期刊文献+
共找到2,561篇文章
< 1 2 129 >
每页显示 20 50 100
Unveiling the challenges encountered by newly graduated nurses during night shifts:A descriptive qualitative study
1
作者 Naomi Kisanuki Miyuki Takase Masako Yamamoto 《International Journal of Nursing Sciences》 CSCD 2024年第4期447-456,共10页
Objectives:Newly graduated nurses commence night shifts during a phase of heightened vulnerability to reality shock,exacerbating the challenges faced by these graduates.Therefore,this study aimed to identify the chall... Objectives:Newly graduated nurses commence night shifts during a phase of heightened vulnerability to reality shock,exacerbating the challenges faced by these graduates.Therefore,this study aimed to identify the challenges experienced by newly graduated nurses when undertaking night shifts in order to help identify a strategy for supporting their adaptation to these shifts.Methods:Semi-structured personal interviews were used to collect data.Fifteen newly graduated nurses were selected to participate in the study by purposive sampling method from November 2021 to March 2022 in one of four general hospitals situated in the southwestern region of Japan.Semi-structured interviews were analyzed by using thematic analysis.Results:The analysis revealedfive central themes and nine subthemes:challenges in task efficiency(task organization challenges,challenges in time-constrained task performance),challenges in responding to patients’changing conditions(challenges in responding to patients’irregular conditions,challenges in responding to nighttime changes in patients’behaviors),challenges in independent practice(challenges in engaging in independent nursing practice,challenges in dealing with unexpected events),challenges in establishing collaborative relationships(challenges in working closely with other staff,challenges in establishing collaborative relationships during night shifts with limited resources),challenges in adapting to shift work(challenges in managing physical conditions for shift work).Conclusions:Newly graduated nurses often encounter challenges in performing their tasks during the transition period.When working night shifts,they face additional hurdles unique to nocturnal duties.Thefindings underscore the necessity for these graduates to develop night shift-specific readiness to effectively navigate the demands inherent in such work schedules. 展开更多
关键词 CHALLENGE Newly graduated nurses Patient care management Qualitative research Shift work schedule Night shifts
下载PDF
Climate-change habitat shifts for the vulnerable endemic oak species(Quercus arkansana Sarg.)
2
作者 Suresh Chandra Subedi Seth Drake +1 位作者 Binaya Adhikari Mark V.Coggeshall 《Journal of Forestry Research》 SCIE EI CAS CSCD 2024年第1期117-127,共11页
Quercus arkansana(Arkansas oak)is at risk of becoming endangered,as the total known population size is represented by a few isolated populations.The potential impact of climate change on this species in the near futur... Quercus arkansana(Arkansas oak)is at risk of becoming endangered,as the total known population size is represented by a few isolated populations.The potential impact of climate change on this species in the near future is high,yet knowledge of its predicted effects is limited.Our study utilized the biomod2 R package to develop habi-tat suitability ensemble models based on bioclimatic and topographic environmental variables and the known loca-tions of current distribution of Q.arkansana.We predicted suitable habitats across three climate change scenarios(SSP1-2.6,SSP2-4.5,and SSP5-8.5)for 2050,2070,and 2090.Our findings reveal that the current suitable habitat for Q.arkansana is approximately 127,881 km^(2) across seven states(Texas,Arkansas,Alabama,Louisiana,Mississippi,Georgia,and Florida);approximately 9.5%is encompassed within state and federally managed protected areas.Our models predict that all current suitable habitats will disap-pear by 2050 due to climate change,resulting in a northward shift into new regions such as Tennessee and Kentucky.The large extent of suitable habitat outside protected areas sug-gests that a species-specific action plan incorporating pro-tected areas and other areas may be crucial for its conserva-tion.Moreover,protection of Q.arkansana habitat against climate change may require locally and regionally focused conservation policies,adaptive management strategies,and educational outreach among local people. 展开更多
关键词 Biomod2 Climate change CONSERVATION Habitat loss Habitat shift Species distribution modeling Oak species
下载PDF
Calculation and Analysis of TVMS Considering Profile Shifts and Surface Wear Evolution Process of Spur Gear
3
作者 Wenzheng Liu Rupeng Zhu +1 位作者 Wenguang Zhou Jingjing Wang 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2024年第3期136-150,共15页
Profile shift is a highly effective technique for optimizing the performance of spur gear transmission systems.However,tooth surface wear is inevitable during gear meshing due to inadequate lubrication and long-term o... Profile shift is a highly effective technique for optimizing the performance of spur gear transmission systems.However,tooth surface wear is inevitable during gear meshing due to inadequate lubrication and long-term operation.Both profile shift and tooth surface wear(TSW)can impact the meshing characteristics by altering the involute tooth profile.In this study,a tooth stiffness model of spur gears that incorporates profile shift,TSW,tooth deformation,tooth contact deformation,fillet-foundation deformation,and gear body structure coupling is established.This model efficiently and accurately determines the time-varying mesh stiffness(TVMS).Additionally,an improved wear depth prediction method for spur gears is developed,which takes into consideration the mutually prime teeth numbers and more accurately reflects actual gear meshing conditions.Results show that consideration of the mutual prime of teeth numbers will have a certain impact on the TSW process.Furthermore,the finite element method(FEM)is employed to accurately verify the values of TVMS and load sharing ratio(LSR)of profile-shifted gears and worn gears.This study quantitatively analyzes the effect of profile shift on the surface wear process,which suggests that gear profile shift can partially alleviate the negative effects of TSW.The contribution of this study provides valuable insights into the design and maintenance of spur gear systems. 展开更多
关键词 Profile shift Tooth surface wear Structure coupling effect Improved wear depth prediction method TVMS
下载PDF
DAO to HANOI via DeSci: AI Paradigm Shifts from AlphaGo to ChatGPT 被引量:16
4
作者 Qinghai Miao Wenbo Zheng +3 位作者 Yisheng Lv Min Huang Wenwen Ding Fei-Yue Wang 《IEEE/CAA Journal of Automatica Sinica》 SCIE EI CSCD 2023年第4期877-897,共21页
From AlphaGo to ChatGPT,the field of AI has launched a series of remarkable achievements in recent years.Analyzing,comparing,and summarizing these achievements at the paradigm level is important for future AI innovati... From AlphaGo to ChatGPT,the field of AI has launched a series of remarkable achievements in recent years.Analyzing,comparing,and summarizing these achievements at the paradigm level is important for future AI innovation,but has not received sufficient attention.In this paper,we give an overview and perspective on machine learning paradigms.First,we propose a paradigm taxonomy with three levels and seven dimensions from a knowledge perspective.Accordingly,we give an overview on three basic and twelve extended learning paradigms,such as Ensemble Learning,Transfer Learning,etc.,with figures in unified style.We further analyze three advanced paradigms,i.e.,AlphaGo,AlphaFold and ChatGPT.Second,to enable more efficient and effective scientific discovery,we propose to build a new ecosystem that drives AI paradigm shifts through the decentralized science(DeSci)movement based on decentralized autonomous organization(DAO).To this end,we design the Hanoi framework,which integrates human factors,parallel intelligence based on a combination of artificial systems and the natural world,and the DAO to inspire AI innovations. 展开更多
关键词 ChatGPT decentralized science(DeSci) decentralized autonomous organization(DAO) machine learning paradigm shift
下载PDF
Discrete Phase Shifts Control and Beam Selection in RIS-Aided MISO System via Deep Reinforcement Learning 被引量:1
5
作者 Dongting Lin Yuan Liu 《China Communications》 SCIE CSCD 2023年第8期198-208,共11页
Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal ... Reconfigurable intelligent surface(RIS)for wireless networks have drawn lots of attention in both academic and industry communities.RIS can dynamically control the phases of the reflection elements to send the signal in the desired direction,thus it provides supplementary links for wireless networks.Most of prior works on RIS-aided wireless communication systems consider continuous phase shifts,but phase shifts of RIS are discrete in practical hardware.Thus we focus on the actual discrete phase shifts on RIS in this paper.Using the advanced deep reinforcement learning(DRL),we jointly optimize the transmit beamforming matrix from the discrete Fourier transform(DFT)codebook at the base station(BS)and the discrete phase shifts at the RIS to maximize the received signal-to-interference plus noise ratio(SINR).Unlike the traditional schemes usually using alternate optimization methods to solve the transmit beamforming and phase shifts,the DRL algorithm proposed in the paper can jointly design the transmit beamforming and phase shifts as the output of the DRL neural network.Numerical results indicate that the DRL proposed can dispose the complicated optimization problem with low computational complexity. 展开更多
关键词 reconfigurable intelligent surface discrete phase shifts transmit beamforming deep reinforcement learning
下载PDF
Dynamic modeling of total ionizing dose-induced threshold voltage shifts in MOS devices
6
作者 陆广宝 刘俊 +2 位作者 张传国 高扬 李永钢 《Chinese Physics B》 SCIE EI CAS CSCD 2023年第1期113-122,共10页
The total ionizing dose(TID) effect is a key cause for the degradation/failure of semiconductor device performance under energetic-particle irradiation. We developed a dynamic model of mobile particles and defects by ... The total ionizing dose(TID) effect is a key cause for the degradation/failure of semiconductor device performance under energetic-particle irradiation. We developed a dynamic model of mobile particles and defects by solving the rate equations and Poisson's equation simultaneously, to understand threshold voltage shifts induced by TID in silicon-based metal–oxide–semiconductor(MOS) devices. The calculated charged defect distribution and corresponding electric field under different TIDs are consistent with experiments. TID changes the electric field at the Si/SiO_(2) interface by inducing the accumulation of oxide charged defects nearby, thus shifting the threshold voltage accordingly. With increasing TID, the oxide charged defects increase to saturation, and the electric field increases following the universal 2/3 power law. Through analyzing the influence of TID on the interfacial electric field by different factors, we recommend that the radiation-hardened performance of devices can be improved by choosing a thin oxide layer with high permittivity and under high gate voltages. 展开更多
关键词 dynamic modeling total ionizing dose threshold voltage shifts radiation-hardening
下载PDF
Large spatial shifts of reflected light beam off biaxial hyperbolic materials
7
作者 沈加国 哈思内恩 +5 位作者 宋浩元 周胜 付淑芳 王选章 王暄 张强 《Chinese Physics B》 SCIE EI CAS CSCD 2023年第11期465-471,共7页
Many optical systems that deal with polarization rely on the adaptability of controlling light reflection in the lithography-free nanostructure. In this study, we explore the Goos–H?nchen(GH) shift and Imbert–Fedoro... Many optical systems that deal with polarization rely on the adaptability of controlling light reflection in the lithography-free nanostructure. In this study, we explore the Goos–H?nchen(GH) shift and Imbert–Fedorov(IF) shift in a biaxial hyperbolic film on a uniaxial hyperbolic substrate. This research statistically calculates and analyzes the GH shift and IF shift for the natural biaxial hyperbolic material(NBHM). We select the surface with the strongest anisotropy within the NBHM and obtain the complex beam-shift spectrum. By incorporating the NBHM film, the GH shift caused by a transversely magnetic incident-beam on the surface increases significantly compared with that on the uniaxial hyperbolic material. The maximum of GH shift can reach 86 λ0at about 841 cm-1when the thickness of NBHM is 90 nm, and the IF shift can approach 2.7 λ0for a circularly-polarized beam incident on a 1700-nm-thick NBHM. It is found that the spatialshift increases when a highly anisotropic hyperbolic polariton is excited in hyperbolic material, where the shift spectrum exhibits an oscillating behaviour accompanied with sharp shift peak(steep slope). This large spatial shift may provide an alternative strategy to develop novel sub-micrometric optical devices and biosensors. 展开更多
关键词 Goos-Hanchen shift Imbert-Fedorov shift α-MoO_(3)
下载PDF
Identifying the Cultural Shifts and Societal Changes That Facilitated the Rise in Box Office Performance of Chinese Women’s Cinema in the 21st Century
8
作者 CUI Yuekun 《Psychology Research》 2023年第12期577-599,共23页
With the gradual improvement of Chinese women’s status in the 21st century,gender studies and gender relations have become one of the hottest topics in Chinese society,which consequently prompted Chinese Women’s Cin... With the gradual improvement of Chinese women’s status in the 21st century,gender studies and gender relations have become one of the hottest topics in Chinese society,which consequently prompted Chinese Women’s Cinema to attract the attention of larger audiences.With regard to the box office performance of Chinese Women’s Cinema,there seems to be a gap in research in finding an association between women’s status and the relevant films’box office performance.The purpose of this research is to outline the underlying reasons for the changes in gender roles and gender representation in the Chinese film industry over the past few decades in order to better understand this expansive social change in the 21st century.This study provides a comprehensive analysis through the use of questionnaires to better understand society’s attitude towards gender representation within the film industry.The questionnaire findings indicate that there is a direct correlation between people’s awareness of women’s changing status and gender equality and their acceptance of materials produced by Chinese Women’s Cinema.At the some time,it highlights that the Chinese government’s support and initiatives for gender equality have had a significant impact on the general popularity of Chinese Women’s Cinema.The significance of this research is to effectively popularize Chinese Women’s Cinema culture and the box office growth by understanding the social attitude towards gender representation in the Chinese film industry and to provide relevant information about the development direction and trend of Chinese Women’s Cinema.Furthermore,this research aims to provide foundational support for gender equality and help to understand the underlying factors that society needs to promote gender equality. 展开更多
关键词 Chinese Women’s Cinema Film Box Office Gender Equality Social Change Cultural shifts
下载PDF
Mean Shift跟踪算法创新实验项目设计
9
作者 王辉 王雪莹 于立君 《实验室科学》 2024年第1期12-16,共5页
视频跟踪算法是计算机视觉实践课程中比较受关注的实验项目。针对突变情况下传统Mean Shift跟踪算法无法实时准确跟踪的问题,设计了基于模板更新和线性预估的Mean Shift跟踪算法创新实验项目。在模板更新策略下,引入背景模板,通过将原... 视频跟踪算法是计算机视觉实践课程中比较受关注的实验项目。针对突变情况下传统Mean Shift跟踪算法无法实时准确跟踪的问题,设计了基于模板更新和线性预估的Mean Shift跟踪算法创新实验项目。在模板更新策略下,引入背景模板,通过将原目标模板和背景模板与设定的阈值进行比较来对干扰因素进行判定,当干扰因素判定目标受到遮挡时,引入线性预估方程进行目标位置预测,有效解决目标在遮挡情况下跟踪丢失的问题。通过对测试视频的跟踪效果和性能进行对比分析,验证了算法在突变情况下相较于传统算法具有更好的抗干扰能力。以算法创新设计为核心,通过开放性创新实验项目的选题、设计、答辩、反馈的闭环实验过程,有效提高了学生算法创新设计能力。 展开更多
关键词 Mean Shift跟踪算法 模板更新 线性预估 抗干扰
下载PDF
Constraints on Characteristics and Distribution of Gas Hydrate and Free Gas Using Broad-Band Processing of Three-Dimensional Seismic Data 被引量:2
10
作者 WANG Xiujuan ZHOU Jilin +7 位作者 LI Sanzhong LI Lixia LI Jie LI Yuanping WANG Linfei SU Pibo JIN Jiapeng GONG Zhi 《Journal of Ocean University of China》 SCIE CAS CSCD 2024年第5期1233-1247,共15页
Gas hydrate drilling expeditions in the Pearl River Mouth Basin,South China Sea,have identified concentrated gas hydrates with variable thickness.Moreover,free gas and the coexistence of gas hydrate and free gas have ... Gas hydrate drilling expeditions in the Pearl River Mouth Basin,South China Sea,have identified concentrated gas hydrates with variable thickness.Moreover,free gas and the coexistence of gas hydrate and free gas have been confirmed by logging,coring,and production tests in the foraminifera-rich silty sediments with complex bottom-simulating reflectors(BSRs).The broad-band processing is conducted on conventional three-dimensional(3D)seismic data to improve the image and detection accuracy of gas hydratebearing layers and delineate the saturation and thickness of gas hydrate-and free gas-bearing sediments.Several geophysical attributes extracted along the base of the gas hydrate stability zone are used to demonstrate the variable distribution and the controlling factors for the differential enrichment of gas hydrate.The inverted gas hydrate saturation at the production zone is over 40% with a thickness of 90 m,showing the interbedded distribution with different boundaries between gas hydrate-and free gas-bearing layers.However,the gas hydrate saturation value at the adjacent canyon is 70%,with 30-m-thick patches and linear features.The lithological and fault controls on gas hydrate and free gas distributions are demonstrated by tracing each gas hydrate-bearing layer.Moreover,the BSR depths based on broad-band reprocessed 3D seismic data not only exhibit variations due to small-scale topographic changes caused by seafloor sedimentation and erosion but also show the upward shift of BSR and the blocky distribution of the coexistence of gas hydrate and free gas in the Pearl River Mouth Basin. 展开更多
关键词 gas hydrate free gas shift of BSR broad-band processing
下载PDF
On the functions of astrocyte-mediated neuronal slow inward currents 被引量:2
11
作者 Balázs Pál 《Neural Regeneration Research》 SCIE CAS CSCD 2024年第12期2602-2612,共11页
Slow inward currents are known as neuronal excitatory currents mediated by glutamate release and activation of neuronal extra synaptic N-met hyl-D-aspartate receptors with the contribution of astrocytes.These events a... Slow inward currents are known as neuronal excitatory currents mediated by glutamate release and activation of neuronal extra synaptic N-met hyl-D-aspartate receptors with the contribution of astrocytes.These events are significantly slower than the excitatory postsynaptic currents.Parameters of slow inward currents are determined by seve ral factors including the mechanisms of astrocytic activation and glutamate release,as well as the diffusion pathways from the release site towards the extra synaptic recepto rs.Astrocytes are stimulated by neuronal network activity,which in turn excite neurons,forming an astrocyte-neuron feedback loop.Mostly as a consequence of brain edema,astrocytic swelling can also induce slow inward currents under pathological conditions.There is a growing body of evidence on the roles of slow inward currents on a single neuron or local network level.These events often occur in synchro ny on neurons located in the same astrocytic domain.Besides synchronization of neuronal excitability,slow inward currents also set synaptic strength via eliciting timing-dependent synaptic plasticity.In addition,slow inward currents are also subject to non-synaptic plasticity triggered by long-la sting stimulation of the excitatory inputs.Of note,there might be important regionspecific differences in the roles and actions triggering slow inward currents.In greater networks,the pathophysiological roles of slow inward currents can be better understood than physiological ones.Slow inward currents are identified in the pathophysiological background of autism,as slow inward currents drive early hypersynchrony of the neural networks.Slow inward currents are significant contributors to paroxysmal depolarizational shifts/interictal spikes.These events are related to epilepsy,but also found in Alzheimer's disease,Parkinson's disease,and stroke,leading to the decline of cognitive functions.Events with features overlapping with slow inward currents(excitatory,N-methyl-Daspartate-receptor mediated currents with astrocytic contribution) as ischemic currents and spreading depolarization also have a well-known pathophysiological role in worsening consequences of stroke,traumatic brain injury,or epilepsy.One might assume that slow inward currents occurring with low frequency under physiological conditions might contribute to synaptic plasticity and memory formation.However,to state this,more experimental evidence from greater neuronal networks or the level of the individual is needed.In this review,I aimed to summarize findings on slow inward currents and to speculate on the potential functions of it. 展开更多
关键词 ASTROCYTE cortical spreading depolarization gliotransmission GLUTAMATE neural synchronization NMDA receptor paroxysmal depolarizational shift slow inward current
下载PDF
High-Precision Doppler Frequency Estimation Based Positioning Using OTFS Modulations by Red and Blue Frequency Shift Discriminator 被引量:1
12
作者 Shaojing Wang Xiaomei Tang +3 位作者 Jing Lei Chunjiang Ma Chao Wen Guangfu Sun 《China Communications》 SCIE CSCD 2024年第2期17-31,共15页
Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Dopple... Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Doppler frequency for positioning is a promising research direction on communication and navigation integration. To tackle the high Doppler frequency and low signal-to-noise ratio(SNR) in satellite communication, this paper proposes a Red and Blue Frequency Shift Discriminator(RBFSD) based on the pseudo-noise(PN) sequence.The paper derives that the cross-correlation function on the Doppler domain exhibits the characteristic of a Sinc function. Therefore, it applies modulation onto the Delay-Doppler domain using PN sequence and adjusts Doppler frequency estimation by red-shifting or blue-shifting. Simulation results show that the performance of Doppler frequency estimation is close to the Cramér-Rao Lower Bound when the SNR is greater than -15dB. The proposed algorithm is about 1/D times less complex than the existing PN pilot sequence algorithm, where D is the resolution of the fractional Doppler. 展开更多
关键词 channel estimation communication and navigation integration Orthogonal Time Frequency and Space pseudo-noise sequence red-blue frequency shift discriminator
下载PDF
基于信令数据的中型城市通勤公交站点优化方法
13
作者 葛浩菁 吕远 焦朋朋 《交通信息与安全》 CSCD 北大核心 2024年第1期142-149,共8页
大中型城市之间的手机通信基站密度和通勤出行结构不同,公交站点布设呈现出显著差异。在此背景下,研究了基于改进Mean Shift聚类算法的中型城市通勤公交站点优化方法。该方法采用荆州市中心城区信令数据中的通勤记录,以系统总成本(包括... 大中型城市之间的手机通信基站密度和通勤出行结构不同,公交站点布设呈现出显著差异。在此背景下,研究了基于改进Mean Shift聚类算法的中型城市通勤公交站点优化方法。该方法采用荆州市中心城区信令数据中的通勤记录,以系统总成本(包括运营成本和乘客步行时间成本)作为主要评价指标。根据中心城区早高峰的通勤出行需求,制定通勤公交站点优化方案。通过对比优化结果和现有公交站点布局,验证了优化方法的有效性;比较不同聚类算法,证明改进的Mean Shift聚类算法的性能优越性;考虑基站和等时圈的影响,对比不同场景,证明了考虑二者影响的必要性。结果表明:①针对荆州市研究区域的早高峰出行需求,优化方法共设置28个公交站,乘客步行时间成本下降51.98%,系统总成本下降17.82%,表明本方法能够得到系统总成本更优的站点布设方案,有效减少研究区域内乘客步行时间成本;②与不同聚类算法的比较中,改进Mean Shift算法得到的方案有明显提升,系统总成本比K-means聚类算法下降8.73%,比近邻传播聚类算法(affinity propagation,AP)下降2.48%;③与未考虑基站和等时圈影响的情况相比,本算法步行时间成本有所下降。上述指标表明改进Mean Shift聚类方法在聚类质量上优于其他方法,可以获得更优的公交站点布设方案,为中型城市的公交线路规划提供基础。 展开更多
关键词 交通规划 中型城市 公交站点布设 改进Mean Shift算法 信令数据
下载PDF
婴幼儿看护机器人的设计与开发
14
作者 徐程远 游国栋 +1 位作者 王一评 赵双乐 《自动化与仪表》 2024年第4期74-78,共5页
在现代科学育婴理念普及以及消费观念升级的影响下,智能母婴产品迎来巨大的发展空间。该文设计了一种婴幼儿看护机器人,基于Jetson Nano,通过激光雷达与ROS集成,可以获取机器人周围环境的信息,并进行地图构建、路径规划等任务。顶端将... 在现代科学育婴理念普及以及消费观念升级的影响下,智能母婴产品迎来巨大的发展空间。该文设计了一种婴幼儿看护机器人,基于Jetson Nano,通过激光雷达与ROS集成,可以获取机器人周围环境的信息,并进行地图构建、路径规划等任务。顶端将舵机二维云台与USB高清摄像头配合使用,结合Mean Shift目标追踪算法自动转动摄像头调整看护角度,并使用YOLO目标检测算法对监控的实时视频流中的婴幼儿人脸进行关键点的定位表情判断等,检测到婴幼儿啼哭、处于消极状态或者危险情况时,及时提醒看护人,看护人还可以通过前端页面实时查看婴幼儿状态。 展开更多
关键词 婴幼儿看护 Jetson Nano ROS YOLO Mean Shift
下载PDF
THE PERSISTENCE OF SOLUTIONS IN A NONLOCAL PREDATOR-PREY SYSTEM WITH A SHIFTING HABITAT
15
作者 赵敏 袁荣 《Acta Mathematica Scientia》 SCIE CSCD 2024年第3期1096-1114,共19页
In this paper,we mainly study the propagation properties of a nonlocal dispersal predator-prey system in a shifting environment.It is known that Choi et al.[J Differ Equ,2021,302:807-853]studied the persistence or ext... In this paper,we mainly study the propagation properties of a nonlocal dispersal predator-prey system in a shifting environment.It is known that Choi et al.[J Differ Equ,2021,302:807-853]studied the persistence or extinction of the prey and of the predator separately in various moving frames.In particular,they achieved a complete picture in the local diffusion case.However,the question of the persistence of the prey and of the predator in some intermediate moving frames in the nonlocal diffusion case was left open in Choi et al.'s paper.By using some a prior estimates,the Arzelà-Ascoli theorem and a diagonal extraction process,we can extend and improve the main results of Choi et al.to achieve a complete picture in the nonlocal diffusion case. 展开更多
关键词 predator-prey system PERSISTENCE nonlocal dispersal shifting environment
下载PDF
Tunable spectral continuous shift of high-order harmonic generation in atoms by a plasmon-assisted shaping pulse
16
作者 王源 李玉龙 +7 位作者 乔月 高娜 郭福明 陈洲 赫兰海 杨玉军 赵曦 王俊 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第3期433-440,共8页
We delve into the phenomenon of high-order harmonic generation within a helium atom under the influence of a plasmon-assisted shaping pulse.Our findings reveal an intriguing manipulation of the frequency peak position... We delve into the phenomenon of high-order harmonic generation within a helium atom under the influence of a plasmon-assisted shaping pulse.Our findings reveal an intriguing manipulation of the frequency peak position in the harmonic emission by adjusting the absolute phase parameter within the frequency domain of the shaping pulse.This phenomenon holds potential significance for experimental setups necessitating precisely tuned single harmonics.Notably,we observe a modulated shift in the created harmonic photon energy,spanning an impressive range of 1.2 eV.This frequency peak shift is rooted in the asymmetry exhibited by the rising and falling edges of the laser pulse,directly influencing the position of the peak frequency emission.Our study quantifies the dependence of this tuning range and the asymmetry of the laser pulse,offering valuable insights into the underlying mechanisms driving this phenomenon.Furthermore,our investigation uncovers the emergence of semi-integer order harmonics as the phase parameter is altered.We attribute this discovery to the intricate interference between harmonics generated by the primary and secondary return cores.This observation introduces an innovative approach for generating semi-integer order harmonics,thus expanding our understanding of high-order harmonic generation.Ultimately,our work contributes to the broader comprehension of complex phenomena in laser-matter interactions and provides a foundation for harnessing these effects in various applications,particularly those involving precise spectral control and the generation of unique harmonic patterns. 展开更多
关键词 high-order harmonic semi-integer-order spectra shift inhomogeneous field
下载PDF
Strong metal-support interactions between highly dispersed Cu^(+) species and ceria via mix-MOF pyrolysis toward promoted water-gas shift reaction
17
作者 Xiao-Chen Sun Xing-Chi Li +7 位作者 Ze-Wei Xie Chen-Yue Yuan De-Jiu Wang Qian Zhang Xiao-Yu Guo Hao Dong Hai-Chao Liu Ya-Wen Zhang 《Journal of Energy Chemistry》 SCIE EI CAS CSCD 2024年第4期475-483,共9页
The modulation of metal-support interfacial interaction is significant but challenging in the design of high-efficiency and high-stability supported catalysts.Here,we report a synthetic strategy to upgrade Cu-CeO_(2)i... The modulation of metal-support interfacial interaction is significant but challenging in the design of high-efficiency and high-stability supported catalysts.Here,we report a synthetic strategy to upgrade Cu-CeO_(2)interfacial interaction by the pyrolysis of mixed metal-organic framework(MOF)structure.The obtained highly dispersed Cu/CeO_(2)-MOF catalyst via this strategy was used to catalyze water-gas shift reaction(WGSR),which exhibited high activity of 40.5μmolCOgcat^(-1).s^(-1)at 300℃and high stability of about 120 h.Based on comprehensive studies of electronic structure,pyrolysis strategy has significant effect on enhancing metal-support interaction and then stabilizing interfacial Cu^(+)species under reaction conditions.Abundant Cu^(+)species and generated oxygen vacancies over Cu/CeO_(2)-MOF catalyst played a key role in CO molecule activation and H2O molecule dissociation,respectively.Both collaborated closely and then promoted WGSR catalytic performance in comparison with traditio nal supported catalysts.This study shall offer a robust approach to harvest highly dispersed catalysts with finely-tuned metal-support interactions for stabilizing the most interfacial active metal species in diverse heterogeneous catalytic reactions. 展开更多
关键词 Cu-based catalyst MOF derivative Water-gas shift reaction Metal-support interaction
下载PDF
The interaction between temperature and precipitation on the potential distribution range of Betula ermanii in the alpine treeline ecotone on the Changbai Mountain
18
作者 Yu Cong Yongfeng Gu +8 位作者 Wen J.Wang Lei Wang Zhenshan Xue Yingyi Chen Yinghua Jin Jiawei Xu Mai-He Li Hong S.He Ming Jiang 《Forest Ecosystems》 SCIE CSCD 2024年第1期42-51,共10页
Alpine treeline ecotones are highly sensitive to climate warming.The low temperature-determined alpine treeline is expected to shift upwards in response to global warming.However,little is known about how temperature ... Alpine treeline ecotones are highly sensitive to climate warming.The low temperature-determined alpine treeline is expected to shift upwards in response to global warming.However,little is known about how temperature interacts with other important factors to influence the distribution range of tree species within and beyond the alpine treeline ecotone.Hence,we used a GF-2 satellite image,along with bioclimatic and topographic variables,to develop an ensemble suitable habitat model based on the species distribution modeling algorithms in Biomod2.We investigated the distribution of suitable habitats for B.ermanii under three climate change scenarios(i.e.,low(SSP126),moderate(SSP370)and extreme(SSP585)future emission trajectories)between two consecutive time periods(i.e.,current-2055,and 2055-2085).By 2055,the potential distribution range of B.ermanii will expand under all three climate scenarios.The medium and high suitable areas will decline under SSP370 and SSP585scenarios from 2055 to 2085.Moreover,under the three climate scenarios,the uppermost altitudes of low suitable habitat will rise to 2,329 m a.s.l.,while the altitudes of medium and high suitable habitats will fall to 2,201 and2,051 m a.s.l.by 2085,respectively.Warming promotes the expansion of B.ermanii distribution range in Changbai Mountain,and this expansion will be modified by precipitation as climate warming continues.This interaction between temperature and precipitation plays a significant role in shaping the potential distribution range of B.ermanii in the alpine treeline ecotone.This study reveals the link between environmental factors,habitat distribution,and species distribution in the alpine treeline ecotone,providing valuable insights into the impacts of climate change on high-elevation vegetation,and contributing to mountain biodiversity conservation and sustainable development. 展开更多
关键词 Biomod2 BIRCH Climate change Climate scenarios Habitat suitability Range shift Treeline species
下载PDF
A Yb optical clock with a lattice power enhancement cavity
19
作者 王春云 姚远 +3 位作者 师浩森 于洪浮 马龙生 蒋燕义 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第3期70-74,共5页
We construct a power enhancement cavity to form an optical lattice in an ytterbium optical clock.It is demonstrated that the intra-cavity lattice power can be increased by about 45 times,and the trap depth can be as l... We construct a power enhancement cavity to form an optical lattice in an ytterbium optical clock.It is demonstrated that the intra-cavity lattice power can be increased by about 45 times,and the trap depth can be as large as 1400Er when laser light with a power of only 0.6 W incident to the lattice cavity.Such high trap depths are the key to accurate evaluation of the lattice-induced light shift with an uncertainty down to~1×10-18.By probing the ytterbium atoms trapped in the power-enhanced optical lattice,we obtain a 4.3 Hz-linewidth Rabi spectrum,which is then used to feedback to the clock laser for the close loop operation of the optical lattice clock.We evaluate the density shift of the Yb optical lattice clock based on interleaving measurements,which is-0.46(62)mHz.This result is smaller compared to the density shift of our first Yb optical clock without lattice power enhancement cavity mainly due to a larger lattice diameter of 344μm. 展开更多
关键词 optical atomic clock optical lattice optical cavity Stark shift
下载PDF
Linking nutrient resorption stoichiometry with plant growth under long-term nitrogen addition
20
作者 Aijun Xing Haihua Shen +3 位作者 Longchao Xu Mengying Zhao Zhengbing Yan Jingyun Fang 《Forest Ecosystems》 SCIE CSCD 2024年第5期642-649,共8页
Increased nitrogen(N)input can potentially lead to secondary phosphorus(P)limitation;however,it remains unclear whether differences in the plant's ability to cope with this P deficiency are related to their growth... Increased nitrogen(N)input can potentially lead to secondary phosphorus(P)limitation;however,it remains unclear whether differences in the plant's ability to cope with this P deficiency are related to their growth responses.Using a long-term experiment of N addition in a boreal forest,we explored the potential role of plant nutrient resorption efficiency and its stoichiometry in mediating plant growth responses to increased N input.We recorded the cover and measured the concentration and resorption efficiency of leaf N and P as well as the photosynthesis of a grass Deyeuxia angustifolia and a shrub Vaccinium vitis-idaea.The cover of the grass D.angustifolia increased with increasing N addition,while that of the shrub V.vitis-idaea decreased with N addition rate and almost disappeared from the high-level N addition over time.P resorption efficiency(PRE)increased in D.angustifolia but decreased in V.vitis-idaea with increasing leaf N:P which was increased by N addition for both species.In addition,photosynthesis increased linearly with N resorption efficiency(NRE)and PRE but was better explained by NRE:PRE,changing nonlinearly with the ratio in a hump-shaped trend.Furthermore,the variance(CV)of NRE:PRE for V.vitis-idaea(123%)was considerably higher than that for D.angustifolia(29%),indicating a more stable nutrient resorption stoichiometry of the grass.Taken together,these results highlight that efficient P acquisition and use strategy through nutrient resorption processes could be a pivotal underlying mechanism driving plant growth and community composition shifts under N enrichment. 展开更多
关键词 Nitrogen deposition Understory layer Community shift Nutrient limitation Phosphorus resorption efficiency Stoichiometric homeostasis
下载PDF
上一页 1 2 129 下一页 到第
使用帮助 返回顶部