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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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Suppressing η-phase development in steel-cemented tungsten carbide: A spark plasma sintering study

We describe the phase stability of a cemented tungsten carbide prepared using a high-vanadium tool steel as the cementing/binder phase and confirm suppression of (Fe, W) 6 C η-phase formation, attributed to the preferential formation of a V 0.78 W 0.22 C 1-x phase that exists as islands within the Fe-rich binder matrix. The samples were prepared using spark plasma sintering (SPS), starting from commercially available WC and A11-LVC tool steel powders. The starting powders were ball milled adding 10, 15, and 20 vol.% steel. An A11-LVC tool steel was chosen as a low-cost hard steel (49 HRC) that does not contain Ni or Co but has a high vanadium (~9 wt.%) and carbon (~1.75 wt.%) content. Our results show that sintering by SPS can produce high-density (>98%) WC-steel specimens in which the matrix wets the WC grain surfaces and formation of the brittle η-phase is avoided. The η phase is often regarded as embrittling and undesirable, and its presence can result in degradation of mechanical properties. Microhardness values for the WC-10 and WC-15 vol.% steel samples were 12.3 ± 1.2 and 13.0 ± 0.9 GPa, respectively, whereas the fracture toughness values were 8.83 ± 0.48 and 8.81 ± 0.61 MPa·m 1/2 , respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electrode Elastic Modulus as the Dominant Factor in the Capping Effect in Ferroelectric Hafnium Zirconium Oxide Thin Films

The discovery of ferroelectricity in hafnia based thin films has catalyzed significant research focused on understanding the ferroelectric property origins and means to increase stability of the ferroelectric phase. Prior studies have revealed that biaxial tensile stress via an electrode “capping effect” is a suspected ferroelectric phase stabilization mechanism. This effect is commonly reported to stem from a coefficient of thermal expansion (CTE) incongruency between the hafnia and top electrode. Despite reported correlations between ferroelectric phase fraction and electrode CTE, the thick silicon substrate dominates the mechanics and CTE-related stresses, negating any dominant contribution from an electrode CTE mismatch toward the capping effect. In this work, these discrepancies are reconciled, and the origin of these differences deriving from electrode elastic modulus, not CTE, is demonstrated. Pt/M/TaN/Hf 0.5 Zr 0.5 O 2 /TaN/Si devices, where M is platinum, TaN, iridium, tungsten, and ruthenium, were fabricated. Sin 2 (ψ)-based X-ray diffraction measurements of biaxial stress in the HZO layer reveal a strong correlation between biaxial stress, remanent polarization, and electrode elastic modulus. Conversely, a low correlation exists between the electrode CTE, HZO biaxial stress, and remanent polarization. A higher elastic modulus enhances the resistance to electrode elastic deformation, which intensifies the capping effect during crystallization, and culminates in the tandem restriction of out-of-plane hafnia volume expansion and preferential orientation of the polar c-axis normal to the plane. These behaviors concomitantly increase the ferroelectric phase stability and polarization magnitude. This work provides electrode material selection guidelines toward the development of high-performing ferroelectric hafnia into microelectronic devices, such as nonvolatile memories.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Space station electrical power system

The purpose of this paper is to describe the design of the Space Station Electrical Power System. This includes the Photovoltaic and Solar Dynamic Power Modules as well as the Power Management and Distribution System (PMAD). In addition, two programmatic options for developing the Electrical Power System will be presented. One approach is defined as the Enhanced Configuration and represents the results of the Phase B studies conducted by the NASA Lewis Research Center over the last two years. Another option, the Phased Program, represents a more measured approach to reaching about the same capability as the Enhanced Configuration.

Labus, Thomas L.↗
NASA NTRS1987

Space Station Electrical Power System

The purpose of this paper is to describe the design of the Space Station Electrical Power System. This includes the Photovoltaic and Solar Dynamic Power Modules as well as the Power Management and Distribution System (PMAD). In addition, two programmatic options for developing the Electrical Power System will be presented. One approach is defined as the Enhanced Configuration and represents the results of the Phase B studies conducted by the NASA Lewis Research Center over the last two years. Another option, the Phased Program, represents a more measured approach to reaching about the same capability as the Enhanced Configuration.

Labus, Thomas L.↗
NASA NTRS2003

Chandra Phase-Resolved X-Ray Spectroscopy of the Crab Pulsar

We present here the first phase-resolved study of the X-ray spectral properties of the Crab Pulsar that covers all pulse phases. The superb angular resolution of the Chandra X-ray Observatory enables distinguishing the pulsar from the surrounding nebulosity, even at pulse minimum. Analysis of the pulse-averaged spectrum measures interstellar photoelectric absorption and scattering by dust grains in the direction of the Crab Nebula. Analysis of the spectrum as a function of pulse phase measures the low-energy X-ray spectral index even at pulse minimum - albeit with large statistical uncertainty. The data are used to set a new upper limit to any thermal component.

Weisskopf, Martin C.↗
NASA NTRS1990

Platform Evolution Studies

Platform evolution studies have focused on developing two types of platforms: the Geostationary Platform, for use as an observatory in NASA's Mission-to-Planet-Earth (MPE) initiative, and a co-orbiting platform, for use as a branching mechanism for the Space Station Freedom manned base. In 1989, platform evolution efforts also documented existing polar platform scares for servicing and for co-orbiting platform configurations. Shown on this viewgraph are various configurations. An Astrophysics Co-Orbiting Platform was studied during Phase B of the Space Station Program. The Stationkeeping Platform was the subject of a Goddard study. Today we will briefly describe the NASA Polar Platform and discuss the evolutionary configurations for geostationary and co-orbiting platforms. General Electric Astro-Space Division was selected to perform these studies because of its role as designer of the Polar Platform.

Walton, Barbara↗
NASA NTRS1996

Application of Doppler Global Velocimetry to Supersonic Flows

The design and implementation of Doppler Global Velocimetry (DGV) for testing in the Langley Unitary Plan Wind Tunnel is presented. The discussion begins by outlining the characteristics of the tunnel and the test environment, with potential problem areas highlighted. Modifications to the optical system design to implement solutions for these problems are described. Since this tunnel entry was the first ever use of DGV in a supersonic wind tunnel, the test series was divided into three phases, each with its own goal. Phase I determined if condensation provided sufficient scattered light for DGV applications. Phase II studied particle lag by measuring the flow about an oblique shock above an inclined flat plate. Phase III investigated the supersonic vortical flow field above a 75-degree delta wing at 24-degrees angle of attack. Example results from these tests are presented.

Meyers, James F.↗
DOE OSTI2023

Magnetic contributions to corundum-eskolaite and corundum-hematite phase equilibria: A DFT cluster expansion study

Magnetic contributions have the potential to significantly influence predicted phase stability within alloy and mineral mixing phase diagrams, yet have been historically challenging to incorporate due to a significant increase to phase space sampling. Here, in this work, we employ a computational protocol that includes spin orientation as an additional configurational component within multi-component cluster expansions between magnetic and non-magnetic metal oxide alloys [calculated using density functional theory (DFT) and the generalized gradient approximation]. This approach was used to determine the effect of magnetic contributions to corundum-eskolaite and corundum-hematite phase equilibria from first principles. Two-component cluster expansions of the magnetic components of eskolaite and hematite were first performed showing the ability of this method to properly calculate their respective magnetic properties. Two-component cluster expansions were then performed for non-magnetic Al(III) and ferromagnetic Cr(III) and Fe(III), and phase diagrams were calculated for later comparison. Finally, a non-magnetic Al(III) and “up” and “down” magnetic configurations for anti-ferromagnetic Cr(III) and Fe(III) were performed. Magnetic contributions to the calculated phase diagram for the corundumeskolaite system were shown to be inconsequential but are vital for accurate determination of the corundum-hematite solvus.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1978

A study of digital holographic filters generation. Phase 2: Digital data communication system, volume 1

An empirical study of the performance of the Viterbi decoders in bursty channels was carried out and an improved algebraic decoder for nonsystematic codes was developed. The hybrid algorithm was simulated for the (2,1), k = 7 code on a computer using 20 channels having various error statistics, ranging from pure random error to pure bursty channels. The hybrid system outperformed both the algebraic and the Viterbi decoders in every case, except the 1% random error channel where the Viterbi decoder had one bit less decoding error.

Ingels, F. M.↗
NASA NTRS2004

Jet Noise Source Localization Using Linear Phased Array

A study was conducted to further clarify the interpretation and application of linear phased array microphone results, for localizing aeroacoustics sources in aircraft exhaust jet. Two model engine nozzles were tested at varying power cycles with the array setup parallel to the jet axis. The array position was varied as well to determine best location for the array. The results showed that it is possible to resolve jet noise sources with bypass and other components separation. The results also showed that a focused near field image provides more realistic noise source localization at low to mid frequencies.

Agboola, Ferni A.↗
NASA NTRS1974

HiMAT - A new approach to the design of highly maneuverable aircraft

Needed improvements in the maneuvering performance of combat aircraft appear to be possible through the simultaneous application of advances in various disciplines in such a way that they complement one another and magnify the benefits derived. The highly maneuverable aircraft technology (HiMAT) program is being conducted to investigate such multidisciplinary concepts. The program has three phases: preliminary studies, conceptual design studies, and the final design and construction of a test airplane. Work is now in the second phase. The test airplane will be a scaled model flown by a remotely piloted research vehicle technique. This paper outlines the HiMAT program and indicates the types of concepts being considered.

Bellman, D. R.↗
NASA NTRS1992

The role of the molecular-metallic transition of hydrogen in the evolution of Jupiter, Saturn, and brown dwarfs

An equation of state for hydrogen which predicts a molecular-metallic phase transition at finite temperatures has become available recently. The effect of this phase transition on the cooling histories of these two giant planets and of substellar brown dwarfs is studied. The phase transition alters the present age of Jupiter and of Saturn by a few percent. Interestingly, the cooling of brown dwarfs is most strongly affected at the time when the interior adiabat crosses the critical point of the phase transition.

Saumon, Didier↗
NASA NTRS1994

US experiments flown on the Soviet biosatellite Cosmos 2044. Volume 1: Mission description, experiments K-7-01 - K-7-15

Cosmos 2044 was launched on September 15, 1989, containing radiation dosimetry experiments and a biological payload including two young male rhesus monkeys, ten adult male Wistar rats, insects, amphibians, protozoa, cell cultures, worms, plants and fish. The biosatellite was launched from the Plesetsk Cosmodrome in the Soviet Union for a mission duration of 14 days, as planned. The major research objectives were: (1) Study adaptive response mechanisms of mammals during flight; (2) Study physiological mechanisms underlying vestibular, motor system and brain function in primates during early and later adaptation phases; (3) Study the tissue regeneration processes of mammals; (4) Study the development of single-celled organisms, cell cultures and embryos in microgravity; (5) Study radiation characteristics during the mission and investigate doses, fluxes and spectra of cosmic radiation for various types of shielding. American and Soviet specialists jointly conducted 29 experiments on this mission including extensive preflight and post flight studies with rhesus monkeys, and tissue processing and cell culturing post flight. Biosamples and data were subsequently transferred to the United States. The U.S. responsibilities for this flight included development of flight and ground-based hardware, the preparation of rat tissue sample procedures, the verification testing of hardware and experiment procedures, and the post flight analysis of biospecimens and data for the joint experiments. The U.S. investigations included four primate experiments, 24 rat experiments, and one radiation dosimetry experiment. Three scientists investigated tissue repair during flight for a subgroup of rats injured preflight by surgical intervention. A description of the Cosmos 2044 mission is presented in this report including preflight, on-orbit and post flight activities. The flight and ground-based bioinstrumentation which was developed by the U.S. and U.S.S.R. is also described, along with the associated preflight testing of the U.S. hardware.

Connolly, James P.↗
NASA NTRS1980

Optimization of solar cells for air mass zero operation and study of solar cells at high temperatures, phase 4

The Pd contact to GaAs was studied using backscattering, Auger analysis, and sheet resistance measurements. Several metallurgical phases were present at low temperatures, but PdGa was the dominant phase in samples annealed at 500 C. Ti/Pd/Ag contacts appeared to have the lowest contact resistance. Etchback epitaxy (EBE) was compared to saturated melt epitaxy (SME) method of growing liquid phase epitaxial layers. The SME method resulted in a lower density of Ga microdroplets in the grown layer, although the best solar cells were made by the EBE method. Photoluminescence was developed as a tool for contactless analysis of GaAs cells. Efficiencies of over 8 percent were measured at 250 C.

Hovel, H. J.↗
DOE OSTI2020

Thermal Stability of π-Conjugated n -Ethylene-Glycol-Terminated Quaterthiophene Oligomers: A Computational and Experimental Study

This work represents a joint computational and experimental study on a series of $\textit{n}$-ethylene glycol (PEO$\textit{n}$)-terminated quaterthiophene (4T) oligomers for 1 < $\textit{n}$ < 10 to elucidate their self-assembly behavior into a smectic-like lamellar phase. This study builds on an earlier study for $\textit{n}$ = 4 that showed that our model predictions were consistent with experimental data on the melting behavior and structure of the lamellar phase, with the latter consisting of crystal-like 4T domains and liquid-like PEO4 domains. The present study aims to understand how the length of the terminal PEO$\textit{n}$ chains modulates the disordering temperature of the lamellar phase and hence the relative stability of the ordered structure. In this work, a simplified bilayer model, where the 4T domains are not explicitly described, is put forward to efficiently estimate the disordering effect of the PEO domains with increasing n; this method is first validated by correctly predicting that layers of alkyl (PE)-capped 4T oligomers (for 1 < $\textit{n}$ < 10) stay ordered at room temperature. Both 4T-domain implicit and explicit model simulations reveal that the order-disorder temperature decreases with the length of the PEO capping chains, as the associated increase in conformational entropy drives a tendency toward disorder that overtakes the cohesive energy, keeping the ordered packing of the 4T domains.

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

The pervasive impact of critical fluctuations in liquid–liquid extraction organic phases

Liquid-liquid extraction is an essential chemical separation technique where polar solutes are extracted from an aqueous phase into a nonpolar organic solvent by amphiphilic extractant molecules. A fundamental limitation to the efficiency of this important technology is third phase formation, wherein the organic phase splits upon sufficient loading of polar solutes. The nanoscale drivers of phase splitting are challenging to understand in the complex hierarchically structured organic phases. In this study, we demonstrate that the organic phase structure and phase behavior are fundamentally connected in a way than can be understood with critical phenomena theory. For a series of binary mixtures of trialkyl phosphate extractants with linear alkane diluents, we combine small angle x-ray scattering and molecular dynamics simulations to demonstrate how the organic phase mesostructure over a wide range of compositions is dominated by critical concentration fluctuations associated with the critical point of the third phase formation phase transition. These findings reconcile many longstanding inconsistencies in the literature where small angle scattering features, also consistent with such critical fluctuations, were interpreted as reverse micellar-like particles. Altogether, this study shows how the organic phase mesostructure and phase behavior are intrinsically linked, deepening our understanding of both and providing a new framework for using molecular structure and thermodynamic variables to control mesostructure and phase behavior in liquid-liquid extraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗