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The synergy of strong spin-orbit coupling and electron-electron interactions gives rise to unconventional topological states, such as topological Mott insulator, Weyl semimetal, and quantum spin liquid. In this study, we have grown single crystals of the pyrochlore iridate Pr$_2$Ir$_2$O$_7$ and explored its magnetic, lattice dynamical, and electronic properties. While Raman spectroscopy data reveal six phonon modes confirming the cubic \textit{Fd$\bar{3}$m} crystal symmetry, dc magnetic susceptibility data show no anomalies and hence indicate the absence of magnetic phase transitions down to 2~K. Both temperature-dependent electric transport and optical conductivity data reveal the metallic character of Pr$_2$Ir$_2$O$_7$. The optical conductivity spectrum contains a mid-infrared absorption band, which becomes more pronounced with decreasing temperature due to spectral weight transfer from high to low energies. The presence of the mid-infrared band hints at the importance of correlation physics. The optical response furthermore suggests that Pr$_2$Ir$_2$O$_7$ is close to the Weyl semimetal phase., Comment: 11 pages, 8 figures, accepted for publication in Phys. Rev. B

In this article, we consider the Chew, Goldberger \& Low (CGL) plasma flow equations, which is a set of nonlinear, non-conservative hyperbolic PDEs modelling anisotropic plasma flows. These equations incorporate the double adiabatic approximation for the evolution of the pressure, making them very valuable for plasma physics, space physics and astrophysical applications. We first present the entropy analysis for the weak solutions. We then propose entropy-stable finite-difference schemes for the CGL equations. The key idea is to rewrite the CGL equations such that the non-conservative terms do not contribute to the entropy equations. The conservative part of the rewritten equations is very similar to the magnetohydrodynamics (MHD) equations. We then symmetrize the conservative part by following Godunov's symmetrization process for MHD. The resulting equations are then discretized by designing entropy conservative numerical flux and entropy diffusion operator based on the entropy scaled eigenvectors of the conservative part. We then prove the semi-discrete entropy stability of the schemes for CGL equations. The schemes are then tested using several test problems derived from the corresponding MHD test cases.

We present a new numerical model for solving the Chew-Goldberger-Low system of equations describing a bi-Maxwellian plasma in a magnetic field. Heliospheric and geospace environments are often observed to be in an anisotropic state with distinctly different parallel and perpendicular pressure components. The CGL system represents the simplest leading order correction to the common isotropic MHD model that still allows to incorporate the latter's most desirable features. However, the CGL system presents several numerical challenges: the system is not in conservation form, the source terms are stiff, and unlike MHD it is prone to a loss of hyperbolicity if the parallel and perpendicular pressures become too different. The usual cure is to bring the parallel and perpendicular pressures closer to one another; but that has usually been done in an ad hoc manner. We present a physics-informed method of pressure relaxation based on the idea of pitch-angle scattering that keeps the numerical system hyperbolic and naturally leads to zero anisotropy in the limit of very large plasma beta. Numerical codes based on the CGL equations can, therefore, be made to function robustly for any magnetic field strength, including the limit where the magnetic field approaches zero. The capabilities of our new algorithm are demonstrated using several stringent test problems that provide a comparison of the CGL equations in the weakly and strongly collisional limits. This includes a test problem that mimics interaction of a shock with a magnetospheric environment in 2D., Comment: Accepted in "The Astrophysical Journal (ApJ)"

Morphological features in galaxies, like spiral arms, bars, rings, tidal tails etc. carry information about their structure, origin and evolution. It is therefore important to catalogue and study such features and to correlate them with other basic galaxy properties the environment in which the galaxies are located and their interactions with other galaxies. Surveys such as SDSS, Pan-STARRS, HSC-SSP have made available very large samples of galaxies for gainful morphological studies. The availability of galaxy images and catalogues will increase manifold with future surveys like LSST. The volume of present and future data is so large that traditional methods, which involve expert astronomers identifying morphological features through visual inspection, are no longer sufficient. It is therefore necessary to use AI based techniques like machine learning and deep learning for finding morphological structures quickly and efficiently. We report in this study the application of deep learning for finding ring like structures in galaxy images from the Sloan Digital Sky Survey (SDSS) data release DR18. We use a catalogue by Buta (2017) of ringed galaxies from the SDSS to train the network reaching good accuracy and recall, and generate a catalogue of 29420 galaxies of which 9805 have ring like structures with prediction confidence exceeding 90 percent. Using a catalogue of barred galaxy images identified by Abraham et. al. (2018) using deep learning techniques, we identify a set of 2087 galaxies with bars as well as rings. The catalogues should be very useful in understanding the origin of these important morphological structures., Comment: 19 pages, 13 figures, 1 Table. Submitted to ApJ

Higher order finite difference Weighted Essentially Non-Oscillatory (WENO) schemes for conservation laws represent a technology that has been reasonably consolidated. They are extremely popular because, when applied to multidimensional problems, they offer high order accuracy at a fraction of the cost of finite volume WENO or DG schemes. They come in two flavors. There is the classical finite difference WENO (FD-WENO) method (Shu and Osher, J. Comput. Phys., 83 (1989) 32-78). However, in recent years there is also an alternative finite difference WENO (AFD-WENO) method which has recently been formalized into a very useful general-purpose algorithm for conservation laws (Balsara et al., Efficient Alternative Finite Difference WENO Schemes for Hyperbolic Conservation Laws, submitted to CAMC (2023)). However, the FD-WENO algorithm has only very recently been formulated for hyperbolic systems with non-conservative products (Balsara et al., Efficient Finite Difference WENO Scheme for Hyperbolic Systems with Non-Conservative Products, to appear CAMC (2023)). In this paper we show that there are substantial advantages in obtaining an AFD-WENO algorithm for hyperbolic systems with non-conservative products. Such an algorithm is documented in this paper. We present an AFD-WENO formulation in fluctuation form that is carefully engineered to retrieve the flux form when that is warranted and nevertheless extends to non-conservative products. The method is flexible because it allows any Riemann solver to be used. The formulation we arrive at is such that when non-conservative products are absent it reverts exactly to the formulation in the second citation above which is in exact flux conservation form. The ability to transition to a precise conservation form when non-conservative products are absent ensures, via the Lax-Wendroff theorem, that shock locations will be exactly ..., Comment: Accepted in Communications on Applied Mathematics and Computation

Higher order finite difference Weighted Essentially Non-Oscillatory (WENO) schemes for conservation laws are extremely popular because, for multidimensional problems, they offer high order accuracy at a fraction of the cost of finite volume WENO or DG schemes. Such schemes come in two formulations. The very popular classical finite difference WENO (FD-WENO) method (Shu and Osher, J. Comput. Phys., 83 (1989) 32-78) relies two reconstruction steps applied to two split fluxes. However, the method cannot accommodate different types of Riemann solvers and cannot preserve free stream boundary conditions on curvilinear meshes. This limits its utility. The alternative finite difference WENO (AFD-WENO) method can overcome these deficiencies, however, much less work has been done on this method. The reasons are three-fold. First, it is difficult for the casual reader to understand the intricate logic that requires higher order derivatives of the fluxes to be evaluated at zone boundaries. The analytical methods for deriving the update equation for AFD-WENO schemes are somewhat recondite. To overcome that difficulty, we provide an easily accessible script that is based on a computer algebra system in Appendix A of this paper. Second, the method relies on interpolation rather than reconstruction, and WENO interpolation formulae have not been documented in the literature as thoroughly as WENO reconstruction formulae. In this paper, we explicitly provide all necessary WENO interpolation formulae that are needed for implementing AFD-WENO up to ninth order. The third reason is that AFD-WENO requires higher order derivatives of the fluxes to be available at zone boundaries. Since those derivatives are usually obtained by finite differencing the zone-centered fluxes, they become susceptible to a Gibbs phenomenon when the solution ..., Comment: Accepted in Communications on Applied Mathematics and Computation

This article proposes entropy stable discontinuous Galerkin schemes (DG) for two-fluid relativistic plasma flow equations. These equations couple the flow of relativistic fluids via electromagnetic quantities evolved using Maxwell's equations. The proposed schemes are based on the Gauss-Lobatto quadrature rule, which has the summation by parts (SBP) property. We exploit the structure of the equations having the flux with three independent parts coupled via nonlinear source terms. We design entropy stable DG schemes for each flux part, coupled with the fact that the source terms do not affect entropy, resulting in an entropy stable scheme for the complete system. The proposed schemes are then tested on various test problems in one and two dimensions to demonstrate their accuracy and stability., Comment: Accepted in Journal of Scientific Computing (JOMP)

The shear shallow water model is an extension of the classical shallow water model to include the effects of vertical shear. It is a system of six non-linear hyperbolic PDE with non-conservative products. We develop a high-order entropy stable finite difference scheme for this model in one dimension and extend it to two dimensions on rectangular grids. The key idea is to rewrite the system so that non-conservative terms do not contribute to the entropy evolution. Then, we first develop an entropy conservative scheme for the conservative part, which is then extended to the complete system using the fact that the non-conservative terms do not contribute to the entropy production. The entropy dissipative scheme, which leads to an entropy inequality, is then obtained by carefully adding dissipative flux terms. The proposed schemes are then tested on several one and two-dimensional problems to demonstrate their stability and accuracy., Comment: Accepted in Journal of Scientific Computing (JOMP)

We introduce a novel approach to the executable semantic object rearrangement problem. In this challenge, a robot seeks to create an actionable plan that rearranges objects within a scene according to a pattern dictated by a natural language description. Unlike existing methods such as StructFormer and StructDiffusion, which tackle the issue in two steps by first generating poses and then leveraging a task planner for action plan formulation, our method concurrently addresses pose generation and action planning. We achieve this integration using a Language-Guided Monte-Carlo Tree Search (LGMCTS). Quantitative evaluations are provided on two simulation datasets, and complemented by qualitative tests with a real robot., Comment: Our code and supplementary materials are accessible at https://github.com/changhaonan/LG-MCTS

The white paper focuses on several candidate technologies that could play a crucial role in the development of 6G systems. Two of the key technologies explored in detail are Orthogonal Time Frequency Division Multiplexing (OTFDM) waveform and Structural MIMO (S-MIMO).

Higher order finite difference Weighted Essentially Non-Oscillatory (WENO) schemes have been constructed for conservation laws. For multidimensional problems, they offer high order accuracy at a fraction of the cost of a finite volume WENO or DG scheme of comparable accuracy. This makes them quite attractive for several science and engineering applications. But, to the best of our knowledge, such schemes have not been extended to non-linear hyperbolic systems with non-conservative products. In this paper, we perform such an extension which improves the domain of applicability of such schemes. The extension is carried out by writing the scheme in fluctuation form. We use the HLLI Riemann solver of Dumbser and Balsara (2016) as a building block for carrying out this extension. Because of the use of an HLL building block, the resulting scheme has a proper supersonic limit. The use of anti-diffusive fluxes ensures that stationary discontinuities can be preserved by the scheme, thus expanding its domain of applicability. Our new finite difference WENO formulation uses the same WENO reconstruction that was used in classical versions, making it very easy for users to transition over to the present formulation. For conservation laws, the new finite difference WENO is shown to perform as well as the classical version of finite difference WENO, with two major advantages:- 1) It can capture jumps in stationary linearly degenerate wave families exactly. 2) It only requires the reconstruction to be applied once. Several examples from hyperbolic PDE systems with non-conservative products are shown which indicate that the scheme works and achieves its design order of accuracy for smooth multidimensional flows. Stringent Riemann ... *Abstract truncated, see PDF*, Comment: Accepted in Communications on Applied Mathematics and Computation

GPU computing is expected to play an integral part in all modern Exascale supercomputers. It is also expected that higher order Godunov schemes will make up about a significant fraction of the application mix on such supercomputers. It is, therefore, very important to prepare the community of users of higher order schemes for hyperbolic PDEs for this emerging opportunity. We focus on three broad and high-impact areas where higher order Godunov schemes are used. The first area is computational fluid dynamics (CFD). The second is computational magnetohydrodynamics (MHD) which has an involution constraint that has to be mimetically preserved. The third is computational electrodynamics (CED) which has involution constraints and also extremely stiff source terms. Together, these three diverse uses of higher order Godunov methodology, cover many of the most important applications areas. In all three cases, we show that the optimal use of algorithms, techniques and tricks, along with the use of OpenACC, yields superlative speedups on GPUs! As a bonus, we find a most remarkable and desirable result: some higher order schemes, with their larger operations count per zone, show better speedup than lower order schemes on GPUs. In other words, the GPU is an optimal stratagem for overcoming the higher computational complexities of higher order schemes! Several avenues for future improvement have also been identified. A scalability study is presented for a real-world application using GPUs and comparable numbers of high-end multicore CPUs. It is found that GPUs offer a substantial performance benefit over comparable number of CPUs, especially when all the methods designed in this paper are used., Comment: 49 pages

Recent observations of Type Ia supernovae (SNe) by SH0ES collaboration (R11 and R16) diverge from the value reported by recent CMBR observations utilising the Planck satellite and application of the $\Lambda CDM$ cosmological model by at least $3 \sigma$. It is among the most challenging problems in contemporary cosmology and is known as the Hubble tension. The SNe Ia in R11 and R16 were calibrated through cepheid variables in three distinct galaxies: Milky Way, LMC, and NGC4258. Carnegie Hubble Program (CHP) observations of type Ia SNe calibrated using the tip of the red giant approach yielded a somewhat different estimate for the Hubble constant. This decreased the Hubble tension from over 3$\sigma$ to below 2$\sigma$. It is a legitimate question to answer whether there are any issues with SNe Ia calibration and to investigate whether the Hubble tension is real or not. We use statistical techniques namely, ANOVA, K-S test, and t-test to examine whether the cepheid calibration is host-dependent. Our analysis shows that (i) both R11 and R16 data suffer from non-Gaussian systematic effects, (ii) $H_0$ values in the sub-samples (different anchor-based) in both R11 and R16 groups are significantly different at a 99\% confidence level, and (iii) neglecting the metal-rich MW sample does not reduce the $H_0$ value significantly, and thus Hubble tension persists. A small reduction in the Hubble constant could be linked to the differences in the host environment. Hence instead of using a single universal relation environment based slope and zero point should be preferred., Comment: 15 pages (single column), 7 figures

Spin-orbit coupling in heavy 5$d$ metal oxides, in particular, iridates have received tremendous interest in recent years due to the realization of exotic electronic and magnetic phases. Here, we report the synthesis, structural, magnetic, thermodynamic, and optical properties of the ternary iridate Pr$_3$IrO$_7$. Single crystals of Pr$_3$IrO$_7$ have been grown by the KF flux method. Structural analysis shows that Pr$_3$IrO$_7$ crystallizes in an orthorhombic phase with $Cmcm$ symmetry. The electron energy loss spectroscopy study indicates that Pr is in a 3+ valence state, which implies a 5+ oxidation state of Ir. Magnetization data measured at high and low magnetic fields do not exhibit any bifurcation between $M_{ZFC}$ and $M_{FC}$, however, a weak hump in $M(T)$ is observed at $T^*$$\sim$10.4~K. The specific heat data reveal two maxima at $\sim$253 K and $\sim$4.8 K. The optical conductivity $\sigma_1(\omega)$ spectrum shows 24 infrared-active phonon modes and reveals an insulating behavior with an optical gap $\Delta_{OP}$ of size $\sim$500~meV. During cooling down, the temperature-dependent reflectivity spectrum reveals eight extra phonon modes below the structural phase transition ($\sim$ 253 K). An anomaly is observed at around $T^*$ in the temperature evolution of infrared-active mode frequencies suggesting the presence of significant spin-phonon coupling in the system., Comment: 18 pages, 8 figures, to appear in J. Phys.: Condens. Matter

In this article, we propose high-order finite-difference entropy stable schemes for the two-fluid relativistic plasma flow equations. This is achieved by exploiting the structure of the equations, which consists of three independent flux components. The first two components describe the ion and electron flows, which are modeled using the relativistic hydrodynamics equation. The third component is Maxwell's equations, which are linear systems. The coupling of the ion and electron flows, and electromagnetic fields is via source terms only. Furthermore, we also show that the source terms do not affect the entropy evolution. To design semi-discrete entropy stable schemes, we extend the RHD entropy stable schemes in Bhoriya et al. to three dimensions. This is then coupled with entropy stable discretization of the Maxwell's equations. Finally, we use SSP-RK schemes to discretize in time. We also propose ARK-IMEX schemes to treat the stiff source terms; the resulting nonlinear set of algebraic equations is local (at each discretization point). These equations are solved using the Newton's Method, which results in an efficient method. The proposed schemes are then tested using various test problems to demonstrate their stability, accuracy and efficiency.

Understanding the explosion mechanism of type Ia supernova is among the most challenging issues in astrophysics. Accretion of matter on a carbon-oxygen white dwarf from a companion star is one of the most important keys in this regard. Our aim is to study the effects of WD composition on various parameters during the accretion of helium rich matter at a slow rate. We have used the computer simulation code Modules for Experiments in Stellar Astrophysics (MESA) to understand the variations in the properties such as specific heat (\textit{$C_P$}) and degeneracy parameter (\textit{$\eta$}). The profile of specific heat shows a discontinuity and that of the degeneracy parameter shows a dip near the ignition region. As expected, the size of WD decreases and \textit{g} increases during the accretion. However, a red-giant-like expansion is observed after the rapid ignition towards the end. Our study explains the reason behind the delay in onset of helium ignition due to the difference in carbon abundance in a CO-WD. We find that white dwarfs of the lower abundance of carbon accrete slightly longer before the onset of helium ignition., Comment: 5 pages, 4 figures, 3 tables. arXiv admin note: substantial text overlap with arXiv:2111.13141

In binary systems, the helium accretion onto carbon-oxygen (CO) white dwarfs (WDs) plays a vital role in many astrophysical scenarios, especially in supernovae type Ia. Moreover, ignition density for accretion rate $\dot{M} \lesssim 10^{-9} M_{\odot}$ $yr^{-1}$ in helium accreting CO white dwarfs decides the triggering mechanism of a supernova explosion which could be either off-centre helium flash or central carbon flash. We aim to study the accretion of helium with a slow accretion rate $5 \times 10^{-10} M_{\odot}$ $yr^{-1}$ onto relatively cool and hot white dwarfs of different abundances of carbon and oxygen. The simulation code Modules for Experiments in Stellar Astrophysics (MESA) has been used for our study. We analyze the variation in several properties like surface gravity (g), helium luminosity ($L_{He}$), and effective temperature ($T_{eff}$) during the accretion phase of the white dwarfs. We also calculate the ignition density (${\rho}_{He}$) and ignition temperature ($T_{He}$) of helium burning. As expected, the size of WD decreases and g increases during the accretion. However, a red-giant-like expansion is observed after the rapid ignition towards the end. The dependence of helium accreting WD evolution on its composition has also been explored in this study. We find that white dwarfs of the lower abundance of carbon accrete slightly longer before the onset of helium ignition., Comment: 5 pages, 6 figures

The 3$d$-5$d$ based double perovskites offer an ideal playground to study the interplay between electron correlation ($U$) and spin-orbit coupling (SOC) effect, showing exotic physics. The Sr$_2$FeIrO$_6$ is an interesting member in this family with ionic distribution of Fe$^{3+}$ (3$d^5$) and Ir$^{5+}$ (5$d^4$) where the later is believed to be nonmagnetic under the picture of strong SOC. Here, we report detailed investigation of structural, magnetic and electronic transport properties along with electronic structure calculations in (Sr$_{1-x}$Ca$_x$)$_2$FeIrO$_6$ series with $x$ from 0 to 1. While the basic interactions such as, $U$ and SOC are unlikely to be modified but a structural modification is expected due to ionic size difference between Sr$^{2+}$ and Ca$^{2+}$ which would influence other properties such as crystal field effect and band widths. While a nonmonotonic changes in lattice parameters are observed across the series, the spectroscopic investigations reveal that 3+/5+ charge state of Fe/Ir continue till end of the series. An analysis of magnetic data suggests similar nonmonotonic evolution of magnetic parameters with doping. Temperature dependent crystal structure as well as low temperature (5 K) magnetic structure have been determined from neutron powder diffraction measurements. The whole series shows insulating behavior. The electronic structure calculations show, SOC enhanced, a noncollinear antiferromagnetic and Mott-type insulating state is the stable ground state for present series with a substantial amount of orbital moment, but less than the spin magnetic moment, at the Ir site and the magnetocrystalline anisotropy. The obtained results imply that the Ca$^{2+}$ has large influence on the magnetic and transport properties, further showing a large agreement between experimental results as well as theoretical calculations., Comment: Accepted in Phys. Rev. B, 19 pages, 18 figures

In this article, we propose high order discontinuous Galerkin entropy stable schemes for ten-moment Gaussian closure equations, which is based on the suitable quadrature rules (see [8]). The key components of the proposed method are the use of an entropy conservative numerical flux [31] in each cell and a suitable entropy stable numerical flux at the cell edges. This is then used in the entropy stable DG framework of [8] to obtain entropy stability of the semi-discrete scheme. We also extend these schemes to a source term that models plasma laser interaction. For the time discretization, we use strong stability preserving schemes. The proposed schemes are then tested on several test cases to demonstrate stability, accuracy, and robustness.

The $f$-$d$ magnetic exchange interaction is considered to be a key ingredient for many exotic topological phases in pyrochlore iridates. Here, we have investigated the evolution of structural, magnetic and electronic properties in doped pyrochlore iridate, (Y$_{1-x}$Pr$_x$)$_2$Ir$_2$O$_7$. Apart from geometrical frustration, pyrochlore iridates are well known for its active spin-orbit coupling effect. The substitution of Pr$^{3+}$ (4$f^2$) for the nonmagnetic Y$^{3+}$ (4$d^0$) acts as a magnetic doping, which provides an ideal platform to study $f$-$d$ exchange interaction without altering the Ir-sublattice. With Pr substitution, system retains its original cubic structural symmetry but the local structural parameters show an evolution with the doping concentration $x$. The robust magnetic-insulating state in Y$_2$Ir$_2$O$_7$ is drastically weakened, while Pr$_2$Ir$_2$O$_7$ ($x$ = 1.0) shows a paramagnetic-metallic behavior. A metal-insulator transition is observed for $x$ = 0.8 sample. This evolution of magnetic and electronic properties are believed to be induced by an exchange interaction between localized Pr-4$f$ and itinerant Ir-5$d$ electrons as well as by an increased hybridization between Ir-$t_{2g}$ and (basal) O-$p$ orbitals as observed in XAS study. The resistivity in insulating materials follows a power-law behavior with a decreasing exponent with $x$. A negative magnetoresistance is observed for present series of samples at low temperature and where the magnetoresistance shows a quadratic field dependence at higher fields., Comment: To appear in Phys. Rev. B, 10 pages, 10 figures

In this article, we present entropy stable discontinuous Galerkin numerical schemes for equations of special relativistic hydrodynamics with the ideal equation of state. The numerical schemes use the summation by parts (SBP) property of Gauss-Lobatto quadrature rules. To achieve entropy stability for the scheme, we use two-point entropy conservative numerical flux inside the cells and a suitable entropy stable numerical flux at the cell interfaces. The resulting semi-discrete scheme is then shown to entropy stable. Time discretization is performed using SSP Runge-Kutta methods. Several numerical test cases are presented to validate the accuracy and stability of the proposed schemes.