ShantanuT01/DACTYL-Pretraining huggingface dataset:
We perform nonlinear MHD simulations to study the propagation of magnetoacoustic waves from the photosphere to the low corona. We focus on a 2D system with a gravitationally stratified atmosphere and three photospheric concentrations of magnetic flux that give rise to a magnetic null point with a magnetic dome topology. We find that a single wavepacket introduced at the lower boundary splits into multiple secondary wavepackets. A portion of the packet refracts towards the null due to the varying Alfv\'en speed. Waves incident on the equipartition contour surrounding the null, where the sound and Alfv\'en speeds coincide, partially transmit, reflect, and mode convert between branches of the local dispersion relation. Approximately $15.5\%$ of the wavepacket's initial energy ($E_{input}$) converges on the null, mostly as a fast magnetoacoustic wave. Conversion is very efficient: $70\%$ of the energy incident on the null is converted to slow modes propagating away from the null, $7\%$ leaves as a fast wave, and the remaining $23\%$ (0.036$E_{input}$) is locally dissipated. The acoustic energy leaving the null is strongly concentrated along field lines near each of the null's four separatrices. The portion of the wavepacket that refracts towards the null, and the amount of current accumulation, depends on the vertical and horizontal wavenumbers and the centroid position of the wavepacket as it crosses the photosphere. Regions that refract towards or away from the null do not simply coincide with regions of open versus closed magnetic field or the local field orientation. We also modeled wavepacket propagation using a WKB method and found that it agrees qualitatively, though not quantitatively, with the results of the numerical simulation.
The existence of the spectral break around $\sim 3 \times 10^{15}$ eV in the cosmic ray spectrum (referred to as the `knee') is one of the biggest questions in cosmic ray astrophysics. At the same time, the origin of cosmic rays above the knee energies (between 10$^{15}$ and 10$^{18}$ eV) is also still unsettled. In this paper, we investigate how the hypothetical extragalactic CRs after modulated by the galactic wind contribute to the knee in the CR spectrum. We numerically calculate the modulated energy spectrum of the hypothetical cosmic rays coming into the galaxy from just outside of the ``galactic sphere'' where the galactic wind terminates. We show that the observed knee structure is reproduced well by a superposition of the modulated component and the galactic cosmic rays originating in supernova remnants.
The frequency of planets in binaries is an important issue in the field of extrasolar planet studies, because of its relevance in estimating of the global planet population of our Galaxy and the clues it can give to our understanding of planet formation and evolution. However, only preliminary estimates are available in the literature. We analyze and compare the frequency of planets in multiple systems to the frequency of planets orbiting single stars. We also try to highlight possible connections between the frequency of planets and the orbital parameters of the binaries (such as the periastron and mass ratio.) A literature search was performed for binaries and multiple systems among the stars of the sample with uniform planet detectability defined by Fischer & Valenti (2005), and 202 of the 850 stars of the sample turned out to be binaries, allowing a statistical comparison of the frequency of planets in binaries and single stars and a study of the run of the planet frequency as a function of the binary separation. We found that the global frequency of planets in the binaries of the sample is not statistically different from that of planets in single stars. Even conservatively taking the probable incompleteness of binary detection in our sample into account, we estimate that the frequency of planets in binaries can be no more than a factor of three lower than that of planets in single stars. There is no significant dependence of planet frequency on the binary separation, except for a lower value of frequency for close binaries. However, this is probably not as low as required to explain the presence of planets in close binaries only as the result of modifications of the binary orbit after the planet formation.
Rauzy-type dynamics are group actions on a collection of combinatorial objects. The first and best known example (the Rauzy dynamics) concerns an action on permutations, associated to interval exchange transformations (IET) for the Poincar\'e map on compact orientable translation surfaces. The equivalence classes on the objects induced by the group action have been classified by Kontsevich and Zorich in [KZ03] and correspond bijectively to the connected components of the strata of the moduli space of abelian differentials.   In a paper [Boi14] Boissy proposed a Rauzy-type dynamics that acts on a subset of the permutations (the standard permutations) and conjectured that the Rauzy classes of this dynamics are exactly the Rauzy classes of the Rauzy dynamics restricted to standard permutations. In this paper, we apply the labelling method introduced in [D18] to classify this dynamics thus proving Boissy's conjecture.   Finally, this paper conclude our serie of three papers on the study of the Rauzy dynamics by presenting two new results on the Rauzy classes: An quadratic algorithm for outputting a path between two connected permutations and a tight $\Theta(n)$ bound on the diameter of the Rauzy classes for the alternating distance.
We present results from two-dimensional, general relativistic, viscous, radiation hydrodynamic numerical simulations of Shakura-Sunyaev thin disks accreting onto stellar mass Schwarzschild black holes. We consider cases on both the gas- and radiation-pressure-dominated branches of the thermal equilibrium curve, with mass accretion rates spanning the range from $\dot{M} = 0.01 L_\mathrm{Edd}/c^2$ to $10 L_\mathrm{Edd}/c^2$. The simulations directly test the stability of this standard disk model on the different branches. We find clear evidence of thermal instability for all radiation-pressure-dominated disks, resulting universally in the vertical collapse of the disks, which in some cases then settle onto the stable, gas-pressure-dominated branch. Although these results are consistent with decades-old theoretical predictions, they appear to be in conflict with available observational data from black hole X-ray binaries. We also find evidence for a radiation-pressure-driven instability that breaks the unstable disks up into alternating rings of high and low surface density on a timescale comparable to the thermal collapse. Since radiation is included self-consistently in the simulations, we are able to calculate lightcurves and power density spectra (PDS). For the most part, we measure radiative efficiencies (ratio of luminosity to mass accretion rate) close to 6%, as expected for a non-rotating black hole. The PDS appear as broken power laws, with a break typically around 100 Hz. There is no evidence of significant excess power at any frequencies, i.e. no quasi-periodic oscillations are observed.
We revisited the short period Type II Cepheids (T2Cs), called the BL Herculis (BLHs), in the Galactic Field to derive a homogeneous analysis of their Fourier parameters. Only V-band data were compiled to make sure that it was directly comparable between the known variables of the OGLE-III catalogue and the 59 individual objects classified as short period Type II Cepheids in the General Catalogue of Variable Stars (GCVS) we had in our sample. The derived Fourier parameters were used to make the distinction between different classes of variables. From the 59 stars we found 19 BLHs, 19 fundamental mode Anomalous Cepheids (ACs) (8 of them were already known from the Catalina Sky Survey (CSS)), 1 first overtone AC, 2 were found to be possible peculiar W Virginis (pWVir), 11 classical Cepheids (DCEPs), and 7 stars were not pulsating variables at all. As a result we created a list of bright BLH stars in the Galactic Field, and separated the ACs, as well as other objects that were misclassified. The number of true BLHs decreased in our sample by more than 50%. We gathered the metallicity from spectroscopic measurements published in the literature. While the number of actual measurements is low, it is highly suggestive that ACs are metal poor. The mean metallicity from 8 measurements in 4 stars (UY Eri having 5 different [Fe/H] data points) is -1.12 dex, but if the higher value metallicity outliers of UY Eri are left out the mean metallicity becomes -1.88 dex, regardless if the AC is in the Milky Way itself or in a cluster. On the other hand, BLHs seem to have a Solar-like metallicity of 0 dex averaged from 21 measurements of 10 stars.
In this paper, we generalize image (texture) statistical descriptors and propose algorithms that improve their efficacy. Recently, a new method showed how the popular Co-Occurrence Matrix (COM) can be modified into a fuzzy version (FCOM) which is more effective and robust to noise. Here, we introduce new fuzzy versions of two additional higher order statistical matrices: the Run Length Matrix (RLM) and the Size Zone Matrix (SZM). We define the fuzzy zones and propose an efficient algorithm to compute the descriptors. We demonstrate the advantage of the proposed improvements over several state-of-the-art methods on three tasks from quantitative cell biology: analyzing and classifying Human Epithelial type 2 (HEp-2) cells using Indirect Immunofluorescence protocol (IFF).
We discuss a little-studied class of weak decay modes sensitive to only one quark topology at leading order in G_F: M --> m gamma, where M,m are mesons with completely distinct flavor quantum numbers. Specifically, they proceed via the annihilation of the valence quarks through a W and the emission of a single hard photon, and thus provide a clear separation between CKM and strong interaction physics. We survey relevant calculations performed to date, discuss experimental discovery potential, and indicate interesting future directions.
Decay of Rabi oscillations of equivalent spins diluted in diamagnetic solid matrix and coupled by magnetic dipole interactions is studied. It is shown that these interactions result in random shifts of spin transient nutation frequencies and thus lead to the decay of the transient signal. Averaging over random spatial distribution of spins within the solid and over their spectral positions within magnetic resonance line, we obtain analytical expressions for the decay of Rabi oscillations. The rate of the decay in the case when the half-width of magnetic resonance line exceeds Rabi frequency is found to depend on the intensity of resonant microwave field and on the spin concentration. The results are compared with the literature data for E1' centers in glassy silica and [AlO4] centers in quartz.
We observe remarkably strong room temperature ferromagnetism (~1.5 Bohr Magneton/Mn) in optically transparent Mn(II)-doped indium tin oxide (ITO) films. The nanocrystalline films with average grain size 10-22 nm and thickness 150-350 nm are prepared by sol-gel coating technique on sodalime silica glass substrate. The ferromagnetic property is, of course, weak for films deposited on pure silica glass substrate. The structural parameters of the films appear to be governing the magnetic property strongly which vary appreciably depending on the substrate. The observation of room temperature ferromagnetism in transparent conducting ITO films may find a plethora of applications in the area of magneto-optics.
We present new spectroscopic identifications of 12 X-shaped radio galaxies and use the spectral data to derive starburst histories and masses of the nuclear supermassive black holes in these galaxies. The observations were done with the 2.1-m telescope of the Observatorio Astron\'omico Nacional at San Pedro M\'artir, M\'exico. The new spectroscopic results extend the sample of X-shaped radio galaxies studied with optical spectroscopy. We show that the combined sample of the X-shaped radio galaxies has statistically higher black-hole masses and older episodes of star formation than a control sample of canonical double-lobed radio sources with similar redshifts and luminosities. The data reveal enhanced star-formation activity in the X-shaped sample on the timescales expected in galactic mergers. We discuss the results obtained in the framework of the merger scenario.
Nanotubular materials inspired by crystalline diborides such as AlB_2 are proposed. The atomic structure, in particular the basic chemical question of where to put Al atoms in order to stabilize nanotubular Al-B systems, is investigated using density-functional calculations for prototype systems. The optimized tubular prototypes are found to be competitive in energy with their bulk crystalline counterparts. All of the tubular Al-B systems investigated are calculated to be metallic.
For the calculation of the partition function $\mathcal{Z}$ of small, isolated and interacting many body systems an improvement with respect to previous formulations is presented. By including anharmonicities and employing a variational approach quantum effects can be treated even at very low temperatures. In order to test its accuracy the novel approach is applied to the exactly solvable Lipkin-Meshkov-Glick model (LMGM). For thermodynamic properties and level densities good agreement with the exact calculations is found.
We show analytically that the collapse and revival in the population dynamics of the atom-cavity coupled system under the rotating wave approximation (RWA), valid only at very weak coupling, is an artifact as the atom-cavity coupling is increased. Even the first-order correction to the RWA is able to bring about the absence of the collapse in the dynamics of atomic population inversion thanks to intrinsic oscillations resulting from the transitions between two levels with the same atomic quantum number. The removal of the collapse is valid for a wide range of coupling strengths which are accessible to current experimental setups. In addition, based on our analytical results that greatly improve upon the conventional RWA, even the strong-coupling power spectrum can now be explained with the help of the numerically exact energy levels.
This paper is an extended version of math.OA/0601528 where we point out and remedy a gap in the proof by P. Julg and G. Kasparov of the Baum-Connes conjecture for discrete subgroups of SU(n,1). In particular, here we explain in details why the non-microlocality of the Heisenberg calculus prevents us from implementing into this framework the classical approach of Seeley to pseudodifferential complex powers, which was the main issue at stake in math.OA/0601528.
We present constraints on the progenitor metallicities of core-collapse supernovae. To date, nearly all metallicity constraints have been inferred from indirect methods such as metallicity gradients in host galaxies, luminosities of host galaxies, or derived global galaxy metallicities. Here, progenitor metallicities are derived from optical spectra taken at the sites of nearby supernovae, from the ratio of strong emission lines found in their host HII regions.We present results from the spectra of 74 host HII regions and discuss the implications that these have on the nature of core-collapse supernova progenitors. Overall, while we find that the mean metallicity of type Ibc environments is higher than that of type II events, this difference is smaller than observed in previous studies. There is only a 0.06 dex difference in the mean metallicity values, at a statistical significance of ~1.5 sigma, while using a KS-test we find that the two metallicity distributions are marginally consistent with being drawn from the same parent population (probability >10%). This argues that progenitor metallicity is not a dominant parameter in deciding supernovae type, with progenitor mass and/or binarity playing a much more significant role.
We analyze the conditions that enable acceleration of particles to ultra-high energies, ~10^{20} eV (UHECRs). We show that broad band photon data recently provided by WMAP, ISOCAM, Swift and Fermi satellites, yield constraints on the ability of active galactic nuclei (AGN) to produce UHECRs. The high energy (MeV - GeV) photons are produced by Compton scattering of the emitted low energy photons and the cosmic microwave background or extra-galactic background light. The ratio of the luminosities at high and low photon energies can therefore be used as a probe of the physical conditions in the acceleration site. We find that existing data excludes core regions of nearby radio-loud AGN as possible acceleration sites of UHECR protons. However, we show that giant radio lobes are not excluded. We apply our method to Cen A, and show that acceleration of protons to ~10^{20} eV can only occur at distances >~ 100 kpc from the core.
Starting with the Green's functions found for normal diffusion, we construct exact time-dependent Green's functions for subdiffusive equation (with fractional time derivatives), with the boundary conditions involving a linear combination of fluxes and concentrations. The method is particularly useful to calculate the concentration profiles in a multi-part system where different kind of transport occurs in each part of it. As an example, we find the solutions of subdiffusive equation for the system composed from two parts with normal diffusion and subdiffusion, respectively.
Einstein's field equations are solved exactly for static charged dust distributions. These solutions generalize the Majumdar Papapetrou metrics. Maxwell's equations lead to the equality of charge and mass densities of the dust distribution. Einstein's equatins reduce to a nonlinear version of Poisson's equation.
In this study, we have found a new random ordered phase in isotropic models with many-body interactions. Spin correlations between neighboring planes are rigorously shown to form a long-range order, namely coplanar order, using a unitary transformation, and the phase transition of this new order has been analyzed on the bases of the mean-field theory and correlation identities. In the systems with regular 4-body interactions, the transition temperature $T_{\text{c}}$ is obtained as $T_{\text{c}}=(z-2)J/k_{\text{B}}$, and the field conjugate to this new order parameter is found to be $H^2$. In contrast, the corresponding physical quantities in the systems with random 4-body interactions are given by $T_{\text{c}}=\sqrt{z-2}J/k_{\text{B}}$ and $H^4$, respectively. Scaling forms of order parameters for regular or random 4-body interactions are expressed by the same scaling functions in the systems with regular or random 2-body interactions, respectively. Furthermore, we have obtained the nonlinear susceptibilities in the regular and random systems, where the coefficient $\chi_{\text{nl}}$ of $H^3$ in the magnetization shows positive divergence in the regular model, while the coefficient $\chi_{7}$ of $H^7$ in the magnetization shows negative divergence in the random model.
We prove that random-cluster models with q larger than 1 on a variety of planar lattices have a sharp phase transition, that is that there exists some parameter p_c below which the model exhibits exponential decay and above which there exists a.s. an infinite cluster. The result may be extended to the Potts model via the Edwards-Sokal coupling.   Our method is based on sharp threshold techniques and certain symmetries of the lattice; in particular it makes no use of self-duality. Part of the argument is not restricted to planar models and may be of some interest for the understanding of random-cluster and Potts models in higher dimensions.   Due to its nature, this strategy could be useful in studying other planar models satisfying the FKG lattice condition and some additional differential inequalities.
During the COVID-19 coronavirus epidemic, almost everyone wears a facial mask, which poses a huge challenge to deep face recognition. In this workshop, we organize Masked Face Recognition (MFR) challenge and focus on bench-marking deep face recognition methods under the existence of facial masks. In the MFR challenge, there are two main tracks: the InsightFace track and the WebFace260M track. For the InsightFace track, we manually collect a large-scale masked face test set with 7K identities. In addition, we also collect a children test set including 14K identities and a multi-racial test set containing 242K identities. By using these three test sets, we build up an online model testing system, which can give a comprehensive evaluation of face recognition models. To avoid data privacy problems, no test image is released to the public. As the challenge is still under-going, we will keep on updating the top-ranked solutions as well as this report on the arxiv.
In this paper we provide explicitly the connection between the hypoelliptic heat kernel for some 3-step sub-Riemannian manifolds and the quartic oscillator. We study the left-invariant sub-Riemannian structure on two nilpotent Lie groups, namely the (2,3,4) group (called the Engel group) and the (2,3,5) group (called the Cartan group or the generalized Dido problem). Our main technique is noncommutative Fourier analysis that permits to transform the hypoelliptic heat equation in a one dimensional heat equation with a quartic potential.
We investigate the maximum caliber variational principle as an inference algorithm used to predict dynamical properties of complex nonequilibrium, stationary, statistical systems in the presence of incomplete information. Specifically, we maximize the path entropy over discrete time step trajectories subject to normalization, stationarity, and detailed balance constraints together with a path-dependent dynamical information constraint reflecting a given average global behavior of the complex system. A general expression for the transition probability values associated with the stationary random Markov processes describing the nonequilibrium stationary system is computed. By virtue of our analysis, we uncover that a convenient choice of the dynamical information constraint together with a perturbative asymptotic expansion with respect to its corresponding Lagrange multiplier of the general expression for the transition probability leads to a formal overlap with the well-known Glauber hyperbolic tangent rule for the transition probability for the stochastic Ising model in the limit of very high temperatures of the heat reservoir.
Characterizing sets of permutations whose associated quasisymmetric function is symmetric and Schur-positive is a long-standing problem in algebraic combinatorics. In this paper we present a general method to construct Schur-positive sets and multisets, based on geometric grid classes and the product operation. Our approach produces many new instances of Schur-positive sets, and provides a broad framework that explains the existence of known such sets that until now were sporadic cases.