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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 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Application of multiple-isotope and groundwater-age data to identify factors affecting the extent of denitrification in a shallow aquifer near a river in South Korea

The extent of denitrification in a small agricultural area near a river in Yangpyeong, South Korea, was determined using multiple isotopes, groundwater age, and physicochemical data for groundwater. The shallow groundwater at one monitoring site had high concentrations of NO{sub 3}-N (74–83 mg L{sup −1}). The δ{sup 15}N-NO{sub 3} values for groundwater in the study area ranged between +9.1 and +24.6‰ in June 2014 and +12.2 to +21.6‰ in October 2014. High δ{sup 15}N-NO{sub 3} values (+10.7 to +12.5‰) in both sampling periods indicated that the high concentrations of nitrate in the groundwater originated from application of organic fertilizers and manure. In the northern part of the study area, some groundwater samples showed elevated δ{sup 15}N-NO{sub 3} and δ{sup 18}O-NO{sub 3} values, which suggest that nitrate was removed from the groundwater via denitrification, with N isotope enrichment factors ranging between −4.8 and −7.9‰ and O isotope enrichment factors varying between −3.8 and −4.9‰. Similar δD and δ{sup 18}O values of the surface water and groundwater in the south appear to indicate that groundwater in that area was affected by surface-water infiltration. The mean residence times (MRTs) of groundwater showed younger ages in the south (10–20 years) than in the north (20–30 years). Hence, it was concluded that denitrification processes under anaerobic conditions with longer groundwater MRT in the northern part of the study area removed considerable amounts of nitrate. This study demonstrates that multi-isotope data combined with physicochemical data and age-dating information can be effectively applied to characterize nitrate contaminant sources and attenuation processes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

MDTri: robust and efficient global mixed integer search of spaces of multiple ternary alloys: A DIRECT-inspired optimization algorithm for experimentally accessible computational material design

Computational materials design has suffered from a lack of algorithms formulated in terms of experimentally accessible variables. Here we formulate the problem of (ternary) alloy optimization at the level of choice of atoms and their composition that is normal for synthesists. Mathematically, this is a mixed integer problem where a candidate solution consists of a choice of three elements, and how much of each of them to use. This space has the natural structure of a set of equilateral triangles. We solve this problem by introducing a novel version of the DIRECT algorithm that (1) operates on equilateral triangles instead of rectangles and (2) works across multiple triangles. We demonstrate on a test case that the algorithm is both robust and efficient. Lastly, we offer an explanation of the efficacy of DIRECT -- specifically, its balance of global and local search -- by showing that 'potentially optimal rectangles' of the original algorithm are akin to the Pareto front of the 'multi-component optimization' of global and local search.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

A mixed-integer PDE-constrained optimization formulation for constructing electromagnetic cloaks with multiple materials

We study the design of an electromagnetic cloak from multiple materials with an additional constraint on the mass of the cloak. Our problem is an example of a topology optimization problem, and we formulate this problem as a mixed-integer partial-differential equation constrained optimization (MIPDECO) problem, where Maxwell’s equation models the propagation of the wave through the cloak and surrounding medium. We use binary variables to model the assignment of the different materials, and their relevant properties (permittivity and density). The mass constraint adds a nontrivial constraint to this problem. We propose a two-phase strategy to solve this problem. In the first phase, we solve a continuous relaxation, and then propose a new variant of the feasibility pump that exploits the structure of the PDE to obtain an initial integral solution candidate. In the second phase, we use a trust-region approach to improve this incumbent. We also consider a continuation or mesh-sequencing approach to find better solutions faster on consecutively finer meshes. We present detailed numerical results to illustrate the effectiveness of our approaches for constructing multi-material cloaks with a mass constraint.

Calculus of Variations and Optimization↗
DOE OSTI2019

Multiple Magnetic Phase Transitions in Mn-deficient Co{sub 0.4}Ni{sub 0.6}Mn{sub 1−x}Ge Compounds

The structural and magnetic transition in Mn-deficient Co{sub 0.4}Ni{sub 0.6}Mn{sub 1−x}Ge was investigated by DC magnetization and temperature-dependent X-ray diffraction measurements. By introducing Mn vacancies in the stoichiometric Co{sub 0.4}Ni{sub 0.6}MnGe compound, multiple magnetic phase transitions and tunable martensitic transitions were observed. A paramagnetic martensite (Ni{sub 2}In-type structure) to ferromagnetic austenite (TiNiSi-type structure) transition was realized in Co{sub 0.4}Ni{sub 0.6}Mn{sub 0.98}Ge around 275 K. A large volume expansion of 2.6% accompanied this transition. In addition, a martensitic transition induced by the magnetic field was also observed near room temperature. Furthermore, a significant magnetic entropy variation of − 21.3 J/kg K at 263 K (∆B = 5 T) was obtained in the Co{sub 0.4}Ni{sub 0.6}Mn{sub 0.98}Ge compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Once More on the Lattice of Subvarieties of the Wreath Product of the Variety of Semilattices and the Variety of Semigroups with Zero Multiplication

It is known that the monoid wreath product of any two semigroup varieties that are atoms in the lattice of all semigroup varieties may have a finite as well as an infinite lattice of subvarieties. If this lattice is finite, then as a rule it has at most eleven elements. This was proved in a paper of the author in 2007. The exclusion is the monoid wreath product Sl w N{sub 2} of the variety of semilattices and the variety of semigroups with zero multiplication. The number of elements of the lattice L(Sl w N{sub 2}) of subvarieties of Sl w N{sub 2} is still unknown. In a previous paper, we have shown that the lattice L(Sl w N{sub 2}) contains a sublattice having 33 elements. In the present paper, it is proved that the lattice under consideration has exactly three maximal subvarieties. As a first application of the obtained results we calculate the finite basis of the lattice union of the variety of all semilattices and the largest variety among subvarieties of our lattice having at least one heterotypic identity. As a second application we show that the considered lattice of subvarieties has at least 39 elements.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Sequential chemical separations and multiple ion counting ICP-MS for 241 Pu– 241 Am– 237 Np dating of environmental collections on a single aliquot

In this study, we have developed a combined sequential chemical separation procedure and multiple ion counting ICP-MS measurement method for isotopic measurements of Am in environmental samples. This, in conjunction with established resin bead TIMS measurements for Pu and Np, allows us to measure long-lived Pu–Np–Am nuclides in environmental samples on a single solution aliquot. This single aliquot method reduces time lines and maximizes sample utility for the measurements, improving sensitivity, precision, and accuracy over prior methods. Finally, we have evaluated this new method with environmental reference materials and have obtained accurate results on samples with > 3E6 atoms 241 Am.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

Representing heterogeneity in structural relationships among multiple choice variables using a latent segmentation approach

Travel model systems often adopt a single decision structure that links several activity-travel choices together. The single decision structure is then used to predict activity-travel choices, with those downstream in the decision-making chain influenced by those upstream in the sequence. The adoption of a singular sequential causal structure to depict relationships among activity-travel choices in travel demand model systems ignores the possibility that some choices are made jointly as a bundle as well as the possible presence of structural heterogeneity in the population with respect to decision-making processes. As different segments in the population may adopt and follow different causal decision-making mechanisms when making selected choices jointly, it would be of value to develop simultaneous equations model systems relating multiple endogenous choice variables that are able to identify population subgroups following alternative causal decision structures. Because the segments are not known a priori, they are considered latent and determined endogenously within a joint modeling framework proposed in this paper. The methodology is applied to a national mobility survey data set to identify population segments that follow different causal structures relating residential location choice, vehicle ownership, and car-share and mobility service usage. It is found that the model revealing three distinct latent segments best describes the data, confirming the efficacy of the modeling approach and the existence of structural heterogeneity in decision-making in the population. Future versions of activity-travel model systems should strive to incorporate such structural heterogeneity to better reflect varying decision processes across population subgroups.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

A parallel evolutionary multiple-try metropolis Markov chain Monte Carlo algorithm for sampling spatial partitions

We develop an Evolutionary Markov Chain Monte Carlo (EMCMC) algorithm for sampling spatial partitions that lie within a large, complex, and constrained spatial state space. Our algorithm combines the advantages of evolutionary algorithms (EAs) as optimization heuristics for state space traversal and the theoretical convergence properties of Markov Chain Monte Carlo algorithms for sampling from unknown distributions. Local optimality information that is identified via a directed search by our optimization heuristic is used to adaptively update a Markov chain in a promising direction within the framework of a Multiple-Try Metropolis Markov Chain model that incorporates a generalized Metropolis-Hastings ratio. We further expand the reach of our EMCMC algorithm by harnessing the computational power afforded by massively parallel computing architecture through the integration of a parallel EA framework that guides Markov chains running in parallel.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

PET Imaging Study of S1PR1 Expression in a Rat Model of Multiple Sclerosis

Upregulation of sphingosine-1-phosphate receptor 1 (S1PR1) expression in multiple sclerosis (MS) lesions is associated with neuroinflammatory response. This study investigated the correlation between neuroinflammation and S1PR1 expression in the spinal cord of an experimental autoimmune encephalomyelitis (EAE) rat model of MS, using the S1PR1 positron emission tomography (PET) radiotracer [11C]TZ3321. MicroPET imaging studies of [11C]TZ3321 were performed to measure uptake of [11C]TZ3321 in the spinal cord of EAE rats. Immunohistochemical staining was performed to confirm the overexpression of S1PR1 and other inflammatory biomarkers. MicroPET imaging demonstrated a 20–30 % increase in [11C]TZ3321 uptake in the lumbar spinal cord of EAE rats versus sham controls at 35–60 min post injection. The increased uptake of [11C]TZ3321 was correlated with the overexpression of S1PR1 in the lumbar spinal cord of EAE rats that was confirmed by immunohistochemical staining. Upregulated S1PR1 expression was associated with glial cell activation and immune cell infiltration. MicroPET imaging modality with a specific radioligand [11C]TZ3321 is able to assess the expression of S1PR1 in EAE rat lumbar spinal cord. This may provide a new approach to the assessment of neuroinflammatory response in MS and other inflammatory diseases.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Effect of oxidation on the release of multiple metals from industrially polluted sediments and synchrotron-based evidence of Cu–S dynamic association

Disposal operations for industrially polluted sediments are usually accompanied by disturbance and resuspension, which can induce metal remobilization and secondary pollution. Evaluating the risk of metal release under various redox conditions is fundamental for predicting contaminant mobilization and guiding remediation measures. An abandoned oxidation pond, Yanjia Lake, China, was selected as a typical industrially polluted site. Re-suspension experiments were carried out by mixing polluted sediments with lake water under oxic or anoxic conditions, then investigating the effect of oxidation conditions on the release of multiple metals. Metal concentrations and aqueous chemistry in the overlying water were monitored. Synchrotron-based methods, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), were used to characterize oxidation states and coordination conditions of metals in sediments. The release of metals, including Cr, Co, Ni, Cu, Zn, Se, Mo, Sn, Cd, and Pb, was enhanced under oxic vs. anoxic conditions. The XANES analysis revealed that elevated Cr and Zn concentrations under oxic conditions likely resulted from the oxidation of Cr(III) and oxidizing dissolution of ZnS, respectively. K-edge Cu XANES, S XANES, and Cu EXAFS analyses reconstructed the Cu–S association, indicating that S-related oxidation promoted Cu release and Cu–O partly replaced Cu–S in the sediment after a 7-day oxic treatment. The release of most metals was promoted under oxic conditions, resulting from the oxidation of sulfides and metals as indicated by aqueous and synchrotron-based evidence. The risk of secondary pollution is greatly enhanced under oxic conditions, which suggests that measures should be taken to minimize the redox disturbance during sediment remediation. This information can guide the management of sediments in Yanjia Lake and other contaminated sites with similar properties.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Rapid Solidification of Sn-Cu-Al Alloys for High-Reliability, Lead-Free Solder: Part II. Intermetallic Coarsening Behavior of Rapidly Solidified Solders After Multiple Reflows

Controlling the size, dispersion, and stability of intermetallic compounds in lead-free solder alloys is vital to creating reliable solder joints regardless of how many times the solder joints are melted and resolidified (reflowed) during circuit board assembly. In this article, the coarsening behavior of Cu x Al y and Cu 6 Sn 5 in two Sn-Cu-Al alloys, a Sn-2.59Cu-0.43Al at. pct alloy produced via drip atomization and a Sn-5.39Cu-1.69Al at. pct alloy produced via melt spinning at a 5-m/s wheel speed, was characterized after multiple (1-5) reflow cycles via differential scanning calorimetry between the temperatures of 293 K and 523 K (20 °C and 250 °C). Little-to-no coarsening of the Cu x Al y particles was observed for either composition; however, clustering of Cu x Al y particles was observed. For Cu 6 Sn 5 particle growth, a bimodal size distribution was observed for the drip atomized alloy, with large, faceted growth of Cu 6 Sn 5 observed, while in the melt spun alloy, Cu 6 Sn 5 particles displayed no significant increase in the average particle size, with irregularly shaped, nonfaceted Cu 6 Sn 5 particles observed after reflow, which is consistent with shapes observed in the as-solidified alloys. The link between original alloy composition, reflow undercooling, and subsequent intermetallic coarsening behavior was discussed by using calculated solidification paths. As a result, the reflowed microstructures suggested that the heteroepitaxial relationship previously observed between the Cu x Al y and the Cu 6 Sn 5 was maintained for both alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Multiple Rejuvenation Cycles on Mechanical Properties and Microstructure of IN-738 Superalloy

The scope of this work is to show the effects of multiple applications of a rejuvenation treatment studied for IN-738 on both the microstructure and the mechanical properties of the creep-damaged superalloy and to check the recovery obtained after one and two rejuvenation cycles through creep and tensile tests, whose results will be compared with the performance of the virgin material. This work will show that this rejuvenation treatment is able to recover the microstructure of creep-damaged specimens after one and two applications and that the mechanical properties of the rejuvenated alloy are very similar to the virgin material even after two rejuvenation cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Residual Stress Distribution and Microstructure of a Multiple Laser-Peened Near-Alpha Titanium Alloy

Laser peening without coating (LPwC) was performed on a Ti-2.5 Cu alloy with multiple passes (1, 3 and 5), using a Nd:YAG laser (1064 nm) at a constant overlap rate of 70% and power density of 6.7 GW cm{sup −2}. Hardness and residual stress profiles indicated thermal softening near the surface (< 100 μm) and bulk softening due to adiabatic heating. Maximum hardness (235 HV at 500 μm) and maximum residual stress (− 890 MPa at 100 μm) were observed for LPwC with 1 pass. Surface roughness and surface 3-D topography imaging showed that the surface roughness increased with the increase in the number of passes. XRD results indicated no significant β phases. However, peak shifts, broadening and asymmetry were observed and interpreted based on dislocation activity. Microstructures indicated no melting or resolidification or refinement of grains at the surface. Twin density was found to increase with the increase in the number of passes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Multiple Local Repairs on Microstructure and Mechanical Properties of T24 Steel Welded Joint

The effect of multiple local repairs on the microstructure and mechanical properties of the T24 steel welded joints was studied. T24 steel tubes were butt-welded by the GTAW method. Peripheral welded joints were made in four locations of the tube. In order to simulate the repair procedure, the welds were cut off from the root and the first local repair was performed. Other two local repairs were carried out in the same way. After each local repair, the microstructure and mechanical properties of the joints were evaluated. The results of the mechanical tests demonstrate that only two local repairs can be performed on the T24 steel peripheral welded joint. After the third local repair, impact energy of the welded joint was lower than required value, which is attributed to the coarser martensite and the coarser carbide precipitates formed in the heat-affected zone, compared with the weld metal.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of ABCB1 polymorphisms on the pharmacokinetics and toxicity of lenalidomide in patients with multiple myeloma

Individual diversity in plasma concentrations of lenalidomide occurs despite dosage modifications based on creatinine clearance (CCr), which can lead to unexpected toxicity. We have previously identified a cutoff value of area under the concentration–time curve (AUC{sub 0–24}) for lenalidomide to avoid severe toxicity. Here, we investigated the association between ABCB1 polymorphisms and pharmacokinetics of lenalidomide in patients with multiple myeloma (MM) treated with lenalidomide and dexamethasone. Plasma concentrations of lenalidomide were analyzed using liquid chromatography–tandem mass spectrometry. Genotyping for ABCB1 1236C>T, 2677G>A/T, and 3435C>T polymorphisms was performed, and the effects of ABCB1 polymorphisms on AUC{sub 0–24} for lenalidomide were compared in 36 patients with MM who were administered lenalidomide according to the drug label based on CCr. Genotyping analysis showed that although there were no differences in AUC{sub 0–24} in 1236C>T and 2677G>A/T polymorphisms. AUC{sub 0–24} was significantly higher in patients with the T allele of 3435C>T (n = 15) than in those without (n = 21) (median 6324.6 ng h/mL vs. 2857.4 ng h/mL, p = 0.028). The AUC{sub 0–24} value exceeded the aforementioned cutoff value in 95% of the patients with the T allele of 3435C>T but in 60% with C/C genotype (p = 0.013). Multivariate logistic analysis confirmed the significance of T allele of ABCB1 3435C>T as a factor due to which the AUC{sub 0–24} cutoff value was exceeded (hazard ratio of 15.0, p = 0.019). We show that lenalidomide pharmacokinetics is influenced by the ABCB1 3435C>T polymorphism, which could be useful to individualize dosage design and reduce unexpected toxicity.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2020

Heterogeneities at multiple length scales in 2D layered materials: From localized defects and dopants to mesoscopic heterostructures

Two-dimensional (2D) materials hold great promise for applications in optoelectronics, quantum information science, and energy conversion due to their remarkable properties imbued by their physical characteristics. Although heterogeneities in their intrinsic structure are the major challenges limiting their synthesis and predictable properties, they also provide a pathway to controllably tune the properties and broaden the potential of 2D materials. Heterogeneities that can be tailored, including defects, dopants, strain, edges, and layer stackings offer transformative opportunities in heterogeneous 2D materials through the introduction of novel properties for technological applications. This article provides a review of recent progress in studying heterogeneities in 2D materials. The review uses examples from our work to develop a strategy to understand the heterogeneities across multiple length scales to link the effect of heterogeneity at the nanoscale with the macroscale properties of 2D materials. We describe specific types of heterogeneities and explore novel synthesis and processing methods for their controlled production with example of the potential impact and applications enabled by their intriguing properties. Finally, we provide a perspective on how to extend the range of tunable properties through further engineering the heterogeneities in 2D materials.

2D materials↗
DOE OSTI2018

Asynchronously parallel optimization solver for finding multiple minima

This paper proposes and analyzes an asynchronously parallel optimization algorithm for finding multiple, high-quality minima of nonlinear optimization problems. Our multistart algorithm considers all previously evaluated points when determining where to start or continue a local optimization run. Theoretical results show that, under certain assumptions, the algorithm almost surely starts a finite number of local optimization runs and identifies, or has a single local optimization run converging to, every minimum. The algorithm is applicable to general optimization settings, but our numerical results focus on the case when derivatives are unavailable. In numerical tests, a PYTHON implementation of the algorithm is shown to yield good approximations of many minima (including a global minimum), and this ability scales well with additional resources. Our implementation’s time to solution is shown also to scale well even when the time to evaluate the function evaluation is highly variable.

97 MATHEMATICS AND COMPUTING↗