Rotating wave approximation: systematic expansion and application to coupled spin pairs

We propose a new treatment of the dynamics of a periodically time-dependent Liouvillian by mapping it onto a time-independent problem and give a systematic expansion for its effective Liouvillian. In the case of a two-level system, the lowest order contribution is equivalent to the well-known rotating wave approximation. We extend the formalism to a pair of coupled two-level systems. For this pair, we find two Rabi frequencies and we can give parameter regimes where the leading order of the expansion is suppressed and higher orders become important. These results might help to investigate the interaction of tunneling systems in mixed crystals by providing a tool for the analysis of echo experiments.Comment: 15 pages, Latex, submitted to European Physical Journal

Glocalizing protest: urban conflicts and the global social movements

The emergence of global social movements is essentially symbolized by the names of cities like Seattle, Genoa or Porto Alegre. This is not accidental, because groups stemming from various parts of the world need places to constitute themselves as movements. But the role of cities in representing great parts of the movements' consciousness also hints at the importance urban struggles have for global protests. The article examines the relationship between urban conflicts and global social movements. By looking for continuities and ruptures between former and current urban conflicts it points out the specificity of the latter: to politicize the contradictions of neoliberal restructuring; to challenge the discursive and institutional terrains of urban politics which were shaped in the 1990s, often with active participation of former movement actors; and, finally, to act simultaneously on various spatial scales. In the last part of the article some examples of 'glocalized' urban protests are presented and analysed, pointing out their ambiguities as well as the specific contribution they can make to the strategic orientation of the global social movements: to fight the destructive influences neoliberal globalization exerts on everyday life and, thereby, to develop alternative forms of societalization. Copyright (c) Joint Editors and Blackwell Publishing Ltd 2003.