Streaming covariance selection with applications to adaptive querying in sensor networks

Sensor networks can be naturally represented as graphical models, where the edge set encodes the presence of sparsity in the correlation structure between sensors. Such graphical representations can be valuable for information mining purposes as well as for optimizing bandwidth and battery usage with minimal loss of estimation accuracy. We use a computationally efficient technique for estimating sparse graphical models which fits a sparse linear regression locally at each node of the graph via the Lasso estimator. Using a recently suggested online, temporally adaptive implementation of the Lasso, we propose an algorithm for streaming graphical model selection over sensor networks. With battery consumption minimization applications in mind, we use this algorithm as the basis of an adaptive querying scheme. We discuss implementation issues in the context of environmental monitoring using sensor networks, where the objective is short-term forecasting of local wind direction. The algorithm is tested against real UK weather data and conclusions are drawn about certain tradeoffs inherent in decentralized sensor networks data analysis. © 2010 The Author. Published by Oxford University Press on behalf of The British Computer Society. All rights reserved.

ROLE OF CHLORINE AND ALKALI PROMOTERS IN ETHYLENE EPOXIDATION OVER SINGLE CRYSTAL SILVER SURFACES.

Experiments with N//2O were carried out with a view to obtaining additional information about the reactivity of oxygen surface species. On clean Ag, N//2O decomposition was found to be an activated process which led exclusively to the deposition of O(a) species. The presence of preadsorbed oxygen or subsurface oxygen served to enhance the deposition rate of O(a). Subsequent dosing with ethylene at 300 K of such an oxygen-populated surface followed by TPR examination showed it to be active for ethylene oxide formation. Control experiments established that adventitious decomposition of N//2O at the reactor walls or specimen supports followed by possible re-absorption of O//2(a) was an entirely negligible process. ) The oxidation activity of N//2O was also investigated at elevated pressures in the batch reactor.

Mechanism And Selectivity In The Epoxidation Of Ethylene Over Silver: The Results Of Single Crystal Measurements

The silver-catalysed oxidation of ethylene has been examined on the (III) face of a single crystal by a combination of electron spectroscopy and kinetic measurements at pressures of up to 50 Torr. The necessary and sufficient conditions for ethylene oxide formation are established, reaction intermediates are identified, kinetic isotope effects are observed and the role of Cs in modifying reaction selectivity is examined. It is shown that surface alkali exhibits opposite effects on the reactions which lead to the further oxidation of ethylene oxide and on the direct combustion of ethylene. © 1984.