Graduate Student Savanah Turner Publishes Study of over 300 L and T dwarfs

Broadband shock-associated noise (BSN) is a major source of high-frequency noise in imperfectly expanded supersonic jets. While BSN has been extensively studied, source characterization from full-scale engines remains limited. This paper investigates BSN source and radiation characteristics from a full-scale, installed GE F404 engine on the T-7A trainer aircraft using acoustic holography. Apparent BSN sources are identified along the nozzle lipline and corroborated with in-situ imaging. The observed shock spacing aligns with similar jets in the literature but deviates significantly from traditional analytical models. Likewise, BSN peak frequencies at forward angles match trends from other full-scale jets but differ from simulations and lab-scale data, likely due to temperature and scale-related differences. A widely used BSN frequency model underperforms when relying on historical analytic shock spacing predictions but yields excellent agreement when corrected with measured spacing. Coherence analysis reveals connections between upstream-directed BSN and downstream Mach wave radiation, and shows elevated coherence between shock cells, indicating a partially coherent, distributed BSN source.

Noise sources in heated, supersonic jets are challenging to measure directly due to the extreme environment. Inverse methods, such as acoustic beamforming, using data collected near these sources can be used to construct equivalent source models that accurately describe the acoustic radiation. However, generating these models for a complex source can require thousands of parameters for a complete description. To address this challenge, a multiple wavepacket decomposition is introduced, reducing the source into a set of analytic wavepackets that recreate the full-rank model. This paper provides an overview of the decomposition procedure and applies it to acoustic data collected near a T-7A-installed GE F404 engine. The decomposition is validated for a peak frequency at military power and physical implications are discussed. It is shown that the downstream radiation at MIL can be accurately reconstructed with as few as five wavepackets with minimal error. The number of wavepackets required to capture the primary radiation region tends to increase with frequency and engine power. Beyond the dominant frequencies, the number of wavepackets per wavelength increases drastically, indicating a rapid decrease in source coherence. Finally, a single wavepacket model is fit to the data at MIL, which captures primary radiation features.

The Carpet Determination In Entirety Measurement (CarpetDIEM) III campaign provided insights into the variability of sonic boom metrics due to atmospheric turbulence. ARray Instrumentation for Sonic Thump Observations in TurbuLEnce (ARISTOTLE) Jr., a 2D array consisting of 23 microphones, recorded 17 sonic booms during the measurement campaign. On average, the Perceived Level (PL) across the array had a range of 7.3 dB and a standard deviation of 1.7 dB. While high wind speeds coincided with the largest PL range, significant variability also occurred during lower wind conditions, suggesting ambient noise and atmospheric turbulence play a role in the variability of metrics. The data further indicated directional dependency in metric variability, affirming the necessity of a 2D measurement approach. Building on these results, a full-scale ARISTOTLE array, consisting of 61 microphones over an area of 1,000 ft x 1,000 ft (305 m x 305 m) is under development and will be used in a future low-boom measurement campaign. Ultimately, ARISTOTLE will support the characterization of signatures generated by the X-59 aircraft, enabling improved understanding of turbulence effects on sonic boom metrics.

In the age of commercial spaceflight, many organizations are designing rockets for reuse. Most designs employ some form of propulsive landing either on land or at sea. The foremost among these organizations is Space Exploration Technologies Corporation (SpaceX) with their Falcon-9 rocket. As such rockets return, they produce audible sonic booms over the surrounding areas. The Falcon-9 booster's sonic boom signature is unique, consisting of three primary shocks instead of the two associated with traditional N-waves. This provides an opportunity to study sonic boom formation from a unique geometry and to see whether the triple boom can be physically explained. This paper considers F-function and computational fluid dynamics methods to model the booster's sonic boom under conditions ranging from Mach 1.5 to 2.5. Results support the conclusion of Anderson and Gee (2025) [JASA Express Lett. 5, 023601 (2025)] that the central shock is the result of a rearward-migrating rarefaction wave produced by the lower portions of the booster merging with a forward-migrating compression wave produced by the grid fins. Although it is clear that both the grid fins and the lower portions of the booster contribute to the central shock, the different models disagree on their relative importance in producing the final shock.

Recently a manifestly gauge invariant formalism for calculating amplitudes in quantum electrodynamics was outlined in which the field strength, rather than the gauge potential, is used as the propagating field. To demonstrate the utility of this formalism we calculate the axial and gauge anomalies explicitly in theories with both electrically and magnetically charged particles. Usually the gauge anomaly is identified as an amplitude that (in certain theories) fails to be gauge invariant, so it seems particularly enlightening to understand it in a manifestly gauge invariant formalism. We find that the three photon amplitude is still anomalous in these same theories because it depends explicitly upon the choice of the Stokes surface needed to couple the field strength to sources, so the gauge anomaly arises from geometric considerations.

We present an M87 molecular line search from archival Atacama Large Millimeter/submillimeter Array imaging, covering the circumnuclear disk (CND) as well as ionized gas filaments and dusty cloud regions. We find no evidence for CO emission in the central ∼kiloparsec and place an upper limit of M⊙ in the atomic gas CND region, a factor of 20× lower than previous surveys. During this search, we discovered extragalactic CO absorption lines in the J = 1−0, 2−1, and 3−2 transitions against the bright (jansky-scale) active nucleus. These CO lines are narrow (∼5 km s−1) and blueshifted with respect to the galaxy’s systemic velocity by −75 to −84 km s−1. This CO absorber appears to be kinematically distinct from outflowing atomic gas seen in absorption. Low integrated opacities ranging from τCO ∼ 0.02−0.06 km s−1 and a column density NCO ≈ (1.2 ± 0.2) × 1015 cm−2 translate to  cm−2. CO excitation temperatures spanning Tex ∼ 8–30 K do not follow local thermodynamic equilibrium (LTE) expectations, and non-LTE radex radiative transfer modeling of the CO absorber is consistent with a number density  cm−3 embedded in a ∼60 K environment. Taken together, the observed CO absorption lines are most consistent with a thin, pressure-confined filament seen slightly off-center from the M87 nucleus. We also explore the impact of residual telluric lines and atmospheric variability on narrow extragalactic line identification and demonstrate how bandpass calibration limitations may introduce broad but very low signal-to-noise ratio and spurious absorption and emission signatures.