New head models extracted from thermal infrared (IR) images for dosimetry computations

In electromagnetic dosimetry, anatomical human models are commonly obtained by segmentation of magnetic resonance imaging or computed tomography scans. In this paper, a human head model extracted from thermal infrared images is examined in terms of its applicability to specific absorption rate (SAR) calculations. Since thermal scans are two-dimensional (2D) representation of surface temperature, this allows researchers to overcome the extensive computational demand associated with 3D simulation. The numerical calculations are performed using the finite-difference time-domain method with mesh sizes of 2 mm at 900 MHz plane wave irradiation. The power density of the incident plane wave is assumed to be 10 W/m(2). Computations were compared with a realistic anatomical head model. The results show that although there were marked differences in the local SAR distribution in the various tissues in the two models, the 1 g peak SAR values are approximately similar in the two models.     

Empirical and theoretical dosimetry in support of whole body resonant RF exposure (100 MHz) in human volunteers

This study reports the dosimetry performed to support an experiment that measured physiological responses of volunteer human subjects exposed to the resonant frequency for a seated human adult at 100 MHz. Exposures were performed in an anechoic chamber which was designed to provide uniform fields for frequencies of 100 MHz or greater. A half wave dipole with a 90 degrees reflector was used to optimize the field at the subject location. The dosimetry plan required measurement of transmitter harmonics, stationary probe drift, field strengths as a function of distance, electric and magnetic field maps at 200, 225, and 250 cm from the dipole antenna, and specific absorption rate (SAR) measurements using a human phantom, as well as theoretical predictions of SAR with the finite difference time domain (FDTD) method. On each exposure test day, a measurement was taken at 225 cm on the beam centerline with a NBS E field probe to assure consistently precise exposures. A NBS 10 cm loop antenna was positioned 150 cm to the right, 100 cm above, and 60 cm behind the subject and was read at 5 min intervals during all RF exposures. These dosimetry measurements assured accurate and consistent exposures. FDTD calculations were used to determine SAR distribution in a seated human subject. This study reports the necessary dosimetry for work on physiological consequences of human volunteer exposures to 100 MHz.     

Empirical and theoretical dosimetry in support of whole body radio frequency (RF) exposure in seated human volunteers at 220 MHz

This study reports the dosimetry performed to support an experiment that measured physiological responses of seated volunteer human subjects exposed to 220 MHz fields. Exposures were performed in an anechoic chamber which was designed to provide uniform fields for frequencies of 100 MHz or greater. A vertical half-wave dipole with a 90 degrees reflector was used to optimize the field at the subject's location. The vertically polarized E field was incident on the dorsal side of the phantoms and human volunteers. The dosimetry plan required measurement of stationary probe drift, field strengths as a function of distance, electric and magnetic field maps at 200, 225, and 250 cm from the dipole antenna, and specific absorption rate (SAR) measurements using a human phantom, as well as theoretical predictions of SAR with the finite difference time domain (FDTD) method. A NBS (National Bureau of Standards, now NIST, National Institute of Standards and Technology, Boulder, CO) 10 cm loop antenna was positioned 150 cm to the right, 100 cm above and 60 cm behind the subject (toward the transmitting antenna) and was read prior to each subject's exposure and at 5 min intervals during all RF exposures. Transmitter stability was determined by measuring plate voltage, plate current, screen voltage and grid voltage for the driver and final amplifiers before and at 5 min intervals throughout the RF exposures. These dosimetry measurements assured accurate and consistent exposures. FDTD calculations were used to determine SAR distribution in a seated human subject. This study reports the necessary dosimetry to precisely control exposure levels for studies of the physiological consequences of human volunteer exposures to 220 MHz.     

Numerical assessment of the performance of a scalp‐implantable antenna: Effects of head anatomy and dielectric parameters

We numerically assess the effects of head properties (anatomy and dielectric parameters) on the performance of a scalp‐implantable antenna for telemetry in the Medical Implant Communications Service band (402.0–405.0 MHz). Safety issues and performance (resonance, radiation) are analyzed for an experimentally validated implantable antenna (volume of 203.6 mm³), considering five head models (3‐ and 5‐layer spherical, 6‐, 10‐, and 13‐tissue anatomical) and seven scenarios (variations ± 20% in the reference permittivity and conductivity values). Simulations are carried out at 403.5 MHz using the finite‐difference time‐domain method. Anatomy of the head model around the implantation site is found to mainly affect antenna performance, whereas overall tissue anatomy and dielectric parameters are less significant. Compared to the reference dielectric parameter scenario within the 3‐layer spherical head, maximum variations of ?19.9%, +3.7%, ?55.1%, and ?39.2% are computed in the maximum allowable net input power imposed by the IEEE Std C95.1‐1999 and Std C95.1‐2005 safety guidelines, return loss, and maximum far‐field gain, respectively. Compliance with the recent IEEE Std C95.1‐2005 is found to be almost insensitive to head properties, in contrast with IEEE Std C95.1‐1999. Taking tissue property uncertainties into account is highlighted as crucial for implantable antenna design and performance assessment. Bioelectromagnetics 34:167–179, 2013. © 2012 Wiley Periodicals, Inc.     

Assessment of SAR and thermal changes near a cochlear implant system for mobile phone type exposures

A cochlear implant system is a device used to enable hearing in people with severe hearing loss and consists of an internal implant and external speech processor. This study considers the effect of scattered radiofrequency fields when these persons are subject to mobile phone type exposure. A worst-case scenario is considered where the antenna is operating at nominal full power, the speech processor is situated behind the ear using a metallic hook, and the antenna is adjacent to the hook and the internal ball electrode. The resultant energy deposition and thermal changes were determined through numerical modelling. With a 900 MHz half-wave dipole antenna producing continuous-wave (CW) 250 mW power, the maximum 10 g averaged SAR was 1.31 W/kg which occurred in the vicinity of the hook and the ball electrode. The maximum temperature increase was 0.33 degrees C in skin adjacent to the hook. For the 1800 MHz antenna, operating at 125 mW, the maximum 10 g averaged SAR was 0.93 W/kg in the pinna whilst the maximum temperature change was 0.16 degrees C. The analysis predicts that the wearer complies with the radiofrequency safety limits specified by the International Commission on Non-Ionizing Radiation Protection (ICNIRP), the Institute of Electrical and Electronics Engineers (IEEE), and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) for 900 and 1800 MHz mobile phone type exposure and thus raises no cause for concern. The resultant temperature increase is well below the maximum rise of 1 degrees C recommended by ICNIRP. Effects in the cochlea were insignificant.     

Setup and dosimetry for exposing anaesthetised pigs in vivo to 900 MHz GSM mobile phone fields

The aim of this study was a dosimetrical analysis of the setup used in the exposure of the heads of domestic pigs to GSM-modulated radio frequency electromagnetic fields (RF-EMF) at 900 MHz. The heads of pigs were irradiated with a half wave dipole using three different exposure routines; short bursts of 1-3 s at two different exposure levels and a continuous 10-min exposure. The electroencephalogram (EEG) was registered continuously during the exposures to search for RF-EMF originated changes. The dosimetry was based on simulations with the anatomical heterogeneous numerical model of the pig head. The simulation results were validated by experimental measurements with the exposure dipole and a homogeneous liquid phantom resembling the pig head. The specific absorption rate (SAR), defined as a maximum average over 10 g tissue mass (SAR(10g)), was 7.3 W/kg for the first set of short bursts and 31 W/kg for the second set of short bursts. The SAR(10g) in the continuous 10-min exposure was 31 W/kg. The estimated uncertainty for the dosimetry was +/-25% (K = 2).     

Development of a rat head exposure system for simulating human exposure to RF fields from handheld wireless telephones

The aim of this project was to develop an animal exposure system for the biological effect studies of radio frequency fields from handheld wireless telephones, with energy deposition in animal brains comparable to those in humans. The finite‐difference time‐domain (FDTD) method was initially used to compute specific absorption rate (SAR) in an ellipsoidal rat model exposed with various size loop antennas at different distances from the model. A 3 × 1 cm rectangular loop produced acceptable SAR patterns. A numerical rat model based on CT images was developed by curve‐fitting Hounsfield Units of CT image pixels to tissue dielectric properties and densities. To design a loop for operating at high power levels, energy coupling and impedance matching were optimized using capacitively coupled feed lines embedded in a Teflon rod. Sprague Dawley rats were exposed with the 3 × 1 cm loop antennas, tuned to 837 or 1957 MHz for thermographically determined SAR distributions. Point SARs in brains of restrained rats were also determined thermometrically using fiberoptic probes. Calculated and measured SAR patterns and results from the various exposure configurations are in general agreement. The FDTD computed average brain SAR and ratio of head to whole body absorption were 23.8 W/kg/W and 62% at 837 MHz, and 22.6 W/kg/W and 89% at 1957 MHz. The average brain to whole body SAR ratio was 20 to 1 for both frequencies. At 837 MHz, the maximum measured SAR in the restrained rat brains was 51 W/kg/W in the cerebellum and 40 W/kg/W at the top of the cerebrum. An exposure system operating at 837 MHz is ready for in vivo biological effect studies of radio frequency fields from portable cellular telephones. Two‐tenths of a watt input power to the loop antenna will produce 10 W/kg maximum SAR, and an estimated 4.8 W/kg average brain SAR in a 300 g medium size rat. Bioelectromagnetics 20:75–92, 1999. © 1999 Wiley‐Liss, Inc.     

Differential scanning calorimetric,circular dichroism,and Fourier transform infrared spectroscopic characterization of the thermal unfolding of xylanase A from Streptomyces lividans

The thermal unfolding of xylanase A from Streptomyces lividans, and of its isolated substrate binding and catalytic domains, was studied by differential scanning calorimetry and Fourier transform infrared and circular dichroism spectroscopy. Our calorimetric studies show that the thermal denaturation of the intact enzyme is a complex process consisting of two endothermic events centered near 57 and 64 degrees C and an exothermic event centered near 75 degrees C, all of which overlap slightly on the temperature scale. A comparison of the data obtained with the intact enzyme and isolated substrate binding and catalytic domains indicate that the lower- and higher-temperature endothermic events are attributable to the thermal unfolding of the xylan binding and catalytic domains, respectively, whereas the higher-temperature exothermic event arises from the aggregation and precipitation of the denatured catalytic domain. Moreover, the thermal unfolding of the two domains of the native enzyme are thermodynamically independent and differentially sensitive to pH. The unfolding of the substrate binding domain is a reversible two-state process and, under appropriate conditions, the refolding of this domain to its native conformation can occur. In contrast, the unfolding of the catalytic domain is a more complex process in which two subdomains unfold independently over a similar temperature range. Also, the unfolding of the catalytic domain leads to aggregation and precipitation, which effectively precludes the refolding of the protein to its native conformation. These observations are compatible with the results of our spectroscopic studies, which show that the catalytic and substrate binding domains of the enzyme are structurally dissimilar and that their native conformations are unaffected by their association in the intact enzyme. Thus, the calorimetric and spectroscopic data demonstrate that the S. lividans xylanase A consists of structurally dissimilar catalytic and substrate binding domains that, although covalently linked, undergo essentially independent thermal denaturation. These observations provide valuable new insights into the structure and thermal stability of this enzyme and should assist our efforts at engineering xylanases that are more thermally robust and otherwise better suited for industrial applications.     

Thermoregulation in normal sleep and insomnia: the role of peripheral heat loss and new applications for digital thermal infrared imaging (DITI)

Sleepiness and changes in body temperature are temporally associated. (2) There is mounting evidence that insomnia may be caused by impaired heat loss capacity. (3) New techniques such as infrared thermal imaging may be useful tools to investigate thermoregulatory changes associated with sleep in humans.     

Thermal characteristics of recombinant green fluorescent protein (GFPuv) extracted from Escherichia coli

AIMS: The thermal stability of isolated and extracted recombinant green fluorescent protein (GFPuv) was evaluated by analysing the loss of fluorescence intensity. METHODS AND RESULTS: GFPuv was expressed by Escherichia coli, extracted by the three-phase partitioning method and purified by elution through an hydrophobic interaction column. The collected fractions were further diluted in Tris-HCl-EDTA (pH 8.0) and subjected to continuous heating at set temperatures (45-95 degrees C). From a standard curve relating fluorescence intensity to GFPuv concentration, the loss of fluorescence intensity was converted to denatured GFPuv concentration (microg ml-1). To determine the extent of the thermal stability of GFPuv, decimal reduction times (D-values), z-value and energy of activation (Ea) were calculated. CONCLUSIONS: For temperatures between 45 and 70 degrees C, extracted native GFPuv activity decreased from 11 to 75% relative to initial native protein concentration above 70 degrees C, the average decrease in GFPuv fluorescence was between 72 to 83%. SIGNIFICANCE AND IMPACT OF THE STUDY: The thermal stability of GFPuv provides the basis for its potential utility as a fluorescent biological indicator to assess the efficacy of the treatment of liquids and materials exposed to steam.     

Discriminating 3(10)- from alpha-helices: vibrational and electronic CD and IR absorption study of related Aib-containing oligopeptides

Model peptides based on -(Aib-Ala)(n)-, and (Aib)(n)-Leu-(Aib)(2) sequences, which have varying amounts of 3(10)-helical character, were studied by use of vibrational and electronic circular dichroism (VCD and ECD) and Fourier transform infrared (FTIR) absorption spectroscopies to test the correlation of spectral response and conformation. The data indicate that these peptides, starting from a length of about four to six residues, predominantly adopt a 3(10)-helical conformation at room temperature. The longest model peptides, depending on the series, may evidence some alpha-helical contribution to the spectra, while the shorter ones, with less than six residues, have much less order. The IR absorption spectra (as supported by theory) showed only small frequency changes between 3(10)- and alpha-helices. By contrast, solvent effects are a source of much bigger perturbations. The ECD results show that the intensity ratio for the approximately 222-nm to approximately 208-nm bands, while useful for distinguishing between these two helical types in some sequences, may have a narrower range of application than VCD. However, the VCD data presented here continue to support the proposed discrimination between alpha- and 3(10)-helices based on qualitative amide I and II bandshape differences. The present study shows the intensities of the 3(10)-helical amide I (peak-to-peak) to its amide II VCD to be of the same order and useful for discriminating them from alpha-helices, whose amide I dominates the amide II in intensity. This qualitative result is experimentally independent of the amount of alphaMe-substituted residues in the sequence. These experimental VCD results are consistent in detail with theoretical spectral simulations for Ac-(Ala)(8)-NH(2), Ac-(Aib-Ala)(4)-NH(2), and Ac-(Aib)(8)-NH(2) in 3(10)- and alpha-helical conformations.     

Effects of temperature on the development and survival of an endangered butterfly,Lycaeides argyrognomon (Lepidoptera: Lycaenidae) with estimation of optimal and threshold temperatures using linear and nonlinear models

The effects of temperature on the development and survival of Lycaeides argyrognomon were examined in the laboratory. The eggs, larvae and pupae were reared at temperatures of 15, 17.5, 20, 25, 30 and 33°C under a long‐day photoperiod of 16‐h light and 8‐h darkness. The survival rates of the first–third instars ranged from 40.0 to 82.4%. The mortalities of the fourth instar were lower than those of the first–third instars. The development time of the overall immature stage decreased from 78.33 days at 15°C to 21.07 days at 30°C, and then increased to 24.33 days at 33°C. The common linear model and the Ikemoto–Takai model were used to estimate the thermal constant (K) and the developmental zero (T₀). The values of T₀ and K for the overall immature stages were 10.50°C and 418.83 degree‐days, and 9.71°C and 451.68 degree‐days by the common model and the Ikemoto–Takai model, respectively. The upper temperature thresholds (T_max) and the optimal temperatures (T_opt) of the egg, the first–third instars and the overall immature stages were estimated by the three nonlinear models. The ranges of T_opt estimated were from 30.33°C to 32.46°C in the overall immature stages and the estimates of T_max of the overall immature stages by the Briere‐1 and the Briere‐2 models were 37.18°C and 33.00°C, respectively. The method to predict the developmental period of L. argyrognomon using the nonlinear models was discussed based on the data of the average temperature per hour.     

Complete mitochondrial genomes from four subspecies of common chaffinch (Fringilla coelebs): New inferences about mitochondrial rate heterogeneity,neutral theory,and phylogenetic relationships within the order Passeriformes

We describe whole mitochondrial genome sequences from four subspecies of the common chaffinch (Fringilla coelebs), and compare them to 31 publicly available mitochondrial genome sequences from other Passeriformes. Rates and patterns of mitochondrial gene evolution are analyzed at different taxonomic levels within this avian order, and evidence is adduced for and against the nearly neutral theory of molecular evolution and the role of positive selection in shaping genetic variation of this small but critical genome. We find evidence of mitochondrial rate heterogeneity in birds as in other vertebrates, likely due to differences in mutational pressure across the genome. Unlike in gadine fish and some of the human mitochondrial work we do not observe strong support for the nearly neutral theory of molecular evolution; instead evidence from molecular clocks, distribution of dN/dS ratios at different levels of the taxonomic hierarchy and in different lineages, McDonald–Kreitman tests within Fringillidae, and site-specific tests of selection within Passeriformes, all point to a role for positive selection, especially for the complex I NADH dehydrogenase genes. The protein-coding mitogenome phylogeny of the order Passeriformes is broadly consistent with previously-reported molecular findings, but provides support for a sister relationship between the superfamilies Muscicapoidea and Passeroidea on a short basal internode of the Passerida where relationships have been difficult to resolve. An unexpected placement of the Paridae (represented by Hume's groundpecker) within the Muscicapoidea was observed. Consistent with other molecular studies the mtDNA phylogeny reveals paraphyly within the Muscicapoidea and a sister relationship of Fringilla with Carduelis rather than Emberiza.