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Winter-spring minimum temperature variations inferred from tree-ringδ13C in southeastern China

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Journal of Forestry Research 2024年第5期35卷 182-190页

作者： Wenli Li Feifei Zhou Heng Zhang Keyan fang Key Laboratory of Humid Subtropical Eco-Geographical Process(MOE) College of Geographic SciencesFujian Normal UniversityFuzhou 350007People’s Republic of China

Long-term temperature variations inferred from high-resolution proxies provide an important context to evaluate the intensity of current ***,tem-perature reconstructions in humid southeastern China are scarce and particularly lack long-term data,limiting us to obtain a complete picture of regional temperature *** this study,we present a well-verified reconstruction of winter-spring(January–April)minimum temperatures over southeastern China based on stable carbon isotopic(δ^(13)C)records of tree rings from Taxus wallichiana *** from 1860 to *** reconstruction accounted for 56.4%of the total observed *** periods occurred during the 1860s–1910s and 1960s–*** temperatures have had an upward trend since the 1920s,most of the cold extremes were in recent *** El Niño-Southern Oscillation(ENSO)variance acted as a key modulator of regional winter-spring minimum temperature ***,teleconnections between them were a nonlinear process,i.e.,a reduced or enhanced ENSO variance may result in a weakened or intensified temperature-ENSO relationship.

关键词： Tree rings Carbon isotope Southeastern China Extreme coldness El nino-southern oscillation

Diophantine equations and Fermat's last theorem for multivariate(skew-)polynomials

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Applied Mathematics(A Journal of Chinese Universities) 2024年第1期39卷 159-173页

作者： PAN Jie JIA Yu-ming LI fang School of Mathematical Sciences Zhejiang UniversityHangzhou 310058China Henan Experimental High School Zhengzhou 450003China

Fermat’s Last Theorem is a famous theorem in number theory which is diﬃcult to ***,it is known that the version of polynomials with one variable of Fermat’s Last Theorem over C can be proved very *** aim of this paper is to study the similar problems about Fermat’s Last Theorem for multivariate(skew)-polynomials with any characteristic.

关键词： Fermat's last theorem polynomial ring skew polynomial ring

Finite Groups with Some Bounded Codegrees

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Acta Mathematica Sinica,English Series 2024年第7期40卷 1778-1784页

作者： Dong fang YANG Yu ZENG Heng LV School of Mathematics and Statistics Southwest UniversityChongqing400715P.R.China Department of Mathematics Changshu Institute of TechnologyChangshu215500P.R.China

For a characterχof a finite group G,the number cod(χ) := ∣G:ker(χ)∣/χ(1)is called the codegree ofχ.In this paper,we give a solvability criterion for a finite group G depending on the minimum of the ratioχ(1)^(... 详细信息

关键词： Finite group codegree degree simple group

Nonlinear metamaterial enabled aeroelastic vibration reduction of a supersonic cantilever wing plate

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Applied Mathematics and Mechanics(English Edition) 2024年第10期45卷 1749-1772页

作者： Peng SHENG Xin fang Dianlong YU Jihong WEN Laboratory of Science and Technology on Integrated Logistics Support College of Intelligence Science and Technology National University of Defense Technology

The violent vibration of supersonic wings threatens aircraft safety. This paper proposes the strongly nonlinear acoustic metamaterial(NAM) method to mitigate aeroelastic vibration in supersonic wing plates. We employ the cantilever plate to simulate the practical behavior of a wing. An aeroelastic vibration model of the NAM cantilever plate is established based on the mode superposition method and a modified third-order piston theory. The aerodynamic properties are systematically studied using both the timedomain integration and frequency-domain harmonic balance methods. While presenting the flutter and post-flutter behaviors of the NAM wing, we emphasize more on the preflutter broadband vibration that is prevalent in aircraft. The results show that the NAM method can reduce the low-frequency and broadband pre-flutter steady vibration by 50%–90%, while the post-flutter vibration is reduced by over 95%, and the critical flutter velocity is also slightly delayed. As clarified, the significant reduction arises from the bandgap, chaotic band, and nonlinear resonances of the NAM plate. The reduction effect is robust across a broad range of parameters, with optimal performance achieved with only10% attached mass. This work offers a novel approach for reducing aeroelastic vibration in aircraft, and it expands the study of nonlinear acoustic/elastic metamaterials.

关键词： 74H45 fluid-structure interaction hypersonic aeroelastic vibration nonlinear acoustic metamaterial (NAM) O328 vibration reduction

Skill enhancement learning with knowledge distillation

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Science China(Information Sciences) 2024年第8期67卷 206-220页

作者： Naijun LIU Fuchun SUN Bin fang Huaping LIU Department of Computer Science and Technology Tsinghua University

Skill learning through reinforcement learning has significantly progressed in recent years. However, it often struggles to efficiently find optimal or near-optimal policies due to the inherent trial-and-error exploration in reinforcement learning. Although algorithms have been proposed to enhance skill learning efficacy, there is still much room for improvement in terms of skill learning performance and training stability. In this paper, we propose an algorithm called skill enhancement learning with knowledge distillation(SELKD), which integrates multiple actors and multiple critics for skill learning. SELKD employs knowledge distillation to establish a mutual learning mechanism among actors. To mitigate critic overestimation bias,we introduce a novel target value calculation method. We also perform theoretical analysis to ensure the convergence of SELKD. Finally, experiments are conducted on several continuous control tasks, illustrating the effectiveness of the proposed algorithm.

关键词： skill learning enhancement learning reinforcement learning knowledge distillation

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Data-driven discovery of linear dynamical systems from noisy data

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Science China(Technological Sciences) 2024年第1期67卷 121-129页

作者： WANG YaSen YUAN Ye fang HuaZhen DING Han School of Mechanical Science and Engineering Huazhong University of Science and TechnologyWuhan 430074China State Key Lab of Digital Manufacturing Equipment and Technology Huazhong University of Science and TechnologyWuhan 430074China School of Artificial Intelligence and Automation Huazhong University of Science and TechnologyWuhan 430074China Department of Mechanical Engineering University of KansasLawrence 66045USA

In modern science and engineering disciplines,data-driven discovery methods play a fundamental role in system modeling,as data serve as the external representations of the intrinsic mechanisms within ***,empirical data contaminated by process and measurement noise remain a significant obstacle for this type of *** this study,we have developed a data-driven method capable of directly uncovering linear dynamical systems from noisy *** method combines the Kalman smoothing and sparse Bayesian learning to decouple process and measurement noise under the expectation-maximization framework,presenting an analytical method for alternate state estimation and system ***,the discovered model explicitly characterizes the probability distribution of process and measurement noise,as they are essential for filtering,smoothing,and stochastic *** have successfully applied the proposed algorithm to several simulation *** results demonstrate its potential to enable linear dynamical system discovery in practical applications where noise-free data are intractable to capture.

关键词： system identification sparse Bayesian learning Kalman smoothing process and measurement noise

Surface engineering with ionic polymers on membranes for boron removal

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Frontiers of Chemical Science and Engineering 2024年第5期18卷 61-69页

作者： Xiting Zhang Chenyi fang J Paul Chen Sui Zhang Department of Chemical and Biomolecular Engineering National University of SingaporeSingapore 117576Singapore Department of Civil and Environmental Engineering National University of SingaporeSingapore 119260Singapore College of Chemistry and Environmental Engineering Shenzhen UniversityShenzhen 518060China

Removal of boric acid from seawater and wastewater using reverse osmosis membrane technologies is imperative and yet remains inadequately addressed by current commercial *** research efforts performed post-modification of reverse osmosis membranes to enhance boron rejection,which is usually accompanied by substantial sacrifice in water *** study delves into the surface engineering of low-pressure reverse osmosis membranes,aiming to elevate boron removal efficiency while maintaining optimal salt rejection and water *** were modified by the self-polymerization and co-deposition of dopamine and polystyrene sulfonate at varying ratios and *** surfaces became smoother and more hydrophilic after *** optimum membrane exhibited a water permeability of 9.2±0.1 L·m^(-2)·h^(-1)·bar^(-1),NaCl rejection of 95.8%±0.3%,and boron rejection of 49.7%±0.1% and 99.6%±0.3% at neutral and alkaline pH,*** water permeability is reduced by less than 15%,while the boron rejection is 3.7 times higher compared to the blank *** research provides a promising avenue for enhancing boron removal in reverse osmosis membranes and addressing water quality concerns in the desalination process.

关键词： membrane low-pressure reverse osmosis boron surface engineering

Grain size effect on the assembly quality of micro-scaled barrel formed by microforming

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Advances in Manufacturing 2024年第1期12卷 19-32页

作者： Dien Hu Jieyichen fang Feng Zeng Ming-Wang Fu Department of Mechanical Engineering Research Institute of Advanced ManufacturingThe Hong Kong Polytechnic UniversityHung HomKowloonHong KongPeople’s Republic of China Xiamen Yulong Machinery Co.Ltd. Xiamen361023FujianPeople’s Republic of China

In this research,a method employing micro-extrusion was designed to produce the micro-scaled barrel-shaped parts with complex geometrical features to study the feasibility of the proposed microforming method and its grain size effect on the formability of the complicated internal features in terms of deformation behavior,material evolution,accuracy of dimensions and final components *** results reveal that the deformation behavior is highly affected by grain size and becomes unpredictable with increased grain *** addition,assembly parameters including feature dimension,tolerance and coaxiality also vary with grain size,and the variation of grain size needs to be accommodated by different assembly types,viz.,clearance fit or transition *** the microstructural evolution aspect,it was identified there were two dead zones and four shear bands,and the formation of these deformation zones was barely affected by the variation in grain *** bulges,cracks,and fracture induced voids were observed on the surface of the final components,tailoring the microstructure of the working material with finer grains could significantly avoid these *** study advances the understanding of forming microparts by extrusion processes and provides guidance for microforming of similar microparts.

关键词： Microformed part Size effect Extrusion Microstructural evolution Dimensions Assembly accuracy

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梅花鹿的微卫星多态性及种群的遗传结构

兽类学报 2008年第2期28卷 109-116页

作者：吴华胡杰万秋红方盛国刘武华章叔岩浙江大学国家濒危野生动植物种质基因保护中心江西省桃红岭国家级自然保护区彭泽332700 浙江省清凉峰国家级自然保护区临安311321

梅花鹿是我国极度濒危的鹿科动物,其野生种群已濒临灭绝。为了探讨我国野生梅花鹿的保护和管理对策,我们选用了16个微卫星位点检测来自东北、四川、江西和浙江种群的122份样品,以此分析我国野生梅花鹿种群的遗传多样性和遗传结构。费希... 详细信息

梅花鹿是我国极度濒危的鹿科动物,其野生种群已濒临灭绝。为了探讨我国野生梅花鹿的保护和管理对策,我们选用了16个微卫星位点检测来自东北、四川、江西和浙江种群的122份样品,以此分析我国野生梅花鹿种群的遗传多样性和遗传结构。费希尔确切性检验表明,四个种群中均存在偏离哈迪-温伯格平衡的现象。与其它的濒危动物相比,中国梅花鹿有着相对较高的遗传多样性:每个位点的平均等位基因数为4个,平均期望杂合度为0.559。四个种群中,东北种群拥有最高的平均等位基因数(n=3.688),东北种群、四川种群、江西种群以及浙江种群的平均期望杂合度分别为0.584,0.477,0.585和0.589,它们之间不存在显著的差异。同时,利用逐步突变模型、双相突变模型和无限等位基因突变模型检测了种群的瓶颈效应,结果表明:除四川种群外,其他种群在近期内都经历过遗传瓶颈。费希尔确切性检验及配对样品FST的结果均表明:四个梅花鹿种群间存在显著的遗传分化(P<0.001)。因此,我们建议将我国梅花鹿的野生种群划分为4个管理单元进行保护和管理。

关键词：梅花鹿微卫星遗传多样性种群遗传结构管理单元