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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Improved band gaps and structural properties from Wannier–Fermi–Löwdin self-interaction corrections for periodic systems

The accurate prediction of band gaps and structural properties in periodic systems continues to be one of the central goals of electronic structure theory. However, band gaps obtained from popular exchange–correlation (XC) functionals (such as LDA and PBE) are severely underestimated partly due to the spurious self-interaction error (SIE) inherent to these functionals. In this work, we present a new formulation and implementation of Wannier function-derived Fermi–Löwdin (WFL) orbitals for correcting the SIE in periodic systems. Since our approach utilizes a variational minimization of the self-interaction energy with respect to the Wannier charge centers (WCC), it is computationally more efficient than the HSE hybrid functional and other self-interaction corrections that require a large number of transformation matrix elements. Here, calculations on several (17 in total) prototypical molecular solids, semiconductors, and wide-bandgap materials show that our WFL self-interaction correction approach gives better band gaps and bulk moduli compared to semilocal functionals, largely due to the partial removal of self-interaction errors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Understanding atom probe’s analytical performance for iron oxides using correlation histograms and ab initio calculations

Abstract Field evaporation from ionic or covalently bonded materials often leads to the emission of molecular ions. The metastability of these molecular ions, particularly under the influence of the intense electrostatic field (10 10 Vm −1 ), makes them prone to dissociation with or without an exchange of energy amongst them. These processes can affect the analytical performance of atom probe tomography (APT). For instance, neutral molecules formed through dissociation may not be detected at all or with a time of flight no longer related to their mass, causing their loss from the analysis. Here, we evaluated the changes in the measured composition of FeO, Fe 2 O 3 and Fe 3 O 4 across a wide range of analysis conditions. Possible dissociation reactions are predicted by density-functional theory calculations considering the spin states of the molecules. The energetically favoured reactions are traced on to the multi-hit ion correlation histograms, to confirm their existence within experiments, using an automated Python-based routine. The detected reactions are carefully analyzed to reflect upon the influence of these neutrals from dissociation reactions on the performance of APT for analysing iron oxides.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Dual-cone variational calculation of the two-electron reduced density matrix

The computation of strongly correlated quantum systems is challenging because of its potentially exponential scaling in the number of electron configurations. Variational calculation of the two-electron reduced density matrix (2-RDM) without the many-electron wave function exploits the pairwise nature of the electronic Coulomb interaction to compute a lower bound on the ground-state energy with polynomial computational scaling. Recently, a dual-cone formulation of the variational 2-RDM calculation was shown to generate the ground-state energy, albeit not the 2-RDM, at a substantially reduced computational cost, especially for higher $\textit{N}$-representability conditions such as the T2 constraint. Here we generalize the dual-cone variational 2-RDM method to compute not only the ground-state energy but also the 2-RDM. The central result is that we can compute the 2-RDM from a generalization of the Hellmann-Feynman theorem. Specifically, we prove that in the Lagrangian formulation of the dual-cone optimization the 2-RDM is the Lagrange multiplier. Further, we apply the method to computing the energies and properties of strongly correlated electrons—including atomic charges, electron densities, dipole moments, and orbital occupations—in an illustrative hydrogen chain and the nitrogen-fixation catalyst FeMoco. The dual variational computation of the 2-RDM with T2 or higher N -representability conditions provides a polynomially scaling approach to strongly correlated molecules and materials with significant applications in atomic and molecular and condensed-matter chemistry and physics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Spontaneous Chirality Flipping in an Orthogonal Spin-Charge Ordered Topological Magnet

The asymmetric distribution of chiral objects with opposite chirality is of great fundamental interest ranging from molecular biology to particle physics. In quantum materials, chiral states can build on inversion-symmetry-breaking lattice structures or emerge from spontaneous magnetic ordering induced by competing interactions. Although the handedness of a chiral state can be changed through external fields, a spontaneous chirality flipping has yet to be discovered. We present experimental evidence of chirality flipping via changing temperature in a topological magnet EuAl 4 , which features orthogonal spin density waves (SDW) and charge density waves (CDW). Using circular dichroism of Bragg peaks in the resonant magnetic x-ray scattering, we find that the chirality of the helical SDW flips through a first-order phase transition with modified SDW wavelength. Intriguingly, we observe that the CDW couples strongly with the SDW and displays a rare commensurate-to-incommensurate transition at the chirality flipping temperature. Combining with first-principles calculations and angle-resolved photoemission spectroscopy, our results support a Fermi surface origin of the helical SDW with intertwined spin, charge, and lattice degrees of freedom in EuAl 4 . Our results reveal an unprecedented spontaneous chirality flipping and lay the groundwork for a new functional manipulation of chirality through momentum-dependent spin-charge-lattice interactions. Published by the American Physical Society 2024

3-dimensional systems↗
DOE OSTI2025

Survey of Thirteen Novel Pseudomonas putida Bacteriophages

Bacteriophages have been widely investigated as a promising treatment of food, medical equipment, and humans colonized by antibiotic-resistant bacteria. Phages pose particular interest in combating those bacteria which form biofilms, such as the medically important human pathogen Pseudomonas aeruginosa and several plant pathogens, including P. syringae . In an undergraduate lab course, P. putida was used as the host to isolate novel anti-pseudomonal bacteriophages. Environmental samples of soil and water were collected, and purified phage isolates were obtained. After Illumina sequencing, genomes of these phages were assembled de novo and annotated. Assembled genomes were compared with known genomes in the literature and GenBank to identify taxonomic relations and to refine their functional annotations. The thirteen phages described are sipho-, myo-, and podoviruses in several families of Caudoviricetes , spanning several novel genera, with genomes ranging from 40,000 to 96,000 bp. One phage (DDSR119) is unique and is the first reported P. putida siphovirus. The remaining 12 can be clustered into four distinct groups. Six are highly related to each other and to previously described Autotranscriptaviridae phages: Waldo5, PlaquesPlease, and Laces98 all belong to the Waldovirus genus, whereas Stalingrad, Bosely, and Stamos belong to the Troedvirus genus. Zuri was previously classified as the founding member of a new genus Zurivirus within the family Schitoviridae . Ebordelon and Holyagarpour each represent different species within Zurivirus , whereas Meara is a more distantly related member of the Schitoviridae . Dolphis and Jeremy are similar enough to form a genus but have only a few distant relatives among sequenced phages and are notable for being temperate. We identified the lysis cassettes in all 13 phages, compared tail spike structures, and found auxiliary metabolic genes in several. Studies like these, which isolate and characterize infectious virions, enable the identification of novel proteins and molecular systems and also provide the raw materials for further study, evaluation, and manipulation of phage proteins and their hosts.

Pseudomonas putida↗
DOE OSTI2020

Homocoupling Reactions of Azoles and Their Applications in Coordination Chemistry

Pyrazole, a member of the structural class of azoles, exhibits molecular properties of interest in pharmaceuticals and materials chemistry, owing to the two adjacent nitrogen atoms in the five-membered ring system. The weakly basic nitrogen atoms of deprotonated pyrazoles have been applied in coordination chemistry, particularly to access coordination polymers and metal-organic frameworks, and homocoupling reactions can in principle provide facile access to bipyrazole ligands. In this context, we summarize recent advances in homocoupling reactions of pyrazoles and other types of azoles (imidazoles, triazoles and tetrazoles) to highlight the utility of homocoupling reactions in synthesizing symmetric bi-heteroaryl systems compared with traditional synthesis. Metal-free reactions and transition-metal catalyzed homocoupling reactions are discussed with reaction mechanisms in detail.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Cavitand-Mediated Photodimerization of Chalcones: The Effect of Supramolecular Influences and Temperature on Reaction Selectivity

The photocycloaddition (PCA) of chalcones represents an important reaction pathway for accessing substituted cyclobutanes, which is a molecular framework with utility in synthetic chemistry, materials science, and medicine. In the past, our group has demonstrated the utility of the large cavity of γ-CD as a container for encapsulating two photo reactants for directing the PCA of several classes of aryl alkenes with high stereo- and regioselectivity: the cavitand-mediated photodimerization (CMP) approach. The CMP of chalcones reported in this work further demonstrates the effectiveness of this approach as high yields of dimers were observed in the photoreactions, while they were non-reactive in the solid state and yielded only the isomerization product in homogeneous media. The γ-CD CMP of chalcones yielded predominantly dimerized products in very good to high yields (>70%), composed of a mixture of three dimers in different proportions with syn HH as the major product. Computational analysis of the ground state complex structures revealed a strong correlation between the stability of the complex and predominance of the stereoisomer in the mixture. Further insights were deduced from temperature-dependence studies, which showed a shift in dimer selectivity tending towards a single stereoisomer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1972

Some scientific criteria for a cometary mission

Scientific data necessary for a successful flyby or rendezvous cometary mission are outlined. Specific material cover photometric profiles of the different molecular bands of various comets and instruments by which such measurements can be made.

Delsemme, A. H.↗
NASA NTRS1984

Process Research of Polycrystalline Silicon Material (PROPSM)

An investigation was begun into the usefulness of molecular hydrogen annealing on polycrystalline solar cells. No improvement was realized even after twenty hours of hydrogenation. Thus, samples were chosen on the basis of: (1) low open circuit voltage; (2) low shunt conductance; and (3) high light generated current. These cells were hydrogenated in molecular hydrogen at 300 C. The differences between the before and after hydrogenation values are so slight as to be negligible. These cells have light generated current densities that indicate long minority carrier diffusion lengths. The open circuit voltage appears to be degraded, and quasi-neutral recombination current enhanced. Therefore, molecular hydrogen is not usful for passivating electrically active defects.

Culik, J. S.↗
NASA NTRS1985

A ground-based experimental test program to duplicate and study the spacecraft glow phenomenon

The use of a plasma device, the Advanced Concepts Torus-I, for producing atoms and molecules to study spacecraft glow mechanisms is discussed. A biased metal plate, located in the plasma edge, is used to accelerate and neutralize plasma ions, thus generating a neutral beam with a flux approx. 5 x 10 to the 14th power/sq cm/sec at the end of a drift tube. Our initial experiments are to produce a 10 eV molecular and atomic nitrogen beam directed onto material targets. Photon emission in the spectral range 2000 to 9000 A from excited species formed on the target surface will be investigated.

Langer, W. D.↗
NASA NTRS1989

Synthesis of organic salts with large second-order optical nonlinearities

The variation of the anion counterion in the presently formulated organic salts, whose cation possesses large molecular hyperpolarizability, will in many cases yield materials with large powder second-harmonic generation efficiencies. The highest such efficiency is three orders of magnitude greater than that of the urea used as a reference compound. It is demonstrated that such nonconventional donors as Br(-) and the pyrenyl moiety can be incorporated into molecules which, in the requisite crystallographic environment, will exhibit substantial bulk susceptibilities.

Marder, Seth R.↗
NASA NTRS1989

Comments on containerless bulk crystal growth and epitaxy in space and on their implications regarding non-contact temperature measurements

Containerless methods are sought for bulk crystal growth and epitaxy which thus far are a less visible component of materials science in space efforts. In the opinion of the author, this is an anomaly which ought to be corrected, because container interactions are a major problem in earth bound materials processing, including crystal growth, and can be avoided or at least significantly reduced in space. The space environment is unique in solving some of these problems, e.g., memory effects in the integration of different classes of materials in high resolution multilayer heterostructures by molecular beam epitaxy or organometallic molecular beam epitaxy. Spectroscopic method of noncontact temperature measurements exist that could be developed in this context. The error in the absolute temperature measurement achieved by these techniques decreases with decreasing substrate temperature and supplements pyrometric measurements that are better suited for high temperature measurements.

Bachmann, Klaus J.↗
NASA NTRS1990

InAs/GaAs and InAs doping superlattices

The extension of the optical response of narrow band gap III-V semiconductors into the long wavelength infrared radiation (LWIR) regime for high sensitivity sensor applications is a challenging problem. Recent advances in nipi doped GaAs superlattices, lattice mismatched epitaxy and the heteroepitaxial growth of III-V compound semiconductors on silicon substrates offer a number of opportunities. Researchers describe two different device approaches based on the molecular beam epitaxy (MBE) growth of superlattice materials which are directed to LWIR focal plane array technology. The first of these uses nipi superlattices fabricated in bulk InAs which has been grown on either GaAs or Si substrates. The second is based on the growth of a new pseudomorphic tetragonal phase of InAs on GaAs to create a semimetal/semiconductor superlattice material.

Grunthaner, Frank J.↗
NASA NTRS1990

N2H(+) in warm and cold clouds

A topic of importance in both cometary and instellar astronomy is the N2/NH3 abundance ratio in star forming regions. A key test for solar system formation models is the N2/NH3 abundance ratio in comets, which are thought to be made up of material from the protostar nebula, and in molecular clouds, from which stars are thought to be approx. 0.1. The N2/NH3 abundance ratio has never been measured in the interstellar medium, but is estimated from theoretical models to be in the range of 100 to 200. If the theoretical models are truly representative of dense molecular clouds then the difference in the abundance ratios of N2/NH3 between comets and the ISM would imply that significant chemical processing must have occurred in the protostar nebula that somehow altered the amount of N2 relative to NH3. A systematic survey was made of star forming regions to establish N2 abundances and N2/NH3 ratios for comparison with cometary data.

Womack, Maria↗
NASA NTRS1991

Synthesis of imide/arylene ether copolymers for adhesives and composite matrices

A series of imide/arylene ether copolymers were prepared from the reaction of an amorphous arylene ether oligomer and a semi-crystalline imide oligomer. These copolymers were thermally characterized and mechanical properties were measured. One block copolymer was endcapped and the molecular weight was controlled to provide a material that displayed good compression moldability and attractive adhesion and composite properties.

Jensen, B. J.↗
NASA NTRS1994

Solventless, curable fluid oligomeric systems for high performance microwave, acoustical and mechanical applications

While establishing the basis for a 'Technology 2000' product plan several years ago we plugged in the usual factors contributing toward product success: price/performance justifiable; profitable, warranting high quality maintenance, enhancement, and specific property improvement; narrow inventory requirements; and raw material integrable backwards with easily variable properties (molecular weight, functionality, and isomer control). We resolved this by selecting radical functional, low molecular weight polybutadiene liquid polymers. Encouraged by the need for solid rocket binders, several companies embarked on various perceptions of binder performance requirements over four decades ago. Initially dominated by progress of liquid polysulfides, soon a few settled primarily upon polybutadiene based binders. Such an approach in a few instances was exploited quite viably with a series of functional group terminated liquid polybutadienes: hydroxyl, mercaptan, carboxyl, vinyl, and amine. Good results are obtained for oligomers, liquid polymers, and their hybrids. The only significant limits on compounded products has been solvent resistance and oxidative sensitivity, unless sufficient proportion of sulfide or nitrile moiety is incorporated. For convenience, they have been grouped under the trademarks Nylane, Seamax, Oligomax, and Castomax.

Lefave, G. M.↗
NASA NTRS1994

Radiative transfer code based estimation of atmospheric parameters for inversion of imaging spectrometer measured radiance to apparent surface reflectance

Surface reflectance is required to quantitatively investigate molecular absorption and particle scattering properties of materials on the Earth's surface. Atmospheric aerosol optical depth, surface pressure and water vapor are required to constrain a radiative transfer code for the inversion of measured spectral radiance to apparent surface reflectance. A suite of algorithms using nonlinear least squares fitting techniques are described that directly estimate these atmospheric parameters from spectral radiance measured by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). The derived atmospheric parameters are used to constrain a radiative transfer code for the inversion of the imaging spectrometer radiance to apparent reflectance. The derived apparent reflectance is validated with respect to in situ measurement on the same target.

Green, Robert O.↗
NASA NTRS1994

Observations of ultraviolet-bright stars in globular clusters with the Hopkins Ultraviolet Telescope

Two UV-bright stars in globular clusters, UV5 in NGC 1851 and vZ 1128 in M3, were observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-1 space shuttle mission in 1990 December. The stars' spectra show weak absorption features and no significant emission features other than well known geocoronal lines. Detailed fitting of Kurucz (1991) stellar atmosphere models using a chi(sup 2) minimization technique indicates T(sub eff) = 16 000 K, log g = 2.5, and abundance (-1.0) (logarithm of abundance of elements heavier than helium relative to solar) for UV5, and T(sub eff) = 35 000 K, log g = 4.0, and abundance (-3.5) for vZ 1128. The Kurucz model which best fits vZ 1128 overpredicts the flux in the region below approximately 1000 A, an effect seen in previous models of O-type stars. Our results are robust (to within approximately 1000 K) with respect to uncertainties in interstellar reddening and atomic and molecular hydrogen column densities. We do not see significant molecular hydrogen absorption, which might have indicated material in a circumstellar shell, in either star's spectrum. We estimate the stellar luminosities to be log L/solar luminosity = 3.33 +/- 0.15 for UV5 and log L/solar luminosity = 3.21 +/- 0.12 for vZ 1128. These atmospheric parameters place both stars on the Schoenberner (post-AGB) tracks, though the stellar masses derived from the best-fitting Kurucz models are somewhat less than those predicted by the Schoenberner models. Examination of individual absorption line strengths reveals no significant abundance anomalies in either star.

Van Dyke Dixon, W.↗