Methods of predicting temperature profiles during local hyperthermia treatment are very important to avoid damage to healthy tissue. With this aim, fundamental solutions of Pennes' bioheat equation are derived in rectangular, cylindrical, and spherical coordinates. The medium is idealised as isotropic with effective thermal properties. Temperature distributions due to space- and time-dependent heat sources are obtained by the solution method presented. Applications of the fundamental solutions are addressed with emphasis on a particular problem of Magnetic Fluid Hyperthermia (MFH) consisting of a thin shell of magnetic nanoparticles in the outer surface of a spherical solid tumour. It is observed from the solution of this particular problem that the temperature profiles are strongly dependent on the distribution of the magnetic nanoparticles within the tissue. An almost uniform temperature profile is obtained inside the tumour with little penetration of therapeutic temperatures to the outer region of healthy tissue. The fundamental solutions obtained can be used to develop boundary element methods to predict temperature profiles with more complicated geometries.

No abstract

Magnetic nanoparticles for magnetocaloric applications should combine small coercivity, low demagnetization temperature, and high pyromagnetic coefficients while keeping the magnetization as high as possible. The strong dependence of the magnetic properties of cobalt-zinc mixed ferrite with specific dopant species enables this material to be considered a promising candidate for magnetocaloric applications. On this basis, pure and Dy-doped Co0.7Zn0.3Fe2O4 cobalt-zinc ferrite nanocrystals have been synthesized by conventional and modified (i.e., flow rate controlled addition of reactants) coprecipitation routes. The modified approach allows the control of ferrite crystal growth at the nanoscale and hence tuning of the corresponding magnetic properties. The magnetic properties of the produced nanocrystals were determined as a function of their structure, nominal dopant concentration, and crystal size. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy analyses suggested both the actual incorporation of the dopants into the host ferrite lattice and the promoting effect on crystal size of the flow rate at which the reactants are contacted. The average crystallite size varied from 13 nm (no control of flow rate) to 28 nm when the ferrite was synthesized at 1 ml/min. Doping caused the maximum magnetization of the ferrite to decrease; this parameter dropped from 60 emu/g (nondoped ferrite) to 55 emu/g when the ferrite was doped with 0.01 at. % of Dy. The maximum magnetization of the Dy (y=0.01) Co–Zn ferrite went up to 62 emu/g when the synthesis was carried out under flow-controlled conditions. The presence of 0.01 at. % Dy in the ferrite caused the demagnetization temperature to decrease from 350 °C (nondoped ferrite) to 320 °C. The demagnetization temperature was further decreased down to 308 °C when the ferrite powders were synthesized under flow rate controlled conditions.

In any cutting processes, the temperature distribution in the cutting tool is intrinsically three-dimensional and very steep temperature gradient can be generated in the vicinity of the tool-chip interface. In this region, where the maximum temperature occurs, the effect of temperature dependent thermal properties may become important. The full three-dimensional nonlinear transient heat conduction equation is solved numerically using a control volume approach to study these nonlinear effects on cutting tool temperatures. The extremely small size of the heat input zone (tool-chip interface), relative to the tool insert rake surface area, requires the mesh to be dense enough in order to obtain accurate solutions. This usually requires very intensive computational efforts. Due to the size of the discretized domain, an optimized algorithm is used in the solution of the problem to significantly reduce the required computing time. This numerical model can be used for process development in an industrial setting. The effect of two different heat flux input profiles, a spatially uniform plane heat flux and a spatially nonuniform parabolic heat flux at the tool-chip interface, on the tool temperatures are also investigated in the present study. Some recommendations are given regarding the condition when these nonlinear effects cannot be ignored.

No abstract