63 research outputs found
A hidden Markov model for describing turbostratic disorder applied to carbon blacks and graphene
A mathematical framework is presented to represent turbostratic disorder in materials like carbon blacks, smectites and twisted n-layer graphene. In particular, the set of all possible disordered layers, including rotated, shifted and curved layers, forms a stochastic sequence governed by a hidden Markov model. The probability distribution over the set of layer types is treated as an element of a Hilbert space and, using the tools of Fourier analysis and functional analysis, expressions are developed for the scattering cross sections of a broad class of disordered materials
Neutron diffraction on methane and hydrogen hydrates under high pressure
Gas hydrates are crystalline solids composed of water and gas. They have attracted considerable attention over the past decade both for their geophysical relevancy [1] and for their possible application to gas storage [2]. Pressure is a key parameter in the study of these systems as gas hydrates are believed to exist at pressure in nature and the gas content is found to increase in gas hydrates as their crystalline structure rearranges upon compression. In addition, high-pressure studies on gas hydrates offer new possibilities to explore water-gas interactions.
We will present recent work on methane and hydrogen hydrates at high pressure performed by neutron diffraction in the GPa range [3]. Several issues including the gas content in the different high-pressure structures will be discussed
A Chiral Gas-Hydrate Structure Common to the Carbon Dioxide-Water and Hydrogen-Water Systems
We
present full in situ structural solutions of carbon dioxide
hydrate-II and hydrogen hydrate <i>C</i><sub>0</sub> at
elevated pressures using neutron and X-ray diffraction. We find both
hydrates adopt a common water network structure. The structure exhibits
several features not previously found in hydrates; most notably it
is chiral and has large open spiral channels along which the guest
molecules are free to move. It has a network that is unrelated to
any experimentally known ice, silica, or zeolite network but is instead
related to two Zintl compounds. Both hydrates are found to be stable
in electronic structure calculations, with hydration ratios in very
good agreement with experiment
Ice structures, patterns, and processes: A view across the ice-fields
We look ahead from the frontiers of research on ice dynamics in its broadest
sense; on the structures of ice, the patterns or morphologies it may assume,
and the physical and chemical processes in which it is involved. We highlight
open questions in the various fields of ice research in nature; ranging from
terrestrial and oceanic ice on Earth, to ice in the atmosphere, to ice on other
solar system bodies and in interstellar space
Chemical physics of air clathrate hydrates
International Symposium on Physics of Ice Core Records. Shikotsukohan, Hokkaido, Japan, September 14-17, 1998
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