摘要:

An aquatic system is described in which marine biota can be exposed under natural conditions for indefinite periods of time to dose‐determinate levels of microwave radiation. A source of 2450‐MHz CW energy is used to feed a standard‐gain horn that radiates a glass‐faced aquarium in the far field; source and aquarium are located in a microwave‐anechoic chamber. Seawater in the 95‐liter aquarium can be maintained at a desired temperature by a high‐capacity heat‐exchange system. By caging sets of one or more small aquatic animals at various distances from the glass face, determinate SARs at different levels can be achieved simultaneously within the aquarium. Reflectometric data on a small marine animal, the molluscAplysia californica, reveal that its presence in seawater does not appreciably change the load that is seen by incident RF waves. The system should prove useful in studying effects of long‐term microwave exposures in animals that are otherwise maintained in a na

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00075

年代:1979

数据来源: WILEY

摘要:

A simple temperature probe is described that is suitable for use in microwave dosimetry. The sensor's tip is a thermocouple junction in which dissimilar nonmetallic conductors form the sensing element. The conductors themselves, although not entirely lossless, are readily available, carbon‐loaded materials such as conductive silicone or conductive fluorocarbon. Secondary thermocouple junctions are formed where metallic leads attach to the nonmetallic conductors and the voltage output from the device is, for certain temperature ranges, proportional to the temperature difference between the primary and secondary junctions. An instrumentation amplifier is described that boosts the output of the probe and eliminates much 60‐Hz interference. Tracking accuracy of the nonmetallic thermocouple (NMT) with the secondary junctions thermally insulated is within 0.1°C, and comparative dosimetric data are given to show that the NMT produces results that compare favorably with those obtained by other, much more expensive, probes. Use of the NMT in the laboratory environment requires the probe to be stationary to avoid noise pickup, a common problem associated with devices using high resistance l

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00081

年代:1979

数据来源: WILEY

摘要:

Membrane‐bound enzyme systems were irradiated with sinusoidally modulated microwave radiation in a spectrophotometric apparatus in which enzyme activity was measured during irradiation. The enzymes chosen for study were cytochrome oxidase, a key enzyme in the electron‐transport chain that is located in the inner membrane of mitochondria, and adenosine triphosphatase (ATPase) from red‐blood‐cell membrane, which is involved in maintaining the sodium‐potassium balance of the cell. The enzyme systems were prepared from rat tissue and were subjected to 2450‐MHz radiation sinusoidally modulated at 16, 30, 90, and 120 Hz; the specific absorption rate was 26 mW g−1. Temperature was controlled at 25±1.0°C in all experiments. Irradiation began immediately after initiation of the reaction and continued for several minutes while the reaction rate was being monitored. Cytochrome oxidase activity was measured directly by monitoring the change in absorbance of its substrate, cytochrome c, at 550 nm. Activity of ATPase was measured by a coupled‐enzyme system in which the rate of conversion of ATP to ADP was followed at 340 nm by stoichiometric oxidation of NADPH. The enzymes pyruvate kinase and lactate dehydrogenase performed the intermediate steps and were always present in excess so that the activity of ATPase was rate controlling. No statistically significant differences in enzyme activities were obtained between irradiated and control samples at any of the modulation frequencies for eit

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00085

年代:1979

数据来源: WILEY

摘要:

Bawin and her coworkers have reported changes in binding of calcium after exposure of avian brain tissue to nonionizing electromagnetic radiation. Because calcium is intimately involved in the electrical activity of the brain, their results reveal a heretofore unrecognized potential for nonionizing radio‐frequency radiation to affect biological function. We have verified and extended their findings. The forebrains of newly hatched chickens, separated at the midline to provide treatment‐control pairs, were labeled invitrowith radioactive calcium. Samples of tissue were exposed for 20 minutes in a Crawford irradiation chamber to 147‐MHz radiation, which was amplitude modulated sinusoidally at selected frequencies between 3 and 30 Hz. Power densities of incident radiation ranged between 0.5 and 2 mW cm−2. Compared with nonirradiated samples, a statistically significant increase in efflux of calcium ions (P<0.01) was observed in irradiated samples at a modulation frequency of 16 Hz and at a power density of 0.75 mW cm−2. Our data confirm the existence of the frequency “window” reported by Bawin et al., as well as a narrow power‐density “window” within which efflux of calci

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00093

年代:1979

数据来源: WILEY

摘要:

A total of 154 male mice of the DBA strain was exposed during a three‐day period for nearly 60 hours to 2.45‐GHz microwaves in multimode cavities or in an electrically anechoic chamber. The estimated effective CW power density in the cavities was 3.3 (±2) mW cm−2; that in the chamber, 4 (±2) mW cm−2. Sham‐irradiated controls numbered 126. Two hours after termination of treatments, mean serum levels of triglycérides were elevated by 30% and 55%, respectively, in cavity‐ and chamber‐irradiated mice. Commensurate elevations of β‐lipoproteins were also observed. While rectal temperatures were not reliably elevated during the exposures, the absence of dosimetric data coupled with the likelihood that resonant absorption took place requires circumspection in interpreting the generality of the data

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00099

年代:1979

数据来源: WILEY

摘要:

The acellular slime moldPhysarum polycephalumhas been exposed continuously to a variety of low‐level, extremely‐low‐frequency (ELF) fields for periods ranging from two months to five years. Changes in several biological parameters have been observed that are significant (P<0.05) and reproducible. Cultures were exposed to 75‐, 60‐, and 45‐Hz CW, and 76‐Hz frequency‐modulated fields. Electric‐field intensities ranged from 0.04 to 0.7 V m−1(rms); magnetic fields, from 0.01 to 0.2 milliteslas (rms). The observed changes are generally those of a slowing of cellular processes. A longer nuclear‐division cycle and depressed respiration rate have been seen under exposure to most CW fields and to all frequency‐modulated fields that have been tested. Additional experiments indicate that lengths of the nuclear‐division cycle of cultures formed by mixing exposed and control samples lie between those of control and exposed cultures. Indirect measurements of chromosomal numbers of this polyploid organism indicate no statistically significant difference between e

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00103

年代:1979

数据来源: WILEY

摘要:

Suspensions of rabbit, human, and dog erythrocytes were irradiated by S‐band microwaves in a WR‐284 waveguide chamber for a period of 20 minutes or three hours. The release of K+and hemoglobin, and the osmotic fragility of the cells, were assayed to determine the effects of microwave and conventional heating on erythrocyte membranes. Conventional heating and microwave radiation resulted in sample temperatures that ranged from 25 to 44°C. There were no statistically significant differences between freshly prepared cells that were irradiated and those heated in a temperature‐controlled water bath at energy absorption rates near 200 mW g−1for three‐hour exposures at a frequency of 3.0 GHz, and near 80 and 100 mW g−1, respectively, for frequencies of 2.45 and 3.95 GHz. Freshly prepared suspensions of rabbit erythrocytes and ouabain‐treated suspensions were also exposed to 3.0‐GHz microwaves at an absorption rate of 170 mW g−1for 20 minutes or for three hours. No statistically signficant differences were detected between irradiated and water‐bath‐heated samples. In addition, effects of 3.0‐GHz microwaves on rabbit erythrocytes that had been held for seven days at 4°C prior to three hours of exposure were studied at a range of absorption rates to 170 mW g−1; no statistically significant effects of microwave irradiation were observed compared with the water‐bath‐heated controls although both modes of heating induced permeability changes relati

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00109

年代:1979

数据来源: WILEY

摘要:

Suspensions of asychronous CHO cells in the log phase of growth were subjected to a water‐bath or to 2450‐MHz‐microwave hyperthermia at a temperature of 44°C for a period of 60 minutes. Immediately following hyperthermic treatment, the cells were equilibrated at 37°C, counted, and plated out for colony assays, to quantitate survival of cells. Microwave heating was performed by inserting the long dimension of a plastic culture tube, which contained 8×105cells in 3 ml of media, into a waveguide parallel to theE‐field vector; CW energy was intermittently applied to maintain the suspension at 44±0.1°C. Hyperthermia was induced in a similar sample of cells from the same culture by immersing the culture tubes into a water bath at 44±0.05°C. Temperature‐rise profiles of the two hyperthermic treatments were matched by monitoring suspensions of cells with the Liquid Crystal Fiberoptic temperature probe. Cells subjected to both sources of hyperthermia under comparable conditions showed no significant difference in survival. TheDo(slope of the exponential region) of the survival curve was 8.3 minutes for the water‐bath treatment compared with 8.1 minutes for the microwave treatment. Similarly, theDq(a measure of the survival curve that indexes cell repair) was 23.4 minutes for the water‐bath treatment and 23.7 minutes for the microwave treatment. Intrasample uniformity of heating and accurate thermometry were found to be highly critical to the dem

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00117

年代:1979

数据来源: WILEY

摘要:

A method is described by which the influence of time‐varying magnetic fields on excitable tissue can be studied in a reproducible way. The retina of the frog (Rana temporaria) was exposed to a time‐varying magnetic field. The field‐generated electrical activity of the ganglion cells was recorded by a microelectrode. The method opens up new possibilities for the study of effects of low‐frequency magnetic fields on excitable

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00125

年代:1979

数据来源: WILEY

摘要:

Frogs (Rana pipiens) were exposed daily for six minutes to pulsed, 2.88‐GHz microwave radiation at an average power density of 10 mW cm−2under controlled conditions in a calibrated anechoic chamber for periods of 20 to 100 days. Single‐fiber preparations ofTibialis anticusmuscle were analyzed for osmotic responses, and the following quantities were determined: osmotically effective cell‐water fraction,Weff; cell‐membrane water permeability,Pw; Staverman's reflection coefficient (σ) for mannitol, sucrose, glycerol, urea, acetamide, ethylene glycol, and formamide; and equivalent pore radius of the membrane. No changes were detected in any of these endpoints as a consequence of repeated exposure to the radiation. Mean values found were:Weff= 0.50;Pw= 0.40 cm4Osm−1s−1; equivalent por

ISSN:0048-6604    

DOI:10.1029/RS014i06Sp00127

年代:1979

数据来源: WILEY