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Posts Tagged ‘ScienceNews.org’

Flawed Diamonds Could Store Quantum Data

25 Mar

DALLAS — Scientists have developed a new way to manipulate atoms inside diamond crystals so that they store information long enough to function as quantum memory, which encodes information not as the 0s and 1s crunched by conventional computers but in states that are both 0 and 1 at the same time. Physicists use such quantum data to send information securely, and hope to eventually build quantum computers capable of solving problems beyond the reach of today’s technology.

sciencenewsFor those developing this quantum memory, the perfect diamonds don’t come from Tiffany & Co. — or Harry Winston, for that matter. Impurities are the key to the technology.

“Oddly enough, perfection may not be the way to go,” said David Awschalom of the University of California, Santa Barbara. “We want to build in defects.”

One of the most common defects in diamond is nitrogen, which turns the stone yellow. When a nitrogen atom sits next to a vacant spot in the carbon crystal, the intruding element provides an extra electron that moves into the hole. Several years ago, scientists learned how to change the spin of such electrons using microwave energy and put them to work as quantum bits, or qubits.

In search of a more stable way to store quantum information, Awschalom has now figured out how to link the spin of a electron to the spin of the nearby nitrogen’s nucleus. This transfer, triggered by magnetic fields, is fast — about 100 nanoseconds, comparable to how long it takes to store information on a stick of RAM.

The technique has “a fidelity of 85 to 95 percent,” Awschalom said March 22 in Dallas at a meeting for the American Physical Society.

In contrast to some other quantum systems under development, which require temperatures close to absolute zero, this diamond memory works at room temperature. The spins inside the diamond can be both changed and measured by shining laser light into the diamond. This could make diamond an attractive material for scientists developing nanophotonic systems designed to move and store information in packets of light.

Unlike a diamond itself, this quantum memory isn’t forever. But it lasts for a very long time by quantum standards. The nuclear spin remains coherent for more than a millisecond, with the potential to improve to seconds.

“You can only do your quantum magic as long as you have coherence,” said Sebastian Loth, a physicist at IBM’s Almaden Research Center in San Jose, Calif. “If you have a lifetime of milliseconds, that lets you do millions of operations.”

In addition to stability, diamond may also overcome another hurdle that has faced quantum computing — it can be scaled up to larger sizes. In a paper published last year in Nano Letters, Awschalom developed a technique for creating customizable patterns of nitrogen atoms inside a diamond, using lasers to implant thousands of atoms in a grid.

Awschalom’s diamond quantum memory could also be useful for building large quantum networks. Currently, quantum information is transmitted by connecting, or entangling, qubits. This scheme is limited to distances of kilometers. Quantum repeaters could potentially use small chips of diamond to catch, store and retransmit this information to extend the range, enabling quantum networks to work over much longer distances.

Image: Jurvetson/Flickr

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Nerve-Electronic Hybrid Could Meld Mind and Machine

21 Mar

Nerve-cell tendrils readily thread their way through tiny semiconductor tubes, researchers find, forming a crisscrossed network like vines twining toward the sun. The discovery that offshoots from nascent mouse nerve cells explore the specially designed tubes could lead to tricks for studying nervous system diseases or testing the effects of potential drugs. Such a system may even bring researchers closer to brain-computer interfaces that seamlessly integrate artificial limbs or other prosthetic devices.

sciencenews“This is quite innovative and interesting,” says nanomaterials expert Nicholas Kotov of the University of Michigan in Ann Arbor. “There is a great need for interfaces between electronic and neuronal tissues.”

To lay the groundwork for a nerve-electronic hybrid, graduate student Minrui Yu of the University of Wisconsin–Madison and his colleagues created tubes of layered silicon and germanium, materials that could insulate electric signals sent by a nerve cell. The tubes were various sizes and shapes and big enough for a nerve cell’s extensions to crawl through but too small for the cell’s main body to get inside.

When the team seeded areas outside the tubes with mouse nerve cells, the cells went exploring, sending their threadlike projections into the tubes and even following the curves of helical tunnels, the researchers report in an upcoming ACS Nano.

“They seem to like the tubes,” says biomedical engineer Justin Williams, who led the research. The approach offers a way to create elaborate networks with precise geometries, says Williams. “Neurons left to their own devices will kind of glom on to one another or connect randomly to other cells, neither of which is a good model for how neurons work.”

At this stage, the researchers have established that nerve cells are game for exploring the tiny tubes, which seem to be biologically friendly, and that the cell extensions will follow the network to link up physically. But it isn’t clear if the nerves are talking to each other, sending signals the way they do in the body. Future work aims to get voltage sensors and other devices into the tubes so researchers can eavesdrop on the cells. The confining space of the little tunnels should be a good environment for listening in, perhaps allowing researchers to study how nerve cells respond to potential drugs or to compare the behavior of healthy neurons with malfunctioning ones such as those found in people with multiple sclerosis or Parkinson’s.

Eventually, the arrangement may make it easier to couple living cells with technology on a larger scale, but getting there is no small task, says neuroengineer Ravi Bellamkonda of the Georgia Institute of Technology in Atlanta.

“There’s a lot of nontrivial engineering that has to happen, that’s the real challenge,” says Bellamkonda. “It’s really cool engineering, but what it means for neuroscience remains to be seen.”

Images: Minrui Yu

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Muscles Remember Past Glory

16 Aug

Pumping up is easier for people who have been buff before, and now scientists think they know why — muscles retain a memory of their former fitness even as they wither from lack of use.

sciencenewsThat memory is stored as DNA-containing nuclei, which proliferate when a muscle is exercised. Contrary to previous thinking, those nuclei aren’t lost when muscles atrophy, researchers report online August 16 in the Proceedings of the National Academy of Sciences. The extra nuclei form a type of muscle memory that allows the muscle to bounce back quickly when retrained.

The findings suggest that exercise early in life could help fend off frailness in the elderly, and also raise questions about how long doping athletes should be banned from competition, says study leader Kristian Gundersen, a physiologist at the University of Oslo in Norway.

Muscle cells are huge, Gundersen says. And because the cells are so big, more than one nucleus is needed to supply the DNA templates for making large amounts of the proteins that give muscle its strength. Previous research has demonstrated that with exercise, muscle cells get even bigger by merging with stem cells called satellite cells, which are nestled between muscle fiber cells. Researchers had previously thought that when muscles atrophy, the extra nuclei are killed by a cell death program called apoptosis.

Memory holding nuclei on muscle fiber light up in green.

In the new study, Gundersen’s team simulated the effect of working out by making a muscle that helps lift the toes work harder in mice. As the muscle worked, the number of nuclei increased, starting on day six. Over the course of 21 days, the hard-working muscle increased the number of nuclei in each fiber cell by about 54 percent. Starting on day nine, the muscle cells also started to plump up, adding an extra 35 percent to their volume. Those results indicate that the nuclei come first and muscle mass is added later.

In another set of experiments, the researchers worked the mice’s muscles for two weeks and then severed nerves leading to the muscle so the tissue would atrophy. As the muscle atrophied, the cells deflated to about 40 percent of their bulked-up volume, but the number of nuclei in the cells did not change.

These results contradict previous studies that show lots of cell death in muscles during atrophy. Gunderson’s team examined individual cells in the wasting muscles and found that there is apoptosis going on, but that other cells are dying, not the muscle fibers or their extra nuclei. The extra nuclei stick around for at least three months — a long time for a mouse, which lives a couple of years on average, Gundersen says.

“I don’t know if it lasts forever,” he says, “but it seems to be a very long-lasting effect.” Since the extra nuclei don’t die, they could be poised to make muscle proteins again, providing a type of muscle memory, he says.

“That’s fascinating thinking, and there’s nice proof in this article to support it,” says Bengt Saltin, a muscle physiologist at the University of Copenhagen in Denmark. “It’s really novel and helps to explain descriptive findings that muscles are quick to respond upon further training.”

The study is likely to provoke strong reaction from some researchers, says Lawrence Schwartz, a cell biologist at the University of Massachusetts Amherst.

“It does fly in the face of a lot of peer-reviewed, published data,” he says. But the selective death of just some of the nuclei in a muscle cell would require a special kind of apoptosis. “The conventional wisdom doesn’t make much sense from a cell and molecular perspective,” Schwartz says. Gunderson’s group has come up with an explanation that seems more plausible. “Their data just feels right.”

If the results hold up in people, sports agencies may want to reconsider how long they ban athletes suspended for taking steroids. Previous research has shown that testosterone boosts the number of nuclei in muscle cells beyond the amount produced by working out. “If you have nuclei that last forever, then you would also have an advantage that could last forever,” Gundersen says.

Well, maybe not exactly forever. As people age, their ability to build muscle mass declines. The new study suggests that pumping muscles full of nuclei early in life could help stave off muscle loss with age. “This could be an argument for mandatory physical training in schools,” Saltin says.

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Images: 1) left to right: Nubret, Schwarzenegger, Lou Ferrigno, ca. 1975. Flickr/d_vdm. 2) J.C. Bruusgaard/University of Oslo

 
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Turbulence Discovery Could Lead to Better Planes

09 Jul

With just a single measurement, a new model may deftly describe turbulent fluid flows near an airplane wing, ship hull or cloud, researchers report in the July 9 Science. If the long-sought model proves successful, it may lead to more efficient airplanes, better ways to curb pollution dispersal and more accurate weather forecasts.

sciencenewsFluid dynamicist Alexander Smits of Princeton University calls the new model “a very significant advance” that opens up a new way of thinking about chaotic, energy-sapping turbulence.

Turbulence is a problem that extends far beyond a bumpy plane ride. Fluid flowing past a body — whether it’s air blowing by a fuselage or water streaming across Michael Phelps’s swimming suit — contorts and twists as it bounces off an edge and interferes with incoming flows, creating highly chaotic patterns. Airliners squander up to half of their fuel just overcoming the turbulence within a foot or so of the aircraft, and turbulent patterns in the bottom 100 meters of the atmosphere confound weather and climate predictions.

Physicists and engineers have had a good grip on the basic behaviors of fluids since the mid-1800s, but have been baffled by the complexity of the tumultuous flows near a boundary. “We don’t really have a handle on the physics,” says study co-author Ivan Marusic of the University of Melbourne in Australia. “So even though the problem is over a hundred years old, we still really haven’t had a major breakthrough.”

In their new study Marusic and his colleagues measured forces in a giant wind tunnel, both near and away from a wall. Data collected by probes suggested a tight link between the small-scale turbulence near a wall and large, smoother patterns of air flow farther from the wall. In particular, newly identified flow patterns called superstructures turn out to have a big effect on the turbulence near the wall. These smooth, predictable flow patterns away from the wall change the turbulence right next to the wall in predictable ways, a link that allowed Marusic and colleagues to write a mathematical formula relating the two.

“The fact is that we were sort of amazed because it’s such a simple formulation,” Marusic says. “Now with this model, all we need to do is measure the outer flow and we can predict what’s happening near the wall.”

If it pans out, the formula may be incorporated into models of climate, weather and pollution dispersal. And now that they have a better understanding of the near-wall turbulence, Marusic and his colleagues are trying to reduce it by manipulating the smooth flow of fluids away from a wall.

One of the strengths of the new model is that it allows the complex flow near boundaries to be reduced to a bare-bones motion that can be easily understood, says engineer Ronald Adrian of Arizona State University in Tempe, who authored an accompanying article in the same issue of Science.

“This model is a breakthrough step, but we’re not ready to say that it’s going to solve all our problems,” he says. “I don’t know if we have enough evidence yet to call it universal, but the hope is that it will be universal.”

Image: zoagli/Flickr

 
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