29Si MAS-NMR investigation of the conversion process of a polytitanocarbosilane into SiC-TiC ceramics

A polytitanocarbosilane has been prepared from polycarbosilane and titanium n-butoxide.²⁹Si MAS-NMR was used to characterize the various steps of the conversion process of the polymer into the final ceramic. The reaction of titanium butoxide with polycarbosilane introduces oxygen into the polymer that seems to play an important role in the pyrolysis process. In the first stage up to 1000 ° C, the study reveals the cleavage of Si-C bonds and the formation of SiC_4-xO_x units. In the second stage, above 1000 ° C, the number of Si-O bonds decreases, probably due to a carbothermal reduction process. At 1500 ° C, the product can be described as a mixture of crystalline SiC and TiC with no excess carbon.     

Limit and shakedown analysis of nozzle/cylinder intersections under internal pressure and in-plane moment loading

A simple technique called the elastic compensation method developed previously by Mackenzie & Boyle is used in combination with full three-dimensional finite-element analysis to obtain limit and shakedown interaction diagrams for nozzle/cylinder intersections subject to combined internal pressure and in-plane nozzle moment loading. The results are compared with solutions from the literature and also with detailed elasto-plastic thin shell finite-element analysis. It is found that the simple elastic compensation procedure can provide good estimates of plastic failure mechanisms for complex three-dimensional structures. A detailed discussion of various issues which arose relates to finite-element modelling and the measures taken to improve the results are also documented.     

Microstructure Effects in Multidipped Tin Oxide Films

Porous ultrafine tin oxide films (particle size 70–90 Å) have been prepared from tin alkoxide by dip coating. The influence of the number of coating applications on the thickness, microstructure, and electrical properties of multidipped tin oxide films was investigated. With an increase in the number of coating applications, the porosity of the multidipped films decreased from 60% to 12%, but the particle size of the films increased. The resistivity of the films decreased from 5.5 × 10^–2 to 5.7 × 10^–3Ω·cm with increasing the number of coating applications from 1 to 10. This tendency of the resistivity to decrease is due to the microstructural change of the films with the number of coating applications. The microstructure, the surface structure, and the composition of the multidipped films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Auger electron spectroscopy (AES).     

Cognitive networks: adaptation and learning to achieve end-to-end performance objectives

In this article we advance the idea of a cognitive network, capable of perceiving current network conditions and then planning, learning, and acting according to end-to-end goals. Cognitive networks are motivated by the complexity, heterogeneity, and reliability requirements of tomorrow's networks, which are increasingly expected to self-organize to meet user and application objectives. We compare and contrast cognitive networks with related research on cognitive radios and cross-layer design. By defining cognitive networks, examining their relationship to other technologies, discussing critical design issues, and providing a framework for implementation, we aim to establish a foundation for further research and discussion     

Reprocessing of thermally oxidized aluminum arsenide (AlAs) in epitaxial multilayers without delamination

Annealing or processing of AlAs that has been subjected to a wet thermal oxidation process can result in severe delamination of material at the oxidation front. This paper reports a procedure for preventing this delamination and presents a possible cause for the delamination.     

Effect of electric fields on solid-state reactions between oxides

The solid-state reaction between CaO and AI₂O₃ in intimately mixed powders and pressed polycrystalline pellets to form a series of calcium aluminates is assisted by the application of external d.c. electric fields. The formation of all the aluminate phases is particularly enhanced in the vicinity of the positive electrode. The major effect of the electric field is probably to assist the diffusion of Ca into AI₂O₃, and the results can be qualitatively explained in terms of a simple diffusional model which takes account of the orientation of the reactant grains relative to each other and to the electric field vector. Possible effects of field-induced sintering and the anion packing density of the various product phases are also discussed.     

CDUL: Class directed unsupervised learning

A novel neural network called Class Directed Unsupervised Learning (CDUL) is introduced. The architecture, based on a Kohonen self-organising network, uses additional input nodes to feed class knowledge to the network during training, in order to optimise the final positioning of Kohonen nodes in feature space. The structure and training of CDUL networks is detailed, showing that (a) networks cannot suffer from the problem of single Kohonen nodes being trained by vectors of more than one class, (b) the number of Kohonen nodes necessary to represent the classes is found during training, and (c) the number of training set passes CDUL requires is low in comparison to similar networks. CDUL is subsequently applied to the classification of chemical excipients from Near Infrared (NIR) reflectance spectra, and its performance compared with three other unsupervised paradigms. The results thereby obtained demonstrate a superior performance which remains relatively constant through a wide range of network parameters.