Tuesday 8 February 2011

Johnald's Fantastical Daily Link Splurge

Johnald's Fantastical Daily Link Splurge

Dr. Seussian Mystery Fluid Could Have Saved Top Kill

Posted: 07 Feb 2011 11:00 AM PST

A mixture of cornstarch and water best known for entertaining kindergartners could have plugged the spewing Macondo oil well in the Gulf of Mexico, say physicists.

Where regular drilling mud failed to stop the flow, oobleck — a complex fluid that seems to switch between liquid and solid — succeeded in simulations published Jan. 31 in Physical Review Letters.

"We couldn't do a full scale experiment on a real well that was blowing out 50,000 barrels a day, but to the extent that you can do a smaller experiment in the laboratory it's basically the same physics," said physicist Jonathan Katz of Washington University in St. Louis. "And it seems to work."

Last May, three weeks after an explosion on the Deepwater Horizon drilling rig left an open well gushing thousands of barrels of oil into the Gulf, the Department of Energy convened a group of independent experts to help stop the flow.

BP, which owned the well, planned to pump heavy drilling mud into the well in a project called "top kill." The plan was for dense mud to sink through the oil and clog the bottom of the pipe. Top kill had worked for other blowouts, where the oil flowed more slowly. But the DOE group saw almost immediately that for Macondo, top kill would fail.

Like paint or ketchup, mud used in drilling thins when it flows quickly, Katz explained. Usually that's an advantage, because thinning mud is easier to pump into a well. But if the oil comes out too fast, and two fluids with different densities rush past each other, turbulence takes over. Whorls and eddies form.

Oil gushed out of Macondo at 3.7 meters per second, causing enough chaos to break up the mud into tiny, useless droplets. "It was sufficiently fast to break up anything descending into small droplets, and sweep them back up and spit them out the top," said Katz, who was part of the DOE team. "That's what ruined the top kill."

 

But even as BP made plans for its doomed top kill, Katz wondered whether oobleck might do the trick.

The half-water, half-cornstarch goop is named after the Dr. Seuss book Bartholomew and the Oobleck, and its quick-change artistry between liquid and solid makes it a kitchen science classic. When it's flowing slowly, oobleck can drip through your fingers as a liquid. But when oobleck flows quickly, it turns suddenly thick, almost solid. YouTube is full of people running across pools of oobleck, and sinking when they run too slowly.

Katz did some quick math and saw that a half-cornstarch drilling mud would suppress the turbulence and sink in one coherent slug. Unfortunately, no one listened.

"I have no idea why they didn't pay attention," said Richard Garwin, a retired IBM physicist who was also part of the DOE-convened team.

The top-kill plan went ahead with the usual drilling mud, and ultimately failed. But Katz went on to team up with Peter Beiersdorfer, David Layne and Edward Magee of Lawrence Livermore National Laboratory to test whether oobleck might really have worked.

The researchers filled a tube 1.6 meters tall and 63 mm in diameter with a transparent mineral oil. They pumped water colored with green dye into the oil at a rate of about 1.15 meters per second, and saw the swirling turbulence they expected.

But when they repeated the experiment with a mixture of cornstarch and water, the goop sank in a single column.

The new paper is "an excellent piece of work," Garwin said. "It should have been done by BP long ago."

Engineer Paulo Arratia of the University of Pennsylvania thinks the experiment is a very good first step, but he would like to see a more systematic follow-up study. "It works in a bench-top experiment, in the lab. I don't know if it works in the real oil well," he said.

In particular, he would like to see more details on the physical properties of the oobleck: how fast it flows, how quickly it switches from liquid to solid, and which kind of cornstarch they used.

"This will not be the last time we have oil spills," he said. "It will be very important to know if this is actually a valid method. Come [the next] disaster, we'll need to know exactly what we're dealing with."

Images: 1) Flickr/thatmushroom. 2) Physical Review Letters/Beiersdorfer et al. 2011. Video: Michigan Technological University

"Viscoelastic Suppression of Gravity-Driven Counterflow Instability." P. Beiersdorfer, D. Layne, E.W. Magee and J. I. Katz. Physical Review Letters, Vol. 106 No. 5, Week ending Feb. 4, 2011. DOI: 10.1103/PhysRevLett.106.058301

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Quantum Fluctuations May Melt Ultracold Glass

Posted: 07 Feb 2011 07:30 AM PST

Just above absolute zero, the coldest temperature possible in the universe, quantum fluctuations can melt some forms of glass into goo.

At the subatomic scale, particles like protons, neutrons and electrons behave like waves, not just infinitesimal points. As a result, particles have jittery positions and can "tunnel" through other particles, among their other abilities.

At everyday temperatures and in ordinary silicate glass, those fluctuations are drowned out. But at ultracold temperatures, in simple glasses made of tiny particles — including hydrogen, helium and even electrons — the chaos of quantum fluctuations may liquefy glass.

"We had a pencil-and-paper result a few years ago, but we didn't believe it. It seemed like a ridiculous prediction," said chemist David Reichman of Columbia University, co-author of a study published Jan. 9 in Nature Physics. "But two quantum simulation experts said they could make large-scale computer simulations to verify it, and they did."

 

Debates about the essential nature of glass have raged for a century. At room temperature, it acts like a solid. Its molecular structure, however, resembles that of a liquid, and at high temperatures it turns molten. The Nobel Prize-winning physicist Philip Anderson has described the nature of glass and its transitions as "the deepest and most interesting unsolved problem in solid state theory."

There's agreement on a few crucial points, though. Glasses have no hint of a crystal structure, and their particles have no order or simple pattern. As temperatures drop, glasses become more brittle.

Reichman and his team thought that as normal particle motion stopped near absolute zero, quantum effects would further weaken simple glasses. Yet their calculations returned two surprises: Quantum fluctuations just above absolute zero melt glass, and weaker quantum fluctuations at slightly warmer temperatures strengthen it.

To make the discoveries, Reichman's team simulated about 1,000 helium-like particles in a glassy state (video above). They kept the temperature within a few degrees of absolute zero, and manipulated the strength of quantum effects by changing particle size. The smaller the particle, the stronger the effects.

The strongest quantum effects allowed particles to tunnel through each another. The solid glass structure turned into a free-flowing liquid. Yet weaker quantum effects, which increased glass density without introducing too much disruptive motion, strengthened the glass.

Aside from matter lurking in deep space, Reichman doesn't see much physical application to the results. But glass particle behavior is analogous to some of the most vexing mathematical problems.

"Glass particles are unsatisfiable. They always want to move to a low-energy state but can't, like hikers walking over mountains that get stuck," he said. "The same is true for some algorithmic problems. The transition from easy to hard is like a liquid-to-glass transition. There's a strong relationship."

As a result, many scientists working on glass have migrated to statistics. Some try to use quantum mechanics to find optimal solutions, but Reichman now warns against doing so.

"Our paper suggests that you have to be careful," he said. "If you're adding quantum effects, it can make it harder, not easier, to search low-energy states and solve these problems."

Video: A simulation of small glass particles at ultra-cold temperatures over the course of about 100 picoseconds. Green and blue blobs represent particles with quantum mechanical laws applied to them (their sizes are similar to helium or hydrogen). The red ring represents the possible positions of a single particle; the same behavior is happening for all other particles, but is hidden for clarity. This quantum "tunneling" effect can weaken glass to the point of being a liquid. (Nature Physics/Thomas Markland et al.)

Citation: "Quantum fluctuations can promote or inhibit glass formation." Thomas E. Markland, Joseph A. Morrone, Bruce J. Berne, Kunimasa Miyazaki, Eran Rabani, David R. Reichman. Nature Physics, Vol. 7, 134-137, January 9, 2011. DOI: 10.1038/nphys1865

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Video: Roiling Sun Captured From All Angles

Posted: 07 Feb 2011 07:05 AM PST

When it comes to solar storms, there's no longer any place to hide. For the first time, solar scientists have obtained simultaneous views of the entire sun, both the front and back sides.

The unprecedented 360-degree panorama, released by NASA on Feb. 6, combines sharp images of the sun's front side recorded by NASA's Solar Dynamics Observatory with those from NASA's twin Stereo spacecraft, which have just begun an eight-year exploration of the rotating sun's far side. Images of the far side, recorded up to 14 days before they rotate into view from Earth, will enable scientists to better predict solar storms that can damage satellites and disrupt communications and power systems on Earth.

The images can also capture eruptions on the back side so short-lived that they disappear before that region of the sun rotates into view, says Stereo scientist Joseph Gurman of NASA's Goddard Space Flight Center in Greenbelt, Maryland. In January, he notes, a solar eruption recorded by Stereo was detected by the Messenger spacecraft as a change in the nearby magnetic field. Messenger, which is about to enter orbit around Mercury, was not harmed by the event.

The new Stereo images resolve features on the sun about 2,400 kilometers [1,500 miles] across.

 

Video: This solar portrait captures the far side of the sun, hidden from Earth's view, as een by NASA's twin Stereo spacecraft. Now that the craft have begun an eight-year exploration of the sun's far side, scientists for the first time have obtained 360-degree panoramas of the sun, as shown in an accompanying video. The dark crack is a narrow region where data still needs to be gathered. (NASA/Goddard Space Flight Center/Stereo/SECCHI)

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