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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Model-independent Exoplanet Transit Spectroscopy

We propose a new data analysis method for obtaining transmission spectra of exoplanet atmospheres and brightness variation across the stellar disk from transit observations. The new method is capable of recovering exoplanet atmosphere absorption spectra and stellar specific intensities without relying on theoretical models of stars and planets. We simultaneously fit both stellar specific intensity and planetary radius directly to transit light curves. This allows stellar models to be removed from the data analysis. Furthermore, we use a data quality weighted filtering technique to achieve an optimal trade-off between spectral resolution and reconstruction fidelity homogenizing the signal-to-noise ratio across the wavelength range. Such an approach is more efficient than conventional data binning onto a low-resolution wavelength grid. We demonstrate that our analysis is capable of reproducing results achieved by using an explicit quadratic limb-darkening equation and that the filtering technique helps eliminate spurious spectral features in regions with strong telluric absorption. The method is applied to the VLT FORS2 observations of the exoplanets GJ 1214 b and WASP-49 b, and our results are in agreement with previous studies. Comparisons between obtained stellar specific intensity and numerical models indicates that the method is capable of accurately reconstructing the specific intensity. The proposed method enables more robust characterization of exoplanetary atmospheres by separating derivation of planetary transmission and stellar specific intensity spectra (that is model-independent) from chemical and physical interpretation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

An Independent Analysis of the Spitzer/IRAC Phase Curves of WASP43 b

We present here a reanalysis of the Spitzer Space Telescope phase curves of the hot Jupiter WASP43 b, using the wavelet pixel-independent component analysis, a blind signal-source separation method. The data analyzed were recorded with the Infrared Array Camera and consisted of two visits at 3.6 μm, and one visit at 4.5 μm, each visit covering one transit and two eclipse events. To test the robustness of our technique we repeated the analysis on smaller portions of the phase curves, and by employing different instrument ramp models. Our reanalysis presents significant updates of the planetary parameters compared to those reported in the original phase curve study of WASP43 b. In particular, we found (1) higher nightside temperatures, (2) smaller hotspot offsets, (3) a greater consistency (∼1σ) between the two 3.6 μm visits, and (4) a greater similarity with the predictions of the atmospheric circulation models. Our parameter results are consistent within 1σ with those reported by a recent reanalysis of the same data sets. For each visit we studied the variation of the retrieved transit parameters as a function of various sets of stellar limb-darkening coefficients, finding significant degeneracy between the limb-darkening models and the analysis output. Furthermore, we performed the analysis of the single transit and eclipse events, and we examined the differences between these results with the ones obtained with the whole phase curve. Finally we provide a formula useful to optimize the trade-off between precision and duration of observations of transiting exoplanets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Model-independent Constraints on Cosmic Curvature and Opacity

In this paper, we propose to estimate the spatial curvature of the universe and the cosmic opacity in a model-independent way with expansion rate measurements, H ( z ), and type Ia supernova (SNe Ia). On the one hand, using a nonparametric smoothing method Gaussian process, we reconstruct a function H ( z ) from opacity-free expansion rate measurements. Then, we integrate the H ( z ) to obtain distance modulus μ {sub H}, which is dependent on the cosmic curvature. On the other hand, distances of SNe Ia can be determined by their photometric observations and thus are opacity-dependent. In our analysis, by confronting distance moduli μ {sub H} with those obtained from SNe Ia, we achieve estimations for both the spatial curvature and the cosmic opacity without any assumptions for the cosmological model. Here, it should be noted that light curve fitting parameters, accounting for the distance estimation of SNe Ia, are determined in a global fit together with the cosmic opacity and spatial curvature to get rid of the dependence of these parameters on cosmology. In addition, we also investigate whether the inclusion of different priors for the present expansion rate ( H {sub 0}: global estimation, 67.74 ± 0.46 km s{sup −1} Mpc{sup −1}, and local measurement, 73.24 ± 1.74 km s{sup −1} Mpc{sup −1}) exert influence on the reconstructed H ( z ) and the following estimations of the spatial curvature and cosmic opacity. Results show that, in general, a spatially flat and transparent universe is preferred by the observations. Moreover, it is suggested that priors for H {sub 0} matter a lot. Finally, we find that there is a strong degeneracy between the curvature and the opacity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Structure of Geobacter OmcZ filaments suggests extracellular cytochrome polymers evolved independently multiple times

While early genetic and low-resolution structural observations suggested that extracellular conductive filaments on metal-reducing organisms such as Geobacter were composed of type IV pili, it has now been established that bacterial c -type cytochromes can polymerize to form extracellular filaments capable of long-range electron transport. Atomic structures exist for two such cytochrome filaments, formed from the hexaheme cytochrome OmcS and the tetraheme cytochrome OmcE. Due to the highly conserved heme packing within the central OmcS and OmcE cores, and shared pattern of heme coordination between subunits, it has been suggested that these polymers have a common origin. We have now used cryo-electron microscopy (cryo-EM) to determine the structure of a third extracellular filament, formed from the Geobacter sulfurreducens octaheme cytochrome, OmcZ. In contrast to the linear heme chains in OmcS and OmcE from the same organism, the packing of hemes, heme:heme angles, and between-subunit heme coordination is quite different in OmcZ. A branched heme arrangement within OmcZ leads to a highly surface exposed heme in every subunit, which may account for the formation of conductive biofilm networks, and explain the higher measured conductivity of OmcZ filaments. This new structural evidence suggests that conductive cytochrome polymers arose independently on more than one occasion from different ancestral multiheme proteins.

Cytochromes/metabolism↗
DOE OSTI2024

Structural and biophysical analysis of a Haemophilus influenzae tripartite ATP-independent periplasmic (TRAP) transporter

Tripartite ATP-independent periplasmic (TRAP) transporters are secondary-active transporters that receive their substrates via a soluble-binding protein to move bioorganic acids across bacterial or archaeal cell membranes. Recent cryo-electron microscopy (cryo-EM) structures of TRAP transporters provide a broad framework to understand how they work, but the mechanistic details of transport are not yet defined. Here we report the cryo-EM structure of the Haemophilus influenzae N-acetylneuraminate TRAP transporter (HiSiaQM) at 2.99 Å resolution (extending to 2.2 Å at the core), revealing new features. The improved resolution (the previous HiSiaQM structure is 4.7 Å resolution) permits accurate assignment of two Na + sites and the architecture of the substrate-binding site, consistent with mutagenic and functional data. Moreover, rather than a monomer, the HiSiaQM structure is a homodimer. We observe lipids at the dimer interface, as well as a lipid trapped within the fusion that links the SiaQ and SiaM subunits. We show that the affinity (K D ) for the complex between the soluble HiSiaP protein and HiSiaQM is in the micromolar range and that a related SiaP can bind HiSiaQM. This work provides key data that enhances our understanding of the ‘elevator-with-an-operator’ mechanism of TRAP transporters.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Tokamak-independent Software Analysis Suite for Multi-Spectral Line-Polarization MSE diagnostics

A tokamak-independent analysis suite has been developed to process data from Motional Stark Effect (MSE) diagnostics. The software supports multi-spectral line-polarization MSE diagnostics which simultaneously measure emission at the MSE sigma and pi lines as well as at two `background' wavelengths that are displaced from the MSE spectrum by a few nanometers. This analysis accurately estimates the amplitude of partially-polarized background light at the sigma and pi wavelengths even in situations where the background light changes rapidly in time and space. The signal amplitude at many frequencies is computed using a numerical-beat algorithm which allows the retardance of the MSE photo-elastic modulators (PEMs) to be monitored during routine operation. It also allows the use of summed intensities at multiple frequencies in the calculation of polarization direction, which increases the effective signal strength and reduces sensitivity to PEM retardance drift. The software allows the polarization angles to be corrected for calibration drift using a system that illuminates the MSE diagnostic with polarized light at four known polarization angles within ten seconds of a plasma discharge The software suite is modular, parallelized, and portable to other facilities. (2016-06-06)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Tokamak-independent Software Analysis Suite for Multi-Spectral Line-Polarization MSE diagnostics

A tokamak-independent analysis suite has been developed to process data from Motional Stark Effect (MSE) diagnostics. The software supports multi-spectral line-polarization MSE diagnostics which simultaneously measure emission at the MSE sigma and pi lines as well as at two `background' wavelengths that are displaced from the MSE spectrum by a few nanometers. This analysis accurately estimates the amplitude of partially-polarized background light at the sigma and pi wavelengths even in situations where the background light changes rapidly in time and space. The signal amplitude at many frequencies is computed using a numerical-beat algorithm which allows the retardance of the MSE photo-elastic modulators (PEMs) to be monitored during routine operation. It also allows the use of summed intensities at multiple frequencies in the calculation of polarization direction, which increases the effective signal strength and reduces sensitivity to PEM retardance drift. The software allows the polarization angles to be corrected for calibration drift using a system that illuminates the MSE diagnostic with polarized light at four known polarization angles within ten seconds of a plasma discharge The software suite is modular, parallelized, and portable to other facilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1966

Concept for passive system to control gas flow independently of temperature

Volumetric flow rate of gas is maintained at a constant value independent of temperature by passing the gas through a parallel or series combination of turbulent flow and laminar flow restrictors. By proper combination of restrictors, the flow rate may be automatically made to vary as an increasing or decreasing function of temperature.

Chavez, E. S.↗