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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Enabling Ultralow Volume Analysis with a High-Resolution Ion Mobility Mass Spectrometry Platform

Of all the molecules thought to exist in the universe, it is estimated that researchers only know the chemical structures of 5% of them. Identifying the chemical structures of the remaining 95% has proven extremely challenging because many molecules exhibit low abundance, are contained in small volumes (e.g., <10 nL), do not readily ionize, exhibit similar structures to other molecules, etc. No single analytical technique exists to definitively identify the structure of an unknown molecule, and thus multiple different molecular measurements are typically made (i.e., multi-modal approach). Ion mobility (IMS) and mass spectrometry (MS) are two key tools that researchers use to determine the chemical structures of unknown molecules, and recently high-resolution and ultrahigh resolution IMS-MS instruments have provided greater confidence than ever before. However, HR-IMS-MS instruments typically exhibit low ion utilization efficiency, meaning they require large amounts of sample for an analysis (e.g., >10 µL). Unfortunately, this limitation prohibits the analysis of small volume samples where many unknown molecules exist. Described herein are the efforts made to enable the analysis of ultralow volumes with an HR-IMS-MS platform. A new scanning technique, termed a ‘stuttered traveling wave scan’, was developed as a replacement for the dual-gated scanning technique and works by halting the traveling waves after allowing ions to separate and then repeatedly restarting and stopping the traveling waves to incrementally move ions from the SLIM to the Orbitrap. Ions were stored inside the SLIM while the TWs were stopped, allowing the Orbitrap to perform high-resolution mass analysis. When the Orbitrap was ready, the TWs were restarted for short periods of time (<10 ms) to move ions from the SLIM to the Orbitrap. It was discovered that lower TW amplitudes and speeds than used during IMS separation were required to produce IMS peaks with the highest signal intensities and best resolving powers. The stuttered TW scan was found to produce similar resolutions and signal intensities compared to the dual-gated scanning technique. A new IMS design possessing an intersecting ‘tee’ with a reversible traveling wave was also developed to improve ion utilization efficiency during cyclic operation, which is necessary when only a single IMS spectrum can be acquired, such as when analyzing ultralow volume samples. The new capabilities described in this report lay the groundwork for acquiring HR-IMS-MS spectra of ultralow volume biological samples, such as single cells, where HR-IMS-MS can help elucidate the structures of unknown compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Manufacturing Bulk Nanocrystalline Al-3Mg Components Using Cryomilling and Spark Plasma Sintering

In the current study, pure aluminum (Al) powders were cryomilled with and without 3 wt.% pure magnesium (Mg) dopant for varying durations followed by spark plasma sintering (SPS) of powders to prepare bulk components with superior mechanical properties. The crystallite sizes were determined for powders and the bulk components by analyzing the X-ray diffraction (XRD) spectrum. The calculations indicated a reduction in crystallite size with the increase in the cryomilling duration. The results also showed a more significant decrease in the crystallite sizes for Al-3Mg samples than that of pure Al. The changes in the surface morphology of powders were characterized using scanning electron microscopy (SEM). The elemental mapping analysis at nanoscale was carried out using Energy-dispersive X-ray spectroscopy (EDX) in Scanning transmission electron microscopy (STEM). The mechanical properties of the bulk components were assessed using a Vickers Microhardness tester. The test results demonstrated an improvement in the hardness of Mg-doped components. Higher hardness values were also reported with an increase in the cryomilling duration. This article discusses the mechanisms for the reduction in crystallite size for pure Al and Al-3Mg and its subsequent impact on improving mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The cosmological evolution of self-interacting dark matter

We study the evolution of cosmological perturbations in dark-matter models with elastic and velocity-independent self interactions. Such interactions are imprinted in the matter-power spectrum as dark acoustic oscillations, which can be experimentally explored to determine the strength of the self scatterings. Models with self interactions have similarities to warm dark matter, as they lead to suppression of power on small scales when the dark-matter velocity dispersion is sizable. Nonetheless, both the physical origin and the extent of the suppression differ for self-interacting dark matter from conventional warm dark matter, with a dark sound horizon controlling the reduction of power in the former case, and a free-streaming length in the latter. We thoroughly analyze these differences by performing computations of the linear power spectrum using a newly developed Boltzmann code. We find that while current Lyman-α data disfavor conventional warm dark matter with a mass less than 5.3 keV, when self interactions are included at their maximal value consistent with bounds from the Bullet Cluster, the limits are relaxed to 4.4 keV. Lastly, we make use of our analysis to set novel bounds on light scalar singlet dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Constraints on dark matter scattering with long lived mediators from observations of the Sun with the Fermi Large Area Telescope

The Sun represents a promising target for indirect dark matter searches, as dark matter particles from the Galactic halo can be gravitationally trapped in its core or in external orbits, and their annihilations can lead to final states with standard model particles that are able to reach the Earth. In this work we have considered a scenario in which dark matter particles can annihilate into pairs of long-lived mediators, which in turn can escape from the Sun and decay into pairs of gamma rays or into the bb̅, τ+τ-, μ+μ- channels, with the production of gamma rays in the final states. All these processes are expected to yield an excess in the energy spectrum of gamma rays towards the Sun. We have therefore analyzed the data collected by the Fermi Large Area Telescope during its first 13.5 years of operation, searching for possible excesses in the solar gamma-ray spectrum. Since no statistically significant excess is found, we have set constraints on the dark matter-nucleon scattering cross sections in both the spin-dependent and spin-independent cases. For all the mediator decay channels explored and for dark matter masses between a few GeV/c 2 and 1 TeV/c 2 , we have found that the upper limits on the spin-dependent and spin-independent cross sections are in the ranges from 10 -45 to 10 -39 cm 2 and from 10 -47 up to 10 -42 cm 2 , respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

A practical method for modeling temporally-averaged ocean wave frequency-directional spectra for characterizing wave energy climates

Wave energy resource characterization investigations have been hindered because frequency-directional wave spectra are not broadly available for many coastal regions due to the insufficient spatial coverage of buoy observation networks and spectral wave model hindcast outputs. We address this problem by developing and validating a practical method for approximating temporally-averaged frequency-directional wave spectra averaged over periods of months or years from bulk wave parameters, which are available at a much greater coverage and resolution than frequency-directional wave spectra. While the temporally averaged frequency-directional wave spectrum over these periods cannot be used for analyzing a single sea state, it aggregates multiple sea states, identifies dominant wave energy systems representing wave climate, and resolves their spectral characteristics. Therefore, modelling temporally averaged frequency-directional wave spectra is of great value for planning and designing wave energy projects, e.g., resource characterization, site assessment, and conceptual design of wave energy converters. Temporally-averaged frequency-directional wave spectra and related important wave energy parameters approximated using this method are found to be more accurate than commonly used parametric wave spectrum models. This method can be applied to a wide range of wave climates given its universality and high accuracy. Also, the availability of bulk wave parameters from multi-decade high-resolution wave model hindcasts is increasing.

16 TIDAL AND WAVE POWER↗
DOE OSTI2024

Unveiling Hidden Shake-Up Features in the Uranyl M 4 -Edge Spectrum

The M 4,5 -edge high energy resolution X-ray absorption near-edge structure (HR-XANES) spectra of actinyls offer valuable insights into the electronic structure and bonding properties of heavy-element complexes. To conduct a comprehensive spectral analysis, it is essential to employ computational methods that accurately account for relativistic effects and electron correlation. In this work, we utilize variational relativistic multireference configurational interaction methods to compute and analyze the X-ray M 4 -edge absorption spectrum of uranyl. By employing these advanced computational techniques, we achieve excellent agreement between the calculated spectral features and experimental observations. Moreover, the calculations unveil significant shake-up features, which arise from the intricate interplay between strongly correlated 3d core-electron and ligand excitations. This research provides important theoretical insights into the spectral characteristics of heavy-element complexes. Furthermore, it establishes the foundation for utilizing M 4,5 -edge spectroscopy as a means to investigate the chemical activities of such complexes. By leveraging this technique, we can gain a deeper understanding of the bonding behavior and reactivity of heavy-element compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Monte Carlo toolkit for designing and validating step-range-filter spectrometer designs

Here, we present a Monte Carlo toolkit for validating step range filter (SRF) spectrometer designs. Geant4 is used to transport charged particles through the SRF filters to generate synthetic SRF data that include realistic CR-39 effects. Synthetic SRF spectra generated by this method inherently account for instrument response and allow for the quantification of SRF performance before shots. The usefulness of this toolkit is demonstrated through its application to a number of problems. A new broadband SRF for the ∼10 MeV wide 3He3He proton spectrum is validated, and an analysis method for analyzing 3He3He-p SRF data that accounts for instrument response is put forth. In addition, an SRF design for the compact recoil-proton spectrometer (CRS) on the Z-machine is validated. Finally, a new calibration technique for the DD-p SRF is proposed and validated.

Johnson, T. M. (ORCID:0000000193032949)↗
DOE OSTI2026

Comparative Evaluation of Spectral Methods for Robust Reactor Noise Estimation

Reactor noise analysis provides a noninvasive means to determine neutron kinetic parameters from stochastic fluctuations in detector signals. However, standard cross-power spectral density (CPSD) analyses can be sensitive to numerical processing choices, which may introduce processing-dependent systematic shifts in estimates of the prompt neutron decay constant (α) and limit reproducibility. This study uses a hybrid multitaper–Welch spectral estimator to analyze subcritical noise measurements from a fast-spectrum critical assembly. The decay constant α was extracted using three frequency-domain methods: the CPSD, the magnitude-squared coherence (MSC), and the generalized magnitude-squared coherence (GMSC). These coherence-based estimators normalize detector auto-spectral structure and are expected to reduce the sensitivity of fitted α values to processing parameters. A Sobol global sensitivity analysis identified which numerical inputs most strongly influence the fitted values of α. All estimators produced a linear dependence of α on inverse count rate, with delayed-critical extrapolations near 1.7 × 10 4 s −1 , in agreement within 8% of MCNP6.3 KOPTS benchmark calculations. Sensitivity results show that while the CPSD depends on both time-bin width and taper selection, the MSC and GMSC are dominated by time-bin width alone, indicating reduced parameter coupling and greater robustness to processing variability. These findings demonstrate the feasibility and practical value of coherence-based spectral estimators for extracting α from reactor noise and support their broader application to multi-detector and irregular datasets in subcritical system characterization.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Uncoordinated Spectrum Sharing in Millimeter Wave Networks Using Carrier Sensing

Here, we propose using Carrier Sensing (CS) for distributed interference management in millimeter-wave (mmWave) cellular networks where spectrum is shared by multiple operators that do not coordinate among themselves. In addition, even the base station sites can be shared by the operators. We describe important challenges in using traditional CS in this setting and propose enhanced CS protocols to address these challenges. Using stochastic geometry, we develop a general framework for downlink coverage probability analysis of our shared mmWave network in the presence of CS and derive the downlink coverage probability expressions for several CS protocols. Our work is the first to investigate and analyze (using stochastic geometry) CS for mmWave networks with spectrum and BS sites shared among non-coordinating operators. We evaluate the downlink coverage probability of our shared mmWave network using simulations as well as numerical examples based on our analysis. Our evaluations show that our proposed approach leads to an improvement in coverage probability, compared to the coverage probability with no CS, for higher values of signal-to-interference and noise ratio (SINR). Interestingly, our evaluations also reveal that for lower values of SINR, not using any CS is the best strategy in terms of the downlink coverage probability.

42 ENGINEERING↗
DOE OSTI2024

Infrared phase-change chiral metasurfaces with tunable circular dichroism

Integrating phase-change materials in metasurfaces has emerged as a powerful strategy to realize optical devices with tunable electromagnetic responses. Here, phase-change chiral metasurfaces based on GST-225 material with the designed trapezoid-shaped resonators are demonstrated to achieve tunable circular dichroism (CD) responses in the infrared regime. The asymmetric trapezoid-shaped resonators are designed to support two chiral plasmonic resonances with opposite CD responses for realizing switchable CD between negative and positive values using the GST phase change from amorphous to crystalline. The electromagnetic field distributions of the chiral plasmonic resonant modes are analyzed to understand the chiroptical responses of the metasurface. Furthermore, the variations in the absorption spectrum and CD value for the metasurface as a function of the baking time during the GST phase transition are analyzed to reveal the underlying thermal tuning process of the metasurface. The demonstrated phase-change metasurfaces with tunable CD responses hold significant promise in enabling many applications in the infrared regime such as chiral sensing, encrypted communication, and thermal imaging.

42 ENGINEERING↗
DOE OSTI2020

Reliability Analysis for Unreliable FSM Computations

Finite State Machines (FSMs) are fundamental in both hardware design and software development. However, the reliability of FSM computations remains poorly understood. This becomes increasingly critical as the technology scaling becomes more aggressive. Existing reliability analyses are mainly designed for generic computations and are unaware of the special error tolerance characteristics in FSM computations. In this work, we introduce RelyFSM – a state-level reliability analysis framework for FSM computations. By qualitatively reasoning about the transition structures in FSM computations, RelyFSM can precisely capture their inherent error tolerance. Basically, RelyFSM takes an FSM specification as input and analyzes its reliability for a specific execution. At the core of the analysis is a set of mathematical models that accurately define the behaviors of unreliable FSM executions. Our evaluation with a spectrum of FSM benchmarks confirms the accuracy and efficiency of RelyFSM in analyzing the reliability of real-world FSM computations.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Design, Detection, and Countermeasure of Frequency Spectrum Attack and Its Impact on Long Short-Term Memory Load Forecasting and Microgrid Energy Management

This paper introduces a frequency-domain false data injection attack called Frequency Spectrum Attack (FSA) and explores its effects on load forecasting and the energy management system (EMS) in a microgrid. The FSA analyzes time-series signals in the frequency domain to identify patterns in their frequency spectrum. It learns the distribution of dominant frequencies in a dataset of healthy signals. Subsequently, it manipulates the amplitudes of dominant frequencies within this healthy distribution, ensuring a stealthy attack against statistical analysis of the signal spectrum. We evaluated the performance of FSA on LSTM, a state-of-the-art network for load forecasting. The results show that FSA can triple the Mean Absolute Error (MAE) of predictions compared to the normal case and increase it by 70% compared to noise injection attacks. Furthermore, FSA indirectly enhances battery utilization in the EMS by 45%. We then proposed a detection method that combines statistical analysis and machine-learning-based classification techniques with features. The model effectively distinguishes FSA from healthy and noisy signals, achieving an accuracy of 98.7% and an F1-score of 98.1% on a load dataset, covering healthy, FSA, and noisy load data. Finally, a countermeasure was introduced based on the statistical analysis of the frequency spectrum of healthy signals to mitigate the impact of FSA. This countermeasure successfully reduces the MAE of the attacked model from 0.135 to 0.053, validating its effectiveness in mitigating FSA.

Nazeri, Amirhossein↗
DOE OSTI2026

Double copy root of Hawking thermality

The Hawking radiation spectrum from a collapsing null shell can be derived via the double copy of a simpler gauge theory calculation. Analyzing the non-abelian Yang-Mills root of this process, we demonstrate that the radiation spectrum is thermal in the color charge eigenvalue 𝜆, not energy. Considering the 𝑆⁢𝑈⁡(𝑁 𝑐 ) gauge theory in the large 𝑁 𝑐 limit, we find the differential spectrum ⅆ⁢𝑁/ⅆ⁢𝜆 is a product of the gravitationally familiar Planck-like factor and the color phase space density, modeled here as the Wigner semicircle from random matrix theory. This reveals that apparent energy thermality in gravity is the direct dual of charge thermality in its underlying non-abelian gauge theory.

Carrasco, John Joseph M. [Northwestern University,↗
DOE OSTI2024

Spin-statistics for black hole microstates

The gravitational path integral can be used to compute the number of black hole states for a given energy window, or the free energy in a thermal ensemble. In this article we explain how to use the gravitational path integral to compute the separate number of bosonic and fermionic black hole microstates. We do this by comparing the partition function with and without the insertion of (–1) F . In particular we introduce a universal rotating black hole that contributes to the partition function in the presence of (–1) F. We study this problem for black holes in asymptotically flat space and in AdS, putting constraints on the high energy spectrum of holographic CFTs (not necessarily supersymmetric). Finally, we analyze wormhole contributions to related quantities.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Experimental investigation of PDI bifurcation of lower hybrid waves during electron density ramp-up in EAST

Abstract The effect of parametric decay instability (PDI) on the current drive efficiency of 4.6 GHz lower hybrid (LH) waves in EAST is investigated experimentally, showing the PDI channel bifurcation of LH waves for the first time in EAST. First, experiments with three platforms of LH power were performed, achieving the LH power required for the PDI occurrence. Second, PDI bifurcation experiments were further carried out by ramping up the plasma electron density. The loop voltage increases with an increase in density, implying a decrease in the current driven by the LH wave. PDI bifurcation during electron density ramp-up was studied by analyzing the parallel refractive index ( n ∥ ) and the frequency spectrum broadening, which is measured with a radio frequency magnetic probe array recently installed close to the LH antenna. It is observed for the first time that they both first increase with density, then there is not much variation and a clear sideband in the frequency spectrum is also observed when the density is up to 4 × 10 19 m − 3 , suggesting a change in the PDI channel. Calculation of the mode growth rate driven by PDI shows that when the edge electron density is up to 1.9 × 10 18 m − 3 , the growth rate of the ion cyclotron quasi-mode (ICQM) will exceed that of the ion sound quasi-mode (ISQM), quantitively explaining that with an increase in density, the PDI channel partly transits from the ISQM to the ICQM channel. Studies provide a possible way to reduce the power deposition in the edge region and improve drive capability by means of mitigating PDI behavior.

Physics↗
DOE OSTI2024

Data Based Shock Test Specification

It is vital that avionic packages used for testing and certifying the reliability and safety of U.S. nuclear weapons with platform aircraft survive exposure to shock environments during transportation and delivery. The objective of this research was to characterize the response to these transportation shock environments delivering accurate shock test specifications in order to set laboratory programming material and device certification rigor. Responses to shock events were analyzed in the frequency domain via the Shock Response Spectrum (SRS). Shocks were then grouped based on respective behavior of maximum response accelerations which were pseudorandomly resampled and compared to test data to form test specifications based on the MinerPalmgren hypothesis. In addition to discovering significant over testing in current shock specifications, a new systematic, data-driven approach to designing shock specifications was formulated.

42 ENGINEERING↗
DOE OSTI2024

Solar Design/Install Labor Quantification (Cooperative Research and Development Final Report)

The goals of this project were to quantify the rate and/or total expected labor expenditure of engineers designing solar arrays and electricians installing solar across a spectrum of project sizes and configurations. Specifically, procuring and analyzing labor data from solar engineering firms relating to the amount of time it takes an engineer to design a solar project, the amount of time it takes an engineer to perform a wiring or stringing design, the amount of time it takes an electrician to install a solar project and the amount of time it takes electricians to install the strings of a solar array. Then these details could be analyzed to evaluate labor intensity for solar design/installation. These goals were unable to be completed because the participant was unable to collect the necessary data for analysis.

14 SOLAR ENERGY↗
DOE OSTI2022

Identification and assignment of rotational spectra using artificial neural networks

A method of identifying molecular parameters may include receiving observed transition frequencies, generating transition frequency sets and a spectral parameter sets, training one or more artificial neural networks by analyzing the transition frequency sets and the spectral parameter sets, analyzing the observed transition frequencies using the one or more trained artificial neural networks to predict estimated spectral parameters, and identifying molecular parameters by analyzing the estimated spectral parameters. A molecular parameter identification system may include a rotational spectrometer, a user interface, and a spectrum analysis application that may retrieve observed transition frequencies, identify a Hamiltonian type by a neural network analyzing the observed transition frequencies, select a second trained artificial neural network based on the identified Hamiltonian type, analyze observed transition frequencies using the second artificial neural network to identify estimated spectral parameters, and identify molecular parameters.

Prozuments, Kirills↗