Scientists outfitted some fake fungi with LEDs and put them in a Brazilian forest to test their theory that light, not some funky mushroom fragrance, was luring bugs.
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The brain’s conversation with itself: neural substrates of dialogic inner speech
Inner speech has been implicated in important aspects of normal and atypical cognition, including the development of auditory hallucinations. Studies to date have focused on covert speech elicited by simple word or sentence repetition, while ignoring richer and arguably more psychologically significant varieties of inner speech. This study compared neural activation for inner speech involving conversations (‘dialogic inner speech’) with single-speaker scenarios (‘monologic inner speech’). Inner speech-related activation differences were then compared with activations relating to Theory-of-Mind (ToM) reasoning and visual perspective-taking in a conjunction design.
Little-known arm of immune system could be key to better vaccines, cancer therapies
For a hiker who unwittingly brushes the leaf of poison ivy, weeks of suffering can start within a few hours, when an itchy red rash appears at the contact site. In the days that follow, blisters erupt and the urge to scratch can become maddening. Even after the blisters begin to burst and crust over, the skin will need days more to heal.
Unpleasant encounters with poison ivy and its noxious relatives are common, but they have long posed a biological puzzle. Immune warriors called T cells drive the inflammation and itch, known as allergic contact dermatitis. Scientists long thought T cells only respond to protein fragments, or peptides. But urushiol, the main skin-irritating substance made by poison ivy and its kin, is a mixture of lipids, compounds related to fats and waxes.
Scientists may now have an explanation that involves an unsung branch of our immune system that keeps track of lipids with help from a cell surface protein called CD1. Lab animal studies suggest components of urushiol bind to CD1 on sentinel cells within the skin. This interaction may ultimately rouse T cells to release inflammation-inducing molecules (see graphic, below). Although that mechanism hasn’t yet been confirmed for poison ivy rash, researchers have amassed strong evidence that the CD1 system drives other human skin conditions, including the painful welt sparked by a bee or wasp sting and the rash some people develop when they encounter dust mites. CD1-sporting cells may also promote gut inflammation in ulcerative colitis and Crohn disease.
Quantum Light Reveals How Solvents Affect Molecules
Understanding how a molecule’s neighbors shape its behavior is essential for explaining chemical reactions and designing molecular systems. Conventional ultrafast spectroscopy can uncover these dependencies. Unfortunately, the technique requires intense laser pulses, which can perturb or damage delicate samples and complicate measurements. Now Tanvir Rajib of Texas A&M University and his colleagues have demonstrated an approach that avoids those problems by using pairs of photons instead of intense laser pulses [1]. Researchers could apply the method to a wide range of chemical, biological, and nanoscale molecular systems.
In the technique, a nonlinear optical crystal transforms laser light into pairs of entangled, identical-frequency photons through a process called spontaneous parametric down-conversion. One photon in each pair interacts with a molecular sample, whose ultrafast molecular dynamics alter that photon’s quantum state and, in turn, its indistinguishability with respect to the other, noninteracting photon. The photons then enter opposite input ports of a four-port beam splitter. How likely they are to emerge from the same output port depends on their indistinguishability through an effect called Hong-Ou-Mandel interference, providing a way to infer the molecular dynamics.
In work published earlier this year, Rajib and his colleagues used the approach to measure a molecule’s coherence time—its ability to maintain a definite phase relationship between its different energy states [2]. Now the researchers have studied how that time varies with the molecule’s neighbors. They investigated a molecular dye known as IR-797 in five solvents—which provided differing dielectric environments—and found that the coherence time ranged from 25 to 60 femtoseconds. In future work, the researchers plan to optimize the method, boosting its speed, efficiency, and sensitivity.
The Unexpected Ubiquity of the Phonon Thermal Hall Effect
The discovery of a thermal version of the Hall effect in common semiconductors challenges our understanding of how magnetic fields and heat fluxes interact within solids.
In the late 19th century, two physicists independently discovered the Righi-Leduc, or thermal Hall, effect: In the presence of a perpendicular magnetic field, a longitudinal heat flux generates a transverse temperature gradient. In metals, the thermal Hall effect is tied to the more familiar electric Hall effect through the Wiedemann-Franz law, which states that electronic thermal conductivity divided by electrical conductivity is directly proportional to temperature.
In electrical insulators, lattice vibrations called phonons carry heat. Until the early 21st century, it was thought that phonons, despite being neutral, could still generate a nonzero thermal Hall signal, provided they are scattered by electron spins. However, since then many experiments worldwide have found that such a signal can be detected even in crystalline insulators with no unpaired electron spins. The decisive discovery was made last year by Xiaobo Jin of Fudan University in China and his colleagues, who found a phonon thermal Hall effect in two simple semiconducting materials: silicon and germanium [1]. Whereas the origin of the effect is hotly debated, its importance in challenging views of how magnetic fields and heat fluxes interact is undisputed.
Bending nanoribbons tunes diamond’s light emission without doping
In a new Physical Review Letters study, researchers have demonstrated that bending diamond nanostructures can tune the light they emit without doping.
Diamond is an ultrawide bandgap semiconductor with high carrier mobility, high thermal conductivity, deep-ultraviolet light emission and stable single-photon emission. These properties make it a potential candidate for next-generation electronic and optoelectronic devices.
However, properties such as its bandgap and light emission are difficult to tune because doping in diamond poses limitations. Elastic strain engineering, which stretches or compresses a material without permanently deforming it, has emerged as an alternative.
Laser-made muons produce first images of dense objects
Muons are constantly being created as cosmic rays collide with molecules in Earth’s upper atmosphere. With their ability to penetrate far into dense, solid materials, these cosmic muons are often used to image the insides of objects that are otherwise hidden from view. However, the flow of these natural particles is far too slow for the technique to become both fast and reliable in practical settings.
Through new research posted to the preprint server arXiv, a team including Madalina Dobre at the Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering in Romania has created images using an artificial muon beam for the first time.
After 20 years, jet diffusion wakes detected in quark-gluon plasmas
Boats passing over smooth water form a pair of diffusion wakes behind them veering off at a certain angle. Turbulence occurs along the line directly behind the boat, but the two diffusion waves are at a theoretical angle of 19.5° from the same line, for deep, ideally smooth water.
Now physicists have for the first time measured diffusion wakes of jets passing through quark-gluon plasmas (QGP), a phenomenon first predicted 20 years ago after it was realized that QGPs are liquid not a plasma (that is, like a gas). In fact, they are the most perfect liquid in the universe. The result, obtained by the CMS Collaboration, is published in Physical Review Letters.
QGPs were the state of the universe for its first few microseconds, from about a trillionth of a second after the Big Bang to a few microseconds after. It is 200,000 times hotter than the center of the sun, and its viscosity was first inferred in 2005 in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York.