Two mechanisms of spiral-pair-source creation in excitable media

Two new modes of generating spiral pairs in an excitable medium have been found. They depend on a geometrical structure (GS) inside the medium. This may be formed e.g. as a result of scars or fibrosis in the heart tissue, or artificially built in a chemical reaction substrate. Both sources involve a GS composed of a circular “convergent lens” bounded by two opaque “walls”. One mode can be induced by a single wave and behaves as a “flip-flop” type of a limit cycle. The other mode is generated by a train of plane waves impinging on the GS, and is created at the focus of the converging wave-fragments.     

Growth and Characteristics of Freestanding Hemispherical Diamond Films by Microwave Plasma Chemical Vapor Deposition

Freestanding hemispherical diamond films have been fabricated by microwave plasma chemical vapor deposition using graphite and molybdenum （Mo） as substrates. Characterized by Raman spectroscopy and scanning electron microscopy, the crystalline quality of the films deposited on Mo is higher than that on graphite, which is attributed to the difference in intrinsic properties of the two substrates. By decreasing the methane concentration, the diamond films grown on the Mo substrate vary from black to white, and the optical transparency is enhanced. After polishing the growth side, the diamond films show an infrared transmittance of 35-60% in the range 400-4000 cm^- 1.