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  • 1
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    An efficient and positivity-preserving layer method for modeling radiation belt diffusion processes (2016)
    Wiley
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    Publication Date: 2016-01-08
    Description: An efficient and positivity-preserving layer method is introduced to solve the radiation belt diffusion equation and is applied to study the bounce resonance interaction between relativistic electrons and magnetosonic waves. The layer method with linear interpolation, denoted by LM-L (layer method-linear), requires the use of a large number of grid points to ensure accurate solutions. We introduce a monotonicity- and positivity-preserving cubic interpolation method to be used with the Milstein-Tretyakov layer method. The resulting method, called LM-MC (layer method-monotone cubic), can be used to solve the radiation belt diffusion equation with a much smaller number of grid points than LM-L, while still being able to preserve the positivity of the solution. We suggest that LM-MC can be used to study long-term dynamics of radiation belts. We then develop a 2D LM-MC code and use it to investigate the bounce resonance diffusion of radiation belt electrons by magnetosonic waves. Using a previously published magnetosonic wave model, we demonstrate that bounce resonance with magnetosonic waves is as important as gyro-resonance; both can cause several orders of magnitude increase of MeV electron fluxes within one day. We conclude that bounce resonance with magnetosonic waves should be taken into consideration together with gyro-resonance.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Glass production rate in electric furnaces for radioactive waste vitrification (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Correlating the melting rates of feeds in electric melters with results of simple laboratory experiments can help evaluate melter feed additives and their effects on melting rate, and support the feed scheduling and plant operation. A recently proposed melting rate correlation (MRC) equation, relating the melting rate to melt viscosity, feed‐to‐glass conversion heat, and cold‐cap bottom temperature, was tested using data from experiments covering various feed compositions and melter operating parameters. The MRC equation is shown to reasonably represent the measured data and thus can be used to quantify how individual variables (melt viscosity, cold‐cap bottom temperature, conversion heat, melter operating temperature, and bubbling flux) affect the glass production rate.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 3
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    Heat transfer from glass melt to cold cap: Gas evolution and foaming (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract In electric melters, the conversion heat is transferred through the foam layer at the cold‐cap bottom. Understanding cold‐cap foaming is thus important for enhancing the efficiency of both commercial and waste glass melters as well as for the development of advanced batch‐to‐glass conversion models. Observing foam behavior is still impossible “in situ,” that is, directly, in glass melters. To investigate the feed foaming behavior in laboratory conditions, we employed the feed volume expansion test, evolved gas analysis, and thermogravimetry. Combining these techniques helps assess the cold‐cap bottom temperature that directly influences the temperature gradient at the melt/cold‐cap interface, and thus the rate of melting. We also discuss the behavior of cavities formed by coalescing primary foam bubbles and ascending secondary bubbles.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 4
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    Formation of Technetium Salts in Hanford Low-Activity Waste Glass (2016)
    Wiley
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    Publication Date: 2016-08-23
    Description: The distribution and physical form of technetium in a Hanford low-activity waste (LAW) glass was examined with scanning electron microscopy (SEM) and X-ray diffraction (XRD). A simulated Hanford LAW glass was spiked with varying amounts of potassium pertechnetate and melted at 1000°C. The glass was melted in a sealed quartz ampoule with the air pumped out, so that volatile material could leave the glass but would not be lost from the system. Previous studies have shown that technetium remains in the glass up to about 2000 ppm, but rises to the top of the melt as a separate salt phase above this concentration. Examination by SEM shows that crystals of technetium compounds appear to grow out of the hot glass, which implies that the hot glass was supersaturated in technetium salts. Some of the technetium compound crystals had apparently melted, but other crystals had obviously not melted and must have formed after the glass had partially cooled. The technetium compounds in the salt layer are KTcO 4 and NaTcO 4 , according to SEM and XRD. No TcO 2 was found in the salt phase, even though Tc(IV) has been previously reported in the glass.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
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    Effect of sucrose on foaming and melting behavior of a low‐activity waste melter feed (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Reductants, such as sucrose (C12H22O11), are added to nuclear waste melter feeds containing high fractions of nitrates and nitrites to reduce excessive foaming during feed‐to‐glass conversion, decrease sulfate segregation, and increase technetium retention. The effect of sucrose on foaming and melting reactions during the conversion was examined using the feed volume expansion test, thermogravimetric analysis, evolved gas analysis, x‐ray diffraction, and scanning electron microscopy with energy dispersive x‐ray spectrometry. Different amounts of sucrose were added to vary the carbon to nitrogen (C/N) ratio in the melter feed. As the C/N ratio increased, the extent of foaming decreased, and the N2/NO ratio increased in the evolved gas. Significant foam suppression, rapid gas release at approximately 250°C, and reduction in transition metal oxides were observed at C/N 〉 1.1.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 6
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    A diagnostic equation for the daily maximum urban heat island effect for cities in northwestern Europe (2016)
    Wiley
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    Publication Date: 2016-04-25
    Description: ABSTRACT The urban heat island (UHI) effect, defined as the air temperature difference between the urban canyon and the nearby rural area, is investigated. Because not all cities around the world are equipped with an extensive measurement network, a need exists for a relatively straightforward equation for the UHI effect. Here, we derive a simple, diagnostic equation for the UHI using dimensional analysis. This equation provides a first-order estimation of the daily maximum UHI based on routine meteorological observations and straightforward urban morphological properties. The equation is tested for 14 cities across northwestern Europe and appears to be robust. The comprehensiveness of this analytical equation allows for applications beyond urban meteorological studies.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 7
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    Conversion of Nuclear Waste to Molten Glass: Cold-Cap Reactions in Crucible Tests (2016)
    Wiley
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    Publication Date: 2016-05-24
    Description: The feed-to-glass conversion, which comprises complex chemical reactions and phase transitions, occurs in the cold cap during nuclear waste vitrification. To investigate the conversion process, we analyzed heat-treated samples of a simulated high-level waste feed using X-ray diffraction, electron probe microanalysis, leaching tests, and residual anion analysis. Feed dehydration, gas evolution, and borate phase formation occurred at temperatures below 700°C before the emerging glass-forming melt was completely connected. Above 700°C, intermediate aluminosilicate phases and quartz particles gradually dissolved in the continuous borosilicate melt, which expanded with transient foam. Knowledge of the chemistry and physics of feed-to-glass conversion will help us control the conversion path by changing the melter feed makeup to maximize the glass production rate.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 8
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    Modeling radiation belt dynamics using a 3D layer method code (2017)
    Wiley
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    Publication Date: 2017-08-16
    Description: A new 3D diffusion code using a recently published layer method has been developed to analyze radiation belt electron dynamics. The code guarantees the positivity of the solution even when mixed diffusion terms are included. Unlike most of previous codes, our 3D code is developed directly in equatorial pitch angle ( α 0 ), momentum ( p ), and L -shell coordinates; this eliminates the need to transform back and forth between ( α 0 , p ) coordinates and adiabatic invariant coordinates. Using ( α 0 , p , L ) is also convenient for direct comparison with satellite data. The new code has been validated by various numerical tests, and we apply the 3D code to model the rapid electron flux enhancement following the geomagnetic storm on March 17, 2013, which is one of the GEM Focus Group challenge events. An event-specific global chorus wave model, an AL-dependent statistical plasmaspheric hiss wave model, and a recently published radial diffusion coefficient formula from Time History of Events and Macroscale Interactions during Substorms (THEMIS) statistics are used. The simulation results show good agreement with satellite observations in general, supporting the scenario that the rapid enhancement of radiation belt electron flux for this event results from an increased level of the seed population by radial diffusion, with subsequent acceleration by chorus waves. Our results prove that the layer method can be readily used to model global radiation belt dynamics in three dimensions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Effects of Heating Rate, Quartz Particle Size, Viscosity, and Form of Glass Additives on High-Level Waste Melter Feed Volume Expansion (2016)
    Wiley
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    Publication Date: 2016-11-01
    Description: Nuclear waste can be vitrified by mixing it with glass-forming and -modifying additives. The resulting feed is charged into an electric glass melter. To comprehend melting behavior of a high-alumina melter feed, we monitored the volume expansion of pellets in response to heating at different heating rates. The feeds were prepared with different particle sizes of quartz (the major additive component) and with varied silica-to-fluxes ratio to investigate the glass melt viscosity effects. Also, we used additional melter feeds with additives premelted into glass frit. The volume of pellets was nearly constant at temperatures 〈600°C. After a short period of volume shrinkage at ~600°C–700°C, foam generation produced massive volume expansion. The low heat conductivity of foam hinders the transfer of heat from molten glass to the reacting feed. The extent of foaming increased with faster heating and higher melt viscosity, and decreased with increasing size of quartz particles and fritting of the additives. Volume expansion data are needed for the mathematical modeling of the cold cap.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
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    Photochemical determination of O densities in the Martian thermosphere: Effect of a revised rate coefficient (2017)
    Wiley
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    Publication Date: 2017-08-05
    Description: We investigate the production and loss rates of O 2 + in the photochemical equilibrium region of the Martian ionosphere near the subsolar point. We adopt neutral and ion densities measured by the MAVEN NGIMS, electron densities and temperatures measured by the LPW, and ion temperatures measured by the STATIC instruments on the MAVEN spacecraft. Contrary to the conventional wisdom, we find that loss of O 2 + by dissociative recombination is balanced mainly by production due to the reaction of O + with CO 2 , with a smaller contribution due to the reaction of CO 2 + with O. We find that the O densities derived from this calculation are larger than those measured by the NGIMS instrument by a factor that averages about 4 over the range 130–155 km. This general conclusion is supported by a newly measured rate coefficient for the reaction of O with CO 2 + , which is smaller by a factor of about six than the only value in the literature, which was measured forty-seven years ago.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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