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Fei Xie

Publications and source records attributed to Fei Xie.

At least 37 records · Page 2Linked to original sources

AutoFly: Vision-Language-Action Model for UAV Autonomous Navigation in the Wild

Vision-language navigation (VLN) requires intelligent agents to navigate environments by interpreting linguistic instructions alongside visual observations, serving as a cornerstone task in Embodied AI. Current VLN research for unmanned aerial vehicles (UAVs) relies on detailed, pre-specified instructions to guide the UAV along predetermined routes. However, real-world outdoor exploration typically occurs in unknown environments where detailed navigation instructions are unavailable. Instead, only coarse-grained positional or directional guidance can be provided, requiring UAVs to autonomously navigate through continuous planning and obstacle avoidance. To bridge this gap, we propose AutoFly, an end-to-end Vision-Language-Action (VLA) model for autonomous UAV navigation. AutoFly incorporates a pseudo-depth encoder that derives depth-aware features from RGB inputs to enhance spatial reasoning, coupled with a progressive two-stage training strategy that effectively aligns visual, depth, and linguistic representations with action policies. Moreover, existing VLN datasets have fundamental limitations for real-world autonomous navigation, stemming from their heavy reliance on explicit instruction-following over autonomous decision-making and insufficient real-world data. To address these issues, we construct a novel autonomous navigation dataset that shifts the paradigm from instruction-following to autonomous behavior modeling through: (1) trajectory collection emphasizing continuous obstacle avoidance, autonomous planning, and recognition workflows; (2) comprehensive real-world data integration. Experimental results demonstrate that AutoFly achieves a 3.9% higher success rate compared to state-of-the-art VLA baselines, with consistent performance across simulated and real environments.

cs.RO↗

ALPBench: A Benchmark for Attribution-level Long-term Personal Behavior Understanding

Recent advances in large language models have highlighted their potential for personalized recommendation, where accurately capturing user preferences remains a key challenge. Leveraging their strong reasoning and generalization capabilities, LLMs offer new opportunities for modeling long-term user behavior. To systematically evaluate this, we introduce ALPBench, a Benchmark for Attribution-level Long-term Personal Behavior Understanding. Unlike item-focused benchmarks, ALPBench predicts user-interested attribute combinations, enabling ground-truth evaluation even for newly introduced items. It models preferences from long-term historical behaviors rather than users' explicitly expressed requests, better reflecting enduring interests. User histories are represented as natural language sequences, allowing interpretable, reasoning-based personalization. ALPBench enables fine-grained evaluation of personalization by focusing on the prediction of attribute combinations task that remains highly challenging for current LLMs due to the need to capture complex interactions among multiple attributes and reason over long-term user behavior sequences.

cs.IR↗

The Interdecadal Bipolar Oscillation: An Atmospheric Water Vapor Mode Driving Asynchronous Polar Climate Change

Climate change is progressing asynchronously between the Arctic and Antarctic, with important implications for global climate dynamics. While the Arctic has experienced rapid warming and pronounced amplification, the Antarctic has exhibited a delayed and heterogeneous response. Here, we identify an Interdecadal Bipolar Oscillation (IBO) in atmospheric water vapor, a coherent internal mode of variability that connects the two polar regions and helps explain their divergent climate trajectories over the past eight decades. Using reanalysis data alongside historical and pre-industrial control simulations from CMIP6, we demonstrate that the IBO is a robust internal variability mode with a quasi-period of 60 ~ 80 years. This oscillation modulates the background warming signal, with a phase shift in the late 1980s amplifying moistening and warming in the Arctic while concurrently suppressing changes in the Antarctic. Crucially, model projections suggest a possible phase reversal, which could slow water vapor increases in the Arctic while accelerating them in the Antarctic, potentially marking the start of rapid Antarctic climate change. While uncertainties remain in how climate models capture polar water vapor, our findings highlight the IBO as a pivotal driver of polar climate evolution and a potential contributor to emerging climate risks in the Southern Hemisphere.

physics.ao-ph↗

X-ray Polarization and Spectral Variations in an Extreme High-Synchrotron-Peaked Blazar 1ES 1101--232

We present the first X-ray polarimetric observation of the extreme high-synchrotron-peaked blazar 1ES 1101--232, conducted by the Imaging X-ray Polarimetry Explorer (IXPE). The data analysis incorporates simultaneous and quasi-simultaneous observations from Swift-XRT and NuSTAR. Our results reveal a significant detection of X-ray polarization in the 2--6 keV band at a confidence level (CL) of 6.6$σ$, with a polarization degree of $Π_{\rm X}=17.9\%\pm2.7\%$ and an electric vector position angle (EVPA) of $ψ_{\rm X}=10^\circ.0\pm4^\circ.4$. An even higher polarization degree of $Π_{\rm X}=38.9\%\pm9.1\%$ with an EVPA of $ψ_{\rm X}=13^\circ.9\pm6^\circ.7$ is observed within a narrower time interval, at a CL of 4.3$σ$. During the IXPE observational campaign, the X-ray spectrum of 1ES 1101--232 exhibits a clear soft-to-hard spectral evolution in the 0.3--10 keV band, although no significant flux variability is detected. Additionally, a clockwise hysteresis loop is identified in the flux--photon index plane. These findings collectively indicate that the X-ray emission from 1ES 1101--232 originates in a region characterized by a well-ordered magnetic field through synchrotron radiation.

astro-ph.HE↗

In-orbit background and sky survey simulation study of POLAR-2/LPD

The Low-Energy X-ray Polarization Detector (LPD) is one of the payloads in the POLAR-2 experiment, designed as an external payload for the China Space Station (CSS) deployment in early 2024. LPD is specifically designed to observe the polarization of Gamma-Ray Bursts (GRBs) prompt emission in the energy range of 2-10 keV, with a wide field of view (FoV) of 90 degrees in preliminary design. This observation is achieved using an array of X-ray photoelectric polarimeters based on gas pixel detectors. Due to the wide FoV configuration, the in-orbit background count rate in the soft X-ray range is high, while GRBs themselves also exhibit a high flux in this energy band. In order to assess the contribution of various background components to the total count rate, we conducted detailed simulations using the GEANT4 C++ package. Our simulations encompassed the main interactions within the instrument materials and provided insights into various background components within the wide FoV scheme. The simulation results reveal that among the background components, the primary contributors are the cosmic X-ray background (CXB) and bright X-ray sources. The total background count rate of LPD, after applying the charged particle background rejection algorithm, is approximately 0.55 counts/cm^2/s on average, and it varies with the detector's orbit and pointing direction. Furthermore, we performed comprehensive simulations and comparative analyses of the CXB and X-ray bright sources under different FoVs and detector pointings. These analyses provide valuable insights into the background characteristic for soft X-ray polarimeter with wide FoV.

astro-ph.IM↗

Wide-Field X-ray Polarimetry for High Energy Astronomical Transients: First results of the pathfinder CXPD Cubesat Mission

The Low Energy Polarization Detector (LPD) is a key component of the next-generation large-scale Gamma-Ray Burst polarimeter, POLAR-2. It is designed for polarization observations of transient sources in the soft X-ray energy range with a wide field of view (FOV). To validate the key technologies required for wide-FOV X-ray polarization measurements, the Cosmic X-ray Polarization Detector (CXPD) CubeSat was developed as a prototype for the LPD. The CXPD is equipped with two Gas Microchannel Plate Pixel Detectors (GMPDs) that measure X-ray polarization via the photoelectric effect, where ejected photoelectrons produce ionization tracks in the gas which are imaged to reconstruct their emission directions. Laboratory calibrations of the modulation factor and energy spectra were successfully performed using linear polarized X-ray sources at 2.98 keV, 4.51 keV, 6.40 keV, and 8.05 keV. Since its launch in June 2023, the CXPD has successfully completed critical in-orbit technology verification. It has also performed polarization observations of two bright X-ray sources Sco X-1 and the transient Swift J1727.8-1613 yielding constraints on their polarization degrees and angles. Notably, this was the first time that an anti-coincidence detector had been implemented in an X-ray polarimeter, enabling in-orbit verification of the charged-particle background rejection algorithm. These results demonstrate the feasibility of wide-field soft X-ray polarization measurements and provide essential guidance for the development of the LPD for the POLAR-2 mission, thereby advancing the frontier of X-ray polarization astronomy.

astro-ph.IM↗

Highly Polarized Intrinsic Emission and its Orthogonal Counterpart in Vela X-1

Vela X-1 is one of the most archetypal wind-fed X-ray pulsars (XRPs), and the emergence of its orthogonal polarization states reveals distinctive polarimetric properties. Using data from Imaging X-ray Polarimetry Explorer (IXPE) observations of Vela X-1, we perform a polarization analysis of Vela X-1 using a triple power-law spectral model absorbed by varying column densities, successfully isolating two physically distinct orthogonal polarized components. The first polarized component corresponds to emission from the accretion mound surface that is not obscured by the wind clumps, with its polarization degree (PD) exceeding 30\%. In specific phase intervals, the PD reaches \(50.9 \pm 10.7\%\). This marks the first detection of such highly polarized neutron star emission in an XRP. The second polarized component likely originates from complex physical processes within or near the accretion mound, with its PD showing a potential negative correlation with column density. Furthermore, by rotating the predicted polarization angle (PA) of the first polarized component by 90$^\circ$, we successfully achieve separate fitting and simultaneous fitting of the two orthogonal polarization states using the rotating vector model (RVM).

astro-ph.HE↗

Retrieval-Augmented Feature Generation for Domain-Specific Classification

Feature generation can significantly enhance learning outcomes, particularly for tasks with limited data. An effective way to improve feature generation is to expand the current feature space using existing features and enriching the informational content. However, generating new, interpretable features usually requires domain-specific knowledge on top of the existing features. In this paper, we introduce a Retrieval-Augmented Feature Generation method, RAFG, to generate useful and explainable features specific to domain classification tasks. To increase the interpretability of the generated features, we conduct knowledge retrieval among the existing features in the domain to identify potential feature associations. These associations are expected to help generate useful features. Moreover, we develop a framework based on large language models (LLMs) for feature generation with reasoning to verify the quality of the features during their generation process. Experiments across several datasets in medical, economic, and geographic domains show that our RAFG method can produce high-quality, meaningful features and significantly improve classification performance compared with baseline methods.

cs.CL↗

Design and Scientific Prospects of the POLAR-2 Mission

The POLAR-2 mission consists of 3 instruments designed with the combined aim of producing a deeper understanding of Gamma-Ray Bursts. To achieve this, POLAR-2 relies on polarisation measurements and, for the first time will provide these using 2 separate polarimeter detectors. The first of these is a payload optimised to perform Compton polarimetry measurements in the 40-1000 keV energy range using a combination of plastic scintillators and SiPMs. The development of this payload, the design of which is based on lessons learned from the POLAR mission, included optimization of plastic scintillator design. In addition, its development included detailed characterization, space qualification and radiation damage and mitigation strategies for the large number of silicon photo-multipliers included in the design. We will present these along with an overview of the readout electronics. These electronics were developed with flexibility in mind, as well as low cost and low power consumption. As such, its design is of interest beyond this polarimeter and is also used on the spectrometer instrument of POLAR-2 where it is used to read out an array of GAGG:Ce scintillators. This readout, in combination with a coded mask, allows this secondary instrument to provide detailed spectral and localization measurements. The final instrument used in the mission aims to use gas-based detectors to perform polarization measurements in the keV energy region. The novelty of this design is that it will be optimized to use these for wide field of view observations. The combination of the three instruments will allow to perform detailed spectral, localization and polarization measurements of these transient phenomena together for the first time. Here we provide an overview of the technologies employed in the mission along with detailed predictions on its capabilities after its launch currently foreseen in 2027.

astro-ph.IM↗

PFEA: An LLM-based High-Level Natural Language Planning and Feedback Embodied Agent for Human-Centered AI

The rapid advancement of Large Language Models (LLMs) has marked a significant breakthrough in Artificial Intelligence (AI), ushering in a new era of Human-centered Artificial Intelligence (HAI). HAI aims to better serve human welfare and needs, thereby placing higher demands on the intelligence level of robots, particularly in aspects such as natural language interaction, complex task planning, and execution. Intelligent agents powered by LLMs have opened up new pathways for realizing HAI. However, existing LLM-based embodied agents often lack the ability to plan and execute complex natural language control tasks online. This paper explores the implementation of intelligent robotic manipulating agents based on Vision-Language Models (VLMs) in the physical world. We propose a novel embodied agent framework for robots, which comprises a human-robot voice interaction module, a vision-language agent module and an action execution module. The vision-language agent itself includes a vision-based task planner, a natural language instruction converter, and a task performance feedback evaluator. Experimental results demonstrate that our agent achieves a 28\% higher average task success rate in both simulated and real environments compared to approaches relying solely on LLM+CLIP, significantly improving the execution success rate of high-level natural language instruction tasks.

cs.RO↗

X-ray spectropolarimetric characterization of the Z-source GX 340+0 in the normal branch

This study presents an X-ray spectropolarimetric characterisation of the Z-source GX 340+0 during the normal branch (NB) and compares it with that obtained for the horizontal branch (HB), using IXPE, NICER and NuSTAR observations. The analysis reveals significant polarisation, with polarisation degrees (PD) of ${\sim}1.4$\% in the NB and ${\sim}3.7$\% in the HB, indicating a notable decrease in polarisation when transitioning from the HB to the NB. The polarisation angles show a consistent trend across the states. Spectropolarimetric analysis favours a dependence of the polarisation on the energy. The Comptonised component shows similar polarisation in both the HB and NB and is higher than the theoretical expectation for a boundary or spreading layer. This suggests a contribution from the wind or the presence of an extended accretion disc corona (ADC) to enhance the polarisation. The results obtained here highlight the importance of using polarimetric data to better understand the accretion mechanisms and the geometry of this class of sources, providing insights into the nature of the accretion flow and the interplay between different spectral components. Overall, the findings advance our understanding of the physical processes governing accretion in low-mass X-ray binaries.

astro-ph.HE↗

Observatory Science with eXTP

Scheduled for launch in 2030, the enhanced X-ray Timing and Polarization (eXTP) telescope is a Chinese space-based mission aimed at studying extreme conditions and phenomena in astrophysics. eXTP will feature three main payloads: Spectroscopy Focusing Arrays (SFAs), Polarimetry Focusing Arrays (PFAs), and a Wide-field Camera (W2C). This white paper outlines observatory science, incorporating key scientific advances and instrumental changes since the publication of the previous white paper [1]. We will discuss perspectives of eXTP on the research domains of flare stars, supernova remnants, pulsar wind nebulae, cataclysmic variables, X-ray binaries, ultraluminous X-ray sources, AGN, and pulsar-based positioning and timekeeping.

astro-ph.IM↗

Physics of Strong Magnetism with eXTP

In this paper we present the science potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission, in its new configuration, for studies of strongly magnetized compact objects. We discuss the scientific potential of eXTP for quantum electrodynamic (QED) studies, especially leveraging on the recent observations made with the NASA IXPE mission. Given eXTP's unique combination of timing, spectroscopy, and polarimetry, we focus on the perspectives for physics and astrophysics studies of strongly magnetized compact objects, such as magnetars and accreting X-ray pulsars. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to launch in early 2030.

astro-ph.HE↗

Prospects for Time-Domain and Multi-Messenger Science with eXTP

In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including advanced polarimetry, high sensitivity & large effective area, and wide energy range coverage, which make it a groundbreaking project in high-energy astrophysics. In this article, we briefly introduce the potential time-domain and multi-messenger targets for eXTP, including gravitational-wave (GW) counterparts, gamma-ray bursts (GRBs), magnetars and fast radio bursts (FRBs), tidal disruption events (TDEs), supernovae, high energy neutrinos and TeV active galactic nucleus (AGNs), and so on. We discuss the advantages of future eXTP observations for detecting these sources, their detection capabilities, the abilities to distinguish theoretical models, and their applications in gravity and cosmology.

astro-ph.HE↗

Multi-Turn Jailbreaks Are Simpler Than They Seem

While defenses against single-turn jailbreak attacks on Large Language Models (LLMs) have improved significantly, multi-turn jailbreaks remain a persistent vulnerability, often achieving success rates exceeding 70% against models optimized for single-turn protection. This work presents an empirical analysis of automated multi-turn jailbreak attacks across state-of-the-art models including GPT-4, Claude, and Gemini variants, using the StrongREJECT benchmark. Our findings challenge the perceived sophistication of multi-turn attacks: when accounting for the attacker's ability to learn from how models refuse harmful requests, multi-turn jailbreaking approaches are approximately equivalent to simply resampling single-turn attacks multiple times. Moreover, attack success is correlated among similar models, making it easier to jailbreak newly released ones. Additionally, for reasoning models, we find surprisingly that higher reasoning effort often leads to higher attack success rates. Our results have important implications for AI safety evaluation and the design of jailbreak-resistant systems. We release the source code at https://github.com/diogo-cruz/multi_turn_simpler

cs.LG↗

VRM: Knowledge Distillation via Virtual Relation Matching

Knowledge distillation (KD) aims to transfer the knowledge of a more capable yet cumbersome teacher model to a lightweight student model. In recent years, relation-based KD methods have fallen behind, as their instance-matching counterparts dominate in performance. In this paper, we revive relational KD by identifying and tackling several key issues in relation-based methods, including their susceptibility to overfitting and spurious responses. Specifically, we transfer novelly constructed affinity graphs that compactly encapsulate a wealth of beneficial inter-sample, inter-class, and inter-view correlations by exploiting virtual views and relations as a new kind of knowledge. As a result, the student has access to richer guidance signals and stronger regularisation throughout the distillation process. To further mitigate the adverse impact of spurious responses, we prune the affinity graphs by dynamically detaching redundant and unreliable edges. Extensive experiments on CIFAR-100, ImageNet, and MS-COCO datasets demonstrate the superior performance of the proposed virtual relation matching (VRM) method, where it consistently sets new state-of-the-art records over a range of models, architectures, tasks, and set-ups. For instance, VRM for the first time hits 74.0% accuracy for ResNet50-to-MobileNetV2 distillation on ImageNet, and improves DeiT-T by 14.44% on CIFAR-100 with a ResNet56 teacher.

cs.CV↗

X-ray Polarization Detection of the Pulsar Wind Nebula in G21.5-0.9 with IXPE

We present the X-ray polarization observation of G21.5-0.9, a young Galactic supernova remnant (SNR), conducted with the Imaging X-ray Polarimetry Explorer (IXPE) in October 2023, with a total livetime of approximately 837 ks. Using different analysis methods, such as a space-integrated study of the entire region of the PWN and a space-resolved polarization map, we detect significant polarization from the pulsar wind nebula (PWN) at the center of the SNR, with an average polarization degree of ~10% oriented at ~33° (north through east). No significant energy-dependent variation in polarization is observed across the IXPE band (2-8 keV). The polarization map, corrected for the effect of polarization leakage, reveals a consistent pattern in both degree and angle, with little change across the nebula. Our findings indicate the presence of a highly polarized central torus, suggesting low levels of turbulence at particle acceleration sites. Unlike Vela, but similar to the Crab Nebula, we observe substantial differences between radio and X-ray polarization maps. This suggests a clear separation in energy of the emitting particle populations and hints at an important, yet poorly understood, role of instabilities in the turbulence dynamics of PWNe.

astro-ph.HE↗

IXPE view of the Sco-like source GX 349+2 in the normal branch

We present a detailed spectropolarimetric study of the Sco-like Z-source GX 349+2, simultaneously observed with the Imaging X-ray Polarimetry Explorer (IXPE) and Nuclear Spectroscopic Telescope Array (NuSTAR). During the observations GX 349+2 was found mainly in the normal branch. A model-independent polarimetric analysis yields a polarisation degree of $1.1\% \pm 0.3\%$ at a polarisation angle of $29° \pm 7°$ in the 2--8 keV band, with ${\sim}4.1σ$ confidence level significance. No variability of polarisation in time and flux has been observed, while an energy-resolved analysis shows a complex dependence of polarisation on energy, as confirmed by a spectropolarimetric analysis. Spectral modeling reveals a dominant disc blackbody component and a Comptonising emitting region, with evidence of a broad iron line associated with a reflection component. Spectropolarimetric fits suggest differing polarisation properties for the disc and Comptonised components, slightly favouring a spreading layer geometry. The polarisation of the Comptonised component exceeds the theoretical expectations, but is in line with the results for other Z-sources with similar inclination. A study of the reflection's polarisation is also reported, with polarisation degree ranging around 10% depending on the assumptions. Despite GX 349+2's classification as a Sco-like source, these polarimetric results align more closely with the Cyg-like system GX 340+0 of similar inclination. This indicates that polarisation is governed primarily by accretion state and orbital inclination, rather than by the subclass to which the source belongs.

astro-ph.HE↗