ForwardThese notes are about discrete constant mean curvature surfaces defined by an approach related to integrable systems techniques. We introduce the notion of discrete constant mean curvature surfaces by first introducing properties of smooth constant mean curvature surfaces. We describe the mathematical structure of the smooth surfaces using conserved quantities, which can be converted into a discrete theory in a natural way. About using quaternions: In following with the historical development of the field, we use a model that involves quaternions. However, the use of a more standard model has some advantages, as it can be applied in more general dimensions and settings (see Chapter 10 here, for example), and sometimes gives less cluttered computations. It would be a good exercise to convert this text into one involving a more standard quaternion-free model, but we do not do that here (see [27]), and instead only make occasional comments about this.
It is common practice today to use IP access control.This seems to be an easy-to-use method, but in fact there are a lot of questionable issues connected to it. A Shibboleth-based authentication and authorization infrastructure (AAI) offers a solution for these issues. For this reason the AAR project was begun in 2005 with the goal of building a Shibboleth infrastructure for both German higher education and research and for the Internet portal for scientific and scholarly information called vascoda. Within just two years, the project attracted a very high level of interest. This article describes how we built the Shibboleth infrastructure and it will show the current status of the DFN-AAI federation for German higher education and research.
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