roduct recovery management (PRM) encompasses the management of all used and discarded products, components, and materials that fail under the responsibility of a manufacturing company. The objective of product recovery management is to recover as much of the economic (and ecological) value as reasonably possible, thereby reducing the ultimate quantities of waste.The traditional approach of many manufacturers towards used products has been to ignore them. Manufacturers typically did not feel responsible for what happened with their products after customer use. Most products were designed in such a way that while materials, assembly, and distribution costs were minimized, the repair, reuse, and disposal requirements were not talcen into account. Manufacturers generally believed that the costs of incorporating these requirements would outweigh the benefits. Most of their customers were not prepared to pay an additional fee for a "green" product. Most purchasing decisions were made with the intention of minimizing the purchasing costs, instead of optimizing life-cycle performance-which includes maintenance, reuse, and disposal issues. Consequently, the majority of used products in "developed countries" were landfilled or incinerated, with considerable damage to the environment. Today, both customers and authorities demand that manufacturers reduce the quantities of waste generated by their products. Customer pressure is triggered by environmental concern in general and by rising product disposal costs

In contrast to vehicle routing problems, little work has been done in ship routing and scheduling, although large benefits may be expected from improving this scheduling process. We will present a real ship planning problem, which is a combined inventory management problem and a routing problem with time windows. A fleet of ships transports a single product (ammonia) between production and consumption harbors. The quantities loaded and discharged are determined by the production rates of the harbors, possible stock levels, and the actual ship visiting the harbor. We describe the real problem and the underlying mathematical model. To decompose this model, we discuss some model adjustments. Then, the problem can be solved by a Dantzig–Wolfe decomposition approach including both ship routing subproblems and inventory management subproblems. The overall problem is solved by branch-and-bound. Our computational results indicate that the proposed method works for the real planning problem.

In this paper we consider the problem of routing trains through railway stations. This problem occurs as a subproblem in a project which the authors are carrying out in cooperation with the Dutch railways. The project involves the analysis of future infrastructural capacity requirements in the Dutch railway network. Part of this project is the automatic generation and evaluation of timetables. To generate a timetable a hierarchical approach is followed: at the upper level in the hierarchy a tentative timetable is generated, taking into account the specific scheduling problems of the trains at the railway stations at an aggregate level. At the lower level in the hierarchy it is checked whether the tentative timetable is feasible with respect to the safety rules and the connection requirements at the stations. To carry out this consistency check, detailed schedules for the trains at the railway yards have to be generated. In this paper we present a mathematical model formulation for this detailed scheduling problem, based on the Node Packing Problem (NPP). Furthermore, we describe a solution procedure for the problem, based on a branch-and-cut approach. The approach is tested in an empirical study with data from the station ofZwolle in The Netherlands.

In the western Pyrenees (Southwest France and Northwest Spain), a narrow hybrid zone exists between the common chiffchaff Phylloscopus (collybita) collybita and the Iberian chiffchaff Phylloscopus (c.) brehmii. In this zone, which is approximately 20 km wide, mixed matings and individuals singing the songs of both taxa occur at substantial frequencies (24 and 8.6%, respectively), suggesting frequent hybridization. Previous studies have shown very weak mitochondrial gene flow (Nm = 0.065), whereas four microsatellites suggested much higher nuclear gene flow (Nm = 4.9). In this study we used the amplified fragment length polymorphism (AFLP) method in order to identify hybrids and early backcrosses. We typed 91 birds from both allopatric and sympatric areas for 12 informative AFLP markers (of > 141 polymorphic fragments), obtained by screening 13 AFLP primer combinations. These individuals were previously typed for song (brehmii, collybita or mixed singers), mitochondrial DNA (mtDNA) haplotype and allelic genotypes at four microsatellite loci. Assignment tests demonstrated that in the zone of sympatry, a substantial number of intermediate genotypes existed among the birds previously believed to be pure collybita and brehmii, based on song and mtDNA haplotype. The majority of the mixed singers had intermediate genotypes. Our data suggest that the fraction of the adult population having a hybrid origin (hybrids or backcrosses) is in the order of 10%. With such a frequency of genetic hybrids, there would have been much more mtDNA introgression than observed, had female hybrids been perfectly fertile/viable. This result is consistent with male-biased gene flow and Haldane's rule.

Mating pattern and gene flow were studied in the contact zone between two morphologically very similar Chiffchaff taxa (Phylloscopus collybita, P. brehmii) in SW France and northern Spain. Mating was assortative in brehmii, but not in collybita. Mixed matings were strongly asymmetric (excess of collybita male × brehmii female pairs), but did produce viable offspring in some cases. Sequence divergence of the mitochondrial cytochrome b gene was 4.6%. Haplotypes segregated significantly with phenotype (only five ‘mismatches’ among 94 individuals), demonstrating that mitochondrial gene flow was very restricted. The estimated proportion of F1 hybrids in the reproductive population was significantly lower than expected under a closed population model, indicating strong selection against hybrids. Genetic typing of 101 individuals at four microsatellite loci also showed significant population differentiation, but nuclear gene flow was estimated to be 75 times higher than mitochondrial gene flow. This strong discrepancy is probably due to unisexual hybrid sterility (Haldane’s rule). Thus, there is a strong, but incomplete, reproductive barrier between these taxa.