Search NASA⌕ Search

SEARCH · Search NASA

Results for “Structural Effects”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Size matters: altering the metal-surface coordination in micropores via structural confinement effects

Solid-state NMR experiments were used to investigate the dynamics of supported complexes grafted to a series of silica gel materials of varied pore sizes. Through dipolar recoupling measurements, we found that ligand dynamics were impeded in the more confined environments, as would be expected. A new form of motion involving the complex as a whole, however, appeared in the most restricted environment consisting of 22 Å diameter pores. These motions persisted down to –100 °C at which point the ligands were frozen on the NMR timescale. The newly observed dynamics could only result from the breaking of secondary dative metal–siloxane interactions that otherwise lock the complex in a preferred orientation on the surface. Crucially, these results show that confinement effects alone can be sufficient to reduce a grafted metal's effective coordination number in direct analogy to the synthesis of undercoordinated complexes using bulky ligands. Finally, this finding could have important implications in the synthesis of more active heterogeneous catalysts.

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

Detecting impurity-specific effects on structure and radiolytic hydrogen production in aluminum hydroxide

While radiolytic hydrogen (H 2 ) generation is an intrinsic property of aqueous and mineral radiolysis in nuclear waste systems, detection of the sub-ns events leading to H 2 generation is challenging. Interfacial processes involving key mineral phases in the sludge, e.g., gibbsite (α-Al(OH) 3 ), have been implicated, with impurities affecting the amount of H 2 generated. To understand why gibbsite synthesized from nitrate precursors produces less H 2 than gibbsite from chloride precursors, we paired 27 Al multiple quantum magic angle spinning (MQMAS) NMR spectroscopy to determine structural heterogeneity with transverse-field muon spin rotation (TF-μSR) to probe electron availability. MQMAS revealed greater structural disorder in the gibbsite synthesized with nitrate (NO 3 -gibbsite). Correspondingly, TF-μSR showed a larger diamagnetic fraction for NO 3 -gibbsite, indicating reduced persistence of μ + -electron bound states (muonium or other radicals) and thus fewer electrons available for reaction on the sub-ns timescale. This establishes a correlation between impurity-induced disorder and electron loss. The diamagnetic fraction serves as a signature for these sub-ns events, as it provides a key constraint for predictive models without currently resolving whether the electron is lost to direct chemical scavenging or trapping at lattice defects.

Graham, Trent R. [Pacific Northwest National Labor↗
DOE OSTI2024

Effects of structural defects on optical properties of In x Ga 1-x N layers and quantum wells

This review concentrates on the microstructure of In x Ga 1-x N layers and quantum wells (QWs) in relation to their optical properties. The microstructure of In x Ga 1-x N, with a constant In(x) concentration, shifts with layer thickness. Only layers below 100 nm for x = 0.1 are nearly defect-free. A photoluminescence peak is observed at 405 nm, in line with ~10% In, suggesting band-edge luminescence. Layers with greater thickness and In content present a corrugated surface with numerous structural defects, including V-defects, causing redshifts and multi-peaks in photoluminescence up to 490 nm. These defects, resembling those in GaN, lead to a corrugated sample surface. Atomic force microscopy shows a 3.7-fold larger corrugation in samples with 20 QWs compared to those with 5 QWs measured on 2 × 2 μm 2 areas. Like in GaN, dual growth on different crystallographic planes results in varied QW thicknesses, influencing optical traits of devices made from In x Ga 1-x N layers. The purpose of this review and the chosen subject is to highlight the significant contribution of Wladek Walukiewicz and his group to the current research on the properties of In x Ga 1-x N, which are crucial alloys in the field of optoelectronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Local structure memory effects in the polar and nonpolar phases of MoTe 2

We use total scattering to study the reversible transition between the polar 1T' and nonpolar T d phases of layered MoTe 2 taking place at 240 K. Whereas, macroscopically, the transition appears to be first order, locally, it is not. In particular, a great deal of the stacking sequence of Te-Mo-Te layers characteristic of the polar 1T' phase persists locally in the nonpolar T d phase, and vice versa, over a broad temperature range extending about 100 K both below and above the transition. The intermixing ratio for the two sequences evolves gradually across the transition temperature, consistent with a second-order transition behavior. Here, the presence of coexisting local polar and nonpolar regions and the resulting variety of internal interfaces where the spatial inversion symmetry is broken may be behind some of the unusual electronic properties of T d –MoTe 2 , including its putative type-II Weyl semimetal state.

2-dimensional systems↗
DOE OSTI2022

Prediction of high-temperature superconductivity in C2/c-24 solid hydrogen

Recent experimental developments in hydrogen-rich materials at high pressures have put this class of materials above others in the race toward room-temperature superconductivity. As it is the basis of all the materials in this class, the efforts to determine the properties of pure solid hydrogen at high pressures remain intense. Most notably, a recent experimental study of the metallization of hydrogen identified the crystal phase of the solid as the C2/c-24 molecular phase up to ~425 GPa [Loubeyre et al., Nature (London) 577, 631 (2020)10.1038/s41586-019-1927-3]. It is possible that the observed metallization is caused by band structure effects and not a structural phase transition, and the material remains in this crystal phase up to higher pressures [Dogan et al., J. Phys.: Condens. Matter 33, 03LT01 (2020)10.1088/1361-648X/abba8a]. Therefore, it is of crucial importance to determine the superconducting properties of the C2/c-24 phase. Here, we employ a Wannier function-based dense k-point and q-point sampling to compute the electron-phonon coupling and superconducting properties of molecular hydrogen in the C2/c-24 phase. We find that the material has a high superconducting transition temperature of 242 K at 500 GPa. We also find that the transition temperature rapidly increases with pressure in the 400-500-GPa range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1986

Effects of Structural Flexibility on Aircraft-Engine Mounts

Analysis extends technique for design of widely used type of vibration-isolating mounts for aircraft engines, in which rubber mounting pads located in plane behind center of gravity of enginepropeller combination. New analysis treats problem in statics. Results of simple approach useful in providing equations for design of vibrationisolating mounts. Equations applicable in usual situation in which engine-mount structure itself relatively light and placed between large mass of engine and other heavy components of airplane.

Phillips, W. H.↗
NASA NTRS1989

An assessment of the structural dynamic effects on the microgravity environment of a reference Space Station

An interim 'Permanently Manned Capability' Space Station configuration and one designated 'Assembly Complete' are modeled by FEM techniques in order to select forcing functions for modal transient response analysis and illustrate sample waveforms. In all, 114 applied-force cases have been executed to simulate such expected operational disturbances as crewmembers' treadmill exercises and EVAs. The present discussion of the results obtained give attention to the acceleration-response environment of the U.S. Laboratory's center grid-point. The magnitude of the acceleration responses obtained indicate that attenuation systems must be incorporated, or operational constraints must be instituted.

Del Basso, Steve↗
NASA NTRS1992

Simulating hypervelocity impact effects on structures using the smoothed particle hydrodynamics code MAGI

Analysis of interaction occurring between space debris and orbiting structures is of great interest to the planning and survivability of space assets. Computer simulation of the impact events using hydrodynamic codes can provide some understanding of the processes but the problems involved with this fundamental approach are formidable. First, any realistic simulation is necessarily three-dimensional, e.g., the impact and breakup of a satellite. Second, the thickness of important components such as satellite skins or bumper shields are small with respect to the dimension of the structure as a whole, presenting severe zoning problems for codes. Thirdly, the debris cloud produced by the primary impact will yield many secondary impacts which will contribute to the damage and possible breakup of the structure. The problem was approached by choosing a relatively new computational technique that has virtues peculiar to space impacts. The method is called Smoothed Particle Hydrodynamics.

Libersky, Larry↗