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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Medium resolution studies of extreme ultraviolet emission from N2 by electron impact - The effect of predissociation on the emission cross section of the b 1Pi(u) state

The electron impact induced fluorescence spectrum of N2 is measured in the 102-134 nm range at a 0.05 nm spectral resolution. The spectral measurements provide the emission cross sections of the transitions of the b 1Pi(u)-X 1Sigma(+)g Birge-Hopfield I-band system. The structure and vibrational population distribution of this system are strongly affected by a configuration interaction of the valence b 1Pi(u) and Rydberg c 1Pi(u) and o 1Pi(u) states. The excitation function (0-400 eV) for the b-X (1,2) transition is measured and a modified Born approximation analytic model is applied to calculate the oscillator strength for the b 1Pi(u)-X band system. With the exception of the v-prime = 1 level, vibrational levels of the b 1Pi(u) state predissociate with a branching ratio of between 0.95 and 1.00. Predissociation of the b 1Pi(u) state contributes approximately six percent of the total dissociation cross section of N2 by electron impact at 100 eV.

James, Geoffrey K.↗
NASA NTRS1982

UV fluxes and effective temperatures of extreme helium stars

Low resolution IUE spectra of a complete ensemble of extreme helium stars are presented and their appearance in comparison with normal stars is discussed. Effective temperatures from these observations by means of line blanketed model atmospheres are determined. It is found that the temperatures are in accordance with earlier results from ground based observations.

Schoenberner, D.↗
NASA NTRS1976

Demonstration of Mg-26 excess in Allende and evidence for Al-26

The observation of a large anomaly in the isotopic composition of Mg in a Ca-Al rich chondrule from the Allende meteorite is discussed. A strong correlation is found in this chondrule between the Mg-26 excess and the Al/Mg ratio. The most plausible cause of the anomaly is attributed to the in situ decay of now extinct Al-26. However, the general pattern of Mg isotopic anomalies is not yet shown to be fully consistent with the Al-26 hypothesis, since an apparently negative Mg-26 anomaly is obtained which cannot be explained by Al-26. A large natural fractionation effect is observed for Mg isotopes. The resolution of the O anomaly and its relation with Mg effects require further investigation.

Lee, T.↗
NASA NTRS1991

Peeking through the picket fence - What astrophysical surprises may be present in the 100-200 A region?

In anticipation of more sensitive EUV and FUV spectroscopic instruments, spectra are simulated including interstellar absorption of solarlike, RS CVn, and flare stars as folded through the instrument parameters of the EUVE, Lyman/FUSE Phase A, and a desirable next-generation spectrometer. Even the relatively insensitive EUVE spectrometer is able to detect sufficient spectral lines from many active binary and dMe stars to determine their coronal-emission-measure distributions. The Lyman/FUSE or next-generation spectrometers are needed to study solar-type stars or flaring stars with high time resolution. The high throughput and effective area of a nex-generation spectrometer is needed for Doppler imaging studies, stellar wind and downflow measurements, and high time and spectral resolution of stellar flares.

Linsky, Jeffrey L.↗
NASA NTRS1988

The C IV doublet ratio intensity effect in symbiotic stars

High-resolution UV spectra in the 1200-2000 wavelength range of the symbiotic variable R Aqr and its nebular jet were obtained in July 1987 with the IUE. The line profile structure of the C IV 1548, 1550 doublet in the jet indicates multicomponent velocity structure from an optically thin emitting gas. The C IV doublet profiles in the compact H II region engulfing the Mira and hot companion binary also suggest multicomponent structure with radial velocities up to about -100 km/s. The value of the doublet intensity ratio in the R Aqr H II region has been observed in other similar symbiotic stars, such as RX Pup. It is suggested that the anomalous behavior of the C IV doublet intensities may be useful for studying the spatial structure and temporal nature of winds in symbiotic stars.

Michalitsianos, A. G.↗
NASA NTRS2007

Accuracy Analysis on Large Blocks of High Resolution Images

Although high altitude frequencies effects are removed at the time of basic image generation, low altitude (Yaw) effects are still present in form of affinity/angular affinity. They are effectively removed by additional parameters. Bundle block adjustment based on properly weighted ephemeris/altitude quaternions (BBABEQ) are not enough to remove the systematic effect. Moreover, due to the narrow FOV of the HRSI, position and altitude are highly correlated making it almost impossible to separate and remove their systematic effects without extending the geometric model (Self-Calib.) The systematic effects gets evident on the increase of accuracy (in terms of RMSE at GCPs) for looser and relaxed ground control at the expense of large and strong block deformation with large residuals at check points. Systematic errors are most freely distributed and their effects propagated all over the block.

Passini, Richardo M.↗
NASA NTRS2019

Improving the AVHRR Long Term Data Record BRDF Correction

The Long Term Data Record (LTDR) project has the goal of developing a quality and consistent surface reflectance product from coarse resolution optical sensors. This paper focuses on the Advanced Very High Resolution Radiometer (AVHRR) part of the record, using the Moderate Resolution Imaging Spectrometer (MODIS) instrument as a reference. When a surface reflectance time series is acquired from satellites with variable observation geometry, the directional variation generates an apparent noise which can be corrected by modeling the bidirectional reflectance distribution function (BRDF). The VJB (Vermote, Justice and Bréon, 2009) method estimates a target’s BRDF shape using 5 years of observation and corrects for directional effects maintaining the high temporal resolution of the measurement using the instantaneous Normalized Difference Vegetation Index (NDVI). The method was originally established on MODIS data but its viability and optimization for AVHRR data have not been fully explored. In this study we analyze different approaches to find the most robust way of applying the VJB correction to AVHRR data, considering that high noise in the red band (B1) caused by atmospheric effect makes the VJB method unstable. Firstly, our results show that for coarse spatial resolution, where the vegetation dynamics of the target don’t change significantly, deriving BRDF parameters from 15+ years of observations reduces the average noise by up to 7% in the Near Infrared (NIR) band and 6% in the NDVI, in comparison to using 3-year windows. Secondly, we find that the VJB method can be modified for AVHRR data to improve the robustness of the correction parameters and decrease the noise by an extra 8% and 9% in the red and NIR bands with respect to using the classical VJB inversion. We do this by using the Stable method, which obtains the volumetric BRDF parameter (V) based on its NDVI dependency, and then obtains the geometric BRDF parameter (R) through the inversion of just one parameter.

LTDR↗
NASA NTRS2000

A Catchment-Based Approach to Modeling Land Surface Processes in a GCM: Model Structure - Part 1

A new strategy for modeling the land surface component of the climate system is described. The strategy is motivated by an arguable deficiency in most state-of-the-art land surface models (LSMs), namely the disproportionately higher emphasis given to the formulation of one-dimensional, vertical physics relative to the treatment of horizontal heterogeneity in surface properties -- particularly subgrid soil moisture variability and its effects on runoff generation. The new strategy calls for the partitioning of the continental surface into a mosaic of hydrologic catchments, delineated through analysis of high-resolution surface elevation data. The effective "grid" used for the land surface is therefore not specified by the overlying atmospheric grid. Within each catchment, the variability of soil moisture is related to characteristics of the topography and to three bulk soil moisture variables through a well-established model of catchment processes. This modeled variability allows the partitioning of the catchment into several areas representing distinct hydrological regimes, wherein distinct (regime-specific) evaporation and runoff parameterizations are applied. Care is taken to ensure that the deficiencies of the catchment model in regions of little to moderate topography are minimized.

Koster, Randal D.↗
NASA NTRS1989

Penning gas mixtures for improving the energy resolution of proportional counters

An experimental investigation of the Penning effect in both argon and xenon has been carried out with a variety of quench gases of different ionization potentials. Acetylene with argon and trimethylamine with xenon show the strongest true Penning effect, returning very high gas gains for a given voltage and improved energy resolution over more conventional mixtures. Data for these mixtures, as well as others exhibiting weaker metastable effects, nonmetastable Penning effects, and charge transfer through photoionization, are presented.

Agrawal, P. C.↗
NASA NTRS1998

Effects of Convective Solute and Impurity Transport in Protein Crystal Growth

High-resolution optical interferometry was used to investigate the effects of forced solution convection on the crystal growth kinetics of the model protein lysozyme. Most experiments were conducted with 99.99% pure protein solutions. To study impurity effects, approx. 1% of lysozyme dimer (covalently bound) was added in some cases. We show that the unsteady kinetics, corresponding to bunching of growth steps, can be characterized by the Fourier components of time traces of the growth rate. Specific Fourier spectra are uniquely determined by the solution conditions (composition, temperature, and flow rate) and the growth layer source activity. We found that the average step velocity and growth rate increase by approx. I0% with increasing flow rate, as a result of the enhanced solute supply to the interface. More importantly, faster convective transport results in lower fluctuation amplitudes. This observation supports our rationale for system-dependent effects of transport on the structural perfection of protein crystals. We also found that solution flow rates greater than 500 microns/s result in stronger fluctuations while the average growth rate is decreased. This can lead to growth cessation at low supersaturations. With the intentionally contaminated solutions, these undesirable phenomena occurred at about half the flow rates required in pure solutions. Thus, we conclude that they are due to enhanced convective supply of impurities that are incorporated into the crystal during growth. Furthermore, we found that the impurity effects are reduced at higher crystal growth rates. Since the exposure time of terraces is inversely proportional to the growth rate, this observation suggests that the increased kinetics instability results from impurity adsorption on the interface. Finally, we provide evidence relating earlier observations of "slow protein crystal growth kinetics" to step bunch formation in response to nonsteady step generation.

Vekilov, Peter G.↗
NASA NTRS1977

Investigation of thematic mapper spatial, radiometric, and spectral resolution

Empirical evidence was provided for the definition of system specifications for the LANDSAT Follow-On Thematic Mapper (TM) and other future space Multispectral Sensor (MSS) systems. Specific sensor parameters addressed were spatial resolution, radiometric sensitivity, and to a lesser degree spectral bandwidths and locations. The study used selected available aircraft MSS data, characterized by narrow spectral bands, fine spatial resolution, and high signal-to-noise, as the basis for simulating spacecraft TM data of various spatial resolutions, radiometric sensitivities, and sets of spectral bands. The primary measure used in evaluating the effects of varying spatial and radiometric resolutions was agricultural crop mensuration accuracy using automatic (computer) information extraction techniques.

Morgenstern, J. P.↗
NASA NTRS1999

Determination of Spectroscopic Properties of Atmospheric Molecules from High Resolution Vacuum Ultraviolet Cross Section and Wavelength Measurements

We have studied the spectroscopy and the cross sections of the simple molecules of atmospheric interest such as oxygen, nitric oxide, carbon dioxide, and water. We have made cross section measurements on an absolute base without the effects from the limited instrumental resolution. We have used the following different instruments- the grating spectrometer (6.65-m at CfA, 3-m at Photon Factory), VUV Fourier transform spectrometer at Imperial College, and then moved the same one to the Photon Factory. Selection of the instruments depend on the appearance of molecular bands, and their wavelength region. For example, the cross section measurements of Doppler limited bands can been done with the Fourier transform spectrometer at the very high resolution (0.025/ cm resolution). All of these spectroscopic measurements are needed for accurate calculations of the production of atomic oxygen penetration of solar radiation into the Earth's atmosphere, and photochemistry of minor molecules.

Parkinson, W. H.↗
NASA NTRS1978

Thorium concentrations in the lunar surface. II - Deconvolution modeling and its application to the regions of Aristarchus and Mare Smythii

The broad angular response which characterized the Apollo gamma ray spectrometer resulted in a loss of spatial resolution and some of the contrast in determining surface concentrations within lunar regions small compared to the field of view. A deconvolution technique has been developed which removes much of this instrumental effect, thereby improving both spatial resolution and accuracy at the cost of a loss in precision. Geometric models of regional thorium distribution are convoluted through the response function of the instrument to yield a predicted distribution which is compared with the observed data field for quality of fit. Application to areas which include Aristarchus and Mare Smythii confirm some geological relationships and fail to support others.

Haines, E. L.↗
NASA NTRS1980

Isoelectric focusing of red blood cells in a density gradient stabilized column

The effects of Ficoll and cell application pH on red blood cell electrophoretic mobility and focusing pH were investigated by focusing cells in a density gradient stabilized column. Sample loading, cell dispersion, column conductivity, resolution of separation, and the effect of Ampholines were examined.

Smolka, A. J. K.↗
NASA NTRS1988

Assessment of recent resolution and parameterization changes in the GLA fourth order GCM

The Goddard Laboratory for Atmospheres' fourth-order GCM is under evaluation for the impact on model integrations of enhanced horizontal and vertical resolution, as well as the effects of such novel parameterization schemes as that of gravity-wave-drag, the Arakawa-Schubert (1974) cumulus parameterization, and an explicitly-resolved planetary boundary layer. While the doubling of the GMC's horizontal resolution to 2 deg in latitude and 2.5 deg in longitude has improved the model's predictive skill for 6-7 day forecasts, systematic errors associated with the model's climate drift lead to a deterioration in predictions for longer forecasts.

Helfand, H. M.↗
NASA NTRS1999

Direct Detection Doppler Lidar for Spaceborne Wind Measurement

The theory of double edge lidar techniques for measuring the atmospheric wind using aerosol and molecular backscatter is described. Two high spectral resolution filters with opposite slopes are located about the laser frequency for the aerosol based measurement or in the wings of the Rayleigh - Brillouin profile for the molecular measurement. This doubles the signal change per unit Doppler shift and improves the measurement accuracy by nearly a factor of 2 relative to the single edge technique. For the aerosol based measurement, the use of two high resolution edge filters reduces the effects of background, Rayleigh scattering, by as much as an order of magnitude and substantially improves the measurement accuracy. Also, we describe a method that allows the Rayleigh and aerosol components of the signal to be independently determined. A measurement accuracy of 1.2 m/s can be obtained for a signal level of 1000 detected photons which corresponds to signal levels in the boundary layer. For the molecular based measurement, we describe the use of a crossover region where the sensitivity of a molecular and aerosol-based measurement are equal. This desensitizes the molecular measurement to the effects of aerosol scattering and greatly simplifies the measurement. Simulations using a conical scanning spaceborne lidar at 355 nm give an accuracy of 2-3 m/s for altitudes of 2-15 km for a 1 km vertical resolution, a satellite altitude of 400 km, and a 200 km x 200 km spatial.

Korb, C. Laurence↗