GraphLab: A New Framework for Parallel Machine Learning

Designing and implementing efficient, provably correct parallel machine learning (ML) algorithms is challenging. Existing high-level parallel abstractions like MapReduce are insufficiently expressive while low-level tools like MPI and Pthreads leave ML experts repeatedly solving the same design challenges. By targeting common patterns in ML, we developed GraphLab, which improves upon abstractions like MapReduce by compactly expressing asynchronous iterative algorithms with sparse computational dependencies while ensuring data consistency and achieving a high degree of parallel performance. We demonstrate the expressiveness of the GraphLab framework by designing and implementing parallel versions of belief propagation, Gibbs sampling, Co-EM, Lasso and Compressed Sensing. We show that using GraphLab we can achieve excellent parallel performance on large scale real-world problems

Collisional Dynamics of Macroscopic Particles in a Viscous Fluid

This thesis presents experimental measurements of the approach and rebound of a particle colliding with a wall in a viscous fluid. Steel, glass, nylon, and Delrin particles were used, with diameters ranging from 3 to 12 mm. The experiments were performed using a thick Zerodur or Lucite wall with various mixtures of glycerol and water. Normal and tangential coefficients of restitution were defined from the ratios of the respective velocity components at the point of contact just prior to and after impact. These coefficients account for losses due to lubrication effects and inelasticity. The experiments clearly show that the rebound velocity depends strongly on the impact Stokes number and weakly on the elastic properties of the materials. Below a Stokes number of approximately 10, no rebound of the particle occurs. Above a Stokes number of approximately 500, the normal coefficient of restitution asymptotically approaches the value for a dry collision. The data collapse onto a single curve of restitution coefficient as a function of Stokes number when normalized by the dry coefficient of restitution. Oblique collisions in a fluid are qualitatively similar to oblique collisions in a dry system, with a lowered friction coefficient dependent on surface roughness. For smooth surfaces the friction coefficient is drastically reduced due to lubrication effects. Values for the friction coefficient are predicted based on elastohydrodynamic lubrication theory. The particle surface roughness was found to affect the repeatability of some measurements, especially for low impact velocities. A significant retardation of a particle approaching a target at a low Stokes number was observed and quantified. The distance at which the particle's trajectory varies due to the presence of the wall is dependent on the impact Stokes number. The observed slowdown can be predicted from hydrodynamic theory to a good approximation. An analysis of the erosion of ductile materials during immersed collisions is presented. The size of the crater formed by the impact of a single particle against a ductile target can be estimated from theory, and these estimates agree well with experimental measurements.</p

Applications of Elastic Modeling, Thermobarometry, and Thermal History Modeling to (Ultra)high-Pressure Metamorphic Rocks

Subduction zones are tectonically active regions that produce seismicity and volcanism during plate convergence and ultimately recycle crustal material into the mantle. Since these regions dictate many global scale tectonic and geochemical processes (i.e. orogenesis, volatile flux into the mantle, etc.), it is important to understand the depth-temperature conditions of mineral reactions during the subduction-exhumation metamorphic cycle. (Ultra)high-pressure ((U)HP) metamorphic rocks, such as blueschists and eclogites, are formed during metamorphism of subducted crust and sediments along relatively cold geothermal gradients. (U)HP metamorphic rocks may be incorporated into the subduction zone accretionary wedge and exhumed, thereby providing a direct records of subduction zone conditions and processes. This PhD research is focused on the determination of pressure (P) – temperature (T) conditions of exhumed (U)HP subduction zone metamorphic rocks in order to better understand the metamorphic conditions of geologic processes within subduction zones. This dissertation contains three separate studies which combine multiple thermobarometric methods to better constrain the petrologic history of exhumed subduction zone metamorphic rocks. Elastic thermobarometry, trace element thermobarometers, and numerical modeling approaches were integrated to determine P–T(–t) histories of (U)HP metamorphic rocks. In the first chapter of this dissertation, multi-diffusion domain numerical modelling of white mica 40Ar/39Ar and thermobarometric data were used to forward model continuous P–T–t paths of blueschist block exhumation from the western Baja terrane of Mexico. Results from this chapter provide new insights into the application of white mica P–T–t numerical modeling to constrain exhumation histories of (U)HP metamorphic rocks. In the second chapter, strain-based quartz-in-garnet elastic thermobarometric data was combined with Ti concentration measurements and a Ti-in-quartz solubility model to estimate P–T conditions of inclusion entrapment in garnet from a quartzofeldspathic gneiss from the (U)HP terrane of eastern Papua New Guinea. The quartz-in-garnet and Ti-in-quartz (QuiG-TiQ) method gives P–T constraints from a single mineral and does not introduce temperature estimates external of the host-inclusion system. Results from this chapter give new insights into the use of elastic thermobarometry to determine conditions of metamorphic mineral growth and inclusion entrapment. In the third chapter, the first characterization of mineralogical evidence for UHP metamorphism in the Appalachian orogen is presented. Multiple thermobarometric methods, including Zr-in-rutile trace element and quartz-in-garnet elastic thermobarometry, were combined with petrologic observations to characterize the prograde metamorphic conditions of garnet growth during subduction