[en] In nuclear power plants, ungrounded low-voltage networks are frequently used. In this type of network it is also usual to have relays for insulation monitoring. These relays employ a saturable inductance of a high value in line with their measuring circuit, which could give rise to a ferro resonance phenomenon with the system capacitances. Ferro resonance could produce temporary overvoltage between each phase and earth which damages the insulation of the equipment connected to this network. This paper presents the theoretical bases of this phenomenon, the electrical resolution of the circuit and the actions which could be undertaken to eliminate or mitigate overvoltage. (Author)

No abstract available

[en] Mechanical alloying technique is used for the decrystallization of Fe_100-xB_x samples with soft magnetic character. Wide angle X-ray scattering (WAXS) and differential scanning calorimetry have been used to monitor the decrystallization kinetics, whose time dependence can be fitted by a stretched exponential function. In all the samples, milling times of around 500 h lead to very low crystallinity percentages (around 5%). This residual crystalline phase corresponds to a mixture of FeB and Fe₂B phases, and the α-Fe phase almost disappeared at the same time. During the decrystallization, the grain size of the α-Fe phase changes appreciably from 40 down to 15 nm. Magnetic properties of the samples in their final lowest crystalline state showed different behaviours for the samples rich in boron or in iron

[en] Tailoring of soft and hard magnetic materials can be performed by nanocrystallisation. Random anisotropy and intergranular exchange govern the macroscopic properties of nanocrystalline ferromagnets. The nature and topology of the intergranular region, matrix or grain boundaries, determine the degree of intergranular coupling. Important information about magnetic and topological properties of grain boundaries can be inferred from Moessbauer spectroscopy. The state of the art of those tailored materials is reviewed paying special attention to the correlation between nanostructure and macroscopic properties

[en] Experimental measurements and micromagnetic simulations of the hysteresis loops of arrays of cobalt nanowires are compared here. Arrays of cobalt nanowires (200 nm in diameter) were electrodeposited into the pores of alumina membranes (thickness 60 μm). Their hysteresis loops along the axial direction of nanowires were measured using vibrating sample magnetometry. Micromagnetic simulations were performed considering dipolar interaction between nanowires leading to similar hysteresis loops as those obtained experimentally

[en] We report on the morphologic and relaxation properties of Co/Ni multilayers having different Ni-layer thickness. These samples evolve with time through a series of intervals during which the system does not change (waiting time) and large moment variations (jumps). The size of the jumps depends on the morphology of the samples

[en] We report on the hysteretic and relaxational behavior of Fe-Ba hexaferrite nanocomposite samples prepared by ball milling. This includes data on the temperature dependence of the coercive force, on the relationship between the field evolution of the isothermal and the demagnetization remanences and on the time evolution of the magnetization at those remanences. Our most remarkable result corresponds to the observation, at room temperature and without field cooling the samples, of a displacement (in the sense of the negative fields) of the hysteresis loops measured under a maximum applied field of 0.8 T. The magnitude of that shift oscillates when the Fe content changes. Our results are analyzed in terms of the occurrence of interphase dipolar interactions

[en] The ''Instituto de Asuntos Nucleares'' of Colombia is responsible for IAN-R1 reactor operation, a 20 Kw. nuclear power machine, which became critical the first time on January 20th, 1965. The introduction of nuclear energy in Colombia has allowed to carry out many peaceful applications, where the reactor has played a significant role in support of these programmes. At this time, the main activities are: Educational and training activities; nuclear research; neutron activation analysis; delayed neutron analysis and radioisotopes production for using in agriculture, industry, hydrology and engineering. A description is made of the reactor aspects that have contributed to scientific and technological improvements

[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] Some effects of visible light on the survival of Escherichia coli in waters of the Butron river were studied by comparing illuminated and nonilluminated systems. The following count methods were used: CFU on a selective medium (eosin-methylene blue agar), CFU on a medium of recuperation (Trypticase soy agar with yeast extract and glucose), number of metabolically active cells by reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT) to INT-formazan, and total number of E. coli cells as determined by the acridine orange direct-count method. In the illuminated systems, decreases in CFU of E. coli and in the number of metabolically active cells were observed. However, no decline of the total number of E. coli cells was observed. By count methods, different stages of progressive dormancy of E. coli cells were determined to exist in illuminated systems. Culturable and recoverable cells were defined as viable cells, and metabolically active cells and morphologically intact cells were defined as somnicells. Indirect activity measurements were also done by using [14C]glucose. In illuminated systems, a decrease of glucose uptake by E. coli cells was observed throughout the experiments. The assimilated fraction of [14C]glucose decreased faster than the respired fraction in illuminated systems. The percentage of respired [14C]glucose (14CO2 production) with respect to the total glucose uptake increased throughout the experiments, and the percentage of assimilated glucose decreased. Therefore, the visible light was also responsible for an additional inhibition of biosynthetic processes