Just as superconductors have no electrical resistance, superfluids have no viscosity, and can flow freely. Like superconductors, which can be used to measure extremely tiny magnetic fields, superfluids could create a new class of ultra-sensitive rotation sensors for use in precision guidance systems and other applications.
But, before new sensors can be built, scientists and engineers must first acquire a better understanding of the odd quirks of superfluids arising in these devices.
In the April 23 issue of Physical Review Letters, U. of I. physicist Paul Goldbart, graduate student David Pekker and postdoctoral research associate Roman Barankov describe a model they developed to explain some of those quirks, which were found in recent experiments conducted by researchers at the University of California at Berkeley.
In the Berkeley experiments, physicist Richard Packard and his students Yuki Sato and Emile Hoskinson explored the behavior of superfluid helium when forced to flow from one reservoir to another through an array of several thousand nano-apertures. Their intent was to amplify the feeble whistling sound of phase-slips associated with superfluid helium passing through a single nano-aperture by collecting the sound produced by all of the apertures acting in concert.
At low temperatures, this amplification turned out, however, to be surprisingly weak, because of an unanticipated loss of synchronicity among the apertures.
"Our model reproduces the key physical features of the Berkeley group's experiments, including a high-temperature synchronous regime, a low-temperature asynchronous regime, and a transition between the two," said Goldbart, who also is a researcher at the university's Frederick Seitz Materials Research Laboratory.
The theoretical model developed by Pekker, Barankov and Goldbart balances a competition between interaction and disorder – two behaviors more commonly associated with magnetic materials and sliding tectonic plates.
The main components of the researchers' model are nano-apertures possessing different temperature-dependent critical flow velocities (the disorder), and inter-aperture coupling mediated by superflow in the reservoirs (the interactions).
For helium, the superfluid state begins at a temperature of 2.18 kelvins. Very close to that temperature, inter-pore coupling tends to cause neighbors of a nano-aperture that already has phase-slipped also to slip. This process may cascade, creating an avalanche of synchronously slipping phases that produces a loud whistle.
However, at roughly one-tenth of a kelvin colder, the differences between the nano-apertures dominate, and the phase-slips in the nano-apertures are asynchronous, yielding a non-avalanching regime. The loss of synchronized behavior weakens the whistle.
"In our model, competition between disorder in critical flow velocities and effective inter-aperture coupling leads to the emergence of rich collective dynamics, including a transition between avalanching and non-avalanching regimes of phase-slips," Goldbart said. "A key parameter is temperature. Small changes in temperature can lead to large changes in the number of phase-slipping nano-apertures involved in an avalanche."
James E. Kloeppel | EurekAlert!
From rocks in Colorado, evidence of a 'chaotic solar system'
23.02.2017 | University of Wisconsin-Madison
Prediction: More gas-giants will be found orbiting Sun-like stars
22.02.2017 | Carnegie Institution for Science
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
24.02.2017 | Life Sciences
24.02.2017 | Life Sciences
24.02.2017 | Trade Fair News