Modular Groups, Visibility Diagram and Quantum Hall Effect

We consider the action of the modular group $\Gamma (2)$ on the set of positive rational fractions. From this, we derive a model for a classification of fractional (as well as integer) Hall states which can be visualized on two ``visibility" diagrams, the first one being associated with even denominator fractions whereas the second one is linked to odd denominator fractions. We use this model to predict, among some interesting physical quantities, the relative ratios of the width of the different transversal resistivity plateaus. A numerical simulation of the tranversal resistivity plot based on this last prediction fits well with the present experimental data.Comment: 17 pages, plain TeX, 4 eps figures included (macro epsf.tex), 1 figure available from reques

Arnol'd Tongues and Quantum Accelerator Modes

The stable periodic orbits of an area-preserving map on the 2-torus, which is formally a variant of the Standard Map, have been shown to explain the quantum accelerator modes that were discovered in experiments with laser-cooled atoms. We show that their parametric dependence exhibits Arnol'd-like tongues and perform a perturbative analysis of such structures. We thus explain the arithmetical organisation of the accelerator modes and discuss experimental implications thereof.Comment: 20 pages, 6 encapsulated postscript figure

A song and dance: branded entertainment and mobile promotion

This article considers the rise of branded entertainment within the contemporary marketing and media environment. Specifically, it examines how mobile phone marketing in the UK has sought to engage consumers and perform the social use of mobile technology through multimedia ad campaigns with an inscribed entertainment value. Focusing on brand campaigns for 3G mobile services that borrow explicitly from reality television (T-Mobile) and Hollywood film (Orange), the article explores the concept of branded entertainment in relation to the ‘popular imagination’ of mobile communication in the late 2000s. In doing so, it examines the particular relation of flash mobs to the production of brand community