UNPs as HEDP simulators

Altermagnets represent a new class of magnetic phases without net magnetization, invariant under a combination of rotation and time reversal. Unlike conventional collinear antiferromagnets (AFM), altermagnets could lead to new correlated states and important material properties deriving from their nonrelativistic spin-split band structure. Indeed, they serve as the magnetic analogue of unconventional superconductors and can yield spin-polarized electrical currents in the absence of external magnetic fields, making them promising candidates for next-generation spintronics. Here, we report altermagnetism in the correlated insulator, magnetically ordered tetragonal oxychalcogenide, La₂O₃Mn₂Se₂. Symmetry analysis reveals a 𝑑_{𝑥2−𝑦2}-wave-like spin-momentum locking arising from the Mn₂O Lieb lattice, supported by density functional theory (DFT) calculations. Magnetic measurements confirm the AFM transition below ∼166K while neutron pair distribution function analysis reveals a 2D short-range magnetic order that persists above the Néel temperature. Single crystals are grown and characterized using x-ray diffraction, optical and electron microscopy, and micro-Raman spectroscopy to confirm the crystal structure, stoichiometry, and uniformity. Our findings establish La₂O₃Mn₂Se₂as a model altermagnetic system realized on a Lieb lattice.

When the SpaceX Falcon-9 rocket booster descends through the atmosphere after a launch, it produces a sonic boom with three shocks in the far field, rather than the usual two-shock N-wave. In this Letter, the additional shock's origin is explained using sonic boom theory, nonlinear propagation modeling, computational fluid dynamics, and photographic evidence. The extra central shock results from a forward-migrating compression wave caused by the grid fins merging with a rearward-migrating rarefaction wave caused by the lower portions of the booster, including the folded landing legs.

Group-theoretical and linear-algebraic methods and tools have recently been developed that aim to exhaustively identify the small-angle rotational rigid-unit modes (RUMs) of a given framework material. But in their current form, they fail to detect RUMs that require a compensating lattice strain which grows linearly with the amplitude of the rigid-unit rotations. Here, we present a systematic approach to including linear strain compensation within the linear-algebraic RUM-search method, so that any geometrically possible small-angle RUM can be detected.

At 7:30 AM on October 6, 2020 Space-X launched a Falcon-9 rocket from Kennedy Space Center. Photographer Trevor Mahlmann had positioned his camera in the location where the rocket would pass in front of the rising sun and took a series of images of that encounter. The high-intensity sound and shock waves originating in the plume are imaged by passing in front of the sun, particularly near the edge of the sun. This can be considered as a type of schlieren imaging system. The sound emitted from a supersonic rocket plume is thought to be due to Mach wave radiation. The images were processed to enhance the visibility of the propagating shock waves, and the propagation of those shock waves was traced back to the plume. This allowed the source location and emission direction of the sound to be determined. The measured shocks were found to be consistent with the predictions of Mach wave radiation from the plume, originating about 15-20 nozzle diameters down the plume, and radiating in a wide lobe peaking at about 70° from the plume direction. There are also indications that lower frequency waves are preferentially emitted at smaller angles relative to the plume.

This paper presents a comprehensive overview of the operation and spectral performance of a novel lab-scale afterburning jet noise rig at Virginia Tech. The study involved steady-state operation at relevant Total Temperature Ratios (TTR) of approximately 6, typical for afterburning jets. The flow was discharged through a scaled-down GE F-404 supersonic nozzle, and far-field noise measurements were acquired using ground microphones positioned at 27 angular locations on a concrete pad. A key focus of the study is to benchmark the rig's performance by comparing its far-field Overall Sound Pressure Level (OASPL) with that of T-7A and F-35B aircraft operating at afterburner power. The investigation revealed that Nozzle Pressure Ratio (NPR) exerts a significant influence on OASPL at relatively close TTRs. Furthermore, the effects of varying TTR and NPR on OASPL were compared with trends observed in F-35A and F-35B operating at two distinct afterburner power levels. Acoustic efficiency in the presented cases lies in the range 0.41% to 0.51%. Phenomena only observed in full scale afterburning jet engine tests were reproduced for the first time in a laboratory scaled rig. This allowed the identification that engine combustion instabilities can convect downstream through the nozzle and impact the far-field noise spectrum. These instabilities manifest as distinct 'instability streaks' in a spatio-spectral map. The present study highlights the importance of conducting high TTR jet noise experiments in a controlled environment with known operating parameters (total pressure, total temperature, mass flow rate, dynamic pressure, etc.) to enhance the understanding of afterburning jet noise phenomena.

his Letter analyzes launch noise from Starship Super Heavy's Flights 5 and 6. While Flight-5 data covered 9.7-35.5 km, the stations during Flight 6 spanned 1.0-35.5 km. A comparison of A-weighted and unweighted maximum and exposure levels is made between flights and with an updated environmental assessment (EA). Key findings include: (a) the two flights' noise levels diverge beyond 10 km, (b) EA models overestimate A-weighted metrics, and (c) the acoustic energy from a Starship launch is equivalent to 2.2 Space Launch System launches or ∼11 Falcon 9 launches. These measurements help predict Starship's noise levels around Kennedy Space Center.