Temperature relaxation in strongly-coupled binary ionic mixtures

The Firefly Alpha launch, featuring an unexpected engine shutdown, offered a unique opportunity to study the acoustic effects of clustered nozzles on rocket noise. Measurements revealed a 0.75 dB drop in overall sound pressure levels (OASPL) and a 30% frequency shift, compared to predictions of 1.2 dB and 20%, respectively. While direct comparisons are limited by the dataset’s uniqueness, the results generally align with existing rocket noise models, highlighting areas for refinement. This study provides valuable data for improving noise prediction methods and deepening the understanding of launch vehicle acoustics.

The far-UV (FUV) reflectance of the state-of-the-art, broadband UV/optical/IR mirrors of XeF2-passivated LiF on Al (Al + XeLiF) is promising for future space telescope missions. To reach their potential, dependable cleaning procedures and storage methods for such reflective surfaces need to be developed. First Contact™ polymer (FCP) formulations have proven to be a reliable method for cleaning conventional mirror surfaces coated with oxides or bare metal and for protecting them in storage. We report here on studies of the cleaning and storage of Al + XeLiF samples using customized FCP formulations designed by Photonic Cleaning Technologies. Cleaning of such mirrors is demanding since fluoride coatings are softer than oxides and can be moisture sensitive. Any damage that marks the overcoat can lead to catastrophic loss of FUV reflectance due to surface roughening and formation of aluminum oxide, which is FUV opaque. We discovered that one formulation could be successfully applied to and removed from Al + XeLiF coatings multiple times. The coatings retained low roughness, minimal aluminum oxide thickness, and high far-UV reflectance. Another of the four FCP formulations successfully cleaned the Al + XeLiF coatings several times. Variable-angle, spectroscopic ellipsometry, tapping-mode atomic force microscopy, x-ray photoelectron spectroscopy, and FUV reflectance allowed us to observe any changes in reflectance and surface roughness, the formation of aluminum oxide, and damage to coating integrity. From the studies of the range of FCP-fluoride interactions, we noted that too much polymer-to-surface adhesion or exposure to trace water in the polymer can result in coating damage.

In this Sound Perspectives essay, I summarize potential impacts of rocket noise and suggest that the Acoustical Society of America (ASA), with its interdisciplinary expertise in acoustics and vibration, is uniquely positioned to help address these growing challenges. 

The search for new useful molecular ferroelectrics is a non-trivial problem. We present the application of an automated symmetry-searching method (FERROSCOPE) to the Cambridge Structural Database (CSD) in order to identify polar structures with a closely-related non-polar phase. Such structures have the possibility of undergoing a polarization-switching phase transition thus forming a ferroelectric-paraelectric pair. FERROSCOPE successfully identifies this relationship in 84% of a curated list of 156 known molecular ferroelectrics from the literature and identifies an additional 17 000 potentially ferroelectric compounds in the CSD. Our analysis shows that the method identifies CSD structures which have potentially been described in incorrect space groups, extending previous analyses. We describe experimental case studies which reveal phase transitions in two polar systems predicted to have related non-polar phases.

Adaptive mesh refinement efficiently facilitates the computation of gravitational waveforms in numerical relativity. However, determining precisely when, where, and to what extent to refine when solving the Einstein equations poses challenges; several ad hoc refinement criteria have been explored in the literature. This work introduces an optimized resolution baseline derived in situ from the inspiral trajectory (ORBIT). This method uses the binary’s orbital frequency as a proxy for anticipated gravitational waves to dynamically refine the grid, satisfying the Nyquist frequency requirements on grid resolution up to a specified spin-weighted spherical harmonic order. ORBIT sustains propagation of gravitational waves while avoiding the more costly alternative of maintaining high resolution across an entire simulation—both spatially and temporally. We find that enabling ORBIT decreases waveform noise by an order of magnitude and better resolves high-order wave amplitudes through merger. Combined with WAMR and other improvements, updates to Dendro-GR decrease waveform noise, decrease constraint violations, and boost refinement efficiency each by factors of 𝒪⁡(100), while reducing computational cost by a factor of 4. ORBIT and other recent improvements to Dendro-GR begin to prepare us for gravitational wave science with next-generation detectors.

Understanding and harnessing X-ray quantum effects could open new, to our knowledge, frontiers in imaging and quantum optics. In this study, we measured the process of X-ray parametric down-conversion, where a single high-energy X-ray photon splits into two lower-energy photons. Using the SACLA X-ray free electron laser in Japan at 9.83 keV, we found clear evidence that pairs of photons were produced along the energy-angle relationship that conserved both energy and momentum, as predicted for down-conversion, and consistent with quantum entanglement of X-ray photons. By matching specific photon pairs for energy and momentum conservation, we observe a signal rate of 1250 pairs per hour, confirming that correlated photon pairs can be generated and observed in the absence of explicit time correlations. Our results show that with further refinement, the number of entangled photons produced per laser pulse could increase by an order of magnitude. This paves the way for demonstrating quantum-enhanced X-ray imaging, and confirmation of X-ray photon entanglement.