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In flight around the world’s brightest laser and the inverse Cheerio effect


By Tushna Commissariat

If you have never been one of the lucky few to have wandered the tunnels of a particle accelerator, but have always wondered what lies within, take a look at the video above. The European X-ray Free Electron Laser (European XFEL) – which is currently under construction in Germany and will come online next year – will provide ultrashort (27,000 X-ray flashes per second) and ultrabright X-ray laser flashes that are needed to study chemical reactions in situ or to study extreme states of matter (you can read more about the kind of research that will be done there in the September issue of Physics World magazine). The XFEL tunnel is 3.4 km long and you can zoom across all of it in the 5 minute long video. I particularly enjoyed watching particular locations where engineers could be seen carrying out tests, as well as watching folks on bicycles wobble out of the camera’s way.

On a slightly related note, if, like me, you occasionally get a bit muddled when it comes to certain details of different particle accelerators – for example which came first, the synchrotron or the cyclotron – take a look at this excellent “primer” over at Symmetry magazine.

The next time you consume a bowl of that ever-popular breakfast cereal Cheerios, do a little experiment. Drop a few of the rings one at a time into the milk and watch as the rings quickly clump together as if drawn in by each other. This “Cheerio effect“, where solid particles floating on a liquid are attracted to one other, was spotted and studied more than a decade ago and is now a mainstay of fluid mechanics. Thanks to the surface tension of a liquid, even objects that are normally too heavy to float if only one of them is placed in a liquid do actually float thanks to the wetting angles. Now, an international team of researchers has looked into the “inverse Cheerio effect” where a liquid is dropped onto a solid – like drops of milk on a bowl of jelly.

The team saw some interesting results. The interactions depended on the thickness of the solid layer. The attraction was attractive for a thick and soft surface like jelly. But if the surface was thin enough, then the drops began to repel each other. The researchers say that this is because both forces of elasticity and capillarity are in play. In case you are left wondering why this admittedly interesting effect is of interest to scientists, interactions between a soft surface and a liquid are involved in some key biological process such as cellular adhesion to soft tissues and have applications in bio-engineering. You can read more about this over at the New York Times website.

For some weekend reading, take a look at this feature on titled “The 7 biggest problems facing science, according to 270 scientists” and bemoan the fact that you could have snapped up Einstein’s leather jacket for a measly $144,000. Finally, go and play a new game released by PBS called “NOVA Black Holes” where you start as a star and work your way towards becoming a black hole over 50 levels.

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