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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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Computational and Experimental 1H-NMR Study of Hydrated Mg-Based Minerals

Magnesium oxide (MgO) can convert to different magnesium-containing compounds depending on exposure and environmental conditions. Many MgO-based phases contain hydrated species allowing 1H-nuclear magnetic resonance (NMR) spectroscopy to be used in the characterization and quantification of proton-containing phases; however, surprisingly limited examples have been reported. Here, 1H-magic angle spinning (MAS) NMR spectra of select Mg-based minerals are presented and assigned. These experimental results are combined with computational NMR density functional theory (DFT) periodic calculations to calibrate the predicted chemical shielding results. This correlation is then used to predict the NMR shielding for a series of different MgO hydroxide, magnesium chloride hydrate, magnesium perchlorate, and magnesium cement compounds to aid in the future assignment of 1H-NMR spectra for complex Mg phases.

1H-NMR↗
DOE OSTI2017

Nanoindenting the Chelyabinsk Meteorite to Learn about Impact Deflection Effects in asteroids

The Chelyabinsk meteorite is a highly shocked, low porosity, ordinary chondrite, probably similar to S- or Q-type asteroids. Therefore, nanoindentation experiments on this meteorite allow us to obtain key data to understand the physical properties of near-Earth asteroids. Tests at different length scales provide information about the local mechanical properties of the minerals forming this meteorite: reduced Young’s modulus, hardness, elastic recovery, and fracture toughness. Those tests are also useful to understand the potential to deflect threatening asteroids using a kinetic projectile. We found that the differences in mechanical properties between regions of the meteorite, which increase or reduce the efficiency of impacts, are not a result of compositional differences. A low mean particle size, attributed to repetitive shock, can increase hardness, while low porosity promotes a higher momentum multiplication. Momentum multiplication is the ratio between the change in momentum of a target due to an impact, and the momentum of the projectile, and therefore, higher values imply more efficient impacts. In the Chelyabinsk meteorite, the properties of the light-colored lithology materials facilitate obtaining higher momentum multiplication values, compared to the other regions described for this meteorite. Also, we found a low value of fracture toughness in the shock-melt veins of Chelyabinsk, which would promote the ejection of material after an impact and therefore increase the momentum multiplication. These results are relevant to the growing interest in missions to test asteroid deflection, such as the recent collaboration between the European Space Agency and NASA, known as the Asteroid Impact and Deflection Assessment mission.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2002

The western red cedar (Thuja plicata) 8-8' DIRIGENT family displays diverse expression patterns and conserved monolignol coupling specificity

The isolation and characterization of a multigene family of the first class of dirigent proteins (namely that mainly involved in 8-8' coupling leading to (+)-pinoresinol in this case) is reported, this comprising of nine western red cedar (Thuja plicata) DIRIGENT genes (DIR1-9) of 72-99.5% identity to each other. Their corresponding cDNA clones had coding regions for 180-183 amino acids with each having a predicted molecular mass of ca. 20 kDa including the signal peptide. Real time-PCR established that the DIRIGENT isovariants were differentially expressed during growth and development of T. plicata (P < 0.05). The phylogenetic relationships and the rates and patterns of nucleotide substitution suggest that the DIRIGENT gene may have evolved via paralogous expansion at an early stage of vascular plant diversification. Thereafter, western red cedar paralogues have maintained an high homogeneity presumably via a concerted evolutionary mode. This, in turn, is assumed to be the driving force for the differential formation of 8-8'-linked pinoresinol derived (poly)lignans in the needles, stems, bark and branches, as well as for massive accumulation of 8-8'-linked plicatic acid-derived (poly)lignans in heartwood.

Non-NASA Center↗
NASA NTRS1998

Co- and/or post-translational modifications are critical for TCH4 XET activity

TCH4 encodes a xyloglucan endotransglycosylase (XET) of Arabidopsis thaliana. XETs endolytically cleave and religate xyloglucan polymers; xyloglucan is one of the primary structural components of the plant cell wall. Therefore, XET function may affect cell shape and plant morphogenesis. To gain insight into the biochemical function of TCH4, we defined structural requirements for optimal XET activity. Recombinant baculoviruses were designed to produce distinct forms of TCH4. TCH4 protein engineered to be synthesized in the cytosol and thus lack normal co- and post-translational modifications is virtually inactive. TCH4 proteins, with and without a polyhistidine tag, that harbor an intact N-terminus are directed to the secretory pathway. Thus, as predicted, the N-terminal region of TCH4 functions as a signal peptide. TCH4 is shown to have at least one disulfide bond as monitored by a mobility shift in SDS-PAGE in the presence of dithiothreitol (DTT). This disulfide bond(s) is essential for full XET activity. TCH4 is glycosylated in vivo; glycosidases that remove N-linked glycosylation eliminated 98% of the XET activity. Thus, co- and/or post-translational modifications are critical for optimal TCH4 XET activity. Furthermore, using site-specific mutagenesis, we demonstrated that the first glutamate residue of the conserved DEIDFEFL motif (E97) is essential for activity. A change to glutamine at this position resulted in an inactive protein; a change to aspartic acid caused protein mislocalization. These data support the hypothesis that, in analogy to Bacillus beta-glucanases, this region may be the active site of XET enzymes.

NASA Discipline Cell Biology↗
NASA NTRS1997

The effects of orbital spaceflight on bone histomorphometry and messenger ribonucleic acid levels for bone matrix proteins and skeletal signaling peptides in ovariectomized growing rats

A 14-day orbital spaceflight was performed using ovariectomized Fisher 344 rats to determine the combined effects of estrogen deficiency and near weightlessness on tibia radial bone growth and cancellous bone turnover. Twelve ovariectomized rats with established cancellous osteopenia were flown aboard the space shuttle Columbia (STS-62). Thirty ovariectomized rats were housed on earth as ground controls: 12 in animal enclosure modules, 12 in vivarium cages, and 6 killed the day of launch for baseline measurements. An additional 18 ovary-intact rats were housed in vivarium cages as ground controls: 8 rats were killed as baseline controls and the remaining 10 rats were killed 14 days later. Ovariectomy increased periosteal bone formation at the tibia-fibula synostosis; cancellous bone resorption and formation in the secondary spongiosa of the proximal tibial metaphysis; and messenger RNA (mRNA) levels for the prepro-alpha2(1) subunit of type 1 collagen, osteocalcin, transforming growth factor-beta, and insulin-like growth factor I in the contralateral proximal tibial metaphysis and for the collagen subunit in periosteum pooled from tibiae and femora and decreased cancellous bone area. Compared to ovariectomized weight-bearing rats, the flight group experienced decreases in periosteal bone formation, collagen subunit mRNA levels, and cancellous bone area. The flight rats had a small decrease in the cancellous mineral apposition rate, but no change in the calculated bone formation rate. Also, spaceflight had no effect on cancellous osteoblast and osteoclast perimeters or on mRNA levels for bone matrix proteins and signaling peptides. On the other hand, spaceflight resulted in an increase in bone resorption, as ascertained from the diminished retention of a preflight fluorochrome label. This latter finding suggests that osteoclast activity was increased. In a follow-up ground-based experiment, unilateral sciatic neurotomy of ovariectomized rats resulted in cancellous bone loss in the unloaded limb in excess of that induced by gonadal hormone deficiency. This additional bone loss was arrested by estrogen replacement. We conclude from these studies that estrogen alters the expression of signaling peptides believed to mediate skeletal adaptation to changes in mechanical usage and likewise modifies the skeletal response to mechanical unloading.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS1992

Identification of a nuclear localization sequence in the polyomavirus capsid protein VP2

A nuclear localization signal (NLS) has been identified in the C-terminal (Glu307-Glu-Asp-Gly-Pro-Gln-Lys-Lys-Lys-Arg-Arg-Leu318) amino acid sequence of the polyomavirus minor capsid protein VP2. The importance of this amino acid sequence for nuclear transport of newly synthesized VP2 was demonstrated by a genetic "subtractive" study using the constructs pSG5VP2 (expressing full-length VP2) and pSG5 delta 3VP2 (expressing truncated VP2, lacking amino acids Glu307-Leu318). These constructs were transfected into COS-7 cells, and the intracellular localization of the VP2 protein was determined by indirect immunofluorescence. These studies revealed that the full-length VP2 was localized in the nucleus, while the truncated VP2 protein was localized in the cytoplasm and not transported to the nucleus. A biochemical "additive" approach was also used to determine whether this sequence could target nonnuclear proteins to the nucleus. A synthetic peptide identical to VP2 amino acids Glu307-Leu318 was cross-linked to the nonnuclear proteins bovine serum albumin (BSA) or immunoglobulin G (IgG). The conjugates were then labeled with fluorescein isothiocyanate and microinjected into the cytoplasm of NIH 3T6 cells. Both conjugates localized in the nucleus of the microinjected cells, whereas unconjugated BSA and IgG remained in the cytoplasm. Taken together, these genetic subtractive and biochemical additive approaches have identified the C-terminal sequence of polyoma-virus VP2 (containing amino acids Glu307-Leu318) as the NLS of this protein.

Non-NASA Center↗

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