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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Coexistence of antiferromagnetic and ferromagnetic spin correlations in Ca ( Fe 1 - x Co x ) 2 As 2 revealed by As 75 nuclear magnetic resonance

Recent nuclear magnetic resonance (NMR) measurements revealed the coexistence of stripe-type antiferromagnetic (AFM) and ferromagnetic (FM) spin correlations in both the hole- and electron-doped BaFe 2 As 2 families of iron-pnictide superconductors by a Korringa ratio analysis. Motivated by the NMR work, we investigate the possible existence of FM fluctuations in another iron-pnictide superconducting family, Ca ( Fe 1 - x Co x ) 2 As 2 . We reanalyzed our previously reported data in terms of the Korringa ratio and found clear evidence for the coexistence of stripe-type AFM and FM spin correlations in the electron-doped CaFe 2 As 2 system. These NMR data indicate that FM fluctuations exist in general in iron-pnictide superconducting families and thus must be included to capture the phenomenology of the iron pnictides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Signatures of pairing in the magnetic excitation spectrum of strongly correlated two-leg ladders [Signatures of pairing in the magnetic excitation spectrum of strongly correlated ladders]

Magnetic interactions are widely believed to play a crucial role in the microscopic mechanism leading to high critical temperature superconductivity. It is therefore important to study the signatures of pairing in the magnetic excitation spectrum of simple models known to show unconventional superconducting tendencies. Using the density matrix renormalization group technique, we calculate the dynamical spin structure factor S(k,ω) of a generalized t–U–J Hubbard model away from half filling in a two-leg ladder geometry. The addition of J enhances pairing tendencies. We analyze quantitatively the signatures of pairing in the magnetic excitation spectra. We found that the superconducting pair-correlation strength, that can be estimated independently from ground state properties, is closely correlated with the integrated low-energy magnetic spectral weight in the vicinity of (π,π). In this wave-vector region, robust spin incommensurate features develop with increasing doping. The branch of the spectrum with rung direction wave vector k rung =0 does not change substantially with doping where pairing dominates and thus plays a minor role. As a result, we discuss the implications of our results for neutron scattering experiments, where the spin excitation dynamics of hole-doped quasi-one-dimensional magnetic materials can be measured and also address implications for recent resonant inelastic x-ray scattering experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Existence of electron and hole pockets and partial gap opening in the correlated semimetal Ca 3 Ru 2 O 7

The electronic band structure of correlated Ca 3 Ru 2 O 7 featuring an antiferromagnetic (AFM) as well as a structural transition has been determined theoretically at high temperatures, which has led to the understanding of the remarkable properties of Ca 3 Ru 2 O 7 , such as the bulk spin-valve effects. However, its band structure and Fermi surface (FS) below the structural transition have not been resolved, even though a FS consisting of electron pockets was found experimentally. Here we report magnetoelectrical transport and thermoelectric measurements with the electric current and temperature gradient directed along the a and b axes, respectively, of an untwined single crystal of Ca 3 Ru 2 O 7 . The thermopowers obtained along the two crystal axes were found to show opposite signs at low temperatures, demonstrating the presence of both electron and hole pockets on the FS. In addition, how the FS evolves across T* = 30K at which a distinct transition from coherent to incoherent behavior occurs was also inferred: the Hall and Nernst coefficient results suggest a temperature- and momentum-dependent partial gap opening in Ca 3 Ru 2 O 7 below the structural transition with a possible Lifshitz transition occurring at T*. In conclusion, the experimental demonstration of a correlated semimetal ground state in Ca 3 Ru 2 O 7 calls for further theoretical studies of this remarkable material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Polaronic correlations and phonon renormalization in La 1–x Sr x MnO 3 (x = 0.2, 0.3)

According to standard theory the magnetoresistance magnitude in ferromagnetic manganites crucially depends on the electron-phonon coupling strength. We showed that in La 0.7 Sr 0.3 MnO 3 the phonon renormalization is strong, despite its relatively small magnetoresistance. Here, we report results of a similar inelastic neutron-scattering investigation of a closely related compound, La 0.8 Sr 0.2 MnO 3 , where the magnetoresistance is enhanced. We find similar phonon renormalization and dynamic CE-type polaron correlations as in La 0.7 Sr 0.3 MnO 3 . Furthermore, quantitative comparison of the results for the two samples shows that only polaron lifetime is well correlated with the strength of the colossal magnetoresistance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Measurement of long-range pseudorapidity correlations and azimuthal harmonics in s N N = 5.02 TeV proton-lead collisions with the ATLAS detector

We present measurements of two-particle correlation functions and the first five azimuthal harmonics, v 1 to v 5 , are presented, using 28 nb -1 of p + Pb collisions at a nucleon-nucleon center-of-mass energy of s N N = 5.02 TeV measured with the ATLAS detector at the LHC. Significant long-range "ridgelike" correlations are observed for pairs with small (|Δ&straightphi;|<π/3) and back-to-back pairs (|Δ&straightphi;|>2π/3) over the transverse momentum range 0.44 GeV. The ν 2 ( p T ), ν 3 ( p T ), and ν 4 ( p T ) are compared to the ν n coefficients in Pb+Pb collisions at s N N = 2.76 TeV with similar event multiplicities. Reasonable agreement is observed after accounting for the difference in the average p T of particles produced in the two collision systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Three-cluster dynamics within the ab initio no-core shell model with continuum: How many-body correlations and α clustering shape He 6 [Three-Cluster Dynamics Within The Ab Initio No-Core Shell Model With Continuum: How Many-Body Correlations And Alpha-Clustering Shape 6He]

We realize the treatment of bound and continuum nuclear systems in the proximity of a three-body breakup threshold within the ab initio framework of the no-core shell model with continuum. Many-body eigenstates obtained from the diagonalization of the Hamiltonian within the harmonic-oscillator expansion of the no-core shell model are coupled with continuous microscopic three-cluster states to correctly describe the nuclear wave function both in the interior and asymptotic regions. We discuss the formalism in detail and give algebraic expressions for the case of core + n + n systems. Using similarity-renormalization-group evolved nucleon-nucleon interactions, we analyze the role of 4 He + n + n clustering and many-body correlations in the ground and low-lying continuum states of the Borromean 6 He nucleus, and study the dependence of the energy spectrum on the resolution scale of the interaction. We show that 6 He small binding energy and extended radii compatible with experiment can be obtained simultaneously, without resorting to extrapolations. Here, we also find that a significant portion of the ground-state energy and the narrow width of the first 2 + resonance stem from many-body correlations that can be interpreted as core-excitation effects.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Effect of the QCD equation of state and strange hadronic resonances on multiparticle correlations in heavy ion collisions

The QCD equation of state at zero baryon chemical potential is the only element of the standard dynamical framework to describe heavy ion collisions that can be directly determined from first principles. Continuum extrapolated lattice QCD equations of state have been computed using 2+1 quark flavors (up/down and strange) as well as 2+1+1 flavors to investigate the effect of thermalized charm quarks on QCD thermodynamics. Lattice results have also indicated the presence of new strange resonances that not only contribute to the equation of state of QCD matter but also affect hadronic afterburners used to model the later stages of heavy ion collisions. We investigate how these new developments obtained from first principles calculations affect multiparticle correlations in heavy ion collisions. We compare the commonly used equation of state S95n-v1, which was constructed using what are now considered outdated lattice results and hadron states, to the current state-of-the-art lattice QCD equations of state with 2+1 and 2+1+1 flavors coupled to the most upto-date hadronic resonances and their decays. New hadronic resonances lead to an enhancement in the hadronic spectra at intermediate p T . Using an outdated equation of state can directly affect the extraction of the shear viscosity to entropy density ratio, η/s , of the quark-gluon plasma and results for different flow observables. The effects of the QCD equation of state on multiparticle correlations of identified particles are determined for both AuAu √ sNN = 200 GeV and PbPb √ sNN = 5.02 TeV collisions. New insights into the v 2 {2} to v 3 {2} puzzle in ultracentral collisions are found. Flow observables of heavier particles exhibit more non-linear behavior regardless of the assumptions about the equation of state, which may provide a new way to constrain the temperature dependence of η/s .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Measurement of the correlation between the polar angles of leptons from top quark decays in the helicity basis at $\sqrt{s}$ = 7 TeV using the ATLAS detector

A measurement of the correlations between the polar angles of leptons from the decay of pair-produced t and $\bar{t}$ quarks in the helicity basis is reported, using proton-proton collision data collected by the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 4.6 fb$^{-1}$ at a center-of-mass energy of $\sqrt{s}$ = 7 TeV collected during 2011. Candidate events are selected in the dilepton topology with large missing transverse momentum and at least two jets. The angles θ$_1$ and θ$_2$ between the charged leptons and the direction of motion of the parent quarks in the $t\bar{t}$ rest frame are sensitive to the spin information, and the distribution of cosθ$_1$ ∙ cosθ$_2$ is sensitive to the spin correlation between the t and $\bar{t}$ quarks. The distribution is unfolded to parton level and compared to the next-to-leading order prediction. A good agreement is observed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Local correlated motions in aqueous solution of sodium chloride

Real-space motions of molecules and ions in an aqueous solution of sodium chloride are studied with high-resolution inelastic x-ray scattering. In this study, we focus on the correlated dynamics of water molecules and salt ions, instead of the instantaneous structure and the rotational and reorientation dynamics that have been studied using scattering techniques and optical spectroscopy, respectively. The real-space analysis in terms of the Van Hove function illustrates the effect of salt ions to slow down the local correlated dynamics of surrounding water in the hydration shells.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Melting rate correlation with batch properties and melter operating conditions during conversion of nuclear waste melter feeds to glasses

The rate of conversion of nuclear waste melter feed to glass is affected by the selection of melter feed materials and by melter design and operation. The melting rate correlation (MRC) is an equation that relates the glass production rate with two types of variables: (1) feed and melt properties: conversion heat, cold-cap bottom temperature, and glass melt viscosity; and (2) melter design and operation parameters: melter geometry, melter operating temperature, and gas bubbling rate. The MRC shows good agreement for an extended melting-rate data set of high-level waste (HLW) melter feeds and a data set generated for low-activity waste (LAW) melter feeds. Laboratory observation of heated melter feed samples is often used to assess the cold-cap bottom temperature of HLW melter feeds (moderately foaming feeds), but this technique appears inadequate for LAW melter feeds (vigorously foaming feeds). For LAW feeds, an adequate assessment of the cold-cap bottom temperature was achieved using evolved gas analysis, which allows identification of the collapse of primary foam for oxidized feeds. This assessment shows that the cold-cap bottom temperature for vigorously foaming LAW feeds is higher than that for moderately foaming HLW feeds. When the results of MRC are compared, LAW feeds are generally less sensitive to the bubbling rate and melt viscosity, and more sensitive to the cold-cap bottom temperature than HLW feeds. The MRC qualifies as a promising tool to support the selection of melter feed materials and melter operating conditions, which is determined from expensive independent scaled melter experiments, and sophisticated mathematical models.

Lee, Seung Min↗
DOE OSTI2017

Measurement of multi-particle azimuthal correlations in pp, p + Pb and low-multiplicity Pb + Pb collisions with the ATLAS detector

Multi-particle cumulants and corresponding Fourier harmonics are measured for azimuthal angle distributions of charged particles in pp collisions at $\sqrt{s}$ = 5.02 and 13 TeV and in p + Pb collisions at $\sqrt{s}$$_ {NN}$ = 5.02 TeV, and compared to the results obtained for low-multiplicity Pb + Pb collisions at $\sqrt{s}$$_ {NN}$ = 2.76 TeV. These measurements aim to assess the collective nature of particle production. The measurements of multi-particle cumulants confirm the evidence for collective phenomena in p + Pb and low-multiplicity Pb + Pb collisions. On the other hand, the pp results for four-particle cumulants do not demonstrate collective behaviour, indicating that they may be biased by contributions from non-flow correlations. A comparison of multi-particle cumulants and derived Fourier harmonics across different collision systems is presented as a function of the charged-particle multiplicity. For a given multiplicity, the measured Fourier harmonics are largest in Pb + Pb, smaller in p + Pb and smallest in pp collisions. Finally, the pp results show no dependence on the collision energy, nor on the multiplicity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Correlation of Electrolyte Volume and Electrochemical Performance in Lithium-Ion Pouch Cells with Graphite Anodes and NMC532 Cathodes

The work herein reports on studies aimed at exploring the correlation between electrolyte volume and electrochemical performance of full cell, pouch-cells consisting of graphite/ Li 1.02 Ni 0.50 Mn 0.29 Co 0.19 O 2 (NMC-532) as the electrodes and 1.2 M LiPF 6 in ethylene carbonate:ethylmethyl carbonate (EC:EMC) as the electrolyte. In addition, it is demonstrated that a minimum electrolyte volume factor of 1.9 times the total pore volume of cell components (cathode, anode, and separator) is needed for long-term cyclability and low impedance. Less electrolyte results in an increase of the measured Ohmic resistances. Increased resistance ratios for charge transfer and passivation layers at cathode, relative to initial values, were 1.5 2.0 after 100 cycles. At the cathode, the resistance from charge transfer was 2-3 times higher than for passivation layers. Lastly, differential voltage analysis showed that anodes were less delithiated after discharging as the cells were cycled.

25 ENERGY STORAGE↗
NASA NTRS1992

Measuring Omega and the real correlation function from the redshift correlation function

Peculiar velocities distort the correlation function of galaxies in redshift space. In the linear regime, the distortion has a characteristic quadrupole plus hexadecapole form. The amplitude of the distortion depends on the cosmological density parameter Omega. Practical formulas are derived here which can be applied to redshift galaxy catalogs to measure Omega in the linear regime. The formulas also yield the real underlying correlation function in the linear regime, corrected for peculiar velocities.

Hamilton, A. J. S.↗
NASA NTRS1992

Scalar rate correlation at a turbulent liquid free surface - A two-regime correlation for high Schmidt numbers

An experimental correlation is derived for gas absorption at a turbulent, shear-free liquid interface. The correlation is expressed in terms of the liquid-side turbulence intensity, liquid-side macroscale, and the properties of the diffusing gas and solvent. The transfer coefficient increases linearly with rms velocity up to a point where the eddy Reynolds number reaches a critical (Schmidt number dependent) value. At higher velocities, there is a more rapid linear rise. The slope of the lower Reynolds number region is proportional to the square root of the diffusivity; at Reynolds numbers much higher than that of the break point, the slope becomes independent of diffusivity.

Khoo, Boo-Cheong↗