Uncertainty quantification for problems in radionuclide transport

The field of radionuclide transport has long recognised the stochastic nature of the problems encountered. Many parameters that are used in computational models are very difficult, if not impossible, to measure with any great degree of confidence. For example, bedrock properties can only be measured at a few discrete points, the properties between these points may be inferred or estimated using experiments but it is difficult to achieve any high levels of confidence. This is a major problem when many countries around the world are considering deep geologic repositories as a disposal option for long-lived nuclear waste but require a high degree of confidence that any release of radioactive material will not pose a risk to future populations. In this thesis we apply Polynomial Chaos methods to a model of the biosphere that is similar to those used to assess exposure pathways for humans and associated dose rates by many countries worldwide. We also apply the Spectral-Stochastic Finite Element Method to the problem of contaminated fluid flow in a porous medium. For this problem we use the Multi-Element generalized Polynomial Chaos method to discretise the random dimensions in a manner similar to the well known Finite Element Method. The stochastic discretisation is then refined adaptively to mitigate the build up errors over the solution times. It was found that these methods have the potential to provide much improved estimates for radionuclide transport problems. However, further development is needed in order to obtain the necessary efficiency that would be required to solve industrial problems

Ultrahigh Energy Cosmic Rays: The state of the art before the Auger Observatory

In this review we discuss the important progress made in recent years towards understanding the experimental data on cosmic rays with energies \agt 10^{19} eV. We begin with a brief survey of the available data, including a description of the energy spectrum, mass composition, and arrival directions. At this point we also give a short overview of experimental techniques. After that, we introduce the fundamentals of acceleration and propagation in order to discuss the conjectured nearby cosmic ray sources. We then turn to theoretical notions of physics beyond the Standard Model where we consider both exotic primaries and exotic physical laws. Particular attention is given to the role that TeV-scale gravity could play in addressing the origin of the highest energy cosmic rays. In the final part of the review we discuss the potential of future cosmic ray experiments for the discovery of tiny black holes that should be produced in the Earth's atmosphere if TeV-scale gravity is realized in Nature.Comment: Final version. To be published in Int. J. Mod. Phys.

Modeling and Simulation in Engineering

The general aim of this book is to present selected chapters of the following types: chapters with more focus on modeling with some necessary simulation details and chapters with less focus on modeling but with more simulation details. This book contains eleven chapters divided into two sections: Modeling in Continuum Mechanics and Modeling in Electronics and Engineering. We hope our book entitled "Modeling and Simulation in Engineering - Selected Problems" will serve as a useful reference to students, scientists, and engineers

Search for an anomalous excess of charged-current electron neutrino interactions with the MicroBooNE detector

Includes bibliographical references.2022 Fall.MicroBooNE is a liquid argon time projection chamber detector designed to address the excess of low-energy electromagnetic events observed by the MiniBooNE detector. Electron neutrinos can create a wide variety of topologies when interacting with liquid argon; this analysis measures events without pions, both with (1eNp0π) and without (1e0p0π) visible protons. This thesis presents a first measurement of pionless charged-current electron neutrino interactions from the Booster Neutrino Beam at Fermilab in the MicroBooNE detector. A model based on the MiniBooNE result is used to quantify the strength of the electron neutrino excess. The analysis suggests that if an excess is present, it is not consistent with a simple scaling of the electronneutrino contribution to the flux. Combined, the 1eNp0π and 1e0p0π channels do not give a conclusive indication of the tested model, but separately they both disfavor the low-energy excess model at > 90% CL. The observation in the most sensitive 1eNp0π channel is below the prediction and is consistent with no excess. In the less sensitive 1e0p0π channel the observation at low energy is above the prediction, while overall there is agreement over the full energy spectrum