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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Lightning-Sensor Data Help In Understanding Thunderstorms

NASA technical memorandum discusses research on use of data from network of ground-based magnetic direction-finding ground-strike lightning sensors to diagnose and predict occurrence and evolution of thunderstorms. Purposes of study to explore applicability and limitations of extrapolation techniques used to generate forecasts from data; to examine physically-based, nonlinear mathematical models for applicability to lightning-forecast problem; and to determine valid extrapolation ranges of such models for various weather scenarios.

Goodman, Steven J.↗
NASA NTRS1999

Multi-Scale Interactions Associated with the Monsoon Onset Over South China Sea and Adjacent Regions during SCSMEX-98

Using data collected during The South China Sea Monsoon Experiment (SCSMEX) (1998) as well as from the TRMM Microwave-Imager (TMI) and precipitation radar (PR), we have studied the multi-scale interactions (meso-synoptic-intraseasonal) associated with monsoon onset over South China Sea (SCS) and its subsequent evolution. Results show that the monsoon onset (defined by development of steady wind direction and heavy precipitation) over the northern SCS occurred around May 15 -17. Prevailing southerlies and southwesterlies developed over the central SCS after May 20. Shortly after, monsoon convection developed over the whole SCS region around May 23-27. The entire onset process appeared to be delayed by about a week to 10 days compared with climatology. During late spring of 1998, mid-latitude frontal systems were particularly active. These systems strongly impacted the northern SCS convection and may have been instrumental in triggering the onset of the SCS monsoon. The Tropical Oceans and Global Atmosphere (TOGA) and Bureau of Meteorology Research Centre (BMRC) radar showed a wide variety of convective systems over the Intensive Flux Array, from frontal bands to shear-banded structure, deep convection, pop-corn type shallow convection, slow moving "fine lines" to water spout. Analysis of SSM/I wind and moisture data suggested that the delayed convective activity over the SCS may be linked to the weakened northward propagation of monsoon rain band, hence contributing to a persistence of the rainband south of the Yangtze River and the disastrous flood that occurred over this region during mid to late June, 1998.

Lau, William K. M.↗
NASA NTRS1997

Etch Profile Simulation Using Level Set Methods

Etching and deposition of materials are critical steps in semiconductor processing for device manufacturing. Both etching and deposition may have isotropic and anisotropic components, due to directional sputtering and redeposition of materials, for example. Previous attempts at modeling profile evolution have used so-called "string theory" to simulate the moving solid-gas interface between the semiconductor and the plasma. One complication of this method is that extensive de-looping schemes are required at the profile corners. We will present a 2D profile evolution simulation using level set theory to model the surface. (1) By embedding the location of the interface in a field variable, the need for de-looping schemes is eliminated and profile corners are more accurately modeled. This level set profile evolution model will calculate both isotropic and anisotropic etch and deposition rates of a substrate in low pressure (10s mTorr) plasmas, considering the incident ion energy angular distribution functions and neutral fluxes. We will present etching profiles of Si substrates in Ar/Cl2 discharges for various incident ion energies and trench geometries.

Hwang, Helen H.↗
NASA NTRS2002

Oxygen Mass Flow Rate Generated for Monitoring Hydrogen Peroxide Stability

Recent interest in propellants with non-toxic reaction products has led to a resurgence of interest in hydrogen peroxide for various propellant applications. Because peroxide is sensitive to contaminants, material interactions, stability and storage issues, monitoring decomposition rates is important. Stennis Space Center (SSC) uses thermocouples to monitor bulk fluid temperature (heat evolution) to determine reaction rates. Unfortunately, large temperature rises are required to offset the heat lost into the surrounding fluid. Also, tank penetration to accomodate a thermocouple can entail modification of a tank or line and act as a source of contamination. The paper evaluates a method for monitoring oxygen evolution as a means to determine peroxide stability. Oxygen generation is not only directly related to peroxide decomposition, but occurs immediately. Measuring peroxide temperature to monitor peroxide stability has significant limitations. The bulk decomposition of 1% / week in a large volume tank can produce in excess of 30 cc / min. This oxygen flow rate corresponds to an equivalent temperature rise of approximately 14 millidegrees C, which is difficult to measure reliably. Thus, if heat transfer were included, there would be no temperature rise. Temperature changes from the surrounding environment and heat lost to the peroxide will also mask potential problems. The use of oxygen flow measurements provides an ultra sensitive technique for monitoring reaction events and will provide an earlier indication of an abnormal decomposition when compared to measuring temperature rise.

Ross, H. Richard↗
NASA NTRS2017

CIRIR Programs: Drilling and Research Opportunities at the Rochechouart Impact Structure

Owing to its size, accessibility and erosional level, the Rochechouart impact structure, dated at ~203 +/- 2 Ma (recalc.), is a unique reser-voir of knowledge within the population of the rare terrestrial analogous to large impacts craters observed on planetary surfaces. The site gives direct access to fundamental mechanisms both in impact-related geology (origin and evolution of planets) and biology (habitability of planets, emergence and evolution of life). For the last decade P. Lambert has been installing Rochechouart as International Natural Laboratory for studying impact processes and collateral effects on planetary surfaces. For this purpose the Center for International Research on Impacts and on Rochechouart (CIRIR) was installed on site in 2016 with twofold objectives and activities. First ones are scientific and dedicated to the scientific community. The second are cultural and educational and are dedi-cated to the public sensu lato. We present here the CIRIR, its scientific programs and the related reseach opportunities.

Lambert, P.↗
NASA NTRS2022

Coupling Carbon Oxidation and Surface Recession in Direct-Simulation Monte Carlo Code, SPARTA

Ablative thermal protection system (TPS) materials for spacecraft are composites that are often made out of carbon-based reinforcement and a polymeric matrix. They endure high-temperature oxidation and surface recession when re-entering Earth’s atmosphere. Ablation is the result of many coupled and competing thermal, mechanical, and chemical phenomena, and it is difficult to isolate the role of each on the overall degradation of the TPS. Here we develop an ablation model for material recession coupled explicitly to finite rate carbon oxidation in complex microstructures. In this work, Stochastic PArallel Rarified-gas Time-accurate Analyzer (SPARTA), a direct-simulation Monte Carlo (DSMC) code, is modified to allow oxidation-driven ablation of implicitly defined carbon surfaces. In SPARTA, implicit surfaces are generated from the grid corner point values via a marching cubes algorithm, therefore creating a new set of surface elements every time ablation is performed. The finite-rate oxidation model developed by Gopalan et. al, was adapted to tally surface reactions and other surface data on a per-grid cell basis. The ablation functionality was also adjusted so once the reactions have occurred, the number of reactions leading to CO formation can be converted to corner point reduction values; therefore, carbon removal is directly proportional to surface recession. We also develop robust algorithms which handle the evolution of the flow cells and solid material regions, including split cells (flow cell divided in two by a solid surface). Finally, we demonstrate our implicit chemistry model for 2D and 3D geometries by producing reaction statistics and detailed visualization of oxidation-induced material recession at the microscale.

V Arias↗
NASA NTRS2006

Atmospheres of Extrasolar Giant Planets

The next decade will almost certainly see the direct imaging of extrasolar giant planets around nearby stars. Unlike purely radial velocity detections, direct imaging will open the door to characterizing the atmosphere and interiors of extrasola planets and ultimately provide clues on their formation and evolution through time. This process has already begun for the transiting planets, placing new constraints on their atmospheric structure, composition, and evolution. Indeed the key to understanding giant planet detectability, interpreting spectra, and constraining effective temperature and hence evolution-is the atmosphere. I will review the universe of extrasolar giant planet models, focusing on what we have already learned from modeling and what we will likely be able to learn from the first generation of direct detection data. In addition to these theoretical considerations, I will review the observations and interpretation of the - transiting hot Jupiters. These objects provide a test of our ability to model exotic atmospheres and challenge our current understanding of giant planet evolution.

Marley, Mark↗
NASA NTRS2001

Etching in Chlorine Discharges Using an Integrated Feature Evolution-Plasma Model

Etching of semiconductor materials is reliant on plasma properties. Quantities such as ion and neutral fluxes, both in magnitude and in direction, are often determined by reactor geometry (height, radius, position of the coils, etc.) In order to obtain accurate etching profiles, one must also model the plasma as a whole to obtain local fluxes and distributions. We have developed a set of three models that simulates C12 plasmas for etching of silicon, ion and neutral trajectories in the plasma, and feature profile evolution. We have found that the location of the peak in the ion densities in the reactor plays a major role in determining etching uniformity across the wafer. For a stove top coil inductively coupled plasma (ICP), the ion density is peaked at the top of the reactor. This leads to nearly uniform neutral and ion fluxes across the wafer. A side coil configuration causes the ion density to peak near the sidewalls. Ion fluxes are thus greater toward the wall's and decrease toward the center. In addition, the ions bombard the wafer at a slight angle. This angle is sufficient to cause slanted profiles, which is highly undesirable.

Hwang, Helen H.↗
NASA NTRS1991

Modeling the pressure-dilatation correlation

It is generally accepted that pressure dilatation, which is an additional compressibility term in turbulence transport equations, may be important for high speed flows. Recent direct simulations of homogeneous shear turbulence have given concrete evidence that the pressure dilatation is important insofar that it contributes to the reduced growth of turbulent kinetic energy due to compressibility effects. The problem of modeling pressure dilatation is addressed. A component of the pressure dilatation is isolated which exhibits temporal oscillations and, using direct numerical simulations of homogeneous shear turbulence and isotropic turbulence, show that it has a negligible contribution to the evolution of turbulent kinetic energy. Then, an analysis for the case of homogeneous turbulence is performed to obtain a model for the nonoscillatory pressure dilatation. This model algebraically relates the pressure dilatation to quantities traditionally obtained in incompressible turbulence closures. The model is validated by direct comparison with the pressure dilatation data obtained from the simulations.

Sarkar, S.↗
NASA NTRS2014

Intercomparison of Large-Eddy Simulations of Arctic Mixed-Phase Clouds: Importance of Ice Size Distribution Assumptions

Large-eddy simulations of mixed-phase Arctic clouds by 11 different models are analyzed with the goal of improving understanding and model representation of processes controlling the evolution of these clouds. In a case based on observations from the Indirect and Semi-Direct Aerosol Campaign (ISDAC), it is found that ice number concentration, Ni, exerts significant influence on the cloud structure. Increasing Ni leads to a substantial reduction in liquid water path (LWP), in agreement with earlier studies. In contrast to previous intercomparison studies, all models here use the same ice particle properties (i.e., mass-size, mass-fall speed, and mass-capacitance relationships) and a common radiation parameterization. The constrained setup exposes the importance of ice particle size distributions (PSDs) in influencing cloud evolution. A clear separation in LWP and IWP predicted by models with bin and bulk microphysical treatments is documented and attributed primarily to the assumed shape of ice PSD used in bulk schemes. Compared to the bin schemes that explicitly predict the PSD, schemes assuming exponential ice PSD underestimate ice growth by vapor deposition and overestimate mass-weighted fall speed leading to an underprediction of IWP by a factor of two in the considered case. Sensitivity tests indicate LWP and IWP are much closer to the bin model simulations when a modified shape factor which is similar to that predicted by bin model simulation is used in bulk scheme. These results demonstrate the importance of representation of ice PSD in determining the partitioning of liquid and ice and the longevity of mixed-phase clouds.

clouds↗
NASA NTRS1972

Large-scale properties of the interplanetary magnetic field

Early theoretical work of Parker is presented along with the observational evidence supporting his Archimedes spiral model. Variations present in the interplanetary magnetic field from the spiral angle are related to structures in the solar wind. The causes of these structures are found to be either nonuniform radial solar wind flow or the time evolution of the photospheric field. Coronal magnetic models are related to the connection between the solar magnetic field and the interplanetary magnetic field. Direct extension of the solar field-magnetic nozzle controversy is discussed along with the coronal magnetic models. Effects of active regions on the interplanetary magnetic field is discussed with particular reference to the evolution of interplanetary sectors. Interplanetary magnetic field magnitude variations are shown throughout the solar cycle. The percentage of time the field magnitude is greater than 10 gamma is shown to closely parallel sunspot number. The sun's polar field influence on the interplanetary field and alternative views of the magnetic field structure out of the ecliptic plane are presented. In addition, a variety of significantly different interplanetary field structures are discussed.

Schatten, K. H.↗
NASA NTRS1980

From inanimate matter to living systems

Since the early part of this century, the Genesis account of the origin and evolution of life has been explained as an extrapolation of astronomical and geochemical processes. The essence of the answer to date is a protoreproductive protocell of much biochemical and cytophysical competance. The processes of its origin, molecular ordering, and its functions are described. A crucial understanding is that of the nonrandomness of evolutionary processes at all stages (with perhaps a minor statistical component). In this way, evolution conflicts with statistical randomness; the latter is a favorite assumption of both scientific and creationistic critics of the proteinoid theory. The principle contribution of the proteinoid theory to the understanding of general biology is to particularize the view that evolutionary direction is rooted in the shapes of molecules, in stereochemistry. After molecules of the right kind first assembled to protocells, life in its various stages of evolution was an inevitable consequence. It is molecules that continue to assemble as part of living process and, in the role of enzymes, continue to direct life cycle of the cell.

Fox, S. W.↗
NASA NTRSDate not supplied

Argon Isotopic Constraints on Planetary Degassing and the Evolution of Earth's Atmosphere: Insights from K-bearing Phases

An enduring question in planetary science is the nature of volatile degassing from rocky planets during their evolution. The reactive nature of planetary volatiles (e.g. H2O, CO2, N, H) make them difficult to directly track through time. Noble gases, like argon, can act as passive tracers of planetary processes, with isotopic ratios providing clues on planetary volatile inventories and fluxes. Previous studies [e.g. 1, 2] use Earth’s argon degassing history to constrain the growth of continental crust. However, that record is limited to the modern 40Ar/36Ar ratio of 298.56 [3] and three time slices recorded in hydrothermal quartz of the Archean Dresser formation [1]: from ~143 (3.5 Ga) to ~212 (2.7 Ga). Due to the paucity of data, partly a result of using nominally K-free minerals, the temporal evolution of atmospheric 40Ar/36Ar remains poorly constrained. K-bearing phases from igneous rocks, forming at high temperature and upper mantle or crustal conditions, are rarely considered viable for recording ancient atmospheric 40Ar/36Ar values. We show that this possible and a potential path to more precise records of ancient atmosphere by leveraging the radiogenic endmember of isotope correlation diagrams. An isochron of coeval biotite grains from the Bushveld Complex [4], with little indication of alteration or excess 40Ar, yield an initial 40Ar/36Ar value that matches the atmospheric 40Ar/36Ar value of ~228 at 2055 Ma in the model of [2]. In addition, new multi-mineral data from the Palisade Sill also match the modelled 40Ar/36Ar value of ~293 at 202 Ma, providing another tie point in the late Triassic. Combined, the Bushveld and Palisades samples provide two new constraints on the ancient atmosphere and help define the history of planetary degassing. These results demonstrate the possibility of accurately and precisely obtaining atmospheric information from igneous rocks, not exclusively K-free phases, thus providing a surplus of ways to reconstruct planetary atmospheres and processes. A robust atmospheric 40Ar/36Ar history also has practical uses and we explore the systematic offsets that arise from using a modern 40Ar/36Ar value in 40Ar/39Ar age calculations of old samples.

J. B. Setera↗
NASA NTRS2010

Proceedings of the Astrobiology Science Conference 2010. Evolution and Life: Surviving Catastrophes and Extremes on Earth and Beyond

The Program of the 2010 Astrobiology Science Conference: Evolution and Life: Surviving Catastrophes and Extremes on Earth and Beyond, included sessions on: 50 Years of Exobiology and Astrobiology: Greatest Hits; Extraterrestrial Molecular Evolution and Pre-Biological Chemistry: From the Interstellar Medium to the Solar System I; Human Exploration, Astronaut Health; Diversity in Astrobiology Research and Education; Titan: Past, Present, and Future; Energy Flow in Microbial Ecosystems; Extraterrestrial Molecular Evolution and Prebiological Chemistry: From the Interstellar Medium to the Solar System II; Astrobiology in Orbit; Astrobiology and Interdisciplinary Communication; Science from Rio Tinto: An Acidic Environment; Can We Rule Out Spontaneous Generation of RNA as the Key Step in the Origin of Life?; How Hellish Was the Hadean Earth?; Results from ASTEP and Other Astrobiology Field Campaigns I; Prebiotic Evolution: From Chemistry to Life I; Adaptation of Life in Hostile Space Environments; Extrasolar Terrestrial Planets I: Formation and Composition; Collaborative Tools and Technology for Astrobiology; Results from ASTEP and Other Astrobiology Field Campaigns II; Prebiotic Evolution: From Chemistry to Life II; Survival, Growth, and Evolution of Microrganisms in Model Extraterrestrial Environments; Extrasolar Terrestrial Planets II: Habitability and Life; Planetary Science Decadal Survey Update; Astrobiology Research Funding; Bioessential Elements Through Space and Time I; State of the Art in Life Detection; Terrestrial Evolution: Implications for the Past, Present, and Future of Life on Earth; Psychrophiles and Polar Environments; Life in Volcanic Environments: On Earth and Beyond; Geochronology and Astrobiology On and Off the Earth; Bioessential Elements Through Space and Time II; Origins and Evolution of Genetic Systems; Evolution of Advanced Life; Water-rich Asteroids and Moons: Composition and Astrobiological Potential; Impact Events and Evolution; A Warm, Wet Mars?; Titan Versus Europa - Potential for Astrobiology; Habitability Potential of Mars; Biosignatures: Tools and Development I; Origins of Molecular Asymmetry, Homochirality, and Life Detection; Deserts and Evaporite Basins and Associated Microbialite Systems; Ancient Life and Synthetic Biology: Crossroad of the Past and Future; Biosignatures: Tools and Development II; Free Oxygen: Proxies, Causes, and Consequences; Life in Modern Microbialite Systems - Function and Adaptation; Hydrothermal Systems and Organosynthesis Processes: Origin and Evolution of Life; Where Should We Go on Mars to Seek Signs of Life?; Search for Intelligent Life I. Innovative SETI Observing Programs and Future Directions; Integrating Astrobiology Research Across and Beyond the Community; Education in Astrobiology in K-12; Search for Intelligent Life II. Global Engagement and Interstellar Message Construction; Poster sessions included: Extraterrestrial Molecular Evolution and Pre-Biological Chemistry; Prebiotic Evolution: From Chemistry to Life; RNA World; Terrestrial Evolution: Implications for the Past, Present, and Future of Life on Earth; Hydrothermal Systems and Organosynthesis Processes: Origin and Evolution of Life; Virology and Astrobiology; Horizontal Genetic Transfer and Properties of Ancestral Organisms; Life in Volcanic Environments: On Earth and Beyond; Impact Events and Evolution; Evolution of Advanced Life; Evolution of Intelligent Life; Education in Astrobiology in K-12; Origins of Molecular Asymmetry, Homochirality, and Life Detection; Astrobiology and Interdisciplinary Communication; Diversity in Astrobiology Research and Education; Integrating Astrobiology Research Across and Beyond the Community; Policy and Societal Issues: Dealing with Potential Bumps in the Astrobiology Road Ahead; Results from ASTEP and Other Astrobiology Field Campaigns; Energy Flow in Microbial Ecosystems; Psychrophiles and Polar Environments; Deserts and Evaporite Basins and Associated Microbialite stems; Life in Modern Microbialite Systems - Function and Adaptation; Free Oxygen: Proxies, Causes, and Consequences; Bioessential Elements Through Space and Time; Water-rich Asteroids and Moons: Composition and Astrobiological Potential; Biosignatures: Tools and Developments; Robotics and Instrumentation for Astrobiology; State of the Art in Life Detection; Astrobiology in Orbit; Survival, Growth, and Evolution of Microrganisms in Model Extraterrestrial Evolution; Search for Intelligent Life; Habitability Potential of Mars; How and Where Should We Seek Signs of Life on Mars?; Titan: Past, Present, and Future; Extrasolar Terrestrial Planets: Formation, Composition, Diversity, Habitability and Life; Human Exploration, Astronaut Health; Science from Rio Tinto: An Acidic Environment and Adaptation of Life in Hostile Space Environments;

Source record↗
NASA NTRS1994

Implications for the evolution of chondrules from Agglomeratic olivine chondrules

There is considerable evidence that chondrules formed by the melting of solid materials and, by default, the early solar nebula is the preferred location for chondrule formation. Agglomeratic olivine (AO) chondrules supply perhaps the most intriguing, direct evidence for chondrule formation from agglomeration of solids. We review the characteristics of AO chondrules and discuss their implications for understanding chondrule precursors and chondrule evolution.

Weisberg, M. K.↗
NASA NTRS1981

Mixing layer simulation by an improved three-dimensional vortex-in-cell algorithm

An extension is presented of the three-dimensional vortex-in-cell (VIC) method that allows for the simulation of incompressible turbulent flows such as plane mixing layers and wakes with exact boundary conditions in the normal direction. The vorticity is assumed to be confined between two parallel planes and the turbulence is assumed to be homogeneous in the two directions parallel to the planes. As an application, an analysis is presented of the evolution of the plane mixing layer subjected to random two- and three-dimensional initial disturbances.

Couet, B.↗
NASA NTRS1985

Evolution and interaction of large interplanetary streams

A computer simulation for the evolution and interaction of large interplanetary streams based on multi-spacecraft observations and an unsteady, one-dimensional MHD model is presented. Two events, each observed by two or more spacecraft separated by a distance of the order of 10 AU, were studied. The first simulation is based on the plasma and magnetic field observations made by two radially-aligned spacecraft. The second simulation is based on an event observed first by Helios-1 in May 1980 near 0.6 AU and later by Voyager-1 in June 1980 at 8.1 AU. These examples show that the dynamical evolution of large-scale solar wind structures is dominated by the shock process, including the formation, collision, and merging of shocks. The interaction of shocks with stream structures also causes a drastic decrease in the amplitude of the solar wind speed variation with increasing heliocentric distance, and as a result of interactions there is a large variation of shock-strengths and shock-speeds. The simulation results shed light on the interpretation for the interaction and evolution of large interplanetary streams. Observations were made along a few limited trajectories, but simulation results can supplement these by providing the detailed evolution process for large-scale solar wind structures in the vast region not directly observed. The use of a quantitative nonlinear simulation model including shock merging process is crucial in the interpretation of data obtained in the outer heliosphere.

Whang, Y. C.↗
NASA NTRS1987

The core mass-radius relation for giants - A new test of stellar evolution theory

It is demonstrated here that the measurable properties of systems containing degenerate dwarfs can be used as a direct test of the core mass-radius relation for moderate-mass giants if the final stages of the loss of the envelope of the progenitor giant occurred via stable critical lobe overflow. This relation directly probes the internal structure of stars at a relatively advanced evolutionary state and is only modestly influenced by adjustable parameters. The measured properties of six binary systems, including such diverse systems as Sirius and Procyon and two millisecond pulsars, are utilized to derive constraints on the empirical core mass-radius relation, and the constraints are compared to the theoretical relation. The possibility that the final stages of envelope ejection of the giant progenitor of Sirius B occurred via critical lobe overflow in historical times is considered.

Joss, P. C.↗