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Research Articles
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Conformal minimal immersions of S2 into HP4
- JIAO Xiaoxiang, CUI Hongbin
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2020, 37 (6):
721-727.
DOI: 10.7523/j.issn.2095-6134.2020.06.001
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Abstract (
219 )
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This work is a generalization of Chen and Jiao's work, where they considered the question of explicit construction of some conformal minimal two-spheres of constant curvature in quaternionic projective space. The crucial point was to find some horizontal immersions derived from Veronese sequence in CP2n+1, which was projected into constant curvature conformal minimal two-spheres by twistor map π:CP2n+1→HPn. They calculated the case n=2. In this work, we deal with the case n=4 and a related geometry phenomenon.
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Inverse prediction of gas concentration based on nonparametric model
- WU Dong, GUO Xiao
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2020, 37 (6):
728-735.
DOI: 10.7523/j.issn.2095-6134.2020.06.002
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Abstract (
234 )
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Gas sensor array is an important and powerful technique for detecting gas and measuring gas concentrations. The conventional strategy to describe the relationship between the response of the sensor and the actual gas concentration is to use some specific nonlinear parametric models. In this work, we use the nonparametric model to depict the change in the gas sensor response with the gas concentrations, which effectively avoids model misspecification. Furthermore, we propose an inverse prediction method based on the nonparametric model to predict gas concentrations. Data-driven selection of tuning parameters is also developed. The simulation results reveal that, when the real model of the sensor array is unknown or misspecified, the nonlinear parametric model is inferior to the nonparametric model in performance. Meanwhile, we verify this with the real data analysis.
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Effects of microwave, glucose, and hydrolyzed urine on phosphorus release and recovery from sewage sludge
- WEN Guoqi, ZHANG Xiangru, HUANG Lijuan, HU Zhengyi
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2020, 37 (6):
744-749.
DOI: 10.7523/j.issn.2095-6134.2020.06.004
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Abstract (
178 )
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Recovery of phosphorus from sewage sludge alleviates the phosphorus crisis. The sludge phosphorus requires to be activated before it is recovered through struvite method. We investigate the effects of microwave, glucose, and hydrolyzed urine on phosphorus release from anaerobic sludge, and also evaluate the feasibility of recovering phosphorus from sludge supernatant through struvite method. Results show that microwave, glucose, and urine promote the phosphorus release from sludge. The phosphorus release rates are 64.57%, 66.93%, 65.63%, and 68.78% for microwave, glucose, 0.2 L urine, and 0.4 L urine, respectively, which are significantly higher than the rate of 40.77% under control treatment. Hydrolyzed urine promotes phosphorus release from sludge mainly because its high concentration of free ammonia nitrogen disintegrates the cells of polyphosphate-accumulating organisms and then accelerates the inside-body inorganic phosphorus release. High-quality struvite precipitation is obtained while magnesium chloride is added into the urine-activated sludge supernatant. The method expressed in this study can be used to well realize the phosphorus recovery from sludge.
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SAR image visual optimization and building damage assessment based on polarimetric decomposition combination
- LIU Shan, ZHANG Fengli, WEI Shiying, LIU Na, SHAO Yun
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2020, 37 (6):
750-759.
DOI: 10.7523/j.issn.2095-6134.2020.06.005
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Abstract (
391 )
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Building damage assessment is of great significance for disaster emergency monitoring. Polarimetric synthetic aperture radar (SAR) records the polarization scattering measurement matrix of ground objects and obtains abundant ground object information. Therefore it can be used for building damage assessment. Based on scattering characteristics of intact and damaged buildings, the scattering angle αs1 in Touzi decomposition, the double-bounce scattering component in Yamaguchi decomposition after deorientation, and the symmetry|τ2|in Touzi decomposition are combined for color composition and optimizing the polarimetric SAR image. This method can be used to quickly identify the building areas with different damage degrees by using single phase polarimetric SAR image. We take the March 11th,2011 earthquake that struck the coast of northeast Japan as an example and use quad-polarimetric ALOS PALSAR data acquired after the disaster for the analysis. The proposed method is verified by using RADARSAT-2 image of Wenchuan earthquake. The results show that the combination of polarimetric parameters not only optimizes the visual display effect of building targets, but also easily identifies the building areas with different damage degrees. This method greatly reduces the limitation and requirements for data source in disaster assessment.
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Danger tree detection and tree number estimation based on UAV LiDAR data
- ZHANG Su, QI Lizhong, HAN Wenjun, ZHU Xiaoxiao, XI Xiaohuan, WANG Cheng, WANG Pu, NIE Sheng
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2020, 37 (6):
760-766.
DOI: 10.7523/j.issn.2095-6134.2020.06.006
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Abstract (
471 )
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The growth of trees in the transmission corridor has a great impact on the transmission line. It is essential to accurately detect the trees that significantly affected the safety of transmission line. Therefore, a method of danger tree detection and tree number estimation based on UAV LiDAR data was proposed in this paper. Firstly, the power line points, ground points, and vegetation points were accurately extracted by rapidly automatic processing the laser point cloud in the transmission corridor. Secondly, the power line was segmented, and then the location and range of tree barrier area were determined by analyzing the safe distance between power lines and vegetation points. Finally, the point clouds in the tree barrier area were divided into single trees, and the number of single trees was counted to achieve accurate estimation of the number of danger trees. The results indicates that the UAV laser point cloud effectively detect the tree barrier in the transmission channel and accurately estimate the number of trees need to be felled with an overall accuracy of 92.3%, which provides not only remote sensing technology support for the safety of transmission line, but also reliable basis for the grid operation and maintenance units to make plan for tree cutting.
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Analysis on the evolution characteristics of rural villages in Japan
- LI Liang, TAN Minghong
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2020, 37 (6):
767-774.
DOI: 10.7523/j.issn.2095-6134.2020.06.007
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Abstract (
392 )
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The decline rural villages caused by the rapid urbanization have become a hot topic in China. Therefore, the government proposed the rural revitalization strategy. How to treat decline rural villages, to rationally plan the distribution of villages in rural revitalization, and to promote rural revitalization, remain questions that deserve consideration. As a highly urbanized country, Japan has experienced the decline, mergers and dissolutions of rural villages, which may have implications for Chinese rural development. This paper first analyzed the changes in the numbers, the population structure, the spatial distribution characteristics of rural villages, and the causing factors of the change of rural villages in different grades in Japan over the past 100 years, and then discussed the implications for Chinese rural development from Japan's experience in four aspects. The results showed that: 1) The larger the rural villages, the more backward the decline in timing sequence, however, the number of all grades of rural villages had decreased from 2000 to 2015 (late stage of urbanization); 2) From 1980 to 2015, the decrease rate of rural villages was higher in southwest and lower in northeast in Japan. The area with the highest decrease rate is on both sides of the Seto Inland Sea, both higher than 80%. 3) During 1980-2015, the villages with rural population growth were distributed in metropolitan areas, including Tokyo Metropolitan Area, Nagoya Metropolitan Area, Osaka Metropolitan Area. 4) The factors causing changes in progress in rural villages mainly included three aspects: the urbanization process, the policy of rural village merging, and the rural revitalization in selected area.
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Influence of South-to-North Water Transfer Project on the changes of terrestrial water storage in North China Plain
- LI Jia, TANG He, RAO Weilong, ZHANG Lan, SUN Wenke
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2020, 37 (6):
775-783.
DOI: 10.7523/j.issn.2095-6134.2020.06.008
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Abstract (
451 )
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The impact of the South-to-North Water Transfer Project on the terrestrial water storage (TWS) depletion in the North China Plain since the formal water supply at the end of 2014 has not been evaluated. Based on the data of GRACE and GRACE Follow-on gravity satellites, this paper calculates the changes of water storage in the North China Plain, and compares it with the water amount (3.08 Gt/a) supplied by the South-to-North Water Transfer Project. It is found that the change rate of TWS in the North China Plain from 2004 to 2015 is (-5.92±0.53) Gt/a, and the change rate in 2015-2019 is (-2.96±2.79) Gt/a. The results show that the change rate of TWS was decreased by 50%, and the trend of long-term depletion was alleviated obviously. At the same time, the trend of TWS in Beijing and Tianjin has also changed significantly. Therefore, the South-to-North Water Transfer Project had significantly improved the situation of TWS in North China, and played an active and effective role.
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Analysis of tectonic evolution characteristics of Wan'an Basin in the southwest of the South China Sea
- WANG Beiyu, ZHANG Jian, AI Yifei
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2020, 37 (6):
784-792.
DOI: 10.7523/j.issn.2095-6134.2020.06.009
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Abstract (
140 )
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The South China Sea Basin is located at the junction of Tethys, Pacific margin, and paleo-Asia tectonic domains. The representative Wan'an Basin in the southwest of the South China Sea Basin has the well-developed Cenozoic strata, but the underappreciated expansion and evolution remains because of a limited understanding of tectonic subsidence and extension mechanism of the basins. Based on the regional geological data, including structural style and stratigraphic sequence, the tectonic evolution history of Wan'an Basin is simulated by utilizing the backstripping method, and the extension factor and extension velocity of Wan'an Basin are obtained after fitting the structural subsidence history through an iterative adjustment of the tensile factor in the McKenzie pure shear tensile model. Furthermore, the heat transfer equation of the lithosphere is used to determine the heat flow of the substrate. The results are given as follows. 1) It is the combined action of the South China Sea expansion, the ridge jump, and the southwest sub-basin expansion that control the sedimentation, extension, and thermal anomalies in Wan'an Basin. 2) Wan'an Basin has unique characteristics of space-time evolution that the left and right rotations of the fracture zone affect the sedimentation which presents a V-shaped transition and that “early east and west, then north and south” is the mainly feature of the extension. 3) Due to the tectonic activity, the extension and thermal anomalies in the basin gradually decline in the directions from the fault to the both sides at different rates.
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Kinetic study of antigorite dehydration using synchrotron X-ray powder diffraction
- LIU Tao, SHEN Kewei, LIU Chuanjiang, WANG Duojun
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2020, 37 (6):
793-797.
DOI: 10.7523/j.issn.2095-6134.2020.06.010
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Abstract (
414 )
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Synchrotron X-ray powder diffraction method was used to study dehydration kinetics of antigorite with particle size of ~5 μm. The isothermal heating method was used to observe antigorite dehydration at 680, 700, 710, and 720 ℃, respectively. It was found that, with the increase of heating time, the characteristic peak of antigorite slowly disappeared and the characteristic peak of forsterite formed, but no enstatite appeared. The reaction order n is 1.1~1.3 by the Avrami equation, indicating that antigorite dehydration is controlled by grain boundary nucleation. Activation energy for the formation of forsterite from antigorite is 105.97 kJ/mol, and the pre-exponential factor is 333.62 s-1 in the Arrhenius equation.
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Stereo localization method for air-borne SAR image based on range equations
- PAN Zhigang, WANG Chao, CAO Ge
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2020, 37 (6):
798-804.
DOI: 10.7523/j.issn.2095-6134.2020.06.011
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Abstract (
252 )
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A method of stereo localization for airborne SAR image based on range equations is proposed. This method uses three SAR images of the same imaging area to implement stereo localization without control points. Firstly, the corresponding image points (CIP) in the three images are determined, and the platform parameters corresponding to the CIP such as instantaneous geographic coordinates, altitude, and slant range are analyzed. The range equations for the CIP of three images are established in the geocentric coordinate system. The geocentric coordinates of the CIP are obtained by solving range equations, the geographic coordinates and altitude are obtained by coordinate transformation, so as to realize the three-dimensional positioning. The system error factors affecting the accuracy of stereo localization are simulated and analyzed. The positioning experiment is carried out using the actual flight airborne SAR image. The results show that the proposed method is effective.
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Resource scheduling algorithm based on beam hopping in LEO satellite network
- LIU Wanying, XIA Shiyi, JIANG Quanjiang, LI Guotong, TIAN Feng, SUN Siyue
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2020, 37 (6):
805-813.
DOI: 10.7523/j.issn.2095-6134.2020.06.012
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Abstract (
544 )
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Low earth orbit (LEO) satellite networks have become the promising approach to provide broadband internet access service and have attracted the interests from both academy and industry. In this paper we review the related work of beam-hopping and find that most of the existing beam-hopping schemes are designed for GEO satellites and cannot be used for LEO satellites. Therefore, the beam-hopping system for the LEO mega-constellation is constructed in this worh. Due to the limited onboard resource and uneven traffic demand distribution, we propose a wide beam combined with dynamic beam-hopping scheme, which acquires signaling information from a wide beam to assist the spot beam to perform a communication scheme of the beam hopping on-demand service. The simulation results show that the beam-hopping scheme achieves better throughput performance than the fixed-beam scheme when the traffic demand distribution is uneven.
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An emergency decision method based on fuzzy linguistic TOPSIS
- LI Haiming, YU Gang, TIAN Chongxin, SHANG Guobin
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2020, 37 (6):
814-819.
DOI: 10.7523/j.issn.2095-6134.2020.06.013
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Abstract (
213 )
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During the process of emergency decision-making, information is frequently hesitant, fuzzy, and unbalanced, and decision makers often present their intuitive and rapid linguistic decision preference. In this work, an emergency decision-making method based on fuzzy linguistic TOPSIS is proposed. It combines the hesitant fuzzy linguistic term set (HFLTS) and 2-tuple linguistic expression to deal with words in highly uncertain context, which not only improves the elicitation of hesitant fuzzy information but also leads to linguistic results easy to understand by decision makers, and it could be helpful to making a rapid and accurate decision judgement. A case study verifies the feasibility and effectiveness of this method and proves its certain practical value.
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Hierarchical label-guided human parsing
- HU Lina, GAO Shenghua
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2020, 37 (6):
820-827.
DOI: 10.7523/j.issn.2095-6134.2020.06.014
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Abstract (
204 )
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Human parsing is a type of semantic segmentation of different human body parts in an image. It is an emerging task in the field of computer vision. Compared with general objects, human body is much more structured but with wide variations in pose and occlusions caused by wearing. In this paper we present a hierarchical label network (HLNet). Firstly, fine categories are merged into body parts with different granularities to obtain multiple parsing maps for each image. Next, a convolutional neural network with a pyramid feature extraction structure is trained under supervision of these maps. Finally, the hierarchical features are fused together to predict the final parsing results. Experimental results on the LIP dataset show that the proposed algorithm achieves higher parsing accuracy and better segmentation performance, compared with common semantic segmentation algorithms.
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Human body joint nodes detection based on DeepPose and Faster RCNN
- YU Baoling, YU Songkun, SUN Yaoran, YANG Zhen, FU Xubo
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2020, 37 (6):
828-834.
DOI: 10.7523/j.issn.2095-6134.2020.06.015
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Abstract (
209 )
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Human body joint nodes detection is a considerably challenging task which has drawn enormous attention in the field of computer vision recently. The challenges of this task include: coping with the complex structure of human body joints, denoting the interdependence between joint nodes, and dealing with the sheltered and overlapped body joint nodes. Among the common solutions to this task, the models based on deep learning are widely applied and provide useful results. However, the existing models have following drawbacks: 1) comparatively low accuracy in prediction; 2) poor performance in multi-objective tasks. In our work, we proposed a novel method aiming at more satisfactory results. We firstly detect the relevant regions of human body with Faster RCNN, and then input the regions into a modified DeepPose algorithm. We achieve the state-of-the-art results in the detection of the wrist and knee on MPII dataset, improving 1.2% and 0.3% in PCKh, respectively. The total PCKh is 87.6% on MPII dataset.
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A software random number generator with entropy monitoring function
- LIU Pan, CHEN Tianyu, LÜ Na, MA Yuan, JING Jiwu
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2020, 37 (6):
835-847.
DOI: 10.7523/j.issn.2095-6134.2020.06.016
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Abstract (
449 )
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Random number generator (RNG) is the foundation and core of modern cryptography. The random number generated by RNG provides basic security for many cryptographic applications, such as cryptographic algorithms and security protocols. With the development of mobile Internet, Internet of things and other technologies,the traditional hardware-based random number generator has the problems of difficult hardware update and high development cost, which limits its application scope. Therefore, software RNG (SRNG) is usually used in computers, mobile terminals and other devices to provide random number services. At present, Linux, Android, Windows, and other typical operating system platforms have their own SRNG, providing software-based random number generation services. The existing research focuses on the lack of entropy of the entropy source and the internal state leakage of the post-processing module, which is the main problem affecting the random number service quality of SRNG. Therefore, a software random number generator with entropy monitoring (entropy monitoring SRNG, EM-SRNG) is designed and implemented in this paper, which uses high-precision nanosecond system clock as non-physical entropy source. The online entropy monitoring module can continuously detect the entropy of the unprocessed data when the generator is running, and call the post-processing module to improve the statistical characteristics of the data when the entropy is insufficient. In addition, the post-processing module of EM-SRNG can choose two post-processing extension algorithms designed based on SM3 and SM4 cryptography algorithms to ensure the forward/backward security of the internal state of the generator. By comparing the EM-SRNG and the Linux random number generator (LRNG, one of the current mainstream SRNGs), the experimental results show that, in terms of security, through SP 800-90B test, it is found that the output quality of EM-SRNG is equal to the data quality provided by LRNG dev/random, but slightly better than that provided by LRNG dev/random, with the minimum entropy of about 0.94/bit per bit; in terms of rate, the data generation rate of EM-SRNG is about 4 orders of magnitude higher than that of LRNG dev/random, but because the 90B statistical suite is embedded in the structure for online entropy estimation, the speed of EM-SRNG is slower than that of LRNG dev/urandom, which is about 4 Mbps.
Brief Report
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Interactions between Cyt c and silver nanoclusters
- ZHANG Chengcheng, LI Xiaoyi
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2020, 37 (6):
848-851.
DOI: 10.7523/j.issn.2095-6134.2020.06.017
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Abstract (
189 )
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Molecular dynamics simulation and path channel analysis were performed to study the main adsorption driving force, conformational change, and electron transfer coupling matrix element of cytochrome c (Cyt c) on the surface of silver nanoclusters. The results show that the surface charge of silver nanoclusters is crucial for electron transfer. The uncharged silver nanoclusters facilitate the adsorption of Cyt c and are prone to electron transfer reactions.
