2021 Vol.27

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    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 0-0.  
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    Shortcuts to adiabatic control of electron states in semiconductor quantum dots
    BAN Yue, LI Xinhe, CHEN Xi
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 1-17.   DOI: 10.12066/j.issn.1007-2861.2273
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    Fast and accurate quantum state preparation and manipulation are important tasks in the field of quantum information processing and solid-state-based quantum computing. In recent years, shortcuts to adiabaticity have been widely used in atom cooling, transfer, and other quantum information processing, aiming to accelerate slow adiabatic processes. In this study, fast, robust control schemes for electron quantum states in different semiconductor quantum dot systems are reviewed using shortcuts to adiabaticity. The different methods include invariant-based inverse engineering and transitionless quantum driving. The various protocols and effects of environmental decoherence and other system factors on quantum state manipulation are analysed.

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    Video colourisation based on voxel flow
    CHEN Yu, DING Youdong, YU Bing, XU Min
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 18-27.   DOI: 10.12066/j.issn.1007-2861.2119
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    Video colourisation methods that transfer colour information in keyframes based on traditional optical flow are time-consuming, while those relying on global colour transfer are prone to desaturation. This paper proposes a new video colourisation method based on voxel flow. In the proposed method, the reference and target images are both converted to the lab colour space, before a double-channel voxel flow is obtained by feeding the luminance channels of the images into a neural network. The voxel flow values indicate the positional colour correspondence between the target frame and the reference frame. Then, the colour of the target frame is obtained by bilinear interpolation of the reference frame utilising the voxel flow. Finally, the colour and luminance channels are combined to synthesise the final colourised image. Experimental results show that the proposed video colourisation method maintains the saturation of the reference image, while also maintaining edge sharpness. Compared with rival video colourisation methods based on traditional optical flow, the proposed method yields a higher peak signal-to-noise ratio (PSNR) and offers a shorter runtime.

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    Method for improving age estimation using age editing
    ZHANG Chenyu, XU Shugong, HUANG Jianbo
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 28-38.   DOI: 10.12066/j.issn.1007-2861.2250
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    As an emerging biometric identification technology, face age estimation is a classic learning problem in computer vision. Based on the powerful data generation ability of a generative adversarial network (GAN), a method to improve age estimation by using age editing is proposed. The training data suitable for age estimation were amplified by combining the training age editing network-StarGAN and the age estimation network-soft stagewise regression network (SSR-Net), in stages. Experimental results show that the method achieves the better age estimation results under unrestricted conditions.

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    Synchronization algorithm for IEEE 802.15.6 protocol in the presence of strong narrowband interference
    JIN Yanliang, WANG Xue, LUO Xuetao, NIE Hong
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 39-48.   DOI: 10.12066/j.issn.1007-2861.2118
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    Impulse radio ultra-wideband (IR-UWB) is a radio technology that transmits information over a broad bandwidth, and which can receive narrowband signals from existing wireless systems with narrowband interference. In this study, a novel synchronisation algorithm is proposed for the IR-UWB receiver, targeting the IEEE 802.15.6 Standard according to the characteristics of the Kasami sequence in the UWB synchronisation header. A Kasami sequence, which is selected as the template, is multiplied by the received signal. The simulation results demonstrate that the proposed algorithm has a higher synchronisation success rate and lower complexity compared with other algorithms that focus on the IEEE 802.15.6 protocol.

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    Cooperative spectrum sensing method based on entropy function
    REN Mengmeng, HU Yanfei, ZHAI Xuping
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 49-58.   DOI: 10.12066/j.issn.1007-2861.2121
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    In cognitive radio, the performance of the spectrum sensing method is closely related to the sensing scene. Research has shown that the Nakagami-Gamma (KG) fading channel model can reliably describe wireless communication channels. A cooperative sensing method based on the entropy function (BEF) is proposed for the sensing scene of heterogeneous nodes (a group of nodes with different performance factors such as sampling number, receiving signal-to-noise ratio (SNR), and geographical location) in the KG fading channel. First, the comprehensive evaluation scores of each node are calculated using the defined entropy function according to the different performance factors of heterogeneous nodes. Then, the nodes with high scores are selected for normalised energy detection. Finally, the OR criterion is used for fusion decision. Simulation results show that the proposed BEF method can effectively reduce the overhead of the sensing system, and the global detection probability is significantly improved when the target false alarm probability of each node is low ($P_{\rm f}<0.1$).

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    Model reduction of linear fast periodically switched systems using balanced truncation
    DU Xin, HU Zheng, WANG Jianying
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 59-77.   DOI: 10.12066/j.issn.1007-2861.2114
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    This study examines the model order reduction of linear fast periodically switched systems within the framework of a balanced truncation approach. The direct current (DC) averaged state-space model is introduced to describe the averaged dynamics of the given periodically switched systems in the presence of a DC input signal. In addition, a balanced truncation-based algorithm is developed to generate the desired reduced periodically switched model. A small-signal averaged state-space model is introduced to deal with cases in which the alternating current input signal is included. Similarly, an algorithm to generate the desired reduced model is proposed by exploiting the singular perturbation-type balanced truncation. Finally, numerical and experimental examples are presented to illustrate the effectiveness of the proposed results.

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    Synthesis of tin-oxygen sulfide compound @poly-aniline@reduced graphene composites with superior electrochemical performance
    ZHU Ying, ZHOU Diwen, TANG Yan, WANG Hao, ZHAO Pandeng, PU Xianjuan, JIAO Zheng, CHENG Lingli
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 78-85.   DOI: 10.12066/j.issn.1007-2861.2104
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    By hydrothermal synthesis of tin disulfide hexagonal wafers, polyaniline was wrapped outside by using oxidative polymerization, and tin-oxygen sulfide compound@polyaniline@reduced graphene oxide composites were prepared by hydrothermal reduction. Characterization instruments of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), and transmission electron microscope (TEM) were used to analyze the morphology and phase of the composites. The results show that the prepared hexagonal tin oxysulfide compound is double-coated by polyaniline and reduced graphene. The electrochemical properties of the composites as a negative electrode of a lithium-ion battery were investigated. The results reveal that the polyaniline and reduced graphene in the multicomponent composite increase the conductivity and buffer the volume expansion of the tin-oxygen sulfide compound during charge and discharge, maintain structural stability, and exhibit superior electrical performance.

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    Spatial distribution of atmospheric carbonyl compounds in the Summer of 2017, Shanghai Area
    CHEN Feng, DUAN Yusen, FENG Yanli, LU Fei
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 86-96.   DOI: 10.12066/j.issn.1007-2861.2060
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    A multi-channel oxygenated volatile organic compound (OVOC) remote control sampler developed in a laboratory and a ternary-mobile phase programme named DNPH- HPLC were used simultaneously to measure the concentration levels of 20 carbonyl compounds in the atmosphere in Shanghai from 4th to 7th August, 2017. The sampling time was 6:00---9:00 a.m. The results indicated that the total concentrations of carbonyls in the atmosphere of the Shanghai area varied from 14.34 to 106.15 $\mu $g/m3, characterised by higher levels in the west and lower levels in the southeast. The concentrations in each area were significantly different. The concentrations in Lingang and Chongming were relatively low, while those of Fengjing and Suzhou Industrial Park were the highest. This pattern was similar to the spatial distribution of VOCs detected in the same periodin the same region. Formaldehyde, acetaldehyde, and acetone were the main carbonyl compounds in the atmosphere, accounting for 68% of the total carbonyl compounds. Suitable correlations were observed among formaldehyde, acetaldehyde, and propionaldehyde. Benzaldehyde, heptanal, octanal, nonanal, and decanal were also correlated, indicating similar sources. The ozone formation potential (OFP) of carbonyl compounds varied from 68.01 to 326.83 $\mu $g/m3, with formaldehyde having the largest contribution and acetaldehyde the second largest. They accounted for 92.93% of the total OFP.

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    Community structure and diversity phytoplankton in the Wujiang River Basin reservoir
    YUE Yihong, FU Zhiwei, CHEN Xueping, YANG Ming, WANG Baoli, WANG Fushun
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 97-105.   DOI: 10.12066/j.issn.1007-2861.2085
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    Phytoplankton plays a crucial role in river ecosystems. To characterise the structure of phytoplankton communities in cascade reservoirs of the Wujiang River Basin, filter samples were collected at 0, 10, and 45 m depth, and two previously reported degenerate primers were applied to amplify the 23S rRNA gene fragment and construct the library for high-throughput sequencing. An efficient identification method was developed through comparison of species coverage between two degenerate primers, and primary information was obtained on the phytoplankton community diversity. This study provides a powerful tool for potential studies on the ecological effect of damming on phytoplankton communities in riverine ecosystems.

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    Experimental methods for characterizing protein-protein interactions
    KONG Wenna, ZHOU Mi, LIN Haixia, WANG Renxiao
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 106-116.   DOI: 10.12066/j.issn.1007-2861.2065
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    Protein molecules usually interact with other partner protein molecules to execute their biological functions. Hence, the characterisation of protein-protein interac- tions (PPIs) plays a significant role inelucidating the molecular mechanism of proteins. With the progress of proteomics comes the development of a variety of experimental methods for characterising protein-protein interactions. This article mainly reviews recently developed biophysical- or biochemical-basedexperimental methods for characterising protein-protein interactions.

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    Synthesis of double layer Co$_{\bf 2.7}$Cu$_{\bf 0.3}$O$_{\bf 4 }$ cubes composites with enhanced lithium ion battery performance
    ZHAO Pandeng, HE Yongchao, HE Xinhua, FENG Xiaoxiao, PU Xianjuan, CHENG Lingli, JIAO Zheng
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 117-124.   DOI: 10.12066/j.issn.1007-2861.2113
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    Co/Cu-BTC solid cube precursors were synthesised by solvent thermal methods, and double-layer Co$_{2.7}$Cu$_{0.3}$O$_{4}$ cube composites were obtained by calcining in air using Co/Cu-BTC as a self-sacrificing template. The phase morphologies of the materials were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). Following this, the prepared double-layer Co$_{2.7}$Cu$_{0.3}$O$_{4}$ cube composites were employed as anode materials for lithium ion batteries, which exhibited excellent cycling stability. This can be attributed to its unique double layer cube structure, which can effectively shorten the electron transfer path and alleviate the volume expansion in the process of charging and discharging, thus maintaining the stability of the structure.

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    Mixed-metal oxide derived from bimetal-organic frameworks for performance lithium-ion batteries
    ZHANG Yanfeng, CAI Chang, TAN Xinyi, SUN Weiwei
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 125-132.   DOI: 10.12066/j.issn.1007-2861.2072
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    Co/Zn bimetal organic framework precursor (Co/Zn-MOF-74) has been obtained by using the one-step facile microwave-assisted solvothermal method. By calcining the Co/Zn-MOF-74 at 500 ${^\circ}$C under air, the mesoporous mixed-metallic Co-Zn-O microrod can be obtained. When applied as the anode materials for lithium-ion batteries, the Co-Zn-O electrode exhibits good electrochemical properties (reversible capacity of 1 137 mA$\cdot$h$\cdot$g-1 after 100 cycles), which could be attributed to its mesoporous nanostructure along with the synergistic effects between two different metal species.

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    Selective degradation of Zn-Ti-O/FTO composite film
    SHI Ji, ZHAO Jiadong, YU Shengwen
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 133-143.   DOI: 10.12066/j.issn.1007-2861.2063
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    The Zn-Ti-O composite film prepared from fluorine-doped tin oxide (FTO) conducting glass with sol-gel technology has been investigated, whose phase structures analyzed by X-ray diffraction (XRD), absorption spectra measured by UV-Vis spectrophotometer, and morphologies characterized by scanning electron microscope (SEM). The photocatalytic reaction of Zn-Ti-O/FTO has been tested by ultraviolet light with wavelength of 255 nm as light source to methyl orange (MO), methylene blue (MB) and rhodamine B (RhB), respectively. Results indicate that the Zn-Ti-O film prepared on FTO substrate shows obvious preference for degradation of organic compounds---the optimal degradation of MB is 90.3%/(6 h). This preference may be related to the relative positions of the bottom of conduction band/the top of valence band of film and substrate, and the lowest unoccupied molecular orbital/highest occupied molecular orbital of the organic degradation.

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    Design and fabrication of silver-coated three-dimensional porous silicon composite anode with high performance for lithium ion battery
    ZHU Delun, PENG Yuqing, BAI Ruicheng, LI Aijun, ZHAO Tianting, SUN Ningxia
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 144-153.   DOI: 10.12066/j.issn.1007-2861.2061
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    Silver-coated three-dimensional porous silicon (3D-porous-Si/Ag) composites were fabricated as anode materials for a lithium-ion battery via a metal-assisted chemical etching (MACE) method and an electroless plating method. Commercial silicon powders were used as substrate material. The composition, microstructure, and specific surface area of 3D-porous-Si and 3D-porous-Si/Ag were analysed via X-ray diffraction, field emission scanning electron microscopy, and surface area and porosity analyses. The electrochemical performance of the 3D-porous-Si/Ag composite was investigated. The results indicate that the aperture size and specific surface area of 3D-porous-Si were 12.5 nm and 6.083 m$^2$/g, respectively. These pores can be attributed to the narrow slit mesopores. The charge-discharge plot under a constant current of 420 mA/g indicates an initial discharge capacity of 2 822 mA$\cdot$h/g for the 3D-porous-Si/Ag electrode. The Coulombic efficiency reached 87.8% after the first cycle, and the capacity of the 3D-porous-Si/Ag electrode reached 832 mA$\cdot$h/g after 50 cycles. This is mainly because the 3D-porous microstructure and silver coating effectively restrain the volume expansion of silicon caused by the insertion of lithium ions. Moreover, the silver coating improves the electrical performance of the Si material.

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    Application of novel porous polyaniline in electrode material of supercapacitor
    JU Ge, KHAN Muhammad Arif, ZHENG Huiwen, AN Zhongxun, WU Mingxia, ZHAO Hongbin, XU Jiaqiang
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 154-160.   DOI: 10.12066/j.issn.1007-2861.2116
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    Porous polyaniline (PANI) is prepared through an efficient and cost-effective method by polymerisation of aniline in a HCl solution containing KCl. The KCl solution serves as a pseudo-template for the formation of porous PANI, thereby avoiding the use of organic solvents and hard/soft templates and thus protecting the environment. Because of its highly porous structure and intercrossed nanorods, PANI provides a large surface area, resulting in good electrochemical performance. The porous PANI electrodes show a high specific capacitance of 800 F$\cdot$g-1 prepared with saturated KCl, which is more than six times than that of PANI prepared without KCl as the pseudo-template. Thus, synthesised PANI is an excellent electrode material for supercapacitors and is of great significance in their practical application.

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    On the construction and performance of high-order smooth boundary elements
    TIAN Yu, HE Donghong, MA Hang
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 161-170.   DOI: 10.12066/j.issn.1007-2861.2108
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    Based on Lagrange interpolation polynomials, this study realizes computer automated generation of coefficients of shape functions for high-order boundary elements. This study constructs the high-order smooth boundary elements based on existing closure elements by utilising the geometrical properties of particles. Numerical examples show that, when compared with the use of traditional quadratic and closure elements, using high-order smooth elements can greatly improve the accuracy and efficiency in simulating particles with elliptical and ellipsoidal shapes.

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    Optimization design of reinforced concrete ribbed floor system
    ZHOU Bolun, ZHU Jiejiang
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 171-180.   DOI: 10.12066/j.issn.1007-2861.2106
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    The eagle strategy is used to optimise a reinforced concrete (RC) ribbed floor system, including floors and underground garage roofs. This study takes the cost as an objective function and satisfies the constrained condition such that an optimal layout is obtained for different column grids. In addition, an optimal section of the beam and slab as well as the corresponding reinforcement are obtained. The RC ribbed floor is optimised according to the Chinese standard, whose two column grids are 8 and 6 m, respectively. The effect of optimisation is determined to be sufficient and applicable to practical engineering.

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    Ageing effect on swelling characteristics of Gaomiaozi (GMZ) bentonite saturated by salt solution
    YANG Kang, SUN Dean, ZHANG Qianyue
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 181-189.   DOI: 10.12066/j.issn.1007-2861.2127
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    There is a long time gap between buffer bentonite block preparation and wetting; thus, it is necessary to study the effect of ageing on swelling characteristics. Gaomiaozi (GMZ) sodium bentonite was used as the test material, and curing periods of 0, 7, 15, 30, and 90 days after preparation were chosen, while maintaining constant dry density and water content. The swelling deformation and pressure tests were performed by saturating the specimens with salt solutions in an odometer. Scanning electron microscope (SEM) was also performed. The test results showed that the swelling deformation and pressure of GMZ bentonite decreased with increasing curing time. The decrease was obvious in the early stage, and it tended to be stable in the later stage. At the same curing time, the ageing effect on the swelling property weakened when the TDS concentration increased. The SEM images revealed that upon increasing the ageing time and TDS concentration, the bentonite was hydrolysed and the pores between the aggregates tended to be homogenised. The variance of pores between the aggregates caused by increasing TDS concentration was larger than that caused by increasing ageing time. This is consistent with the conclusion for the swelling force attenuation rate: under the condition of low TDS concentration and short ageing time, the TDS concentration may have a more obvious influence than the ageing time.

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    Multi-criteria decision-making method based on an interval-valued Pythagorean triangular fuzzy linguistic set
    DING Xuefeng, ZHONG Junhui
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 190-207.   DOI: 10.12066/j.issn.1007-2861.2175
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    To improve the accuracy of information descriptions in uncertain environments, an interval-valued Pythagorean triangular fuzzy linguistic set is proposed, and basic theories of interval-valued Pythagorean triangular fuzzy linguistic variables (IVPTrFLVs) are critically examined. In addition, an improved combinative distance-based assessment (CODAS) method for solving multi-criteria decision-making problems is developed. First, this study defines the IVPTrFLVs, operational rules, score function, accuracy function, and the formulas for calculating Hamming, Euclidean, and Taxicab distances. An IVPTrFL weighted arithmetic averaging (IVPTrFLPWAA) operator is proposed. Then, by calculating the relative importance coefficient of criteria weight, the study establishes an improved CODAS method based on IVPTrFLVs. Finally, the validity and stability of the proposed method are verified through an example.

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    Weak delay-dependent stability of Rosenbrock methods for neutral delay differential equations
    ZHANG Mingkun, WANG Yanpei, ZHAO Huanhuan
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 208-217.   DOI: 10.12066/j.issn.1007-2861.2115
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    The weak delay-dependent stability of the Rosenbrock methods for neutral delay differential equations is studied under the condition that the equations are delay-dependent asymptotically stable. Based on the argument principle, a sufficient condition for the weak delay asymptotic stability of Rosenbrock methods is given. Finally, numerical examples are provided to verify the effectiveness of the theoretical results.

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    Bayesian inference for semiparametric ordinal regression
    ZHAO Huanli, HE Youhua
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (1): 218-226.   DOI: 10.12066/j.issn.1007-2861.2124
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    This study combines the proportional odds and semiparametric regression models to establish a general form of a semiparametric ordinal regression model. For the parametric and nonparametric parts of the model, a Bayesian estimator based on the finite dimensional distribution of the stochastic process is constructed, and the analytical expression of the estimator is given under normal conditions. Numerical simulation results reveal that, even in the case of small samples, the estimated values of the model parameters are close to the true values, and the estimated values of the non-parametric parts can describe the shape of the real function. An empirical analysis of predicted income levels based on household consumption structures shows that a difference exists in the consumption structures between urban residents and rural households at the same income level, and a better performance under extrapolation is identified.

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    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 226-410.  
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    Rapid determination of TOC, TN and BSi content in reservoir sediments based FTIR
    MEI Lin, FAN Xinyi, YUE Yihong, LIU Liu, CHU Yongsheng, WANG Fushun
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 227-235.   DOI: 10.12066/j.issn.1007-2861.2290
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    Fourier transform infrared spectroscopy (FTIR) was used to analyse sediments from Yantan (YT) Reservoir in Southwest China, and a rapid analysis method for sediment total organic carbon (TOC), total nitrogen (TN) and biogenic silica (BSi) content based on FTIR was investigated. The FTIR prediction models of TOC/TN/BSi contents were established by partial least squares regression (PLSR) method, respectively. The prediction accuracy of this model was verified based on the measured data. This method can effectively extract geochemical information from reservoir sediments and can be applied to the study of high-resolution paleoenvironmental changes. The method requires small sample size and simple pretreatment process to rapidly and economically determine the content of various sediments components, which is of great advantage in determining a large number of sediment samples.

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    Distribution characteristics, influencing factors and sources of heavy metals in karst deep-water reservoirs: a case study of Longtan Reservoir
    GUAN Tianhao, LI Xiaodong, WANG Yiyao, YANG Mengdi, CUI Gaoyang, DING Shiyuan, ZHANG Xuecheng
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 236-249.   DOI: 10.12066/j.issn.1007-2861.2289
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    In order to reveal the influencing factors and sources of the temporal and spatial variation of dissolved heavy metals in karst deep-water reservoirs, this paper selected Longtan Reservoir in Pearl River basin as the research object, and analysed the dissolved heavy metals in stratified water, surface water of tributaries flowing into the reservoir area and discharged water in July 2019 and January 2020, as well as the hydrochemical parameters of the reservoir area in April, July, October 2019 and January 2020. Through Piper diagram of main ions, Pearson correlation analysis among the different kinds of heavy metals, cluster analysis and canonical correlation analysis (CCA) between environmental factors and dissolved heavy metals, the results showed that the weathering of carbonate rocks in the basin was an important external source of dissolved heavy metals in Longtan Reservoir. The change in relative water column stability (RWCS) caused by the seasonal thermal stratification of reservoir water body was the main factor affecting the spatial and temporal distribution of dissolved heavy metals in the study area. Higher RWCS usually promoted the release of Cr and Cu, whereas lower RWCS promoted the release of Fe and As. This study provided a theoretical basis for exploring the relationship between hydrodynamic conditions and dissolved heavy metals, and had important guiding significance for scientific utilization and protection of water resources in karst deep-water reservoirs.

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    Spatial and seasonal variability of particulate organic carbon in the Wujiang River
    ZHANG Jinhua, HUANG Jiaqi, LIN Xin, WANG Fushun, MA Jing
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 250-259.   DOI: 10.12066/j.issn.1007-2861.2145
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    Surface water samples were collected from seven cascade reservoirs across the mainstream Wujiang River and Hongfeng Reservoir on the tributary of Maotiao River, to measure the concentration of total suspended matter (TSM). Samples were analysed for elemental and stable carbon isotopic ($\delta ^{13}$C) composition and lignin phenols to investigate the variability in the spatial and seasonal distribution of particulate organic carbon (POC). The TSM in surface water varied greatly across the seasons. It was higher in the spring and summer than in autumn and winter. POC and lignin content ($\Sigma $8 and $\Lambda $8, respectively) in surface water showed high variability that were greatly influenced by season. POC in upstream waters was higher than in downstream waters in the autumn and winter, reflecting dam interception. $\Sigma $8 and $\Lambda $8 in the TSM samples exhibited a significant linear relationship, stronger in autumn and winter than in spring and summer. The $\delta ^{13}$C of TSM was significantly negative. This was potentially due to the more depleted $\delta ^{13}$C of terrestrial plant debris and freshwater plankton, that was likely to exist in surface water. Angiosperms were the dominant vegetation species reflected by lignin. There was a high diversity in the plant sources of terrestrial organic matter in surface particulate matter samples. The extent of degradation of TSM samples was relatively low, and aggravated degradation was observed in July and October, likely related to vigorous microbial activity.

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    Impact of dam construction on land-use change at the catchment and landscape scale: a case study of Hongjiadu Reservoir
    FU Junjie, WANG Wei, LI Wei, SUN Junyao
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 260-270.   DOI: 10.12066/j.issn.1007-2861.2291
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    Land-use change is closely related to the human disturbance. Dam construction alters the land-use of a reservoir's surroundings, ultimately affecting the transport of matters from terrestrial ecosystem to the ocean through inland waters. Taking the Hongjiadu Reservoir in Wujiang River as an example, a land-use transfer matrix was applied to discuss the dam-induced change in land-use in the Hongjiadu Reservoir catchment at both the catchment scale and landscape scale. Results showed as follows. From a time scale perspective, land-use change mainly occurred in the second stage after reservoir impoundment. In the first stage, the overall change of Hongjiadu Reservoir catchment was that the cropland area decreased by 91.33 km$^{2}$, while the forest, grassland, water and urban areas increased by 26.54, 8.84, 55.51 and 0.45 km$^{2}$, respectively. In the second stage, the cropland, forest and grassland areas decreased by 230.98, 30.17 and 42.88 km$^{2}$, respectively, while water and urban areas increased by 9.07 and 295.46 km$^{2}$, respectively. At the spatial scale, the land-use change was mainly concentrated in the vicinity of Hongjiadu Reservoir, in the decrease of cropland areas and the increase of grassland areas. The land-use type changed the most within the 0-1 km buffer zone at the reservoir's landscape scale, mainly manifested as water becoming grassland and urban becoming cropland. Different land-use types were inundated to form the reservoir area after the construction of Hongjiadu dam, which with the greatest impact on the land-use change within the 0-1 km buffer zone of the reservoir.

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    Characteristics of lignin in sediment cores from cascade reservoirs downstream of the Wujiang River and[1mm] source analysis of organic carbon
    HUANG Jiaqi, LIN Xin, WANG Fushun, MA Jing
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 271-279.   DOI: 10.12066/j.issn.1007-2861.2280
    Abstract557)   HTML312)    PDF(pc) (750KB)(91)       Save

    The terrestrial organic carbon (OC) in sediment cores from two large deep-water reservoirs (Silin and Pengshui) located in the lower reaches of the Wujiang River in the karst landscape of Southwest China were analysed and quantified using lignin biomarker technology. Qualitative analysis and quantitative calculations of terrestrial-derived organic carbon in sediment cores using the lignin biomarker technique showed that the lignin content index $\Sigma 8$ ranged from 0.55 to 2.97 mg/10 g dw (dry weight) and $\Lambda 8$ ranged from 0.38 to 1.42 mg/100 mg OC. The lignin in the sediment cores was derived mainly from the herbaceous tissues of angiosperms, and had been degraded via demethylation, demethoxylation, and oxidative degradation of the side chains by white rot and brown rot bacteria. The end-member model showed that the contribution of exogenous organic carbon to the sediment cores was slightly greater than that of endogenous organic carbon, with soil organic carbon contributing the most. The influence of river cascade damming on sedimentary organic carbon was manifested in the interception of exogenous organic carbon and the accmulation of endogenous organic carbon, and there was obvious spatial heterogeneity in the distribution of both types of organic carbon.

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    Effects of boron content on microstructure and mechanical properties of FeCoNiCrAl$_{\bf 0.1}$B$_{ x }$ high-entropy alloy
    XIE Yaxi, CHEN Yexin, MA Xingxing
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 280-288.   DOI: 10.12066/j.issn.1007-2861.2161
    Abstract1244)   HTML344)    PDF(pc) (12310KB)(119)       Save

    The effects of boron content on the microstructure and mechanical properties of FeCoNiCrAl$_{0.1}$B$_{x }(x = 0{\sim}$0.1) high-entropy alloy were investigated in this study. The results suggested that the FeCoNiCrAl$_{0.1}$B$_{x}$ high-entropy alloy consisted of single face-centered cubic (FCC) $\gamma $ phases when $x\le 0.03$, whereas it consisted of FCC $\gamma $ phase, trace of ordered FCC phase, and boride when $x\ge 0.05$. With the addition of boron atoms in the alloy, the grain size of the alloy refined, tensile strength of the alloy increased, and elongation of the alloy decreased with an increase in the boron content. The fractographs of the FeCoNiCrAl$_{0.1}$B$_{x}$ high-entropy alloy exhibited all transgranular fracture patterns during tensile testing in vacuum.

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    Quasi-twisted codes achieving the Gilbert-Varshamov bound
    LU Xiaohua, WANG Yongchao, DING Yang
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 289-297.   DOI: 10.12066/j.issn.1007-2861.2129
    Abstract1315)   HTML19)    PDF(pc) (230KB)(84)       Save

    Quasi-twisted codes are regarded as a generalisation of cyclic codes. The Gilbert-Varshamov bound is an important criterion for measuring the quality of quasi-twisted codes. A class of randomized one-generator quasi-twisted codes was presented. Furthermore, it was proved that, using the properties of irreducible polynomials, random one-generator quasi-twisted codes asymptotically achieved the Gilbert-Varshamov bound with high probability and identified a one-generator module of a polynomial quotient ring.

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    First-principles calculation of the rectification characteristic of single-molecule diodes
    YUAN Ying, LI Weiju, CHEN Jingzhe
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 298-306.   DOI: 10.12066/j.issn.1007-2861.2148
    Abstract1396)   HTML20)    PDF(pc) (2669KB)(189)       Save

    In the field of molecular electronics, structural design of a molecule is necessary to achieve different functionalities. The rectification behaviour of single-molecule diodes is one of the most attractive device features. The electron transport of symmetric and asymmetric single molecular junctions was studied, which correspond to tetraphenyl and dipyrimidiny-diphenyl monomolecular junctions, respectively. Both of them were covalently bonded to two gold electrodes. Asymmetric diblock molecules exhibited significant rectifying behaviour compared to their homologous symmetric blocks, and the electrons flow from diphenyl to dipyrimidinyl. The first-principles method was used, including density functional theory (DFT) and the non-equilibrium Green's function (NEGF) method, to study the electronic structure and quantum transport of single-molecule junctions. The asymmetry in the $I$-$V$ could be explained by the localisation of the electron density at one end of the asymmetric molecule, leading to a nonequilibrium effect under bias voltage. Theoretical results agreed qualitatively with the experimental works reported in the literature. Moreover, upon investigating different contacting ends, it was found that the scanning tunneling microscope (STM)-tip setup in the experiment would cancel the rectification effect to some extent; meanwhile, the STM-tip results also confirmed the previous theoretical prediction.

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    Numerical simulation of the supersonic flow/jet flow and their interaction at different flight altitudes
    DENG Fang, HAN Guilai, LIU Meikuan, DING Jue, WENG Peifen, JIANG Zonglin
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 307-324.   DOI: 10.12066/j.issn.1007-2861.2147
    Abstract1434)   HTML21)    PDF(pc) (2705KB)(86)       Save

    The two-dimensional Navier-Stokes equations were solved using high-precision schemes, and the basic structure of the flow field in the supersonic flow and jet flow at different flight altitudes was studied. The three-order Runge-Kutta scheme was adopted in the time-marching scheme. The five-order weighted essentially non-oscillatory (WENO) and the six-order central difference schemes were used to discretize the convection term and viscous term, respectively. The parallel computation was performed using MPI non-blocking communication. The basic structural characteristics of backward-facing step flow and jet flow under backward-facing steps at different flight altitudes were studied. Furthermore, by combining the two flows, the flow field structure of the interaction between the supersonic flow and jet flow was studied. The supersonic flow above the backward-facing step was changed to simulate the environment of different flight altitudes, and the environment affected structures such as vortices, shear layers, and shock waves in the flow field. It was observed that after the interaction between the supersonic flow and jet flow, a recirculation zone was generated near the back step, and the presence of supersonic flow affected the structures of the jet flow.

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    Progressive damage analysis of the bearing capacity of L-type carbon fibre reinforced composite connectors
    DU Yapeng, HU Xiaoyu, CHU Haijian
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 325-335.   DOI: 10.12066/j.issn.1007-2861.2126
    Abstract1282)   HTML17)    PDF(pc) (5438KB)(90)       Save

    The failure modes and bearing capacities of L-type carbon fibre reinforced composite connectors (CFRCC) were studied through experimental testing and computational simulation. The results demonstrated the following. ① Delamination at the corner and matrix damage around bolt holes were the dominant failure modes of L-type CFRCC under tensile loading. ② Comparing the different combinations of two strength failure criteria and two material degradation criteria revealed that the combination of mixed strength failure criteria and the Camanho-Mathews stiffness degradation criteria was more suitable for analysing the progressive damage to the connectors. ③ The predictions from the finite element simulation were in good agreement with the experimental results, and the relative error of the bearing capacity was 9.4%. The strategy of "design-test-simulation-prediction-validation" and the results obtained in this study may provide reliable guidance for the design of L-type CFRCC.

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    Numerical simulation of particle flow during a drawing test of a ribbed geomembrane and sandy soil interface under different temperatures
    GAO Junli, XU Hongfei, YUAN Chuan, CAO Wei
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 336-346.   DOI: 10.12066/j.issn.1007-2861.2128
    Abstract1087)   HTML14)    PDF(pc) (3826KB)(75)       Save

    The features of a ribbed geomembrane and sandy soil interface in a landfill liner system were studied by comparing the results of an indoor experiment and a two-dimensional particle flow code (PFC$^{\rm 2D})$ simulation using the discrete element method. An interface drawing test of the ribbed geomembrane and sandy soil interface was conducted under different combinations of ribbed heights and temperatures. Then, the macroscopic stress-strain curves of the ribbed geomembrane and sandy soil interface, the changing rule of the displacement field of microscopic particles, and the stress field were investigated. The results showed that the tensile stress of the ribbed geomembrane and sandy soil interface was superior to that of the smooth geomembrane ($h =0$ mm) and sandy soil interface. The drawing stress limit of the interface increased with the increase in rib height, and decreased with the increase in temperature. In addition, the friction coefficient of the interface decreased with the increase in temperature. Simulation of the microscopic aspects (particle displacement and internal contact force) also corresponded with the results of the ribbed geomembrane and sandy soil interface drawing experiment. The soil particle displacement near the ribbed geomembrane and sandy soil interface was larger, and the overall particles moved to the top left. The sandy soil at the top after the rib had downward movement owing to the normal stress. With an increase in temperature or decrease in rib height, the displacement of sand particles near the ribbed geomembrane and sandy soil interface increased, and the interface stability between the ribbed geomembrane and sandy soil became negligible. The contact forces on the left side of the drawing model and near the ribbed geomembrane were larger, and gradually decreased to the upper and lower sides. With an increase in rib height or a decrease in temperature, the contact force around the interface between the ribbed geomembrane and sandy soil increased. The entire process of drawing the ribbed geomembrane and sandy soil interface from macroscopic to microscopic was described.

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    Seismic test and finite element analysis of bolted joints connecting concrete-filled square steel tubular column and H-type steel beam
    CHEN Jingyuan, YANG Feng, DING Xinbiao, WANG Peicheng
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 347-359.   DOI: 10.12066/j.issn.1007-2861.2130
    Abstract1253)   HTML17)    PDF(pc) (7470KB)(81)       Save

    Three concrete-filled square steel tubular column and H-type steel beam for two-sided all-bolted connections were fabricated according to the specifications of two countries, China and America. Repeated low cyclic loading tests were conducted on different loading systems. The results showed that the hysteretic loop curves and skeleton curves of the welded joint had obvious characteristics because of the relative slip in the clapboard flange, and the hysteretic loop curve in the horizontal section showed a pinch shrink shape. The test results indicated that the loading system controlled by the displacement angle was more complete and better than the loading system controlled by "two stages" owing to the existence of the slip section in tests on all the bolted joints. At the same time, using the finite element software, ABAQUS, for repeated low cyclic loads on the steel beam and concrete-filled steel tube, the stress performance of the bolt connection node was calculated and analysed. These results verified the accuracy of the test results. Further, the stiffness degradation, ductility performance, and overall strength degradation coefficient of the seismic performance of the nodes were analysed. In addition, because of the existence of the relative slip in the plate flange, a revised evaluation of these indicators was proposed.

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    An improved genetic algorithm based mixed-model U-shaped assembly line balancing problem of type-Ⅱ
    PENG Yunfang, LIANG Yuzhen, XIA Beixin
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 360-368.   DOI: 10.12066/j.issn.1007-2861.2165
    Abstract1397)   HTML20)    PDF(pc) (1092KB)(173)       Save

    To solve the type-Ⅱ balancing problem of a mixed-model U-shaped assembly line to minimise the cycle time, a mathematical model was established and an improved genetic algorithm was designed. In the decoding process of the genetic algorithm, three search techniques were used to assign tasks to workstations, and workstation times under these search techniques were compared. The optimal assignment was selected according to the expected cycle time. The task assignment result determined whether to update the value of the expected cycle time automatically. The performance of the proposed improved genetic algorithm was proved by a set of benchmark instances. Finally, a practical balancing problem was analysed and effectively solved by the proposed method.

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    Design and application of Co-Mn metal-organic-frameworks derived bimetallic sulfides as anode for lithium-ion batteries
    CHEN Hengqiao, LÜ Liping, WU Minghong
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 369-378.   DOI: 10.12066/j.issn.1007-2861.2157
    Abstract1407)   HTML21)    PDF(pc) (9699KB)(190)       Save

    The facile synthesis of a Co-Mn metal-organic-framework (MOF) with a porous structure is reported. The prepared bimetallic MOF was then vulcanized to obtain a porous CoS$_{2}$/MnS bimetallic composite. By comparing single metal MnS and CoS$_{2}$ materials prepared by the same method, it was observed that the CoS$_{2}$/MnS bimetal composite exhibited a petal-like porous sheet structure and a smaller particle size than that of single metal composites. When used as an electrode material in lithium-ion batteries, the CoS$_{2}$/MnS composite exhibited the best lithium storage performance among contemporary composites. It was believed that the porous petal-like structure provided a short transport pathway for lithium-ions. The synergistic combination of the two metal sulfides also effectively inhibited the rapid capacity decay caused by volume changes during cycling. In addition, the carbon skeleton derived from the MOF organic ligands further played a positive role in the enhancement of the electronic conductivity of the material.

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    Preparation of lactic acid by catalytic conversion of glucose by dual-metal ions
    LI Hangwei, YANG Xiang, LUO Xiaofei, GUO Xiaoya, KONG Lingzhao-
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 379-388.   DOI: 10.12066/j.issn.1007-2861.2152
    Abstract1441)   HTML17)    PDF(pc) (1340KB)(132)       Save

    Different dual-metal ions were selected as catalysts to prepare lactic acid (LA) by hydrothermal conversion of glucose under alkaline conditions, and Sn$^{2+}$ and Cu$^{2+}$ were found to have a certain synergistic effect. The effects of reaction temperature, time, alkali addition amount, and metal ion ratio on lactic acid yield were studied to optimise the experimental conditions. The optimum process conditions were as follows: 0.025 g glucose, 2 mmol sodium hydroxide, $n$(Sn$^{2+})$:$n$(Cu$^{2+})$=0.25:0.75 (1 mmol total), 20 mL water, reaction temperature 200 ${^\circ}$C, and reaction time 3 h. Under optimal conditions, the yields of lactic acid, formic acid (FA), and acetic acid (AA) were 64.1%, 20.3% and 11%, respectively. Several model compounds were selected as intermediate products for the hydrothermal transformation experiments. According to the experimental results, the conversion mechanism of the hydrothermal conversion of glucose was investigated. Important intermediates detected in the conversion process were fructose, 1,3-dihydroxyacetone and pyruvaldehyde. There was a synergistic effect between the two metal ions, as Cu$^{2+}$ inhibited the decomposition of lactic acid, and Sn$^{2+}$ increased the conversion efficiency of pyruvaldehyde to lactic acid, finally increasing the yield of lactic acid.

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    Physicochemical characterization of ambient particulate matter emitted from solid fuel combustion in high lung cancer incidence areas in Xuanwei, Yunnan
    XIAO Kai, PENG Jiaxian, XIE Tingting, ZENG Junyang, YAO Chuanhe, MYAT Sandar Win, LÜ Senlin, WANG Qingyao, YONEMOCHI Shinich
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 389-399.   DOI: 10.12066/j.issn.1007-2861.2156
    Abstract1504)   HTML26)    PDF(pc) (1102KB)(89)       Save

    Samples of atmospheric particulate matter from solid fuel (coal and wood) combustion were collected in the high lung cancer incidence area of Xuanwei, Yunnan, and 796 particles emitted by combustion were analysed by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). According to the microscopic characteristics and chemical element compositions of the particles, the particles were divided into four categories, namely mineral particles, fly ash, soot aggregates, and unidentified particles. The $P$(X) method was used to further classify the mineral particles into eight different types, namely Si-rich, S-rich, Ca-rich, Fe-rich, Ti-rich, Al-rich, Na-rich, and others. The percentages of Si-rich, Ca-rich, Fe-rich, and S-rich particles in coal-fired particulate matter and combustion biomass particles accounted for 44.47%, 20.49%, 8.85%, 1.22% and 55.91%, 17.27%, 6.36%, 2.27%, respectively. The chemical analysis results showed that the mass concentrations of the crustal elements Al, Fe, Ca, and Mg in the particles were relatively high, and the mass concentrations of heavy metal elements were relatively low. There was a positive correlation ($R^{2}=0.63$) between the results of the chemical analysis of particulate matter emitted from coal combustion and the results of single particle analysis.

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    Preparation and electrochemical properties as anode materials for lithium-ion batteries of MnO@CoMn$_{\textbf{2}}$O$_{\textbf{4}}$/N-C nanowire composites
    CHENG Erbo, WANG Shangdai, HUANG Shoushuang, CHEN Dayong, HU Zhangjun, CHEN Zhiwen
    Journal of Shanghai University(Natural Science Edition)    2021, 27 (2): 400-410.   DOI: 10.12066/j.issn.1007-2861.2155
    Abstract1461)   HTML16)    PDF(pc) (2392KB)(161)       Save

    Transition metal oxides have a higher theoretical capacity as anode materials for lithium-ion batteries (LIBs). However, they often suffer from poor capacity retention owing to their low electrical conductivity and large volume variations during the charge/discharge process. Carbon coating is an effective way to enhance the electrical conductivity of metal oxides. The synergistic effects of the two components can also effectively improve the electrochemical performance of the material. In this study, MnO$_{2}$@ZIF-67 organic-inorganic hybrid nanostructures were prepared using MnO$_{2}$ nanowires as a template. N-doped carbon-coated MnO@CoMn$_{2}$O$_{4}$ nanowire composites (MnO@CoMn$_{2}$O$_{4}$@N-C) were synthesised by annealing. The organic ligand of ZIF-67 underwent carbonisation during high-temperature calcination to produce N-doped carbon, which improved the electrical conductivity. When MnO@CoMn$_{2}$O$_{4}$/N-C nanowire composites were used as the anode material for LIBs, a discharge capacity of 1 594.6 mA$\cdot$h/g was achieved in the first cycle, with a retention capacity of 925.8 mA$\cdot$h/g even after 100 cycles at current density of 0.1 A/g and a reversible capacity of 837.6 mA$\cdot$h/g at 0.5 A/g. It also had an excellent rate cycling performance. The outstanding electrochemical performance was attributed to the unique structure as well as the coating effect of N-doped carbon.

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