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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 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Synthesis, modular composition, and electrochemical properties of lamellar iron sulfides

Transition metal chalcogenides with layered structures are promising materials for energy storage, catalysis, and electronics, among other areas. We have identified a new layered phase of iron sulfide containing interlayer solvated cations. We present an optimized synthesis for the Li + -containing material from an Fe(III) xanthate complex. Structure and composition data indicate the material consists of poorly-ordered iron sulfide layers separated by solvated cations. The lamellar spacing in these materials can be tuned by changing the identity of the cation. Furthermore, the lamellar spacing can also be reversibly tuned by the degree of solvation of the material. The material is electrically conductive and can serve as a pseudocapacitor with comparable performance to commercial materials such as MnO 2 . Finally, these materials also show promise as lithium or sodium ion battery cathodes with good capacity and reversibility.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Enhanced current collection in 1.7 eV GaInAsP solar cells grown on GaAs by metalorganic vapor phase epitaxy

Quaternary GaInAsP solar cells with a bandgap of ~1.7 eV offer an attractive Al-free alternative to AlGaAs solar cells for integration in next generation of III-V multijunction solar cells with five or more junctions. Development of a high quality 1.7 eV solar cell is also highly sought for III-V/Si tandem solar cells. In this work, we systematically investigate the impact of varying base thicknesses and doping concentrations on the carrier collection and performance of 1.7 eV GaInAsP solar cells. The photoresponse of these cells is found to be very sensitive to p-type zinc doping concentration in the base layer. Prototype 1.7 eV GaInAsP n-i-p solar cell designs are demonstrated that leverage enhanced depletion width as an effective method to achieve peak quantum efficiency exceeding 90%. We also show the importance of optimal i-layer thickness as a critical parameter to reduce the drop in fill-factor (FF) due to field-aided collection. Furthermore, we demonstrate substantial improvement in the cell performance when the GaInAsP base layer is grown at 650 degrees C instead of 600 degrees C. The best GaInAsP solar cell (Eg ~ 1.65 eV) in this study achieved JSC of 21.1 mA/cm 2 , VOC of 1.18 V, FF of 83.8%, and an efficiency of 20.8 +/- 1% under AM1.5D spectrum (21.5 +/- 1% under AM1.5G spectrum). Finally, these results highlight the potential of Al-free GaInAsP solar cells for integration in the next generation of III-V multijunction solar cells.

14 SOLAR ENERGY↗
DOE OSTI2021

Energy demand reduction in the built environment using shallow geothermal integrated energy systems: Part II – Hybrid ground source heat pump for building heating

The research collection aims at finding the various possible opportunities for the effective integration of shallow geothermal energy (SGE) to decrease the energy demand in the built environment and to reduce emission associated with it. The direct utilization of SGE using a ground source heat pump (GSHP) has been reviewed in comprehensive review part I and part II. From the extensive review, we have found that the hybrid GSHP is needed to avoid ground thermal imbalance and peak demand. Hybrid GSHP can adopt various supplemental heat sources and sinks according to the local climatic conditions and the balance of energy demands. The primary focus on the integration of subsystems such as biomass, solar energy (PV, PVT, and collector), phase change material, micro gas turbine, and absorption heat pump with GSHP is presented for heating application. This comprehensive review part III highlights the recent research findings and a potential gap in hybrid GSHP for further research and developments

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS1977

Interpretation of Beta Lyrae. III - A study of the disk around the secondary component

Light curves of Beta Lyrae available in the far-ultraviolet, visual, and infrared regions of the spectrum at numerous phases in eclipse are analyzed in order to investigate the physical and radiative nature of the disk surrounding the secondary component. The results of this analysis together with those of other investigators lead to the proposal that the outer regions of the disk are dominated by free electrons. This electron-scattering envelope is most likely the source of infrared radiation as well as the cause of the observed polarization. However, the radiation in the region from the optical to the far-ultraviolet comes mainly from submerged layers where local thermodynamic equilibrium prevails. These layers represent the photosphere of either the disk or the secondary component itself.

Brown, D. A.↗
NASA NTRS1988

Macrosegregation in undercooled Pb-Sn eutectic alloys

A novel technique resulting in large undercoolings in bulk samples (23g) of lead-tin eutectic alloy is described. Samples of eutectic composition were processed with undercoolings ranging from 4 to 20 K and with cooling rates varying between 0.04 to 4 K/sec. The final macrostructure of undercooled samples depends on both the initial undercooling of the melt and the cooling rate. Gravity-driven segregation is found to increase with increasing undercooling. A eutectic Pb-Sn alloy undercooled at 20 K and cooled at 4 K/sec had a composition of about Pb-72 wt pct Sn at the top and 55 pct Sn at the bottom. Macrosegregation in these undercooled lead-tin eutectic alloys is shown to be primarily due to a sink/float mechanism caused by the difference in density of the solid and liquid phases and the undercooling and nucleation behavior of the alloy.

De Groh, H. C., III↗
NASA NTRS2005

Temperature Scale of Central Stars Planetary Nebulae

The goal of this project was to gain new insight into both the true temperatures of the central stars of planetary nebulae and their evolutionary histories. The temperature scale of the hottest central stars of planetary nebulae is poorly known. The temperature diagnostics available at visible wavelengths are not useful for these very hot stars, or suffer from as-yet unresolved systematic uncertainties. However, the combination of FUSE FUV spectra and HST NUV spectra allows precise temperature determinations by utilizing ionization balances of C III, C IV and O V, O VI lines. The sample comprises hot hydrogen-rich central stars covering the hottest phase of post-AGB evolution (T_eff greater than 70,000K). The spectra were analyzed with fully metal line blanketed NLTE model atmospheres in order to determine T_eff, surface gravity, and chemical composition. In addition to the temperature scale, the spectra help address the question of metal abundances at the surface of these stars. Depending on the particular star, the metal abundances are either dominated by ongoing diffusion processes or they originate from dredge-up phases during previous AGB evolution. The sample was selected so as to include objects that were expected to exhibit both processes, in order to assess their relative importance and to gain insight into the evolutionary history of the stars. The objects that show qualitatively a metal abundance pattern which points at dredge-up phases, can be used to quantitatively check against abundance predictions of stellar evolution theory. The other objects, where gravitational diffusion and radiative acceleration determine the photospheric metal abundances, will be used to check our NLTE models which for the first time include diffusion processes self-consistently.

Kruk, Jeffry↗
NASA NTRS2009

FPGA-Based Networked Phasemeter for a Heterodyne Interferometer

A document discusses a component of a laser metrology system designed to measure displacements along the line of sight with precision on the order of a tenth the diameter of an atom. This component, the phasemeter, measures the relative phase of two electrical signals and transfers that information to a computer. Because the metrology system measures the differences between two optical paths, the phasemeter has two inputs, called measure and reference. The reference signal is nominally a perfect square wave with a 50- percent duty cycle (though only rising edges are used). As the metrology system detects motion, the difference between the reference and measure signal phases is proportional to the displacement of the motion. The phasemeter, therefore, counts the elapsed time between rising edges in the two signals, and converts the time into an estimate of phase delay. The hardware consists of a circuit board that plugs into a COTS (commercial, off-the- shelf) Spartan-III FPGA (field-programmable gate array) evaluation board. It has two BNC inputs, (reference and measure), a CMOS logic chip to buffer the inputs, and an Ethernet jack for transmitting reduced-data to a PC. Two extra BNC connectors can be attached for future expandability, such as external synchronization. Each phasemeter handles one metrology channel. A bank of six phasemeters (and two zero-crossing detector cards) with an Ethernet switch can monitor the rigid body motion of an object. This device is smaller and cheaper than existing zero-crossing phasemeters. Also, because it uses Ethernet for communication with a computer, instead of a VME bridge, it is much easier to use. The phasemeter is a key part of the Precision Deployable Apertures and Structures strategic R&D effort to design large, deployable, segmented space telescopes.

Rao, Shanti↗
NASA NTRS2019

Chandra X-Ray Spectroscopy of the Focused Wind in the Cygnus X-1 System III. Dipping in the Low/Hard State

We present an analysis of three Chandra High Energy Transmission Gratings observations of the black hole binary CygX-1/HDE 226868 at different orbital phases. The stellar wind that is powering the accretion in this system is characterized by temperature and density in homogeneities including structures, or “clumps”, of colder, more dense material embedded in the photoionized gas. As these clumps pass our line of sight, absorption dips appear in the light curve. We characterize the properties of the clumps through spectral changes during various dip stages. Comparing the silicon and sulfur absorption line regions (1.6–2.7 keV Ξ 7.7–4.6 Å) in four levels of varying column depth reveals the presence of lower ionization stages, i.e., colder or denser material, in the deeper dip phases. The Doppler velocities of the lines are roughly consistent within each observation, varying with the respective orbital phase. This is consistent with the picture of a structure that consists of differently ionized material, in which shells of material facing the black hole shield the inner and back shells from the ionizing radiation. The variation of the Doppler velocities compared to a toy model of the stellar wind, however, does not allow us to pin down an exact location of the clump region in the system. This result, as well as the asymmetric shape of the observed lines, point at a picture of a complex wind structure.

Cyg X-1↗
DOE OSTI2023

Sub-quarter micrometer periodically poled Al 0.68 Sc 0.32 N for ultra-wideband photonics and acoustic devices

In this study, we demonstrate the ability of polarity inversion of sputtered aluminum scandium nitride thin films through post-fabrication processes with domain widths as small as 220 nm at a periodicity of 440 nm. An approach using photo- and electron-beam lithography to generate sub-quarter micrometer feature size with adjustable duty cycle through a lift-off process is presented. Here, the film with a coercive field $E_c^+$ of 5.35 MV/cm was exercised first with a 1 kHz triangular double bipolar wave and ultimately poled with a 0.5 kHz double monopolar wave using a Radiant Precision Premier II tester. The metal polar (M-polar) and nitrogen polar (N-polar) domains were identified and characterized through potassium hydroxide wet etching as well as piezoresponse force microscopy (PFM). Well-distinguished boundaries between the oppositely polarized domain regions were confirmed through the phase diagram of the PFM results. The relationship between the electrode width, poling voltage, and domain growth was experimentally studied and statistically analyzed, where 7.96 nm/V domain width broadening vs escalating poling voltage was observed. This method produces extremely high domain spatial resolution in III-nitride materials via poling and is transferable to a CMOS-compatible photolithography process. The spatial resolution of the periodically poled Al 0.68 Sc 0.32 N is suitable for second-harmonic generation of deep ultraviolet through quasi-phase-matching and RF MEMS operating in the X-Band spectrum.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Interstellar absorption lines in high-resolution IUE spectra of cataclysmic variables

High-resolution ultraviolet spectra of five cataclysmic variables obtained with the IUE are used to investigate the character of the interstellar medium in the vicinity of the sun. These spectra reveal narrow absorption features of neutral and singly ionized interstellar species, and, in SS Cyg, narrow velocity-shifted absorption features of C IV, Si IV, and Si III. Using the column densities implied by the absorption features of the neutral and singly ionized species, values for the depletion of Si, Mg, Mn, and Fe from the gas phase of the interstellar medium in the vicinity of the sun are obtained. These hydrogen column densities are of particular importance in constraining the soft X-ray luminosity of cataclysmic variables because of the severe attenuation of the soft X-ray flux of cataclysmic variables by photoelectric absorption in the interstellar medium. In addition, using the column densities implied by the absorption features of C IV, Si IV, and Si III in the spectrum of SS Cyg, the existence of an expanding H II region of interstellar gas photoionized by he EUV and soft X-ray flux of this cataclysmic variable are inferred.

Mauche, Christopher W.↗
DOE OSTI2024

Properties of a fading AGN from SDSS-IV MaNGA

ABSTRACT We identify a fading AGN SDSS J220141.64+115124.3 from the internal Product Launch-11 (MPL-11) in Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. The central region with a projected radius of $\sim$2.4 kpc is characterized as LINER-like line ratios while the outskirts extended to $\sim$15 kpc show Seyfert-like line ratios. The ${\rm{[O {\small III}]}}$$\lambda$5007 luminosity of the Seyfert regions is a factor of 37 (2) higher than the LINER regions without (with) dust attenuation correction, suggesting that the AGN activity decreases at least $\sim$8 $\times$ 10$^3$ yr ($\sim$2.4 kpc/light-speed) ago. We model the emission line spectra in the central region with double Gaussian components (a narrow core and a broad wing) and analyse the properties of each component. The narrow core component mostly co-rotates with the stellar disc, whereas the broad wing component with a median of the velocity dispersion $\sim$300 km s$^{-1}$ is related to a wind outflow. The kinematic position angle (PA) of the ionized gas shows an $\sim 20^{\circ }$ twist from the galaxy centre to 1.5 effective radius. The median of the PA difference between the gas and stellar components is as large as $\sim 50^{\circ }$ within 0.4 effective radius. The tidal feature in DESI image and star–gas misalignment suggest this galaxy is a merger remnant. Combining all these observational results as well as public available X-ray and MIR luminosities, we confirm this is a fading AGN, the merger process kick-started the central engine to quasar phase which ionized gas composed of tidal debris, and now the activity of the central black hole decreases. The discontinuity in ${\rm{[O {\small III}]}}$$\lambda$5007 flux and EQW maps is due to multiple AGN outbursts triggered by merger remnant gas inflows.

Mo, Hao (ORCID:0000000234430768)↗
NASA NTRS1986

Ultraviolet and visual variability of Theta CrB during a normal B-phase following a shell phase (1980-1985)

Based on far-UV and visual observations made between 1980 and 1985, the phenomena characterizing the end of a shell phase of Theta-CrB, and the normal B-phase following it, are described as part of a long-term study of Be stars. The strength, shape, and velocity of the C IV, Si IV, and Al III resonance lines, and the Fe III lines of low excitation, show associated variability patterns over the whole range of ionization observable in the IUE and visual spectra. The observed variability pattern consists of a one-year narrow-line stage where the lines show narrow absorption cores close to rest wavelength, a two-year series of abrupt changes between a weak and a strong line, and a damping out of these variations leaving the observed spectrum in a lower ionization state. The existence of a phase-lag between similar phenomena occurring in the superionized and subionized/normally ionized regions, is noted.

Doazan, V.↗
DOE OSTI2023

Natural fiber-derived gas diffusion layers for high performance, lower cost PEM fuel cells

The gas diffusion layer (GDL) is a critical component of proton exchange membrane fuel cells. GDL manufacture is dominated by the use of polyacrylonitrile (PAN) fibers, resulting in high production costs. Those costs contribute to the high cost of fuel cell stacks. Thus, reducing GDL manufacturing costs without sacrificing performance, should help reduce the overall cost of the fuel cell stack. Using inexpensive, natural fiber-based papers and fabric as substrates, here we examine the inherent performance these materials as GDLs, and the improvements enabled by the addition of a microporous layer, gas-phase hydrophobic treatment, and densification. The resulting GDLs achieve equivalent performance the commercial baseline GDL and demonstrate the potential of lower cost GDLs.

25 ENERGY STORAGE↗
DOE OSTI2016

Structural and thermodynamic properties of the Cm III ion solvated by water and methanol

The geometric and electronic structures of the 9-coordinate Cm 3+ ion solvated with both water and methanol are systematically investigated in the gas phase at each possible solvent-shell composition and configuration using density functional theory and second-order Møller–Plesset perturbation theory. Ab initio molecular dynamics simulations are employed to assess the effects of second and third solvent shells on the gas-phase structure. The ion–solvent dissociation energy for methanol is greater than that of water, potentially because of increased charge donation to the ion made possible by the electron-rich methyl group. Further, the ion–solvent dissociation energy and the ion–solvent distance are shown to be dependent on the solvent-shell composition. Furthermore, this has implications for solvent exchange, which is generally the rate-limiting step in complexation reactions utilized in the separation of curium from complex metal mixtures that derive from the advanced nuclear fuel cycle.

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

Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system: III. Dipping in the low/hard state

We present an analysis of three Chandra High Energy Transmission Gratings observations of the black hole binary Cyg X-1/HDE 226868 at different orbital phases. The stellar wind that is powering the accretion in this system is characterized by temperature and density inhomogeneities including structures, or “clumps”, of colder, more dense material embedded in the photoionized gas. As these clumps pass our line of sight, absorption dips appear in the light curve. We characterize the properties of the clumps through spectral changes during various dip stages. Comparing the silicon and sulfur absorption line regions (1.6–2.7 keV ≡ 7.7–4.6 Å) in four levels of varying column depth reveals the presence of lower ionization stages, i.e., colder or denser material, in the deeper dip phases. The Doppler velocities of the lines are roughly consistent within each observation, varying with the respective orbital phase. This is consistent with the picture of a structure that consists of differently ionized material, in which shells of material facing the black hole shield the inner and back shells from the ionizing radiation. The variation of the Doppler velocities compared to a toy model of the stellar wind, however, does not allow us to pin down an exact location of the clump region in the system. This result, as well as the asymmetric shape of the observed lines, point at a picture of a complex wind structure.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1979

A theory of stationary long waves. III - Quasi-normal modes in a singular waveguide

The present paper deals with the fundamental issue of whether one can treat waves as normal modes when critical surface, where the phase speed of the wave matches the zonal wind speed, are present. In particular the question of whether a Rossby critical level (such as the zero-wind line for stationary waves) is absorbing or reflecting is raised and subsequently addressed. It is found that the critical level is never totally absorbing; Rossby waves are partially reflected even if the critical layer is dominated by dissipative processes. The relevance of nonlinearity in planetary-scale Rossby wave critical layers is also discussed and it is found to be the dominant mechanism. With the relative magnitudes of nonlinearity versus viscosity relevant to the earth's atmosphere it is found that the steady-state critical level should be almost perfectly reflecting to incident Rossby waves. Consequently, normal-mode solutions can be found; the quantization condition for these waves is also derived.

Tung, K. K.↗
NASA NTRS1980

Asteroid rotation. III - 1978 observations

Photoelectric observations of 32 asteroids observed from Table Mountain Observatory during the second half of 1978 are reported. Rotation periods were obtained for most objects. Absolute magnitudes and phase functions were not determined for any of these asteroids. The geometric mean rotation period of the 32 asteroids observed is 14.2 + or - 1.6 hr, as compared to 9.38 + or - 0.35 hr for 182 asteroids analyzed in Harris and Burns (1979). This difference is attributed to an observational selection effect which favors detection of fast rotation. If this is true, then the present sample contains the reverse bias, since it is complete in that a period (in some cases very approximate) was obtained for each object observed, but fast rotators are underrepresented due to prior discovery of their rotation properties.

Harris, A. W.↗