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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Tunable Collective Excitations in Epitaxial Perovskite Nickelates

The formation of plasmons through the collective excitation of charge density has generated intense discussions, offering insights to fundamental sciences and potential applications. While the underlying physical principles have been well-established, the effects of multibody interactions and orbital hybridization on plasmonic dynamics remain understudied. Here, in this work, we present the observation of conventional metallic and correlated plasmons in epitaxial La 1-x Sr x NiO 3 (LSNO) films with varying Sr doping concentrations (x = 0, 0.125, 0.25), unveiling their intriguing evolution. Unlike samples at other doping concentrations, the x = 0.125 intermediate doping sample does not exhibit the correlated plasmons despite showing high optical conductivity. Through experimental investigation using spectroscopic ellipsometry and X-ray absorption spectroscopy, that is further supported by theoretical calculations, the O2p-Ni3d orbital hybridization for x = 0.125 is found to be significantly enhanced, alongside a considerable weakening of its effective interaction comprising long-range Coulomb and variable interaction, U*. These factors account for the absence of correlated plasmons and the high optical conductivity observed in LSNO(0.125). Our findings highlight the significant impact of orbital hybridization on the electronic structures and the formation of quasiparticles in strongly correlated systems, opening new paths for plasmonic-based engineering research.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Formation of Phenanthrene via Recombination of Indenyl and Cyclopentadienyl Radicals: A Theoretical Study

This work presents quantum chemical G3(MP2,CC)//B2PLYPD3/6-311G(d,p) calculations of the potential energy surface for the indenyl (C 9 H 7 ) + cyclopentadienyl (C 5 H 5 ) reaction followed by unimolecular decomposition of the C 14 H 11 radicals formed as the primary products, as well as the Rice–Ramsperger–Kassel–Marcus master equation (RRKM-ME) calculations to predict temperature- and pressure-dependent reaction rate constants and product branching ratios. The reaction begins with the barrierless recombination of indenyl and cyclopentadienyl forming a C 14 H 12 molecule with a new C–C bond connecting two five-membered rings, which subsequently dissociates to C 14 H 11 radicals by H losses. The primary products of the C 9 H 7 + C 5 H 5 → C 14 H 11 + H reaction can directly decompose by another H loss to benzofulvalene, and this pathway is most favorable in terms of the entropy factor and hence is preferable at higher temperatures. Otherwise, the initial C 14 H 11 isomers can undergo significant structural rearrangements before eliminating an H atom and producing phenanthrene, anthracene, or benzoazulenes, among which the formation of phenanthrene via the “spiran” pathway is clearly preferred. The calculated barriers along the computed favorable dissociation pathways are relatively low, in the ~30–40 kcal/mol range, making the C 14 H 11 radicals unstable at temperatures above 1000–1250 K at 1 atm. The results of RRKM-ME calculations show that, under typical combustion conditions, the decomposition of the C 14 H 11 radicals predominantly leads to benzofulvalene. However, the latter can be rapidly converted to phenanthrene via H-assisted isomerization with the rate constant for the benzofulvalene + H → phenanthrene + H reaction being close to 10 –11 cm 3 molecule –1 s –1 at 1000–1500 K and 1 atm. Here, the results provide further support for the hypothesis that recombination of two π radicals containing five-membered rings can lead to a growth of PAH with the formation of two fused six-membered rings, but the reaction mechanism may not be direct and is likely to involve two consecutive H atom losses leading to a fulvalene-like product, with subsequent H-assisted isomerization of the latter to a benzenoid PAH.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2016

The Habitability of Proxima Centauri b: I. Irradiation, Rotation and Volatile Inventory From Formation to the Present

Proxima b is a planet with a minimum mass of 1.3 M(sub ⨁) orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass, active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet and show that the planet currently receives 30 times more extreme-UV radiation than Earth and 250 times more X-rays. We compute the time evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima b’s obliquity is likely null, and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and level of triaxiality. Next, we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity, we find that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EO(sub H)) before it reached the HZ 100–200 Myr after its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We conclude that Proxima b is a viable candidate habitable planet.

Proxima Cen↗
DOE OSTI2025

Nickel hydroxide–nickel carbonate competitive growth on carbonate surfaces

The thermodynamic and kinetic factors controlling the competitive heterogeneous nucleation and growth of ubiquitous metal carbonate and hydroxide phases are poorly understood. In this work, calcite (CaCO 3 ) and magnesite (MgCO 3 ) powders were reacted with NiCl 2 (0–600 μM) for 7 days at 22 °C and 5 °C. The reacted powders were analyzed with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and energy-dispersive X-ray spectroscopy to characterize the Ni surface precipitates formed. Evidence from these techniques pointed to the formation of mixed Ni carbonate-Ni hydroxide amorphous surface precipitates. On calcite, XPS detected primarily Ni(OH) 2 despite the initial solutions being more supersaturated with respect to gaspéite (NiCO 3 ) than to theophrastite (Ni(OH) 2 ) by a factor of 17–18. In contrast, NiCO 3 was the dominant component detected by XPS on magnesite in the same conditions. Decreasing the temperature had the effect of increasing the proportion of NiCO 3 to the detriment of Ni(OH) 2 . The experimental observations were consistent with low lattice/cation size mismatch favoring NiCO 3 nucleation and temperature most influencing Ni(OH) 2 nucleation. Comparison to previous work on Co-reacted powders indicated the differences in lattice/cation size mismatch and/or water exchange rate impacted the composition of the surface precipitates more than the relative thermodynamic stabilities of the competing minerals. This work explored the heterogeneous growth regime of Ni carbonate and hydroxide phases on carbonate surfaces and shed light on the factors that control the competition between surface precipitates when mineral surfaces are in contact with aqueous solutions supersaturated with respect to multiple mineral phases. In conclusion, these results contribute to geochemists’ efforts toward interpreting data from geochemical systems with elevated Ni concentrations, improving Ni environmental remediation and recovery strategies, and predicting the fate and transport of Ni in geochemical systems.

Heterogeneous nucleation↗
DOE OSTI2021

Alkali Metal Alkoxides in Noyori-Type Hydrogenations

Chemical modification of the catalyst via the formation of the amidate HM-N-M a + complexes and/or physical activation of the substrate through C=O…M a + non-covalent interactions are two factors responsible for the rate acceleration in Noyori-type hydrogenations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Simultaneously characterization of tumoral angiogenesis and vasculogenesis in stem cell-derived teratomas

Highlights: • CAM supports the growth and differentiation of embryonic stem cells into teratomas. • In teratomas, parenchymal Embryonic stem cell-derived endothelial cells form chimeric vessels with stromal endothelial cells. • CAM allows the simultaneously characterization of vasculogenesis and angiogenesis processes. Tumor neovascularization may occur via both angiogenic and vasculogenic events. In order to investigate the vessel formation during tumor growth, we developed a novel experimental model that takes into account the differentiative and tumorigenic properties of Embryonic Stem cells (ESCs). Leukemia Inhibitory Factor-deprived murine ESCs were grafted on the top of the chick embryo chorionallantoic membrane (CAM) in ovo. Cell grafts progressively grew, forming a vascularized mass within 10 days. At this stage, the grafts are formed by cells with differentiative features representative of all three germ layers, thus originating teratomas, a germinal cell tumor. In addition, ESC supports neovascular events by recruiting host capillaries from surrounding tissue that infiltrates the tumor mass. Moreover, immunofluorescence studies demonstrate that perfused active blood vessels within the tumor are of both avian and murine origin because of the simultaneous occurrence of angiogenic and vasculogenic events. In conclusion, the chick embryo ESC/CAM-derived teratoma model may represent a useful approach to investigate both vasculogenic and angiogenic events during tumor growth and for the study of natural and synthetic modulators of the two processes.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Valence Disproportionation of GeS in the PbS Matrix Forms Pb 5 Ge 5 S 12 Inclusions with Conduction Band Alignment Leading to High n-Type Thermoelectric Performance

Converting waste heat into useful electricity using solid-state thermoelectrics has a potential for enormous global energy savings. Lead chalcogenides are among the most prominent thermoelectric materials, whose performance decreases with an increase in chalcogen amounts (e.g., PbTe>PbSe>PbS). Herein, we demonstrate the simultaneous optimization of the electrical and thermal transport properties of PbS-based compounds by alloying with GeS. The addition of GeS triggers a complex cascade of beneficial events as follows: Ge 2+ substitution in Pb 2+ and discordant off-center behavior; formation of Pb 5 Ge 5 S 12 as stable second phase inclusions through valence disproportionation of Ge 2+ to Ge0 and Ge 4+ . PbS and Pb 5 Ge 5 S 12 exhibit good conduction band energy alignment that preserves the high electron mobility; the formation of Pb 5 Ge 5 S 12 increases the electron carrier concentration by introducing S vacancies. Sb doping as the electron donor produces a large power factor and low lattice thermal conductivity (κ lat ) of ~0.61 Wm -1 K -1 . The highest performance was obtained for the 14% GeS-alloyed samples, which exhibited an increased room temperature electron mobility of ~121 cm 2 V -1 s -1 for 3 × 10 19 cm -3 carrier density, and a ZT, of 1.32 at 923 K. This is ~ 55% greater that the corresponding Sb-doped PbS sample and is one of the highest reported for the n-type PbS system. Moreover, the average ZT (ZT avg ) of ~0.76 from 400 to 923 K is the highest for PbS-based systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Enhancement of double-close-binary quadruples

ABSTRACT Double-close-binary quadruples (2 + 2 systems) are hierarchical systems of four stars where two short-period binary systems move around their common centre of mass on a wider orbit. Using Gaia Early Data Release 3, we search for comoving pairs where both components are eclipsing binaries. We present eight 2 + 2 quadruple systems with inner orbital periods of <0.4 d and with outer separations of ≳1000 au. All of these systems but one are newly discovered by this work, and we catalogue their orbital information measured from their light curves. We find that the occurrence rate of 2 + 2 quadruples is 7.3 ± 2.6 times higher than what is expected from random pairings of field stars. At most a factor of ∼2 enhancement may be explained by the age and metallicity dependence of the eclipsing binary fraction in the field stellar population. The remaining factor of ∼3 represents a genuine enhancement of the production of short-period binaries in wide-separation (>103 au) pairs, suggesting a close-binary formation channel that may be enhanced by the presence of wide companions.

Fezenko, Gavin B. (ORCID:0000000217169430)↗
DOE OSTI2024

Geranylgeranylated-chlorophyll-protein complexes in lhl3 mutant of the green alga Chlamydomonas reinhardtii

Chlorophylls a and b (Chl a and b) are involved in light harvesting, photochemical reactions, and electron transfer reactions in plants and green algae. The core complexes of the photosystems (PSI and PSII) associate with Chl a, while the peripheral antenna complexes (LHCI and LHCII) bind Chls a and b. One of the final steps of Chl biosynthesis is the conversion of geranylgeranylated Chls (Chls GG ) to phytylated Chls by geranylgeranyl reductase (GGR). Here, we isolated and characterized a pale green mutant of the green alga Chlamydomonas reinhardtii that was very photosensitive and was unable to grow photoautotrophically. This mutant has a 16-bp deletion in the LHL3 gene, which resulted in the loss of LHL3 and GGR and accumulated only Chls GG . The lhl3 mutant cells grown in the dark accumulated PSII and PSI proteins at 25–50% of WT levels, lacked PSII activity, and retained a decreased PSI activity. The PSII and PSI proteins were depleted to trace amounts in the mutant cells grown in light. In contrast, the accumulation of LHCI and LHCII was unaffected except for LHCA3. Our results suggest that the replacement of Chls with Chls GG strongly affects the structural and functional integrity of PSII and PSI complexes but their associating LHC complexes to a lesser extent. Affinity purification of HA-tagged LHL3 confirmed the formation of a stable LHL3-GGR complex, which is vital for GGR stability. The LHL3-GGR complex contained a small amount of PSI complex assembly factors, suggesting a putative coupling between Chl synthesis and PSI complex assembly.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

SIF and Vegetation Indices in the US Midwestern Agroecosystems, 2016-2021, Carbon Monitoring System (CMS)

This dataset contains half-hourly ground solar-induced chlorophyll fluorescence (SIF) and vegetation indices including NDVI, EVI, Red edge chlorophyll index, green chlorophyll index, and photochemical reflectance index at seven crop sites in Nebraska and Illinois for the period 2016-2021. Four sites were located at Eddy Covariance (EC) tower sites (sites US-Ne2, US-Ne3, US-UiB, and US-UiC), and three sites were located on private farms (sites Reifsteck, Rund, and Reinhart). The sites were either miscanthus, corn-soybean rotation or corn-corn-soybean rotation. The spectral data for SIF retrieval and hyperspectral reflectance for vegetation index calculation were collected by the FluoSpec2 system, installed near planting, and uninstalled after harvest to collect whole growing-season data. Raw nadir SIF at 760 nm from different algorithms (sFLD, 3FLD, iFLD, SFM) are included. SFM_nonlinear and SFM_linear represent the Spectral fitting method (SFM) with the assumption that fluorescence and reflectance change with wavelength non-linearly and linearly, respectively. Additional data include two SIF correction factors including calibration coefficient adjustment factor (f_cal_corr_QEPRO) and upscaling nadir SIF to eddy covariance footprint factor (ratio_EC footprint, SIF pixel), and measured FPAR from quantum sensors and Rededge NDVI calculated FPAR. The data are provided in comma-separated values (CSV) format.

Ameriflux↗
DOE OSTI2022

The (Un)reasonable Effectiveness of Neural Network in Cherenkov Calorimetry

We report a greater than factor of two improvement in the hadronic energy resolution of a simulated Cherenkov calorimeter by estimating the energy with machine learning over traditional techniques. The prompt signal formation and energy threshold properties of Cherenkov radiation provide identifiable features that machine learning techniques can exploit to produce a superior model for energy reconstruction. We simulated a quartz-fiber calorimeter via the GEANT4 framework to study the reconstruction techniques in single events. We compared the machine learning-based reconstruction performance to the traditional simple sum of signal and dual-readout techniques that use both Cherenkov and scintillation signals. We describe why this game-changing approach to Cherenkov hadron calorimetry excels and our plans for a dedicated beam test to validate these findings with a fast, radiation-hard hadron calorimeter prototype.

Akchurin, Nural↗
DOE OSTI2025

Review of Layered Transition Metal Oxide Materials for Cathodes in Sodium-Ion Batteries

The growing interest in sodium-ion batteries (SIBs) is driven by scarcity and the rising costs of lithium, coupled with the urgent need for scalable and sustainable energy storage solutions. Among various cathode materials, layered transition metal oxides have emerged as promising candidates due to their structural similarity to lithium-ion battery (LIB) counterparts and their potential to deliver high energy density at reduced costs. However, significant challenges remain, including limited capacity at high charge/discharge rates and structural instability during extended cycling. Addressing these issues is critical for advancing SIB technology toward industrial applications, particularly for large-scale energy storage systems. This review provides a comprehensive analysis of layered sodium transition metal oxides, focusing on their structural properties, electrochemical performance, and degradation mechanisms. Special attention is given to the intrinsic and extrinsic factors contributing to their instability, such as structural phase transitions, and cationic/anionic redox behavior. Additionally, recent advancements in material design strategies, including doping, surface modifications, and composite formation, are discussed to highlight the progress toward enhancing the stability and performance of these materials. This work aims to bridge the knowledge gaps and inspire further innovations in the development of high-performance cathodes for sodium-ion batteries.

Ahangari, Mehdi (ORCID:0000000345803969)↗
NASA NTRS1971

Heavy ion plasma confinement in an RF quadrupole trap

The confinement of an electron free plasma in a pure quadrupole RF electric trap was considered. The ultimate goal was to produce a large density of mercury ions, in order to realize a trapped ion frequency standard using the hyperfine resonance of 199 Hg(+) at 40.7 GHz. An attempt was made to obtain an iodine plasma consisting of equal numbers of positive and negative ions of atomic iodine, the positive iodine ions, being susceptible to charge-exchange with mercury atoms, will produce the desired mercury ions. The experiment showed that the photoproduction of ions pairs in iodine using the necessary UV radiation occurs with a small cross-section, making it difficult to demonstrate the feasibility of space charge neutralization in a quadrupole trap. For this reason it was considered expedient to choose thallium iodide, which has a more favorable absorption spectrum (in the region of 2000 to 2100 A). The results indicate that, although the ionic recombination is a serious limiting factor, a considerable improvement can be obtained in practice for the density of trapped ions, with a considerable advantage in lifetimes for spectroscopic purposes. The ion pair formation by photoionization is briefly reviewed.

Schermann, J.↗
NASA NTRS1971

Remote Sensing of Sea Ice from Earth Satellites

The application of meteorological satellite data for mapping ice fields is discussed. The characteristics of the photographic records of sea ice formations are described. The derivation of the composite minimum brightness chart by computer processing of the mapped satellite vidicon data for several successive days is explained. The factors which create a quantitative delimiting of the sea ice conditions are explained.

Mcclain, E. P.↗
NASA NTRS1984

Investigation of Satellite Measurements in the Presence of Clouds, Forcing Influences on Clouds and Feedback to the Large Scale Following Convection

Satellite measurements during cloudy conditions, forces influencing clouds and large scale feedback following convection were investigated. The following conditions were studied: (1) passing marked thermal features aloft near the northern Bay of Bengal at the time of formation of the July 1979 monsoon depression; (2) recognition of regions of dense high overcast clouds in satellite radiances; (3) evolution of monsoon cloud systems and controlling factors on the clouds, and the effects of the clouds on thermodynamic and wind structures for improvements for numerical models are suggested.

Warner, C.↗
NASA NTRS1985

Defects in silicon effect on device performance and relationship to crystal growth conditions

A relationship between material defects in silicon and the performance of electronic devices will be described. A role which oxygen and carbon in silicon play during the defects generation process will be discussed. The electronic properties of silicon are a strong function of the oxygen state in the silicon. This state controls mechanical properties of silicon efficiency for internal gettering and formation of defects in the device's active area. In addition, to temperature, time, ambience, and the cooling/heating rates of high temperature treatments, the oxygen state is a function of the crystal growth process. The incorporation of carbon and oxygen into silicon crystal is controlled by geometry and rotation rates applied to crystal and crucible during crystal growths. Also, formation of nucleation centers for oxygen precipitation is influenced by the growth process, although there is still a controversy which parameters play a major role. All these factors will be reviewed with special emphasis on areas which are still ambiguous and controversial.

Jastrzebski, L.↗
NASA NTRS1991

Parametric entry corridors for lunar/Mars aerocapture missions

Parametric atmospheric entry corridor data are presented for Earth and Mars aerocapture. Parameter ranges were dictated by the range of mission designs currently envisioned as possibilities for the Human Exploration Initiative (HEI). This data, while not providing a means for exhaustive evaluation of aerocapture performance, should prove to be a useful aid for preliminary mission design and evaluation. Entry corridors are expressed as ranges of allowable vacuum periapse altitude of the planetary approach hyperbolic orbit, with chart provided for conversion to an approximate flight path angle corridor at entry interface (125 km altitude). The corridor boundaries are defined by open-loop aerocapture trajectories which satisfy boundary constraints while utilizing the full aerodynamic control capability of the vehicle (i.e., full lift-up or full lift-down). Parameters examined were limited to those of greatest importance from an aerocapture performance standpoint, including the approach orbit hyperbolic excess velocity, the vehicle lift to drag ratio, maximum aerodynamic load factor limit, and the apoapse of the target orbit. The impact of the atmospheric density bias uncertainties are also included. The corridor data is presented in graphical format, and examples of the utilization of these graphs for mission design and evaluation are included.

Ling, Lisa M.↗
NASA NTRS1991

Options for Martian propellant production

A quantitative evaluation methodology for utilizing in-situ resources on Mars for the production of useful substances. The emphasis is on the chemical processes. Various options considering different feedstock (mostly, carbon dioxide, water, and iron oxides) are carefully examined for the product mix and the energy needs. Oxygen, carbon monoxide, alcohols, and other chemicals are the end products. The chemical processes involve electrolysis, methanation, and variations. It is shown that maximizing the product utility is more important than the production of oxygen, methane, or alcohols. An important factor is the storage of the chemicals produced. The product utility is dependent, to some extent, upon the mission. A combination of the stability, the enthalpy of formation, and the mass fraction of the products is seen to yield a fairly good quantitative feel for the overall utility and maximum mission impact.

Dowler, Warren↗