Journal of University of Chinese Academy of Sciences

Heterogeneous oceanographic exploration system based on USV and AUV:a survey of developments and challenges

XU Huixi, JIANG Chenglin

2021, 38 (2): 145-159. DOI: 10.7523/j.issn.2095-6134.2021.02.001

With sufficient literature retrieval and summery, this paper reviews the heterogeneous oceanographic exploration system based on the synergy of unmanned surface vehicle (USV) and multiple autonomous underwater vehicles (AUVs). Firstly, latest progress and achievements of heterogeneous oceanic exploration system are summarized and compared in terms of technical features and design ideas. In the following, research status of key technologies in coordinated control of the heterogeneous systems are elaborated. The task assignment, path planning and formation control are discussed in detail. Then the paper analyzes the technical problems of the exploration system from the aspects of external constraints from environment and hardware and the auxiliary technology of ocean exploration system. Finally, the future vision for the oceanographic exploration system is prospected based on the analysis of the current progress and actual requirements.

Stochastic Poisson integrators based on Padé approximations for linear stochastic Poisson systems

WANG Pengjun, WANG Lijin

2021, 38 (2): 160-170. DOI: 10.7523/j.issn.2095-6134.2021.02.002

Abstract ( 455 ) PDF (0KB) ( 0 )

We propose a class of stochastic Poisson integrators based on Padé approximations for linear stochastic Poisson systems. The root mean-square convergence orders of the schemes are analyzed, and the structure preserving properties are investigated. Numerical tests are performed to verify the theoretical results and illustrate the numerical behavior of the proposed methods.

A unified theory of confidence intervals for high-dimensional precision matrix

WANG Yue, LI Yang, ZHENG Zemin

2021, 38 (2): 171-180. DOI: 10.7523/j.issn.2095-6134.2021.02.003

Abstract ( 451 ) PDF (0KB) ( 0 )

Precision matrix inference is of fundamental importance nowadays in high-dimensional data analysis for measuring conditional dependence. Despite the fast growing literature, developing approaches to make simultaneous inference for precision matrix with low computational cost is still in urgent need. In this paper, we apply bootstrap-assisted procedure to conduct simultaneous inference for high-dimensional precision matrix based on the recent de-biased nodewise Lasso estimator, which does not require the irrepresentability condition and is easy to implement with low computational cost. Furthermore, we summary a unified framework to perform simultaneous confidence intervals for high-dimensional precision matrix under the sub-Gaussian case. We show that as long as some precision matrix estimation effects are satisfied, our procedure can focus on different precision matrix estimation methods which owns great flexibility. Besides, distinct from earlier Bonferroni-Holm procedure, this bootstrap method is asymptotically nonconservative. Both numerical results confirm the theoretical results and computational advantage of our method.

Imbalanced data credit scoring model based on Group-Lasso method

WEI Yongfeng, XIANG Yibo

2021, 38 (2): 181-188. DOI: 10.7523/j.issn.2095-6134.2021.02.004

Abstract ( 642 ) PDF (0KB) ( 0 )

In view of the complexity of the customers' credit risk faced by commercial banks at the present, how to manage customers' credit risk is very important. Customers' credit risk modeling is a key step. We use the credit card data of a commercial bank to construct a credit scoring model and predict the default probability. We construct a credit scoring model on the basis of Logistic regression, using the group-Lasso (AUC criterion) method to select variables and using the ROSE (random over sampling examples) method to deal with the unbalanced categories. The results are compared and analyzed, and the new model constructed in this work has certain advantages in discriminating ability and predictive ability. It can play a guiding role for banks and other financial institutions in evaluating customer credit risk and can be used as an effective basis for customer credit evaluation decision. In practice, it also has good operability.

Numerical research on mechanisms of the mercury capture by activated carbon injection within an electrostatic precipitator

FENG Yuxuan, LUO Kun, FAN Jianren

2021, 38 (2): 189-197. DOI: 10.7523/j.issn.2095-6134.2021.02.005

Abstract ( 360 ) PDF (0KB) ( 0 )

Based on the Ansys Fluent platform along with its secondary development programs, this research developed a comprehensive numerical model for mercury capture by activated carbon injection and particle migration within an electrostatic precipitator (ESP). The multi-field model coupled sub-models such as flow field, electric field, mercury adsorption, particle charging, and particle motion. The mechanisms and crucial operation parameters of mercury adsorption by suspended activated carbon particles in electrostatic precipitators are fully discussed. The results show that both activated carbon particle size and ion wind effects have great impacts on combined removal efficiency of the mercury and particles. Reducing the size of sorbent particles (activated carbon) can promote mercury removal efficiency while decreasing the particle collection efficiency,the mercury removal efficiency will be 89.6% while the particle size is 5 μm. Additionally, the ion wind has distinct effects on the two mercury adsorption mechanisms in an ESP where the adsorption mechanism of mercury by suspended activated carbon particles is dominant, while the mercury capture efficiency near the wall is at a low level which is below 9%. The comparison between the experimental data and numerical results demonstrates that this model is able to predict the mercury removal efficiency by powdered sorbent injection with acceptable accuracy.

Effect of the gap width between tray and box wall on the precooling effectiveness of apples

GONG Yafang, CAO Yuhui

2021, 38 (2): 198-206. DOI: 10.7523/j.issn.2095-6134.2021.02.006

Abstract ( 396 ) PDF (0KB) ( 0 )

Rapidly removing field heat after harvest is a key step in food cold chain logistics to ensure the good quality of fruits and vegetables and consequently extend their storage and shelf life. The internal structure of package filled with trays and products is complex, resulting in serious cooling heterogeneity. The present study focuses on the effect of tray design on the precooling process of apples and attempts to give the optimal gap width between tray and box wall. The widely-used corrugated double-layered apple packaging box in the market was chosen as the research object, a three-dimensional model was established, and the precooling process of apples was studied by using the direct computational fluid dynamics (CFD) simulation method. Results indicate that increasing the gap width is an effective way to shorten the precooling time and improve the precooling uniformity. However, the gap width can not be increased infinitely. Therefore, considering the influence of the gap width increment on both the precooling time and the uniformity of apple temperature, the optimal gap width increment between the tray and the box wall should be 7.5 mm. This results in shorter precooling time and better precooling uniformity.

Dissociative photoionization of methyl crotonate: experimental and theoretical insights

SUN Ruirui, LI Yanbo, CHEN Jun, MENG Qinghui, WANG Huanhuan, ZHANG Hang, SHAN Xiaobin, LIU Fuyi, SHENG Liusi

2021, 38 (2): 207-216. DOI: 10.7523/j.issn.2095-6134.2021.02.007

Abstract ( 310 ) PDF (0KB) ( 1 )

The photoionization and dissociation of methyl crotonate have been studied by tunable vacuum ultraviolet synchrotron radiation coupled with time-of-flight mass spectrometer in the photon energy region 9.0-14.5 eV. The ionization energy of methyl crotonate and the appearance energies for major fragments C₄H₅O₂⁺, C₄H₅O⁺,C₄H₄O⁺, C₂H₃O₂⁺, C₃H₅⁺, and C₂H₅⁺ are determined to be 10.11, 10.73, 10.88, 12.2, 11.93(12.77), and 12.44 eV, respectively, according to the photoionization efficiency curves. Based on the experimental AEs and energies predicted by ab initio G3B3 calculations, possible formation channels for the major fragments C₄H₅O₂⁺+CH₃, C₄H₅O⁺+CH₃O, C₄H₄O⁺+CH₄O, C₂H₃O₂⁺+C₃H₅, C₃H₅⁺+C₂H₃O₂(CO+CH₃O), and C₂H₅⁺+C₃H₃O₂ are proposed. Transition states and intermediates involved in the dissociation channels are also located. The majority of the proposed channels occur through isomerization processes prior to dissociations. Hydrogen shift and ring closing/opening are found to be the dominant processes during photoionization and dissociation of methyl crotonate.

Preparation of grape peel based biochar by orthogonal design and its adsorption performance

CHANG Chun, BAI Yang, SONG Xinyi, SHAN Shuang, LI Mingzhe

2021, 38 (2): 217-227. DOI: 10.7523/j.issn.2095-6134.2021.02.008

Abstract ( 384 ) PDF (0KB) ( 0 )

The biochar was prepared by the limited oxygen pyrolysis method using agricultural waste grape peel as raw materials. The best activation conditions were selected for activated biochar through the orthogonal test table of three factors and three levels, and the activated biochar was obtained for adsorption experiment. The effects of initial concentration of reactants, reaction temperature and contact time on adsorption were investigated and analyzed through batch experiments. According to the kinetic fitting results, it could be concluded that the adsorption process of grape peel-based biochar on methyl orange could be well described by the quasi-second-order kinetic equation. It indicated that the adsorption process of activated biochar on methyl orange was not a single monolayer adsorption process. The intraparticle diffusion equation showed that intraparticle diffusion was not the only limiting factor, and the adsorption process was controlled by two processes:liquid film diffusion and intraparticle diffusion. The two-chamber model showed that the fast adsorption reaction played a leading role in the whole adsorption process. The adsorption of methyl orange by activated biochar was well fitted by Temkin-Pyzhev model, which showed that the adsorption of methyl orange by activated carbon was more prone to irregular surface adsorption. The adsorption thermodynamic data proved that adsorption reaction was easy to occur.

Effects of NaHCO₃ and Na₂CO₃ stress on seed germination, seedling growth, and physiological indexes of Puccinelia chinampoensis and Elymus dahuricus

ZHENG Yiru, ZHAO Junchao, GONG Shufang, WANG Jin

2021, 38 (2): 228-239. DOI: 10.7523/j.issn.2095-6134.2021.02.009

Abstract ( 418 ) PDF (0KB) ( 0 )

Saline-alkali soil restricts the normal growth of plants. Understanding the adaptation mechanism of grasses to NaHCO₃ and Na₂CO₃ stress is important for the utilization of saline-alkali soil and the cultivation of crops. In this experiment, Puccinelia chinampoensis and Elymus dahuricus were treated with NaHCO₃ and Na₂CO₃ mixtures. The seed germination rate, seedling dry weight, a series of leaf physiological parameters, including cell membrane permeability, photosynthetic gas exchange parameters, chlorophyll fluorescence parameters, superoxide dismutase activity and malondialdehyde (MDA) content, as well as leaf and root Na⁺, K⁺ ion contents were measured. The results showed that stress treatment reduced the seed germination rate, dry matter accumulation of seedlings, leaf net photosynthetic rate and electron transfer quantum efficiency, and increased the relative conductivity and MDA content of the two plant species. Under stress, the damage of the leaf cell plasma membrane of P. chinampoensis was greater than that of E. dahuricus, and the photosynthetic gas exchange parameters were more affected. E. dahuricus maintained higher SOD enzyme activity and lower MDA content than P. chinampoensis under stress treatments. In conclusion, the mixed treatment of NaHCO₃ and Na₂CO₃ inhibited the normal growth of P. chinampoensis and E. dahuricus, but E. dahuricus was more resistant than P. chinampoensis. This study provides theoretical basis for soil bioremediation and planting of grasses in saline-alkali areas.

Spatial distribution of agricultural production from perspective of water footprint: a case study of north-piedmont major agriculture production regions of Tianshan Mountains, Xinjiang

CHEN Hongxing, LI Jiangyue, YANG Degang, LI Xiaohu, CAI Tianyi, XIA Fuqiang

2021, 38 (2): 240-251. DOI: 10.7523/j.issn.2095-6134.2021.02.010

Abstract ( 298 ) PDF (0KB) ( 0 )

For the arid regions, it is necessary to implement a water-saving strategy. Water footprint strategy has been viewed as a vital countermeasure to solve the issues of grain and water security. In our research, first, the agricultural water footprint was calculated from 2000 to 2017, which presents the current actual level of agricultural development. Second, we established the regional agricultural production advantage model to explore the potential of agricultural development. Then we established the WF-APA (water footprint-agricultural production advantage) gap index to illustrate agricultural types of each county. Additionally, in order to more directly explore the matching relationship between water footprint and economy, technology, environment and resources, taking 2017 as an example, we computed the imbalance index of water footprint versus above mentioned factors. Specifically, agricultural irrigation water, cultivated land area, agricultural labor productivity, consumption of chemical fertilizers, and total power of cultivated land agricultural machinery were included. Results indicated that:1) The index of water footprint showed a large instability from 2000 to 2017, showing a spatial distribution that the total water footprint of middle counties is higher than those of eastern and western counties. 2) Regional agricultural production advantage can be divided into five types:high, relatively high, middle, low, relatively low, and general decrease in 2017. 3) Regional agricultural production can be divided into three types, which are reasonable, over-dense and over-sparse. 4) The outside fairness of the water footprint for agricultural products was found to be relatively low, suggesting that Shawan and Wusu counties were the most prominent areas. In any case, the findings of research would assist policy makers in formulating reasonable agricultural policies to guarantee food-water security and at the same time to answer for regional sustainability.

Joint transmitter-receiver hybrid beamforming design for multi-user mmWave massive MIMO systems

YIN Feng, QIU Ling, LIANG Xiaowen

2021, 38 (2): 252-259. DOI: 10.7523/j.issn.2095-6134.2021.02.011

Abstract ( 512 ) PDF (0KB) ( 0 )

Millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems can achieve several orders of magnitude improvement in spectral efficiency and energy efficiency. However, due to limitations of hardware complexity and energy cost, the conventional fully digital beamforming methods which require one radio frequency chain per antenna element are no longer viable. To address this challenge, hybrid digital and analog beamforming architectures are proposed. In this paper, we consider the practical partially-connected hybrid beamforming structure and propose to jointly design the hybrid beamformers of both the base station and the users for a multi-user massive MIMO system. For the purpose of achieving a high array gain, a sparse principal component analysis based algorithm is utilized to obtain the corresponding analog precoding and combining matrices. Then we develop an iterative algorithm to jointly design the digital precoding and combining matrices under a weighted minimum mean square error criteria. Simulations over mmWave channels demonstrate that our scheme can approach the performance of those with fully-connected structures, with rather high energy efficiency.

Imaging method of space-frequency TR-MUSIC in random medium

MA Tian, CHEN Kunshan, LIU Yu, LI Tingting, XU Zhen

2021, 38 (2): 260-269. DOI: 10.7523/j.issn.2095-6134.2021.02.012

Abstract ( 396 ) PDF (0KB) ( 0 )

A time reversal imaging algorithm, based on the space-frequency decomposition, namely space-frequency TR-MUSIC, is proposed in an attempt to improve the focusing of the target obscured by complex random media, where TR-MUSIC algorithm may perform poorly when the signal to noise ratio (SNR) is low and the acquisition of the space-space multistatic data matrix (SS-MDM) is difficult. Using the backscattered data collected by an antenna array, a space-frequency multistatic data matrix (SF-MDM) is configured. Then the singular value decomposition is applied to the matrix to obtain the noisy subspace vector, which is then employed to image the target. The imaging function based on the full backscattered data includes the contributions of multiple sub-matrix and is found to be statistically stable. Numerical simulations show that the imaging performance of the space-frequency TR-MUSIC is better than that of the traditional space-space TR-MUSIC in both free space and random media, with fine resolution and good geometric accuracy under SNR as low as 10 dB.

Financial network construction and analysis based on event correlation extraction under Chinese context

LI Pengyuan, YU Hua, JIANG Cheng

2021, 38 (2): 270-279. DOI: 10.7523/j.issn.2095-6134.2021.02.013

Abstract ( 426 ) PDF (0KB) ( 0 )

In recent years, researches on the construction and analysis of financial network have been widely concerned. The existing researches mainly focus on the use of transaction data in the financial market. However, in the era of big data, how to use non-financial market data, such as news texts, to carry out researches still be a large space for exploration. Based on the idea of co-occurrence analysis, this paper proposes a method of constructing financial network based on event association mining in Chinese context. Based on the constructed network, we carry out the analysis of topological structure, financial event path transitivity, and event entity association. The experimental results show that our proposed approach based on financial networks can not only help to understand the evolution of financial markets, but also better realize the relationship between the entities involved in financial markets in some situations.

Missing data imputing algorithm based on modified neural process

SUN Xiaoli, GUO Yan, LI Ning, SONG Xiaoxiang

2021, 38 (2): 280-287. DOI: 10.7523/j.issn.2095-6134.2021.02.014

Abstract ( 296 ) PDF (0KB) ( 0 )

Missing data imputing is a serious problem in the field of data analysis and process, which is extremely intractable in the case of the small dataset especially. In view of this problem, a missing data imputing algorithm based on modified neural process is proposed, which can improve the imputing performance in the background of the small dataset. Firstly, the observed time series is single-represented and then obtain the symptomatic vector respectively through the neural network. Secondly, it can acquire the distribution function of the data via the neural process and introduce the correction coefficient α to determine the sampling rate more exactly based on missing rate in the training stage. Finally, it imported the imputing process and estimated the missing data via trained model. Experiments are carried out on the sea surface temperature dataset and the Beijing PM_2.5 dataset to verify the performance of the algorithm. The experiments show that the algorithm has an excellent performance in the context of small datasets, and it has a lower root mean square error compared with other algorithms.

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