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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
DOE OSTI2025

Enhanced chloroplast FtsZ-ring constriction by the ARC6–ARC3 module in Arabidopsis

Chloroplast division, a process tightly linked to the energy demands of plants, is initiated by the formation of the stromal filamenting temperature-sensitive Z (FtsZ) ring. The Z ring is highly dynamic, and its constriction provides the essential force for chloroplast division. However, the regulatory mechanisms governing Z-ring dynamics and constriction remain poorly understood. Here, we report that the chloroplast inner envelope membrane (IEM) protein ACCUMULATION AND REPLICATION OF CHLOROPLASTS6 (ARC6) interacts with the chloroplast stromal protein ARC3, and this interaction is negatively regulated by the conserved J-like domain of ARC6. ARC3 is found both distributed throughout the stroma and localized to a ring-like structure at the chloroplast division site. We demonstrate that ARC6 recruits ARC3 to the division site to form a ring-like structure, likely through direct interaction. This ARC6–ARC3 interaction enables ARC3 to bind FtsZs. Furthermore, we show that the ARC6–ARC3 complex significantly promotes the dynamics of chloroplast Z rings reconstituted in a heterologous system. Finally, the constriction of these reconstituted Z rings is markedly enhanced by ARC6–ARC3. Our findings reveal a regulatory mechanism that governs Z-ring dynamics and constriction, shedding light on the molecular mechanisms underlying chloroplast division.

Science & Technology - Other Topics↗
NASA NTRS1979

The vertical structure and thickness of Saturn's rings

The steady state thickness and vertical structure of Saturn's rings are discussed with regard to whether a collapse to a monolayer due to particle collisions may be prevented by various mechanisms. The differences between thick rings and wavy monolayers are outlined and used to show that such coherent perturbations to the rings as satellite and solar gravitational effects would produce a wavy monolayer while such dispersive mechanisms as meteoroid impact, radiation pressure, Kepler shear and radial spreading, which would produce the random particle motions necessary to maintain a thick layer, are probably insignificant. Given a typical power law distribution of particle sizes, it is found that gravitational scattering of small particles by large ones would maintain a ring thickness of several times the radius of the largest particles. A steady state ring thickness of 20 to 50 meters, derived from energy considerations, would imply a maximum particle size of a few meters.

Cuzzi, J. N.↗
NASA NTRS2004

Potential of Radar Imaging and Sounding Methods in Mapping Heavily Eroded Impact Craters: Mapping Some Structural Elements of the Hico Crater, TX

Shuttle Radar Topography Mission (SRTM) and Ground Penetrating Radar (GPR) data collected over an area north of the town of Hico, central Texas, have been used to map disturbances in the surface topography and subsurface stratigraphy. The Radar topography results confirm the presence of multiple rings suggestive of an impact crater. Correlation between the orbital SRTM and on-the-ground GPR field data are affected by different biases related to variations in terrain and vegetation cover. Nevertheless, the correspondence of the two data sets supports the earlier conclusions that a complex, multiple ring impact structure is reflected in the topography of this area. The SRTM data reveal three previously unrecognized rings; with the outermost ring some 5-6 km in diameter. The crater appears to be significantly larger than the size (2.5 km diameter) previously inferred on the basis of aerial images. In addition, the GPR data suggest the presence of subsurface faulting that spatially coincides with the two inner rings of the crater. This suggests that the topographic rings are structurally controlled by faulting.

Heggy, E.↗
DOE OSTI2022

Bond Length Alternation and Internal Dynamics in Model Aromatic Substituents of Lignin

In this report broadband microwave spectra were recorded over the 2-18 GHz frequency range for a series of four model aromatic components of lignin; namely, guaiacol (ortho-methoxy phenol, G), syringol (2,6-dimethoxy phenol, S), 4-methyl guaiacol (MG), and 4-vinyl guaiacol (VG), under jet-cooled conditions in the gas phase. Using a combination of 13 C isotopic data and electronic structure calculations, distortions of the phenyl ring by the substituents on the ring are identified. In all four molecules, the r C(1)-C(6) bond between the two substituted C-atoms lengthens, leading to clear bond alternation that reflects an increase in the phenyl ring resonance structure with double bonds at r C(1)-C(2) , r C(3)-C(4) and r C(5)-C(6) . Syringol, with its symmetric methoxy substituents, possesses a microwave spectrum with tunneling doublets in the a-type transitions associated with H-atom tunneling. These splittings were fit to determine a barrier to hindered rotation of the OH group of 1975 cm -1 , a value nearly 50% greater than that in phenol, due to the presence of the intramolecular OH…OCH 3 H-bonds at the two equivalent planar geometries. In 4-methyl guaiacol, methyl rotor splittings are observed and used to confirm and refine an earlier measurement of the three-fold barrier V 3 = 67 cm -1 . Finally, 4-vinyl guaiacol shows transitions due to two conformers differing in the relative orientations of the vinyl and OH groups.

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

Ring Size Effects on the Structures of Sandwich Compounds with a Stoichiometry of C 12 H 12 M (M = Ti–Ni)

Ring size effects on geometries and electronic structures were investigated for the (C n H n )M(C m H m ) (n = 4, 5, or 6; m = 8, 7, or 6; m + n = 12; M = Ti–Ni) systems using density functional theory. The lowest-energy C 12 H 12 M structures for the early transition metals titanium, vanadium, and chromium are the experimentally known singlet (η 5 -C 5 H 5 )Ti(η 7 -C 7 H 7 ), doublet (η 5 -C 5 H 5 )V(η 7 -C 7 H 7 ), and singlet (η 6 -C 6 H 6 ) 2 Cr, respectively. The likewise experimentally known singlet (η 6 -C 6 H 6 ) 2 Ti, doublet (η 6 -C 6 H 6 ) 2 V, and singlet (η 5 -C 5 H 5 )Cr(η 7 -C 7 H 7 ) are the secondlowest- energy structures with only a small energy difference between the two vanadium structures. For the later transition metals, dibenzenemetal complexes are the lowest-energy C 12 H 12 M species with two fully bonded hexahapto benzene rings in the lowest-energy manganese and iron derivatives and one hexahapto and one dihapto benzene ring in the lowest-energy cobalt and nickel derivatives. The lowest-energy (C 5 H 5 )M(C 7 H 7 ) structures for the later transition metals iron, cobalt, and nickel have partially bonded nonplanar C 7 H 7 rings with one or two uncomplexed C=C bonds. The (C 4 H 4 )M(C 8 H 8 ) (M = Ti–Ni) structures with the metal sandwiched between four- and eight-membered rings were found to be much higher in energy than their (C 5 H 5 )M(C 7 H 7 ) and (C 6 H 6 ) 2 M isomers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1999

Experiments on Diffusion Flame Structure of a Laminar Vortex Ring

The study of flame-vortex interactions provides one of the means to better understand turbulent combustion, and allows for canonical configurations that contain the fundamental elements found in turbulent flames, These include concentrated vorticity, entrainment and mixing, strain and nonequilibrium phenomena, diffusion and differential diffusion, partial premixing and diluent effects, and heat release effects. In flame- vortex configurations, these fundamental elements can be studied under more controlled conditions than is possible in direct investigations of turbulent flames. Since the paper of Marble, the problem of the flame-vortex interaction has received considerable attention theoretically, numerically and experimentally. Several configurations exist for study of the premixed flame/vortex ring interaction but more limited results have been obtained to date for the diffusion flame/vortex ring case. The setup of Chen and Dahm, which is conceptually similar to that of Karagozian and Manda and Karagozian, Suganuma and Strom where the ring is composed of fuel and air and combustion begins during the ring formation process, is used in the current study. However, it is essential to conduct the experiments in microgravity to remove the asymmetries caused by buoyancy and thus obtain highly symmetric and repeatable interactions. In previous studies it was found that the flame structure of the vortex ring was similar to that obtained analytically by Karagozian and Manda. Dilution of propane with nitrogen led mainly to a reduction in flame luminosities, flame burnout times were affected by both fuel volumes and amount of dilution, and a simple model of the burnout times was developed. In this paper, a discussion on reacting ring displacement and flame burnout time will be given, and the flame structures of vortex rings containing ethane and air will be compared to those of propane reacting in air.

Chen, Shin-Juh↗
DOE OSTI2025

Structural basis for ring-opening fluorescence by the RhoBAST RNA aptamer

Abstract Tagging RNAs with fluorogenic aptamers has enabled imaging of transcripts in living cells, revealing novel aspects of RNA metabolism and dynamics. While a diverse set of fluorogenic aptamers has been developed, a new generation of aptamers uses the ring-opening of spirocyclic rhodamine dyes to achieve robust performance in live mammalian cells. These fluorophores have two chemical states: a cell-permeable spirocyclic state and a fluorescent zwitterionic state. The SpyRho555 dye is mostly non-fluorescent in solution and becomes fluorescent in complex with the RhoBAST aptamer. To understand the basis for RhoBAST-SpyRho555 fluorogenicity, we have determined crystal structures of RhoBAST in complex with 5-carboxytetramethylrhodamine and a SpyRho555 analogue, MaP555. RhoBAST is organized by a perfect four-way junction that positions two loops to form the dye-binding pocket. The core of the ligand resides between a tri-adenine floor and a single guanine base, largely driven by π-stacking interactions. Importantly, the unpaired guanine interacts with the 3-position group of MaP555 to stabilize the open conformation, supported by mutagenesis data, and may play an active role in promoting the open conformation of the dye. This work has implications for the development of new fluorogenic aptamers with improved properties using structure-guided design approaches.

Biochemistry & Molecular Biology↗
DOE OSTI2024

Using Data Science Tools to Reveal and Understand Subtle Relationships of Inhibitor Structure in Frontal Ring-Opening Metathesis Polymerization

The rate of frontal ring-opening metathesis polymerization (FROMP) using the Grubbs generation II catalyst is impacted by both the concentration and choice of monomers and inhibitors, usually organophosphorus derivatives. Herein we report a data-science-driven workflow to evaluate how these factors impact both the rate of FROMP and how long the formulation of the mixture is stable (pot life). Using this workflow, we built a classification model using a single-node decision tree to determine how a simple phosphine structural descriptor (V bur-near ) can bin long versus short pot life. Additionally, we applied a nonlinear kernel ridge regression model to predict how the inhibitor and selection/concentration of comonomers impact the FROMP rate. Furthermore, the analysis provides selection criteria for material network structures that span from highly cross-linked thermosets to non-cross-linked thermoplastics as well as degradable and nondegradable materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1976

Degradation of small mare surface features

Ring-moat structures are interpreted as remnants of flow topography associated with mare emplacement. Measurements of narrow moats characterizing these small mare features reveal a contradiction between their inferred preservation and the degree of surface degradation predicted by theoretical erosional models. Moat widths smaller than 50 m are recorded in areas where erosional models predict that walls of craters three to four times as large should be degraded to slopes of 1 deg. Crater statistics in such regions provide estimates of equilibrium conditions for impact crater formation that are consistent with the degree of preservation of the narrow moats. Although relative ages determined by observation of crater wall slopes near 20 deg, may be appropriate, it is concluded that current erosional models are not valid down to impact-degraded slopes of 1 deg. Relative age estimates based on the inferred degraded state of highly subdued craters are believed to be invalid, particularly for late Eratosthenian-age and Copernican-age mare units. In regions displaying ring-moat structures, highly subdued craters larger than the average moat widths are intepreted as either endogenic features associated with the emplacement of mare flow units or degraded secondary craters, which are typically subdued at the outset.

Schultz, P. H.↗
NASA NTRS1974

Structure of Saturn's rings: Optical and dynamical considerations

The photometric phase curves of Saturn's rings are considered, as well as a conflict between dynamical and photometric models of the rings. The dependence of ring brightness on angular separation of the earth and sun as viewed from Saturn is discussed. The nonlinear brightness surge is interpreted. Some quantitative calculations were carried out for bodies in and near the asteroidal belt. Predicted density profiles of the ring obtained with Mimas in an eccentric orbit and in a circular orbit are also included.

Franklin, F. A.↗
NASA NTRS1981

On the radial structure of Saturn's rings

Voyager 1 cameras revealed that Saturn's B ring appears to be subdivided into hundreds of chaotically spaced narrow rings in a hierarchy that extends to the limit of resolution. A disk model is proposed and applied to Saturn's rings: it is shown that the radial diffusion in a particulate Keplerian disk, under the influence of a viscosity law that decreases more steeply with a certain surface density than with another, will promote the breakdown of the system into an ensemble of thin rings.

Ward, W. R.↗
NASA NTRS1983

The fine structure of the Saturnian ring system

A dust disk within a planetary magnetosphere constitutes a novel type of dust-ring current. Such an azimuthal current carrying dust disk is subject to the dusty plasma analog of the well known finite-resistivity 'tearing' mode instability in regular plasma current sheets, at long wavelengths. It is proposed that the presently observed fine ringlet of the Saturnian ring system is a relic of this process operating at cosmogonic times and breaking up the initial proto-ring (which may be regarded as an admixture of fine dust and plasma) into an ensemble of thin ringlets. It is shown that this instability develops at a rate that is many orders of magnitude faster than any other known instability, when the disk thickness reaches a value that is comparable to its present observed value.

Houpis, H. L. F.↗
NASA NTRS1984

Structure of the Uranian rings. I - Square-well model and particle-size constraints

A least squares fitting is added to the diffraction model for the Uranian rings and the model is then used to determine the relative optical depths of the rings at visible and near-IR wavelengths. Light transmission is assumed constant on a scale of a few radial km in the rings. The amount of starlight passing through the rings is calculated from occultations with account taken of a monolayer ring, diffraction effects, and multiple ring layers. A diffracted occultation profile is generated with consideration given to the angular diameter of the star, the impulse response of the detector, and atmospheric aberrations. Calculation procedures which remove noise are outlined and results are compared with the observational data base. The wavelength dependence of optical depth is formulated. It is shown that occultation data do not support the presence of a large fraction of submicron particles. No optical depth variations are projected for 0.88-2.2 microns wavelengths. Unchopped data are needed to verify the model predictions.

Elliot, J. L.↗