A MARKET COVERAGE MODEL FOR PRODUCER SERVICES

ABSTRACT We present a model of the optimum market size of a producer service firm that is based on that contact requirements of its service as well as the firm's distance to its prospective clients. The effects on market size of differing contact requirements are discussed from a comparative statics perspective. Optimum market sizes are shown to vary with different values of service duration and demand frequency. These differences may exist between producer service industries, and they may also arise from changes over time in the market requirements of a particular industry. The paper concludes with suggestions for improving the muscle. An impartial agenda for advancing the modeling interests of service-sector researchers also presented.     

Representing the socioeconomic world

This paper considers the potential of geographic information systems as a tool for the analysis of the socioeconomic environment. To obtain the maximum benefit from spatial data, it is necessary to find a structure which allows analysis at a wide range of scales, and this is a severe limitation to conventional vector-based systems. Raster models may be constructed that overcome many of these difficulties. This approach serves to illustrate a number of ways in which GIS can be used as a basis for spatial statistics and modeling of socioeconomic phenomena.     

Dynamic analysis and optimal feedback control synthesis applied to biological waste treatment

The dynamics and optimal feedback control of biological waste treatment processes are examined. Modern feedback control theory is applied and results are obtained for both proportional and proportional plus integral control. A dynamic mathematical model of the system is developed by employing a Monod kinetic model, which is modified to account for endogenous metabolism, and a complete mixing flow model in the growth chamber. The feedback control is implemented via the flow rate so as to maintain desired effluent concentrations. External disturbances which cause changes in substrate concentration and/or cell concentration are considered and optimal control effort is applied. Results are also presented for impulse and step changes in the influent substrate concentration. It is found that by changing the values of the weighting factors in the objective function, it is possible to obtain good control of either the effluent substrate concentration or cell concentration.     

THE INCREASING EFFECTS OF ZEBRA MUSSELS ON WATER INSTALLATIONS IN ENGLAND

The zebra mussel, Dreissena polymorpha, is a major biofouling pest of water treatment works, irrigation systems and power stations in Europe and North America. This paper documents current problems associated with zebra mussels in English waterworks. Questionnaires and manual surveys conducted between 2001 and 2003 have revealed that over 30 water treatment works in England suffer problems associated with zebra mussels. Hundreds of tonnes of mussels are being removed each year from raw water intakes, pipelines and reservoirs. Problems have increased in. the last five years, due to a spread in the range of zebra mussels around England and the cessation of chemical treatment at the intakes of many treatment facilities during the 1990s. The importance of taking control of zebra mussels into account in planning new water supply schemes is highlighted.     

Book reviews

Edge of Empire: Postcolonialism and the City. Jane M. Jacobs. London and New York, Routledge, 1996, 193 pp., £12.99 pb, ISBN 0–415–12007–1

Land for Industrial Development. David Adams, Lynne Russell & Clare Taylor‐Russell. London, E.&F.N. Spon, 1994, 289 pp., £37.50 hb, ISBN 0–419–19180–1

Urban Policy in Practice. Tim Blackman. London, Routledge, 1994, 320 pp., £14.99 pb, ISBN 0–415–09300–7

Planning, the Market and Private House‐building. G. Bramley, W. Bartlett & C. Lambert London, UCL Press, 1995, 192 pp., £11.95 pb, ISBN 1–85728–163–2

Retail Planning Policies in Western Europe. Ross Davies. London, Routledge, 1995, 304 pp., £45.00 hb, ISBN 0–415–10997–3

Transport Concepts in European Cities. Tim Pharoah & Dieter Apel. Aldershot, Avebury, 1995, 291 pp., £42.50 hb, ISBN 1–859–72094–3

Building a New Heritage: Tourism, Culture and Identity in the New Europe. G.J. Ashworth & P.J. Larkham (Eds). London, Routledge, 1994, 278 pp., hb (out of print), ISBN 0–415–07931–4

Fractal Cities: A Geometry of Form and Function. Michael Batty & Paul Longley. London, Academic Press, 1994, 394 pp., £38.00 hb, ISBN 0–124–55570–5     

Virtual reality systems and research on the perception, simulation and presentation of environmental change

The ability of evolving data visualization techniques (e.g. video image-capture technology) to portray realistically both the sensuous and connotative properties of the molar environment and change within the environment has produces an abundance of environmental perception studies using various visualization technologies. Future growth in the application of these technologies to environmental change perception research requires consideration of three sets of issues: (1) the nature of the perceptual experiencing of environment; (2) simulation of thise experience; and (3) presentation of environmental displays to people engaged in the studies.     

Biodegradation of urea in river waters under controlled laboratory conditions

The biodegradation of urea in river waters has been evaluated under laboratory conditions. Urea will degrade to ammonia at a rate depending on the bacterial state of the river water and on the water temperature. Under normal conditions no breakdown may be expected to occur at temperatures below 8°C for 14 days contact. In river waters with a high suspended solids content, simulating extreme winter river conditions, a maximum breakdown of 3–6 per cent daily of the original urea levels was found for temperatures not exceeding 8°C during the first 7 days contact.     

A computer technique for predicting smoke movement in tall buildings

An approach to the analysis of stack effect has been developed which allows the prediction of internal air flow quantities and associated pressure differentials for specific buildings prior to construction. An example of the application of this analysis is presented for a hypothetical 75-story office building. Note: The authors presented this paper at a symposium on “The Control of Smoke Movement on Escape Routes in Buildings,” sponsored by the Joint Fire Research Organization and held on April 9 and 10, 1969 in Hertfordshire, England.