Vogtle Electric Generating Plant ETE Analysis Review (open access)

Vogtle Electric Generating Plant ETE Analysis Review

Under contract with the Nuclear Regulatory Commission (NRC), staff from Pacific Northwest National Laboratory (PNNL) and Sandia National Laboratory (SNL)-Albuquerque reviewed the evacuation time estimate (ETE) analysis dated April 2006 prepared by IEM for the Vogtle Electric Generating Plant (VEGP). The ETE analysis was reviewed for consistency with federal regulations using the NRC guidelines in Review Standard (RS)-002, Supplement 2 and Appendix 4 to NUREG-0654, and NUREG/CR-4831. Additional sources of information referenced in the analysis and used in the review included NUREG/CR-6863 and NUREG/CR-6864. The PNNL report includes general comments, data needs or clarifications, and requests for additional information (RAI) resulting from review of the ETE analysis.
Date: December 9, 2006
Creator: Diediker, Nona H. & Jones, Joe A.
Object Type: Report
System: The UNT Digital Library
Climate change uncertainty for daily minimum and maximum temperatures: a model inter-comparison (open access)

Climate change uncertainty for daily minimum and maximum temperatures: a model inter-comparison

Several impacts of climate change may depend more on changes in mean daily minimum (T{sub min}) or maximum (T{sub max}) temperatures than daily averages. To evaluate uncertainties in these variables, we compared projections of T{sub min} and T{sub max} changes by 2046-2065 for 12 climate models under an A2 emission scenario. Average modeled changes in T{sub max} were slightly lower in most locations than T{sub min}, consistent with historical trends exhibiting a reduction in diurnal temperature ranges. However, while average changes in T{sub min} and T{sub max} were similar, the inter-model variability of T{sub min} and T{sub max} projections exhibited substantial differences. For example, inter-model standard deviations of June-August T{sub max} changes were more than 50% greater than for T{sub min} throughout much of North America, Europe, and Asia. Model differences in cloud changes, which exert relatively greater influence on T{sub max} during summer and T{sub min} during winter, were identified as the main source of uncertainty disparities. These results highlight the importance of considering separately projections for T{sub max} and T{sub min} when assessing climate change impacts, even in cases where average projected changes are similar. In addition, impacts that are most sensitive to summertime T{sub min} or wintertime …
Date: November 9, 2006
Creator: Lobell, D; Bonfils, C & Duffy, P
Object Type: Article
System: The UNT Digital Library
Development of Improved Chemicals and Plastics from Oilseeds (open access)

Development of Improved Chemicals and Plastics from Oilseeds

The overall objective of this program was to develop technology that can be applied to the production of various chemicals and plastics from seed oils. This research and development program included activities in all four key barrier areas identified in the US DOE Technology Roadmap for Plant/Crop-Based Renewable Resources, namely Plant Science, Production, Processing, and Utilization. Participants in the project included The Dow Chemical Company, Castor Oil, Inc., and the USDA Western Regional Research Center (WRRC). The objective of this production task was to evaluate and develop metathesis catalyst technology as a means of utilizing seed oils as feedstocks for the chemical industry. Specifically, ethenolysis of fatty acid methyl esters, FAME’s, leads to functionalized derivatives. These serve as valuable starting points for materials which cascade into a variety of applications, many of which have a current market presence. The relatively recent discovery and commercial availability of a family of metathesis catalysts which are tolerant of polar functional groups and the acquisition and implementation of high throughput synthesis and screening infrastructure led to a prime opportunity to investigate this project area.
Date: November 9, 2006
Creator: Nugent, Patricia A. & Lysenko, Zenon
Object Type: Report
System: The UNT Digital Library
Dissimilar behavior of technetium and rhenium in borosilicatewaste glass as determined by X-ray absorption spectroscopy (open access)

Dissimilar behavior of technetium and rhenium in borosilicatewaste glass as determined by X-ray absorption spectroscopy

Technetium-99 is an abundant, long-lived (t1/2 = 213,000 yr)fission product that creates challenges for the safe, long-term disposalof nuclear waste. While 99Tc receives attention largely due to its highenvironmental mobility, it also causes problems during its incorporationinto nuclear waste glass due to the volatility of Tc(VII) compounds. Thisvolatility decreases the amount of 99Tc stabilized in the waste glass andcauses contamination of the waste glass melter and off-gas system. Theapproach to decrease the volatility of 99Tc that has received the mostattention is reduction of the volatile Tc(VII) species to less volatileTc(IV) species in the glass melt. On engineering scale experiments,rhenium is often used as a non-radioactive surrogate for 99Tc to avoidthe radioactive contamination problems caused by volatile 99Tc compounds.However, Re(VII) is more stable towards reduction than Tc(VII), so morereducing conditions would be required in the glass melt to produceRe(IV). To better understand the redox behavior of Tc and Re in nuclearwaste glass, a series of glasses were prepared under different redoxconditions. The speciation of Tc and Re in the resulting glasses wasdetermined by X-ray absorption fine structure spectroscopy. Surprisingly,Re and Tc do not behave similarly in the glass melt. Although Tc(0),Tc(IV), and Tc(VII) were observed in these samples, only Re(0) andRe(VII) …
Date: November 9, 2006
Creator: Lukens, Wayne W.; McKeown, David A.; Buechele, Andrew C.; Muller,Isabelle S.; Shuh, David K. & Pegg, Ian L.
Object Type: Article
System: The UNT Digital Library
Fusion of X-Ray and Ultrasound Images for As-Built Modeling (open access)

Fusion of X-Ray and Ultrasound Images for As-Built Modeling

None
Date: November 9, 2006
Creator: Clark, G A & Jackson, J A
Object Type: Article
System: The UNT Digital Library
Millimeter-wave Radiometer for High Sensitivity Water Vapor Profiling in Arid Regions (open access)

Millimeter-wave Radiometer for High Sensitivity Water Vapor Profiling in Arid Regions

Abstract - ProSensing Inc. has developed a G-band (183 GHz) water Vapor Radiometer (GVR) for long-term, unattended measurements of low concentrations of atmospheric water vapor and liquid water. Precipitable water vapor and liquid water path are estimated from zenith brightness temperatures measured from four double-sideband receiver channels, centered at 183.31 1, 3 and 7, and 14 GHz. A prototype ground-based version of the instrument was deployed at the DOE ARM program?s North Slope of Alaska site near Barrow AK in April 2005, where it collected data continuously for one year. A compact, airborne version of this instrument, packaged to operate from a standard 2-D PMS probe canister, has been tested on the ground and is scheduled for test flights in the summer of 2006. This paper presents design details, laboratory test results and examples of retrieved precipitable water vapor and liquid water path from measured brightness temperature data.
Date: November 9, 2006
Creator: Pazmany, Andrew
Object Type: Report
System: The UNT Digital Library
Particle Splitting for Monte-Carlo Simulation of the National Ignition Facility (open access)

Particle Splitting for Monte-Carlo Simulation of the National Ignition Facility

The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory is scheduled for completion in 2009. Thereafter, experiments will commence in which capsules of DT will be imploded, generating neutrons, gammas, x-rays, and other reaction products that will interact in the facility's structure. In order to understand and minimize the exposure of workers within the facility to prompt and delayed (activation) dose, they have developed a model for the facility using the three-dimensional Monte Carlo particle transport code, TART. To obtain acceptable statistics in a reasonable amount of time, biasing techniques are employed. In an effort to improve efficiency, they are studying the optimization of particle splitting using geometrically similar, but much simpler models. They are discussing their techniques and results.
Date: November 9, 2006
Creator: Dauffy, L S & Latkowski, J F
Object Type: Article
System: The UNT Digital Library
Report on coating from Teer (open access)

Report on coating from Teer

A trial coating run has been performed at Teer Coating LTD to assess the use of a barrel coating system as a viable option to coat multilayer spheres. Hollow glass spheres (3M K15) ranging in diameter from 70-120 microns were cleaned in a process using a 0.1 M HCl solution. Comparative photos before and after the cleaning process are shown in figure 1. Approximately, 2 liters of cleaned spheres were sent to Teer for the trial coating in their barrel coater. A picture of barrel coating system is shown in figure 2. The coating process was one layer of titanium followed by one layer of aluminum. The target thickness for each layer is 500 nm, however, no rate runs were performed to calibrate the parameters. Each layer was sputtered for 10 hours, for a total of 20 hours. After the coating process, the coated spheres were sent back to LLNL for SEM analysis. In order to quickly examine the coating in cross-section, the spheres were broken with a spatula. Photos of the broken spheres are shown in Fig 3. One sphere was chosen to look at the uniformity around the sphere. As can be seen in Figure 4, there is …
Date: November 9, 2006
Creator: Florando, J
Object Type: Report
System: The UNT Digital Library
Search for Small Trans-Neptunian Objects by the TAOS Project (open access)

Search for Small Trans-Neptunian Objects by the TAOS Project

None
Date: November 9, 2006
Creator: Chen, W.; Alcock, C.; Axelrod, T.; Bianco, F.; Byun, Y.; Chang, Y. et al.
Object Type: Article
System: The UNT Digital Library
Super-Resolution Algorithms for Nondestructive Evaluation Imaging (open access)

Super-Resolution Algorithms for Nondestructive Evaluation Imaging

None
Date: November 9, 2006
Creator: Clark, G A; Jackson, J A & Benson, S E
Object Type: Article
System: The UNT Digital Library
Three Dimensional Holographic Archival Memory (open access)

Three Dimensional Holographic Archival Memory

To address the DOE need for the storage and handling of terabyte of nuclear physics data, Physical Optics Corporation (POC) developed a new multi-terabit, 90° recording geometry 3D holographic archival optical memory storage and search system. In contrast to state-of-the-art memory approaches, 3DHAM handles the data through highly parallel optical processing in conjunction with highly redundant hologram multiplexing. The 3DHAM system advantages also stem from its unique 3D volume-recording medium, which theoretically has a significantly greater data density than diskbased systems.
Date: November 9, 2006
Creator: Gibbard, Bruce
Object Type: Report
System: The UNT Digital Library
A micromechanical basis for partitioning the evolution of grainbridging in brittle materials (open access)

A micromechanical basis for partitioning the evolution of grainbridging in brittle materials

A micromechanical model is developed for grain bridging inmonolithic ceramics. Specifically, bridge formation of a single,non-equiaxed grain spanning adjacent grains is addressed. A cohesive zoneframework enables crack initiation and propagation along grainboundaries. The evolution of the bridge is investigated through avariance in both grain angle and aspect ratio. We propose that thebridging process can be partitioned into five distinct regimes ofresistance: propagate, kink, arrest, stall, and bridge. Although crackpropagation and kinking are well understood, crack arrest and subsequent"stall" have been largely overlooked. Resistance during the stall regimeexposes large volumes of microstructure to stresses well in excess of thegrain boundary strength. Bridging can occur through continued propagationor reinitiation ahead of the stalled crack tip. The driving forcerequired to reinitiate is substantially greater than the driving forcerequired to kink. In addition, the critical driving force to reinitiateis sensitive to grain aspect ratio but relatively insensitive to grainangle. The marked increase in crack resistance occurs prior to bridgeformation and provides an interpretation for the rapidly risingresistance curves which govern the strength of many brittle materials atrealistically small flaw sizes.
Date: October 9, 2006
Creator: Foulk, J. W., III; Cannon, R. M.; Johnson, G. C.; Klein, P. A. & Ritchie, R. O.
Object Type: Article
System: The UNT Digital Library
AN OVERVIEW OF CESIUM-137 CONTAMINATION IN A SOUTHEASTERN SWAMP ENVIRONMENT (open access)

AN OVERVIEW OF CESIUM-137 CONTAMINATION IN A SOUTHEASTERN SWAMP ENVIRONMENT

In the early 1960s, an area of privately owned swamp adjacent to the Savannah River Site (SRS) was contaminated by site operations. Studies conducted in 1974 estimated that approximately 925 GBq of {sup 137}Cs and 37 GBq of {sup 60}Co were deposited in the swamp. Subsequently, a series of surveys was initiated to characterize the contaminated environment. These surveys--composed of 52 monitoring locations--allow for continued monitoring at a consistent set of locations. Initial survey results indicated maximum {sup 137}Cs concentrations of 19.5 Bq g{sup -1} in soil and 8.7 Bq g{sup -1} in vegetation. By the 2004-2005 surveys, maximum concentrations had declined to 1-2 Bq g{sup -1} in soil and 0.4 Bq g{sup -1} in vegetation.
Date: October 9, 2006
Creator: Fledderman, P; Tim Jannik, T & Michael Paller, M
Object Type: Article
System: The UNT Digital Library
Particle and Energy Transport in the SOL of DIII-D and NSTX (open access)

Particle and Energy Transport in the SOL of DIII-D and NSTX

The far scrape-off layer (SOL) radial transport and plasma-wall contact is mediated by intermittent and ELM-driven transport. Experiments to characterize the intermittent transport and ELMs have been performed in both DIII-D and NSTX under similar conditions. Both intermittent transport and ELMs are comprised of filaments of hot, dense plasma (n{sub e} {approx} 1 x 10{sup 13} cm{sup -3}, T{sub e} {approx} 400 eV) originating at the edge, transport both particles and heat into the SOL by convection, increasing wall interaction and causing sputtering and impurity release. Both intermittent filaments and ELMs leave the pedestal region at speeds of {approx}0.5-3 km/s, losing heat and particles by parallel transport as they travel through the SOL. The intermittency shows many similarities in NSTX and DIII-D, featuring similar size (2-5 cm), large convective radial velocity, ''holes'' inside and peaks outside the LCFS which quickly decay and slow down with radius. Whereas in DIII-D the intermittency decays in both intensity and frequency in H-mode, it chiefly decays in frequency in NSTX. In the low collisionality (v* = {pi}R{sub q{sub 95}}/{lambda}C) (v* {approx} 0.1, N{sub G} {approx} 0.3) case, the ELMs impact the walls quite directly and account for {approx}90% of the wall particle flux, decreasing …
Date: October 9, 2006
Creator: Boedo, J.; Maqueda, R.; Rudakov, D.; McKee, G.; Kugel, H.; Maingi, R. et al.
Object Type: Article
System: The UNT Digital Library
Performance Criteria for Residential Zero Energy Windows (open access)

Performance Criteria for Residential Zero Energy Windows

This paper shows that the energy requirements for today's typical efficient window products (i.e. ENERGY STAR{trademark} products) are significant when compared to the needs of Zero Energy Homes (ZEHs). Through the use of whole house energy modeling, typical efficient products are evaluated in five US climates and compared against the requirements for ZEHs. Products which meet these needs are defined as a function of climate. In heating dominated climates, windows with U-factors of 0.10 Btu/hr-ft{sup 2}-F (0.57 W/m{sup 2}-K) will become energy neutral. In mixed heating/cooling climates a low U-factor is not as significant as the ability to modulate from high SHGCs (heating season) to low SHGCs (cooling season).
Date: October 9, 2006
Creator: Arasteh, Dariush; Goudey, Howdy; Huang, Joe; Kohler, Christian & Mitchell, Robin
Object Type: Article
System: The UNT Digital Library
Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure (open access)

Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure

In this paper, we investigated the effects of substrate creep on the fatigue behavior of a model dental multilayer structure, in which a top glass layer was bonded to a polycarbonate substrate through a dental adhesive. The top glass layers were ground using 120 grit or 600 grit sand papers before bonding to create different sub-surface crack sizes and morphologies. The multilayer structures were tested under cyclic Hertzian contact loading to study crack growth and obtain fatigue life curves. The experiment results showed that the fatigue lives of the multilayer structures were impaired by increasing crack sizes in the sub-surfaces. They were also significantly reduced by the substrate creep when tested at relatively low load levels i.e. P{sub m} < 60 N (Pm is the maximum magnitude of cyclic load). But at relatively high load levels i.e. P{sub m} > 65 N, slow crack growth (SCG) was the major failure mechanisms. A modeling study was then carried out to explore the possible failure mechanisms over a range of load levels. It is found that fatigue life at relatively low load levels can be better estimated by considering the substrate creep effect (SCE).
Date: October 9, 2006
Creator: Zhou, J; Huang, M; Niu, X & soboyejo, W
Object Type: Article
System: The UNT Digital Library
Development of a Method for Measuring Carbon Balance in Chemical Sequestration of CO2 (open access)

Development of a Method for Measuring Carbon Balance in Chemical Sequestration of CO2

Anthropogenic CO2 released from fossil fuel combustion is a primary greenhouse gas which contributes to “global warming.” It is estimated that stationary power generation contributes over one-third of total CO2 emissions. Reducing CO2 in the atmosphere can be accomplished either by decreasing the rate at which CO2 is emitted into the atmosphere or by increasing the rate at which it is removed from it. Extensive research has been conducted on determining a fast and inexpensive method to sequester carbon dioxide. These methods can be classified into two categories, CO2 fixation by natural sink process for CO2, or direct CO2 sequestration by artificial processes. In direct sequestration, CO2 produced from sources such as coal-fired power plants, would be captured from the exhausted gases. CO2 from a combustion exhaust gas is absorbed with an aqueous ammonia solution through scrubbing. The captured CO2 is then used to synthesize ammonium bicarbonate (ABC or NH4HCO3), an economical source of nitrogen fertilizer. In this work, we studied the carbon distribution after fertilizer is synthesized from CO2. The synthesized fertilizer in laboratory is used as a “CO2 carrier” to “transport” CO2 from the atmosphere to crops. After biological assimilation and metabolism in crops treated with ABC, a …
Date: September 9, 2006
Creator: Cheng, Zhongxian; Pan, Wei-Ping & Riley, John T.
Object Type: Report
System: The UNT Digital Library
Hybrid Solar Cells with Prescribed Nanoscale Morphologies Based onHyperbranched Semiconductor Nanocrystals (open access)

Hybrid Solar Cells with Prescribed Nanoscale Morphologies Based onHyperbranched Semiconductor Nanocrystals

In recent years, the search to develop large-area solar cells at low cost has led to research on photovoltaic (PV) systems based on nanocomposites containing conjugated polymers. These composite films can be synthesized and processed at lower costs and with greater versatility than the solid state inorganic semiconductors that comprise today's solar cells. However, the best nanocomposite solar cells are based on a complex architecture, consisting of a fine blend of interpenetrating and percolating donor and acceptor materials. Cell performance is strongly dependent on blend morphology, and solution-based fabrication techniques often result in uncontrolled and irreproducible blends, whose composite morphologies are difficult to characterize accurately. Here we incorporate 3-dimensional hyper-branched colloidal semiconductor nanocrystals in solution-processed hybrid organic-inorganic solar cells, yielding reproducible and controlled nanoscale morphology.
Date: September 9, 2006
Creator: Gur, Ilan; Fromer, Neil A.; Chen, Chih-Ping; Kanaras, AntoniosG. & Alivisatos, A. Paul
Object Type: Article
System: The UNT Digital Library
Passivation of Aluminum in Lithium-ion Battery Electrolytes withLiBOB (open access)

Passivation of Aluminum in Lithium-ion Battery Electrolytes withLiBOB

A combination of cyclic polarization tests, electrochemical impedance spectroscopy, and electrochemical quartz crystal microbalance (EQCM) measurements indicate a film is formed when aluminum is polarized above 4.5V in 1:1 EC+DMC with 1M LiBOB. The quantity of film that is formed increases with increasing applied potential. Results of EQCM tests suggest the film is AlBO{sub 3}. The film is very protective against corrosion and inhibits pitting corrosion of aluminum in normally corrosive 1M LiTFSI.
Date: September 9, 2006
Creator: Zhang, Xueyuan & Devine, Thomas M.
Object Type: Article
System: The UNT Digital Library
Surfactant Based Enhanced Oil Recovery and Foam Mobility Control (open access)

Surfactant Based Enhanced Oil Recovery and Foam Mobility Control

Surfactant flooding has the potential to significantly increase recovery over that of conventional waterflooding. The availability of a large number of surfactant structures makes it possible to conduct a systematic study of the relation between surfactant structure and its efficacy for oil recovery. A mixture of two surfactants was found to be particularly effective for application in carbonate formations at low temperature. The mixture is single phase for higher salinity or calcium concentrations than that for either surfactant used alone. This makes it possible to inject the surfactant slug with polymer close to optimal conditions and yet be single phase. A formulation has been designed for a particular field application. It uses partially hydrolyzed polyacrylamide for mobility control. The addition of an alkali such as sodium carbonate makes possible in situ generation of naphthenic soap and significant reduction of synthetic surfactant adsorption. The design of the process to maximize the region of ultra-low IFT takes advantage of the observation that the ratio of soap to synthetic surfactant is a parameter in the conditions for optimal salinity. Even for a fixed ratio of soap to surfactant, the range of salinity for low IFT was wider than that reported for surfactant systems …
Date: September 9, 2006
Creator: Hirasaki, George J. & Miller, Clarence A.
Object Type: Report
System: The UNT Digital Library
Automated High Throughput Protein Crystallization Screening at Nanoliter Scale and Protein Structural Study on Lactate Dehydrogenase (open access)

Automated High Throughput Protein Crystallization Screening at Nanoliter Scale and Protein Structural Study on Lactate Dehydrogenase

The purposes of our research were: (1) To develop an economical, easy to use, automated, high throughput system for large scale protein crystallization screening. (2) To develop a new protein crystallization method with high screening efficiency, low protein consumption and complete compatibility with high throughput screening system. (3) To determine the structure of lactate dehydrogenase complexed with NADH by x-ray protein crystallography to study its inherent structural properties. Firstly, we demonstrated large scale protein crystallization screening can be performed in a high throughput manner with low cost, easy operation. The overall system integrates liquid dispensing, crystallization and detection and serves as a whole solution to protein crystallization screening. The system can dispense protein and multiple different precipitants in nanoliter scale and in parallel. A new detection scheme, native fluorescence, has been developed in this system to form a two-detector system with a visible light detector for detecting protein crystallization screening results. This detection scheme has capability of eliminating common false positives by distinguishing protein crystals from inorganic crystals in a high throughput and non-destructive manner. The entire system from liquid dispensing, crystallization to crystal detection is essentially parallel, high throughput and compatible with automation. The system was successfully demonstrated by …
Date: August 9, 2006
Creator: Li, Fenglei
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Biomimetic Nanocomposites of Calcium Phosphate and Self-Assembling Triblock and Pentablock Copolymers (open access)

Biomimetic Nanocomposites of Calcium Phosphate and Self-Assembling Triblock and Pentablock Copolymers

In an effort to mimic the growth of natural bone, self-assembling, micelle and gel-forming copolymers were used as a template for calcium phosphate precipitation. Because of the cationic characteristics imparted by PDEAEM end group additions to commercially available Pluronic{reg_sign} Fl27, a direct ionic attraction mechanism was utilized and a polymer-brushite nanocomposite spheres were produced. Brushite coated spherical micelles with diameters of {approx}40 nm, and agglomerates of these particles (on the order of 0.5 {mu}m) were obtained. Thickness and durability of the calcium phosphate coating, and the extent of agglomeration were studied. The coating has been shown to be robust enough to retain its integrity even below polymer critical micelle concentration and/or temperature. Calcium phosphate-polymer gel nanocomposites were also prepared. Gel samples appeared as a single phase network of agglomerated spherical micelles, and had a final calcium phosphate concentration of up to 15 wt%. Analysis with x-ray diffraction and NMR indicated a disordered brushite phase with the phosphate groups linking inorganic phase to the polymer.
Date: August 9, 2006
Creator: Enlow, Drew Lenzen
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Computational Fluid Dynamics Simulation of Fluidized Bed Polymerization Reactors (open access)

Computational Fluid Dynamics Simulation of Fluidized Bed Polymerization Reactors

Fluidized beds (FB) reactors are widely used in the polymerization industry due to their superior heat- and mass-transfer characteristics. Nevertheless, problems associated with local overheating of polymer particles and excessive agglomeration leading to FB reactors defluidization still persist and limit the range of operating temperatures that can be safely achieved in plant-scale reactors. Many people have been worked on the modeling of FB polymerization reactors, and quite a few models are available in the open literature, such as the well-mixed model developed by McAuley, Talbot, and Harris (1994), the constant bubble size model (Choi and Ray, 1985) and the heterogeneous three phase model (Fernandes and Lona, 2002). Most these research works focus on the kinetic aspects, but from industrial viewpoint, the behavior of FB reactors should be modeled by considering the particle and fluid dynamics in the reactor. Computational fluid dynamics (CFD) is a powerful tool for understanding the effect of fluid dynamics on chemical reactor performance. For single-phase flows, CFD models for turbulent reacting flows are now well understood and routinely applied to investigate complex flows with detailed chemistry. For multiphase flows, the state-of-the-art in CFD models is changing rapidly and it is now possible to predict reasonably well …
Date: August 9, 2006
Creator: Fan, Rong
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Couples Magnetic and Structural Transitions in High-Purity Dy and Gd5SbxGe4-x (open access)

Couples Magnetic and Structural Transitions in High-Purity Dy and Gd5SbxGe4-x

Magnetic materials exhibiting magnetic phase transitions simultaneously with structural rearrangements of their crystal lattices hold a promise for numerous applications including magnetic refrigeration, magnetomechanical devices and sensors. We undertook a detailed study of a single crystal of dysprosium metal, which is a classical example of a system where magnetic and crystallographic sublattices can be either coupled or decoupled from one another. Magnetocaloric effect, magnetization, ac magnetic susceptibility, and heat capacity of high purity single crystals of dysprosium have been investigated over broad temperature and magnetic field intervals with the magnetic field vector parallel to either the a- or c-axes of the crystal. Notable differences in the behavior of the physical properties when compared to Dy samples studied in the past have been observed between 110 K and 125 K, and between 178 K and {approx}210 K. A plausible mechanism based on the formation of antiferromagnetic clusters in the impure Dy has been suggested in order to explain the reduction of the magnetocaloric effect in the vicinity of the Neel point. Experimental and theoretical investigations of the influence of commensurability effects on the magnetic phase diagram and the value of the magnetocaloric effect have been conducted. The presence of newly found …
Date: August 9, 2006
Creator: Chernyshov, Alexander S.
Object Type: Thesis or Dissertation
System: The UNT Digital Library