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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Increase in the resolution of the method of surface nanostructuring by femtosecond-laser impact through a layer of colloidal microparticles

It is experimentally demonstrated that by converting a few percent of the fundamental frequency pulse energy into the second harmonic one can obtain surface structures using dielectric microspheres with the dimension of the order of the second harmonic wavelength. Structuring by means of the second harmonic solely requires a significantly greater energy density in the pulse than using bichromatic irradiation. It is impossible to obtain structures using only the fundamental frequency radiation pulses, because radiation at the fundamental frequency is not focused by the system of microspheres. Therefore, the use of bichromatic pulses allows an essential increase in the structure recording density. Theoretical calculations demonstrating the possibility of further improvement of the structure recording density by using nonspherical microlenses of a smaller size made of a material with a higher refractive index are presented. (extreme light fields and their applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Influence of Surfactants on Noble Metal Liquid-Gas Interface Mass Transfer in Molten Salt Reactors

Noble metals, a group of insoluble fission products (FPs), can accumulate in molten salt reactors (MSRs) and influence system performance and safety through deposition. Upon generation in fission, noble metals are transported by circulating salt and may either deposit on structural surfaces or enter the circulating gas bubble interfaces. While sparging was primarily designed for xenon and krypton removal, the mass transfer of noble metals into bubble interfaces highlights a potential pathway for their transport and partial extraction. The properties of the liquid-gas interface therefore play an important role in noble metal deposition and removal behaviors. Observations from earlier studies suggest that noble metals accumulated at the bubble interface can act as surfactants, making the bubble interface partially immobile. This behavior reduces the mass transfer capacity of circulating bubbles and affects both the overall distribution of noble metals in the loop and their removal efficiency. To investigate the influence of surfactants on noble metal transport, deposition, and extraction behaviors in MSRs, a previously developed and validated species transport model incorporating noble metal interphase mass transfer was used to simulate these behaviors. Two designed cases were studied to predict the distribution of 132Te along the Molten Salt Reactor Experiment (MSRE) loop under different bubble interface conditions. The results show that the mass transfer coefficients at the liquid-gas interface, determined by bubble interface characteristics, significantly influence noble metal distribution within the reactor loop. These findings emphasize the importance of continuously introducing fresh circulating bubbles into the molten salt to improve the removal efficiency of insoluble FPs from the MSR primary loop.

MSR↗
DOE OSTI2020

A Facile Degumming Method of Kenaf Fibers Using Deep Eutectic Solution

An eco-friendly and effective degumming method needed to be developed for producing kenaf bast fibers. As such, this study devised a novel deep eutectic solvent (DES) method coupled with microwave and alkaline-ultrasonic treatment. The novel method could effectively remove the gummy matters, providing a smooth and clean fiber surface. The properties of the fibers were assessed including chemical compositions, surface structure, crystallinity index (66.68%) and thermal properties. The residual gum content (9.419%), fiber fineness (4.125tex), breaking tenacity (13.650 cn/tex) of the refined dry fibers produced by the novel treatment were comparable with the fibers produced by the traditional two-step alkali boiling method. Besides, the novel method could reduce the usage of chemical, water and time by 48.9%, by 66.7% and 66.8%, respectively. These results revealed that the novel combined DES pretreatment is a practical and feasible pretreatment method for kenaf bast degumming, demonstrating its facile, green energy-saving and fast properties in the degumming process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

MATERIALS, FABRICATION, AND MANUFACTURING OF MICRO/NANOSTRUCTURED SURFACES FOR PHASE-CHANGE HEAT TRANSFER ENHANCEMENT

This article describes the most prominent materials, fabrication methods, and manufacturing schemes for micro- and nanostructured surfaces that can be employed to enhance phase-change heat transfer phenomena. The numerous processes include traditional microfabrication techniques such as thin-film deposition, lithography, and etching, as well as template-assisted and template-free nanofabrication techniques. The creation of complex, hierarchical, and heterogeneous surface structures using advanced techniques is also reviewed. Additionally, research needs in the field and future directions necessary to translate these approaches from the laboratory to high-performance applications are identified. Particular focus is placed on the extension of these techniques to the design of micro/nanostructures for increased performance, manufacturability, and reliability. The current research needs and goals are detailed, and potential pathways forward are suggested.

McCarthy, M↗
DOE OSTI2014

Multi-wavelength high-resolution observations of a small-scale emerging magnetic flux event and the chromospheric and coronal response

State-of-the-art solar instrumentation is now revealing magnetic activity of the Sun with unprecedented temporal and spatial resolutions. Observations with the 1.6 m aperture New Solar Telescope (NST) of the Big Bear Solar Observatory are making next steps in our understanding of the solar surface structure. Granular-scale magnetic flux emergence and the response of the solar atmosphere are among the key research topics of high-resolution solar physics. As part of a joint observing program with NASA's Interface Region Imaging Spectrograph (IRIS) mission on 2013 August 7, the NST observed active region NOAA 11,810 in the photospheric TiO 7057 Å band with a resolution of pixel size of 0.''034 and chromospheric He I 10830 Å and Hα 6563 Å wavelengths. Complementary data are provided by the Solar Dynamics Observatory (SDO) and Hinode space-based telescopes. The region displayed a group of solar pores, in the vicinity of which we detect a small-scale buoyant horizontal magnetic flux tube causing granular alignments and interacting with the preexisting ambient field in the upper atmospheric layers. Following the expansion of distorted granules at the emergence site, we observed a sudden appearance of an extended surge in the He I 10830 Å data (bandpass of 0.05 Å). The IRIS transition region imaging caught ejection of a hot plasma jet associated with the He I surge. The SDO/HMI data used to study the evolution of the magnetic and Doppler velocity fields reveal emerging magnetic loop-like structures. Hinode/Ca II H and IRIS filtergrams detail the connectivities of the newly emerged magnetic field in the lower solar chromosphere. From these data, we find that the orientation of the emerging magnetic field lines from a twisted flux tube formed an angle of ∼45° with the overlying ambient field. Nevertheless, the interaction of emerging magnetic field lines with the pre-existing overlying field generates high-temperature emission regions and boosts the surge/jet production. The localized heating is detected before and after the first signs of the surge/jet ejection. We compare the results with previous observations and theoretical models and propose a scenario for the activation of plasma jet/surges and confined heating triggered by buoyant magnetic flux tubes rising up into a magnetized upper environment. Such process may play a significant role in the mass and energy flow from the interior to the corona.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G): MULTI-COMPONENT DECOMPOSITION STRATEGIES AND DATA RELEASE

The Spitzer Survey of Stellar Structure in Galaxies (S{sup 4}G) is a deep 3.6 and 4.5 μm imaging survey of 2352 nearby (<40 Mpc) galaxies. We describe the S{sup 4}G data analysis pipeline 4, which is dedicated to two-dimensional structural surface brightness decompositions of 3.6 μm images, using GALFIT3.0. Besides automatic 1-component Sérsic fits, and 2-component Sérsic bulge + exponential disk fits, we present human-supervised multi-component decompositions, which include, when judged appropriate, a central point source, bulge, disk, and bar components. Comparison of the fitted parameters indicates that multi-component models are needed to obtain reliable estimates for the bulge Sérsic index and bulge-to-total light ratio (B/T), confirming earlier results. Here, we describe the preparations of input data done for decompositions, give examples of our decomposition strategy, and describe the data products released via IRSA and via our web page (www.oulu.fi/astronomy/S4G-PIPELINE4/MAIN). These products include all the input data and decomposition files in electronic form, making it easy to extend the decompositions to suit specific science purposes. We also provide our IDL-based visualization tools (GALFIDL) developed for displaying/running GALFIT-decompositions, as well as our mask editing procedure (MASK-EDIT) used in data preparation. A detailed analysis of the bulge, disk, and bar parameters derived from multi-component decompositions will be published separately.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Understanding the pseudocapacitance of RuO 2 from joint density functional theory

Pseudocapacitors have been experimentally studied for many years in electric energy storage. However, first principles understanding of the pseudocapacitive behavior is still not satisfactory due to the complexity involved in modeling electrochemistry. In this paper, we applied joint density functional theory (JDFT) to simulate the pseudocapacitive behavior of RuO 2 , a prototypical material, in a model electrolyte. Additionally, we obtained from JDFT a capacitive curve which showed a redox peak position comparable to that in the experimental cyclic voltammetry (CV) curve. We found that the experimental turning point from double-layer to pseudocapacitive charge storage at low scan rates could be explained by the hydrogen adsorption at low coverage. As the electrode voltage becomes more negative, H coverage increases and causes the surface-structure change, leading to bended –OH bonds at the on-top oxygen atoms and large capacitance. This H coverage-dependent capacitance can explain the high pseudocapacitance of hydrous RuO 2 . In conclusion, our work here provides a first principles understanding of the pseudocapacitance for RuO 2 in particular and for transition-metal oxides in general.

double layer capacitance↗
DOE OSTI2022

Reaction–drift–diffusion models from master equations: application to material defects

We present a general method to produce well-conditioned continuum reaction–drift–diffusion equations directly from master equations on a discrete, periodic state space. We assume the underlying data to be kinetic Monte Carlo models (i.e. continuous-time Markov chains) produced from atomic sampling of point defects in locally periodic environments, such as perfect lattices, ordered surface structures or dislocation cores, possibly under the influence of a slowly varying external field. Our approach also applies to any discrete, periodic Markov chain. Here, the analysis identifies a previously omitted non-equilibrium drift term, present even in the absence of external forces, which can compete in magnitude with the reaction rates, thus being essential to correctly capture the kinetics. To remove fast modes which hinder time integration, we use a generalized Bloch relation to efficiently calculate the eigenspectrum of the master equation. A well conditioned continuum equation then emerges by searching for spectral gaps in the long wavelength limit, using an established kinetic clustering algorithm to define a proper reduced, Markovian state space.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of layer thickness on structural, morphological and superconducting properties of Nb 3 Sn films fabricated by multilayer sequential sputtering

Superconducting Nb3Sn films can be synthesized by controlling atomic concentration of Sn. Multilayer sequential sputtering of Nb and Sn thin films followed by high temperature annealing is considered as a method to fabricate Nb3Sn films where Sn composition of deposited films can be controlled by controlling the thickness of alternating Nb and Sn layers. We report on the structural, morphological and superconducting properties of Nb3Sn films fabricated by multilayer sequential sputtering of Nb and Sn films on sapphire substrates with ex-situ annealing at 950 °C for 3 h. We have investigated the effect of Nb and Sn layer thickness on the properties of Nb3Sn films. The thicknesses of Nb and Sn layers were varied in two ways: (1) varied Nb:Sn thickness ratio (1:1, 2:1, 3:1, 4:1), and (2) varied layer thickness of both Nb and Sn layers, while keeping constant Nb:Sn thickness ratio of 2:1. The crystal structure, surface morphology, topography, and film composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDS) respectively. The results showed Sn loss from the surface due to evaporation during annealing. Superconducting Nb3Sn films of critical temperature up to 17.93 K have been achieved.

Sayeed, M. N.↗
DOE OSTI2020

Characterization with dense array data of seismic sources in the shallow part of the San Jacinto fault zone

SUMMARY We analyse dominant sources identified in a catalogue of more than 156 000 localizations performed using a 26-d data set recorded by a dense array set on the San Jacinto fault near Anza, in California. Events were localized using an array processing technique called Match Field Processing. As for all array processing techniques, the quality of the event position decrease when the events are outside of the array. We thus separate localizations in and outside the array using simple geometrical conditions. We compare the time distribution of the localization to additional data such as meteorological data, day of human activity as well as existing catalogues to determine the nature of the dominant events located using our method. We find that most of the events located outside of the array could be attributed to a surface structure excited by wind. On the other hand, part of the localizations under the array occur during regional earthquakes and could correspond to diffraction on the fault's heterogeneities. The rest of the localizations inside the array could be generated by the fault itself.

Geochemistry & Geophysics↗
DOE OSTI2018

Broad-band trajectory mechanics

We present here a trajectory-based solution to the elastodynamic equation of motion that is valid across a wide range of seismic frequencies. That is, the derivation of the solution does not invoke a high-frequency assumption or require that the medium have smoothly varying properties. The approach, adopted from techniques used in quantum dynamics, produces a set of coupled ordinary differential equations for the trajectory, the slowness vector and the elastic wave amplitude along the ray path. The trajectories may be determined by a direct solution of the governing equations or derived as the by-product of a numerical wavefield simulation. Synthetic tests with interfaces and layers containing increasingly narrow transition zones indicate that the conventional high-frequency trajectories associated with the eikonal equation bend too sharply into high-velocity regions as the wavelength exceeds the transition zone width. Tests in a velocity model, based upon mapped structural surfaces from the Geysers geothermal field in California, indicate that discrepancies between high-frequency and broad-band trajectories can exceed several hundred metres at wavelengths of 1 Hz. An application to a crosswell tomographic imaging experiment demonstrates that the technique provides a basis for the seismic monitoring of fluid flow along narrow features such as fracture zones.

58 GEOSCIENCES↗
DOE OSTI2020

Universal dynamics of coarsening during polymer-polymer thin-film spinodal dewetting kinetics

The dewetting dynamics of a supported bilayer polymer thin film on a solid substrate is investigated using grazing incidence x-ray photon correlation spectroscopy. We find that the top layer dewets via the spinodal mechanism. The kinetics of the dewetting is studied by monitoring the time evolution of the surface diffuse x-ray scattering intensity. We study the time evolution of fluctuations about the average surface structure by measuring the two-time x-ray intensity fluctuation correlation functions. Using these two-time correlation functions we quantify the crossover from early-time diffusive dynamics to hydrodynamics. The early diffusive regime satisfies dynamic universality. The two-time correlation functions also quantify the onset of hydrodynamic effects. The hydrodynamic regime is observed during the spinodal dewetting process as these interactions are not screened.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Boron nitride on SiC(0001)

Here, in the field of van der Waals heterostructures, the twist angle between stacked two-dimensional layers has been identified to be of utmost importance for the properties of the heterostructures. In this context, we previously reported the growth of a single layer of unconventionally oriented epitaxial graphene that forms in a surfactant atmosphere [F. C. Bocquet et al., Phys. Rev. Lett. 125, 106102 (2020)]. The resulting G-R0° layer is aligned with the SiC lattice, and hence represents an important milestone towards high-quality twisted bilayer graphene, a frequently investigated model system in this field. Here, we focus on the surface structures obtained in the same surfactant atmosphere, but at lower preparation temperatures at which a boron nitride template layer forms on SiC(0001). In a comprehensive study based on complementary experimental and theoretical techniques, we find—in contrast to the literature—that this template layer is a hexagonal B x N y layer, but not high-quality hBN. It is aligned with the SiC lattice and gradually replaced by low-quality graphene in the 0° orientation of the B x N y template layer upon annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Connect the Dots: In Situ 4-D Seismic Monitoring of CO 2 Storage With Spatio-Temporal CNNs

4-D seismic imaging has been widely used in CO 2 sequestration projects to monitor the fluid flow in the volumetric subsurface region that is not sampled by wells. Ideally, real-time monitoring and near-future forecasting would provide site operators with great insights to understand the dynamics of the subsurface reservoir and assess any potential risks. However, due to obstacles such as high deployment cost, availability of acquisition equipment, exclusion zones around surface structures, only very sparse seismic imaging data can be obtained during monitoring. That leads to an unavoidable and growing knowledge gap over time. The operator needs to understand the fluid flow throughout the project lifetime and the seismic data are only available at a limited number of times. This is insufficient for understanding reservoir behavior. To overcome those challenges, we have developed spatio-temporal neural-network-based models that can produce high-fidelity interpolated or extrapolated images effectively and efficiently. Specifically, our models are built on an autoencoder, and incorporate the long short-term memory (LSTM) structure with a new loss function regularized by optical flow. We validate the performance of our models using real 4-D post-stack seismic imaging data acquired at the Sleipner CO 2 sequestration field. We employ two different strategies in evaluating our models. Numerically, we compare our models with different baseline approaches using classic pixel-based metrics. We also conduct a blind survey and collect a total of 20 responses from domain experts to evaluate the quality of data generated by our models. Finally, via both numerical and expert evaluation, we conclude that our models can produce high-quality 2-D/3-D seismic imaging data at a reasonable cost, offering the possibility of real-time monitoring or even near-future forecasting of the CO 2 storage reservoir.

4-D seismic imaging↗
DOE OSTI2020

Topological controls on aluminosilicate glass dissolution: Complexities induced in hyperalkaline aqueous environments

Abstract Fly ash, an aluminosilicate composite consisting of disordered (major) and crystalline (minor) compounds, is a low‐carbon alternative that can partially replace ordinary portland cement (OPC) in the binder fraction of concrete. Therefore, understanding the reactivity of fly ash in the hyperalkaline conditions prevalent in concrete is critical to predicting concrete's performance; including setting and strength gain. Herein, temporal measurements of the solution composition (using inductively coupled plasma‐optical emission spectrometry: ICP‐OES) are used to assess the aqueous dissolution rate of monophasic synthetic aluminosilicate glasses analogous to those present in technical fly ashes, under hyperalkaline conditions (10 ≤ pH ≤ 13) across a range of temperatures (25°C ≤ T≤45°C). The dissolution rate is shown to depend on the average number of topological constraints per atom within the glass network (n c , unitless), but this dependence weakens with increasing pH (>10). This is postulated to be on account of: (a) time‐dependent changes in the glass’ surface structure, that is, the number of topological constraints; and/or (b) a change in the dissolution mechanism (eg from network hydrolysis to transport control). The results indicate that the topological description of glass dissolution is most rigorously valid only at very short reaction times (ie at high undersaturations), especially under conditions of hyperalkalinity. These findings provide an improved basis to understand the underlying factors that affect the initial and ongoing reactivity of aluminosilicate glasses such as fly ash in changing chemical environments, for example, when such materials are utilized in cementitious composites.

Oey, Tandré↗
DOE OSTI2021

X-ray and electron spectroscopy of (photo)electrocatalysts: Understanding activity through electronic structure and adsorbate coverage

Electronic structure plays a critical role in the kinetics of (photo)electrocatalytic reactions. X-ray and electron spectroscopies provide key determinants—electronic structure, surface adsorbate speciation and coverage quantification, valence state, coordination chemistry, etc.—of catalytic activity and selectivity. Here, we provide an introduction to the fundamental physical concepts, capabilities, and limitations of x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and electron energy-loss spectroscopy as well as provide discussions of (photo)electrocatalysis-relevant publications utilizing each of these techniques. Our objective is to provide those new to x-ray and electron spectroscopies with sufficient information to assess which techniques probe desired material parameters, while also providing experts in each of these spectroscopic fields a bridge to view the importance of these spectroscopies to (photo)electrocatalysis research.

Carvalho, Oliver Quinn (ORCID:0000000344205203)↗
DOE OSTI2025

Synthesis and characterization of electron beam irradiation-induced damage in polycrystalline metal thin films

High-energy physics research, industrial sterilizing, and material processing depend extensively on electron beam accelerators. Exit windows are crucial components of such electron accelerator systems, maintaining vacuum integrity inside the machine while providing mechanical strength, thermal stability, and radiation resistance at the beam-target interface. In this study, thin metallic films of Ni, Ti, Cr, and V were explored for use in electron beam exit windows, and their properties were compared with the properties of their bulk counterparts. Simulation results of metal foils predicted Ti to exhibit less beam power dissipation compared to Ni. However, Ni possesses superior mechanical and structural properties compared to Ti. The performance of these films under electron beam irradiation was examined by depositing thin layers of these films on silicon and metallic substrates using magnetron sputtering and exposing them to e-beam irradiation in a controlled setup. The deposited films were subjected to a dose of approximately 66 kGy at a beam energy of 10 MeV and characterized prior to and postexposure to the beam using field emission scanning electron microscopy, atomic force microscopy, x-ray diffraction (XRD), and nanoindentation. Particular emphasis was given to characteristics like the grain structure, surface morphology, dislocation density, and hardness. XRD patterns revealed irradiation-induced changes in peak intensities, while the crystallinity remained largely unchanged. Nanoindentation results showed that the pristine and irradiated Ti and Ni films were twice as hard when compared to bulk Ti and Ni samples, regardless of the substrate type used (Si or bulk Ti, or Ni). These results emphasize the superior mechanical properties of thin metal films compared to their bulk counterparts. In conclusion, this study advances the optimization of thin film materials for robust and efficient e-beam applications, ensuring improved durability and operational reliability.

AFM↗
DOE OSTI2015

SU-E-T-234: Daily Quality Assurance for a Six Degrees of Freedom Couch Using a Novel Phantom

Purpose: To test the accuracy and reproducibility of both translational and rotational movements for a couch with six degrees of freedom (6DoF) using a novel phantom design Methods: An end-to-end test was carried out using two different phantoms. A 6 cm3 cube with a central fiducial BB (WL-QA Sun Nuclear) and a custom fabricated rectangular prism (31 cm x 8 cm x 8 cm), placed on a baseplate with known angular offsets for pitch, roll and yaw with a central fiducial BB and unique surface structures for registration purposes, were used. The end-to-end test included an initial CT simulation for a reference study, setup to an offset mark on each phantom, registration of the reference CT to the acquired cone-beam CT, and final Winston-Lutz delivery at four cardinal gantry angles. Results for both translational and rotational movements were recorded and compared for both phantoms. Results: Translational and rotational measurements were performed with a PerfectPitch (Varian) couch for 10 trials for both phantoms. Distinct translational shifts were [−5.372±0.384mm, −10.183±0.137mm, 14.028±0.155mm] for the cube and [7.520±0.159mm, −9.117±0.101mm, 16.273±0.115mm] for the prototype phantom for lateral, longitudinal, and vertical shifts, respectively. Distinct rotational adjustments were [1.121±0.102o, −1.067±0.235o, −2.662±0.380o] for the cube and [2.534±0.059o, 1.994±0.025o, 2.094±0.076o] for the prototype for pitch, roll, and yaw, respectively. Winston-Lutz test results performed after 6DoF couch correction from each cardinal gantry angle ranged from 0.26–0.72mm for the cube and 0.55–0.86mm for the prototype. Conclusion: The prototype phantom is more precise for both translational and rotational adjustments compared to a commercial phantom. The design of the prototype phantom allows for a more discernible visual confirmation of correct translational and rotational adjustments with the prototype phantom. Winston-Lutz results are more accurate for the commercial phantom but are still within tolerance for the prototype phantom.

60 APPLIED LIFE SCIENCES↗