Iterative solution of field problems with a varying physical parameter

In this paper, linear field problems with a varying physical parameter are solved with the conjugate gradient method and a dedicated extrapolation procedure for generating the initial estimate. The scheme is formulated in detail, and its application to three-dimensional scattering problems for a rectangular conducting plate and an inhomogeneous, dispersive dielectric body are discussed

A head and neck hyperthermia applicator: Theoretical antenna array design

Purpose: Investigation into the feasibility of a circular array of dipole antennas to deposit RF-energy centrally in the neck as a function of: (1) patient positioning, (2) antenna ring radius, (3) number of antenna rings, (4) number of antennas per ring and (5) distance between antenna rings. Materials and Methods: Power absorption (PA) distributions in realistic, head and neck, anatomy models are calculated at 433 MHz. Relative PA distributions corresponding to different set-ups were analysed using the ratio of the average PA (aPA) in the target and neck region. Results: Enlarging the antenna ring radius from 12.5cm to 25 cm resulted in a ~21% decrease in aPA. By changing the orientation of the patients with respect to the array an increase by ~11% was obtained. Increase of the amount of antenna rings led to a better focussing of the power (1 - 2 / 3: ~17%). Increase of the distance between the antenna rings resulted in a smaller (more target region conformal) focus but also a decreased power penetration. Conclusions: A single optimum array setup suitable for all patients is difficult to define. Based on the results and practical limitations a setup consisting of two rings of six antennas with a radius of 20 cm and 6 cm array spacing is considered a good choice providing the ability to heat the majority of patients

Semi-quantitative proteomics of mammalian cells upon short-term exposure to nonionizing electromagnetic fields

The potential effects of non-ionizing electromagnetic fields (EMFs), such as those emitted by power-lines (in extremely low frequency range), mobile cellular systems and wireless networking devices (in radio frequency range) on human health have been intensively researched and debated. However, how exposure to these EMFs may lead to biological changes underlying possible health effects is still unclear. To reveal EMF-induced molecular changes, unbiased experiments (without a priori focusing on specific biological processes) with sensitive readouts are required. We present the first proteome-wide semi-quantitative mass spectrometry analysis of human fibroblasts, osteosarcomas and mouse embryonic stem cells exposed to three types of non-ionizing EMFs (ELF 50 Hz, UMTS 2.1 GHz and WiFi 5.8 GHz). We performed controlled in vitro EMF exposures of metabolically labeled mammalian cells followed by reliable statistical analyses of differential protein-and pathway-level regulations using an array of established bioinformatics methods. Our results indicate that less than 1% of the quantitated human or mouse proteome responds to the EMFs by small changes in protein abundance. Further network-based analysis of the differentially regulated proteins did not detect significantly perturbed cellular processes or pathways in human and mouse cells in response to ELF, UMTS or WiFi exposure. In conclusion, our extensive bioinformatics analyses of semi-quantitative mass spectrometry data do not support the notion that the short-time exposures to non-ionizing EMFs have a consistent biologically significant bearing on mammalian cells in culture

Marching on in anything: solving electromagnetic field equations with a varying physical parameter

In this paper, we consider the determination of electromagnetic fields for a (large) number of values of a physical parameter. We restrict ourselves to the case where the linear system originates from one or more integral equations. We apply an iterative procedure based on the minimization of an integrated squared error, and start this procedure from an initial estimate that is a linear combination of the last few "final" results. When the coefficients in this extrapolation are determined by minimizing the integrated squared error for the actual value of the parameter, the built-in orthogonality in this type of scheme ensures that only a few iteration steps are required to obtain the solution. The paper is organized as follows. We first describe the general approach. Second, we give an overview of various practical applications. Third, the iterative procedure is illustrated for scattering by a two-dimensional dielectric cylinder in free space. For that example, finally, we outline the use of the algorithm in transient scattering, in linearized and nonlinear inverse-scattering algorithms, and in scattering by an object in a more general environment. Results for all four applications are available, but cannot be included because of space limitations

Scattering by objects with electric contrast

Electrical Engineering, Mathematics and Computer Scienc

Marching on in anything : Solving electromagnetic field equations with a varying physical parameter

In this paper, we consider the determination of electromagnetic flelds for a (large) number of values of a physical parameter. We restrict ourselves to the case where the linear system originates from one or more integral equations. we apply an iterative procedure based on the minimization of an integrated squared error, and start this procedure from an initial estimate that is a linear combination of the last few "final" ræults. When the coefficients in this extrapolation is determined by minimizing the integrated squared error for the actual value of the parameter, the built-in orthogonality in this type of scheme ensures that only a few iteration steps are required to obtain the solution