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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

The luminous, slow-rising orphan afterglow AT2019pim as a candidate moderately relativistic outflow

ABSTRACT Classical gamma-ray bursts (GRBs) have two distinct emission episodes: prompt emission from ultrarelativistic ejecta and afterglow from shocked circumstellar material. While both components are extremely luminous in known GRBs, a variety of scenarios predict the existence of luminous afterglow emission with little or no associated high-energy prompt emission. We present AT 2019pim, the first spectroscopically confirmed afterglow with no observed high-energy emission to be identified. Serendipitously discovered during follow-up observations of a gravitational-wave trigger and located in a contemporaneous TESS sector, it is hallmarked by a fast-rising ($t \approx 2$ h), luminous ($M_{\rm UV,peak} \approx -24.4$ mag) optical transient with accompanying luminous X-ray and radio emission. No gamma-ray emission consistent with the time and location of the transient was detected by Fermi-GBM or by Konus, placing constraining limits on an accompanying GRB. We investigate several independent observational aspects of the afterglow in the context of constraints on relativistic motion and find all of them are consistent with an initial Lorentz factor of $\Gamma _0 \approx$ 10–30 for the on-axis material, significantly lower than in any well-observed GRB and consistent with the theoretically predicted ‘dirty fireball’ scenario in which the high-energy prompt emission is stifled by pair production. However, we cannot rule out a structured jet model in which only the line-of-sight material was ejected at low-$\Gamma$, off-axis from a classical high-$\Gamma$ jet core, and an on-axis GRB with below-average gamma-ray efficiency also remains a possibility. This event represents a milestone in orphan afterglow searches, demonstrating that luminous optical afterglows lacking detected GRB counterparts can be identified and spectroscopically confirmed in real time.

Perley, Daniel A. (ORCID:0000000184721996)↗
DOE OSTI2016

Tepidibacillus decaturensis sp. nov., a microaerophilic, moderately thermophilic iron-reducing bacterium isolated from 1.7 km depth groundwater

Here, a Gram-stain-negative, microaerophilic rod-shaped organism designated as strain Z9 T was isolated from groundwater of 1.7 km depth from the Mt. Simon Sandstone of the Illinois Basin, Illinois, USA. Cells of strain Z9 T were rod shaped with dimensions of 0.3×(1–10) µm and stained Gram-negative. Strain Z9 T grew within the temperature range 20–60 °C (optimum at 30–40 °C), between pH 5 and 8 (optimum 5.2–5.8) and under salt concentrations of 1–5 % (w/v) NaCl (optimum 2.5 % NaCl). In addition to growth by fermentation and nitrate reduction, this strain was able to reduce Fe(III), Mn(IV), Co(III) and Cr(VI) when H 2 or organic carbon was available as the electron donor, but did not actively reduce oxidized sulfur compounds (e.g. sulfate, thiosulfate or S 0 ). The G+C content of the DNA from strain Z9 T was 36.1 mol%. Phylogenetic analysis of the 16S rRNA gene from strain Z9 T showed that it belongs to the class Bacilli and shares 97 % sequence similarity with the only currently characterized member of the genus Tepidibacillus , T. fermentans . Based on the physiological distinctness and phylogenetic information, strain Z9 T represents a novel species within the genus Tepidibacillus , for which the name Tepidibacillus decaturensis sp. nov. is proposed. The type strain is Z9 T (=ATCC BAA-2644 T =DSM 103037 T ).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2011

Electron-impact ionization of moderately charged atomic ions in excited states

Nonperturbative R-matrix and perturbative distorted-wave methods are used to calculate electron-impact ionization cross sections for C{sup 3+} in excited states. Convergence studies for the cross sections of the 1s{sup 2}5s excited configuration reveal that both the R-matrix and distorted-wave methods need fairly high ejected electron angular momenta. Reasonable agreement is found between the converged R-matrix and distorted-wave cross sections. Thus, the use of the computationally less demanding distorted-wave method as a tool for the n scaling of excited-state ionization cross sections appears to be reasonable for atomic ions with charge q{>=}3.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Bond-Peierls polaron: Moderate mass enhancement and current-carrying ground state

We study polarons in the one-dimensional Bond-Peierls electron-phonon model in which phonons on bonds of a lattice modulate the hopping of electrons between lattice sites and contrast the results to those known for the breathing-mode Peierls problem. By inspecting the atomic limit, we show that polaronic dressing and mass enhancement of Bond-Peierls polarons depend on the momentum dependence of the phonons. For dispersionless phonons, Bond-Peierls polarons are perfectly localized in the atomic limit, unlike their breathing-mode counter-parts because the carrier creates a string of phonon excitations that can only be annihilated via processes that retrace the carrier to its original site. Furthermore, inclusion of phonon dispersion leads to a nondivergent polaron mass even in the atomic limit and depending on the form of the phonon dispersion may lead to a transition to a non-zero-momentum ground state akin to that found in the breathing-mode Peierls model.

1-dimensional systems↗
DOE OSTI2011

Electroweak nuclear response at moderate momentum transfer

We discuss the convergence of the expansion of the nuclear electroweak current in powers of |k|/M, where M is the nucleon mass and k denotes either the momentum transfer or the momentum of the struck nucleon. We have computed the electron and neutrino scattering cross sections off uniform nuclear matter at equilibrium density using correlated wave functions and the cluster expansion formalism. The results of our work suggest that the proposed approach provides accurate estimates of the measured electron scattering cross sections. On the other hand, the description of the current based on the widely used leading-order approximation does not appear to be adequate, even at momentum transfer as low as 300 MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Precise determination of the deuteron spin structure at low to moderate Q 2 with CLAS and extraction of the neutron contribution

In this study, we present the final results for the deuteron spin structure functions obtained from the full data set collected with Jefferson Lab's CLAS in 2000-2001. Polarized electrons with energies of 1.6, 2.5, 4.2 and 5.8 GeV were scattered from deuteron ( 15 ND 3 ) targets, dynamically polarized along the beam direction, and detected with CLAS. From the measured double spin asymmetry, the virtual photon absorption asymmetry A d 1 and the polarized structure function g d 1 were extracted over a wide kinematic range (0.05 GeV2 < Q2 < 5 GeV2 and 0.9 GeV < W < 3 GeV). We use an unfolding procedure and a parametrization of the corresponding proton results to extract from these data the polarized structure functions A n 1 and g 1 n of the (bound) neutron, which are so far unknown in the resonance region, W < 2 GeV. We compare our final results, including several moments of the deuteron and neutron spin structure functions, with various theoretical models and expectations as well as parametrizations of the world data. The unprecedented precision and dense kinematic coverage of these data can aid in future extractions of polarized parton distributions, tests of perturbative QCD predictions for the quark polarization at large x, a better understanding of quark-hadron duality, and more precise values for higher-twist matrix elements in the framework of the Operator Product Expansion.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Structure of a highly acidic β-lactamase from the moderate halophile Chromohalobacter sp. 560 and the discovery of a Cs{sup +}-selective binding site

The tertiary structure of a β-lactamase derived from the halobacterium Chromohalobacter sp. 560 (HaBLA) was determined by X-ray crystallography. Three unique Sr{sup 2+}-binding sites and one Cs{sup +}-binding site were discovered in the HaBLA molecule. Environmentally friendly absorbents are needed for Sr{sup 2+} and Cs{sup +}, as the removal of the radioactive Sr{sup 2+} and Cs{sup +} that has leaked from the Fukushima Nuclear Power Plant is one of the most important problems in Japan. Halophilic proteins are known to have many acidic residues on their surface that can provide specific binding sites for metal ions such as Cs{sup +} or Sr{sup 2+}. The crystal structure of a halophilic β-lactamase from Chromohalobacter sp. 560 (HaBLA) was determined to resolutions of between 1.8 and 2.9 Å in space group P3{sub 1} using X-ray crystallography. Moreover, the locations of bound Sr{sup 2+} and Cs{sup +} ions were identified by anomalous X-ray diffraction. The location of one Cs{sup +}-specific binding site was identified in HaBLA even in the presence of a ninefold molar excess of Na{sup +} (90 mM Na{sup +}/10 mM Cs{sup +}). From an activity assay using isothermal titration calorimetry, the bound Sr{sup 2+} and Cs{sup +} ions do not significantly affect the enzymatic function of HaBLA. The observation of a selective and high-affinity Cs{sup +}-binding site provides important information that is useful for the design of artificial Cs{sup +}-binding sites that may be useful in the bioremediation of radioactive isotopes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Stomatal behaviour moderates the water cost of CO 2 acquisition for 21 boreal and temperate species under experimental climate change

Abstract The linkage of stomatal behaviour with photosynthesis is critical to understanding water and carbon cycles under global change. The relationship of stomatal conductance (g s ) and CO 2 assimilation (A net ) across a range of environmental contexts, as represented in the model parameter (g 1 ), has served as a proxy of the marginal water cost of carbon acquisition. We useg 1 to assess species differences in stomatal behaviour to a decade of open‐air experimental climate change manipulations, asking whether generalisable patterns exist across species and climate contexts.A net ‐g s measurements (17 727) for 21 boreal and temperate tree species under ambient and +3.3°C warming, and ambient and ~40% summer rainfall reduction, provided >2700 estimates ofg 1 . Warming and/or reduced rainfall treatments both loweredg 1 because those treatments resulted in lower soil moisture and because stomatal behaviour changed more in warming when soil moisture was low. Species tended to respond similarly, although, in species from warmer and drier habitats, g 1 tended to be slightly higher and to be the least sensitive to the decrease in soil water. Overall, both warming and rainfall reduction consistently made stomatal behaviour more conservative in terms of water loss per unit carbon gain across 21 species and a decade of experimental observation.

Plant Sciences↗
DOE OSTI2018

Uranium polyhydrides at moderate pressures: Prediction, synthesis, and expected superconductivity

Hydrogen-rich hydrides attract great attention due to recent theoretical (1) and then experimental discovery of record high-temperature superconductivity in H 3 S [T c = 203 K at 155 GPa (2)]. Here we search for stable uranium hydrides at pressures up to 500 GPa using ab initio evolutionary crystal structure prediction. Chemistry of the U-H system turned out to be extremely rich, with 14 new compounds, including hydrogen-rich UH 5 , UH 6 , U 2 H 13 , UH 7 , UH 8 , U 2 H 17 , and UH 9 . Their crystal structures are based on either common face-centered cubic or hexagonal close-packed uranium sublattice and unusual H 8 cubic clusters. Our high-pressure experiments at 1 to 103 GPa confirm the predicted UH 7 , UH 8 , and three different phases of UH 5 , raising confidence about predictions of the other phases. Many of the newly predicted phases are expected to be high-temperature superconductors. The highest-T c superconductor is UH 7 , predicted to be thermodynamically stable at pressures above 22 GPa (with T c = 44 to 54 K), and this phase remains dynamically stable upon decompression to zero pressure (where it has T c = 57 to 66 K).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Analysis of the uncertainties in the physical calculations of water-moderated power reactors of the VVER type by the parameters of models of preparing few-group constants

The article covers the uncertainty analysis of the physical calculations of the VVER reactor core for different meshes of the reference values of the feedback parameters (FBP). Various numbers of nodes of the parametric axes of FBPs and different ranges between them are investigated. The uncertainties of the dynamic calculations are analyzed using RTS RCCA ejection as an example within the framework of the model with the boundary conditions at the core inlet and outlet.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

Electron–ion relaxation time in moderately degenerate plasma

A formula is derived for the electron–ion relaxation time in a partially degenerate plasma with electron-ion interaction via a central field. The resulting expression in the form of an integral of the transport cross section generalizes the well-known Landau and Brysk approximations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗