期刊文献+
共找到18,087篇文章
< 1 2 250 >
每页显示 20 50 100
Food-borne parasitic zoonosis: Distribution of trichinosis in Thailand 被引量:6
1
作者 Natthawut Kaewpitoon Soraya Jatesadapattaya Kaewpitoon Prasit Pengsaa 《World Journal of Gastroenterology》 SCIE CAS CSCD 2008年第22期3471-3475,共5页
Trichinosis is among the most common food-borne parasitic zoonoses in Thailand and many outbreaks are reported each year. This paper investigates the distribution of the disease in regions of north, north-east, centra... Trichinosis is among the most common food-borne parasitic zoonoses in Thailand and many outbreaks are reported each year. This paper investigates the distribution of the disease in regions of north, north-east, central and south Thailand. Between the earliest recorded of outbreak of trichinosis in Mae Hong Son Province in 1962 and 2006, there have been 135 outbreaks involving 7340 patients and 97 deaths in Thailand. The highest number of cases, 557, was recorded in 1983. Most infected patients were in the 35-44 year age group, and the disease occurred more frequently in men than women during 1962-2003, with no significant sex difference during 2004-2006. Outbreaks were most common in the northern areas, especially in rural areas where raw and under-cooked pork and/or wild animals are eaten. Human infections occur annually in northern Thailand during communal feasts celebrating the Thai New Year. Trichinosis causes have been reported every year, supporting the need for planning education programs. 展开更多
关键词 food-born parasitic ZOONOSIS TRICHINOSIS Thailand
下载PDF
Bio-control of Some Food-Borne Pathogenic Bacteria by Bacteriophage 被引量:1
2
作者 S. Kalkan E. UEnal Z. Erginkaya 《Journal of Food Science and Engineering》 2011年第4期237-244,共8页
In recent years, researchers tended to bring new alternative to biological protective systems used in conservation of food and production of safe food. Use of bacteriophage against to pathogen bacteria in food was the... In recent years, researchers tended to bring new alternative to biological protective systems used in conservation of food and production of safe food. Use of bacteriophage against to pathogen bacteria in food was the most hopeful system in these methods about bio-control. Controls of bacteriophage for each pathogen species and subspecies and determination of phage-host originality are important because efficient bio-control was achieved. Researches concentrated on some food-borne pathogen bacteria such as E. coli O157:H7, Campylobacter, Salmonella and Listeria. In a consequence of these studies made as in vitro and in vivo, first commercial production of phage which will be used in foods was made in Netherlands. Also, it has been informed that use of phage is cost-efficient alternative as compared with other preservatives. This review, discussed application of bacteriophages as bio-control agents in food and advantages and disadvantages about uses of bacteriophages by taking into account antimicrobial characteristics of them. 展开更多
关键词 BACTERIOPHAGE food-born pathogenic bacteria BIO-CONTROL ANTIMICROBIAL FOOD review.
下载PDF
Smart prediction of liquefaction-induced lateral spreading 被引量:1
3
作者 Muhammad Nouman Amjad Raja Tarek Abdoun Waleed El-Sekelly 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2024年第6期2310-2325,共16页
The prediction of liquefaction-induced lateral spreading/displacement(Dh)is a challenging task for civil/geotechnical engineers.In this study,a new approach is proposed to predict Dh using gene expression programming(... The prediction of liquefaction-induced lateral spreading/displacement(Dh)is a challenging task for civil/geotechnical engineers.In this study,a new approach is proposed to predict Dh using gene expression programming(GEP).Based on statistical reasoning,individual models were developed for two topographies:free-face and gently sloping ground.Along with a comparison with conventional approaches for predicting the Dh,four additional regression-based soft computing models,i.e.Gaussian process regression(GPR),relevance vector machine(RVM),sequential minimal optimization regression(SMOR),and M5-tree,were developed and compared with the GEP model.The results indicate that the GEP models predict Dh with less bias,as evidenced by the root mean square error(RMSE)and mean absolute error(MAE)for training(i.e.1.092 and 0.815;and 0.643 and 0.526)and for testing(i.e.0.89 and 0.705;and 0.773 and 0.573)in free-face and gently sloping ground topographies,respectively.The overall performance for the free-face topology was ranked as follows:GEP>RVM>M5-tree>GPR>SMOR,with a total score of 40,32,24,15,and 10,respectively.For the gently sloping condition,the performance was ranked as follows:GEP>RVM>GPR>M5-tree>SMOR with a total score of 40,32,21,19,and 8,respectively.Finally,the results of the sensitivity analysis showed that for both free-face and gently sloping ground,the liquefiable layer thickness(T_(15))was the major parameter with percentage deterioration(%D)value of 99.15 and 90.72,respectively. 展开更多
关键词 Lateral spreading Intelligent modeling Gene expression programming(GEP) Closed-form solution Feature importance
下载PDF
Individual dynamics and local heterogeneity provide a microscopic view of the epidemic spreading
4
作者 朱友源 沈瑞哲 +1 位作者 董昊 王炜 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第5期656-663,共8页
The COVID-19 pandemic has caused severe global disasters,highlighting the importance of understanding the details and trends of epidemic transmission in order to introduce efficient intervention measures.While the wid... The COVID-19 pandemic has caused severe global disasters,highlighting the importance of understanding the details and trends of epidemic transmission in order to introduce efficient intervention measures.While the widely used deterministic compartmental models have qualitatively presented continuous “analytical” insight and captured some transmission features,their treatment usually lacks spatiotemporal variation.Here,we propose a stochastic individual dynamical(SID)model to mimic the random and heterogeneous nature of epidemic propagation.The SID model provides a unifying framework for representing the spatiotemporal variations of epidemic development by tracking the movements of each individual.Using this model,we reproduce the infection curves for COVID-19 cases in different areas globally and find the local dynamics and heterogeneity at the individual level that affect the disease outbreak.The macroscopic trend of virus spreading is clearly illustrated from the microscopic perspective,enabling a quantitative assessment of different interventions.Seemingly,this model is also applicable to studying stochastic processes at the “meter scale”,e.g.,human society’s collective dynamics. 展开更多
关键词 Brownian motion epidemic spreading HETEROGENEITY
下载PDF
Influence of network structure on spreading dynamics via tie range
5
作者 李敏 宋玉蓉 +3 位作者 宋波 李汝琦 蒋国平 张晖 《Chinese Physics B》 SCIE EI CAS CSCD 2024年第8期606-613,共8页
There are various phenomena of malicious information spreading in the real society, which cause many negative impacts on the society. In order to better control the spreading, it is crucial to reveal the influence of ... There are various phenomena of malicious information spreading in the real society, which cause many negative impacts on the society. In order to better control the spreading, it is crucial to reveal the influence of network structure on network spreading. Motifs, as fundamental structures within a network, play a significant role in spreading. Therefore, it is of interest to investigate the influence of the structural characteristics of basic network motifs on spreading dynamics.Considering the edges of the basic network motifs in an undirected network correspond to different tie ranges, two edge removal strategies are proposed, short ties priority removal strategy and long ties priority removal strategy. The tie range represents the second shortest path length between two connected nodes. The study focuses on analyzing how the proposed strategies impact network spreading and network structure, as well as examining the influence of network structure on network spreading. Our findings indicate that the long ties priority removal strategy is most effective in controlling network spreading, especially in terms of spread range and spread velocity. In terms of network structure, the clustering coefficient and the diameter of network also have an effect on the network spreading, and the triangular structure as an important motif structure effectively inhibits the spreading. 展开更多
关键词 network spreading network motifs tie range edge removal strategy
下载PDF
Possible Cortical Spreading Depression Recorded Intraoperatively Following a Generalized Seizure: Illustrative Case
6
作者 Greg Schaublin Romina Shirka +4 位作者 Nabil Azar Callan Broderick Jayson Neil George R. Lee Kiara Ebinger 《Neuroscience & Medicine》 2024年第3期119-128,共10页
Background: We present a compelling case fitting the phenomenon of cortical spreading depression detected by intraoperative neurophysiological monitoring (IONM) following an intraoperative seizure during a craniotomy ... Background: We present a compelling case fitting the phenomenon of cortical spreading depression detected by intraoperative neurophysiological monitoring (IONM) following an intraoperative seizure during a craniotomy for revascularization. Cortical spreading depression (CSD, also called cortical spreading depolarization) is a pathophysiological phenomenon whereby a wave of depolarization is thought to propagate across the cerebral cortex, creating a brief period of relative neuronal inactivity. The relationship between CSD and seizures is unclear, although some literature has made a correlation between seizures and a cortical environment conducive to CSD. Methods: Intraoperative somatosensory evoked potentials (SSEPs) and electroencephalography (EEG) were monitored continuously during the craniotomy procedure utilizing standard montages. Electrophysiological data from pre-ictal, ictal, and post-ictal periods were recorded. Results: During the procedure, intraoperative EEG captured a generalized seizure followed by a stepwise decrease in somatosensory evoked potential cortical amplitudes, compelling for the phenomenon of CSD. The subsequent partial recovery of neuronal function was also captured electrophysiologically. Discussion: While CSD is considered controversial in some aspects, intraoperative neurophysiological monitoring allowed for the unique analysis of a case demonstrating a CSD-like phenomenon. To our knowledge, this is the first published example of this phenomenon in which intraoperative neurophysiological monitoring captured a seizure, along with a stepwise subsequent reduction in SSEP cortical amplitudes not explained by other variables. 展开更多
关键词 Cortical spreading Depression ELECTROENCEPHALOGRAPHY Intraoperative Neurophysiological Monitoring SEIZURE
下载PDF
DiriNet:An Estimation Network for Spectral Response Function and Point Spread Function
7
作者 Ting Hu Siyuan Cheng Chang Liu 《Journal of Beijing Institute of Technology》 EI CAS 2024年第4期287-297,共11页
Hyper-and multi-spectral image fusion is an important technology to produce hyper-spectral and hyper-resolution images,which always depends on the spectral response function andthe point spread function.However,few wo... Hyper-and multi-spectral image fusion is an important technology to produce hyper-spectral and hyper-resolution images,which always depends on the spectral response function andthe point spread function.However,few works have been payed on the estimation of the two degra-dation functions.To learn the two functions from image pairs to be fused,we propose a Dirichletnetwork,where both functions are properly constrained.Specifically,the spatial response function isconstrained with positivity,while the Dirichlet distribution along with a total variation is imposedon the point spread function.To the best of our knowledge,the neural network and the Dirichlet regularization are exclusively investigated,for the first time,to estimate the degradation functions.Both image degradation and fusion experiments demonstrate the effectiveness and superiority of theproposed Dirichlet network. 展开更多
关键词 Dirichlet network point spread function spectral response function hyper-spectralimage multi-spectral image
下载PDF
Adaptive Video Dual Domain Watermarking Scheme Based on PHT Moment and Optimized Spread Transform Dither Modulation
8
作者 Yucheng Liang Ke Niu +2 位作者 Yingnan Zhang Yifei Meng Fangmeng Hu 《Computers, Materials & Continua》 SCIE EI 2024年第11期2457-2492,共36页
To address the challenges of video copyright protection and ensure the perfect recovery of original video,we propose a dual-domain watermarking scheme for digital video,inspired by Robust Reversible Watermarking(RRW)t... To address the challenges of video copyright protection and ensure the perfect recovery of original video,we propose a dual-domain watermarking scheme for digital video,inspired by Robust Reversible Watermarking(RRW)technology used in digital images.Our approach introduces a parameter optimization strategy that incre-mentally adjusts scheme parameters through attack simulation fitting,allowing for adaptive tuning of experimental parameters.In this scheme,the low-frequency Polar Harmonic Transform(PHT)moment is utilized as the embedding domain for robust watermarking,enhancing stability against simulation attacks while implementing the parameter optimization strategy.Through extensive attack simulations across various digital videos,we identify the optimal low-frequency PHT moment using adaptive normalization.Subsequently,the embedding parameters for robust watermarking are adaptively adjusted to maximize robustness.To address computational efficiency and practical requirements,the unnormalized high-frequency PHT moment is selected as the embedding domain for reversible watermarking.We optimize the traditional single-stage extended transform dithering modulation(STDM)to facilitate multi-stage embedding in the dual-domain watermarking process.In practice,the video embedded with a robust watermark serves as the candidate video.This candidate video undergoes simulation according to the parameter optimization strategy to balance robustness and embedding capacity,with adaptive determination of embedding strength.The reversible watermarking is formed by combining errors and other information,utilizing recursive coding technology to ensure reversibility without attacks.Comprehensive analyses of multiple performance indicators demonstrate that our scheme exhibits strong robustness against Common Signal Processing(CSP)and Geometric Deformation(GD)attacks,outperforming other advanced video watermarking algorithms under similar conditions of invisibility,reversibility,and embedding capacity.This underscores the effectiveness and feasibility of our attack simulation fitting strategy. 展开更多
关键词 Dual-domain H.264 group of pictures polar harmonic transform spread transform dither modulation
下载PDF
Bearing Capacity Analysis of Spread Footing on Massif in the “Corniche Ouest” of the Dakar Peninsula (Senegal, West Africa)
9
作者 Moussa Sawadogo Déthie Sarr Oustasse A. Sall 《Open Journal of Civil Engineering》 2024年第3期421-434,共14页
This study presents various approaches to calculating the bearing capacity of spread footings applied to the rock mass of the western corniche at the tip of the Dakar peninsula. The bearing capacity was estimated usin... This study presents various approaches to calculating the bearing capacity of spread footings applied to the rock mass of the western corniche at the tip of the Dakar peninsula. The bearing capacity was estimated using empirical, analytical and numerical approaches based on the parameters of the rock mass and the foundation. Laboratory tests were carried out on basanite, as well as on the other facies detected. The results of these studies give a range of allowable bearing capacity values varying between 1.92 and 11.39 MPa for the empirical methods and from 7.13 to 25.50 MPa for the analytical methods. A wide dispersion of results was observed according to the different approaches. This dispersion of results is explained by the use of different rock parameters depending on the method used. The allowable bearing capacity results obtained with varying approaches of calculation remain admissible to support the loads. On the other hand, the foundation calculations show acceptable settlement of the order of a millimeter for all the layers, especially in the thin clay layers resting on the bedrock at shallow depths, where the rigidity of the rock reduces settlement. 展开更多
关键词 Peninsula of Dakar Bearing Capacity Basanites Rock Mass spread Footings
下载PDF
双圈图的Laplace spread 被引量:1
10
作者 李平 施劲松 李瑞林 《华东师范大学学报(自然科学版)》 CAS CSCD 北大核心 2010年第1期6-9,共4页
图的Laplace spread定义为图的最大Laplace特征值与次小Laplace特征值之差.利用多项式函数的性质,得到了具有最大Laplace spread的双圈图.
关键词 LAPLACE特征值 双圈图 LAPLACE spread
下载PDF
中性风在中低纬Spread-F中的作用 被引量:4
11
作者 谢红 刘滨莎 萧佐 《北京大学学报(自然科学版)》 CAS CSCD 北大核心 1996年第1期78-88,共11页
讨论了中低纬度电离层F区中有碰撞的Rayleigh-Taylor不稳定性的线性增长率,着重考察背景中性风对增长率的影响,首先建立了适合于描述中低纬地区R-T不稳定性的基本方程,其中包括背景中性风和电场。在此基础上导出了色散关系和不稳定性增... 讨论了中低纬度电离层F区中有碰撞的Rayleigh-Taylor不稳定性的线性增长率,着重考察背景中性风对增长率的影响,首先建立了适合于描述中低纬地区R-T不稳定性的基本方程,其中包括背景中性风和电场。在此基础上导出了色散关系和不稳定性增长率γ。结果表明,γ随纬度增加而逐渐减小,虽然东西方向和垂直向下的中性风分量有利于不稳定性增长,但在比30度更高的纬度,正常的背景中性风很难使γ为正值,除非存在合适的东西方向电场,亦即电场在中纬度Spread F的形成方面起着重要的作用。文中还根据比较合乎实际的电离层电子密度分布模式估算了线性增长率γ的季节变化。 展开更多
关键词 中纬扩展F 中性风 电离层 R-T不稳定性 spread-F
下载PDF
基于Spread业务支撑系统的拓扑构造
12
作者 董立岩 殷涵 +2 位作者 王利民 毛锐 黄乐 《吉林大学学报(理学版)》 CAS CSCD 北大核心 2011年第6期1073-1078,共6页
基于Spread具有的高度灵活性和自动发现功能,构造一个基于Spread的业务支撑系统,并研究了该系统的拓扑构造,给出了系统拓扑常见的4种情况:服务节点加入、服务节点离开、动态拓扑增加和动态拓扑减少的算法.仿真实验表明,该系统具有良好... 基于Spread具有的高度灵活性和自动发现功能,构造一个基于Spread的业务支撑系统,并研究了该系统的拓扑构造,给出了系统拓扑常见的4种情况:服务节点加入、服务节点离开、动态拓扑增加和动态拓扑减少的算法.仿真实验表明,该系统具有良好的稳定性、扩展性和容灾抗毁能力. 展开更多
关键词 拓扑构造 spread中间件 算法 业务支撑系统
下载PDF
一种类Spreadsheet结构的信息汇聚方法
13
作者 魏永山 韩燕波 +2 位作者 孙忠林 张峰 陈欣 《计算机科学》 CSCD 北大核心 2010年第5期134-138,共5页
SpreadSheet样式的数据操作具有很好的可用性,但在SpreadSheet结构中如何表示并操纵XML数据以及如何使用复制、粘贴、移动等简单操作表示复杂的XQuery查询是两个难点问题。提出一种基于XML模式的操作表示方法,将复杂的XQuery查询语句分... SpreadSheet样式的数据操作具有很好的可用性,但在SpreadSheet结构中如何表示并操纵XML数据以及如何使用复制、粘贴、移动等简单操作表示复杂的XQuery查询是两个难点问题。提出一种基于XML模式的操作表示方法,将复杂的XQuery查询语句分解为XML模式上的粘贴节点、移动节点等操作,从而可以表示XQuery语言的核心语句FLOWR。在Spreadsheet结构中将XML模式显示为嵌套表格,用户在嵌套表格上的操作转换为XML模式上的操作。使用该方法可以构造多数据源的XQuery查询,并实现了概念验证的原型系统。与当前流行的XQuery查询构造工具相比较,原型系统更适合于无编程经验的最终用户构造XQuery查询。 展开更多
关键词 spread SHEET XQUERY 信息集成 信息资源汇聚
下载PDF
声重波激发的赤道Spread—F的拓扑特性研究 被引量:1
14
作者 谢红 萧佐 王宪民 《空间科学学报》 CAS CSCD 北大核心 1997年第4期309-316,共8页
本文对声重波激发的Spread-F扰动的非线性制约方程的拓扑特性进行了定性讨论和数值计算.研究了Spread-F的混沌特征及参数范围.结果表明声重波在不同条件时对Spread-F的激发作用有本质的不同.
关键词 spread-F 声重波 混沌 拓扑 赤道 电离层
下载PDF
声重波激发的赤道 Spread—F 不稳定性 被引量:8
15
作者 肖佐 谢红 《空间科学学报》 CAS CSCD 北大核心 1994年第3期183-190,共8页
本文导出了声重波扰动与赤道电离层扩展F层相互作用的基本方程,并对数值模拟结果进行了讨论.结果表明当声重波扰动与Kavleigh-Taylor不稳定性共同作用于赤道F层时,将导致大尺度波状结构的Spread-F.其特征... 本文导出了声重波扰动与赤道电离层扩展F层相互作用的基本方程,并对数值模拟结果进行了讨论.结果表明当声重波扰动与Kavleigh-Taylor不稳定性共同作用于赤道F层时,将导致大尺度波状结构的Spread-F.其特征为以一定速度漂移的准周期不规则性,发展到后期伴有羽柱形状的bubble(电子密度低区)产生.这种现状的bubble可上升至F层顶部并发生倾斜.声重波波矢量的方向决定着羽柱的倾斜方向.这些结果与实验观测特征相符,说明声重波扰动不仅是大尺度Saread-F的触发源,而且对其整个形态发展过程起着重要的作用. 展开更多
关键词 声重波扰动 稳定性 赤道
下载PDF
Spread-F的经度效应 被引量:2
16
作者 张天华 肖佐 《北京大学学报(自然科学版)》 CAS CSCD 北大核心 2001年第3期348-352,共5页
从三维地理坐标系出发建立模型 ,考虑了地磁倾角和偏角的影响 ,研究Spread F现象的全球分布特点 ,是对以前的研究从赤道地区向中、低纬度地区的推广。从该三维模型中可以看到地磁场的大小和位型的影响 (包括磁倾角和磁偏角的效应 )。由... 从三维地理坐标系出发建立模型 ,考虑了地磁倾角和偏角的影响 ,研究Spread F现象的全球分布特点 ,是对以前的研究从赤道地区向中、低纬度地区的推广。从该三维模型中可以看到地磁场的大小和位型的影响 (包括磁倾角和磁偏角的效应 )。由于地磁位型的不同 ,发生率的分布并不具有经度对称性 ,即使在磁赤道附近也如此。在某些特殊的经度和纬度地区 ,会达到发生率的峰值。 展开更多
关键词 spread-F 三维地理坐标系 经度效应 地磁效应 电离层风
下载PDF
确定美式Spread期权自由边界的一种算法
17
作者 吴雄华 余屹 《同济大学学报(自然科学版)》 EI CAS CSCD 北大核心 2002年第6期749-754,共6页
Spread期权是一种新型两维美式差价期权 ,即客户有权以价格E ,一份标的资产s2 交换一份标的资产s1.这种期权涉及到两标的资产且可提前执行 ,其数学模型是抛物型方程的自由边界问题 .确定期权价格的关键在于自由边界位置的确定 .通过坐... Spread期权是一种新型两维美式差价期权 ,即客户有权以价格E ,一份标的资产s2 交换一份标的资产s1.这种期权涉及到两标的资产且可提前执行 ,其数学模型是抛物型方程的自由边界问题 .确定期权价格的关键在于自由边界位置的确定 .通过坐标变换、高精度分裂算法及奇性消除方法等手段 ,计算出可靠的数值结果 . 展开更多
关键词 美式spread期权 最优执行价格 自由边界 消除奇性
下载PDF
The burden of upper motor neuron involvement is correlated with the bilateral limb involvement interval in patients with amyotrophic lateral sclerosis:a retrospective observational study
18
作者 Jieying Wu Shan Ye +2 位作者 Xiangyi Liu Yingsheng Xu Dongsheng Fan 《Neural Regeneration Research》 SCIE CAS 2025年第5期1505-1512,共8页
Amyotrophic lateral sclerosis is a rare neurodegenerative disease characterized by the involvement of both upper and lower motor neurons.Early bilateral limb involvement significantly affects patients'daily lives ... Amyotrophic lateral sclerosis is a rare neurodegenerative disease characterized by the involvement of both upper and lower motor neurons.Early bilateral limb involvement significantly affects patients'daily lives and may lead them to be confined to bed.However,the effect of upper and lower motor neuron impairment and other risk factors on bilateral limb involvement is unclear.To address this issue,we retrospectively collected data from 586 amyotrophic lateral sclerosis patients with limb onset diagnosed at Peking University Third Hospital between January 2020 and May 2022.A univariate analysis revealed no significant differences in the time intervals of spread in different directions between individuals with upper motor neuron-dominant amyotrophic lateral sclerosis and those with classic amyotrophic lateral sclerosis.We used causal directed acyclic graphs for risk factor determination and Cox proportional hazards models to investigate the association between the duration of bilateral limb involvement and clinical baseline characteristics in amyotrophic lateral sclerosis patients.Multiple factor analyses revealed that higher upper motor neuron scores(hazard ratio[HR]=1.05,95%confidence interval[CI]=1.01–1.09,P=0.018),onset in the left limb(HR=0.72,95%CI=0.58–0.89,P=0.002),and a horizontal pattern of progression(HR=0.46,95%CI=0.37–0.58,P<0.001)were risk factors for a shorter interval until bilateral limb involvement.The results demonstrated that a greater degree of upper motor neuron involvement might cause contralateral limb involvement to progress more quickly in limb-onset amyotrophic lateral sclerosis patients.These findings may improve the management of amyotrophic lateral sclerosis patients with limb onset and the prediction of patient prognosis. 展开更多
关键词 amyotrophic lateral sclerosis bilateral limb involvement Cox proportional hazards regression model horizontal spread restricted cubic spline analysis time interval upper motor neuron vertical spread
下载PDF
中低纬Spread-F的数值模拟 被引量:15
19
作者 谢红 肖佐 《地球物理学报》 SCIE EI CAS CSCD 北大核心 1993年第1期18-26,共9页
本文导出了中低纬地区电离层F区中的Rayleigh-Taylor不稳定性的线性增长率,并对一些典型情况进行了数值模拟研究.结果表明,Ravleigh-Taylor不稳定性的线性增长率随纬度的增加而降低,在中纬度地区,如果没有合适的东西向水平外电场,纯Rayl... 本文导出了中低纬地区电离层F区中的Rayleigh-Taylor不稳定性的线性增长率,并对一些典型情况进行了数值模拟研究.结果表明,Ravleigh-Taylor不稳定性的线性增长率随纬度的增加而降低,在中纬度地区,如果没有合适的东西向水平外电场,纯Rayleiyh-Taylor模难于增长,初始扰动将被稳定化.在这些区域,线性增长率的表达式还表明,外电场导致的E×B模的增长率虽然随纬度的增加而减小,但其减小的速率慢于R-T模增长率的减小.非线性的数值模拟则显示,中纬非线性E×B漂移不能象在赤道地区那样使电子密度减小的区域抬升到F区顶部以上,亦即在中纬地区,F顶部以上通常不出现电离层泡,但在F区较低部分可以演化出较大范围的电子密度增强区,这与中低纬地区Spread-F的某些观测特征一致.这说明Rayleigh-Taylor不稳定性与东向水平外电场一起可以成为导致中纬Spread-F发展的一种机制. 展开更多
关键词 中低纬地区 电离层 扩展F层
下载PDF
数字测高仪对海南地区Spread—F的观测(摘要)
20
作者 张奇伟 郭兼善 +1 位作者 徐楚孚 王作桂 《天文研究与技术》 CSCD 1990年第4期314-314,共1页
用数字测高仪DGS—256在海南地区进行了夜间距离扩展Spread—F的观测。充分利用DGS—256的多参数测量能力,我们从振幅频高图和Doppler频高图中看到了Spread—F的多描迹结构,即由一条从正常电离层反射的主描迹和几条在主描迹之上的辅描... 用数字测高仪DGS—256在海南地区进行了夜间距离扩展Spread—F的观测。充分利用DGS—256的多参数测量能力,我们从振幅频高图和Doppler频高图中看到了Spread—F的多描迹结构,即由一条从正常电离层反射的主描迹和几条在主描迹之上的辅描迹组成的Spread—F描迹。从时间顺序上。 展开更多
关键词 测高仪 spread 电离层反射 海南地区 幅频 时间顺序 多参数测量 以正
下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部