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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Cofactorless oxygenases guide anthraquinone-fused enediyne biosynthesis

The anthraquinone-fused enediynes (AFEs) combine an anthraquinone moiety and a ten-membered enediyne core capable of generating a cytotoxic diradical species. AFE cyclization is triggered by opening the F-ring epoxide, which is also the site of the most structural diversity. Previous studies of tiancimycin A, a heavily modified AFE, have revealed a cryptic aldehyde blocking installation of the epoxide, and no unassigned oxidases could be predicted within the tnm biosynthetic gene cluster. Here, in this study, we identify two consecutively acting cofactorless oxygenases derived from methyltransferase and α/β-hydrolase protein folds, TnmJ and TnmK2, respectively, that are responsible for F-ring tailoring in tiancimycin biosynthesis by comparative genomics. Further biochemical and structural characterizations reveal that the electron-rich AFE anthraquinone moiety assists in catalyzing deformylation, epoxidation and oxidative ring cleavage without exogenous cofactors. These enzymes therefore fill important knowledge gaps for the biosynthesis of this class of molecules and the underappreciated family of cofactorless oxygenases. Cofactorless oxygenases are rare in nature and natural product biosynthesis. Here the authors describe the biochemical and structural characterization of two such oxygenases catalyzing deformylation, ring cleavage and epoxidation in the biosynthesis of the enediyne natural product tiancimycin A.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1983

Ladder supported ring bar circuit

An improved slow wave circuit especially useful in backward wave oscillators includes a slow wave circuit in a waveguide. The slow wave circuit is comprised of rings disposed between and attached to respective stubs. The stubs are attached to opposing sidewalls of the waveguide. To the end that opposed, interacting magnetic fields will be established to provide a very high coupling impedance for the slow wave structure, axially orientated bars are connected between rings in alternate spaces and adjacent to the attachment points of stubs. Similarly, axial bars are connected between rings in the spaces which do not include bars and at points adjacent to the attachment of bars.

Kosmahl, H. G.↗
DOE OSTI2026

Resolving Competing Ultraviolet Photoinduced Ring-Opening and Dissociation Pathways in Iodothiophenes by Ultrafast Electron Diffraction

The ultraviolet photochemistry of halothiophenes is thought to proceed via competing pathways, prompt C–X (X = halogen) bond fission, and parent ring opening followed by fragmentation, yet direct structural evidence distinguishing these mechanisms is limited. Here, time-resolved gas-phase ultrafast electron diffraction (UED) has been used to directly follow the structural dynamics of 2- and 3-iodothiophene following photoexcitation at 247 nm. For both isomers, the time-resolved pair distribution functions reveal the appearance of new interatomic distances that cannot be explained by simple C–I bond cleavage and formation of C 4 SH 3 radical cofragments. The signatures, particularly those for 2-iodothiophene, are consistent with a rival ring-opening channel of the intact parent, which evolve on time scales distinct from those associated with the direct C–I bond cleavage. In addition, the extracted kinetics indicate that the ring-opening channel occurs faster in 2-iodothiophene than in the 3-isomer at this excitation wavelength. Furthermore, these measurements provide direct geometric evidence for competing pathways leading to different structures following photodissociation in a model heteroaromatic and further establish UED as a sensitive probe of complex excited-state chemistry.

Bond cleavage↗
DOE OSTI2023

Determination of the Interfacial Energy between Graphene Nanoplatelets and Deuterated or Hydrogenated Polystyrene

The tracer diffusion coefficients of various graphene nanoplatelet-polystyrene (GNP-PS) systems were determined by using dynamic secondary ion mass spectrometry, which provided insights into the interactions within the polymer nanocomposite system. Bilayer films, where one contained trace amounts of deuterated polystyrene (dPS), were produced, and the interdiffusion was measured by detecting the position of the dPS interface. GNPs were placed in both or only one of the two layers. The diffusion coefficient was decreased when GNPs were present in both layers as compared to the samples without GNP, indicating an attractive interaction between GNP and polystyrene. Surprisingly, the coefficient increased relative to the control when GNPs were present only in the PS containing layer, whereas it decreased most strongly when GNP and dPS were present only in the same layer, indicating that an additional preference existed for GNPs and dPS. A significant difference in interfacial energies was measured using contact angle goniometry of PS or dPS droplets on flat GNP layers, confirming the preferential interaction. DFT calculations were used to calculate the interfacial interaction between GNP and dPS or PS, and they showed an attractive potential which was maximal when the PS rings were conformal with the GNP structure. Furthermore, the differential energy between PS and dPS at the GNP interface was in excellent agreement with the measured value. In contrast, contact angle goniometry indicated that the interaction between GNP and poly(methyl methacrylate) (PMMA) was unfavorable, and no difference in interfacial energy between dPMMA and PMMA was observed. Therefore, these techniques can provide a means for determining the relative affinity between GNP and different polymer hosts, which can be an important consideration in the mechanics and adhesion properties of the compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Au as a Surrogate for F: The Case of UAu 6 vs UF 6

Here, anion photoelectron spectroscopy and first-principles quantum chemistry are used to demonstrate to what degree Au can act as a surrogate for F in UF6 and its anion. Unlike UF6, UAu6 exhibits strong ligand–ligand, i.e., Au–Au, interactions, resulting in three low-lying isomers, two of which are three-dimensional while the third isomer has a ring-like quasi two-dimensional structure. Additionally, all the UAu6 isomers have open-shell electrons, which in nearly all cases are localized on the central U atom. As a result, the adiabatic electron affinity and vertical detachment energy are measured to be 3.05 ± 0.05 and 3.28 ± 0.05 eV, respectively, and are in very good agreement with calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Finite-difference time-domain methods

The finite-difference time-domain (FDTD) method is a widespread numerical tool for full-wave analysis of electromagnetic fields in complex media and for detailed geometries. Applications of the FDTD method cover a range of time and spatial scales, extending from subatomic to galactic lengths and from classical to quantum physics. Technology areas that benefit from the FDTD method include biomedicine — bioimaging, biophotonics, bioelectronics and biosensors; geophysics — remote sensing, communications, space weather hazards and geolocation; metamaterials — sub-wavelength focusing lenses, electromagnetic cloaks and continuously scanning leaky-wave antennas; optics — diffractive optical elements, photonic bandgap structures, photonic crystal waveguides and ring-resonator devices; plasmonics — plasmonic waveguides and antennas; and quantum applications — quantum devices and quantum radar. This Primer summarizes the main features of the FDTD method, along with key extensions that enable accurate solutions to be obtained for different research questions. Additionally, hardware considerations are discussed, plus examples of how to extract magnitude and phase data, Brillouin diagrams and scattering parameters from the output of an FDTD model. Furthermore, the Primer ends with a discussion of ongoing challenges and opportunities to further enhance the FDTD method for current and future applications.

42 ENGINEERING↗
DOE OSTI2023

Trimethyltriazacyclohexane coordination chemistry of simple rare-earth metal salts

Reactions of 1,3,5-trimethyl-triazacyclohexane (Me 3 tach) with common rare-earth metal iodide, chloride, and triflate salts were examined to determine the capacity of this inexpensive chelate to provide alternative precursors for THF-free reactions. The reaction of LaI 3 (THF) 4 and CeI 3 (THF) 4 with 1,3,5-trimethyl-triazacyclohexane in THF generated toluene soluble (Me 3 tach) 2 LnI 3 , 1-Ln , in which the Ln center has a tri-capped trigonal prismatic geometry with two eclipsed Me 3 tach rings. Reaction with NdI 3 (THF) 3.5 forms the analogous 1-Nd , but a different structure with one outer sphere iodide, [(Me 3 tach) 2 NdI 2 ][I], 2-Nd , is also accessible and has a structure reminiscent of bent metallocenes. The reaction of LaCl 3 and Me 3 tach forms the less soluble (Me 3 tach) 2 LaCl 3 , which has a structure analogous to 1-Ln with eclipsed Me 3 tach rings. The mono-ring yttrium complex, (Me 3 tach)YCl 3 (THF) 2 , could be isolated from the reaction of YCl 3 with Me 3 tach. Reactions of La(OTf) 3 with Me 3 tach were sensitive to the presence of residual proton sources as exemplified by the isolation of {[(Me 3 tach)La(μ-OH)(μ-OTf)] 2 (μ-OTf) 2 } 2 , 5-La , and [HMe 3 tach][(Me 3 tach) 2 La-(OTf) 4 ], 6-La . SmI 2 reacts with Me 3 tach to produce the Sm( II ) complex, (Me 3 tach) 2 SmI 2 (THF), 7-Sm , but 2-Sm can also form in this reaction. Complexes of the larger 1,4,7-trimethyltriazacyclononane (Me 3 tacn) ligand, namely (Me 3 tacn)LaI 3 (THF), (Me 3 tacn)YCl 3 , and (Me 3 tacn)SmI 2 (THF) were synthesized for comparison. Several examples of the protonated ligands with simple counteranions, [HMe 3 tach][X] (X = Cl, Br, I) and [HMe 3 tacn][OTf], were identified in the course of these studies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Co-free gradient lithium-rich cathode for high-energy batteries with optimized cyclability

Lithium-rich layered oxides (LLOs) hold the promise for high-energy battery cathodes. However, its application has been hindered by voltage decay associated with irreversible reactions at high voltages despite decades of intensive efforts. Here, we first theoretically studied the molecular orbitals of Mn-based Li-rich configurations. We found that the π-bond ring formed within the LiMn 6 structure could participate in stable redox reactions as one unit, but Co could disrupt its symmetry. We thus designed and synthesized Co-free concentration-gradient LLOs (CF-CG-LLOs) materials. The combination of concentration gradient and Co removal leads to exceptional capacity retention without any fading over 100 cycles of the pouch cell. More importantly, it exhibits an extraordinarily low voltage decay of 0.15 mV/cycle, accompanied by a high Coulombic efficiency of 99.86%. This concept and demonstration of CF-CG-LLO cathodes reveal a viable avenue toward low-cost, high-energy-density battery cathodes.

25 ENERGY STORAGE↗
NASA NTRS1974

Ruemker Hills - A lunar volcanic dome complex

The Ruemker Hills, a volcanic dome-flow complex in the northern Oceanus Procellarum, is characterized by overlapping plains-forming units with lobate scarps, volcanic domes, a 60-km ring, and a scarp which separates the plateau from surrounding mare materials. Plains-forming units are interpreted as fluid volcanic flows, and domes as viscous extrusions. One dome may be a stratovolcano. The ring system is discordant with regional structural trends and probably has a local origin. The Ruemker Hills is the closest lunar analog to the large Martian shield structures revealed on the Mariner 9 photographs of Mars.

Smith, E. I.↗
NASA NTRS1974

Cytogenic studies of blood (experiment M111)

The Skylab M111 experiment was a continuation of the preflight and postflight chromosomal analyses of the flight crews that have been performed since the Gemini 3 mission. The experiment was designed to determine whether some space flight parameter produces cytogenetic effects in human cells and to provide biological radiation dosimetric capability in the event of significant radiation exposure to a flight crew. On each of the Skylab flights, blood lymphocytes for analysis of chromosomes for structural defects were obtained from each of the prime crewmembers and from a ground-based control group before and after flight. Two types of defects were recorded. The minor defects included the following aberrations: chromatid fragments, chromosome fragments, and deletions. Structural rearrangements such as dicentrics, exchanges, ring chromosomes, and translocations were photographed, and the cells were karyotyped to delineate, when possible, the chromosome or chromosomes involved in the rearrangement. Result seems to indicate that the flight itself was not a major contributing factor.

Lockhart, L. H.↗
NASA NTRS1975

Reentry static stability characteristics of a (Model 471) .005479-scale 146-inch solid rocket booster tested in the NASA/MSFC 14 by 14 inch TWT (SA8F)

A force test of a scale model of the Space Shuttle Solid Rocket Booster was conducted in a trisonic wind tunnel. The model was tested with such protuberances as a camera capsule, electrical tunnel, attach rings, aft separation rockets, ET attachment structure, and hold-down struts. The model was also tested with the nozzle at gimbal angles of 0, 2.5, and 5 degrees. The influence of a unique heat shield configuration was also determined. Some photographs of model installations in the tunnel were taken and are included. Schlieren photography was utilized for several angles of attack.

Johnson, J. D.↗
NASA NTRS1978

Finite element microscopic stress analysis of cracked composite systems

This paper considers the stress concentration problems of two types of cracked composite systems: (1) a composite system with a broken fiber (a penny-shaped crack problem), and (2) a composite system with a cracked matrix (an annular crack problem). The cracked composite systems are modeled with triangular and trapezoidal ring finite elements. Using NASTRAN (NASA Structural Analysis) finite element computer program, the stress and deformation fields in the cracked composite systems are calculated. The effect of fiber-matrix material combination on the stress concentrations and on the crack opening displacements is studied.

Ko, W. L.↗
NASA NTRS1981

Cylindrical bearing analysis

Program CYBEAN computes behavior of rolling-element bearings including effects of bearing geometry, shaft misalinement, and temperature. Accurate assessment is possible for various outer-ring and housing configurations. CYBEAN is structured for coordinated execution of modules that perform specific analytical tasks. It is written in FORTRAN IV for use on the UNIVAC 1100/40 computer.

Kleckner, R. J.↗
NASA NTRS1983

On long-wavelength magnetic anomalies over Indian region

A data set composed of vector magnetic measurements obtained by MAGSAT and very accurate altitude determinations made using Sun sensors and star cameras was used to obtain data for very quiet days over the Indian region at 10 S to 40 N and 60 E to 110 E in an effort to determine the validity of quantitative estimates made from aeromagnetic data obtained by removing the core field. To further account for the external effects, the ring current contributions estimated using both X and Z variations were subtracted from the observed values. Before this, the core contribution was eliminated through a spherical harmonic expansion with terms up to N=13. Analysis of the residual measurements using Fast Fourier techniques indicates that the anomalies contain substantial power for wavelengths of about 1500 kms. Because the ring current effect has a spatial structure of this dimension over India, efforts are being made to exactly eliminate these two interfering effects from the data.

Srinivasan, S.↗
NASA NTRS1984

Exploration of the Solar System by Airborne Astronomy

The contributions of airborne astronomy to the knowledge of our solar system are reviewed, beginning in 1967 when planetary observations became a vigorous part of NASA's airborne astronomy initiatives using aircraft outfitted with 30 cm diameter telescopes for infrared observations at altitudes between 12 and 15 km. These early facilities and their successor, the Kuiper airborne observatory (KAO), profoundly influenced many areas of planetary science by providing optimized platforms for the conduct of certain types of remote sensing experiments that were incompatible with both ground-based and spacecraft environments. Specific topics reviewed include energy balance in the outer planets, the composition and structure of planetary atmospheres, and planetary ring systems.

Larson, H. P.↗
NASA NTRS1990

Liquid-Ring Attitude-Control System For Spacecraft

Angular momentum transferred to liquid flowing in rings of tubing. Proposed fluid-ring actuator used to orient spacecraft. Used instead of rotating inertia wheels. Meets need for pointing system of low mass, low power, and high resolution. Advantage of actuator, rings of tubing routed through existing structures, minimizing required space and mass.

Lurie, Boris J.↗