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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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9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Differences in the temporal variations of solar UV flux, 10.7-cm solar radio flux, sunspot number, and Ca-K plage data caused by solar rotation and active region evolution

Attention is given to two types of temporal variations in the solar UV spectral irradiance caused by solar rotation and active region evolution. It is noted that the first type of dissimilar temporal behavior occurs when concentrations of solar active regions evolve at solar longitudes nearly 180 deg apart. Both the UV observations and modeled UV fluxes based on Ca-K plage data then exhibit pronounced 13-day periodicity, whereas the 10.7-cm solar radio flux and sunspot number exhibit quite dissimilar temporal variations. This type of dissimilarity is related to the modeled UV flux and has a dependence on the solar central meridian distance that is narrower than that for the 10.7-cm radio flux or for sunspot numbers. A second case of marked dissimilarity is seen when major new solar active regions arise and dominate the full-disk fluxes for several rotations. It is found that the strongest peaks in 10.7 cm and sunspot numbers tend to occur on their first rotation, for example, during major dips in the total solar irradiance, whereas the Ca-K plages and UV enhancements peak on the next rotation and then decay more slowly on subsequent rotations.

Donnelly, R. F.↗
NASA NTRS1991

Modelling solar irradiances using ground-based measurements

The first results of photometric measurements of Ca-K plage remnants are presented. They show that during the fall of 1986 the remnants gave a significant contribution to the irradiance variations and that the averaged remnant component is less than assumed in the present UV models. The contribution of the plage remnants to the combined plage and remnant index was on average about 13 percent, and it changed with time.

Pap, J. M.↗
NASA NTRS1991

Solar irradiance variability from modern measurements

Direct measurements from satellites of the solar 'constant' (the total irradiance at mean sun-earth distance) during more than ten years show variations over time scales from minutes to years and decades. At high frequencies, solar oscillations contribute to the variance. The most important influences are related to solar activity: during the passage of active regions on the solar disk (sunspots and faculae) changes of a few 0.1 percent lasting for several days are observed. The effects of spots can be well reproduced by the projected sunspot index, whereas the influence of faculae have to be modeled from proxy data like the Ca-K plage index or the He I index. Long-term trends are detected which are connected to the 11-yr solar activity cycle.

Froehlich, C.↗
NASA NTRS1992

Variations in solar Lyman alpha irradiance on short time scales

Variations in solar UV irradiance at Lyman alpha are studied on short time scales (from days to months) after removing the long-term changes over the solar cycle. The SME/Lyman alpha irradiance is estimated from various solar indices using linear regression analysis. In order to study the nonlinear effects, Lyman alpha irradiance is modeled with a 5th-degree polynomial as well. It is shown that the full-disk equivalent width of the He line at 1083 nm, which is used as a proxy for the plages and active network, can best reproduce the changes observed in Lyman alpha. Approximately 72 percent of the solar-activity-related changes in Lyman alpha irradiance arise from plages and the network. The network contribution is estimated by the correlation analysis to be about 19 percent. It is shown that significant variability remains in Lyman alpha irradiance, with periods around 300, 27, and 13.5d, which is not explained by the solar activity indices. It is shown that the nonlinear effects cannot account for a significant part of the unexplained variation in Lyman alpha irradiance. Therefore, additional events (e.g., large-scale motions and/or a systematic difference in the area and intensity of the plages and network observed in the lines of Ca-K, He 1083, and Lyman alpha) may explain the discrepancies found between the observed and estimated irradiance values.

Pap, J. M.↗
DOE OSTI2020

Materials Data on K3Ca by Materials Project

K3Ca is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. K is bonded to eight equivalent K and four equivalent Ca atoms to form KK8Ca4 cuboctahedra that share corners with twelve equivalent KK8Ca4 cuboctahedra, edges with eight equivalent CaK12 cuboctahedra, edges with sixteen equivalent KK8Ca4 cuboctahedra, faces with four equivalent CaK12 cuboctahedra, and faces with fourteen equivalent KK8Ca4 cuboctahedra. All K–K bond lengths are 4.47 Å. All K–Ca bond lengths are 4.47 Å. Ca is bonded to twelve equivalent K atoms to form CaK12 cuboctahedra that share corners with twelve equivalent CaK12 cuboctahedra, edges with twenty-four equivalent KK8Ca4 cuboctahedra, faces with six equivalent CaK12 cuboctahedra, and faces with twelve equivalent KK8Ca4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KCa3 by Materials Project

KCa3 is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. K is bonded in a body-centered cubic geometry to eight equivalent Ca atoms. All K–Ca bond lengths are 3.93 Å. There are two inequivalent Ca sites. In the first Ca site, Ca is bonded in a body-centered cubic geometry to four equivalent K and four equivalent Ca atoms. All Ca–Ca bond lengths are 3.93 Å. In the second Ca site, Ca is bonded in a body-centered cubic geometry to eight equivalent Ca atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KCa3 by Materials Project

KCa3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. K is bonded to twelve Ca atoms to form KCa12 cuboctahedra that share corners with four equivalent KCa12 cuboctahedra, corners with eight equivalent CaK4Ca8 cuboctahedra, edges with eight equivalent KCa12 cuboctahedra, edges with sixteen equivalent CaK4Ca8 cuboctahedra, faces with four equivalent KCa12 cuboctahedra, and faces with fourteen CaK4Ca8 cuboctahedra. There are four shorter (4.03 Å) and eight longer (4.08 Å) K–Ca bond lengths. There are two inequivalent Ca sites. In the first Ca site, Ca is bonded to four equivalent K and eight Ca atoms to form CaK4Ca8 cuboctahedra that share corners with twelve equivalent CaK4Ca8 cuboctahedra, edges with eight equivalent KCa12 cuboctahedra, edges with sixteen CaK4Ca8 cuboctahedra, faces with four equivalent KCa12 cuboctahedra, and faces with fourteen CaK4Ca8 cuboctahedra. There are four shorter (4.03 Å) and four longer (4.08 Å) Ca–Ca bond lengths. In the second Ca site, Ca is bonded to four equivalent K and eight equivalent Ca atoms to form CaK4Ca8 cuboctahedra that share corners with four equivalent CaK4Ca8 cuboctahedra, corners with eight equivalent KCa12 cuboctahedra, edges with twenty-four CaK4Ca8 cuboctahedra, faces with six equivalent KCa12 cuboctahedra, and faces with twelve CaK4Ca8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3Ca by Materials Project

K3Ca is alpha bismuth trifluoride structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded in a body-centered cubic geometry to four equivalent K and four equivalent Ca atoms. All K–K bond lengths are 4.36 Å. All K–Ca bond lengths are 4.36 Å. In the second K site, K is bonded in a body-centered cubic geometry to eight equivalent K atoms. Ca is bonded in a body-centered cubic geometry to eight equivalent K atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KCa3 by Materials Project

KCa3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. K is bonded to twelve equivalent Ca atoms to form KCa12 cuboctahedra that share corners with twelve equivalent KCa12 cuboctahedra, edges with twenty-four equivalent CaK4Ca8 cuboctahedra, faces with six equivalent KCa12 cuboctahedra, and faces with twelve equivalent CaK4Ca8 cuboctahedra. All K–Ca bond lengths are 4.07 Å. Ca is bonded to four equivalent K and eight equivalent Ca atoms to form CaK4Ca8 cuboctahedra that share corners with twelve equivalent CaK4Ca8 cuboctahedra, edges with eight equivalent KCa12 cuboctahedra, edges with sixteen equivalent CaK4Ca8 cuboctahedra, faces with four equivalent KCa12 cuboctahedra, and faces with fourteen equivalent CaK4Ca8 cuboctahedra. All Ca–Ca bond lengths are 4.07 Å.

36 MATERIALS SCIENCE↗