Optical properties of ZrZn2 from 0.6 to 3.8 eV

In this paper we report ellipsometry measurements on ZrZn2 at room temperature under ultra-high vacuum conditions. The optical constants have been determined in the energy range 0.6-3.8 eV. The results are compared with calculated optical conductivity curves based on recent band-structure calculation. Peaks in the experimental optical conductivity at 0.92, 1.22 and 3.02 eV could be assigned to direct transitions, in agreement with the band model

Pyrrolizidine alkaloid poisoning of yaks: identification of the plants involved.

A search was undertaken in the most eastern part of the Himalayan kingdom of Bhutan for the plants which are causing severe losses of yaks due to pyrrolizidine alkaloid poisoning. Two Senecio and three Ligularia species were found on yak pastures at altitudes between 3000 and 4000 m, including one so far underscribed Ligularia species. None was previously known to contain pyrrolizidine alkaloids. Another Senecio species was found between 2500 and 3000 m, an altitude too low for yaks to be kept but significant for other cattle. The search was supported by field chemical tests for the alkaloids and the diagnosis was later confirmed by thin layer chromatography and high pressure liquid chromatography. Two of the Senecio species had exceptionally high concentrations of pyrrolizidine alkaloids of about 0.5 per cent in the dry matter