Area coverage maximization in service facility siting

Traditionally, models for siting facilities in order to optimize coverage of area demand have made use of discrete space representations to efficiently handle both candidate facility locations and demand. These discretizations of space are often necessary given the linear functional forms of many siting models and the complexities associated with evaluating continuous space. Recently, several spatial optimization approaches have been proposed to address the more general problem of identifying facility sites that maximize regional coverage for the case where candidate sites and demand are continuously distributed across space. One assumption of existing approaches is that only demand falling within a prescribed radius of the facility can be effectively served. In many practical applications, however, service areas are not necessarily circular, as terrain, transportation, and service characteristics of the facility often result in irregular shapes. This paper develops a generalized service coverage approach, allowing a sited facility to have any continuous service area shape, not simply a circle. Given that demand and facility sites are assumed to be continuous throughout a region, geometrical properties of the demand region and the service facility coverage area are exploited to identify a facility site to optimize the correspondence between the two areas. In particular, we consider the case where demand is uniformly distributed and the service area is translated to maximize coverage. A heuristic approach is proposed for efficient model solution. Application results are presented for siting a facility given differently shaped service areas.

The Big Circles in Jordan: First absolute ages using rock luminescence surface dating

In this study, we provide the first absolute ages for a Big Circle megalithic structure in Jordan, using rock surface luminescence dating of the buried surface of rocks collected from circle J4 in southern Jordan. Five rocks were used for this study. All rocks showed evidence of previous daylight exposure before being used in the construction of the circle. The exposure was sufficient to bleach the latent luminescence signal to a negligible level compared to the subsequent burial dose. Three rocks gave indistinguishable ages, and were last exposed to daylight in 1500 ± 100 BCE; this is very likely to be the date of circle construction. Two others gave younger ages, indicating later disturbance or reworking. These new results provide very strong evidence for construction during the Late Bronze Age, and refute the earlier hypothesis of construction during Umayyad period (661–750 CE) as a hunting trap.