Anisotropic stress inhibits crystallization in Cu-Zr glass-forming liquids

Liquids attain a metastable state without crystallizing by cooling rapidly to a given temperature below the melting point. With increasing supercooling, the nucleation rate would show an increase based on the prediction of the classical nucleation theory. It is generally thought that the nucleation rate will reach the maximum upon approaching the glass transition temperature, T_g, for glass-forming liquids. We report that there exists a supercooled region above T_g in which the crystallization has actually been severely suppressed. Our molecular dynamics simulations show that the growth of embryos in the supercooled Cu₆₀Zr₄₀ melt is subjected to a strong anisotropic stress associated with the dynamic heterogeneity. Its long-range effect drives the embryo to grow into a ramified morphology so that the interface energy dominates over the embryo growth, leading to the suppression of nucleation.

Polymorphism and genetic relatedness among wild and cultivated rice species determined by AP-PCR analysis

We have applied the arbitrarily primed polymerase chain reaction (AP-PCR) technique to the analysis of the relationships among six japonica and indica cultivars, and four wild species of rice. Chosen were four primers of arbitrary sequence that gave multiple amplification products when rice DNA was used as template. Among a total of 50 bands scored, 44 were polymorphic, which was sufficient to distinguish the species used in this study. It is apparent from the comparisons of genetic distances that cultivated rice (Oryza sativa) exhibits closest molecular affinity to wild O. rufipogon, suggesting that the origin of cultivated rice is from O. rufipogon. In a dendrogram of cultivated rice and O. rufipogon from different regions, japonica and indica rice were most closely clustered with O. rufipogon from China and India, respectively. Japonica and indica subspecies showed closer affinity with O. rufipogon from different origins than with each other, supporting a hypothesis of multi-centers of the origin of rice cultivation.