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W F Pickard

Publications and source records attributed to W F Pickard.

At least 19 recordsLinked to original sources
PubMed2000

Experimental and numerical determination of SAR distributions within culture flasks in a dielectric loaded radial transmission line.

The effect of dielectric loading on the cell layer specific absorption rate (SAR) within a T-75 culture flask being irradiated within a transverse electromagnetic (TEM) cell was studied both experimentally and numerically. Direct thermal measurements of a T-75 containing 40 mL of culture medium and resting upon a 3-mm-thick slab of alumina ceramic (epsilon r = 9.6) revealed that, compared to the same flask resting upon a foam slab (epsilon r = 1.0) of the same thickness, the average SAR at the cell layer was increased roughly fourfold. This fourfold increase is significant experimentally because it allows biologists to perform experiments over a larger range of SAR values needed to determine possible dose-response curves without the costs and difficulties of a fourfold increase in amplifier power. Finite-difference time-domain (FDTD) simulations of the SAR distribution were in good quantitative agreement with the experimental measurements. It is concluded that FDTD modeling can be a cost effective and scientifically acceptable means of obviating the thermal measurement of SAR.

Absorption↗
PubMed1999

The radial transmission line as a broad-band shielded exposure system for microwave irradiation of large numbers of culture flasks.

The problem of simultaneously exposing large numbers of culture flasks at nominally equivalent incident power densities and with good thermal control is considered, and the radial transmission line (RTL) is proposed as a solution. The electromagnetic design of this structure is discussed, and an extensively bench-tested realization is described. Referred to 1 W of net forward power, the following specific absorption rate (SAR) data were obtained: at 835.62 MHz, 16.0+/-2.5 mW/kg (mean+/-SD) with range (11-22); at 2450 MHz, 245+/-50 mW/kg with range (130-323). Radio-frequency interference from an RTL driven at roughly 100 W is so low as to be compatible with a cellular base station only 500 m distant. To avoid potential confounding by temperature differences among as many as 144 T-75 flasks distributed over 9 RTLs (six irradiates and three shams), temperature within all flasks was controlled to 37.0+/-0.3 degrees C. Experience with over two years of trouble-free operation suggests that the RTL offers a robust, logistically friendly, and environmentally satisfactory solution to the problem of large-scale in vitro experiments in bioelectromagnetics.

Absorption↗
PubMed1999

Simplified model and measurement of specific absorption rate distribution in a culture flask within a transverse electromagnetic mode exposure system.

In vitro experiments in bioelectromagnetics frequently require the determination of specific absorption rate (SAR) within a layer of cells on the bottom of a culture flask when the SAR has rapid spatial variation both horizontally within the cell layer and vertically in the medium bathing the cells. This problem has only recently been treated in the literature; and it is here approached differently for another irradiation system. It is shown that a simple two-dimensional frequency-domain guided-wave treatment yields results qualitatively comparable to those of more computationally intensive three-dimensional time-domain free-field scattering treatments. The problem of inferring local SARs from temperature-vs.-time curves is shown to be seriously confounded by thermal diffusion; and specific analytic and numerical results are presented to aid in understanding this effect. A novel experimental technique is introduced for measuring millikelvin temperature offsets with subsecond resolution, and illustrative experimental data are presented. Finally, present experimental and theoretical uncertainties are considered; and it is pessimistically asserted that, in a culture flask where spatial SAR variation is rapid, point SAR measurements by thermal methods may be in error by as much as +/- 3 dB. More reliable thermal determinations will require extreme care, challenging technological innovations, or both.

Cells, Cultured↗
PubMed1999

Compact shielded exposure system for the simultaneous long-term UHF irradiation of forty small mammals. II. Dosimetry.

A four-antenna collinear array in an electromagnetically shielded chamber was designed and constructed to preferentially irradiate the brains of a large number of small mammals using cellular telephony microwave signals. Ten animals in special restrainers were positioned symmetrically around a centrally located antenna. These restrainers are resting on a circular structure made of acrylic plastic called a "carousel." Four carousels are stacked vertically, forming the array, inside a microwave anechoic chamber called a "chamberette." (Details of the design of this irradiator and of a 12-chamberette irradiation facility are given in a previous article.) In this article, the dosimetry on rats is reported. Both thermometric and thermographic measurements were performed. The average specific absorption rate (SAR) in brain tissue measured thermometrically was 0.85+/-0.34 W/kg per watt of net input power into the radiating antenna. This range agrees with the SAR levels reported in the literature for cellular telephones. Thermographic evaluation using splittable phantoms showed that most of the energy absorbed by the rats is concentrated in and around the brain. Moreover, it was found that the SAR in brain tissue can vary considerably for rats of similar weights, depending on position of the rats' heads inside the restrainers, and that there exists a significant dependence of SAR on animal weight. These variations may be of importance in the interpretation of results of lifelong studies. The data presented clearly show that the chamberette is, dosimetrically, a suitable irradiation system for electromagnetic bioeffects studies in the cellular communication frequency range, especially when a large number of laboratory animals is required.

Animals↗
PubMed1999

Proto-oncogene mRNA levels and activities of multiple transcription factors in C3H 10T 1/2 murine embryonic fibroblasts exposed to 835.62 and 847.74 MHz cellular phone communication frequency radiation.

This study was designed to determine whether two differently modulated radiofrequencies of the type generally used in cellular phone communications could elicit a general stress response in a biological system. The two modulations and frequencies studied were a frequency-modulated continuous wave (FMCW) with a carrier frequency of 835.62 MHz and a code division multiple-access (CDMA) modulation centered on 847.74 MHz. Changes in proto-oncogene expression, determined by measuring Fos, Jun, and Myc mRNA levels as well as by the DNA-binding activity of the AP1, AP2 and NF-kappaB transcription factors, were used as indicators of a general stress response. The effect of radiofrequency exposure on proto-oncogene expression was assessed (1) in exponentially growing C3H 10T 1/2 mouse embryo fibroblasts during their transition to plateau phase and (2) during transition of serum-deprived cells to the proliferation cycle after serum stimulation. Exposure of serum-deprived cells to 835.62 MHz FMCW or 847.74 MHz CDMA microwaves (at an average specific absorption rate, SAR, of 0.6 W/kg) did not significantly change the kinetics of proto-oncogene expression after serum stimulation. Similarly, these exposures did not affect either the Jun and Myc mRNA levels or the DNA-binding activity of AP1, AP2 and NF-kappaB in exponential cells during transit to plateau-phase growth. Therefore, these results suggest that the radiofrequency exposure is unlikely to elicit a general stress response in cells of this cell line under these conditions. However, statistically significant increases (approximately 2-fold, P = 0.001) in Fos mRNA levels were detected in exponential cells in transit to the plateau phase and in plateau-phase cells exposed to 835.62 MHz FMCW microwaves. For 847.74 MHz CDMA exposure, the increase was 1.4-fold (P = 0.04). This increase in Fos expression suggests that expression of specific genes could be affected by radiofrequency exposure.

Animals↗
PubMed1999

Cell phones and cancer: what is the evidence for a connection?

There have been allegations in the media and in the courts that cell phones and other types of hand-held transceivers are a cause of cancer. There have also been numerous public objections to the siting of TV, radio and cell phone transmission facilities because of a fear of cancer induction. A recent publication in Radiation Research by Repacholi et al. (147, 631-640, 1997) which suggests that exposure to radiofrequency (RF) radiation may increase lymphoma incidence in mice has contributed to this controversy. The goal of this review is to provide biomedical researchers a brief overview of the existing RF radiation-cancer studies. This article begins with a brief review of the physics and technology of cell phones. It then reviews the existing epidemiological studies of RF radiation, identifying gaps in our knowledge. Finally, the review discusses the cytogenetics literature on RF radiation and the whole-animal RF-radiation carcinogenesis studies. The epidemiological evidence for an association between RF radiation and cancer is found to be weak and inconsistent, the laboratory studies generally do not suggest that cell phone RF radiation has genotoxic or epigenetic activity, and a cell phone RF radiation-cancer connection is found to be physically implausible. Overall, the existing evidence for a causal relationship between RF radiation from cell phones and cancer is found to be weak to nonexistent.

Animals↗
PubMed1999

On the assumption of negligible heat diffusion during the thermal measurement of a nonuniform specific absorption rate.

The problem of measuring a spatially varying specific absorption rate (SAR) by thermal techniques is treated both analytically and numerically. It is shown that, unless the measurement is attempted at an inflection point of the SAR distribution, it will be confounded by thermal diffusion within the medium. Rules of thumb are provided to enable the experimenter to gauge the thermal conduction contributions (i.e. error) to the thermally determined SAR near a spatial extremum. The simplest of these is that the width t(m) [s] of the time window, over which temperature variation associated with SAR is measured, should satisfy the inequality t(m) </approximately alpha(2)/pi(2)D, where alpha [m] is a characteristic length scale of the spatial variation of the SAR and D [m(2)/s] is the thermal diffusivity of the medium. The above considerations are valid, independent of the source of the deposited energy.

Absorption↗
PubMed1999

Radiofrequency electromagnetic fields have no effect on the in vivo proliferation of the 9L brain tumor.

The intracranial 9L tumor model was used to determine if exposure to a radiofrequency (RF) electromagnetic field similar to those used in cellular telephone has any effects on the growth of a central nervous system tumor. Fischer 344 rats implanted with different numbers of 9L gliosarcoma cells were exposed to 835.62 MHz frequency-modulated continuous wave (FMCW) or 847.74 MHz code division multiple access (CDMA) RF field with nominal slot-average specific absorption rates in the brain of 0.75 +/- 0.25 W/kg. The animals were exposed to the RF field for 4 h a day, 5 days a week starting 4 weeks prior to and up to 150 days after the implantation of tumor cells. Among sham-exposed animals injected with 2 to 10 viable cells (group 1), the median survival was 70 days, with 27% of the animals surviving at 150 days. The median survival length and final survival fraction for animals injected with 11 to 36 viable cells (group 2) were 52 days and 14%, respectively, while the values for those injected with 37 to 100 cells (group 3) were 45 days and 0%. The animals exposed to CDMA or FMCW had similar survival parameters, and the statistical comparison of the survival curves for each of the groups 1, 2 and 3 showed no significant differences compared to sham-exposed controls.

Animals↗
PubMed1998

DNA damage in rat brain cells after in vivo exposure to 2450 MHz electromagnetic radiation and various methods of euthanasia.

The present study was done to confirm the reported observation that low-intensity acute exposure to 2450 MHz radiation causes DNA single-strand breaks (Lai and Singh, Bioelectromagnetics 16, 207-210, 1995). Male Sprague-Dawley rats weighing approximately 250 g were irradiated with 2450 MHz continuous-wave (CW) microwaves for 2 h at a specific absorption rate of 1.2 W/kg in a cylindrical waveguide system (Guy et al., Radio Sci. 14, 63-74, 1979). There was no associated rise in the core body temperature of the rats. After the irradiation or sham treatments, rats were euthanized by either CO2 asphyxia or decapitation by guillotine (eight pairs of animals per euthanasia group). After euthanasia the brains were removed and immediately immersed in cold Ames medium and the cells of the cerebral cortex and the hippocampus were dissociated separately and subjected to the alkaline comet assay. Irrespective of whether the rats were euthanized by CO2 asphyxia or decapitated by guillotine, no significant differences were observed between either the comet length or the normalized comet moment of cells from either the cerebral cortex or the hippocampus of sham-treated rats and those from the irradiated rats. However, the data for the rats asphyxiated with CO2 showed more intrinsic DNA damage and more experiment-to-experiment variation than did the data for rats euthanized by guillotine. Therefore, the guillotine method of euthanasia is the most appropriate in studies relating to DNA damage. Furthermore, we did not confirm the observation that DNA damage is produced in cells of the rat cerebral cortex or the hippocampus after a 2-h exposure to 2450 MHz CW microwaves or at 4 h after the exposure.

Animals↗
PubMed1998

A compact shielded exposure system for the simultaneous long-term UHF irradiation of forty small mammals: I. Electromagnetic and environmental design.

To carry out in vivo studies of the possible health effects of radiation from cellular telephone handsets, it is necessary to expose large numbers of small mammals at realistic power densities, modulations, and frequencies. Because even microwatt leakage could compromise the local cellular system, extreme care in shielding is required. Experimental logistics dictate, however, that the irradiated animals be easily accessed and that it be possible to irradiate them in small groups, while other groups are being loaded into or unloaded from the irradiators. This problem has been resolved by exposing the animals in aluminum-sheathed rectangular parallelepipeds, lined with microwave absorber and having doors that can be opened readily. Inside each of these microwave anechoic "chamberettes" is a vertical, four-element collinear array of dipole antennas; and around each antenna, 10 animal restrainers can be arranged like spokes on a wheel. The system has worked efficiently in studies of up to 480 rats. There is negligible coupling between antennas, and back reflection at an antenna's feed line is down 7-9 dB. Received CDMA power at the local base station is below the receiver's noise floor. Interior illumination reinforces the rats' diurnal rhythms, and the rats sleep during irradiation. Experimental logistics are excellent. In this paper, the irradiator design is presented.

Absorption↗
PubMed1997

Measurement of DNA damage after exposure to 2450 MHz electromagnetic radiation.

Recent reports suggest that exposure to 2450 MHz electromagnetic radiation causes DNA single-strand breaks (SSBs) and double-strand breaks (DSBs) in cells of rat brain irradiated in vivo (Lai and Singh, Bioelectromagnetics 16, 207-210, 1995; Int. J. Radiat. Biol. 69, 513-521, 1996). Therefore, we endeavored to determine if exposure of cultured mammalian cells in vitro to 2450 MHz radiation causes DNA damage. The alkaline comet assay (single-cell gel electrophoresis), which is reportedly the most sensitive method to assay DNA damage in individual cells, was used to measure DNA damage after in vitro 2450 MHz irradiation. Exponentially growing U87MG and C3H 10T1/2 cells were exposed to 2450 MHz continuous-wave (CW) radiation in specially designed radial transmission lines (RTLs) that provided relatively uniform microwave exposure. Specific absorption rates (SARs) were calculated to be 0.7 and 1.9 W/kg. Temperatures in the RTLs were measured in real time and were maintained at 37 +/- 0.3 degrees C. Every experiment included sham exposure(s) in an RTL. Cells were irradiated for 2 h, 2 h followed by a 4-h incubation at 37 degrees C in an incubator, 4 h and 24 h. After these treatments samples were subjected to the alkaline comet assay as described by Olive et al. (Exp. Cell Res. 198, 259-267, 1992). Images of comets were digitized and analyzed using a PC-based image analysis system, and the "normalized comet moment" and "comet length" were determined. No significant differences were observed between the test group and the controls after exposure to 2450 MHz CW irradiation. Thus 2450 MHz irradiation does not appear to cause DNA damage in cultured mammalian cells under these exposure conditions as measured by this assay.

Animals↗
PubMed1997

Measurement of DNA damage after exposure to electromagnetic radiation in the cellular phone communication frequency band (835.62 and 847.74 MHz).

Mouse C3H 10T1/2 fibroblasts and human glioblastoma U87MG cells were exposed to cellular phone communication frequency radiations to investigate whether such exposure produces DNA damage in in vitro cultures. Two types of frequency modulations were studied: frequency-modulated continuous-wave (FMCW), with a carrier frequency of 835.62 MHz, and code-division multiple-access (CDMA) centered on 847.74 MHz. Exponentially growing (U87MG and C3H 10T1/2 cells) and plateau-phase (C3H 10T1/2 cells) cultures were exposed to either FMCW or CDMA radiation for varying periods up to 24 h in specially designed radial transmission lines (RTLs) that provided relatively uniform exposure with a specific absorption rate (SAR) of 0.6 W/kg. Temperatures in the RTLs were monitored continuously and maintained at 37 +/- 0.3 degrees C. Sham exposure of cultures in an RTL (negative control) and 137Cs gamma-irradiated samples (positive control) were included with every experiment. The alkaline comet assay as described by Olive et al. (Exp. Cell Res. 198, 259-269, 1992) was used to measure DNA damage. No significant differences were observed between the test group exposed to FMCW or CDMA radiation and the sham-treated negative controls. Our results indicate that exposure of cultured mammalian cells to cellular phone communication frequencies under these conditions at an SAR of 0.6 W/kg does not cause DNA damage as measured by the alkaline comet assay.

Animals↗
PubMed1995

Trivial influences: a doubly stochastic Poisson process model permits the detection of arbitrarily small electromagnetic signals.

If a weak, exogenous, extremely low-frequency (ELF) electric or magnetic field is to produce biological sequelae, then there must exist averaging sufficient to lift some primary effect of that field above the endogenous stochastic variations of the biological system. One way in which a field could accomplish this is by changing the intensity of some stochastic operation that controls an important and not trivially reversible biological transformation. In this paper, this operation is modeled as a doubly stochastic Poisson process. It is then shown, first, that (in theory) even a minuscule exogenous influence might appreciably shift the incidence of a sufficiently rare transformation and, second, that this shift might be observable if a trial were allowed to run long enough over a sufficiently large population of exposed entities.

Algorithms↗
PubMed1986

A theory of the saturable ohmic channel.

Let the passage of type-lambda ions through a type-sigma channel be determined only by the ionic valence z lambda, by the thermal energy kT, by the ion concentrations on the out- and in- sides [S lambda]o and [S lambda]i, by the inside with-respect-to outside voltage of the channel E, by a single descriptor of channel saturation [S sigma lambda], and by a single descriptor (permeance) the ease of channel transit P sigma lambda. Then, if the channel current i sigma lambda, due to lambda-ions is ohmic about the Nernst potential, is a function of the sum ([S lambda]o + [S lambda]i) and not of [S lambda]o or [S lambda]i independently, and saturates in a Michaelis-Menten fashion, it follows that (Formula: see text) where F is the Faraday constant.

Biological Transport↗
PubMed1985

Low-power 2.45-GHz microwave radiation affects neither the vacuolar potential nor the low frequency excess noise in single cells of characean algae.

Single, giant cells of the eukaryotic green algae Chara braunii and Nitella flexilis were subjected to short-, intermediate-, and long-term irradiations with 2.45-GHz microwaves. A search was carried out for radiation-correlated shifts (i) in both the dc level and the rms low-frequency excess noise of the vacuolar potential and (ii) in the membrane resistivity. No reliable shifts were observed, either in normal cells or in cells subjected to reduced temperatures or the poison ethacrynic acid.

Chlorophyta↗
PubMed1984

Offset of the vacuolar potential of Characean cells in response to electromagnetic radiation over the range 250 Hz-250 kHz.

Measurements were made of the small, transient offsets of vacuolar potential produced in single cells of Nitella flexilis and Chara braunii by isolated bursts of audio frequency electromagnetic radiation. The offsets increased in magnitude with decreasing frequency of the electromagnetic radiation and, below about 6 kHz, seemed to approach a low-frequency asymptote. This frequency dependence for the offset is shown to be in accordance with a previously developed model in which the incident radiation is weakly rectified by the cell's membrane system.

Animals↗