Benchmarking access methods for time-evolving regional data

In this paper we present a performance comparison of access methods for time-evolving regional data. Initially, we briefly review four temporal extensions of the Linear Region Quadtree: the Time-Split Linear Quadtree, the Multiversion Linear Quadtree, the Multiversion Access Structure for Evolving Raster Images and Overlapping Linear Quadtrees. These methods comprise a family of specialized access methods that can efficiently store and manipulate consecutive raster images. A new simpler implementation solution that provides efficient support for spatio-temporal queries referring to the past through these methods, is suggested. An extensive experimental space and time performance comparison of all the above access methods follows. The comparison is made under a common and flexible benchmarking environment in order to choose the best technique depending on the application and on the image characteristics. These experimental results show that in most cases the Overlapping Linear Quadtrees method is the best choice.     

A Convergence-Free Predistortion Technique for Adaptive Linearisation of RF Power Amplifiers

Adaptive digital baseband predistortion is a well-known linearisation technique for removing intermodulation products that radio frequency power amplifiers (PAs) introduce. This paper proposes a new baseband predistortion method that is based on a non-iterative, fast adaptation algorithm without convergence restrictions. The response of the PA in a batch of training magnitude stimuli is used for the computation of the predistortion gain. The latter is directly extracted in rectangular form without prior transformations and AM/AM and AM/PM non-linearities sequential estimation. The influence of the gain table size and the imperfections of the modulator and demodulator in the method's performance are examined. Experimental measurements of an in-house prototype show a linearity improvement of about 25 dB.     

A sensitivity study for an indoor channel

The context of this paper is the 3D wave propagation simulation with a software based on a ray tracing technique in typical indoor environments. The presented works are complementary to these of the literature which propose the validation of a propagation model in comparison with measurements. Indeed, the presented study consists of a sensitivity analysis of an already validated propagation model. The considered parameters are electromagnetic, geometric and electric; they directly intervene in the two parts of a simulation: the modelling of the wave propagation and of the environment. The aim of this study is to contribute to the setting up of parameterisation rules of a simulation software according to two criteria: the accuracy and the compromise between accuracy and computation time.     

Une optimisation en temps de calcul pour la prédiction de zones de couverture radioélectriques

This article presents a method which optimises the computation time for the prediction of a radio coverage, whatever the propagation model used. The principle consists in reducing the number of application points of the propagation model in relation to a classical technique. The proposed method is based on a multi resolution analysis of measured signals carried out around 2 GHz, and on an electromagnetic analysis of the propagation environment. The performances of the method are evaluated in term of reduction in computation time and of accuracy, in comparaison with the classical technique.     

The plastic spin concept and a simple illustration of its role in finite plastic transformations

The basic kinematics and the rate constitutive equations are briefly presented within the framework of a macroscopic formulation of finite plastic transformations for structured media, employing the concept of tensorial structure variables. The key feature is the necessity to provide constitutive relations for the plastic spin according to the proposition of Mandel and Kratochvil. After obtaining these relations for a transversely isotropic medium employing the representation theorems for isotropic second order antisymmetric tensor-valued functions, the role of the plastic spin is illustrated by the analysis of large simple shear for such a medium.     

Automated design of robust discriminant analysis classifier for foot pressure lesions using kinematic data

In the recent years, the use of motion tracking systems for acquisition of functional biomechanical gait data, has received increasing interest due to the richness and accuracy of the measured kinematic information. However, costs frequently restrict the number of subjects employed, and this makes the dimensionality of the collected data far higher than the available samples. This paper applies discriminant analysis algorithms to the classification of patients with different types of foot lesions, in order to establish an association between foot motion and lesion formation. With primary attention to small sample size situations, we compare different types of Bayesian classifiers and evaluate their performance with various dimensionality reduction techniques for feature extraction, as well as search methods for selection of raw kinematic variables. Finally, we propose a novel integrated method which fine-tunes the classifier parameters and selects the most relevant kinematic variables simultaneously. Performance comparisons are using robust resampling techniques such as Bootstrap 632+ and k-fold cross-validation. Results from experimentations with lesion subjects suffering from pathological plantar hyperkeratosis, show that the proposed method can lead to approximately 96% correct classification rates with less than 10% of the original features.     

Experimenting with pattern-matching algorithms

Two new pattern-matching algorithms based on the Boyer-Moore algorithm are presented. Their performance is compared to that of earlier relevant variants in terms of the number of character comparisons and the required running time by exhaustive simulation. Experimental results show the efficiency of both these two new algorithms.