Pressure infiltration of boron nitride preforms with molten aluminum

The infiltration of compacted cubic BN (cBN) with molten aluminum has been investigated as a potential route for a cheap and easy method of manufacturing cBN/metal composites. CBN compacts have been infiltrated with molten Al at a temperature between 670 and 800 °C and pressure of 15 MPa in vacuum. At these temperatures no pronounced interactions between hexagonal and cubic BN with Al was observed, allowing the complete infiltration of cBN with 12 μm mean grain size. After infiltration at 800 °C, the temperature was increased without pressure to convert aluminum into borides and AlN. The hardness of the resulting materials depends on the content of hexagonal, cubic BN and the rate of conversion of Al into borides and AlN. The infiltration height of less than 1 mm obtained from infiltrating the 3 μm cBN powder green compacts gave a hardness of 22.0 ± 0.6 GPa after heat treatment.     

A bounded distance metric for comparing tree structure

Comparing tree-structured data for structural similarity is a recurring theme and one on which much effort has been spent. Most approaches so far are grounded, implicitly or explicitly, in algorithmic information theory, being approximations to an information distance derived from Kolmogorov complexity. In this paper we propose a novel complexity metric, also grounded in information theory, but calculated via Shannon's entropy equations. This is used to formulate a directly and efficiently computable metric for the structural difference between unordered trees. The paper explains the derivation of the metric in terms of information theory, and proves the essential property that it is a distance metric. The property of boundedness means that the metric can be used in contexts such as clustering, where second-order comparisons are required. The distance metric property means that the metric can be used in the context of similarity search and metric spaces in general, allowing trees to be indexed and stored within this domain. We are not aware of any other tree similarity metric with these properties.     

Functionalised hybrid Poly(ether ether ketone) containing MnO2: Investigation of operative conditions for hydrogen sorption

A composite material synthesis, based on Manganese oxide (MnO₂) anchored to a functionalized polymeric matrix, was optimized. For this investigation two different MnO₂ loadings were selected (16 and 80 wt%) in order to understand the relation between the oxide content, chemical-physical characteristic and the H₂ sorption properties. SEM, XRD were carried out and the obtained results were correlated to the H₂ sorption/desorption characterizations by Sievert apparatus.From these measurements at 50 °C/40 bar, the sample containing 16 wt% of metal oxide content has revealed a low H₂ sorption capability (0,04 wt%), while the 80 wt% sample showed a very high H₂ storage value (3 wt%). A short sorption/desorption cycles were carried out and a good reversibility was revealed.A modelling study, ab-initio Density Functional Theory (DFT) calculations, was carried out. The starting unit cell was MnO₂ while Mn₂₄O₄₈ was considered as a supercell. The number of H atoms was gradually increased and desorption energy was calculated. Desorption energy starts from 366 kJ/mol and decreases by increasing the number of H atoms. For the experimental H₂ sorption value (1,7 wt%) it was calculated the number of the respective H atoms (36) and the corresponding desorption energy (150 kJ/mol).     

Al2O3-Ta2O5-rich glass-ceramic with interconnected pores and its sintering

Substitution of SiO₂ in the ternary sodium borosilicate system with Al₂O₃ plus Ta₂O₅ was found to produce glass which decomposed into microphases and/or crystallized after heat treatment. At least one of the phases present was water soluble. The structure of the material was glassy with the presence of a small crystalline content. Crystalline forms found during powder X-ray diffraction analysis of heat treated, leached and then sintered materials were orthorhombic NaTaO₃ plus AIBO₃, orthorhombic NaTaO₃ and orthorhombic Na₂O · 4Ta₂O₅ plus rhombic 9AI₂O₃ · 2B₂O₃, respectively. The specific surface areas of the leached materials ranged between 96 and 304 m²g^–1, while the mean pore radii of interconnected pores were calculated to be between 2.0 and 8.4 nm. A sintering rate of between 1520 and 1580° C for 5 min were estimated from void volume and bulk density measurements.     

Dielectric waveguides in two-dimensional photonic bandgap materials

We investigate the performance and guiding properties of waveguides fabricated in a finite two-dimensional (2-D) photonic bandgap (PBG) structure. Confinement in the direction perpendicular to the plane of periodicity is achieved by fabricating the 2-D PBG structure in a high dielectric layer enclosed by two lower dielectric layers. Simulations using the finite-difference time-domain (FDTD) method are performed to investigate the energy transport in such waveguides. Good qualitative agreement is found with the experimental observations     

Preparation, Hardness, and Fracture Toughness of Tantalum Oxynitride Ceramics

Tantalum oxynitride powder with a baddeleyite crystal structure was synthesized and densified by hot pressing in Ar and under high pressure using a belt-type high-pressure apparatus. The tantalum oxynitride powder could not be densified completely under hot-pressing conditions at 1400°C. The use of high pressure resulted in dense materials. The samples showed a hardness of 16–17 GPa and a fracture toughness of 3–4 MPa·m^1/2. The hardness is higher compared with that of ZrO₂ and HfO₂ ceramics. The fracture toughness corresponds to the value of fully stabilized ZrO₂ due to the absence of any transformation toughening mechanism.     

Parlay‐based service provision in circuit‐ and packet‐switched telecommunications networks

The spectrum of potential value added services over Internet telephony is wide, but the current service provision solutions are inadequate or proprietary. The nature of Internet differs significantly from that of circuit switched network, however, VoIP architectures can capitalize service control architectures in the PSTN world. We describe such an architecture based on the intelligent network and the Parlay, employing distributed objects and mobile agents as enabling technologies. This architecture has been implemented in the PSTN and the Internet and it has provided a framework for service provisioning, augmenting the space of supported services. Copyright © 2004 John Wiley & Sons, Ltd.