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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Consistency between reflection momentum-resolved electron energy loss spectroscopy and optical spectroscopy measurements of the long-wavelength density response of Bi 2 Sr 2 CaCu 2 O 8 + x

The density fluctuation spectrum captures many fundamental properties of strange metals. Using momentum-resolved electron energy-loss spectroscopy (M-EELS), we recently showed that the density response of the strange metal Bi 2 Sr 2 CaCu 2 O 8+x (Bi-2212) at large momentum, q, exhibits a constant-in-frequency continuum reminiscent of the marginal Fermi liquid (MFL) hypothesis of the late 1980s. However, reconciling this observation with infrared (IR) optics experiments, which show a well-defined plasmon excitation at q ~ 0, has been challenging. Here we report M-EELS measurements of Bi-2212 using 4× improved momentum resolution, allowing us to reach the optical limit. For momenta q < 0.04 r.l.u., the M-EELS data show a plasmon feature that is quantitatively consistent with IR optics. For q > 0.04 r.l.u., the spectra become incoherent with an MFL-like, constant-in-frequency form. Here we speculate that, at finite frequency, ω, and nonzero q, some attribute of this Planckian metal randomizes the probe electron, causing it to lose information about its own momentum.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Mirror at the edge of the universe: Reflections on an accelerated boundary correspondence with de Sitter cosmology

An accelerated boundary correspondence (ABC) is solved for the de Sitter moving mirror cosmology. The beta Bogoliubov coefficients reveal the particle spectrum is a Planck distribution with temperature inversely proportional to horizon radius. The quantum stress tensor indicates a constant emission of energy flux consistent with eternal equilibrium, while the total energy carried by the particles remains finite. In conclusion, the curved spacetime transformation to flat spacetime with an accelerated boundary is illustrated, and also shown for anti-de Sitter (AdS) spacetime.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Reflections on Noether’s second theorem and the energy-momentum tensor

Through symmetry of the action under global spacetime translations, Noether’s first theorem infamously entails an energy-momentum tensor (EMT) that is neither symmetric nor gauge-invariant. In a prior work [Phys. Rev. D 106, 125012 (2022)], I had obtained a symmetric and gauge-invariant EMT by using Noether’s second theorem instead, with local spacetime translations as the symmetry group. However, the derivation therein was flawed, containing a faulty assumption about the transformation rule for spinor fields. In this work, I revisit the derivation of the previous work, both correcting the faulty step and simplifying the derivation for broader accessibility. The end result is an EMT for quantum chromodynamics that is gauge-invariant, but not symmetric.

Quantum chromodynamics↗
DOE OSTI2020

Two-stage reflective self-seeding scheme for high-repetition-rate X-ray free-electron lasers

X-ray free-electron lasers (XFELs) open a new era of X-ray based research by generating extremely intense X-ray flashes. To further improve the spectrum brightness, a self-seeding FEL scheme has been developed and demonstrated experimentally. As the next step, new-generation FELs with high repetition rates are being designed, built and commissioned around the world. A high repetition rate would significantly speed up the scientific research; however, alongside this improvement comes new challenges surrounding thermal management of the self-seeding monochromator. Here, a new configuration for self-seeding FELs is proposed, operated under a high repetition rate which can strongly suppress the thermal effects on the monochromator and provides a narrow-bandwidth FEL pulse. Three-dimension time-dependent simulations have been performed to demonstrate this idea. Finally, with this proposed configuration, high-repetition-rate XFEL facilities are able to generate narrow-bandwidth X-ray pulses without obvious thermal concern on the monochromators.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Distribution and abundance of tetraether lipid cyclization genes in terrestrial hot springs reflect pH

Many Archaea produce membrane-spanning lipids that enable life in extreme environments. These isoprenoid glycerol dibiphytanyl glycerol tetraethers (GDGTs) may contain up to eight cyclopentyl and one cyclohexyl ring, where higher degrees of cyclization are associated with more acidic, hotter or energy-limited conditions. Recently, the genes encoding GDGT ring synthases, grsAB, were identified in two Sulfolobaceae; however, the distribution and abundance of grs homologs across environments inhabited by these and related organisms remain a mystery. To address this, we examined the distribution of grs homologs in relation to environmental temperature and pH, from thermal springs across Earth, where sequences derive from metagenomes, metatranscriptomes, single-cell and cultivar genomes. The abundance of grs homologs shows a strong negative correlation to pH, but a weak positive correlation to temperature. Archaeal genomes and metagenome-assembled genomes (MAGs) that carry two or more grs copies are more abundant in low pH springs. We also find grs in 12 archaeal classes, with the most representatives in Thermoproteia, followed by MAGs of the uncultured Korarchaeia, Bathyarchaeia and Hadarchaeia, while several Nitrososphaeria encodes >3 copies. Furthermore, our findings highlight the key role of grs-catalysed lipid cyclization in archaeal diversification across hot and acidic environments.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Linking leaf dark respiration to leaf traits and reflectance spectroscopy across diverse forest types

Leaf dark respiration (R dark ), an important yet rarely quantified component of carbon cycling in forest ecosystems, is often simulated from leaf traits such as the maximum carboxylation capacity (V cmax ), leaf mass per area (LMA), nitrogen (N) and phosphorus (P) concentrations, in terrestrial biosphere models. However, the validity of these relationships across forest types remains to be thoroughly assessed. Here, in this study, we analyzed R dark variability and its associations with V cmax and other leaf traits across three temperate, subtropical and tropical forests in China, evaluating the effectiveness of leaf spectroscopy as a superior monitoring alternative. We found that leaf magnesium and calcium concentrations were more significant in explaining cross-site R dark than commonly used traits like LMA, N and P concentrations, but univariate trait–R dark relationships were always weak (r 2 ≤ 0.15) and forest-specific. Although multivariate relationships of leaf traits improved the model performance, leaf spectroscopy outperformed trait–R dark relationships, accurately predicted cross-site R dark (r 2 = 0.65) and pinpointed the factors contributing to R dark variability. Our findings reveal a few novel traits with greater cross-site scalability regarding R dark , challenging the use of empirical trait–R dark relationships in process models and emphasize the potential of leaf spectroscopy as a promising alternative for estimating R dark , which could ultimately improve process modeling of terrestrial plant respiration.

59 BASIC BIOLOGICAL SCIENCES↗