Leakage properties of photonic crystal fibers.

An analysis of the con.nement losses in photonic crystal fibers due to the finite numbers of air holes is performed by means of the finite element method. The high flexibility of the numerical method allows us to consider fibers with regular lattices, like the triangular and the honeycomb ones, and circular holes, but also fibers with more complicated cross sections like the cobweb fiber. Numerical results show that by increasing the number of air hole rings the attenuation constant decreases. This dependence is very strong for triangular and cobweb fibers, whereas it is very weak for the honeycomb one.

[Cohen syndrome. Contribution to its clinical delineation]. / La sindrome di Cohen. Contributo alla sua delineazione clinica.

The authors report a case with features of the Cohen syndrome: characteristic cranio-facial appearance with prominent nasal bridge, short philtrum, prominent upper central incisors, micrognathia, truncal obesity of mid-childhood onset, muscle hypotonia, mental deficiency, limb anomalies associated with other clinical expressivity present among the previous reported cases. The reported case is of particular interest: the distal limbs anomalies are peculiar with marked shortening of metacarpals and metatarsals. A review of the other cases is also reported and discussed in order to stress the most frequent manifestations of the syndrome and delineate the major clinical characteristics.