Journal of University of Chinese Academy of Sciences

The K₁ group of integral group ring and its maximal order for a commutative p group

YANG Quanli, TANG Guoping

2020, 37 (5): 577-581. DOI: 10.7523/j.issn.2095-6134.2020.05.001

Group rings are very important rings in algebra and many other branches of mathematics. It is also one of the main research subjects of algebraic K-theory. In this work, we mainly deal with integral group rings ZG for some abelian p(p is prime) groups G. We can regard ZG as a Z-order of the semi-simple algebra QG and embed it into the maximal Z-order Γ. Then we use the properties of the kernel group to study the exponential problem of K₁(ZG) in K₁(Γ). In this paper, there are two main results. First, the explicit formula of[(Γ_p)^×:(Z_pG)^×] is obtained for some abelian p groups. Secondly,by using the formula,we get the specific result of[K₁(Γ):K₁(ZG)] for some abelian p groups.

Breakdown point of penalized logistic regression

DONG Yulin, GUO Xiao

2020, 37 (5): 582-592. DOI: 10.7523/j.issn.2095-6134.2020.05.002

Abstract ( 410 ) PDF (KB) ( 1 )

Breakdown point is regarded as an important measure of robustness in regression analysis. At the same time, sparse model estimation is a hot topic in data analysis. In the case of less attention to the breakdown point of robust estimates in nonlinear models, we study it in binary response models. We prove that the penalized estimate of logistic models always stays bounded, which means the finite explosive breakdown point of it is 1. Moreover, we give an upper bound of the implosive breakdown point of the slope parameter. Both simulation study and real data application verify this point while we use the approximation method and coordinate descent algorithm.

Preparation of Fe₃O₄@PCDP nanocomposite and its application in Fenton-like system

CHEN Fengxia, MA Jiahai

2020, 37 (5): 593-598. DOI: 10.7523/j.issn.2095-6134.2020.05.003

Abstract ( 390 ) PDF (KB) ( 79 )

In this study, a Fe₃O₄@PCDP nanocomposite is prepared as a highly efficient and eco-friendly heterogeneous Fenton-like catalyst that is used for the degradation of Rhodamine (RhB). The structure of the Fe₃O₄@PCDP nanocomposite is characterized by XRD, FTIR, and SEM, and the results demonstrate that it is synthesized successfully. The catalytic capacity of Fe₃O₄@PCDP is evaluated on the basis of various parameters, including the concentration of H₂O₂ and the pH value. The removal rate of RhB reaches 87.25% 42 h after the reaction under the optimal condition. The structure of Fe₃O₄@PCDP does not change and the catalytic performance is stable after the third cycle.

Oligomerization of isobutene catalyzed by combined proton acidic ionic liquids

YU Xiaojia, LIU Ying, WANG Hui, WU Youqing, GUO Yanqiu

2020, 37 (5): 599-605. DOI: 10.7523/j.issn.2095-6134.2020.05.004

Abstract ( 347 ) PDF (KB) ( 1 )

Two proton acidic imidazolium-based ionic liquids(ILs) of 1-(4-sulfobutyl)-3-methylimidazolium trifluoromethanesulfonate ([NNS][CF₃SO₃]) and 1-(4-sulfobutyl)-3-methylimidazolium hydrosulfate ([NNS][HSO₄])， were synthesized and applied in the oligomerization of isobutene. Some important parameters, including the types of ionic liquids, amount of catalysts, the reaction temperature, the reaction time, molar ratios of two ILs, stirring method and speeds, were screened. The optimized reaction conditions were determined as follows, 5 mmol of catalyst, 100 ℃, 3 h, and molar ratio of 1：1 for the two ILs. Under these conditions, the catalytic activity of the complexed ILs reached the highest with conversion rate of 84% for isobutene and selectivity of 77% for C₈⁼. The complex ILs could be recycled six times without obvious loss of catalytic activities, and conversion rate of isobutene remained 70% with above 90% selectivity of C₈⁼. The reaction was monitored on NMR and the formation process was further determined.

Effects of composition and spatial distribution of patches on microclimate in the urban riparian zone：a case study of riparian zone along Yongding River in Beijing

WANG Xin, ZHANG Na, YUE Rongwu, ZHENG Xiaorou

2020, 37 (5): 606-618. DOI: 10.7523/j.issn.2095-6134.2020.05.005

Abstract ( 280 ) PDF (KB) ( 0 )

We discuss the effects of composition and spatial distribution of patches on microclimate in the riparian zone from Mencheng Lake to Lianshi Lake along Yongding River in Beijing. In August 2017, we measured the three microclimate indexes, land surface temperature (LST), air temperature (TP), and relative humidity (RH), within each vegetation patch in the morning, at noon, and at dusk, respectively, on the same sunny days.Redundancy analysis and stepwise regression analysis are used to determine the main factors affecting the three microclimate indexes for different vegetation patch types and how they affect. The results show that, compared with roads, plants significantly reduce LST and TP and increase RH within the vegetation patches. However, the differences among the three vegetation patch types are not significant. LST, TP, and RH at the three times are affected by the characteristics of both vegetation patches themselves and their adjacent patches. However, these relationships at the same time are not always the same for different vegetation patch types. At noon, as the height of herb increases by 0.1 m, LST within herb patches reduces by 5.11%. As the shrub coverage increases by 10%, TP within shrub patches reduces by 2.50% and RH increases by 10.82%. As the adjacent tree coverage increases by 10%, LST within the mixed herb and broad-leaved patches and the herb patches reduces by 8.26% and 44.98%, respectively. As the adjacent road area increases by 10%, LST within the mixed herb and broad-leaved patches increases by up to 6.00%. As the distance from the river decreases by 10 m, RH within herb patches and shrub patches increases by up to 9.32% and 2.01%, respectively. In general, the index interactions or additions among different patches have more significant influence on microclimate than single patch index. The results provide useful information for ecological restoration of riparian zone and landscape design and planning.

CNN remote sensing crop classification based on time series spectral reconstruction

FENG Qixin, YANG Liao, WANG Weisheng, CHEN Tao, HUANG Shuangyan

2020, 37 (5): 619-628. DOI: 10.7523/j.issn.2095-6134.2020.05.006

Abstract ( 578 ) PDF (KB) ( 1 )

At the present, the crop classification method based on time series feature extraction needs much prior knowledge and manual intervention. It is difficult to automate the classification and it is easy to reduce the accuracy due to neglecting some effective features. We propose a convolutional neural network crop classification method based on time series spectral reconstruction. The method constructs a time-series image for every ground pixel, with the time dimension as the vertical axis and the spectral dimension as the horizontal axis, and then uses CNN, optimized by using the Adam gradient descent method and 40% connection rate dropout, to classify the time-series images. The experimental results show that the method reduces the salt-and-pepper noise, and the boundary of the plot is clear. The overall classification accuracy reaches 95.12%, which is higher than those of the time series multispectral + random forest method(88.58%), time-series NDVI + random forest method(90.25%), and time-series NDVI + convolutional neural network method(91.79%). For spring corn and tomato with close spectral similarity, the F₁-scores of our method reach 95.9% and 89.9% respectively, which are significantly improved compared with the control groups. The results of this study provide useful information for the automatic and fine mapping of croplands.

Network structure characteristics and spatial pattern evolution of educational facilities in mountainous towns：a case study of Wanzhou District of Chongqing

DENG Liangkai, HUANG Yong, SHI Yaling, WAN Dan, LI Lin

2020, 37 (5): 629-639. DOI: 10.7523/j.issn.2095-6134.2020.05.007

Abstract ( 234 ) PDF (KB) ( 1 )

In order to explore the evolution of the network structure and spatial pattern of educational facilities in mountainous cities and towns, taking Wanzhou District of Chongqing, China as a case study, using complex network analysis methods to construct collaboration network models of multi-period educational facilities, we calculate their degree distribution, network density, node strength, and network hinterland. Indicators such as the network hinterland reflect the integrity of the network, the level of hierarchy, and the functional structure of the core facilities. The research shows that: 1)the overall spatial pattern of the network evolves from “one core and many wings” to “multi-core and multi-wing”; 2)influenced by multiple factors such as policies, facility functions, location, etc., different levels of educational facilities appear to be “overall crushing-local agglomeration” in spatial distribution; 3)core facility functions are divided into “pair-assisted type” and “group core type”, and the “pair-assisted type” facility network hinterland is less restricted by space distance, while the “group core type” facility network hinterland is subject to space, namely, the distance limit is obvious. Based on this, combined with the influence mechanism of spatial pattern, this research refines the evolution pattern of educational facility spatial pattern and discusses the planning orientation.

Viscoelastic relaxation of lithospheric flexure and its influence on determining thickness of elastic lithosphere

SHAO Cuifa, WANG Shimin

2020, 37 (5): 640-649. DOI: 10.7523/j.issn.2095-6134.2020.05.008

Abstract ( 276 ) PDF (KB) ( 0 )

It is of significant importance to determine the thickness of elastic lithosphere in geoscience. The traditional method of inverting the thickness of elastic lithosphere constrained by the location of peripheral bulge in the flexural lithosphere based on the analytical solution of elastic plate flexure has far-reaching influence. In this work, the viscoelastic relaxation of the lithosphere flexure under vertical surface loads is studied quantitatively by means of a compressible viscoelastic finite element model with variable viscosities. The simulation results show that the position of the peripheral bulge moves first to the bending center and then to the outside of the bending, and the reverse motion occurs about 9 Ma after the loading. Compared with the elastic lithospheric thickness defined by relaxation time, the method of determining the thickness of the elastic lithosphere by the position of the peripheral bulge based on elastic plate bending solution gives reasonable results only in the period of 0.2-5.0 Ma after loading.

The first-principles study of elastic wave velocities of Mg-pyroxene under high pressures

MA Maining, ZHANG Jikai, HAN Lin, ZHANG Yuxin, ZHANG Linyi

2020, 37 (5): 650-656. DOI: 10.7523/j.issn.2095-6134.2020.05.009

Abstract ( 268 ) PDF (KB) ( 1 )

Pyroxene, including orthorhombic and monoclinic structures, is a common mineral in the crust and upper mantle, and the study of its elastic wave velocities is helpful to well understand the seismic velocity anomaly and dynamic process. Natural orthopyroxene is dominated by magnesium pyroxene (Mg-pyroxene). So, in this study, magnesium pyroxene was chosen as the object. The elastic wave velocities of the four structure phases of Mg-pyroxene, including orthoenstatite (space group, Pbca), low-pressure clinoenstatite (P2₁/c), high-pressure clinoenstatite (C2/c), and high-pressure orthoenstatite (P2₁ca), have been calculated based on the first-principles theory. The major conclusions are summarized as follows. 1) The elastic wave velocities of the four structures show obvious anisotropy. 2) The calculations of compressional wave velocity anisotropy indicate that C2/c has the largest seismic anisotropy below 12 GPa(almost the upper mantle condition), and above 12 GPa it is Pbca that has a steep increase in the anisotropy. 3) Shear wave velocity anisotropy along the a-axis is apparent compared to those along the b- and c-axises in enstatites except for C2/c. The results provide new evidence for the interpretation of seismic wave velocity anomalies in the upper mantle.

Joint detection and decoding algorithm based on partial response and SCMA

LIU Meng, LIU Wei, ZHOU Zhigang

2020, 37 (5): 657-662. DOI: 10.7523/j.issn.2095-6134.2020.05.010

Abstract ( 229 ) PDF (KB) ( 1 )

Sparse code multiple access (SCMA) is a new type of non-orthogonal multiple access technology with overload communication. In the high signal to noise ratio(E_b/N₀)scenario, based on the message passing (MPA) decoding algorithm, the bit error rate performance is not ideal. Therefore, a joint modulation and decoding model based on partial response and sparse code division multiple access is proposed. The scheme inherits the low complexity of SCMA at the decoding end and the high fault tolerance of partial response. In order to further reduce the bit error rate of the joint decoding, the Viterbi decoding of the partial response is cascaded into the MPA iterative decoding process, that is, the variable node performs a Viterbi decoding during each iteration, to form a new joint decoding module. The theoretical and simulation results show that the improved joint coding and decoding model effectively reduces the system’s demand for E_b/N₀ and maintains a low bit error rate.

Degree of freedom of MIMO multiway relay channel in full data exchange model

LI Yong, YUAN Xiaojun

2020, 37 (5): 663-672. DOI: 10.7523/j.issn.2095-6134.2020.05.011

Abstract ( 277 ) PDF (KB) ( 1 )

Recently, much research interest was focused on the degree of freedom (DoF) analysis of multiple input multiple output (MIMO) multiway relay channel (mRC). In this work, we investigate the achievable DoF of the half duplex MIMO mRC with two clusters each of which contains K users. Also, we focus on full data exchange model, which means that each user in a cluster wants to exchange information with all the other users in the same cluster. To achieve efficient DoF, signal alignment techniques are developed to jointly construct the beamforming matrices at the user and the relay. Also, we design signal alignments for uplink and downlink, respectively, as that the uplink and downlink are asymmetry in the full data exchange model. Combining with the optimized uplink and downlink time allocations, we derive an achievable DoF for the half duplex model. Further, we expand our analysis to full duplex model considering equal uplink and downlink time allocations, and show that one can use our signal alignment scheme to obtain the optimized achievable DoF in full duplex model.

Information fusion algorithm based on improved particle swarm BP neural network in WSN

WANG Hong, XU Youyu, TAN Chong, LIU Hong, ZHENG Min

2020, 37 (5): 673-680. DOI: 10.7523/j.issn.2095-6134.2020.05.012

Abstract ( 318 ) PDF (KB) ( 13 )

Back-propagation (BP) neural network has low convergence speed, is sensitive to the initial value, and easily falls into the local optimal solution in data fusion algorithms in wireless sensor network (WSN). To solve these problems, a data fusion algorithm based on improved particle swarm optimization BP neural network in WSN (BSO-BP) is proposed. The beetle antennae search(BAS) algorithm is used to improve the particle swarm optimization. Then the imporved particle swarm optimization is used to optimize the BP neural network weights and thresholds, which are applied to WSN data fusion. The cluster head nodes extract the feature of the collected data by optimizing the trained BP neural network, and send the merged data to the sink node. Simulation results show that BSO-BP algorithm effectively improves the fusion accuracy and convergence speed, decreases the redundant data communication and prolongs network lifetime. BSO-BP algorithm reduces the relative error by 12.4% and the root-mean-square error by 11%, compared to BP and PSO-BP algorithms.

Path planning and obstacle avoidance for UAV based on Laplacian potential field

GU Yujin, SONG Xiaocheng, LIU Xiaopei, LU Jie

2020, 37 (5): 681-687. DOI: 10.7523/j.issn.2095-6134.2020.05.013

Abstract ( 384 ) PDF (KB) ( 1 )

We propose a method for autonomous navigation of unmanned aerial vehicles (UAVs) in cluttered environment utilizing Laplacian potential field. With suitable boundary conditions for obstacles and goal in the map, Laplace’s equations are solved by boundary element method (BEM). Then we establish artificial potential field which is capable of handling obstacles with complex configuration and guarantees nonexistence of local minima. Since such a kind of potential field has easy access to the gradient of arbitrary point in the map, a linear quadratic Gaussian controller (LQG) is designed for velocity tracking to help complete attitude control. The simulation is conducted on Airsim platform with different scenarioes, and the results illustrate that this method is valid for path planning and obstacle avoidance and has adaptability to unexpected disturbance.

Online learning-based task offloading algorithms for dynamic fog networks

TAN Youyu, CHEN Lei, ZHOU Mingtuo, WANG Kunlun, YANG Yang, ZHANG Wuxiong

2020, 37 (5): 688-698. DOI: 10.7523/j.issn.2095-6134.2020.05.014

Abstract ( 293 ) PDF (KB) ( 1 )

Task offloading is one of the main techniques of the fog computing, and it means that the computation-limited nodes offload the tasks to the capable nodes for help. Firstly, we propose TOD (online learning-based task offloading algorithm for the dynamic fog networks under stationary status) using the MAB (multi-armed bandit) theory, which aims at minimizing the long term offloading delay and improving the task offloading success ratio. Then, we propose TOD-N (online learning-based task offloading algorithm for the dynamic fog networks under non-stationary status) to efficiently track the changes of the sharing computing resources and the channel environment. Moreover, we analyze the performances of the two algorithms on the optimality, the computational complexity, and the memory usage. Simulation results show that the long term average offloading delays achieved by the two algorithms are almost as good as the one achieved by the Oracle algorithm, and the offloading success ratios are also efficiently promoted. Moreover, TOD-N tracks the optimal resources efficiently under non-stationary network status.

Online task offloading in non-stationary fog-enabled networks

ZHU Zhaowei, LIU Ting, QIAN Hua, LUO Xiliang

2020, 37 (5): 699-707. DOI: 10.7523/j.issn.2095-6134.2020.05.015

Abstract ( 260 ) PDF (KB) ( 0 )

To fully exploit the computational resources in different fog nodes, task offloading is emerging. In this work, under the fog computing scenario, an efficient online task offloading strategy is investigated to minimize the long-term cost of task offloading. To achieve this goal, the problem is modeled as a stochastic optimization problem. Moreover, the system parameters are characterized by random variables, and their expectations may change abruptly at unknown time slot. Besides, the information about the system parameters is only available through the feedbacks after the task finishes. Using the non-stationary multi-armed bandit framework, we propose an efficient algorithm to handle this challenging stochastic programming. Furthermore, theoretical analyses are presented to prove the asymptotic optimality of the proposed algorithm. Numerical results reveal the advantages of this algorithm.

A conformal focusing microwave hyperthermia system based on differential algorithm

XU Lifan, WANG Xiong

2020, 37 (5): 708-713. DOI: 10.7523/j.issn.2095-6134.2020.05.016

Abstract ( 343 ) PDF (KB) ( 0 )

Focusing microwave hyperthermia, as a new non-invasive treatment, can be applied to the treatment of breast cancer. A prototype of conformal focusing microwave hyperthermia based on differential evolution algorithm is proposed. The operating frequency of the focusing antenna array is 2.45 GHz, and a real-time compressive sensing thermoacoustic imaging system is integrated to improve the visibility of focusing state. The focusing thermotherapy strategy of the prototype is expounded, and the focusing effect of the prototype is compared with that of the common prototype. Finally, joint simulation indicates that the focusing effect of the prototype based on differential evolution algorithm is better than that of the conventional prototype.

Design and implementation of a generic parallel architecture for LDPC codes based on FPGA

ZHANG Xue, JIANG Quanjiang, LIANG Guang, YU Jinpei

2020, 37 (5): 714-719. DOI: 10.7523/j.issn.2095-6134.2020.05.017

Abstract ( 276 ) PDF (KB) ( 0 )

In order to meet the requirements of FPGA implementation of spaceborne ultra-high speed data transmission equipment and to make full advantage of the abundant parallel resources of FPGA devices to solve the problem of low work processing clock frequency, we propose and design a general parallel architecture of LDPC coding with N-bit configurable. The architecture is designed based on FPGA according to the characteristics of LDPC structure. The equivalence between parallel architecture and traditional serial architecture is theoretically analyzed and successfully validated by simulation. Taking N=8 as an example, the LDPC code with a throughput of 2.5 Gbps is implemented on the FPGA development platform, which verifies the feasibility of the proposed architecture.

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