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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Visualizing Size-Dependent Dynamics of CeO 2-δ {100}-Supported CoO x Nanoparticles Under CO 2 Hydrogenation Conditions

Carbon dioxide is a major greenhouse gas. In order to optimize processes focused on its chemical valorization, one needs detailed information about the effects of CO 2 and/or CO 2 /H 2 mixtures on the structure and morphology of metal/oxide catalysts. Here, in this study, the evolution of a catalyst with cobalt supported on CeO 2 -cube nanostructures under CO 2 hydrogenation conditions was investigated by using a set of in situ characterization techniques (X-ray absorption fine structure, X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, and environmental transmission electron microscopy (TEM)). The {100} facets of the ceria support displayed an unexpectedly high stability due to strong interactions with the aggregates of cobalt oxide. A significant influence of interfacial bonding between CoO x and CeO 2-δ {100} is evident through a clear preference in the orientation of CoO x nanoparticles (NPs) with respect to the substrate. For initially reduced Co/CeO 2 -cube nanostructures, a kinetically controlled oxidation of cobalt upon the introduction of CO 2 was observed during the early stages of CO 2 hydrogenation. Environmental TEM revealed the size-dependent morphological behavior of cobalt oxide NPs due to strong interactions with the CeO 2 {100} surface. When the environment was switched from H 2 to a mixture of H 2 and CO 2 at 250 °C, small CoO x NPs (in the largest dimension < 2.5 nm) rapidly transformed from a pyramidal three-dimensional (3D) form to a planar, monatomic layer attached to the concurrently oxidized CeO 2-δ {100} surface. This maximizes the number of sites available for the binding of CO 2 or reaction intermediates. The shape transformation reflected the oxophilic character of cobalt and strong metal–support interactions. The removal of CO 2 from the gas phase led to a reduction of the cobalt oxide NPs by hydrogen and a reversible two-dimensional → 3D transformation. In contrast, no significant morphological changes, apart from further oxidation, were observed for big CoO x NPs (in the largest dimension > 3 nm). These trends are not seen for nanoparticles of noble metals. The observed morphological and structural changes in the small CoO x NPs affected the stability of reaction intermediates and modified the selectivity of the CoO x /CeO 2 catalyst system for methane production.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Dynamics of Emergent Crystallinity in Photonic Quantum Materials

This proposal will employ a revolutionary cold atom/photon hybrid material that combines the advantages of cold atom and semiconductor approaches: By confining a thin layer of Rydberg-EIT dressed atoms in the waist of a confocal optical resonator, a new synthetic material will emerge, akin to an exciton-polariton gas, but with stronger interactions and exquisite control: In the resonator, photons and Rydbergs hybridize, producing quasi-particles whose low mass is inherited from photons, and strong interactions from the Rydbergs. These particles have adjustable mass, interactions, and confinement, allowing tuning from a BEC to an unexplored regime expected to exhibit crystallinity. By studying non-equilibrium evolution near this transition, it will be possible to investigate quantum dynamics in a non-classical crystal, where quantum zero-point motion is substantial. Such a regime offers a unique opportunity to probe the universality of quantum dynamics, and also to study, for the first time, a form of quantum “soft-matter”, where the lattice structure is emergent, and competes with quantum fluctuations through the introduction of strongly interacting topological defects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Fermions in Two Dimensions: Scattering and Many-Body Properties

Ultracold atomic Fermi gases in two dimensions (2D) are an increasingly popular topic of research. The interaction strength between spin-up and spin-down particles in two-component Fermi gases can be tuned in experiments, allowing for a strongly interacting regime where the gas properties are yet to be fully understood. We have probed this regime for 2D Fermi gases by performing T = 0 ab initio diffusion Monte Carlo calculations. The many-body dynamics are largely dependent on the two-body interactions; therefore, we start with an in-depth look at scattering theory in 2D. We show the partial-wave expansion and its relation to the scattering length and effective range. Then, we discuss our numerical methods for determining these scattering parameters. Here, we close out this discussion by illustrating the details of bound states in 2D. Transitioning to the many-body system, we also use variationally optimized wave functions to calculate ground-state properties of the gas over a range of interaction strengths. We show results for the energy per particle and parametrize an equation of state. We then proceed to determine the chemical potential for the strongly interacting gas.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Promoting Noncovalent Intermolecular Interactions Using a C 60 Core Particle in Aqueous PC60s-Covered Colloids for Ultraefficient Photoinduced Particle Activity

We report that noncovalent intermolecular interactions in nanomaterials, such as van der Waals effects, allow adjustment of the nanoscopic size of compounds and their conformation in molecular crystal regimes. These strong interactions permit small particle sizes to be maintained as the crystals grow. In particular, these effects can be leveraged in the confined/reinforcing phase of molecules. With this in mind, we used C 60 molecules as a core particle in single-PC60 surfactant-covered colloid in a water-processable system. Compared with our previous results based on a PC 61 BM core-PC60 shell particle, the PC60-C 60 colloid had a considerably smaller spherical structure due to the increased intermolecular interactions between C 60 (fullerene) molecules. Interestingly, the conformation of C 60 aggregates was altered depending on the mixed solvents and their volume fraction in the organic phase, which strongly affected the structural properties of the PC60-C 60 colloids. The particle facilitated strong interactions with a p-type core sphere when it was introduced as the shell part of a p-n heterojunction particle. This direct interaction provided effective electronic communication between p- and n-type particles, resulting in ultraefficient photonic properties, particularly in charge separation in aqueous heterostructured colloids. Lastly, this enabled the development of an extremely efficient photovoltaic device with a 6.74% efficiency, which could provide the basis for creating high-performance water-processable solar cells based on p-n heterostructured NPs.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Interaction of magnetic resonators studied by the magnetic field enhancement

It is the first time that the magnetic field enhancement (MFE) is used to study the interaction of magnetic resonators (MRs), which is more sensitive than previous parameters–shift and damping of resonance frequency. To avoid the coherence of lattice and the effect of Bloch wave, the interaction is simulated between two MRs with same primary phase when the distance is changed in the range of several resonance wavelengths, which is also compared with periodic structure. The calculated MFE oscillating and decaying with distance with the period equal to resonance wavelength directly shows the retardation effect. Simulation also shows that the interaction at normal incidence is sensitive to the phase correlation which is related with retardation effect and is ultra-long-distance interaction when the two MRs are strongly localized. When the distance is very short, the amplitude of magnetic resonance is oppressed by the strong interaction and thus the MFE can be much lower than that of single MR. This study provides the design rules of metamaterials for engineering resonant properties of MRs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Charge transfer excitations, pair density waves, and superconductivity in moiré materials

Transition-metal dichalcogenide (TMD) bilayers are a new class of tunable moiré systems attracting interest as quantum simulators of strongly interacting electrons in two dimensions. In particular, recent theory predicts that the correlated insulator observed in WSe 2 /WS 2 at half filling is a charge-transfer insulator similar to cuprates and, upon further hole doping, exhibits a transfer of charge from anionlike to cationlike orbitals at different locations in the moiré unit cell. In this work, we demonstrate that in this doped charge-transfer insulator, tightly bound charge-2$\textit{e}$ excitations can form to lower the total electrostatic repulsion. This composite excitation, which we dub a trimer, consists of a pair of holes bound to a charge-transfer exciton. When the bandwidth of doped holes is small, trimers crystallize into insulating pair density waves at a sequence of commensurate doping levels. Further, when the bandwidth becomes comparable to the pair binding energy, itinerant holes and charge-2$\textit{e}$ trimers interact resonantly, leading to unconventional superconductivity similar to superfluidity in an ultracold Fermi gas near Feshbach resonance. Our theory is broadly applicable to strongly interacting charge-transfer insulators, such as WSe 2 /WS 2 or TMD homobilayers under an applied electric field.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Orientational Dependence of Cofacial Porphyrin–Quinone Electronic Interactions within the Strong Coupling Regime

We examine the relative magnitudes of electronic coupling HDA in two face-to-face rigid and diastereomeric (porphinato)zinc(II)–quinone (PZn–Q) as-semblies, 1β-ZnA and 1β-ZnB, in which the six quinonyl carbon atoms lie in virtually identical arrangements relative to the PZn plane at sub-van der Waals donor–acceptor (D–A) interplanar separations. Steady-state and time-resolved transient optical data and computational studies show that minor differences in relative D–A cofacial orientation give rise to disparate H DA magnitudes for both photoinduced charge separation (CS) and thermal charge recombination (CR). Here, time-dependent density functional theory (TDDFT) computations illuminate the nature of direct charge transfer states and the electronic structural factors that give rise to these differential H DA s. These data show more extensive mixing of locally excited (LE) and CS states in 1β-ZnA relative to 1β-ZnB and that these H DA differences track the magnitudes of electronic coupling matrix elements determined from steady-state electronic spectral data and thermal CR rate constants measured via pump–probe spectroscopy. Collectively, this work shows that electron transfer dynamics may be manipulated in cofacial D–A systems, even at sub-van der Waals contact, provided that conformational rigidity precludes structural fluctuations that modulate D–A interactions on the charge transfer time scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Probing earth-bound dark matter with nuclear reactors

Strongly-interacting dark matter can be accumulated in large quantities inside the Earth, and for dark matter particles in a few GeV mass range, it can exist in large quantities near the Earth’s surface. We investigate the constraints imposed on such dark matter properties by its upscattering by fast neutrons in nuclear reactors with subsequent scattering in nearby well-shielded dark matter detectors, schemes which are already used for searches of the coherent reactor neutrino scattering. We find that the existing experiments cover new parameter space on the spin-dependent interaction between dark matter and the nucleon. Similar experiments performed with research reactors, and lesser amount of shielding, may provide additional sensitivity to strongly-interacting dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Systematic analysis of transverse momentum distribution and non-extensive thermodynamics theory

A systematic analysis of transverse momentum distribution of hadrons produced in ultrarelativistic p+p and A+A collisions is presented. We investigate the effective temperature and the entropic parameter from the non-extensive thermodynamic theory of strong interaction. We conclude that the existence of a limiting effective temperature and of a limiting entropic parameter is in accordance with experimental data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Møller–Plesset and Density-Fixed Adiabatic Connections for a Model Diatomic System at Different Correlation Regimes

In recent years, adiabatic connection (AC) interpolations developed within density functional theory (DFT) have been found to provide good performances in the calculation of interaction energies when used with Hartree–Fock (HF) ingredients. The physical and mathematical reasons for such unanticipated performance have been clarified, to some extent, by studying the strong-interaction limit of the Møller–Plesset (MP) AC. In this work, we calculate both the MP and the DFT AC integrand for the asymmetric Hubbard dimer, which allows for a systematic investigation of different correlation regimes by varying two simple parameters in the Hamiltonian: the external potential, Δv, and the interaction strength, U. Notably, we find that, while the DFT AC integrand appears to be convex in the full parameter space, the MP integrand may change curvature twice. Furthermore, we discuss different aspects of the second-order expansion of the correlation energy in each AC, and we demonstrate why the derivative of the λ-dependent density in the MP AC at λ = 0 (i.e., at the HF density) is zero in the model. Concerning the strong-interaction limit of both ACs in the Hubbard dimer setting, we show that the asymptotic value of the MP AC, W ∞ HF , is lower than (or equal to) its DFT analogue, W ∞ KS , if the two are compared at a given density, just like in real space. Furthermore, we also show that this is not always the case if the two quantities are compared at a given external potential.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A Biomimetic Approach to New Adsorptive Hydrogen Storage Metal-Organic Frameworks

In the past decades, there has been an escalation of interest in the study of MOFs due to their fascinating structures and intriguing application potentials. Their exceptionally high surface areas, uniform yet tunable pore sizes, and well-defined adsorbate-MOF interaction sites make them suitable for hydrogen storage. Various strategies to increase the hydrogen capacity of MOFs, such as constructing pore sizes comparable to hydrogen molecules, increasing surface area and pore volume, utilizing catenation, and introducing coordinatively unsaturated metal centers (UMCs) have been widely explored to increase the hydrogen uptake of the MOFs. MOFs with hydrogen uptake approaching the DOE gravimetric storage goal under reasonable pressure but cryo- temperature (typically 77 K) were achieved. However, the weak interaction between hydrogen molecules and MOFs has been the major hurdle limiting the hydrogen uptake of MOFs at ambient temperature. Along the road, we have realized both high surface area and strong interaction between framework and hydrogen are equally essential for porous materials to be practically applicable in Hydrogen storage. Increasing the isosteric heats of adsorption for hydrogen through the introduction of active centers into the framework could have great potential on rendering the framework with strong interaction toward hydrogen. Approaches on increasing the surface areas and improving hydrogen affinity by optimizing size and structure of the pores and the alignment of active centers around the pores in frameworks have been pursued, for example: (a) the introduction of coordinatively UMC (represents a metal center missing multiple ligands) with potential capability of multiple dihydrogen-binding (Kubas type, non-dissociative) per UMC, (b) the design and synthesis of proton-rich MOFs in which a + H3 binds dihydrogen just like a metal ion does, and (c) the preparation of MOFs and PPNs with well aligned internal electric fields. We believe the accomplishments of this DOE supported research will greatly benefit the future pursuit of hydrogen storage materials. The ultimate goal to increase the gravimetric and volumetric hydrogen storage capacity to meet DOE targets for Light-Duty Vehicles is achievable.

08 HYDROGEN↗
DOE OSTI2019

RIKEN/RBRC Scientific Review Committee Meeting (Vol. 132)

The RIKEN BNL Research Center (RBRC) was established in April 1997 at Brookhaven National Laboratory*. It is funded by RIKEN, "Rikagaku Kenkyusho", of Japan and the U. S. Department of Energy’s Office of Science. The Memorandum of Understanding between RIKEN and BNL, initiated in 1997, has been renewed in 2002, 2007, 2012 and 2018. The Center is dedicated to the study of strong interactions, including spin physics, lattice QCD, and RHIC physics through the nurturing of a new generation of young physicists. The RBRC has an active workshop program on strong interaction physics with each workshop focused on a specific physics problem. For most of these workshops, the talks are made available on the RBRC website. To date there are over 116 proceedings volumes available. In 2017 RBRC celebrated its 20th anniversary since its inauguration in 1997. This was also the year of the 100th anniversary of RIKEN. The RBRC is well matured and moves into the new generation with dismantling of the PHENIX detector and construction of the new sPHENIX detector at RHIC. We are on track with growth plans in place. On April 1st 2017, Hideto En’yo, Director of RIKEN Nishina Center for Accelerator-Based Science, was named Acting Director of the RBRC, preceded by Samuel Aronson, Nicholas Samios and Tsung-Dao Lee.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Strong interlayer interactions in bilayer and trilayer moiré superlattices

Moiré superlattices constructed from transition metal dichalcogenides have demonstrated a series of emergent phenomena, including moiré excitons, flat bands, and correlated insulating states. All of these phenomena depend crucially on the presence of strong moiré potentials, yet the properties of these moiré potentials, and the mechanisms by which they can be generated, remain largely open questions. Here, we use angle-resolved photoemission spectroscopy with submicron spatial resolution to investigate an aligned WS 2 /WSe 2 moiré superlattice and graphene/WS 2 /WSe 2 trilayer heterostructure. Our experiments reveal that the hybridization between moiré bands in WS 2 /WSe 2 exhibits an unusually large momentum dependence, with the splitting between moiré bands at the Γ point more than an order of magnitude larger than that at K point. In addition, we discover that the same WS 2 /WSe 2 superlattice can imprint an unexpectedly large moiré potential on a third, separate layer of graphene (g/WS 2 /WSe 2 ), suggesting new avenues for engineering two-dimensional moiré superlattices.

36 MATERIALS SCIENCE↗
NASA NTRS1989

The far-infrared structure of the luminous interacting galaxy Arp 299

The strongly interacting galaxies NGC 3690 and IC 694 (or Arp 299) exhibit extensive star formation, a large infrared luminosity, and possible nuclear activity. To determine the origin of the infrared luminosity in this system, high-resolution far-infrared profiles have been obtained in which two distinct sources can clearly be discerned; these observations reveal that 60 percent of the far-infrared luminosity comes from an unresolved source in the center of IC 694, with the remaining 40 percent originating in a compact source in NGC 3690. A new high-resolution 20-micron image of the Arp 299 system is compared with the far-infrared profiles, revealing that NGC 3690 is substantially hotter than IC 694 in the thermal infrared; the observed temperature gradient is opposite to that which is expected if the putative active nucleus in IC 694 generates a significant fraction of the total luminosity.

Joy, Marshall↗
NASA NTRS1974

International Cosmic Ray Conference, 13th, University of Denver, Denver, Colo., August 17-30, 1973, Proceedings. Volumes 3 & 4

Volumes 3 and 4 contain papers dealing with measurements of muons and neutrinos, ultrahigh-energy interactions, extensive air showers, and details of experimental techniques and instrumentation. Attention is given to the zenith angle and underground depth dependence of cosmic ray muons, muon charge ratios and energy spectra, extraterrestrial sources of neutrinos, strong interaction data from new accelerators, searches for quarks and other new particles, hadron fluxes and propagation in the atmosphere, high-energy gamma-ray measurements, and new models and theories for high-energy strong interactions. Extensive air showers are examined in papers dealing with associated Cerenkov light, radio emission, structure, the hadron content, and primaries. The design, operation, and performance of various detectors are explained. Individual items are announced in this issue.

Source record↗
NASA NTRS1982

Analysis of separated boundary-layer flows

A method for predicting the strong interaction between the viscous and inviscid flows which occurs in flow separation is reviewed. An inverse boundary-layer procedure approximately accounts for normal pressure gradients that may be important in strongly interacting flows. Transformed boundary-layer equations are written in which the pressure gradient is set equal to the inviscid pressure gradient. As the boundary-layer edge is approached and the viscous shear and heat conduction terms vanish, the viscous flow solution is required to asymptotically approach the inviscid solution over the generalized displacement body. Attention is then focused on viscous-inviscid interacting flows with a first-order viscous formulation and constant pressure across the boundary layer. Results obtained with this procedure are presented for: (1) transitional separation bubbles near an airfoil leading edge, (2) subsonic boattail separated turbulent flow, and (3) transonic turbulent shock wave boundary-layer interaction on an axisymmetric bump configuration.

Carter, J. E.↗
DOE OSTI2014

Excitation picture of an interacting Bose gas

Atomic Bose–Einstein condensates (BECs) can be viewed as macroscopic objects where atoms form correlated atom clusters to all orders. Therefore, the presence of a BEC makes the direct use of the cluster-expansion approach–lucrative e.g. in semiconductor quantum optics–inefficient when solving the many-body kinetics of a strongly interacting Bose. An excitation picture is introduced with a nonunitary transformation that describes the system in terms of atom clusters within the normal component alone. The nontrivial properties of this transformation are systematically studied, which yields a cluster-expansion friendly formalism for a strongly interacting Bose gas. Its connections and corrections to the standard Hartree–Fock–Bogoliubov approach are discussed and the role of the order parameter and the Bogoliubov excitations are identified. The resulting interaction effects are shown to visibly modify number fluctuations of the BEC. Even when the BEC has a nearly perfect second-order coherence, the BEC number fluctuations can still resolve interaction-generated non-Poissonian fluctuations. - Highlights: • Excitation picture expresses interacting Bose gas with few atom clusters. • Semiconductor and BEC many-body investigations are connected with cluster expansion. • Quantum statistics of BEC is identified in terms of atom clusters. • BEC number fluctuations show extreme sensitivity to many-body correlations. • Cluster-expansion friendly framework is established for an interacting Bose gas.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗