Properties of poly(ethylene terephthalate)–poly(ethylene naphthalene 2,6‐dicarboxylate) blends with montmorillonite clay

The production and properties of blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) with three modified clays are reported. Octadecylammonium chloride and maleic anhydride (MAH) are used to modify the surface of the montmorillonite–Na⁺ clay particles (clay–Na⁺) to produce clay–C18 and clay–MAH, respectively, before they are mixed with the PET/PEN system. The transesterification degree, hydrophobicity and the effect of the clays on the mechanical, rheological and thermal properties are analysed. The PET–PEN/clay–C18 system does not show any improvements in the mechanical properties, which is attributed to poor exfoliation. On the other hand, in the PET–PEN/clay–MAH blends, the modified clay restricts crystallization of the matrix, as evidenced in the low value of the crystallization enthalpy. The process‐induced PET–PEN transesterification reaction is affected by the clay particles. Clay–C18 induces the largest proportion of naphthalate–ethylene–terephthalate (NET) blocks, as opposed to clay–Na⁺ which renders the lowest proportion. The clay readily incorporates in the bulk polymer, but receding contact‐angle measurements reveal a small influence of the particles on the surface properties of the sample. The clay–Na⁺ blend shows a predominant solid‐like behaviour, as evidenced by the magnitude of the storage modulus in the low‐frequency range, which reflects a high entanglement density and a substantial degree of polymer–particle interactions. Copyright © 2005 Society of Chemical Industry     

Wavelength-switchable fiber laser using acoustic waves

We report a wavelength-switchable fiber ring laser that includes a Bragg grating-based acoustooptic superlattice modulator. Wavelength switching of the laser emission is achieved by controlling the peak reflectivity of the different reflection bands that appear on both sides of the Bragg wavelength when a longitudinal acoustic wave propagates along the grating.     

Importance of out-of-plane dispersion of the excitation spectrum of superconducting bilayers with Josephson coupling

We study the effect of Josephson coupling between adjacent superconducting layers on the BCS energy spectrum. We find that the interference between the gap functions of two layers can lead to vanishing condensation energy for perpendicular momenta corresponding to the formation of standing waves. We therefore predict a conventional energy spectrum for large interlayer spacings, if the gap of the single layers has no nodes, and in all cases a gapless spectrum for small spacings. Within the experimental error, our numerical results account for the low-temperature dependence of the penetration depth reported in Nd_1.85Ce_0.15CuO₄ and YBa₂Cu₃O_6.9.     

Lithium reactivity with III–VI layered compounds

The reactivity of lithium with layered chalcogenides InSe and In₂Se₃ is studied using transmission electron microscopy (TEM), electrochemical potential spectroscopy (EPS) and Raman scattering (RS). It is found that for x(Li)≥0.1 in Li_xInSe, the host material decomposes with the formation of lithium selenide. The presence of Li₂Se is confirmed by Raman spectroscopy. The insertion of Li into In₂Se₃ appears more stable with the occurrence of a superlattice formation at x(Li)≈0.25. The superstructure corresponding to the 2a×2a lattice is consistent with the EPS measurements of Li_xIn₂Se₃.     

Optimization of the properties obtained by quenching in martensitic stainless steels X30-40Cr13 and X40-60CrMoV14

An experimental study of the effects produced by different parameters of the heat-quenching cycle permitted the optimization of the properties typical of these martensitic stainless steels: hardness and corrosion resistance. The results obtained demonstrate that the heating temperatures currently used in industrial quenching treatment of these steels should be modified.     

Analysis of an interferometric optical fibre detection technique applied to silicon vibrating sensors

A simple and accurate analysis of a single-mode optical fibre interferometric displacement detection technique is resented. This analysis is in good agreement with experimental measurements, and shows that angular alignment between the fibre and the sensor is the most critical parameter.     

Optically pumped rubidium as a frequency standard at 196 THz

The performance of 196.0-THz (1529-nm) DFB lasers frequency-locked to absorption lines of a rubidium vapor optically pumped at 384.2 THz (780.2 nm) is studied. The absorption profiles of the pumped vapor are measured under various conditions and compared with theoretical predictions. A bright resonance resulting from the cascade of two cycling transitions is characterized both experimentally and theoretically. The measured frequency stability of a DFB laser frequency-locked to this line reaches a level of 2×10^-10 for an averaging time of 100 s when compared to a similar laser locked to an acetylene line     

Pedestrian Reactive Navigation for Crowd Simulation: a Predictive Approach

This paper addresses the problem of virtual pedestrian autonomous navigation for crowd simulation. It describes a method for solving interactions between pedestrians and avoiding inter-collisions. Our approach is agent-based and predictive: each agent perceives surrounding agents and extrapolates their trajectory in order to react to potential collisions. We aim at obtaining realistic results, thus the proposed model is calibrated from experimental motion capture data. Our method is shown to be valid and solves major drawbacks compared to previous approaches such as oscillations due to a lack of anticipation. We first describe the mathematical representation used in our model, we then detail its implementation, and finally, its calibration and validation from real data.     

Thermodynamic equations of state for hydrazine and monomethylhydrazine

Thermodynamic equations of state are evaluated for the aerospace fuels hydrazine and monomethylhydrazine using Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) formulations. The PR formulation is shown to be the best fit for hydrazine, and the SRK formulation to be the best fit for monomethylhydrazine, based on available critical property data and evaluations of thermodynamic consistency. The adequacy of the differing property data for these fuels in the literature is discussed, and the methodology used to validate the formulations is outlined. The importance of using appropriate real fluid equations of state in thermodynamic safety and hazards analysis of fuel systems is demonstrated by considering an adiabatic compression of gaseous fuels previously postulated in accident scenarios of aerospace propulsion systems. Calculation of isentropic compression temperatures for pure components using ideal gas constant heat capacity, ideal gas with variable heat capacity, and real fluid equations of state are compared to illustrate the need for real fluid equations of state. In addition, three separate approaches are used for estimating isentropic compression temperatures for mixtures involving these fuels, again illustrating the importance of treating these mixtures as real fluids for design and safety analysis.