©2019. American Geophysical Union. All Rights Reserved. It has been widely recognized that the cross-correlation function of ambient seismic noise data recorded at two stations approximates to the part of Greens function between two stations. Therefore, the cross-correlation function should include higher modes, aside from the fundamental mode. However, the problem of measuring or extracting overtones from ambient seismic noise data remains. In this paper, we propose the frequency-Bessel transform method (F-J method) for extracting the dispersion curves of higher modes from ambient seismic noise data. We then assess the validity, accuracy, and applicability of the F-J method by conducting extensive numerical simulations and processing the observed ambient seismic noise data of the USArray. As demonstrated in this study, the F-J method is a convenient, practical, and accurate method for extracting the dispersion curves of multimodes from ambient seismic noise data and therefore has significant potentiality in the field of ambient seismic noise tomography.

Persistent dynamics in colloidal glasses suggest the existence of a non-equilibrium driving force for structural relaxation during glassy aging. But the implicit assumption in the literature that colloidal glasses form within the metastable state bypasses the search for a driving force for vitrification and glassy aging and its connection with a metastable state. The natural relation of osmotic pressure to number-density gradients motivates us to investigate the osmotic pressure as this driving force. We use dynamic simulation to quench a polydisperse hard-sphere colloidal liquid into the putative glass region while monitoring structural relaxation and osmotic pressure. Following quenches to various depths in volume fractionϕ(whereϕRCP≈ 0.678 for 7% polydispersity), the osmotic pressure overshoots its metastable value, then decreases with age toward the metastable pressure, driving redistribution of coordination number and interparticle voids that smooths structural heterogeneity with age. For quenches to 0.56 ⩽ϕ⩽ 0.58, accessible post-quench volume redistributes with age, allowing the glass to relax into a strong supercooled liquid and easily reach a metastable state. At higher volume fractions, 0.59 ⩽ϕ< 0.64, this redistribution encounters a barrier that is subsequently overcome by osmotic pressure, allowing the system to relax toward the metastable state. But forϕ⩾ 0.64, the overshoot is small compared to the high metastable pressure; redistribution of volume stops as particles acquire contacts and get stuck, freezing the system far from the metastable state. Overall, the osmotic pressure drives structural rearrangements responsible for both vitrification and glassy age-relaxation. The connection of energy, pressure, and structure identifies the glass transition, 0.63 <ϕg⩽ 0.64. We leverage the connection of osmotic pressure to energy density to put forth the mechanistic view that relaxation of structural heterogeneity in colloidal glasses occurs via individual particle motion driven by osmotic pressure, and is a spontaneous energy minimization process that drives the glass off and back to the metastable state.

The application of inorganic nanostructures for solar water splitting is currently limited by our understanding of photochemical charge transfer on the nanoscale, where space charge layers are less effective for carrier separation. Here we employ surface photovoltage spectroscopy to measure the internal photovoltages in single crystalline platinum/ruthenium-modified Rh-doped SrTiO3 nanocrystals for the first time. Voltages of -0.88 V and -1.13 V are found between the absorber and the Ru and Pt cocatalysts, respectively, and a voltage of -1.48 V for a Rh:SrTiO3 film on an Au substrate. This shows that the Pt and Ru cocatalysts not only improve the redox kinetics but also aid charge separation in the absorber. Voltages of +0.4 V, +0.6 V, and +1.2 V are found for hole injection into KI, K4[Fe(CN)6], and methanol, respectively, and a voltage of -0.7 V for electron injection into K3[Fe(CN)6]. These voltages correlate well with the photocatalytic performance of the catalyst; they are influenced by the built-in potentials of the donor-acceptor configurations, the physical separation of donors and acceptors, and the reversibility of the redox reaction. The photovoltage data also allowed the identification of a photosynthetic system for hydrogen evolution (80 μmol g-1 h-1) under visible light illumination (>400 nm) from 0.05 M aqueous K4[Fe(CN)6].