Direct and indirect contacts between cattle farms in north-west England

Little is known regarding the types and frequencies of contact that exist between farms and which of these may act as pathogen transmission routes; however it is likely that farms demonstrate considerable heterogeneity in such contacts. In this cross-sectional study, we explored the direct and indirect contact types and frequencies that exist between cattle farms within a region, focusing on potential routes of pathogen transmission. The owners/managers of 56 farms located in a 10 km by 10 km study area in north-west England were administered an interview-based questionnaire between June and September 2005. Information was obtained relating to contact types and frequencies, including those involving animal movements, equipment sharing between farms and any contractors or companies visiting the farms. The data was explored using hierarchical cluster analysis and network analysis. There was considerable variation between farms arising from different contact types. Some networks exhibited great connectivity, incorporating approximately 90% of the farms interviewed in a single component, whilst other networks were more fragmented, with multiple small components (sets of connected farms not linked with other farms). A range of factors influencing contact between farms were identified. For example, contiguous farms were more likely to be linked via other contacts, such as sharing of equipment and direct farm-to-farm animal movements (p < 0.001 and p = 0.02, respectively). The frequency of contacts was also investigated; it is likely that the amount of contact a farm receives from a company or contractor and whether or not biosecurity is performed after contact would impact on disease transmission potential. We found considerable heterogeneity in contact frequency and that many company and contractor personnel undertook little biosecurity. These findings lead to greater understanding of inter-farm contact and may aid development of appropriate biosecurity practices and control procedures, and inform mathematical modelling of infectious diseases

The allocation of value for jointly provided services

Caller I.D. service, whereby the telephone number of the calling party is visually displayed to the called party during ringing, is now available in some areas of the U.S., but it is restricted to calls within a local calling area, and for which the calling and called party are customers of the same local telephone company. If Caller I.D. service is extended nationwide, identification of a long-distance call will, in a typical case, require the participation of three companies: the local exchange carrier originating the call, the long-distance carrier, and the local exchange carrier terminating the call. How shall the revenues from the service be divided among the participating firms? We apply cooperative game theory to address this question

Semantics of Agent Communication: An Introduction

Communication has been one of the salient issues in the research on concurrent and distributed systems. This holds no less for the research on multiagent systems. Over the last few years the study of agent communication, and in particular the semantics of agent communication, has attracted increased interest. The present paper provides an introduction to this area. Since agent communication builds upon concepts and techniques from concurrency theory , we start by giving a short historical overview that covers shared-variable concurrency, message-passing, rendezvous, concurrent constraint programming and agent communication. Standard approaches of agent communication identify three different layers: a content layer, message layer and communication layer. To this model we add an extra level, namely the layer of the multi-agent system. Subsequently, we discern three approaches in developing the semantics of programming languages: the axiomatic, operational and denotational approach. Additionally, we discuss semantic aspects of agent communication, including communication histories, compositionality, observable behaviour, failure sets and full abstractness. We illustrate these issues by means of the framework ACPL (Agent Communication Programming Language). Finally, we briefly consider the specification and verification of agent communication