[en] Applications of radioactive materials to peaceful uses in Mexico, is the responsibility of the Instituto Nacional de Investigaciones de Nucleares. This paper describes how the Institute monitors one such use of radioactive tracers, namely their application to measuring fluid flow rates and residence time in industrial equipment. (author)

[en] We present a micromagnetic analysis of the field and thermally induced magnetization reversal occurring in ultra-thin films having in-plane anisotropy. We used for that purpose a Monte Carlo algorithm which allowed us to work at finite temperature and to simulate the effect on the demagnetization of the thermal fluctuations. Our results show that, for the examined system sizes, demagnetization is ruled by the ratio of the lateral dimension of the system to the magnetostatic correlation length associated with magnetization. When that ratio is small the coherent rotation mechanism is prefered by both the hysteretic and relaxational reversal. The increase of that ratio is accompanied by the occurrence of different incoherent collective reversal mechanisms (which try to minimize the magnetostatic energy). We evidence that those mechanisms can coexist in a given system due to the very similar involved energies. Finally, when the magnetization correlation length becomes small compared to the system size a nucleation-propagation mechanism rules the reversal processes

[en] By means of the hybrid FEM-BEM method formulated by Koehler and Fredkin (IEEE Trans. Magn. 28 (1992) 1239), we have simulated a transverse biased initial susceptibility (TBIS) experiment in a 3D system. We discuss the relationship between the anisotropy fields obtained from the TBIS simulations by using the Hoffmann's ripple theory and the characteristics of the microstructure of the system