arXiv subjects

Ning Jiang

Publications and source records attributed to Ning Jiang.

At least 181 records · Page 10Linked to original sources

arXiv2022

Discovery of ATLAS17jrp as an Optical, X-ray and Infrared Bright TDE in a Star-forming Galaxy

We hereby report the discovery of ATLAS17jrp as an extraordinary TDE in star-forming galaxy SDSSJ162034.99+240726.5 in our recent sample of mid-infrared outbursts in nearby galaxies. Its optical/UV light curves rise to a peak luminosity $\sim1.06\times10^{44}\rm\,erg\,s^{-1}$ in about a month and then decay as $\rm t^{-5/3}$ with a roughly constant temperature around 19000~K, and the optical spectra show a blue continuum and very broad Balmer lines with FWHM$\sim$15000 km/s which gradually narrowed to 1400 km/s within 4 years, all agreeing well with other optical TDEs. A delayed and rapidly rising X-ray flare with a peak luminosity $\rm \sim 1.27\times10^{43}\,erg\,s^{-1}$ was detected at $\rm \sim$ 170 days after the optical peak. The high MIR luminosity of ATLAS17jrp ($\sim2\times10^{43} \rm\,erg\,s^{-1}$) has revealed a distinctive dusty environment with covering factor as high as $\sim0.2$, that is comparable with that of torus in active galactic nuclei but at least one order of magnitude higher than normal optical TDEs. Therefore, ATLAS17jrp turns out to be one of the rare unambiguous TDE found in star-forming galaxies and its high dust covering factor implies that the dust extinction could play an important role in the absence of optical TDEs in star-forming galaxies.

astro-ph.GA↗

arXiv2022

Communication and Computation Assisted Sensing Information Freshness Performance Analysis in Vehicular Networks

The timely sharing of raw sensing information in the vehicular networks (VNETs) is essential to safety. In order to improve the freshness of sensing information, joint scheduling of multi-dimensional resources such as communication and computation is required. However, the complex relevance among multi-dimensional resources is still unclear, and it is difficult to achieve efficient resource utilization. In this paper, we present a theoretical analysis for a novel metric Age of Information (AoI) on a communication and computation assisted spatial-temporal model. An uplink VNETs scenario where Road Side Units (RSUs) are deployed with computational resource is considered. The transmission and computation process is unified into a two-stage tandem queue and the expression of the average AoI is derived. The network interference is analyzed by modeling the VNETs as Cox Poisson Point Process based on stochastic geometry and the closed-form solution of the coverage probability and the expected data rate performance under the constraints of transmission resources is obtained. The simulation results reveal the basic relationship between communication and computation capacity and show that communication and computation should reach a tradeoff to improve resource utilization while ensuring real-time information requirement.

cs.NI↗

arXiv2022

The Prospects of Finding Tidal Disruption Events with 2.5-Metre Wide-Field Survey Telescope (WFST) Based on Mock Observations

Optical time-domain survey has been the dominant means of hunting for rare tidal disruption events (TDEs) in the past decade and remarkably advanced the TDE study. Particularly, the Zwicky Transient Facility (ZTF) has opened the era of population studies and the upcoming Large Synoptic Survey Telescope (LSST) at the Vera Rubin Observatory (VRO) is believed to further revolutionize the field soon. Here we present the prospects of finding TDEs with another powerful survey to be performed by 2.5-metre Wide-Field Survey Telescope (WFST). The WFST, located in western China, will be the most advanced facility dedicated to optical time-domain surveys in the northern hemisphere once commissioning. We choose to assess its TDE detectability on the basis of mock observations, which is hitherto closest to reality by taking into consideration of site conditions, telescope parameters, survey strategy and transient searching pipeline. Our mock observations on 440 deg$^2$ field (CosmoDC2 catalogue) show that $29\pm6$ TDEs can be robustly found per year if observed at $u, g, r, i$ bands with 30-second exposure every 10 days, in which a discovery is defined as $\geq$10 epochal detections in at least two filters. If the WFST survey is fully optimized for discovering TDE, we would expect to identify $392\pm74$ of TDEs every year, with the redshift up to $z\sim0.8$, which poses a huge challenge to follow-up resources.

astro-ph.HE↗

arXiv2022

Hydrodynamic limit of the incompressible Navier-Stokes-Fourier-Maxwell System with Ohm's Law from the Vlasov-Maxwell-Boltzmann system: Hilbert expansion approach

We prove a global-in-time limit from the two-species Vlasov-Maxwell-Boltzmann system to the two-fluid incompressible Navier-Stokes-Fourier-Maxwell system with Ohm's law. Besides the techniques developed for the classical solutions to the Vlasov-Maxwell-Boltzmann equations in the past years, such as the nonlinear energy method and micro-macro decomposition are employed, key roles are played by the decay properties of both the electric field and the wave equation with linear damping of the divergence free magnetic field. This is a companion paper of [N. Jiang and Y.-L. Luo, \emph{Ann. PDE} 8 (2022), no. 1, Paper No. 4, 126 pp] in which Hilbert expansion is not employed.

math.AP↗

arXiv2022

Tick-Tock: The Imminent Merger of a Supermassive Black Hole Binary

Supermassive black hole binaries (SMBHs) are a fascinating byproduct of galaxy mergers in the hierarchical universe. In the last stage of their orbital evolution, gravitational wave radiation drives the binary inspiral and produces the loudest siren awaiting to be detected by gravitational wave observatories. Periodically varying emission from active galactic nuclei has been proposed as a powerful approach to probe such systems, although none of the identified candidates are close to their final coalescence such that the observed periods stay constant in time. In this work, we report on the first system with rapid decaying periods revealed by its optical and X-ray light curves, which has decreased from about one year to one month in three years. Together with its optical hydrogen line spectroscopy, we propose that the system is an uneven mass-ratio, highly eccentric SMBH binary which will merge within three years, as predicted by the trajectory evolution model. If the interpretation is true, coordinated, multi-band electromagnetic campaign should be planned for this first binary SMBH merger event observed in human history, together with possible neutrino measurements. Gravitational wave memory from this event may also be detectable by Pulsar Timing Array with additional five-to-ten year observation.

astro-ph.HE↗

arXiv2022

Open Access Dataset for Electromyography based Multi-code Biometric Authentication

Recently, surface electromyogram (EMG) has been proposed as a novel biometric trait for addressing some key limitations of current biometrics, such as spoofing and liveness. The EMG signals possess a unique characteristic: they are inherently different for individuals (biometrics), and they can be customized to realize multi-length codes or passwords (for example, by performing different gestures). However, current EMG-based biometric research has two critical limitations: 1) a small subject pool, compared to other more established biometric traits, and 2) limited to single-session or single-day data sets. In this study, forearm and wrist EMG data were collected from 43 participants over three different days with long separation while they performed static hand and wrist gestures. The multi-day biometric authentication resulted in a median EER of 0.017 for the forearm setup and 0.025 for the wrist setup, comparable to well-established biometric traits suggesting consistent performance over multiple days. The presented large-sample multi-day data set and findings could facilitate further research on EMG-based biometrics and other gesture recognition-based applications.

cs.CR↗

arXiv2021

Mid-InfraRed Outbursts in Nearby Galaxies (MIRONG). II. Optical Spectroscopic Follow-up

Infrared echo has proven to be an effective means to discover transient accretion events of supermassive black holes (SMBHs), such as tidal disruption events (TDEs) and changing-look active galactic nuclei (AGNs), in dusty circumnuclear environments. To explore the dusty populations of SMBH transient events, we have constructed a large sample of Mid-infrared Outbursts in Nearby Galaxies (MIRONG) and performed multiwavelength observations. Here we present the results of multiepoch spectroscopic follow-up observations of a subsample of 54 objects spanning a time scale of 4 yr. Emission-line variability was detected in 22 of them with either emergence or enhancement of broad Balmer emission lines in comparison with pre-outburst spectra. Coronal lines, HeIIλ4686 and Bowen line NIIIλ4640 appeared in the spectra of nine,seven and two sources, respectively. These results suggest that MIRONG is a mixed bag of different transient sources. We have tentatively classified them into different subclass according to their spectral evolution and light curves. Two sources have been in a steady high broad Hα flux up to the latest observation and might be turn-on AGNs. Broad lines faded out in the remaining sources, indicating a transient ionizing source ignited by TDE or sporadic gas accretion. Thirty-one sources do not show noticeable spectral change with respect to their pre-outburst spectra. They have a statistically redder MIR color and lower MIR luminosity of the outbursts,which are consistent with heavily obscured events.

astro-ph.GA↗

arXiv2021

The Compressible Euler and Acoustic Limits from quantum Boltzmann Equation with Fermi-Dirac Statistics

This paper justifies the compressible Euler and acoustic limits from quantum Boltzmann equation with Fermi-Dirac statistics (briefly, BFD) rigorously. This limit was formally derived in Zakrevskiy's thesis \cite{Zakrevskiy} by moment method. We employ the Hilbert approach. The forms of the classical compressible Euler system and the one derived from BFD are different. Our proof is based on the analysis of the nonlinear implicit transformation of these two forms, and a few novel nonlinear estimates.

math.AP↗

arXiv2021

On the Vlasov-Poisson-Boltzmann limit of the Vlasov-Maxwell-Boltzmann system

For the whole range of cutoff intermolecular interactions, we give a rigorous mathematical justification of the limit from the Vlasov-Maxwell-Boltzmann system to the Vlasov-Poisson-Boltzmann system as the light speed tends to infinity.Such a limit is shown to hold global-in-time in the perturbative framework.The key point in our analysis is to deduce certain a priori estimates which are independent of the light speed and the main difficulty is due to the degeneracy of the dissipative effect of the electromagnetic field for large light speed.

math.AP↗

arXiv2021

Evidence of a tidal disruption event in GSN 069 from the abnormal carbon and nitrogen abundance ratio

GSN 069 is an ultra-soft X-ray active galactic nucleus that previously exhibited a huge X-ray outburst and a subsequent long-term decay. It has recently presented X-ray quasi-periodic eruptions (QPEs). We report the detection of strong nitrogen lines but weak or undetectable carbon lines in its far ultraviolet spectrum. With a detailed photoionization model, we use the C IV/N IV] ratio and other ratios between nitrogen lines to constrain the [C/N] abundance of GSN 069 to be from -3.33 to -1.91. We argue that a partially disrupted red giant star can naturally explain the abnormal C/N abundance in the UV spectrum, while the surviving core orbiting the black hole might produce the QPEs.

astro-ph.GA↗

arXiv2021

Dense Semantic Contrast for Self-Supervised Visual Representation Learning

Self-supervised representation learning for visual pre-training has achieved remarkable success with sample (instance or pixel) discrimination and semantics discovery of instance, whereas there still exists a non-negligible gap between pre-trained model and downstream dense prediction tasks. Concretely, these downstream tasks require more accurate representation, in other words, the pixels from the same object must belong to a shared semantic category, which is lacking in the previous methods. In this work, we present Dense Semantic Contrast (DSC) for modeling semantic category decision boundaries at a dense level to meet the requirement of these tasks. Furthermore, we propose a dense cross-image semantic contrastive learning framework for multi-granularity representation learning. Specially, we explicitly explore the semantic structure of the dataset by mining relations among pixels from different perspectives. For intra-image relation modeling, we discover pixel neighbors from multiple views. And for inter-image relations, we enforce pixel representation from the same semantic class to be more similar than the representation from different classes in one mini-batch. Experimental results show that our DSC model outperforms state-of-the-art methods when transferring to downstream dense prediction tasks, including object detection, semantic segmentation, and instance segmentation. Code will be made available.

cs.CV↗

arXiv2021

PIMNet: A Parallel, Iterative and Mimicking Network for Scene Text Recognition

Nowadays, scene text recognition has attracted more and more attention due to its various applications. Most state-of-the-art methods adopt an encoder-decoder framework with attention mechanism, which generates text autoregressively from left to right. Despite the convincing performance, the speed is limited because of the one-by-one decoding strategy. As opposed to autoregressive models, non-autoregressive models predict the results in parallel with a much shorter inference time, but the accuracy falls behind the autoregressive counterpart considerably. In this paper, we propose a Parallel, Iterative and Mimicking Network (PIMNet) to balance accuracy and efficiency. Specifically, PIMNet adopts a parallel attention mechanism to predict the text faster and an iterative generation mechanism to make the predictions more accurate. In each iteration, the context information is fully explored. To improve learning of the hidden layer, we exploit the mimicking learning in the training phase, where an additional autoregressive decoder is adopted and the parallel decoder mimics the autoregressive decoder with fitting outputs of the hidden layer. With the shared backbone between the two decoders, the proposed PIMNet can be trained end-to-end without pre-training. During inference, the branch of the autoregressive decoder is removed for a faster speed. Extensive experiments on public benchmarks demonstrate the effectiveness and efficiency of PIMNet. Our code will be available at https://github.com/Pay20Y/PIMNet.

cs.CV↗

arXiv2021

Mask is All You Need: Rethinking Mask R-CNN for Dense and Arbitrary-Shaped Scene Text Detection

Due to the large success in object detection and instance segmentation, Mask R-CNN attracts great attention and is widely adopted as a strong baseline for arbitrary-shaped scene text detection and spotting. However, two issues remain to be settled. The first is dense text case, which is easy to be neglected but quite practical. There may exist multiple instances in one proposal, which makes it difficult for the mask head to distinguish different instances and degrades the performance. In this work, we argue that the performance degradation results from the learning confusion issue in the mask head. We propose to use an MLP decoder instead of the "deconv-conv" decoder in the mask head, which alleviates the issue and promotes robustness significantly. And we propose instance-aware mask learning in which the mask head learns to predict the shape of the whole instance rather than classify each pixel to text or non-text. With instance-aware mask learning, the mask branch can learn separated and compact masks. The second is that due to large variations in scale and aspect ratio, RPN needs complicated anchor settings, making it hard to maintain and transfer across different datasets. To settle this issue, we propose an adaptive label assignment in which all instances especially those with extreme aspect ratios are guaranteed to be associated with enough anchors. Equipped with these components, the proposed method named MAYOR achieves state-of-the-art performance on five benchmarks including DAST1500, MSRA-TD500, ICDAR2015, CTW1500, and Total-Text.

cs.CV↗

arXiv2021

GMH: A General Multi-hop Reasoning Model for KG Completion

Knowledge graphs are essential for numerous downstream natural language processing applications, but are typically incomplete with many facts missing. This results in research efforts on multi-hop reasoning task, which can be formulated as a search process and current models typically perform short distance reasoning. However, the long-distance reasoning is also vital with the ability to connect the superficially unrelated entities. To the best of our knowledge, there lacks a general framework that approaches multi-hop reasoning in mixed long-short distance reasoning scenarios. We argue that there are two key issues for a general multi-hop reasoning model: i) where to go, and ii) when to stop. Therefore, we propose a general model which resolves the issues with three modules: 1) the local-global knowledge module to estimate the possible paths, 2) the differentiated action dropout module to explore a diverse set of paths, and 3) the adaptive stopping search module to avoid over searching. The comprehensive results on three datasets demonstrate the superiority of our model with significant improvements against baselines in both short and long distance reasoning scenarios.

cs.AI↗

arXiv2021

On kinetic and macroscopic models for the stripe formation in engineered bacterial populations

We study the well-posedness of the biological models with AHL-dependent cell mobility on engineered Escherichia coli populations. For the kinetic model proposed by Xue-Xue-Tang recently, the local existence for large initial data is proved first. Furthermore, the positivity and local conservation laws for density $ρ(t,x,z)$ and nutrient $n(t,x)$ with initial assumptions are justified. Based on these properties, it can be extended globally in time near the equilibrium $(0,0,0)$. Considering the asymptotic behaviors of faster response CheZ turnover rate (i.e.,$\varepsilon\rightarrow 0$), one formally derives an anisotropic diffusion engineered Escherichia coli populations model (in short, AD-EECP) for which we find a key extra a priori estimate to overcome the difficulties coming from the nonlinearity of the diffusion structure. The local well-posedness and the positivity and local conservation laws for density and nutrient of the AD-EECP are justified. Furthermore, the global existence around the steady state $(\varrho_a, h_a, 0)$ with $\varrho_a \in [0, Λ_b)$ is obtained.

math.AP↗

arXiv2021

Compressible Euler limit from Boltzmann equation with Maxwell reflection boundary condition in half-space

Starting from the local-in-time classical solution to the compressible Euler system with impermeable boundary condition in half-space, by employing the coupled weak viscous layers (governed by linearized compressible Prandtl equations with Robin boundary condition) and linear kinetic boundary layers, and the analytical tools in \cite{Guo-Jang-Jiang-2010-CPAM} and some new boundary estimates both for Prandtl and Knudsen layers, we proved the local-in-time existence of Hilbert expansion type classical solutions to the scaled Boltzmann equation with Maxwell reflection boundary condition with accommodation coefficient $α_\varepsilon=O(\sqrt{\varepsilon})$ when the Knudsen number $\varepsilon$ small enough. As a consequence, this justifies the corresponding case of formal analysis in Sone's books \cite{Sone-2002book, Sone-2007-Book}. This also extends the results in \cite{GHW-2020} from specular to Maxwell reflection boundary condition. Both of this paper and \cite{GHW-2020} can be viewed as generalizations of Caflisch's classic work \cite{Caflish-1980-CPAM} to the cases with boundary.

math.AP↗

arXiv2021

On a Reversible Gray-Scott Type System from Energetic Variational Approach and Its Irreversible Limit

Most of the previous studies on the well-known Gray-Scott model view it as an irreversible chemical reaction system. In this paper, we derive a four-species reaction-diffusion system using the energetic variational approach based on the law of mass action. This is a reversible Gray-Scott type model, which has a natural entropy structure. We establish the local well-posedness of this system, and justify the limit to the corresponding irreversible Gray-Scott type system as some backward coefficients tend to zero. Furthermore, under some smallness assumption on the initial data, we obtain the global-in-time existence of classical solutions of the reversible system.

math.AP↗

arXiv2021

Mrk 1239: a Type-2 Counterpart of Narrow-line Seyfert-1?

We present new spectrophotometric and spectropolarimetric observations of Mrk 1239, one of the 8 prototypes that defines type-1 narrow-line Seyfert galaxies (NLS1s). Unlike the other typical NLS1s though, a high degree of polarization ($P\sim$5.6%) and red optical-IR ($g-W_4$ = 12.35) colors suggest that Mrk 1239 is more similar to type-2 active galactic nuclei like NGC 1068. Detailed analysis of spectral energy distribution in the UV-optical-IR yields two components from the nucleus: a direct and transmitted component that is heavily obscured ($E_{B-V} \approx 1.6$), and another indirect and scattered one with mild extinction ($E_{B-V} \sim$ 0.5). Such a two-light-paths scenario is also found in previous reports based on the X-ray data. Comparison of emission lines and the detection of He\,{\footnotesize I}*$λ$10830 BAL at [-3000,-1000] km s$^{-1}$ indicates that the obscuring clouds are at physical scale between the sublimation radius and that of the narrow emission line regions. The potential existence of powerful outflows is found as both the obscurer and scatterer are outflowing. Similar to many other type-2s, jet-like structure in the radio band is found in Mrk 1239, perpendicular to the polarization angle, suggesting polar scattering. We argue that Mrk 1239 is very probably a type-2 counterpart of NLS1s. The identification of 1 out of 8 prototype NLS1s as a type-2 counterpart implies that there can be a substantial amount of analogs of Mrk 1239 misidentified as type-1s in the optical band. Properties of these misidentified objects are going to be explored in our future works.

astro-ph.GA↗