How do grains flow out of an emptying silo? And what about sugar poured out by a pastry chef? Like liquids (2), grains can flow, but there is no attraction between the grains to trigger cohesion. However, by studying the waves that form and propagate on the surface of flowing sand, the physicists have observed telltale signs of cohesion.
Like the very small ripples that form on the surface of water, these waves point to the existence of a “taut elastic skin” on the surface of volumes of grain.This “skin” on flowing grain is its surface tension.
By measuring wave propagation speed, the researchers have shown that this cohesion effect is a result of a decrease in air pressure between flowing grains. Therefore, when a mass of grains flows, there is a depressed area at the middle of the flow, which pulls straying grains back towards the mass. These results should improve our understanding of the details of what happens in grain flows –materials which are common, but not yet well understood.
(1) CPMOH(2) The surface of a liquid is similar to an elastic membrane under
DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)
New quantum liquid crystals may play role in future of computers
21.04.2017 | California Institute of Technology
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
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25.04.2017 | Earth Sciences