ShantanuT01/DACTYL-Pretraining huggingface dataset:
The ubiquitous relativistic jet phenomena associated with black holes play a major role in high and very-high-energy (VHE) astrophysics. In particular, observations have demonstrated that blazars show VHE emission with time-variability from days (in the GeV band) to minutes (in the TeV band), implying very compact emission regions. The real mechanism able to explain the particle acceleration process responsible for this emission is still debated, but magnetic reconnection has been lately discussed as a strong potential candidate and, in some circumstances, as the only possible one. In this work, we present the results of three-dimensional special relativistic magnetohydrodynamic simulations of the development of reconnection events driven by turbulence induced by current-driven kink instability along a relativistic jet. We have performed a systematic identification of all reconnection regions in the system, characterizing their local magnetic field topology and quantifying the reconnection rates. We obtained average rates of $0.051\pm0.026$ (in units of the Alfv\'{e}n speed) which are comparable to the predictions of the theory of turbulence-induced fast reconnection. Detailed statistical analysis also demonstrated that the fast reconnection events follow a log-normal distribution, which is a signature of its turbulent origin. To probe the robustness of our method, we have applied our results to the blazar Mrk 421. Building a synthetic light curve from the integrated power of the magnetic reconnection events, we evaluated the time-variability from a power spectral density analysis, obtaining a good agreement with the observations in the GeV band. This suggests that turbulent fast magnetic reconnection driven by kink instability can be a possible process behind the high energy emission variability phenomena observed in blazars.
We show that the maximal number of equal entries in a totally positive (resp. totally nonsingular) $n\textrm{-by-}n$ matrix is $\Theta(n^{4/3})$ (resp. $\Theta(n^{3/2}$)). Relationships with point-line incidences in the plane, Bruhat order of permutations, and $TP$ completability are also presented. We also examine the number and positionings of equal $2\textrm{-by-}2$ minors in a $2\textrm{-by-}n$ $TP$ matrix, and give a relationship between the location of equal $2\textrm{-by-}2$ minors and outerplanar graphs.
We explore the abundance of light clusters in asymmetric nuclear matter at subsaturation density. With increasing density, binding energies and wave functions are modified due to medium effects. The method of Albergo, Costa, Costanzo and Rubbino (ACCR) for determining the temperature and free nucleon density of a disassembling hot nuclear source from fragment yields is modified to include, in addition to Coulomb effects and flow, also effects of medium modifications of cluster properties, which become of importance when the nuclear matter density is above 10$^{-3}$ fm$^{-3}$. We show how the analysis of cluster yields, to infer temperature and nucleon densities, is modified if the shifts in binding energies of in medium clusters are included. While, at low densities, the temperature calculated from given yields changes only modestly if medium effects are taken into account, larger discrepancies are observed when the nucleon densities are determined from measured yields.
A model of fast radio bursts, which enlists young, short period extragalactic magnetars satisfying $B/P > 2 \times 10^{16}$~G~s$^{-1}$ (1~G = 1~statvolt~cm$^{-1}$) as the source, is proposed. When the parallel component $\bE_\parallel$ of the surface electric field (under the scenario of a vacuum magnetosphere) of such pulsars approaches 5 \% of the critical field $E_c = m_e^2 c^3/(e\hbar)$, in strength, the field can readily decay via the Schwinger mechanism into electron-positron pairs, the back reaction of which causes $\bE_\parallel$ to oscillate on a characteristic timescale smaller than the development of a spark gap. Thus, under this scenario, the open field line region of the pulsar magnetosphere is controlled by Schwinger pairs, and their large creation and acceleration rates enable the escaping pairs to coherently emit radio waves directly from the polar cap. The majority of the energy is emitted at frequencies $\lesssim 1$~GHz where the coherent radiation has the highest yield, at a rate large enough to cause the magnetar to lose spin significantly over timescale $\ap$ a few $\times 10^{-3}$~s, the duration of a fast radio burst. Owing to circumstellar environment of a young magnetar, however, the $\lesssim 1$~GHz radiation is likely to be absorbed or reflected by the overlying matter. It is shown that the brightness of the remaining (observable) frequencies of $\ap 1$~GHz and above are on par with a typical fast radio burst. Unless some spin-up mechanism is available to recover the original high rotation rate that triggered the Schwinger mechanism, the fast radio burst will not be repeated again in the same magnetar.
We have studied the ground state of a simple cubic magnetic cluster, which contains a spin s at each corner site. The ground state of such cluster depends on the competition between nearest, next-nearest and next-next-nearest-neighbor exchange interactions. We have calculated the "phase" diagrams for the Izing clusters with s=1/2;1;3/2;5/2;\infty and for the Heisenberg clusters with s=1/2 and s=1. We have found that the "phase" diagram is remarkably independent on the s value. It is important also that the Izing "phase" diagram can be used as a rough approximation for the Heisenberg model.
Starting from the parametric representation of a Feynman diagram, we obtain it's well defined value in dimensional regularisation by changing the integrals over parameters into contour integrals. That way we eventually arrive at a representation consisting of well-defined compact integrals. The result is a simple transformation of the integrand which gives the analytic continuation of a wide class of Feynmanintegrals. The algorithm will especially be fit for numerical calculation of general massive multi-loop integrals. An important advantage of this method is that it allows us to calculate both infinite and finite parts independently.
We propose a new mechanism of indirect exchange interaction, which can be responsible for the ferromagnetic ordering in Mn-doped semiconductors (like GaMnAs) at low carrier concentration. The mechanism is based on the interplay of the hybridization of band states (conduction or valence) with localized impurity (donor or acceptor) states and the direct exchange interaction between localized spins and the band states. The indirect exchange coupling between two impurities occurs when the wavefunctions of the corresponding localized donor (acceptor) states overlap. This coupling is independent of the free carrier concentration and therefore may be responsible for ferromagnetic transition at low or vanishing carrier concentration.
We present an analysis of scattering by a fluid-mechanical `black hole analogue', known as the draining bathtub vortex: a two-dimensional flow which possesses both a sonic horizon and an ergoregion. We consider the scattering of a plane wave of fixed frequency impinging upon the vortex. At low frequency, we encounter a modified Aharonov-Bohm effect. At high frequencies, we observe regular `orbiting' oscillations in the scattering length, due to interference between contra-orbiting rays. We present approximate formulae for both effects, and a selection of numerical results obtained by summing partial-wave series. Finally, we examine interference patterns in the vicinity of the vortex, and highlight the prospects for experimental investigation.
I review recent insights and open questions connected with the production of eta--mesons from hadrons.
The attenuation of ultrasound waves in photoacoustic and thermoacoustic imaging presents an important drawback in the applicability of these modalities. This issue has been addressed previously in the applied and theoretical literature, and some advances have been made on the topic. In particular, stability inequalities have been proposed for the inverse problem of initial source recovery with partial observations under the assumption of unique determination of the initial pressure. The main goal of this work is to fill this gap, this is, we prove the uniqueness property for the inverse problem and establish the associated stability estimates as well. The problem of reconstructing the initial condition of acoustic waves in the complete-data setting is revisited and a new Neumann series reconstruction formula is obtained for the case of partial observations in a semi-bounded geometry. A numerical simulation is also included to test the method.
We report on a double quantum dot which is formed in a width-modulated etched bilayer graphene nanoribbon. A number of lateral graphene gates enable us to tune the quantum dot energy levels and the tunneling barriers of the device over a wide energy range. Charge stability diagrams and in particular individual triple point pairs allow to study the tunable capacitive inter-dot coupling energy as well as the spectrum of the electronic excited states on a number of individual triple points. We extract a mutual capacitive inter-dot coupling in the range of 2 - 6 meV and an inter-dot tunnel coupling on the order of 1.5 {\mu}eV.
Light hole doping of lanthanum cuprate strongly suppresses the onset of antiferromagnetic (AF) order. Surprisingly, it simultaneously suppresses the extrapolated zero temperature sub-lattice magnetization. 139La NQR results in lightly Li-doped lanthanum cuprate have demonstrated that these effects are independent of the details of the mobility of the added holes. We propose a model in which doped holes phase separate into charged domain walls that surround ``anti-phase'' domains. These domains are mobile down to ~30 K where they either become pinned to the lattice or evaporate as their constituent holes become pinned to dopant impurities.
Using a large collection of near-infrared spectra (2.5-5.4 um) of Galactic HII regions and HII region-like objects, we perform a systematic investigation of the astronomical polycyclic aromatic hydrocarbon (PAH) features. 36 objects were observed by the use of the infrared camera onboard the AKARI satellite as a part of a directer's time program. In addition to the well-known 3.3-3.6 um features, most spectra show a relatively-weak emission feature at 5.22 um with sufficient signal-to-noise ratios, which we identify as the PAH 5.25 um band previously reported. By careful analysis, we find good correlations between the 5.25 um band and both the aromatic hydrocarbon feature at 3.3 um and the aliphatic ones at around 3.4-3.6 um. The present results give us convincing evidence that the astronomical 5.25 um band is associated with C-H vibrations as suggested by previous studies and show its potential to probe the PAH size distribution. The analysis also shows that the aliphatic to aromatic ratio of I(3.4-3.6)/I(3.3) decreases against the ratio of the 3.7 um continuum intensity to the 3.3 um band, I(3.7 cont)/I(3.3), which is an indicator of the ionization fraction of PAHs. The mid-infrared color of I(9)/I(18) also declines steeply against the ratio of the hydrogen recombination line Bralpha at 4.05 um to the 3.3 um band, I(Bralpha)/I(3.3). These facts indicate possible dust processing inside or at the boundary of ionized gas.
Several discrete geometry problems are equivalent to estimating the size of the largest homogeneous sets in graphs that happen to be the union of few comparability graphs. An important observation for such results is that if $G$ is an $n$-vertex graph that is the union of $r$ comparability (or more generally, perfect) graphs, then either $G$ or its complement contains a clique of size $n^{1/(r+1)}$.   This bound is known to be tight for $r=1$. The question whether it is optimal for $r\ge 2$ was studied by Dumitrescu and T\'oth. We prove that it is essentially best possible for $r=2$, as well: we introduce a probabilistic construction of two comparability graphs on $n$ vertices, whose union contains no clique or independent set of size $n^{1/3+o(1)}$.   Using similar ideas, we can also construct a graph $G$ that is the union of $r$ comparability graphs, and neither $G$, nor its complement contains a complete bipartite graph with parts of size $\frac{cn}{(\log n)^r}$. With this, we improve a result of Fox and Pach.
We report the controlled integration, via Dip Pen Nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 Bohr magnetons) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 100, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.
Building on the initial results of the nIFTy simulated galaxy cluster comparison, we compare and contrast the impact of baryonic physics with a single massive galaxy cluster, run with 11 state-of-the-art codes, spanning adaptive mesh, moving mesh, classic and modern SPH approaches. For each code represented we have a dark matter only (DM) and non-radiative (NR) version of the cluster, as well as a full physics (FP) version for a subset of the codes. We compare both radial mass and kinematic profiles, as well as global measures of the cluster (e.g. concentration, spin, shape), in the NR and FP runs with that in the DM runs. Our analysis reveals good consistency (<= 20%) between global properties of the cluster predicted by different codes when integrated quantities are measured within the virial radius R200. However, we see larger differences for quantities within R2500, especially in the FP runs. The radial profiles reveal a diversity, especially in the cluster centre, between the NR runs, which can be understood straightforwardly from the division of codes into classic SPH and non-classic SPH (including the modern SPH, adaptive and moving mesh codes); and between the FP runs, which can also be understood broadly from the division of codes into those that include AGN feedback and those that do not. The variation with respect to the median is much larger in the FP runs with different baryonic physics prescriptions than in the NR runs with different hydrodynamics solvers.
We give a new characterisation of elliptic curves of Shimura type in terms commuting families of Frobenius lifts and also strengthen an old principal ideal theorem for ray class fields. These two results combined yield the existence of global minimal models for elliptic curves of Shimura type, generalising a result of Gross. Along the way we also prove a handful of small but new results regarding elliptic curves with complex multiplication.
Leveraging on the recent developments in convolutional neural networks (CNNs), matching dense correspondence from a stereo pair has been cast as a learning problem, with performance exceeding traditional approaches. However, it remains challenging to generate high-quality disparities for the inherently ill-posed regions. To tackle this problem, we propose a novel cascade CNN architecture composing of two stages. The first stage advances the recently proposed DispNet by equipping it with extra up-convolution modules, leading to disparity images with more details. The second stage explicitly rectifies the disparity initialized by the first stage; it couples with the first-stage and generates residual signals across multiple scales. The summation of the outputs from the two stages gives the final disparity. As opposed to directly learning the disparity at the second stage, we show that residual learning provides more effective refinement. Moreover, it also benefits the training of the overall cascade network. Experimentation shows that our cascade residual learning scheme provides state-of-the-art performance for matching stereo correspondence. By the time of the submission of this paper, our method ranks first in the KITTI 2015 stereo benchmark, surpassing the prior works by a noteworthy margin.
We consider unimodular random rooted trees (URTs) and invariant forests in Cayley graphs. We show that URTs of bounded degree are the same as the law of the component of the root in an invariant percolation on a regular tree. We use this to give a new proof that URTs are sofic, a result of Elek. We show that ends of invariant forests in the hyperbolic plane converge to ideal boundary points. We also prove that uniform integrability of the degree distribution of a family of finite graphs implies tightness of that family for local convergence, also known as random weak convergence.
We compute the supersymmetric contribution to   $R_{b}\equiv \Gamma (Z\to b{\bar b})/\Gamma (Z\to {\rm hadrons})$ in a variety of supergravity models. We find $R^{\rm susy}_b\lsim0.0004$, which does not shift significantly the Standard Model prediction   ($R^{\rm SM}_b=0.2162$ for $m_t=160\GeV$). An improvement in experimental precision by a factor of four would be required to be sensitive to such an effect.
Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC) detected the gamma-ray afterglow of GRB 190114C, which can constrain microscopic parameters of the shock-heated plasma emitting non-thermal emission. Focusing on the early afterglow of this event, we numerically simulate the spectrum and multi-wavelength light curves with constant and wind-like circumstellar medium using a time-dependent code. Our results show that the electron acceleration timescale at the highest energies is likely shorter than 20 times the gyroperiod to reproduce the GeV gamma-ray flux and its spectral index reported by {\it Fermi}. This gives an interesting constraint on the acceleration efficiency for Weibel-mediated shocks. We also constrain the number fraction of non-thermal electrons $f_{\rm e}$, and the temperature of the thermal electrons. The early optical emission can be explained by the thermal synchrotron emission with $f_{\rm e} \lesssim 0.01$. On the other hand, the X-ray light curves restrict efficient energy transfer from protons to the thermal electrons, and $f_{\rm e}\sim1$ is required if the energy fraction of the thermal electrons is larger than $\sim10$\%. The parameter constraints obtained in this work give important clues to probing plasma physics with relativistic shocks.
We prove that if X, X' are closed subschemes of a torus T over a non-Archimedean field K, of complementary codimension and with finite intersection, then the stable tropical intersection along a (possibly positive-dimensional, possibly unbounded) connected component C of Trop(X) \cap Trop(X') lifts to algebraic intersection points, with multiplicities. This theorem requires potentially passing to a suitable toric variety X(\Delta) and its associated extended tropicalization N_R(\Delta); the algebraic intersection points lifting the stable tropical intersection will have tropicalization somewhere in the closure of C in N_R(\Delta). The proof involves a result on continuity of intersection numbers in the context of non-Archimedean analytic spaces.
We present a brief review of the modified Brans-Dicke theory (MBDT) in arbitrary dimensions, whereby the ($N+1$)-dimensional field equations reduce to the $N$-dimensional $(ND)$ configuration with sources and an effective induced scalar potential. We then investigate a generalized Bianchi type~I anisotropic cosmology in $5D$ BD theory that leads to an extended Kasner solution. By employing the original equations of MBDT, we probe the reduced Kasner cosmology on the hypersuface with proceeding the investigations for a few cosmological quantities, explaining their properties for some cosmological models.}
X-ray counterparts for 35 galaxy clusters contained in the PF catalog of galaxy clusters and groups were found in XMM-Newton archive. 22 ones (all from ACO catalogue) have extended elliptic X-ray haloes appropriate for determination of orientation. Position angles and eccentricities were calculated and compared with cluster orientations optical band.
In this article we prove the $e$-positivity of $G_{\mathbf{\nu}}[X;q+1]$ when $G_{\mathbf{\nu}}[X;q]$ is a vertical strip LLT polynomial. This property has been conjectured by Alexandersson and Panova, and by Garsia, Haglund, Qiu and Romero, and it implies several $e$-positivities conjectured by them and also by Bergeron.   We make use of a result of Carlsson and Mellit that shows that a vertical strip LLT polynomial can be obtained by applying certain compositions of operators of the Dyck path algebra to the constant $1$. Our proof gives in fact an algorithm to expand these symmetric functions in the elementary basis, and it shows, as a byproduct, that these compositions of operators are actually multiplication operators.
While egocentric video is becoming increasingly popular, browsing it is very difficult. In this paper we present a compact 3D Convolutional Neural Network (CNN) architecture for long-term activity recognition in egocentric videos. Recognizing long-term activities enables us to temporally segment (index) long and unstructured egocentric videos. Existing methods for this task are based on hand tuned features derived from visible objects, location of hands, as well as optical flow.   Given a sparse optical flow volume as input, our CNN classifies the camera wearer's activity. We obtain classification accuracy of 89%, which outperforms the current state-of-the-art by 19%. Additional evaluation is performed on an extended egocentric video dataset, classifying twice the amount of categories than current state-of-the-art. Furthermore, our CNN is able to recognize whether a video is egocentric or not with 99.2% accuracy, up by 24% from current state-of-the-art. To better understand what the network actually learns, we propose a novel visualization of CNN kernels as flow fields.
Neutrino reactions on $^{40}$Ar via charged and neutral currents for detecting solar and core collapsing supernovae (SNe) neutrinos and the Gamow Teller strength are calculated by considering the high-lying excited states up to a few tens of MeV region. The nucleus was originally exploited to identify the solar neutrino emitted from $^{8}$B produced in the pp-chains on the Sun. With the higher energy neutrinos emitted from the core collapsing SNe, contributions from higher multi-pole transitions including the spin dipole resonances (SDR) as well as the Gamow Teller (GT) and Fermi transitions are shown to be important ingredients for understanding reactions induced by the SNe as well as solar neutrinos. In this work, we focused on the role of high-lying excited states which are located beyond a few low-lying states known in the experiment. Expected large difference between the cross sections of $\nu_e$ and ${\bar \nu_e}$ reactions on $^{40}$Ar, which difference has been anticipated in previous calculations because of the large Q value in the ${\bar \nu}_e$ reaction, is significantly diminished. The reduction leads only to about 2 times difference between them. Our calculations are carried out by the Quasi-particle Random Phase Approximation (QRPA), which takes account of the neutron-proton pairing as well as proton-proton and neutron-neutron pairing correlations. They were successfully applied in the description of the nuclear beta decay and relevant neutrino reaction data on $^{12}$C and $^{56}$Fe, and the GT data on the $^{138}$La and $^{180}$Ta.