摘要:

AbstractThe 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 at 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 resona

ISSN:0197-8462    

DOI:10.1002/bem.2250010302

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

年代:1980

数据来源: WILEY

摘要:

AbstractTo explain a carrier frequency dependence reported for radiofrequency (RF)‐induced calcium‐ion efflux from brain tissue, a chick‐brain hemisphere bathed in buffer solution is modeled as a sphere within the uniform field of the incident electromagnetic wave. Calculations on a spherical model show that the average electric‐field intensity within the sample remains the same at different carrier frequencies if the incident power density (Pi) is adjusted by an amount that compensates for the change in complex permittivity (ϵ r*) and the change of wavelength, as a function of carrier frequency. The resulting formula for transforming Piis seen to follow the pattern of both positive and negative demonstrations of calcium‐ion efflux that have been observed at carrier frequencies of 50, 147, and 450 MHz. Indeed, all results obtained at these three frequencies, when related by Pi's that produce the same average electric‐field intensity within the sample, are seen to be in agreement; no prediction is contradicted by

ISSN:0197-8462    

DOI:10.1002/bem.2250010303

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

年代:1980

数据来源: WILEY

摘要:

AbstractIn previous experiments changes were found in calcium‐ion efflux from chickbrain tissue that had been exposed in vitro to 147‐MHz radiation across a specific range of power densities when the field was amplitude modulated at 16 Hz. In the present study, 50‐MHz radiation, similarly modulated as a sinusoid, was found to produce changes in calcium‐ion efflux from chick brains exposed in vitro in a Crawford cell. Exposure conditions were optimized to broaden any power‐density window and to enhance the opportunity to detect changes in the calcium‐ion efflux. The results of a power‐density series demonstrated two effective ranges: One spanning a range from 1.44 to 1.67 mW/cm2, and the other including 3.64 mW/cm2, which were bracketed by no‐effect results at 0.72, 2.17, and 4.32 mW/cm2. Peaks of positive findings are associated with near‐identical rates of energy absorption: 1.4 μW/g at 147 MHz, and 1.3 μW/g at 50 MHz, which indicates that the enhanced‐efflux phenomenon is more dependent on the intensity of fields in the brain than on the power density of incident radiation. In addition, the phenomenon appears to occur at multiples of some, as yet unknown, rate of radiofrequency (RF) energy absorption. Because of the extremely small increments of temperature associated with positive findings (<4 × 10−4°C), and the existence of more than one productive absorption rate, a solely thermal explanation a

ISSN:0197-8462    

DOI:10.1002/bem.2250010304

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

年代:1980

数据来源: WILEY

摘要:

AbstractA solid‐state computer‐controlled system has been used to make swept‐frequency measurements of absorption of biological specimens from 26.5 to 90.0 GHz. A wide range of samples was used, including solutions of DNA and RNA, and suspensions of BHK‐21/C13 cells, Candida albicans, C krusei, and Escherichia coli. Sharp spectra reported by other workers were not observed. The strong absorbance of water (10–30 dB/mm) caused the absorbance of all aqueous preparations that we examined to have a water‐like dependence on frequency. Reduction of incident power (to below 1.0 μW), elimination of modulation, and control of temperature to assure cell viability were not found to significantly alter the water‐dominated absorbance. Frozen samples of BHK‐21/C13 cells tested at dry ice and liquid nitrogen temperatures were found to have average insertion loss reduced to 0.2 dB/cm but still showed no reproducible peaks that could be attributed to absorption spectra. It is concluded that the spectral resonances reported by others are likel

ISSN:0197-8462    

DOI:10.1002/bem.2250010305

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

年代:1980

数据来源: WILEY

摘要:

AbstractIn repeated short‐term tests (four sessions, each of 45‐minute duration), and one longer test (a 23.5‐hour session), behavior of rats was evaluated in a long, narrow shuttlebox. One side of the box was exposed to an electric field at various strengths, while a visually identical opposite side was shielded from exposure. In the short‐term tests, rats generally remained shielded from electric fields of 90 kV/m and greater during the first session, and maintained this response in subsequent sessions. In the longer test, this same preference response was demonstrated at field strengths of 75 kV/m and greater; however, at 25 and 50 kV/m, rats exhibited a statistically significant preference for the exposed region of the shuttlebox, but only during the light portion of a 12‐hour light: 12‐hour dark cycle. Exposed animals made more traverses than sham‐exposed controls between the two ends of the shuttlebox during the first hour of the test. The experimental data support the hypothesis that the observed behavioral effects are the result of direct interaction of the electric field with the animal, and not the result of secondary factors such as electric shock, corona discharge, audible noise, ozone, or vibration of the experimen

ISSN:0197-8462    

DOI:10.1002/bem.2250010306

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

年代:1980

数据来源: WILEY

摘要:

AbstractThis investigation was aimed at correlating changes of blood‐brain‐barrier permeability with the quantity and distribution of absorbed microwave energy inside the brain of adult Wistar rats anesthetized by sodium pentobarbital. Through use of thermographic methods and a direct‐contact applicator at the animal's head, the pattern of absorbed microwave energy was determined. Indwelling catheters were placed in the femoral vein and in the left external carotid artery. Evans blue and sodium fluorescein in isotonic saline were used as visual indicators of barrier permeation. Exposure to pulsed 2,450‐MHz radiation for 20 min at average power densities of 0.5, 1, 5, 20, 145 or 1,000 mW/cm2, which resulted in average specific absorption rates (SARs) of 0.04, 0.08, 0.4, 1.6, 11.5 or 80.0 mW/g in the brain, did not produce staining, except in the pineal body, the pituitary gland, and the choroid plexus — regions that normally are highly permeable. Except for these regions, staining was also absent in the brains of sham‐exposed animals. The rectal temperature, as monitored by a copper‐constantan thermocouple, showed a maximum increase of less than 0.75°C from a mean pre‐exposure temperature of 36.6°C. The highest brain temperature recorded in a similar group of animals using a thickfilm carbon thermistor was

ISSN:0197-8462    

DOI:10.1002/bem.2250010307

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

年代:1980

数据来源: WILEY

摘要:

AbstractIn order to determine the effects of microwave radiation on the testis, it is necessary to express the physical insult in animal studies in a way that can be replicated elsewhere and ultimately used as a basis for extrapolation to man. However, there is conflict — especially in chronic experiments — between the desire for precise dosimetry and the need to minimise alteration of the normal physiological functions of the animals. The compromise arrangement used in this study was to house the mice singly, in cages with limited food and water, and to irradiate them for up to 30 days (16 h/day) in an anechoic chamber. The only measurements taken routinely were of power density in the positions normally occupied by the cages. In addition, a series of absorption measurements was made in mouse carcasses: Whole‐body specific absorption rate (SAR); energy‐deposition patterns (determined thermographically); and local SAR in testis (using a miniature electric (E)‐field probe). It was concluded that the SAR in testis was considerably less than the whole‐body SAR. Exposure for 16 h at 50 mW/cm2elevated rectal but not testis temperature, thus demonstrating the ability of the conscious mouse to regulate the temperature of

ISSN:0197-8462    

DOI:10.1002/bem.2250010308

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe temperature distribution inside a lossy sphere resulting from the absorption of microwave energy was approximated by successive numerical iterations, of the thermal energy equation. Heat transfer within the sphere by conduction was considered. In the model energy was not dissipated by convection but was contained in the sphere for over 200 seconds. Exposure of a 5‐cm sphere to 3,000 MHz at 30 mW/cm2for 200 seconds was calculated to produce a temperature rise of 0.56°C near the front surfa

ISSN:0197-8462    

DOI:10.1002/bem.2250010309

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

年代:1980

数据来源: WILEY

摘要:

AbstractDutch rabbits were acutely exposed to electromagnetic pulsed (EMP) fields (pulse duration 0.4μs, field strengths of 1–2 kV/cm and pulse repetition rates in the range of 10 to 38 Hz) for periods of up to two hours. The dependent variables investigated were pentobarbital‐induced sleeping time and serum chemistry (including serum triglycerides, creatine phosphokinase (CPK) isoenzymes, and sodium and potassium). Core temperature measured immediately pre‐exposure and postexposure revealed no exposure‐related alterations. Over the range of field strengths and pulse durations investigated no consistent, statistically significant alterations were found in the end‐points in

ISSN:0197-8462    

DOI:10.1002/bem.2250010310

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

年代:1980

数据来源: WILEY

ISSN:0197-8462    

DOI:10.1002/bem.2250010301

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

年代:1980

数据来源: WILEY