We describe the application of the molecular dynamics (MD) method to simulate structures and physical properies, including volume compressibilities, volume thermal expansivities, enthalpies, and atomic thermal vibrations, for the MgSiO3 polymorphs and iron. The MD simulation is shown to be very useful and powerful for predecting properties especially under conditions unavailable in the laboratory, such as extremes of temperatures and pressures prevailing in the Earth's deep-interior. We use the MD technique to investigate the possibility of high-pressure or high-temperature phase transitions in MgSiO3 and Fe, which might occur in the deep Earth.
A density modification technique for phase determination and refinement is described which replaces all density less than one-fifth of the average peak height by zero. Its effectiveness is demonstrated by applications to small proteins. With high resolution data, the method is successfully applied to phase refinement for Ribonuclease Apl. It has also been shown that for a small protein it is possible to obtain an ab initio solution of the structure by refining from a complete set of random phases for all reflexions.
The perovskite form of Mg0.981Fe0.028Cr0.011Si0.979O3, quenched from 26 GPa and 1900°C in a uniaxial split-sphere-type high-pressure apparatus, was studied. The result of structural refinement indicates that Fe and a small amount of Cr substitute for Mg rather than for Si, contrary to the result of Jackson et al. (1987) who reported Fe in the octahedral site of a perovskite synthesized at 50 GPa and 2000 K in a diamond-anvil cell with laser heating.
New phases which contain mixed-valent vanadium; SrV6O11, SrTxV6-xO11 (T=Ti, Cr, Fe) and NaFe3V9O19 were synthesized. Crystal structures of them and NaV6O11 were determined and discussed in comparison with the magnetoplumbite structure. Random cation distributions in SrTxV6-xO11 suggest that AT6O11 phases contain itinerant d-electrons. NaV6O11, SrV6O11 and NaFe3V9O19 were revealed to show spontaneous magnetization.
Quasi-elastic neutron scattering has been applied to characterize the surface-mobile layer of films of HD (an isotope of molecular hydrogen) condensed on MgO powder in the coverage range 1.6-9 layers and the temperature range 7-17K (Tm=16.6K) . The close-packed surface has a diffusivity from about 8K, with 0.3 mobile layers and a diffusion coefficient of 1/3 that of bulk liquid HD at Tm. The mobile quantity increases with temperature. The diffusion coefficients are in the range (0.8-3.0) ×10-5cm2/s. The partial order remains in the mobile layer where HD molecules jump from site to site on a hexagonal lattice.
It has been introduced that trehalose has a possible role in cryptobionts, which are able to be back to life after complete dryness when it become wet again. The simple disaccharide prevents cell components such as proteins, cell membrane and nucleic acid from any damage of denaturation by dryness. It seemes that bonded water is replaced by trehalose on the surface of biomolecules without damage. The understanding for the mechanism is not known yet. Trehalose is a perfect preservative for the storage of unstable biological materials.