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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

ON THE PROPERTIES OF SLOW MHD SAUSAGE WAVES WITHIN SMALL-SCALE PHOTOSPHERIC MAGNETIC STRUCTURES

The presence of magnetoacoustic waves in magnetic structures in the solar atmosphere is well-documented. Applying the technique of solar magneto-seismology (SMS) allows us to infer the background properties of these structures. Here, we aim to identify properties of the observed magnetoacoustic waves and study the background properties of magnetic structures within the lower solar atmosphere. Using the Dutch Open Telescope and Rapid Oscillations in the Solar Atmosphere instruments, we captured two series of high-resolution intensity images with short cadences of two isolated magnetic pores. Combining wavelet analysis and empirical mode decomposition (EMD), we determined characteristic periods within the cross-sectional (i.e., area) and intensity time series. Then, by applying the theory of linear magnetohydrodynamics (MHD), we identified the mode of these oscillations within the MHD framework. Several oscillations have been detected within these two magnetic pores. Their periods range from 3 to 20 minutes. Combining wavelet analysis and EMD enables us to confidently find the phase difference between the area and intensity oscillations. From these observed features, we concluded that the detected oscillations can be classified as slow sausage MHD waves. Furthermore, we determined several key properties of these oscillations such as the radial velocity perturbation, the magnetic field perturbation, and the vertical wavenumber using SMS. The estimated range of the related wavenumbers reveals that these oscillations are trapped within these magnetic structures. Our results suggest that the detected oscillations are standing harmonics, and this allows us to estimate the expansion factor of the waveguides by employing SMS. The calculated expansion factor ranges from 4 to 12.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Small scale H I structure and the soft X-ray background

The observed anticorrelation between diffuse soft X-ray flux and H I column density has been explained as absorption of soft X-rays produced in a hot galactic halo, assuming that the neutral interstellar material is sufficiently clumped to reduce the soft X-ray absorption cross section by a factor of two to three. A 21 cm emission line study of H I column density variations at intermediate and high galactic latitudes to 10' spatial resolution has been done. The results confirm conclusions from preliminary work at coarser resolution, and in combination with other data appear to rule out the hypothesis that clumping of neutral interstellar matter on any angular scale significantly reduces X-ray absorption cross sections in the 0.13 - 0.28 keV energy range. It is concluded therefore that the observed anticorrelation is not primarily a consequence of absorption of soft X-rays produced in a hot galactic halo.

Jahoda, K.↗
NASA NTRS1986

Small-scale H I structure and the soft X-ray background

The observed anticorrelation between diffuse soft X-ray flux and H I column density has been explained as absorption of soft X-rays produced in a hot Galactic halo, assuming that the neutral interstellar material is sufficiently clumped to reduce the soft X-ray absorption cross section by a factor of two to three. A 21-cm emission-line study of H I column density variations at intermediate and high Galactic latitudes is extended to 10 arcmin spatial resolution. The results confirm conclusions from preliminary work at coarser resolution, and, in combination with other data, appear to rule out, on any angular scale, the hypothesis that clumping of neutral interstellar matter significantly reduces X-ray absorption cross sections in the 0.13-0.28 keV energy range. It is concluded therefore that the observed anticorrelation is not primarily a consequence of absorption of soft X-rays produced in a hot Galactic halo.

Jahoda, Keith↗
NASA NTRS1987

Small Al clusters. II - Structure and binding in Al(n) (n = 2-6, 13)

The structure and stability of aluminum clusters containing up to six atoms have been studied using correlated wave functions and extended basis sets. The lowest energy structure is planar for Al4 and Al5, but three dimensional for Al6. The icosahedral, hcp, fcc, and two planar structures of Al13 were considered at the SCF level. The lowest energy structure is the icosahedron, but the planar structures are fairly low lying even in this case. A simplified description using two- and three-body interaction potentials is found to agree well with the ab initio structures and binding energies.

Pettersson, Lars G. M.↗
NASA NTRS2003

Towards the Structure Determination of a Modulated Protein Crystal: The Semicrystalline State of Profilin:Actin

One of the remaining challenges to structural biology is the solution of modulated structures. While small molecule crystallographers have championed this type of structure, to date, no modulated macromolecular structures have been determined. Modulation of the molecular structures within the crystal can produce satellite reflections or a superlattice of reflections in reciprocal space. We have developed the data collection methods and strategies that are needed to collect and analyze these data. If the macromolecule's crystal lattice is composed of physiologically relevant packing contacts, structural changes induced under physiological conditions can cause distortion relevant to the function and biophysical processes of the molecule making up the crystal. By careful measurement of the distortion, and the corresponding three-dimensional structure of the distorted molecule, we will visualize the motion and mechanism of the biological macromolecule(s). We have measured the modulated diffraction pattern produced by the semicrystalline state of profilin:actin crystals using highly parallel and highly monochromatic synchrotron radiation coupled with fine phi slicing (0.001-0.010 degrees) for structure determination. These crystals present these crystals present a unique opportunity to address an important question in structural biology. The modulation is believed to be due to the formation of actin helical filaments from the actin beta ribbon upon the pH-induced dissociation of profilin. To date, the filamentous state of actin has resisted crystallization and no detailed structures are available. The semicrystalline state profilin:actin crystals provides a unique opportunity to understand the many conformational states of actin. This knowledge is essential for understanding the dynamics underlying shape changes and motility of eukaryotic cells. Many essential processes, such as cytokinesis, phagocytosis, and cellular migration depend upon the capacity of the actin microfilament system to be restructured in a controlled manner via polymerization, depolymerization, severing, cross-linking, and anchorage. The structure the semicrystalline state of profilin:actin will challenge and validate current models of muscle contraction and cell motility. The methodology and theory under development will be easily extendable to other systems.

Borgstahl, G.↗
DOE OSTI2017

Spatial Variations of Turbulent Properties of Neutral Hydrogen Gas in the Small Magellanic Cloud Using Structure-function Analysis

We investigate spatial variations of turbulent properties in the Small Magellanic Cloud (SMC) by using neutral hydrogen (H i) observations. With the goal of testing the importance of stellar feedback on H i turbulence, we define central and outer SMC regions based on the star formation rate (SFR) surface density, as well as the H i integrated intensity. We use the structure function and the velocity channel analysis to calculate the power-law index ( γ ) for both underlying density and velocity fields in these regions. In all cases, our results show essentially no difference in γ between the central and outer regions. This suggests that H i turbulent properties are surprisingly homogeneous across the SMC when probed at a resolution of 30 pc. Contrary to recent suggestions from numerical simulations, we do not find a significant change in γ due to stellar feedback as traced by the SFR surface density. This could be due to the stellar feedback being widespread over the whole of the SMC, but more likely due to a large-scale gravitational driving of turbulence. We show that the lack of difference between central and outer SMC regions cannot be explained by the high optical depth H I.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Effect of the chlorine substitution position of the end-group on intermolecular interactions and photovoltaic performance of small molecule acceptors

The structure–property relationships of small molecular acceptors (SMAs) are a key issue in the molecular design of new-generation acceptor materials for further improving the device efficiencies of polymer solar cells (PSCs). Herein, three couples of SMA isomers were synthesized, based on three central fused ring units and two 1,1-dicyanomethylene-3-indanone (IC) isomer electron-withdrawing terminal units with chlorine substitutions in different positions of its benzene ring: Cl-1 with chlorine on the same side as a C=O group of IC and Cl-2 with chlorine on the same side as the CN groups of IC. Through systematical investigation, we found that the chlorine substitution position of the terminal groups has a regular and significant influence on the molecular packing and photovoltaic performance of the SMAs. The molecular packing behavior of the SMAs is closely related to and determined by the configuration of their terminal groups, no matter which central fused ring of the SMAs is used. In particular, the Cl-1-based SMAs possess a stronger crystallinity with long range ordering packing in their molecular plane direction, while the more abundant and stereoscopic π–π intermolecular interaction in the Cl-2-based SMAs promotes the molecules to form three-dimensional charge transporting channels and leads to their red-shifted absorption and higher electron mobilities. Therefore, the Cl-2-based PSCs exhibit a higher power conversion efficiency (PCE) compared to that of the Cl-1-based devices, and the best PCE of a Cl-2 SMA-based PSC reached 16.42%. These results highlight the importance of the investigation of intermolecular interactions, packing and the arrangement of the SMAs in the solid-state, which may provide direct insights for exploring the relationship between the molecular structure and property of the photovoltaic materials. Moreover, we envision that if fragments such as end groups or side chains with more diverse molecular interactions are added into the design and the subsequent synthesis of the SMAs, this may be beneficial to promoting molecular π–π accumulation and further improving the molecular order, forming suitable molecular packing and morphology in the resulting blend films, and finally affecting the efficiency of the PSCs.

14 SOLAR ENERGY↗
DOE OSTI2013

Structure, stability, and dissociation of small ionic silicon oxide clusters [SiO{sub n}{sup +}(n = 3, 4)]: Insight from density functional and topological exploration

The structures, energies, isomerization, and decomposition pathways of small ionic silicon oxide clusters, SiO{sub n}{sup +} (n = 3, 4), on doublet and quartet energy surfaces are investigated by density functional theory. New structural isomers of these ionic clusters have been obtained with this systematic study. The energy ordering of the isomeric cluster ions on doublet spin surface is found to follow the same general trend as that of the neutral ones, while it differs on the quartet surface. Our computational results reveal the energetically most preferred decomposition pathways of the ionic clusters on both spin surfaces. To comprehend the reaction mechanism, bonding evolution theory has also been employed using atoms in molecules formalism. The possible reasons behind the structural deformation of some isomers on quartet surface have also been addressed. Our results are expected to provide important insight into the decomposition mechanism and relative stability of the SiO{sub n}{sup +} clusters on both the energy surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

High-throughput screening identifies small molecules that bind to the RAS:SOS:RAS complex and perturb RAS signaling

K-RAS is mutated in approximately 30% of human cancers, resulting in increased RAS signaling and tumor growth. Thus, RAS is a highly validated therapeutic target, especially in tumors of the pancreas, lung and colon. Although directly targeting RAS has proven to be challenging, it may be possible to target other proteins involved in RAS signaling, such as the guanine nucleotide exchange factor Son of Sevenless (SOS). We have previously reported on the discovery of small molecules that bind to SOS1, activate SOS-mediated nucleotide exchange on RAS, and paradoxically inhibit ERK phosphorylation. In this paper, we describe the discovery of additional, structurally diverse small molecules that also bind to SOS1 in the same pocket and elicit similar biological effects. We tested>160,000 compounds in a fluorescence-based assay to assess their effects on SOS-mediated nucleotide exchange. X-Ray structures revealed that these small molecules bind to the CDC25 domain of SOS1. Compounds that elicited high levels of nucleotide exchange activity in vitro increased RAS-GTP levels in cells, and inhibited phospho ERK levels at higher treatment concentrations. The identification of structurally diverse SOS1 binding ligands may assist in the discovery of new molecules designed to target RASdriven tumors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

The system with zwitterionic lactose-based surfactant for complexation and delivery of small interfering ribonucleic acid—A structural and spectroscopic study

Systems suitable for the effective preparation of complexes with siRNA (small interfering RNA) are at the center of interest in the area of research work on the delivery of the RNA-based drugs (RNA-therapeutics). This article presents results of a study on the structural effects associated with siRNA complexation by a surfactant comprising a lactose group (N-(3-propanesulfone)-N-dodecyl-amino-beta-D-lactose hydrochloride, LA12). The double stranded siRNA oligomer (21 base pairs) used in this study is responsible for silencing a gene that can be important in the therapy of myotonic dystrophy type 1. The obtained siRNA/LA12 lipoplexes were studied using the methods of small angle scattering of synchrotron radiation, circular dichroism spectroscopy, Fourier transform infrared spectroscopy, and electrophoretic mobility tests. Lipoplexes form in solution stable lamellar or cubic phases. The surfactant selected for the study shows much lower cytotoxicity and good complexation abilities of siRNA than dicationic or polycationic surfactants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Structure, Stability, and Mobility of Small Pd Clusters on the Stoichiometric and Defective TiO2 (110) Surfaces

We report on the structure and adsorption properties of Pdn (n = 1–4) clusters supported on the rutile TiO2 (110) surfaces with the possible presence of a surface oxygen vacancy or a subsurface Ti-interstitial atom. As predicted by the density functional theory, small Pd clusters prefer to bind to the stoichiometric titania surface or at sites near subsurface Ti-interstitial atoms. The adsorption of Pd clusters changes the electronic structure of the underlying surface. For the surface with an oxygen vacancy, the charge localization and ferromagnetic spin states are found to be largely attenuated owing to the adsorption of Pd clusters. The potential energy surfaces of the Pd monomer on different types of surfaces are also reported. The process of sintering is then simulated via the Metropolis Monte Carlo method. The presence of oxygen vacancy likely leads to the dissociation of Pd clusters. On the stoichiometric surface or surface with Ti-interstitial atom, the Pd monomers tend to sinter into larger clusters, whereas the Pd dimer, trimer, and tetramer appear to be relatively stable below 600 K. This result agrees with the standard sintering model of transition metal clusters and experimental observations.

Environmental Molecular Sciences Laboratory↗