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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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NASA NTRS1984

Mid-infrared Spectroscopy of Planetary Nebulae

The application of infrared spectral lines observed in part of the broadened spectral range (18 to 36 microns) to planetary nebula studies is discussed. Infrared spectral lines in the mid-infrared supply information about planetary nebulae which both supplement and complement optical results. Their utility lies mainly in the insensitivity of the line intensities to temperature variations or uncertainties, in contrast to the behavior of optical emission. This in turn leads to more accurate ionic abundances than presently available from optical lines. Although densities from optical line ratios are not very sensitive to temperature, the lines are weighted toward regions of higher temperatures. A comparison with infrared densities from the same ions therefore provide clues to the density and/or temperature variations within nebulae. Temperatures from OIV and NeV ions show a part of high-excitation nebulae previously inaccessible. They verify the picture of physical processes in the HeIII zone.

Shure, M. A.↗
NASA NTRS2016

Enabling the Direct Detection of Earth-Sized Exoplanets with the LBTI HOSTS Project: A Progress Report

NASA has funded a project called the Hunt for Observable Signatures of Terrestrial Systems (HOSTS) to survey nearby solar type stars to determine the amount of warm zodiacal dust in their habitable zones. The goal is not only to determine the luminosity distribution function but also to know which individual stars have the least amount of zodiacal dust. It is important to have this information for future missions that directly image exoplanets as this dust is the main source of astrophysical noise for them. The HOSTS project utilizes the Large Binocular Telescope Interferometer (LBTI), which consists of two 8.4-m apertures separated by a 14.4-m baseline on Mt. Graham, Arizona. The LBTI operates in a nulling mode in the mid-infrared spectral window (8-13 micrometers), in which light from the two telescopes is coherently combined with a 180 degree phase shift between them, producing a dark fringe at the location of the target star. In doing so the starlight is greatly reduced, increasing the contrast, analogous to a coronagraph operating at shorter wavelengths. The LBTI is a unique instrument, having only three warm reflections before the starlight reaches cold mirrors, giving it the best photometric sensitivity of any interferometer operating in the mid-infrared. It also has a superb Adaptive Optics (AO) system giving it Strehl ratios greater than 98% at 10 micrometers. In 2014 into early 2015 LBTI was undergoing commissioning. The HOSTS. project team passed its Operational Readiness Review (ORR) in April 2015. The team recently published papers on the target sample, modeling of the nulled disk images, and initial results such as the detection of warm dust around eta Corvi. Recently a paper was published on the data pipeline and on-sky performance. An additional paper is in preparation on Beta Leo. We will discuss the scientific and programmatic context for the LBTI project, and we will report recent progress, new results, and plans for the science verification phase that started in February 2016, and for the survey.

Hunt for Observable Signatures of Terrestrial Syst↗
NASA NTRS1994

Hydrodynamics of binary coalescence. 1: Polytropes with stiff equations of state

We performed a series of three-dimensional hydrodynamic calculations of binary coalescence using the smoothed particle hydrodynamics (SPH) method. The initial conditions are exact polytropic equilibrium configurations on the verge of dynamical instability. We consider synchronized equilbria only and concentrate on stiff equations of state, with adiabatic Gamma greater than 5/3. We assume that the polytropic constants (K identically equal to P/(rho(exp Gamma)) are the same for both components. These conditions apply well to models of neutron star binaries. Accordingly, we discuss our results in the context of the Laser Interferometer Gravitational-Wave Observatory (LIGO) project, and we calculate the emission of gravitational radiation in the quadruple approximation. The fully nonlinear development of the instability is followed using SPH until a new equilibrium configuration is reached by the system. We find that the properties of this final configuration depend sensitively on both the compressibility and mass ratio. An axisymmetric merged configuration is always produced when the adiabatic exponent Gamma approximately less than 2.3. As a consequence, the emission of gravitational radiation shuts off abruptly right after the onset of dynamical instability. In contrast, triaxial merged configurations are obtained when Gamma approximately greater than 2.3, and the system continues to emit gravitational waves after the final coalescence. Systems with mass ratios q not equal to 1 typically become dynamically unstable before the onset of mass transfer. Stable mass transfer from one neutron star to another in a close binary is therefore probably ruled out. For a mass ratio q approximately less than 0.5, however, dynamical mass transfer can temporarily retard the coalescence by causing a rapid reexpansion of the binary into a new, slightly eccentric but dynamically stable orbit. The maximum amplitude h(sub max) and peak luminosity L(sub max) of the gravitational waves emitted during the final coalescence are nearly independent of Gamma, but depend sensitively on the mass ratio q. The approximate scalings we find are h(sub max) varies as q(exp 2) and L(sub max) varies as q(exp 6) for q close to unity.

Rasio, Frederic A.↗
NASA NTRS1982

Influence of gravity driven convection on the directional solidification of Bi/MnBi eutectic composites

The role of gravity on Bridgman-Stockharger directional solidification of eutectic Bi/MnBi has been studied in reduced gravity aboard NASA sounding rocket SPAR flight experiments and contrasted with normal gravity investigations. The directional solidification of eutectic Bi/MnBi results in a low volume fraction, faceted/nonfaceted aligned rod eutectic whose MnBi rod size, interrod spacing, thermal and magnetic properties are sensitive functions of solidification processing conditions. The morphology of the low-gravity samples showed striking differences compared with identically processed, normal gravity samples grown in the same apparatus. The MnBi rod diameter and interrod spacing distributions were significantly smaller, approximately 50 percent, for the low gravity samples compared with identically processed one gravity samples. Accompanying the smaller MnBi rod diameters observed in the flight samples, was an increase in permanent magnet properties which reached greater than 97 percent of the theoretical maximum. Gravitationally induced thermal instabilities in one-gravity which result in irregular interface movement and associated difficulty of the faceted MnBi phase to branch are suggested to explain the morphological differences between one and low gravity solidification.

Pirich, R. G.↗
NASA NTRSDate not supplied

TPSAS-NF1676L-27509-DND

The information about composition of aerosols has a great importance for monitoring and understanding of climate and environment dynamics. Such information can be obtained using situ measurements or chemical transport models. However, in situ sampling has limited spatial and temporal coverage, while estimations have large uncertainties. The present work enables the monitoring of aerosol chemical species from space-borne observations, providing observationally-based results with spatial and temporal coverage. Following the ideas of Schuster et al.(2005, 2009, 2016), we retrieve chemical composition directly from satellite observations without intermediate retrieval of the refractive index (in contrast with Schuster's approach). This approach is expected to reduce the influence of modeling uncertainties, and to provide additional constraints in situations where remote sensing observations do not have enough spectral sensitivity to refractive index. One of principal difficulties is the identification of an adequate model for linking refractive index to chemical composition. Therefore, the initial effort of this work has focused on identifying an optimal physico-chemistry to refractive index conversion model. With that purpose, we first tested the retrieval approach using a simplified volume-weighting model and updated by the Maxwell Garnett mixing model. This concept was incorporated into the GRASP algorithm designed to retrieve an extended set of atmospheric parameters from remote sensing observations. Then a series of sensitivity tests using synthetic data of POLDER/PARASOL were conducted, and followed by inversion of real PARASOL observations over Africa. The sensitivity tests showed that these two models allow the retrieval to distinguish amongst the assumed chemical species. Results obtained from real PARASOL data demonstrated good agreement with the optical characteristics provided by AERONET. In addition, the obtained patterns of chemical component distribution agreed with known physical expectations. We also compared the chemical composition retrievals to GOCART model simulations and obtained good consistencies.

Lei Li↗
NASA NTRS1981

Earth rotation from lunar laser ranging

Since the time when the first laser retroreflector was placed on the lunar surface by the Apollo 11 astronauts, lunar laser ranging (LLR) has led to advances in a wide range of disciplines, including the study of variations in the rotation of the earth. The conventional techniques used to monitor earth rotation suffer from lack of precision on time scales of a few months and less. LLR, by contrast, makes it possible to monitor small changes in earth rotation with a temporal resolution of the order of 1 day. Studies of earth rotation by LLR are discussed, taking into account data sensitivity, aspects of data analysis, the variation of latitude, and UTO, the mean solar time at the site as affected by polar motion.

Langley, R. B.↗
NASA NTRS1990

Age effects on rat hindlimb muscle atrophy during suspension unloading

The effects of hindlimb unloading on muscle mass and biochemical responses were examined and compared in adult (450-g) and juvenile (200-g) rats after 1, 7, or 14 days of whole-body suspension. Quantitatively and qualitatively the soleus, gastrocnemius, plantaris, and extensor digitorum longus (EDL) muscles of the hindlimb exhibited a differential sensitivity to suspension and weightlessness unloading in both adults and juveniles. The red slow-twitch soleus exhibited the most pronounced atrophy under both conditions, with juvenile responses being greater than adult. In contrast, the fast-twitch EDL hypertrophied during suspension and atrophied during weightlessness, with no significant difference between adults and juveniles. Determination of biochemical parameters (total protein, RNA, and DNA) indicates a less rapid rate of response in adult muscles.

Steffen, Joseph M.↗
NASA NTRS1997

Global Geodetic Signatures of the Antarctic Ice Sheet

Four scenarios of present day Antarctic ice sheet mass change are developed from comprehensive reviews of the available glaciological and oceanographic evidence. The gridded scenarios predict widely varying contributions to secular sea level change xi ranging from -1.1 to 0.45 mm/yr, and predict polar motion m and time-varying low-degree gravitational coefficients J(sub l) that differ significantly from earlier estimates. A reasonably linear relationship between the rate of sea level change from Antarctica xi(sub A) and the predicted Antarctic J(sub l) is found for the four scenarios. This linearity permits a series of forward models to be constructed that incorporate the effects of ice mass changes in Antarctica, Greenland, and distributed smaller glaciers, as well as postglacial rebound (assuming the ICE-3G deglaciation history), with the goal of obtaining optimum reconciliation between observed constraints on J(sub l) and sea level rise xi. Numerous viable combinations of lower mantle viscosity and hydrologic sources are found that safely "observed" in the range of 1 to 2-2.5 mm/yr and observed J(sub l) for degrees 2, 3, and 4. In contrast, rates of global sea level rise above 2.5 mm/yr are inconsistent with available J(sub l) observations. The successful composite models feature a pair of lower mantle viscosity solutions arising from the sensitivity of J(sub l) to glacial rebound. The paired values are well separated at xi = 1 mm/yr, but move closer together as xi is increased, and, in fact, merge around xi = 2 - 2.5 mm/yr, revealing an intimate relation between xi and preferred lower mantle viscosity. This general pattern is quite robust and persists for different J(sub l) solutions, for variations in source assumptions, and for different styles of lower mantle viscosity stratification. Tighter J(sub l) constraints for l greater than 2 may allow some viscosity stratification schemes and source assumptions to be excluded in the future. For a given total observed xi the sea level rise from Antarctica xi(sub A) is tightly constrained and ranges from 0 to + 1 mr/yr (corresponding to an ablating ice sheet) as estimates of xi are raised from 1 to 2.5 mm/yr. However, when the degree 3 zonal harmonic constraint is removed, the solutions show little sensitivity to Antarctic mass balance, emphasizing the need for a well determined odd-degree secular zonal harmonic for determining polar ice mass balance.

James, Thomas S.↗
NASA NTRS2024

Decreased Northern Hemisphere Precipitation from Consecutive CO 2 Doublings Is Associated with Significant AMOC Weakening

Previous studies found many climate properties such as northern hemisphere (NH) surface temperature and precipitation respond non-monotonically when CO2 is increased from 1× to 8×CO2 relative to pre-industrial levels. Here, we explore the robustness of the non-monotonicity in the NH precipitation response in 11 coupled climate models. Eight models show a decrease in NH precipitation under repeated CO2 doubling, indicating that the non-monotonic response is a common but not universal result. Although common, the critical CO2 level where the NH precipitation decrease first occurs differs widely across models, ranging from 2×CO2 to 8×CO2. These models also show a prominent weakening in the Atlantic meridional overturning circulation (AMOC) at the same critical CO2 level, with the AMOC weakening leading the precipitation decrease. The sensitivities of NH precipitation and the AMOC to CO2 doublings are positively correlated, especially when the AMOC weakens beyond 10 Sv. This suggests that the differences in models' AMOC response can explain their contrasting NH precipitation responses, where models with a large AMOC weakening have decreased NH precipitation. Regionally, this decrease in NH precipitation is the most prominent over the North Atlantic, Europe and the tropical Pacific. Our results suggest that special care must be taken with the use of pattern scaling to inform regional climate decision-making.

Atlantic meridional overturning circulation↗
NASA NTRS1994

Ice nucleation in the upper troposphere: Sensitivity to aerosol number density, temperature, and cooling rate

We have investigated the processes that control ice crystal nucleation in the upper troposphere using a numerical model. Nucleation of ice resulting from cooling was simulated for a range of aerosol number densities, initial temperatures, and cooling rates. In contrast to observations of stratus clouds, we find that the number of ice crystals that nucleate in cirrus is relatively insensitive to the number of aerosols present. The ice crystal size distribution at the end of the nucleation process is unaffected by the assumed initial aerosol number density. Essentially, nucleation continues until enough ice crystals are present such that their deposition growth rapidly depletes the vapor and shuts off any further nucleation. However, the number of ice crystals nucleated increases rapidly with decreasing initial temperature and increasing cooling rate. This temperature dependence alone could explain the large ice crystal number density observed in very cold tropical cirrus.

Jensen, E. J.↗
NASA NTRS2019

TPSAS-NF1676L-34013-DND

Currently, many experiments pursuing comprehensive characterization of the atmosphere include coordinated observations by both lidar and polarimeters in order to obtain important complimentary information about aerosol properties. The most advanced passive observations by space-based multi-angle polarimeters are sensitive to the properties of aerosol in total atmospheric column, but have very limited sensitivity to vertical structure of the atmosphere. Polarimeter observations can be used not only for retrieval of aerosol optical thickness, but also for deriving microphysical information about aerosol particle shape, size distribution, complex refractive index, and the properties of underlying surface (Dubovik et al., 2019). In a contrast, the lidar observations of atmospheric responses from different altitudes to laser pulses are designed to provide vertical profiles of atmospheric characteristics. Here we present the recent advancement in GRASP algorithm (Generalized Aerosol Retrieval of Atmospheric and Surface Properties) (Dubovik et al., 2011, 2014) that allows simultaneous inversion of co-incident lidar and polarimeter spaceborne observations and derives a united set of vertically resolved aerosol and surface parameters. Such synergetic retrieval is an extension to satellite data of the approach for synergetic processing of active and passive measurements developed earlier by (Lopatin et al., 2013) for ground-based observations. Another addition to these developments is the inclusion of Raman-shifted and volume depolarization backscattering observations that improve sensitivity to the vertical properties of aerosol, while polarimetric observations provide sufficient constraints on aerosol type and loading that generally are missing in lidar signals. The potential and limitations of such synergetic processing is illustrated by application to co-incident PARASOL and CALIPSO data.

Anton Lopatin↗
NASA NTRS1984

Ultraviolet spectral morphology of the O stars - The remarkable luminosity dependence of the Si IV stellar wind effect

An extensive survey of ultraviolet O type spectra, by means of high-resolution data from the International Ultraviolet Explorer archives, shows a strong correlation between both the photospheric and stellar wind features, and the optical spectral types. In particular, the stellar wind effect in the Si IV resonance doublet displays a strong luminosity dependence which has not been completely described before: there is no effect anywhere on the main sequence, but it develops gradually through the intermediate luminosity classes into a full P Cygni profile in the supergiants. This behavior is in sharp contrast to that of the C IV and N V, which have strong P Cygni profiles throughout most of the O type domain, including the main sequence. The Si IV effect simultaneously provides a sensitive classification criterion and poses an outstanding problem for detailed astrophysical interpretation. In addition, a new emission feature at 1574 A, possibly due to N III or to N IV forbidden line, is reported.

Walborn, N. R.↗
NASA NTRS1994

Noise Analysis of Spatial Phase coding in analog Acoustooptic Processors

Optical beams can carry information in their amplitude and phase; however, optical analog numerical calculators such as an optical matrix processor use incoherent light to achieve linear operation. Thus, the phase information is lost and only the magnitude can be used. This limits such processors to the representation of positive real numbers. Many systems have been devised to overcome this deficit through the use of digital number representations, but they all operate at a greatly reduced efficiency in contrast to analog systems. The most widely accepted method to achieve sign coding in analog optical systems has been the use of an offset for the zero level. Unfortunately, this results in increased noise sensitivity for small numbers. In this paper, we examine the use of spatially coherent sign coding in acoustooptical processors, a method first developed for digital calculations by D. V. Tigin. This coding technique uses spatial coherence for the representation of signed numbers, while temporal incoherence allows for linear analog processing of the optical information. We show how spatial phase coding reduces noise sensitivity for signed analog calculations.

Gary, Charles K.↗
NASA NTRS1987

Sensitivity of LFC techniques in the non-linear regime

For all the Laminar Flow Control (LFC) techniques examined, finite-amplitude effects are destabilizing, i.e., finite-amplitude 2-D Tollmien-Schlichting (TS) waves grow faster than predicted by linear theory. It was also found, in direct contrast to the results from linear theory for low-amplitude waves, that temperature fluctuations exert a further destabilizing influence on finite amplitude 2-D TS waves. The controlled boundary layers are, of course, subject to intense 3-D secondary instabilities. The instantaneous growth rates of both the fundamental and subharmonic instabilities are strongly tied to the amplitude of the primary 2-D wave. The principal finite-amplitude effects upon the 3-D secondary instabilities occur through the faster growth of the 2-D waves.

Bushnell, Dennis M.↗
NASA NTRS1988

Discrete analysis of spatial-sensitivity models

Procedures for reducing the computational burden of current models of spatial vision are described, the simplifications being consistent with the prediction of the complete model. A method for using pattern-sensitivity measurements to estimate the initial linear transformation is also proposed which is based on the assumption that detection performance is monotonic with the vector length of the sensor responses. It is shown how contrast-threshold data can be used to estimate the linear transformation needed to characterize threshold performance.

Nielsen, Kenneth R. K.↗
NASA NTRS1990

Eustatic sea level fluctuations induced by polar wander

It is shown here that polar wander of a viscoelastic, stratified earth can induce global sea level fluctuations comparable to the short-term component in eustatic sea-level curves. The sign of these fluctuations, which are very sensitive to the rheological stratification, depends on the geographical location of the observation point; rises and falls in sea level can thus be coeval in different parts of the world. This finding is a distinct contrast to the main assumption underlying the reconstruction of eustatic curves, namely that global sea-level events produce the same depositional sequence everywhere. It is proposed that polar wander should be added to the list of geophysical mechanisms that can control the third-order cycles in sea level.

Sabadini, Roberto↗
NASA NTRS1994

A three-dimensional transport model for the middle atmosphere

In this paper we describe fundamental properties of an 'off-line' three-dimensional transport model, that is, a model which uses prescribed rather than predicted winds. The model is currently used primarily for studying problems of the middle atmosphere because we have not (yet) incorporated a formulation for the convective transport of trace species, a prerequisite for many tropospheric problems. The off-line model is simpler and less expensive than a model which predicts the wind and mass evolution (an 'on-line' model), but it is more complex than the two-dimensional (2-D) zonally averaged transport models often used in the study of chemistry and transport in the middle atmosphere. It thus serves as a model of intermediate complexity and can fill a useful niche for the study of transport and chemistry. We compare simulations of four tracers, released in the lower stratosphere, in both the on- and off-line models to document the difference resulting from differences in modeling the same problem with this intermediate model. These differences identify the price to be paid in going to a cheaper and simpler calculation. The off-line model transports a tracer in three dimensions. For this reason, it requires fewer approximations than 2-D transport model, which must parameterize the effects of mixing by transient and zonally asymmetric wind features. We compare simulations of the off-line model with simulations of a 2-D model for two problems. First, we compare 2-D and three-dimensional (3-D) models by simulating the emission of an NO(x)-like tracer by a fleet of high-speed aircraft. The off-line model is then used to simulate the transport of C-14 and to contrast its simulation properties to that of the host of 2-D models which participated in an identical simulation in a recent NASA model intercomparison. The off-line model is shown to be somewhat sensitive to the sampling strategy for off-line winds. Simulations with daily averaged winds are in very good qualitative agreement but are less diffusive than when driven with instantaneous winds sampled at half-hour intervals. Simulations with the off-line and 2-D models are quite similar in the middle and upper stratosphere but behave quite differently in the lower stratosphere, where the 3-D model has a substantially more vigorous circulation. The off-line model is quite realistic in its simulation of C-14. While there are still systematic differences between the 3-D calculation and the observations, the differences seem to be substantially reduced when compared with the body of 2-D simulations documented in the above mentioned NASA intercomparison, particularly at 31 deg N.

Rasch, Philip J.↗