Browsing by Author "Mackey, Mark"
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Item Accelerating a Simulation of Type-I X-ray Bursts from Accreting Neutron Stars(2012-04-18) Mackey, MarkThe goal of my project was to develop an optimized linear system solver to shorten the runtime of a computer simulation. The simulation was created to study the thermonuclear burning of Type I X-ray Bursts in low-mass X-ray binary star systems (LMXBs). To study these systems, thousands of X-ray bursts need to be simulated. Currently, the simulation can complete around one X-ray burst per day. I worked on accelerating the main bottleneck of the simulation by using very powerful graphics cards (GPUs) instead of the central processing unit (CPU) to perform the necessary calculations. I made steady progress over the summer towards this goal and eventually developed a solution that was four to five times faster than the original code.Item End-Effects in Diblock Copolymer Melts(2018-01) Mackey, MarkModern understanding of block copolymer systems relies heavily on coarse-grained models and mean-field theories such as self-consistent field theory (SCFT) and Fredrickson-Helfand (FH) theory. These models simplify the system, ignoring the finer structural details of the underlying polymers. One often ignored detail is the difference in the chemistry of the last monomer on the chain. Polymer synthesis re- quires the end-monomer to have a different chemistry than the other monomers in the chain. The effect that this difference has on equilibrium properties of the system has not been thoroughly explored. This work is an attempt to quantify these effects using course-grained simulations. We report on a number of simulation measurements designed to characterize the local environment of the end-monomer. The local composition distributions of monomers around the end-monomer was measured and compared to the other monomers. Additionally the composition profile of all monomer types was measured and compared to 1-dimensional SCFT simulations. Our second focus was to quantify the shift in position of the Order-Disorder Tran- sition (ODT) due to an end-monomer that was more repulsive than the other beads in the chain. Upper and lower bounds on the new position of the ODT were calculated using conventional scattering structure factor hysteresis loop methods. A subsequent Claperyon-style approximation of the new position of the ODT agreed nicely with the range that was measured. The precise location of the ODT was then obtained using well-tempered metadynamics simulations. Finally, we estimated the effective interaction parameter χe by fitting disordered phase scattering measurements to Renormalized One Loop (ROL) theory predictions. This was used to determine the effect that the repulsive end-monomer had on the value χeN at the ODT. Our results indicate that the effect is small enough to go unnoticed when the calibration of χe is constrained to scattering data from a single chain-length.