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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Thermospheric meridional winds and atomic oxygen depletion at high latitudes

Rocket vapor trail measurements of the properties of the high latitude wind system are compared with Ogo 6 measurements, the atomic densities being studied as a function of geomagnetic local time at three seasons for three ranges of magnetic activity. It is found that the atomic oxygen densities at altitudes in the region of 120 km are about 35% lower in the post-midnight sector than in the afternoon and evening sectors, decrease with increasing magnetic activity, and are lower in summer than in winter. The variations are related to vertical velocities in the 95-150 km altitude range and to the meridional fluxes at 70 deg geomagnetic latitude. The upward average vertical velocity of atomic oxygen in the region poleward of 70 deg is calculated to be of the order of 0.3 m/s at 120 km and the energy transported by the winds out of this region is calculated to be of the order of 10 to the 10th W for Kp levels of 2.

Nisbet, J. S.↗
NASA NTRS1973

Explorer 18 study of the stability of the magnetopause using a Kelvin-Helmholtz instability criterion

Explorer 18 magnetometer and plasma probe data are used to calculate the magnitude of the Kelvin-Helmholtz instability criterion for 42 crossings of the magnetopause. The 30 crossings through the dipole field region show that for low levels of geomagnetic disturbance ( Kp less than or equal to 2) large regions of the magnetopause near the nose are stable, whereas for higher levels of geomagnetic disturbance (Kp greater than 2) only a small region near the nose is stable. The unstable regions are found further downstream. Similarly, the 12 crossings through the tail show that the unstable regions are downstream of the stable regions. The Kelvin-Helmholtz mechanism might be the 'viscous interaction' discussed by Axford and Hines (1961) and the relevant parameter for worldwide geomagnetic disturbance, just as the southward interplanetary field has been firmly established as the major relevant parameter in the case of substorm activity.

Boller, B. R.↗
NASA NTRS1993

Development of a prototype kinestatic platform for application to space and ground servicing tasks. Phase 1: Concept Modeling

The Center for Intelligent Machines and Robotics (CIMAR) of the University of Florida, in conjunction with Rockwell International is developing an electro-mechanical device called a Kinestatic Platform (KP) for aerospace applications. The goal of the current project is to develop a prototype KP which is capable of manipulating a 50 lb. payload. This prototype will demonstrate the feasibility of implementing a scaled up version to perform high precision manipulation of distributed systems and to control contact forces and allowable motions (rotations and translations), which is defined here as Kinestatic Control, in a six dimensional, partially constrained environment, simultaneously and independently. The objectives of the Phase 1 effort were as follows: (1) Identify specific NASA applications where the KP technology can be applied. (2) Select one application for development. (3) Develop a conceptual design of the KP specifically for the selected application. This includes the steps of developing a set of detailed performance criteria, establishing and making selection of the mechanism design parameters, and evaluating the expected system response. (4) Develop a computer graphics animation of the KP as it performs the selected application. This report will proceed by providing a technical description of the KP followed by how each of these objectives was addressed.

Duffy, J.↗
NASA NTRS1974

Average high latitude magnetic field - Variation with interplanetary sector and with season. II

Average high-latitude magnetic-field data from northern observatories are examined for three ranges of magnetic disturbance level, Kp = 1- to 1+, 2- to 3+ and greater than or equal to 4-. Except for 0 to 0800 hr MLT, 55 to 78 deg invariant latitude, during away interplanetary magnetic field sectors, the variations between season and sector have the same characteristics at all Kp ranges. Because the amplitude of sector differences is much larger at sunlit local times than in the midnight sector, it is concluded that the current system of Svalgaard (1973) is not adequate to describe the sector variations in magnetic disturbance. Other current systems are discussed briefly. The disturbance morphology and seasonal variation at all Kp levels confirms the results of previous studies which indicate that latitudinally broad current systems and nonionospheric sources are present in addition to latitudinally narrow electrojet currents.

Langel, R.↗
NASA NTRS1973

Average high latitude magnetic field: Variations with interplanetary sector and with season. 2: Comparison of disturbance levels and discussion of ionospheric currents

Average high latitude magnetic field data from northern observatories are examined for three ranges of magnetic disturbance level, Kp = 1 minus to 1+,2 minus to 3+, and or = 4 minus. Except for 0-8h MLT, 55-78 deg invariant latitude, during away interplanetary magnetic field sectors, the variations between season and sector have the the same characteristics at all Kp ranges. Because the amplitude of sector differences is much larger at sunlit local times than in the midnight sector, it is concluded that the current system of Svalgaard (1973) is not adequate to describe the sector variations in magnetic disturbance, other current systems are discussed briefly. The disturbance morphology and seasonal variation at all Kp levels confirms the results of previous studies which indicate that latitudinally broad current systems and non-ionospheric sources are present in addition to latitudinally narrow electrojet currents. Comparison of data between Kp levels indicates that the Harang discontinuity shifts toward earlier MLT with increasing Kp level.

Langel, R. A.↗
NASA NTRS1975

Quiet time inflation of the inner magnetosphere in the afternoon and evening quadrants

The quiet-time depression of the magnetic field magnitude in the equatorial inner magnetosphere was studied for the interval Nov. 1971-June 1972. For periods when Kp was less than 2 and Dst was between +10 and -20 gamma, an inflated field region near the magnetic equator was found between noon and midnight. The inflation was greatest at the lowest altitude studied (L = 3) and appeared to be somewhat greater near midnight (-40 gamma) than near noon (-20 gamma). Protons of energy above 100 keV observed on the same satellite appeared to be sufficient to produce the quiet-time inflation.

Lee, Y. C.↗
DOE OSTI2021

Thermochemical Modeling in Molten Fluoride Salts for Radionuclide Speciation

An important aspect of the licensing process for nuclear reactors is providing a reasonable assurance of safety to the general public. This includes modeling potential radionuclide releases from the reactor during normal operations and accident scenarios, which is known as the reactor’s source term. A new class of advanced (non-LWR) reactors are being developed which use molten salts as the coolant fluid. Because the molten salt coolant represents a credited barrier for radionuclide transport between the fuel and the environment, a necessary aspect of mechanistic source term (MST) analysis for the KP-FHR is modeling the thermochemistry of molten salts. Provided here is a review of the theory of the thermodynamic principles governing multicomponent phase equilibria, the background of molten salt thermochemistry research, and a summary of the thermochemical data relevant to the KP-FHR coolant salt, Li 2 BeF 4 , commonly referred to as “FLiBe”. A review of literature is followed by a brief introduction to methods that can be used to model the thermochemical behavior of molten salt mixtures. The methodology outlined is based on the use of a commercial thermodynamic modeling software called FactSage, which is one of only a few available softwares based on the modified quasichemical model(MQM), which is the recommended solution model for molten salts.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Predicting Volume of Distribution in Humans: Performance of In Silico Methods for a Large Set of Structurally Diverse Clinical Compounds

Volume of distribution at steady state (V D,ss ) is one of the key pharmacokinetic parameters estimated during the drug discovery process. Despite considerable efforts to predict V D,ss , accuracy and choice of prediction methods remain a challenge, with evaluations constrained to a small set (<150) of compounds. To address these issues, a series of in silico methods for predicting human V D,ss directly from structure were evaluated using a large set of clinical compounds. Machine learning (ML) models were built to predict V D,ss directly and to predict input parameters required for mechanistic and empirical V D,ss predictions. In addition, log D, fraction unbound in plasma (fup), and blood-to-plasma partition ratio (BPR) were measured on 254 compounds to estimate the impact of measured data on predictive performance of mechanistic models. Furthermore, the impact of novel methodologies such as measuring partition (Kp) in adipocytes and myocytes (n = 189) on V D,ss predictions was also investigated. In predicting V D,ss directly from chemical structures, both mechanistic and empirical scaling using a combination of predicted rat and dog V D,ss demonstrated comparable performance (62%–71% within 3-fold). The direct ML model outperformed other in silico methods (75% within 3-fold, r 2 = 0.5, AAFE = 2.2) when built from a larger data set. Scaling to human from predicted V D,ss of either rat or dog yielded poor results (<47% within 3-fold). Measured fup and BPR improved performance of mechanistic V D,ss predictions significantly (81% within 3-fold, r 2 = 0.6, AAFE = 2.0). Adipocyte intracellular Kp showed good correlation to the V D,ss but was limited in estimating the compounds with low V D,ss .

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1994

High charge state carbon and oxygen ions in Earth's equatorial quasi-trapping region

Observations of energetic (1.5 - 300 keV/e) medium-to-high charge state (+3 less than or equal to Q less than or equal to +7) solar wind origin C and O ions made in the quasi-trapping region (QTR) of Earth's magnetosphere are compared to ion trajectories calculated in model equatorial magnetospheric magnetic and electric fields. These comparisons indicate that solar wind ions entering the QTR on the nightside as an energetic component of the plasma sheet exit the region on the dayside, experiencing little or no charge exchange on the way. Measurements made by the CHarge Energy Mass (CHEM) ion spectrometer on board the Active Magnetospheric Particle Tracer Explorer/Charge Composition Explorer (AMPTE/CCE) spacecraft at 7 less than L less than 9 from September 1984 to January 1989 are the source of the new results contained herein: quantitative long-term determination of number densities, average energies, energy spectra, local time distributions, and their variation with geomagnetic disturbance level as indexed by Kp. Solar wind primaries (ions with charge states unchanged) and their secondaries (ions with generally lower charge states produced from primaries in the magnetosphere via charge exchange)are observed throughout the QTR and have distinctly different local time variations that persist over the entire 4-year analysis interval. During Kp larger than or equal to 3 deg intervals, primary ion (e.g., O(+6)) densities exhibit a pronounced predawn maximum with average energy minimum and a broad near-local-noon density minimum with average energy maximum. Secondary ion (e.g., O(+5)) densities do not have an identifiable predawn peak, rather they have a broad dayside maximum peaked in local morning and a nightside minimum. During Kp less than or equal to 2(-) intervals, primary ion density peaks are less intense, broader in local time extent, and centered near midnight, while secondary ion density local time variations diminish. The long-time-interval baseline helps to refine and extend previous observations; for example, we show that ionospheric contribution to O(+3)) is negligible. Through comparison with model ion trajectories, we interpret the lack of pronounced secondary ion density peaks colocated with the primary density peaks to indicate that: (1) negligible charge exchange occurs at L greater than 7, that is, solar wind secondaries are produced at L less than 7, and (2) solar wind secondaries do not form a significant portion of the plasma sheet population injected into the QTR. We conclude that little of the energetic solar wind secondary ion population is recirculated through the magnetosphere.

Christon, S. P.↗
NASA NTRS1980

Improved definition of crustal anomalies for Magsat data

Final editing and reduction of the equatorial ground observatory data set was completed. Plots of delineation, and the vertical and horizontal components of the time varying field were generated from these data. Appropriate baselines were derived and deviations from these levels can be used as a continuous measure of the external variations at ground level in the sub-auroral zones. They may also be useful as quantitative measures of the intensity of external field activity. Other data sets assembled for dissemination include (1) Kp and Ap - the planetary magnetic indexes; (2) the international magnetic character indexes-Cp; (3) compilations of magnetic storm sudden commencements; (4) time of interplanetary magnetic sector changes; and (5) Dst - the storm disturbance measure. Fine attitude component data with its increased pointing resolution is reducing residuals by an order of magnitude.

Source record↗
NASA NTRS1987

Average spatial distributions of energetic O(+), O(2+), O(6+), and C(6+) ions in the magnetosphere observed by AMPTE CCE

Measurements with the charge energy mass spectrometer of the AMPTE CCE spacecraft are used to determine the relative fluxes of these ions near the equatorial plane as a function of the drift shell parameter L, the magnetic activity index Kp, and the local time LT. The O(+) and O(2+) ions have radial profiles with maxima at about L = 5 and diurnal variations with a broad maximum on the dayside. The O(6+) and C(6+) ion fluxes increase with L between L = 5 and L = 7 and level off farther out. The diurnal variations of the relative O(6+) and C(6+) fluxes exhibit a pronounced minimum on the dayside. The observations can be interpreted in terms of ion convection from the tail onto quasi-trapped drift orbits and further radial diffusion onto closed drift shells. The maximum of the O(+) and O(2+) fluxes as well as the minimum of the O(6+) and C(6+) fluxes on the dayside can be explained by drift shell splitting. The inward transport is associated with ion losses, mainly by charge exchange. O(6+) and C(6+) ions are removed already at larger distances than O(+) and O(2+). As a result, the ionosphere contributes most of the oxygen ions in the magnetosphere. Important contributions from the solar wind are encountered in the outer magnetosphere.

Kremser, G.↗
DOE OSTI2022

Setup and verification of a SCALE/KENO platform for generic FHR benchmark calculations

The work presented in this article is preliminary to downstream analysis of a generic fluoride salt-cooled high-temperature reactor (gFHR) core performed by the University of Tennessee in collaboration with Kairos Power (KP). A Monte Carlo transport model of the publicly available gFHR equilibrium core is developed in SCALE/KENO with multigroup energy treatment. Several output quantities of interest are used to verify the simulations against a benchmark model developed by KP using the continuous energy Monte Carlo code Serpent 2. Good agreement is seen in flux and fission rate profiles with a maximum relative difference of 1.4% and 2.8% respectively. Furthermore, an effective multiplication factor bias of 44 pcm was observed between the two simulations. The fuel temperature reactivity coefficient calculated with SCALE is within uncertainty to the reference model. This verification acts as a publicly reproducible benchmark for the gFHR in SCALE/KENO. A simplified depletion model is also presented where a single fuel pebble is depleted to discharge burnup through the equilibrium core while the equilibrium core is assumed to be invariant. This method produces results that intercept the equilibrium core concentrations in every case, however, an interesting artifact of this particular depletion model is uncovered. The phenomenon is shown to be a fundamental feature of the differential rate equations and inspires questions about how this system behaves when the time evolution of the equilibrium core is considered. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1991

Thermodynamics of acetylene van der Waals dimerization

Integrated band intensities of the 620/cm absorption in (C2H2)2 are measured by FTIR spectroscopy at constant acetylene pressure between 198 and 273 K. These data, in conjunction with ab initio results for (C2H2)2, are used for the statistical evaluation of the equilibrium constant Kp(T) for acetylene-cluster dimerization. The present results are used to clarify the role of molecular clusters in chemical systems at or near equilibrium, in particular in Titan's stratosphere.

Colussi, A. J.↗
NASA NTRS1991

Model and observation comparison of the universal time and IMF by dependence of the ionospheric polar hole

The polar ionospheric F-region often exhibits regions of marked density depletion. These depletions have been observed by a variety of polar orbiting ionospheric satellites over a full range of solar cycle, season, magnetic activity, and universal time (UT). An empirical model of these observations has recently been developed to describe the polar depletion dependence on these parameters. Specifically, the dependence has been defined as a function of F10.7 (solar), summer or winter, Kp (magnetic), and UT. Polar cap depletions have also been predicted /1, 2/ and are, hence, present in physical models of the high latitude ionosphere. Using the Utah State University Time Dependent Ionospheric Model (TDIM) the predicted polar depletion characteristics are compared with those described by the above empirical model. In addition, the TDIM is used to predict the IMF By dependence of the polar hole feature.

Sojka, J. J.↗
NASA NTRS2005

Comparison of Two IRI Plasmasphere Extensions with GPS-TEC Observations

Two plasmasphere extensions of the International Reference Ionosphere are made available for the users. It is aimed to estimate the effect of charged particles on technical devices in the Earth's environment and to define the ionosphere-plasmasphere operational conditions compatible with existing and future systems of radio communication, radio navigation and other relevant radio technologies in the ranges of medium and higher frequencies. The Global Core Plasma Model (GCPM-2000) of Gallagher et al. (2000) is an empirical description of thermal plasma densities in the plasmasphere, plasmapause, magnetospheric trough, and polar cap. GCPM-2000 uses the Kp index and is coupled to IRI in the transition region 500-600 km. The IZMIRAN plasmasphere model (Chasovitin et al., 1998; Gulyaeva et al., 2002) is an empirical model based on whistler and satellite observations. It presents global vertical analytical profiles of electron density smoothly fitted to IRI electron density profile at 1000 km altitude and extended towards the plasmapause (up to 36,000 km). For the smooth fitting of the two models, the shape of the IRI topside electron density profile is improved using ISIS 1, ISIS 2, and IK19 satellite inputs (Gulyaeva, 2003). The plasmasphere model depends on solar activity and magnetic activity (kp-index). The two IRI plasmasphere extensions are compared in the present study with the total electron content derived from records of Global Positioning Satellites (GPS-TEC) observations for different latitudinal, solar activity, magnetic activity, diurnal and seasonal conditions. The differences of model TEC with observed TEC in the topside ionosphere and plasmasphere are discussed.

Gulyacva, Tamara↗
NASA NTRS2017

Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars. II. Planetary Systems Observed During Campaigns 1-7

We recently used near-infrared spectroscopy to improve the characterization of 76 low-mass stars around which K2 had detected 79 candidate transiting planets. 29 of these worlds were new discoveries that had not previously been published. We calculate the false positive probabilities that the transit-like signals are actually caused by non-planetary astrophysical phenomena and reject five new transit-like events and three previously reported events as false positives. We also statistically validate 17 planets (7 of which were previously unpublished), confirm the earlier validation of 22 planets, and announce 17 newly discovered planet candidates. Revising the properties of the associated planet candidates based on the updated host star characteristics and refitting the transit photometry, we find that our sample contains 21 planets or planet candidates with radii smaller than 1.25 solar radii, 18 super-Earths (1.25-2 solar radii), 21 small Neptunes (2-4 solar radii), three large Neptunes (4-6 solar radii), and eight giant planets (greater than 6 solar radii). Most of these planets are highly irradiated, but EPIC 206209135.04 (K2-72e, 1.29 from plus 0.19 to minus 0.18 solar radii), EPIC 211988320.01 (perihelion radius equals 2.86 from plus 0.16 to minus 0.15 solar radii), and EPIC 212690867.01 (2.20 from plus 0.19 to minus 0.18 solar radii) orbit within optimistic habitable zone boundaries set by the "recent Venus" inner limit and the "early Mars" outer limit. In total, our planet sample includes eight moderately irradiated 1.5-3 solar radii planet candidates (planetary flux greater than or approximately 20 times Earth's flux) orbiting brighter stars (Ks less than 11) that are well-suited for atmospheric investigations with the Hubble, Spitzer, and/or James Webb Space Telescopes. Five validated planets orbit relatively bright stars (Kp less than 12.5) and are expected to yield radial velocity semi-amplitudes of at least 2 meters per second. Accordingly, they are possible targets for radial velocity mass measurement with current facilities or the upcoming generation of red optical and near-infrared high-precision RV (Radial Velocity) spectrographs.

Dressing, Courtney D.↗
DOE OSTI2025

Post-Irradiation Examination on MiniFuel UCO and UO 2 TRISO Particles Irradiated in HFIR at High Power

Post-irradiation examination (PIE) of MiniFuel compacts was conducted at Oak Ridge National Laboratory (ORNL) under the Nuclear Science User Facilities project in collaboration with Kairos Power (KP) to evaluate the performance of tristructural-isotropic (TRISO) particles under high particle power and fluoride-salt-cooled high-temperature reactor (FHR)-relevant conditions. MiniFuel compacts containing low-enriched uranium oxide-uranium carbide (LEUCO), low-enriched uranium dioxide (LEUO 2 ), and natural UCO (NUCO) kernels were irradiated for four cycles at ORNL’s High Flux Isotope Reactor (HFIR) at target temperatures between 500°C and 900°C. Post irradiation, the experiment was disassembled at ORNL to recover the MiniFuel subcapsules, which were subsequently punctured to measure fission gas release. Subcapsule disassembly allowed the recovery of components of interest, such as silicon carbide (SiC) thermometry, fuel specimens, fission product sinks, and SiC spacers. The experimental irradiation temperature was confirmed by analyzing the SiC thermometry via dilatometry. PIE on the fuel specimens included gamma spectrometry and deconsolidation leach burn leach, which were complemented by imaging techniques such as x-ray computed tomography, optical microscopy, and electron microscopy. The PIE results provide insight into TRISO particle integrity, fission product retention, coating performance, and kernel migration, informing fuel qualification for application in KP’s FHR concept.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1991

An evaluation of the Tsyganenko magnetic field model

A data set of more than 22,000 vector averages of the magnetosphere magnetic field over 0.5 R(E) regions is used to evaluate Tsyganenko's 1982 and 1987 magnetospheric magnetic field models. The magnetic field predicted by the model in various regions is compared to observations to find systematic discrepancies which future models might address. While agreement is generally good, discrepancies are noted which include: (1) a lack of adequate field line stretching in the tail and ring current regions; (2) an inability to predict weak enough fields in the polar cusps; and (3) a deficiency of Kp as a predictor of the field configuration.

Fairfield, D. H.↗