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Special Spin State Triggered by Curved Surface

The field of magnonics aims to take advantage of spin waves, which are waves of precessing spins that can propagate in certain magnetic materials. A spin wave containing many equally spaced frequencies—called a magnon frequency comb (MFC)—would be especially useful for information processing and magnetic-field detection. Unfortunately, generating such waves is complicated. Now Peng Yan and his colleagues at the University of Electronic Science and Technology of China have shown theoretically that MFCs could be produced by simply creating a tiny bump in a thin magnetic layer [1].

Creating an MFC in a magnetic material usually entails creating an intricate pattern or “texture” of spin orientations in a small region—such as a spin vortex—and irradiating those spins with monochromatic microwaves. To avoid the complexities of spin textures, Yan and his colleagues propose introducing a bump in a few-nanometer-thick magnetic film. Previous research showed that material curvature can affect spin waves, for example, by modifying the frequency–wavelength relationship.

Exploiting another curvature effect, the theorists showed that a bump between 4 and 64 nm high can spontaneously create a set of spin waves that remain restricted to the bump region. Irradiating the bump with microwaves of a specific frequency then excites these waves and launches an MFC that travels away from the bump. Adjusting the height of the bump changes the spacing of the comb frequencies. Team member Hao Zhao says that in addition to possibly making MFCs more widely available, the work shows the potential for using geometry to manipulate spin waves in new ways.

Trios of quantum particles form checkerboard layouts when particle density hits sweet spot

Trions form when three particles, like quarks or electrons, come together. This formation occurs in quantum particles in nuclear physics, semiconductors and magnets, and understanding its behavior can be challenging. Rice University’s Kaden Hazzard and his team recently developed a theory on how these formations occur and behave, which was published in Physical Review Letters.

“Our theory sheds light on how trions form and interact with each other,” said Hazzard, associate professor of physics and astronomy and corresponding author on the paper. “It predicts the strength of the interactions needed to form the trions, and that, after formation, they arrange themselves in a checkerboard pattern.”

If you imagine a space full of equal amounts of red, blue and yellow balls, a trion would form when a red, blue and yellow ball all stuck to each other, Hazzard explained. Once all the balls, or particles, are bound together, he was curious about how these trions would arrange themselves in space.

A thermodynamic approach to gravity could explain cosmic acceleration without dark energy

Gravity, the force that attracts objects toward each other, is currently framed by Albert Einstein’s theory of general relativity. This framework describes gravity as the curvature of spacetime, the invisible four-dimensional fabric of the universe.

While general relativity is now the central theory of gravity, it fails to explain some cosmological phenomena and mysteries, such as the so-called cosmological constant problem. This is the unexplained mismatch between the observed energy of empty space and the far greater values predicted by quantum theories.

In a recent paper published in Physical Review Letters, researchers at Imperial College London tried to frame gravity using thermodynamics, the framework that describes how energy and heat transform. Their study builds on a seminal paper by theoretical physicist Ted Jacobson, published more than three decades ago.

The universe should look the same in all directions at large scales, but DESI data suggest otherwise

Earlier this year, the Dark Energy Spectroscopic Instrument (DESI) completed observations that mapped 47 million galaxies across 11 billion light-years, allowing astronomers to better evaluate the large-scale structure of the visible universe. After studying these data, astronomers Francesco Sylos Labini and Marco Galoppo say the universe may not look the same in all directions. Their results, published in Nature, contradict a fundamental assumption in modern cosmology.

At the scale of a single galaxy or local groups of galaxies, the universe clearly appears to be anisotropic, meaning the structure is different depending on which direction you look. In one direction, there may be more void space, while another direction may have a cluster of galaxies.

However, the cosmological principle says that at larger scales, the universe consists of matter that is more or less distributed evenly in all directions. This is based on the Copernican principle, which states that there should be no “special observers” in the universe, meaning that at large scales, the universe should look the same from anywhere else in the universe.

Scientists find molecular-level evidence for two structures in liquid water

A study published in Nature Physics provides new molecular-level evidence from simulations that liquid water is not a single uniform substance, but a constantly shifting mixture of two distinct microscopic structures.

The idea that water might exist in two distinct structural states is not new. For decades, scientists have theorized that liquid water is composed of two interconvertible local structures—one denser and more disordered, the other less dense and more ordered.

This “two-state model” has been invoked to explain water’s many anomalous properties, including why it becomes easier to compress as it cools and why it reaches maximum density at 4°C (39°F) rather than at its freezing point. But the model has remained controversial because direct molecular-level evidence for the two structures has been elusive.

Thirsty desert lizards inspire a new water-harvesting system

When the desert horned lizard (Phrynosoma platyrhinos) is thirsty, it cannot just lap up water or scoop it up like a bird because it lives in environments where water is extremely scarce. Typically, it’s found in damp soil or, even more rarely, in drops of rain.

Instead, its skin contains microscopic channels between overlapping scales that pull in moisture by capillary action. But how it gets that water from these channels into its mouth has remained a mystery until now.

Scientists have discovered how that happens, and it inspired them to design a water-harvesting system that borrows from how the reptiles do it.

It only takes one fake web page to fool AI shopping bots, study finds

AI shopping assistants are popping up all over the internet, changing how we browse, compare and discover products. However, these helpful tools appear to have a serious security flaw. According to a paper published on the arXiv preprint server, a single manipulated web page can trick an AI assistant into promoting a fake product to unsuspecting customers.

Considering that fake goods and fake reviews are everywhere online, researchers Minghao Luo and Liang Chen decided to test how easily search-augmented AI systems can be tricked into promoting bogus brands.

Quantum waves reveal one-sided motion marking elusive critical states

Sound waves, light waves and other types of waves, generally spread freely through space and over time. In 1958, physicist Philip W. Anderson first described a phenomenon via which irregularities or other sources of disorder in materials would prevent waves from propagating freely, which is now known as Anderson localization.

In quantum systems, one can observe quantum states that are spread throughout a system (i.e., extended), confined to a small region (i.e., localized) or somewhere between the two (i.e., critical). Critical quantum states have so far proved to be very difficult to identify and study using Anderson’s localization theory.

Researchers at the International Quantum Academy and Southern University of Science and Technology in China recently set out to further explore critical quantum states in a quantum processor based on superconducting qubits.

Microscale hydrogel fibers could enable imaging inside tiny tissue structures

Researchers have developed light-transmitting hydrogel fibers that are just hundreds of micrometers in diameter. With further development, these soft fibers could one day make it possible to use imaging techniques to detect early breast cancer hidden inside very small breast ducts.

“While traditional, relatively rigid fiber probes may cause mechanical damage when entering narrow, curved or soft tissue spaces, our fibers are very soft with mechanical properties more similar to those of human soft tissues,” said research team leader Yu Zhang from Harbin Engineering University in China. “We made these fibers using a draw-spinning method that was inspired by spider-silk spinning.”

In research appearing in Optics Express, the researchers describe how they tested the new hydrogel fibers by incorporating them into an imaging system and using it to analyze standard pathology-stained breast tissue sections. The imaging system successfully reconstructed the microscopic features used by pathologists to evaluate tumors and, when combined with artificial intelligence algorithms, distinguished tumor subtypes with an accuracy of 93.97%.

Tiny water droplets transmutate aniline into pyridine in ambient and catalyst-free conditions

Aniline can now be transformed into pyridine without adding any catalysts, oxidants or toxic reagents. In a recent study published in the Journal of the American Chemical Society, researchers achieved skeletal editing, involving the reorganization of the carbon-nitrogen bonds within an aromatic ring, by turning an aqueous solution of aniline into a mist of microdroplets.

During its millisecond-long airborne lifespan, aniline underwent rapid molecular rearrangement, inserting nitrogen into the aromatic ring and forming pyridine, driven by the uniquely active air-water interface in microdroplets. The green, reagent-free reaction converted up to 80% of the starting material into the product under ambient conditions, eliminating the added energy cost often required to carry out such conversion reactions.

By testing droplets of different sizes, charges and acidity levels, researchers found that the reaction is boosted at the droplet’s interface, a zone that is rich in protons and highly polarized. The smaller the droplet, the larger its reactive surface area relative to its volume, and the better the reaction outcome.

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