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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Impact of the plasma geometry on divertor power exhaust: experimental evidence from $\mathrm{TCV}$ and simulations with SolEdge2D and $\mathrm{TOKAM3X}$

A deep understanding of plasma transport at the edge of magnetically confined fusion plasmas is needed for the handling and control of heat loads on the machine first wall. Experimental observations collected on a number of tokamaks over the last three decades taught us that heat flux profiles at the divertor targets of X-point configurations can be parametrized by using two scale lengths for the scrape-off layer (SOL) transport, separately characterizing the main SOL (λ q ) and the divertor SOL (S q ). Here in this work we challenge the current interpretation of these two scale lengths as well as their dependence on plasma parameters by studying the effect of divertor geometry modifications on heat exhaust in the Tokamak à Configuration Variable. In particular, a significant broadening of the heat flux profiles at the outer divertor target is diagnosed while increasing the length of the outer divertor leg in lower single null, Ohmic, L-mode discharges. Efforts to reproduce this experimental finding with both diffusive (SolEdge2D-EIRENE) and turbulent (TOKAM3X) modelling tools confirm the validity of a diffusive approach for simulating heat flux profiles in more traditional, short leg, configurations while highlighting the need of a turbulent description for modified, long leg, ones in which strongly asymmetric divertor perpendicular transport develops.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Impact of the magnetic horizon on the interpretation of the Pierre Auger Observatory spectrum and composition data

The flux of ultra-high energy cosmic rays reaching Earth above the ankle energy (5 EeV) can be described as a mixture of nuclei injected by extragalactic sources with very hard spectra and a low rigidity cutoff.Extragalactic magnetic fields existing between the Earth and the closest sources can affect the observed CR spectrum by reducing the flux of low-rigidity particles reaching Earth. We perform a combined fit of the spectrum and distributions of depth of shower maximum measured with the Pierre Auger Observatory including the effect of this magnetic horizon in the propagation of UHECRs in the intergalactic space.We find that, within a specific range of the various experimental and phenomenological systematics, the magnetic horizon effect can be relevant for turbulent magnetic field strengths in the local neighbourhood in which the closest sources lieof order B$_{rms}$ ≃ (50–100) nG (20 Mpc/d$_{s}$)( 100 kpc/L$_{coh}$)$^{1/2}$, with d$_{s}$ the typical intersource separation and L$_{coh}$ the magnetic field coherence length. When this is the case,the inferred slope of the source spectrum becomes softer and can be closer to the expectations of diffusive shock acceleration, i.e., ∝ E$^{-2}$.An additional cosmic-ray population with higher source density and softer spectra, presumably also extragalactic and dominating the cosmic-ray flux at EeV energies, is also required to reproduce the overall spectrum and composition results for all energies down to 0.6 EeV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Persistent short-range spin fluctuation in rare-earth substituted square lattice Sr 2 ⁢Ir 0.89 ⁢Tb 0.11⁢ O 4

Sr 2 ⁢IrO 4 , a prototypical 𝐽 eff = 1/2 square lattice system, is widely studied for novel physics. While transition metal substitution effects are well explored, rare-earth doping at the Ir 4+ site is less explored. Here we present a detailed magnetization and neutron diffraction study on Sr 2 ⁢Ir 1−𝑥 ⁢Tb 𝑥 ⁢O 4 (𝑥 = 0.11). The system tends to adopt an in-plane antiferromagnetic configuration with a “++++” stacking sequence. Strong spin fluctuations persist down to the lowest measured temperature, consistent with the concave shape order parameter. A pronounced magnetic diffuse scattering rod develops along the 𝐿 direction at low temperature, indicating the formation of short-range magnetic correlations with a characteristic length of ∼ 24⁢(2) ⁢Å. In conclusion, this work provides a new pathway to exotic quantum phases in the strongly spin-orbit-coupled iridates.

Iridates↗
DOE OSTI2015

MO-FG-BRA-08: A Preliminary Study of Gold Nanoparticles Enhanced Diffuse Optical Tomography

Purpose: To develop an imaging method by using gold nanoparticles (GNP) to enhance diffuse optical tomography (DOT) for better tumor detection. Methods: Experiments were performed on a tissue-simulating cylindrical optical phantom (30mm diameter, 60mm length). The GNP used are gold nanorods (10nm diameter, 44nm length) with peak light absorption at 840nm. 0.085ml GNP colloid of 96nM concentration was loaded into a 6mm diameter cylindrical hole in the phantom. An 856nm laser beam (14mW) was used as light source to irradiate the phantom at multiple locations through rotating and elevating the phantom. A CCD camera captured the light transmission through the phantom for each irradiation with total 40 projections (8 rotation angles in 45degree steps and 5 elevations with 3mm apart). Cone beam CT of the phantom was used to generate the three-dimensional mesh for DOT reconstruction and to identify the true location of the GNP volume. A forward simulation was performed with known phantom optical properties to establish a relationship between the absorption coefficient and concentration of the GNP by matching the simulated and measured transmission. DOT image reconstruction was performed to restore the GNP within the phantom. In addition, a region-constrained reconstruction was performed by confining the solutions within the GNP volume detected from CT. Results: The position of the GNP volume was reconstructed with <2mm error. The reconstructed average GNP concentration within an identical volume was 104nM, 8% difference from the truth. When the CT was used as “a priori”, the reconstructed average GNP concentration was 239nM, about 2.5 times of the true concentration. Conclusion: This study is the first to demonstrate GNP enhanced DOT with phantom imaging. The GNP can be differentiated from their surrounding background. However, the reconstruction methods needs to be improved for better spatial and quantification accuracy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Solid State Characterizations of Long-Term Leached Cast Stone Monoliths

This report describes the results from the solid phase characterization of six Cast Stone monoliths from the extended leach tests recently reported on (Serne et al. 2016),that were selected for characterization using multiple state-of-the-art approaches. The Cast Stone samples investigated were leached for > 590 d in the EPA Method 1315 test then archived for > 390 d in their final leachate. After reporting the long term leach behavior of the monoliths (containing radioactive 99 Tc and stable 127 I spikes and for original Westsik et al. 2013 fabricated monoliths, 238 U), it was suggested that physical changes to the waste forms and a depleting inventory of contaminants of potential concern may mean that effective diffusivity calculations past 63 d should not be used to accurately represent long-term waste form behavior. These novel investigations, in both length of leaching time and application of solid state techniques, provide an initial arsenal of techniques which can be utilized to perform such Cast Stone solid phase characterization work, which in turn can support upcoming performance assessment maintenance. The work was performed at Pacific Northwest National Laboratory (PNNL) for Washington River Protection Solutions (WRPS) to characterize several properties of the long- term leached Cast Stone monolith samples.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Computational Modeling of Fluctuations in Energy and Metabolic Pathways of Methanogenic Archaea

The methanogenic archaea, anaerobic microbes that convert CO2 and H2 and/or other small organic fermentation products into methane, play an unusually large role in the global carbon cycle. As they perform the final step in the anaerobic breakdown of biomass, methanogens are a biogenic source of an estimated one billion tons methane each year. Depending on the location, produced methane can be considered as either a greenhouse gas (agricultural byproduct), sequestered carbon storage (methane hydrate deposits), or a potential energy source (organic wastewater treatment). These microbes therefore represent an important target for biotechnology applications. Computational models of methanogens with predictive power are useful aids in the adaptation of methanogenic systems, but need to connect processes of wide-ranging time and length scales. In this project, we developed several computational methodologies for modeling the dynamic behavior of entire cells that connects stochastic reaction-diffusion dynamics of individual biochemical pathways with genome-scale modeling of metabolic networks. While each of these techniques were in the realm of well-defined computational methods, here we integrated them to develop several entirely new approaches to systems biology. The first scientific aim of the project was to model how noise in a biochemical pathway propagates into cellular phenotypes. Genetic circuits have been optimized by evolution to regulate molecular processes despite stochastic noise, but the effect of such noise on a cellular biochemical networks is currently unknown. An integrated stochastic/systems model of Escherichia coli species was created to analyze how noise in protein expression gives—and therefore noise in metabolic fluxes—gives rise to multiple cellular phenotype in isogenic population. After the initial work developing and validating methods that allow characterization of the heterogeneity in the model organism E. coli, the project shifted toward investigations of the methanogen Methanosarcina acetivorans. By integrating an unprecedented transcriptomics dataset for growth of the methanogen on many substrates with an in silico model, heterogeneity in metabolic pathway usage and methane production were examined. This lent insight into the physiological requirements of the organism under different environmental conditions and uncovered the unique regulatory role that mRNA half-life has in shaping metabolic flux distributions in this organism.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1973

High-speed leading edge problem.

The sharp leading edge problem has been studied for both monatomic and diatomic gases using the Boltzmann equation with the Bhatnagar-Gross-Krook type models as the governing equation and the discrete ordinate method with a closed-boundary value approach as a tool. Plate length relative to the freestream mean free path is taken to be 52. The gas-surface interaction law is assumed to be diffuse reflection. The local distribution functions of molecular velocities and internal energies (for the diatomic gas) for the entire flowfield have been calculated for a freestream Mach number of 6.1. Comparisons are made between the calculated results and experimental data.

Huang, A. B.↗
NASA NTRS1976

Modeling of short channel MOS transistors

Higher frequency response in MOS technology can be obtained by shortening the channel length. One approach for doing this involves an employment of higher resolution lithography technology. A second approach makes use of a double-diffused MOS transistor (DMOS). It is pointed out that the ordinary method of modeling the transistors used in both approaches is not accurate. An investigation is conducted of the questions which have to be considered for DMOS modeling. The modeling of a short channel MOS transistor is discussed, taking into account the derivation of the threshold voltage equation. Excellent agreement between theoretical and experimental data shows the accuracy of the described modeling approach.

Lin, H. C.↗
NASA NTRS1978

Performance characteristics of two annular dump diffusers using suction-stabilized vortex flow control

The two diffusers employed in the investigation had the same overall area ratio but different prediffuser area ratios and suction slot geometries. Velocity profile and diffuser pressure recovery performance data were obtained at ambient pressure and temperature, with inlet Mach numbers ranging from 0.18 to 0.41 and suction rate varying from zero to 18% of total inlet mass flow rate. On the basis of the reported investigation it is concluded that suction stabilized vortex flow diffusers show promise for application in combustors because of relatively high static pressure recovery and low total pressure loss obtained in a short length. Performance obtained using a narrow angle (7 degree) prediffuser was superior to that obtained with a prediffuser having a 14 degree included angle.

Juhasz, A. J.↗
NASA NTRS1980

Ice crystal growth in a dynamic thermal diffusion chamber

Ice crystals were grown in a supersaturated environment produced by a dynamic thermal diffusion chamber, which employed two horizontal plates separated by a distance of 2.5 cm. Air was circulated between and along the 1.2 m length of the plates past ice crystals which nucleated and grew from a fiber suspended vertically between the two plates. A zoom stereo microscope with a magnification which ranged from 3X to 80X and both 35 mm still photographs and 16 mm time lapse cine films taken through the microscope were used to study the variation of the shape and linear growth rate of ice crystals as a function of the ambient temperature, the ambient supersaturation, and the forced ventilation velocity. The ambient growth conditions were varied over the range of temperature 0 to -40 C, over the range of supersaturation 4% to 50% with respect to ice, and over the range of forced ventilation velocities 0 cm/s to 20 cm/s.

Keller, V. W.↗
NASA NTRS1981

Analytical description of charged particles transport along arbitrary guiding-field configurations

A new description of focused transport was developed which is valid for arbitrary spatial dependences of both the scattering mean free path and the focusing length. In particular, it describes the supercoherent transition from the coherent modes that occurs when focusing is strong compared to scattering to the diffusive mode that occurs when focusing is weak. Because it specifies the pitch angle distribution in terms of relatively simple functions, the new formulation facilitates not only the detailed interpretation of solar particle events, but also the qualitative understanding of focused transport. In the steady state, it predicts that the angular distribution consists of a highly collimated 'strahl' which is superimposed on an anisotropic 'halo'. This picture provides new insight into observed configurations of steady-state particle fluxes.

Earl, J. A.↗
DOE OSTI2020

The Influence of Aqueous Dispersivity on Transport of Radiological Material at LANL MDA G - 20450

Aqueous dispersivity is a phenomenon by which a solute moving in groundwater mixes with water that does not contain the solute and becomes diluted. Solutes take paths of varying lengths through pore networks or experience slower velocities due to interactions with pore walls. Aqueous dispersivity leads to breakthrough curves with earlier arrival than expected in purely advective systems and persistent 'tails,' or late-arriving, dilute concentrations of the solute. Dispersivity can be longitudinal (in the direction of flow) or transverse (orthogonal to flow). LANL has disposed of radioactive material at Material Disposal Area (MDA) G since the late 1950's. Most of the disposed materials at MDA G are low-level waste (LLW), but other types of radioactive wastes are disposed or stored at the site. For example, there is a collection of remote-handled transuranic waste (RH-TRU) waste in 33 shafts, which were intended to be stored retrievably. Aqueous-phase radionuclides included in models of contaminant transport at MDA G are subject to dispersive processes in porous media of the vadose zone and saturated zone. To model dispersivity at MDA G probabilistically, we created site-specific distributions of aqueous dispersivity. First, we performed a comprehensive review of peer-reviewed publications, reports from other performance assessments of MDA G, and documentation from sites that were considered similar based on expert opinion, such as Yucca Mountain. Data were included from a wide range of sources, so that distributions developed based on the data reflect the current state of knowledge in properties of the subsurface environment. Data were grouped based on value type (e.g., determined via experiment or used in a different model), rock type, zone type (saturated or unsaturated), and site, and were weighted in the distributions according to their relevance to the site and zone type. We combined Monte Carlo simulation and bootstrapping techniques to produce approximate distributions of mean aqueous dispersivity. Distributions of dispersivity for saturated and unsaturated zone transport are differentiated by data weight and the length scales over which transport occurs. We find that underestimating or disregarding transverse dispersivity may lead to overstating simulated well capture in the saturated zone at MDA G. Neglecting transverse dispersivity is a common assumption due in part to use of one-dimensional transport models that do not consider solute spreading orthogonal to flow. Also, we find that variability in longitudinal dispersivity is associated with substantial travel time alterations in the MDA G unsaturated zone and in simulated contaminant breakthrough times at a downstream observation plane in the MDA G saturated zone. Finally, at large scales (>1000 m), a linear trend between the dispersivity coefficient and length over which transport occurs may overestimate the dispersivity coefficient. Future modeling work with application to solute spreading could include interacting advective and diffusive zones in the highly fractured basalt below MDA G. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1981

Application of aerial photography to the study of small scale upper ocean phenomena

The industrial waste dumped 180 n. miles south of Galveston was monitored in July 1977 by water sampling, hydrographic measurements, acoustic tracking on board two vessels, and by aerial photography. The plume of the waste diffused vertically and horizontally. Photodensitometry of aerial photos of the plume showed lateral dispersion of the plume in agreement with two other methods: acoustic tracking of the waste suspensoid and transmissometer sampling. In addition, the method showed small scale features like the lateral and longitudinal variations in the photodensity, indicating the waste concentration. This waste concentration showed periodic changes in its axial distance, with the spectral peak at about 160 m wave length. It shows a sharp increase at the windward edge of the plume as do the acoustic records. This phenomenon is explained in terms of the shearing current near the surface together with vertical diffusion. The periodic change along the axis is explained in terms of the Langmuir circulation and in terms of internal ship waves.

Ichiye, T.↗
DOE OSTI2019

Dynamics of Water Molecules and Ions in Concentrated Lithium Chloride Solutions Probed with Ultrafast 2D IR Spectroscopy

Water and ion dynamics in concentrated LiCl solutions were studied using ultrafast 2D IR spectroscopy with the methyl thiocyanate (MeSCN) CN stretch as the vibrational probe. The IR absorption spectrum of MeSCN has two peaks, one peak for water associated with the nitrogen lone pair of MeSCN (W) and the other peak corresponding to Li + associated with the lone pair (L). To extract the spectral diffusion (structural dynamics) of W and L species, we developed a method that isolates the peak of interest by subtracting the 2D Gaussian proxies of multiple interfering peaks. Center line slope data (normalized frequency–frequency correlation function) for 2D bands from the W and L are fit with triexponential functions. The fastest component (1.1–1.6 ps) is assigned to local hydrogen bond length fluctuations. The intermediate timescale (~4.0 ps) corresponds to the hydrogen bond network rearrangement. The slowest component decays in ~40 ps and corresponds to ion pair and ion cluster dynamics. The very similar W and L spectral diffusion indicates that the motions of the water and ions are strongly coupled. Orientational relaxations of the W and L species were extracted using a new method to eliminate the effects of overlapping peaks. The results show that MeSCN bound to water undergoes orientational relaxation significantly faster than MeSCN bound to Li + . The orientational and spectral diffusion results are compared. In conclusion, a Stark coupling model is used to extract the root mean square average electric field caused by the ion clouds along the CN moiety as a function of concentration.

14 SOLAR ENERGY↗
DOE OSTI2025

Extending the capillary wave model to include the effect of bending rigidity: X-ray reflectivity and diffuse scattering

The surface roughness of a thin film at a liquid interface exhibits contributions of thermally excited fluctuations. This thermal roughness depends on temperature (𝑇), surface tension (𝛾), and elastic material properties, specifically the bending modulus (𝜅) of the film. A nonzero 𝜅 suppresses the thermal roughness at small length scales compared to an interface with zero 𝜅, as expressed by the power spectral density of the thermal roughness. The description of the x-ray scattering of the standard capillary wave model (CWM), which is valid for zero 𝜅, is extended to include the effect of 𝜅. The extended CWM (eCWM) provides a single analytical form for both the specular x-ray reflectivity (XRR) and the diffuse scattering around the specular reflection, and recovers the expression of the CWM at its zero 𝜅 limit. This theoretical approach enables the use of single-shot grazing incidence x-ray off-specular scattering (GIXOS) measurements for characterizing the structure of thin films on a liquid surface. The eCWM analysis approach decouples the thermal roughness factor from the surface scattering signal, providing direct access to the intrinsic surface-normal structure of the film and its bending modulus. Moreover, the eCWM facilitates the calculation of reflectivity at any desired resolution (pseudo-XRR approach). The transformation into pseudo-XRR provides the benefit of using widely available XRR software to perform GIXOS analysis. The extended range of the vertical scattering vector (𝑄 𝑧 ) available with the GIXOS pseudo-XRR approach allows for a higher spatial resolution than with conventional XRR. Experimental results are presented for various lipid systems, showing strong agreement between conventional specular XRR and pseudo-XRR methods. This agreement validates the proposed approach and highlights its utility for analyzing soft, thin films.

36 MATERIALS SCIENCE↗
NASA NTRS1993

A model of concurrent flow flame spread over a thin solid fuel

A numerical model is developed to examine laminar flame spread and extinction over a thin solid fuel in lowspeed concurrent flows. The model provides a more precise fluid-mechanical description of the flame by incorporating an elliptic treatment of the upstream flame stabilization zone near the fuel burnout point. Parabolic equations are used to treat the downstream flame, which has a higher flow Reynolds number. The parabolic and elliptic regions are coupled smoothly by an appropriate matching of boundary conditions. The solid phase consists of an energy equation with surface radiative loss and a surface pyrolysis relation. Steady spread with constant flame and pyrolysis lengths is found possible for thin fuels and this facilitates the adoption of a moving coordinate system attached to the flame with the flame spread rate being an eigen value. Calculations are performed in purely forced flow in a range of velocities which are lower than those induced in a normal gravity buoyant environment. Both quenching and blowoff extinction are observed. The results show that as flow velocity or oxygen percentage is reduced, the flame spread rate, the pyrolysis length, and the flame length all decrease, as expected. The flame standoff distance from the solid and the reaction zone thickness, however, first increase with decreasing flow velocity, but eventually decrease very near the quenching extinction limit. The short, diffuse flames observed at low flow velocities and oxygen levels are consistent with available experimental data. The maximum flame temperature decreases slowly at first as flow velocity is reduced, then falls more steeply close to the quenching extinction limit. Low velocity quenching occurs as a result of heat loss. At low velocities, surface radiative loss becomes a significant fraction of the total combustion heat release. In addition, the shorter flame length causes an increase in the fraction of conduction downstream compared to conduction to the fuel. These heat losses lead to lower flame temperatures, and ultimately, extinction. This extinction mechanism differs from that of blowoff, where the flame is unable to be stabilized due to the high flow velocity.

Ferkul, Paul V.↗
DOE OSTI2015

Searching for low percolation thresholds within amphiphilic polymer membranes: The effect of side chain branching

Percolation thresholds for solvent diffusion within hydrated model polymeric membranes are derived from dissipative particle dynamics in combination with Monte Carlo (MC) tracer diffusion calculations. The polymer backbones are composed of hydrophobic A beads to which at regular intervals Y-shaped side chains are attached. Each side chain is composed of eight A beads and contains two identical branches that are each terminated with a pendant hydrophilic C bead. Four types of side chains are considered for which the two branches (each represented as [C], [AC], [AAC], or [AAAC]) are splitting off from the 8th, 6th, 4th, or 2nd A bead, respectively. Water diffusion through the phase separated water containing pore networks is deduced from MC tracer diffusion calculations. The percolation threshold for the architectures containing the [C] and [AC] branches is at a water volume fraction of ∼0.07 and 0.08, respectively. These are much lower than those derived earlier for linear architectures of various side chain length and side chain distributions. Control of side chain architecture is thus a very interesting design parameter to decrease the percolation threshold for solvent and proton transports within flexible amphiphilic polymer membranes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗