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Gas-surface interaction features under effects of gas-gas molecules interaction in high-speed flows

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Chinese Journal of Aeronautics 2024年第5期37卷 228-242页

作者： Ruiling TAO Zhihui WANG school of engineering Science University of Chinese Academy of SciencesBeijing 100049China

Understanding interactions between gas molecules and solid surface is key to the aerodynamic design of high-speed,high-altitude aerospace vehicles,but there is a large dispersion of gas-surface interaction parameters or namely accommodation *** uncertainty results partly from different considerations of the interaction between gas molecules in various experimental and numerical *** this study,effects of gas-gas molecules interaction are systematically discussed by comparing two different approaches of molecular dynamics simulation of high-speed argon molecules scattering on a graphite *** popularly-used“single scattering”approach repeats the scattering process of a single gas molecule without considering the gas-gas molecules *** newly-developed“continual scattering”approach continually shoots gas molecules at the surface,considering collisions between gas molecules in addition to gas molecules’collisions with ***-surface interaction features in the two approaches are compared and discussed under various affecting factors including rarefaction degree,gas-surface interaction strength,surface temperature and incident *** is shown that these two approaches usually produce different accommodation coefficients,and the corresponding mechanisms are *** study could help clarify some doubts about the selection of accommodation coefficients in engineering practice,and also provide an instruction on design of an appropriate molecular dynamics simulation approach.

关键词： Gas-surface interaction Molecular dynamics Accommodation coefficient Aerospace vehicles High-speed flow

Luminescent enhancement and multi-mode optical thermometry of erbium doped halide Cs2（Na/Ag）BiCl6 microcrystals

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Journal of Rare Earths 2024年第11期42卷 2018-2026页

作者： Shuang Zhao Jinpeng Zou Hanqi Xu Qichuan Hu Qiuju Han Wenzhi Wu school of Electronic engineering Heilongjiang University school of Arts and sciences Northeast Agricultural University

Lanthanum-doped double halide perovskite has attracted increasing interest due to its distinctive upconversion and near-infrared（NIR） luminous ***,erbium ion(Er3+) doped Cs2（Na/Ag）BiCl6microcrystals（MCs） were synthesized and proved to be one of the most prospective candidates for optical *** enhancement of both white light from self-trapped exciton emission and NIR emission from Er3+ion of Cs2AgBiCl6microcrystals is caused by lattice distortion due to Na+ion *** intensity ratio and lifetime methods provide self-referenced and sensitive thermometry under 405 and/or 980 nm laser excitation at the temperatures from 80 to 480 ***,the maximum values of relative and absolute sensitivity of 3.62%/K and 27//K can be achieved in the low to high temperature range under 980 and 405 nm laser *** the experimental analysis,Er3+doped Cs2（Na/Ag）BiCl6double perovskite is considered to be an ideal self-calibrating thermometric material due to its good long-term stability and multi-mode function of excitation and detection.

关键词： Double halide perovskite Rare earths Near-infrared emission Multi-mode thermometry Up-conversion luminescence 980 and 405 nm laser co-excitation

Forced boiling of nonazeotropic immiscible mixture in a supercapillary microchannel array for ultra-high heat flux removal with chip junction temperature below 85℃

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Science China(Technological sciences) 2024年第5期67卷 1364-1380页

作者： SUN Bo BAO YuChen TIAN Tong LI Ji school of engineering Science University of Chinese Academy of SciencesBeijing100049China Laboratory of Advanced Thermal Management Technologies School of Engineering ScienceUniversity of Chinese Academy of SciencesBeijing100049China

In this study,a structure-optimized two-phase microchannel heat sink with sintered submicron nucleation sites was developed and *** copper-based microchannels had a rectangular cross-section with an equivalent hydraulic diameter of 222μ*** subcooled flow boiling characteristics were comprehensively compared between pure HFE-7100 and a non-azeotropic,immiscible binary mixture of HFE-7100 and water,considering heating areas of 1 and 5 cm^(2).The total heating power input to the test section were 100–1500 and 250–3000 W for a 1 and 5 cm^(2)heat source,respectively,with a flow rate ranging from 50 to150 L/*** to pure HFE-7100,the non-azeotropic immiscible binary mixture of HFE-7100/water in the sintered porous microchannels exhibited a much higher overall heat transfer coefficient and lower power *** maintain the junction temperature of a high power electronic chip below 85℃,the proposed supercapillary microchannel heat sink could effectively dissipate the heat flux of 1275 W/cm^(2)over 1 cm^(2)heat source and 500 W/cm^(2)over 5 cm^(2)heat *** addition,the volume ratio of the binary mixture strongly influence the two-phase flow heat transfer *** optimal volume ratio exist in terms of the thermal resistance–pumping power minimization(HFE-7100:water=2:8 is recommended in this study).The findings of this investigation on the flow boiling properties of non-azeotropic immiscible mixtures help fill a gap in the related field.

关键词： microchannel sintered powder coating submicron nucleation cavities nonazeotropic immiscible ultra-high heat flux

Atomically self-healing of structural defects in monolayer WSe2

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Chinese Physics B 2024年第9期33卷 53-59页

作者：李康舒李俊贤韩小藏周武赵晓续 school of Materials Science and engineering Peking University school of Physical sciences University of Chinese Academy of Sciences AI for Science Institute

Minimizing disorder and defects is crucial for realizing the full potential of two-dimensional transition metal dichalcogenides(TMDs) materials and improving device performance to desired properties. However, the methods in defect control currently face challenges with overly large operational areas and a lack of precision in targeting specific defects. Therefore,we propose a new method for the precise and universal defect healing of TMD materials, integrating real-time imaging with scanning transmission electron microscopy(STEM). This method employs electron beam irradiation to stimulate the diffusion migration of surface-adsorbed adatoms on TMD materials grown by low-temperature molecular beam epitaxy(MBE),and heal defects within the diffusion range. This approach covers defect repairs ranging from zero-dimensional vacancy defects to two-dimensional grain orientation alignment, demonstrating its universality in terms of the types of samples and defects. These findings offer insights into the use of atomic-level focused electron beams at appropriate voltages in STEM for defect healing, providing valuable experience for achieving atomic-level precise fabrication of TMD materials.

关键词： atom manipulation design fabrication nanoscale materials and structures: fabrication and characterization new materials: theory scanning transmission electron microscopy (STEM)

Quasi-static and dynamic compressive behaviour of additively manufactured Menger fractal cube structures

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Defence Technology（防务技术） 2024年第7期37卷 39-49页

作者： Damith Mohotti Dakshitha Weerasinghe Madhusha Bogahawaththa Hongxu Wang Kasun Wijesooriya Paul JHazell school of engineering and Technology UNSWCanberraACT2600Australia school of Civil Mining and Environmental EngineeringFaculty of Engineering and Information SciencesUniversity of WollongongWollongongNSWAustralia

This paper presents the first-ever investigation of Menger fractal cubes'quasi-static compression and impact *** cubes with different void ratios were 3D printed using polylactic acid(PLA)with dimensions of 40 mm×40 mm×40 *** different orders of Menger cubes with different void ratios were considered,namely M1 with a void ratio of 0.26,M2 with a void ratio of 0.45,and M3with a void ratio of ***-static Compression tests were conducted using a universal testing machine,while the drop hammer was used to observe the behaviour under impact *** fracture mechanism,energy efficiency and force-time histories were *** the structured nature of the void formation and predictability of the failure modes,the Menger geometry showed some promise compared to other alternatives,such as foams and *** the increasing void ratio,the Menger geometries show force-displacement behaviour similar to hyper-elastic materials such as rubber and *** third-order Menger cubes showed the highest energy absorption efficiency compared to the other two geometries in this *** findings of the present work reveal the possibility of using additively manufactured Menger geometries as an energy-efficient system capable of reducing the transmitting force in applications such as crash barriers.

关键词： Additive manufacturing Fractal geometries Menger cube Energy absorption Quasi-static

Metal-organic framework-derived CoSe_(2)@N-doped carbon nanocubes for high-performance lithium-ion capacitors

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Rare Metals 2024年第5期43卷 2150-2160页

作者： Lei Wang Xiong Zhang Yan-Yan Kong Chen Li Ya-Bin An Xian-Zhong Sun Kai Wang Yan-Wei Ma Institute of Electrical engineering Chinese Academy of SciencesBeijing 100190China school of engineering sciences University of Chinese Academy of SciencesBeijing 100190China Institute of Electrical engineering and Advanced Electromagnetic Drive Technology Qilu ZhongkeJinan 250013China school of Materials Science and engineering Zhengzhou UniversityZhengzhou 450001China

Cobalt selenide(CoSe_(2))has garnered considerable attention as a prospective anode candidate for advanced lithium-ion storage,prompting comprehensive ***,CoSe_(2)-based anodes usually suffer from significant volume variation upon lithiation leading to unsatisfactory cycling ***,a versatile synthesis route is proposed for the in-situ fabrication of CoSe2nanoparticles embedded in N-dope carbon skeleton(CoSe_(2)@NC)through annealing treatment and selenization of a metal–organic framework-derived(MOF)*** N-doped carbon derived from the MOF serves not only as an excellent conductive substrate but also as a confined reactor,effectively inhibiting the structural instability and alleviating the inevitable volume change of CoSe_(2).Owing to their unique nanostructure,the as-prepared CoSe_(2)@NC exhibits a high capacity of 745.9mAh·g^(-1)at 0.1 A·g^(-1),while maintaining excellent rate capability and an impressive ***,the assembled lithium-ion capacitor(LIC)based on CoSe_(2)@NC demonstrates an energy density of 130Wh·kg^(-1),a power density of 24.6 kW·kg^(-1),and remarkable capacity retention of 90.8%after 8000 *** results highlight the great potential of CoSe_(2)@NC for practical applications.

关键词： Lithium capacitors Cobalt selenide Metal-organic frameworks N-doped carbon

Steady-state multiscale CFD simulation of a circulating fluidized bed riser

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Particuology 2024年第10期93卷 54-64页

作者： Zhaojie Ke Yujie Tian Fei Li Bona Lu Wei Wang State Key Laboratory of Mesoscience and engineering Institute of Process EngineeringChinese Academy of SciencesBeijing100190China school of Chemical engineering University of Chinese Academy of SciencesBeijing100049China

Compared to transient simulation,steady-state simulation of circulating fluidized bed risers is more efficient,but is also harder to perform due to the complex scale-dependency of dense gas-solid *** this work,steady-state computational fluid dynamics(CFD)simulation of a riser is performed using the steady energy-minimization multi-scale(EMMS)*** is found that the steady state corresponds to an extremely large scale of length and time,thus the grid size required in steady-state simulation is larger than that in transient *** time-averaged two-fluid model(TFM)coupled with the steady-state EMMS/1M drag model enables a good prediction of the S-shaped,axial solids distribution and the choking transition,whereas the two-phase turbulence and solids stress models are important in predicting the radially core-annular distribution of *** far as we know,this is the first time that one can predict the choking transition in a steady-state CFD *** improvement may need an EMMS modeling of the time-averaged solid stresses.

关键词： Fluidization Drag force Steady state Simulation Mesoscale

High-rate metal-free MXene microsupercapacitors on paper substrates

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Carbon Energy 2024年第5期6卷 94-104页

作者： Han Xue Po‐Han Huang Lee‐Lun Lai Yingchun Su Axel Strömberg Gaolong Cao Yuzhu Fan Sergiy Khartsev Mats Göthelid Yan‐Ting Sun Jonas Weissenrieder Kristinn BGylfason Frank Niklaus Jiantong Li school of Electrical engineering and Computer Science KTH Royal Institute of TechnologyStockholmSweden school of engineering sciences KTH Royal Institute of TechnologyStockholmSweden

MXene is a promising energy storage material for miniaturized microbatteries and microsupercapacitors(MSCs).Despite its superior electrochemical performance,only a few studies have reported MXene-based ultrahigh-rate(>1000 mV s^(−1))on-paper MSCs,mainly due to the reduced electrical conductance of MXene films deposited on ***,ultrahigh-rate metal-free on-paper MSCs based on heterogeneous MXene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)-stack electrodes are fabricated through the combination of direct ink writing and femtosecond laser *** a footprint area of only 20 mm^(2),the on-paper MSCs exhibit excellent high-rate capacitive behavior with an areal capacitance of 5.7 mF cm^(−2)and long cycle life(>95%capacitance retention after 10,000 cycles)at a high scan rate of 1000 mV s^(−1),outperforming most of the present on-paper ***,the heterogeneous MXene/PEDOT:PSS electrodes can interconnect individual MSCs into metal-free on-paper MSC arrays,which can also be simultaneously charged/discharged at 1000 mV s^(−1),showing scalable capacitive *** heterogeneous MXene/PEDOT:PSS stacks are a promising electrode structure for on-paper MSCs to serve as ultrafast miniaturized energy storage components for emerging paper electronics.

关键词： direct ink writing femtosecond laser scribing MXene on-paper microsupercapacitors PEDOT:PSS ultrahigh rate capability

Identifying malicious traffic under concept drift based on intraclass consistency enhanced variational autoencoder

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Science China(Information sciences) 2024年第8期67卷 238-252页

作者： Xiang LUO Chang LIU Gaopeng GOU Gang XIONG Zhen LI Binxing FANG Institute of Information engineering Chinese Academy of Sciences school of Cyber Security University of Chinese Academy of Sciences school of Computer Science and Technology Harbin Institute of Technology (Shenzhen)

Accurate identification of malicious traffic is crucial for implementing effective defense countermeasures and has led to extensive research efforts. However, the continuously evolving techniques employed by adversaries have introduced the issues of concept drift, which significantly affects the performance of existing methods. To tackle this challenge, some researchers have focused on improving the separability of malicious traffic representation and designing drift detectors to reduce the number of false ***, these methods often overlook the importance of enhancing the generalization and intraclass consistency in the representation. Additionally, the detectors are not sufficiently sensitive to the variations among different malicious traffic classes, which results in poor performance and limited robustness. In this paper, we propose intraclass consistency enhanced variational autoencoder with Class-Perception detector(ICE-CP) to identify malicious traffic under concept drift. It comprises two key modules during training:intraclass consistency enhanced(ICE) representation learning and Class-Perception(CP) detector construction. In the first module, we employ a variational autoencoder(VAE) in conjunction with Kullback-Leibler(KL)-divergence and cross-entropy loss to model the distribution of each input malicious traffic flow. This approach simultaneously enhances the generalization, interclass consistency, and intraclass differences in the learned representation. Consequently, we obtain a compact representation and a trained classifier for nondrifting malicious traffic. In the second module, we design the CP detector, which generates a centroid and threshold for each malicious traffic class separately based on the learned representation, depicting the boundaries between drifting and non-drifting malicious traffic. During testing, we utilize the trained classifier to predict malicious traffic classes for the testing samples. Then, we use the CP det

关键词： concept drift malicious traffic identification variational autoencoder intrusion detection cyberspace security