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arXiv 2022年

作者： Tang, Yihong Qu, Ao Chow, Andy H.F. Lam, William H.K. Wong, S.C. Ma, Wei Department of Urban Planning and Design University of Hong Kong Hong Kong Laboratory for Information and Decision Systems Massachusetts Institute of Technology Boston United States Department of Advanced Design and Systems Engineering City University of Hong Kong Hong Kong Department of Civil and Environmental Engineering The Hong Kong Polytechnic University Hong Kong Department of Civil Engineering University of Hong Kong Hong Kong Department of Civil and Environmental Engineering Research Institute for Sustainable Urban Development The Hong Kong Polytechnic University Hong Kong

Accurate real-time traffic forecast is critical for intelligent transportation systems (ITS) and it serves as the cornerstone of various smart mobility applications. Though this research area is dominated by deep learning, recent studies indicate that the accuracy improvement by developing new model structures is becoming marginal. Instead, we envision that the improvement can be achieved by transferring the "forecasting-related knowledge" across cities with different data distributions and network topologies. To this end, this paper aims to propose a novel transferable traffic forecasting framework: Domain Adversarial Spatial-Temporal Network (DastNet). DastNet is pre-trained on multiple source networks and fine-tuned with the target network's traffic data. Specifically, we leverage the graph representation learning and adversarial domain adaptation techniques to learn the domain-invariant node embeddings, which are further incorporated to model the temporal traffic data. To the best of our knowledge, we are the first to employ adversarial multi-domain adaptation for network-wide traffic forecasting problems. DastNet consistently outperforms all state-of-the-art baseline methods on three benchmark datasets. The trained DastNet is applied to Hong Kong's new traffic detectors, and accurate traffic predictions can be delivered immediately (within one day) when the detector is available. Overall, this study suggests an alternative to enhance the traffic forecasting methods and provides practical implications for cities lacking historical traffic data. Source codes of DastNet are available at https://***/YihongT/DASTNet. Copyright © 2022, The Authors. All rights reserved.

关键词： Network topology

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Bayesian Optimization Framework for Efficient Fleet design in Autonomous Multi-Robot Exploration

arXiv

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arXiv 2024年

作者： Concha, David Molina Li, Jiping Yin, Haoran Park, Kyeonghyeon Lee, Hyun-Rok Lee, Taesik Sirohi, Dhruv Lee, Chi-Guhn The Dynamic Optimization and Reinforcement Learning Laboratory The Department of Mechanical & Industrial Engineering University of Toronto TorontoONM5S3G8 Canada The Department of Electrical & Computer Engineering University of Toronto TorontoONM5S3G8 Canada The Division of Engineering Science The Faculty of Applied Science and Engineering University of Toronto TorontoONM5S3G8 Canada The Complex System Design Laboratory The Department of Industrial and Systems Engineering Korea Advanced Institute of Science and Technology Daejeon34141 Korea Republic of The Department of Industrial Engineering Inha University Incheon22212 Korea Republic of

This study addresses the challenge of fleet design optimization in the context of heterogeneous multi-robot fleets, aiming to obtain feasible designs that balance performance and costs. In the domain of autonomous multi-robot exploration, reinforcement learning agents play a central role, offering adaptability to complex terrains and facilitating collaboration among robots. However, modifying the fleet composition results in changes in the learned behavior, and training multi-robot systems using multi-agent reinforcement learning is expensive. Therefore, an exhaustive evaluation of each potential fleet design is infeasible. To tackle these hurdles, we introduce Bayesian Optimization for Fleet design (BOFD), a framework leveraging multiobjective Bayesian Optimization to explore fleets on the Pareto front of performance and cost while accounting for uncertainty in the design space. Moreover, we establish a sub-linear bound for cumulative regret, supporting BOFD’s robustness and efficacy. Extensive benchmark experiments in synthetic and simulated environments demonstrate the superiority of our framework over state-of-the-art methods, achieving efficient fleet designs with minimal fleet evaluations. Copyright © 2024, The Authors. All rights reserved.

关键词： Multipurpose robots

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Modeling and Analysis of Mtj Array with Shielding Layer

SSRN

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SSRN 2023年

作者： Qu, Ying-Hui Xiong, Jing-Ya Zuo, Chao Dong, Kai-Feng Song, Jun-Lei Mo, Wen-Qin Hui, Ya-Juan Jin, Fang School of Automation China University of Geosciences Wuhan430074 China Hubei key Laboratory of Advanced Control and Intelligent Automation for Complex Systems Wuhan430074 China Geological Exploration Intelligent Technology Engineering Research Center The Ministry of Education Wuhan Second Ship Design and Research Institute Hubei Province Wuhan China

In STT-MRAM, data is stored in a magnetic tunnel structure (MTJ) containing multiple ferromagnetic layers. Each ferromagnetic layer generates a stray field, which affects the critical switching current, switching time, thermal stability, and the density of the MTJ array. These factors have a direct impact on the performance and storage capacity of STT-MRAM. Previously, we have studied that hexagonal MTJ arrays can improve storage density. However, this improvement also leads to increased intracellular and intercellular stray fields, which in turn affects the device's performance. This paper aims to reduce the intercellular stray field by covering each MTJ unit with a soft magnetic shielding layer and investigates the performance of the MTJ array with a shielding layer. Firstly, a simulation model of a single MTJ stack is built using the simulation software COMSOL. Then, based on modeling the MTJ stack, square and hexagonal MTJ arrays are established. The intercellular magnetic coupling coefficient (Ψ) is quoted, and Ψ=2% is defined as the threshold below which the intercellular magnetic coupling can be considered negligible. The results indicate that the soft magnetic shielding layer can effectively shield the stray field, reducing its impact on MTJ performance. Specifically, a thicker shielding layer with higher magnetic permeability provides better shielding efficacy. However, comparing square and hexagonal MTJ array after magnetic shielding reveals a larger stray field between the hexagonal array. © 2023, The Authors. All rights reserved.

关键词： Ferromagnetic materials

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Anisotropic lattice Boltzmann-phase-field modeling of crystal growth with melt convection induced by solid-liquid density change

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Journal of Materials Science & Technology 2020年第22期54卷 26-32页

作者： Hui Xing Xianglei Dong Dongke Sun Yongsheng Han MOE Key Laboratory of Material Physics and Chemistry Under Extraordinary Shaanxi Key Laboratory for Condensed Matter Structure and PropertiesNorthwestern Polytechnical University710129Xi'anChina College of Materials Science and Engineering Zhengzhou University450001ZhengzhouChina Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments School of Mechanical EngineeringSoutheast UniversityNanjing211189China State Key Laboratory of Advanced Special Steel Shanghai Key Laboratory of Advanced FerrometallurgyShanghai UniversityShanghaiChina The EMMS Group State Key Laboratory of Multiphase Complex Systems.Institute of Process EngineeringChinese Academy of Science100190BeijingChina

Density change is ubiquitous in phase transformation, and it can induce melt convection which strongly influences the crystal growth. Here, an anisotropic lattice Boltzmann-phase-field method was extended to predict the dendritic growth under the shrinkage or expansion melt convection by density change induced. A novel LB equation with an anisotropic coefficient was constructed to model the advancement of ordering parameter, coupling with the passive scalar LB equation for convective and diffusive heat transfer during phase transition. We studied dendritic growth and shape selection with melt convection induced by density change in crystal growth. Results show that the melt convection induced by density change affects strongly the dendritic growth. The shrinkage flow results in a higher tip velocity while the expansion flow leads to a slower one. Predicted Péclet number with respect to the relative density change was compared with an analytical solution. Moreover, the modified selection parameter has been verified by numerical simulations.

关键词： Dendritic growth Density change Melt convection Phase-field method

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Privacy-preserving Intelligent Resource Allocation for Federated Edge Learning in Quantum Internet

arXiv

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arXiv 2022年

作者： Xu, Minrui Niyato, Dusit Yang, Zhaohui Xiong, Zehui Kang, Jiawen Kim, Dong In Shen, Xuemin The School of Computer Science and Engineering Nanyang Technological University Singapore The College of Information Science and Electronic Engineering Zhejiang University Hangzhou310007 China Hangzhou310007 China Zhejiang Laboratory Hangzhou31121 China The Pillar of Information Systems Technology and Design Singapore University of Technology and Design Singapore 487372 Singapore The School of Automation Guangdong University of Technology China Department of Electrical and Computer Engineering Sungkyunkwan University Suwon16419 Korea Republic of The Department of Electrical and Computer Engineering University of Waterloo Waterloo ON N2L 3G1 Canada

Federated edge learning (FEL) is a promising paradigm of distributed machine learning that can preserve data privacy while training the global model collaboratively. However, FEL is still facing model confidentiality issues due to eavesdropping risks of exchanging cryptographic keys through traditional encryption schemes. Therefore, in this paper, we propose a hierarchical architecture for quantum-secured FEL systems with ideal security based on the quantum key distribution (QKD) to facilitate public key and model encryption against eavesdropping attacks. Specifically, we propose a stochastic resource allocation model for efficient QKD to encrypt FEL keys and models. In FEL systems, remote FEL workers are connected to cluster heads via quantum-secured channels to train an aggregated global model collaboratively. However, due to the unpredictable number of workers at each location, the demand for secret-key rates to support secure model transmission to the server is unpredictable. The proposed systems need to efficiently allocate limited QKD resources (i.e., wavelengths) such that the total cost is minimized in the presence of stochastic demand by formulating the optimization problem for the proposed architecture as a stochastic programming model. To this end, we propose a federated reinforcement learning-based resource allocation scheme to solve the proposed model without complete state information. The proposed scheme enables QKD managers and controllers to train a global QKD resource allocation policy while keeping their private experiences local. Numerical results demonstrate that the proposed schemes can successfully achieve the cost-minimizing objective under uncertain demand while improving the training efficiency by about 50% compared to state-of-the-art schemes. © 2022, CC BY.

关键词： Stochastic systems

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Adhesive-less bonding of incompatible thermosetting materials

RSC Applied Polymers

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RSC Applied Polymers 2024年第1期3卷 247-256页

作者： Khairkkar, Shhyam Pansare, Amol V. Pansare, Shubham V. Chhatre, Shraddha Y. Sakamoto, Junji Barbezat, Michel Terrasi, Giovanni P. Patil, Vishwanath R. Nagarkar, Amit A. Naito, Masanobu Data-Driven Polymer Design Group Research and Services Division of Materials Data and Integrated System (MaDIS) National Institute for Materials Science (NIMS) 1-2-1 Sengen Ibaraki Tsukuba 305-0047 Japan Composites Group Mechanical Systems Engineering Swiss Federal Laboratories for Materials Science and Technology-Empa ETH Domain Dübendorf 8600 Switzerland Department of Chemistry University of Mumbai Santacruz (E) Mumbai 400098 India National Chemical Laboratory (NCL) Dr Homi Bhabha Road Pune 411008 India Advanced Material Technology Center Technology Division Panasonic Holdings Corporation 1006 Kadoma Kadoma City Osaka 571-8508 Japan Datacule Inc. 529 Main St. Boston 02129 MA United States

We show that dynamic covalent exchange at the interface of two thermosetting polymers results in strong bonding between the materials via creation of a new material at the interface. Thus, polymers of significantly different polarities can be bonded without the use of adhesives. We also show that such dynamic covalent exchange is not only limited to the interface but also penetrates into the bulk material (ca. 20 microns), thereby creating a strong bond. The creation of a new material at the interface was confirmed by Energy Dispersive X-ray (EDX) elemental mapping as well as a new glass transition temperature at the interface. Using this phenomenon, we show that hydrophobic, compliant polymers can also be used as adhesives for polar, stiff materials. We also show that such dynamic exchange also takes place in the presence of fillers like nano-silica. Lastly, using this technique, we demonstrate the adhesive-less fabrication of layered materials where each layer has vastly different polarities and mechanical properties, thereby tuning the failures modes of the resulting composite material. © 2025 RSC.

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Analysis of Electro-mechanical Actuator Transmission Clearance under High-temperature Conditions

Analysis of Electro-mechanical Actuator Transmission Clearan...

引用

International Conference on Fluid Power and Mechatronics (FPM)

作者： Zhicheng Liu Tian Yu Rui Hong Li Liu Hao Su Jionghui Lin Chaofan Jiang Yaoxing Shang School of Automation Science and Electrical Engineering Beihang University Beijing China Technology on Aircraft Control Laboratory Beihang University Beijing China Research Institute for Frontier Science Beihang University Beijing China Tianmushan Laboratory Xixi Octagon City Yuhang District Hangzhou China Chengdu Aircraft Design and Research Institute Chengdu China Ningbo Institute of Technology Beihang University Ningbo China Key Laboratory of Advanced Aircraft Systems (Beihang University) Ministry of Industry and Information Technology

ISBN: (数字)9798350304947

ISBN: (纸本)9798350304954

More Electric Aircraft with electro-mechanical actuator(EMA) or electro-hydrostatic actuator(EHA) is the development trend of new aircraft. In high temperature conditions, the transmission clearance of EMA transmission system may change because of thermal deformation. If the transmission clearance decreases, the EMA may get stuck; If the transmission clearance increases, it will affect the control accuracy of the aircraft control. This paper investigates the transmission clearance of EMA transmission system when subjected to the combined effects of an external high-temperature environment and internal heat sources. To calculate the temperature distribution of EMA transmission system, A heat transfer model of the EMA is established. Based on this temperature distribution, the EMA transmission clearance can be calculated. an EMA dynamic model, involved nonlinear clearance, is established to analysis the effects of the transmission clearance on the actuator's output performance. This research provides a reference for studying the design clearances of EMA under high temperature conditions.

关键词： Deformable models Temperature distribution Analytical models Thermodynamics Gears Deformation Time series analysis

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Nitrogen-Doping Induced Local Chemical Heterogeneity and the Enhanced Mechanical Properties In Cocrmow Alloys Manufactured Via Laser Powder Bed Fusion

SSRN

引用

SSRN 2024年

作者： Jiang, Wenting Li, Ruidi He, Junyang Ni, Song Wang, Li Chen, Zibin Huang, Yi Li, Caiju Yi, Jianhong Song, Min State Key Laboratory of Powder Metallurgy Central South University Changsha410083 China Research Institute for Advanced Manufacturing Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hong Kong Department of Design and Engineering Faculty of Science and Technology Bournemouth University Poole DorsetBH12 5BB United Kingdom Materials Research Group Department of Mechanical Engineering University of Southampton SouthamptonSO17 1BJ United Kingdom Faculty of Materials Science and Engineering Kunming University of Science and Technology Kunming650093 China

CoCrMoW alloys with different nitrogen (N) additions (0, 0.05, 0.1 and 0.2 wt.%) were prepared via laser powder bed fusion (LPBF). The effects of N content on the microstructure and mechanical properties were investigated. The results indicate that the LPBFed CoCrMoW alloy with 0.1 wt.% N addition (0.1N alloy) shows the best combination of mechanical properties with a yield strength of ~ 983 MPa and an elongation of ~ 19%. Both the LPBF process and the N addition impose great effects on suppressing the γ to Ε martensitic transformation, resulting in a decrease in the width and amount of Ε laths/stacking faults. Besides, the N addition promotes the segregation of elements Mo, W, and Si along the cellular sub-grain boundaries (CBs), forming fine and discontinuous precipitates rich in Mo, W and Si along the CBs in the 0.1N alloy, but dense and continuous (Mo,W)5Si3 precipitates along the CBs in the 0.2N alloy. The (Mo,W)5Si3 precipitates with a tetragonal structure were observed and characterized for the first time in the Co-Cr based alloys. The negative mixing enthalpy between the non-metallic elements N, Si and the metallic elements Mo, W, Cr, and the rapid solidification induced segregation of high melting point elements such as Mo and W along CBs during LPBF process, synergistically contribute to the chemical heterogeneity in the alloys. The pure FCC matrix, the slightly increased segregation of Mo, W, Si elements and fine precipitates along the CBs contribute to the good combination of strength and elongation of the 0.1N alloy. However, though pure FCC phase was present in the 0.2N alloy, the dense and continuous (Mo,W)5Si3 precipitates along CBs acted as nucleation sites for cracks, deteriorating the elongation of the alloy. Overall, it is possible to tune the mechanical properties of the LPBFed CoCrMoW alloy by adjusting the local chemical heterogeneity. © 2024, The Authors. All rights reserved.

关键词： Chromium alloys

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Nitrogen-Doping Assisted Local Chemical Heterogeneity and Mechanical Properties In Cocrmow Alloys Manufactured Via Laser Powder Bed Fusion

SSRN

引用

SSRN 2024年

CoCrMoW alloys with different nitrogen (N) additions (0, 0.05, 0.1 and 0.2 wt.%) were prepared via laser powder bed fusion (LPBF). The effects of N content on the microstructure and mechanical properties were investigated. The results indicate that the LPBFed CoCrMoW alloy with 0.1 wt.% N addition (0.1N alloy) shows the best combination of mechanical properties with a yield strength of ~ 983 MPa and an elongation of ~ 19%. Both the LPBF process and the N addition impose great effects on suppressing the g to e martensitic transformation, resulting in a decrease in the width and amount of e laths/stacking faults. Besides, the N addition promotes the segregation of elements Mo, W, and Si along the cellular sub-grain boundaries (CBs), forming fine and discontinuous precipitates rich in Mo, W and Si along the CBs in the 0.1N alloy, but dense and continuous (Mo,W)5Si3 precipitates along the CBs in the 0.2N alloy. The (Mo,W)5Si3 precipitates with a tetragonal structure were observed and characterized for the first time in the Co-Cr based alloys. The negative mixing enthalpy between the non-metallic elements N, Si and the metallic elements Mo, W, Cr, and the rapid solidification induced segregation of high melting point elements such as Mo and W along CBs during LPBF process, synergistically contribute to the chemical heterogeneity in the alloys. The pure FCC matrix, the slightly increased segregation of Mo, W, Si elements and fine precipitates along the CBs contribute to the good combination of strength and elongation of the 0.1N alloy. However, though pure FCC phase was present in the 0.2N alloy, the dense and continuous (Mo,W)5Si3 precipitates along CBs acted as nucleation sites for cracks, deteriorating the elongation of the alloy. Overall, it is possible to tune the mechanical properties of the LPBFed CoCrMoW alloy by adjusting the local chemical heterogeneity. © 2024, The Authors. All rights reserved.

关键词： Chromium alloys

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Crystal Thermal Transport in Altermagnetic RuO2

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Physical Review Letters 2024年第5期132卷 056701-056701页

作者： Xiaodong Zhou Wanxiang Feng Run-Wu Zhang Libor Šmejkal Jairo Sinova Yuriy Mokrousov Yugui Yao Centre for Quantum Physics Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) School of Physics Beijing Institute of Technology Beijing 100081 China Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing 100081 China Laboratory of Quantum Functional Materials Design and Application School of Physics and Electronic Engineering Jiangsu Normal University Xuzhou 221116 China Institute of Physics Johannes Gutenberg University Mainz 55099 Mainz Germany Institute of Physics Czech Academy of Sciences Cukrovarnická 10 162 00 Praha 6 Czech Republic Peter Grünberg Institut and Institute for Advanced Simulation Forschungszentrum Jülich and JARA 52425 Jülich Germany

We demonstrate the emergence of a pronounced thermal transport in the recently discovered class of magnetic materials—altermagnets. From symmetry arguments and first-principles calculations performed for the showcase altermagnet, RuO2, we uncover that crystal Nernst and crystal thermal Hall effects in this material are very large and strongly anisotropic with respect to the Néel vector. We find the large crystal thermal transport to originate from three sources of Berry’s curvature in momentum space: the Weyl fermions due to crossings between well-separated bands, the strong spin-flip pseudonodal surfaces, and the weak spin-flip ladder transitions, defined by transitions among very weakly spin-split states of similar dispersion crossing the Fermi surface. Moreover, we reveal that the anomalous thermal and electrical transport coefficients in RuO2 are linked by an extended Wiedemann-Franz law in a temperature range much wider than expected for conventional magnets. Our results suggest that altermagnets may assume a leading role in realizing concepts in spin caloritronics not achievable with ferromagnets or antiferromagnets.

关键词： Magnetism Nernst effect Thermal Hall effect Topological materials First-principles calculations

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