arXiv subjects

Xiao Fan

Publications and source records attributed to Xiao Fan.

At least 19 recordsLinked to original sources

arXiv2026

Provenance Before Prose: Claim-Locked Reporting

Large language models (LLMs) can fluently verbalize statistical evidence, yet statistical reports can still drift numerical values, invert effect directions, or restate thresholded contrasts as categorical effects. We frame these failures as a control problem: the evidence-bearing content of a scientific report should be fixed by structured statistical results rather than sampled during prose generation. We therefore use cross-run reproducibility to stress-test whether report-visible numbers and claims are bound before prose generation. Existing controls operate at the text or slot level; a deterministic hybrid template reproduces only 61.1% of report-visible numerical content across seeds because the LLM still selects which findings and numbers the template renders. We propose claim-locked reporting, a provenance-before-prose protocol that fixes the evidence source, numbers, direction, and allowed language strength of each reportable claim before the LLM writes only connective prose. Across fMRI functional-connectivity reporting and randomized controlled trial reporting on Evidence Inference 2.0, claim-locked reporting improves reproducibility over the hybrid template by 37.4 and 20.5 points, respectively. Blinded human audits support the observed direction-preservation and governance trends. In an fMRI cost analysis with DeepSeek, claim-locked reporting also yields the lowest observed token use and median generation latency.

cs.CL↗

arXiv2026

Frequency-Decorrelated Temporal Ensembles for EEG--fNIRS Imagined-Handwriting Decoding

Imagined handwriting offers a temporally rich paradigm for non-invasive neural decoding, yet reliable recognition across unseen participants remains difficult because scalp EEG is noisy and internally generated stroke sequences vary across individuals. The Multimodal Brain-Computer Interface Grand Challenge provides synchronized EEG and fNIRS for four-class subject-independent handwriting-trajectory classification. We propose FRED, a task-adapted system that models imagined handwriting as a multi-second motor sequence and trains a compact multi-scale temporal network on three complementary EEG frequency views. With three seeds per view, cross-band members produce substantially less-correlated errors than same-band replicas, yielding a clean nine-member ensemble accuracy of 0.8076/0.7242/0.7492 on the public/private/overall test partitions without test-set adaptation or output constraints. The submitted pipeline further incorporates transductive pseudo-label training, three EEG-Conformer members, posterior aggregation, and a paradigm-aware decoder. Because every 12-trial randomization block contains three instances of each class, the final predictions are obtained by Hungarian assignment under the known block quota. On one fixed posterior pool, independent, session-constrained, and block-constrained decoding achieve 0.7600, 0.7758, and 0.7952 overall accuracy, respectively. The complete system reaches 0.8498/0.7718/0.7952, ranking fourth on the private split. A modality audit finds fNIRS-only decoding at chance (0.2511 overall), while adding fNIRS to EEG changes accuracy by only +0.0025. These results identify frequency-diverse temporal EEG modeling and protocol-matched structured inference as the principal sources of performance in this sparse-montage EEG--fNIRS setting. The source code is available at https://github.com/XiuFan719/EEG-fNIRS-fuse-method-for-MM-challenge.

cs.CV↗

arXiv2026

Stable X-ray reverberation lags in the black hole X-ray binary Swift J1727.8-1613

Aims. We investigate the evolution of X-ray reverberation lags in the black hole X-ray binary Swift J1727.8-1613 during its 2023 outburst, with the aim of probing the inner accretion flow geometry across spectral states. Methods. We analyzed NICER observations covering the low-hard state (LHS) and hard-intermediate state (HIMS). The time lags were computed using Fourier-based techniques, and we constructed lag-frequency and lag-energy spectra. To obtain a robust estimate of the soft lag amplitude, we focused on a frequency range in which the reverberation signal dominates and remains stable, thereby minimizing contamination from hard lags and phase-wrapping effects. Results. The soft lag amplitude increases rapidly from the LHS to the early HIMS and then stays near 10 ms throughout the HIMS. In the frequency range in which reverberation lags prevail, the lag shows little dependence on Fourier frequency. On the other hand, the observed low-frequency lags change from hard-lag dominated to soft-lag dominated, with amplitudes comparable to those measured at higher frequencies. Conclusions. These results suggest that the reverberation lag varies little during the HIMS, consistent with a relatively stable inner accretion geometry during this state. The apparent evolution of the lag amplitude from the LHS to the HIMS can be largely explained by the diminishing effect of hard lags and does not necessarily require significant changes in the intrinsic light-travel timescale. Swift J1727.8-1613 therefore provides a case in which the reverberation signal can be studied with reduced contamination over a broad frequency range, offering new insight into the evolution of the accretion geometry in black hole X-ray binaries.

astro-ph.HE↗

arXiv2026

X-rays breaking out of pre-explosion ejecta mark a supernova's first light

Massive stars die as core-collapse supernovae, whose optical light emerges days after the implosion. Theory predicts that the initial collapse-driven shock, upon breaking through the star and dense circumstellar medium, emits a brief thermal flash of soft X-rays and ultraviolet. Yet these elusive first signals have remained largely undetected, owing to limited wide-field soft X-ray monitoring. Here we report the discovery of a soft X-ray flash, EP260321a, followed days later by a broad-lined supernova from an envelope-stripped progenitor. Its X-ray spectrum, best modeled with blackbody, establishes it as the long-sought archetypal shock breakout. The burst's duration and energetics place the breakout at a radius of 300 solar radii, tracing a dense surrounding shell and revealing abrupt mass ejection within the final month before collapse.

astro-ph.HE↗

arXiv2026

QPEs from Warped Disk Collisions with EMRIs: Brightness-Recurrence Diagram and Gravitational-Wave Follow-up

Quasi-Periodic Eruptions (QPEs) display correlated long/short and strong/weak patterns that remain unexplained by existing flat-disk collision models. We propose that these features arise from an extreme-mass-ratio inspiral (EMRI) colliding with a warped accretion disk, likely formed after a tidal disruption event. The warp modulates both recurrence time and burst energy, encoding the disk geometry -- and thus the spin of the central supermassive black hole (SMBH) -- into the X-ray light curve. We introduce the Brightness-Recurrence Diagram (BRD) to visualize this correlation, where QPE bursts trace an elliptical trajectory driven by the EMRI's apsidal precession; the tilt of this ellipse encodes whether the EMRI is prograde or retrograde relative to the SMBH spin. Applying this model to the prototypical QPE source GSN 069 successfully reproduces the observed patterns. The data are consistent with either a prograde stellar secondary or a retrograde stellar-mass black hole. In the stellar-mass black hole scenario, ongoing orbital decay could render the EMRI detectable by LISA within a few decades, facilitating gravitational-wave follow-up and independent multimessenger constraints on the system.

astro-ph.HE↗

arXiv2026

BrainRing: An Interactive Web-Based Tool for Brain Connectivity Chord Diagram Visualization

Visualizing brain functional connectivity (FC) patterns is essential for understanding neural organization, yet existing tools such as Circos and BrainNet Viewer require complex configuration files or proprietary software environments. We present BrainRing, a free, open-source, browser-based interactive tool for generating publication-quality chord diagrams of brain connectivity data. BrainRing requires no installation, backend server, or programming knowledge. Users simply open a single HTML file in any modern browser. The tool supports 8 widely-used brain atlases (Brainnetome 246, AAL-90/116, Schaefer 100/200/400, Power 264, and Dosenbach 160), provides real-time parameter adjustment through an intuitive graphical interface, and offers comprehensive edge management including click-to-connect, per-edge color customization, and Circos link file import. BrainRing supports both Chinese and English interfaces and enables researchers to produce publication-ready SVG and PNG figures with full control over visual styling, all within seconds rather than the minutes-to-hours workflow typical of script-based approaches. BrainRing is freely available at https://github.com/XiuFan719/brain-connectivity-viz with a live demo at https://XiuFan719.github.io/brain-connectivity-viz/.

cs.HC↗

arXiv2026

Air-to-Ground Communications for Internet of Things: UAV-based Coverage Hole Detection and Recovery

Uncrewed aerial vehicles (UAVs) play a pivotal role in ensuring seamless connectivity for Internet of Things (IoT) devices, particularly in scenarios where conventional terrestrial networks are constrained or temporarily unavailable. However, traditional coverage-hole detection approaches, such as minimizing drive tests, are costly, time-consuming, and reliant on outdated radio-environment data, making them unsuitable for real-time applications. To address these limitations, this paper proposes a UAV-assisted framework for real-time detection and recovery of coverage holes in IoT networks. In the proposed scheme, a patrol UAV is first dispatched to identify coverage holes in regions where the operational status of terrestrial base stations (BSs) is uncertain. Once a coverage hole is detected, one or more UAVs acting as aerial BSs are deployed by a satellite or nearby operational BSs to restore connectivity. The UAV swarm is organized based on Delaunay triangulation, enabling scalable deployment and tractable analytical characterization using stochastic geometry. Moreover, a collision-avoidance mechanism grounded in multi-agent system theory ensures safe and coordinated motion among multiple UAVs. Simulation results demonstrate that the proposed framework achieves high efficiency in both coverage-hole detection and on-demand connectivity restoration while significantly reducing operational cost and time.

cs.IT↗

arXiv2025

MoETTA: Test-Time Adaptation Under Mixed Distribution Shifts with MoE-LayerNorm

Test-Time adaptation (TTA) has proven effective in mitigating performance drops under single-domain distribution shifts by updating model parameters during inference. However, real-world deployments often involve mixed distribution shifts, where test samples are affected by diverse and potentially conflicting domain factors, posing significant challenges even for SOTA TTA methods. A key limitation in existing approaches is their reliance on a unified adaptation path, which fails to account for the fact that optimal gradient directions can vary significantly across different domains. Moreover, current benchmarks focus only on synthetic or homogeneous shifts, failing to capture the complexity of real-world heterogeneous mixed distribution shifts. To address this, we propose MoETTA, a novel entropy-based TTA framework that integrates the Mixture-of-Experts (MoE) architecture. Rather than enforcing a single parameter update rule for all test samples, MoETTA introduces a set of structurally decoupled experts, enabling adaptation along diverse gradient directions. This design allows the model to better accommodate heterogeneous shifts through flexible and disentangled parameter updates. To simulate realistic deployment conditions, we introduce two new benchmarks: potpourri and potpourri+. While classical settings focus solely on synthetic corruptions, potpourri encompasses a broader range of domain shifts--including natural, artistic, and adversarial distortions--capturing more realistic deployment challenges. Additionally, potpourri+ further includes source-domain samples to evaluate robustness against catastrophic forgetting. Extensive experiments across three mixed distribution shifts settings show that MoETTA consistently outperforms strong baselines, establishing SOTA performance and highlighting the benefit of modeling multiple adaptation directions via expert-level diversity.

cs.LG↗

arXiv2025

Semantic-Space Exploration and Exploitation in RLVR for LLM Reasoning

Reinforcement Learning with Verifiable Rewards (RLVR) for LLM reasoning is often framed as balancing exploration and exploitation in action space, typically operationalized with token-level proxies (e.g., output entropy or confidence). We argue that this apparent trade-off is largely a measurement artifact: token-level statistics reflect next-token uncertainty rather than how reasoning progresses over multi-token semantic structures. We therefore study exploration and exploitation in the hidden-state space of response trajectories. We use Effective Rank (ER) to quantify representational exploration and introduce its temporal derivatives, Effective Rank Velocity (ERV) and Effective Rank Acceleration (ERA), to characterize exploitative refinement dynamics. Empirically and theoretically, ER and ERV exhibit near-zero correlation in semantic space, suggesting the two capacities can be improved simultaneously. Motivated by this, we propose Velocity-Exploiting Rank Learning (VERL), which shapes the RLVR advantage with an auxiliary signal derived from ER/ERV and uses the more stable ERA as a meta-control variable to adaptively balance the incentives. Across multiple base models, RLVR algorithms, and reasoning benchmarks, VERL yields consistent improvements, including large gains on challenging tasks (e.g., 21.4\% in Gaokao 2024). The code is available at https://github.com/hf618/VERL.

cs.LG↗

arXiv2025

On the optical emission in the mini-outburst of the black hole X-ray binary MAXI J1348-630

We investigate the optical emission of the black hole X-ray binary MAXI J1348-630 during its 2019 minioutburst. Using optical data from the Las Cumbres Observatory Global Telescope and X-ray data from Insight-HXMT, we performed time delay analysis, optical-X-ray correlation analysis, and spectral energy distribution (SED) fitting. Our key findings are as follows: (1) The X-ray Comptonization flux lags behind the optical emission by about 8.5 days, a delay naturally explained by the disk instability model (DIM). (2) The optical and X-ray fluxes show a power-law correlation with a slope about 0.4, which lies between the predicted values for viscous heating and X-ray reprocessing, consistent with the DIM framework. (3) SED fitting with the irradiated disk model successfully reproduces the quasi-simultaneous optical and X-ray data, and the contribution of the jet is negligible. Our results indicate that the optical emission during the mini-outburst originates from the disk, rather than the jet or hot accretion flow, and highlight the critical role of the DIM in understanding the mini-outburst of X-ray binaries.

astro-ph.HE↗

arXiv2025

Composite spectrum of Little Red Dot from a standard inner disk and an unstable outer disk

James Webb Space Telescope (JWST) has revealed a new class of high-redshift, very red, compact broad-line sources, termed as "little red dots" (LRDs). The physical mechanism driving these properties remains elusive. We construct spectral energy distributions (SEDs) with spectroscopic redshift for 28 LRDs and find they exhibit V-shaped SEDs with a common break frequency of $\nu_{\rm b}\simeq10^{14.96\pm0.06}$ Hz. We propose that the unique SEDs can be well explained by the combination of an inner standard disk and an outer gravitationally unstable accretion disk with Toomre parameter $Q\sim1$, where the outer disk has a temperature of $\sim2000-4000 K$ and mainly radiates in near-infrared to optical wavebands. The composite spectrum from this model naturally explains the V-shaped continuum and reproduces intrinsically luminous infrared-optical emission without requiring extreme dust extinction or unusual stellar populations. Even considering possible dense gas around the disk to account for pronounced Balmer breaks in some LRDs, the intrinsic optical-UV emission is only suppressed by factors of $\lesssim2-3$, which suggests that most LRDs are sub-Eddington and intrinsically weak. These results provide new insights into early-phase black hole growth and galaxy evolution.

astro-ph.HE↗

arXiv2024

Exploring variation of double-peak broad-line profile in strongly variable AGNs

The geometry and kinematics of the broad-line region (BLR) in AGNs are still unclear, which is crucial for studying the physics and evolution of supermassive black holes (SMBHs) and AGNs. The broad-line profile provides valuable information on BLR geometry and kinematics. In this work, we explore the evolution of line profiles in variable AGNs based on the BLR model of Czerny \& Hryniewicz, where the BLR is driven by the radiation pressure acting on dust at the surface layers of the accretion disk. The line profiles in the low-Eddington-ratio regime show a double-peak profile, which will become a single peak at high Eddington ratios. The high metallicity of $Z\gtrsim 5Z_{\odot}$ is required to reproduce the observational anti-correlation between the peak separation of broad lines and the Eddington ratio for a sample of AGNs. For the broad lines in variable AGNs, it will take several years to several decades to change their line profile if the disk luminosity suffers strong variation in a much shorter timescale. More monitoring of the broad line and continuum in strongly variable AGNs can shed special light on BLR physics.

astro-ph.GA↗

arXiv2024

Simulations on the collision between debris stream and outer dusty torus: a possible channel for forming fast-rise and long-delayed radio outburst in tidal disruption events

The geometrically thick dusty torus structure is believed to exist in the nuclear region of galaxies (especially in active galactic nuclei, AGNs). The debris stream from a tidal disruption event (TDE) will possibly collide with the dusty torus and produce a transient flare. We perform three-dimensional hydrodynamic simulations to model the dynamical evolution of the interaction between unbound debris and dusty torus. During the continuous interaction, the shocked material will be spilled out from the interaction region and form an outflow. We calculate the temporal evolution of synchrotron emission by assuming that the shock accelerates a fraction of electrons in the outflow into a non-thermal distribution. We find that radio emission from the debris-torus collision generates a steep-rise and slow-decline radio light curve due to the sharp edge and dense gas of dusty torus, where the radio outburst delays the main optical/X-ray outburst by several years or even several tens of years. We apply our model to a TDE that happened in a narrow-line Seyfert I (PS16dtm), where both the radio spectrum and the light curve can be roughly reproduced. Future high-sensitivity, wide-field-of-view radio surveys have the opportunity to detect more such radio flares.

astro-ph.HE↗

arXiv2024

The Interaction Between Stars and Past AGN Disk: Possible Explanation for the Kinematic Distributions of S-stars in the Galactic Center

The presence of young stars, aged around several million years and situated within the range of $\sim 0.04-1$ pc from our Galactic center raises a question about their origins and dynamical evolutions. Their kinematics provide an opportunity to explore their formation or possible subsequent dynamical evolution. If Sagittarius A* was active in the past as suggested by several observations, the accretion disk may have a significant impact on the dynamics of stars in the Galactic center. The drag force exerted on stars during star-disk interaction could lead some of them to sink into the accretion disk, and these embedded stars will rapidly migrate inward and eventually be disrupted within $\sim10^5$ yr. This could roughly explain the absence of stars within $2.5 \times 10^4 R_{\rm g}$ ($\sim$ 1000 au). Additionally, Kozai-Lidov oscillations, induced by the gravitational perturbation of the disk, could contribute to the bimodal distribution of S-star inclinations and drive a majority of stars into high eccentricity orbits.

astro-ph.GA↗

arXiv2024

The weakness of soft X-ray intensity: possible physical reason for weak line quasars

Weak-line quasars (WLQs) are a notable group of active galactic nuclei (AGNs) that show unusually weak UV lines even though their optical-UV continuum shapes are similar to those of typical quasars. The physical mechanism for WLQs is an unsolved puzzle in the AGN unified model. We explore the properties of UV emission lines by performing extensive photoionization calculations based on Cloudy simulation with different spectral energy distributions (SEDs) of AGNs. The AGN continua are built from several observational empirical correlations, where the black-body emission from the cold disk, the power-law emission from the hot corona, and a soft X-ray excess component are considered. We find that the equivalent width (EW) of C {\footnotesize IV} from our models is systematically lower than observational values if the component of soft X-ray excess is neglected. The EW will increase several times and is roughly consistent with the observations after considering the soft X-ray excess component as constrained from normal type I AGNs. We find that the UV lines are weak for QSOs with quite large BH mass (e.g., $M_{\rm BH}>10^9M_{\odot}$) and weak soft X-ray emission due to the deficit of ionizing photons. As an example, we present the strength of C {\footnotesize IV} based on the multi-band SEDs for three nearby weak-line AGNs, where the weaker soft X-ray emission normally predicts the weaker lines.

astro-ph.HE↗

arXiv2024

The Devil is in the Details: Boosting Guided Depth Super-Resolution via Rethinking Cross-Modal Alignment and Aggregation

Guided depth super-resolution (GDSR) involves restoring missing depth details using the high-resolution RGB image of the same scene. Previous approaches have struggled with the heterogeneity and complementarity of the multi-modal inputs, and neglected the issues of modal misalignment, geometrical misalignment, and feature selection. In this study, we rethink some essential components in GDSR networks and propose a simple yet effective Dynamic Dual Alignment and Aggregation network (D2A2). D2A2 mainly consists of 1) a dynamic dual alignment module that adapts to alleviate the modal misalignment via a learnable domain alignment block and geometrically align cross-modal features by learning the offset; and 2) a mask-to-pixel feature aggregate module that uses the gated mechanism and pixel attention to filter out irrelevant texture noise from RGB features and combine the useful features with depth features. By combining the strengths of RGB and depth features while minimizing disturbance introduced by the RGB image, our method with simple reuse and redesign of basic components achieves state-of-the-art performance on multiple benchmark datasets. The code is available at https://github.com/JiangXinni/D2A2.

cs.CV↗

arXiv2023

Air-to-Ground Communications Beyond 5G: UAV Swarm Formation Control and Tracking

Unmanned aerial vehicle (UAV) communications have been widely accepted as promising technologies to support air-to-ground communications in the forthcoming sixth-generation (6G) wireless networks. This paper proposes a novel air-to-ground communication model consisting of aerial base stations served by UAVs and terrestrial user equipments (UEs) by integrating the technique of coordinated multi-point (CoMP) transmission with the theory of stochastic geometry. In particular, a CoMP set consisting of multiple UAVs is developed based on the theory of Poisson-Delaunay tetrahedralization. Effective UAV formation control and UAV swarm tracking schemes for two typical scenarios, including static and mobile UEs, are also developed using the multi-agent system theory to ensure that collaborative UAVs can efficiently reach target spatial positions for mission execution. Thanks to the ease of mathematical tractability, this model provides explicit performance expressions for a typical UE's coverage probability and achievable ergodic rate. Extensive simulation and numerical results corroborate that the proposed scheme outperforms UAV communications without CoMP transmission and obtains similar performance to the conventional CoMP scheme while avoiding search overhead.

cs.IT↗

arXiv2023

Core Collapse Supernova Explosions in Active Galactic Nucleus Accretion Disks

Astrophysical events that occur in active galactic nucleus (AGN) disks are believed to differ significantly from the ordinary in the interstellar medium. We show that stars located in the outer region of the AGN disk would explode near the original migration starting points instead of being accreted by the central supermassive black hole due to the effect of viscosity. AGN disks provide a dense environment for supernova (SN) explosions, which inevitably involve ejecta-disk interactions. In this paper, we investigate the light curves (LCs) of core-collapse SN exploded in AGN disks. In addition to the fundamental energy source of $^{56} \mathrm{Ni}$--$^{56} \mathrm{Co}$--$^{56} \mathrm{Fe}$ decay reaction powering the SN LCs, the forward-reverse shock produced during interactions may contribute significantly to the observed flux. If the stellar winds manage to create a cavity surrounded by a shell near the star before the SN explosion, the ejecta-winds-disk configurations are expected. We present various SN LCs from different types of progenitors and find that the SN LCs are dominated by the radiation of ejecta-disk interaction-induced shocks. The resulting SNe in the AGN disk is a promising transient source for UV and optical band detection by the Neil Gehrels Swift Observatory (Swift), the Ultraviolet Explorer (UVEX) and wide field survey telescopes such as Ultraviolet Transient Astronomy Satellite (ULTRASAT), Wide Field Survey Telescope (WFST) and Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory. These detections could aid in the investigation of AGN discs and the associated high-energy transient occurrences.

astro-ph.HE↗