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Influence and optimization of the electrodes position in a piezoelectric energy harvesting flag
No full textInternational audienceFluttering piezoelectric plates may harvest energy from a fluid flow by converting the plate's mechanical deformation into electric energy in an output circuit. This work focuses on the influence of the arrangement of the piezoelectric electrodes along the plate's surface on the energy harvesting efficiency of the system, using a combination of experiments and numerical simulations. A weakly non-linear model of a plate in axial flow, equipped with a discrete number of piezoelectric patches is derived and confronted to experimental results. Numerical simulations are then used to optimize the position and dimensions of the piezoelectric electrodes. These optimal configurations can be understood physically in the limit of small and large electromechanical coupling
Preface.: Extended versions of selected papers presented at Computational methods for Structural RNAs (CMSR'14)
No full textInternational audienceThis preface introduces to the extended versions of selected papers presented at Computational methods for Structural RNAs (CMSR'14
A mid-infrared Mueller ellipsometer with pseudo-achromatic optical elements
No full textInternational audienceThe purpose of this article is to present a new broadband Mueller ellipsometer designed to work in the mid-infrared range, from 3 to 14 microns. The Mueller ellipsometer, which can be mounted in reflection or in transmission configuration, consists of a polarization state generator (PSG), a sample holder, and a polarization state analyzer (PSA). The PSG consists in one linear polarizer and a retarder sequentially rotated to generate a set of four optimal polarization states. The retarder consists in a bi-prism made of two identical Fresnel rhombs disposed symmetrically and joined by optical contact, giving the ensemble a " V " shape. Retardation is induced by the four total internal reflections that the beam undergoes when it propagates through the bi-prism. Total internal reflection allows to generate a quasi-achromatic retardation. The PSA is identical to the PSG, but with its optical elements mounted in reverse order. After a measurement run, the instrument yields a set of sixteen independent values, which is the minimum amount of data required to calculate the Mueller matrix of the sample. The design of the Mueller ellipsometer is based on the optimization of an objective criterion that allows minimizing the propagation of errors from raw data to the Mueller matrix of the sample. The pseudo-achromatic optical elements ensure a homogeneous quality of the measurements for all wavelengths. The performance of the Mueller ellipsometer in terms of precision, and accuracy, is discussed and illustrated with a few examples
Mechanical and statistical study of the laminar hole formation in transitional plane Couette flow
No full textInternational audienceThis article is concerned with the numerical study and modelling of two aspects the formation of laminar holes in transitional turbulence of plane Couette flow (PCF). On the one hand, we consider quenches: sudden decreases of the Reynolds number R which force the formation of holes. The Reynolds number is decreased from featureless turbulence to the range of existence of the oblique laminar-turbulent bands [Rg; Rt]. The successive stages of the quench are studied by means of visualisations and measurements of kinetic energy and turbulent fraction. The behaviour of the kinetic energy is explained using a kinetic energy budget: it shows that viscosity causes quasi modal decay until lift-up equals it and creates a new balance. Moreover, the budget confirms that the physical mechanisms at play are independent of the way the quench is performed. On the other hand we consider the natural formation of laminar holes in the bands, near Rg. The Direct Numerical simulations (DNS) show that holes in the turbulent bands provide a mechanism for the fragmented bands regime and orientation fluctuations near Rg. Moreover the analysis of the fluctuations of kinetic energy toward low values demonstrates that the disappearance of turbulence in the bands can be described within the framework of Large Deviations. A Large Deviation function is extracted from the Probability Density Function of the kinetic energ
Controllability of spin-boson systems
No full textInternational audienceIn this paper we study the so-called spin-boson system, namely {a two-level system} in interaction with a distinguished mode of a quantizedbosonic field. We give a brief description of the controlled Rabi and Jaynes--Cummings models and we discuss their appearance in the mathematics and physics literature. We then study the controllability of the Rabi model when the control is an external fieldacting on the bosonic part.Applying geometric control techniques to the Galerkin approximation andusing perturbation theory to guarantee non-resonance of the spectrum ofthe drift operator, we prove approximate controllability of thesystem, for almost every value of the interaction parameter
Ordered choice probabilities in random utility models
No full textWe prove a general identity which states that any element of a tuple (ordered set) can be obtained as an alternating binomial weighted sum of rst elements of some sub-tuples. The identity is then applied within the random utility models framework where any alternative's ordered choice probability (the probability that it has a given rank) is expressed with respect to standard best choice probabilities. The logit and the logsum formulas are extended to their ordered choice counterparts. In a symmetric case, we compare for the probit and the logit, the surplus loss due to the withdrawal of a product with the damage due to the loss of a rank
Coherence between geodetic and seismic deformation in a context of slow tectonic activity (SW Alps, France)
No full textInternational audienceA dense, local network of 30 geodetic markers covering a 50 × 60 km2 area in the southwestern European Alps (Briançon region) has been temporarily surveyed in 1996, 2006 and 2011 by GPS. The aim is to measure the current deformation in this seismically active area. The study zone is characterized by a majority of extensional and dextral focal mechanisms, along north–south to N160 oriented faults. The combined analysis of the three measurement campaigns over 15 years and up to 16 years of permanent GPS data from the French RENAG network now enables to assess horizontal velocities below 1 mm/year within the local network. The long observation interval and the redundancy of the dense campaign network measurement help to constrain a significant local deformation pattern in the Briançon region, yielding an average E–W extension of 16 ± 11 nanostrain/year. We compare the geodetic deformation field to the seismic deformation rate cumulated over 37 years, and obtain good coherencies both in amplitude and direction. Moreover, the horizontal deformation localized in the Briançon region represents a major part of the Adriatic-European relative plate motion. However, the average uplift of the network in an extensional setting needs the presence of buoyancy forces in addition to plate tectonics
Half a billion simulations: evolutionary algorithms and distributed computing for calibrating the SimpopLocal geographical model
No full textMulti-agent geographical models integrate very large numbers of spatial interactions. In order to validate those models large amount of computing is necessary for their simulation and calibration. Here a new data processing chain including an automated calibration procedure is experimented on a computational grid using evolutionary algorithms. This is applied for the first time to a geographical model designed to simulate the evolution of an early urban settlement system. The method enables us to reduce the computing time and provides robust results. Using this method, we identify several parameter settings that minimise three objective functions that quantify how closely the model results match a reference pattern. As the values of each parameter in different settings are very close, this estimation considerably reduces the initial possible domain of variation of the parameters. The model is thus a useful tool for further multiple applications on empirical historical situations
