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All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Interstellar abundances derived from IUE data. I - Silicon depletions toward reddened stars

Surveys of abundances for species well suited to IUE's wavelength coverage and spectral resolution are undertaken to acquire interstellar line data for a large number of stars and column densities greater than those of previous instruments. A complex set of interactive computer programs has been developed for the efficient analysis of the IUE data, which is described along with results on Si II column densities toward two moderately reddened stars. Silicon depletions are inferred in the cases of the two stars, HD 42088 and HD 151804, and their H I column density determinations are used to estimate the total hydrogen column density.

Snow, T. P., Jr.↗
NASA NTRS2012

Longitudinal Differences of Ionospheric Vertical Density Distribution and Equatorial Electrodynamics

Accurate estimation of global vertical distribution of ionospheric and plasmaspheric density as a function of local time, season, and magnetic activity is required to improve the operation of space-based navigation and communication systems. The vertical density distribution, especially at low and equatorial latitudes, is governed by the equatorial electrodynamics that produces a vertical driving force. The vertical structure of the equatorial density distribution can be observed by using tomographic reconstruction techniques on ground-based global positioning system (GPS) total electron content (TEC). Similarly, the vertical drift, which is one of the driving mechanisms that govern equatorial electrodynamics and strongly affect the structure and dynamics of the ionosphere in the low/midlatitude region, can be estimated using ground magnetometer observations. We present tomographically reconstructed density distribution and the corresponding vertical drifts at two different longitudes: the East African and west South American sectors. Chains of GPS stations in the east African and west South American longitudinal sectors, covering the equatorial anomaly region of meridian approx. 37 deg and 290 deg E, respectively, are used to reconstruct the vertical density distribution. Similarly, magnetometer sites of African Meridian B-field Education and Research (AMBER) and INTERMAGNET for the east African sector and South American Meridional B-field Array (SAMBA) and Low Latitude Ionospheric Sensor Network (LISN) are used to estimate the vertical drift velocity at two distinct longitudes. The comparison between the reconstructed and Jicamarca Incoherent Scatter Radar (ISR) measured density profiles shows excellent agreement, demonstrating the usefulness of tomographic reconstruction technique in providing the vertical density distribution at different longitudes. Similarly, the comparison between magnetometer estimated vertical drift and other independent drift observation, such as from VEFI onboard Communication/Navigation Outage Forecasting System (C/NOFS) satellite and JULIA radar, is equally promising. The observations at different longitudes suggest that the vertical drift velocities and the vertical density distribution have significant longitudinal differences; especially the equatorial anomaly peaks expand to higher latitudes more in American sector than the African sector, indicating that the vertical drift in the American sector is stronger than the African sector.

total electron content↗
NASA NTRS2010

Methods for Estimating Environmental Effects and Constraints on NexGen: High Density Case Study

This document provides a summary of the current methods developed by Metron Aviation for the estimate of environmental effects and constraints on the Next Generation Air Transportation System (NextGen). This body of work incorporates many of the key elements necessary to achieve such an estimate. Each section contains the background and motivation for the technical elements of the work, a description of the methods used, and possible next steps. The current methods described in this document were selected in an attempt to provide a good balance between accuracy and fairly rapid turn around times to best advance Joint Planning and Development Office (JPDO) System Modeling and Analysis Division (SMAD) objectives while also supporting the needs of the JPDO Environmental Working Group (EWG). In particular this document describes methods applied to support the High Density (HD) Case Study performed during the spring of 2008. A reference day (in 2006) is modeled to describe current system capabilities while the future demand is applied to multiple alternatives to analyze system performance. The major variables in the alternatives are operational/procedural capabilities for airport, terminal, and en route airspace along with projected improvements to airframe, engine and navigational equipment.

Augustine, S.↗
NASA NTRS1974

Kinematics of the Orion A molecular cloud

Examination of the velocity structure of J = 1 to J = 0 emission of CO in the Orion A molecular cloud, including a presentation of extended strip maps in both declination and right ascension intersecting at the position of peak intensity. The results in declination show evidence for large-scale rotation, while the right ascension maps show features which can be interpreted as gravitational condensations. The observed rotation is found to be sufficient to support a density equal to that estimated for the cloud (an H2 number density of about 2000 per cu cm).

Linke, R. A.↗
NASA NTRS1984

The electron density in M82 from the S III mid-infrared line ratio

Strong detections have been made of both the 18.7 microns and 33.4 microns lines of S III in the irregular galaxy M82. This represents the first detection of the 33.4 microns line in an extragalactic object. These measurements sample the ionized gas component which dominates the observed infrared forbidden line and infrared hydrogen recombination line emission. From the ratio of the line fluxes an electron density of 120 (+ 280, - 120) per cu cm is deduced. This result is in agreement with previous estimates of the density derived from high-frequency radio continuum measurements and an assumed emitting volume. They impose further constraints on possible starburst models.

Houck, J. R.↗
NASA NTRS1995

Lithospheric bending at subduction zones based on depth soundings and satellite gravity

A global study of trench flexure was performed by simultaneously modeling 117 bathymetric profiles (original depth soundings) and satellite-derived gravity profiles. A thin, elastic plate flexure model was fit to each bathymetry/gravity profile by minimization of the L(sub 1) norm. The six model parameters were regional depth, regional gravity, trench axis location, flexural wavelength, flexural amplitude, and lithospheric density. A regional tilt parameter was not required after correcting for age-related trend using a new high-resolution age map. Estimates of the density parameter confirm that most outer rises are uncompensated. We find that flexural wavelength is not an accurate estimate of plate thickness because of the high curvatures observed at a majority of trenches. As in previous studies, we find that the gravity data favor a longer-wavelength flexure than the bathymetry data. A joint topography-gravity modeling scheme and fit criteria are used to limit acceptable parameter values to models for which topography and gravity yield consistent results. Even after the elastic thicknesses are converted to mechanical thicknesses using the yield strength envelope model, residual scatter obscures the systematic increase of mechanical thickness with age; perhaps this reflects the combination of uncertainties inherent in estimating flexural wavelength, such as extreme inelastic bending and accumulated thermoelastic stress. The bending moment needed to support the trench and outer rise topography increases by a factor of 10 as lithospheric age increases from 20 to 150 Ma; this reflects the increase in saturation bending moment that the lithosphere can maintain. Using a stiff, dry-olivine rheology, we find that the lithosphere of the GDH1 thermal model (Stein and Stein, 1992) is too hot and thin to maintain the observed bending moments. Moreover, the regional depth seaward of the oldest trenches (approximately 150 Ma) exceeds the GDH1 model depths by about 400 m.

Levitt, Daniel A.↗
NASA NTRS2004

Physical Properties of a Coronal Hole from a Coronal Diagnostics Spectrometer, Mauna Loa Coronagraph, and LASCO Observations during the Whole Sun Month

Until recently, inference of electron density distribution in the solar corona was limited by the field of view of white-light coronagraphs (typically out to 6 Rs). Now, for the first time we have a series of white- light coronagraphs (SOHO/LASCO) whose combined field of view extends from 1.1 - 30 Rs. Quantitative information on electron density distribution of coronal hole and coronal plumes/rays are estimated by using white-light, polarized brightness (pB) observations from the SOHO/LASCO/C2 and C3 and HAO/Mauna Loa Mark III coronagraphs from 1.15 to 8.0 Rs. Morphological information on the boundary of the polar coronal hole and streamer interface is determined from the white-light observations in a manner similar to the Skylab polar coronal hole boundary estimate. The average coronal hole electron density in the region 1 - 1.15 Rs is estimated from the density-sensitive EUV line ratios of Si IX 3501342 A observed by the SOHO/coronal diagnostic spectrometer (CDS). We combine these numbers with the estimate from white-light (WL) observations to obtain a density profile from 1 to 8 Rs for the plumes and the polar coronal hole. We find that white light and spectral analysis produce consistent density information. Extrapolated densities inferred from SOHO observations are compared to Ulysses in situ observations of density. Like the density inferred from the Spartan 201-03 coronagraph, the current SOHO density profiles suggest that the acceleration of the fast solar wind takes place very close to the Sun, within 10-15 Rs. The density information is used to put constraints on solar wind flow velocities and effective temperatures. Finally, these results are compared to the recent analysis of the Spartan 201-03 white-light observations.

Guhathakurta, M.↗
DOE OSTI2020

Predicting Biological Cleanliness: An Empirical Bayes Approach for Spacecraft Bioburden Accounting

To comply with the international planetary protection policy set forth by the Committee on Space Research and NASA Agency level requirements, spacecraft destined to biologically sensitive planetary bodies have to minimize terrestrial biological contamination. Analysis, testing and inspection are the standard forward verification activities that are used to demonstrate compliance with the biological contamination requirements. For testing of spacecraft surface areas, a swab or wipe sample is collected from surfaces prior to last access and subsequently processed in the lab using NASA Approved Planetary Protection Methods for Culture Based Assays. Raw data resulting from this assay is then statistically treated employing a mathematical paradigm stemming from the 1970’s Viking Lander Project to generate the bioburden density and total microbial bioburden present. This standard approach arbitrarily accounts for error and provides an upper conservative bound as it reports the maximum number of spores estimated to be present on flight hardware surfaces. A bioburden density estimate factors in the following variables: the observed bioburden count, representative volume processed, sampling efficiencies. Notably, to account for error in the approach, a 0 observed count is arbitrarily changed to a count of 1 for each hardware grouping. The data generated by spacecraft bioburden verification campaigns in the past have resulted in <80% of wipes and <90% of swabs containing a bioburden count of 0. As such, having a robust and well documented statistical approach for dealing with the probability of low incident rates is necessary to be able to estimate spacecraft bioburden. Being able to statistically describe the bioburden distribution and associated confidence level is a gamechanger for the development of bioburden allocations during mission design and will allow for tighter management of risk throughout spacecraft build. Thus, Empirical Bayes statistical approach was evaluated to estimate the microbial bioburden on spacecraft to mitigate the aforementioned mathematical concerns and provide a probabilistic bioburden distribution of the flight hardware surface. For application of this approach to performing bioburden calculations, a range of non-informative prior assumptions on hardware surfaces are explored for Bayesian analyses while informative priors using posterior distributions from prior assays are utilized for Empirical Bayes analyses. Several non-informative priors are currently under investigation to assess fitness including use of these priors to serve as a foundation to build off of NASA specification values or a basis of risk to account for unknowns during the integration and testing process. Informative priors under consideration are generated using sampled bioburden values from hardware originating within like processing environments (e.g. vendor cleaning process or similar assembly process), temporal spacecraft status events as a prediction for hardware cleanliness of future samples, and heritage system bioburden actuals to predict allocation for subsequent missions. Informative priors and probabilistic bioburden distributions are then validated using data sets from the Mars Exploration Rover, Mars Science Laboratory, and InSight missions. Using Empirical Bayes approach to generate a probabilistic bioburden distribution as demonstrated through mission use cases provides a valid approach for use in the end-to-end requirements verification process.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

The Poisson tensor completion non-parametric differential entropy estimator

We introduce the Poisson tensor completion (PTC) estimator, a non-parametric differential entropy estimator. The PTC estimator leverages inter-sample relationships to compute a low-rank Poisson tensor decomposition of the frequency histogram. Our crucial observation is that the histogram bins are an instance of a space partitioning of counts and thus can be identified with a spatial Poisson process. The Poisson tensor decomposition leads to a completion of the intensity measure over all bins—including those containing few to no samples—and leads to our proposed PTC differential entropy estimator. A Poisson tensor decomposition models the underlying distribution of the count data and guarantees non-negative estimated values and so can be safely used directly in entropy estimation. Our estimator is the first tensor-based estimator that exploits the underlying spatial Poisson process related to the histogram explicitly when estimating the probability density with low-rank tensor decompositions for the purpose of tensor completion. Furthermore, we demonstrate that our PTC estimator is a substantial improvement over standard histogram-based estimators for sub-Gaussian probability distributions because of the concentration of norm phenomenon.

42 ENGINEERING↗
NASA NTRS1988

High-peak-power low-threshold AlGaAs/GaAs stripe laser diodes on Si substrates grown by migration-enhanced molecular beam epitaxy

A high-peak-power low-threshold AlGaAs/GaAs double-heterostructure stripe laser diode on Si substrats, grown by hybrid migration-enhanced molecular beam epitaxy (MEMBE) and metalorganic chemical vapor deposition (MOCVD) has been demonstrated for the first time. These devices showed the highest peak powers of up to 184 mW per facet reported so far for double-heterostructure stripe laser diodes on Si substrates, room-temperature pulsed threshold currents as low as 150 mA, and differential quantum efficiencies as high as 30 percent without mirror facet coating. An intrinsic threshold current density has been estimated to be about 2 kA/sq cm when taking current spreading and lateral diffusion effects into account. Low dislocation density shows that MEMBE can be a useful method to grow high-quality GaAs and AlGaAs/GaAs layers on Si substrates by combining with MOCVD.

Kim, Jae-Hoon↗
NASA NTRS1994

Properties of an H I-selected galaxy sample

We analyze the properties of a sample of galaxies identified in a 21cm, H I-line survey of selected areas in the Perseus-Pisces supercluster and its foreground void. Twelve fields were observed in the supercluster, five of them (target fields) centered on optically bright galaxies, and the other seven (blank fields) selected to contain no bright galaxies within 45 min. of their centers. We detected nine previously uncatalogued, gas-rich galaxies, six of them in the target fields. We also detected H I from seven previously catalogued galaxies in these fields. Observations in the void covered the same volume as the 12 supercluster fields at the same H I-mass sensitivity, but no objects were detected. Combining out H I data with optical broadband and H alpha imaging, we conclude that the properties of H I-selected galaxies do not differ substantially from those of late-type galaxies found in optical surveys. In particular, the galaxies in our sample do not appear to be unusually faint for their H I mass, or for their circular velocity. We find tentative evidence for a connection between optical surface brightness and degree of isolation, in the sense that low surface brightness galaxies tend to be more isolated. The previously catalogued, optically bright galaxies in our survey volume dominate the total H I mass density and cross section; the uncatalogued galaxies contribute only approximately 19 percent of the mass and approximately 12 percent of the cross section. Thus, existing estimates of the density and cross section of neutral hydrogen, most of which are based on optically selected galaxy samples, are probably accurate. Such estimates can be used to compare the nearby universe to the high-redshift universe probed by quasar absorption lines.

Szomoru, Arpad↗
DOE OSTI2020

Vadose Zone Flow and Transport Parameters Data Package for the Hanford Site Composite Analysis

This report provides a description of the basis for the development and implementation of a conceptual model for vadose zone flow and transport for the Hanford Site composite analysis (CA) groundwater pathway analysis. The parameterization for a numerical model is intimately linked to the conceptual model framework. This report describes the basis for the selection of hydraulic and transport parameters for the hydrostratigraphic units (HSUs) identified in the 200 East and 200 West Areas. The following three-step process was used to develop the hydraulic properties and transport parameters for the CA modeling: 1. Breakdown of existing database on hydraulic properties by HSUs 2. Constitutive model parameters for laboratory, core-scale hydraulic properties 3. Upscaling for macroscopic, field-scale flow, and transport parameters This document provides data and information on the following items: A brief description and technical basis for the conceptual model selected to represent vadose zone flow and transport for the CA modeling. Variation in sediment particle size distribution for representative sites in the 200 East and West Areas. A summary of effective (upscaled) moisture retention, and saturated and unsaturated hydraulic conductivity estimates for the HSUs in the 200 East and West Areas. A summary of effective transport parameters, including sediment bulk density and macrodispersivity estimates for various HSUs. The 200 East Area B Complex perched water aquifer hydraulic properties

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1997

Estimation of Snow Parameters from Dual-Wavelength Airborne Radar

Estimation of snow characteristics from airborne radar measurements would complement In-situ measurements. While In-situ data provide more detailed information than radar, they are limited in their space-time sampling. In the absence of significant cloud water contents, dual-wavelength radar data can be used to estimate 2 parameters of a drop size distribution if the snow density is assumed. To estimate, rather than assume, a snow density is difficult, however, and represents a major limitation in the radar retrieval. There are a number of ways that this problem can be investigated: direct comparisons with in-situ measurements, examination of the large scale characteristics of the retrievals and their comparison to cloud model outputs, use of LDR measurements, and comparisons to the theoretical results of Passarelli(1978) and others. In this paper we address the first approach and, in part, the second.

Liao, Liang↗
NASA NTRS1972

Atmospheric density variations related to internal gravity waves

Report describes method for estimating gravity-wave density variation from wind speed profile between 60 and 100 km. Single profile is inadequate for valid determination of mean or background values and ensemble averaging over several related profiles is recommended.

Miller, E. B.↗
DOE OSTI2024

Rapid recovery of invasive wild pig (Sus scrofa) populations following density reduction

Abstract Trapping is an effective strategy for control of invasive wild pig (Sus scrofa), but eradication of populations via trapping alone typically is impractical throughout much of the species’ introduced range. Consequently, recovery of wild pig populations to pre-trapping levels following control is a major impediment to success of long-term control. In this study, we conducted camera-trap surveys to monitor recovery of two wild pig populations immediately following density reductions achieved via trapping on two sites on the Savannah River Site, SC. We used spatial capture-recapture models to estimate wild pig density during seven 3 week periods spanning 12 months to: (1) determine the time required for populations to recover to pre-trapping levels; and (2) evaluate trends in population growth, density, and distribution during recovery. Recovery of both wild pig populations started immediately after trapping ceased, with populations reaching pre-trapping levels in 3 and 5 months. Threeweek population growth rates for each wild pig population during recovery averaged 1.28 (range = 1.11–1.39 on site 1) and 1.24 (range = 0.64–1.92 on site 2), which corresponded to a 345% and 132% increase in abundance (an increase of 141 and 126 individual wild pigs on site 1 and 2, respectively) of each population by the last survey period. Rapid recovery and growth beyond pre-trapping levels of wild pig populations likely were driven by residual wild pigs not removed by trapping and compensatory reproduction and immigration. Our study is one of the first to provide information on how quickly wild pig populations can recover following overall density reductions of 54–68% and indicates practitioners should be prepared to reinitiate trapping efforts in as little as 3 months to prevent recovery of wild pig populations following control.

Biodiversity & Conservation↗
NASA NTRS1985

The unexpected ultraviolet variability of Herbig-Haro object 1

The line fluxes of the C IV 1550 A and semiforbidden C III 1909 A emission lines in HH 1 are noted to have monotonically decreased by factors of 4-6 between 1979 and 1983, despite a lack of indications of optical range changes. The thickness of the shocked layers and preshock density can be estimated on the basis of these rapid changes, with results suggesting a clumpy medium that leads to truncated shock waves with column densities insufficient for the development of complete recombination zones.

Brugel, E. W.↗
NASA NTRS1976

Detectability of auditory signals presented without defined observation intervals

Ability to detect tones in noise was measured without defined observation intervals. Latency density functions were estimated for the first response following a signal and, separately, for the first response following randomly distributed instances of background noise. Detection performance was measured by the maximum separation between the cumulative latency density functions for signal-plus-noise and for noise alone. Values of the index of detectability, estimated by this procedure, were approximately those obtained with a 2-dB weaker signal and defined observation intervals. Simulation of defined- and non-defined-interval tasks with an energy detector showed that this device performs very similarly to the human listener in both cases.

Watson, C. S.↗
NASA NTRS1980

Radiative cooling efficiencies and predicted spectra of species of the Io plasma torus

Calculations of the physical condition of the Io plasma torus have been made based on the recent Voyager EUV observations. The calculations represent an assumed thin plasma collisional ionization equilibrium among the states within each species. The observations of the torus are all consistent with this condition. The major energy loss mechanism is radiative cooling in discrete transitions. Calculations of radiative cooling efficiencies of the identified species leads to an estimated energy loss rate of at least 1.5 x 10 to the 12th watts. The mean electron temperature and density of the plasma are estimated to be 100,000 K and 2100/cu cm. The estimated number densities of S III, S IV, and O III are roughly 95, 80, and 190-740/cu cm. Upper limits have been placed on a number of other species based on the first published Voyager EUV spectrum of the torus. The assumption that energy is supplied to the torus through injection of neutral particles from Io leads to the conclusion that ion loss rates are controlled by diffusion, and relative species abundances consequently are not controlled by collisional ionization equilibrium.

Shemansky, D. E.↗