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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 361 records · Page 20

Counterion Dynamics in Polyester-Sulfonate Ionomers with Ionic Liquid Counterions

Conventional sodium cations (Na{sup +}) in sulfonated polyester ionomers were replaced with ammonium-based ionic liquid counterions. Counterion dynamics were measured by dielectric spectroscopy and linear viscoelastic response via oscillatory shear. Ion exchange from sodium counterions to ionic liquid counterions such as tetramethylammonium and tetrabutylammonium showed an order of 10{sup 4} increase in conductivity compared with sodium counterions, primarily attributed to weaker ionic interactions that lower the glass transition temperature. Electrode polarization was used in conjunction with the 1953 Macdonald model to determine the number density of conducting counterions and their mobility. Conductivity and mobility exhibit Vogel-Fulcher-Tammann (VFT) temperature dependences and both increased with counterion size. Conducting counterion concentrations showed Arrhenius temperature dependences, with activation energy reduced as counterion size increased. When ether-oxygen was incorporated into the mobile cation structure, self-solvating ability notably increased the conducting ion concentration. Weakened ion pairing interactions prove favorable for fundamental design of single-ion conductors for actuators, as ionic liquid counterions can provide both larger and faster strains, required by such electro-active devices.

36 MATERIALS SCIENCE↗

Activation of microcarrier-attached lymphocytes in microgravity

A technology has been developed to achieve optimal attachment of adhesion-independent lymphocytes to microcarrier beads. The activation of T-lymphocytes by concanavalin A was tested under microgravity conditions in an experiment carried out in space during the first Spacelab Life Science Mission. Activation, measured as the synthesis of deoxyribonucleic acid (DNA) and the production of interferon-gamma, more than doubled in attached lymphocytes in microgravity. The depression of the activation discovered in previous space experiments is due to an impairment not of the lymphocyte but of the macrophage function. The system described here may be useful for radiobiological investigations on the effect of high-energy particles and for testing the efficiency of the immune system in humans during the long-duration space flight planned in the future. The biotechnological significance of the increased lymphokine production in space remains to be assessed.

Non-NASA Center↗

Microstructural characterization of weld joints of 9Cr reduced activation ferritic martensitic steel fabricated by different joining methods

This paper presents a detailed electron microscopy study on the microstructure of various regions of weldment fabricated by three welding methods namely tungsten inert gas welding, electron beam welding and laser beam welding in an indigenously developed 9Cr reduced activation ferritic/martensitic steel. Electron back scatter diffraction studies showed a random micro-texture in all the three welds. Microstructural changes during thermal exposures were studied and corroborated with hardness and optimized conditions for the post weld heat treatment have been identified for this steel. Hollomon–Jaffe parameter has been used to estimate the extent of tempering. The activation energy for the tempering process has been evaluated and found to be corresponding to interstitial diffusion of carbon in ferrite matrix. The type and microchemistry of secondary phases in different regions of the weldment have been identified by analytical transmission electron microscopy. - Highlights: • Comparison of microstructural parameters in TIG, electron beam and laser welds of RAFM steel • EBSD studies to illustrate the absence of preferred orientation and identification of prior austenite grain size using phase identification map • Optimization of PWHT conditions for indigenous RAFM steel • Study of kinetics of tempering and estimation of apparent activation energy of the process.

36 MATERIALS SCIENCE↗

Activity gradient mass transport accelerated corrosion of stainless steel in molten salt

Advanced energy systems based on molten salt technologies have gained increasing interest, and their design and construction are likely going to involve the use of materials of dissimilar chemistries. With dissimilar materials being used, galvanic coupling induced corrosion acceleration is one of the mechanisms believed to be an issue for the deployment of molten salt systems. However, non-galvanic interaction mechanisms such as activity gradient mass transport have also been theorized to represent a potential challenge. Unfortunately, the two effects have often been compounded in the literature, such that it is still unclear which degradation mechanisms are at play in these systems. In the following study, electrochemical measurements are used to predict the effect that galvanic coupling would have on dissimilar materials submerged in the same molten salt medium. Dissimilar material salt exposure tests are then performed to investigate whether galvanic coupling or activity gradient driven processes account for the levels of materials degradation observed. Finally, these separate effect electrochemical and corrosion experiments uniquely elucidate the degradation mechanisms in dissimilar materials systems.

36 MATERIALS SCIENCE↗

Effect of trifluoperazine on toxicity, HIF-1α induction and hepatocyte regeneration in acetaminophen toxicity in mice

Oxidative stress and mitochondrial permeability transition (MPT) are important mechanisms in acetaminophen (APAP) toxicity. The MPT inhibitor trifluoperazine (TFP) reduced MPT, oxidative stress, and toxicity in freshly isolated hepatocytes treated with APAP. Since hypoxia inducible factor-one alpha (HIF-1α) is induced very early in APAP toxicity, a role for oxidative stress in the induction has been postulated. In the present study, the effect of TFP on toxicity and HIF-1α induction in B6C3F1 male mice treated with APAP was examined. Mice received TFP (10 mg/kg, oral gavage) prior to APAP (200 mg/kg IP) and at 7 and 36 h after APAP. Measures of metabolism (hepatic glutathione and APAP protein adducts) were comparable in the two groups of mice. Toxicity was decreased in the APAP/TFP mice at 2, 4, and 8 h, compared to the APAP mice. At 24 and 48 h, there were no significant differences in toxicity between the two groups. TFP lowered HIF-1α induction but also reduced the expression of proliferating cell nuclear antigen, a marker of hepatocyte regeneration. TFP can also inhibit phospholipase A{sub 2}, and cytosolic and secretory PLA{sub 2} activity levels were reduced in the APAP/TFP mice compared to the APAP mice. TFP also lowered prostaglandin E{sub 2} expression, a known mechanism of cytoprotection. In summary, the MPT inhibitor TFP delayed the onset of toxicity and lowered HIF-1α induction in APAP treated mice. TFP also reduced PGE{sub 2} expression and hepatocyte regeneration, likely through a mechanism involving PLA{sub 2}. -- Highlights: ► Trifluoperazine reduced acetaminophen toxicity and lowered HIF-1α induction. ► Trifluoperazine had no effect on the metabolism of acetaminophen. ► Trifluoperazine reduced hepatocyte regeneration. ► Trifluoperazine reduced phospholipase A{sub 2} activity and prostaglandin E{sub 2} levels.

60 APPLIED LIFE SCIENCES↗

Friction-mediated phase transition in confined active nematics

Using a minimal continuum model, we investigate the interplay between circular confinement and substrate friction in active nematics. Upon increasing the friction from low to high, we observe a dynamical phase transition from a circulating flow phase to an anisotropic flow phase in which the flow tends to align perpendicular to the nematic director at the boundary. We demonstrate that both the flow structure and dynamic correlations in the latter phase differ from those of an unconfined, active turbulent system and may be controlled by the prescribed nematic boundary conditions. Here, our results show that substrate friction and geometric confinement act as valuable control parameters in active nematics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Deformation of the surface of gallium arsenide during the deposition of gold

Deformation phenomena of near-surface GaAs layers are studied using surface acoustic waves during the deposition of Au and the irradiation of the semiconductor surface by the light of a heated evaporator. It is shown that, in the case of Au deposition, the near-surface layers are plasticized due to the phase transformations in the Au-Ga-As system, while upon irradiation of the GaAs surface with light, a coarse-grained layer with liquid-like interlayers is formed. As a result, the type of surface deformations and their relaxation time change. The integral temporal characteristics of the surface acoustic wave, such as the variation integrals of its rate and dissipated power, reflect the processes occurring on the surface in the real-time mode. In summary, they reflect the current magnitude of the resulting deformation. The parameters of occurring processes such as activation energy and relaxation time are determined.

36 MATERIALS SCIENCE↗

Interaction of Intercalated Li+ Ions with Oxygen Vacancies in Rutile TiO2

Point defects are known to affect transport properties of materials. The effect of oxygen vacancies on the diffusion of Li+ ions in rutile TiO2 is investigated using an embedded cluster method. The calculated Li+ diffusion pathway in vacancy-containing lattice is similar to that found for the ideal lattice. However, vacancies strongly modify the shape of the Li+ potential energy surface and increase the diffusion activation energies by the factor of two.

36 MATERIALS SCIENCE↗

Synthesis, structural, magnetic and electrical properties of Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (x = 0.0, 0.2) nanoparticles

Graphical abstract: The variations of imaginary part of dielectric permittivity (ε″) of TEG@Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} nanocomposite as a function of temperature and frequency for (A) x = 0.0 and (B) x = 0.2. Display Omitted Highlights: ► Nearly monodisperse Zn{sub x}Co{sub 1−x}Fe{sub 2}O{sub 4} nanocomposite were prepared via hydrothermal method. ► The ac conductivity showed a temperature dependent behavior at low frequencies. ► dc conductivity of Co{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} nanoparticle are found to obey the Arrhenius plot. ► Also these materials may be used in electronic devices and microwave devices. -- Abstract: Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} spinel nanoparticles with Zn concentrations of x = 0.0, 0.2 were prepared by a hydrothermal route in the presence of triethylene glycol (TEG). The structural, magnetic, electrical and dielectric properties of the prepared nanoparticles were studied. The XRD results confirmed the formation of single spinel ferrite structure with crystallite size 9 and 10 nm for x = 0.0 and 0.2 compositions respectively. The lattice parameter (a) increased with increasing Zn concentration. Temperature and frequency dependent electrical and dielectric properties of the prepared ferrites have also been investigated. Our findings show that overall conductivity of Co{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} nanoparticle is lower than that of CoFe{sub 2}O{sub 4} and roughly in the range of 10{sup −11}–10{sup −7} S cm{sup −1} depending strongly temperature and frequency owing to the formation of stable electric bonds between the Zn{sup 2+} and Fe{sup 2+} ions, which localizes Fe{sup 2+} charge carriers. The ac conductivity showed a temperature dependent behavior at low frequencies and temperature independent behavior at high frequencies, which is an indication of ionic conductivity. dc conductivity of Co{sub 0.8}Zn{sub 0.2}Fe{sub 2}O{sub 4} nanoparticle are found to obey the Arrhenius plot and can be classified into two regions over with activation energy of 0.113 and 0.163 eV in the ranges of 20–40 °C and 70–120 °C, respectively when CoFe{sub 2}O{sub 4} has an activation energy of 0.245 eV.

36 MATERIALS SCIENCE↗

Highly polarized photoluminescence and its dynamics in semipolar (202{sup ¯}1{sup ¯}) InGaN/GaN quantum well

Very high polarization degree of 0.98, considerably larger than theoretical predictions, has been measured in (202{sup ¯}1{sup ¯}) In{sub 0.24}Ga{sub 0.76}N/GaN quantum well by low temperature photoluminescence. With increasing temperature, the polarization degree decreases due to thermal population of the excited valence band level. This effect suggests an accurate method to determine the interlevel energy, which, for the studied well, is 32 meV. Time-resolved photoluminescence measurements set radiative recombination times between 2 and 12 ns for temperatures from 3 to 300 K. Nonradiative recombination was found to be slow, over 2 ns at 300 K, taking place via traps with activation energy of 0.19 eV.

36 MATERIALS SCIENCE↗

Sodium diffusion in 4H-SiC

Sodium diffusion has been studied in p-type 4H-SiC. Heat treatments have been performed from 1200 °C to 1800 °C for 1 min to 4 h. Secondary ion mass spectrometry has been used to measure the sodium distribution. We show that sodium has a considerable mobility at 1200 °C in p-type 4H-SiC. On the other hand for sodium atoms trapped at suitable sites the mobility is limited up to 1800 °C. Trap limited diffusion kinetics is suggested and an effective diffusivity has been extracted with an activation energy of 4 eV for sodium diffusion in p-type 4H-SiC.

36 MATERIALS SCIENCE↗

Rectified Rotational Dynamics of Mobile Inclusions in Two-Dimensional Active Nematics

We investigate the dynamics of mobile inclusions embedded in 2D active nematics. The interplay between the inclusion shape, boundary-induced nematic order, and autonomous flows powers the inclusion motion. Disks and achiral gears exhibit unbiased rotational motion, but with distinct dynamics. In comparison, chiral gear-shaped inclusions exhibit long-term rectified rotation, which is correlated with dynamics and polarization of nearby +1/2 topological defects. Furthermore, the chirality of defect polarities and the active nematic texture around the inclusion correlate with the inclusion’s instantaneous rotation rate. Inclusions provide a promising tool for probing the rheological properties of active nematics and extracting ordered motion from their inherently chaotic motion.

36 MATERIALS SCIENCE↗

Feedbacks Between Surface Deformation and Permafrost Degradation in Ice Wedge Polygons: Modeling Archive

This Modeling Archive is in support of an NGEE Arctic publication "Feedbacks between surface deformation and permafrost degradation in ice wedge polygons," submitted for review to the Journal of Geophysical Research: Earth Surface. The goals of the study were: 1) to determine how variability in microtopographic conditions (i.e., rim height, trough width, and trough depth) and hydrologic conditions in the trough (i.e., inundated or well-drained) of an ice wedge polygon impact active layer thickness above an ice wedge; and 2) to determine how microtopographic and hydrologic controls on active layer thickness may influence thermokarst trajectories in ice wedge polygon terrain. Toward these objectives, an ensemble of fine-scale simulations of the hydrologic and thermal regimes in ice wedge polygons of variable microtopography was conducted, each polygon being subjected to identical meteorological forcing data, characteristic of the last twenty years near Prudhoe Bay, Alaska. Simulations incorporated solutions of conservation of water and mass at the surface, in the subsurface, and in the snowpack. Active layer thickness in the trough (i.e., above the ice wedge) was extracted from each simulation at the end of a 19 year spin-up, and at the end of a markedly warm summer which followed the spin-up. This archive includes mesh files, meteorological forcing data, and input files needed to reproduce the analysis described in the paper. Due to the large file sizes, raw model output has been omitted. However, post-processing scripts and time series of several variables extracted from the raw output have been included. All data are included in one zipped file with a user guide as a pdf. All simulations were conducted using Amanzi-ATS, v 0.86 (https://doi.org/10.11578/dc.20190911.1).The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research.The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska.Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

54 ENVIRONMENTAL SCIENCES↗

Hot Ductility and Compression Deformation Behavior of TRIP980 at Elevated Temperatures

The hot ductility tests of a kind of 980 MPa class Fe-0.31C (wt pct) TRIP steel (TRIP980) with the addition of Ti/V/Nb were conducted on a Gleeble-3500 thermomechanical simulator in the temperatures ranging from 873 K to 1573 K (600 °C to 1300 °C) at a constant strain rate of 0.001 s{sup −1}. It is found that the hot ductility trough ranges from 873 K to 1123 K (600 °C to 850 °C). The recommended straightening temperatures are from 1173 K to 1523 K (900 °C to 1250 °C). The isothermal hot compression deformation behavior was also studied by means of Gleeble-3500 in the temperatures ranging from 1173 K to 1373 K (900 °C to 1100 °C) at strain rates ranging from 0.01 s{sup −1} to 10 s{sup −1}. The results show that the peak stress decreases with the increasing temperature and the decreasing strain rate. The deformation activation energy of the test steel is 436.7 kJ/mol. The hot deformation equation of the steel has been established, and the processing maps have been developed on the basis of experimental data and the principle of dynamic materials model (DMM). By analyzing the processing maps of strains of 0.5, 0.7, and 0.9, it is found that dynamic recrystallization occurs in the peak power dissipation efficiency domain, which is the optimal area of hot working. Finally, the factors influencing hot ductility and thermal activation energy of the test steel were investigated by means of microscopic analysis. It indicates that the additional microalloying elements play important roles both in the loss of hot ductility and in the enormous increase of deformation activation energy for the TRIP980 steel.

36 MATERIALS SCIENCE↗

Oxidative Dehydrogenation of Isobutane on Phosphorous-Modified Graphitic Mesoporous Carbon

Phosphorous heteroatoms were added in order to tune the selectivity and investigate the roles of different oxygen species in graphitic mesoporous carbons for the oxidative dehydrogenation reaction of isobutane to isobutene. Small changes in the apparent isobutane activation energy are consistent with the notion that the phosphorous groups do not change the nature of the active sites but they interfere with the availability of the sites. Our results show that the improvement on selectivity is not proportional to the amount of phosphorous added. Small phosphorous content improved the selectivity by suppressing the combustion of isobutane. However, a higher amount of phosphorous groups lead to coverage of selective quinone sites and/or creation of active sites favorable to total oxidation.

2-METHYLPROPANE↗