Rudolf Röckelein

A High Field Gradient Magnet for Magnetic Drug Targeting

A magnet for Magnetic Drug Targeting was designed, built and tested. The magnet applies a magnetic force on ferrofluids coupled with therapeutic agents for medical and biological applications, e.g. for regional treatment of cancer. The application for cancer treatment requires a high magnetic field gradient in the application volume around and inside the tumor. Furthermore the magnet should have low mass and size combined with an appropriate geometry for easy handling and positioning near the patient, as well as a surface temperature below 40 degC. The gradient of the magnetic field, which determines the magnetic force for small single-domain ferromagnetic particles, ranges from 100 T/m at the pole tip to a minimum of 10 T/m in an application volume of (20 mm)3 and points inwardly to the center of the pole tip

On the finite element simulation of fluid motion with high Reynolds or Grashof number

Abstract Numerical Simulation of free convection problems with usual Finite Element (FE) formulations run into stability problems for large Grashof numbers. This is true even for simple models. In regions where the stream velocity or the temperature field is constant along the stream lines, the stiffness matrix may become ill-conditioned for large stream velocities although its physical contribution vanishes. Besides a costly increase in the number of elements and corresponding decrease of the length unit, a change in the unit system can not improve the matrix condition. The ill-conditioning arises from the usual decomposition of the nonlinear convective terms into a velocity-dependent stiffness matrix which represents a differential operator and a solution vector on which the stiffness matrix operates. The problem should be solved by an adapted choice of the matrix representation of the nonlinear convective terms. Alternatively - and necessarily for Newton-Raphson iteration of the nonlinear equations - the ill-conditioning terms may be neglected within those elements, where their physical contribution is negligible.