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Category: particle physics – Page 25

Waiting in line: Why six feet of social distancing may not be enough to stop airborne virus spread

We all remember the advice frequently repeated during the COVID pandemic: maintain six feet of distance from every other human when waiting in a line to avoid transmitting the virus. While reasonable, the advice did not take into account the complicated fluid dynamics governing how the airborne particles actually travel through the air if people are also walking and stopping. Now, a team of researchers led by two undergraduate physics majors at the University of Massachusetts Amherst has modeled how aerosol plumes spread when people are waiting and walking in a line.

The results, published recently in Science Advances, grew out of a question that many of us may have asked ourselves when standing in marked locations six-feet apart while waiting for a vaccine, to pay for groceries or to get a cup of coffee: what’s the science behind six-feet of separation? If you are a physicist, you might even have asked yourself, “What is happening physically to the aerosol plumes we’re all breathing out while waiting in a line, and is the six-foot guideline the best way to design a queue?”

To find answers to these questions, two UMass Amherst undergrads, Ruixi Lou and Milo Van Mooy, took the lead.

A dual ion beam tests new steel under fusion energy-producing conditions

A new class of advanced steels needs more fine-tuning before use in system components for fusion energy—a more sustainable alternative to fission that combines two light atoms rather than splitting one heavy atom. The alloy, a type of reduced activation ferritic/martensitic or RAFM steel, contains billions of nanoscale particles of titanium carbide meant to absorb radiation and trap helium produced by fusion within a single component.

When subjected to and concentrations representative of fusion, the titanium-carbide precipitates initially helped trap helium but later dissolved under high damage levels. After dissolving, the alloy swelled as it was no longer able to disperse and trap helium, which could compromise system components.

The first-of-its-kind systematic investigation led by University of Michigan engineers was published in Acta Materialia and the Journal of Nuclear Materials in a series of three papers.

Scientists Were Wrong: Apollo 16 Rocks Rewrite the Story of the Moon’s Exosphere

The Moon’s surface is constantly exposed to the solar wind, a stream of charged particles emitted by the Sun. These energetic ions can dislodge atoms from the Moon’s outermost rocky layer, contributing to the formation of a very sparse layer of gas around the Moon known as the exosphere. However, the exact mechanism behind the creation of this exosphere has remained unclear.

Researchers at TU Wien, working with international collaborators, have now shown that a major contributing process, sputtering caused by the solar wind, has been greatly overestimated in earlier studies. This discrepancy stems from previous models overlooking the Moon’s actual surface texture, which is rough and porous.

For the first time, the team used original Apollo 16 samples in high-precision laboratory experiments, along with advanced 3D modeling, to calculate more accurate sputtering rates. Their findings are published in Communications Earth & Environment.

New model explains plutonium’s peculiar behavior

Normally, materials expand when heated. Higher temperatures cause atoms to vibrate, bounce around and take up a larger volume. However, for one specific phase of plutonium—called delta-plutonium—the opposite inexplicably occurs: it shrinks above room temperature.

As part of its national security mission, Lawrence Livermore National Laboratory (LLNL) aims to predict the behavior of plutonium in all of its phases. Unraveling the mystery behind delta-plutonium’s abnormal behavior at high temperatures is an important piece of the picture.

In a new study, published in Reports on Progress in Physics, researchers from LLNL demonstrate a model that can reproduce and explain delta-plutonium’s thermal behavior and unusual properties. The model calculates the material’s free energy, a quantity that reflects the amount of available or useful energy in a system.

Researchers discover universal rules of quantum entanglement across all dimensions

A team of theoretical researchers used thermal effective theory to demonstrate that quantum entanglement follows universal rules across all dimensions. Their study was published online in Physical Review Letters.

“This study is the first example of applying thermal effective theory to quantum information. The results of this study demonstrate the usefulness of this approach, and we hope to further develop this approach to gain a deeper understanding of quantum structures,” said lead author and Kyushu University Institute for Advanced Study Associate Professor Yuya Kusuki.

In , two particles that are far apart behave independently. However, in , two particles can exhibit strong correlations regardless of the distance between them. This quantum correlation is known as quantum entanglement.

Ghost particles may secretly decide the fate of collapsing stars

Neutrinos are cosmic tricksters, paradoxically hardly there but lethal to stars significantly more massive than the sun. These elementary particles come in three known “flavors”: electron, muon and tau. Whatever the flavor, neutrinos are notoriously slippery, and much about their properties remains mysterious. It is almost impossible to collide neutrinos with each other in the lab, so it is not known if neutrinos interact with each other according to the standard model of particle physics, or if there are much-speculated “secret” interactions only among neutrinos.

Now a team of researchers from the Network for Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS), including several from UC San Diego, have shown, through theoretical calculations, how collapsing massive stars can act as a “neutrino collider.” Neutrinos steal thermal energy from these stars, forcing them to contract and causing their electrons to move near light speed. This drives the stars to instability and collapse.

Eventually the collapsing star’s density becomes so high that the neutrinos are trapped and collide with each other. With purely standard model interactions, the neutrinos will be mostly electron flavor, the matter will be relatively “cold,” and the collapse will likely leave a neutron star remnant. However, secret interactions that change neutrino flavor radically alter this scenario, producing neutrinos of all flavors and leading to a mostly neutron “hot” core that may lead to a black hole remnant.

‘Neglected’ particles that could rescue quantum computing

One of the most promising approaches to overcoming this challenge is topological quantum computing, which aims to protect quantum information by encoding it in the geometric properties of exotic particles called anyons. These particles, predicted to exist in certain two-dimensional materials, are expected to be far more resistant to noise and interference than conventional qubits.

“Among the leading candidates for building such a computer are Ising anyons, which are already being intensely investigated in condensed matter labs due to their potential realization in exotic systems like the fractional quantum Hall state and topological superconductors,” said Aaron Lauda, professor of mathematics, physics and astronomy at the USC Dornsife College of Letters, Arts and Sciences and the study’s senior author. “On their own, Ising anyons can’t perform all the operations needed for a general-purpose quantum computer. The computations they support rely on ‘braiding,’ physically moving anyons around one another to carry out quantum logic. For Ising anyons, this braiding only enables a limited set of operations known as Clifford gates, which fall short of the full power required for universal quantum computing.”

But in a new study published in Nature Communications, a team of mathematicians and physicists led by USC researchers has demonstrated a surprising workaround. By adding a single new type of anyon, which was previously discarded in traditional approaches to topological quantum computation, the team shows that Ising anyons can be made universal, capable of performing any quantum computation through braiding alone. The team dubbed these rescued particles “neglectons,” a name that reflects both their overlooked status and their newfound importance. This new anyon emerges naturally from a broader mathematical framework and provides exactly the missing ingredient needed to complete the computational toolkit.

Research examines how ripples affect nanoscopic materials

When materials are created on a nanometer scale — just a handful of atoms thick — even the thermal energy present at room temperature can cause structural ripples. How these ripples affect the mechanical properties of these thin materials can limit their use in electronics and other key systems.

New research validates theoretical models about how elasticity is scale-dependent — in other words, the elastic properties of a material are not constant, but vary with the size of the piece of material.

Assistant Professor Jian Zhou, PhD ’18, collaborated with researchers from Argonne National Laboratory, Harvard University, Princeton University and Penn State University for a recently published paper in the Proceedings of the National Academy of Sciences.

Using a semiconductor manufacturing process, the team created alumina structures 28 nanometers thick (more than 1,000 times thinner than the diameter of a human hair) on the silicon wafer with thermal-like static ripples, then tested them with lasers to measure their behavior. To remove possible stress to the material that could affect the results, cantilevers held the wafers during testing.

Understanding how thin materials behave is key to electronics and other technology.

Heavy fermions entangled: Discovery of Planckian time limit opens doors to novel quantum technologies

A joint research team from Japan has observed “heavy fermions,” electrons with dramatically enhanced mass, exhibiting quantum entanglement governed by the Planckian time—the fundamental unit of time in quantum mechanics. This discovery opens up exciting possibilities for harnessing this phenomenon in solid-state materials to develop a new type of quantum computer. The findings are published in npj Quantum Materials.

Heavy fermions arise when conduction electrons in a solid interact strongly with localized magnetic electrons, effectively increasing their mass. This phenomenon leads to unusual properties like unconventional superconductivity and is a central theme in condensed matter physics. Cerium-rhodium-tin (CeRhSn), the material studied in this research, belongs to a class of heavy fermion systems with a quasi-kagome lattice structure, known for its geometrical frustration effects.

Researchers investigated the electronic state of CeRhSn, known for exhibiting non-Fermi liquid behavior at relatively high temperatures. Precise measurements of CeRhSn’s reflectance spectra revealed non-Fermi liquid behavior persisting up to near room temperature, with heavy electron lifetimes approaching the Planckian limit. The observed spectral behavior, describable by a single function, strongly indicates that heavy electrons in CeRhSn are quantum entangled.

Experiment Recreates The Universe’s Very First Chemical Reactions

The first chemical reactions in the wake of the Big Bang have been recreated for the first time in conditions similar to those in the baby Universe.

A team of physicists led by Florian Grussie of the Max Planck Institute for Nuclear Physics (MPIK) in Germany has reproduced the reactions of the helium hydride ion (HeH+), a molecule made from a neutral helium atom fusing with an ionized atom of hydrogen.

These are the first steps that lead to the formation of molecular hydrogen (H2), the most abundant molecule in the Universe and the stuff from which stars are born. The new work, therefore, elucidates some of the earliest processes that gave rise to the Universe as we know it today.

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