Recent progress in theoretical modeling of a sunspot is reviewed. The observed properties of umbral dots are well reproduced by realistic simulations of magnetoconvection in a vertical, monolithic magnetic field. To understand the penumbra, it is useful to distinguish between the inner penumbra, dominated by bright filaments containing slender dark cores, and the outer penumbra, made up of dark...

We present a domain-theoretic model of parametric polymorphism based on admissible per’s over a domain-theoretic model of the untyped lambda calculus. The model is shown to be a model of Abadi & Plotkin’s logic for parametricity, by the construction of an LAPL-structure as defined by the authors in [7, 5]. This construction gives formal proof of solutions to a large class of recursive domain eq...

By definition, brown dwarfs never reach the main-sequence, cooling and dimming over their entire lifetime, thus making substellar models challenging to test because of the strong dependence on age. Currently, most brown dwarfs with independently determined ages are companions to nearby stars, so stellar ages are at the heart of the effort to test substellar models. However, these models are onl...

This note is based on my invited talk at the 4th Intl. Colloq. on Structural Information and Communication Complexity (SIROCCO'97). In it, I discuss a few \meta-issues" concerning theoretical research on networks, and I illustrate these issues with some recent research of mine (so that all critical remarks can be focused in my direction). My central foci are the selection of problems and models...