Evaluation and comparison of 50 Hz current threshold of electrocutaneous sensations using different methods

Leakage currents, tiny currents flowing from an everyday-life appliance through the body to the ground, can cause a non-adequate perception (called electrocutaneous sensation, ECS) or even pain and should be avoided. Safety standards for low-frequency range are based on experimental results of current thresholds of electrocutaneous sensations, which however show a wide range between about 50 microA (rms) and 1000 microA (rms). In order to be able to explain these differences, the perception threshold was measured repeatedly in experiments with test persons under identical experimental setup, but by means of different methods (measuring strategies), namely: direct adjustment, classical threshold as amperage of 50% perception probability, and confidence rating procedure of signal detection theory. The current is injected using a 1 cm2 electrode at the highly touch sensitive part of the index fingertip. These investigations show for the first time that the threshold of electrocutaneous sensations is influenced both by adaptation to the non-adequate stimulus and individual, emotional factors. Therefore, classical methods, on which the majority of the safety investigations are based, cannot be used to determine a leakage current threshold.The confidence rating procedure of the modern signal detection theory yields a value of 179.5 microA (rms) at 50 Hz power supply net frequency as the lower end of the 95% confidence range considering the variance in the investigated group. This value is expected to be free of adaptation influences, and is distinctly lower than the European limits and supports the stricter regulations of Canada and USA.

Cationic silica nanoparticles as gene carriers: synthesis, characterization and transfection efficiency in vitro and in vivo

The potential of cationic SiO2 nanoparticles was investigated for in vivo gene transfer in this study. Cationic SiO2 nanoparticles with surface modification were generated using amino-hexyl-amino-propyltri-methoxysilane (AHAPS). The zeta potential of the nanoparticles at pH = 7.4 varied from -31.4 mV (unmodified particles; 10 nm) to +9.6 mV (modified by AHAPS). Complete immobilization of DNA at the nanoparticle surface was achieved at a particle ratio of 80 (w/w nanoparticle/DNA ratio). The surface modified nanoparticle had a size of 42 nm with a distribution from 10-100 nm. The ability of these particles to transfect pCMVbeta reporter gene was tested in Cos-1 cells, and optimum results were obtained in the presence of FCS and chloroquine at a particle ratio of 80. These nanoparticles were tested for their ability to transfer genes in vivo in the mouse lung, and a two-times increase in the expression levels was found with silica particles in comparison to EGFP alone. Very low or no cell toxicity was observed, suggesting silica nanoparticles as potential alternatives for gene transfection.

Electrical phosphenes: on the influence of conductivity inhomogeneities and small-scale structures of the orbita on the current density threshold of excitation

Electrical and magnetic phosphenes, perceptions of light as a result of non-adequate stimulation of the eye by electrical current or magnetic induction, respectively, are one of the cornerstones to justify limit values for extreme low-frequency fields specified by statutory regulations. However, the mechanism and place of action, as well as the excitation threshold, remain unknown until now. We suggest that the origin of phosphene excitation is the synaptic layer of the eye. The current density threshold value for electrical phosphene excitation was numerically quantified for this area on the basis of a detailed geometrical model in original submillimetre resolution and specifically measured conductivities in the LF range. The threshold values found were 1.8 A m-2 at 60 Hz and 0.3 A m-2 at 25 Hz. These values are comparable with values of other excitable tissues. It has been shown that the current density threshold for phosphene generation depends on small-scale structures not taken into account by previous models.

A model of the electrical volume conductor in the region of the eye in the ELF range

Electrical and magnetic phosphenes are irritations of the eye caused by electric currents or magnetic fields. These are well known effects initially investigated in the early 1900s. Available estimations of the current densities in the eye, based on the assumption of a homogeneous volume conductor, show low thresholds. These outdated thresholds are still an important cornerstone when justifying today's limit values for extremely low-frequency (ELF) fields specified by statutory regulations. In vitro measurements of the complex conductivity of cattle eye are carried out for the ELF range (5-2000 Hz) separated for the different tissues of the eyeball. They do not show peculiarities at 20 Hz which is the threshold minimum for the phosphene generation. The reported conductivity data of the eye region show variations of two orders of magnitude regarding the electrical conductivity of the individual tissue layers. Starting with these new data, a model of the orbita is introduced describing the eye and its periphery as an electrically inhomogeneous volume conductor. This model contains small-scale structures which are expected to behave as good electrical conductors yielding regions of higher field values within the eye. Therefore, earlier models assuming a homogeneous volume conductor can be regarded as oversimplistic.

Thermal diffusion and soret feedback of gold-doped polyorganosiloxane nanospheres in toluene

We have investigated diffusion and thermal diffusion properties of light-absorbing colloidal polyorganosiloxane microgels containing tiny nanometer-sized gold clusters dispersed in toluene. Transient holographic gratings allow for very subtle perturbations in the linear regime where Soret feedback is negligible. Gold-doped colloids of different size and crosslink ratios show different Soret coefficients but identical thermal diffusion coefficients D(T). Undoped colloids tend to aggregate, but a consistent interpretation is obtained if an identical D(T) is assumed for the doped, the undoped, and the aggregated particles. Previously reported Soret feedback measurements on similar systems incidentally yielded comparable Soret coefficients. We show, however, that they suffer from strong convective perturbations.