arXiv subjects

Bo Lan

Publications and source records attributed to Bo Lan.

At least 19 recordsLinked to original sources

arXiv2026

Study of $\chi _{c1,2}$ decays to $PPP$ via light meson resonances

The three-body decays of charmonium states provide a valuable laboratory for probing non-perturbative QCD dynamics and investigating light meson resonances. Three-body decays $\chi _{c1,2} \to P_{1}P_{2}P_{3}$ are studied in this work ($P$ denotes the light pseudoscalar meson). Branching ratio analysis is performed for the $\chi _{c1,2} \to P_{1}P_{2}P_{3}$ decays incorporating light vector ($V$) meson resonance, light tensor ($T$) meson resonance and light scalar ($S$) meson resonance contributions. Based on the SU(3) flavor symmetry approach, we calculate the branching ratios under both the narrow width approximation and the finite width effect, and provide the predict results in the $\chi _{c1,2}\to (V/T)P_{3} \to P_{1}P_{2}P_{3}$ processes. Furthermore, based on the significant $a^{+}_{0}(980)$ resonance signal in $\chi _{c1} \to \pi^{+ }\pi^{- }\eta$ decay, the predict results for $\chi _{c1}\to SP_{3} \to P_{1}P_{2}P_{3}$ are also obtained. While the resonance signals observed in current experiments are mainly concentrated in the $\chi_{c1} \to \pi^+ \pi^- \eta$ decay, our results suggest potential resonance contributions in other channels. Especially in $\chi _{c1,2}\to KK\pi$ channels, the predicted results show the significant resonance contributions from $V$ mesons and $T$ mesons, which is worth further experimental verification and exploration.

hep-ph↗

arXiv2026

SkillAudit: From Fixed-Suite Benchmarking to Skill-Centered Assessment

Agent skills have become a practical way to extend large language model agents, but the growing skill ecosystem still lacks a reliable way to judge whether a skill is worth deploying. Existing evaluation methods remain largely anchored to fixed task suites, assessing skills through performance on predefined tasks and environments. As skill marketplaces expand, this paradigm becomes inadequate: fixed suites can conflate a skill's marginal contribution with backbone strength and miss its value when tasks fall outside the skill's intended scope. We introduce SkillAudit, an end-to-end framework for skill-centered assessment that takes an arbitrary agent skill as input and automatically generates a comprehensive, multi-dimensional evaluation report spanning utility, efficiency/cost, and safety. SkillAudit focuses on the skill artifact itself and constructs capability-aligned evaluation tasks directly from the skill package. The generated tasks are conducted in isolated sandbox environments to collect execution evidence, followed by automated checks with LLM-based judging to produce auditable results. To dissect the agent skills, we propose the baseline comparison principle to measure utility and efficiency/cost, and introduce a two-stage detection paradigm combining static semantic analysis with dynamic runtime verification to assess safety risks. After scanning top-ranked real-world skill packages spanning 23 occupational categories, we found that over 7% of skills are at risky status.

cs.AI↗

arXiv2026

A pure stress formulation for modeling elastic waves using central finite differences

A pure stress-based finite difference formulation is introduced for modeling elastic wave propagation in linear elastic solids with spatial heterogeneity. The approach derives from the strong form of the elastodynamic equation of motion, in which stress is the only dependent variable. A standard second-order central difference scheme is applied to discretize the equation of motion, allowing the space-time-dependent evolution of stress components to be modeled. Numerical dispersion analysis is performed for homogeneous, elastically isotropic materials. Simulations are then carried out for a spatially heterogeneous case consisting of a bimaterial with stiffness heterogeneity. This bimaterial case allows comparison with known closed-form solutions for reflection and transmission coefficients and with an analogous displacement-based finite difference model. Simulations are executed on modern graphics processing unit architectures, enabling stress-based modeling of large-scale three-dimensional problems exceeding one billion degrees of freedom. The approach shows promise for ultrasonic simulations in materials with stiffness heterogeneity and uniform mass density, conditions common in polycrystalline metals used in engineering applications. The formulation offers a potential alternative means of modeling wave propagation and scattering in heterogeneous materials, with possible applications in nondestructive evaluation, materials characterization, biomedical ultrasound, and geosciences.

physics.class-ph↗

arXiv2026

A Reciprocity-Based Signal Compensation Framework for Ultrasonic Backscatter Measurements in Heterogeneous Scattering Media

Ultrasonic backscatter measurements are widely used for microstructural characterisation. However, in materials containing strong anisotropy and spatial heterogeneity, the interpretation of backscatter signals becomes challenging because distance-dependent propagation effects can obscure genuine microstructural variations across depth. In this paper, a cross-directional compensation method is presented for ultrasonic backscatter measurements acquired from opposing inspection surfaces. The method exploits the reciprocal constraint that the dominant through-thickness propagation bias should contain a shared component between opposing inspection directions. A shared distance-dependent baseline is estimated in the logarithmic amplitude domain using an anchor-based fitting approach and subsequently used to compensate the measured backscatter profiles with depth. The method is demonstrated on two macrozone-containing Ti--6Al--4V samples, where conventional attenuation-based compensation is shown to be insufficient to consistently reconcile opposing-face backscatter profiles. Across six opposing-face signal pairs, the proposed method reduces the mean standard deviation of the directional mismatch profile from $0.367$ to $0.120$ and the mean absolute fitted gradient from $0.171$ to $0.0067$, outperforming conventional attenuation compensation. These results demonstrate that reciprocity-based compensation can reduce propagation-related bias while preserving local direction-dependent scattering variations, providing a practical signal-normalisation framework for backscatter analysis in heterogeneous anisotropic materials.

physics.app-ph↗

arXiv2025

Study the decays of $\chi_{cJ}(J=0,1,2)$ to light meson pairs with SU(3) flavor symmetry/breaking analysis

Based on available experimental results on $\chi _{cJ}(J=0,1,2)$ decays, we investigate the $\chi_{cJ}\to PP$, $VV$, $PV$, and $PT$ decays by using SU(3) flavor symmetry/breaking approach, where $P$, $V$, and $T$ denote light pseudoscalar, vector, and tensor mesons, respectively. With the decay amplitude relations determined by SU(3) flavor symmetry/breaking, we present the branching ratios for all $\chi_{cJ}\to PP$ and $\chi_{cJ}\to VV$ modes, including ones without experimental data. While theoretical considerations strongly suppress or even forbid most $\chi_{cJ}\to PV$ and $PT$ decays, we also provide quantitative predictions constrained by existing experimental data. Our results are expected to be accessible in future experiments at BESIII and the planned Super Tau-Charm Facility.

hep-ph↗

arXiv2025

FastDriveVLA: Efficient End-to-End Driving via Plug-and-Play Reconstruction-based Token Pruning

Vision-Language-Action (VLA) models have demonstrated significant potential in complex scene understanding and action reasoning, leading to their increasing adoption in end-to-end autonomous driving systems. However, the long visual tokens of VLA models greatly increase computational costs. Current visual token pruning methods in Vision-Language Models (VLM) rely on either visual token similarity or visual-text attention, but both have shown poor performance in autonomous driving scenarios. Given that human drivers concentrate on relevant foreground areas while driving, we assert that retaining visual tokens containing this foreground information is essential for effective decision-making. Inspired by this, we propose FastDriveVLA, a novel reconstruction-based vision token pruning framework designed specifically for autonomous driving. FastDriveVLA includes a plug-and-play visual token pruner called ReconPruner, which prioritizes foreground information through MAE-style pixel reconstruction. A novel adversarial foreground-background reconstruction strategy is designed to train ReconPruner for the visual encoder of VLA models. Once trained, ReconPruner can be seamlessly applied to different VLA models with the same visual encoder without retraining. To train ReconPruner, we also introduce a large-scale dataset called nuScenes-FG, consisting of 241K image-mask pairs with annotated foreground regions. Our approach achieves state-of-the-art results on the nuScenes open-loop planning benchmark across different pruning ratios.

cs.CV↗

arXiv2025

Improving Retrospective Language Agents via Joint Policy Gradient Optimization

In recent research advancements within the community, large language models (LLMs) have sparked great interest in creating autonomous agents. However, current prompt-based agents often heavily rely on large-scale LLMs. Meanwhile, although fine-tuning methods significantly enhance the capabilities of smaller LLMs, the fine-tuned agents often lack the potential for self-reflection and self-improvement. To address these challenges, we introduce a novel agent framework named RetroAct, which is a framework that jointly optimizes both task-planning and self-reflective evolution capabilities in language agents. Specifically, we develop a two-stage joint optimization process that integrates imitation learning and reinforcement learning, and design an off-policy joint policy gradient optimization algorithm with imitation learning regularization to enhance the data efficiency and training stability in agent tasks. RetroAct significantly improves the performance of open-source models, reduces dependency on closed-source LLMs, and enables fine-tuned agents to learn and evolve continuously. We conduct extensive experiments across various testing environments, demonstrating RetroAct has substantial improvements in task performance and decision-making processes.

cs.CL↗

arXiv2025

XRF V2: A Dataset for Action Summarization with Wi-Fi Signals, and IMUs in Phones, Watches, Earbuds, and Glasses

Human Action Recognition (HAR) plays a crucial role in applications such as health monitoring, smart home automation, and human-computer interaction. While HAR has been extensively studied, action summarization using Wi-Fi and IMU signals in smart-home environments , which involves identifying and summarizing continuous actions, remains an emerging task. This paper introduces the novel XRF V2 dataset, designed for indoor daily activity Temporal Action Localization (TAL) and action summarization. XRF V2 integrates multimodal data from Wi-Fi signals, IMU sensors (smartphones, smartwatches, headphones, and smart glasses), and synchronized video recordings, offering a diverse collection of indoor activities from 16 volunteers across three distinct environments. To tackle TAL and action summarization, we propose the XRFMamba neural network, which excels at capturing long-term dependencies in untrimmed sensory sequences and achieves the best performance with an average mAP of 78.74, outperforming the recent WiFiTAD by 5.49 points in mAP@avg while using 35% fewer parameters. In action summarization, we introduce a new metric, Response Meaning Consistency (RMC), to evaluate action summarization performance. And it achieves an average Response Meaning Consistency (mRMC) of 0.802. We envision XRF V2 as a valuable resource for advancing research in human action localization, action forecasting, pose estimation, multimodal foundation models pre-training, synthetic data generation, and more. The data and code are available at https://github.com/aiotgroup/XRFV2.

cs.CV↗

arXiv2024

Accurate wave velocity measurement from diffuse wave fields

Directional wave speeds variations in anisotropic elastic solids enables material characterisation capabilities, such as determination of elastic constants and volumetric measurement of crystallographic texture. However, achieving such measurements is challenging especially on samples with complex geometries. Here we propose the use of Green's Function reconstruction from diffuse ultrasonic wave fields for accurate velocity measurements on components with arbitrary geometries. Strategies for accurate reconstruction, including averaging over an increased number of different source locations, using longer window lengths of diffuse fields, and accurately deconvolving a source-dependent factor, were implemented to achieve satisfactory convergence towards Green's Function. Additionally, low signal intensity challenges from laser interferometers were overcome to enable non-contact measurement of the wave speeds, by making use of simultaneous excitation of sources to increase signal-to-noise ratio and signal normalisation to account for energy dissipation of diffuse fields. With successful demonstration using both phased array and laser receivers, this advancement fundamentally broadens acoustic wave velocity measurement capabilities to a wider range of environments and holds promise for future material characterisation of complex-shaped components.

physics.app-ph↗

arXiv2024

Efficient numerical frameworks for modelling ultrasonic beams propagating across interfaces

Two different frameworks are developed to model the wave field generated by a transducer and propagating through one or more interfaces, and a Quasi-Monte Carlo (QMC) integration scheme is used to numerically evaluate their results. The first method is based on the Rayleigh-Sommerfeld Integral (RSI), further developing a formulation in the literature and improving its capabilities, while the second relies on a high-frequency approximation, using a ray tracing principle. The advantages and limitations of each model are then compared via in-depth investigations on several use cases, culminating in an efficiency and scope assessment. It was found that the RSI-based model performs well if a large number of field points is needed, such as when modelling a full image of the field. Conversely, for a large number of interfaces, such as when modelling the field through a thin-layered material, the most efficient model was the ray tracing formulation, since it was unnecessary to propagate the field between all the interfaces first. This was especially noticeable for applications requiring only the evaluation of the field at a few points on the other side of multiple interfaces.

physics.class-ph↗

arXiv2024

CodexGraph: Bridging Large Language Models and Code Repositories via Code Graph Databases

Large Language Models (LLMs) excel in stand-alone code tasks like HumanEval and MBPP, but struggle with handling entire code repositories. This challenge has prompted research on enhancing LLM-codebase interaction at a repository scale. Current solutions rely on similarity-based retrieval or manual tools and APIs, each with notable drawbacks. Similarity-based retrieval often has low recall in complex tasks, while manual tools and APIs are typically task-specific and require expert knowledge, reducing their generalizability across diverse code tasks and real-world applications. To mitigate these limitations, we introduce CodexGraph, a system that integrates LLM agents with graph database interfaces extracted from code repositories. By leveraging the structural properties of graph databases and the flexibility of the graph query language, CodexGraph enables the LLM agent to construct and execute queries, allowing for precise, code structure-aware context retrieval and code navigation. We assess CodexGraph using three benchmarks: CrossCodeEval, SWE-bench, and EvoCodeBench. Additionally, we develop five real-world coding applications. With a unified graph database schema, CodexGraph demonstrates competitive performance and potential in both academic and real-world environments, showcasing its versatility and efficacy in software engineering. Our application demo: https://github.com/modelscope/modelscope-agent/tree/master/apps/codexgraph_agent.

cs.SE↗

arXiv2024

Probing $\chi _{cJ}(J=0,1,2)$ decay into baryon and anti-baryon with SU(3) flavor analysis

With the accurate measurements of $\chi _{cJ}(J=0,1,2)$ charmonium decays, we explore $\chi _{cJ}\to \mathcal{B}_{8}\bar{\mathcal{B}}_{8}$ and $\mathcal{B}_{10}\bar{\mathcal{B}}_{10}$ decays based on the SU(3) flavor symmetry model, where $\mathcal{B}_{8}$ and $\mathcal{B}_{10}$ are light octet and decuplet baryons, respectively. The decay amplitude relations are determined by an effective interaction Hamiltonian. Then using experimental data and the amplitude relations of $\chi _{cJ}\to \mathcal{B}_{8}\bar{\mathcal{B}}_{8}$, $\mathcal{B}_{10}\bar{\mathcal{B}}_{10}$ decays, relative nonperturbative coefficients are constrained, and the branching ratios of unmeasured $\chi _{cJ}\to \mathcal{B}_{8}\bar{\mathcal{B}}_{8},\mathcal{B}_{10}\bar{\mathcal{B}}_{10}$, for examples, $\chi _{cJ}\to n\bar{n}$ and $\chi _{cJ}\to\Lambda \bar{\Sigma}^{0}+\bar{\Lambda} \Sigma^{0}$ channels, are predicted. Moreover, we discuss the case of adding a mixing angle between $\Lambda $ and $\Sigma ^{0}$, which is determined by the quark mass differences. Our results provide valuable insights that will aid in advancing our understanding of the mechanisms and characteristics of $\chi _{cJ}$ decays.

hep-ph↗

arXiv2024

GMPC: Geometric Model Predictive Control for Wheeled Mobile Robot Trajectory Tracking

The configuration of most robotic systems lies in continuous transformation groups. However, in mobile robot trajectory tracking, many recent works still naively utilize optimization methods for elements in vector space without considering the manifold constraint of the robot configuration. In this letter, we propose a geometric model predictive control (MPC) framework for wheeled mobile robot trajectory tracking. We first derive the error dynamics of the wheeled mobile robot trajectory tracking by considering its manifold constraint and kinematic constraint simultaneously. After that, we utilize the relationship between the Lie group and Lie algebra to convexify the tracking control problem, which enables us to solve the problem efficiently. Thanks to the Lie group formulation, our method tracks the trajectory more smoothly than existing nonlinear MPC. Simulations and physical experiments verify the effectiveness of our proposed methods. Our pure Python-based simulation platform is publicly available to benefit further research in the community.

eess.SY↗

arXiv2023

Ultrasonic backscattering model for Rayleigh waves in polycrystals with Born and independent scattering approximations

This paper presents theoretical and numerical models for the backscattering of 2D Rayleigh waves in single-phase, untextured polycrystalline materials with statistically equiaxed grains. The theoretical model, based on our prior inclusion-induced Rayleigh wave scattering model and the independent scattering approximation, considers single scattering of Rayleigh-to-Rayleigh (R-R) waves. The numerical finite element model is established to accurately simulate the scattering problem and evaluate the theoretical model. Good quantitative agreement is observed between the theoretical model and the finite element results, especially for weakly scattering materials. The agreement decreases with the increase of the anisotropy index, owing to the reduced applicability of the Born approximation. However, the agreement remains generally good when weak multiple scattering is involved. In addition, the R-R backscattering behaviour of 2D Rayleigh waves is similar to the longitudinal-to-longitudinal and transverse-to-transverse backscattering of bulk waves, with the former exhibiting stronger scattering. These findings establish a foundation for using Rayleigh waves in quantitative characterisation of polycrystalline materials.

physics.app-ph↗

arXiv2023

Investigation of the Influence of Macrozones in Titanium Alloys on the Propagation and Scattering of Ultrasound

The presence of macrozones (or micro-textured regions) in Ti-6Al-4V (Ti64) was shown to be a potential cause to the onset of cold dwell fatigue which reduces fatigue life significantly. Past research has demonstrated the potential of using ultrasonic testing for macrozone characterisation, with the variation of ultrasound attenuation, backscatter, and velocity in the presence of macrozones. However, due to the complexity of the microstructure, some physical phenomena that were observed are still not well understood. In this study, we propose the use of Finite Element (FE) polycrystalline models to provide us with a means to systematically study the wave-macrozone interaction. Through this investigation performed using two-dimensional (2D) models, we are able to identify important correlations between macrozone characteristics (size, shape, and texture) and ultrasound responses (attenuation, backscatter, and velocity). The observed behaviours are then validated experimentally, and we also highlight how this understanding can potentially aid with the characterisation of macrozones in Ti-64 samples.

physics.app-ph↗

arXiv2023

Stiffness matrix method for modelling wave propagation in arbitrary multilayers

Natural and engineered media usually involve combinations of solid, fluid and porous layers, and accurate and stable modelling of wave propagation in such complex multilayered media is fundamental to evaluating their properties with wave-based methods. Here we present a general stiffness matrix method for modelling waves in arbitrary multilayers. The method first formulates stiffness matrices for individual layers based on the governing wave equations for fluids and solids, and the Biot theory for porous materials. Then it utilises the boundary conditions considered at layer interfaces to assemble the layer matrices into a global system of equations, to obtain solutions for reflection and transmission coefficients at any incidence. Its advantage over existing methods is manifested by its unconditional computational stability, and its validity is proved by experimental validations on single solid sheets, porous layers, and porous-solid-porous battery electrodes. This establishes a powerful theoretical platform that allows us to develop advanced wave-based methods to quantitatively characterise properties of the layers, especially for layers of porous materials.

physics.class-ph↗

arXiv2023

Frustrated total internal reflection of ultrasonic waves at a fluid-coupled elastic plate

A complete treatment regarding frustrated total internal reflection (FTIR) of ultrasonic waves is presented and validated against experiments, providing a theoretical explanation for the physics behind this phenomenon. Two different approaches are used to develop a theoretical model capable of studying transmission in fluid-coupled elastic plates. One is the multiple reflections approach (analogous to the study of FTIR in electromagnetic/optical waves), which is shown to have limited applicability for incident angles beyond the first critical angle. This prompted us to address the problem using the second, potentials-based approach, which is established and validated against experimental data with correct predictions for a thin air-coupled steel sheet. A relation between the transmitted power and the dispersion curves for guided waves in the plate is established, highlighting the two fundamental causes of FTIR in such systems. First, a thin plate, when compared to the wavelength of the wave incident on it, will always be subjected to the effects of FTIR. This is because the evanescent wave created inside the plate will never assume negligible values, thus always allowing transmission to the other side. Second, and more surprisingly, the excitation of the fundamental antisymmetric mode $A_0$ of the plate is shown to be a direct enabler of FTIR, even for thicker plates.

physics.class-ph↗

arXiv2022

Coupled three-mode squeezed vacuum: Gaussian steering and remote generation of Wigner negativity

Multipartite Einstein-Podolsky-Rosen (EPR) steering and multimode quantum squeezing are essential resources for various quantum applications. The paper focuses on studying a coupled three-mode squeezed vacuum (C3MSV), which is a typical multimode squeezed Gaussian state and will exhibit peculiar steering property. Using the technique of integration within ordered products, we give the normal-ordering form for the coupled three-mode squeezing operator and derive the general analytical expressions of the statistical quantities for the C3MSV. Under Gaussian measurements, we analyze all bipartite Gaussian steerings (including no steering, one-way steering and two-way steering) in details and study the monogamy relations for the C3MSV. Then, we study the decoherence of all these steerings in noisy channels and find that sudden death will happen in a certain threshold time. Through the steerings shared in the C3MSV, we propose conceptual (and ideal) schemes of remotely generating Wigner negativity (WN) by performing appropriate photon subtraction(s) in the local position. Our obtained results may lay a solid theoretical foundation for a future practical study. We also believe that the C3MSV will be one of good candidate resources in future quantum protocols.

quant-ph↗