摘要:

AbstractWe have previously reported that in vitro exposure of chick forebrain tissue to 50‐MHz radiofrequency (RF) electromagnetic radiation, amplitude modulated (AM) at 16 Hz, would enhance the efflux of calcium ions within only two power‐density ranges: one from 1.44 to 1.67 mW/cm2, and the other including 3.64 mW/cm2. No effect on efflux occurred at 0.37, 0.72, 2.17, and 4.32 mW/cm2. We confirmed and extended these results by testing at another set of power densities, which included the range of the previous study. Forebrain tissue from 1–7‐day‐old chickens was labeled in vitro with radioactive calcium ions (30 min, at 37 °C), rinsed, placed in a physiological salt solution, and then exposed for 20 min to 50‐MHz radiation, AM at 16 Hz, in a transverse electric and magnetic field (TEM) cell maintained at 37 °C. The solution was then assayed for radioactive calcium activity. A power‐density series was tested. An enhanced efflux of calcium ions was found at 1.75, 3.85, 5.57, 6.82, 7.65, 7.77, and 8.82 mW/cm2; no change was observed at 0.75, 2.30, 4.50, 5.85, 7.08, 8.19, 8.66, 10.6, and 14.7 mW/cm2. Power density is converted to specific absorption rate (SAR) by 0.36 mW/kg per mW/cm2. Even the highest SAR tested (0.005 W/kg) is much too low to result in generalized heating of the sample and thus to be the underlying cause of the enhanced response. A hypothetical mechanism is proposed involving dynamic systems that may account for the power‐density dependency as well as for part of the frequency dependency observed with both modulated RF radiation and extremely‐low‐f

ISSN:0197-8462    

DOI:10.1002/bem.2250100202

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

年代:1989

数据来源: WILEY

摘要:

AbstractThere are a number of reports of the plasma membrane transport of Ca2+in biological systems being enhanced by low frequency electromagnetic fields (EMF), including reports that the enhancement involves a resonance‐type response at the cyclotron frequency for Ca2+ions for geomagnetic values of the magnetic field. Using the fluorescent probe fura2, we find no evidence for changes in cytosolic calcium concentration in BALB/c3T3, L929, V‐79, and ROS, a rat osteosarcoma cell line, at the application of both resonant and nonresonant

ISSN:0197-8462    

DOI:10.1002/bem.2250100203

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

年代:1989

数据来源: WILEY

摘要:

AbstractAction potentials of neurons in cat dorsal and posteroventral cochlear nuclei were recorded extracellularly with glass microelectrodes while the head of the cat was exposed to microwave pulses at 915 MHz using a diathermy applicator. Response thresholds to acoustic tones, acoustic clicks, and microwave pulses were determined for auditory units with characteristic frequencies (CFs) from 278 Hz to 39.2 kHz. Tests with pulsatile stimuli were performed for durations of 20–700 μs, principally 20, 70, and 200 μs. Brainstem midline specific absorption rate (SAR) threshold was as small as 11.1 mW/g per pulse, and specific absorption (SA) threshold was as small as 0.6 μJ/g per pulse. Microwave thresholds were generally lower for CF less than 9 kHz, as were most acoustic thresholds. However, microwave threshold was only weakly related to click threshold and CF‐tone threshold of eac

ISSN:0197-8462    

DOI:10.1002/bem.2250100204

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

年代:1989

数据来源: WILEY

摘要:

AbstractLocalized and averaged specific absorption rates (SARs) were obtained in a full‐size muscle‐equivalent human model exposed to near‐field 29.9 MHz irradiation at an outdoor facility. The model was positioned erect on a metallic groundplane 1.22 m (4 ft) from the base of a 10.8‐m (35 ft) whip antenna with an input power of 1.0 kW. For whole‐body SAR, a mean value of 0.83 W/kg was determined using two gradient‐layer calorimeters in a twin‐well configuration. The localized SARs at 12 body locations were measured using nonperturbing temperature probes and were highest in the ankle region. We conclude that averaged SAR measurements in a full‐size phantom are feasible using a twin‐calorimeter approach; measurements in the field are practical when human‐size (183 × 61 × 46 cm)

ISSN:0197-8462    

DOI:10.1002/bem.2250100205

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

年代:1989

数据来源: WILEY

摘要:

AbstractSpecific absorption rate (SAR) was measured in models of the human head exposed to hand‐held portable radios (“transceivers”) transmitting at frequencies in the 800‐MHz band. An isotropic implantable electric‐field probe was used to measure internal fields induced in the head models, and SARs were determined by calculation. As well as determining representative values and distributions for SARs under various conditions, it was shown that antenna type and orientation with respect to the head are important factors affecting energy a

ISSN:0197-8462    

DOI:10.1002/bem.2250100206

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

年代:1989

数据来源: WILEY

摘要:

AbstractA residential neighborhood in Buffalo, NY, was surveyed with a magnetic field meter to evaluate whether or not spot measurements are reliable predictors of the 60‐Hz fields at street corners and residences. The results of repeated measurements over 7 days at 33 street corners in this neighborhood indicate that day‐to‐day variation in power line magnetic fields is negligible (intraclass correlation coefficient = 0.94). Multivariate linear regression analysis of the data indicates that transmission lines and thick, three‐phase primary wires near the field measurement site are strong predictors and account for the majority of the ambient magnetic field variance between locations (multiple correlation coefficient squared = 0.60; F ratio = 22.2,P<.001). Magnetic fields measured at the front sidewalk were highly correlated with fields at the front doorsteps of 45 homes in this neighborhood (γ = 0.81). These results suggest that ambient power line magnetic field levels at urban residences can be reliably characterized on a one‐time site inspection using a hand‐held magnetic field meter and a simple wiring classific

ISSN:0197-8462    

DOI:10.1002/bem.2250100207

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

年代:1989

数据来源: WILEY

摘要:

AbstractTo test the generality of radiofrequency radiation‐induced changes in45Ca2+efflux from avian and feline brain tissues, human neuroblastoma cells were exposed to electromagnetic radiation at 147 MHz, amplitude‐modulated (AM) at 16 Hz, at specific absorption rates (SAR) of 0.1, 0.05, 0.01, 0.005, 0.001, and 0.0005 W/kg. Significant45Ca2+efflux was obtained at SAR values of 0.05 and 0.005 W/kg. Enhanced efflux at 0.05 W/kg peaked at the 13–16 Hz and at the 57.5–60 Hz modulation ranges. A Chinese hamster‐mouse hybrid neuroblastoma was also shown to exhibit enhanced radiation‐induced45Ca2+efflux at an SAR of 0.05 W/kg, using 147 MHz, AM at 16 Hz. These results confirm that amplitude‐modulated radiofrequency radiation can induce responses in cells of nervous tissue origin from widely different animal species, including humans. The results are also consistent with the reports of similar findings in avian and feline brain tissues and indicate the general nature of t

ISSN:0197-8462    

DOI:10.1002/bem.2250100208

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

年代:1989

数据来源: WILEY

摘要:

AbstractRats were irradiated with circularly polarized, 2,450‐MHz pulsed microwaves (2‐μs pulses, 500 pulses per second [pps]) for 45 min in the cylindrical waveguide system of Guy et al:(Radio Sci14:63–74, 1979). Immediately after exposure, sodium‐dependent high‐affinity choline uptake, an indicator of cholinergic activity in neural tissue, was measured in the striatum, frontal cortex, hippocampus, and hypothalamus. The power density was set to give average whole‐body specific absorption rates (SAR) of 0.3, 0.45, 0.6, 0.75, 0.9, or 1.2 W/kg to study the dose‐response relationship between the rate of microwave energy absorption and cholinergic activity in the different areas of the brain. Decrease in choline uptake was observed in the striatum at a SAR of 0.75 W/kg and above, whereas for the frontal cortex and hippocampus, decreases in choline uptake were observed at a SAR of 0.45 W/kg and above. No significant effect was observed in the hypothalamus at the irradiation power densities studied. The probit analysis was used to determine the SAR50in each brain area, i.e., the SAR at which 50% of maximum response was elicited. SAR50values for the striatum, frontal cortex, and hippocampus were 0.65, 0.38, and 0.44 W/kg

ISSN:0197-8462    

DOI:10.1002/bem.2250100209

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe present a simple readout device that fills the void produced by the gradual disappearance of the Vitek model 101 Electrothermia Monitor. The new device uses commercially available probes that are similar to Bowman's (IEEE Trans Microwave Theory Tech MTT‐24:43–45, 1976) original design. As described, the device covers the range of 7 ° to 45 °C with an accuracy and resolution of better than 0.1 °C throughout. The digital readout (3½ digits) is proportional to the thermistor resistance in the tip of the probe; it is converted to temperature through a formula or printed table. Outdoor dosimetric comparisons between the new and Vitek devices were conducted. Results showed no significant difference in the calculated specific absorption rates (SARs); moreover, variance was lower in the data collected from the new

ISSN:0197-8462    

DOI:10.1002/bem.2250100210

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

年代:1989

数据来源: WILEY

ISSN:0197-8462    

DOI:10.1002/bem.2250100201

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

年代:1989

数据来源: WILEY