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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

Effect of q-nonextensive parameter and saturation time on electron density steepening in electron-positron-ion plasmas

The effect of q-nonextensive parameter and saturation time on the electron density steepening in electron-positron-ion plasmas is studied by particle in cell method. Phase space diagrams show that the size of the holes, and consequently, the number of trapped particles strongly depends on the q-parameter and saturation time. Furthermore, the mechanism of the instability and exchange of energy between electron-positron and electric field is explained by the profiles of the energy density. Moreover, it is found that the q-parameter, saturation time, and electron and positron velocities affect the nonlinear evolution of the electron density which leads to the steepening of its structure. The q-nonextensive parameter or degree of nonextensivity is the relation between temperature gradient and potential energy of the system. Therefore, the deviation of q-parameter from unity indicates the degree of inhomogeneity of temperature or deviation from equilibrium. Finally, using the kinetic theory, a generalized q-dispersion relation is presented for electron-positron-ion plasma systems. It is found that the simulation results in the linear regime are in good agreement with the growth rate results obtained by the kinetic theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

The structural and electronic properties of cubic AgMO{sub 3} (M=Nb, Ta) by first principles calculations

We report the electronic structure of the AgMO{sub 3}(M=Nb, Ta) within the frame work of density functional theory and calculations are performed within the generalized gradient approximation (GGA) by using ultrasoft pseudopotentials. The calculated equilibrium lattice parameters and volumes are extracted from fitting of Birch third order equation of state and which are reasonable agreement with the available experimental results. The density of states,band structure of Ag(Nb,Ta)O{sub 3} reveals that the valance bands mostly occupied with O-2p and O-2s states and whereas conduction band occupied with Nb (Ta) 4d(5d) states including less contribution from Ag 5s states.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Multi-site reaction dynamics through multi-fragment density matrix embedding

The practical description of disordered chemical reactions, where the reactions involve multiple species at multiple sites, is presently a challenge using correlated electronic structure methods due to their high computational cost and steep scaling. Here, we describe the gradient theory of multi-fragment density matrix embedding theory, which potentially provides a minimal computational framework to model such processes at the correlated electron level. We present the derivation and implementation of the gradient theory, its validation on model systems and chemical reactions using density matrix embedding, and its application to a molecular dynamics simulation of proton transport in a small water cluster, a simple example of multi-site reaction dynamics.

Chemistry↗
DOE OSTI2012

CONSEQUENCES OF MAGNETIC FIELD STRUCTURE FOR HEAT TRANSPORT IN MAGNETOHYDRODYNAMICS

Interfaces between hot and cold magnetized plasmas exist in various astrophysical contexts, for example, where hot outflows impinge on an ambient interstellar medium. It is of interest to understand how the structure of the magnetic field spanning the interface affects the temporal evolution of the temperature gradient. Here, we explore the relation between the magnetic field topology and the heat transfer rate by adding various fractions of tangled versus ordered field across a hot-cold interface that allows the system to evolve to a steady state. We find a simple mathematical relation for the rate of heat conduction as a function of the initial ratio of ordered-to-tangled field across the interface. We discuss potential implications for the astrophysical context of magnetized wind blown bubbles around evolved stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The effect of saturated thermal conduction on clouds in a hot plasma

We numerically investigate the internal evolution of multiphase clouds, which are at rest with respect to an ambient, highly ionized medium (HIM) representing the hot component of the circumgalactic medium. Time-dependent saturated thermal conduction and its implications like condensation rates and mixing efficiency are assessed in multiphase clouds. Our simulations are carried out by using the adaptive mesh refinement code FLASH. The model clouds are initially in both hydrostatic and thermal equilibrium and are in pressure balance with the HIM. Thus, they have steep gradients in both temperature and density at the interface to HIM leading to non-negligible thermal conduction. Several physical processes are considered numerically or semi-analytically: thermal conduction, radiative cooling and external heating of gas, self-gravity, mass diffusion, and dissociation of molecules and ionization of atoms. It turns out that saturated thermal conduction triggers a continuous condensation irrespective of cloud mass. Dynamical interactions with ambient HIM all relate to the radial density gradient in the clouds: (1) mass flux due to condensation is the higher the more homogeneous the clouds are; (2) mixing of condensed gas with cloud gas is easier in low-mass clouds, because of their shallower radial density gradient; and thus (3) accreted gas is distributed more efficiently. A distinct and sub-structured transition zone forms at the interface between cloud and HIM, which starts at smaller radii and is much narrower as deduced from analytical theory.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Role of iron in the incorporation of uranium in ferric garnet matrices

The structural relaxations and electronic structure of U-containing Ca₃(Ti,Zr,Hf,Sn)₂(Fe₂Si)O₁₂ garnet systems have been investigated using ab initio methods within density functional theory (DFT) in the generalized gradient approximation with a Hubbard correction U (GCA + U). The calculations provide a fundamental understanding of the role of Fe in the incorporation and stability of U in the garnet structure. The atomic relaxations around U are controlled by a delicate balance between the Coulomb interactions among the ions and the size effect of the large U atom. The relaxation pattern indicates that when U occupies the A site, a charge transfer occurs from U to its nearest-neighbor (NN) Fe atom. This is further verified by the detailed analysis of the electronic band structures and charge density distribution. The double exchange coupling of the U f and the NN Fe d shells via the transfer of electrons lowers the energy of the system when the spins of the f and d shells are antiparallel. The incorporation energy of U at the A site (substituting Ca) increases dramatically with the decrease in the number of Fe atoms in the neighboring tetrahedral sites. The presence of Fe is crucial, since it accommodates the extra valence electrons introduced by U and the electron transfer allows the lowering of the total energy of the structure. Comparing the incorporation energies at the A and B site (octahedral site), U clearly prefers the A site, provided that there are sufficient Fe atoms in its vicinity to facilitate the charge transfer.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Power Plant Testing of Ultrasonic Measurements of Temperature Distributions and Heat Fluxes to Heat Exchange Surfaces

Extreme environmental conditions are common in energy conversion applications, in which the most hardened insertion sensors often do not perform reliably for long. On the other hand, ultrasonic measurements can be acquired noninvasively, with sensitive components kept away from the damaging environment. We have previously developed the ultrasonic method for measuring the spatial distribution of temperatures in solid materials applicable when large thermal gradients are present. In the developed approach, we use the echogenically segmented ultrasound propagation path, structured to contain engineered or naturally occurring echogenic features, to produce a train of echoes in response to an external pulse of ultrasonic excitation. This paper outlines the testing results of this approach applied to the temperature distribution measurements to a waterwall of a 500 MW power-plant utility boiler. The validation results obtained over the prolonged power plant test show that the estimated temperature profile is correctly captured, and the measurement accuracy can be comparable with traditional insertion sensors, such as thermocouples. Overall, the testing has confirmed that the developed approach has matured to become an attractive alternative to conventional sensing in solving challenging problems of long-term temperature measurements in extreme environments. Heat fluxes and thermal stresses in the structure can then be characterized noninvasively using the measured temperature distribution as the basis.

Walton, Kenneth↗
DOE OSTI2019

Ultrasonic Measurements of Temperature Distribution and Heat Fluxes Across Containments of Extreme Environments

Extreme conditions are common in energy conversion, material processing, nuclear, airspace, and military applications. In such environments, the most hardened insertion sensors do not perform reliably for long. Ultrasonic measurements, on the other hand, can be acquired noninvasively, with sensitive components kept away from the damaging environment. We have previously developed the ultrasonic method for measuring the spatial distribution of temperatures in solid materials applicable in the cases when large thermal gradients are present. In the developed approach, we use the echogenically segmented ultrasound propagation path, structured to contain engineered or naturally occurring echogenic features, to produce a train of echoes in response to an external pulse of ultrasonic excitation. The delays between the echoes, which encode the information on the temperature distribution in the corresponding segments, is used to reconstruct unknown temperature profile. In this paper, we outline the results of pilot-scale testing of the developed approach and demonstrate its application to the measurements of the temperature distribution across the containment of a high-temperature combustion process. The validation results show that the estimated temperature profile is correctly captured, and the measurement accuracy can be comparable with traditional insertion sensors, such as thermocouples. Overall, the testing has confirmed that the developed approach has matured to become an attractive alternative to conventional sensing in solving challenging problems of long-term temperature measurements in extreme environments. Heat fluxes and thermal stresses in the structure can then be characterized noninvasively using the measured temperature distribution as the basis.

Jia, Yunlu↗
DOE OSTI2015

Linearity Response of Ca2+- Doped CeBr3 as a Function of Gamma-Ray Energy

An aliovalently calcium-doped cerium tribromide (CeBr3:Ca2+) crystal was prepared with a gamma-energy resolution (FWHM) of 3.2% at the 137Cs 662 keV gamma energy. We completed a crystal assessment and calculated the predictive performance and physical characteristics using density functional theory (DFT) formalism. Detector performance, characteristics, calcium doping concentration, and crystal strength are reported. The structural, electronic, and optical properties of CeBr3 crystals were investigated using the DFT within generalized gradient approximation. Specifically, we see excellent linearity of photons per unit energy with the aliovalent CeBr3:Ca2+ crystal. Proportionality of light yield is one area of performance in which Ce-doped and Ce-based lanthanide halides excel. Maintaining proportionality is the key to producing a strong, high-performance scintillator. Relative light yield proportionality was measured for both doped and undoped samples of CeBr3 to ensure no loss in performance was incurred by doping. The light output and proportionality for doped CeBr3, however, appears to be similar to that of undoped CeBr3. The new crystal was subjected to additional testing and evaluation, including a benchmark spectroscopy assessment. Results, which present energy resolution as a function of energy, are summarized. Typical spectroscopy results using a 137Cs radiation source are shown for our crystallites with diameters <1 cm. We obtain energy resolution of 3.2% before packing the crystallite in a sealed detector container and 4.5% after packing. Spectra were also obtained for 241Am, 60Co, 228Th, and background to illustrate the spectrosocopic quality of CeBr3:Ca2+ over a broader energy range.

aliovalent substitution↗
DOE OSTI2023

Multipulse Optical-Rectification-Based THz Source for Accelerator Applications

THz sources offer the potential for higher frequencies and higher breakdown thresholds in accelerating structures in comparison with conventional RF sources. They also benefit from larger field strengths, field gradients, better beam synchronization and compactness. In this work, we first present the development of a 49μJ single-cycle THz source centered at 0.6 THz that provides fields over 30 MV/m. With further modifications, multicycle pulses were produced, narrowing the bandwidth of the source and potentially easing the coupling of THz radiation to relativistic electron beams and increasing the usability in other areas of research.

Lenz, Maximilian (ORCID:0009000579693042)↗
DOE OSTI2016

SIGNATURE OF AN INTERMEDIATE-MASS BLACK HOLE IN THE CENTRAL MOLECULAR ZONE OF OUR GALAXY

We mapped the high-velocity compact cloud CO–0.40–0.22 in 21 molecular lines in the 3 mm band using the Nobeyama Radio Observatory 45 m radio telescope. Eighteen lines were detected from CO–0.40–0.22. The map of each detected line shows that this cloud has a compact appearance (d ≃ 3 pc) and extremely broad velocity width (ΔV ≃ 100 km s{sup −1}). The mass and kinetic energy of CO–0.40–0.22 are estimated to be 10{sup 3.6} M{sub ⊙} and 10{sup 49.7} erg, respectively. The representative position–velocity map along the major axis shows that CO–0.40–0.22 consists of an intense region with a shallow velocity gradient and a less intense high-velocity wing. Here, we show that this kinematical structure can be attributed to a gravitational kick to the molecular cloud caused by an invisible compact object with a mass of ∼10{sup 5} M{sub ⊙}. Its compactness and the absence of counterparts at other wavelengths suggest that this massive object is an intermediate-mass black hole.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Production of the thermal scattering law and neutron scattering cross sections for ice from first principles - 14503

Water ice can exist in many polymorphic phases as a result of the wide range of geometric ordering possible for the hydrogen bonds between H{sub 2}O molecules. Ice Ih, which can form under normal atmospheric pressure at 273 K, is the most common type. Ab initio density functional theory, incorporating the generalized gradient approximation (GGA) for the exchange-correlation energy, is used to simulate the hexagonal structure of ice Ih and calculate phonon dispersion relations with harmonic lattice dynamics. While the unit cell for ice Ih contains four molecules with particular alignments of the H{sub 2}O molecules possible, the structure has globally disordered proton arrangement. To improve capturing this random distribution, a 12-molecule unit cell is incorporated along with a 2x2x2 supercell. The total phonon density of states is determined by randomly sampling dispersion relations in the first Brillouin zone. The translational, librational, bending, and stretching modes are produced with high-quality resolution and are consistent with the optical peaks and ranges observed in Raman, infrared, and inelastic neutron scattering experiments [1]. The phonon spectrum is used to calculate the S(α,β) thermal scattering law for ENDF [2] publication in the incoherent approximation, which is appropriate due to the relatively small coherent nuclear scattering cross section for H{sub 2}O. These theoretical results are compared to experimental S(α,β) at 268 K [3] and trends are found to be in good agreement. Finally, total scattering cross sections are calculated by integrating over S(α,β) to determine the incoherent inelastic cross sections and then separately adding the absorption and incoherent elastic components. These results are compared to experimental total cross sections for ice Ih at 115 K over a range of incident energies [4] and found to provide excellent agreement. (authors)

42 ENGINEERING↗
DOE OSTI2017

Coherent structures in wind shear induced wave–turbulence–vegetation interaction in water bodies

Flume experiments with particle imaging velocimetry (PIV) were conducted recently to study a complex flow problem where wind shear acts on the surface of a static water body in presence of flexible emergent vegetation and induces a rich dynamics of wave–turbulence–vegetation interaction inside the water body without any gravitational gradient. The experiments were aimed at mimicking realistic vegetated wetlands and the present work is targeted to improve the understanding of the coherent structures associated with this interaction by employing a combination of techniques such as quadrant analysis, proper orthogonal decomposition (POD), Shannon entropy and mutual information content (MIC). The turbulent transfer of momentum is found to be dominated by organized motions such as sweeps and ejections, while the wave component of vertical momentum transport does not show any such preference. Furthermore, by reducing the data using POD we see that wave energy for large flow depths and turbulent energy for all water depths is concentrated among the top few modes, which can allow development of simple reduced order models. Vegetation flexibility is found to induce several roll type structures, however if the vegetation density is increased, drag effects dominate over flexibility and organize the flow. The interaction between waves and turbulence is also found to be highest among flexible sparse vegetation. But, rapidly evolving parts of the flow such as the air–water interface reduces wave–turbulence interaction.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Electric fields and stationary drift flows in the island divertor SOL of Wendelstein 7-X

Abstract In the island divertor scrape-off layer (SOL) of the Wendelstein 7-X stellarator, 2D-resolved Langmuir probe measurements uncover a complex spatial structure of electron temperature, density, and floating potential. Depending on details of magnetic island size and position, significant poloidal gradients and non-monotonic radial profiles are observed. The resulting electric fields imply the presence of sheared stationary drift flows with poloidal velocities of a few km/s, with flow channels as narrow as one cm. Such flows are observed with a gas puff imaging diagnostic in qualitative agreement with the probe results and imply a significant transport channel in the SOL. The 2D distribution of plasma parameters is intricately associated to the unique magnetic structure of the island divertor SOL and highlights the necessity for more accurate magnetic field reconstructions.

Killer, Carsten (ORCID:0000000177473066)↗
DOE OSTI2020

Re-evaluation of the TSL for Yttrium Hydride

Yttrium hydride (YH x ) is of interest as a high-temperature moderator material in advanced nuclear reactor systems because of its superior ability to retain hydrogen at elevated temperatures. Thermal neutron scattering laws (TSL) for hydrogen bound in yttrium hydride (H-YH 2 ) and yttrium bound in yttrium hydride (Y-YH 2 ) were previously evaluated by Naval Nuclear Laboratory using the ab initio approach and released in ENDF/B-VIII.0. In that work, density functional theory, incorporating the generalized gradient approximation (GGA) for the exchange-correlation energy, was used to simulate the face-centered cubic structure of YH 2 and calculate the interatomic Hellmann-Feynman forces for a 2×2×2 supercell containing 96 atoms. Lattice dynamics calculations using PHONON were used to determine the phonon density of states. The calculated phonon density of states for H and Y in YH 2 were then used to prepare H-YH 2 and Y-YH 2 TSL evaluations, in the incoherent approximation, using the LEAPR module of NJOY. In addition, elastic scattering was assumed to be incoherent for both H and Y. While the incoherent elastic scattering approximation is appropriate for H-YH 2 , it introduces an undesirable approximation for Y-YH 2 . In this work, we re-evaluate the TSL for Y-YH 2 using FLASSH (Full Law Analysis Scattering System Hub). Y-YH 2 is evaluated using the FLASSH generalized coherent elastic scattering capability in order to capture the Bragg peaks associated with the YH 2 crystal structure which were neglected in the prior NJOY-based evaluation due to limitations in LEAPR. An experimental approach to validate the Y-YH 2 TSL using neutron transmission measurements is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

UNVEILING THE DETAILED DENSITY AND VELOCITY STRUCTURES OF THE PROTOSTELLAR CORE B335

We present an observational study of the protostellar core B335 harboring a low-mass Class 0 source. The observations of the H{sup 13}CO{sup +}(J = 1-0) line emission were carried out using the Nobeyama 45 m telescope and Nobeyama Millimeter Array. Our combined image of the interferometer and single-dish data depicts detailed structures of the dense envelope within the core. We found that the core has a radial density profile of n(r){proportional_to}r {sup -p} and a reliable difference in the power-law indices between the outer and inner regions of the core: p Almost-Equal-To 2 for r {approx}> 4000 AU and p Almost-Equal-To 1.5 for r {approx}< 4000 AU. The dense core shows a slight overall velocity gradient of {approx}1.0 km s{sup -1} over the scale of 20, 000 AU across the outflow axis. We believe that this velocity gradient represents a solid-body-like rotation of the core. The dense envelope has a quite symmetrical velocity structure with a remarkable line broadening toward the core center, which is especially prominent in the position-velocity diagram across the outflow axis. The model calculations of position-velocity diagrams do a good job of reproducing observational results using the collapse model of an isothermal sphere in which the core has an inner free-fall region and an outer region conserving the conditions at the formation stage of a central stellar object. We derived a central stellar mass of {approx}0.1 M{sub Sun }, and suggest a small inward velocity, v{sub r{>=}r{sub i{sub n{sub f}}}}{approx}0 km s{sup -1} in the outer core at {approx}> 4000 AU. We concluded that our data can be well explained by gravitational collapse with a quasi-static initial condition, such as Shu's model, or by the isothermal collapse of a marginally critical Bonnor-Ebert sphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Reversible ratchet effects for vortices in conformal pinning arrays

A conformal transformation of a uniform triangular pinning array produces a structure called a conformal crystal which preserves the sixfold ordering of the original lattice but contains a gradient in the pinning density. Here we use numerical simulations to show that vortices in type-II superconductors driven with an ac drive over gradient pinning arrays produce the most pronounced ratchet effect over a wide range of parameters for a conformal array, while square gradient or random gradient arrays with equivalent pinning densities give reduced ratchet effects. In the conformal array, the larger spacing of the pinning sites in the direction transverse to the ac drive permits easy funneling of interstitial vortices for one driving direction, producing the enhanced ratchet effect. In the square array, the transverse spacing between pinning sites is uniform, giving no asymmetry in the funneling of the vortices as the driving direction switches, while in the random array, there are numerous easy-flow channels present for either direction of drive. We find multiple ratchet reversals in the conformal arrays as a function of vortex density and ac amplitude, and correlate the features with a reversal in the vortex ordering, which is greater for motion in the ratchet direction. In conclusion, the enhanced conformal pinning ratchet effect can also be realized for colloidal particles moving over a conformal array, indicating the general usefulness of conformal structures for controlling the motion of particles.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Energetic and structural control of polyspecificity in a multidrug transporter

Multidrug efflux pumps are dynamic molecular machines that drive antibiotic resistance by harnessing ion gradients to export chemically diverse substrates. Despite their clinical importance, the molecular principles underlying multidrug promiscuity and energy efficiency remain poorly understood. Using multiparametric deep mutational scanning across eight substrates and two energy conditions, we deconvolute the contributions of substrate recognition, energetic coupling, and protein stability, providing an integrated, high-resolution view of multidrug transport. We find that substrate specificity arises from a distributed network of residues extending beyond the binding site, with mutations that reshape binding, coupling, conformational flexibility, and membrane interactions. Further, we apply a pH-based selection scheme to measure the effect of mutation on pH-dependent transport efficiency. By integrating these data, we reveal a fundamental relationship between efficiency and promiscuity: Highly efficient variants exhibit broad substrate profiles, while inefficient variants are narrower. In conclusion, these findings establish a direct link between energy coupling and polyspecificity, uncovering the biochemical logic underlying multidrug transport.

Biological Sciences↗