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At least 523 records · Page 29
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NASA NTRS2002

CRYSTAL-FACE: A Field Experiment and Modeling Program Focused on Tropical Anvils and Cirrus Layers

The Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE) is a measurement campaign designed to investigate tropical Cirrus cloud physical properties and formation processes. Understanding the production of upper tropospheric cirrus clouds is essential for the successful modeling of 'he Earth's climate. The deployment phase will occur in July, 2002 in southern Florida, USA. Several aircraft will be used, including the ER-2 and Proteus for cloud remote sensing, the WB-57 and Citation for in situ cloud measurements, the P-3 with a Doppler radar for characterization of convective systems, and the Twin otter for sampling of inflow airmasses. In addition, numerous ground-based and satellite remote sensing measurements will be contributing. A central focus of the mission is improvement of our ability to model cirrus clouds with numerical models. Several research groups with a variety of model types (cloud-resolving models, mesoscale models, weather-prediction models, and general circulation models) will be participating. Our hope is to fully characterize several mulonimbus/cirrus anvil systems that can be used as case studies for testing and improvement of the models. The models will be used for investigating cirrus generation and dissipation processes and the sensitivity of tropical cirrus to convective intensity and aerosol properties. Ultimately, we expect this effort to improve our ability to represent tropical cirrus in GCMs. A general description of the CRYSTAL-FACE program will be presented, with an emphasis on the cloud modeling approach.

Jenson, Eric↗
NASA NTRS2002

Dynamical Evolution of Planetary Embryos

During the past decade, progress has been made by relating the 'standard model' for the formation of planetary systems to computational and observational advances. A significant contribution to this has been provided by this grant. The consequence of this is that the rigor of the physical modeling has improved considerably. This has identified discrepancies between the predictions of the standard model and recent observations of extrasolar planets. In some cases, the discrepancies can be resolved by recognition of the stochastic nature of the planetary formation process, leading to variations in the final state of a planetary system. In other cases, it seems more likely that there are major deficiencies in the standard model, requiring our identifying variations to the model that are not so strongly constrained to our Solar System.

Wetherill, George W.↗
NASA NTRS2002

Geology and Origin of Europa's Mitten Feature (Murias Chaos)

The "Mitten" (provisionally named Murias Chaos by the International Astronomical Union) is a region of elevated chaos-like terrain in the leading hemisphere of Europa. Its origin had been explained under the currently debated theories of melting through a thin lithosphere or convection within a thick one. Galileo observations reveal several characteristics that suggest that the Mitten is distinct from typical chaos terrain and point to a different formational process. Photoclinometric elevation estimates suggest that the Mitten is slightly elevated with respect to the surrounding terrain; geologic relations indicate that it must have raised significantly from the plains in its past, resembling disrupted domes on Europa's trailing hemisphere. Moreover, the Mitten material appears to have extruded onto the plains and flowed for tens of kilometers. The area subsequently subsided as a result of isostatic adjustment, viscous relaxation, and/or plains loading. Using plate flexure models, we estimated the elastic lithosphere in the area to be several kilometers thick. We propose that the Mitten originated by the ascent and extrusion of a large thermal diapir. Thermal-mechanical modeling shows that a Mitten-sized plume would remain sufficiently warm and buoyant to pierce through the crust and flow unconfined on the surface. Such a diapir probably had an initial radius between 5 and 8 km and an initial depth of 20-40 km, consistent with a thick-lithosphere model. In this scenario the Mitten appears to represent the surface expression of the rare ascent of a large diapir, in contrast to lenticulae and chaos terrain, which may form by isolated and clustered small diapirs, respectively.

Figueredo, P. H.↗
NASA NTRS2002

New Insights into the X-Ray Spectra of Heliumlike and Neonlike Ions

Recent measurements of the K-shell and L-shell x-ray spectra of highly charged helium- like and neonlike ions are presented that were performed on the Livermore electron beam ion traps and the Princeton tokamaks. These measurements provide new insights into collisional and indirect line formation processes, identifications of forbidden lines, and a new plasma line diagnostic of magnetic field strength.

IONS↗
NASA NTRS2003

Protoplanetary Nebula Evolution using the Beta Viscosity Model

The evolutionary dynamics of a protoplanetary disk is an important component of the planet formation process. In particular, the dynamic and thermodynamic field plays a critical role in chemical evolution, the migration of dust particles in the nebula, and the radial transport of meteoritic components. The dynamic evolution is investigated using analytical solutions of the surface density transport equations using a turbulence model based on hydrodynamic generation of turbulence. It captures the major properties of the disk including region of separation between radial inflow and-outflow and the evolution of the central plane temperature. The analytical formulas are compared with available numerical solutions based on the alpha viscosity model. The beta viscosity model, heretofore used for steady-state disks, is shown to be a useful approximation for unsteady problems.

Davis, Sanford S.↗
NASA NTRS2003

Hydrodynamic Instability and Enhanced Transport in Protoplanetary Nebulae

The nature of turbulence (and the enhanced transport it provides) is a key element to comprehend the dynamics, physics and chemistry of the protoplanetary nebulae and consequently the planet formation process. Early accretion disk models postulated the turbulent transport through the well-known "alpha-viscosity" model, introduced by Shakura and Sunyaev in 1973. Since then, the nature of the turbulence in disks has been a subject of investigation. In 1991, the rediscovery by Balbus and Hawley of Chandrasekhar's linear instability in magnetized disks was a breakthrough in the discipline. Unfortunately, the mechanisms leading to turbulence in non-magnetized disks, such as protoplanetary nebulae, remain poorly understood. We will present results from laboratory experiments along with analytical arguments showing that, despite skepticism in the Astrophysical community, differential rotation may indeed be sufficient to trigger and sustain turbulence. We will also propose an alternative viscosity prescription derived from both experiments and analysis.

Richard, Denis T.↗
NASA NTRS2003

The Logical Extension

The same software controlling autonomous and crew-assisted operations for the International Space Station (ISS) is enabling commercial enterprises to integrate and automate manual operations, also known as decision logic, in real time across complex and disparate networked applications, databases, servers, and other devices, all with quantifiable business benefits. Auspice Corporation, of Framingham, Massachusetts, developed the Auspice TLX (The Logical Extension) software platform to effectively mimic the human decision-making process. Auspice TLX automates operations across extended enterprise systems, where any given infrastructure can include thousands of computers, servers, switches, and modems that are connected, and therefore, dependent upon each other. The concept behind the Auspice software spawned from a computer program originally developed in 1981 by Cambridge, Massachusetts-based Draper Laboratory for simulating tasks performed by astronauts aboard the Space Shuttle. At the time, the Space Shuttle Program was dependent upon paper-based procedures for its manned space missions, which typically averaged 2 weeks in duration. As the Shuttle Program progressed, NASA began increasing the length of manned missions in preparation for a more permanent space habitat. Acknowledging the need to relinquish paper-based procedures in favor of an electronic processing format to properly monitor and manage the complexities of these longer missions, NASA realized that Draper's task simulation software could be applied to its vision of year-round space occupancy. In 1992, Draper was awarded a NASA contract to build User Interface Language software to enable autonomous operations of a multitude of functions on Space Station Freedom (the station was redesigned in 1993 and converted into the international venture known today as the ISS)

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NASA NTRS2003

Discovery of an Obscured Supernova in Arp 299

The galaxy merger Arp 299, at a distance of 40 Mpc, is one of the most extensively studied interacting starburst galaxies known. It has been the site of 4 known supernovae (SNe) since 1990. Arp 299 contains a number of strong radio and infrared condensations, with the strongest starburst occurring in 'Source A,' in the nuclear region of the eastern galaxy. Source A has an inferred supernova rate of 0.5-0.7/yr, and its star formation peaked 6-8 Myr ago. Our recent observations identify a new radio-loud SN in Source A, which occurred sometime between April 2002 and February 2003. We imaged Arp 299 at milliarcsecond resolution at two epochs, in April 2002 and February 2003, using the Very Long Baseline Array and (at the first epoch) the Green Bank Telescope. In 2002, four compact radio sources were found in Source A at 2.3 GHz, with flux densities ranging from 0.3 to 1.7 mJy. In 2003, 8.4 GEz images revealed a new 3 mJy source, as well as the four objects detected a year earlier. The new radio SN is more than 1000 times more powerful than the galactic supernova remnant Cassiopeia A and is located located only 12 milliarcseconds (2.5 pc projected) from the strongest source seen in 2002. Milliarcsecond radio imaging is the only technique that could have detected this supernova, since it is embedded within an 80 mJy VLA source and buried in gas and dust (Av 15-25 mag). We suggest that both the new supernova and its nearest neighbor are occurring within a super star cluster, perhaps a newly formed globular cluster akin to those seen in a number of nearby galaxies and particularly galaxy mergers. If so, we are observing this cluster just as its massive stars have begun to explode into a very dense surrounding medium. The likelihood that most supernovae in such a medium will be radio-loud implies that future VLBI imaging over a number of years could lead to a direct measurement of the supernova rate in the Source A starburst, placing powerful constraints on models of present-day star formation processes.

Neff, Susan↗
NASA NTRS2004

Measuring the Internal Structure and Physical Conditions in Star and Planet Forming Clouds Cores: Towards a Quantitative Description of Cloud Evolution

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular cloud cores and investigate the physical conditions which give rise to star and planet formation. The goals of this program are to acquire, reduce and analyze deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds in order to determine the detailed initial conditions for star formation from quantitative measurements of the internal structure of starless cloud cores and to quantitatively investigate the evolution of such structure through the star and planet formation process.

Lada, Charles J.↗
NASA NTRS2004

Numerical Modeling of the South Pole-Aitkin Impact

The South Pole-Aitkin (SPA) basin, on the far side of the Moon, is the largest and oldest impact structure still preserved in the solar system. The crater is about 2500 km in diameter and formed in the Pre-Nectarian era of lunar history, over 4 Gyr ago. At this time, the thermal state of the Moon was much hotter than it is today. Accretional energy from the rapidly forming Moon melted the outermost few hundred kilometers of the Moon. As this magma ocean differentiated and cooled a 60 100-km thick low-density crust formed at the surface; below this the residual melt, with a higher density, cooled to form the lunar mantle. The giant SPA impact event punctured the Moon some time during the cooling of the magma ocean and thus provides a unique window for studying the lunar interior and the early formative processes of the Moon. The impact excavated otherwise inaccessible samples of the deep crust and (possibly) upper mantle, which has inspired proposed sample return missions. Furthermore, the thermal and rheologic state of the early Moon played a role in shaping the final structure of the basin. To aid in site selection for future sample return missions to the SPA basin, and to investigate the effect of thermal state on final crater structure, we performed some numerical simulations of the SPA impact event.

Collins, G. S.↗
NASA NTRS2004

Metal-Silicate Segregation in Deforming Dunitic Rocks: Applications to Core Formation in Europa and Ganymede

Core formation is an important event in the evolution of a planetary body, affecting both the geochemical and geophysical properties of the body. Metal-silicate segregation could have proceeded either by settling of liquid metal through a magma ocean or by percolation of liquid metal through a solid silicate mantle. Percolation of metallic melt had previously been excluded as a viable segregation mechanism because metallic melts do not form an interconnected network under hydrostatic conditions, except at high melt fraction (>5 vol%), due to the high dihedral angle between metals and silicates (>60 ). Without an interconnected network, porous flow of metallic melt is impossible, leaving the magma ocean scenario as the only mechanism to form the core. Moment-of-inertia measurements of Europa and Ganymede from the Galileo probe indicate that they are differentiated. This evidence suggests that a method for segregating metals and silicates at temperatures low enough to retain volatile compounds must exist. We have investigated the effect of deformation on the distribution of metallic melts in silicates. We have deformed samples of olivine + 5-9 vol% Fe-S to strains of 2.5 in simple shear and find that the metallic melt segregates into melt-rich planes oriented at 20 to the shear plane. These metallic melt-rich bands are similar in structure to the silicate melt-rich bands reported by Holtzman, indicating that deformation can interconnect isolated metallic melt pockets and allow porous flow of non-wetting melts. Such a core formation process could have occurred in the jovian satellites.

Hustoft, J. W.↗
NASA NTRS2004

Contemporaneous Formation of Chondrules in the Al-26-MG-26 System for Ordinary and CO Chondrites

Chronometer using the short-lived extinct-nuclide (26)Al has been applied to chondrules in order to obtain of their formation ages. Previous studies were mostly performed on Al-rich chondrules, which constitute only 1% of all chondrules, because of their high Al/Mg ratios. Recently, (26)Al ages of major ferromagnesian chondrules in least equilibrated ordinary chondrites (OC) have been obtained. However, (26)Al ages of ferromagnesian chondrules in least equilibrated carbonaceous chondrites (CC) are very limited. Particularly, age data of FeO-poor (Type I) chondrules in CC have been scarcely obtained, because of their fine textures and lack of phases with high Al/Mg (>100) ratios. In order to clarify the origin and formation processes of chondrules, we started systematic investigations on Type I chondrules in the most pristine CC (CO3.0 Yamato-81020), by examining textures, bulk chemical compositions, (26)Al ages and oxygen isotopic compositions. We find Type I chondrules in CC formed contemporaneously with ferromagnesian chondrules in OC.

Kurahashi, E.↗
NASA NTRS2004

Modeling Images of Natural 3D Surfaces: Overview and Potential Applications

Generative models of natural images have long been used in computer vision. However, since they only describe the of 2D scenes, they fail to capture all the properties of the underlying 3D world. Even though such models are sufficient for many vision tasks a 3D scene model is when it comes to inferring a 3D object or its characteristics. In this paper, we present such a generative model, incorporating both a multiscale surface prior model for surface geometry and reflectance, and an image formation process model based on realistic rendering, the computation of the posterior model parameter densities, and on the critical aspects of the rendering. We also how to efficiently invert the model within a Bayesian framework. We present a few potential applications, such as asteroid modeling and Planetary topography recovery, illustrated by promising results on real images.

Jalobeanu, Andre↗
NASA NTRS2005

Plasma in a Pulsed Discharge Environment

The plasma generated in a pulsed slit discharge nozzle is used to form molecular ions in an astrophysically relevant environment. The plasma has been characterized as a glow discharge in the abnormal regime. Laboratory studies help understand the formation processes of polycyclic aromatic hydrocarbon (PAH) ions that are thought to be the source of the ubiquitous unidentified infrared bands.

Remy, J.↗
NASA NTRS2005

Measuring the Internal Structure and Physical Conditions in Star and Planet Forming Clouds Core: Toward a Quantitative Description of Cloud Evolution

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular cloud cores and investigate the physical conditions which give rise to star and planet formation. The goals of this program are to acquire, reduce and analyze deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds in order to internal structure of starless cloud cores and to quantitatively investigate the evolution of such structure through the star and planet formation process. During the second year of this grant, progress toward these goals is discussed.

Lada, Charles J.↗
NASA NTRS2005

Irregular Satellites of the Planets

This proposal is directed towards the observational exploration of the irregular satellite systems of the planets. Primarily we use large-format CCD cameras on the world's largest telescopes, on Mauna Kea, to discover new irregular satellites and then to monitor their positions in order to ascertain their orbital characteristics. Separate observations are taken to determine the physical properties of the irregular satellites. The big picture science objective is to determine how these satellites were captures, and to use the properties of the satellites and their orbits to place constraints on early solar system (including formation) processes. Work in the first year has focussed on a major investigation of the Saturn irregular satellite system. We secured observing time on the Subaru and Gemini 8-m diameter telescopes in December 2004, January, February and March 2005 for the conduct of a deep, wide-area survey. This has resulted in the detection and orbit determination for 12 new satellites to be announced in the next week or two. Additional satellites were lost, temporarily, due to unusually poor weather conditions on Mauna Kea. These objects will be recovered and their orbits published next year. A separate survey of the Uranus irregular satellites was published (Sheppard, Jewitt and Kleyna 2005). Away from the telescope, we have discovered the amazing result that the four giant planets possess similar numbers of irregular satellites. This flies in the face of the standard gas-drag model for satellite capture, since only two of the giant planets are gas giants and the others (Uranus and Neptune) formed by a different process and in the absence of much gas. The constancy of the satellite number (each giant holds approximately 100 irregular satellites measured down to the kilometer scale) is either a coincidence, with different capture mechanisms at different planets giving by chance the same total numbers of irregular satellites, or indicates that the satellites were captured by a completely different process. We favor the latter (Jewitt and Sheppard 2005).

Jewitt, David↗
NASA NTRS2005

The CRYSTAL-FACE Mission

The Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE) was a measurement campaign designed to investigate tropical cirrus cloud physical properties and formation processes. Understanding the production of upper tropospheric cirrus clouds is essential for the successful modeling of the Earth's climate. The mission was staged in July 2002 with flights of 6 aircraft from Key West, Florida. Several aircraft were used for in situ and remote sensing of aerosols, ice crystals, meteorological fields, radiative fluxes, and gas concentrations. The NASA ER-2 and WB-57, the Proteus aircraft, owned by Northrop Grumman and operated by Scaled Composites, CIRPAS provided the DeHavilland UV-l8A, "Twin Otter" aircraft, the University of North Dakota provided a Cessna Citation II aircraft , and NSF supported the ELDORA radar onboard the Naval Research Laboratory P-3 aircraft. In this presentation, I will describe some of the flights, the conditions, and some of the results from the mission.

Newman, P.↗
NASA NTRS1997

BFS Method for Alloys Optimized and Verified for the Study of Ordered Intermetallic Material

The aerospace industry has a need for new metallic alloys that are lightweight and have high strength at elevated temperatures. The BFS (Bozzolo, Ferrante, and Smith) method is a new, computationally efficient and physically sound quantum semi-perturbative approach for describing metals and their defects. Based on a simple interpretation of the alloy formation process that identifies strain and chemical contributions to the energy of the alloy, the method provides an atom-by-atom description of an alloy. Its implementation requires little more than algebra and the solution of transcendental equations. At the NASA Lewis Research Center, we have demonstrated that BFS can investigate the properties of a large number of alloys with a minimum computational effort on low-level computers. This screening allows the selection of the best alloy candidates for a particular application and, therefore, promises large cost savings over current approaches.

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