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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 OSTI2021

Understanding the Correlation between Ga Speciation and Propane Dehydrogenation Activity on Ga/H-ZSM-5 Catalysts

H-ZSM-5 zeolite-supported Ga (Ga/H-ZSM-5) has been considered as a selective catalyst for nonoxidative propane dehydrogenation (PDH) for decades; however, the reaction mechanism remains a topic of considerable discussion. In particular, the correlation between various Ga species present on the catalyst at the reaction conditions and the PDH activity has yet to be established. In this work, intrinsic PDH rates and activation energies were determined on Ga + –H + pair sites and isolated Ga + sites on Ga/H-ZSM-5 samples with a wide range of Si/Al and Ga/Al ratios. Here, the turnover frequency on Ga + –H + pair sites in the PDH is higher than that of isolated Ga + sites by a factor of ~15. Experimental measurements combined with a dual-site model show the activation energy in the PDH on the Ga + –H + pair sites and isolated Ga + sites to be 90.8 ± 1.5 and 117 ± 4.7 kJ·mol –1 , respectively. These results demonstrate that Ga+–H+ pair sites are much more active in the PDH than isolated Ga + sites. The activation energy of GaH x decomposition to form H 2 was determined to be 40–60 kJ·mol –1 higher than that of the PDH on Ga species, suggesting that the GaH x decomposition is unlikely to be part of the PDH mechanism. Although both Brønsted acid and Ga sites interact with propane, Fourier transform infrared spectroscopy results provide strong evidence suggesting that the alkyl mechanism is more likely in the PDH on Ga/H-ZSM-5 catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1933

Wind-tunnel tests on model wing with Fowler flap and specially developed leading-edge slot

An investigation was made in the NACA 7 by 10 foot wind tunnel to find the increase in maximum lift coefficient which could be obtained by providing a model wing with both a Fowler trailing-edge extension flap and a Handley Page type leading-edge slot. A conventional Handley page slot proportioned to operate on the plain wing without a flap gave but a slight increase with the flap; so a special form of slot was developed to work more effectively with the flap. With the best combined arrangement the maximum lift coefficient based on the original area was increased from 3.17, for the Fowler wing, to 3.62. The minimum drag coefficient with both devices retracted was increased in approximately the same proportion. Tests were also made with the special-type slot on the plain wing without the flap. The special slot, used either with or without the Fowler flap, gave definitely higher values of the maximum lift coefficient than the slots of conventional form, with an increase of the same order in the minimum drag coefficient.

WING SLOTS & FLAPS, FOWLER↗
NASA NTRS1990

Ion beam heating in the auroral zone

Recent satellite observations at high altitudes (above 5000 km) in the auroral zone have shown the existence of hybrid or bimodal ion beam distributions that are evidence of both parallel and perpendicular ion acceleration. To study the nonlinear effects of the ion-ion instability in terms of plasma heating, a numerical simulation parametric study has been performed. It was found that the parallel acceleration that forms the ion beams occurs on a time scale faster than ion-ion wave growth at low drifts; thus ion-ion wave growth is expected to occur primarily for higher drift speeds, which results in strong oblique heating of the ions (both hydrogen and oxygen) forming elevated ion conics.

Schriver, David↗
NASA NTRS1977

Noncausal propagation in spin-0 theories with external field interactions

The two-component Sakata-Taketani (ST) spin-0 theory and the single-component Klein-Gordon theory are obtained from the five-component Duffin-Kemmer-Petiau (DKP) theory with six types of external field interactions by means of a Peirce decomposition. Whereas the DKP equation manifests the covariance, the ST equation manifests the causal properties. In particular, the presence of noncausal wave propagation when there is coupling to a second-rank tensor field is apparent from the form of the ST equation, in which the coefficients of all the space derivatives depend on the external field. The results indicate that the causal properties of higher-spin equations should also be obvious when they are expressed in 2(2J + 1)-component Schroedinger form

Guertin, R. F.↗
DOE OSTI2020

Production and Fuel properties of Iso-Olefins with Controlled Molecular Structure and Obtained from Butene Oligomerization

The ability to control the molecular structure (e.g., degree of branching) of iso-olefins produced from oligomerizing light olefins is a valuable tool for tuning the final compositions of hydrocarbon fuels and targeting specific fuel properties. In this study, we demonstrated that the degree of branching of iso-olefins obtained from butene(s) oligomerization can be controlled by tuning process conditions (i.e., temperature, weight hourly space velocity [WHSV], and nature of butene feedstock) and by choosing the proper catalyst (i.e., Amberlyst-36 vs. Y/ZSM-22). In this study, we produced three types of iso-olefin mixtures: 1) a methyl-heptenes rich (74 wt.%) mixture, 2) dimethyl-hexenes rich (80–96 wt.%) mixtures, and 3) highly branched (i.e., more than three methyl substitutions) iso-olefins rich (>50 wt.%) mixtures. While dimethyl-hexenes are preferentially formed at lower temperatures (60–100°C) and WHSV (i.e., 2 hr-1), methyl-heptenes are favorably produced at higher temperatures (>100°C) and WHSVs (i.e., 7 hr-1) over Amberlyst-36. The use of either 1-butene or 2-butene as feedstock resulted in liquid products with similar branching because facile intramolecular isomerization occurs prior to oligomerization. However, the use of isobutylene feedstock forms a significantly more branched olefin product. The formation of highly branched iso-olefins also is favored at higher temperature (140°C) over Amberlyst-36. Using Y/ZSM-22 instead of Amberlyst-36 allowed preferential formation of less-branched methyl-heptenes. For each type of iso-olefins mixture, we determined fuel properties including research octane number (RON), motor octane number (MON), and octane sensitivity (S), which is the difference between RON and MON. We found that not only RON and MON but also S values increased with the degree of branching of these complex mixtures of iso-olefins. The highest RON of 99.7 and S value of 9.3 were obtained for a mixture of highly branched iso-olefins.

Dagle, Vanessa↗
NASA NTRS1981

Computing aerodynamic sound using advanced statistical turbulence theories

It is noted that the calculation of turbulence-generated aerodynamic sound requires knowledge of the spatial and temporal variation of Q sub ij (xi sub k, tau), the two-point, two-time turbulent velocity correlations. A technique is presented to obtain an approximate form of these correlations based on closure of the Reynolds stress equations by modeling of higher order terms. The governing equations for Q sub ij are first developed for a general flow. The case of homogeneous, stationary turbulence in a unidirectional constant shear mean flow is then assumed. The required closure form for Q sub ij is selected which is capable of qualitatively reproducing experimentally observed behavior. This form contains separation time dependent scale factors as parameters and depends explicitly on spatial separation. The approximate forms of Q sub ij are used in the differential equations and integral moments are taken over the spatial domain. The velocity correlations are used in the Lighthill theory of aerodynamic sound by assuming normal joint probability.

Hecht, A. M.↗
NASA NTRS1996

Multipath analysis diffraction calculations

This report describes extensions of the Kirchhoff diffraction equation to higher edge terms and discusses their suitability to model diffraction multipath effects of a small satellite structure. When receiving signals, at a satellite, from the Global Positioning System (GPS), reflected signals from the satellite structure result in multipath errors in the determination of the satellite position. Multipath error can be caused by diffraction of the reflected signals and a method of calculating this diffraction is required when using a facet model of the satellite. Several aspects of the Kirchhoff equation are discussed and numerical examples, in the near and far fields, are shown. The vector form of the extended Kirchhoff equation, by adding the Larmor-Tedone and Kottler edge terms, is given as a mathematical model in an appendix. The Kirchhoff equation was investigated as being easily implemented and of good accuracy in the basic form, especially in phase determination. The basic Kirchhoff can be extended for higher accuracy if desired. A brief discussion of the method of moments and the geometric theory of diffraction is included, but seems to offer no clear advantage in implementation over the Kirchhoff for facet models.

Statham, Richard B.↗
DOE OSTI2022

BrzostekEcologyLab/CORPSE-soil-jars

Efforts to manage soils for carbon (C) sequestration remain limited by our understanding of how differences in plant traits and microbial traits mechanistically drive soil organic C (SOC) storage. Addressing this uncertainty is particularly critical in bioenergy agriculture, due to its potential to enhance soil C and provide a C neutral fuel. As such, we examined differences between two contrasting feedstocks, Zea mays (corn) and Miscanthus x giganteus (miscanthus), in the ability of their litter to form new chemically resistant particulate SOC vs. physically protected mineral associated SOC and used this data to improve the parameterization of a microbial SOC model. We tested a hypothesized conceptual model whereby easy to decompose corn litters drive greater microbial carbon use efficiency (CUE) and the formation of more mineral associated SOC over particulate SOC than more complex miscanthus litters. To do this, we performed a soil microcosm experiment where we added 13C enriched aboveground and belowground litters to soils and traced the fate of the 13C into microbial respiration and SOC pools. We found that corn litters promoted higher microbial CUE (0.37) than miscanthus litters (0.24). In turn, corn litter formed approximately 50% more mineral associated SOC than miscanthus litters. Similarly, structurally complex root litters promoted a lower CUE and formed less mineral associated SOC than leaf and shoot litters for both crops. When we used our data to parameterize the SOC model, we found that modeling microbial trait differences uniquely allowed the model to capture the fate of litter C in SOC. Collectively, we found a robust link between litter quality, microbial efficiency, and the formation of SOC. This link bridges the empirical uncertainty in how different crops can form new soil C and provides an empirical basis for modeling SOC transformations.

Ridgeway, Joanna↗
DOE OSTI2022

Plant litter traits control microbial decomposition and drive soil carbon stabilization

Efforts to manage soils for carbon (C) sequestration remain limited by our understanding of how differences in plant traits and microbial traits mechanistically drive soil organic C (SOC) storage. Addressing this uncertainty is particularly critical in bioenergy agriculture, due to its potential to enhance soil C and provide a C neutral fuel. As such, we examined differences between two contrasting feedstocks, Zea mays (corn) and Miscanthus x giganteus (miscanthus), in the ability of their litter to form new chemically resistant particulate SOC vs. physically protected mineral associated SOC and used this data to improve the parameterization of a microbial SOC model. We tested a hypothesized conceptual model whereby easy to decompose corn litters drive greater microbial carbon use efficiency (CUE) and the formation of more mineral associated SOC over particulate SOC than more complex miscanthus litters. To do this, we performed a soil microcosm experiment where we added 13 C enriched aboveground and belowground litters to soils and traced the fate of the 13 C into microbial respiration and SOC pools. We found that corn litters promoted higher microbial CUE (0.37) than miscanthus litters (0.24). In turn, corn litter formed approximately 50% more mineral associated SOC than miscanthus litters. Similarly, structurally complex root litters promoted a lower CUE and formed less mineral associated SOC than leaf and shoot litters for both crops. When we used our data to parameterize the SOC model, we found that modelling microbial trait differences uniquely allowed the model to capture the fate of litter C in SOC. Collectively, we found a robust link between litter quality, microbial efficiency, and the formation of SOC. This link bridges the empirical uncertainty in how different crops can form new soil C and provides an empirical basis for modelling SOC transformations.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1991

Robust fault diagnosis of physical systems in operation

Ideas are presented and demonstrated for improved robustness in diagnostic problem solving of complex physical systems in operation, or operative diagnosis. The first idea is that graceful degradation can be viewed as reasoning at higher levels of abstraction whenever the more detailed levels proved to be incomplete or inadequate. A form of abstraction is defined that applies this view to the problem of diagnosis. In this form of abstraction, named status abstraction, two levels are defined. The lower level of abstraction corresponds to the level of detail at which most current knowledge-based diagnosis systems reason. At the higher level, a graph representation is presented that describes the real-world physical system. An incremental, constructive approach to manipulating this graph representation is demonstrated that supports certain characteristics of operative diagnosis. The suitability of this constructive approach is shown for diagnosing fault propagation behavior over time, and for sometimes diagnosing systems with feedback. A way is shown to represent different semantics in the same type of graph representation to characterize different types of fault propagation behavior. An approach is demonstrated that threats these different behaviors as different fault classes, and the approach moves to other classes when previous classes fail to generate suitable hypotheses. These ideas are implemented in a computer program named Draphys (Diagnostic Reasoning About Physical Systems) and demonstrated for the domain of inflight aircraft subsystems, specifically a propulsion system (containing two turbofan systems and a fuel system) and hydraulic subsystem.

Abbott, Kathy Hamilton↗
NASA NTRS2006

The Evolution of the Cluster X-ray Scaling Relations in the Wide Angle ROSAT Pointed Survey Sample at 0.6 < z < 1.0

The X-ray properties of a sample of 11 high-redshift (0.6 < z < 1 .O) clusters observed with Chardm and/or XMM-Newton are used to investigate the evolution of the cluster scaling relations. The observed evolution in the normalization of the L-T, M-T, M(sub 2)-T and M-L relations is consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the Universe at their redshift of observation. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L-T relation is consistent with the high-z clusters having virialized at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material. The slope of the L-T relation at high redshift (B = 3.32 +/- 0.37) is consistent with the local relation, and significantly steeper than the self-similar prediction of B = 2. This suggests that the same non-gravitational processes are responsible for steepening the local and high-z relations, possibly occurring universally at z is approximately greater than 1 or in the early stages of the cluster formation, prior to their observation. The properties of the intracluster medium at high redshift are found to be similar to those in the local Universe. The mean surface-brightness profile slope for the sample is Beta = 0.66 +/- 0.05, the mean gas mass fractions within R(sub 2500(z)) and R(200(z)) are 0.069 +/- 0.012 and 0.11 +/- 0.02, respectively, and the mean metallicity of the sample is 0.28 +/- 0.11 Z(sub solar).

Maughan, B. J.↗
DOE OSTI2021

Flume and single-pass washing systems for fresh-cut produce processing: Disinfection by-products evaluation

Free chlorine is widely used in fresh-cut produce washing to minimize microbial cross-contamination, but its application can also lead to the formation of harmful disinfection byproducts (DBPs). This study compared DBPs in process water and washed produce during commercial operation. Samples of shredded lettuce and diced cabbages washed in chlorinated water in the traditional double-flume wash and novel immersion-free single-pass wash systems were collected at multiple time points and locations from the processing lines. A suite of 33 conventional and emerging DBPs, including 4 trihalomethanes (THMs), 9 haloacetic acids (HAAs), 9 nitrogenous DBPs (N-DBPs), and 11 carbonaceous DBPs (C-DBPs), were investigated. Overall, N-DBPs and HAAs dominated the concentration of detected DBPs. Wash water in the flumes contained 7–111 folds higher DBP levels compared to that in the single-pass system, with the abundance of DBPs following the order of N-DBPs > HAAs > C-DBPs > THMs. DBPs were detected on washed produce, presenting primarily in the forms of N-DBPs and HAAs followed by C-DBPs and THMs. While higher levels of DBPs were detected in flume-washed produce, the final potable water rinse significantly reduced the DBP concentration in these products. The concentrations of THMs and HAAs on these washed products were used to estimate potential exposure via consumption of fresh-cut produce and the levels were below the daily allowable exposure for drinking water standard established by the U.S. Environmental Protection Agency. The detected high concentration and potential toxicity of N-DBPs indicate the need for further research. Here, the findings of this study advance the understanding of the formation and removal of DBPs during wash processes, and identify additional research opportunities for further reduction in DBPs and food safety improvement.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2009

Finding the First Galaxies

Astronomers study distant galaxies by taking long exposures in deep survey fields. They choose fields that are empty of known sources, so that they are statistically representative of the Universe as a whole. Astronomers can compare the distribution of the detected galaxies in brightness, color, morphology and redshift to theoretical models, in order to puzzle out the processes of galaxy evolution. In 2004, the Hubble Space Telescope was pointed at a small, deep-survey field in the southern constellation Fornax for more than 500 hours of exposure time. The resulting Hubble Ultra-Deep Field could see the faintest and most distant galaxies that the telescope is capable of viewing. These galaxies emitted their light less than 1 billion years after the Big Bang. From the Ultra Deep Field and other galaxy surveys, astronomers have built up a history of star formation in the universe. the peak occurred about7 billion years ago, about half of the age of the current universe, then the number of stars that were forming was about 15 time the rate today. Going backward in time to when the very first starts and galaxies formed, the average star-formation rate should drop to zero. but when looking at the most distant galaxies in the Ultra Deep field, the star formation rate is still higher than it is today. The faintest galaxies seen by Hubble are not the first galaxies that formed in the early universe. To detect these galaxies NASA is planning the James Webb Space Telescope for launch in 2013. Webb will have a 6.5-meter diameter primary mirror, much bigger than Hubble's 2.4-meter primary, and will be optimized for infrared observations to see the highly redshifted galaxies.

Gardner, Jonathan P.↗
DOE OSTI2020

Pitting behavior of friction stir repair-welded 304L stainless steel in 3.5% NaCl solution at room temperature: role of grain and defect structures

Stainless steel (SS) canisters used for storing spent nuclear waste are prone to chloride-induced stress corrosion cracking. Friction stir welding (FSW), being a low heat input process, can be used for repair welding of these canisters. In this study, an artificial crack was introduced on the 304L SS coupons by an electric discharge machining process. The artificial crack was repair-welded by FSW by maintaining the tool temperature a constant at two levels (725 and 825 °C). Friction stirring significantly reduced the grain size of the stirred zone (SZ) from about 47 to 2–4 μm. The fraction of low-angle grain boundaries increased in the SZ from 2 to 37–43%. Here, on the other hand, the fraction of special grain boundaries (Σ3 and Σ9) that was ~ 50% in the base metal reduced to < 10% in the SZ. During friction stirring, the oxide layer of artificial crack was broken and aligned to form a spiral defect called lazy-S structure. All these microstructural changes affected the corrosion behavior of the FSW specimens when tested in 3.5% NaCl at room temperature using cyclic polarization, chronoamperometry, and electrochemical impedance spectroscopy. The FSW specimens showed lower polarization resistance and lower transpassive potential than those of the base metal specimens. However, the pitting protection potentials of the FSW specimens were higher than that of the base metal. The pitting behavior of the FSW specimens was influenced more by the preferential attack on the lazy-S region than by passive film breakdown. The flat band potentials of the passive film formed on the FSW specimens were more positive than that of base metal. The charge carrier density of passive film formed on the FSW specimens was higher than that of the base metal. The higher fraction of low-angle grain boundaries present in the FSW specimens could supply more number of misorientation dislocations at the metal/film interface which could form anion vacancies by a climb process leading to formation of oxide at these locations without stressing the substrate. Therefore, low-angle boundaries are considered helpful for formation of stress-free passive films that will be highly stable and enhance both pitting and stress corrosion cracking resistance.

Dry storage canister↗
DOE OSTI2020

Advances in High Resolution Ultrafast Scintillators for Fast timing Applications

Scintillation detectors exhibiting high spatial resolution and fast timing capabilities are of vital importance for synchrotron sources. These detectors may be exposed to a variety of X-ray energies (up to 140 keV) and used in high frame rate applications. Here, we describe the advances in the development of thin-film LuI3:Ce scintillators for higher energy X-ray imaging, with fast timing and high spatial resolution. When grown in a single crystalline form, these scintillators are bright, producing 115 000 photons/MeV. However, to achieve high spatial resolution, these scintillators are grown in thin-film form with a microcolumnar structure, controllable to column diameters of <1-30 mu m. Thus, a much thicker scintillator layer (10 mu m-3 mm or higher) may be grown, providing superior X-ray absorption while achieving high resolutions of 50 mu m or better, at the cost of reduced light yield. To study the timing characteristics of the scintillator, time-resolved X-ray excited optical luminescence (TR-XEOL) was performed on two different sets of three samples of LuI3 at the 1-BM beamline of the Advanced Photon Source at Argonne National Laboratory. Besides, we report timing measurements obtained using a photomultiplier tube (PMT) and oscilloscope at Radiation Monitoring Devices (RMD) Inc. Using the TR-XEOL, we determined the decay constants of LuI3 as a function of Ce doping, recording a fast decay component as low as 3.6 ns (39%), one of the fastest values recorded in inorganic scintillators. This fast decay opens up numerous novel applications, where ultrahigh frame rates are important using synchrotron X-rays. This article will discuss fabrication, characterization, and potential applications for this novel scintillator.

fast timing↗
DOE OSTI2021

A new spin on the Weak Gravity Conjecture

The mild form of the Weak Gravity Conjecture states that quantum or higher-derivative corrections should decrease the mass of large extremal charged black holes at fixed charge. This allows extremal black holes to decay, unless protected by a symmetry (such as supersymmetry). We reformulate this conjecture as an integrated condition on the effective stress tensor capturing the effect of quantum or higher-derivative corrections. In addition to charged black holes, we also consider rotating BTZ black holes and show that this condition is satisfied as a consequence of the $\textit{c}$-theorem, proving a spinning version of the Weak Gravity Conjecture. We also apply our results to a five-dimensional boosted black string with higher-derivative corrections. The boosted black string has a BTZ×$S^2$ near-horizon geometry and, after Kaluza-Klein reduction, describes a four-dimensional charged black hole. Combining the spinning and charged Weak Gravity Conjecture we obtain positivity bounds on the five-dimensional Wilson coefficients that are stronger than those obtained from charged black holes alone.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

D614G Spike Mutation Increases SARS CoV-2 Susceptibility to Neutralization

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein acquired a D614G mutation early in the pandemic that confers greater infectivity and is now the globally dominant form. To determine whether D614G might also mediate neutralization escape that could compromise vaccine efficacy, sera from spike-immunized mice, nonhuman primates, and humans were evaluated for neutralization of pseudoviruses bearing either D614 or G614 spike. In all cases, the G614 pseudovirus was moderately more susceptible to neutralization. The G614 pseudovirus also was more susceptible to neutralization by receptor-binding domain (RBD) monoclonal antibodies and convalescent sera from people infected with either form of the virus. Here, negative stain electron microscopy revealed a higher percentage of the 1-RBD “up” conformation in the G614 spike, suggesting increased epitope exposure as a mechanism of enhanced vulnerability to neutralization. Based on these findings, the D614G mutation is not expected to be an obstacle for current vaccine development.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Gradient flow based phase-field modeling using separable neural networks

Allen–Cahn equation is a reaction–diffusion equation and is widely used for modeling phase separation. Machine learning methods for solving the Allen–Cahn equation in its strong form suffer from inaccuracies in collocation techniques, errors in computing higher-order spatial derivatives, and the large system size required by the space–time approach. To overcome these challenges, we propose solving the gradient flow of the Ginzburg–Landau free energy functional, which is equivalent to the Allen–Cahn equation, thereby avoiding the second-order spatial derivatives associated with the Allen–Cahn equation. A minimizing movement scheme is employed to solve the gradient flow problem, eliminating the complexities of a space–time approach. We utilize a separable neural network that efficiently represents the phase field through low-rank tensor decomposition. As we use the minimizing movement scheme to numerically solve the gradient flow problem, we thus, refer to the proposed method as the Separable Deep Minimizing Movement (SDMM) method. The evaluation of the functional in the minimizing movement scheme using the Gauss quadrature technique bypasses the inaccuracies associated with collocation techniques traditionally used to solve partial differential equations. A hyperbolic tangent transformation is introduced on the phase field prior to the evaluation of the functional to ensure that it remains strictly bounded within the values of the two phases. For this transformation, theoretical guarantee for energy stability of the minimizing movement scheme is established. Our results suggest that this transformation helps to improve the accuracy and efficiency significantly. The proposed method resolves the challenges faced by state-of-the-art machine learning techniques, outperforming them in both accuracy and efficiency. It is also the first machine learning method to achieve an order of magnitude speed improvement over the finite element method. In addition to its formulation and computational implementation, several case studies illustrate the applicability of the proposed method.

42 ENGINEERING↗