Détection d’un signal déterministe après réflexions aléatoires

In active signal detection (e.g., radar, sonar, geophysics, etc.), the objective is to extract in the presence of background noise a signal which is known at the transmission but randomly reflected by the target. The received signal is, therefore, no longer deterministic, and the optimum receiver is not a simple matched filter even if the noise is white Gaussian. By introducing appropriate probability distributions for the random reflection, the authors make a mathematical model of the received signal and calculate the likelihood ratio for the Gaussiannoise case. The optimum receiver consists of the matched filter followed by a nonlinear device, which can be represented by a series of filters, and a time-integrator. In a special case of impulse-like signals, the nonlinearity is virtually memoryless. In the case of low signal-to-noise ratio, the series can be approximated by the first two terms, namely, the linear and the quadratic filters.     

Simple iterative receivers for MIMO LP-OFDM systems

In this paper,Lp-ofdm is combined with differentMimo schemes in order to improve performance in terms of diversity gain and to exploit capacity brought by theMimo channel. The original contribution is the development of a generic iterative receiver designed forLp mimo transmission able to work whatever the antenna configuration and the spatial coding scheme. By using a globalMmse criterion, interference terms coming from space-time coding and linear precoding are jointly treated leading to a very good trade-off between performance and complexity compared to trellis based detectors particularly for high order modulations, high number of antennas and/or large size of precoding matrices.     

Punch-through impact ionization MOSFET (PIMOS): From device principle to applications

In the present work a punch-through impact ionization MOSFET (PIMOS) is presented, which exploits impact ionization in low-doped body-tied Ω- and tri-gate structures to obtain abrupt switching (3–10 mV/decade) combined with a hysteresis in the I_D(V_DS) and I_D(V_GS) characteristics. The PIMOS device shows an extraordinary temperature stability up to 125 °C. The influence of various parameters on device performance as abrupt switch or memory cell is investigated. Reduction of the electrical channel length, i.e. of gate length and/or substrate doping, reduces the breakdown voltage and hence the DRAM operating voltage, but also increase the I_off. Two architectures for a capacitor-less DRAM cell are demonstrated and evaluated. In addition, a PIMOS n-type hysteretic inverter is demonstrated, which may serve as a 1T SRAM cell.     

Indoor wood dust analysis during machining with an original experimental device

Particles generated by wood machining have a proven impact on the health of users and woodworkers. The aim of this study was to quantify and describe wood particles in solid and gas phases to reliably and reproducibly characterise these emissions. First, we developed an experimental device that produced particles from solid wood and wood-based panels using portable machine tools. The objective was to study the particles emitted by wood machining while avoiding ambient pollution. Based on own technical specifications, the experimental system was defined and composed of various elements that integrated treatment of inlet air through wood machining to the analysis section that allows solid and gas phases. The first experiments were carried out in sanding and sawing modes on materials used in construction, including solid wood (spruce) and composite panels (particle board (PB), oriented strand board (OSB), and medium density fibreboard (MDF)). Wood-based panels showed more emissive behaviour than solid wood, both for the solid phase and the gas phase. These tests validate the feasibility of generating and measuring particles and emissions of volatile organic compounds (VOCs). Further modifications to the experimental device would enable us to integrate additional devices, such as toxicological ones, to better understand the impact of these wood particles on the health of woodworkers.

     

Synthesis and characterization of (co)polymers containing a phosphonate function for use in dental composites

Novel monomers 1a, 1b, in which a phosphonate function is incorporated in both aromatic rings, were synthesized from the addition reaction of tetraisopropyl [2,2′-disulfanyl-5,5′-thiodiphenyl]-1,1′-diphosphonate and diisopropyl (2-sulfanylphenyl)-1-phosphonate with the glycidylmethacrylate. Free radical homo- and copolymerizations of phosphonate monomers containing methacrylate groups were first carried out in bulk and in THF solution. They offered (co)polymers for potential use in dental resins, in high yields and moderate to high inherent viscosities. The components and structure of the (co)polymers were confirmed by FTIR, SEC, ¹H, ³¹P NMR spectra.

Thermal analysis by using differential scanning calorimetry indicated an amorphous structure of the (co)polymers obtained by polymerization in solution. Upon UV-radiation the composite resins have been synthesized by cross-linking reaction.     

Effect of electrode potential on the tribocorrosion of tungsten

The tribocorrosion behavior of tungsten sliding against an alumina ball was evaluated in sulfuric acid under applied electrode potential. Surface chemistry of worn and unworn surfaces was evaluated using XPS and AES. Quasi-potentiostatic polarization curves and potential step measurements were performed under mass transport control to assess relevant corrosion factors. It was found that the tribocorrosion rate of tungsten varies with the applied electrode potential and goes through a maximum for a potential of 0.5 V MSE. Different material removal mechanisms were identified. In the wear track, materials deterioration proceeds by cyclic mechanical removal of the passive oxide film followed by anodic oxidation. The removal rate was found to be proportional to the passivation charge density determined in independent electrochemical experiments. At higher potential (1 V MSE) a thick WO₃ tribolayer forms and by covering the wear track reduces the tribocorrosion damage. Outside the wear track the stirring of the solution induced by the moving alumina ball leads to an enhancement of the dissolution rate of the WO₃ passive film and thus to higher material wastage.     

Experimental investigation of impact on composite laminates with protective layers

This paper presents an experimental study of low energy impacts on composite plates covered with a protective layer. In service, composite materials are subjected to low energy impacts. Such impacts can generate damage in the material that results in significant reduction in material strength. In order to reduce the damage severity, one solution is to add a mechanical protection on composite structures. The protection layer is made up of a low density energy absorbent material (hollow spheres) of a certain thickness and a thin layer of composite laminate (Kevlar). Energy absorption ability of these protective layers can be deduced from the load/displacement impact curves. First, two configurations of protection are tested on an aluminium plate in order to identify their performance against impact, then the same are tested on composite plates. Test results from force–displacement curves and C-scan control are compared and discussed and finally a comparison of impact on composite plates with and without protection is made for different configurations.     

Low velocity impact modeling in composite laminates capturing permanent indentation

This paper deals with impact damage and permanent indentation modeling. A numerical model has been elaborated in order to simulate the different impact damage types developing during low velocity/low energy impact. The three current damage types: matrix cracking, fiber failure and delamination, are simulated. Inter-laminar damage, i.e. interface delamination, is conventionally simulated using interface elements based on fracture mechanics. Intra-laminar damage, i.e. matrix cracks, is simulated using interface elements based on failure criterion. Fiber failure is simulated using degradation in the volume elements. The originality of this model is to simulate permanent indentation after impact with a “plastic-like” model introduced in the matrix cracking elements. This model type is based on experimental observations showing matrix cracking debris which block crack closure. Lastly, experimental validation is performed, which demonstrates the model’s satisfactory relevance in simulating impact damage. This acceptable match between experiment and modeling confirms the interest of the novel approach proposed in this paper to describe the physics behind permanent indentation.