Synthesis of Oxynitride Powders via Fluidized-Bed Ammonolysis, Part I: Large, Porous, Silica Particles

Reaction of silica (SiO₂) with triethanolamine (TEA, N(CH₂CH₂OH)₃) and ethylene glycol (EG) under conditions (∼200°C) where byproduct water is removed resulted in the formation of the neutral silatrane glycolate complex, N(CH₂CH₂O)₃SiOCH₂CH₂OH (or TEASiOCH₂CH₂OH) in essentially quantitative yield. Solutions of this neutral precursor in EG, when rapidly pyrolyzed and then oxidized at 500°C, formed porous ceramic powders with high specific surface areas (>500 m²/g). These powders were nitrided via ammonolysis in a fluidized-bed reactor at temperatures of 700°-1000°C. The resulting nitrided powders were characterized by thermal and chemical analyses, diffuse reflectance infrared spectroscopy, gas sorption, and X-ray photoelectron spectroscopy. The apparent activation energy for the nitridation process was determined to be 54 kJ/mol. Following nitridation, the powders were amorphous and had nitrogen contents as high as 21 wt% with retained surface areas >300 m²/g at 1000°C. Under the nitridation conditions used, the extent of nitrogen incorporation correlated linearly with increases in material density. This linearity suggested that the change in density occurred primarily because of changes in coordination that occurred as trivalent nitrogen replaced divalent oxygen in the glass structure and nominally because of viscous flow. The linear density increase also suggested that pore trapping did not occur under these processing conditions. This work serves as a model for ongoing studies on the nitridation of high-surface-area ceramic powders produced by the rapid pyrolysis of mixed-metal TEA alkoxides.     

Adaptive Transmission for Direct-Sequence Spread-Spectrum Communications over Multipath Channels

A method is proposed and evaluated for energy-efficient adaptive transmission in direct-sequence spread-spectrum packet communications over specular multipath channels. The power, code rate, and symbol rate are adapted to match the multipath profile and propagation loss of the wireless communications channel. The adaptation of the transmission parameters is based on several statistics that can be derived in a spread-spectrum receiver. The transmission parameters are selected to optimize a performance measure that is related to the energy consumption and time duration of a packet transmission.     

Synthesis of macroporous silica from solid-stabilised emulsion templates

We have investigated the microstructures of the solid residue left behind after the evaporation of solid-stabilised emulsions. The correlation between the microstructure and the properties and preparation conditions of the emulsions will be thoroughly discussed. The type of microstructure is related to the conditions (oil type, oil content, particle type, particle concentration and emulsion type) of the initial emulsion. Solid residues left after evaporation of oil-in-water emulsions containing volatile oils (relative to water) show a “knobbly” microstructure. When oils with similar or lower vapour pressure to that of water were used, “sponge-like” structures were obtained. For emulsions containing volatile oils, the mean drop diameter is similar to the mean pore diameter, whereas when oils with low vapour pressure are used, the pores are much smaller. Finally, this paper will illustrate that stable toluene-in-water emulsions leave porous microstructures, whereas water-in-toluene emulsions and emulsions close to the phase inversion show sheet-like or “knobbly” structure.     

Distributed coordination space: Toward a theory of distributed team process and performance

This paper discusses a theoretical framework designed to elucidate the many issues surrounding distributed team performance, emphasizing how work characteristics associated with such teams may alter both the processes and the products emerging from distributed interaction. It is suggested that distributed team performance can best be understood through conceptualization of a coordination space within which distributed interaction occurs over time and distance. The goal is to take a socio-technical approach to distributed team research so that one can explicate both the cognitive consequences of a lack of co-location as well as the social consequences affecting interaction and team development when work is technology-mediated. The overall objective is to present a framework of 'distributed coordination' such that the principles most appropriate for distributed team performance can be developed.     

Opportunities for Sustainable Mining Pit Lakes in Australia

Abstract.  Due to operational and regulatory practicalities, pit lakes will continue to be common legacies of mine lease relinquishments. Unplanned or inappropriate management of these geographical features can lead to both short- and long-term liability to mining companies, local communities, and the nearby environment during mining operations or after lease relinquishment. However, the potential for pit lakes to provide benefit to companies, communities, and the environment is frequently unrecognised and yet may be a vital contribution to the sustainability of the open-cut mining industry. Sustainable pit lake management aims to minimise short and long term pit lake liabilities and maximise short and long term pit lake opportunities. Improved remediation technologies are offering more avenues for pit lakes resource exploitation than ever before, at the same time mining companies, local communities, and regulatory authorities are becoming more aware of the benefit these resources can offer.     

On the VC Dimension of Bounded Margin Classifiers

In this paper we prove a result that is fundamental to the generalization properties of Vapnik's support vector machines and other large margin classifiers. In particular, we prove that the minimum margin over all dichotomies of k n + 1 points inside a unit ball in R ⁿ is maximized when the points form a regular simplex on the unit sphere. We also provide an alternative proof directly in the framework of level fat shattering.     

Program proving: Jumps and functions

Summary Proof methods adequate for a wide range of computer programs have been expounded in [1] and [2]. This paper develops a method suitable for programs containing functions, and a certain kind Of jump. The method is illustrated by the proof of a useful and efficient program for table lookup by logarithmic search.     

Program proving: Coroutines

Summary Proof methods adequate for a wide range of computer programs have been given in [1–6]. This paper develops a method suitable for programs which incorporate coroutines. The implementation of coroutines described follows closely that given in SIMULA [7, 8], a language in which such features may be used to great advantage. Proof rules for establishing the correctness of coroutines are given and the method is illustrated by the proof of a useful program for histogram compilation.