Suchergebnisse

This paper is concerned with solution procedures for the p-median problem: the well-established heuristic of Teitz and Bart, and the GRIA (Global/Regional Interchange Algorithm) technique developed more recently by Densham and Rushton. A computational scheme is presented which facilitates efficient implementations in both cases. The mathematical basis for the computational scheme is explained concisely by means of set-theory notation, and implementation of the Teitz—Bart heuristic is discussed with particular reference to search and storage considerations in large networks and in trees. In addition, it is shown that the two procedures in general do not terminate at solutions of equivalent local optimality.

AbstractDespite known risks associated with aberrant social skill development, there has been a relative dearth of literature on typical developmental changes in social skills over time. In this study, we examine systematic changes in social skills from kindergarten (typical age of 5–6 years) to third grade (typical age of 8–9 years), and focus on systematic heterogeneity across these developmental trajectories. Data came from the National Head Start—Public School Early Childhood Transition Demonstration Project (N = 6964). Mixture models provide evidence for multiple classes of individuals representing heterogeneity in the development of social skills. Classes were defined as a majority class (whose trajectories remained relatively stable over time), an increasing class (whose trajectories increased at a faster rate than the majority class), and a decreasing class (whose trajectories decreased at a faster rate than the majority class). Developmental trends accounted for a substantial proportion of the variance in social skill components. Implications and limitations of the study are discussed.

Under a contract from the Federal Ministry for Economics and Employment, the DIW Berlin, the Engler-Bunte-Institut and the Fraunhofer-Institut für Systemtechnik und Innovationsforschung, both in Karlsruhe, have investigated influence of the environmental requirements prevailing in Germany and other EU member states on the competitive situation of the German oil industry. The costs of environmental protection measures were analyzed in the refining, storage and retail sectors in Germany and 13 other European countries (Austria, Belgium, Denmark, France, Italy, The Netherlands, Sweden, Spain, The United Kingdom, Poland, Slovakia, The Czech Republic and Hungary). Existing regulations for allowable emissions to the air, water and soil (including TA Luft, the 13. BImSchV and the EU directive for limitation of VOC emissions in storage facilities) as well as requirements for product qualities (e.g. reduction of sulphur in transport fuels and the introduction of biofuels) were considered. Those measures which only have to be implemented by 2009 were also included in the analysis. Starting from the state of plant in the industry (to the extent that this data was available) and the state of national legislation at the end of 2002, the costs to the national oil industries of implementing these requirements in the different countries were determined. In 2002 Germany had stricter requirements in many areas in comparison with other countries investigated and so requires less investment in future to meet these requirements. On the basis of this data the additional cost to the German oil industry (including filling stations) was estimated to be 1,9 Euro per ton of crude processed, of which 0,4 Euro could be attributed to the refining sector and 1,5 Euro to the filling stations. The additional costs in the storage area were relatively small. If the oil industries in all the countries investigated actually reached the same degree of environmental protection by 2009, then the costs would be equal at this time. In fact, however, current legislation shows that Germany intends to maintain its position of "early deployer", so that these cost differences will not be eliminated. The later deployers have the advantage over the early deployers that they invest later and can therefore profit from interest gains. Furthermore they are also able to benefit from the technical progress made over the intervening period.

The measurement of diversity in biological systems is an increasingly important requirement in environmental planning at regional, national, and even international levels. Phylogenetic diversity indicates the biological variety present in a set of species by reference to the phylogenetic relationships amongst the species. A new diversity measure is proposed which for a given group indicates how well a given set of extant taxa represent the group as a whole. The new measure is called the phylogenetic moment, and is related to the p-median definition of locational efficiency in location—allocation analysis. Several analytical techniques for the new measure are described: an evaluation procedure, an heuristic optimisation procedure designed to select a representationally efficient set of taxa, and an exact algorithm for the special case where only one taxon is to be selected. The authors describe the application of the procedures in conservation planning for Australian bat fauna, and report the results of performance tests on a variety of other data sets. Because of their efficient performance and modest storage requirements, the procedures are well suited to the analysis of large taxonomic trees.