Cilia are characterized by slender, threadlike projections, which are used by biological organisms to control fluid flows at the microscale. Attempts to mimic these structures and engineer cilia-like systems to have broad applications have proved problematic. In this week’s issue, Wei Wang and colleagues present electronically controlled artificial cilia that can be used to create flow patterns in near-surface liquids. The researchers use surface-mounted platinum strips, each about 50 micrometres long, 5 micrometres wide and 10 nanometres thick, and capped on one side with titanium. Applying an oscillating potential with an amplitude of around 1 volt to the cilia drives ions on to and off of the exposed platinum surface. These ions create asymmetric forces that generate a beating pattern that can be used to pump surface liquids in various flow geometries. The cover shows an artist’s impression of the artificial cilia in action.

At industrial scales, chemical reactions are typically driven by applying continuous heat to the reactants. In this week’s issue, Liangbing Hu and his colleagues show that pulsed heating and quenching can enhance synthetic performance while also saving energy. The researchers use a programmable electric current to switch between high and low temperatures very quickly — typically 0.02 seconds on, 1.08 seconds off. Rapidly quenching the reaction gives high selectivity, maintains catalyst stability and reduces energy usage. The cover image illustrates the heater in action for the pyrolysis of methane — the model reaction the team tested. Methane molecules travel through the pores of the high-temperature heater and are selectively converted into useful products.

Nova explosions occur when a runaway thermonuclear reaction is triggered in a white dwarf that is accreting hydrogen from a companion star. The massive amount of energy released ultimately creates the bright light source that can be seen with a naked eye as a nova. But some of the energy has been predicted to be lost during the initial stages of the reaction as a flash of intense luminosity — a fireball phase — detectable as low-energy X-rays. In this week’s issue, Ole König and his colleagues present observations that corroborate this prediction. Using scans taken by the instrument eROSITA, the researchers identified a short, bright X-ray flash from the nova YZ Reticuli a few hours before it became visible in the optical spectrum. The cover shows an artist’s impression of the nova in the fireball phase.

Conservation efforts for waterbirds, such as the Dalmatian pelicans (Pelecanus crispus) pictured on the cover, have centred on creating protected areas to maintain suitable habitats. But it has been unclear to what extent protected areas affect species’ population levels. In this week’s issue, Hannah Wauchope and her colleagues present an analysis that suggests protected areas have a mixed impact on waterbird populations. The researchers examined 1,506 protected areas to assess how they affected 27,055 waterbird populations across the globe. By assessing population levels before and after the implementation of protection, and comparing this change between protected and unprotected areas, the researchers identified the mixed impact, but also saw a strong indication that areas that were managed for waterbirds or their habitats were more likely to benefit populations. As a result, the team suggests that conservation strategies will require not only an increase in the number of protected areas, but active management of those areas to have the best chance of success.