复合结构偏心的缓变截面波导开放式同轴谐振腔电磁特性仿真研究     

谢永超  孔艳岩 《科技通报》2015,(7)

利用三维电磁仿真软件CST Microwave Studio,数值模拟了复合结构偏心对缓变截面波导开放式同轴谐振腔电磁特性的影响。结果表明:当内外导体的轴线同时存在平行偏心和倾斜偏心时,改变了腔体的边界条件,从而导致开放式同轴谐振腔的谐振频率、品质因数和场振幅下降,使谐振腔的有效长度(即形成驻波的长度)变短,减小了开放式同轴谐振腔回旋管振荡器中电子束与电磁波的互作用强度,使得起振时所需要的电流增大,器件的输出功率减小。复合结构偏心产生的影响比平行偏心或者倾斜偏心单独存在时更为严重。因此,在开放式缓变截面波导同轴谐振腔的实际制作过程中,应尽力避免发生复合结构偏心。  相似文献   

个性化服务中用户兴趣建模与更新研究   总被引：1，自引：0，他引：1  

李珊 《情报学报》2010,29(1)

目的:为了使用户兴趣模型更好地被推荐系统理解,实现个性化服务.方法:引入领域本体,对特征项语义进行扩展,构建电影领域本体.根据信息论思想,改进相似度的计算方法,构建基于本体的用户四元组多兴趣细粒度表示模型和相应更新机制.结果:随着用户欣赏同类电影的数量的不断增加,用户兴趣模型能进行累加学习,推荐的准确性不断提高.当用户的兴趣爱好发生转移时,用户兴趣模型能随着用户兴趣的转移合理地"遗忘"掉用户过去的爱好,而积累用户新近感兴趣的电影主题.结论:实验表明该用户兴趣模型能够准确及时地跟踪用户多种兴趣及其变化,保证用户模型的可靠性.  相似文献   

To Establish the Reference Intervals of Lipid Profile in Punjab     

Vaneet Kaur  Minni Verma  Amandeep Kaur  Shalini Gupta  Kamaljit Singh 《Indian journal of clinical biochemistry : IJCB》2012,27(3):290-295

Overnight fasting samples of 1,031 apparently healthy people of Punjab visiting the hospital over a period of 3 years were tested for serum lipid profile. The mean ± SD of serum total cholesterol, triglycerides, high density lipoprotein cholesterol, low density lipoprotein cholesterol and very low density lipoprotein cholesterol in mg/dl were 182.2 ± 33.9, 122.4 ± 33.4, 44.1 ± 6.8, 113.9 ± 32.0, 24.6 ± 7.1 respectively. When these subjects were grouped according to age and sex, no appreciable difference was observed between most of the groups. Serum triglycerides were found to be low and HDL-C was high in females when compared with males of similar age and vice versa. With advancing age, total cholesterol and low density lipoprotein cholesterol levels were found to be higher in women. The present study suggests that the obtained lipid values should be taken into consideration during clinical evaluation.  相似文献   

Web环境下的个性化信息检索技术   总被引：5，自引：0，他引：5  

崔建海  程妮  王军 《现代图书情报技术》2005,21(9):45-49

对当前网络环境下应用的若干典型的个性化信息检索技术进行了研究和分析。介绍了个性化信息检索的一般模型，从四个不同的角度对各种个性化检索技术做了分类，列举了主要的个性化检索个案，描述了个性化检索系统的核心模块，并简单介绍了如何提高个性化检索的效率。  相似文献   

基于Z39.50数据库更新扩展服务的联合目录规程*     

赵英  陈文飞 《现代图书情报技术》2000,16(6):32-35

讨论了一种基于Z39. 50 数据库更新扩展服务的联合目录规程, 它可以确保创建者在本地系统
环境下方便地应用本地的软件进行目录的创建或更新, 为联合目录的高效维护提供了可能。  相似文献   

Determining optimal trial size using sequential analysis     

Paul Geoffrey Taylor  Kwee-Yum Lee  Raul Landeo  Damien Michael O'Meara  Emma Millett 《Journal of sports sciences》2015,33(3):300-308

When characterising typical human movement profiles, the optimal number of trials analysed for each participant should ensure a stable mean. Sequential analysis is one method able to establish the number of trials to stability by assessing a moving point mean against a set bandwidth. As the total trial number determining this bandwidth is selected arbitrarily, the effect of applying different total trial numbers on the results of sequential analysis was investigated. Twenty participants performed 30 trials of overarm throwing, and sequential analyses were applied to three dimensional (3-D) kinematic data over 10, 20 and 30 trial numbers. We found a total of 20 to be the preferred trial number for sequential analyses. Erroneous results were produced consistently by 10 trial number groups, while moving point means were statistically unchanged after the 10th trial. Subsequently, sequential analyses were applied to 20 trials to establish trials to stability in discrete and time series elements of the 3-D kinematic data. The results suggest that a trial size between 13 and 17 provides stable means for overarm throwing kinematics.  相似文献   

渐开线圆柱齿轮参数化三维实体建模系统研究     

江方记 《深圳职业技术学院学报》2014,(3):43-47

通过分析机械零件参数化设计的特点,利用Microsoft Visual Studio和AutoCAD-次开发工具,设计了渐开线圆柱齿轮参数化三维建模软件系统.基于渐开线齿廓曲线的关键算法,根据渐开线极坐标和笛卡尔坐标数学方程,使用旋转和拉伸等三维建模方法完成渐开线齿轮参数化实体建模的程序设计.使用该软件系统,可根据不同结构型号的齿轮几何参数要求,实现单联滑移、双联滑移和轮毂腹板式等常见齿轮的三维实体建模.该系统须在Windows环境下的AutoCAD中运行,具有使用简单、人机界面友好和运行速度快等特点.  相似文献   

基于用户画像和视频兴趣标签的个性化推荐          下载免费PDF全文

吴剑云  胥明珠 《情报科学》2021,39(1):128-134

【目的/意义】用户画像深刻地描述了视频用户的个体和群体行为特征,为视频的个性化推荐服务提供参 考。【方法/过程】通过文本挖掘对爬取的视频、用户及其观影数据分析,构建单个用户画像,并通过K-Means和LDA 模型对用户聚类并提取主题,挖掘群体用户特征。基于用户画像和时间指数衰减的视频兴趣标签,并结合视频喜 爱度和协同过滤,进行视频推荐。【结果/结论】考虑时间指数衰减的个性化推荐,提高了系统对用户兴趣的感知。 结合视频喜爱度和协同过滤,推荐视频评分达0.87,有助于提高用户对网站的忠诚度和活跃度。【创新/局限】基于用 户生成内容的文本挖掘结果,进行单个和群体用户画像,并创新性采用时间指数衰减构建用户视频兴趣标签,以捕 获用户兴趣的变化。由于网络爬虫的限制,实验数据量有一定的局限性,且特征提取兴趣范围有限。  相似文献   

基于用户画像的学术期刊精准服务研究          下载免费PDF全文

韩云惠 《编辑学报》2021,33(2):142-146

对学术期刊而言,其价值的实现有赖于用户.构建用户画像能够使学术期刊全方位了解自己的核心读者、作者和专家群体,掌握相关群体的信息,为用户提供精准服务.通过梳理学术期刊精准服务和用户画像理论等相关研究成果,分析基于用户画像理论的学术期刊精准服务的意义、理论内核和价值表征,并阐释其运行机制,最后提出基于用户画像的学术期刊精准服务策略,有利于拓展期刊领域学术研究思维和方法,提升学术期刊用户服务的质量和水平.  相似文献   

Modeling of a novel fish passage-way using coupled spatially varied flow     

M.M. Mortula 《Journal of The Franklin Institute》2011,348(7):1627-1637

An innovative hydraulic structure was proposed for passage of fish in surface water. The structure consisted of identical ‘cells’ throughout its length and was designed to create coupled spatially varied flow for optimization of depth and velocity of water. The objective of this paper was to simulate the hydraulics of a single cell of this fish passage structure. A numerical model was developed to simulate the water surface profiles and longitudinal variation of 1-D velocity through one cell. The transition in the water surface profile between longitudinally adjacent cells (chamber) was also investigated. It was found that numerical convergence was usually achieved after three iterations with 2% discretization. The difference in depth arising from cell vs. chamber analysis was found to be small. The experimental results indicated turbulence in the water surface. The water surface profile matched the results obtained from numerical results. However, there were errors observed in estimation of flow rate. It is concluded that the mathematical approach used for the numerical simulation is reliable and can be used to analyze coupled spatially varied flow for any hydraulic structures aimed at controlling depth and velocity of water. Innovative approach to the interface between can potentially be used to achieve hydraulic goal of any structure.  相似文献