Archive for the ‘Physics’ Category

MIT scientists: Heat can act like sound wave when moving through pencil lead

March 16th, 2019
Pile of tiny gray rods.

Enlarge / Graphite rods ready to be encased in wood to make pencils. MIT scientists have shown that heat behaves like sound when moving through graphite. (credit: Jean-Christophe Verhaegen/AFP/Getty Images)

A boiling tea kettle diffuses its heat to gradually warm surrounding air, yet it will still be the warmest region even as it, too, slowly cools. But what if the kettle cooled down to room temperature almost instantly, losing its heat in a wave traveling through the material close to the speed of sound? MIT researchers have observed this rare, counterintuitive phenomenon—known as "second sound"—in graphite, the stuff of pencil lead. They described their results in a paper published earlier this week in Science.

Chances are you've never heard of the concept of "second sound," even though the phenomenon has been known for decades. "It's been confined to only a handful of materials that are really very low temperature," said co-author Keith Nelson, severely limiting its potential usefulness. There might be a paragraph or two on the topic in your average solid-state textbook, but the field "has been kind of a backwater."

With the results of this new research, that may be about to change. Graphite is a very common material, and the effect was observed at a relatively balmy (by low-temperature physics standards) temperature of around -240 degrees F. The team's theoretical models indicate it might be possible to produce the effect in graphene at something closer to room temperature in the future, thereby opening up any number of potential practical applications. For instance, microelectronics just keep getting smaller, making heat management a daunting challenge. If room-temperature graphene could rapidly carry off heat as waves, it might allow even more miniaturization.

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Posted in graphene, graphite, materials science, Physics, science, sound | Comments (0)

Study: hacking 10 percent of self-driving cars would cause gridlock in NYC

March 13th, 2019
Cars are seen in a traffic jam in their evening commute on the 5th Avenue on February 27, 2019 in New York City.

Enlarge / Cars are seen in a traffic jam in their evening commute on the 5th Avenue on February 27, 2019 in New York City. (credit: Johannes Eisele/AFP/Getty Images)

In 2015, a pair of hackers demonstrated just how easy it was to break into the UConnect system of a Jeep Cherokee, remotely manipulating the speed, braking, steering, even shutting the car down entirely. Vehicles on the road will only have greater interconnectivity from this point forward, with self-driving cars on the horizon. That poses a unique potential risk: if someone can hack one car, what happens if they manage to hack many at once in a major metropolitan city?

That question inspired scientists at the Georgia Institute of Technology to quantify the likely impact of such a large-scale hack on traffic flow in New York City. Skanda Vivek, a postdoctoral researcher at Georgia Tech, described the study's findings at the American Physical Society's 2019 March meeting, held last week in Boston. Worst-case scenario: a small-scale hack affecting just ten percent of cars on the road would be sufficient to cause city-wide gridlock, essentially cutting half of Manhattan off from the rest of the city. And unlike compromised data, compromised vehicles can lead to physical injury.

Vivek and his colleagues performed computer simulations of traffic flow in Manhattan, using a statistical method called percolation theory. If that reminds you of brewing coffee, that's exactly the right image. Percolation theory a mathematical model of a smooth, continuous phase transition (as opposed to a rapid one, like flicking a light switch), similar to water seeping through roasted ground coffee beans, until it shifts into a new state: "coffee." Hot water seeping through packed coffee grains will hunt for the most viable path. The more connected routes that are open, the more likely it is the water will filter through. Traffic works much the same way. Cut off too many routes, and there won't be sufficient connectivity for cars to filter through.

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Posted in Physics, science, self driving cars, traffic, traffic physics | Comments (0)

The secret of how the mako shark swims so fast lies in its flexible scales

March 8th, 2019
A shortfin mako shark off the coast of Cancun, Mexico. Tiny flexible scales on its skin control flow separation as it swims, reducing pressure drag.

Enlarge / A shortfin mako shark off the coast of Cancun, Mexico. Tiny flexible scales on its skin control flow separation as it swims, reducing pressure drag. (credit: YouTube/Guy Harvey)

Mako sharks can swim as fast as 70 to 80 MPH, earning them the moniker "cheetahs of the ocean." Now scientists at the University of Alabama have determined one major factor in how mako sharks are able to move so fast: the unique structure of their skin, especially around the flank and fin regions of their bodies. The team described their work at the American Physical Society's 2019 March meeting this week in Boston.

University of Alabama engineer Amy Lang conducted a series water tunnel experiments in her lab to test samples of real mako shark skin from the animal's flanks, using a technique called particle image velocimetry to measure the velocity of the water flowing over and around the skin. Anyone who has touched a shark knows the skin feels smooth if you stroke from nose to nail. Reverse the direction, however, and it feels like sandpaper. That's because of tiny translucent scales, roughly 0.2 millimeters in size, called "denticles" (because they strongly resemble teeth) all over the shark's body, especially concentrated in the animal's flanks and fins. It's like a suit of armor for sharks.

Mako sharks have evolved a distinct passive "bristling" aspect on some of their scales to swim faster. Lang's lab coordinated their project with biologists at the University of South Florida, who imaged shark skin and mapped out the scales, noting particularly how many of the scales were capable of this passive bristling and the angles at which such bristling occurs. They found that near regions like the nose, the scales aren't especially flexible, more like molars embedded in the skin. But near the flanks and fins, the scales are much more flexible.

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Posted in APS March Meeting, biophysics, fluid dynamics, mako shark, Physics, science | Comments (0)

Physicists are decoding math-y secrets of knitting to make bespoke materials

March 8th, 2019
Introducing topological defects into knitted patterns can shape the (a) out-of-plane elasticity of a stuffed rabbit (left), and (b) the in-plane deformations of knitted textiles (right).

Enlarge / Introducing topological defects into knitted patterns can shape the (a) out-of-plane elasticity of a stuffed rabbit (left), and (b) the in-plane deformations of knitted textiles (right). (credit: Elisabetta Matsumoto)

Knitted fabrics like a scarf or socks are highly elastic, capable of stretching as much as twice their length, but individual strands of yarn hardly stretch at all. It's the way those strands form an interlocking network of stitches that give knitted fabrics their stretchiness. Physicists are trying to unlock the knitting "code"—the underlying mathematical rules that govern how different stitch combinations give rise to different properties, like stretchiness—in hopes of creating new "tunable" materials whose properties can be tailored for specific purposes.

"Knitting is this incredibly complex way of converting one-dimensional yarn into complex fabric," said Elisabetta Matsumoto, a physicist at the Georgia Institute of Technology. "So basically this is a type of coding." Figuring out how different stitch types determine shape and mechanical strength could help create designer materials for future technologies—everything from better materials for the aerospace industry to making stretchable materials to replace torn ligaments. The models her team is developing may also be useful in improving the realistic animation of clothing and hair in computer game graphics. Matsumoto described her research during the American Physical Society's 2019 March meeting taking place this week in Boston.

Knitted fabrics can technically be considered a type of metamaterial (engineered materials that get their properties not from the base materials, but from their designed structures), according to Matsumoto, who points to the medieval embroidery technique known as "smocking" as an early example. From a physics standpoint, smocking uses knots to essentially convert local bending energy into bulk stretching energy.

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Posted in geometry, knitting, materials science, mathematics, Physics, science, topology | Comments (0)

JPL scientist analyzes pros and cons of the science in dystopian drama IO

March 3rd, 2019
Micah (Anthony Mackie) and Sam (Margaret Qualley) are two of the last people on a toxic Earth in the Netflix original movie <em>IO</em>.

Enlarge / Micah (Anthony Mackie) and Sam (Margaret Qualley) are two of the last people on a toxic Earth in the Netflix original movie IO. (credit: Netflix)

Much of the human race has decamped to a distant colony, leaving behind an uninhabitable Earth, in IO, Netflix's modest follow-up to its post-apocalyptic thriller, Bird Box. Directed by Jonathan Halpert, it's an ambitious film that doesn't quite work, with glacial pacing, little dramatic tension, and a rather flat tone. But it still has some lovely moments and a thought-provoking premise. It made us wonder how much of the film is based in real science, and we turned to Kevin Hand, an astrobiologist and planetary scientist at the Jet Propulsion Laboratory, for answers.

Hand is an ideal person to comment on the film's science. His research interests include studying the ocean worlds of the outer solar system, most notably Jupiter's moon Europa, considered to be one promising site for extraterrestrial life. He's attempted to recreate the conditions on Europa in the laboratory—what he dubs "Europa in a can"—to see if any telltale forms of life might form. (It hasn't so far, but who knows when a breakthrough might occur?) And Hand is part of NASA/JPL's Europa Clipper mission to send a robotic spacecraft to perform repeated close flybys of the distant moon. He even consulted on the 2013 sci-fi "found footage" film, Europa Report, which dramatized a fictional crewed mission to Jupiter's moon.

(Spoilers below for IO.)

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Posted in climate chage, dystopia, Entertainment, film, Gaming & Culture, Netflix, Physics, science | Comments (0)

Physicists set world record in tabletop plasma acceleration with laser drill

February 27th, 2019
Wakefield acceleration can use different drivers. In the laser-driven case (top), a strong laser pulse is fired into a preformed plasma. In the proton-driven scenario (bottom), a high-energy proton bunch is sent into a gas.

Enlarge / Wakefield acceleration can use different drivers. In the laser-driven case (top), a strong laser pulse is fired into a preformed plasma. In the proton-driven scenario (bottom), a high-energy proton bunch is sent into a gas. (credit: APS/Alan Stonebraker)

Particle accelerators can speed up subatomic particles almost to the speed of light. The tradeoff is that this requires miles-long tunnels, so such machines are typically enormous and very expensive to build. Physicists are keen to build a viable tabletop version capable of accelerating particles over mere centimeters. Researchers at Lawrence Berkeley National Laboratory have now achieved the highest energy yet recorded using these so-called "plasma wakefield accelerators," and they describe their work in a new paper in Physical Review Letters.

Typical particle accelerators use modulated electric fields inside metal cavities to speed up electrons. The Large Hadron Collider at CERN in Switzerland is the largest ever built, with a 16-mile ring of superconducting magnets serving to boost electrons to near-light speeds. In contrast, plasma wakefield acceleration involves firing very intense, short bursts of laser light into a cloud of ionized gas (the plasma).

The resulting "wave" rippling through the plasma leaves a "wake" of charged particles behind it, just like a speed boat will churn up a wake of water as it zooms across a lake. Then a second laser pulses more electrons into the plasma. If this is done at just the right time, those electrons can "surf" along the wakefield. The electrons draw off the wakefield's energy to pick up more speed, just like a surfer can pick up speed skimming down the face of a wave.

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Posted in Physics, plasma physics, plasma wakefield acceleration, science | Comments (0)

Happy Death Day 2 U, Russian Doll give us time loops with a multiverse twist

February 20th, 2019
(left) Natasha Lyonne as Nadia Vulvokov in <em>Russian Doll</em>. (right) Jessica Rothe as Theresa "Tree" Gelbman in <em>Happy Death Day 2 U</em>.  Both women find themselves caught in a time loop where they die over and over on their birthday.

Enlarge / (left) Natasha Lyonne as Nadia Vulvokov in Russian Doll. (right) Jessica Rothe as Theresa "Tree" Gelbman in Happy Death Day 2 U. Both women find themselves caught in a time loop where they die over and over on their birthday. (credit: Netflix/Blumhouse Productions)

The time loop is pretty much a classic science fiction trope, thanks in large part to the enormous success of the 1993 film Groundhog Day. It's been used so often, in fact, that it's challenging to come up with a fresh take. But the Netflix series Russian Doll and the new film Happy Death Day 2 U manage to do just that, giving us time loops with a multiverse twist.

Wikipedia has amassed an impressive list of films featuring time loops: 49 so far, and that's not counting TV shows, like The X-Files episode "Monday" (in turn referenced on a Buffy the Vampire episode, "Life Serial"). The earliest film dates back to 1933: Turn Back the Clock, in which a tobacconist named Joe is killed in a hit-and-run and wakes up 20 years earlier. But it's not a true time loop tale, having more in common with It's a Wonderful Life.

A 1987 Russian film, Zerkalo dlya geroya (Mirror for a Hero), does have a lot of the key elements in place. But the real original source material is probably Richard A. Lupoff's 1973 short story, "12:01 PM," adapted into an Oscar-nominated short film in 1990 and a full-length feature in 1993—the same year Groundhog Day came out. (Lupoff definitely noticed the similarities and considered suing for plagiarism, but eventually dropped the idea.) It's pretty much been a sci-fi mainstay ever since.

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Posted in Entertainment, film, film review, Gaming & Culture, Happy Death Day, Happy Death Day 2 U, multiverse, Netflix, Physics, Russian Doll, science, television review, television streaming, time loops | Comments (0)

The wrath of grapes: A tale of 12 dead microwaves and plasma-spewing grapes

February 18th, 2019
Not just for grapes: plasma formed between a pair of hydrogel beads irradiated in a household microwave oven.

Enlarge / Not just for grapes: plasma formed between a pair of hydrogel beads irradiated in a household microwave oven. (credit: Hamza K. Khattak)

DIY science enthusiasts know that, if you put a halved grape into a microwave with just a bit of skin connecting the halves, it'll produce sparks and a fiery plume of ionized gas known as a plasma. There are thousands of YouTube videos documenting the effect. But the standard explanation offered for why this occurs isn't quite right, according to a new paper in the Proceedings of the National Academy of Sciences. And its authors only needed to destroy a dozen microwaves to prove it.

"Many microwaves were in fact harmed during the experiments," admitted co-author Hamza Khattak of Trent University in Canada. "At one point, we had a microwave graveyard in the lab before disposing of the many early iterations in electronic waste."

Co-author Aaron Slepkov first became interested in the phenomenon when, as an undergraduate in 1995, he noticed there was no formal (i.e., scientifically rigorous and peer-reviewed) explanation for how the plasma was being generated. Once he'd finished his PhD and established his own research group at Trent University, he started doing his own experiments (microwaving grapes for science) with one of his undergraduate students. They used thermal imaging and computer simulations of both grapes and hydrogel beads in their experiments.

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Posted in microwaving grapes, Physics, plasma physics, science | Comments (0)

Dance Your PhD’s 2018 winner mixes superconductivity and swing dancing

February 18th, 2019

Cooper pairs and impurities come to life in a superconductor and dance their little particle hearts out in Pramodh Yapa's "Superconductivity: The Musical."

Pairs of swing-dancing electrons do the Lindy Hop in "Superconductivity: The Musical," the winning video for this year's geektastic Dance Your PhD contest. Pramodh Yapa, a graduate student at the University of Alberta, Canada, beat out roughly 50 other entries for the interpretive dance based on his master's thesis, "Non-Local Electrodynamics of Superconducting Wires: Implications for Flux Noise and Inductance."

The Dance Your PhD contest was established in 2008 by science journalist John Bohannon, and is sponsored by Science magazine and the American Association for the Advancement of Science (AAAS). Bohannon told Slate in 2011 that he came up with the idea while trying to figure out how to get a group of stressed-out PhD students in the middle of defending their theses to let off a little steam. So he put together a dance party at Austria's Institute of Molecular Biotechnology, including a contest for whichever candidate could best explain their thesis topics with interpretive dance.

Science kicked in a free one-year subscription as a reward. It was such a hit, Bohannon started getting emails asking when the next such contest would be. And Dance Your PhD has continued ever since. There are four broad categories: physics, chemistry, biology, and social science, with a fairly liberal interpretation of what topics fall under each.

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Posted in Dance Your PhD, Gaming & Culture, nerd culture, Physics, science, superconductivity | Comments (0)

Georgia Tech scientists figured out how maggots can eat so much, so fast

February 17th, 2019
Studying the collective feeding behavior of black soldier fly larvae.

Enlarge / Studying the collective feeding behavior of black soldier fly larvae. (credit: Hu lab/Georgia Tech)

How do the larvae of black soldier flies eat so much, so fast, despite their tiny size? Scientists at Georgia Tech have been studying this "collective feeding" behavior and found that one strategy for maximizing the larvae's feeding rate involves forming maggot "fountains." The scientists described the results in a recent paper in the Journal of the Royal Society Interface, along with an entertaining video showing a swarm of larvae consuming an entire pizza in just two hours.

"This is the first time, as far as I know, that we've really tried to quantify how much they were able to eat, and how they are able to do it," said graduate student and co-author Olga Shishkov, who demonstrated the research on Saturday at the American Association for the Advancement of Science meeting in Washington, DC. It's not the first time she's had fun demonstrating the maggots' hearty appetite in creative ways: last year, she videotaped the critters devouring a heart-shaped donut for Valentine's Day.

Shishkov's advisor is David Hu, who runs a biolocomotion laboratory at the Georgia Institute of Technology studying how various creatures move. He is perhaps best known for his work with fire ants, but his lab also studies cat tongues, water striders, snakes, various climbing insects, mosquitos, and, of course, black soldier fly larvae.

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Posted in Biology, collective behavior, fluid dynamics, Physics, science | Comments (0)