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The imaging condition is a crucial component of the reverse time migration. In its conventional form, it involves cross‐correlating the extrapolated source‐ and receiver‐side wavefields. Effective imaging conditions are usually developed to suppress imaging artefacts (e.g. low‐wavenumber artefacts) and enhance the image quality. For acoustic reverse time migration, not only the scalar pressure but also their spatial and/or time derivatives are used in the imaging condition, similar to the gradient terms of adjoint tomography. These operations implicitly introduce additional angle‐domain weighting factors to the image results. In this study, based on an analysis of angle‐dependent properties of the existing imaging conditions, we propose a new imaging condition tailored for acoustic reverse time migration. It can be implemented efficiently using the variables within the finite‐difference solver. Without explicitly measuring wave propagation directions, the proposed imaging condition can naturally suppress the low‐wavenumber artefacts while maintaining a relatively wider imaging aperture, thereby corresponding to a broader wavenumber sampling range. Additionally, the evolved imaging conditions for imaging elastic P–P and S–S scattering and reflections are also formulated. In the angle domain, we conduct a comparative analysis between existing imaging conditions and the newly proposed ones. Various numerical examples are provided to demonstrate the advantages of the new imaging conditions. A comprehensive understanding of their angle‐domain properties may be further beneficial to constructing reasonable inversion strategies for full waveform inversion. [ABSTRACT FROM AUTHOR]

Epinephrine (EP) is a very important chemical transmitter in the transmission of nerve impulses in the central nervous system of mammals. Ascorbic acid (AA) is considered to be the most important extracellular fluid antioxidant and has important antioxidant properties in the cell. In this study, a series of transition metal–polyhistidine-carboxylated multi-wall carbon nanotube nanocomposites were synthesized, and their simultaneous catalytic effects on epinephrine and ascorbic acid were investigated. The results showed that nanocomposites based on iron ions had the highest catalytic activity. The prepared biosensor expressed high selectivity toward EP and AA with LOD values of 0.1 μΜ (AA) and 0.01 μΜ (EP), and sensitivity values of 4.18 μA mM−1 with a range of 0.001–5 mM (AA), 50.98 μA mM−1 with a range of 0.2–100 μM (EP), and 265.75 μA mM−1 with a range of 0.1–1.0 mM (EP). Moreover, it showed good stability, good repeatability and high selectivity in real sample detection. This work is a reference for the design of new electrochemical enzyme-free biosensors and the detection of biomarkers. [ABSTRACT FROM AUTHOR]

The determinations of detailed stress states are of great importance for various environmental and engineering investigations, which makes numerical stress modelling a key issue in many fields. We developed a new stress modelling method governed by elastic wave equations using finite-difference scheme. By introducing an artificial damping factor to the particle velocity in wave modelling, the proposed method is able to solve both the dynamic stress evolution and the static stress state of equilibrium. We validate the proposed method both in body force and surface force benchmarks in different scales. With the proposed method, we are able to substantially improve the modelling accuracy of models in unbounded domain by using the perfectly matched layer as the artificial boundary conditions. A 3-D concrete-faced rockfill dam model is further presented as a numerical example of practical investigation. The consistent results with the finite-element method further illustrate the proposed method's applicability. As a minor modification to wave modelling scheme, the proposed stress modelling method is not only accurate for geological models through different scales, but also physically reasonable and easy to implement for geophysicists. [ABSTRACT FROM AUTHOR]