摘要:

AbstractBees exposed to 60‐Hz electric (E) fields>150 kV/m show field‐induced vibrations of wings, antennae, and body hairs. They also show altered behavior if exposed while in contact with a conductive substrate. Measurements indicate that approximately 240 nA is coupled to a bee standing on a conductive substrate in a 100‐kV/m E field. In lab experiments, bee disturbance and sting result from exposure to E field>200 kV/m (bee current>480 nA) and reduced voluntary movements at>300 kV/m (>720 nA bee current)onlyif the bee is on a conductive substrate. It is hypothesized that in the latter situation coupled bee current drains through the lower thorax and legs to the conductive substrate, and that the resulting enhanced current density in these regions is the cause of observed responses. The observation that bees exposed to intense E fields on an insulator show vibration of body parts but no behavioral response suggests that vibration contributes little to the disturbance of bees in intense E fields.Lab measurements of bee impedance from front‐to‐rear leg pairs were made on wet and dry conductors. Measurements validate the selection of 1 MΩ as a middle value for bee impedance used in the design of devices used to generate step‐potential‐induced cu

ISSN:0197-8462    

DOI:10.1002/bem.2250100102

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe relative locations and characteristics of the distribution lines feeding 434 residences in the Denver metropolitan area were recorded and classified according to the Wertheimer‐Leeper code (WL code) as a part of an epidemiological study of the incidence of childhood cancer. The WL code was found to place the mean values of the fields in rank order. However, the standard deviations were approximately the same size as the means. Theoretical calculations indicate that a significant fraction of the low‐power magnetic fields can be generated by the distribution lines, especially in the cases where the distribution lines are within 50 feet of the residence. Thus, the wiring code was shown to be a useful method for making a first‐order approximation to predict long‐term, low‐level magnetic fields in r

ISSN:0197-8462    

DOI:10.1002/bem.2250100103

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

年代:1989

数据来源: WILEY

摘要:

AbstractA large proportion of scientific effort in investigating the possible biological effects of exposure to extremely‐low‐frequency (ELF) fields consists of laboratory studies on experimental animals. Most experiments in which hematologic properties are measured show no statistically significant effect due to exposure. However, some studies show significant effects which, in general, are not clearly reproducible. A difficult question must then be addressed: Are these relatively few indications of ELF effects statistical artifacts due to the increased risk of a type I error in multiple studies, or is there a real biological effect that is undetected in most studies due to the relatively small sample sizes commonly used? A statistical approach for examining the accumulated results of multiple experiments which results in a single test for treatment effect is presented. The technique requires very mild assumptions, and is valid for experiments that vary widely in specific characteristics such as exposure level, duration, and laboratory. The method is applied to the results of a collection of hematologic and serum chemistry experiments, and the combined results indicate the existence of experimental effects on some end poi

ISSN:0197-8462    

DOI:10.1002/bem.2250100104

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe responses of a plane‐wave pulse train irradiating a lossy dispersive dielectric half‐space are investigated. The incident pulse train is expressed as a Fourier series with summing done by the inverse fast Fourier transform. The Fourier series technique is adopted to avoid the many difficulties often encountered in finding the inverse Fourier transform when transform analyses are used. Calculations are made for propagation in pure water, and typical waveforms inside the dielectric half‐space are presented. Higher harmonics are strongly attenuated, resulting in a single continuous sinusoidal waveform at the frequency of the fundamental depth in the material. The time‐averaged specific absorption rate (SAR) for pulse‐train propagation is shown to be the sum of the time‐averaged SARs of the individual harmonic components of the pulse train. For the same average power, calculated SARs reveal that pulse trains generally penetrate deeper than carrier‐frequency continuous waves but not deeper than continuous waves at frequencies approaching the fundamental of the pulse train. The effects of rise time on the propagating pulse train in the dielectrics are shown and explained. Since most practical pulsed systems are very limited in bandwidth, no pronounced differences between their response and continuous wave (CW) response would be expected. Typical results for pulse‐train propagation in arrays of dispersive planar dielectric slabs are presented. Expressing the pulse train as a Fourier series provides a practical way of interpreting the dispersion characteristics from the spectra

ISSN:0197-8462    

DOI:10.1002/bem.2250100105

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

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper presents a theoretical analysis of electromagnetic environments in power substations in service. A new analytical method is developed and applied to magnetic field calculations in 187‐kV and 66‐kV substations. Experimental results verify that the method offers a good prediction of the magnetic field profiles in the substations except for the areas where localized field sources exist. The analytical results show that the magnetic field strength depends to a great extent on how the load powers distribute on individual lines and buses, that the magnetic fields in substations have a three‐dimensional characteristic, and that the predominant field component depends on the position of interest. Moreover, it is suggested that objects placed in substations are exposed not only to magnetic fields of high strength in comparison to those in houses or near the distribution networks but also to fields with several percent of harmonic disto

ISSN:0197-8462    

DOI:10.1002/bem.2250100106

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe current safety standards for radiofrequency and microwave exposure do not limit the peak power of microwave pulses for general or occupational exposures. While some biological effects, primarily the auditory effect, depend on pulsed microwaves, hazards associated with very high peak‐power microwave pulses in the absence of whole‐body heating are unknown. Five rhesus monkeys,Macaca mulatta, were exposed to peak‐power densities of 131.8 W/cm2(RMS) while performing a time‐related behavioral task. The task was composed of a multiple schedule of reinforcement consisting of three distinct behavioral components: inter‐response time, time discrimination, and fixed interval. Trained monkeys performed the multiple schedule during exposure to 1.3‐GHz pulses at low pulse‐repetition rates (2–32 Hz). No significant change was observed in any behavior during irradiation as compared to sham‐irradiation sessions. Generalization of these findings to experimental results with higher peak‐power densities, other pulse rates, different carrier frequencies, or other b

ISSN:0197-8462    

DOI:10.1002/bem.2250100107

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe heat uptake that resulted from immersing the hand and wrist into a water‐filled calorimeter maintained at temperatures between 37–40 °C was measured under standard conditions in a group of eight subjects of either sex. The rate of heat transfer (W) increased exponentially with temperature and was a function of hand or body size and age, but not sex. The heat transfer rate normalized to hand mass (W.kg−1) was determined by temperature and age: best‐fit mean values (and 95% confidence limits of the population) were 6.0 W.kg−1(3.2–11.2 W.kg−1) at an immersion temperature of 37 °C and 25.4 W.kg−1(13.7–47.0 W.kg−1) at 40 °C. The application of these results to limits on specific energy absorption rate induced in the hands and wrists by radiofrequency dielectric heat seale

ISSN:0197-8462    

DOI:10.1002/bem.2250100108

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

年代:1989

数据来源: WILEY

摘要:

AbstractMagnetic field systems were added to existing electric field exposure apparatuses for exposing cell suspensions in vitro and small animals in vivo. Two horizontally oriented, rectangular coils, stacked one directly above the other, have opposite electric currents. This configuration minimizes leakage fields and allows sham‐ and field‐exposure systems to be placed in the same room or incubator. For the in vitro system, copper plates formed the loop‐pair, with up to 900 A supplied by a 180:1 transformer. Electric fields were supplied via electrodes at the ends of cell‐culture tubes, eight of which can be accommodated by each exposure system. Two complete systems are situated in an incubator to allow simultaneous sham and field exposure up to 1 mT. For the in vivo system, four pairs of 0.8 × 2.7‐m coils made of copper bus bar are employed. This arrangement is energized from the power grid via a 30:1 transformer; horizontal magnetic flux densities up to 1 mT can be generated. Pairs of electrode plates spaced 30.5 cm apart provide electric field exposure of up to 130 kV/m. Four systems with a capacity of 48 rats each are located in one room. For both the in vitro and in vivo systems, magnetic exposure fields are uniform to within ± 2.5%, and sham levels are at least 2,500‐fold lower than exposure levels. Potential confounding factors, such as heating and vibration, were examined and found

ISSN:0197-8462    

DOI:10.1002/bem.2250100109

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

年代:1989

数据来源: WILEY

摘要:

AbstractRats were exposed to two procedures which enabled them to press a lever to turn off a 90 or 100 kV/m 60‐Hz electric field or, later in the study, illumination from an incandescent lamp. Under one procedure, a response turned off the stimulus for a fixed duration, after which the stimulus was turned on again. A response during the off‐period restarted the fixed duration. None of the rats turned the field off reliably. Next, under an alternative procedure, pressing one lever turned the field off; pressing the other lever turned it back on; responding under those conditions differed little from that seen at 0 kV/m. Under both procedures, when illumination from an incandescent lamp served as the stimulus, each rat did turn the stimulus off, and performances varied with stimulus intensity. The results show that a 100 kV/m 60‐Hz electric field is not sufficient to function as an aversive stimulus under two procedures where illumination from a lamp does function as an aversive sti

ISSN:0197-8462    

DOI:10.1002/bem.2250100110

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

年代:1989

数据来源: WILEY

摘要:

AbstractExperiments were conducted to further investigate the effect of 60‐Hz cyclotron‐resonance exposures on rats performing on a multiple FR‐DRL schedule. The previously reported temporary loss of DRL baseline response, when measured as a function of A.C. magnetic intensity, was found to have a threshold. Utilizing the component of A.C. magnetic intensity parallel to the D.C. field, we report this threshold as (0.27 ± 0.10) × 1

ISSN:0197-8462    

DOI:10.1002/bem.2250100111

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

年代:1989

数据来源: WILEY