11,212 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
Recommended from our members
An evaluation framework for stereo-based driver assistance
This is the post-print version of the Article - Copyright @ 2012 Springer VerlagThe accuracy of stereo algorithms or optical flow methods is commonly assessed by comparing the results against the Middlebury
database. However, equivalent data for automotive or robotics applications
rarely exist as they are difficult to obtain. As our main contribution, we introduce an evaluation framework tailored for stereo-based driver assistance able to deliver excellent performance measures while
circumventing manual label effort. Within this framework one can combine several ways of ground-truthing, different comparison metrics, and use large image databases.
Using our framework we show examples on several types of ground truthing techniques: implicit ground truthing (e.g. sequence recorded without a crash occurred), robotic vehicles with high precision sensors, and to a small extent, manual labeling. To show the effectiveness of our evaluation framework we compare three different stereo algorithms on
pixel and object level. In more detail we evaluate an intermediate representation
called the Stixel World. Besides evaluating the accuracy of the Stixels, we investigate the completeness (equivalent to the detection rate) of the StixelWorld vs. the number of phantom Stixels. Among many findings, using this framework enables us to reduce the number of phantom Stixels by a factor of three compared to the base parametrization. This base parametrization has already been optimized by test driving vehicles for distances exceeding 10000 km
Evidence for A Two-dimensional Quantum Wigner Solid in Zero Magnetic Field
We report the first experimental observation of a characteristic nonlinear
threshold behavior from dc dynamical response as an evidence for a Wigner
crystallization in high-purity GaAs 2D hole systems in zero magnetic field. The
system under increasing current drive exhibits voltage oscillations with
negative differential resistance. They confirm the coexistence of a moving
crystal along with striped edge states as observed for electrons on helium
surfaces. However, the threshold is well below the typical classical levels due
to a different pinning and depinning mechanism that is possibly related to a
quantum process
Optimizing crop loading of apples and pears - results 2004-2006 (foliar fertilizers, thinning)
Main topics of the research-project FuE 03OE088 of āBundesprogramm Ćkologischer
Landbauā (30.04.2004-31.12.2006) were the testing of foliar fertilizers in organic apples
and pears, optimizing lime sulphur for blossom thinning, looking for alternatives to lime
sulphur for blossom thinning and looking at different combinations of thinning measures.
Only the results of testing foliar fertilizers (carried out by KoGa Ahrweiler and OVB/ĆON
Jork) and combinations of thinning measures (carried out by LVWO Weinsberg) are
described in this article. Over three years only a small increase in yield was evaluated for
the fertilizers Aminosol PS and Wuxal Ascofol (site Ahrweiler, apple variety āElstarā). In
Jork (apple variety āHolsteiner Coxā) yield could only be judged in 2005 and 2006. Wuxal
Ascofol showed some advantage in comparison to the control. At pear variety āConferenceā
no clear tendencies could be seen, the control had the highest yield. In 2005 the fruitsetting
of āConferenceā was very low because of bad conditions during blossom
Field-induced resonant tunneling between parallel two-dimensional electron systems
Resonant tunneling between two high-mobility two-dimensional (2D) electron systems in a double quantum well structure has been induced by the action of an external Schottky gate field. Using one 2D electron gas as source and the other as drain, the tunnel conductance between them shows a strong resonance when the gate field aligns the ground subband edges of the two quantum wells
- ā¦