Lifeboat Foundation

Experiments verify a theory that explains why paint doesn’t dry any faster on a dry day than on a wet day.

You might think that polymer solutions like paint dry more slowly on a humid day than on a dry day. But researchers have now verified a theory that explains why the evaporation rate of the water or another solvent in a polymer solution can be independent of the ambient humidity [1]. The experiments show that, as predicted, water evaporation drives the polymer molecules toward the surface, where they form a dense layer that hinders evaporation and shields the surface from humidity effects. This phenomenon may affect the rate at which virus-containing respiratory droplets evaporate and thus could help explain the seasonal dependence of viral infections.

Humidity-independent evaporation is an advantage in many situations. For example, to preserve the body’s hydration, human skin maintains a nearly constant evaporation rate thanks to cell membranes whose lipid molecules can be reconfigured to adjust the sweat evaporation rate. This reconfiguration is an example of an active process. In 2017, Jean-Baptiste Salmon, a chemical engineer at the University of Bordeaux in France, proposed that humidity-independent evaporation does not require an active response [2]. Instead, his theory suggested that it occurs whenever the solvent evaporates from a solution of large molecules, a process that was already known to draw those molecules toward the drying interface. He predicted that, after the large molecules form a dense layer, the solvent’s evaporation rate will remain unchanged whether the surroundings are bone dry or at 100% humidity. However, the theory has not been tested with a nonactive polymer solution.

Researchers in China have produced a phenomenon known as the giant skyrmion topological Hall effect in a two-dimensional material using only a small amount of current to manipulate the skyrmions responsible for it. The finding, which a team at Huazhong University of Science and Technology in Hubei observed in a ferromagnetic crystal discovered in 2022, comes about thanks to an electronic spin interaction known to stabilize skyrmions. Since the effect was apparent at a wide range of temperatures, including room temperature, it could prove useful for developing two-dimensional topological and spintronic devices such as racetrack memory, logic gates and spin nano-oscillators.

Skyrmions are quasiparticles with a vortex-like structure, and they exist in many materials, notably magnetic thin films and multilayers. They are robust to external perturbations, and at just tens of nanometres across, they are much smaller than the magnetic domains used to encode data in today’s hard disks. That makes them ideal building blocks for future data storage technologies such as “racetrack” memories.

Skyrmions can generally be identified in a material by spotting unusual features (for example, abnormal resistivity) in the Hall effect, which occurs when electrons flow through a conductor in the presence of an applied magnetic field. The magnetic field exerts a sideways force on the electrons, leading to a voltage difference in the conductor that is proportional to the strength of the field. If the conductor has an internal magnetic field or magnetic spin texture, like a skyrmion does, this also affects the electrons. In these circumstances, the Hall effect is known as the skyrmion topological Hall effect (THE).

Result draws on 50-year-old theorem from quantum field theory to make entanglement measurement more efficient.

New type of fibre reversibly changes its shape in response to temperature and can be spun into threads to make entire morphing garments. Potential applications for the technology include compression garments for post-surgical recovery, adaptive architectural interiors and even clothing that “hugs” its wearer on activation.

Each year at its annual meeting, the American Physical Society’s Division of Fluid Dynamics sponsors a contest for the best images in a variety of categories, all related to the flow of fluids.

This year’s Gallery was presented at the Division’s 76th meeting in November in Washington, D.C., with 12 artistic videos and images being selected in four different categories. Here are some of the winners.

Materials with enhanced thermal conductivity are critical for the development of advanced devices to support applications in communications, clean energy and aerospace. But in order to engineer materials with this property, scientists need to understand how phonons, or quantum units of the vibration of atoms, behave in a particular substance.

“Phonons are quite important for studying new materials because they govern several material properties such as thermal conductivity and carrier properties,” said Fuyang Tay, a graduate student in applied physics working with the Rice Advanced Magnet with Broadband Optics (RAMBO), a tabletop spectrometer in Junichiro Kono’s laboratory at Rice University. “For example, it is widely accepted that superconductivity arises from electron–phonon interactions.

Recently, there has been growing interest in the magnetic moment carried by phonon modes that show circular motion, also known as chiral phonons. But the mechanisms that can lead to a large phonon magnetic moment are not well understood.

Virtual reality, or VR, is not just for fun-filled video games and other visual entertainment. This technology, involving a computer-generated environment with objects that seem real, has found many scientific and educational applications as well.

Sean Preins, a doctoral student in the Department of Physics and Astronomy at the University of California, Riverside, has created a VR application called VIRTUE, for “Virtual Interactive Reality Toolkit for Understanding the EIC,” that is a game changer in how particle and nuclear physics data can be seen.

Made publicly available on Christmas Day, VIRTUE can be used to visualize experiments and simulated data from the upcoming Electron-Ion Collider, or EIC, a planned major new nuclear physics research facility at Brookhaven National Lab in Upton, New York. EIC will explore mysteries of the “strong force” that binds the atomic nucleus together. Electrons and ions, sped up to almost the speed of light, will collide with one another in the EIC.

When two lead ions collide at the Large Hadron Collider (LHC), they produce an extremely hot and dense state of matter in which quarks and gluons are not confined inside composite particles called hadrons. This fireball of particles—known as quark–gluon plasma and believed to have filled the universe in the first few millionths of a second after the Big Bang—expands and cools down rapidly. The quarks and gluons then transform back into hadrons, which fly out of the collision zone towards particle detectors.

In collisions where the two lead ions do not collide head on, the overlap region between the ions has an elliptic shape that leaves an imprint on the flow of hadrons. Measurements of such elliptic flow provide a powerful way to study quark–gluon plasma. In a recent paper posted to the arXiv preprint server, the ALICE collaboration reported a new measurement of the elliptic flow of hadrons containing heavy quarks, which are particularly powerful probes of the plasma.

Unlike the gluons and light quarks that make up the bulk of the quark–gluon plasma created in heavy-ion collisions, heavy charm and beauty quarks are produced in the initial stages of the collisions, before the plasma forms. They therefore interact with the plasma throughout its entire evolution, from its expansion and cooling to its transformation into hadrons.

Liquid crystal is a state of matter that exhibits properties of both liquid and solid. It can flow like a liquid, while its constituent molecules are aligned as in a solid. Liquid crystal is widely used nowadays, for example, as a core element of LCD devices.

The magnetic analog of this kind of material is dubbed the “spin-nematic phase,” where spin moments play the role of the molecules. However, it has not yet been directly observed despite its prediction a half-century ago. The main challenge stems from the fact that most conventional experimental techniques are insensitive to spin quadrupoles, which are the defining features of this spin-nematic phase.

But now, for the first time in the world, a team of researchers led by Professor Kim Bumjoon at the IBS Center for Artificial Low-Dimensional Electronic Systems in South Korea has succeeded at directly observing spin quadrupoles. This work was made possible through remarkable achievements over the last decades in synchrotron facility development.