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DOE OSTI2021

Emergent properties at oxide interfaces controlled by ferroelectric polarization

Abstract Ferroelectric materials are characterized by the spontaneous polarization switchable by the applied fields, which can act as a “gate” to control various properties of ferroelectric/insulator interfaces. Here we review the recent studies on the modulation of oxide hetero-/homo-interfaces by ferroelectric polarization. We discuss the potential applications of recently developed four-dimensional scanning transmission electron microscopy and how it can provide insights into the fundamental understanding of ferroelectric polarization-induced phenomena and stimulate future computational studies. Finally, we give the outlook for the potentials, the challenges, and the opportunities for the contribution of materials computation to future progress in the area.

Chemistry↗

DOE OSTI2015

A generalized reconstruction framework for unconventional PET systems

Purpose: Quantitative estimation of the radionuclide activity concentration in positron emission tomography (PET) requires precise modeling of PET physics. The authors are focused on designing unconventional PET geometries for specific applications. This work reports the creation of a generalized reconstruction framework, capable of reconstructing tomographic PET data for systems that use right cuboidal detector elements positioned at arbitrary geometry using a regular Cartesian grid of image voxels. Methods: The authors report on a variety of design choices and optimization for the creation of the generalized framework. The image reconstruction algorithm is maximum likelihood-expectation–maximization. System geometry can be specified using a simple script. Given the geometry, a symmetry seeking algorithm finds existing symmetry in the geometry with respect to the image grid to improve the memory usage/speed. Normalization is approached from a geometry independent perspective. The system matrix is computed using the Siddon’s algorithm and subcrystal approach. The program is parallelized through open multiprocessing and message passing interface libraries. A wide variety of systems can be modeled using the framework. This is made possible by modeling the underlying physics and data correction, while generalizing the geometry dependent features. Results: Application of the framework for three novel PET systems, each designed for a specific application, is presented to demonstrate the robustness of the framework in modeling PET systems of unconventional geometry. Three PET systems of unconventional geometry are studied. (1) Virtual-pinhole half-ring insert integrated into Biograph-40: although the insert device improves image quality over conventional whole-body scanner, the image quality varies depending on the position of the insert and the object. (2) Virtual-pinhole flat-panel insert integrated into Biograph-40: preliminary results from an investigation into a modular flat-panel insert are presented. (3) Plant PET system: a reconfigurable PET system for imaging plants, with resolution of greater than 3.3 mm, is shown. Using the automated symmetry seeking algorithm, the authors achieved a compression ratio of the storage and memory requirement by a factor of approximately 50 for the half-ring and flat-panel systems. For plant PET system, the compression ratio is approximately five. The ratio depends on the level of symmetry that exists in different geometries. Conclusions: This work brings the field closer to arbitrary geometry reconstruction. A generalized reconstruction framework can be used to validate multiple hypotheses and the effort required to investigate each system is reduced. Memory usage/speed can be improved with certain optimizations.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2016

Microbiome-wide association studies link dynamic microbial consortia to disease

Rapid advances in DNA sequencing, metabolomics, proteomics and computational tools are dramatically increasing access to the microbiome and identification of its links with disease. In particular, time-series studies and multiple molecular perspectives are facilitating microbiome-wide association studies, which are analogous to genome-wide association studies. Early findings point to actionable outcomes of microbiome-wide association studies, although their clinical application has yet to be approved. An appreciation of the complexity of interactions among the microbiome and the host's diet, chemistry and health, as well as determining the frequency of observations that are needed to capture and integrate this dynamic interface, is paramount for developing precision diagnostics and therapies that are based on the microbiome.

Gilbert, Jack A.↗

DOE OSTI2026

What Is the Agent Doing? Visualizing Agentic AI Querying Workflows

We explore how visualizations can help users understand what an AI agent is doing as it builds and runs queries over data. As part of the LinkQ system, a natural language interface for querying knowledge graphs with a large language model (LLM), we designed two complementary views: A State Diagram that shows where the agent is within a larger workflow, and a Live Action Display that gives real-time updates about the agent's current task. In a study with 14 practitioners, we found that these visuals helped participants build stronger mental models of the agent's behavior while also increasing their confidence in the system. However, we also observed that users sometimes trusted incorrect outputs simply because the agent appeared to be doing the "right" thing. Our findings point to both the value and risk of visualizing agent behavior in interactive AI systems.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2022

An automated fast neutron computed tomography instrument with on-line focusing for non-destructive evaluation

A fast neutron tomography imaging instrument has been designed, built, and tested at The Ohio State University 500 kW Research Reactor on a fast neutron beamline with a peak neutron flux ≈5.4 × 107 n·cm−2·s−1 at 1.6 MeV median neutron energy. The instrument and beamline are also configurable for thermal neutron imaging. The imaging apparatus is composed of a lens coupled, water-cooled Electron Multiplying Charge Coupled Device camera, a front-surface mirror, and a high light yield plastic Polyvinyl toluene scintillator. The instrument sits on a mobile cart. A total of 5 motion-control stages are built into the system for XYZ and rotational degrees of freedom for sample positioning; the fifth stage fine tunes the focal distance between the camera and the scintillator to achieve on-line focusing. A Python code with a user-friendly graphical user interface controls the fully automated image acquisition, not requiring user interaction, yet facilitating tracking of the image acquisition. A complete fast neutron computed tomography dataset with 360 projections requires less than 3 h, with 30 s per projection. On-line focusing is accomplished with a commercial, off-the-shelf, dielectrically actuated liquid lens. Finally, tomographic reconstructions are visualized using the Livermore Tomography Tools software package. The effective pixel size (width and height) is ≈0.1058 mm, yielding a minimum voxel size of 0.1058 × 0.1058 × 0.1058 mm3, and produces a spatial resolution of 231 μm when calculated from knife-edge measurements.

Bisbee, M. G. (ORCID:0000000313466697)↗

DOE OSTI2026

Photoresponsive Rotaxanes Switch Lipid Bilayer Neuromorphic Behavior with Light

A rotaxane consisting of a macrocycle ring with two azobenzene units mechanically interlocked onto a bolaamphiphilic axle was incorporated into droplet interface bilayers (DIBs). The azobenzene groups on the ring underwent quasi-reversible, photoisomerization-induced cycling between 1-E and 1-Z configurations when irradiated with 370 and 467 nm light, respectively, enabling programmable access to different history-dependent electrical behaviors from the same membrane. In the 1-E configuration, bilayers exhibited type-IIactive memristance that coincided with increasingly elevated ionic conduction, associated with progressively enhanced bilayer permeability during voltage cycling. In the 1-Z configuration, bilayers displayed type-I, passive memcapacitive behavior, reflecting tighter lipid packing and reduced ionic permeability. Photoswitching also yielded a nonvolatile, photoresponsive memcapacitor that could be modulated repetitively with negligible loss, likely via reversible changes in membrane thickness. Concurrent ohmic leakage currents across the membrane were less than 0.3%. These results agree with previous studies with increasing membrane permeability using photoswitchable rotaxanes and provide new insights into the coupling between volatile and nonvolatile memcapacitance during photoisomerization. More broadly, they demonstrate a new strategy for the manipulation of neuromorphic behaviors in soft materials using light, with implications for brain-inspired computation and sensing.

droplet interface bilayers↗

DOE OSTI2014

High-resolution X-ray diffraction analysis of Al{sub x}Ga{sub 1−x}N/In{sub x}Ga{sub 1−x}N/GaN on sapphire multilayer structures: Theoretical, simulations, and experimental observations

The work presents a comparative study on the effects of In incorporation in the channel layer of AlGaN/GaN type-II heterostructures grown on c-plane sapphire by Plasma Assisted Molecular Beam Epitaxy. The structural characterizations of these samples were performed by High-Resolution X-Ray Diffraction (HRXRD), X-ray Reflectivity (XRR), Field Emission Scanning Electron Microscopy, and High Resolution Transmission Electron Microscopy. The two-dimensional electron gas in the AlGaN/GaN and AlGaN/InGaN interface was analyzed by electrochemical capacitance voltage and compared with theoretical results based on self-consistent solution of Schördinger–Poisson equations. The carrier profile shows enhanced confinement in InGaN channel (1.4393 × 10{sup 13} cm{sup −2} compared to 1.096 × 10{sup 13} cm{sup −2} in GaN). On the basis of HRXRD measurements, the stress-strain of the layers was examined. The c- and a-lattice parameters of the epilayers as well as in-plane and out-of plane strains were determined from the ω-2θ for symmetric scan and ω-Xθ (X represents the coupling coefficient) for asymmetric scan. Strain, tilt, and correlation lengths were calculated from Williamson–Hall plots, whereas stress was examined from modified plot of the same data assuming Uniform Stress Deformation Model. Moreover, the twist angle was measured from skew symmetric scan of (102), (103), and (105) plane along with (002) symmetric plane. The composition and strain/relaxation state of the epilayers were observed in detail by reciprocal space mapping (RSM). The symmetric (002) triple axis RSM and asymmetric (105 and 114) double axis RSM of grazing incidence and exit geometry were carried out on each sample. The defect density was measured from HRXRD curves of skew symmetric (002) and (102) reflection plane. The Al and In mole fraction and strain states of the layers were calculated by fitting the experimental curves with computer simulations and compared with theoretical findings based on elastic theory. The thicknesses of the layers and roughness of the interfaces were measured from simulation of the nominal structure by fitting with XRR experimental curves. The HRXRD measured thicknesses of the layers were further confirmed by cross sectional electron micrographs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

A simple grand canonical approach to compute the vapor pressure of bulk and finite size systems

In this article we introduce a simple grand canonical screening (GCS) approach to accurately compute vapor pressures from molecular dynamics or Monte Carlo simulations. This procedure entails a screening of chemical potentials using a conventional grand canonical scheme, and therefore it is straightforward to implement for any kind of interface. The scheme is validated against data obtained from Gibbs ensemble simulations for water and argon. Then, it is applied to obtain the vapor pressure of the coarse-grained mW water model, and it is shown that the computed value is in excellent accord with the one formally deduced using statistical thermodynamics arguments. Finally, this methodology is used to calculate the vapor pressure of a water nanodroplet of 94 molecules. Interestingly, the result is in perfect agreement with the one predicted by the Kelvin equation for a homogeneous droplet of that size.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Numerical comparison of bubbling in a waste glass melter

Radioactive tank waste is scheduled for vitrification at the Hanford Tank Waste Treatment and Immobilization Plant, also known as the Vit Plant, being constructed at the Hanford Site. Testing of the pilot-scale, joule-heated DuraMelter 1200 at the Vitreous State Laboratory has shown that bubbling increases the melt rate, and as a result, melter throughput. Computational fluid dynamics (CFD) models of this pilot-scale waste glass melter were developed to improve our understanding of the processes that occur within the melter to aid in process optimization and troubleshooting of the Vit Plant melters. Unfortunately, model validation is complicated by the difficulty of obtaining suitable experimental data for operational melters attributed to the large-scale, radioactivity and high temperatures at which these melters are operated. This study focuses on confirming the fidelity of the CFD models to accurately reproduce the bubbling behavior. Because of the paucity of experimental data at the resolution required for CFD validation, a code-to-code comparison was used to evaluate two common approaches for simulating flows of immiscible fluids on numerical grids and resolving multiphase interfaces. Here, the volume of fluid and level set methods are used to track the dynamically evolving interfaces between the molten glass and the air bubbles. To aid in the verification of the results of these codes, a comparison of the bubble behavior, growth, and frequency of bubble generation are presented and a grid convergence study is performed for the two approaches. In addition to comparing the numerical results to available experimental data and observations from pilot-scale testing, the results are evaluated in relation to laboratory experiments with bubbles injected into viscous fluids, empirical correlations obtained from the published literature, and the basic laws of fluid dynamics. Furthermore, the results of this work can assist in validating waste glass melter models and provide a better understanding of the flow patterns within the WTP melters.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2018

Enhancing Clean Energy Innovation Ecosystem Discovery Tool

During March 2016, the DOE’s Office of Energy Policy and Systems Analysis (EPSA) sought a methodology to identify and quantify the strength of the existing clean energy innovation ecosystems (IE) in the U.S. and their characteristics. Oak Ridge National Lab (ORNL) did a pilot study (Phase 1) and demonstrated the feasibility of an application comprised of natural language processing, link analysis, and other computational techniques to transform text and numerical data into metrics on clean energy innovation activity and geography. The data-collection, ingest and analytics pipelines were combined with an advanced user interface, together known as the Ecosystem Discovery Tool, to enhance DOE’s understanding of existing geographic innovation clusters. During Phase 2 of this project, this tool has been further enhanced by integrating new data sets and through backend software architecture changes, validation and bug fixing, making it a much more robust and powerful application. The tool’s user interface is a lot more intuitive, which enables a user to visualize the IE rankings for various geographic regions(CBSA, state level) for different clean energy technologies and seek automated insights. ORNL also created a DOE-specific dashboard that allows the user to visualize and analyze federal funding from various offices including Energy Efficiency and Renewable Energy(EERE), Office of Electricity(OE), Fossil Energy(FE), and Nuclear Energy(NE). During Phase 1 of this project, EPSA defined a clean energy innovation ecosystem as the overlap of five Ecosystem Components: 1) nascent clean energy Indicators, 2) investors, 3) enabling environment, 4) networking assets and 5) large companies. EPSA and ORNL worked together to collect data for each component: 1) small and medium companies, ARPA-E awardees, SBIR awardees, patents, publications, ERCs for Nascent Clean Energy Indicators; 2) qualified investors; 3) the Clean Edge Policy Index/DSIRE for the Enabling Environment; 4) universities, national laboratories, ERCs and incubators for Networking Assets; and 5) large companies and a subset of the Russell 1000 list for Large Companies. The ORNL team created a visual tool based on Tableau that integrated ecosystem component data to score, rank and map IEs. The tool was created with the flexibility to allow the user to choose the weights of each of the five ecosystem components and the subcomponents. This flexibility allows the user to visualize different subsets and to use the underlying data for different types of analysis. During Phase 2 of this project, the backend database and computation process have undergone major changes to provide a much more refined user-interface and added new features into the scoring algorithm. This phase also involved addition of newer databases such as a list of Energy Research Centers (ERC) ,DSIRE, and funding data from EERE, FE, NE, and OE to provide more granular information and more accurate/better quantification.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2016

Phonon Transport at the Interfaces of Vertically Stacked Graphene and Hexagonal Boron Nitride Heterostructures

Hexagonal boron nitride (h-BN) is a substrate for graphene based nano-electronic devices. We investigate the ballistic phonon transport at the interface of vertically stacked graphene and h-BN heterostructures using first principles density functional theory and atomistic Green's function simulations considering the influence of lattice stacking. We compute the frequency and wave-vector dependent transmission function and observe distinct stacking-dependent phonon transmission features for the h-BN/graphene/h-BN sandwiched systems. We find that the in-plane acoustic modes have the dominant contributions to the phonon transmission and thermal boundary conductance (TBC) for the interfaces with the carbon atom located directly on top of the boron atom (C–B matched) because of low interfacial spacing. The low interfacial spacing is a consequence of the differences in the effective atomic volume of N and B and the difference in the local electron density around N and B. For the structures with the carbon atom directly on top of the nitrogen atom (C–N matched), the spatial distance increases and the contribution of in-plane modes to the TBC decreases leading to higher contributions by out-of-plane acoustic modes. We find that the C–B matched interfaces have stronger phonon–phonon coupling than the C–N matched interfaces, which results in significantly higher TBC (more than 50%) in the C–B matched interface. The findings in this study will provide insights to understand the mechanism of phonon transport at h-BN/graphene/h-BN interfaces, to better explain the experimental observations and to engineer these interfaces to enhance heat dissipation in graphene based electronic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2014

PhytoPET, PhytoBeta and PhytoSPECT: Radioisotope Imaging Systems Being Developed for Plant Biology Research

The Radiation Detector and Imaging Group at Thomas Jefferson National Accelerator Facility (Jefferson Lab) is developing radioisotope imaging systems designed and constructed to facilitate plant biology studies at the Duke University Phytotron. The imaging systems utilize nuclear medicine imaging methodologies used in positron emission tomography (PET) and single photon emission computed tomography (SPECT) but designed specifically for plant biology. The range of plant shapes and the environmental conditions in plant growth chambers pose a technological challenge. Description: Jefferson Lab is collaborating with the Duke University Phytotron and the Triangle Universities Nuclear Laboratory (TUNL) in the construction and operation of PhytoPET and PhytoBeta (for direct beta particle detection) for plant and/or microbe imaging. The TUNL tandem Van de Graaff accelerator (maximum terminal voltage of 10 MV) has been used to generate 11C and 13N for plant biology research. The PhytoPET and PhytoBeta have been used with 11C as a 11CO2 tracer for plant ecophysiology imaging with corn, poplar, oak and barley utilizing technologies developed for nuclear physics research and nuclear medicine. The imaging detectors are based on position sensitive photomultiplier tubes coupled to scintillators. Additionally, the collaboration is investigating a methodology using single photon emitting radioisotope tracers for imaging the distribution of molecular compounds of interest in the rhizosphere, the interface between root and soil, without disturbing the root or soil habitat. Plans are underway to develop a single photon emission computed tomography (SPECT) system (PhytoSPECT) to image the bio-distribution of fungi in association with a host plant's roots. In addition to a description of the technology an overview will be given of the application of PhytoPET, PhytBeta and PhytoSPECT to plant biology research at Duke University. Conclusions: We have developed and used radioisotope imaging technologies based on PET and SPECT to visualize plant function in changing environments. There are many opportunities to provide radioisotope based imaging tools for plant ecophysiology imaging. Keywords: radioisotope detection, plant biology, carbon-11, accelerator produced isotopes

Weisenberger, Andrew↗

DOE OSTI2015

Human Factors and Technical Considerations for a Computerized Operator Support System Prototype

A prototype computerized operator support system (COSS) has been developed in order to demonstrate the concept and provide a test bed for further research. The prototype is based on four underlying elements consisting of a digital alarm system, computer-based procedures, PI&D system representations, and a recommender module for mitigation actions. At this point, the prototype simulates an interface to a sensor validation module and a fault diagnosis module. These two modules will be fully integrated in the next version of the prototype. The initial version of the prototype is now operational at the Idaho National Laboratory using the U.S. Department of Energy’s Light Water Reactor Sustainability (LWRS) Human Systems Simulation Laboratory (HSSL). The HSSL is a full-scope, full-scale glass top simulator capable of simulating existing and future nuclear power plant main control rooms. The COSS is interfaced to the Generic Pressurized Water Reactor (gPWR) simulator with industry-typical control board layouts. The glass top panels display realistic images of the control boards that can be operated by touch gestures. A section of the simulated control board was dedicated to the COSS human-system interface (HSI), which resulted in a seamless integration of the COSS into the normal control room environment. A COSS demonstration scenario has been developed for the prototype involving the Chemical & Volume Control System (CVCS) of the PWR simulator. It involves a primary coolant leak outside of containment that would require tripping the reactor if not mitigated in a very short timeframe. The COSS prototype presents a series of operator screens that provide the needed information and soft controls to successfully mitigate the event.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2016

Multigroup Transport Equations Derived via Homogeneity and Isotropy Restoration Theory

The multigroup neutron transport calculation at a cell-level or assembly-level is a key step in conventional deterministic reactor analysis. As the computing power grows, it is contemplated that the multigroup transport equation itself be used in whole-core calculation. While the continuous-energy transport equation is derived straightforwardly and rigorously, the multigroup transport equation currently in use involves several approximations during its derivation. Recently, we proposed the Homogeneity and Isotropy Restoration (HIRE) theory in a preliminary form for deriving a multigroup transport equation that maintains angle-independence in the total cross section and homogeneity in the material region (originally each material region is usually homogeneous by design). As a byproduct, only the isotropic scattering term remained, which also relieved the computational burden significantly. In the Homogeneity and Isotropy Restoration (HIRE) theory, we introduced a discontinuity factor in the form of partial current discontinuity factor (PCDF) at the material interface. In this paper, we elaborate on the HIRE theory and apply it to several typical pin-cell problems. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Investigating Scientific Workload Acceleration using BlueField SmartNICs [Slides]

Modern computing platforms whose workloads generate large amounts of network traffic, such as cloud and HPC systems, often suffer from performance bottlenecks associated with the network interface. In order to alleviate the effects of this obstacle, a new generation of accelerators known as ‘SmartNICs’, which are designed to offload low level networking tasks from the processor into the NIC, have emerged.

42 ENGINEERING↗

DOE OSTI2020

In-plane selective area InSb–Al nanowire quantum networks

Abstract Strong spin–orbit semiconductor nanowires coupled to a superconductor are predicted to host Majorana zero modes. Exchange (braiding) operations of Majorana modes form the logical gates of a topological quantum computer and require a network of nanowires. Here, we utilize an in-plane selective area growth technique for InSb–Al semiconductor–superconductor nanowire networks. Transport channels, free from extended defects, in InSb nanowire networks are realized on insulating, but heavily mismatched InP (111)B substrates by full relaxation of the lattice mismatch at the nanowire/substrate interface and nucleation of a complete network from a single nucleation site by optimizing the surface diffusion length of the adatoms. Essential quantum transport phenomena for topological quantum computing are demonstrated in these structures including phase-coherence lengths exceeding several micrometers with Aharonov–Bohm oscillations up to five harmonics and a hard superconducting gap accompanied by 2 e -periodic Coulomb oscillations with an Al-based Cooper pair island integrated in the nanowire network.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Multi-solid and multi-fluid diffuse interface model: Applications to dynamic fracture and fragmentation

We extend the model of diffuse solid–fluid interfaces developed earlier by authors of this paper to the case of arbitrary number of interacting hyperelastic solids. Plastic transformations of solids are taken into account through a Maxwell type model. The specific energy of each solid is given in separable form: it is the sum of a hydrodynamic part of the energy depending only on the density and the entropy, and an elastic part of the energy which is unaffected by the volume change. It allows us to naturally pass to the fluid description in the limit of vanishing shear modulus. In spite of a large number of governing equations, the model has a quite simple mathematical structure: it is a duplication of a single visco-elastic model. The model is well posed both mathematically and thermodynamically: it is hyperbolic and compatible with the second law of thermodynamics. The resulting model can be applied in the situations involving an arbitrary number of fluids and solids. In particular, we show the ability of the model to describe spallation and penetration phenomena occurring during high velocity impacts.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

MCNPs Easy Sources for (α,n) (MESA):Verification with Sources4c

MESA is intended to be a direct re-implementation of the algorithms documented in the Sources manual in C++. However, some fundamental changes to the computational structure and logic were made to avoid the use of goto, require consistency in input definition, and reduce computational approximations in later steps of three-layer problems. In addition, MESA uses α-decay information from ISC libraries (based on ENDF). In most cases, differences between Sources4c and MESA are dominated by differences in decay energy spectra and intensities. To verify this we have reproduced 6 problems that are documented examples or samples in Sources4c. These problems cover the three types of problems MESA currently supports: homogeneous, interface, and three-layer.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗