Developmental regulation of dental regeneration and morphogenesis in Fishes

The study of odontogenesis has been limited by the lack of established developmental models which regenerate their teeth continuously throughout life. Furthermore, our understanding of dental morphogenesis is primarily based on research on the mouse. Evolutionary developmental biology seeks to comparatively study natural morphological diversity in order to identify the developmental mechanisms which underpin their evolution. Throughout this thesis, I investigate the process of dental morphogenesis and successional regeneration in both cartilaginous fishes (Chondrichthyes) and bony fishes (Osteichthyes), in order to provide a more detailed picture of the evolution of odontogenesis, and a reference point for the comparative study of dental regeneration in humans. I show that odontogenesis is widely conserved from sharks through to mammals, and that the most usual vertebrate dentitions develop from only subtle modification of the ancestral bauplan. Furthermore, the process of dental regeneration appears to be important, not only for the replacement of lost or damaged dentition, but also in the evolution of dental morphological diversification. Given that successional dental regeneration is an ancestral gnathostome characteristic, I also investigate the regulation of dental regeneration in a basal gnathostome lineage. Our de novo transcriptome sequencing and predictive gene regulatory network analysis reveals novel candidate markers involved in the regulation of successional dental regeneration, previously undescribed during odontogenesis. This thesis lays the groundwork for the comparative study of these novel markers in mammalian models

Experimental study of the recombination of a drifting low temperature plasma in the divertor simulator Mistral-B

In a new divertor simulator, an ultra-cold (Te<1 eV) high density recombining magnetized laboratory plasma is studied using probes, spectroscopic measurements, and ultra-fast imaging of spontaneous emission. The Mistral-B device consists in a linear high density magnetized plasma column. The ionizing electrons originate from a large cathode array located in the fringing field of the solenoid. The ionizing electrons are focused in a 3 cm diameter hole at the entrance of the solenoid. The typical plasma density on the axis is close to 2.10^18 m-3. The collector is segmented into two plates and a transverse electric field is applied through a potential difference between the plates. The Lorentz force induces the ejection of a very-low temperature plasma jet in the limiter shadow. The characteristic convection time and decay lengths have been obtained with an ultra-fast camera. The study of the atomic physics of the recombining plasma allows to understand the measured decay time and to explain the emission spectra.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Consistency and fluctuations for stochastic gradient Langevin dynamics

Applying standard Markov chain Monte Carlo (MCMC) algorithms to large data sets is computationally expensive. Both the calculation of the acceptance probability and the creation of informed proposals usually require an iteration through the whole data set. The recently proposed stochastic gradient Langevin dynamics (SGLD) method circumvents this problem by generating proposals which are only based on a subset of the data, by skipping the accept-reject step and by using decreasing step-sizes sequence (δm)m≥0. We provide in this article a rigorous mathematical framework for analysing this algorithm. We prove that, under verifiable assumptions, the algorithm is consistent, satisfies a central limit theorem (CLT) and its asymptotic bias-variance decomposition can be characterized by an explicit functional of the step-sizes sequence (δm)m≥0. We leverage this analysis to give practical recommendations for the notoriously difficult tuning of this algorithm: it is asymptotically optimal to use a step-size sequence of the type δm = m-1/3, leading to an algorithm whose mean squared error (MSE) decreases at rate O(m-1/3)