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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} and Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63}: The diversity of pseudo 5-fold symmetries in the Na–Au–Ga system

The Na-rich part (∼30% Na) of the Na–Au–Ga system between NaAu{sub 2}, NaGa{sub 4}, and Na{sub 22}Ga{sub 39} has been found to contain the ternary phases Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} (I) and Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63} (II), according to the results of single crystal X-ray diffraction measurements. I is orthorhombic, Cmcm, a=5.3040(1), b=24.519(5), c=14.573(3) Å, and contains a network of clusters with local 5-fold symmetry along the a-axis. Such clusters are frequent building units in decagonal quasicrystals and their approximants. II is rhombohedral, R3{sup ¯}m, a=16.325(2), c=35.242(7) Å, and contains building blocks that are structurally identical to the Bergman-type clusters as well as fused icosahedral units known with active metals, triels and late transition elements. II also contains a polycationic network with elements of the clathrate V type structure. Tight-binding electronic structure calculations using linear muffin–tin-orbital (LMTO) methods on idealized models of I and II indicate that both compounds are metallic with evident pseudogaps at the corresponding Fermi levels. The overall Hamilton bond populations are generally dominated by Au–Ga and Au–Au bonds in I and by Ga–Ga bonds in II; moreover, the Na–Au and Na–Ga contributions in I are unexpectedly large, ∼20% of the total. A similar involvement of sodium in covalent bonding has also been found in the electron-richer i-Na{sub 13}Au{sub 12}Ga{sub 15} quasicrystal approximant. - Graphical abstract: Multiply-endohedral Bergman-related clusters in the structure of Na{sub 17}Au{sub 5.9(1)}Ga{sub 46.6.} Display Omitted - Highlights: • Two new compounds with the local 5-fold symmetry have been investigated. • Na{sub 8}Au{sub 9.8(4)}Ga{sub 7.2} is an orthorhombic approximant of the Na{sub 13}Au{sub 12}Ga{sub 15} quasicrystal. • Na{sub 17}Au{sub 5.87(2)}Ga{sub 46.63} represents a rhombohedral distortion of the Bergman-type phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Analysis of the Frequency and Diversity of 1,3-Dialkylimidazolium Ionic Liquids Appearing in the Literature

The hypothetical assertion that there are potentially millions of ionic liquids (ILs) can be validated using basic knowledge of IL precursors and simple calculations. While it is an interesting thought exercise to ponder the possibilities of ILs, it is important to investigate how many discrete ILs (i.e., unique cation and anion pairings) have actually been synthesized and reported in the literature. A complete analysis of all ILs is a daunting task, especially if the definition of what constitutes an IL is broad. Nonetheless, insight can be gained into the use of ILs over the past ~20 years from a focused analysis of systematically varied 1,3-dialkylimidazolium-based ILs (i.e., [R 1 R 2 im][X], where R 1 and R 2 are n-alkyl chains and X is either a halide or molecular anion). This family of ILs includes many of the most widely used and most thoroughly studied IL substances, including 1-butyl-3-methylimidazolium hexafluorophosphate ([C 4 mim][PF 6 ]) and 1-ethyl-3-methylimidazolium bistriflimide ([C 2 mim][Tf 2 N]). Using data retrieved from SciFinder searches, we analyzed the variety and frequency of 1,3-dialkylimidazolium-based ILs appearing in the literature. Our analysis reveals that there is a relatively large number of simple 1,3-dialkylimidazolium cations which have not yet been synthesized. Our findings indicate that despite the broad possibilities of IL structures available, there are but a handful of ILs that are commonly used and studied. Within the 1248 [R 1 R 2 im][X] ILs studied, there were only 12 cations extensively used, which included [R 1 R 2 im] + (R 1 = C 1 and R 2 = C 1 –C 12 ). Of the 16 anions studied, only 5, including [BF 4 ] – , [Cl] – , [PF 6 ] – , [Tf 2 N] – , and [Br] – , were used significantly. Thus, it appears that although ILs can be used as designer solvents with task-specific properties, there is a small default subset of ILs, which are “go-to” or “one-size-fits-all.” Here, we rationalize the current state of the IL landscape in terms of the historical perceptions (and misconceptions) around ILs, familiarity, availability and cost of starting materials, commercial availability of ILs, and the motivations from which researchers choose to synthesize and characterize new ILs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Structural basis for selectivity and diversity in angiotensin II receptors

The angiotensin II receptors AT 1 R and AT 2 R serve as key components of the renin–angiotensin–aldosterone system. AT 1 R has a central role in the regulation of blood pressure, but the function of AT 2 R is unclear and it has a variety of reported effects. To identify the mechanisms that underlie the differences in function and ligand selectivity between these receptors, here we report crystal structures of human AT 2 R bound to an AT 2 R-selective ligand and to an AT 1 R/AT 2 R dual ligand, capturing the receptor in an active-like conformation. Unexpectedly, helix VIII was found in a non-canonical position, stabilizing the active-like state, but at the same time preventing the recruitment of G proteins or β-arrestins, in agreement with the lack of signalling responses in standard cellular assays. Structure–activity relationship, docking and mutagenesis studies revealed the crucial interactions for ligand binding and selectivity. Finally, our results thus provide insights into the structural basis of the distinct functions of the angiotensin receptors, and may guide the design of new selective ligands.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

N= 4 mechanics with diverse (4, 4, 0) multiplets: Explicit examples of hyper-Kähler with torsion, Clifford Kähler with torsion, and octonionic Kähler with torsion geometries

We present simple models of N= 4 supersymmetric mechanics with ordinary and mirror linear (4, 4, 0) multiplets that give a transparent description of Hyper-Kähler with Torsion (HKT), Clifford Kähler with Torsion (CKT), and Octonionic Kähler with Torsion (OKT) geometries. These models are treated in the N= 4 and N=2 superfield approaches, as well as in the component approach. Our study makes manifest that the CKT and OKT supersymmetric sigma models are distinguished from the more simple HKT models by the presence of extra holomorphic torsion terms in the supercharges.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗