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At least 1,441 records · Page 80

All sources NASA NTRS DOE OSTI

DOE OSTI2016

Optical properties and carrier dynamics of GaAs/GaInAs multiple-quantum-well shell grown on GaAs nanowire by molecular beam epitaxy

GaAs/GaInAs multiple-quantum-well (MQW) shells having different GaInAs shell width formed on the surface of self-catalyzed GaAs core nanowires (NWs) are grown on (100) Si substrate using molecular beam epitaxy. The photoluminescence emission from GaAs/GaInAs MQW shells and the carrier lifetime could be varied by changing the width of GaInAs shell. Time-resolved photoluminescence measurements showed that the carrier lifetime had a fast and slow decay owing to the mixing of wurtzite and zinc-blende structures of the NWs. Furthermore, strain relaxation caused the carrier lifetime to decrease beyond a certain thickness of GaInAs quantum well shells.

14 SOLAR ENERGY↗

DOE OSTI2014

Hydrogen cluster/network in tobermorite as studied by multiple-quantum spin counting {sup 1}H NMR

Proton multiple-quantum (MQ) spin-counting experiment has been employed to study arrangement of hydrogen atoms in 9 Å/11 Å natural/synthetic tobermorites. Even though all tobermorite samples give similar characterless, broad static-powder {sup 1}H NMR spectra, their MQ spin-counting spectra are markedly different; higher quanta in 11 Å tobermorite do not grow with the MQ excitation time, while those in 9 Å one do. A statistical analysis of the MQ results recently proposed [26] is applied to show that hydrogens align in 9 Å tobermorite one dimensionally, while in 11 Å tobermorite they exist as a cluster of 5–8 hydrogen atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2019

The multiple depleted mantle components in the Hawaiian-Emperor chain

Oceanic island basalts are targeted for geochemical study because they provide a direct window into mantle composition and a wealth of information on the dynamics and timescales associated with Earth mixing. Previous studies mainly focused on the shield volcanic stage of oceanic islands and the more fusible, enriched mantle components that are easily distinguished in those basalts. Mantle depleted compositions are typically more difficult to resolve unless large amounts of this material participated in mantle melting (e.g., mid-ocean ridges), or unique processes allow for their compositions to be erupted undiluted, such as very small degrees of melting of a source with minimal fusible enriched components (e.g., rejuvenated basalts) or as xenoliths (e.g., abyssal peridotites). Mantle depleted components, defined here as material with low time-integrated Rb/Sr (low 87 Sr/ 86 Sr) and high time-integrated Sm/Nd and Lu/Hf ratios (high 143 Nd/ 144 Nd and 176 Hf/ 177 Hf) relative to primitive mantle, derive from a potentially very large volume reservoir (up to 80% of the mantle), and therefore need adequate characterization in order estimate the composition of the Earth and mantle-derived melts. Here, this review focuses on mantle depleted compositions in oceanic island basalts using the Hawaiian-Emperor chain as a case study. The Hawaiian-Emperor chain is the ~6000 km long geological record of the deeply sourced Hawaiian mantle plume, active for >81 Myr. Hawaiian volcanism evolves through four volcanic stages as a volcano traverses the Hawaiian plume: alkalic preshield, tholeiitic shield (80–90% volcano volume), alkalic postshield (~1%), and silica undersaturated rejuvenated (<0.1%). We report Pb-Sr-Nd-Hf isotope compositions and trace element concentrations of three rejuvenated Northwest Hawaiian Ridge basalts and compare them to an exhaustive compiled dataset of basalts from the Hawaiian Islands to the Emperor Seamounts. The Northwest Hawaiian Ridge (NWHR) includes 51 volcanoes spanning ~42 m.y. between the bend in the Hawaiian-Emperor chain and the Hawaiian Islands where there is no high-precision isotopic data published on the rejuvenated-stage over ~47% of the chain. NWHR and Hawaiian Island rejuvenated basalts are geochemically similar, indicating a consistent source for rejuvenated volcanism over ~12.5 million years. In contrast, shield-stage basalts from the oldest Emperor Seamounts are more depleted in isotopic composition (i.e., higher 176 Hf/ 177 Hf, and 143 Nd/ 144 Nd with lower 87 Sr/ 86 Sr and 208 Pb*/ 206 Pb*) and trace element concentrations (i.e., much lower concentrations of highly incompatible elements) than all other depleted Hawaiian basalts younger than the bend, including NWHR rejuvenated basalts. The strongly depleted source for the oldest Emperor Seamounts (>70 Ma) was likely related to interaction with the Kula-Pacific-Izanagi mid-ocean ridge spreading system active near the Hawaiian plume in the Late Cretaceous. In contrast, the incompatible trace element ratios of NWHR rejuvenated basalts require a distinct source in the Hawaiian mantle plume that was imprinted by ancient (>1 Ga) partial melting, likely ancient recycled oceanic lithosphere. This review of the geochemistry of Hawaiian depleted components documents the need for the sampling of multiple distinctive depleted compositions, each preferentially melted during specific periods of Hawaiian plume activity. This suggests that the composition of depleted components can evolve during the lifetime of the mantle plume, as observed for enriched components in the Hawaiian mantle plume. Changes in the composition of depleted components are dominantly controlled by the upper mantle tectonic configurations at the time of eruption (i.e., proximity to a mid-ocean ridge), as this effect overwhelms the signal imparted by potentially sampling different lower mantle components through time.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2017

Comparing multiple statistical methods for inverse prediction in nuclear forensics applications

Forensic science seeks to predict source characteristics using measured observables. Statistically, this objective can be thought of as an inverse problem where interest is in the unknown source characteristics or factors ( X ) of some underlying causal model producing the observables or responses (Y = g ( X ) + error ). Here, this paper reviews several statistical methods for use in inverse problems and demonstrates that comparing results from multiple methods can be used to assess predictive capability. Motivation for assessing inverse predictions comes from the desired application to historical and future experiments involving nuclear material production for forensics research in which inverse predictions, along with an assessment of predictive capability, are desired.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2010

Multiple mapping conditioning of velocity in turbulent jet flames

Multiple mapping conditioning (MMC) has emerged as a new approach to model turbulent reacting flows. This study revises the standard MMC closure for velocity in turbulent jet flows from linearity in the reference space to linearity in the composition space. This modeling amendment ensures that the standard velocity model in conditional moment closure studies can now be used for MMC computation as well. A simplified model for the velocity-dependence of MMC drift coefficients is derived without loss of generality and is implemented for the revised velocity closure. Modeling results have been corroborated against the Direct Numerical Simulation database of a spatially evolving, planar turbulent jet flame. The revised model shows marked improvement over standard MMC closure in predicting velocity statistics close to the nozzle. (author)

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

The effect of variable fuel staging transients on self-excited instabilities in a multiple-nozzle combustor

Combustion instability in gas turbine engines is often mitigated using fuel staging. Fuel staging, sometimes referred to as fuel splitting, is a strategy by which fuel is unevenly distributed between different nozzles of a multiple-nozzle combustor. These fuel splits are conducted in a transient manner in real engines, and the effects of these transients on instability are not well characterized. This work fills this gap by systematically studying the effects of transient fuel staging on self-excited combustion instability by varying the amount of staging fuel (staging amplitude), timescale in which the fuel is added (transient duration), and whether staging fuel is added or subtracted (transient direction). In this work, three staging amplitudes, five transient durations, and both transient directions are considered. The transient timescales are broadly divided into “short” duration transients, which have fuel delivery timescales shorter than the characteristic instability decay or onset timescales, and “long” duration transients, which have fuel delivery timescales longer than the characteristic instability decay or onset timescales. For short duration transients, we find the instability decay timescale depends on staging amplitude but does not depend on transient duration. For long duration transients, we find the instability decay timescale does not strongly depend on staging amplitude. The instability onset timescale is found to be longer and more variable between runs than the instability decay timescale for a given fuel delivery timescale. The onset timescale is also longer in duration and more variable than the decay timescale at a given fuel delivery timescale, implying that the instability rise process is overall more variable and slower than the instability decay process. Analysis of combustor damping rates show a strong dependence of damping rate on staging amplitude but no strong dependence on transient duration or direction. Instantaneous phase difference images between p' and are used to differentiate regions in the combustor that have constructive versus destructive interference between heat release rate oscillations and pressure fluctuations. Furthermore, the phase images show that p' and q . ' become in-phase early in the transient for the onset transients.

20 FOSSIL-FUELED POWER PLANTS↗

DOE OSTI2016

GPU acceleration of the Locally Selfconsistent Multiple Scattering code for first principles calculation of the ground state and statistical physics of materials

The Locally Self-consistent Multiple Scattering (LSMS) code solves the first principles Density Functional theory Kohn–Sham equation for a wide range of materials with a special focus on metals, alloys and metallic nano-structures. It has traditionally exhibited near perfect scalability on massively parallel high performance computer architectures. In this paper, we present our efforts to exploit GPUs to accelerate the LSMS code to enable first principles calculations of O(100,000) atoms and statistical physics sampling of finite temperature properties. We reimplement the scattering matrix calculation for GPUs with a block matrix inversion algorithm that only uses accelerator memory. Finally, using the Cray XK7 system Titan at the Oak Ridge Leadership Computing Facility we achieve a sustained performance of 14.5PFlop/s and a speedup of 8.6 compared to the CPU only code.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Multiple charging and chemical stability of tripodal catholyte redoxmers

Macromolecular catholyte materials store multiple positive charges in all-organic redox flow cells. Presently, little is known about the electronic structure and chemical stability of these macromolecules in different states of charge. Here we demonstrate that in propeller-like catholyte trimers (tripods), chemical stability increases when they become fully charged.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Trophic structure and metal bioaccumulation differences in multiple fish species exposed to coal ash-associated metals

On December 22, 2008 a dike containing coal fly ash from the Tennessee Valley Authority Kingston Fossil Plant near Kingston Tennessee USA failed and resulted in the largest coal ash spill in U.S. history. Coal ash, the by-product of coal combustion, is known to contain multiple contaminants of concern, including arsenic and selenium. The purpose of this study was to investigate the bioaccumulation of arsenic and selenium and to identify possible differences in trophic dynamics in feral fish at various sites in the vicinity of the Kingston coal ash spill. Elevated levels of arsenic and selenium were observed in various tissues of largemouth bass, white crappie, bluegill and redear sunfish from sites associated with the Kingston coal ash spill. Highest concentrations of selenium were found in redear sunfish with liver concentrations as high as 24.83 mg/kg dry weight and ovary concentrations up to 10.40 mg/kg dry weight at coal ash-associated sites. To help explain the elevated selenium levels observed in redear sunfish, investigations into the gut pH and trophic dynamics of redear sunfish and bluegill were conducted which demonstrated a large difference in the gut physiology between these two species. Redear sunfish stomach and intestinal pH was found to be 1.1 and 0.16 pH units higher than in bluegill, respectively. In addition, fish from coal ash-associated sites showed enrichment of 15N & 13C compared to no ash sites, indicating differences in food web dynamics between sites. These results imply the incorporation of coal ash-associated compounds into local food webs and/or a shift in diet at ash sites compared to the no ash reference sites. Based on these results, further investigation into a broader food web at ash-associated sites is warranted.

Otter, Ryan↗

DOE OSTI2022

Approximating a linear multiplicative objective in watershed management optimization

Implementing management practices in a cost-efficient manner is critical for regional efforts to reduce the amount of pollutants entering the Chesapeake Bay. We study the problem of selecting a subset of practices that minimizes pollutant load—subject to budgetary and environmental constraints—as simulated in a widely used regulatory watershed model. Mimicking the computation of pollutant load in the regulatory model, we formulate this problem as a continuous optimization model with a linear multiplicative objective function and linear constraints. To lay the groundwork for incorporating additional stakeholder requirements in the future, especially those that would require integer variables, we present and study a continuous linear optimization model that approximates the nonlinear model. The linear model, which requires an exponential number of variables, arises naturally as an alternative model for the same underlying physical process. We examine the theoretical behavior of these optimization models and investigate restrictions of the linear model to handle its large number of variables. Through extensive computational tests on real and randomly generated instances, we demonstrate that the linear model and its restrictions provide optimal solutions close to those of the nonlinear model in practice, despite poor approximation properties in the worst case. We conclude that the linear model—together with our approach to handling its large number of variables—provides a viable framework from which to extend the optimization model to better meet the needs of the Chesapeake Bay watershed management stakeholders.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

A techno-economic assessment framework for hydrogen energy storage toward multiple energy delivery pathways and grid services

Hydrogen energy storage (HES) transforms and stores electric energy from the grid into hydrogen, and supplements other energy storage and demand response resources in addressing challenges in renewable-intensive power systems. Understanding how to optimally utilize an HES system to maximize its economic benefits from stacked value streams is highly important to its development and deployment. Here, in this paper, we present a techno-economic assessment framework for an HES system considering three common energy delivery pathways and multiple grid and end-user services. Models are developed to capture the operational capability, flexibility, and constraints associated with hydrogen production, compression, storage, and utilization as well as different grid services in an economic assessment. To define the technically achievable benefits, an optimal dispatch formulation is proposed to maximize the economic benefits over a representative year with an hourly time step considering the trade-offs among different value streams. Representative case studies are designed and carried out to show how system configuration, energy delivery pathways, and grid services may affect economic benefits. It was found that value streams from bundling grid services account for up to 76% of the total benefits and are critical for an HES project to be financially viable.

25 ENERGY STORAGE↗

DOE OSTI2018

Urban residential greenspace and mental health in youth: Different approaches to testing multiple pathways yield different conclusions

Highlights: • We compared single and parallel mediation models to serial mediation models. • Single mediation models suggested mediation through neighborhood restorative quality. • Parallel mediation models did not find any mediation through restorative quality. • There was serial mediation through restorative quality, physical activity and social cohesion. • Testing mediators alone or in parallel may lead to incorrect inferences. Urban greenspace can benefit mental health through multiple mechanisms. They may work together, but previous studies have treated them as independent.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

Ozone, NO2 and PM10 are associated with the occurrence of multiple sclerosis relapses. Evidence from seasonal multi-pollutant analyses

Highlights: • Season-dependent associations between short term exposure to NO{sub 2} and O{sub 3} and risk of MS relapses were observed. • Confirmation of PM10-associated risk of MS relapses. • A multi-pollutant approach should be systematically intended, especially when assessing level of PM{sub 10} and NO{sub 2.} • Individual characteristics should be considered alongside other MS relapses risk factors. Triggers of multiple sclerosis (MS) relapses are essentially unknown. PM{sub 10} exposure has recently been associated with an increased risk of relapses.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

Long-term exposure to air pollution and the incidence of multiple sclerosis: A population-based cohort study

Highlights: • No associations of MS incidence with PM{sub 2.5} and NO{sub 2} were observed. • There was a tendency for increasing MS incidence in relation to O{sub 3.} • Females exhibited a higher risk of developing MS in association with O{sub 3} than males. Evidence of the adverse neurological effects of exposure to ambient air pollution is emerging, but little is known about its effect on the development of multiple sclerosis (MS), the most common autoimmune disease of the central nervous system.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

Joint estimation of biogeochemical model parameters from multiple experiments: A bayesian approach applied to mercury methylation

Here, to characterize complex biogeochemical systems, results from multiple experiments, where each targets a specific subprocess, are commonly combined. The resulting datasets are interpreted through the calibration of biogeochemical models for process inference and predictions. Commonly used calibration approaches of fitting datasets from individual experiments to subprocess models one at a time is prone to missing information shared between datasets and incomplete uncertainty propagation. We propose a Bayesian joint-fitting scheme addressing the above-mentioned concerns by jointly fitting all the available datasets, thus calibrating the entire biogeochemical model in one go using Markov Chain Monte Carlo (MCMC). The identification of null spaces in the parameter distributions from MCMC guided the simplification of certain subprocess models. For example, fast kinetic sorption was replaced by equilibrium sorption, and Monod demethylation was replaced by first-order demethylation. Joint fitting of datasets resulted in complete uncertainty propagation with parameter estimates informed by all available data.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2012

High-Yield Secretion of Multiple Client Proteins in Aspergillus

Production of pure and high-yield client proteins is an important technology that addresses the need for industrial applications of enzymes as well as scientific experiments in protein chemistry and crystallization. Fungi are utilized in industrial protein production because of their ability to secrete large quantities of proteins. In this study, we engineered a high-expression-secretion vector, pEXPYR that directs proteins towards the extracellular medium in two Aspergillii host strains, examine the effect of maltose-induced over-expression and protein secretion as well as time and pH-dependent protein stability in the medium. We describe five client proteins representing a core set of hemicellulose degrading enzymes that accumulated up to 50-100 mg/L of protein. Using a recyclable genetic marker that allows serial insertion of multiple genes, simultaneous hyper-secretion of three client proteins in a single host strain was accomplished.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2018

Experimental and numerical studies of helium-cooled modular divertors with multiple jets

As part of the US-Japan PHENIX program, the helium-cooled modular divertor with multiple jets (HEMJ) and a simpler “flat” variant were experimentally studied in a closed helium loop with a redesigned test chamber at coolant inlet temperatures as great as 425 °C, incident heat fluxes as great as 2.2 MW/m 2 and prototypical inlet pressures of ~10 MPa. The data were used to develop correlations for the average Nusselt number and loss coefficient for a range of mass flow rates; these correlations were used in turn to predict the thermal-hydraulic performance of a single divertor module at prototypical conditions. The experimental results suggest that a flat jet array with six holes surrounding one central hole, all of the same diameter, can provide similar average heat transfer coefficients as the HEMJ divertor, albeit with higher pumping power requirements. Because of its smaller cooled surface area, however, this design has lower maximum allowable heat fluxes compared with the HEMJ divertor. Nevertheless, the flat variant could potentially simplify manufacturing and reduce the costs required to fabricate O(10 6 ) “finger” modules.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

QoS-aware edge AI placement and scheduling with multiple implementations in FaaS-based edge computing

Resource constraints on the computing continuum require that we make smart decisions for serving AI-based services at the network edge. AI-based services typically have multiple implementations (e.g., image classification implementations include SqueezeNet, DenseNet, and others) with varying trade-offs (e.g., latency and accuracy). The question then is how should AI-based services be placed across Function-as-a-Service (FaaS) based edge computing systems in order to maximize total Quality-of-Service (QoS). To address this question, we propose a problem that jointly aims to solve (i) edge AI service placement and (ii) request scheduling. These are done across two time-scales (one for placement and one for scheduling). Here we first cast the problem as an integer linear program. We then decompose the problem into separate placement and scheduling subproblems and prove that both are NP-hard. We then propose a novel placement algorithm that places services while considering device-to-device communication across edge clouds to offload requests to one another. Our results show that the proposed placement algorithm is able to outperform a state-of-the-art placement algorithm for AI-based services, and other baseline heuristics, with regard to maximizing total QoS. Additionally, we present a federated learning-based framework, FLIES, to predict the future incoming service requests and their QoS requirements. Our results also show that our FLIES algorithm is able to outperform a standard decentralized learning baseline for predicting incoming requests and show comparable predictive performance when compared to centralized training.

97 MATHEMATICS AND COMPUTING↗