ShantanuT01/DACTYL-Pretraining huggingface dataset:
The hard X-ray (HXR) emission in solar flares comes almost exclusively from a very small part of the flaring region, the footpoints of magnetic loops. Using RHESSI observations of solar flare footpoints, we determine the radial positions and sizes of footpoints as a function of energy in six near-limb events to investigate the transport of flare accelerated electrons and the properties of the chromosphere. HXR visibility forward fitting allows to find the positions/heights and the sizes of HXR footpoints along and perpendicular to the magnetic field of the flaring loop at different energies in the HXR range. We show that in half of the analyzed events, a clear trend of decreasing height of the sources with energy is found. Assuming collisional thick-target transport, HXR sources are located between 600 and 1200 km above the photosphere for photon energies between 120 and 25 keV respectively. In the other events, the position as a function of energy is constant within the uncertainties. The vertical sizes (along the path of electron propagation) range from 1.3 to 8 arcseconds which is up to a factor 4 larger than predicted by the thick-target model even in events where the positions/heights of HXR sources are consistent with the collisional thick-target model. Magnetic mirroring, collisional pitch angle scattering and X-ray albedo are discussed as potential explanations of the findings.
A variety of periodic phenomena have been observed in conjunction with large solar jets. We aim to find further evidence for {(quasi-)}periodic behaviour in solar jets and determine what the periodic behaviour can tell us about the excitation mechanism and formation process of the large solar jet. Using the 304 {\AA} (He-II), 171 {\AA} (Fe IX), 193 {\AA} (Fe XII/XXIV) and 131 {\AA} (Fe VIII/XXI) filters on-board the Solar Dynamic Observatory (SDO) Atmospheric Imaging Assembly (AIA), we investigate the intensity oscillations associated with a solar jet. Evidence is provided for multiple magnetic reconnection events occurring between a pre-twisted, closed field and open field lines. Components of the jet are seen in multiple SDO/AIA filters covering a wide range of temperatures, suggesting the jet can be classified as a blowout jet. Two bright, elongated features are observed to be co-spatial with the large jet, appearing at the jet's footpoints. Investigation of these features reveal they are defined by multiple plasma ejections. The ejecta display (quasi-)periodic behaviour on timescales of 50 s and have rise velocities of 40-150 km\,s$^{-1}$ along the open field lines. Due to the suggestion that the large jet is reconnection-driven and the observed properties of the ejecta, we further propose that these ejecta events are similar to type-II spicules. The bright features also display (quasi)-periodic intensity perturbations on the timescale of 300 s. Possible explanations for the existence of the (quasi-)periodic perturbations in terms of jet dynamics and the response of the transition region are discussed.
We report first-principles static and dynamic calculations that clarify the microscopic mechanism of carbon annihilation due to phosphorous treatment upon oxidation of silicon carbide (SiC). We identify the most stable form of the phosphorus (P) in the oxide as the four-fold coordinated with the dangling PO unit and find that the unit attracts carbon ejected from the interface, thus operating as a carbon absorber. This finding provides a microscopic reasoning for the first time for the promotion of the oxidation reaction on one hand and the annihilation of the C-related defects at the interface on the other. Secondary ion mass spectrometry measurements are also performed and the obtained carbon profile corroborates the theoretical finding above.
We report measurements of spin pumping and the inverse spin Hall effect in Ni80Fe20/Uranium bilayers designed to study the efficiency of spin-charge interconversion in a super-heavy element. We employ broad-band ferromagnetic resonance on extended films to inject a spin current from the Ni80Fe20 (permalloy) into the uranium layer, which is then converted into an electric field by the inverse spin Hall effect. Surprisingly, our results suggest a spin mixing conductance of order 2x10 e19 m-2 and a positive spin Hall angle of 0.004, which are both merely comparable to those of several transition metals. These results thus support the idea that the electronic configuration may be at least as important as the atomic number in governing spin pumping across interfaces and subsequent spin Hall effects. In fact, given that both the magnitude and the sign are unexpected based on trends in d-electron systems, materials with unfilled f-electron orbitals may hold additional exploration avenues for spin physics.
We present photometric and polarimetric observations of a new magnetic cataclysmic variable, presumably a polar, USNO-A2.0 0825-18396733. The photometric observations were carried out with the SAO RAS Zeiss-1000 telescope, and the polarimetry was performed with the 6-m BTA telescope. The redefined orbital period P = 0:d08481(2); the brightness of the system varied from 17:5 to 20:0 in the Rc filter. Polarimetric observations of the object in the V filter revealed strong variable circular polarization: -2% to over -31%. This indicates that the variable USNO-A2.0 0825-18396733 is a polar.
In view of the numerous experimental results recently released, we provide in this letter an update on the performance of our simple Regge model for strangeness electroproduction on the nucleon. Without refitting any parameters, a decent description of all measured observables and channels is achieved. We also give predictions for spin transfer observables, recently measured at Jefferson Lab which have high sensitivity to discriminate between different theoretical approaches.
Modern machine learning models for computer vision exceed humans in accuracy on specific visual recognition tasks, notably on datasets like ImageNet. However, high accuracy can be achieved in many ways. The particular decision function found by a machine learning system is determined not only by the data to which the system is exposed, but also the inductive biases of the model, which are typically harder to characterize. In this work, we follow a recent trend of in-depth behavioral analyses of neural network models that go beyond accuracy as an evaluation metric by looking at patterns of errors. Our focus is on comparing a suite of standard Convolutional Neural Networks (CNNs) and a recently-proposed attention-based network, the Vision Transformer (ViT), which relaxes the translation-invariance constraint of CNNs and therefore represents a model with a weaker set of inductive biases. Attention-based networks have previously been shown to achieve higher accuracy than CNNs on vision tasks, and we demonstrate, using new metrics for examining error consistency with more granularity, that their errors are also more consistent with those of humans. These results have implications both for building more human-like vision models, as well as for understanding visual object recognition in humans.
Asymmetric X-ray emission and powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field, including 128 member galaxies (called sample I).A large velocity dispersion in the rest frame suggests a merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ~ 10' NW to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ~ 20 mag. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h=19.0 are newly selected as member candidates. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time scales, older stellar ages, and higher ISM metallicities. For the merging cluster A2319, local surface density is a better environmental indicator rather than the clustercentric distance. Compared with the well-relaxed cluster A2589, a higher fraction of star-forming galaxies is found in A2319, indicating that the galaxy-scale turbulence stimulated by the subcluster merger might have played a role in triggering the star formation activity.
We show how to use quantum mechanics on the group manifold U(N) as a tool for problems in U(N) representation theory. The quantum mechanics reduces to free fermions on the circle, which in the large N limit become relativistic. The theory can be bosonized giving the Das-Jevicki-Sakita collective field theory. The formalism is particularly suited to problems involving tensor product multiplicity (Littlewood-Richardson) coefficients. As examples, we discuss the partition function of two-dimensional Yang-Mills theory on the sphere, and the zero magnetic field limit of D-dimensional Eguchi-Kawai Yang-Mills theory. We give the leading O(N^0) solution of the latter theory, using a method which allows computing corrections. Largely (but not completely) superseded by hep-th/9311130.
Ryser conjectured that $\tau\le(r-1)\nu$ for $r$-partite hypergraphs, where $\tau$ is the covering number and $\nu$ is the matching number. We prove this conjecture for $r\le9$ in the special case of linear intersecting hypergraphs, in other words where every pair of lines meets in exactly one vertex. Aharoni formulated a stronger version of Ryser's conjecture which specified that each $r$-partite hypergraph should have a cover of size $(r-1)\nu$ of a particular form. We provide a counterexample to Aharoni's conjecture with $r=13$ and $\nu=1$. We also report a number of computational results. For $r=7$, we find that there is no linear intersecting hypergraph that achieves the equality $\tau=r-1$ in Ryser's conjecture, although non-linear examples are known. We exhibit intersecting non-linear examples achieving equality for $r\in\{9,13,17\}$. Also, we find that $r=8$ is the smallest value of $r$ for which there exists a linear intersecting $r$-partite hypergraph that achieves $\tau=r-1$ and is not isomorphic to a subhypergraph of a projective plane.
Near- and mid-infrared interferometers have resolved the dusty parsec-scale obscurer (torus) around nearby active galactic nuclei (AGNs). With the arrival of extremely large single-aperture telescopes, the emission morphology will soon be resolvable unambiguously, without modeling directly the underlying brightness distribution probed by interferometers today. Simulations must instead deliver the projected 2D brightness distribution as a result of radiative transfer through a 3D distribution of dusty matter around the AGN. We employ such physically motivated 3D dust distributions in tori around AGNs to compute 2D images of the emergent thermal emission using CLUMPY, a dust radiative transfer code for clumpy media. We demonstrate that CLUMPY models can exhibit morphologies with significant polar elongation in the mid-infrared (i.e. the emission extends perpendicular to the dust distribution) on scales of several parsecs, in line with observations in several nearby AGNs. We characterize the emission and cloud distribution morphologies. The observed emission from near- to mid-infrared wavelengths generally does not trace the bulk of the cloud distribution. The elongation of the emission is sensitive to the torus opening angle or scale height. For cloud distributions with a flat radial profile, polar extended emission is realized only at wavelengths shorter than ~18 micron, and shorter than ~5 micron for steep profiles. We make the full results available through HYPERCAT, a large hypercube of resolved AGN torus brightness maps computed with CLUMPY. HYPERCAT also comprises software to process and analyze such large data cubes and provides tools to simulate observations with various current and future telescopes.
The immediate vicinity of T Tauri was observed with the new high-contrast imaging instrument SPHERE at the VLT to resolve remaining mysteries of the system, such as the putative small edge-on disk around T Tauri Sa, and the assignment of the complex outflow patterns to the individual stars. We used SPHERE IRDIS narrow-band classical imaging in Pa$\beta$, Br$\gamma$, and the $\nu$ = 1-0 S(1) line of H$_2$, as well as in the nearby continua to obtain high spatial resolution and high contrast images over the NIR spectral range. Line maps were created by subtracting the nearby continuum. We also re--analyzed coronagraphic data taken with SPHERE's integral field spectrograph in $J$- and $H$-band with the goal to obtain a precise extinction estimate to T Tauri Sb, and to verify the recently reported claim of another stellar or substellar object in the system. A previously unknown coiling structure is observed southwest of the stars in reflected light, which points to the vicinity of T Tauri N. We map the circumbinary emission from T Tauri S in $J$- and $H$-band scattered light for the first time, showing a morphology which differs significantly from that observed in $K$-band. H$_2$ emission is found southwest of the stars, near the coiling structure. We also detect the H$_2$ emitting region T Tauri NW. The motion of T Tauri NW with respect to T Tauri N and S between previous images and our 2014 data, provides strong evidence that the Southeast-Northwest outflow triggering T Tauri NW is likely to be associated with T Tauri S. We further present accurate relative photometry of the stars, confirming that T Tauri Sa is brightening again. Our analysis rules out the presence of the recently proposed companion to T Tauri N with high confidence.
Fluid states of matter can locally exhibit characteristics of the onset of crystalline order. Traditionally this has been theoretically investigated using multipoint correlation functions. However new measurement techniques now allow multiparticle configurations of cold atomic systems to be observed directly. This has led to a search for new techniques to characterize the configurations that are likely to be observed. One of these techniques is the configuration density (CD), which has been used to argue for the formation of "Pauli crystals" by non-interacting electrons in e.g. a harmonic trap. We show here that such Pauli crystals do not exist, but that other other interesting spatial structures can occur in the form of an "anti-Crystal", where the fermions preferentially avoid a lattice of positions surrounding any given fermion. Further, we show that configuration densities must be treated with great care as naive application can lead to the identification of crystalline structures which are artifacts of the method and of no physical significance. We analyze the failure of the CD and suggest methods that might be more suitable for characterizing multiparticle correlations which may signal the onset of crystalline order. In particular, we introduce neighbour counting statistics (NCS), which is the full counting statistics of the particle number in a neighborhood of a given particle. We test this on two dimensional systems with emerging triangular and square crystal structures.
We study the impact on leptogenesis of Higgs portal couplings to a new scalar singlet. These couplings open up additional $CP$-violating decay channels for the higher mass singlet neutrinos $N_2$ and $N_3$. We analyze the simplest case of two-level $N_1-N_2$ leptogenesis, including significant mass hierarchies, in which the $CP$ asymmetry is generated in part by singlet-mediated decays of $N_2$. For these models, provided the lightest singlet neutrino $N_1$ is sufficiently weakly coupled to avoid excessive washout, its mass scale is not directly constrained by the Davidson-Ibarra bound.
We confirm a prediction that the recently introduced shadow kink defect in the theory of light-matter interaction in nematic liquid crystals is described to main order by a solution of the Painlev\'e-II equation which changes sign once in the whole real line. Our result implies that such a solution of the latter equation is energy minimizing with respect to compactly supported perturbations.
We present a numerical estimate of the $\gamma^* \gamma^*$ total cross section at the designed 500 GeV $e^+e^-$ Linear Collider, based upon the BFKL Pomeron. We find that the event rate is substantial provided electrons scattered under small angles can be detected, and a measurement of this cross section provides an excellent test of the BFKL Pomeron.
We present three dimensional spectroscopy of eleven E+A galaxies, selected for their strong H-delta absorption but weak (or non-existent) [OII]3727 and H-alpha emission. This selection suggests that a recent burst of star-formation was triggered but subsequently abruptly ended. We probe the spatial and spectral properties of both the young (~1Gyr) and old (few Gyr) stellar populations. Using the H-delta equivalent widths we estimate that the burst masses must have been at least 10% by mass (Mburst~10^10Mo), which is also consistent with the star-formation history inferred from the broad-band SEDs. On average the A-stars cover ~33% of the galaxy image, extending over 2-15kpc^2, indicating that the characteristic E+A signature is a property of the galaxy as a whole and not due to a heterogeneous mixture of populations. In approximately half of the sample, we find that the A-stars, nebular emission, and continuum emission are not co-located, suggesting that the newest stars are forming in a different place than those that formed ~1Gyr ago, and that recent star-formation has occurred in regions distinct from the oldest stellar populations. At least ten of the galaxies (91%) have dynamics that class them as "fast rotators" with magnitudes and dynamics comparable to local ellipticals and S0's. We also find a correlation between the spatial extent of the A-stars and dynamics such that the fastest rotators tend to have the most compact A-star populations, providing new constraints on models that aim to explain the transformation of later type galaxies into early types. Finally, we show that there are no obvious differences between the line extents and kinematics of E+A galaxies detected in the radio (AGN) compared to non-radio sources, suggesting that AGN feedback does not play a dramatic role in defining their properties, or that its effects are short.
Realization of wafer-scale single-crystal films of transition metal dichalcogenides (TMDs) such as tungsten sulfide requires epitaxial growth and coalescence of oriented domains to form a continuous monolayer. The domains must be oriented in the same crystallographic direction on the substrate to avoid the formation of metallic inversion domain boundaries (IDBs) which are a common feature of layered chalcogenides. Here we demonstrate fully-coalesced single orientation tungsten sulfide monolayers on 2-inch diameter c-plane sapphire by metalorganic chemical vapor deposition using a multi-step growth process. High growth temperatures and sulfur/metal ratios were required to reduce domain misorientation and achieve epitaxial tungsten sulfide monolayers with low in-plane rotational twist (0.09 deg). Transmission electron microscopy analysis reveals that the tungsten sulfide monolayers lack IDBs but instead have translational boundaries that arise when tungsten sulfide domains with slightly off-set lattices merge together. By adjusting the monolayer growth rate, the density of translational boundaries and bilayer coverage were significantly reduced. The preferred orientation of domains is attributed to the presence of steps on the sapphire surface coupled with growth conditions promote surface diffusion and oriented attachment. The transferred tungsten sulfide monolayers show neutral and charged exciton emission at 80K with negligible defect-related luminescence. Back-gated tungsten sulfide field effect transistors exhibited mobility of 16 cm2/Vs. The results demonstrate the potential of achieving wafer-scale TMD monolayers free of inversion domains with properties approaching that of exfoliated flakes.
Segmentation of medical images using seeded region growing technique is increasingly becoming a popular method because of its ability to involve high-level knowledge of anatomical structures in seed selection process. Region based segmentation of medical images are widely used in varied clinical applications like visualization, bone detection, tumor detection and unsupervised image retrieval in clinical databases. As medical images are mostly fuzzy in nature, segmenting regions based intensity is the most challenging task. In this paper, we discuss about popular seeded region grow methodology used for segmenting anatomical structures in CT Angiography images. We have proposed a gradient based homogeneity criteria to control the region grow process while segmenting CTA images.
We report the first-ever discovery of a Wolf-Rayet (WR) star in the Large Magellanic Cloud via detection of a circular shell with the Spitzer Space Telescope. Follow-up observations with Gemini-South resolved the central star of the shell into two components separated from each other by approx 2 arcsec (or approx 0.5 pc in projection). One of these components turns out to be a WN3 star with H and He lines both in emission and absorption (we named it BAT99 3a using the numbering system based on extending the Breysacher et al. catalogue). Spectroscopy of the second component showed that it is a B0 V star. Subsequent spectroscopic observations of BAT99 3a with the du Pont 2.5-m telescope and the Southern African Large Telescope revealed that it is a close, eccentric binary system, and that the absorption lines are associated with an O companion star. We analyzed the spectrum of the binary system using the non-LTE Potsdam Wolf-Rayet (PoWR) code, confirming that the WR component is a very hot (approx 90 kK) WN star. For this star, we derived a luminosity of log L/Lsun =5.45 and a mass-loss rate of 10^{-5.8} Msun/yr, and found that the stellar wind composition is dominated by helium with 20 per cent of hydrogen. Spectroscopy of the shell revealed an He iii region centred on BAT99 3a and having the same angular radius (approx 15 arcsec) as the shell. We thereby add a new example to a rare class of high-excitation nebulae photoionized by WR stars. Analysis of the nebular spectrum showed that the shell is composed of unprocessed material, implying that the shell was swept-up from the local interstellar medium. We discuss the physical relationship between the newly identified massive stars and their possible membership of a previously unrecognized star cluster.