Electrostrictive polymer harvesting using a nonlinear approach

This paper presents a new application of the ‘synchronized switch harvesting on inductor’ (SSHI) applied to electrostrictive polymers for DC energy harvesting. It is demonstrated that this technique is very effective for harvesting energy from ambient vibrations using electrostrictive polymers. The method consists in adding an electrical switching device connected in parallel with the electrostrictive elements. The switch triggers on maxima or minima of the voltage and realizes a voltage inversion through an inductor. It is shown that, when applied to electrostrictive polymers, the SSHI technique increases the harvesting process efficiency by 700% compared to the classical approach.     

Influence of woven ply degradation on fatigue crack growth in thin notched composites under tensile loading

This paper deals with the fatigue of the through-the-thickness crack propagation in thin notched composite laminates made of two glass woven plies. It highlights the different crack growths between warp and weft directions of the woven ply. Experimental results show a decrease of the crack growth rate per cycle with the increase of the crack initiation time. Moreover, it has been shown that it is necessary to take into account the fatigue damage of the woven plies in term of loss of rigidity in the initiation phase. The fatigue crack growth rates are then quantified using Paris law type equations and linear elastic fracture mechanics (LEFM).     

Fabrication and mechanical testing of glass fiber entangled sandwich beams: A comparison with honeycomb and foam sandwich beams

The aim of this paper is the fabrication and mechanical testing of entangled sandwich beam specimens and the comparison of their results with standard sandwich specimens with honeycomb and foam as core materials. The entangled sandwich specimens have glass fiber cores and glass woven fabric as skin materials. The tested glass fiber entangled sandwich beams possess low compressive and shear modulus as compared to honeycomb and foam sandwich beams of the same specifications. Although the entangled sandwich beams are heavier than the honeycomb and foam sandwich beams, the vibration tests show that the entangled sandwich beams possess higher damping ratios and low vibratory levels as compared to honeycomb and foam sandwich beams, making them suitable for vibro-acoustic applications where structural strength is of secondary importance, e.g., internal paneling of a helicopter.     

Spin Diffusion Measurements in Spin-Polarised Liquid 3He-4He Mixtures

We report on investigations of spin diffusion in isotopic helium liquid mixtures using a multi-echo technique in applied magnetic field gradients. Samples (up to 1 cm ³ in volume) are obtained by liquefaction of optically polarised gas. NMR measurements are performed at saturated vapour pressure in a low magnetic field (2.2 mT). Signal-to-noise ratios stay high down to ³ He concentrations of order a few parts per thousand at 1K for instance. We demonstrate that the experimental accuracy of spin diffusion measurements is substantially improved using optically polarised mixtures. We have observed that the dynamics of the precession of the transverse magnetisation can be altered due to large dipolar fields at high magnetisation densities. Effects on spin-echo signals and implications for the extension of spin diffusion measurements with our technique are discussed.     

Low-temperature growth of nano-structured silicon thin films on ITO initiated by metal catalysts

Nano-structured silicon thin films have been grown on tin-doped indium oxide (ITO) by Plasma-Enhanced Chemical Vapor Deposition (PECVD) at temperatures lower than 200 °C. Nanometer-scaled aggregates of metal (copper or gold) obtained from evaporated layers were necessary to initiate the nano-structuring growth. Different deposition conditions have been investigated. The highest aspect ratio was obtained with copper and high-pressure plasmas with SiH₄ diluted in H₂. The metals help dissociating silane so the deposition starts faster on the aggregates than around them, which leads to nano-structuration. It is likely that the metal remains confined at the interface between ITO and silicon and do not diffuse in the silicon layer.     

Fibre remote optoelectronic gamma dosimetry based on optically stimulated luminescence of Al2O3:C

Optically stimulated luminescence dosimetry (OSL-D) used in conjunction with fibre optics enables a remote measurement of dose, for the purpose of radioprotection in the nuclear industry and in medicine (radiology, radiotherapy). Alumina OSL crystals are used because of their low Z, low fading and optical transparency, which improves the sensitivity. An optoelectronic portable dosemeter has been designed and tested that shows a dose detection of 50 microGy with a 20 metre-long fibre. Following irradiation, all trapped electrons are released under light stimulation while the OSL is integrated to provide dose-equivalent measurements. A compensation technique is designed with the help of the MCNP4b code, so that both angular and photon energy characteristics comply with international standards (CEI 61066) for photon dose equivalent Hp(10). Two sensors are described that allow measurements over a wide solid angle (95% of 4piSr), for photon energies ranging from 15 keV to 3 MeV.     

Influence of High-Speed Machine Tool Control Parameters on the Contouring Accuracy. Application to Linear and Circular Interpolation

In this paper, we investigate the servo parameters and axis dynamics influences on the contouring accuracy for practical applications such as contouring control of manufacturing systems (robot, machine tool...). The analytical formulation of contouring error in the case of straight line, circle and corner crossing is derived using a simplified axis drive model including the main servo parameters and dominating mechanical mode. The effectiveness of the proposed formulation in estimating the evolution of the final contour error is demonstrated experimentally on a two-axis machine tool.     

Heat conduction in spin-polarized gaseous3He at low temperature

A dilute gas of³He exhibits an interesting dependence of its transport properties on the nuclear spin polarization, resulting from the indistinguishability of the fermions during binary collisions. This article reports experimental results on the heat conductivity of gaseous³He in the 1.2–4.2 K range, the gas being polarized by laser optical pumping. The heat conductivity is found to change with the nuclear polarization. Compared to preliminary data already reported, the present work has been carried out with more care to control all the heat fluxes reaching the measurement cell, and the temperature range has been extended. The results are compared to recently improved calculations. The temperature dependence of the effect is now found to be in satisfactory agreement with theory.     

Modelisation de l'evolution du parathion dans le milieu naturel sur un pilote de laboratoire

The evolution of parathion in a river, and its degradation by the principal natural factors (hydrolysis, photochemical oxidation, biological transformations and retention by sludge and sediments) has been studied on a laboratory pilot plant. The experimental period was 55 days. On the first 34 days, the plant was fed with a solution containing 13 mg l⁻¹ of the pesticide, and during the following 21 days, the effluent was continuously recycled.In the condition in which our experiences were conducted, the main phenomena were biological degradation of the pesticide into non poisonous amino-parathion and its adsorption on the sediments. The quantity of the parathion reduced is proportionated to the quantity of the ATP found in the activated sludge tank.This biological method being the more important, the shock effect of the parathion on a bacterial population was studied by varying the organo-phosphorous concentration (5-10-15 mg l⁻¹) and the quantity of volatile suspended solid (1-2-3 mg l⁻¹).The microorganisms were not affected by the poison and a reduction to aminoparathion was obtained. The quantitative results may be expressed by the following equation On the other hand a very large dose of parathion (1 mg l⁻¹) destroyed the living organism.The presence of anionic or cationic surfactant plays no part in the toxicity of the parathion (15 mg l⁻¹) on the biomass but the degradation of the organo-phosphorous pesticide is totally inhibited.