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Elucidating the role of precipitated phase particles in modifying creep properties of as-cast Mg-Bi/Sn-based alloys

Journal of Magnesium and Alloys 2024年第11期12卷 4682-4693页

作者： Gang Xu Wei-li Cheng Yi-hao Luo Hui Yu Li-fei Wang Hang Li Hong-xia Wang Jin-hui Wang School of Materials Science and Engineering Taiyuan University of TechnologyTaiyuan 030024China b School of Materials Science and Engineering Hebei University of TechnologyTianjin 300132China Qinghai Provincial Key Laboratory of New Light Alloys Qinghai Provincial Engineering Research Center of High Performance Light Metal Alloys and FormingQinghai UniversityXining 810016China School of Materials Science and Engineering Zhejiang UniversityHangzhou 310000China

The study developed the three alloy systems with different precipitates and examined the role of precipitated phase particles in modifying the creep properties of as-cast Mg^(-1)0Bi-0.5Mn-0.5Ag(BMQ1000),Mg-5Bi-5Sn-0.5Mn-0.5Ag(BTMQ5500)and Mg^(-1)0Sn-0.5Mn-0.5Ag(TMQ1000)alloys at temperatures ranging from 423 to 473 K and stresses of 45-85 *** values of n for the BMQ1000,BTMQ5500,and TMQ1000 alloys were determined as 6.67,5.75,and 5.92,***,the activation energy for these alloys was found to be 164.71,134.68,and 135.93 k J/mol,*** results suggested that the creep properties followed the order of BTMQ5500>TMQ1000>BMQ1000.A coarse and uneven distribution of the Mg_(3)Bi_(2)precipitated phase in the BMQ1000 alloy leads to a feeble pining effect on dislocation slipping and generates substantial stress *** TMQ1000 alloy,while the nanoscale Mg_(2)Sn precipitates have a stronger barrier effect on dislocations than the Mg_(3)Bi_(2)in the BMQ1000 alloy,their ability to inhibit dislocation climbing is comparatively ***,it was found that Mg_(2)Sn precipitates andα-Mg exhibited a preferential orientation relationship of(020)Mg_(2)Sn//(-1010)Mg,and the morphology of the precipitated phase transformed in a way that hinders dislocation movement *** addition,elastic interactions between the precipitated phases are *** above-mentioned factors are largely responsible for the notable enhancement in creep ***,it is ascertained that cross-slip and pyramidal(c+a)slip are primary creep mechanisms in the BMQ1000 *** contrast,the dominant mechanisms in TMQ1000 and BTMQ5500 alloys are dislocation climb and pyramidal(c+a)***,stacking faults(SFs)and twinning assist in the creep deformation of the BTMQ5500 alloy.

关键词： Magnesium alloy Microstructural characteristics Creep properties Precipitates Creep mechanism

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Dynamic Task Allocation for Heterogeneous Multi-Robot System under Communication Constraints 6

Dynamic Task Allocation for Heterogeneous Multi-Robot System...

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6th IEEE Information technology, Networking, Electronic and Automation Control Conference, ITNEC 2023

作者： Li, Jun Cai, Zhongxuan Li, Minglong Huang, Wanrong Zhang, Yongjun National University of Defense Technology Institute for Quantum Information State Key Laboratory of High Performance Computing College of Computer China

ISBN: (纸本)9781665460033

Multi-robot system has important application potential in disaster rescue and other dangerous scenarios, in which task allocation is the basis for multi-robot cooperation to complete tasks. Due to the limited ability of individual robots, many complex scenarios requires coordination of different types of robot, e.g. robots for search, communication, rescue and so on. At the same time, communication is often limited in a wide range of scenarios. This brings two challenges in the realistic environment: heterogeneous multi-robot cooperation problem and communication constraint problem. This paper proposes a task allocation method based on hierarchical auction and dynamic grouping. By introducing a dynamic grouping algorithm to the general allocation procedure, we simultaneously optimize the number of robots in each group and the communication distance between robots. Then the communication loss rate can be reduced to improve task execution efficiency. Simulations of a communication constrained search and rescue scenario are conducted to verify the proposed algorithm, which are compared with the vanilla auction algorithm and a hierarchical approach on static grouping. The results show that our method surpasses the baseline on both task achievement and communication performance. © 2023 IEEE.

关键词： Multipurpose robots

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LprViT:An Efficient ViT for LiDAR-Based Place Recognition Using Range Image 8

LprViT:An Efficient ViT for LiDAR-Based Place Recognition Us...

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8th International Conference on Communication, Image and Signal Processing, CCISP 2023

作者： He, Rui Xiao, Yunzhe Yang, Shaowu College of Computer Science and Technology National University of Defense Technology Quantum Information & State Key Laboratory of High Performance Computing Changsha China

ISBN: (纸本)9798350305838

Place recognition is a crucial component in the realm of simultaneous localization and mapping (SLAM) and autonomous driving. It can also enhance the performance of loop closure detection and global localization. LiDAR-based place recognition usually relies on global feature descriptors to accurately express the similarity between LiDAR scans. However, it is time-consuming to extract and generate the global feature descriptors from the original LiDAR data. As a result, treating LiDAR-based point clouds place recognition as a 2D image problem using range projection is becoming an increasingly common and successful strategy. Vision Transformer (ViT) is a Transformer model based on self-attention mechanism for image classification. Through self-attention mechanism, ViT out-performs CNN at modeling the global information of images. We investigate that whether ViT can be transferred to LiDAR-based place recognition tasks. Firstly, we introduce a new convolutional stem to replace the original linear embedding layer in ViT. Secondly, we establish synergy by integrating low-level fine-grained features from new convolution layer with high-level coarse-grained features from ViT by skip connections. Thirdly, we aggregate these features to construct the global feature descriptor via the NetVLAD technique. The results of experiments on KITTI confirm that our method can operate online and achieve superior performance on par with existing approaches. © 2023 IEEE.

关键词： Convolution

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A Unity-Gain Buffer Assisted Noise-Shaping SAR ADC Based on Error-Feedback Structure

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Chinese Journal of Electronics 2022年第4期31卷 658-664页

作者： YI Pinyun ZHU Zhangming XU Nuo FANG Liang HAO Yue State Key Laboratory of High Performance Computing College of ComputerNational University of Defense Technology School of Microelectronics Xidian University College of Computer National University of Defense Technology State Key Discipline Laboratory of Wide Band Gap Semiconductor Technology School of MicroelectronicsXidian University

The passive noise-shaping successive approximation register(NS-SAR) analog-to-digital converter(ADC) demonstrates high performance in resolution improvement, power reduction, and process scaling, while its charge-sharing loss and limited bandwidth weaken the noise-shaping effect. This paper presents a first-order NSSAR ADC based on error-feedback(EF) structure to realize high-efficiency noise shaping. It employs a lossless EF path by using a set of ping-pong switching capacitors with passive signal-residue summation technique. The proposed first-order EF NS-SAR prototype can be promoted to multi-order structure with the minor modification. Verified by simulation in 65-nm CMOS process, the proposed 9-bit NS-SAR ADC consumes 183.66 μW when operating at 20 MS/s with the supply voltage of 1.2 V. At the oversampling ratio of 16, it achieves a peak signal-tonoise-and-distortion ratio of 81 d B, yielding Schreier figure of merit of 176.32 d B.

关键词： Noise-shaping SAR ADC Error feedback Unity-gain buffer Lossless integration Ping-pong manner Full-resolution switching

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A Study on CFL Conditions for the DG Solution of Conservation Laws on Adaptive Moving Meshes

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Numerical Mathematics(Theory,Methods and Applications) 2023年第1期16卷 111-139页

作者： Min Zhang Weizhang Huang Jianxian Qiu School of Mathematical Sciences Peking UniversityBeijing 100871China Department of Mathematics University of KansasLawrenceKansas 66045USA School of Mathematical Sciences Fujian Provincial Key Laboratory of Mathematical ModelingHigh-Performance Scientific ComputingXiamen UniversityXiamenFujian 361005China

The selection of time step plays a crucial role in improving stability and efficiency in the Discontinuous Galerkin(DG)solution of hyperbolic conservation laws on adaptive moving meshes that typically employs explicit stepping.A commonly used selection of time step is a direct extension based on Courant-Friedrichs-Levy(CFL)conditions established for fixed and uniform *** this work,we provide a mathematical justification for those time step selection strategies used in practical adaptive DG computations.A stability analysis is presented for a moving mesh DG method for linear scalar conservation *** on the analysis,a new selection strategy of the time step is proposed,which takes into consideration the coupling of theα-function(that is related to the eigenvalues of the Jacobian matrix of the flux and the mesh movement velocity)and the heights of the mesh *** analysis also suggests several stable combinations of the choices of theα-function in the numerical scheme and in the time step *** results obtained with a moving mesh DG method for Burgers’and Euler equations are *** comparison purpose,numerical results obtained with an error-based time step-size selection strategy are also given。

关键词： Discontinuous Galerkin method adaptive mesh moving mesh CFL condition stability

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Self-distillation Enhanced Vertical Wavelet Spatial Attention for Person Re-identification 1

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30th International Conference on MultiMedia Modeling, MMM 2024

作者： Zhang, Yuxuan Tan, Huibin Lan, Long Teng, Xiao Ren, Jing Zhang, Yongjun Institute for Quantum Information & State Key Laboratory of High Performance Computing College of Computer Science and Technology National University of Defense Technology Changsha410073 China Beijing100071 China

ISBN: (数字)9783031533082

ISBN: (纸本)9783031533075

Person re-identification is a challenging problem in computer vision, aiming to accurately match and recognize the same individual across different viewpoints and cameras. Due to significant variations in appearance under different scenes, person re-identification requires highly discriminative features. Wavelet features contain richer phase and amplitude information as well as rotational invariance, demonstrating good performance in various visual tasks. However, through our observations and validations, we have found that the vertical component within wavelet features exhibits stronger adaptability and discriminability in person re-identification. It better captures the body contour and detailed information of pedestrians, which is particularly helpful in distinguishing differences among individuals. Based on this observation, we propose a vertical wavelet spatial attention only with the vertical component in the high frequency specifically designed for feature extraction and matching in person re-identification. To enhance spatial semantic consistency and facilitate the transfer of knowledge between different layers of wavelet attention in the neural network, we introduce a self-distillation enhancement method to constrain shallow and deep spatial attention. Experimental results on Market-1501 and DukeMTMC-reID datasets validate the effectiveness of our model. © 2024, The Author(s), under exclusive license to Springer Nature Switzerland AG.

关键词： Distillation

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ISpliter:an intelligent and automatic surface mesh generator using neural networks and splitting lines

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Advances in Aerodynamics 2023年第1期5卷 362-386页

作者： Zengsheng Liu Shizhao Chen Xiang Gao Xiang Zhang Chunye Gong Chuanfu Xu Jie Liu State Key Laboratory of High Performance Computing National University of Defense TechnologyChangsha 410073China College of Computer National University of Defense TechnologyChangsha 410073China Laboratory of Digitizing Software for Frontier Equipment National University of Defense TechnologyChangsha 410073China

In this paper,we present a novel surface mesh generation approach that splits B-rep geometry models into isotropic triangular meshes based on neural networks and splitting *** the first stage,a recursive method is designed to generate plentiful data to train the neural network model *** the second stage,the implemented mesh generator,ISpliter,maps each surface patch into the parameter plane,and then the trained neural network model is applied to select the optimal splitting line to divide the patch into subdomains continuously until they are all *** the third stage,ISpliter remaps the 2D mesh back to the physical space and further optimizes *** typical cases are evaluated to compare the mesh quality generated by ISpliter and two baselines,Gmsh and *** results show that ISpliter can generate isotropic triangular meshes with high average quality,and the generated meshes are comparable to those generated by the other two software under the same configuration.

关键词： Surface mesh generation Artificial neural network Splitting line Triangular element Feature extraction

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Polymer-on-HOF:a new strategy for fabricating“armour-plated”HOFs to sequester radioactive anions

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Science China Chemistry 2024年第9期67卷 2958-2967页

作者： Hai-Ruo Li Shitao Wu Xuezhuo Jing Zhengyi Di Kun Liu Lu Wang Cheng-Peng Li Zhong Liu Miao Du College of Chemistry Tianjin Key Laboratory of Structure and Performance for Functional MoleculesTianjin Normal UniversityTianjin 300387China Shanghai Key Laboratory of High-Resolution Electron Microscopy School of Physical Science and TechnologyShanghaiTech UniversityShanghai 201210China Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources Qinghai Provincial Key Laboratory of Resources and Chemistry of Salt LakesQinghai Institute of Salt LakesChinese Academy of SciencesXining 810008China College of Material and Chemical Engineering Institute of New Energy Science and TechnologySchool of Future Hydrogen Energy TechnologyZhengzhou University of Light IndustryZhengzhou 450001China

The development of hydrogen-bonded organic frameworks(HOFs)faces significant constraints,primarily attributed to their fragile architectures and limited functionalization *** overcome these limitations,this work presents a new polymeron-HOF strategy by covalently tethering armor-like polymers onto the surface of *** application of this approach not only bolsters the stability of HOFs,but also facilitates the customization of their functional expansion in radionuclide *** optimized HOF-polymer materials display extraordinary ability in radionuclide sequestration,achieving uptake of I^(-)(0.699 g g^(-1)),IO_(3)^(-)(0.285 g g^(-1))and ReO_(4)^(-)(1.616 g g^(-1),setting a world record),fast adsorption kinetics(~100% removal within 45 s),and exceptional regeneration capability(>30 cycles)under continuous flow *** outstanding performances benefit from the internal porous channels and surface imidazolium polymer coatings of HOFs,as proved by density functional theory calculation and molecular dynamics *** work paves the way for the rational design of HOF-based hybrid materials tailored to versatile applications.

关键词： hydrogen-bonded organic frameworks(HOFs) post-synthetic modification radionuclide sequestration

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A large scale parallel fluid-structure interaction computing platform for simulating structural responses to a detonation shock

A large scale parallel fluid-structure interaction computing...

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作者： Zhang, Sen Guo, Xiao-Wei Li, Chao Liu, Yi Fan, Sijiang Zhao, Ran Yang, Canqun Institute for Quantum Information & State Key Laboratory of High Performance Computing College of Computer Science and Technology National University of Defense Technology Changsha China

Due to the intrinsic nature of multi-physics, it is prohibitively complex to design and implement a simulation software platform for study of structural responses to a detonation shock. In this article, a partitioned fluid-structure interaction computing platform is designed for parallel simulating structural responses to a detonation shock. The detonation and wave propagation are modeled in an open-source multi-component solver based on OpenFOAM and blastFoam, and the structural responses are simulated through the finite element library ***. To capture the interaction dynamics between the fluid and the structure, both solvers are adapted to preCICE. For improving the parallel performance of the computing platform, the inter-solver data is exchanged by peer-to-peer communications and the intermediate server in conventional multi-physics software is eliminated. Furthermore, the coupled solver with detonation support has been deployed on a computing cluster after considering the distributed data storage and load-balancing between solvers. The 3D numerical result of structural responses to a detonation shock is presented and analyzed. On 256 processor cores, the speedup ratio of the simulations for a detonation shock reach 178.0 with 5.1 million of mesh cells and the parallel efficiency achieve 69.5%. The results demonstrate good potential of massively parallel simulations. Overall, a general-purpose fluid-structure interaction software platform with detonation support is proposed by integrating open source codes. And this work has important practical significance for engineering application in fields of construction blasting, mining, and so forth. © 2021 John Wiley & Sons, Ltd.

关键词： Detonation

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OL-CBBA: An Online Task Allocation Algorithm under Weak Communication Conditions 29

OL-CBBA: An Online Task Allocation Algorithm under Weak Comm...

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29th IEEE International Conference on Parallel and Distributed Systems, ICPADS 2023

作者： Li, Jun Huang, Wanrong Wu, Honglin Cai, Zhongxuan Zhang, Yongjun National University of Defense Technology Institute for Quantum Information State Key Laboratory of High Performance Computing College of Computer Science and Technology Changsha China

ISBN: (纸本)9798350330717

Multiple unmanned aerial vehicles (UAVs) and multiple tasks allocation problem is difficult to solve. Existing task allocation algorithms assume that the UAVs' position is static, and cannot assign tasks with the changing UAVs' position simultaneously during task execution. Those algorithms reduce the efficiency of task allocation. In this paper, we propose an online consensus-based bundle algorithm (OL-CBBA) under weak communication for dynamic task allocation. We consider the situation that the location information of UAVs will constantly change during the dynamic execution of tasks. The algorithm first improves the static CBBA to an online algorithm by updating the task marginal score in task path. Moreover, we specify a flag for the convergence of individual tasks, allowing UAVs to start executing tasks earlier. Extensive comparative experiments prove the highly consistent efficiency of OL-CBBA under weak communication conditions. Specifically, the proposed OL-CBBA attains up to 22% improvement compared with CBBA. © 2023 IEEE.

关键词： Auction Algorithm Decentralized System Dynamic Task Allocation Weak Communication

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