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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Natural Variability Has Concealed Increases in Western US Flood Hazard Since the 1970s

Flood hazard across the western United States (US) has generally shown decreasing trends in recent decades. This region's extreme streamflow is highly influenced by natural variability, which could either mask or amplify anthropogenic streamflow trends. Here, in this study, we utilize a technique known as dynamical adjustment to assess historical (1970–2020) annual maximum 1-day streamflow (Qx1d) from unregulated basins across the western US with and without the impact of natural variability. After removing natural variability, the fraction of basins with a positive (>5%) trend in Qx1d shifts from 25% to 53%. Basins with increasing (decreasing) Qx1d trends after dynamical adjustment exhibit weak (strong) drying, and furthermore are associated with intensifying precipitation extremes and/or large decreases in snowpack. Increasing flood hazard will likely emerge for such basins as the current phase of natural decadal variability shifts, and anthropogenic signals continue to intensify.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Evaluation of Phase Change Plaster/Paste Composites for Building Envelopes

Thermal energy storage (TES) materials increase a building’s thermal mass and provide the flexibility to shave and time-shift energy use. These materials are needed to enable grid-interactive efficient buildings, allowing building occupants to lower costs by leveraging free ambient heating/cooling as well as shifting consumption to cheaper electricity periods. Phase change materials (PCMs) that store heat through a solid-liquid/solid-solid transformation are of particular interest for TES because of their ability to store large amounts of energy across a constant temperature or very small temperature range. Furthermore, previous studies on PCM building envelopes evaluated products that may only be incorporated as part of new construction and are not easily applicable to existing, energy-intensive buildings. In this work, we leverage laboratory PCM characterization and whole-building energy simulation to study the energy and cost savings of PCM plaster/paste coatings, which can be applied post construction to both new builds and retrofits of existing buildings (about 40% of residential buildings in the United States fall into the retrofit category). We evaluated the energy impact of PCM plaster/paste composites for a single-family residential building in the United States, including layer design (location and thickness), composite properties (phase change temperature, energy density, and shape of the enthalpy curve), and U.S. climate zone. The enthalpy curve shape of PCM shows that phase change temperature and energy density are not the only two parameters that must be considered for PCM selection. Maximizing the energy density amid the effective TES zone is key to boosting energy savings. We also studied PCM price targets with the aim of achieving reasonable payback periods based on both block and time-of-use electricity rates. Moreover, we developed an empirical equation to provide a rough estimate of the energy savings potential of incorporating PCM without the need to perform detailed simulations. These results will help guide the selection and design of PCM plaster/paste composite elements for residential building envelopes.

ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION↗
DOE OSTI2021

Quantum optimal control of ten-level nuclear spin qudits in Sr 87

We study the ability to implement unitary maps on states of the I = 9 / 2 nuclear spin in Sr 87 , a d = 10 dimensional (qudecimal) Hilbert space, using quantum optimal control. Through a combination of nuclear spin resonance and a tensor ac Stark shift, by solely modulating the phase of a radio-frequency magnetic field, the system is quantum controllable. Alkaline-earth-metal atoms, such as Sr 87 , have a very favorable figure of merit for such control due to narrow intercombination lines and the large hyperfine splitting in the excited states. We numerically study the quantum speed limit, optimal parameters, and the fidelity of arbitrary state preparation and full SU(10) maps, including the presence of decoherence due to optical pumping induced by the light-shifting laser. We also study the use of robust control to mitigate some dephasing due to inhomogeneities in the light shift. We find that with an rf Rabi frequency of Ω rf and 0.5% inhomogeneity in the the light shift we can prepare an arbitrary Haar-random state in a time T = 4.5 π / Ω rf with average fidelity ( F ψ ) = 0.9992 , and an arbitrary Haar-random SU(10) map in a time T = 24 π / Ω rf with average fidelity ( F U ) = 0.9923 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Elucidate the Thermal Degradation Mechanism of Y6‐Based Organic Solar Cells by Establishing Structure‐Property Correlation

Abstract Organic solar cells (OSCs) achieved performance booming benefiting from the emerging of non‐fullerene acceptors, while inadequate device stability hampers their further application. At present, the prevalent belief attributes the inevitable thermal degradation of OSC device to morphological instability caused by excessive phase separation and crystallization in the active layer during device operation. However, it is inapplicable for state‐of‐art Y6‐based devices which strongly degrade before large‐scale morphology change. Herein, an alternative degradation mechanism is elucidated wherein molecular orientation change and demixing induced performance degradation in Y6‐based devices. Distinct from IT‐4F‐based counterpart, Y6‐based devices suffer severe thermal degradation dominated by open‐circuit voltage (V OC ) and fill factor (FF) losses. TheV OC loss is attributed to molecular orientation transition of polymer donors from edge‐on to face‐on, leading to a strong built‐in potential reduction and increase in non‐radiative loss due to energy level shifting. As forFFdecay, discontinuous acceptor phases result in electron mobility decrease by over orders of magnitude, originating from the increased molecular stacking and phase separation. This work reveals the thermal degradation mechanism for Y6‐based devices and correlates the photoelectric properties with morphology instability, which will offer guidance for improving the stability of high‐performance OSCs.

Chemistry↗
DOE OSTI2025

The possibility of hydrogen-water demixing in Uranus, Neptune, K2-18 b and TOI-270 d

Context. The internal structures of Uranus and Neptune remain unknown. In addition, sub-Neptunes are now thought to be the most common type of exoplanets. Improving our understanding of the physical processes that govern the interiors of such planets is therefore essential. Phase separation between planetary constituents may occur, in particular, hydrogen-water immiscibility in cold, water-rich intermediate-mass planets. Aims. We assess whether hydrogen-water demixing could occur in Uranus, Neptune, K2-18 b and TOI-270 d, and investigate its effect on the planetary evolution and inferred internal structure. Methods. We couple planetary evolution models with recent ab initio calculations of the hydrogen-water phase diagram, allowing for temperature shifts to account for uncertainties in miscibility gaps. Results. We find that demixing may occur and could lead to a complete depletion of water in the outermost regions of Uranus and Neptune. Temperature offsets of up to 1100 K lead to a depleted region comprising as much as 16% of the planet’s mass, and an increase in planetary radius by nearly 20%. For K2-18 b, our models suggest that hydrogen-water demixing is ongoing and may explain the absence of water features in its JWST spectrum. A temperature offset of 500 K is required to get a complete depletion of water in the atmosphere of K2-18b. TOI-270d may also have experienced hydrogen-water demixing. When applying a similar temperature offset on the phase diagram as for K2-18 b, we find a partial depletion of water in the atmosphere of TOI-270 d, consistent with JWST’s detection of water. Conclusions. Hydrogen-water immiscibility may play a key role in shaping the structure and evolution of both Solar System giant planets like Uranus and Neptune, and cold/temperate exoplanets such as K2-18 b and TOI-270 d. Accounting for such internal processes is crucial to accurately interpret atmospheric observations from current (e.g., JWST) and upcoming (e.g., ARIEL) missions.

planets and satellites: composition↗
DOE OSTI2020

X-ray scattering signatures of early-time accelerations in iodine dissociation

Ultrafast time-resolved x-ray scattering (TRXS) from a photoexcited molecular ensemble measures a distribution $S(Q, τ)$ of the x-ray momentum transfer Q and pump-probe delay τ in which all modes of motion induced by the excitation overlap. Frequency-resolved x-ray scattering (FRXS) based on $\tilde {S}\left(Q,\omega \right)$ separates each oscillation and dissociation channel in the TRXS data, enabling measurements of vibrational frequencies and phases, and dissociation velocities and time shifts. In this work, we extend FRXS analysis to study early-time accelerations as well. We show how these appear as diffuse scattering patterns with characteristic phase evolution in FXRS and we develop a set of transformations that isolate individual channels to measure the early-time accelerated motion. This procedure is used to analyze diatomic iodine x-ray scattering data with multiple dissociations, and the ability of this technique to characterize early-time accelerations of one dissociation channel even in the presence of another dissociation is demonstrated.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Composites of (C4F)n and (CF)n Synthesized by Uncatalyzed Fluorination of Graphite

A new solid-state 19F magic-angle spinning NMR signal at an isotropic 19F chemical shift of −53 ppm is measured from graphite fluoride synthesized by reaction of graphite with F2 at temperatures above 750 K with no catalyst. Two-dimensional NMR suggests the −53 ppm 19F NMR signal originates from covalent fluoromethanetriyl groups belonging to ordered (CyF)n bulk domains composited with the major (CF)n domains. Quantitative 19F and 13C NMR find y=4.32±0.64. DFT calculations of NMR chemical shifts for unsaturated fluorographene models show that a (C4F)n phase with fluorine bound covalently to a single side of the carbon layer best explains the observed NMR chemical shifts. We assign the new phase to this (C4F)n structure, which constitutes up to 15% of the carbon in our graphite fluoride composites. The (C4F)n content of the composite affects bulk electrochemical properties in a manner similar to graphite fluorides produced by conventional, catalyzed fluorination processes.

Walder, Brennan J. (ORCID:0000000274539143)↗
DOE OSTI2026

Phase change material-to-refrigerant heat exchangers: Experimental validation and uneven melting analysis

Thermal energy storage (TES) using phase change materials (PCMs) enables load shifting and reduces mismatches between the building's thermal demand and the heat pump (HP) system's thermal capacity. While most TES studies have focused on single-phase heat transfer fluids, PCM-to-refrigerant heat exchangers (PRHX), in which the refrigerant undergoes liquid-vapor phase change, remain largely underexplored. Here, to address this gap, this study systematically investigates a shell-and-tube PRHX operating as the condenser in an HP through experiments and simulations. A two-dimensional enthalpy-based finite-volume PRHX model was developed and validated against experimental data, including refrigerant and PCM temperature profiles, PRHX capacity, and system-level performance. Results show three characteristic stages: Stage I, the condenser temperature rapidly increases with PCM in the solid state absorbing sensible heat; Stage II, stable operation during PCM phase change; and Stage III, performance decline once part of the PCM becomes fully melted. Heat transfer analysis revealed that uneven PCM melting along the condenser length was driven primarily by variations in the refrigerant-side heat transfer coefficient, rather than local approach temperature differences. Further study demonstrated that minimizing refrigerant outlet subcooling led to more uniform PCM melting and extended Stages I and II by up to 89%. This paper provides a validated PRHX model, clarifies the mechanisms of uneven PCM melting, and highlights subcooling control as an effective strategy to improve TES performance in HP systems without requiring secondary loops.

Graphite matrix↗
DOE OSTI2021

An underestimated negative cloud feedback from cloud lifetime changes

As the atmosphere warms, part of the cloud population shifts from ice and mixed phase (“cold”) to liquid (“warm”) clouds. Because warm clouds are more reflective and longerlived, this phase change reduces the solar flux absorbed by Earth and constitutes a negative radiative feedback. This cooling feedback is weaker in CMIP6 than in CMIP5, contributing to greater greenhouse warming. While this change is often attributed to improvements in simulated cloud phase, another model bias persists: warm clouds precipitate too readily, potentially leading to underestimated negative lifetime feedbacks. In this work, we modify a climate model to better simulate warm rain probability and find it exhibits a cloud lifetime feedback nearly three times larger than the default model. This suggests model errors in cloud-precipitation processes may bias cloud feedbacks as much as CMIP5–CMIP6 climate sensitivity differences. Reliable climate model projections therefore require improved cloud process realism guided by process-oriented observations and observational constraints.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Noncollinear, inelastic four-wave mixing in the extreme ultraviolet

Driving four-wave mixing (FWM) processes with extreme ultraviolet (EUV) pulses could enable experimental approaches that have the potential to provide unique information on dynamics and correlations. In this work, we demonstrate inelastic FWM obtained by noncollinear mixing of two EUV pulses with different photon energies and an optical pulse in a diamond sample. This three-pulse interaction leads to the emission of an optical signal, propagating in the phase-matching direction and blue shifted by the photon energy difference of the two EUV pulses. The presented results demonstrate the feasibility of experiments such as the soft X-ray analogue of coherent anti-Stokes Raman scattering, so far only theoretically conceived [ Phys. Rev. Lett. 89 , 043001 ( 2002 ) PRLTAO 0031-9007 10.1103/PhysRevLett.89.043001 ], which can be further extended for studying vibrational and electronics dephasing in solid, liquid, or gaseous samples.

Mincigrucci, R. (ORCID:0000000163436256)↗
DOE OSTI2023

The impact of non-ideal phase change properties on phase change thermal energy storage device performance

Phase change materials have been known to improve the performance of energy storage devices by shifting or reducing thermal/electrical loads. While an ideal phase change material is one that undergoes a sharp, reversible phase transition, real phase change materials do not exhibit this behavior and often have one or more non-idealities – glide, hysteresis, supercooling – associated with them. Experimental and modeling techniques to characterize these non-ideal properties are reasonably well understood, however, their impact on the performance of a thermal energy storage system is not fully understood. Herein, we analyze the performance of a heat exchanger with a phase change material as a function of the different non-idealities, for a heating and a cooling application. We focus on the impact of these non-ideal behaviors on different modes of operation of the thermal energy storage device, which will serve as a useful guide to researchers on the relative importance of the non-ideal properties, along with the necessary accuracy required during an experimental characterization.

25 ENERGY STORAGE↗
DOE OSTI2024

Voltage and temperature effects on low cobalt lithium-ion battery cathode degradation

Degradation of low cobalt lithium-ion cathodes was tested using a full factorial combination of upper cut-off voltage (4.0 V and 4.3 V vs. Li/Li + ) and operating temperature (25 °C and 60 °C). Half-cell batteries were analyzed with electrochemical and microstructural characterization methods. Electrochemical performance was assessed with galvanostatic cycling, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) supported by distribution of relaxation times (DRT) analysis. Electrode microstructure was characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray absorption near edge structure (XANES) imaging. Higher cut-off voltage cycling shows presence of NiO x formation, a low diffusivity rock-salt phase, in both CV and XRD data. XRD patterns confirmed that the rock-salt phase was beginning to form at the low cut-off voltage at high temperature, but in much lower intensity than at the high cut-off voltage. Higher temperature accelerates degradation processes at both voltages. Degradation factors at high temperature include NiO x formation, cathode material dissolution, and electrolyte decomposition. SEM analysis suggests that supporting phases may isolate and disconnect active material particles reducing capacity retention and battery life cycle. DRT analysis and XANES imaging show that both high temperature samples revealed a NiO x phase based on an increased diffusive impedance and a visible shift in the XANES spectra. The low cut-off voltage, high temperature sample showed a split peak and shift to lower energies indicating early formation of the NiO x phase. The diffusive impedance, which hinders intercalation and deintercalation, is driven by the formation of the NiO x phase. While primarily driven by cut-off voltage, elevated temperature also contributes to this degradation mechanism.

electrochemical impedance spectroscopy↗
DOE OSTI2026

Nanometer-scale prebunched electron beams generated from all-optical plasma-based acceleration

High-quality and prebunched electron beams can produce coherent x-rays with high intensity and narrow bandwidth, which are essential for modern light sources. An all-optical scheme based on plasma-based acceleration for producing bright electron beams that are prebunched on the nanometer scale is proposed. By using a density modulation created by two low intensity counterpropagating lasers, the phase velocity of the plasma wake excited by an intense driver laser in a uniform plasma can be modulated at a frequency twice that of the colliding lasers, thus turning the injection on and off. The injected electrons are microbunched at the Doppler-shifted modulated wavelength, corresponding to the phase velocity of the gradually expanding wakefield. It is demonstrated that by controlling the properties of the drive and colliding lasers, beams with exotic prebunched structures can be produced, which may have critical applications in ultrafast high power x-rays. This extremely compact, all-optical scheme for producing ultrabright prebunched electron beams may therefore enable novel applications for ultrafast x-ray users and arouse general interest in various fields.

Beam injection, extraction & transport↗
DOE OSTI2023

Robust Vector BOTDA Signal Processing with Probabilistic Machine Learning

This paper presents a novel probabilistic machine learning (PML) framework to estimate the Brillouin frequency shift (BFS) from both Brillouin gain and phase spectra of a vector Brillouin optical time-domain analysis (VBOTDA). The PML framework is used to predict the Brillouin frequency shift (BFS) along the fiber and to assess its predictive uncertainty. We compare the predictions obtained from the proposed PML model with a conventional curve fitting method and evaluate the BFS uncertainty and data processing time for both methods. The proposed method is demonstrated using two BOTDA systems: (i) a BOTDA system with a 10 km sensing fiber and (ii) a vector BOTDA with a 25 km sensing fiber. The PML framework provides a pathway to enhance the VBOTDA system performance.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Photon phase-space dynamics in a plasma wakefield accelerator

Frequency up-shifting of laser light in a beam-driven plasma wakefield has the potential to provide high-intensity sources of short wavelength radiation. Simulations have demonstrated that a laser pulse can undergo large frequency shifts, limited only by the drive beam energy, when the plasma density is tailored to match the accelerating phase of the wake to the group velocity of the pulse. Here, we study the dynamical evolution of photons in the 1D1P phase-space vicinity of the plasma wake-phase matching condition. Numerical calculations using a photon kinetic model are validated by direct comparison with 1D and quasi-3D particle-in-cell simulations. These calculations form the basis of a linear theory of the photon dynamics which reveals several important results, including scalings for the properties of the witness pulse and a self-similar solution for the photon phase-space dynamics. One prediction of the analytic theory is that the pulse can be compressed indefinitely, though the amount of compression would ultimately be limited by practical constraints. These results suggest that photon acceleration can provide a novel source of sub-femtosecond, short wavelength radiation.

XUV generation↗
DOE OSTI2022

Improving magnitude and phase comparison metrics for frequency response functions using cross-correlation and log-frequency shifting

This paper provides a new method for matching dominant features of Frequency Response Functions (FRFs). In particular, this paper proposes a slicing and shifting method where the key features (in this case, resonant amplitudes) of a baseline FRF are compared with a similar FRF using cross-correlation and a Log-Frequency Shift (LFS). Here, the goal is to provide an alternative to classic point-to-point methods for FRF comparison and instead to match the dominant features of two FRFs in a way similar to visual inspection. This enables existing FRF comparison metrics to then be applied with greater fidelity. Additionally, this paper introduces the Phase Similarity Metric (PSM) for comparing phases of two FRFs and illustrates the improvement of using LFS for phase comparisons as well. This paper uses a cantilever beam experiment in multiple configurations to provide a benchmark case for FRF comparison improvements.

42 ENGINEERING↗
DOE OSTI2021

Rate capability and Ragone plots for phase change thermal energy storage

Phase change materials can improve the efficiency of energy systems by time shifting or reducing peak thermal loads. The value of a phase change material is defined by its energy and power density—the total available storage capacity and the speed at which it can be accessed. These are influenced by material properties but cannot be defined with these properties alone. In this work, we show the close link between energy and power density by developing thermal rate capability and Ragone plots, a framework widely used to describe the trade-off between energy and power in electrochemical storage systems (that is, batteries). Our results elucidate how material properties, geometry and operating conditions influence the performance of phase change thermal storage. This research sets a clear framework for comparing thermal storage materials and devices and can be used by researchers and designers to increase clean energy use with storage.

25 ENERGY STORAGE↗
DOE OSTI2021

Radiocarbon Analyses Quantify Peat Carbon Losses With Increasing Temperature in a Whole Ecosystem Warming Experiment

Abstract Climate warming is expected to accelerate peatland degradation and release rates of carbon dioxide (CO 2 ) and methane (CH 4 ). Spruce and Peatlands Responses Under Changing Environments is an ecosystem‐scale climate manipulation experiment, designed to examine peatland ecosystem response to climate forcings. We examined whether heating up to +9 °C to 3 m‐deep in a peat bog over a 7‐year period led to higher C turnover and CO 2 and CH 4 emissions, by measuring 14 C of solid peat, dissolved organic carbon (DOC), CH 4 , and dissolved CO 2 (DIC). DOC, a major substrate for heterotrophic respiration, increased significantly with warming. There was no 7‐year trend in the DI 14 C of the ambient plots which remained similar to their DO 14 C. At +6.75 °C and +9 °C, the 14 C of DIC, a product of microbial respiration, initially resembled ambient plots but became more depleted over 7 years of warming. We attributed the shifts in DI 14 C to the increasing importance of solid phase peat as a substrate for microbial respiration and quantified this shift via the radiocarbon mass balance. The mass‐balance model revealed increases in peat‐supported respiration of the catotelm depths in heated plots over time and relative to ambient enclosures, from a baseline of 20%–25% in ambient enclosures, to 35%–40% in the heated plots. We find that warming stimulates microorganisms to respire ancient peat C, deposited under prior climate (cooler) conditions. This apparent destabilization of the large peat C reservoir has implications for peatland‐climate feedbacks especially if the balance of the peatland is tipped from net C sink to C source.

54 ENVIRONMENTAL SCIENCES↗