ShantanuT01/DACTYL-Pretraining huggingface dataset:
We present a study of internal stellar population gradients in early-type cluster galaxies. Using the VLT VIMOS integral field unit, we observed 19 galaxies in the core of the Shapley Supercluster (z = 0.048). The radial trends in nine absorption lines (HdF to Fe5406) were measured to the effective radius for 14 galaxies, from which we derived the gradients in age, total metallicity and alpha-element over-abundance. We combine these with results from 11 galaxies studied in our previous VIMOS work (Rawle et al 2008). We observe a mean metallicity gradient of -0.13 +/- 0.04 per dex and, in common with the findings of previous studies, galaxies with log(sigma) > 2.1 have a sizeable intrinsic scatter in metallicity gradient. The mean log(age/Gyr) gradient is -0.02 +/- 0.06 per dex, although several galaxies have significant positive or negative age gradients. The mean gradient in alpha-element enhancement is -0.10 +/- 0.04 per dex. We find that stellar population gradients are primarily related to the central metallicity: early-type galaxies with super-solar centres have steep negative metallicity gradients and positive age gradients; those with solar metallicity centres have negligible [Z/H] gradients and negative age gradients. There is a strong observed anti-correlation between the gradients in age and metallicity. While a part of this trend can be attributed to the correlation of measurement errors, we demonstrate that there is an underlying intrinsic relation. For the Shapley galaxies, B-R colour gradients predicted from spectroscopic age and metallicity generally agree well with those measured directly from photometry.
We define a L\'evy process on a smooth manifold $M$ with a connection as a projection of a solution of a Marcus stochastic differential equation on a holonomy bundle of $M$, driven by a holonomy-invariant L\'evy process on a Euclidean space. On a Riemannian manifold, our definition (with Levi-Civita connection) generalizes the Eells-Elworthy-Malliavin construction of the Brownian motion and extends the class of isotropic L\'evy process introduced in Applebaum and Estrade [AE00]. On a Lie group with a surjective exponential map, our definition (with left-invariant connection) coincides with the classical definition of a (left) L\'evy process given in terms of its increments.   Our main theorem characterizes the class of L\'evy processes via their generators on $M$, generalizing the fact that the Laplace-Beltrami operator generates Brownian motion on a Riemannian manifold. Its proof requires a path-wise construction of the stochastic horizontal lift and anti-development of a discontinuous semimartingale, leading to a generalization of Pontier and Estrade [PE92] to smooth manifolds with non-unique geodesics between distinct points.
In this paper we study the existence of doubly-connected rotating patches for Euler equations when the classical non-degeneracy conditions are not satisfied. We prove the bifurcation of the V-states with two-fold symmetry, however for higher $m-$fold symmetry with $m\geq3$ the bifurcation does not occur. This answers to a problem left open in \cite{H-F-M-V}. Note that, contrary to the known results for simply-connected and doubly-connected cases where the bifurcation is pitchfork, we show that the degenerate bifurcation is actually transcritical. These results are in agreement with the numerical observations recently discussed in \cite{H-F-M-V}. The proofs stem from the local structure of the quadratic form associated to the reduced bifurcation equation.
In this paper, we prove that there are more than 66.036% of zeros of the Riemann zeta-function are distinct.
This overview discusses issues relevant to modeling nucleosynthesis in type II supernovae and implications of detailed studies of the ejecta. After a brief presentation of the most common approaches to stellar evolution and parameterized explosions, the relevance of a number of nuclei to obtain information on the evolution and explosion mechanisms is discussed. The paper is concluded by an outlook on multi-dimensional simulations.
Some solutions of the Maxwell equations with Dirac particles for the source in FRW spacetime are discussed. The Green's function of the equation for the radial component of the Maxwell fields, F_{r\eta} and F_{\theta\phi} is solved. Green's function is found to reduce to that of Minkowskian spacetime in the appropriate limit. Also, the Lienard-Wiechert type solution is derived. Also, the solutions with the Dirac particle current is also presented. It is found that the F_{r\eta} is composed of even angular momentum states while the odd states constitue F_{\theta\phi} .
We give conditions under which a scalar random variable T can be coupled to a random scaling factor $\xi$ such that T and $\xi$T are rendered stochastically independent. A similar result is obtained for random measures. One consequence is a generalization of a result by Pitman and Yor on the Poisson-Dirichlet distribution to its negative parameter range. Another application are diffusion excursions straddling an exponential random time.
In this paper, we derive eight basic identities of symmetry in three variables related to Euler polynomials and alternating power sums. These and most of their corollaries are new, since there have been results only about identities of symmetry in two variables. These abundance of symmetries shed new light even on the existing identities so as to yield some further interesting ones. The derivations of identities are based on the $p$-adic integral expression of the generating function for the Euler polynomials and the quotient of integrals that can be expressed as the exponential generating function for the alternating power sums.
Ensembles of magnetic skyrmions in confined geometries are shown to exhibit thermally driven motion on two different time scales. The intrinsic fluctuating dynamics ($t\sim 1~$ps) is governed by short-range symmetric and antisymmetric exchange interactions, whereas the long-time limit ($t\gtrsim10\,$ns) is determined by the coaction of skyrmion-skyrmion-repulsion and the system's geometry. Micromagnetic simulations for realistic island shapes and sizes are performed and analyzed, indicating the special importance of skyrmion dynamics at finite temperatures. We demonstrate how the competition between skyrmion mobility and observation time directly affects the addressability of skyrmionic bits, which is a key challenge on the path of developing skyrmion-based room-temperature applications. The presented quasiparticle Monte Carlo approach offers a computationally efficient description of the diffusive motion of skyrmion ensembles in confined geometries, like racetrack memory setups.
We present an implementation of an efficient algorithm for the calculation of the spectrum of one-dimensional quantum systems with periodic boundary conditions. This algorithm is based on a matrix product representation for quantum states (MPS), and a similar representation for Hamiltonians and other operators (MPO). It is significantly more efficient for systems of about 100 sites and more than for small quantum systems. We apply the formalism to calculate the ground state and first excited state of a spin-1 Heisenberg ring and deduce the size of the Haldane gap. The results are compared to previous high-precision DMRG calculations. Furthermore, we study spin-1 systems with a biquadratic nearest-neighbor interaction and show first results of an application to a mesoscopic Hubbard ring of spinless Fermions which carries a persistent current.
This paper is concerned with the classical two-species Lotka-Volterra diffusion system with strong competition. The sharp dynamical behavior of the solution is established in two different situations: either one species is an invasive one and the other is a native one or both are invasive species. Our results seem to be the first that provide a precise spreading speed and profile for such a strong competition system. Among other things, our analysis relies on the construction of new types of supersolution and subsolution, which are optimal in certain sense.
We study charge transport in a two dimensional hybrid systems consisting of nonmagnetic two dimensional electron gas with spin-orbit interaction sandwiched between a Ferromagnetic lead and a normal metallic lead (FM/2DEG/NM). An {\it absolute spin valve effect} is shown to exist. It is shown that the conductance of such a hybrid system changes upon rotating the magnetization such that it always stays perpendicular to the current direction. An ASVC ({\it Absolute Spin Valve Coefficient}) is defined to quantify this effect and its dependence on various parameter is studied.
The electric, magnetic, and thermal properties of three perovskite cobaltites with the same 30% hole doping and ferromagnetic ground state were investigated down to very low temperatures. With decreasing size of large cations, the ferromagnetic Curie temperature and spontaneous moments of cobalt are gradually suppressed - $T_C=130$ K, 55 K and 25 K and $m = 0.68 \mu_B$, 0.34 $\mu_B$ and 0.23 $\mu_B$ for Nd$_{0.7}$Sr$_{0.3}$CoO$_3$, Pr$_{0.7}$Ca$_{0.3}$CoO$_3$ and Nd$_{0.7}$Ca$_{0.3}$CoO$_3$, respectively. The moment reduction with respect to moment of the conventional ferromagnet La$_{0.7}$Sr$_{0.3}$CoO$_3$ ($T_C=230$ K, $m = 1.71 \mu_B$) in so-called IS/LS state for Co$^{3+}$/Co$^{4+}$, was originally interpreted using phase-separation scenario. Based on the present results, mainly the analysis of Schottky peak originating in Zeeman splitting of the ground state Kramers doublet of Nd$^{3+}$, we find, however, that ferromagnetic phase in Nd$_{0.7}$Ca$_{0.3}$CoO$_3$ and likely also Pr$_{0.7}$Ca$_{0.3}$CoO$_3$ is uniformly distributed over all sample volume, despite the severe drop of moments. The ground state of these compounds is identified with the LS/LS-related phase derived theoretically by Sboychakov \textit{et al.} [Phys. Rev. B \textbf{80}, 024423 (2009)]. The ground state of Nd$_{0.7}$Sr$_{0.3}$CoO$_3$ with an intermediate cobalt moment is inhomogeneous due to competing of LS/LS and IS/LS phases. In the theoretical part of the study, the crystal field split levels for $4f^3$ (Nd$^{3+}$), $4f^2$ (Pr$^{3+}$) and $4f^1$ (Ce$^{3+}$ or Pr$^{4+}$) are calculated and their magnetic characteristics are presented.
Over a decade ago, a group of supernova explosions with peak luminosities far exceeding (often by >100) those of normal events, has been identified. These superluminous supernovae (SLSNe) have been a focus of intensive study. I review the accumulated observations and discuss the implications for the physics of these extreme explosions. SLSNe can be classified into hydrogen poor (SLSNe-I) and hydrogen rich (SLSNe-II) events. Combining photometric and spectroscopic analysis of samples of nearby SLSNe-I and lower-luminosity events, a threshold of M_g<-19.8 mag at peak appears to separate SLSNe-I from the normal population. SLSN-I light curves can be quite complex, presenting both early bumps and late post-peak undulations. SLSNe-I spectroscopically evolve from an early hot photospheric phase with a blue continuum and weak absorption lines, through a cool photospheric phase resembling spectra of SNe Ic, and into the late nebular phase. SLSNe-II are not nearly as well studied, lacking information based on large sample studies. Proposed models for the SLSN power source are challenged to explain all the observations. SLSNe arise from massive progenitors, with some events associated with very massive stars (M>40 solar). Host galaxies of SLSNe in the nearby universe tend to have low mass and sub-solar metallicity. SLSNe are rare, with rates <100 times lower than ordinary SNe. SLSN cosmology and their use as beacons to study the high-redshift universe offer exciting future prospects.
We present observations of SDF-05M05, an unusual optical transient discovered in the Subaru Deep Field (SDF). The duration of the transient is > ~800 d in the observer frame, and the maximum brightness during observation reached approximately 23 mag in the i' and z' bands. The faint host galaxy is clearly identified in all 5 optical bands of the deep SDF images. The photometric redshift of the host yields z~0.6 and the corresponding absolute magnitude at maximum is ~-20. This implies that this event shone with an absolute magnitude brighter than -19 mag for approximately 300 d in the rest frame, which is significantly longer than a typical supernova and ultra-luminous supernova. The total radiated energy during our observation was 1x10^51 erg. The light curves and color evolution are marginally consistent with some of luminous IIn supernova. We suggest that the transient may be a unique and peculiar supernova at intermediate redshift.
In a cool neutron star (T < 1.e6 K) endowed with a rather high magnetic field (B > 1.e13 G), a phase transition may occur in the outermost layers. As a consequence the neutron star becomes `bare', i.e. no gaseous atmosphere sits on the top of the crust. The surface of a cooling, bare neutron star does not necessarily emit a blackbody spectrum because the emissivity is strongly suppressed at energies below the electron plasma frequency, omega_p. Since omega_p ~ 1 keV under the conditions typical of the denseelectron gas in the condensate, the emission from a T ~ 100 eV bare neutron star will be substantially depressed with respect to that of a perfect Planckian radiator at most energies. Here we present a detailed analysis of the emission properties of a bare neutron star. In particular, we derive the surface emissivity for a Fe composition in a range of magnetic fields and temperatures representative of cooling isolated neutron stars, like RX J1856.5-3754. We find that the emitted spectrum is strongly dependent on the electron conductivity in the solid surface layers. In the cold electron gas approximation (no electron-lattice interactions), the spectrum turns out to be a featureless depressed blackbody in the 0.1-2 keV band with a steeper low-energy distribution. When damping effects due to collisions between electrons and the ion lattice (mainly due to electron-phonon interactions) are accounted for, the spectrum is more depressed depending on the magnetic field strength. Details of the emitted spectrum are found, however, to be strongly dependent of the assumed treatment of the transition from the external vacuum to the metallic surface. The implications of out results to RX J1856.5-3754 and other isolated neutron stars are discussed.
A formalism based on a chiral quark model ($\chi$QM) approach complemented with a one-gluon exchange model, to take into account the breakdown of the $SU(6)\otimes O(3)$ symmetry, is presented. The configuration mixing of wave functions for nucleon and resonances are derived. % With few adjustable parameters, differential cross-section and polarized beam asymmetry for the $\gamma p \to \eta p$ process are calculated and successfully compared with the data in the centre-of-mass energy range from threshold up to 2 GeV. The known resonances $S_{11}(1535)$, $S_{11}(1650)$, $P_{13}(1720)$, $D_{13}(1520)$, and $F_{15}(1680)$, as well as two new $S_{11}$ and $D_{15}$ resonances are found to be dominant in the reaction mechanism. Besides, connections among the scattering amplitudes of the $\chi$QM approach and the helicity amplitudes, as well as decay widths of resonances are established. Possible contributions from the so-called "missing resonances" are investigated and found to be negligible.
We study close approaches in hierarchical triple systems with comparable masses using full N-body simulations, motivated by a recent model for type Ia supernovae involving direct collisions of white dwarfs (WDs). For stable hierarchical systems where the inner binary components have equal masses, we show that the ability of the inner binary to achieve very close approaches, where the separation between the components of the inner binary reaches values which are orders of magnitude smaller than the semi-major axis, can be analytically predicted from initial conditions. The rate of close approaches is found to be roughly linear with the mass of the tertiary. The rate increases in systems with unequal inner binaries by a marginal factor of $\lesssim 2$ for mass ratios ${0.5<m_1/m_2<1}$ relevant for the inner white-dwarf binaries. For an average tertiary mass of $\sim 0.3 M_{\odot}$ which is representative of typical M-dwarfs, the chance for clean collisions is $\sim 1$% setting challenging constraints on the collisional model for type Ia's.
The gas needed to sustain star formation in galaxies is supplied by the circumgalactic medium (CGM), which in turn is affected by accretion from large scales. In a series of two papers, we examine the interplay between a galaxy's ambient CGM and central star formation within the context of the large-scale environment. We use the IllustrisTNG-100 simulation to show that the influence exerted by the large-scale galaxy environment on the CGM gas angular momentum results in either enhanced (Paper I) or suppressed (Paper II, this paper) star formation inside a galaxy. We find that for present-day quenched galaxies, both the large-scale environments and the ambient CGM have always had higher angular momenta throughout their evolutionary history since at least $z=2$, in comparison to those around present-day star-forming disk galaxies, resulting in less efficient gas inflow into the central star-forming gas reservoirs. A sufficiently high CGM angular momentum, as inherited from the larger-scale environment, is thus an important factor in keeping a galaxy quenched, once it is quenched. The process above naturally renders two key observational signatures: (1) a coherent rotation pattern existing across multiple distances from the large-scale galaxy environment, to the circumgalactic gas, to the central stellar disk; and (2) an anti-correlation between galaxy star-formation rates and orbital angular momenta of interacting galaxy pairs or groups.
Despite the outstanding success of self-supervised pretraining methods for video representation learning, they generalise poorly when the unlabeled dataset for pretraining is small or the domain difference between unlabelled data in source task (pretraining) and labeled data in target task (finetuning) is significant. To mitigate these issues, we propose a novel approach to complement self-supervised pretraining via an auxiliary pretraining phase, based on knowledge similarity distillation, auxSKD, for better generalisation with a significantly smaller amount of video data, e.g. Kinetics-100 rather than Kinetics-400. Our method deploys a teacher network that iteratively distills its knowledge to the student model by capturing the similarity information between segments of unlabelled video data. The student model meanwhile solves a pretext task by exploiting this prior knowledge. We also introduce a novel pretext task, Video Segment Pace Prediction or VSPP, which requires our model to predict the playback speed of a randomly selected segment of the input video to provide more reliable self-supervised representations. Our experimental results show superior results to the state of the art on both UCF101 and HMDB51 datasets when pretraining on K100 in apple-to-apple comparisons. Additionally, we show that our auxiliary pretraining, auxSKD, when added as an extra pretraining phase to recent state of the art self-supervised methods (i.e. VCOP, VideoPace, and RSPNet), improves their results on UCF101 and HMDB51. Our code is available at https://github.com/Plrbear/auxSKD.
We revisit the computation of the 1-loop string correction to the "latitude" minimal surface in $AdS_5 \times S^5$ representing 1/4 BPS Wilson loop in planar $\cal N$=4 SYM theory previously addressed in arXiv:1512.00841 and arXiv:1601.04708. We resolve the problem of matching with the subleading term in the strong coupling expansion of the exact gauge theory result (derived previously from localization) using a different method to compute determinants of 2d string fluctuation operators. We apply perturbation theory in a small parameter (angle of the latitude) corresponding to an expansion near the $AdS_2$ minimal surface representing 1/2 BPS circular Wilson loop. This allows us to compute the corrections to the heat kernels and zeta-functions of the operators in terms of the known heat kernels on $AdS_2$. We apply the same method also to two other examples of Wilson loop surfaces: generalized cusp and $k$-wound circle.
Approximating radiance fields with volumetric grids is one of promising directions for improving NeRF, represented by methods like Plenoxels and DVGO, which achieve super-fast training convergence and real-time rendering. However, these methods typically require a tremendous storage overhead, costing up to hundreds of megabytes of disk space and runtime memory for a single scene. We address this issue in this paper by introducing a simple yet effective framework, called vector quantized radiance fields (VQRF), for compressing these volume-grid-based radiance fields. We first present a robust and adaptive metric for estimating redundancy in grid models and performing voxel pruning by better exploring intermediate outputs of volumetric rendering. A trainable vector quantization is further proposed to improve the compactness of grid models. In combination with an efficient joint tuning strategy and post-processing, our method can achieve a compression ratio of 100$\times$ by reducing the overall model size to 1 MB with negligible loss on visual quality. Extensive experiments demonstrate that the proposed framework is capable of achieving unrivaled performance and well generalization across multiple methods with distinct volumetric structures, facilitating the wide use of volumetric radiance fields methods in real-world applications. Code Available at \url{https://github.com/AlgoHunt/VQRF}
We report results of a spectral and timing analysis of the poorly studied transient X-ray pulsar 2S 1553-542 using data collected with the NuSTAR and Chandra observatories and the Fermi/GBM instrument during an outburst in 2015. Properties of the source at high energies (>30 keV) are studied for the first time and the sky position had been essentially improved. The source broadband spectrum has a quite complicated shape and can be reasonably described by a composite model with two continuum components - a black body emission with the temperature about 1 keV at low energies and a power law with an exponential cutoff at high energies. Additionally an absorption feature at $\sim23.5$ keV is discovered both in phase-averaged and phase-resolved spectra and interpreted as the cyclotron resonance scattering feature corresponding to the magnetic field strength of the neutron star $B\sim3\times10^{12}$ G. Based on the Fermi/GBM data the orbital parameters of the system were substantially improved, that allowed us to determine the spin period of the neutron star P = 9.27880(3) s and a local spin-up $\dot P \simeq -7.5\times10^{-10}$ s s$^{-1}$ due to the mass accretion during the NuSTAR observations. Assuming accretion from the disk and using standard torque models we have estimated the distance to the system $d=20\pm4$ kpc.
We describe conditions on non-gradient drift diffusion Fokker-Planck equations for its solutions to converge to equilibrium with a uniform exponential rate in Wasserstein distance. This asymptotic behaviour is related to a functional inequality, which links the distance with its dissipation and ensures a spectral gap in Wasserstein distance. We give practical criteria for this inequality and compare it to classical ones. The key point is to quantify the contribution of the diffusion term to the rate of convergence, which to our knowledge is a novelty.