R. Hergt

Temperature distribution as function of time around a small spherical heat source of local magnetic hyperthermia

A spherical region containing magnetic particles embedded in extended muscle tissue is taken as model of small breast carcinomas. Using analytically derived equations the spatial temperature distribution is calculated as function of the time for exposing to an alternating magnetic field. In vitro measurements with muscle tissue yielded such an agreement with the calculations that treatment of small tumors in slightly vascularized tissues on the base of mathematical predictions seems now to be more promising than in the past.

High-pressure synthesis of MgB2 with addition of Ti

Abstract Magnesium diboride-based material high-pressure synthesized at 2 GPa and 800 °C for 1 h from Mg and B (taken in the stoichiometry ratio of MgB 2 ) with addition of 2–10 wt.% of Ti demonstrated the critical current density ( j c ) higher than 100 kA/cm 2 at 20 K up to 3 T and at 33 K in 0 T field. At 20 K the critical current density higher than 10 kA/cm 2 was observed up to 5 T field. In the magnetic fields up to 2 T high-pressure synthesized MgB 2 (with 10% of Ti) at 20 K has a critical current density comparable to that of Nb 3 Sn at 4.2 K. XRD patterns of magnesium diboride with Ti addition exhibited no evidence of unreacted titanium and only one compound with titanium was identified, namely, titanium dihydride TiH 2 (or more strictly TiH 1.924 ). The sample with the highest critical current density and the irreversibility field in the temperature range of 25–10 K contained some amount of rather homogeneously dispersed pure Mg and high amount of Mg–B inclusions.

Magnetic Nanoparticles for Biomedical Heating Applications

Summary In the past, magnetic nanoparticles have found increasing interest in different biomedical applications, e.g. the magnetic hyperthermia of tumor cells or the remote controlled drug delivery to the gut. These applications are based on a magnetically induced heating effect caused by different magnetic loss mechanisms in the nanoparticles. To advance the present state of the art of these methods, it is important to use particles with a higher specific heating power (SHP) at lower magnetic field amplitudes. To this aim, several iron oxide nanoparticle powders, consisting of particles in the diameter range from 10 nm up to 100 nm, were prepared by two different chemical methods and magnetically as well as morphologically characterized. The magnetic characterization was done by using a vibrating sample magnetometer and the calorimetrical determination of SHP. The dependence of the magnetic losses on the morphological properties was investigated. Magnetic characterization showed that several suitable iron oxide absorbers can be utilized. With decreasing particle size, hysteresis loss underestimates SHP at higher frequencies as measured calorimetrically. The effect of measurement frequency on the hysteresis losses is shown experimentally. Experimental results are discussed in the frame of known theoretical models of nanoparticle magnetism.

Precipitated iron oxide particles by cyclic growth

Summary Magnetic fluids show heating effects in ac-magnetic fields which may be useful for application in magnetic hyperthermia proposed as a tumour therapy. Enhancement of the specific loss power (SLP) of magnetic ac-losses would allow a reduction of the tissue load with magnetic material (iron oxide). The several types of loss processes depend strongly on the mean particle size [1] and the size distribution width [2]. To influence and improve the mean size as well as size distribution new approaches in preparation are promising where nucleation and growth of the particles can be influenced independently or where a further growing is possible on small given particles without further nucleation. First experiments on iron oxide powders by a cyclic method based on “conventional” precipitation from Fe-salt solution have shown the feasibility of cyclic growth in an aqueous system. An increasing mean particle size (in the range from about 10 to 30 nm) with increasing number of cycles (up to four) is confirmed by XRD. Magnetic parameters of the saturation hysteresis loop and magnetic hysteresis losses calculated from minor loops are shown. The coercivity increases with the particle size, whereas the hysteresis losses at small applied fields (11 kA/m) reveal lower values again if the particles are magnetically too hard.

Magnetic Measurements of Local Passage Velocity through the Gut

Arguments are given for the pressing need to measure the local passage velocity, especially in the small intestine. Current velocity measurement methods are reviewed and a new magnetic method is presented. First results of “in vitro” experiments yielded a spatial resolving power in the order of 1 cm in any direction and demonstrate the feasibility of automatically imaging the trace of a magnetic marker moving through the gut and to measuring its local velocity.