ShantanuT01/DACTYL-Pretraining huggingface dataset:
We present data from long ROSAT HRI observations of the intermediate polars YY Dra and V709 Cas which show that V709 Cas, like YY Dra, exhibits a double-peaked X-ray pulse profile. Neither system shows evidence for X-ray beat period or orbital modulation, so both must be disc-fed accretors seen at low inclination angles. We argue that the short spin periods of the white dwarfs in these objects indicate that they have weak magnetic fields, so the radius at which material is captured by the field lines is relatively small. Consequently the footprints of the disc-fed accretion curtains on the white dwarf surface are large. The optical depths to X-ray emission within the accretion curtains are therefore lowest in the direction along the magnetic field lines, and highest in the direction parallel to the white dwarf surface, such that the emission from the two poles conspires to produce double-peaked X-ray pulse profiles. We emphasise that such a pulse profile is not a unique indicator of two-pole accretion however. Indeed, two-pole accretion onto smaller regions of the white dwarf surface may be considered the `normal' mode of behaviour in a disc-fed intermediate polar with a longer white dwarf spin period (and therefore a higher field strength), resulting in a single-peaked pulse profile. Collating data on other intermediate polars, we may classify them into two subsets. Fast rotators, with relatively weak fields, show double-peaked pulse profiles (AE Aqr, DQ Her, XY Ari, GK Per, V709 Cas, YY Dra, V405 Aur), whilst slower rotators, with larger fields and therefore larger magnetospheres, have been seen to exhibit an X-ray beat period modulation at some time (FO Aqr, TX Col, BG CMi, AO Psc, V1223 Sgr, RX J1712.6-2414).
A rook path is a path on lattice points in the plane in which any proper horizontal step to the right or vertical step north is allowed. If, in addition, one allow bishop steps, that is, proper diagonal steps of slope 1, then one has queen paths. A rook or queen path is Catalan if it starts at the origin and stays strictly to the left of the line y = x-1. We give explicit formulas for the ordinary generating function of the number of Catalan rook and queen paths finishing at $(n,n).$ These generating functions are algebraic; indeed, they satisfy quadratic equations. In the second version, we also consider paths with "spider steps", that is, proper steps on lattice points with slope strictly greater than one. In the third version, we give step-enumerator versions of our results.
The scattering polarization in the solar spectrum is traditionally modeled with each spectral line treated separately, but this is generally inadequate for multiplets where J-state interference plays a significant role. Through simultaneous observations of all the 3 lines of a Cr I triplet, combined with realistic radiative transfer modeling of the data, we show that it is necessary to include J-state interference consistently when modeling lines with partially interacting fine structure components. Polarized line formation theory that includes J-state interference effects together with partial frequency redistribution for a two-term atom is used to model the observations. Collisional frequency redistribution is also accounted for. We show that the resonance polarization in the Cr I triplet is strongly affected by the partial frequency redistribution effects in the line core and near wing peaks. The Cr I triplet is quite sensitive to the temperature structure of the photospheric layers. Our complete frequency redistribution calculations in semi-empirical models of the solar atmosphere cannot reproduce the observed near wing polarization or the cross-over of the Stokes Q/I line polarization about the continuum polarization level that is due to the J-state interference. When however partial frequency redistribution is included, a good fit to these features can be achieved. Further, to obtain a good fit to the far wings, a small temperature enhancement of the FALF model in the photospheric layers is necessary.
The near-surface layers of cool main-sequence stars are structured by convective flows, which are overshooting into the atmosphere. The flows and the associated spatio-temporal variations of density and temperature affect spectral line profiles and thus have an impact on estimates of stellar properties such as effective temperature, gravitational acceleration, and abundances. We aim at identifying distinctive properties of the thermodynamic structure of the atmospheres of different stars and understand their causes. We ran comprehensive 3D radiation hydrodynamics simulations of the near-surface layers of six simulated stars of spectral type F3V to M2V with the MURaM code. We carry out a systematic parameter study of the mean stratifications, flow structures, and the energy flux in these stars.\par Results: We find monotonic trends along the lower main sequence in granule size, flow velocity, and intensity contrast. The convection in the M-star models differs substantially from that of the hotter stars, mainly owing to the more gradual transition from convective to radiative energy transport. While the basic mechanisms driving surface convection in cool stars are the same, the properties of the convection vary along the main sequence. Apart from monotonic trends in rms velocity, intensity contrast, granule size, etc., there is a transition between "naked" and "hidden" granulation around spectral type K5V caused by the (highly non-linear) temperature dependence of the opacity. These variations have to be taken into account when stellar parameters are derived from spectra.
For a $k$-graph $\mathcal{F}\subset \binom{[n]}{k}$, the clique number of $\mathcal{F}$ is defined to be the maximum size of a subset $Q$ of $[n]$ with $\binom{Q}{k}\subset \mathcal{F}$. In the present paper, we determine the maximum number of edges in a $k$-graph on $[n]$ with matching number at most $s$ and clique number at least $q$ for $n\geq 8k^2s$ and for $q \geq (s+1)k-l$, $n\leq (s+1)k+s/(3k)-l$. Two special cases that $q=(s+1)k-2$ and $k=2$ are solved completely.
We present modelling of ~0.1arcsec resolution Atacama Large Millimetre/sub-millimeter Array imaging of seven strong gravitationally lensed galaxies detected by the Herschel Space Observatory. Four of these systems are galaxy-galaxy scale strong lenses, with the remaining three being group-scale lenses. Through careful modelling of visibilities, we infer the mass profiles of the lensing galaxies and by determining the magnification factors, we investigate the intrinsic properties and morphologies of the lensed sub-millimetre sources. We find that these sub-millimetre sources all have ratios of star formation rate to dust mass that is consistent with or in excess of the mean ratio for high-redshift sub-millimetre galaxies and low redshift ultra-luminous infrared galaxies. The contribution to the infrared luminosity from possible AGN is not quantified and so could be biasing our star formation rates to higher values. The majority of our lens models have mass density slopes close to isothermal, but some systems show significant differences.
We study effects of an external magnetic field on charge ordering in the one-dimensional extended Hubbard model at quarter filling by means of the quantum Monte Carlo method. We find that the Zeeman coupling enhances the charge order correlation, which is prominent when the system is located in the critical regime near the charge ordering transition at zero magnetic field. This behavior is interpreted in terms of the crossover to the fully spin-polarized limit where the model is exactly solvable. Furthermore, by incorporating the interchain Coulomb repulsion, we show that the charge-ordering transition temperature is raised by the magnetic field. We also discuss the relevance of our results to magnetoresistance effects observed in molecular conductors.
We calculate the junction resistance for a metal-barrier-metal device with the barrier tuned to lie just on the insulating side of the metal-insulator transition. We find that the crossover from tunneling behavior in thin barriers at low temperature to incoherent transport in thick barriers at higher temperature is governed by a generalized Thouless energy. The crossover temperature can be estimated from the low temperature resistance of the device and the bulk density of states of the barrier.
We investigate triphoton signals of the Randall-Sundram model at the Large Hadron Collider. Such a signal can be an important probe to the RS model as these are relatively cleaner from the hadronic activity and bear significant rate. The corresponding standard model background has also been studied in detail. We also show that a clear graviton reconstruction is possible in such signal.
For each nonprincipal Dirichlet character $\chi$, let $n_\chi$ be the least $n$ with $\chi(n) \notin \{0,1\}$. We show that as the average of $n_\chi$ over all nonprincipal characters $\chi$ modulo $q$ is $\ell(q) + o(1)$, where $\ell(q)$ denotes the least prime not dividing $q$. Moreover, if one averages over all nonprincipal characters of modulus at most $x$, the average approaches a particular limiting value 2.5350541804. We also prove a result of this type for cubic number fields: If one averages over all cubic fields $K$, ordered by the absolute value of their discriminant, then the mean value of the least rational prime that does not split completely in $K$ is another particular constant 2.1211027269.
Gravitational collapse of matter in the presence of rotation is a mostly unexplored topic but it might have important implications for cosmic censorship. Recently a convenient setup was identified to address this problem, by considering thin matter shells at the interface between two equal angular momenta Myers-Perry spacetimes in five dimensions. This note provides more details about the matching of such cohomogeneity-1 spacetimes and extends the results obtained therein to arbitrary higher odd dimensions. It is also pointed out that oscillatory orbits for shells in asymptotically flat spacetimes can be naturally obtained if the matter has a negative pressure component.
Recent work has shown that depth estimation from a stereo pair of images can be formulated as a supervised learning task to be resolved with convolutional neural networks (CNNs). However, current architectures rely on patch-based Siamese networks, lacking the means to exploit context information for finding correspondence in illposed regions. To tackle this problem, we propose PSMNet, a pyramid stereo matching network consisting of two main modules: spatial pyramid pooling and 3D CNN. The spatial pyramid pooling module takes advantage of the capacity of global context information by aggregating context in different scales and locations to form a cost volume. The 3D CNN learns to regularize cost volume using stacked multiple hourglass networks in conjunction with intermediate supervision. The proposed approach was evaluated on several benchmark datasets. Our method ranked first in the KITTI 2012 and 2015 leaderboards before March 18, 2018. The codes of PSMNet are available at: https://github.com/JiaRenChang/PSMNet.
Let $G$ be a finite, connected graph. The eccentricity of a vertex $v$ of $G$ is the distance from $v$ to a vertex farthest from $v$. The average eccentricity of $G$ is the arithmetic mean of the eccentricities of the vertices of $G$. We show that the average eccentricity of a connected graph $G$ of girth at least six is at most $\frac{9}{2} \lceil \frac{n}{2\delta^2 - 2\delta+2} \rceil + 7$, where $n$ is the order of $G$ and $\delta$ its minimum degree. We construct graphs that show that whenever $\delta-1$ is a prime power, then this bound is sharp apart from an additive constant. For graphs containing a vertex of large degree we give an improved bound. We further show that if the girth condition on $G$ is relaxed to $G$ having neither a $4$-cycle nor a $5$-cycle as a subgraph, then similar and only slightly weaker bounds hold.
We report the discovery of four massive ($M > 0.8\,M_\odot$) ZZ Ceti white dwarfs, including an ultramassive $1.16\,M_\odot$ star. We obtained ground based, time-series photometry for thirteen white dwarfs from the Sloan Digital Sky Survey Data Release 7 and Data Release 10 whose atmospheric parameters place them within the ZZ Ceti instability strip. We detect mono-periodic pulsations in three of our targets (J1053, J1554, and J2038) and identify three periods of pulsation in J0840 (173, 327, and 797 s). Fourier analysis of the remaining nine objects do not indicate variability above the $4\langle{A}\rangle$ detection threshold. Our preliminary asteroseismic analysis of J0840 yields a stellar mass $M=1.14\pm 0.01\,M_{\odot}$, hydrogen and helium envelope masses of $M_H = 5.8 \times 10^{-7}\,M_{\odot}$ and $M_{He}=4.5 \times 10^{-4}\,M_{\odot}$, and an expected core crystallized mass ratio of 50-70\%. J1053, J1554, and J2038 have masses in the range $0.84-0.91 M_\odot$ and are expected to have a CO core; however, the core of J0840 could consist of highly crystallized CO or ONeMg given its high mass. These newly discovered massive pulsators represent a significant increase in the number of known ZZ Ceti white dwarfs with mass $M > 0.85\,M_\odot$, and detailed asteroseismic modeling of J0840 will allow for significant tests of crystallization theory in CO and ONeMg core white dwarfs.
The d-wave pairing correlations along with spin correlation are calculated with quantum Monte Carlo method for the two-dimensional Hubbard model on lattice structures representing organic superconductors $\kappa$-(BEDT-TTF)$_2$X and (TMTSF)$_2$X. In both cases the pairing correlations for superconducting order parameters with nodes are found to be enhanced. The symmetry and the enhancement of the pairing is systematically correlated with the spin structure factor, suggesting a spin-fluctuation mediated pairing. We have further found that, as we deform the Fermi surface to make the system approach the half-filled square lattice, the coherence of the pairing saturates while the local pairing amplitude continues to increase.
I provide a frequency domain reduced order model (ROM) for the aligned-spin effective-one-body (EOB) model "SEOBNRv2" for data analysis with second and third generation ground based gravitational wave (GW) detectors. SEOBNRv2 models the dominant mode of the GWs emitted by the coalescence of black hole (BH) binaries. The large physical parameter space (dimensionless spins $-1 \leq \chi_i \leq 0.99$ and symmetric mass-ratios $0.01 \leq \eta \leq 0.25$) requires sophisticated reduced order modeling techniques, including patching in the parameter space and in frequency. I find that the time window over which the inspiral-plunge and the merger-ringdown waveform in SEOBNRv2 are connected is discontinuous when the spin of the deformed Kerr BH $\chi=0.8$ or the symmetric mass-ratio $\eta \sim 0.083$. This discontinuity increases resolution requirements for the ROM. The ROM can be used for compact binary systems with total masses of $2 M_\odot$ or higher for the advanced LIGO (aLIGO) design sensitivity and a $10$ Hz lower cutoff frequency. The ROM has a worst mismatch against SEOBNRv2 of $\sim 1\%$, but in general mismatches are better than $\sim 0.1\%$. The ROM is crucial for key data analysis applications for compact binaries, such as GW searches and parameter estimation carried out within the LIGO Scientific Collaboration (LSC).
Transient reflectivity measurements of thin films, ranging from 6 to 40 nm in thickness, of the topological insulator Bi2Se3 revealed a strong dependence of the carrier relaxation time on the film thickness. For thicker films the relaxation dynamics are similar to those of bulk Bi2Se3, where the contribution of the bulk insulating phase dominates over that of the surface metallic phase. The carrier relaxation time shortens with decreasing film thickness, reaching values comparable to those of noble metals. This effect may result from the hybridization of Dirac cone states at the opposite surfaces for the thinnest films.
Recent hydrodynamical simulations predict that stellar feedback in intermediate mass galaxies (IMGs) can drive strong fluctuations in structure (e.g., half-light radius, $R_e$). This process operates on timescales of only a few hundred Myr and persists even at late cosmic times. One prediction of this quasi-periodic, galactic-scale "breathing" is an $anti$-correlation between star formation rate (SFR) and half-light radius as central gas overdensities lead to starbursts whose feedback drags stars to larger radii while star formation dwindles. We test this prediction with a sample of 322 $isolated$ IMGs with stellar masses of $10^{9.0} \leq M/M_{\odot} \leq 10^{9.5}$ at $0.3<z<0.4$ in the HST $I_{814}$ COSMOS footprint. We find that IMGs with higher specific SFRs (SSFR $>10^{-10}$ yr$^{-1}$) are the most extended with median sizes of $R_e \sim 3-3.4$ kpc and are mostly disk-dominated systems. In contrast, IMGs with lower SSFRs ($<10^{-10}$ yr$^{-1}$) are a factor of $\sim 2-3$ more compact with median sizes of $R_e \sim 0.9-1.6$ kpc and have more significant bulge contributions to their light. These observed trends are opposite the predictions for stellar feedback that operate via the "breathing" process described above. We discuss various paths to reconcile the observations and simulations, all of which likely require a different implementation of stellar feedback in IMGs that drastically changes their predicted formation history.
The effect of nonequilibrium solute trapping by a growing solid under rapid solidification conditions is studied using a phase-field model. Considering a continuous steady-state concentration profile across the diffuse solid-liquid interface, a new definition of the nonequilibrium partition coefficient in the phase-field context is introduced. This definition leads, in particular for high growth velocities, to a better description of the available experimental data in comparison with other diffuse interface and sharp-interface predictions.
We calculate the angular power spectrum of the Cosmic Microwave Background (CMB) temperature fluctuations induced by the kinetic Sunyaev-Zel'dovich (kSZ) effect from the epoch of reionization (EOR). We use detailed N-body+radiative transfer simulations to follow inhomogeneous reionization of the intergalactic medium (IGM). For the first time we take into account the "self-regulation" of reionization: star formation in low-mass dwarf galaxies (10^8 M_\sun \lesssim M \lesssim 10^9 M_\sun) or minihalos (10^5 M_\sun \lesssim M \lesssim 10^8 M_\sun) is suppressed if these halos form in the regions that were already ionized or Lyman-Werner dissociated. Some previous work suggested that the amplitude of the kSZ power spectrum from the EOR can be described by a two-parameter family: the epoch of half ionization and the duration of reionization. However, we argue that this picture applies only to simple forms of the reionization history which are roughly symmetric about the half-ionization epoch. In self-regulated reionization, the universe begins to be ionized early, maintains a low level of ionization for an extended period, and then finishes reionization as soon as high-mass atomically-cooling halos dominate. While inclusion of self-regulation affects the amplitude of the kSZ power spectrum only modestly (\sim 10 %), it can change the duration of reionization by a factor of more than two. We conclude that the simple two-parameter family does not capture the effect of a physical, yet complex, reionization history caused by self-regulation. When added to the post-reionization kSZ contribution, our prediction for the total kSZ power spectrum is below the current upper bound from the South Pole Telescope. Therefore, the current upper bound on the kSZ effect from the EOR is consistent with our understanding of the physics of reionization.
Within a Kondo lattice, the strong hybridization between electrons localized in real space (r-space) and those delocalized in momentum-space (k-space) generates exotic electronic states called 'heavy fermions'. In URu2Si2 these effects begin at temperatures around 55K but they are suddenly altered by an unidentified electronic phase transition at To = 17.5 K. Whether this is conventional ordering of the k-space states, or a change in the hybridization of the r-space states at each U atom, is unknown. Here we use spectroscopic imaging scanning tunnelling microscopy (SI-STM) to image the evolution of URuSi2 electronic structure simultaneously in r-space and k-space. Above To, the 'Fano lattice' electronic structure predicted for Kondo screening of a magnetic lattice is revealed. Below To, a partial energy gap without any associated density-wave signatures emerges from this Fano lattice. Heavy-quasiparticle interference imaging within this gap reveals its cause as the rapid splitting below To of a light k-space band into two new heavy fermion bands. Thus, the URu2Si2 'hidden order' state emerges directly from the Fano lattice electronic structure and exhibits characteristics, not of a conventional density wave, but of sudden alterations in both the hybridization at each U atom and the associated heavy fermion states.
We study weak convergence of a sequence of point processes to a scale-invariant simple point process. For a deterministic sequence $(z_n)_{n\in\mathbb{N}}$ of positive real numbers increasing to infinity as $n \to \infty$ and a sequence $(X_k)_{k\in\mathbb{N}}$ of independent non-negative integer-valued random variables, we consider the sequence of point processes   \begin{equation*}   \nu_n=\sum_{k=1}^\infty X_k \delta_{z_k/z_n}, \quad n\in \mathbb{N},   \end{equation*} and prove that, under some general conditions, it converges vaguely in distribution to a scale-invariant Poisson process $\eta_c$ on $(0,\infty)$ with the intensity measure having the density $ct^{-1}$, $t\in(0,\infty)$. An important motivating example from probabilistic number theory relies on choosing $X_k \sim {\rm Geom}(1-1/p_k)$ and $z_k=\log p_k$, $k\in \mathbb{N}$, where $(p_k)_{k \in \mathbb{N}}$ is an enumeration of the primes in increasing order. We derive a general result on convergence of the integrals $\int_0^1 t \nu_n(dt)$ to the integral $\int_0^1 t \eta_c(dt)$, the latter having a generalized Dickman distribution, thus providing a new way of proving Dickman convergence results.   We extend our results to the multivariate setting and provide sufficient conditions for vague convergence in distribution for a broad class of sequences of point processes obtained by mapping the points from $(0,\infty)$ to $\mathbb{R}^d$ via multiplication by i.i.d. random vectors. In addition, we introduce a new class of multivariate Dickman distributions which naturally extends the univariate setting.
We prove that the variety of complete flags for any semisimple algebraic group is rigid in any smooth family of Fano manifolds.