ShantanuT01/DACTYL-Pretraining huggingface dataset:
Resonant soft x-ray Bragg diffraction at the Tb M4,5 edges and non resonant Bragg diffraction have been used to investigate orbitals in TbB2C2. The Tb 4f quadrupole moments are ordered in zero field below T_N and show a ferroquadrupolar alignment dictated by the antiferromagnetic order. With increasing applied field along [110] the Tb 4f magnetic dipole moments rotate in a gradual manner toward the field. The quadrupole moment is rigidly coupled to the magnetic moment and follows this field-induced rotation. The quadrupolar pair interaction is found to depend on the specific orientation of the orbitals as predicted theoretically and can be manipulated with an applied magnetic field.
Aims and Methods: We present the results of VLBI observations of nineteen GHz-Peaked-Spectrum (GPS) radio sources at 1.6 GHz. Of them, 15 sources are selected from the Parkes Half Jansky (PHJ) sample (Snellen 2002), 4 others are from our previous observation list. We aimed at imaging the structure of GPS sources, searching for Compact Symmetric Objects (CSOs) and studying the absorption for the convex radio spectra of GPS sources.   Results: We obtained total intensity 1.6 GHz VLBI images of 17 sources for the first time. Of them, 80% show mini-double-lobe radio structure, indicating that they are CSOs or candidates, and their host AGNs could be edge-on to us. This result suggests that there is a high incidence of mini double-lobe sources (or CSOs) in the PHJ sample. The sources J0323+0534, J1135-0021, J1352+0232, J2058+0540, J2123-0112 and J2325-0344 with measured redshift, showing double-lobe structure with sizes of <1 kpc, are classified as CSOs. Three sources J1057+0012, J1600-0037 and J1753+2750 are considered as core-jet sources according to their morphologies and flux variability.
We present observations from the Small Array of the Arcminute Microkelvin Imager (AMI) of eight high X-ray luminosity galaxy cluster systems selected from the Local Cluster Substructure Survey (LoCuSS) sample.We detect the Sunyaev-Zel'dovich (SZ) effect in seven of these clusters. With the assumptions that galaxy clusters are isothermal, have a density profile described by a spherical b -model and obey the theoretical M-T relation, we are able to derive cluster parameters at r200 from our SZ data. With the additional assumption of hydrostatic equilibrium we are able to derive parameters at r500. We present posterior probability distributions for cluster parameters such as mass, radius and temperature (TSZ, MT). Combining our sample with that of AMI Consortium: Rodr'\iguez-Gonz\'alvez et al. (2011) and using large-radius X-ray temperature estimates (TX) from Chandra and Suzaku observations, we find that there is reasonable correspondence between TX and TSZ,MT values at low TX, but that for clusters with TX above around 6keV the correspondence breaks down with TX exceeding TSZ, MT; we stress that this finding is based on just ten clusters.
We follow the galaxy stellar mass assembly by morphological and spectral type in the COSMOS 2-deg^2 field. We derive the stellar mass functions and stellar mass densities from z=2 to z=0.2 using 196,000 galaxies selected at F(3.6 micron) > 1 microJy with accurate photometric redshifts (sigma_((zp-zs)/(1+zs))=0.008 at i<22.5). Using a spectral classification, we find that z~1 is an epoch of transition in the stellar mass assembly of quiescent galaxies. Their stellar mass density increases by 1.1 dex between z=1.5-2 and z=0.8-1 (Delta t ~2.5 Gyr), but only by 0.3 dex between z=0.8-1 and z~0.1 (Delta t ~ 6 Gyr). Then, we add the morphological information and find that 80-90% of the massive quiescent galaxies (log(M)~11) have an elliptical morphology at z<0.8. Therefore, a dominant mechanism links the shutdown of star formation and the acquisition of an elliptical morphology in massive galaxies. Still, a significant fraction of quiescent galaxies present a Spi/Irr morphology at low mass (40-60% at log(M)~9.5), but this fraction is smaller than predicted by semi-analytical models using a ``halo quenching'' recipe. We also analyze the evolution of star-forming galaxies and split them into ``intermediate activity'' and ``high activity'' galaxies. We find that the most massive ``high activity'' galaxies end their high star formation rate phase first. Finally, the space density of massive star-forming galaxies becomes lower than the space density of massive elliptical galaxies at z<1. As a consequence, the rate of ``wet mergers'' involved in the formation of the most massive ellipticals must decline very rapidly at z<1, which could explain the observed slow down in the assembly of these quiescent and massive sources.
Using density functional theory (DFT)-based calculations, we propose a family of metastable, as-yet unmade V5+ and Cr6+ double perovskite compounds with low band gaps spanning much of the visible region of the solar spectrum. Through analysis of a related set of measured optical gaps of d0 ABO3 perovskites and A2B'BO6 double perovskites, an ad hoc procedure is developed to correct DFT and many-body perturbation theory gaps, bringing them into quantitative agreement with experiment for measured compounds, and predicting that V5+ and Cr6+ double perovskites would have gaps ranging from approximately 1.1-2.4 eV, significantly lower than previous materials studied in this class. DFT calculations also establish that these V5+ and Cr6+ compounds are likely able to be synthesized, either in bulk form or as epitaxial thin films. These compounds would comprise a new class of semiconducting double perovskites for potential use in solar energy conversion and other optoelectronic applications.
In the literature, most existing graph-based semi-supervised learning (SSL) methods only use the label information of observed samples in the label propagation stage, while ignoring such valuable information when learning the graph. In this paper, we argue that it is beneficial to consider the label information in the graph learning stage. Specifically, by enforcing the weight of edges between labeled samples of different classes to be zero, we explicitly incorporate the label information into the state-of-the-art graph learning methods, such as the Low-Rank Representation (LRR), and propose a novel semi-supervised graph learning method called Semi-Supervised Low-Rank Representation (SSLRR). This results in a convex optimization problem with linear constraints, which can be solved by the linearized alternating direction method. Though we take LRR as an example, our proposed method is in fact very general and can be applied to any self-representation graph learning methods. Experiment results on both synthetic and real datasets demonstrate that the proposed graph learning method can better capture the global geometric structure of the data, and therefore is more effective for semi-supervised learning tasks.
Pulsar spin frequencies and their time evolution are an important source of information on compact stars and their internal composition. Oscillations of the star can reduce the rotational energy via the emission of gravitational waves. In particular unstable oscillation modes, like r-modes, are relevant since their amplitude becomes large and can lead to a fast spin-down of young stars if they are saturated by a non-linear saturation mechanism. We present a novel mechanism based on the pronounced large-amplitude enhancement of the bulk viscosity of dense matter. We show that the enhanced damping due to non-linear bulk viscosity can saturate r-modes of neutron stars at amplitudes appropriate for an efficient spin-down.
The velocity anisotropy of particles inside dark matter (DM) haloes is an important physical quantity, which is required for the accurate modelling of mass profiles of galaxies and clusters of galaxies. It is typically measured using the ratio of the radial-to-tangential velocity dispersions at a given distance from the halo centre. However, this measure is insufficient to describe the dynamics of realistic haloes, which are typically quite elongated. Studying the velocity distribution in massive DM haloes in cosmological simulations, we find that in the inner parts of the haloes the local velocity ellipsoids are strongly aligned with the major axis of the halo, the alignment being stronger for more relaxed haloes. In the outer regions of the haloes, the alignment becomes gradually weaker and the orientation is more random. These two distinct regions of different degree of the alignment coincide with two characteristic regimes of the DM density profile: shallower and steeper than \rho r^{-2}. This alignment of the local velocity ellipsoids requires reinterpretation of features found in measurements based on the spherically averaged ratio of the radial-to-tangential velocity dispersions. In particular, we show that the velocity distribution in the central halo regions is highly anisotropic. For cluster-size haloes with mass 10^{14}-10^{15} h^-1 Msun, the velocity anisotropy along the major axis is nearly independent of radius and is equal to \beta=1-\sigma^2_{perp}/\sigma^2_{radial}=0.4, which is significantly larger than the previously estimated spherically averaged velocity anisotropy. The alignment of density and velocity anisotropies, and the radial trends may also have some implications for the mass modelling based on kinematical data of such objects as galaxy clusters or dwarf spheroidals, where the orbital anisotropy is a key element in an unbiased mass inference.
H2CO is one of the most readily detected organic molecules in protoplanetary disks. Yet its distribution and dominant formation pathway(s) remain largely unconstrained. To address these issues, we present ALMA observations of two H2CO lines (3_{12}-2_{11} and 5_{15}-4_{14}) at 0".5 (~30 au) spatial resolution toward the disk around the nearby T Tauri star TW Hya. Emission from both lines is spatially resolved, showing a central depression, a peak at 0".4 radius, and a radial decline at larger radii with a bump at ~1", near the millimeter continuum edge. We adopt a physical model for the disk and use toy models to explore the radial and vertical H2CO abundance structure. We find that the observed emission implies the presence of at least two distinct H2CO gas reservoirs: (1) a warm and unresolved inner component (<10 au), and (2) an outer component that extends from ~15 au to beyond the millimeter continuum edge. The outer component is further constrained by the line ratio to arise in a more elevated disk layer at larger radii. The inferred H2CO abundance structure agrees well with disk chemistry models, which predict efficient H2CO gas-phase formation close to the star, and cold H2CO grain surface formation, through H additions to condensed CO, followed by non-thermal desorption in the outer disk. The implied presence of active grain surface chemistry in the TW Hya disk is consistent with the recent detection of CH3OH emission, and suggests that more complex organic molecules are formed in disks, as well.
Classically, the projective duality between joins of varieties and the intersections of varieties only holds in good cases. In this paper, we show that categorically, the duality between joins and intersections holds in the framework of homological projective duality (HPD) [K07], as long as the intersections have expected dimensions. This result together with its various applications provide further evidences for the proposal of homological projective geometry of Kuznetsov and Perry [KP18]. When the varieties are inside disjoint linear subspaces, our approach also provides a new proof of the main result "formation of categorical joins commutes with HPD" of [KP18]. We also introduce the concept of an $n$-HPD category, and study its properties and connections with joins and HPDs.
We study diffusive shock acceleration (DSA) of electrons in non-relativistic quasi-perpendicular shocks using self-consistent one-dimensional particle-in-cell (PIC) simulations. By exploring the parameter space of sonic and Alfv\'{e}nic Mach numbers we find that high Mach number quasi-perpendicular shocks can efficiently accelerate electrons to power-law downstream spectra with slopes consistent with DSA prediction. Electrons are reflected by magnetic mirroring at the shock and drive non-resonant waves in the upstream. Reflected electrons are trapped between the shock front and upstream waves and undergo multiple cycles of shock drift acceleration before the injection into DSA. Strong current-driven waves also temporarily change the shock obliquity and cause mild proton pre-acceleration even in quasi-perpendicular shocks, which otherwise do not accelerate protons. These results can be used to understand nonthermal emission in supernova remnants and intracluster medium in galaxy clusters.
A sequence of nonnegative integers $\pi =(d_1,d_2,...,d_n)$ is graphic if there is a (simple) graph $G$ of order $n$ having degree sequence $\pi$. In this case, $G$ is said to realize or be a realization of $\pi$. Given a graph $H$, a graphic sequence $\pi$ is potentially $H$-graphic if there is some realization of $\pi$ that contains $H$ as a subgraph.   In this paper, we consider a degree sequence analogue to classical graph Ramsey numbers. For graphs $H_1$ and $H_2$, the potential-Ramsey number $r_{pot}(H_1,H_2)$ is the minimum integer $N$ such that for any $N$-term graphic sequence $\pi$, either $\pi$ is potentially $H_1$-graphic or the complementary sequence $\overline{\pi}=(N-1-d_N,\dots, N-1-d_1)$ is potentially $H_2$-graphic.   We prove that if $s\ge 2$ is an integer and $T_t$ is a tree of order $t> 7(s-2)$, then $$r_{pot}(K_s, T_t) = t+s-2.$$ This result, which is best possible up to the bound on $t$, is a degree sequence analogue to a classical 1977 result of Chv\'{a}tal on the graph Ramsey number of trees vs. cliques. To obtain this theorem, we prove a sharp condition that ensures an arbitrary graph packs with a forest, which is likely to be of independent interest.
Higher-dimensional Dedekind sums are defined as a generalization of a recent 1-dimensional probability model of Dilcher and Girstmair to a d-dimensional cube. The analysis of the frequency distribution of marked lattice points leads to new formulae in certain special cases, and to new bounds for the classical Dedekind sums. Upper bounds for the generalized Dedekind sums are defined in terms of 1-dimensional moments. In the classical two-dimensional case, the ratio of these sums to their upper bounds are cosines of angles between certain vectors of n-dimensional cones, conjectured to have a largest spacial angle of pi/6.
It was recently proposed that the stress state of a material can also be altered via electron or hole doping, a concept termed electronic stress (ES), which is different from the traditional mechanical stress (MS) due to lattice contraction or expansion. Here we demonstrate the equivalence of ES and MS in structural stabilization, using In wires on Si(111) as a prototypical example. Our systematic density-functional theory calculations reveal that, first, for the same degrees of carrier doping into the In wires, the ES of the high-temperature metallic 4x1 structure is only slightly compressive, while that of the low-temperature insulating 8x2 structure is much larger and highly anisotropic. As a consequence, the intrinsic energy difference between the two phases is significantly reduced towards electronically phase-separated ground states. Our calculations further demonstrate quantitatively that such intriguing phase tunabilities can be achieved equivalently via lattice-contraction induced MS in the absence of charge doping. We also validate the equivalence through our detailed scanning tunneling microscopy experiments. The present findings have important implications in understanding the underlying driving forces involved in various phase transitions of simple and complex systems alike.
The paper is withdrawn since the results are included in arXiv:math/0403364.
We present the discovery and timing of the young (age $\sim 28.6$ kyr) pulsar PSR J0837$-$2454. Based on its high latitude ($b = 9.8^{\circ}$) and dispersion measure (DM $ = 143$~pc~cm$^{-3}$), the pulsar appears to be at a $z$-height of $>$1 kpc above the Galactic plane, but near the edge of our Galaxy. This is many times the observed scale height of the canonical pulsar population, which suggests this pulsar may have been born far out of the plane. If accurate, the young age and high $z$-height imply that this is the first pulsar known to be born from a runaway O/B star. In follow-up imaging with the Australia Telescope Compact Array (ATCA), we detect the pulsar with a flux density $S_{1400} = 0.18 \pm 0.05$ mJy. We do not detect an obvious supernova remnant around the pulsar in our ATCA data, but we detect a co-located, low-surface-brightness region of $\sim$1.5$^\circ$ extent in archival Galactic and Extragalactic All-sky MWA Survey data. We also detect co-located H$\alpha$ emission from the Southern H$\alpha$ Sky Survey Atlas. Distance estimates based on these two detections come out to $\sim$0.9 kpc and $\sim$0.2 kpc respectively, both of which are much smaller than the distance predicted by the NE2001 model ($6.3$ kpc) and YMW model ($>25$ kpc) and place the pulsar much closer to the plane of the Galaxy. If the pulsar/remnant association holds, this result also highlights the inherent difficulty in the classification of transients as "Galactic" (pulsar) or "extragalactic" (fast radio burst) toward the Galactic anti-center based solely on the modeled Galactic electron contribution to a detection.
A gauge theory of gravity based on a nonlinear realization (NLR) of the local Conform-Affine (CA) group of symmetry transformations is presented. The coframe fields and gauge connections of the theory are obtained. The tetrads and Lorentz group metric are used to induce a spacetime metric. The inhomogenously transforming (under the Lorentz group) connection coefficients serve as gravitational gauge potentials used to define covariant derivatives accommodating minimal coupling of matter and gauge fields. On the other hand, the tensor valued connection forms serve as auxillary dynamical fields associated with the dilation, special conformal and deformational (shear) degrees of freedom inherent in the bundle manifold. The bundle curvature of the theory is determined. Boundary topological invariants are constructed. They serve as a prototype (source free) gravitational Lagrangian. The Bianchi identities, covariant field equations and gauge currents are obtained.
The role of bipolar jets in the formation of stars, and in particular how they are launched, is still not well understood. We probe the protostellar jet launching mechanism, via high resolution observations of the near-IR [FeII] 1.53,1.64 micron lines. We consider the bipolar jet from the Classical T Tauri star, DO Tau, & investigate jet morphology & kinematics close to the star, using AO-assisted IFU observations from GEMINI/NIFS. The brighter, blue-shifted jet is collimated quickly after launch. This early collimation requires the presence of magnetic fields. We confirm velocity asymmetries between the two jet lobes, & confirm no time variability in the asymmetry over a 20 year interval. This sustained asymmetry is in accordance with recent simulations of magnetised disk-winds. We examine the data for jet rotation. We report an upper limit on differences in radial velocity of 6.3 & 8.7 km/s for the blue & red-shifted jets, respectively. Interpreting this as an upper limit on jet rotation implies that any steady, axisymmetric magneto-centrifugal model of jet launching is constrained to a launch radius in the disk-plane of 0.5 & 0.3 au for the blue & red-shifted jets, respectively. This supports an X-wind or narrow disk-wind model. This pertains only to the observed high velocity [FeII] emission, & does not rule out a wider flow launched from a wider radius. We report detection of small amplitude jet axis wiggling in both lobes. We rule out orbital motion of the jet source as the cause. Precession can better account for the observations but requires double the precession angle, & a different phase for the counter-jet. Such non-solid body precession could arise from an inclined massive Jupiter companion, or a warping instability induced by launching a magnetic disk-wind. Overall, our observations are consistent with an origin of the DO Tau jets from the inner regions of the disk.
We look for collective excitations originating from the strong surface pairing in unstable nuclei near the neutron drip-line. The soft dipole excitation is such a pairing mode as it exhibits a character of core-vs-dineutron motion. Possibility of the hydrodynamic phonon mode (the Anderson-Bogoliubov mode) is also discussed.
We overcome one of Bell's objections to `quantum measurement' by generalizing the definition to include systems outside the laboratory. According to this definition a {\sl generalized quantum measurement} takes place when the value of a classical variable is influenced significantly by an earlier state of a quantum system. A generalized quantum measurement can then take place in equilibrium systems, provided the classical motion is chaotic. This paper deals with this classical aspect of quantum measurement, assuming that the Heisenberg cut between the quantum dynamics and the classical dynamics is made at a very small scale. For simplicity, a gas with collisions is modelled by an `Arnold gas'.
We present the far-infrared (IR) maps of a bipolar planetary nebula (PN), NGC 650, at 24, 70, and 160 micron taken with the Multiband Imaging Photometer for Spitzer (MIPS) on-board the Spitzer Space Telescope. While the two-peak emission structure seen in all MIPS bands suggests the presence of a near edge-on dusty torus, the distinct emission structure between the 24 micron map and the 70/160 micron maps indicates the presence of two distinct emission components in the central torus. Based on the spatial correlation of these two far-IR emission components with respect to various optical line emission, we conclude that the 24 micron emission is largely due to the [O IV] line at 25.9 micron arising from highly ionized regions behind the ionization front, whereas the 70 and 160 micron emission is due to dust continuum arising from low-temperature dust in the remnant asymptotic giant branch (AGB) wind shell. The far-IR nebula structure also suggests that the enhancement of mass loss at the end of the AGB phase has occurred isotropically, but has ensued only in the equatorial directions while ceasing in the polar directions. The present data also show evidence for the prolate spheroidal distribution of matter in this bipolar PN. The AGB mass loss history reconstructed in this PN is thus consistent with what has been previously proposed based on the past optical and mid-IR imaging surveys of the post-AGB shells.