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Between low-end stellar-mass black holes and top-end supermassive black holes, lie the elusive intermediate black holes. Jenny Greene reviews the search for these black holes in galaxy centres, which should indicate if supermassive black holes grew from stellar-mass ones or if a more complex process was needed.
Hydrogels are water-containing polymer networks that have been applied in various biological settings. Burdick and Murphy review recent advances in the development of dynamic hydrogels whose properties and mechanics change in response to biological signals.
The diffraction limit of light constrains the achievable resolution of conventional optical systems, but metamaterials provide numerous avenues to beat it. Lu and Liu review recent advances in super-resolution imaging with hyperlenses and metalenses, and discuss future directions and hurdles for the field.
Quantum-mechanical tunnelling currents across nanometre-scale gaps between electrodes are sensitive to the medium in the gap. Albrecht reviews progress towards using tunnelling currents to probe single-molecule processes, and in biosensor and sequencing applications.
High-valent iron–oxo and –nitrido complexes are intermediates in the catalytic cycles of various metalloenzymes that activate dioxygen and dinitrogen. Hohenbergeret al. review the advances in the chemistry of model high-valent iron–oxo and –nitrido systems and relate them to our understanding of related enzymes.
