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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Study of a Flexible Low Profile Tunable Dipole Antenna Using Barium Strontium Titanate Varactors

In this paper a flexible low profile dipole antenna using a frequency selective surface (FSS) with interdigital barium strontium titanate (BST) varactor-tuned unit cells is presented. The varactor chips were placed only along one dimension of the FSS to avoid the use of vias and simplify the DC bias network. The antenna uses overlapping metallic plates that resemble fish scales as a ground plane to improve the flexibility of the multi-material stack structure. The measured data of the antenna demonstrate tunability from 2.42 GHz to 2.66 GHz and 1.3 dB gain drop when using overlapping metallic plates instead of continuous ground plane. The total antenna thickness is approximately lambda/24.

Flexible antennas↗
NASA NTRS1968

Rubidium-strontium age of hypersthene

Rubidium, Sr and Sr isotopic composition of normal gray hypersthene chondrite falls, noting Rb/Sr and Sr87/Sr86 ratio determination of Bath Furnace L chondrite isochron

Gopalan, K.↗
NASA NTRS1972

Rubidium-strontium isotope characteristics of lunar soils.

Evaluation of K, Rb, and Sr concentrations and Sr isotopic composition for hand-picked fractions from the 175- to 1000-micron Apollo 12 fines samples 12032 and 12070 and for two less than 1-mm bulk fines samples, 14163,160 and 14259,21, from Apollo 14 which have model Rb-Sr ages close to 4.6 b.y. The Apollo 14 data indicate the presence of a radiogenic component of 4.6 b.y. model age like the Apollo 12 fines, confirming a very early geochemical differentiation of the moon. Progressively greater enrichment in K and Rb relative to the bulk fines is shown by microbreccia from both samples, ropy brown glass from 12032, and light-grey lithic fragments from 12032. Model Rb-Sr ages, based on a basaltic achondrite initial ratio, are generally close to 4.6 b.y. The microbreccias and ropy brown glass have model ages that are younger but indistinguishable from 4.6 b.y. within analytical error. Light grey lithic fragments from 12032 have a model age of 5.1 b.y. and must have had a multistage Rb/Sr evolution. The data are broadly compatible with two-component mixing models of the Apollo 12 fines. On the basis of modal composition, the microbreccia is considered the major nonbasaltic constituent.

Cliff, R. A.↗
NASA NTRS1974

Isotopic composition of lithium, potassium, rubidium, and strontium in lunar surface material

The isotopic composition of alkali and alkaline earth elements in the Luna 16 regolith was investigated by the method of thermionic emission, without chemical separation. The isotopic composition of the lithium in two regolith samples did not differ (within the limits 0.5 percent) from the mean of the terrestrial reference standard. At the same time, the observed difference (1 percent) in the isotopic composition of lithium between the samples requires further investigation and confirmation. The isotopic compositions of K and Rb did not differ within the limits of experimental error from the isotopic composition of the reference standard.

Zaslavskiy, V. G.↗
NASA NTRS1976

Rb, Sr and strontium isotopic composition, K/Ar age and large ion lithophile trace element abundances in rocks and glasses from the Wanapitei Lake impact structure

Shock metamorphosed rocks and shock-produced melt glasses from the Wanapitei Lake impact structure have been examined petrographically and by electron microprobe. Eleven clasts exhibiting varying degrees of shock metamorphism and eight impact-produced glasses have been analyzed for Rb, Sr and Sr isotopic composition. Five clasts and one glass have also been analyzed for large ion lithophile (LIL) trace element abundances including Li, Rb, Sr, and Ba and the REE's. The impact event forming the Wanapitei Lake structure occurred 37 m.y. ago based on K/Ar dating of glass and glassy whole-rock samples. Rb/Sr isotopic dating failed to provide a meaningful whole-rock or internal isochron. The isotopic composition of the glasses can be explained by impact-produced mixing and melting of metasediments.

Winzer, S. R.↗
NASA NTRS1975

Lead and strontium isotopes in post-glacial basalts from Iceland

We report here our Pb and Sr isotopic study of some post-glacial basalts (less than 12,000 yr old) from the southern part of Iceland, and use our new data to evaluate various proposed models for the genesis of volcanic rocks on Iceland. The interpretation for Icelandic rocks is also extended to the genesis of volcanic rocks on other oceanic islands of the world.

Sun, S.-S.↗
NASA NTRS1976

Neutral calcium, strontium and barium - Determination of f values of the principal series by the hook method

The hook method is used to measure the absolute gf values of the following lines: the first 13 members of the principal series, the ground-level transition at 2275.46 A, and the intercombination line at 6572.78 A in Ca I; the first 22 members of the principal series, the ground-level transitions at 2428.1 and 2680.08 A, and the intercombination line at 6892.6 A in Sr I; and the members from principal quantum numbers 12 to 21, inclusive, as well as the ground-level transitions at 2432.5, 2444.6, and 2454.06 A in Ba I. The results are compared with those of previous measurements, and the quantum-defect method is applied to plot the oscillator strengths of the discrete transitions in the principal series of Mg I, Ca I, and Sr I in order to obtain estimates of the photoionization cross sections at the first ionization limit. The resulting cross sections are found to be about twice as large as previous values based on vapor-pressure data.

Parkinson, W. H.↗
NASA NTRS1978

On strontium isotopic anomalies and odd-A p-process abundances

Several aspects of the nucleosynthesis of Sr isotopes are considered in an attempt to shed light on the problem of the Sr isotopic anomalies discovered in an inclusion of the Allende meteorite. Decomposition of the Sr isotopes into average r-, s-, and p-process nucleosynthetic classes is performed. It is suggested that the Allende inclusion most likely has an excess of s-process Sr and that the initial Sr-87/Sr-86 isotopic ratio is probably slightly more primitive than basaltic achondrites. The results also show that Sn-115 is mostly due to the r-process and that odd-A yields are very small. It is concluded that if the Sr anomaly in the inclusion is an average s enhancement, it argues somewhat in favor of a model of gas/dust fractionation of s and r isotopes during accumulation of the inclusion parent in the protosolar cloud.

Clayton, D. D.↗