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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 OSTI2012

Persistence of soil organic matter in eroding versus depositional landform positions

The terrestrial biosphere is dominated by sloping landscapes [Staub and Rosenzweig, 1986] where biogeochemical cycling of essential elements is controlled by interaction of geomorphic, pedogenic, and ecological processes that shape them. Recent studies have highlighted the important role of soil erosion in dynamics of soil organic matter (SOM) [Berhe et al., 2007, 2008; Boix-Fayos et al., 2009; Harden et al.,1999; Smith et al., 2001; Stallard, 1998a; Van Oost et al., 2007]. However, most process level studies of SOM cycling are dominantly located on nonsloping sites that experience minimal soil erosion and deposition and thus they fail to capture the influence of topography on SOM dynamics.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2012

Lagrangian perturbations and the matter bispectrum II: the resummed one-loop correction to the matter bispectrum

This is part two in a series of papers in which we investigate an approach based on Lagrangian perturbation theory (LPT) to study the non-linear evolution of the large-scale structure distribution in the universe. Firstly, we compute the matter bispectrum in real space using LPT up one-loop order, for both Gaussian and non-Gaussian initial conditions. In the initial position limit, we find that the one-loop bispectrum computed in this manner is identical to its counterpart obtained from standard Eulerian perturbation theory (SPT). Furthermore, the LPT formalism allows for a simple reorganisation of the perturbative series corresponding to the resummation of an infinite series of perturbations in SPT. Applying this method, we find a resummed one-loop bispectrum that compares favourably with results from N-body simulations. We generalise the resummation method also to the computation of the redshift-space bispectrum up to one loop.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Searching for MeV-mass neutrinophilic dark matter with large scale dark matter detectors

The indirect detection of dark matter (DM) through its annihilation products is one of the primary strategies for DM detection. One of the least constrained classes of models is neutrinophilic DM, because the annihilation products, weakly interacting neutrinos, are challenging to observe. Here, we consider a scenario where MeV-mass DM exclusively annihilates to the third neutrino mass eigenstate, which is predominantly of tau and muon flavor. In such a scenario, the potential detection rate of the neutrinos originating from the DM annihilation in our Galaxy in the conventional detectors would be suppressed by up to approximately two orders of magnitude. This is because the best sensitivity of such detectors for neutrinos with energies below approximately 100 MeV is for electron neutrino flavor. In this work, we highlight the potential of large-scale DM detectors in uncovering such signals in the tens of MeV range of DM masses. In addition, we discuss how coincident signals in direct detection DM experiments and upcoming neutrino detectors such as DUNE, Hyper-Kamiokande, and JUNO could provide new perspectives on the DM problem. Published by the American Physical Society 2025

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Observations of Continuum Depression in Warm Dense Matter with X-Ray Thomson Scattering

Detailed measurements of the electron densities, temperatures, and ionization states of compressed CH shells approaching pressures of 50 Mbar are achieved with spectrally resolved x-ray scattering. Laser- produced 9 keV x-rays probe the plasma during the transient state of three-shock coalescence. High signal- to-noise x-ray scattering spectra show direct evidence of continuum depression in highly degenerate warm dense matter states with electron densities $n_e$ > 10 24 cm –3 . Furthermore, the measured densities and temperatures agree well with radiation-hydrodynamic modeling when accounting for continuum lowering in calculations that employ detailed configuration accounting.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

First Results on Dark Matter Substructure from Astrometric Weak Lensing

Low-mass structures of dark matter (DM) are expected to be entirely devoid of light-emitting regions and baryons. Precisely because of this lack of baryonic feedback, small-scale substructures of the Milky Way are a relatively pristine testing ground for discovering aspects of DM microphysics and primordial fluctuations on subgalactic scales. In this work, we report results from the first search for Galactic DM subhalos with time-domain astrometric weak gravitational lensing. The analysis is based on a matched-filter template of local lensing corrections to the proper motion of stars in the Magellanic Clouds. We describe a data analysis pipeline detailing sample selection, background subtraction, and handling outliers and other systematics. For tentative candidate lenses, we identify a signature based on an anomalous parallax template that can unequivocally confirm the presence of a DM lens, opening up prospects for robust discovery potential with full time-series data. We present our constraints on substructure fraction f l ≲5 at 90% CL (and f l ≲2 at 50% CL) for compact lenses with radii r l <1pc, with best sensitivity reached for lens masses M l around 10 7 -10 8 M ⊙ . Parametric improvements are expected with future astrometric data sets; by end of mission, Gaia could reach f l ≲10 -3 for these massive point-like objects, and be sensitive to lighter and/or more extended subhalos for O(1) substructure fractions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The Vanishing Superfluid Density in Cuprates—and Why It Matters

Recently, we have released the results of a comprehensive study of a couple thousand single-crystal La{sub 2−x}Sr{sub x}CuO{sub 4} films, covering densely the entire overdoped side of the phase diagram (Božović et al. Nature 536, 309–311, 2016; Wu et al. Nature 547, 432–435, 2017). Here, we review the key experimental findings, place them in the context of other important well-established facts and observations, and discuss their implications for our understanding of high-temperature superconductivity in cuprates. We conclude that it involves some new physics that requires going beyond the standard Fermi liquid description of the normal state and Bardeen-Cooper-Schrieffer description of the superconducting state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Gamma-ray bounds from EAS detectors and heavy decaying dark matter constraints

The very high energy Galactic γ-ray sky is partially opaque in the (0.1–10) PeV energy range. In the light of the recently detected high energy neutrino flux by IceCube, a comparable very high energy γ-ray flux is expected in any scenario with a sizable Galactic contribution to the neutrino flux. Here we elaborate on the peculiar energy and anisotropy features imposed upon these very high energy γ-rays by the absorption on the cosmic microwave background photons and Galactic interstellar light. As a notable application of our considerations, we study the prospects of probing the PeV-scale decaying DM scenario, proposed as a possible source of IceCube neutrinos, by extensive air shower (EAS) cosmic ray experiments. In particular, we show that anisotropy measurements at EAS experiments are already sensitive to τ{sub DM}∼O(10{sup 27}) s and future measurements, using better gamma/hadron separation, can improve the limit significantly.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗