Effects Of Low-frequency Fields Research Articles

Study on the magnetic field influence around of the overhead power lines regarding the general public exposure level

This paper analyzes the distribution of the dimensions of the magnetic field in the vicinity of the high voltage overhead power lines (400 kV), in the context in which the effects of the electromagnetic field on living organisms and especially on humans are currently being analyzed. Electromagnetic fields of different frequencies interact with the human body in different ways, just as the effects of low frequency fields are not the same as those of the high frequency fields. Analysis of the electromagnetic field values near a high voltage overhead power line is very important for determining the degree of exposure to the electromagnetic field. The measurements are performed with the magnetic field tester, Hioki FT 3470-50 and the values obtained are compared with those indicated by current standards.

Quantum path controlling in the presence of a low frequency field to generate isolated attosecond pulse

In this article, an efficient method is presented to generate an isolated attosecond pulse based on synthesized laser field. The 1D time-dependent Schrödinger equation is numerically solved for a helium atom exposed in a strong laser field. Two color fields containing a chirped laser pulse and its half harmonic as control pulse are modulated by a low frequency field to construct the configuration of strong laser field. The effect of low frequency field dominates the effect of the chirp parameter and extremely affects the acceleration step of high-order harmonic generation process. The low frequency field, in the optimized conditions, eliminates the long quantum path completely and only the short quantum path contributes in the higher harmonics emission mechanism. With such scheme, an extra supercontinuum with 700eV bandwidth can be generated which supports the creation of a 64 attosecond isolated pulse. Moreover, the classical electron dynamics and the time–frequency analysis for explaining the underlying physics of atom–pulse interaction are also presented.

Periodic forcing of intracellular calcium oscillators Theoretical studies of the effects of low frequency fields on the magnitude of oscillations

In many types of cell the signal transduction from plasmalemma to intracellular targets is linked to the oscillatory behaviour of intracellular Ca 2+. Experimental investigations of the effects of low frequency electromagnetic fields on living systems seem to indicate that calcium signalling pathways, and a cytosolic calcium oscillator in particular, may be the processes which are affected by external fields. In accordance with these findings the external forcing of a cytosolic calcium oscillator was studied numerically on two models of intracellular Ca 2+ oscillations: the `minimal' model suggested by Goldbeter et al. [A. Goldbeter, G. Dupont, M.J. Berridge, Minimal model for signal-induced Ca 2+ oscillations and for their frequency encoding through protein phosphorylation, Proc. Natl. Acad. Sci. USA 87 (1990) 1461–1465.], and a three-dimensional model with chaos [P. Shen, R. Larter, Chaos in intracellular Ca 2+ oscillations in a new model for non-excitable cells, Cell Calcium 17 (1995) 225–232.]. The results obtained previously [J. Galvanovskis, J. Sandblom, B. Bergqvist, S. Galt, Y. Hamnerius, Cytoplasmic Ca 2+ oscillations in human leukemia T-cells are reduced by 50 Hz magnetic fields, Bioelectromagnetics, in press.] in experiments on periodic forcing by 50 Hz magnetic fields of Ca 2+ oscillations in Jurkat cells were qualitatively reproduced with simulations on the `minimal' model. Simulations revealed that the most sensitive part in the chain of reactions involved in Ca 2+ oscillations was the Ca 2+ release from internal stores by calcium induced calcium release. The analysis further showed that the effect of forcing depends on the level of cell stimulation by the external application of agonist depending on the strength of this stimulus opposite field effects could be achieved. A multitude of frequency and amplitude `windows' was also demonstrated in the response of a cytosolic oscillator quantified by the use of the total spectral power of Ca 2+ oscillations. The occurrence of maxima in the forcing effect at the basic Ca 2+ oscillator frequency and its higher harmonics shows that it may be possible to explain the experimentally observed resonance effects on a basis of non-linear dynamics. Simulations on the three-dimensional model revealed the extreme sensitivity of a chaotic state to periodic forcing, suggesting a possible role of chaotic processes in detection of weak signals within cells.

A theoretical approach to the question of biological effects of low frequency fields

A human body in the vicinity of an overhead cable is subject to two kinds of electrical effects, inductive and capacitive, which together are responsible for tiny currents. Recent concerns about possible biological effects of such currents have made their accurate computation necessary. The author address the mathematical modeling that has to precede such computations. By an asymptotic analysis of the full set of Maxwell's equations (displacement currents not neglected), which takes into account the smallness of the electrical permittivity and the large penetration depth, the author arrives at a standard conduction problem, to which both kinds of effect contribute source terms: inductive effects give a right-hand side, and capacitive effects give a nonhomogeneous boundary condition. Numerical results are displayed. >