Sökresultat

We present a-posteriori analysis of higher order finite element approximations (hp-FEM) for quadratic Fredholm-valued operator functions. Residual estimates for approximations of the algebraic eigenspaces are derived and we reduce the analysis of the estimator to the analysis of an associated boundary value problem. For the reasons of robustness we also consider approximations of the associated in

We present an algorithm for approximating an eigensubspace of a spectral component of an analytic Fredholm valued function. Our approach is based on numerical contour integration and the analytic Fredholm theorem. The presented method can be seen as a variant of the FEAST algorithm for infinite dimensional nonlinear eigenvalue problems. Numerical experiments illustrate the performance of the algor

Metallic nano-antennas are devices used to concentrate the energy in light into regions that are much smaller than the wavelength. These structures are currently used to develop new measurement and printing techniques, such as optical microscopy with sub-wavelength resolution, and high-resolution lithography. Here, we analyze and design a nano-antenna in a two-dimensional setting with the source b

Galerkin spectral approximation theory for non-self-adjoint quadratic operator polynomials with periodic coefficients is considered. The main applications are complex band structure calculations in metallic photonic crystals, periodic waveguides, and metamaterials. We show that the spectrum of the considered operator polynomials consists of isolated eigenvalues of finite multiplicity with a nonzer

The meshless radial point interpolation method (RPIM) in frequency domain for electromagnetic scattering problems is presented. This method promises high accuracy in a simple collocation approach using radial basis functions. The treatment of high-order non-reflecting boundary conditions for open waveguides is discussed and implemented up to fourth-order. RPIM allows the direct calculation of high

Meshless methods are a promising new field in computational electromagnetics. Instead of relying on an explicit mesh topology, a numerical solution is computed on an unstructured set of collocation nodes. This allows to model fine geometrical details with high accuracy and facilitates the adaptation of node distributions for optimization or refinement purposes. The radial point interpolation metho

Band structure calculations for photonic crystals require the numerical solution of eigenvalue problems. In this paper, we consider crystals composed of lossy materials with frequency-dependent permittivities. Often, these frequency dependencies are modeled by rational functions, such as the Lorentz model, in which case the eigenvalue problems are rational in the eigenvalue parameter. After spatia

In this paper a high-order finite element method with curvilinear elements is proposed for the simulation of plasmonic structures. Most finite element packages use low order basis functions and non-curved elements, which is very costly for demanding problems such as the simulation of nanoantennas. To enhance the performance of finite elements, we use curvilinear quadrilateral elements to calculate

Meshless methods are numerical methods that have the advantage of high accuracy without the need of an explicitly described mesh topology. In this class of methods, the Radial Point Interpolation Method (RPIM) is a promising collocation method where the application of radial basis functions yields high interpolation accuracy for even strongly unstructured node distributions. For electromagnetic si

Three different meshless methods based on radial basis functions are investigated for the numerical solution of electromagnetic eigenvalue problems. The three algorithms, the non-symmetric Kansa approach, the symmetric Kansa method and the radial point interpolation method, are first described putting emphasis on the influence of their formalism on practical implementation. The convergence rate of

A meshless method based on a radial basis collocation approach is presented to calculate eigenvalues for the second-order wave equation. Instead of an explicit mesh topology only a node distribution is required to calculate electric fields, thus facilitating dynamic alteration of the discretization of an electromagnetic problem. An algorithm is presented that automatically adapts an initially very

The concept of an adaptive meshless eigenvalue solver is presented and implemented for two-dimensional structures. Based on radial basis functions, eigenmodes are calculated in a collocation approach for the second-order wave equation. This type of meshless method promises highly accurate results with the simplicity of a node-based collocation approach. Thus, when changing the discrete representat

The rescue operations’ environment can impair firefighters’ performance and increase the risk of injuries, e.g., burns and hyperthermia. The bulk and carried weight of heavy protection contributes to lower physical performance, higher metabolic load and internal body heat production. For recommending optimal protection for the tasks and incident scenarios, knowledge of clothing thermal properties

This study utilizes ethnographic methods to inquire how ideas of masculinities are perceived by English-language media professionals and media audiences in Egypt. Using semi-structured interviews and a survey, the aim is to find common narratives on how masculinity is perceived on personal levels and what terms are used to describe men and masculinities, which in turn can be used as the basis for

Cement augmentation of pedicle screws is one of the most promising approaches to enhance the anchoring of screws in the osteoporotic spine. To date, there is no ideal cement for pedicle screw augmentation. The purpose of this study was to investigate whether an injectable, bioactive, and degradable calcium sulfate/hydroxyapatite (CaS/HA) cement could increase the maximum pull-out force of pedicle

Large Eddy Simulation (LES) has rapidly developed into a powerful computational methodology for fluid dynamic studies, between Reynolds-Averaged Navier–Stokes (RANS) and Direct Numerical Simulation (DNS) in both accuracy and cost. High-speed combustion applications, such as ramjets, scramjets, dual-mode ramjets, and rotating detonation engines, are promising propulsion systems, but also challengin

The discovery of the Higgs boson by the ATLAS and CMS collaborations in 2012 concluded the longest search for a particle in the history of particle physics and was based on the largest and most complex physics experiments ever conducted, involving thousands of scientists and engineers from around the world. It provided crucial evidence for a theory developed in the 1960s that describes the existen

The aviation sector is facing a massive change in terms of replacing the currently used fossil jet fuels (Jet A, JP5, etc.) with non-fossil jet fuels from sustainable feedstocks. This involves several challenges and, among them, we have the fundamental issue of current jet engines being developed for the existing fossil jet fuels. To facilitate such a transformation, we need to investigate the sen

Several alkaline earth or rare earth binary monosilicides and -germanides possess complex bonding properties, such as polycation formation exceeding the scope of classical electron counting rules. In this study, we present characterization by powder and single-crystal diffraction and thermal analysis of CeGe, one of the few monogermanides crystallizing in the FeB-type structure. Comparative comput