ShantanuT01/DACTYL-Pretraining huggingface dataset:
Many black holes (BHs) detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) and the Virgo detectors are multiple times more massive than those in X-ray binaries. One possibility is that some BBHs merge within a few Schwarzschild radii of a supermassive black hole (SMBH), such that the gravitational waves (GWs) are highly redshifted, causing the mass inferred from GW signals to appear higher than the real mass. The difficulty of this scenario lies in the delivery of BBH to such a small distance to a SMBH. Here we revisit the theoretical models for the migration of compact objects (COs) in the accretion discs of active galactic nuclei (AGNs). We find that when the accretion rate is high so that the disc is best described by the slim disc model, the COs in the disc could migrate to a radius close to the innermost stable circular orbit (ISCO) and be trapped there for the remaining lifetime of the AGN. The exact trapping radius coincides with the transition region between the sub- and super-Keplerian rotation of the slim disc. We call this region "the last migration trap" because inside it COs can no longer be trapped for a long time. We pinpoint the parameter space which could induce such a trap and we estimate that the last migration trap contributes a few per cent of the LIGO/Virgo events. Our result implies that a couple of BBHs discovered by LIGO/Virgo could have smaller intrinsic masses.
We study the evacuation process from a smoky room by means of experiments and simulations. People in a dark or smoky room are mimicked by ``blind'' students wearing eye masks. The evacuation of the disoriented students from the room is observed by video cameras, and the escape time of each student is measured. We find that the disoriented students exhibit a distinctly different behavior compared with a situation in which people can see and orient themselves. Our experimental results are reproduced by an extended lattice gas model taking into account the empirically observed behavior. Our particular focus is on the mean value and distribution of escape times. For a large number of people in the room, the escape time distribution is wide because of jamming. Surprisingly, adding more exits does not improve the situation in the expected way, since most people use the exit that is discovered first, which may be viewed as ``herding effect'' based on accoustic interactions. Moreover, the average escape time becomes minimal for a certain finite number of people in the dark or smoky room. These non-linear effects have practical implications for emergency evacuation and the planning of safer buildings.
There is now compelling evidence in favour of the hierarchical structure formation paradigm. Semi-analytic modelling is a powerful tool which allows the formation and evolution of galaxies to be followed in a hierarchical framework. We review some of the latest developments in this area before discussing how such models can help us to interpret observations of the high redshift Universe.
We discuss power corrections to infrared safe cross sections and event shapes, and identify a nonperturbative function that governs 1/Q corrections to these quantities.
By extracting spatial and temporal characteristics in one network, the two-stream ConvNets can achieve the state-of-the-art performance in action recognition. However, such a framework typically suffers from the separately processing of spatial and temporal information between the two standalone streams and is hard to capture long-term temporal dependence of an action. More importantly, it is incapable of finding the salient portions of an action, say, the frames that are the most discriminative to identify the action. To address these problems, a \textbf{j}oint \textbf{n}etwork based \textbf{a}ttention (JNA) is proposed in this study. We find that the fully-connected fusion, branch selection and spatial attention mechanism are totally infeasible for action recognition. Thus in our joint network, the spatial and temporal branches share some information during the training stage. We also introduce an attention mechanism on the temporal domain to capture the long-term dependence meanwhile finding the salient portions. Extensive experiments are conducted on two benchmark datasets, UCF101 and HMDB51. Experimental results show that our method can improve the action recognition performance significantly and achieves the state-of-the-art results on both datasets.
Multi-Weyl semimetals(WSMs) have an anisotropic non-linear dispersion along a 2-D plane and a linear dispersion in an orthogonal direction. They have topological charge $\lq n $' and are created when two or multiple Weyl points or nodes with nonzero net monopole charge are brought together onto a high-symmetry point. We study the perturbation corrections up to second order of such multi-WSMs in crossed electric($\mathcal{E}$) and magnetic (B) fields in the low electric field approximation. As a result, the first order correction lifts only n-fold degeneracy of the lowest Landau levels(LLs) while the higher Landau levels are modified due to the second order perturbation. We study the signatures of these corrections due to electric fields on the density of states (DOS) subjected to a magnetic field.
We investigate the molecular gas properties of galaxies across the main sequence of star-forming (SF) galaxies in the local Universe using $^{12}$CO($J=1-0$) (hereafter $^{12}$CO) and $^{13}$CO($J=1-0$) ($^{13}$CO) mapping data of 147 nearby galaxies obtained in the COMING project, a legacy project of the Nobeyama Radio Observatory. In order to improve signal-to-noise ratios of both lines, we stack all the pixels where $^{12}$CO emission is detected after aligning the line center expected from the first-moment map of $^{12}$CO. As a result, $^{13}$CO emission is successfully detected in 80 galaxies with a signal-to-noise ratio larger than three. The error-weighted mean of integrated-intensity ratio of $^{12}$CO to $^{13}$CO lines ($R_{1213}$) of the 80 galaxies is $10.9$ with a standard deviation of $7.0$. We find that (1) $R_{1213}$ positively correlates to specific star-formation rate (sSFR) with a correlation coefficient of $0.46$, and (2) both flux ratio of IRAS 60~$\mu$m to 100~$\mu$m ($f_{60}/f_{100}$) and inclination-corrected linewidth of $^{12}$CO stacked spectra ($\sigma_{{\rm ^{12}CO},i}$) also correlate with sSFR for galaxies with the $R_{1213}$ measurement. Our results support the scenario where $R_{1213}$ variation is mainly caused by the changes in molecular-gas properties such as temperature and turbulence. The consequent variation of CO-to-H$_2$ conversion factor across the SF main sequence is not large enough to completely extinguish the known correlations between sSFR and $M_{\rm mol}/M_{\rm star}$ ($\mu_{\rm mol}$) or star-formation efficiency (SFE) reported in previous studies, while this variation would strengthen (weaken) the sSFR-SFE (sSFR-$\mu_{\rm mol}$) correlation.
We propose a method to construct universal order parameters for quantum phase transitions in many-body lattice systems. The method exploits the $H$-orthogonality of a few near-degenerate lowest states of the Hamiltonian describing a given finite-size system, which makes it possible to perform finite-size scaling and take full advantage of currently available numerical algorithms. An explicit connection is established between the fidelity per site between two $H$-orthogonal states and the energy gap between the ground state and low-lying excited states in the finite-size system. The physical information encoded in this gap arising from finite-size fluctuations clarifies the origin of the universal order parameter.We demonstrate the procedure for the one-dimensional quantum formulation of the $q$-state Potts model, for $q=2,3,4$ and 5, as prototypical examples, using finite-size data obtained from the density matrix renormalization group (DMRG) algorithm.
This paper focuses on improved edge model based on Curvelet coefficients analysis. Curvelet transform is a powerful tool for multiresolution representation of object with anisotropic edge. Curvelet coefficients contributions have been analyzed using Scale Invariant Feature Transform (SIFT), commonly used to study local structure in images. The permutation of Curvelet coefficients from original image and edges image obtained from gradient operator is used to improve original edges. Experimental results show that this method brings out details on edges when the decomposition scale increases.
We prove a regularity result for the Poisson problem $-\Delta u = f$, $u |\_{\pa \PP} = g$ on a polyhedral domain $\PP \subset \RR^3$ using the \BK\ spaces $\Kond{m}{a}(\PP)$. These are weighted Sobolev spaces in which the weight is given by the distance to the set of edges \cite{Babu70, Kondratiev67}. In particular, we show that there is no loss of $\Kond{m}{a}$--regularity for solutions of strongly elliptic systems with smooth coefficients. We also establish a "trace theorem" for the restriction to the boundary of the functions in $\Kond{m}{a}(\PP)$.
The person re-identification (Re-ID) task requires to robustly extract feature representations for person images. Recently, part-based representation models have been widely studied for extracting the more compact and robust feature representations for person images to improve person Re-ID results. However, existing part-based representation models mostly extract the features of different parts independently which ignore the relationship information between different parts. To overcome this limitation, in this paper we propose a novel deep learning framework, named Part-based Hierarchical Graph Convolutional Network (PH-GCN) for person Re-ID problem. Given a person image, PH-GCN first constructs a hierarchical graph to represent the pairwise relationships among different parts. Then, both local and global feature learning are performed by the messages passing in PH-GCN, which takes other nodes information into account for part feature representation. Finally, a perceptron layer is adopted for the final person part label prediction and re-identification. The proposed framework provides a general solution that integrates local, global and structural feature learning simultaneously in a unified end-to-end network. Extensive experiments on several benchmark datasets demonstrate the effectiveness of the proposed PH-GCN based Re-ID approach.
We analyze the fragmentation behavior of random clusters on the lattice under a process where bonds between neighboring sites are successively broken. Modeling such structures by configurations of a generalized Potts or random-cluster model allows us to discuss a wide range of systems with fractal properties including trees as well as dense clusters. We present exact results for the densities of fragmenting edges and the distribution of fragment sizes for critical clusters in two dimensions. Dynamical fragmentation with a size cutoff leads to broad distributions of fragment sizes. The resulting power laws are shown to encode characteristic fingerprints of the fragmented objects.
We consider the energy critical four dimensional semi linear heat equation \partial tu-\Deltau-u3 = 0. We show the existence of type II finite time blow up solutions and give a sharp description of the corresponding singularity formation. These solutions concentrate a universal bubble of energy in the critical topology u(t,r)-1/{\lambda} Q(r/{\lambda})\rightarrow u* in $\dot{H}^1$ where the blow up profile is given by the Talenti Aubin soliton Q(r)= 1/(1 +r^2/8) and with speed {\lambda}(t) ~(T-t)/|log(T - t)|^2 as t\rightarrowT. Our approach uses a robust energy method approach developped for the study of geometrical dispersive problems, and lies in the continuation of the study of the energy critical harmonic heat flow and the energy critical four dimensional wave equation.
We have carried out a survey of the Andromeda galaxy for unresolved microlensing (pixel lensing). We present a subset of four short timescale, high signal-to-noise microlensing candidates found by imposing severe selection criteria: the source flux variation exceeds the flux of an R=21 magnitude star and the full width at half maximum timescale is less than 25 days. Remarkably, in three out of four cases, we have been able to measure or strongly constrain the Einstein crossing time of the event. One event, which lies projected on the M31 bulge, is almost certainly due to a stellar lens in the bulge of M31. The other three candidates can be explained either by stars in M31 and M32 or by MACHOs.
For a non-isotrivial family of surfaces of general type over a complex projective curve, we give upper bounds for the degree of the direct images of powers of the relative dualizing sheaf. They imply that, fixing the curve and the possible degeneration locus, the induced morphisms to the moduli scheme of stable surfaces of general type are parameterized by a scheme of finite type. The method extends to families of canonically polarized manifolds, but the modular interpretation requires the existence of relative minimal models.
Uniform random numbers, not Gaussian random numbers, should have been used with Standard Solar Models to estimate the effect on the neutrino flux of uncertainties in input data. The observed discrepancy is therefore probably quite smaller than currently accepted.
Elaborating on previous theoretical treatments of the roughening transition, we provide the exact mapping of a surface model which undergoes both roughening and preroughening onto a mixture of unit and double charges living on the square lattice. Depending on the model parameters, the preroughening transition of the surface can be either continuous or discontinuous. Using the surface temperature as a control parameter, the dual Coulomb gas accordingly undergoes two consecutive phase transitions through equilibrium phases whose dielectric behavior is analysed in terms of Monte Carlo simulation and exact finite-size calculations. Right at the preroughening point of the surface model, the charged mixture behaves like an electric insulator (provided preroughening is second-order), while showing metallic behavior below and above that temperature, at least up to the roughening temperature where the conventional metal-insulator transition occurs.
It has been suggested that chaotic motion inside the nucleus may significantly limit the accuracy with which nuclear masses can be calculated. Using a power spectrum analysis we show that the inclusion of additional physical contributions in mass calculations, through many-body interactions or local information, removes the chaotic signal in the discrepancies between calculated and measured masses. Furthermore, a systematic application of global mass formulas and of a set of relationships among neighboring nuclei to more than 2000 nuclear masses allows to set an unambiguous upper bound for the average errors in calculated masses which turn out to be almost an order of magnitude smaller than estimated chaotic components.
We investigate weak convergence of measures generated by solutions of stochastic equations with local time and small diffusion while the last one tends to zero. In case the correspondent ordinary differential equation has infinitely many solutions we prove that limit measure concentrated with some weights on its extreme solutions. Formulae for weights are obtained.
In certain configurations, the aromatic properties of benzene ring structured molecules allow for unpaired, reactive valence electrons (known as radicals). Clar's goblets are such molecules. With an even number of unpaired radicals, these nanographenes are topologically frustrated hydrocarbons in which pi-bonding network and topology of edges give rise to the magnetism. Clar's goblets are therefore valued as prospective qubits provided they can be modulated between magnetic states. Using first principles DFT, we demonstrate the effects of adsorption on both molecule and substrate in a graphene-Clar's goblet heterostructure. We look at the energy difference bewteen FM and AFM states of the system and discuss underlying physical and chemical mechanisms in reference to the highest occupied molecular orbital (HOMO) and second HOMO (HOMO-1). We find that the HOMO of the molecule in the FM state is right at the Fermi surface, which leads to the hybridization between molecular state and the graphene state near the Dirac point. Furthermore, we investigate qualitative changes in charge realignment and magnetic state under variable electric field. Transitions from FM to AFM and back to FM states are observed.
Deep learning based 3D stereo networks give superior performance compared to 2D networks and conventional stereo methods. However, this improvement in the performance comes at the cost of increased computational complexity, thus making these networks non-practical for the real-world applications. Specifically, these networks use 3D convolutions as a major work horse to refine and regress disparities. In this work first, we show that these 3D convolutions in stereo networks consume up to 94% of overall network operations and act as a major bottleneck. Next, we propose a set of "plug-&-run" separable convolutions to reduce the number of parameters and operations. When integrated with the existing state of the art stereo networks, these convolutions lead up to 7x reduction in number of operations and up to 3.5x reduction in parameters without compromising their performance. In fact these convolutions lead to improvement in their performance in the majority of cases.
There are very strong observed correlations between the specific star-formation rates (sSFR) of galaxies and their mean surface mass densities, {\Sigma}, as well as other aspects of their internal structure. These strong correlations have often been taken to indicate that the internal structure of a galaxy must play a major physical role, directly or indirectly, in the control of star-formation. In this paper we show by means of a very simple toy model that these correlations can arise naturally without any such physical role once the observed evolution of the size-mass relation for star-forming galaxies is taken into account. In particular, the model reproduces the sharp threshold in {\Sigma} between galaxies that are star-forming and those that are quenched, and the evolution of this threshold with redshift. Similarly, it produces iso-quenched-fraction contours in the ${f_Q(m,R_e)}$ plane that are almost exactly parallel to lines of constant {\Sigma} for centrals and shallower for satellites. It does so without any dependence on quenching on size or {\Sigma}, and without invoking any differences between centrals and satellites, beyond the different mass-dependences of their quenching laws. The toy-model also reproduces several other observations, including the sSFR gradients within galaxies and the appearance of inside-out build-up of passive galaxies. Finally, it is shown that curvature in the Main Sequence sSFR-mass relation can produce curvature in the apparent B/T ratios with mass. Our analysis therefore suggests that many of the strong correlations that are observed between galaxy structure and sSFR may well be a consequence of things unrelated to quenching and should not be taken as evidence of the physical processes that drive quenching.
It is shown that the H$\alpha$ luminosity and the Thomson optical depth of the iPTF14hls on day 600 after the detection provide us with the estimate of the envelope age which turns to be about 1000 days. I propose a model that suggests an explosion of a massive star with the radius of $\sim 2\times10^{13}$ cm at 450 days prior to the discovery. For the optimal model the ejected mass is $30\,M_{\odot}$, and the kinetic energy is $8\times10^{51}$ erg. The energy source at the dominant luminosity stage is presumably related to the relativistic bipolar outflow originated from a disk accretion onto the black hole. The [O\,I] 6300, 6364 \AA\ doublet in the spectrum on day 600 is shown to be the result of the emission of at least $1-3\,M_{\odot}$ of oxygen in the ejecta inner zone. The oxygen distribution is non-spherical and can be represented either by two components with blue and red shifts (in the optically thin case), or by one blue shifted component, in the case of optically thick lines for the filling factor of $\sim 2\times10^{-3}$.
Recent observations of tidal debris around galaxies have revealed that the structural properties of the spheroidal components of tidally disturbed galaxies are similar to those found in non-interacting early-type galaxies(ETGs), likely due to minor merging events that do not strongly affect the bulge region or to major mergers that happened a long time ago. We show that independently of merger events, tidal features like shells or rings can also arise if the the dark matter is an ultra light scalar field of mass ~10$^{-22}$eV/c$^2$. In the scalar field dark matter (SFDM) model the small mass precludes halo formation below ~10$^8$ M$_{\odot}$ reducing the number of small galaxies today, it produces shallow density profiles due to the uncertainty principle in contrast to the steep profiles found in the standard cold dark matter (CDM) paradigm, in addition to the usual soliton solution there exists dark matter haloes in multistates, characterized by ripples in their density profiles, which are stable provided that most of the halo mass resides in the ground state. We use the hydrodynamics code ZEUS to track the gas evolution in a background potential given by a superposition of the ground and first excited state of the scalar field, we study this configuration when it is initially unstable (excited state more massive than ground state) but by a population inversion in the states it eventually becomes stable, this could happen when haloes decoupled from the expansion of the universe and collapse to reach a state of equilibrium. We found that tidal structures like rings are formed at a particular radii as a direct consequence of the wavelike structure of the dark matter halo(abridged)
A new renormalization group approach that maps lattice problems to tensor networks may hold the key to solving seemingly intractable models of strongly correlated systems in any dimension. A Physics Viewpoint on arXiv:0903.1069
The dependence of inter-particle correlations on the orientation of particle relative-momentum can yield unique information on the space-time features of emission in reactions with multiparticle final states. In the present paper, the benefits of a representation and analysis of the three-dimensional correlation information in terms of surface spherical harmonics is presented. The harmonics include the standard complex tesseral harmonics and the real cartesian harmonics. Mathematical properties of the lesser-known cartesian harmonics are illuminated. The physical content of different angular harmonic components in a correlation is described. The resolving power of different final-state effects with regarding to determining angular features of emission regions is investigated. The considered final-state effects include identity interference and strong and Coulomb interactions. The correlation analysis in terms of spherical harmonics is illustrated with the cases of gaussian and blast-wave sources for proton-charged meson and baryon-baryon pairs.
We discuss the inverse problem of determining the, possibly anisotropic, conductivity of a body $\Omega\subset\mathbb{R}^{n}$ when the so-called Neumann-to-Dirichlet map is locally given on a non empty curved portion $\Sigma$ of the boundary $\partial\Omega$. We prove that anisotropic conductivities that are \textit{a-priori} known to be piecewise constant matrices on a given partition of $\Omega$ with curved interfaces can be uniquely determined in the interior from the knowledge of the local Neumann-to-Dirichlet map.
In this paper, we first present a Gearhardt-Pr\"uss type theorem with a sharp bound for m-accretive operators. Then we give two applications: (1) give a simple proof of the result proved by Constantin et al. on relaxation enhancement induced by incompressible flows; (2) show that shear flows with a class of Weierstrass functions obey logarithmically fast dissipation time-scales.