ShantanuT01/DACTYL-Pretraining huggingface dataset:
We demonstrate with a nonlinear MHD code that angular momentum can be transported due to the magnetic instability of toroidal fields under the influence of differential rotation, and that the resulting effective viscosity may be high enough to explain the almost rigid-body rotation observed in radiative stellar cores. Only stationary current-free fields and only those combinations of rotation rates and magnetic field amplitudes which provide maximal numerical values of the viscosity are considered. We find that the dimensionless ratio of the effective over molecular viscosity, $\nu_T/\nu$;, linearly grows with the Reynolds number of the rotating fluid multiplied with the square-root of the magnetic Prandtl number - which is of order unity for the considered red sub-giant KIC 7341231.   For the considered interval of magnetic Reynolds numbers - which is restricted by numerical constraints of the nonlinear MHD code - there is a remarkable influence of the magnetic Prandtl number on the relative importance of the contributions of the Reynolds stress and the Maxwell stress to the total viscosity, which is magnetically dominated only for Pm $\gtrsim$ 0.5. We also find that the magnetized plasma behaves as a non-Newtonian fluid, i.e. the resulting effective viscosity depends on the shear in the rotation law. The decay time of the differential rotation thus depends on its shear and becomes longer and longer during the spin-down of a stellar core.
In this study, we report a parallel algorithm for the infinite-size density matrix renormalization group (iDMRG) that is applicable to one-dimensional (1D) quantum systems with $\ell$-site periods, where $\ell$ is an even number. It combines Hida's iDMRG applied to random 1D spin systems with a variant of McCulloch's wavefunction prediction. This allows us to apply $\ell/2$ times of computational power to accelerate the investigation of multi-leg frustrated quantum systems in the thermodynamic limit, which is a challenging simulation. We performed benchmark calculations for a spin-1/2 Heisenberg model on a Kagome cylinder YC8 using the parallel iDMRG, and found that the proposed iDMRG was efficiently parallelized for shared memory and distributed memory systems, and provided such bulk physical quantities as total energy, bond strength on nearest neighbor spins, and spin--spin correlation functions and their correlation lengths without finite-size effects. Moreover, the variant of the wavefunction prediction sped up Lanczos methods in the parallel iDMRG by approximately three times.
We investigate the interacting, one-dimensional Rice-Mele model, a prototypical fermionic model of topological properties. To set the stage, we firstly compute the single-particle spectral function, the local density, and the boundary charge in the absence of interactions. The boundary charge is fully determined by bulk properties indicating a bulk-boundary correspondence. In a large parameter regime it agrees with the one obtained from an effective low-energy theory (arXiv:2004.00463). Secondly, we investigate the robustness of our results towards two-particle interactions. To resum the series of leading logarithms for small gaps, which dismantle plain perturbation theory in the interaction, we use an essentially analytical renormalization group approach. It is controlled for small interactions and can directly be applied to the microscopic lattice model. We benchmark the results against numerical density matrix renormalization group data. The main interaction effect in the bulk is a power-law renormalization of the gap with an interaction dependent exponent. The important characteristics of the boundary charge are unaltered and can be understood from the renormalized bulk properties, elevating the bulk-boundary correspondence to the interacting regime. This requires a consistent treatment not only of the low-energy gap renormalization but also of the high-energy band width one. In contrast to low-energy field theories our renormalization group approach also provides the latter. We show that the interaction spoils the relation between the bulk properties and the number of edge states, consistent with the observation that the Rice-Mele model with finite potential modulation does not reveal any zero-energy edge states.
A revision is presented of the sunspot observations made by Charles Malapert from 1618 to 1626, studying several documentary sources that include those observations. The revised accounting of the group numbers recorded by Malapert for that period shows new information unavailable in the current sunspot group database. The average solar activity level calculated from these revised records of Malapert is by almost one third greater than that calculated from his records included in the current group database. Comparison of the sunspot observations made by Malapert and by other astronomers of that time with regard to the number of recorded groups and sunspot positions on the solar disk shows good agreement. Malapert reported that he only recorded one sunspot group in each sunspot drawing presented in Austriaca Sidera Heliocyclia (the documentary source which includes most of the sunspot records made by Malapert), although he sometimes observed several groups. Therefore, the sunspot counts obtained in this present work on Malapert's sunspot observations represents the lower limit of the solar activity level corresponding to those records.
We consider the production of $Z$ bosons associated with heavy (charm and beauty) jets at the LHC energies using two scenarios based on the transverse momentum dependent (TMD) parton densities in a proton. The first of them employs the Catani-Ciafaloni-Fiorani-Marchesini gluon evolution and is implemented in the Monte-Carlo event generator PEGASUS. Here, the heavy quarks are always produced in the hard partonic scattering. The second scheme is based on the parton branching approach, currently implemented into the Monte-Carlo event generator CASCADE. In this scenario, the $Z$ + jets sample is generated and then events containing the heavy flavor jet in a final state are selected. We compare the predictions obtained within these two TMD-based approaches to each other, investigate their sensitivity to the TMD gluon densities in a proton and estimate the effects coming from parton showers and double parton scattering mechanism. Additionally, we compare our predictions with the results of traditional (collinear) pQCD calculations performed at NLO accuracy. It is shown that the TMD-based results agree with the LHC experimental data collected at $\sqrt s = 8$ and $13$ TeV. We discuss the sensitivity of observables to the quark distributions in a proton and present predictions to search for the intrinsic charm signal in forthcoming analyses of the LHC experimental data.
We establish the existence of rank two Ulrich vector bundles on surfaces that are either of maximal Albanese dimension or with irregularity 1, under many embeddings. In particular we get the first known examples of Ulrich vector bundles on irregular surfaces of general type. Another consequence is that every surface such that either $q \le 1$ or $q \ge 2$ and its minimal model has rank one, carries a simple rank two Ulrich vector bundle.
We systematically investigate the mergers of neutron star-white dwarf binaries from beginning to end, with focus on the properties of the inflows and outflows in accretion disks and their electromagnetic emissions. Using population synthesis models, we determine a subset of these binaries in which the white dwarf companion undergoes unstable mass transfer and complete tidal disruption, forming a large accretion disk around the neutron star. The material evolves according to an advection-dominated accretion disk model with nuclear burning, neutrino-emissions, and disk-surface wind ejection. The extreme dynamics of the entire process has proven difficult for analytic analysis, and thus currently the properties are poorly understood. The outflows from the mergers are iron- and nickel-rich, giving rise to optical and infrared emissions powered from the decay of the radioactive iron-type isotopes, calculated via the SuperNu light-curve code. We find these systems capable of powering bright, yet short-lived, optical transients with the potential to power gamma-ray bursts.
Oxygen incorporation has been reported to increase the current-induced spin-orbit torque in ferromagnetic heterostructures, but the underlying mechanism is still under active debate. Here, we report on an in-situ study of the oxygen exposure effect on spin-orbit torque in Pt/Co bilayers via controlled oxygen exposure, Co and Mg deposition, and electrical measurements in ultrahigh vacuum. We show that the oxygen exposure on Pt/Co indeed leads to an increase of spin-orbit torque, but the enhancement is not as large as those reported previously. Similar enhancement of spin-orbit torque is also observed after the deposition of an MgO capping layer. The results of ab initio calculations on the Rashba splitting of Pt/Co and Pt/Co/O suggest that the enhancement is due to enhanced Rashba-Edelstein effect by surface-adsorbed oxygen. Our findings shed some light on the varying roles of oxygen in modifying the spin torque efficiency reported previously.
Accurate long-term trajectory prediction in complex scenes, where multiple agents (e.g., pedestrians or vehicles) interact with each other and the environment while attempting to accomplish diverse and often unknown goals, is a challenging stochastic forecasting problem. In this work, we propose MUSE, a new probabilistic modeling framework based on a cascade of Conditional VAEs, which tackles the long-term, uncertain trajectory prediction task using a coarse-to-fine multi-factor forecasting architecture. In its Macro stage, the model learns a joint pixel-space representation of two key factors, the underlying environment and the agent movements, to predict the long and short-term motion goals. Conditioned on them, the Micro stage learns a fine-grained spatio-temporal representation for the prediction of individual agent trajectories. The VAE backbones across the two stages make it possible to naturally account for the joint uncertainty at both levels of granularity. As a result, MUSE offers diverse and simultaneously more accurate predictions compared to the current state-of-the-art. We demonstrate these assertions through a comprehensive set of experiments on nuScenes and SDD benchmarks as well as PFSD, a new synthetic dataset, which challenges the forecasting ability of models on complex agent-environment interaction scenarios.
The theorem of Pusey, Barrett, and Rudolph proves that different quantum states describe different physical realities. Their proof is based on the construction of entanglement measurement bases of two, and more than two qbits. In this note, I show that a two-qubit entanglement base is sufficient for a general proof.
For 89 galaxies, mostly spirals, in the Virgo cluster region, we have obtained optical long-slit major axis spectra of the ionized gas. We find: (1) One-half of the Virgo galaxies we observed have regular rotation patterns, while the other 50% exhibit kinematic disturbances ranging from mild to major. Velocity complexities are generally consistent with those resulting from tidal encounters or accretion events. Since kinematic disturbances are expected to fade within ~10^9 years, many Virgo galaxies have experienced several significant kinematic disturbances during their lifetimes. (2) A few Virgo galaxies have ionized gas of limited extent, with velocities exceptionally low for their luminosities. In these galaxies the gas must be not rotationally supported. (3) There is a remarkable difference in the distribution of galaxy systemic velocity for galaxies with Regular rotation curves and galaxies with Disturbed rotation curves. Galaxies with regular rotation patterns show a flat distribution with systemic velocity, while galaxies with disturbed kinematics have a Gaussian distribution very similar to that for the elliptical galaxies in Virgo. This suggests that spirals with disturbed kinematics are preferentially on radial orbits, which bring them to the cluster core, where tidal interactions are strong and/or more common. These interactions may alter the morphology of the galaxy, and may also play a role in driving the Virgo cluster toward dynamical equilibrium.
Within the framework of the dynamical recombination approach implemented in the partonic/hadronic quark Molecular Dynamics (qMD) model, we investigate numerous QGP signals constructed from the correlations and fluctuations of conserved charges, namely charged particle ratio fluctuations, charge transfer fluctuations as well as various ratios of susceptibilities. We argue that more generally, the covariances and the variances of the conserved charges divided by the number of charged particles are a measure of the quark number susceptibilities and are thus sensitive to the phase of the system. Computations carried within samples of central qMD events from low AGS energies on ($E_{lab}=2$ AGeV) up to the highest RHIC energies available ($\sqrt{s_{NN}}=200$ GeV) show that the final state calculations are always compatible with the hadronic result. From analyses performed as a function of time with our sample of events at $\sqrt{s_{NN}}=200$ GeV, we find the recombination-like hadronization process the qMD system undergoes to be responsible for the vanishing of the early stage QGP correlations and fluctuations. These results might explain the compatibility of the measurements on charged particle ratio fluctuations with the hadronic expectations and leave no room for the experimental observation of any QGP fluctuation/correlation signals based upon the susceptibilities of the conserved charges.
Nova explosions occur on the white dwarf component of a Cataclysmic Variable binary stellar system that is accreting matter lost by its companion. When sufficient material has been accreted by the white dwarf, a thermonuclear runaway occurs and ejects material in what is observed as a Classical Nova explosion. We describe both the recent advances in our understanding of the progress of the outburst and outline some of the puzzles that are still outstanding. We report on the effects of improving both the nuclear reaction rate library and including a modern nuclear reaction network in our one-dimensional, fully implicit, hydrodynamic computer code. In addition, there has been progress in observational studies of Supernovae Ia with implications about the progenitors and we discuss that in this review.
We present a study of the connection between the galactic spin parameter $\lambda_{d}$ and the bar fraction in a volume-limited sample of 10,674 disk galaxies drawn from the Sloan Digital Sky Survey Data Release 7. The galaxies in our sample are visually classified into galaxies hosting long or short bars, and non-barred galaxies. We find that the spin distributions of these three classes are statistically different, with galaxies hosting long bars with the lowest $\lambda_{d}$ values, followed by non-barred galaxies, while galaxies with short bars present typically high spin parameters. The bar fraction presents its maximum at low to intermediate $\lambda_{d}$ values for the case of long bars, while the maximum for short bars is at high $\lambda_{d}$. This bi-modality is in good agreement with previous studies finding longer bars hosted by luminous, massive, red galaxies with low content of cold gas, while short bars are found in low luminosity, low mass, blue galaxies, usually gas rich. In addition, the rise and fall of the bar fraction as a function of $\lambda_{d}$, within the long-bar sample, shown in our results, can be explained as a result of two competing factors: the self-gravity of the disk that enhances bar instabilities, and the support by random motions instead of ordered rotational motion, that prevents the formation/growth of bars.
We study the spin-1/2 Heisenberg antiferromagnet on a bilayer honeycomb lattice including interlayer frustration. Using a set of complementary approaches, namely Schwinger bosons, dimer series expansion, bond operators, and exact diagonalization, we map out the quantum phase diagram. Analyzing ground state energies and elementary excitation spectra, we find four distinct phases, corresponding to three collinear magnetic long range ordered states, and one quantum disordered interlayer dimer phase. We detail, that the latter phase is adiabatically connected to an "exact" singlet product ground state of the the bilayer which exists along a line of maximum interlayer frustration. The order within the remaining three phases will be clarified.
This paper is complete proof of one method for obtaining the generalized Ito-Wentzell formula, its basic idea was announced earlier in a pre-print (arXiv:1309.3038v1). This proof sets the approach which uses the Ito formula and the stochastic approximation theory.
Here a short synthesis is presented of the work, developed in the last two years by the Brescia Collaboration, on the phenomenology of antinucleon-nucleon and antinucleon-nucleus annihilation at small momenta (below 300 MeV/c in the laboratory), with special stress on the role of general principles.
The gravitational effect of vacuum polarization in space exterior to a particle in (2+1)-dimensional Einstein theory is investigated. In the weak field limit this gravitational field corresponds to an inverse square law of gravitational attraction, even though the gravitational mass of the quantum vacuum is negative. The paradox is resolved by considering a particle of finite extension and taking into account the vacuum polarization in its interior.
We prove that the formula giving the exact value of the irrationality exponent of regular continued fractions remains valid for semi-regular continued fractions satisfyiong certain conditions.
We characterize in detail the radial structure of the stellar population properties of 300 galaxies in the nearby universe, observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, from spheroidal to spiral galaxies, ranging in stellar masses from $M_\star \sim 10^9$ to $7 \times 10^{11}$ $M_\odot$. We derive the stellar mass surface density ($\mu_\star$), light-weighted and mass-weighted ages ($\langle {\rm log}\,age\rangle _L$, $\langle {\rm log}\,age\rangle _M$), and mass-weighted metallicity ($\langle {\rm log}\,Z_\star\rangle _M$), applying the spectral synthesis technique. We study the mean trends with galaxy stellar mass, $M_\star$, and morphology (E, S0, Sa, Sb, Sbc, Sc and Sd). We confirm that more massive galaxies are more compact, older, more metal rich, and less reddened by dust. Additionally, we find that these trends are preserved spatially with the radial distance to the nucleus. Deviations from these relations appear correlated with Hubble type: earlier types are more compact, older, and more metal rich for a given M$_\star$, which evidences that quenching is related to morphology, but not driven by mass.
Sketch recognition remains a significant challenge due to the limited training data and the substantial intra-class variance of freehand sketches for the same object. Conventional methods for this task often rely on the availability of the temporal order of sketch strokes, additional cues acquired from different modalities and supervised augmentation of sketch datasets with real images, which also limit the applicability and feasibility of these methods in real scenarios.   In this paper, we propose a novel sketch-specific data augmentation (SSDA) method that leverages the quantity and quality of the sketches automatically. From the aspect of quantity, we introduce a Bezier pivot based deformation (BPD) strategy to enrich the training data. Towards quality improvement, we present a mean stroke reconstruction (MSR) approach to generate a set of novel types of sketches with smaller intra-class variances. Both of these solutions are unrestricted from any multi-source data and temporal cues of sketches. Furthermore, we show that some recent deep convolutional neural network models that are trained on generic classes of real images can be better choices than most of the elaborate architectures that are designed explicitly for sketch recognition. As SSDA can be integrated with any convolutional neural networks, it has a distinct advantage over the existing methods. Our extensive experimental evaluations demonstrate that the proposed method achieves the state-of-the-art results (84.27%) on the TU-Berlin dataset, outperforming the human performance by a remarkable 11.17% increase. Finally, more experiments show the practical value of our approach for the task of sketch-based image retrieval.
A squaregraph is a plane graph in which each internal face is a $4$-cycle and each internal vertex has degree at least 4. This paper proves that every squaregraph is isomorphic to a subgraph of the semi-strong product of an outerplanar graph and a path. We generalise this result for infinite squaregraphs, and show that this is best possible in the sense that "outerplanar graph" cannot be replaced by "forest".
The current induced magnetization reversal in nanoscale spin valves is a potential alternative to magnetic field switching in magnetic memory devices. We show that the critical switching current can be decreased by an order of magnitude by strategically distributing the resistances in the magnetically active region of the spin valve. In addition, we simulate full switching curves and predict a new precessional state.
The study of galaxies has changed dramatically over the past few decades with the advent of large-scale astronomical surveys. These large collaborative efforts have made available high-quality imaging and spectroscopy of hundreds of thousands of systems, providing a body of observations which has significantly enhanced our understanding not only of cosmology and large-scale structure in the universe but also of the astrophysics of galaxy formation and evolution. Throughout these changes, one thing that has remained constant is the role of galaxy morphology as a clue to understanding galaxies. But obtaining morphologies for large numbers of galaxies is challenging; this topic, "Morphology in the era of large surveys", was the subject of a recent discussion meeting at the Royal Astronomical Society, and this "Astronomy and Geophysics" article is a report on that meeting.
Optical emission is detected from filaments around the central galaxies of clusters of galaxies. These filaments have lengths of tens of kiloparsecs. The emission is possibly due to heating caused by the dissipation of mechanical energy and by cosmic ray induced ionisation. CO millimeter and submillimeter line emissions as well as H$_{2}$ infrared emission originating in such filaments surrounding NGC~1275, the central galaxy of the Perseus cluster, have been detected. Our aim is to identify those molecular species, other than CO, that may emit detectable millimeter and submillimeter line features arising in these filaments, and to determine which of those species will produce emissions that might serve as diagnostics of the dissipation and cosmic ray induced ionisation. The time-dependent UCL photon-dominated region modelling code was used in the construction of steady-state models of molecular filamentary emission regions at appropriate pressures, for a range of dissipation and cosmic ray induced ionisation rates and incident radiation fields.HCO$^+$ and C$_2$H emissions will potentially provide information about the cosmic ray induced ionisation rates in the filaments. HCN and, in particular, CN are species with millimeter and submillimeter lines that remain abundant in the warmest regions containing molecules. Detections of the galaxy cluster filaments in HCO$^{+}$, C$_{2}$H, and CN emissions and further detections of them in HCN emissions would provide significant constraints on the dissipation and cosmic ray induced ionisation rates.