Archive for the ‘Physics’ Category

Scientists found that these old photographs contain metallic nanoparticles

June 12th, 2019
The earliest reliably dated photograph of people, taken by Louis Daguerre one spring morning in 1838.

Enlarge / The earliest reliably dated photograph of people, taken by Louis Daguerre one spring morning in 1838. (credit: Public domain)

Daguerreotypes are one of the earliest forms of photography, producing images on silver plates that look subtly different, depending on viewing angle. For instance they can appear positive or negative, or the colors can shift from bluish to brownish-red tones. Now an interdisciplinary team of scientists has discovered that these unusual optical effects are due to the presence of metallic nanoparticles in the plates. They described their findings in a new paper in the Proceedings of the National Academy of Sciences.

Co-author Alejandro Manjavacas—now at the University of New Mexico in Albuquerque—was a postdoc at Rice University, which boasts one of the top nanophotonics research groups in the US. That's where he met his co-author, Andrea Schlather, who ended up in the scientific research department at the Metropolitan Museum of New York. The Met has a valuable collection of daguerreotypes, and her new colleagues were keen to find better methods for preserving these valuable artifacts.

Schlather contacted Manjavacas and suggested this might be a great place to apply their combined expertise in nanoplasmonics—a field dedicated to detailing how nanoparticles interact with light. Think of it this way: light is an optical oscillation made up of photons. Sound is a mechanical oscillation made up of quasiparticles known as phonons. And plasma (ionized gas, the fourth fundamental state of matter) oscillations consist of plasmons. Surface plasmons play a critical role in determining the optical properties of metals in particular.

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Posted in History, history of science, nanoparticles, optics, photography, Physics, plasmonics, science | Comments (0)

Rat brains provide even more evidence our brains operates near tipping point

June 7th, 2019
A real human brain suspended in liquid within a human silhouette carved into acrylic, on display at the Bristol Science Centre in England. New research finds more evidence that the brain operates near a critical point.

Enlarge / A real human brain suspended in liquid within a human silhouette carved into acrylic, on display at the Bristol Science Centre in England. New research finds more evidence that the brain operates near a critical point. (credit: Ben Birchall/PA Images/Getty Images)

The human brain doesn't seem like it would have much in common with how water freezes into ice, or heats up into a gas. But over the last decade, evidence has been mounting that the brain as a system functions much like water approaching the critical point of a phase transition. Now a team of Brazilian scientists has found additional evidence in rat brains that this might indeed be the case. The team described its findings in a recent paper in Physical Review Letters.

The notion of so-called "self-organized criticality" dates back to a landmark paper in 1987, when the late Danish physicist Per Bak concluded that nature's exquisite order was the result of a kind of phase transition. That precise moment of transition is colloquially known as the "tipping point" or "critical point."

A brain's the thing

Typically, a classical phase transition only occurs when the temperature and pressure are just right for a given system. Self-organized criticality emerges spontaneously as the result of many local interactions between the many elements of a system, like millions of grains of sand running from the top to the bottom of an hourglass. The pile grows, grain by grain, until it becomes sufficiently unstable that the next grain to drop makes the pile collapse in an avalanche. The base of the pile widens, restoring stability, and the pile-up begins anew, until the sand pile hits the critical point again. Those avalanches follow a so-called "power law," meaning smaller ones happen more often than larger ones.

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Posted in brain, brain activity, criticality, neurophysics, Neuroscience, phase transitions, Physics, science, self-organized criticality | Comments (0)

Researchers balance Casimir effects, make tiny hoverboard

June 6th, 2019
Researchers balance Casimir effects, make tiny hoverboard

Enlarge (credit: Wikimedia Commons)

Empty space isn't actually empty. Even if you somehow managed to suck every single atom out of it, the Universe is filled with various fields that dictate the behavior of particles and forces. These fields even create pairs of "virtual particles" that pop into existence briefly before annihilating each other.

This counterintuitive view of the nature of the Universe is an outgrowth of quantum field theory, but it was difficult to figure out any obvious consequences. That changed in 1948, when Dutch physicist Hendrik Casimir figured out a specific situation where the contents of empty space matter. Now called the Casimir effect, it creates a tiny force when two conductive metal plates are placed in close proximity.

In a new paper published in today's edition of Science, researchers show that the Casimir effect can also be repulsive and use the balance between attractive and repulsive forces to cause a tiny flake of metal to levitate above a surface.

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Posted in Casimir effect, Physics, quantum mechanics, science | Comments (0)

Following Schrödinger’s cat to its death and giving it a reprieve

June 5th, 2019
Two-state cat.

Enlarge / Two-state cat. (credit: RBerteig on Flickr)

One thing I dislike about quantum mechanics is that it encourages journalists to overuse words like "mysterious" and "spooky." Given that we can model quantum systems to an accuracy that would make a god cry, where is the mystery?

I personally blame Schrödinger and his eponymous cat. That thought experiment, combined with an ever-increasing body of experimental results, shows just how subtle quantum mechanics is. Rather than admitting a lack of understanding, some journalists seem to use Schrödinger’s cat as a get-out-of-explaining-for-free card.

No doubt the words "mysterious" and "spooky" are going to turn up again regarding an experiment that, according to its press release, shows how to predict when Schrödinger’s cat is about to die. The experiment is really only tangentially related to Schrödinger’s cat; instead, it shows how no matter how well you understand quantum mechanics, there is always another layer to peel back and explore.

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Posted in artificial atoms, Cats, Physics, quantum mechanics, science, superposition state | Comments (0)

A tale of lost WW2 uranium cubes shows why Germany’s nuclear program failed

June 3rd, 2019
This is one of the 664 uranium cubes from the failed nuclear reactor that German scientists tried to build in Haigerloch during World War II.

Enlarge / This is one of the 664 uranium cubes from the failed nuclear reactor that German scientists tried to build in Haigerloch during World War II. (credit: John T. Consoli/University of Maryland)

When University of Maryland physicist Timothy Koeth received a mysterious heavy metal cube from a friend as a birthday gift several years ago, he instantly recognized it as one of the uranium cubes used by German scientists during World War II in their unsuccessful attempt to build a working nuclear reactor. Had there been any doubt, there was an accompanying note on a piece of paper wrapped around the cube: "Taken from Germany, from the nuclear reactor Hitler tried to build. Gift of Ninninger."

Thus began Koeth's six-year quest to track down the cube's origins, as well as several other similar cubes that had somehow found their way across the Atlantic. Koeth and his partner in the quest, graduate student Miriam "Mimi" Hiebert, reported on their progress to date in the May issue of Physics Today. It's quite the tale, replete with top-secret scientific intrigue, a secret Allied mission, and even black market dealers keen to hold the US hostage over uranium cubes in their possession. Small wonder Hollywood has expressed interest in adapting the story for the screen.

Until quite recently, Koeth ran the nuclear reactor program at UMD, which is how he met his co-author. Hiebert is completing a PhD in materials science and engineering, specializing in the study of historical materials in museum collections (glass in particular) and the methods used to preserve them, using the reactor facility for neutron imaging of a few samples. Koeth told her about his research into his cube's origins, and she started collaborating with him as a side project.

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Posted in History, history of science, Nuclear Reactor, Physics, science, World War II | Comments (0)

Sonic black holes produce “Hawking radiation,” may confirm famous theory

May 30th, 2019
Simulated view of a black hole in front of the Large Magellanic Cloud.

Enlarge / Simulated view of a black hole in front of the Large Magellanic Cloud. (credit: Wikimedia Commons/Alain r)

Israeli physicists think they have confirmed one of the late Stephen Hawking's most famous predictions by creating the sonic equivalent of a black hole out of an exotic superfluid of ultra-cold atoms. Jeff Steinhauer and colleagues at the Israel Institute of Technology (Technion) described these intriguing experimental results in a new paper in Nature.

The standard description of a black hole is an object with such a strong gravitational force that light can't even escape once it moves behind a point of no return known as the event horizon. But in the 1970s, Hawking demonstrated that—theoretically, at least—black holes should emit tiny amounts of radiation and gradually evaporate over time.

Blame the intricacies of quantum mechanics for this Hawking radiation. From a quantum perspective, the vacuum of space continually produces pairs of virtual particles (matter and antimatter) that pop into existence and just as quickly annihilate away. Hawking proposed that a virtual particle pair, if it popped up at the event horizon of a black hole, might have different fates: one might fall in, but the other could escape, making it seem as if the black hole were emitting radiation. The black hole would lose a bit of its mass in the process. The bigger the black hole, the longer it takes to evaporate. (Mini-black holes the size of a subatomic particle would wink out of existence almost instantaneously.)

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Posted in analogue black holes, astronomy, black holes, Hawking radiation, Physics, quantum simulations, science | Comments (0)

Superconductivity reported at the temperature of a good freezer

May 22nd, 2019
Superconductivity reported at the temperature of a good freezer

Enlarge (credit: Manmohan Singh | Getty Images)

Superconductivity offers the promise of hyper-efficient electric motors, ultra powerful magnets, and the transmission of electricity without losses. The reality, however, has fallen considerably short of that promise, as superconducting materials are difficult and expensive to manufacture, requiring a constant bath of liquid nitrogen to keep them cold enough to operate. And progress at identifying new high-temperature superconductors went through an extended stall, with no new contenders for decades.

But behind that stall, researchers were getting a better understanding of the physics involved with superconductivity, and that understanding seems to be paying off. A few years back, researchers found that a high-pressure form of hydrogen sulfide would superconduct at 203K (-70°C), roughly 65K higher than any previous material. Now, following up on suggestions from computer modeling, researchers have discovered that a metal-hydrogen compound (LaH10) can superconduct all the way up to 250K. That's roughly -25°C, a temperature that can be reached by a good freezer.

Unfortunately, its superconductivity is dependent upon pressure and required compressing the sample between two diamonds. But the results do tell us that our understanding is on the right track, and there are undoubtedly additional chemicals worth examining.

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Posted in chemistry, Physics, science, superconductivity | Comments (0)

Dribble no more: Physics can help combat that pesky “teapot effect”

May 17th, 2019
Dribble no more: Physics can help combat that pesky “teapot effect”

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Tea drinkers know all too well that annoying dribble from the kettle spout that so often occurs as one pours a nice refreshing cuppa. It's even known as the "teapot effect," and it usually happens when the tea is poured too slowly. Potters usually design their pots—giving the spout a thin lip, for instance—to reduce the likelihood of dribbling, based on centuries of accrued knowledge derived from trial and error.

Now a group of Dutch physicists has come up with quantitative model to accurately predict the precise flow rate for how much (or how little) a teapot will dribble as it pours, described in a recent paper in Physical Review Letters. The model accurately describes both the simple teapot effect and more complex behavior—notably, the formation of a helix as a water stream swirls around a cylinder. That should be a boon not to just for teapot design, but for 3D printing and similar industrial applications, which are also plagued by inconvenient dribbling.

Physicists have long been fascinated by the phenomenon. The late Stanford engineer and mathematician Joseph B. Keller once recalled attending a lecture by an Israeli scientist who mentioned that he'd posed the question of why teapots dribble to 100 physicists. All opined that it must be due to surface tension, but when the Israeli scientist performed experiments to test that theory, this proved not to be the case.

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

Mapping Notre Dame’s unique sound will be a boon to reconstruction efforts

May 14th, 2019
Protective tarps displayed on the roof of Notre-Dame de Paris cathedral, two weeks after a fire devastated it in Paris.

Enlarge / Protective tarps displayed on the roof of Notre-Dame de Paris cathedral, two weeks after a fire devastated it in Paris. (credit: KENZO TRIBOUILLARD/AFP/Getty Images)

When the iconic Notre Dame cathedral in Paris caught fire last month, people found some hope in the news that scientist Andrew Tallon had used laser scanning to create precisely detailed maps of the interior and exterior of the cathedral—an invaluable aid as Paris rebuilds this landmark structure.

The acoustics of the cathedral—how it sounds—are also part of its cultural heritage, and given the ephemeral nature of sound, acoustical characteristics can be far trickier to preserve or reproduce. Fortunately, a group of French acousticians made detailed measurements of Notre Dame's "soundscape" over the last few years, along with two other cathedrals. That data will now be instrumental in helping architects factor acoustics into their reconstruction plans.

Dialing in the reverb

"We have a snapshot of the acoustics from two years ago and a computer model that can reproduce that," said Brian FG Katz, research director of the National Center for Scientific Research (CNRS) at Sorbonne University in Paris, who worked in tandem with Tallon's laser scanning project. "The idea is if they want to, for example, change the materials, we can tell them what the impact of those changes will be on the acoustics. We're not trying to force anybody to restore it one way versus another, but they should be able to make an informed decision about the acoustic impact."

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Posted in acoustics, notre dame, Physics, science, soundscapes | Comments (0)

Study finds ultimate fate of Leidenfrost droplets depends on their size

May 12th, 2019
A new study shows the ultimate fate of Leidenfrost droplets, liquid drops that levitate above very hot surfaces. Larger drops explode violently with an audible crack. Smaller ones simple shrink and fly away.

Enlarge / A new study shows the ultimate fate of Leidenfrost droplets, liquid drops that levitate above very hot surfaces. Larger drops explode violently with an audible crack. Smaller ones simple shrink and fly away. (credit: Lyu/Mathai)

In 1756, a German scientist named Johann Gottlob Leidenfrost reported his observation of an unusual phenomenon. Normally, water splashed onto a very hot pan sizzles and evaporates very quickly. But if the pan's temperature is well above water's boiling point, "gleaming drops resembling quicksilver" will form and will skitter across the surface. It's known as the "Leidenfrost effect" in his honor.

In the ensuing 250 years, physicists came up with a viable explanation for why this occurs. If the surface is at least 40 degrees Fahrenheit (well above the boiling point of water), cushions of water vapor, or steam, form underneath them, keeping them levitated. The Leidenfrost effect also works with other liquids, including oils and alcohol, but the temperature at which it manifests will be different. In a 2009 Mythbusters episode, for instance, the hosts demonstrated how someone could wet their hand and dip it ever so briefly into molten lead without injury, thanks to this effect.

But nobody had been able to identify the source of the accompanying cracking sound Leidenfrost reported. Now, an international team of scientists has filled in that last remaining gap in our knowledge with a recent paper in Science Advances.

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Posted in Leidenfrost effect, Physics, science | Comments (0)