Geometry of a corelation coefficient under a copula

Spearman's rank correlation coefficient is shown to be a measure of distance on the unit square, which characterizes the concentration of the probability density under a copula. A distance function offers insight into structuring copulas with a desired degree of association.     

RUTA: A framework for assessing and selecting additive value functions on the basis of rank related requirements

In this paper, we present a new preference disaggregation method, called RUTA, which infers a set of additive value functions from the preference information referring to the desired ranks of some reference alternatives. Real-life experience indicates that people willingly refer to the range of allowed ranks that a particular alternative should attain, or to constraints on the final scores of the alternatives. We develop a mathematical model for incorporating such preference information via mixed-integer linear programming (MILP). Then, we discuss how decision making could be supported with the use of the already proposed extreme ranking analysis (ERA), which indicates the best and worst ranks gained by each alternative over the set of compatible preference model instances. We also introduce a new interactive UTA-like technique, which aims at selecting a single value function representing the outcomes of ERA. In the interactive process, the decision maker (DM) is assigning priorities to different pre-defined targets, which are built on results of ERA, and refer to the comparison of the best and/or worst ranks for pairs of alternatives. In particular, the DM may choose to emphasize or neglect the advantage of some alternatives over the others, in terms of results of ERA. In this way, one obtains a synthetic representation of extreme ranking analysis at a higher level of abstraction.     

COUNTERVAILING POWER AND DYNAMIC EFFICIENCY

This paper studies the impact of buyer power on dynamic efficiency. We consider a bargaining model in which buyer power arises endogenously from size and may impact on a supplier’s incentives to invest in lower marginal cost. We challenge the view frequently expressed in policy circles that the exercise of buyer power stifles suppliers’ incentives. Instead, we find that the presence of larger buyers keeps a supplier “more on his toes” and induces him to improve the competitiveness of his offering, in terms of both price and quality, relative to buyers’ alternative options.     

Heuristics for the network design problem with connectivity requirements

We consider the NP-complete problem of finding a spanning \(k\)-tree of minimum weight in a complete weighted graph. This problem has a number of applications in designing reliable backbone telecommunication networks. We propose effective algorithms based on a greedy strategy and several variable neighborhood search metaheuristics. We also develop an integer linear programming model for calculating a lower bound. Preliminary numerical experiments using random and real-word data sets are reported to show the effectiveness of our approach. In addition, we compare our approach with known metaheuristics.     

Cognitive antecedents of business models: Exploring the link between attention and business model design over time

A firm's ability to conceive performance-enhancing business models (BMs) has become a cornerstone of competitive advantage. There is consensus that external triggers spur such BM change, but the literature has remained silent on the role of internal and cognitive antecedents such as managerial attention. In our inductive case study of four corporate spin-offs, we find that top management teams (TMTs) with a specific set of attention patterns are more likely to develop performance-enhancing BM designs. However, our findings provide evidence that specific attention foci are not sufficient to enhance particular BM designs, as it is also a matter of the intensity of attention. We further find that, over time, TMTs attention patterns shift and cause changes in BM designs. The emergent theoretical framework highlights that attention is an antecedent in explaining BM designs.     

How to improve urban greenspace for woodland birds: site and local-scale determinants of bird species richness

Wooded habitats represent hotspots of urban biodiversity, however, urban development imposes pressure on biota in these refuges. Identification of the most influential habitat attributes and the role of local urban characteristics is crucial for proper decisions on management practices supporting biodiversity. We aimed to identify well manageable fine-scale habitat attributes to suggest specific, feasible and affordable management recommendations for green space in cities. We analysed species richness of woodland-associated bird communities and incidence of individual species at 290 sites in a wide variety of green areas scattered across the city of Prague, Czech Republic. Generalized linear mixed models (GLMM) and regression tree analyses were used to identify site-scale (100 m radius sampling sites) and local-scale (200 m and 500 m radius plots) habitat attributes shaping the bird communities at individual sites. Logistic regression was used to assess the responses of individual species to habitat characteristics. Our results imply that at the site scale, management practices should focus on maintenance and promoting species-diverse and older tree stands, with a mixture of coniferous and deciduous trees. Water-bodies and accompanying riparian habitats should be maintained and carefully managed to preserve high-quality remnants of natural vegetation. Presence of a few old trees (about 12 % of tree cover with DBH?>?50 cm) or small urban standing water and watercourses enrich the bird community by at least two species. Species richness of woodland avifauna at particular sites is further supported by the total amount of tree cover in the surroundings, including scattered greenery of public spaces and private gardens. We conclude that proper management at site scale has the potential to increase biodiversity of the urban environment.