摘要:

AbstractPower‐frequency electric fields are strongly perturbed in the vicinity of human beings and experimental animals. As a consequence, the extrapolation of biological data from laboratory animals to human‐exposure situations cannot use the unperturbed exposure field strength as a common exposure parameter. Rather, comparisons between species must be based on the actual electric fields at the outer surfaces of and inside the bodies of the subjects. Experimental data have been published on surface and internal fields for a few exposure situations, but it is not feasible to characterize experimentally more than a small fraction of the diverse types of exposures which occur in the laboratory and in the field. A predictive numerical model is needed, one whose predictions have been verified in situations where experimental data are available, and one whose results can be used with confidence in new exposure situations. This paper describes a numerical technique which can be used to develop such a model, and it carries out this development for a test case, that of a homogeneous right‐circular cylinder resting upright on‐end on a ground plane and exposed to a vertical, uniform, 60‐Hz electric field. The accuracy of the model is tested by comparing short‐circuit currents and induced current densities predicted by it to measured values: Agreem

ISSN:0197-8462    

DOI:10.1002/bem.2250060302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe present study was undertaken to investigate the thermal adjustments of squirrel monkeys exposed in a cold environment to relatively high energy levels of microwave fields. The animals (Saimiri sciureus) were equilibrated for 90 min to a cool environment (Ta= 20°C) to elevate metabolic heat production (M). They were then exposed for brief (10‐min) or long (30‐min) periods to 2,450‐MHz continuous‐wave microwaves. Power densities (MPD) were 10, 14, 19, and 25 mW/cm2during brief exposures and 30, 35, 40, and 45 mW/cm2during long exposures (rate of energy absorption: SAR = 0.15 [W/kg]/ [mW/cm2]). Individual exposures were separated by enough time to allow physiological variables to return to baseline levels. The results confirm that each microwave exposure induced a rapid decrease in M. In a 20°C environment, the power density of a 10‐min exposure required to lower M to approximate the resting level was 35 mW/cm2(SAR = 5.3 W/kg). During the long exposures, 20 min was needed to decrease M to its lowest level. Cessation of irradiation was associated with persistence of low levels of M for periods that depended on the power density of the preceding microwave exposure. Vasodilation, as indexed by changes in local skin temperature, occurred at a high rate of energy absorption (SAR = 4.5 W/kg) and was sufficient to prevent a dramatic increase in storage of thermal energy by the body; vasoconstriction was reinstated after termination of irradiation. Patterns of thermophysiological responses confirm the influence both of peripheral and of internal inputs to thermoregulation in squirrel monkeys exposed to microwaves in a cool

ISSN:0197-8462    

DOI:10.1002/bem.2250060303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe dielectric properties of developing rabbit brain were measured at 37°C between 10 MHz and 18 GHz using time domain and frequency domain systems. The results show a variation with age of the dielectric properties of brain. An analysis of the data suggests that the water dispersion in the brain of newly born animals can be represented by a Debye equation. This dispersion increases in complexity with age, and there is evidence of a smaller additional relaxation process centered around 1 GHz. It is concluded that the principal contribution to this subsidiary dispersion region arises from water of hydration

ISSN:0197-8462    

DOI:10.1002/bem.2250060304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe electrical properties (variation of capacitance and conductance with frequency) of a plant stem can be conveniently measured in vivo by time domain dielectric spectroscopy. In this technique a voltage step is applied to a stem. The resulting polarization current is sampled by a microprocessor and Fourier‐transformed to yield these properties. Spectra were obtained for seven electrode separations along a Poinsettia stem. The inverse capacitance and conductance were plotted vs separation for 50 frequencies from .35 to 350 Hz. Least‐square fits yielded the effective dielectric constant and conductivity of the stem over this frequency range. In this way electrode effects were eliminated. A similar procedure was carried out for Coleus.A log‐log plot of dielectric constant vs frequency shows a two‐stage linear decrease for both plants. The conductivity is primarily DC. The dielectric loss decreases smoothly with frequency for Coleus. These results are compared to those for bone and the inorganic material hollandite. The dielectric properties seem best described by a cooperative, manybody a

ISSN:0197-8462    

DOI:10.1002/bem.2250060305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractHelix aspersa neurons were irradiated with continuous‐wave (CW) and noise‐amplitudemodulated microwaves (carrier frequency 2450 MHz, 20% AM, 2 Hz‐20 kHz) in a specially designed waveguide exposure system. Continuous‐wave microwave irradiations were conducted at 8°, 21°, and 28°C, while noise‐modulated irradiation was performed at 21°C. The results showed that exposure of snail neurons to CW microwaves for 60 min at 12.9 W/kg inhibited spontaneous activity and reduced input resistance at 8° and 21°C but not at 28°C. The relative decrease in resistance at 21°C was half that at 8°C. Exposure of neurons to noise‐modulated microwaves at 6.8 and 14.4 W/kg predominately caused excitatory responses characterized by augmented membrane resistance and the appearance of greater activity. The effect differed qualitatively from the inhibition observed with continuous, unmodulated m

ISSN:0197-8462    

DOI:10.1002/bem.2250060306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractFertile eggs of the Coturnix quail were exposed twice a day for 30 min to 2.45‐GHz continuous wave radiation at power densities of 25 or 50 mW cm−2throughout the 17‐day incubation period. Other eggs were exposed to 20°C or 24°C temperatures twice daily. Repeated exposures to 20°C, 24°C, or 25 mW cm−2did not reduce hatchability. Irradiation at 50 mW cm−2lowered hatchability, probably as a result of high egg temperatures. Hatchlings that had been irradiated by microwaves as embryos had normal growth rates and no obvious developmental

ISSN:0197-8462    

DOI:10.1002/bem.2250060307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractRoots of Pisum sativum were exposed for 48 h to 60‐Hz electric fields of 430 V/m in an aqueous inorganic growth medium. The growth in length of the exposed roots was 44% of that for control roots. Root tips were analyzed for mitotic index and cell cycle duration. Mature, differentiated root sections from tissue produced after electrode energization were analyzed for cell lengths and number of files. The major reason for the observation that exposed roots are shorter than control roots is that cell elongation in the former is greatly diminished relative to control

ISSN:0197-8462    

DOI:10.1002/bem.2250060308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractGrowth, mitotic index, and growth rate recovery were determined forVicia fabaL. roots exposed to 60‐Hz electric fields of 200, 290, and 360 V/m in an aqueous inorganic nutrient medium (conductivity 0.07–0.09 S/m). Root growth rate decreased in proportion to the increasing strength; the electric field threshold for a growth rate effect was about 230 V/m. The induced transmembrane potential at the threshold exposure was about 4–7 mV. The mitotic index was not affected by an electric field exposure sufficient to reduce root growth rate to about 35% of control. Root growth rate recovery from 31–96% of control occurred in 4 days after cessation of the 360 V/m exposure. The results support the postulate that the site of action of the applied electric fields is the cell m

ISSN:0197-8462    

DOI:10.1002/bem.2250060309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractBy use of fluorescence probes 1‐anilinonaphthalene‐8‐sulfonic acid, 2‐toluidinylnaphthal‐ene‐6‐sulfonate, pyrene, perylene and chemical label phosphatidylethanolamine 2,4,6‐trinitrobenzele sulfonic acid, the effect of microwave radiation on the erythrocyte membrane was studied. The studies with the fluorescence probes were carried out on erythrocyte ghosts and with 2,4,6‐trinitrobenzene sulfonic acid on whole erythrocytes. The fluorescence was measured during irradiation of the membranes with 340‐MHz microwaves at an SAR of 100 W/kg. Trinitrophenylation of phosphatidylethanolamine from whole erythrocytes was performed simultaneously with microwave irradiation at 900 MHz (10 mW/cm2). It was shown that the microwave field decreased lipid viscosity, altered the structural state of lipid‐protein contact regions, and decreased the protein shielding of lipids. These changes corresponded to those produced by thermal

ISSN:0197-8462    

DOI:10.1002/bem.2250060310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractA field‐strength‐dependent hemolytic effect of continuous‐wave radiofrequency (RF) exposure in vitro has been demonstrated. Erythrocytes in whole heparinized rabbit blood were hemolyzed by a 2‐h exposure to 50‐ or 100‐MHz RF fields at field strengths of greater than 4 V/cm. An effect of comparable magnitude resulted from exposure to 10‐MHz RF at a field strength of 9 V/cm. Sample temperatures were maintainted at 22.5° ± 0.2°C. There was no apparent involvement of heating or temperature gradients, nor were there any RF exposure effects on cellular K+or Na+concentration, nor on pH. The mechanism of the hemolytic effect is not known. Since the percentage of lysed erythrocytes was less than 1% and there was an absence of effects on cellular cation concentrations, RF radiation may have irreversibly altered the plasma membrane permeability of a sensitive subpopulation of red cells (possibly aged cells) leading to osmotic lysis. RF radiation at these frequencies appears to affect red cells in a manner that is qualitatively and quantitatively different from mic

ISSN:0197-8462    

DOI:10.1002/bem.2250060311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY