2,367 research outputs found
Extension of the Finite Integration Technique including dynamic mesh refinement and its application to self-consistent beam dynamics simulations
An extension of the framework of the Finite Integration Technique (FIT)
including dynamic and adaptive mesh refinement is presented. After recalling
the standard formulation of the FIT, the proposed mesh adaptation procedure is
described. Besides the linear interpolation approach, a novel interpolation
technique based on specialized spline functions for approximating the discrete
electromagnetic field solution during mesh adaptation is introduced. The
standard FIT on a fixed mesh and the new adaptive approach are applied to a
simulation test case with known analytical solution. The numerical accuracy of
the two methods are shown to be comparable. The dynamic mesh approach is,
however, much more efficient. This is also demonstrated for the full scale
modeling of the complete RF gun at the Photo Injector Test Facility DESY
Zeuthen (PITZ) on a single computer. Results of a detailed design study
addressing the effects of individual components of the gun onto the beam
emittance using a fully self-consistent approach are presented.Comment: 33 pages, 14 figures, 4 table
Contemporary Group Piano Instruction Seminar
News release announces that a Contemporary Group Piano Instruction seminar will be held at the University of Dayton
Discontinuous Galerkin Methods with Trefftz Approximation
We present a novel Discontinuous Galerkin Finite Element Method for wave
propagation problems. The method employs space-time Trefftz-type basis
functions that satisfy the underlying partial differential equations and the
respective interface boundary conditions exactly in an element-wise fashion.
The basis functions can be of arbitrary high order, and we demonstrate spectral
convergence in the \Lebesgue_2-norm. In this context, spectral convergence is
obtained with respect to the approximation error in the entire space-time
domain of interest, i.e. in space and time simultaneously. Formulating the
approximation in terms of a space-time Trefftz basis makes high order time
integration an inherent property of the method and clearly sets it apart from
methods, that employ a high order approximation in space only.Comment: 14 pages, 12 figures, preprint submitted at J Comput Phy
A Space-Time Discontinuous Galerkin Trefftz Method for time dependent Maxwell's equations
We consider the discretization of electromagnetic wave propagation problems
by a discontinuous Galerkin Method based on Trefftz polynomials. This method
fits into an abstract framework for space-time discontinuous Galerkin methods
for which we can prove consistency, stability, and energy dissipation without
the need to completely specify the approximation spaces in detail. Any method
of such a general form results in an implicit time-stepping scheme with some
basic stability properties. For the local approximation on each space-time
element, we then consider Trefftz polynomials, i.e., the subspace of
polynomials that satisfy Maxwell's equations exactly on the respective element.
We present an explicit construction of a basis for the local Trefftz spaces in
two and three dimensions and summarize some of their basic properties. Using
local properties of the Trefftz polynomials, we can establish the
well-posedness of the resulting discontinuous Galerkin Trefftz method.
Consistency, stability, and energy dissipation then follow immediately from the
results about the abstract framework. The method proposed in this paper
therefore shares many of the advantages of more standard discontinuous Galerkin
methods, while at the same time, it yields a substantial reduction in the
number of degrees of freedom and the cost for assembling. These benefits and
the spectral convergence of the scheme are demonstrated in numerical tests
Large, Single Institution Review of Prognostic Factors in Oligodendroglioma
Studies have demonstrated an association between loss of heterozygosity on chromosome 1p and chromosome 19q in oligodendrogliomas with both chemosensitivity and prolonged survival. This represents the first time genetic mutations have been utilized to guide clinical decision making. Studies have also found these genetic mutations to be associated with magnetic resonance imaging (MRI) features including indistinct tumor borders on T1-weighted imaging, susceptibility effect, and mixed signal intensity. However, no study has yet demonstrated an association between imaging features and survival. We seek to confirm the clinical utility of known prognostic factors such as age and tumor grade while investigating the potential importance of imaging characteristics in predicting survival. We conducted a large, single-institution retrospective chart review of patients with tissue diagnoses of oligodendroglioma. Pathology reports, allelic status studies, MR imaging, and survival information were reviewed. Survival curves, Two-sided chi-square tests, and generalized linear models failed to reveal an association between survival and gender, age, tumor grade, allelic status, or imaging characteristics. We found no association between imaging characteristics and allelic status. The failure to confirm even well-accepted prognostic factors suggests limitations in the study largely attributable to small sample size. This limitation was due to availability of necessary information, rarity of the tumor, and only recent availability of genetic testing. Further studies with larger populations need to be conducted to fully determine the prognostic utility of MRI features
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A highly scalable Met Office NERC Cloud model
Large Eddy Simulation is a critical modelling tool for scien- tists investigating atmospheric flows, turbulence and cloud microphysics. Within the UK, the principal LES model used by the atmospheric research community is the Met Office Large Eddy Model (LEM). The LEM was originally devel- oped in the late 1980s using computational techniques and assumptions of the time, which means that the it does not scale beyond 512 cores. In this paper we present the Met Office NERC Cloud model, MONC, which is a re-write of the existing LEM. We discuss the software engineering and architectural decisions made in order to develop a flexible, extensible model which the community can easily customise for their own needs. The scalability of MONC is evaluated, along with numerous additional customisations made to fur- ther improve performance at large core counts. The result of this work is a model which delivers to the community signifi- cant new scientific modelling capability that takes advantage of the current and future generation HPC machine
Senior Citizen Day Celebration to be Held at University of Dayton
News release announces that Senior Citizens Day will be held at the University of Dayton
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