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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Advanced ACTPol TES Device Parameters and Noise Performance in Fielded Arrays

The Advanced ACTPol (AdvACT) upgrade to the Atacama Cosmology Telescope (ACT) features arrays of aluminum manganese transition-edge sensors (TESes) optimized for ground-based observations of the cosmic microwave background (CMB). Array testing shows highly responsive detectors with anticipated in-band noise performance under optical loading. We report on TES parameters measured with impedance data taken on a subset of TESes. We then compare modeled noise spectral densities to measurements. We find excess noise at frequencies around 100 Hz, nearly outside of the signal band of CMB measurements. In addition, we describe full-array noise measurements in the laboratory and in the field for two new AdvACT mid-frequency arrays, sensitive at bands centered on 90 and 150 GHz, and data for the high-frequency array (150/230 GHz) as deployed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Development of a Small-Pixel Ir-TES for Optical Applications

We designed and fabricated a photon-number-resolving detector based on an iridium (Ir) transition-edge sensors (TES) with small timing jitter time for coherent optical communication. The current–voltage relationship of the small Ir-TES, with an effective area of 7 μm × 7 μm, was measured, and its electrothermal feedback operation was confirmed. This device had a transition temperature of 280 mK, which is higher than that of bulk Ir, because of the wide contact area.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Brain in situ hybridization maps as a source for reverse-engineering transcriptional regulatory networks: Alzheimer's disease insights

Microarray data have been a valuable resource for identifying transcriptional regulatory relationships among genes. As an example, brain region-specific transcriptional regulatory events have the potential of providing etiological insights into Alzheimer Disease (AD). However, there is often a paucity of suitable brain-region specific expression data obtained via microarrays or other high throughput means. The Allen Brain Atlas in situ hybridization (ISH) data sets (Jones et al., 2009) represent a potentially valuable alternative source of high-throughput brain region-specific gene expression data for such purposes. In this study, Allen BrainAtlasmouse ISH data in the hippocampal fields were extracted, focusing on 508 genes relevant to neurodegeneration. Transcriptional regulatory networkswere learned using three high-performing network inference algorithms. Only 17% of regulatory edges from a network reverse-engineered based on brain region-specific ISH data were also found in a network constructed upon gene expression correlations inmousewhole brain microarrays, thus showing the specificity of gene expression within brain sub-regions. Furthermore, the ISH data-based networks were used to identify instructive transcriptional regulatory relationships. Ncor2, Sp3 and Usf2 form a unique three-party regulatory motif, potentially affecting memory formation pathways. Nfe2l1, Egr1 and Usf2 emerge among regulators of genes involved in AD (e.g. Dhcr24, Aplp2, Tia1, Pdrx1, Vdac1, andSyn2). Further, Nfe2l1, Egr1 and Usf2 are sensitive to dietary factors and could be among links between dietary influences and genes in the AD etiology. Thus, this approach of harnessing brain region-specific ISH data represents a rare opportunity for gleaning unique etiological insights for diseases such as AD.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Highly efficient and stable p-type ZnO nanowires with piezotronic effect for photoelectrochemical water splitting

Unremitting efforts have been made to develop high-performance photoelectrochemical (PEC) water-splitting system to produce clean hydrogen fuel using sunlight. In this research, a novel way, combining highly-ordered nanowires (NWs) structure and piezotronic effect of p-type ZnO has been demonstrated to dramatically enhance PEC hydrogen evolution performance. Systematic characterizations indicate that the Sb atoms uniformly dope into ZnO NWs and substitute Zn sites with the introduction of two zinc vacancies to form the shallow acceptor Sb Zn –2V Zn complex. Detailed synchrotron-based X-ray absorption near-edge structure (XANES) experiments in O K-edge and Zn L-edge further confirm the formation of the complex, and theoretical calculation verifies the Sb 5+ state dominating the complex. The optimal photocurrent density of the 0.2Sb/ZnO-anneal NWs can reach –0.85 mA/cm 2 (0 V RHE ) which is 17.2 times larger than that of the n-ZnO NWs under sunlight illumination (100 mW/cm 2 ). Furthermore, the piezotronic effect can be introduced to regulate the charge separation and transfer in the ZnO NWs through modulating the band structure near the interface. The photocurrent density can further increase to –1.08 mA/cm 2 (0 V RHE ) under a 0.6% tensile strain, which is 27.4% enhancement with respect to the ZnO sample without strain. These conclusions provide an efficient way to design and develop high-performance photoelectrodes toward PEC hydrogen evolution.

08 HYDROGEN↗
DOE OSTI2020

Digital force prediction for milling

This paper presents a fully digital, integrated approach for milling force prediction with arbitrary end mill-work material combinations. The approach includes: 1) structured light scanning to identify the end mill’s cutting edge macro-geometry along the tool axis; 2) structured light scanning to measure the cutting edge cross-sectional rake and relief profiles; 3) finite element analysis of orthogonal cutting to determine the force model coefficients that relate the force to chip area using the work material’s constitutive model and tool’s rake and relief profiles; and 4) time domain simulation with inputs that include the measured cutting edge macro-geometry, finite element-based force model, and measured structural dynamics. Milling force predictions are compared to in-process measurements to validate the method.

42 ENGINEERING↗
DOE OSTI2017

Noninvasive Synchrotron-Based X-ray Raman Scattering Discriminates Carbonaceous Compounds in Ancient and Historical Materials [ In situ synchrotron-based X-Ray Raman scattering discriminates carbonaceous compounds in ancient and historical materials]

Carbon compounds are ubiquitous and occur in a diversity of chemical forms in many systems including ancient and historic materials ranging from cultural heritage to paleontology. Determining their speciation cannot only provide unique information on their origin but may also elucidate degradation processes. Synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the carbon K-edge (280–350 eV) is a very powerful method to probe carbon speciation. However, the short penetration depth of soft X-rays imposes stringent constraints on sample type, preparation, and analytical environment. A hard X-ray probe such as X-ray Raman scattering (XRS) can overcome many of these difficulties. Here we report the use of XRS at ~6 keV incident energy to collect carbon K-edge XANES data and probe the speciation of organic carbon in several specimens relevant to cultural heritage and natural history. This methodology enables the measurement to be done in a nondestructive way, in air, and provides information that is not compromised by surface contamination by ensuring that the dominant signal contribution is from the bulk of the probed material. Using the backscattering geometry at large photon momentum transfer maximizes the XRS signal at the given X-ray energy and enhances nondipole contributions compared to conventional XANES, thereby augmenting the speciation sensitivity. The capabilities and limitations of the technique are discussed. As a result, we show that despite its small cross section, for a range of systems the XRS method can provide satisfactory signals at realistic experimental conditions. XRS constitutes a powerful complement to FT-IR, Raman, and conventional XANES spectroscopy, overcoming some of the limitations of these techniques.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Tracking the Local Effect of Fluorine Self-Doping in Anodic TiO 2 Nanotubes

Here, we report herein a study in which we reveal the role of F – incorporated in the very anodic TiO 2 nanotubes prepared electrochemically from a Ti foil using a fluoride based electrolyte. X-ray absorption near edge structure (XANES), resonant X-ray emission spectroscopy (RXES), and X-ray photoelectron spectroscopy (XPS) have been used to examine the as-prepared and the annealed TiO 2 nanotubes. It is found that the additional electron resulting from the substitution of O 2– by self-doped F – in the TiO 2 lattice is localized in the t 2g state. Consequently, a localized Ti 3+ state can be tracked by a d–d energy loss peak with a constant energy of 1.6 eV in the RXES, in contrast to TiO 2 nanostructures where this peak is hardly noticeable when F – is driven out of the lattice upon annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Statistical White-Line Analysis in High-Throughput TXM-XANES for Chemical State Quantification

The transmission X-ray microscopy (TXM) based X-ray absorption near-edge structure (XANES) technique provides three-dimensional mapping of element-specific chemical states at nanometer-scale spatial resolution and micrometer-scale fields of view. However, compared to conventional volume-averaged XANES (VA-XANES) measurements, the inherently small voxel size in TXM-XANES leads to a lower signal-to-noise ratio, making full-spectrum analysis computationally demanding and less robust. Here, we present the structural and compositional conditions for a statistical white-line analysis framework under which chemical state information can be directly extracted from the white-line peak position in voxel spectra without the need for voxel-wise background subtraction or normalization, under well-defined structural and compositional conditions. The method is validated on layered oxide cathode materials, where low-order polynomial fitting accurately reproduces white-line features, and the extracted energy distributions correlate strongly with VA-XANES results. This statistical approach enables high-throughput, dose-efficient, and noise-robust chemical state quantification in TXM-XANES, offering broad applicability to functional materials requiring nanoscale oxidation-state mapping.

TXM↗
DOE OSTI2020

Rapid assessment of structural and compositional changes during early stages of zirconium alloy oxidation

A multimodal chemical imaging approach has been developed and applied to detail the dynamic, atomic-scale changes associated with oxidation of a zirconium alloy (Zircaloy-4). Scanning transmission electron microscopy, a gas-phase reactor chamber attached to an atom probe tomography instrument, and synchrotron-based X-ray absorption near-edge spectroscopy were employed to reveal morphology, composition, crystal, and electronic structure changes that occur during initial stages of oxidation at 300 °C. Oxidation was carried out in 10 mbar O 2 gas for short exposure times of 1 and 5 min. A multilayered oxide film with a cubic ZrO adjacent to the oxide/metal interface, a nanoscopic transition region with a graded composition of ZrO 2-x (where 0 < x < 1), and tetragonal ZrO 2 in the outermost oxide were formed. Partitioning of the major alloying element (tin) to the oxide/metal interface and heterogeneously within the oxide accompanied the development of the layered oxide. Our work provides a rapid, high-throughput approach for detailed characterisation of initial stages of zirconium alloy oxidation at an accelerated time scale, with implications for several other alloy systems.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Alkaline-stable nickel manganese oxides with ideal band gap for solar fuel photoanodes

Combinatorial (photo)electrochemical studies of the (Ni–Mn)O x system reveal a range of promising materials for oxygen evolution photoanodes. X-ray diffraction, quantum efficiency, and optical spectroscopy mapping reveal stable photoactivity of NiMnO 3 in alkaline conditions with photocurrent onset commensurate with its 1.9 eV direct band gap. The photoactivity increases upon mixture with 10–60% Ni 6 MnO 8 providing an example of enhanced charge separation via heterojunction formation in mixed-phase thin film photoelectrodes. Further, density functional theory-based hybrid functional calculations of the band edge energies in this oxide reveal that a somewhat smaller than typical fraction of exact exchange is required to explain the favorable valence band alignment for water oxidation.

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

Mechanism for spontaneous oxygen and hydrogen evolution reactions on CoO nanoparticles

Overall photocatalytic water splitting with a high efficiency of ~5% has recently been observed for CoO nanoparticle suspensions in the absence of an applied bias or co-catalyst. Although experimental measurements indicate that the overall photocatalytic water splitting is caused by optimal band edge alignments with respect to the redox potentials of water, the mechanism by which H 2 and O 2 simultaneously evolve on these nanoparticles is unknown. Here, we used first-principles density functional theory (DFT) calculations to elucidate the mechanisms for the charge separation and H 2 and O 2 evolution on CoO nanoparticles under illumination in aqueous solution. We demonstrated that electrons are driven to the CoO(100) facet and holes are driven to the hydroxylated CoO(111) facet (OH*–CoO(111)) as a result of the built-in potential arising from the difference in the band edge positions on the two facets. Furthermore, based on a set of criteria, depending on if the photoexcited electrons and holes have sufficient energy to overcome the kinetic barrier along the H 2 and O 2 evolution reaction pathways, respectively, on the relevant surface facet, we show that H 2 evolution preferentially occurs on the CoO(100) facet, while O 2 evolution occurs on the OH*–CoO(111) surface. Our understanding of the overall water splitting mechanism on CoO nanoparticles provides a general explanation for the experimentally observed overall water splitting phenomena on a variety of self-standing photocatalysts, including γ-Ga 2 O 3 , Cu 2 O, and KTaO 3 , without an external driving potential or co-catalyst. In addition, we provide a new strategy for designing novel photocatalysts with high efficiency by controlling their surface configurations and morphologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Turbulent electron transport in edge pedestal by electron temperature gradient turbulence

We present a model for turbulent electron thermal transport at the edge pedestal in high (H)-mode plasmas based on electron temperature gradient (ETG) turbulence. A quasi-linear analysis of electrostatic toroidal ETG modes shows that both turbulent electron thermal diffusivity and hyper-resistivity exhibits the Ohkawa scaling in which the radial correlation length of turbulence becomes the order of electron skin depth. Combination of the Ohkawa scales and the plasma current dependence results in a novel confinement scaling inside the pedestal region. It is also shown that ETG turbulence induces a thermoelectric pinch, which may accelerate the density pedestal formation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Cathode fall thickness of abnormal glow discharges between parallel-plane electrodes in different radii at low pressure

In order to investigate the influence of electrode radius on the characteristics of cathode fall thickness, experiments of low-pressure (20 Pa ≤ p ≤ 30 Pa) abnormal glow discharge were carried out between parallel-plane electrodes in different radii keeping gap distance unchanged. Axial distributions of light intensity were obtained from the discharge images captured using a Charge Coupled Device camera. The assumption that the position of the negative glow peak coincides with the edge of cathode fall layer was verified based on a two-dimensional model, and the cathode fall thicknesses, d{sub c}, were calculated from the axial distributions of light intensity. It was observed that the position of peak emission shifts closer to the cathode as current or pressure grows. The dependence of cathode fall thickness on the gas pressure and normalized current J/p{sup 2} was presented, and it was found that for discharges between electrodes in large radius the curves of pd{sub c} against J/p{sup 2} were superimposed on each other, however, this phenomenon will not hold for discharges between the smaller electrodes. The reason for this phenomenon is that the transverse diffusions of charged particles are not the same in two gaps between electrodes with different radii.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca{sub 0.9}La{sub 0.1}FeAs{sub 2}

CaFeAs{sub 2} is a parent compound of recently discovered 112-type iron-based superconductors. It is predicted to be a staggered intercalation compound that naturally integrates both quantum spin Hall insulating and superconducting layers and an ideal system for the realization of Majorana modes. We performed a systematical angle-resolved photoemission spectroscopy and first-principles calculation study of the slightly electron-doped CaFeAs{sub 2}. We found that the zigzag As chain of 112-type iron-based superconductors play a considerable role in the low-energy electronic structure, resulting in the characteristic Dirac-cone like band dispersion as the prediction. Our experimental results further confirm that these Dirac cones only exist around the X but not Y points in the Brillouin zone, breaking the S{sub 4} symmetry at iron sites. Our findings present the compelling support to the theoretical prediction that the 112-type iron-based superconductors might host the topological nontrivial edge states. The slightly electron doped CaFeAs{sub 2} would provide us a unique opportunity to realize and explore Majorana fermion physics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Instability-enhanced transport in low temperature magnetized plasma

It is shown that the transport in low temperature, collisional, bound plasma is enhanced by instabilities at a high magnetic field. While the magnetic field confines the electrons in a stable plasma, the instability completely destroys the confinement such that the transport becomes independent of the magnetic field in the highly magnetized limit. Finally, an analytical expression of the instability-enhanced collision frequency is proposed, based on a magnetic field independent edge-to-center density ratio.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Development of five-moment two-fluid modeling for Z-pinch physics

The Z-pinch m = 0 instability as well as its stabilization by radially sheared axial flow is studied using the nonlinear ideal five-moment twofluid (5M2F) model with an extension of that model to include Braginskii heat and momentum transport. Using the ideal 5M2F model, linear growth rate results are compared with prior work using MHD and Hall MHD. At small normalized wavenumber, 1 < k a < 4 , where a is the effective pinch radius, 5M2F results agree with Hall MHD within 20% in scenarios without radially sheared axial flow. With the sheared flow and focusing on ka = 10/3, agreement with Hall MHD is excellent. In the limit of small ion inertial length, results also match with MHD. A comparison with PIC modeling of shear-free m = 0 stability focuses on a plasma scenario based on recent experimental results. In a scan of mode wavenumber, ideal 5M2F results are qualitatively similar to PIC: the growth rate rises to a peak at a moderate wavenumber and declines at a large wavenumber in contrast to MHD results, which show the saturation of the growth rate with the increasing wavenumber rather than a decline. The peak normalized 5M2F growth rate is &#x3B3; &#x3C4; A = 1.5 , where sA is the Alfven transit time across the pinch. The peak occurs at normalized wavenumber ka = 10. For comparison, PIC results have a peak growth of &#x3B3; &#x3C4; A = 0.77 at ka = 5. Including Braginskiibased closure of the 5M2F model does not qualitatively change the ideal results in this particular case. Nonlinear saturation is studied using the 5M2F model with the dissipative Braginskii-based closure in cases with pinch-edge sheared-flow speed equal to half the Alfven speed. Nonlinear mixing due to the sheared flow yields a quasi-steady state after modest losses of pinch ion inventory and pinch thermal energy, approximately 30% and 10%, respectively. 5M2F modeling captures the essential physics of m = 0 instability and offers a computationally tractable route to high-fidelity modeling of 3D Z-pinch behavior, including m = 1 instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗