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. This advancement not only broadens fundamental knowledge, it also provides new avenues to a number of practical areas that ranges from materials innovation to medicine. The study, currently available on the Nature Physics Web site, will be published in the journal’s print edition on May 1.

“We started this research by looking at the behavior of dry powders as solid lubricants as well as the behavior of a powdered rock in fault zones called gouge during an earthquake. What we found led us to a model that can accurately predict the behavior of dense granular flows. What we realized soon after was that the granular particles interact similarly to that of molecules in materials that jam, such as colloids and foam” said study’s author Pirouz Kavehpour, an assistant professor of mechanical and aerospace engineering and director of the Complex Fluids & Interfacial Physics Laboratory at UCLA. “From there, we were able to find a universal law that can predict the jamming behavior for the first time.”

According to Emily Brodsky, associate professor of earth and planetary sciences at UC Santa Cruz and also an author of the study, “We understand how water flows. We understand how honey flows. We even understand how elastic bands deform. But granular flows are complicated and hard to understand. If you’re pouring sand down a hill or in an hour glass, there was never a good formula for the strain or the strain rate as a function of stress. This formula is definitely new and unique.”

Kevin Lu, UCLA graduate student and lead author of the study, showed that the formula also quantified glass-transition. “Glass is a solid that flows. But structurally, it’s a liquid. The molecules in a glass are jammed and unable to flow past each other so the material actually flows sluggishly. One evidence of this can be found in the window panes of old churches in Europe. Studies have shown that the bottom of the windows are consistently thicker than the top. Glassy liquids flow very much in the same manner as granular media.” said Lu.

This new theoretical framework, the authors believe, can be applied to many different areas. Pharmaceutical companies can use the new equation to decide the size and quantities of pills that may or may not fit through a shoot that fills containers. Also, from knowing the fundamentals of jamming, scientists can now engineer materials that are both durable and strong. Instead of working with composites or alloys, the jamming theory provides a roadmap to tune material properties from pure substances.

“It can also help us to better understand certain diseases in medicine. In sickle cell anemia, for example, the abnormal blood cells are long and skinny, resulting in the obstruction of blood flow to various organs. Now we can do more to reduce the likeliness of death-threatening implications to benefit the medical community,” said Lu.

As a geologist who studies fault zones and earthquakes, Brodsky is particularly interested in the granular flow of gouge found in fault zones and having a formula to figure out when the rock is jammed and when it’s free flowing can be significant.

“Knowing how things flow and the granular behavior in a fault zone is one of the very important steps in trying to figure out how exactly faults slip,” said Brodsky.

The study was partially funded by the Air Force Office of Scientific Research.

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A team of astronomers looking at the universe’s distant past found nine young, unusually compact galaxies, each weighing in at 200 billion times the mass of the Sun. These young galaxies are the equivalent of a human baby that is 20 inches long, yet weighs 180 pounds.

“Seeing the compact sizes of these galaxies is a puzzle,” said Pieter G. van Dokkum of Yale, who led the study. “No massive galaxy at this distance has ever been observed to be so compact, and it is not yet clear how one of these would build itself up to be the size of the galaxies we see today.” The findings appeared in the April 10 issue of The Astrophysical Journal Letters.

The galaxies, each only 5,000 light-years across, are a fraction of the size of today’s “grownup” galaxies but contain approximately the same number of stars. Each could fit inside the central hub of the Milky Way. “These ultra-dense galaxies, forming the building blocks of today’s largest galaxies, might comprise half of all galaxies of that mass at this early time,” van Dokkum said.

But, van Dokkum noted that they would have to change a lot over 11 billion years — they would have to grow five times bigger, “While they could get larger by colliding with other galaxies, such collisions may not be the complete answer,” he said.

Astronomers used NASA’s Hubble Space Telescope and the W.M. Keck Observatory on Mauna Kea, Hawaii, to study the galaxies whose light has been traveling toward us for 11 billion years. “What we see now is the way these compact galaxies existed 11 billion years ago, when the universe was less than 3 billion years old,” van Dokkum explained. “Only Hubble and Keck can see the sizes of these galaxies because they are very small and far away.”

In 2006, the research team also studied the galaxies with the Gemini South Telescope Near-Infrared Spectrograph, on Cerro Pachon in the Chilean Andes. Those observations provided the galaxies’ distances and showed that the stars are a half a billion to a billion years old, and that the most massive stars had already exploded as supernovae.

“In the Hubble Deep Field, astronomers found that star-forming galaxies are small,” said Marijn Franx of Leiden University, The Netherlands. “However, these galaxies were also very low in mass. They weigh much less than our Milky Way. Our study, which surveyed a much larger area than in the Hubble Deep Field, surprisingly shows that galaxies with the same weight as our Milky Way were also very small in the past. All galaxies look really different in early times, even massive ones that formed their stars early.”

Van Dokkum speculated on how these small, crowded galaxies formed. He said, one way could have involved an interaction in the emerging universe between hydrogen gas and dark matter — an invisible form of matter that accounts for most of the universe’s mass. Shortly after the Big Bang, the universe contained an uneven landscape of dark matter. He said that hydrogen gas could have been trapped in puddles of the invisible material which began spinning rapidly in dark matter’s gravitational whirlpool, forming stars at a furious rate.

The astronomers estimated that the stars in the compact galaxies are spinning around their galactic disks at roughly 1 million miles an hour (500 kilometers a second). Stars in today’s galaxies, by contrast, are traveling at about half that speed because they are larger and rotate more slowly.

These galaxies are ideal targets for the Wide Field Camera 3, which is scheduled to be installed aboard Hubble during Servicing Mission 4 in the fall of 2008. The team says that the new images should lead to a better understanding of the evolution of galaxies early in the life of the universe.

The authors of the paper are Pieter van Dokkum (Yale University), Marijn Franx (Leiden University, The Netherlands), Mariska Kriek (Princeton University), Bradford Holden, Garth Illingworth, Daniel Magee, and Rychard Bouwens (University of California, Santa Cruz and Lick Observatory), Danilo Marchesini (Yale University), Ryan Quadri (Leiden University), Greg Rudnick (National Optical Astronomical Observatory, Tucson), Edward Taylor (Leiden University), and Sune Toft (European Southern Observatory, Germany).

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