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Co-training and Self-training for Word Sense Disambiguation

Description: This paper investigates the application of co-training and self-training to word sense disambiguation. Optimal and empirical parameter selection methods for co-training and self-training are investigated, with various degrees of error reduction. A new method that combines co-training with majority voting is introduced, with the effect of smoothing the bootstrapping learning curves, and improving the average performance.
Date: May 2004
Creator: Mihalcea, Rada, 1974-
Partner: UNT College of Engineering

Finding Semantic Associations on Express Lane

Description: This paper introduces a new codification scheme for efficient computation of measures in semantic networks. The scheme is particularly useful for fast computation of semantic associations between words and implementation of an informational retrieval operator for efficient search in semantic spaces. Other applications may also be possible.
Date: May 2004
Creator: Nastase, Vivi & Mihalcea, Rada, 1974-
Partner: UNT College of Engineering

Thermophysical Properties of Fluids and Fluid Mixtures

Description: The major goal of the project was to study the effect of critical fluctuations on the thermophysical properties and phase behavior of fluids and fluid mixtures. Long-range fluctuations appear because of the presence of critical phase transitions. A global theory of critical fluctuations was developed and applied to represent thermodynamic properties and transport properties of molecular fluids and fluid mixtures. In the second phase of the project, the theory was extended to deal with critical fluctuations in complex fluids such as polymer solutions and electrolyte solutions. The theoretical predictions have been confirmed by computer simulations and by light-scattering experiments. Fluctuations in fluids in nonequilibrium states have also been investigated.
Date: May 3, 2004
Creator: Sengers, Jan V. & Anisimov, Mikhail A.
Partner: UNT Libraries Government Documents Department

Density, Distribution and Habitat Requirements for the Ozark Pocket Gopher (Geomys Bursarius Ozarkensis)

Description: A new subspecies of the plains pocket gopher (Geomys bursarius ozarkensis), located in the Ozark Mountains of north central Arkansas, was recently described by Elrod et al. (2000). Current range for G. b. ozarkensis was established, habitat preference was assessed by analyzing soil samples, vegetation and distance to stream and potential pocket gopher habitat within the current range was identified. A census technique was used to estimate a total density of 3, 564 pocket gophers. Through automobile and aerial survey 51 known fields of inhabitance were located extending the range slightly. Soil analyses indicated loamy sand as the most common texture with a slightly acidic pH and a broad range of values for other measured soil parameters and 21 families of vegetation were identified. All inhabited fields were located within an average of 107.2m from waterways and over 1,600 hectares of possible suitable habitat was identified.
Date: May 2004
Creator: Kershen, Audrey Allbach
Partner: UNT Libraries

Performance characteristics of the Cray X1 and their implicationsfor application performance tuning

Description: During the last decade the scientific computing community has optimized many applications for execution on superscalar computing platforms. The recent arrival of the Japanese Earth Simulator has revived interest in vector architectures especially in the US. It is important to examine how to port our current scientific applications to the new vector platforms and how to achieve high performance. The success of porting these applications will also influence the acceptance of new vector architectures. In this paper, we first investigate the memory performance characteristics of the Cray X1, a recently released vector platform, and determine the most influential performance factors. Then, we examine how to optimize applications tuned on superscalar platforms for the Cray X1 using its performance characteristics as guidelines. Finally, we evaluate the different types of optimizations used, the effort for their implementations, and whether they provide any performance benefits when ported back to superscalar platforms.
Date: May 11, 2004
Creator: Shan, Hogzhang & Strohmaier, Erich
Partner: UNT Libraries Government Documents Department

Measurement of {gamma}{sub T} with the {gamma}{sub T} quads on and off

Description: An experimental procedure for measuring {gamma}{sub T} has been developed and tested in two different measurements, with the {gamma}{sub T} quads on and off. The results were compared to MAD calculations. The discrepancy between the measured {gamma}{sub T} and the calculated {gamma}{sub T} is less than 5%.
Date: May 24, 2004
Creator: Xi Yang, James MacLachlan and Charles M. Ankenbrandt
Partner: UNT Libraries Government Documents Department

Imaging of Acoustically Coupled Oscillations Due to Flow Past a Shallow Cavity: Effect of Cavity Length Scale

Description: Flow-acoustic interactions due to fully turbulent inflow past a shallow axisymmetric cavity mounted in a pipe, which give rise to flow tones, are investigated using a technique of high-image-density particle image velocimetry in conjunction with unsteady pressure measurements. This imaging leads to patterns of velocity, vorticity, streamline topology, and hydrodynamic contributions to the acoustic power integral. Global instantaneous images, as well as time-averaged images, are evaluated to provide insight into the flow physics during tone generation. Emphasis is on the manner in which the streamwise length scale of the cavity alters the major features of the flow structure. These image-based approaches allow identification of regions of the unsteady shear layer that contribute to the instantaneous hydrodynamic component of the acoustic power, which is necessary to maintain a flow tone. In addition, combined image analysis and pressure measurements allow categorization of the instantaneous flow patterns that are associated with types of time traces and spectra of the fluctuating pressure. In contrast to consideration based solely on pressure spectra, it is demonstrated that locked-on tones may actually exhibit intermittent, non-phase-locked images, apparently due to low damping of the acoustic resonator. Locked-on flow tones (without modulation or intermittency), locked-on flow tones with modulation, and non-locked-on oscillations with short-term, highly coherent fluctuations are defined and represented by selected cases. Depending on which of these regimes occur, the time-averaged Q (quality)-factor and the dimensionless peak pressure are substantially altered.
Date: May 24, 2004
Creator: Oshkai, P; Geveci, M; Rockwell, D & Pollack, M
Partner: UNT Libraries Government Documents Department

Reaction selectivity studies on nanolithographically-fabricated platinum model catalyst arrays

Description: In an effort to understand the molecular ingredients of catalytic activity and selectivity toward the end of tuning a catalyst for 100% selectivity, advanced nanolithography techniques were developed and utilized to fabricate well-ordered two-dimensional model catalyst arrays of metal nanostructures on an oxide support for the investigation of reaction selectivity. In-situ and ex-situ surface science techniques were coupled with catalytic reaction data to characterize the molecular structure of the catalyst systems and gain insight into hydrocarbon conversion in heterogeneous catalysis. Through systematic variation of catalyst parameters (size, spacing, structure, and oxide support) and catalytic reaction conditions (hydrocarbon chain length, temperature, pressures, and gas composition), the data presented in this dissertation demonstrate the ability to direct a reaction by rationally adjusting, through precise control, the design of the catalyst system. Electron beam lithography (EBL) was employed to create platinum nanoparticles on an alumina (Al{sub 2}O{sub 3}) support. The Pt nanoparticle spacing (100-150-nm interparticle distance) was varied in these samples, and they were characterized using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM), both before and after reactions. The TEM studies showed the 28-nm Pt nanoparticles with 100 and 150-nm interparticle spacing on alumina to be polycrystalline in nature, with crystalline sizes of 3-5 nm. The nanoparticle crystallites increased significantly after heat treatment. The nanoparticles were still mostly polycrystalline in nature, with 2-3 domains. The 28-nm Pt nanoparticles deposited on alumina were removed by the AFM tip in contact mode with a normal force of approximately 30 nN. After heat treatment at 500 C in vacuum for 3 hours, the AFM tip, even at 4000 nN, could not remove the platinum nanoparticles. The increase of adhesion upon heat treatment indicates stronger bonding between the Pt and the support at the metal-oxide interface.
Date: May 15, 2004
Creator: Grunes, Jeffrey Benjamin
Partner: UNT Libraries Government Documents Department

A study on chemical interactions between waste fluid, formation water, and host rock during deep well injection

Description: A new disposal well was drilled in the vicinity of an injection well that had been in operation for 12 years. The drilling activities provided an opportunity to assess the fate and transport of waste products injected in the nearby well, and the impact, if any, on the host geologic formation. The origin of the fluid collected while drilling the new well and the interaction between injected waste and the formation were investigated using analyses of formation waters, waste, and formation minerals, by applying traditional graphical methods and sophisticated numerical models. This approach can be used to solve a wide range of geochemical problems related to deep well injection of waste. Trilinear Piper diagrams, Stiff diagrams, and correlation plots show that the chemical characteristics of recovered fluid at the new well are similar to those of formation water. The concentrations of most major constituents in the fluid appear diluted when compared to formation water sampled at other locations. This could be explained by mixing with waste, which is less saline than formation water. However, the waste injected near the new well consists primarily of ammonia and sulfate, and these waste constituents are not found at concentrations elevated enough to suggest that significant mixing of formation water with waste has occurred. To determine whether chemical interactions between injected waste and formation could explain the chemistry of fluid recovered from the new well, we simulated the chemical reaction between waste, formation water, and the formation rock by numerical modeling. Initial modeling calculations were done using a multicomponent geochemical reaction-path model to simulate fresh waste reacting with the formation. A more complex simulation coupling flow, transport, and reaction was then run using a multicomponent geochemical reactive transport model. These numerical simulations were carried out to calculate porosity changes and evaluate chemical processes resulting ...
Date: May 14, 2004
Creator: Spycher, Nicolas & Larkin, Randy
Partner: UNT Libraries Government Documents Department

From Sequential Extraction to Transport Modeling, Monitored Natural Attenuation as a Remediation Approach for Inorganic Contaminants

Description: Implementation of monitored natural attenuation (MNA) as a remediation method requires a mechanistic understanding of the natural attenuation processes occurring at a given site. For inorganic contaminants, natural attenuation typically involves a decrease in metal toxicity and/or mobility. These natural processes include dilution, dispersion, sorption (including adsorption, absorption, and precipitation), and redox processes. In order to better quantify these processes in terms of metal availability, sequential extraction experiments were carried out on subsurface soil samples impacted by a low pH, high sulfate, metals (Be, Ni, U, As) plume associated with the long-term operation of a coal plant at the Savannah River Site. These laboratory scale studies provide mechanistic information regarding the solid phases in the soils associated with natural attenuation of the contaminant metals. This data provides input to be evaluated in the definition of the contaminant source term as well as transport of contaminants for site transport models.
Date: May 25, 2004
Creator: POWELL, KIMBERLYR.
Partner: UNT Libraries Government Documents Department

Real Time Pricing and the Real Live Firm

Description: Energy economists have long argued the benefits of real time pricing (RTP) of electricity. Their basis for modeling customers response to short-term fluctuations in electricity prices are based on theories of rational firm behavior, where management strives to minimize operating costs and optimize profit, and labor, capital and energy are potential substitutes in the firm's production function. How well do private firms and public sector institutions operating conditions, knowledge structures, decision-making practices, and external relationships comport with these assumptions and how might this impact price response? We discuss these issues on the basis of interviews with 29 large (over 2 MW) industrial, commercial, and institutional customers in the Niagara Mohawk Power Corporation service territory that have faced day-ahead electricity market prices since 1998. We look at stories interviewees told about why and how they respond to RTP, why some customers report that they can't, and why even if they can, they don't. Some firms respond as theorized, and we describe their load curtailment strategies. About half of our interviewees reported that they were unable to either shift or forego electricity consumption even when prices are high ($0.50/kWh). Reasons customers gave for why they weren't price-responsive include implicit value placed on reliability, pricing structures, lack of flexibility in adjusting production inputs, just-in-time practices, perceived barriers to onsite generation, and insufficient time. We draw these observations into a framework that could help refine economic theory of dynamic pricing by providing real-world descriptions of how firms behave and why.
Date: May 26, 2004
Creator: Moezzi, Mithra; Goldman, Charles; Sezgen, Osman; Bharvirkar, Ranjit & Hopper, Nicole
Partner: UNT Libraries Government Documents Department

Pilot-Scale Testing of a Spin Tek Rotary Microfilter With Welded Disks and Simulated Savannah River Site High Level Waste

Description: The Department of Energy is developing processes to treat Savannah River Site (SRS) radioactive waste. In the first step, personnel contact the incoming salt solution that contains entrained sludge with monosodium titanate (MST) to adsorb strontium and select actinides. They filter the resulting slurry to remove the sludge and MST. The filtrate receives further treatment to remove cesium. Previously, personnel conducted a review of solid-liquid separation technologies and identified the rotary microfilter as a plausible improvement over the tubular crossflow filter in the current baseline. The Savannah River National Laboratory (SRNL) received funding from the DOE to continue developing the rotary microfilter for SRS high level waste applications. As part of this task, the authors developed a protocol to weld stainless steel and ceramic filter disks. After they welded the disks, they placed them in the pilot-scale rotary microfilter and tested them with simulated SRS waste. The conclusions are: the rotary microfilter has now operated for over 2400 hours with no significant operational problems; filter flux with the welded disks was significantly less than the flux in comparable tests with filter disks fabricated using epoxy; the ceramic filter media produced the highest flux; the Pall filter media produced higher flux than the Mott filter media; MST-only feed filtered at a higher rate than sludge plus MST feed; the Lasaentec(R) data provide insight into the settling behavior of the sludge and MST particles; when agitation resumed, the settled particles re-suspended within a few minutes; the MST-only solids settled more rapidly than the sludge plus MST solids; particle size measurements showed a 25 - 50 percent median particle size reduction during the tests; the median particle size was as much as 35 percent smaller than in previous tests.
Date: May 21, 2004
Creator: POIRIER, MICHAEL
Partner: UNT Libraries Government Documents Department

Microwave Scattering System Design for {rho}{sub i}e-Scale Turbulence Measurements on NSTX

Description: Despite suppression of {rho}{sub i}-scale turbulent fluctuations, electron thermal transport remains anomalous in NSTX. For this reason, a microwave scattering system will be deployed to directly observe the w and k spectra of {rho}{sub e}-scale turbulent fluctuations and characterize the effect on electron thermal transport. The scattering system will employ a Gaussian probe beam produced by a high power 280 GHz microwave source. A five-channel heterodyne detection system will measure radial turbulent spectra in the range |k{sub r}| = 0-20 cm{sup -1}. Inboard and outboard launch configurations cover most of the normalized minor radius. Improved spatial localization of measurements is achieved with low aspect ratio and high magnetic shear configurations. This paper will address the global design of the scattering system, such as choice of frequency, size, launching system, and detection system.
Date: May 19, 2004
Creator: Smith, D.R.; Mazzucato, E.; Munsat, T.; Park, H.; Johnson, D.; Lin, L. et al.
Partner: UNT Libraries Government Documents Department

Supernova/Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy

Description: The Supernova/Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the dark energy and alternative explanations of the acceleration of the Universes expansion by performing a series of complementary systematics-controlled astrophysical measurements. We here describe a self-consistent reference mission design that can accomplish this goal with the two leading measurement approaches being the Type Ia supernova Hubble diagram and a wide-area weak gravitational lensing survey. This design has been optimized to first order and is now under study for further modification and optimization. A 2-m three-mirror anastigmat wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high efficiency low-resolution integral field spectrograph. The instrumentation suite provides simultaneous discovery and light-curve measurements of supernovae and then can target individual objects for detailed spectral characterization. The SNAP mission will discover thousands of Type Ia supernovae out to z = 3 and will obtain high-signal-to-noise calibrated light-curves and spectra for a subset of > 2000 supernovae at redshifts between z = 0.1 and 1.7 in a northern field and in a southern field. A wide-field survey covering one thousand square degrees in both northern and southern fields resolves {approx} 100 galaxies per square arcminute, or a total of more than 300 million galaxies. With the PSF stability afforded by a space observatory, SNAP will provide precise and accurate measurements of gravitational lensing. The high-quality data available in space, combined with the large sample of supernovae, will enable stringent control of systematic uncertainties. The resulting data set will be used to determine the energy density of dark energy and parameters that describe its dynamical behavior. The data also provide a direct test of theoretical models for the dark energy, including discrimination of vacuum energy due to ...
Date: May 12, 2004
Creator: Aldering, G.; Althouse, W.; Amanullah, R.; Annis, J.; Astier, P.; Baltay, C. et al.
Partner: UNT Libraries Government Documents Department

Benchmarking optimization software with COPS 3.0.

Description: The authors describe version 3.0 of the COPS set of nonlinearly constrained optimization problems. They have added new problems, as well as streamlined and improved most of the problems. They also provide a comparison of the FILTER, KNITRO, LOQO, MINOS, and SNOPT solvers on these problems.
Date: May 24, 2004
Creator: Dolan, E. D.; More, J. J. & Munson, T. S.
Partner: UNT Libraries Government Documents Department

Valence band hybridization in N-rich GaN1-xAsx alloys

Description: We have used photo-modulated transmission and optical absorption spectroscopies to measure the composition dependence of interband optical transitions in N-rich GaN{sub 1-x}As{sub x} alloys with x up to 0.06. The direct bandgap gradually decreases as x increases. In the dilute x limit, the observed band gap approaches 2.8 eV; this limiting value is attributed to a transition between the As localized level, which has been previously observed in As-doped GaN at 0.6 eV above the valence band maximum in As-doped GaN, and the conduction band minimum. The structure of the valence band of GaN{sub 1-x}As{sub x} is explained by the hybridization of the localized As states with the extended valence band states of GaN matrix. The hybridization is directly confirmed by soft x-ray emission experiments. To describe the electronic structure of the GaN{sub 1-x}As{sub x} alloys in the entire composition range a linear interpolation is used to combine the effects of valence band hybridization in N-rich alloys with conduction band anticrossing in As-rich alloys.
Date: May 4, 2004
Creator: Wu, J.; Walukiewicz, W.; Yu, K.M.; Denlinger, J.D.; Shan, W.; Ager III, J.W. et al.
Partner: UNT Libraries Government Documents Department

Corrective Action Investigation Plan for Corrective Action Unit 543: Liquid Disposal Units Nevada Test Site, Nevada, Rev. No.: 0 with ROTC 1 and 2

Description: This Corrective Action Investigation Plan (CAIP) contains project-specific information including facility descriptions, environmental sample collection objectives, and criteria for conducting site investigation activities at Corrective Action Unit (CAU) 543: Liquid Disposal Units, Nevada Test Site (NTS), Nevada. This CAIP has been developed in accordance with the ''Federal Facility Agreement and Consent Order'' (FFACO) (1996) that was agreed to by the State of Nevada, the U.S. Department of Energy (DOE), and the U.S Department of Defense (DoD). Corrective Action Unit 543 is located in Area 6 and Area 15 of the NTS, which is approximately 65 miles (mi) northwest of Las Vegas, Nevada (Figure 1-1). Seven corrective action sites (CASs) comprise CAU 543 and are listed below: (1) 06-07-01, Decon Pad; (2) 15-01-03, Aboveground Storage Tank; (3) 15-04-01, Septic Tank; (4) 15-05-01, Leachfield; (5) 15-08-01, Liquid Manure Tank; (6) 15-23-01, Underground Radioactive Material Area; and (7) 15-23-03, Contaminated Sump, Piping. Corrective Action Site 06-07-01, Decon Pad, is located in Area 6 and consists of the Area 6 Decontamination Facility and its components that are associated with decontamination of equipment, vehicles, and materials related to nuclear testing. The six CASs in Area 15 are located at the U.S. Environmental Protection Agency (EPA) Farm and are related to waste disposal activities at the EPA Farm. The EPA Farm was a fully-functional dairy associated with animal experiments conducted at the on-site laboratory. The corrective action investigation (CAI) will include field inspections, video-mole surveys, and sampling of media, where appropriate. Data will also be obtained to support waste management decisions. The CASs within CAU 543 are being investigated because hazardous and/or radioactive constituents may be present at concentrations that could potentially pose a threat to human health and the environment. The seven CASs in CAU 543 primarily consist of sanitary and process waste collection, storage, ...
Date: May 1, 2004
Creator: Strand, David A.
Partner: UNT Libraries Government Documents Department

Photometry of SN 2002ic and implications for the progenitor mass-loss history

Description: We present new pre-maximum and late-time optical photometry of the Type Ia/IIn supernova 2002ic. These observations are combined with the published V-band magnitudes of Hamuy et al. (2003) and the VLT spectrophotometry of Wang et al. (2004) to construct the most extensive light curve to date of this unusual supernova. The observed flux at late time is significantly higher relative to the flux at maximum than that of any other observed Type Ia supernova and continues to fade very slowly a year after explosion. Our analysis of the light curve suggests that a non-Type Ia supernova component becomes prominent {approx}20 days after explosion. Modeling of the non-Type Ia supernova component as heating from the shock interaction of the supernova ejecta with pre-existing circumstellar material suggests the presence of a {approx}1.7 x 1015 cm gap or trough between the progenitor system and the surrounding circumstellar material. This gap could be due to significantly lower mass-loss {approx}15 (nu{sub omega}/10 km/s) -1 years prior to explosion or evacuation of the circumstellar material by a low-density fast wind. The latter is consistent with observed properties of proto-planetary nebulae and with models of white-dwarf + asymptotic giant branch star progenitor systems with the asymptotic giant branch star in the proto-planetary nebula phase.
Date: May 6, 2004
Creator: Wood-Vasey, W.M.; Wang, L. & Aldering, G.
Partner: UNT Libraries Government Documents Department

After-hours power status of office equipment and energy use of miscellaneous plug-load equipment

Description: This research was conducted in support of two branches of the EPA ENERGY STAR program, whose overall goal is to reduce, through voluntary market-based means, the amount of carbon dioxide emitted in the U.S. The primary objective was to collect data for the ENERGY STAR Office Equipment program on the after-hours power state of computers, monitors, printers, copiers, scanners, fax machines, and multi-function devices. We also collected data for the ENERGY STAR Commercial Buildings branch on the types and amounts of miscellaneous plug-load equipment, a significant and growing end use that is not usually accounted for by building energy managers. For most types of miscellaneous equipment, we also estimated typical unit energy consumption in order to estimate total energy consumption of the miscellaneous devices within our sample. This data set is the first of its kind that we know of, and is an important first step in characterizing miscellaneous plug loads in commercial buildings. The main purpose of this study is to supplement and update previous data we collected on the extent to which electronic office equipment is turned off or automatically enters a low power state when not in active use. In addition, it provides data on numbers and types of office equipment, and helps identify trends in office equipment usage patterns. These data improve our estimates of typical unit energy consumption and savings for each equipment type, and enables the ENERGY STAR Office Equipment program to focus future effort on products with the highest energy savings potential. This study expands our previous sample of office buildings in California and Washington DC to include education and health care facilities, and buildings in other states. We report data from sixteen commercial buildings in California, Georgia, and Pennsylvania: four education buildings, two medical buildings, two large offices (> 500 employees each), ...
Date: May 27, 2004
Creator: Roberson, Judy A.; Webber, Carrie A.; McWhinney, Marla C.; Brown, Richard E.; Pinckard, Marageret J. & Busch, John F.
Partner: UNT Libraries Government Documents Department

A proposal for a UPC memory consistency model, v1.0

Description: The memory consistency model in a language defines the order in which the results of write operations maybe observed through read operations. The behavior of a UPC program may depend on the timing of accesses to shared variables, so a program defines a set of possible executions, rather than a single execution. The memory consistency model constrains the set of possible executions for a given program; the user may then rely on properties that are true of all of those executions. The memory consistency model is defined in terms of the read and write operations issued by each thread in naive translation of the code, i.e., without any code transformations by the compiler, with each thread issuing operations as defined by the abstract machine defined in ISO C 5.1.2.3. A UPC compiler or run time system may perform various code transformations to improve performance, so long as they are not visible to the programmer - i.e., provided the set of externally-visible behaviors (the input/output dynamics and volatile behavior defined in ISO C 5.1.2.3) from any execution of the transformed program are identical to those of the original program executing on the abstract machine and adhering to the consistency model defined in this document.
Date: May 5, 2004
Creator: Yelick, Katherine; Bonachea, Dan & Wallace, Charles
Partner: UNT Libraries Government Documents Department

Tracer Testing for Estimating Heat Transfer Area in Fractured Reservoirs

Description: A key parameter governing the performance and life-time of a Hot Fractured Rock (HFR) reservoir is the effective heat transfer area between the fracture network and the matrix rock. We report on numerical modeling studies into the feasibility of using tracer tests for estimating heat transfer area. More specifically, we discuss simulation results of a new HFR characterization method which uses surface-sorbing tracers for which the adsorbed tracer mass is proportional to the fracture surface area per unit volume. Sorption in the rock matrix is treated with the conventional formulation in which tracer adsorption is volume-based. A slug of solute tracer migrating along a fracture is subject to diffusion across the fracture walls into the adjacent rock matrix. Such diffusion removes some of the tracer from the fluid in the fractures, reducing and retarding the peak in the breakthrough curve (BTC) of the tracer. After the slug has passed the concentration gradient reverses, causing back-diffusion from the rock matrix into the fracture, and giving rise to a long tail in the BTC of the solute. These effects become stronger for larger fracture-matrix interface area, potentially providing a means for estimating this area. Previous field tests and modeling studies have demonstrated characteristic tailing in BTCs for volatile tracers in vapor-dominated reservoirs. Simulated BTCs for solute tracers in single-phase liquid systems show much weaker tails, as would be expected because diffusivities are much smaller in the aqueous than in the gas phase, by a factor of order 1000. A much stronger signal of fracture-matrix interaction can be obtained when sorbing tracers are used. We have performed simulation studies of surface-sorbing tracers by implementing a model in which the adsorbed tracer mass is assumed proportional to the fracture-matrix surface area per unit volume. The results show that sorbing tracers generate stronger tails in ...
Date: May 12, 2004
Creator: Pruess, Karsten; van Heel, Ton & Shan, Chao
Partner: UNT Libraries Government Documents Department

Erosion Modeling Analysis For DWPF MFT/SME Tanks

Description: This report presents the application of computational fluid dynamics (CFD) methods to qualitative estimate of the erosion phenomena expected in the actual Slurry Mixer Evaporator (SME) and MFT (Melter Feed Tank) process facilities by calculating erosion drivers. Using the transport equations governing the slurry flow, two erosion mechanisms were considered to evaluate high erosion sites and to investigate the primary cause of erosion damage for the modeling domain representative of the actual mixing process in the SME/MFT vessels. One of the two erosion mechanisms is the abrasive erosion which is worn by high wall shear of viscous liquid or by continuous contact or low-angle collision of the moving solids with rough surface, and the other is the chip-off erosion which is mainly governed by high-angle impingement of particles. Ductile wall material such as stainless steel is damaged by wall mechanism when particles are impinged on the ductile surface of the present coil guide geometry with wide-open space and no closed- and curved-flow path. The previous results show that the primary locations of high erosion due to particle impingement are at the occurrence of sudden change of flow direction, sudden contraction, and flow obstruction.
Date: May 3, 2004
Creator: LEE, SI
Partner: UNT Libraries Government Documents Department