14,922 research outputs found
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
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