Journal of University of Chinese Academy of Sciences

Krull dimension and primary decomposition of Rep(F[C_2^α])

LU Xin, TANG Guoping

2025, 42 (2): 145-152. DOI: 10.7523/j.ucas.2023.057

Let F be a field with characteristic 2 and C_2^α be a cyclic group with order 2^α. The ring, which has a Z-basis by finite dimensional indecomposable F[C_2^α] modules and multiplications by tensor product of F module, is called representation ring and denoted by Rep(F[C_2^α]). Based on Higman’s work, we further get the Krull dimension and the concrete forms of all prime ideals of Rep(F[C_2^α]). And then, we prove that Rep(F[C_2^α]) is a reduced ring and find the minimal primary decomposition of the zero ideal. At last, we prove that Spec(Rep(F[C_2^α])) is a connected topological space.

A new cross-domain recommendation method with cluster effect

ZHAI Haoran, ZHANG Sanguo

2025, 42 (2): 153-158. DOI: 10.7523/j.ucas.2023.040

Abstract ( 228 ) PDF (0KB) ( 0 )

In recent years, the recommender system has been widely used in online platforms, which can extract useful information from giant volumes of data and recommend suitable items to the user according to user preferences. In this article, we put forward a crossdomain recommendation method based on the rating data of the different projects from similar users, introducing project cluster effect in the target domain of the study, the use of this specific group of singular value decomposition with the method of extracting information associated with a project with similar characteristics. This method could effectively solve the problem of data sparsity. Due to the sparsity of the target domain, most items in the test set of the target domain have few scores, and their information is challenging to obtain from the training set. A strictly related problem is the one of collaborative filtering in recommender systems, where an algorithm tries to extrapolate missing information about the items from the rating activity of the users in order to provide a specific ad-hoc ranking for each user also on the items that have not been rated (on this see discuss how to aggregate the information from multilayer networks, while showing the importance of centrality measures for this issue). MovieLens data analysis indicated that, compared with the existing recommendation methods and cross-domain recommendation methods, the proposed new method of cross-domain recommendation with cluster effect has a significant improvement in the prediction accuracy.

Thermoelectric effect on the flow and heat transfer of liquid metal in a conducting pipe under the magnetic field

CHEN Zhaoqi, WANG Zenghui

2025, 42 (2): 159-166. DOI: 10.7523/j.ucas.2023.036

Abstract ( 248 ) PDF (0KB) ( 0 )

The seebeck effect produced by metal fluid under the influence of a stable magnetic field and temperature gradient can effectively enhance its heat transfer efficiency. The flow phenomena of liquid lithium and stainless steel in partially conducting pipes are simulated by using the consistent conservative numerical scheme developed for magnetohydrodynamics and the partitioned iterative algorithm for multi-domain coupled physical problems. The magnetic field direction is along the span of the pipe. The flow phenomena of liquid metal in the partially conductive tube under the action of the thermoelectric effect at Reynolds number (Re=745.6) are studied. It is found that the Lorentz force produced by the thermoelectric effect and magnetic field forms the reverse flow vortex structure at the four corners of the square tube. The reverse flow vortex increases the velocity in the central region and promotes the convective heat transfer of the liquid metal in the vortex structure at the four corners of the square tube. The reverse flow vortex increases the velocity in the central region and promotes the convective heat transfer of the liquid metal in the central region. With the increase of magnetic field intensity, the flow changes from unsteady flow to steady flow, the flow in the central region is dominated by the magnetic damping effect, the scale of the thermoelectric effect gradually shrinks to the vicinity of the boundary, and the relationship between velocity and temperature changes from two-way coupling under weak magnetic field to one-way coupling under strong magnetic field.

Rice plant density inversion using polarimetric SAR considering planting methods

XU Jingxuan, LI Kun, QIN Yi, ZHANG Bolin, ZHANG Fengli

2025, 42 (2): 167-175. DOI: 10.7523/j.ucas.2023.032

Abstract ( 344 ) PDF (0KB) ( 0 )

Plant density is an important factor affecting rice growth and yield. Because planting methods affect the distribution characteristics of rice in the field, and then cause the difference in density, it is necessary to consider the influence of planting methods in the inversion of rice plant density. Synthetic aperture radar (SAR) has been proved to be one of the important means of rice monitoring due to its advantages of all-day, all-weather and penetrability. Polarimetric SAR not only has the advantages of traditional SAR, but also is very sensitive to target structure and distribution characteristics. It has greater application potential in rice plant density inversion. Based on RADARSAT-2 full polarimetric SAR data, this study fully excavates the polarimetric information, considers the planting methods of transplanting and sowing, and uses the elastic network model to realize the inversion of rice plant density. The results show that polarimetric SAR has a good effect on the inversion of rice plant density. The RMSE of plant density in transplanting and sowing fields is 25 and 39 plants/m² respectively. Compared with the inversion results without considering planting methods, the accuracy is improved by more than 30%.

Characterization of lake area and number change in western Mongolia from 1992 to 2021

YANG Song, ZHOU Hongfei, YAN Yingjie

2025, 42 (2): 176-185. DOI: 10.7523/j.ucas.2023.083

Abstract ( 273 ) PDF (0KB) ( 0 )

Climate change and human activities have impacted greatly on many lakes in western Mongolia, whereas they were seldom studied. Using Landsat images as the data source, lakes with an area larger than 1 km² from 1992 to 2021 were extracted based on Google Earth Engine (GEE). Spatio-temporal changes of lake area were characterized, and causes were analyzed combining meteorological data and socioeconomic data. The results showed that: 1) The change of lake area could be divided into two phases, i.e., the expansion phase from 1992 to 1996 and the shrinking phase after 1996; 2) There are obvious spatial variations in lake area change. In Khovd Province and Gobi-Altai Provinces lake area shows a trend of decreasing first and then increasing, whereas the trend is opposite in Uvs Province and Zavkhan Provinces; 3) The causes are obvious different temporally and spatially. The increase of summer mean temperature and potential evapotranspiration had a negative impact on the decrease of lake area in Khovd Province and Gobi-Altai Provinces during 1992-2001. However, human activities, including agricultural irrigation and overgrazing, were the dominant negative drivers for the shrinkage of lakes in Uvs Province and Zavkhan Provinces from 1996 to 2019.

Medical accessibility of affordable housing and commercial housing in Xiamen from the perspective of equity

LIU Wenhui, ZHANG Guoqin, WANG Yang

2025, 42 (2): 186-198. DOI: 10.7523/j.ucas.2023.059

Abstract ( 234 ) PDF (0KB) ( 0 )

The rational planning and equitable allocation of medical facilities are closely related to public health and social justice. This paper takes Xiamen as an example and combines real-time traffic data from Baidu Maps to measure the medical accessibility of affordable housing and commercial housing by driving and public transportation, and explores the spatial equity of medical services for different housing groups by analyzing the differences in accessibility between the two types of housing and their characteristics under different zoning and transportation modes in the city. The results indicate that: 1) Compared with commercial housing, affordable housing is more disadvantaged in terms of site selection and the construction of supporting medical facilities in the surrounding area; 2) Regardless of the travel mode and regional scale, the accessibility of affordable housing is lower than that of commercial housing, and the spatial inequity between the two is more obvious in the peripheral urban areas and when using public transportation; 3) Even in the core urban areas where medical facilities are adequate, the accessibility of housing is better, and the spatial equity of medical care is better by car, the spatial inequity of medical services exists when using public transportation. The results of the study reflect the uneven and biased spatial allocation of medical facilities among different housing types in Xiamen, and also show the lower spatial equity of medical services faced by people living in affordable housing in the peripheral urban areas and are more dependent on public transportation. The relevant government departments should focus on strengthening the construction of medical facilities around affordable housing in the peripheral urban areas, and pay attention to the construction of the public transportation system around affordable housing. In addition, when planning new affordable housing in the future, the fairness of site selection should be emphasized, and the planning of public service facilities should be done at the same time to put the concept of social equity into practice in planning.

Medium-term prediction of earthquakes in Southern California using LSTM neural network

WANG Yixuan, ZHANG Huai, SHI Yaolin, CHENG Shu

2025, 42 (2): 199-208. DOI: 10.7523/j.ucas.2023.068

Abstract ( 371 ) PDF (0KB) ( 0 )

This paper explores earthquake prediction using neural networks, focusing mainly on using long-short-time memory (LSTM) neural networks to construct an earthquake prediction model. Based on the Southern California earthquake catalog data from 1932 to 2021, the earthquake catalog from January 1932 to March 2002 was used as the training set(80% of the entire earthquake catalog), and the earthquake catalog from March 2002 to September 2021 was used as the test set (the remaining 20%). The LSTM neural network was selected, and 11 earthquake prediction factors reflecting the spatiotemporal intensity distribution characteristics of the earthquake time series data were calculated from the training set. The maximum magnitude label corresponding to these factors was used to construct the model. The test set was then used for retrospective prediction testing. The model’s prediction performance was evaluated using metrics such as accuracy, precision, and R-value, which were calculated based on the values in the confusion matrix. The results show that the prediction has achieved certain results, predicting the M7.2 earthquake in April 2010. The R-value of some models is significantly higher than China’s current medium-term prediction level. However, the value of the evaluation model is still not ideal, and further exploration is needed.

Classification of S- and I-type detrital zircon by machine learning and its application to supercontinental evolution

SUN Zhihan, ZHANG Yigang

2025, 42 (2): 209-220. DOI: 10.7523/j.ucas.2023.065

Abstract ( 244 ) PDF (0KB) ( 0 )

Supercontinent evolution and distribution of detrital zircon with time is a long-term hot research topic. By using the stacking framework involving eight different machine learning methods and the area under curve (AUC) and accuracy proxy, a model is established to classify S- and I-type zircons. Applying the model to global detrital zircon dataset gives the distribution of S- and I-type zircon with time. After comparing the distribution with paleomagnetism and geological records, it is found that the S-type zircon distribution peak corresponds to the end of a supercontinent breakup and the start of assembly of the next supercontinent, and that the S-type zircon distribution valley (also the small peak of I-type zircon) is related to the maximum packing of a supercontinent and the start of its breakup. Based on the correlation of S-type zircon peak with global zircon big peak and the valley of S-type zircon with the global zircon small peak, it is proposed that big peaks of global zircon distribution with time represent a dispersive state of continents, during which magmatic activity is high producing both I- and S-type granites with also a high velocity of continent movement. By comparison, the small peaks in global zircon distribution represent a packing state of continents during which the supercontinent is stable with low magmatic activity producing mainly I-type granites and with a low velocity of continent movement. Finally, a high-accuracy decision function is provided to judge S- and I-type zircons and can be applied in related studies.

“Caochi” in Dunhuang and Turpan document

CHEN Tao, AILIJIANG Aisha, JIANG Hong'en

2025, 42 (2): 221-226. DOI: 10.7523/j.ucas.2023.023

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

Based on the historical literature, unearthed documents, and plant morphology, this paper made a detailed study on the word “Caochi” from the aspects of function, origin, and plant trait. The result showed that “Caochi” was Nigella glandulifera and it was used as medicine and condiment by the inhabitant in Dunhuang and Turpan during the period of Tang and Five Dynasties.

A fast recursive calculation method of projection coefficients without starting point constraint

WANG Ping, ZHOU Mei, CHEN Jiuying, ZHOU Chuncheng

2025, 42 (2): 227-235. DOI: 10.7523/j.ucas.2023.018

Abstract ( 247 ) PDF (0KB) ( 0 )

The two-dimensional gas concentration distribution obtained based on mobile laser gas telemetry technology is mainly achieved through an image reconstruction algorithm. Fast calculation of the projection coefficient is the key for such algorithm. However, the telemetry starting point based on mobile laser gas telemetry technology is randomly distributed in the grid or on the grid line of the reconstruction area, and the existing fast recursive calculation methods of projection coefficient are not applicable. This paper proposes a fast recursive calculation method of projection coefficient without starting point constraint. Three optical path accumulation factors are designed, which unify the recursive process of telemetry starting point in the grid and on the grid line without increasing the amount of calculation and realize the fast calculation of projection coefficient without starting point constraint. Algebraic reconstruction technology is used for reconstruction experiments, which verifies the effectiveness of this method. The minimum relative root mean square error is about 0.113%, and the maximum calculation speed is about 13.9 times that of the classical Siddon algorithm. The recursive calculation method proposed in this paper has a wider range of applications. It is the first time to realize the recursive calculation of projection coefficients without starting point constraints.

Cross-modal retrieval method based on MFF-SFE for remote sensing image-text

ZHONG Jinyan, CHEN Jun, LI Yu, WU Yewei, GE Xiaoqing

2025, 42 (2): 236-247. DOI: 10.7523/j.ucas.2024.025

Abstract ( 343 ) PDF (0KB) ( 0 )

Remote sensing image-text cross-modal retrieval technology can quickly obtain valuable information from massive remote sensing data. However, existing remote sensing image-text retrieval methods have limitations in utilizing multi-scale information within remote sensing images, and the weak recognition of target information leads to relatively low retrieval accuracy. To address these issues, this paper proposes a new method for remote sensing image-text cross-modal retrieval. This method mainly comprises a multi-scale feature fusion module and a salient feature enhancement module, which are designed to integrate multi-scale information of remote sensing images and enhance the expression of target information in remote sensing images, so as to improve the precision of remote sensing image-text cross-modal retrieval. Experimental validation was conducted on two publicly available remote sensing image-text datasets. The results demonstrate that the proposed method outperforms other methods across most evaluation metrics in the remote sensing image-text cross-modal retrieval task and exhibits the best overall retrieval performance.

Flow aggregation with constrained resource for in-network computation

SHENG Jiahua, HONG Peilin, WANG Hang

2025, 42 (2): 248-259. DOI: 10.7523/j.ucas.2023.044

Abstract ( 119 ) PDF (0KB) ( 0 )

In-network computation can greatly reduce the traffic generated during many-to-one transmission by establishing aggregation trees to merge data streams at the aggregation nodes. In this paper, we consider finding the minimum-cost aggregation tree under the constraints of a given amount of resources and the capacity of switch nodes. Since this problem is an NP-hard problem, a linear integer programming model and a heuristic algorithm called greedy cost aggregation tree (GCAT) are given to solve it. Simulation results show that the GCAT algorithm can generate a tree with less cost and utilize the resource more efficiently than other heuristics, and the performance is close to the optimal solution for small-scale networks.

Industrial MCU oriented transcendental function unit design

SONG Minte, LIU Nan, RU Zhanqiang, YIN Zhizhen, DING Peng, WANG Zhengguang, CHENG Suzhen, SONG Helun

2025, 42 (2): 260-267. DOI: 10.7523/j.ucas.2023.009

Abstract ( 246 ) PDF (0KB) ( 0 )

The calculation of transcendental functions is one of the necessary steps in industrial control algorithms. As the complexity of industrial control systems increases, calculating the transcendental function by software approximation algorithm takes up a large number of CPU cycles, compressing the computational resources of real-time control algorithms and reducing the accuracy of closed-loop control. Equipped with hardware accelerating units, industrial microcontroller unit architecture becomes the preferred solution to solve this contradiction. In this paper, a multi-threaded, high-performance, configurable transcendental function unit based on digital iterative algorithms was designed, which supports trigonometric function, exponential, and logarithmic calculations. The design was synthesized by standard cell library of SMIC 40 nm eFlash platform, resulting in a clock frequency of 200 MHz and an area of 301 074 μm².

Solutions of cross-entropy loss with spectral decoupling regularization

HU Yinhan, GUO Tiande, HAN Congying

2025, 42 (2): 268-275. DOI: 10.7523/j.ucas.2023.071

Abstract ( 204 ) PDF (0KB) ( 0 )

In this paper, we study the effect of spectral decoupling with different strengths on over-parameterized models. In the absence of weight decay, we show that the models obtained by spectral decoupling of different strengths are equivalent. When there is a small weight decay, we use the second-order Taylor expansion of the objective function to obtain an approximate solution. Analyzing the approximate solution, we find that reducing the spectral decoupling has the effect of enhancing the weight decay, which is directly equivalent in the binary classification problem. Finally, we verify our analytical conclusions through experiments.

Impact and mechanism of relocation of urban administrative center on spatial expansion: taking Qingdao as an example

XU Shaojie, WANG Kaiyong, WANG Fuyuan

2025, 42 (2): 276-288. DOI: 10.7523/j.ucas.2023.075

Abstract ( 419 ) PDF (0KB) ( 0 )

The administrative center is a core element in the framework of administrative division research. The location, adjustment, and change of a city’s administrative center can significantly impact the spatial form and structure of the city. This paper takes Qingdao City as a case study and utilizes the CLCD dataset, along with GIS spatial analysis methods, to quantitatively measure the spatial and temporal patterns of urban construction land expansion after the relocation of the administrative center. It analyzes the differences in urban built-up area spatial expansion before and after the relocation and explores the mechanisms of how the relocation of the administrative center influences urban spatial expansion. The results show that：1) After relocating the administrative center, Qingdao’s construction land area exhibits higher average values for the number, rate, and intensity of expansion compared to before relocation, indicating that the relocation of the administrative center accelerates urban construction land expansion in Qingdao; 2) The relocation of the administrative center has led to an agglomeration trend in Qingdao’s urban spatial expansion, with a shift towards polycentric agglomeration, and the primary hotspot of spatial expansion lies along the Jiaozhou Bay Ring; 3) Land finance is the direct cause of urban spatial expansion following the relocation of Qingdao’s administrative center. The strengthening of land finance enhances the spatial governance capacity of the government, further promoting the reconfiguration of production factors, urban planning, and urban functions in Qingdao. As a result, this process indirectly influences the city’s spatial expansion. The findings of this study emphasize the significance of incorporating the spatial impact of administrative center relocation into urban planning and development strategies. These findings can serve as a reference for the strategic relocation of urban administrative centers and the planning of future urban development directions.

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