检索结果-南通市图书馆

Journal of Systems Engineering and Electronics 2005年第4期16卷 908-916页

作者： leng xin Liu Degui Song Xiaoqiu Chen Lirong Beijing Inst. of Computer Application and Simulation Technology Beijing 100854 P. R. China Beijing Inst. of Applied Physics and Computational Mathematics Beijing 100088 P. R. China

An idea of relaxing the effect of delay when computing the Runge-Kutta stages in the current step and a class of two-step continuity Runge-Kutta methods （TSCRK） is presented. Their construction, their order conditions and their convergence are studied. The two-step continuity Runge-Kutta methods possess good numerical stability properties and higher stage-order, and keep the explicit process of computing the Runge-Kutta stages. The numerical experiments show that the TSCRK methods are efficient.

关键词： convergence singular delay differential equations two-step continuity Runge-Kutta methods.

A CLASS OF TWO-STEP CONTINUITY RUNGE-KUTTA METHODS FOR SOLVING SINGULAR DELAY DIFFERENTIAL EQUATIONS AND ITS STABILITY ANALYSIS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2005年第6期23卷 647-656页

作者： xin leng De-gui Liu Xiao-qiu Song Li-rong Chen Beijing Institute of Computer Application and Simulation Technology 100854 China Beijing Institute of Applied Physics and Computational Mathematics 100088 China

In this paper, a class of two-step continuity Runge-Kutta（TSCRK） methods for solving singular delay differential equations（DDEs） is presented. Analysis of numerical stability of this methods is given. We consider the two distinct cases：（i）τ≥ h, （ii）τ 〈 h, where the delay τ and step size h of the two-step continuity Runge-Kutta methods are both constant. The absolute stability regions of some methods are plotted and numerical examples show the efficiency of the method.

关键词： Analysis of numerical stability Singular delay differential equations Two-step continuity Runge-Kutta methods

An Improved YOLOv8-Based Method for Real-Time Detection of Harmful Tea Leaves in Complex Backgrounds

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Phyton-International Journal of Experimental Botany 2024年第11期93卷 2963-2981页

作者： xin leng Jiakai Chen Jianping Huang Lei Zhang Zongxuan Li College of Computer and Control Engineering Northeast Forestry UniversityHarbin150040China

Tea,a globally cultivated crop renowned for its uniqueﬂavor proﬁle and health-promoting properties,ranks among the most favored functional beverages ***,diseases severely jeopardize the production and quality of tea leaves,leading to signiﬁcant economic *** early and accurate identiﬁcation coupled with the removal of infected leaves can mitigate widespread infection,manual leaves removal remains time-con-suming and *** robots for pruning can signiﬁcantly enhance efﬁciency and reduce ***-ever,the accuracy of object detection directly impacts the overall efﬁciency of pruning *** complex tea plantation environments,complex image backgrounds,the overlapping and occlusion of leaves,as well as small and densely harmful leaves can all introduce interference *** algorithms perform poorly in detecting small and densely packed *** address these challenges,this paper collected a dataset of 1108 images of harmful tea leaves and proposed the YOLO-DBD *** model excels in efﬁciently identifying harmful tea leaves with various poses in complex backgrounds,providing crucial guidance for the posture and obstacle avoidance of a robotic arm during the pruning *** improvements proposed in this study encompass the Cross Stage Partial with Deformable Convolutional Networks v2(C2f-DCN)module,Bi-Level Routing Atten-tion(BRA),Dynamic Head(DyHead),and Focal Complete Intersection over Union(Focal-CIoU)Loss function,enhancing the model’s feature extraction,computation allocation,and perception *** to the baseline model YOLOv8s,mean Average Precision at IoU 0.5(mAP0.5)increased by 6%,and Floating Point Operations Per second(FLOPs)decreased by 3.3 G.

关键词： Harmful tea leaves YOLO-DBD Focal-CIoU Loss dynamic head Bi-Level Routing Attention

Spatiotemporal propagation dynamics of intense optical pulses in loosely confined gas-filled hollow-core fibers

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics B 2017年第1期26卷 224-228页

作者： Rui-rui Zhao Ding Wang Zhi-yuan Huang Yu-xin leng Ru-xin Li State Key Laboratory of High Field Laser Physics Shanghai Institute of Optics and Fine Mechanics Chinese Academy of Sciences Shanghai 201800 China University of Chinese Academy of Sciences Beijing 100049 China

We numerically study the propagation dynamics of intense optical pulses in gas-filled hollow-core fibers（HCFs）. The spatiotemporal dynamics of the pulses show a transition from tightly confined to loosely confined characteristics as the fiber core is increased, which manifests as a deterioration in the spatiotemporal uniformity of the beam. It is found that using the gas pressure gradient does not enhance the beam quality in large-core HCFs, while inducing a positive chirp in the pulse to lower the peak power can improve the beam quality. This indicates that the self-focusing effect in the HCFs is the main driving force for the propagation dynamics. It also suggests that pulses at longer wavelengths are more suitable for HCFs with large cores because of the lower critical power of self-focusing, which is justified by the numerical simulations. These results will benefit the generation of energetic few-cycle pulses in large-core HCFs.

关键词： spatiotemporal dynamics hollow-core fiber longer wavelengths

Dispersal of invasive Phytolacca americana seeds by birds in an urban garden in China

在线全文

学校读者我要写书评

暂无评论

Integrative Zoology 2017年第1期12卷 26-31页

作者： Ning LI Wen YANG Shubo FANG xinhai LI Zhanchen LIU xin leng Shuqing AN School of Life Science Nanjing UniversityNanjingChina Fisheries and Life Science School Shanghai Ocean UniversityShanghaiChina Institute of Zoology Chinese Academy of SciencesBeijingChina College of Biology and the Environment Nanjing Forestry UniversityNanjingChina

Although seed dispersal is a key process determining the regeneration and spread of invasive plant populations,few studies have explicitly addressed the link between dispersal vector behavior and seedling recruitment to gain insight into the invasion process within an urban garden *** evaluated the role of bird vectors in the dispersal of pokeweed(Phytolacca americana),a North American herb that is invasive in urban gardens in *** *** attracted both generalist and specialist bird species that fed on and dispersed its *** generalist species Pycnonotus sinensis and Urocissa erythrorhyncha were the most frequent *** numbers of *** were strongly associated with the perching behavior of frugivorous *** newly recruited bird species use seedling-safe perching sites,the *** will regenerate faster,which would enhance its invasive *** on our observations,we conclude that the 2 main bird vectors,*** and ***,provide potential effective dispersal agents for *** results highlight the role of native birds in seed dispersal of invasive plants in urban gardens.

关键词： dispersal patterns frugivorous bird Phytolacca americana seed dispersal urban ecosystem

Generation of few-cycle radially-polarized infrared pulses in a gas-filled hollow-core fiber

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics B 2018年第10期27卷 333-340页

作者： Rui-Rui Zhao Zhi-Yuan Huang Ding Wang Yu Zhao Yu-xin leng Ru-xin Li State Key Laboratory of High Field Laser Physics Shanghai Institute of Optics and Fine Mechanics Chinese Academy of Sciences Shanghai 201800 China University of Chinese Academy of Sciences Beijing 100049 China

We perform a numerical study for temporally compressing radially-polarized（RP） infrared pulses in a gas-filled hollow-core fiber（HCF）. The dynamic transmission and nonlinear compression of RP pulses centered at wavelengths of0.8 m, 1.8 m, 3.1 m, and 5.0 m in HCFs are simulated. By comparing the propagation of pulses with the same optical cycles and intensity, we find that under proper conditions these pulses can be compressed down to 2–3 cycles. In the transverse direction, the spatiotemporal beam profile ameliorates from 0.8-m to 1.8-m and 3.1-m pulses before the appearance of high-order dispersion. These results show an alternative method of scaling generation for delivering RP infrared pulses in gas-filled HCFs, which can obtain energetic few-cycle pulses, and will be beneficial for relevant researches in the infrared scope.

关键词： pulse compression polarization infrared pulses hollow-core fibers

Observations of carbon–carbon coupling of 4,4''-dibromo-p-terphenyl on Cu(110) surface at molecular level

在线全文

学校读者我要写书评

暂无评论

Chinese Chemical Letters 2017年第1期28卷 24-28页

作者： xin-Li leng Li-Li Song Yan Lu Xiao-Qing Liu Li Wang Department of Physics Nanchang University Nanchang 330031 China Department of Chemistry Nanchang University Nanchang 330031 China

The carbon–carbon couplings of 4,4＇＇-dibromo-p-terphenyl（DBTP） on Cu（110） surface have been investigated at a single molecular level by scanning tunneling microscopy. After annealing at 353 K, a mixture of parallel non-organometallic and organometallic intermediates of DBTP molecules along the[1–10] direction of the surface has been observed. Further annealing at 393 K causes one group of molecules to form oligomers with para-para and para-meta motifs via Ullmann reaction and the other group of molecules to synthesize oligomers with meta-meta motifs via direct carbon–carbon coupling reaction. Statistical results directly reveal that the occurrence of reaction type is strongly related to the initial binding configuration of DBTP molecules.

关键词： Carbon-carbon coupling Ullmann coupling Organometallic intermediate Selective C-H activation Oligomer

Energetic few-cycle pulse compression in gas-filled hollow core fiber with concentric phase mask

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2019年第6期28卷 213-222页

作者： Yu Zhao Zhi-Yuan Huang Rui-Rui Zhao Ding Wang Yu-xin leng State Key Laboratory of High Field Laser Physics Shanghai Institute of Optics and Fine MechanicsChinese Academy of SciencesShanghai 201800China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing 100049China

The compression of high-energy, linearly polarized pulses in a gas-filled hollow core fiber(HCF) by using a concentric phase mask is studied theoretically. Simulation results indicate that using a properly designed concentric phase mask, a40-fs input pulse centered at 800 nm with energy up to 10.0 mJ can be compressed to a full width at half maximum(FWHM) of less than 5 fs after propagating through a neon-filled HCF with a length of 1 m and diameter of 500 μm with a transmission efficiency of 67%, which is significantly higher than that without a concentric phase mask. Pulses with energy up to 20.0 mJ can also be efficiently compressed to less than 10 fs with the concentric phase mask. The higher efficiency due to the concentric phase mask can be attributed to the redistribution of the transverse intensity profile, which reduces the effect of ionization. The proposed method exhibits great potential for generating few-cycle laser pulse sources with high energy by the HCF compressor.

关键词： pulse compression hollow-core fiber phase mask

Effects of Logging on the Genetic Diversity of Quercus tiaoloshanica Chun et Ko in a Tropical Montane Forest of Hainan Island, Southern China

在线全文

学校读者我要写书评

暂无评论

Journal of Integrative Plant Biology 2005年第10期47卷 1184-1192页

作者： Jian-Wei ZHENG Shu-Qing AN Lin CHEN xin leng Zhong-Sheng WANG Hua-Jun XIANG Laboratory of Forest Ecology and Global Changes School of Life Science Nanjing University Nanjing 210093 China

Quercus tiaoloshanica Chun et Ko, which has a narrow range of distribution, is one of the important endemic species of the tropical montane rain forest on Hainan Island, southern China. Long-term logging and habitat destruction have resulted in population decline and distribution retreat of Q. tiaoloshanica. To determine the impact of logging on the genetic diversity of Q. tiaoloshanica, the authors investigated the genetic structures using amplified fragment length polymorphism markers in four regenerated stands after logging and in one unlogged stand. Compared with the unlogged stand, the effective number of alleles per locus dropped by 1.0% in selective logging stands and by 2.0% in clear logging stands, corresponding to reductions of 3.8% and 5.2%, respectively, in mean Nei＇s gene diversity and 2.9% and 3.5%, respectively, in mean Shannon diversity index. No substantial genetic erosion was detected in any of the regenerated stands owing to the high tree density and high heterogeneity of the Q. tiaoloshanica stands investigated. Meanwhile, there was no natural regeneration of the species observed in a Dacrydium pierrei Hickel plantation 700 m away from the regenerated stands, suggesting the limited ability of seed dispersal of Q. tiaoloshanica. Clear logging should be undertaken cautiously because the total number of plant species dropped by 15.2% in the clear-logged stands compared with the unlogged stand. To conserve the genetic diversity of this species, as well as the plant biodiversity of tropical forests, the habitats of Q. tiaoloshanica should be protected against exploitation in terms of agricultural or other forms of land use, and some mature trees should be preserved as seed sources to maintain an adequate regeneration base for this species in the management of logging.

关键词： amplified fragment length polymorphism genetic erosion logging Quercus tiaoloshanica tropical forest.

High-precision X-ray polarimeter based on channel-cut crystals

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Nuclear Science and Techniques 2024年第3期35卷 30-39页

作者： Shang-Yu Si Zhong-Liang Li Wen-Hong Jia Lian Xue Hong-xin Luo Jian-Cai Xu Bai-Fei Shen Lin-Gang Zhang Liang-Liang Ji Yu-xin leng Ren-Zhong Tai Shanghai Institute of Applied Physics Chinese Academy of SciencesShanghai 201800China University of Chinese Academy of Sciences Beijing 100049China Shanghai Synchrotron Radiation Facility Shanghai Advanced Research InstituteChinese Academy of SciencesShanghai 201204China Shanghai Institute of Optics and Fine Mechanics Chinese Academy of SciencesShanghai 201800China

We report on using synthetic silicon for a high-precision X-ray polarimeter comprising a polarizer and an analyzer,each based on a monolithic channel-cut crystal used at multiple Brewster reflections with a Bragg angle very close to 45°.Experiments were performed at the BL09B bending magnet beamline of the Shanghai Synchrotron Radiation Facility using a Si(800)crystal at an X-ray energy of 12.914 keV.A polarization purity of 8.4×10^(-9)was *** result is encouraging,as the measured polarization purity is the best-reported value for the bending magnet ***,this is the firstly systematic study on the hard X-ray polarimeter in China,which is crucial for exploring new physics,such as verifying vacuum birefringence.

关键词： X-ray polarimeter Vacuum birefringence Synchrotron radiation Channel-cut crystal