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China Communications 2022年第3期19卷 129-131页

作者： Depeng Jin Xiaoming Tao Xiaofeng Zhong Jintao Wang Department of Electronic Engineering Tsinghua University Department Council Electronic Engineering Dept. Tsinghua Univ Department of Electronic Engineering at Tsinghua University Department of Electronic Engineering at Tsinghua University

AI-Empowered Future Communication Networks Recently, the fifth-generation(5G) of wireless network has been developed to support enhanced mobile broadband(eMBB), massive machine-type communications(mMTC) and ultra-reliable and low-latency communications(uRLLC). However, with the tremendous increase of data services,

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A Joint Activity and Data Detection Scheme for Asynchronous Grant-Free Rateless Multiple Access

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China Communications 2024年第1期21卷 34-52页

作者： Wei Zhang Xiaofeng Zhong Shidong Zhou Department of Electronic Engineering Tsinghua UniversityBeijing 100084China

This paper considers the frameasynchronous grant-free rateless multiple access(FAGF-RMA)scenario,where users can initiate access at any symbol time,using shared channel resources to transmit data to the base station.Rateless coding is introduced to enhance the reliability of the system.Previous literature has shown that FA-GFRMA can achieve lower access delay than framesynchronous grant-free rateless multiple access(FSGF-RMA),with extreme reliability enabled by rateless coding.To support FA-GF-RMA in more practical scenarios,a joint activity and data detection(JADD)scheme is proposed.Exploiting the feature of sporadic traffic,approximate message passing(AMP)is exploited for transmission signal matrix estimation.Then,to determine the packet start points,a maximum posterior probability(MAP)estimation problem is solved based on the recovered transmitted signals,leveraging the intrinsic power pattern in the codeword.An iterative power-pattern-aided AMP algorithm is devised to enhance the estimation performance of AMP.Simulation results verify that the proposed solution achieves a delay performance that is comparable to the performance limit of FA-GF-RMA.

关键词： asynchronous grant-free JADD rateless codes

Optimizing the electronic spin state and delocalized electron of NiCo_(2)(OH)_(x)/MXene composite by interface engineering and plasma boosting oxygen evolution reaction

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Journal of Energy Chemistry 2022年第8期31卷 129-140,I0004页

作者： Jingyao Xu Xia zhong xiaofeng Wu Ying Wang Shouhua Feng State Key Laboratory of Inorganic Synthesis and Preparative Chemistry College of ChemistryJilin UniversityChangchun 130012JilinChina Chinese Acad Sci Inst Met ResShenyang Natl Lab Mat SciShenyang 110016LiaoningChina Univ Sci&Technol China Sch Mat Sci&EngnShenyang 110016LiaoningChina State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied ChemistryChinese Academy of SciencesChangchun 130022JilinChina

The electrocatalytic activity of transition-metal-based compounds is closely related to the electronic configuration.However,optimizing the surface electron spin state of catalysts remains a challenge.Here,we developed a spin-state and delocalized electron regulation method to optimize oxygen evolution reaction(OER)performance by in-situ growth of NiCo_(2)(OH)_(x) using Oswald ripening and coordinating etching process on MXene and plasma treatment.X-ray absorption spectroscopy,magnetic tests and electron paramagnetic resonance reveal that the coupling of NiCo_(2)(OH)_(x) and MXene can induce remarkable spin-state transition of Co^(3+)and transition metal ions electron delocalization,plasma treatment further optimizes the 3 d orbital structure and delocalized electron density.The unique Jahn-Teller phenomenon can be brought by the intermediate spin state(t2 _(g)^(5) e_(g)^(1))of Co^(3+),which benefits from the partial electron occupied egorbitals.This distinct electron configuration(t2_(g)^(5) e_(g)^(1))with unpaired electrons leads to orbital degeneracy,that the adsorption free energy of intermediate species and conductivity were further optimized.The optimized electrocatalyst exhibits excellent OER activity with an overpotential of 268 m V at 10 m A cm^(-2).DFT calculations show that plasma treatment can effectively regulate the d-band center of TMs to optimize the adsorption and improve the OER activity.This approach could guide the rational design and discovery of electrocatalysts with ideal electron configurations in the future.

关键词： Transition metal compounds Electronic state control of surface/interface Electron spin state Delocalized electron Electrocatalytic material

Efficient Preconstruction of Three‑Dimensional Graphene Networks for Thermally Conductive Polymer Composites

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Nano-Micro Letters 2022年第8期14卷 72-111页

作者： Hao‑Yu Zhao Ming‑Yuan Yu Ji Liu xiaofeng Li Peng Min zhong‑Zhen Yu Beijing Key Laboratory of Advanced Functional Polymer Composites Beijing University of Chemical TechnologyBeijing 100029People’s Republic of China College of Materials Science and Engineering Beijing University of Chemical TechnologyBeijing 100029People’s Republic of China School of Chemistry CRANN and AMBERTrinity College DublinDublinIreland

Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation.Featured by its exceptional thermal conductivity,graphene is an ideal functional filler for fabricating thermally conductive polymer composites to provide efficient thermal management.Extensive studies have been focusing on constructing graphene networks in polymer composites to achieve high thermal conductivities.Compared with conventional composite fabrications by directly mixing graphene with polymers,preconstruction of three-dimensional graphene networks followed by backfilling polymers represents a promising way to produce composites with higher performances,enabling high manufacturing flexibility and controllability.In this review,we first summarize the factors that affect thermal conductivity of graphene composites and strategies for fabricating highly thermally conductive graphene/polymer composites.Subsequently,we give the reasoning behind using preconstructed three-dimensional graphene networks for fabricating thermally conductive polymer composites and highlight their potential applications.Finally,our insight into the existing bottlenecks and opportunities is provided for developing preconstructed porous architectures of graphene and their thermally conductive composites.

关键词： Graphene networks Thermal conductivity Thermal interface materials Phase change composites Anisotropic aerogels

Constructing central hollow cylindrical reduced graphene oxide foams with vertically and radially orientated porous channels for highly efficient solar-driven water evaporation and purification

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Nano Research 2023年第5期16卷 6343-6352页

作者： Changjun Li Wei Li Hao-Yu Zhao Xin-Yue Feng xiaofeng Li zhong-Zhen Yu State Key Laboratory of Organic-Inorganic Composites College of Materials Science and EngineeringBeijing University of Chemical TechnologyBeijing 100029China Beijing Key Laboratory of Advanced Functional Polymer Composites Beijing University of Chemical TechnologyBeijing 100029China College of Materials Science and Engineering Shandong University of Science and TechnologyQingdao 266590China

Although solar steam generation is an eco-friendly approach for desalinating seawater and purifying wastewater,there are still issues on how to improve the efficiency of solar energy utilization and accelerate the water and heat transport inside the solardriven water evaporators.Herein,we design a central hollow cylindrical reduced graphene oxide(RGO)foam with vertically and radially orientated channels as a solar steam generation device for efficient water evaporation and purification.The vertically aligned porous channels accelerate upward transport of water to the top evaporation surface,while the radially aligned porous channels facilitate water transport and heat transfer along the radial directions for fully utilizing the heat accumulated inside the central cylindrical hole of the foam.The central hole of the foam plays a highly positive role in accumulating more heat for accelerating the water evaporation,the newly generated inner sidewall resulted from the central hole can gain extra thermal energy from surrounding environment in the same way as the outer sidewall of the foam due to the surface cooling effect of the water evaporation.As a result,the vertically and radially aligned RGO foam evaporator with central hollow cylinder achieves a high solar steam generation rate of 2.32 kg·m^(−2)·h^(−1)with an exceptional energy conversion efficiency of 120.9%under 1-sun irradiation,superior to the vertically aligned RGO foam without the central hole(1.83 kg·m^(−2)·h^(−1),96.9%)because of the enhanced water and heat transfer inside the porous channels,the efficient utilization of environmental energy.

关键词： hollow cylindrical foams reduced graphene oxide solar steam generation water evaporation rate seawater desalination

A Storage Optimization Scheme for Blockchain Transaction Databases

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Computer Systems Science & Engineering 2021年第3期36卷 521-535页

作者： Jingyu Zhang Siqi zhong Jin Wang xiaofeng Yu Osama Alfarraj School of Computer and Communication Engineering Changsha University of Science and TechnologyChangsha410114China School of Systems Engineering National University of Defense TechnologyChangsha410000China School of Information Science and Engineering Fujian University of TechnologyFuzhou350000China School of Business Nanjing UniversityNanjing210093China Computer Science Department Community CollegeKing Saud UniversityRiyadh11437Saudi Arabia

As the typical peer-to-peer distributed networks, blockchain systemsrequire each node to copy a complete transaction database, so as to ensure newtransactions can by verified independently. In a blockchain system (e.g., bitcoinsystem), the node does not rely on any central organization, and every node keepsan entire copy of the transaction database. However, this feature determines thatthe size of blockchain transaction database is growing rapidly. Therefore, with thecontinuous system operations, the node memory also needs to be expanded tosupport the system running. Especially in the big data era, the increasing networktraffic will lead to faster transaction growth rate. This paper analyzes blockchaintransaction databases and proposes a storage optimization scheme. The proposedscheme divides blockchain transaction database into cold zone and hot zone usingexpiration recognition method based on Least Recently Used (LRU) algorithm. Itcan achieve storage optimization by moving unspent transaction outputs outsidethe in-memory transaction databases. We present the theoretical analysis on theoptimization method to validate the effectiveness. Extensive experiments showour proposed method outperforms the current mechanism for the blockchaintransaction databases.

关键词： Blockchain distributed systems transaction databases

Nucleation and growth of L1_(2)-Al_(3)RE particles in aluminum alloys:A first-principles study

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Journal of Rare Earths 2023年第7期41卷 1116-1126,I0005页

作者： Touwen Fan Zixiong Ruan Feng zhong Chaoyang Xie xiaofeng Li Dongchu Chen Pingying Tang Yuanzhi Wu College of Science Hunan Institute of TechnologyHengyang 421002China Research Institute of Automobile Parts Technology Hunan Institute of TechnologyHengyang 421002China School of Materials Science and Engineering North University of Chin1Taiyuan 030051China School of Material Science and Hydrogen Energy Engineering Foshan UniversityFoshan 528001China Key Laboratory of New Electric Functional Materials of Guangxi Colleges and Universities Nanning Normal UniversityNanning 530023China

The internal mechanisms of nucleation and growth of L1_(2)-AI_(3)RE(RE=Sc,Y,La-Lu) second phases in Al alloys were investigated by combining first-principles calculations with quasi-harmonic approximation(QHA).The calculated results show that the diffusion rate D_s and chemical potential AG_V increase with the increase of temperature.With the increase of atomic number,the D_s and the strain energy ΔE_(CS)increase firstly from Sc to La,and then decreases,while the calculated interface energy γ_(α/β) and ΔG_V show opposite tendency.Based on above calculated results,the critical nucleation radius R*and coarsening rate K_(LSW) are obtained from the classical nucleation theory(CNT) and LSW model of the Ostwald ripening of particles,respectively.With the increase of atomic number,the R*increases firstly,and then decreases for all planes at finite temperatures.Whereas the K_(LSW) shows opposite variation to the R^(*).From this point of view,it is reasonably speculated that Y and later RE elements can replace the expensive Sc for heat-resistance Al alloys.The solubility c_(∞) of particles is usually very small at low temperature,and there is obvious solubility only when the temperature reaches 600 K.The surface energies E_(sur) of AI_(3)RE compounds and Al solid solution are respectively larger and smaller than that of pure Al,respectively,except for the surface(001) and(110) of Al_(3)La.For all planes,with the increase of atomic number of RE,E_(sur) decreases firstly from Sc to La,and then increases linearly to Lu.These results are helpful for designing high performance heat-resistance Al alloys.

关键词： First-principles calculations Diffusion rate Quasi-harmonic approximation Particle nucleation and growth Rare earths

3D Lamellar-Structured Graphene Aerogels for Thermal Interface Composites with High Through-Plane Thermal Conductivity and Fracture Toughness

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Nano-Micro Letters 2021年第2期13卷 13-27页

作者： Pengfei Liu xiaofeng Li Peng Min Xiyuan Chang Chao Shu Yun Ding zhong-Zhen Yu Beijing Key Laboratory of Advanced Functional Polymer Composites Beijing University of Chemical TechnologyBeijing 100029People’s Republic of China State Key Laboratory of Organic-Inorganic Composites College of Materials Science and EngineeringBeijing University of Chemical TechnologyBeijing 100029People’s Republic of China Beijing Advanced Innovation Center for Soft Matter Science and Engineering Beijing University of Chemical TechnologyBeijing 100029People’s Republic of China

Although thermally conductive graphene sheets are efficient in enhancing in-plane thermal conductivities of polymers,the resulting nanocomposites usually exhibit low through-plane thermal conductivities,limiting their application as thermal interface materials.Herein,lamellarstructured polyamic acid salt/graphene oxide(PAAS/GO)hybrid aerogels are constructed by bidirectional freezing of PAAS/GO suspension followed by lyophilization.Subsequently,PAAS monomers are polymerized to polyimide(PI),while GO is converted to thermally reduced graphene oxide(RGO)during thermal annealing at 300℃.Final graphitization at 2800℃ converts PI to graphitized carbon with the inductive effect of RGO,and simultaneously,RGO is thermally reduced and healed to high-quality graphene.Consequently,lamellar-structured graphene aerogels with superior through-plane thermal conduction capacity are fabricated for the first time,and its superior through-plane thermal conduction capacity results from its vertically aligned and closely stacked high-quality graphene lamellae.After vacuum-assisted impregnation with epoxy,the resultant epoxy composite with 2.30 vol% of graphene exhibits an outstanding through-plane thermal conductivity of as high as 20.0 W m^−1 K^−1,100 times of that of epoxy,with a record-high specific thermal conductivity enhancement of 4310%.Furthermore,the lamellar-structured graphene aerogel endows epoxy with a high fracture toughness,~1.71 times of that of epoxy.

关键词： Anisotropic aerogels Graphene Thermal conductivity Epoxy composites Fracture toughness

Reservoir Characteristics and Genetic Mechanisms of the Mesozoic Granite Buried Hills in the Deep-water of the Qiongdongnan Basin,Northern South China Sea

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Acta Geologica Sinica(English Edition) 2021年第1期95卷 259-267页

作者： YOU Li XU Shouli MAO Xuelian zhong Jia JIAO Yaoqi XIONG xiaofeng Chinese National Offshore Oil Limited Corporation(Zhanjiang) ZhanjiangGuangdong 524057China

Due to its structure,rock and mineral composition,fluid and other factors,the granite Buried Hill Reservoir is highly heterogeneous with a complex longitudinal structure and a reservoir space made up of a combination of dissolution pores and fractures.This paper is based on current understanding of tectonic evolution in the northern part of the South China Sea,in conjunction with the seismic phase characteristics.It is determined that the meshed fault system was formed by three stages of movement-tectonic compression orogeny during the Indochinese epoch,strike-slip compression-tension during the Yanshanian Period,early fracture extension activation during the Himalayan-which controlled the distribution of the Buried Hill Reservoir.Drilling revealed two types of buried hills,faulted anticline and fault horst,their longitudinal structure and the reservoir space type being significantly different.The mineral composition,reservoir space and diagenetic characteristics of the reservoir rocks and minerals were analyzed by lithogeochemistry,micro section and logging etc.,it thus being determined that the Mesozoic rocks of the Songnan Low Uplift in the Qiongdongnan Basin are mainly composed of syenogranite,granodiorite,monzogranite,which is the material basis for the development of the Buried Hill Reservoir.The content of felsic and other brittle minerals is more than 70%,making it easy for it to be transformed into fractures.At the same time,the weathering resistance of granodiorite and monzogranite is weaker than that of syenogranite,which is easily weathered and destroyed,forming a thick sand gravel weathering zone.With increasing depth of burial,weathering and dissolution gradually weaken,the deep acidic fluid improving the reservoir property of internal fractures and expanding the vertical distribution range of the reservoirs.The research results lay a foundation for the exploration of Buried Hill in the deep-water area of the Qiongdongnan Basin.

关键词： granite buried hill weathering structure deep-water genetic mechanism Qiongdongnan Basin