Browsing by Author "Koza, MM"

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    Neutron scattering study of water confined in periodic mesoporous organosilicas
    (Elsevier, 2010-07) Levy, E; Chan, LK; Yu, DH; Koza, MM; Mastai, Y; Ford, RC; Li, JC
    A series of quasi-elastic neutron scattering measurements were performed using IN6 at the Institute Laue Langevin for a mesoporous organosilica material with phenyl functions, called phenyltriethoxysilane (PTES). The aim of the experiment was to study the diffusion dynamics of nano-scale water clusters inside the hydrophobic pores as a function of temperature and hydration. By fitting the Debye–Waller factor, the data show clearly the different behavior between water, both inside and outside the hydrophobic pores, which resembles bulk water. The mean thermal displacement u2 of the external water increases with T almost linearly up to 353 K, while the internal water quickly reaches the maximum at T323 K, indicating the confinement by an averaged pore diameter of the porous organosilica. © 2010, Elsevier Ltd.
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    Novel rattling of K atoms in aluminium-doped defect pyrochlore tungstate
    (IOP Science, 2014-07-04) Shoko, E; Kearley, GJ; Peterson, VK; Mutka, H; Koza, MM; Yamaura, J; Hiroi, Z; Thorogood, GJ
    Rattling dynamics have been identified as fundamental to superconductivity in defect pyrochlore osmates and aluminium vanadium intermetallics, as well as low thermal conductivity in clathrates and filled skutterudites. Combining inelastic neutron scattering (INS) measurements and ab initio molecular dynamics (MD) simulations, we use a new approach to investigate rattling in the Al-doped defect pyrochlore tungstates: AAl0.33W1.67O6 (A = K, Rb, Cs). We find that although all the alkali metals rattle, the rattling of the K atoms is unique, not only among the tungstates but also among the analogous defect osmates, KOs2O6 and RbOs2O6. Detailed analysis of the MD trajectories reveals that two unique features set the K dynamics apart from the rest, namely, (1) quasi one-dimensional local diffusion within a cage, and (2) vibration at a range of frequencies. The local diffusion is driven by strongly anharmonic local potentials around the K atoms exhibiting a double-well structure in the direction of maximum displacement, which is also the direction of local diffusion. On the other hand, vibration at a range of frequencies is a consequence of the strong anisotropy in the local potentials around the K atoms as revealed by directional magnitude spectra. We present evidence to show that it is the smaller size rather than the smaller mass of the K rattler which leads to the unusual dynamics. Finally, we suggest that the occurrence of local diffusion and vibration at a range of frequencies in the dynamics of a single rattler, as found here for the K atoms, may open new possibilities for phonon engineering in thermoelectric materials. © 2014, IOP Publishing Ltd.
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    Picosecond dynamics in haemoglobin from different species: a quasielastic neutron scattering study
    (Elsevier, 2014-10) Stadler, AM; Garvey, CJ; Embs, JP; Koza, MM; Unruh, T; Artmann, GM; Zaccai, G
    Background Dynamics in haemoglobin from platypus (Ornithorhynchus anatinus), chicken (Gallus gallus domesticus) and saltwater crocodile (Crocodylus porosus) were measured to investigate response of conformational motions on the picosecond time scale to naturally occurring variations in the amino acid sequence of structurally identical proteins. Methods Protein dynamics was measured using incoherent quasielastic neutron scattering. The quasielastic broadening was interpreted first with a simple single Lorentzian approach and then by using the Kneller–Volino Brownian dynamics model. Results Mean square displacements of conformational motions, diffusion coefficients of internal dynamics and residence times for jump-diffusion between sites and corresponding effective force constants (resilience) and activation energies were determined from the data. Conclusions Modifications of the physicochemical properties caused by mutations of the amino acids were found to have a significant impact on protein dynamics. Activation energies of local side chain dynamics were found to be similar between the different proteins being close to the energy, which is required for the rupture of single hydrogen bond in a protein. General significance The measured dynamic quantities showed significant and systematic variations between the investigated species, suggesting that they are the signature of an evolutionary adaptation process stimulated by the different physiological environments of the respective protein. © 2014,Elsevier B.V.
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    Quasi-elastic neutron scattering study of water confined in periodic mesoporous organosilicas
    (Physical Society of Japan, 2012-12-18) Yu, DH; Page, DE; Li, JC; Mastau, Y; Koza, MM; Kearley, GJ
    Water confined in nanoscale space behaves significantly differently from bulk water. We have applied the Quasi-Elastic Neutron Scattering technique to investigate diffusive properties of water confined in porous silicate coated with hydrophobic organic functional groups, at two different levels of hydration. The measurements were performed over a wide range of temperatures, and although we cannot exclude subdiffusion, the data are more easily understood from a distribution in the diffusive dynamics ranging from static water monolayer at the pore surface to much greater mobility towards the pore centre. There is some evidence for a local diffusive motion with an effective radius of about 3.5 Å. The overall diffusion constants are significantly less than bulk water over the same temperature ranges. © 2013, The Physical Society of Japan.