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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Metabolic Interactions between Brachypodium and Pseudomonas fluorescens under Controlled Iron-Limited Conditions

Plant iron (Fe) nutritional status has a significant impact on rhizosphere microbial communities. While this effect has been attributed to alterations in the composition of root exudates, the underlying mechanisms are not known. Here, we investigated the effect of Fe deficiency on the interactions between the grass Brachypodium distachyon and the common soil bacteria Pseudomonas fluorescens SBW25. Increased phytosiderophore production was the most significant response of Brachypodium root exudation to Fe deficiency. We observed upregulated expression of phytosiderophore biosynthesis genes but lower accumulated exudate concentrations in the presence of Pseudomonas, indicating that the bacteria degrade these phytosiderophores. Pseudomonas did not produce endogenous siderophores under the low Fe conditions. Rather, the bacterial transcriptome revealed upregulation of four genes in response to Fe deficiency that contain motifs associated with cellular uptake of small molecules. Collectively, these results suggest that rhizosphere Pseudomonas fluorescens may take up phytosiderophores produced by grasses in response to Fe deficiency, and we propose target genes that may be involved. Our findings provide insight into the molecular basis for the exchange of C, N, and Fe between plants and bacteria under Fe deficient conditions. These interactions may contribute to differences in the rhizosphere microbial community structure across soil pH regimes.

Boiteau, Rene M.↗
DOE OSTI2018

Preliminary disposal limits, plume interaction factors, and final disposal limits

In the 2008 E-Area Performance Assessment (PA), each final disposal limit was constructed as the product of a preliminary disposal limit and a plume interaction factor. The following mathematical development demonstrates that performance objectives are generally expected to be satisfied with high confidence under practical PA scenarios using this method. However, radionuclides that experience significant decay between a disposal unit and the 100-meter boundary, such as H-3 and Sr-90, can challenge performance objectives, depending on the disposed-of waste composition, facility geometry, and the significance of the plume interaction factor. Pros and cons of analyzing single disposal units or multiple disposal units as a group in the preliminary disposal limits analysis are also identified.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1977

Limitations on oceanographic use of beam-limited target-referenced radars

A general development is undertaken to determine the limitations on the use of beam-limited target-referenced radars in the measurement of ocean wave height. This class of radars is concerned only with the range extent of the target, not the range to the target. The nonzero range extent of a flat waveless sea and the compounding effect of pointing errors due to radar platform instability cause difficulty in measuring low wave heights and impose a maximum operating altitude on such systems. It is seen that it is impractical to obtain accurate measurements for wave heights of interest at altitudes above those used by commercial aircraft (10,000 m). Additionally, the typical ratio of dominant wavelength to significant wave height (SWH) of 30 for wind-driven gravity waves imposes an upper limit on the SWH measurable for a given altitude and beamwidth.

Walsh, E. J.↗
NASA NTRS1998

A Framework for a Supervisory Expert System for Robotic Manipulators with Joint-Position Limits and Joint-Rate Limits

This report addresses the problem of path planning and control of robotic manipulators which have joint-position limits and joint-rate limits. The manipulators move autonomously and carry out variable tasks in a dynamic, unstructured and cluttered environment. The issue considered is whether the robotic manipulator can achieve all its tasks, and if it cannot, the objective is to identify the closest achievable goal. This problem is formalized and systematically solved for generic manipulators by using inverse kinematics and forward kinematics. Inverse kinematics are employed to define the subspace, workspace and constrained workspace, which are then used to identify when a task is not achievable. The closest achievable goal is obtained by determining weights for an optimal control redistribution scheme. These weights are quantified by using forward kinematics. Conditions leading to joint rate limits are identified, in particular it is established that all generic manipulators have singularities at the boundary of their workspace, while some have loci of singularities inside their workspace. Once the manipulator singularity is identified the command redistribution scheme is used to compute the closest achievable Cartesian velocities. Two examples are used to illustrate the use of the algorithm: A three link planar manipulator and the Unimation Puma 560. Implementation of the derived algorithm is effected by using a supervisory expert system to check whether the desired goal lies in the constrained workspace and if not, to evoke the redistribution scheme which determines the constraint relaxation between end effector position and orientation, and then computes optimal gains.

Mutambara, Arthur G. O.↗
NASA NTRS1999

The Performance Capabillities and Limitations of Gain-Limitated Propulsion Systems

Omniplanetary space flight requires new high-performance propulsion systems based on nuclear energy. Over the last several decades, many propulsion concepts have been discussed which will allow one-month missions to Mars and one-year missions to the outer planets. Such missions entail large mission velocities and vehicle accelerations, which in turn require both high exhaust velocities (and therefore, and extremely low mass-power ratios. High performance electric propulsion appears capable of enabling multi-month transits to Mars and the near-earth asteroids; however, the mass-power ratio of these systems appears too high to achieve large accelerations for outer planet missions. This presentation analyzed the round-trip mission times and distances. This analysis has shown that even high-performance power-limited systems cannot achieve the higher accelerations needed to meet fast missions to the outer planets. Gain-limited missions are necessary for those extremely aggressive missions. An analysis of spacecraft power systems via a power balance and examination of gain vs mass-power ratio has shown: (1) A minimum gain is needed to have enough power for thrust production and driver operation; (2) Increases in gain result in decreases in mass-power ratio, which in turn leads to greater achievable accelerations. However, there is an absolute minimum mass-power ratio for a given set of subsystems, even in the limit of infinite gain.

Schmidt, G. R.↗
DOE OSTI2019

Structure‐based control of the rate limitation of photosynthetic electron transport

The 2.5 Å structure of the cytochrome (cyt) b 6 f complex provides a basis for control of the rate‐limiting electron transfer step of oxygenic photosynthesis associated with the plastoquinol/quinone exchange pathway. Here, a structural change was made at a site containing two proline residues which border the intra‐cyt pathway for plastoquinol/quinone exchange. The proline side chains confer a larger aperture for passage of plastoquinol/quinone. Change of these prolines to alanine in the cyanobacterium Synechococcus sp. PCC 7002 results in attenuation of this rate‐limiting step, observed by a two‐fold reduction in the rate of cell growth, O 2 evolution, and plastoquinol‐mediated reduction of cyt f . This study demonstrates modification by site‐directed mutagenesis of photosynthetic energy transduction based on rational application of information in the atomic structure.

Ness, Jillian↗
DOE OSTI2017

Increasing Biomass Production on Limited Land Area Through an Optimal Planting Arrangement

Planting density is a primary consideration in silviculture; however, planting arrangement is often ignored. Most, if not all, forest plantations are arranged in rectangular or square lattices (i.e., grids). Using a simple mathematical model, we investigate the potential influence of planting arrangement on planting density, biomass yield, and rotation period by assuming that efficiently arranging trees is similar to packing congruent circles on a plane. The hexagonal lattice achieves the densest circle packing on a plane; therefore, a hexagonal or triangular lattice arrangement of stems provides the highest planting density for a given spacing. Using packing density to quantify arrangement efficiency, tree crowns in a hexagonal lattice fill approximately 90.7% of available area at initial canopy contact, while tree crowns in a square lattice fill approximately 78.5% of available area at initial canopy contact. The hexagonal lattice permits about a 15% higher density than the square lattice, which allows canopy closure to occur earlier without any change in individual tree growth. Short rotation woody crop (SRWC) systems are excellent candidates under the model's assumptions of level stand with even-age monoculture. If belowground resources are non-limiting, a hexagonal lattice arrangement shortens rotation period and thus optimizes the biomass yield per land area over time. Lastly, higher productivity over time is central to sustainable and efficient use of limited area for bioenergy and biomass products.

09 BIOMASS FUELS↗
DOE OSTI2020

Optimal Orbital Selection for Full Configuration Interaction (OptOrbFCI): Pursuing the Basis Set Limit under a Budget

Full configuration interaction (FCI) solvers are limited to small basis sets due to their expensive computational costs. An optimal orbital selection for FCI (OptOrbFCI) is proposed to boost the power of existing FCI solvers to pursue the basis set limit under a computational budget. The optimization problem coincides with that of the complete active space SCF method (CASSCF), while OptOrbFCI is algorithmically quite different. OptOrbFCI effectively finds an optimal rotation matrix via solving a constrained optimization problem directly to compress the orbitals of large basis sets to one with a manageable size, conducts FCI calculations only on rotated orbital sets, and produces a variational ground-state energy and its wave function. Coupled with coordinate descent full configuration interaction (CDFCI), we demonstrate the efficiency and accuracy of the method on the carbon dimer and nitrogen dimer under basis sets up to cc-pV5Z. We also benchmark the binding curve of the nitrogen dimer under the cc-pVQZ basis set with 28 selected orbitals, which provide consistently lower ground-state energies than the FCI results under the cc-pVDZ basis set. Furthermore, the dissociation energy in this case is found to be of higher accuracy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

U.S. Manufacturing Water Use Data and Estimates: Current State, Limitations, and Future Needs for Supporting Manufacturing Research and Development

Water is essential to manufacturing operations; without it, many facilities could not operate or meet production demands. Physical, reputational, and regulatory risks to water supplies compounded by climate change-induced impacts on hydrological conditions threaten the adequacy of water supplies for manufacturing. Manufacturing water use has not been a major focus of either water or manufacturing-related research. Research and development (R&D) aimed at helping manufacturers use water more sustainably and adapt to changing water conditions is needed to ensure a thriving sector and economy. However, the ability to identify R&D needs is severely limited due to a lack of current, statistically representative data on manufacturing water use and its environmental implications. In this Perspective, we outline four key questions to inform R&D on manufacturing use and highlight how the current state of water data in the United States does not support the adequate investigation of these questions. We make recommendations for the water data characteristics needed to explore the research questions and knowledgeably inform R&D on manufacturing water use.

McCall, James↗
DOE OSTI2018

Reorientation of the Methyl Group in MAs(III) is the Rate-Limiting Step in the ArsM As(III) S -Adenosylmethionine Methyltransferase Reaction

The most common biotransformation of trivalent inorganic arsenic (As(III)) is methylation to mono-, di-, and trimethylated species. Methylation is catalyzed by As(III) S-adenosylmethionine (SAM) methyltransferase (termed ArsM in microbes and AS3MT in animals). Methylarsenite (MAs(III)) is both the product of the first methylation step and the substrate of the second methylation step. When the rate of the overall methylation reaction was determined with As(III) as the substrate, the first methylation step was rapid, whereas the second methylation step was slow. In contrast, when MAs(III) was used as the substrate, the rate of methylation was as fast as the first methylation step when As(III) was used as the substrate. These results indicate that there is a slow conformational change between the first and second methylation steps. The structure of CmArsM from the thermophilic alga Cyanidioschyzon merolae sp. 5508 was determined with bound MAs(III) at 2.27 Å resolution. The methyl group is facing the solvent, as would be expected when MAs(III) is bound as the substrate rather than facing the SAM-binding site, as would be expected for MAs(III) as a product. We propose that the rate-limiting step in arsenic methylation is slow reorientation of the methyl group from the SAM-binding site to the solvent, which is linked to the conformation of the side chain of a conserved residue Tyr70.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Niobium in the clean limit: An intrinsic type-I superconductor

Niobium is one of the most researched superconductors, both theoretically and experimentally. It is enormously significant in all branches of superconducting applications, from powerful magnets to quantum computing. It is therefore imperative to understand its fundamental properties in great detail. In this work, we use the results of recent microscopic calculations of anisotropic electronic, phonon, and superconducting properties, and apply a thermodynamic criterion for the type of superconductivity, more accurate and straightforward than a conventional Ginzburg-Landau parameter κ-based delineation, to show that pure niobium is a type-I superconductor in the clean limit. However, disorder (impurities, defects, strain, stress) pushes it to become a type-II superconductor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Upper limit for the effect of elastic bending stress on the saturation magnetization of L a 0.8 S r 0.2 Mn O 3

In this study, using polarized neutron reflectometry, we measured the influence of elastic bending stress on the magnetization depth profile of a La 0.8 Sr 0.2 MnO 3 (LSMO) epitaxial film grown on a SrTiO 3 substrate. The elastic bending strain of ±0.03% has no obvious effect on the magnetization depth profile at saturation. This result is in stark contrast to that of (La 1-x Pr x )1-yCayMnO 3 (LPCMO) films for which strain of ±0.01% produced dramatic changes in the magnetization profile and Curie temperature. We attribute the difference between the influence of strain on the saturation magnetization in LSMO (weak or none) and LPCMO (strong) to a difference in the ability of LSMO (weak or none) and LPCMO (strong) to phase separate. Our observation provides an upper limit of tuning LSMO saturation magnetization via elastic strain effect.

36 MATERIALS SCIENCE↗
DOE OSTI2019

PREDICTION OF CYCLIC VARIABILITY AND KNOCK-LIMITED SPARK ADVANCE (KLSA) IN SPARK-IGNITION (SI) ENGINE

Engine knock remains one of the major barriers to further improve the thermal efficiency of spark-ignition (SI) engines. SI engine is usually operated at knock-limited spark advance (KLSA) to achieve possibly maximum efficiency with given engine hardware and fuel properties. Co-optimization of fuels and engines is promising to improve engine efficiency, and predictive computational fluid dynamics (CFD) models can be used to facilitate this process. However, cyclic variability of SI engine demands that multi cycle results are required to capture the extreme conditions. In addition, Mach Courant Friedrichs-Lewy (CFL) number of 1 is desired to accurately predict the knock intensity (KI), resulting in unaffordable computational cost. In this study, a new approach to numerically predict KLSA using large Mach CFL of 50 with ten consecutive cycle simulation is proposed. This approach is validated against the experimental data for a boosted SI engine at multiple loads and spark timings with good agreements in terms of cylinder pressure, combustion phasing, and cyclic variation. Engine knock is predicted with early spark timing, indicated by significant pressure oscillation and end-gas heat release. Maximum amplitude of pressure oscillation analysis is performed to quantify the KI, and the slope change point in KI extrema is used to indicate the KLSA accurately. Using a smaller Mach CFL number of 5 also results in the same conclusions, thus demonstrating that this approach is insensitive to the Mach CFL number. The use of large Mach CFL number allows us to achieve fast turn-around time for multicycle engine CFD simulations.

CCV↗
DOE OSTI2022

Cross-biome synthesis of source versus sink limits to tree growth

Uncertainties surrounding tree carbon allocation to growth are a major limitation to projections of forest carbon sequestration and response to climate change. The prevalence and extent to which carbon assimilation (source) or cambial activity (sink) mediate wood production are fundamentally important and remain elusive. We quantified source-sink relations across biomes by combining eddy-covariance gross primary production with extensive on-site and regional tree ring observations. We found widespread temporal decoupling between carbon assimilation and tree growth, underpinned by contrasting climatic sensitivities of these two processes. Substantial differences in assimilation-growth decoupling between angiosperms and gymnosperms were determined, as well as stronger decoupling with canopy closure, aridity, and decreasing temperatures. Our results reveal pervasive sink control over tree growth that is likely to be increasingly prominent under global climate change.

Science & Technology - Other Topics↗
DOE OSTI2025

pbd-industrial-limit-of-performance (PBD limit of performance) v1.0.0

Software repository that contains models used for a paper about Platform-Based Design with limit of performance analysis for an industrial pilot study. This repository contains process and control models in Modelica and IDAES and scripts to develop an ML based controller that computes the control function that maximizes the techno-economic performance of cost and energy computed by the model. This software is meant to be released to reproduce the work described in a Journal publication that is now drafted with the working title "Energy System Limit of Performance Analysis using an Online Machine Learning Multi-Resolution Optimization Framework".

Amusat, Oluwamayowa [Lawrence Berkeley National La↗