The use of smartphones is expanding rapidly around the world, thus raising the concern of possible harmful effects of radiofrequency generated by smartphones. We hypothesized that Wi-Fi signals from smartphones may have harmful influence on adipose-derived stem cells (ASCs). An in vitro study was performed to assess the influence of Wi-Fi signals from smartphones. The ASCs were incubated under a smartphone connected to a Wi-Fi network, which was uploading files at a speed of 4.8 Mbps for 10 hours a day, for a total of 5 days. We constructed 2 kinds of control cells, one grown in 37°C and the other grown in 39°C. After 5 days of Wi-Fi exposure from the smartphone, the cells underwent cell proliferation assay, apoptosis assay, and flow cytometry analysis. Three growth factors, vascular endothelial growth factor, hepatocyte growth factor, and transforming growth factor-β, were measured from ASC-conditioned media. Cell proliferation rate was higher in Wi-Fi-exposed cells and 39°C control cells compared with 37°C control cells. Apoptosis assay, flow cytometry analysis, and growth factor concentrations showed no remarkable differences among the 3 groups. We could not find any harmful effects of Wi-Fi electromagnetic signals from smartphones. The increased proliferation of ASCs under the smartphone, however, might be attributable to the thermal effect.

Epoxy coating in nuclear fuel storage degrades with aging and hazardous radiation. In order to evaluate the deterioration of the epoxy, the dependence of acoustic impedance on mechanical properties is studied. Unlike metals, the epoxy is hard to measure the acoustic velocity because the surface of epoxy coating applied on a concrete wall is wavy and highly attenuative for the ultrasound. In this paper, simulated annealing (SA) algorithm is used to calculate the acoustic impedance using a multiple reflection waves from the rough epoxy surface. Epoxy films coated on small concrete cubes are subjected to the accelerated aging conditions and tested by SA method to calculate acoustic impedance of the epoxy film. The experimental results show that the acoustic impedance has a good correlation with the degradation of epoxy coating and the method developed in this study can be applied effectively to monitor the aging of the epoxy coating in the nuclear fuel storage.

Polymeric materials such as epoxy are widely used as coating layers for the containment building of the nuclear power plant. These layers may be damaged through a hygrothermal process and residual stresses can reach significant levels near the free edges, possibly leading to interface debonding or delamination. Interfacial stress singularities induced in a laminate model consisting of the epoxy coating layer and the concrete substrate is investigated using the time-domain boundary element method. The epoxy layer is assumed to be a linear viscoelastic material and moisture effects are assumed to be analogous to thermal effects. The overall stress intensity factor for the case of a small interfacial edge crack of length a has been computed.

This paper deals with the stress singularity induced at the interface corner between the viscoelastic thin film and the elastic substrate as the film absorbs moisture from the ambient environment. The thin film is assumed to be a linear viscoelastic material and moisture effects are assumed to be analogous to thermal effects. The time-domain boundary element method is employed to investigate the behavior of interface stresses. The order of the singularity is obtained numerically for a given viscoelastic model. The numerical results exhibit the relaxation of interface stresses and large stress gradients are observed in the vicinity of the free surface. It is shown that the stress singularity factor is relaxed with time, while the order of the singularity increases with time for the viscoelastic model considered.

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