Constraints on the Ultra High Energy Photon flux using inclined showers from the Haverah Park array

We describe a method to analyse inclined air showers produced by ultra high energy cosmic rays using an analytical description of the muon densities. We report the results obtained using data from inclined events (60^{\circ}<\theta<80^{\circ}) recorded by the Haverah Park shower detector for energies above 10^19 eV. Using mass independent knowledge of the UHECR spectrum obtained from vertical air shower measurements and comparing the expected horizontal shower rate to the reported measurements we show that above 10^19 eV less than 48 % of the primary cosmic rays can be photons at the 95 % confidence level and above 4 X 10^19 eV less than 50 % of the cosmic rays can be photonic at the same confidence level. These limits place important constraints on some models of the origin of ultra high-energy cosmic rays.Comment: 45 pages, 25 figure

Lacunae Infills for in Situ Treatment of Historic Glazed Tiles

Knowledge of current conservation materials and methods together with those adopted in the past is essential to aid research and improve or develop better conservation options. The infill and painting of tile lacunae are subjected to special requirements mainly when used in outdoor settings. A selection of the most commonly used materials was undertaken and performed based on inquiries to practitioners working in the field. The infill pastes comprised organic (epoxy, polyester), inorganic (slaked lime,hydraulic lime and zinc hydroxychloride) and mixed organic–inorganic (slaked lime mixed with a vinylic resin)binders. The selected aggregates were those most commonly used or those already present in the commercially formulated products. The infill pastes were characterised by SEM, MIP, open porosity, water absorption by capillarity, water vapour permeability, thermal and hydric expansibilities and adhesion to the ceramic body. Their performance was assessed after curing, artificial ageing (salt ageing and UV–Temp–RH cycles) and natural ageing. The results were interpreted in terms of their significance as indicators of effectiveness, compatibility and durabilit

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