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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Exceptional Fluorocarbon Uptake with Mesoporous Metal-Organic Frameworks for Adsorption-Based Cooling Systems

For the first time, a series of well-reported mesoporous metal–organic frameworks (MOFs) have been tested for R134a fluorocarbon adsorption. Differences in sorption behavior were attributed to varying porosities and topologies. All mesoporous MOFs exhibited excellent, reversible R134a adsorption capacities and among them, NU-1000 provided an exceptional fluorocarbon uptake of ~170 wt% near saturation, which is among the highest values reported so far for MOFs. N2 sorption, high-resolution STEM, and micro calorimetry were used to further explore the relation between the features of NU-1000 and the exceptionally high R134a uptake capacity. Such high performance materials with the appropriate equilibrium isotherm behavior provide significant potential for adsorption cooling systems operating on pressure swing cycles. These results provide evidence that mesoporous MOFs, especially those with hierarchical structure, are promising candidates for chiller applications.

adsorption cooling, fluorocarbons, mesoporous, met↗
DOE OSTI2019

Machine Learning Accelerates the Discovery of Design Rules and Exceptions in Stable Metal–Oxo Intermediate Formation

Metal–oxo moieties are important catalytic intermediates in the selective partial oxidation of hydrocarbons and in water splitting. Stable metal–oxo species have reactive properties that vary depending on the spin state of the metal, complicating the development of structure–property relationships. To overcome these challenges, we train machine-learning (ML) models capable of predicting metal–oxo formation energies across a range of first-row metals, oxidation states, and spin states. Using connectivity-only features tailored for inorganic chemistry as inputs to kernel ridge regression or artificial neural network (ANN) ML models, we achieve good mean absolute errors (4–5 kcal/mol) on set-aside test data across a range of ligand orientations. Analysis of feature importance for oxo formation energy prediction reveals the dominance of nonlocal, electronic ligand properties in contrast to other transition metal complex properties (e.g., spin-state or ionization potential). We enumerate the theoretical catalyst space with an ANN, revealing expected trends in oxo formation energetics, such as destabilization of the metal–oxo species with increasing d-filling, as well as exceptions, such as weak correlations with indicators of oxidative stability of the metal in the resting state or unexpected spin-state dependence in reactivity. We carry out uncertainty-aware evolutionary optimization using the ANN to explore a >37 000 candidate catalyst space. New metal and oxidation state combinations are uncovered and validated with density functional theory (DFT), including counterintuitive oxo formation energies for oxidatively stable complexes. This approach doubles the density of confirmed DFT leads in originally sparsely populated regions of property space, highlighting the potential of ML-model-driven discovery to uncover catalyst design rules and exceptions.

transition metal catalysis↗
DOE OSTI2016

Exceptionally Long-Lived Charge Separated State in Zeolitic Imidazolate Framework: Implication for Photocatalytic Applications

Zeolitic Imidazolate Frameworks (ZIFs) have emerged as a novel class of porous metal-organic frameworks (MOFs) for catalysis application because of their exceptional thermal and chemical stability. Inspired by the broad absorption of ZIF-67 in UV-visible-near IR region, we explored its excited state and charge separation dynamics, properties essential for photocatalytic applications, using optical (OTA) and X-ray transient absorption (XTA) spectroscopy. OTA results show that an exceptionally long-lived excited state is formed after photoexcitation. This long-lived excited state was confirmed to be the charge separated state with ligandto-metal charge transfer character using XTA. The surprisingly long-lived charge separated state, together with its intrinsic hybrid nature, all point to its potential application in heterogeneous photocatalysis and energy conversion.

Pattengale, Brian↗
DOE OSTI2017

Hyperconnected molecular glass network architectures with exceptional elastic properties

Hyperconnected network architectures can endow nanomaterials with remarkable mechanical properties that are fundamentally controlled by designing connectivity into the intrinsic molecular structure. For hybrid organic–inorganic nanomaterials, here we show that by using 1,3,5 silyl benzene precursors, the connectivity of a silicon atom within the network extends beyond its chemical coordination number, resulting in a hyperconnected network with exceptional elastic stiffness, higher than that of fully dense silica. The exceptional intrinsic stiffness of these hyperconnected glass networks is demonstrated with molecular dynamics models and these model predictions are calibrated through the synthesis and characterization of an intrinsically porous hybrid glass processed from 1,3,5(triethoxysilyl) benzene. Altogether, the proposed molecular design strategy applies to any materials system wherein the mechanical properties are controlled by the underlying network connectivity.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Robust lasing modes in coupled colloidal quantum dot microdisk pairs using a non-Hermitian exceptional point

Evanescently coupled pairs of microdisk lasers have emerged as a useful platform for studying the non-Hermitian physics of exceptional points. It remains an open question how scalable and versatile such phenomena can be when carried over to other designs. Here we have studied the effect of gain/loss modulation in an evanescently coupled pair of microdisk optical resonators fabricated from solution-processed colloidal quantum dots. The emission spectra of these structures are sensitive to small imperfections, which cause frequency-splitting of the whispering gallery modes. Despite this inherent disorder, we found that when spatially modulating the optical pump to vary the gain differential between the coupled microdisks, the coupling drives the split parasitic intra-cavity modes into coalescence at an exceptional point of the resulting three-mode system. This unusual behavior is rationalized via a Hamiltonian that incorporates the intra-cavity coupling as well as the anisotropic inter-cavity coupling between modes in the microdisk pair.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Exceptionally crystalline and conducting acid doped polyaniline films by level surface assisted solution casting approach

Emeraldine salt form of polyaniline (PANI) was synthesized by chemical oxidative polymerisation method using ammonium persulfate as oxidant. Resultant emeraldine salt form of PANI was dedoped using ammonia solution and then re-doped with camphor sulphonic acid (CSA), naphthaline sulphonic acid (NSA), hydrochloric acid (HCl), and m-cresol. Thin films of these doped PANI samples were deposited on glass substrates using solution casting method with m-cresol as solvent. A level surface was employed to get homogeneous thin films of uniform thickness. Detailed X-ray diffraction studies have shown that the films are exceptionally crystalline. The crystalline peaks observed in the XRD spectra can be indexed to simple monoclinic structure. FTIR and Raman spectroscopy studies provide convincing explanation for the exceptional crystallinity observed in these polymer films. FESEM and AFM images give better details of surface morphology of doped PANI films. The DC electrical conductivity of the samples was measured using four point probe technique. It is seen that the samples also exhibit quite high DC electrical conductivity, about 287 S/cm for CSA doped PANI, 67 S/cm for NSA doped PANI 65 S/cm for HCl doped PANI, and just below 1 S/cm for m-cresol doped PANI. Effect of using the level surface for solution casting is studied and correlated with the observed crystallinity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

The blob crashes into the mirror: modeling the exceptional γ-ray flaring activity of 3C 454.3 in 2010 November

3C 454.3 is a prominent flat-spectrum radio quasar that in recent years attracted considerable attention because of its variable high-energy emissions. In this paper, we focus on the exceptional flaring activity of 3C 454.3 that was detected by AGILE and by Fermi-LAT in 2010 November. In the light of the time-varying data ranging from the radio, optical, and X-ray up to GeV γ-ray bands, we discuss a theoretical framework addressing all data in their overall evolution. For two weeks, the source has shown a plateau of enhanced GeV emission preceding a sudden major flare lasting about three days before decaying. The γ-ray flare onset is abrupt (about six hours), and is characterized by a prominent 'Compton dominance' with the GeV flux exceeding the pre-flare values by a factor of four to five. During this episode, the optical and X-ray fluxes increased by a factor of around two. Within the standard framework of a jet launched with a Lorentz bulk factor Γ ∼ 10 from a central black hole, we explore the yields of two alternatives. Case 1, with high-energy emission originating within the broad line region (BLR); and Case 2, with most of it produced outside at larger distances of a few parsecs. We show that Case 1 has considerable problems in explaining the whole set of multifrequency data. Case 2, instead, leads to a consistent and interesting interpretation based on the enhanced inverse Compton radiation that is produced as the jet crashes onto a mirror cloud positioned at parsec scales. This model explains the γ-ray versus optical/X-ray behavior of 3C 454.3, including the otherwise puzzling phenomena such as the prominent 'rphan' optical flare, and the enhanced line emission with no appreciable γ-ray counterpart that preceded the GeV γ-ray flare. It also accounts for the delayed onset of the latter on top of the long plateau. Our modeling of the exceptional 3C 454.3 γ-ray flare shows that while emission inside the canonical BLR is problematic, major and rapid variations can be produced at parsec scales with moderate bulk Lorentz factors Γ ≈ 15. Our 'crashed mirror' model is also applicable to other blazar flares marked by large Compton dominance of the emitted radiation such as the flare of PKS 1830–211 in 2010 October.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Neutron stars with exceptionally light QCD axions

We present a comprehensive study of axion condensed neutron stars that arise in models of an exceptionally light axion that couples to quantum chromodynamics (QCD). These axions solve the strong-charge-parity (𝐶⁢𝑃) problem, but have a mass-squared lighter than that due to QCD by a factor of 𝜖 < 1. Inside dense matter, the axion potential is altered, and much of the matter in neutron stars resides in the axion condensed phase where the strong-𝐶⁢𝑃 parameter 𝜃 = 𝜋 and 𝐶⁢𝑃 remains a good symmetry. In these regions, masses and interactions of nucleons are modified, in turn changing the equation of state (EOS), structure, and phenomenology of the neutron stars. We take the first steps toward the study of the EOS of neutron star matter at 𝜃 = 𝜋 within chiral effective field theory and use relativistic mean field theory to deduce the resulting changes to nuclear matter and the neutron star low-density EOS. We derive constraints on the exceptionally light axion parameter space based on observations of the thermal relaxation of accreting neutron stars, isolated neutron star cooling, and pulsar glitches, excluding the region up to 5 ×10 −7 ≲ 𝜖 ≲ 0.2 for 𝑚 𝑎 ≳ 2 × 10 −9 eV. We comment on potential changes to the neutron star mass-radius relationship, and discuss the possibility of novel, nuclear-density compact objects with 𝜃 = 𝜋 that are stabilized not by gravity but by the axion potential.

axions↗
DOE OSTI2026

Squeezing-Enhanced Sensing at an Exceptional Point

Pushing the boundaries of measurement precision is central for sensing and metrology, pursued by nonclassical resources such as squeezing, as well as non-Hermitian degeneracies with distinct spectral response. Their convergence, however, remains challenging. We find extraordinary enhancement of sensitivity by unifying both effects in a general framework for quantum sensing in open systems. At the parametric oscillation threshold and an exceptional point, the sensing precision exhibits a unique quartic scaling with the perturbation strength. The result generalizes to multimode squeezed-state sensors with higher-order exceptional points catered to various quantum sensing platforms.

Wang, Changqing [Fermilab] (ORCID:0000000198073045↗
DOE OSTI2022

Exceptional fracture toughness of CrCoNi-based medium- and high-entropy alloys at 20 kelvin

Medium- and high-entropy alloys based on the CrCoNi-system have been shown to display outstanding strength, tensile ductility and fracture toughness (damage-tolerance properties), especially at cryogenic temperatures. Here we examine the J Ic and (back-calculated) K JIc fracture toughness values of the face-centered cubic, equiatomic CrCoNi and CrMnFeCoNi alloys at 20 K. At flow stress values of ~1.5 GPa, crack-initiation K JIc toughnesses were found to be exceptionally high, respectively 235 and 415 MPa√m for CrMnFeCoNi and CrCoNi, with the latter displaying a crack-growth toughness K ss exceeding 540 MPa√m after 2.25 mm of stable cracking, which to our knowledge is the highest such value ever reported. Characterization of the crack-tip regions in CrCoNi by scanning electron and transmission electron microscopy reveal deformation structures at 20 K that are quite distinct from those at higher temperatures and involve heterogeneous nucleation, but restricted growth, of stacking faults and fine nanotwins, together with transformation to the hexagonal closed-packed phase. The coherent interfaces of these features can promote both the arrest and transmission of dislocations to generate respectively strength and ductility which strongly contributes to sustained strain hardening. Indeed, we believe that these nominally single-phase, concentrated solid-solution alloys develop their fracture resistance through a progressive synergy of deformation mechanisms, including dislocation glide, stacking-fault formation, nano-twinning and eventually in situ phase transformation, all of which serve to extend continuous strain hardening which simultaneously elevates strength and ductility (by delaying plastic instability), leading to truly exceptional resistance to fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2025

FloatGuard: Efficient Whole-Program Detection of Floating-Point Exceptions in AMD GPUs

FloatGuard is a tool that captures floating-point exceptions in AMD HIP kernels. FloatGuard leverages AMD GPU hardware registers to detect floating-point exceptions, overcoming the limitations of AMD's built-in trapping mechanisms through a novel algorithm that combines assembly- and source-level instrumentation with debugger-guided execution.

MIAO, WENJUN [Lawrence Livermore National Laborato↗
NASA NTRS2013

A Short-Range Distance Sensor with Exceptional Linearity

A sensor has been demonstrated that can measure distance over a total range of about 300 microns to an accuracy of about 0.1 nm (resolution of about 0.01 nm). This represents an exceptionally large dynamic range of operation - over 1,000,000. The sensor is optical in nature, and requires the attachment of a mirror to the object whose distance is being measured. This work resulted from actively developing a white light interferometric system to be used to measure the depths of defects in the Space Shuttle Orbiter windows. The concept was then applied to measuring distance. The concept later expanded to include spectrometer calibration. In summary, broadband (i.e., white) light is launched into a Michelson interferometer, one mirror of which is fixed and one of which is attached to the object whose distance is to be measured. The light emerging from the interferometer has traveled one of two distances: either the distance to the fixed mirror and back, or the distance to the moving mirror and back. These two light beams mix and produce an interference pattern where some wavelengths interfere constructively and some destructively. Sending this light into a spectrometer allows this interference pattern to be analyzed, yielding the net distance difference between the two paths. The unique feature of this distance sensor is its ability to measure accurately distance over a dynamic range of more than one million, the ratio of its range (about 300 microns) to its accuracy (about 0.1 nanometer). Such a large linear operating range is rare and arises here because both amplitude and phase-matching algorithms contribute to the performance. The sensor is limited by the need to attach a mirror of some kind to the object being tracked, and by the fairly small total range, but the exceptional dynamic range should make it of interest.

Simmons, Steven↗
NASA NTRS2016

Two Exceptions in the Large SEP Events of Solar Cycles 23 and 24

We discuss our findings from a survey of all large solar energetic particle (SEP) events of Solar Cycles 23 and 24, i.e. the SEP events where the intensity of greater than 10 megaelectronvolts protons observed by GOES (Geostationary Operational Environmental Satellite) was greater than 10 proton flux units. In our previous work (Gopalswamy et al. in Geophys.Res.Lett. 41, 2673, 2014) we suggested that ground level enhancements (GLEs) in Cycles 23 and 24 also produce an intensity increase in the GOES greater than 700 megaelectronvolts proton channel. Our survey, now extended to include all large SEP events of Cycle 23, confirms this to be true for all but two events: i) the GLE of 6 May 1998 (GLE57) for which GOES did not observe enhancement in greater than 700 megaelectronvolts protons intensities and ii) a high-energy SEP event of 8 November 2000, for which GOES observed greater than 700 megaelectronvolts protons but no GLE was recorded. Here we discuss these two exceptions. We compare GLE57 with other small GLEs, and the 8 November 2000 SEP event with those that showed similar intensity increases in the GOES greater than 700 megaelectronvolts protons but produced GLEs. We find that, because GOES greater than 700 megaelectronvolts proton intensity enhancements are typically small for small GLEs, they are difficult to discern near solar minima due to higher background. Our results also support that GLEs are generally observed when shocks of the associated coronal mass ejections (CMEs) form at heights 1.2-1.93 solar radii [R (sub solar)] and when the solar particle release occurs between 2-6 solar radii [R (sub solar)]. Our secondary findings support the view that the nose region of the CME-shock may be accelerating the first-arriving GLE particles and the observation of a GLE is also dependent on the latitudinal connectivity of the observer to the CME-shock nose. We conclude that the GOES greater than 700 megaelectronvolts proton channel can be used as an indicator of GLEs excluding some rare exceptions, such as those discussed here.

Thakur, N.↗
NASA NTRS2020

Unprecedented Atmospheric Conditions (1948–2019) Drive the 2019 Exceptional Melting Season Over the Greenland Ice Sheet

Understanding the role of atmospheric circulation anomalies on the surface mass balance of the Greenland ice sheet (GrIS) is fundamental for improving estimates of its current and future contributions to sea level rise. Here, we show, using a combination of remote sensing observations, regional climate model outputs, reanalysis data, and artificial neural networks, that unprecedented atmospheric conditions (1948–2019) occurring in the summer of 2019 over Greenland promoted new record or close-to-record values of surface mass balance (SMB), runoff, and snowfall. Specifically, runoff in 2019 ranked second within the 1948–2019 period (after 2012) and first in terms of surface mass balance negative anomaly for the hydrological year 1 September 2018–31 August 2019. The summer of 2019 was characterized by an exceptional persistence of anticyclonic conditions that, in conjunction with low albedo associated with reduced snowfall in summer, enhanced the melt–albedo feedback by promoting the absorption of solar radiation and favored advection of warm, moist air along the western portion of the ice sheet towards the north, where the surface melt has been the highest since 1948. The analysis of the frequency of daily 500 hPa geopotential heights obtained from artificial neural networks shows that the total number of days with the five most frequent atmospheric patterns that characterized the summer of 2019 was 5 standard deviations above the 1981–2010 mean, confirming the exceptional nature of the 2019 season over Greenland.

Greenland ice sheet↗
DOE OSTI2022

Observation of Weyl exceptional rings in thermal diffusion

A non-Hermitian Weyl equation indispensably requires a three-dimensional (3D) real/synthetic space, and it is thereby perceived that a Weyl exceptional ring (WER) will not be present in thermal diffusion given its purely dissipative nature. Here, we report a recipe for establishing a 3D parameter space to imitate thermal spinor field. Two orthogonal pairs of spatiotemporally modulated advections are employed to serve as two synthetic parameter dimensions, in addition to the inherent dimension corresponding to heat exchanges. We first predict the existence of WER in our hybrid conduction–advection system and experimentally observe the WER thermal signatures verifying our theoretical prediction. When coupling two WERs of opposite topological charges, the system further exhibits surface-like and bulk topological states, manifested as stationary and continuously changing thermal processes, respectively, with good robustness. Our findings reveal the long-ignored topological nature in thermal diffusion and may empower distinct paradigms for general diffusion and dissipation controls.

42 ENGINEERING↗
DOE OSTI2021

Non-Hermitian topological states in 2D line-graph lattices: evolving triple exceptional points on reciprocal line graphs

Non-Hermitian (NH) topological states, such as the doubly-degenerate nodes dubbed as exceptional points (EPs) in Bloch band structure of 2D lattices driven by gain and loss, have attracted much recent interest. We demonstrate theoretically that in the three-site edge-centered lattices, i.e. the so-called line-graph lattices, such as kagome lattice which is a line graph of hexagonal lattice, there exist three types of triply-degenerate EPs evolving intriguingly on another set of line graphs in the reciprocal space. A single TEP (STEP) with ±1/3 topological charge moves faithfully along the edges of reciprocal line graphs with varying gain and loss, while two STEPs merge distinctively into one unconventional orthogonal double TEP (DTEP) with ±2/3 charge at the vertices, which is characterized with two ordinary self-orthogonal eigenfunctions but one surprising 'orthogonal' eigenfunction. Differently, in a modified line-graph lattice with an off-edge-center site, the ordinary coalesced state of DTEPs emerges with three identical self-orthogonal eigenfunctions. Such NH states and their evolution can be generally realized in various artificial systems, such as photonic and sonic crystals, where light and sonic vortex beams with different fractional twisting can be found. Our findings shed new light on fundamental understanding of gapless topological states in NH systems in terms of creation and evolution of high-order EPs, and open up new research directions to further link line graph and flow network theory coupled with topological physics, especially under non-equilibrium gain/loss conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Bi-stability and period-doubling cascade of frequency combs in exceptional-point lasers

Abstract Recent studies have demonstrated that a laser can self-generate frequency combs when tuned near an exceptional point (EP), where two cavity modes coalesce. These EP combs induce periodic modulation of the population inversion in the gain medium, and their repetition rate is independent of the laser cavity’s free spectral range. In this work, we perform a stability analysis that reveals two notable properties of EP combs, bi-stability and a period-doubling cascade. The period-doubling cascade enables halving of the repetition rate while maintaining the comb’s total bandwidth, presenting opportunities for the design of highly compact frequency comb generators.

exceptional points↗
DOE OSTI2023

Solar Uncertainty Management and Mitigation for Exceptional Reliability in Grid Operations (SUMMER-GO): Project Final Report

The Solar Uncertainty Management and Mitigation for Exceptional Reliability in Grid Operation (SUMMER-GO) project was recently completed through a collaboration among the National Renewable Energy Laboratory, Maxar, the Electric Reliability Council of Texas (ERCOT), the University of Texas at Dallas, the University of California Berkeley, and the University of Colorado Boulder. The project made significant advances in probabilistic solar power forecasting, both through the development of Bayesian model averaging methods for ensemble forecasting and in bringing these and other advancements into practice with Maxar's delivery of operational forecasts to ERCOT. In addition to creating more reliable solar power forecasts, the project developed methods for their utilization in power system operations. These include the development of risk-aware unit commitment and economic dispatch algorithms and methods to reformulate probabilistic forecasts to be used in these power system operational models. Dynamic power system reserve methods were also developed, which have been shown in silico to create economic savings and reliability improvements on an ERCOT-like system as well as financial savings in the ERCOT system through more granular consideration of the uncertainty associated with solar power forecasts. Finally, a situational awareness tool to help grid operators better understand solar power forecast uncertainty in daily operations was developed and extensively vetted.

14 SOLAR ENERGY↗