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1,565 Matching Results
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Adsorption and Precipitation of Aqueous Zn(II) on Hematite Nano- and Microparticles
As part of a study of the effect of particle size on reactivity of hematite to aqueous metal ions, the sorption of Zn(II) on hematite nanoparticles and microparticles was examined over a wide range of Zn(II) concentrations using Zn K-edge EXAFS. When reacted with nanoparticles at pH 5.5 and low Zn(II) sorption densities (0.04 {le} {Lambda} < 2.76 imol/m{sup 2}), Zn(II) formed five-coordinated or a mixture of four- and six-coordinated surface complexes with an average Zn-O distance of 2.04({+-}0.02){angstrom}. At pH 5.5 and high Zn(II) sorption densities (2.76 {ge} {Lambda} {le} 3.70 mol/m{sup 2}), formation of surface precipitates is suggested based on the presence of second-shell Zn and multiple scattering features in the Fourier transform (FT) of the EXAFS spectra. EXAFS fitting of these high {Lambda} samples yielded an average first-shell Zn-O distance of 2.10({+-}0.02){angstrom}, with second-shell Zn-Fe and Zn-Zn distances of 3.23({+-}0.03){angstrom} and 3.31({+-}0.03){angstrom}, respectively. Qualitative comparison between the EXAFS spectra of these sorption samples and that of amorphous zinc hydroxide and Zn-bearing hydrotalcite indicates the development of surface precipitates with increasing {Lambda}. EXAFS spectra of Zn(II) sorbed on hematite microparticles under similar experimental conditions showed no evidence for surface precipitates even at the highest Zn surface coverage ({Lambda} …
Date:
December 13, 2006
Creator:
Ha, Juyong; /Stanford U., Geo. Environ. Sci.; Farges, Francois; /Stanford U., Geo. Environ. Sci. /Museum Nat. Hist., Paris; Brown, Gordon E., Jr. & /SLAC, SSRL
Object Type:
Article
System:
The UNT Digital Library
Adsorption Mechanisms of Trivalent Gold onto Iron Oxy-Hydroxides: From the Molecular Scale to the Model
Gold is a highly valuable metal that can concentrate in iron-rich exogenetic horizons such as laterites. An improved knowledge of the retention mechanisms of gold onto highly reactive soil components such as iron oxyhydroxides is therefore needed to better understand and predict the geochemical behavior of this element. In this study, we use EXAFS information and titration experiments to provide a realistic thermochemical description of the sorption of trivalent gold onto iron oxy-hydroxides. Analysis of Au L{sub III}-edge XAFS spectra shows that aqueous Au(III) adsorbs from chloride solutions onto goethite surfaces as inner-sphere square-planar complexes (Au(III)(OH,Cl){sub 4}), with dominantly OH ligands at pH > 6 and mixed OH/Cl ligands at lower pH values. In combination with these spectroscopic results, Reverse Monte Carlo simulations were used to constraint the possible sorption sites on the surface of goethite. Based on this structural information, we calculated sorption isotherms of Au(III) on Fe oxy-hydroxides surfaces, using the CD-MUSIC (Charge Distribution--Multi Site Complexation) model. The various Au(III)-sorbed species were identified as a function of pH, and the results of these EXAFS+CD-MUSIC models are compared with titration experiments. The overall good agreement between the predicted and measured structural models shows the potential of this combined approach …
Date:
December 13, 2006
Creator:
Cances, Benjamin; Benedetti, Marc; Farges, Francois; Brown, Gordon E., Jr. & /Stanford U., Geo. Environ. Sci. /SLAC, SSRL
Object Type:
Article
System:
The UNT Digital Library
Advanced Fuel Cycle Economic Sensitivity Analysis
A fuel cycle economic analysis was performed on four fuel cycles to provide a baseline for initial cost comparison using the Gen IV Economic Modeling Work Group G4 ECON spreadsheet model, Decision Programming Language software, the 2006 Advanced Fuel Cycle Cost Basis report, industry cost data, international papers, the nuclear power related cost study from MIT, Harvard, and the University of Chicago. The analysis developed and compared the fuel cycle cost component of the total cost of energy for a wide range of fuel cycles including: once through, thermal with fast recycle, continuous fast recycle, and thermal recycle.
Date:
December 1, 2006
Creator:
Shropshire, David; Williams, Kent; Smith, J. D. & Boore, Brent
Object Type:
Report
System:
The UNT Digital Library
Advanced Measurement and Modeling Techniques for Improved SOFC Cathodes
The goal of this project was to develop an improved understanding of factors governing performance and degradation of mixed-conducting SOFC cathodes. Two new diagnostic tools were developed to help achieve this goal: (1) microelectrode half-cells for improved isolation of cathode impedance on thin electrolytes, and (2) nonlinear electrochemical impedance spectroscopy (NLEIS), a variant of traditional impedance that allows workers to probe nonlinear rates as a function of frequency. After reporting on the development and efficacy of these tools, this document reports on the use of these and other tools to better understand performance and degradation of cathodes based on the mixed conductor La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (LSC) on gadolinia or samaria-doped ceria (GDC or SDC). We describe the use of NLEIS to measure O{sub 2} exchange on thin-film LSC electrodes, and show that O{sub 2} exchange is most likely governed by dissociative adsorption. We also describe parametric studies of porous LSC electrodes using impedance and NLEIS. Our results suggest that O{sub 2} exchange and ion transport co-limit performance under most relevant conditions, but it is O{sub 2} exchange that is most sensitive to processing, and subject to the greatest degradation and sample-to-sample variation. We recommend further work that focuses on …
Date:
December 31, 2006
Creator:
Adler, Stuart; Dunyushkina, L.; Huff, S.; Lu, Y. & Wilson, J.
Object Type:
Report
System:
The UNT Digital Library
Advanced Multi-Product Coal Utilization By-Product Processing Plant
The objective of the project is to build a multi-product ash beneficiation plant at Kentucky Utilities 2,200-MW Ghent Generating Station, located in Carroll County, Kentucky. This part of the study includes an investigation of the secondary classification characteristics of the ash feedstock excavated from the lower ash pond at Ghent Station. The market study for the products of the processing plant (Subtask 1.6), conducted by Cemex, is reported herein. The study incorporated simplifying assumptions and focused only on pozzolan and ultra fine fly ash (UFFA). It found that the market for pozzolan in the Ghent area was oversupplied, with resultant poor pricing structure. Reachable export markets for the Ghent pozzolan market were mostly locally served with the exception of Florida. It was concluded that a beneficiated material for that market may be at a long term disadvantage. The market for the UFFA was more complex as this material would compete with other beneficiated ash and potential metakaolin and silica fume as well. The study concluded that this market represented about 100,000 tons of sales per year and, although lucrative, represented a widely dispersed niche market.
Date:
December 31, 2006
Creator:
Jackura, Andrew; Groppo, John & Robl, Thomas
Object Type:
Report
System:
The UNT Digital Library
Advanced Test Reactor LEU Fuel Conversion Feasibility Study (2006 Annual Report)
The Advanced Test Reactor (ATR) is a high power density and high neutron flux research reactor operating in the United States. Powered with highly enriched uranium (HEU), the ATR has a maximum thermal power rating of 250 MWth with a maximum unperturbed thermal neutron flux rating of 1.0 x 1015 n/cm2–s. Because of these operating parameters, and the large test volumes located in high flux areas, the ATR is an ideal candidate for assessing the feasibility of converting an HEU driven reactor to a low-enriched core. The present work investigates the necessary modifications and evaluates the subsequent operating effects of this conversion. A detailed plate-by-plate MCNP ATR 1/8th core model was developed and validated for a fuel cycle burnup comparison analysis. Using the current HEU U 235 enrichment of 93.0 % as a baseline, an analysis can be performed to determine the low-enriched uranium (LEU) density and U-235 enrichment required in the fuel meat to yield an equivalent K-eff between the HEU core and the LEU core versus effective full power days (EFPD). The MCNP ATR 1/8th core model will be used to optimize the U-235 loading in the LEU core, such that the differences in K-eff and heat profile …
Date:
December 1, 2006
Creator:
Chang, Gray S.; Ambrosek, Richard G. & Lillo, Misti A.
Object Type:
Report
System:
The UNT Digital Library
Advancing the Science of Natural and Enhanced Attenuation for Chlorinated Solvents
This report summarizes the results of a three-year program that addressed key scientific and technical aspects related to natural and enhanced attenuation of chlorinated organics. The results from this coordinated three-year program support a variety of technical and regulatory advancements. Scientists, regulators, engineers, end-users and stakeholders participated in the program, which was supported by the U.S. Department of Energy (DOE) and the Interstate Technology and Regulatory Council (ITRC). The overarching objective of the effort was to examine environmental remedies that are based on natural processes--remedies such as Monitored Natural Attenuation (MNA) or Enhanced Attenuation (EA). A key result of the recent effort was the general affirmation of the approaches and guidance in the original U.S. Environmental Protection Agency (EPA) chlorinated solvent MNA protocols and directives from 1998 and 1999, respectively. The research program did identify several specific opportunities for advances based on: (1) mass balance as the central framework for attenuation based remedies, (2) scientific advancements and achievements during the past ten years, (3) regulatory and policy development and real-world experience using MNA, and (4) exploration of various ideas for integrating attenuation remedies into a systematic set of ''combined remedies'' for contaminated sites. These opportunities are summarized herein and are …
Date:
December 27, 2006
Creator:
Looney, B.; Early, Thomas O.; Gilmore, Tyler; Chapelle, Francis H.; Cutshall, Norman H.; Ross, Jeff et al.
Object Type:
Report
System:
The UNT Digital Library
Afghanistan: Narcotics and U.S. Policy
This report provides current statistical information, profiles the Afghanistan narcotics trade's participants, explores linkages between narcotics, insecurity, and corruption, and reviews U.S. and international policy responses since late 2001. The report also considers ongoing policy debates regarding the counternarcotics role of coalition military forces, poppy eradication, alternative livelihoods, and funding issues for Congress.
Date:
December 10, 2006
Creator:
Blanchard, Christopher M.
Object Type:
Report
System:
The UNT Digital Library
[After a Fashion, December 29, 2006]
Article about various events that took place in Austin, Texas throughout 2006.
Date:
December 29, 2006
Creator:
Moser, Stephen MacMillan
Object Type:
Article
System:
The UNT Digital Library
Agricultural Issues in the 110th Congress
This report considers the issues the 110th Congress was confronted with in relation to agriculture and the issues inherited from the 109th Congress. The report also includes details about the upcoming farm bill and the usual problems that are examined with the creation of a new farm bill.
Date:
December 11, 2006
Creator:
Chite, Ralph M.
Object Type:
Report
System:
The UNT Digital Library
The Albany News (Albany, Tex.), Vol. 131, No. 28, Ed. 1 Thursday, December 7, 2006
Weekly newspaper from Albany, Texas that includes local, county, and state news along with extensive advertising.
Date:
December 7, 2006
Creator:
Lucas, Melinda L.
Object Type:
Newspaper
System:
The Portal to Texas History
The Albany News (Albany, Tex.), Vol. 131, No. 30, Ed. 1 Thursday, December 14, 2006
Weekly newspaper from Albany, Texas that includes local, county, and state news along with extensive advertising.
Date:
December 14, 2006
Creator:
Lucas, Melinda L.
Object Type:
Newspaper
System:
The Portal to Texas History
The Albany News (Albany, Tex.), Vol. 131, No. 30, Ed. 1 Thursday, December 21, 2006
Weekly newspaper from Albany, Texas that includes local, county, and state news along with extensive advertising.
Date:
December 21, 2006
Creator:
Lucas, Melinda L.
Object Type:
Newspaper
System:
The Portal to Texas History
The Alternative Minimum Tax for Individuals: Legislative Initiatives in the 109th Congress
This report describes the Alternative Minimum Tax (AMT), specifically revenue effects of modifying the AMT and Legislative Initiatives.
Date:
December 28, 2006
Creator:
Esenwein, Gregg A.
Object Type:
Report
System:
The UNT Digital Library
Alternative Mortgages: Risks to Consumers and Lenders in the Current Housing Cycle
This report consists of alternative mortgages: risks to consumers and lenders in the current housing cycle.
Date:
December 27, 2006
Creator:
Murphy, Edward Vincent
Object Type:
Report
System:
The UNT Digital Library
Altus Times (Altus, Okla.), Vol. 108, No. 210, Ed. 1 Friday, December 1, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 1, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Altus Times (Altus, Okla.), Vol. 108, No. 212, Ed. 1 Sunday, December 3, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 3, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Altus Times (Altus, Okla.), Vol. 108, No. 213, Ed. 1 Monday, December 4, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 4, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Altus Times (Altus, Okla.), Vol. 108, No. 214, Ed. 1 Tuesday, December 5, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 5, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Altus Times (Altus, Okla.), Vol. 108, No. 215, Ed. 1 Wednesday, December 6, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 6, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Altus Times (Altus, Okla.), Vol. 108, No. 216, Ed. 1 Thursday, December 7, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 7, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
Altus Times (Altus, Okla.), Vol. 108, No. 217, Ed. 1 Friday, December 8, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 8, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
The Altus Times (Altus, Okla.), Vol. 108, No. 218, Ed. 1 Sunday, December 10, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 10, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History
The Altus Times (Altus, Okla.), Vol. 108, No. 219, Ed. 1 Monday, December 11, 2006
Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date:
December 11, 2006
Creator:
Bush, Michael
Object Type:
Newspaper
System:
The Gateway to Oklahoma History