Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Surprising transition observed when flowing grains become too jam packed to move

31.01.2007
Using color-shifting cylinders as substitutes for sand grains or coal lumps, a Duke University-led team of physicists has pinpointed a critical density level where granular materials suddenly cease flowing like a liquid and instead congeal into a state of rigidity.

That magic moment -- described as a "jamming transition" -- is announced by a kind of phase change analogous to the freezing of water, the scientists showed in experiments.

"The transition does not occur at the point that the particles are as dense as they can possibly be," said Robert Behringer, the Duke physics professor who led the research team. "Actually, they are just beginning to get densely packed. So you don't need that much compaction to make them like solids. You just need this sort of magical amount.

"That's really very peculiar," he said. "Experience wouldn't suggest that there would be this magic point where there would suddenly be this leap."

The findings could help engineers resolve when grainlike coal pieces will clump together and when they will flow like a liquid. "If you open the door to a coal hopper, you don't want the coal to be like a solid," Behringer said. "You want it to flow."

The report was posted online on Monday, Jan. 29, in the journal Physical Review Letters.

The research was funded by the National Science Foundation; the U.S.-Israel Binational Science Foundation; and Deutsche Forschungsgemeinschaft, the German equivalent of the NSF.

Behringer has spent years overseeing experimental studies of granular materials, a group that includes sand, coal, cereal, sugar, pills, powders, gravel and ice cubes.

Such materials exhibit uncanny group behavior in which they sometimes flow but other times clump rigidly in a mass, he said. This behavior is unpredictable, with examples occurring in such diverse events as coal jams and avalanches.

A previous Behringer-led experiment demonstrated that small plastic beads exhibiting grainlike behavior can be made to "freeze" into crystallike solids or "melt" into loose and fluidlike irregularity, depending on how they are stirred or shaken.

In the new study, the researchers provided an unprecedented analysis detailing what happens as free-flowing grains begin to get jammed by each other.

The experiment relied on plastic cylinders as grain substitutes. The cylinders changed color where squeezed, giving researchers a glimpse of jagged "force chains" that transmit the group effects of grain-on-grain influences within a closed system.

The researchers compressed the cylinders within an adjustable frame and analyzed what happened using special computational mathematics developed by Trushant Majmudar, the first author of the journal report, who is a former Duke graduate student and now a postdoctoral researcher at the Massachusetts Institute of Technology.

"When a container is really large, there's lots of space between the particles so they don't touch very much and the system acts like a fluid," Behringer said. "But as you shrink the container, the number of contacts grows. And the prediction was that when there are enough contacts per particle, the system will make this transition from fluid to solid."

Confirming the almost-decade-old predictions of theoreticians from the University of Pennsylvania and the University of Chicago as well as Princeton, Yale and Brandeis universities, the Duke team documented that at a critical confluence, pressure and particle-density readings suddenly increase and then diverge -- a change mathematically known as a "power law."

Such power laws are also expressed in phase transitions, such as the point at which water and steam become indistinguishable, Behringer said.

Comparative digital images of the system in "almost jammed" versus "highly jammed" states graphically documented the difference, with a network of glowing force chains clearly visible in the highly jammed image, he said.

Monte Basgall | EurekAlert!
Further information:
http://www.duke.edu

More articles from Physics and Astronomy:

nachricht NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>