ShantanuT01/DACTYL-Pretraining huggingface dataset:
Aircraft detection in Synthetic Aperture Radar (SAR) imagery is a challenging task in SAR Automatic Target Recognition (SAR ATR) areas due to aircraft's extremely discrete appearance, obvious intraclass variation, small size and serious background's interference. In this paper, a single-shot detector namely Attentional Feature Refinement and Alignment Network (AFRAN) is proposed for detecting aircraft in SAR images with competitive accuracy and speed. Specifically, three significant components including Attention Feature Fusion Module (AFFM), Deformable Lateral Connection Module (DLCM) and Anchor-guided Detection Module (ADM), are carefully designed in our method for refining and aligning informative characteristics of aircraft. To represent characteristics of aircraft with less interference, low-level textural and high-level semantic features of aircraft are fused and refined in AFFM throughly. The alignment between aircraft's discrete back-scatting points and convolutional sampling spots is promoted in DLCM. Eventually, the locations of aircraft are predicted precisely in ADM based on aligned features revised by refined anchors. To evaluate the performance of our method, a self-built SAR aircraft sliced dataset and a large scene SAR image are collected. Extensive quantitative and qualitative experiments with detailed analysis illustrate the effectiveness of the three proposed components. Furthermore, the topmost detection accuracy and competitive speed are achieved by our method compared with other domain-specific,e.g., DAPN, PADN, and general CNN-based methods,e.g., FPN, Cascade R-CNN, SSD, RefineDet and RPDet.
We consider the time evolution of two-dimensional Levy flights in a finite area with periodic boundary conditions. From simulations we show that the fractal path dimension d_f and thus the degree of area coverage grows in time until it reaches the saturation value d_f=2 at sufficiently long times. We also investigate the time evolution of the probability density function and associated moments in these boundary conditions. Finally we consider the mean first passage time as function of the stable index. Our findings are of interest to assess the ergodic behavior of Levy flights, to estimate their efficiency as stochastic search mechanisms and to discriminate them from other types of search processes.
The second order perturbations in Friedmann-Robertson-Walker universe filled with a perfect fluid are completely formulated in the gauge invariant manner without any gauge fixing. All components of the Einstein equations are derived neglecting the first order vector and tensor modes. These equations imply that the tensor and the vector mode of the second order metric perturbations may be generated by the non-linear effects of the Einstein equations from the first order density perturbations.
We discuss a scenario of short Gamma-Ray Bursts (GRBs) following a merger of a massive ONeMg white dwarf (WD) with a CO WD, and an ensuing accretion induced collapse (AIC). An initial system with the primary mass $M_1 \sim 6-10 \, M_\odot$ and the secondary mass $M_2 \sim 3-6\, M_\odot$ forms, via two distinct evolutionary channels, a double degenerate CO-ONeMg WD system. For sufficiently large mass ratio $q \equiv M_2/M_1 > q_{crit} \sim 0.25$ the ensuing gravitational wave-driven mass transfer is unstable, whereby the less massive CO WD is disrupted and transfers its mass to the primary ONeMg WD on a few orbital time scales. The merger product ignites shell CO burning, adding mass to the degenerate core; at the same time mass and angular momentum is lost due to powerful winds. For an ONeMg WD sufficiently close to the Chandrasekhar mass an electron-capture accretion induced collapse (AIC) follows $\sim 10^4$ years afterwards. We associate the prompt short GRB emission with a direct collapse of an ONeMg WD to a neutron star, without formation of an accretion disk. After the collapse the accretion of the unburnt part of the shell onto the newly formed NS powers the extended emission (EE). During the collapse the neutron star is spun to millisecond periods and produce long lasting relativistic winds that shock against the material lost during the shell-burning stage, and produce afterglow emission from the wind termination shock.
We study the quantum phase diagram of spinful fermions on kagome lattice with half-filled lowest flat bands. To understand the competition between magnetism, flat band frustration, and repulsive interactions, we adopt an extended $t$-$J$ model, where the hopping energy $t$, antiferromagnetic Heisenberg interaction $J$, and short-range neighboring Hubbard interaction $V$ are considered. In the weak $J$ regime, we identify a fully spin-polarized phase, which can further support the spontaneous Chern insulating phase driven by the short-range repulsive interaction. This phase still emerges with in-plane ferromagnetism, whereas the non-interacting Chern insulator disappears constrained by symmetry. As $J$ gradually increases, the ferromagnetism is suppressed and the system first becomes partially-polarized with large magnetization and then enters a non-polarized phase with the ground state exhibiting vanishing magnetization. We identify this non-polarized phase as an insulator with a nematic charge density wave. In the end, we discuss the potential experimental observations of our theoretical findings.
The tunable properties of molecular materials place them among the favorites for a variety of future generation devices. In addition, to maintain the current trend of miniaturization of those devices, a departure from the present top-down production methods may soon be required and self-assembly appears among the most promising alternatives. On-surface synthesis unites the promises of molecular materials and of self-assembly, with the sturdiness of covalently bonded structures: an ideal scenario for future applications. Following this idea, we report the synthesis of functional extended nanowires by self-assembly. In particular, the products correspond to one-dimensional organic semiconductors. The uniaxial alignment provided by our substrate templates allows us to access with exquisite detail their electronic properties, including the full valence band dispersion, by combining local probes with spatial averaging techniques. We show how, by selectively doping the molecular precursors, the product's energy level alignment can be tuned without compromising the charge carrier's mobility.
We show that the analytic continuations of Helson zeta functions $ \zeta_\chi (s)= \sum_1^{\infty}\chi(n)n^{-s} $ can have essentially arbitrary poles and zeroes in the strip $ 21/40 < \Re s < 1 $ (unconditionally), and in the whole critical strip $ 1/2 < \Re s <1 $ under Riemann Hypothesis for the function $ \chi $ taking values in cubic roots of unity. If the sets are symmetric with respect to the real axis, the same can be achieved with $ \chi $ taking values $ \pm 1 $.
Epitaxial Fe/magnesium gallium spinel oxide (MgGa2O4)/Fe(001) magnetic tunnel junctions (MTJs) were fabricated by magnetron sputtering. Tunnel magnetoresistance (TMR) ratio up to 121% at room temperature (196% at 4 K) was observed, suggesting a TMR enhancement by the coherent tunneling effect in the MgGa2O4 barrier. The MgGa2O4 layer had a spinel structure and it showed good lattice matching with the Fe layers owing to slight tetragonal lattice distortion of MgGa2O4. Barrier thickness dependence of the tunneling resistance and current-voltage characteristics revealed that the barrier height of the MgGa2O4 barrier is much lower than that in an MgAl2O4 barrier. This study demonstrates the potential of Ga-based spinel oxides for MTJ barriers having a large TMR ratio at a low resistance area product.
Although deep learning approaches have achieved performance surpassing humans for still image-based face recognition, unconstrained video-based face recognition is still a challenging task due to large volume of data to be processed and intra/inter-video variations on pose, illumination, occlusion, scene, blur, video quality, etc. In this work, we consider challenging scenarios for unconstrained video-based face recognition from multiple-shot videos and surveillance videos with low-quality frames. To handle these problems, we propose a robust and efficient system for unconstrained video-based face recognition, which is composed of modules for face/fiducial detection, face association, and face recognition. First, we use multi-scale single-shot face detectors to efficiently localize faces in videos. The detected faces are then grouped respectively through carefully designed face association methods, especially for multi-shot videos. Finally, the faces are recognized by the proposed face matcher based on an unsupervised subspace learning approach and a subspace-to-subspace similarity metric. Extensive experiments on challenging video datasets, such as Multiple Biometric Grand Challenge (MBGC), Face and Ocular Challenge Series (FOCS), IARPA Janus Surveillance Video Benchmark (IJB-S) for low-quality surveillance videos and IARPA JANUS Benchmark B (IJB-B) for multiple-shot videos, demonstrate that the proposed system can accurately detect and associate faces from unconstrained videos and effectively learn robust and discriminative features for recognition.
Let $X$ be a continuous time random walk on a weighted graph. Given the on-diagonal upper bounds of transition probabilities at two vertices $x_1$ and $x_2$, we use an adapted metric initiated by Davies, and obtain Gaussian upper estimates for the off-diagonal transition probability $P_{x_1}(X_t=x_2)$.
We revisit the question of hadronic decays of a GeV-mass Higgs-like scalar. A number of extensions of the Standard Model predict Higgs sector with additional light scalars. Currently operating and planned Intensity Frontier experiments will probe for the existence of such particles, while theoretical computations are plagued by uncer- tainties. The goal of this paper is to bring the results in a consolidated form that can be readily used by experimental groups. To this end we provide a physically motivated fitting ansatz for the decay width that reproduces the previous non-perturbative nu- merical analysis. We describe systematic uncertainties of the non-perturbative method and provide explicit examples of the influence of extra resonances above 1.4 GeV onto the total decay width.
RR Lyr is one of the most studied variable stars. Its light curve has been regularly monitored since the discovery of the periodic variability in 1899. Analysis of all observed maxima allows us to identify two primary pulsation states defined as pulsation over a long (P0 longer than 0.56684 d) and a short (P0 shorter than 0.56682 d) primary pulsation period. These states alternate with intervals of 13-16 yr, and are well defined after 1943. The 40.8 d periodical modulations of the amplitude and the period (i.e. Blazhko effect) were noticed in 1916. We provide homogeneous determinations of the Blazhko period in the different primary pulsation states. The Blazhko period does not follow the variations of P0 and suddenly diminished from 40.8 d to around 39.0 d in 1975. The monitoring of these periodicities deserved and deserves a continuous and intensive observational effort. For this purpose we have built dedicated, transportable and autonomous small instruments, Very Tiny Telescopes (VTTs), to observe the times of maximum brightness of RR Lyr. As immediate results the VTTs recorded the last change of P0 state in mid-2009 and extended the time coverage of the Kepler observations, thus recording a maximum O-C amplitude of the Blazhko effect at the end of 2008, followed by the historically smallest O-C amplitude in late 2013. This decrease is still ongoing and VTT instruments are ready to monitor the expected increase in the next few years.
In this paper we investigate vacuum nonlinear electrodynamics corrections on rapidly rotating pulsar radiation and spin-down in the perturbative QED approach (post-Maxwellian approximation). An analytical expression for the pulsar's radiation intensity has been obtained and analyzed.
Recently a new class of hot subluminous stars strongly enriched in C and O have been discovered (CO-sdOs). These stars show abundances very similar to those observed in PG1159 stars but at lower temperatures. Moreover, it has been recently suggested that C and O enrichment might be the key ingredient driving the pulsations in He-rich hot subdwarf stars (He-sdBVs). Here we argue that these two types of rare stars can be explained by a variant of one of the main channels forming hot subdwarf stars. The scenario involves the formation and merging of a He-core white dwarf and a less massive CO-core white dwarf. We have constructed a simple merger models and computed their subsequent evolution. The merger products are in agreement with the surface parameters and composition of CO-sdOs. In addition, we have performed simulations including the effects of element diffusion and the excitation of pulsations. These simulations show that less massive merger products can form stellar structures that have surface parameters, abundances, and pulsation periods similar to those displayed by He-sdBVs. We conclude that the proposed scenario, or some variant of it, offers a very plausible explanation for the formation of CO-sdOs, pulsating He-sdBs and low-luminosity PG1159 stars.
The black hole candidate MAXI J1348-630 was discovered on January 26th, 2019, with the Gas Slit Camera (GSC) on-board \textit{MAXI}. We report a detailed spectral analysis of this source by using the archived data of \textit{NuSTAR}. A total of 9 observations covered the complete outburst evolution of MAXI J1348-630 from the hard state to the soft state and finally back to the hard state. Additionally, the intermediate state is found in the transition from the hard state to the soft state. We use the state-of-art reflection model \verb'relxill' family to fit all the 9 spectra, and the spectra from two focal plane module detectors of \textit{NuSTAR} are jointly fitted for each observation. In particular, we concentrate on the results of the black hole spin parameter and the inclination of the accretion disk. Based on the analysis of the inner radius of the accretion disk, we obtain the spin parameter $a_* =0.78_{-0.04}^{+0.04}$, and the inclination angle of the inner disk $i = 29.2_{-0.5}^{+0.3}$ degrees. Furthermore, we also find that when the black hole is in the hard state, the accretion disk would show a significant truncation. The high iron abundance and ionization of the accretion disk obtained in the fitting results can be possibly explained by the high density of the accretion disk.
We prove that a family $\mathcal{T}$ of distinct triangles on $n$ given vertices that does not have a rainbow triangle (that is, three edges, each taken from a different triangle in $\mathcal{T}$, that form together a triangle) must be of size at most $\frac{n^2}{8}$. We also show that this result is sharp and characterize the extremal case. In addition, we discuss a version of this problem in which the triangles are not necessarily distinct, and show that in this case, the same bound holds asymptotically. After posting the original arXiv version of this paper, we learned that the sharp upper bound of $\frac{n^2}{8}$ was proved much earlier by Gy\H{o}ri (2006) and independently by Frankl, F\"uredi and Simonyi (unpublished). Gy\H{o}ri also obtained a stronger version of our result for the case when repetitions are allowed.
A method allowing analysis of the overpopulation of phase-space in heavy ion collisions in a model independent way is proposed within the hydrodynamic approach. It makes it possible to extract a chemical potential of thermal pions at freeze out irrespective of the form of freeze-out (isothermal) hypersurface in Minkowski space and transverse flows on it. The contributions of resonance (with masses up to 2 GeV) decays to spectra, interferometry volumes and phase-space densities are calculated and discussed in detail. The estimates of average phase-space densities and chemical potentials of thermal pions are obtained for SPS and RHIC energies. They demonstrate that multibosonic phenomena at those energies might be considered as a correction factor rather than as a significant physical effect. The analysis of the evolution of the pion average phase-space density in chemically frozen hadron systems shows that it is almost constant or slightly increases with time while the particle density and phase-space density at each space point drops down rapidly during the system's expansion. We found that, unlike the particle density, the average phase-space density has no direct link to the freeze-out criterion and final thermodynamic parameters, being connected rather to the initial phase-space density of hadronic matter formed in relativistic nucleus-nucleus collisions.
We study the general form of the equations for isotropic single-scalar, multi-scalar and dyonic $p$-branes in superstring theory and M-theory, and show that they can be cast into the form of Liouville, Toda (or Toda-like) equations. The general solutions describe non-extremal isotropic $p$-branes, reducing to the previously-known extremal solutions in limiting cases. In the non-extremal case, the dilatonic scalar fields are finite at the outer event horizon.
We consider a fixed-point equation for a non-negative integer-valued random variable, that appears in branching processes with state-independent immigration. A similar equation appears in the analysis of a single-server queue with a homogeneous Poisson input, feedback and permanent customer(s).   It is known that the solution to this equation uniquely exists under mild first and logarithmic moments conditions. We find further the tail asymptotics of the distribution of the solution when the immigration size and branch size distributions are heavy-tailed. We assume that the distributions of interest are dominantly varying and have a long tail. This class includes, in particular, (intermediate, extended) regularly varying distributions.   We consider also a number of generalisations of the model.
Flattened bulges with disk-like properties are considered to be the end product of secular evolution processes at work in the inner regions of galaxies. On the contrary, classical bulges are characterized by rounder shapes and thought to be similar to low-luminosity elliptical galaxies. We aim at testing the variety of observational diagnostics which are commonly adopted to separate classical from disk-like bulges in nearby galaxies. We select a sample of eight unbarred lenticular galaxies to be morphologically and kinematically undisturbed with no evidence of other components than bulge and disk. We analyze archival data of broad-band imaging from SDSS and integral-field spectroscopy from the ATLAS$^{\rm 3D}$ survey to derive the photometric and kinematic properties, line-strength indices, and intrinsic shape of the sample bulges. We argue that the bulge S\'ersic index is a poor diagnostics to discriminate different bulge types. We find that the combination of line-strength with either kinematic or photometric diagnostics does not provide a clear separation for half of the sample bulges. We include for the first time the intrinsic three-dimensional shape of bulges as a possible discriminant of their nature. All bulges turn out to be thick oblate spheroids, but only one has a flattening consistent with that expected for outer disks. We conclude that bulge classification may be difficult even adopting all observational diagnostics proposed so far and that classical and disk-like bulges could be more confidently identified by considering their intrinsic shape.
The one-QRPA method is used to describe simultaneously both double decay beta modes, giving special attention to the partial restoration of spin-isospin SU(4) symmetry. To implement this restoration and to fix the model parameters, we resort to the energetics of Gamow-Teller resonances and to the minima of the single $\beta^+$-decay strengths. This makes the theory predictive regarding the $\beta\beta_{2\nu}$-decay, producing the $2\nu$ moments in $^{48}$Ca, $^{76}$Ge, $^{82}$Se, $^{96}$Zr, $^{100}$Mo, $^{128,130}$Te, and $^{150}$Nd, that are of the same order of magnitude as the experimental ones; however, the agreement with $\beta\beta_{2\nu}$ data is only modest. To include contributions coming from induced nuclear weak currents, we extend the $\beta\beta_{0\nu}$-decay formalism employed previously in C. Barbero et. al, Nuc. Phys. A628, 170 (1998). The numerical results for the $\beta\beta_{0\nu}$ moments in the above mentioned nuclei are similar to those obtained in other theoretical studies although smaller on averag by $\sim 40\%$. We attribute this difference basically to the one-QRPA-method, employed here for the first time, instead of the currently used two-QRPA-method. The difference is partially due to the way of carrying out the restoration of the spin-isospin symmetry. It is hard to say which is the best way to make the restoration, since the $\beta\beta_{0\nu}$ moments are not experimentally measurable. The numerical uncertainties in the $\beta\beta$ moments, related with i) their strong dependence on the residual interaction in the p-p channel when evaluated within the QRPA, and ii) lack of proper knowledge of single-particle energies, have been quantified. It is concluded that the partial restoration of the SU (4) symmetry is crucial in the description of the $\beta\beta$-decays, regardless of the nuclear model used.
We investigate spontaneous symmetry breaking within the linear sigma model with the SU(2)xU(1) internal symmetry at finite chemical potential, which was suggested as a model for kaon condensation in the CFL phase of dense quark matter. One-loop corrections to the scalar field effective potential as well as its propagator are calculated. Particular attention is paid to the type-II Goldstone boson that appears in the Bose--Einstein condensed phase. Furthermore, we show that the type-I Goldstone boson -- the superfluid phonon -- is allowed to decay due to the nonlinearity of its dispersion relation at high momentum, and determine its decay width.
We demonstrate transport rectification in a hermitian Hamiltonian quantum ratchet by a dissipative, dynamic impurity. While the bulk of the ratchet supports transport in both directions, the properly designed loss function of the local impurity acts as a direction-dependent filter for the moving states. We analyse this scheme theoretically by making use of Floquet-S-Matrix theory. In addition, we provide the direct experimental observation of one-way transmittance in periodically modulated plasmonic waveguide arrays containing a local impurity with engineered losses.
We present LOFAR imaging observations from the April/May 2020 active episode of magnetar SGR 1935+2154. We place the earliest radio limits on persistent emission following the low-luminosity fast radio burst FRB 200428 from the magnetar. We also perform an image-plane search for transient emission and find no radio flares during our observations. We examine post-FRB radio upper limits in the literature and find that all are consistent with the multi-wavelength afterglow predicted by the synchrotron maser shock model interpretation of FRB 200428. However, early optical observations appear to rule out the simple versions of the afterglow model with constant-density circumburst media. We show that these constraints may be mitigated by adapting the model for a wind-like environment, but only for a limited parameter range. In addition, we suggest that late-time non-thermal particle acceleration occurs within the afterglow model when the shock is no longer relativistic, which may prove vital for detecting afterglows from other Galactic FRBs. We also discuss future observing strategies for verifying either magnetospheric or maser shock FRB models via rapid radio observations of Galactic magnetars and nearby FRBs.