Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World's team of editors and reporters
Tornado mystery solved at long last
In 1955, Scottsbluff, Nebraska, US, a group of broadcasters was forced to take shelter from a tornado in the basement of a stone building. But they weren’t completely safe from the violent storm. As the funnel of the tornado passed overhead, the temperature dropped and suddenly they found it difficult to breathe. Sixty-two years on, Georgios Vatistas and his students at Concordia University in Canada have developed a new mathematical model that can explain what happened that day. While past studies have focused on laminar (smooth) vortices, the current study looked at vortices with more complex turbulent flow. In a laminar vortex, the converging flow cools down consistently with decreasing radius. The new model, however, takes into account density variation and turbulence. The team found that the temperature first rises before cooling to a minimum at the vortex centre. This is the result of competition between the air heating because of mechanical friction and cooling because of expanding air pockets. The result is a cooler vortex centre, with lower air pressure. Vatistas and colleagues could work out that during the 1955 tornado, the temperature went from 27 °C to 12 °C and the air pressure dropped to 80% of that found at an altitude of 8000 m (known as the “death zone”). Thankfully, it passed quickly before the broadcasters were suffocated. The findings, published in the Journal of Aircraft, will help to improve the operation of refrigeration vortex tubes used to cool equipment such as electronic components and cutting tools. It also sheds some light on the mysterious world of tornados and water spouts.
Nanoparticles self-heal after absorbing hydrogen
Researchers at Stanford University in the US have used state-of-the-art electron-microscopy techniques to watch tiny particles of palladium absorb hydrogen ions in real time. Jen Dionne and colleagues first created palladium nanocubes that were 15–80 nm in size. The nanocubes were then placed in a scanning transmission electron microscope in the presence of hydrogen. The team watched as hydrogen molecules reacted with the surface of the palladium, creating hydrogen ions that entered the bulk of the nanocubes in a process called intercalation. Studies that lasted more than 24 h revealed that imperfections in the palladium-crystal structure developed as the nanocube filled up with hydrogen. However, once the material can absorb no more hydrogen, these imperfections appeared to be “pushed-out” of the nanocube. “The nanoparticle has the ability to self-heal,” explains Dionne. “When you first introduce hydrogen, the particle deforms and loses its perfect crystallinity. But once the particle has absorbed as much hydrogen as it can, it transforms itself back to a perfect crystal again.” The storage of hydrogen in metals plays an important role in advanced energy sources such as fuel cells. The research – described in Nature Communications – could help to boost the performance of such systems.
Amec Foster Wheeler bags £35m nuclear-propulsion contract
UK-based engineering firm Amec Foster Wheeler has been awarded a five-year contract to provide research and technology services to the UK Ministry of Defence’s Naval Nuclear Propulsion Programme (NNPP). The deal is worth £35m and involves analysis and laboratory testing at the firm’s facilities in Warrington and Dorchester. Programme, project and technical management services will also be provided by Amec Foster Wheeler. “Long-term investment in innovative research and technology like this is absolutely essential to ensuring that Britain’s nuclear programme remains cutting-edge,” says UK defence minister Harriet Baldwin.