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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Constraints on 5 f -electron magnetism in Ga-stabilized $δ$-Pu from x-ray magnetic circular dichroism

Density-functional theory models of δ-Pu accurately predict crystal structure, phonon density of states, and unit cell volumes but require magnetic degrees of freedom which have never been experimentally verified. Some models invoke an on-site cancellation of spin and orbital moments, engendering a near-zero bulk magnetization, undetectable by most probes. Here, we employ x-ray magnetic circular dichroism at the Pu M 4,5 edges to directly probe spin and orbital moments using the magneto-optical sum rules. The data show no dichroism within experimental error, constraining polarized moments at 6 T and 3 K to μ L,S <0.1⁢μ B . Finally, these experiments point to the absence of even unconventional spin-orbit compensated order in δ-Pu.

36 MATERIALS SCIENCE↗
DOE OSTI2015

General microscopic model of magnetoelastic coupling from first principles

Magnetoelastic coupling, i.e., the change of crystal lattice induced by a spin order, is not only scientifically interesting, but also technically important. In this work, we propose a general microscopic model from firstprinciples calculations to describe the magnetoelastic coupling and provide a way to construct the microscopic model from density functional theory calculations. Based on this model, we reveal that there exists a previously unexpected contribution to the electric polarization induced by the spin order in multiferroics due to the combined effects of magnetoelastic coupling and piezoelectric effect. Interestingly and surprisingly, we find that this latticedeformation contribution to the polarization is even larger than that from the pure electronic and ion-displacement contributions in BiFeO 3 . We conclude this model of magnetoelastic coupling can be generally applied to investigate the other magnetoelastic phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Bright and dark singlet excitons via linear and two-photon spectroscopy in monolayer transition metal dichalcogenides

We discuss the linear and two-photon spectroscopic selection rules for spin-singlet excitons in monolayer transition-metal dichalcogenides. Our microscopic formalism combines a fully k-dependent few-orbital band structure with a many-body Bethe-Salpeter equation treatment of the electron-hole interaction, using a model dielectric function. We show analytically and numerically that the single-particle, valley-dependent selection rules are preserved in the presence of excitonic effects. Furthermore, we definitively demonstrate that the bright (one-photon allowed) excitons have s-type azimuthal symmetry and that dark p-type excitons can be probed via two-photon spectroscopy. Thus, the screened Coulomb interaction in these materials substantially deviates from the 1/ε₀r form; this breaks the “accidental” angular momentum degeneracy in the exciton spectrum, such that the 2p exciton has a lower energy than the 2s exciton by at least 50 meV. We compare our calculated two-photon absorption spectra to recent experimental measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High-resolution hypernuclear spectroscopy at Jefferson Lab, Hall A

The experiment E94-107 in Hall A at Jefferson Lab started a systematic study of high resolution hypernuclear spectroscopy in the 0 p -shell region of nuclei such as the hypernuclei produced in electroproduction on 9 Be, 12 C and 16 O targets. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a ring-imaging Cherenkov detector were added to the Hall A standard equipment. The high-quality beam, the good spectrometers and the new experimental devices allowed us to obtain very good results. Here, measurable strength with sub-MeV energy resolution was recorded for the core-excited states of $^{12}_{Λ}$B. A high-quality$^{16}_{Λ}N hypernuclear spectrum was likewise obtained. A first measurement of the Λ binding energy for Lambda 16N, calibrated against the elementary reaction on hydrogen, was obtained with high precision, 13.76 ± 0.16 MeV. Similarly, the first$^{9}_{Λ}Li hypernuclear spectrum shows general agreement with theory (distorted-wave impulse approximation with the SLA and BS3 electroproduction models and shell-model wave functions). Some disagreement exists with respect to the relative strength of the states making up the first multiplet. A Λ separation energy of 8.36 MeV was obtained, in agreement with previous results. It has been observed that the electroproduction of hypernuclei can provide information complementary to that obtained with hadronic probes and the γ-ray spectroscopy technique.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Heavy quarkonium correlators at finite temperature: QCD sum rule approach

We investigate the properties of heavy quarkonia at finite temperature in detail using QCD sum rules. Extending previous analyses, we take into account a temperature-dependent effective continuum threshold and derive constraints on the mass, the width, and the varying effective continuum threshold. We find that at least one of these quantities of a charmonium changes abruptly in the vicinity of the phase transition. We also calculate the ratio of the imaginary time correlator to its reconstructed one, G/G{sub rec}, by constructing a model spectral function and compare it to the corresponding lattice QCD results. We demonstrate that the almost constant unity of G/G{sub rec} can be obtained from the destructive interplay of the changes in each part of the spectral modification which are extracted from QCD sum rules.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Nonglobal correlations in collider physics

Despite their importance for precision QCD calculations, correlations between in- and out-of-jet regions of phase space have never directly been observed. These so-called non-global effects are present generically whenever a collider physics measurement is not explicitly dependent on radiation throughout the entire phase space. In this paper, we introduce a novel procedure based on mutual information, which allows us to isolate these non-global correlations between measurements made in different regions of phase space. We study this procedure both analytically and in Monte Carlo simulations in the context of observables measured on hadronic final states produced in e+e- collisions, though it is more widely applicable.The procedure exploits the sensitivity of soft radiation at large angles to non-global correlations, and we calculate these correlations through next-to-leading logarithmic accuracy. The bulk of these non-global correlations are found to be described in Monte Carlo simulation. They increase by the inclusion of non-perturbative effects, which we show can be incorporated in our calculation through the use of a model shape function. As a result, this procedure illuminates the source of non-global correlations and has connections more broadly to fundamental quantities in quantum field theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Amplitude analysis of B - → D + π - π - decays

The Dalitz plot analysis technique is used to study the resonant substructures of B - → D + π - π - decays in a data sample corresponding to 3.0 fb -1 of pp collision data recorded by the LHCb experiment during 2011 and 2012. A model-independent analysis of the angular moments demonstrates the presence of resonances with spins 1, 2 and 3 at high D + π - mass. The data are fitted with an amplitude model composed of a quasi-model-independent function to describe the D + π - S wave together with virtual contributions from the D*(2007) 0 and B* 0 states, and components corresponding to the D$*\atop{2}$(2460) 0 , D$*\atop{1}$(2680) 0 , D$*\atop{3}$(2760) 0 and D$*\atop{2}$(3000) 0 resonances. The masses and widths of these resonances are determined together with the branching fractions for their production in B- → D + π - π - decays. The D + π - S wave has phase motion consistent with that expected due to the presence of the D$*\atop{0}$(2400) 0 state. These results constitute the first observations of the D$*\atop{3}$(2760) 0 and D$*\atop{2}$(3000) 0 resonances, with significances of 10σ and 6.6σ, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Suppression of Tritium Retention in Remote Areas of ITER by Nonperturbative Reactive Gas Injection

A technique based on reactive gas injection in the afterglow region of the divertor plasma is proposed for the suppression of tritium-carbon codeposits in remote areas of ITER when operated with carbon-based divertor targets. Experiments in a divertor simulator plasma device indicate that a 4 nm/min deposition can be suppressed by addition of 1 Pa{center_dot}m{sup 3} s{sup -1} ammonia flow at 10 cm from the plasma. These results bolster the concept of nonperturbative scavenger injection for tritium inventory control in carbon-based fusion plasma devices, thus paving the way for ITER operation in the active phase under a carbon-dominated, plasma facing component background.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Extreme Decoherence and Quantum Chaos

Here, we study the ultimate limits to the decoherence rate associated with dephasing processes. Fluctuating chaotic quantum systems are shown to exhibit extreme decoherence, with a rate that scales exponentially with the particle number, thus exceeding the polynomial dependence of systems with fluctuating k -body interactions. Our findings suggest the use of quantum chaotic systems as a natural test bed for spontaneous wave function collapse models. Lastly, we further discuss the implications on the decoherence of AdS/CFT black holes resulting from the unitarity loss associated with energy dephasing.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Dirac Fermion Hierarchy of Composite Fermi Liquids

Composite Fermi liquids (CFLs) are compressible states that can occur for 2D interacting fermions confined in the lowest Landau level at certain Landau level fillings. They have been understood as Fermi seas formed by composite fermions which are bound states of electromagnetic fluxes and electrons as reported by Halperin, Lee, and Read [Phys. Rev. B 47, 7312 (1993)]. At half filling, an explicitly particle-hole symmetric theory based on Dirac fermions was proposed by Son [Phys. Rev. X 5, 031027 (2015)] as an alternative low energy description. In this work, we investigate the Berry curvature of CFL model wave functions at a filling fraction of one-quarter, and observe that it is uniformly distributed over the Fermi sea except at the center where an additional π phase was found. Motivated by this, we propose an effective theory which generalizes Son’s half filling theory, by internal gauge flux attachment, to all filling fractions in which fermionic CFLs can occur. As a result, the numerical results support the idea of internal gauge flux attachment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Universality in the Near-Side Energy-Energy Correlator

We investigate the energy-energy correlator (EEC) of hadrons produced on the same side in e + e − annihilation or in leading jets in p p collisions. We observe a remarkable universality of the correlator. Using a nonperturbative transverse momentum dependent (TMD) fragmentation function to model the transition from the “free-hadron” region to the perturbative collinear region, we are able to describe the near-side shapes and peaks over a wide range of energy for both the e + e − annihilation and the p p jet substructure measurements in terms of just two parameters. We present further predictions for the ratio of the projected three-point energy correlator to the EEC. The excellent agreement between our calculations and the experimental data may provide new insights into the role of nonperturbative physics for EECs, and suggests the possibility of exploring nonperturbative TMDs using theoretical tools developed for the energy correlators. Published by the American Physical Society 2025

Liu, Xiaohui (ORCID:0000000277011205)↗
DOE OSTI2024

XaaS: Acceleration as a Service to Enable Productive High-Performance Cloud Computing

High-performance computing (HPC) and the cloud have evolved independently, specializing their innovations into performance or productivity. Acceleration as a Service (XaaS) is a recipe to empower both fields with a shared execution platform that provides transparent access to computing resources, regardless of the underlying cloud or HPC service provider. Bridging HPC and cloud advancements, XaaS presents a unified architecture built on performance-portable containers. Here, our converged model concentrates on low-overhead, high-performance communication and computing, targeting resource-intensive workloads from climate simulations to machine learning. XaaS lifts the restricted allocation model of Function as a Service (FaaS), allowing users to benefit from the flexibility and efficient resource utilization of serverless computing while supporting long-running and performance-sensitive workloads from HPC.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Measurement-based Power System Dynamic Model Reduction Using ARX Equivalents

The increasing complexity of power system has made it difficult to simulate large-scale power system in detail. Therefore, to improve computational efficiency, model reduction techniques has been applied to reduce the external area and focus on the dynamics of the internal area. This paper proposes a measurement-based model reduction method which reduces the external system by replacing external system with ARX equivalents. The modeled transfer function parameters are obtained using system identification approach. Case studies on the NPCC system and EI system are carried out. Results show that the proposed reduction method can effectively retain the dynamic behavior of the study area while mitigating computation burden.

Jiang, Zhihao↗
DOE OSTI2020

Arsenic Doping of Polycrystalline CdSeTe Devices for Microsecond Life-times with High Carrier Concentrations

We report seminal advances in fabrication and understanding of group V (As) doped thin-film polycrystalline CdTe-based solar cells. The devices are fabricated using a novel approach, by sublimating layers of CdSeTe and CdSeTe:As. This new method allowed us to achieve minority carrier lifetime of over 1 μs, carrier concentration of more than 5×l0 15 cc -1 and external radiative efficiency of over 2 % in a device configuration. We find an increase in open-circuit voltage when comparing As-doped, Cu-doped and undoped devices. The choice of CdSeTe instead of a CdTe-only absorber has been explained using first-principle density functional theory model. A SCAPS device model is used to analyze the potential causes for lower open-circuit voltage.

Munshi, Amit H.↗