On explicit solutions to the stationary axisymmetric Einstein-Maxwell equations describing dust disks

We review explicit solutions to the stationary axisymmetric Einstein-Maxwell equations which can be interpreted as disks of charged dust. The disks of finite or infinite extension are infinitesimally thin and constitute a surface layer at the boundary of an electro-vacuum. The Einstein-Maxwell equations in the presence of one Killing vector are obtained by using a projection formalism. The SU(2,1) invariance of the stationary Einstein-Maxwell equations can be used to construct solutions for the electro-vacuum from solutions to the pure vacuum case via a so-called Harrison transformation. It is shown that the corresponding solutions will always have a non-vanishing total charge and a gyromagnetic ratio of 2. Since the vacuum and the electro-vacuum equations in the stationary axisymmetric case are completely integrable, large classes of solutions can be constructed with techniques from the theory of solitons. The richest class of physically interesting solutions to the pure vacuum case due to Korotkin is given in terms of hyperelliptic theta functions. The Harrison transformed hyperelliptic solutions are discussed.Comment: 44 pages, 11 figures, revie

Psy-expertise, therapeutic culture and the politics of the personal in development

Expertise stemming from the psy disciplines is increasingly and explicitly shaping international development policy and practice. Whilst some policy makers see the use of psy expertise as a new way to reduce poverty, increase economic efficiency, and promote wellbeing, others raise concerns that psychocentric development promotes individual over structural change, pathologises poverty, and depoliticises development. This paper specifically analyses four aspects of psy knowledge used in contemporary development policy: child development/developmental psychology, behavioural economics, positive psychology, and global mental health. This analysis illuminates the co-constitutive intellectual and colonial histories of development and psy-expertise: a connection that complicates claims that development has been psychologized; the uses and coloniality of both within a neoliberal project; and the potential for psychopolitics to inform development

Numerical study of a multiscale expansion of KdV and Camassa-Holm equation

We study numerically solutions to the Korteweg-de Vries and Camassa-Holm equation close to the breakup of the corresponding solution to the dispersionless equation. The solutions are compared with the properly rescaled numerical solution to a fourth order ordinary differential equation, the second member of the Painlev\'e I hierarchy. It is shown that this solution gives a valid asymptotic description of the solutions close to breakup. We present a detailed analysis of the situation and compare the Korteweg-de Vries solution quantitatively with asymptotic solutions obtained via the solution of the Hopf and the Whitham equations. We give a qualitative analysis for the Camassa-Holm equationComment: 17 pages, 13 figure

Numerical study of blow-up and stability of line solitons for the Novikov-Veselov equation

We study numerically the evolution of perturbed Korteweg-de Vries solitons and of well localized initial data by the Novikov-Veselov (NV) equation at different levels of the "energy" parameter $E$. We show that as $|E| \to \infty$, NV behaves, as expected, similarly to its formal limit, the Kadomtsev-Petviashvili equation. However at intermediate regimes, i.e. when $| E |$ is not very large, more varied scenarios are possible, in particular, blow-ups are observed. The mechanism of the blow-up is studied