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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The effects of TiO opacity on the atmospheric structure of cool stars

A quantitative investigation is conducted concerning the effect of TiO opacities on the atmospheric temperature structure in late-type stars. Model atmospheres are computed, taking into account opacity-sampling (OS) or straight-mean (SM) opacities for three singlet and three triplet band systems of TiO. Model atmospheres using OS and SM opacities for TiO are compared with models having no TiO, giving attention to the effects of TiO opacities on the temperature structures of various atmospheres and the usefulness of straight-mean TiO opacities in model atmosphere calculations. The results of the model-atmosphere calculations are presented in two graphs. TiO opacities produce a global atmospheric heating which may reach several hundred kelvins. It is shown quantitatively that the TiO molecule is an important source of atmospheric opacity in cool stars of solar composition. The relative importance of TiO opacities to the thermal structure of a stellar atmosphere is influenced in the outer layers by CO and H2O cooling effects and in the deeper layers by CO, CN, and metal line absorption.

Krupp, B. M.↗
NASA NTRS2008

Obtaining Electron Temperatures and Flow Speeds from Thomson Scattered Coronal Emission Observed during the 29 March 2006 Total Solar Eclipse in Libya

An experiment to measure the electron temperature and flow speed in the solar corona by observing the visible K-coronal spectrum was conducted during the total solar eclipse on 29 March 2006 in Libya. New corona1 models accounting for the effect of electron temperature and flow on the resulting K-corona spectrum were used to interpret the observations. Results show electron temperatures of 1.10 +/- 0.05, 0.98 +/- 0.12, and 0.70 +/- 0.08 MK, at l.l{\it R)$-{\odot)$ in the solar north, east and west, respectively, and 0.93 +/- 0.12 MK, at 1.2 R(sub sun) in the solar east. The corresponding outflow speeds obtained from the spectral fit are 103 +/- 92, 0 + 10, 0 + 10, and 0 + 10 km/s. Since the observations are taken only at 1.1 and 1.2 R(sub sun) these velocities , consistent with zero outflow, are in agreement with expectations and provide additional confirmation that the spectral fitting method is working.

Davila, Joseph M.↗
NASA NTRS1984

Relative abundance of the light ions in the winter nighttime topside ionosphere

Ion concentration measurements with the retarding potential analyzer onboard OGO 6 satellite have served as basis for investigation of the distribution of the light ions, H(+) and He(+), relative to that of O(+) in the 500- to 800-km height range in the winter nighttime ionosphere. This concentration ratio exhibits distinct large-scale horizontal variations, with a relative depression in the ratio observed over a broad region about -45 deg longitude northward of approximately 40 deg dip latitude. The lower ratios are associated primarily with well-defined relative increases in the abundance of O(+), and occur in the same longitude sector that has been characterized in an earlier study by both an observed concurrent relative enhancement in ion temperature and the presence of large fluxes of energetic electrons. Comparisons are presented for the altitude distributions of the concentration ratio between regions representing extremes of the horizontal variation. A simple diffusive-equilibrium model demonstrates that the effects of ion temperature on the O(+) vertical distribution are a significant factor leading to the observed variation of the concentration ratio.

Sanatani, S.↗
NASA NTRS1975

The NATA code: Theory and analysis, volume 1

A computer program for calculating quasi-one-dimensional gas flow in axisymmetric and two-dimensional nozzles and rectangular channels is presented. Flow is assumed to start from a state of thermochemical equilibrium at a high temperature in an upstream reservoir. The program provides solutions based on frozen chemistry, chemical equilibrium, and nonequilibrium flow with finite reaction rates. Electronic nonequilibrium effects can be included using a two-temperature model. An approximate laminar boundary layer calculation is given for the shear and heat flux on the nozzle wall. Boundary layer displacement effects on the inviscid flow are considered also. Chemical equilibrium and transport property calculations are provided by subroutines. The code contains precoded thermochemical, chemical kinetic, and transport cross section data for high-temperature air, CO2-N2-Ar mixtures, helium, and argon. It provides calculations of the stagnation conditions on axisymmetric or two-dimensional models, and of the conditions on the flat surface of a blunt wedge. The primary purpose of the code is to describe the flow conditions and test conditions in electric arc heated wind tunnels.

Bade, W. L.↗
NASA NTRS1982

Analysis of the effect of heated jet flow on the far field radiation from a noise source

The influence on jet noise radiation of the interaction with the heated moving flow of a parallel twin jet is investigated. An analytical model of jet shielding is developed which consists of the sound field emitted from a stationary, discrete frequency point source impinging on a cylinder of locally parallel flow. The zones in which the various shielding mechanisms dominate are analyzed using the model. The effects of parameters such as jet temperature and flow speed are examined. It is found that the results obtained using the model are comparable to the experimental results for a point noise source impinging on a subsonic isothermal air jet.

Gerhold, C.↗
NASA NTRS1981

Some examples of the utility of HCMM data in geologic remote sensing

Examples of HCMM (Heat Capacity Mapping Mission) data in geologic remote sensing are presented, and the data set is composed of HCMM and aircraft digital scanner data and ground truth data from four western U.S. test sites. Data are used in the thermal model to test thermal data effectiveness, and changes in temperature with depth and time for dry soils are described by the model. It is found that the HCMM thermal inertia image is useful in the separability of bedrock and alluvium in Death Valley, and aa and pahoehoe flows in the Pisgah basalt flow. In a color composite of HCMM day temperature, night temperature, and day visible images of the Pisgah Crater test site, it is possible to distinguish alluvium, playa, aa and pahoehoe basalt flow, rhyolite intrusives, and other elements. Ground checking of units at a few points will extend capabilities to large areas and assist in creating telegeologic maps.

Kahle, A. B.↗
NASA NTRS2007

A Stellar-mass Black Hole in the Ultra-luminous X-ray Source M82 X-1

We have analyzed the archival XMM-Newton data of the archetypal Ultra-Luminous X-ray Source (ULX) M82 X-1 with an LO5 ksec exposure when the source was in the steady state. Thanks to the high photon statistics from the large effective area and long exposure, we were able to discriminate different X-ray continuum spectral models. Neither the standard accretion disk model (where the radial dependency of the disk effective temperature is T(r) proportional to r(sup -3/4)) nor a power-law model gives a satisfactory fit. In fact, observed curvature of the M82 X-1 spectrum was just between those of the two models. When the exponent of the radial dependence (p in T(r) proportional to r(sup -P)) of the disk temperature is allowed to be free, we obtained p = 0.61 (sup +0.03)(sub -0.02). Such a reduction of p from the standard value 3/4 under extremely high mass accretion rates is predicted from the accretion disk theory as a consequence of the radial energy advection. Thus, the accretion disk in M82 X-1 is considered to be in the Slim disk state, where an optically thick Advection Dominant Accretion Flow (ADAF) is taking place. We have applied a theoretical slim disk spectral model to M82 X-1, and estimated the black hole mass approximately equal to 19 - 32 solar mass. We conclude that M82 X-1 is a stellar black hole which has been produced through evolution of an extremely massive star, shining at a several times the super-Eddington luminosity.

Okajima, Takashi↗
NASA NTRS1983

A unified mathematical theory of electrophoretic processes

A mathematical theory is presented which shows that each of the four classical electrophoretic modes (zone electrophoresis, moving boundary electrophoresis, isotachophoresis, and isoelectric focusing) is based on the same general principles and can collectively be described in terms of a single set of equations. This model can predict the evolution of the four electrophoretic modes as a function of time. The model system is one-dimensional, neglecting the effects of electroosmosis, temperature gradients, and any bulk flows of liquid. The model is based on equations which express the components' dissociation equilibria, the mass transport due to electromigration and diffusion, electroneutrality, and the conservation of mass and charge. The model consists of a system of coupled partial differential and nonlinear algebraic equations which can be solved numerically by use of a computer. The versatility of this model was verified using an example of a three-component system containing cacodylate, tris hydroxylmethylaminomethane, and histidine. Results show that this model not only correctly predicts the characteristic features of each electrophoretic mode, but also gives details of the concentration, pH, and conductivity profiles not easily amenable to direct experimental measurement.

Bier, M.↗
NASA NTRS1996

Quantifying energy and mass transfer in crop canopies: sensors for measurement of temperature and air velocity

Here we report on the in situ performance of inexpensive, miniature sensors that have increased our ability to measure mass and energy fluxes from plant canopies in controlled environments: 1. Surface temperature. Canopy temperature measurements indicate changes in stomatal aperture and thus latent and sensible heat fluxes. Infrared transducers from two manufacturers (Exergen Corporation, Newton, MA; and Everest Interscience, Tucson, AZ, USA) have recently become available. Transducer accuracy matched that of a more expensive hand-held infrared thermometer. 2. Air velocity varies above and within plant canopies and is an important component in mass and energy transfer models. We tested commercially-available needle, heat-transfer anemometers (1 x 50 mm cylinder) that consist of a fine-wire thermocouple and a heater inside a hypodermic needle. The needle is heated and wind speed determined from the temperature rise above ambient. These sensors are particularly useful in measuring the low wind speeds found within plant canopies. 3. Accurate measurements of air temperature adjacent to plant leaves facilitates transport phenomena modeling. We quantified the effect of radiation and air velocity on temperature rise in thermocouples from 10 to 500 micrometers. At high radiation loads and low wind speeds, temperature errors were as large as 7 degrees C above air temperature.

NASA Program CELSS↗
NASA NTRS1978

Aircraft HO sub x and NO sub x emission effects on stratospheric ozone and temperature

A simplified two-dimensional steady-state photochemical model of the atmosphere was developed. The model was used to study the effect on the thermal and chemical structure of the atmosphere of two types of pollution cases: (1) injection of NOx and HOx from a hypothetical fleet of supersonic and subsonic aircraft and (2) injection of HOx from a hypothetical fleet of liquid-fueled hydrogen aircraft. The results are discussed with regard to stratospheric perturbations in ozone, water vapor and temperature.

Glatt, L.↗
NASA NTRS1971

A model for analysis of the temperature field downstream of a heated jet injected into an isothermal crossflow at an angle of 90 deg

The temperature distribution downstream of a heated jet entering an isothermal crossflow at an angle of 90 deg is predicted using two conduction models with energy sources above the point of injection, in one case a point source and in the second a line source. The models use effective turbulent diffusivities that are determined empirically from previous measurements. Temperatures predicted by the models are compared to experimental results.

Eriksen, V. L.↗
NASA NTRS1978

A Radiative Transfer Model for Microwave Emission from Soils

The radiative transfer equation for an absorbing medium is used to develop a model for microwave emission from soils. The model calculates the microwave emission intensity in terms of the brightness temperature as a function of the soil moisture and temperature. The consistency of the model is verified by a comparative study of the present model with other microwave emission models. The effect of surface roughness on the brightness temperature is studied by modifying the Fresnel reflection coefficient and by including the surface depolarization effect. The quantitative effect of the surface roughness is studied and it is demonstrated that the brightness temperatures observed for a natural agricultural terrain can be explained through the inclusion of the roughness effect. The surface roughness effect is further analyzed to obtain formulae which are useful in the analysis of the brightness temperatures, particularly, to obtain soil moisture information from the brightness. temperatures. The sensitivity of the brightness temperature to the soil temperature variations is studied both qualitatively and quantitatively. A simple formula is obtained to calculate the soil temperature dependence of the brightness temperature in terms of the surface and the deep soil temperatures. An algorithm to normalize the brightness temperatures so as to compare microwave observations under different soil temperature conditions is also discussed. A program listing of the model is given in the appendix.

Choudhury, B. J.↗
NASA NTRS1979

Analysis of Viking infrared thermal mapping data of Mars. The effects of non-ideal surfaces on the derived thermal properties of Mars

The thermal interia of the surface of Mars varies spatially by a factor of eight. This is attributable to changes in the average particle size of the fine material, the surface elevation, the atmospheric opacity due to dust, and the fraction of the surface covered by rocks and fine material. The effects of these non-ideal properties on the surface temperatures and derived thermal inertias are modeled, along with the the effects of slopes, CO2 condensed onto the surface, and layering of fine material upon solid rock. The non-ideal models are capable of producing thermal behavior similar to that observed by the Viking Infrared Thermal Mapper, including a morning delay in the post-dawn temperature rise and an enhanced cooling in the afternoon relative to any ideal, homogeneous model. The enhanced afternoon cooling observed at the Viking-1 landing site is reproduced by the non-ideal models while that atop Arsia Mons volcano is not, but may be attributed to the observing geometry.

Muhleman, D. O.↗
NASA NTRS1998

Models of Solar Irradiance Variability and the Instrumental Temperature Record

The effects of decade-to-century (Dec-Cen) variations in total solar irradiance (TSI) on global mean surface temperature Ts during the pre-Pinatubo instrumental era (1854-1991) are studied by using two different proxies for TSI and a simplified version of the IPCC climate model.

solar variability climate change global warming↗
NASA NTRS2019

The Southern Ocean Sea Surface Temperature Response to Ozone Depletion: A Multi-Model Comparison

The effect of the Antarctic ozone hole extends downwards from the stratosphere, with clear signatures in surface weather patterns including a positive trend in the Southern Annular Mode (SAM). Several recent studies have used coupled climate models to investigate the impact of these changes on Southern Ocean sea surface temperature (SST), notably motivated by the observed cooling from the late 1970s. Here we examine the robustness of these model results through comparison of both previously published and new simulations. We focus on the calculation of ‘climate response functions' (CRFs), transient responses to an instantaneous step-change in ozone concentrations. The CRF for most models consists of a rapid cooling of SST, followed by a slower warming trend. However, inter-model comparison reveals large uncertainties, such that even the sign of the impact of ozone depletion on historical SST, when reconstructed from the CRF, remains unconstrained. Comparison of these CRFs with SST responses to a hypothetical step-change in the SAM, inferred through lagged linear regression, shows broadly similar results. Causes of uncertainty are explored by examining relationships between model climatologies and their CRFs. The inter-model spread in CRFs can be reproduced by varying a single subgrid-scale mixing parameter within a single model. Antarctic sea-ice CRFs are also calculated: these do not generally exhibit the two-time-scale behavior of SST, suggesting a complex relationship between the two. Finally, by constraining model climatology-response relationships with observational values, we conclude that ozone depletion in unlikely to have been the primary driver of the observed SST cooling trend.

Climate response functions (CRF)↗
NASA NTRS2014

On Helium-Dominated Stellar Evolution: The Mysterious Role of the O(He)-Type Stars

Context. About a quarter of all post-asymptotic giant branch (AGB) stars are hydrogen-deficient. Stellar evolutionary models explain the carbon-dominated H-deficient stars by a (very) late thermal pulse scenario where the hydrogen-rich envelope is mixed with the helium-rich intershell layer. Depending on the particular time at which the final flash occurs, the entire hydrogen envelope may be burned. In contrast, helium-dominated post-AGB stars and their evolution are not yet understood. Aims. A small group of very hot, helium-dominated stars is formed by O(He)-type stars. A precise analysis of their photospheric abundances will establish constraints to their evolution. Methods. We performed a detailed spectral analysis of ultraviolet and optical spectra of four O(He) stars by means of state-of-the-art non-LTE model-atmosphere techniques. Results. We determined effective temperatures, surface gravities, and the abundances of H, He, C, N, O, F, Ne, Si, P, S, Ar, and Fe. By deriving upper limits for the mass-loss rates of the O(He) stars, we found that they do not exhibit enhanced mass-loss. The comparison with evolutionary models shows that the status of the O(He) stars remains uncertain. Their abundances match predictions of a double helium white dwarf (WD) merger scenario, suggesting that they might be the progeny of the compact and of the luminous helium-rich sdO-type stars. The existence of planetary nebulae that do not show helium enrichment around every other O(He) star precludes a merger origin for these stars. These stars must have formed in a different way, for instance via enhanced mass-loss during their post-AGB evolution or a merger within a common-envelope (CE) of a CO-WD and a red giant or AGB star. Conclusions. A helium-dominated stellar evolutionary sequence exists that may be fed by different types of mergers or CE scenarios. It appears likely that all these pass through the O(He) phase just before they become WDs.

evolution↗
NASA NTRS1980

Synthetic line profiles in early-type stellar winds. I - H and He/+/

Statistical equilibrium calculations for the first 10 levels of H and He(+) were carried out for several model atmospheres of a star with an effective temperature of 40,000 deg K and log g equal to 3.5. Atomic level populations and line profiles were computed for a wind model (Klein and Castor, 1978) with a mass-loss rate of about 1.2 x 10 to the -5th solar mass per yr. A comoving frame method was applied and the radiative transfer problem in the expanding atmosphere is treated. Two variants of the Klein-Castor model produce He II at 4686 A in emission with 3203 A in absorption, as is commonly observed in Of spectra.

Kunasz, P. B.↗