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At least 1,459 records · Page 81Linked to original sources
PubMed1980

A thermal model of the human body exposed to an electromagnetic field.

The human body was modeled by numerical procedures to determine the thermal response under varied electromagnetic (EM) exposures. The basic approach taken was to modify the heat transfer equations for man in air to account for thermal loading due to the energy absorbed from the EM field. The human body was represented in an EM model by a large number of small cubical cells of tissue, and the energy density was determined for each cell. This information was then analyzed by a thermal response model consisting of a series of two-dimensional transient conduction equations with internal heat generation due to metabolism, internal convective heat transfer due to blood flow, external interaction by convection and radiation, and cooling of the skin by sweating and evaporation. This model simulated the human body by a series of cylindrical segments. The local temperature of 61 discrete locations as well as the thermoregulatory responses of vasodilatation and sweating were computed for a number of EM field intensities and two frequencies, one near whole-body resonance.

Absorption↗
PubMed2005

Modeling electromagnetic fields detectability in a HH-like neuronal system: stochastic resonance and window behavior.

Noise has already been shown to play a constructive role in neuronal processing and reliability, according to stochastic resonance (SR). Here another issue is addressed, concerning noise role in the detectability of an exogenous signal, here representing an electromagnetic (EM) field. A Hodgkin-Huxley like neuronal model describing a myelinated nerve fiber is proposed and validated, excited with a suprathreshold stimulation. EM field is introduced as an additive voltage input and its detectability in neuronal response is evaluated in terms of the output signal-to-noise ratio. Noise intensities maximizing spiking activity coherence with the exogenous EM signal are clearly shown, indicating a stochastic resonant behavior, strictly connected to the model frequency sensitivity. In this study SR exhibits a window of occurrence in the values of field frequency and intensity, which is a kind of effect long reported in bioelectromagnetic experimental studies. The spatial distribution of the modeled structure also allows to investigate possible effects on action potentials saltatory propagation, which results to be reliable and robust over the presence of an exogenous EM field and biological noise. The proposed approach can be seen as assessing biophysical bases of medical applications funded on electric and magnetic stimulation where the role of noise as a cooperative factor has recently gained growing attention.

Action Potentials↗
PubMed1999

Penetration of electromagnetic fields of an open-ended coaxial probe between 1 MHz and 1 GHz in dielectric skin measurements.

An open-ended coaxial probe is often used for investigating the dielectric properties of biological tissues. The present study indicates that in addition to the probe size, the penetration of the electromagnetic (EM) fields of an open-ended coaxial probe in contact with the skin is dependent on the applied frequency between 1 MHz and 1 GHz. At high frequencies, above 100 MHz, the measured dielectric parameters are functions of the dielectric properties of different cutaneous layers and subcutaneous fat. At lower frequencies, less than 10 MHz, the measurement is mainly dependent on the dielectric properties of superficial structures of the skin. The reason for this is that the probe, the surface of the skin, mainly stratum corneum, and underlying skin form a capacitance where the stratum corneum with low water content lies between the well-conducting dermis and the probe. The situation is equivalent to the frequency-dependent Maxwell-Wagner interfacial polarization. This result is verified by experimental dielectric measurements and with human skin in vivo.

Electromagnetic Fields↗
PubMedDate not supplied

[Influence of electromagnetic fields on the emotional behaviour of rats].

The effects of ultra low power pulse-width + modulation electromagnetic radiation (EMR, power density 10 mc/Wt/cm2, carrying frequency 915 MHz, modulating pulses with frequency 4, 6, 16 and 20 Hz, duration 10 min) on the rat emotional behavior and motor activity in the elevated plus-maze were studied. It was established that EMR (frequency of modulation 4 and 6 Hz) significantly decreased the emotionally negative reactions of anxiety and fear by a factor of 3.7 (p < 0.01) and 4.5 (p < 0.01) correspondingly and increased by a factor of 1.9-2.2 (p < 0.05) exploratory activity. On the contrary EMR (frequency of modulation 20 Hz) significantly increased by a factor of (p < 0.05) emotionally negative reactions of anxiety and fear and decreased by a factor of 1.8 (p < 0.05) the exploratory activity in rats.

Animals↗
PubMed1997

Magnetic isotope effects in biology: a marker for radical pair reactions and electromagnetic field effects?

PURPOSE: To explore the possible usefulness of magnetic isotope effects, especially to detect processes affected by magnetic fields. MATERIALS AND METHODS: The theoretical model of Brocklehurst and McLauchlan is used to estimate the effects of isotopic substitution (e.g. 13C for 12C) on the yields of chemical reactions involving radical pairs. RESULTS: It is demonstrated that in some circumstances isotope effects on the yields from initially singlet pairs (bond breaking to give radicals) could be very large and easily detected. The effects on radical pairs formed by random encounters are necessarily much smaller but may be detectable. Illustrative calculations are presented for carbon, hydrogen and oxygen isotopes; deuterium substitution also produces very large mass effects but its study could be useful to support work on carbon. CONCLUSIONS: Effects may be small but worth looking for: distinguishing them from mass effects will be aided by measuring distributions within product molecules. In laboratory experiments (especially tomography) a combination of isotopic substitution and applied fields is a potentially powerful technique.

Electromagnetic Fields↗
PubMed2003

[Recent concept of protection of workers and general population against electromagnetic fields in the European countries].

In 1994, guidelines for protection against EM fields were elaborated by the International Commission for Non-Ionizing Radiation Protection (ICNIRP). In 1998, they were slightly modified and became the base for the 1999 recommendation of the UE Commission. The ICNIRP recommendations are based on few selected criteria, and thus provide good protection in the case of short-term exposures to EM fields, but possible effects of EM fields at intensities lower than those admissible by the ICNIPR standards raise still growing doubts. Over a couple of years, well educated and organized groups of citizens and non-governmental organizations call attention to risks of long-term exposure of humans to weak EM fields. In their reviews, the members of these groups/organizations draw attention to the need for a precautionary approach on the one hand, and postulate better protection of the general population and workers from weak EM fields on the other. The evaluation of the present situation indicates that the range of the influence of independent groups/organizations supporting the modification of ICNIPR guidelines to include the effects of low-level EM fields is steadily growing.

Electromagnetic Fields↗