Jürg Fröhlich

The association between exposure determined by radiofrequency personal exposimeters and human exposure: a simulation study.

The selection of an adequate exposure assessment approach is imperative for the quality of epidemiological studies. The use of personal exposimeters turned out to be a reasonable approach to determine exposure profiles, however, certain limitations regarding the absolute values delivered by the devices have to be considered. Apart from the limited dynamic range, it has to be taken into account that these devices give only an approximation of the exposure due to the influence of the body of the person carrying the exposimeter, the receiver characteristics of the exposimeter, as well as the dependence of the measured value on frequency band, channel, slot configuration, and communication traffic. In this study, the relationship between the field strength measured close to the human body at the location of the exposimeter and the exposure, that is, the field strength at the location of the human body without the human body present, is investigated by numerical means using the Visible Human model as an anatomical phantom. Two different scenarios were chosen: (1) For FM, GSM, and UMTS an urban outdoor scenario was examined that included a transmitting antenna mounted on the roof of one of four buildings at a street crossing, (2) For WLAN an indoor scenario was investigated. For GSM the average degree of underestimation by the exposimeter (relation of the average field levels at the location of the exposimeter to the field level averaged over the volume of the human body without the body present) was 0.76, and for UMTS 0.87; for FM no underestimation was found, the ratio was 1. In the case of WLAN the degree of underestimation was more pronounced, the ratio was 0.64. This study clearly suggests that a careful evaluation of correction factors for different scenarios is needed prior to the definition of the study protocol. It has to be noted that the reference scenario used in this study does not allow for final conclusions on general correction factors.

Low Intensity and Frequency Pulsed Electromagnetic Fields Selectively Impair Breast Cancer Cell Viability

Introduction A common drawback of many anticancer therapies is non-specificity in action of killing. We investigated the potential of ultra-low intensity and frequency pulsed electromagnetic fields (PEMFs) to kill breast cancer cells. Our criteria to accept this technology as a potentially valid therapeutic approach were: 1) cytotoxicity to breast cancer cells and; 2) that the designed fields proved innocuous to healthy cell classes that would be exposed to the PEMFs during clinical treatment. Methods MCF7 breast cancer cells and their normal counterparts, MCF10 cells, were exposed to PEMFs and cytotoxic indices measured in order to design PEMF paradigms that best kill breast cancer cells. The PEMF parameters tested were: 1) frequencies ranging from 20 to 50 Hz; 2) intensities ranging from 2 mT to 5 mT and; 3) exposure durations ranging from 30 to 90 minutes per day for up to three days to determine the optimum parameters for selective cancer cell killing. Results We observed a discrete window of vulnerability of MCF7 cells to PEMFs of 20 Hz frequency, 3 mT magnitude and exposure duration of 60 minutes per day. The cell damage accrued in response to PEMFs increased with time and gained significance after three days of consecutive daily exposure. By contrast, the PEMFs parameters determined to be most cytotoxic to breast cancer MCF-7 cells were not damaging to normal MCF-10 cells. Conclusion Based on our data it appears that PEMF-based anticancer strategies may represent a new therapeutic approach to treat breast cancer without affecting normal tissues in a manner that is non-invasive and can be potentially combined with existing anti-cancer treatments.

Genome-wide transcription analysis of Escherichia coli in response to extremely low-frequency magnetic fields

The widespread use of electricity raises the question of whether or not 50 Hz (power line frequency in Europe) magnetic fields (MFs) affect organisms. We investigated the transcription of Escherichia coli K-12 MG1655 in response to extremely low-frequency (ELF) MFs. Fields generated by three signal types (sinusoidal continuous, sinusoidal intermittent, and power line intermittent; all at 50 Hz, 1 mT) were applied and gene expression was monitored at the transcript level using an Affymetrix whole-genome microarray. Bacterial cells were grown continuously in a chemostat (dilution rate D = 0.4 h(-1)) fed with glucose-limited minimal medium and exposed to 50 Hz MFs with a homogenous flux density of 1 mT. For all three types of MFs investigated, neither bacterial growth (determined using optical density) nor culturable counts were affected. Likewise, no statistically significant change (fold-change > 2, P ≤ 0.01) in the expression of 4,358 genes and 714 intergenic regions represented on the gene chip was detected after MF exposure for 2.5 h (1.4 generations) or 15 h (8.7 generations). Moreover, short-term exposure (8 min) to the sinusoidal continuous and power line intermittent signal neither affected bacterial growth nor showed evidence for reliable changes in transcription. In conclusion, our experiments did not indicate that the different tested MFs (50 Hz, 1 mT) affected the transcription of E. coli.

Evolutionary optimization of non-periodic coupled-cavity semiconductor laser diodes

The analysis of different types of non-periodic multi-cavity laser structures will be presented. Deterministic non-periodic cavity concepts such as self-similar Cantor- or quasi-periodic Fibonacci sequences offer a distinct mode selectivity whilst having a significantly lower number of coupled cavities compared to an equivalent periodic solution. A heuristic numerical optimization procedure based on a breeder genetic algorithm scheme is favoured, also to give a sort of general information as to which kind of structures are well suited in terms of our requirements. By investigating the evolutionary optimized laser topologies according to the evolution of characteristic patterns, we propose a sort of superior meta-optimization strategy which relies on a population based information gathering.

An evolutionary optimization procedure applied to the synthesis of integrated spot-size converters

An evolutionary algorithm is applied to the synthesis of an integrated spot-size converter. Evolutionary algorithms turned out to be well suited for the solution of very complex problems having strongly non-linear cost functions defined over the solution space. They mostly work faster than other optimization techniques like random search or the Monte-Carlo method because of their parallel search mechanism, also referred to as implicit parallelism. The intrinsic behaviour of the optimization is demonstrated using an example of a spot-size converter that is implemented as a non-periodic segmented waveguide structure. Only a small number of structures have to be evaluated to achieve a coupling loss below 1.3dB that is considered to be very good. A supervising method is proposed, introducing an evolution quality figure. This figure is used to visualize and to qualify the evolution of the algorithm. Based on this figure a termination condition is suggested.

Experimental system for real-time assessment of potential changes in protein conformation induced by electromagnetic fields.

A novel experimental system to distinguish between potential thermal and non-thermal effects of electromagnetic fields (EMFs) on the conformational equilibrium and folding kinetics of proteins is presented. The system comprises an exposure chamber installed within the measurement compartment of a spectropolarimeter and allows real-time observation of the circular dichroism (CD) signal of the protein during EMF exposure. An optical temperature probe monitors the temperature of the protein solution at the site of irradiation. The electromagnetic, thermal, and fluid-dynamic behavior of the system is characterized by numerical and experimental means. The number of repeated EMF on/off cycles needed for achieving a certain detection limit is determined on the basis of the experimentally assessed precision of the CD measurements. The isolated thermosensor protein GrpE of the Hsp70 chaperone system of Eschericha coli serves as the test protein. Long-term experiments show high thermal reproducibility as well as thermal stability of the experimental setup.

Treatment of resistant fever: new method of local cerebral cooling.

BackgroundFever in neurocritical care patients is common and has a negative impact on neurological outcome. The purpose of this prospective observational study was (1) to evaluate the practicability of cooling with newly developed neck pads in the daily setting of neurointensive care unit (NICU) patients and (2) to evaluate its effectiveness as a surrogate endpoint to indicate the feasibility of neck cooling as a new method for intractable fever.MethodsNine patients with ten episodes of intractable fever and aneurysmal subarachnoid hemorrhage were treated with one of two different shapes of specifically adapted cooling neck pads. Temperature values of the brain, blood, and urinary bladder were taken close meshed after application of the cooling neck pads up to hourxa08.ResultsThe brain, blood, and urinary bladder temperatures decreased significantly from hourxa00 to a minimum in hourxa05 (Pxa0<xa00.01). After hourxa05, instead of continuous cooling in all the patients, the temperature of all the three sites remounted.ConclusionThis study showed the practicability of local cooling for intractable fever using the newly developed neck pads in the daily setting of NICU patients.

Towards a realistic dielectric tissue model: A multiscale approach

In the past, mainly analytical mixing formulas were used for modeling of dielectric properties of biological cells. General drawbacks of such formulas are the restriction to simple shapes and small cellular volume fractions. Assuming cell suspensions or tissues being quasi-periodic the problem size can be reduced to a cubic unit cell containing a single biological cell. Under this assumption numerical, e.g. Finite- Element models of such unit cells provide effective dielectric parameters for the entire tissue or cell suspension. In this work a flexible shape parametrization method allowing for a realistic representation of biological cells is applied to eight different cell types. A non-axisymmetric columnar epithelium cell occurring e.g. in the epidermis is chosen as an example. Numerical simulations of the columnar cell exposed to a time-harmonic electric field are performed for two different, high volume fractions, followed by the extraction of effective dielectric parameters of the bulk material. The simulation results are compared to two analytical approximations for ellipsoidal particles. The results suggest, that the calculation of effective dielectric properties of arbitrarily shaped cells in the frequency range between 100kHz and 1GHz requires at least a numerical cell model.