Rigid and Non-rigid Point-based Medical Image Registration

The primary goal of this dissertation is to develop point-based rigid and non-rigid image registration methods that have better accuracy than existing methods. We first present point-based PoIRe, which provides the framework for point-based global rigid registrations. It allows a choice of different search strategies including (a) branch-and-bound, (b) probabilistic hill-climbing, and (c) a novel hybrid method that takes advantage of the best characteristics of the other two methods. We use a robust similarity measure that is insensitive to noise, which is often introduced during feature extraction. We show the robustness of PoIRe using it to register images obtained with an electronic portal imaging device (EPID), which have large amounts of scatter and low contrast. To evaluate PoIRe we used (a) simulated images and (b) images with fiducial markers; PoIRe was extensively tested with 2D EPID images and images generated by 3D Computer Tomography (CT) and Magnetic Resonance (MR) images. PoIRe was also evaluated using benchmark data sets from the blind retrospective evaluation project (RIRE). We show that PoIRe is better than existing methods such as Iterative Closest Point (ICP) and methods based on mutual information. We also present a novel point-based local non-rigid shape registration algorithm. We extend the robust similarity measure used in PoIRe to non-rigid registrations adapting it to a free form deformation (FFD) model and making it robust to local minima, which is a drawback common to existing non-rigid point-based methods. For non-rigid registrations we show that it performs better than existing methods and that is less sensitive to starting conditions. We test our non-rigid registration method using available benchmark data sets for shape registration. Finally, we also explore the extraction of features invariant to changes in perspective and illumination, and explore how they can help improve the accuracy of multi-modal registration. For multimodal registration of EPID-DRR images we present a method based on a local descriptor defined by a vector of complex responses to a circular Gabor filter.

Stated versus observed performance levels in patients with chronic low back pain

This study examined the relationship between chronic low back pain (CLBP) patients' perceived (stated) levels of function and their measured (observed) performance in squatting and stair climbing activities as compared to healthy volunteers. Twenty patients with CLBP and 20 healthy subjects were asked through an interview to self-assess their ability to comfortably perform stair climbing and squatting as well as other tolerances. The subjects were then asked to perform the activities and their performance levels were recorded. Results of the t-tests and Analysis of Variance (ANOVA) procedures revealed that patients' estimate of squatting and stair climbing abilities as well as their demonstrated levels were significantly lower (p < 0.001) than those of the healthy subjects. There was a significant difference between groups in terms of the time required to perform squatting but not stair climbing. Both healthy subjects and patients with CLBP underestimated their physical capabilities. Findings indicate that the use of actual performance measurement combined with self-report of functional abilities is needed when assessing performance levels of both healthy as well as patients with CLBP.

Seguridad en prácticas de andinismo : formación docente en Educación Física

El Profesorado de Educación Física con Orientación en Actividades Regionales en Montaña de la Universidad Nacional del Comahue. (En adelante PEF-CRUB-UNCo) es el único en el país que posee una trayectoria con más de 20 años de formación de profesores de Educación Física con orientación. Fue a través de un trabajo dinámico y continuo a lo largo de los años que se fueron definiendo qué contenidos teórico-prácticos eran los apropiados para la Educación Física (Palacio, López, Schneider, 2011). Se observan coincidencias con las experiencias realizadas en otros Países como España y Alemania en los que las actividades de escalada forman parte de la Formación Docente y de la currícula educativa (Saez Padilla, Gimenez, Fuentes Guerra 2005; Arribas Cubero 2008; Winter, 2000). Se determinó en paralelo con otros autores (Hepp, Güllich y Heidorn, 2001) que los contenidos relacionados con Trekking y Escalada son apropiados para desarrollar en un profesorado de estas características. Una preocupación permanente que desafía a la actividad como contenido educativo es el manejo de las condiciones de seguridad. En el presente trabajo se explicarán las condiciones de Seguridad que a lo largo de los años desde la experiencia, la interrogación permanente, la consulta de bibliografía especializada y las acciones realizadas en la formación docente han sido recopiladas.

Seguridad en prácticas de andinismo : formación docente en Educación Física

El Profesorado de Educación Física con Orientación en Actividades Regionales en Montaña de la Universidad Nacional del Comahue. (En adelante PEF-CRUB-UNCo) es el único en el país que posee una trayectoria con más de 20 años de formación de profesores de Educación Física con orientación. Fue a través de un trabajo dinámico y continuo a lo largo de los años que se fueron definiendo qué contenidos teórico-prácticos eran los apropiados para la Educación Física (Palacio, López, Schneider, 2011). Se observan coincidencias con las experiencias realizadas en otros Países como España y Alemania en los que las actividades de escalada forman parte de la Formación Docente y de la currícula educativa (Saez Padilla, Gimenez, Fuentes Guerra 2005; Arribas Cubero 2008; Winter, 2000). Se determinó en paralelo con otros autores (Hepp, Güllich y Heidorn, 2001) que los contenidos relacionados con Trekking y Escalada son apropiados para desarrollar en un profesorado de estas características. Una preocupación permanente que desafía a la actividad como contenido educativo es el manejo de las condiciones de seguridad. En el presente trabajo se explicarán las condiciones de Seguridad que a lo largo de los años desde la experiencia, la interrogación permanente, la consulta de bibliografía especializada y las acciones realizadas en la formación docente han sido recopiladas.

Leaving and Coming Back to Canada : Evidence from Longitudinal Data (Working Paper 32)

The paper exploits the unique strengths of Statistics Canada's Longitudinal Administrative Database ("LAD"), constructed from individuals' tax records, to shed new light on the extent and nature of the emigration of Canadians to other countries and their patterns of return over the period 1982-1999. The empirical evidence begins with some simple graphs of the overall rates of leaving over time, and follows with the presentation of the estimation results of a model that essentially addresses the question: "who moves?" The paper then analyses the rates of return for those observed to leave the country - something for which there is virtually no existing evidence. Simple return rates are reported first, followed by the results of a hazard model of the probability of returning which takes into account individuals' characteristics and the number of years they have already been out of the country. Taken together, these results provide a new empirical basis for discussions of emigration in general, and the brain drain in particular. Of particular interest are the ebb and flow of emigration rates observed over the last two decades, including a perhaps surprising turndown in the most recent years after climbing through the earlier part of the 1990s; the data on the number who return after leaving, the associated patterns by income level, and the increases observed over the last decade.

Efficient Learning of Bayesian Networks with Bounded Tree-width

Learning Bayesian networks with bounded tree-width has attracted much attention recently, because low tree-width allows exact inference to be performed efficiently. Some existing methods \cite{korhonen2exact, nie2014advances} tackle the problem by using $k$-trees to learn the optimal Bayesian network with tree-width up to $k$. Finding the best $k$-tree, however, is computationally intractable. In this paper, we propose a sampling method to efficiently find representative $k$-trees by introducing an informative score function to characterize the quality of a $k$-tree. To further improve the quality of the $k$-trees, we propose a probabilistic hill climbing approach that locally refines the sampled $k$-trees. The proposed algorithm can efficiently learn a quality Bayesian network with tree-width at most $k$. Experimental results demonstrate that our approach is more computationally efficient than the exact methods with comparable accuracy, and outperforms most existing approximate methods.

Barn utforskar sin förskolegård : Förskolebarns perspektiv på sin utemiljö

Vårt intresse för utemiljön uppstod då vi såg, genom erfarenheter av arbete på förskolor, att många förskolegårdar inte alltid tilltalade barnen. Några gårdar såg inte inspirerande ut och barnen visste inte vet vad de skulle göra. Syftet med studien är att skapa kunskap om hur barn utforskar sin förskolegård och vad som styr deras val av hur de placerar sig själva på gården när de leker. Utifrån en etnografisk, induktiv studie, vill vi lyfta fram vad barnen berättar om sin förskolegård. Vi har utgått från barndomsgeografi vilken ses inom forskningen som en del av barndomssociologin. Barndomen ses här som socialt konstruerad och frågor uppkommer om vilka platser som betraktas som bra för barn. Vi har sett utifrån våra samtalspromenader och observationer att barnen använder sig av olika rörelsestrategier såsom att klättra i träden, åka rutschkana och gunga samt att de använder sig av fysiska aktiviteter som till exempel att bygga kojor, samla naturmaterial och hoppar i lövhögar men att de även styrs av sin nyfikenhet och plötsligt kan stanna till för att titta på insekter etc. när de utforskar områden på gården. Resultaten av vår studie visar att rörelse är något som barnen ofta berättar om att de ägnar sig åt på sin förskolegård.

No Woman's Land

Willkommen Damen and Gentlemen! Roll up, stroll in and join us on a spectacular stagger through the post-apocalyptical wasteland of 1945. Before your very eyes the bearded ladies run on treadmills as they conjure up past and present digital landscapes. Masquerading as men for your entertainment, and their own protection, the bearded duo use gallows humour to launch you on an unimaginable, unconceivable plight of flight and migration. 1945. Lucia Rippel, expelled from her place of birth, walked 220 miles across the fractured landscape of Europe, with her two children and all her belongings dragged in a cart. In 2015, Ildikó Rippel and Rosie Garton retraced her footsteps, crossing borders, climbing fences, bleeding, crying, and blistering, and carrying their flat-pack children. No Woman’s Land is a politically charged, darkly humorous nod to 1920’s Kabarett, entwining the duo’s experience of the walk with Lucia’s story.

Multiple-Retrieval Case-Based Reasoning for Course Timetabling Problems

The structured representation of cases by attribute graphs in a Case-Based Reasoning (CBR) system for course timetabling has been the subject of previous research by the authors. In that system, the case base is organised as a decision tree and the retrieval process chooses those cases which are sub attribute graph isomorphic to the new case. The drawback of that approach is that it is not suitable for solving large problems. This paper presents a multiple-retrieval approach that partitions a large problem into small solvable sub-problems by recursively inputting the unsolved part of the graph into the decision tree for retrieval. The adaptation combines the retrieved partial solutions of all the partitioned sub-problems and employs a graph heuristic method to construct the whole solution for the new case. We present a methodology which is not dependant upon problem specific information and which, as such, represents an approach which underpins the goal of building more general timetabling systems. We also explore the question of whether this multiple-retrieval CBR could be an effective initialisation method for local search methods such as Hill Climbing, Tabu Search and Simulated Annealing. Significant results are obtained from a wide range of experiments. An evaluation of the CBR system is presented and the impact of the approach on timetabling research is discussed. We see that the approach does indeed represent an effective initialisation method for these approaches.

Case-Based Reasoning as a Heuristic Selector in a Hyper-Heuristic for Course Timetabling Problems

This paper studies Knowledge Discovery (KD) using Tabu Search and Hill Climbing within Case-Based Reasoning (CBR) as a hyper-heuristic method for course timetabling problems. The aim of the hyper-heuristic is to choose the best heuristic(s) for given timetabling problems according to the knowledge stored in the case base. KD in CBR is a 2-stage iterative process on both case representation and the case base. Experimental results are analysed and related research issues for future work are discussed.

Multiple-retrieval case-based reasoning for course timetabling problems

The structured representation of cases by attribute graphs in a Case-Based Reasoning (CBR) system for course timetabling has been the subject of previous research by the authors. In that system, the case base is organised as a decision tree and the retrieval process chooses those cases which are sub attribute graph isomorphic to the new case. The drawback of that approach is that it is not suitable for solving large problems. This paper presents a multiple-retrieval approach that partitions a large problem into small solvable sub-problems by recursively inputting the unsolved part of the graph into the decision tree for retrieval. The adaptation combines the retrieved partial solutions of all the partitioned sub-problems and employs a graph heuristic method to construct the whole solution for the new case. We present a methodology which is not dependant upon problem specific information and which, as such, represents an approach which underpins the goal of building more general timetabling systems. We also explore the question of whether this multiple-retrieval CBR could be an effective initialisation method for local search methods such as Hill Climbing, Tabu Search and Simulated Annealing. Significant results are obtained from a wide range of experiments. An evaluation of the CBR system is presented and the impact of the approach on timetabling research is discussed. We see that the approach does indeed represent an effective initialisation method for these approaches.

Dynamically balanced and plausible trajectory planning for human-like characters

International audience

Réseau calculant asynchrone dédié à la segmentation d'images

National audience

Detección y aplicación de T-Patterns en la escalada de élite

El presente trabajo constituye un ejemplo de la potencia informativa de los T-patterns -estructuras regulares y temporales de conductas obtenidas mediante el software Theme, versión 6.0- y de su aplicación, por primera vez, al conocimiento estratégico-táctico de un deporte que ha sido residualmente estudiado como es la escalada deportiva. En el seno de la metodología observacional se ha construido ad hoc el instrumento de observación Sport Climbing Observation Tool (SCOT) que ha permitido detectar T-patterns que reflejan el comportamiento desarrollado en la ascensión de la vía -presa, mano de agarre, inicio y final de contacto, chapaje, uso de magnesio y descansos- por los mejores escaladores -modalidad Lead- que participaron en el Campeonato del Mundo de 2011, celebrado en Arco (Italia). Mediante la información contenida en los T-patterns detectados se ha caracterizado la ascensión en tramos (inicial, medio y final), describiéndose operativamente la manera en la que los mejores escaladores del mundo cumplimentan la ascensión de la vía.

An Indirect Genetic Algorithm for Set Covering Problems

This paper presents a new type of genetic algorithm for the set covering problem. It differs from previous evolutionary approaches first because it is an indirect algorithm, i.e. the actual solutions are found by an external decoder function. The genetic algorithm itself provides this decoder with permutations of the solution variables and other parameters. Second, it will be shown that results can be further improved by adding another indirect optimisation layer. The decoder will not directly seek out low cost solutions but instead aims for good exploitable solutions. These are then post optimised by another hill-climbing algorithm. Although seemingly more complicated, we will show that this three-stage approach has advantages in terms of solution quality, speed and adaptability to new types of problems over more direct approaches. Extensive computational results are presented and compared to the latest evolutionary and other heuristic approaches to the same data instances.