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Category: physics – Page 244

When energy is added to uranium under pressure, it creates a shock wave, and even a tiny sample will be vaporized like a small explosion. By using smaller, controlled explosions, physicists can test on a microscale in a safe laboratory environment what could previously be tested only in larger, more dangerous experiments with bombs.

“In our case, it’s the laser depositing energy into a target, but you get the same formation and time-dependent evolution of plasma,” author Patrick Skrodzki said. “With these small-scale explosions in the lab, we can understand similar physics.”

In a recent experiment, scientists working with Skrodzki used a laser to ablate atomic uranium, stealing its electrons until it ionized and turned to plasma, all while recording as the plasma cooled, oxidized and formed species of more complex uranium. Their work puts uranium species and the reaction pathways between them onto a map of space and time to discover how many nanoseconds they take to form and at which part of the plasma’s evolution.

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It’s not like the one in your car, but a team of physicists at Trinity College Dublin have built what they claim is the world’s smallest engine. The engine is the size of a single calcium ion — about ten billion times smaller than an automobile engine.

Rather than powering your next road trip, the atomic engine could one day be used to lay the foundation for extraordinary, futuristic nanotechnologies.

Here’s how it works: the calcium ion holds an electrical charge, which makes it spin. This angular momentum is then used to convert heat from a laser beam into vibrations.

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By Rachel Courtland

The crust of neutron stars is 10 billion times stronger than steel, according to new simulations. That makes the surface of these ultra-dense stars tough enough to support long-lived bulges that could produce gravitational waves detectable by experiments on Earth.

Neutron stars are the cores left behind when relatively massive stars explode in supernovae. They are incredibly dense, packing about as much mass as the sun into a sphere just 20 kilometres or so across, and some rotate hundreds of times per second.

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The Universe is expanding, and that expansion is speeding up over time. These two facts have been well established through observation, but we don’t know what’s causing that expansion. It seems to be some mysterious, unknown energy that acts like the opposite of gravity.

We call this hypothetical energy “dark energy”, and it’s been calculated to constitute around 72 percent of all the stuff that makes up the Universe. We don’t know what it actually is. But a new experiment has just allowed us to rule out one more thing that it isn’t: a new force.

“This experiment, connecting atomic physics and cosmology, has allowed us to rule out a wide class of models that have been proposed to explain the nature of dark energy, and will enable us to constrain many more dark energy models,’‘said physicist Ed Copeland of the University of Nottingham.

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Theoretical physicists at Trinity College Dublin are among an international collaboration that has built the world’s smallest engine—which, as a single calcium ion, is approximately ten billion times smaller than a car engine.

Work performed by Professor John Goold’s QuSys group in Trinity’s School of Physics describes the science behind this tiny motor. The research, published today in international journal Physical Review Letters, explains how random fluctuations affect the operation of microscopic machines. In the future, such devices could be incorporated into other technologies in order to recycle and thus improve .

The engine itself—a single calcium ion—is electrically charged, which makes it easy to trap using electric fields. The working substance of the engine is the ion’s “intrinsic spin” (its angular momentum). This spin is used to convert heat absorbed from laser beams into oscillations, or vibrations, of the trapped ion.

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A group of researchers led by Skoltech Professor Pavel Troshin studied coordination polymers, a class of compounds with scarcely explored applications in metal-ion batteries, and demonstrated their possible future use in energy storage devices with a high charging/discharging rate and stability. The results of their study were published in the journal Chemistry of Materials.

The charging/discharging rate is one of the key characteristics of lithium-ion batteries. Most modern commercial batteries need at least an hour to get fully charged, which certainly limits the scope of their application, in particular, for electric vehicles. The trouble with active materials, such as the most popular anode material, graphite, is that their capacity decays significantly, as their charging rate increases. To retain the battery capacity at high charging rates, the active electrode materials must have high electronic and ionic conductivity, which is the case with the newly-discovered coordination polymers that are derived from and salts of , such as nickel or copper. Although these compounds hold a great promise, their application in lithium-ion batteries remains virtually unexplored.

A recent study undertaken by a group of scientists from Skoltech and the Institute for Problems of Chemical Physics of RAS led by Professor P. Troshin in collaboration with the University of Cologne (Germany) and the Ural Federal University, focused on tetraaminobenzene-based linear polymers of nickel and copper. Although the linear polymers exhibited much lower initial electronic conductivity as compared to their two-dimensional counterparts, it transpired that they can be used as anode materials that get charged/discharged in less than a minute, because their conductivity increases dramatically after the first discharge due to lithium doping.

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This could lead to self-healing cars.

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a mathematical framework that can turn any sheet of material into any prescribed shape, inspired by the paper craft termed kirigami (from the Japanese, kiri, meaning to cut and kami, meaning paper).

Unlike its better-known cousin origami, which uses folds to shape , kirigami relies on a pattern of cuts in a flat paper sheet to change its flexibility and allow it to morph into 3D shapes. Artists have long used this artform to create everything from pop-up cards to castles and dragons.

“We asked if it is possible to uncover the basic mathematical principles underlying kirigami and use them to create algorithms that would allow us to design the number, size and orientation of the cuts in a flat sheet so that it can morph into any given shape,” said L. Mahadevan, de Valpine Professor of Applied Mathematics, Physics, and Organismic and Evolutionary Biology, the senior author on the paper.

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He solved a 127-year-old physics problem on paper and proved that off-centered boat wakes could exist. Five years later, practical experiments proved him right.

“Seeing the pictures appear on the computer screen was the best day at work I’ve ever had,” says Simen Ådnøy Ellingsen, an associate professor at NTNU’s Department of Energy and Process Engineering.

That was the day that Ph.D. candidate Benjamin Keeler Smeltzer and master’s student Eirik Æsøy had shown in the lab that Ellingsen was right and sent him the photos from the experiment. Five years ago, Ellingsen had challenged accepted knowledge from 1887, armed with a pen and paper, and won.

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In the same decade when gravitational waves and a neutron star merger have been observed, astronomers have now observed what they believe to be the first detection of a black hole swallowing a neutron star.

Last Wednesday, gravitational wave detectors in Italy and the US, called LIGO and Virgo, detected telltale ripples in space and time, traced to an event that happened 8,550 million trillion kilometers away from Earth.

Astronomers are analyzing the data from the detection to confirm the size of the two objects that came together to form such cataclysmic ripples, but the event is likely a black hole eating a neutron star.

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