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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Contrasting Perspectives Of Junior versus Senior NASA ISS Flight Controllers On Leadership And Cultural Issues

NASA flight controllers have always worked in a very demanding environment, but the International Space Station (ISS) poses even more challenges than prior missions. A recent NASA/Ames survey by Parke and Orasanu of NASA/Johnson flight controllers uncovered concerns about communications problems between American personnel and their international counterparts. To better understand these problems, we interviewed 14 senior and 12 junior ISS flight controllers at NASA/Johnson about leadership and cultural challenges they face and strategies for addressing these challenges. The qualitative interview data were coded and tabulated. Here we present quantitative analyses testing for differences between junior and senior controllers. Based on nonparametric statistical tests comparing responses across groups, the senior controllers were significantly more aware of the impact of working in dispersed teams, the context of constant change, and the upcoming multilateral challenges, while junior controllers were more aware of language and cultural issues. We consider our findings in light of other studies of controllers and other known differences between senior and junior controllers. For example, the fact that senior controllers had their formative early experience controlling pre-ISS short-duration Shuttle missions seems to have both positive and negative aspects, which are supported by our data. Our findings may also reflect gender differences, but we cannot unconfound this effect in our data because all the senior respondents were males. Many of the junior-senior differences are not only due to elapsed time on the job, but also due to a cohort effect. The findings of this study should be used for training curricula tailored differently for junior and senior controllers.

Clement, James L.↗
NASA NTRS2016

Tropical Cyclone Activity in the North Atlantic Basin During the Weather Satellite Era, 1960-2014

This Technical Publication (TP) represents an extension of previous work concerning the tropical cyclone activity in the North Atlantic basin during the weather satellite era, 1960-2014, in particular, that of an article published in The Journal of the Alabama Academy of Science. With the launch of the TIROS-1 polar-orbiting satellite in April 1960, a new era of global weather observation and monitoring began. Prior to this, the conditions of the North Atlantic basin were determined only from ship reports, island reports, and long-range aircraft reconnaissance. Consequently, storms that formed far from land, away from shipping lanes, and beyond the reach of aircraft possibly could be missed altogether, thereby leading to an underestimate of the true number of tropical cyclones forming in the basin. Additionally, new analysis techniques have come into use which sometimes has led to the inclusion of one or more storms at the end of a nominal hurricane season that otherwise would not have been included. In this TP, examined are the yearly (or seasonal) and 10-year moving average (10-year moving average) values of the (1) first storm day (FSD), last storm day (LSD), and length of season (LOS); (2) frequencies of tropical cyclones (by class); (3) average peak 1-minute sustained wind speed ( ) and average lowest pressure ( ); (4) average genesis location in terms of north latitudinal ( ) and west longitudinal ( ) positions; (5) sum and average power dissipation index ( ); (6) sum and average accumulated cyclone energy ( ); (7) sum and average number of storm days ( ); (8) sum of the number of hurricane days (NHD) and number of major hurricane days (NMHD); (9) net tropical cyclone activity index (NTCA); (10) largest individual storm (LIS) PWS, LP, PDI, ACE, NSD, NHD, NMHD; and (11) number of category 4 and 5 hurricanes (N4/5). Also examined are the December-May (D-M) and June-November (J-N) averages and 10-year moving average values of several climatic factors, including the (1) oceanic Nino index ( ); (2) Atlantic multi-decadal oscillation ( ) index; (3) Atlantic meridional mode ( ) index; (4) global land-ocean temperature index ( ); and (5) quasi-biennial oscillation ( ) index. Lastly, the associational aspects (using both linear and nonparametric statistical tests) between selected tropical cyclone parameters and the climatic factors are examined based on their 10-year moving average trend values.

satellite↗
NASA NTRS2020

Threats to Resiliency of Redundant Systems Due to Destructive SEE

Destructive SEE pose serious challenges for the reliable use of COTS devices in space systems. We used system-level modeling to determine SEL rates that would likely compromise system reliability, resilience and capabilities. We then assembled a representative dataset of COTS CMOS parts and used nonparametric statistical techniques to assess the threat posed to redundant systems by destructive SEE.

single-event effects↗
DOE OSTI2023

Bayesian projection pursuit regression

In projection pursuit regression (PPR), a univariate response variable is approximated by the sum of $M$ “ridge functions,” which are flexible functions of one-dimensional projections of a multivariate input variable. Traditionally, optimization routines are used to choose the projection directions and ridge functions via a sequential algorithm, and $M$ is typically chosen via cross-validation. Here, we introduce a novel Bayesian version of PPR, which has the benefit of accurate uncertainty quantification. To infer appropriate projection directions and ridge functions, we apply novel adaptations of methods used for the single ridge function case ($M$=1), called the Bayesian Single Index Model; and use a Reversible Jump Markov chain Monte Carlo algorithm to infer the number of ridge functions $M$. We evaluate the predictive ability of our model in 20 simulated scenarios and for 23 real datasets, in a bake-off against an array of state-of-the-art regression methods. Finally, we generalize this methodology and demonstrate the ability to accurately model multivariate response variables. Its effective performance indicates that Bayesian Projection Pursuit Regression is a valuable addition to the existing regression toolbox.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

Asymptotic inconsistency of the cumulative algorithm for laser-induced damage probability analysis

The “cumulative algorithm” is a data analysis method that has been proposed to provide an objective, nonparametric determination of laser-induced damage probability as a function of fluence from experimental data that contain both damaged sites and undamaged sites (i.e., 1-on-1 or S-on-1 testing protocols). In this work, the limitations of this approach are explored by considering the asymptotic limit of a large number of test sites. It is shown that the cumulative algorithm does not converge to the true probability distribution and significantly underestimates the damage probability near the damage onset. Here, based on the results of this work, the cumulative algorithm is not recommended for accurate estimation of damage probability.

Computational methods↗
NASA NTRS2003

Lumbar spine disc heights and curvature: upright posture vs. supine compression harness

INTRODUCTION: Spinal lengthening in microgravity is thought to cause back pain in astronauts. A spinal compression harness can compress the spine to eliminate lengthening but the loading condition with harness is different than physiologic conditions. Our purpose was to compare the effect of spine compression with a harness in supine position on disk height and spinal curvature in the lumbar spine to that of upright position as measured using a vertically open magnetic resonance imaging system. METHODS: Fifteen healthy subjects volunteered. On day 1, each subject lay supine for an hour and a baseline scan of the lumbar spine was performed. After applying a load of fifty percent of body weight with the harness for thirty minutes, the lumbar spine was scanned again. On day 2, after a baseline scan, a follow up scan was performed after kneeling for thirty minutes within the gap between two vertically oriented magnetic coils. Anterior and posterior disk heights, posterior disk bulging, and spinal curvature were measured from the baseline and follow up scans. RESULTS: Anterior disk heights increased and posterior disk heights decreased compared with baseline scans both after spinal compression with harness and upright posture. The spinal curvature increased by both loading conditions of the spine. DISCUSSION: The spinal compression with specially designed harness has the same effect as the physiologic loading of the spine in the kneeling upright position. The harness shows some promise as a tool to increase the diagnostic capabilities of a conventional MR system.

Non-NASA Center↗
NASA NTRS1997

Angiogenesis and osteogenesis in an orthopedically expanded suture

The purpose of this study was to examine the angiogenic and the subsequent osteogenic responses during a 96-hour time-course after sutural expansion. Fifty rats were divided into: (1) a control group that received only angiogenic induction through injection of 5 ng/gm recombinant human endothelial cell growth factor (rhECGF); (2) an experimental group that received orthopedic expansion and rhECGF; (3) a sham group that received expansion and sodium chloride (NaCl) injection; and (4) a baseline group that received no expansion or injection. All rats were injected with 3H-thymidine (1.0 microCi/gm) 1 hour before death to label the DNA of S-phase cells. Demineralized sections (4 microm thick) were stained with hematoxylin and eosin. Angiogenesis and cell migration were analyzed with a previously established cell kinetics model. Analysis of variance was used to test the hypothesis that enhancement of angiogenesis stimulates reestablishment of osteogenic capability. Blood vessel number, area, and endothelial cell-labeled index significantly increased in experimental groups, but no difference was found between control and baseline groups. Labeled-pericyte index and activated pericyte numbers in the experimental group were also higher than in the sham groups. These results show that supplemental rhECGF enhances angiogenesis in expanded sutures but not in nonexpanded sutures. Data also suggest that pericytes are the source of osteoblasts in an orthopedically expanded suture.

NASA Discipline Musculoskeletal↗
NASA NTRS2018

A Comparative Analysis of Micrometeorological Determinants of Evapotranspiration Rates Within a Heterogeneous Urban Environment

Variability in micrometeorological conditions and their influence on estimated reference evapotranspiration (RET) rates were evaluated across a heterogeneous urban environment. Micrometeorological data sets (incoming solar radiation, air temperature, relative humidity and wind speed) were collected over a one-year period at six weather stations in New York City, NY (USA). Weather stations are located at four new urban green space monitoring sites and two airports. Reference evapotranspiration (RET) rates were estimated from the micrometeorological data sets for a short reference surface at a daily time-step using the ASCE Standardized Reference Evapotranspiration Equation, a Penman-Monteith based combination equation. Nonparametric comparative statistical analyses (Kruskal-Wallis) revealed statistically significant differences (at significance level α = 0.05) in micrometeorological conditions and estimated RET rates between the six sites. On a cumulative annual basis, estimated RET varied by up to 40 percent between the sites. A new technique for adjusting weather data collected at one location (e.g. regional airports) for use at another location (e.g. interior engineered urban green spaces) was evaluated. The study highlights the importance, for accurate estimation of ET, of onsite micrometeorological data sets, but concludes that additional research is needed to more thoroughly characterize micrometeorological variability across heterogeneous urban environments, and also to evaluate the influence of non-meteorological determinants, e.g. vegetation type, soil/media type, media moisture conditions and anthropogenic heat fluxes, on urban ET.

Urban environment↗
DOE OSTI2021

Statistical Uncertainty in Paleoclimate Proxy Reconstructions

A quantitative analysis of any environment older than the instrumental record relies on proxies. Uncertainties associated with proxy reconstructions are often underestimated, which can lead to artificial conflict between different proxies, and between data and models. In this paper, using ordinary least squares linear regression as a common example, we describe a simple, robust and generalizable method for quantifying uncertainty in proxy reconstructions. We highlight the primary controls on the magnitude of uncertainty, and compare this simple estimate to equivalent estimates from Bayesian, nonparametric and fiducial statistical frameworks. We discuss when it may be possible to reduce uncertainties, and conclude that the unexplained variance in the calibration must always feature in the uncertainty in the reconstruction. This directs future research toward explaining as much of the variance in the calibration data as possible. We also advocate for a “data-forward” approach, that clearly decouples the presentation of proxy data from plausible environmental inferences.

58 GEOSCIENCES↗
DOE OSTI2020

Stochastic nonlinear analysis of unidirectional fiber composites using image-based microstructural uncertainty quantification

Here, we present a data-driven nonlinear uncertainty quantification and propagation framework to study the microstructure-induced stochastic performance of unidirectional (UD) carbon fiber reinforced polymer (CFRP) composites. The proposed approach integrates (1) microscopic image characterization, (2) stochastic microstructure reconstruction, and (3) efficient multiscale finite element simulations enabled by self-consistent clustering (SCA) analysis. To model the complex microstructural variability, the proposed UQ methods take the non-Gaussian uncertainty sources into account through a distribution-free sampling approach leveraging nonparametric and asymptotic statistical tools. A hierarchical conditional sampling strategy enables the simultaneous sampling of multiple sources of uncertainties. Our approach provides insights into the impact of microstructural variabilities, which are shown to have an increasing impact on the nonlinear responses of UD CFRP parts under progressive compression loading and ultimately on the failure rate over time. We discover that before CFRP parts start to fail, a characteristic time period emerges with distinctive uncertainty distributions specific to the microstructure variability and the probability of failure. Identifying the failure time period is crucial to the reliability prediction, which is an essential component of CFRP design.

36 MATERIALS SCIENCE↗