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Excellent dynamic yield and spall strength of single crystal NiAlCo alloy under shock compression

Materials Science and engineering: A 2025年 939卷

作者： Pan, X.T. Dong, J.L. Chen, X.M. Luo, B.Q. Shui, R.J. Xu, C. Wu, G. Wang, G.J. Wu, H.A. Tan, F.L. Zhao, J.H. Sun, C.W. CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern Mechanics CAS Center for Excellence in Complex System Mechanics University of Science and Technology of China Hefei230027 China Institute of Fluid Physics China Academy of Engineering Physics Mianyang621999 China Institute of Applied Electronics China Academy of Engineering Physics Mianyang621999 China

A fundamental understanding of the mechanical behaviors and deformation mechanism of materials subjected to dynamic loading is critical for developing outstanding structural materials. This work focuses on the experimental investigation into the dynamic mechanical behaviors, deformation mechanisms, and damage characteristics of single-crystal NiAlCo which was regarded as a potential structure material at high pressure and strain rate. The shock responses of the single-crystal NiAlCo alloy were tested over a range of shock pressure from 10 to 50 GPa at a strain rate of 105/s utilizing the technique of magnetically driven high-velocity flyer plates on high pulsed power generator CQ-4. Based on the analyses of free surface velocity profiles, a linear Hugoniot relationship between shock wave speed and particle velocity was obtained, and the spall strength gradually increased from 2.61 GPa to 6.98 GPa with increasing shock pressure. The yield strength was calculated from the Hugoniot elastic limit, and it reaches 1.80 GPa over the wide range of shock pressure. Further, the relationship between dynamic strength and strain rate was depicted by empirical formulas in power exponential form. Finally, the detailed transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) microscopic characterization results of recovered samples disclose that single-crystal NiAlCo have abundant micro-deformation mechanisms under high pressure and high strain rate, including dislocation tangle, high-density stacking faults, and Lomer-Cottrell locks. The results show that both spall and yield strength are significantly higher than those of most alloys, exhibiting superior mechanical properties, which may be attributed to the coupling of multiple deformation mechanisms. © 2025 Elsevier B.V.

关键词： Strain rate

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Disentangle the intrinsic line tension from the nano-corrugations induced by surface lateral roughness

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International Communications in Heat and Mass Transfer 2025年 164卷

作者： Long, Zhilin Yuan, Zifeng Wang, Hao Lab of Heat Mass Transfer and Carbon Cycling College of Engineering Peking University Beijing100871 China Center for Applied Physics and Technology Peking University Beijing100871 China Department of Mechanics and Engineering Science Peking University Beijing100871 China State Key Laboratory for Turbulence & Complex System Peking University Beijing100871 China

Line tension of the contact line plays an important role in microscopic wetting, but its understanding remains vague and the reported values are far from convergence. We note in most studies the contact lines are treated as smooth lines as the droplets are considered as smooth spherical caps. Here using helium ion microscopy, we confirm ubiquitous nano-corrugations along the contact lines even on smooth solids like mica. The corrugation size is correlated with the lateral roughness, which represents the lateral characteristic size of the solid roughness elements. A remodified Young's equation for line tension is therefore derived by including the corrugations and the droplet deformation in the surface energy calculations. By applying the remodified Young's equation, the nonlinear relationship between the apparent contact angle and the droplet radius reported in experiments can be well explained, and a converged line tension value is given around 10−10 J/m. © 2025 Elsevier Ltd

关键词： Linewidth

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Joint Secure and Covert Communications for Active STAR-RIS Assisted ISAC systems

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IEEE Transactions on Wireless Communications 2025年

作者： Guo, Liang Jia, Jie Mu, Xidong Liu, Yuanwei Chen, Jian Wang, Xingwei Northeastern University School of Computer Science and Engineering China Northeastern University Engineering Research Center of Security Technology of Complex Network System Ministry of Education China Northeastern University Key Laboratory of Intelligent Computing in Medical Image Ministry of Education Shenyang110819 China BelfastBT3 9DT United Kingdom Department of Electrical and Electronic Engineering China

This paper investigates the design of jointly supporting physical layer security (PLS) and covert communications (CCs) in an active simultaneously transmitting and reflecting reconfigurable intelligent surface (a-STAR-RIS) assisted integrated sensing and communication (ISAC) system. Due to the unified waveform design of ISAC signals, we consider a challenging scenario with two targets being suspicious attackers, where one warden target potentially detects the confidential transmission behavior of covert users and another eavesdropper target attempts to intercept the broadcasted confidential information of security users. We investigate the joint beamforming design at the base station (BS) and the a-STAR-RIS to achieve a high-quality sensing beampattern while meeting covertness and security communication requirements. (1) For the ideal scenario with perfect channel state information (CSI) and precise target locations, we propose an alternative optimization (AO) method to address the optimization problem involving highly coupled variables. Specifically, the optimal beamforming design at the BS is handled using the semi-definite relaxation (SDR) technique, while the beamforming design at the a-STAR-RIS is addressed through a penalty-based iterative algorithm. (2) A more practical case with uncertain target locations and imperfect CSI is considered to achieve a robust beamforming design, where the non-deterministic outage probability constraints are effectively transformed by employing the Bernstein-type inequality. Numerical results demonstrate the superiority of the a-STAR-RIS over the baseline cases and certify that the proposed algorithms can effectively balance the tradeoff among the sensing quality, covert and secure communication requirements. Besides, results also show that the proposed robust beamforming scheme can construct adequate sensing beampattern, even with imperfect CSI and uncertain target locations. © 2002-2012 IEEE.

关键词： Beamforming

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Data-Driven Learning and Control with Event-Triggered Measurements

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IEEE Transactions on Automatic Control 2025年

作者： Feng, Shilun Shi, Dawei Chen, Tongwen Shi, Ling Beijing Institute of Technology State Key Laboratory of Intelligent Control and Decision of Complex Systems MIIT Key Laboratory of Servo Motion System Drive and Control School of Automation Beijing100081 China University of Alberta Department of Electrical and Computer Engineering EdmontonABT6G 1H9 Canada Hong Kong University of Science and Technology Department of Electronic and Computer Engineering Clear Water Bay Kowloon Hong Kong

Event-triggered control has attracted considerable attention for its effectiveness in resource-restricted applications. To make event-triggered control as an end-to-end solution, a key issue is how to effectively learn unknown system dynamics from event-triggered measurements and consequently, develop a learning-based event-triggered controller. Existing works learn system dynamics based on periodic time-triggered measurements, and it is yet to know how to learn a controller with performance guarantee based on event-triggered measurements. To address this issue, we consider the problem of learning an event-triggered state feedback controller for an unknown linear system based on event-triggered state measurements in this work. In particular, we first analyze the event-triggered measurements within a set-membership framework. We prove that the estimation error belongs to a bounded ellipsoid determined by the historical measurements and the event-triggering condition. Subsequently, we demonstrate that all admissible systems compatible with the collected data samples can be explicitly represented in the form of quadratic matrix inequalities using the state estimates. With the acquired set of admissible systems, a co-design problem for the data-driven controller and event-triggering condition is solved using the linear matrix inequality technique, with guaranteed closed-loop stability and L2-gain performance. Finally, numerical examples and comparisons are provided to illustrate the effectiveness of the proposed event-triggered learning and control approach. © 1963-2012 IEEE.

关键词： Networked control systems

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Less Yet Robust: Crucial Region Selection for Scene Recognition

Less Yet Robust: Crucial Region Selection for Scene Recognit...

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International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

作者： Jianqi Zhang Mengxuan Wang Jingyao Wang Lingyu Si Changwen Zheng Fanjiang Xu National Key Laboratory of Space Integrated Information System Institute of Software Chinese Academy of Sciences Beijing China University of Chinese Academy of Sciences Beijing China Shien-Ming Wu School of Intelligent Engineering South China University of Technology Guangzhou China

ISBN: (数字)9798350368741

ISBN: (纸本)9798350368758

Scene recognition, particularly for aerial and underwater images, often suffers from various types of degradation, such as blurring or overexposure. Previous works that focus on convolutional neural networks have been shown to be able to extract panoramic semantic features and perform well on scene recognition tasks. However, low-quality images still impede model performance due to the inappropriate use of high-level semantic features. To address these challenges, we propose an adaptive selection mechanism to identify the most important and robust regions with high-level features. Thus, the model can perform learning via these regions to avoid interference. implement a learnable mask in the neural network, which can filter high-level features by assigning weights to different regions of the feature matrix. We also introduce a regularization term to further enhance the significance of key high-level feature regions. Different from previous methods, our learnable matrix pays extra attention to regions that are important to multiple categories but may cause misclassification and sets constraints to reduce the influence of such regions. This is a plug-and-play architecture that can be easily extended to other methods. Additionally, we construct an Underwater Geological Scene Classification dataset to assess the effectiveness of our model. Extensive experimental results demonstrate the superiority and robustness of our proposed method over state-of-the-art techniques on two datasets.

关键词： Adaptation models Scene classification Image recognition Semantics Speech recognition Signal processing Feature extraction Robustness Sensors Speech processing

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Noise reduction of add-on acoustic black holes with different topologies based on combined Reduced Multibody system Transfer Matrix Method and Elementary Radiators Method

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Thin-Walled Structures 2025年 214卷

作者： Liu, Jianghong Zhang, Yanni Jia, Huiliang Rui, Xiaoting Yan, Xiaowei Wang, Guoping Liu, Yang Institute of Launch Dynamics Nanjing University of Science and Technology Jiangsu Nanjing China National Key Laboratory of Complex Multibody System Dynamics China China State Shipbuilding Corporation Systems Engineering Research Institute Beijing 100094 China School of Energy and Power Jiangsu University of Science and Technology Zhenjiang212003 China

Recently, add-on acoustic black holes (ABHs) have received increasing attentions since they would not reduce the thickness/stiffness of the main structure and are flexible to install. Most of the studies, nevertheless, were conducted from the numerical simulation and experimental perspectives. Efficient theoretical computational methods are still lacking, especially for noise characteristics of a host structure with an add-on ABH as a dynamics vibration absorber (DVA), also known as an ABH-DVA. Herein, a theoretical method is proposed for calculating the noise radiation from a combined system formed by a host structure and an ABH-DVA via combining the Reduced Multibody system Transfer Matrix Method (RMSTMM) and the Elementary Radiators Method (ERM) or RMSTMM-ERM. The RMSTMM-ERM is applied to combined systems with ABH-DVAs of three topologies (unilateral, tree-shaped, spiral), and the results are compared with those from two finite element methods (FEMs). It is revealed that for combined systems with ABH-DVA of all three topologies, the RMSTMM-ERM reduces the computation time by >100 times compared with FEMs, while maintaining a high computational accuracy. Besides, remarkable and broadband low-frequency noise reductions are observed for all three ABH-DVAs, especially the spiral one with a deep-subwavelength dimension (λ/200). The vibration spatial distributions and wavenumber spectra with and without the ABH-DVAs are further investigated to disclose the noise reduction mechanisms. This paper provides an efficient and versatile theoretical computation method and design tool for noise studies of ABHs with complex geometries and topologies. © 2025 Elsevier Ltd

关键词： Finite element method

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A comparative study of piezoelectric unimorph and multilayer actuators as stiffness sensors via contact resonance

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Acta Mechanica Sinica 2016年第4期32卷 633-639页

作者： Ji Fu Fa-Xin Li State Key Laboratory for Turbulence and Complex System College of Engineering Peking University

Piezoelectric bar-shaped resonators were proposed to act as hardness sensors in the 1960 s and stiffness sensors in the 1990 s based on the contact impedance *** this work, we point out that both multilayer and unimorph（or bimorph） piezoelectric actuators could act as stiffness/modulus sensors based on the principle of mechanical contact resonance. First, the practical design and the performance of a piezoelectric unimorph actuator–based stiffness sensor were presented. Then the working principle of piezoelectric multilayer actuator–based stiffness sensors was given and verified by numerical investigation. It was found that for these two types of resonance-based sensors, the shift of the resonance frequency due to contact is always positive, which is different from that of the contact impedance method. Further comparative sensitivity study indicated that the unimorph actuator–based stiffness sensor is very suitable for measurement on soft materials, whereas the multilayer actuator–based sensor is more suitable for hard materials.

关键词： piezoelectric stiffness multilayer actuator modulus hardness impedance shaped diamond verified

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Continual Test-Time Adaptation for Single Image Defocus Deblurring via Causal Siamese Networks

arXiv

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arXiv 2025年

作者： Cui, Shuang Li, Yi Li, Jiangmeng Tang, Xiongxin Su, Bing Xu, Fanjiang Xiong, Hui National Key Laboratory of Space Integrated Information System Institute of Software Chinese Academy of Sciences University of Chinese Academy of Sciences China Beijing Key Laboratory of Big Data Management and Analysis Methods Gaoling School of Artificial Intelligence Renmin University of China China Department of Computer Science & Engineering the Hong Kong University of Science and Technology Hong Kong

Single image defocus deblurring (SIDD) aims to restore an all-in-focus image from a defocused one. Distribution shifts in defocused images generally lead to performance degradation of existing methods during out-of-distribution inferences. In this work, we gauge the intrinsic reason behind the performance degradation, which is identified as the heterogeneity of lens-specific point spread functions. Empirical evidence supports this finding, motivating us to employ a continual test-time adaptation (CTTA) paradigm for SIDD. However, traditional CTTA methods, which primarily rely on entropy minimization, cannot sufficiently explore task-dependent information for pixel-level regression tasks like SIDD. To address this issue, we propose a novel Siamese networks-based continual test-time adaptation framework, which adapts source models to continuously changing target domains only requiring unlabeled target data in an online manner. To further mitigate semantically erroneous textures introduced by source SIDD models under severe degradation, we revisit the learning paradigm through a structural causal model and propose Causal Siamese networks (CauSiam). Our method leverages large-scale pre-trained vision-language models to derive discriminative universal semantic priors and integrates these priors into Siamese networks, ensuring causal identifiability between blurry inputs and restored images. Extensive experiments demonstrate that CauSiam effectively improves the generalization performance of existing SIDD methods in continuously changing domains. Copyright © 2025, The Authors. All rights reserved.

关键词： Semantics

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Nondestructive testing method based on lamb waves for localization and extent of damage

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Acta Mechanica Solida Sinica 2017年第1期30卷 65-74页

作者： Jianlin Chen Zheng Li Kezhuang Gong State Key Laboratory of Turbulence and Complex System College of EngineeringPeking University

Based on Lamb wave analysis of propagation in plate-like structures, a damage detection method is proposed that not only locates the position of the damage accurately but also estimates its size. Similar damage detection methods focus only on localization giving no quantitative estimation of extent. To improve detection, we propose two predictive circle methods for size estimation. Numerical simulations and experiments were performed for an aluminum plate with a hole. Two PZT configurations of different sizes were designed to excite and detect Lamb waves. From cross-correlation analysis, the damage location and extent can be determined. Results show that the proposed method enables a better quantitative resolution in detection, the size of the inspection area influences the accuracy of damage identification, and the closer is the inspected area to the damage, the more accurate are the results. The method proposed can be developed into a multiple-step detection method for multi-scale analysis with prospective accuracy.

关键词： Lamb wave Damage detection Cross correlation PZT wafer Aluminum plate

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Multiplexed model predictive attitude control for nadir-pointing satellite using only magnetorquers

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Control engineering Practice 2025年 162卷

作者： Yang, Sen Ling, Keck Voon Wang, Zhenhua Li, Huiping School of Astronautic Harbin Institute of Technology Harbin150001 China School of Electrical and Electronic Engineering Nanyang Technological University Singapore639798 Singapore National Key Laboratory of Complex System Control and Intelligent Agent Cooperation Harbin150001 China School of Marine Science and Technology Northwestern Polytechnical University Xi'an710072 China

Due to the low failure risk of magnetorquers, the control strategy based on magnetic actuators can significantly enhance the reliability of the satellite attitude control system. In light of this advantage, this paper conducts research on model predictive control (MPC) algorithm for nadir-pointing satellites equipped only with magnetorquers. Firstly, to facilitate controller design, the linear time-varying (LTV) model for nadir-pointing satellites is derived by linearizing the nonlinear equations around the operating point. Then, leveraging this linearized representation, an LTV multiplexed MPC (MMPC) method with exponential weighting is proposed. The MMPC scheme allows for faster sampling rates and quicker responses to disturbances, thereby enhancing the overall performance of the satellite attitude control system while retaining the benefits of MPC. Finally, compared with a state-of-the-art SMPC method, the proposed method is particularly advantageous in situations where computational resources are limited, specifically for satellites that rely only on onboard computing capabilities. © 2025

关键词： Nonlinear equations

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