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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Enhancement of magnetodielectric coupling in 6H-perovskites Ba 3 R Ru 2 O 9 for heavier rare-earth cations ( R = Ho , Tb )

The role of rare-earth ( R ) ions in magnetodielectric (MD) coupling is always intriguing and markedly different for different systems. Although many reports are available concerning this aspect in frustrated 3 d -transition metal oxides, no such reports exist on higher d ( 4 d /5 d )-orbital based systems due to the rare availability of highly insulating 4 d /5 d systems. Here, we systematically investigated the magnetic, dielectric, ferroelectric, and magnetodielectric behavior of the 6H-perovskites Ba 3 R Ru 2 O 9 for different R -ions, namely R = Sm , Tb , and Ho, which magnetically order at 12, 9.5, and 10.2 K, respectively. For R = Tb and Ho, the temperature and magnetic-field-dependent complex dielectric constant traces the magnetic features, which manifests MD coupling in this system. A weak magnetic-field ( H ) induced transition is observed for ~ 30 kOe , which is clearly captured in H -dependent dielectric measurements. No MD coupling is observed for Ba 3 SmRu 2 O 9 . The MD coupling is enhanced by a factor of 3 and 20 times for R = Tb and Ho, respectively, when compared to that of the Nd-counterpart. Here, these results evidence the gradual enhancement of MD coupling with the introduction of heavier R -ions in this series, which is attributed to their larger moment values. Our investigation establishes dominating 4 d (Ru)-4ƒ( R ) magnetic correlation in this series for the heavier R -members.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Tuning the interlayer coupling in La 0.7 Sr 0.3 Mn 0.95 Ru 0.05 O 3 / LaNiO 3 multilayers with perpendicular magnetic anisotropy

In ferromagnetic oxide epitaxial multilayers, magnetic properties and interlayer coupling are determined by a variety of factors. Beyond the contribution of interlayer exchange coupling, strain and interfacial effects, such as structural reconstructions or charge transfer, play significant roles, resulting in complex magnetic behavior. In this study, the interlayer coupling of ferromagnetic La 0.7 ⁢Sr 0.3⁢ Mn 0.95 ⁢Ru 0.05 ⁢O 3 (LSMRO) layers (8 nm thick) was investigated, when separated by epitaxial spacers of paramagnetic metallic LaNiO 3 (LNO), in stacks exhibiting perpendicular magnetic anisotropy. By varying the thickness of the spacer, it was found that the coupling between two LSMRO layers changes from antiferromagnetic (with a 4-unit-cell-thick LNO spacer) to ferromagnetic (with a 6-unit-cell-thick LNO spacer). For multilayers comprising five LSMRO layers and a 4-unit-cell-thick LNO spacer, the antiferromagnetic coupling was preserved. However, the effective magnetic anisotropy changed, causing the magnetization to cant more towards the in-plane direction. Further, this behavior was corroborated by X-ray magnetic circular dichroism (XMCD) investigations at the Mn and Ni L 3 edges. The XMCD results indicated that the 4-unit-cell-thick LNO spacer in the multilayer become magnetically ordered, closely following the magnetization of adjacent LSMRO layers.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Structure and dynamics of open-shell nuclei from spherical coupled-cluster theory

We extend the spherical coupled-cluster ab initio method for open-shell nuclei where two nucleons are removed from a shell subclosure. Following the recent implementation of the two-particle-attached approach [Phys. Rev. C 110, 044306 (2024)], we focus on the two-particle-removed method. Using the equations-of-motion framework, we address both nuclear structure and dipole response functions by coupling coupled-cluster theory with the Lorentz integral transform technique. We perform calculations using chiral interactions, including three-nucleon forces, and estimate many-body uncertainties by comparing different coupled-cluster truncation schemes. Here, we validate our approach by studying ground-state energies, excited states, and electric dipole polarizabilities in the oxygen and calcium isotopic chains. For binding energies and selected low-lying excited states, we achieve an accuracy comparable to that of the established closed-shell coupled-cluster theory and generally agree with experiment. Finally, we underestimate experimental data for electric dipole polarizabilities, particularly in calcium isotopes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Multi-phase Coupled and Integrated Inductors for Critical Conduction Mode Totem-Pole PFC Converter

Coupled inductor has been widely used in voltage regulator (VR) applications for many years because it can help reducing current ripple and improving transient performance. In this paper, the coupled inductor concept is applied to interleaved totem-pole critical conduction mode (CRM) PFC converter for 6.6kW on board battery charger. The difference between negative coupling and positive coupling will be discussed. The benefit of positive coupling for battery charger will be presented, such as reducing switching frequency range and reducing input differential mode (DM) noise. In addition, balance technique is applied to help minimize common mode (CM) noise. Last but not least, the inductor will be integrated into PCB winding with a little sacrifice on loss. With the inductor integration, the converter can avoid labor intensive production and achieve fully automated manufacture. The analysis is verified by both simulation and experiment.

Yang, Yuchen↗
DOE OSTI2019

Coupled Inductor Design for Interleaved Three-level Active Neutral Point Clamped Inverters Considering EMI Noise Reduction

This paper presents the coupled inductor design for interleaved three-level active neutral point clamped (ANPC) inverter considering electromagnetic interference (EMI) noise reduction. Compared to two-level case, the scenarios involved in the three-level space vector modulation (SVM) are more complicated when analyzing the volt-seconds of the coupled inductor for paralleled three-level inverter. At system level, the purpose of converter interleaving is to reduce EMI noise and ripple current in most applications, and coupled inductor design should consider the needs of EMI noise reduction and EMI filter design. These issues are discussed in this paper. The relationship between circulating current and EMI noise is illustrated. EMI filter corner frequency as a function of interleaving angle is analytically derived, and optimal interleaving angle for maximum common-mode (CM) filter and differential-mode (DM) filter corner frequencies is discussed. Coupled inductor design methodology for interleaved three-level inverters with SVM is then presented. Experiments on two interleaved ANPC inverters are conducted. The results verify the coupled inductor design. With the derived optimal interleaving angle, the CM and DM EMI noise are significantly reduced.

Chen, Ruirui↗
DOE OSTI2016

In-Staging Data Placement for Asynchronous Coupling of Task-Based Scientific Workflows, In: 2016 Second International Workshop on Extreme Scale Programming Models and Middlewar (ESPM2)

Coupled application workflows composed of applications implemented using task-based models present new coupling and data exchange challenges, due to the asynchronous interaction and coupling behaviors between tasks of the component applications. In this paper, we present an adaptive data placement approach that addresses these challenges by dynamically adjusting to the asynchronous coupling patterns. Specifically, it places data across a set of staging cores/nodes with an awareness of the application-specific data locality requirements and the runtime task executions at these staging cores/nodes, with the goal of reducing end-to-end execution time and data movement overhead of the workflow. We experimentally demonstrate the effectiveness of our approach on the Titan Cray XK7 system using representative data coupling patterns derived from current scientific workflows. The evaluation demonstrates that our approach efficiently improves performance by reducing the time-to-solution and increasing the quality of insights for scientific discovery.

Computer Science↗
DOE OSTI2018

Using a Dynamic Substructuring Approach to Model the Effects of Acoustic Damping in Coupled Acoustic-Structure Systems

Acoustic-structure coupling can substantially alter the frequency response of air-filled structures. Coupling effects typically manifest as two resonance peaks at frequencies above and below the resonant frequency of the uncoupled structural system. In this study, a dynamic substrucuring approach is applied to a simple acoustic-structure system to expose how the system response depends on the damping in the acoustic subsystem. Parametric studies show that as acoustic damping is increased, the frequencies and amplitudes of the coupled resonances in the structural response undergo a sequence of changes. For low levels of acoustic damping, the two coupled resonances have amplitudes approximating the corresponding in vacuo resonance. As acoustic damping is increased, resonant amplitudes decrease dramatically while the frequency separation between the resonances tends to increase slightly. When acoustic damping is increased even further, the separation of the resonant frequencies decreases below their initial separation. Finally, at some critical value of acoustic damping, one of the resonances abruptly disappears, leaving just a single resonance. Counterintuitively, increasing acoustic damping beyond this point tends to increase the amplitude of the remaining resonance peak. Finally, these results have implications for analysts and experimentalists attempting to understand, mitigate, or otherwise compensate for the confounding effects of acoustic-structure coupling in fluid-filled test structures.

42 ENGINEERING↗
DOE OSTI2024

Constraining effects of aerosol-cloud interaction by accounting for coupling between cloud and land surface

Aerosol-cloud interactions (ACIs) are vital for regulating Earth’s climate by influencing energy and water cycles. Yet, effects of ACI bear large uncertainties, evidenced by systematic discrepancies between observed and modeled estimates. This study quantifies a major bias in ACI determinations, stemming from conventional surface or space measurements that fail to capture aerosol at the cloud level unless the cloud is coupled with land surface. We introduce an advanced approach to determine radiative forcing of ACI by accounting for cloud-surface coupling. By integrating field observations, satellite data, and model simulations, this approach reveals a drastic alteration in aerosol vertical transport and ACI effects caused by cloud coupling. In coupled regimes, aerosols enhance cloud droplet number concentration across the boundary layer more homogeneously than in decoupled conditions, under which aerosols from the free atmosphere predominantly affect cloud properties, leading to marked cooling effects. Our findings spotlight cloud-surface coupling as a key factor for ACI quantification, hinting at potential underassessments in traditional estimates.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Coupled Air Quality and Boundary-Layer Meteorology in Western U.S. Basins during Winter: Design and Rationale for a Comprehensive Study

The wintertime episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys worldwide. These episodes often arise following development of persistent cold-air pools (PCAPs) that limit mixing and modify chemistry. While field campaigns targeting either basin meteorology or wintertime pollution chemistry have been conducted, coupling between interconnected chemical and meteorological processes remains an insufficiently studied research area. Gaps in understanding the coupled chemical–meteorological interactions that drive high-pollution events make identification of the most effective air-basin specific emission control strategies challenging. To address this, a September 2019 workshop occurred with the goal of planning a future research campaign to investigate air quality in western U.S. basins. Approximately 120 people participated, representing 50 institutions and five countries. Workshop participants outlined the rationale and design for a comprehensive wintertime study that would couple atmospheric chemistry and boundary layer and complex-terrain meteorology within western U.S. basins. Participants concluded the study should focus on two regions with contrasting aerosol chemistry: three populated valleys within Utah (Salt Lake, Utah, and Cache Valleys) and the San Joaquin Valley in California. This paper describes the scientific rationale for a campaign that will acquire chemical and meteorological datasets using airborne platforms with extensive range, coupled to surface-based measurements focusing on sampling within the near-surface boundary layer, and transport and mixing processes within this layer, with high vertical resolution at a number of representative sites. No prior wintertime basin-focused campaign has provided the breadth of observations necessary to characterize the meteorological–chemical linkages outlined here, nor to validate complex processes within coupled atmosphere–chemistry models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

A Novel Method for Diagnosing Land–Atmosphere Coupling Sensitivity in a Single-Column Model

The response of boundary layer properties and cloudiness to changes in surface evaporative fraction (EF) is investigated in a single-column model to quantify the locally coupled impact of subgrid surface variations on the atmosphere during summer. Sensitive coupling days are defined when the model atmosphere exhibits large variations across a range of EFs centered on the analyzed value. Coupling sensitivity exists as both positive feedback (cloudiness increases with EF) and negative feedback (clouds increase with decreasing EF) regimes. The positive regime manifests in shallow convection situations, which are capped by a strengthened inversion and subsidence, restricting the vertical extent of convection to just above the boundary layer. Surfaces with larger EF (greater surface latent heat flux) can inject more moisture into the vertically confined system, lowering the cloud base and an increasing cloud liquid water path (LWP). Negative feedback regimes tend to manifest when large-scale deep convection, such as from mesoscale convective systems and fronts, is advected through the domain, where convection strengthens over surfaces with a lower EF (greater surface sensible heat flux). The invigoration of these systems by the land surface leads to an increase in LWP through strengthened updrafts and stronger coupling between the boundary layer and the free atmosphere. These results apply in the absence of heterogeneity-induced mesoscale circulations, providing a one-dimensional dynamical perspective on the effect of surface heterogeneity. Finally, this study provides a framework of intermediate complexity, lying between parcel theory and high-resolution coupled land–atmosphere modeling, and therefore isolates the relevant first-order processes in land–atmosphere interactions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Determining the electron-phonon coupling strength from Resonant Inelastic X-ray Scattering at transition metal L-edges

We show that high-resolution Resonant Inelastic X-ray Scattering (RIXS) provides direct, element-specific and momentum-resolved information on the electron-phonon (e-p) coupling strength. Our theoretical analysis indicates how the e-p coupling can be extracted from RIXS spectra by determining the differential phonon scattering cross-section. An alternative manner to extract the coupling is to use the one- and two-phonon loss ratio, which is governed by the e-p coupling strength and the core-hole lifetime. This allows the determination of the e-p coupling on an absolute energy scale.

Ament, L. J.P.↗
DOE OSTI2025

Photon-magnon coupling using gain-assisted spoof-localized surface plasmons

Improving the photon-magnon coupling strength can be done by tuning the structure of microwave resonators to better interact with the magnon counterpart. Planar resonators accommodating unconventional photon modes beyond the half- and quarter-wavelength designs have been explored due to their optimized mode profiles and potentials for on-chip integration. Here, we designed and fabricated an actively controlled ring resonator supporting the spoof localized surface plasmons (LSPs), and implemented it in the investigation of photon-magnon coupling for hybrid magnonic applications. We demonstrated gain-assisted photon-magnon coupling with the YIG magnon mode under several different sample geometries. The achieved coupling amplification largely benefits from the high quality factor (Q-factor) due to the additional gain provided by a semiconductor amplifier, which effectively increases the Q-factor from a nearly null state (passive resonance) to more than 1000 for a quadrupole LSP mode. Our results suggest an additional control knob for manipulating photon-magnon coupled systems exploiting external controls of gain and loss.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Mechanical coupling in the nitrogenase complex

The enzyme nitrogenase reduces dinitrogen to ammonia utilizing electrons, protons, and energy obtained from the hydrolysis of ATP. Mo-dependent nitrogenase is a symmetric dimer, with each half comprising an ATP-dependent reductase, termed the Fe Protein, and a catalytic protein, known as the MoFe protein, which hosts the electron transfer P-cluster and the active-site metal cofactor (FeMo-co). A series of synchronized events for the electron transfer have been characterized experimentally, in which electron delivery is coupled to nucleotide hydrolysis and regulated by an intricate allosteric network. We report a graph theory analysis of the mechanical coupling in the nitrogenase complex as a key step to understanding the dynamics of allosteric regulation of nitrogen reduction. This analysis shows that regions near the active sites undergo large-scale, large-amplitude correlated motions that enable communications within each half and between the two halves of the complex. Computational predictions of mechanically regions were validated against an analysis of the solution phase dynamics of the nitrogenase complex via hydrogen-deuterium exchange. These regions include the P-loops and the switch regions in the Fe proteins, the loop containing the residue β-188Ser adjacent to the P-cluster in the MoFe protein, and the residues near the protein-protein interface. In particular, it is found that: (i) within each Fe protein, the switch regions I and II are coupled to the [4Fe-4S] cluster; (ii) within each half of the complex, the switch regions I and II are coupled to the loop containing β-188Ser; (iii) between the two halves of the complex, the regions near the nucleotide binding pockets of the two Fe proteins (in particular the P-loops, located over 130 Å apart) are also mechanically coupled. Notably, we found that residues next to the P-cluster (in particular the loop containing β-188Ser) are important for communication between the two halves.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Wire scanner assessment of transverse beam size in the Fermilab side-coupled linac

The Fermilab Side-Coupled Linac contains seven 805 MHz modules accelerating H- beam from 116 MeV to 400 MeV. Each module contains at least one wire scanner, yielding beam intensity at positions along a transverse direction. These wire scanners each contain three wires, mounted at different angles: "X", "Y", and 45° between "X" and "Y" to analyze coupling. Recently, a significant amount of transverse X-Y coupling was identified within wire scanner data from the Side-Coupled Linac, which has been present in data from the past decade. This realization has prompted an investigation into the wire scanner's utility as a diagnostic tool in the Fermilab Linac. This work presents efforts to better characterize the wire scanners' limitations and the phenomenon occurring in the Side-Coupled Linac.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

GRIZZLY MODEL OF FULLY COUPLED HEAT TRANSFER, MOISTURE DIFFUSION, ALKALI-SILICA REACTION AND FRACTURING PROCESSES IN CONCRETE

Idaho National Laboratory (INL) has been developing a fully coupled thermo-hydro-mechanical-chemical (THMC) concrete model, referred as Grizzly, with the ultimate goal of reliably simulating and predicting the long-term performance of concrete structures subjected to various aging and degradation mechanisms. In this paper, we present a fully coupled concrete model implemented in our Grizzly code for simulating coupled moisture/heat transfer, stress-dependent ASR swelling and elastic/inelastic mechanics. Example simulation results and preliminary model validation results against experimental data reported in the literature will be provided also in this paper. The close matches between the simulation results and experiments clearly reveal the potential of the fully coupled solution strategy for solving tightly coupled THMC concrete models. We also present simulation results of using a rate-dependent damaging mechanics model for simulating the ASR swelling induced degradation of concrete structures and its feedback to moisture and heat transport processes.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2013

User's guide of TOUGH2-EGS-MP: A Massively Parallel Simulator with Coupled Geomechanics for Fluid and Heat Flow in Enhanced Geothermal Systems VERSION 1.0

TOUGH2-EGS-MP is a parallel numerical simulation program coupling geomechanics with fluid and heat flow in fractured and porous media, and is applicable for simulation of enhanced geothermal systems (EGS). TOUGH2-EGS-MP is based on the TOUGH2-MP code, the massively parallel version of TOUGH2. In TOUGH2-EGS-MP, the fully-coupled flow-geomechanics model is developed from linear elastic theory for thermo-poro-elastic systems and is formulated in terms of mean normal stress as well as pore pressure and temperature. Reservoir rock properties such as porosity and permeability depend on rock deformation, and the relationships between these two, obtained from poro-elasticity theories and empirical correlations, are incorporated into the simulation. This report provides the user with detailed information on the TOUGH2-EGS-MP mathematical model and instructions for using it for Thermal-Hydrological-Mechanical (THM) simulations. The mathematical model includes the fluid and heat flow equations, geomechanical equation, and discretization of those equations. In addition, the parallel aspects of the code, such as domain partitioning and communication between processors, are also included. Although TOUGH2-EGS-MP has the capability for simulating fluid and heat flows coupled with geomechanical effects, it is up to the user to select the specific coupling process, such as THM or only TH, in a simulation. There are several example problems illustrating applications of this program. These example problems are described in detail and their input data are presented. Their results demonstrate that this program can be used for field-scale geothermal reservoir simulation in porous and fractured media with fluid and heat flow coupled with geomechanical effects.

15 GEOTHERMAL ENERGY↗
DOE OSTI2017

SIERRA Code Coupling Module: Arpeggio User Manual Version 4.44

The SNL Sierra Mechanics code suite is designed to enable simulation of complex multiphysics scenarios. The code suite is composed of several specialized applications which can operate either in standalone mode or coupled with each other. Arpeggio is a supported utility that enables loose coupling of the various Sierra Mechanics applications by providing access to Framework services that facilitate the coupling. More importantly Arpeggio orchestrates the execution of applications that participate in the coupling. This document describes the various components of Arpeggio and their operability. The intent of the document is to provide a fast path for analysts interested in coupled applications via simple examples of its usage.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
DOE OSTI2018

Merging symmetry projection methods with coupled cluster theory: Lessons from the Lipkin model Hamiltonian

Coupled cluster and symmetry projected Hartree-Fock are two central paradigms in electronic structure theory. However, they are very different. Single reference coupled cluster is highly successful for treating weakly correlated systems, but fails under strong correlation unless one sacrifices good quantum numbers and works with broken-symmetry wave functions, which is unphysical for finite systems. Symmetry projection is effective for the treatment of strong correlation at the mean-field level through multireference non-orthogonal configuration interaction wavefunctions, but unlike coupled cluster, it is neither size extensive nor ideal for treating dynamic correlation. We here examine different scenarios for merging these two dissimilar theories. We carry out this exercise over the integrable Lipkin model Hamiltonian, which despite its simplicity, encompasses non-trivial physics for degenerate systems and can be solved via diagonalization for a very large number of particles. We show how symmetry projection and coupled cluster doubles individually fail in different correlation limits, whereas models that merge these two theories are highly successful over the entire phase diagram. Despite the simplicity of the Lipkin Hamiltonian, the lessons learned in this work will be useful for building an ab initio symmetry projected coupled cluster theory that we expect to be accurate in the weakly and strongly correlated limits, as well as the recoupling regime.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗