An inequality for the Perron and Floquet eigenvalues of monotone differential systems and age structured equations

For monotone linear differential systems with periodic coefficients, the (first) Floquet eigenvalue measures the growth rate of the system. We define an appropriate arithmetico-geometric time average of the coefficients for which we can prove that the Perron eigenvalue is smaller than the Floquet eigenvalue. We apply this method to Partial Differential Equations, and we use it for an age-structured systems of equations for the cell cycle. This opposition between Floquet and Perron eigenvalues models the loss of circadian rhythms by cancer cells.Comment: 7 pages, in English, with an abridged French versio

Facing the organic reality : the diversity of development models and their consequences on research policies

While OF&F specificity or diversity are acknowledged in many studies, the process of selecting development models is still a pending issue. Based on literature review and our experience, we propose a comprehensive description of such models. Two main axes determine four models. The first axis refers to governance patterns, whether individual or collective. The second one opposes means-based OF to system redesign. Four models are then described, and potential transitions among them are discussed. The role and nature of public policies likely to support candidate models is finally examined. On this basis, this paper intends to openly lay down the stakes of a public research policy for OF&F. As the current poli-cies generally consider implicitly OF&F as an homoge-nous entity, the authors emphasize it’s the diversity and show how the research agendas are strongly connected to the development models for OF&F

Client-based and Cross-layer Optimized Flow Mobility for Android Devices in Heterogeneous Femtocell/Wi-Fi Networks*

AbstractThe number of subscribers accessing Internet resources from mobile and wireless devices has been increasing continually since i-mode, the first mobile Internet service launched in 1999. The handling and support of dramatic growth of mobile data traffic create serious challenges for the network operators. Due to the spreading of WLAN networks and the proliferation of multi-access devices, offloading from 3G to Wi-Fi seems to be a promising step towards the solution. To solve the bandwidth limitation and coverage issues in 3G/4G environments, femtocells became key players. These facts motivate the design and development of femtocell/Wi-Fi offloading schemes. Aiming to support advanced offloading in heterogeneous networks, in this paper we propose a client-based, cross-layer optimized flow mobility architecture for Android devices in femtocell/Wi-Fi access environments. The paper presents the design, implementation and evaluation details of the aforementioned mechanisms

Anharmonicity and asymmetry of Landau levels for a two-dimensional electron gas

We calculate the density of states of a two dimensional electron gas located at the interface of a GaAlAs/GaAs heterojunction. The disorder potential which is generally created by a single doping layer behind a spacer, is here enhanced by the presence of a second delta doped layer of scatterers which can be repulsive or attractive impurities. We have calculated the density of states by means of the Klauder's approximation, in the presence of a magnetic field of arbitrary strength. At low field either band tails or impurity bands are observed for attractive potentials, depending on the impurity concentration. At higher field, impurity bands are observed for both repulsive and attractive potentials. We discuss the effect of such an asymmetrical density of states on the transport properties in the quantum Hall effect regime.Comment: 22 pages, 12 figures. submitted to Phys. Rev.

Mini-bâteau récupérateur de micro-énergie de vaguelette

This paper introduces an original research work on experimental demonstration of micro-energy harvesting from water wave. To implement this demonstrator, commercial piezo-electric elements are used as an electromechanical aquatic energy transducer. The proof-of-concept is constituted by electrical micro-energy sensor circuit implemented on a mini-boat external surface. The water wave is generated by the valve oscillating motion placed in a water tank. Because of the wave interaction with the piezo, it was shown that the electrical circuit placed on the micro-boat surface generates instantaneous electrical power with microwatt amplitude under some Volts amplitude instantaneous voltage. The influence of the boat orientation in function of the water wave propagation direction is investigated

ASIRPA - Analyse des Impacts de la Recherche Publique Agronomique. Rapport final

Le rapport fait le bilan de trois années de recherche concernant les méthodologies d'évaluation d'un organisme public de recherche finalisée. Au cours de trois années de recherche, l’équipe ASIRPA a construit une approche d’évaluation fondée sur la réalisation d’études de cas standardisées, conciliant analyse qualitative et quantitative des impacts des recherches selon cinq dimensions d’analyse. La démarche a été utilisée avec succès par les départements de recherche de l’institut. Une analyse transversale des 30 études réalisées à ce jour a permis de construire une typologie de 5 familles de chemins d’impact caractéristiques de l’institut. Le présent rapport démontre la pertinence des études ex post pour permettre à un organisme finalisé de mieux connaître l’impact de ses recherches, et favoriser les échanges avec les chercheurs et les partenaires autour de cette questio

Application of a Relative Visual Performance Model in a Virtual Reality Immersive System

As part of an evaluation process of user experience realism in a Virtual Reality (VR) system, we focus in this paper on one of the core characteristics of vision: the relationship between contrast and luminance. The experiment aims at validating in VR reaction time predictions given by Rea and Ouellette's model. The subjects have to distinguish, as fast as they can, a target object from an uniform background. Our results did not match the predictions of the model. Our subjects showed higher performance in performing the task than expected. At low level of contrast, our subjects could easily perceive a target they should not have been able to see at all. This is explained by the size of the visual field surrounding the target: at low level of visibility, the larger the surrounding, the easier perception the is. We conclude that the Rea and Ouellette's model could be applied in VR if a specific visual field size factor was added

Dephasing effects on coherent exciton-polaritons and the breakdown of the strong coupling regime

International audienceUsing femtosecond pump-probe spectroscopy, we identify excitation-induced dephasing as a major mechanism responsible for the breakdown of the strong coupling between excitons and photons in a semiconductor microcavity. The effects of dephasing are observed on the transmitted probe-pulse spectrum as a density-dependent broadening of the exciton-polariton resonances and the emergence of a third resonance at high excitation density. A striking asymmetry in the energy shift between the upper and the lower polaritons is also evidenced. Using the excitonic Bloch equations, we quantify the respective contributions to the energy shift of many-body effects associated with Coulomb fermion exchange and photon assisted exchange processes and the contribution to collisional broadening