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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

COMPOSITION STRUCTURE OF INTERPLANETARY CORONAL MASS EJECTIONS FROM MULTISPACECRAFT OBSERVATIONS, MODELING, AND COMPARISON WITH NUMERICAL SIMULATIONS

We present an analysis of the ionic composition of iron for two interplanetary coronal mass ejections (ICMEs) observed on 2007 May 21-23 by the ACE and STEREO spacecraft in the context of the magnetic structure of the ejecta flux rope, sheath region, and surrounding solar wind flow. This analysis is made possible due to recent advances in multispacecraft data interpolation, reconstruction, and visualization as well as results from recent modeling of ionic charge states in MHD simulations of magnetic breakout and flux cancellation coronal mass ejection (CME) initiation. We use these advances to interpret specific features of the ICME plasma composition resulting from the magnetic topology and evolution of the CME. We find that, in both the data and our MHD simulations, the flux ropes centers are relatively cool, while charge state enhancements surround and trail the flux ropes. The magnetic orientations of the ICMEs are suggestive of magnetic breakout-like reconnection during the eruption process, which could explain the spatial location of the observed iron enhancements just outside the traditional flux rope magnetic signatures and between the two ICMEs. Detailed comparisons between the simulations and data were more complicated, but a sharp increase in high iron charge states in the ACE and STEREO-A data during the second flux rope corresponds well to similar features in the flux cancellation results. We discuss the prospects of this integrated in situ data analysis and modeling approach to advancing our understanding of the unified CME-to-ICME evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Magneto-acoustic study near the quantum critical point of the frustrated quantum antiferromagnet Cs{sub 2}CuCl{sub 4}

Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs{sub 2}CuCl{sub 4} were performed for the longitudinal modes c{sub 11} and c{sub 33} in magnetic fields along the a-axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at T{sub N}. Isothermal measurements at T < T{sub N} of the sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at B{sub s} ≈ 8.5 T for B || a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature T{sub N}(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material's spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/k{sub B} ≈ 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Laser-induced selective local patterning of vanadium oxide phases

The same elements can form different compounds with widely different physical properties. Synthesis of a single-phase material is commonly achieved by controlling experimental conditions. Synthesizing materials that incorporate multiple specific spatially distributed chemical phases is often challenging, especially if different phases must be organized into well-defined spatial patterns. Here, we present an efficient solid reaction laser annealing (SRLA) approach to directly write regions of different local chemical compositions. We demonstrate the practical utility of our approach by locally writing microscale patterns of distinct chemical phases in vanadium oxide thin films. Specifically, we achieved the controlled local recrystallization of a uniform V 2 O 3 matrix into VO 2 , V 3 O 5 , and V 4 O 7 regions exhibiting sharp 1st- and 2nd-order metal–insulator phase transitions over a wide range of critical temperatures, i.e., a characteristic feature of select vanadium oxides that is extremely sensitive to even minute structural or compositional imperfections. We utilized the local chemical phase writing to pattern spiking oscillators with distinct electrical behavior directly in the thin film sample without employing elaborate lithography fabrication. Our laser tuning local chemical composition opens a pathway to synthesize a wide range of artificially micropatterned composite materials, with precision and control unattainable in conventional material synthesis methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Resonance Raman Study of Shell Morphology in InP/ZnSe/ZnS Core/Shell/Shell Nanocrystals

Resonance Raman spectra and absolute cross sections of InP/ZnSe/ZnS core/shell/shell nanocrystals have been obtained at excitation wavelengths of 501.7, 457.9, and 410 nm. Eight different structures having nearly the same lowest excitonic absorption wavelength but significantly different stoichiometries are compared. The Raman spectra show phonon features attributable to both the InP core and the ZnSe shell. The largest differences among the structures are seen in the ZnSe phonon region by using excitation at 457.9 nm, on the low-energy edge of the absorption features having significant contributions from the ZnSe shell. Here, structures that are nearly stoichiometric (In:P ratio ≈1.0) show a sharp, strongly polarized peak near the bulk ZnSe phonon frequency (~250 cm –1 ) and a weak lower-frequency shoulder with a higher depolarization ratio. Structures having excess indium show a stronger low-frequency shoulder near 225 cm –1 and lower integrated Raman intensities throughout the ZnSe phonon region. These changes are attributed to the presence of indium atoms in the ZnSe shell. Furthermore, these results support a previous assignment of a slow rise component in the time-resolved photoluminescence spectra of nonstoichiometric structures to transient trapping of holes at indium defects in the shell.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Radical Polymer-Based Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) are an emerging platform for bioelectronic applications. Significant effort has been placed in designing advanced polymers that simultaneously transport both charge and ions (i.e., macromolecules that are mixed conductors). Furthermore, the considerations for mixed organic conductors are often different from the established principles that are well-known in the solid-state organic electronics field; thus, the discovery of new OECT macromolecular systems is highly desired. Here, we demonstrate a new materials system by blending a radical polymer (i.e., a macromolecule with a nonconjugated backbone and with stable open-shell sites at its pendant group) with a frequently used conjugated polymer. Specifically, poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO) was blended with poly(3-hexylthiophene) (P 3 HT) to create thin films with distinct closed-shell and open-shell domains. Importantly, the sharp and unique oxidation–reduction (redox) potential associated with the radical moieties of the PTEO chain provided a distinct actuation feature to the blended films that modulated the ionic transport of the OECT devices. In turn, this led to controlled regulation of the doping of the P 3 HT phase in the composite film. By decoupling the ionic and electronic transport into two distinct phases and by using an ion transport phase with well-controlled redox activity, never-before-seen performance for a P3HT-based OECT was observed. That is, at loadings as low as 5% PTEO (by weight) OECTs achieved figure-of-merit (i.e., μC*) values >150 F V –1 cm –1 s –1 , which place the performance on the same order as state-of-the-art conjugated polymers despite the relatively common conjugated macromolecular moiety implemented. As such, this effort presents a design platform by which to readily create a tailored OECT response through strategic macromolecular selection and polymer processing.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microlensing constraints on broad absorption and emission line flows in the quasar H1413+117

We present new integral field spectroscopy of the gravitationally lensed broad absorption line (BAL) quasar H1413+117, covering the ultraviolet restframe spectral range. We observe strong microlensing signatures in lensed image D, and we use this microlensing to simultaneously constrain both the broad emission and broad absorption line gas. The wavelength independence of image D magnifications across the broad emission lines (BELs) indicates a lower limit on the broad emission line region (BELR) size equal to the Einstein radius (ER) of the system: ≳11 (〈M〉/M{sub ⊙}){sup 0.5} lt-day for a lens redshift of 1.4 and ≳15 (〈M〉/M{sub ⊙}){sup 0.5} lt-day for z{sub L} = 0.94. Lensing simulations verify that the observed wavelength independence is very unlikely for BELRs with significant velocity stratification at size scales below an ER. We perform spectral decomposition to derive the intrinsic BEL and continuum spectrum, subject to BAL absorption. We reconstruct the intrinsic BAL absorption profile, whose features allow us to constrain outflow kinematics in the context of a disk-wind model. We find a very sharp, blueshifted onset of absorption of 1500 km s{sup −1} in both C iv and N v, which may correspond to an inner edge of a disk-wind’s radial outflow. The lower ionization Si iv and Al iii have higher-velocity absorption onsets, consistent with a decreasing ionization parameter with radius in an accelerating outflow. There is evidence of strong absorption in the BEL component, which indicates a high covering factor for absorption over two orders of magnitude in outflow radius.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak

The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without an accompanying particle barrier and with broadband instabilities, known as weakly coherent modes (WCM), believed to regulate particle transport at the edge. Recent experiments on the DIII-D tokamak exhibit I-mode characteristics in various physical quantities. These DIII-D plasmas evolve over long periods, lasting several energy confinement times, during which the edge electron temperature slowly evolves towards an H-mode-like profile, while maintaining a typical L-mode edge density profile. During these periods, referred to as I-mode phases, the radial electric field at the edge also gradually reaches values typically observed in H-mode. Density fluctuations measured with the phase contrast imaging diagnostic during I-mode phases exhibit three features typically observed in H-mode on DIII-D, although they develop progressively with time and without a sharp transition: the intensity of the fluctuations is reduced; the frequency spectrum is broadened and becomes non-monotonic; two dimensional space-time spectra appear to approach those in H-mode, showing phase velocities of density fluctuations at the edge increasing to about 10 km s -1 . However, in DIII-D there is no clear evidence of the WCM. Preliminary linear gyro-kinetic simulations are performed in the pedestal region with the GS2 code and its recently upgraded model collision operator that conserves particles, energy and momentum. The increased bootstrap current and flow shear generated by the temperature pedestal are shown to decrease growth rates, thus possibly generating a feedback mechanism that progressively stabilizes fluctuations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Effects of strain and defects on the topological properties of HfTe 5

Manipulating topological states is a topic of vigorous research. However, the impact of such topological phase transitions on the quasiparticle dynamics remains elusive. Here, in this work, we present the effects of a transition from a strong to weak topological insulator in HfTe 5 as a function of Te vacancy concentration. We observed a significant transition from distinct sharp surface states and Dirac crossing to a Fermi-liquid-like quasiparticle state in which these surface-localized features are heavily suppressed. Additionally, by inducing the same effect through applied uniaxial stress, we demonstrate that changes in the lattice constants play the foremost role in determining the electronic structure, self-energy, and topological states of HfTe 5 . Our results demonstrate the possibility of using both defect chemistry and strain as control parameters for topological phase transitions and associated many-body physics.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Using photoelectron spectroscopy to measure resonant inelastic X-ray scattering: a computational investigation

Resonant inelastic X-ray scattering (RIXS) has become an important scientific tool. Nonetheless, conventional high-resolution (few hundred meV or less) RIXS measurements, especially in the soft X-ray range, require low-throughput grating spectrometers, which limits measurement accuracy. Here, the performance of a different method for measuring RIXS, i.e. photoelectron spectrometry for analysis of X-rays (PAX), is computationally investigated. This method transforms the X-ray measurement problem of RIXS to an electron measurement problem, enabling use of high-throughput, compact electron spectrometers. X-rays to be measured are incident on a converter material and the energy distribution of the resultant photoelectrons, the PAX spectrum, is measured with an electron spectrometer. A deconvolution algorithm for analysis of such PAX data is proposed. It is shown that the deconvolution algorithm works well on data recorded with ~0.5 eV resolution. Additional simulations show the potential of PAX for estimation of RIXS features with smaller widths. For simulations using the 3d levels of Ag as a converter material, and with 10 5 simulated detected electrons, it is estimated that features with a few hundred meV width can be accurately estimated in a model RIXS spectrum. For simulations using a sharp Fermi edge to encode RIXS spectra, it is estimated that one can accurately distinguish 100 meV FWHM peaks separated by 45 meV with 10 5 simulated detected electrons that were photoemitted from within 0.4 eV of the Fermi level.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Constraints on iron sulfate and iron oxide mineralogy from ChemCam visible/near-infrared reflectance spectroscopy of Mt. Sharp basal units, Gale Crater, Mars

Relative reflectace point spectra (400–840 nm) were acquired by the Chemistry and Camera (ChemCam) instrument on the Mars Science Laboratory (MSL) rover Curiosity in passive mode (no laser) of drill tailings and broken rock fragments near the rover as it entered the lower reaches of Mt. Sharp and of landforms at distances of 2–8 km. Freshly disturbed surfaces are less subject to the spectral masking effects of dust, and revealed spectral features consistent with the presence of iron oxides and ferric sulfates. Here, we present the first detection on Mars of a ~433 nm absorption band consistent with small abundances of ferric sulfates, corroborated by jarosite detections by the Chemistry and Mineralogy (CheMin) X-ray diffraction instrument in the Mojave, Telegraph Peak, and Confidence Hills drilled samples. The disturbed materials near the Bonanza King region also exhibited strong 433 nm bands and negative near-infrared spectral slopes consistent with jarosite. ChemCam passive spectra of the Confidence Hills and Mojave drill tailings showed features suggestive of the crystalline hematite identified by CheMin analyses. The Windjana drill sample tailings exhibited flat, low relative reflectance spectra, explained by the occurrence of magnetite detected by CheMin. Passive spectra of Bonanza King were similar, suggesting the presence of spectrally dark and neutral minerals such as magnetite. Long-distance spectra of the “Hematite Ridge” feature (3–5 km from the rover) exhibited features consistent with crystalline hematite. The Bagnold dune field north of the Hematite Ridge area exhibited low relative reflectance and near-infrared features indicative of basaltic materials (olivine, pyroxene). Light-toned layers south of Hematite Ridge lacked distinct spectral features in the 400–840 nm region, and may represent portions of nearby clay minerals and sulfates mapped with orbital near-infrared observations. The presence of ferric sulfates such as jarosite in the drill tailings suggests a relatively acidic environment, likely associated with flow of iron-bearing fluids, associated oxidation, and/or hydrothermal leaching of sedimentary rocks. Combined with other remote sensing data sets, mineralogical constraints from ChemCam passive spectra will continue to play an important role in interpreting the mineralogy and composition of materials encountered as Curiosity traverses further south within the basal layers of the Mt. Sharp complex.

58 GEOSCIENCES↗
DOE OSTI2019

Submicron Sodium Banding in Cultured Planktic Foraminifera Shells

The calcite shells, or tests, of foraminifera provide a window into Earth history because they are well preserved in marine sediments and contain useful geochemical proxies for paleoceanography. Previous observations of diurnal heterogeneity in proxies like Mg/Ca demonstrate a complex relationship between environmental conditions and test composition. The definitive causes for this diurnal banding and the potential impact for proxy interpretation in systems other than Mg/Ca have yet to be determined. Here we use time-of-flight secondary ion mass spectrometry (ToF-SIMS), a chemical and isotope mapping technique with a spatial resolution of 300 nm, to show that Na banding is a consistent feature in the tests of cultured Orbulina universa, a species of planktic foraminifer. This banding occurs in two distinct forms: (1) sharp Na bands associated with embedded organic sheets and (2) regular, thicker, but lower-amplitude Na bands that are found throughout the test. In Orbulina bilobata, a morphotype of O. universa that develops a second partial spherical chamber attached to the primary sphere, we use the first type of banding to show that a second organic sheet is used as a template to form this second chamber. Thus, sodium banding links test geochemistry with foraminiferal growth models, allowing us to explain the pattern and timing of chamber formation as well as a specific type of geochemical banding in foraminifera. Furthermore, the magnitude, timing, and coherency between Na and Mg bands can help constrain mechanistic explanations for geochemical banding in foraminifera in general.

paleoclimate, Foraminifera, biomineralization, pal↗
DOE OSTI2015

Stabilization of gene expression and cell morphology after explant recycling during fin explant culture in goldfish

The development of fin primary cell cultures for in vitro cellular and physiological studies is hampered by slow cell outgrowth, low proliferation rate, poor viability, and sparse cell characterization. Here, we investigated whether the recycling of fresh explants after a first conventional culture could improve physiological stability and sustainability of the culture. The recycled explants were able to give a supplementary cell culture showing faster outgrowth, cleaner cell layers and higher net cell production. The cells exhibited a highly stabilized profile for marker gene expression including a low cytokeratin 49 (epithelial marker) and a high collagen 1a1 (mesenchymal marker) expression. Added to the cell spindle-shaped morphology, motility behavior, and actin organization, this suggests that the cells bore stable mesenchymal characteristics. This contrast with the time-evolving expression pattern observed in the control fresh explants during the first 2 weeks of culture: a sharp decrease in cytokeratin 49 expression was concomitant with a gradual increase in col1a1. We surmise that such loss of epithelial features for the benefit of mesenchymal ones was triggered by an epithelial to mesenchymal transition (EMT) process or by way of a progressive population replacement process. Overall, our findings provide a comprehensive characterization of this new primary culture model bearing mesenchymal features and whose stability over culture time makes those cells good candidates for cell reprogramming prior to nuclear transfer, in a context of fish genome preservation. - Highlights: • Recycled fin explants outgrow cells bearing stable mesenchymal traits. • Cell production and quality is enhanced in the recycled explant culture system. • Fresh fin primary culture is highly variable and loose epithelial traits over time.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

The glass-ceiling convective regime and the origin and diversity of coronae on Venus

Venus and Earth are rocky planets of roughly the same size and bulk density, yet their surface volcanic and tectonic features appear substantially different. On Venus, the coexistence of large volcanic highlands—interpreted as the surface expression of long-lived mantle plumes—alongside coronae, smaller features thought to be caused by transient thermal diapirs, remains enigmatic. Using two-dimensional numerical models of mantle convection with sharp and broad mineral phase transitions for pyrolite, we show that both scales of upwellings can be generated in a stagnant lid planet with an interior temperature 250 to 400 K warmer than Earth’s. The smaller plumes originate from a ~600 km deep internal layer that exists as a consequence of the different sequence of mineral phase transitions that occur in warmer mantles less processed and differentiated by partial melting and volcanism. Future models that include melting will provide further tests of our hypothesis.

Science & Technology - Other Topics↗
DOE OSTI2014

Investigation on the pyroelectric property of polycrystalline GdMnO{sub 3}

Pyroelectric property of orthorhomic GdMnO{sub 3} polycrystalline samples was investigated. Two pyrocurrent peaks were observed with the sharp one near 20 K and the broad one at around 120 K. The dependences of these two peaks on magnetic field, heating rate, and poling voltage were explored systematically. The sharp peak is related to the ferroelectric transition, while the behavior of the broad one corresponds to dipole reorientation. Some key pyroelectric features are proposed to separate the spin-induced ferroelectricity from other effects. This work is helpful for understanding the pyroelectric property of multiferroic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets

Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (Δν > 100 cm{sup −1}) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Edge-Confined Excitons in Monolayer Black Phosphorus

Quantum confinement of two-dimensional excitons in van der Waals materials via electrostatic trapping, lithographic patterning, Moiré potentials, and chemical implantation has enabled significant advances in tailoring light emission from nanostructures. While such approaches rely on complex preparation of materials, natural edges are a ubiquitous feature in layered materials and provide a different approach for investigating quantum-confined excitons. Here, we observe that certain edge sites of monolayer black phosphorus (BP) strongly localize the intrinsic quasi-one-dimensional excitons, yielding sharp spectral lines in photoluminescence, with nearly an order of magnitude line width reduction. Through structural characterization of BP edges using transmission electron microscopy and first-principles GW plus Bethe–Salpeter equation (GW-BSE) calculations of exemplary BP nanoribbons, we find that certain atomic reconstructions can strongly quantum-confine excitons resulting in distinct emission features, mediated by local strain and screening. Here we observe linearly polarized luminescence emission from edge reconstructions that preserve the mirror symmetry of the parent BP lattice, in agreement with calculations. Furthermore, we demonstrate efficient electrical switching of localized edge excitonic luminescence, whose sites act as excitonic transistors for emission. Localized emission from BP edges motivates exploration of nanoribbons and quantum dots as hosts for tunable narrowband light generation, with future potential to create atomic-like structures for quantum information processing applications as well as exploration of exotic phases that may reside in atomic edge structures.

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

Antiferromagnetic and nematic phase transitions in BaF e 2 ( A s 1 - x P x ) 2 studied by ac microcalorimetry and SQUID magnetometry

In this work, we study the antiferromagnetic (AFM) and structural phase transitions in single-crystal BaF e 2 ( A s 1 – x P x ) 2 ( x = 0 , 0.3 ) at temperatures T N and T S , respectively, by high-resolution ac microcalorimetry and SQUID magnetometry. The specific heat measurements of both as-grown and annealed BaF e 2 A s 2 display a sharp peak at the AFM-structural transitions. A kink in the entropy of annealed BaF e 2 A s 2 gives evidence for splitting of the two transitions by approximately 0.5 K. No additional features could be identified in the specific heat of both BaF e 2 A s 2 and BaF e 2 ( A s 0.7 P 0.3 ) 2 in the temperature regions around T * > T S where torque measurements had revealed the “true” nematic phase transition, even though the Ginzburg-Landau model used to fit the magnetic torque data indicates that the expected thermal anomaly should be easily observable with our experimental resolution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗