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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 OSTI2015

Rapid selective sweep of pre-existing polymorphisms and slow fixation of new mutations in experimental evolution of Desulfovibrio vulgaris

To investigate the genetic basis of microbial evolutionary adaptation to salt (NaCl) stress, populations of Desulfovibrio vulgaris Hildenborough (DvH), a sulfate-reducing bacterium important for the biogeochemical cycling of sulfur, carbon and nitrogen, and potentially the bioremediation of toxic heavy metals and radionuclides, were propagated under salt stress or non-stress conditions for 1200 generations. Whole-genome sequencing revealed 11 mutations in salt stress-evolved clone ES9-11 and 14 mutations in non-stress-evolved clone EC3-10. Whole-population sequencing data suggested the rapid selective sweep of the pre-existing polymorphisms under salt stress within the first 100 generations and the slow fixation of new mutations. Population genotyping data demonstrated that the rapid selective sweep of pre-existing polymorphisms was common in salt stress-evolved populations. In contrast, the selection of pre-existing polymorphisms was largely random in EC populations. Consistently, at 100 generations, stress-evolved population ES9 showed improved salt tolerance, namely increased growth rate (2.0-fold), higher biomass yield (1.8-fold) and shorter lag phase (0.7-fold) under higher salinity conditions. The beneficial nature of several mutations was confirmed by site-directed mutagenesis. All four tested mutations contributed to the shortened lag phases under higher salinity condition. In particular, compared with the salt tolerance improvement in ES9-11, a mutation in a histidine kinase protein gene lytS contributed 27% of the growth rate increase and 23% of the biomass yield increase while a mutation in hypothetical gene DVU2472 contributed 24% of the biomass yield increase. Our results suggested that a few beneficial mutations could lead to dramatic improvements in salt tolerance.

Zhou, Aifen↗
DOE OSTI2019

Actinyl-cation interactions: experimental and theoretical assessment of [Np(vi)O 2 Cl 4 ] 2– and [U(vi)O 2 Cl 4 ] 2– systems

The interaction of the actinyl (AnO 2 2+ ) oxo group with low-valent cations influences the chemical and physical properties of hexavalent actinides, but the impact of these intermolecular interactions on the actinyl bond and their occurrence in solution and solid state phases remain unclear. In this study, we explore the coordination of alkali cations (Li + , Na + , K + ) with the [NpO 2 Cl 4 ] 2– coordination complexes using single-crystal X-ray diffraction, Raman spectroscopy, and density functional theory (DFT) calculations and compare to the related uranyl system. Three solid-state coordination compounds ([Li(12-crown-4)] 2 [NpO 2 Cl 4 ] (LiNp), [Na(18-crown-6)H 2 O] 2 [NpO 2 Cl 4 ] (NaNp), and [K(18-crown- 6 )] 2 [NpO 2 Cl 4 ] (KNp) have been synthesized and characterized using single-crystal X-ray diffraction and Raman spectroscopy. Only Li + cations interact with the neptunyl oxo in the solid-state compounds and this results in a red-shift of the NpO 2 2+ symmetric stretch (ν 1 ). Raman spectra of Np(VI) solutions containing lower Li + concentrations display a single peak at ~854 cm –1 and increasing the amount of Li + results in the ingrowth of a second band at 807 cm –1 . DFT calculations and vibrational analysis indicate the lower frequency vibrational band is the result of interactions between the Li + cation and the neptunyl oxo. Here, comparison to the related uranyl system shows similar interactions occur in the solid state, but subtle differences in the actinyl-cation modes in solution phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The sensitive surface chemistry of Co-free, Ni-rich layered oxides: identifying experimental conditions that influence characterization results

Recent studies have suggested that Co-free, Ni-rich layered cathodes (e.g., doped LiNiO2) can provide promising battery performance for practical applications. However, these layered cathodes suffer from significant surface instability during various stages of the sample history, which generates inherent challenges for achieving stable battery performance and obtaining statistically representative characterization results. To reliably report the surface chemistry of these materials, delicate controls of stepwise sample preparation are required. In this study, we aim to reveal how the surface chemistry of LiNiO2 based materials changes with various environments, including human exhalation, sample storage, sample preparation, electrochemistry cycling, and surface doping. Our results demonstrate that the surface of these materials is highly reactive and prone to alter at various stages of sample handling and characterization. The sensitive surface could impact the interpretation of the surface chemical and structural information, including surface carbonate formation, transition metal reduction and dissolution, and surface reconstruction. Importantly, the heterogeneity of the surface degradation calls for a consolidation of nanoscale, high-resolution characterization, and ensemble-averaged methods in order to improve statistical representation. Furthermore, the doping chemistry can effectively mitigate the surface degradation and improve overall battery performance due to the enhanced surface oxygen retention. Our study highlights the necessity of strict measurements through complementary characterizations at multiple length scales to eliminate unintentional biased conclusions.

surface chemistry, Co-free Ni-rich cathodes, Istab↗
DOE OSTI2021

Computational and experimental search for potential polyanionic K-ion cathode materials

Discovering high-energy cathode materials is critical to construct K-ion batteries for practical applications. Owing to the great success of layered oxides in Li- and Na-ion systems, K layered cathodes have also been investigated in recent years. However, the much larger size of K + compared to Li or Na introduces strong K + –K + interaction within the layer, which results in a sloped voltage profile thereby limiting the specific capacity and operating voltage. In contrast, polyanionic materials with a three-dimensional K + arrangement can effectively mitigate K + –K + interaction. In this work, ten K polyanionic compounds with theoretical capacity >100 mA h g –1 are screened from the Inorganic Crystal Structure Database as potential cathode materials for K-ion batteries. Among the ten proposed compounds, K 2 MnP 2 O 7 , K 2 Mn 2 P 2 O 7 F 2 , K 2 Fe 2 P 2 O 7 F 2 , and K 6 V 2 (PO 4 ) 4 with average voltage <4.5 V are synthesized and evaluated electrochemically. While the re-insertion of K into these compounds is not fully reversible, it may be related to the very high migration barrier that we compute for K ions. In addition, we show the successful synthesis of a series of K 3 V 3–x Cr x (PO 4 ) 4 (x = 0, 1, 2, 3) compounds. Among these, K 3 V 2 Cr(PO 4 ) 4 exhibits the largest reversible capacity, as revealed by the in situ investigation. Lastly, we find that the redox couples in many of these compounds sit at remarkably high potential, even higher than in equivalent Li compounds, which brings both opportunities and challenges in the future research of K polyanion cathodes.

25 ENERGY STORAGE↗
DOE OSTI2010

Experimental Background Studies in the Two Photon Exchange (TPE) Experiment at Jefferson Lab

This work is based on the improvement of an existing simulation for the two photon exchange (TPE) experiment at Jefferson Lab developed within the GEANT4 framework. This experiment will determine the ratio of the positron-proton elastic scattering cross section and the electron-proton elastic scattering cross section with high precision. To accomplish this measurement requires the use of a variety of devices and complex arrangements, creating background particles that manage to reach the detector system (CLAS). A number of test runs have identified the sources of background in the detector guided by previous simulations. Even so, the remaining background can be reduced considerably by the microscopic identification and locating of the background sources performed by our new simulation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Work Towards Experimental Evidence Of Hard X-Ray Photoionization In Highly Charged Krypton

Ions of almost any charge state can be produced through electron-impact ionization. Here we describe our first experiments designed to photoionize these highly charged ions with hard x-rays by pairing an electron and photon beam. A spectral line at 12.7(1) keV with an intensity corroborated by theory may be the first evidence of hard x-ray photoionization of a highly charged ion.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Experimental Results in DIS, SIDIS and DES from Jefferson Lab

Jefferson Lab's electron accelerator in its present incarnation, with a maximum beam energy slightly above 6 GeV, has already enabled a large number of experiments expanding our knowledge of nucleon and nuclear structure (especially in Deep Inelastic Scattering--DIS--at moderately high x, and in the resonance region). Several pioneering experiments have yielded first results on Deeply Virtual Compton Scattering (DVCS) and other Deep Exclusive Processes (DES), and the exploration of the rich landscape of transverse momentum-dependent (TMD) structure functions using Semi-Inclusive electron scattering (SIDIS) has begun. With the upgrade of CEBAF to 12 GeV now underway, a significantly larger kinematic space will become available. The 12 GeV program taking shape will complete a detailed mapping of inclusive, TMD and generalized distribution functions for quarks, antiquarks and gluons in the valence region and beyond.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Bulk Modulus of Sc2O3: Ab Initio Calculations and Experimental Results

The bulk modulus of scandia is evaluated by ab initio calculation, based on density functional theory, and compared with bulk modulus measurement on nearly fully dense scandia and with the value attained from the equation of state based on diamond anvil cell measurements. The current results are in the upper range of the bulk moduli results in the literature. The scatter in the literature results might be explained by the differences in the specific volumes of the measured and calculated cases. For the specific volume of 59.65 {+-} 0.07 {angstrom}{sup 3} the average measured isothermal bulk modulus of scandia from the present study and recent literature results is 188 {+-} 10 GPa.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗