Lossless InAsP-InGaP modulator at 1.3 /spl mu/m for optical conversion of radio signals up to 40 GHz

We report on an InAsP-InGaP electroabsorption modulator at 1.3 /spl mu/m integrated with a semiconductor amplifier. The fiber-to-fiber insertion gain reaches +10 dB. The 50-/spl mu/m-long modulator section exhibits a bandwidth of 36 GHz and a -17-dB extinction ratio with 3-V drive voltage. The integrated amplifier produced an RF-link efficiency of -26 dB at 20 GHz without any external amplification.     

The conducting behavior and stability of conducting polymer composites

Results of measurements of the electrical conductivity of low density polyethylene/polypyrrole and polystyrene/polypyrrole composites are reported. It is observed that the electrical conductivity of the composite vs. concentration follows the power law predicted by the percolation theory. The manufacturing process influences the homogeneity of the composite at microscopic scale and thus the percolation threshold. Annealing studies show that the stability of the electrical conductivity of the composite is related to the thermal expansion of the polymers and the relaxation of the polymer chains. The decrease of the electrical conductivity of the composite is attributed to the interruption of the percolation path.     

Recognition of discharge sources using UHF PD signatures

This paper investigates utilizing zero span UHF PD detection. The findings suggest that the technique is a practical solution for on-line PD monitoring of transformers in the presence of noise and also permits the use of existing knowledge on PD defect signatures.     

20 Gbit/s operation of a high-efficiency InGaAsP/InGaAsP MQWelectroabsorption modulator with 1.2-V drive voltage

The authors have fabricated a ridge waveguide electroabsorption modulator based on the quantum-confined Stark effect in InGaAsP/InGaAsP multiple quantum wells. The drive voltage for 12-dB extinction ratio is 1.2 V, and the frequency response is flat within 2 dB from DC to 20 GHz. Operation at 20 Gb/s is reported. Extensive data concerning the parasitic phase modulation (chirping) are obtained as a function of applied bias acid operating wavelength     

Microstructural and magnetic characterization of alumina-iron nanocomposites

Iron-alumina nanocomposite powders containing 10 wt % iron were prepared by selective reduction of alumina-haematite solid solutions. Microstructural study showed three types of metal dispersion in the alumina matrix according to the elaboration process: iron grains that were >70 nm, most of the iron particles were <10 nm and directly epitaxied in the alumina matrix, and iron particles that were surrounded by an interfacial phase. In agreement with transmission electron miscroscopy (TEM) observations, magnetic study confirmed a distribution of the iron particles size, showing the superposition of a ferromagnetic behaviour (larger particles) and a superantiferromagnetic behaviour (smaller particles). Furthermore, analysis of thermoremanent behaviour, coercive field and dissymmetry of hysteresis loops allowed the interfacial phase surrounding some iron particles to be identified as an antiferromagnetic phase, Fe_1+x Al_2–x O₄. Nevertheless, at the interface of metallic iron epitaxied on the alumina matrix some atomic planes always existed where iron was ionic (even if no other phase was detected). As a consequence the mean magnetic moment of iron in these nanocrystals is larger than that in bulk metallic iron.     

Theoretical analysis and experimental applications of barelling and folding in cylinder upsetting tests

By using the finite-element method in the elastic-plastic large-strain range, a new modelling of the upsetting test with sticking and dry friction conditions has been made. The unsteady plastic flow which occurs during experimental upsetting causes the bulging and the folding of the free surface. An appropriate initial meshing which allows the material near the corner of the specimen to be folded is employed in combination with an updated Lagrangian method. These arrangements of the finite-element method describe the flow irregularities with a very good accuracy. The results obtained are highly significant for large strains, especially for the flow localization which gives the high strains required for the coalescence of voids. This localization is described in relation with the friction conditions and some of the theories of ductile fracture have been applied to the problem of fracture in upsetting. We have shown that the theories based on the critical energy accumulated up to the moment of the fracture, like the ones based on the growth of holes are strongly dependent on the strain path at the equatorial free surface. At last, the localization mode depends on the degree of friction, and we may conclude that localization occurs by local necking in high friction conditions.     

A local criterion for cleavage fracture of a nuclear pressure vessel steel

Experiments were performed on three heats of A508 class 3 steel in order to determine the mechanical conditions for cleavage fracture. These tests were carried out on various geometries including 4-point bend specimens and axisymmetric notched tensile bars with different notch radii which have been modelized using the finite element method. In one heat, the temperature range investigated was from 77 K to 233 K. It is shown that the cleavage resistance is increased by tensile straining. Moreover, the probability of fracture obeys the Weibull statistical distribution. All the results can be accounted for in terms of a local criterion based on Weibull theory and which takes into account the effect of plastic strain. In this criterion, the parameters which were experimentally determined are found to be temperature independent over the range 77 K to 170 K. The applicability of the approach proposed for cleavage fracture at the crack tip is also examined. It is shown that the experimental results published in the literature giving the variation of fracture toughness with temperature can be explained by the proposed criterion which predicts reasonably well both the scatter in the experimental results and theK _ICtemperature dependence.     

Solubilisation of dye-loaded zeolite L nanocrystals

Solubilisation of zeolite L nanocrystals in different solvents is reported. Grafting alkoxysilane derivatives with a hydrophobic part leads to transparent suspensions in non-polar solvents while modification with a positively charged complex leads to solubilisation in water.     

The transesterification of bisphenol-a polycarbonate (PC) and polybutylene terephthalate (PBTP): A new route to block copolycondensates

In this work, the exchange reaction taking place in molten blends of bisphenol-A polycarbonate and polybutylene terephthalate was studied. A direct transesterification mechanism catalyzed by titanium residues, present in commercial PBTP, was deduced. The transesterification reaction can be -stopped at various levels by additives capable of complexing the titanium catalyst. This work enhances the possibility of a new approach in macromolecular engineering by directly combining polycondensates in a processing machine such as an extruder.