Showing papers by "Altran published in 2008"

Electrodes for transcutaneous (surface) electrical stimulation

Abstract: In therapeutic and functional applications transcutaneous electrical stimulation (TES) is still the most frequently applied technique for muscle and nerve activation despite the huge efforts made to improve implantable technologies. Stimulation electrodes play the important role in interfacing the tissue with the stimulation unit. Between the electrode and the excitable tissue there are a number of obstacles in form of tissue resistivities and permittivities that can only be circumvented by magnetic fields but not by electric fields and currents. However, the generation of magnetic fields needed for the activation of excitable tissues in the human body requires large and bulky equipment. TES devices on the other hand can be built cheap, small and light weight. The weak part in TES is the electrode that cannot be brought close enough to the excitable tissue and has to fulfill a number of requirements to be able to act as efficient as possible. The present review article summarizes the most important factors that influence efficient TES, presents and discusses currently used electrode materials, designs and configurations, and points out findings that have been obtained through modeling, simulation and testing.

First-order macroscopic modelling of human crowd dynamics

Abstract: This paper deals with the mathematical modelling of crowd dynamics within the framework of continuum mechanics. The method uses the mass conservation equation closed by phenomenological models linking the local velocity to density and density gradients. The closures take into account movement in more than one space dimension, presence of obstacles, pedestrian strategies, and modelling of panic conditions. Numerical simulations of the initial-boundary value problems visualize the ability of the models to predict several interesting phenomena related to the complex system under consideration.

The 100-ka and rapid sea level changes recorded by prograding shelf sand bodies in the Gulf of Lions (western Mediterranean Sea)

Abstract: Thick forced regressive units on the wide continental shelf of the Gulf of Lions (western Mediterranean) recorded the composite effect of sea level changes during the Quaternary. They are mostly composed of coastal siliciclastic and bioclastic wedges showing clinoform geometry. These deposits have been intensively explored through high-resolution seismic investigations, but only recently it was possible to ground truth seismic interpretations, based on a long (100 m) borehole that crossed the succession and recovered a large part of the mainly sandy deposits (similar to 84% recovery). A multiproxy analysis of the sedimentary succession shows that (1) the stratal architecture of the shelf margin is defined by major bounding surfaces that are polygenic erosion surfaces associated with coarse-grained material incorporating abundant and diverse shells, including cold-water fauna (presently absent from the Mediterranean Sea). Between each surface, coarsening upward units with steep (up to 5 degrees) foresets are made of massive (more than 20 m thick) sands with possible swaley and hummocky cross-stratification, passing seaward to sands with muddy intervals and, further offshore, alternating highly boiturbated sands and silts. Each prograding wedge corresponds to a forced-regressive shoreface (or delta front/prodelta), deposited during the overall sea level falls occurring at (relatively slow) interglacial/glacial transition and therefore represents the record of 100 ka cyclicity. Higher-frequency Milankovitch cyclicities are also probably represented by distinct shoreface/delta front wedges; (2) detailed examination of the architecture and chronostratigraphy of the most recent sequence shows that minor bounding surfaces, corresponding to abrupt shallowing of sedimentary facies, separate downward stepping parasequences within the last 100 ka sequence...

CFRP-based broad-band Radar Absorbing Materials

Abstract: Strong interest in radar absorbing materials (RAMs) took place with years due to their extensive sectors of application. RAMs are coatings whose electric and magnetic properties allow the absorption of microwave energy over certain frequencies. In particular, RAMs are very effective means of Radar Cross Section (RCS) reduction in the context of stealth technology. RCS reduction requires absorbers with broad-band characteristics since surveillance radars often employ wide bandwidths. Carbon fiber reinforced plastic (CFRP) composites are made of short carbon fibers embedded in a polymer matrix. They allow broad-band radar absorbing materials (RAMs) characterized by low reflection coefficient against impinging electromagnetic fields, and high resistance against environmental hazards.

Channel estimation for iterative MIMO OFDM/OQAM transceivers

Abstract: OFDM/OQAM modulation scheme is an alternative to the conventional cyclic-prefix OFDM (CP-OFDM) modulation. It allows a larger theoretical spectral efficiency as it does not require the use of any guard interval. In this paper we investigate and evaluate channel estimation for OFDM/OQAM modulations in multiple-input multiple-output (MIMO) context. We focus on transmission over radio channels and use a two transmit antenna spatial data multiplexing (SDM) scheme. Direct compared in this paper.

Parametric Estimation Procedures in Multivariate Generalized Pareto Models

Abstract: . Modelling the tails of a multivariate distribution can be reasonably done by multivariate generalized Pareto distributions (GPDs). We present several methods of parametric estimation in these models, which use decompositions of the corresponding random vectors with the help of different versions of Pickands coordinates. The estimators are compared to each other with simulated data sets. To show the practical value of the methods, they are applied to a real hydrological data set.

Ethanol Sensors for Flex Fuel Operation

Abstract: Motor fuels are increasingly being mixed with ethanol, i. e. plant production alcohol, to reduce CO2 emissions. “Flex Fuel” vehicles are particularly good at running on high ethanol levels (up to 85 % vol. — also known as E85). The engine’s control system must, however, be adjusted to the mixture poured into the tank; the precise determination of the ethanol amount is a critical issue here. At Altran the combination of a virtual and an electrical sensor is currently considered to be the best way forward in this respect. The different measurement methods are examined in more detail in the following.

Wind Evaluation Breadboard: mechanical design and analysis, control architecture, dynamic model, and performance simulation

Abstract: The Wind Evaluation Breadboard (WEB) for the European Extremely Large Telescope (ELT) is a primary mirror and telescope simulator formed by seven segments simulators, including position sensors, electromechanical support systems and support structures. The purpose of the WEB is to evaluate the performance of the control of wind buffeting disturbance on ELT segmented mirrors using an electro-mechanical set-up which simulates the real operational constrains applied to large segmented mirrors. The instrument has been designed and developed by IAC, ALTRAN, JUPASA and ESO, with FOGALE responsible of the Edge Sensors, and TNO of the Position Actuators. This paper describes the mechanical design and analysis, the control architecture, the dynamic model generated based on the Finite Element Model and the close loop performance achieved in simulations. A comparison in control performance between segments modal control and actuators local control is also presented.

Long memory models for the analysis and simulation of multi-channel airborne radar measurement (MCARM) data

Abstract: The performance of STAP algorithms are usually evaluated using both simulated and measured airborne radar data. Data simulation allows the effectiveness of STAP methods to be estimated on larger data sets which normally rely on an assumption of spatial homogeneity and temporal stationarity. Further, synthetic data corresponding to particular radar or terrain characteristics that contribute to degrade STAP performance (e.g. internal clutter motion (ICM), antenna array misalignment and channel mismatch) can be easily generated. Simulated clutter space-time snapshots usually rely on an assumption of identical distribution and statistical independency (IID). The aim of this paper is to analyze multi-channel airborne radar measurement (MCARM) data in order to estimate the spatial correlation of space-time snapshots in real clutter environments. Our experimental results show that clutter measured space-time steering vectors exhibit long-range dependence (LRD) characteristics. The final goal of this work is to define a reliable LRD model for strong correlated clutter space-time snapshots. An accurate characterization of clutter in multi-channel airborne/spaceborne radar data is important, because it can lead to the development of STAP algorithms with improved performance. The presented method demonstrates reliable results when applied to MCARM data files including either spatially homogeneous or nonhomogeneous clutter.

Ethanolsensoren für den Flex-Fuel-Betrieb

Abstract: Zur CO2-Minderung wird Ottokraftstoffen zunehmend Ethanol beigemischt. Flex-Fuel-Fahrzeuge konnen besonders hohe Ethanolanteile (bis 85 % Vol., auch als E85 bezeichnet) verarbeiten. Allerdings muss die Motorsteuerung an das jeweils getankte, immer wieder wechselnde Gemisch aktuell angepasst werden — unter anderem mittels Sensoren. Altran favorisiert derzeit die Kombination eines virtuellen und eines elektrischen Sensors. Im Folgenden werden die verschiedenen Mess methoden naher betrachtet.

Wind Evaluation Breadboard electronics and software

Abstract: WEB, the Wind Evaluation Breadboard, is an Extremely Large Telescope Primary Mirror simulator, developed with the aim of quantifying the ability of a segmented primary mirror to cope with wind disturbances. This instrument supported by the European Community (Framework Programme 6, ELT Design Study), is developed by ESO, IAC, MEDIA-ALTRAN, JUPASA and FOGALE. The WEB is a bench of about 20 tons and 7 meter diameter emulating a segmented primary mirror and its cell, with 7 hexagonal segments simulators, including electromechanical support systems. In this paper we present the WEB central control electronics and the software development which has to interface with: position actuators, auxiliary slave actuators, edge sensors, azimuth ring, elevation actuator, meteorological station and air balloons enclosure. The set of subsystems to control is a reduced version of a real telescope segmented primary mirror control system with high real time performance but emphasizing on development time efficiency and flexibility, because WEB is a test bench. The paper includes a detailed description of hardware and software, paying special attention to real time performance. The Hardware is composed of three computers and the Software architecture has been divided in three intercommunicated applications and they have been implemented using Labview over Windows XP and Pharlap ETS real time operating system. The edge sensors and position actuators close loop has a sampling and commanding frequency of 1KHz.

Airborne radar STAP using long-memory clutter models

Abstract: Traditional analysis of airborne adaptive radars usually assumes the ideal condition of statistically independent and identically distributed (IID) secondary data. To the contrary, measured clutter data are spatially correlated and exhibit long-memory characteristics. In addition, clutter can appear heterogeneous and so the secondary data are no longer IID. The aim of this paper is to define an efficient simulator of long-range dependence (LRD) homogeneous or non-homogeneous clutter space-time steering vectors. To this end, multi-channel airborne radar measurement (MCARM) data have been analyzed to estimate the power spectral density (PSD) of space-time snapshots in real clutter environments. In this paper we will refer to the considered long-memory clutter models as to the LRDSTAP clutter models. LRDSTAP models extend the simplified general clutter model (GCM) by including the LRD characteristics of clutter PSDs. Simulated data from LRDSTAP are used to evaluate the impact of long-memory data on the convergence measure of effectiveness (MOE) of the sample matrix inversion (SMI) STAP processor. The presented method demonstrates reliable results when applied to MCARM data files including either spatially homogeneous or nonhomogeneous clutter.

Analyse vibratoire de modifications de structures. L'approche des cercles de Vincent revisitée

Abstract: Nous traitons ici de la conception de systemes anti-vibratoires venant modifier des structures complexes. L'approche developpee utilise en entree des modeles en elements-finis condenses, ou bien des systemes representes sous une forme simplifiee a partir de modeles fonctionnels, ou bien encore de donnees experimentales. Cette approche peut s'utiliser pour evaluer rapidement le potentiel de concepts et proceder a un premier dimensionnement, mais aussi pour dimensionner finement ces memes concepts au cours des cycles de conception. Nous utilisons comme point de depart les formules classiques de raccord impedanciel, que nous exploitons avec les proprietes homographiques identifiees par A.H. Vincent [A note on the properties of the variation of structural res-ponse with respect to a single structural parameter when plotted in the complex plane, Technical report, Westland Helicopters Ltd., September 1973]. La methode proposee permet notamment de prendre en compte des amortissements, de controler les effets de la modification sur l'ensemble de la bande de frequences d'etude, ainsi que d'evaluer la sensibilite aux parametres de conception. Nous donnons ici une application de cette methode au dimensionnement d'un joint anti-vibratoire pour une culasse de moteur Diesel.

Analyse vibro-acoustique des structures sandwich en NIDA micro-perforées utilisées dans le spatial

Abstract: Les antennes paraboliques ultra legeres des satellites de telecommunication, sont fabriquees en materiaux composites a partir de coques multicouches tres minces obtenues par tissage. Pendant la premiere phase de vol du lanceur, lors de la traversee des premieres couches atmospheriques, les excitations vibro-acoustiques dues au systeme de propulsion et aux forces aerodynamiques sont les plus critiques. La charge acoustique de type aleatoire induite sur la structure de l'antenne, devient alors tres importante et peut provoquer des dommages aux structures et aux equipements. Pour reduire les charges acoustiques, les concepteurs utilisent des coques micro-perforees pour permettre a la structure de "respirer" et de reduire ainsi la charge acoustique. Le dimensionnement et l'optimisation de ces structures necessitent des outils de calcul numerique. La prise en compte de la perforation du materiau pour le calcul de la charge induite par l'excitation acoustique aleatoire n'est pas classique. L'objet de cette etude est de proposer un modele d'impedance locale representatif de la micro-perforation pouvant etre utilise dans un code de calcul vibro-acoustique.