Editor’s Note

With this issue, Law and Contemporary Problems initiates a new practice of offering occasional mini-symposia on topics which deserve treatment, but may not fill an entire issue. The topics we have chosen certainly deserve treatment. The questions of policy posed by the prospect of additional urban growth in the eighties demand far more thoughtful attention than they have yet had. The relevance of an examination into the control of political and ideological dissent is manifest as we contemplate world events of the past year. We are pleased to offer these two brief symposia. We will introduce others from time to time in future issues. David Lang

Kelvin force in a layer of magnetic fluid

The Kelvin force in a layer of magnetic fluid subjected to a homogeneous magnetic field and local heating is studied. The study is motivated by the question about the corresponding Kelvin force density [M. Liu, Phys. Rev. Lett., 2762 (2000)]. It is shown that the usual and the newly proposed formulation of the Kelvin force are entirely equivalent. It is only when approximations are introduced that differences arise.Comment: 7 pages, 1 figur

Recent Progress on 3D Silicon Detectors

3D silicon detectors, in which the electrodes penetrate the sensor bulk perpendicular to the surface, have recently undergone a rapid development from R\&D over industrialisation to their first installation in a real high-energy-physics experiment. Since June 2015, the ATLAS Insertable B-Layer is taking first collision data with 3D pixel detectors. At the same time, preparations are advancing to install 3D pixel detectors in forward trackers such as the ATLAS Forward Proton detector or the CMS-TOTEM Proton Precision Spectrometer. For those experiments, the main requirements are a slim edge and the ability to cope with non-uniform irradiation. Both have been shown to be fulfilled by 3D pixel detectors. For the High-Luminosity LHC pixel upgrades of the major experiments, 3D detectors are promising candidates for the innermost pixel layers to cope with harsh radiation environments up to fluences of $2\times10^{16}$\,n$_{eq}$/cm$^2$ thanks to their excellent radiation hardness at low operational voltages and power dissipation as well as moderate temperatures. This paper will give an overview on the recent developments of 3D detectors related to the projects mentioned above and the future plans.Comment: Proceedings of the 24th International Workshop on Vertex Detectors, 1-5 June 2015, Santa Fe, US

The Arity Hierarchy in the Polyadic μ\mu-Calculus

The polyadic mu-calculus is a modal fixpoint logic whose formulas define relations of nodes rather than just sets in labelled transition systems. It can express exactly the polynomial-time computable and bisimulation-invariant queries on finite graphs. In this paper we show a hierarchy result with respect to expressive power inside the polyadic mu-calculus: for every level of fixpoint alternation, greater arity of relations gives rise to higher expressive power. The proof uses a diagonalisation argument.Comment: In Proceedings FICS 2015, arXiv:1509.0282