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Category: physics – Page 224

The ultimate goal of the Old World alchemist was to turn inexpensive metals into gold. Modern-day physicists at the University of Rochester’s Institute of Optics (Rochester, NY), have turned aluminum and other metals gold—in color if not chemistry. A femtosecond laser processing technique created by professor Chunlei Guo and his assistant Anatoliy Vorobeyv alters the surface properties of aluminum, platinum, titanium, tungsten, silver, and gold to create tints of gold, blue, gray, black, and even multicolored irridescence.

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Advanced optoelectronics require materials with newly engineered characteristics. Examples include a class of materials named metal-halide perovskites that have tremendous significance to form perovskite solar cells with photovoltaic efficiencies. Recent advances have also applied perovskite nanocrystals in light-emitting devices. The unusually efficient light emission of cesium lead-halide perovskite may be due to a unique excitonic fine structure made of three bright triplet states that minimally interact with a proximal dark singlet state. Excitons are electronic excitations responsible for the emissive properties of nanostructured semiconductors, where the lowest-energy excitonic state is expected to be long lived and hence poorly emitting (or ‘dark’).

In a new report now published in Science Advances, Albert Liu and a team of scientists in physics and chemistry at the University of Michigan, U.S., and Campinas State University, Brazil, used multidimensional coherent spectroscopy at cryogenic (ultra-cold) temperatures to study the fine structure without isolating the cube-shaped single . The work revealed coherences (wave properties relative to space and time) involving the triplet states of a cesium lead-iodide (CsPbI3) nanocrystal ensemble. Based on the measurements of triplet and inter-triplet coherences, the team obtained a unique exciton fine structure level ordering composed of a dark state, energetically positioned within the bright triplet manifold.

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Although no list like this can be definitive, we polled dozens of researchers over the past year to develop a diverse line-up of ten software tools that have had a big impact on the world of science. You can weigh in on our choices at the end of the story.

From Fortran to arXiv.org, these advances in programming and platforms sent biology, climate science and physics into warp speed.

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Researchers from the Max Planck Society assessed humans’ capabilities for controlling killer AI. Read the details.

Researchers from Osaka University propose a concept for next-generation ultra-intense lasers, possibly increasing the current record from 10 Petawatts to 500 Petawatts.

Ultra-intense lasers with ultra-short pulses and ultra-high energies are powerful tools for exploring unknowns in physics, cosmology, material science, etc. With the help of the famous technology “Chirped Pulse Amplification (CPA)” (2018 Nobel Prize in Physics), the current record has reached 10 Petawatts (or 1016 Watts). In a study recently published in Scientific Reports, researchers from Osaka University proposed a concept for next-generation ultra-intense lasers with a simulated peak power up to the Exawatt class (1 Exawatt equals 1000 Petawatts).

The laser, which was invented by Dr. T. H. Maiman in 1960, has one important characteristic of high intensity (or high peak power for pulse lasers): historically, laser peak power has experienced two-stage development. Just after the birth of the laser, Q-switching and mode-locking technologies increased laser peak power to Kilowatt (103 Watt) and Gigawatt (109 Watt) levels. After CPA technology was invented by Gérard Mourou and Donna Strickland in 1985, by which material damage and optical nonlinearity were avoided, laser peak power was dramatically increased to Terawatt (1012 Watt) and Petawatt (1015 Watt) levels. Today, two 10-Petawatt CPA lasers have been demonstrated in Europe (ELI-NP laser) and China (SULF laser), respectively.

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The Milky Way houses 8292 recently discovered stellar streams—all named Theia. But Theia 456 is special.

A stellar stream is a rare linear pattern—rather than a cluster—of stars. After combining multiple datasets captured by the Gaia space telescope, a team of astrophysicists found that all of Theia 456’s 468 stars were born at the same time and are traveling in the same direction across the sky.

“Most stellar clusters are formed together,” said Jeff Andrews, a Northwestern University astrophysicist and member of the team. “What’s exciting about Theia 456 is that it’s not a small clump of stars together. It’s long and stretched out. There are relatively few streams that are nearby, young and so widely dispersed.”

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On the path to writing his Ph.D. dissertation, Lucio Milanese made a discovery—one that refocused his research, and will now likely dominate his thesis.

Milanese studies , a gas-like flow of ions and electrons that comprises 99 percent of the visible universe, including the Earth’s ionosphere, interstellar space, the , and the environment of stars. Plasmas, like other fluids, are often found in a turbulent state characterized by chaotic, unpredictable motion, providing multiple challenges to researchers who seek to understand the cosmic universe or hope to harness burning plasmas for fusion energy.

Milanese is interested in what physicist Richard Feynman called “the most important unsolved problem of classical physics”—turbulence. In this case, the focus is plasma turbulence, its nature and structure.

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Scientists have used a “galaxy-sized” space observatory to find possible hints of a unique signal from gravitational waves, or the powerful ripples that course through the universe and warp the fabric of space and time itself.

The new findings, which appeared recently in The Astrophysical Journal Letters, hail from a U.S. and Canadian project called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).

For over 13 years, NANOGrav researchers have pored over the light streaming from dozens of pulsars spread throughout the Milky Way Galaxy to try to detect a “gravitational wave background.” That’s what scientists call the steady flux of gravitational radiation that, according to theory, washes over Earth on a constant basis. The team hasn’t yet pinpointed that target, but it’s getting closer than ever before, said Joseph Simon, an astrophysicist at the University of Colorado Boulder and lead author of the new paper.

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Understanding the dynamics of granular materials—such as sand flowing through an hourglass or salt pouring through a shaker—is a major unsolved problem in physics. A new paper describes a pattern for how record-sized “shaking” events affect the dynamics of a granular material as it moves from an excited to a relaxed state, adding to the evidence that a unifying theory underlies this behavior.

The Proceedings of the National Academy of Sciences (PNAS) published the work by Stefan Boettcher, an Emory , and Paula Gago, an expert in modeling the statistical mechanics of granular matter in the Department of Earth Science and Engineering at the Imperial College of London.

“Our work marks another small step forward to describing the behavior of granular materials in a uniform way,” says Boettcher, professor and chair of Emory’s Department of Physics.

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