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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Tnseq to identify catabolism of b-5 linked aromatics by Novosphingobium aromaticivorans

This study investigates the catabolism of the b-5 linked aromatic dimer dehydrodiconiferyl alcohol (DC-A) by the bacterium Novosphingobium aromaticivorans. We used genome wide screens to identify candidate genes involved in DC-A catabolism. Subsequent in vivo and in vitro analyses of these candidates elucidated a catabolic pathway composed of four required gene products and several partially redundant dehydrogenases that convert DC-A to aromatic monomers that can be funneled into the central aromatic metabolic pathway of N. aromaticivorans.

Noguera, Daniel R.↗
DOE OSTI2024

Tnseq to identify catabolism of b-5 linked aromatics by Novosphingobium aromaticivorans

This study investigates the catabolism of the b-5 linked aromatic dimer dehydrodiconiferyl alcohol (DC-A) by the bacterium Novosphingobium aromaticivorans. We used genome wide screens to identify candidate genes involved in DC-A catabolism. Subsequent in vivo and in vitro analyses of these candidates elucidated a catabolic pathway composed of four required gene products and several partially redundant dehydrogenases that convert DC-A to aromatic monomers that can be funneled into the central aromatic metabolic pathway of N. aromaticivorans.

aromatic compounds↗
NASA NTRS1972

Polyimidazopyrrolone model compounds.

Study of model reactions between phthalic anhydride and o-phenylenediamine under conditions analogous to the polymerization and post cyclization of dianhydrides with bis(o-diamines) to form polyimidazopyrrolones (Pyrrones). Solid-state thermal conversion of the amide-acid-amine affords a unique dimeric species containing amide, imide, and benzimidazole functions. It was confirmed that melt techniques lead to disproportionation products. The application of these findings to related polymer syntheses is discussed.

Young, P. R.↗
NASA NTRS1972

Polyimidazopyrrolone model compounds.

The model reactions between phthalic anhydride and o-phenylenediamine were studied under conditions analogous to the polymerization and post-cyclization of dianhydrides with bis(o-diamines) to form polyimidazopyrrolones (Pyrrones). The route from the initial amide-acid-amine to the tetracyclic Pyrrone model when the reactions are conducted in aprotic solvents is highly competitive between isolatable benzimidazole-acid and imide-amine intermediates. Solid-state thermal conversion of the amide-acid-amine affords a unique dimeric species containing amide, imide, and benzimidazole functions. It was confirmed that melt techniques lead to disproportionation products. The application of these findings to related polymer synthesis is discussed.

Young, P. R.↗
NASA NTRS1973

Condensation in CO2 free jet expansions. II - Growth of small clusters.

An investigation into the kinetics of molecular clustering processes which occur in the highly supersaturated vapor of a CO2 free jet is described. Terminal cluster concentrations in expansions from room temperature and reservoir pressures in the range from 400 to 900 torr were determined for trimeric CO2 for nozzle diameters of .0076 cm, .015 cm, and .023 cm and in the case of CO2 tetramer and pentamer for .015 cm nozzle diameter. The measurements were made mass spectrometrically in a supersonic molecular beam apparatus. A kinetic analysis was developed from an extension of the critical nucleus concept of nucleation theory and rate equations based on intermolecular collisions. The observed cluster populations could be accounted for by the theory by adopting sticking probabilities of approximately .03 for monomer impinging on dimer, trimer, and tetramer.

Dorfeld, W. G.↗
NASA NTRS1972

Photochromism of heterocyclic systems

The preparations of photochromic dimers of a 2-aryl-4,5-di-phenylimidazyl radical and of a 2,5-diphenyl-3,4-isobenzopyrrole with different substituents in the homocyclic ring are reported. Of the dienes investigated, only 1-4-diphenyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene gave isolable amounts of the Diels-Adler adducts.

Silversmith, E. F.↗
NASA NTRS1974

The polarizability of diatomic helium

The calculation of the electric dipole polarizability tensor of the He 2 dimer is described, and the results are used in the computation of several dielectric and optical properties of helium gas, at both high (322 K) and low (4 K) temperatures. The properties considered are the second dielectric virial coefficient, the second Kerr virial coefficient, and the depolarization ratio of the integrated intensities for the Raman scattering experiments. The thesis consists of five parts: the polarizability and various properties are defined; the calculation of the polarizability in the long-range region in terms of a quantum mechanical multipole expansion is described; the calculation of the He2 polarizability in the overlap region via coupled Hartree-Fock perturbation theory is described; the calculation of the quantum pair distribution function for both the He-3 and He-4 isotopes at 4 K is discussed; and the calculated values of the properties of helium gas are given.

Fortune, P. J.↗
NASA NTRS1975

Anomalous volume change of gramicidin A in ethanol solutions

Results of studies aimed at clarifying the failure of gramicidin A (GA) to sediment in early experiments are analyzed. In the present work, no sedimentation was observed in pure pentanol or ethanol, while normal sedimentation was observed in ethanol-water mixtures. It is concluded that GA exists in two conformations that differ in volume. Since the apparent specific volume in absolute ethanol sinks to its lowest values on increasing concentration, the GA molecule probably unfolds completely in conditions favorable for dimerization.

Derechin, M.↗
NASA NTRS1976

Ice crystal growth in water vapor at high saturation

A simple technique is presented for estimating the energy of formation of monolayer icelike clusters at ice-vapor interfaces. Under the assumptions that the ice surfaces are smooth and sparsely covered with monomers, dimers, etc., in near equilibrium with the vapor, and that the bond energies and configurational entropy dominate the energy of formation, it is found that the basal surfaces prefer triangular embryos with an orientation which reverses from layer to layer, whereas the most stable clusters on the prism surfaces are rectangular in configuration. The preferred prism clusters are determined to have a significantly lower critical energy of formation than the basal clusters due to differences in both corner free energy and configurational entropy. This phenomenon provides a mechanism for strongly anisotropic crystal growth at high saturations.

Bartley, D. L.↗
NASA NTRS1976

A parylene coating process for hybrid circuits

The parylene coating process developed during this program consists of (1) obtaining a hybrid cover with a hole in it, (2) sealing of the circuit with a hole in the cover, (3) parylene coating through the hole with the external leads protected from parylene by appropriate fixturing, and (4) sealing of the hole by soldering a pretinned kovar tab. Development of the above process required optimization of the parylene coater parameters to obtain a uniform consistent coating which could offer adequate protection to the circuits, fixture design for packages of various types, determination of the size of the deposition hole, and the amount of dimer charge per run, a process to hermetically seal the deposition holes and establishment of quality control techniques or acceptance criteria for the deposited film.

Source record↗
NASA NTRS1977

Collision-induced absorption of O2 in the Herzberg continuum

Using a one meter normal incidence grating monochromator, the total absorption of radiation for O2 has been reinvestigated between 2000-2500 A. The absorption cross sections of O2 and O4 are then derived from total absorption measurements and compared with other available data. Additional measurements of O2 absorption have been made in the presence of Ar which does not absorb in this spectral region and is chemically inactive with O2. It is found that the absorption of oxygen increases in the presence of Ar, which is interpreted as due to the formation of O2-Ar dimers.

SHARDANAND↗
NASA NTRS1976

Extinction coefficients of NO2 and N2O4

The extinction coefficient of NO2 has been measured in the spectral range from 185 to 410 nm as a function of temperature between 235 and 298 K. In order to correct for the effect of dimer absorption, the extinction coefficient of N2O4 has also been measured. The effect of a decrease in temperature on NO2 absorption is a reduction in the extinction coefficient of approximately 10% in the range from 320 to 380 nm.

Bass, A. M.↗