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Suspension calcination and alkali leaching of low-grade high-sulfur bauxite:Desulfurization, mineralogical evolution and desilication

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International Journal of Minerals,Metallurgy and Materials 2020年第5期27卷 602-610页

作者： Hong-fei Wu Jun-qi Li Chao-yi Chen fei-long Xia Zhen-shan Xie Department of Metallurgical Engineering College of Materials and MetallurgyGuizhou UniversityGuiyang 550025China Guizhou Province Key Laboratory of Metallurgical Engineering and Process Energy Saving Guiyang 550025China

To enable the utilization of low-grade and high-sulfur bauxite, the suspension calcination was used to remove the sulfur and the activate silica minerals, and the calcinated bauxite was subjected to a desilication process in Na OH solution under atmospheric pressure. The desulfurization and desilication properties and mineralogical evolution were studied by X-ray diffraction, thermogravimetry–differential thermal analysis, scanning electron microscopy, and FactSage methods. The results demonstrate that the suspension calcination method is efficient for sulfur removal: 84.21% of S was removed after calcination at 1000°C for 2 min. During the calcination process, diaspore and pyrite were transferred to α-Al2O3, magnetite, and hematite. The phase transformation of pyrite follows the order FeS2 → Fe3O4 → Fe2O3, and the iron oxides and silica were converted into iron silicate. In the alkali-soluble desilication process, the optimum condition was an alkali solution concentration of 110 g/L, a reaction time of 20 min, and a reaction temperature of 95°C. The corresponding desilication ratio and alumina loss ratio were 44.9% and 2.4%, respectively, and the alumina-to-silica mass ratio of the concentrate was 7.9. The Al2O3·2SiO2, SiO2, and Al2O3 formed during the calcination process could react with Na OH solution, and their activity decreased in the order of Al2O3·2 SiO2, SiO2, and Al2O3.

关键词： low-grade bauxite sulfur suspension calcination alkali-soluble desilication Bayer process

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Towards reinforcement learning in UAV relay for anti-jamming maritime communications

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Digital Communications and Networks 2023年第6期9卷 1477-1485页

作者： Chuhuan Liu yi Zhang Guohang niu Luliang Jia Liang Xiao Jiangxia Luan Department of Information and Communication Engineering Xiamen UniversityXiamen361005China School of Space Information Space Engineering UniversityBeijing101400China Xiamen Meiya Pico Information Co. Ltd.Xiamen361005China

Maritime communications with sea surface reflections and sea wave occlusions are susceptible to jamming attacks due to the wide geographical area and intensive wireless communication *** Aerial Vehicles(UAVs)help relay messages to improve communication performance,but the relay policy that depends on the rapidly changing maritime environments is difficult to *** this paper,a reinforcement learning-based UAV relay policy for maritime communications is proposed to resist jamming *** on previous transmission performance,the relay location,the received power of the transmitted signal and the received jamming power,this scheme optimizes the UAV trajectory and relay power to save the energy consumption and decrease the Bit-Error-Rate(BER)of the maritime signals.A deep reinforcement learning-based scheme is also proposed,which designs a deep neural network with dueling architecture to further improve the communication performance and computational *** performance bounds regarding the signal to interference plus noise ratio,energy consumption and the communication utility are provided based on the Nash equilibrium of the game against jamming,and the computational complexity of the proposed schemes is *** results show that the proposed schemes improve the energy efficiency and decrease the BER compared with the benchmark.

关键词： Maritime communications Jamming Unmanned aerial vehicle Relay Reinforcement learning

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Preparation and evaluation of α-Al2O3 supported lithium ion sieve membranes for Li^+ extraction

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Chinese Journal of Chemical Engineering 2020年第9期28卷 2312-2318页

作者： Feng Xue Xiaoxian Zhang Yue niu Chenhao yi Shengui Ju Weihong Xing College of Chemical Engineering Nanjing Tech UniversityNanjing 211816China

Spinel lithium manganese oxide ion-sieves have been considered the most promising adsorbents to extract Li^+ from brines and sea ***,we report a lithium ion-sieve which was successfully loaded onto tubular α-Al2 O3 ceramic substrates by dipping crystallization and post-calcination *** lithium manganese oxide Li4 Mn5 O(12)was first synthesized onto tubular α-Al2 O3 ceramic substrates as the ion-sieve precursor(i.e.L-AA),and the corresponding lithium ion-sieve(i.e.H-AA) was obtained after acid *** chemical and morphological properties of the ion-sieve were confirmed by X-ray diffraction(XRD) and scanning electron microscopy(SEM).Both L-AA and H-AA showed characteristic peaks of α-Al2 O3 and cubic phase Li4 Mn5 O(12) and the peaks representing cubic phase could still exist after *** lithium manganese oxide Li4 Mn5 O(12) could be uniformly loaded not only on the surface of α-Al2 O3 ubstrates but also inside the ***,we found that the equilibrium adsorption capacity of H-AA was 22.9 mg·g^-*** 12 h adsorption,the adsorption balance was *** 5 cycles of adsorption,the adsorption capacity of H-AA was 60.88% of the initial adsorption *** process of H-AA adsorption for Li^+correlated with pseudo-second order kinetic model and Langmuir *** thermodynamic parameters regarding enthalpy(△N), Gibbs free energy(△G) and entropy(AS) were *** the dynamic adsorptiondesorption process of H-AA,the H-AA exhibited excellent adsorption performance to Li^+ with the Li^+ dynamic adsorption capacity of 9.74 mg·g^-1 and the Mn^2+dissolution loss rate of 0.99%.After 3 dynamic adsorption-desorption cycles,80% of the initial dynamic adsorption capacity was still kept.

关键词： Lithium α-Al2O3 tube Ion sieve Adsorption Li4Mn5O(12)

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Master event based backazimuth estimation and its application to downhole microseismic monitoring

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Petroleum Science 2022年第6期19卷 2675-2682页

作者： Xiao-Bo Meng Hai-Chao Chen Feng-Lin niu yi-Jing Du Department of Geophysics Chengdu University of TechnologyChengduSichuan610059China Unconventional Petroleum Research Institute and State Key Laboratory of Petroleum Resources and ProspectingChina University of PetroleumBeijing102249China Department of Earth Environmental and Planetary SciencesRice UniversityHoustonTX77005USA Petro China Research Institute of Petroleum Exploration and Development Beijing100083China

Microseismic monitoring provides a valuable tool for evaluating the effectiveness of hydraulic fracturing ***,robust detection and accurate location of microseismic events are challenging due to the low signal to noise ratio(SNR)of their signals on *** a downhole monitoring setting,P-wave polarization direction measured from 3-component records is usually considered as the backazimuth of the microseismic event,i.e.,the direction of the *** direction and arrival time difference between the P and S waves is used to locate the seismic *** SNR is low,an accurate estimate of event backazimuth becomes very challenging with the traditional covariance matrix *** we propose to employ a master event and use a grid search method to find the backazimuth of a target event that maximizes the dot product of the two backazimuthal vectors of the master and target *** compared the backazimuths measured with the proposed grid-search and the conventional covariance-matrix methods using a large synthetic *** found that the grid-search method yields more accurate backazimuth estimates from low SNR records when measurements are made at single geophone *** array data are combined,the proposed method also has some advantage over the covariance-matrix method,especially when the number of geophones is *** also applied the method to a microseismic dataset acquired by a hydraulic fracturing project at a shale play site in southwestern China and found that the relocated microseismic events tend to align along existing faults more tightly than those in the original catalog.

关键词： Hydraulic fracturing Microseismic event Back azimuth Master event Grid search Covariance-matrix

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Experimental investigation of expansion effect on shock wave boundary layer interaction near a compression ramp

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Chinese Journal of Aeronautics 2022年第12期35卷 89-101页

作者： Junjie HUO Shihe yi Wenpeng ZHENG Haibo niu Xiaoge LU Dundian GANG College of Aerospace Science and Engineering National University of Defense TechnologyChangsha 410073China

The experiment is conducted to investigate the effect of expansion on the shock wave boundary layer interaction near a compression ramp. The small-angle expansion with an angle degree of 5° occurs at different positions in front of the compression ramp. The particle image velocimetry and flow visualization technology show the flow structures, velocity field, and velocity fluctuation near the compression ramp. The mean pressure distribution, pressure fluctuation, and power spectral density are measured by high-frequency response pressure transducers. The experimental results indicate that the expansion before the compression ramp position affects the shock wave boundary layer interaction to induce a large-scale separation. But the velocity fluctuation and pressure fluctuation are attenuated near the large-scale flow separation region. When the expansion occurs closer to the compression ramp, the expansion has a more significant impact on the flow. The fluctuation of velocity and pressure is significantly attenuated, and the wall pressure rise of the separation point is reduced obviously. And the characteristic low-frequency spectrum signal related to the unsteadiness of the shock wave boundary layer interaction is significantly suppressed. In addition, variation of the separation region scale at different compression angle degrees is distinctive with the effect of expansion.

关键词： Boundary layers Flow visualization Fluid dynamic Pressure measurement Shock waves Supersonic aerodynamics Velocity measurement

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Excellent Terahertz shielding performance of ultrathin flexible Cu/graphene nanolayered composites with high stability

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Journal of Materials Science & Technology 2020年第17期52卷 136-144页

作者： Shengyue Hou Wenle Ma Guanghao Li yi Zhang Yunyun Ji fei Fan yi Huang National Institute for Advanced Materials Tianjin Key Laboratory of Metal and Molecule Based Material ChemistryKey Laboratory of Functional Polymer MaterialsCollaborative Innovation Center of Chemical Science and Engineering(Tianjin)School of Materials Science and EngineeringNankai UniversityTianjin 300350China Beijing Institute of Aeronautical Materials Beijing 100095China Institute of Modern Optics Nankai UniversityTianjin 300350China

Electromagnetic interference(EMI)shielding at Terahertz(THz)frequency range attracts increasing attention due to the rapid development of THz science and *** shielding materials with small thickness,high shielding effectiveness(SE),good flexibility and stability are highly ***,an ultrathin flexible copper/graphene(Cu/Gr)nanolayered composite are prepared,which can reach the average EMI SE of 60.95 dB at 0.1–1.0 THz with a thickness of only 160 nm,indicating that more than 99.9999%of the THz wave power can be ***,the Cu/Gr nanolayered composite also exhibits excellent oxidation resistance,with a 93.09%maintenance rate for EMI SE value after heating at 120℃for 3 h in air,far higher than that of the bare Cu film(62.15%).Besides,the Cu/Gr nanolayered composite exhibits good mechanical flexibility and flexural fatigue *** EMI SE value of the Cu/Gr nanolayered composite shows a maintenance rate of 98.87%even after 1500 times bending cycles,obviously higher than that of multilayer Cu film(93.07%).These results demonstrate that the ultrathin flexible Cu/Gr nanolayered composites with excellent shielding performance and good stability have a broad application prospect in THz shielding for wearable devices and next generation mobile communication equipment.

关键词： Terahertz shielding Ultrathin flexible Cu/grapheme nano composites High stability

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Arbitrary-Order Fractance Approximation Circuits With High Order-Stability Characteristic and Wider Approximation Frequency Bandwidth

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IEEE/CAA Journal of Automatica Sinica 2020年第5期7卷 1425-1436页

作者： Qiu-Yan He yi-fei Pu Bo Yu Xiao Yuan College of Computer Science Sichuan UniversityChengdu 610065China College of Physics and Engineering Chengdu Normal UniversityChengdu 611130China College of Electronics and Information Engineering Sichuan UniversityChengdu 610065China

This paper discusses a novel rational approximation algorithm of arbitrary-order fractances,which has high orderstability characteristic and wider approximation frequency *** fractor has been exploited extensively in various scientific *** well-known shortcoming of the existing fractance approximation circuits,such as the oscillation phenomena,is still in great need of special research *** by this need,a novel algorithm with high orderstability characteristic and wider approximation frequency bandwidth is *** order to better understand the iterating process,the approximation principle of this algorithm is investigated at ***,features of the iterating function and frequency-domain characteristics of the impedance function calculated by this algorithm are researched,***,approximation performance comparisons have been made between the corresponding circuit and other types of fractance approximation ***,a fractance approximation circuit with the impedance function of negative2/3-order is *** high order-stability characteristic and wider approximation frequency bandwidth are fundamental important advantages,which make our proposed algorithm competitive in practical applications.

关键词： Fractal fractance fractional calculus fractional-order systems

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Effect of process parameters on the microstructure and properties of laser-clad FeNiCoCrTi0.5 high-entropy alloy coating

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International Journal of Minerals,Metallurgy and Materials 2020年第5期27卷 630-639页

作者： ying Zhang Teng-fei Han Meng Xiao yi-fu Shen College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics(NUAA)Nanjing 210016China Nanjing Institute of Advanced Laser Technology Nanjing 210038China

FeNiCoCrTi0.5 coatings with different process parameters were fabricated by laser cladding. The macro-morphology, phase, microstructure, hardness, and wear resistance of each coating were studied. The smoothness and dilution rate of the FeNiCoCrTi0.5 coating generally increased with the increase of specific energy(Es), which is the laser irradiation energy received by a unit area. FeNiCoCrTi0.5 coatings at different parameters had bcc, fcc, and Ti-rich phases as well as equiaxed, dendritic, and columnar structures. When Es increased, the size of each structure increased and the distribution area of the columnar and dendritic structures changed. The prepared FeNiCoCrTi0.5 coating with the Es of 72.22 J·mm-2 had the highest hardness and the best wear resistance, the highest hardness of the coating reached HV 498.37, which is twice the substrate hardness. The average hardness of the FeNiCoCrTi0.5 coating with the Es of 72.22 J·mm-2 was 15.8% higher than the lowest average hardness of the coating with the Es of 108.33 J·mm-2. The worn surface morphologies indicate that the FeNiCoCrTi0.5 coatings exhibited abrasive wear.

关键词： high-entropy alloy coating 45 steel laser cladding microstructure wear resistance

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Oxidation damage zone formed in creep fatigue crack growth of GH4169 alloy at 650℃

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Journal of Iron and Steel Research International 2023年第12期30卷 2582-2592页

作者： Lan-zhou Liu yi-fei Gao Jin-hui Du Teng An Central Iron and Steel Research Institute Beijing100081China NCS Testing Technology Co. Ltd.Beijing100081China Beijing Cisri-Gaona Materials and Technology Co. Ltd.Beijing100081China

In the creep fatigue crack growth of GH4169 alloy,oxidation is a prominent damage source,which is mainly manifested as the oxidation damage zone in front of crack *** order to investigate the property of the oxidation damage zone formed in the creep fatigue crack growth,crack growth tests of directly aged GH4169 alloy were conducted at 650℃ in air under various load *** tests were performed to observe the damage characteristics at crack *** tests were systematically executed to quantify the dependency of oxidation damage zone size on load and holding *** crack propagation of the GH4169 alloy has a close relationship with grain boundary oxidation at 650℃.An oxidation damage zone in front of crack tip includes intergranular microcracks and oxidised but uncracked grain *** size has been calculated from transient crack growth rate and described as a function of maximum stress intensity factor and holding *** on oxidation damage zone size,a novel model has been developed to predict the creep fatigue crack growth rate of the GH4169 alloy at 650℃.

关键词： Performance evaluation Creep fatigue crack growth-Directly aged GH4169 alloy Intergranular crack propagation Oxidation damage zone

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Region coverage control for multiple stratospheric airships with combined self-/event-triggered mechanism

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Defence Technology（防务技术） 2023年第6期24卷 254-268页

作者： yi-fei Zhang Ming Zhu Tian Chen Ze-wei Zheng School of Aeronautic Science and Engineering Beihang UniversityBeijing100191China Institute of Unmanned System Beihang UniversityBeijing100191China School of Electronic and Information Engineering Beihang UniversityBeijing100191China School of Automation Science and Electrical Engineering Beihang UniversityBeijing100191China

The region coverage control problem of multiple stratospheric airships system is firstly addressed in this *** it,we propose a two-layer control framework with the artificial potential field(APF)-based region coverage control law and the adaptive tracking control *** APF-based region coverage control law ensures the coverage task is achieved until every single stratospheric airship ends up performing station keeping where near the respective global minimum point,in which an innovative solution to the local minimum problem is put *** adaptive tracking control law is designed to realize motion control using tracking the desired velocity and angular velocity given by coverage control law,with the consideration of several practical control problems as unknown individual differences and external *** save resources,the combined self-/event-triggered mechanism designed therein significantly reduces the times of state information transmission and control law *** effectiveness of the proposed control framework is verified through simulations.

关键词： Formation coverage control Combined self-/event-triggered control Improved artificial potential field

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