2,569 research outputs found
PRELIMINARY STUDY OF CERAMICS FOR IMMOBILIZATION OF ADVANCED FUEL CYCLE REPROCESSING WASTES
The Savannah River National Laboratory (SRNL) developed a series of ceramic waste forms for the immobilization of Cesium/Lanthanide (CS/LN) and Cesium/Lanthanide/Transition Metal (CS/LN/TM) waste streams anticipated to result from nuclear fuel reprocessing. Simple raw materials, including Al{sub 2}O{sub 3}, CaO, and TiO{sub 2} were combined with simulated waste components to produce multiphase ceramics containing hollandite-type phases, perovskites (particularly BaTiO{sub 3}), pyrochlores, zirconolite, and other minor metal titanate phases. Identification of excess Al{sub 2}O{sub 3} via X-ray Diffraction (XRD) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) in the first series of compositions led to a Phase II study, with significantly reduced Al{sub 2}O{sub 3} concentrations and increased waste loadings. Three fabrication methodologies were used, including melting and crystallizing, pressing and sintering, and Spark Plasma Sintering (SPS), with the intent of studying phase evolution under various sintering conditions. XRD and SEM/EDS results showed that the partitioning of the waste elements in the sintered materials was very similar, despite varying stoichiometry of the phases formed. The Phase II compositions generally contained a reduced amount of unreacted Al{sub 2}O{sub 3} as identified by XRD, and had phase assemblages that were closer to the initial targets. Chemical composition measurements showed no significant issues with meeting the target compositions. However, volatilization of Cs and Mo was identified, particularly during melting, since sintering of the pressed pellets and SPS were performed at lower temperatures. Partitioning of some of the waste components was difficult to determine via XRD. SEM/EDS mapping showed that those elements, which were generally present in small concentrations, were well distributed throughout the waste forms. Initial studies of radiation damage tolerance using ion beam irradiation at Los Alamos National Laboratory (LANL) showed little if any modification of the material after irradiation. Additional study in this area is needed. Chemical durability was briefly studied using the Product Consistency Test (PCT). Most of the elements measured were retained by the ceramic waste forms, indicating good chemical durability. Cs, Mo, and Rb were released at somewhat higher rates as compared to the matrix components, although benchmark compositions and additional characterization are needed in order to qualify the PCT results
Transport and thermoelectric properties of the LaAlO/SrTiO interface
The transport and thermoelectric properties of the interface between
SrTiO and a 26-monolayer thick LaAlO-layer grown at high
oxygen-pressure have been investigated at temperatures from 4.2 K to 100 K and
in magnetic fields up to 18 T. For 4.2 K, two different electron-like
charge carriers originating from two electron channels which contribute to
transport are observed. We probe the contributions of a degenerate and a
non-degenerate band to the thermoelectric power and develop a consistent model
to describe the temperature dependence of the thermoelectric tensor. Anomalies
in the data point to an additional magnetic field dependent scattering.Comment: 7 pages, 4 figure
Correlated enhancement of Hc2 and Jc in carbon nanotube-doped MgB2
The use of MgB2 in superconducting applications still awaits for the
development of a MgB2-based material where both current-carrying performance
and critical magnetic field are optimized simultaneously. We achieved this by
doping MgB2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in
polycrystalline samples. The optimum nominal DWCNT content for increasing the
critical current density, Jc is in the range 2.5-10%at depending on field and
temperature. Record values of the upper critical field, Hc2(4K) = 41.9 T (with
extrapolated Hc2(0) ~ 44.4 T) are reached in a bulk sample with 10%at DWCNT
content. The measured Hc2 vs T in all samples are successfully described using
a theoretical model for a two-gap superconductor in the dirty limit first
proposed by Gurevich et al.Comment: 12 pages, 3 figure
MSS D Multispectral Scanner System
The development and acceptance testing of the 4-band Multispectral Scanners to be flown on LANDSAT D and LANDSAT D Earth resources satellites are summarized. Emphasis is placed on the acceptance test phase of the program. Test history and acceptance test algorithms are discussed. Trend data of all the key performance parameters are included and discussed separately for each of the two multispectral scanner instruments. Anomalies encountered and their resolutions are included
The establishment of a future NESP dredging research investment framework: NESP TWQ Hub Project 1.9
The purpose of this project was to conduct a facilitated workshop with key researchers and stakeholders to establish priorities for future research investment of the NESP Tropical Water Quality Hub (NESP TWQ) into dredging and disposal of dredged sediments in the GBR.
A recent independent review of potential impacts of dredging on the biological values of the Great Barrier Reef (GBR) identified a number of key knowledge gaps that need to be addressed to improve management of dredging1 activities. That review, together with the findings of the currently underway dredging science node of the Western Australian Marine Institution (WAMSI), informed the subsequent prioritisation of research topics to address the most important knowledge gaps
Josephson supercurrent in a topological insulator without a bulk shunt
A Josephson supercurrent has been induced into the three-dimensional
topological insulator Bi1.5Sb0.5Te1.7Se1.3. We show that the transport in
Bi1.5Sb0.5Te1.7Se1.3 exfoliated flakes is dominated by surface states and that
the bulk conductivity can be neglected at the temperatures where we study the
proximity induced superconductivity. We prepared Josephson junctions with
widths in the order of 40 nm and lengths in the order of 50 to 80 nm on several
Bi1.5Sb0.5Te1.7Se1.3 flakes and measured down to 30 mK. The Fraunhofer patterns
unequivocally reveal that the supercurrent is a Josephson supercurrent. The
measured critical currents are reproducibly observed on different devices and
upon multiple cooldowns, and the critical current dependence on temperature as
well as magnetic field can be well explained by diffusive transport models and
geometric effects
Bogoliubov - de Gennes versus Quasiclassical Description of Josephson Structures
The applicability of the quasiclassical theory of superconductivity in
Josephson multi-layer structures is analyzed. The quasiclassical approach is
compared with the exact theory based on the Bogoliubov - de Gennes equation.
The angle and energy resolved (coarse-grain) currents are calculated using both
techniques. It is shown that the two approaches agree in geometries
after the coarse-grain averaging. A quantitative discrepancy, which exceeds the
quasiclassical accuracy, is observed when three or more interfaces are present.
The invalidity of the quasiclassical theory is attributed to the presence of
closed trajectories formed by sequential reflections on the interfaces.Comment: revtex4,12 pages, 12 figure
High Resolution Spectroscopy of the X-ray Photoionized Wind in Cygnus X-3 with the Chandra High Energy Transmission Grating Spectrometer
We present a preliminary analysis of the 1--10 keV spectrum of the massive
X-ray binary Cyg X-3, obtained with the High Energy Transmission Grating
Spectrometer on the Chandra X-ray Observatory. The source reveals a richly
detailed discrete emission spectrum, with clear signatures of
photoionization-driven excitation.
Among the spectroscopic novelties in the data are the first astrophysical
detections of a number of He-like 'triplets' (Si, S, Ar) with emission line
ratios characteristic of photoionization equilibrium, fully resolved narrow
radiative recombination continua of Mg, Si, and S, the presence of the H-like
Fe Balmer series, and a clear detection of a ~ 800 km/s large scale velocity
field, as well as a ~1500 km/s FWHM Doppler broadening in the source. We
briefly touch on the implications of these findings for the structure of the
Wolf-Rayet wind.Comment: 11 pages, 3 figures; Accepted for publication in ApJ Letter
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