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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

IUE and Einstein observations of NGC5204

The use of both the Einstein and IUE observations of NGC5204 to test some of the hypotheses put forward as a result of an X-ray survey of blue peculiar late type galaxies is discussed. In particular the hypothesis that binary X-ray sources of Pop I progenitors are responsible for most of the X-ray emission, is strengthened by the IUE short wavelength spectrum of NGC5204. This spectrum suggests a number of OB stars in agreement with the inferred from the X-ray luminosity. It also shows an ultraviolet excess in agreement with the large X-ray to blue flux ratio.

Fabbiano, G.↗
NASA NTRS1987

A gamma-ray constraint on the nature of dark matter

If even a small component of the Galactic spheroid consists of the weakly interacting majorana fermions that are cold-dark-matter candidate particles for the Galactic halo, there should be a substantial flux of annihilation gamma rays from a source of about 1-deg extent at the Galactic center. COS B observations already constrain the halo cold-dark-matter (CDM) content entrained in the inner spheroid to be less than about 10 percent. A somewhat weaker constraint applies to the CDM believed to be present in the Galactic disk, but still only about 15 percent can be in such particles. Monochromatic line photons of energy 3-10 GeV are also predicted, and future experiments may be capable of improving these limits. Since both theoretical models of galaxy formation in a CDM-dominated universe and mass models for the rotation curve in the inner Galaxy suggest that a substantial fraction of the spheroid component should be nonluminous and incorporate entrained halo CDM, the hypothesis that the halo CDM consists predominantly of weakly interacting fermions such as photinos or heavy majorana mass neutrinos or higgsinos may already be subject to observational test.

Silk, Joseph↗
DOE OSTI2020

Neurosensory and Sinus Evolution as Tyrannosauroid Dinosaurs Developed Giant Size: Insight from the Endocranial Anatomy of Bistahieversor sealeyi

Tyrannosaurus rex and other tyrannosaurid dinosaurs were apex predators during the latest Cretaceous, which combined giant size and advanced neurosensory systems. Computed tomography (CT) data have shown that tyrannosaurids had a trademark system of a large brain, large olfactory bulbs, elongate cochlear ducts, and expansive endocranial sinuses surrounding the brain and sense organs. Older, smaller tyrannosauroid relatives of tyrannosaurids developed some, but not all, of these features, raising the hypothesis that tyrannosaurid-style brains evolved before the enlarged tyrannosaurid-style sinuses, which might have developed only with large body size. This has been difficult to test, however, because little is known about the brains and sinuses of the first large-bodied tyrannosauroids, which evolved prior to Tyrannosauridae. Here we present the first CT data for one of these species, Bistahieversor sealeyi from New Mexico. Bistahieversor had a nearly identical brain and sinus system as tyrannosaurids like Tyrannosaurus, including a large brain, large olfactory bulbs, reduced cerebral hemispheres, and optic lobes, a small tab-like flocculus, long and straight cochlear ducts, and voluminous sinuses that include a supraocciptal recess, subcondyar sinus, and an anterior tympanic recess that exits the braincase via a prootic fossa. When characters are plotted onto tyrannosauroid phylogeny, there is a two-stage sequence in which features of the tyrannosaurid-style brain evolved first (in smaller, nontyrannosaurid species like Timurlengia), followed by features of the tyrannosaurid-style sinuses (in the first large-bodied nontyrannosaurid tyrannosauroids like Bistahieversor). This suggests that the signature tyrannosaurid sinus system evolved in concert with large size, whereas the brain did not.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

How to improve scaling from traits to ecosystem processes

Scaling approaches in ecology assume that traits are the main attributes by which organisms influence ecosystem functioning. However, several recent empirical papers have found only weak links between traits and ecosystem functioning, questioning the usefulness of trait-based ecology (TBE). Here, we argue that these studies often suffer from one or more widespread misconceptions. Specifically, these studies often (i) conflict with the conceptual foundations of TBE, (ii) lack theory- or hypothesis-driven selection and use of traits, (iii) tend to ignore intraspecific variation, and (iv) use experimental or study designs that are not well suited to make strong tests of TBE assumptions. Addressing these aspects could significantly improve our ability to scale from traits to ecosystem functioning.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Sugar loading is not required for phloem sap flow in maize plants

We report phloem transport of photoassimilates from leaves to non-photosynthetic organs, such as the root and shoot apices and reproductive organs, is crucial to plant growth and yield. For nearly 90 years, evidence has been generally consistent with the theory of a pressure-flow mechanism of phloem transport. Central to this hypothesis is the loading of osmolytes, principally sugars, into the phloem to generate the osmotic pressure that propels bulk flow. Here we used genetic and light manipulations to test whether sugar import into the phloem is required as the driving force for phloem sap flow. Using carbon-11 radiotracer, we show that a maize sucrose transporter1 (sut1) loss-of-function mutant has severely reduced export of carbon from photosynthetic leaves (only ~4% of the wild type level). Yet, the mutant remarkably maintains phloem pressure at ~100% and sap flow speeds at ~50–75% of those of wild type. Potassium (K+) abundance in the phloem was elevated in sut1 mutant leaves. Fluid dynamic modelling supports the conclusion that increased K+ loading compensated for decreased sucrose loading to maintain phloem pressure, and thereby maintained phloem transport via the pressure-flow mechanism. Furthermore, these results suggest that sap flow and transport of other phloem-mobile nutrients and signalling molecules could be regulated independently of sugar loading into the phloem, potentially influencing carbon–nutrient homoeostasis and the distribution of signalling molecules in plants encountering different environmental conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The Effects of Lithium Ions and pH on the Function of Polyacrylic Acid Binder for Silicon Anodes

Binder plays a critical role in the performance of silicon anodes for lithium-ion batteries, specifically by connecting particles of active material and promoting adhesion to the current collector. Recent studies have differed on the relative cycle life of silicon anodes made from water-based polyacrylic acid (PAA) vs LiOH-PAA binders. Differences between the two may be due to the pH value or the extra Li + in the binder, both of which change when LiOH is added to PAA. Here we investigate the impact of these two variables on the performance of silicon anodes. Regarding the effect of Li + , cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results confirm our hypothesis that the extra Li + facilitates ion transport. Regarding pH, we find that high pH in binders is detrimental to the electrode mechanical integrity, as observed in peeling tests and cross-sectional imaging. However, viscosity tests reveal that increased pH benefits the coating and mixing process. Further, our cycling results show that LiOH-PAA binder maintains greater cell capacity than does PAA, and further that LiOH-PAA at pH 4.5 leads to a cell with the highest capacity. Therefore, an intermediate pH is an optimal compromise between benefits observed for the low and high pH experiments.

25 ENERGY STORAGE↗
NASA NTRS1993

Follow-up on the effects of the space environment on UHCRE thermal blankets

An overview of the effects of the space environment on the thermal blanket of the UHCRE experiment is presented with an emphasis on atomic oxygen (AO) erosion. A more accurate value for FEP Teflon reaction efficiency is given and corresponds, at normal incidence, to 3.24 10(exp -25) cu cm/atomic, therefore, the FEP Teflon erosion corresponding to the Long Duration Exposure Facility (LDEF) total mission is 29.5 microns. A power 1.44 of the cosine of the incident angle of the oxygen atoms is found. It is shown that this value is not far from the power found using Fergusson's relationship between efficiency and energy of the O-atoms. An hypothesis concerning the effect of oxygen ions (O(+)) is also presented. The presence of oxygen ions may explain the different results obtained from different flights and from laboratory tests. Finally an XPS analysis of Chemglaze Z306(tm) black paint demonstrates the presence of silicone in the paint which may explain part of the contamination found on LDEF.

Levadou, Francois↗
NASA NTRS1998

Modeling of a Two-Phase Jet Pump with Phase Change, Shocks and Temperature-Dependent Properties

One of the primary motivations behind this work is the attempt to understand the physics of a two-phase jet pump which constitutes part of a flow boiling test facility at NASA-Marshall. The flow boiling apparatus is intended to provide data necessary to design highly efficient two-phase thermal control systems for aerospace applications. The facility will also be capable of testing alternative refrigerants and evaluate their performance using various heat exchangers with enhanced surfaces. The test facility is also intended for use in evaluating single-phase performance of systems currently using CFC refrigerants. Literature dealing with jet pumps is abundant and covers a very wide array of application areas. Example application areas include vacuum pumps which are used in the food industry, power station work, and the chemical industry; ejector systems which have applications in the aircraft industry as cabin ventilators and for purposes of jet thrust augmentation; jet pumps which are used in the oil industry for oil well pumping; and steam-jet ejector refrigeration, to just name a few. Examples of work relevant to this investigation includes those of Fairuzov and Bredikhin (1995). While past researchers have been able to model the two-phase flow jet pump using the one-dimensional assumption with no shock waves and no phase change, there is no research known to the author apart from that of Anand (1992) who was able to account for condensation shocks. Thus, one of the objectives of this work is to model the dynamics of fluid interaction between a two-phase primary fluid and a subcooled liquid secondary fluid which is being injected employing atomizing spray injectors. The model developed accounts for phase transformations due to expansion, compression, and mixing. It also accounts for shock waves developing in the different parts of the jet pump as well as temperature and pressure dependencies of the fluid properties for both the primary two-phase mixture and the secondary subcooled liquid. The research effort on which this document partly reports described a relatively simple model capable of describing the performance of a two-phase flow jet pump. The model is based on the isentropic homogeneous expansion/compression hypothesis and is capable of fully incorporating the effects of shocks in both the mixing chamber and the throat/diffuser parts of the pump. The physical system chosen is identical to that experimentally tested by Fairuzov and Bredikhin (1995) and should therefore be relatively easy to validate.

Sherif, S. A.↗
DOE OSTI2024

Methods and stability tests associated with the sterile neutrino search using improved high-energy ν μ event reconstruction in IceCube

We provide supporting details for the search for a 3 + 1 sterile neutrino using data collected over 10.7 years at the IceCube Neutrino Observatory. The analysis uses atmospheric muon-flavored neutrinos from 0.5 to 100 TeV that traverse Earth to reach the IceCube detector and finds a best-fit point at sin 2 ( 2 θ 24 ) = 0.16 and Δ m 41 2 = 3.5 eV 2 with a goodness-of-fit p value of 12% and consistency with the null hypothesis of no oscillations to sterile neutrinos with a p value of 3.1%. Several improvements were made over past analyses, which are reviewed in this article, including upgrades to the reconstruction and the study of sources of systematic uncertainty. We provide details of the fit quality and discuss stability tests that split the data for separate samples, comparing results. We find that the fits are consistent between split datasets. Published by the American Physical Society 2024

Abbasi, R.↗
NASA NTRS1991

A comparison of photointerpretation and ground measurements of forest structure

Traditional forest inventory methods are compared with photointerpreted results. The accuracy of photointerpretation for forest-type classification is assessed in test locations in northern California. If the accuracy of photointerpretation is not sufficiently high, then the traditional practice of comparing satellite classification to photointerpretation is not justified. If this hypothesis is true, it is speculated that spectral analysis of advanced digital satellite data (SPOT and TM) can be used in conjunction with ancillary ground data to produce forest classifications of the same or better accuracy than by traditional photointerpretation techniques. Results of the accuracy assessment of three levels of classification - species, size class, and density - are presented in tables.

Biging, Greg S.↗
NASA NTRS1992

Fatigability and blood flow in the rat gastrocnemius-plantaris-soleus after hindlimb suspension

The hypothesis that hindlimb suspension (HS) increases the fatigability of the soleus during intense contractile activity and that the increased fatigue is associated with a reduced muscle blood flow was tested using caged control rats and rats subjected to HS for 15 days. After 15 days, either the soleus or the gastrocnemius-plantaris-soleus (G-P-S) muscle group was stimulated in situ (10 min at 100 Hz, 100 ms trains at 120/min), and in the G-P-S preparation, blood flow was measured with radiolabeled microspheres before and at 2 min and 10 min after the start of contractile activity. The results indicate that 15 days of HS resulted in increased fatigability of the soleus, but the effect was not caused by a reduced muscle blood flow.

Mcdonald, K. S.↗
DOE OSTI2026

Validation Studies of RELAP5-3D for High-Temperature Gas-Cooled Reactor Analysis Using a Refined RELAP5-3D Model of the High Temperature Test Facility

RELAP5-3D has been used extensively for high-temperature gas-cooled reactor (HTGR) analysis, but such analysis lies outside the validation basis for the code. Oregon State University (OSU) and the United States Department of Energy’s (DOE) Advanced Reactor Technologies (ART) – Gas-cooled reactor campaign worked together to design and operate the High Temperature Test Facility (HTTF) at OSU to provide validation data for prismatic HTGR thermal hydraulics analysis. Work using a previous RELAP5-3D model of HTTF demonstrated the ability to reproduce trends in HTTF data but an inability to reproduce the values measured in multiple experiments within the uncertainty. It was hypothesized that a new model with a finer radial nodalization would perform better for HTTF analysis. In this paper, we present the development of that more refined model and analyze HTTF experiments PG-27 and PG-29, a pressurized (PCC) and depressurized conduction cooldown (DCC) transient. Comparing PG-27 results to experimental data shows a better prediction of steady state and transient temperatures; however, a deeper dive reveals that better transient temperature predictions are a result of better initial conditions. The transient temperature rise in the core is comparable between the two models, but the legacy model predicts temperatures in the reflectors better. The new model demonstrates the ability to predict unique temperatures in each sector of the core during PG-29, capturing the azimuthal asymmetry; however, the temperature predictions still differ from measured temperatures. One hypothesis is that differences between the assumed and actual power distribution leads to the underprediction of the individual block temperatures. These results suggest that gaps and uncertainties in the measured boundary conditions for the HTTF tests do not allow to fully validate RELAP5-3D for prismatic HTGR analyses. The authors suspect that some of the differences between predicted and measured temperatures may be a result of uncertainties associated with HTTF itself rather than RELAP5-3D. We demonstrated improved validation for steady-state analysis, but significantly improved transient performance has yet to be recognized.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Graph-based machine learning improves just-in-time defect prediction

The increasing complexity of today’s software requires the contribution of thousands of developers. This complex collaboration structure makes developers more likely to introduce defect-prone changes that lead to software faults. Determining when these defect-prone changes are introduced has proven challenging, and using traditional machine learning (ML) methods to make these determinations seems to have reached a plateau. In this work, we build contribution graphs consisting of developers and source files to capture the nuanced complexity of changes required to build software. By leveraging these contribution graphs, our research shows the potential of using graph-based ML to improve Just-In-Time (JIT) defect prediction. We hypothesize that features extracted from the contribution graphs may be better predictors of defect-prone changes than intrinsic features derived from software characteristics. We corroborate our hypothesis using graph-based ML for classifying edges that represent defect-prone changes. This new framing of the JIT defect prediction problem leads to remarkably better results. We test our approach on 14 open-source projects and show that our best model can predict whether or not a code change will lead to a defect with an F1 score as high as 77.55% and a Matthews correlation coefficient (MCC) as high as 53.16%. This represents a 152% higher F1 score and a 3% higher MCC over the state-of-the-art JIT defect prediction. We describe limitations, open challenges, and how this method can be used for operational JIT defect prediction.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1980

A stochastic model of cumulus clumping

Observations show that cumulus clouds often occur in long-lived mesoscale groups, or clumps. Five possible explanations of clumping are surveyed. The 'mutual protection hypothesis,' that clumps occur because cumulus clouds create and maintain, in their near environments, relatively favorable conditions for the development of succeeding clouds, is examined at length. This idea is tested through the use of a simple time-dependent model in which clouds, triggered at randomly selected locations, tend to stabilize their environment in the face of a prescribed constant forcing. Results show that clumping occurs when the cloud-induced stabilization rate is strongest at an intermediate distance from a cloud, and that it does not occur when the stabilization rate decreases monotonically away from a cloud.

Randall, D. A.↗
NASA NTRS1987

Results from a compound semiconductor crystal growth experiment in a low gravity environment

A directional solidification experiment in the compound semiconductor lead tin telluride has been carried out in a low-gravity environment on board the Space Shuttle during a flight in October, 1985. Optical etching techniques and concentration profiles from wavelength dispersive electron microscopy indicate that there was a significant amount of convection during the solidifcation of the sample. A preliminary hypothesis of this result, that even at gravity levels on the order of 0.0001 g, the convective forces can be significant compared to mass transport due to diffusion, is being tested.

Crouch, Roger K.↗
NASA NTRS1992

Stratospheric evidence of relativistic electron precipitation

The hypothesis of Thorne (1977, 1980) and Baker et al. (1986, 1987) that the precipitation of energetic electrons is modifying the high-latitude ozone distribution in the Southern Hemisphere is tested by comparing electron density data from a ground-based partial reflection sounder with simultaneous satellite data on ozone mixing ratios taken at the 40 to 50 km altitude. The results do not support the theory that large electron densities coincide with ozone destruction. There is no evidence, for instance, that the January 15, 1984 ionization event had an associated ozone loss. Further experiments for investigating the relationship between the precipitating electrons and ozone depletion are suggested.

Aikin, Arthur C.↗
NASA NTRS1995

Assessment of the Polycyclic Aromatic Hydrocarbon-Diffuse Interstellar Band Proposal

The potential link between neutral and/or ionized polycyclic aromatic hydrocarbons (PAHs) and the diffuse interstellar band (DIB) carriers is examined. Based on the study of the general physical and chemical properties of PAHs, an assessment is made of their possible contribution to the DIB carriers. It is found that, under the conditions reigning in the diffuse interstellar medium, PAHs can be present in the form of neutral molecules as well as positive and/or negative ions. The charge distribution of small PAHs is dominated, however, by two charge states at one time with compact PAHs present only in the neutral and cationic forms. Each PAH has a distinct spectral signature depending on its charge state. Moreover, the spectra of ionized PAHs are always clearly dominated by a single band in the DIB spectral range. In the case of compact PAH ions, the strongest absorption band is of type A (i.e., the band is broad, falls in the high energy range of the spectrum, and possess a large oscillator strength), and seems to correlate with strong and broad DIBs. In the case of non-compact PAH ions, the strongest absorption band is of type I (i.e., the band is narrow, falls in the low energy range of the spectrum, and possess a small oscillator strength), and seems to correlate with weak and narrow DIBs. Potential molecular size and structure constraints for interstellar PAHs are derived by comparing known DIB characteristics to the spectroscopic properties of PAHs. It is found that: (i) Only neutral PAHs larger than about 30 carbon atoms could, if present, contribute to the DIBs. (ii) For compact PAHs, only ions with less than about 250 carbon atoms could, if present, contribute to the DIBs. (iii) The observed distribution of the DIBs between strong/moderate and broad bands on the one hand and weak and narrow bands on the other hand can easily be interpreted in the context of the PAH proposal by a distribution between compact and non-compact PAH ions, respectively. A plausible correlation between PAH charge states and DIB "families" is thus provided by the PAH-DIB proposal. Following this proposal, DIB families would provide tracers of conditions within a cloud which globally determine the relative importance of cations, anions, and neutral species, rather than tracers of a specific species. Observational predictions are given to establish the viability of the PAH hypothesis. It is concluded that small PAH ions are very promising candidates as DIB carriers provided their population is dominated by a finite number (100-200) of species. A key test for the PAH proposal, consisting of laboratory and astronomical investigations of the ultraviolet range, is called for.

Salama, Farid↗
NASA NTRS1996

Assessment of the polycyclic aromatic hydrocarbon-diffuse interstellar band proposal

The potential link between neutral and/or ionized polycyclic aromatic hydrocarbons (PAHs) and the diffuse interstellar band (DIB) carriers is examined. Based on the study of the general physical and chemical properties of PAHs, an assessment is made of their possible contribution to the DIB carriers. It is found that, under the conditions reigning in the diffuse interstellar medium, PAHs can be present in the form of neutral molecules as well as positive and/or negative ions. The charge distribution of small PAHs is dominated, however, by two charge states at one time with compact PAHs present only in the neutral and cationic forms. Each PAH has a distinct spectral signature depending on its charge state. Moreover, the spectra of ionized PAHs are always clearly dominated by a single band in the DIB spectral range. In the case of compact PAH ions, the strongest absorption band is of type A (i.e., the band is broad, falls in the high-energy range of the spectrum, and possesses a large oscillator strength), and seems to correlate with strong and broad DIBs. For noncompact PAH ions, the strongest absorption band is of type I (i.e., the band is narrow, falls in the low-energy range of the spectrum, and possesses a small oscillator strength), and seems to correlate with weak and narrow DIBs. Potential molecular size and structure constraints for interstellar PAHs are derived by comparing known DIB characteristics to the spectroscopic properties of PAHs. It is found that (i) only neutral PAHs larger than about 30 carbon atoms could, if present, contribute to the DIBs. (ii) For compact PAHs, only ions with less than about 250 carbon atoms could, if present, contribute to the DIBs. (iii) The observed distribution of the DIBs between strong/moderate and broad bands on the one hand and weak and narow bands on the other can easily be interpreted in the context of the PAH proposal by a distribution of compact and noncompact PAH ions, respectively. A plausible correlation between PAH charge states and DIB "families" is thus provided by the PAH-DIB proposal. Following this proposal, DIB families would reflect conditions within a cloud which locally determine the relative importance of cations, anions, and neutral species, rather than tracers of a specific species. Observational predictions are given to establish the viability of the PAH hypothesis. It is concluded that small PAH ions are very promising candidates as DIB carriers provided their population is dominated by a finite number (100-200) of species. A key test for the PAH proposal, consisting of laboratory and astronomical investigations in the ultraviolet range, is called for.

NASA Discipline Number 52-10↗