Relatively Nearby Active Galaxy

Shock-bubble interactions (SBIs) are important across a wide range of physical systems. In inertial confinement fusion, interactions between laser-driven shocks and micro-voids in both ablators and foam targets generate instabilities that are a major obstacle in achieving ignition. Experiments imaging the collapse of such voids at high energy densities (HED) are constrained by spatial and temporal resolution, making simulations a vital tool in understanding these systems. In this study, we benchmark several radiation and thermal transport models in the xRAGE hydrodynamic code against experimental images of a collapsing mesoscale void during the passage of a 300 GPa shock. We also quantitatively examine the role of transport physics in the evolution of the SBI. This allows us to understand the dynamics of the interaction at timescales shorter than experimental imaging framerates. We find that all radiation models examined reproduce empirical shock velocities within experimental error. Radiation transport is found to reduce shock pressures by providing an additional energy pathway in the ablation region, but this effect is small (similar to 1% of total shock pressure). Employing a flux-limited Spitzer model for heat conduction, we find that flux limiters between 0.03 and 0.10 produce agreement with experimental velocities, suggesting that the system is well-within the Spitzer regime. Higher heat conduction is found to lower temperatures in the ablated plasma and to prevent secondary shocks at the ablation front, resulting in weaker primary shocks. Finally, we confirm that the SBI-driven instabilities observed in the HED regime are baroclinically driven, as in the low energy case.

An intensive reverberation mapping campaign of the Seyfert 1 galaxy Mrk 817 using the Cosmic Origins Spectrograph on the Hubble Space Telescope revealed significant variations in the response of broad UV emission lines to fluctuations in the continuum emission. The response of the prominent UV emission lines changes over an similar to 60 day duration, resulting in distinctly different time lags in the various segments of the light curve over the 14 month observing campaign. One-dimensional echo-mapping models fit these variations if a slowly varying background is included for each emission line. These variations are more evident in the C iv light curve, which is the line least affected by intrinsic absorption in Mrk 817 and least blended with neighboring emission lines. We identify five temporal windows with a distinct emission-line response, and measure their corresponding time delays, which range from 2 to 13 days. These temporal windows are plausibly linked to changes in the UV and X-ray obscuration occurring during these same intervals. The shortest time lags occur during periods with diminishing obscuration, whereas the longest lags occur during periods with rising obscuration. We propose that the obscuring outflow shields the broad UV lines from the ionizing continuum. The resulting change in the spectral energy distribution of the ionizing continuum, as seen by clouds at a range of distances from the nucleus, is responsible for the changes in the line response.

Far-field acoustical characterization of blast wave propagation from explosives is often carried out using relatively small shot sizes (less than 1 kg). This paper describes a series of eleven Composition C4 detonations, with shot charge mass varying from 13.6 kg to 54.4 kg (30 to 120 lbs.) that were recently measured at the Big Explosives Experimental Facility (BEEF) at the Nevada National Security Site. Pressure waveform data were recorded at up to nine different stations, ranging from 23 m to 2.7 km from the blast origin, with some angular variation. As part of examining blast overpressure decay with distance and comparing with literature, the data were analyzed from the context of human safety regulations. To provide improved guidance for BEEF personnel working distances, an empirical model equation was developed for the distance, as a function of shot size, at which the peak pressure level drops below 140 dB. A preliminary investigation into peak level variability due to wind was also conducted.

During a rocket’s liftoff, its extreme sound levels can damage launch structures, payload electronics, and even the rocket itself.

Sound power, a standard metric used to quantify product noise, is determined through the vibration -based sound power (VBSP) method. This method involves measuring surface velocities and utilizing an acoustic radiation resistance matrix, R, dependent on the structure's geometry. While R matrix expressions have been established for baffled flat plates, fully closed cylinders, and fully closed spheres, this work presents the first analytical expression tailored for baffled simply curved plates with uniform curvature. This development, based on eigenfunction expansion and the uniform theory of diffraction, extends the VBSP method's capabilities for accurate sound power assessment from these structures. Experimental validation involved testing three plates of varying curvature in a reverberation chamber, comparing the VBSP method with the ISO 3741 pressure-based standard. One of the curved plates underwent additional testing in an anechoic chamber following the ISO 3745 standard, confi rming the VBSP method's accurate sound power measurements down to the 160 Hz one-third octave band. The same plate was tested in uncontrolled acoustic environments - a busy hallway and an outdoor location. The VBSP results showed strong agreement with ISO 3741, af fi rming the method's robustness for measuring sound power from baf fl ed simply curved plates in acoustically challenging real -world conditions. This underscores the practicality of the VBSP method, enabling accurate sound power measurements of baffled curved plates in the presence of substantial background noise and environmental variability. (c) 2024 Institute of Noise Control Engineering.

We present the methods and results from the discovery and photometric measurement of 26 bright VR > 24 trans-Neptunian objects (TNOs) during the first year (2019–20) of the DECam Ecliptic Exploration Project (DEEP). The DEEP survey is an observational TNO survey with wide sky coverage, high sensitivity, and a fast photometric cadence. We apply a computer vision technique known as a progressive probabilistic Hough transform to identify linearly moving transient sources within DEEP photometric catalogs. After subsequent visual vetting, we provide a photometric and astrometric catalog of our TNOs. By modeling the partial lightcurve amplitude distribution of the DEEP TNOs using Monte Carlo techniques, we find our data to be most consistent with an average TNO axis ratio b/a < 0.5, implying a population dominated by non-spherical objects. Based on ellipsoidal gravitational stability arguments, we find our data to be consistent with a TNO population containing a high fraction of contact binaries or other extremely non-spherical objects. We also discuss our data as evidence that the expected binarity fraction of TNOs may be size-dependent.