ABSTRACT
We review a strategy for low- and least-order Galerkin models suitable for the design of closed-loop stabilization of wakes. These low-order models are based on a fixed set of dominant coherent structures and tend to be incurably fragile owing to two challenges. Firstly, they miss the important stabilizing effects of interactions with the base flow and stochastic fluctuations. Secondly, their range of validity is restricted by ignoring mode deformations during natural and actuated transients. We address the first challenge by including shift mode(s) and nonlinear turbulence models. The resulting robust least-order model lives on an inertial manifold, which links slow variations in the base flow and coherent and stochastic fluctuation amplitudes. The second challenge, the deformation of coherent structures, is addressed by parameter-dependent modes, allowing smooth transitions between operating conditions. Now, the Galerkin model lives on a refined manifold incorporating mode deformations. Control design is a simple corollary of the distilled model structure. We illustrate the modelling path for actuated wake flows.
ABSTRACT
Wandering spleen in children is a rare condition. The diagnosis is difficult, and any delay can cause splenic ischemia. An epidemiologic, semiological, and surgical diagnosis questionnaire on incidence of wandering spleen in children was sent to several French surgical teams. We report the results of this multicenter retrospective study. Fourteen cases (6 girls, 8 boys) were reported between 1984 and 2009; the age range varies between 1-day-old and 15 years; 86% were seen in the emergency department. Ninety-three percent had diffuse abdominal pain. For 57% of the cases, it was their first symptomatic episode of this type. No diagnosis was established based on the clinical results alone. All patients had presurgical imaging diagnosis. Open surgery was performed on 64% cases. Forty-three had splenectomy for splenic ischemia. Thirty-six percent had splenopexy, 14% had laparoscopic gastropexy, and 7% had spleen repositioning and regeneration. Complications were noted in 60% of the cases resulting in postsplenopexy splenic ischemia. Early diagnosis and surgery are the best guarantee for spleen preservation. Even if the choice of one technique, splenopexy or gastropexy, can be argued, gastropexy has the advantage of avoiding splenic manipulation and restoring proper physiologic anatomy. When there is no history of abdominal surgery, laparoscopy surgery seems the best procedure.
