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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Extensive sampling of basidiomycete genomes demonstrates inadequacy of the white-rot/brown-rot paradigm for wood decay fungi

Basidiomycota (basidiomycetes) make up 32% of the described fungi and include most wood-decaying species, as well as pathogens and mutualistic symbionts. Wood-decaying basidiomycetes have typically been classified as either white rot or brown rot, based on the ability (in white rot only) to degrade lignin along with cellulose and hemicellulose. Prior genomic comparisons suggested that the two decay modes can be distinguished based on the presence or absence of ligninolytic class II peroxidases (PODs), as well as the abundance of enzymes acting directly on crystalline cellulose (reduced in brown rot). To assess the generality of the white-rot/brown-rot classification paradigm, we compared the genomes of 33 basidiomycetes, including four newly sequenced wood decayers, and performed phylogenetically informed principal-components analysis (PCA) of a broad range of gene families encoding plant biomass-degrading enzymes. The newly sequenced Botryobasidium botryosum and Jaapia argillacea genomes lack PODs but possess diverse enzymes acting on crystalline cellulose, and they group close to the model white-rot species Phanerochaete chrysosporium in the PCA. Furthermore, laboratory assays showed that both B. botryosum and J. argillacea can degrade all polymeric components of woody plant cell walls, a characteristic of white rot. We also found expansions in reducing polyketide synthase genes specific to the brown-rot fungi. Our results suggest a continuum rather than a dichotomy between the white-rot and brown-rot modes of wood decay. A more nuanced categorization of rot types is needed, based on an improved understanding of the genomics and biochemistry of wood decay.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Quantification of the transferability of a designed protein specificity switch reveals extensive epistasis in molecular recognition

Re-engineering protein–protein recognition is an important route to dissecting and controlling complex interaction networks. Experimental approaches have used the strategy of “second-site suppressors,” where a functional interaction is inferred between two proteins if a mutation in one protein can be compensated by a mutation in the second. Mimicking this strategy, computational design has been applied successfully to change protein recognition specificity by predicting such sets of compensatory mutations in protein–protein interfaces. To extend this approach, it would be advantageous to be able to “transplant” existing engineered and experimentally validated specificity changes to other homologous protein–protein complexes. Here, we test this strategy by designing a pair of mutations that modulates peptide recognition specificity in the Syntrophin PDZ domain, confirming the designed interaction biochemically and structurally, and then transplanting the mutations into the context of five related PDZ domain–peptide complexes. We find a wide range of energetic effects of identical mutations in structurally similar positions, revealing a dramatic context dependence (epistasis) of designed mutations in homologous protein–protein interactions. To better understand the structural basis of this context dependence, we apply a structure-based computational model that recapitulates these energetic effects and we use this model to make and validate forward predictions. The context dependence of these mutations is captured by computational predictions, our results both highlight the considerable difficulties in designing protein–protein interactions and provide challenging benchmark cases for the development of improved protein modeling and design methods that accurately account for the context.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Modelling multiple occurrences of activities during a day: An extension of the MDCEV model

The increased interest in time use among transport researchers has led to a search for flexible but tractable models of time use, such as Bhat's Multiple Discrete Continuous Extreme Value (MDCEV) model. MDCEV formulations typically model aggregate time allocation into different activity types during a given period, such as the amount of time spent working and shopping in a day. While these applications provide valuable insights into activity participation, they ignore disaggregate activity-episodes, that is the fact that people might split their total time spent working in multiple separate blocks, with breaks or other activities in between. Insights into this splitting into episodes are necessary for predicting trips and understanding time use satiation. We propose a modified MDCEV model where an activity-episode, rather than an activity type, is the basic choice alternative, using a modified utility function to capture the reduced likelihood of individuals performing a very large number of episodes of the same activity. Results from two large revealed preference datasets exhibit equivalent forecast accuracy between the traditional and proposed approach at an aggregate level, but the latter also provides insights on the number and duration of activity-episodes with significant accuracy.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Temporal evolution of solar wind ion composition and their source coronal holes during the declining phase of cycle 23. I. Low-latitude extension of polar coronal holes

We analyzed 27 solar wind (SW) intervals during the declining phase of cycle 23, whose source coronal holes (CHs) can be unambiguously identified and are associated with one of the polar CHs. We found that the SW ions have a temporal trend of decreasing ionization state, and such a trend is different between the slow and fast SW. The photospheric magnetic field, both inside and at the outside boundary of the CH, also exhibits a trend of decrease with time. However, EUV line emissions from different layers of the atmosphere exhibit different temporal trends. The coronal emission inside the CH generally increases toward the CH boundary as the underlying field increases in strength and becomes less unipolar. In contrast, this relationship is not seen in the coronal emission averaged over the entire CH. For C and O SW ions that freeze-in at lower altitude, stronger correlation between their ionization states and field strength (both signed and unsigned) appears in the slow SW, while for Fe ions that freeze-in at higher altitude, stronger correlation appears in the fast SW. Such correlations are seen both inside the CH and at its boundary region. On the other hand, the coronal electron temperature correlates well with the SW ion composition only in the boundary region. Our analyses, although not able to determine the likely footpoint locations of the SW of different speeds, raise many outstanding questions for how the SW is heated and accelerated in response to the long-term evolution of the solar magnetic field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The AstraLux multiplicity survey: Extension to late M-dwarfs

The distribution of multiplicity among low-mass stars is a key issue to understanding the formation of stars and brown dwarfs, and recent surveys have yielded large enough samples of nearby low-mass stars to study this issue statistically to good accuracy. Previously, we have presented a multiplicity study of ∼700 early/mid M-type stars observed with the AstraLux high-resolution Lucky Imaging cameras. Here, we extend the study of multiplicity in M-type stars through studying 286 nearby mid/late M-type stars, bridging the gap between our previous study and multiplicity studies of brown dwarfs. Most of the targets have been observed more than once, allowing us to assess common proper motion to confirm companionship. We detect 68 confirmed or probable companions in 66 systems, of which 41 were previously undiscovered. Detections are made down to the resolution limit of ∼100 mas of the instrument. The raw multiplicity in the AstraLux sensitivity range is 17.9%, leading to a total multiplicity fraction of 21%-27% depending on the mass ratio distribution, which is consistent with being flat down to mass ratios of ∼0.4, but cannot be stringently constrained below this value. The semi-major axis distribution is well represented by a log-normal function with μ{sub a} = 0.78 and σ{sub a} = 0.47, which is narrower and peaked at smaller separations than for a Sun-like sample. This is consistent with a steady decrease in average semi-major axis from the highest-mass binary stars to the brown dwarf binaries.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Classical bulges, supermassive black holes, and AGN feedback: Extension to low-mass galaxies

The empirical model of Lu et al. for the relation between star formation rate and halo mass growth is adopted to predict the classical bulge mass (M{sub cb})–total stellar mass (M{sub ⋆}) relation for central galaxies. The assumption that the supermassive black hole (SMBH) mass (M{sub BH}) is directly proportional to the classical bulge mass, with the proportionality given by that for massive galaxies, predicts a M{sub BH}−M{sub ⋆} relation that matches well the observed relation for different types of galaxies. In particular, the model reproduces the strong transition at M{sub ⋆}=10{sup 10.5}−10{sup 11} M{sub ⊙}, below which M{sub BH} drops rapidly with decreasing M{sub ⋆}. Our model predicts a new sequence at M{sub ⋆}<10{sup 10.5} M{sub ⊙}, where M{sub BH}∝M{sub ⋆} but the amplitude is a factor of ∼50 lower than the amplitude of the sequence at M{sub ⋆}>10{sup 11} M{sub ⊙}. If all SMBHs grow through similar quasar modes with a feedback efficiency of a few percent, then the energy produced in low-mass galaxies at redshift z≳2 can heat the circumgalactic medium up to a specific entropy level that is required to prevent excessive star formation in low-mass dark matter halos.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE HYPERFINE STRUCTURE OF THE ROTATIONAL SPECTRUM OF HDO AND ITS EXTENSION TO THE THz REGION: ACCURATE REST FREQUENCIES AND SPECTROSCOPIC PARAMETERS FOR ASTROPHYSICAL OBSERVATIONS

The rotational spectrum of the mono-deuterated isotopologue of water, HD{sup 16}O, has been investigated in the millimeter- and submillimeter-wave frequency regions, up to 1.6 THz. The Lamb-dip technique has been exploited to obtain sub-Doppler resolution and to resolve the hyperfine (hf) structure due to the deuterium and hydrogen nuclei, thus enabling the accurate determination of the corresponding hf parameters. Their experimental determination has been supported by high-level quantum-chemical calculations. The Lamb-dip measurements have been supplemented by Doppler-limited measurements (weak high-J and high-frequency transitions) in order to extend the predictive capability of the available spectroscopic constants. The possibility of resolving hf splittings in astronomical spectra has been discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The distances to open clusters from main-sequence fitting. V. Extension of color calibration and test using cool and metal-rich stars in NGC 6791

We extend our effort to calibrate stellar isochrones in the Johnson–Cousins (BVI{sub C}) and the 2MASS (JHK{sub s}) filter systems based on observations of well-studied open clusters. Using cool main-sequence (MS) stars in Praesepe, we define empirical corrections to the Lejeune et al. color–effective temperature (T{sub eff}) relations down to T{sub eff}∼3600 K, complementing our previous work based on the Hyades and the Pleiades. We apply empirically corrected isochrones to existing optical and near-infrared photometry of cool (T{sub eff}≲5500 K) and metal-rich ([Fe/H]= +0.37) MS stars in NGC 6791. The current methodology relies on an assumption that color–T{sub eff} corrections are independent of metallicity, but we find that estimates of color excess and distance from color–magnitude diagrams with different color indices converge on each other at the precisely known metallicity of the cluster. Along with a satisfactory agreement with eclipsing binary data in the cluster, we view the improved internal consistency as a validation of our calibrated isochrones at super-solar metallicities. For very cool stars (T{sub eff}≲4800 K), however, we find that B − V colors of our models are systematically redder than the cluster photometry by ∼0.02 mag. We use color–T{sub eff} transformations from the infrared flux method and alternative photometry to examine a potential color-scale error in the input cluster photometry. After excluding B − V photometry of these cool MS stars, we derive E(B − V)=0.105±0.014, [M/H] = +0.42±0.07, (m − M){sub 0}=13.04±0.08, and the age of 9.5 ± 0.3 Gyr for NGC 6791.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE BOLOCAM GALACTIC PLANE SURVEY. IX. DATA RELEASE 2 AND OUTER GALAXY EXTENSION

We present a re-reduction and expansion of the Bolocam Galactic Plane Survey (BGPS), first presented by Aguirre et al. and Rosolowsky et al. The BGPS is a 1.1 mm survey of dust emission in the Northern galactic plane, covering longitudes –10° < l < 90° and latitudes |b| < 0.°5 with a typical 1σ rms sensitivity of 30-100 mJy in a ∼33'' beam. Version 2 of the survey includes an additional ∼20 deg{sup 2} of coverage in the third and fourth quadrants and ∼2 deg{sup 2} in the first quadrant. The new data release has improved angular recovery, with complete recovery out to ∼80'' and partial recovery to ∼300'', and reduced negative bowls around bright sources resulting from the atmospheric subtraction process. We resolve the factor of 1.5 flux calibration offset between the v1.0 data release and other data sets and determine that there is no offset between v2.0 and other data sets. The v2.0 pointing accuracy is tested against other surveys and is demonstrated to be accurate and an improvement over v1.0. We present simulations and tests of the pipeline and its properties, including measurements of the pipeline's angular transfer function. The Bolocat cataloging tool was used to extract a new catalog, which includes 8594 sources, with 591 in the expanded regions. We have demonstrated that the Bolocat 40'' and 80'' apertures are accurate even in the presence of strong extended background emission. The number of sources is lower than in v1.0, but the amount of flux and area included in identified sources is larger.

79 ASTRONOMY AND ASTROPHYSICS↗