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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
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↗
DOE OSTI2011

High-pressure Study of Silane to 150 GPa

We present an extensive study of the optical, electronic, and structural properties of silane (SiH{sub 4}) to 150 GPa through the use of Raman spectroscopy, optical microscopy, synchrotron infrared reflectivity, optical absorption, and synchrotron x-ray diffraction measurements. To mitigate possible contamination from previously reported metal hydride formation, we performed experiments using gold-lined sample gaskets, finding molecular silane remains in the transparent and insulating P2{sub 1}/c structure until {approx}40 GPa. Silane shows a partial loss of crystallinity above {approx}50 GPa and appears to visibly darken. The darkening is plausibly the result of a loss of molecular character with many enthalpically competitive pathways available, including decomposition, combined with the absorptive nature of the sample. Above 100 GPa we observed crystallization into structures partially consistent with the previously reported nonmolecular I4{sup -} 2d and I4{sub 1}/a types. In the absence of decomposition, silane remains partially transparent and nonmetallic to at least 150 GPa with a band gap constrained between 0.6 and 1.8 eV. Under pressure, silane is sensitive to irradiation from x-rays and lasers, and may easily decompose into metallic silicon. We suggest that previous reports of metallization starting from molecular SiH{sub 4} arise from decomposition, and superconductivity may originate from hydrogen-doped silicon. While silane may readily decompose, the inherent metastability provides access to a wide range of path- and sample-history-dependent states and suggests a unique range of physical properties for hydrogen-rich silicon alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Experimental and theoretical study of Ti-6Al-4V to 220 GPa

We report results from an experimental and theoretical study of the ternary alloy Ti-6Al-4V to 221 GPa. We observe a phase transition to the hexagonal {omega} phase at approximately 30 GPa, and then a further transition to the cubic {beta} phase starting at 94-99 GPa. We do not observe the orthorhombic {gamma} and {delta} phases reported previously in pure Ti. Computational studies show that this sequence is possible only if there is significant local atomic ordering during the compression process, yet insufficient atomic diffusion to reach the phase-separated thermodynamic equilibrium state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Antiferromagnetic and nematic phase transitions in BaF e 2 ( A s 1 - x P x ) 2 studied by ac microcalorimetry and SQUID magnetometry

In this work, we study the antiferromagnetic (AFM) and structural phase transitions in single-crystal BaF e 2 ( A s 1 – x P x ) 2 ( x = 0 , 0.3 ) at temperatures T N and T S , respectively, by high-resolution ac microcalorimetry and SQUID magnetometry. The specific heat measurements of both as-grown and annealed BaF e 2 A s 2 display a sharp peak at the AFM-structural transitions. A kink in the entropy of annealed BaF e 2 A s 2 gives evidence for splitting of the two transitions by approximately 0.5 K. No additional features could be identified in the specific heat of both BaF e 2 A s 2 and BaF e 2 ( A s 0.7 P 0.3 ) 2 in the temperature regions around T * > T S where torque measurements had revealed the “true” nematic phase transition, even though the Ginzburg-Landau model used to fit the magnetic torque data indicates that the expected thermal anomaly should be easily observable with our experimental resolution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Numerical study of the temperature dependence of the NMR relaxation rate across the superfluid–Bose glass transition in one dimension

Here, we study the nuclear magnetic resonance (NMR) spin-lattice relaxation rate 1/ T 1 1 in random one-dimensional spin chains as a function of the temperature and disorder strength. In the zero temperature limit, the system displays a disorder-induced quantum phase transition between a critical Tomonaga-Luttinger liquid (TLL) phase and a localized Bose glass phase. The 1/ T 1 is investigated across this transition using large-scale simulations based on matrix product state techniques. We find that this quantity can detect the transition and probe the value of the dimensionless TLL parameter K . We also compute the NMR relaxation rate distributions for each temperature and disorder strength considered. In particular, we discuss the applicability of the stretched exponential fit to the return-to-equilibrium function to extract the 1/ T 1 experimentally. The results presented here should provide valuable insights in regards of future NMR experiments in realistic disordered spin compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Experimental study of Ar 38 + α reaction cross sections relevant to the Ca 41 abundance in the solar system [Experimental study of Ar 38 + α induced cross sections relevant to the Ca 41 abundance in the solar system]

In massive stars, the 41 Ca(n,α) 38 Ar and 41 K(p,α) 38 Ar reactions have been identified as the key reactions governing the abundance of 41 Ca, which is considered as a potential chronometer for solar system formation. So far, due to experimental limitations, the 41 Ca(n,α) 38 Ar reaction rate is solely based on statistical model calculations. In the present study, we have measured the time-inverse 38 Ar(α,n) 41 Ca and 38 Ar(α,p) 41 K reactions using an active target detector. The reactions were studied in inverse kinematics using a 133-MeV 38 Ar beam and 4 He as the active-gas target. Both excitation functions were measured simultaneously in the energy range of 6.8 ≤ E c.m. ≤ 9.3 MeV. Furthermore by using detailed balance the 41 Ca(n,α) 38 Ar and 41 K(p,α) 38 Ar reaction rates were determined, which suggested a 20% increase in the 41 Ca yield from massive stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Separability of the Dirac equation in the STU black hole spacetime: Pairwise-equal charge case study

We study the separability of the Dirac equation in the background of four dimensional charged rotating asymptotically flat black hole solution of supergravity and the low energy string theory known as STU black hole. In particular, we analyze in detail the separability conditions in the pairwise equal charge STU black hole space-time. While in the latter case the minimally coupled Dirac equation is not separable, the introduction of a specific torsion term ensures the separability. The source of the torsion is the Kalb-Ramond field, which is an integral part of string theory, but further aspects of its properties and coupling to fermionic fields remain to be studied. To derive the torsion, two different approaches are used in conformally related frames, showing that the torsion is not unique. The correspondingly modified Dirac equations in the Einstein and string frames are shown to be separable. Furthermore, the massless radial and angular wave equations are examined; they show close similarity with corresponding equations for the standard Kerr background. A generalization of the Teukolsky equation for the pairwise equal case is conjectured. We also briefly analyze a technically sophisticated radial equation in the massive case.

Dirac equation↗
DOE OSTI2013

Study of exclusive B → X u ℓ ν decays and extraction of | V u b | using full reconstruction tagging at the Belle experiment

Here, we report the results of a study of the exclusive semileptonic decays B - → π 0 ℓ - ν ¯ ℓ , B ¯ 0 → π + ℓ - ν ¯ ℓ , B - → ρ 0 ℓ - ν ¯ ℓ , B ¯ 0 → ρ + ℓ - ν ¯ ℓ and B - → ω ℓ - ν ¯ ℓ , where ℓ represents an electron or a muon. The events are tagged by fully reconstructing a second B meson in the event in a hadronic decay mode. The measured branching fractions are B ( B - → π 0 ℓ - ν ¯ ℓ ) = ( 0.80 ± 0.08 ± 0.04 ) × 10 - 4 , B ( B ¯ 0 → π + ℓ - ν ¯ ℓ ) = ( 1.49 ± 0.09 ± 0.07 ) × 10 - 4 , B ( B - → ρ 0 ℓ - ν ¯ ℓ ) = ( 1.83 ± 0.10 ± 0.10 ) × 10 - 4 , B ( B ¯ 0 → ρ + ℓ - ν ¯ ℓ ) = ( 3.22 ± 0.27 ± 0.24 ) × 10 - 4 , and B ( B - → ω ℓ - ν ¯ ℓ ) = ( 1.07 ± 0.16 ± 0.07 ) × 10 - 4 , where the first error is statistical and the second one is systematic. The obtained branching fractions are inclusive of soft photon emission. Furthermore, we determine the branching fractions as a function of the 4-momentum transfer squared to the leptonic system q 2 = ( p ℓ + p ν ) 2 , where p ℓ and p ν are the lepton and neutrino 4-momenta, respectively. Using the pion modes, a recent light cone sum rule calculation, lattice QCD results and a model-independent description of the hadronic form factor, a value of the Cabibbo-Kobayashi-Maskawa matrix element | V u b | = ( 3.52 ± 0.29 ) × 10 - 3 is extracted. A structure in the two-pion invariant mass distribution near 1.3 GeV / c 2 , which might be dominated by the decay B - → f 2 ( 1270 ) ℓ - ν ¯ ℓ , f 2 → π + π - , is seen. These results are obtained from a 711 fb - 1 data sample that contains 772 × 10 6 B B ¯ pairs, collected near the Υ ( 4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Semi-inclusive studies of semileptonic B s decays at Belle

We present an analysis of the semi-inclusive decays B s → D s - X ℓ + ν and B s → D s * - X ℓ + ν , where X denotes a final state that may consist of additional hadrons or photons and ℓ is an electron or muon. The studied B s decays are contained in the 121.4 fb - 1 Υ ( 5 S ) data sample collected by the Belle detector at the KEKB asymmetric-energy e + e - collider. The branching fractions of the decays are measured to be B ( B s → D s - X ℓ + ν ) = [ 8.2 ± 0.2 ( stat ) ± 0.6 ( syst ) ± 1.4 ( ext ) ] % and B ( B s → D s * - X ℓ + ν ) = [ 5.4 ± 0.4 ( stat ) ± 0.4 ( syst ) ± 0.9 ( ext ) ] % , where the first two uncertainties are statistical and systematic and the last is due to external parameters. The measurement also provides an estimate of the B s ( * ) B ¯ s ( * ) production cross section, σ ( e + e - → B s ( * ) B ¯ s ( * ) ) = [ 53.8 ± 1.4 ( stat ) ± 4.0 ( syst ) ± 3.4 ( ext ) ] pb , at the center-of-mass energy s = 10.86 GeV .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Study of η and dipion transitions in Υ ( 4 S ) decays to lower bottomonia

Here, we study hadronic transitions between bottomonium states using 496 fb - 1 data collected at the Υ ( 4 S ) resonance with the Belle detector at the KEKB asymmetric energy e + e - collider. We measure B ( Υ ( 4 S ) → π + π - Υ ( 1 S ) ) = ( 8.2 ± 0.5 ( stat ) ± 0.4 ( syst ) ) × 10 - 5 , B ( Υ ( 4 S ) → π + π - Υ ( 2 S ) ) = ( 7.9 ± 1.0 ( stat ) ± 0.4 ( syst ) ) × 10 - 5 , and B ( Υ ( 4 S ) → η Υ ( 1 S ) ) = ( 1.70 ± 0.23 ( stat ) ± 0.08 ( syst ) ) × 10 - 4 . We measure the ratio of branching fractions R = B ( Υ ( 4 S ) → η Υ ( 1 S ) ) / B ( Υ ( 4 S ) → π + π - Υ ( 1 S ) ) = 2.07 ± 0.30 ( stat ) ± 0.11 ( syst ) . We search for the decay Υ ( 1 D 3 1 , 2 ) → η Υ ( 1 S ) , but do not find significant evidence for such a transition. We also measure the initial-state radiation production cross sections of the Υ ( 2 S , 3 S ) resonances and we find values compatible with the expected ones. Finally, the analysis of the Υ ( 4 S ) → π + π - Υ ( 1 S ) events reflects indications for a resonant contribution due to the f 0 ( 980 ) meson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗