Dynamics of pyroclastic density currents : : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Sciences at Massey University, Palmerston North, New Zealand

Listed in 2016 Dean's List of Exceptional ThesesPyroclastic density currents (PDCs) are the most dangerous mass flows on Earth. Yet they remain poorly understood because internal measurements and observations are hitherto non-existent. In this thesis, the first measurements and views into experimental large-scale PDCs synthesized by “column collapse” provide insights into the internal structure, transport and emplacement dynamics of dense PDCs or pyroclastic flows. While from an outside point of view, PDCs resemble dilute gravity currents, the internal flow structure shows longitudinal and vertical complexities that greatly influence the PDCs‟ propagation and emplacement dynamics. Internal velocity and concentration profiles from direct observations provide the evidence of an unforeseen intermediate zone that plays an important role into the transfer of mass from the ash-cloud to the underflow. The intermediate zone is a “dense suspension” where particle cluster in bands to form mesoscale structures. These reduce particle drag and yield an extreme sedimentation rate of particles onto the newly-formed underflow. These findings call into question the existing paradigm of a continuous vertical concentration profile to explain the formation of massive layers and an underflow from ash-clouds. Instead, a sharp concentration jump occurs between the intermediate zone, with concentrations of the order of few volume percent, and the underflow, with concentrations of c.45%. PDCs were found to be composed of 4 main zones identified as the underflow, and the ash-cloud head, body and wake. Following the evolution of the PDC structure over time allows the formation of a complex ignimbrite deposit sequence to be uncovered, reproducing experimentally the “standard ignimbrite sequence” reported from field studies. Experiments revealed that each flow zone deposited the particulate load under contrasting emplacement timescales (spanning up to 5 orders of magnitude), which are primarily controlled by the concentration of the zone. The ash-cloud head is the most dynamic zone of the PDC, where proximally mass is intensively transferred downward and feeds the underflow front, while at all times, the finest particles are entrained upward and feed the wake through detachment of large Kelvin-Helmholtz instabilities. Subsequently, kinematic coupling between the moving underflow and overriding ash-cloud leads to a forced-supercriticality, preferentially affecting the head. The wide range of particle sizes and densities yield a spectrum of gas-transport behaviours ranging from a poorly coupled and rapid-sedimenting mesoscale regime up to a homogeneously coupled long-lived suspending regime. Internal velocity and concentration profiles illuminate the role of boundary velocity, which yields forced-acceleration of the ash-cloud. Kinematic coupling of the ash-cloud with the underflow induces a velocity at the lower flow boundary, while shear stress at the ash-cloud/underflow wanes and results in the shrinking of the maximum velocity and concentration heights. Therefore, the ash-cloud can reach high velocities and multiply its destruction potential. The experimental work presented in this thesis provides the first datasets of the internal physical properties of PDCs, which can be used to test the validity of current numerical models and highlight their limitations. This thesis also presents the study of a small hydrothermal blast that occurred at Mt. Tongariro, New Zealand, on the 6th of August 2012. The study of the blast is subdivided into two phases: the PDC phase and the ballistic phase. The detailed study of the PDC along the main propagation axis highlighted the role of the longitudinal zoning of the current, which was reflected in the complex tripartite deposit architecture. The study of the blast-derived ballistic crater field revealed a zone of high crater density that was related to the focus of ballistic trajectories around the main explosion direction. Simple inverse ballistic modelling provided evidence for a shallow blast (c. 5° above horizontal) from Te Maari. Furthermore, a comparison of ballistic block lithologies confirmed the origin of the elongated succession of craters or fissures formed by successive blasting during the eruption

Implementing vertex dynamics models of cell populations in biology within a consistent computational framework

The dynamic behaviour of epithelial cell sheets plays a central role during development, growth, disease and wound healing. These processes occur as a result of cell adhesion, migration, division, differentiation and death, and involve multiple processes acting at the cellular and molecular level. Computational models offer a useful means by which to investigate and test hypotheses about these processes, and have played a key role in the study of cell–cell interactions. However, the necessarily complex nature of such models means that it is difficult to make accurate comparison between different models, since it is often impossible to distinguish between differences in behaviour that are due to the underlying model assumptions, and those due to differences in the in silico implementation of the model. In this work, an approach is described for the implementation of vertex dynamics models, a discrete approach that represents each cell by a polygon (or polyhedron) whose vertices may move in response to forces. The implementation is undertaken in a consistent manner within a single open source computational framework, Chaste, which comprises fully tested, industrial-grade software that has been developed using an agile approach. This framework allows one to easily change assumptions regarding force generation and cell rearrangement processes within these models. The versatility and generality of this framework is illustrated using a number of biological examples. In each case we provide full details of all technical aspects of our model implementations, and in some cases provide extensions to make the models more generally applicable

Use of a Laser Scanning System for Professional Preparation and Scene Assessment of Fire Rescue Units

The paper presents results of a study focused on usability of a 3D laser scanning system by fire rescue units during emergencies, respectively during preparations for inspection and tactical exercises. The first part of the study focuses on an applicability of a 3D scanner in relation to an accurate evaluation of a fire scene through digitization and creation of virtual walk-through of the fire scene. The second part deals with detailed documentation of access road to the place of intervention, including a simulation of the fire vehicle arrival

Involvement of fast-spiking cells in ictal sequences during spontaneous seizures in rats with chronic temporal lobe epilepsy

Epileptic seizures represent altered neuronal network dynamics, but the temporal evolution and cellular substrates of the neuronal activity patterns associated with spontaneous seizures are not fully understood. We used simultaneous recordings from multiple neurons in the hippocampus and neocortex of rats with chronic temporal lobe epilepsy to demonstrate that subsets of cells discharge in a highly stereotypical sequential pattern during ictal events, and that these stereotypical patterns were reproducible across consecutive seizures. In contrast to the canonical view that principal cell discharges dominate ictal events, the ictal sequences were predominantly composed of fast-spiking, putative inhibitory neurons, which displayed unusually strong coupling to local field potential even before seizures. The temporal evolution of activity was characterized by unique dynamics where the most correlated neuronal pairs before seizure onset displayed the largest increases in correlation strength during the seizures. These results demonstrate the selective involvement of fast spiking interneurons in structured temporal sequences during spontaneous ictal events in hippocampal and neocortical circuits in experimental models of chronic temporal lobe epilepsy

A convergence acceleration operator for multiobjective optimisation

A novel multiobjective optimisation accelerator is introduced that uses direct manipulation in objective space together with neural network mappings from objective space to decision space. This operator is a portable component that can be hybridized with any multiobjective optimisation algorithm. The purpose of this Convergence Acceleration Operator (CAO) is to enhance the search capability and the speed of convergence of the host algorithm. The operator acts directly in objective space to suggest improvements to solutions obtained by a multiobjective evolutionary algorithm (MOEA). These suggested improved objective vectors are then mapped into decision variable space and tested. The CAO is incorporated with two leading MOEAs, the Non-Dominated Sorting Genetic Algorithm (NSGA-II) and the Strength Pareto Evolutionary Algorithm (SPEA2) and tested. Results show that the hybridized algorithms consistently improve the speed of convergence of the original algorithm whilst maintaining the desired distribution of solutions

Multi crteria decision making and its applications : a literature review

This paper presents current techniques used in Multi Criteria Decision Making (MCDM) and their applications. Two basic approaches for MCDM, namely Artificial Intelligence MCDM (AIMCDM) and Classical MCDM (CMCDM) are discussed and investigated. Recent articles from international journals related to MCDM are collected and analyzed to find which approach is more common than the other in MCDM. Also, which area these techniques are applied to. Those articles are appearing in journals for the year 2008 only. This paper provides evidence that currently, both AIMCDM and CMCDM are equally common in MCDM