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Self-diffusion of Pb210 and Cl36 in Molten PbCl2-KCl Mixtures in the Region of the Compound 2PbCl2-KCl

Description: The specific goal of the investigation was the measurement, as a function of temperature, of the self-diffusion coefficients of Pb210 and Cl36 in PbCl2-KCl compositions in the region of the first compound, and to calculate from these data the activation energy necessary for the diffusion of these ions.
Date: June 1960
Creator: Tidwell, Troy Haskell
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Impurity Diffusion Coefficients of Al and Zn in Mg Determined from Solid-to-Solid Diffusion Couples

Description: Increasing use and development of lightweight Mgalloys have led to the desire for more fundamental research in and understanding of Mg-based systems. As property enhancing components, Al and Zn are two of the most important and common alloying elements for Mg-alloys. We have investigated the concentration dependent interdiffusion of Al and Zn in Mg using diffusion couples of pure polycrystalline Mg mated to Mg solid solutions containing either <9 at.% Al or <3 at.% Zn. Concentration profiles were determined by electron micro-probe microanalysis of the diffusion zone. The interdiffusion coefficients were determined by the classical Boltzmann-Matano method within the Mg solid solution. As the concentration of Al or Zn approaches the dilute ends, we employ an analytical approach based on the Hall method to estimate the impurity diffusion coefficients. Results of Al and Zn impurity diffusion in Mg are reported and compared to published impurity diffusion coefficients typically determined by thin film techniques.
Date: August 1, 2013
Creator: Kammerer, Catherine; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Perry, Kelly A; Belova, Irina; Murch, Prof. Graeme et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Experimental Investigation of Radio-Turbulence Induced Diffusion -- Final Report

Description: The outcome of this research project suggests that the transport of radon in water is significantly greater than that predicted solely by molecular diffusion. The original study was related to the long term storage of {sup 226}Ra-bearing sand at the DOE Fernald site and determining whether a barrier of water covering the sand would be effective in reducing the emanation of {sup 222}Rn from the sand. Initial observations before this study found the transport of radon in water to be greater than that predicted solely by molecular diffusion. Fick's law on diffusion was used to model the transport of radon in water including the impact associated with radioactive decay. Initial measurements suggested that the deposition of energy in water associated with the radioactive decay process influences diffusion and enhances transport of radon. A multi-region, one-dimensional, steady-state transport model was used to analyze the movement of radon through a sequential column of air, water and air. An effective diffusion coefficient was determined by varying the thickness of the water column and measuring the time for transport of {sup 222}Rn through of the water barrier. A one-region, one-dimensional transient diffusion equation was developed to investigate the build up of radon at the end of the water column to the time when a steady-state, equilibrium condition was achieved. This build up with time is characteristic of the transport rate of radon in water and established the basis for estimating the effective diffusion coefficient for {sup 222}Rn in water. Several experiments were conducted using different types and physical arrangements of water barriers to examine how radon transport is influenced by the water barrier. Results of our measurements confirm our theoretical analyses which suggest that convective forces other than pure molecular diffusion impact the transport of {sup 222}Rn through the water barrier. An effective diffusion …
Date: July 7, 2005
Creator: Spitz, H. B. & Usman, S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Mega et al. Reply

Description: This article is a reply to a comment by A. Helmstetter and D. Sornette about the article 'Power-Law Time Distribution of Large Earthquakes' from 2003.
Date: March 26, 2004
Creator: Mega, Mirko S.; Allegrini, Paolo; Grigolini, Paolo; Latora, Vito; Palatella, Luigi; Rapisarda, Andrea et al.
Item Type: Refine your search to only Article
Partner: UNT College of Arts and Sciences
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Timescales of spherulite crystallization in obsidian inferred from water concentration profiles

Description: We determined the kinetics of spherulite growth in obsidians from Krafla volcano, Iceland. We measured water concentration profiles around spherulites in obsidian by synchrotron Fourier transform infrared spectroscopy. The distribution of OH? groups surrounding spherulites decreases exponentially away from the spherulite-glass border, reflecting expulsion of water during crystallization of an anhydrous paragenesis (plagioclase + SiO2 + clinopyroxene + magnetite). This pattern is controlled by a balance between the growth rate of the spherulites and the diffusivity of hydrous solute in the rhyolitic melt. We modeled advective and diffusive transport of the water away from the growing spherulites by numerically solving the diffusion equation with a moving boundary. Numerical models fit the natural data best when a small amount of post-growth diffusion is incorporated in the model. Comparisons between models and data constrain the average spherulite growth rates for different temperatures and highlight size-dependent growth among a small population of spherulites.
Date: June 25, 2008
Creator: Castro, Jonathan M.; Beck, Pierre; Tuffen, Hugh; Nichols, Alexander R.L.; Dingwell, Donald B. & Martin, Michael C
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Sulfidation of Cadmium at the Nanoscale

Description: We investigate the evolution of structures that result when spherical Cd nanoparticles of a few hundred nanometers in diameter react with dissolved molecular sulfur species in solution to form hollow CdS. Over a wide range of temperatures and concentrations, we find that rapid Cd diffusion through the growing CdS shell localizes the reaction front at the outermost CdS/S interface, leading to hollow particles when all the Cd is consumed. When we examine partially reacted particles, we find that this system differs significantly from others in which the nanoscale Kirkendall effect has been used to create hollow particles. In previously reported systems, partial reaction creates a hollow particle with a spherically symmetric metal core connected to the outer shell by filaments. In contrast, here we obtain a lower symmetry structure, in which the unreacted metal core and the coalesced vacancies separate into two distinct spherical caps, minimizing the metal/void interface. This pattern of void coalescence is likely to occur in situations where the metal/vacancy self-diffusivities in the core are greater than the diffusivity of the cations through the shell.
Date: May 22, 2008
Creator: Cabot, Andreu; Smith, Rachel; Yin, Yadong; Zheng, Haimei; Reinhard, Bjorn; Liu, Haitao et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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A Simple Single Step diffusion and Emitter Etching Process for High Efficiency Gallium Antimonide Thermophotovoltaic Devices

Description: A single step diffusion followed by precise etching of the diffused layer has been developed to obtain a diffusion profile appropriate for high efficiency GaSb thermophotovoltaic cells. The junction depth was controlled through monitoring of light current-voltage (I-V) curves (photovoltaic response) during the post diffusion emitter etching process. The measured photoresponses (prior to device fabrication) have been correlated with the quantum efficiencies and the open circuit voltages in the fabricated devices. An optimum junction depth for obtaining highest quantum efficiency and open circuit voltage is presented based on diffusion lengths (or monitoring carrier lifetimes), carrier mobility and typical diffused impurity profile in GaSb.
Date: August 29, 2003
Creator: Rajagopalan, G.; Reddy, N. S.; Ehsani, E.; Bhat, I. B.; Dutta, P. S.; Gutmann, R. J. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Measurement of lateral charge diffusion in thick, fully depleted, back-illuminated CCDs

Description: Lateral charge diffusion in back-illuminated CCDs directly affects the point spread function (PSF) and spatial resolution of an imaging device. This can be of particular concern in thick, back-illuminated CCDs. We describe a technique of measuring this diffusion and present PSF measurements for an 800 x 1100, 15 mu m pixel, 280 mu m thick, back-illuminated, p-channel CCD that can be over-depleted. The PSF is measured over a wavelength range of 450 nm to 650 nm and at substrate bias voltages between 6 V and 80 V.
Date: June 30, 2004
Creator: Karcher, Armin; Bebek, Christopher J.; Kolbe, William F.; Maurath, Dominic; Prasad, Valmiki; Uslenghi, Michela et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Diffusion of Xenon in Columbium

Description: The diffusion coefficient was calculated for the diffusion of Xe through Nb and found to be 0.064 exp (-18,600/RT).
Date: November 20, 1959
Creator: Gregory, D. P. (Derek P.) & Leavenworth, H. W. (Howard W.)
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Advances in radiation modeling in ALEGRA :a final report for LDRD-67120, efficient implicit mulitgroup radiation calculations.

Description: The original LDRD proposal was to use a nonlinear diffusion solver to compute estimates for the material temperature that could then be used in a Implicit Monte Carlo (IMC) calculation. At the end of the first year of the project, it was determined that this was not going to be effective, partially due to the concept, and partially due to the fact that the radiation diffusion package was not as efficient as it could be. The second, and final year, of the project focused on improving the robustness and computational efficiency of the radiation diffusion package in ALEGRA. To this end, several new multigroup diffusion methods have been developed and implemented in ALEGRA. While these methods have been implemented, their effectiveness of reducing overall simulation run time has not been fully tested. Additionally a comprehensive suite of verification problems has been developed for the diffusion package to ensure that it has been implemented correctly. This process took considerable time, but exposed significant bugs in both the previous and new diffusion packages, the linear solve packages, and even the NEVADA Framework's parser. In order to manage this large suite of problem, a new tool called Tampa has been developed. It is a general tool for automating the process of running and analyzing many simulations. Ryan McClarren, at the University of Michigan has been developing a Spherical Harmonics capability for unstructured meshes. While still in the early phases of development, this promises to bridge the gap in accuracy between a full transport solution using IMC and the diffusion approximation.
Date: November 1, 2005
Creator: Mehlhorn, Thomas Alan; Kurecka, Christopher J. (University of Michigan, Ann Arbor, MI); McClarren, Ryan (University of Michigan, Ann Arbor, MI); Brunner, Thomas A. & Holloway, James Paul (University of Michigan, Ann Arbor, MI)
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Flux Control in Networks of Diffusion Paths

Description: A class of optimization problems in networks of intersecting diffusion domains of a special form of thin paths has been considered. The system of equations describing stationary solutions is equivalent to an electrical circuit built of intersecting conductors. The solution of an optimization problem has been obtained and extended to the analogous electrical circuit. The interest in this network arises from, among other applications, an application to wave-particle diffusion through resonant interactions in plasma.
Date: July 8, 2009
Creator: Fisch, A. I. Zhmoginov and N. J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Moisture Transport in Silica Gel Particle Beds: I. Theoretical Study

Description: Diffusion mechanisms of moisture within silica gel particles are investigated. It is found that for microporous silica gel surface diffusion is the dominant mechanism of moisture transport, while for macroporous silica gel both Knudsen and surface diffusion are important.
Date: August 1, 1986
Creator: Pesaran, A. A. & Mills, A. F.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Diffusion and precipitation of inert gases in metals. Final report

Description: The behavior of inert gases, particularly helium, in metals was studied in aluminum, copper, niobium and stainless steel. Emphasis was upon characterizing the state of helium in the metals and upon following the kinetics of precipitation and coalescence. Experimental techniques that are, in most cases, new to studies of inert gases in metals were employed. These include low- temperature specific heat, precision lattice parameter measurement, internal friction, computer simulation, and residual resistivit gamma , in addition to confirmatory electron microscopy. The single most important finding is that bubble coalescence takes place at rates which are much slower than was previously supposed and that the slow coalescence fits a model in which the bubble mobility required for coalescence is rate-limited by nucleation of facets on the bubble surface. The further understanding and subsequent potential ability to control rates of bubble and/or void coalescence will be important to the design of nuclear fuel and cladding materials. (auth)
Date: September 25, 1973
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Self-Diffusion in Gamma Uranium

Description: The self-diffusion coefficient or uranium was measured at four temperatures in the gamma phase. The data are fitted by an Arrhenius-tyoe equation D = 2.33 x well with previously reported results. The value of D/sub o/ is lower than that predicted by Zener's theory, and the activation energy is much less than the value expected from various empirical codelations. (auth)
Date: July 1, 1959
Creator: Rothman, S. J.; Lloyd, L. T.; Weil, R. & Harkness, A. L.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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