Journal of University of Chinese Academy of Sciences

Collins effect at super tau-charm facility

WANG Binlong, Lü Xiaorui, ZHENG Yangheng

2021, 38 (4): 433-441. DOI: 10.7523/j.issn.2095-6134.2021.04.001

The super tau-charm facility is a future project of high luminosity electron-positron collider, which will achieve the luminosity of 100 times of the current running facility BEPCⅡ in Beijing. In this work, we present a sensitivity study on the Collins asymmetry measurement of e⁺e^-→ππX and KKX using 2.5 fb^-1 e⁺e^-→qq Monte Carlo simulation sample generated at the center-of-mass energy of 7 GeV. Extrapolating to the integrated luminosity of 1 ab^-1, the statistical sensitivities of the Collins asymmetries of charged ππ pairs are at the level of 10^-4, while for the charged KK pairs, the sensitivities are in the range of 10^-3. Research shows that the accuracy of the asymmetry measurement is affected to a large extent by the background level (mostly from weak processes) and K-π misidentification. So an improved particle discrimination power using Cherenkov detector is very important for this project.

Liquid metal drop impingement on an electrolyte solution pool surface under the influence of a horizontal magnetic field

REN Dongwei, YANG Juancheng, NI Mingjiu

2021, 38 (4): 442-449. DOI: 10.7523/j.issn.2095-6134.2021.04.002

Abstract ( 356 ) PDF (0KB) ( 0 )

In the present paper, we experimentally investigate the impingements of a liquid metal drop on the electrolyte solution pool. The experimental setup consists of an electromagnet, liquid metal droplet generating system, argon-protecting vessel for drop impact, and high-speed imaging system. The setup can capture the dynamic phenomena of droplet impact upon and below the free surface of the electrolyte pool under different conditions (with or without a magnetic field, different droplet diameters, and impact velocities). Upon the surface of pool, we observed three typical outcomes after drop impact on the pool, namely, thin jet with second droplet, prompt splash with a thick jet, and thick jet with second droplet, among which the prompt splash with the thick jet is only observed in the presence of horizontal magnetic field. The horizontal magnetic field can inhibit the height of central jet and the occurrence of second droplet, and such effect becomes stronger when the strength of magnetic field increases. On the other hand, several phenomena were observed below the surface of pool, i.e. ellipsoid vibration, flat vibration, bowl deformation, the collapse and second bowl deformation with or without magnetic field. The horizontal magnetic field, which promotes a "bulge" of the flat vibration and bowl deformation, affects the critical We of the occurrence of bowl deformation, the collapse and second bowl deformation. In addition, we found the relationships between the motion of liquid metal drop upon and below the surface of pool. Experimental results reveal that the complex phenomena can be observed when the liquid metal drop impacts on the electrolyte solution pool under the influence of an external magnetic field, it is worthy of further investigations both by detailed experiments and numerical simulations.

Co-propagation of femtosecond vortex beam and the generated third harmonic in air

ZHAN Lindi, ZHONG Zhiping, XU Litong, XI Tingting, HAO Zuoqiang

2021, 38 (4): 450-458. DOI: 10.7523/j.issn.2095-6134.2021.04.003

Abstract ( 351 ) PDF (0KB) ( 0 )

The third harmonic (TH) vortex generated by the filamentation of femtosecond vortex beam in air is simulated. The influences of perturbation distribution and peak power of the initial fundamental wave (FW) on the evolution of the two-color vortex are investigated. For the initial FW with symmetrical perturbation, the intensity annulus of the two-color vortex is not influenced by the initial peak power and can be kept in the filamentation regime. But the spiral phase distribution is influenced by multiple filamentation under the high peak power condition. In this case, the spiral phase distribution of the two-color vortex is destroyed due to the phase accumulation of the multiple filaments. For the initial FW with asymmetrical perturbation, both the spatial annulus and the spiral phase distribution of the two-color vortex are destroyed when multiple filaments are formed.

Experimental study of flow pattern and heat transfer of liquid metal in microchannel under the magnetic field

LEI Tianyang, MENG Xu, WANG Zenghui, NI Mingjiu

2021, 38 (4): 459-466. DOI: 10.7523/j.issn.2095-6134.2021.04.004

Abstract ( 411 ) PDF (0KB) ( 0 )

The first wall of facing plasma of fusion reactor needs to bear high-intensity neutron irradiation and heat load, so it is difficult for ordinary materials to meet the requirements. It is an effective way to use the liquid metal as the first wall of facing plasma. Taking liquid metal as the first wall, it is necessary to solve the problem that how to evenly spread the liquid metal on the wall and study the heat transfer characteristics between liquid metal and the wall under a perpendicular magnetic field. Previous studies have shown that the structure of microchannel surface contributes to the even spreading of liquid metal. In this paper, liquid metal alloy GaInSn works as the working fluid. The flow pattern and heat transfer characteristics of the liquid metal in microchannel plate under the condition of uniform magnetic field and no magnetic field are studied experimentally. The influence of a perpendicular magnetic field on the flow pattern and heat transfer of liquid metal in a microchannel is studied by comparing the experimental results of two different working conditions.

Temporal-spatial distribution characteristics and protection countermeasures of cultural heritage sites in Northern Pakistan based on GIS spatial analysis method

JIANG Chun, LUO Lei, SHAHINA Tariq, MUHAMMAD Ali, YAO Ya, WANG Xinyuan

2021, 38 (4): 467-477. DOI: 10.7523/j.issn.2095-6134.2021.04.005

Abstract ( 550 ) PDF (0KB) ( 0 )

The northern Pakistan is the central area of the Gandhara culture in history, where a large number of Hinduist, Buddhist and Islamic cultural heritage sites are located. Based on multisource data such as historical sources, DEM data, and field survey, the spatial and temporal distribution characteristics and preservation of Hinduist, Buddhist, and Islamic cultural heritage sites have been studied by using spatial analysis methods of GIS, and the reasonable protection countermeasures have been suggested. The research results indicate that Northern Pakistan has witnessed the coming, rising, and falling of Hinduist, Buddhist, and Islamic cultures. The kernel density estimate shows that these three types of cultural heritage sites have different distribution ranges and aggregation degree, but they all gather around Islamabad with the highest aggregation degree. High resolution DEM analysis shows that more than 90% of these three types of cultural heritage sites are no farther than 800 m away from the river, which confirms the great significance of the river in history when these culture sites were selected. It also can be known from DEM that the location of these three types of sites is mainly no higher than 800 m, and the slope range is mainly between 0° and 10°, along rivers and main roads. Of the statistical data, the number of Islamic sites is the largest, followed by Buddhist sites and Hinduist sites respectively, reflecting the change of the number of preserved sites over time. Due to nature factors and human activities, at present, many sites such as Bhera and Vijhi are in a bad condition, which demands more efforts and better strategies to preserve. As to the current preservation and risks of the cultural heritage sites in Northern Pakistan, the corresponding protection strategies are put forward.

Substrate phosphorus removal for contaminated water treatment in constructed wetlands by integrating static adsorption experiments with seepage sand tank tests

WANG Di, WANG Mingyu

2021, 38 (4): 478-485. DOI: 10.7523/j.issn.2095-6134.2021.04.006

Abstract ( 359 ) PDF (0KB) ( 0 )

In order to solve the problem of decreasing for the removal rate of phosphorus and consider the optimal design and maintenance of the substrate structure in constructed wetlands, it is necessary to understand the phosphorus adsorption characteristics for different substrates and obtain the evolution trend and law regarding the actual dephosphorization effect for specific phosphorus-containing wastewater. In this study, three substrates including zeolite, medical stone, and magnetite, were selected, which are commonly used in constructed wetlands with good phosphorus removal performance, to study their adsorption kinetics and isothermal adsorption characteristics of phosphorus and to investigate the effects of different substrates and particle sizes on phosphorus adsorption. Further, zeolite with the best phosphorus adsorption performance among the three substrates was selected to carry out the seepage sand tank test for phosphorus removal, so as to simulate and obtain the phosphorus removal and purification effects of the subsurface flow wetland. By integrating the static experiment with seepage sand tank test for the phosphorus removal, the mechanisms of dephosphorization and the evolution trend and law of actual dephosphorization effects of the zeolite substrates with different particle sizes were identified. The results show that the adsorption process of phosphorus on the three substrates consists of the fast adsorption, slow adsorption, and gradual equilibrium. Furthermore, the Langmuir equation can accurately describes the isothermal process of phosphorus adsorption on the substrates. The adsorption phosphorus removal efficiency and the overall phosphorus removal efficiency of the zeolite substrate with different particle sizes are significantly different. Additionally, the phosphorus removal efficiency of the zeolite substrates fluctuates with the particle size, and the overall phosphorus removal efficiency initially increases and then decreases considerably. The analysis of the achieved data sets indicates that, in addition to the significant mechanism of phosphorus adsorption removal, the microbial effect is also considerable on the phosphorus removal. Based on this type of integrated investigations, the phosphorus removal mechanisms with their relative importance and the overall phosphorus removal efficiency can be identified.

Spatiotemporal evolution of urban eco-efficiency in China and its influencing factors based on super-efficiency SBM model

YAN Tao, ZHANG Xiaoping, ZHAO Yanyan

2021, 38 (4): 486-493. DOI: 10.7523/j.issn.2095-6134.2021.04.007

Abstract ( 1221 ) PDF (0KB) ( 0 )

Urban eco-efficiency is an effective indicator to show the relationship between regional economic development and its impact on resources and environment. The spatiotemporal evolution of the eco-efficiency of 285 cities above the prefecture level in China from 2005 to 2017 was calculated by the super-efficiency SBM model containing the undesirable outputs. The panel regression models were further constructed to analyze the factors that significantly influenced the urban eco-efficiency. The conclusions are as follows. 1) The average urban eco-efficiency across China fluctuated slightly and showed a rising trend. 2) Even though the gap of eco-efficiency between cities decreased gradually from 2005 to 2017, the regional disparity in the whole country was still obvious. 3) The spatiotemporal pattern of urban eco-efficiency among different regions and cities has evolved significantly. The cities with higher ecological efficiency in 2005 were mainly distributed in the Pearl River Delta, the Yangtze River Delta, and Shandong Province. By contrast, the territorial ranges of cities with higher urban eco-efficiency in 2017 were greatly expanded. 4) Results from the regression models showed that factors as urbanization rate, economic development level, openness to foreign economies, science and technology investments, and industrial transition were important determinants promoting the urban eco-efficiency in China. Therefore, high priorities should be given to upgrade industrial structure, increase investments in science and technology, and reduce resources consumption and pollutants emissions when authorities make policies towards regional sustainable development.

Efficient machine learning methods for hardware Trojan detection using instruction-level power character

LI Ying, CHEN Lan, TONG Xin

2021, 38 (4): 494-502. DOI: 10.7523/j.issn.2095-6134.2021.04.008

Abstract ( 329 ) PDF (0KB) ( 0 )

Integrated circuits (IC) are vulnerable to hardware Trojans (HTs) due to the globalization of semiconductor design and outsourcing fabrication. Stealthy HTs which activate malicious aging operations are ususlly hide in normal behaviors.Therefore, it is a challenge to detect those HTs by general test and verification approaches. In this paper, we build an efficient machine learning (ML) framework to classify the genuine and Trojan-insert chips using instruction-level side-channel power characters. Different instructions and HTs are used as feature sets to construct the algorithm models. In order to evaluate the performance of the method, we implemented five HTs benchmarks of MC8051 micro-controller in Altera Stratix II FPGA, and presented analysis on five formulated ML models in both supervised and unsupervised modes. The test results showed that the detection accuracy of supervised Naïve Bayes is 95% in average, which is the highest among the ML models. The supervised SVM consumed the shortest running time, with an average of 0.04 s. We also verified that one-class SVM can be a valuable method without golden reference, which has accuracy in the range from 17% to 72% even in Harsh learning condition.

An algorithm for multi-target detection in multi-temporal remote sensing images

XI Yanxin, JI Luyan, GENG Xiurui

2021, 38 (4): 503-510. DOI: 10.7523/j.issn.2095-6134.2021.04.009

Abstract ( 376 ) PDF (0KB) ( 0 )

With the rapid development of remote sensing technology, the remote sensing data become valuable in many practical applications. Among them, target detection has always been an important topic. However, most of the target detection algorithms in remote sensing images merely concentrate on single-temporal data, and there are few algorithms for multi-temporal data. In the field of target detection in multi-temporal remote sensing data, filter tensor analysis (FTA) has achieved great success which outperforms other target detection algorithms for single-temporal data. Yet FTA is designed only for single target detection, which means it can not meet the need for practical applications in circumstances where it has to detect more than one target simultaneously. So, in this paper, a modified algorithm for multi-target detection in multi-temporal data has been proposed based on the target constraints in multiple target constrained energy minimization and the tensor filter in FTA. Both the experiment results on simulation data and real remote sensing data from Landsat 8 prove that the algorithm proposed in this paper can effectively detect several targets in multi-temporal data.

Two-step imaging algorithm of bistatic sliding-spotlight SAR based on hyperbolic equivalent method

XIANG Jianbing, Lü Xiaolei, FU Xikai

2021, 38 (4): 511-518. DOI: 10.7523/j.issn.2095-6134.2021.04.010

Abstract ( 354 ) PDF (0KB) ( 0 )

Bistatic sliding-spotlight synthetic aperture radar (SAR) can not only maintains the flexibility, reliability and stability of the bistatic SAR, but also produce high-resolution image pairs with great potential for observation and mapping. This mode should consider both characteristics of bistatic imaging and a significant increase in Doppler bandwidth. In this paper, the Doppler characteristics of the target in bistatic sliding-spotlight SAR system are analyzed, then, a two-step imaging algorithm based on hyperbolic equivalent method is proposed by combining the bistatic imaging algorithm with the spectrum analysis method. At the same time, for the degradation of the focus quality caused by the error of hyperbolic equivalent model, the model error compensation method is proposed, and the complete algorithm processing flow is given. Finally, the proposed algorithm is verified by simulation experiments.

A stereo positioning method of GaoFen-3 SAR images under different time and space conditions

LI Dan, LIU Jiayin

2021, 38 (4): 519-523. DOI: 10.7523/j.issn.2095-6134.2021.04.011

Abstract ( 415 ) PDF (0KB) ( 0 )

This paper introduces a reliable stereo positioning method of GaoFen-3 synthetic aperture radar (SAR) images. The method can achieve high positioning accuracy even if the spatial and temporal conditions of the stereo image differ greatly. Firstly, the stereo positioning equations are established according to the range-Doppler model, and then the polynomial fitting method is used to obtain the state vectors of the satellite. Finally, the equations are solved by Newton's method. In this paper, stereo location experiments are carried out with 7 SAR images of Beijing, Shanghai, and Suzhou with different imaging times. The resolutions of these images are within 5 m. Verification based on Google Earth image shows that the plane errors of all the targets are within 30 m, and the height errors are within 34 m. It is proved that even if the imaging time intervals of the stereo SAR image pairs are long, the 3D information with high accuracy can also be obtained. Besides, the localization accuracy of the SAR image pair from spotlight mode is the highest.

Range spread target adaptive detector for distributed MIMO radar in nonhomogeneous environment

LAN Yun, TANG Liang, BU Zhiyong, CAO Leban

2021, 38 (4): 524-531. DOI: 10.7523/j.issn.2095-6134.2021.04.012

Abstract ( 332 ) PDF (0KB) ( 0 )

With the increase of radar resolutions, point source models at low resolutions are no longer applicable. And the target range spread phenomenon brought by the improvement of radar resolution has an increasingly greater impact on radar detection probability. Therefore, this paper aims at the problem of detecting range spread targets in distributed MIMO radar. We model the problem as a binary hypothesis testing problem, and suppose the interference clutter covariance matrices corresponding to different transmit-receive pairs is random matrices. The prior probability density functions are also supposed as inverse complex Wishart distributions. By setting different power levels to simulate the nonhomogeneous clutter power between different transmit-receive antenna pairs. Two new detectors were derived based on the detection criteria of Rao and Wald detectors and the Bayesian frame with the nonhomogeneous clutter. The detectors mainly have two advantages:firstly, no training data is needed; secondly, the prior information of clutter is included in the decision rule which increase the performance. The simulation results show that in a nonhomogeneous clutter environment, our detectors perform better than the existing detection performance and have lower computational complexity.

Solution method of satellite navigation positioning based on cubature Kalman filter

ZHANG Jie, LI Jinghua, HU Chao

2021, 38 (4): 532-537. DOI: 10.7523/j.issn.2095-6134.2021.04.013

Abstract ( 464 ) PDF (0KB) ( 0 )

Due to the nonlinear characteristics of satellite navigation positioning equations, the traditional positioning methods need to linearize the equations before solving, which would reduce the accuracy of positioning. Cubature Kalman filter (CKF) algorithm based on Bayesian estimation and cubature transformation could effectively improve the accuracy of nonlinear filtering estimation. In this paper, cubature Kalman filter algorithm is applied to satellite positioning solution. The transfer and measurement models of the positioning solution system are established. The three-dimensional position coordinates of the receiver are recursively solved by time update and measurement update. The positioning solution algorithm based on cubature Kalman filter is verified by IGS observation data tests, and compared with the least square method and extended Kalman filter algorithm. The results show that the application of CKF algorithm in satellite positioning is of higher precision and faster convergence speed.

Hierarchical Gaussian loss based object detection in open world

WANG Lin, CHEN Xilin

2021, 38 (4): 538-548. DOI: 10.7523/j.issn.2095-6134.2021.04.014

Abstract ( 354 ) PDF (0KB) ( 0 )

Object detection targets both object localization and categorization. Most of existing object detection methods are category-dependent, and can not deal with the detection task in open world with unknown categories. In aware that the difficulties of localization and categorization are different during transfer from known categories to unknown ones, and the localization is more universal than categorization, and inspired by the process of human categorization on unknown objects, we propose a Gaussian hierarchical loss model which applies an hierarchical modeling of object categories in object detection. KL divergence is used to describe the hierarchical relationship among categories while learning all the class multidimensional Gaussian distributions and enhance the transfer ability from the known classes to the unknown classes. Therefore the proposed method can extend the existing object detection methods to unknown categories in open world. Experimental results show that the proposed method can improve the detection ability of unknown categories without losing the performance on known categories.

Combination algorithm of spectrum sensing in vehicle network based on neural network

JI Yufeng, ZHENG Min, TAN Chong, LIU Hong

2021, 38 (4): 549-556. DOI: 10.7523/j.issn.2095-6134.2021.04.015

Abstract ( 334 ) PDF (0KB) ( 0 )

In this paper, a multi-conditional spectrum sensing combination algorithm based on neural network is proposed to address the current shortage of spectrum resources in vehicular network. The algorithm combines signal energy, the maximum-minimum of eigenvalues, traces, and the average eigenvalue of the covariance matrix as neural network characteristic parameters, which are achieved through the strong multi-classification ability of neural network. To improve the successful rate of spectrum sensing and the utilization rate of the spectrum, we focus on analyzing the selection of parameter in theory as well as the low signal-to-noise ratio caused by channel fading and shadow effect. Meanwhile, the Doppler effective caused by car moving is also our consideration. Under low signal-to-noise ratio, the simulation results show that the proposed algorithm has better detection performance than existing spectrum sensing algorithms.

Research and design of fog computing-enabled mobile robots fleet tracking

SHEN Guofeng, ZHOU Mingtuo, LI Jian, WANG Huajun, LI Kai, YANG Yang

2021, 38 (4): 557-566. DOI: 10.7523/j.issn.2095-6134.2021.04.016

Abstract ( 270 ) PDF (0KB) ( 0 )

Tracking control in multi-robot systems has always been a research hotspot, and the emerging fog/edge computing technology provides new ideas for the design of robot systems. A novel robot formation control scheme that requires no global positioning information is proposed in this article. Fog computing technology is also introduced to offload computing tasks when implementing the system. A fog node is responsible for providing wireless network and executing the tracking control program. As for the tracking control scheme, the desired tracking trajectory is calculated utilizing the speed information of the leader robot, and the real-time tracking error is obtained by vision based measurement. The trajectory tracking control is implemented by a combination of speed replay and PD-type iterative learning control method. The experimental results of our prototype system shows that the network provided by fog node can meet the needs of distributed real-time control applications. Local computing power requirement can be eased and 25% of computing energy is saved due to task offloading. The mean tracking error of the system is less than 0.05 m during field tests.

Diurnal variation of energy flux of Haloxylon ammodendron community in the southern margin of Gurbantunggut Desert under different weather conditions

LI Chuanjin, HU Shunjun

2021, 38 (4): 567-575. DOI: 10.7523/j.issn.2095-6134.2021.04.017

Abstract ( 278 ) PDF (0KB) ( 0 )

Based on the meteorological and energy data measured by the Bowen ratio system on the southern edge of the Gurbantunggut Desert in the summer of 2018, the diurnal variation of the energy exchange and its components of the Haloxylon ammodendron community under different weather conditions was analyzed. The results show:1) The diurnal curve of energy exchange is highly similar unimodal type in sunny and cloudy days in this area. Soil heat flux is the smallest, while sensible heat is slightly higher than latent heat in sunny and partly cloudy days. In cloudy days sensible heat energy transfer is the main component. In rainy days, the overall heat flux is the smallest and characterized by multi-modal curve, in which latent heat transmission is the dominated component. 2) The daytime Bowen ratio is below 1 and the smallest in rainy days. It exceeds 1 in other three weather conditions, increasing from sunny, partly cloudy to cloudy days. During nighttime, the Bowen ratios are lower than 1 in all the days, increasing from sunny, cloudy, partly cloudy to rainy days. 3) The energy partitioning curve is relatively stable in daytime and unstable during nighttime. It fluctuates dramatically in twilight, which differs in starting time among the diverse weather conditions.

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