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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Cr/B{sub 4}C multilayer mirrors: Study of interfaces and X-ray reflectance

We present an experimental study of the effect of layer interfaces on the x-ray reflectance in Cr/B{sub 4}C multilayer interference coatings with layer thicknesses ranging from 0.7 nm to 5.4 nm. The multilayers were deposited by magnetron sputtering and by ion beam sputtering. Grazing incidence x-ray reflectometry, soft x-ray reflectometry, and transmission electron microscopy reveal asymmetric multilayer structures with a larger B{sub 4}C-on-Cr interface, which we modeled with a 1–1.5 nm thick interfacial layer. Reflectance measurements in the vicinity of the Cr L{sub 2,3} absorption edge demonstrate fine structure that is not predicted by simulations using the currently tabulated refractive index (optical constants) values for Cr.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Transition state region in the A-Band photodissociation of allyl iodide—A femtosecond extreme ultraviolet transient absorption study

Femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy based on a high-harmonic generation source is used to study the 266 nm induced A-band photodissociation dynamics of allyl iodide (CH{sub 2} =CHCH{sub 2}I). The photolysis of the C—I bond at this wavelength produces iodine atoms both in the ground ({sup 2}P{sub 3/2}, I) and spin-orbit excited ({sup 2}P{sub 1/2}, I*) states, with the latter as the predominant channel. Using XUV absorption at the iodine N{sub 4/5} edge (45–60 eV), the experiments constitute a direct probe of not only the long-lived atomic iodine reaction products but also the fleeting transition state region of the repulsive n{sub I}σ{sup ∗}{sub C—I} excited states. Specifically, three distinct features are identified in the XUV transient absorption spectrum at 45.3 eV, 47.4 eV, and 48.4 eV (denoted transients A, B, and C, respectively), which arise from the repulsive valence-excited nσ{sup ∗} states and project onto the high-lying core-excited states of the dissociating molecule via excitation of 4d(I) core electrons. Transients A and B originate from 4d(I) → n(I) core-to-valence transitions, whereas transient C is best assigned to a 4d(I) →σ{sup ∗}(C—I) transition. The measured differential absorbance of these new features along with the I/I* branching ratios known from the literature is used to suggest a more definitive assignment, albeit provisional, of the transients to specific dissociative states within the A-band manifold. The transients are found to peak around 55 fs–65 fs and decay completely by 145 fs–185 fs, demonstrating the ability of XUV spectroscopy to map the evolution of reactants into products in real time. The similarity in the energies of transients A and B with analogous features observed in methyl iodide [Attar et al. J. Phys. Chem. Lett. 6, 5072, (2015)] together with the new observation of transient C in the present work provides a more complete picture of the valence electronic structure in the transition state region. The results provide a benchmark for theoretical calculations on the nature of core-excited states in halogenated hydrocarbons, especially in the transition state region along the C—I reaction coordinate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

UV + V UV double-resonance studies of autoionizing Rydberg states of the hydroxyl radical

The hydroxyl radical (OH) is a key oxidant in atmospheric and combustion chemistry. Recently, a sensitive and state-selective ionization method has been developed for detection of the OH radical that utilizes UV excitation on the A{sup 2}Σ{sup +}–X{sup 2}Π transition followed by fixed 118 nm vacuum ultraviolet (VUV) radiation to access autoionizing Rydberg states [J. M. Beames et al., J. Chem. Phys. 134, 241102 (2011)]. The present study uses tunable VUV radiation generated by four-wave mixing to examine the origin of the enhanced ionization efficiency observed for OH radicals prepared in specific A{sup 2}Σ{sup +} intermediate levels. The enhancement is shown to arise from resonant excitation to distinct rotational and fine structure levels of two newly identified {sup 2}Π Rydberg states with an A{sup 3}Π cationic core and a 3d electron followed by ionization. Spectroscopic constants are derived and effects due to uncoupling of the Rydberg electron are revealed for the OH {sup 2}Π Rydberg states. The linewidths indicate a Rydberg state lifetime due to autoionization on the order of a picosecond.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

A molecular dynamics study of the effect of thermal boundary conductance on thermal transport of ideal crystal of n-alkanes with different number of carbon atoms

Phase change materials such as n-alkanes that exhibit desirable characteristics such as high latent heat, chemical stability, and negligible supercooling are widely used in thermal energy storage applications. However, n-alkanes have the drawback of low thermal conductivity values. The low thermal conductivity of n-alkanes is linked to formation of randomly oriented nano-domains of molecules in their solid structure that is responsible for excessive phonon scattering at the grain boundaries. Thus, understanding the thermal boundary conductance at the grain boundaries can be crucial for improving the effectiveness of thermal storage systems. The concept of the ideal crystal is proposed in this paper, which describes a simplified model such that all the nano-domains of long-chain n-alkanes are artificially aligned perfectly in one direction. In order to study thermal transport of the ideal crystal of long-chain n-alkanes, four (4) systems (C{sub 20}H{sub 42}, C{sub 24}H{sub 50}, C{sub 26}H{sub 54}, and C{sub 30}H{sub 62}) are investigated by the molecular dynamics simulations. Thermal boundary conductance between the layers of ideal crystals is determined using both non-equilibrium molecular dynamics (NEMD) and equilibrium molecular dynamics (EMD) simulations. Both NEMD and EMD simulations exhibit no significant change in thermal conductance with the molecular length. However, the values obtained from the EMD simulations are less than the values from NEMD simulations with the ratio being nearly three (3) in most cases. This difference is due to the nature of EMD simulations where all the phonons are assumed to be in equilibrium at the interface. Thermal conductivity of the n-alkanes in three structures including liquid, solid, and ideal crystal is investigated utilizing NEMD simulations. Our results exhibit a very slight rise in thermal conductivity values as the number of carbon atoms of the chain increases. The key understanding is that thermal transport can be significantly altered by how the molecules and the nano-domains are oriented in the structure rather than by the length of the n-alkane molecules.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A multi-scale study of the adsorption of lanthanum on the (110) surface of tungsten

In this study, we utilize a multi-scale approach to studying lanthanum adsorption on the (110) plane of tungsten. The energy of the system is described from density functional theory calculations within the framework of the cluster expansion method. It is found that including two-body figures up to the sixth nearest neighbor yielded a reasonable agreement with density functional theory calculations as evidenced by the reported cross validation score. The results indicate that the interaction between the adsorbate atoms in the adlayer is important and cannot be ignored. The parameterized cluster expansion expression is used in a lattice gas Monte Carlo simulation in the grand canonical ensemble at 773 K and the adsorption isotherm is recorded. Implications of the obtained results for the pyroprocessing application are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Dynamic-range studies and improvements for multiplexed photonic Doppler velocimetry

This paper presents studies of the dynamic range achievable with multiplexed photonic Doppler velocimetry (MPDV) measurements, and demonstrates techniques to extend the dynamic range. Improved dynamic range for MPDV measurements is needed in order to track the velocity of the free surface behind a cloud of ejecta. Therefore, the authors have undertaken theoretical and experimental studies of factors affecting dynamic range, particularly in cases where the large number of MPDV probe points precludes high illumination power on each channel. To quantify the potential dynamic range of a given MPDV configuration, they introduce a metric called the frequency-domain number of bits, FNOB, which is less stringent than the formally defined equivalent number of bits (ENOB). This new metric is simple to compute in the lab, and it is well suited to conventional PDV analysis, which does not require digitizer phase coherence beyond tens of nanoseconds.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A benchmark photoelectron spectroscopic and theoretical study of the electronic stability of [B12H12]2-

We report a joint benchmark study on the electronic stability of closo-dodecaborate [B12H12]2- employing negative ion photoelectron spectroscopy and high level electronic structure methods. The photoelectron spectra of [B12H12]2-, measured at 266, 193 and 157 nm, yield the Adiabatic and Vertical Detachment Energies (ADE and VDE) of this dianion at 0.93 ± 0.05 eV and 1.15 ± 0.05 eV, respectively, along with a ~ 3 eV Repulsive Coulomb Barrier (RCB) against electron detachment. Theoretical calculations at various levels of electronic structure theory confirm the high stability of this dianion. The ADE and VDE values calculated at the CCSD(T)/aug-cc-PVQZ level are 0.92, and 1.16 eV, in excellent agreement with the experimental benchmark values. The comparison between the experimental and the theoretical values obtained at different levels of theory indicate that the PBE0 density functional represents a cost-effective method of sufficient accuracy to describe the molecular properties of this dianion and associated compounds. The theoretical RCB was modelled after the electrostatic potential (ESP) and point charge method (PCM) along three different detachment pathways, viz. along the B-H bond, perpendicular to a B-B bond, and normal to a B-B-B triangle. It was found that detachment of the electron along the B-H bond is preferred, as this pathway is associated with RCBs between 2.3 eV (PCM) and 3.3 eV (ESP), values that bracket the experimental estimate of ~ 3 eV.

Apra, Edoardo↗
DOE OSTI2020

Rethinking the magnetic properties of lepidocrocite: A density functional theory and cluster expansion study

The iron oxyhydroxide lepidocrocite (g-FeOOH) is an abundant mineral critical to a number of chemical and technological applications. Of particular interest is the ground state and nite temperature magnetic order, and the subsequent impact this has upon crystal properties. The magnetic properties, investigated in this work are governed primarily through superexchange interactions, and have been calculated using density functional theory and cluster expansion methods. Quantication of these exchange terms has facilitated the determination of the ground state magneto-crystalline structure and subsequent calculation of its lattice constants, elastic moduli, cohesive enthalpy, and electronic density of states. Further, using a collinear magnetic conguration model, the magnetic heat capacity versus temperature has been studied and the Neel temperature obtained.

Pope, Daniel J.↗
DOE OSTI2019

Design Studies for the Optimization of 238 Pu Production in NpO 2 Targets Irradiated at the High Flux Isotope Reactor

Efforts to reestablish a domestic 238 Pu production capability in support of National Aeronautics and Space Administration mission objectives are ongoing throughout the U.S. Department of Energy complex. The Plutonium-238 Supply Project (PSP) was initiated in response to a report published by the National Research Council in 2011 stating that “without a restart of 238 Pu production, it will be impossible for the United States, or any other country, to conduct certain important types of planetary missions after this decade.” The PSP is targeting a sustained, constant production rate of 1.5 kg/year of heat source PuO 2 for several years. Design and optimization studies of 237 Np-bearing targets are underway at Oak Ridge National Laboratory (ORNL). It is anticipated that targets will be irradiated in ORNL’s High Flux Isotope Reactor (HFIR) and in the Advanced Test Reactor (ATR) at Idaho National Laboratory. A variety of target materials, containments, arrangements, and irradiation histories have been analyzed, and the results indicate that a sufficient quantity of 238 Pu can be produced in HFIR and ATR to fulfill the PSP’s constant production rate target. This paper focuses on the design and optimization of new target configurations containing pellets that are (1) ~93% of the theoretical density of NpO 2 , (2) loaded into pins of cladding materials that can be handled as solid waste following postirradiation 238 Pu recovery operations, (3) irradiated in various vertical experiment facility (VXF) locations in the HFIR permanent beryllium reflector, and (4) rotated within and/or moved to another VXF location following each HFIR operational cycle to maximize 238Pu production and minimize peak heat generation rates.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

Liquid–Liquid Mixing Studies in Annular Centrifugal Contactors Comparing Stationary Mixing Vane Options

Comparative studies of multiphase operation of annular centrifugal contactors showing the impact of housing stationary mixing vane configuration. A number of experimental results for several different mixing vane options are reported with selected measurements in a lab-scale 5 cm contactor and 12.5 cm engineering-scale unit. Fewer straight vanes give greater mixingzone hold-up compared to curved vanes. Quantitative comparison of droplet size distribution also showed a significant decrease in mean diameter for four straight vanes versus eight curved vanes. This set of measurements gives a compelling case for careful consideration of mixing vane geometry when evaluating hydraulic operation and extraction process efficiency of annular centrifugal contactors.

Wardle, Kent E.↗
DOE OSTI2013

STUDYING INTERCLUSTER GALAXY FILAMENTS THROUGH STACKING gmBCG GALAXY CLUSTER PAIRS

We present a method to study the photometric properties of galaxies in filaments by stacking the galaxy populations between pairs of galaxy clusters. Using Sloan Digital Sky Survey data, this method can detect the intercluster filament galaxy overdensity with a significance of {approx}5{sigma} out to z = 0.40. Using this approach, we study the g - r color and luminosity distribution of filament galaxies as a function of redshift. Consistent with expectation, filament galaxies are bimodal in their color distribution and contain a larger blue galaxy population than clusters. Filament galaxies are also generally fainter than cluster galaxies. More interestingly, the observed filament population seems to show redshift evolution at 0.12 < z < 0.40: the blue galaxy fraction has a trend to increase at higher redshift; such evolution is parallel to the ''Butcher-Oemler effect'' of galaxy clusters. We test the dependence of the observed filament density on the richness of the cluster pair: richer clusters are connected by higher density filaments. We also test the spatial dependence of filament galaxy overdensity: this quantity decreases when moving away from the intercluster axis between a cluster pair. This method provides an economical way to probe the photometric properties of filament galaxies and should prove useful for upcoming projects like the Dark Energy Survey.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Extreme blazars studied with Fermi-lat and Suzaku: 1ES 0347–121 and blazar candidate HESS J1943+213

We report on our study of high-energy properties of two peculiar TeV emitters: the 'extreme blazar' 1ES 0347–121 and the 'extreme blazar candidate' HESS J1943+213 located near the Galactic plane. Both objects are characterized by quiescent synchrotron emission with flat spectra extending up to the hard X-ray range, and both were reported to be missing GeV counterparts in the Fermi Large Area Telescope (LAT) two-year Source Catalog. We analyze a 4.5 yr accumulation of the Fermi-LAT data, resulting in the detection of 1ES 0347–121 in the GeV band, as well as in improved upper limits for HESS J1943+213. We also present the analysis results of newly acquired Suzaku data for HESS J1943+213. The X-ray spectrum is well represented by a single power law extending up to 25 keV with photon index 2.00 ± 0.02 and a moderate absorption in excess of the Galactic value, which is in agreement with previous X-ray observations. No short-term X-ray variability was found over the 80 ks duration of the Suzaku exposure. Under the blazar hypothesis, we modeled the spectral energy distributions of 1ES 0347–121 and HESS J1943+213, and we derived constraints on the intergalactic magnetic field strength and source energetics. We conclude that although the classification of HESS J1943+213 has not yet been determined, the blazar hypothesis remains the most plausible option since, in particular, the broadband spectra of the two analyzed sources along with the source model parameters closely resemble each other, and the newly available Wide-field Infrared Survey Explorer and UKIRT Infrared Deep Sky Survey data for HESS J1943+213 are consistent with the presence of an elliptical host at the distance of approximately ∼600 Mpc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Carbon diffusion in molten uranium: an ab initio molecular dynamics study

In this work we used ab initio molecular dynamics (AIMD) within the framework of density functional theory (DFT) and the projector-augmented wave (PAW) method to study carbon diffusion in liquid uranium at temperatures above 1600 K. The electronic interactions of carbon and uranium were described using the local density approximation (LDA). The self-diffusion of uranium based on this approach is compared with literature computational and experimental results for liquid uranium. The temperature dependence of carbon and uranium diffusion in the melt was evaluated by fitting the resulting diffusion coefficients to an Arrhenius relationship. We found that the LDA calculated activation energy for carbon was nearly twice that of uranium: 0.55±0.03 eV for carbon compared to 0.32±0.04 eV for uranium. Structural analysis of the liquid uranium-carbon system is also discussed.

Molecular dynamics computer simulation, Nuclear Pr↗
DOE OSTI2016

High-pressure studies with x-rays using diamond anvil cells

Pressure profoundly alters all states of matter. The symbiotic development of ultrahigh-pressure diamond anvil cells, to compress samples to sustainable multi-megabar pressures; and synchrotron x-ray techniques, to probe materials' properties in situ, has enabled the exploration of rich high-pressure (HP) science. In this article, we first introduce the essential concept of diamond anvil cell technology, together with recent developments and its integration with other extreme environments. We then provide an overview of the latest developments in HP synchrotron techniques, their applications, and current problems, followed by a discussion of HP scientific studies using x-rays in the key multidisciplinary fields. These HP studies include: HP x-ray emission spectroscopy, which provides information on the filled electronic states of HP samples; HP x-ray Raman spectroscopy, which probes the HP chemical bonding changes of light elements; HP electronic inelastic x-ray scattering spectroscopy, which accesses high energy electronic phenomena, including electronic band structure, Fermi surface, excitons, plasmons, and their dispersions; HP resonant inelastic x-ray scattering spectroscopy, which probes shallow core excitations, multiplet structures, and spin-resolved electronic structure; HP nuclear resonant x-ray spectroscopy, which provides phonon densities of state and time-resolved Mössbauer information; HP x-ray imaging, which provides information on hierarchical structures, dynamic processes, and internal strains; HP x-ray diffraction, which determines the fundamental structures and densities of single-crystal, polycrystalline, nanocrystalline, and non-crystalline materials; and HP radial x-ray diffraction, which yields deviatoric, elastic and rheological information. Integrating these tools with hydrostatic or uniaxial pressure media, laser and resistive heating, and cryogenic cooling, has enabled investigations of the structural, vibrational, electronic, and magnetic properties of materials over a wide range of pressure-temperature conditions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Resonant particle production during inflation: a full analytical study

We revisit the study of the phenomenology associated to a burst of particle production of a field whose mass is controlled by the inflaton field and vanishes at one given instance during inflation. This generates a bump in the correlators of the primordial scalar curvature. We provide a unified formalism to compute various effects that have been obtained in the literature and confirm that the dominant effects are due to the rescattering of the produced particles on the inflaton condensate. We improve over existing results (based on numerical fits) by providing exact analytic expressions for the shape and height of the bump, both in the power spectrum and the equilateral bispectrum. We then study the regime of validity of the perturbative computations of this signature. Finally, we extend these computations to the case of a burst of particle production in a sector coupled only gravitationally to the inflaton.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Experimental study of high-k turbulence during an energy confinement degradation phase in EAST ohmic plasmas

In this paper, we present experimental studies of both high-k(r) ( cm(-1), and , respectively; ) and high- ( cm(-1), and , respectively; ) turbulence behavior during an ohmic energy confinement degradation phase in experimental advanced superconducting tokamak (EAST). High-k(r) turbulence from density fluctuation at and high- turbulence from density fluctuation at -0.97 were measured by tangential and poloidal CO2 laser collective scattering diagnostics, respectively. Note that k(r), , and are radial wavenumber, poloidal wavenumber, perpendicular wavenumber and ion gyroradius at electron temperature, respectively. Both high-k(r)/ turbulence power and energy confinement time are found to be temporally correlated to line-averaged electron density n(e) in the plasma current flat-top phase (I-p = 0.4 MA): when the n(e) shows continuous increase/decrease, the high-k(r)/ turbulence power increases/decreases correspondingly and the shows corresponding decrease/increase; the stable n(e) is related to stable both and high-k(r)/ turbulence power. Statistical results of high-k(r)/ turbulence power versus further imply that high-k(r)/ turbulence shows a strong correlation with plasma energy confinement degradation in high line-averaged n(e) condition, but high-k(r) and high- turbulence have relatively weak and no dependence on the transition between linear range in low-n(e) condition and energy confinement degradation in the high-n(e) condition, respectively. Moreover, profiles of electron temperature T-e and n(e) as well as their normalized gradients in a part of high- density fluctuation measurement region also have been given to qualitatively explain the enhancement of turbulence power with the increase of line-averaged n(e).

EAST tokamak↗
DOE OSTI2023

The use of synchrotron X-ray fluorescent imaging to study distribution and content of elements in chemically fixed single cells: a case study using mouse pancreatic beta-cells

Synchrotron X-ray fluorescence microscopy (SXRF) presents a valuable opportunity to study the metallome of single cells because it simultaneously provides high-resolution subcellular distribution and quantitative cellular content of multiple elements. Different sample preparation techniques have been used to preserve cells for observations with SXRF, with a goal to maintain fidelity of the cellular metallome. In this case study, mouse pancreatic beta-cells have been preserved with optimized chemical fixation. We show that cell-to-cell variability is normal in the metallome of beta-cells due to heterogeneity and should be considered when interpreting SXRF data. Additionally, we determined the impact of several immunofluorescence (IF) protocols on metal distribution and quantification in chemically fixed beta-cells and found that the metallome of beta-cells was not well preserved for quantitative analysis. However, zinc and iron qualitative analysis could be performed after IF with certain limitations. To help minimize metal loss using samples that require IF, we describe a novel IF protocol that can be used with chemically fixed cells after the completion of SXRF.

59 BASIC BIOLOGICAL SCIENCES↗