(Press-News.org) DURHAM, N.C. -- High-speed video of projectiles slamming into a bed of disks has given scientists a new microscopic picture of the way a meteorite or missile transfers the energy of its impact to sand and dirt grains.
The transfer is jerky, not smooth. "It was surprising just how unsmooth the slow-down of the intruding object was," Duke physicist Robert Behringer said. His team describes their new videos and impact analysis in the Dec. 7 Physical Review Letters. The research may change the way scientists model meteorite and missile impacts and their effects.
Scientists previously assumed that the slowing down would be smooth and that any sound wave would travel through a granular material in a regular, uniform pattern, similar to the way noise from a clap of the hands diffuses evenly in all directions through the air. But using high-speed video, Behringer, his graduate student Abram Clark and Lou Kondic of the New Jersey Institute of Technology have shown a very different behavior for the sound wave and grains during a collision.
In the study, supported by the Defense Threat Reduction Agency, the team shot bronze disks into a narrow bed of photoelastic grains and used an ultrafast camera to track the collision energy as it shifted from the disk to the beads. The footage shows that the bronze disk loses most of its energy in intense, sporadic acoustic pulses along networks of grains, or force chains, in the bed of beads.
"This phenomenon was so hard to observe before because of how fast the force chains travel," Behringer said. The standard movie rate is about 30 frames per second. To capture the path of energy down the force chains, the scientists had to use a camera that could capture 40,000 frames per second, 1300 times faster than a normal video, because the sound pulses move at such high speeds.
The scientists shot the intruding disks into the photoelastic grains at speeds up to 6.5 meters per second, about 15 miles per hour. On impact, the force chains in the disks started moving the energy away from the intruding object, dumping it down deep in the bed of disks like the drainpipes of a septic system carrying water and waste away from a house, Behringer said.
The speed of the bronze disk was well under sonic or super-sonic speed, which could make the patterns of energy transfer substantially different, the team noted in the paper. "For supersonic speeds, it's kind of like the car chases that happen in markets in movies. People can't get out of the way fast enough. Similarly the pulses wouldn't clear the chain networks and the forces would back up rather than get carried away from the intruder," Behringer said.
Studying the impacts at sonic and supersonic speeds, however, is a set of experiments that requires different grain particles, Behringer said, adding it's one the team may try soon. He also explained that once a missile or meteor drops below sonic speeds, the grains absorbing its impact would carry the energy and momentum away jerkily and sporadically, just as the team's new microscopic picture shows.
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Citation:
"Particle Scale Dynamics in Granular Impact." Clark, A., Kondic, L., and Behringer, R. 2012. Physical Review Letters, 5:137. DOI: 10.1103/Physics.5.137
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WASHINGTON (Dec. 11, 2012) – New research, presented this morning at the 54th Annual Meeting of the American Society of Hematology (ASH), has identified important associations between Plasmodium falciparum (Pf) malaria and endemic Burkitt Lymphoma (eBL) that may help researchers identify young children who are more susceptible to eBL.
Unlike previous studies in which malaria infection alone was considered the important factor, this study approached the evolving complexity and heterogeneity of the humoral immune response to Pf as a key component for risk of developing ...
Rose madder – a natural plant dye once prized throughout the Old World to make fiery red textiles – has found a second life as the basis for a new "green" battery.
Chemists from The City College of New York teamed with researchers from Rice University and the U.S. Army Research Laboratory to develop a non-toxic and sustainable lithium-ion battery powered by purpurin, a dye extracted from the roots of the madder plant (Rubia species).
More than 3500 years ago, civilizations in Asia and the Middle East first boiled madder roots to color fabrics in vivid oranges, reds ...
LEXINGTON, Ky. (Dec. 10, 2012) — A research team composed of University of Kentucky researchers has published a paper which provides the first direct evidence that activated astrocytes could play a harmful role in Alzheimer's disease. The UK Sanders-Brown Center on Aging has also received significant new National Institutes of Health (NIH) funding to further this line of study.
Chris Norris, an associate professor in the UK College of Medicine Department of Molecular and Biomedical Pharmacology, as well as a member of the faculty at the UK Sanders-Brown Center on Aging, ...
Hot flushes affect millions of people, and not just women. Yet, it is still unclear what causes the episodes of temperature discomfort, often accompanied by profuse sweating.
Now a team of researchers around Dr. Naomi Rance, a professor in the department of pathology at the UA College of Medicine, has come closer to understanding the mechanism of hot flushes, a necessary step for potential treatment options down the road. This research was published recently in the Proceedings of the National Academy of Sciences.
The team identified a group of brain cells known as KNDy ...
HOUSTON – (Dec. 11, 2012) – Here's a reason to be glad about madder: The climbing plant has the potential to make a greener rechargeable battery.
Scientists at Rice University and the City College of New York have discovered that the madder plant, aka Rubia tinctorum, is a good source of purpurin, an organic dye that can be turned into a highly effective, natural cathode for lithium-ion batteries. The plant has been used since ancient times to create dye for fabrics.
The discovery is the subject of a paper that appears today in Nature's online, open-access journal ...
When we're faced with things that seem threatening, whether it's a hairy spider or an angry mob, our goal is usually to get as far away as we can. Now, new research suggests that our visual perception may actually be biased to help motivate us to get out of harm's way.
When we're faced with a threat our bodies respond in ways that engage our fight-or-flight response and enable us to act quickly: Our heart rate and blood pressure ramp up, and we produce more of the stress hormone cortisol. But research suggests that the body may also demonstrate its preparedness through ...
ANN ARBOR—A glass plate with a nanoscale roughness could be a simple way for scientists to capture and study the circulating tumor cells that carry cancer around the body through the bloodstream.
Engineering and medical researchers at the University of Michigan have devised such a set-up, which they say takes advantage of cancer cells' stronger drive to settle and bind compared with normal blood cells.
Circulating tumor cells are believed to contribute to cancer metastasis, the grim process of the disease spreading from its original site to distant tissues. Blood tests ...
When you walk into a darkened room, your first instinct is to feel around for a light switch. You slide your hand along the wall, feeling the transition from the doorframe to the painted drywall, and then up and down until you find the metal or plastic plate of the switch. During the process you use your sense of touch to develop an image in your mind of the wall's surface and make a better guess for where the switch is.
Sliman Bensmaia, PhD, assistant professor of organismal biology and anatomy at the University of Chicago, studies the neural basis of tactile perception, ...
A University of British Columbia researcher has helped create a gel – based on the mussel's knack for clinging to rocks, piers and boat hulls – that can be painted onto the walls of blood vessels and stay put, forming a protective barrier with potentially life-saving implications.
Co-invented by Assistant Professor Christian Kastrup while a postdoctoral student at the Massachusetts Institute of Technology, the gel is similar to the amino acid that enables mussels to resist the power of churning water. The variant that Kastrup and his collaborators created, described in ...
ANN ARBOR—Vega, a star astronomers have used as a touchstone to measure other stars' brightness for thousands of years, may be more than 200 million years older than previously thought. That's according to new findings from the University of Michigan.
The researchers estimated Vega's age by precisely measuring its spin speed with a tool called the Michigan Infrared Combiner, developed by John Monnier, associate professor of astronomy in U-M's College of Literature, Science, and the Arts.
MIRC collects the light gathered by six telescopes to make it appear to be coming ...
