Physical Sciences and Mathematics Commons^™

Microstructure And Critical Current Of Hot-Pressed Ybco Ceramics, Şadan Özcan, Tezer Firat, Engi̇n Özdaş

Turkish Journal of Physics

The effect of hot-pressing (HPing) on the densification and the superconducting properties of YBCO were investigated. The phases and microstructure were analysed by XRD and SEM and transport properties were studied by I-V and AC susceptibility measurements. Relative density up to 93% and critical current density of 509 A/cm^{2} at 77 K were achieved through uniaxial HPing at 800°C under 325 kg/cm^{2} pressure for 4 hours. HPing raised the J_{c} from 80 A/cm^{2} to 509 A/cm^{2}. These results and AC susceptibility measurements reveal that the weak links or pinning forces were improved by increasing HPing pressure.

Characterization Of The Sno_{2}/P Contact Resistance And Sno_{2} Properties In Operating A-Si:H P-I-N Solar Cells, Ruhi̇ Kaplan, Bengü Kaplan

Turkish Journal of Physics

A method is presented to characterize the TCO/p contact and the TCO sheet resistance in a-Si TCO/p-i-n superstrate devices. It is extremely useful for understanding resistance losses in modulus and diagnosing how plasma processing influences the TCO layers. Analysis of 4-terminal dark J-V measurements as a function of temperature on devices with varying TCO geometry yields the TCO/p contact resistance R_{TCO/p}, its activation energy E_{a} or barrier height, and the TCO sheet resistance R_{SH} in an integrated device structure. The method is applied to devices fabricated on different brands of commercial SnO_{2} substrates with different p-layers. Important new results are …

The Temperature Dependence Of The Electronic Structure Of Si \Delta-Doped Gaas, Emi̇ne Öztürk

Turkish Journal of Physics

We investigated theoretically the change of electronic properties of Si \delta-doped GaAs layer as a function of temperature. We studied the influence of temperature on the donor concentration for a nonuniform distribution, which is taken as different from the known Gaussian distribution. In order to obtain the electronic structure we have calculated self-consistent Schrödinger - Poisson equations. We have seen that the change of the electronic properties as dependent on temperature is less pronounced at higher doping concentration.

Defect Structure Of Glow Peak 1 In Lif:Mg,Ti (Tld-100), A. Necmeddi̇n Yazici

Turkish Journal of Physics

The possible defect structure of peak 1 of LiF:Mg,Ti (TLD-100) was studied in the present work after different pre-irradiation heat treatments between 80°C and 150°C using the computer glow curve deconvolution (CGCD) method. It was shown that the defect structure of peak 1 is based on colloid centers, Ti^{+4}-3O_{2}^{-}-mixed centers and U_{1}-centers.

The Effect Of Surface Curvature On Wound Healing In Bone, J. A. Adam

Mathematics & Statistics Faculty Publications

The time-independent nonhomogeneous diffusion equation is solved for the equilibrium distribution of wound-induced growth factor over a hemispherical surface. The growth factor is produced at the inner edge of a circular wound and stimulates healing in regions where the concentration exceeds a certain threshold value. An implicit analytic criterion is derived for complete healing of the wound. (C) 2001 Elsevier Science Ltd. All rights reserved.

Advances In Space Radiation Shielding Codes, John W. Wilson, Ram K. Tripathi, Garry D. Qualls, Francis A. Cucinotta, Richard E. Prael, John W. Norbury, John H. Heinbockel, John Tweed, Giovanni De Angelis

Mathematics & Statistics Faculty Publications

Early space radiation shield code development relied on Monte Carlo methods and made important contributions to the space program. Monte Carlo methods have resorted to restricted one-dimensional problems leading to imperfect representation of appropriate boundary conditions. Even so, intensive computational requirements resulted and shield evaluation was made near the end of the design process. Resolving shielding issues usually had a negative impact on the design. Improved spacecraft shield design requires early entry of radiation constraints into the design process to maximize performance and minimize costs. As a result, we have been investigating high-speed computational procedures to allow shield analysis from …

A High Resolution Gravity Survey Of The Lake St. Martin Impact Structure, Manitoba, Canada, Christina Davids

Theses and Dissertations

There are roughly 160 known impact craters listed in the Cratering Database (Earth Impact Database, 2002) of these approximately 20% are buried structures. Geophysical methods of investigation are used to study buried impact structures and add to the growing knowledge base of crater properties. Approximately three to five craters are discovered each year, some of which may be identified through gravity anomalies. A high-resolution gravity survey of the Lake St. Martin impact structure, southern Manitoba, Canada, was conducted to further interpret the structure's gravity anomaly. Previous studies have suggested two different crater diameters for Lake St. Martin, one of 23-km …

Southern Nevada Interagency Science & Research Program, Public Lands Institute

Interagency Science and Research Strategy

Conduct and support high quality, relevant, up-to-date research that is needed to solve problems and make effective decisions to enhance conservation, restoration, and adaptive management of public lands.

Spatial And Temporal Patterns Of Eastern White Pine Regeneration In The Northwestern Ohio Oak Stand, Scott R. Abella, Neil W. Macdonald

Public Policy and Leadership Faculty Research

Eastern white pine (Pinus strobus L.) was often associated with oaks (Quercus spp.) on upland sites in presettlement forests of the upper Great Lakes region, but widespread logging and subsequent fires in the late 1800s converted these upland sites to fire-tolerant oak forests. Although white pine regeneration is occurring in these second-growth oak forests, white pine regeneration patterns in oak forests of the Great Lakes region are not well documented. We examined white pine regeneration in the southern Great Lakes region in an oak stand within the Oak Openings region of northwestern Ohio, where white pine plantations established in the …

Bonytail (Gila Elegans) May Enhance Survival Of Razorback Suckers (Xyrauchen Texanus) In Rearing Ponds By Preying On Exotic Crayfish, Nathan Lenon, Krystyna Anne Stave, Tom Burke, James E. Deacon

Public Policy and Leadership Faculty Research

This study examined the potential of bonytail (Gila elegans) to enhance survival of young razorback sucker (Xyrauchen texanus) in rearing ponds by serving as a biological control agent for young stages of Red Swamp Crayfish (Procambarus clarki). Large populations of crayfish in rearing ponds negatively affect the survival of razorback suckers, through predation and competition for food. Traps made with 6.34 mm (0.25 inch) mesh have been used in an effort to reduce crayfish populations, however crayfish less than 17 mm carapace length (CPL) are able to escape. Juvenile bonytail in experimental trials ate young crayfish ranging in size from …

Optical And Magnetic Behaviour Of Low Dimensional Structures, Francis Pedreschi

Doctoral

Low dimensional structures can exhibit unusual properties due to the quantum confinement of electrons. This may manifest itself in any effects that depend on electron behaviour. In this study, the optical and magnetic properties in particular of two types of low dimensional structures are examines. Quantum wires are structures that have macroscopic length scales along one dimension and nanometre length scales in the others. Two Indium induced reconstructions of Silicon surfaces were grown and examined to determine if quantum confinement, a necessary requirement for a quantum wire, did exist for their structures. A UHV compatible Reflectance Anisotropy Spectroscopy (RAS) instrument, …

Atmospheric Stability And Gravity Wave Dissipation In The Mesopause Region, Chester S. Gardner, Yucheng Zhao, Alan Z. Liu

Physical Sciences - Daytona Beach

High-resolution temperature profile data collected at the Urbana Atmospheric Observatory (40ºN, 88ºW) and Starfire Optical Range, NM (35ºN, 106.5ºW) with a Na lidar are used to assess the stability of the mesopause region between 80 and 105 km. The mean diurnal and annual temperature profiles demonstrate that in the absence of gravity wave and tidal perturbations, the background atmosphere is statically stable throughout the day and year. Thin layers of instability can be generated only when the combined perturbations associated with tides and gravity waves induce large vertical shears in the horizontal wind and temperature profiles. There is a region …

Nitrate Anomaly In The Upper Nutricline In The Northern South China Sea - Evidence For Nitrogen Fixation, George T. F. Wong, Shi-Wei Chung, Fuh-Kwo Shiah, Chung-Chi Chen, Liang-Saw Wen, Kon-Kee Liu

OES Faculty Publications

[1] Up to 2 μM of nitrate anomaly, N*, were found in the upper nutricline at the South East Asia Time-series Study (SEATS) site in the northern South China Sea (SCS). These concentrations were among the higher values reported in the Pacific and indicate the significant contribution of the remineralization of nitrogen-rich organic matter formed by nitrogen fixation to the nutrient dynamics of the area. The concentrations were systematically higher, by up to 2.5 μM, in the Fall through the early Spring, during the northeast monsoon, than in the Summer, suggesting that the impact of nitrogen fixation was higher during …

The Transformation Of Iodate To Iodide In Marine Phytoplankton Cultures, George T. F. Wong, Ajcharaporn U. Piumsomboon, William M. Dunstan

OES Faculty Publications

Six species of phytoplankton, representing 6 major phylogenetic groups (2 oceanic species: a cyanobacteria, Synechococcus sp., and a coccolithophorid, Emiliania huxleyi; and 4 coastal species: a prasinophyte, Tetraselmis sp., the green algae Dunaliella tertiolecta, the diatom Skeletonema costatum and a dinoflagellate Amphidinium carterae) were tested for their ability to reduce iodate to iodide in batch cultures. They all did so to varying degrees. Thus, the reduction of iodate to iodide by phytoplankton may be a general phenomenon in the marine environment. At ambient concentrations of iodate, the rates of depletion of iodate and appearance of …

Arctic Ice Export Events And Their Potential Impact On Global Climate During The Late Pleistocene, Dennis A. Darby, Jens F. Bischof, Robert F. Spielhagen, Steven A. Marshall, Stephen W. Herman

OES Faculty Publications

Ice sheets in the North American Arctic and, to a lesser extent, those in northern Eurasia calved large quantities of icebergs that drifted through Fram Strait into the Greenland Sea several times during the late Pleistocene. These icebergs deposited Fe oxide grains (45-250 mum) and coarse lithic clasts >250 mum matched to specific circum-Arctic sources. Four massive Arctic iceberg export events are identified from the Laurentide and the Innuitian ice sheets, between 14 and 34 ka (calendar years) in a sediment core from Fram Strait. These relatively short duration (<1-4 kyr) events contain 3-5 times the background levels of Fe oxide grains. They began suddenly, as indicated by a steep rise in the number of grains matched to an ice sheet source, suggesting rapid purges of ice through Fram Strait, due perhaps to collapse of ice sheets. The larger events from the northwestern Laurentide ice sheet are preceded by events from the Innuitian ice sheet. Despite the chronological uncertainties, the Arctic export events appear to occur prior to Heinrich events.

Peptide Hydrolysis, Amino Acid Oxidation, And Nitrogen Uptake In Communities Seasonally Dominated By Aureococcus Anophagefferens, Margaret R. Mulholland, Christopher J. Gobler, Cindy Lee

OES Faculty Publications

Elevated levels of dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) are among the factors implicated in the initiation of algal blooms. However, the degree to which phytoplankton augment their autotrophic metabolism with heterotrophic uptake of organic carbon that is associated with DON is unknown. We evaluated the relative importance of peptide hydrolysis, amino acid oxidation, and amino acid uptake over a seasonal cycle in an embayment on Long Island, New York, that had high concentrations of dissolved organic matter (DOM) and a bloom of the brown tide pelagophyte, Aureococcus anophagefferens. Amino acids were a significant component (up …

Effects Of Nonequilibrium Atmospheric Pressure Plasmas On The Heterotrophic Pathways Of Bacteria And On Their Cell Morphology, Mounir Laroussi, J. Paul Richardson, Fred C. Dobbs

OES Faculty Publications

To date, most research on the interaction of nonequilibrium, atmospheric pressure plasma discharges with bacteria has concentrated on the germicidal effects. Therefore, published results deal mainly with killing efficacy and little attention is given to physical mechanisms and biochemical pathways and their potential alterations when cells of microorganisms are exposed to the plasma. In this letter, an attempt to investigate the effects of plasma exposure on the biochemical pathways of bacteria is presented. In addition, using electron microscopy, we investigate if any gross morphological changes take place when cells are exposed to a lethal dose of plasma. We are testing …

Microbial Ecology Of Ballast Water During A Transoceanic Voyage And The Effects Of Open-Ocean Exchange, Lisa A. Drake, Gregory M. Ruiz, Bella S. Galil, Timothy L. Mullady, Daniela O. Friedmann, Fred C. Dobbs

OES Faculty Publications

The only procedure used frequently to reduce the risk of invasion by ballast-mediated biota is open-ocean exchange of ballast water, a procedure in which vessels release coastal water and replace it with oceanic water. Limited information exists concerning the effects of transport upon the aquatic microbial community throughout transit and following open-ocean exchange, A transoceanic voyage aboard a commercial bulk carrier afforded us the opportunity to sample the microbial community in exchanged and unexchanged ballast-water holds during the journey from Hadera, Israel to Baltimore, USA. Five days following the exchange process, all microbial metrics tested (i.e. bacteria concentration, virus-like particle …

Impact Of Sea Grass Density On Carbonate Dissolution In Bahamian Sediments, David J. Burdige, Richard C. Zimmerman

OES Faculty Publications

Carbonate dissolution has been widely observed in shallow water tropical sediments. However, sediment budgets C have generally not been closed with respect to the amount of acid required to produce the observed carbonate dissolution. Recently it has been suggested that enhanced oxygen transport into sediments through the roots and rhizomes of sea grasses might play a role in resolving this mass balance problem. We conducted studies of sea grass-carbonate sediment interactions around Lee Stocking Island, Exuma Islands, Bahamas to further examine this problem. Our studies showed that alkalinity, total dissolved inorganic carbon (ΣCO₂) and Ca²⁺ increased with …

Project Continuation Proposal: Radiation Transport Modeling Of Beam-Target Experiments For The Aaa Project, William Culbreth

Reactor Campaign (TRP)

The AAA program will rely on the use of an accelerator-based transmuter1 to expose spent nuclear fuel to high-energy neutrons. The neutron flux will be sufficient to activate or fission the long-lived isotopes of Tc, I, Pu, Am, Cm, and Np that present a significant radiological hazard in commercial spent fuel. Transmuter fuel will be subcritical and a high-energy proton accelerator is needed to maintain the necessary neutron flux through the use of a neutron spallation target. The maximum neutron energy produced by spallation (~ 800 MeV) is significantly higher than that produced by a commercial light water reactor (~ …

Radiation Transport Modeling Of Beam-Target Experiments, William Culbreth, Denis Beller

Reactor Campaign (TRP)

In the first year of the UNLV effort, researchers planned to develop the models of the experimental systems to predict the neutron flux and leakage from the experimental targets using the MCNPX code suite in order to help determine these missing parameters. To support these models, the researchers project, or estimate, values for the unknown parameters describing various events and phenomena occurring within the beam-target experiment. The results of these simulations will then be compared against the observed neutron leakage rates and energies. The estimates for the unknown parameters are then revised to correlate with the observed values (these parameters …

University Of Nevada, Las Vegas Transmutation Research Program Annual Report 2001, Anthony Hechanova, Elizabeth Johnson, Gary Cerefice

Transmutation Research Program Reports (TRP)

The UNLV Transmutation Research Program was established in March 2001 as part of the national Advanced Accelerator Applications program to develop the technologies necessary for the ecological and economical treatment of spent nuclear fuel.

The primary role of the UNLV program in the national effort is the training of graduate and undergraduate students in nuclear engineering and other related fields to support the augmentation of the U.S. human infrastructure for transmutation technologies.

To accomplish this role, UNLV has developed the TRP with the primary focus of supporting student research into transmutation and supporting technologies. This focus is realized through the …

Experimental Investigation Of Steel Corrosion In Lead Bismuth Eutectic (Lbe): Characterization, Species Identification, And Chemical Reactions, John Farley, Dale L. Perry, Allen L. Johnson

Transmutation Sciences Materials (TRP)

The goal of the present research is to achieve a basic understanding of corrosion of steels by Lead Bismuth Eutectic (LBE). Liquid LBE is under consideration in the transmuter as both a spallation target and as a blanket coolant. There have been previous studies of LBE, especially by the Russians, who have over 80 reactor-years experience with LBE coolant in their Alpha-class submarine reactors. However, a fundamental understanding and verification of its role in the corrosion of steels is still very incomplete. We have begun a program of post-experiment testing and analysis on steel samples that have been in intimate …

Corrosion Of Steel By Lead Bismuth Eutectic, John Farley, Dale L. Perry, Allen L. Johnson

Transmutation Sciences Materials (TRP)

This research program will analyze various steel samples that have been exposed to LBE as part of the national program to develop LBE and transmutation technologies. This information will be paramount in developing engineering efforts to control, avoid, and/or minimize the effect of corrosion of steels by LBE in transmuter and LBE systems. Additionally, this program provides UNLV researchers with hands-on experience that will be crucial in developing the UNLV LBE program, supporting the University’s mission with the ISTC target complex, and the future development of additional facilities to examine LBE systems.

The research group plans to test the hypothesis …

Corrosion Of Steel By Lead Bismuth Eutectic: Year 1 Annual Report, John Farley

Transmutation Sciences Materials (TRP)

The goal is to investigate the corrosion of stainless steel by lead-bismuth eutectic (LBE), which has been proposed for use as a blanket coolant and a spallation target in the transmuter.

Hydrogen-Induced Embrittlement Of Candidate Target Materials For Applications In Spallation-Neutron-Target Systems, Ajit K. Roy, Brendan O'Toole, Zhiyong Wang, David W. Hatchett

Transmutation Sciences Materials (TRP)

Spallation-neutron-sources, such as those under investigation for use in accelerator-driven transmutation systems, generate neutrons through the collision of high-energy protons, or charged hydrogen atoms, with heavy metal targets such as lead. As a result, these systems also tend to deposit a significant amount of hydrogen in the materials of the transmuter target and superstructure. This can result in accelerated corrosion and changes in the properties of the exposed materials. Of particular importance is a phenomenon called hydrogen embrittlement, in which materials lose their ductility (ability to deform under stress) and become brittle (more susceptible to fracture) after reacting with hydrogen. …

Modeling Corrosion In Oxygen Controlled Lbe Systems With Coupling Of Chemical Kinetics And Hydrodynamics: Task V 4th Quarterly Report, Samir Moujaes

Transmutation Sciences Materials (TRP)

The project is moving on target with the newly realigned objective set for the Phase I. Through close communications with Dr. Li and Dr. Jinsuo Zhang from LANL a realignment of the simulation work has been recommended. The reason for that is the vendor of STAR-CD/CHEMKIN had not perfected yet the final coupling of the post processing of output for any potential surface chemistry reaction taking place on the inside pipe surface of the LBE loop. This is because the coupling of CHEMKIN and STAR-CD has been done fairly recently.

Our final effort has been to generate using an innovative …

Modeling Corrosion In Oxygen Controlled Lbe Systems With Coupling Of Chemical Kinetics And Hydrodynamics, Samir Moujaes, Yitung Chen

Transmutation Sciences Materials (TRP)

Many of the international efforts to develop transmutation technology, including the U.S., Russian, and European scientific communities, have determined that lead bismuth eutectic (LBE) is a potential material for use as a both a spallation target and a coolant. To exploit this potential, a more thorough understanding of the effect and rates of corrosion on steels, particularly non-Russian alloys, inside the LBE systems is required. Properly controlling the oxygen content in LBE systems has been observed to drastically reduce the corrosion of structural steels in LBE. However, the transport of oxygen and formation of corrosion products is not well understood; …

Development Of A Mechanistic Understanding Of High-Temperature Deformation Of Alloy Ep-823, Ajit K. Roy, Brendan O'Toole

Transmutation Sciences Materials (TRP)

Alloy EP-823 has been developed as a structural material for Lead Bismuth Eutectic (LBE) systems, such as those under development for nuclear transmutation systems, as well as other applications. However, very little data regarding the mechanical properties of this alloy exists in the open literature, particularly in the temperature regime of interest for transmutation systems. To address this need, the UNLV research team, in collaboration with researchers from Los Alamos National Laboratory, has developed a research program to evaluate tensile properties of Alloy EP-823 stainless steel at elevated temperatures, which is not being performed at any other facility to date. …

Neutron Multiplicity Measurements Of Target/Blanket Materials, Carter D. Hull, William H. Johnson

Transmutation Sciences Physics (TRP)

To begin developing the database necessary for the validation and benchmarking of the LAHET component of the MCNPX code suite, the UNLV research program has set forth the following objectives. First, the current MCNPX suite will be used to develop models of multi-element neutron detector systems. These models of the detector systems will be incorporated into the design of detailed models for the entire detector-target system. These models will first be used to help design the irradiation experiments, and then will be used to model the behavior of the system. Irradiation experiments corresponding to the detector-target system models will be …