Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Dependability”

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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Size-dependent characteristics of ultra-fine oxygen-enriched nanoparticles in austenitic steels

Here, a coordinated investigation of the elemental composition and morphology of ultra-fine-scale nanoparticles as a function of size within a variety of austenitic oxide dispersion-strengthened (ODS) steels is reported. Atom probe tomography was utilized to evaluate the elemental composition of these nanoparticles. Meanwhile, the crystal structures and orientation relationships were determined by high resolution transmission electron microscopy. The nanoparticles with sufficient size (>4 nm) to maintain a Y2Ti2-xO7-2x stoichiometry were found to have a pyrochlore structure, whereas smaller YxTiyOz nanoparticles lacked a well-defined structure. The size-dependent characteristics of the nanoparticles in austenitic ODS steels differ from those in ferritic/martensitic ODS steels.

atom probe tomography↗
DOE OSTI2018

Synthesis-dependent properties of barlowite and Zn-substituted barlowite

The mineral barlowite, Cu4(OH)6FBr, has been the focus of recent attention due to the possibility of substituting the interlayer Cu2+ site with non-magnetic ions to develop new quantum spin liquid materials. We re-examine previous methods of synthesizing barlowite and describe a novel hydrothermal synthesis method that produces large single crystals of barlowite and Zn-substituted barlowite (Cu3ZnxCu1–x(OH)6FBr). The two synthesis techniques yield barlowite with indistinguishable crystal structures and spectroscopic properties at room temperature; however, the magnetic ordering temperatures differ by 4 K, and the thermodynamic properties are clearly different. The dependence of properties upon synthetic conditions implies that the defect chemistry of barlowite and related materials is complex and significant. Zn-substituted barlowite exhibits a lack of magnetic order down to T = 2 K, characteristic of a quantum spin liquid, and we provide a synthetic route towards producing large crystals suitable for neutron scattering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Temperature dependence of irradiation-induced nanocrystallization in amorphous silicon carbide

Ion irradiation induced nucleation and growth in amorphous SiC at elevated temperatures are investigated in this study. Both as-deposited amorphous and Kr ion irradiation-amorphized SiC films are used for the investigation. Similar behavior of particle precipitation in the two types of the films is observed. It is found that the threshold temperature for nucleation is between 550 and 700 K, which is considerably higher than the critical temperature for full amorphization in SiC irradiated with Kr ions. There is a temperature regime up to at least 900 K, where the growth rates are only weakly dependent of the irradiation temperature. This temperature regime is potentially useful to tailor the size and density of nanocrystalline SiC precipitates by optimizing the ion irradiation conditions.

Ion irradiation, Nucleation and Growth, Silicon Ca↗
DOE OSTI2018

Dose-Dependent Enrichments and Improved Redox Status in Tissues of Broiler Chicks under Heat Stress by Dietary Supplemental Microalgal Astaxanthin

Here, astaxanthin (AST) is a well-known carotenoid with a high antioxidant capacity. This study was designed to evaluate the nutritional and metabolic effects of microalgal AST added to the diets of broiler chicks under heat stress. A total of 240 Cornish male chicks (1 day old) were divided into six cages per treatment (eight chicks per cage) and fed a corn-soybean meal diet supplemented with AST from Haematococcus pluvialis at 0, 10, 20, 40, and 80 mg/kg for 6 weeks. Heat stress was employed during weeks 4-6. The supplementation led to dose-dependent enrichments ( P < 0.05) of AST and total carotenoids in the plasma, the liver, and the breast and thigh muscles. There were similar enhancements ( P < 0.05) of oxygen-radical-absorbance capacities, but there were decreases or mixed responses ( P < 0.05) of glutathione concentrations and glutathione peroxidase activities in the tissues. In conclusion, supplemental dietary microalgal AST was bioavailable to the chicks and enriched in their tissues independent of heat stress, leading to coordinated changes in their endogenous antioxidant defense and meat quality.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Orientational Dependence of Cofacial Porphyrin–Quinone Electronic Interactions within the Strong Coupling Regime

We examine the relative magnitudes of electronic coupling HDA in two face-to-face rigid and diastereomeric (porphinato)zinc(II)–quinone (PZn–Q) as-semblies, 1β-ZnA and 1β-ZnB, in which the six quinonyl carbon atoms lie in virtually identical arrangements relative to the PZn plane at sub-van der Waals donor–acceptor (D–A) interplanar separations. Steady-state and time-resolved transient optical data and computational studies show that minor differences in relative D–A cofacial orientation give rise to disparate H DA magnitudes for both photoinduced charge separation (CS) and thermal charge recombination (CR). Here, time-dependent density functional theory (TDDFT) computations illuminate the nature of direct charge transfer states and the electronic structural factors that give rise to these differential H DA s. These data show more extensive mixing of locally excited (LE) and CS states in 1β-ZnA relative to 1β-ZnB and that these H DA differences track the magnitudes of electronic coupling matrix elements determined from steady-state electronic spectral data and thermal CR rate constants measured via pump–probe spectroscopy. Collectively, this work shows that electron transfer dynamics may be manipulated in cofacial D–A systems, even at sub-van der Waals contact, provided that conformational rigidity precludes structural fluctuations that modulate D–A interactions on the charge transfer time scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Measuring Relative Energies of Ligand Binding Conformations on Nanocluster Surfaces with Temperature-Dependent FTIR Spectroscopy

We present a method to measure relative energies between binding conformations of carboxylate ligands on InP magic-sized clusters in solution. Using Markov chain Monte Carlo global fitting analysis on temperature-dependent vibrational spectra of cluster-bound ligands, we observe significantly different relative energies between various bidentate and monodentate binding motifs. Relative to the monodentate motif, the chelating conformation is 0.7 ± 0.3 kcal/mol more stable and the syn–syn bridging conformation is 1.1 ± 0.5 kcal/mol more stable, but the syn–anti bridging conformation exhibits no significant difference. Our results demonstrate that the relative energy between monodentate-bound carboxylates and unbound carboxylic acids is 4.52 ± 0.05 kcal/mol, or 1582 ± 19 cm –1 , nearly identical to the carboxylate asymmetric stretching frequency. Here, we suggest that the ligand vibrational energy may play a key role in ligand dissociation by compensating for energy differences between bound and dissociated ligand states. This approach gives important experimental insights into ligand binding and can inform future nanocrystal surface engineering.

Conformation↗
DOE OSTI2016

A family of metal-dependent phosphatases implicated in metabolite damage-control

DUF89 family proteins occur widely in pro- and eukaryotes but their functions are unknown. Here we define three DUF89 subfamilies (I, II, and III), subfamily II being split into standalone proteins and proteins fused to pantothenate kinase (PanK). We demonstrated that DUF89 proteins have metaldependent phosphatase activity against reactive phosphoesters or their damaged forms, notably sugar phosphates (subfamilies II and III), phosphopantetheine and its S-sulfonate or sulfonate (subfamily II-PanK fusions), and nucleotides (subfamily I). Genetic and comparative genomic data strongly associated DUF89 genes with phosphoester metabolism. The crystal structure of the yeast (Saccharomyces cerevisiae) subfamily III protein YMR027W revealed a novel phosphatase active site with fructose 6-phosphate and Mg 2+ bound near conserved signature residues Asp254 and Asn255 that are critical for activity. These findings indicate that DUF89 proteins are previously unrecognized hydrolases whose characteristic in vivo function is to limit potentially harmful buildups of normal or damaged phosphometabolites.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Multiresolution quantum chemistry in multiwavelet bases: excited states from time-dependent Hartree–Fock and density functional theory via linear response

Using the fully numerical method for time-dependent Hartree–Fock and density functional theory (TD-HF/DFT) with the Tamm–Dancoff (TD) approximation we use a multiresolution analysis (MRA) approach to present our findings. From a reformulation with effective use of the density matrix operator, we obtain a general form of the HF/DFT linear response equation in the first quantization formalism. It can be readily rewritten as an integral equation with the bound-state Helmholtz (BSH) kernel for the Green's function. The MRA implementation of the resultant equation permits excited state calculations without virtual orbitals. Moreover, the integral equation is efficiently and adaptively solved using a numerical multiresolution solver with multiwavelet bases. Our implementation of the TD-HF/DFT methods is applied for calculating the excitation energies of H 2 , Be, N 2 , H 2 O, and C 2 H 4 molecules. The numerical errors of the calculated excitation energies converge in proportion to the residuals of the equation in the molecular orbitals and response functions. The energies of the excited states at a variety of length scales ranging from short-range valence excitations to long-range Rydberg-type ones are consistently accurate. It is shown that the multiresolution calculations yield the correct exponential asymptotic tails for the response functions, whereas those computed with Gaussian basis functions are too diffuse or decay too rapidly. Finally, we introduce a simple asymptotic correction to the local spin-density approximation (LSDA) so that in the TDDFT calculations, the excited states are correctly bound.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

History-dependent ion transport through conical nanopipettes and the implications in energy conversion dynamics at nanoscale interfaces

The dynamics of ion transport at nanostructured substrate–solution interfaces play vital roles in high-density energy conversion, stochastic chemical sensing and biosensing, membrane separation, nanofluidics and fundamental nanoelectrochemistry. Advancements in these applications require a fundamental understanding of ion transport at nanoscale interfaces. The understanding of the dynamic or transient transport, and the key physical process involved, is limited, which contrasts sharply with widely studied steady-state ion transport features at atomic and nanometer scale interfaces. Here we report striking time-dependent ion transport characteristics at nanoscale interfaces in current–potential (I–V) measurements and theoretical analyses. First, a unique non-zero I–V cross-point and pinched I–V curves are established as signatures to characterize the dynamics of ion transport through individual conical nanopipettes. Moreoever, ion transport against a concentration gradient is regulated by applied and surface electrical fields. The concept of ion pumping or separation is demonstrated via the selective ion transport against concentration gradients through individual nanopipettes. Third, this dynamic ion transport process under a predefined salinity gradient is discussed in the context of nanoscale energy conversion in supercapacitor type charging–discharging, as well as chemical and electrical energy conversion. Our analysis of the emerging current–potential features establishes the urgently needed physical foundation for energy conversion employing ordered nanostructures. The elucidated mechanism and established methodology can be generalized into broadly-defined nanoporous materials and devices for improved energy, separation and sensing applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗