On the dynamics and breakup of a bubble immersed in a turbulent flow

Experimental investigations of the dynamics of a deformable bubble rising in a uniform turbulent flow are reported. The turbulence is characterized by fast PIV. Time-resolved evolutions of bubble translation, rotation and deformation are determined by three-dimensional shape recognition from three perpendicular camera views. The bubble dynamics involves three mechanisms fairly decoupled: (i) average shape is imposed by the mean motion of the bubble relative to liquid; (ii) wake instability generates almost periodic oscillations of velocity and orientation; (iii) turbulence causes random deformations that sometimes lead to breakup. The deformation dynamics is radically different from that observed in the absence of a significant sliding motion due to buoyancy. Large deformations that lead to breakup are not axisymmetric and correspond to elongations in the horizontal direction. The timescale of decay of shape oscillations is of the same order as their natural frequency f2, so that breakup always results from the interaction with a single turbulent eddy. This overdamping causes the statistics of large deformations and the statistics of breakup identical to the statistics of turbulence. The bubble response time f2 however controls the duration of individual breakup events

Advances in quantitative coronary and vascular angiography

The main objective of this thesis is to develop new, accurate and reproducible automated methods for the detection and quantification of lesions in coronary and peripheral X-ray angiograms, which make it possible to extend the straight segment analysis to analyses of sidebranches and bifurcations. We introduce new methods for the detection of pathlines (Wavepath), the detection of arterial contours (Wavecontour) and the measurement of diameter sizes in straight segments, sidebranches and bifurcations. These methods are designed to increase reproducibility and decrease the influence of user interaction. These new methods are validated extensively in coronary and vascular angiograms, proving their accuracy and reproducibility. Furthermore we developed two new bifurcation models (Y-shape and T-shape) in order to accurately measure the diameters and lesion parameters of an entire bifurcation. The models, including their edge segment analyses, are validated extensively in a clinical validation study in order to assess the inter- and intra-observer variability on pre- and post-intervention data. Overall we can conclude that our goal of improving the QCA analysis and extend it towards the new morphologies and new intervention techniques has been met.Nederlandse Hartstichting Stichting inz. Doelfonds Beeldverwerking Medis medical imaging systems bv, LeidenUBL - phd migration 201