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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Manipulating the Energetics and Rates of Electron Transfer in Rhodobacter capsulatus Reaction Centers with Asymmetric Pigment Content

Seemingly redundant parallel pathways for electron transfer (ET) – comprised of identical sets of cofactors – are a cornerstone feature of photosynthetic reaction centers (RCs) involved in light-energy conversion. In native bacterial RCs, both the A and B branches house one bacteriochlorophyll (BChl) and one bacteriopheophytin (BPh), but the A branch is used exclusively. Described herein are results obtained for two Rhodobacter capsulatus RCs with an unnaturally high degree of cofactor asymmetry – two BPh on the RC’s B side and two BChl on the A side. These pigment changes derive, respectively, from the His(M180)Leu mutation [a BPh (Φ B ) replaces the B-side BChl (B B )], and the Leu(M212)His mutation [a BChl (β A ) replaces the A-side BPh (H A )]. Additionally, Tyr(M208)Phe was employed to disfavor ET to the A branch and in one mutant Val(M131)Glu creates a hydrogen bond to H B to enhance ET to H B . In both Φ B mutants, the decay kinetics of the excited primary ET donor (P*) resolve three populations with lifetimes of ~9 ps (50-60%), ~40 ps (10-20%) and ~200 ps (20-30%), with P + Φ B - formed predominately from the 9-ps fraction. The 50-60% yield of P + Φ B - is the highest yet observed for a Φ B -containing RC. Here, the results provide insight into factors needed for efficient multi-step ET.

14 SOLAR ENERGY↗
DOE OSTI2014

Molecular Characterization of Organic Content of Soot along the Centerline of a Coflow Diffusion Flame

High-resolution mass spectrometry coupled with nanospray desorption electrospray ionization was used to probe chemical constituents of young soot particles sampled along the centerline of a coflow diffusion flame of a three-component Jet-A1 surrogate. In lower positions where particles are transparent to light extinction (n= 632.8 nm), peri-condensed polycyclic aromatic hydrocarbons (PAHs) are found to be the major components of the particle material. These particles become enriched with aliphatic components as they grow in mass and size. Before carbonization occurs, the constituent species in young soot particles are aliphatic and aromatic compounds 200-600 amu in mass, some of which are oxygenated. Particles dominated by PAHs or mixtures of PAHs and aliphatics can both exhibit liquid-like appearance observed by electron microscopy and be transparent to visible light. The variations in chemical composition observed here indicate that the molecular processes of soot formation in coflow diffusion flames may be more complex than previously thought. For example, the mass growth and enrichment of aliphatic components in an initially, mostly aromatic structure region of the flame that is absent of H atoms or other free radicals indicates that there must exist at least another mechanism of soot mass growth in addition to the hydrogen-abstraction-carbon addition mechanism currently considered in fundamental models of soot formation.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2014

Induced anisotropy in FeCo-based nanocomposites: Early transition metal content dependence

Soft magnetic nanocomposites variants of FeCo-based (HTX002) alloys (Fe65Co35)(81+x)B12Nb4-xSi2Cu1, exhibiting high inductions (up to 1.9 T), low losses, and high temperature stability are studied for high frequency inductors and current sensors. For alloys with x 0, 1, 1.5, 2, and 3, we report field induced anisotropy, K-U, after annealing at temperatures of 340-450 degrees C for 1 h in a 2 T transverse magnetic field. The anisotropy field, H-K, measured by AC permeametry on toroidal cores, and by first order reversal curves on square sections of ribbon, decreases with annealing temperature and saturates at high annealing temperatures suggesting a nanostructure related anisotropy mechanism in which the amorphous phase exhibits a higher H-K than the crystalline phase. A high saturation induction nanocrystalline phase and high H-K amorphous phase were achieved by low temperature annealing resulting in a value of K-U exceeding 14 X 10(3) erg/cm(3), more than twice that reported previously for Fe-rich amorphous and nanocomposite alloys. (C) 2014 AIP Publishing LLC.

Shen, S↗
DOE OSTI2015

Spectroscopic investigations of band offsets of MgO|Al x Ga 1-x N epitaxial heterostructures with varying AlN content.

Epitaxial (111) Mg0 films were prepared on (0001) Al x Ga 1-x N via molecular-beam epitaxy for x=0 to x=0.67. Valence band offsets of Mg0 to Al x Ga 1-x N were measured using X-ray photoelectron spectroscopy as 1.65 ± 0.07 eV, 1.36 ± 0.05 eV, and1.05 ± 0.09 eV for x=0, 0.28, and 0.67, respectively. This yielded conduction band offsets of 2.75 eV, 2.39 eV, and 1.63 eV for x=0, 0.28, and 0.67, respectively. All band offsets measured between Mg0 and Al x Ga 1-x N provide a > 1 eV barrier height to the semiconductor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of Ni content on the morphological evolution of Ni-YSZ solid oxide fuel cell electrodes

The coarsening of Ni in Ni–yttria-stabilized zirconia (YSZ) anodes is a potential cause of long term solid oxide fuel cells (SOFC) performance degradation. The specifics of the Ni-YSZ structure—including Ni/YSZ ratio, porosity, and particle size distributions—are normally selected to minimize anode polarization resistance, but they also impact long-term stability. A better understanding of how these factors influence long-term stability is important for designing more durable anodes. The effect of structural details, e.g., Ni-YSZ ratio, on Ni coarsening has not been quantified. Furthermore, prior measurements have been done by comparing evolved structures with control samples, such that sample-to-sample variations introduce errors. Here in this paper, we report a four dimensional (three spatial dimensions and time) study of Ni coarsening in Ni-YSZ anode functional layers with different Ni/YSZ ratios, using synchrotron x-ray nano-tomography. The continuous structural evolution was observed and analyzed at sub-100 nm resolution. It is shown quantitatively that increasing the Ni/YSZ ratio increases the Ni coarsening rate. This is due to both increased pore volume and a decrease in the YSZ volume fraction, such that there is more free volume and a less obtrusive YSZ network, both of which allow greater Ni coarsening. The results are shown to be in good agreement with a power-law coarsening model. In conclusion, the finding is critical for informing the design of SOFC electrode microstructures that limit coarsening and performance degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Influence of iron doping on tetravalent nickel content in catalytic oxygen evolving films

Iron doping of nickel oxide films results in enhanced activity for promoting the oxygen evolution reaction (OER). Whereas this enhanced activity has been ascribed to a unique iron site within the nickel oxide matrix, we show here that Fe doping influences the Ni valency. The percent of Fe3+ doping promotes the formation of formal Ni4+, which in turn directly correlates with an enhanced activity of the catalyst in promoting OER. The role of Fe3+ is consistent with its behavior as a superior Lewis acid.

electrocatalysis↗
DOE OSTI2012

ON THE BARYONIC CONTENTS OF LOW-MASS GALAXIES

The baryonic Tully-Fisher relation is an important observational constraint on cosmological and galactic models. However, it is critical to keep in mind that in observations only stars and molecular and atomic gas are counted, while the contribution of the ionized gas is almost universally missed. The ionized gas is, however, expected to be present in the gaseous disks of dwarf galaxies simply because they are exposed to the cosmic ionizing background and to the stellar radiation that manages to escape from the central regions of the galactic disks into their outer layers. Such an expectation is, indeed, born out both by cosmological numerical simulations and by simple analytical models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Baryon content of massive galaxy clusters at 0.57 < z < 1.33

We study the stellar, brightest cluster galaxy (BCG) and intracluster medium (ICM) masses of 14 South Pole Telescope (SPT) selected galaxy clusters with median redshift z = 0.9 and mass M-500 = 6 x 10(14) M-circle dot. We estimate stellar masses for each cluster and BCG using six photometric bands, the ICM mass using X-ray observations and the virial masses using the SPT Sunyaev-Zel'dovich effect signature. At z = 0.9, the BCG mass M-*(BCG) constitutes 0.12 +/- 0.01 per cent of the halo mass for a 6 x 10(14) M-circle dot cluster, and this fraction falls as M-500(-0.58 +/- 0.07). The cluster stellar mass function has a characteristic mass M-0 = 10(11.0 +/- 0.1) M-circle dot, and the number of galaxies per unit mass in clusters is larger than in the field by a factor of 1.65 +/- 0.20. We combine our SPT sample with previously published samples at low redshift and correct to a common initial mass function and for systematic virial mass differences. We then explore mass and redshift trends in the stellar fraction f(*), the ICM fraction f(ICM), the collapsed baryon fraction f(c) and the baryon fraction f(b). At a pivot mass of 6 x 10(14) M-circle dot and redshift z = 0.9, the characteristic values are f(*) = 1.1 +/- 0.1 per cent, f(ICM) = 9.6 +/- 0.5 per cent, f(c) = 10.7 +/- 1.1 per cent and f(b) = 10.7 +/- 0.6 per cent. These fractions all vary with cluster mass at high significance, with higher mass clusters having lower f(*) and f(c) and higher f(ICM) and f(b). When accounting for a 15 per cent systematic virial mass uncertainty, there is no statistically significant redshift trend at fixed mass. Our results support the scenario where clusters grow through accretion from subclusters (higher f(*), lower f(ICM)) and the field (lower f(*), higher f(ICM)), balancing to keep f(*) and f(ICM) approximately constant since z similar to 0.9.

Chiu, I.↗
DOE OSTI2020

Effect of Mg Content in Melt-Spun Mn–Bi–Mg–Sb–In Alloys on the Structure and Properties of Field-Annealed Magnets

Mn-Bi alloys modified with Mg and other elements were recently developed into promising rare-earth-free permanent magnets through successive melt-spinning, warm compaction, and short magnetic-field annealing. This letter reports herein on the crystal structures, texture, and magnetic properties observed in Mn 50 Bi 49-x Mg x Sb 0.5 In 0.5 alloys (x = 0, 1.5, 3.0, 4.5) throughout these processing steps. The Mg substitution favors MnBi-based intermetallic phases over the Bi- and Mn-based solid solutions and the stable α intermetallic phase over the metastable β' intermetallic phase. Magnesium increases the c/a ratio of the α phase lattice parameters for all studied x values and it increases the degree of the field-annealing-induced texture for x ≤ 3. The effect of Mg on coercivity is explained as combination of a positive one via the α phase magnetocrystalline anisotropy and a negative one via the development of texture. The effect of the substitution on the maximum energy product additionally involves the decreasing density of the alloys; the optimum x is found to be ≈3. Additionally reported are the thermal properties of selected alloys. The mechanism of field-annealing effect on the coercivity is briefly discussed.

36 MATERIALS SCIENCE↗