Search NASA⌕ Search

SEARCH · Search NASA

Results for “Control”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Using controlled disorder to probe the interplay between charge order and superconductivity in NbSe 2

The interplay between superconductivity and charge-density wave (CDW) in 2H-NbSe2 is not fully understood despite decades of study. Artificially introduced disorder can tip the delicate balance between two competing long-range orders, and reveal the underlying interactions that give rise to them. Here in this paper we introduce disorder by electron irradiation and measure in-plane resistivity, Hall resistivity, X-ray scattering, and London penetration depth. With increasing disorder, the superconducting transition temperature, T c , varies non-monotonically, whereas the CDW transition temperature, T CDW , monotonically decreases and becomes unresolvable above a critical irradiation dose where T c drops sharply. Our results imply that the CDW order initially competes with superconductivity, but eventually assists it. We argue that at the transition where the long-range CDW order disappears, the cooperation with superconductivity is dramatically suppressed. X-ray scattering and Hall resistivity measurements reveal that the short-range CDW survives above the transition. Superconductivity persists to much higher dose levels, consistent with fully gapped superconductivity and moderate interband pairing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Dislocation interactions in olivine control postseismic creep of the upper mantle

Changes in stress applied to mantle rocks, such as those imposed by earthquakes, commonly induce a period of transient creep, which is often modelled based on stress transfer among slip systems due to grain interactions. However, recent experiments have demonstrated that the accumulation of stresses among dislocations is the dominant cause of strain hardening in olivine at temperatures ≤600 °C, raising the question of whether the same process contributes to transient creep at higher temperatures. Here, we demonstrate that olivine samples deformed at 25 °C or 1150–1250 °C both preserve stress heterogeneities of ~1 GPa that are imparted by dislocations and have correlation lengths of ~1 μm. The similar stress distributions formed at these different temperatures indicate that accumulation of stresses among dislocations also provides a contribution to transient creep at high temperatures. The results motivate a new generation of models that capture these intragranular processes and may refine predictions of evolving mantle viscosity over the earthquake cycle.

58 GEOSCIENCES↗
DOE OSTI2019

Controlling protein assembly on inorganic crystals through designed protein interfaces

The ability of proteins and other macromolecules to interact with inorganic surfaces is critical to biological function. The proteins involved in these interactions are highly charged and often rich in carboxylic acid side chains1–5, but the structures of most protein-inorganic interfaces are unknown. We explored the possibility of systematically designing structured protein-mineral interfaces guided by the example of ice-binding proteins, which present arrays of threonine residues matched to the ice lattice that order clathrate waters into an ice-like structure6. We designed proteins displaying arrays of up to 54 carboxylate residues geometrically matched to the K+ sub-lattice on muscovite mica (001). At low [K+] individual molecules bind independently to mica in the designed orientations, while at high [K+], the designs form 2D liquid-crystal phases, which accentuate the inherent structural bias in the muscovite lattice to produce protein arrays ordered over tens of millimeters. Incorporation of designed protein-protein interactions preserving the match between the proteins and the K+ lattice led to extended self-assembled structures on mica: designed end-to-end interactions produced micron long single protein-diameter wires, and a designed trimeric interface yielded extensive honeycomb arrays. The nearest neighbor distances in these hexagonal arrays could be set digitally between 7.5 and 15.9 nm with 2.1 nm selectivity by changing the number of repeat units in the monomer. These results demonstrate that protein-inorganic lattice interactions can be systematically programmed and set the stage for designing protein-inorganic hybrid materials.

Pyles, Harley↗
DOE OSTI2017

Controlling the magnetic and optical responses of a MoS 2 monolayer by lanthanide substitutional doping: a first-principles study

Here, the electronic, magnetic and optical properties of lanthanide substitutional doping (~2% concentration) on the MoS 2 monolayer have been investigated within the density functional theory formalism together with the Hubbard correction (DFT+U). The dopants investigated include Ce, Eu, Gd, Lu and Tm. The calculated dopant substitutional energies under both Mo-rich and S-rich conditions suggest that it is possible to experimentally realize the lanthanide doped MoS 2 monolayer systems. The Eu, Gd and Tm dopants induce strong magnetization in the host lattice. The electronic structure calculations reveal that the dopants have a p-type character and they exhibit a half-metallic behavior in the Gd and Eu doped systems. A dilute magnetic semiconducting behavior can also be realized in Gd, Eu and Tm doped systems by slightly tuning the Fermi level. All the dopants refine the optical responses of the host system with the onset of the optical absorption edge shifting to lower energies within the visible range (red shift phenomenon). We observe an optical anisotropy for two different directions of the electric field (E) polarizations, i.e. parallel, E∥, and perpendicular, E⊥, to the xy-plane. Lanthanide substitutional doping significantly influences the electron energy loss spectra (EELS), absorption spectra, and dielectric properties of the host MoS 2 monolayer. Furthermore, we notice that lanthanide substitutional doping could enhance the photocatalytic properties of the MoS 2 monolayer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗