From intracardiac electrograms to electrocardiograms: Models and metamodels

International audienceWe consider the problem of building a standard electrocardiogram (ECG) from the electrical potential provided by a pacemaker in a few points of the heart (electrogram). We use a 3D mathematical model of the heart and the torso electrical activity, able to generate "computational ECG", and a "metamodel" based on a kernel ridge regression. The input of the metamodel is the electrogram, its output is the ECG. The 3D model is used to train and test the metamodel. We illustrate the performance of the proposed strategy on simulated bundle branch blocks of various severities and a few clinical dat

Innovation Cycles and Urban Dynamics

International audienceUrban systems are adaptive systems, in the sense that they continuously renew their structure while fulfilling very different functionalities. Many examples of adaptation in city size, spacing, and their social and functional components have been given in Chapter 6 of this book. There, we defined the structure of urban systems as a rather persistent configuration of relative and relational properties differentiating cities, which, over long periods, maintains the same cities in categories of size or socio-economic specialization. The content of these categories changes in terms ofthe quantitative thresholds or the qualitative attributes used for defining them at each date, but they retain the same meaning in terms of the relative situation of cities in the urban systems. Hierarchical differentiation and socio-economic specialization are the major structural features shared by all city systems. On the scale of national, continental, or world urban systems, the structures result mainly from self-organization processes, even if intentional decisions made by individuals or institutions (for instance, the choice of Brussels for the seat of many European Union institutions) may sometimes influence the general configuration