Flux Limit Research Articles

The 700 ks Chandra Spiderweb Field

Aims. We present an analysis of the 700 ks Chandra ACIS-S observation of the field around the radio galaxy J1140-2629 (the Spiderweb Galaxy) at z = 2.156, focusing on the nuclear activity in the associated large-scale environment. Methods. We identified unresolved X-ray sources in the field down to flux limits of 1.3 × 10−16 and 3.9 × 10−16 erg s−1 cm−2 in the soft (0.5–2.0 keV) and hard (2–10 keV) band, respectively. We searched for counterparts in the optical, near-infrared, and submillimeter catalogs available in the literature to identify X-ray sources belonging to the protocluster and derived their X-ray properties. Results. We detect 107 X-ray unresolved sources within 5 arcmin (corresponding to 2.5 Mpc) of J1140-2629, among which 13 have optical counterparts with spectroscopic redshift 2.11 < z < 2.20, and 1 source has a photometric redshift consistent with this range. The X-ray-emitting protocluster members are distributed approximately over a ∼3.2 × 1.3 Mpc2 rectangular region. An X-ray spectral analysis for all the sources within the protocluster shows that their intrinsic spectral slope is consistent with an average ⟨Γ⟩∼1.84 ± 0.04. Excluding the Spiderweb Galaxy, the best-fit intrinsic absorption for five protocluster X-ray members is NH > 1023 cm−2, while another six have upper limits of the order of a few times 1022 cm−2. Two sources can only be fitted with very flat Γ ≤ 1, and are therefore considered Compton-thick candidates. The 0.5–10 keV rest-frame luminosities of the 11 Compton-thin protocluster members corrected for intrinsic absorption are greater than 2 × 1043 erg s−1. These values are typical for the bright end of a Seyfert-like distribution and significantly greater than X-ray luminosities expected from star formation activity. The X-ray luminosity function of the AGN in the volume associated to the Spiderweb protocluster in the range 1043 < LX < 1044.5 erg s−1 is at least ten times higher than that in the field at the same redshift and significantly flatter, implying an increasing excess at the bright end. The X-ray AGN fraction is measured to be 25.5 ± 4.5% of the spectroscopically confirmed members in the stellar mass range log(M*/M⊙) > 10.5. This value corresponds to an enhancement factor of 6.0−3.0+9.0 for the nuclear activity with L0.5 − 10 keV > 4 × 1043 erg s−1 with respect to the COSMOS field at comparable redshifts and stellar mass range. Conclusions. We conclude that the galaxy population in the Spiderweb protocluster is characterized by enhanced X-ray nuclear activity triggered by environmental effects on megaparsec scales.

Blow-up phenomena for a chemotaxis system with flux limitation

In this paper we consider nonnegative solutions of the following parabolic-elliptic cross-diffusion system{ut=Δu−∇(uf(|∇v|2)∇v),0=Δv−μ+u,∫Ωv=0,μ:=1|Ω|∫Ωudx,u(x,0)=u0(x), in Ω×(0,∞), with Ω a ball in RN, N≥3 under homogeneous Neumann boundary conditions and f(ξ)=(1+ξ)−α, 0<α<N−22(N−1), which describes gradient-dependent limitation of cross diffusion fluxes. Under conditions on f and initial data, we prove that a solution which blows up in finite time in L∞-norm, blows up also in Lp-norm for some p>1. Moreover, a lower bound of blow-up time is derived.

Comparative Analysis of Methods for Calculating the Energy Flux Density used in Assessing the Permissible Level of Environmental Pollution by Electromagnetic Radiation

In this article, the results of measurements and calculations of the power flux density in the frequency range 670 MHz-766 MHz (46th and 57th television channels) of digital broadcasting of the DVBT2 standard were presented. Experimental data on the power flux density were obtained by the selective electromagnetic field meters NARDA SRM-3000 with an isotropic antenna. The radiating system consists of 16 panel antennas (four-storey panel antennas) with a circular radiation pattern in the horizontal plane. Calculations were carried out in the ПК АЭМО (Software package for electromagnetic environment analysis) and MMANA programs. The data obtained were compared with the permissible exposure limit (PEL) of energy flux density (EFD) set by health and safety rules and standards (2.1.8/2.2.4.1383-03), which operate on the territory of Russia.The values obtained are significantly less than the acceptable levels. In the USA, Japan, European countries, Canada, China, and the PEL of energy flux density in the frequency range 300 MHz – 300 GHz are higher than in Russia.

Time–dependent Hamilton–Jacobi equations on networks

We study well posedness of time–dependent Hamilton–Jacobi equations on a network, coupled with a continuous initial datum and a flux limiter. We show existence and uniqueness of solutions as well as stability properties. The novelty of our approach is that comparison results are proved linking the equation to a suitable semidiscrete problem, bypassing doubling variable method. Further, we do not need special test functions, and perform tests relative to the equations on different arcs separately.

Oceanic emissions of dimethyl sulfide and methanethiol and their contribution to sulfur dioxide production in the marine atmosphere

Abstract. Oceanic emissions of dimethyl sulfide (CH3SCH3, DMS) have long been recognized to impact aerosol particle composition and size, the concentration of cloud condensation nuclei (CCN), and Earth's radiation balance. The impact of oceanic emissions of methanethiol (CH3SH, MeSH), which is produced by the same oceanic precursor as DMS, on the volatile sulfur budget of the marine atmosphere is largely unconstrained. Here we present direct flux measurements of MeSH oceanic emissions using the eddy covariance (EC) method with a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToFMS) detector and compare them to simultaneous flux measurements of DMS emissions from a coastal ocean site. Campaign mean mixing ratios of DMS and MeSH were 72 ppt (28–90 ppt interquartile range) and 19.1 ppt (7.6–24.5 ppt interquartile range), respectively. Campaign mean emission fluxes of DMS (FDMS) and MeSH (FMeSH) were 1.13 ppt m s−1 (0.53–1.61 ppt m s−1 interquartile range) and 0.21 ppt m s−1 (0.10–0.31 ppt m s−1 interquartile range), respectively. Linear least squares regression of observed MeSH and DMS flux indicates the emissions are highly correlated with each other (R2=0.65) over the course of the campaign, consistent with a shared oceanic source. The campaign mean DMS to MeSH flux ratio (FDMS:FMeSH) was 5.5 ± 3.0, calculated from the ratio of 304 individual coincident measurements of FDMS and FMeSH. Measured FDMS:FMeSH was weakly correlated (R2=0.15) with ocean chlorophyll concentrations, with FDMS:FMeSH reaching a maximum of 10.8 ± 4.4 during a phytoplankton bloom period. No other volatile sulfur compounds were observed by PTR-ToFMS to have a resolvable emission flux above their flux limit of detection or to have a gas-phase mixing ratio consistently above their limit of detection during the study period, suggesting DMS and MeSH are the dominant volatile organic sulfur compounds emitted from the ocean at this site. The impact of this MeSH emission source on atmospheric budgets of sulfur dioxide (SO2) was evaluated by implementing observed emissions in a coupled ocean–atmosphere chemical box model using a newly compiled MeSH oxidation mechanism. Model results suggest that MeSH emissions lead to afternoon instantaneous SO2 production of 2.5 ppt h−1, which results in a 43 % increase in total SO2 production compared to a case where only DMS emissions are considered and accounts for 30% of the instantaneous SO2 production in the marine boundary layer at the mean measured FDMS and FMeSH. This contribution of MeSH to SO2 production is driven by a higher effective yield of SO2 from MeSH oxidation and the shorter oxidation lifetime of MeSH compared to DMS. This large additional source of marine SO2 has not been previously considered in global models of marine sulfur cycling. The field measurements and modeling results presented here demonstrate that MeSH is an important contributor to volatile sulfur budgets in the marine atmosphere and must be measured along with DMS in order to constrain marine sulfur budgets. This large additional source of marine–reduced sulfur from MeSH will contribute to particle formation and growth and CCN abundance in the marine atmosphere, with subsequent impacts on climate.

A generalized Eulerian-Lagrangian discontinuous Galerkin method for transport problems

We propose a generalized Eulerian-Lagrangian (GEL) discontinuous Galerkin (DG) method. The method is a generalization of the Eulerian-Lagrangian (EL) DG method for transport problems proposed in Cai et al. (2021) [5], which tracks solution along approximations to characteristics in the DG framework, allowing extra large time stepping size with stability. The newly proposed GEL DG method in this paper is motivated for solving linear hyperbolic systems with variable coefficients, where the velocity field for adjoint problems of the test functions is frozen to constant. In this paper, in a simplified scalar setting, we propose the GEL DG methodology by freezing the velocity field of adjoint problems, and by formulating the semi-discrete scheme over the space-time region partitioned by linear lines approximating characteristics. The fully-discrete schemes are obtained by method-of-lines Runge-Kutta methods. We further design flux limiters for the schemes to satisfy the discrete geometric conservation law (DGCL) and maximum principle preserving (MPP) properties. Numerical results on 1D and 2D linear transport problems are presented to demonstrate great properties of the GEL DG method. These include the high order spatial and temporal accuracy, stability with extra large time stepping size, and satisfaction of DGCL and MPP properties.

Global boundedness and large time behavior of solutions to a chemotaxis system with flux limitation

This paper deals with the following cross-diffusion system{ut=∇⋅((u+1)m−1∇u)−∇⋅(u∇v(1+|∇v|2)α),x∈Ω,t>0,0=Δv−v+u,x∈Ω,t>0, in a bounded domain Ω⊂Rn, n≥2 with smooth boundary. In this framework, it is shown that the problem possesses a unique global bounded classical solution under the condition that α>2n−2−mn2(n−1) and m≥1. Moreover, it is asserted that the corresponding solution exponentially converges to the constant stationary solution (u0‾,u0‾) when the initial data u0 is sufficiently small, where u0‾:=∫Ωu0|Ω|.

Energy conserving and well-balanced discontinuous Galerkin methods for the Euler–Poisson equations in spherical symmetry

ABSTRACT This paper presents high-order Runge–Kutta (RK) discontinuous Galerkin methods for the Euler–Poisson equations in spherical symmetry. The scheme can preserve a general polytropic equilibrium state and achieve total energy conservation up to machine precision with carefully designed spatial and temporal discretizations. To achieve the well-balanced property, the numerical solutions are decomposed into equilibrium and fluctuation components that are treated differently in the source term approximation. One non-trivial challenge encountered in the procedure is the complexity of the equilibrium state, which is governed by the Lane–Emden equation. For total energy conservation, we present second- and third-order RK time discretization, where different source term approximations are introduced in each stage of the RK method to ensure the conservation of total energy. A carefully designed slope limiter for spherical symmetry is also introduced to eliminate oscillations near discontinuities while maintaining the well-balanced and total-energy-conserving properties. Extensive numerical examples – including a toy model of stellar core collapse with a phenomenological equation of state that results in core bounce and shock formation – are provided to demonstrate the desired properties of the proposed methods, including the well-balanced property, high-order accuracy, shock-capturing capability, and total energy conservation.

The eROSITA Final Equatorial-Depth Survey (eFEDS)

Context.In November 2019, eROSITA on board of the Spektrum-Roentgen-Gamma (SRG) observatory started to map the entire sky in X-rays. After the four-year survey program, it will reach a flux limit that is about 25 times deeper than ROSAT. During the SRG performance verification phase, eROSITA observed a contiguous 140 deg2area of the sky down to the final depth of the eROSITA all-sky survey (eROSITA Final Equatorial-Depth Survey; eFEDS), with the goal of obtaining a census of the X-ray emitting populations (stars, compact objects, galaxies, clusters of galaxies, and active galactic nuclei) that will be discovered over the entire sky.Aims.This paper presents the identification of the counterparts to the point sources detected in eFEDS in the main and hard samples and their multi-wavelength properties, including redshift.Methods.To identifyy the counterparts, we combined the results from two independent methods (NWAYandASTROMATCH), trained on the multi-wavelength properties of a sample of 23kXMM-Newtonsources detected in the DESI Legacy Imaging Survey DR8. Then spectroscopic redshifts and photometry from ancillary surveys were collated to compute photometric redshifts.Results.Of the eFEDS sources, 24 774 of 27 369 have reliable counterparts (90.5%) in the main sample and 231 of 246 sourcess (93.9%) have counterparts in the hard sample, including 2514 (3) sources for which a second counterpart is equally likely. By means of reliable spectra,Gaiaparallaxes, and/or multi-wavelength properties, we have classified the reliable counterparts in both samples into Galactic (2695) and extragalactic sources (22 079). For about 340 of the extragalactic sources, we cannot rule out the possibility that they are unresolved clusters or belong to clusters. Inspection of the distributions of the X-ray sources in various optical/IR colour-magnitude spaces reveal a rich variety of diverse classes of objects. The photometric redshifts are most reliable within the KiDS/VIKING area, where deep near-infrared data are also available.Conclusions.This paper accompanies the eROSITA early data release of all the observations performed during the performance and verification phase. Together with the catalogues of primary and secondary counterparts to the main and hard samples of the eFEDS survey, this paper releases their multi-wavelength properties and redshifts.

The eROSITA Final Equatorial Depth Survey (eFEDS)

Context.The eROSITA X-ray telescope on board the Spectrum-Poentgen-Gamma (SPG) observatory combines a large field of view and a large collecting area in the energy range between ~0.2 and ~8.0 keV. This gives the telescope the capability to perform uniform scanning observations of large sky areas.Aims.SRG/eROSITA performed scanning observations of the ~140 square degree eROSITA Final Equatorial Depth Survey field (the eFEDS field) as part of its performance verification phase ahead of the planned four year of all-sky scanning operations. The observing time of eFEDS was chosen to slightly exceed the depth expected in an equatorial field after the completion of the all-sky survey. While verifying the capability of eROSITA to perform large-area uniform surveys and saving as a test and training dataset to establish calibration and data analysis procedures, the eFEDS survey also constitutes the largest contiguous soft X-ray survey at this depth to date, supporting a range of early eROSITA survey science investigations. Here we (i) present a catalogue of detected X-ray sources in the eFEDS field providing information about source positions and extent, as well as fluxes in multiple energy bands, and (ii) document the suite of tools and procedures developed for eROSITA data processing and analysis, which were validated and optimised by the eFEDS work.Methods.The data were fed through a standard data processing pipeline, which appltes X-ray event calibration and provides a set of standard calibrated data products. A mutiti-stage source detection procedure, building in part on experience fromXMM-Newton,was optimised and calibrated by performing realistic simulations of the eROSITA eFEDS observations. Source fluxes were computed in multiple standard energy bands by forced point source fitting and aperture photometry. We cross-matched the eROSITA eFEDS source catalogue with previous XMM-ATLAS observations, which confirmed the excellentt agreement of the eROSITA and XMM-ATLAS source fluxes. Astrometric corrections were performed by cross-matching the eROSITA source positions with an optical reference catalogue of quasars.Results.We present a primary catalogue of 27 910 X-ray sources (542 of which are significantly spatially extended) detected in the 0.2–2.3 keV energy range with detection likelihoods ≥6, corresponding to a (point source) flux limit of 6.5 × 10–15erg cm–2s–1in the 0.5–2.0 keV energy band (80% completeness). A supplementary catalogue contains 4774 low-significance source candidates with detection likelihoods between 5 and 6. In addition, a hard-band sample of 246 sources detected in the energy range 22.3–5.0 keV above a detection likelihood of 10 is provided. In an appendix, we finally describe the dedicated data analysis software package, the eROSITA calibration database, and the standard calibrated data products.

The eROSITA Final Equatorial-Depth Survey (eFEDS)

Context.During the performance verification phase of the Spectrum-Roentgen-Gamma eROSITA telescope, the eROSITA Final Equatorial-Depth Survey (eFEDS) was carried out. It covers a 140 deg2field located at 126° &lt; RA &lt; 146° and–3° &lt; Dec &lt; + 6° with a nominal unvignetted exposure over the field of 2.2 ks. Five hundred and forty-two candidate clusters and groups were detected in this field, down to a flux limitFX~10–14erg s–1cm–2in the 0.5–2 keV band.Aims.In order to understand radio-mode feedback in galaxy clusters, we study the radio emission of brightest cluster galaxies (BCGs) of eFEDS clusters and groups, and we relate it to the X-ray properties of the host cluster.Methods.Using LOFAR, we identified 227 radio galaxies hosted in the BCGs of the 542 galaxy clusters and groups detected in eFEDS. We treated non-detections as radio upper limits. We analysed the properties of radio galaxies, such as redshift and luminosity distribution, offset from the cluster centre, largest linear size, and radio power. We studied their relation to the intracluster medium of the host cluster.Results.We find that BCGs with radio-loud active galactic nucleus (AGN) are more likely to lie close to the cluster centre than radioquiet BCGs. There is a clear relation between the cluster X-ray luminosity and the 144 MHz radio power of the BCG. Statistical tests indicate that this correlation is not produced by biases or selection effects in the radio band. We see no apparent link between largest linear size of the radio galaxy and the central density in the host cluster. Converting the radio luminosity into kinetic luminosity, we find that radiative losses of the intracluster medium are in an overall balance with the heating provided by the central AGN. Finally, we tentatively classify our objects into disturbed and relaxed based on different morphological parameters, and we show that the link between the AGN and the ICM apparently holds for both subsamples, regardless of the dynamical state of the cluster.

The eROSITA Final Equatorial-Depth Survey (eFEDS)

Aims. The eROSITA Final Equatorial-Depth Survey (eFEDS), executed during the performance verification phase of the Spectrum-Roentgen-Gamma (SRG)/eROSITA telescope, was completed in November 2019. One of the science goals of this survey is to demonstrate the ability of eROSITA to detect samples of clusters and groups at the final depth of the eROSITA all-sky survey.Methods. Because of the sizeable (≈26″ HEW FOV average) point-spread function of eROSITA, high-redshift clusters of galaxies or compact nearby groups hosting bright active galactic nuclei (AGN) can be misclassified as point sources by the source detection algorithms. A total of 346 galaxy clusters and groups in the redshift range of 0.1 &lt; z &lt; 1.3 were identified based on their red sequenc in the eFEDS point source catalog.Results. We examine the multiwavelength properties of these clusters and groups to understand the potential biases in our selection process and the completeness of the extent-selected sample. We find that the majority of the clusters and groups in the point source sample are indeed underluminous and compact compared to the extent-selected sample. Their faint X-ray emission, well below the flux limit of the extent-selected eFEDS clusters, and their compact X-ray emission are likely to be the main reason for this misclassification. In the sample, we confirm that 10% of the sources host AGN in their brightest cluster galaxies (BCGs) through optical spectroscopy and visual inspection. By studying their X-ray, optical, infrared, and radio properties, we establish a method for identifying clusters and groups that host AGN in their BCGs. We successfully test this method on the current point source catalog through the Sloan Digital Sky Survey optical spectroscopy and find eight low-mass clusters and groups with active radio-loud AGN that are particularly bright in the infrared. They include eFEDS J091437.8+024558, eFEDS J083520.1+012516, and eFEDS J092227.1+043339 at redshifts 0.3−0.4.Conclusions. This study helps us to characterize and understand our selection process and assess the completeness of the eROSITA extent-selected samples. The method we developed will be used to identify high-redshift clusters, AGN-dominated groups, and low-mass clusters that are misclassified in the future eROSITA all-sky survey point source catalogs.

The Low-redshift Lyman Continuum Survey. I. New, Diverse Local Lyman Continuum Emitters

The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a z = 0.2–0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.

Anti‐diffusive alternate‐directions schemes for the transport of step functions

AbstractThe purpose in this article is to design finite‐volume schemes on structured grids for the transport of piecewise‐constant functions (typically, indicator functions) with as low diffusion as possible. We first propose an extension of the so‐called Lagrange‐projection algorithm, or downwind scheme with an Ultrabee limiter, for the transport equation in one space dimension with a non‐constant velocity; as its constant velocity counterpart, this scheme is designed to capture the discontinuities separating two plateaus in only one cell, and is referred to as “anti‐diffusive.” It is shown to preserve the bounds of the solution. Then, for two and three dimensional problems, we introduce a conservative alternate‐directions algorithm, an show that this latter enjoys a discrete maximum principle, provided that the underlying one‐dimensional schemes satisfy a property which may be seen as a flux limitation, possibly incorporated a posteriori in any explicit scheme. Numerical tests of this alternate‐directions algorithm are performed, with a variety of one‐dimensional embedded schemes including the anti‐diffusive scheme developed here and the so called THINC scheme. The observed numerical diffusion is indeed very low. With the anti‐diffusive scheme, the above‐mentioned a posteriori limitation is necessary to preserve the solution bounds, but, in the performed tests, does not introduce any visible additional diffusion.

Galaxy clustering in the VVV near-IR galaxy catalogue

ABSTRACTMapping galaxies at low Galactic latitudes and determining their clustering status are fundamental steps in defining the large-scale structure in the nearby Universe. The VISTA Variables in the Vía Láctea (VVV) near-IR galaxy catalogue (VVV NIRGC) allows us to explore this region in great detail. Our goal is to identify galaxy overdensities and characterize galaxy clustering in the Zone of Avoidance. We use different clustering algorithms to identify galaxy overdensities: the Voronoi tessellations, the minimum spanning tree, and the ordering points to identify the clustering structure. We studied the membership, isolation, compactness, and flux limits to identify compact groups of galaxies. Each method identified a variety of galaxy systems across the Galactic plane that are publicly available. We also explore the probability that these systems are formed by concordant galaxies using mock catalogues. 19 galaxy systems were identified in all of the four methods. They have the highest probability to be real overdensities. We stress the need for spectroscopic follow-up observations to confirm and characterize these new structures.

Limiting Flux versus Redshift as a Flag of New Physics

Abstract I show that General Relativity sets an absolute upper limit on the energy flux observed from a cosmological source as a function of its redshift. Detecting a brighter source in gravitational waves, neutrinos or light, would flag new physics. The derived flux limit can also be used to determine the maximum redshift possible for any source with an unknown origin.

Topography measurement of helical grooves on a hemisphere based on stitching interference microscopy

Hemispherical bearings fabricated with helical grooves on the working surface show improved aerodynamic performance which depends to a large extent on the machining accuracy of the grooves. Topography measurement of the entire groove from macro to micro scale is thus important to evaluate the bearing performance. White light interference microscopy is widely used in topography measurement. However, subaperture stitching is necessary to extend the field of view (FOV) for large area measurement but limited to planar surfaces. This paper presents a method of interference microscopy combined with subaperture stitching. The long groove is divided into a series of subapertures with overlapping regions. Each subaperture meets the requirement of FOV and measurable slope limit of the microscope. We show that the helical curve is approximately located on a geodesic circle of the hemisphere. Accordingly a special fixture is designed with a rotary table to rotate the groove around the axis perpendicular to the geodesic circle. A four-axis scanning platform is integrated with the interference microscope. Based on the principle of minimal deviations in overlapping regions, six-degree-of-freedom motion error introduced in subaperture scanning is simultaneously corrected through an iterative stitching algorithm. It is experimentally verified by measuring a real part with helical grooves etched on a hemisphere bearing rotor. Complete high-resolution topography of the entire groove is reconstructed and the stitching map shows no overlap sliding effect, which is instructive for assessment of the machining error and further evaluation of the bearing performance.

Effects of Different Slope Limiters on Stratified Shear Flow Simulation in a Non-hydrostatic Model

To simulate the dynamical structures of stratified shear flows, the high-resolution Total Variation Diminishing (TVD) method is necessary and widely-used due to its high-order spatial accuracy, oscillation control, and ability to capture the well-defined structures of vortices. Lack of understanding the TVD slope limiters usually results in inaccurate numerical simulation on stratified shear flows in terms of shear instability and spatiotemporal variations of mixing. In this study, the performances of four typical TVD slope limiters, namely the minmod, van Leer, Monotonized Central (MC), and superbee limiters, were investigated on modelling stratified shear flows based on the open-source non-hydrostatic model, NHWAVE. The four slope limiters are all commonly-used and have the typical numerical characteristics. All the limiters were respectively applied in two classical test cases, namely, shear instability and lock-exchange problem. The simulation results showed that the effects of slope limiters were correlated with their characteristics of numerical dissipation (or anti-dissipation), which can influence notably the model predictions of the generation of shear instability, the development of interfacial structures, and the mixing process. In the test cases, MC limiter’s performance was the best, because it could simulate the well-defined structures of instability while not introducing noticeable error. Minmod has an excessively large dissipation, which introduced noticeable numerical errors that can influence the model accuracy and can even suppress or omit the generation of interfacial vortices. Superbee limiter, the most anti-dissipative one, usually over-predicted the instability and mixing effects in time and space domain, and was likely to cause computational instability in some cases. The performances of van Leer and MC were similar, but their predictions of the evolutions of interfacial structures and mixing could be significantly different. Besides, the co-effects of grid resolution and slope limiters were also investigated; it was found that the refinement of grids may not help to reproduce a higher-quality result with a specific slope limiter.

Impact of different electron thermal conductivity models on the performance of cryogenic implosions

The electron thermal conduction strongly affects the hot-spot formation and the hydrodynamic instability growth in inertial confinement fusion implosions. A harmonic-mean flux-limited conductivity model has been widely used in implosion simulations. In this paper, using the high foot implosion N140520 as an example, we have performed a series of one-dimensional (1D) no-alpha simulations to quantify the impact of different conductivity models including the Spitzer–Harm model, the Lee–More model, and the recently proposed coupled Gericke-Murillo-Schlanges model [Ma et al., Phys. Rev. Lett. 122, 015001 (2019)] with the flux limiter fe ranging from 0.03 to 0.15 on the performance of cryogenic implosions. It is shown that varying fe has a bigger impact on the performance than changing conductivity models. Therefore, we have only performed two-dimensional (2D) no-alpha simulations using the Lee–More model with different flux limiters feLM to quantify the effect of the electron thermal conduction on the performance, with single-mode velocity perturbations with different mode numbers L seeded on the inner shell surface near the peak implosion velocity. We find that in both the 1D implosions and the 2D implosions with the same L, increasing fe leads to more hot-spot mass and lower hot-spot-averaged ion temperature, resulting in approximately constant hot-spot internal energy. In addition, the no-alpha yield Ynα is dominated by the neutron-averaged ion temperature Tn in these two cases. Increasing feLM from 0.0368 to 0.184 reduces Tn by ∼15% in 1D and by ∼20% for the 2D implosions with the same L, both leading to a ∼20% reduction in Ynα.

A new 3D OpenFoam solver with improved resolution for hyperbolic systems on hybrid unstructured grids

Although the accuracy and the robustness of discretized schemes solving hyperbolic systems have been greatly improved over the last two decades, devising a low-dissipative and non-oscillatory method remains a challenge. Especially, it is algorithmically complicated and computationally expensive to extend and apply high-resolution non-oscillatory schemes to 3D hybrid unstructured grids. Therefore, in this work we develop accurate, practical, and robust 3D hybrid unstructured OpenFoam solvers which can be applied in wide industrial applications. Different from existing 3D high order numerical solvers of which reconstruction schemes are based on polynomials of high degree, the proposed 3D scheme employs a polynomial function and a hyperbolic tangent basis function as two candidates for reconstruction functions. The MUSCL (Monotone Upstream-centered Schemes for Conservation law) scheme with the MLP (Multi-dimensional Limiting Process) slope limiter is adopted as the polynomial function. The multi-dimensional THINC (Tangent of Hyperbola for INterface Capturing) function with quadratic surface representation and Gaussian quadrature, so-called THINC/QQ, is used as the non-polynomial reconstruction candidate. With these reconstruction candidates, a multi-stage boundary variation diminishing (BVD) algorithm which significantly minimizes numerical dissipation is designed on 3D unstructured grids to select the final reconstruction function. With this accurate and robust reconstruction scheme, then we developed new solvers for simulating inviscid high speed compressible single-phase flow and two-phase flow via the implementation of the proposed scheme and algorithm into the open-source computational fluid dynamics (CFD) software, OpenFOAM. The solver with the proposed low-dissipative scheme, named as EulerEquationFoam-M-TQ-BVD, is constructed with the density-based solver for inviscid high speed compressible flow simulations. To simulate compressible multi-material flow with moving material interfaces, a solver named as FiveEquationFoam-M-TQ-BVD is developed based on mechanical-equilibrium diffusive interface model and MieGrüneisen equation of state. The performance of new solvers is evaluated through wide range benchmark tests and are compared with existing high order schemes such as the third-order WENO (Weighted Essentially Non-Oscillatory) scheme. The new solvers produce superior solution across critical points, contact discontinuities and material interfaces. Moreover, in comparison with WENO schemes, the proposed solver enjoys algorithmic simplicity and greater flexibility in 3D hybrid unstructured grids. Thus, this work provides accurate, practical and robust numerical solvers for high speed compressible single- and multi-material flow simulations.