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The Shifty Nature of Grains
June 24, 2005In separate papers appearing in this week's Nature, researchers announce findings regarding the little-understood world of granular materials, systems of particles that can dictate the flow of avalanches, the quality of concrete and even the mixing of pharmaceuticals.
In both studies, the researchers developed new analytical tools that combine laboratory simulators with advanced computer simulations and mathematics, bringing additional quantitative methods to a field that relies mostly upon qualitative observations.
Duke University physics and engineering professor Robert Behringer and his graduate student, Trushant Majmudar, used a novel system that includes a bed of thousands of light-bending plastic cylinders to trace the flow of stress, particle by particle, in a 2-dimensional granular set up. The researchers found that stresses applied to one dimension across the bed transferred along jagged pathways from one particle to the next when the other dimension was free from strain. However, when the system was compressed equally on both sides, the pathways, or "force chains," were much shorter.
The findings could prove important for understanding natural hazards such as the recent slope failures at La Conchita and Laguna Beach in California. Strongly shear states with long force chains occur just before the granular material fails, similar to the collapsing sandy cliffs.
The second report comes from the Chicago Materials Research Center at the University of Chicago, one of nearly 30 NSF-supported Materials Research Science and Engineering Center. Physicists Heinrich Jaeger and Sidney Nagel worked with graduate student Eric Corwin to develop a different testing system, in this case comprised of a cylinder filled with up to 100,000 glass beads compressed over hour-long periods by a rotating piston. Their goal was to study shear forces in granular materials.
The Chicago researchers were able to quantify a characteristic change in the way stresses propagate through the materials when the grains shift from a jammed state to a flowing one. The researchers suspect the underlying mechanism, whereby grains acquire an "effective temperature" in their flowing state, has wide-reaching implications for better understanding materials that are jammed at the atomic level, such as glass.
Glass behaves like a solid but can flow like a liquid, particularly at higher temperatures. If the granular studies hold true, this project may have resolved decades-old questions regarding the transition of solids into the more fluid glass-like state.
National Science Foundation
The findings could prove important for understanding natural hazards such as the recent slope failures at La Conchita and Laguna Beach in California. Strongly shear states with long force chains occur just before the granular material fails, similar to the collapsing sandy cliffs.
The second report comes from the Chicago Materials Research Center at the University of Chicago, one of nearly 30 NSF-supported Materials Research Science and Engineering Center. Physicists Heinrich Jaeger and Sidney Nagel worked with graduate student Eric Corwin to develop a different testing system, in this case comprised of a cylinder filled with up to 100,000 glass beads compressed over hour-long periods by a rotating piston. Their goal was to study shear forces in granular materials.
The Chicago researchers were able to quantify a characteristic change in the way stresses propagate through the materials when the grains shift from a jammed state to a flowing one. The researchers suspect the underlying mechanism, whereby grains acquire an "effective temperature" in their flowing state, has wide-reaching implications for better understanding materials that are jammed at the atomic level, such as glass.
Glass behaves like a solid but can flow like a liquid, particularly at higher temperatures. If the granular studies hold true, this project may have resolved decades-old questions regarding the transition of solids into the more fluid glass-like state.
National Science Foundation
Granular Materials Current Events and Granular Materials News RSSSo-called 'sandfish' could help materials handling and process technology specialists
It moves as quickly in sand as a fish moves through water, which is why this lizard, a species of skink (Scincus scincus) that grows to about 15 cm long and lives in the deserts of North Africa and the Near East, is commonly known by the name "sandfish."
Researchers at UCLA engineering discover theoretical model to predict jamming
Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have come up with a theoretical model to predict when granular materials become jammed.
Earthquake 'memory' could spur aftershocks
Using a novel device that simulates earthquakes in a laboratory setting, a Los Alamos researcher and his colleagues have shown that seismic waves-the sounds radiated from earthquakes-can induce earthquake aftershocks, often long after a quake has subsided.
Physicists see similarities in stream of sand grains, exotic plasma at birth of universe
Streams of granular particles bouncing off a target in a simple tabletop experiment produce liquid-like behavior also witnessed in a massive research apparatus that simulates the birth of the universe.
Physicists describe strange new fluid-like state of matter
University of Chicago physicists have created a novel state of matter using nothing more than a container of loosely packed sand and a falling marble. They have found that the impacting marble produces a jet of sand grains that briefly behaves like a special type of dense fluid.
Latest papers from Royal Society`s Proceedings B (Biological Sciences) and Proceedings A (Mathematical, Physical & Engineering Sciences) journals
Proceedings B (Biological Sciences) http://www.catchword.com/rsl/09628452/previews/contp1-1.htm Age- and density-dependent reproductive effort in male red deer by Dr NG Yoccoz, Dr A Mysterud, Dr R Langvatn and Professor NC Stenseth Male ungulates spend a large amount of their body reserves when fighting with other males for access to females during the rut. In this study of red deer stags in Norway, weight loss during rut is quantified for the first time. Relative weight loss peaked at prime age, and was lower in younger and senescent males. An average 8 year old stag weighing 135 kg lost an impressive 30 kg in 3-4 weeks time. Weight loss was smaller as density increased, and more so for old
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