Lifeboat Foundation

The amplitude mode is a ubiquitous collective excitation in condensed-matter systems with broken continuous symmetry. It is expected in antiferromagnets, short coherence length superconductors, charge density waves, and lattice Bose condensates. Its detection is a valuable test of the corresponding field theory, and its mass gap measures the proximity to a quantum critical point. However, since the amplitude mode can decay into low-energy Goldstone modes, its experimental visibility has been questioned. Here we show that the visibility depends on the symmetry of the measured susceptibility. The longitudinal susceptibility diverges at low frequency as Im χ σ σ ∼ ω − 1 (d = 2) or log (1 / | ω |) (d = 3), which can completely obscure the amplitude peak. In contrast, the scalar susceptibility is suppressed by four extra powers of frequency, exposing the amplitude peak throughout the ordered phase. We discuss experimental setups for measuring the scalar susceptibility. The conductivity of the O (2 ) theory (relativistic superfluid) is a scalar response and therefore exhibits suppressed absorption below the Higgs mass threshold, σ ∼ ω 2 d + 1. In layered, short coherence length superconductors, (relevant, e.g., to cuprates) this threshold is raised by the interlayer plasma frequency.

O.,o circa 2014.

Researchers in China are reporting that they’ve taken a big step towards creating a supersonic submarine. This technology, which could just as easily be applied to weaponized torpedoes as military or civilian submarines, could theoretically get from Shanghai to San Francisco — about 6,000 miles — in just 100 minutes. If all this doesn’t sound crazy enough, get this: This new advance by the Chinese is based on supercavitation, which was originally developed by the Soviets in the ’60s, during the Cold War.

As you may already know, it’s a lot harder for an object to move quickly through water than air. This is mostly due to increased drag. Without getting into the complexities of fluid dynamics, water is simply much thicker and more viscous than air — and as a result it requires a lot more energy for an object to push through it. You can experience the increased drag of water yourself next time you’re in a swimming pool: Raise your hand above your head, and then let it fall towards the water. (Or alternatively, if there are people sunbathing nearby, do a belly flop.)

Continue reading “China’s supersonic submarine, which could go from Shanghai to San Francisco in 100 minutes, creeps ever closer to reality” »

In light of the ongoing shift toward renewable energy technologies and the growing number of Internet of Things (IoT) devices, researchers worldwide have been trying to develop batteries that can operate more efficiently and for longer periods of time. Lithium-ion batteries (LIBs) are currently the preferred energy-storage technology for portable electronics, as they contain organic electrolytes, which typically enable high operating voltages and energy densities.

Despite their widespread use, further increasing the performance of existing LIBs could have a significant impact on their safety. In fact, these batteries contain highly volatile and flammable organic carbonates, which, if ignited, can cause considerable damage.

In recent years, researchers have made significant efforts toward overcoming these safety issues, for instance, by using additional substances or by optimizing the materials separating battery components. While some of these strategies successfully reduced the risk of the battery catching fire, as long as LIBs are made with highly flammable electrolytes, accidents may still occur.

Justin Thomas considers bidets to be “a key green technology” because they eliminate the use of toilet paper. According to his analysis, Americans use 36.5 billion rolls of toilet paper every year, representing the pulping of some 15 million trees. Says Thomas: “This also involves 473,587,500,000 gallons of water to produce the paper and 253,000 tons of chlorine for bleaching.” He adds that manufacturing requires about 17.3 terawatts of electricity annually and that significant amounts of energy and materials are used in packaging and in transportation to retail outlets.

That’s a lot of water, far more than is actually used by the bidet itself.

Lloyd Alter/ toto toilet with washlet/CC BY 2.0

Lasers o.o

They could supply energy to far-flung bases, power laser weapons and charge electric vehicles.

Science and technology Mar 14th 2020 edition.

Continue reading “Nuclear power plants are coming to the battlefield” »

The new approach could even pave the way for 100 percent self-sufficiency in power, heat, and water.

Hybrid “power capacitors” that can store as much energy as lithium batteries, but with much higher charge/discharge rates, a huge range of safe operating temperatures, super-long lifespans and no risk of explosion are already in production, says a small Belgian company that’s been testing them and selling them for some time.

Chinese family-owned company Shenzhen Toomen New Energy is tough to find, at least on the English-language internet, but Belgian electronic engineer Eric Verhulst bumped into Toomen representatives on a tiny stand at the Hannover Messe expo in Germany back in 2018, while looking for next-gen battery solutions for an electric mobility startup he was running.

The Toomen team made a hell of a claim, saying they’d managed to manufacture powerful supercapacitors with the energy density of lithium batteries. “Of course, that’s an unbelievable claim,” Verhulst told us. “It’s a factor of 20 better than what, for example, Maxwell had at the time. So I took my time, went over there, looked at their tests, did some tests myself, and I got convinced this is real. So at the end of 2018, we made an agreement to become their exclusive partner.”

Nematic superconductivity with spontaneously broken rotation symmetry has recently been reported in doped topological insulators, M x Bi 2 Se 3 (M = Cu, Sr, Nb). Here we show that the electromagnetic (EM) response of these compounds provides a spectroscopy for bosonic excitations that reflect the pairing channel and the broken symmetries of the ground state. Using quasiclassical Keldysh theory, we find two characteristic bosonic modes in nematic superconductors: the nematicity mode and the chiral Higgs mode. The former corresponds to the vibrations of the nematic order parameter associated with broken crystal symmetry, while the latter represents the excitation of chiral Cooper pairs. The chiral Higgs mode softens at a critical doping, signaling a dynamical instability of the nematic state towards a new chiral ground state with broken time reversal and mirror symmetry. Evolution of the bosonic spectrum is directly captured by EM power absorption spectra. We also discuss contributions to the bosonic spectrum from subdominant pairing channels to the EM response.