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At least 487 records · Page 27

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DOE OSTI2025

Disorder driven crossover between anomalous Hall regimes in Fe 3 GaTe 2

The large anomalous Hall conductivity (AHC) of the Fe 3 ⁢(Ge,Ga)⁢Te 2 compounds has attracted considerable attention. Here, we expose the intrinsic nature of the AHC in Fe 3 ⁢GaTe 2 crystals characterized by high conductivities, which show disorder-independent AHC with a pronounced value 𝜎$^{c}_{𝑥⁢𝑦}$≈ 420 Ω −1 ⁢cm −1 . In the low-conductivity regime, we observe the scaling relation 𝜎 𝑥⁢𝑦 ∝ 𝜎$^{1.6}_{𝑥⁢𝑥}$, which crosses over to 𝜎 𝑥⁢𝑦 ≃ 𝜎$^{c}_{𝑥⁢𝑦}$ as 𝜎 𝑥⁢𝑥 increases. Disorder in low-conductivity crystals is confirmed by the broadening of a first-order transition between ferromagnetism and the ferrimagnetic ground state. Through density functional theory (DFT) calculations, we reveal that the dominant sources of Berry curvature are located a few hundred meV below the Fermi energy around the Γ point. Furthermore, Fe 3⁢ GaTe 2 clearly exposes the disorder-induced crossover among distinct AHC regimes, previously inferred from measurements on different ferromagnets located on either side of the crossover region.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Raman spectroscopy of thermally perturbed carbon fibers: Discriminating spectral responses of modulus classes and defect types

The mechanical strength properties of carbon fibers are generally thought to be correlated with the presence of underlying atomic-level defects. These defects serve to break the underlying translational symmetry of the graphitic or graphene subunits of the fiber construction, resulting in the emergence of new Raman-active spectral features. However, historical attempts to classify the precise origin of defect contributions to the Raman spectra have been challenging because of indistinct and overlapping features in the carbon fiber Raman spectra. Further, while substantial research exists on high-temperature exposure in inert atmospheres for carbon fiber composites, comparatively less addresses microscale behaviors and Raman spectral alterations to monofilament carbon fibers exposed to high-temperature atmospheric environments. Here, we report Raman spectral responses of nine commercially available high-performance, polyacrylonitrile-based carbon fibers exposed to various atmospheric heat treatments. In this work, we introduce a model-independent characterization method, the integrated absolute difference, to quantify the spectral responses to heat treatment of different fiber modulus classes. We combine this new method with a newly reported strategy to standardize spectral fitting for carbon fibers. With this approach, we show that atomic-scale defects in the underlying fiber microstructure manifest in measurably distinct manners and have distinct responses to thermal perturbation. These combined approaches may lay the foundation for disentangling contributions from specific defects in the Raman spectra of carbon fibers.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Detection of diffusion limited oxidation in thermally aged ethylene propylene rubber cable insulation material

The lifetime prediction of electrical cable insulation in nuclear power plants (NPPs) is primarily based on accelerated aging. Polymeric insulation exposed to accelerated aging at high temperatures may demonstrate diffusion limited oxidation (DLO) where oxygen within the material is consumed faster than can be supplied by diffusion from the surrounding air. This situation leads to equilibrium oxidation at the exposed surfaces and limited oxidation away from the surfaces. Therefore, DLO results in a heterogeneously aged material which can lead to underestimation of lifetime for in-service cable insulation. In this study, the presence of inhomogeneous aging caused by DLO was evaluated on cross-sectioned cable insulation specimens made of ethylene propylene rubber (EPR). The studies were performed on thermally aged specimens (165 °C, 1 day and 165 °C, 16 days) using local measurement techniques including nanoindentation, micro-Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) - energy dispersive spectroscopy (EDS). All the results indicate some degree of heterogenous aging, with 165 °C, 16 days, aging demonstrating highest degree of oxidative degradation on the inside edges presumably caused due to copper catalyzed oxidation.

Pallaka, Madhusudhan Reddy↗

DOE OSTI2023

Effect of Measurement Temperature on Electrical Cable Frequency Domain Reflectometry Response

In nuclear power plants, electrical cables are exposed to stressors, such as elevated temperature and radiation. Evaluation of the effect of stressors on the lifetime of electrical cables can be conducted using offline electrical reflectometry techniques, such as frequency domain reflectometry (FDR). However, recent work has raised the concern that FDR measurements at temperatures higher than ambient may diminish or reduce the response due to stressors, potentially leading to incorrect predictions of electrical cable damage and lifetime. In this work, we explore the FDR response of an electrical cable exposed to an oven-based thermal stressor up to 140°C, including both ramping up and ramping down temperature. It was observed that, for both the oven entrance and exit, an increase in the FDR measurement temperature led to a decrease in the FDR reflection coefficient. In particular, it was found that the reflection coefficient at the oven entrance decreased from the ambient measurement by approximately 7%, 22%, and 36% at a temperature of 60°C, 100°C, and 140°C, respectively.

Spencer, Mychal P.↗

DOE OSTI2022

3D Frequency Domain Reflectometry Digital Twin of an Electrical Cable: A First Glance

Electrical cables within nuclear power plants (NPPs) are critical components required for power, control, and instrumentation systems which may be exposed to stressors, such as elevated temperatures and gamma radiation. Such stressors can lead to a reduction in the remaining useful life of electrical cables, jeopardizing the safety of NPP systems. To evaluate the effect of stressors on the degradation of electrical cables, electrical reflectometry methods are commonly employed. Frequency domain reflectometry (FDR) is a non-destructive electrical reflectometry method that uses transmission line theory to detect degradation or impedance changes within electrical cables. However, in most cases FDR is only applied to de-energized cables, limiting the application in NPPs as the cable system must be taken offline. In this work, we explore the development of an FDR digital twin to predict the degradation of an electrical cable exposed to elevated temperature, which is expected to reduce the need for offline FDR. A 3-conductor low-voltage electrical cable was selected for evaluation of the digital twin. The fully three-dimensional digital twin was developed in COMSOL using the RF module. A cable length of 30-m and frequency bandwidth of 400 MHz was selected to mimic real-world application of FDR. Over a 1-m region, the permittivity of the insulation was varied by up to 20% to model thermal degradation. The results demonstrate accurate detection of the insulation damage region, supporting further investigation of the FDR digital twin using real-world data and machine learning for predictive damage estimation or remaining lifetime.

Spencer, Mychal P.↗

DOE OSTI2021

Quasi-Dynamic Electromagnetic Field Safety Analysis and Mitigation for High-Power Dynamic Wireless Charging of Electric Vehicles

Dynamic wireless charging of electric vehicles (EV) is an emerging charging technology to enable non-contact wireless charging while the vehicle is moving. Compared to stationary wireless charging, in-motion wireless charging involves dynamic processes in which an EV is passing over the charging pads (transmitters). This in motion process makes the dynamic electromagnetic (EM) environment more complicated, and EM safety needs to be ensured under all circumstances. This is due to the fact that the entire vehicle body may be exposed to magnetic fields while the vehicle moves over the energized transmitter. This paper investigates several typical charging scenarios when EVs approach, pass over, and move away from the charging pads. Quasi-dynamic models, which are preliminarily verified by coils’ inductance measurements, are developed to analyze the dynamic process. Based on the quasi-dynamic analysis, shielding solutions are also studied to ensure EM safety for the dynamic wireless charging processes.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2023

Severe Temperature Impact Study on Ferrite Electromagnetic Shielding for Wireless Electric Vehicle Charging

Wireless charging of an electric vehicle (EV) is an emerging technology that enables noncontact charging, which has advantages in terms of convenience and flexibility. However, the embedded charging pads under and on the ground expose the charging coils, ferrite shielding, and related components to a potentially severe external environment. To study the electromagnetic shielding performance under such extreme temperature conditions, ferrite shielding material's permeability characteristics are tested under temperatures as low as -50°C to as high as 240°C. Referring to the official recorded lowest and highest temperature of the United States, in this paper, it is assumed that the operation temperature ranges from -50°C to 57°C as the coldest winter and hottest summer environment for WPT application. Electromagnetic performance, shielding, and associated stray magnetic emissions are simulated by using three-dimensional (3D) transient simulations to study the impact of low and high temperature on electromagnetic shielding performance. Based on ferrite testing data, from -50°C low temperature to 57°C high temperature, the ferrite's relative permeability ranges from 2550 to 3727. The simulation study indicates that there won't be significant impact on the EM shielding performance for WPT operated under those severe environment temperature conditions.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2020

An Adaptive Reference Scheme to Extend the Functional Range of Optical Backscatter Reflectometry in Extreme Environments

Optical frequency domain reflectometry (OFDR) measurements are performed by recording the interference pattern of light backscattered by density fluctuations or Bragg gratings along the length of an optical fiber. Changes in local temperature or strain in the fiber cause shifts in the backscattered light spectrum, which can be calibrated to the applied temperature or strain. Comparing the backscattered optical spectra from each reflection site with a reference (unstrained) spectrum allows for quantification of local spectral shifts. While mature OFDR-based technologies can provide high-precision spatially distributed measurements over kilometer lengths, the post-processing approaches used to recover spectral shifts from raw optical intensity data can limit the use of OFDR in harsh environments. This paper presents a novel approach to post-processing OFDR data which extends the usability of optical fibers exposed to harsh environments. This approach is the first to use the spectral shift quality, calculated for two OFDR measurements, to identify an appropriate reference scan from which the spectral shift can be determined. Here, three experimental data sets are used to test the algorithm: (1) an optical fiber heated to >950°C, (2) an aluminum-embedded optical fiber under strain from differential thermal expansion, and (3) an optical fiber exposed to a total neutron flux of 2×10 13 n/cm 2 /s over 40 hours in a nuclear test reactor. Results show that using a metric of quality to select an appropriate reference measurement extends the functional range of OFDR strain and temperature sensors. Furthermore, this algorithm can be applied to existing OFDR data.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Case Study of Using Kokkos and SYCLs Performance-Portable Frameworks for Milc-Dslash Benchmark on NVIDIA, AMD and Intel GPUs

Six of the top ten supercomputers in the TOP500 list from June 2021 rely on NVIDIA GPUs to achieve their peak compute bandwidth. With the announcement of Aurora, Frontier, and El Capitan, Intel and AMD have also entered the domain of providing GPUs for scientific computing. A consequence of the increased diversity in the GPU landscape is the emergence of portable programming models such as Kokkos, SYCL, OpenCL, and OpenMP, which allow application developers to maintain a single-source code across a diverse range of hardware architectures. While the portable frameworks try to optimize the compute resource usage on a given architecture, it is the programmers responsibility to expose parallelism in an application that can take advantage of thousands of processing elements available on GPUs. In this paper, we introduce a GPU-friendly parallel implementation of Milc-Dslash that exposes multiple hierarchies of parallelism in the algorithm. Milc-Dslash was designed to serve as a benchmark with highly optimized matrix-vector multiplications to measure the resource utilization on the GPU systems. The parallel hierarchies in the Milc-Dslash algorithm are mapped onto a target hardware using Kokkos and SYCL programming models. We present the performance achieved by Kokkos and SYCL implementations of Milc-Dslash on NVIDIA A100 GPU, AMD MI100 GPU, and Intel Gen9 GPU. Additionally, we compare the Kokkos and SYCL performances with those obtained from the versions written in CUDA and HIP programming models on NVIDIA A100 GPU and AMD MI100 GPU, respectively.

Dufek, Amanda S↗

DOE OSTI2020

Enhanced Photovoltaic Soiling in an Urban Environment

Natural soiling, or the deposition of ambient particulate matter (PM) onto the surface of solar glass, causes losses in PV production around the world. Much work in the PV community has focused on soiling in dusty desert environments. However, PV systems in urban environments are exposed to different contaminants and thus soil differently. We present an analysis of PV soiling in such an urban environment considering the impacts of meteorological parameters. We present 1 year of results from a soiling station in an urban location in Colorado. Bare glass samples were exposed outdoors for 11 days alongside the station; results from microscopy and light transmittance measurements show how moisture and dew affect the morphology and optics of contamination on glass. The coupon results suggest that natural (rain) cleanings may not be sufficient to clean solar panels in urban environments. Ion chromatography of soiling on the reference cell surfaces suggest that dry brush cleanings may not sufficiently clean chemicals deposited on solar panel surfaces in urban environments.

14 SOLAR ENERGY↗

DOE OSTI2021

The Role of Water on the Interfacial Adhesion in Si Solar Modules

Delamination of solar module interfaces often occurs in field-tested solar modules after decades of service due to environmental stressors such as humidity. As water diffuses into the module, failure mechanisms like corrosion and delamination are significantly affected. In the presence of water, the interfaces between EVA and the cell, glass, and backsheet all experience losses of adhesion exposing the module to accelerated degradation. Understanding the relation between interfacial adhesion and water content inside PV modules can help mitigate detrimental power losses. Water content measurements via short wave infrared reflectometry combined with 180 degrees peel tests were used to study and quantify the effect of water ingress and egress on adhesion. Changes in adhesion strength for different module interfaces are quantified, correlating spatial distribution of water content to adhesion for damp heat and dry heat exposed samples. After 1000 hours of damp heat exposure, decreases in adhesion strength of approximately 1 N/mm were noted for all interfaces.

adhesion↗

DOE OSTI2022

Overall Performance Losses and Activated Mechanisms in Double Glass and Glass-backsheet Photovoltaic Modules with Monofacial and Bifacial PERC Cells, under Accelerated Exposures

Commercial PV modules have various packaging choices nowadays, which influence their long-term reliability. This study compared the degradation behaviors of sixteen module variants from two brands with varying encapsulant materials (EVA or POE), encapsulant types, module architectures (GB or DG), and cell types (monofacial or bifacial) using null hypothesis testing to determine statistical significant findings. The modules were exposed for 2,520 hours under two accelerated exposures: modified damp heat (mDH) and modified damp heat with full-spectrum light (mDH+FSL). For both brands, two DG module variants with UV-Cutoff rear encapsulant are found to have significantly lower average power loss than the module variants of EVA+GB with opaque rear encapsulant after each accelerated exposure. Metallization interconnect corrosion is identified as the primary degradation mechanism. Furthermore, unsupervised hierarchical clustering finds that the degradation behaviors of modules from one brand with a more strict manufacturing quality control depends on module architectures only.

14 SOLAR ENERGY↗

DOE OSTI2020

Analysis of Threading Libraries for High Performance Computing

With the appearance of multi-/many core machines, applications and runtime systems have evolved in order to exploit the new on-node concurrency brought by new software paradigms. POSIX threads (Pthreads) was widely-adopted for that purpose and it remains as the most used threading solution in current hardware. Lightweight thread (LWT) libraries emerged as an alternative offering lighter mechanisms to tackle the massive concurrency of current hardware. In this article, we analyze in detail the most representative threading libraries including Pthread- and LWT-based solutions. In addition, to examine the suitability of LWTs for different use cases, we develop a set of microbenchmarks consisting of OpenMP patterns commonly found in current parallel codes, and we compare the results using threading libraries and OpenMP implementations. Moreover, we study the semantics offered by threading libraries in order to expose the similarities among different LWT application programming interfaces and their advantages over Pthreads. This article exposes that LWT libraries outperform solutions based on operating system threads when tasks and nested parallelism are required.

GLT↗

DOE OSTI2021

Simulation and Modeling of Time-Resolved X-Ray Detector for the Saturn Accelerator

In this work, we present the technology-aided computer design (TCAD) device simulation and modeling of a silicon p-i-n diode for detecting time-dependent X-ray radiation. We show that the simulated forward and reverse breakdown current–voltage characteristics agree well with the measured data under nonradiation environment by only calibrating carrier lifetimes for the forward bias case and avalanche model critical fields for the reverse bias condition. Using the calibrated parameters and other nominal material properties, we simulated the radiation responses of the p-i-n diode and compared with experimental data when the diode was exposed to X-ray radiation at Sandia’s Saturn facility and the Idaho State University (ISU) TriMeV facility. For Saturn’s Gaussian dose-rate pulses, we show three findings from TCAD simulations. First, the simulated photocurrents are in excellent agreement with the measured data for two dose-rate pulses with peak values of 1.16×10 10 and 1.88×10 10 rad(Si)/s. Second, the simulation results of high dose-rate pulses predict increased delayed photocurrents with longer time tails in the diode electrical responses due to excess carrier generation. Third, simulated peak values of diode radiation responses versus peak dose rates at different bias conditions provide useful guidance to determine the dose-rate range that the p-i-n diode can reliably detect in experiment. For TriMeV’s non-Gaussian dose-rate pulse, our simulated diode response is in decent agreement with the measured data without further calibration. We also studied the effects of device geometry, recombination process, and dose-rate enhancement via TCAD simulations to understand the higher measured response in the time after the peak dose-rate radiation for the p-i-n diode exposed to TriMeV irradiation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2024

MOLLER Spectrometer Magnet Design With Measured Mechanical Properties of Irradiated S2-Glass Reinforced Cyanate Ester Resin at Elevated Temperature

Here, the aim of this study was to retire the risk of maintaining the integrity of S2-glass reinforced CTD-403 (a cyanate ester resin) that is exposed to radiation and elevated temperature over the life of the measurement of a lepton–lepton electroweak reaction (MOLLER) experiment in experimental Hall A at Jefferson Lab, Newport News, VA. In this article, the shear strength and flexural modulus of irradiated S2-glass reinforced CTD-403 specimens were measured at 65 °C (the magnets are to operate at less than 65 °C) under two scenarios: vacuum and gaseous nitrogen. The testing method is the short-beam shear (SBS) test according to ASTM D2344. The specimens were exposed to neutrons and gamma rays up to 124 MGy. The results show that specimens have excellent resistance against radiation, only 23% degradation of apparent shear strength with 124 MGy at 65 °C under vacuum. At the highest dose areas of the coils, tungsten plates are used to reduce the radiation dose to the resin system. The conclusion is that S2-glass reinforced CTD-403 is well-suited for electrical insulation of MOLLER magnets.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Transient computational and experimental thermal analysis of graphite foam monoblock

A densified graphite foam is being explored for its applicability as plasma-facing material in fusion devices. Three different graphite foam monoblocks are constructed and tested in the Garching Large Divertor Sample Testing Facility. The monoblock samples consist of graphite foam press-fit to a single tube, graphite foam cubes brazed to a single, and graphite foam cubes press-fit to a single tube. The tube is composed of CuCrZr with a steel twisted tape. The monoblocks are exposed to the heat fluxes of 5, 6, and 8 MW/m 2 for 30 s to determine the maximum surface and body temperatures measured with thermocouple for each monoblock design. The press-fit monoblocks are exposed to 8 MW/m 2 for 15 s for 100 cycles to determine the effect of thermal cycling on the contact between the graphite foam and the tube. STAR-CCM+ is used to predict how much the contact between the foam and tubes varies as a result of thermal cycling. In addition, the 6 MW/m 2 loading is modeled in STAR-CCM+ to compare the transient cooldown curves of the computational results to the recorded temperatures at the surface and two different thermocouple locations. This comparison is used to validate the temperature-dependent thermal conductivity and specific heat capacity used in the models of the graphite foam. The computational modeling of the experiment has been used to hypothesize ways to use and improve upon the graphite foam as a suitable material for fusion applications.

Gehrig, Monica↗

DOE OSTI2020

Relative reproductive phenology and synchrony affect neonate survival in a nonprecocial ungulate

Abstract Degree of reproductive synchronization in prey is hypothesized as a predator defense strategy reducing prey risk via predator satiation or predator avoidance. Species with precocial young, especially those exposed to specialist predators, should be highly synchronous to satiate predators (predator satiation hypothesis), while prey with nonprecocial (i.e. altricial) young, especially those exposed to generalist predators, should become relatively asynchronous to avoid predator detection (predator avoidance hypothesis). The white‐tailed deer Odocoileus virginianus in North America is an example of a nonprecocial ungulate that uses the hider strategy early in life; its primary predator (coyote; Canis latrans ) is a generalist, making white‐tailed deer a good model species to test the predator avoidance hypothesis. We used birth dates and known fates of white‐tailed deer neonates ( n = 1,032) across nine study sites varying in relative synchrony and predator assemblages to test the predator avoidance hypothesis. We predicted that relative birthing asynchrony of the population would increase relative survival at the population level; therefore, at the individual scale, neonate birth date nearer to mean birthing date in a respective population would not influence individual survival. Coyotes were responsible for the majority of predation events, and survival of those neonates increased the closer the individual was born to peak birthing season in each respective population. Also, at the population level, reproductive asynchronization negatively affected survival. Contrary to the predator avoidance hypothesis, our data indicate patterns in neonate survival for white‐tailed deer better support the predator satiation hypothesis at the individual and population level. Additionally, coyotes may present a selective force great enough to shift reproductive synchrony such that predator satiation may become a feasible defense strategy for neonates at local spatial scales. Our results indicate that synchronizing reproduction may still be the most effective strategy to reduce individual predation risk from generalist predators, particularly when the window of heightened resource availability to the prey is narrow. A free Plain Language Summary can be found within the Supporting Information of this article.

Michel, Eric S.↗

DOE OSTI2022

The safety of pranlukast and montelukast during the first trimester of pregnancy: A prospective, two‐centered cohort study in Japan

Abstract For leukotriene receptor antagonists (LTRAs), especially pranlukast, safety data during pregnancy is limited. Therefore, we conducted a prospective, two‐centered cohort study using data from teratogen information services in Japan to clarify the effects of LTRA exposure during pregnancy on maternal and fetal outcomes. Pregnant women who being counseled on drug use during pregnancy at two facilities were enrolled. The primary outcome of this study was major congenital anomalies. The incidence of major congenital anomalies in women exposed to montelukast or pranlukast during the first trimester of pregnancy was compared with that of controls. Logistic regression analysis was performed to analyze the effects of maternal LTRA use during the first trimester of pregnancy on major congenital anomalies. The outcomes of 231 pregnant women exposed to LTRAs (montelukast n = 122; pranlukast n = 106; both n = 3) and 212 live births were compared with those of controls. The rate of major congenital anomalies in the LTRA group was 1.9%. Multivariable logistic regression analysis revealed that LTRA exposure was not a risk factor for major congenital anomalies (adjusted odds ratio, 0.78; 95% confidence interval, 0.23–2.05; p = 0.653). In addition, no significant difference was detected in stillbirth, spontaneous abortion, preterm birth, and low birth weight between the two groups. The present study revealed that montelukast and pranlukast were not associated with the risk of major congenital anomalies. Our findings suggest that LTRAs could be safely employed for asthma therapy during pregnancy.

Hatakeyama, Shiro↗