Showing papers by "Grenoble Institute of Technology published in 2002"

Solution of Some One- and Two-Dimensional Master Equation Models for Thermal Dissociation: The Dissociation of Methane in the Low-Pressure Limit

Abstract: Using three formulations of the master equation (ME), we have investigated theoretically the dissociation of methane in the low-pressure limit. The three forms of the ME are as follows: (1) A one-dimensional model in which E, the total energy, is the independent variable (the E model). (2) The two-dimensional strong-collision-in-J model of Smith and Gilbert (Int. J. Chem. Kinet. 1988, 20, 307−329) in which e, the energy in the active degrees of freedom, and J, the total angular momentum quantum number, are the independent variables (the e,J model). (3) A two-dimensional variant of the e,J model in which E and J are the independent variables (the E,J model). The third form of the ME is the most physically realistic, and for this model we investigate the dependence of values of the energy transfer moments (〈ΔEd〉, −〈ΔE〉, and 〈ΔE2〉1/2) deduced from experiment on assumed forms of the energy transfer function, P(E,E‘), and on temperature. All three moments increase as the temperature rises; −〈ΔE〉 increases fro...

Accuracy of solitary wave generation by a piston wave maker. Précision de la génération d'une onde solitaire par un batteur piston.

Abstract: A new experimental procedure to generate solitary waves in a flume using a piston type wave maker is derived from Rayleigh’s (1876, [18]) solitary wave solution. Resulting solitary waves for dimensionless amplitudes e ranging from 0.05 to 0.5 are as pure as the ones generated using Goring’s (1978, [7]) procedure which is based on Boussinesq (1871a, [1]) solitary wave, with trailing waves of amplitude lower tha n3%o f themain pulse amplitude. In contrast with Goring’s procedure, the new procedure results in very little loss of amplitude in the initial stage of the propagation of the solitary waves. We show that solitary waves generated using this new procedure are more rapidly established. This is attributed to the better description of the outskirts decay coefficient in a solitary wave given by Rayleigh’s solution rather than by a Boussinesq expression. Two other generation procedures based on first-order (KdV) and second order shallow water theories are also tested. Solitary waves generated by the latter are of much lower quality than those generated with Rayleigh or Boussinesq-based procedures.

FlexWare : A Flexible Firmware Development Environment for Embedded Systems

Abstract: The Flexware system is a software/firmware development environment for application specific instruction set processors (ASIPs) and commercial processors. It is currently composed of two main tools : 1. An instruction set simulator, INSULIN, which provides a cycle true VHDL based simulation environment for a user defined instruction set. The use of INSULIN has allowed to model in-house (two DSPs and one microcontrol ASIP) and commercial processors (e.g. the Intel 80C196 and SGS-Thomson ST7291 microcontrollers, as well as the SGS-Thomson ST18950 DSP) in a fraction of the time required for a manually developed model. Execution times are in the order of thousands of instructions per second on a Sparc 2. 2. A retargetable code generator, CODESYN, which takes one or more algorithms expressed in a high-level language and maps them onto a user defined instruction set to produce optimized machine code for a target ASIP or a commercial processor core. The development of a CODESYN based compiler for a DSP ASIP produced results within 20% of hand coded assembler.

Fuzzy and Neural Control of an Induction Motor

Abstract: This paper presents some design approaches to hybrid control systems combining conventional control techniques with fuzzy logic and neural networks. Such a mixed implementation leads to a more effective control design with improved system performance and robustness. While conventional control allows different design objectives such as steady state and transient characteristics of the closed loop system to be specified, fuzzy logic and neural networks are integrated to overcome the problems with uncertainties in the plant parameters and structure encountered in the classical model-based design. Induction motors are characterised by complex, highly non-linear and time-varying dynamics and inaccessibility of some states and outputs for measurements, and hence can be considered as a challenging engineering problem. The advent of vector control techniques has partially solved induction motor control problems, because they are sensitive to drive parameter variations and performance may deteriorate if conventional controllers are used. Fuzzy logic and neural network-based controllers are considered as potential candidates for such an application. Three control approaches are developed and applied to adjust the speed of the drive system. The first control design combines the variable structure theory with the fuzzy logic concept. In the second approach neural networks are used in an internal model control structure. Finally, a fuzzy state feedback controller is developed based on the pole placement technique. A simulation study of these methods is presented. The effectiveness of these controllers is demonstrated for different operating conditions of the drive system.

Extension of the lugre dynamic tire friction model to 2d motion

Abstract: An extension of the LuGre dynamic friction model from longitudinal motion to longitudinal/lateral motion is developed. Applying this model to the motion of a tire we derive a model for tire-road contact forces and moments. A comparison of the steadystate behaviour of the dynamic model with existing static tire friction models is also presented. This comparison allows one to determine the values of the parameters for the new model. Introducing a set of mean states we reduce the order of the system and derive a model in lumped form which is useful for control purposes.

Inverted blister test to measure adhesion energy of thermal oxide scales on metals or alloys

Abstract: A blister test experiment, used in an inverted configuration, has been developed in an attempt to quantify the interfacial fracture energy of oxide scales thermally grown on metallic materials. The practical use of this test is described for two systems: TiO2 on Ti and chromia rich oxide on stainless steel. Provided that experimental problems of good oxide gluing to the sample holder and regular propagation of the interfacial crack could be controlled, adhesion energy values may be obtained with good accuracy. Values between 3 and 170 J m-2 were measured, depending on the metal-oxide system and on the oxidation conditions.

Fragile and robust watermarking by histogram specification

Abstract: This paper presents new results on regional image watermarking by exact histogram specification. Image is split in regions and for each region a watermark is specified. Watermarks are selected such as image original histogram is preserved. Main improvement of proposed regional scheme consists in the marking of the entire image (all the regions) with complementary watermarks. This procedure considerably increases watermarking robustness. The region selection strategy is discussed so that direct identification of regions and bordering effects are eliminated. Robustness/fragility of the proposed scheme depends on the specified histograms. In a general setting, exact histogram specification allows only certain graylevel values for the pixels of each region. Fragile watermarking is obtained when sentinel pixels' region is allowed to take only certain discrete values. Thus, using sparse histograms, one achieves not only image authentication, but also, in case of any attack or malicious editing, the detection of the area where image has been altered. On the contrary, robust watermarking against many attacks is obtained when pixels of each region are allowed to take values on compact intervals of graylevels.

Discontinuous exponential stabilization of chained form systems

Abstract: A transformation is proposed for single chained form systems. This transformation puts chained form systems in a form close to the Brunovsky linear canonical form and can be utilized to derive an almost stabilizing feedback. This feedback is then extended in order to treat the singularity that arises for some initial conditions in the previous approach. The so obtained feedback is static and discontinuous and globally exponentially stabilizes chained form systems. This feedback law has the advantageous property of being bounded for bounded states and converging to zero along the trajectories of the closed-loop system. This work is straightforwardly extendable to multi-input chained systems.

Natural scene perception: visual attractors and images processing

Abstract: This paper aims at identifying the regions of interest in natural scenes. These regions have been defined by a behavioural measure of eye movement and by a model of saliency map constructed in a biologically plausible manner. The saliency map codes the local region of interest in terms of signal properties such as contrast, orientation, colour, curvature etc. In our approach, pictures are processed using a retinal model, simulating the parvocellular output of the retina. The result is then filtered by a bank of Gabor filters, in mutual interaction in order to lower noise, enhance contour, and sharpen filter selectivity. Subjects’ eye positions were recorded as they explored static black and white images in order to categorize these images. All fixations during one scene were averaged in order to make a density map coding the time spent for subjects on each pixel. Statistics were computed on the regions around the fixation point to evaluate an index of predictability of our saliency map. The saliency map and the density map select similar areas. Furthermore, statistics based on eye-selected regions show greater values than for randomly-selected ones.

New viscoplastic model to simulate hot isostatic pressing

Abstract: Most of the numerical simulation software on the hot isostatic pressing (hipping) process is based on viscoplastic modelling of densification, such as the well known Abouaf's model. These constitutive equations are generally obtained from a viscoplastic potential depending on Green's equivalent stress. An implicit coupling between isotropic and deviator parts is therefore only defined by an equivalent stress. A new viscoplastic formulation proposed by Stutz introduces an explicit coupling between isotropic and deviator parts of the stress state, allowing then more flexibility to take into account the experimental results achieved from isotropic, die compaction, and creep tests. This paper deals with the presentation of this new formulation which has been implemented in the finite elements software PreCAD, and the subsequent changes observed in numerical simulations. These simulations achieved with PreCAD software, are compared with an experiment on a complex part manufactured by CEA Grenoble.

Learning the Hidden Structure of Intonation: Implementing Various Functions of Prosody

Abstract: This paper introduces a new model-constrained, data-driven method to generate prosody from metalinguistic information. We refer here to the general ability of intonation to demarcate speech units and convey information about the propositional and interactional functions of these units within the discourse. Our strong hypothesis are that (1) these functions are directly implemented as prototypical prosodic contours that are coextensive to the unit(s) they apply to, (2) the prosody of the message is obtained by superposing and adding all the contributing contours [2]. We describe here an analysis-bysynthesis scheme that consists in both identifying these prototypical contours and separating out their contributions in the prosodic contours of the training data. The scheme is applied to databases designed to evidence various functions of intonation. Experimental results show that the model generates faithful prosodic contours with very few prototypical movements.

Searching for the embedded manifolds in high- dimensional data, problems and unsolved questions

Abstract: Starting from a recall of several classical - and less classical - remarks about high dimensional data spaces, this paper gives a bird's eye view over various techniques of data reduction, from linear multidimensional scaling to non-linear and non-parametric methods. Two kinds of approaches will be presented, the first one operating in the feature space, the second one operating in the dissimilarity space. A special attention will be devoted to the CCA algorithm, in a version which aims at capturing the mean manifold spanned by the data vectors. Some examples from artificial and real data are given.

Video shot detection based on linear prediction of motion

Abstract: This paper describes an approach for video shot detection. It relies on the temporal analysis of frame to frame optical flow measurements. These measures, which are motion wavelet coefficients directly estimated from the image sequence, exhibit discontinuities when shot boundaries occur. These transitions are detected by considering the temporal trajectories of the linear prediction errors of wavelet coefficients. Experimental results and performance evaluation using videos with reference segmentations are presented to demonstrate the efficiency of the approach.

Snow Toughness Measurements and Possible Applications to Avalanche Triggering

Abstract: A snow slab avalanche release usually results from the unstable expansion of a basal crack at the interface between an upper layer (slab) and an underlying substrate, followed by crown crack nucleation and propagation. Despite the fact that many models proposed so far to predict this kind of rupture were only based on continuum mechanics, the use of fracture mechanics seems to be more appropriate to deal with the possible unstable propagation of such defects. For this purpose, a precise knowledge of snow fracture toughnesses in both tensile and shear modes is needed. In the present work, we developed an experimental set similar to Kirchner and Michot's, in order to measure mode I toughness. The experimental campaign carried out in the Alps during the 2000-2001 and 2001-2002 winters on homogeneous sintered snow with different densities gave toughness results of the same order of magnitude as Michot's. However, an unexpected and reproducible dependence of toughness on cantilever length was evidenced. Discrete element simulations of the toughness experiment, considering snow as a cohesive granular material, showed that the elastic energy was stored along a branching pattern. These findings suggest that the classical toughness should be replaced by a generalised toughness defined on the basis of the fractal dimension of this force line pattern.

Seismic waves in fractured porous media

Abstract: A fractured porous medium is a dual-porosity medium, i.e.,itconsistsoftwointeractingporoussystemswhosepermeabil-ities are very different. The purpose of this paper is to math-ematically model seismic wave propagation in saturated frac-turedporousmediawhenthewavelengthislargecomparedtothe fracture characteristic length.The acoustics of porous saturated media are of first impor-tanceinnumerousengineeringareas,e.g.,seismicexploration,property testings in paper manufacturing, designing antinoisedevices. When modeling transport processes in porous media,wecandistinguishtwokindofapproaches(1)phenomenolog-ical approaches, i.e., macroscopic approaches, and (2) homog-enization methods by which the macroscopic equations arederived by starting with the detailed microscale physical de-scription. The acoustics of single-porosity media, i.e., porousmedia with a single pore-size characteristic length, was pio-neered by Biot, who derived his model on the basis of phe-nomenological reasoning (Biot, 1956). In Biot’s theory, theporous matrix is assumed to be elastic, and the fluid is vis-cous and Newtonian. Biot’s model is a two-phase model: theporoussaturatedmediumisdescribedbytwomacroscopicdis-placement fields,

Audiovisual speech synthesis. from ground truth to models.

Abstract: We present here the main approaches used to synthesize and drive talking faces. Illustrative systems are described. We distinguish between facial synthesis itself (i.e the manner in which facial movements are rendered on a computer screen), and the way these movements may be controlled and predicted using phonetic input. We then focus on the necessity to capture, model and render with maximum fidelity the intimate coherence of the facial deformations observed on a human face.

Minimización del tiempo total de flujo de tareas en una sola máquina: Estado del arte

Abstract: La programacion de operaciones en una sola maquina es un problema clasico de la investigacion de operaciones. Numerosos metodos han sido propuestos para resolver diferentes instancias del problema, dependiendo de las restricciones impuestas y del objetivo del mismo. En este articulo estamos interesados en ilustrar el estado actual de desarrollo de los metodos y algoritmos existentes en la literatura para el problema de minimizacion del flujo total de tareas sujetas a fechas de llegadas, tanto en problemas estaticos como dinamicos. Ademas, las posibilidades de trabajo y las preguntas abiertas seran igualmente expuestas.

Standardisation d'une famille ordonnée de composants dont le coût d'obtention est concave

Abstract: The standardization problem studied in this paper can be described as follows. There are n components. The component i is characterized by a certain parameter U(i) (for example: the braking capacity). The set of components can be completely ordered so that U(i)

Wide-area measurements for power system oscillations and facts interactions

Abstract: The potential of wide-area measurements in increasing system performances for damping power oscilla- tions - as inter-area oscillations (1) - and dealing with FACTS (2) interactions has been studied. For this purpose, a Remote Feedback Controller (RFC) (3) is used for both cases. The RFC uses input signals from the generator (or FACTS) where it is installed and also from a remote gen- erator (or remote FACTS). These input signals, both local and remote, are synchronized via the Global Positioning System (GPS) satellites (4, 5). The RFC is tuned via the use of residues, as well as recent convex programming tech- niques that include the application of Linear Matrix Ine- quality (LMI) constraints (6). Simulation tests have been carried out by using a 4- machines test system and a STATCOM via optimal siting of a RFC containing local and remote input signals. The RFC has showed higher performances in damping inter- area oscillation and in limiting adverse FACTS interactions (7).

Implémentation d'un système de tatouage pour la transmission de données

Abstract: Audio watermarking is a method that allows the insertion of an imperceptible mark on an audio data set. Although the watermarking is often used to guarantee copyrights, it can also be used to increase the information transmitted in a communication context. In this paper, this idea is derived from a classical data transmission technique. Then, this model has been modified by controlling the transmitted power and by adapting the spectral coefficients of embedded codes according to the voice signal. This watermarking technique allows us to provide robust system to several treatment, specially to MP3 compression technique

Grain Refinement in an Aluminium-Magnesium Alloy by Severe Plastic Deformation

Abstract: A commercial Al-Mg alloy (AA5083) with an initial grain size of 40 )m was deformed by Equal Channel Angular Extrusion (ECAE). Eight passes, leading to an equivalent strain of 9.2, were performed at 150°C. The yield stress is substantially increased in cold forming conditions while a nearly superplastic behaviour is promoted at a remarkably low temperature (260°C). The structural evolution was investigated. The final structure consists in a mixture of submicronic cells and/or grains that are hardly distinguishable. The local crystallographic orientation was measured with the help of a dedicated experimental procedure based on TEM diffraction pattern recording and computer indexing. The average grain size appears to decrease gradually down to 1 )m for eight passes. This means that misorientations between adjacent cells progressively increases and leads to the formation of high angle grain boundaries.

Towards a Linguistic Validation of a Prosodic Generation Model

Abstract: This paper deals with an approach of prosody evaluation and modelisation, tested together a prosodic model and a prosodic generator, to produce a compared diagnostic of their linguistic competencies. Three evaluation experiments are succinctly described. The first one consists in an online measurement by listeners of the prosodic quality; the second one uses tuned stimuli to test the differences perceived by subjects, and the last one uses delexicalised stimuli to present separately a pure prosodic stimulus and a syntactic stimulus. Their efficiency and disadvantages are analysed along a compared analysis of their results.