hp-adaptive discontinuous Galerkin solver for elliptic equations in numerical relativity

A considerable amount of attention has been given to discontinuous Galerkin methods for hyperbolic problems in numerical relativity, showing potential advantages of the methods in dealing with hydrodynamical shocks and other discontinuities. This paper investigates discontinuous Galerkin methods for the solution of elliptic problems in numerical relativity. We present a novel hp-adaptive numerical scheme for curvilinear and non-conforming meshes. It uses a multigrid preconditioner with a Chebyshev or Schwarz smoother to create a very scalable discontinuous Galerkin code on generic domains. The code employs compactification to move the outer boundary near spatial infinity. We explore the properties of the code on some test problems, including one mimicking Neutron stars with phase transitions. We also apply it to construct initial data for two or three black holes

A 4-neutrino model with a Higgs triplet

We take as a starting point the Gelmini -- Roncadelli model enlarged by a term with explicit lepton number violation in the Higgs potential and add a neutrino singlet field coupled via a scalar doublet to the usual leptons. This scenario allows us to take into account all three present indications in favour of neutrino oscillations provided by the solar, atmospheric and LSND neutrino oscillation experiments. Furthermore, it suggests a model which reproduces naturally one of the two 4-neutrino mass spectra favoured by the data. In this model the solar neutrino problem is solved by large mixing MSW \nu_e\to\nu_\tau transitions and the atmospheric neutrino problem by transitions of \nu_\mu into a sterile neutrino.Comment: Latex, 14 pages, no figure

Stability of exact force-free electrodynamic solutions and scattering from spacetime curvature

Recently, a family of exact force-free electrodynamic (FFE) solutions was given by Brennan, Gralla and Jacobson, which generalizes earlier solutions by Michel, Menon and Dermer, and other authors. These solutions have been proposed as useful models for describing the outer magnetosphere of conducting stars. As with any exact analytical solution that aspires to describe actual physical systems, it is vitally important that the solution possess the necessary stability. In this paper, we show via fully nonlinear numerical simulations that the aforementioned FFE solutions, despite being highly special in their properties, are nonetheless stable under small perturbations. Through this study, we also introduce a three-dimensional pseudospectral relativistic FFE code that achieves exponential convergence for smooth test cases, as well as two additional well-posed FFE evolution systems in the appendix that have desirable mathematical properties. Furthermore, we provide an explicit analysis that demonstrates how propagation along degenerate principal null directions of the spacetime curvature tensor simplifies scattering, thereby providing an intuitive understanding of why these exact solutions are tractable, i.e. why they are not backscattered by spacetime curvature.Comment: 33 pages, 21 figures; V2 updated to match published versio

Black hole initial data on hyperboloidal slices

We generalize Bowen-York black hole initial data to hyperboloidal constant mean curvature slices which extend to future null infinity. We solve this initial value problem numerically for several cases, including unequal mass binary black holes with spins and boosts. The singularity at null infinity in the Hamiltonian constraint associated with a constant mean curvature hypersurface does not pose any particular difficulties. The inner boundaries of our slices are minimal surfaces. Trumpet configurations are explored both analytically and numerically.Comment: version for publication in Phys. Rev.

A Critical Consideration of the Introduction of Community-Service Learning Projects to Courses in the Sociology of Social Problems

This paper examines the introduction of community service learning activities in lower division (200 level) undergraduate Sociology of Social Problems courses. Data from student evaluations and grades are presented for five semesters of this class between 1994-1996 (n=98), prior to the introduction of a community service learning option. This data is contrasted with five semesters of the class between 1996-1998 (n=141), following the introduction of service learning activities. Despite generally positive feedback from students and increased enrollments, results suggest that student performance as measured by grades has not significantly changed with the introduction of community service activities. Also student evaluations of the class are somewhat lower. The community service learning option itself is discussed, and examples and descriptions of community service sites are presented. A discussion of implications for future research on community service learning outcomes concludes the paper

Assessing composition gradients in multifilamentary superconductors by means of magnetometry methods

We present two magnetometry-based methods suitable for assessing gradients in the critical temperature and hence the composition of multifilamentary superconductors: AC magnetometry and Scanning Hall Probe Microscopy. The novelty of the former technique lies in the iterative evaluation procedure we developed, whereas the strength of the latter is the direct visualization of the temperature dependent penetration of a magnetic field into the superconductor. Using the example of a PIT Nb3Sn wire, we demonstrate the application of these techniques, and compare the respective results to each other and to EDX measurements of the Sn distribution within the sub-elements of the wire.Comment: 7 pages, 8 figures; broken hyperlinks are due to a problem with arXi