Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Phase III”

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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Digital single-sideband mixer.

Description of a simple single-sideband (SSB) mixer design that yields either a sum-frequency output with the difference-frequency output suppressed or vice-versa, and uses only 'digital' logic devices and no reactive or frequency-selective 'analog' (linear) circuit elements. A pair of outputs is generated in phase quadrature. It is shown that SSB frequency conversion can be accomplished for many applications much more efficiently with simple digital circuitry than in the usual way with complicated linear frequency selective filter and phasing circuits.

Counselman, C. C., III↗
NASA NTRS1979

Eliminating ambiguity in digital signals

Multiamplitude minimum shift keying (mamsk) transmission system, method of differential encoding overcomes problem of ambiguity associated with advanced digital-transmission techniques with little or no penalty in transmission rate, error rate, or system complexity. Principle of method states, if signal points are properly encoded and decoded, bits are detected correctly, regardless of phase ambiguities.

Weber, W. J., III↗
NASA NTRS1981

Matrix spectroscopic studies of chlorine atom-ozone reaction products

A spectroscopic study is presented of the matrix-isolated products of the direct combination reaction of chlorine atoms with ozone and of the microwave discharge reaction of chlorine and oxygen. Infrared spectra in the wavenumber range 2000 to 200 per cm were recorded for reaction products trapped by the condensation of a matrix of solid argon. Evidence for the formation of the ClO radical as well as the ClOO and ClClO radicals during the direct chlorine-ozone reaction is obtained, however no evidence is found for the presence of asymmetric ClO3 under conditions thought favorable for its formation. The ClO molecule is also observed following the microwave discharge reaction of chlorine and oxygen in argon in the isotopic forms (Cl-35)(O-16), (Cl-37)(O-16), (Cl-35)(O-18), and (Cl-37)(O-18). It is noted that the vibrational frequency for the (Cl-35)(O-16) radical at 849.2 per cm is blue-shifted 5 per cm above its gas-phase fundamental.

Carter, R. O., III↗
DOE OSTI2018

Elastic anomalies across phase transitions of praseodymium to 12 GPa

The elastic properties of praseodymium (Pr) were investigated at pressures up to 12 GPa at room temperature using ultrasonic interferometry technique. Softening and discontinuities in compressional (P) and shear (S) wave velocities were observed at around 2.5, 6.5 and 10.5 GPa, which are interpreted as indications of the phase transitions from Pr-I (dhcp) to Pr-II (fcc), Pr-II (fcc) to Pr-III (d-fcc) and Pr-III (d-fcc) to Pr-VII (monoclinic or orthorhombic), respectively. Very small discontinuities in compressibility have been observed across the phase transitions of I-II and II-III of Pr, which are unlikely visible in the X-ray diffraction studies. Finally, a comparison with the elastic behaviors of other lanthanide elements (e.g., Ce and La) suggests that the elastic anomalies associated with these phase transitions are likely to be caused by the 6s-5d electron transfer and the softening of acoustic phonon mode facilitated by decreased atomic distances under pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2022

(110)-Oriented GaAs Devices and Spalling as a Platform for Low-Cost III-V Photovoltaics

Here, we demonstrate the growth of GaAs solar cells by hydride vapor phase epitaxy (HVPE) on epi-ready and previously spalled (110) GaAs wafers as an advance towards a potentially low-cost (110)-based device platform. Controlled spalling offers a fracture-based path to substrate cost amortization, enabling device exfoliation and substrate reuse, but the faceted surface generated during the spalling of (100)-oriented GaAs presents hurdles to direct regrowth of subsequent devices. Spalling of (110) substrates instead eliminates faceting by aligning the substrate surface with the predominant crystal cleavage plane. III-V epitaxy of solar cells is significantly less developed on (110)-oriented substrates, however. Here, we develop (110)-based GaAs solar cells grown by HVPE on epi-ready substrates, demonstrating equal performance to devices grown on the more standard (100) orientation. We also characterize the surface of spalled, (110)-oriented substrates, revealing flat terraces separated by steps with sub-micron-scale height on average. Finally, we present an initial device grown on a previously spalled surface without additional surface re-preparation with nearly 16% efficiency under a simulated AM1.5G spectrum. Together, these results provide preliminary evidence of a potentially low-cost path to enable terrestrial III-V photovoltaics via the (110) substrate orientation.

14 SOLAR ENERGY↗
DOE OSTI2018

Iron and Arsenic Speciation During As(III) Oxidation by Manganese Oxides in the Presence of Fe(II): Molecular-Level Characterization Using XAFS, Mössbauer, and TEM Analysis

The redox state and speciation of the metalloid arsenic (As) determine its toxicity and mobility. Knowledge of biogeochemical processes influencing the As redox state is therefore important to understand and predict its environmental behavior. Many previous studies examined As(III) oxidation by various Mn-oxides, but little is known concerning environmental influences (e.g., coexisting ions) on the process. As such, in this study we investigated the mechanisms of As(III) oxidation by a poorly crystalline hexagonal birnessite (δ-MnO 2 ) in the presence of dissolved Fe(II) using X-ray absorption spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The As K-edge X-ray absorption near edge spectroscopy (XANES) analysis revealed that, at low Fe(II) concentration (100 μM), As(V) was the predominant As species on the solid phase, whereas at higher Fe(II) concentrations (200–1000 μM), both As(III) and As(V) were sorbed on the solid phase. As K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) analysis showed an increasing As–Mn/Fe distance over time, indicating As prefers to bind with the newly formed Fe(III)-(hydr)oxides. Both As(III) and (V) adsorbed on Fe(III)-(hydr)oxides as a bidentate binuclear corner-sharing complex. Both Mössbauer and TEM-EDS investigations demonstrated that oxidized Fe(III) products formed during Fe(II) oxidation by δ-MnO 2 were predominantly ferrihydrite-, goethite-, and ferric arsenate-like compounds. However, Fe EXAFS analysis also suggested the formation of a small amount of lepidocrocite. The Mn K-edge XANES data indicated that As(III) oxidation occurs as a two electron transfer with δ-MnO 2 and that the observed Mn(III) is due to conproportionation of surface-sorbed Mn(II) with Mn(IV) in the δ-MnO 2 structure. This study reveals that the mechanisms of As(III) oxidation by δ-MnO 2 in the presence of Fe(II) are very complex, involving many simultaneous reactions, and the formation of Fe(III)-(hydr)oxides plays a very important role in reducing As mobility.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Solution Phase Synthesis of Indium Gallium Phosphide Alloy Nanowires

The tunable physical and electronic structure of III–V semiconductor alloys renders them uniquely useful for a variety of applications, including biological imaging, transistors, and solar energy conversion. However, their fabrication typically requires complex gas phase instrumentation or growth from high-temperature melts, which consequently limits their prospects for widespread implementation. Furthermore, the need for lattice matched growth substrates in many cases confines the composition of the materials to a narrow range that can be epitaxially grown. In this work, we present a solution phase synthesis for indium gallium phosphide (In x Ga 1–x P) alloy nanowires, whose indium/gallium ratio, and consequently, physical and electronic structure, can be tuned across the entire x = 0 to x = 1 composition range. We demonstrate the evolution of structural and optical properties of the nanowires, notably the direct to indirect band gap transition, as the composition is varied from InP to GaP. Our scalable, low-temperature synthesis affords compositional, structural, and electronic tunability and can provide a route for realization of broader In x Ga 1–x P applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Skyrmion transport and annihilation in funnel geometries

Using atomistic simulations, we have investigated the transport and annihilation of skyrmions interacting with a funnel array under a current applied perpendicular to the funnel axis. We find that transport without annihilation is possible at low currents, when the motion is dominated by skyrmion–skyrmion interactions and skyrmions push each other through the funnel opening. Skyrmion annihilation occurs for higher currents when skyrmions in the upper half of the sample exert pressure on skyrmions in the bottom half of the sample due to the external current. Upon interacting with the funnel wall, the skyrmions undergo a size reduction that makes it easier for them to pass through the funnel opening. We find five phases as a function of the applied current and the size of the funnel opening: (i) pinned, (ii) transport without annihilation, (iii) transport with annihilation, (iv) complete annihilation, and (v) a reentrant pinning phase that only occurs for very narrow openings. Finally, our findings provide insight into how to control skyrmion transport using funnel arrays by delineating regimes in which transport of skyrmions is possible as well as the conditions under which annihilation occurs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

QUASI-PERIODIC ACCELERATION OF ELECTRONS IN THE FLARE ON 2012 JULY 19

Quasi-periodic pulsations (QPPs) of nonthermal emission in an M7.7 class flare on 2012 July 19 are investigated with spatially resolved observations at microwave and HXR bands and with spectral observations at decimetric, metric waves. Microwave emission at 17 GHz of two footpoints, HXR emission at 20–50 keV of the north footpoint and loop top, and type III bursts at 0.7–3 GHz show prominent in-phase oscillations at 270 s. The microwave emission of the loop leg has less pulsation but stronger emission. Through the estimation of plasma density around the loop top from EUV observations, we find that the local plasma frequency would be 1.5 GHz or even higher. Thus, type III bursts at 700 MHz originate above the loop top. Quasi-periodic acceleration or injection of energetic electrons is proposed to dominate these in-phase QPPs of nonthermal emission from footpoints, loop top, and above. In the overlying region, drifting pulsations (DPS) at 200–600 MHz oscillate at a distinct period (200 s). Its global structure drifts toward lower frequency, which is closely related to upward plasmoids observed simultaneously from EUV emission. Hence, nonthermal emission from overlying plasmoids and underlying flaring loops show different oscillating periods. Two individual systems of quasi-periodic acceleration of electrons are proposed to coincide in the bi-direction outflows from the reconnection region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Planck intermediate results: XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck $\star$

The nearby Chamaeleon clouds have been observed in γ rays by the Fermi Large Area Telescope (LAT) and in thermal dust emission by Planck and IRAS. Cosmic rays and large dust grains, if smoothly mixed with gas, can jointly serve with the H i and 12 CO radio data to (i) map the hydrogen column densities, N H , in the different gas phases, in particular at the dark neutral medium (DNM) transition between the H i -bright and CO-bright media; (ii) constrain the CO-to-H 2 conversion factor, X CO ; and (iii) probe the dust properties per gas nucleon in each phase and map their spatial variations across the clouds. We have separated clouds at local, intermediate, and Galactic velocities in H i and 12 CO line emission to model in parallel the γ-ray intensity recorded between 0.4 and 100 GeV; the dust optical depth at 353 GHz, τ 353 ; the thermal radiance of the large grains; and an estimate of the dust extinction, A VQ , empirically corrected for the starlight intensity. Furthermore, the dust and γ-ray models have been coupled to account for the DNM gas. The consistent γ-ray emissivity spectra recorded in the different phases confirm that the GeV–TeV cosmic rays probed by the LAT uniformly permeate all gas phases up to the 12 CO cores. The dust and cosmic rays both reveal large amounts of DNM gas, with comparable spatial distributions and twice as much mass as in the CO-bright clouds. We give constraints on the H i -DNM-CO transitions for five separate clouds. CO-dark H 2 dominates the molecular columns up to AV ≃ 0.9 and its mass often exceeds the one-third of the molecular mass expected by theory. The corrected A VQ extinction largely provides the best fit to the total gas traced by the γ rays. Nevertheless, we find evidence for a marked rise in A VQ /N H with increasing N H and molecular fraction, and with decreasing dust temperature. The rise in τ 353 /NH is even steeper. Here, we observe variations of lesser amplitude and orderliness for the specific power of the grains, except for a coherent decline by half in the CO cores. This combined information suggests grain evolution. We also provide average values for the dust properties per gas nucleon in the different phases. The γ rays and dust radiance yield consistent X CO estimates near 0.7 × 10 20 cm -2 K -1 km -1 s. The A VQ and τ 353 tracers yield biased values because of the large rise in grain opacity in the CO clouds. These results clarify a recurrent disparity in the γ-ray versus dust calibration of X CO , but they confirm the factor of 2 difference found between the X CO estimates in nearby clouds and in the neighbouring spiral arms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

BC8 Silicon (Si-III) is a Narrow-Gap Semiconductor

Large-volume, phase-pure synthesis of BC8 silicon ($Ia\bar{3}$, cI16) has allowed bulk measurements of optical, electronic, and thermal properties. Unlike previous reports that conclude BC8-Si is semimetallic, we demonstrate that this phase is a direct band gap semiconductor with a very small energy gap and moderate carrier concentration and mobility at room temperature, based on far- and midinfrared optical spectroscopy, temperature-dependent electrical conductivity, Seebeck and heat capacity measurements. Samples exhibit a plasma wavelength near 11 μm, indicating potential for infrared plasmonic applications. Thermal conductivity is reduced by 1–2 orders of magnitude depending on temperature as compared with the diamond cubic (DC-Si) phase. The electronic structure and dielectric properties can be reproduced by first-principles calculations with hybrid functionals after adjusting the level of exact Hartree–Fock (HF) exchange mixing. These results clarify existing limited and controversial experimental data sets and ab initio calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1991

Electron beams and associated rapid fluctuations in solar flares

Recent observations show that the rapid fluctuations in radio, hard X-ray, and H-alpha emissions are closely associated with type III and microwave (or decimetric) bursts during the impulsive and/or preimpulsive phases of solar flares. In order to clarify the physical processes of these observed phenomena, this paper proposes a tentative model of two acceleration regions A (source of type III bursts) and B (source of microwave or decimetric bursts) formed in the neutral sheet and at the top of a flaring loop, respectively; and also suggests that the electron beams streaming from region A and/or region B downward to the chromosphere are responsible for the rapid fluctuations in the different emissions mentioned above during the impulsive and/or preimpulsive phases of solar flares.

Li, C. S.↗
DOE OSTI2016

On the role of the ΩΓ limit in the formation of population III massive stars

We explore the role of the modified Eddington limit due to rapid rotation (the so-called ΩΓ limit) in the formation of Population III stars. We performed one-dimensional stellar evolution simulations of zero-metallicity protostars accreting mass at a very high rate ( M-dot ∼10{sup −3} M{sub ⊙} yr{sup −1}) and dealt with stellar rotation as a separate post-process. The protostar would reach the Keplerian rotation very soon after the onset of mass accretion, but mass accretion would continue as stellar angular momentum is transferred outward to the accretion disk by viscous stress. The envelope of the protostar expands rapidly when the stellar mass reaches ∼5–7 M{sub ⊙} and the Eddington factor increases sharply. This makes the protostar rotate critically at a rate that is significantly below the Keplerian value (i.e., the ΩΓ limit). The resultant positive gradient of the angular velocity in the boundary layer between the protostar and the Keplerian disk prohibits angular momentum transport from the star to the disk, and consequently further rapid mass accretion. This would prevent the protostar from growing significantly beyond 20–40 M{sub ⊙}. Another important consequence of the ΩΓ limit is that the protostar can remain fairly compact (R ≲ 50 R{sub ⊙}) and avoid a fluffy structure (R ≳ 500 R{sub ⊙}) that is usually found with a very high rate of mass accretion. This effect would make the protostar less prone to binary interactions during the protostar phase. Although our analysis is based on Population III protostar models, this role of the ΩΓ limit would be universal in the formation process of massive stars, regardless of metallicity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

GOTTCHA Database, Version 1

One major challenge in the field of shotgun metagenomics is the accurate identification of the organisms present within the community, based on classification of short sequence reads. Though microbial community profiling methods have emerged to attempt to rapidly classify the millions of reads output from contemporary sequencers, the combination of incomplete databases, similarity among otherwise divergent genomes, and the large volumes of sequencing data required for metagenome sequencing has led to unacceptably high false discovery rates (FDR). Here we present the application of a novel, gene-independent and signature-based metagenomic taxonomic profiling tool with significantly smaller FDR, which is also capable of classifying never-before seen genomes into the appropriate parent taxa.The algorithm is based upon three primary computational phases: (I) genomic decomposition into bit vectors, (II) bit vector intersections to identify shared regions, and (III) bit vector subtractions to remove shared regions and reveal unique, signature regions.In the Decomposition phase, genomic data is first masked to highlight only the valid (non-ambiguous) regions and then decomposed into overlapping 24-mers. The k-mers are sorted along with their start positions, de-replicated, and then prefixed, to minimize data duplication. The prefixes are indexed and an identical data structure is created for the start positions to mimic that of the k-mer data structure.During the Intersection phase -- which is the most computationally intensive phase -- as an all-vs-all comparison is made, the number of comparisons is first reduced by four methods: (a) Prefix restriction, (b) Overlap detection, (c) Overlap restriction, and (d) Result recording. In Prefix restriction, only k-mers of the same prefix are compared. Within that group, potential overlap of k-mer suffixes that would result in a non-empty set intersection are screened for. If such an overlap exists, the region which intersects is first reduced by performing a binary search of the boundary suffixes of the smaller set into the larger set, which defines the limits of the zipper-based intersection process. Rather than recording the actual k-mers of the intersection, another data structure of identical "shape" is created which consists of only bit vectors so that only a 1 or 0 will be stored in the location of the k-mer suffix that was found in the intersection. This reduces the amount of data generated and stored considerably.During the Subtraction phase, relevant intersection bitmasks are first unionized together to form a single bitmask which is then applied over the original genome to reveal only those regions of the genome that are unique. These regions are then exported to disk in FASTA format and used in the application of determining the constituents of an unknown metagenomic community.The DATABASE provided is the result of the algorithm described.

Freitas, Tracey↗
DOE OSTI2015

GOTTCHA Database, Version 1

One major challenge in the field of shotgun metagenomics is the accurate identification of the organisms present within the community, based on classification of short sequence reads. Though microbial community profiling methods have emerged to attempt to rapidly classify the millions of reads output from contemporary sequencers, the combination of incomplete databases, similarity among otherwise divergent genomes, and the large volumes of sequencing data required for metagenome sequencing has led to unacceptably high false discovery rates (FDR). Here we present the application of a novel, gene-independent and signature-based metagenomic taxonomic profiling tool with significantly smaller FDR, which is also capable of classifying never-before seen genomes into the appropriate parent taxa.The algorithm is based upon three primary computational phases: (I) genomic decomposition into bit vectors, (II) bit vector intersections to identify shared regions, and (III) bit vector subtractions to remove shared regions and reveal unique, signature regions.In the Decomposition phase, genomic data is first masked to highlight only the valid (non-ambiguous) regions and then decomposed into overlapping 24-mers. The k-mers are sorted along with their start positions, de-replicated, and then prefixed, to minimize data duplication. The prefixes are indexed and an identical data structure is created for the start positions to mimic that of the k-mer data structure.During the Intersection phase -- which is the most computationally intensive phase -- as an all-vs-all comparison is made, the number of comparisons is first reduced by four methods: (a) Prefix restriction, (b) Overlap detection, (c) Overlap restriction, and (d) Result recording. In Prefix restriction, only k-mers of the same prefix are compared. Within that group, potential overlap of k-mer suffixes that would result in a non-empty set intersection are screened for. If such an overlap exists, the region which intersects is first reduced by performing a binary search of the boundary suffixes of the smaller set into the larger set, which defines the limits of the zipper-based intersection process. Rather than recording the actual k-mers of the intersection, another data structure of identical "shape" is created which consists of only bit vectors so that only a 1 or 0 will be stored in the location of the k-mer suffix that was found in the intersection. This reduces the amount of data generated and stored considerably.During the Subtraction phase, relevant intersection bitmasks are first unionized together to form a single bitmask which is then applied over the original genome to reveal only those regions of the genome that are unique. These regions are then exported to disk in FASTA format and used in the application of determining the constituents of an unknown metagenomic community.The DATABASE provided is the result of the algorithm described.

Freitas, Tracey↗
DOE OSTI2015

Spin-glass behaviors in carrier polarity controlled Fe{sub 3−x}Ti{sub x}O{sub 4} semiconductor thin films

Carrier-type control of spin-glass (cluster spin-glass) is studied in order to engineer basic magnetic semiconductor elements using the memory functions of spin-glass. A key of carrier-polarity control in magnetite is the valence engineering between Fe(II) and Fe(III) that is achieved by Ti(IV) substitution. Single phases of (001)-oriented Fe{sub 3−x}Ti{sub x}O{sub 4} thin films have been obtained on spinel MgAl{sub 2}O{sub 4} substrates by pulsed laser deposition. Thermoelectric power measurements reveal that Ti-rich films (x = 0.8) show p-type conduction, while Ti-poor films (x = 0.6–0.75) show n-type conduction. The systematic Fe(III) reduction to Fe(II) followed by Ti(IV) substitution in the octahedral sublattice is confirmed by the X-ray absorption spectra. All of the Fe{sub 3−x}Ti{sub x}O{sub 4} films (x = 0.6–0.8) exhibit ferrimagnetism above room temperature. Next, the spin-glass behaviors of Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film are studied, since this magnetically diluted system is expected to exhibit the spin-glass behaviors. The DC magnetization and AC susceptibility measurements for the Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film reveal the presence of the spin glass phase. Thermal- and magnetic-field-history memory effects are observed and are attributed to the long time-decay nature of remanent magnetization. The detailed analysis of the time-dependent thermoremanent magnetization reveals the presence of the cluster spin glass state.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

EuNi 5 InH 1.5-x (x = 0–1.5): hydrogen induced structural and magnetic transitions

The new quaternary hydride EuNi 5 InH 1.5 has been obtained by hydrogenation of the intermetallic parent EuNi5In under extremely mild conditions, hence, at room temperature and low hydrogen pressure. Hydrogenation at slightly elevated temperatures and pressures allows for the growth of large crystals, which is a rare observation for intermetallic hydrides. EuNi 5 InH 1.5 crystallizes in its own structure type ( hP 17, P6¯m2 , a = 4.9437(6), c = 10.643(1) Å) with a unique arrangement of the intermetallic host. The hydrogen atoms prefer Ni-surrounded positions, occupying {EuNi 3 } and {Eu 2 Ni 2 } tetrahedral voids in the structure. Upon hydrogenation of EuNi 5 In an anisotropic volume expansion accompanied with a decrease of symmetry is observed. Magnetic measurements reveal antiferromagnetic ordering in the hydride below 4 K and indicate an intermediate +II/+III oxidation state for Eu both in the intermetallic phase and the hydride. X-ray photoemission spectroscopy confirms the existence of the two different oxidation states of Eu. The hydrogenation does not affect the oxidation state of Eu and the type of magnetic ordering, but exerts a strong influence on the transition temperature, crystal structure, mechanical and electrical properties. Crystallographic analysis suggests that Eu(II) and Eu(III) do not order but rather mix homogeneously on crystallographic sites. Electronic structure calculations reveal the metallic character of the hydride with several different types of chemical bonding interactions being present in the compound ranging from the formally ionic Eu–H to covalent Ni–H and delocalized metal–metal. As a result, geometry optimization confirm the thermodynamic instability of the intermetallic host lattice for the hydride and supports a transformation into the parental structure as observed experimentally.

36 MATERIALS SCIENCE↗