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Category: physics – Page 64

Simulating KH-, RT-, or RM-driven mixing using direct numerical simulations (DNS) can be prohibitively expensive because all the spatial and temporal scales have to be resolved, making approaches such as Reynolds-averaged Navier–Stokes (RANS) often the more favorable engineering option for applications like ICF. To this day, no DNS has been performed for ICF even on the largest supercomputers, as the resolution requirements are too stringent.8 However, RANS approaches also face their own challenges: RANS is based on the Reynolds decomposition of a flow where mean quantities are intended to represent an average over an ensemble of realizations, which is often replaced by a spatial average due to the scarcity of ensemble datasets. Replacing ensemble averages by space averages may be appropriate for flows that are in homogenous-, isotropic-, and fully developed turbulent states in which spatial, temporal, and ensemble averaging are often equivalent. However, most HED hydrodynamic experiments involve transitional periods in which the flow is neither homogeneous nor isotropic nor fully developed but may contain large-scale unsteady dynamics; thus, the equivalency of averaging can no longer be assumed. Yet, RANS models often still require to be initialized in such states of turbulence, and knowing how and when to initialize them in a transitional state is, therefore, challenging and is still poorly understood.

The goal of this paper is to develop a strategy allowing the initialization of a RANS model to describe an unsteady transitional RM-induced flow. We seek to examine how ensemble-averaged quantities evolve during the transition to turbulence based on some of the first ensemble experiments repeated under HED conditions. Our strategy involves using 3D high-resolution implicit large eddy simulations (ILES) to supplement the experiments and both initialize and validate the RANS model. We use the Besnard–Harlow–Rauenzahn (BHR) model,9–12 specifically designed to predict variable-density turbulent physics involved in flows like RM. Previous studies have considered different ways of initializing the BHR model.

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Reliably guiding and capturing optical waves is central to the functioning of various contemporary technologies, including communication and information processing systems. The most conventional approach to guide light waves leverages the total internal reflection of optical fibers and other similar structures, yet recently physicists have been exploring the potential of techniques based on other physical mechanisms.

Researchers at University of Southern California recently devised a highly innovative approach for trapping light. This method, introduced in Nature Physics, exploits the exotic properties of Lagrange points, the same equilibrium points that govern the orbits of primordial celestial bodies, such as so-called Trojan asteroids in the sun-Jupiter system.

“The discovery of Lagrange points, which happens to be pivotal in this research, can be traced back to the early work of Leonhard Euler and Joseph-Louis Lagrange, which found that at these locations, the exerted by two large bodies can be precisely counterbalanced by centrifugal forces,” Mercedeh Khajavikhan and Demetrios N. Christodoulides, co-authors of the paper, told Phys.org.

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A collaborative research team co-led by Professor Shuang ZHANG, the Interim Head of the Department of Physics, The University of Hong Kong (HKU), along with Professor Qing DAI from National Center for Nanoscience and Technology, China, has introduced a solution to a prevalent issue in the realm of nanophotonics – the study of light at an extremely small scale. Their findings, recently published in the prestigious academic journal Nature Materials, propose a synthetic complex frequency wave (CFW) approach to address optical loss in polariton propagation. These findings offer practical solutions such as more efficient light-based devices for faster and more compact data storage and processing in devices such as computer chips and data storage devices, and improved accuracy in sensors, imaging techniques, and security systems.

Surface plasmon polaritons and phonon polaritons offer advantages such as efficient energy storage, local field enhancement, and high sensitivities, benefitting from their ability to confine light at small scales. However, their practical applications are hindered by the issue of ohmic loss, which causes energy dissipation when interacting with natural materials.

Over the past three decades, this limitation has impeded progress in nanophotonics for sensing, superimaging, and nanophotonic circuits. Overcoming ohmic loss would significantly enhance device performance, enabling advancement in sensing technology, high-resolution imaging, and advanced nanophotonic circuits.

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For example, a video of a swinging pendulum would look the same if you played it backward. We see time as irreversible because of another law of nature, the second law of thermodynamics. This law says that the disorder in a system always increases. If the broken glass reassembled itself, the disorder would decrease.

The same law applies to the aging of materials. But physicists from Darmstadt have found out that this is not the case. They have discovered that the motion of molecules in glass or plastic can be reversed in time if you look at it from a special angle.

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MIT physicists have discovered a surprising twist in the Milky Way’s rotation curve that challenges our understanding of dark matter. By tracking the speed of stars across the galaxy, they’ve uncovered a potential deficit of dark matter at the galactic core.

Traditionally, astronomers believed that dark matter was responsible for the galaxy’s rotation. Still, the new analysis raises the possibility that the Milky Way’s gravitational center may be lighter in mass than previously thought.

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Physicists in Darmstadt are investigating aging processes in materials. For the first time, they have measured the ticking of an internal clock in glass. When evaluating the data, they discovered a surprising phenomenon.

We experience time as having only one direction. Who has ever seen a cup smash on the floor, only to then spontaneously reassemble itself? To , this is not immediately self-evident because the formulae that describe movements apply irrespective of the direction of time.

A video of a pendulum swinging unimpeded, for instance, would look just the same if it ran backwards. The everyday irreversibility we experience only comes into play through a further law of nature, the second law of thermodynamics. This states that the disorder in a system grows constantly. If the smashed cup were to reassemble itself, however, the disorder would decrease.

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The U.S. Naval Research Laboratory and the Fermi Large Area Telescope Collaboration have discovered nearly 300 gamma ray pulsars, advancing pulsar research and contributing to gravitational wave studies and navigation applications. The findings also include insights into “spider” pulsars, where a neutron star interacts intensively with its binary companion.

The U.S. Naval Research Laboratory (NRL), in conjunction with the international Fermi Large Area Telescope Collaboration, has announced the discovery of almost 300 gamma ray pulsars. This announcement was made in their Third Catalog of Gamma Ray Pulsars, marking a significant achievement 15 years after the 2008 launch of the Fermi telescope. At the time of Fermi’s launch, there were less than ten known gamma-ray pulsars.

“Work on this important catalog has been going on in our group for years,” said Paul Ray, Ph.D., head of the High Energy Astrophysics and Applications Section at NRL. “Our scientists and postdocs have been able to both discover and analyze the timing behavior and spectra of many of these newfound pulsars as part of our quest to further our understanding of these exotic stars that we are able to use as cosmic clocks.”

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The branch of mathematics known as topology has become a cornerstone of modern physics thanks to the remarkable—and above all reliable—properties it can impart to a material or system. Unfortunately, identifying topological systems, or even designing new ones, is generally a tedious process that requires exactly matching the physical system to a mathematical model.

Researchers at the University of Amsterdam and the École Normale Supérieure of Lyon have demonstrated a model-free method for identifying topology, enabling the discovery of new topological materials using a purely experimental approach. The research is published in the journal Proceedings of the National Academy of Sciences.

Topology encompasses the properties of a system that cannot be changed by any “smooth deformation.” As you might be able to tell from this rather formal and abstract description, topology began its life as a branch of mathematics. However, over the last few decades physicists have demonstrated that the mathematics underlying topology can have very real consequences. Topological effects can be found in a wide range of physical systems, from individual electrons to large-scale .

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