Space efficient system for small animal, whole body microwave exposure at 1.6 GHz

A space efficient, whole body microwave exposure system for unrestrained laboratory animals utilizing a flared parallel plate waveguide is described. The system comprises an Iridium wireless signal source, signal generator, power supply and amplifier (400 W), a coax to waveguide transition, an open ended, flared parallel plate waveguide, and animal exposure area with a dipole field sensing antenna. Across the waveguide aperture the system provides uniform exposure (+/-3 dB incident RF power density) for small animals (rats, mice or hamsters) in up to 18 standard cages for housing groups of animals. Overall system dimensions are 3.6 m (d)x2.4 m (w)x1.6 m (h). Operating at 1.62 GHz, the system provided average power density of 3.7 W/m(2) in the cage area, resulting in a calculated whole body dose of 0.07 W/kg and a calculated average brain dose of 0.19 W/kg.     

Specific absorption rate in electrically coupled biological samples between metal plates

The specific absorption rate (SAR) in a biological sample irradiated by electromagnetic fields between the metal plates of a transmission line can be altered significantly by the spacing of the metal plates and the distance between neighboring samples. The SAR in spherical biological samples is calculated for a number of neighboring sample arrangements and metal-plate spacings by using the method of images and induced dipole coupling. For a decrease in metal-plate spacing, the derived equations predict an increase in SAR within a sample and a decrease in SAR with a decrease in neighboring-sample spacing. The calculations are compared with measurements made with the aid of an array of 1-in radius metal hemispheres on the lower plate of two parallel plates (thus forming an image system). The hemisphere on which measurements are taken is insulated from the metal plate and is connected via a coaxial center conductor to an HP 3582A spectrum analyzer that measures the voltage and hence the electric field intensity at the hemisphere. Measurements made at a frequency where wavelength is large compared with sample size (48 Hz) are in good agreement with calculations.     

Millimeter wave dosimetry at exposure of cell monolayers

The specific absorption rate, the amplitude of the electric field and the power flux density of millimeter waves in a cell monolayer within a well of a multi-well plate or a Petri dish are calculated. The radiation power absorption decrease in the cell layer compared to the solution is shown. The presence of the cells causes a slight increase of the electric field amplitude in the medium. The dielectric of the bottom of the well or Petri dish plays the role of a coupling layer that results in complex frequency dependences of the power reflection coefficient and the specific absorption rate.     

SAR and efficiency evaluation of a 900 MHz waveguide chamber for cell exposure

In this work we present the results of numerical and experimental dosimetry carried out for an in vitro exposure device to irradiate sample groups at 900 MHz. The cells are kept in 8 and 15 ml cell cultures, contained, respectively in T25 and T75 rectangular flasks. The dosimetric assessment of the distribution of the specific absorption rate (SAR) is performed for both the bottom of the flask and the whole volume of the sample to provide results for experiments on either the cell layer or the cell suspension. The irradiating chamber is a rectangular waveguide (WG). Different configurations are considered to assess the optimum orientation and positioning of the cell cultures inside the WG. The system performance is optimal when the electric field is parallel to the sample and the WG is terminated by a matched load. In this condition two 15 or four 8 ml cells cultures can be exposed. The efficiency (ratio between the power absorbed by the sample and the incident power) and the non-uniformity degree (ratio between the standard deviation of SAR values and the average SAR over the sample) are calculated and successfully verified through measurements of the scattering parameters and local temperature increases. In the chosen exposure configuration, the efficiency is 0.40 and the non-uniformity degree is 39% for the 15 ml samples. For the 8 ml samples, the efficiency is 0.19 and a low non-uniformity degree (15%) is found.     

Analysis of electromagnetic heating patterns inside a cryopreserved organ

Computer analysis of the induced electromagnetic field and heating distribution inside cryopreserved organs subjected to electromagnetic illumination at frequencies of 84 MHz 434 MHz and 2.45 GHz were carried out using a spherical model for the organ, with special reference to heating in a single-mode resonant cavity. The interaction between the frequency of the incident field and the size and dielectric properties of the sample was investigated. It is shown that uniform heating of organs is likely to be achieved at lower frequencies, as might be expected. However, the ratio between the power penetration depth for plane waves and the size of the organ is not a sufficient basis on which to judge quantitatively the uniformity of the power absorption. Hot or cold spots can occur within the organ even when this ratio is greater than unity; the wavelength in the material is also an important factor. The results from this study indicate that the use of a resonant cavity as a heating applicator has advantages over plane-wave illumination. A sharp upper limit can be set to the frequency suitable for rapid and uniform heating of a given organ.     

Simple method to measure power density entering a plane biological sample at millimeter wavelengths

A simple method for measuring microwave power density is described. It is applicable to situations where exposure of samples in the near field of a horn is necessary. A transmitted power method is used to calibrate the power density entering the surface of the sample. Once the calibration is available, the power density is known in terms of the incident and reflected powers within the waveguide. The calibration has been carried out for liquid samples in a quartz cell. Formulas for calculating specific absorption rate (SAR) are derived in terms of the power density and the complex dielectric constant of the sample. An error analysis is also given.     

Determination of the induced ELF electric field distribution in a two layer in vitro system simulating biological cells in nutrient solution

In-vitro studies of biological effects of electromagnetic fields are often conducted with cultured cells either in suspension or grown in a monolayer. In the former case, the exposed medium can be assumed to be homogeneous; however, eventually the cells settle to the bottom of the container forming a two layer system with different dielectric and conductive properties. In the present work the effect of this separation on the electric field distribution is calculated and experimentally measured at selected positions for a commonly used exposure configuration. The settled cell suspension is modeled by a well-defined two layer system placed in a rectangular container with the base of the container parallel to the direction of the magnetic field. Theoretical calculations based on numerical techniques are done for various two layer systems with different conductivities in each layer. The agreement between the theoretical calculations and the experimental measurements is within ± 1.5 mV/m, or 10% of the maximum induced field when the conductivity of the lower layer is ten times that of the upper layer. This result is well within experimental error. When the thickness of one of the layers is small compared to the thickness of the other layer, it is found that the electric field distribution is essentially that of the homogeneous case. The latter situation corresponds to a typical cell exposure condition. © 1993 Wiley-Liss, Inc.     

Theoretical evaluation of the distributed power dissipation in biological cells exposed to electric fields

The paper deals with the power dissipation caused by exposure of biological cells to electric fields of various frequencies. With DC and sub-MHz AC frequencies, power dissipation in the cell membrane is of the same order of magnitude as in the external medium. At MHz and GHz frequencies, dielectric relaxation leads to dielectric power dissipation gradually increasing with frequency, and total power dissipation within the membrane rises significantly. Since such local increase can lead to considerable biochemical and biophysical changes within the membrane, especially at higher frequencies, the bulk treatment does not provide a complete picture of effects of an exposure. In this paper, we theoretically analyze the distribution of power dissipation as a function of field frequency. We first discuss conductive power dissipation generated by DC exposures. Then, we focus on AC fields; starting with the established first-order model, which includes only conductive power dissipation and is valid at sub-MHz frequencies, we enhance it in two steps. We first introduce the capacitive properties of the cytoplasm and the external medium to obtain a second-order model, which still includes only conductive power dissipation. Then we enhance this model further by accounting for dielectric relaxation effects, thereby introducing dielectric power dissipation. The calculations show that due to the latter component, in the MHz range the power dissipation within the membrane significantly exceeds the value in the external medium, while in the lower GHz range this effect is even more pronounced. This implies that even in exposures that do not cause a significant temperature rise at the macroscopic, whole-system level, the locally increased power dissipation in cell membranes could lead to various effects at the microscopic, single-cell level.     

Numerical simulation of the effect of superparamagnetic nanoparticles on microwave rewarming of cryopreserved tissues

In this study, the microwave rewarming process of cryopreserved samples with embedded superparamagnetic (SPM) nanoparticles was numerically simulated. The Finite Element Method (FEM) was used to calculate the coupling of the electromagnetic field and the temperature field in a microwave rewarming system composed of a cylindrical resonant cavity, an antenna source, and a frozen sample phantom with temperature-dependent properties. The heat generated by the sample and the nanoparticles inside the electromagnetic field of the microwave cavity was calculated. The dielectric properties of the biological tissues were approximated using the Debye model, which is applicable at different temperatures. The numerical results showed that, during the rewarming process of the sample phantom without nanoparticles, the rewarming rate was 29.45 °C/min and the maximum temperature gradient in the sample was 3.58 °C/mm. If nanoparticles were embedded in the sample, and the cavity power was unchanged, the rewarming rate was 47.76 °C/min and the maximum temperature gradient in the sample was 1.64 °C/mm. In the presence of SPM nanoparticles, the rewarming rate and the maximum temperature gradient were able to reach 20.73 °C/min and 0.68 °C/mm at the end of the rewarming under the optimized cavity power setting, respectively. The ability to change these temperature behaviors may prevent devitrification and would greatly diminish thermal stress during the rewarming process. The results indicate that the rewarming rate and the uniformity of temperature distribution are increased by nanoparticles. This could be because nanoparticles generated heat in the sample homogeneously and the time-dependent parameters of the sample improved after nanoparticles were homogeneously embedded within it. We were thus able to estimate the positive effect of SPM nanoparticles on microwave rewarming of cryopreserved samples.     

Further investigations concerning the applicability of laser analysis in quantitative histochemistry

Summary Further investigations on the applicability of the laser technique for qantitative purposes in histochemistry were conducted. Special attention has been paid to the relationship between the volume of the crater burnt out in the tissue by laser ray treatment and the photometric readings of the spectral bands. A statistical evalution of the measurements of crater volumes for quantitative histochemistry as well as determination of the error of the former method used and previously described (Kozik et al., 1970b) have been performed. Special agar standards containing known amounts of Pb(NO₃)₂ and appropriately prepared photographic plates were used. From the results obtained it appeared that the variances calculated for the differences between density of spectral bands for the Pb present in the investigated sample and the density of the respective band for the Ag present in the photographic plate fall in the range of between 14.1 and 19.7%, whereas the error of the method in which the density of spectral bands was related to the crater volumes covered a range from 3.45–7.7%.Based on the discussion of results the authors conclude that both methods of acP assay in histological slices by means of laser microanalysis may be successfully used.     

Near-field dosimetry for in vitro exposure of human cells at 60 GHz

Due to the expected mass deployment of millimeter‐wave wireless technologies, thresholds of potential millimeter‐wave‐induced biological and health effects should be carefully assessed. The main purpose of this study is to propose, optimize, and characterize a near‐field exposure configuration allowing illumination of cells in vitro at 60 GHz with power densities up to several tens of mW/cm². Positioning of a tissue culture plate containing cells has been optimized in the near‐field of a standard horn antenna operating at 60 GHz. The optimal position corresponds to the maximal mean‐to‐peak specific absorption rate (SAR) ratio over the cell monolayer, allowing the achievement of power densities up to 50 mW/cm² at least. Three complementary parameters have been determined and analyzed for the exposed cells, namely the power density, SAR, and temperature dynamics. The incident power density and SAR have been computed using the finite‐difference time‐domain (FDTD) method. The temperature dynamics at different locations inside the culture medium are measured and analyzed for various power densities. Local SAR, determined based on the initial rate of temperature rise, is in a good agreement with the computed SAR (maximal difference of 5%). For the optimized exposure setup configuration, 73% of cells are located within the ±3 dB region with respect to the average SAR. It is shown that under the considered exposure conditions, the maximal power density, local SAR, and temperature increments equal 57 mW/cm², 1.4 kW/kg, and 6 °C, respectively, for the radiated power of 425 mW. Bioelectromagnetics 33:55–64, 2012. © 2011 Wiley Periodicals, Inc.     

The effect of excluding taxa with low abundances or taxa with small distribution ranges on ecological assessment

The present study aims to investigate whether taxa with a small distribution range or taxa with low abundances indicate specific habitats or a high ecological quality and what the effect is if these taxa are excluded from ecological assessment. We compared autecological features between stream dwelling taxa with a mean abundance >5 individuals per sample and a mean abundance ≤5 individuals per sample as well as between taxa with a small distribution range and taxa with a large distribution range. The number of rare taxa (either with a small distribution range or with low abundances) in a sample was related to the ecological quality classes. To test the effect of exclusion of rare taxa we constructed 8 data sets all including 142 samples of Dutch lowland streams. From each data set we stepwise excluded taxa that had low abundances or taxa that were known to be restricted in their distribution range. With help of the AQEM assessment software we calculated the final ecological quality classes and the metrics that were included in the multimetric for the original data and the 8 selected data sets. Autecological features of the taxa within the different selections showed that taxa with small distribution ranges were often running water taxa, living on stones and gravel and indicating oligosaprobic water conditions in contrast to taxa that had a large distribution range. There were only small differences between taxa with low and high abundances. However, current velocity preference was lower for taxa with abundance ≤5 individuals per sample, saprobic values were higher and scores for typical stream habitats, such as lithal, psammal and akal were lower compared to high abundant taxa. If taxa with low abundances were excluded a higher ecological quality class was achieved in most cases, while excluding taxa with a small distribution range resulted in lower ecological quality classes. In conclusion, excluding taxa with a small distribution range led to worse ecological quality classes because these taxa have special autecological features that often indicate natural streams. On the other hand, excluding taxa with low abundances resulted in higher ecological quality classes because these taxa indicate more disturbed situations and because the number of taxa per sample was strongly reduced. Although the documentation of rare taxa (either with low abundances or with small distribution ranges) is often time and cost-intensive regarding field work, laboratory work, data processing, and analyses, the indicative power of these taxa for natural circumstances is essential and therefore rare taxa should be included in ecological assessment studies.     

The effect of a variable dielectric coefficient and finite ion size on Poisson-Boltzmann calculations of DNA-electrolyte systems.

The results of variable dielectric coefficient Poisson-Boltzmann calculations of the counter-ion concentration in the vicinity of an all-atom model of the B-form of DNA are presented with an emphasis on the importance of spatial variations in the dielectric properties of the solvent, particularly at the macro-ion-solvent interface. Calculations of the distribution of hard-sphere electrolyte ions of various dimensions are reported. The presence of a dielectric boundary significantly increases the magnitude of the electrostatic potential with a concomitant increase in the accumulation of small counter-ions in the groove regions of DNA. Because ions with radii greater than 2 A have restricted access to the minor groove, the effect there is less significant than it is within the major groove. Changes in the dielectric coefficient for the electrolyte solution, allowing variation from 10 to 25, 40, 60, and 78.5 within the first 7.4 A of the surface of DNA, substantially increases the calculated surface concentration of counter-ions of all sizes. A lower dielectric coefficient near the macro-ion surface also tends to increase the counter-ion density in regions where the electrostatic potential is more negative than -kT. Regardless of the choice of dielectric coefficient, the number of ions in regions where the electrostatic potential is less than -kT remains the same for 0.153 M added 1-1 monovalent electrolyte as for the case without added salt.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of spatial inhomogeneity in dielectric permittivity on DNA double layer formation

In solutions of tetramethylammonium (TMA+) DNA (double stranded) without added low-molecular-weight salt, the counterion radial density is calculated using the cylindrical Poisson-Boltzmann equation with a distance-dependent quasimacroscopic dielectric permittivity. Comparisons with small-angle neutron scattering data indicate that any inhomogeneity in dielectric permittivity is confined to one or two solvent layers from the DNA surface. At least for TMA+, which may be too large to penetrate the grooves of DNA to any significant extent, dielectric inhomogeneity modeled in this way has no detectable effect on the radial distribution.     

Multipactor discharge on a dielectric at different inclination angles of the microwave electric field relative to the dielectric surface

Multipactor discharge on a dielectric is studied numerically and analytically for different inclination angles α of the microwave electric field with respect to the dielectric surface. The power absorbed in the discharge is calculated, and analytic estimates for the average current density of secondary electrons and the average energy of electrons bombarding the dielectric surface are obtained as functions of the angle α and the electron oscillation energy in the microwave field. It is found that the dependence of the absorbed power on the inclination angle of the external microwave field has a minimum at α ～20°–30°.     

Real-time measurements of quartz erosion in experiments modeling heat loads on divertor plates during disruption in tokamaks

Time-resolved measurements of quartz erosion are carried out to determine the density of the energy flux incident onto the sample surface. These data are needed to create a reliable code describing the interaction of a thermonuclear plasma with a solid surface. Experiments were performed in the 2MK-200 facilityunder the program of modeling heat loads on divertor plates during disruptions in tokamaks. A 10-mm-thick plate of fused quartz was exposed to a high-temperature deuterium-plasma stream with the temperature T _i +T _e ≤1 keV, density (5–10)×10¹⁵ cm⁻³ β=0.25, energy density up to 200 J/cm², and power density ∼10 MW/cm². It is shown that the quartz erosion begins almost immediately after the stream reaches the surface. The eroded material shields the quartz surface from further destruction. Under the given experimental conditions, the integral shielding factor (the ratio of the stream energy to the energy reaching the surface) was rather high (about seventeen). As a result, at a stream energy density of ∼150 J/cm², the total erosion depth was about 0.75 μm over 35 μs. Based on the measured time dependence of the erosion depth and the reference data on the thermal conductivity of the fused quartz, the power density incident onto the quartz sample was numerically calculated. __________ Translated from Fizika Plazmy, Vol. 27, No. 3, 2001, pp. 243–250. Original Russian Text Copyright ? 2001 by Arkhipov, Bakhtin, Vasenin, Zhitlukhin, Safronov, Toporkov.     

Approaches for sampling the twospotted spider mite (Acari: Tetranychidae) on clementines in Spain

Tetranychus urticae Koch (Acari: Tetranychidae) is an important pest of clementine mandarins, Citrus reticulata Blanco, in Spain. As a first step toward the development of an integrated crop management program for clementines, dispersion patterns of T. urticae females were determined for different types of leaves and fruit. The study was carried out between 2001 and 2003 in different commercial clementine orchards in the provinces of Castelló and Tarragona (northeastern Spain). We found that symptomatic leaves (those exhibiting typical chlorotic spots) harbored 57.1% of the total mite counts. Furthermore, these leaves were representative of mite dynamics on other leaf types. Therefore, symptomatic leaves were selected as a sampling unit. Dispersion patterns generated by Taylor's power law demonstrated the occurrence of aggregated patterns of spatial distribution (b > 1.21) on both leaves and fruit. Based on these results, the incidence (proportion of infested samples) and mean density relationship were developed. We found that optimal binomial sample sizes for estimating low populations of T. urticae on leaves (up to 0.2 female per leaf) were very large. Therefore, enumerative sampling would be more reliable within this range of T. urticae densities. However, binomial sampling was the only valid method for estimating mite density on fruit.     

Monitoring changes in lichen resources for range management purposes in reindeer husbandry

Mat-forming lichens are important as food source for reindeer during the winter, and thus a vital resource to manage in reindeer husbandry. In this paper we suggest a method for monitoring of changes in lichen height with the purpose to early detect changes in lichen abundance in reindeer grazing areas. The method is intended for measuring geographically uniform lichen areas, evenly used for reindeer grazing. We analysed spatial variations in lichen height at the meter and 100 m scales, and calculated sample size requirements, and estimated effects of forest density and age, lichen moisture and lichen density on lichen height, and assessed the correspondence between lichen height and biomass. The variation in lichen height differed considerably between sites and, hence, the required sample size to detect a 5 mm change in lichen height with a power of 0.95 ranged from 200 to 2000, depending on the standard deviation of measured heights. Based on the autocorrelation in lichen height found between adjacent measurement points, a minimum distance of 4 m between measurement points is also recommended. Lichen height was significantly affected by lichen moisture, and the results suggest that this effect of moisture might vary with lichen density. Lichen height varied spatially within the study sites, and the spatial variations were partly caused by forest age and density. Thus, gradual changes in the forest characteristics are likely to alter the spatial variation in lichen height and it is therefore important to regularly re-evaluate the locations of measurement points within the monitored area. This study provides suggestions for a variable that could be used as an indicator of changes in the lichen resource, and aspects that should be considered when designing a monitoring program. The accuracy of detecting changes depends on the monitoring efforts, i.e. the number and distribution of measurement points and how often an area is monitored. In conclusion, our results indicate that measurements of lichen height have considerable potential for monitoring of changes in lichen resources within reindeer husbandry.     

Consequences for seed distributions of intra-crop variation in wing-loading of wind-dispersed species

We used a computer simulation to quantify how intra-crop variation in wing-loading in a wind-dispersed species affects the seed distribution around a parent plant. We used a data set of seed distributions generated from a previous field study using artificial fruits varying in seed mass or fruit area dispersed from a tower into a tropical forest. For this study, the spatial distribution from each hypothetical parent's fruit crop of 1000 was calculated by randomly drawing locations of dispersed fruits from the previous data base. Three parents with contrasting fruit crops were used to test two hypotheses: 1) Increasing within-parent variance in wing-loading (= weight/area), while maintaining the mean, will lead to an increase in the area and uniformity of the seed distribution, without changing the mean dispersal distance. 2) Decreasing within-parent mean wing-loading, (which also decreases variance), will lead to an increase in mean dispersal distance, area, and uniformity of the seed distribution. The hypotheses were tested under four wind speeds.Increasing variance in wing-loading resulted in increasing the area and uniformity of density of the seed distribution without changing mean dispersal distance. Decreasing mean and variance in wing-loading resulted in increasing the area and uniformity of density of the seed distribution, as well as increasing the mean dispersal distance. Similar results occurred whether the differences in wing-loading arose by altering seed mass or fruit area. The effect of wind speed was consistently greater than the effect of parent. Generally, the same pattern of parent effects on seed distributions occurred, regardless of wind condition.The effects on seed distributions differed for alterations in mean versus variance, specifically in whether mean dispersal distance was increased. How selection may act on intra-crop mean and variance in wing-loading will depend on additional factors, e.g. the relative importance of distance, area, and density on seedling recruitment and the relative costs for crop size and seedling establishment of making fruit crops of a given mean and variance.