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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

High-Resolution Genuinely Multidimensional Solution of Conservation Laws by the Space-Time Conservation Element and Solution Element Method

In this overview paper, we review the basic principles of the method of space-time conservation element and solution element for solving the conservation laws in one and two spatial dimensions. The present method is developed on the basis of local and global flux conservation in a space-time domain, in which space and time are treated in a unified manner. In contrast to the modern upwind schemes, the approach here does not use the Riemann solver and the reconstruction procedure as the building blocks. The drawbacks of the upwind approach, such as the difficulty of rationally extending the 1D scalar approach to systems of equations and particularly to multiple dimensions is here contrasted with the uniformity and ease of generalization of the Conservation Element and Solution Element (CE/SE) 1D scalar schemes to systems of equations and to multiple spatial dimensions. The assured compatibility with the simplest type of unstructured meshes, and the uniquely simple nonreflecting boundary conditions of the present method are also discussed. The present approach has yielded high-resolution shocks, rarefaction waves, acoustic waves, vortices, ZND detonation waves, and shock/acoustic waves/vortices interactions. Moreover, since no directional splitting is employed, numerical resolution of two-dimensional calculations is comparable to that of the one-dimensional calculations. Some sample applications displaying the strengths and broad applicability of the CE/SE method are reviewed.

Himansu, Ananda↗
NASA NTRS2014

Core-Mantle Partitioning of Volatile Elements and the Origin of Volatile Elements in Earth and Moon

Depletions of volatile siderophile elements (VSE; Ga, Ge, In, As, Sb, Sn, Bi, Zn, Cu, Cd) in mantles of Earth and Moon, constrain the origin of volatile elements in these bodies, and the overall depletion of volatile elements in Moon relative to Earth. A satisfactory explanation has remained elusive [1,2]. We examine the depletions of VSE in Earth and Moon and quantify the amount of depletion due to core formation and volatility of potential building blocks. We calculate the composition of the Earth's PUM during continuous accretion scenarios with constant and variable fO2. Results suggest that the VSE can be explained by a rather simple scenario of continuous accretion leading to a high PT metal-silicate equilibrium scenario that establishes the siderophile element content of Earth's PUM near the end of accretion [3]. Core formation models for the Moon explain most VSE, but calculated contents of In, Sn, and Zn (all with Tc < 750 K) are all still too high after core formation, and must therefore require an additional process to explain the depletions in the lunar mantle. We discuss possible processes including magmatic degassing, evaporation, condensation, and vapor-liquid fractionation in the lunar disk.

Righter, Kevin↗
NASA NTRS1973

A Comparison of the Measured Scattering Matrix Elements of Polydisperse Systems of Irregular Particles with the Matrix Elements Calculated for Spheres that Have the Same Distribution of Projected Areas

The elements of the scattering or Mueller Matrix for three polydisperse systems of irregular, randomly-oriented particles have been measured in absolute terms as a function of scattering angle for several visible wavelengths. The samples consisted of commercially available silicon dioxide particles that fit three distinct lognormal size distributions. The measured matrix elements were compared with the matrix elements calculated for spheres that had the same refractive index and fitted the same distribution of projected areas. Correlations and discrepancies between the two sets of matrix elements will be discussed.

Holland, A. C.↗
DOE OSTI2015

Bioleaching of rare earth elements from monazite sand: Bioleaching of Rare Earth Elements from Monazite

Three fungal strains were found to be capable of bioleaching rare earth elements from monazite, a rare earth phosphate mineral, utilizing the monazite as a phosphate source and releasing rare earth cations into solution. These organisms include one known phosphate solubilizing fungus, Aspergillus niger ATCC 1015, as well as two newly isolated fungi: an Aspergillus terreus strain ML3-1 and a Paecilomyces spp. strain WE3-F. Although monazite also contains the radioactive element Thorium, bioleaching by these fungi preferentially solubilized rare earth elements over Thorium, leaving the Thorium in the solid residual. Adjustments in growth media composition improved bioleaching performance measured as rare earth release. Cell-free spent medium generated during growth of A. terreus strain ML3-1 and Paecilomyces spp. strain WE3-F in the presence of monazite leached rare earths to concentrations 1.7-3.8 times those of HCl solutions of comparable pH, indicating that compounds exogenously released by these organisms contribute substantially to leaching. Organic acids released by the organisms included acetic, citric, gluconic, itaconic, oxalic, and succinic acids. Abiotic leaching with laboratory prepared solutions of these acids was not as effective as bioleaching or leaching with cell-free spent medium at releasing rare earths from monazite, indicating that compounds other than the identified organic acids contribute to leaching performance.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

EDS-PhaSe: Phase Segmentation and Analysis from EDS Elemental Map Images Using Markers of Elemental Segregation

Scanning electron microscopy (SEM), combined with energy-dispersive spectroscopy (EDS), is an extensively used technique for in-depth microstructural analysis. Here, we present the EDS-Phase Segmentation (EDS-PhaSe) tool that enables phase segmentation and phase analysis using the EDS elemental map images. Importantly, it converts the EDS map images into estimated composition maps for calculating markers of selective elemental redistribution in the scanned area and creates a phase-segmented micrograph while providing approximate fraction and composition of each identified phase. EDS-PhaSe offers two unique advantages. Firstly, it enables the direct processing of EDS elemental map images without requiring any raw or proprietary data/software, thereby allowing the analysis of EDS results available in the published literature as images. Secondly, it enables segmentation and analysis of phases even when the phase contrast is missing in backscattered micrographs, assisting in correlating the XRD and SEM-EDS data as shown in this work for a AlCoCrFeNi high-entropy alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evaluation of trace elements in U.S. coals using the USGS COALQUAL database version 3.0. Part I: Rare earth elements and yttrium (REY)

Coal is a potential source of valuable elements such as rare earth elements and yttrium (REY). In this work, REY concentrations in U.S. domestic coals were evaluated using data from the USGS COALQUAL Database Version 3.0. The database contains a total of 7657 non-weathered, full-bed coal samples. The number of samples containing REY data points varies among elements. Assessment of data quality indicates that some of the REY data are semi-quantitative and should be used with caution. Different analytical instruments and methods with varying accuracies and precisions are thought to be the main sources of errors. Inclusion of qualified data also accounts for the sawtooth pattern of the UCC-normalized REY distribution. A new set of Q factor values was thus proposed to adjust qualified data. Consequently, mean concentrations of REY in U.S. coals were obtained with a total REY concentration of 65.5 ppm on a moisture-free whole coal basis. Further evaluation of REY in 5378 selected coal samples indicates that about 9–13% of the samples fall into the combined category of promising and highly promising coals for REY, according to the classification of Dai et al. (2017). Taking sampling bias into consideration, we further found that bituminous coal, particularly from the central Appalachian region, has the highest probability of being a source for beneficial recovery of REY. More specifically, bituminous coal from eastern Kentucky is likely to be the best option. Lastly, we conclude that U.S. domestic coal is a promising, alternative source for beneficial recovery of REY to meet the U.S. REY demand for economic growth.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2016

A non-locking composite tetrahedron element for the combined finite discrete element method

Here, a number of validation cases considering different loading and boundary conditions and different materials for the proposed element are presented. A practical application of the use of the composite tetrahedral finite element is presented by quantitative comparisons of numerical model results against simple theoretical estimates and results from acrylic fracturing experiments. All of these examples clearly show the capability of the composite element in eliminating volumetric locking.

42 ENGINEERING↗
DOE OSTI2016

Nanomineralogy as a new dimension in understanding elusive geochemical processes in soils: The case of low-solubility-index elements

Nanomineralogical studies of mineral surface coatings in soils reveal insights into biogeochemical processes that heretofore were not known to exist. This is a new dimension in understanding past and present biogeochemical processes in soils, and in this study it is a way to better understand the behavior of low-solubility-index elements such as Al, Ti, and Zr. Soils were sampled from selected sites in Sudbury (Ontario, Canada) that have been affected by acidification and particulate matter emissions from base-metal smelters with subsequent remediation within the past century. These anthropogenic processes have affected an entire landscape, but are now recorded in assemblages of nano-size phases that can be only studied using a combination of focused ion beam technology (for sample preparation) and high-resolution analytical transmission electron microscopy (for phase identification). A first generation of clay minerals (pre-acidification phase), their partial replacement by nano-size hematite and amorphous silica (anthropogenic acidification), and a second generation of clay minerals (post-acidification, including soil remediation) are products of changes in soil biogeochemical processes during these natural and anthropogenic-induced weathering stages. Furthermore, complex assemblages of nanophases formed prior to the second generation of clay minerals depict underlying mechanisms for the mobilization and sequestration of the low-solubility-index elements Zr and Ti under acidic conditions. The occurrence of baddeleyite (ZrO 2 ), anatase (TiO 2 ), and the Magneli phases Ti 4 O 7 and Ti 5 O 9 (all present at the nanoscale) suggest an influx of nanocolloidal Zr and Ti oxides during weathering of smelter-derived particulate matter. Kelyshite {NaZr[Si 2 O 6 (OH)]}, authigenic zircon (ZrSiO 4 ), and kleberite [Fe 3+ Ti 6 O 11 (OH) 5 ] are most likely products of the sequestration of the Zr- and Ti-bearing nanocolloids.

58 GEOSCIENCES↗
DOE OSTI2017

Process evaluation and flowsheet development for the recovery of rare earth elements from coal and associated byproducts

Coal and coal byproducts produced annually contain enough rare earth elements (REEs) to meet current U.S. demand. Here, the REEs exist in the form of minerals, ion-exchanged elements associated with clays and chemically bonded elements within the organic coal matrix. Researchers at three universities have collaborated to evaluate the effectiveness of existing physical and chemical concentration processes for the recovery of the REEs. The efforts have found that physical separation processes can increase the total REE content in the thickener underflow material collected from a Central Appalachian coal cleaning facility from around 300 ppm to values greater than 17,500 ppm on an ash basis. Leaching followed by solvent extraction was found to be the most effective to recover the REEs from coarse middlings materials collected from multiple coal basins as indicated by recovery values exceeding 80%. Based on material characterization data and process evaluations conducted for several potential feed coal sources, economic recovery of the REEs will require byproduct production of both clean coal and REE concentrate using a process flowsheet that is unique for each source.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2017

Final Report of the Project "From the finite element method to the virtual element method"

The Finite Element Method (FEM) is a powerful numerical tool that is being used in a large number of engineering applications. The FEM is constructed on triangular/tetrahedral and quadrilateral/hexahedral meshes. Extending the FEM to general polygonal/polyhedral meshes in straightforward way turns out to be extremely difficult and leads to very complex and computationally expensive schemes. The reason for this failure is that the construction of the basis functions on elements with a very general shape is a non-trivial and complex task. In this project we developed a new family of numerical methods, dubbed the Virtual Element Method (VEM) for the numerical approximation of partial differential equations (PDE) of elliptic type suitable to polygonal and polyhedral unstructured meshes. We successfully formulated, implemented and tested these methods and studied both theoretically and numerically their stability, robustness and accuracy for diffusion problems, convection-reaction-diffusion problems, the Stokes equations and the biharmonic equations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

X-ray Fluorescence Microscopy to Develop Elemental Classifiers and Investigate Elemental Signatures in BALB/c Mouse Intestine a Week after Exposure to 8 Gy of Gamma Rays

Iron redistribution in the intestine after total body irradiation is an established phenomenon. However, in the literature, there are no reports about the use of X-ray fluorescence microscopy or equivalent techniques to generate semi-quantitative 2D maps of iron in sectioned intestine samples from irradiated mice. In this work, we used X-ray fluorescence microscopy (XFM) to map the elemental content of iron as well as phosphorus, sulfur, calcium, copper and zinc in tissue sections of the small intestine from eight-week-old BALB/c male mice that developed gastrointestinal acute radiation syndrome (GI-ARS) in response to exposure to 8 Gray of gamma rays. Seven days after irradiation, we found that the majority of the iron is localized as hot spots in the intercellular regions of the area surrounding crypts and stretching between the outer perimeter of the intestine and the surface cell layer of villi. In addition, this study represents our current efforts to develop elemental cell classifiers that could be used for the automated generation of regions of interest for analyses of X-ray fluorescence maps. Once developed, such a tool will be instrumental for studies of effects of radiation and other toxicants on the elemental content in cells and tissues. While XFM studies cannot be conducted on living organisms, it is possible to envision future scenarios where XFM imaging of single cells sloughed from the human (or rodent) intestine could be used to follow up on the progression of GI-ARS.

X-ray fluorescence microscopy↗
DOE OSTI2025

Production of anhydrous ƒ-element fluorides through the ionothermal treatment of ƒ-element oxalates

The pivotal role of uranium and plutonium fluorides in the nuclear fuel cycle, particularly in the pyrochemical reduction process, is well recognized. Traditionally, the fluorination of uranium and plutonium materials relies on the use of highly toxic and corrosive gases (e.g., HF (g) , F 2(g) ). Herein, we present an alternative approach using the ionic liquid 1‑butyl‑3-methylimidazolium hexafluorophosphate ([Bmim][PF 6 ] (l) ) and/or hexafluorophosphoric acid (HPF 6(aq) ) as fluorinating agents for the ƒ-element oxalates M$^{III}_{2}$(C 2 O 4 ) 3 ∙ 9H 2 O (s) M$^{III}_{2}$(C 2 O 4 ) 3 ∙ 9H 2 O (s) (M III = Ce, Pu) and M IV (C 2 O 4 ) 2 ∙ 6H 2 O (s) (M IV = Th, U). Our findings demonstrate that [Bmim][PF 6 ] (l) and HPF 6(aq) enable the ionothermal fluorination of ƒ-element oxalates, resulting in the formation of anhydrous CeF 3(s) , ThF 4(s) , and UF 4(s) within 2 hours at 200 °C. This method also facilitates the partial fluorination of plutonium(III) oxalate, yielding a mixture of anhydrous PuF 3(s) and an unidentified phase. Overall, the ionothermal treatment approach offers a safer and more efficient means of producing anhydrous ƒ-element fluorides than conventional methods involving hazardous gases. In addition, we describe the morphology of UF 4(s) materials as a function of production route and demonstrate the presence of morphological signatures that could be used during a nuclear forensic investigation.

Cerium↗
DOE OSTI2016

Design and expected performance of a fast neutron attenuation probe for light element density measurements

In this paper, we present the design and expected performance of a proof-of-concept 32 channel material identification system. Our system is based on the energy-dependent attenuation of fast neutrons for four elements: hydrogen, carbon, nitrogen and oxygen. We describe a new approach to obtaining a broad range of neutron energies to probe a sample, as well as our technique for reconstructing the molar densities within a sample. The system's performance as a function of time-of-flight energy resolution is explored using a Geant4-based Monte Carlo. Our results indicate that, with the expected detector response of our system, we will be able to determine the molar density of all four elements to within a 20–30% accuracy in a two hour scan time. In many cases this error is systematically low, thus the ratio between elements is more accurate. This degree of accuracy is enough to distinguish, for example, a sample of water from a sample of pure hydrogen peroxide: the ratio of oxygen to hydrogen is reconstructed to within 8±0.5% of the true value. Lastly, with future algorithm development that accounts for backgrounds caused by scattering within the sample itself, the accuracy of molar densities, not ratios, may improve to the 5–10% level for a two hour scan time.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1972

Evaluation of the use of a singularity element in finite element analysis of center-cracked plates

Two different methods are applied to the analyses of finite width linear elastic plates with central cracks. Both methods give displacements as a primary part of the solution. One method makes use of Fourier transforms. The second method employs a coarse mesh of triangular second-order finite elements in conjunction with a single singularity element subjected to appropriate additional constraints. The displacements obtained by these two methods are in very good agreement. The results suggest considerable potential for the use of a cracked element for related crack problems, particularly in connection with the extension to nonlinear material behavior.

Mendelson, A.↗