Production of the radioisotope 18F in novae is severely constrained by the rate of the 18F(p,alpha)15O reaction. A resonance at E(c.m.)=330 keV may strongly enhance the 18F(p,alpha)15O reaction rate, but its strength has been very uncertain. We have determined the strength of this important resonance by measuring the 18F(p,alpha)15O cross section on and off resonance using a radioactive 18F beam at the ORNL Holifield Radioactive Ion Beam Facility. We find that its resonance strength is 1.48+/-0.46 eV, and that it dominates the 18F(p,alpha)15O reaction rate over a significant range of temperatures characteristic of ONeMg novae.

Proton capture by 17 F plays an important role in the synthesis of nuclei in nova explosions. A revised rate for this reaction, based on a measurement of the 1 H( 17 F,p) 17 F excitation function using a radioactive 17 F beam at ORNL's Holifield Radioactive Ion Beam Facility, is used to calculate the nucleosynthesis in nova outbursts on the surfaces of 1.25 M ⊙ and 1.35 M ⊙ ONeMg white dwarfs and a 1.00 M ⊙ CO white dwarf. We find that the new 17 F (p,γ) 18 Ne reaction rate changes the abundances of some nuclides (e.g., 17 O) synthesized in the hottest zones of an explosion on a 1.35 M ⊙ white dwarf by more than a factor of 10 4 compared to calculations using some previous estimates for this reaction rate, and by more than a factor of 3 when the entire exploding envelope is considered. In a 1.25 M ⊙ white dwarf nova explosion, this new rate changes the abundances of some nuclides synthesized in the hottest zones by more than a factor of 600, and by more than a factor of 2 when the entire exploding envelope is considered. Calculations for the 1.00 M ⊙ white dwarf nova show that this new rate changes the abundance of 18 Ne by 21%, but has negligible effect on all other nuclides. Comparison of model predictions with observations is also discussed.

Joining a research group is like joining a family. I have been very fortunate in the academic family that I have found at the University of Tennessee and Oak Ridge National Laboratory. I would like to thank my advisors Raph Hix and Mike Guidry for their guidance, time, patience, and support throughout the process of this work. I would also like to express my appreciation to my committee members (Witek Nazarewic, Mark Littmann, and Kate Jones) for taking the time to be on my committee, review my work, and provide helpful insight. I would like to thank Bronson Messer for help with FLASH and insightful discussions. Great thanks to Mark Littman, Marissa Mills, Betty Mansfield, Catherine Longmire, and Jack Neely for guiding my development as a science writer and introducing me to the world of science journalism. I would also like to thank my many academic siblings and cousins (Marc, Reuben,

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The importance of computing facilities is heralded every six months with the announcement of the new Top500 list, showcasing the world's fastest supercomputers. Unfortunately, with great computing capability does not come great long-term data storage capacity, which often means users must move their data to their local site archive, to remote sites where they may be doing future computation or analysis, or back to their home institution, else face the dreaded data purge that most HPC centers employ to keep utilization of large parallel filesystems low to manage performance and capacity. At HPC centers, data transfer is crucial to the scientific workflow and will increase in importance as computing systems grow in size. The Energy Sciences Network (ESnet) recently launched its fifth generation network, a 100 Gbps high-performance, unclassified national network connecting more than 40 DOE research sites to support scientific research and collaboration. Despite the tenfold increase in bandwidth to DOE research sites amenable to multiple data transfer streams and high throughput, in practice, researchers often under-utilize the network and resort to painfully-slow single stream transfer methods such as scp to avoid the complexity of using multiple stream tools such as GridFTP and bbcp, and contend with frustration from the lack of consistency of available tools between sites. In this study we survey and assess the data transfer methods provided at several DOE supported computing facilities, including both leadership-computing facilities, connected through ESnet. We present observed transfer rates, suggested optimizations, and discuss the obstacles the tools must overcome to receive wide-spread adoption over scp.

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