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Results for “Greens function”

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 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Application of boundary integral method to elastic analysis of V-notched beams

A semidirect boundary integral method, using Airy's stress function and its derivatives in Green's boundary integral formula, is used to obtain an accurate numerical solution for elastic stress and strain fields in V-notched beams in pure bending. The proper choice of nodal spacing on the boundary is shown to be necessary to achieve an accurate stress field in the vicinity of the tip of the notch. Excellent agreement is obtained with the results of the collocation method of solution.

Rzasnicki, W.↗
NASA NTRS1986

Factors that affect reliability of nondestructive detection of flaws in structural ceramics

The factors that affect reliability of nondestructive detection of flaws in structural ceramics by microfocus radiography and scanning laser acoustic microscopy (SLAM) were investigated. Reliability of void detection in silicon nitride and silicon carbide by microfocus X-rays was affected by photon energy level, material chemistry in the immediate vicinity of the void, and the presence of loose powder aggregates inside the void cavity. The sensitivity of SLAM to voids was affected by material microstructure, the level of porosity, and the condition of the specimen surfaces. Statistical results are presented in the form of probability of detection as a function of void diameter for green compacts and sintered materials.

Klima, S. J.↗
DOE OSTI2023

Identification and preliminary characterization of conserved uncharacterized proteins from Chlamydomonas reinhardtii , Arabidopsis thaliana , and Setaria viridis

Abstract The rapid accumulation of sequenced plant genomes in the past decade has outpaced the still difficult problem of genome‐wide protein‐coding gene annotation. A substantial fraction of protein‐coding genes in all plant genomes are poorly annotated or unannotated and remain functionally uncharacterized. We identified unannotated proteins in three model organisms representing distinct branches of the green lineage (Viridiplantae): Arabidopsis thaliana (eudicot), Setaria viridis (monocot), and Chlamydomonas reinhardtii (Chlorophyte alga). Using similarity searching, we identified a subset of unannotated proteins that were conserved between these species and defined them as Deep Green proteins. Bioinformatic, genomic, and structural predictions were performed to begin classifying Deep Green genes and proteins. Compared to whole proteomes for each species, the Deep Green set was enriched for proteins with predicted chloroplast targeting signals predictive of photosynthetic or plastid functions, a result that was consistent with enrichment for daylight phase diurnal expression patterning. Structural predictions using AlphaFold and comparisons to known structures showed that a significant proportion of Deep Green proteins may possess novel folds. Though only available for three organisms, the Deep Green genes and proteins provide a starting resource of high‐value targets for further investigation of potentially new protein structures and functions conserved across the green lineage.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1980

Surface reflectance measurements in the UV from an airborne platform. I

The reflectance of naturally occurring surfaces is measured from a twin engine Cessna 402B aircraft both spectrally (0.29-0.40 micron) with a compact double monochromator and broadband (0.29-1.2 micron) with a UV enhanced photodiode. The measurement system, which is computer controlled and electrically isolated from the aircraft, consists of upward and downward looking hemispheric diffusers, filters, a rotating 90 deg mirror, a focusing lens, and a double monochromator/PMT or the UV photodiode. Measurements are taken at several altitudes enabling the empirical determination of backscatter and attenuation effects on the reflectance. The results are presented for pine forest canopy, green farmland, open ocean, and brown farmland as a function of wavelength and altitude.

Doda, D. D.↗
DOE OSTI2025

Exploring Micro-Environmental Conditions of Urban Agrivoltaics: Advancing Sustainable Green Spaces and Agriculture in Temperate Cities

Agrivoltaics, the integrated land use combining renewable energy production and agriculture, can potentially address key challenges faced by urban communities, including limited access to vacant land, fresh produce, and electricity. However, urban agrivoltaics has rarely been considered a viable solution, primarily due to a lack of experimental systems demonstrating the functionality of urban food production or green spaces alongside solar energy production. To evaluate the potential of solar photovoltaics to help mitigate heat stress on urban agriculture and green spaces in a temperate climate, we examined the microclimatic changes introduced by an urban agrivoltaics system (UrAV) when combined with vegetable crops and turfgrass, respectively. Accordingly, we installed an experimental setup instrumented with environmental sensors to compare full-sun conditions with those of an agrivoltaics system designed for urban environments. We found minimal differences for both land cover types between the control and agrivoltaics sites in air and soil temperature. However, during periods of intensified summer heat, temperatures beneath the panels cooled due to reductions in wind speed and relative humidity, which impeded the movement of hot, moist air and reduced reference evapotranspiration. Further, soil moisture in UrAV was highly spatially heterogeneous, influenced by the layout of the photovoltaic panels and their support structure, which redistributed rainfall and controlled where solar radiation could penetrate and drive evapotranspiration. Overall, our results suggest that PV-induced environmental changes in temperate climates are compatible with cultivating turfgrass or appropriate crops. These findings can help planners and designers integrate agrivoltaics into community gardens, farms, and green spaces in temperate cities.

14 SOLAR ENERGY↗
NASA NTRS1981

Spectral properties /0.04 to 0.75 microns/ of soils exposed at the Viking 1 landing site

The bidirectional reflectance and photometric function (Hapke, 1981) was determined for seven patches of soil located near the Viking Lander 1 spacecraft. The soil photometric function has a prominent opposition effect in addition to a phase function that is strongly backscattering. The ratio of reflectances at a 1 deg phase angle to that at a 10 deg phase angle averages 1.25, 1.24, and 1.19 for blue, green, and red wavelengths respectively. The photometric function has a wavelength dependence, which causes color ratios to vary by up to 33% as a function of phase angle. Estimates of soil reflectance at a 5 deg phase angle averaged over the blue and green passbands of the Viking Lander cameras are 0.11 and 0.17, respectively, while estimates over the red channel range from 0.30 to 0.39. Brightness and color variations within the soil can be correlated with particle size, finer-grained soil being brighter and redder than coarser-grained soil. Lander soils, homogeneous in nature, are typical of brighter soils covering a large portion of the Martian surface.

Guinness, E. A.↗
NASA NTRS1973

The auroral green line in Perseid spectra near sunspot maximum

Thirty-one spectra photographed during the Perseid showers of 1969 and 1970 are found to exhibit greater ionization and stronger, more frequent appearance of the forbidden oxygen line at 5577 A than Perseid spectra obtained with the same instrument in 1961. Data from 13 Perseid showers indicate a relationship between the frequency of occurrence of the oxygen line and solar activity. In 1969-70, near sunspot maximum, the strength of this auroral green line is greatest near shower maximum, as though the nature of the meteoroids were a function of their distance from the core of the stream, or, alternatively, the strength of the green line were a function of the altitude of the radiant.

Russell, J. A.↗
NASA NTRS1985

Experimental methods for quenching structures in lunar-analog silicate melts: Variations as a function of quench media and composition

Compositions analogous to lunar green, organge, and brown glasses were synthesized under consistent conditions, then quenched into a variety of different media when the samples were removed from the furnace. Iron valence and coordination are a direct function of quench media used, spanning the range from brine/ice (most effective quench), water, butyl phthalate, silicone oil, liquid nitrogen, highly reducing CO-CO2 gas, to air (least efficient quench). In the green and brown glasses, Fe(3+) in four-fold and six-fold coordination is observed in the slowest-quenched samples; Fe(2+) coordination varies directly with quench efficiency. Less pronounced changes were observed in the Ti-rich orange glass. Therefore the remote-sensed spectrum of a glass-bearing regolith on the Moon may be influenced by the process by which the glass cooled, and extreme caution must be used when comparing spectra of synthetic glass analogs with real lunar glasses.

Dyar, M. D.↗
NASA NTRS1984

Experimental methods for quenching structures in lunar-analog silicate melts - Variations as a function of quench media and composition

Compositions analogous to lunar green, orange, and brown glasses were synthesized under consistent conditions, then quenched into a variety of different media when the samples were removed from the furnace. Iron valence and coordination are a direct function of quench media used, spanning the range from brine/ice (most effective quench), water, butyl phthalate, silicone oil, liquid nitrogen, highly reducing CO-CO2 gas, to air (least efficient quench). In the green and brown glasses, Fe(3+) in four-fold and six-fold coordination is observed in the slowest-quenched samples; Fe(2+) coordination varies directly with quench efficiency. Less pronounced changes were observed in the Ti-rich orange glass. Therefore the remote-sensed spectrum of a glass-bearing regolith on the moon may be influenced by the process by which the glass cooled, and extreme caution must be used when comparing spectra of synthetic glass analogs with real lunar glasses.

Dyar, M. D.↗
NASA NTRS2012

Alternative Green Solvents Project

Necessary for safe and proper functioning of equipment. Mainly halogenated solvents. Tetrachloride, Trichloroethylene (TCE), CFC-113. No longer used due to regulatory/safety concerns. Precision Cleaning at KSC: Small % of total parts. Used for liquid oxygen (LOX) systems. Dual solvent process. Vertrel MCA (decafluoropentane (DFP) and trons-dichloroethylene) HFE-7100. DFP has long term environmental concerns. Project Goals: a) Identify potential replacements. b) 22 wet chemical processes. c) 3 alternative processes. d) Develop test procedures. e) Contamination and cleaning. f) Analysis. g) Use results to recommend alternative processes. Conclusions: a) No alternative matched Vertrel in this study. b) No clear second place solvent. c) Hydrocarbons- easy; Fluorinated greases- difficult. d) Fluorinated component may be needed in replacement solvent. e) Process may need to make up for shortcoming of the solvent. f) Plasma and SCC02 warrant further testing.

Maloney, Phillip R.↗
DOE OSTI2014

A large catalog of accurate distances to molecular clouds from PS1 photometry

Distance measurements to molecular clouds are important but are often made separately for each cloud of interest, employing very different data and techniques. We present a large, homogeneous catalog of distances to molecular clouds, most of which are of unprecedented accuracy. We determine distances using optical photometry of stars along lines of sight toward these clouds, obtained from PanSTARRS-1. We simultaneously infer the reddenings and distances to these stars, tracking the full probability distribution function using a technique presented in Green et al. We fit these star-by-star measurements using a simple dust screen model to find the distance to each cloud. We thus estimate the distances to almost all of the clouds in the Magnani et al. catalog, as well as many other well-studied clouds, including Orion, Perseus, Taurus, Cepheus, Polaris, California, and Monoceros R2, avoiding only the inner Galaxy. Typical statistical uncertainties in the distances are 5%, though the systematic uncertainty stemming from the quality of our stellar models is about 10%. The resulting catalog is the largest catalog of accurate, directly measured distances to molecular clouds. Our distance estimates are generally consistent with available distance estimates from the literature, though in some cases the literature estimates are off by a factor of more than two.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Reviewing Flexibility in Industrial Electrification: U.S. Green Ammonia and Steel Industries [Slides]

The renewable energy transition in the power sector involves a paradigm shift for flexibility. Supply flexibility faces new constraints due to the increased share of variable renewable resources. Increased demand flexibility can allow less use of peaking power plants and delay need for additional capacity and transmission. Industrial customers are larger on average than residential and commercial consumers and have typically provided the largest share of demand response in the United States. We consider industrial demand, studying characteristics of flexible industrial loads. We examine the dynamics of change occurring around industrial load flexibility by focusing on two case studies: green ammonia and steel production via electric arc furnaces. Electric arc furnace steel production is an important component of current demand response programs, whereas green ammonia and green fuels offer new paradigms for flexibility. We analyze the structure and functions of the technological innovation systems of load flexibility in those two industries via interviews with twenty-two stakeholders. We conclude that the technological innovation systems are not well-functioning for flexibility in EAF based steelmaking, but are in the green ammonia space. Explicit connections between scope two greenhouse gas emissions reporting and flexibility are lacking, and industry stakeholders do not appear to make a connection between decarbonization and load flexibility.

25 ENERGY STORAGE↗
DOE OSTI2021

Two-color pyrometry based flame to fuel surface radiative heat flux diagnostic using flamelets

In this study, a non-intrusive two-color pyrometry based radiative heat flux diagnostic is presented that accounts for the self-absorption effects. This diagnostic relies on looking up the flame temperature and soot volume fraction using the ratio of color intensities obtained from digital cameras and numerical solutions of 1D steady-state diffusion flames. Virtual two color pyrometry of computed flame show a unique one-to-one mapping of strained flames with intensity ratio; thereby allowing flames to be indexed and creation of a two-color flamelet manifold (TCFM). The TCFM is a function of two variables; the ratio of red to green intensities (flame index) and physical distance to the stoichiometric surface defined using a level-set function. The developed diagnostic is used in upward flame spread experiments where an approximate flame hull reconstruction method is applied to provide the 3D level-set function and intensity ratio for use of TCFM to provide radiative absorption properties for 3D ray tracing. Accounting for self- absorption effects provide improved soot volume fraction estimates. In conclusion, the radiative heat flux estimates are found to be in very good agreement with literature and improved results are obtained near the flame base.

42 ENGINEERING↗
DOE OSTI2017

Ground State and Excited State Tuning in Ferric Dipyrrin Complexes Promoted by Ancillary Ligand Exchange

Three ferric dipyrromethene complexes featuring different ancillary ligands were synthesized by one electron oxidation of ferrous precursors. Four-coordinate iron complexes of the type ( Ar L)FeX 2 [ Ar L = 1,9-(2,4,6-Ph 3 C 6 H 2 ) 2 -5-mesityldipyrromethene] with X = Cl or t BuO were prepared and found to be high-spin (S = 5/2), as determined by superconducting quantum interference device magnetometry, electron paramagnetic resonance, and 57 Fe Mössbauer spectroscopy. The ancillary ligand substitution was found to affect both ground state and excited properties of the ferric complexes examined. While each ferric complex displays reversible reduction and oxidation events, each alkoxide for chloride substitution results in a nearly 600 mV cathodic shift of the Fe III/II couple. The oxidation event remains largely unaffected by the ancillary ligand substitution and is likely dipyrrin-centered. While the alkoxide substituted ferric species largely retain the color of their ferrous precursors, characteristic of dipyrrin-based ligand-to-ligand charge transfer (LLCT), the dichloride ferric complex loses the prominent dipyrrin chromophore, taking on a deep green color. Time-dependent density functional theory analyses indicate the weaker-field chloride ligands allow substantial configuration mixing of ligand-to-metal charge transfer into the LLCT bands, giving rise to the color changes observed. Furthermore, the higher degree of covalency between the alkoxide ferric centers is manifest in the observed reactivity. Delocalization of spin density onto the tert-butoxide ligand in ( Ar L)FeCl(O t Bu) is evidenced by hydrogen atom abstraction to yield ( Ar L)FeCl and HOtBu in the presence of substrates containing weak C–H bonds, whereas the chloride ( Ar L)FeCl 2 analogue does not react under these conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Viscoelastic Response of Dispersed Entangled Polymer Melts

Any polymer synthesis routes result in molecular weight dispersity DAI, depending on the polymerization mechanism. The lowest dispersity polymers are those made by anionic and atom-transfer radical polymerization, which exhibit relatively narrow distributions DM=g,„1A172 — 1.02-1.04. This small divergence from monodispersity results in significant number of molecules that differ in their molecular weight from the average and their impact on the viscoelastic response remains an open question. Here the effects of low dispersity on stress relaxation and shear viscosity of entangled melts are studied using a coarse-grained model for polyethylene. Polymer melts with chain length dispersity set to follow a Schulz-Zimm distribution of Dm = 1.0 — 1.16 for an entangled polyethylene melt using molecular dynamic simulations. The systems were studied to times up to 800 ,us which is beyond the terminal time. These systems are compared to those with binary and ternary distributions. The stress relaxation functions were extracted from the Green-Kubo relation and from stress-strain relaxation following a uniaxial extension. We find on the entanglement time scale, both the mean squared displacement and the stress relaxation are independent of D m . The tube diameter and the rubbery plateau for entangled dynamics do not depend on D m . At longer times, the terminal relaxation time decreases as the faster motion of the shorter chains results in constraint release for the longer chains. Probing this low dispersity regime opens the way to evaluate the degree of dispersity that affects mechanical properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Active Learning Guided Computational Discovery of Plant-Based Redoxmers for Organic Nonaqueous Redox Flow Batteries

Organic nonaqueous redox flow batteries (ONRFBs) are promising energy storage devices due to their scalability and reliance on sourceable materials. However, finding suitable redox-active organic molecules (redoxmers) for these batteries remains a challenge. Using plant-based compounds as precursors for these redoxmers can decrease their costs and environmental toxicity. In this computational study, flavonoid molecules have been examined as potential redoxmers for ONRFBs. Flavone and isoflavone derivatives were selected as catholyte (positive charge carrier) and anolyte (negative charge carrier) molecules, respectively. To drive their redox potentials to the opposite extremes, in silico derivatization was performed using a novel algorithm to generate a library of > 40000 candidate molecules that penalizes overly complex structures. A multiobjective Bayesian optimization based active learning algorithm was then used to identify best redoxmer candidates in these search spaces. Furthermore, our study provides methodologies for molecular design and optimization of natural scaffolds and highlights the need of incorporating expert chemistry awareness of the natural products and the basic rules of synthetic chemistry in machine learning.

25 ENERGY STORAGE↗
DOE OSTI2020

The concept of spin ice graphs and a field theory for their charges

Originally detected in rare earth pyrochlores, spin ice physics is now being artificially extended to a variety of geometries that control collective behavior and exotic properties, making graph theory their proper framework. We relate spin ice notions, such as ice rule, ice manifold, Coulomb phases, charges, and monopoles, to graph-theoretical notions, such as balance, in/out-degrees, and Euler paths. We then propose a field-theoretical treatment in which topological charges and monopoles are the degrees of freedom, while the binary spins are subsumed in an entropic interaction among charges. We show that for a spin ice on a graph in a Gaussian approximation, the kernel of the entropic interaction is the inverse of the graph Laplacian, and we compute screening functions from the graph spectra as Green operators for the screened Poisson problem on a graph. We then apply the treatment to star graphs, tournaments, cycles, and regular spin ice in different dimensions. Our aim is twofold: to set spin ice physics in a proper graph setting, where only topological rather than geometrical notions hold, and to invite graph theorists to contribute their powerful tools to the field of spin ice.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗