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The Trickle‐Down model has been developed and applied to Vandercook Lake, Wisconsin, for an acidic deposition assessment. Three years of field data were simulated. Field data of lake stage and groundwater level at the nearshore piezometer were used for hydrological model calibration. Field alkalinity and pH data were used for alkalinity/pH model calibration. Hydrological budget calculations showed that almost all of the water in the lake came from precipitation falling directly on its surface. Alkalinity budget calculations indicated that 76% of the alkalinity produced came from internal processes, and the remainder of the alkalinity (24%) was supplied from groundwater inputs. Model results were within one standard deviation of field data for alkalinity at all times except the winter period of 1981–1982. Simulations of a doubling of the acid deposition to Vandercook Lake indicate that an acidification of the lake would occur over a 5–20 yr period.

A compact, light weight cavity-backed slot radiator operating at 2450 MHz is described. The near field patterns and the axial energy density are presented as a function of distance from the slot.

In most experimental investigations of the biological effects of microwave radiation, it is necessary to use low-loss dielectric materials for restraining animals under irradiation. Because of the complexity of the aualysis of the animal-restrainer combination, an analysis is made of the scattering of microwave fields by a simplified model of the restrainer with no animal present. The model chosen is that of a plane wave incident at an arbitrary angle upon a rectangular slab of finite width and thickness. Numerical results indicate that the scattered fields within a square region of one wavelength in distance from the slab surfaces are greatly enhanced and highly nonuniform. In particular, the maxima for parallel incidence exceed those for normal incidence by almost a factor of 2.

The perturbation introduced by low-loss dielectric materials in a microwave field was assessed through experiment and analysis. The model chosen was that of a plane wave incident at an arbitrary angle upon a rectangular Plexiglas slab of finite width and thickness. It is shown that the perturbation produced by a slab parallel to the direction of propagation is at least as great as the normal incident case. Good agreement between theory and experiment was obtained.

Integral equations describing the multiple‐scattering effects of waves propagating in a discrete random medium are solved using Fourier transform techniques. The average intensity in the medium for a given source radiation is expressed in terms of a Green's function which consists of residue contribution at a pole representing diffusion and a branch cut integration pertaining to nearfield. It is shown that for a plane wave, multiple scattering becomes significant when the particles are mostly scattering (albedo, b > 0.5) for all distances greater than a fraction of an optical depth Z. When the particles are mostly absorbing, multiple scattering will not take effect until at least Z > 2. For a spherical wave, the multiple‐scattering influence does not become significant until several optical depths, except when the scatterers are extremely low loss (b → 1).

The human body was modeled by a finite difference numerical procedure to determine the effect of simulating the sweating rate by different analytical models. Six different models were used in which the hypothalamus, muscle, average skin, and local skin temperatures were used as the controlling parameters for the rate of local sweating. These different models were tested by comparing their predictions of local temperatures for an exercising man with measured values. The computer program was then used to compute the thermal response of a man subjected to microwave irradiation of the entire body and the head only. Transient head and body temperatures and sweating rates were computed and compared with the temperature changes due to an equivalent exercise level. Significant differences in the results found by using the different sweat models point out the need for further work in determining accurate analytical descriptions of this major mode of body heat loss.

Microwave power deposition patterns and temperature distributions were measured for rabbit eyes exposed to localized near zone 2450 MHz radiation and good agreement was obtained between the measured and predicted transient temperature fields. The lenses were biomicroscopically examined to determine the minimum exposure times necessary to produce posterior lens opacity (cataracts) and these times are correlated with the temperature calculations to suggest that a threshold temperature level exists.

The effect of angle of incidence on the transmission electromagnetic pulse with Gaussion character in biological material is studied. The model assumed is a layer of soft tissue over a semi-infinite medium of boney structure governed by alpha dispersion. The numerical results demonstrate that the transmitted pulse strength is the greatest when the pulse is incident normally on the air-tissue interface. The coupling efficiency for a one microsecond pulse is three times as big as that for a ten microsecond pulse.

A popular neuron encoder model is cast into the form of an information channel, and the encoder state is shown to be measured in probability by a Markov chain. Channel capacity of the model is calculated under the assumption that the neuron threshold follows an approximately Gaussian distribution. The model is also shown to be characterized in information theory terms as a finite-state indecomposable channel subject to intersymbol interference and fading. From experiments on snail neurons which were the stimulus for the modelling efforts, the hypothesis is suggested that, to the extent the model captures the actual performance of neurons, microwave radiation could significantly alter the information processing ability of neurons.

Microwave-induced acoustic pressures in the spherical models of human and animal heads are measured using a small hydrophone transducer. The measured acoustic frequencies that correspond to mechanical resonance of the head model agree with those predicted by the thermoelastic theory of interaction. Further, a three-pulse burst applied at the appropriate pulse repetition frequencies could effectively drive the model to respond in such a manner that the microwave-induced pressure amplitude would be increased by threefold or more.

Rabbits, irradiated by known cataractogenic levels of 2.45 GHz radiation at 5 cm, did not develop cataracts if kept under general hypothermia. Radiation-induced temperature elevation appears to be essential for the cataractogenic effect of microwaves.

When human subjects are exposed to rectangular pulses of microwave radiation, an audible sound occurs which appears to originate from within or behind the head. It has been shown that electrophysiological auditory activity may be elicited by exposing the brains of laboratory animals to rectangular pulses of microwave energy. These results suggest that a microwave auditory phenomenon is evoked by a mechanism similar to that responsible for conventional sound reception and that the primary site of interaction resides peripheral to the cochlea. A comparison of the pressure amplitudes, such as those produced in a homogeneous planar layer of brain matter that is irradiated by a microwave pulse, indicates that the peak pressure due to thermal expansion is much greater than either radiation pressure or electrostriction. Theoretical analyses for a spherical brain based on the thermoelastic mechanism of interaction were found to agree with experimentally observed characteristics and indicate also that the induced sound frequency is only a function of the size and acoustic property of the brain. A few suggestions have been made for future research aimed at furthering our knowledge on microwave auditory effect and its health implications.

Human marrow cells were irradiated with 2450-MHz CW microwaves in a fluid-filled waveguide irradiation system. Cell exposure was conducted by placing a marrow cell suspension in 20-microliter glass microcapillary tubes were positioned in the exposure chamber, and irradiated at power densities from 31 to 1,000 mW/cm2 (with corresponding specific absorption rates of 62 to 2,000 mW/g) for 15 minutes. The temperature of the sample was maintained at a fixed point. Sham-irradiated (SI) and microwave-irradiated (MWI) cells were cultured in a methylcellulose culture system for neutrophil colony proliferation. There was no reduction in neutrophil colony number on days 6-7 or 12-14 in cells exposed at 31 or 62 mW/cm2, but as the power density was increased to 1,000 mW/cm2, there was a reduction in colony number of MWI cells compared with SI cells. The microwave interaction with the human neutrophil colony-forming cells was apparently not related to temperature rise, or to the state of cells cycle, and was irreversible.

Microwave pulse-evoked potentials at the vertex show a series of waves occurring in the first 10 ms following delivery of the pulse. The sources of these waves, as in the case of acoustic click-evoked responses, are action potentials generated in the cochlea and auditory brain stem nuclei. We shall show, using microwave-induced auditory brain stem responses, that the experimentally observed characteristics agree with previously derived theoretical predictions in regard to pulse width and frequency of impinging microwaves, pattern of absorbed microwave energy, frequency of vibration, and threshold of sensation.

The cataractogenic effects of near-zone 2450-MHz radiation in rabbits are presented. The power deposition pattern inside the eyes and head of rabbits has been determined using a thermocouple technique. It was found that a peak absorption of 0.92 W/kg occurred between the lens of the eye and the retina for each milliwatt/square centimeter incident. Time and power-density studies indicated a cataractogenic threshold of a 150-mW/cm2 incident, or 138-W/kg peak absorption behind the lens for 100 min. The threshold time decreased with increasing power density. Agreement between in vivo intraocular temperature measurements and finite-element computer predictions reinforces the suggestion of a thermal mechanism for microwave-induced lens opacities.

Patterns of thermalized energy of rat carcasses exposed to 918-MHz CW radiation in the near zone have been determined using a computerized thermograph. Peak absorption of energy in the body was estimated to be 0.9 W/kg per mW/cm/sup 2/ of incident energy. Operant responses of irradiated rats to schedules of fixed-ratio (food) reinforcement under the same conditions as the dosimetric test were observed to occur at averaged power densities of 30-40 mW/cm/sup 2/. This range of densities corresponds to absorbed peaks of energy of 27-36 W/kg. No change in behavior was observed for incident power densities and peaks of absorbed energy to 20-30 mW/cm/sup 2/ and to 18-27 W/kg, respectively, and all changes at higher values were reversible.

A “vertical” condensation scheme for discrete probability distribution (DPD) calculations is presented as an alternative to the earlier “horizontal” scheme, an example of which was presented recently by Kurth and Cox. When applied to DPDs over a space of curves, the vertical condensation results in a “regularization” of the “spaghetti” of curves that results from combination operations on such DPDs.

Microwaves (pulsed, 2,450 MHz) at an average power density of 3 W/cm2 were applied directly to the head for 5, 10, or 20 min, producing a peak specific absorption rate of 240 W/kg in the brain, which, after a 10-min exposure, resulted in brain temperatures in excess of 43 degrees C. A bolus of 86Rb in isotonic saline was injected intravenously and an arterial sample was collected for 20 s to determine cardiac output. Compared with unexposed controls, uptake of 86Rb increased most in those regions directly in the path of the irradiation, namely, the occipital and parietal cortex, as well as the dorsal hippocampus, midbrain, and basal ganglia. In a separate group of animals, regional brain-vascular spaces were found to increase with brain temperature. These results support previous observations indicating that reliably demonstrable increases of blood-brain barrier permeability are associated with intense, microwave-induced hyperthermia, and that the observed changes are not due to field-specific interaction.

The transmission characteristics of transient electromagnetic pulses in biological material are studied using a plane wave pulse incident normally on a semi-infinite layer model. With the dispersion properties of complex tissue dielectric constants taken into account, the steady state transfer function was examined as a function of frequency. Integral solutions for the transmitted field of a Gaussian pulse were obtained through Fourier transformation. The transmitted waveforms inside muscle were determined numerically for various depths pertinent to biological situations. The results suggest that incident pulse experiences severe reflection at the airtissue interface and, shorter pulses are transmitted more readily than longer ones. For an incident pulse of 50 kV/m and 1 us in pulsewidth, the transmitted amplitude is 221 V/m.

It has been shown that ultrasonic Doppler signals can be obtained easily and transcutaneously from many blood vessels in both normal and atherosclerotic subjects. The Doppler spectrum changes with time, giving rise toa distnbution of frequencies whose envelope has a waveform that is characteristic of the vessel site and closely folows the events of the cardiac cycle. This makes it very useful in diagnosing lesions of the arterial system. The paper presents a coherent optical technique for displaying and analyzing a blood-flow-generated ultrasonic Doppler spectrum. The system is highly cost-effective and produces spectrograms on-line. Other advantages include a large, continuously variable bandwidth, an instantaneous display of velocity profile, and simultaneous display of temporal spectra. The system makes use of the Fourier transformation property of converging lens and its use of processing time signals. The spectrum obtained from the brachial artery of a normal subject compares favorably with the spectrograms obtained using electronic spectrum analyzers.

Helix aspersa neurons were irradiated with continuous-wave (CW) and noise-amplitude-modulated 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 degrees, 21 degrees, and 28 degrees C, while noise-modulated irradiation was performed at 21 degrees 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 degrees and 21 degrees C but not at 28 degrees C. The relative decrease in resistance at 21 degrees C was half that at 8 degrees 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 microwave irradiation.

A new Doppler microwave device designed for noninvasive arterial pulse detection by assessment of arterial wall motion was clinically evaluated. Carotid pulse tracings obtained with the microwave device were compared with simultaneously obtained intra-aortic pressure pulse waves. Ease and quality of the recording were also evaluated in 25 consecutive patients undergoing echocardiography. In 92% of the patients tested, good quality carotid pulse tracings could be obtained. T1/2 values and systolic time intervals were calculated from these recordings and correlated well with the known disease states of these patients, which ranged from aortic stenosis and aortic insufficiency to chronic heart failure. Finally, microwave tracings were faithful reproductions of invasive recordings of arterial pressures when compared on the basis of left ventricular ejection times and pulse contour.

A class of new direct-contact microwave applicators has been developed for diathermy and hyperthermia applications. They consist of three concentric, circular, cylindrical tubes. The inner cylinder may serve as a port for circulating coolant to reduce surface temperature or as a port for introducing ionizing radiation in combination therapy for cancer. The coaxial waveguides formed by the inner and middle cylinders and by the middle and outer cylinders permit the propagation of TE11 and TE21 modes, respectively, for dual-beam, single-frequency use. The combinations give relatively uniform, circularly symmetric heating distributions in the tissue. Heating pattern and leakage level measurements obtained for a 10-cm-diameter dual-beam 2450±50-MHz applicator show that the maximum leakage level at a distance of 5 cm from the surface of the applicator in contact with planar fat-muscle phantoms is less than 4 mW/cm2 for a therapeutic specific absorption rate (SAR) of 235 W/kg. This value corresponds to a net forward power of 26 W. The measured VSWR is about 1.25. The width of the heating pattern is about 4 cm at a depth of 2.2 cm into the simulated muscle, where the SAR is half the maximum, and decreases slowly as the depth into the muscle increases, thus giving it a fairly uniform distribution.

Power deposition at the implant and elsewhere inside a head model during inductive thermocoagulation procedures has been studied. A quasistatic approximation is employed to estimate the absorbed power. The model consists of a small solid metallic cylinder implanted inside a homogeneous brain sphere. Results indicate that absorption by the brain is a strong function of location. The implant power absorption is at least two orders of magnitude greater than the rest of the head. The predicted magnetic field squared dependence of the implant power deposition agrees well with reported experimental observations.

The transmitted field strengths in homogeneous spherical models of human and animal heads are determined as a function of time and position, using frequency analytic techniques for an impinging pulse of Gaussian character. A relaxation process and constant conductivity are assumed for the electrical behavior of brain matter. The constant conductivity process predicts continued decrease in pulse amplitude as it advances in the head starting from the leading surface; however, the relaxation process predicts reduction only from the surface to the center. Moreover, it appears that the transmitted pulse in a spherical model of the head is always related to the time derivative of the incident radiation. Numerical results indicate that the transmitted pulse amplitude is quite small and can be estimated using the constant conductivity model.

A microwave-induced thermoelastic tissue imaging system is proposed as a new and promising imaging modality. lt possesses unique features that permit noninvasive imaging of tissue characteristics which are not identifiable by otber techniques. It uses nonionizing radiation and relies on a beam of impinging microwave energy to launch an acoustic wavefront into tissue. This thermoelastic wave of pressure propagates through the tissue and is detected by a two-dimensional array of piezoelectric transducers positioned on the body surface to give an image of the intervening tissue structure. Signals from the output of this transducer array are amplified and band-limited. A computer-controlled data acquisition system samples and converts them to digital form for further processing. A hybrid paralleljserial design for dividing the array into segments and collecting data from each segment sequentially is used. The area image sensor offers inherent geometric stability essential for reliable measurement. Error in scan position is not a conctrn, since mechanical scanning is not involved. The gray Ievel resolution is 256 after digitization, and the spatial resolution is 5 x 5 mm. These resolutions, along with a calculated signal-to-noise ratio (SNR) greater than 2500, are sufficient to provide structural information needed to render microwave-induced thermoelastic imaging a useful, noninvasive method for imaging biological tissues.

Microwave induced heating patterns in mammalian brains have been studied using spherical models through theory and experiment. Differential absorption by various portions of the brain produces local hyperthermia. Though microwave heating is extremely rapid, the precise temperature rise depends on the intensity of incident radiation and the duration of exposure. Preliminary animal experiments indicate that a temperature of 43°C is attained in 90 seconds without tissue damage, thus suggesting the possibility of using microwave differential hyperthermia as an adjunct for combination therapy for brain cancer.

The induced fields and the associated power deposition in mail exposed to HF electromagnetic (EM) fields have been investigated theoretically using spherical models. The induced electric fields inside the model exposed to either plane wave or near fields can be described adequately by a combination of quasi-static electric and magnetic induction solutions. It is shown that for field impedances less than 1200/spl pi//spl Omega/ the magnetically induced energy absorption predominates. Therefore, H fields must be measured to obtain any estimate of the hazards due to HF exposure. For a 70-kg model of man exposed to a plane wave field, the theory indicates that the time-average power absorption per unit volume is less than 2.5x10/sup -3/ mW/g for each milliwatt per square centimeter incident at 20 MHz and below. This suggests that the thermal safe-exposure levels for the HF band are many orders of magnitude in excess of the 10-mW/cm/sup 2/ level recommended for the microwave region.

Background Alcohol screening and brief intervention for unhealthy alcohol use has not been consistently delivered in primary care as part of preventive healthcare. Objective To explore whether telephone-based intervention delivered by a health educator is efficacious in reducing at-risk drinking among older adults in primary care settings. Design Secondary analyses of data from a randomized controlled trial. Participants Subjects randomized to the intervention arm of the trial (n = 310). Interventions Personalized risk reports, advice from physicians, booklet about alcohol and aging, and up to three telephone calls from a health educator. All interventions were completed before the three-month follow-up. Measurements Risk outcomes (at-risk or not at-risk) at 3 and 12 months after enrollment. Main results In univariate analyses, compared to those who remained at risk, those who achieved not at-risk outcome at 3 months were more likely to be women, Hispanic or non-white, have lower levels of education, consume less alcohol, drink less frequently, and have lower baseline number of risks. In mixed-effects logistic regression models, completing all three health educator calls increased the odds of achieving not at-risk outcome compared to not completing any calls at 3 months (OR 5.31; 95% CI 1.92–14.7; p = 0.001), but not at 12 months (OR 2.01; 95% CI 0.71–5.67; p = 0.18). Conclusions Telephone-based intervention delivered by a health educator was moderately efficacious in reducing at-risk drinking at 3 months after enrollment among older adults receiving a multi-faceted intervention in primary care settings; however, the effect was not sustained at 12 months.

The effect of the cell membrane on the scattering and absorption of light by a red blood cell is investigated theoretically using spherical models. It is shown that although the backscattering cross section varies considerably with cell membrane refractive index, cell membrane has very little to do with other scattering and absorption characteristics in general.

The complex dielectric constant of human, primate, canine, ovine, and swine brain tissues at 37°C was measured in S band using a slotted waveguide section. The in vitro measurements indicate that mammalian brains exhibit very little dispersion within the frequency range of 2.25 to 3.95 GHz. The dielectric constant was found between 30 and 35 and the conductivity varied from 1.1 to 3.1 mho/m.

Pulsed microwaves impinging on the head of animals and man produce auditory sensations. Theoretical analyses indicate a series of resonant frequencies occurring inside the head. This is supported by previous observations of characteristic oscillations recorded from the round window of mammals during pulsed microwave irradiation.

Real-time cortical and colonic temperature changes in rats irradiated for 20 min by a 2450 MHz contact radiator at the animals head were measured. Ten ?s pulses were delivered to the radiator at pulse repetition rates of 25-500 pulses/s and at energy rates of 0.3 to 1325 mW that corresponded to incident power densities of 0.18 to 875 mW/cm2. Lower power densities yielded a small cortical temperature increase below that for the body core whereas higher power densities produced a greater cortical temperature rise. Even at an incident power density as high as 875 mW/cm2 that resulted in a specific absorption rate of 70 mW/g in the brain, the cortical temperature increased by less than 3.0°C while the colonic temperature rose by 0.5°C. The cortical temperature rapidly rose during the initial transient period of irradiation. It soon became nonlinear and achieved a steady-state level around 39°C. From these observations we concluded that the brain temperature was lowered by thermoregulatory processes involving blood circulation, temperature, and mass differences between the brain and the nonirradiated body of the anesthetized rat, and furthermore, the irradiated brain received significant protection from the nonirradiated body.

Carbohydrate consumption regulates pancreatic amylase synthesis in rats. The Lieber-DeCarli 36% alcohol diet employed in chronic alcohol studies and the isocaloric control diet contain 11 and 47% of total calories from carbohydrates, respectively. Young rats fed ad libitum the 36% ethanol diet for 2 weeks obtained 1.2 g/day of carbohydrate, whereas those pair-fed with control diet received 5.8 g/day. Rats fed the 36% ethanol diet and given an intramuscular injection of a solution of 1.5 g of glucose daily for 2 weeks received twofold greater amounts of carbohydrate than saline-injected controls (2.7 versus 1.2 g). These changes in carbohydrate intake produced proportionate changes in pancreatic amylase levels. The secretory responses to cholecystokinin-octapeptide (CCK8) of acini from control and glucose-injected rats were significantly higher compared with those in the saline-injected or noninjected alcohol groups. The blood alcohol levels in glucose-injected rats were markedly reduced compared with other alcohol groups (71.7 versus 274.9 mg/dl) despite similar amounts of ethanol ingestion daily (2.4 g) in the three groups. In vitro experiments with acini from rats fed a nutritionally optimal diet revealed that high pharmacologic concentrations of ethanol, while inducing basal secretion, inhibited CCK8-stimulated amylase secretion. These results indicate that: (a) the amount of alcohol consumption does not correlate with either the levels of blood alcohol or of pancreatic amylase; (b) the carbohydrate availability in rats regulates pancreatic amylase levels despite significant levels of alcohol in blood; (c) blood alcohol levels observed in vivo may not affect synthetic and secretory processes of amylase in pancreatic acini.

From anatomical and physiological aspects, it is appropriate to consider the skin in a review of the pathophysiological consequences of exposure to RF/MW energy. Because the skin covers the entire body, it has the greatest potential for most immediate exposure; it also contains the nerve endings for thermal sensation of microwave energy and plays an important part in thermal regulation of animals.

A new technique to monitor brain edema is described that uses microwave energy to detect increased intracranial water content. By recording the phase of a transmitted microwave signal, increases in intracranial water content on the order of 1% are detected in vivo. These findings suggest that the progression of brain edema on a long-term basis can be assessed by progression of brain edema on a long-term basis can be assessed by our technique. Furthermore, phase changes related to small intracranial pressure variations are observed, indicating that the detection of pathologic pressure variations such as Traube-Hering-Mayer waves and plateau waves is possible by a noninvasive microwave technique.

In recent years, considerable interest has developed on the relationship between microwave exposure and alteration of the immune response. The immune system is a physiological defense against a large spectrum of pathogens, including bacteria, viruses, fungi, parasites, tumors, toxins from organisms, and miscellaneous chemical substances. There is considerable adaptability and redundancy in the immune system. Thus, many perturbations of the immune response may not have clinical significance (Roberts, 1983). The immune response is initiated by the introduction of a foreign substance, called an antigen. The immune system can respond specifically and nonspecifically to challenge. It can recognize nonspecifically (as nonself) an offender that the host has not encountered previously. The responsive cells can produce antigen-specific or nonspecific mediators that recruit other immunocompetent cells. In fact, recruitment of cells and so-called “arming”or activation of cells are major features of the immune response. The true immune system consists of cells that are specialized for defense, broadly classified into phagocytic cells and lymphoid cells, and cell-derived humoral substances such as antibodies and complement (Roberts, 1983; Roberts et al., 1986).

The effect of repeated exposure of C3H mice to radio frequency (RF) energy (148 MHz) was investigated. The animals were exposed to 0.5 mW/sq cm (63. 25 V/m) in a TEM exposure chamber. They were exposed for one hour a day, five days a week, beginning on the 4th to 7th day postpartum, for 10 weeks. Both RF and sham irradiated animals were weighed daily from the beginning of irradiation treatments for ten weeks, and weekly thereafter. Blood was drawn from tail vessels of the mice for analysis at 28, 70, 100, 250, 300, 360, and 600 days of age. Necropsy and histopathological examinations were performed on randomly selected animals from each group. The results indicated that the formed elements in the blood were not affected by the exposure. The means of body mass of the irradiated and control animals were comparable. No significant differences in lesion onset, incidence, prevalence, extent, or type were observed when repeated RF-exposed animals were compared with sham-control groups. The study thus suggested that at the exposure levels studies, biological effects do not occur or are not detectable from the parameters used.

Cataract is the best known of all eye diseases, but despite wide public awareness and research that has been devoted to elucidation of its etiology, knowledge of the biochemistry of the normal and pathological lens is still somewhat fragmentary. During the past 25 years, numerous investigations in animals and several surveys among human populations have been devoted to assessing the relationship between exposure to microwaves and subsequent development of cataracts. It is significant that of the many experiments on rabbits by several investigators using various techniques, power density >100 mW/cm2 for 1 hr or longer appears to be the lowest time—power threshold in the frequency range of 2450 to 10,000 Hz. In other species of animals such as dogs and nonhuman primates, the threshold for experimental microwave-induced cataract appears to be even higher. Data that are presented to indicate nonthermal, cumulative, or direct cellular effects are equivocal. If one carefully reviews the human data that are presently available, little is added to our knowledge of microwave cataractogenesis.

The efficacy of magnetic necklaces (maximum static magnetic field 0.13 T) in controlling chronic neck and shoulder pain was studied. A double-blind experiment was performed on four groups of human adults (Total N = 101). The experimental design involved 52 subjects with chronic pain (35 women, 17 men) and 49 without symptoms of pain (20 women, 29 men). They were assigned in near-equal numbers into subgroups in which magnetic or nonmagnetic necklaces were worn 24 hr. a day for 4 wk. Subjective reports and psychological testing indicated that there were no statistically significant differences among treatment subgroups before treatment. Subjects in the pain group reported a statistically significant reduction in frequency and severity of pain immediately after treatment. However, treatment condition (magnetic vs nonmagnetic) did not significantly affect subjective reports, indicating that the reported improvement is attributable to the placebo effect.

In vivo and in vitro studies of nervous tissues exposed to microwave radiation are reported. It is shown that the conduction and transmission latencies and amplitudes of evoked potentials in both the CNS of anesthetized cats, isolated nerves of cats, and ganglia of rabbits are affected by CW microwaves in a manner very similar to that of localized conduction heat. Temperature rises are always associated with any observable changes of the measured characteristics in the nervous tissues exposed to CW irradiation. The threshold of occurrence of latency changes falls between 2.5 – 5.0 W/kg of absorbed power density in the affected tissues which is about one-quarter to one-half of the normal metabolic rate of brain tissue. This absorbed power corresponds to 5 –10 mW/cm2 and 10 – 25 mW/cm2 incident upon a cat head and a human head, respectively. Pulsed microwaves of high peak intensity and low average power induce a hearing phenomenon in man. Electrophysiological studies on cats indicate that pulsed microwaves interact with mammalian auditory systems in a manner similar to that of conventional acoustic perception. A possible mechanism of microwave interaction is the acoustic energy release from rapid thermal expansion due to power absorption in the gross structure of the head.

This paper presents a new microwave antenna design with improved heating at the tip for interstitial hyperthermia and thermocoagulation. Temperature distribution patterns surrounding a conventional insulated antenna and the new sleeved coaxial slot radiator are measured in a saline phantom under transient and steady-state conditions. The new design provides an improved steady-state temperature distribution over the active region of the radiator. In contrast to the cold zone at the tip of a conventional insulated antenna the new sleeved coaxial slot antenna provides maximal (sixfold greater) power deposition at its tip.