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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Numerical Simulations and Diagnostic Studies Relating Meteorology To Atmospheric Chemistry during TRACE-P

The Florida State University (FSU) team participated extensively in the pre-mission planning for TRACE-P through meetings, telephone calls, and e-mails. During Spring 2001, Prof. Fuelberg served as DC-8 Mission Meteorologist during the field campaign. He prepared meteorological guidance for each flight of the DC-8 and flew on each mission. After the field phase, FSU prepared various meteorological products, included backward air trajectories, for each flight of the DC-8 and P-3B. These were posted on the FSU and NASA-GTE web sites for use by all the Science Team. During the two-year post mission period, FSU conducted research relating meteorology to atmospheric chemistry during TRACE-P. This led to three journal articles in the Journal of Geophysical Research. FSU personnel were the lead authors on each of these articles. Abstracts of these articles are attached. In addition, the FSU team collaborated with other members of the TRACE-P Science Team to incorporate meteorological factors into their research. A list of publications resulting from these interactions is included.

Fuelberg, Henry E.↗
NASA NTRS2010

Conditions of Core Formation in the Early Earth: Single Stage or Heterogeneous Accretion?

Since approx.1990 high pressure and temperature (PT) experiments on metal-silicate systems have showed that partition coefficients [D(met/sil)] for siderophile (iron-loving) elements are much different than those measured at low PT conditions [1,2]. The high PT data have been used to argue for a magma ocean during growth of the early Earth [3,4]. In the ensuing decades there have been hundreds of new experiments carried out and published on a wide range of siderophile elements (> 80 experiments published for Ni, Co, Mo, W, P, Mn, V, Cr, Ga, Cu and Pd). At the same time several different models have been advanced to explain the siderophile elements in Earth's mantle: a) shallow depth magma ocean 25-30 GPa [3,5]; b) deep magma ocean; up to 50 GPa [6,7], and c) early reduced and later oxidized magma ocean [8,9]. Some studies have drawn conclusions based on a small subset of siderophile elements, or a set of elements that provides little leverage on the big picture (like slightly siderophile elements), and no single study has attempted to quantitatively explain more than 5 elements at a time. The purpose of this abstract is to identify issues that have lead to a difference in interpretation, and to present updated predictive expressions based on new experimental data. The resulting expressions will be applied to the siderophile element depletions in Earth's upper mantle.

Righter, Kevin↗
DOE OSTI2024

Advances in Mixed Tin‐Lead Narrow‐Bandgap Perovskites for Single‐Junction and All‐Perovskite Tandem Solar Cells

Abstract Organic–inorganic metal‐halide perovskites have received great attention for photovoltaic (PV) applications owing to their superior optoelectronic properties and the unprecedented performance development. For single‐junction PV devices, although lead (Pb)‐based perovskite solar cells have achieved 26.1% efficiency, the mixed tin‐lead (Sn‐Pb) perovskites offer more ideal bandgap tuning capability to enable an even higher performance. The Sn‐Pb perovskite (with a bandgap tuned to ≈1.2 eV) is also attractive as the bottom subcell for a tandem configuration to further surpass the Shockley–Queisser radiative limit for the single‐junction devices. The performance of the all‐perovskite tandem solar cells has gained rapid development and achieved a certified efficiency up to 29.1%. In this article, the properties and recent development of state‐of‐the‐art mixed Sn‐Pb perovskites and their application in single‐junction and all‐perovskite tandem solar cells are reviewed. Recent advances in various approaches covering additives, solvents, interfaces, and perovskite growth are highlighted. The authors also provide the perspective and outlook on the challenges and strategies for further development of mixed Sn‐Pb perovskites in both efficiency and stability for PV applications.

14 SOLAR ENERGY↗
DOE OSTI2016

A Theoretical Investigation of the Structure and Reactivity of the Molecular Constituents of Oil Sand and Oil Shale

We used a variety of small organic models of asphaltenes to investigate the molecular mechanism for the high temperature decomposition that would take place as part of the oil refinery process. We determined that the decomposition is initiated via four different types of hydrogen migration reactions. According to the energetics of the reactions, the dominant 1,2-H shift mechanism involves two competitive product channels, namely, C 2 H 2 + CH 2 CS and CS + CH 3 CCH. The minor channels include the formation of CS + CH 2 CCH 2 , H 2 S + C 4 H 2 , HCS + CH 2 CCH, CS + CH 2 CHCH, H + C 4 H 3 S, and HS + C 4 H 3 . We also investigated the alkyl substitution effect by exploring the decomposition pathways of models with alkyl arms. The energetics of such systems were very similar to that for unsubstituted model compounds, which suggests that asphaltene alkylation may not play a significant role in the decomposition of asphaltene compounds. This work was published in the Journal of Physical Chemistry A 2011, 115, 2882-2891. A MECHANISTIC STUDY OF THE 2-THIENYLMETHYL + HO2 RADICAL RECOMBINATION REACTION Radicals are molecules which contain single electrons. They are very reactive. Radical recombination reactions are important in the combustion of fuel oils. Shale oil contains radicals. We used quantum mechanics to explore the reactivity of shale oil model radical compounds. Seventeen product channels corresponding to either addition/elimination or direct hydrogen abstraction were characterized. Direct hydrogen abstraction proceeds via a weakly bonded complex, which leads to 2-methylthiophene, 2-methylene-2,3-dihydrothiophene or 2-methylene-2,5-dihydrothiophene depending upon the 2-thienylmethyl radical reaction site. The addition pathway for the two radical reactants is barrierless with the formation of three adducts, as distinguished by HO 2 reaction at three different sites on the 2-thienylmethyl radical. The addition is exothermic by 37 ~ 55 kcal mol-1 relative to the entrance channel. These excess energies are available to promote further decomposition or rearrangement of the adducts that lead to nascent products such as H, OH, H 2 O and CH 2 O. The reaction surfaces are characterized by relatively low barriers (most are lower than 10 kcal mol-1). Based upon a careful analysis of the overall barrier heights and reaction exothermicities, the formation of O2, OH and H2O is likely to be an important pathway in the radical recombination reactions of 2-thienylmethyl + HO 2 . This work was published in the Journal of Physical Chemistry A, 2011, 115, 14546-14557. REACTION OF THIOPHENE AND METHYLTHIOPHENE WITH SINGLET AND TRIPLET MOLECULAR OXYGEN Mechanisms for the reaction of thiophene and 2-methylthiophene with molecular oxygen on both the triplet and singlet potential energy surfaces (PESs) were investigated using ab initio methods. Thiophene and 2-methylthiophene where shown to react with O 2 via two types of mechanisms; namely, direct hydrogen abstraction and addition/elimination. The barriers for reaction with triplet oxygen are all significantly large (i.e., > 30 kcal mol-1), which indicates that the direct oxidation of thiophene by ground state oxygen might be important only in high temperature processes. Reaction of thiophene with singlet oxygen via a 2+4 cycloaddition leading to endoperoxides is the most favorable channel. Moreover, it was found that alkylation of the thiophene ring (i.e., methyl-substituted thiophene) is capable of lowering the barrier height for the addition pathway. The implication of the current theoretical results may shed new light on the initiation mechanisms for combustion of asphaltenes. This work was published in the Journal of Physical Chemistry A, 2012 116, 4934-4946. JAHN-TELLER STABILIZATION IN POSS CATIONS We have a long standing interest in polyoligomeric silsesquioxane (POSS) molecules. 1-2 These molecules have recently been used as advanced surface coatings for photovoltaic devices and have potential as molecular-based energy storage devices as well as magnetically controllable liquid marbles. 3-5 We have been investigating the small molecule encapsulation properties of POSS and discovered some interesting symmetry breaking processes that need to be better understood in order to use POSS in advanced materials. We have investigated this symmetry breaking mechanism in POSS monocations Si8O12(C(CH3)3)8+ and Si8O12Cl8+, using density functional theory (DFT) and group theory. Under Oh symmetry, these ions possess 2T2g and 2Eg electronic states, respectively, and undergo different symmetry breaking mechanisms. The ground states of Si 8 O 12 (C(CH 3 ) 3 ) 8 + and Si 8 O 12 Cl 8 + belong to the C 3v and D 4h point groups and are characterized by Jahn-Teller stabilization energies of 3959 and 1328 cm-1, respectively, at the B3LYP/def2-SVP level of theory. The symmetry distortion mechanism in Si 8 O 12 Cl 8 + is Jahn-Teller type, whereas in Si 8 O 12 (C(CH 3 ) 3 ) 8 + the distortion is a combination of both Jahn-Teller and pseudo-Jahn-Teller effects. The distortion force acting in Si 8 O 12 (C(CH 3 ) 3 ) 8 + is mainly localized on one Si-(tert-butyl) group while in Si 8 O 12 Cl 8 + it is distributed over the oxygen atoms. The main distortion forces acting on the Si8O12 core arise from the coupling between the electronic state and the vibrational modes; identified as 9t 2g +1e g +3a 2u for the Si 8 O 12 (C(CH 3 ) 3 ) 8 + and 1e g +2e g for Si 8 O 12 Cl 8 + . This work was published in the Journal of Physical Chemistry A, 2015, 119, 4237-4243.

04 OIL SHALES AND TAR SANDS↗
DOE OSTI2018

HOCO formation in astrochemical environments by radical-induced H-abstraction from formic acid

Rate constants for the radical-induced hydrogen abstraction from formic acid, HCOOH, are presented here. Only those reactions leading to the formation of HOCO were investigated. The astrochemically relevant radicals OH, NH 2 , and H were considered to induce the H-abstraction. Tunnelling was taken into account by using the instanton method for rate constant calculations. For reactions relevant on grain surfaces, the unimolecular rate constant is of particular importance. For the reactions with OH and NH 2 , a corresponding deep pre-reactive minimum can be found that contributes to the barrier height and thus slows down the reaction. In general though, abstraction induced by OH radicals is found to be the fastest. The reaction with the H atoms becomes increasingly important at low temperatures, because of the narrow barrier through which tunnelling is efficient. In conclusion, the reaction with NH 2 radicals has both a high and broad barrier and consequently shows significantly smaller low-temperature rate constants.

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

Transcription Factors Controlling the Rhizobium–Legume Symbiosis: Integrating Infection, Organogenesis and the Abiotic Environment

Abstract Legume roots engage in a symbiotic relationship with rhizobia, leading to the development of nitrogen-fixing nodules. Nodule development is a sophisticated process and is under the tight regulation of the plant. The symbiosis initiates with a signal exchange between the two partners, followed by the development of a new organ colonized by rhizobia. Over two decades of study have shed light on the transcriptional regulation of rhizobium–legume symbiosis. A large number of transcription factors (TFs) have been implicated in one or more stages of this symbiosis. Legumes must monitor nodule development amidst a dynamic physical environment. Some environmental factors are conducive to nodulation, whereas others are stressful. The modulation of rhizobium–legume symbiosis by the abiotic environment adds another layer of complexity and is also transcriptionally regulated. Several symbiotic TFs act as integrators between symbiosis and the response to the abiotic environment. In this review, we trace the role of various TFs involved in rhizobium–legume symbiosis along its developmental route and highlight the ones that also act as communicators between this symbiosis and the response to the abiotic environment. Finally, we discuss contemporary approaches to study TF-target interactions in plants and probe their potential utility in the field of rhizobium–legume symbiosis.

Cell Biology↗
DOE OSTI2018

Warming‐Induced Earlier Greenup Leads to Reduced Stream Discharge in a Temperate Mixed Forest Catchment

Abstract The phenological response of vegetation to ongoing climate change may have great implications for hydrological regimes in the eastern United States. However, there have been few studies that analyze its resultant effect on catchment discharge dynamics, separating from dominant climatic controls. In this study, we examined the net effect of phenological variations on the long‐term and interannual gross primary production (GPP) and evapotranspiration (ET) fluxes in a temperate deciduous forest, as well as on the catchment discharge behavior in a mixed deciduous‐conifer forest catchment. First, we calibrated the spring and autumn leaf phenology models for the Harvard Forest in the northeastern United States, where the onsets of greenup and senescence have been significantly advanced and delayed, 10.3 and 6.0 days respectively, over the past two decades (1992–2011). We then integrated the phenology models into a mechanistic watershed ecohydrological model (RHESSys), which improved the interannual and long‐term simulations of both the plot‐scale daily GPP and ET fluxes and the catchment discharge dynamics. We found that the phenological changes amplified the long‐term increases in GPP and ET driven by the climatic controls. In particular, the earlier greenup onsets resulted in increases in annual ET significantly, while the delayed senescence onsets had less influence. Consequently, the earlier greenup onsets reduced stream discharge not only during the growing season but also during the following dormant season due to soil water depletion. This study highlights the importance of understanding vegetation response to ongoing climate change in order to predict the future hydrological nonstationarity in this region.

Kim, Ji Hyun↗
DOE OSTI2020

Altered climate leads to positive density‐dependent feedbacks in a tropical wet forest

Abstract Climate change is predicted to result in warmer and drier Neotropical forests relative to current conditions. Negative density‐dependent feedbacks, mediated by natural enemies, are key to maintaining the high diversity of tree species found in the tropics, yet we have little understanding of how projected changes in climate are likely to affect these critical controls. Over 3 years, we evaluated the effects of a natural drought and in situ experimental warming on density‐dependent feedbacks on seedling demography in a wet tropical forest in Puerto Rico. In the +4°C warming treatment, we found that seedling survival increased with increasing density of the same species (conspecific). These positive density‐dependent feedbacks were not associated with a decrease in aboveground natural enemy pressure. If positive density‐dependent feedbacks are not transient, the diversity of tropical wet forests, which may rely on negative density dependence to drive diversity, could decline in a future warmer, drier world.

Bachelot, Benedicte↗