Doctor of Philosophy in Computing

dissertationThe aim of direct volume rendering is to facilitate exploration and understanding of three-dimensional scalar fields referred to as volume datasets. Improving understanding is done by improving depth perception, whereas facilitating exploration is done by speeding up volume rendering. In this dissertation, improving both depth perception and rendering speed is considered. The impact of depth of field (DoF) on depth perception in direct volume rendering is evaluated by conducting a user study in which the test subjects had to choose which of two features, located at different depths, appeared to be in front in a volume-rendered image. Whereas DoF was expected to improve perception in all cases, the user study revealed that if used on the back feature, DoF reduced depth perception, whereas it produced a marked improvement when used on the front feature. We then worked on improving the speed of volume rendering on distributed memory machines. Distributed volume rendering has three stages: loading, rendering, and compositing. In this dissertation, the focus is on image compositing, more specifically, trying to optimize communication in image compositing algorithms. For that, we have developed the Task Overlapped Direct Send Tree image compositing algorithm, which works on both CPU- and GPU-accelerated supercomputers, which focuses on communication avoidance and overlapping communication with computation; the Dynamically Scheduled Region-Based image compositing algorithm that uses spatial and temporal awareness to efficiently schedule communication among compositing nodes, and a rendering and compositing pipeline that allows both image compositing and rendering to be done on GPUs of GPU-accelerated supercomputers. We tested these on CPU- and GPU-accelerated supercomputers and explain how these improvements allow us to obtain better performance than image compositing algorithms that focus on load-balancing and algorithms that have no spatial and temporal awareness of the rendering and compositing stages

Using Depth Perception to Enhance Volume Rendering

poste

Optimizing Error-Bounded Lossy Compression for Three-Dimensional Adaptive Mesh Refinement Simulations

Today's scientific simulations require a significant reduction of data volume because of extremely large amounts of data they produce and the limited I/O bandwidth and storage space. Error-bounded lossy compression has been considered one of the most effective solutions to the above problem. However, little work has been done to improve error-bounded lossy compression for Adaptive Mesh Refinement (AMR) simulation data. Unlike the previous work that only leverages 1D compression, in this work, we propose to leverage high-dimensional (e.g., 3D) compression for each refinement level of AMR data. To remove the data redundancy across different levels, we propose three pre-process strategies and adaptively use them based on the data characteristics. Experiments on seven AMR datasets from a real-world large-scale AMR simulation demonstrate that our proposed approach can improve the compression ratio by up to 3.3X under the same data distortion, compared to the state-of-the-art method. In addition, we leverage the flexibility of our approach to tune the error bound for each level, which achieves much lower data distortion on two application-specific metrics.Comment: 13 pages, 17 figures, 3 tables, accepted by ACM HPDC 202

Diagnostic et prise en charge des hypovitaminoses D chez l'adulte. Enquête auprès des médecins généralistes de Gironde

Introduction : La vitamine D suscite un intérêt grandissant, mais est-elle réellement un enjeu de santé publique ? Objectif : Il s'agissait de réaliser un état des lieux des opinions et pratiques des médecins généralistes concernant le diagnostic et la prise en charge des hypovitaminoses D chez l'adulte. Méthode : Nous avons réalisé une enquête auprès de 1776 médecins généralistes de Gironde, sous la forme d'un questionnaire envoyé par courriel d'avril à mai 2013. Résultats : L'analyse a porté sur une population de 241 médecins. Les résultats révèlent un intérêt de la majorité d'entre eux pour le sujet d'étude et un souhait de recommandation de bonnes pratiques. Ils suggèrent par ailleurs une grande disparité des pratiques et l'existence de nombreuses incertitudes et de multiples questionnements. Discussion : L'hétérogénéité des résultats est le reflet des controverses existantes et de l'absence de recommandation officielle des autorités de santé. Conclusion : Dans l'état actuel des connaissances, il convient de définir avec clarté les seuils d'interventions tant diagnostiques que thérapeutiques ayant une balance bénéfices-risques favorable pour les patients.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Infinite Zoom

posterAny image (apart from a fractal) has a finite resolution. On zooming in, we eventually see pixels. The aim of this project is to allow users to infinitely zoom in on an image

Evaluation of Depth of Field for Depth Perception in DVR

International audienceIn this paper, we present a user study on the use of Depth of Field for depth perception in Direct Volume Rendering. Direct Volume Rendering with Phong shading and perspective projection is used as the baseline. Depth of Field is then added to see its impact on the correct perception of ordinal depth. Accuracy and response time are used as the metrics to evaluate the usefulness of Depth of Field. The on site user study has two parts: static and dynamic. Eye tracking is used to monitor the gaze of the subjects. From our results we see that though Depth of Field does not act as a proper depth cue in all conditions, it can be used to reinforce the perception of which feature is in front of the other. The best results (high accuracy & fast response time) for correct perception of ordinal depth is when the front feature (out of the users were to choose from) is in focus and perspective projection is used

A complete methodology for determining the influence of the design for 3.3 kV silicon carbide diodes : JBS compared to Schottky

The paper presents the design and the characterization of Schottky and JBS diodes, for high voltage matching. Design for manufacturing has been preferred and diodes have been fabricated following a semi-industrial methodology. Then electrical characterization was performed on devices : static characterization, including temperature influence, dynamic characterization in a buck-like con-figuration to evaluate the behavior in switching mode and C-V characterization to identify some parameters like the junction area. Whereas forward conduction is provided with low on-state re-sistance, 3.3 kV capability is demonstrated with low leakage current, low turn-on and low turn-off delays

High-Voltage SiC-JFET Fabrication and Full Characterization

International audienc

High-Voltage SiC-JFET Fabrication and Full Characterization

International audienceThis paper reports the design, the processing, the static characterisation, the switching behaviour and the high current stress test of 10 kV aimed 4H-SiC bipolar diodes. The actual breakdown voltage of the selected devices is between 7 kV and 8 kV. The switching characterisations show a good behaviour with a t rr of only 90 ns. No degradation was observed after the application of 10 000 high current pulses during the stress tests