It was recently suggested that the periodic and fractal precipitation of calcium salts and proteins in cholesterol gallstonesis closely related to the process of stone formation. The present study is to mimic the process of gallstone growth in vitro. We demonstrate for the first time that a three-dimensional structure of periodic rings (Liesegang ring) and/or fractal patterns can be produced by metal ion and deoxycholate precipitation, which are similar to gallstones. Precipitation in a periodic pattern occurs more often than in a fractal structure. Using X-ray diffraction, polarized light microscope, Fourier transform-infrared (FT-IR), and extended X-ray absorption fine structure (EXAFS), we studied the pattern formation mechanisms of both types of structures. The results indicate that the rate of nucleation in the crystal growth is a crucial element to affect the pattern formation. The pattern selection between periodic and fractal type depends on the crystal growth speed and the rate of nucleation.

Magnesium diboride (MgB2) is a good candidate material for superconducting RF cavities because of its higher transition temperature of ∼39 K and because of the absence of weak links between grains which prevents other high-Tc superconducting materials, such as YBCO, from being used for SRF cavities. Differently from MgB2 films fabricated on Cu or stainless steel(SS), we have fabricated MgB2 films on Mo substrate by hybrid physical–chemical vapor deposition. The films are about 0.7 µm thick and the Tc (onset) is as high as 38 K, with a corresponding transition width of 0.9 K. The upper critical field at T = 0 K, HC2(0), is extrapolated as 13.5 T and the critical current density at 5 K, JC (5 K, 0 T), is 6.5 × 105 A cm−2. Analysis results indicate that MgB2 film on molybdenum substrate has suitable superconducting properties and does not show the problems which often occur for MgB2 films fabricated on other metal substrates, such as the large cracks on SS substrate and the reaction between the substrate and the Mg on Cu substrate.

No abstract