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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Long-term, large-scale experiment reveals the effects of seed limitation, climate, and anthropogenic disturbance on restoration of plant communities in a biodiversity hotspot

Ecological restoration is essential for maintaining biodiversity in the face of dynamic, global changes in climate, human land use, and disturbance regimes. Effective restoration requires understanding bottlenecks in plant community recovery that exist today, while recognizing that these bottlenecks may relate to complex histories of environmental change. Such understanding has been a challenge because few long-term, well-replicated experiments exist to decipher the demographic processes influencing recovery for numerous species against the backdrop of multiyear variation in climate and management. Here we address this challenge through a long-term and geographically expansive experiment in longleaf pine savannas, an imperiled ecosystem and biodiversity hotspot in the southeastern United States. Using 48 sites at three locations spanning 480 km, the 8-y experiment manipulated initial seed arrival for 24 herbaceous plant species and presence of competitors to evaluate the impacts of climate variability and management actions (e.g., prescribed burning) on plant establishment and persistence. Adding seeds increased plant establishment of many species. Cool and wet climatic conditions, low tree density, and reduced litter depth also promoted establishment. Once established, most species persisted for the duration of the 8-y experiment. Plant traits were most predictive when tightly coupled to the process of establishment. Our results illustrate how seed additions can restore plant diversity and how interannual climatic variation affects the dynamics of plant communities across a large region. The significant effects of temperature and precipitation inform how future climate may affect restoration and conservation via large-scale changes in the fundamental processes of establishment and persistence.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1984

Arabidopsis seed production limited by CO2 in simulated space experiments

Several generations of Arabidopsis thaliana were grown axenically from seed to seed on nutrient agar medium. The Arabidopsis plants produce seeds within 30 days after seeding, when grown either in containers open to the ambient atmosphere or in large sealed jars, but not in sealed test tubes. Moreover, the plant height was directly proportional to the size of the sealed container. Periodic analyses of the CO2 levels in the sealed containers has shown a decrease during the first week, but a tenfold increase in the following weeks. It is speculated that, by the end of the second week, the cotyledons entering the senescence stage would release ethylene into the culture atmosphere with a concomitant release of CO2, which in turn would induce further release of ethylene, hastening the senescence process in other tissues. Thus, in a controlled ecological life-support system of a space station, various components of the plant atmosphere may have to be maintained within the prescribed limits.

Hoshizaki, T.↗
NASA NTRS1984

Radiographic detectability limits for seeded voids in sintered silicon carbide and silicon nitride

Conventional and microfocus X-radiographic techniques were compared to determine relative detectability limits for voids in green and sintered SiC and Si3N4. The relative sensitivity of the techniques was evaluated by comparing their ability to detect voids that were artificially introduced by a seeding process. For projection microfocus radiography the sensitivity of void detection at a 90/95 probability of detection/confidence level is 1.5% of specimen thickness in sintered SiC and Si3N4. For conventional contact radiography the sensitivity is 2.5% of specimen thickness. It appears that microfocus projection radiography is preferable to conventional contact radiography in cases where increased sensitivity is required and where the additional complexity of the technique can be tolerated.

Baaklini, G. Y.↗
NASA NTRS1986

Radiographic detectability limits for seeded voids in sintered silicon carbide and silicon nitride

Conventional and microfocus X-radiographic techniques were compared to determine relative detectability limits for voids in green and sintered SiC and Si3N4. The relative sensitivity of the techniques was evaluated by comparing their ability to detect voids that were artificially introduced by a seeding process. For projection microfocus radiography the sensitivity of void detection at a 90/95 probability of detection/confidence level is 1.5 percent of specimen thickness in sintered SiC and Si3N4. For conventional contact radiography the sensitivity is 2.5 percent of specimen thickness. It appears that microfocus projection radiography is preferable to conventional contact radiography in cases where increased sensitivity is required and where the additional complexity of the technique can be tolerated.

Baaklini, G. Y.↗
DOE OSTI2021

Increased seminal root number associated with domestication improves nitrogen and phosphorus acquisition in maize seedlings

Abstract Background and Aims Domesticated maize (Zea mays ssp. mays) generally forms between two and six seminal roots, while its wild ancestor, Mexican annual teosinte (Zea mays ssp. parviglumis), typically lacks seminal roots. Maize also produces larger seeds than teosinte, and it generally has higher growth rates as a seedling. Maize was originally domesticated in the tropical soils of southern Mexico, but it was later brought to the Mexican highlands before spreading to other parts of the continent, where it experienced different soil resource constraints. The aims of this study were to understand the impacts of increased seminal root number on seedling nitrogen and phosphorus acquisition and to model how differences in maize and teosinte phenotypes might have contributed to increased seminal root number in domesticated maize. Methods Seedling root system architectural models of a teosinte accession and a maize landrace were constructed by parameterizing the functional–structural plant model OpenSimRoot using plants grown in mesocosms. Seedling growth was simulated in a low-phosphorus environment, multiple low-nitrogen environments, and at variable planting densities. Models were also constructed to combine individual components of the maize and teosinte phenotypes. Key Results Seminal roots contributed ~35 % of the nitrogen and phosphorus acquired by maize landrace seedlings in the first 25 d after planting. Increased seminal root number improved plant nitrogen acquisition under low-nitrogen environments with varying precipitation patterns, fertilization rates, soil textures and planting densities. Models suggested that the optimal number of seminal roots for nutrient acquisition in teosinte is constrained by its limited seed carbohydrate reserves. Conclusions Seminal roots can improve the acquisition of both nitrogen and phosphorus in maize seedlings, and the increase in seed size associated with maize domestication may have facilitated increased seminal root number.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Past and present disturbances generate spatial variation in seed predation

Seed survival is a key process for plant populations; variation in the activity and abundance of animals that consume seeds can lead to dramatic shifts in seed fate. Because granivores may respond to contemporary disturbance as well as to enduring changes in habitats caused by past disturbances, understanding seed fate requires studies capable of evaluating how past and present disturbances modify granivore communities, foraging activity, and ultimately, seed predation. Historic agricultural land use and contemporary canopy harvesting are widespread disturbances that could generate large-scale patterns of seed fate by modifying environmental characteristics that determine granivore identity and behavior. Here, to evaluate whether land-use history and canopy harvesting affect seed–animal interactions, we conducted an experiment distributed across 80,000 ha of longleaf pine woodlands that coupled large-scale canopy harvesting at seven 4-ha sites containing both post-agricultural land use and nonagricultural land use in South Carolina, United States. We deployed a total of 28,000 nail-tagged seeds and recovered the tags to quantify seed fate. Past agricultural land use and contemporary canopy harvesting interacted to affect the rate of seed predation. Seed predation rates in harvested sites depended on land-use history: Seed predation was 30% lower in post-agricultural plots than in nonagricultural plots. This interaction was driven by the differential effect of land-use history and canopy harvesting on rodent activity. Camera traps revealed that Sigmodon hispidus only foraged in harvested plots and was most active in nonagricultural plots. In harvested plots, seed removal increased with S. hispidus activity. In unharvested plots, seed removal increased with Sciurus niger activity, but S. niger was not affected by land-use history. In finding that land-use history and canopy harvesting determine the outcomes of seed–animal interactions, we show that understanding patterns of seed predation is contingent upon the interplay of disturbances in both the distant past and recent past. These results suggest that patterns of past land use and present land use may help reconcile the considerable variation in seed fate observed in ecological communities.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Temperature measurements in heavily-sooting ethylene/air flames using synchrotron x-ray fluorescence of krypton

High-fidelity temperature field measurements have been made for several heavily-sooting ethylene/air flames that have historically been challenging environments for conventional optical diagnostics. These challenges have largely been overcome here, in this study, by conducting x-ray fluorescence (XRF) measurements of a Kr fluorescent agent in the hard x-ray regime (15 keV). The current methodology presents a more economical diagnostic than a previously reported implementation of the Kr-XRF method, by limiting seeding of the expensive fluorescent agent to only the fuel stream flows. Detailed reacting flow simulations have been used to interpret experimental signals by tracking the mole fraction of the fluorescent agent in the flow field. Simulated Kr densities are in excellent agreement with measurements throughout the flow field. Temperature measurements of the flow field also agree well with simulations and recent literature studies. However, uncertainties in the measurements become increasingly large downstream of the burner surface as the krypton fraction drops due to mixing of the fuel and co-flow streams. Additionally, we demonstrate that soot particles in the heavily sooting flames studied do not impede the Kr-XRF measurements.

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

The radiated power limit in impurity seeded JET-ILW plasmas

The total radiated fraction is examined in high density H-mode plasmas (Greenwald fraction of about 85 %) in JET by the variation of the auxiliary heating power of Pheat = 14 MW-29 MW. An achieved radiation fraction of about 75 % at most has been observed in JET-ILW, which is less than the highest achievable (≈90 %) fraction in JET-C during the high radiative power scenarios with N2 seeding. It is shown that the maximal achievable total radiation fraction averaged over ELM cycles has a strong dependence on the radiation efficiency of the ELM energy, $θ_{rad}$: $\gamma^{max}_{rad,total}$ = 1 -$\frac {f_{ELM} x ΔW_{ELM}} {P_heat}$ (1- $θ_{rad}$). About 50 % and 16 % of the ELM induced diamagnetic energy drop (ΔW ELM ) radiates during the ELM in JET-C and JET-ILW, respectively, which corresponds to the maximum total radiated powers of $\gamma^{max}_{rad,JET-C}$ = 0.87 and $\gamma^{max}_{rad,JET-ILW}$ = 0.77. These values of the maximum of the radiative power fractions are in good agreement with $\gamma^{max}_{rad}$ experimentally observed in JET-C (90 %) and JET-ILW (75 %).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2003

Oxygen requirement of germinating flax seeds

Plant experiments in earth orbit are typically prepared on the ground and germinated in orbit to study gravity effects on the developing seedlings. Germination requires the breakdown of storage compounds, and this metabolism depends upon respiration, making oxygen one of the limiting factors in seed germination. In microgravity lack of run-off of excess water requires careful testing of water dispensation and oxygen availability. In preparation for a shuttle experiment (MICRO on STS-107) we studied germination and growth of flax (Linum usitatissimum L.) seedlings in the developed hardware (Magnetic Field Chamber, MFC). We tested between four to 32 seeds per chamber (air volume=14 mL) and after 36 h measured the root length. At 90 microliters O2 per seed (32 seeds/chamber), the germination decreased from 94 to 69%, and the root length was reduced by 20%, compared to 8 seeds per chamber. Based on the percent germination and root length obtained in controlled gas mixtures between 3.6 and 21.6% O2 we determined the lower limit of reliable germination to be 10 vol. % O2 at atmospheric pressure. Although the oxygen available in the MFC's can support the intended number of seeds, the data show that seed storage and microgravity-related limitations may reduce germination. c2003 Published by Elsevier Ltd on behalf of COSPAR.

NASA Discipline Plant Biology↗
DOE OSTI2020

Thermal loading on self-seeding monochromators in x-ray free electron lasers

One approach to achieve longitudinally coherent hard X-ray free electron laser (XFEL) radiation is to introduce a single-crystal monochromator in the beam path to generate a co-propagating, time-synchronized self-seeding radiation pulse. For modern high-repetition rate XFELs, however, thermal loading on the crystal can degrade the quality of the seed pulse. To assess limitations on the maximum XFEL pulse repetition rate imposed by the seeding crystal, a comprehensive study of thermomechanical, and X-ray diffraction effects within the crystal is presented in this paper for two consecutive self-amplified spontaneous emission pulses incident on both reflective and transmissive crystal monochromators.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Impact of nutritional history, prey quality, and quantity on grazing and photophysiological responses in the mixoplanktonic dinoflagellate Karenia brevis

The mixotrophic toxic dinoflagellate Karenia brevis forms red tides almost annually along Florida's Gulf coast. We hypothesize that the nutritional status and abundance of its prey, the picocyanobacterium Synechococcus , will affect its feeding rates and growth responses, with implications for bloom dynamics. This study investigated how prey nutritional quality and quantity (absolute and relative) impact grazing rates by K. brevis initially exponentially growing and in nitrogen (N)-limited conditions, and how grazing, in turn, affects the photophysiological responses of predator and prey. Prey quality was manipulated by providing Synechococcus grown under different ratios of N : phosphorus (P). Synechococcus quality did not significantly affect ingestion rates (measured as prey death rate) but grazing rates increased with increasing prey : grazer ratios (R 2 = 0.7). Compared to control, the growth of exponentially growing grazers doubled when Synechococcus was provided, whereas there was no growth enhancement when Synechococcus of varying qualities was provided to N-limited, chemostat-seeded grazers. Despite this doubled growth, 15 N labeling of the prey and nanoscale secondary ion mass spectrometry (nanoSIMS) detected low Synechococcus -N transfer into grazer biomass after 3 d (< 1% on a cell basis). This suggests the potential of grazers benefiting from alternative N sources (e.g., microbiome-N) or other constituents (e.g., vitamins or metals) not measured in this study. Prey photosynthetic efficiency declined under grazing conditions, demonstrating that grazers can directly affect prey abundance through grazing and indirectly affect prey photophysiology, potentially via allelopathy, supporting previous findings of an inverse relationship between grazers and prey along the Florida Gulf Coast.

Ahn, So Hyun [Univ. of Maryland, Cambridge, MD (Un↗
DOE OSTI2024

Numerical implications of including drifts in SOLPS-ITER simulations of EAST

The inclusion of drifts in plasma edge codes like SOLPS-ITER is required to match simulation data with experimental profiles. However, this remains numerically challenging. In this paper, the effect of some numerical factors on the final plasma solution is investigated. This study is performed on three EAST simulations in the upper single null configuration: an attached purely deuterium case, an attached case with limited Ne-seeding, and a detached Ne-seeded case. The effects of the anomalous conductivity and anomalous thermo-electric coefficient on the plasma potential are investigated. Next, the effect of the employed grids is shown. In order to investigate these effects, accurate drift simulations are needed. Therefore, the employed time step and numerical parameters are discussed for the three studied simulations. For all presented simulations, it is verified that the restriction of the grid to the first flux surface tangent to the main chamber wall is sufficient within the context of non-extended simulations. This means that the main power dissipation takes place inside the simulated domain, and only a small fraction of the power is leaving the B2.5 grid through the grid boundary closest to the first wall. Finally, the effect of drifts on the asymmetry between the inner and outer target for EAST simulations is demonstrated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1997

Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects. I: Properties of the Corona and the Spectrum of Escaping Radiation

We present the properties of accretion disk corona (ADC) models in which the radiation field, the temperature, and the total opacity of the corona are determined self-consistently. We use a nonlinear Monte Carlo code to perform the calculations. As an example, we discuss models in which the corona is situated above and below a cold accretion disk with a plane-parallel (slab) geometry, similar to the model of Haardt & Maraschi. By Comptonizing the soft radiation emitted by the accretion disk, the corona is responsible for producing the high-energy component of the escaping radiation. Our models include the reprocessing of radiation in the accretion disk. Here the photons either are Compton-reflected or photoabsorbed, giving rise to fluorescent line emission and thermal emission. The self- consistent coronal temperature is determined by balancing heating (due to viscous energy dissipation) with Compton cooling, determined using the fully relativistic, angle-dependent cross sections. The total opacity is found by balancing pair productions with annihilations. We find that, for a disk temperature kT(sub BB) approx. less than 200 eV, these coronae are unable to have a self-consistent temperature higher than approx. 140 keV if the total optical depth is approx. less than 0.2, regardless of the compactness parameter of the corona and the seed opacity. This limitation corresponds to the angle-averaged spectrum of escaping radiation having a photon index approx. greater than 1.8 within the 5-30 keV band. Finally, all models that have reprocessing features also predict a large thermal excess at lower energies. These constraints make explaining the X-ray spectra of persistent black hole candidates with ADC models very problematic.

Dove, James B.↗
NASA NTRS2005

Real-Time Simulation for Verification and Validation of Diagnostic and Prognostic Algorithms

To verify that a health management system (HMS) performs as expected, a virtual system simulation capability, including interaction with the associated platform or vehicle, very likely will need to be developed. The rationale for developing this capability is discussed and includes the limited capability to seed faults into the actual target system due to the risk of potential damage to high value hardware. The capability envisioned would accurately reproduce the propagation of a fault or failure as observed by sensors located at strategic locations on and around the target system and would also accurately reproduce the control system and vehicle response. In this way, HMS operation can be exercised over a broad range of conditions to verify that it meets requirements for accurate, timely response to actual faults with adequate margin against false and missed detections. An overview is also presented of a real-time rocket propulsion health management system laboratory which is available for future rocket engine programs. The health management elements and approaches of this lab are directly applicable for future space systems. In this paper the various components are discussed and the general fault detection, diagnosis, isolation and the response (FDIR) concept is presented. Additionally, the complexities of V&V (Verification and Validation) for advanced algorithms and the simulation capabilities required to meet the changing state-of-the-art in HMS are discussed.

Aguilar, Robet↗
DOE OSTI2024

Efficacy and Costs of Restoring Wetland Breeding Habitat for Imperiled Amphibians in the Southeastern U.S.

Herbaceous isolated wetlands in the North American Southeastern Coastal Plain are important breeding sites for many imperiled amphibians. However, most are degraded from alterations to historic fire disturbance and hydrologic regimes. Without fire, encroaching woody vegetation can transition wetlands to more terrestrial conditions and negatively impact amphibian breeding habitat, yet few studies have experimentally tested the efficacy, cost, or temporal requirement of current methods to restore herbaceous wetland vegetation. Here, we tested the interaction of manipulating wetland canopy and leaf litter/duff to promote herbaceous vegetation within one year (i.e., one breeding season) in degraded herbaceous wetlands in South Carolina. We assessed plant response via herbaceous cover, composition, and species similarity to the wetland seed bank and then related treatment performance to treatment cost. Removing trees combined with burning, disturbing, or removing duff significantly increased herbaceous cover and proportions of wetland plants and graminoids. Removing trees alone did not improve herbaceous cover compared to closed-canopy controls, and manipulating duff alone had limited positive effects on plant cover and composition. The most expensive yet effective treatment was Tree Removal-Duff Removal, while Tree Removal-Duff Disturbance was the most cost-effective. At a minimum, we recommend removing trees and burning to kickstart herbaceous recovery. Promisingly, comparisons of our data with previous seed bank studies from these same wetlands indicate there was limited seed bank attrition during 30 years of woody encroachment. Results from this study should aid practitioners in choosing wetland restoration techniques to better conserve at-risk species in the Southeastern Coastal Plain.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Can magnetogenesis driven by dynamo instabilities in chiral fermion plasmas, favor Einstein–Cartan AdS cosmology?

In this letter we show that the magnetic field (MF) bounds induced by Einstein–Cartan–de Sitter (EC) with AdS anti-de Sitter spacetime geometry and fermionic torsion with chiral dynamo plasmas instabilities, with inhomogeneous uniform chiral chemical potential, indicates that there is a possibility, as far as magnetogenesis is concerned, that we may obtain more stringent results within ECAdS gravity, compared with general relativity (GR) limits obtained by Tsagas using torsionless magnetogenesis. Spinorial fermionic source with torsion induces a chiral plasmas oscillation. The time dependent chiral chemical potential, sometimes associated formally with torsion, (de Andrade, 2018), is obtained from chiral flipping equation. The MFs obtained from the present universe ECdS chiral dynamo model, meet the criteria of galactic seed fields with better limits within Tsagas range (Tsagas, 2015) seed galactic magnetic fields for dynamo mechanisms, than the bound obtained by chiral dynamos in torsionless AdS cosmology. Majorana neutrinos are used as spatial components of axial spin-torsion source of dynamo instability from neutrino asymmetry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Why Seeding Works When Nucleation Barriers Vanish

This paper explains why seeds can speed up crystallization even when the formation of new crystal nuclei is not the slow step. In zeolite synthesis, local crystalline order can form relatively early, but the material may still appear poorly crystalline by X-ray diffraction because many small crystallites are misoriented and lack long-range coherence. Using coarse-grained molecular simulations, the study showed that seeds help solve this coherence problem. Rather than primarily lowering a nucleation barrier, seeds impose a common orientation on nearby growing crystallites, allowing them to merge into larger, better aligned domains. This accelerates the development of X-ray-detectable crystallinity even if the total amount of locally ordered material has not changed much. The work changes how induction times in zeolite synthesis should be interpreted: the delay before X-ray crystallinity appears can reflect the time needed to build long-range structural coherence, not simply the time needed to form crystalline material. This provides a new explanation for why seeding is effective in growth-limited crystallization and offers design principles for controlling crystallization rate and crystal quality.

36 MATERIALS SCIENCE↗