Using first principles variable cell shape molecular dynamics, we predict a new structure for silica. This structure results from annealing a-quartz at pressures near a major phonon instability. The new phase is obtained by rotations of SiO4 tetrahedra producing edge-sharing SiO6 octahedra and SiO5 cuboids. This type of mechanism was proposed to account for structural transitions in silicate me...

plant tissue culture techniques are used as basic requirement of common plant transformation systems. in most cases of plant transformation, a reproducible regeneration protocol is the limiting step due to long time lasting, specialized facilities and well experienced persons. furthermore, tissue culture procedures induce somaclonal variation among regenerated transgenic plants. therefore, rece...

Coesite is an important pressure indicator for metamorphic rocks of ultra-high pressure origin. However, it often does not survive exhumation, but reacts back to quartz. Although it was shown experimentally that hydrogen incorporation in coesite increases with increasing pressure, the few coesite relics, which are found in nature, are “dry”. Thus, does the incorporation of hydrogen promote the ...

Plastic shear significantly reduces the phase transformation (PT) pressure when compared to hydrostatic conditions. Here, a paradoxical result was obtained: PT of graphitelike hexagonal boron nitride (hBN) to superhard wurtzitic boron nitride under pressure and shear started at about the same pressure ( approximately 10 GPa) as under hydrostatic conditions. In situ x-ray diffraction measurement...

Strain-induced phase transformations (PTs) in a sample under compression, unloading, and reloading in a diamond anvil cell are investigated in detail, by applying finite element method. In contrast to previous studies, the kinetic equation includes the pressure range in which both direct and reverse PTs occur simultaneously. Results are compared to the case when “no transformation” region in th...

In the past two decades, the geometric pathways involved in the transformations between inverse bicontinuous cubic phases in amphiphilic systems have been extensively theoretically modeled. However, little experimental data exists on the cubic-cubic transformation in pure lipid systems. We have used pressure-jump time-resolved X-ray diffraction to investigate the transition between the gyroid Q...

There is interest in identifying novel materials for use in radioactive waste applications and studying their behavior under high pressure conditions. The mineral zirconolite (CaZrTi(2)O(7)) exists naturally in trace amounts in diamond-bearing deep-seated metamorphic/igneous environments, and it is also identified as a potential ceramic phase for radionuclide sequestration. However, it has been...

In-situ high-energy X-ray diffraction and molecular dynamic simulation were employed to study the structural evolution of a B2 phase reinforced CuZr-based bulk metallic glass composite in different states during cryogenic treatment between 300 K 100 K. No transformation occurs as-cast sample treatment, while pre-strained undergoes martensitic reverse transformation. The ambient temperature, uni...

Thermal mismatch stresses in the ceramic particles of a Cu–ZrW2O8 composite were calculated using a finite-element model, and found to be high enough to trigger a pressure-induced phase transformation, in agreement with previous measurements by X-ray diffraction. The calculated thermal expansion/contraction curves also agree with previous experimental dilatometric results. 2004 Elsevier Ltd. Al...