The presence and the phase of an ischemic stroke lesion, as well as the configuration of electrode montages affect the distribution and the maximum value of the electric field induced in tissues. Moreover, patients whom seem to benefit most from tDCS are those in the chronic phase of an ischemic stroke, since contrasts in the tissue conductivity result in a higher electric field induced around the lesion volume, which could stimulate the remaining healthy tissue in the area.

Transcranial alternating current stimulation (tACs) is an important new technique that allows to modulate non-invasively high-order cortical processes. The underlying mechanisms of activation of this brain stimulation technique are still poorly understood. Herein, we use a finite difference time domain (FDTD) technique to investigate the penetration and focality of tACs in comparison to a time invariant (DC) stimulation. We show that stimulation using 10 Hz generates cerebral fields that are larger (× 2.5) and more focused than DC stimulation and that faster oscillating stimuli of 100 Hz and 1000 Hz, generate smaller and less focused cerebral fields than 10 Hz. The outcomes of this study may help tACs users to design better protocols and interpret experimental results.

Organic coatings form an effective barrier between metals and their environment, providing them protection against corrosion. Corrosion on coated metals depends mainly on the diffusion of water through the coating, the loss of adhesion at the interface between the coating and the metal (delamination), the rate of the chemical and electrochemical reactions under the coating and the treatment of the metal surface before the coating application. Many aggressive ions are transported toward and inside the coating through water. In organic coatings, typically, the water absorbed by the coating affects the polymer matrix structure, and it causes swelling and stresses, which may result in cracks. Swelling and cracks enhance the transport of water into the solid polymer, and concurrently the diffusion of ions. Over time also, the chemical structure of the polymer may change, adversely affecting its barrier properties and overall performance. In this chapter, we focus on methods to quantify the transport of electrolyte in organic coatings. We mark out the main characteristics, advantages and limitations of each one of them.

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