Study of the dispersion of natural gas issuing from compressor stations through silencers with upper cover

The aim of the present study is the simulation of the dispersion of natural gas issuing from the silencer of compressor stations during vent operations. The objective is to analyze the dispersion of the gas emitted under different conditions of mass flow rate at the exit and ambient cross-flow velocity. We have considered a silencer with an upper cover to protect it from the rain and the fall of objects. The influence of the upper cover of the silencer on the dispersion of natural gas has also been studied, and non-dimensional approaches of the model have been proposed to simplify the problem. Seven different cases have been solved, using two models: a 3D model based on the commercial code FLUENT, and a simplified quasi-one-dimensional model. The results obtained in both cases have been compared, and the range of validity of the one-dimensional model in non-dimensional form has been discussed.     

Electron microscopic characterization of Cr/silica catalyst for ethylene polymerization

Ethylene polymerization was carried out over both porous and non-porous 5 wt% Cr/silica catalysts in a slurry reactor. The polymerization was stopped at selected times to obtain samples for SEM and TEM characterization. Despite the different physical characteristics of the two silica-supported catalysts and their different behavior in the early stages of reaction, high resolution SEM micrographs (taken after runs of longer duration) revealed similar, fibrous and very porous polymer layers on both. This accessibility of the ethylene enables transport of monomer to the active sites at the very high reaction rates.     

A further investigation of the pretest-treatment interaction effect.

What effect does a pretest have on a study of an attitude-treatment when the topic is of great concern to the Ss? Segregation and vivisection were the topics in comparing pretest-treatment interaction. 224 college students plus 100 others were used as Ss. "Apparently, an attitudinal pretest has no effect on the reception of a succeeding persuasive communication within the limits of involvement of S with the topical continuum represented by vivisection… at one point and ethnic prejudice at another." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Synergy Between PAV and AdaBoost

Schapire and Singer's improved version of AdaBoost for handling weak hypotheses with confidence rated predictions represents an important advance in the theory and practice of boosting. Its success results from a more efficient use of information in weak hypotheses during updating. Instead of simple binary voting a weak hypothesis is allowed to vote for or against a classification with a variable strength or confidence. The Pool Adjacent Violators (PAV) algorithm is a method for converting a score into a probability. We show how PAV may be applied to a weak hypothesis to yield a new weak hypothesis which is in a sense an ideal confidence rated prediction and that this leads to an optimal updating for AdaBoost. The result is a new algorithm which we term PAV-AdaBoost. We give several examples illustrating problems for which this new algorithm provides advantages in performance. Editor: Robert Schapire     

Locomotor experience and use of social information are posture specific.

The authors examined the effects of locomotor experience on infants' perceptual judgments in a potentially risky situation--descending steep and shallow slopes--while manipulating social incentives to determine where perceptual judgments are most malleable. Twelve-month-old experienced crawlers and novice walkers were tested on an adjustable sloping walkway as their mothers encouraged and discouraged descent. A psychophysical procedure was used to estimate infants' ability to crawl/walk down slopes, followed by test trials in which mothers encouraged and discouraged infants to crawl/walk down. Both locomotor experience and social incentives affected perceptual judgments. In the encourage condition, crawlers only attempted safe slopes within their abilities, but walkers repeatedly attempted impossibly risky slopes, replicating previous work. The discourage condition showed where judgments are most malleable. When mothers provided negative social incentives, crawlers occasionally avoided safe slopes, and walkers occasionally avoided the most extreme 50? increment, although they attempted to walk on more than half the trials. Findings indicate that both locomotor experience and social incentives play key roles in adaptive responding, but the benefits are specific to the posture that infants use for balance and locomotion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Book reviews

Urban Planning in a Multicultural Society

Michael A. Burayidi (ed.) Praeger, Westport, Conn., 2000 ISBN 0275961257 (hardback) 280 pp.; index RRP $123.85

The Community Planning Handbook: How People Can Shape Their Cities, Towns and Villages

Nick Wates (ed.) Earthscan, London, 2000 ISBN 1853836540 (paperback) 230 pp. RRP $42.85

City Against Suburb: The Culture Wars in an American Metropolis

Joseph A. Rodriguez Praeger, Westport, Conn., 1999 ISBN 027596406X (hardback) 144 pp.; bibliographic essay RRP $96.97

Community Development in the Market Economy

Jeremy McArdle Vista, Melbourne, 1999 ISBN 0958649677 (paperback) 117 pp.; bibliography RRP $16.50

Ethnicity and Housing: Accommodating Difference

Frederick W. Boal (ed.) Ashgate, Aldershot, 2000 ISBN 1859725961 (hardcover) 318 pp.; bibliography and index RRP $101.08

Computer‐Aided Policymaking: Lessons from Strategic Planning Software

Ray Wyatt, E. & F. N. Spon, London, 1999 ISBN 0419244808 (paperback) 244 pp.; bibliography and index RRP $79.95

Making Common Ground: Public‐Private Partnership in Land for Housing.

Geoffrey Payne (ed.). Intermediate Technology Publications, London, 1999. ISBN 1853394793 (paperback). 256 pp.; bibliography and index. RRP $45.86