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NASA NTRS1990

Coronae of Mnemosyne Regio - Morphology and origin

The Mnemosine Regio area of Venus contains seven of the circular-to-elliptical structures, characterized by an annulus of concentric ridges, that are known as 'coronae'. Several corona-origin models are presently considered, and it is found that the processes associated with diapirism or hot-spots, and the gravitational relaxation of high topography, are most consistent with the topography and morphology of these coronae. The sequence of the formation and evolution of the coronae proceeds from regional volcanic and tectonic activity, through localized uplift and volcanism, to annulus and trough formation related to gravitational relaxation, and finally local volcanic flooding of the corona, annulus, and trough.

Stofan, Ellen R.↗

NASA NTRS1990

Comparative morphological analysis of Puppis A at radio, infrared, optical, and X-ray wavelengths

This paper presents a new radio image of the supernova remnant Puppis A obtained with the Molonglo Observatory synthesis telescope (MOST) and the Parkes telescope, and infrared images of Puppis A and its surrounding medium obtained with the IRAS, and compares the remnant morphologies at radio, infrared, optical, and X-ray wavelengths. The radio image, which includes large-scale emission, shows a clumpy shell of emission with moderate central brightness. The infrared observations have the advantage of offering a detailed look at the medium into which the remnant is expanding. From the IR data, evidence is found of the remnant's expansion into a strong density gradient (distinct from the more gentle gradient of the Galactic plane). A strong isolated knot of enhanced X-ray and radio emission is a region of enhanced infrared emission as well. Detailed correlative analysis of the infrared, radio, and X-ray emission shows that the IR emission correlates very well with the X-ray emission, confirming the idea that the IR emission arises from dust that is collisionally heated by the shocked gas.

Arendt, Richard G.↗

NASA NTRS1990

Freeze drying for morphological control of inter-penetrating polymer networks

The intrinsic brittleness of BMI resins can be reduced through the creation of an interpenetrating network (IPN) of BMI with a reactive-encapped thermoplastic, such as the presently considered polyimidesulfone, PISO2. The PISO2 and BMI were dissolved in a common solvent, which was then removed from the constituents by freeze drying; in an alternative method, an IPN was formed through dissolution of the constituent in a common solvent with either high or low melting point, followed by evaporative removal of the solvent. The effectiveness of the freeze-drying approach for morphological control is evaluated.

Hansen, Marion G.↗

NASA NTRS1990

Investigation of the asymmetric misfit dislocation morphology in epitaxial layers with the zinc-blende structure

The source of the asymmetry in the dislocation morphology exhibited in the epitaxial growth of compound semiconductors on (100) was investigated. A thickness wedge of p- and n-type GaAs(0.95)P(0.05) was grown on GaAs by metalorganic chemical vapor deposition, and the effect of misorientation on the resolved shear stress for each slip system was calculated and eliminated as the source of the asymmetry. Another potential source of asymmetry, the thickness gradient, was also eliminated. Results show that the substrate misorientation and the thickness gradient do not significantly contribute to the asymmetry and that the dominant contributor to the asymmetry of misfit dislocations in the (001) epitaxial interface can be attributed to the differences in the Peierls barriers between the two types of dilocations in GaAsP/GaAs.

Fox, Bradley A.↗

NASA NTRS1990

Optical and morphological properties of Cirrus clouds determined by the high spectral resolution lidar during FIRE

Cirrus clouds reflect incoming solar radiation and trap outgoing terrestrial radiation; therefore, accurate estimation of the global energy balance depends upon knowledge of the optical and physical properties of these clouds. Scattering and absorption by cirrus clouds affect measurements made by many satellite-borne and ground based remote sensors. Scattering of ambient light by the cloud, and thermal emissions from the cloud can increase measurement background noise. Multiple scattering processes can adversely affect the divergence of optical beams propagating through these clouds. Determination of the optical thickness and the vertical and horizontal extent of cirrus clouds is necessary to the evaluation of all of these effects. Lidar can be an effective tool for investigating these properties. During the FIRE cirrus IFO in Oct. to Nov. 1986, the High Spectral Resolution Lidar (HSRL) was operated from a rooftop site on the campus of the University of Wisconsin at Madison, Wisconsin. Approximately 124 hours of fall season data were acquired under a variety of cloud optical thickness conditions. Since the IFO, the HSRL data set was expanded by more than 63.5 hours of additional data acquired during all seasons. Measurements are presented for the range in optical thickness and backscattering phase function of the cirrus clouds, as well as contour maps of extinction corrected backscatter cross sections indicating cloud morphology. Color enhanced images of range-time indicator (RTI) displays a variety of cirrus clouds with approximately 30 sec time resolution are presented. The importance of extinction correction on the interpretation of cloud height and structure from lidar observations of optically thick cirrus are demonstrated.

Grund, Christian John↗

NASA NTRS1990

Interpretation of the optical and morphological properties of Cirrus clouds from lidar measurements

Lidar measurements can provide a great deal of information about the structure, location, and scattering properties of cirrus clouds. However, caution must be used when interpreting raw lidar backscatter profiles in terms of relative or absolute extinction distribution, internal cloud structure, and, at times, cloud location. The problem arises because the signal measured from a range by any monostatic lidar system depends on the backscatter cross section at that range and the 2-way optical thickness to the scattering volume. Simple lidar systems, however, produce only one measurement of attenuated backscatter from each range. The general FIRE research community is given aid in interpretation of lidar measurements, and the special capabilities of the High Spectral Resolution Lidar (HSRL) is explained. Some examples are given of conditions under which direct interpretation of cirrus cloud morphology from simple lidar profiles could be misleading.

Grund, Christian John↗

NASA NTRS1990

An experimental study of high Tc superconducting microstrip transmission lines at 35 GHz and the effect of film morphology

Microstrip transmission lines in the form of ring resonators were fabricated from a number of in-situ grown laser ablated films and post-annealed co-sputtered YBa2Cu3O(7-x) films. The properties of these resonators were measured at 35 GHz and the observed performance is examined in light of the critical temperature (Tc) and film thickness and also the film morphology which is different for the two deposition techniques. It is found that Tc is a major indicator of the film performance for each growth type with film thickness becoming important as it decreases towards 100 A. It is also found that the films with a mixed grain orientation (both a axis and c axis oriented grains) have poorer microwave properties as compared with the primarily c axis oriented material. This is probably due to the significant number of grain boundaries between the different crystallites, which may act as superconducting weak links and contribute to the surface resistance.

Chorey, C. M.↗

NASA NTRS1990

The ratio of molecular to atomic gas in spiral galaxies as a function of morphological type

In order to gain an understanding of the global processes which influence cloud and star formation in disk galaxies, it is necessary to determine the relative amounts of atomic, molecular, and ionized gas both as a function of position in galaxies and from galaxy to galaxy. With observations of the CO distributions in over 200 galaxies now completed as part of the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey (Young et al. 1989), researchers are finally in a position to determine the type dependence of the molecular content of spiral galaxies, along with the ratio of molecular to atomic gas as a function of type. Do late type spirals really have more gas than early types when the molecular gas content is included. Researchers conclude that there is more than an order of magnitude decrease in the ratio of molecular to atomic gas mass as a function of morphological type from Sa-Sd; an average Sa galaxy has more molecular than atomic gas, and an average Sc has less. Therefore, the total interstellar gas mass to blue luminosity ratio, M sub gas/L sub B, increases by less than a factor of two as a function of type from Sa-Sd. The dominant effect found is that the phase of the gas in the cool interstellar medium (ISM) varies along the Hubble sequence. Researchers suggest that the more massive and centrally concentrated galaxies are able to achieve a molecular-dominated ISM through the collection of more gas in the potential. That gas may then form molecular clouds when a critical density is exceeded. The picture which these observations support is one in which the conversion of atomic gas to molecular gas is a global process which depends on large scale dynamics (cf Wyse 1986). Among interacting and merging systems, researchers find considerable scatter in the M(H2)/M(HI) ratio, with the mean ratio similar to that in the early type galaxies. The high global ratio of molecular to atomic gas could result from the removal of HI gas, the enhanced conversion of HI into H2, or both.

Knezek, Patricia M.↗

NASA NTRS1990

The morphology-density relation for dwarf galaxies

The morphology-density relation is examined for dwarf galaxies with absolute magnitudes -18 less than or equal to M sub B sub T less than or equal to -12.5, based on a deep photographic survey of nearby groups and clusters of galaxies. Results are given. Compared to dwarf ellipticals, dwarf irregulars form a more extended population in nearby clusters, and may in fact be entirely absent from the cluster cores. The spatial distribution of dwarf ellipticals in clusters depends on luminosity and the presence or absence of nucleation. Nucleated dE's and non-nucleated dE's fainter than M sub B sub T approx. -13.5 are concentrated toward the centers of clusters like the giant E and S0 galaxies. In contrast, non-nucleated dE's brighter than M sub B sub T approx. -14.5 are distributed like the spirals and irregulars. The intrinsic shapes of the bright non-nucleated dE's are similar to those of the dwarf irregulars, suggesting a possible evolutionary connection between these two classes of galaxies.

Ferguson, H. C.↗

NASA NTRS1990

The morphology of Sersic-Pastoriza galaxies

The authors present the preliminary results of their radio-continuum and neutral hydrogen observations of Sersic-Pastoriza (S-P) galaxies. They show that the central regions contain a population of compact features thought to be young supernova remnants (SNRs) and discuss the overall morphology of the nuclei.

Yates, G. J.↗

NASA NTRS1990

The kinematics and morphology of NGC 520: One, two, or three galaxies

The peculiar galaxy NGC 520 (Arp 157) is often interpreted as an interacting pair of galaxies. The identification of the two bulges and overall morphology of the two galaxies has long been a puzzle which the authors attempt to solve here. New longslit optical spectroscopy and near-infrared images of NGC 520 are presented. These data suggest that the northwest peak is the bulge of one of two galaxies in the system. The other larger bulge is clearly evident in the K band image in the middle of the dust lane. The stellar radial velocity profile in the central 10 seconds of the larger bulge is consistent with counterrotation seen in the molecular gas component. This kinematic subsystem could be the remains of a merged gas-rich irregular.

Stanford, S. A.↗

NASA NTRS1991

Evaluating some computer enhancement algorithms that improve the visibility of cometary morphology

The observed morphology of cometary comae is determined by ejection circumstances and the interaction of the ejected material with the local environment. Anisotropic emission can provide useful information on such things as orientation of the nucleus, location of active areas on the nucleus, and the formation of ion structure near the nucleus. However, discrete coma features are usually diffuse, of low amplitude, and superimposed on a steep intensity gradient radial to the nucleus. To improve the visibility of these features, a variety of digital enhancement algorithms were employed with varying degrees of success. They usually produce some degree of spatial filtering, and are chosen to optimize visibility of certain detail. Since information in the image is altered, it is important to understand the effects of parameter selection and processing artifacts can have on subsequent interpretation. Using the criteria that the ideal algorithm must enhance low contrast features while not introducing misleading artifacts (or features that cannot be seen in the stretched, unprocessed image), the suitability of various algorithms that aid cometary studies were assessed. The strong and weak points of each are identified in the context of maintaining positional integrity of features at the expense of photometric information.

Larson, S. M.↗

NASA NTRS1990

Spectral synthesis in the ultraviolet. III - The spectral morphology of normal stars in the mid-ultraviolet

The morphology of 218 mid-UV spectra of stars ranging from O through K in spectral type is examined. Several new line and continuum indices are defined and their usefulness as temperature, luminosity, and metallicity discriminants is discussed. Mid-UV stellar continua are found to be markedly affected by abundance. A UV excess, delta(2600-V), is computed which is more sensitive by a factor of 10 to (Fe/H) than is delta(U-B). The relative strength of spectral lines in the mid-UV is not as strongly affected by abundance. Mid-UV spectra are much more sensitive to the temperature of the stellar population than to either metallicity or the dwarf/giant ratio. Mg II 2800 shows unexpected behavior, displaying no sensitivity to abundance for cool stars and a reversed sensitivity in FG dwarfs such that metal-poor stars have stronger Mg II strengths at the same temperature than more metal-rich stars.

Fanelli, Michael N.↗

NASA NTRS1990

The effect of an electric field on the morphological stability of the crystal-melt interface of a binary alloy. III - Weakly nonlinear theory

The effect of a constant electric current on the crystal-melt interface morphology during directional solidification at constant velocity of a binary alloy is considered. A linear temperature field is assumed, and thermoelectric effects and Joule heating are neglected; electromigration and differing electrical conductivities of crystal and melt are taken into account. A two-dimensional weakly nonlinear analysis is carried out to third order in the interface amplitude, resulting in a cubic amplitude equation that describes whether the bifurcation from the planar state is supercritical or subcritical. For wavelengths corresponding to the most dangerous mode of linear theory, the demarcation between supercritical and subcritical behavior is calculated as a function of processing conditions and material parameters. The bifurcation behavior is a sensitive function of the magnitude and direction of the electric current and of the electrical conductivity ratio.

Wheeler, A. A.↗

NASA NTRS1990

Effect of anisotropic thermal conductivity on the morphological stability of a binary alloy

A linear morphological stability analysis is presented for a planar interface during unidirectional solidification of a binary alloy, in the case of a crystal having an anisotropic thermal conductivity. A dispersion relation shows that the onset of instability depends on the orientation of the growth direction with respect to principal crystallographic axes and on the orientation of the wavevector of the perturbation. The onset of instability can be either oscillatory (traveling waves) or nonoscillatory in time. For growth along a principal axis of the crystal there is an exchange of stabilities, and the onset of instability is nonoscillatory.

Coriell, S. R.↗

NASA NTRS1990

Cumulus cloud field morphology and spatial patterns derived from high spatial resolution Landsat imagery

Using high-spatial-resolution Landsat MSS imagery, the cumulus cloud morphology, cloud nearest-neighbor distributions, and cloud clumping scales were investigated. It is shown that the cloud-size distribution can be represented by a mixture of two power laws; clouds of diameters less than 1 km have power-law slope range of 1.4-2.3, while larger clouds have slopes from 2.1 to 4.75. The break in power-law slope occurs at the cloud size that makes the largest contribution to cloud cover. Results suggest that larger clouds grow at the expense of smaller clouds. It was also found that the cloud inhomogeneities have significant impact on radiative fluxes.

Sengupta, S. K.↗

NASA NTRS1991

Peculiar morphologies of four IRAS galaxies

Optical and radio data that reveal the peculiar morphologies of four IRAS galaxies are discussed. NGC 1620 is shown to have an off-center arclike structure of 3 kpc radius that may be the largest supernova-blown bubble known. UGC 2982 is an ongoing merger of two gas-rich galaxies. It is shown that the UGC 3004/3005 pair is not interacting despite the proximity of its components. UGC 3004 is a regular barred spiral galaxy. A second nucleus in the edge-on system UGC 3005 suggests a recent merger. Finally, IRAS 23385 + 0300 is one of the most infrared-luminous galaxies known.

Chaboyer, Brian↗

NASA NTRS1991

Population studies in groups and clusters of galaxies. IV - Comparison of the luminosity functions and morphological-type distributions in seven nearby groups

Published observational data on the Leo, Dorado, NGC 1400, NGC 5044, Antlia, Fornax, and Virgo groups of galaxies are analyzed in terms of the luminosity functions and morphological types of their members. The data sets employed are characterized, and the results are presented in extensive tables and graphs and discussed in detail. While the fractions of early and late galaxies in the groups are similar, the ratio of dwarfs to giants (D/G) in the early galaxies varies monotonically with the richness of the cluster, leading to artificial flattening at the faint end of the total luminosity function in environments with low D/G. The luminosity function for dwarfs in all environments is found to have a slope of about -1.3.

Ferguson, Henry C.↗