The evolution of strength,elasticity and rupture behaviour of birch tar made with ‘double-pot’ techniques during tar cooking

Birch tar was the first adhesive produced by humans. Its study has consequences for our understanding of human evolution and the development of specialised craftsmanship. One of the better-documented birch tar making methods is the ‘double-pot’ technique, where two containers are used, one containing bark, the other collecting the tar. Birch tar made with double-pots has low viscosity and bad adhesive properties. To obtain a usable adhesive, it must be reduced in volume by cooking. We investigate the evolution of tar’s mechanical properties during cooking. We use lap-shear tests to investigate strength, stiffness and failure behaviour. We found that tar must be cooked for 90 min to acquire adhesive properties. When cooked for longer, strength and stiffness increase over a 30 min lasting time span. Cooking for even longer, beyond this 30 min window, produced a substance that could no longer be used as an adhesive. The implications are that tar cooking requires a high level of skill because specific signs indicating the desired properties must be recognised during the process. Tar cooking constitutes a supplementary investment in time and resources and appears to be associated with a certain degree of risk.     

Review Article: Is there a French way of Explaining African Politics?

This article seeks to uncover the extent to which our ways of understanding contemporary Africa are influenced by our national (historical, cultural, political, intellectual) traditions through an examination of the influential French journal Politique Africaine , whose twentieth anniversary falls this year. In a wide-ranging review article that discusses in detail the 1999 issues of Politique Africaine but is informed by a consideration of the 'deep history' of that journal, the author argues that the French Africanist political scientists whose views appear in the journal are somewhat reluctant to open up to some of the new analysis of Africa available today.     

Approaches to violent death: a case study from early medieval Cambridge

This paper examines one of a number of weapon‐injury victims from the cemetery at Church End in Cherry Hinton, Cambridge (Hertfordshire Archaeological Trust/Archaeological Solutions site HAT358), which was in use from the late Anglo‐Saxon period until after the Norman Conquest. Drawing on precedents set by forensic studies, palaeopathology and more traditional spatial cemetery analysis, assertions are made about the nature of the attack and its context. Copyright © 2006 John Wiley & Sons, Ltd.     

European Corridors as Carriers of Dynamic Agglomeration Externalities?

Transport corridors are viewed as a promising way forward in European Union (EU) transport policy, assumed to contribute positively to regional economic development. However, the validity of this assumption is not evident. The aim of this paper is to empirically test whether agglomeration economies in European transport corridor regions are positively related to indicators of regional economic development compared to regions outside the scope of corridors. The results build on the notion that the type of agglomeration economy in combination with the structure of the economy matters for prospects of structural economic growth in different regions. In this way, the analysis not only contributes to enhancing the empirical scrutiny of the corridor concept in EU transport policy, but also provides new insights into how corridors contribute to regional economic growth. We find only limited evidence for a corridor effect across European regions on productivity and employment growth externalities. Instead, we find a large degree of spatial heterogeneity interacting with corridors—a heterogeneity that has been little recognized in EU policies. We suggest that recent attention to place-based development strategies may accord well with the kinds of agglomeration effects related to corridor development observed in this study.