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RHEOLOGICAL AND ELEMENTAL ANALYSES OF SIMULANT SB5 SLURRY MIX EVAPORATOR-MELTER FEED TANK SLURRIES

Description: The Defense Waste Processing Facility (DWPF) will complete Sludge Batch 5 (SB5) processing in fiscal year 2010. DWPF has experienced multiple feed stoppages for the SB5 Melter Feed Tank (MFT) due to clogs. Melter throughput is decreased not only due to the feed stoppage, but also because dilution of the feed by addition of prime water (about 60 gallons), which is required to restart the MFT pump. SB5 conditions are different from previous batches in one respect: pH of the Slurry Mix Evaporator (SME) product (9 for SB5 vs. 7 for SB4). Since a higher pH could cause gel formation, due in part to greater leaching from the glass frit into the supernate, SRNL studies were undertaken to check this hypothesis. The clogging issue is addressed by this simulant work, requested via a technical task request from DWPF. The experiments were conducted at Aiken County Technology Laboratory (ACTL) wherein a non-radioactive simulant consisting of SB5 Sludge Receipt and Adjustment Tank (SRAT) product simulant and frit was subjected to a 30 hour SME cycle at two different pH levels, 7.5 and 10; the boiling was completed over a period of six days. Rheology and supernate elemental composition measurements were conducted. The caustic run exhibited foaming once, after 30 minutes of boiling. It was expected that caustic boiling would exhibit a greater leaching rate, which could cause formation of sodium aluminosilicate and would allow gel formation to increase the thickness of the simulant. Xray Diffraction (XRD) measurements of the simulant did not detect crystalline sodium aluminosilicate, a possible gel formation species. Instead, it was observed that caustic conditions, but not necessarily boiling time, induced greater thickness, but lowered the leach rate. Leaching consists of the formation of metal hydroxides from the oxides, formation of boric acid from the boron oxide, and dissolution ...
Date: February 8, 2010
Creator: Fernandez, A.
Partner: UNT Libraries Government Documents Department

Magnetic domain structure and magnetization reversal in submicron-scale Co dots

Description: We present a magnetic force microscopy (MFM) analysis of arrays of submicron-scale Co dots fabricated by interference lithography. The dots are thin (180-300 A) and are elliptical in shape. MFM of these structures reveals that they relax into highly ordered remanent states whose symmetry and configuration are governed by their shape anisotropy. In particular, when the dots are saturated along the easy-axis, a uniformly magnetized state persists at remanence. However, when the dots are saturated in hard-axis, they relax into a single-vortex state in which the circulation can have either sign. Both remanent states are characterized by smoothly varying magnetization patterns and a high degree of uniformity across the array. We attribute the ordered behavior of these structures to the film microstructure, which allows the shape anisotropy to dominate over magnetocrystalline anisotropy. By imaging a series of minor-loop remanent states, we show that magnetization reversal in these structures occurs via the nucleation and annihilation of a single vortex. Magnetic hysteresis loop measurements are consistent with these observations and provide additional details. Furthermore, we present the results of micromagnetic simulations, which are in excellent agreement with both the MFM images and the hysteresis loop measurements.
Date: February 17, 1998
Creator: Fernandez, A.
Partner: UNT Libraries Government Documents Department

Sludge Batch Supplemental Srat Runs Effects of Yield Stress and Cycle Time Increase

Description: The Defense Waste Processing Facility (DWPF) has transitioned from Sludge Batch 5 (SB5) processing to Sludge Batch 6 (SB6) processing. Phase III-Tank 40 Chemical Process Cell (CPC) flowsheet simulations have been completed to determine the initial processing conditions for the DWPF transition. The impact of higher yield stress (SB-25) and cycle time extension (SB6-26) on the physical and chemical effects of SB6 processing during the SRAT (Sludge Receipt and Adjustment Tank) cycle were evaluated. No significant impacts on the SRAT chemistry were noted during the higher yield stress run. In particular, no impact on mercury stripping was noted, indicating that settling of elemental mercury was not the primary factor in the low mercury recovery noted in the flowsheet testing. The SRAT product from this run retained the higher yield stress of the starting sludge. The run indicated that ultrasonication is an effective tool to increase the yield stress of simulants to targeted values and the chemistry of downstream processing is not impacted. Significant differences were noted in the cycle time extension test compared to the Phase III flowsheet baseline runs. Large decreases in the ammonia and hydrogen generation rates were noted along with reduced mercury stripping efficiency. The latter effect is similar to that of operating under a high acid stoichiometry. It is conceivable that, under the distinctly different conditions of high formic acid concentration (high acid run) or slow formic acid addition (extended run), that mercury could form amalgams with noble metals, possibly rendering both inert. Thus, the removal of free mercury and noble metals could decrease the rate of catalytic formic acid reactions which would decrease generation of ammonium and hydrogen. The potential underlying reasons for the behavior noted during this run would require additional testing.
Date: August 10, 2010
Creator: Fernandez, A.
Partner: UNT Libraries Government Documents Department

Size reduction of complex networks preserving modularity

Description: The ubiquity of modular structure in real-world complex networks is being the focus of attention in many trials to understand the interplay between network topology and functionality. The best approaches to the identification of modular structure are based on the optimization of a quality function known as modularity. However this optimization is a hard task provided that the computational complexity of the problem is in the NP-hard class. Here we propose an exact method for reducing the size of weighted (directed and undirected) complex networks while maintaining invariant its modularity. This size reduction allows the heuristic algorithms that optimize modularity for a better exploration of the modularity landscape. We compare the modularity obtained in several real complex-networks by using the Extremal Optimization algorithm, before and after the size reduction, showing the improvement obtained. We speculate that the proposed analytical size reduction could be extended to an exact coarse graining of the network in the scope of real-space renormalization.
Date: December 24, 2008
Creator: Arenas, A.; Duch, J.; Fernandez, A. & Gomez, S.
Partner: UNT Libraries Government Documents Department

Analysis of the structure of complex networks at different resolution levels

Description: Modular structure is ubiquitous in real-world complex networks, and its detection is important because it gives insights in the structure-functionality relationship. The standard approach is based on the optimization of a quality function, modularity, which is a relative quality measure for a partition of a network into modules. Recently some authors have pointed out that the optimization of modularity has a fundamental drawback: the existence of a resolution limit beyond which no modular structure can be detected even though these modules might have own entity. The reason is that several topological descriptions of the network coexist at different scales, which is, in general, a fingerprint of complex systems. Here we propose a method that allows for multiple resolution screening of the modular structure. The method has been validated using synthetic networks, discovering the predefined structures at all scales. Its application to two real social networks allows to find the exact splits reported in the literature, as well as the substructure beyond the actual split.
Date: February 28, 2008
Creator: Arenas, A.; Fernandez, A. & Gomez, S.
Partner: UNT Libraries Government Documents Department

A coupled THMC model of a heating and hydration laboratory experiment in unsaturated compacted FEBEX bentonite

Description: Unsaturated compacted bentonite is foreseen by several countries as a backfill and sealing material in high-level radioactive waste repositories. The strong interplays between thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes during the hydration stage of a repository call for fully coupled THMC models. Validation of such THMC models is prevented by the lack of comprehensive THMC experiments and the difficulties of experimental methods to measure accurately the chemical composition of bentonite porewater. We present here a non-isothermal multiphase flow and multicomponent reactive solute transport model for a deformable medium of a heating and hydration experiment performed on a sample of compacted FEBEX bentonite. Besides standard solute transport and geochemical processes, the model accounts for solute cross diffusion and thermal and chemical osmosis. Bentonite swelling is solved with a state-surface approach. The THM model is calibrated with transient temperature, water content and porosity data measured at the end of the experiment. The reactive transport model is calibrated with porewater chemical data derived from aqueous extract data. Model results confirm that thermal osmosis is relevant for the hydration of FEBEX bentonite while chemical osmosis can be safely neglected. Dilution and evaporation are the main processes controlling the concentration of conservative species. Dissolved cations are mostly affected by calcite dissolution-precipitation and cation exchange reactions. Dissolved sulphate is controlled by gypsum/anhydrite dissolution-precipitation. pH is mostly buffered by protonation/deprotonation via surface complexation. Computed concentrations agree well with inferred aqueous extract data at all sections except near the hydration boundary where cation data are affected by a sampling artifact. The fit of Cl{sup -} data is excellent except for the data near the heater. The largest deviations of the model from inferred aqueous extract data occur for dissolved SO{sub 4}{sup 2-} which is underpredicted by the model. There are uncertainties on the amount ...
Date: May 1, 2010
Creator: Zheng, L.; Samper, J.; Montenegro, L. & Fernandez, A.M.
Partner: UNT Libraries Government Documents Department

Report of preliminary analysis of data from dew-point hygrometer profiles during the ARM 1996 WVIOP

Description: Unique commercial light-weight chilled-mirror dew-point sensors were flown on tethered balloons during the Water Vapor Intensive Operation Period (WVIOP) in September 1996. Comparisons were made between in situ and remote sensing instruments that detect water vapor. We obtained a special waiver to fly the sensors up to 1 km both day and night from the FAA. Preliminary comparisons with tower mounted, surface-based temperature/relative humidity probes, rawinsonde, air-borne chilled-mirror dew point, and Raman lidar profiles are included. Profiles during nocturnal boundary layer wind jet occurrences are presented as special cases along with balloon-borne nephelometer light scattering profile comparisons.
Date: March 1, 1997
Creator: Porch, W.; Fernandez, A. & Spurgeon, W.
Partner: UNT Libraries Government Documents Department

Scaling behavior in interference lithography

Description: Interference lithography is an emerging, technology that provides a means for achieving high resolution over large exposure areas (approximately 1 m{sup 2}) with virtually unlimited depth of field. One- and two-dimensional arrays of deep submicron structures can be created using near i-line wavelengths and standard resist processing. In this paper, we report on recent advances in the development of this technology, focusing, in particular, on how exposure latitude and resist profile scale with interference period We present structure width vs dose curves for periods ranging from 200 nm to 1 um, demonstrating that deep submicron structures can be generated with exposure latitudes exceeding 30%. Our experimental results are compared to simulations based on PROLITIV2.
Date: February 27, 1998
Creator: Agayan, R.R.; Banyai, W.C. & Fernandez, A.
Partner: UNT Libraries Government Documents Department

Continuosly Stirred Tank Reactor Parameters That Affect Sludge Batch 6 Simulant Properties

Description: The High Level Radioactive Waste (HLW) Sludge in Savannah River Site (SRS) waste tanks was produced over a period of over 60 years by neutralizing the acidic waste produced in the F and H Separations Canyons with sodium hydroxide. The HLW slurries have been stored at free hydroxide concentrations above 1 M to minimize the corrosion of the carbon steel waste tanks. Sodium nitrite is periodically added as a corrosion inhibitor. The resulting waste has been subjected to supernate evaporation to minimize the volume of the stored waste. In addition, some of the waste tanks experienced high temperatures so some of the waste has been at elevated temperatures. Because the waste is radioactive, the waste is transforming through the decay of shorter lived radioactive species and the radiation damage that the decay releases. The goal of the Savannah River National Laboratory (SRNL) simulant development program is to develop a method to produce a sludge simulant that matches both the chemical and physical characteristics of the HLW without the time, temperature profile, chemical or radiation exposure of that of the real waste. Several different approaches have been taken historically toward preparing simulated waste slurries. All of the approaches used in the past dozen years involve some precipitation of the species using similar chemistry to that which formed the radioactive waste solids in the tank farm. All of the approaches add certain chemical species as commercially available insoluble solid compounds. The number of species introduced in this manner, however, has varied widely. All of the simulant preparation approaches make the simulated aqueous phase by adding the appropriate ratios of various sodium salts. The simulant preparation sequence generally starts with an acidic pH and ends up with a caustic pH (typically in the 10-12 range). The current method for making sludge simulant involves ...
Date: May 28, 2010
Creator: Newell, J.; Lambert, D.; Stone, M. & Fernandez, A.
Partner: UNT Libraries Government Documents Department

Small-angle neutron scattering from polystyrene-DVB networks containing a delta fraction of deuterated polystyrene: evidence for aggregation during polymerization

Description: Sample No. 1 yielded a mol wt of 70,000 g/mole and a Z-average radius of gyration of 121 A. The delta fraction of polystyrene of interest has a mol wt of 50,000-72,000 g/mole, depending on position, and suggestive of aggregation. Some speculation is made on the aggregation mechanism. (DLC)
Date: January 1, 1983
Creator: Fernandez, A.M.; Widmaier, J.M.; Wignall, G.D. & Sperling, L.H.
Partner: UNT Libraries Government Documents Department

Magnetic force microscopy of single-domain cobalt dots patterned using interference lithography

Description: We have fabricated arrays of Co dots of diameters 100 and 70 nm using interference lithography. Density of these arrays is 7.2x10{sup 9}/in{sup 2}. Magnetic force microscopy indicate that the Co dots are single domain with moments that can be controlled to point either in-plane or out-of-plane. Interference lithography is a process that is easily scaled to large areas and is potentially capable of high throughput. Large, uniform arrays of single-domain structures are potentially useful for high-density, low-noise data storage.
Date: March 20, 1996
Creator: Fernandez, A.; Bedrossian, P.J.; Baker, S.L.; Vernon, S.P. & Kania, D.R.
Partner: UNT Libraries Government Documents Department

Magnetic domain structure and magnetization reversal in submicron-scale Co dots

Description: We present a magnetic force microscopy (MFM) analysis of arrays of submicron-scale Co dots fabricated by interference lithography. The dots are thin (180--300 Å) and elliptical in shape. MFM reveals that these structures relax into highly ordered remanent states whose symmetry and configuration are governed by their shape anisotropy. In particular, when the dots are saturated along their long-axis, a uniformly magnetized state persists at remanence. However, when the dots are saturated along their short-axis, they relax into a single-vortex state in which the circulation can have either sign. Both states are characterized by smoothly varying magnetization patterns and a high degree of uniformity across the array. We attribute the ordered behavior of these.structures to the film microstructure, which allows the shape anisotropy to dominate over magnetocrystalline anjsotropy. By imaging a series of minor-loop remanent states, we show that magnetization reversal in these structures occurs via the nucleation and annihilation of a single vortex. Magnetic hysteresis loop measurements are consistent with these observations and provide additional details. Furthermore, we present the results of micromagnetic simulations, which are in excellent agreement with both the MFM images and the hysteresis loop measurements. © 1998 Elsevier Science B.V. All rights reserved.
Date: September 24, 1998
Creator: Cerjan, C J; Fernandez, A; Gibbons, M & Wall, M A
Partner: UNT Libraries Government Documents Department

Undergraduate research semester internship spring 1999 abstracts and research papers

Description: This report consists of the following titles: (1) Development of Sieving Media for DNA Sequencing; (2) Protein-Protein Interaction Specificity of a Human Exonuclease; (3) Cascading Modular Biotreatment System--From Conceptual Design to Field Tests; (4) Detecting the Unseen Enemies--Biological Warfare; and (5) Development of a Functional Chip for High-Throughput Screening of Protein-DNA Interactions.
Date: May 1, 1999
Creator: Dibble, S; Fernandez, A; Mayers, C; Omikunle, A & Weiss, O
Partner: UNT Libraries Government Documents Department

Methods for fabricating arrays of holes using interference lithography

Description: Optical interference lithography offers a robust patterning technology capable of achieving high spatial resolution over extremely large field sizes ( {approx}1 m ). Here, we compare two different approaches for fabricating arrays of holes using interferometric techniques. We show that by applying an image reversal process to standard two-beam interference lithography, arrays of high aspect ratio holes can be generated. This process scales to submicron periods and allows holes as small as 0.1 micron to be patterned. Next, we present an analysis of the multiple-beam approach for patterning holes. We demonstrate that while the formation of higher contrast intensity patterns is possible by interfering four or more beams, the shape and modulation depth of such patterns are inherently sensitive to relative phase variations.
Date: May 28, 1997
Creator: Fernandez, A.; Decker, J.Y.; Herman, S.M.; Phillion, D.W.; Sweeny, D.W. & Perry, M.D.
Partner: UNT Libraries Government Documents Department

Model independent measurement of S-wave K- pi+ systems using D+ ---> K pi pi decays from Fermilab E791

Description: A model-independent partial-wave analysis of the S-wave component of the K{pi} system from decays of D{sup +} mesons to the three-body K{sup -}{pi}{sup +}{pi}{sup +} final state is described. Data come from the Fermilab E791 experiment. Amplitude measurements are made independently for ranges of K{sup -}{pi}{sup +} invariant mass, and results are obtained below 825 MeV/c{sup 2}, where previous measurements exist only in two mass bins. This method of parametrizing a three-body decay amplitude represents a new approach to analyzing such decays. Though no model is required for the S-wave, a parametrization of the relatively well-known reference P- and D-waves, optimized to describe the data used, is required. The observed phase variation for the S-, P- and D-waves do not match existing measurements of I = 1/2 K{sup -} {pi}{sup +} scattering in the invariant mass range in which scattering is predominantly elastic. If the data are mostly I = 1/2, this observation indicates that the Watson theorem, which requires these phases to have the same dependence on invariant mass, does not apply to these decays. The production rate of K{sup -}{pi}{sup +} from these decays, if assumed to be predominantly I = 1/2, is also found to have a significant dependence on invariant mass in the region above 1.25 GeV/c{sup 2}. These measurements can provide a relatively model-free basis for future attempts to determine which strange scalar amplitudes contribute to the decays.
Date: July 1, 2005
Creator: Aitala, E.M.; Amato, S.; Anjos, J.C.; Appel, J.A.; Ashery, D.; Banerjee, S. et al.
Partner: UNT Libraries Government Documents Department