Search NASA⌕ Search

SEARCH · Search NASA

Results for “sequence variations”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Bacterial endophyte communities in Pinus flexilis are structured by host age, tissue type, and environmental factors

Background and aims: Forest tree microbiomes are vital to forest dynamics, diversity, and ecosystem processes. Mature limber pines ( Pinus flexilis ) host a core microbiome of acetic acid bacteria in their foliage, but the bacterial endophyte community structure, variation, and assembly across tree ontogeny is unknown. The aims of this research were to test if the core microbiome observed in adult P. flexilis is established at the seedling stage, if seedlings host different endophyte communities in root and shoot tissues, and how environmental factors structure seedling endophyte communities. Methods: The 16S rRNA gene was sequenced to characterize the bacterial endophyte communities in roots and shoots of P. flexilis seedlings grown in plots at three elevations at Niwot Ridge, Colorado, subjected to experimental treatments (watering and heating). The data was compared to previously sequenced endophyte communities from adult tree foliage sampled in the same year and location. Results: Seedling shoots hosted a different core microbiome than adult tree foliage and were dominated by a few OTUs in the family Oxalobacteraceae , identical or closely related to strains with antifungal activity. Shoot and root communities significantly differed from each other but shared major OTUs. Watering but not warming restructured the seedling endophyte communities. Conclusions: The results indicate differences in assembly and ecological function across conifer life stages. Seedlings may recruit endophytes to protect against fungi under increased soil moisture.

16S rRNA↗
NASA NTRS1984

An attitude reorientation algorithm for the Galileo spacecraft

This paper presents an onboard closed loop attitude reorientation algorithm for a dual-spin spacecraft, Galileo. The basic concept for the design uses the despun stator as a reference and fires a sequence of fixed duration thruster pulses to precess the angular momentum vector to its commanded orientation. The error signals used to despin the stator and to perform the turn are derived from the stator error quaternion which is computed using gyro outputs. Constraints considered in the design include gyro rate saturation, plume impingement effects, system parameter variations, as well as software reliability and flexibility. The performance of the algorithm was predicted by analysis and confirmed by computer simulation results. It was concluded that a reorientation accuracy of better than 1 milliradian with a nutation angle of less than 1 degree during the turn can be achieved.

Lin, H.-S.↗
NASA NTRS1987

Postbuckling of laminated anisotropic panels

A two-part study of the buckling and postbuckling of laminated anisotropic plates with bending-extensional coupling is presented. The first part involves the development and application of a modified Rayleigh-Ritz analysis technique. Modifications made to the classical technique can be grouped into three areas. First, known symmetries of anisotropic panels are exploited in the selection of approximation functions. Second, a reduced basis technique based on these same symmetries is applied in the linear range. Finally, geometric boundary conditions are enforced via an exterior penalty function approach, rather than relying on choice of approximation functions to satisfy these boundary conditions. Numerical results are presented for both the linear and nonlinear range, with additional studies made to determine the effect of variation in penalty parameter and number of basis vectors. In the second part, six panels possessing anisotropy and bending-extensional coupling are tested. Detailed comparisons are made between experiment and finite element results in order to gain insight into the postbuckling and failure characteristics of such panels. The panels are constructed using two different lamination sequences, and panels with three different aspect ratios were constructed for each lamination sequence.

Jeffrey, Glenda L.↗
NASA NTRS1988

Apollo 14 regolith breccias - Different glass populations and their potential for charting space time variations

Apollo 14 regolith breccias (14313, 14307, 14301, 14049, 14047) have been found to have different populations of nonagglutinitic, mare-derived glasses. These variations appear to not only reflect different source regoliths but also different closure ages for these breccias. Based upon these different glass populations, 14301 is inferred to have a closure age sometime during the epoch of mare volcanism. All of the other four breccias were formed after the termination of mare volcanism with a possible age sequence from old to young of the following: 14307, 14313, 14049, 14047. Due to the relative simplicity of acquiring high-quality chemical data on large numbers of glasses by electron microprobe, mare glass populations allow: (1) classification of regolith breccias with respect to provenance and (2) estimation of their relative and absolute closure ages. The determination of (Ar-40)-(Ar-39) ages on individual glass spherules within breccias using the laser probe should in the future prove to be a promising extension of the present study.

Delano, John W.↗
NASA NTRS2004

Cyclic Oxidation Modeling and Life Prediction

The cyclic oxidation process can be described as an iterative scale growth and spallation sequence by a number of similar models. Model input variable include oxide scale type and growth parameters, spalling geometry, spall constant, and cycle duration. Outputs include net weight change, the amounts of retained and spalled oxide, the total oxygen and metal consumed, and the terminal rates of weight loss and metal consumption. All models and their variations produce a number of similar characteristic features. In general, spalling and material consumption increase to a steady state rate, at which point the retained scale approaches a constant and the rate of weight loss becomes linear. For one model, this regularity was demonstrated as dimensionless, universal expressions, obtained by normalizing the variables by critical performance factors. These insights were enabled through the use of the COSP for Windows cyclic oxidation spalling program.

Smialek, James L.↗
DOE OSTI2019

Ancient polymorphisms contribute to genome-wide variation by long-term balancing selection and divergent sorting in Boechera stricta

Genomic variation is widespread, and both neutral and selective processes can generate similar patterns in the genome. These processes are not mutually exclusive, so it is difficult to infer the evolutionary mechanisms that govern population and species divergence. Boechera stricta is a perennial relative of Arabidopsis thaliana native to largely undisturbed habitats with two geographic and ecologically divergent subspecies. Here, we delineate the evolutionary processes driving the genetic diversity and population differentiation in this species. Using whole-genome re-sequencing data from 517 B. stricta accessions, we identify four genetic groups that diverged around 30-180 thousand years ago, with long-term small effective population sizes and recent population expansion after the Last Glacial Maximum. We find three genomic regions with elevated nucleotide diversity, totaling about 10% of the genome. These three regions of elevated nucleotide diversity show excess of intermediate-frequency alleles, higher absolute divergence ( d XY ), and lower relative divergence ( F ST ) than genomic background, and significant enrichment in immune-related genes, reflecting long-term balancing selection. Scattered across the genome, we also find regions with both high F ST and d XY among the groups, termed F ST -islands. Population genetic signatures indicate that F ST -islands with elevated divergence, which have experienced directional selection, are derived from divergent sorting of ancient polymorphisms. Our results suggest that long-term balancing selection on disease resistance genes may have maintained ancestral haplotypes across different geographical lineages, and unequal sorting of balanced polymorphisms may have generated genomic regions with elevated divergence. This study highlights the importance of ancestral balanced polymorphisms as crucial components of genome-wide variation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Homogenous Voltage-Matched Strings Using Three-Terminal Tandem Solar Cells: Fundamentals and End Losses

Strings constructed from three-terminal tandem (3TT) solar cells offer the performance benefits of voltage-matching (which reduces sensitivity to spectral variation), but without the subcell voltage isolation required by four-terminal cells. However, the circuitry for a 3TT string can become complex, making circuit analysis more challenging. Here, we illustrate the essential features of “homogenous” voltage-matched (VM) 3TT strings, for which all 3TT cells in the string are nominally identical (with the same design/doping sequence, such that they can be fabricated on the same manufacturing line). Several representative VM string configurations are explicitly considered, and used to describe the general construction of string I(V) curves. End losses intrinsic to these strings are discussed in detail, along with mitigation strategies to minimize their impact. Our analysis agrees with experimental results for eight-cell strings constructed from GaInP/GaAs 3TT devices.

14 SOLAR ENERGY↗
DOE OSTI2018

Features of the Emission Spectra of Ni-Like Ions. Application to Calculating the Wavelengths of Self-Photo-Pumped X-Ray Lasers

The energy levels and probabilities of radiative transitions to the ground state of Ni-like ions with Z = 36–51 are calculated. The energies of the upper working level 3d{sub 3/2}4f{sub 5/2} [J = 1] and the lower working level 3d{sub 3/2}4d{sub 3/2} [J = 1] of self-photo-pumped X-ray lasers along the sequence of Ni-like ions are studied. It is shown that, at the points of intersection of levels of the same parity, a strong interaction of these levels takes place, which leads to a redistribution of the oscillator strengths of the radiative transitions from these levels. Near the intersection points, the emission spectra change abruptly with variation in the nuclear charge Z.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1988

Impact wave deposits provide new constraints on the location of the K/T boundary impact

All available evidence is consistent with an impact into oceanic crust terminating the Cretaceous Period. Although much of this evidence is incompatible with an endogenic origin, some investigators still feel that a volcanic origin is possible for the Cretaceous/Tertiary (K/T) boundary clay layers. The commonly cited evidence for a large impact stems from delicate clay layers and their components and the impact site has not yet been found. Impact sites have been suggested all over the globe. The impact is felt to have occurred near North America by: the occurrence of a 2 cm thick ejecta layer only at North American locales, the global variation of shocked quartz grain sizes peaking in North America, the global variation of spinel compositions with most refractory compositions occurring in samples from the Pacific region and possibly uniquely severe plant extinctions in the North American region. The K/T boundary interval was investigated as preserved on the banks of the Brazos River, Texas. The K/T fireball and ejecta layers with associated geochemical anomalies were found interbedded with this sequence which apparently allows a temporal resolution 4 orders of magnitude greater than typical K/T boundary sections. A literature search reveals that such coarse deposits are widely preserved at the K/T boundary. Impact wave deposits have not been found elsewhere on the globe, suggesting the impact occurred between North and South America. The coarse deposits preserved in Deep Sea Drilling Project (DSDP) holes 151-3 suggest the impact occurred nearby. Subsequent tectonism has complicated the picture.

Hildebrand, A. R.↗
NASA NTRS1989

Numerical studies of asymmetric adiabatic accretion flow - The effect of velocity gradients

A numerical study of the time variation of the angular momentum and mass capture rates for a central object accreting from a uniform medium with a velocity gradient transverse to the direction of the mean flow is presented, covering a range of velocity asymmetries and Mach numbers in the incident flow. It is found that the mass accretion rate in a given evolutionary sequence varies in an irregular manner, with the matter accreting onto the central object from either a continuously moving accretion wake or from an accretion disk. The implications of the results from the study of short-term fluctuations observed in the pulse period and luminosity of X-ray pulsars are discussed.

Taam, Ronald E.↗
NASA NTRS1990

Numerical and experimental simulations of the postbuckling response of laminated anisotropic panels

Numerical simulations are used in conjuction with experiments to study the buckling and postbuckling responses and failure initiation of flat unstiffened composite panels. The numerical simulations are conducted using two-dimensional shear-flexible finite elements. The effect of the laminate stacking sequence on the buckling and postbuckling responses is studied. Correlation between numerical and experimental results is good through buckling, but the numerical models overestimate the postbuckling stiffness of the panels. To explain the discrepancies in the postbuckling stiffnesses, analytic sensitivity derivatives are calculated and are used to study the sensitivity of the buckling and postbuckling responses to variations in different material and lamination parameters of the panel. Experimental results indicate that failure occurs along a nodal line. Numerical results show that the location of failure initiation corresponds to that of the maximum transverse shear strain energy density in the panel, which occurs at the edge of the panel at a nodal line.

Noor, Ahmed K.↗
NASA NTRS2010

High-Resolution Spectroscopy of Stratospheric Ethane Following the Jupiter Impact of 2009

We report on high-resolution infrared spectroscopy of ethane (C2H6) performed at the latitude of an impact site on Jupiter discovered on 19 July 2009 by A. Wesley from a location in Murrumbateman, Australia. The observations used the NASA Goddard Space Flight Center's Heterodyne Instrument for Planetary Wind and Composition (HIPWAC) at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. HIPWAC is a mid-infrared (9-12 microns) heterodyne spectrometer operating at the highest limit of spectral resolving power (lambda\Delta\lambda > l06), providing information on atmospheric constituent abundance and temperature through fully resolved tine shapes. Ethane is a stable trace product of methane photochemistry that is nearly uniformly mixed in Jupiter's stratosphere, providing an effective probe of that altitude region. Ethane emission line profiles near 11,74 microns in the Ug band were measured in Jupiter's stratosphere at 25 MHz (11.00083/cm) resolution. A sequence of spectra of ethane acquired over a range of longitude at the impact latitude (56S planetocentric) probes constituent abundance and temperature profile, both on and off the impact region. Near the site of the impact, ethane emission increased above levels measured well outside the impact region. Radiative transfer analysis indicates increased ethane mole fraction (30% greater). Variation in the measured continuum level and line intensities within 75deg of the impact longitude indicate the presence of an opacity source (haze) at altitudes near and above the tropopause and as high as the 10-mbar level near the impact site. The indication of possible haze opacity up to the 10-mbar level in the atmosphere is consistent with measurements made by HIPWAC's predecessor as part of the IRTF Shoemaker Levy-9 campaign in 1994.

Fast, Kelly↗
NASA NTRSDate not supplied

Dynamics and Structure of Main-Sequence Stars with Shallow Convection Zones

A dramatic increase in observational data from NASA’s Kepler, K2, and TESS missions and supporting ground-based observatories has opened new opportunities to investigate the internal structure, dynamics, and evolution of stars and their atmospheres. We present 3D radiative MHD simulations for several main-sequence stars with masses from 1.4 to 1.5M sun. The simulations are performed using the "StellarBox" code developed for modeling stellar turbulent convection and atmospheres with a high degree of realism. This presentation discusses similarities and differences between 3D realistic-type and 1D mixing-length models with regard to structural, thermodynamic, and turbulent property variations from the radiative zone to the convection zone and photosphere.

SMD↗
NASA NTRS2004

Phylogenetic and physiological diversity of microorganisms isolated from a deep greenland glacier ice core

We studied a sample from the GISP 2 (Greenland Ice Sheet Project) ice core to determine the diversity and survival of microorganisms trapped in the ice at least 120,000 years ago. Previously, we examined the phylogenetic relationships among 16S ribosomal DNA (rDNA) sequences in a clone library obtained by PCR amplification from genomic DNA extracted from anaerobic enrichments. Here we report the isolation of nearly 800 aerobic organisms that were grouped by morphology and amplified rDNA restriction analysis patterns to select isolates for further study. The phylogenetic analyses of 56 representative rDNA sequences showed that the isolates belonged to four major phylogenetic groups: the high-G+C gram-positives, low-G+C gram-positives, Proteobacteria, and the Cytophaga-Flavobacterium-Bacteroides group. The most abundant and diverse isolates were within the high-G+C gram-positive cluster that had not been represented in the clone library. The Jukes-Cantor evolutionary distance matrix results suggested that at least 7 isolates represent new species within characterized genera and that 49 are different strains of known species. The isolates were further categorized based on the isolation conditions, temperature range for growth, enzyme activity, antibiotic resistance, presence of plasmids, and strain-specific genomic variations. A significant observation with implications for the development of novel and more effective cultivation methods was that preliminary incubation in anaerobic and aerobic liquid prior to plating on agar media greatly increased the recovery of CFU from the ice core sample.

Bacteria/classification/genetics/isolation & purif↗
DOE OSTI2018

Novel brain-expressed noncoding RNA, HSTR1, identified at a human-specific variable number tandem repeat locus with a human accelerated region

Highlights: • A novel noncoding RNA gene HSTR1 is expressed in human brain and testis. • The evolutionary accelerated region showed enhanced promoter activity in human. • The variable number tandem repeat in HSTR1 is associated with its RNA stability. The evolutionary conserved genomic sequences that have acquired significantly increased number of nucleotide substitutions specifically in the human lineage, called human accelerated regions (HARs), have been identified as candidate genomic regions that have contributed to the evolution of human-specific traits. A number of HARs were indeed shown to have novel enhancer activity and be associated with human-specific brain development and with cognition and social behavior. It is therefore of great importance to investigate the details of genomic function of each HAR to understand the roles of HARs as critical contributors to the genetic basis of human evolution. In this study, we identified a previously unannotated brain-expressed noncoding RNA gene, HSTR1, at a human-specific tandem repeat locus. Notably, the 5′ flanking sequence of HSTR1 showed the signature of HARs and the dramatic human-specific enhancement of promoter activity, providing the evidence of positive selection to increase the expression level of HSTR1 during human evolution. We also revealed that the tandem repeat number in HSTR1 was highly variable among individual alleles and affected the stability of HSTR1 RNA, suggesting variation in the activity of HSTR1 between human individuals. Our work thus provides a novel candidate gene that potentially contributed to the evolution of the human brain. It may also underpin some of the variation between human brains.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

The Fecal Microbial Community of Breast-fed Infants from Armenia and Georgia

Multiple factors help shape the infant intestinal microbiota early in life. Environmental conditions such as the presence of bioactive molecules from breast milk dictate gut microbial growth and survival. Infants also receive distinct, personalized, bacterial exposures leading to differential colonization. Microbial exposures and gut environmental conditions differ between infants in different locations, as does the typical microbial community structure in an infant’s gut. Here we evaluate potential influences on the infant gut microbiota through a longitudinal study on cohorts of breast-fed infants from the neighboring countries of Armenia and Georgia, an area of the world for which the infant microbiome has not been previously investigated. Marker gene sequencing of 16S ribosomal genes revealed that the gut microbial communities of infants from these countries were dominated by bifidobacteria, were different from each other, and were marginally influenced by their mother’s secretor status. Species-level differences in the bifidobacterial communities of each country and birth method were also observed. These community differences suggest that environmental variation between individuals in different locations may influence the gut microbiota of infants.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1979

Martian soil stratigraphy and rock coatings observed in color-enhanced Viking Lander images

Subtle color variations of martian surface materials were enhanced in eight Viking Lander (VL) color images. Well-defined soil units recognized at each site (six at VL-1 and four at VL-2), are identified on the basis of color, texture, morphology, and contact relations. The soil units at the Viking 2 site form a well-defined stratigraphic sequence, whereas the sequence at the Viking 1 site is only partially defined. The same relative soil colors occur at the two sites, suggesting that similar soil units are widespread on Mars. Several types of rock surface materials can be recognized at the two sites; dark, relatively 'blue' rock surfaces are probably minimally weathered igneous rock, whereas bright rock surfaces, with a green/(blue + red) ratio higher than that of any other surface material, are interpreted as a weathering product formed in situ on the rock. These rock surface types are common at both sites. Soil adhering to rocks is common at VL-2, but rare at VL-1. The mechanism that produces the weathering coating on rocks probably operates planet-wide.

Strickland, E. L., III↗