E.E. Mola

Electrical trees in silicone gel: A combination of liquid and solid behaviour patterns

Electrical trees in liquids (streamers) occur on the nano-second timescale and produce structures that dissipate on voltage removal and sometimes even during voltage application. In AC fields the structures are a combination of fine filaments from the positive half-cycle and spheroidal cavities from the negative half-cycle. In contrast electrical trees in solids are permanent filamentary structures with a fractal geometry that grow on timescales of hours or longer at typical field values. Here we present the results of tree formation in a silicone gel under an AC applied electric field. These grow on timescales of minutes and possess a fine branched filamentary structure as well as spheroidal cavities. As in liquids, the cavities can collapse during tree growth. In contrast the filamentary structure is permanent as in solids. However the whole tree contracts following the removal of the applied voltage. The observed stability of the partial self-healing tree features are discussed in terms of the mixed liquid and solid features of the gel structure.

Increase in the embedding dimension in the heart rate variability associated with left ventricular abnormalities

In the present study, the authors report evidence that the existence of premature ventricular contractions increases the embedding dimension of the cardiac dynamics. They also analyze patients with congestive heart failure, a severe clinical condition associated with abnormal left ventricular function. Results also show an increase in the embedding dimension of the heart rate variability. They used electrocardiograms collected by themselves with quality standards that make them comparable with other databases.

How to find the sunrise and sunset times from a Sun clock and calendar

The purpose of this article is to describe the construction of a Sun clock and calendar (SCandC) that will allow an observer to not only see the time but also the symmetry properties of the Sun–Earth relative movement. A set of circles drawn on the SCandC will allow the observer to see their associated dates as well as to perform a visual interpolation between any pair of consecutive circles to estimate an intermediate date. By introducing the sunrise and sunset horizon lines in the SCandC the observer will be able to find the sunrise and sunset times during most of the year. The observer will also be able to appreciate the difference in time duration between the spring–summer and autumn–winter periods, as a consequence of Keplers second law, as well as to observe that there is a small difference between the circle radii of equidistant dates from the solstices in the spring–summer versus autumn–winter periods as a consequence also of Keplers second law. The equations derived in the present article will be tested against data from a particular lighthouse.