Wednesday, August 26, 2015

On Pi and Tau

In 2010, physicist and educator Michael Hartl published something he called The Tau Manifesto, a piece of writing which put forth arguments for a surprisingly controversial assertion: π is wrong.

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Monday, August 24, 2015

Danger! High Voltage

A few weeks ago, we put up a "Fermi problem Friday" post about the odds of being struck by lightning. That post was met with some criticism in the comments section, so it's currently down while we revise it to reflect our readers' concerns. But last Friday, we made a discovery here at PhysicsCentral headquarters: your odds of getting zapped go up exponentially if your boss brings her old Van de Graaff generator to work!

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Wednesday, August 19, 2015

Liftoff: Hydrophobic Fibers Fling Condensation From Their Strands

I recently moved to the DC area in the middle of the summer where, on a bad day, being outdoors is a lot like being inside a rice cooker; sometimes I wish I could stop sweating, because evaporative cooling doesn’t really work when the air is already practically saturated with moisture. As such, the dehumidifier has become my new best friend. This miracle of modern technology that keeps the mildew out of my apartment works by blowing air over a refrigerated mesh of wires, where the water condenses and falls into a bucket, sometimes at the surprising rate of a few liters per day.

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Monday, August 17, 2015

The Heavyweight Champion of the Universe

About 3.4 billion light-years away, in the general direction of the constellation Draco, lies one of the heaviest singular objects in the known universe. Designated H1821+643, it has roughly 30 billion times the mass of the sun, with an event horizon that could swallow our solar system—28 times over.

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Friday, August 14, 2015

What's more radioactive than a nuclear power plant?

A lot of things, it turns out. But the one you'd probably least expect? Waste from a non-nuclear power plant, by a factor of 100.

Would we feel different about fossil fuels if this 
warning were mandatory on coal-fired power plants? 
Image courtesy Torsten Henning, Public Domain
On Wednesday, we published a Physics+ article about radiation, written in memory of the bombing of Hiroshima, 70 years prior. While the author did a fantastic job in describing the state of the art on low-dose radiation research, I was troubled by a line where he cited "widespread deployment of nuclear power" along with medical scans and air travel as a potential contributor to chronic low-dose radiation. I took issue with the line because, counterintuitive as it might be, widespread deployment of nuclear power is acting to decrease the radiation burden of the average individual. To understand how, we'll need a smidge of radiation biophysics knowledge, along with a touch of nuclear engineering. If that sounds scary, don't worry; I promise to keep it simple.

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Tuesday, August 11, 2015

The Disappointing Truth About Lexus' New Hoverboard

By now you've probably seen the latest video of Lexus' hoverboard technology, a two-minute spot produced as part of their "Amazing in Motion" advertising campaign. The board itself is incredibly cool—literally—the technology relies on superconductors, cooled using liquid nitrogen to somewhere below -200°C, and as a result it emits a trail of futuristic-looking fog (actually condensing water vapor) wherever it goes. Unfortunately, the video, which shows a number of skateboarders trying out their favorite sport sans wheels, is more than a little misleading.

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Wednesday, August 05, 2015

Blue Smoke, Red Sun

I was living in Indiana back in June when I got a surprise lesson in optics, simply by looking out my window to see the golden-orange glow of sunset bathing our lawn. That’s odd, I thought to myself, seems like the day just flew by.

I checked my watch; it was 3 P.M. I blinked hard, wondering to myself what could be going on. I checked my phone; still 3 P.M. I stepped outside for a better look around.
There was no mistaking it; this was the kind of color scheme I was used to seeing an hour or two before the last light of the day, but the sun was hanging stubbornly far above the horizon, at its usual 3 o’clock position.

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Tuesday, August 04, 2015

String Theory (No, not that kind!)

Creating a slow-motion effect in real life takes some creativity, but with the help of a few strobe lights and a frequency generator, the folks at Pasco put together one that’s truly mesmerizing, on top of being educational. Watch the video of it below, and then read on to find out how it’s done!

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Friday, July 31, 2015

Allotropy: Why Winter Spells Trouble for the Tin Man

Tin is a commonplace metal that’s used industrially in a thousand different ways. From the solder that holds your computer’s motherboard together to the PVC plumbing under your sink, tin compounds are everywhere. In spite of its versatility, tin possesses an interesting physical property which is responsible for its tendency to wear down over time outdoors. This phenomenon, known as “tin pest”, is certainly not due a biological organism, but is widely mistaken for an oxidation reaction. Instead, tin pest happens thanks to something called allotropy—the metal’s atomic lattice can take on multiple different shapes, depending on the temperature it’s kept at. 

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Thursday, July 30, 2015

How Insects' Legs Can Improve Man-Made Materials

In an effort to improve materials used in aviation and medicine, a team of Irish researchers is studying the legs of certain insects. Some features that appear to contribute to the legs' sturdiness don’t actually do so, they found, while others that would be expected to weaken the legs don’t have that effect.

These null results provide fresh insight into the surprising ways that nature works. But the new understanding also has the potential to contribute to applications of engineering materials shaped like the insects’ legs.
David Taylor’s team examined how the insects’ legs, which consist of light, thin, tubelike structures of cuticle material, buckle and bend in response to pressure.
“Many materials in nature have evolved to perform some mechanical purpose. So my research group is looking at insects, crabs, plant stems, eggs, etc.,” explained Taylor, a professor of mechanical engineering at Trinity College, Dublin.
In addition to studying how the natural materials work, said Taylor, engineers must also be sure they understand how they might fail.
Long, thin-walled tubes tend to maintain strength despite weighing less than other types of structures.
That provides an obvious benefit for designers of aircraft parts and hospital equipment such as catheters. But the tubes’ tendency to buckle, in the way that a drinking straw gives when bent, counters that advantage.
Taylor’s team set out to understand how differences in the detailed structure of insects’ legs influence their buckling behavior. They began with locusts, which are large and easy to work with, before moving on to other largish insects that live different lifestyles, including bees, stick insects and cockroaches.
Those insects not only use their legs in different ways in their natural environments; they also have different leg structures.
“The interesting aspect I found [in the Taylor group’s work] was the observation of the different cross-section shapes of the insect legs,” said Ahmer Wadee, a professor of nonlinear mechanics at Imperial College, London, who studies why metals and other materials buckle.
Stick insects have five ridges running down their legs. Bees’ legs have triangular cross-sections, with one large, flat surface used to carry pollen. And the legs of locusts and cockroaches have almost circular cross-sections.
Taylor and his team obtained their subjects locally. “We buy our locusts from a pet shop where they are normally used as food for the snakes. So we feel they get a slightly nicer and longer life with us,” he said. “In our care they live much longer than they normally would, even in the wild. And at the end of our work they are euthanized in a humane way."
To test the buckling behavior of a leg, on a living insect or detached from it, the team fixed one end by putting it in quick-drying polymer cement.
“We held it horizontally and pressed down on the other end using a testing machine which can record the applied force,” Taylor noted. “You can do something similar for yourself with a drinking straw or, better still, those tubes of plastic foam that are used to insulate water pipes.”
Timing was critical. “We needed to test the legs within a few minutes of cutting them off because they quickly dry out and become more stiff and brittle,” Taylor recalled.
The team found that buckling is a complex process that can occur in several different ways. Under a growing force, a leg suddenly becomes unstable, said Taylor, which can quickly lead to deformation and failure. In addition to experiments with the actual legs, they use computer simulations.
The experiments and simulations revealed that two types of buckling occur more or less simultaneously. These are local buckling, which is what happens when you press on the ends of a beer can, and ovalization buckling that occurs when the circular tube becomes oval and bends more easily.
Further investigation showed that different tube shapes confer no apparent advantage or disadvantage on insects’ legs.
“The ridges running along a stick insect’s legs look as if they are there to make the leg stiffer and more resistant to bending; we expected them to make the tubes about two-and-a-half times stronger,” Taylor said. “But we found out that they don’t; the leg would be just as good without them. So those ridges must have evolved for some other purpose that we don’t know about yet.”
The team also expected that pollen baskets might make bees’ legs weaker and more prone to buckling. “But we found they were just as good as if they had been circular,” Taylor said. “This shows that it’s possible to design non-circular cross sections that work well.”
A related piece of research compared the forces that insects’ legs experience with those that predictions indicate will cause the legs to break. Graduate student Eoin Parle found that when locusts jump, their legs experience more than half the failure force.
“That means there is a safety factor of less than two,” Taylor said. “That’s much smaller than you will find in most engineering structures.”
However, locusts have a safety mechanism, according to recent research by Malcolm Burrows, emeritus professor of biology at the University of Cambridge. “This is a specialized region in the tibia which buckles if the leg over-extends, but which contains the elastic protein resilin that returns the leg to its original shape,” Burrows said.
What does the Trinity College team’s research, which it presented at a meeting of the Society for Experimental Biology, suggest for the design of man-made structures?
“We’ve made a small contribution there by showing how certain types of buckling can be predicted using computer programs, and by showing that non-circular cross sections can be effective,” Taylor said. “Certainly a possible future application of this knowledge could be in the development of new designs for aircraft and other fields.”
--Peter Gwynne, Inside Science News Service

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