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Hydroxylation of wadsleyite, β-(Mg,Fe)2SiO4, is associated with divalent cation defects and well known to afect its physical properties. However, an atomic-scale understanding of the defect structure and hydrogen bonding at high pressures is needed to interpret the influence of water on the behavior of wadsleyite in the mantle transition zone. We have determined the pressure evolution of the wadsleyite crystal symmetry and structure, including all O∙∙∙O interatomic distances, up to 32 GPa using single-crystal X-ray difraction on two well-characterized, Fe-bearing (Fo90) samples containing 0.25(4) and 2.0(2) wt% H2O. Both compositions undergo a pressure-dependent monoclinic distortion from orthorhombic symmetry above 9 GPa, with the less hydrous sample showing a larger increase in distortion at increased pressures due to the diference in compressibility of the split M3 site in the monoclinic setting arising from preferred vacancy ordering at the M3B site. Although hydrogen positions cannot be modeled from the X-ray difraction data, the pressure evolution of the longer O1∙∙∙O4 distance in the structure characterizes the primary hydrogen bond length. We observe the hydrogen-bonded O1∙∙∙O4 distance shorten gradually from 3.080(1) Å at ambient pressure to about 2.90(1) Å at 25 GPa, being still much longer than is defined as strong hydrogen bonding (2.5–2.7 Å). Above 25 GPa and up to the maximum pressure of the experiment at 32.5 GPa, the hydrogen-bonded O1∙∙∙O4 distance decreases no further, despite the fact that previous spectroscopic studies have shown that the primary O-H stretching frequencies continuously drop into the regime of strong hydrogen bonding (<3200 cm–1) above ~15 GPa. We propose that the primary O1-H∙∙∙O4 hydrogen bond in wadsleyite becomes highly nonlinear at high pressures based on its deviation from frequency-distance correlations for linear hydrogen bonds. One possible explanation is that the hydrogen position shifts from being nearly on the long O1-O4 edge of the M3 site to a position more above O1 along the c-axis.

A high resolution X-ray scattering method is used to measure spectra of the collective density oscillations propagating along the axis of a rod-like supra-molecular system made of a shear-aligned columnar hexagonal liquid crystalline phase of DNA dispersed in water. The dynamic structure factor is extracted from the spectrum using a generalized three effective eigenmode (GTEE) theory. The dynamic structure factor consists of three Lorentzian lines, one central Rayleigh and two symmetrically shifted Brillouin peaks, from which the phonon frequency and damping can be obtained. We investigated two systems: a 40 wt.% calf-thymus Na–DNA of molecular weight 8.4 × 106 Da (13 000 base pairs) in water, and 40 wt.% Na–DNA in 0.085 M MgCl₂. The phonon dispersion relations obtained show an oscillatory behavior as a function of Q (magnitude of the scattering vector) in the range of 2 nm−1 to 30 nm−1, similar to that obtained from lipid bilayers before. The dispersion relation of 40 wt.% DNA rods in pure water, for example, starts with a linear dispersion at low Q with a high-frequency sound speed of about 3100 m s−1, similar to that observed in bulk water, reaching a maximum of ω = 12 meV at Q = 9 nm−1, going down to a valley at Q = 18.7 nm−1, coming up to a secondary (lower) maximum at Q = 25 nm−1 and eventually going down at Q = 30 nm−1. One major distinctive feature of the DNA systems from liquids is that the dispersion relation in the shear aligned DNA extends to a considerably higher Q than that observed in liquids. The extended range of Q includes values corresponding to those in the second Brillouin zone in a crystalline system. This latter feature implies that a DNA rod can be regarded approximately as a one-dimensional crystal, as far as the density oscillations are concerned. In the system with 40 wt.% Na–DNA in 0.085 M MgCl₂, we observe a significantly greater phonon damping compared to the one in water.

A high resolution X-ray scattering method is used to measure spectra of the collective density oscillations propagating along the axis of a rod-like supra-molecular system made of a shear-aligned columnar hexagonal liquid crystalline phase of DNA dispersed in water. The dynamic structure factor is extracted from the spectrum using a generalized three effective eigenmode (GTEE) theory. The dynamic structure factor consists of three Lorentzian lines, one central Rayleigh and two symmetrically shifted Brillouin peaks, from which the phonon frequency and damping can be obtained. We investigated two systems: a 40 wt. calf-thymus Na–DNA of molecular weight 8.4 × 106Da 13 000 base pairs in water, and 40 wt. Na–DNA in 0.085 M MgCl2. The phonon dispersion relations obtained show an oscillatory behavior as a function of Qmagnitude of the scattering vector in the range of 2 nm−1to 30 nm−1, similar to that obtained from lipid bilayers before. The dispersion relation of 40 wt. DNA rods in pure water, for example, starts with a linear dispersion at low Qwith a high-frequency sound speed of about 3100 m s−1, similar to that observed in bulk water, reaching a maximum of ω  12 meV at Q  9 nm−1, going down to a valley at Q  18.7 nm−1, coming up to a secondary lower maximum at Q  25 nm−1and eventually going down at Q  30 nm−1. One major distinctive feature of the DNA systems from liquids is that the dispersion relation in the shear aligned DNA extends to a considerably higher Qthan that observed in liquids. The extended range of Qincludes values corresponding to those in the second Brillouin zone in a crystalline system. This latter feature implies that a DNA rod can be regarded approximately as a one-dimensional crystal, as far as the density oscillations are concerned. In the system with 40 wt. Na–DNA in 0.085 M MgCl2, we observe a significantly greater phonon damping compared to the one in water.

We investigated the application of inelastic x-ray scattering (IXS) to lipid bilayers. This technique directly measures the dynamic structure factor S(q,ω) which is the space-time Fourier transform of the electron density correlation function of the measured system. For a multiatomic system, the analysis of S(q,ω) is usually complicated. But for multiple bilayers of lipid, S(q,ω) is dominated by chain-chain correlations within individual bilayers. Thus IXS provides a unique probe for the collective dynamics of lipid chains in a bilayer that cannot be obtained by any other method. IXS of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylcholine+cholesterol at two different concentrations were measured. S(q,ω) was analyzed by three-mode hydrodynamic equations, including a thermal diffusive mode and two propagating acoustic modes. We obtained the dispersion curves for the phonons that represent the collective in-plane excitations of lipid chains. The effect of cholesterol on chain dynamics was detected. Our analysis shows the importance of having a high instrument resolution as well as the requirement of sufficient signal-to-noise ratio to obtain meaningful results from such an IXS experiment. The requirement on signal-to-noise also applies to molecular dynamics simulations.

A novel laser angular‐encoder system has been developed based on the principles of radar, the Doppler effect, optical heterodyning and self‐aligning multiple‐reflection optics. Using this novel three‐dimensional multiple‐reflection optical path, an increase in resolution of 10 to 20 times has been reached compared with commercially available laser Doppler displacement meters or laser interferometer systems. With the new angular encoder, sub‐nrad resolution has been attained in the 8° measuring range in a compact set‐up [about 60 (H) × 150 (W) × 370 mm (L)] for high‐energy‐resolution applications at the Advanced Photon Source undulator beamline 3‐ID.