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Standing detonation engines are a promising detonation-based propulsion technology. The most commonly studied standing detonation configuration involves a straight-sided wedge that induces an oblique detonation wave. A recently introduced standing-detonation-engine concept entails a curved ramp that leads to formation of a curved detonation wave. The continuous compression or expansion induced by the ramp curvature can have significant influence on the flow characteristics and wave patterns of the detonation wave, offering greater flexibility in engine design than conventional wedge geometries. This study aims to further explore this relatively new standing-detonation-engine concept by examining the effect of ignition promoters, namely ozone, on the flow characteristics and reflection patterns of curved detonation waves induced by convex or concave ramps inside a confined combustion chamber. Simulations are performed using a positivity-preserving and entropy-bounded discontinuous Galerkin method with curved elements to exactly represent the ramp geometries. In the context of wedge-induced oblique detonation waves, ozone addition has been found to decrease the initiation length and lead to a smoother shock-detonation transition. This can then attenuate the detonation and reduce stagnation-pressure losses, thus improving the potential propulsion performance. In the context of detonation waves induced by curved ramps, although ozone addition similarly shortens the initiation zone, the curvature of the ramp introduces additional effects that can amplify or counteract both the ozone-induced contraction of the initiation zone and the aforementioned detonation attenuation. Furthermore, specific examples are presented wherein ozone addition changes the type of reflection pattern (e.g., regular reflection, stationary Mach reflection, and non-stationary Mach reflection).

This paper presents a conservative discontinuous Galerkin method for the simulation of supercritical and transcritical real-fluid flows without phase separation. A well-known issue associated with the use of fully conservative schemes is the generation of spurious pressure oscillations at contact interfaces, which are exacerbated when a cubic equation of state and thermodynamic relations appropriate for this high-pressure flow regime are considered. To reduce these pressure oscillations, which can otherwise lead to solver divergence in the absence of additional dissipation, an L2-projection of primitive variables is performed in the evaluation of the flux. We apply the discontinuous Galerkin formulation to a variety of test cases. The first case is the advection of a sinusoidal density wave, which is used to verify the convergence of the scheme. The next two involve one- and two-dimensional advection of a nitrogen/n-dodecane thermal bubble, in which the ability of the methodology to reduce pressure oscillations and maintain solution stability is assessed. The final test cases consist of two- and three-dimensional injection of an n-dodecane jet into a nitrogen chamber.

Mathematical and statistical models underlie many of the world's most important fisheries management decisions. Since the 19th century, difficulty calibrating and fitting such models has been used to justify the selection of simple, stationary, single-species models to aid tactical fisheries management decisions. Whereas these justifications are reasonable, it is imperative that we quantify the value of different levels of model complexity for supporting fisheries management, especially given a changing climate, where old methodologies may no longer perform as well as in the past. Here we argue that cost-benefit analysis is an ideal lens to assess the value of model complexity in fisheries management. While some studies have reported the benefits of model complexity in fisheries, modeling costs are rarely considered. In the absence of cost data in the literature, we report, as a starting point, relative costs of single-species stock assessment and marine ecosystem models from two Australian organizations. We found that costs varied by two orders of magnitude, and that ecosystem model costs increased with model complexity. Using these costs, we walk through a hypothetical example of cost-benefit analysis. The demonstration is intended to catalyze the reporting of modeling costs and benefits.

Generative adversarial networks (GANs) generate photorealistic faces that are often indistinguishable by humans from real faces. While biases in machine learning models are often assumed to be due to biases in training data, we find pathological internal color and luminance biases in the discriminator of a pre-trained StyleGAN3-r model that are not explicable by the training data. We also find that the discriminator systematically stratifies scores by both image- and face-level qualities and that this disproportionately affects images across gender, race, and other categories. We examine axes common in research on stereotyping in social psychology.

Measurements of chemical abundances in high-$z$ star-forming (SF) galaxies place important constraints on the enrichment histories of galaxies and the physical conditions in the early universe. JWST is beginning to enable direct chemical abundance measurements in galaxies at $z$$>$2 via the detection of the faint T$_e$-sensitive auroral line [O III]$\lambda$4364. However, abundances of other elements (e.g., S and Ar) in high-$z$ galaxies remain unconstrained due to a lack of T$_e$ data and wavelength coverage. Here, we present multiple direct abundances in Q2343-D40, a galaxy at $z=$2.9628$\pm$0.0001 observed with JWST/NIRSpec as part of the CECILIA program. We report the first simultaneous measurement of T$_e$[O III] and T$_e$[S III] in a high-$z$ galaxy, finding good agreement with the temperature trends in local SF systems. We measure a gas-phase metallicity of 12+log(O/H) $=8.07\pm0.06$, and the N/O abundance, log(N/O) $=-1.37\pm0.21$, is indicative of primary nucleosynthesis. The S/O and Ar/O relative abundances, log(S/O)$=-1.88\pm0.10$ and log(Ar/O)$=-2.80\pm0.12$, are both $>$0.3 dex lower than the solar ratios. However, the relative Ar$^{2+}$/S$^{2+}$ abundance is consistent with the solar ratio, suggesting that the relative S-to-Ar abundance does not evolve significantly with redshift. Recent nucleosynthesis models find that a significant amount of S and Ar are produced in Type Ia supernovae, such that the S/O and Ar/O abundances in Q2343-D40 could be the result of predominantly core-collapse supernovae enrichment. Future JWST observations of high-$z$ galaxies will uncover whether S/O and Ar/O are sensitive to the timescales of these different enrichment mechanisms., Comment: 14 pages, 3 figures, accepted for publication in The Astrophysical Journal Letters

Active feedback control in magnetic confinement fusion devices is desirable to mitigate plasma instabilities and enable robust operation. Optical high-speed cameras provide a powerful, non-invasive diagnostic and can be suitable for these applications. In this study, we process fast camera data, at rates exceeding 100kfps, on $\textit{in situ}$ Field Programmable Gate Array (FPGA) hardware to track magnetohydrodynamic (MHD) mode evolution and generate control signals in real-time. Our system utilizes a convolutional neural network (CNN) model which predicts the $n$=1 MHD mode amplitude and phase using camera images with better accuracy than other tested non-deep-learning-based methods. By implementing this model directly within the standard FPGA readout hardware of the high-speed camera diagnostic, our mode tracking system achieves a total trigger-to-output latency of 17.6$\mu$s and a throughput of up to 120kfps. This study at the High Beta Tokamak-Extended Pulse (HBT-EP) experiment demonstrates an FPGA-based high-speed camera data acquisition and processing system, enabling application in real-time machine-learning-based tokamak diagnostic and control as well as potential applications in other scientific domains., Comment: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Rev. Sci. Instrum. 95, 073509 (2024) and may be found at https://doi.org/10.1063/5.0190354

A well-known issue associated with the use of fully conservative schemes in multicomponent-flow simulations is the generation of spurious pressure oscillations at contact interfaces. These oscillations can rapidly lead to solver divergence even in the presence of smooth interfaces that are not fully resolved. In this note, we compare various strategies for reducing such oscillations that do not (a) introduce conservation error, (b) rely on artificial viscosity or limiting, or (c) degrade order of accuracy in smooth regions of the flow. The considered test case is one-dimensional advection of a high-pressure nitrogen/n-dodecane thermal bubble using the thermally perfect gas model. Several results are presented that contradict those corresponding to the more conventional hydrogen/oxygen thermal-bubble case.

This article concerns the development of a fully conservative, positivity-preserving, and entropy-bounded discontinuous Galerkin scheme for the multicomponent, chemically reacting, compressible Navier-Stokes equations with complex thermodynamics. In particular, we extend to viscous flows the fully conservative, positivity-preserving, and entropy-bounded discontinuous Galerkin method for the chemically reacting Euler equations that we previously introduced. An important component of the formulation is the positivity-preserving Lax-Friedrichs-type viscous flux function devised by Zhang [J. Comput. Phys., 328 (2017), pp. 301-343], which was adapted to multicomponent flows by Du and Yang [J. Comput. Phys., 469 (2022), pp. 111548] in a manner that treats the inviscid and viscous fluxes as a single flux. Here, we similarly extend the aforementioned flux function to multicomponent flows but separate the inviscid and viscous fluxes, resulting in a different dissipation coefficient. This separation of the fluxes allows for use of other inviscid flux functions, as well as enforcement of entropy boundedness on only the convective contribution to the evolved state, as motivated by physical and mathematical principles. We also detail how to account for boundary conditions and incorporate previously developed techniques to reduce spurious pressure oscillations into the positivity-preserving framework. Furthermore, potential issues associated with the Lax-Friedrichs-type viscous flux function in the case of zero species concentrations are discussed and addressed. The resulting formulation is compatible with curved, multidimensional elements and general quadrature rules with positive weights. A variety of multicomponent, viscous flows is computed, ranging from a one-dimensional shock tube problem to multidimensional detonation waves and shock/mixing-layer interaction.

High-temperature superconductivity is reported in a series of compositionally-complex cuprates with varying degrees of size and spin disorder. Three compositions of Y-site alloyed YBa$_2$Cu$_3$O$_{7-x}$, i.e., (5Y)BCO, were prepared using solid-state methods with different sets of rare earth ions on the Y-site. Synchrotron X-ray diffraction and energy-dispersive X-ray spectroscopy confirm these samples have high phase-purity and homogeneous mixing of the Y-site elements. The superconducting phase transition was probed using electrical resistivity and AC magnetometry measurements, which reveal the transition temperature, T$_C$, is greater than 91 K for all series when near optimal oxygen doping. Importantly, these T$_C$ values are only $\approx$1$\%$ suppressed relative to pure YBCO (T$_C$ = 93 K). This result highlights the robustness of pairing in the YBCO structure to specific types of disorder. In addition, the chemical flexibility of compositionally-complex cuprates allows spin and lattice disorder to be decoupled to a degree not previously possible in high-temperature superconductors. This feature makes compositionally-complex cuprates a uniquely well-suited materials platform for studying proposed pairing interactions in cuprates., Comment: 6 pages, 3 figures, 1 table

In ecological and environmental contexts, management actions must sometimes be chosen urgently. Value of information (VoI) analysis provides a quantitative toolkit for projecting the improved management outcomes expected after making additional measurements. However, traditional VoI analysis reports metrics as expected values (i.e. risk-neutral). This can be problematic because expected values hide uncertainties in projections. The true value of a measurement will only be known after the measurement's outcome is known, leaving large uncertainty in the measurement's value before it is performed. As a result, the expected value metrics produced in traditional VoI analysis may not align with the priorities of a risk-averse decision-maker who wants to avoid low-value measurement outcomes. In the present work, we introduce four new VoI metrics that can address a decision-maker's risk-aversion to different measurement outcomes. We demonstrate the benefits of the new metrics with two ecological case studies for which traditional VoI analysis has been previously applied. Using the new metrics, we also demonstrate a clear mathematical link between the often-separated environmental decision-making disciplines of VoI and optimal design of experiments. This mathematical link has the potential to catalyse future collaborations between ecologists and statisticians to work together to quantitatively address environmental decision-making questions of fundamental importance. Overall, the introduced VoI metrics complement existing metrics to provide decision-makers with a comprehensive view of the value of, and risks associated with, a proposed monitoring or measurement activity. This is critical for improved environmental outcomes when decisions must be urgently made., Comment: 53 pages, 3 figures

We present the first results from CECILIA, a Cycle 1 JWST NIRSpec/MSA program that uses ultra-deep ~30 hour G235M/F170LP observations to target multiple electron temperature-sensitive auroral lines in the spectra of 33 galaxies at z~1-3. Using a subset of 23 galaxies, we construct two ~600 object-hour composite spectra, both with and without the stellar continuum, and use these to investigate the characteristic rest-optical (5700-8500 Angstrom) spectrum of star-forming galaxies at the peak epoch of cosmic star formation. Emission lines of eight different elements (H, He, N, O, Si, S, Ar, and Ni) are detected, with most of these features observed to be <3% the strength of H-alpha. We report the characteristic strength of three auroral lines ([NII]5756, [SIII]6313, and [OII]7322,7332), as well as other semi-strong and faint emission lines, including forbidden [NiII]7380,7414 and the OI 8449 recombination line, some of which have never before been observed outside of the local universe. Using these measurements, we find T_e[NII]=13630+/-2540 K, representing the first measurement of electron temperature using [NII] in the high-redshift universe. We also see evidence for broad line emission with a FWHM of ~536 km/s; the broad component of H-alpha is 6.01-28.31% the strength of the narrow component and likely arises from star-formation driven outflows. Finally, we briefly comment on the feasibility of obtaining large samples of faint emission lines using JWST in the future., Comment: Published in ApJL in November 2023

Strong coupling between light and matter generates hybrid polaritons. We present a continuum model that describes the polaritons by light and matter densities of states (DOS) that only depend on the refractive index of the material. This model is applied to molecular polaritons derived from molecules with broad spectral absorption. While the photonic DOS has a complex spectral distribution, the matter DOS is largely unmodified by strong coupling. We argue that bright states cannot be partitioned from dark states, and instead the photonic DOS is shared over a vast number of matter states.

In this second part of our two-part paper, we extend to multiple spatial dimensions the one-dimensional, fully conservative, positivity-preserving, and entropy-bounded discontinuous Galerkin scheme developed in the first part for the chemically reacting Euler equations. Our primary objective is to enable robust and accurate solutions to complex reacting-flow problems using the high-order discontinuous Galerkin method without requiring extremely high resolution. Variable thermodynamics and detailed chemistry are considered. Our multidimensional framework can be regarded as a further generalization of similar positivity-preserving and/or entropy-bounded discontinuous Galerkin schemes in the literature. In particular, the proposed formulation is compatible with curved elements of arbitrary shape, a variety of numerical flux functions, general quadrature rules with positive weights, and mixtures of thermally perfect gases. Preservation of pressure equilibrium between adjacent elements, especially crucial in simulations of multicomponent flows, is discussed. Complex detonation waves in two and three dimensions are accurately computed using high-order polynomials. Enforcement of an entropy bound, as opposed to solely the positivity property, is found to significantly improve stability. Mass, total energy, and atomic elements are shown to be discretely conserved.

In this paper, we develop a fully conservative, positivity-preserving, and entropy-bounded discontinuous Galerkin scheme for simulating the chemically reacting, compressible Euler equations with complex thermodynamics. The proposed formulation is an extension of the conservative, high-order numerical method previously developed by Johnson and Kercher [J. Comput. Phys., 423 (2020), 109826] that maintains pressure equilibrium between adjacent elements. In this first part of our two-part paper, we focus on the one-dimensional case. Our methodology is rooted in the minimum entropy principle satisfied by entropy solutions to the multicomponent, compressible Euler equations, which was proved by Gouasmi et al. [ESAIM: Math. Model. Numer. Anal., 54 (2020), 373--389] for nonreacting flows. We first show that the minimum entropy principle holds in the reacting case as well. Next, we introduce the ingredients required for the solution to have nonnegative species concentrations, positive density, positive pressure, and bounded entropy. We also discuss how to retain the aforementioned ability to preserve pressure equilibrium between elements. Operator splitting is employed to handle stiff chemical reactions. To guarantee satisfaction of the minimum entropy principle in the reaction step, we develop an entropy-stable discontinuous Galerkin method based on diagonal-norm summation-by-parts operators for solving ordinary differential equations. The developed formulation is used to compute canonical one-dimensional test cases, namely thermal-bubble advection, multicomponent shock-tube flow, and a moving hydrogen-oxygen detonation wave with detailed chemistry. We find that the enforcement of an entropy bound can considerably reduce the large-scale nonlinear instabilities that emerge when only the positivity property is enforced, to an even greater extent than in the monocomponent, calorically perfect case.

The resonantly scattered Lyman-$\alpha$ line illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Ly$\alpha$ emission in 12 relatively low-mass ($M_{\star} \sim10^9 \, M_{\odot}$) $z\sim2$ galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Ly$\alpha$ blue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak separation and trough depth with radius, and broadly reconcile outflow velocities inferred from Ly$\alpha$ and absorption lines. The galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (ICM), whose residual neutral content produces absorption at the systemic redshift. The peak ratio, peak separation and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the HI column density, and the residual neutral density in the ICM respectively. Azimuthal asymmetries in the line profile further suggest non-radial gas motions at large radii and variations in the HI column density in the outer halos., Comment: 43 pages, 13 figures. This version corrects an error in the ordering of column headings in Table 3. Table data have not changed