Effects of turbulence on alkaline phosphatase activity of phytoplankton and bacterioplankton in Lake Taihu

Alkaline phosphatase (AP), an inducible and hydrolytic enzyme, plays a key role in the biogeochemical cycle of phosphorus (P) in lakes. Activity and regulation of AP has been suggested to be affected by hydrodynamic turbulence. However, many aspects of the coupling of the AP activity (APA) and turbulence are still to be investigated and understood. In this study, mesocosm experiments were carried out to further understand the effects of turbulence on APA and the relative contribution of the different microbial groups to the total APA (TAPA). Specifically, we focused on evaluating the APA of phytoplankton (2–112 µm) and bacterioplankton (0.2–2 µm) and its relationship with P fractions under four turbulence levels. Results showed that turbulent conditions enhanced planktonic APA (PAPA) which dominated TAPA by comprising 66–93% of the total fraction. In particular, PAPA was almost two times higher in the turbulence treatments than in still-water control. On the other hand, bacterioplanktonic APA (BAPA) decreased which could be associated with the competitive advantage of bacteria in nutrient-limited conditions due to surface-to-volume ratio. The results suggest that turbulence can accelerate the biogeochemical cycle of P and plays an important role in P strategies of plankton

Aquatic ecological modelling with TELEMAC3D: performance of the ecological library AED2 in a natural ecosystem

Hydrodynamic

Control of a Multi-Stage Continuous Fermentor for the study of the wine fermentation

APPLICATION PAPER PRIZE (APP)International audienceYeasts play a central role in the wine making process. To study the yeasts in a stable environment and physiological state, a Multi-Stage Continuous Fermentor (MSCF) has been designed that mimics steps of the batch fermentation process. In this paper, the problem of the control of the sugar concentrations in each of the four reactors of the MSCF is considered. The cascade structure of the device leads to a constraint on the input flow rates (the control variables). A control strategy based on a linearizing control law coupled with a state observer and an anti windup component is proposed and finally implemented on the experimental process

Équations différentielles linéaires

Engineering schoo

Représentation diffusive et inversion opératorielle pour l'analyse et la résolution de problèmes dynamiques non locaux

The first part of the thesis is devoted to the mathematical and numerical problem of inversion of dynamic convolutive operators formulated in terms of diffusive symbols. After having introduced an adapted algebraic framework, we first establish several mathematical results allowing to regularize this problem, in fact ill-posed in the Hadamard sense. Namely, the continuity of the inversion operation is proved for a suitably weakened topology. Then, we propose numerical methods based on the above theoretical study and test them on a few concrete examples. In the second part, various dynamic problems are formulated in an original way by means of the tools introduced in the first part. In particular, identification methods based on both the notions of diffusif symbol and symbolic inversion are proposed and studied for nonlinear Volterra models. For illustration, these methods are implemented on some non trivial numerical examples.La première partie de la thèse est consacrée au problème de l'inversion d'opérateurs dynamiques de convolution formulé en termes de symboles diffusifs. Après avoir introduit un cadre algébrique adapté, on établit plusieurs résultats garantissant la résolubilité concrète du problème de l'inversion opératorielle, en fait mal posé au sens de Hadamard, mais régularisable. La continuité de l'opération d'inversion est en particulier obtenue pour un mode de convergence convenablement affaibli. Diverses méthodes d'inversion numérique sont ensuite proposées et testées sur quelques exemples. Dans la seconde partie, divers problèmes dynamiques sont abordés de façon originale au moyen des outils développés dans la première partie. Plus particulièrement, plusieurs techniques d'identification de modèles de Volterra basées sur la paramétrisation de l'opérateur dynamique via son symbole diffusif, sont proposées et étudiées sur la base d'exemples numériques non triviaux

Identification of a Nonlinear Dynamic Model of MEMS with Unstable Switching Zone

This paper focuses on the identification of nonlinear dynamic models for physical systems such as Micro-Electro-Mechanical Systems (MEMS). A first approach consists in transforming the specific inputoutput differential model of the system elaborated from physical analysis in such a way that we get a new equivalent model formulation specifically adapted to the identification problem. Thanks to the equivalence between the dynamic model and the derived identification model, the latter remains in continuous-time, with a clear physical meaning of any of its components. In this paper, we propose to compare this method with two other ones: the first one is also based on global transformation of the model and application of the least-squares minimization and the second one is the well known Continuous-Discrete Extended Kalman Filter. The comparison is made first on simulated data and then on real measurement ones

Identification of a Nonlinear Dynamic Model of MEMS with Unstable Switching Zone

This paper focuses on the identification of nonlinear dynamic models for physical systems such as Micro-Electro-Mechanical Systems (MEMS). A first approach consists in transforming the specific inputoutput differential model of the system elaborated from physical analysis in such a way that we get a new equivalent model formulation specifically adapted to the identification problem. Thanks to the equivalence between the dynamic model and the derived identification model, the latter remains in continuous-time, with a clear physical meaning of any of its components. In this paper, we propose to compare this method with two other ones: the first one is also based on global transformation of the model and application of the least-squares minimization and the second one is the well known Continuous-Discrete Extended Kalman Filter. The comparison is made first on simulated data and then on real measurement ones

Controllability of SISO Volterra Models via Diffusive Representation

International audienceThe problem under consideration is the controllability of a wide class of convolution Volterra systems, namely the class of "diffusive" systems, for which there exists an input-output state realization whose state evolves in the so-called diffusive representation space. We first show that this universal state variable is approximately controllable, and then deduce that such Volterra systems always possess suitable controllability properties, stated and proved. Then, we show how to solve the optimal null control problem in an LQ sense. A numerical example finally highlights these results