Researchers at ETH Zurich and the Paul Scherrer Institute in Villigen, Switzerland, have produced a high-intensity beam of muonium atoms in a cold state, an experimental advance that could enable a direct test of whether gravity acts differently on second-generation matter. The peer-reviewed study in Nature Physics describes a new method for generating muonium in superfluid helium. The resulting atoms travel at similar speeds and almost parallel to one another, properties required for a future interferometer that would measure the tiny influence of gravity on muonium.

The study did not conduct that gravitational measurement or find evidence that gravity departs from its expected behavior for ordinary matter; it instead developed the beam source needed for the proposed test. The experiment is designed to examine the universality of free fall and the equivalence of gravitational and inertial mass, a cornerstone of Albert Einstein’s theory of gravitation. In ordinary matter, bodies fall at the same rate at a given point within a gravitational field, while the equivalence principle links gravitational mass with inertial mass.

According to the research team, this principle has so far been demonstrated only with ordinary matter or first-generation antimatter. Muonium is a neutral atom formed from a positively charged antimuon and a negatively charged electron, making it a second-generation probe. A gravity experiment with this exotic atom would test whether the equivalence continues to hold for particles outside the first generation.

Muonium has two characteristics that make it useful for this test: it is neutral, and it belongs to a heavier and less familiar generation of particles. A neutral object allows gravitational behavior to be studied without the weak gravitational signal being masked by stray electromagnetic fields, which can dominate the behavior of charged particles. At the same time, muonium is exceptionally difficult to produce and control.

Its constituent muon decays after only about 2.2 microseconds. Earlier sources generated muonium atoms that flew off in many directions at different speeds and were therefore unsuitable for the precision required in a gravity experiment. The researchers addressed this problem by creating a cold, intense and well-directed beam.

The antimuons were directed into a thin layer of superfluid helium that had been cooled close to absolute zero, at minus 273 degrees Celsius. Superfluid helium is a quantum fluid in which individual helium atoms lose their identity and in which impurities are not tolerated. Lead author Jesse Zhang said the researchers used the superfluid as an “atomic cannon,” exploiting the conversion of chemical potential into kinetic energy to propel the newly formed muonium atoms out of the liquid.

When an antimuon encounters a free electron in the superfluid helium, it forms a neutral muonium atom with positive chemical potential. The atom is forced out of the liquid, and as it reaches the surface, that chemical potential is converted into kinetic energy. The resulting boost sends the muonium vertically out of the helium.

Importantly, the atoms must move through the quantum liquid at a suitable speed without collisions, because excessive scattering would prevent them from reaching the surface within their very short lifetime. The high-intensity antimuon beam from PSI allows many muonium atoms to be generated for the planned experiments. Anna Soter, a professor of physics at ETH Zurich and member of the research team, said the cold state is what makes the proposed gravity experiment possible.

In this context, “cold” does not mean that the atoms are motionless; it means that they propagate at similar speeds and nearly parallel to one another. This improved control over direction and velocity is important because the planned instrument will use the wave properties of the atoms to create an interference pattern. A very small shift in that pattern caused by Earth’s gravitational pull would provide a measure of gravity’s effect on muonium.

The study establishes the upstream beam capability rather than reporting the result of that comparison. The next stage of the program is the development of a muonium interferometer. According to the researchers, they hoped to test the method for the first time with the atomic beam in the year of the announcement and, if that worked as expected, to carry out the actual gravity experiment two or three years later.

Those are planned milestones rather than completed measurements. If the interference pattern of muonium shifts differently from the pattern expected for ordinary matter, Soter said the result would be surprising and could, among other theoretical possibilities, point toward the existence of a fifth force. No fifth force has been proven, and the present work provides no evidence for one.

The team’s primary aim is to measure whether the equivalence between gravitational and inertial mass applies to a second-generation particle. Physics recognizes four fundamental interactions: gravity, electromagnetism, the strong interaction and the weak interaction. A fifth force has been proposed repeatedly, but it has never been established.

Soter emphasized that the researchers are open-minded about what the measurement may show while keeping the immediate objective focused on the first such test. The new beam is therefore an enabling experimental result, not a demonstration that Einstein’s theory has been challenged or overturned. Beyond the planned gravity measurement, the high-intensity muonium beam is expected to enable more precise laser-spectroscopy experiments.

These could allow muonium to be measured more accurately than in previous work and provide information about the muon’s mass and fundamental physical constants, which are stated goals of the research group. The same experimental source can thus serve two purposes: supplying a cold, directed beam for a gravitational comparison and providing a larger, better-controlled population of muonium for detailed spectroscopic study. The reported advance addresses a major technical obstacle while leaving the central scientific question unresolved.

A successful gravitational test will still require an interferometer capable of resolving a minuscule shift in an interference pattern while dealing with muonium’s short lifetime, beam quality and other sources of uncertainty. The study’s demonstrated result is the generation of a high-intensity, superthermal muonium beam in superfluid helium, with atoms emerging in the cold state needed for future work. Whether muonium falls exactly as expected for ordinary matter remains to be measured.

The beam nevertheless supplies the experimental foundation for testing gravitational universality in a second-generation particle, a comparison that had not previously been carried out with muonium.

Subject of Research: A cold muonium beam developed for future tests of gravitational universality and laser spectroscopy

Article Title: Novel particle beam could challenge Einstein’s Theory of Gravity

Article References: Novel particle beam could challenge Einstein’s Theory of Gravity. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: muonium, muon beam, gravity, gravitational universality, equivalence principle, interferometry, superfluid helium, laser spectroscopy, ETH Zurich, Paul Scherrer Institute, Novel, particle

New active ingredients for drugs to treat infections, cancer or other serious diseases are often based on substances originally discovered in microorganisms, plants or other living organisms. Producing or improving such active ingredients in a targeted manner using microorganisms is often challenging because the underlying biological processes are extremely complex.

New active ingredients for drugs to treat infections, cancer or other serious diseases are often based on substances originally discovered in microorganisms, plants or other living organisms. Producing or improving such active ingredients in a targeted manner using microorganisms is often challenging because the underlying biological processes are extremely complex.

From rejected batches to renewable fuels, researchers are exploring how ice cream makers could reuse ingredients they discard.

The Northern suburbs of Toledo, Ohio turned into a real life Don DeLillo novel overnight, after an explosion at a chemical facility sent plumes of industrial compounds billowing into the sky.

According to the local station WTOL11, the blast happened at a chemical distribution site in Ohio’s Lucas County on Tuesday night, prompting an immediate evacuation order for anybody living within one mile of the disaster zone. Those within three miles were given an order to shelter in place.

In a press conference on Wednesday, city emergency officials explained that the leaking chemical exhaust is glycidyl methacrylate, an industrial manufacturing chemical broadly suspected to be carcinogenic to humans.

Maps show numerous residential neighborhoods in the immediate vicinity, the closest being a trailer park just 0.25 miles as the crow flies from the site of the chemical explosion. The nearby Ottawa river, a tributary of Lake Erie, is situated under a half mile to the South.

Complicating matters for first responders and any broader evacuation order is the onset of a fog alert, which combined with the hazmat emergency has turned Toledo into America’s apocalypse zone du jour.

Images circulated by WTOL11 on Facebook show the cataclysmic scenes unfolding across the city, with commenters expressing confusion over whether the clouds of haze were caused by the airborne chemical leak, the fog, or a noxious mix of both.

“I can’t see out my window,” one Toledo resident wrote. “Should I and my dog leave?”

More on disasters: Giant Oil Tanker Runs Aground in Marine Nature Preserve, Spills Nonstop for Weeks

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Just like gloves, molecules can have left- and right-handed—or mirror-image—forms. Because the left- and right-handed molecules are still very similar, scientists have had trouble separating them from each other. But a team of researchers in Japan might have found a solution. In their new study, published in Science Advances, the team successfully separated an equal mixture of mirror-image molecules created by replacing hydrogen with deuterium in one form.

Scientists have developed a new material that helps a costly catalyst survive for thousands of hours while producing hydrogen from water. The advance could address one of the problems holding back a promising method of making low-emission hydrogen. Researchers at Tohoku University designed a structure that keeps tiny particles of iridium firmly in place and […]

The post New catalyst could make clean hydrogen production last much longer appeared first on Knowridge Science Report.

A new study suggests that hydrogen could be produced from natural gas while capturing most of the carbon dioxide generated during the process. In detailed computer models, some designs captured between 90% and 99% of those emissions. Researchers at the University of Manchester assessed a technology called chemical looping reforming. Their work, published in Carbon […]

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Where did it start? How did it grow complex? Why did it get big? Three moments in Earth’s early history when evolution suddenly, inexplicably turned up the dial.

 

In 2004, physicists isolated graphene, a sheet of carbon just one atom thick. It launched the study of two-dimensional (2D) materials: crystals a few atoms thick in which electrons are confined to a plane and can behave quite differently from those in ordinary solids. The family of known and predicted 2D crystals has since grown to thousands of members. Two recent studies show how computation can search that family for the most promising ones, the first for unusual electronic “topology”, the second for crystals well suited to twisting.

A hidden property of electrons

Electrons in a crystal can only have energies within allowed ranges called bands, separated by forbidden gaps. If a gap separates the filled electrons from the empty states, the material is an insulator. In a semimetal, filled and empty bands just touch, so a few electrons can move freely.

Two insulators can still differ at a deeper level, described by topology: a property of the whole set of electron states that cannot change smoothly, only by closing the gap or breaking a protecting symmetry. A doughnut and a coffee mug are topologically alike because each has one hole, and neither can become a sphere without tearing.

The idea took off with the quantum spin Hall effect. Proposed for graphene in 2005, it proved unobservable there because the effect is far too weak. A 2006 proposal for thin layers of mercury telluride was confirmed in 2007. In such a topological insulator the interior blocks current, yet the edges conduct, with electrons of opposite spin travelling in opposite directions, which protects them against many kinds of imperfection.

Symmetry-based methods known as topological quantum chemistry in 2017 made it possible to decide whether a computed electronic structure is topological. Applied to three-dimensional crystals, they pointed to thousands of candidates. Flat crystals lagged behind, with only about 400 known topological or related monolayers.

The first study, “Two-dimensional Topological Quantum Chemistry and Catalog of Topological Materials” ¹, adapts these methods to 2D crystals and applies them to 8,872 entries in two computational databases. It finds 4,073 with nontrivial topology or a related property called obstruction, including 905 topological insulators, 2,129 topological semimetals and 1,003 obstructed atomic insulators, plus 36 close variants. In an obstructed insulator the electrons are centred on empty positions between the atoms rather than on the atoms themselves. The bulk looks ordinary, but cutting the crystal along certain lines produces edge states, and small flakes can carry fractions of an electron’s charge at their corners. The study also calculates edge states for selected materials. Its catalogue includes over 100 monolayers already made in laboratories, but most entries are computer predictions whose properties remain to be tested.

Twisting layers

Stack two atomic sheets and rotate one slightly, and the mismatch creates a large interference pattern, called a moiré pattern, much like two overlapping window screens. Electrons feel this longer repeating pattern, and under the right conditions their bands become nearly flat. Electrons in a flat band have little energy of motion, so their mutual repulsion dominates and strongly correlated behaviour can emerge.

In 2011, calculations predicted that two graphene sheets twisted by about 1.1 degrees, a “magic angle”, would have such flat bands. In 2018, experiments at that angle revealed insulating states caused by electron repulsion, and superconductivity. Twisted layers of other materials, such as MoTe₂ and WSe₂, have since shown many correlated phases, though the mechanisms are still debated.

Most work has focused on these few materials, because most crystals have electronic structures too complicated to predict once twisted. The second study, “2D theoretically twistable material database” ², therefore defines a material as theoretically twistable if its low-energy electrons admit a simple description. In a metal, the relevant electrons must sit at isolated points, as in graphene. In an insulator, the top of the filled band or the bottom of the empty band must stand clear of other bands. Insulators must also have gaps between 0.2 and 3 electronvolts, because larger gaps make electrical contacts difficult. The search was limited to crystals with at most 12 atoms in the repeating cell and four chemical elements.

Starting from the first study’s database, it identifies 61 semimetals and 1,568 insulators. It ranks them with a score and sorts them by lattice shape (about half are hexagonal), by where in momentum space the relevant electrons sit, and by the strength of spin-orbit coupling, the link between an electron’s spin and its motion. These choices shape the moiré pattern, which can resemble honeycomb, kagome or square lattices. Square-lattice moiré systems have been proposed but not yet realized, and could help simulate models relevant to cuprate superconductors.

Calculations on twisted bilayers of SnSe₂, SnS₂, ZrS₂, HfS₂ and Sc₂CCl₂ at a twist of about 7 degrees show isolated flat bands, as the database predicts. Experiments connect the theory to the laboratory. Bulk crystals of SnSe₂, SnS₂, HfS₂, GaTe and ZrNCl were grown. Single layers of several candidates, including SnSe₂, HfSe₂, ZrS₂ and WS₂, were peeled off with a gold-assisted technique that yields larger, cleaner flakes. A dual-gated two-layer SnSe₂ device was built for electrical measurements, and a twisted two-layer HfS₂ device was used for scanning tunnelling measurements near absolute zero.

The direction is clear. Instead of discovering materials by trial and error, it is becoming possible to search systematically for crystals with chosen properties, then test them layer by layer.

 

Author: César Tomé López is a science writer and the editor of Mapping Ignorance

Disclaimer: Parts of this article may have been copied verbatim or almost verbatim from the referenced research paper/s.

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Scientists have developed remarkably long, precisely patterned molecular threads that could open new possibilities for designing advanced materials. The scientists also discovered these threads — called supramolecular polymers — can dramatically enhance brain cell activity. ¹

Built from self-assembling molecules, the longest threads reach dimensions greater than the diameter of a cell. By molecular standards, they are giant — roughly 100 times more massive than even very large conventional polymers and the largest known proteins in biology. Yet despite their enormous size, scientists can precisely control their lengths and organize them into chemically distinct segments with defined dimensions carrying opposite electrical charges.

That precision also produced an unexpected biological effect. In cell culture studies, the structures enhanced the growth and organization of neurons and increased synapse formation.

The findings introduce a new way to use self-assembly to build highly controlled supramolecular materials with precise physical arrangement of chemical structures. Ultimately, the work could inform materials’ design for a range of applications, including biomaterials for regenerative medicine.

“These structures represent a breakthrough in materials design, and we already discovered one useful application: their superbioactivity toward neurons, which will bring new opportunities in regenerative medicine,” said Northwestern’s Samuel I. Stupp, who led the study. “Typically, when we design a regenerative material, we add biological signals, designed to activate cell receptors. Here, the material itself becomes highly bioactive simply through the precise organization of electrical charges and its dynamic behavior. That introduces a very different way of thinking about how materials can communicate with cells.”

Bringing precision to self-assembly

The new study builds on Stupp’s long history working with supramolecular materials, dynamic structures that form when molecules spontaneously organize through weak, reversible interactions. While conventional polymers, like plastics, hold together using strong, permanent chemical bonds, supramolecular polymers are dynamic, allowing their components to move and reconfigure, which generates life-like properties in synthetic systems. Supramolecular polymers exist in all living organisms, where they perform essential functions and hold promise for future soft matter technologies.

That flexible, dynamic nature can be useful for interacting with living cells in biomedical applications, but it also makes the structures difficult to control. Scientists can design the individual molecular building blocks but then struggle to control how long the resulting structures grow and how they organize their chemical components.

Stupp’s team overcame that limitation by using novel designs of molecules and carefully controlling their assembly process. With this strategy, the researchers could dictate the threads’ lengths and keep them uniform. Once the growth stopped, the structures maintained their precise lengths rather than fusing together or rearranging.

“We let these filaments sit in a test tube for months, and they surprisingly didn’t change,” Stupp said. “They remained the same length and retained their segmented structures.”

Grow, stop, grow again

Stupp and his team traced that unusual ability to a previously unknown process his laboratory calls “self-capping supramolecular polymerization.” As a thread grows, flexible portions at the ends remain highly dynamic and, at proper temperatures, allow new molecules to join in a synchronized manner. Once the available building blocks are consumed, those flexible portions fold over and protect the ends. This effectively shuts down further growth by preventing threads from fusing together or undergoing “Ostwald Ripening,” a process in which smaller structures disappear while larger ones grow.

“To make them longer and longer, we just kept adding new molecules,” Stupp said. “The new molecules stick with strong noncovalent bonds to the growing thread and elongate the assembly, which led to a breakthrough in terms of size control.

“The collective molar mass of their noncovalently bonded monomers reaches billions of daltons, and thus they are ‘giga-assemblies.’ These are the largest supramolecular polymers ever made with this degree of precision. Once the monomer is fully consumed, they finish growing and their dimensions remain stable.”

Approximately the size of one proton or neutron, a dalton is a tiny unit that scientists use to measure the mass of molecules and atoms. More than a billion daltons is enormous by molecular standards. For comparison, the largest common polymers of plastics have molar masses in the range of 10 million daltons, and the largest proteins in nature reach approximately 3 to 5 million daltons.

Researchers can later restart growth by supplying more building blocks. By adding different types of molecules in sequence, the researchers can create precisely defined segments with different chemical properties. In the study, Stupp and his team created threads with positively and negatively charged segments. Because opposites attract, the researchers expected the threads to clump together. Instead, they remained stable in water because the “capping” mechanism prevented the assemblies from fusing together.

Small anchor, big difference

To explore how the pattern of electrical charges might interact with living cells, Stupp and his team turned to neurons, which carry a strong negative charge. The team exposed several threads with different designs to cellular cultures containing cortical neurons.

“The first thing we did was make a structure with only positively charged segments, and it basically killed the neurons,” Stupp said. “Then, we tried a structure with only negatively charged segments, and nothing happened because the neurons repelled the materials.”

When Stupp’s team used supramolecular assemblies with randomly mixed positive and negative charges, the neurons didn’t respond in a notable way. But then the team designed a thread with the breakthrough polymerization strategy comprising a small positively charged segment sandwiched between two negatively charged segments of different lengths. Something interesting and unexpected occurred.

The small positive region anchored the thread to the negatively charged surface of a neuron. Repelled by the neuron’s negative charge, the thread’s negative segments remained highly mobile and in constant motion since they could not escape.

“When we used only positively charged segments, they suffocated the neuron and killed it,” Stupp said. “But with only one positively charged segment surrounded by negative ones, it couldn’t do that anymore. And the negative segments, which ordinarily couldn’t get near the neuron, were forced to stay near it because they were anchored.”

Neurons grow and spring to life

Neurons treated with the precisely segmented threads grew longer neurites — the long projections neurons use to communicate with other cells. The treated neurons also formed more elaborate branches, gaining the ability to connect with neighboring cells.

“The neurons matured to an amazing level,” Stupp said. “They grew long and highly branched neurites, which is how they can start making synaptic connections in the brain and in the spinal cord.”

After just seven days, treated neurons were much more active than untreated neurons. When stimulated, treated neurons produced a calcium response — a sign of neuronal activity. Their overall calcium activity was four times greater. And, after 14 days, treated neurons formed more synapses than untreated neurons.

Stupp and his team saw another striking effect in cultures of human neural progenitor cells, which are immature cells that can develop into neurons. Although these cultures typically grow in flat layers, the cells instead organized into raised, three-dimensional clusters connected by axons. This organization resembled aspects of the brain’s white and gray matter, where somas are separated from axons.

No signals required

Perhaps most surprisingly, the molecular threads produced these effects without carrying biological signals specifically designed to encourage neurons to grow. Stupp posits the negatively charged segments recruit specific proteins already present around the cells that help neurons survive, grow and communicate. These proteins, called neurotrophic factors, have positively charged domains. Stupp’s team also found laminin — an important protein that holds tissues together and has positively charged domains — accumulating along the supramolecular threads near neurons.

Stupp hypothesizes that the interplay between attraction and repulsion causes the threads’ negative segments to rapidly move toward and away from the neurons in a “tapping” motion. Proteins recruited by the negative segments may be drawn toward receptors on the neurons, while electrostatic forces push the segments away. This repeated tapping, occurring on millisecond timescales, could help enhance biological signaling. A live cell movie included in the Science paper has captured this phenomenon.

Beyond neurons, Stupp says the new polymerization strategy could eventually enable scientists to build long molecular structures containing many carefully positioned chemical segments. That could open opportunities to create new materials and devices with features that extend over very long distances.

“We discovered something we had never seen before in chemistry or in biology,” Stupp said. “This work gives us a new level of control over supramolecular materials. In the future, we can imagine creating many segments with different properties. The unknown functions of these structures are likely to be as surprising as the superbioactivity observed on neurons. We’re just beginning to imagine the possibilities.”

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Pyrolysis (noun, “Py-RAW-leh-sis”)

Pyrolysis is a process though which heat breaks down large molecules into smaller ones. It is just one of the chemical reactions that occurs when something is burning.

Picture a campfire. The flame may look like a single chemical reaction. But in reality, it comes from multiple reactions that occur step by step.

The first step is pyrolysis. In this step, heat breaks open the fuel’s chemical bonds. In the case of a campfire, that fuel is wood. But pyrolysis doesn’t create the campfire’s flame. The next step — combustion — does that. Combustion occurs when the broken-open fuel molecules react with oxygen in the air.

Pyrolysis can occur without combustion. For example, if you seal wood in an oxygen-free container and heat it, the wood won’t ignite. Instead, pyrolysis will slowly transform it into charcoal. Pyrolysis typically does not break down fuel as completely as combustion does. That’s why charcoal can still burn to heat up a grill. In contrast, soot collected from a cold campfire typically cannot be burned.

Pyrolysis also plays a crucial role in cooking up a popular sweet treat: caramel.

To make caramel, a chef heats sugar and water on a stovetop into a syrup. As the syrup gets hotter and hotter, the sugar molecules begin to break open. This causes the clear syrup to turn yellow-gold and then a deep, caramel brown. That’s the chef’s cue to take the caramel off the heat. They may then add butter and cream to the hot, gurgling caramel. Much of the chemical transformation that turned syrup into caramel occurred through heat alone. Therefore, it is an example of pyrolysis.

In a sentence

Pyrolysis can produce biochar, a valuable, carbon-rich substance that farmers use to improve soil quality.

Check out the full list of Scientists Say.