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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Novel Hybrid Current Limiter for Grid-Forming Inverter Control During Unbalanced Faults

Grid-forming (GFM) inverter controls have illustrated many desirable features to enable the bulk integration of renewable resources into the future power grid; however, the performance of GFM inverters during unbalanced faults remains underexplored. This paper proposes a novel current-limiting method for GFM inverters to handle unbalanced fault conditions while providing voltage support to the main grid. The proposed current limiter combines concepts of dynamic virtual-impedance and current-reference saturation limiting, all built in the stationary reference frame, to achieve improved current-limiting performance under unbalanced load/fault conditions. System-wide full-order transient simulations with multiple GFM inverters demonstrate the potential of the method and benchmark the performance against state-of-the-art current limiters. Simulation results portray improved voltage balancing performance of the proposed method compared to both current-reference saturation and virtual-impedance limiting.

controller anti windup↗
DOE OSTI2019

A New Model for Electron-capture Supernovae in Galactic Chemical Evolution

We examine the contribution of electron-capture supernovae (ECSNe), low-mass SNe from collapsing Fe cores (FeCCSNe), and rotating massive stars to the chemical composition of the Galaxy. Our model includes contributions to chemical evolution from both thermonuclear ECSNe (tECSNe) and gravitational collapse ECSNe (cECSNe). We show that if ECSNe are predominantly gravitational collapse SNe but about 15% are partial thermonuclear explosions, the model is able to reproduce the solar abundances of several important and problematic isotopes including ${}^{48}\mathrm{Ca}$, ${}^{50}\mathrm{Ti}$, and 54 Cr together with 58 Fe, 64 Ni, 82 Se, and 86 Kr and several of the Zn–Zr isotopes. A model in which no cECSNe occur, only tECSNe with low-mass FeCCSNe or rotating massive stars, proves also very successful at reproducing the solar abundances for these isotopes. Despite the small mass range for the progenitors of ECSNe and low-mass FeCCSNe, the large production factors suffice for the solar inventory of the above isotopes. Our model is compelling because it introduces no new tensions with the solar abundance distribution for a Milky Way model—only tending to improve the model predictions for several isotopes. Here, the proposed astrophysical production model thus provides a natural and elegant way to explain one of the last uncharted territories on the periodic table of astrophysical element production.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1966

The greenhouse effect in a gray planetary atmosphere.

Hopf analytical solution for values of ratio of gray absorption coefficients for insolating and escaping radiation /greenhouse parameter/ assumed constant at all depths, presenting temperature distribution graphs

ABSORPTION COEFFICIENT↗
NASA NTRS1973

LLL electron and proton spectrometer on NASA's Orbiting Geophysical Observatory 5

The LLL energetic electron and proton spectrometer on NASA's Orbiting Geophysical Observatory 5 (OGO-5) operated successfully from launch - March 4, 1968 - until retirement in August 1971. Data recovery during this time was about 95% of the orbit except for the last few months. The electron spectrometer used a magnetic field for electron momentum selection which served also as an electron broom for a proton range - energy telescope. The energy range was approximately 60 to 2950 keV for electrons (seven channels) and 0.10 to approximately 94 MeV for protons (seven channels). The experiment was scanned relative to the stabilized OGO-5 for obtaining directional information. Excellent data were taken throughout the magnetosphere and in the interplanetary region. Studies were carried out in the areas of equatorial pitch-angle distributions, substorm dynamics and field topology, particle spectra (time history), particle spatial distributions, and solar particle events.

West, H. I., Jr.↗
NASA NTRS1974

The albedo of Titan

The irradiance of Titan has been measured from 0.50 to 1.08 micron in 30 A bandpasses spaced 0.01 to 0.02 micron apart. Geometric albedos have been computed at the wavelengths of measurement using a standard solar flux distribution after Labs and Neckel (1967). The maximum value of p sub lambda (0) is 0.37 at 0.68, 0.75, and 0.834 micron; the minimum value, in the centers of the strongest methane absorption bands, is 0.10 at 0.887 and 1.012 micron. The brightness of Titan at the time of the present measurements has been compared with that of previous modern photoelectric measurements. Within the apparent consistency of the different photoelectric systems, the brightness of Titan appears to undergo changes with time.

Younkin, R. L.↗
NASA NTRS1974

Pioneer 10: Observations of energetic electrons in the Jovian magnetosphere

Results are given of a study of the intensities, energy spectra, and angular distribution of energetic particles in the magnetosphere of Jupiter; the heliocentric radial gradient of the intensity of galactic cosmic rays; and the occurrence, intensity, and angular distribution of solar flare particles and their propagation through the interplanetary medium at large heliocentric distances.

Randall, B. A.↗