Coupling of the 4f Electrons in Lanthanide Molecules (open access)

Coupling of the 4f Electrons in Lanthanide Molecules

(C5Me5)2LnOTf where Ln = La, Ce, Sm, Gd, and Yb have been synthesized and these derivatives are good starting materials for the synthesis of (C5Me5)2LnX derivatives. (C5Me5)2Ln(2,2'-bipyridine), where Ln = La, Ce, Sm, and Gd, along with several methylated bipyridine analogues have been synthesized and their magnetic moments have been measured as a function of temperature. In lanthanum, cerium, and gadolinium complexes the bipyridine ligand ligand is unequivocally the radical anion, and the observed magnetic moment is the result of intramolecular coupling of the unpaired electron on the lanthanide fragment with the unpaired electron on the bipyridine along with the intermolecular coupling between radicals. Comparison with the magnetic moments of the known compounds (C5Me5)2Sm(2,2'-bipyridine) and (C5Me5)2Yb(2,2'-bipyridine) leads to an understanding of the role of the Sm(II)/Sm(III) and Yb(II)/Yb(III) couple in the magnetic properties of (C5Me5)2Sm(2,2'-bipyridine) and (C5Me5)2Yb(2,2'-bipyridine). In addition, crystal structures of (C5Me5)2Ln(2,2'-bipyridine) and [(C5Me5)2Ln(2,2'-bipyridine)][BPh4](Ln= Ce and Gd), where the lanthanide is unequivocally in the +3 oxidation state, give the crystallographic characteristics of bipyridine as an anion and as a neutral ligand in the same coordination environment, respectively. Substituted bipyridine ligands coordinated to (C5Me5)2Yb are studied to further understand how the magnetic coupling in (C5Me5)2Yb(2,2'-bipyridine) changes with substitutions. In the …
Date: September 12, 2008
Creator: Kazhdan, Daniel
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Anthrax Sampling and Decontamination: Technology Trade-Offs (open access)

Anthrax Sampling and Decontamination: Technology Trade-Offs

The goal of this project was to answer the following questions concerning response to a future anthrax release (or suspected release) in a building: 1. Based on past experience, what rules of thumb can be determined concerning: (a) the amount of sampling that may be needed to determine the extent of contamination within a given building; (b) what portions of a building should be sampled; (c) the cost per square foot to decontaminate a given type of building using a given method; (d) the time required to prepare for, and perform, decontamination; (e) the effectiveness of a given decontamination method in a given type of building? 2. Based on past experience, what resources will be spent on evaluating the extent of contamination, performing decontamination, and assessing the effectiveness of the decontamination in abuilding of a given type and size? 3. What are the trade-offs between cost, time, and effectiveness for the various sampling plans, sampling methods, and decontamination methods that have been used in the past?
Date: September 12, 2008
Creator: Price, Phillip N.; Hamachi, Kristina; McWilliams, Jennifer & Sohn, Michael D.
Object Type: Report
System: The UNT Digital Library
Energetic Particle-induced Geodesic Acoustic Mode (open access)

Energetic Particle-induced Geodesic Acoustic Mode

A new energetic particle-induced Geodesic Acoustic Mode (EGAM) is shown to exist. The mode frequency, mode structure, and mode destabilization are determined non-perturbatively by energetic particle kinetic effects. In particular the EGAM frequency is found to be substantially lower than the standard GAM frequency. The radial mode width is determined by the energetic particle drift orbit width and can be fairly large for high energetic particle pressure and large safety factor. These results are consistent with the recent experimental observation of the beam- driven n=0 mode in DIII-D. The new mode is important since it can degrade energetic particle confinement as shown in the DIII-D experiments. The new mode may also affect the thermal plasma confinement via its interaction with plasma micro-turbulence.
Date: September 12, 2008
Creator: Fu, G. Y.
Object Type: Report
System: The UNT Digital Library
The ecology and genomics of C02 fixation in oceanic river plumes (open access)

The ecology and genomics of C02 fixation in oceanic river plumes

The ocean/atmosphere interface is the major conduit for the entry of atmospheric CO2 into oceanic carbon pools that can lead to sequestration or recycled release. The surface layers of the temperate and tropical oceans are often too oligotrophic to result in significant primary production that might lead to carbon sequestration. However, nutrient-rich river plumes can alter the primary production schemes of oligotrophic ocean basins, resulting in increased phytoplankton biomass and carbon fixation. The ultimate goal of this proposal is to understand these carbon cycling processes in major river plumes from the molecular processes involved in biological DIC uptake to contribution to basin-wide production and potential sequestration. Our research efforts include a field component to answer the questions raised concerning DIC in plumes entering ocean basins and an intensive genomics approach to understanding these processes on the cellular level using genomic fragments obtained from plume biota. This project is actually composed of 3 separate PI-initiated projects, including projects at the University of South Florida (USF) College of Marine Science, the University of Puerto Rico, and The Ohio State University. This report concerns research conducted at The Ohio State University and studies performed in collaboration with USF. In order to understand what …
Date: September 12, 2008
Creator: Tabita, F. Robert
Object Type: Report
System: The UNT Digital Library
Cathode Effects in Cylindrical Hall Thrusters (open access)

Cathode Effects in Cylindrical Hall Thrusters

Stable operation of a cylindrical Hall thruster (CHT) has been achieved using a hot wire cathode, which functions as a controllable electron emission source. It is shown that as the electron emission from the cathode increases with wire heating, the discharge current increases, the plasma plume angle reduces, and the ion energy distribution function shifts toward higher energies. The observed effect of cathode electron emission on thruster parameters extends and clarifies performance improvements previously obtained for the overrun discharge current regime of the same type of thruster, but using a hollow cathode-neutralizer. Once thruster discharge current saturates with wire heating, further filament heating does not affect other discharge parameters. The saturated values of thruster discharge parameters can be further enhanced by optimal placement of the cathode wire with respect to the magnetic field.
Date: September 12, 2008
Creator: Granstedt, E.M.; Raitses, Y. & Fisch, N. J.
Object Type: Report
System: The UNT Digital Library
POLYMER ELECTROLYTE MEMBRANE ELECTROLYZER OPERATION WITH VARYING INLET WATER FEED CONFIGURATIONS (open access)

POLYMER ELECTROLYTE MEMBRANE ELECTROLYZER OPERATION WITH VARYING INLET WATER FEED CONFIGURATIONS

Proton Exchange Membrane (PEM) electrolysis is a potential alternative technology to crack water in specialty applications where a dry gas stream is needed, such as isotope production. One design proposal is to feed the cathode of the electrolyzer with vapor phase water. This feed configuration would allow isotopic water to be isolated on the cathode side of the electrolyzer and the isotope recovery system could be operated in a closed loop. Tests were performed to characterize the difference in the current-voltage behavior between a PEM electrolyzer operated with a cathode water vapor feed and with an anode liquid water feed. The cathode water vapor feed cell had a maximum limiting current density of 100 mA/cm2 at 70 C compared to a current density of 800 mA/cm2 for the anode liquid feed cell at 70 C. The limiting current densities for the cathode water vapor feed cell were approximately 3 times lower than predicted by a water mass transfer model. It is estimated that a cathode water vapor feed electrolyzer system will need to be between 8-14 times larger in active area or number of cells than an anode liquid feed system.
Date: September 12, 2008
Creator: Fox, E
Object Type: Article
System: The UNT Digital Library
ALTERNATIVE MATERIALS TO PD MEMBRANES FOR HYDROGEN PURIFICATION (open access)

ALTERNATIVE MATERIALS TO PD MEMBRANES FOR HYDROGEN PURIFICATION

Development of advanced hydrogen separation membranes in support of hydrogen production processes such as coal gasification and as front end gas purifiers for fuel cell based system is paramount to the successful implementation of a national hydrogen economy. Current generation metallic hydrogen separation membranes are based on Pd-alloys. Although the technology has proven successful, at issue is the high cost of palladium. Evaluation of non-noble metal based dense metallic separation membranes is currently receiving national and international attention. The focal point of the reported work was to evaluate two different classes of materials for potential replacement of conventional Pd-alloy purification/diffuser membranes. Crystalline V-Ni-Ti and Amorphous Fe- and Co-based metallic glass alloys have been evaluated using gaseous hydrogen permeation testing techniques.
Date: September 12, 2008
Creator: Korinko, P & Adams, T.
Object Type: Article
System: The UNT Digital Library
Lost Opportunities in the Buildings Sector: Energy-Efficiency Analysis and Results (open access)

Lost Opportunities in the Buildings Sector: Energy-Efficiency Analysis and Results

This report summarizes the results and the assumptions used in an analysis of the potential “lost efficiency opportunities” in the buildings sector. These targets of opportunity are those end-uses, applications, practices, and portions of the buildings market which are not currently being addressed, or addressed fully, by the Building Technologies Program (BTP) due to lack of resources. The lost opportunities, while a significant increase in effort and impact in the buildings sector, still represent only a small portion of the full technical potential for energy efficiency in buildings.
Date: September 12, 2008
Creator: Dirks, James A.; Anderson, David M.; Hostick, Donna J.; Belzer, David B. & Cort, Katherine A.
Object Type: Report
System: The UNT Digital Library
Design and Fabrication of a Radiation-Hard 500-MHz Digitizer Using Deep Submicron Technology (open access)

Design and Fabrication of a Radiation-Hard 500-MHz Digitizer Using Deep Submicron Technology

The proposed International Linear Collider (ILC) will use tens of thousands of beam position monitors (BPMs) for precise beam alignment. The signal from each BPM is digitized and processed for feedback control. We proposed the development of an 11-bit (effective) digitizer with 500 MHz bandwidth and 2 G samples/s. The digitizer was somewhat beyond the state-of-the-art. Moreover we planned to design the digitizer chip using the deep-submicron technology with custom transistors that had proven to be very radiation hard (up to at least 60 Mrad). The design mitigated the need for costly shielding and long cables while providing ready access to the electronics for testing and maintenance. In FY06 as we prepared to submit a chip with test circuits and a partial ADC circuit we found that IBM had changed the availability of our chosen IC fabrication process (IBM 6HP SiGe BiCMOS), making it unaffordable for us, at roughly 3 times the previous price. This prompted us to change our design to the IBM 5HPE process with 0.35 µm feature size. We requested funding for FY07 to continue the design work and submit the first prototype chip. Unfortunately, the funding was not continued and we will summarize below the work …
Date: September 12, 2008
Creator: Gan, K.K.; Johnson, M.O.; Kass, R.D. & Moore, J.
Object Type: Report
System: The UNT Digital Library
Improvement in Plasma Performance with Lithium Coatings in NSTX (open access)

Improvement in Plasma Performance with Lithium Coatings in NSTX

Lithium as a plasma-facing material has attractive features, including a reduction in the recycling of hydrogenic species and the potential for withstanding high heat and neutron fluxes in fusion reactors. Dramatic effects on plasma performance with lithium-coated plasma-facing components (PFCOs) have been demonstrated on many fusion devices, including TFTR, [1] T-11M, [2] and FT-U. [3] Using a liquid-lithium-filled tray as a limiter, the CDX-U device achieved very significant enhancement in the confinement time of ohmically heated plasmas. [4] The recent NSTX experiments reported here have demonstrated, for the first time, significant and recurring benefits of lithium PFC coatings on divertor plasma performance in both L- and H- mode regimes heated by neutral beams.
Date: September 12, 2008
Creator: Kaita, R.; Ahn, J.-W.; Allain, J. P.; Bell, M. G.; Bell, R.; Boedo, J. et al.
Object Type: Article
System: The UNT Digital Library
A technique for estimating the time-of-track distribution of optical vehicle tracking systems (open access)

A technique for estimating the time-of-track distribution of optical vehicle tracking systems

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Date: September 12, 2008
Creator: Roberts, R. S.; Carrano, C. J. & Bulaevskaya, V. L.
Object Type: Article
System: The UNT Digital Library