Joint Cohort Detection & Predictive Modelling alongside Safe Model Updating

A common objective provided by stakeholders, given a supervised dataset, is to construct a predictive model of the response given the covariates. If a clustering structure is suspected (such that different clusters interact with the response in different ways) then an additional objective may be given to detect these clusters, or cohorts, such that interventions based on the predictive model can be adapted for each group. The solution to this problem requires a balanced handling of both objectives through a joint cohort detection and predictive modelling method. Previous solutions to this issue often favour one objective over the other. Indeed, cohort detection takes prevalence for unsupervised clustering methods such as K-means (which are followed by cluster-specific models for prediction), whereas accurate prediction takes prevalence for supervised clustering methods such as mixture models (which use clustering solely as a tool for more accurate modelling). This thesis aims to provide a method that focuses on cohort detection by providing a non-probabilistic partitioning of the data whilst simultaneously focusing on accurate predictive modelling by allowing the Bayesian evidence of the model to dictate the partition. A graphical representation of the data is constructed to ensure the partitioning both respects the structure in covariate space and reduces the number of possible partitions (and hence models) one would have to consider. The latter point is particularly important as the Bayesian evidence is determined through Sequential Monte Carlo, a computationally expensive but necessary process used to ensure the estimated measure that selects the partition is accurate. This method has an associated R package (UNCOVER) for implementation. Finally, a separate contribution is discussed in this thesis surrounding the topic of safe modelling updating. Specifically, this refers to the use of hold-out sets when updating a model to avoid interventions negatively impacting model quality. Contributions to this field are: a method of locating the minimum hold-out set size through Gaussian process emulation of a total cost function and a discussion on the impacts of clustering in this setting

The Role of Bed Shear Stress in Sediment Sorting Patterns in a Reconstructed, Gravel Bed River

The role of bed shear stress in bed surface grain size sorting was investigated on a reconstructed reach of the Merced River in the Central Valley of California. Pebble count data were collected at the inside, middle, and outside of ten bends in April 2015 and compared to data from pebble counts conducted in previous years. Output from a previously developed 2D flow model (FaSTMECH) was compared to critical shear stresses calculated from median grain-size data. Comparison of pebble count results from 2002 through 2015 showed that there was no temporally consistent pattern of coarsening or fining along the study reach; however, the bed surface coarsened between 2002 and 2015. Pebble count data from April 2015 revealed a distinct spatial distribution of grain sizes with a larger median grain size (D50) at the outside of bends and a smaller D50 at the inside of bends. Regression analyses performed on pebble count data from point bars revealed statistically significant downstream changes in surface grain size on two of the seven bars. Analysis of shear stress data showed a weak relationship between the modeled bed shear stress (τb) and the calculated critical shear stress (τcr). The weak relationship between τb and τcr indicated that bed shear stress was not solely responsible for the grain size sorting in the study reach. It is likely that the observed grain size sorting patterns resulted from helical secondary flows at the bends

Future Exploration of the South Pole as Enabled by the Lunar Reconnaissance Orbiter

The Lunar Reconnaissance Orbiter (LRO) launched in 2009 to collect the dataset required for future surface missions and to answer key questions about the lunar surface environment. In the first seven years of operations, the Lunar Reconnaissance Orbiter Camera (LROC) acquired over a million images of the lunar surface and collected key stereo observations for the production of meter-scale digital terrain models. Due to the configuration of the LRO orbit, LROC and the other onboard instruments have the opportunity to acquire observations at or near the poles every two hours. The lunar south polar region is an area of interest for future surface missions due to the benign thermal environment and areas of near-continuous illumination. These persistently illuminated regions are also adjacent to permanently shadowed areas (e.g. floors of craters and local depressions) that are of interest to both scientists and engineers prospecting for cold-trapped volatiles on or near the surface for future in situ resource utilization. Using a terramechanics model based on surface properties derived during the Apollo and Luna missions, we evaluated the accessibility of different science targets and the optimal traverse paths for a given set of waypoints. Assuming a rover that relies primarily on solar power, we identified a traverse that would keep the rover illuminated for 94.43% of the year between 1 January 2021 and 31 December 2021. Throughout this year-long period, the longest eclipse endured by the rover would last only 101 hours and the rover would move a total of 22.11 km with an average speed of 2.5 m/hr (max speed=30 m/hr). During this time the rover would be able to explore a variety of targets along the connecting ridge between Shackleton and de Gerlache craters. In addition to the southern polar regions, we are also examining traverses around other key exploration sites such as Marius Hills, Ina-D, Rima Parry, and the Mairan Domes in efforts to aid future mission planners and assess the requirements for future roving prospectors (e.g., maximum speed, maximum slope, etc.)

Luces y sombras del urbanismo táctico. Análisis de dos proyectos de Urbanismo táctico en ciudad de Barranquilla, Colombia

La demanda por espacios urbanos dignos y adecuados a las dinámicas cotidianas y a la sociabilidad de los ciudadanos, ha llevado al surgimiento de artefactos de naturaleza efímera, que vienen a sustituir una acción más contundente de parte de las instituciones administrativas del Estado en los procesos de producción de la ciudad. Se trata de intervenciones de bajo coste, que batallan por un lugar en los métodos que facilitan el hacer las ciudades. A estas expresiones se les conoce como urbanismo táctico. Este artículo explora ese concepto y sus efectos en la humanización del espacio público. Para eso, aborda sus luces y sombras, así como su implementación en espacios de la ciudad de Barranquilla, Colombia, como un mecanismo de transformación de realidades urbanas. En ese contexto, este trabajo se constituye como una reflexión crítica desde un enfoque constructivista y cualitativo. Además, realiza una exploración práctica de observación y análisis del desarrollo de dos proyectos de urbanismo táctico en Barranquilla, desarrollados a través de laboratorios de ciudad con el Semillero Acupuntura Urbana y el Colectivo de Profesores Cityzen de la Universidad de la Costa

Estado del arte del proyecto

Con la presente investigación se pretende ilustrar la problemática de la contaminación visual causada por las estaciones y/o antenas de telefonía celular o telecomunicaciones en la ciudad de Barranquilla. Debido al aumento sostenido de la demanda por los servicios de la telefonía celular en Colombia, el cual se ha concentrado en las ciudades principales, tal como Barranquilla; los operadores del servicio han instalado sus estaciones y/o antenas en las esquinas de las manzanas de los barrios, o en los predios en donde antes existía una residencia o lotes desocupados, en los jardines de casas o hasta dentro de las mismas edificaciones con tal de satisfacer las necesidades de comunicación de sus usuarios. Sin embargo, actualmente se ha visto como su servicio es más deficiente día a día, debido a que las autoridades responsables los han limitado en su crecimiento al imponer mayores restricciones para la obtención de licencias de construcción, como consecuencia de las constantes quejas de los habitantes por la instalación de antenas cerca a sus domicilios, y aún así se tiene un alto porcentaje de ilegalidad en dichas instalaciones. Es por esto que se hace necesario reconocer los aspectos normativos y las posibles soluciones sobre el tema que permitan gestionar de la mejor forma esta problemática que genera contaminación visual en la ciudad, el deterioro del paisaje urbano y la descualificación del suelo urbano en los barrio

Model updating after interventions paradoxically introduces bias

Machine learning is increasingly being used to generate prediction models for use in a number of real-world settings, from credit risk assessment to clinical decision support. Recent discussions have highlighted potential problems in the updating of a predictive score for a binary outcome when an existing predictive score forms part of the standard workflow, driving interventions. In this setting, the existing score induces an additional causative pathway which leads to miscalibration when the original score is replaced. We propose a general causal framework to describe and address this problem, and demonstrate an equivalent formulation as a partially observed Markov decision process. We use this model to demonstrate the impact of such `naive updating' when performed repeatedly. Namely, we show that successive predictive scores may converge to a point where they predict their own effect, or may eventually tend toward a stable oscillation between two values, and we argue that neither outcome is desirable. Furthermore, we demonstrate that even if model-fitting procedures improve, actual performance may worsen. We complement these findings with a discussion of several potential routes to overcome these issues.Comment: Sections of this preprint on 'Successive adjuvancy' (section 4, theorem 2, figures 4,5, and associated discussions) were not included in the originally submitted version of this paper due to length. This material does not appear in the published version of this manuscript, and the reader should be aware that these sections did not undergo peer revie

DEIXE-ME TOCÁ-LO MAIS UMA VEZ: O DISCURSO HOMOERÓTICO NO ROMANCE EM NOME DO DESEJO, DE JOÃO SILVÉRIO TREVISAN

This article investigates the novel Em nome do desejo, of the São Paulo writer João Silvério Trevisan, having as touchstone, primordially, the Bakhtinian theory on the polyphonic novel. At the same time, questions concerning literary homoeroticism, which, in the novel in question, are articulated with religion, adolescence and abandonment are investigated.Este artigo investiga o romance Em nome do desejo, do escritor paulista João Silvério Trevisan, tendo como pedra de toque, primordialmente, a teoria bakhtiniana sobre o romance polifônico. Concomitantemente, são averiguadas questões concernentes ao homoerotismo literário, que, no romance em questão, articula-se junto à religião, à adolescência e ao abandono

Sticking under wet conditions: the remarkable attachment abilities of the torrent frog, staurois guttatus

Tree frogs climb smooth surfaces utilising capillary forces arising from an air-fluid interface around their toe pads, whereas torrent frogs are able to climb in wet environments near waterfalls where the integrity of the meniscus is at risk. This study compares the adhesive capabilities of a torrent frog to a tree frog, investigating possible adaptations for adhesion under wet conditions. We challenged both frog species to cling to a platform which could be tilted from the horizontal to an upside-down orientation, testing the frogs on different levels of roughness and water flow. On dry, smooth surfaces, both frog species stayed attached to overhanging slopes equally well. In contrast, under both low and high flow rate conditions, the torrent frogs performed significantly better, even adhering under conditions where their toe pads were submerged in water, abolishing the meniscus that underlies capillarity. Using a transparent platform where areas of contact are illuminated, we measured the contact area of frogs during platform rotation under dry conditions. Both frog species not only used the contact area of their pads to adhere, but also large parts of their belly and thigh skin. In the tree frogs, the belly and thighs often detached on steeper slopes, whereas the torrent frogs increased the use of these areas as the slope angle increased. Probing small areas of the different skin parts with a force transducer revealed that forces declined significantly in wet conditions, with only minor differences between the frog species. The superior abilities of the torrent frogs were thus due to the large contact area they used on steep, overhanging surfaces. SEM images revealed slightly elongated cells in the periphery of the toe pads in the torrent frogs, with straightened channels in between them which could facilitate drainage of excess fluid underneath the pad