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

A Continuous Learning Strategy for Self-Organizing Maps Based on Convergence Windows

A self-organizing map (SOM) is a type of artificial neural network that has applications in a variety of fields and disciplines. The SOM algorithm uses unsupervised learning to produce a low-dimensional representation of high- dimensional data. This is done by \u27fitting\u27 a grid of nodes to a data set over a fixed number of iterations. With each iteration, the nodes of the map are adjusted so that they appear more like the data points. The low-dimensionality of the resulting map means that it can be presented graphically and be more intuitively interpreted by humans. However, it is still essential to evaluate the \u27quality\u27 of a map to ensure that the model is indeed representative of the underlying data. There are several quality measures used with self-organizing maps. The traditional method is to compute the quantization error of the map by summing the distances between the nodes and the data points, with smaller values representing a better fit. However, it has been shown that the quantization error approaches zero as the number of training iterations is increased, and therefore can result in overfitting. For this reason, we choose to use a population based convergence criterion for map evaluation. This method treats the nodes of the SOM and the points in the data set as two populations and uses a statistical test to determine if they appear to be drawn from the same probability distribution. If they do, we say the model is converged and has a \u27good fit.\u27 If not, the map requires more training. With both evaluation methods, and in SOM construction in general, the quality of the model is directly related to the predetermined number of training iterations. We propose that the efficiency of the algorithm would be improved by eliminating the current guess-and-check method that is associated with arbitrarily picking the number of iterations to train a map. This is done by combining the processes of construction and evaluation. That is, the amount of training necessary for a good fit can be more accurately determined by periodically evaluating the quality of the model. We automate this procedure using both fixed and variable length training windows. The convergence of the map is calculated after each window; and construction is halted when the change between windows has stagnated or the target value has been reached. This completely removes the necessity to know in advance how much training is required for an accurate model. We attempt to validate this hypothesis by analyzing SOMs built on both synthetic and real-world data sets using the traditional algorithm and our convergence window algorithm

Superconductivity in a new hexagonal high entropy alloy

High entropy alloys (HEAs) are the new class of materials with an attractive combination of tunable mechanical and physicochemical properties. They crystallize mainly in cubic structures, however, for practical applications, HEAs with hexagonal close-packed (hcp) structure are highly desirable in connection to their in general high hardness. Herein, we report the synthesis, structure and detailed superconducting properties of Re$_{0.56}$Nb$_{0.11}$Ti$_{0.11}$Zr$_{0.11}$Hf$_{0.11}$-the first hexagonal superconducting high entropy alloy (HEA) composed of five randomly distributed transition-metals. Combination of room temperature precession electron diffraction, precession electron diffraction tomography and powder X-ray diffraction is utilized to determine the room temperature crystal structure. Transport, magnetic and heat capacity measurements show that the material is a type-II superconductor with the bulk superconducting transition at $T_{c}$ = 4.4 K, lower critical field $H_{c1}$(0) = 2.3 mT and upper critical field $H_{c2}$(0) = 3.6 T. Low-temperature specific heat measurement indicates that Re$_{0.56}$Nb$_{0.11}$Ti$_{0.11}$Zr$_{0.11}$Hf$_{0.11}$ is a phonon-mediated superconductor in the weak electron-phonon coupling limit with a normalized specific heat jump $\frac{\Delta C_{el}}{\gamma_{n}T_{c}}$ = 1.32. Further, hexagonal to cubic structural transition is observed by lowering the valence electron counts and $T_{c}$ follows crystalline-like behaviour.Comment: 6 Pages, 9 Figures. arXiv admin note: text overlap with arXiv:1804.1009

Problemas y desafíos de las políticas académicas e institucionales para garantizar la calidad y excelencia académica de los Doctorados en Derecho

El presente artículo trata de reflejar algunos avances iniciales de nuestra investigación sobre el contexto académico del desarrollo de los posgrados en la UNNE y se revisa el registro de actividades curriculares a nivel de otras universidades de la región, con especial interés en la reflexión sobre la universidad y la investigación social

Rendimiento académico de las estudiantes de la facultad de derecho. Un análisis preliminar del desarrollo de los estudios en ciencias jurídicas

El presente artículo se enmarca dentro del Proyecto de Investigación “Evolución del rendimiento académico de los estudiantes de la Facultad de Derecho de la UNNE (período 1995-2010). Diagnóstico, análisis de las políticas académicas y propuestas de incidencia para la gestión universitaria”, del cual forman parte todos los autores. Por tratarse de una propuesta de investigación en ejecución, en esta oportunidad se reflejarán sintéticamente algunos análisis preliminares y los resultados parciales obtenidos en los primeros meses de tarea investigativa (hasta los últimos meses del año 2011)

Sincretismo reflexivo, recíproco y anticausativo en mbayá-eyiguayegui (flia. guaycurú)

Este trabajo analiza un sincretismo presente en mbayá-eyiguayegui (flia. guaycurú) entre construcciones reflexivas, recíprocas y anticausativas, derivadas a partir de la prefijación del morfema modificador de valencia din-, el cual fue documentado por el jesuita José Sánchez Labrador a mediados del siglo XVIII. El mbayá-eyiguayegui es considerada una lengua extinta y fue registrada por el padre Sánchez Labrador entre 1760 y 1767, en la época colonial, en la Provincia Jesuítica del Paraguay. A su vez, el mbayá está emparentado con la lengua kadiwéu-ejiwajegi, la cual se habla actualmente en el estado de Mato Grosso del sur, en Brasil. Este artículo aborda la documentación del jesuita Sánchez Labrador sobre el mbayá con el fin de examinar los mecanismos de modificación de la valencia verbal identificados cuando se utiliza el prefijo din- con verbos transitivos. Además, se expone un proceso de verbalización que se observa cuando dicho prefijo ocurre con nombres

The nonstructural protein NSs of Schmallenberg virus is targeted to the nucleolus and induces nucleolar disorganization

Schmallenberg virus (SBV) was discovered in Germany in late 2011 and then spread rapidly to many European countries. SBV is an orthobunyavirus that causes abortion and congenital abnormalities in ruminants. A virus-encoded nonstructural protein, termed NSs, is a major virulence factor of SBV, and it is known to promote the degradation of Rpb1, a subunit of the RNA polymerase II (Pol II) complex, and therefore hampers global cellular transcription. In this study, we found that NSs is mainly localized in the nucleus of infected cells and specifically appears to target the nucleolus through a nucleolar localization signal (NoLS) localized between residues 33 and 51 of the protein. NSs colocalizes with nucleolar markers such as B23 (nucleophosmin) and fibrillarin. We observed that in SBV-infected cells, B23 undergoes a nucleolus-to-nucleoplasm redistribution, evocative of virus-induced nucleolar disruption. In contrast, the nucleolar pattern of B23 was unchanged upon infection with an SBV recombinant mutant with NSs lacking the NoLS motif (SBVΔNoLS). Interestingly, unlike wild-type SBV, the inhibitory activity of SBVΔNoLS toward RNA Pol II transcription is impaired. Overall, our results suggest that a putative link exists between NSs-induced nucleolar disruption and its inhibitory function on cellular transcription, which consequently precludes the cellular antiviral response and/or induces cell death