Latest news with #RichardFletcher
Yahoo
5 days ago
- General
- Yahoo
Physicists capture 'second sound' for the first time — after nearly 100 years of searching
When you buy through links on our articles, Future and its syndication partners may earn a commission. Scientists have captured direct images of heat behaving like sound — an elusive phenomenon called 'second sound' — for the very first time. Imaged within an exotic superfluid state of cold lithium-6 atoms by a new heat-mapping technique, the phenomenon shows heat moving as a wave, bouncing like sound around its container. Understanding the way that second sound moves could help scientists predict how heat flows inside ultradense neutron stars and high-temperature superconductors — one of the "holy grails" of physics whose development would enable near-lossless energy transmission. The researchers published their findings in the journal Science. "It's as if you had a tank of water and made one half nearly boiling," study co-author Richard Fletcher, an assistant professor of physics at Massachusetts Institute of Technology (MIT), said in a statement. "If you then watched, the water itself might look totally calm, but suddenly the other side is hot, and then the other side is hot, and the heat goes back and forth, while the water looks totally still." Typically heat spreads from a localized source, slowly dissipating across an entire material as it raises the temperature across it. But exotic materials called superfluids needn't play by these rules. Created when clouds of fermions (which include protons, neutrons and electrons) are cooled to temperatures approaching absolute zero, atoms inside superfluids pair up and travel frictionlessly throughout the material. Related: Physicists make record-breaking 'quantum vortex' to study the mysteries of black holes As a result, heat flows differently through the material: instead of spreading through the movements of particles within the fluid, as it typically flows, heat sloshes back and forth within superfluids like a sound wave. This second sound was first predicted by the physicist László Tisza in 1938, but heat-mapping techniques have, until now, proven unable to observe it directly. "Second sound is the hallmark of superfluidity, but in ultracold gases so far you could only see it in this faint reflection of the density ripples that go along with it," study senior-author Martin Zwierlein, a professor of physics at MIT, said in the statement. "The character of the heat wave could not be proven before." To capture second sound, the researchers had to solve a daunting problem in tracking the flow of heat inside ultracold gases. These gases are so cold that they do not give off infrared radiation, upon which typical heat-mapping, or thermography, techniques rely. Instead, the physicists developed a method to track the fermion pairs through their resonant frequencies. Lithium-6 atoms resonate at different radio frequencies as their temperatures change, with warmer atoms vibrating at higher frequencies. RELATED STORIES — Scientists turn light into a 'supersolid' for the 1st time ever: What that means, and why it matters — Government scientists discover new state of matter that's 'half ice, half fire' — Scientists unveil new type of 'time crystal' that defies our traditional understanding of time and motion By applying resonant radio frequencies corresponding to warmer atoms, the scientists made these atoms ring in response, enabling them to track the particles' flow frame by frame. "For the first time, we can take pictures of this substance as we cool it through the critical temperature of superfluidity, and directly see how it transitions from being a normal fluid, where heat equilibrates boringly, to a superfluid where heat sloshes back and forth," Zwierlein said. The physicists say that their groundbreaking technique will enable them to better study the behaviors of some of the universe's most extreme objects, such as neutron stars, and measure the conductivity of high-temperature superconductors to make even better designs. "There are strong connections between our puff of gas, which is a million times thinner than air, and the behavior of electrons in high-temperature superconductors, and even neutrons in ultradense neutron stars," Zwierlein said. "Now we can probe pristinely the temperature response of our system, which teaches us about things that are very difficult to understand or even reach."
BBC News
16-05-2025
- Health
- BBC News
Bristol City Council allocates £2.8m for work on diseased trees
Up to 4,000 trees infected with a deadly disease that pose a risk to public safety will be felled or made safe after councillors allocated £2.8m for the City Council has agreed to spend the money on felling ash trees that are in the latter stages of ash dieback - a windblown fungus that makes trees brittle - focusing on those that could collapse near roads and of the money will be spent on replacement tree planting, which will eventually increase Bristol's tree canopy, the council three Labour members on the public health and communities committee refused to support the plans while the other three parties voted in favour. A report to the meeting said 10,000 trees owned by the council were in an advanced state of decline, with about a third of those identified as requiring urgent committee allocated £930,000 to chop the trees down and £1.9m for replacement tree planting, according to the Local Democracy Reporting report said the work would result in a "short term" reduction in the city's tree cover and estimated it would take 15 to 20 years to return to current levels. Public safety Labour councillor Tom Blenkinsop said: "I'm struggling to get my head around 15 to 20 years being a temporary situation."The council's head of parks and green spaces, Richard Fletcher, said the trees would be lost anyway as a result of ash dieback and not because of the decision to cut them Democrat committee chairman Stephen Williams said the decision was down to public safety. "We would be even more concerned if a branch fell on a bus, pedestrian or a cyclist."Williams said he would write to the government to ask for money to deal with the disease because it is a national problem.
