equation, arising in the small-segregation-coefficient, large-surface-energy limit. This equation links both of the former and describes the change from the sub- to super-critical bifurcations. This study sets the previous long-wave analyses into a logical framework.

Riley, D. S.↗
NASA NTRS1990

The kinematics and morphology of NGC 520

New long-slit optical spectroscopy and optical and NIR images of NGC 520 are presented. Velocity-dispersion and radial-velocity profiles are obtained from the spectra with the Fourier quotient and cross-correlation techniques. At the NW optical emission peak, a sharp rise in the velocity dispersions implies a concentration of mass. The NW optical peak is also apparent as a peak in the K-band image, whose NIR colors are consistent with the presence of a typical bulge steller population. These data suggest that the NW peak may be the bulge of one of two galaxies in the system. A larger bulge is clearly evident in the K-band image in the middle of an optical dust lane. The optical colors and H-alpha emission imply that both bulges and the disk of the NW galaxy have experienced recent star formation. The radial-velocity profile in the central 10 arcsec at the larger bulge is consistent with a counterrotating core, in agreement with the CO radial-velocity profile (Sanders et al., 1988). This core could be explained as an accreted gas-rich irregular galaxy which is forming a counterrotating stellar disk.

Standord, S. A.↗
NASA NTRS1990

The morphology of star clusters in the SMC

The projected ellipticities of 34 populous SMC star clusters have been derived by means of PDS 1010A scans and a computer interactive method of reduction implemented on an Apollo 570 workstation. A pair of J and R plates taken with the 1.2 m UK Schmidt telescope in Australia were used. Radial ellipticity variations within individual globular clusters seem to be a common phenomenon for the SMC clusters, similar to that observed in the LMC clusters where the innerparts are more elliptical than the outer ones in 95 percent of the cases. The derived ellipticities which correspond to the innermost part of the cluster at radial distances near to half-mass radii have been found to be statistically more elliptical than those of the LMC, known to be more elliptical than those of the Galaxy. The dynamical masses of the clusters seem to correlate with ellipticities supporting the hypothesis that, either the gravitational field of the parent galaxy being a dominant factor affect slower the shape of the high mass clusters and/or the most massive clusters, being dynamically younger, retain their original shape.

Kontizas, E.↗
NASA NTRS1990

Geochemical evolution of the northern plains of Mars - Early hydrosphere, carbonate development, and present morphology

An equilibrium geochemical model of the primitive Martian atmosphere-regolith-ocean system that could have existed early in the history of Mars is developed. The results of this model are used to examine the evolution of the volatile budget of Mars and the processes occurring in the Martian ocean that may have contributed to the deposition of large carbonate beds on the northern plains. Results of this model are compared to those of the Pollack et al. (1987) model.

Schaefer, Martha W.↗
NASA NTRS1990

Dentritic morphology and microsegregation in directionally solidified superalloy, PWA-1480, single crystal: Effect of gravity; center director's discretionary fund report

Primary dendrite spacings, secondary dendrite spacings, and microsegregation have been examined in PWA-1480 single crystal specimens which were directionally solidified during parabolic maneuvers on the KC-135 aircraft. Experimentally observed growth rate and thermal gradient dependence of primary dendrite spacings are in good agreement with predictions from dendrite growth models for binary alloys. Secondary dendrite coarsening kinetics show a reasonable fit with the predictions from an analytical model proposed by Kirkwood for a binary alloy. The partition coefficients of tantalum, titanium, and aluminum are observed to be less than unity, while that for tungsten and cobalt are greater than unity. This is qualitatively similar to the nickel base binaries. Microsegregation profiles experimentally observed for PWA-1480 superalloy show a good fit with Bower, Brody, and Flemings model developed for binary alloys. Transitions in gravity levels do not appear to affect primary dendrite spacings. A trend of decreased secondary arm spacings with transition from high gravity to the low gravity period was observed at a growth speed of 0.023 cm s(exp -1). However, definite conclusions can only be drawn by experiments at lower growth speeds which make it possible to examine the side-branch coarsening kinetics over a longer duration. Such experiments, not possible due to the insufficient low-gravity time of the KC-135, may be carried out in the low-gravity environment of space.

Tewari, S. N.↗
NASA NTRS1991

COSMOS 2044: Lung morphology study, experiment K-7-28

Researchers examined the effect of microgravity during spaceflight on lung tissue. The ultrastructure of the left lungs of 5 Czechoslovakian Wister rats flown on the 13 day, 19+ hour Cosmos 2044 mission was examined and compared to 5 vivarium and 5 synchronous controls at 1-g conditions, and 5 rats exposed to 14 days of tail suspension. Pulmonary hemorrage and alveolar adema of unknown origin occurred to a greater extent in the flight, tail-suspended, and synchronous control animals, and in the dorsal regions of the lung when compared with the vivarium controls. The cause of these changes, which are possibly due to an increase in pulmonary vascular pressure, requires further investigation.

Elliott, Ann R.↗
NASA NTRS1990

Coronae on Venus - Morphology, classification, and distribution

Venera 15/16 radar images of Venus show two circular features having no analog among the terrestrial planets: 21 coronae, which have a complex interior zone, and 11 corona-like features, which lack the ridge annuli of the coronae. Each of these two groups of features is subdivisible into three classes; coronae may be symmetrical, asymmetrical, and subdued, while corona-like structures are double, irregular, and heart-shaped. The various classes of both types of classes are interpreted as having a similar mode of origin, namely the uplift and volcanism generated by a thermal anomaly at depth, followed by gravitational relaxation.

Pronin, A. A.↗
NASA NTRS1990

Studies of the local interstellar medium. VIII - Morphology and kinematics of the diffuse interstellar clouds toward Orion

Interstellar clouds in the direction of the Orion association show only positive velocities for target stars within 190 pc of the sun, and both positive and negative velocities for more distant target stars, confirming an earlier prediction by Cowie, Songaila, and York (1979). The nearby positive velocity cloud, designated here as Orion-Lepus 70 (OL 70), is a standard diffuse interstellar cloud: it is subject to the ambient galactic radiation field, with properties consistent with T about equal to 100 K and n about equal to 3/cu cm. Combined with a column density log N(H) = 19.8-20.0/sq cm, these values imply a cloud thickness of about 7 pc. The kinematics of OL 70 are consistent with either an origin as part of the expanding Loop I superbubble shell, or as part of Lindbald's expanding ring, or a synthesis of the two models. The negative velocity interstellar components seen in stars at d not less than 200 pc are caused by interstellar matter accelerated by the expanding Ori-Eri superbubble. Relatively dense interstellar gas at positive LSR velocities is also found within the Orion association, so that it is difficult to pick out OL 70 components in the spectra of the distant stars.

Frisch, P. C.↗
NASA NTRS1990

Morphological instability in rapid directional solidification

Mullins and Sekerka (1964) showed for fixed temperature gradient that the planar interface is linearly stable for all pulling speeds V above some critical value, the absolute stability limit. Near this limit, where solidification rates are rapid, the assumption of local equilibrium at the interface may be violated. Here, nonequilibrium effects are incorporated into a linear stability analysis of the planar front by allowing the segregation coefficient and interface temperature to depend on V in a thermodynamically consistent way. The absolute stability limit of the cellular mode is modified. A new oscillatory state is formed which, in the absence of latent heat, has a critical wavenumber of zero; by itself this instability would lead to the formation of solute bands in the solid. This mode has its own absolute-stability limit determined by solute trapping and kinetics. Under certain conditions, there exists a window of stability above the steady absolute-stability boundary and below the oscillatory-stability boundary; here the planar segregation-free state is restabilized.

Merchant, G. J.↗
NASA NTRS1990

A numerical and analytical study of nonlinear bifurcations associated with the morphological stability of two-dimensional single crystals

The nonlinear stability of a two-dimensional single crystal of pure material in an undercooled melt is studied both analytically and numerically. The quasi-steady state approximation is used for the thermal fields, and the effects of different solid and liquid thermal conductivities, isotropic interfacial growth kinetics, and isotropic surface tension are included. The bifurcation analysis is performed by calculating the instantaneous value of the fundamental component of the local normal growth speed for an interface perturbed by a single Fourier shape component. Numerically, the fundamental component of the interfacial growth speed is found by Fourier analysis of the solution to an integrodifferential equation obeyed at the interface. Analytically, an expansion technique is used to derive a solvability condition defining each of these bifurcation points. The analytical and numerical results are in very close agreement. Almost all of the bifurcations are subcritical, and the results are presented by giving values of the Landau coefficient as a function of the different dimensionless parameters used in the model.

Brush, L. N.↗
NASA NTRS1991

Fluid volcanism on Miranda and Ariel - Flow morphology and composition

Several types of volcanic units have been recognized on the icy Uranian satellites Miranda and Ariel. On Miranda, ridges characterized by crest grooves are up to 10 km wide and 500 m high. A continuous flat-topped flow band also 10 km wide and 500 m high forms the outer southern margin of Elsinore Corona, which appears to comprise coalesced flow bands and ridges. On Ariel, in addition to at least one ridge unit similar to those on Miranda, flood plains material has covered the floors of deep chasmata (grabens) and an irregular depression. Flows on both satellites are characterized by linear vent geometries and distinct topographic margins, which indicate extrusion of a relatively viscous material. The topography of the flows can be used to estimate flow viscosity or yield strength using a Bingham plastic model. Extrusion viscosity estimates, incorporating plausible volcanologically based emplacement time scales and a rigid crust correction, range from 10 MP to 1 GP (10 TP in the unlikely absence of a chilled crust). Viscosity estimates are dependent on the assumed emplacement time scale, however, and could be as high as 10 PP, if a solid-state-based time scale is assumed.

Schenk, Paul M.↗
NASA NTRS1991

A comparison of ULF fluctuations in the solar wind, magnetosheath, and dayside magnetosphere. I - Magnetosheath morphology. II - Field and plasma conditions in the magnetosheath

Simultaneous data from ISEE 1 and 2 in the upstream solar wind, from AMPTE IRM in the subsolar magnetosheath, and from AMPTE CCE in the dayside magnetosphere are used to investigate the properties of the magnetosheath responsible for the transmission into the magnetosphere the ULF waves generated in the solar wind upstream of a quasi-parallel bow shock. The data are used to characterize the magnetosheath both during the periods when azimuthally polarized resonant harmonic ULF magnetic pulsations were observed in the dayside outer maagnetosphere, and when they were not. In addition, a detailed analysis is carried out of magnetic field and plasma conditions in the subsolar magnetosheath during these and other periods.

Engebretson, M. J.↗
NASA NTRS1991

A morphological study of vertical ionospheric flows in the high-latitude F region

The vertical bulk-ion-drift data between 200 and 1000 km, obtained by DE 2 satellite were used to examine ion flows in the high-latitude F region. The data indicated that field-aligned ion flows between 100 m/s and 3 km/s are a common occurrence in the F region. The ion flows were predominantly upward near the cusp region and throughout the auroral zone, with occasionally observed downward flows of smaller magnitude over the polar cap. The results on bulk-ion flows in F region are compared with the published characteristics of the magnetospheric ion outflow, and the possibility that the two flows are physically linked is discussed.

Loranc, M.↗
NASA NTRS1991

Growth morphologies of crystal surfaces

A previously proposed Monte Carlo model (Xiao et al., 1988, 1990) is extended to three dimensions, and reevaporation after accommodation and growth on dislocation-induced steps are included. It is found again that, for a given set of growth parameters, the critical size beyond which a crystal cannot retain its macroscopically faceted shape scales linearly with the mean free path in the vapor. However, the three-dimensional systems show increased shape stability as compared with the corresponding two-dimensional cases. The experimental observation that the critical size of a growing crystal depends on the prevailing growth mechanism is confirmed, and detailed insight into the processes leading to the loss of face and facet stability is obtained.

Xiao, Rong-Fu↗
NASA NTRS1991

The X-ray morphology of the relaxed cluster of galaxies A2256. II - Sources around the extended cluster emission

The X-ray observation of A2256 with the imaging proportional counter on board the X-ray observatory Rosat revealed significantly more sources in the field around the extended cluster emission than expected by chance. In a preliminary investigation, 14 sources were discovered at the limiting flux for this exposure whereas about 7 sources would have been expected by chance. At least two of those sources are coincident with cluster-member galaxies, having X-ray luminosities of approximately 10 to the 42nd erg/s in the Rosat energy band from 0.1 to 2.4 keV, but at least four more are from 'dark' objects. The similarity of these objects to those in A1367 suggests the existence of a new class of X-ray sources in clusters.

Henry, J. P.↗