On Cristobalite (Part I)

Compressional pathways of α-cristobalite, structure of cristobalite X-I, and towards the understanding of seifertite formation

In various shocked meteorites, low-pressure silica polymorph α-cristobalite is commonly found in close spatial relation with the densest known SiO2 polymorph seifertite, which is stable above ∼80 GPa. We demonstrate that under hydrostatic pressure α-cristobalite remains untransformed up to at least 15 GPa. In quasi-hydrostatic experiments, above 11 GPa cristobalite X-I forms-a monoclinic polymo...

Notes on Sandflies. Part I

Part] I I

Pressure-induced transformations of cristobalite

X-ray in situ studies in electrically and laser-heated diamond anvil cells (DACs) at pressures over 80 GPa and temperatures above 2500 K were used to determine stable silica phase at extreme conditions. We demonstrate that so far unidenti®ed phases obtained on the compression of a-cristobalite, new dense silica polymorph in the Martian Shergotty meteorite, and controversial post-stishovite phas...

Lecture Notes on Pseudorandomness { Part I

A fresh view at the question of randomness was taken in the theory of computing: It has been postulated that a distribution is pseudorandom if it cannot be told apart from the uniform distribution by any e cient procedure. This paradigm, originally associating e cient procedures with polynomial-time algorithms, has been applied also with respect to a variety of other classes of distinguishing p...