Utilisation d’un analyseur syntaxique pour la reconnaissance de la parole continue

The author describes the syntactic analyzer which is used in the system keal for continuous speech recognition. After detection of the words in an utterance by a lexical analyzer, the syntactic analyzer builds all the possible syntactic structures according to a context free grammar previously defined by means of a compiled metalanguage. This analyzer allows, in some cases, to correct some errors such as omission and insertion of phonemes by the phonemic analyzer, or non-detection of short words by the lexical analyzer. This program enables presently the recognition of 65 % of utterances in simple dialogs. A few seconds are enough to recognize a sentence.     

Codage différentiel de la parole: algorithmes de prédiction adaptative et performances

This paper describes several speech coding algorithms using adaptive differential pulse code modulation (adpcm) and gives subjective and objective results without and with transmission errors. Subjective results show that these algorithms allow a reduction of the standardpcm bit rate by a factor 2. The best results are obtained by adaptive lattice predictors. The behaviour of the described algorithms in some configuration that will appear in the telephone network, i.e. multiple codings and transcodings frompcm, is also studied.     

Modification de la théorie géométrique de la diffraction pour supprimer la divergence sur l’axe,d’une ouverture rayonnante circulaire en zone proche

All the versions of the Geometrical Theory of Diffraction (GTD)which had been proposed up to now diverged on and near the axial caustic. This paper shows that the axial causticcorrection factor used by Keller gives different results in the planes E and H. By demonstrating a hypothesis concerning the invariability of the average of the fields diffracted on the axis by two pairs of orthogonal points on the outline, the author proposes a new method for calculating the axial field. The numerical results calculated with the new method very well agree with the results obtained with Kottler’s formulas, and that in a far larger zone than that in which the GTD was diverging.     

Amélioration de la sensibilité de détection et de la qualité du radargramme d’un radar pénétrant GPR par une modulation micro-onde

The primary effect of the field continuously capted by aGpr is the production of a class which limits the contrast of the reflections on the targets. The target response becomes illegible sight the influence of certain disturbances which are due to the reflections caused by certain parasitic elements which are randomly distributed in the soil and the dispersion phenomenon. We present in this paper an approach based on a μ-wave modulation which allowed stage this problem. The technique suggested makes it possible to do a classification of capted signals. It will be shown that the frequency of modulation f_m must be higher than a cut-off frequency f_c which depends on the electric parameters of the ground. In a second part of this paper, we show how to improve quality of the radargram of a systemGpr by a simple convolution between the collected signal and a wavelet with a defined parameters.     

Utilisation de la corrélation pondérée dans un processus de détection d’intrusions

Generally, an intruder must perform several actions, organized in an intrusion scenario, to achieve his or her malicious objectives. Actions are modeled by their pre and post conditions, which are a set of logical predicates or negations of predicates. Pre conditions of an action correspond to conditions the system’s state must satisfy to perform the action. Post conditions correspond to the effects of executing the action on the system’s state. When an intruder begins his intrusion, we can deduce, from the alerts generated byidss (Intrusion Detection Systems), several possible scenarios, by correlating attacks, that lead to multiple intrusion objectives. However, with no further analysis, we are not able to decide which are the most plausible ones among the possible scenarios. We propose in this paper to define an order over the possible scenarios by weighting the correlation relations between successive attacks composing the scenarios. These weights reflect to what level executing some actions are necessary to execute some action B. We will see that to be satisfactory, the comparison operator between two scenarios must satisfy some properties.