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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Origins of Solar Systems Program

The chondrites are aggregates of components (e.g. chondrules, chondrule rims and matrix) that formed in the nebula but, at present, there is no consensus on how any of these components formed or whether their formation produced or post dated the chemical fractionations between the chondrites. Chondrites are, at present, the most primitive Solar System objects available for laboratory study and the conditions under which their principle components formed would provide the most direct constraints for models of nebula formation and evolution. The conditions under which chondrules formed is of particular importance because, if their relative abundance in chondrites approximates that in the nebula, they are the products of one of the most energetic and pervasive processes that operated in the early Solar System. The goal of this proposal was to combine theoretical modeling with a comprehensive study of the elemental and isotopic compositions of the major components in unequilibrated ordinary chondrites (UOCs), with the aim of determining the conditions in the nebula at the time of their formation. The isotopes of volatile and moderately volatile elements should be particularly revealing of conditions during chondrule formation, as evaporation under most conditions would lead to isotopic mass fractionation. Modeling of chondrule and matrix formation requires the development of a kinetic model of evaporation and condensation, and calibration of this model against experiments.

O'D. Alexander, Conel↗
NASA NTRS2003

Final Summary of Research Report to the National Aeronautics and Space Administration Origins of Solar Systems Program

The chondrites are aggregates of components (e.g. chondrules, chondrule rims and matrix) that formed in the nebula but, at present, there is no consensus on how any of these components formed or whether their formation produced or post dated the chemical fractionations between the chondrites. Chondrites are, at present, the most primitive Solar System objects available for laboratory study and the conditions under which their principle components formed would provide the most direct constraints for models of nebula formation and evolution. The conditions under which chondrules formed is of particular importance because, if their relative abundance in chondrites approximates that in the nebula, they are the products of one of the most energetic and pervasive processes that operated in the early Solar System. The goal of this proposal was to combine theoretical modeling with a comprehensive study of the elemental and isotopic compositions of the major components in unequilibrated ordinary chondrites (UOCs), with the aim of determining the conditions in the nebula at the time of their formation. The isotopes of volatile and moderately volatile elements should be particularly revealing of conditions during chondrule formation, as evaporation under most conditions would lead to isotopic mass fractionation. Modeling of chondrule and matrix formation requires the development of a kinetic model of evaporation and condensation, and calibration of this model against experiments. Cosmic spherules present an opportunity to test our evaporation models under flash heating conditions that would be difficult to simulate experimentally. However, there is surprisingly little known about the isotopic compositions of silicate cosmic spherules, and a number of questions need to be addressed. Is the range of compositions they exhibit due to evaporation? If they are, are the relative volatilities consistent with the models/experiments and are the isotopic fractionations consistent with Rayleigh conditions? For instance, do the alkalis and S evaporate prior to significant melting so that conditions did not meet the Rayleigh criteria of rapid diffusion? If so, their isotopic fractionation might be considerably suppressed. Could this mechanism of K loss apply to chondrule formation? The Fe isotopic fractionation during evaporation of silicates has not been measured, so cosmic spherules might provide a clue to whether FeO diffusion is fast enough to maintain Rayleigh conditions during evaporation. And so on.

O'D. Alexander, Conel↗
NASA NTRS2007

The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005

We report on the evolution of key spectral and temporal parameters of SGR 1806-20 prior to and following the highly energetic giant flare of 2004 December 27. Using RXTE, we track the pulse frequency of the SGR and find that the spin-down rate varied erratically in the months before and after the flare. Contrary to the giant flare in SGR 1900+14, we find no evidence for a discrete jump in spin frequency at the time of the December 27th flare (Absolute value of (Delta * upsilon/upsilon) < 5 10 (exp -6)). In the months surrounding the flare, we find a strong correlation between pulsed flux and torque consistent with the model for magnetar magnetosphere electrodynamics proposed. As with the flare in SGR 1900+14, the pulse morphology of SGR 1806-20 changes drastically following the flare. Using Chandra and other publicly available imaging X-ray detector observations, we construct a spectral history of SGR 1806-20 from 1993 to 2005. The usual magnetar persistent emission spectral model of a power law plus a blackbody provides an excellent fit to the data. We confirm the earlier finding of increasing spectral hardness of SGR 1806-20 between 1993 and 2004. However, our results indicate significant differences in the temporal evolution of the spectral hardening. Rather than a direct correlation between torque and spectral hardness, we find evidence for a sudden torque change that preceded a gradual hardening of the energy spectrum on a timescale of years. Interestingly, the spectral hardness, spin-down rate, phase-averaged flux, and pulsed flux of SGR 1806-20 all peak months before the flare epoch.

Woods, Peter M.↗
NASA NTRS2017

On the Magnetic Protection of the Atmosphere of Proxima Centauri b

The discovery of exoplanets orbiting red dwarfs, such as Proxima Centauri b, has led to questions of their habitability and capacity to retain liquid surface water. While Proxima b is in a ''temperate orbit,'' i.e., an Earth at that location would not freeze or boil its oceans, its proximity to a parent star with quite high magnetic activity is likely to influence its atmospheric evolution and habitability. Planetary magnetic fields can prevent direct stripping away of the planetary atmosphere by the stellar wind, but ion escape can still occur at the magnetic poles. This process, the polar wind, is well known to occur at Earth and may have contributed to the habitability of Earth's early atmosphere. The polar wind is highly variable and sensitive to both ionizing radiation and geomagnetic activity. The higher ionizing radiation levels of M dwarfs at habitable zone distances are expected to increase the polar wind by orders of magnitude and, instead of helping create a habitable atmosphere, may strip away enough volatiles to render the planet inhospitable. Here, we compute the ionospheric outflow of an Earth-twin subject to the enhanced stellar EUV flux of Proxima b, and the effect on atmospheric escape timescales. We show that an Earth-like planet would not survive the escape of its atmosphere at that location, and therefore the pathway to habitability for Proxima b requires a very different atmospheric history than that of Earth.

planets and satellites↗
NASA NTRS2020

The Artemis Challenge: Another Revolution in Structural Dynamics

The National Aeronautics and Space Administration (NASA) is embarking on an exciting evolution in human exploration and spaceflight. Space Policy Directive (SPD) 1 provides the overarching narrative for returning humans to the Moon and then to Mars. We are challenged to “Lead an innovative and sustainable program with commercial and international partners to enable human expansion across the solar system and to bring back to Earth new knowledge and opportunities. Beginning with missions beyond low Earth orbit, the United States will lead the return of humans to the Moon for long-term exploration and utilization, followed by human missions to Mars and other destinations…” Here we explore some of the key technical challenges that this new era of human exploration brings with a focus on the challenges and opportunities in the structural dynamics discipline.

Structural Dynamics↗
NASA NTRS2022

Impact of 3D Structure on Magnetic Reconnection

Results from 2.5D and 3D studies of the onset and development of the tearing instability are presented, using high fidelity resistive MHD simulations. A limited parameter study of the strength of the reconnecting field (or shear angle) was performed. An initially simple 1D equilibrium was used, consisting of a modified force-free current sheet, with periodic boundary conditions in all directions. In all cases, the linear and nonlinear evolution led to a primary current sheet between two large flux ropes. The global reconnection rate during this later stage was analyzed in all simulations. It was found that in 2.5D the primary current sheet fragmented owing to plasmoids, and as expected, the global reconnection rate, calculated using multiple methods, increases with the strength of the reconnecting field owing to a stronger Alfvén speed. In 3D, the presence of interacting oblique modes of the tearing instability complicates the simple 2.5D picture, entangling the magnetic field of the inflow and introducing a negative effect on the reconnection rate. The two competing effects of stronger Alfvén speed and entangling, which both increase with the strength of the reconnecting field, resulted in a decrease in the reconnection rate with increasing reconnecting field. For all simulations, the 3D rates were less than in 2.5D but suggest that as one goes to weak reconnecting field (or strong guide field) the system becomes more 2.5D-like and the 2.5D and 3D rates converge. These results have relevance to situations like nanoflare heating and flare current sheets in the corona.

Lars K S Daldorff↗
NASA NTRS1993

Origins of Solar Systems Workshop: The Origin, Evolution, and Detectability of Short Period Comets

The origin of the short period comets (SPC) (periods less than 200 years), the dynamical formation of their present reservoir(s), the cause and rate of their transport to the inner planetary region where they can be detected, and the magnitude of selection effects in their discovery are important research questions directly coupled to the goals of understanding the origin and evolution of the Solar System. To address these questions in an intensive way, an interdisciplinary, five month long Workshop from Jan. to May 1993 at Southwest Research Institute (SwRI) in San Antonio was convened. The goal of this Workshop was to advance the state of understanding about the origins, dynamical evolution, and present location of short period comets and their reservoir(s).

Stern, S. Alan↗
NASA NTRS2009

Landform Erosion and Volatile Redistribution on Ganymede and Callisto

We have been modeling landscape evolution on the Galilean satellites driven by volatile transport. Our work directly addresses some of the most fundamental issues pertinent to deciphering icy Galilean satellite geologic histories by employing techniques currently at the forefront of terrestrial, martian, and icy satellite landscape evolution studies [e.g., 1-6], including modeling of surface and subsurface energy and volatile exchanges, and computer simulation of long-term landform evolution by a variety of processes. A quantitative understanding of the expression and rates of landform erosion, and of volatile redistribution on landforms, is especially essential in interpreting endogenic landforms that have, in many cases, been significantly modified by erosion [e.g., 7-9].

Moore, Jeffrey Morgan↗
NASA NTRSDate not supplied

The Foundations of Modern Magnetic Reconnection Research

Magnetic reconnection is a fundamental process operating in laboratory, space, and astrophysical plasmas. We understand today that it is the mechanism behind the often explosive release of the stored magnetic energy, and that it directly or indirectly powers as diverse a set of phenomena as solar eruptions, stellar flares, geomagnetic storms, the aurora, and even disruption events in fusion machines. It is also the mechanism powering the majority of the deleterious space effects collectively referred to as “space weather.” Owing to its importance, reconnection has been a research focus for many years, culminating in the research based on NASA’s Magnetospheric Multiscale mission. A major component of foundational research involved studies of the stability and disruption of current sheets by collisionless tearing, which still plays a major role in the dynamical evolution of the interfaces between magnetic fields of different directions. This presentation will illuminate these beginnings, with special focus on the seminal work of Academician A. A. Galeev, and also provide a summary of the present state of knowledge. It will conclude with an outlook toward future reconnection research targets.

Plasma↗
NASA NTRS1983

Space station architectural issues - The view from science

The evolution from current missions in space from Shuttle-directed to space station-directed is projected, with consideration given to space station missions that will affect the station architecture. The Shuttle science mission is basically to support astronomy and astrophysics work into the 1990s, particularly in launching and refurbishing satellites such as the SMM, the Space Telescope, and the Gamma Ray Observatory. Various new observational facilities are being planned and may be carried by the Shuttle for assembly in orbit. The assembly crews could live on a space station if sufficient capabilities and size were built into the station. The construction of large instruments in orbit, instruments that cannot be launched by any current booster, could permit enough data to be gathered to successfully characterize the evolution of the Universe.

Mcdonald, F. B.↗
NASA NTRS1991

Anisotropy and minimum variance directions of solar wind fluctuations in the outer heliosphere

Voyager 2 magnetic field and plasma data are examined over time intervals of 1 to 12 hours in the heliospheric range of 1 to 10 AU to study the evolution of the anisotropy of solar wind fluctuations. Consistent with previous results, the directions of minimum variance vectors of magnetic fluctuations are found to be close to the mean magnetic field direction with an increasing component along the field at larger scales. At large radial distances there is more spread in the minimum variance directions than at smaller radial distances. The power in smaller-scale fluctuations in the magnetic field components perpendicular to the local mean field B(0) is in the ratio of about 5:1 near 1 AU at the scale of 1 hour but decreases to about 3:1 further out. No evidence for selective enhancement of out-of-the-ecliptic components of fluctuations is found. In contrast to results for field fluctuations, analysis of velocity fluctuations shows that the minimum variance direction systematically remains more radially oriented and becomes increasingly less oriented along B(0) with increasing heliocentric distance. The velocity fluctuations are generally more isotropic than the magnetic fluctuations. The observations cannot be explained by a superposed wave picture, and thus are consistent with the view that nonlinear turbulent evolution is responsible for the anisotropy in the fluctuations.

Klein, Larry W.↗
DOE OSTI2026

Direct estimation of the density of states for fermionic systems

Simulating time evolution is one of the most natural applications of quantum computers and is thus one of the most promising prospects for achieving practical quantum advantage. Here, we develop quantum algorithms to extract thermodynamic properties by estimating the density of states (DOS), which is a central object in quantum statistical mechanics. We introduce several key innovations that significantly improve the practicality and extend the generality of previous techniques. First, our approach allows one to estimate the DOS only for a specific subspace of the full Hilbert space. This is crucial for fermionic systems, since both canonical and grand canonical ensemble thermal equilibrium properties depend on subspaces of fixed number. Second, in our approach, by time evolving very simple, random initial states, such as randomly chosen computational basis states, we can exactly recover the DOS on average. Third, due to circuit-depth limitations, we only reconstruct the DOS up to a convolution with a Gaussian window—thus all imperfections that shift the energy levels by less than the width of the convolution window will not significantly affect the estimated DOS. For these reasons, we find the approach is a promising candidate for early quantum advantage as even short-time, noisy dynamics can yield a semiquantitative reconstruction of the DOS (convolution with a broad Gaussian window), while early fault-tolerant devices will likely enable higher-resolution DOS reconstruction through longer time evolutions. We demonstrate the practicality of our approach in representative Fermi-Hubbard and spin models and indeed find that our approach is highly robust against algorithmic errors in the time evolution and against gate noise. We further demonstrate that our approach is compatible with noisy intermediate-scale quantum (NISQ) computing NISQ-friendly variational techniques, introducing and leveraging a technique for variational time evolution.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1992

Evolution of near UV Halley's spectrum in the inner coma

A direct way to observe the photodissociation of water vapor in a cometary coma is to detect the OH prompt emission. This emission is shifted of delta lambda = 4 nm with respect to the OH 309 nm fluorescence band. The extended data set obtained with the three-channel spectrometer on-board Vega 2 reveals at short distance of the nucleus (i.e., less than 600 km) an excess of emission on the right wing of the OH band which may be interpreted as being mainly due to prompt emission.

Rousselot, Phillippe↗
NASA NTRS1999

Numerical Modeling and In-Situ Observations of the Dynamics of the Solid/Liquid Interface Morphology During Directional Solidification of Alloys

The departure from interface planarity and the subsequent evolution to a periodic array of cells or dendrites is a fundamental process that characterizes most microstructures in solidified alloys. The growing demand for high quality alloys and semiconductor crystals requires a precise methodology to predict and subsequently control both the interface morphology and the distribution of impurities, additives, and phases in the grown crystal. Apart from its practical significance, the study of morphological evolution has also been viewed as a means to unearth a general paradigm for pattern formation in nature. A previously developed 2D numerical model for the solid/liquid interface tracking has been further refined and used to simulate the time-evolution of the perturbations on the interface. The dynamics of the local growth velocity, interface undercooling and solute concentration at the interface has been theoretically predicted by means of the numerical model for Al-Cu and Pb-Sn alloys. The model shows that perturbations with a wavelengths, lambda greater than a critical wavelength lambda(sub c) continue to grow in time whereas perturbations with lambda < lambda(sub c) cease to propagate. The model further predicts that under certain conditions perturbation can also propagate along the interface. Comparison of these predictions with existing theories of pattern formation and experimental results will be discussed.

Catalina, Adrian V.↗
DOE OSTI2024

Understanding Formation of Irradiation-Induced Defects through 4D-STEM, Electron Tomography, and WBDF-STEM

A major challenge in advancing nuclear materials for next-generation fission and proposed fusion reactors is to comprehensively understand the formation of irradiation-induced defects. Here it is essential to correlate the evolution of irradiation-induced defects and the degradation of mechanical properties, as they collectively dictate the material's lifespan and ensure nuclear safety. Scanning transmission electron microscopy (STEM) based techniques have emerged as indispensable tools for irradiation-induced defect characterization, offering high spatial resolution imaging and chemical analysis, such as electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS). These techniques have been effectively used to obtain an atomic-scale view of the defect structure. Recent advances in electron microscopy, particularly in 4D-STEM, offer detailed insight into microstructural evolution by capturing full 2D diffraction patterns at every pixel position. Using high-speed direct electron detectors, this technology generates a four-dimensional dataset, overcoming the limitations of traditional STEM imaging.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Collisional evolution of mass-distribution spectrum of planetesimals

The early growth of planetesimals by mutual direct collisions is numerically simulated with a Monte Carlo technique to show how planetesimals with specific mass and velocity distributions evolve into a full-size planet. Four types of collisions are taken into account: rebound, erosion, catastrophic break-up, and coagulation. It is shown that evolution of mass-distribution spectrum is expressed by an inverse power relation. It is also suggested that whether or not a planetesimal can survive catastrophic collision is primarily dependent on mean relative velocity and mechanical properties of planetesimals. It is necessary for the early growth of rocky (basaltic) materials that mean relative velocity be much smaller than 0.1 km/s. Otherwise it is necessary to introduce something like nucleating agents (such as iron bodies which have plastic properties at temperatures higher than 200 K) for the formation of terrestrial planets.

Matsui, T.↗
NASA NTRS1987

Non-enzymatic transcription of an oligodeoxynucleotide 14 residues long

Nonenzymatic synthesis of oligodeoxynucleotides up to 14 residues long from 2-MeImpG and 2-MeImpC mononucleotides was demonstrated. The synthesis is primed by 14-mer and 15-mer oligonucleotides d(C3GC3GC3GC2) and d(C3GC3GC3GC3) as templates. The predominant products are a series of 3-prime-5-prime-linked oligonucleotides, complementary to the template, ranging in length from GGC to GGCGGGCGGGCGGG. The 15-mer template directed the synthesis of the same family of products that were formed on the 14-mer template. This finding is explained by the preferential conversion of the dimer GG to GGC rather than to GGG. In the context of molecular evolution, these results suggest that the detailed kinetics of template-directed synthesis could form the basis for the selection of one replicating oligonucleotide from a family of closely related oligonucleotides.

Acevedo, Oscar L.↗