Posts Tagged ‘Physics’

Why are clouds white? [Madscience]

10 Jul
Water is clear. The sky is blue. So why are clouds white? And if regular clouds are white, why are rain clouds gray? More »

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


How do we measure gravitational waves? [Mad Science]

03 Jul
"Gravitational telescopes" let scientists observe fluctuations in spacetime itself. They are, in a word, crazystupidamazing. More »

Carbon Nanotube Manufacturing Breakthrough Could Mean Bye-Bye Steel [Nanotubes]

30 Sep

Carbon nanotubes have been popping on Giz for a while, touted as one of the next wonder-materials—but a new development in their manufacture means they may not remain "future technology" for long. In fact the work of a team at CSIRO and the University of Texas at Dallas means that commercial-scale production of sheets of carbon nanotube "textile" is possible at up to seven meters per minute.

And these are no ordinary textiles either: they're transparent and way stronger than a sheet of steel. The team's technique involves chemically-growing "forests" of nanotubes that self-assemble, and is reported in Science currently. If it proves true we may see nanotube materials replacing metals like steel pretty soon—though I'm not sure how many people would balk at flying in a plane with wings you can partly see through. [Physorg]

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Earth: A Very Special Place In the Void [Dark Energy]

29 Sep

You know that "I'm an insignificant dot in the middle of this enormous universe" feeling you get when you stare up into the night sky a little too long? Well, some Oxford scientists think you might be a little more special than that - or at least, the planet you live on is. Their radical new theory would not only obviate the need for dark energy to explain observed patterns of galactic motion, it would overturn the centuries-old Copernican Principle. Not bad for a day's work.

In the 16th century, Copernicus hypothesized that the Earth is not the center of the solar system, but rather the sun is. Later, cosmologists expanded this idea into the Copernican Principle: Earth is not in a special place in the universe, therefore our observations of local space can be used to infer data about the rest of the universe. When astronomers observed that the universe appears to be expanding at an accelerating rate, they needed to add something to their equations to make it all make sense. That something is dark energy, which would have to exist in massive quantities (as yet, pretty much undetectable) to explain this expansion.

Here's the thing - the universe is really, really, really huge. Just the part we can see is almost incomprehensibly big, and there's a whole lot of universe we can't see. No one knows how big the whole universe is, but it's entirely possible that our part of the universe is just a tiny fraction of the whole. Physicists from Oxford University are considering the idea that the universe we can observe is actually anomalous, a giant void with a low density of matter. The rest of the universe may look substantially different. Doing some number crunching revealed that their model of the universe works without dark energy, but isn't quite as accurate as the current dark energy model. However, they need more observations of certain types of supernovae to refine their numbers - in a few months, their equations may look better with more data.

What's particularly cool is that this maverick theory that tosses a very accepted tenet of astronomy right out the window is being published in Physical Review Letters, one of the most respected physics journals. It sure beats excommunication. Image by: NASA.

Overturning Copernicus, eliminating dark energy. [Nobel Intent]

Tsunami invisibility cloak, dark energy v. the void, sorting nanotubes with light, and more. [EurekAlert!]

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