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At least 253 records · Page 14

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NASA NTRS2001

A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

Roeder, Jeffrey F.↗

NASA NTRS2004

A-SITE-AND/OR B-SITE-MODIFIED PBZRTIO3 MATERIALS AND (PB, SR, CA, BA, MG) (ZR, TI,NB, TA)O3 FILMS HAVING UTILITY IN FERROELECTRIC RANDOM ACCESS MEMORIES AND HIGH PERFORMANCE THIN FILM MICROACTUATORS

Roeder, Jeffrey F.↗

NASA NTRS2009

Fuel-Cell Power Systems Incorporating Mg-Based H2 Generators

Two hydrogen generators based on reactions involving magnesium and steam have been proposed as means for generating the fuel (hydrogen gas) for such fuel-cell power systems as those to be used in the drive systems of advanced motor vehicles. The hydrogen generators would make it unnecessary to rely on any of the hydrogen storage systems developed thus far that are, variously, too expensive, too heavy, too bulky, and/or too unsafe to be practical. The two proposed hydrogen generators are denoted basic and advanced, respectively. In the basic hydrogen generator (see figure), steam at a temperature greater than or equals 330 C would be fed into a reactor charged with magnesium, wherein hydrogen would be released in the exothermic reaction Mg + H2O yields MgO + H2. The steam would be made in a flash boiler. To initiate the reaction, the boiler could be heated electrically by energy borrowed from a storage battery that would be recharged during normal operation of the associated fuel-cell subsystem. Once the reaction was underway, heat from the reaction would be fed to the boiler. If the boiler were made an integral part of the hydrogen-generator reactor vessel, then the problem of transfer of heat from the reactor to the boiler would be greatly simplified. A pump would be used to feed water from a storage tank to the boiler.

Kindler, Andrew↗

NASA NTRS2009

Characterizing the Effect of Shock on Isotopic Ages: Mg-Suite Troctolite Major Elements - 2

Two troctolites from the lunar magnesium suite (Mg-suite), 76335 and 76535, have Sm-147-ND-143 and Rb-87- Sr-87 ages that do not indicate the same age for their respective sample. In the case of 76335, the Sm-147-ND-143 age is 4278 +/- 60 Ma, but the Rb-87-Sr-87 data does not reveal an isochron]. For 76535, the Sm-147-ND-143 age is significantly younger (4260 +/- 60 Ma) than the Rb-87- Sr-87 age (4570 +/- 70 Ma, Lambda = 1.402x10(exp -11)). This study was designed to discover why the Sm-147-ND-143 and Rb-87-Sr-87 ages did not match for each individual sample.

Edmunson, Jennifer↗

NASA NTRS2012

Organic Combustion in the Presence of Ca-Carbonate and Mg-Perchlorate: A Possible Source for the Low Temperature CO2 Release Seen in Mars Phoenix Thermal and Evolved Gas Analyzer Data

Two of the most important discoveries of the Phoenix Lander were the detection of approx.0.6% perchlorate [1] and 3-5% carbonate [2] in landing site soils. The Thermal and Evolved Gas Analyzer (TEGA) instrument on the Phoenix lander could heat samples up to approx.1000 C and monitor evolved gases with a mass spectrometer. TEGA detected a low (approx.350 C) and high (approx.750 C) temperature CO2 release. The high temp release was attributed to the thermal decomposition of Ca-carbonate (calcite). The low temperature CO2 release could be due to desorption of CO2, decomposition of a different carbonate mineral, or the combustion of organic material. A new hypothesis has also been proposed that the low temperature CO2 release could be due to the early breakdown of calcite in the presence of the decomposition products of certain perchlorate salts [3]. We have investigated whether or not this new hypothesis is also compatible with organic combustion. Magnesium perchlorate is stable as Mg(ClO4)2-6H2O on the martian surface [4]. During thermal decomposition, this perchlorate salt releases H2O, Cl2, and O2 gases. The Cl2 can react with water to form HCl which then reacts with calcite, releasing CO2 below the standard thermal decomposition temperature of calcite. However, when using concentrations of perchlorate and calcite similar to what was detected by Phoenix, the ratio of high:low temperature CO2 evolved is much larger in the lab, indicating that although this process might contribute to the low temp CO2 release, it cannot account for all of it. While H2O and Cl2 cause calcite decomposition, the O2 evolved during perchlorate decomposition can lead to the combustion of any reduced carbon present in the sample [5]. We investigate the possible contribution of organic molecules to the low temperature CO2 release seen on Mars.

Archer, Douglas↗

NASA NTRS2010

K-shell Photoionization of Na-like to Cl-like Ions of Mg, Si, S, Ar, and Ca

We present R-matrix calculations of photoabsorption and photoionization cross sections across the K edge of Mg, Si, S, Ar, and Ca ions with more than 10 electrons. The calculations include the effects of radiative and Auger damping by means of an optical potential. The wave functions are constructed from single-electron. orbital bases obtained using a Thomas-Fermi-Dirac statistical model potential. Configuration interaction is considered among all states up to n = 3. The damping processes affect the resonances converging to the K-thresholds causing them to display symmetric profiles of constant width that smear the otherwise sharp edge at the photoionization threshold. These data are important for the modeling of features found in photoionized plasmas.

Witthoeft, M. C.↗

NASA NTRS2013

Character of Mg(ClO4)2 Brines Under Mars Regolith Conditions

Elsewhere, we report on our investigation of the initiation and growth of ice lenses under Mars like conditions. In that work, we assume that the soil-water-ice system is gas and solute free. We conclude that initiation of lens initiation - the unloading of particle-particle contacts by thermomolecular forces at a given soil horizon - may be a common process in the shallow Martian regolith, and that the dominant property controlling the rate of lens growth is the freezing point depression (Delta-T(sub f)) associated with the interfacial forces of the soil. Lens growth is thus favored in clay-sized soils over silt soils due to the greater Delta-T(sub f), but segregated ice was observed at the Phoenix site, where soils were predominantly siltsized.. Perchlorate salts were also observed at the Phoenix site, and will strongly affect some of the properties associated with potential ice lens growth, over and above increases to Delta-T(sub f),. Here, we investigate the nature of Mg(ClO4)2 brines under Mars-like conditions, with particular emphasis on those aspects that might influence the in situ segregation of residual liquids during phase change, potentially leading to the formation of subsurface excess ice. We also discuss cyclic variations in the water activity (a(sub w)) that might affect the habitability of solutions in the shallow regolith.

soil-water-ice system↗

NASA NTRS2017

CLASP2: High-Precision Spectro-Polarimetery in Mg II h & k

The international team is promoting the CLASP2 (Chromospheric LAyer Spectro-Polarimeter 2) sounding rocket experiment, which is the re-flight of CLASP (2015). In this second flight, we will refit the existing CLASP instrument to measure all Stokes parameters in Mg II h k lines, and aim at inferring the magnetic field information in the upper chromosphere combining the Hanle and Zeeman effects. CLASP2 project was approved by NASA in December 2016, and is now scheduled to fly in 2019.

spectropolarimetry↗

NASA NTRS2018

Relative Sputtering Rates of FeS, MgS, and Mg Silicates: Implications for ISM Gas Phase Depletions of Rock-Forming Elements

Astronomical measurements of S abundances in the diffuse interstellar medium (ISM) indicate ionized S is a dominant species with little (< 5%) S residing in grains (e.g. Jenkins 2009). This is an enigmatic result, given that abundant Fe-sulfide grains are observed in dust around pre- and post-main sequence stars and are also observed as major components of primitive meteoritic and cometary samples. These disparate observations suggest that the lifetime of sulfide grains in the ISM is short because of destruction processes. Our previous work has shown that FeS and MgS retain their crystallinity and do not amorphize during radiation processing, whereas enstatite and forsterite are readily amorphized. We have extended this study to measure the relative sputtering rates of FeS and MgS compared to enstatite and forsterite. Irradiation of FeS with 4 keV He+ results in preferential sputtering of S and the formation of a thin 2-3 nm, compact Fe metal layer that armors the surface. The zone of S loss extends to a depth of ~8-10 nm below the exposed surface. Despite this S loss, the FeS retains its crystallinity and shows no sign of incipient amorphization. Irradiation of FeS with 5kV Ga+ in a focused ion beam (FIB) instrument resulted in preferential sputtering of S and the formation of a 5-8-nm thick surface layer of nanophase Fe metal. X-ray mapping shows that the zone of S sputtering extends to a depth of nearly 20 nm, but there is no evidence for FeS amorphization, consistent with our previous work. The irradiation experiments show that the relative sputtering rate of FeS and MgS are much higher than olivine or enstatite. Sputtering experiments utilizing 30 kV and 5 kV Ga ions in the FIB produced volume loss in troilite that was ~4X greater than in enstatite or forsterite. The sputter yield under these conditions is such that for every Si atom sputtered from enstatite, ~14 S atoms are sputtered from FeS. We have performed similar sputtering experiments on Fe-bearing niningerite (MgS) and co-existing enstatite from the ALH 84170 EH3 chondrite. MgS also sputters much more rapidly than enstatite with a relative Si:S sputter yield of 1:8. For MgS, sulfur is highly depleted at the surface and the S-depletion zone extends to a depth of ~15 nm (using 5 kV Ga+). There is a corresponding zone of Mg and especially Fe enrichment that extends from 5 to ~10 nm below the surface, respectively. The dominant grain destruction mechanism in the ISM is sputtering from passage of supernova-generated shock waves. This process also results in the amorphization of crystalline silicates in the ISM. Our results indicate that FeS and MgS grains produced in evolved stars and injected into the ISM will be destroyed more rapidly than crystalline silicates. This process may account for the lack of significant depletion of S from the gas phase in the ISM. However, rare nanophase FeS grains occur as inclusions in circumstellar amorphous silicate grains found in comet dust particles analyzed in the laboratory. These results show that a finite amount of S in the ISM is sequestered in solid grains.

SPUTTERING RATES↗

NASA NTRS2019

Center-to-Limb Variation of the Polarization of Mg II H & K Lines as Measured by CLASP2

Who cares? Magnetograms in the upper chromosphere are needed for accurate magnetic coronal extrapolations. The CLASP2 sounding rocket took spatially resolved spectropolarimetric data of Mg II h & k in the upper chromosphere, that can be used as a pathfinder to routine magnetograms. This work: Preliminary results of the center-to-limb variation (CLV) of the linear polarization in the quiet sun. We compare the signals to recent theoretical calculations of the expected polarization which include PRD, J-state interference, and magneto-optical effects.

Rachmeler, Laurel↗

NASA NTRSDate not supplied

Mineralogical and Al-Mg Isotopic Study of Fine-Grained Ca-Al-Rich Inclusions

Fine-grained Ca-Al-rich inclusions (FGIs) in carbonaceous chondrites are interpreted as aggregates of nebular gas-solid condensates that escaped significant melting.Thus far, a small number of FGIs from CV3 chondrites have been analyzed, showing a range of (26Al/27Al)0=~5.4×10−5to ~3.4×10−5.These values are similar to (26Al/27Al)0inferred from coarse-grained, igneous CAIs (CGIs) from CV3 chondrites.This observed spread in (26Al/27Al)0values indicates the CAI formation over an extended time period. However, more analyses are needed to determine if the FGIs formed continuously over a significant time period or by multiple episodic events of nebular condensation. In this study, we present high-precision Al-Mg isotopic data of FGIs from reduced CV3 chondrites to better constrain their formation timescale relative to CGIs in CV3 chondrites, as well as to smaller FGIs in CO3 chondrites. This isotopic study is coordinated with a FIB/TEM study to elucidate the origin and nature of FGIs in the petrologic and mineralogical context.

J Han↗

NASA NTRSDate not supplied

Observational Evidence for the Hanle and Magneto-Optical Effects in the Polarization of the Mg II h & k Lines Observed by CLASP2

CLASP2 (Chromospheric LAyer Spectro-Polarimeter) - Demonstration of the UV spectro-polarimetery as a diagnostic tool of magnetic fields in upper chromosphere - High-precision (<0.1%) spectro-polarimetry across the Mg II h & k around 280 nm - Aim at measuring magnetic field in top chromosphere - International NASA sounding rocket program - Refitted the instrument: CLASP (Lya @ 122 nm) → CLASP2) - Launched at White Sands Missile Range, NM, USA on April 11, 2019

R. Ishikawa↗

NASA NTRSDate not supplied

Al-Mg Isotopic Constraints on the Condensation Age of Fine-Grained Refractory Inclusions in Reduced Cv3 Chondrites

Fine-grained Ca-Al-rich inclusions (FGIs) in carbonaceous chondrites are interpreted as aggregates of direct condensates from the solar nebula that escaped extensive melting. Thus far, a few high-precision SIMS Al-Mg chronology studies of FGIs from CV3 chondrites have been reported. Argued that (26Al/27Al)0 of all FGIs are close to the bulk refractory inclusion value of ~5.2×10−5 which may define a time zero for the FGI condensation. A similar (26Al/27Al)0 value was also inferred from an amoeboid olivine aggregate (AOA), which also represents a direct condensate from the solar nebula. In contrast, reported significant variations in (26Al/27Al)0 of FGIs, ranging from ~5.2×10−5 to ~3.4×10−5, and concluded that their formation continued over at least ~0.4 Ma after the canonical value. These contrasting results suggest that the chronological significance for the formation age spread of FGIs in CV3 chondrites is still poorly constrained.

J. Han↗

NASA NTRS1997

Electron-Impact Ionization of Mg

A pulsed crossed beam technique is used to measure inonization cross-sections of metallic atoms. Relative values of cross-sections of single, double and triple inonization of magnesium have been successfully measured with good accuracy over the o-700 eV range. Absolute values of cross sections have been obtained by normalization to a theoretical value at high electron energy. Results are compared to previously published values and, for single inonization in particular, a comparison with theoretical cross-extions is perfomed.

Ionization of Mg↗

NASA NTRSDate not supplied