Quick method of obtaining the power curve of a wind energy conversion system

This study proposes a method which makes it possible to reduce the number of tests needed to obtain the power curve of a Wind Energy Conversion System (WECS) by extracting more useful information from a test. When using the method of bins, recommended by the International Energy Agency, to determine the power curve, the pre-average occults the wind's irregularity. The study of this irregularity allows to give a weighting to each test data. Before defining this method two lines of study were developed.

The first one concerns the regularity of a function and its application to the variation, for a given machine, of the wind vector module over time. The second one deals with the estimation of the mean value of a random variable by the calculation of the mean of the observed values, given a weighting by a coefficient allowing the diminution or increase then importance of a result.

For a given place, whose turbulence intensity during the measurements is known, the weighted curve and the unweighted curve should be the same. Using the weighting brings either increase in the accuracy or decrease in the number of tests. This method has been tested on two WECS. The tests were carried out at the Centre National d'Essais Eoliens de Lannion (CNEEL France). Then the results are set out and commented.     

Modeling the effective viscoelastic properties of PEEK matrix reinforced by arbitrary oriented short glass fibers

Mechanics of Time-Dependent Materials - The aim of this work consists in estimating and modeling the viscoelastic behavior at small strain of KetaSpire® KT-880 PEEK fiber composites reinforced...     

Structure/properties relationship of nadimide-terminated fluorinated polyimides. Part II. New thermostable systems

We have established the chemical structure/mechanical properties relationships of new nadimide-terminated polyimides. Initially, the prepolymers were synthesized by polycondensation of nadic anhydride (NA), hexafluoroisopropylidene-2,2-bis(phthalic acid anhydride) (6HFDA) and two phenylene diamines, meta (mPDA) and para (pPDA) in N-methylpyrrolidone (NMP). After characterizing the microstructure and composition of these systems using chromatographic (HPLC, SEC) and spectroscopic techniques (¹H and ¹³C NMR), we determined their thermomechanical properties. The rheology curves obtained showed the presence of two transitions, α and β, associated with the glass transition and a second, sub-vitreous transition, because of local molecular movements. By studying the relationship between chemical structures and mechanical properties, we have shown the influence of endo/exo isomerization of nadimide extremities on the glass transition temperature T_g. In a given polymer, the value of T_g increases with increasing percentage of exo isomers. ©1997 SCI     

Control of Al-implantation doping in 4H–SiC

We report results of high-dose Al-ion implantation in 4H–SiC. Using multiple energy implantation techniques, box profiles were realized with targeted concentrations: 3.33×10¹⁸ to 10²¹ cm⁻³. The depths were 190 and 420 nm. The implantation energies ranged from 30 to 200 keV. The implantation and annealing temperatures were 650 and 1670°C, respectively. First, infrared investigations were done to assess the surface quality of the samples before and after annealing. Next, the conduction mechanism was investigated. Performing Hall measurements, we found that the room temperature free hole concentration varies like p_H=C_t/105 (cm⁻³), where C_t is the targeted Al-concentration, with a high level of electronic mobility. For the targeted concentration 10²¹ cm⁻³, this resulted in an active layer with 95 mΩ cm resistivity and, at room temperature, a free hole concentration of 10¹⁹ cm⁻³.     

Electrostatic immobilization of polyoxometallates on silicon: X-ray Photoelectron Spectroscopy and electrochemical studies

Keggin-type dodecatungstosilicates polyoxometallates (POMs) ([SiW₁₂O₄₀]⁴⁻) were immobilized in a straightforward manner by electrostatic interactions on ammonium layers covalently grafted on silicon. This method does not require any POM modification synthetical steps. The presence of [SiW₁₂O₄₀]⁴⁻ on the surface is demonstrated by X-ray Photoelectron Spectroscopy from a specific modification of the tungsten 4f_7/2 signal. Moreover the surface coverage of [SiW₁₂O₄₀]⁴⁻ has been improved by 35% upon changing the nature of the anchoring ammonium groups from protonated to methylated amino groups. The organic-inorganic composite films have also been characterized by cyclic voltammetry showing that POMs have a specific behavior on silicon surfaces. In addition the use of a polyallylamine capping layer proved to stabilize efficiently the POM electrochemical response.     

Innovative scheme for selective carbon nanotubes integration in via structures

Thanks to their outstanding electrical properties [1] and [2], carbon nanotubes (CNTs) are promising candidate to replace Cu in advanced interconnects [3], [4], [5], [6], [7] and [8]. In damascene based CNT via integration scheme, CNTs growth occurs on the whole surface of the wafers: in vias, but also on top surfaces [5]. CNTs on top are subsequently removed by polishing. In this paper, an alternative integration scheme is proposed which avoids CNTs on top. Thanks to careful choice of top surface (TiN) and bottom electrode (doped silicon) materials, CNT growth occurs only in vias. Dense growth (6 × 10¹¹ CNTs/cm²) of small multi wall CNTs is achieved in vias over doped poly-silicon lines. Good encapsulation of CNTs is obtained with SACVD SiO₂ or ALD Al₂O₃ materials. Thanks to polishing of emerging CNTs, planarized CNT vias are obtained. Initial electrical measurements by conductive AFM show the conductivity of these CNT vias.     

Functional biohybrid materials synthesized via surface-initiated MADIX/RAFT polymerization from renewable natural wood fiber: Grafting of polymer as non leaching preservative

Crude wood fibers represent a wide class of renewable resources. The surface modification of such materials via covalent grafting of polymer offers new surface properties with non-leaching coating. The grafting of the polymer chains was achieved by surface-initiated controlled radical polymerization through a grafted xanthate chain transfer agent. Macromolecular design via interchange of xanthate (MADIX) technique was chosen to graft poly(vinyl acetate), polystyrene, poly(n-butyl acrylate) and poly(4-vinylbenzyl chloride)-polystyrene amphiphilic cationic copolymers. Water contact angle measurements highlighted the hydrophobization of the wood fiber surface with a nanoscaled polymer monolayer indicating the appropriate coverage of the fiber. X-ray photoelectron spectroscopy showed the successful grafting of the polymer after drastic washing procedure. The quaternization of the grafted polystyrene-co-poly(4-vinyl benzyl chloride) copolymers with tertiary amine allows the introduction of biocide quaternary ammonium functions while preserving the hydrophobic character of the modified wood fiber when introducing a long alkyl chain in the statistical copolymer. Finally, the cationic copolymer was subjected to Coniophora Puteana to evaluate its propensity to limit the fungi expansion.     

Spherulitic structure development during crystallization in confined space II. Effect of spherulite nucleation at borders

This paper is devoted to the formation of a spherulitic pattern in polymers that are spatially confined. The nucleation at sample boundaries influences the spherulitic structure and accelerates the local conversion of melt into spherulites. A model of the spherulitic pattern formation in narrow strips of polymer based on the probability theory was developed to account for the effect of spherulite nucleation at sample borders. The model allows us to predict the rates of formation of the interspherulitic boundaries and also the distributions of distances from spherulite centers to the boundaries for an isothermal as well as a nonisothermal crystallization. The final length of interspherulitic lines and the final number of triple points between spherulites can also be calculated. The predictions of the model were verified by computer simulation, which reproduces spherulitic patterns observed experimentally in strips of thin films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2319–2329, 2005     

Transcrystallinity effects in high‐density polyethylene. II. Determination of kinetics parameters

Transcrystallinity may occur during differential scanning calorimetry analysis at the surfaces of the samples. In such a case, measurements may be unsuitable. We propose simple methods for the determination of intrinsic crystallization data that are accurate for the polymer and for the determination of the nucleating ability of the surfaces. These methods are based on the experimental analysis of the crystallization of samples with different and calibrated thicknesses during experiments at different constant cooling rates. Analysis of thin samples allowed the characterization of transcrystallinity, whereas analysis of at least three samples of different thicknesses allowed us to determine the true crystallization kinetics of the bulk material. These two techniques were independent of each other and were successfully applied to the case of a high‐density polyethylene. The determinations were verified with simple analytical models. A further extension could be the study of the nucleating ability of different substrates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 734–742, 2002     

Fluorenone‐Based Molecules for Bulk‐Heterojunction Solar Cells: Synthesis,Characterization, and Photovoltaic Properties

A series of four conjugated molecules consisting of a fluorenone central unit symmetrically coupled to different oligothiophene segments are conceptually designed and synthesized to provide new electroactive materials for application in photovoltaic devices. The combination of electron‐donating oligothiophene building blocks with an electron‐accepting fluorenone unit results in the emergence of a new band assigned to an intramolecular charge transfer transition that gives rise to the extension of the absorption spectral range of the resulting molecules. Detailed spectroscopic and voltammetric investigations show that all studied molecules have highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) level positions, which make them good candidates for the application as electron‐donors in bulk‐heterojunction photovoltaic cells, with (6,6)‐phenyl‐C61‐butyric acid methyl ester (PCBM)‐C₆₀ as electron acceptor component. Moderate device performances, with power conversion efficiencies (PCEs) comprised between 0.3 and 0.6%, were obtained with rigid molecules, containing either the bridging units between the thiophene rings, i.e., (2,7‐bis(4,4′‐dioctyl‐cyclopenta[2,1‐b:3,4‐b′]dithiophen‐2‐yl)‐fluoren‐9‐one (SCPTF) and 2,7‐bis(4‐(dioctylmethylene)‐cyclopenta[2,1‐b:3,4‐b′]dithiophen‐5‐yl)‐fluoren‐9‐one (MCPTF) or a vinylene unit 2,7‐bis(5‐[(E)‐1,2‐bis(3‐octylthien‐2‐yl)ethylene])‐fluoren‐9‐one (TVF), whereas with (2,7‐bis‐(3,3?‐dioctyl‐[2,2′;5′,2″;5″,2?]quaterthiophen‐5‐yl)‐fluoren‐9‐one (QTF) PCE up to 1.2% (under AM 1.5 illumination, 100 mW cm^?2, active area 0.28 cm²) was obtained. The strong π‐stacking interactions in the solid state for this oligomer leading to improved morphology could explain the good performances of QTF‐based devices, which rank among the highest recorded for non‐polymeric materials. Consequently, fluorenone‐based non‐polymeric molecules constitute highly attractive materials for solution‐processable solar cell applications.