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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Conversion of Domestic US Coal into Exceedingly High-Quality Graphene

The Recipient will study how flash Joule heating (FJH) from anthracite coal can afford high value graphene in gram scales in less than 1 second per conversion step. The graphene is termed flash graphene (FG). The process uses no furnace and no solvent or reactive gases, and the yields from anthracite coal are 85-95% with a purity >99%. The scaled electrical energy cost is projected at $100 per metric ton. FG can be among the lowest defect graphene ever reported (2D/G = 17:1) and turbostratic by powder X-ray diffraction (XRD) analysis, meaning that is has little order between the graphene layers, thereby facilitating its dispersion in composites. FG might provide the long-sought method to make graphene in bulk with industrially acceptable economics: inexpensive coal, furnace-free, solvent-free and chemical-free processing, and low-energy input to render it suitable for bulk plastic, metal and even concrete composites.

01 COAL, LIGNITE, AND PEAT↗
NASA NTRS2014

Integration of the Total Lightning Jump Algorithm into Current Operational Warning Environment Conceptual Models

The presence and rates of total lightning are both correlated to and physically dependent upon storm updraft strength, mixed phase precipitation volume and the size of the charging zone. The updraft modulates the ingredients necessary for electrification within a thunderstorm, while the updraft also plays a critical role in the development of severe and hazardous weather. Therefore utilizing this relationship, the monitoring of lightning rates and jumps provides an additional piece of information on the evolution of a thunderstorm, more often than not, at higher temporal resolution than current operational radar systems. This correlation is the basis for the total lightning jump algorithm that has been developed in recent years. Currently, the lightning jump algorithm is being tested in two separate but important efforts. Schultz et al. (2014; AMS 10th Satellite Symposium) is exploring the transition of the algorithm from its research based formulation to a fully objective algorithm that includes storm tracking, Geostationary Lightning Mapper (GLM) Proxy data and the lightning jump algorithm. Chronis et al. (2014; this conference) provides context for the transition to current operational forecasting using lightning mapping array based products. However, what remains is an end to end physical and dynamical basis for relating lightning rates to severe storm manifestation, so the forecaster has a reason beyond simple correlation to utilize the lightning jump algorithm within their severe storm conceptual models. Therefore, the physical basis for the lightning jump algorithm in relation to severe storm dynamics and microphysics is a key component that must be further explored. Many radar studies have examined flash rates and their relation to updraft strength, updraft volume, precipitation‐sized ice mass, etc.; however, relation specifically to lightning jumps is fragmented within the literature. Thus the goal of this study is to use multiple Doppler techniques to resolve the physical and dynamical storm characteristics specifically around the time of the lightning jump. This information will help forecasters anticipate lightning jump occurrence, or even be of use to determine future characteristics of a given storm (e.g., development of a mesocyclone, downdraft, or hail signature on radar), providing additional lead time/confidence in the severe storm warning paradigm.

Shultz, Christopher J.↗
NASA NTRS2011

Nanoparticle Filtration in a RTM Processed Epoxy/Carbon Fiber Composite

Several epoxy matrix composite panels were fabricated by resin transfer molding (RTM) E862/W resin onto a triaxially braided carbon fiber pre-form. Nanoparticles including carbon nanofiber, synthetic clay, and functionalized graphite were dispersed in the E862 matrix, and the extent of particle filtration during processing was characterized. Nanoparticle dispersion in the resin flashing on both the inlet and outlet edges of the panel was compared by TEM. Variation in physical properties such as Tg and moisture absorption throughout the panel were also characterized. All nanoparticle filled panels showed a decrease in Tg along the resin flow path across the panel, indicating nanoparticle filtration, however there was little change in moisture absorption. This works illustrates the need to obtain good nano-particle dispersion in the matrix resin to prevent particle agglomeration and hence particle filtration in the resultant polymer matrix composites (PMC).

Miller, Sandi G.↗
NASA NTRSDate not supplied

The International Space Station Lightning Imaging Sensor: Performance, Applications, and Cross-Platform Science

The Lightning Imaging Sensor (LIS), an optically based lightning detector developed at NASA Marshall Space Flight Center, was launched to the International Space Station (ISS) in February 2017, detecting optical signatures of lightning with storm-scale horizontal resolution (4-km) during both day and night. ISS LIS data are available 1 March 2017 to present. Millisecond timing allows detailed intercalibration and validation with other spaceborne and ground-based lightning sensors. Initial comparisons with those other sensors suggest flash detection efficiency around 60% (diurnal variability of 51-75%), false alarm rate under 5%, timing accuracy better than 2 ms, and horizontal location accuracy around 3 km. The spatially uniform flash detection capability of ISS LIS from low-Earth orbit allows assessment of spatially varying flash detection efficiency for other sensors and networks, particularly the Geostationary Lightning Mappers (GLMs). ISS LIS provides research data suitable for investigations of lightning physics, climatology, thunderstorm processes, and atmospheric composition, as well as realtime lightning data for operational forecasting and aviation weather interests. ISS LIS enables enrichment and extension of the long-term global climatology of lightning from space, and is the only recent platform that extends the global record to higher latitudes (± 55°). The global spatial distribution of lightning from ISS LIS is broadly similar to previous datasets, with globally averaged seasonal/annual flash rates (3-year average: ~44 s) about 5-10% lower. This difference is likely due to reduced flash detection efficiency that will be mitigated in future ISS LIS data processing, as well as the shorter ISS LIS period of record. The expected land/ocean contrast in the diurnal variability of global lightning is also observed. The near-realtime ISS LIS data make the instrument important to operational weather forecasting and related applications, including public safety. Finally, ISS LIS is demonstrating utility as part (or potential part) of cross-platform studies examining a diverse array of topics, including lightning physics, thunderstorm processes, convective precipitation, and atmospheric composition.

Timothy Lang↗
DOE OSTI2022

Using an Explainable Machine Learning Approach to Characterize Earth System Model Errors: Application of SHAP Analysis to Modeling Lightning Flash Occurrence

Abstract Computational models of the Earth System are critical tools for modern scientific inquiry. Efforts toward evaluating and improving errors in representations of physical and chemical processes in these large computational systems are commonly stymied by highly nonlinear and complex error behavior. Recent work has shown that these errors can be effectively predicted using modern Artificial Intelligence (A.I.) techniques. In this work, we go beyond these previous studies to apply an explainable A.I. technique to not only predict model errors but also move toward understanding the underlying reasons for successful error prediction. We use XGBoost classification trees and SHapley Additive exPlanations analysis to explore the errors in the prediction of lightning occurrence in the NASA Goddard Earth Observing System model, a widely used Earth System Model. This explainable error prediction system can effectively predict the model error and indicates that the errors are strongly related to convective processes and the characteristics of the land surface.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

A two-dimensional numerical study of the magneto-Rayleigh–Taylor instability with FLASH: Application to the staged Z-pinch concept

Magnetically driven implosions involving a liner collapsing onto a target are inherently vulnerable to the magneto-Rayleigh–Taylor instability (MRTI). Among the various approaches proposed to achieve fusion conditions within the target, the staged Z-pinch (SZP) concept employs a high-Z liner, the advantages of which remain an active area of investigation. Consequently, ongoing design optimization efforts are essential, while critical physical processes such as magnetic field (B-field) diffusion and radiation transport increase the complexity of required simulations. In this study, we utilize the new capabilities of the FLASH code to simulate in 2D, for the first time using this code, staged Z-pinch configurations (designated SZP1 and SZP1*), focusing on their stability. First, a comparison of simulation results with theoretical predictions of MRTI growth provide new insights into the often-overlooked influences of high mesh resolution and initial perturbation seeding on instability dynamics. These findings then lead to a discussion on potential improvements for future SZP experiments. These include the use of an axial B-field stabilization and the optimization of radiation transport processes during the implosion. The results presented herein establish the framework for simulating multi-dimensional Z pinches using the FLASH code and pave the way for the development of innovative experimental configurations leveraging its advanced simulation capabilities.

Adaptive mesh refinement↗
DOE OSTI2018

Exploiting Internal Parallelism for Address Translation in Solid-State Drives

Solid-state Drives (SSDs) have changed the landscape of storage systems and present a promising storage solution for data-intensive applications due to their low latency, high bandwidth, and low power consumption compared to traditional hard disk drives. SSDs achieve these desirable characteristics using internal parallelism—parallel access to multiple internal flash memory chips—and a Flash Translation Layer (FTL) that determines where data are stored on those chips so that they do not wear out prematurely. However, current state-of-the-art cache-based FTLs like the Demand-based Flash Translation Layer (DFTL) do not allow IO schedulers to take full advantage of internal parallelism, because they impose a tight coupling between the logical-to-physical address translation and the data access. In this study to address this limitation, we introduce a new FTL design called Parallel-DFTL that works with the DFTL to decouple address translation operations from data accesses. Parallel-DFTL separates address translation and data access operations into different queues, allowing the SSD to use concurrent flash accesses for both types of operations. We also present a Parallel-LRU cache replacement algorithm to improve the concurrency of address translation operations. To compare Parallel-DFTL against existing FTL approaches, we present a Parallel-DFTL performance model and compare its predictions against those for DFTL and an ideal page-mapping approach. We also implemented the Parallel-DFTL approach in an SSD simulator using real device parameters, and used trace-driven simulation to evaluate Parallel-DFTL’s efficacy. Our evaluation results show that Parallel-DFTL improved the overall performance by up to 32% for the real IO workloads we tested, and by up to two orders of magnitude with synthetic test workloads. Finally, we also found that Parallel-DFTL is able to achieve reasonable performance with a very small cache size and that it provides the best benefit for those workloads with large request size or with high write ratio.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Code-to-code comparison between FLASH and HYDRA in gas-puff Z-pinch modeling

The numerical modeling of gas-puff Z pinches involves the nonlinear coupling of a broad range of complex, multi-physics phenomena that makes such simulations challenging. The challenge is further compounded by nonlinear instabilities that can impact the dynamics of imploding gas-puff Z pinches, such as the magneto Rayleigh–Taylor instability (MRTI). If the growth rate and amplitude of the latter is comparable to the relevant timescales and properties of the imploding plasma, the MRTI can dramatically alter implosion dynamics, dictate pinch stability, and govern the plasma properties achievable in pulsed-power-driven laboratory experiments. National Laboratories and academic teams have developed numerical tools that can accurately model Z-pinch configurations and provide reliable design capabilities that can guide experimental choices and assist in interpreting experimental results. Most such tools, however, are not broadly available. Here, we present newly developed Z-pinch simulation capabilities of the publicly available FLASH code, applied in the study of MRTI growth and dynamical effects in gas-puff implosions. To verify the new implementations, we perform a comparison of FLASH gas-puff implosion simulations with previously published calculations with the HYDRA code from Lawrence Livermore National Laboratory, which have been validated with experimental data from the CESZAR pulsed-power driver at the University of California, San Diego. The experiments involved double- and triple-nozzle configurations, in an experimental attempt to stabilize the pinch to the MRTI. The code-to-code comparison shows similar results between the FLASH and HYDRA simulations, supporting the use of FLASH in the modeling of future gas-puff Z-pinch experiments at CESZAR.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2020

Using GLM Flash Density, Flash Area, and Flash Energy to Diagnose Tropical Cyclone Structure and Intensification

Increased lightning in tropical cyclones (TCs) is typically associated with intensification, but significant lightning outbreaks are also observed in weakening storms. The total number of lightning flashes in a TC is not always a reliable indicator of TC intensity evolution. Issues with the range and detection efficiency of ground-based networks, particularly for intracloud lightning. Physical processes such as vertical wind shear can intensify asymmetric convection while also weakening the TC. The commissioning of the Geostationary Lightning Mapper (GLM) aboard GOES-16 and GOES-17 marked, for the first time, the presence of an operational lightning detector in geostationary orbit. In addition to flash density (the number of flashes per unit area per unit time), GLM also provides continuous observations of flash area and total optical energy.

Duran, Patrick↗
DOE OSTI2020

Characterization of an imploding cylindrical plasma for electron transport studies using x-ray emission spectroscopy

We report here on the characterization of the conditions of an imploding cylindrical plasma by time-resolved x-ray emission spectroscopy. Knowledge about this implosion platform can be applied to studies of particle transport for inertial confinement fusion schemes or to astrophysical plasmas. A cylindrical Cl-doped CH foam within a tube of solid CH was irradiated by 36 beams (I total ~5×10 14 W/cm 2 , 1.5ns square pulse, and E total ~ 16.2kJ) of the OMEGA-60 laser to radially compress the CH toward the axis. The analysis of the time-resolved spectra showed that the compression can be described by four distinct phases, each presenting different plasma conditions. First the ablation of the cylinder is dominant; second, the foam is heated and induces a significant jump in emission intensities; third, the temperature and density of the foam reaches a maximum; and finally, the plasma expands. Ranges for the plasma temperature were inferred with the atomic physics code SCRAM (Spectroscopic Collisional-Radiative Atomic Model) and the experimental data have been compared to hydrodynamic simulations performed with the 2D code FLASH, which showed a similar implosion dynamic over time.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Metal-poor stars. IV - The evolution of red giants.

Detailed evolutionary calculations for six Population-II red giants are presented. The first five of these models are followed from the zero age main sequence to the onset of the helium flash. The sixth model allows the effect of direct electron-neutrino interactions to be estimated. The updated input physics and evolutionary code are described briefly. The results of the calculations are presented in a manner pertinent to later stages of evolutions and suitable for comparison with observations.

Rood, R. T.↗
NASA NTRS1989

Triggered lightning strikes to aircraft and natural intracloud discharges

The physical model of Mazur (1989) for triggering lightning strikes by aircraft was used to interpret the initiation of intracloud flashes observed by the French UHF-VHF interferometric system. It is shown that both the intracloud discharges and airplane-triggered lightning strikes were initiated by simultaneous bidirectional development of the negative stepped leader and the positive leader-continous current process. However, the negative stepped leader phase in triggered flashes is of shorter duration (tens of milliseconds), than that in intracloud flashes (usually hundreds of milliseconds). This is considered to be due to the fact that, on the aircraft there is a single initiation process, versus the numerous initiation processes that occur inside the cloud.

Mazur, Vladislav↗
NASA NTRS1995

Pressure Dependence and Metastable State Formation in the Photolysis of Dichlorine Monoxide (Cl2O)

Physics%K photolysis, dichlorine monoxide, pressure%U http://techreports.jpl.nasa.gov/1995/95-0924.pdfThe photodissociation of dichlorine monoxide (Cl2O) was studied using broadband flash photolysis to investigate the influence of variations in the photolysis wavelength domain, bath gas pressure, and bath gas identity on the yield and temporal dependence of the ClO product. ClO yields were independent of bath gas pressure when the photolysis spectral band extended to 200 nm (quartz cutoff) but for photolysis restricted to wavelengths longer than about 250 nm, ClO yields decreased with increasing bath gas pressure and there was a pressure-dependent delay in the formation of ClO.!.

photolysis↗
DOE OSTI2020

Pool boiling critical heat flux studies of accident tolerant fuel cladding materials

Pool boiling experiments have been performed at atmospheric pressure on potential accident tolerant fuel (ATF) cladding materials (Zirlo®, Cr coated Zirlo®, FeCrAl coated Zirlo®, and monolithic SiC) to evaluate the Critical Heat Flux (CHF) points. Corrosion resistant coatings of Cr and FeCrAl alloy were deposited on flat Zirlo® samples using cold spray technology. The as-prepared samples after uniform surface polishing were subjected to autoclave tests at 360 °C water and 18.6 MPa for 360 h to simulate prototypic corrosion of the ATF cladding materials in LWR normal operation. Surface characteristics potentially influencing CHF such as surface morphology, roughness, static contact angle, and surface chemistry were characterized using a suite of characterization methods including scanning electron microscopy, 3D optical profilometry, optical contact angle measurements, and x-ray photoelectron spectroscopy (XPS). Thermo-physical properties of the samples such as density, thermal conductivity, and heat capacity were measured by differential scanning calorimetry and laser flash thermal diffusivity measurement. FeCrAl coatings showed CHF values comparable to bare Zirlo® samples, while slightly lower CHF values were observed for Cr coated samples and bulk SiC flats (produced by chemical vapor deposition, CVD). As-deposited Cr coatings showed 67% higher CHF than the as-polished Cr coatings due to its higher surface roughness level. The autoclave testing for the prepared samples generally increased the CHF except for the surface polished Cr coatings. Similar CHF values of bare Zirlo®, FeCrAl coating, and CVD SiC samples were observed after autoclave test but there were negligible change CHF of Cr coatings. XPS studies indicated that the formation or deposition of a few monolayers of hydrophobic carbonaceous species on surface can affect CHF values. The trends in CHF data are discussed in terms of evolution of the surface characteristics of the ATF materials.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Highlights from the STAR Experiment

Despite the challenges of pandemic, the years 2020-21 were quite successful for STAR. We completed the Beam Energy Scan program phase 2 and installed the forward upgrade with which STAR finished data-taking for polarized p+p collisions at 510 GeV. In this contribution, we discuss STAR results on five different topics that were presented in twenty-one parallel talks, forty-seven posters, and two flash talks at the Quark Matter 11 2022 conference.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1973

Can oscillations grow in a sunspot umbra.

Umbral flashes and running penumbral waves have been attributed by Moore (1972) to overstable oscillations in the umbra. His numerical results were derived by inserting physical conditions at two particular depths beneath the umbral surface. Seven variables must be specified at each point. We have extended Moore's analysis to examine the depth-dependence of overstable oscillations in a recently computed umbral model. Electrical conductivity is evaluated taking full account of partial ionization and magnetic fields. In the surface layers, within 250 km of the top of the umbral convection zone, the conductivity is so low that Joule dissipation is more rapid than the growth rate of oscillations. In these layers, Moore's results are therefore not applicable. At greater depths, oscillations can grow and we agree with Moore that both umbral flashes and penumbral waves may be due to overstable oscillations. However, we suggest that both phenomena can arise at the same depth in the spot, and not in two layers, as Moore suggests.

Mullan, D. J.↗