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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Quantum tensor network algorithms for evaluation of spectral functions on quantum computers

We investigate quantum algorithms derived from tensor networks to simulate the static and dynamic properties of quantum many-body systems. Using a sequentially prepared quantum circuit representation of a matrix product state (MPS) that we call a quantum tensor network (QTN), we demonstrate algorithms to prepare ground and excited states on a quantum computer and apply them to molecular nanomagnets (MNMs) as a paradigmatic example. In this setting, we develop two approaches for extracting the spectral correlation functions measured in neutron-scattering experiments: (a) a generalization of the SWAP test for computing wave function overlaps and, (b) a generalization of the notion of matrix product operators to the QTN setting which generates a linear combination of unitaries. The latter method is discussed in detail for translationally invariant spin-half systems, where it is shown to reduce the qubit resource requirements compared with the SWAP method and may be generalized to other systems. We demonstrate the versatility of our approaches by simulating spin-1/2 and spin-3/2 MNMs, with the latter being an experimentally relevant model of a Cr$^{3+}_{8}$ ring. Here, our approach has qubit requirements that are independent of the number of constituents of the many-body system and scale only logarithmically with the bond dimension of the MPS representation, making them appealing for implementation on near-term quantum hardware with mid-circuit measurement and reset.

Neutron scattering↗
DOE OSTI2019

Electronic Structure, Lattice Dynamics, and Superconducting Properties of Mercury-Alkaline Earth Metal Compounds: a First-Principles Study

The electronic structure, lattice dynamics, and superconducting properties of SrHg and BaHg intermetallic compounds are investigated using plane wave pseudo-potential and linear response methods based on density functional theory. The ground state properties such as lattice parameters are in good agreement with previously reported results. The positive phonon frequencies reveal the stability of both compounds in B{sub 2} (CsCl-type) structure. The metallic nature of SrHg and BaHg is confirmed by the electronic band structure as well as phonon dispersion curves. The superconducting behavior described in terms of Eliashberg spectral function (α{sup 2}F(ω)) and electron-phonon coupling constant (λ). The calculated values of superconducting transition temperatures (T{sub c}) show good agreement with available experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Electronic Excitation‐Driven β‐Ga 2 O 3 Metastability Transformation and Self‐Organization Mechanism: β→κ/γ/δ Phases

Here, irradiation-driven multiphase self-organization presents emergent opportunities for the customization of nanoscale engineering properties, dynamically tuning strain-field distributions and interfacial electronic structures. Responding to intense electronic excitation-induced energy deposition, the dominant phase transformations, with varying Gibbs free energy $Δ,G^o_f$ are confirmed as β → κ → γ → δ that are located in specific microregions for Gallium (III) oxide (Ga 2 O 3 ), as follows: (i) Surface-localized interstitial accumulation under compressive stress triggers β → δ via semi-coherent interface formation. (ii) Tensile stress within latent tracks drives vacancy-mediated oxygen layer truncation (4/12 periodicity along ⟨0001⟩), stabilizing coherent 4H (ABCB) κ and 3C (ABC) β (ABC) interfaces through strain-compensated octahedral distortion. (iii) Screw dislocation-mediated lattice relaxation induces β → γ via cation disordering (Ga 3+ occupancy at β-interstitial sites), forming metastable spinel γ with mixed occupancy across 16d/8a Wyckoff sites. Irradiation-driven β-Ga 2 O 3 →κ/γ/δ transitions, as mechanistically revealed via inelastic thermal spike (i-TS) calculations and molecular dynamics simulations, induce defect-mediated nonlinear photoresponse, critical for optoelectronic engineering.

Han, Xinqing [Shandong Univ., Jinan (China)]↗
DOE OSTI2019

Insights into Structural Evolution of Lithium Peroxides with Reduced Charge Overpotential in Li–O 2 System

Reducing charge-discharge overpotential is of great significance to enhance efficiency and cyclability of Li–O 2 batteries. Here we successfully achieve dramatically reduced charge overpotential (0.4 V) via a rational design of cathode architecture, which features highly uniform Pt and Pt 3 Co nanocrystals embedding within nitrogen-doped cobalt@graphene heterostructures. Because of the improvement on the catalytic efficiency for optimizing the electrical and dynamic properties, the cathode design enables promising electrochemical performance. More importantly, the results reveal different overpotential prompted by different structural evolution of bulk Li 2 O 2 , which depends on the Pt modification approach (surface-coating and bulk-doping). This dependence is found to be attributed to the influence of Pt nanocomponents and their dispersion on the formation and decomposition mechanism of Li 2 O 2 . Density functional theory calculations provide mechanistic insights into the promotional effect of Pt and Pt 3 Co on the reduction of the charge overpotential. Lastly, an inner relationship between overpotential and electrochemical kinetics is proposed.

25 ENERGY STORAGE↗
DOE OSTI2020

Active Learning A Neural Network Model For Gold Clusters & Bulk From Sparse First Principles Training Data

Small metal clusters are of fundamental scientific interest and of tremendous significance in catalysis. These nanoscale clusters display diverse geometries and structural motifs depending on the cluster size; a knowledge of this size-dependent structural motifs and their dynamical evolution has been of longstanding interest. Given the high computational cost of first-principles calculations, molecular modeling and atomistic simulations such as molecular dynamics (MD) has proven to be an important complementary tool to aid this understanding. Classical MD typically employ predefined functional forms which limits their ability to capture such complex size-dependent structural and dynamical transformation. Neural Network (NN) based potentials represent flexible alternatives and in principle, well-trained NN potentials can provide high level of flexibility, transferability and accuracy on-par with the reference model used for training. A major challenge, however, is that NN models are interpolative and requires large quantities (similar to 10 4 or greater) of training data to ensure that the model adequately samples the energy landscape both near and far-from-equilibrium. A highly desirable goal is minimize the number of training data, especially if the underlying reference model is first-principles based and hence expensive. In this work, we introduce an active learning (AL) scheme that trains a NN model on-the-fly with minimal amount of first-principles based training data. Our AL workflow is initiated with a sparse training dataset (similar to 1 to 5 data points) and is updated on-the-fly via a Nested Ensemble Monte Carlo scheme that iteratively queries the energy landscape in regions of failure and updates the training pool to improve the network performance. Using a representative system of gold clusters, we demonstrate that our AL workflow can train a NN with similar to 500 total reference calculations. Using an extensive DFT test set of similar to 1100 configurations, we show that our AL-NN is able to accurately predict both the DFT energies and the forces for clusters of a myriad of different sizes. Our NN predictions are within 30 meV/atom and 40 meV/angstrom of the reference DFT calculations. Moreover, our AL-NN model also adequately captures the various size-dependent structural and dynamical properties of gold clusters in excellent agreement with DFT calculations and available experiments. We finally show that our AL-NN model also captures bulk properties reasonably well, even though they were not included in the training data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Multi‐fidelity digital twin structural model for a sub‐scale downwind wind turbine rotor blade

Abstract This paper presents the development of a multi‐fidelity digital twin structural model (virtual model) of an as‐built wind turbine blade. The goal is to develop and demonstrate an approach to produce an accurate and detailed model of the as‐built blade for use in verifying the performance of the operating two‐bladed, downwind rotor. The digital twin model development methodology, presented herein, involves a novel calibration process to integrate a wide range of information including design specifications, manufacturing information, and structural testing data (modal and static) to produce a multi‐fidelity digital twin structural model: a detailed high‐fidelity model (i.e., 3D finite element analysis [FEA]) and consistent beam‐type models for aeroelastic simulation. A key element is that the multi‐fidelity structural digital twin method follows the rotor from the stages of design, to manufacturing, then to the ground testing and field operation. The result of this comprehensive approach is an accurate multi‐fidelity digital twin structural model for the geometric, structural, and structural dynamic properties of the as‐built blade within a 1% match in mass properties, 3.2% in blade frequencies, and 6% in deflection. The different stages of processing this information within the methodology are discussed. The rotor examined is the SUMR‐Demonstrator (SUMR‐D), which was installed on the Controls Advanced Research Testbed (CART‐2) wind turbine at the National Wind Technology Center. The digital twin model developed here was utilized to design controllers to safely operate SUMR‐D in field tests, which are providing additional data for further evaluation and development of the multi‐fidelity digital twin structural model.

Chetan, Mayank↗
DOE OSTI2019

Effects of Thermal Fluctuations on Dynamics of Josephson Junction with Unconventional Current-Phase Relation

In this study, we carried out the analysis of the thermal fluctuations on Josephson junction (JJ) dynamics with unconventional current-phase relation (CPR). We analyzed two cases of CPR: the anharmonic term case and the case of Majorana term. An expression was obtained for the delay time and the critical current fluctuations in the case of linear growth of current via junction in two limits: low and high growth rate. The dynamical properties of JJ with unconventional CPR are determined by the renormalized critical current of JJ.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Strain-Rate Effect and Constitutive Models for Q550 High-Strength Structural Steel

High-strength structural steel is the tendency in modern construction practice. In this study, quasi-static tension tests and dynamic tests for Q550 with strain rate from 0.00025 to 3831 s{sup −1} were conducted. The results showed that Q550 is dependent on the strain rate, keeping the flow stress increased as the strain rate increases, while Q550 has lower strain-rate sensitivity of flow stress than that of normal mild steel. Based on the experimental data, a proper constant for the key parameter, C, in Johnson–Cook model (J–C) was suggested. Then, a modified J–C model based on a rate-dependent parameter C( ε-dot ) was recommended to consider the influence of strain-rate effect. New constants of D and p governing the dynamic response of steel in the Cowper–Symonds (C–S) model were also suggested. The C–S model and J–C models with suggested constants provided in the paper were proven to have acceptable prediction accuracy for the dynamic increase factor of Q550. These results may be applied to study the dynamical properties of Q550 and related structural components for future engineering applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mammalian nonmuscle myosin II comes in three flavors

Highlights: • Nonmuscle myosin II executes numerous mechanical tasks in cells including cytoskeleton organization and cell migration. • Three mammalian nonmuscle myosin II paralogs have distinct kinetic and dynamic properties in vitro and in vivo. • Mammalian nonmuscle myosin II paralogs mix and match their abilities to perform both individual and joint tasks in the cell. Nonmuscle myosin II is an actin-based motor that executes numerous mechanical tasks in cells including spatiotemporal organization of the actin cytoskeleton, adhesion, migration, cytokinesis, tissue remodeling, and membrane trafficking. Nonmuscle myosin II is ubiquitously expressed in mammalian cells as a tissue-specific combination of three paralogs. Recent studies reveal novel specific aspects of their kinetics, intracellular regulation and functions. On the other hand, the three paralogs also can copolymerize and cooperate in cells. Here we review the recent advances from the prospective of how distinct features of the three myosin II paralogs adapt them to perform specialized and joint tasks in the cell.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Electromechanical memcapacitor model offering biologically plausible spiking.

In this article, we introduce a new nanoscale electromechanical device - a leaky memcapacitor - and show that it may be useful for the hardware implementation of spiking neurons. The leaky memcapacitor is a movableplate capacitor that becomes quite conductive when the plates come close to each other. The equivalent circuit of the leaky memcapacitor involves a memcapacitive and memristive system connected in parallel. In the leaky memcapacitor, resistance and capacitance depend on the same internal state variable, which is the displacement of the movable plate. We have performed a comprehensive analysis showing that several types of spiking observed in biological neurons can be implemented with the leaky memcapacitor. Significant attention is paid to the dynamic properties of the model. As in leaky memcapacitors the capacitive, leaking resistive, and reset functionalities are implemented naturally within the same device structure, their use will simplify the creation of spiking neural networks.

Zhang, Zixi↗
DOE OSTI2018

Evaluating methane adsorbed film densities on activated carbon in dynamic systems

Dynamic methane loading and discharge experiments on a 40 L adsorbed natural gas tank containing 20.5 kg of monolithic carbon adsorbent have been combined with pore volume data from subcritical nitrogen isotherms to evaluate the density and dynamic properties associated with adsorbed methane. The time-dependent density of the adsorbed gas was evaluated for narrow and wide micropores. The temperature-dependent adsorbed film volume was determined from the Ono-Kondo model and compared with the total micropore volume. The resulting adsorbed methane density evolves in two distinct parts. The density increases rapidly during the beginning of the loading process and increases slowly after narrow pores reach saturation. The narrow pores’ saturated adsorbed gas densities ranged from 0.26 – 0.35 kg/L, depending on the choice of film volume. The density of wide micropores was found to be highly dependent on the loading procedure due to the expected temperature dependence of the film volume. During discharge, it was found that the wide micropores deplete early while narrow micropores deplete slowly which causes the less than 100% efficient discharges seen in adsorbed natural gas systems. These density models have been applied to accurately predict the gravimetric excess adsorption of other carbon adsorbents at 35 bar and explain previously published pressure and temperature relations during tank loading.

25 ENERGY STORAGE↗
DOE OSTI2022

Sodium diffusion in heterogeneous porous media: Connecting laboratory experiments and simulations

Sodium has been suggested as a tracer for brine in reservoir formations where a significant amount of sodium ion is found mainly in the aqueous phase. Fortunately, the most abundant sodium isotope, 23 Na, is Nuclear Magnetic Resonance (NMR) active, making it possible to study the structure and dynamical properties of both bulk and pore confined fluid systems. We investigated the diffusion of key dissolved sodium species in bulk solution and porous media as a function of composition, ionic strength, and permeability of the carbonate samples using NMR relaxometry and pulsed-field gradient (PFG) NMR techniques. We use Indiana limestone as an example of natural porous media and water as a freely diffusible tracer and carrier. We demonstrate apparent diffusion measurement of sodium based on changes in spin–spin relaxation time (T 2 ) signal in pore confinement. The diffusion rate of sodium decreases with increasing counter-ion size. This effect is greater at higher ionic strengths and lower chemical potentials in porous media. The reactive transport code, CrunchFlow, was used to complement the NMR experiments to simulate diffusion behavior in porous media. Combining these two methods provides a powerful approach to estimating effective diffusion coefficients in heterogeneous matrices. The modeling considers the influence of physical properties (porosity and tortuosity) and chemical properties (geochemical composition and chemical gradients). The results presented in this work highlight the advantage of measuring apparent diffusivity using NMR T 2 relaxometry in conjunction with numerical simulation to derive effective diffusivity and the corresponding matrix properties (i.e., tortuosity) of the system.

58 GEOSCIENCES↗
DOE OSTI2019

Comparison of anion and cation dynamics in a carbon-substituted closo-hydroborate salt: 1 H and 23 Na NMR studies of solid-solution Na 2 (CB 9 H 10 )(CB 11 H 12 )

The hexagonal mixed-anion solid solution Na 2 (CB 9 H 10 )(CB 11 H 12 ) shows the highest room-temperature ionic conductivity among all known Na-ion conductors. To study the dynamical properties of this compound, we have measured the 1 H and 23 Na nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates in Na 2 (CB 9 H 10 )(CB 11 H 12 ) over the temperature range of 80-435 K. It is found that the diffusive motion of Na+ ions can be described in terms of two jump processes: the fast localized motion within the pairs of tetrahedral interstitial sites of the hexagonal close-packed lattice formed by large anions and the slower jump process via octahedral sites leading to long-range diffusion. Below 350 K, the slower Na + jump process is characterized by the activation energy of 353(11) meV. Although Na + mobility in Na 2 (CB 9 H 10 )(CB 11 H 12 ) found from our NMR experiments is higher than in other ionic conductors, it appears to be an order-of-magnitude lower than that expected on the basis of the conductivity measurements. This result suggests that the complex diffusion mechanism and/or correlations between Na + jumps should be taken into account. The measured 1H spin-lattice relaxation rates for Na 2 (CB 9 H 10 )(CB 11 H 12 ) are consistent with a coexistence of at least two anion reorientational jump processes occurring at different frequency scales. Near room temperature, both reorientational processes are found to be faster than the Na + jump process responsible for the long-range diffusion.

25 ENERGY STORAGE↗
DOE OSTI2021

Giant anisotropic in-plane thermal conduction induced by Anomalous phonons in pentagonal PdSe 2

In two-dimensional materials, different atomic stacking induces anisotropic atomic interactions and phonon dispersions, leading to the anisotropy of in-plane thermal transport. In this work, we report an exceptional case in layered pentagonal PdSe 2 , where the bonding, force constants, and lattice constants are nearly-equal along the in-plane crystallographic axis directions, while the thermal conductivity is surprisingly much greater along b-axis than along a-axis with a ratio up to 1.8. Such strong anisotropy is not only unexpected in in-plane uniform structured materials, but also 2 comparable to the record high in-plane anisotropic thermal conductivity in the nonuniform structured material reported to date (the ratio is ~2.0 in TiS 3 ). By combining the inelastic X-ray scattering measurement and the first-principles calculations, we attribute such high anisotropy to the low-energy phonons along a-axis, particularly their lower group velocities and “avoided-crossing” behavior. The different buckling structures between a- (zigzag-type) and b-axis (flat-type) are mainly responsible for such unique phonon dynamics properties of PdSe 2 . This finding helps to discover materials with high anisotropic in-plane thermal conductivity in uniform structures and reveals new physics of anisotropy of in-plane thermal conduction. Due to the unique features in structure and thermal transport properties, PdSe 2 may serve as a new platform for designing novel devices to route heat flow precisely at the nanoscale.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optical Microscopic Techniques for Synthetic Polymer Characterization

In this paper, we discuss how state-of-the-art optical microscopic techniques enhance our understanding of the morphological and dynamic properties of synthetic polymers. Microscopic/nanoscopic properties obtained using these techniques can be linked to the macroscopic rheological, mechanical, optical, electrical and/or chemical properties of synthetic polymers that are widely used in scientific research and/or in daily life. Lastly, detailed knowledge of nanoscale polymer properties is thus anticipated to facilitate designing novel polymers for various applications, including surface coating, chemical separations, chemical sensing, bioimaging, and organic electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Lattice Dynamics and Structural Phase Transitions in Eu 2 O 3

Using the density functional theory, we study the structural and lattice dynamical properties of europium sesquioxide (Eu 2 O 3 ) in the cubic, trigonal, and monoclinic phases. The obtained lattice parameters and energies of the Raman modes show a good agreement with the available experimental data. The Eu-partial phonon density of states calculated for the cubic structure is compared with the nuclear inelastic scattering data obtained from a 20 nm thick Eu 2 O 3 film deposited on a YSZ substrate. A small shift of the experimental spectrum to higher energies results from a compressive strain induced by the substrate. On the basis of lattice and phonon properties, we analyze the mechanisms of structural transitions between different phases of Eu 2 O 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗