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Wang, F.

Publications and source records attributed to Wang, F..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Morphology and Mechanical, Corrosive, and Antibacterial Behaviors of Indirectly Extruded Zn-0.05wt.%Mg-(0.5, 1 wt.%)Ag Alloys

Biodegradable Zn-0.05Mg-(0.5, 1 wt.%) Ag alloy was manufactured by indirectly extruding the alloy ingot at 200 °C with an extrusion ratio of 16:1. Dynamic recrystallization took place during the extrusion process, leading to the formation of equiaxed crystals with twins in both cross-sectional and longitudinal direction. There was no detectable Ag-related phase present except the Mg{sub 2}Zn{sub 11} in the alloys. Tensile strength was increased with an increase in Ag content, reaching 202 MPa when Ag content is 1 wt.%. As-extruded Zn-0.05Mg-0.5Ag showed better corrosion performance with a low corrosion current density of 2.2 A/cm{sup 2} and low corrosion rate of 0.15 mm/year. The antibacterial property improved for both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) by addition of Ag. The antibacterial rates were more than 99% when Ag content is up to 1 wt.%. The biodegradable Zn-Mg-Ag alloys with high antibacterial behavior show great potential in medical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

First beam tests of prototype silicon modules for the CMS High Granularity Endcap Calorimeter

The High Luminosity phase of the Large Hadron Collider will deliver 10 times more integrated luminosity than the existing collider, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry. As part of its upgrade program, the Compact Muon Solenoid collaboration is designing a high-granularity calorimeter (HGCAL) to replace the existing endcap calorimeters. It will feature unprecedented transverse and longitudinal readout and triggering segmentation for both electromagnetic and hadronic sections. The electromagnetic section and a large fraction of the hadronic section will be based on hexagonal silicon sensors of 0.5–1 cm 2 cell size, with the remainder of the hadronic section being based on highly-segmented scintillators with silicon photomultiplier readout. The intrinsic high-precision timing capabilities of the silicon sensors will add an extra dimension to event reconstruction, especially in terms of pileup rejection. First hexagonal silicon modules, using the existing Skiroc2 front-end ASIC developed for CALICE, have been tested in beams at Fermilab and CERN in 2016. Here, we present results from these tests, in terms of system stability, calibration with minimum-ionizing particles and resolution (energy, position and timing) for electrons, and the comparisons of these quantities with GEANT4-based simulation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2018

Performance of the QWIP Focal Plane Array for NASA's Landsat 9 Mission

The flight focal plane array (FPA) for the Thermal Infrared Sensor 2 (TIRS-2) instrument, to be flown on Landsat 9, was built and characterized at NASA Goddard Space Flight Center (GSFC). The FPA was assembled using GaAs quantum well infrared photodetector (QWIP) arrays from the same lot as the TIRS instrument on Landsat 8. Each QWIP array is hybridized to an Indigo ISC9803 readout integrated circuit (ROIC) with 640 x 512, 25µm by 25µm pixels. Each QWIP hybrid was tested at the NASA/GSFC Detector Characterization Laboratory (DCL) as a single sensor chip assembly (SCA). The best SCAs in terms of performance were then built up into an FPA consisting of three SCAs, required to provide the necessary 15-degree field of view of the instrument. The FPA was tested to determine if project requirements were being met as a fully assembled unit. The performance of the QWIP SCAs and the fully assembled, NASA flight-qualified FPA will be reviewed.

Quantum well infrared photodiode↗
DOE OSTI2018

The Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Release Two and Three

This is the second installment for the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey, which includes quasars observed from 2013 September to 2015 June. There are 9024 confirmed quasars in DR2 and 10911 in DR3. After cross-match with the Sloan Digital Sky Survey (SDSS) quasar catalogs and NED, 12126 quasars are discovered independently. Among them, 2225 quasars were released by SDSS DR12 QSO catalog in 2014 after we finalized the survey candidates. 1801 sources were identified by SDSS DR14 as QSOs. The remaining 8100 quasars are considered as newly founded, and among them, 6887 quasars can be given reliable emission line measurements and the estimated black hole masses. Quasars found in LAMOST are mostly located at low-to-moderate redshifts, with a mean value of 1.5. The highest redshift observed in DR2 and DR3 is 5. We applied emission line measurements to Hα, Hβ, Mg ii, and C iv. We deduced the monochromatic continuum luminosities using photometry data, and estimated the virial black hole masses for the newly discovered quasars. Results are compiled into a quasar catalog, which will be available online.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Ultraviolet (UV) Oxidation Final Report CRADA No. TC-0350-92

This CRADA was a collaborative agreement between the above parties to develop a more efficient ultraviolet (UV) oxidation process than the existing commercial processes. The proposed new process would be capable of completely mineralizing the organic constiruents in aqueous mixedwastes (wastes that contain both radioactive and organic constiruents) and converting them into ordinary radioactive wastes, which would mean cheaper and easier disposal.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

Microstructures of chemical vapor deposited high-purity tungsten achieved by two different precursors

Highlights: • CVD tungsten used as electron emitters of thermionic fuel elements was investigated. • Microstructures were characterized with metallography analysis. • The preferred orientation was determined with XRD and EBSD. • The surface morphology was observed with SEM and WLI. • Tungsten via thermolysis of WCl{sub 6} is better for thermionic fuel elements. - Abstract: Chemical vapor deposited (CVD) high-purity tungsten can be manufactured as electron emitters in thermionic fuel elements. Exposed surface planes of the emitter emit electrons and affect the efficiency and load capacity of the thermionic fuel element. In order to determine the electron emission planes of the emitter, the metallurgic structures, the preferred orientation and the as-deposited surface morphology of CVD tungsten have been investigated. In this work, high-purity (over 99.99%) tungsten was achieved by two different precursors: hydrogen reduction of tungsten hexafluoride (WF{sub 6}) and thermolysis of tungsten hexachloride (WCl{sub 6}). The microstructures of CVD tungsten were characterized by metallography analysis, X-ray diffraction (XRD), electron backscattered diffraction (EBSD), and white light interference (WLI). Tungsten fabricated by hydrogen reduction of WF{sub 6} and thermolysis of WCl{sub 6} has <100>-preferred columnar microstructures. However, the latter exhibits larger columnar grains and preferred <100> less. The preferred orientation is caused by the higher growth rate of the <100> orientation and competition between the <100> orientations of different grains. The as-deposited surface consists of tiny pyramids, with <100> axis and {111} side faces. In contrast to tungsten produced by hydrogen reduction of WF{sub 6}, the pyramid on tungsten synthesized via thermolysis of WCl{sub 6} contains small {110} facets on the four edges. Therefore, tungsten made via thermolysis of WCl{sub 6} is a better candidate for thermionic fuel elements, because the higher work function of {110} planes enables better output efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2016

The Pan-STARRS1 distant z > 5.6 quasar survey: More than 100 quasars within the first GYR of the universe

Luminous quasars at z>5.6 can be studied in detail with the current generation of telescopes and provide us with unique information on the first gigayear of the universe. Thus far, these studies have been statistically limited by the number of quasars known at these redshifts. Such quasars are rare, and therefore, wide-field surveys are required to identify them, and multiwavelength data are required to separate them efficiently from their main contaminants, the far more numerous cool dwarfs. In this paper, we update and extend the selection for the z∼6 quasars presented in Bañados et al. (2014) using the Pan-STARRS1 (PS1) survey. We present the PS1 distant quasar sample, which currently consists of 124 quasars in the redshift range 5.6≲z≲6.7 that satisfy our selection criteria. Of these quasars, 77 have been discovered with PS1, and 63 of them are newly identified in this paper. We present the composite spectra of the PS1 distant quasar sample. This sample spans a factor of ∼20 in luminosity and shows a variety of emission line properties. The number of quasars at z>5.6 presented in this work almost doubles the previously known quasars at these redshifts, marking a transition phase from studies of individual sources to statistical studies of the high-redshift quasar population, which was impossible with earlier, smaller samples.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Exascale Storage Systems the SIRIUS Way

As the exascale computing age emerges, data related issues are becoming critical factors that determine how and where we do computing. Popular approaches used by traditional I/O solution and storage libraries become increasingly bottlenecked due to their assumptions about data movement, re-organization, and storage. While, new technologies, such as "burst buffers", can help address some of the short-term performance issues, it is essential that we reexamine the underlying storage and I/O infrastructure to effectively support requirements and challenges at exascale and beyond. In this paper we present a new approach to the exascale Storage System and I/O (SSIO), which is based on allowing users to inject application knowledge into the system and leverage this knowledge to better manage, store, and access large data volumes so as to minimize the time to scientific insights. Central to our approach is the distinction between the data, metadata, and the knowledge contained therein, transferred from the user to the system by describing "utility" of data as it ages.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Landau level splitting in nitrogen-seeded epitaxial graphene

We present a new form of semiconducting graphene grown on C-face silicon carbide, SiC(0001), seeded with a sub-monolayer of nitrogen. This graphene exhibits a gap of 0.3-0.7 eV from the Fermi level to the valence band dependent on lm thickness as measured via angle resolved photo-emission spectroscopy (ARPES). Scanning tunneling microscopy (STM) images imply that the bandgap may be the result of strain-induced confinement. STM indicates that much of the graphene consists of wide at hexagonal plateaus, 8-20 nm2 on average, surrounded by both smooth and disordered folds of length scales from 0.5-2 nm tall, 1-4 nm thick, and 1-20 nm long. The remainder of the surface is covered in smooth or disordered ripples and folds intermixed. Scanning tunneling spectroscopy (STS) measurements on all features show peaks suggestive of Landau levels, and have been analyzed to give pseudo-magnetic field magnitudes. The magnetic lengths associated with these fields are less than the average plateau diameter but comparable to typical fold widths. We consider a growth process whereby the graphene grows pinned to the substrate by the interface nitrogen. The graphene experiences compressive strain as a result of both this pinning as well as competing thermal expansion forces between the substrate and lm. As a result, graphene on nitrogen-seeded SiC has a more concentrated network of strained ripples and folds than seen on C-face SiC graphene without nitrogen.

36 MATERIALS SCIENCE↗