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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Transcription initiation as a control point in plastid gene expression

The extensive processing and protein-assisted stabilization of transcripts have been taken as evidence for a viewpoint that the control of gene expression had shifted entirely in evolution from transcriptional in the bacterial endosymbiont to posttranscriptional in the plastid. This suggestion is however at odds with many observations on plastid gene transcription. Chloroplasts of flowering plants and mosses contain two or more RNA polymerases with distinct promoter preference and division of labor for the coordinated synthesis of plastid RNAs. Plant and algal plastids further possess multiple nonredundant sigma factors that function as transcription initiation factors. The controlled accumulation of plastid sigma factors and modification of their activity by sigma-binding proteins and phosphorylation constitute additional transcriptional regulatory strategies. Plant and algal plastids also contain dedicated one- or two-component transcriptional regulators. Finally, transcription initiation thus continues to form a critical control point at which varied developmental and environmental signals intersect with plastid gene expression.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Modeling copper precipitation hardening and embrittlement in a dilute Fe-0.3at.%Cu alloy under neutron irradiation

The neutron irradiation in light water reactors can induce precipitation of nanometer sized Cu clusters in reactor pressure vessel steels. The Cu precipitates impede dislocation gliding, leading to increase of yield strength (hardening) and upward shift of ductile-to-brittle transition temperature (embrittlement). In this work, cluster dynamics modeling is used to model the entire Cu precipitation process (nucleation, growth, and coarsening) in a Fe-0.3at.%Cu alloy under neutron irradiation at 300 °C. The evolution of the Cu cluster number density and mean radius predicted by the modeling agrees well with experimental data reported in literature for the same alloy under the same irradiation conditions. The predicted precipitation kinetics are used as input for a dispersed barrier hardening model to correlate the microstructural evolution with the radiation hardening and embrittlement in this alloy. The predicted radiation hardening agrees well with the mechanical test results in literature. In conclusion, the limitation of the model and future improvement directions are also discussed in this work.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

{sup 13}C dynamic nuclear polarization for measuring metabolic flux in endothelial progenitor cells

Endothelial progenitor cells (EPCs) represent a heterogeneous cell population that is believed to be involved in vasculogenesis. With the purpose of enhancing endothelial repair, EPCs could have a potential for future cell therapies. Due to the low amount of EPCs in the peripheral circulating blood, in vitro expansion is needed before administration to recipients and the effects of in vitro culturing is still an under-evaluated field with little knowledge of how the cells change over time in culture. The aim of this study was to use hyperpolarised carbon-13 magnetic resonance spectroscopy to profile important metabolic pathways in a population of progenitor cells and to show that cell culturing in 3D scaffolds seem to block the metabolic processes that leads to cell senescence. The metabolic breakdown of hyperpolarized [1-{sup 13}C]pyruvate was followed after injection of the substrate to a bioreactor system with EPCs either adhered to 3D printed scaffolds or kept in cell suspension. The pyruvate-to-lactate conversion was elevated in suspension of EPCs compared to the EPCs adhered to scaffolds. Furthermore in the setup with EPCs in suspension, an increase in lactate production was seen over time indicating that the older the cultures of EPCs was before using the cells for cell suspension experiments, the more lactate they produce, compared to a constant lactate level in the cells adhered to scaffolds. It could therefore be stated that cells grown first in 2D culture and subsequent prepared for cell suspension show a metabolism with higher lactate production consistent with cells senescence processes compared to cells grown first at 2D culture and subsequent in the 3D printed scaffolds, where metabolism shows no sign of metabolic shifting during the monitored period. - Highlights: • Hyperpolarized 13C MRS detects EPCs metabolic changes associated with ageing and cultivating conditions. • Increased lactate production in EPC’s correlates positively with aging. • 2D cultivation show an increased lactate production, while 3D cultivation show a maintained lactate production.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Synthesis of Self-Assembled Porphyrin Nanoparticle Photosensitizers

The use of nanoparticles as a potential building block for photosensitizers has recently become a focus of interest in the field of photocatalysis and photodynamic therapy. Porphyrins and their derivatives are effective photosensitizers due to extended π-conjugated electronic structure, high molar absorption from visible to near-infrared spectrum, and high singlet oxygen quantum yields as well as chemical versatility. In this work, we report a synthesis of self-assembled porphyrin nanoparticle photosensitizers using zinc meso-tetra(4-pyridyl)porphyrin (ZnTPyP) through a confined noncovalent self-assembly process. Scanning electron microscopy reveals formation of monodisperse cubic nanoparticles. UV–vis characterizations reveal that optical absorption of the nanoparticles exhibits a red shift due to noncovalent self-assembly of porphyrins, which not only effectively increase intensity of light absorption but also extend light absorption broadly covering visible light for enhanced photodynamic therapy. Electron spin-resonance spectroscopy (ESR) studies show the resultant porphyrin nanoparticles release a high yield of singlet oxygen. Nitric oxide (NO) coordinates to central metal Zn ions to form stabilized ZnTPyP@NO nanoparticles. We show that under light irradiation ZnTPyP@NO nanoparticles release highly reactive peroxynitrite molecules that exhibit enhanced antibacterial photodynamic therapy (APDT) activity. Finally, the ease of the synthesis of self-assembled porphyrin nanoparticles and light-triggered release of highly reactive moieties represent a completely different photosensitizer system for APDT application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Probing the proton exchange kinetics of BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3− δ ceramic electrolyte by operando diffuse reflectance infrared Fourier transform spectroscopy

Proton exchange kinetics plays an important role in governing the performance of intermediate-temperature protonic ceramic electrolysis cells (PCECs) for hydrogen production. Our understanding of the nature of the surface hydration reaction at the single-cell level, however, remains very limited, hampering further efficiency improvements. Here, in this study, we developed a custom operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) platform that operates under high temperature and steam conditions with applied bias. Quantitative investigations of surface H 2 O/D 2 O isotope exchange in a BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ (BZCYYb1711) protonic electrolyte-based single cell were conducted under different applied voltages using this DRIFTS platform, to gain molecular-level insight into hydration kinetics. The findings show that the application of an external voltage significantly enhances the surface proton exchange rate, decreasing the apparent activation energy from 29.1 kJ mol −1 at open-circuit voltage (OCV) to 6.8 kJ mol −1 at 1.3 V. In addition, distinct voltage-induced spectral shifts in O–D vibrations point to dynamic changes in surface hydration. These findings demonstrate a sensitive spectroscopic platform for probing interfacial proton processes and reveal strong electrochemical control over surface proton kinetics, offering new opportunities for probing electrolyte hydration behavior in PCECs.

36 - MATERIALS SCIENCE↗
DOE OSTI2012

Cyclic powder formation during pulsed injection of hexamethyldisiloxane in an axially asymmetric radiofrequency argon discharge

A new approach of periodic production of dusty plasma consisting of pulsed injection of hexamethyldisiloxane (HMDSO) in argon axially asymmetric radiofrequency (RF) discharge was investigated in this work. The range of plasma operating conditions in which this dusty plasma can exist was closely examined. The obtained results clearly show that a net periodicity in the formation/disappearance of dust particles in the plasma can be maintained on a very large scale of discharge duration. The significance of discharge axial asymmetry to the dust particles behaviour in the plasma is revealed by the development of an asymmetric in shape void shifted towards the powered RF electrode. The key role of the reactive gas and its pulsed injection on each stage of the oscillating process of formation/disappearance of dust particles is disclosed by optical and electrical measurements. It is shown that the period of dusty plasma formation/disappearance is inversely related to the HMDSO injection time. Moreover, the impact of time injection over short period (5 s) is examined. It indicates the conflicting role played by the HMDSO on the reduction of dusty plasma during the reactive gas injection and the reappearance of particles in the plasma during the time off. The electronegative behavior of the plasma in the presence of negatively charged particles seems to explain the energetic modifications in the discharge. A frequency analysis of the floating potential reveals all these cyclic processes. Particularly, in the 10-200 Hz frequency range, the presence and the evolution of dust particles in the plasma over one generation can be observed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Boundary-Aware Adversarial Learning Domain Adaption and Active Learning for Cross-Sensor Building Extraction

The use of convolutional neural networks (CNNs) for building extraction from remote sensing images has been widely studied and many public datasets have been made available for accelerating development of these CNN models. Yet adapting pretrained models at scale in real-world scenarios remains a challenging task. The main barrier is that certain new labels are still needed to compensate for domain shifting between the labeled data and new images that potentially cover new geographic locations or that are from a different sensor. In this article, we propose to add informatively labeled samples from a new image pool under the paradigm of active learning. To select the most useful samples based on model uncertainty, we first tackle the problem of uncalibrated uncertainty estimation due to distribution shifting by adapting feature extractors with boundary-based adversarial learning. Calibrated uncertainty is used as the query criterion in the active learning process, where the most uncertain samples are selected for annotation and included for model retraining. The proposed workflow was tested with three data pairs in which each workflow represents a scenario often encountered in real-world applications, including adapting pretrained models to new images collected with different sensors or to new geographic areas where appearances and types of buildings are very different. Compared to several baselines, including random sampling, temperature scaling (a well-known uncertainty calibration technique), different query strategies, and active domain adaptation methods, the proposed workflow shows that strategically querying a smaller set of samples for labeling achieves comparable or better building extraction performance. The proposed method reduces the number of labeled samples required to achieve sufficient model accuracy, thus significantly reducing hundreds of person-hours for labeled data creation. In addition, we include a few considerations when deploying this workflow in a GPU cluster that can be easily adapted to achieve operational building extraction model retraining.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Imaging Bragg Edge Analysis TooLs for Engineering Structures (iBeatles)

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) provides pulsed neutrons with energies varying from epithermal to cold. In preparation for VENUS, the neutron imaging beamline to be located at beam port 10, we have performed a series of experiments focused on wavelength-dependent radiography and computed tomography for a broad range of applications, from materials science to biological tissues.One of the time-of-flight (TOF) techniques that is of interest to the scientific community is the 2-dimensional mapping of phases and average crystalline plane orientation in samples both ex-situ and during applied stresses such as tensile loading and heating. This technique is known as Bragg edgeimaging and relies on the identification of changes of transmission values, fitting of the edge to measure its displacement, and thus identify the shift in lattice parameter due to stresses. One of the challenges of TOF imaging measurements is the amount of data and the inability to observe Bragg edge shifts in real time during an experiment. Thus, we have been focusing on creating a Python-based interface that allows fast data processing and instantaneous mapping and fitting of the Bragg edges, and their evolution through time. Python libraries and Jupyter notebooks have been implemented to facilitate decision making during an experiment. The advantage of the notebooks is the possibility to guide an experiment as they can quickly process and display Bragg edge data. These notebooks can be used independently, or can be combined in a Python Graphical User Interface (GUI) tool called iBeatles. This interface permits visualization and fitting of the Bragg edges, and ultimately back-projects the fitting results onto the radiographs to display a strain map. Assuming data collection has sufficient statistics, the strain mapping analysis can be performed on a pixel-by-pixel basis. This development is a step forward toward a better user experience at the future VENUS beamline in terms of live feedback and productivity. Analysis that used to take days of switching between different applications can now be done in minutes within the

Bilheux, JeanChristophe [Oak Ridge National Labora↗
DOE OSTI2012

A Stochastic Conceptual Modeling Approach for Examining the Effects of Climate Change on Streamflows in Mountain Basins

Abstract This study presents a modeling approach for examining how changes in climate affect streamflow in mesoscale mountain basins dominated by snowmelt runoff. A conceptual snowmelt-runoff model was developed that is forced by daily time series of temperature and precipitation. The model can be run using either observed climate data or artificial climate data generated from a GCM or a stochastic model. The model was applied to a case-study basin, the north fork of the Clearwater River in Idaho, using stochastically generated climate scenarios. Climate scenarios were generated using a contemporaneous auto-regressive integrated moving average (CARIMA) model for temperature and a precipitation model based on a two-state first-order Markov process. A baseline climate scenario was developed that represents recently observed temperature and precipitation conditions and then 15 additional climate scenarios that represent shifts in recent conditions. For each scenario, model application produced an ensemble of 50 streamflow traces each spanning 30 yr. Results show that an increase in temperature among scenarios leads to a decrease in streamflow and vice versa. Decreases in temperature shift the basin runoff to fully snowmelt dominated, whereas increases in temperature increase the frequency of midwinter runoff events. Increasing precipitation leads to increased runoff in cases where the temperature remains the same as the observed record, but not in cases where the temperature increases. The modeling approach presented here can be used by water managers to examine which types of climate change could require modifications in water planning and operations.

13 HYDRO ENERGY↗
DOE OSTI2019

Development of 211-Astatine Production in the Crocker Nuclear Laboratory Cyclotron

There is a great deal of interest in the medical community in the use of the alpha-emitter 211-At as a therapeutic isotope. Among other things, its 7.2 hour half life is long enough to allow for recovery and labeling, but short enough to avoid long term activity in patients. Unfortunately, the only practical technique for its production is to bombard a 209-Bi target with a ~29 MeV alpha beam, so it is not accessible to commercial isotope production facilities, which all use fixed energy proton beams. The US Department of Energy is therefore supporting the development of a "University Isotope Network" (UIN) to satisfy this need. Our prposoal is to retrofit the variable-energy, multi-species cyclotron at the Crocker Nuclear Laboratory at the University of California Davis with an internal Bi-209 target, such that we can put at least 100 uA of 29 MeV alpha particles on target without concerns about extraction efficiency. Using very conservative assumptions, we are confident we will be able to produce 60 mCi of 211-At in solution in an eight hour shift, which includes setup, exposure, and chemical recovery. This poster will cover the design of the target, as well as the required chemical processing and reliability upgrades.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

DVMDOSTEM v0.8.3: a terrestrial ecosystem model designed to represent arctic, boreal and permafrost ecosystem dynamics

The impacts of climate change on natural ecosystems are the result of complex physical and ecological processes operating and interacting at a variety of spatio-temporal scales, that can be represented in process-based ecosystem models. DVMDOSTEM is an advanced process-based terrestrial ecosystem model (TEM) designed to study ecosystem responses to climate changes and disturbances. It has a particular focus on permafrost regions (i.e. regions characterized by soils that stay partially frozen all year round for at least two consecutive years), encompassing boreal, arctic, and alpine landscapes. The model couples two previous versions of the Terrestrial Ecosystem Model (TEM) (McGuire et al., 1992): DVMTEM that includes a dynamic vegetation module (DVM) (E. S. Euskirchen et al., 2009), and DOSTEM that includes a dynamic organic soil module (DOS) (H. Genet et al., 2013; Yi et al., 2010). DVMDOSTEM simulates processes at yearly and monthly scales, with some physical processes operating at an even finer temporal resolution. Its versatility allows for site-specific to regional simulations, making it valuable for predicting shifts in permafrost, vegetation, and carbon (C) and nitrogen (N) dynamics. While DVMDOSTEM has been described in the methods sections of many manuscripts, this paper is the first stand alone description of DVMDOSTEM, independent of a particular scientific investigation.

Carman, Tobey B. [Univ. of Alaska, Fairbanks, AK (↗
DOE OSTI2016

Theory and Modeling of Petawatt Laser Pulse Propagation in Low Density Plasmas

Report describing accomplishments in all-optical control of self-injection in laser-plasma accelerators and in developing advanced numerical models of laser-plasma interactions. All-optical approaches to controlling electron self-injection and beam formation in laser-plasma accelerators (LPAs) were explored. It was demonstrated that control over the laser pulse evolution is the key ingredient in the generation of low-background, low-phase-space-volume electron beams. To this end, preserving a smooth laser pulse envelope throughout the acceleration process can be achieved through tuning the phase and amplitude of the incident pulse. A negative frequency chirp compensates the frequency red-shift accumulated due to wake excitation, preventing evolution of the pulse into a relativistic optical shock. This reduces the ponderomotive force exerted on quiescent plasma electrons, suppressing expansion of the bubble and continuous injection of background electrons, thereby reducing the charge in the low-energy tail by an order of magnitude. Slowly raising the density in the pulse propagation direction locks electrons in the accelerating phase, boosting their energy, keeping continuous injection at a low level, tripling the brightness of the quasi-monoenergetic component. Additionally, propagating the negatively chirped pulse in a plasma channel suppresses diffraction of the pulse leading edge, further reducing continuous injection. As a side effect, oscillations of the pulse tail may be enhanced, leading to production of low-background, polychromatic electron beams. Such beams, consisting of quasi-monoenergetic components with controllable energy and energy separation, may be useful as drivers of polychromatic x-rays based on Thomson backscattering. These all-optical methods of electron beam quality control are critically important for the development of future compact, high-repetition-rate, GeV-scale LPA using 10 TW-class, ultra-high bandwidth pulses and mm-scale, dense plasmas. These results emphasize that investment into new pulse amplification techniques allowing for ultrahigh frequency bandwidth is as important for the design of future LPA as are the current efforts directed to increasing the pulse energy.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Uranium Mining and Milling

The starting point for material accountancy under INFCIRC/153-type comprehensive safeguards agreements (paragraph 34(c)) with an Additional Protocol envisions a shifting toward earlier in the nuclear fuel cycle than current practice. The design of effective and efficient safeguards requires a more detailed process-level understanding of front-end activities, to include conducting a survey of uranium mining, concentration, and purification processes in commercial use to catalog technological options for producing uranium ore concentrate, also known as yellow cake. Based on this survey, a process flow diagram (PFD) illustrating front-end process options will be created to illustrate pre-34(c) material flows and support the identification of material control points.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Soil Metabolomics Predict Microbial Taxa as Biomarkers of Moisture Status in Soils from a Tidal Wetland

We present observations from a laboratory-controlled study on the impacts of extreme wetting and drying on a wetland soil microbiome. Our approach was to experimentally challenge the soil microbiome to understand impacts on anaerobic carbon cycling processes as the system transitions from dryness to saturation and vice-versa. Specifically, we tested for impacts on stress responses related to shifts from wet to drought conditions. We used a combination of high-resolution data for small organic chemical compounds (metabolites) and biological (community structure based on 16S rRNA gene sequencing) features. Using a robust correlation-independent data approach, we further tested the predictive power of soil metabolites for the presence or absence of taxa. Here, we demonstrate that taking an untargeted, multidimensional data approach to the interpretation of metabolomics has the potential to indicate the causative pathways selecting for the observed bacterial community structure in soils.

16S rRNA gene↗
NASA NTRS1972

Services provided in support of the planetary quarantine requirements of the National Aeronautics and Space Administration

The evaluation is discussed of the terminal sterilization process for unmanned lander spacecraft. Results of biochemical test deviations encountered with the identification schemes are tabulated. Studies to examine the possibility of shifts in biochemical reaction patterns during storage and subculture of the environmental Bacillius isolates are also reported.

Favero, M. S.↗
NASA NTRS1972

Utilization of FSK communications for time

The method of time control at a radio station for time signal transmission using frequency shift keying, is discussed. Methods for extracting a recovered clock at the receiver are described. Results of a test involving the methods of processing time signals are presented. The requirements for adapting Precise Time and Time Interval control to a communications system are analyzed. A method for reducing the time required for synchronization or identification of messages and the fallout from the communication system to passive timekeeping users are reported.

Stone, R. R., Jr.↗
NASA NTRS1973

Instrumentation for one-way satellite PTTI applications

A review of general principles and operational procedures illustrates how the typical passive user and omni receiving antenna can recover Precise Time and Time Interval (PTTI) information from a low altitude navigation satellite system for clock calibration and synchronization. Detailed discussions of concepts and theory of the receiver design are presented. The importance of RF correlation of the received and local PN encoded sequences is emphasized as a means of reducing delay uncertainties of the instrumentation to values compatible with nanosecond to submicrosecond PTTI objectives. Two receiver configurations were fabricated for use in satellite-to-laboratory experiments. In one receiver the delay-locked loop for PN signals synchronization used a dithered amplitude detection process while the second receiver used a complex sums phase detection method for measurement of delay error. The necessity for compensation of Doppler shift is discussed. Differences in theoretical signal acquisition and tracking performance of the design concepts are noted.

Osborne, A. E.↗
NASA NTRS1992

Fractals and cosmological large-scale structure

Observations of galaxy-galaxy and cluster-cluster correlations as well as other large-scale structure can be fit with a 'limited' fractal with dimension D of about 1.2. This is not a 'pure' fractal out to the horizon: the distribution shifts from power law to random behavior at some large scale. If the observed patterns and structures are formed through an aggregation growth process, the fractal dimension D can serve as an interesting constraint on the properties of the stochastic motion responsible for limiting the fractal structure. In particular, it is found that the observed fractal should have grown from two-dimensional sheetlike objects such as pancakes, domain walls, or string wakes. This result is generic and does not depend on the details of the growth process.

Luo, Xiaochun↗